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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2012	Oct. 30, 2012
Document and Entity Information [Abstract]
Entity Registrant Name	WHITE MOUNTAINS INSURANCE GROUP LTD
Entity Central Index Key	0000776867
Document Type	10-Q
Document Period End Date	Sep. 30, 2012
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		6,583,653
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q3
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2012	Dec. 31, 2011
Assets
Fixed maturity investments, at fair value	$ 4,912.4	$ 6,221.9
Short-term investments, at amortized cost (which approximates fair value)	917.3	846.0
Common equity securities, at fair value	1,004.8	755.0
Convertible fixed maturity investments, at fair value	142.0	143.8
Other long-term investments	307.1	301.3
Total investments	7,283.6	8,268.0
Cash (restricted: $341.7 and $453.5)	549.2	705.4
Reinsurance recoverable on unpaid losses	356.8	2,507.3
Reinsurance recoverable on paid losses	14.8	30.5
Insurance and reinsurance premiums receivable	678.1	489.2
Funds held by ceding companies	102.7	106.5
Investments in unconsolidated affiliates	376.3	275.3
Deferred acquisition costs	211.3	187.0
Deferred Income Tax Assets	555.0	536.9
Ceded unearned insurance and reinsurance premiums	113.6	87.3
Accrued investment income	45.5	51.4
Accounts receivable on unsettled investment sales	167.2	4.7
Other assets	626.5	681.9
Assets held for sale	2,388.2	132.6
Total assets held for sale	13,468.8	14,064.0
Liabilities
Loss and loss adjustment expense reserves	3,059.8	5,702.3
Unearned insurance and reinsurance premiums	1,067.1	846.9
Variable annuity benefit guarantee	672.4	768.5
Debt	676.6	677.5
Deferred tax liability	399.7	365.5
Accrued incentive compensation	144.7	187.9
Ceded reinsurance payable	138.6	134.6
Funds held under reinsurance treaties	33.8	42.9
Accounts payable on unsettled investment purchases	47.7	34.6
Other liabilities	461.8	527.8
Liabilities held for sale	2,388.2	107.6
Total liabilities	9,090.4	9,396.1
Equity
White Mountains' common shares at $1 par value per share - authorized 50,000,000 shares; issued and outstanding 6,583,653 and 7,577,855 shares	6.6	7.6
Paid-in surplus	1,095.6	1,253.7
Retained earnings	2,577.4	2,789.7
Accumulated other comprehensive income, after-tax:
Equity in net unrealized losses from investments in unconsolidated affiliates	59.3	0.0
Net unrealized foreign currency translation gains	80.8	46.1
Pension liability and other	(10.4)	(9.4)
Total White Mountains' common shareholders' equity	3,809.3	4,087.7
Noncontrolling interests
Noncontrolling interest - OneBeacon Ltd.	259.7	273.1
Noncontrolling interest - SIG Preference Shares	250.0	250.0
Noncontrolling Interest Subsidiary HG Global	16.6	0.0
Noncontrolling Interest Subsidiary BAM	(18.0)	0.0
Noncontrolling interest - other	60.8	57.1
Total noncontrolling interests	569.1	580.2
Total equity	4,378.4	4,667.9
Total liabilities and equity	$ 13,468.8	$ 14,064.0

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2012	Dec. 31, 2011
Cash (in dollars)	$ 341.7	$ 453.5
Common shares, par value per share (in dollars per share)	$ 1	$ 1
Common shares, authorized shares	50,000,000	50,000,000
Common shares, issued shares	6,583,653	7,577,855
Common shares, outstanding shares	6,583,653	7,577,855

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($)
$ in Millions

3 Months Ended

9 Months Ended

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2012

Sep. 30, 2011

Revenues:

Earned insurance and reinsurance premiums

$ 536.8

$ 491.1

$ 1,545.3

$ 1,433.5

Net investment income

37.6

42.8

119.8

138.1

Net realized and unrealized investment gains (losses)

72.7

2.9

123.2

36.4

Other revenue

50.3

(35.0)

81.0

(28.3)

Total revenues

697.4

501.8

1,869.3

1,579.7

Expenses:

Loss and loss adjustment expenses

308.1

280.2

821.7

920.4

Insurance and reinsurance acquisition expenses

107.6

107.0

326.2

296.6

Other underwriting expenses

76.6

64.3

228.4

203.9

General and administrative expenses

58.7

36.2

146.3

120.4

Interest expense on debt

11.3

12.8

33.1

38.8

Total expenses

562.3

500.5

1,555.7

1,580.1

Pre-tax income (loss) from continuing operations

135.1

1.3

313.6

(0.4)

Income tax (expense) benefit

(47.8)

0.6

(85.3)

(0.8)

Net income (loss) from continuing operations

87.3

1.9

228.3

(1.2)

Gain (loss) on sale of discontinued operation, net of tax

(91.0)

(18.2)

(91.0)

(18.2)

Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest

(15.8)

(12.0)

(24.5)

(7.8)

Income (loss) before equity in earnings of unconsolidated affiliates

(19.5)

(28.3)

112.8

(27.2)

Equity in earnings of unconsolidated affiliates

7.7

1.5

24.4

16.1

Net income (loss)

(11.8)

(26.8)

137.2

(11.1)

Net (Income) Loss Attributable to Noncontrolling Interest

30.9

11.0

2.0

(21.2)

Net income (loss) attributable to White Mountains' common shareholders

19.1

(15.8)

139.2

(32.3)

Comprehensive income (loss), net of tax:

Change in equity in net unrealized losses from investments in unconsolidated affiliates

32.3

55.1

59.3

77.2

Other Comprehensive Income (Loss) Foreign Currency Translation and Other

39.6

(81.8)

33.3

(25.3)

Comprehensive income

91.0

(42.5)

231.8

19.6

Comprehensive income attributable to noncontrolling interests

0.4

0.0

0.4

0.0

Comprehensive income attributable to White Mountains’ common shareholders

$ 91.4

$ (42.5)

$ 232.2

$ 19.6

Basic income (loss) per share

Continuing operations (in dollars per share)

$ 19.11

$ 1.81

$ 36.96

$ (0.80)

Discontinued operations (in dollars per share)

(16.21)

(3.81)

(16.77)

(3.26)

Total consolidated operations (in dollars per share)

2.90

(2.00)

20.19

(4.06)

Diluted income (loss) per share

Continuing operations (in dollars per share)

19.11

1.81

36.96

(0.80)

Discontinued operations (in dollars per share)

(16.21)

(3.81)

(16.77)

(3.26)

Total consolidated operations (in dollars per share)

2.90

(2.00)

20.19

(4.06)

Dividends declared per White Mountains' common share (in dollars per share)

$ 0.00

$ 1.00

Segment, Discontinued Operations [Member]

Revenues:

Earned insurance and reinsurance premiums

$ (0.4)

$ 233.3

$ 10.0

$ 701.9

Net investment income

0.0

3.8

0.0

11.8

Net realized and unrealized investment gains (losses)

0.0

(6.4)

0.0

1.4

Other revenue

0.0

17.5

0.0

54.0

Total revenues

(0.4)

248.2

10.0

769.1

Expenses:

Loss and loss adjustment expenses

27.7

177.4

48.4

512.3

Insurance and reinsurance acquisition expenses

(0.8)

51.4

(1.3)

154.1

Other underwriting expenses

(1.1)

35.0

1.1

83.9

General and administrative expenses

0.0

1.7

0.0

37.5

Total expenses

25.8

265.5

48.2

787.8

Gain (loss) on sale of discontinued operation, net of tax

(91.0)

(18.2)

(91.0)

18.2

Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest

(15.8)

(12.0)

(24.5)

(7.8)

Net income (loss) attributable to White Mountains' common shareholders

^[1]

$ (105.3)

$ (29.9)

$ (114.0)

$ (25.8)

[1]	(2) Net loss attributable to White Mountains’ common shareholders, net of restricted share amounts, is equal to undistributed loss for the three and nine months ended September 30, 2012 and 2011.

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions	Total	Common shareholders' equity.	Common shares and paid-in surplus	Retained earnings	Accum. Other comprehensive income (loss),after-tax	Non-controlling interest
Balances at Dec. 31, 2010		$ 3,653.0	$ 1,359.0	$ 2,175.6	$ 118.4	$ 607.8
Increase (Decrease) in Shareholders' Equity
Net income (loss)	$ (11.1)	(32.3)	0.0	(32.3)	0.0	21.2
Other comprehensive income, after-tax		52.0	0.0	0.0	52.0	0.0
Dividends declared on common shares		(8.0)	0.0	(8.0)	0.0	0.0
Dividends to noncontrolling interests		0.0	0.0	0.0	0.0	(47.2)
Repurchases and retirements of common shares	(93.2)	(229.8)	(98.5)	(131.3)	0.0	0.0
Issuances of common shares		0.9	0.9	0.0	0.0	0.0
Net distributions to noncontrolling interests		0.0	0.0	0.0	0.0	(7.7)
Amortization of restricted share and option awards		8.9	8.9	0.0	0.0	0.3
Balances at Sep. 30, 2011		3,444.7	1,270.3	2,004.0	170.4	574.4
Balances at Dec. 31, 2010		3,653.0	1,359.0	2,175.6	118.4	607.8
Balances at Dec. 31, 2011	4,667.9	4,087.7	1,261.3	2,789.7	36.7	580.2
Increase (Decrease) in Shareholders' Equity
Net income (loss)	137.2	139.2	0.0	139.2	0.0	(2.0)
Other comprehensive income, after-tax		93.0	0.0	0.0	93.0	(0.4)
Dividends declared on common shares		(6.6)	0.0	(6.6)	0.0	0.0
Dividends to noncontrolling interests		0.0	0.0	0.0	0.0	(24.5)
Repurchases and retirements of common shares	(107.6)	(517.5)	(172.6)	(344.9)	0.0	0.0
Issuances of common shares		5.8	5.8	0.0	0.0	0.0
Net distributions to noncontrolling interests		0.0	0.0	0.0	0.0	13.0
Amortization of restricted share and option awards		9.9	9.9	0.0	0.0	0.6
Balances at Sep. 30, 2012	$ 4,378.4	3,809.3	1,102.2	2,577.4	129.7	569.1
Increase (Decrease) in Shareholders' Equity
Fair Value of Net Assets Acquired		$ (2.2)	$ (2.2)	$ 0.0	$ 0.0	$ 2.2

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Cash flows from operations:
Net income (loss)	$ (11.8)	$ (26.8)	$ 137.2	$ (11.1)
Charges (credits) to reconcile net income to net cash (used for) provided from operations:
Net realized and unrealized investment gains (losses)	(72.7)	(2.9)	(123.2)	(36.4)
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	15.8	12.0	24.5	7.8
Gain (loss) on sale of discontinued operation, net of tax	91.0	18.2	91.0	18.2
Undistributed equity in earnings from unconsolidated affiliates, net of tax	(7.7)	(1.5)	(24.4)	(16.1)
Deferred income tax expense (benefit)			50.4	(45.6)
Other operating items:
Net change in loss and loss adjustment expense reserves			(241.6)	46.3
Net change in reinsurance recoverable on paid and unpaid losses			98.1	102.9
Net change in unearned insurance and reinsurance premiums			206.6	190.8
Net change in funds held by ceding companies			5.3	(17.2)
Net change in variable annuity benefit guarantee liabilities			(96.1)	151.1
Net change in variable annuity derivative instruments			48.3	(6.3)
Net change in deferred acquisition costs			(21.9)	(31.2)
Net change in ceded unearned premiums			(22.1)	(25.4)
Net change in funds held under reinsurance treaties			1.9	(46.0)
Net change in insurance and reinsurance premiums receivable			(206.9)	(165.0)
Net change in ceded reinsurance payable			31.5	44.2
Net change in other assets and liabilities, net			68.4	13.5
Net cash used for operations - continuing operations			27.0	174.5
Net cash (used for) provided from operations - discontinued operations			(155.6)	(133.9)
Net cash used for operations			(128.6)	40.6
Cash flows from investing activities:
Net change in short-term investments			(127.3)	112.6
Sales of fixed maturity and convertible fixed maturity investments			4,918.8	2,905.7
Maturities, calls and paydowns of fixed maturity and convertible fixed maturity investments			408.7	1,015.3
Sales of common equity securities			99.7	125.4
Distributions and redemptions of other long-term investments			20.9	90.0
Proceeds from Divestiture of Interest in Subsidiaries and Affiliates			9.8	0.0	$ 1,010.0
Purchases of other long-term investments			(28.8)	(30.6)
Contributions to discontinued operations			(155.6)	(248.5)
Purchases of common equity securities			(284.2)	(189.0)
Purchases of fixed maturity and convertible fixed maturity investments			(4,239.0)	(3,497.6)
Net change in unsettled investment purchases and sales			(149.5)	54.0
Net acquisitions of property and equipment			(1.5)	(3.3)
Net cash provided from investing activities - continuing operations			472.0	334.0
Net cash used for investing activities - discontinued operations			155.6	325.1
Net cash provided from investing activities			627.6	659.1
Cash flows from financing activities:
Repayment of debt			0.0	(161.6)
Cash dividends paid to the Company's common shareholders			(6.6)	(8.0)
Cash dividends paid to OneBeacon Ltd.'s noncontrolling common shareholders			(14.9)	(37.9)
Cash dividends paid on SIG Preference Shares			(9.4)	(9.4)
Common shares repurchased			(517.5)	(229.7)
Proceeds from issuances of common shares			0.0	0.9
Net cash used for financing activities - continuing operations			(548.4)	(445.7)
Net cash provided from financing activities - discontinued operations			0.0	0.0
Net cash used for financing activities			(548.4)	(445.7)
Effect of exchange rate changes on cash			3.0	(2.0)
Net change in cash during the period			(46.4)	252.0
Net change in cash from discontinued operations			0.0	(191.2)
Cash reclassified from assets held for sale (net of cash sold of $3.5 and $0)			2.0	0.0
Cash balances at beginning of period (excludes restricted cash balances of $453.5 and $286.7 and AutoOne cash of $0 and $4.7)			251.9	103.6	103.6
Cash balances at end of period (excludes restricted cash balances of $ 341.7 and $393.3)	$ 207.5	$ 164.4	207.5	164.4	$ 251.9
Supplemental cash flows information:
Interest paid			(21.4)	(38.5)
Net income tax payments to national governments			$ (6.5)	$ (6.4)

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
CashIncluedInAssetsHeldForSale		$ 0.0
Restricted cash balances, beginning of period	$ 453.5
Restricted cash balances, end of period	341.7
Cash reclassified from assets held for sale, cash sold	3.5
AutoOne Cash, beginning of period	0.0
AutoOne Cash, end of period	$ 0.0

- Definition

For the disposal group, including a component of the entity (discontinued operation), cash includes currency on hand as well as demand deposits with banks or financial institutions. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

+ References + Details

Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2012
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation These interim consolidated financial statements include the accounts of White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”) and its subsidiaries (collectively, with the Company, “White Mountains”) and have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”). The Company is an exempted Bermuda limited liability company whose principal businesses are conducted through its property and casualty insurance and reinsurance subsidiaries and affiliates. The Company’s headquarters is located at 14 Wesley Street, Hamilton, Bermuda HM 11, its principal executive office is located at 80 South Main Street, Hanover, New Hampshire 03755-2053 and its registered office is located at Clarendon House, 2 Church Street, Hamilton, Bermuda HM 11. White Mountains’ reportable segments are OneBeacon, Sirius Group and Other Operations. As discussed further in Note 2, on October 7, 2011, White Mountains completed its sale of Esurance Holdings, Inc. and its subsidiaries (“Esurance Insurance”) and Answer Financial Inc. and its subsidiaries (“AFI”) (collectively, “Esurance”). Esurance has been presented as discontinued operations. (See Note 14 for discontinued operations). The OneBeacon segment consists of OneBeacon Insurance Group, Ltd. (“OneBeacon Ltd.”), an exempted Bermuda limited liability company that owns a family of U.S.-based property and casualty insurance companies (collectively “OneBeacon”), most of which operate in a multi-company pool. OneBeacon is a specialty property and casualty insurance writer that offers a wide range of insurance products through independent agencies, regional and national brokers, wholesalers and managing general agencies. As of September 30, 2012 and December 31, 2011, White Mountains owned 75.2% and 75.5% of OneBeacon Ltd.’s outstanding common shares. As discussed further in Note 2, OneBeacon entered into a definitive agreement to sell its runoff business in October 2012 and sold its AutoOne Insurance business (“AutoOne”) in February 2012. The runoff business and AutoOne are presented as discontinued operations. Assets and liabilities associated with the runoff business as of September 30, 2012 and AutoOne as of December 31, 2011 have been presented as held for sale in the financial statements. Prior year income statement and cash flow amounts have been reclassified to conform to the current year’s presentation. (See Note 14 for discontinued operations). The Sirius Group segment consists of Sirius International Insurance Group, Ltd., an exempted Bermuda limited liability company, and its subsidiaries (collectively, “Sirius Group”). Sirius Group provides insurance and reinsurance products for property, accident and health, aviation and space, trade credit, marine, agriculture and certain other exposures on a worldwide basis through its subsidiaries, Sirius International Insurance Corporation (“Sirius International”), Sirius America Insurance Company (“Sirius America”) and Lloyds Syndicate 1945 (“Syndicate 1945”). Sirius Group also specializes in the acquisition and management of runoff insurance and reinsurance companies both in the United States and internationally through its White Mountains Solutions division. On December 31, 2011, Sirius Group completed a transaction led by White Mountains Solutions to acquire the runoff loss reserve portfolio of Old Lyme Insurance Company Ltd. (“Old Lyme”). Sirius Group also includes Scandinavian Reinsurance Company, Ltd. (“Scandinavian Re”) and Central National Insurance Company of Omaha (“Central National”), which are both in runoff. White Mountains’ Other Operations segment consists of the Company and its intermediate holding companies, its wholly-owned investment management subsidiary, White Mountains Advisors LLC (“WM Advisors”), White Mountains’ variable annuity reinsurance business, White Mountains Life Reinsurance (Bermuda) Ltd. (“WM Life Re”), which is in runoff, as well as various other entities not included in other segments. For 2011, the Other Operations segment also included the consolidated results of the Tuckerman Capital, LP fund (“Tuckerman Fund I”). On December 31, 2011, Tuckerman Fund I liquidated and distributed all of its assets, which consisted of shares of two small manufacturing companies, Hamer, LLC (“Hamer”) and Bri-Mar Manufacturing, LLC (“Bri-Mar”), to its partners, including White Mountains. Commencing on January 1, 2012, the consolidated results of Hamer and Bri-Mar are included in the Other Operations segment. In July 2012, White Mountains capitalized HG Global Ltd. ("HG Global") to fund Build America Mutual Assurance Company ("BAM"), a newly formed mutual municipal bond insurer, and HG Re, Ltd. ("HG Re"), a wholly-owned subsidiary of HG Global. As of September 30, 2012, White Mountains owned 97% of HG Global's preferred equity and 89% of its common equity. HG Global provided the initial capitalization of BAM through the purchase of surplus notes. Through HG Re, HG Global provides first loss reinsurance protection for policies underwritten by BAM of 15% of par outstanding, on a per policy basis. HG Re's obligations to BAM are collateralized in trusts, and there is an aggregate loss limit that is equal to the total assets in the collateral trusts at any point in time. HG Global and BAM are both included in the Other Operations segment. U.S. GAAP requires White Mountains to consolidate the results of BAM. However, BAM is a mutual insurance company owned by its members and its equity and results of operations are included in noncontrolling interests. White Mountains’ discontinued operations consist of Esurance Insurance, AFI, OneBeacon's runoff business and AutoOne. Esurance Insurance wrote personal auto insurance directly to customers in 30 states through its website and over the phone and also sold other lines of personal insurance for unaffiliated insurance companies. Esurance Insurance also wrote personal auto policies through select online agents and provided other insurance products through partnerships with industry leading online providers. Esurance Insurance earned commissions and fees by referring to unaffiliated insurance companies those shoppers that it could not underwrite because of pricing or underwriting eligibility. AFI sold insurance online and through call centers for both Esurance Insurance and unaffiliated companies utilizing a comparison quoting platform. AutoOne was formed by OneBeacon in 2001 to provide products and services to automobile assigned risk markets primarily in New York and New Jersey. All significant intercompany transactions have been eliminated in consolidation. These interim financial statements include all adjustments considered necessary by management to fairly present the financial position, results of operations and cash flows of White Mountains. These interim financial statements may not be indicative of financial results for the full year and should be read in conjunction with the Company’s 2011 Annual Report on Form 10-K. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Refer to the Company’s 2011 Annual Report on Form 10-K for a complete discussion regarding White Mountains’ significant accounting policies. Noncontrolling Interests Noncontrolling interests consist of the ownership interests of noncontrolling parties in consolidated entities and are presented separately as a component of equity on the balance sheet. The percentage of the noncontrolling equity interests in OneBeacon Ltd. at September 30, 2012 and December 31, 2011 was 24.8% and 24.5%. In July 2012, HG Global was capitalized with $594.5 million from White Mountains and $14.5 million from certain management members of BAM, the latter of which is included in noncontrolling interest. Upon closing, certain BAM management members also received additional common and preferred shares of HG Global that resulted in a $2.2 million allocation of the carrying value of White Mountains' investment in HG Global to the noncontrolling interest, which was recorded as an adjustment to paid-in surplus in White Mountains' consolidated statement of changes in equity. White Mountains is required to consolidate BAM in its GAAP financial statements. However, since BAM is a mutual insurance company that is owned by its members and not White Mountains, BAM's results do not affect White Mountains' common shareholders' equity as they are attributable to noncontrolling interests. For the third quarter of 2012, BAM reported $18 million in pre-tax losses that have been allocated to noncontrolling interest. In May 2007, Sirius International Group, Ltd. (“SIG”), an intermediate holding company of Sirius Group, issued $250 million non-cumulative perpetual preference shares with a $1,000 per share liquidation preference (the “SIG Preference Shares”). Proceeds of $245.7 million, net of $4.3 million of issuance costs and commissions, were received from the issuance. The SIG Preference Shares are included in noncontrolling interests on the balance sheet. At September 30, 2012 and December 31, 2011, the noncontrolling equity interest in limited partnerships that are consolidated with White Mountains (the Prospector Offshore Fund, the Prospector Turtle Fund and Tuckerman Fund I prior to December 31, 2011) was $52.8 million and $54.2 million. On December 31, 2011, Tuckerman Fund I was dissolved and all of the net assets of the fund, which consisted of common stock of Hamer and Bri-Mar, were distributed. At September 30, 2012, the noncontrolling equity interest in Hamer and Bri-Mar was $4.5 million. At September 30, 2012 and December 31, 2011, the noncontrolling equity interest in A.W.G. Dewar Inc, a subsidiary of OneBeacon, was $3.2 million and $2.3 million. At September 30, 2012 and December 31, 2011, the noncontrolling equity interest in Passage2Health Limited, a subsidiary of Sirius Group, was $0.3 million and $0.6 million. Recently Adopted Changes in Accounting Principles Policy Acquisition Costs On January 1, 2012, White Mountains adopted ASU 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts (ASC 944). The new standard changes the types of policy acquisition costs that are eligible for deferral. Specifically, the new guidance limits deferrable costs to those that are incremental direct costs of contract acquisition and certain costs related to acquisition activities performed by the insurer, such as underwriting, policy issuance and processing, medical and inspection costs and sales force contract selling. The ASU defines incremental direct costs as those costs that result directly from and were essential to the contract acquisition and would not have been incurred absent the acquisition. Accordingly, under the new guidance, deferrable acquisition costs are limited to costs related to successful contract acquisitions. Acquisition costs that are not eligible for deferral are to be charged to expense in the period incurred. White Mountains adopted ASU 2010-26 prospectively. Upon adoption, certain acquisition costs, primarily a portion of the profit sharing commissions associated with OneBeacon’s collector car and boats business, no longer meet the criteria for deferral. Deferred acquisition costs of $5.6 million at January 1, 2012 that no longer meet the criteria for deferral under ASU 2010-26 will be recognized in expense over the original amortization periods. For the three and nine months ended September 30, 2012, White Mountains recognized $0.9 million and $5.3 million of expense related to such previously deferrable acquisition costs. If White Mountains had adopted ASU 2010-26 retrospectively, $1.4 million and $5.7 million of acquisition costs that were deferred would have been recognized in expense for the three and nine months ended September 30, 2011. Fair Value Measurements On January 1, 2012, White Mountains adopted ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRS. The ASU clarifies existing guidance with respect to the concepts of highest and best use and valuation premise and measuring instruments classified within a reporting entity’s shareholders’ equity. The ASU also clarifies disclosure requirements, requiring disclosure of quantitative information about unobservable inputs used in Level 3 fair value measurements. The ASU also amends existing guidance. In circumstances where a reporting entity manages a portfolio of financial assets and liabilities based on the net market and counterparty credit risk exposures, the ASU permits determination of the fair value of those instruments to be based on the net risk exposure. In addition, the ASU permits the application of premiums or discounts to be applied in a fair value measurement to the extent that market participants would consider them in valuing the financial instruments. The ASU also expands the required disclosures for Level 3 measurements, requiring that reporting entities provide a narrative description of the sensitivity of Level 3 fair value measurements to changes in unobservable inputs and the interrelationships between those inputs, if any. As a result of adopting ASU 2011-04, White Mountains expanded its fair value disclosures. (See Note 5). Comprehensive Income For fiscal periods beginning after December 15, 2011, ASU 2011-05, Comprehensive Income, became effective, which requires all components of comprehensive income to be reported in a continuous financial statement or in consecutive statements displaying the components of net income and the components of other comprehensive income. Since White Mountains previously presented comprehensive income in a continuous financial statement, adoption of ASU 2011-05 had no effect on White Mountains’ financial statement presentation. Recently Issued Accounting Pronouncements Offsetting Assets and Liabilities On December 16, 2011, the FASB issued ASU 2011-11, Disclosures about Offsetting Assets and Liabilities (ASC 210). The new standard expands the required disclosures in circumstances where either balances have been offset or the right of offset exists. The required disclosures are intended to provide information to enable financial statement users to evaluate the effect or potential effect of netting arrangements on a reporting entity’s financial position. Disclosures required under the new standard include the gross amount of assets and liabilities recognized; the amounts that have been offset to arrive at the amounts presented in the statement of financial position; and for any amounts subject to an enforceable master netting arrangement, whether such amounts have been offset. In addition, a description of the rights of offset should be disclosed. ASU 2011-11 is effective for periods beginning on or after January 1, 2013. White Mountains is party to master netting arrangements in connection with the derivative instruments held by WM Life Re and is currently evaluating the effect of adoption will have on its disclosures, but does not expect adoption to have a material effect on its financial position, results of operations or cash flows.

Significant Transactions	9 Months Ended
Significant Transactions	Sep. 30, 2012
Significant Transactions Disclosure
Significant Transactions	Significant Transactions Formation of HG Global and BAM In July 2012, White Mountains capitalized HG Global with $594.5 million to fund BAM, a newly formed mutual municipal bond insurer. As of September 30, 2012, White Mountains owned 97% of HG Global's preferred equity and 89% of its common equity. HG Global provided the initial capitalization of BAM through the purchase of $503.0 million of BAM surplus notes. Through HG Re, HG Global provides first loss reinsurance protection for policies underwritten by BAM of 15% of par outstanding, on a per policy basis. HG Re's obligations to BAM are collateralized in trusts, and there is an aggregate loss limit that is equal to the total assets in the collateral trusts at any point in time. U.S. GAAP requires White Mountains to consolidate BAM in its financial statements. However, since BAM is a mutual insurance company that is owned by its members and not White Mountains, BAM's results do not affect White Mountains' common shareholders' equity as they are attributable to noncontrolling interests. For the three and nine months ended September 30, 2012, HG Global had pre-tax income of $4.8 million, which included $8.3 million of interest income on the BAM surplus notes. For the three and nine months ended September 30, 2012, BAM had a pre-tax loss of $18.0 million that was recorded in net loss attributable to noncontrolling interests, which included $8.3 million of interest expense on its surplus notes. Sale of OneBeacon runoff business On October 17, 2012, one of OneBeacon's indirect wholly-owned subsidiaries, OneBeacon Insurance Group LLC, entered into a definitive agreement with Trebuchet US Holdings, Inc. (“Trebuchet”), a wholly-owned subsidiary of Armour Group Holdings Limited (together with Trebuchet, “Armour”), to sell its runoff business (the "Runoff Transaction"). Pursuant to the terms of the agreement, at closing OneBeacon will transfer to Trebuchet all of the issued and outstanding shares of common stock of certain legal entities that will contain the assets, liabilities (including gross and ceded loss reserves) and capital supporting the runoff business as well as certain elements of the runoff business infrastructure, including staff and office space. Additionally, as part of the Runoff Transaction, OneBeacon may provide financing in the form of surplus notes. The transaction is subject to regulatory approvals and is expected to close in the second half of 2013. During the third quarter of 2012, OneBeacon recorded $100.5 million in after-tax losses related to the Runoff Transaction. These losses are presented in discontinued operations and are composed of a $91.5 million after-tax loss on sale and a $9.0 million after-tax loss related to an reduction in the workers compensation loss reserve discount rate on reserves being transferred as part of the sale. OneBeacon also recognized $6.5 million of after-tax underwriting losses primarily related to unfavorable loss reserve development from a legacy assumed reinsurance treaty, which is presented in discontinued operations (see Note 14). Sale of AutoOne On February 22, 2012, OneBeacon completed the sale of AutoOne to Interboro Holdings, Inc. (“Interboro”). OneBeacon formed AutoOne in 2001 to provide products and services to automobile assigned risk markets primarily in New York and New Jersey. OneBeacon transferred to the buyer AutoOne Insurance Company (“AOIC”) and AutoOne Select Insurance Company (“AOSIC”), which contained the assets, liabilities (including loss reserves and unearned premiums), and the capital of the AutoOne business, and transferred substantially all of the AutoOne infrastructure including systems and office space as well as certain staff. As a result of the sale, AutoOne is reported as discontinued operations (see Note 14). Sale of Esurance On October 7, 2011, White Mountains completed the sale of Esurance Insurance and AFI to The Allstate Corporation (“Allstate”) for $700 million plus tangible book value. White Mountains recorded a gain on the sale of $677.5 million in discontinued operations in the fourth quarter of 2011. The transaction is subject to a true-up of the estimated tangible book value of the entities sold through the date of closing and certain other contingencies (see Note 14). Share Repurchases On March 22, 2012, White Mountains completed a fixed-price tender offer and repurchased 816,829 of its common shares at $500 per share. The total cost of the share repurchase was $408.6 million, including fees and expenses. During 2011, White Mountains completed two “modified Dutch auction” self-tender offers and repurchased 332,346 of its common shares at an average price of $418 per share. The total cost of the share repurchases was $138.8 million, including fees and expenses. In addition to the tender offers, which were separately authorized, the board of directors has authorized the Company to repurchase its common shares, from time to time, subject to market conditions. In 2006, White Mountains’ board of directors authorized the Company to repurchase up to 1,000,000 of its common shares and in 2010 White Mountains’ board of directors authorized the Company to repurchase an additional 600,000 of its common shares. On May 25, 2012, White Mountains' board of directors authorized the Company to repurchase an additional 1,000,000 of its common shares. Shares may be repurchased on the open market or through privately negotiated transactions. The repurchase authorization does not obligate the Company to acquire any specific number of shares, nor is there a stated expiration date. During the three and nine months ended September 30, 2012, the Company repurchased 50,000 and 217,801 common shares for $26.4 million and $107.6 million under this program. During the nine months ended September 30, 2011, the Company repurchased 265,768 common shares for $93.2 million. Since the inception of this authorization through September 30, 2012, the Company repurchased 1,629,504 common shares for $645.1 million. At September 30, 2012, the Company may repurchase an additional 970,496 shares under this authorization.

Loss and Loss Adjustment Expense Reserves

9 Months Ended

Sep. 30, 2012

Insurance Loss Reserves [Abstract]

Loss and Loss Adjustment Expense Reserves

The following table summarizes the loss and loss adjustment expense (“LAE”) reserve activities of White Mountains’ insurance and reinsurance subsidiaries for the three and nine months ended September 30, 2012 and 2011:



	Three Months Ended						Nine Months Ended
	September 30,						September 30,
Millions	2012			2011			2012			2011
Gross beginning balance	$	5,329.8		$	5,642.4		$	5,702.3		$	5,736.8
Less beginning reinsurance recoverable on unpaid losses	(2,369.4		)	(2,193.0		)	(2,507.3		)	(2,344.0		)
Net loss and LAE reserves	2,960.4			3,449.4			3,195.0			3,392.8

Less: Beginning net loss and LAE reserves for AutoOne and OneBeacon's runoff business⁽¹⁾	(296.0		)	(503.2		)	(384.1		)	(620.6		)

Loss and LAE incurred relating to:
Current year losses	318.2			307.1			842.9			968.0
Prior year losses	(10.1		)	(26.9		)	(21.2		)	(47.6		)
Total incurred losses and LAE	308.1			280.2			821.7			920.4

Accretion of fair value adjustment to loss and LAE reserves	1.1			2.1			9.4			6.2
Foreign currency translation adjustment to loss and LAE reserves	12.0			(25.5		)	11.7			5.7

Loss and LAE paid relating to:
Current year losses	(101.1		)	(109.7		)	(223.9		)	(226.3		)
Prior year losses	(181.5		)	(186.9		)	(726.8		)	(571.8		)
Total loss and LAE payments	(282.6		)	(296.6		)	(950.7		)	(798.1		)

Plus: Ending net loss and LAE reserves for AutoOne and OneBeacon's runoff business (1)	—			394.4			—			394.4

Net ending balance	2,703.0			3,300.8			2,703.0			3,300.8
Plus ending reinsurance recoverable on unpaid losses	356.8			2,581.2			356.8			2,581.2
Gross ending balance	$	3,059.8		$	5,882.0		$	3,059.8		$	5,882.0
⁽¹⁾Loss and LAE reserve balances for OneBeacon's run-off business prior to September 30, 2012 and AutoOne prior to September 30, 2011 were not classified as held for sale. Adjustment is to present loss and LAE reserve activities from continuing operations.

Loss and LAE incurred relating to prior year losses for the three and nine months ended September 30, 2012

During the three and nine months ended September 30, 2012, White Mountains experienced $10.1 million and $21.2 million of net favorable loss reserve development.

For the three and nine months ended September 30, 2012, OneBeacon had net favorable loss reserve development of $2.3 million and $7.6 million, primarily related to professional liability lines, multiple peril liability lines and other general liability lines.

For the three and nine months ended September 30, 2012, Sirius Group had net favorable loss reserve development of $7.8 million and $13.6 million. With the completion of a ground-up asbestos reserve study in the quarter, Sirius Group increased asbestos loss reserves by $33.0 million and $45.0 million in the three and nine months ended September 30, 2012. These increases were more than offset by reductions in liability and property loss reserves.

Loss and LAE incurred relating to prior year losses for the three and nine months ended September 30, 2011

During the three and nine months ended September 30, 2011, White Mountains experienced $26.9 million and $47.6 million of net favorable loss reserve development.

For the three and nine months ended September 30, 2011, OneBeacon had net favorable loss reserve development of $6.0 million and $14.4 million, primarily related to professional liability lines, multiple peril liability lines and other general liability lines.

For the three and nine months ended September 30, 2011, Sirius Group had net favorable loss reserve development of $20.9 million and $33.2 million, primarily attributable to property lines.

Fair value adjustment to loss and LAE reserves

In connection with purchase accounting for acquisitions, White Mountains was required to adjust loss and LAE reserves and the related reinsurance recoverables to fair value on their respective acquired balance sheets. The net reduction to loss and LAE reserves is being recognized through an income statement charge ratably with and over the period the claims are settled. White Mountains recognized $1.1 million and $9.4 million of such charges, recorded as loss and LAE for the three and nine months ended September 30, 2012, and $2.1 million and $6.2 million for the three and nine months ended September 30, 2011. Accretion of fair value adjustment to losses and LAE reserves for the nine months ended September 30, 2012 included $5.0 million from the first quarter of 2012 due to the acceleration of the amortization of the purchase accounting established for the acquisition of Scandinavian Re. This acceleration was a result of a final settlement and commutation of Scandinavian Re’s multi-year retrocessional Casualty Aggregate Stop Loss Agreement with St. Paul Fire & Marine Insurance Company (“St Paul”). As of September 30, 2012, the remaining unamortized fair value adjustment for Scandinavian Re was $2.0 million.

- Definition

The entire disclosure for liabilities related to future policy benefits and unpaid claims and claim adjustments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 6
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 94-5
-Paragraph 11
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 60
-Paragraph 60
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 13
-Article 7

+ Details

Third Party Reinsurance

9 Months Ended

Sep. 30, 2012

Reinsurance Disclosures [Abstract]

Third Party Reinsurance

Note 4. Third Party Reinsurance

In the normal course of business, White Mountains’ insurance and reinsurance subsidiaries may seek to limit losses that may arise from catastrophes or other events by reinsuring with third party reinsurers. White Mountains remains liable for risks reinsured in the event that the reinsurer does not honor its obligations under reinsurance contracts.

OneBeacon

At September 30, 2012, OneBeacon had $2.0 million of reinsurance recoverables on paid losses and $41.3 million that will become recoverable if claims are paid in accordance with current reserve estimates. The reinsurance balances associated with the runoff business are included in discontinued operations (see Note 14). OneBeacon is selective with its reinsurers, placing reinsurance with only those reinsurers having a strong financial condition. OneBeacon monitors the financial strength of its reinsurers on an ongoing basis. Uncollectible amounts historically have not been significant.

Effective May 1, 2012, OneBeacon renewed its property catastrophe reinsurance program through April 30, 2013. The program provides coverage for OneBeacon’s property business as well as certain acts of terrorism. Under the program, the first $25 million of losses resulting from any single catastrophe are retained and the next $155 million of losses resulting from the catastrophe are reinsured in three layers, OneBeacon retains a co-participation of 55% of losses from $25 million to $40 million, 15% of losses from $40 million to $80 million and 10% of losses from $80 million to $180 million. Thus, for a $180 million loss, OneBeacon would retain $49.3 million. Any loss above $180 million would be retained in full. In the event of a catastrophe, OneBeacon’s property catastrophe reinsurance program is reinstated for the remainder of the original contract term by paying a reinstatement premium that is based on the percentage of coverage reinstated and the original property catastrophe coverage premium.

The following table provides a listing of OneBeacon’s top reinsurers, based upon recoverable amounts, the percentage of total paid and unpaid reinsurance recoverables and the reinsurer’s A.M Best Company, Inc. (“A.M. Best”) rating.



Top Reinsurers (Millions)	Balance at September 30, 2012		% of Total		A.M. Best Rating ⁽¹⁾
Hannover Ruckversich	$	6.4	15	%	A+
Hartford Steam Boiler	4.6		11	%	A++
Munich Reinsurance America	4.5		10	%	A+
Platinum Underwriters Re	4.1		9	%	A
Transatlantic Reinsurance	2.0		5	%	A

¹⁾A.M. Best ratings as detailed above are: “A++” (Superior, which is the highest of fifteen financial strength ratings), “A+” (Superior, which is the second highest of fifteen financial strength ratings) and “A” (Excellent, which is the third highest of fifteen financial strength ratings).

Sirius Group

At September 30, 2012, Sirius Group had $12.7 million of reinsurance recoverables on paid losses and $315.5 million of reinsurance that will become recoverable if claims are paid in accordance with current reserve estimates. Because reinsurance contracts do not relieve Sirius Group of its obligation to its ceding companies, the collectability of balances due from its reinsurers is important to Sirius Group’s financial strength. Sirius Group monitors the financial strength of its reinsurers on an ongoing basis.

The following table provides a listing of Sirius Group’s top reinsurers based upon recoverable amounts, the percentage of total paid and unpaid reinsurance recoverables and the reinsurers’ A.M. Best ratings.



Top Reinsurers (Millions)	Balance at September 30, 2012		% of Total		A.M. Best Rating ⁽¹⁾	% Collateralized
General Reinsurance Corporation	$	42.3	13	%	A++	1	%
Swiss Re Group	33.7		10	%	A+	5	%
Lloyds of London ⁽²⁾	29.9		9	%	A	4	%
Olympus⁽³⁾	28.8		9	%	NR-5	100	%
Michigan Catastrophic Claims Association ⁽⁴⁾	14.6		4	%	N/A	—	%

⁽¹⁾A.M. Best ratings as detailed above are: “A++” (Superior, which is the highest of fifteen financial strength ratings), “A+” (Superior, which is the second highest of fifteen financial strength ratings), “A” (Excellent, which is the third highest of fifteen financial strength ratings) and “NR-5” (Not formally followed).

⁽²⁾Represents the total of reinsurance recoverables due to Sirius Group from all Lloyds Syndicates.

⁽³⁾Non-U.S. insurance entity. The balance is fully collateralized through funds held, letters of credit or trust agreements.

⁽⁴⁾ Michigan Catastrophic Claims Association ("MCCA") is a non-profit unincorporated association., established by the State of Michigan with the power to issue and collect assessments, to which every insurance company that sells automobile coverage in Michigan is required to be a member. A.M. Best does not rate MCCA. Sirius Group acquired its recoverable from MCCA in the acquisition of Stockbridge Insurance Company. As part of the acquisition, Sirius Group obtained $25.0 of reinsurance protection from the seller (currently rated A+ by A.M. Best) for unfavorable loss reserve development, including uncollectible reinsurance.

- Definition

The entire disclosure pertaining to the existence, magnitude and information about insurance that has been ceded to or assumed from another insurance company, including the methodologies and assumptions used in determining recorded amounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 50
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 113
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 12: http://www.xbrl.org/2003/role/presentationRef
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Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 13
-Article 7

+ Details

Investment Securities

9 Months Ended

Sep. 30, 2012

Investments, Debt and Equity Securities [Abstract]

Investment Securities

White Mountains’ invested assets consist of securities and other long-term investments held for general investment purposes. The portfolio of investment securities includes short-term investments, fixed maturity investments, convertible fixed maturity investments and equity securities which are all classified as trading securities. Trading securities are reported at fair value as of the balance sheet date. Realized and unrealized investment gains and losses on trading securities are reported in pre-tax revenues. White Mountains’ investments in debt securities, including mortgage-backed and asset-backed securities, are generally valued using industry standard pricing models. Key inputs include benchmark yields, benchmark securities, reported trades, issuer spreads, bids, offers, credit ratings and prepayment speeds. Income on mortgage-backed and asset-backed securities is recognized using an effective yield based on anticipated prepayments and the estimated economic life of the securities. When actual prepayments differ significantly from anticipated prepayments, the estimated economic life is recalculated and the remaining unamortized premium or discount is amortized prospectively over the remaining economic life.

Realized investment gains and losses resulting from sales of investment securities are accounted for using the specific identification method. Premiums and discounts on all fixed maturity investments are amortized or accreted to income over the anticipated life of the investment. Short-term investments consist of money market funds, certificates of deposit and other securities which, at the time of purchase, mature or become available for use within one year. Short-term investments are carried at amortized or accreted cost, which approximated fair value as of September 30, 2012 and December 31, 2011.

Other long-term investments primarily comprise White Mountains’ investments in hedge funds and private equity funds.

Net Investment Income

Pre-tax net investment income for the three and nine months ended September 30, 2012 and 2011 consisted of the following:



	Three Months Ended						Nine Months Ended
	Sept 30,						Sept 30,
Millions	2012			2011			2012			2011
Investment income:
Fixed maturity investments	$	33.0		$	38.5		$	105.1		$	127.0
Short-term investments	.5			.9			2.3			3.2
Common equity securities	4.8			3.6			13.8			10.1
Convertible fixed maturity investments	2.0			1.3			5.9			3.9
Other long-term investments	.7			1.2			2.2			1.9
Interest on funds held under reinsurance treaties	—			.2			—			(.6		)
Total investment income	41.0			45.7			129.3			145.5
Less third-party investment expenses	(3.4		)	(2.9		)	(9.5		)	(7.4		)
Net investment income, pre-tax	$	37.6		$	42.8		$	119.8		$	138.1

Net Realized and Unrealized Investment Gains and Losses

Net realized and unrealized investment gains and losses for the three and nine months ended September 30, 2012 and 2011 consisted of the following:



	Three Months Ended						Nine Months Ended
	Sept 30,						Sept 30,
Millions	2012			2011			2012			2011
Net realized investment gains, pre-tax	$	23.7		$	38.3		$	40.5		$	67.7
Net unrealized investment (losses) gains, pre-tax	49.0			(35.4		)	82.7			(31.3		)
Net realized and unrealized investment gains, pre-tax	72.7			2.9			123.2			36.4
Income tax expense attributable to net realized and unrealized investment gains (losses)	(12.3		)	(1.4		)	(28.3		)	(12.7		)
Net realized and unrealized investment gains, after tax	$	60.4		$	1.5		$	94.9		$	23.7

Net realized investment gains (losses)

Net realized investment gains (losses) for the three and nine months ended September 30, 2012 and 2011 consisted of the following:



	Three Months Ended						Nine Months Ended
	Sept 30,						Sept 30,
Millions	2012			2011			2012			2011
Fixed maturity investments	$	29.0		$	14.1		$	69.5		$	3.3
Short-term investments	(3.4		)	.4			(3.9		)	(10.9		)
Common equity securities	3.9			23.1			(2.2		)	41.0
Convertible fixed maturity investments	1.1			(.7		)	3.2			6.3
Other long-term investments	(7.2		)	1.4			(26.4		)	28.0
Forward contracts	.3			—			.3			—
Net realized investment gains, pre-tax	23.7			38.3			40.5			67.7
Income tax expense attributable to net realized investment gains	(7.4		)	(8.3		)	(12.8		)	(20.7		)
Net realized investment gains, after tax	$	16.3		$	30.0		$	27.7		$	47.0

Net unrealized investment gains (losses)

The following table summarizes changes in the carrying value of investments measured at fair value:



	Three Months Ended									Nine Months Ended
	September 30, 2012									September 30, 2012
Millions	Net unrealized gains (losses)			Net foreign exchange gains (losses)			Total changes in fair value reflected in earnings			Net unrealized gains (losses)			Net foreign exchange gains (losses)			Total changes in fair value reflected in earnings
Fixed maturity investments	$	27.2		$	(40.6	)	$	(13.4	)	$	35.5		$	(36.9	)	$	(1.4	)
Short-term investments	—			.1			.1			—			.1			.1
Common equity securities	65.1			(.1		)	65.0			71.5			(.1		)	71.4
Convertible fixed maturity investments	(.6		)	—			(.6		)	(2.9		)	—			(2.9		)
Other long-term investments	1.6			(3.7		)	(2.1		)	18.2			(2.7		)	15.5
Net unrealized investment gains (losses), pre-tax	93.3			(44.3		)	49.0			122.3			(39.6		)	82.7
Income tax expense attributable to net unrealized investment (losses) gains	(16.7		)	11.8			(4.9		)	(25.9		)	10.4			(15.5		)
Net unrealized investment gains (losses), after tax	$	76.6		$	(32.5	)	$	44.1		$	96.4		$	(29.2	)	$	67.2



	Three Months Ended									Nine Months Ended
	September 30, 2011									September 30, 2011
Millions	Net unrealized gains (losses)			Net foreign exchange gains (losses)			Total changes in fair value reflected in earnings			Net unrealized gains (losses)			Net foreign exchange gains (losses)			Total changes in fair value reflected in earnings
Fixed maturity investments	$	3.5		$	67.5		$	71.0		$	12.6		$	77.7		$	90.3
Short-term investments	(.1		)	(.4		)	(.5		)	(.1		)	(1.4		)	(1.5		)
Common equity securities	(101.0		)	(.9		)	(101.9		)	(95.1		)	(1.8		)	(96.9		)
Convertible fixed maturity investments	(11.2		)	—			(11.2		)	(19.3		)	—			(19.3		)
Other long-term investments	(1.2		)	8.4			7.2			(8.4		)	4.5			(3.9		)
Net unrealized investment (losses) gains, pre-tax	(110.0		)	74.6			(35.4		)	(110.3		)	79.0			(31.3		)
Income tax benefit (expense) attributable to net unrealized investment gains (losses)	26.4			(19.5		)	6.9			28.5			(20.5		)	8.0
Net unrealized investment (losses) gains, after tax	$	(83.6	)	$	55.1		$	(28.5	)	$	(81.8	)	$	58.5		$	(23.3	)

The following table summarizes the amount of total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments for the three and nine months ended September 30, 2012 and 2011:



	Three Months Ended						Nine Months Ended
	Sept 30,						Sept 30,
Millions	2012			2011			2012		2011
Fixed maturity investments	$	(1.0	)	$	(13.5	)	$	7.3	$	(14.9	)
Common equity securities	.8			(17.5		)	1.8		(17.0		)
Convertible fixed maturities	—			—			—		—
Other long-term investments	2.9			(3.2		)	11.3		(6.5		)
Total unrealized investment losses, pre-tax - Level 3 investments	$	2.7		$	(34.2	)	$	20.4	$	(38.4	)

Investment Holdings

The cost or amortized cost, gross unrealized investment gains and losses, net foreign currency gains and losses and carrying values of White Mountains’ fixed maturity investments as of September 30, 2012 and December 31, 2011, were as follows:



	September 30, 2012
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency gains (losses)			Carrying value
U.S. Government and agency obligations	$	393.7	$	1.2	$	(.1	)	$	(.1	)	$	394.7
Debt securities issued by corporations	2,213.8		91.6		(3.0		)	(21.1		)	2,281.3
Municipal obligations	3.8		—		—			—			3.8
Mortgage-backed and asset-backed securities	2,023.3		30.3		(1.1		)	(5.1		)	2,047.4
Foreign government, agency and provincial obligations	475.2		8.0		(.4		)	(6.4		)	476.4
Preferred stocks	79.8		6.3		—			—			86.1
Total fixed maturity investments including assets held for sale	$	5,189.6	$	137.4	$	(4.6	)	$	(32.7	)	$	5,289.7
Fixed maturity investments reclassified to assets held for sale related the Runoff Transaction											(377.3		)
Total fixed maturity investments											$	4,912.4



	December 31, 2011
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency gains (losses)			Carrying value
U.S. Government and agency obligations	$	299.4	$	5.3	$	(.1	)	$	.4		$	305.0
Debt securities issued by corporations	2,072.1		73.7		(7.8		)	(2.9		)	2,135.1
Municipal obligations	2.7		—		—			—			2.7
Mortgage-backed and asset-backed securities	3,190.5		25.9		(3.9		)	10.4			3,222.9
Foreign government, agency and provincial obligations	581.2		11.0		(.1		)	(2.9		)	589.2
Preferred stocks	82.3		3.2		(6.7		)	—			78.8
Total fixed maturity investments including assets held for sale	$	6,228.2	$	119.1	$	(18.6	)	$	5.0		$	6,333.7
Fixed maturity investments reclassified to assets held for sale related to AutoOne											(111.8		)
Total fixed maturity investments											$	6,221.9

The cost or amortized cost, gross unrealized investment gains and losses, net foreign currency gains and losses and carrying values of White Mountains’ common equity securities, convertible fixed maturities and other long-term investments as of September 30, 2012 and December 31, 2011, were as follows:



	September 30, 2012
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency losses			Carrying value
Common equity securities	$	870.0	$	139.7	$	(4.9	)	$	—		$	1,004.8
Convertible fixed maturity investments	$	140.2	$	7.6	$	(5.8	)	$	—		$	142.0
Other long-term investments	$	264.8	$	57.1	$	(8.6	)	$	(6.2	)	$	307.1



	December 31, 2011
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency losses			Carrying value
Common equity securities	$	691.7	$	72.0	$	(8.7	)	$	—		$	755.0
Convertible fixed maturity investments	$	139.2	$	6.2	$	(1.6	)	$	—		$	143.8
Other long-term investments	$	274.4	$	55.5	$	(25.2	)	$	(3.4	)	$	301.3

Other long-term investments

White Mountains holds investments in hedge funds and private equity funds, which are included in other long-term investments. The fair value of these investments has been estimated using the net asset value of the funds. At September 30, 2012, White Mountains held investments in 17 hedge funds and 36 private equity funds. The largest investment in a single fund was $19.2 million at September 30, 2012. The following table summarizes investments in hedge funds and private equity interests by investment objective and sector at September 30, 2012 and December 31, 2011:



	September 30, 2012				December 31, 2011
Millions	Fair Value		Unfunded Commitments		Fair Value		Unfunded Commitments
Hedge funds
Long/short equity	$	58.6	$	—	$	48.8	$	—
Long/short credit & distressed	33.8		—		32.3		—
Long diversified strategies	2.3		—		16.9		—
Long/short equity REIT	15.2		—		14.5		—
Long/short equity activist	14.0		—		12.3		—
Long bank loan	.4		—		.5		—
Total hedge funds	124.3		—		125.3		—

Private equity funds
Multi-sector	29.3		6.4		26.9		8.2
Energy infrastructure & services	32.9		11.7		28.0		9.9
Distressed residential real estate	19.2		—		27.4		—
Real estate	12.2		3.3		9.5		3.3
Private equity secondaries	11.0		3.2		11.3		4.0
International multi-sector, Europe	4.3		4.9		7.8		4.7
Manufacturing/Industrial	10.6		29.1		6.2		—
Healthcare	4.3		5.4		2.3		7.0
International multi-sector, Asia	.4		2.7		3.6		2.6
Insurance	3.2		41.3		3.5		41.3
Venture capital	2.4		.5		2.4		.5
Total private equity funds	129.8		108.5		128.9		81.5

Total hedge and private equity funds included in other long-term investments	$	254.1	$	108.5	$	254.2	$	81.5

Redemption of investments in certain hedge funds is subject to restrictions including lock-up periods where no redemptions or withdrawals are allowed, restrictions on redemption frequency and advance notice periods for redemptions. Amounts requested for redemptions remain subject to market fluctuations until the redemption effective date, which generally falls at the end of the defined redemption period.

The following summarizes the September 30, 2012 fair value of hedge funds subject to restrictions on redemption frequency and advance notice period requirements for investments in active hedge funds:



	Notice Period
Millions Redemption frequency	30-59 days notice		60-89 days notice		90-119 days notice		120+ days notice		Total
Monthly	$	—	$	—	$	—	$	6.8	$	6.8
Quarterly	27.1		29.3		19.9		9.4		85.7
Semi-annual	—		20.6		—		—		20.6
Annual	2.3		—		8.5		.4		11.2
Total	$	29.4	$	49.9	$	28.4	$	16.6	$	124.3

Certain of the hedge fund investments in which White Mountains is invested are no longer active and are in process of disposing of their underlying investments. Distributions from such funds are remitted to investors as the fund’s underlying investments are liquidated. At September 30, 2012, distributions of $3.3 million were outstanding from these investments. The actual amount of the final distribution remittances remain subject to market fluctuations. The date at which such remittances will be received is not determinable at September 30, 2012.

White Mountains has also submitted redemption requests for certain of its investments in active hedge funds. At September 30, 2012, redemptions of $13.9 million are outstanding and are subject to market fluctuations. The majority of such remittances are expected to be received in the fourth quarter of 2012. Redemptions are recorded as receivables when approved by the hedge funds and no longer subject to market fluctuations.

Investments in private equity funds are generally subject to a “lock-up” period during which investors may not request a redemption. Distributions prior to the expected termination date of the fund may be limited to dividends or proceeds arising from the liquidation of the fund’s underlying investments. In addition, certain private equity funds provide an option to extend the lock-up period at either the sole discretion of the fund manager or upon agreement between the fund and the investors.

At September 30, 2012, investments in private equity funds were subject to lock-up periods as follows:



Millions	1-3 years	3 – 5 years	5 – 10 years	>10 years	Total
Private Equity Funds — expected lock-up period remaining	$27.7	$15.6	$75.9	$10.6	$129.8

Fair value measurements at September 30, 2012

White Mountains’ invested assets measured at fair value include fixed maturity investments, common and preferred equity securities, convertible fixed maturity investments and other long-term investments which primarily consist of hedge funds and private equity funds. Fair value measurements reflect management’s best estimate of the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value measurements fall into a hierarchy with three levels based on the nature of the inputs. Fair value measurements based on quoted prices in active markets for identical assets are at the top of the hierarchy (“Level 1”), followed by fair value measurements based on observable inputs that do not meet the criteria for Level 1, including quoted prices in inactive markets and quoted prices in active markets for similar, but not identical instruments (“Level 2”). Measurements based on unobservable inputs, including a reporting entity’s estimates of the assumptions that market participants would use are at the bottom of the hierarchy (“Level 3”).

White Mountains uses quoted market prices or other observable inputs to estimate fair value for the vast majority of its investment portfolio. Investments valued using Level 1 inputs include fixed maturity investments, primarily investments in U.S. Treasuries, common equities and short-term investments, which include U.S. Treasury Bills. Investments valued using Level 2 inputs consist of fixed maturity investments including corporate debt, state and other governmental debt, convertible fixed maturity securities and mortgage and asset-backed securities. Fair value estimates for investments that trade infrequently and have few or no observable market prices are classified as Level 3 measurements. Level 3 fair value estimates based upon unobservable inputs include White Mountains’ investments in hedge funds and private equity funds, as well as investments in certain debt securities where quoted market prices are unavailable. White Mountains uses brokers and outside pricing services to assist in determining fair values. For investments in active markets, White Mountains uses the quoted market prices provided by outside pricing services to determine fair value. The outside pricing services used by White Mountains have indicated that if no observable inputs are available for a security, they will not provide a price. In those circumstances, White Mountains estimates the fair value using industry standard pricing models and observable inputs such as benchmark interest rates, matrix pricing, market comparables, broker quotes, issuer spreads, bids, offers, credit rating, prepayment speeds and other relevant inputs. White Mountains performs procedures to validate the market prices obtained from the outside pricing sources. Such procedures, which cover substantially all of its fixed maturity investments include, but are not limited to, evaluation of model pricing methodologies and review of the pricing services’ quality control processes and procedures on at least an annual basis, comparison of market prices to prices obtained from different independent pricing vendors on at least a semi-annual basis, monthly analytical reviews of certain prices, and review of assumptions utilized by the pricing service for selected measurements on an ad hoc basis throughout the year. White Mountains also performs back-testing of selected sales activity to determine whether there are any significant differences between the market price used to value the security prior to sale and the actual sale price on an ad-hoc basis throughout the year. Prices provided by the pricing services that vary by more than 5% and $1.0 million from the expected price based on these procedures are considered outliers. In circumstances where the results of White Mountains’ review process do not appear to support the market price provided by the pricing services, White Mountains challenges the price. If White Mountains cannot gain satisfactory evidence to support the challenged price, it relies upon its own pricing methodologies to estimate the fair value of the security in question. The fair values of such securities are considered to be Level 3 measurements.

White Mountains’ investments in debt securities are generally valued using matrix and other pricing models. Key inputs include benchmark yields, benchmark securities, reported trades, issuer spreads, bids, offers, credit ratings and prepayment speeds. Income on mortgage-backed and asset-backed securities is recognized using an effective yield based on anticipated prepayments and the estimated economic life of the securities. When actual prepayments differ significantly from anticipated prepayments, the estimated economic life is recalculated and the remaining unamortized premium or discount is amortized or accreted prospectively over the remaining economic life.

White Mountains employs a number of procedures to assess the reasonableness of the fair value measurements for its other long-term investments, including obtaining and reviewing the audited annual financial statements of each hedge fund and private equity fund and periodically discussing each fund’s pricing with the fund manager. However, since the fund managers do not provide sufficient information to evaluate the pricing inputs and methods for each underlying investment, the inputs are considered to be unobservable. Accordingly, the fair values of White Mountains’ investments in hedge funds and private equity funds have been classified as Level 3 measurements. The fair value of White Mountains’ investments in hedge funds and private equity funds has been determined using net asset value.

In addition to the investments described above, White Mountains has $77.1 million and $68.1 million of investment-related liabilities recorded at fair value and included in other liabilities as of September 30, 2012 and December 31, 2011. These liabilities relate to securities that have been sold short by limited partnerships in which White Mountains has investments and is required to consolidate under GAAP. All of the liabilities included have a Level 1 designation.

Fair Value Measurements by Level

The following tables summarize White Mountains’ fair value measurements for investments at September 30, 2012 and December 31, 2011, by level.



	September 30, 2012
Millions	Fair value		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs
Fixed maturity investments:
US Government and agency obligations	$	394.7	$	340.5	$	54.2	$	—

Debt securities issued by corporations:
Consumer	597.2		—		597.2		—
Industrial	488.1		—		488.1		—
Financials	405.4		1.1		404.3		—
Communications	217.1		—		217.1		—
Basic materials	175.1		—		175.1		—
Energy	172.9		—		172.9		—
Utilities	204.4		—		204.4		—
Technology	21.1		—		21.1		—
Diversified	—		—		—		—
Total debt securities issued by corporations:	2,281.3		1.1		2,280.2		—

Municipal obligations	3.8		—		3.8		—
Mortgage-backed and asset-backed securities	2,047.4		—		2,041.9		5.5
Foreign government, agency and provincial obligations	476.4		56.9		419.5		—
Preferred stocks	86.1		—		15.5		70.6
Total fixed maturity investments ⁽¹⁾	5,289.7		398.5		4,815.1		76.1

Short-term investments	917.3		917.3		—		—

Common equity securities:
Financials	316.1		277.9		2.3		35.9
Consumer	249.7		249.6		.1		—
Basic materials	118.2		118.2		—		—
Energy	96.8		96.8		—		—
Technology	51.6		51.6		—		—
Utilities	42.9		42.7		.2		—
Other	129.5		73.2		56.3		—
Total common equity securities	1,004.8		910.0		58.9		35.9

Convertible fixed maturity investments	142.0		—		142.0		—
Other long-term investments ⁽²⁾	272.6		—		—		272.6
Total investments	$	7,626.4	$	2,225.8	$	5,016.0	$	384.6

⁽¹⁾Carrying value includes $377.3 that is classified as assets held for sale relating to discontinued operations.

⁽²⁾Excludes carrying value of $34.3 associated with other long-term investment limited partnerships accounted for using the equity method and $0.3 related to forward contracts.



	December 31, 2011
Millions	Fair value		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs
Fixed maturity investments:
US Government and agency obligations	$	305.0	$	296.2	$	8.8	$	—

Debt securities issued by corporations:
Consumer	790.7		—		790.7		—
Industrial	359.4		—		359.4		—
Financials	239.6		3.8		235.8		—
Communications	225.8		—		225.8		—
Basic materials	195.7		—		195.7		—
Energy	155.8		—		155.8		—
Utilities	140.1		—		140.1		—
Technology	24.5		—		24.5		—
Diversified	3.5		—		3.5		—
Total debt securities issued by corporations:	2,135.1		3.8		2,131.3		—

Municipal obligations	2.7		—		2.7		—
Mortgage-backed and asset-backed securities	3,222.9		—		3,207.8		15.1
Foreign government, agency and provincial obligations	589.2		65.7		523.5		—
Preferred stocks	78.8		—		15.0		63.8
Total fixed maturity investments ⁽¹⁾	6,333.7		365.7		5,889.1		78.9

Short-term investments	846.0		846.0		—		—

Common equity securities:
Financials	219.2		185.8		1.5		31.9
Consumer	188.8		188.5		.3		—
Basic materials	121.0		119.9		1.1		—
Energy	72.6		72.6		—		—
Utilities	42.0		41.8		.2		—
Technology	25.8		25.8		—		—
Other	85.6		33.0		52.2		.4
Total common equity securities	755.0		667.4		55.3		32.3

Convertible fixed maturity investments	143.8		—		143.8		—
Other long-term investments ⁽²⁾	268.3		—		—		268.3
Total investments	$	8,346.8	$	1,879.1	$	6,088.2	$	379.5

⁽¹⁾Carrying value includes $111.8 that is classified as assets held for sale relating to AutoOne discontinued operations.

⁽²⁾Excludes carrying value of $33.0 associated with other long-term investments accounted for using the equity method.

Debt securities issued by corporations

The following table summarizes the ratings of the corporate debt securities held in White Mountains’ investment portfolio as of September 30, 2012 and December 31, 2011:



Millions	September 30, 2012		December 31, 2011
AAA	$	—	$	—
AA	165.5		206.8
A	992.8		802.8
BBB	1,108.5		1,110.8
BB	7.6		6.2
Other	6.9		8.5
Debt securities issued by corporations ⁽¹⁾	$	2,281.3	$	2,135.1

⁽¹⁾Credit ratings are assigned based on the following hierarchy: 1) Standard & Poor’s, 2) Moody’s

and 3) Bloomberg (Composite rating).

Mortgage-backed, Asset-backed Securities

White Mountains purchases commercial and residential mortgage-backed securities with the goal of maximizing risk adjusted returns in the context of a diversified portfolio. White Mountains’ non-agency commercial mortgage-backed portfolio (“CMBS”) is generally short tenor and structurally senior, with more than 25 points of subordination on average for fixed rate CMBS and more than 50 points of subordination on average for floating rate CMBS as of September 30, 2012. In general, subordination represents the percentage principal loss on the underlying collateral that would be absorbed by other securities lower in the capital structure before the more senior security incurs a loss. White Mountains believes these levels of protection will mitigate the risk of loss tied to the refinancing challenges facing the commercial real estate market. As of September 30, 2012, on average less than 1.0% of the underlying loans were reported as non-performing for all non-agency CMBS held by White Mountains. White Mountains is not an originator of residential mortgage loans and did not hold any residential mortgage-backed securities (“RMBS”) categorized as sub-prime as of September 30, 2012. White Mountains’ investments in hedge funds and private equity funds contain negligible amounts of sub-prime mortgage-backed securities at September 30, 2012. White Mountains considers sub-prime mortgage-backed securities as those that have underlying loan pools that exhibit weak credit characteristics, or those that are issued from dedicated sub-prime shelves or dedicated second-lien shelf registrations (i.e., White Mountains considers investments backed primarily by second-liens to be sub-prime risks regardless of credit scores or other metrics).

White Mountains categorizes mortgage-backed securities as “non-prime” (also called “Alt A” or “A-”) if they are backed by collateral that has overall credit quality between prime and sub-prime based on White Mountains’ review of the characteristics of their underlying mortgage loan pools, such as credit scores and financial ratios. White Mountains’ non-agency residential mortgage-backed portfolio is generally short tenor and structurally senior. White Mountains does not own any collateralized debt obligations, including residential mortgage-backed collateralized debt obligations.

The following table summarizes mortgage and asset-backed securities as of September 30, 2012 and December 31, 2011:



	September 30, 2012						December 31, 2011
Millions	Fair Value		Level 2		Level 3		Fair Value		Level 2		Level 3
Mortgage-backed securities:
Agency:
GNMA	$	1,165.5	$	1,165.5	$	—	$	1,365.8	$	1,365.8	$	—
FNMA	97.2		97.2		—		712.6		712.6		—
FHLMC	37.6		37.6		—		35.9		35.9		—
Total Agency ⁽¹⁾	1,300.3		1,300.3		—		2,114.3		2,114.3		—
Non-agency:
Residential	160.5		160.5		—		83.1		68.0		15.1
Commercial	389.3		383.8		5.5		276.7		276.7		—
Total Non-agency	549.8		544.3		5.5		359.8		344.7		15.1

Total mortgage-backed securities	1,850.1		1,844.6		5.5		2,474.1		2,459.0		15.1
Other asset-backed securities:
Credit card receivables	80.8		80.8		—		380.6		380.6		—
Vehicle receivables	80.3		80.3		—		345.6		345.6		—
Other	36.2		36.2		—		22.6		22.6		—
Total other asset-backed securities	197.3		197.3		—		748.8		748.8		—
Total mortgage and asset- backed securities	$	2,047.4	$	2,041.9	$	5.5	$	3,222.9	$	3,207.8	$	15.1

⁽¹⁾Represents publicly traded mortgage-backed securities which carry the full faith and credit guaranty of the U.S. government (i.e., GNMA) or are guaranteed by a government sponsored entity (i.e., FNMA, FHLMC).

Non-agency Mortgage-backed Securities

The security issuance years of White Mountains’ investments in non-agency RMBS and non-agency CMBS securities as of September 30, 2012 are as follows:



			Security Issuance Year
Millions	Fair Value		2003		2006		2007		2009		2010		2011		2012
Non-agency RMBS	$	160.5	$	2.2	$	21.4	$	7.1	$	1.7	$	53.2	$	74.9	$	—
Non-agency CMBS	389.3		—		4.5		15.3		11.9		6.1		127.4		224.1
Total	$	549.8	$	2.2	$	25.9	$	22.4	$	13.6	$	59.3	$	202.3	$	224.1

Non-agency Residential Mortgage-backed Securities

The classification of the underlying collateral quality and the tranche levels of White Mountains’ non-agency RMBS securities are as follows as of September 30, 2012:



Millions	Fair Value		Super Senior ⁽¹⁾		Senior ⁽²⁾		Subordinate ⁽³⁾
Prime	$	160.0	$	13.0	$	147.0	$	—
Non-prime	.5		—		.5		—
Sub-prime	—		—		—		—
Total	$	160.5	$	13.0	$	147.5	$	—

⁽¹⁾At issuance, Super Senior were rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were senior to

other AAA or Aaa bonds.

⁽²⁾At issuance, Senior were rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were senior to non-AAA

or non-Aaa bonds.

⁽³⁾At issuance, Subordinate were not rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were junior to

AAA or Aaa bonds.

Non-agency Commercial Mortgage-backed Securities

The amount of fixed and floating rate securities and their tranche levels of White Mountains’ non-agency CMBS securities are as follows as of September 30, 2012:



Millions	Fair Value		Super Senior ⁽¹⁾		Senior ⁽²⁾		Subordinate ⁽³⁾
Fixed rate CMBS	$	367.1	$	253.0	$	109.6	$	4.5
Floating rate CMBS	22.2		15.3		1.4		5.5
Total	$	389.3	$	268.3	$	111.0	$	10.0

⁽¹⁾At issuance, Super Senior were rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were

senior to other AAA or Aaa bonds.

⁽²⁾At issuance, Senior were rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were senior to

non-AAA or non-Aaa bonds.

⁽³⁾At issuance, Subordinate were not rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were

junior to AAA or Aaa bonds.

Rollforward of Fair Value Measurements by Level

White Mountains uses quoted market prices where available as the inputs to estimate fair value for its investments in active markets. Such measurements are considered to be either Level 1 or Level 2 measurements, depending on whether the quoted market price inputs are for identical securities (Level 1) or similar securities (Level 2). Level 3 measurements for fixed maturity investments, common equity securities, convertible fixed maturity investments and other long-term investments at September 30, 2012 and 2011 consist of securities for which the estimated fair value has not been determined based upon quoted market price inputs for identical or similar securities.

The following tables summarize the changes in White Mountains’ fair value measurements by level for the three and nine months ended September 30, 2012 and 2011:



							Level 3 Investments
Millions	Level 1 Investments			Level 2 Investments			Fixed Maturities			Common equity securities			Convertible fixed maturities		Other long-term investments			Total
Balance at January 1, 2012	$	1,879.1		$	6,088.2		$	78.9		$	32.3		$	—	$	268.3		$	8,346.8		⁽¹⁾⁽²⁾
Total realized and unrealized gains (losses)	57.8			53.8			8.4			11.4			—		(8.2		)	123.2
Foreign currency gains (losses) through OCI	13.2			75.5			.7			.1			—		3.1			92.6
Amortization/Accretion	(.7		)	(34.0		)	(.7		)	—			—		—			(35.4		)
Purchases	6,712.0			3,823.7			144.3			2.5			—		40.6			10,723.1
Sales	(6,435.6		)	(5,048.1		)	(99.2		)	(9.8		)	—		(31.2		)	(11,623.9		)
Transfers in	—			56.9			—			—			—		—			56.9
Transfers out	—			—			(56.3		)	(.6		)	—		—			(56.9		)
Balance at September 30, 2012	$	2,225.8		$	5,016.0		$	76.1		$	35.9		$	—	$	272.6		$	7,626.4		⁽¹⁾⁽²⁾

⁽¹⁾Excludes carrying value of $33.0 and $34.3 at January 1, 2012 and September 30, 2012 associated with other long-term investments accounted for using the equity method and $0.3 at September 30, 2012 related to forward contracts.

⁽²⁾Carrying value includes $111.8 and $377.3 at January 1, 2012 and September 30, 2012 that is classified as assets held for sale relating to discontinued operations.



							Level 3 Investments
Millions	Level 1 Investments			Level 2 Investments			Fixed Maturities			Common equity securities			Convertible fixed maturities		Other long-term investments				Total
Balance at January 1, 2011	$	1,894.4		$	5,477.4		$	128.4		$	71.2		$	—	$	330.2		⁽¹⁾	$	7,901.6		⁽¹⁾
Total realized and unrealized gains (losses)	(50.5		)	115.9			(10.6		)	(4.9		)	—		22.5				72.4
Foreign currency gains (losses) through OCI	.3			(84.4		)	(4.4		)	1.6			—		(5.0		)		(91.9		)
Amortization/Accretion	2.4			(40.7		)	(.1		)	—			—		—				(38.4		)
Purchases	6,690.7			3,987.4			212.8			19.7			—		27.9				10,938.5
Sales	(6,782.1		)	(4,596.9		)	1.6			(55.5		)	—		(83.4		)		(11,516.3		)
Transfers in	—			111.8			1.0			—			—		—				112.8
Transfers out	—			(1.0		)	(111.8		)	—			—		—				(112.8		)
Balance at September 30, 2011	$	1,755.2		$	4,969.5		$	216.9		$	32.1		$	—	$	292.2		⁽¹⁾	$	7,265.9		⁽¹⁾

⁽¹⁾Excludes carrying value of $36.6 and $41.9 at September 30, 2011 and January 1, 2011 associated with other long-term investment limited partnerships accounted for using the equity method.

Fair Value Measurements — transfers between levels - Three-month period ended September 30, 2012 and 2011

During the first nine months of 2012, one security classified as Level 3 measurements in the prior period was recategorized as Level 2 measurements because quoted market prices for similar securities that were considered reliable and could be validated against an alternative source were available at September 30, 2012. These measurements comprise “Transfers out” of Level 3 and “Transfers in” to Level 2 of $56.9 million in fixed maturities for the period ended September 30, 2012.

During the first nine months of 2011, seven securities which had been classified as Level 3 measurements at January 1, 2011 were recategorized as Level 2 measurements because quoted market prices for similar securities that were considered reliable and could be validated against an alternative source were available at September 30, 2011. These measurements comprise “Transfers out” of Level 3 and “Transfers in” to Level 2 of $111.8 million in fixed maturities for the period ended September 30, 2011. One security that was classified as a Level 2 investment at January 1, 2011 was priced with unobservable inputs and represents “Transfers in” of $1.0 million in Level 3 investments. The fair value of this security was estimated using industry standard pricing models, in which management selected inputs using its best judgment. The pricing models used by White Mountains use the same valuation methodology for all Level 3 measurements for fixed maturities. The security is considered to be Level 3 because the measurements are not directly observable. At September 30, 2011, the estimated fair value for this security determined using the industry standard pricing models was $0.8 million less than the estimated fair value based upon quoted prices provided by a third party pricing vendor.

Significant Unobservable Inputs

The following summarizes significant unobservable inputs used in estimating the fair value of investment securities classified within Level 3 at September 30, 2012:



($ in Millions)	September 30, 2012
Description	Fair Value	Rating⁽¹⁾	Valuation Technique(s)	Unobservable Input	Range⁽¹⁾
Non-agency commercial mortgage-backed securities	$5.5	A2	Discounted cash flow	Prepayment Rate	0.0	%	CPY ⁽²⁾
				Discount Margin over LIBOR	2.1	%
Preferred Stock	$70.6	NR	Discounted cash flow	Discount yield	8.0	%

⁽¹⁾Each asset type consists of one security.

⁽²⁾CPY refers to the market convention for CMBS prepayment.

The assumed prepayment rate is a significant unobservable input used to estimate the fair value of investments in non-agency commercial mortgage-backed securities (“CMBS”). Generally for bonds priced at a premium, increases in prepayment speeds will result in a lower fair value, while decreases in prepayment speed may result in a higher fair value.

- Definition

The entire disclosure for investments in certain debt and equity securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-Glossary Debt Security
-URI http://asc.fasb.org/extlink&oid=6509901

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27290-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-Glossary Equity Security
-URI http://asc.fasb.org/extlink&oid=6511694

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27232-111563

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 320
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27357-111563

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27161-111563

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27405-111563

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 3, 19, 20, 21, 22, 137
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Debt

9 Months Ended

Sep. 30, 2012

Debt Disclosure [Abstract]

Debt

White Mountains’ debt outstanding as of September 30, 2012 and December 31, 2011 consisted of the following:



Millions	September 30, 2012			December 31, 2011
OBH Senior Notes, at face value	$	269.9		$	269.9
Unamortized original issue discount	(.1		)	(.1		)
OBH Senior Notes, carrying value	269.8			269.8
SIG Senior Notes, at face value	400.0			400.0
Unamortized original issue discount	(.6		)	(.7		)
SIG Senior Notes, carrying value	399.4			399.3
WTM Bank Facility	—			—
Old Lyme	2.1			2.1
Other debt ⁽¹⁾	5.3			6.3
Total debt	$	676.6		$	677.5

⁽¹⁾Other debt relates to White Mountains’ consolidation of Hamer and Bri-Mar.

Bank Facility

White Mountains has a revolving credit facility with a total commitment of $375.0 million (the “WTM Bank Facility”) with a syndicate of lenders administered by Bank of America, N.A. As of September 30, 2012, the WTM Bank Facility was undrawn.

Debt Covenants

At September 30, 2012, White Mountains was in compliance with all of the covenants under the WTM Bank Facility, the OneBeacon U.S. Holdings, Inc. (“OBH”) Senior Notes and the SIG Senior Notes.

Old Lyme

On December 31, 2011, Sirius Group acquired the runoff loss reserve portfolio of Old Lyme. As part of the acquisition, Sirius Group entered into a five year $2.1 million purchase note. The principal amount of the purchase note is subject to upward adjustments for favorable loss reserve development (up to 50% of $6.0 million) and downward adjustments for any adverse loss reserve development.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References + Details

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2012
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company and its Bermuda domiciled subsidiaries are not subject to Bermuda income tax under current Bermuda law. In the event there is a change in the current law such that taxes are imposed, the Company and its Bermuda domiciled subsidiaries would be exempt from such tax until March 31, 2035, pursuant to the Bermuda Exempted Undertakings Tax Protection Act of 1966. The Company has subsidiaries and branches that operate in various other jurisdictions around the world that are subject to tax in the jurisdictions in which they operate. The jurisdictions in which the Company’s subsidiaries and branches are subject to tax are Australia, Belgium, Canada, Denmark, Germany, Gibraltar, Luxembourg, the Netherlands, Singapore, Sweden, Switzerland, the United Kingdom and the United States. White Mountains' income tax expense for the three months ended September 30, 2012 represented an effective tax rate of 35.4%, which is in line with the U.S. statutory rate of 35%. White Mountains’ income tax expense for the nine months ended September 30, 2012 represented effective tax rate of 27.2%, which differed from the U.S. statutory rate of 35% primarily due to income generated in jurisdictions other than the United States. White Mountains' effective tax rate for the three and nine months ended September 30, 2011 was not meaningful as pre-tax income was near break-even. In arriving at the effective tax rate for the three and nine months ended September 30, 2012 and 2011, White Mountains forecasted the change in unrealized investment gains (losses) and realized investment gains (losses) for the years ending December 31, 2012 and 2011 and included these gains (losses) in the effective tax rate calculation pursuant to ASC 740-270. White Mountains records a valuation allowance against deferred tax assets if it becomes more likely than not that all or a portion of a deferred tax asset will not be realized. Changes in valuation allowances from period to period are included in income tax expense in the period of change. In determining whether a valuation allowance, or change therein, is warranted, White Mountains considers factors such as prior earnings history, expected future earnings, carryback and carryforward periods and strategies that if executed would result in the realization of a deferred tax asset. During the next twelve months, it is possible that certain planning strategies will no longer be sufficient to utilize the entire deferred tax asset, which could result in material changes to White Mountains’ deferred tax assets and tax expense. Upon completion of the Runoff Transaction, it is expected that the unrecognized tax benefits associated with tax positions where the deductibility is certain but the timing is uncertain, will decrease by approximately $11.5 million. White Mountains does not expect the decrease to result in a material change to its financial position. With few exceptions, White Mountains is no longer subject to U.S. federal, state or non-U.S. income tax examinations by tax authorities for years before 2005. The IRS is conducting an examination of income tax returns for 2005 and 2006 for certain U.S. subsidiaries of OneBeacon. On January 5, 2011, White Mountains received Form 4549-A (Income Tax Discrepancy Adjustments) from the IRS relating to the examination of tax years 2005 and 2006. The estimated total assessment, including interest and utilization of alternative minimum and foreign tax credit carryovers, is $20.6 million. White Mountains disagrees with the adjustments proposed by the IRS and intends to defend its position. The timing of the resolution of these issues is uncertain, however, it is reasonably possible that the resolution could occur within the next twelve months. An estimate of the range of potential outcomes cannot be made at this time. When ultimately settled, White Mountains does not expect the resolution of this examination to result in a material change to its financial position. On July 28, 2011, the IRS commenced an examination of the income tax returns for 2007, 2008 and 2009 for certain U.S. subsidiaries of OneBeacon. White Mountains does not expect the resolution of this examination to result in a material change to its financial position. On December 15, 2011, the IRS commenced an examination of the income tax returns for 2010 for certain U.S. subsidiaries of AFI. Pursuant to a Stock Purchase Agreement dated as of May 17, 2011 between White Mountains and Allstate, White Mountains is required to indemnify Allstate for any changes in pre-closing taxes. White Mountains does not expect the resolution of this examination to result in a material change to its financial position. The IRS conducted an examination of income tax returns for 2006 and 2007 for certain U.S. subsidiaries of Sirius Group. On October 26, 2011, the Sirius Group received and signed the IRS Revenue Agent’s Report, which contained no proposed adjustments. The IRS also examined the U.S. income tax return filed by WM Belvaux S.à r.l., a Luxembourg subsidiary, for tax year 2007. On May 3, 2011, the exam was completed with no proposed adjustments. The Ministry of Finance in Sweden has proposed reducing the corporate income tax rate in Sweden to 22.0% from 26.3%. If this proposal is enacted, the reduction in the Swedish corporate income tax rate would reduce the White Mountains' net deferred tax liability by approximately $60 million. The Ministry of Finance in Sweden has also proposed tax legislation that, if enacted, would limit the deductibility of interest paid on certain intra-group debt instruments after January 1, 2013. At September 30, 2012, White Mountains has $272.1 million of deferred tax assets related to net operating loss carryforwards that are being utilized from interest income on intra-group debt instruments that would be affected by the proposed tax legislation. However, management does not expect that the proposed tax legislation will adversely affect the carrying value of these deferred tax assets as management believes it has alternate strategies to utilize the deferred tax assets.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h))
-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32639-109319

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32537-109319

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 109
-Paragraph 136, 172
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 08
-Paragraph h
-Article 4

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 109
-Paragraph 43, 44, 45, 46, 47, 48, 49
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Derivatives

9 Months Ended

Sep. 30, 2012

Derivatives Disclosure [Abstract]

Derivative [Text Block]

Variable Annuity Reinsurance

White Mountains has entered into agreements to reinsure death and living benefit guarantees associated with certain variable annuities in Japan. At September 30, 2012 and December 31, 2011, the total guarantee value was approximately ¥230.5 billion (approximately $3.0 billion at exchange rates on that date) and ¥233.7 billion (approximately $3.0 billion at exchange rates on that date). The collective account values of the underlying variable annuities were approximately 80% and 78% of the guarantee value at September 30, 2012 and December 31, 2011.

The following table summarizes the pre-tax operating results of WM Life Re for the three and nine months ended September 30, 2012 and 2011:



	Three Months Ended						Nine Months Ended
	September 30,						September 30,
Millions	2012			2011			2012			2011
Fees, included in other revenues	$	8.1		$	8.4		$	24.1		$	24.3
Change in fair value of variable annuity liability, included in other revenues	(11.3		)	(164.4		)	89.4			(148.0		)
Change in fair value of derivatives, included in other revenues	(11.0		)	148.9			(122.0		)	105.4
Foreign exchange, included in other revenues	9.0			14.8			(6.4		)	17.1
Other investment income and gains (losses)	3.8			.5			2.9			(.1		)
Total revenues	(1.4		)	8.2			(12.0		)	(1.3		)
Change in fair value of variable annuity death benefit liabilities, included in other expenses	.7			(5.6		)	6.7			(3.1		)
Death benefit claims paid, included in other expenses	(1.5		)	(.7		)	(4.9		)	(2.4		)
General and administrative expenses	(1.1		)	(1.1		)	(3.8		)	(3.2		)
Pre-tax (loss) income	$	(3.3	)	$	.8		$	(14.0	)	$	(10.0	)

All of White Mountains’ variable annuity reinsurance liabilities were classified as Level 3 measurements at September 30, 2012 and 2011. The following tables summarize the changes in White Mountains’ variable annuity reinsurance liabilities and derivative instruments for the three and nine months ended September 30, 2012 and 2011:



	Three Months Ended September 30, 2012
	Variable Annuity (Liabilities)			Derivative Instruments
Millions	Level 3			Level 3 ⁽¹⁾			Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total ⁽⁴⁾
Beginning of period	$	(661.8	)	$	213.0		$	61.0		$	(23.7	)	$	250.3
Purchases	—			—			—			—			—
Realized and unrealized (losses) gains	(10.6		)	6.7			(15.3		)	(2.4		)	(11.0		)
Transfers in	—			—			—			—			—
Sales/settlements	—			(6.7		)	(12.5		)	22.0			2.8
End of period	$	(672.4	)	$	213.0		$	33.2		$	(4.1	)	$	242.1



	Nine Months Ended September 30, 2012
	Variable Annuity (Liabilities)			Derivative Instruments
Millions	Level 3			Level 3 ⁽¹⁾			Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total ⁽⁴⁾
Beginning of period	$	(768.5	)	$	247.1		$	39.2		$	4.1		$	290.4
Purchases	—			6.1			—			—			6.1
Realized and unrealized gains (losses)	96.1			(24.1		)	(71.8		)	(26.1		)	(122.0		)
Transfers in	—			—			—			—			—
Sales/settlements	—			(16.1		)	65.8			17.9			67.6
End of period	$	(672.4	)	$	213.0		$	33.2		$	(4.1	)	$	242.1



	Three Months Ended September 30, 2011
	Variable Annuity (Liabilities)			Derivative Instruments
Millions	Level 3			Level 3 ⁽¹⁾		Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total ⁽⁴⁾
Beginning of period	$	(591.3	)	$	232.7	$	48.2		$	(11.9	)	$	269.0
Purchases	—			—		—			—			—
Realized and unrealized (losses) gains	(170.0		)	45.6		75.7			27.6			148.9
Transfers in	—			—		—			—			—
Sales/settlements	—			—		(48.4		)	(15.7		)	(64.1		)
End of period	$	(761.3	)	$	278.3	$	75.5		$	—		$	353.8



	Nine Months Ended September 30, 2011
	Variable Annuity (Liabilities)			Derivative Instruments
Millions	Level 3			Level 3 ⁽¹⁾			Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total ⁽⁴⁾
Beginning of period	$	(610.2	)	$	275.3		$	72.2		$	—		$	347.5
Purchases	—			5.0			—			—			5.0
Realized and unrealized (losses) gains	(151.1		)	27.1			67.5			10.8			105.4
Transfers in	—			—			—			—			—
Sales/settlements	—			(29.1		)	(64.2		)	(10.8		)	(104.1		)
End of period	$	(761.3	)	$	278.3		$	75.5		$	—		$	353.8

⁽¹⁾Consists of over-the-counter instruments.

⁽²⁾Consists of interest rate swaps, total return swaps, foreign currency forward contracts, and bond forwards. Fair value measurement based upon bid/ask pricing quotes for similar instruments that are actively traded, where available. Swaps for which an active market does not exist have been priced using observable inputs including the swap curve and the underlying bond index.

⁽³⁾Consists of exchange traded equity index, foreign currency and interest rate futures. Fair value measurements based upon quoted prices for identical instruments that are actively traded.

⁽⁴⁾In addition to derivative instruments, WM Life Re held cash, short-term and fixed maturity investments of $477.5 and $419.7 at September 30, 2012 and 2011 posted as collateral to its reinsurance counterparties.

The fair value of White Mountains’ variable annuity reinsurance liabilities are estimated using actuarial and capital market assumptions related to the projected discounted cash flows over the term of the reinsurance agreement. Assumptions regarding future policyholder behavior, including surrender and lapse rates, are generally unobservable inputs and significantly impact the fair value estimates. Market conditions including, but not limited to, changes in interest rates, equity indices, market volatility and foreign currency exchange rates as well as the variations in actuarial assumptions regarding policyholder behavior may result in significant fluctuations in the fair value estimates. Generally, the liabilities associated with these guarantees increase with declines in the equity markets, interest rates and currencies against the Japanese yen, as well as with increases in market volatilities. White Mountains uses derivative instruments, including put options, interest rate swaps, total return swaps on bond and equity indices and forwards and futures contracts on major equity indices, currency pairs and government bonds, to mitigate the risks associated with changes in the fair value of the reinsured variable annuity guarantees. The types of inputs used to estimate the fair value of these derivative instruments, with the exception of actuarial assumptions regarding policyholder behavior and risk margins, are generally the same as those used to estimate the fair value of variable annuity liabilities.

The following summarizes quantitative information about significant unobservable inputs associated with the fair value estimates for variable annuity reinsurance liabilities and derivative instruments that have been classified as Level 3 measurements:



	September 30, 2012
($ in Millions) Description	Fair Value		Valuation Technique(s)	Unobservable Input	Range					Weighted Average
Variable annuity benefit guarantee liabilities	$	672.4	Discounted cash flows	Surrenders	0.1	%	-	3.0	%	0.4	%
				Mortality	0.0	%	-	6.4	%	0.9	%
				Foreign exchange volatilities	10.8	%	-	17.4	%	12.8	%
				Index volatilities	13.1	%	-	23.9	%	19.5	%

Foreign exchange and equity index options	$	213.0	Black-Scholes option pricing model	Expected equity dividends	1.9	%	-	5.2	%	3.1	%
			Black-Scholes option pricing model	Foreign exchange volatilities	10.8	%	-	17.4	%	12.8	%
				Index volatilities	13.1	%	-	23.9	%	19.5	%

The following summarizes realized and unrealized derivative gains (losses) recognized in other revenues for the three and nine months ended September 30, 2012 and 2011 and the carrying values, included in other assets, at September 30, 2012 and December 31, 2011, by type of instrument:



	Gains (Losses)										Carrying Value
	Three Months Ended					Nine Months Ended					As of
	Sept 30,					Sept 30,					Sept 30, 2012		Dec 31, 2011
Millions	2012			2011		2012			2011		Sept 30, 2012		Dec 31, 2011
Fixed income/Interest rate	$	(22.6	)	$	29.8	$	(73.1	)	$	17.3	$	29.1	$	31.1
Foreign exchange	6.5			63.0		(21.0		)	32.8		127.9		161.3
Equity	5.1			56.1		(27.9		)	55.3		85.1		98.0
Total	$	(11.0	)	$	148.9	$	(122.0	)	$	105.4	$	242.1	$	290.4

WM Life Re enters into both over-the-counter (“OTC”) and exchange traded derivative instruments to economically hedge the liability from the variable annuity benefit guarantee. In the case of OTC derivatives, WM Life Re has exposure to credit risk for amounts that are uncollateralized by counterparties. WM Life Re’s internal risk management guidelines establish net counterparty exposure thresholds that take into account OTC counterparties’ credit ratings. WM Life Re has entered into master netting agreements with certain of its counterparties whereby the collateral provided (held) is calculated on a net basis. The following summarizes collateral provided to WM Life Re from counterparties:



Millions	September 30, 2012		December 31, 2011
Short-term investments	$	63.3	$	73.2
Fixed maturity securities	—		—
Total	$	63.3	$	73.2

Collateral held by or provided by WM Life Re in the form of fixed maturity securities comprise U.S. Treasury securities, which are recorded at fair value. Collateral in the form of short-term investments consists of money-market instruments, carried at amortized cost, which approximates fair value. The following summarizes the value, collateral (held) provided by WM Life Re and net exposure to credit losses on OTC derivative instruments recorded within other assets:



Millions	September 30, 2012			December 31, 2011
OTC derivative instruments ⁽¹⁾	$	251.4		$	295.4
Collateral held	(63.3		)	(73.2		)
Collateral provided	85.6			83.0
Net exposure to credit losses on fair value of OTC instruments	$	273.7		$	305.2

⁽¹⁾Value of OTC derivative instruments as of September 30, 2012 and December 31, 2011 excludes adjustments for counterparty credit risk of $(5.2)

and $(9.1) included in fair value under GAAP.

The following table summarizes uncollateralized amounts due under WM Life Re’s OTC derivative contracts:



	Uncollateralized balance as of
Millions	September 30, 2012		S&P Rating⁽¹⁾
Citigroup ⁽²⁾	$	63.4	A
Royal Bank of Scotland	58.5		A
Bank of America	50.3		A
JP Morgan ⁽²⁾	40.8		A+
Nomura ⁽²⁾	35.9		BBB+
Barclays	20.7		A+
Goldman Sachs ⁽²⁾	4.1		A-
Total	$	273.7

⁽¹⁾Standard & Poor’s (“S&P”) ratings as detailed above are: “A+” (Strong, which is the fifth highest of

twenty-two creditworthiness ratings), “A” (Strong, which is the sixth highest of

twenty-two creditworthiness ratings), “A-” (Strong, which is the seventh highest of twenty-two creditworthiness

ratings) and “BBB+” (Adequate, which is the eighth highest of twenty-two creditworthiness ratings).

⁽²⁾Collateral provided (held) calculated under master netting agreement.

The OTC derivative contracts are subject to restrictions on liquidation of the instruments and distribution of proceeds under collateral agreements. In addition, WM Life Re held cash, short-term and fixed maturity investments posted as collateral to its reinsurance counterparties. The additional collateral consists of the following:



Millions	September 30, 2012		December 31, 2011
Cash	$	341.7	$	453.5
Short-term investments	14.6		.6
Fixed maturity investments	121.2		31.2
Total	$	477.5	$	485.3

Forward Contracts

Beginning in September 2012, White Mountains has entered into forward contracts as a tool to assist in maintaining currency positions within pre-defined ranges at Sirius Group. White Mountains monitors its exposure to foreign currency and adjusts its forward positions within the risk guidelines and ranges established by senior management for each currency, as necessary. While White Mountains actively manages its forward positions, mismatches between movements in foreign currency rates and its forward contracts may result in currency positions being outside the pre-defined ranges and/or foreign currency losses. At September 30, 2012, White Mountains held approximately $38.8 million (SEK 254.0 million) total gross notional value of foreign currency forward contracts.

All of White Mountains' forward contracts are traded over-the-counter. The fair value of the contracts has been estimated using OTC quotes for similar instruments and accordingly, the measurements have been classified as Level 2 measurements at September 30, 2012.

The following tables summarize the changes in White Mountains' forward contracts for the three and nine months ended September 30, 2012:



	Forward contracts
	Three Months Ended		Nine Months Ended
Millions	September 30, 2012		September 30, 2012
Beginning of period	$	—	$	—
Purchases	—		—
Realized and unrealized gains(losses)	.3		.3
Sales/settlements	—		—
End of period	$	.3	$	.3

The following summarizes realized and unrealized derivative gains (losses) recognized in net realized and unrealized investment gains for the three and nine months ended September 30, 2012 and the carrying values, included in other long-term investments, at September 30, 2012 by type of currency:



	Gains (Losses)
	Three Months Ended			Nine Months Ended			Carrying Value As of
	September 30,			September 30,			September 30,
Millions	2012			2012			2012
USD	$	.4		$	.4		$	.4
SEK	—			—			—
EUR	(.1		)	(.1		)	(.1		)
GBP	—			—			—
Currency Translation	—			—			—
Total	$	.3		$	.3		$	.3

White Mountains does not hold or provide any collateral for the forward contracts. The following table summarizes uncollateralized notional amounts associated with forward currency contracts:



	Uncollateralized balance as of
Millions	September 30, 2012		S&P Rating(1)
Deutsche Bank	$	5.5	A+
Royal Bank of Canada	8.0		A+
HSBC Bank plc	12.4		AA-
JP Morgan	7.3		A
Goldman Sachs	5.6		AA-
Total	$	38.8

⁽¹⁾Standard & Poor's (“S&P”) ratings as detailed above are: “AA-” (Very Strong, which is the sixth highest of

twenty-two creditworthiness ratings), “A+” (Strong, which is the seventh highest of twenty-two creditworthiness

ratings) and “A” (Strong, which is the eighth highest of twenty-two creditworthiness ratings).

Earnings (Loss) Per Share

9 Months Ended

Sep. 30, 2012

Earnings Per Share [Abstract]

Earnings per share

Earnings (Loss) Per Share

Basic earnings (loss) per share amounts are based on the weighted average number of common shares outstanding including unvested restricted shares that are considered participating securities. Diluted earnings (loss) per share amounts are based on the weighted average number of common shares including unvested restricted shares and the net effect of potentially dilutive common shares outstanding. The following table outlines the Company’s computation of earnings (loss) per share from continuing operations for the three and nine months ended September 30, 2012 and 2011 (see Note 14 for earnings per share amounts for discontinued operations):



	Three Months Ended						Nine Months Ended
	Sept 30,						Sept 30,
	2012			2011			2012			2011
Basic and diluted earnings (loss) per share numerators (in millions):
Net income (loss) from continuing operations attributable to White Mountains’ common shareholders	$	125.9		$	14.3		$	254.6		$	(6.3	)
Allocation of (income) loss for unvested restricted common shares	(1.8		)	(.1		)	(3.3		)	.1
Dividends declared on participating restricted common shares ⁽¹⁾	—			—			(.1		)	(.1		)
Total allocation to restricted common shares	(1.8		)	(.1		)	(3.4		)	—
Net income (loss) attributable to White Mountains’ common shareholders, net of restricted common share amounts	$	124.1		$	14.2		$	251.2		$	(6.3	)
Undistributed net earnings (loss) (in millions):
Net income (loss) attributable to White Mountains’ common shareholders, net of restricted common share amounts	$	124.1		$	14.2		$	251.2		$	(6.3	)
Dividends declared net of participating restricted common share amounts ⁽¹⁾	—			—			(6.5		)	(7.9		)
Total undistributed net earnings (loss), net of restricted common share amounts	$	124.1		$	14.2		$	244.7		$	(14.2	)
Basic earnings (loss) per share denominators (in thousands):
Total average common shares outstanding during the period	6,590.4			7,919.3			6,885.9			7,970.0
Average unvested restricted shares ⁽²⁾	(96.5		)	(73.5		)	(89.5		)	(68.0		)
Basic earnings (loss) per share denominator	6,493.9			7,845.8			6,796.4			7,902.0
Diluted earnings (loss) per share denominator (in thousands):
Total average common shares outstanding during the period	6,590.4			7,919.3			6,885.9			7,970.0
Average unvested restricted common shares⁽²⁾	(96.5		)	(73.5		)	(89.5		)	(68.0		)
Average outstanding dilutive options to acquire common shares ⁽³⁾	—			—			—			—
Diluted earnings (loss) per share denominator	6,493.9			7,845.8			6,796.4			7,902.0
Basic earnings (loss) per share (in dollars):
Net income (loss) attributable to White Mountains’ common shareholders	$	19.11		$	1.81		$	36.96		$	(.80	)
Dividends declared	—			—			(1.00		)	(1.00		)
Undistributed earnings (loss)	$	19.11		$	1.81		$	35.96		$	(1.80	)
Diluted earnings (loss) per share (in dollars)
Net income (loss) attributable to White Mountains’ common shareholders	$	19.11		$	1.81		$	36.96		$	(.80	)
Dividends declared	—			—			(1.00		)	(1.00		)
Undistributed earnings (loss)	$	19.11		$	1.81		$	35.96		$	(1.80	)

⁽¹⁾ Restricted shares issued by White Mountains receive dividends, and therefore, are considered participating securities.

⁽²⁾Restricted shares outstanding vest either in equal annual installments or upon a stated date (see Note 12).

⁽³⁾The diluted earnings (loss) per share denominator for the three and nine months ended September 30, 2012 and 2011 do not include common shares issuable upon exercise of the Non-Qualified Options as they are anti-dilutive to the calculation.

Segment Information

9 Months Ended

Sep. 30, 2011

Segment Reporting [Abstract]

Segment Information

White Mountains has determined that its reportable segments are OneBeacon, Sirius Group, and Other Operations.

White Mountains has made its segment determination based on consideration of the following criteria: (i) the nature of the business activities of each of the Company’s subsidiaries and affiliates; (ii) the manner in which the Company’s subsidiaries and affiliates are organized; (iii) the existence of primary managers responsible for specific subsidiaries and affiliates; and (iv) the organization of information provided to the chief operating decision makers and the Board of Directors.

Significant intercompany transactions among White Mountains’ segments have been eliminated herein. Financial information for White Mountains’ segments follows:



Millions	OneBeacon			Sirius Group			Other Operations		Total
Three Months Ended September 30, 2012
Earned insurance and reinsurance premiums	$	293.9		$	242.9		$	—	$	536.8
Net investment income	12.8			16.7			8.1		37.6
Net realized and unrealized investment gains (losses)	40.0			(8.9		)	41.6		72.7
Other revenue	(.4		)	48.2			2.5		50.3
Total revenues	346.3			298.9			52.2		697.4
Losses and loss adjustment expenses	164.7			143.4			—		308.1
Insurance and reinsurance acquisition expenses	66.6			41.0			—		107.6
Other underwriting expenses	47.4			29.1			.1		76.6
General and administrative expenses	4.4			10.2			44.1		58.7
Interest expense on debt	4.1			6.5			.7		11.3
Total expenses	287.2			230.2			44.9		562.3
Pre-tax income	$	59.1		$	68.7		$	7.3	$	135.1



Millions	OneBeacon			Sirius Group			Other Operations			Total
Three Months Ended September 30, 2011
Earned insurance and reinsurance premiums	$	259.1		$	232.0		$	—		$	491.1
Net investment income	16.1			22.1			4.6			42.8
Net realized and unrealized investment gains (losses)	(47.4		)	65.9			(15.6		)	2.9
Other revenue	.1			(29.3		)	(5.8		)	(35.0		)
Total revenues	227.9			290.7			(16.8		)	501.8
Losses and loss adjustment expenses	149.7			130.5			—			280.2
Insurance and reinsurance acquisition expenses	58.6			48.4			—			107.0
Other underwriting expenses	36.0			28.3			—			64.3
General and administrative expenses	2.5			7.4			26.3			36.2
Interest expense on debt	4.1			6.5			2.2			12.8
Total expenses	250.9			221.1			28.5			500.5
Pre-tax (loss) income	$	(23.0	)	$	69.6		$	(45.3	)	$	1.3



Millions	OneBeacon			Sirius Group		Other Operations			Total
Nine Months Ended September 30, 2012
Earned insurance and reinsurance premiums	$	846.0		$	699.3	$	—		$	1,545.3
Net investment income	41.5			50.9		27.4			119.8
Net realized and unrealized investment gains (losses)	57.9			22.9		42.4			123.2
Other revenue	(.1		)	48.9		32.2			81.0
Total revenues	945.3			822.0		102.0			1,869.3
Losses and loss adjustment expenses	452.5			369.2		—			821.7
Insurance and reinsurance acquisition expenses	185.6			140.6		—			326.2
Other underwriting expenses	146.2			82.1		.1			228.4
General and administrative expenses	9.6			35.4		101.3			146.3
Interest expense on debt	12.2			19.6		1.3			33.1
Total expenses	806.1			646.9		102.7			1,555.7
Pre-tax income (loss)	$	139.2		$	175.1	$	(.7	)	$	313.6



Millions	OneBeacon			Sirius Group			Other Operations			Total
Nine Months Ended September 30, 2011
Earned insurance and reinsurance premiums	$	748.0		$	685.5		$	—		$	1,433.5
Net investment income	55.8			68.3			14.0			138.1
Net realized and unrealized investment gains (losses)	(13.3		)	60.7			(11.0		)	36.4
Other revenue	(12.2		)	(13.8		)	(2.3		)	(28.3		)
Total revenues	778.3			800.7			.7			1,579.7
Losses and loss adjustment expenses	421.3			499.1			—			920.4
Insurance and reinsurance acquisition expenses	161.5			135.1			—			296.6
Other underwriting expenses	124.5			79.4			—			203.9
General and administrative expenses	7.4			23.3			89.7			120.4
Interest expense on debt	16.4			19.6			2.8			38.8
Total expenses	731.1			756.5			92.5			1,580.1
Pre-tax income (loss)	$	47.2		$	44.2		$	(91.8	)	$	(.4	)

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8981-108599

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9038-108599

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8971-108599

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8595-108599

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8380-108599

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8933-108599

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 26
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8844-108599

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8984-108599

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9031-108599

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9054-108599

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8538-108599

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8864-108599

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8924-108599

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8906-108599

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 131
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Investments in Unconsolidated Affiliates

9 Months Ended

Sep. 30, 2012

Equity Method Investments and Joint Ventures [Abstract]

Investments in Unconsolidated Affiliates

Note 11. Investments in Unconsolidated Affiliates

White Mountains’ investments in unconsolidated affiliates represent investments in other companies in which White Mountains has a significant voting and economic interest but does not control the entity.



Millions	September 30, 2012		December 31, 2011
Symetra common shares	$	284.0	$	261.0
Unrealized gains from Symetra's fixed maturity portfolio	64.6		—
GAAP Carrying value of Symetra common shares	348.6		261.0
Symetra warrants	26.2		12.6
Total investment in Symetra	374.8		273.6
Pentelia Capital Management	1.5		1.7
Total investments in unconsolidated affiliates	$	376.3	$	275.3

Symetra

At September 30, 2012 and December 31, 2011, White Mountains owned 17.4 million common shares of Symetra Financial Corporation (“Symetra”) and warrants to acquire an additional 9.5 million common shares. White Mountains accounts for its investment in common shares of Symetra using the equity method. At December 31, 2011, due to the prolonged low interest rate environment in which life insurance companies currently operate, White Mountains concluded that its investment in Symetra common shares was other-than-temporarily impaired and wrote down the GAAP book value of the investment to its estimated fair value of $261.0 million, or $15 per share at December 31, 2011. White Mountains recorded $45.9 million of after-tax equity in losses of unconsolidated affiliates and $136.6 million of after-tax equity in net unrealized losses of unconsolidated affiliates.

Under the equity method, the GAAP carrying value of White Mountains’ investment in Symetra common shares is normally equal to the percentage of Symetra’s GAAP book value represented by White Mountains’ common share ownership, which was 15% at September 30, 2012. As a result of recording the write-down, White Mountains’ carrying value of its investment in Symetra differs from the carrying value by applying its ownership share against Symetra’s GAAP equity as normally done under the equity method. The pre-tax basis difference of $195.8 million as of December 31, 2011 is being amortized over a 30 year period pro rata based on estimated future cash flows associated with Symetra’s underlying assets and liabilities to which the basis difference has been attributed. White Mountains continues to record its equity in Symetra’s earnings and net unrealized gains (losses). In addition, White Mountains recognizes the amortization of the basis difference through equity in earnings of unconsolidated affiliates and equity in net unrealized gains (losses) from investments in unconsolidated affiliates consistent with the original attribution of the writedown between equity in earnings and equity in net unrealized gains (losses). For the three and nine months ended September 30, 2012, White Mountains recognized after-tax amortization of $0.8 million and $2.4 million through equity in earnings of unconsolidated affiliates and $3.0 million and $9.1 million through equity in net unrealized gains from investments in unconsolidated affiliates. At September 30, 2012, the pre-tax unamortized basis difference was $183.3 million.

White Mountains accounts for its Symetra warrants as derivatives with changes in fair value recognized through the income statement as a gain or loss recognized through other revenues. White Mountains uses a Black Scholes valuation model to determine the fair value of the Symetra warrants. The major assumptions used in valuing the Symetra warrants at September 30, 2012 were a risk free rate of 0.22%, volatility of 36.5%, an expected life of 1.82 years, a strike price of $11.49 per share and a share price of $12.30 per share.

The following table summarizes amounts recorded by White Mountains relating to its investment in Symetra for the three months ended September 30, 2012 and 2011:



	Three Months Ended									Three Months Ended
	September 30, 2012									September 30, 2011
Millions	Common Shares			Warrants			Total			Common Shares			Warrants			Total
Carrying value of investment in Symetra as of June 30	$	305.9		$	29.8		$	335.7		$	388.5		$	32.5		$	421.0
Equity in earnings⁽¹⁾⁽²⁾	8.8			—			8.8			1.6			—			1.6
Equity in net unrealized gains from Symetra’s fixed maturity portfolio ⁽³⁾	35.2			—			35.2			59.9			—			59.9
Dividends received	(1.3		)	—			(1.3		)	(1.0		)	—			(1.0		)
Increase (decrease) in value of warrants	—			(3.6		)	(3.6		)	—			(24.8		)	(24.8		)
Carrying value of investment in Symetra as September 30⁽⁴⁾⁽⁵⁾	$	348.6		$	26.2		$	374.8		$	449.0		$	7.7		$	456.7

⁽¹⁾Equity in earnings excludes tax expense of $0.7 and $0.1.

⁽²⁾Equity in earnings includes $0.9 increase relating to the pre-tax amortization of Symetra common share impairment from September 30, 2012

⁽³⁾Net unrealized gains includes $3.3 increase relating to the pre-tax amortization of Symetra common share impairment from September 30, 2012.

⁽⁴⁾Includes White Mountains’ equity in net unrealized gains from Symetra’s fixed maturity portfolio of $35.2 and $147.7 as of September 30, 2012 and 2011, which exclude tax expense of $2.8 and $12.3.

⁽⁵⁾The aggregate value of White Mountains’ investment in common shares of Symetra was $214.0 based upon the quoted market price of $12.30 per share

at September 30, 2012.

The following table summarizes amounts recorded by White Mountains relating to its investment in Symetra for the nine months ended September 30, 2012 and 2011:



	Nine Months Ended								Nine Months Ended
	September 30, 2012								September 30, 2011
Millions	Common Shares			Warrants		Total			Common Shares			Warrants			Total
Carrying value of investment in Symetra as of January 1	$	261.0		$	12.6	$	273.6		$	350.4		$	37.1		$	387.5
Equity in earnings ⁽¹⁾⁽²⁾	26.7			—		26.7			17.5			—			17.5
Equity in net unrealized gains from Symetra’s fixed maturity portfolio⁽³⁾	64.6			—		64.6			84.0			—			84.0
Dividends received	(3.7		)	—		(3.7		)	(2.9		)	—			(2.9		)
Increase (decrease) in value of warrants	—			13.6		13.6			—			(29.4		)	(29.4		)
Carrying value of investment in Symetra as September 30 ⁽⁴⁾⁽⁵⁾	$	348.6		$	26.2	$	374.8		$	449.0		$	7.7		$	456.7

⁽¹⁾Equity in earnings excludes tax expense of $2.2 and $1.4.

⁽²⁾Equity in earnings includes $0.9 increase relating to the pre-tax amortization of Symetra common share impairment from September 30, 2012.

⁽³⁾Net unrealized gains includes $9.9 increase relating to the pre-tax amortization of Symetra common share impairment from September 30, 2012.

⁽⁴⁾Includes White Mountains’ equity in net unrealized gains from Symetra’s fixed maturity portfolio of $64.6 and $147.7 as of September 30, 2012 and 2011, which exclude tax expense of $5.2 and $24.2.

⁽⁵⁾The aggregate value of White Mountains’ investment in common shares of Symetra was $214.0 based upon the quoted market price of $12.30 per share at

September 30, 2012.

During the three and nine months ended September 30, 2012, White Mountains received cash dividends from Symetra of $1.3 million and $3.7 million on its common share investment that was recorded as a reduction of White Mountains’ investment in Symetra. During the three and nine months ended September 30, 2012, White Mountains also received cash dividends of $0.7 million and $2.0 million from Symetra on its investment in Symetra warrants that was recorded in net investment income.

- Definition

The entire disclosure for equity method investments and joint ventures. Equity method investments are investments that give the investor the ability to exercise significant influence over the operating and financial policies of an investee. Joint ventures are entities owned and operated by a small group of businesses as a separate and specific business or project for the mutual benefit of the members of the group.

+ References + Details

Employee Share-Based Incentive Compensation Plans

9 Months Ended

Sep. 30, 2012

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Employee Share-Based Incentive Compensation Plans

White Mountains’ Long-Term Incentive Plan (the “WTM Incentive Plan”) provides for grants of various types of share-based and non share-based incentive awards to key employees and service providers of the Company and certain of its subsidiaries. White Mountains’ share-based compensation incentive awards consist of performance shares, restricted shares and stock options.

Share-Based Compensation Based on White Mountains Common Shares

WTM Performance Shares

Performance shares are conditional grants of a specified maximum number of common shares or an equivalent amount of cash. Performance share awards vest, subject to the attainment of performance goals, at the end of a three-year period and are valued based on the market value of common shares at the time awards are paid. The following table summarizes performance share activity for the three and nine months ended September 30, 2012 and 2011 for performance shares granted under the WTM Incentive Plan and phantom performance shares granted under the Sirius Group Performance Plan (the “WTM Phantom Share Plan”):



	Three Months Ended September 30,									Nine Months Ended September 30,
	2012					2011				2012					2011
Millions, except share amounts	Target Performance Shares Outstanding		Accrued Expense			Target Performance Shares Outstanding	Accrued Expense			Target Performance Shares Outstanding		Accrued Expense			Target Performance Shares Outstanding		Accrued Expense
Beginning of period	118,450		$	32.7		150,064	$	56.5		150,064		$	66.1		163,184		$	29.4
Shares paid or expired⁽¹⁾	—		—			—	—			(68,357	)	(48.4		)	(51,131	)	—
New grants	2,500		—			—	—			38,432		—			37,675		—
Assumed forfeitures and cancellations ⁽²⁾	(1,359	)	(.4		)	—	—			(548	)	.4			336		(.6		)
Expense recognized	—		6.6			—	(1.0		)	—		20.8			—		26.7
Ending September 30,	119,591		$	38.9		150,064	$	55.5		119,591		$	38.9		150,064		$	55.5

⁽¹⁾WTM performance share payments in 2012 for the 2009-2011 performance cycle ranged from147% to 155% of target. There were no payments made in 2011 for the 2008-2010 performance cycle; those performance shares did not meet the threshold performance goals and expired.

⁽²⁾Amounts include changes in assumed forfeitures, as required under GAAP.

For the 2009-2011 performance cycle, the Company issued common shares for 9,577 performance shares earned and all other performance shares earned were settled in cash.

If the outstanding WTM performance shares had vested on September 30, 2012, the total additional compensation cost to be recognized would have been $26.6 million, based on accrual factors at September 30, 2012 (common share price and payout assumptions).

Performance Shares granted under the WTM Incentive Plan

The following table summarizes performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan at September 30, 2012 for each performance cycle:



Millions, except share amounts	Target Performance Shares Outstanding		Accrued Expense
Performance cycle:
2010 – 2012	42,320		$	19.0
2011 – 2013	37,255		12.9
2012 – 2014	38,092		5.4
Sub-total	117,667		37.3
Assumed forfeitures	(2,941	)	(1.0		)
Total at September 30, 2012	114,726		$	36.3

Phantom Performance Shares granted under WTM Phantom Share Plan

The following table summarizes phantom performance shares outstanding and accrued expense for grants made under WTM Phantom Share Plan at September 30, 2012 for each performance cycle:



Millions, except share amounts	Target WTM Phantom Performance Shares Outstanding		Accrued Expense
Performance cycle:
2010 – 2012	4,990		$	2.7
2011 – 2013 ⁽¹⁾	—		—
2012 – 2014 ⁽¹⁾	—		—
Sub-total	4,990		2.7
Assumed forfeitures	(125	)	(.1		)
Total at September 30, 2012	4,865		$	2.6

⁽¹⁾ All performance shares for the 2011–2013 and 2012–2014 performance cycles were granted from

the WTM Incentive Plan.

Restricted Shares

The following outlines the unrecognized compensation cost associated with the outstanding restricted share awards for the three and nine months ended September 30, 2012 and 2011:



	Three Months Ended September 30,									Nine Months Ended September 30,
	2012					2011				2012					2011
Millions, except share amounts	Restricted Shares		Unamortized Issue Date Fair Value			Restricted Shares	Unamortized Issue Date Fair Value			Restricted Shares		Unamortized Issue Date Fair Value			Restricted Shares	Unamortized Issue Date Fair Value
Non-vested,
Beginning of period	93,460		$	21.5		73,500	$	18.9		72,000		$	13.3		46,250	$	14.1
Issued	3,700		2.0			—	—			32,160		15.7			27,250	9.9
Vested	—		—			—	—			(7,000	)	—			—	—
Forfeited	(1,065	)	(.2		)	—	—			(1,065	)	(.2		)	—	—
Expense recognized	—		(3.2		)	—	(2.8		)	—		(8.7		)	—	(7.9		)
Non-vested at September 30,	96,095		$	20.1		73,500	$	16.1		96,095		$	20.1		73,500	$	16.1

During the third quarter of 2012, White Mountains issued 2,500 restricted shares that vest on January 1, 2015 and 1,200 restricted shares that vest on July 16, 2015. During the first quarter of 2012, White Mountains issued 25,460 restricted shares that vest on January 1, 2015 and 3,000 restricted shares that vest in two equal annual installments beginning in February 2014. During the second quarter of 2011, White Mountains issued 250 restricted shares that vest on January 1, 2014. During the first quarter of 2011, White Mountains issued 27,000 restricted shares that vest on January 1, 2014. During the first quarter of 2010, White Mountains issued 19,750 restricted shares that vest on December 31, 2012. The unrecognized compensation cost at September 30, 2012 is expected to be recognized ratably over the remaining vesting periods.

Non-Qualified Options

In January 2007, the Company issued 200,000 seven year Non-Qualified Options to the Company’s Chairman and CEO that vested in equal annual installments over five years and that had an initial exercise price of $650 per common share that escalated at an annual rate of 5% less the annual regular dividend rate. At the 2010 Annual General Meeting of Members held on May 26, 2010, the Company’s shareholders approved the following amendments to the Non-Qualified Options: (1) extend the term of the Non-Qualified Options by three years to January 20, 2017; (2) freeze the exercise price at $742 per common share, the exercise price on February 24, 2010; (3) extinguish 75,000 of the 200,000 Non-Qualified Options; and (4) limit the potential in-the-money value of the Non-Qualified Options in excess of $100.0 million to 50% of the amount in excess of $100.0 million. For the nine months ended September 30, 2011, White Mountains recognized a total of $0.1 million of expense related to amortizing the Non-Qualified Options. As of the first quarter of 2011 the Non-Qualified Options were fully amortized.

Share-Based Compensation Based on OneBeacon Ltd. Common Shares

The OneBeacon Long-Term Incentive Plan (the “OneBeacon Incentive Plan”) provides for grants of various types of share-based and non share-based incentive awards to key employees of OneBeacon Ltd. and certain of its subsidiaries. OneBeacon’s share-based incentive awards consist of OneBeacon performance shares, stock options granted in connection with OneBeacon’s initial public offering, restricted shares and restricted stock units (“RSUs”).

OneBeacon Performance Shares

OneBeacon performance shares are conditional grants of a specified maximum number of common shares or an equivalent amount of cash. OneBeacon performance share awards vest, subject to the attainment of performance goals, at the end of a three-year period and are valued based on the market value of OneBeacon Ltd. common shares at the time awards are paid.

The following table summarizes performance share activity for the three and nine months ended September 30, 2012 and 2011 for OneBeacon performance shares granted under the OneBeacon Incentive Plan:



	Three Months Ended September 30,										Nine Months Ended September 30,
	2012					2011					2012					2011
Millions, except share amounts	Target Performance Shares Outstanding		Accrued Expense			Target Performance Shares Outstanding		Accrued Expense			Target Performance Shares Outstanding		Accrued Expense			Target Performance Shares Outstanding		Accrued Expense
Beginning of period	560,577		$	3.1		671,727		$	10.0		642,667		$	9.7		1,464,295		$	18.5
Payments and deferrals⁽¹⁾⁽²⁾	—		—			—		—			(258,901	)	(7.8		)	(936,150	)	(10.5		)
New awards	—		—			—		—			181,290		—			194,900		—
Assumed forfeitures and cancellations⁽³⁾	(3,354	)	—			(19,583	)	.1			(7,833	)	—			(70,901	)	(.2		)
Expense recognized	—		(2.2		)	—		(.5		)	—		(1.0		)	—		1.8
Ending September 30,	557,223		$	.9		652,144		$	9.6		557,223		$	.9		652,144		$	9.6

⁽¹⁾ OneBeacon performance share payments in 2012 for the 2009-2011 performance cycle were at 138.6% of target. OneBeacon performance shares payments in 2011 for the 2008-2010 performance cycle were at 68.5% of target. Amounts include deposits into OneBeacon’s deferred compensation plan.

⁽²⁾ OneBeacon performance share payments also include accelerated payments resulting from the OneBeacon Personal Lines and Commercial Lines Transactions. The accelerated OneBeacon performance shares payments for the 2009-2011 and 2010-2012 performance cycles were on a pro rata basis and at a performance factor of 100%.

⁽³⁾ Amounts include changes in assumed forfeitures, as required under GAAP.

If the outstanding OneBeacon performance shares had been vested on September 30, 2012, the total additional compensation cost to be recognized would have been $1.7 million, based on accrual factors at September 30, 2012 (common share price and payout assumptions).

The following table summarizes OneBeacon performance shares outstanding awarded under the OneBeacon Incentive Plan at September 30, 2012 for each performance cycle:



Millions, except share amounts	Target OneBeacon Performance Shares Outstanding		Accrued Expense
Performance cycle:
2010 – 2012	238,658		$	—
2011 – 2013	151,563		.4
2012 – 2014	181,290		.5
Sub-total	571,511		.9
Assumed forfeitures	(14,288	)	—
Total at September 30, 2012	557,223		$	.9

OneBeacon Restricted Shares

The following outlines the unrecognized compensation cost associated with the outstanding restricted share awards for the three and nine months ended September 30, 2012:



	Three Months Ended September 30,								Nine Months Ended September 30,
	2012				2011				2012				2011
Millions, except share amounts	Restricted Shares	Unamortized Issue Date Fair Value			Restricted Shares	Unamortized Issue Date Fair Value			Restricted Shares	Unamortized Issue Date Fair Value			Restricted Shares	Unamortized Issue Date Fair Value
Non-vested,
Beginning of period	930,000	$	11.2		630,000	$	8.5		630,000	$	7.7		630,000	$	8.6
Issued	—	—			—	—			300,000	4.6			—	—
Vested	—	—			—	—			—	—			—	—
Forfeited	—	—			—	—			—	—			—	—
Expense recognized	—	(.8		)	—	(.4		)	—	(1.9		)	—	(.5		)
Non-vested at September 30,	930,000	$	10.4		630,000	$	8.1		930,000	$	10.4		630,000	$	8.1

On March 1, 2012, OneBeacon issued 300,000 restricted shares that vest in two equal annual installments on February 28, 2014 and 2015.

On May 25, 2011, OneBeacon issued 630,000 restricted shares to its CEO that vest in four equal annual installments beginning on February 22, 2014. Concurrently with the grant of the restricted shares, 35,000 OneBeacon performance shares issued to OneBeacon’s CEO for the 2011-2013 performance share cycle were forfeited and performance share awards to OneBeacon’s CEO for the subsequent five years will also be reduced by 35,000 shares.

The unrecognized compensation cost at September 30, 2012 is expected to be recognized ratably over the remaining vesting periods.

Non-Qualified Options

In November 2006, in connection with its initial public offering, OneBeacon Ltd. issued to its key employees 1,420,000 OneBeacon Non-Qualified Options to acquire OneBeacon Ltd. common shares at an above-market fixed exercise price.

The following table summarizes option activity for the three and nine months ended September 30, 2012 and 2011:



	Three Months Ended September 30,			Nine Months Ended September 30,
	2012	2011		2012		2011
Millions, except share amounts	Target Options Outstanding	Target Options Outstanding		Target Options Outstanding		Target Options Outstanding
Beginning of period	—	750,130		740,870		768,652
New awards	—	—		—		—
Forfeitures and cancellations	—	(9,260	)	—		(27,782	)
Vested and expired	—	—		(740,870	)	—
Exercised	—	—		—		—
Expense recognized	—	—		—		—
Ending September 30,	—	740,870		—		740,870

The fair value of each option award at grant was estimated using a Black-Scholes option pricing model using an expected volatility assumption of 30%, a risk-free interest rate assumption of 4.6%, a forfeiture assumption of 5%, an expected dividend rate assumption of 3.4% and an expected term assumption of 5.5 years. The options originally had a per share exercise price of $30.00. On May 27, 2008, the OneBeacon Compensation Committee of the Board of Directors (the “OB Compensation Committee”) amended the exercise price to $27.97 as a result of the $2.03 per share special dividend paid in the first quarter of 2008. On November 16, 2010, the OB Compensation Committee adjusted the exercise price to $25.47 as a result of the $2.50 per share special dividend paid in the third quarter of 2010. The compensation expense associated with the options and the incremental fair value of the award modifications were recognized ratably over the vesting period.

For the three and nine months ended September 30, 2011, White Mountains recognized $0.1 million and $0.4 million of expense related to amortizing the OneBeacon Non-Qualified Options. As of December 31, 2011, the OneBeacon Non-Qualified Options were fully amortized. The options expired unexercised in the second quarter of 2012.

Restricted Stock Units

The Non-Qualified Options granted by OneBeacon Ltd., in connection with its initial public offering, did not include a mechanism in the options to reflect the contribution to total return from the regular quarterly dividend. As a result, during the first quarter of 2008, OneBeacon granted 116,270 Restricted Stock Units (“RSUs”) to actively employed option holders that were scheduled to vest equally on November 9, 2009, 2010 and 2011 subject to, for each vesting tranche of units, the attainment of 4% growth in OneBeacon’s book value per share from January 1, 2008 through the end of the calendar year immediately following the applicable vesting date. Consistent with the terms of the RSU plan, all of the RSUs have vested and were deferred into a OneBeacon non-qualified deferred compensation plan that were paid out in May 2012.

- Definition

The entire disclosure for compensation-related costs for equity-based compensation, which may include disclosure of policies, compensation plan details, allocation of equity compensation, incentive distributions, equity-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 50
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6406099&loc=d3e25284-112666

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6418621&loc=d3e17540-113929

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 718
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5444-113901

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 14

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph 64, 65, A240
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 93-6
-Paragraph 53
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Fair Value of Financial Instruments

9 Months Ended

Sep. 30, 2012

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

White Mountains carries its financial instruments on its balance sheet at fair value with the exception of its fixed-rate, long-term indebtedness and the SIG Preference Shares, which are recorded as noncontrolling interest.

The following table summarizes the fair value and carrying value of financial instruments as of September 30, 2012 and December 31, 2011:



	September 30, 2012				December 31, 2011
Millions	Fair Value		Carrying Value		Fair Value		Carrying Value
OBH Senior Notes	$	276.3	$	269.8	$	277.4	$	269.8
SIG Senior Notes	442.9		399.4		418.6		399.3
SIG Preference Shares	257.5		250.0		217.5		250.0

The fair value estimate for the OBH Senior Notes has been determined using observable inputs for similar instruments and is considered a Level 2 measurement. The fair value estimates for the SIG Senior Notes and the SIG Preference Shares have been determined based on indicative broker quotes and are considered to be Level 3 measurements.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 12: http://www.xbrl.org/2003/role/presentationRef
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+ Details

Discontinued Operations

9 Months Ended

Sep. 30, 2012

Discontinued Operations and Disposal Groups [Abstract]

Discontinued operations

Discontinued Operations

Esurance

On October 7, 2011, White Mountains completed the sale of Esurance Insurance and AFI to Allstate (see Note 2). As a result of the transaction, Esurance Insurance, AFI and the business Esurance Insurance cedes to Sirius Group (collectively, “the Esurance Disposal Group”) are reported as discontinued operations. White Mountains recognized a gain of $677.5 million on the Esurance Sale which is recorded net of tax in discontinued operations. Effective as of December 31, 2011, the results of operations for the Esurance Disposal Group have been classified as discontinued operations and are presented, net of related income taxes, in the statement of comprehensive income.

AutoOne

On February 22, 2012, OneBeacon completed the sale of the AutoOne business to Interboro. AutoOne operated as a division within OneBeacon that offered products and services to automobile assigned risk markets. The transaction included the sale of two insurance entities, AOIC and AOSIC, through which substantially all of the AutoOne business was written on a direct basis. The results of operations for the AutoOne business have been classified as discontinued operations and are presented, net of related income taxes, in the statement of comprehensive income. The assets and liabilities associated with the AutoOne business as of December 31, 2011 have been presented in the balance sheet as held for sale.

During the third quarter of 2012, OneBeacon and Interboro finalized the post-closing adjustments to the closing balance sheet resulting in OneBeacon recording a net gain of $0.5 million after tax. This after-tax net gain is included in loss from sale of discontinued operations in the statements of comprehensive income (loss) for the three and nine months ended September 30, 2012. During the third quarter of 2011, OneBeacon recorded an after-tax loss of $18.2 million in loss from sale of discontinued operations for the estimated loss on sale of AutoOne.

OneBeacon runoff business

On October 17, 2012, OneBeacon entered into an agreement to sell its runoff business to Armour. For the nine months ended September 30, 2012, the results of operations for the runoff business have been classified as discontinued operations and are presented, net of related income taxes, in the statement of comprehensive income. Prior year results of operations have been reclassified to conform to the current period’s presentation. The assets and liabilities associated with the runoff business as of September 30, 2012 have been presented in the balance sheet as held for sale. The amounts classified as discontinued operations exclude investing and financing activities that are conducted on an overall consolidated level and, accordingly, there were no separately identifiable investments associated with the runoff business. Therefore, the prior period balance sheet has not been reclassified to conform to the current period's presentation.

During the third quarter of 2012, OneBeacon recorded $100.5 million in after-tax losses related to the Runoff Transaction. These losses are presented in discontinued operations and are composed of a $91.5 million after-tax loss on sale and a $9.0 million after-tax loss related to a reduction in the workers compensation loss reserve discount rate on reserves being transferred as part of the sale. OneBeacon also recognized $6.5 million of after-tax underwriting losses primarily related to unfavorable loss reserve development from a legacy assumed reinsurance treaty, which is presented in discontinued operations.

Reinsurance

Included in the assets held for sale are reinsurance recoverables from two reinsurance contracts with subsidiaries of Berkshire Hathaway Inc. that OneBeacon was required to purchase in connection with White Mountains' acquisition of OneBeacon in 2001: a reinsurance contract with National Indemnity Company (“NICO”) for up to $2.5 billion in old asbestos and environmental (“A&E”) claims and certain other exposures (the “NICO Cover”) and an adverse loss reserve development cover from General Reinsurance Corporation (“GRC”) for up to $570.0 million, comprised of $400.0 million of adverse loss reserve development occurring in years 2000 and prior (the “GRC Cover”) in addition to $170.0 million of reserves ceded as of the date of the OneBeacon Acquisition. The NICO Cover and GRC Cover, which were contingent on and occurred contemporaneously with the OneBeacon Acquisition, were put in place in lieu of a seller guarantee of loss and LAE reserves and are therefore accounted for under GAAP as a seller guarantee. As of September 30, 2012, the total reinsurance recoverables on paid and unpaid losses of $1,449.2 million related to both the NICO cover and the GRC cover has been included in assets held for sale. Both NICO and GRC have an A.M Best rating of A++, Superior, which is the highest of fifteen ratings.

The total reinsurance recoverables on paid and unpaid losses in assets held for sale were $17.6 million and $2,110.0 million as of September 30, 2012. The reinsurance recoverable on unpaid amount is gross of $153.4 million in purchase accounting adjustments that will become recoverable if claims are paid in accordance with current reserve estimates. In addition, $36.7 million of the amount that is currently included in assets held for sale on the balance sheet will be reported in reinsurance recoverables on unpaid losses when the Runoff Transaction closes (at the then current value) as a result of a related reinsurance contract.

Net Assets Held for Sale

The following summarizes the assets and liabilities associated with the businesses classified as held for sale:



Millions	September 30, 2012		December 31, 2011
Assets held for sale
Fixed maturity investments, at fair value	$	377.3	$	111.8
Cash	—		5.5
Reinsurance recoverable on unpaid losses	1,956.6		—
Reinsurance recoverable on paid losses	17.6		—
Insurance premiums receivable	13.6		8.8
Deferred acquisition costs	—		2.2
Deferred tax asset	6.1		1.9
Other assets	17.0		2.4
Total assets held for sale	$	2,388.2	$	132.6
Liabilities held for sale
Loss and loss adjustment expense reserves	$	2,212.9	$	64.7
Unearned insurance premiums	.6		34.1
Ceded reinsurance payable	19.5		—
Other liabilities	155.2		8.8
Total liabilities held for sale	2,388.2		107.6
Net assets held for sale	$	—	$	25.0

Loss from Discontinued Operations

The following summarizes the results of operations, including related income taxes associated with the businesses classified as discontinued operations:



	Three Months Ended						Nine Months Ended
Millions, except per share amounts	Sept 30,						Sept 30,
	2012			2011			2012			2011
Revenues
Earned insurance premiums	$	(.4	)	$	233.3		$	10.0		$	701.9
Net investment income	—			3.8			—			11.8
Net realized and unrealized investment gains (losses)	—			(6.4		)	—			1.4
Other revenue	—			17.5			—			54.0
Total revenues	(.4		)	248.2			10.0			769.1
Expenses
Loss and loss adjustment expenses	27.7			177.4			48.4			512.3
Insurance and reinsurance acquisition expenses	(.8		)	51.4			(1.3		)	154.1
Other underwriting expenses	(1.1		)	35.0			1.1			83.9
General and administrative expenses	—			1.7			—			37.5
Total expenses	25.8			265.5			48.2			787.8
Pre-tax loss	(26.2		)	(17.3		)	(38.2		)	(18.7		)
Income tax benefit	10.4			5.3			13.7			10.9
Loss from discontinued operations	(15.8		)	(12.0		)	(24.5		)	(7.8		)
Loss from sale of discontinued operations	(91.0		)	(18.2		)	(91.0		)	(18.2		)
Net loss from discontinued operations	$	(106.8	)	$	(30.2	)	$	(115.5	)	$	(26.0	)

Loss Per Share

Basic loss per share amounts are based on the weighted average number of common shares outstanding including unvested restricted shares that are considered participating securities. Diluted loss per share amounts are based on the weighted average number of common shares including unvested restricted shares and the net effect of potentially dilutive common shares outstanding.

The following table outlines the computation of loss per share for discontinued operations for the three and nine months ended September 30, 2012 and 2011:



	Three Months Ended						Nine Months Ended
	Sept 30,						Sept 30,
	2012			2011			2012			2011
Basic and diluted loss per share numerators (in millions):
Net loss attributable to White Mountains’ common shareholders	$	(106.8	)	$	(30.2	)	$	(115.5	)	$	(26.0	)
Allocation of income for participating unvested restricted common shares ⁽¹⁾	1.5			.3			1.5			.2
Net loss attributable to White Mountains’ common shareholders, net of restricted common share amounts⁽²⁾	$	(105.3	)	$	(29.9	)	$	(114.0	)	$	(25.8	)
Basic loss per share denominators (in thousands):
Total average common shares outstanding during the period	6,590.4			7,919.3			6,885.9			7,970.0
Average unvested restricted common shares⁽³⁾	(96.5		)	(73.5		)	(89.5		)	(68.0		)
Basic loss per share denominator	6,493.9			7,845.8			6,796.4			7,902.0
Diluted loss per share denominator (in thousands):
Total average common shares outstanding during the period	6,590.4			7,919.3			6,885.9			7,970.0
Average unvested restricted common shares	(96.5		)	(73.5		)	(89.5		)	(68.0		)
Average outstanding dilutive options to acquire common shares	—			—			—			—
Diluted loss per share denominator	6,493.9			7,845.8			6,796.4			7,902.0
Basic and diluted loss per share (in dollars):	$	(16.21	)	$	(3.81	)	$	(16.77	)	$	(3.26	)

⁽¹⁾Restricted shares issued by White Mountains contain dividend participation features, and therefore, are considered participating securities.

⁽²⁾Net loss attributable to White Mountains’ common shareholders, net of restricted share amounts, is equal to undistributed loss for the three and nine months ended September 30, 2012 and 2011.

⁽³⁾ Restricted common shares outstanding vest either in equal annual installments or upon a stated date (see Note 12)

- Definition

The entire disclosure for the facts and circumstances leading to the completed or expected disposal, manner and timing of disposal, the gain (loss) recognized in the income statement and the income statement caption that includes that gain (loss), amounts of revenues and pretax profit or loss reported in discontinued operations, the segment in which the disposal group was reported, and the classification (whether sold or classified as held for sale) and carrying value of the assets and liabilities comprising the disposal group. Includes all disposal groups, including those classified as components of the entity (discontinued operations).

+ References

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+ Details

Contingencies	9 Months Ended
Contingencies	Sep. 30, 2012
Note 15. Contingencies [Abstract]
Contingencies Disclosure [Text Block]	Note 15. Contingencies Legal Contingencies White Mountains, and the insurance and reinsurance industry in general, are routinely subject to claims related litigation and arbitration in the normal course of business, as well as litigation and arbitration that do not arise from, or are directly related to, claims activity. White Mountains' estimates of the costs of settling matters routinely encountered in claims activity are reflected in the reserves for unpaid loss and LAE. See Note 3. Except as described below, White Mountains is not a party to any material non-claims litigation or arbitration. White Mountains considers the requirements of ASC 450 when evaluating its exposure to non-claims related litigation and arbitration. ASC 450 requires that accruals be established for litigation and arbitration if it is probable that a loss has been incurred and it can be reasonably estimated. ASC 450 also requires that litigation and arbitration be disclosed if it is probable that a loss has been incurred or if there is a reasonable possibility that a loss may have been incurred. Although the ultimate outcome of claims and non-claims related litigation and arbitration, and the amount or range of potential loss at any particular time, is often inherently uncertain, management does not believe that the ultimate outcome of such claims and non-claims related litigation and arbitration will have a material adverse effect on White Mountains' financial condition, results of operations or cash flows. Esurance Sale In 2011, the Company sold its Esurance and Answer Financial businesses (the "Transferred Companies") to The Allstate Corporation ("Allstate") for a purchase price of approximately $1.01 billion. The purchase price consisted of $700 million plus the tangible book value of the Transferred Companies at the closing, which was estimated to be $308 million. Following closing, Allstate was required to prepare a final closing statement, including an audited balance sheet for the Transferred Companies as of the closing date. The Company believes this final closing statement was required to be prepared and audited no later than January 5, 2012. Allstate did not deliver the final closing statement to the Company until June 6, 2012, with an audit report dated June 1, 2012. The Company is disputing Allstate's calculation of tangible book value in the closing statement. The amount in dispute is approximately $20 million, after tax. The dispute principally relates to (i) the elimination of $24.7 million (pre-tax) of deferred acquisition costs ($16.0 million, after tax) and (ii) the inclusion of a liability equal to the costs associated with an Esurance extra-contractual (“ECO”) matter settled in April 2012 of $5.2 million ($3.4 million, after tax). The Company believes that Allstate's failure to have the final closing statement prepared and audited by the required date constitutes a breach of Allstate's obligations under the agreement governing the sale of the Transferred Companies. The Company has brought suit in the United States District Court for the Southern District of New York in connection with such breach. Tribune Company In June 2011, Deutsche Bank Trust Company Americas, Law Debenture Company of New York and Wilmington Trust Company (collectively referred to as "Plaintiffs"), in their capacity as trustees for certain senior notes issued by the Tribune Company ("Tribune"), filed lawsuits in various jurisdictions (the “Noteholder Actions”) against numerous defendants including OneBeacon, OBIC-sponsored benefit plans and other affiliates of White Mountains in their capacity as former shareholders of Tribune seeking recovery of the proceeds from the sale of common stock of Tribune in connection with Tribune's leveraged buyout in 2007 (the "LBO"). Tribune filed for bankruptcy in 2008 in the Delaware bankruptcy court (the "Bankruptcy Court"). The Bankruptcy Court granted Plaintiffs permission to commence these LBO-related actions. Plaintiffs seek recovery of the proceeds received by the former Tribune shareholders on a theory of constructive fraudulent transfer asserting that Tribune purchased or repurchased its common shares without receiving fair consideration at a time when it was, or as a result of the purchases of shares, was rendered, insolvent. OneBeacon has entered into a joint defense agreement with other affiliates of White Mountains that are defendants in the action. OneBeacon and OBIC-sponsored benefit plans received approximately $32 million for Tribune common stock tendered in connection with the LBO. In December 2011, the Judicial Panel on Multidistrict Litigation granted a motion to consolidate all of the Noteholder Actions for pretrial matters and transfer all such proceedings to the United States District Court for the Southern District of New York. In addition, OneBeacon, OBIC-sponsored benefit plans and other affiliates of White Mountains in their capacity as former shareholders of Tribune, along with thousands of former Tribune shareholders, have been named as defendants in an adversary proceeding brought by the Official Committee of Unsecured Creditors of the Tribune Company, on behalf of the Tribune Company, which seeks to avoid the repurchase of shares by Tribune in the LBO on a theory of intentional fraudulent transfer (the “Committee Action”). The Committee Action has since been consolidated with the Noteholder Actions. In September 2012, a case management order was entered in the consolidated cases, setting forth, among other things, a briefing schedule for an omnibus motion to dismiss in the Noteholder Actions. The court is expected to hear oral argument on that motion in March 2013. Discovery and other motion practice (other than motions to amend the complaints) in the Committee Action and the Noteholder Actions is stayed until further order of the court. Ace American Insurance Company A subsidiary of OneBeacon, OneBeacon U.S. Holdings, Inc. ("OBH"), was sued in Federal Court in the Eastern District of Pennsylvania on August 17, 2012 by Ace American Insurance Company ("Ace"). The complaint alleges that OBH, through a professional recruiting firm, improperly hired a group of Ace employees from Ace's surety division. The complaint seeks injunctive relief and unspecified damages. Upon motions of both parties, the court ordered expedited discovery, which has been completed. OBH's response to Ace's motion for preliminary injunction is due at the end of October. OneBeacon believes that Ace's motion is without merit and intends to vigorously defend the lawsuit.

- Definition

The entire disclosure for loss and gain contingencies. Describes any existing condition, situation, or set of circumstances involving uncertainty as of the balance sheet date (or prior to issuance of the financial statements) as to a probable or reasonably possible loss incurred by an entity that will ultimately be resolved when one or more future events occur or fail to occur, and typically discloses the amount of loss recorded or a range of possible loss, or an assertion that no reasonable estimate can be made.

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+ Details

Subsequent Event	9 Months Ended
Subsequent Event	Sep. 30, 2012
Subsequent Events [Abstract]
Subsequent Events	Note 16. Subsequent Event On October 16, 2012, OneBeacon announced it entered into an agreement to terminate its exclusive underwriting agreement with Hagerty Insurance Agency and to sell one of its insurance entities to Markel Corporation. OneBeacon anticipates recording an after-tax gain of $15 million related to this transaction. The sale is subject to regulatory approvals and is expected to close during the first quarter of 2013. The business associated with this agreement generated written premiums of approximately $179 million, or 16% of OneBeacon's consolidated written premiums for the twelve months prior to September 30, 2012.

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2012
Accounting Policies [Abstract]
Comprehensive Income	Comprehensive Income For fiscal periods beginning after December 15, 2011, ASU 2011-05, Comprehensive Income, became effective, which requires all components of comprehensive income to be reported in a continuous financial statement or in consecutive statements displaying the components of net income and the components of other comprehensive income. Since White Mountains previously presented comprehensive income in a continuous financial statement, adoption of ASU 2011-05 had no effect on White Mountains’ financial statement presentation.
Offsetting Assets and Liabilities	Offsetting Assets and Liabilities On December 16, 2011, the FASB issued ASU 2011-11, Disclosures about Offsetting Assets and Liabilities (ASC 210). The new standard expands the required disclosures in circumstances where either balances have been offset or the right of offset exists. The required disclosures are intended to provide information to enable financial statement users to evaluate the effect or potential effect of netting arrangements on a reporting entity’s financial position. Disclosures required under the new standard include the gross amount of assets and liabilities recognized; the amounts that have been offset to arrive at the amounts presented in the statement of financial position; and for any amounts subject to an enforceable master netting arrangement, whether such amounts have been offset. In addition, a description of the rights of offset should be disclosed. ASU 2011-11 is effective for periods beginning on or after January 1, 2013. White Mountains is party to master netting arrangements in connection with the derivative instruments held by WM Life Re and is currently evaluating the effect of adoption will have on its disclosures, but does not expect adoption to have a material effect on its financial position, results of operations or cash flows.
Noncontrolling Interest	Noncontrolling Interests Noncontrolling interests consist of the ownership interests of noncontrolling parties in consolidated entities and are presented separately as a component of equity on the balance sheet. The percentage of the noncontrolling equity interests in OneBeacon Ltd. at September 30, 2012 and December 31, 2011 was 24.8% and 24.5%. In July 2012, HG Global was capitalized with $594.5 million from White Mountains and $14.5 million from certain management members of BAM, the latter of which is included in noncontrolling interest. Upon closing, certain BAM management members also received additional common and preferred shares of HG Global that resulted in a $2.2 million allocation of the carrying value of White Mountains' investment in HG Global to the noncontrolling interest, which was recorded as an adjustment to paid-in surplus in White Mountains' consolidated statement of changes in equity. White Mountains is required to consolidate BAM in its GAAP financial statements. However, since BAM is a mutual insurance company that is owned by its members and not White Mountains, BAM's results do not affect White Mountains' common shareholders' equity as they are attributable to noncontrolling interests. For the third quarter of 2012, BAM reported $18 million in pre-tax losses that have been allocated to noncontrolling interest. In May 2007, Sirius International Group, Ltd. (“SIG”), an intermediate holding company of Sirius Group, issued $250 million non-cumulative perpetual preference shares with a $1,000 per share liquidation preference (the “SIG Preference Shares”). Proceeds of $245.7 million, net of $4.3 million of issuance costs and commissions, were received from the issuance. The SIG Preference Shares are included in noncontrolling interests on the balance sheet. At September 30, 2012 and December 31, 2011, the noncontrolling equity interest in limited partnerships that are consolidated with White Mountains (the Prospector Offshore Fund, the Prospector Turtle Fund and Tuckerman Fund I prior to December 31, 2011) was $52.8 million and $54.2 million. On December 31, 2011, Tuckerman Fund I was dissolved and all of the net assets of the fund, which consisted of common stock of Hamer and Bri-Mar, were distributed. At September 30, 2012, the noncontrolling equity interest in Hamer and Bri-Mar was $4.5 million. At September 30, 2012 and December 31, 2011, the noncontrolling equity interest in A.W.G. Dewar Inc, a subsidiary of OneBeacon, was $3.2 million and $2.3 million. At September 30, 2012 and December 31, 2011, the noncontrolling equity interest in Passage2Health Limited, a subsidiary of Sirius Group, was $0.3 million and $0.6 million.
Policy Acquisition Costs	Policy Acquisition Costs On January 1, 2012, White Mountains adopted ASU 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts (ASC 944). The new standard changes the types of policy acquisition costs that are eligible for deferral. Specifically, the new guidance limits deferrable costs to those that are incremental direct costs of contract acquisition and certain costs related to acquisition activities performed by the insurer, such as underwriting, policy issuance and processing, medical and inspection costs and sales force contract selling. The ASU defines incremental direct costs as those costs that result directly from and were essential to the contract acquisition and would not have been incurred absent the acquisition. Accordingly, under the new guidance, deferrable acquisition costs are limited to costs related to successful contract acquisitions. Acquisition costs that are not eligible for deferral are to be charged to expense in the period incurred. White Mountains adopted ASU 2010-26 prospectively. Upon adoption, certain acquisition costs, primarily a portion of the profit sharing commissions associated with OneBeacon’s collector car and boats business, no longer meet the criteria for deferral. Deferred acquisition costs of $5.6 million at January 1, 2012 that no longer meet the criteria for deferral under ASU 2010-26 will be recognized in expense over the original amortization periods. For the three and nine months ended September 30, 2012, White Mountains recognized $0.9 million and $5.3 million of expense related to such previously deferrable acquisition costs. If White Mountains had adopted ASU 2010-26 retrospectively, $1.4 million and $5.7 million of acquisition costs that were deferred would have been recognized in expense for the three and nine months ended September 30, 2011.
Fair Value Measurements	Fair Value Measurements On January 1, 2012, White Mountains adopted ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRS. The ASU clarifies existing guidance with respect to the concepts of highest and best use and valuation premise and measuring instruments classified within a reporting entity’s shareholders’ equity. The ASU also clarifies disclosure requirements, requiring disclosure of quantitative information about unobservable inputs used in Level 3 fair value measurements. The ASU also amends existing guidance. In circumstances where a reporting entity manages a portfolio of financial assets and liabilities based on the net market and counterparty credit risk exposures, the ASU permits determination of the fair value of those instruments to be based on the net risk exposure. In addition, the ASU permits the application of premiums or discounts to be applied in a fair value measurement to the extent that market participants would consider them in valuing the financial instruments. The ASU also expands the required disclosures for Level 3 measurements, requiring that reporting entities provide a narrative description of the sensitivity of Level 3 fair value measurements to changes in unobservable inputs and the interrelationships between those inputs, if any. As a result of adopting ASU 2011-04, White Mountains expanded its fair value disclosures. (See Note 5).

Loss and Loss Adjustment Expense Reserves (Tables)

9 Months Ended

Sep. 30, 2012

Insurance Loss Reserves [Abstract]

Loss and loss adjustment expense ("LAE") reserve activities



	Three Months Ended						Nine Months Ended
	September 30,						September 30,
Millions	2012			2011			2012			2011
Gross beginning balance	$	5,329.8		$	5,642.4		$	5,702.3		$	5,736.8
Less beginning reinsurance recoverable on unpaid losses	(2,369.4		)	(2,193.0		)	(2,507.3		)	(2,344.0		)
Net loss and LAE reserves	2,960.4			3,449.4			3,195.0			3,392.8

Less: Beginning net loss and LAE reserves for AutoOne and OneBeacon's runoff business⁽¹⁾	(296.0		)	(503.2		)	(384.1		)	(620.6		)

Loss and LAE incurred relating to:
Current year losses	318.2			307.1			842.9			968.0
Prior year losses	(10.1		)	(26.9		)	(21.2		)	(47.6		)
Total incurred losses and LAE	308.1			280.2			821.7			920.4

Accretion of fair value adjustment to loss and LAE reserves	1.1			2.1			9.4			6.2
Foreign currency translation adjustment to loss and LAE reserves	12.0			(25.5		)	11.7			5.7

Loss and LAE paid relating to:
Current year losses	(101.1		)	(109.7		)	(223.9		)	(226.3		)
Prior year losses	(181.5		)	(186.9		)	(726.8		)	(571.8		)
Total loss and LAE payments	(282.6		)	(296.6		)	(950.7		)	(798.1		)

Plus: Ending net loss and LAE reserves for AutoOne and OneBeacon's runoff business (1)	—			394.4			—			394.4

Net ending balance	2,703.0			3,300.8			2,703.0			3,300.8
Plus ending reinsurance recoverable on unpaid losses	356.8			2,581.2			356.8			2,581.2
Gross ending balance	$	3,059.8		$	5,882.0		$	3,059.8		$	5,882.0
⁽¹⁾Loss and LAE reserve balances for OneBeacon's run-off business prior to September 30, 2012 and AutoOne prior to September 30, 2011 were not classified as held for sale. Adjustment is to present loss and LAE reserve activities from continuing operations.

Third Party Reinsurance (Tables)

9 Months Ended

Sep. 30, 2012

Reinsurance Disclosures [Abstract]

Listing of OneBeacon's top reinsurers



Top Reinsurers (Millions)	Balance at September 30, 2012		% of Total		A.M. Best Rating ⁽¹⁾
Hannover Ruckversich	$	6.4	15	%	A+
Hartford Steam Boiler	4.6		11	%	A++
Munich Reinsurance America	4.5		10	%	A+
Platinum Underwriters Re	4.1		9	%	A
Transatlantic Reinsurance	2.0		5	%	A

Listing of Sirius's top reinsurers



Top Reinsurers (Millions)	Balance at September 30, 2012		% of Total		A.M. Best Rating ⁽¹⁾	% Collateralized
General Reinsurance Corporation	$	42.3	13	%	A++	1	%
Swiss Re Group	33.7		10	%	A+	5	%
Lloyds of London ⁽²⁾	29.9		9	%	A	4	%
Olympus⁽³⁾	28.8		9	%	NR-5	100	%
Michigan Catastrophic Claims Association ⁽⁴⁾	14.6		4	%	N/A	—	%

⁽²⁾Represents the total of reinsurance recoverables due to Sirius Group from all Lloyds Syndicates.

⁽³⁾Non-U.S. insurance entity. The balance is fully collateralized through funds held, letters of credit or trust agreements.

Investment Securities (Tables)

9 Months Ended

Sep. 30, 2012

Investments, Debt and Equity Securities [Abstract]

Pre-tax net investment income

Pre-tax net investment income for the three and nine months ended September 30, 2012 and 2011 consisted of the following:



	Three Months Ended						Nine Months Ended
	Sept 30,						Sept 30,
Millions	2012			2011			2012			2011
Investment income:
Fixed maturity investments	$	33.0		$	38.5		$	105.1		$	127.0
Short-term investments	.5			.9			2.3			3.2
Common equity securities	4.8			3.6			13.8			10.1
Convertible fixed maturity investments	2.0			1.3			5.9			3.9
Other long-term investments	.7			1.2			2.2			1.9
Interest on funds held under reinsurance treaties	—			.2			—			(.6		)
Total investment income	41.0			45.7			129.3			145.5
Less third-party investment expenses	(3.4		)	(2.9		)	(9.5		)	(7.4		)
Net investment income, pre-tax	$	37.6		$	42.8		$	119.8		$	138.1

Net Realized and Unrealized Investment Gains and Losses

Net realized and unrealized investment gains and losses for the three and nine months ended September 30, 2012 and 2011 consisted of the following:



	Three Months Ended						Nine Months Ended
	Sept 30,						Sept 30,
Millions	2012			2011			2012			2011
Net realized investment gains, pre-tax	$	23.7		$	38.3		$	40.5		$	67.7
Net unrealized investment (losses) gains, pre-tax	49.0			(35.4		)	82.7			(31.3		)
Net realized and unrealized investment gains, pre-tax	72.7			2.9			123.2			36.4
Income tax expense attributable to net realized and unrealized investment gains (losses)	(12.3		)	(1.4		)	(28.3		)	(12.7		)
Net realized and unrealized investment gains, after tax	$	60.4		$	1.5		$	94.9		$	23.7

Net realized investment gains (losses)

Net realized investment gains (losses) for the three and nine months ended September 30, 2012 and 2011 consisted of the following:



	Three Months Ended						Nine Months Ended
	Sept 30,						Sept 30,
Millions	2012			2011			2012			2011
Fixed maturity investments	$	29.0		$	14.1		$	69.5		$	3.3
Short-term investments	(3.4		)	.4			(3.9		)	(10.9		)
Common equity securities	3.9			23.1			(2.2		)	41.0
Convertible fixed maturity investments	1.1			(.7		)	3.2			6.3
Other long-term investments	(7.2		)	1.4			(26.4		)	28.0
Forward contracts	.3			—			.3			—
Net realized investment gains, pre-tax	23.7			38.3			40.5			67.7
Income tax expense attributable to net realized investment gains	(7.4		)	(8.3		)	(12.8		)	(20.7		)
Net realized investment gains, after tax	$	16.3		$	30.0		$	27.7		$	47.0

Unrealized Gain (Loss) on Investments [Table Text Block]

The following table summarizes changes in the carrying value of investments measured at fair value:



	Three Months Ended									Nine Months Ended
	September 30, 2012									September 30, 2012
Millions	Net unrealized gains (losses)			Net foreign exchange gains (losses)			Total changes in fair value reflected in earnings			Net unrealized gains (losses)			Net foreign exchange gains (losses)			Total changes in fair value reflected in earnings
Fixed maturity investments	$	27.2		$	(40.6	)	$	(13.4	)	$	35.5		$	(36.9	)	$	(1.4	)
Short-term investments	—			.1			.1			—			.1			.1
Common equity securities	65.1			(.1		)	65.0			71.5			(.1		)	71.4
Convertible fixed maturity investments	(.6		)	—			(.6		)	(2.9		)	—			(2.9		)
Other long-term investments	1.6			(3.7		)	(2.1		)	18.2			(2.7		)	15.5
Net unrealized investment gains (losses), pre-tax	93.3			(44.3		)	49.0			122.3			(39.6		)	82.7
Income tax expense attributable to net unrealized investment (losses) gains	(16.7		)	11.8			(4.9		)	(25.9		)	10.4			(15.5		)
Net unrealized investment gains (losses), after tax	$	76.6		$	(32.5	)	$	44.1		$	96.4		$	(29.2	)	$	67.2



	Three Months Ended									Nine Months Ended
	September 30, 2011									September 30, 2011
Millions	Net unrealized gains (losses)			Net foreign exchange gains (losses)			Total changes in fair value reflected in earnings			Net unrealized gains (losses)			Net foreign exchange gains (losses)			Total changes in fair value reflected in earnings
Fixed maturity investments	$	3.5		$	67.5		$	71.0		$	12.6		$	77.7		$	90.3
Short-term investments	(.1		)	(.4		)	(.5		)	(.1		)	(1.4		)	(1.5		)
Common equity securities	(101.0		)	(.9		)	(101.9		)	(95.1		)	(1.8		)	(96.9		)
Convertible fixed maturity investments	(11.2		)	—			(11.2		)	(19.3		)	—			(19.3		)
Other long-term investments	(1.2		)	8.4			7.2			(8.4		)	4.5			(3.9		)
Net unrealized investment (losses) gains, pre-tax	(110.0		)	74.6			(35.4		)	(110.3		)	79.0			(31.3		)
Income tax benefit (expense) attributable to net unrealized investment gains (losses)	26.4			(19.5		)	6.9			28.5			(20.5		)	8.0
Net unrealized investment (losses) gains, after tax	$	(83.6	)	$	55.1		$	(28.5	)	$	(81.8	)	$	58.5		$	(23.3	)

Net unrealized investment gains (losses) for Level 3 investments



	Three Months Ended						Nine Months Ended
	Sept 30,						Sept 30,
Millions	2012			2011			2012		2011
Fixed maturity investments	$	(1.0	)	$	(13.5	)	$	7.3	$	(14.9	)
Common equity securities	.8			(17.5		)	1.8		(17.0		)
Convertible fixed maturities	—			—			—		—
Other long-term investments	2.9			(3.2		)	11.3		(6.5		)
Total unrealized investment losses, pre-tax - Level 3 investments	$	2.7		$	(34.2	)	$	20.4	$	(38.4	)

Investment holdings, fixed maturity investments



	September 30, 2012
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency gains (losses)			Carrying value
U.S. Government and agency obligations	$	393.7	$	1.2	$	(.1	)	$	(.1	)	$	394.7
Debt securities issued by corporations	2,213.8		91.6		(3.0		)	(21.1		)	2,281.3
Municipal obligations	3.8		—		—			—			3.8
Mortgage-backed and asset-backed securities	2,023.3		30.3		(1.1		)	(5.1		)	2,047.4
Foreign government, agency and provincial obligations	475.2		8.0		(.4		)	(6.4		)	476.4
Preferred stocks	79.8		6.3		—			—			86.1
Total fixed maturity investments including assets held for sale	$	5,189.6	$	137.4	$	(4.6	)	$	(32.7	)	$	5,289.7
Fixed maturity investments reclassified to assets held for sale related the Runoff Transaction											(377.3		)
Total fixed maturity investments											$	4,912.4



	December 31, 2011
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency gains (losses)			Carrying value
U.S. Government and agency obligations	$	299.4	$	5.3	$	(.1	)	$	.4		$	305.0
Debt securities issued by corporations	2,072.1		73.7		(7.8		)	(2.9		)	2,135.1
Municipal obligations	2.7		—		—			—			2.7
Mortgage-backed and asset-backed securities	3,190.5		25.9		(3.9		)	10.4			3,222.9
Foreign government, agency and provincial obligations	581.2		11.0		(.1		)	(2.9		)	589.2
Preferred stocks	82.3		3.2		(6.7		)	—			78.8
Total fixed maturity investments including assets held for sale	$	6,228.2	$	119.1	$	(18.6	)	$	5.0		$	6,333.7
Fixed maturity investments reclassified to assets held for sale related to AutoOne											(111.8		)
Total fixed maturity investments											$	6,221.9

Investment holdings, equity securities, convertible fixed maturities and other long-term investments



	September 30, 2012
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency losses			Carrying value
Common equity securities	$	870.0	$	139.7	$	(4.9	)	$	—		$	1,004.8
Convertible fixed maturity investments	$	140.2	$	7.6	$	(5.8	)	$	—		$	142.0
Other long-term investments	$	264.8	$	57.1	$	(8.6	)	$	(6.2	)	$	307.1



	December 31, 2011
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency losses			Carrying value
Common equity securities	$	691.7	$	72.0	$	(8.7	)	$	—		$	755.0
Convertible fixed maturity investments	$	139.2	$	6.2	$	(1.6	)	$	—		$	143.8
Other long-term investments	$	274.4	$	55.5	$	(25.2	)	$	(3.4	)	$	301.3

Other long-term investments

The following table summarizes investments in hedge funds and private equity interests by investment objective and sector at September 30, 2012 and December 31, 2011:



	September 30, 2012				December 31, 2011
Millions	Fair Value		Unfunded Commitments		Fair Value		Unfunded Commitments
Hedge funds
Long/short equity	$	58.6	$	—	$	48.8	$	—
Long/short credit & distressed	33.8		—		32.3		—
Long diversified strategies	2.3		—		16.9		—
Long/short equity REIT	15.2		—		14.5		—
Long/short equity activist	14.0		—		12.3		—
Long bank loan	.4		—		.5		—
Total hedge funds	124.3		—		125.3		—

Private equity funds
Multi-sector	29.3		6.4		26.9		8.2
Energy infrastructure & services	32.9		11.7		28.0		9.9
Distressed residential real estate	19.2		—		27.4		—
Real estate	12.2		3.3		9.5		3.3
Private equity secondaries	11.0		3.2		11.3		4.0
International multi-sector, Europe	4.3		4.9		7.8		4.7
Manufacturing/Industrial	10.6		29.1		6.2		—
Healthcare	4.3		5.4		2.3		7.0
International multi-sector, Asia	.4		2.7		3.6		2.6
Insurance	3.2		41.3		3.5		41.3
Venture capital	2.4		.5		2.4		.5
Total private equity funds	129.8		108.5		128.9		81.5

Total hedge and private equity funds included in other long-term investments	$	254.1	$	108.5	$	254.2	$	81.5

Fair value of hedge funds subject to restrictions on redemption frequency and advance notice period requirements for investments in active hedge funds

The following summarizes the September 30, 2012 fair value of hedge funds subject to restrictions on redemption frequency and advance notice period requirements for investments in active hedge funds:



	Notice Period
Millions Redemption frequency	30-59 days notice		60-89 days notice		90-119 days notice		120+ days notice		Total
Monthly	$	—	$	—	$	—	$	6.8	$	6.8
Quarterly	27.1		29.3		19.9		9.4		85.7
Semi-annual	—		20.6		—		—		20.6
Annual	2.3		—		8.5		.4		11.2
Total	$	29.4	$	49.9	$	28.4	$	16.6	$	124.3

Fair Value of private equity funds subject to lock-up periods

At September 30, 2012, investments in private equity funds were subject to lock-up periods as follows:



Millions	1-3 years	3 – 5 years	5 – 10 years	>10 years	Total
Private Equity Funds — expected lock-up period remaining	$27.7	$15.6	$75.9	$10.6	$129.8

Fair value measurements by level, investment securities

The following tables summarize White Mountains’ fair value measurements for investments at September 30, 2012 and December 31, 2011, by level.



	September 30, 2012
Millions	Fair value		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs
Fixed maturity investments:
US Government and agency obligations	$	394.7	$	340.5	$	54.2	$	—

Debt securities issued by corporations:
Consumer	597.2		—		597.2		—
Industrial	488.1		—		488.1		—
Financials	405.4		1.1		404.3		—
Communications	217.1		—		217.1		—
Basic materials	175.1		—		175.1		—
Energy	172.9		—		172.9		—
Utilities	204.4		—		204.4		—
Technology	21.1		—		21.1		—
Diversified	—		—		—		—
Total debt securities issued by corporations:	2,281.3		1.1		2,280.2		—

Municipal obligations	3.8		—		3.8		—
Mortgage-backed and asset-backed securities	2,047.4		—		2,041.9		5.5
Foreign government, agency and provincial obligations	476.4		56.9		419.5		—
Preferred stocks	86.1		—		15.5		70.6
Total fixed maturity investments ⁽¹⁾	5,289.7		398.5		4,815.1		76.1

Short-term investments	917.3		917.3		—		—

Common equity securities:
Financials	316.1		277.9		2.3		35.9
Consumer	249.7		249.6		.1		—
Basic materials	118.2		118.2		—		—
Energy	96.8		96.8		—		—
Technology	51.6		51.6		—		—
Utilities	42.9		42.7		.2		—
Other	129.5		73.2		56.3		—
Total common equity securities	1,004.8		910.0		58.9		35.9

Convertible fixed maturity investments	142.0		—		142.0		—
Other long-term investments ⁽²⁾	272.6		—		—		272.6
Total investments	$	7,626.4	$	2,225.8	$	5,016.0	$	384.6

⁽¹⁾Carrying value includes $377.3 that is classified as assets held for sale relating to discontinued operations.

⁽²⁾Excludes carrying value of $34.3 associated with other long-term investment limited partnerships accounted for using the equity method and $0.3 related to forward contracts.



	December 31, 2011
Millions	Fair value		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs
Fixed maturity investments:
US Government and agency obligations	$	305.0	$	296.2	$	8.8	$	—

Debt securities issued by corporations:
Consumer	790.7		—		790.7		—
Industrial	359.4		—		359.4		—
Financials	239.6		3.8		235.8		—
Communications	225.8		—		225.8		—
Basic materials	195.7		—		195.7		—
Energy	155.8		—		155.8		—
Utilities	140.1		—		140.1		—
Technology	24.5		—		24.5		—
Diversified	3.5		—		3.5		—
Total debt securities issued by corporations:	2,135.1		3.8		2,131.3		—

Municipal obligations	2.7		—		2.7		—
Mortgage-backed and asset-backed securities	3,222.9		—		3,207.8		15.1
Foreign government, agency and provincial obligations	589.2		65.7		523.5		—
Preferred stocks	78.8		—		15.0		63.8
Total fixed maturity investments ⁽¹⁾	6,333.7		365.7		5,889.1		78.9

Short-term investments	846.0		846.0		—		—

Common equity securities:
Financials	219.2		185.8		1.5		31.9
Consumer	188.8		188.5		.3		—
Basic materials	121.0		119.9		1.1		—
Energy	72.6		72.6		—		—
Utilities	42.0		41.8		.2		—
Technology	25.8		25.8		—		—
Other	85.6		33.0		52.2		.4
Total common equity securities	755.0		667.4		55.3		32.3

Convertible fixed maturity investments	143.8		—		143.8		—
Other long-term investments ⁽²⁾	268.3		—		—		268.3
Total investments	$	8,346.8	$	1,879.1	$	6,088.2	$	379.5

⁽¹⁾Carrying value includes $111.8 that is classified as assets held for sale relating to AutoOne discontinued operations.

⁽²⁾Excludes carrying value of $33.0 associated with other long-term investments accounted for using the equity method.

Debt securities issued by corporations, credit ratings

The following table summarizes the ratings of the corporate debt securities held in White Mountains’ investment portfolio as of September 30, 2012 and December 31, 2011:



Millions	September 30, 2012		December 31, 2011
AAA	$	—	$	—
AA	165.5		206.8
A	992.8		802.8
BBB	1,108.5		1,110.8
BB	7.6		6.2
Other	6.9		8.5
Debt securities issued by corporations ⁽¹⁾	$	2,281.3	$	2,135.1

⁽¹⁾Credit ratings are assigned based on the following hierarchy: 1) Standard & Poor’s, 2) Moody’s

and 3) Bloomberg

Mortgage-backed, asset-backed securities

The following table summarizes mortgage and asset-backed securities as of September 30, 2012 and December 31, 2011:



	September 30, 2012						December 31, 2011
Millions	Fair Value		Level 2		Level 3		Fair Value		Level 2		Level 3
Mortgage-backed securities:
Agency:
GNMA	$	1,165.5	$	1,165.5	$	—	$	1,365.8	$	1,365.8	$	—
FNMA	97.2		97.2		—		712.6		712.6		—
FHLMC	37.6		37.6		—		35.9		35.9		—
Total Agency ⁽¹⁾	1,300.3		1,300.3		—		2,114.3		2,114.3		—
Non-agency:
Residential	160.5		160.5		—		83.1		68.0		15.1
Commercial	389.3		383.8		5.5		276.7		276.7		—
Total Non-agency	549.8		544.3		5.5		359.8		344.7		15.1

Total mortgage-backed securities	1,850.1		1,844.6		5.5		2,474.1		2,459.0		15.1
Other asset-backed securities:
Credit card receivables	80.8		80.8		—		380.6		380.6		—
Vehicle receivables	80.3		80.3		—		345.6		345.6		—
Other	36.2		36.2		—		22.6		22.6		—
Total other asset-backed securities	197.3		197.3		—		748.8		748.8		—
Total mortgage and asset- backed securities	$	2,047.4	$	2,041.9	$	5.5	$	3,222.9	$	3,207.8	$	15.1

Schedule of security issuance years of investments in non-agency RMBS and non-agency CMBS securities

The security issuance years of White Mountains’ investments in non-agency RMBS and non-agency CMBS securities as of September 30, 2012 are as follows:



			Security Issuance Year
Millions	Fair Value		2003		2006		2007		2009		2010		2011		2012
Non-agency RMBS	$	160.5	$	2.2	$	21.4	$	7.1	$	1.7	$	53.2	$	74.9	$	—
Non-agency CMBS	389.3		—		4.5		15.3		11.9		6.1		127.4		224.1
Total	$	549.8	$	2.2	$	25.9	$	22.4	$	13.6	$	59.3	$	202.3	$	224.1

Non-agency residential mortgage securities, collateral quality and tranche levels

The classification of the underlying collateral quality and the tranche levels of White Mountains’ non-agency RMBS securities are as follows as of September 30, 2012:



Millions	Fair Value		Super Senior ⁽¹⁾		Senior ⁽²⁾		Subordinate ⁽³⁾
Prime	$	160.0	$	13.0	$	147.0	$	—
Non-prime	.5		—		.5		—
Sub-prime	—		—		—		—
Total	$	160.5	$	13.0	$	147.5	$	—

⁽¹⁾At issuance, Super Senior were rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were senior to

other AAA or Aaa bonds.

⁽²⁾At issuance, Senior were rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were senior to non-AAA

or non-Aaa bonds.

⁽³⁾At issuance, Subordinate were not rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were junior to

AAA or Aaa bonds.

Non-agency commercial mortgage securities, type of interest rate and tranche levels

The amount of fixed and floating rate securities and their tranche levels of White Mountains’ non-agency CMBS securities are as follows as of September 30, 2012:



Millions	Fair Value		Super Senior ⁽¹⁾		Senior ⁽²⁾		Subordinate ⁽³⁾
Fixed rate CMBS	$	367.1	$	253.0	$	109.6	$	4.5
Floating rate CMBS	22.2		15.3		1.4		5.5
Total	$	389.3	$	268.3	$	111.0	$	10.0

⁽¹⁾At issuance, Super Senior were rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were

senior to other AAA or Aaa bonds.

⁽²⁾At issuance, Senior were rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were senior to

non-AAA or non-Aaa bonds.

⁽³⁾At issuance, Subordinate were not rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were

junior to AAA or Aaa bonds.

Rollforward of fair value investments by level

The following tables summarize the changes in White Mountains’ fair value measurements by level for the three and nine months ended September 30, 2012 and 2011:



							Level 3 Investments
Millions	Level 1 Investments			Level 2 Investments			Fixed Maturities			Common equity securities			Convertible fixed maturities		Other long-term investments			Total
Balance at January 1, 2012	$	1,879.1		$	6,088.2		$	78.9		$	32.3		$	—	$	268.3		$	8,346.8		⁽¹⁾⁽²⁾
Total realized and unrealized gains (losses)	57.8			53.8			8.4			11.4			—		(8.2		)	123.2
Foreign currency gains (losses) through OCI	13.2			75.5			.7			.1			—		3.1			92.6
Amortization/Accretion	(.7		)	(34.0		)	(.7		)	—			—		—			(35.4		)
Purchases	6,712.0			3,823.7			144.3			2.5			—		40.6			10,723.1
Sales	(6,435.6		)	(5,048.1		)	(99.2		)	(9.8		)	—		(31.2		)	(11,623.9		)
Transfers in	—			56.9			—			—			—		—			56.9
Transfers out	—			—			(56.3		)	(.6		)	—		—			(56.9		)
Balance at September 30, 2012	$	2,225.8		$	5,016.0		$	76.1		$	35.9		$	—	$	272.6		$	7,626.4		⁽¹⁾⁽²⁾

⁽²⁾Carrying value includes $111.8 and $377.3 at January 1, 2012 and September 30, 2012 that is classified as assets held for sale relating to discontinued operations.



							Level 3 Investments
Millions	Level 1 Investments			Level 2 Investments			Fixed Maturities			Common equity securities			Convertible fixed maturities		Other long-term investments				Total
Balance at January 1, 2011	$	1,894.4		$	5,477.4		$	128.4		$	71.2		$	—	$	330.2		⁽¹⁾	$	7,901.6		⁽¹⁾
Total realized and unrealized gains (losses)	(50.5		)	115.9			(10.6		)	(4.9		)	—		22.5				72.4
Foreign currency gains (losses) through OCI	.3			(84.4		)	(4.4		)	1.6			—		(5.0		)		(91.9		)
Amortization/Accretion	2.4			(40.7		)	(.1		)	—			—		—				(38.4		)
Purchases	6,690.7			3,987.4			212.8			19.7			—		27.9				10,938.5
Sales	(6,782.1		)	(4,596.9		)	1.6			(55.5		)	—		(83.4		)		(11,516.3		)
Transfers in	—			111.8			1.0			—			—		—				112.8
Transfers out	—			(1.0		)	(111.8		)	—			—		—				(112.8		)
Balance at September 30, 2011	$	1,755.2		$	4,969.5		$	216.9		$	32.1		$	—	$	292.2		⁽¹⁾	$	7,265.9		⁽¹⁾

⁽¹⁾Excludes carrying value of $36.6 and $41.9 at September 30, 2011 and January 1, 2011 associated with other long-term investment limited partnerships accounted for using the equity method.

Schedule of significant unobservable inputs used in estimating the fair value of investment securities

The following summarizes significant unobservable inputs used in estimating the fair value of investment securities classified within Level 3 at September 30, 2012:



($ in Millions)	September 30, 2012
Description	Fair Value	Rating⁽¹⁾	Valuation Technique(s)	Unobservable Input	Range⁽¹⁾
Non-agency commercial mortgage-backed securities	$5.5	A2	Discounted cash flow	Prepayment Rate	0.0	%	CPY ⁽²⁾
				Discount Margin over LIBOR	2.1	%
Preferred Stock	$70.6	NR	Discounted cash flow	Discount yield	8.0	%

⁽¹⁾Each asset type consists of one security.

⁽²⁾CPY refers to the market convention for CMBS prepayment.

Debt (Tables)

9 Months Ended

Sep. 30, 2012

Debt Disclosure [Abstract]

Schedule of debt outstanding

White Mountains’ debt outstanding as of September 30, 2012 and December 31, 2011 consisted of the following:



Millions	September 30, 2012			December 31, 2011
OBH Senior Notes, at face value	$	269.9		$	269.9
Unamortized original issue discount	(.1		)	(.1		)
OBH Senior Notes, carrying value	269.8			269.8
SIG Senior Notes, at face value	400.0			400.0
Unamortized original issue discount	(.6		)	(.7		)
SIG Senior Notes, carrying value	399.4			399.3
WTM Bank Facility	—			—
Old Lyme	2.1			2.1
Other debt ⁽¹⁾	5.3			6.3
Total debt	$	676.6		$	677.5

⁽¹⁾Other debt relates to White Mountains’ consolidation of Hamer and Bri-Mar.

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21538-112644

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28541-108399

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21506-112644

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21521-112644

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 22
-Article 5

+ Details

Derivatives (Tables)

9 Months Ended

Sep. 30, 2012

Derivatives Disclosure [Abstract]

Derivative [Text Block]

Variable Annuity Reinsurance

The following table summarizes the pre-tax operating results of WM Life Re for the three and nine months ended September 30, 2012 and 2011:



	Three Months Ended						Nine Months Ended
	September 30,						September 30,
Millions	2012			2011			2012			2011
Fees, included in other revenues	$	8.1		$	8.4		$	24.1		$	24.3
Change in fair value of variable annuity liability, included in other revenues	(11.3		)	(164.4		)	89.4			(148.0		)
Change in fair value of derivatives, included in other revenues	(11.0		)	148.9			(122.0		)	105.4
Foreign exchange, included in other revenues	9.0			14.8			(6.4		)	17.1
Other investment income and gains (losses)	3.8			.5			2.9			(.1		)
Total revenues	(1.4		)	8.2			(12.0		)	(1.3		)
Change in fair value of variable annuity death benefit liabilities, included in other expenses	.7			(5.6		)	6.7			(3.1		)
Death benefit claims paid, included in other expenses	(1.5		)	(.7		)	(4.9		)	(2.4		)
General and administrative expenses	(1.1		)	(1.1		)	(3.8		)	(3.2		)
Pre-tax (loss) income	$	(3.3	)	$	.8		$	(14.0	)	$	(10.0	)



	Three Months Ended September 30, 2012
	Variable Annuity (Liabilities)			Derivative Instruments
Millions	Level 3			Level 3 ⁽¹⁾			Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total ⁽⁴⁾
Beginning of period	$	(661.8	)	$	213.0		$	61.0		$	(23.7	)	$	250.3
Purchases	—			—			—			—			—
Realized and unrealized (losses) gains	(10.6		)	6.7			(15.3		)	(2.4		)	(11.0		)
Transfers in	—			—			—			—			—
Sales/settlements	—			(6.7		)	(12.5		)	22.0			2.8
End of period	$	(672.4	)	$	213.0		$	33.2		$	(4.1	)	$	242.1



	Nine Months Ended September 30, 2012
	Variable Annuity (Liabilities)			Derivative Instruments
Millions	Level 3			Level 3 ⁽¹⁾			Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total ⁽⁴⁾
Beginning of period	$	(768.5	)	$	247.1		$	39.2		$	4.1		$	290.4
Purchases	—			6.1			—			—			6.1
Realized and unrealized gains (losses)	96.1			(24.1		)	(71.8		)	(26.1		)	(122.0		)
Transfers in	—			—			—			—			—
Sales/settlements	—			(16.1		)	65.8			17.9			67.6
End of period	$	(672.4	)	$	213.0		$	33.2		$	(4.1	)	$	242.1



	Three Months Ended September 30, 2011
	Variable Annuity (Liabilities)			Derivative Instruments
Millions	Level 3			Level 3 ⁽¹⁾		Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total ⁽⁴⁾
Beginning of period	$	(591.3	)	$	232.7	$	48.2		$	(11.9	)	$	269.0
Purchases	—			—		—			—			—
Realized and unrealized (losses) gains	(170.0		)	45.6		75.7			27.6			148.9
Transfers in	—			—		—			—			—
Sales/settlements	—			—		(48.4		)	(15.7		)	(64.1		)
End of period	$	(761.3	)	$	278.3	$	75.5		$	—		$	353.8



	Nine Months Ended September 30, 2011
	Variable Annuity (Liabilities)			Derivative Instruments
Millions	Level 3			Level 3 ⁽¹⁾			Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total ⁽⁴⁾
Beginning of period	$	(610.2	)	$	275.3		$	72.2		$	—		$	347.5
Purchases	—			5.0			—			—			5.0
Realized and unrealized (losses) gains	(151.1		)	27.1			67.5			10.8			105.4
Transfers in	—			—			—			—			—
Sales/settlements	—			(29.1		)	(64.2		)	(10.8		)	(104.1		)
End of period	$	(761.3	)	$	278.3		$	75.5		$	—		$	353.8

⁽¹⁾Consists of over-the-counter instruments.

⁽³⁾Consists of exchange traded equity index, foreign currency and interest rate futures. Fair value measurements based upon quoted prices for identical instruments that are actively traded.



	September 30, 2012
($ in Millions) Description	Fair Value		Valuation Technique(s)	Unobservable Input	Range					Weighted Average
Variable annuity benefit guarantee liabilities	$	672.4	Discounted cash flows	Surrenders	0.1	%	-	3.0	%	0.4	%
				Mortality	0.0	%	-	6.4	%	0.9	%
				Foreign exchange volatilities	10.8	%	-	17.4	%	12.8	%
				Index volatilities	13.1	%	-	23.9	%	19.5	%

Foreign exchange and equity index options	$	213.0	Black-Scholes option pricing model	Expected equity dividends	1.9	%	-	5.2	%	3.1	%
			Black-Scholes option pricing model	Foreign exchange volatilities	10.8	%	-	17.4	%	12.8	%
				Index volatilities	13.1	%	-	23.9	%	19.5	%



	Gains (Losses)										Carrying Value
	Three Months Ended					Nine Months Ended					As of
	Sept 30,					Sept 30,					Sept 30, 2012		Dec 31, 2011
Millions	2012			2011		2012			2011		Sept 30, 2012		Dec 31, 2011
Fixed income/Interest rate	$	(22.6	)	$	29.8	$	(73.1	)	$	17.3	$	29.1	$	31.1
Foreign exchange	6.5			63.0		(21.0		)	32.8		127.9		161.3
Equity	5.1			56.1		(27.9		)	55.3		85.1		98.0
Total	$	(11.0	)	$	148.9	$	(122.0	)	$	105.4	$	242.1	$	290.4



Millions	September 30, 2012		December 31, 2011
Short-term investments	$	63.3	$	73.2
Fixed maturity securities	—		—
Total	$	63.3	$	73.2



Millions	September 30, 2012			December 31, 2011
OTC derivative instruments ⁽¹⁾	$	251.4		$	295.4
Collateral held	(63.3		)	(73.2		)
Collateral provided	85.6			83.0
Net exposure to credit losses on fair value of OTC instruments	$	273.7		$	305.2

⁽¹⁾Value of OTC derivative instruments as of September 30, 2012 and December 31, 2011 excludes adjustments for counterparty credit risk of $(5.2)

and $(9.1) included in fair value under GAAP.

The following table summarizes uncollateralized amounts due under WM Life Re’s OTC derivative contracts:



	Uncollateralized balance as of
Millions	September 30, 2012		S&P Rating⁽¹⁾
Citigroup ⁽²⁾	$	63.4	A
Royal Bank of Scotland	58.5		A
Bank of America	50.3		A
JP Morgan ⁽²⁾	40.8		A+
Nomura ⁽²⁾	35.9		BBB+
Barclays	20.7		A+
Goldman Sachs ⁽²⁾	4.1		A-
Total	$	273.7

⁽¹⁾Standard & Poor’s (“S&P”) ratings as detailed above are: “A+” (Strong, which is the fifth highest of

twenty-two creditworthiness ratings), “A” (Strong, which is the sixth highest of

twenty-two creditworthiness ratings), “A-” (Strong, which is the seventh highest of twenty-two creditworthiness

ratings) and “BBB+” (Adequate, which is the eighth highest of twenty-two creditworthiness ratings).

⁽²⁾Collateral provided (held) calculated under master netting agreement.



Millions	September 30, 2012		December 31, 2011
Cash	$	341.7	$	453.5
Short-term investments	14.6		.6
Fixed maturity investments	121.2		31.2
Total	$	477.5	$	485.3

Forward Contracts

The following tables summarize the changes in White Mountains' forward contracts for the three and nine months ended September 30, 2012:



	Forward contracts
	Three Months Ended		Nine Months Ended
Millions	September 30, 2012		September 30, 2012
Beginning of period	$	—	$	—
Purchases	—		—
Realized and unrealized gains(losses)	.3		.3
Sales/settlements	—		—
End of period	$	.3	$	.3



	Gains (Losses)
	Three Months Ended			Nine Months Ended			Carrying Value As of
	September 30,			September 30,			September 30,
Millions	2012			2012			2012
USD	$	.4		$	.4		$	.4
SEK	—			—			—
EUR	(.1		)	(.1		)	(.1		)
GBP	—			—			—
Currency Translation	—			—			—
Total	$	.3		$	.3		$	.3

White Mountains does not hold or provide any collateral for the forward contracts. The following table summarizes uncollateralized notional amounts associated with forward currency contracts:



	Uncollateralized balance as of
Millions	September 30, 2012		S&P Rating(1)
Deutsche Bank	$	5.5	A+
Royal Bank of Canada	8.0		A+
HSBC Bank plc	12.4		AA-
JP Morgan	7.3		A
Goldman Sachs	5.6		AA-
Total	$	38.8

⁽¹⁾Standard & Poor's (“S&P”) ratings as detailed above are: “AA-” (Very Strong, which is the sixth highest of

twenty-two creditworthiness ratings), “A+” (Strong, which is the seventh highest of twenty-two creditworthiness

ratings) and “A” (Strong, which is the eighth highest of twenty-two creditworthiness ratings).

Pre-tax operating results of WM Life Re

The following table summarizes the pre-tax operating results of WM Life Re for the three and nine months ended September 30, 2012 and 2011:



	Three Months Ended						Nine Months Ended
	September 30,						September 30,
Millions	2012			2011			2012			2011
Fees, included in other revenues	$	8.1		$	8.4		$	24.1		$	24.3
Change in fair value of variable annuity liability, included in other revenues	(11.3		)	(164.4		)	89.4			(148.0		)
Change in fair value of derivatives, included in other revenues	(11.0		)	148.9			(122.0		)	105.4
Foreign exchange, included in other revenues	9.0			14.8			(6.4		)	17.1
Other investment income and gains (losses)	3.8			.5			2.9			(.1		)
Total revenues	(1.4		)	8.2			(12.0		)	(1.3		)
Change in fair value of variable annuity death benefit liabilities, included in other expenses	.7			(5.6		)	6.7			(3.1		)
Death benefit claims paid, included in other expenses	(1.5		)	(.7		)	(4.9		)	(2.4		)
General and administrative expenses	(1.1		)	(1.1		)	(3.8		)	(3.2		)
Pre-tax (loss) income	$	(3.3	)	$	.8		$	(14.0	)	$	(10.0	)

Fair Value of Assets and Liabilities Measured on Recurring and Non-recurring Basis Table [Text Block]

The following tables summarize the changes in White Mountains’ variable annuity reinsurance liabilities and derivative instruments for the three and nine months ended September 30, 2012 and 2011:



	Three Months Ended September 30, 2012
	Variable Annuity (Liabilities)			Derivative Instruments
Millions	Level 3			Level 3 ⁽¹⁾			Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total ⁽⁴⁾
Beginning of period	$	(661.8	)	$	213.0		$	61.0		$	(23.7	)	$	250.3
Purchases	—			—			—			—			—
Realized and unrealized (losses) gains	(10.6		)	6.7			(15.3		)	(2.4		)	(11.0		)
Transfers in	—			—			—			—			—
Sales/settlements	—			(6.7		)	(12.5		)	22.0			2.8
End of period	$	(672.4	)	$	213.0		$	33.2		$	(4.1	)	$	242.1



	Nine Months Ended September 30, 2012
	Variable Annuity (Liabilities)			Derivative Instruments
Millions	Level 3			Level 3 ⁽¹⁾			Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total ⁽⁴⁾
Beginning of period	$	(768.5	)	$	247.1		$	39.2		$	4.1		$	290.4
Purchases	—			6.1			—			—			6.1
Realized and unrealized gains (losses)	96.1			(24.1		)	(71.8		)	(26.1		)	(122.0		)
Transfers in	—			—			—			—			—
Sales/settlements	—			(16.1		)	65.8			17.9			67.6
End of period	$	(672.4	)	$	213.0		$	33.2		$	(4.1	)	$	242.1



	Three Months Ended September 30, 2011
	Variable Annuity (Liabilities)			Derivative Instruments
Millions	Level 3			Level 3 ⁽¹⁾		Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total ⁽⁴⁾
Beginning of period	$	(591.3	)	$	232.7	$	48.2		$	(11.9	)	$	269.0
Purchases	—			—		—			—			—
Realized and unrealized (losses) gains	(170.0		)	45.6		75.7			27.6			148.9
Transfers in	—			—		—			—			—
Sales/settlements	—			—		(48.4		)	(15.7		)	(64.1		)
End of period	$	(761.3	)	$	278.3	$	75.5		$	—		$	353.8



	Nine Months Ended September 30, 2011
	Variable Annuity (Liabilities)			Derivative Instruments
Millions	Level 3			Level 3 ⁽¹⁾			Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total ⁽⁴⁾
Beginning of period	$	(610.2	)	$	275.3		$	72.2		$	—		$	347.5
Purchases	—			5.0			—			—			5.0
Realized and unrealized (losses) gains	(151.1		)	27.1			67.5			10.8			105.4
Transfers in	—			—			—			—			—
Sales/settlements	—			(29.1		)	(64.2		)	(10.8		)	(104.1		)
End of period	$	(761.3	)	$	278.3		$	75.5		$	—		$	353.8

⁽¹⁾Consists of over-the-counter instruments.

⁽³⁾Consists of exchange traded equity index, foreign currency and interest rate futures. Fair value measurements based upon quoted prices for identical instruments that are actively traded.

The following tables summarize the changes in White Mountains' forward contracts for the three and nine months ended September 30, 2012:



	Forward contracts
	Three Months Ended		Nine Months Ended
Millions	September 30, 2012		September 30, 2012
Beginning of period	$	—	$	—
Purchases	—		—
Realized and unrealized gains(losses)	.3		.3
Sales/settlements	—		—
End of period	$	.3	$	.3

Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]



	Gains (Losses)
	Three Months Ended			Nine Months Ended			Carrying Value As of
	September 30,			September 30,			September 30,
Millions	2012			2012			2012
USD	$	.4		$	.4		$	.4
SEK	—			—			—
EUR	(.1		)	(.1		)	(.1		)
GBP	—			—			—
Currency Translation	—			—			—
Total	$	.3		$	.3		$	.3

Schedule of significant unobservable inputs associated with the fair value estimates for variable annuity reinsurance liabilities and derivative instruments



	September 30, 2012
($ in Millions) Description	Fair Value		Valuation Technique(s)	Unobservable Input	Range					Weighted Average
Variable annuity benefit guarantee liabilities	$	672.4	Discounted cash flows	Surrenders	0.1	%	-	3.0	%	0.4	%
				Mortality	0.0	%	-	6.4	%	0.9	%
				Foreign exchange volatilities	10.8	%	-	17.4	%	12.8	%
				Index volatilities	13.1	%	-	23.9	%	19.5	%

Foreign exchange and equity index options	$	213.0	Black-Scholes option pricing model	Expected equity dividends	1.9	%	-	5.2	%	3.1	%
			Black-Scholes option pricing model	Foreign exchange volatilities	10.8	%	-	17.4	%	12.8	%
				Index volatilities	13.1	%	-	23.9	%	19.5	%

Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values, by the type of instrument



	Gains (Losses)										Carrying Value
	Three Months Ended					Nine Months Ended					As of
	Sept 30,					Sept 30,					Sept 30, 2012		Dec 31, 2011
Millions	2012			2011		2012			2011		Sept 30, 2012		Dec 31, 2011
Fixed income/Interest rate	$	(22.6	)	$	29.8	$	(73.1	)	$	17.3	$	29.1	$	31.1
Foreign exchange	6.5			63.0		(21.0		)	32.8		127.9		161.3
Equity	5.1			56.1		(27.9		)	55.3		85.1		98.0
Total	$	(11.0	)	$	148.9	$	(122.0	)	$	105.4	$	242.1	$	290.4

Summary of collateral provided to WM Life Re from counterparties

The following summarizes collateral provided to WM Life Re from counterparties:



Millions	September 30, 2012		December 31, 2011
Short-term investments	$	63.3	$	73.2
Fixed maturity securities	—		—
Total	$	63.3	$	73.2

Summary of value, collateral provided (held) by WM Life Re and net exposure on OTC derivative instruments

The following summarizes the value, collateral (held) provided by WM Life Re and net exposure to credit losses on OTC derivative instruments recorded within other assets:



Millions	September 30, 2012			December 31, 2011
OTC derivative instruments ⁽¹⁾	$	251.4		$	295.4
Collateral held	(63.3		)	(73.2		)
Collateral provided	85.6			83.0
Net exposure to credit losses on fair value of OTC instruments	$	273.7		$	305.2

⁽¹⁾Value of OTC derivative instruments as of September 30, 2012 and December 31, 2011 excludes adjustments for counterparty credit risk of $(5.2)

and $(9.1) included in fair value under GAAP.

Schedule of Uncollateralized Amounts Due [Table Text Block]

The following table summarizes uncollateralized amounts due under WM Life Re’s OTC derivative contracts:



	Uncollateralized balance as of
Millions	September 30, 2012		S&P Rating⁽¹⁾
Citigroup ⁽²⁾	$	63.4	A
Royal Bank of Scotland	58.5		A
Bank of America	50.3		A
JP Morgan ⁽²⁾	40.8		A+
Nomura ⁽²⁾	35.9		BBB+
Barclays	20.7		A+
Goldman Sachs ⁽²⁾	4.1		A-
Total	$	273.7

⁽¹⁾Standard & Poor’s (“S&P”) ratings as detailed above are: “A+” (Strong, which is the fifth highest of

twenty-two creditworthiness ratings), “A” (Strong, which is the sixth highest of

twenty-two creditworthiness ratings), “A-” (Strong, which is the seventh highest of twenty-two creditworthiness

ratings) and “BBB+” (Adequate, which is the eighth highest of twenty-two creditworthiness ratings).

⁽²⁾Collateral provided (held) calculated under master netting agreement.

The following table summarizes uncollateralized notional amounts associated with forward currency contracts:



	Uncollateralized balance as of
Millions	September 30, 2012		S&P Rating(1)
Deutsche Bank	$	5.5	A+
Royal Bank of Canada	8.0		A+
HSBC Bank plc	12.4		AA-
JP Morgan	7.3		A
Goldman Sachs	5.6		AA-
Total	$	38.8

⁽¹⁾Standard & Poor's (“S&P”) ratings as detailed above are: “AA-” (Very Strong, which is the sixth highest of

twenty-two creditworthiness ratings), “A+” (Strong, which is the seventh highest of twenty-two creditworthiness

ratings) and “A” (Strong, which is the eighth highest of twenty-two creditworthiness ratings).

Summary of additional collateral posted for variable reinsurance counterparties

The additional collateral consists of the following:



Millions	September 30, 2012		December 31, 2011
Cash	$	341.7	$	453.5
Short-term investments	14.6		.6
Fixed maturity investments	121.2		31.2
Total	$	477.5	$	485.3

Earnings (Loss) Per Share (Tables)

9 Months Ended

Sep. 30, 2012

Earnings Per Share [Abstract]

Computation of earnings per share

The following table outlines the Company’s computation of earnings (loss) per share from continuing operations for the three and nine months ended September 30, 2012 and 2011 (see Note 14 for earnings per share amounts for discontinued operations):



	Three Months Ended						Nine Months Ended
	Sept 30,						Sept 30,
	2012			2011			2012			2011
Basic and diluted earnings (loss) per share numerators (in millions):
Net income (loss) from continuing operations attributable to White Mountains’ common shareholders	$	125.9		$	14.3		$	254.6		$	(6.3	)
Allocation of (income) loss for unvested restricted common shares	(1.8		)	(.1		)	(3.3		)	.1
Dividends declared on participating restricted common shares ⁽¹⁾	—			—			(.1		)	(.1		)
Total allocation to restricted common shares	(1.8		)	(.1		)	(3.4		)	—
Net income (loss) attributable to White Mountains’ common shareholders, net of restricted common share amounts	$	124.1		$	14.2		$	251.2		$	(6.3	)
Undistributed net earnings (loss) (in millions):
Net income (loss) attributable to White Mountains’ common shareholders, net of restricted common share amounts	$	124.1		$	14.2		$	251.2		$	(6.3	)
Dividends declared net of participating restricted common share amounts ⁽¹⁾	—			—			(6.5		)	(7.9		)
Total undistributed net earnings (loss), net of restricted common share amounts	$	124.1		$	14.2		$	244.7		$	(14.2	)
Basic earnings (loss) per share denominators (in thousands):
Total average common shares outstanding during the period	6,590.4			7,919.3			6,885.9			7,970.0
Average unvested restricted shares ⁽²⁾	(96.5		)	(73.5		)	(89.5		)	(68.0		)
Basic earnings (loss) per share denominator	6,493.9			7,845.8			6,796.4			7,902.0
Diluted earnings (loss) per share denominator (in thousands):
Total average common shares outstanding during the period	6,590.4			7,919.3			6,885.9			7,970.0
Average unvested restricted common shares⁽²⁾	(96.5		)	(73.5		)	(89.5		)	(68.0		)
Average outstanding dilutive options to acquire common shares ⁽³⁾	—			—			—			—
Diluted earnings (loss) per share denominator	6,493.9			7,845.8			6,796.4			7,902.0
Basic earnings (loss) per share (in dollars):
Net income (loss) attributable to White Mountains’ common shareholders	$	19.11		$	1.81		$	36.96		$	(.80	)
Dividends declared	—			—			(1.00		)	(1.00		)
Undistributed earnings (loss)	$	19.11		$	1.81		$	35.96		$	(1.80	)
Diluted earnings (loss) per share (in dollars)
Net income (loss) attributable to White Mountains’ common shareholders	$	19.11		$	1.81		$	36.96		$	(.80	)
Dividends declared	—			—			(1.00		)	(1.00		)
Undistributed earnings (loss)	$	19.11		$	1.81		$	35.96		$	(1.80	)

⁽¹⁾ Restricted shares issued by White Mountains receive dividends, and therefore, are considered participating securities.

⁽²⁾Restricted shares outstanding vest either in equal annual installments or upon a stated date (see Note 12).

Segment Information (Tables)

9 Months Ended

Sep. 30, 2012

Segment Reporting [Abstract]

Financial information for White Mountains' segments

Significant intercompany transactions among White Mountains’ segments have been eliminated herein. Financial information for White Mountains’ segments follows:



Millions	OneBeacon			Sirius Group			Other Operations		Total
Three Months Ended September 30, 2012
Earned insurance and reinsurance premiums	$	293.9		$	242.9		$	—	$	536.8
Net investment income	12.8			16.7			8.1		37.6
Net realized and unrealized investment gains (losses)	40.0			(8.9		)	41.6		72.7
Other revenue	(.4		)	48.2			2.5		50.3
Total revenues	346.3			298.9			52.2		697.4
Losses and loss adjustment expenses	164.7			143.4			—		308.1
Insurance and reinsurance acquisition expenses	66.6			41.0			—		107.6
Other underwriting expenses	47.4			29.1			.1		76.6
General and administrative expenses	4.4			10.2			44.1		58.7
Interest expense on debt	4.1			6.5			.7		11.3
Total expenses	287.2			230.2			44.9		562.3
Pre-tax income	$	59.1		$	68.7		$	7.3	$	135.1



Millions	OneBeacon			Sirius Group			Other Operations			Total
Three Months Ended September 30, 2011
Earned insurance and reinsurance premiums	$	259.1		$	232.0		$	—		$	491.1
Net investment income	16.1			22.1			4.6			42.8
Net realized and unrealized investment gains (losses)	(47.4		)	65.9			(15.6		)	2.9
Other revenue	.1			(29.3		)	(5.8		)	(35.0		)
Total revenues	227.9			290.7			(16.8		)	501.8
Losses and loss adjustment expenses	149.7			130.5			—			280.2
Insurance and reinsurance acquisition expenses	58.6			48.4			—			107.0
Other underwriting expenses	36.0			28.3			—			64.3
General and administrative expenses	2.5			7.4			26.3			36.2
Interest expense on debt	4.1			6.5			2.2			12.8
Total expenses	250.9			221.1			28.5			500.5
Pre-tax (loss) income	$	(23.0	)	$	69.6		$	(45.3	)	$	1.3



Millions	OneBeacon			Sirius Group		Other Operations			Total
Nine Months Ended September 30, 2012
Earned insurance and reinsurance premiums	$	846.0		$	699.3	$	—		$	1,545.3
Net investment income	41.5			50.9		27.4			119.8
Net realized and unrealized investment gains (losses)	57.9			22.9		42.4			123.2
Other revenue	(.1		)	48.9		32.2			81.0
Total revenues	945.3			822.0		102.0			1,869.3
Losses and loss adjustment expenses	452.5			369.2		—			821.7
Insurance and reinsurance acquisition expenses	185.6			140.6		—			326.2
Other underwriting expenses	146.2			82.1		.1			228.4
General and administrative expenses	9.6			35.4		101.3			146.3
Interest expense on debt	12.2			19.6		1.3			33.1
Total expenses	806.1			646.9		102.7			1,555.7
Pre-tax income (loss)	$	139.2		$	175.1	$	(.7	)	$	313.6



Millions	OneBeacon			Sirius Group			Other Operations			Total
Nine Months Ended September 30, 2011
Earned insurance and reinsurance premiums	$	748.0		$	685.5		$	—		$	1,433.5
Net investment income	55.8			68.3			14.0			138.1
Net realized and unrealized investment gains (losses)	(13.3		)	60.7			(11.0		)	36.4
Other revenue	(12.2		)	(13.8		)	(2.3		)	(28.3		)
Total revenues	778.3			800.7			.7			1,579.7
Losses and loss adjustment expenses	421.3			499.1			—			920.4
Insurance and reinsurance acquisition expenses	161.5			135.1			—			296.6
Other underwriting expenses	124.5			79.4			—			203.9
General and administrative expenses	7.4			23.3			89.7			120.4
Interest expense on debt	16.4			19.6			2.8			38.8
Total expenses	731.1			756.5			92.5			1,580.1
Pre-tax income (loss)	$	47.2		$	44.2		$	(91.8	)	$	(.4	)

- Definition

Tabular disclosure of the profit or loss and total assets for each reportable segment. An entity discloses certain information on each reportable segment if the amounts (a) are included in the measure of segment profit or loss reviewed by the chief operating decision maker or (b) are otherwise regularly provided to the chief operating decision maker, even if not included in that measure of segment profit or loss.

+ References + Details

Investments in Unconsolidated Affiliates (Tables)

9 Months Ended

Sep. 30, 2012

Equity Method Investments and Joint Ventures [Abstract]

Investments in and Advances to Affiliates



Millions	September 30, 2012		December 31, 2011
Symetra common shares	$	284.0	$	261.0
Unrealized gains from Symetra's fixed maturity portfolio	64.6		—
GAAP Carrying value of Symetra common shares	348.6		261.0
Symetra warrants	26.2		12.6
Total investment in Symetra	374.8		273.6
Pentelia Capital Management	1.5		1.7
Total investments in unconsolidated affiliates	$	376.3	$	275.3

Schedule of Changes in Investments in Unconsolidated Affiliates

The following table summarizes amounts recorded by White Mountains relating to its investment in Symetra for the three months ended September 30, 2012 and 2011:



	Three Months Ended									Three Months Ended
	September 30, 2012									September 30, 2011
Millions	Common Shares			Warrants			Total			Common Shares			Warrants			Total
Carrying value of investment in Symetra as of June 30	$	305.9		$	29.8		$	335.7		$	388.5		$	32.5		$	421.0
Equity in earnings⁽¹⁾⁽²⁾	8.8			—			8.8			1.6			—			1.6
Equity in net unrealized gains from Symetra’s fixed maturity portfolio ⁽³⁾	35.2			—			35.2			59.9			—			59.9
Dividends received	(1.3		)	—			(1.3		)	(1.0		)	—			(1.0		)
Increase (decrease) in value of warrants	—			(3.6		)	(3.6		)	—			(24.8		)	(24.8		)
Carrying value of investment in Symetra as September 30⁽⁴⁾⁽⁵⁾	$	348.6		$	26.2		$	374.8		$	449.0		$	7.7		$	456.7

⁽¹⁾Equity in earnings excludes tax expense of $0.7 and $0.1.

⁽²⁾Equity in earnings includes $0.9 increase relating to the pre-tax amortization of Symetra common share impairment from September 30, 2012

⁽³⁾Net unrealized gains includes $3.3 increase relating to the pre-tax amortization of Symetra common share impairment from September 30, 2012.

⁽⁵⁾The aggregate value of White Mountains’ investment in common shares of Symetra was $214.0 based upon the quoted market price of $12.30 per share

at September 30, 2012.

The following table summarizes amounts recorded by White Mountains relating to its investment in Symetra for the nine months ended September 30, 2012 and 2011:



	Nine Months Ended								Nine Months Ended
	September 30, 2012								September 30, 2011
Millions	Common Shares			Warrants		Total			Common Shares			Warrants			Total
Carrying value of investment in Symetra as of January 1	$	261.0		$	12.6	$	273.6		$	350.4		$	37.1		$	387.5
Equity in earnings ⁽¹⁾⁽²⁾	26.7			—		26.7			17.5			—			17.5
Equity in net unrealized gains from Symetra’s fixed maturity portfolio⁽³⁾	64.6			—		64.6			84.0			—			84.0
Dividends received	(3.7		)	—		(3.7		)	(2.9		)	—			(2.9		)
Increase (decrease) in value of warrants	—			13.6		13.6			—			(29.4		)	(29.4		)
Carrying value of investment in Symetra as September 30 ⁽⁴⁾⁽⁵⁾	$	348.6		$	26.2	$	374.8		$	449.0		$	7.7		$	456.7

⁽¹⁾Equity in earnings excludes tax expense of $2.2 and $1.4.

⁽²⁾Equity in earnings includes $0.9 increase relating to the pre-tax amortization of Symetra common share impairment from September 30, 2012.

⁽³⁾Net unrealized gains includes $9.9 increase relating to the pre-tax amortization of Symetra common share impairment from September 30, 2012.

⁽⁵⁾The aggregate value of White Mountains’ investment in common shares of Symetra was $214.0 based upon the quoted market price of $12.30 per share at

September 30, 2012.

Employee Share-Based Incentive Compensation Plans (Tables)

9 Months Ended

Sep. 30, 2012

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of performance share activity

The following table summarizes performance share activity for the three and nine months ended September 30, 2012 and 2011 for performance shares granted under the WTM Incentive Plan and phantom performance shares granted under the Sirius Group Performance Plan (the “WTM Phantom Share Plan”):



	Three Months Ended September 30,									Nine Months Ended September 30,
	2012					2011				2012					2011
Millions, except share amounts	Target Performance Shares Outstanding		Accrued Expense			Target Performance Shares Outstanding	Accrued Expense			Target Performance Shares Outstanding		Accrued Expense			Target Performance Shares Outstanding		Accrued Expense
Beginning of period	118,450		$	32.7		150,064	$	56.5		150,064		$	66.1		163,184		$	29.4
Shares paid or expired⁽¹⁾	—		—			—	—			(68,357	)	(48.4		)	(51,131	)	—
New grants	2,500		—			—	—			38,432		—			37,675		—
Assumed forfeitures and cancellations ⁽²⁾	(1,359	)	(.4		)	—	—			(548	)	.4			336		(.6		)
Expense recognized	—		6.6			—	(1.0		)	—		20.8			—		26.7
Ending September 30,	119,591		$	38.9		150,064	$	55.5		119,591		$	38.9		150,064		$	55.5

⁽²⁾Amounts include changes in assumed forfeitures, as required under GAAP.

Summary of performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan

The following table summarizes performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan at September 30, 2012 for each performance cycle:



Millions, except share amounts	Target Performance Shares Outstanding		Accrued Expense
Performance cycle:
2010 – 2012	42,320		$	19.0
2011 – 2013	37,255		12.9
2012 – 2014	38,092		5.4
Sub-total	117,667		37.3
Assumed forfeitures	(2,941	)	(1.0		)
Total at September 30, 2012	114,726		$	36.3

Summary of performance shares outstanding and accrued expense for performance shares awarded under the Phantom Plan

The following table summarizes phantom performance shares outstanding and accrued expense for grants made under WTM Phantom Share Plan at September 30, 2012 for each performance cycle:



Millions, except share amounts	Target WTM Phantom Performance Shares Outstanding		Accrued Expense
Performance cycle:
2010 – 2012	4,990		$	2.7
2011 – 2013 ⁽¹⁾	—		—
2012 – 2014 ⁽¹⁾	—		—
Sub-total	4,990		2.7
Assumed forfeitures	(125	)	(.1		)
Total at September 30, 2012	4,865		$	2.6

⁽¹⁾ All performance shares for the 2011–2013 and 2012–2014 performance cycles were granted from

the WTM Incentive Plan

Summary of restricted share activity

The following outlines the unrecognized compensation cost associated with the outstanding restricted share awards for the three and nine months ended September 30, 2012 and 2011:



	Three Months Ended September 30,									Nine Months Ended September 30,
	2012					2011				2012					2011
Millions, except share amounts	Restricted Shares		Unamortized Issue Date Fair Value			Restricted Shares	Unamortized Issue Date Fair Value			Restricted Shares		Unamortized Issue Date Fair Value			Restricted Shares	Unamortized Issue Date Fair Value
Non-vested,
Beginning of period	93,460		$	21.5		73,500	$	18.9		72,000		$	13.3		46,250	$	14.1
Issued	3,700		2.0			—	—			32,160		15.7			27,250	9.9
Vested	—		—			—	—			(7,000	)	—			—	—
Forfeited	(1,065	)	(.2		)	—	—			(1,065	)	(.2		)	—	—
Expense recognized	—		(3.2		)	—	(2.8		)	—		(8.7		)	—	(7.9		)
Non-vested at September 30,	96,095		$	20.1		73,500	$	16.1		96,095		$	20.1		73,500	$	16.1

Summary of performance share activity for OneBeacon performance shares granted under OneBeacon Incentive Plan

The following table summarizes performance share activity for the three and nine months ended September 30, 2012 and 2011 for OneBeacon performance shares granted under the OneBeacon Incentive Plan:



	Three Months Ended September 30,										Nine Months Ended September 30,
	2012					2011					2012					2011
Millions, except share amounts	Target Performance Shares Outstanding		Accrued Expense			Target Performance Shares Outstanding		Accrued Expense			Target Performance Shares Outstanding		Accrued Expense			Target Performance Shares Outstanding		Accrued Expense
Beginning of period	560,577		$	3.1		671,727		$	10.0		642,667		$	9.7		1,464,295		$	18.5
Payments and deferrals⁽¹⁾⁽²⁾	—		—			—		—			(258,901	)	(7.8		)	(936,150	)	(10.5		)
New awards	—		—			—		—			181,290		—			194,900		—
Assumed forfeitures and cancellations⁽³⁾	(3,354	)	—			(19,583	)	.1			(7,833	)	—			(70,901	)	(.2		)
Expense recognized	—		(2.2		)	—		(.5		)	—		(1.0		)	—		1.8
Ending September 30,	557,223		$	.9		652,144		$	9.6		557,223		$	.9		652,144		$	9.6

⁽³⁾ Amounts include changes in assumed forfeitures, as required under GAAP.

Summary of OneBeacon performance shares outstanding and accrued expense for OneBeacon performance shares awarded under the OneBeacon Incentive Plan

The following table summarizes OneBeacon performance shares outstanding awarded under the OneBeacon Incentive Plan at September 30, 2012 for each performance cycle:



Millions, except share amounts	Target OneBeacon Performance Shares Outstanding		Accrued Expense
Performance cycle:
2010 – 2012	238,658		$	—
2011 – 2013	151,563		.4
2012 – 2014	181,290		.5
Sub-total	571,511		.9
Assumed forfeitures	(14,288	)	—
Total at September 30, 2012	557,223		$	.9

Summary of OneBeacon Restricted Shares activity

The following outlines the unrecognized compensation cost associated with the outstanding restricted share awards for the three and nine months ended September 30, 2012:



	Three Months Ended September 30,								Nine Months Ended September 30,
	2012				2011				2012				2011
Millions, except share amounts	Restricted Shares	Unamortized Issue Date Fair Value			Restricted Shares	Unamortized Issue Date Fair Value			Restricted Shares	Unamortized Issue Date Fair Value			Restricted Shares	Unamortized Issue Date Fair Value
Non-vested,
Beginning of period	930,000	$	11.2		630,000	$	8.5		630,000	$	7.7		630,000	$	8.6
Issued	—	—			—	—			300,000	4.6			—	—
Vested	—	—			—	—			—	—			—	—
Forfeited	—	—			—	—			—	—			—	—
Expense recognized	—	(.8		)	—	(.4		)	—	(1.9		)	—	(.5		)
Non-vested at September 30,	930,000	$	10.4		630,000	$	8.1		930,000	$	10.4		630,000	$	8.1

Summary of OneBeacon option activity

The following table summarizes option activity for the three and nine months ended September 30, 2012 and 2011:



	Three Months Ended September 30,			Nine Months Ended September 30,
	2012	2011		2012		2011
Millions, except share amounts	Target Options Outstanding	Target Options Outstanding		Target Options Outstanding		Target Options Outstanding
Beginning of period	—	750,130		740,870		768,652
New awards	—	—		—		—
Forfeitures and cancellations	—	(9,260	)	—		(27,782	)
Vested and expired	—	—		(740,870	)	—
Exercised	—	—		—		—
Expense recognized	—	—		—		—
Ending September 30,	—	740,870		—		740,870

Fair Value of Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2012

Fair Value Disclosures [Abstract]

Summary of the fair value and carrying value of financial instruments

The following table summarizes the fair value and carrying value of financial instruments as of September 30, 2012 and December 31, 2011:



	September 30, 2012				December 31, 2011
Millions	Fair Value		Carrying Value		Fair Value		Carrying Value
OBH Senior Notes	$	276.3	$	269.8	$	277.4	$	269.8
SIG Senior Notes	442.9		399.4		418.6		399.3
SIG Preference Shares	257.5		250.0		217.5		250.0

- Definition

Tabular disclosure of the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments, assets, and liabilities. Such certain disclosures about the financial instruments, assets, and liabilities include: (1) the fair value of the required items together with their carrying amounts (as appropriate) and (2) the methodology and assumptions used in developing such estimates of fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13476-108611

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13467-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6447952&loc=d3e13220-108610

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14172-108612

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 159
-Paragraph 19
-Subparagraph a, b, c(1), d(1)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 14
-Subparagraph a
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 15
-Subparagraph b-d
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 159
-Paragraph 18
-Subparagraph c(2), d, e, f
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 157
-Paragraph 32
-Subparagraph a, c(1), c(2), c(3), d
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 10
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Discontinued Operations (Tables)

9 Months Ended

Sep. 30, 2012

Discontinued Operations and Disposal Groups [Abstract]

Schedule of discontinued operations balance sheet

Net Assets Held for Sale

The following summarizes the assets and liabilities associated with the businesses classified as held for sale:



Millions	September 30, 2012		December 31, 2011
Assets held for sale
Fixed maturity investments, at fair value	$	377.3	$	111.8
Cash	—		5.5
Reinsurance recoverable on unpaid losses	1,956.6		—
Reinsurance recoverable on paid losses	17.6		—
Insurance premiums receivable	13.6		8.8
Deferred acquisition costs	—		2.2
Deferred tax asset	6.1		1.9
Other assets	17.0		2.4
Total assets held for sale	$	2,388.2	$	132.6
Liabilities held for sale
Loss and loss adjustment expense reserves	$	2,212.9	$	64.7
Unearned insurance premiums	.6		34.1
Ceded reinsurance payable	19.5		—
Other liabilities	155.2		8.8
Total liabilities held for sale	2,388.2		107.6
Net assets held for sale	$	—	$	25.0

Schedule of discontinued operations income statement

The following summarizes the results of operations, including related income taxes associated with the businesses classified as discontinued operations:



	Three Months Ended						Nine Months Ended
Millions, except per share amounts	Sept 30,						Sept 30,
	2012			2011			2012			2011
Revenues
Earned insurance premiums	$	(.4	)	$	233.3		$	10.0		$	701.9
Net investment income	—			3.8			—			11.8
Net realized and unrealized investment gains (losses)	—			(6.4		)	—			1.4
Other revenue	—			17.5			—			54.0
Total revenues	(.4		)	248.2			10.0			769.1
Expenses
Loss and loss adjustment expenses	27.7			177.4			48.4			512.3
Insurance and reinsurance acquisition expenses	(.8		)	51.4			(1.3		)	154.1
Other underwriting expenses	(1.1		)	35.0			1.1			83.9
General and administrative expenses	—			1.7			—			37.5
Total expenses	25.8			265.5			48.2			787.8
Pre-tax loss	(26.2		)	(17.3		)	(38.2		)	(18.7		)
Income tax benefit	10.4			5.3			13.7			10.9
Loss from discontinued operations	(15.8		)	(12.0		)	(24.5		)	(7.8		)
Loss from sale of discontinued operations	(91.0		)	(18.2		)	(91.0		)	(18.2		)
Net loss from discontinued operations	$	(106.8	)	$	(30.2	)	$	(115.5	)	$	(26.0	)

Discontinued operations, computation of earnings per share

The following table outlines the computation of loss per share for discontinued operations for the three and nine months ended September 30, 2012 and 2011:



	Three Months Ended						Nine Months Ended
	Sept 30,						Sept 30,
	2012			2011			2012			2011
Basic and diluted loss per share numerators (in millions):
Net loss attributable to White Mountains’ common shareholders	$	(106.8	)	$	(30.2	)	$	(115.5	)	$	(26.0	)
Allocation of income for participating unvested restricted common shares ⁽¹⁾	1.5			.3			1.5			.2
Net loss attributable to White Mountains’ common shareholders, net of restricted common share amounts⁽²⁾	$	(105.3	)	$	(29.9	)	$	(114.0	)	$	(25.8	)
Basic loss per share denominators (in thousands):
Total average common shares outstanding during the period	6,590.4			7,919.3			6,885.9			7,970.0
Average unvested restricted common shares⁽³⁾	(96.5		)	(73.5		)	(89.5		)	(68.0		)
Basic loss per share denominator	6,493.9			7,845.8			6,796.4			7,902.0
Diluted loss per share denominator (in thousands):
Total average common shares outstanding during the period	6,590.4			7,919.3			6,885.9			7,970.0
Average unvested restricted common shares	(96.5		)	(73.5		)	(89.5		)	(68.0		)
Average outstanding dilutive options to acquire common shares	—			—			—			—
Diluted loss per share denominator	6,493.9			7,845.8			6,796.4			7,902.0
Basic and diluted loss per share (in dollars):	$	(16.21	)	$	(3.81	)	$	(16.77	)	$	(3.26	)

⁽¹⁾Restricted shares issued by White Mountains contain dividend participation features, and therefore, are considered participating securities.

⁽³⁾ Restricted common shares outstanding vest either in equal annual installments or upon a stated date (see Note 12)

Summary of Significant Accounting Policies (Basis of Presentation) (Details) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended		9 Months Ended
	Dec. 31, 2011 USD ($) company	May 31, 2007 USD ($) shares	Sep. 30, 2012 USD ($) state	Sep. 30, 2011 USD ($)	Sep. 30, 2012 USD ($) state	Sep. 30, 2011 USD ($)	May 24, 2007 USD ($) $ / shares
Basis of Presentation
Number of small manufacturing companies owned by the Tuckerman Fund I from whom the entity received shares \| company	2
Percentage of par value of policy reinsured			15.00%		15.00%
Number of states in which Esurance insurance directly writes insurance \| state			30		30
Net (Income) Loss Attributable to Noncontrolling Interest			$ 30.9	$ 11.0	$ 2.0	$ (21.2)
Noncontrolling interest - other	$ 57.1		$ 60.8		$ 60.8
OneBeacon Ltd.
Basis of Presentation
Ownership percentage in outstanding common shares	75.50%		75.20%		75.20%
Noncontrolling equity percentage in OneBeacon Ltd.	24.50%		24.80%		24.80%
White Mountains [Member]
Basis of Presentation
Funds to Capitalized HG Global					$ 594.5
HG Global [Member]
Basis of Presentation
Fair Value of Net Assets Acquired					2.2
White Mountains Consolidated Limited Partnership [Member]
Basis of Presentation
Noncontrolling interest - other	$ 54.2		$ 52.8		52.8
Hamer and Bri-Mar [Member]
Basis of Presentation
Noncontrolling interest - other			4.5		4.5
A W G Dewar Inc [Member]
Basis of Presentation
Noncontrolling interest - other	2.3		3.2		3.2
Passage 2 Health Limited [Member]
Basis of Presentation
Noncontrolling interest - other	$ 0.6		$ 0.3		$ 0.3
Preferred Stock \| Sirius Internation Group Ltd [Member]
Basis of Presentation
Non-cumulative perpetual preference shares issued \| shares		250,000,000
Non-cumulative perpetual preference shares per share liquidation preference (in dollars per share) \| $ / shares							$ 1,000
Proceeds from non-cumulative perpetual preference shares		$ 245.7
Non-cumulative perpetual preference shares issuance cost and commission							$ 4.3
Preferred Stock \| HG Global [Member]
Basis of Presentation
Ownership interest (as a percent)			97.00%		97.00%
Common Stock \| HG Global [Member]
Basis of Presentation
Ownership interest (as a percent)			89.00%		89.00%
Percentage of par value of policy reinsured			15.00%		15.00%
Non-controlling interest
Basis of Presentation
Fair Value of Net Assets Acquired					$ 2.2
Non-controlling interest \| Build America Mutual [Member]
Basis of Presentation
Net (Income) Loss Attributable to Noncontrolling Interest			$ 18.0
Non-controlling interest \| HG Global [Member]
Basis of Presentation
Funds to Capitalized HG Global					$ 14.5

Summary of Significant Accounting Policies (Recently Adopted Changes in Accounting Principles) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Jan. 02, 2012	Dec. 31, 2011
Accounting Policies [Abstract]
Deferred acquisition costs	$ 211.3		$ 211.3		$ 5.6	$ 187.0
Deferred policy acquisition costs, amortization expense	$ 0.9	$ 1.4	$ 5.3	$ 5.7

- Definition

Amount of deferred policy acquisition costs charged to expense in the period, generally in proportion to related revenue earned, estimated gross profits, or over the customer relationship or some other period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 30
-Section 35
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=7473040&loc=d3e10157-158409

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
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-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6480726&loc=d3e6691-158385

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Subparagraph (SX 210.7-04.7(a))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-SubTopic 30
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-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6967983&loc=d3e11264-158415

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 97
-Paragraph 22, 23, 24, 25, 26
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 7
-Article 7

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 18
-Article 12

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 16
-Article 12

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 60
-Paragraph 60
-Subparagraph c
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Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 95-1
-Paragraph 19, 20, 21, 22, 23
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

- Definition

Net amount of deferred policy acquisition costs capitalized on contracts remaining in force as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 825
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6487548&loc=d3e32546-158582

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 30
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-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6481648&loc=d3e11198-158413

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.(a),7)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 60
-Paragraph 28, 29, 30, 31
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 97
-Paragraph 22
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-Name Statement of Financial Accounting Standard (FAS)
-Number 120
-Paragraph 5, 6
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-Publisher AICPA
-Name Statement of Position (SOP)
-Number 95-1
-Paragraph 19-23
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 7
-Article 7

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 60
-Paragraph 60
-Subparagraph c
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Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 16
-Article 12

+ Details

Significant Transactions (Sale of Esurance) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2011	Dec. 31, 2011
Significant Transactions
Gain on sale of business in discontinued operations		$ 700.0
Esurance
Significant Transactions
Consideration in excess of tangible book value	$ 700.0
Gain on sale of business in discontinued operations	$ 677.5

Significant Transactions (Share Repurchases) (Details) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended		12 Months Ended	81 Months Ended
	Mar. 31, 2012 USD ($) $ / shares shares	Sep. 30, 2012 USD ($) shares	Sep. 30, 2012 USD ($) shares	Sep. 30, 2011 USD ($) shares	Dec. 31, 2011 USD ($) Auction $ / shares shares	Sep. 30, 2012 USD ($) shares	May 25, 2012 shares	Dec. 31, 2010 shares	Nov. 17, 2006 shares
Significant Transactions
Common shares repurchased and retired during the period		50,000	217,801	265,768		1,629,504
Value of common shares repurchased and retired during the period \| $		$ 26.4	$ 107.6	$ 93.2		$ 645.1
Authorized repurchase of common shares									1,000,000
Additional authorized repurchase of common shares							1,000,000	600,000
Shares remaining under share repurchase authorization		970,496	970,496			970,496
Tender Offer
Significant Transactions
Common shares repurchased and retired during the period	816,829				332,346
Value of common shares repurchased and retired during the period \| $	$ 408.6				$ 138.8
Average price per share \| $ / shares	$ 500				$ 418
Number of modified Dutch auction \| Auction					2

Significant Transactions Formation of HG and BAM (Details) $ in Millions	9 Months Ended
	Sep. 30, 2012 USD ($) shares
Significant Transactions
Shares remaining under share repurchase authorization \| shares	970,496
Percentage of par value of policy reinsured	15.00%
White Mountains [Member]
Significant Transactions
Funds to Capitalized HG Global	$ 594.5
HG Global [Member]
Significant Transactions
Interest income, surplus notes	8.3
Income (Loss) from Continuing Operations before Income Taxes, Foreign	4.8
Surplus Notes	$ 503.0
HG Global [Member] \| Common Stock
Significant Transactions
Ownership interest (as a percent)	89.00%
Percentage of par value of policy reinsured	15.00%
HG Global [Member] \| Preferred Stock
Significant Transactions
Ownership interest (as a percent)	97.00%
Build America Mutual [Member]
Significant Transactions
Interest income, surplus notes	$ (8.3)
Income (Loss) from Continuing Operations before Income Taxes, Foreign	$ 18.0

Significant Transactions OneBeacon runoff business (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Significant Transactions
Gain (loss) on sale of discontinued operation, net of tax	$ (91.0)	$ (18.2)	$ (91.0)	$ (18.2)
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(15.8)	$ (12.0)	$ (24.5)	$ (7.8)
OneBeacon Runoff [Member]
Significant Transactions
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	(100.5)
Gain (loss) on sale of discontinued operation, net of tax	(91.5)
Loss attributable to change in discount rate [Member]
Significant Transactions
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(9.0)
Loss attributable to prior year reserve devolopment [Member]
Significant Transactions
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ (6.5)

- Definition

Amount of income (loss) from a disposal group, net of income tax before extraordinary items allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.12)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.14)
-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1361-107760

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6892542&loc=d3e957-107759

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 13
-Article 7

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
-Paragraph 29
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 144
-Paragraph 43
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 144
-Paragraph 47
-Subparagraph c
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 15
-Article 5

+ Details

- Definition

Amount of income (loss) from a disposal group, net of income tax, reported as a separate component of income before extraordinary items after deduction or consideration of the amount allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

+ References + Details

Loss and Loss Adjustment Expense Reserves Details (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Loss and Loss Adjustment, Expense Reserves [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims, Prior Years	$ 10.1	$ 26.9	$ 21.2	$ 47.6
Accretion of fair value adjustment to net loss and LAE reserves	1.1	2.1	9.4	6.2
Accretion of fair value adjustment to net loss and LAE reserves increase			5.0
Remaining unamortized fair value adjustment			2.0
One Beacon Segment [Member]
Loss and Loss Adjustment, Expense Reserves [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims, Prior Years	(2.3)	(6.0)	(7.6)	(14.4)
Sirius
Loss and Loss Adjustment, Expense Reserves [Line Items]
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims, Prior Years	(7.8)	$ (20.9)	(13.6)	$ (33.2)
Net Unfavorable Loss Reserve Development Due To Asbestos And Environmental Reserves Additions	$ 33.0		$ 45.0

Loss and Loss Adjustment Expense Reserves (Loss and Loss Adjustment Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Mar. 31, 2012	Mar. 31, 2011
Loss and Loss Adjustment Expense Reserve
Gross beginning balance	$ 5,329.8	$ 5,642.4	$ 5,702.3	$ 5,736.8
Less beginning reinsurance recoverable on unpaid losses			(2,507.3)	(2,344.0)
Net loss and LAE reserves			3,195.0	3,392.8
Loss and LAE incurred relating to current year losses	318.2	307.1	842.9	968.0
Net favorable and unfavorable loss reserve development	(10.1)	(26.9)	(21.2)	(47.6)
Total incurred losses and LAE	308.1	280.2	821.7	920.4
Accretion of fair value adjustment to net loss and LAE reserves	1.1	2.1	9.4	6.2
Foreign currency translation adjustment to net loss and LAE reserves	12.0	(25.5)	11.7	5.7
Current year losses	(101.1)	(109.7)	(223.9)	(226.3)
Prior year losses	(181.5)	(186.9)	(726.8)	(571.8)
Total loss and LAE payments	(282.6)	(296.6)	(950.7)	(798.1)
Net loss and LAE reserves	2,703.0	3,300.8	2,703.0	3,300.8
Plus ending reinsurance recoverable on unpaid losses	356.8	2,581.2	2,507.3	2,344.0	$ 2,369.4	$ 2,193.0
Gross ending balance	3,059.8	5,882.0	3,059.8	5,882.0
One Beacon
Loss and Loss Adjustment Expense Reserve
Net favorable and unfavorable loss reserve development	2.3	6.0	7.6	14.4
Sirius
Loss and Loss Adjustment Expense Reserve
Net favorable and unfavorable loss reserve development	7.8	20.9	13.6	33.2
Net Unfavorable Loss Reserve Development Due To Asbestos And Environmental Reserves Additions	33.0		45.0
Total incurred losses and LAE	143.4	130.5	369.2	499.1
Plus ending reinsurance recoverable on unpaid losses	315.5
Segment, Discontinued Operations [Member]
Loss and Loss Adjustment Expense Reserve
Gross beginning balance			64.7
Less beginning reinsurance recoverable on unpaid losses			0.0
Net loss and LAE reserves	(296.0)	(503.2)	(384.1)	(620.6)
Total incurred losses and LAE	27.7	177.4	48.4	512.3
Net loss and LAE reserves	0.0	$ 394.4	0.0	$ 394.4
Plus ending reinsurance recoverable on unpaid losses	1,956.6		0.0
Gross ending balance	$ 2,212.9		$ 2,212.9

Third Party Reinsurance (Details) $ in Millions	9 Months Ended
Third Party Reinsurance (Details) $ in Millions	Sep. 30, 2012 USD ($) Contract Rating	Mar. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)	Sep. 30, 2011 USD ($)	Mar. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)
Reinsurance [Line Items]
Reinsurance recoverable on paid losses	$ 14.8		$ 30.5
Reinsurance recoverable on unpaid losses	356.8	$ 2,369.4	$ 2,507.3	$ 2,581.2	$ 2,193.0	$ 2,344.0
Purchase accounting adjustments	153.0
Amount Retained Under Reinsurance Cover	$ 49.3
OneBeacon
Reinsurance [Line Items]
Number of ratings in A.M. Best ratings \| Rating	15
Reinsurance recoverable on paid losses	$ 2.0
Reinsurance recoverable on unpaid losses	41.3
Reinsurance recoverables	$ 1,449.2
Number of Contracts Seller Caused One Beacon to Purchase Prior to Acquisition \| Contract	2
OneBeacon \| Property catastrophe reinsurance program
Reinsurance [Line Items]
Amount of loss on a single catastrophe retained, first layer	$ 25.0
Amount of loss on a single catastrophe reinsured, second layer	$ 155.0
Property catastrophe reinsurance program second layer first retention percentage	55.00%
Second retention percentage of loss on a single catastrophe reinsured, second layer	15.00%
Property catastrophe reinsurance program second layer third retention percentage	10.00%
Amount of loss on a single catastrophe retained, third layer	$ 180.0
OneBeacon \| Property catastrophe reinsurance program \| Minimum
Reinsurance [Line Items]
Amount of loss on a single catastrophe reinsured, first retention slab for second layer	25.0
Amount of loss on a single catastrophe reinsured, second retention slab for second layer	40.0
Property catastrophe reinsurance program third retention slab for second layer	80.0
OneBeacon \| Property catastrophe reinsurance program \| Maximum
Reinsurance [Line Items]
Amount of loss on a single catastrophe reinsured, first retention slab for second layer	40.0
Amount of loss on a single catastrophe reinsured, second retention slab for second layer	80.0
Property catastrophe reinsurance program third retention slab for second layer	180.0
OneBeacon \| Hannover Ruversich [Member]
Reinsurance [Line Items]
Reinsurance recoverables	$ 6.4
Percentage of total paid and unpaid reinsurance recoverables	15.00%
OneBeacon \| Hartford Steam Boiler [Member]
Reinsurance [Line Items]
Reinsurance recoverables	$ 4.6
Percentage of total paid and unpaid reinsurance recoverables	11.00%
OneBeacon \| Munich Reinsurance America
Reinsurance [Line Items]
Reinsurance recoverables	$ 4.5
Percentage of total paid and unpaid reinsurance recoverables	10.00%
OneBeacon \| Platinum Underwriters Re [Member]
Reinsurance [Line Items]
Reinsurance recoverables	$ 4.1
Percentage of total paid and unpaid reinsurance recoverables	9.00%
OneBeacon \| Transatlantic Reinsurance [Member]
Reinsurance [Line Items]
Reinsurance recoverables	$ 2.0
Percentage of total paid and unpaid reinsurance recoverables	5.00%

Third Party Reinsurance (Sirius Group) (Details)
$ in Millions

9 Months Ended

Sep. 30, 2012

USD ($)

Rating

Mar. 31, 2012

USD ($)

Dec. 31, 2011

USD ($)

Sep. 30, 2011

USD ($)

Mar. 31, 2011

USD ($)

Dec. 31, 2010

USD ($)

Reinsurance [Line Items]

Reinsurance recoverable on paid losses

$ 14.8

$ 30.5

Reinsurance recoverable on unpaid losses

356.8

$ 2,369.4

$ 2,507.3

$ 2,581.2

$ 2,193.0

$ 2,344.0

Seller Note From Acquisition

25.0

OneBeacon

Reinsurance [Line Items]

Reinsurance recoverable on paid losses

2.0

Reinsurance recoverable on unpaid losses

41.3

Reinsurance Recoverables

$ 1,449.2

Number of ratings in A.M. Best ratings | Rating

Sirius

Reinsurance [Line Items]

Reinsurance recoverable on paid losses

$ 12.7

Reinsurance recoverable on unpaid losses

315.5

General Reinsurance Corporation [Member] | Sirius

Reinsurance [Line Items]

Reinsurance Recoverables

$ 42.3

Percentage of total paid and unpaid reinsurance recoverables

13.00%

Percentage Collateralized

1.00%

Swiss Re Group [Member] | Sirius

Reinsurance [Line Items]

Reinsurance Recoverables

$ 33.7

Percentage of total paid and unpaid reinsurance recoverables

10.00%

Percentage Collateralized

5.00%

Olympus [Member] | Sirius

Reinsurance [Line Items]

Reinsurance Recoverables

^[1]

$ 28.8

Percentage of total paid and unpaid reinsurance recoverables

^[1]

9.00%

Percentage Collateralized

^[1]

100.00%

Lloyds of London [Member] | Sirius

Reinsurance [Line Items]

Reinsurance Recoverables

^[2]

$ 29.9

Percentage of total paid and unpaid reinsurance recoverables

^[2]

9.00%

Percentage Collateralized

^[2]

4.00%

Michigan Catastorphic Claims Association [Member] | Sirius

Reinsurance [Line Items]

Reinsurance Recoverables

$ 14.6

Percentage of total paid and unpaid reinsurance recoverables

4.00%

Percentage Collateralized

0.00%

[1]

(4) Michigan Catastrophic Claims Association ("MCCA") is a non-profit unincorporated association., established by the State of Michigan with the power to issue and collect assessments, to which every insurance company that sells automobile coverage in Michigan is required to be a member. A.M. Best does not rate MCCA. Sirius Group acquired its recoverable from MCCA in the acquisition of Stockbridge Insurance Company. As part of the acquisition, Sirius Group obtained $25.0 of reinsurance protection from the seller (currently rated A+ by A.M. Best) for unfavorable loss reserve development, including uncollectible reinsurance.

[2]

(3) Non-U.S. insurance entity. The balance is fully collateralized through funds held, letters of credit or trust agreements.

Investment Securities (Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Investment income
Total investment income	$ 41.0	$ 45.7	$ 129.3	$ 145.5
Third-party investment expenses	(3.4)	(2.9)	(9.5)	(7.4)
Net investment income	37.6	42.8	119.8	138.1
Fixed maturity investments.
Investment income
Total investment income	33.0	38.5	105.1	127.0
Short-term investments
Investment income
Total investment income	0.5	0.9	2.3	3.2
Common shareholders' equity.
Investment income
Total investment income	4.8	3.6	13.8	10.1
Convertible fixed maturity investments
Investment income
Total investment income	2.0	1.3	5.9	3.9
Other long-term investments
Investment income
Total investment income	0.7	1.2	2.2	1.9
Interest on funds held under reinsurance treaties
Investment income
Total investment income	$ 0.0	$ 0.2	$ 0.0	$ (0.6)

(Net Realized and Unrealized Gains and Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Gain (Loss) on Investments [Abstract]
Net realized investment gains (losses), pre-tax	$ 23.7	$ 38.3	$ 40.5	$ 67.7
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings	49.0	(35.4)	82.7	(31.3)
Net Realized and Unrealized Gain (Loss) on Trading Securities	72.7	2.9	123.2	36.4
Trading Securities, Tax on Realized and Unrealized Holding Gain (Loss) on Investments	12.3	1.4	28.3	12.7
Trading Securities Realized and Unrealized Holding Gain (Loss) on Investments after Tax	$ 60.4	$ 1.5	$ 94.9	$ 23.7

Investment Securities (Net Realized Investment Gains (Losses)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Investment securities
Trading Securities, Realized Gain (Loss)	$ 23.7	$ 38.3	$ 40.5	$ 67.7
Trading Securities, Realized Gain (Loss) Tax	7.4	8.3	12.8	20.7
Trading Securities, Realized Gain (Loss) Net of Tax	16.3	30.0	27.7	47.0
Fixed maturity investments.
Investment securities
Trading Securities, Realized Gain (Loss)	29.0	14.1	69.5	3.3
Short-term investments
Investment securities
Trading Securities, Realized Gain (Loss)	(3.4)	0.4	(3.9)	(10.9)
Common equity securities
Investment securities
Trading Securities, Realized Gain (Loss)	3.9	23.1	(2.2)	41.0
Convertible Debt Securities [Member]
Investment securities
Trading Securities, Realized Gain (Loss)	1.1	(0.7)	3.2	6.3
Other long-term investments
Investment securities
Trading Securities, Realized Gain (Loss)	(7.2)	1.4	(26.4)	28.0
Forward Contracts [Member]
Investment securities
Trading Securities, Realized Gain (Loss)	$ 0.3	$ 0.0	$ 0.3	$ 0.0

Investment Securities (Net Unrealized Investment Gains (Losses)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Investment securities
Net unrealized gains (losses), pre-tax	$ 93.3	$ (110.0)	$ 122.3	$ (110.3)
Trading Securities, Unrealized Gain (Loss) Tax	16.7	(26.4)	25.9	(28.5)
Trading Securities, Unrealized Gain (Loss), Net of Tax	76.6	(83.6)	96.4	(81.8)
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	(44.3)	74.6	(39.6)	79.0
Trading Securities, Unrealized Foreign Currency Transaction Gain (Loss) Tax	(11.8)	19.5	(10.4)	20.5
Trading Securities, Unrealized Foreign Currency Gain (Loss) Net of Tax	(32.5)	55.1	(29.2)	58.5
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	49.0	(35.4)	82.7	(31.3)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Tax	4.9	(6.9)	15.5	(8.0)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	44.1	(28.5)	67.2	(23.3)
Fixed maturity investments.
Investment securities
Net unrealized gains (losses), pre-tax	27.2	3.5	35.5	12.6
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	(40.6)	67.5	(36.9)	77.7
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(13.4)	71.0	(1.4)	90.3
Short-term investments
Investment securities
Net unrealized gains (losses), pre-tax	0.0	(0.1)	0.0	(0.1)
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	0.1	(0.4)	0.1	(1.4)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	0.1	(0.5)	0.1	(1.5)
Common equity securities
Investment securities
Net unrealized gains (losses), pre-tax	65.1	(101.0)	71.5	(95.1)
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	(0.1)	(0.9)	(0.1)	(1.8)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	65.0	(101.9)	71.4	(96.9)
Convertible Debt Securities [Member]
Investment securities
Net unrealized gains (losses), pre-tax	(0.6)	(11.2)	(2.9)	(19.3)
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	0.0	0.0	0.0	0.0
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(0.6)	(11.2)	(2.9)	(19.3)
Other long-term investments
Investment securities
Net unrealized gains (losses), pre-tax	1.6	(1.2)	18.2	(8.4)
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	(3.7)	8.4	(2.7)	4.5
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	$ (2.1)	$ 7.2	$ 15.5	$ (3.9)

Investment Securities (Investment gains (losses) for Level 3) (Details) - Level 3 Inputs - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	$ 2.7	$ (34.2)	$ 20.4	$ (38.4)
Fixed maturity investments.
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	(1.0)	(13.5)	7.3	(14.9)
Common equity securities
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	0.8	(17.5)	1.8	(17.0)
Other long-term investments
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	0.0	0.0	0.0	0.0
Convertible fixed maturity investments
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	$ 2.9	$ (3.2)	$ 11.3	$ (6.5)

Investment Securities (Investment Holdings) (Details) - USD ($) $ in Millions	Sep. 30, 2012	Dec. 31, 2011
Investment securities
Cost or amortized cost	$ 5,189.6	$ 6,228.2
Gross unrealized gains	137.4	119.1
Gross unrealized losses	(4.6)	(18.6)
Net foreign currency gains (losses)	(32.7)	5.0
Total fixed maturity investments including assets held for sale	5,289.7	6,333.7
Fixed maturity investments, at fair value	4,912.4	6,221.9
U.S. Government and agency obligations
Investment securities
Cost or amortized cost	393.7	299.4
Gross unrealized gains	1.2	5.3
Gross unrealized losses	(0.1)	(0.1)
Net foreign currency gains (losses)	(0.1)	0.4
Fixed maturity investments, at fair value	394.7	305.0
Debt securities issued by corporations
Investment securities
Cost or amortized cost	2,213.8	2,072.1
Gross unrealized gains	91.6	73.7
Gross unrealized losses	(3.0)	(7.8)
Net foreign currency gains (losses)	(21.1)	(2.9)
Fixed maturity investments, at fair value	2,281.3	2,135.1
Municipal obligations
Investment securities
Cost or amortized cost	3.8	2.7
Gross unrealized gains	0.0	0.0
Gross unrealized losses	0.0	0.0
Net foreign currency gains (losses)	0.0	0.0
Fixed maturity investments, at fair value	3.8	2.7
Mortgage-backed and asset-backed securities
Investment securities
Cost or amortized cost	2,023.3	3,190.5
Gross unrealized gains	30.3	25.9
Gross unrealized losses	(1.1)	(3.9)
Net foreign currency gains (losses)	(5.1)	10.4
Fixed maturity investments, at fair value	2,047.4	3,222.9
Foreign government, agency and provincial obligations
Investment securities
Cost or amortized cost	475.2	581.2
Gross unrealized gains	8.0	11.0
Gross unrealized losses	(0.4)	(0.1)
Net foreign currency gains (losses)	(6.4)	(2.9)
Fixed maturity investments, at fair value	476.4	589.2
Non-cumulative perpetual preference shares
Investment securities
Cost or amortized cost	79.8	82.3
Gross unrealized gains	6.3	3.2
Gross unrealized losses	0.0	(6.7)
Net foreign currency gains (losses)	0.0	0.0
Fixed maturity investments, at fair value	86.1	78.8
Common shareholders' equity.
Investment securities
Cost or amortized cost	870.0	691.7
Gross unrealized gains	139.7	72.0
Gross unrealized losses	(4.9)	(8.7)
Net foreign currency gains (losses)	0.0	0.0
Convertible fixed maturity investments
Investment securities
Cost or amortized cost	140.2	139.2
Gross unrealized gains	7.6	6.2
Gross unrealized losses	(5.8)	(1.6)
Net foreign currency gains (losses)	0.0	0.0
Other long-term investments.
Investment securities
Cost or amortized cost	264.8	274.4
Gross unrealized gains	57.1	55.5
Gross unrealized losses	(8.6)	(25.2)
Net foreign currency gains (losses)	$ (6.2)	(3.4)
OneBeacon Runoff [Member]
Investment securities
Fixed maturity investments reclassified to assets held for sale		377.3
AutoOne
Investment securities
Fixed maturity investments reclassified to assets held for sale		$ 111.8

Investment Securities (The Cost or Amortized Cost, Gross Unrealized Investment Gains and Losses) (Details) - USD ($) $ in Millions	Sep. 30, 2012	Dec. 31, 2011
Investment securities
Cost or amortized cost	$ 5,189.6	$ 6,228.2
Gross unrealized gains	137.4	119.1
Trading Securities, Gross Unrealized Loss	4.6	18.6
Net foreign currency gains (losses)	(32.7)	5.0
Fixed maturity investments, at fair value	4,912.4	6,221.9
Common equity securities, at fair value	1,004.8	755.0
Convertible fixed maturity investments, at fair value	142.0	143.8
Other long-term investments	307.1	301.3
Common shareholders' equity.
Investment securities
Cost or amortized cost	870.0	691.7
Gross unrealized gains	139.7	72.0
Trading Securities, Gross Unrealized Loss	4.9	8.7
Net foreign currency gains (losses)	0.0	0.0
Common equity securities, at fair value	1,004.8	755.0
Convertible Debt Securities [Member]
Investment securities
Cost or amortized cost	140.2	139.2
Gross unrealized gains	7.6	6.2
Trading Securities, Gross Unrealized Loss	5.8	1.6
Net foreign currency gains (losses)	0.0	0.0
Convertible fixed maturity investments, at fair value	142.0	143.8
Other long-term investments.
Investment securities
Cost or amortized cost	264.8	274.4
Gross unrealized gains	57.1	55.5
Trading Securities, Gross Unrealized Loss	8.6	25.2
Net foreign currency gains (losses)	(6.2)	(3.4)
Other long-term investments	$ 307.1	301.3
OneBeacon Runoff [Member]
Investment securities
Fixed maturity investments reclassified to assets held for sale		$ 377.3

Investment Securities (Other long-term investments) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2012 USD ($) Entity	Dec. 31, 2011 USD ($)
Investment securities
Distributions from Inactive Hedge Funds	$ 3.3
Maximum percentage of price difference provided by pricing services	5.00%
Maximum price difference provided by pricing services	$ 1.0
Fair value, investment-related liabilities	77.1	$ 68.1
Hedge and private equity funds included in other long-term investments
Investment securities
Largest single fund investment	$ 19.2
Hedge funds
Investment securities
Number of investments \| Entity	17
Redemption requests	$ 13.9
Private equity funds
Investment securities
Number of investments \| Entity	36

Investment Securities (Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency) (Details) - USD ($) $ in Millions	Sep. 30, 2012	Dec. 31, 2011
Hedge funds
Investment securities
Other long-term investments	$ 124.3
Private equity funds
Investment securities
Other long-term investments	129.8
Hedge and private equity funds included in other long-term investments
Investment securities
Other long-term investments	254.1	$ 254.2
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	108.5	81.5
Private equity funds \| Private Equity Multi Sector [Member]
Investment securities
Other long-term investments	29.3	26.9
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	6.4	8.2
Private equity funds \| Private Equity Energy Infrastructure and Services [Member]
Investment securities
Other long-term investments	32.9	28.0
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	11.7	9.9
Private equity funds \| Private Equity Distressed Residential Real Estate [Member]
Investment securities
Other long-term investments	19.2	27.4
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0.0	0.0
Private equity funds \| Real Estate Funds [Member]
Investment securities
Other long-term investments	12.2	9.5
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	3.3	3.3
Private equity funds \| Private Equity Secondaries [Member]
Investment securities
Other long-term investments	11.0	11.3
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	3.2	4.0
Private equity funds \| Private Equity Funds Multi Sector Europe [Member]
Investment securities
Other long-term investments	4.3	7.8
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	4.9	4.7
Private equity funds \| Private Equity Funds Manufacturing and Industrial [Member]
Investment securities
Other long-term investments	10.6	6.2
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	29.1	0.0
Private equity funds \| Private Equity Healthcare [Member]
Investment securities
Other long-term investments	4.3	2.3
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	5.4	7.0
Private equity funds \| Private Equity Funds Multi Sector Asia [Member]
Investment securities
Other long-term investments	0.4	3.6
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	2.7	2.6
Private equity funds \| Private Equity Insurance [Member]
Investment securities
Other long-term investments	3.2	3.5
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	41.3	41.3
Private equity funds \| Venture Capital Funds [Member]
Investment securities
Other long-term investments	2.4	2.4
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0.5	0.5
Private equity funds \| Private equity funds
Investment securities
Other long-term investments	129.8	128.9
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	108.5	81.5
Hedge funds \| Hedge Funds, Equity [Member]
Investment securities
Other long-term investments	58.6	48.8
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0.0	0.0
Hedge funds \| Hedge Funds Credit and Distressed [Member]
Investment securities
Other long-term investments	33.8	32.3
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0.0	0.0
Hedge funds \| Hedge Funds Diversified Strategies [Member]
Investment securities
Other long-term investments	2.3	16.9
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0.0	0.0
Hedge funds \| Hedge Funds Equity R E I T [Member]
Investment securities
Other long-term investments	15.2	14.5
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0.0	0.0
Hedge funds \| Hedge Funds Equity Activist [Member]
Investment securities
Other long-term investments	14.0	12.3
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0.0	0.0
Hedge funds \| Hedge Funds Bank Loan [Member]
Investment securities
Other long-term investments	0.4	0.5
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	0.0	0.0
Hedge funds \| Hedge funds
Investment securities
Other long-term investments	124.3	125.3
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share, Unfunded Commitments	$ 0.0	$ 0.0

Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) $ in Millions	Sep. 30, 2012 USD ($)
Investment securities
Distributions from Inactive Hedge Funds	$ 3.3
Hedge funds
Investment securities
Other long-term investments	124.3
Monthly \| Hedge funds
Investment securities
Other long-term investments	6.8
Quarterly \| Hedge funds
Investment securities
Other long-term investments	85.7
Semi-annual \| Hedge funds
Investment securities
Other long-term investments	20.6
Annual \| Hedge funds
Investment securities
Other long-term investments	11.2
90-119 days notice \| Hedge funds
Investment securities
Other long-term investments	28.4
90-119 days notice \| Monthly \| Hedge funds
Investment securities
Other long-term investments	0.0
90-119 days notice \| Quarterly \| Hedge funds
Investment securities
Other long-term investments	19.9
90-119 days notice \| Semi-annual \| Hedge funds
Investment securities
Other long-term investments	0.0
90-119 days notice \| Annual \| Hedge funds
Investment securities
Other long-term investments	8.5
30-59 days notice \| Hedge funds
Investment securities
Other long-term investments	29.4
30-59 days notice \| Monthly \| Hedge funds
Investment securities
Other long-term investments	0.0
30-59 days notice \| Quarterly \| Hedge funds
Investment securities
Other long-term investments	27.1
30-59 days notice \| Semi-annual \| Hedge funds
Investment securities
Other long-term investments	0.0
30-59 days notice \| Annual \| Hedge funds
Investment securities
Other long-term investments	2.3
60-89 days notice \| Hedge funds
Investment securities
Other long-term investments	49.9
60-89 days notice \| Monthly \| Hedge funds
Investment securities
Other long-term investments	0.0
60-89 days notice \| Quarterly \| Hedge funds
Investment securities
Other long-term investments	29.3
60-89 days notice \| Semi-annual \| Hedge funds
Investment securities
Other long-term investments	20.6
60-89 days notice \| Annual \| Hedge funds
Investment securities
Other long-term investments	0.0
120+ days notice \| Hedge funds
Investment securities
Other long-term investments	16.6
120+ days notice \| Monthly \| Hedge funds
Investment securities
Other long-term investments	6.8
120+ days notice \| Quarterly \| Hedge funds
Investment securities
Other long-term investments	9.4
120+ days notice \| Semi-annual \| Hedge funds
Investment securities
Other long-term investments	0.0
120+ days notice \| Annual \| Hedge funds
Investment securities
Other long-term investments	$ 0.4

Investment Securities (Investments In Private Equity Funds Subject to Lock-Up Periods) (Details) $ in Millions	Sep. 30, 2012 USD ($)
Investment securities
Distributions from Inactive Hedge Funds	$ 3.3
Private equity funds
Investment securities
Other long-term investments	129.8
1-3 years \| Private equity funds
Investment securities
Other long-term investments	27.7
3-5 years \| Private equity funds
Investment securities
Other long-term investments	15.6
5-10 years \| Private equity funds
Investment securities
Other long-term investments	75.9
Greater than 10 years \| Private equity funds
Investment securities
Other long-term investments	$ 10.6

Investment Securities (Fair Value Measurements) (Details) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Investments, Debt and Equity Securities [Abstract]
Maximum percentage of price difference provided by pricing services	5.00%
Maximum price difference provided by pricing services	$ 1.0
Fair value, investment-related liabilities	$ 77.1	$ 68.1

- Definition

Fair value of obligations incurred from short sales.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
-Section 35
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6475908&loc=d3e42429-110968

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Audit and Accounting Guide (AAG)
-Number AAG-BRD
-Paragraph 2
-IssueDate 2006-05-01
-Chapter 7
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Audit and Accounting Guide (AAG)
-Number AAG-BRD
-Paragraph 40
-IssueDate 2006-05-01
-Chapter 7
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Audit and Accounting Guide (AAG)
-Number AAG-BRD
-Paragraph 38
-IssueDate 2006-05-01
-Chapter 4
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Audit and Accounting Guide (AAG)
-Number AAG-BRD
-Paragraph 19
-IssueDate 2006-05-01
-Chapter 7
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

Investment Securities (Debt securities issued by corporation) (Details) - Debt securities issued by corporations - USD ($) $ in Millions	Sep. 30, 2012	Dec. 31, 2011
Investment securities
Fair value investments	$ 2,281.3	$ 2,135.1
AAA
Investment securities
Fair value investments	0.0	0.0
AA
Investment securities
Fair value investments	165.5	206.8
A
Investment securities
Fair value investments	992.8	802.8
BBB
Investment securities
Fair value investments	1,108.5	1,110.8
BB
Investment securities
Fair value investments	7.6	6.2
Other rating
Investment securities
Fair value investments	$ 6.9	$ 8.5

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents investment securities as of the balance sheet date which may include marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References + Details

Investment Securities (Mortgage-backed, Asset-backed Securities) (Details)	9 Months Ended
	Sep. 30, 2012
Commercial Mortgage Backed Securities Fixed Rate [Member]
Investment securities
Average basis points of subordination (as a percent)	25.0000
Commercial Mortgage Backed Securities Floating Rate [Member]
Investment securities
Average basis points of subordination (as a percent)	50.0000
Maximum \| Commercial Mortgage Backed Securities [Member]
Investment securities
Percentage of underlying loans reported as non-performing	1.00%

Investment Securities (Mortgage-backed Asset Securities) (Details) - USD ($)
$ in Millions

Sep. 30, 2012

Dec. 31, 2011

Sep. 30, 2011

Dec. 31, 2010

Level 2 Inputs

Investment securities

Fair value investments

$ 5,016.0

$ 6,088.2

$ 4,969.5

$ 5,477.4

Level 2 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA) [Member]

Investment securities

Fair value investments

1,165.5

1,365.8

Level 2 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]

Investment securities

Fair value investments

97.2

712.6

Level 2 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]

Investment securities

Fair value investments

37.6

35.9

Level 2 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]

Investment securities

Fair value investments

^[1]

1,300.3

2,114.3

Level 2 Inputs | Residential Mortgage Backed Securities [Member]

Investment securities

Fair value investments

160.5

68.0

Level 2 Inputs | Commercial Mortgage Backed Securities [Member]

Investment securities

Fair value investments

383.8

276.7

Level 2 Inputs | Mortgage-backed Securities, Issued by Private Enterprises [Member]

Investment securities

Fair value investments

544.3

344.7

Level 2 Inputs | Collateralized Mortgage Backed Securities [Member]

Investment securities

Fair value investments

1,844.6

2,459.0

Level 2 Inputs | Collateralized Credit Card Securities [Member]

Investment securities

Fair value investments

80.8

380.6

Level 2 Inputs | Collateralized Auto Loans [Member]

Investment securities

Fair value investments

80.3

345.6

Level 2 Inputs | Collateralized Securities, Other [Member]

Investment securities

Fair value investments

36.2

22.6

Level 2 Inputs | Asset-backed Securities, Securitized Loans and Receivables [Member]

Investment securities

Fair value investments

197.3

748.8

Level 2 Inputs | Mortgage-backed and asset-backed securities

Investment securities

Fair value investments

2,041.9

3,207.8

Level 3 Inputs

Investment securities

Fair value investments

0.0

Level 3 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA) [Member]

Investment securities

Fair value investments

0.0

Level 3 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]

Investment securities

Fair value investments

0.0

Level 3 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]

Investment securities

Fair value investments

0.0

Level 3 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]

Investment securities

Fair value investments

^[1]

0.0

Level 3 Inputs | Residential Mortgage Backed Securities [Member]

Investment securities

Fair value investments

0.0

15.1

Level 3 Inputs | Commercial Mortgage Backed Securities [Member]

Investment securities

Fair value investments

5.5

0.0

Level 3 Inputs | Mortgage-backed Securities, Issued by Private Enterprises [Member]

Investment securities

Fair value investments

5.5

15.1

Level 3 Inputs | Collateralized Mortgage Backed Securities [Member]

Investment securities

Fair value investments

5.5

15.1

Level 3 Inputs | Collateralized Credit Card Securities [Member]

Investment securities

Fair value investments

0.0

Level 3 Inputs | Collateralized Auto Loans [Member]

Investment securities

Fair value investments

0.0

Level 3 Inputs | Collateralized Securities, Other [Member]

Investment securities

Fair value investments

0.0

Level 3 Inputs | Asset-backed Securities, Securitized Loans and Receivables [Member]

Investment securities

Fair value investments

0.0

Level 3 Inputs | Mortgage-backed and asset-backed securities

Investment securities

Fair value investments

5.5

15.1

Fair Value

Investment securities

Fair value investments

^[2]

7,626.4

8,346.8

^[3]

$ 7,265.9

$ 7,901.6

Fair Value | Government National Mortgage Association Certificates and Obligations (GNMA) [Member]

Investment securities

Fair value investments

1,165.5

1,365.8

Fair Value | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]

Investment securities

Fair value investments

97.2

712.6

Fair Value | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]

Investment securities

Fair value investments

37.6

35.9

Fair Value | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]

Investment securities

Fair value investments

^[1]

1,300.3

2,114.3

Fair Value | Residential Mortgage Backed Securities [Member]

Investment securities

Fair value investments

160.5

83.1

Fair Value | Commercial Mortgage Backed Securities [Member]

Investment securities

Fair value investments

389.3

276.7

Fair Value | Mortgage-backed Securities, Issued by Private Enterprises [Member]

Investment securities

Fair value investments

549.8

359.8

Fair Value | Collateralized Mortgage Backed Securities [Member]

Investment securities

Fair value investments

1,850.1

2,474.1

Fair Value | Collateralized Credit Card Securities [Member]

Investment securities

Fair value investments

80.8

380.6

Fair Value | Collateralized Auto Loans [Member]

Investment securities

Fair value investments

80.3

345.6

Fair Value | Collateralized Securities, Other [Member]

Investment securities

Fair value investments

36.2

22.6

Fair Value | Asset-backed Securities, Securitized Loans and Receivables [Member]

Investment securities

Fair value investments

197.3

748.8

Fair Value | Mortgage-backed and asset-backed securities

Investment securities

Fair value investments

$ 2,047.4

$ 3,222.9

[1]	(1) Represents publicly traded mortgage-backed securities which carry the full faith and credit guaranty of the U.S. government (i.e., GNMA) or are guaranteed by a government sponsored entity (i.e., FNMA, FHLMC).
[2]	(1) Excludes carrying value of $33.0 and $34.3 at January 1, 2012 and September 30, 2012 associated with other long-term investments accounted for using the equity method
[3]	(2) Carrying value includes $111.8 and $377.3 at January 1, 2012 and September 30, 2012 that is classified as assets held for sale relating to discontinued operations. Level 3 Investments MillionsLevel 1InvestmentsLevel 2InvestmentsFixedMaturitiesCommonequitysecuritiesConvertiblefixedmaturitiesOther long-terminvestments Total Balance at January 1, 2011$1,894.4$5,477.4$128.4$71.2$—$330.2(1) $7,901.6(1) Total realized and unrealized gains (losses)(50.5)115.9(10.6)(4.9)—22.5 72.4 Foreign currency gains (losses) through OCI.3(84.4)(4.4)1.6—(5.0) (91.9) Amortization/Accretion2.4(40.7)(.1)——— (38.4) Purchases6,690.73,987.4212.819.7—27.9 10,938.5 Sales(6,782.1)(4,596.9)1.6(55.5)—(83.4) (11,516.3) Transfers in—111.81.0——— 112.8 Transfers out—(1.0)(111.8)——— (112.8) Balance at September 30, 2011$1,755.2$4,969.5$216.9$32.1$—$292.2(1) $7,265.9(1) (1) Excludes carrying value o

Investment Securities (Non-agency Mortgage-backed Securities) (Details) - Fair Value - USD ($)
$ in Millions

Sep. 30, 2012

Dec. 31, 2011

Sep. 30, 2011

Dec. 31, 2010

Investment securities

Fair value investments

^[1]

$ 7,626.4

$ 8,346.8

^[2]

$ 7,265.9

$ 7,901.6

Residential Mortgage Backed Securities [Member]

Investment securities

Fair value investments

160.5

83.1

Commercial Mortgage Backed Securities [Member]

Investment securities

Fair value investments

389.3

276.7

Mortgage-backed Securities, Issued by Private Enterprises [Member]

Investment securities

Fair value investments

549.8

$ 359.8

Securities Issued In2007 [Member] | Residential Mortgage Backed Securities [Member]

Investment securities

Fair value investments

7.1

Securities Issued In2007 [Member] | Commercial Mortgage Backed Securities [Member]

Investment securities

Fair value investments

15.3

Securities Issued In2007 [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]

Investment securities

Fair value investments

22.4

Securities Issued In2009 [Member] | Residential Mortgage Backed Securities [Member]

Investment securities

Fair value investments

1.7

Securities Issued In2009 [Member] | Commercial Mortgage Backed Securities [Member]

Investment securities

Fair value investments

11.9

Securities Issued In2009 [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]

Investment securities

Fair value investments

13.6

Securities Issued in 2012 [Member] | Residential Mortgage Backed Securities [Member]

Investment securities

Fair value investments

0.0

Securities Issued in 2012 [Member] | Commercial Mortgage Backed Securities [Member]

Investment securities

Fair value investments

224.1

Securities Issued in 2012 [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]

Investment securities

Fair value investments

224.1

Securities Issued In2010 [Member] | Residential Mortgage Backed Securities [Member]

Investment securities

Fair value investments

53.2

Securities Issued In2010 [Member] | Commercial Mortgage Backed Securities [Member]

Investment securities

Fair value investments

6.1

Securities Issued In2010 [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]

Investment securities

Fair value investments

59.3

Securities Issued In2011 [Member] | Residential Mortgage Backed Securities [Member]

Investment securities

Fair value investments

74.9

Securities Issued In2011 [Member] | Commercial Mortgage Backed Securities [Member]

Investment securities

Fair value investments

127.4

Securities Issued In2011 [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]

Investment securities

Fair value investments

202.3

Securities Issued In2003 [Member] | Residential Mortgage Backed Securities [Member]

Investment securities

Fair value investments

2.2

Securities Issued In2003 [Member] | Commercial Mortgage Backed Securities [Member]

Investment securities

Fair value investments

0.0

Securities Issued In2003 [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]

Investment securities

Fair value investments

2.2

Securities Issued In 2006 [Member] | Residential Mortgage Backed Securities [Member]

Investment securities

Fair value investments

21.4

Securities Issued In 2006 [Member] | Commercial Mortgage Backed Securities [Member]

Investment securities

Fair value investments

4.5

Securities Issued In 2006 [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]

Investment securities

Fair value investments

$ 25.9

[1]

(1) Excludes carrying value of $33.0 and $34.3 at January 1, 2012 and September 30, 2012 associated with other long-term investments accounted for using the equity method

[2]

(2) Carrying value includes $111.8 and $377.3 at January 1, 2012 and September 30, 2012 that is classified as assets held for sale relating to discontinued operations. Level 3 Investments MillionsLevel 1InvestmentsLevel 2InvestmentsFixedMaturitiesCommonequitysecuritiesConvertiblefixedmaturitiesOther long-terminvestments Total Balance at January 1, 2011$1,894.4$5,477.4$128.4$71.2$—$330.2(1) $7,901.6(1) Total realized and unrealized gains (losses)(50.5)115.9(10.6)(4.9)—22.5 72.4 Foreign currency gains (losses) through OCI.3(84.4)(4.4)1.6—(5.0) (91.9) Amortization/Accretion2.4(40.7)(.1)——— (38.4) Purchases6,690.73,987.4212.819.7—27.9 10,938.5 Sales(6,782.1)(4,596.9)1.6(55.5)—(83.4) (11,516.3) Transfers in—111.81.0——— 112.8 Transfers out—(1.0)(111.8)——— (112.8) Balance at September 30, 2011$1,755.2$4,969.5$216.9$32.1$—$292.2(1) $7,265.9(1) (1) Excludes carrying value o

Investment Securities (Non-agency Residential Mortgage-backed Securities) (Details) - USD ($)
$ in Millions

Sep. 30, 2012

Dec. 31, 2011

Sep. 30, 2011

Dec. 31, 2010

Fair Value

Investment securities

Fair value investments

^[1]

$ 7,626.4

$ 8,346.8

^[2]

$ 7,265.9

$ 7,901.6

Residential Mortgage Backed Securities [Member] | Fair Value

Investment securities

Fair value investments

160.5

$ 83.1

Residential Mortgage Backed Securities [Member] | Residential, Prime, Financing Receivable [Member] | Fair Value

Investment securities

Fair value investments

160.0

Residential Mortgage Backed Securities [Member] | Residential Nonprime Financing Receivable [Member] | Fair Value

Investment securities

Fair value investments

0.5

Residential Mortgage Backed Securities [Member] | Residential, Subprime, Financing Receivable [Member] | Fair Value

Investment securities

Fair value investments

0.0

Residential Mortgage Backed Securities [Member] | Super Senior [Member]

Investment securities

Fair value investments

^[3]

13.0

Residential Mortgage Backed Securities [Member] | Super Senior [Member] | Residential, Prime, Financing Receivable [Member]

Investment securities

Fair value investments

^[3]

13.0

Residential Mortgage Backed Securities [Member] | Super Senior [Member] | Residential Nonprime Financing Receivable [Member]

Investment securities

Fair value investments

^[3]

0.0

Residential Mortgage Backed Securities [Member] | Super Senior [Member] | Residential, Subprime, Financing Receivable [Member]

Investment securities

Fair value investments

^[3]

0.0

Residential Mortgage Backed Securities [Member] | Senior [Member]

Investment securities

Fair value investments

^[4]

147.5

Residential Mortgage Backed Securities [Member] | Senior [Member] | Residential, Prime, Financing Receivable [Member]

Investment securities

Fair value investments

^[4]

147.0

Residential Mortgage Backed Securities [Member] | Senior [Member] | Residential Nonprime Financing Receivable [Member]

Investment securities

Fair value investments

^[4]

0.5

Residential Mortgage Backed Securities [Member] | Senior [Member] | Residential, Subprime, Financing Receivable [Member]

Investment securities

Fair value investments

^[4]

0.0

Residential Mortgage Backed Securities [Member] | Subordinate [Member]

Investment securities

Fair value investments

^[5]

0.0

Residential Mortgage Backed Securities [Member] | Subordinate [Member] | Residential, Prime, Financing Receivable [Member]

Investment securities

Fair value investments

^[5]

0.0

Residential Mortgage Backed Securities [Member] | Subordinate [Member] | Residential Nonprime Financing Receivable [Member]

Investment securities

Fair value investments

^[5]

0.0

Residential Mortgage Backed Securities [Member] | Subordinate [Member] | Residential, Subprime, Financing Receivable [Member]

Investment securities

Fair value investments

^[5]

$ 0.0

[1]	(1) Excludes carrying value of $33.0 and $34.3 at January 1, 2012 and September 30, 2012 associated with other long-term investments accounted for using the equity method
[2]	(2) Carrying value includes $111.8 and $377.3 at January 1, 2012 and September 30, 2012 that is classified as assets held for sale relating to discontinued operations. Level 3 Investments MillionsLevel 1InvestmentsLevel 2InvestmentsFixedMaturitiesCommonequitysecuritiesConvertiblefixedmaturitiesOther long-terminvestments Total Balance at January 1, 2011$1,894.4$5,477.4$128.4$71.2$—$330.2(1) $7,901.6(1) Total realized and unrealized gains (losses)(50.5)115.9(10.6)(4.9)—22.5 72.4 Foreign currency gains (losses) through OCI.3(84.4)(4.4)1.6—(5.0) (91.9) Amortization/Accretion2.4(40.7)(.1)——— (38.4) Purchases6,690.73,987.4212.819.7—27.9 10,938.5 Sales(6,782.1)(4,596.9)1.6(55.5)—(83.4) (11,516.3) Transfers in—111.81.0——— 112.8 Transfers out—(1.0)(111.8)——— (112.8) Balance at September 30, 2011$1,755.2$4,969.5$216.9$32.1$—$292.2(1) $7,265.9(1) (1) Excludes carrying value o
[3]	(1) At issuance, Super Senior were rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were senior to other AAA or Aaa bonds.
[4]	(2) At issuance, Senior were rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were senior to non-AAA or non-Aaa bonds.
[5]	(3) At issuance, Subordinate were not rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were junior to AAA or Aaa bonds.

Investment Securities (Non-agency Commercial Mortgage-backed Securities) (Details) - USD ($)
$ in Millions

Sep. 30, 2012

Dec. 31, 2011

Sep. 30, 2011

Dec. 31, 2010

Commercial Mortgage Backed Securities Fixed Rate [Member] | Subordinate [Member]

Investment securities

Fair value investments

^[1]

$ 4.5

Commercial Mortgage Backed Securities Fixed Rate [Member] | Super Senior [Member]

Investment securities

Fair value investments

^[2]

253.0

Commercial Mortgage Backed Securities Fixed Rate [Member] | Senior [Member]

Investment securities

Fair value investments

^[3]

109.6

Commercial Mortgage Backed Securities Floating Rate [Member] | Subordinate [Member]

Investment securities

Fair value investments

^[1]

5.5

Commercial Mortgage Backed Securities Floating Rate [Member] | Super Senior [Member]

Investment securities

Fair value investments

^[2]

15.3

Commercial Mortgage Backed Securities Floating Rate [Member] | Senior [Member]

Investment securities

Fair value investments

^[3]

1.4

Commercial Mortgage Backed Securities [Member] | Subordinate [Member]

Investment securities

Fair value investments

^[1]

10.0

Commercial Mortgage Backed Securities [Member] | Super Senior [Member]

Investment securities

Fair value investments

^[2]

268.3

Commercial Mortgage Backed Securities [Member] | Senior [Member]

Investment securities

Fair value investments

^[3]

111.0

Fair Value

Investment securities

Fair value investments

^[4]

7,626.4

$ 8,346.8

^[5]

$ 7,265.9

$ 7,901.6

Fair Value | Commercial Mortgage Backed Securities Fixed Rate [Member]

Investment securities

Fair value investments

367.1

Fair Value | Commercial Mortgage Backed Securities Floating Rate [Member]

Investment securities

Fair value investments

22.2

Fair Value | Commercial Mortgage Backed Securities [Member]

Investment securities

Fair value investments

$ 389.3

$ 276.7

[1]	(3) At issuance, Subordinate were not rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were junior to AAA or Aaa bonds.
[2]	(1) At issuance, Super Senior were rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were senior to other AAA or Aaa bonds.
[3]	(2) At issuance, Senior were rated AAA by Standard & Poor’s, Aaa by Moody’s or AAA by Fitch and were senior to non-AAA or non-Aaa bonds.
[4]	(1) Excludes carrying value of $33.0 and $34.3 at January 1, 2012 and September 30, 2012 associated with other long-term investments accounted for using the equity method
[5]	(2) Carrying value includes $111.8 and $377.3 at January 1, 2012 and September 30, 2012 that is classified as assets held for sale relating to discontinued operations. Level 3 Investments MillionsLevel 1InvestmentsLevel 2InvestmentsFixedMaturitiesCommonequitysecuritiesConvertiblefixedmaturitiesOther long-terminvestments Total Balance at January 1, 2011$1,894.4$5,477.4$128.4$71.2$—$330.2(1) $7,901.6(1) Total realized and unrealized gains (losses)(50.5)115.9(10.6)(4.9)—22.5 72.4 Foreign currency gains (losses) through OCI.3(84.4)(4.4)1.6—(5.0) (91.9) Amortization/Accretion2.4(40.7)(.1)——— (38.4) Purchases6,690.73,987.4212.819.7—27.9 10,938.5 Sales(6,782.1)(4,596.9)1.6(55.5)—(83.4) (11,516.3) Transfers in—111.81.0——— 112.8 Transfers out—(1.0)(111.8)——— (112.8) Balance at September 30, 2011$1,755.2$4,969.5$216.9$32.1$—$292.2(1) $7,265.9(1) (1) Excludes carrying value o

- Definition

+ References + Details

(Rollforward of Fair Value Measurements by Level) (Details) - USD ($)
$ in Millions

9 Months Ended

Sep. 30, 2012

Sep. 30, 2011

Dec. 31, 2011

Dec. 31, 2010

Level 1 Inputs

Investment securities

Fair value investments

$ 2,225.8

$ 1,755.2

$ 1,879.1

$ 1,894.4

Total realized and unrealized gains (losses)

57.8

(50.5)

Foreign currency gains (losses) through OCI

13.2

0.3

Amortization/Accretion

(0.7)

2.4

Purchases

6,712.0

6,690.7

Sales

(6,435.6)

(6,782.1)

Transfers in

0.0

Transfers out

0.0

Level 2 Inputs

Investment securities

Fair value investments

5,016.0

4,969.5

6,088.2

5,477.4

Total realized and unrealized gains (losses)

53.8

115.9

Foreign currency gains (losses) through OCI

75.5

(84.4)

Amortization/Accretion

(34.0)

(40.7)

Purchases

3,823.7

3,987.4

Sales

(5,048.1)

(4,596.9)

Transfers in

56.9

111.8

Transfers out

0.0

(1.0)

Securities of level 3 measurements recategorized as level 2 measurements

56.9

111.8

Level 3 Inputs

Investment securities

Fair value investments

0.0

Total realized and unrealized gains (losses)

0.0

Foreign currency gains (losses) through OCI

0.0

Amortization/Accretion

0.0

Purchases

0.0

Sales

0.0

Fair Value

Investment securities

Fair value investments

^[1]

7,626.4

7,265.9

8,346.8

^[2]

7,901.6

Total realized and unrealized gains (losses)

123.2

72.4

Foreign currency gains (losses) through OCI

92.6

(91.9)

Amortization/Accretion

(35.4)

(38.4)

Purchases

10,723.1

10,938.5

Sales

(11,623.9)

(11,516.3)

Transfers in

56.9

112.8

Transfers out

(56.9)

(112.8)

Fixed maturity investments.

Investment securities

Difference in value between securities determined using the industry standard pricing models and securities based upon quoted prices provided by a third party

0.8

Fixed maturity investments. | Level 3 Inputs

Investment securities

Fair value investments

76.1

216.9

78.9

128.4

Total realized and unrealized gains (losses)

8.4

(10.6)

Foreign currency gains (losses) through OCI

0.7

(4.4)

Amortization/Accretion

(0.7)

(0.1)

Purchases

144.3

212.8

Sales

(99.2)

1.6

Transfers in

0.0

1.0

Transfers out

(56.3)

(111.8)

Common equity securities | Level 3 Inputs

Investment securities

Fair value investments

35.9

32.1

32.3

71.2

Total realized and unrealized gains (losses)

11.4

(4.9)

Foreign currency gains (losses) through OCI

0.1

1.6

Amortization/Accretion

0.0

Purchases

2.5

19.7

Sales

(9.8)

(55.5)

Transfers in

0.0

Transfers out

(0.6)

0.0

Convertible Debt Securities [Member] | Level 3 Inputs

Investment securities

Fair value investments

0.0

Total realized and unrealized gains (losses)

0.0

Foreign currency gains (losses) through OCI

0.0

Amortization/Accretion

0.0

0.0

0.0

0.0

0.0

Other long-term investments | Level 3 Inputs

Investment securities

Fair value investments

^[1]

272.6

292.2

268.3

330.2

Total realized and unrealized gains (losses)

(8.2)

22.5

Foreign currency gains (losses) through OCI

3.1

(5.0)

Amortization/Accretion

0.0

Purchases

40.6

27.9

Sales

(31.2)

(83.4)

Transfers in

0.0

Transfers out

0.0

Fair value measured on a recurring basis | Level 1 Inputs

Investment securities

Fair value investments

2,225.8

1,879.1

Fair value measured on a recurring basis | Level 2 Inputs

Investment securities

Fair value investments

5,016.0

6,088.2

Fair value measured on a recurring basis | Level 3 Inputs

Investment securities

Fair value investments

384.6

379.5

Fair value measured on a recurring basis | Fair Value

Investment securities

Fair value investments

7,626.4

8,346.8

Fair value measured on a recurring basis | Fixed maturity investments. | Level 1 Inputs

Investment securities

Fair value investments

398.5

365.7

^[3]

Fair value measured on a recurring basis | Fixed maturity investments. | Level 2 Inputs

Investment securities

Fair value investments

4,815.1

5,889.1

^[3]

Fair value measured on a recurring basis | Fixed maturity investments. | Level 3 Inputs

Investment securities

Fair value investments

76.1

78.9

^[3]

Fair value measured on a recurring basis | Fixed maturity investments. | Fair Value

Investment securities

Fair value investments

5,289.7

6,333.7

^[3]

Fair value measured on a recurring basis | Convertible Debt Securities [Member] | Level 1 Inputs

Investment securities

Fair value investments

0.0

Fair value measured on a recurring basis | Convertible Debt Securities [Member] | Level 2 Inputs

Investment securities

Fair value investments

142.0

143.8

Fair value measured on a recurring basis | Convertible Debt Securities [Member] | Level 3 Inputs

Investment securities

Fair value investments

0.0

Fair value measured on a recurring basis | Convertible Debt Securities [Member] | Fair Value

Investment securities

Fair value investments

142.0

143.8

Fair value measured on a recurring basis | Other long-term investments | Level 1 Inputs

Investment securities

Fair value investments

0.0

^[3]

0.0

^[4]

Fair value measured on a recurring basis | Other long-term investments | Level 2 Inputs

Investment securities

Fair value investments

0.0

^[3]

0.0

^[4]

Fair value measured on a recurring basis | Other long-term investments | Level 3 Inputs

Investment securities

Fair value investments

272.6

^[3]

268.3

^[4]

Carrying value of investment accounted for using the equity method

34.3

$ 36.6

33.0

$ 41.9

Fair value measured on a recurring basis | Other long-term investments | Fair Value

Investment securities

Fair value investments

$ 272.6

^[3]

$ 268.3

^[4]

[1]	(1) Excludes carrying value of $33.0 and $34.3 at January 1, 2012 and September 30, 2012 associated with other long-term investments accounted for using the equity method
[2]	(2) Carrying value includes $111.8 and $377.3 at January 1, 2012 and September 30, 2012 that is classified as assets held for sale relating to discontinued operations. Level 3 Investments MillionsLevel 1InvestmentsLevel 2InvestmentsFixedMaturitiesCommonequitysecuritiesConvertiblefixedmaturitiesOther long-terminvestments Total Balance at January 1, 2011$1,894.4$5,477.4$128.4$71.2$—$330.2(1) $7,901.6(1) Total realized and unrealized gains (losses)(50.5)115.9(10.6)(4.9)—22.5 72.4 Foreign currency gains (losses) through OCI.3(84.4)(4.4)1.6—(5.0) (91.9) Amortization/Accretion2.4(40.7)(.1)——— (38.4) Purchases6,690.73,987.4212.819.7—27.9 10,938.5 Sales(6,782.1)(4,596.9)1.6(55.5)—(83.4) (11,516.3) Transfers in—111.81.0——— 112.8 Transfers out—(1.0)(111.8)——— (112.8) Balance at September 30, 2011$1,755.2$4,969.5$216.9$32.1$—$292.2(1) $7,265.9(1) (1) Excludes carrying value o
[3]	September 30, 2012MillionsFair value Level 1 Inputs Level 2 Inputs Level 3 InputsFixed maturity investments: US Government and agency obligations$394.7 $340.5 $54.2 $— Debt securities issued by corporations: Consumer597.2 — 597.2 —Industrial488.1 — 488.1 —Financials405.4 1.1 404.3 —Communications217.1 — 217.1 —Basic materials175.1 — 175.1 —Energy172.9 — 172.9 —Utilities204.4 — 204.4 —Technology21.1 — 21.1 —Diversified— — — —Total debt securities issued by corporations:2,281.3 1.1 2,280.2 — Municipal obligations3.8 — 3.8 —Mortgage-backed and asset-backed securities2,047.4 — 2,041.9 5.5Foreign government, agency and provincial obligations476.4 56.9 419.5 —Preferred stocks86.1 — 15.5 70.6Total fixed maturity investments (1)5,289.7 398.5 4,815.1 76.1 Short-term investments917.3 917.3 — — Common equity securities: Financials316.1 277.9 2.3 35.9Consumer249.7 249.6 .1 —Basic materials118.2 118.2 — —Energy96.8 96.8 — —Technology51.6 51.6 — —Utilities42.9 42.7 .2 —Other129.5 73.2 56.3 —Total common equity securities1,004.8 910.0 58.9 35.9 Convertible fixed maturity investments142.0 — 142.0 —Other long-term investments (2) 272.6 — — 272.6Total investments$7,626.4 $2,225.8 $5,016.0 $384.6 (1) Carrying value includes $377.3 that is classified as assets held for sale relating to discontinued operations. (2) Excludes carrying value of $34.3 associated with other long-term investment limited partnerships accounted for using the equity method and $0.3 related to forward contrac
[4]

Investment Securities (Significant Unobservable Inputs) (Details) - Discounted cash flows $ in Millions	9 Months Ended
	Sep. 30, 2012 USD ($)
Agency CMBS \| AA+
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value Assets	$ 5.5
Prepayment rate (as a percent)	0.00%
Discount Yield (as a percent)	2.10%
Preferred Stock \| NR
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value Assets	$ 70.6
Discount Yield (as a percent)	8.00%

Debt (Details)
$ in Millions

Sep. 30, 2012

USD ($)

Dec. 31, 2011

USD ($)

Dec. 30, 2011

USD ($)

Aug. 12, 2011

USD ($)

Debt Instrument

Total debt

$ 676.6

$ 677.5

OBH Senior Notes

Debt Instrument

Debt instrument at face value

269.9

Unamortized original issue discount

(0.1)

Total debt

269.8

SIG Senior Notes

Debt Instrument

Debt instrument at face value

400.0

Unamortized original issue discount

(0.6)

(0.7)

Total debt

399.4

399.3

WTM Bank Facility

Debt Instrument

Total debt

0.0

Total commitment under revolving credit facility

$ 375.0

Old Lyme

Debt Instrument

Total debt

2.1

Debt Instrument Term (in years) | yr

Percentage of principal amount of debt subject to upward or downward adjustments

50.00%

Cash to be paid on acquisition

$ 6.0

Other debt

Debt Instrument

Total debt

^[1]

$ 5.3

$ 6.3

[1]	(1) Other debt relates to White Mountains’ consolidation of Hamer and Bri-Mar.

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Income Taxes (Details) - USD ($) $ in Millions	Sep. 30, 2012	Sep. 30, 2012	Dec. 31, 2011
Income Tax Contingency [Line Items]
Deferred tax liability	$ 399.7	$ 399.7	$ 365.5
Deferred Income Tax Assets	$ 555.0	$ 555.0	$ 536.9
Effective tax rates (as a percent)	35.40%	27.20%
U.S. statutory rate (as a percent)	35.00%	35.00%
Unrecognized Tax Benefits, Decreases Resulting from Prior Period Tax Positions		$ 11.5
Foreign tax credit carryforwards	$ 20.6	$ 20.6
Sweden proposed corporate income tax rate		22.00%
Sweden corporate income tax rate		26.30%
Sirius Group Segment [Member]
Income Tax Contingency [Line Items]
Deferred tax liability	60.0	$ 60.0
Deferred Income Tax Assets	$ 272.1	$ 272.1

Derivatives (Details) ¥ in Billions, $ in Billions	Sep. 30, 2012 JPY (¥)	Sep. 30, 2012 USD ($)	Dec. 31, 2011 JPY (¥)	Dec. 31, 2011 USD ($)
Derivatives Disclosure [Abstract]
Total guarantee value	¥ 230.5	$ 3.0	¥ 233.7	$ 3.0
Collective account values of underlying variable annuities as a percentage of the guarantee value	80.00%	80.00%	78.00%	78.00%

Derivatives (Pre-Tax Operating Results of WM Life Re) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Pre-tax operating results of WM Life Re
Revenues	$ 697.4	$ 501.8	$ 1,869.3	$ 1,579.7
General and administrative expenses	(58.7)	(36.2)	(146.3)	(120.4)
Pre-tax income (loss) from continuing operations	135.1	1.3	313.6	(0.4)
White Mountains Life Re [Member]
Pre-tax operating results of WM Life Re
Policy Charges, Insurance	8.1	8.4	24.1	24.3
Gain (Loss) on Variable Annuity Liabilities	(11.3)	(164.4)	89.4	(148.0)
Derivative, Gain (Loss) on Derivative, Net	(11.0)	148.9	(122.0)	105.4
Foreign Exchange Derivatives Gain (Loss)	9.0	14.8	(6.4)	17.1
Other Investment Income and Gain (Loss) on Investments	3.8	0.5	2.9	(0.1)
Revenues	(1.4)	8.2	(12.0)	(1.3)
Gain (Loss) on Liability for Death Benefit	0.7	(5.6)	6.7	(3.1)
Liability for Future Policy Benefits, Benefits Paid	(1.5)	(0.7)	(4.9)	(2.4)
General and administrative expenses	(1.1)	(1.1)	(3.8)	(3.2)
Pre-tax income (loss) from continuing operations	$ (3.3)	$ 0.8	$ (14.0)	$ (10.0)

Derivatives (Variable Annuity Reinsurance Liabilities and Derivative Instruments (Details) - White Mountains Life Re [Member] - USD ($)
$ in Millions

3 Months Ended

9 Months Ended

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2012

Sep. 30, 2011

Dec. 31, 2011

Changes in variable annuity liabilities

Derivative, Fair Value, Net

$ 290.4

Derivative, Gain (Loss) on Derivative, Net

$ (11.0)

$ 148.9

(122.0)

$ 105.4

Derivative, Fair Value, Net

242.1

Collateral Cash and Investments

477.5

419.7

477.5

419.7

$ 485.3

Fair Value

Changes in variable annuity liabilities

Derivative, Fair Value, Net

250.3

269.0

^[1]

290.4

347.5

^[1]

Fair Value Derivatives Measured on Recurring Basis, Asset Purchases

0.0

^[1]

6.1

5.0

^[1]

Derivative, Gain (Loss) on Derivative, Net

(11.0)

148.9

^[1]

(122.0)

105.4

^[1]

Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements

2.8

(64.1)

^[1]

67.6

(104.1)

^[1]

Derivative, Fair Value, Net

242.1

353.8

^[1]

242.1

353.8

^[1]

Level 3 Inputs

Changes in derivative instruments

Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value

(661.8)

(591.3)

(768.5)

(610.2)

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases

0.0

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings

(10.6)

(170.0)

96.1

(151.1)

Fair Value Measurement with Unobservable Inputs, Reconciliation, Recurring Basis, Liability Sales or Settlements

0.0

Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value

(672.4)

(761.3)

(672.4)

(761.3)

Changes in variable annuity liabilities

Derivative, Fair Value, Net

^[2]

213.0

232.7

247.1

275.3

Fair Value Derivatives Measured on Recurring Basis, Asset Purchases

^[2]

0.0

6.1

5.0

Derivative, Gain (Loss) on Derivative, Net

^[2]

6.7

45.6

(24.1)

27.1

Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements

^[2]

(6.7)

0.0

(16.1)

(29.1)

Derivative, Fair Value, Net

^[2]

213.0

278.3

213.0

278.3

Level 2 Inputs

Changes in variable annuity liabilities

Derivative, Fair Value, Net

^[2]

61.0

48.2

^[3]

39.2

72.2

^[3]

Fair Value Derivatives Measured on Recurring Basis, Asset Purchases

^[2]

0.0

^[3]

0.0

^[3]

Derivative, Gain (Loss) on Derivative, Net

^[2]

(15.3)

75.7

^[3]

(71.8)

67.5

^[3]

Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements

^[2]

(12.5)

(48.4)

^[3]

65.8

(64.2)

^[3]

Derivative, Fair Value, Net

^[2]

33.2

75.5

^[3]

33.2

75.5

^[3]

Level 1 Inputs

Changes in variable annuity liabilities

Derivative, Fair Value, Net

(23.7)

(11.9)

^[4]

4.1

0.0

^[4]

Fair Value Derivatives Measured on Recurring Basis, Asset Purchases

0.0

^[4]

0.0

^[4]

Derivative, Gain (Loss) on Derivative, Net

(2.4)

27.6

^[4]

(26.1)

10.8

^[4]

Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements

22.0

(15.7)

^[4]

17.9

(10.8)

^[4]

Derivative, Fair Value, Net

$ (4.1)

$ 0.0

^[4]

$ (4.1)

$ 0.0

^[4]

[1]	(4) In addition to derivative instruments, WM Life Re held cash, short-term and fixed maturity investments of $477.5 and $419.7 at September 30, 2012 and 2011 posted as collateral to its reinsurance counterparties.
[2]	(1) Consists of over-the-counter instruments.
[3]	(2) Consists of interest rate swaps, total return swaps, foreign currency forward contracts, and bond forwards. Fair value measurement based upon bid/ask pricing quotes for similar instruments that are actively traded, where available. Swaps for which an active market does not exist have been priced using observable inputs including the swap curve and the underlying bond index.
[4]	(3) Consists of exchange traded equity index, foreign currency and interest rate futures. Fair value measurements based upon quoted prices for identical instruments that are actively traded.

Derivatives (Level 3 Derivative Instruments) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2012 USD ($)
Variable annuity benefit guarantee liabilities
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value Liabilities	$ 672.4
Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	0.10%
Mortality (as a percent)	0.00%
Foreign exchange volatilities (as a percent)	10.80%
Index volatilities (as a percent)	13.10%
Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	3.00%
Mortality (as a percent)	6.40%
Foreign exchange volatilities (as a percent)	17.40%
Index volatilities (as a percent)	23.90%
Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	0.40%
Mortality (as a percent)	0.90%
Foreign exchange volatilities (as a percent)	12.80%
Index volatilities (as a percent)	19.50%
Foreign exchange and equity index options
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value Liabilities	$ 213.0
Foreign exchange and equity index options \| Black-Scholes option pricing model \| Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	10.80%
Expected equity dividends (as a percent)	1.90%
Index volatilities (as a percent)	13.10%
Foreign exchange and equity index options \| Black-Scholes option pricing model \| Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	17.40%
Expected equity dividends (as a percent)	5.20%
Index volatilities (as a percent)	23.90%
Foreign exchange and equity index options \| Black-Scholes option pricing model \| Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	12.80%
Expected equity dividends (as a percent)	3.10%
Index volatilities (as a percent)	19.50%

Derivatives (Realized and Unrealized Gains (Losses) (Details) - White Mountains Life Re [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Derivative, Gain (Loss) on Derivative, Net	$ (11.0)	$ 148.9	$ (122.0)	$ 105.4
Derivative, Fair Value, Net	242.1		242.1		$ 290.4
Interest Rate Contract [Member]
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Derivative, Gain (Loss) on Derivative, Net	(22.6)	29.8	(73.1)	17.3
Derivative, Fair Value, Net	29.1		29.1		31.1
Foreign Exchange Contract [Member]
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Derivative, Gain (Loss) on Derivative, Net	6.5	63.0	(21.0)	32.8
Derivative, Fair Value, Net	127.9		127.9		161.3
Equity Contract [Member]
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Derivative, Gain (Loss) on Derivative, Net	5.1	$ 56.1	(27.9)	$ 55.3
Derivative, Fair Value, Net	$ 85.1		$ 85.1		$ 98.0

Derivatives (Collateral Provided to WM Life Re from Counterparties) (Details) - White Mountains Life Re [Member] - USD ($) $ in Millions	Sep. 30, 2012	Dec. 31, 2011
Variable Annuity Reinsurance [Line Items]
Derivative Collateral Obligation to Return	$ 85.6	$ 83.0
Derivative Collateral Right to Reclaim	63.3	73.2
Short-term investments
Variable Annuity Reinsurance [Line Items]
Derivative Collateral Obligation to Return	63.3	73.2
Derivative Collateral Right to Reclaim	14.6	0.6
Fixed maturity investments.
Variable Annuity Reinsurance [Line Items]
Derivative Collateral Obligation to Return	0.0	0.0
Derivative Collateral Right to Reclaim	$ 121.2	$ 31.2

Derivatives (Value, Collateral (held) provided by WM Life Re and Net Exposure to Credit Losses on OTC Derivative Instruments) (Details) - USD ($)
$ in Millions

Sep. 30, 2012

Dec. 31, 2011

Credit risk on derivative instruments

Derivative Counterparty Credit Risk

$ (5.2)

$ (9.1)

White Mountains Life Re [Member]

Credit risk on derivative instruments

Derivative Assets (Liabilities), at Fair Value, Net

^[1]

251.4

295.4

Derivative Collateral Right to Reclaim

(63.3)

(73.2)

Derivative Collateral Obligation to Return

85.6

83.0

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

$ 273.7

$ 305.2

[1]	(1) Value of OTC derivative instruments as of September 30, 2012 and December 31, 2011 excludes adjustments for counterparty credit risk of $(5.2) and $(9.1) included in fair value under GAAP.The following table

Derivatives (Uncollateralized Amounts Due Under WM Life Re's OTC Derivative Contracts) (Details) - White Mountains Life Re [Member]
$ in Millions

Sep. 30, 2012

USD ($)

Rating

Dec. 31, 2011

USD ($)

Credit risk on derivative instruments

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

$ 273.7

$ 305.2

S&P Credit Ratings | Rating

Citigroup [Member]

Credit risk on derivative instruments

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

^[1]

$ 63.4

Royal Bank of Scotland [Member]

Credit risk on derivative instruments

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

58.5

Bank of America [Member]

Credit risk on derivative instruments

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

50.3

J P Morgan Chase [Member]

Credit risk on derivative instruments

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

^[1]

40.8

Nomura [Member]

Credit risk on derivative instruments

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

^[1]

35.9

Barclays [Member]

Credit risk on derivative instruments

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

20.7

Goldman Sachs [Member]

Credit risk on derivative instruments

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

^[1]

$ 4.1

[1]	(2) Collateral provided (held) calculated under master netting agreement.

Derivatives Additional Collateral (Details) - White Mountains Life Re [Member] - USD ($) $ in Millions	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Credit risk on derivative instruments
Derivative Collateral Right to Reclaim	$ 63.3	$ 73.2
Collateral Cash and Investments	477.5	485.3	$ 419.7
Cash and Cash Equivalents [Member]
Credit risk on derivative instruments
Derivative Collateral Right to Reclaim	341.7	453.5
Short-term investments
Credit risk on derivative instruments
Derivative Collateral Right to Reclaim	14.6	0.6
Fixed maturity investments.
Credit risk on derivative instruments
Derivative Collateral Right to Reclaim	$ 121.2	$ 31.2

Derivatives Forward Contracts (Details) - Forward Contracts [Member]
kr in Millions, $ in Millions

3 Months Ended

9 Months Ended

Sep. 30, 2012

USD ($)

Sep. 30, 2012

USD ($)

Sep. 30, 2012

SEK (kr)

Rating

Sep. 30, 2012

USD ($)

Rating

Jun. 30, 2012

USD ($)

Dec. 31, 2011

USD ($)

Derivative Instruments, Gain (Loss) [Line Items]

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

^[1]

$ 38.8

Fair Value Derivatives Measured on Recurring Basis, Asset Purchases

$ 0.0

Derivative, Notional Amount

kr 254.0

38.8

Derivative, Gain (Loss) on Derivative, Net

0.3

Derivative, Fair Value, Net

$ 0.3

$ 0.0

Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements

0.0

S&P Credit Ratings | Rating

United States of America, Dollars

Derivative Instruments, Gain (Loss) [Line Items]

Derivative, Gain (Loss) on Derivative, Net

0.4

Derivative, Fair Value, Net

$ 0.4

United Kingdom, Pounds

Derivative Instruments, Gain (Loss) [Line Items]

Derivative, Gain (Loss) on Derivative, Net

0.0

Derivative, Fair Value, Net

0.0

Euro Member Countries, Euro

Derivative Instruments, Gain (Loss) [Line Items]

Derivative, Gain (Loss) on Derivative, Net

(0.1)

Derivative, Fair Value, Net

(0.1)

Sweden, Kronor

Derivative Instruments, Gain (Loss) [Line Items]

Derivative, Gain (Loss) on Derivative, Net

0.0

Derivative, Fair Value, Net

0.0

Foreign Currency Gain (Loss) [Member]

Derivative Instruments, Gain (Loss) [Line Items]

Derivative, Gain (Loss) on Derivative, Net

$ 0.0

Derivative, Fair Value, Net

0.0

Goldman Sachs [Member]

Derivative Instruments, Gain (Loss) [Line Items]

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

^[1]

5.6

J P Morgan Chase [Member]

Derivative Instruments, Gain (Loss) [Line Items]

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

^[1]

7.3

HSBS Bank plc [Member]

Derivative Instruments, Gain (Loss) [Line Items]

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

^[1]

12.4

Royal Bank of Canada [Member]

Derivative Instruments, Gain (Loss) [Line Items]

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

^[1]

8.0

Deutsche Bank [Member]

Derivative Instruments, Gain (Loss) [Line Items]

Net Exposure On Fair Value Of Over The Counter Derivative Instruments

^[1]

$ 5.5

[1]	(2) Collateral provided (held) calculated under master netting agreement.

Earnings (Loss) Per Share (Details) - USD ($)
$ / shares in Units, $ in Millions

3 Months Ended

9 Months Ended

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2012

Sep. 30, 2011

Basic and diluted earnings per share numerators (in millions):

Net income (loss) from continuing operations attributable to White Mountains’ common shareholders

$ 125.9

$ 14.3

$ 254.6

$ (6.3)

Allocation of (income) loss for unvested restricted common shares

(1.8)

(0.1)

(3.3)

0.1

Dividends declared on participating restricted common shares

^[1]

0.0

0.1

Total allocation to restricted common shares

(1.8)

(0.1)

(3.4)

0.0

Net income (loss) attributable to White Mountains' common shareholders, net of restricted share amounts

124.1

14.2

251.2

(6.3)

Undistributed net earnings (in millions):

Net income (loss) attributable to White Mountains' common shareholders, net of restricted common share amounts

124.1

14.2

251.2

(6.3)

Dividends declared net of restricted common share amounts

^[1]

0.0

6.5

7.9

Total undistributed net earnings (loss), net of restricted common share amounts

$ 124.1

$ 14.2

$ 244.7

$ (14.2)

Basic earnings per share denominators (in thousands):

Total average common shares outstanding during the period

6,590,400

7,919,300

6,885,900

7,970,000

Average unvested restricted common shares

^[2],[3]

(96,500)

(73,500)

(89,500)

(68,000)

Basic earnings (loss) per share denominator

6,493,900

7,845,800

6,796,400

7,902,000

Diluted earnings per share denominator (in thousands):

Total average common shares outstanding during the period

6,590,400

7,919,300

6,885,900

7,970,000

Average unvested restricted common shares

^[2],[3]

(96,500)

(73,500)

(89,500)

(68,000)

Average outstanding dilutive options to acquire common shares

^[3]

Diluted earnings (loss) per share denominator

6,493,900

7,845,800

6,796,400

7,902,000

Basic earnings per share (in dollars):

Net income (loss) attributable to White Mountains' common shareholders

$ 19.11

$ 1.81

$ 36.96

$ (0.80)

Undistributed earnings (loss) (in dollars per share)

19.11

1.81

35.96

(1.80)

Earnings Per Share, Diluted [Abstract]

Net income (loss) attributable to White Mountains' common shareholders (in dollars per share)

19.11

1.81

36.96

(0.80)

Dividends declared per White Mountains' common share (in dollars per share)

0.00

1.00

Undistributed earnings (loss) (in dollars per share)

$ 19.11

$ 1.81

$ 35.96

$ (1.80)

[1]	(1) Restricted shares issued by White Mountains receive dividends, and therefore, are considered participating securities.
[2]	(2) Restricted shares outstanding vest either in equal annual installments or upon a stated date (see Note 12).
[3]	(3) The diluted earnings (loss) per share denominator for the three and nine months ended September 30, 2012 and 2011 do not include common shares issuable upon exercise of the Non-Qualified Options as they are anti-dilutive to the calculation.

Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Segment Information (Details) - USD ($) $ in Millions	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment reporting information
Earned insurance and reinsurance premiums	$ 536.8	$ 491.1	$ 1,545.3	$ 1,433.5
Net investment income	37.6	42.8	119.8	138.1
Net realized and unrealized investment gains (losses)	72.7	2.9	123.2	36.4
Other revenue	50.3	(35.0)	81.0	(28.3)
Revenues	697.4	501.8	1,869.3	1,579.7
Loss and loss adjustment expenses	308.1	280.2	821.7	920.4
Insurance and reinsurance acquisition expenses	107.6	107.0	326.2	296.6
Other underwriting expenses	76.6	64.3	228.4	203.9
General and administrative expenses	58.7	36.2	146.3	120.4
Interest expense on debt	11.3	12.8	33.1	38.8
Total expenses	562.3	500.5	1,555.7	1,580.1
Pre-tax income (loss)	135.1	1.3	313.6	(0.4)
OneBeacon
Segment reporting information
Earned insurance and reinsurance premiums	293.9	259.1	846.0	748.0
Net investment income	12.8	16.1	41.5	55.8
Net realized and unrealized investment gains (losses)	40.0	(47.4)	57.9	(13.3)
Other revenue	(0.4)	0.1	(0.1)	(12.2)
Revenues	346.3	227.9	945.3	778.3
Loss and loss adjustment expenses	164.7	149.7	452.5	421.3
Insurance and reinsurance acquisition expenses	66.6	58.6	185.6	161.5
Other underwriting expenses	47.4	36.0	146.2	124.5
General and administrative expenses	4.4	2.5	9.6	7.4
Interest expense on debt	4.1	4.1	12.2	16.4
Total expenses	287.2	250.9	806.1	731.1
Pre-tax income (loss)	59.1	(23.0)	139.2	47.2
Sirius
Segment reporting information
Earned insurance and reinsurance premiums	242.9	232.0	699.3	685.5
Net investment income	16.7	22.1	50.9	68.3
Net realized and unrealized investment gains (losses)	(8.9)	65.9	22.9	60.7
Other revenue	48.2	(29.3)	48.9	(13.8)
Revenues	298.9	290.7	822.0	800.7
Loss and loss adjustment expenses	143.4	130.5	369.2	499.1
Insurance and reinsurance acquisition expenses	41.0	48.4	140.6	135.1
Other underwriting expenses	29.1	28.3	82.1	79.4
General and administrative expenses	10.2	7.4	35.4	23.3
Interest expense on debt	6.5	6.5	19.6	19.6
Total expenses	230.2	221.1	646.9	756.5
Pre-tax income (loss)	68.7	69.6	175.1	44.2
Other Operations
Segment reporting information
Earned insurance and reinsurance premiums	0.0	0.0	0.0	0.0
Net investment income	8.1	4.6	27.4	14.0
Net realized and unrealized investment gains (losses)	41.6	(15.6)	42.4	(11.0)
Other revenue	2.5	(5.8)	32.2	(2.3)
Revenues	52.2	(16.8)	102.0	0.7
Loss and loss adjustment expenses	0.0	0.0	0.0	0.0
Insurance and reinsurance acquisition expenses	0.0	0.0	0.0	0.0
Other underwriting expenses	0.1	0.0	0.1	0.0
General and administrative expenses	44.1	26.3	101.3	89.7
Interest expense on debt	0.7	2.2	1.3	2.8
Total expenses	44.9	28.5	102.7	92.5
Pre-tax income (loss)	$ 7.3	$ (45.3)	$ (0.7)	$ (91.8)

Investments in Unconsolidated Affiliates (Details) - USD ($)
$ in Millions

3 Months Ended

9 Months Ended

12 Months Ended

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2012

Sep. 30, 2011

Dec. 31, 2011

Jun. 30, 2012

Mar. 31, 2012

Jun. 30, 2011

Mar. 31, 2011

Dec. 31, 2010

Investments in unconsolidated affiliates

Total investments in unconsolidated affiliates

$ 376.3

$ 275.3

Symetra

Investments in unconsolidated affiliates

Total investments in unconsolidated affiliates

374.8

^[1],[2]

$ 456.7

^[1],[2]

374.8

^[1],[2]

$ 456.7

^[1],[2]

273.6

$ 421.0

$ 335.7

$ 387.5

Equity in Unrealized Gains (Losses) from Investments in Unconsolidated Affiliates

35.2

147.7

64.6

147.7

0.0

Symetra | Common shareholders' equity.

Investments in unconsolidated affiliates

Symetra Common Shares excluding unrealized gains (losses)

284.0

261.0

Total investments in unconsolidated affiliates

348.6

^[1],[2]

449.0

^[1],[2]

348.6

^[1],[2]

449.0

^[1],[2]

261.0

$ 305.9

$ 388.5

350.4

Symetra | Warrants

Investments in unconsolidated affiliates

Total investments in unconsolidated affiliates

26.2

^[1],[2]

$ 7.7

^[1],[2]

26.2

^[1],[2]

$ 7.7

^[1],[2]

12.6

$ 29.8

$ 32.5

$ 37.1

Pentelia Capital Management

Investments in unconsolidated affiliates

Total investments in unconsolidated affiliates

$ 1.5

$ 1.7

[1]	Includes White Mountains’ equity in net unrealized gains from Symetra’s fixed maturity portfolio of $64.6 and $147.7 as of September 30, 2012 and 2011, which exclude tax expense of $5.2 and $24.2.
[2]	The aggregate value of White Mountains’ investment in common shares of Symetra was $214.0 based upon the quoted market price of $12.30 per share at September 30, 2012.

Investments in Unconsolidated Affiliates (Symetra) (Details) - Symetra $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012 USD ($) $ / shares shares	Sep. 30, 2011 USD ($)	Sep. 30, 2012 USD ($) Year yr $ / shares shares	Sep. 30, 2011 USD ($)	Dec. 31, 2011 USD ($) $ / shares shares
Investments in unconsolidated affiliates
Shares of Symetra Financial Corporation owned (in shares) \| shares	17.4		17.4		17.4
Investments in unconsolidated affiliates on conversion of warrants \| shares	9.5		9.5		9.5
Fair value of investment					$ 261.0
Estimated fair value of investment per share \| $ / shares					$ 15
After-tax equity in losses of unconsolidated affiliates					$ 45.9
Equity in net unrealized losses increase relating to amortization of common share impairment					136.6
Equity in Unrealized Gains (Losses) from Investments in Unconsolidated Affiliates	$ 35.2	$ 147.7	$ 64.6	$ 147.7	0.0
Ownership interest (as a percent)	15.00%		15.00%
Difference between fair value and carrying amount					$ 195.8
Term of amortization (in years) \| yr			30
After tax amortization through equity in earnings	$ 0.8		$ 2.4
After tax amortization through equity in net unrealized losses	3.0		9.1
Pre-tax unamortized basis difference	$ 183.3		$ 183.3
Risk free interest rate (as a percent)			0.22%
Volatility rate (as a percent)			36.50%
Expected life (in years) \| Year			1.82
Class of warrant or right fair value assumptions per strike price \| $ / shares	$ 11.49		$ 11.49
Market Price Per Share \| $ / shares	$ 12.30		$ 12.30
Common Stock
Investments in unconsolidated affiliates
Equity in net unrealized losses increase relating to amortization of common share impairment	$ 3.3		$ 9.9

Investments in Unconsolidated Affiliates (Investments in Symetra) (Details) - USD ($)
$ / shares in Units, $ in Millions

3 Months Ended

9 Months Ended

12 Months Ended

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2012

Sep. 30, 2011

Dec. 31, 2011

Changes in carrying value of investment in Symetra

Carrying value at the beginning of the period

$ 275.3

Equity in earnings

$ 7.7

$ 1.5

24.4

$ 16.1

Carrying value at the end of the period

376.3

$ 275.3

Symetra

Changes in carrying value of investment in Symetra

Carrying value at the beginning of the period

421.0

273.6

387.5

Equity in earnings

^[1],[2]

8.8

1.6

26.7

17.5

Equity in net unrealized losses from Symetra's fixed maturity portfolio

^[3]

35.2

59.9

64.6

84.0

Dividends received

(1.3)

(1.0)

(3.7)

(2.9)

Increase (decrease) in value of warrants

(3.6)

(24.8)

13.6

(29.4)

Carrying value at the end of the period

374.8

^[4],[5]

456.7

^[4],[5]

374.8

^[4],[5]

456.7

^[4],[5]

273.6

Tax on equity in earnings

0.7

0.1

2.2

1.4

Equity in net unrealized losses increase relating to amortization of common share impairment

136.6

Equity in Unrealized Gains (Losses) from Investments in Unconsolidated Affiliates

35.2

147.7

64.6

147.7

0.0

Tax on equity in net unrealized gains (losses)

2.8

12.3

5.2

24.2

Aggregate value of White Mountains common shares of Symetra at quoted market price

$ 214.0

Quoted market price (in dollars per share)

$ 12.30

Symetra | Common shareholders' equity.

Changes in carrying value of investment in Symetra

Carrying value at the beginning of the period

$ 305.9

388.5

$ 261.0

350.4

Equity in earnings

^[1],[2]

8.8

1.6

26.7

17.5

Equity in net unrealized losses from Symetra's fixed maturity portfolio

^[3]

35.2

59.9

64.6

84.0

Dividends received

(1.3)

(1.0)

(3.7)

(2.9)

Increase (decrease) in value of warrants

0.0

Carrying value at the end of the period

348.6

^[4],[5]

449.0

^[4],[5]

348.6

^[4],[5]

449.0

^[4],[5]

261.0

Equity in earnings increase relating to amortization of common share impairment

0.9

Equity in net unrealized losses increase relating to amortization of common share impairment

3.3

9.9

Symetra | Warrants

Changes in carrying value of investment in Symetra

Carrying value at the beginning of the period

12.6

37.1

Equity in earnings

^[1],[2]

0.0

Equity in net unrealized losses from Symetra's fixed maturity portfolio

^[3]

0.0

Dividends received

0.0

Increase (decrease) in value of warrants

(3.6)

(24.8)

13.6

(29.4)

Carrying value at the end of the period

$ 26.2

^[4],[5]

$ 7.7

^[4],[5]

26.2

^[4],[5]

7.7

^[4],[5]

$ 12.6

Cash dividends received on warrants

$ 0.7

$ 2.0

[1]	Equity in earnings excludes tax expense of $2.2 and $1.4.
[2]	Equity in earnings includes $0.9 increase relating to the pre-tax amortization of Symetra common share impairment from September 30, 2012.
[3]	Net unrealized gains includes $9.9 increase relating to the pre-tax amortization of Symetra common share impairment from September 30, 2012
[4]	Includes White Mountains’ equity in net unrealized gains from Symetra’s fixed maturity portfolio of $64.6 and $147.7 as of September 30, 2012 and 2011, which exclude tax expense of $5.2 and $24.2.
[5]	The aggregate value of White Mountains’ investment in common shares of Symetra was $214.0 based upon the quoted market price of $12.30 per share at September 30, 2012.

Employee Share-Based Incentive Compensation Plans (WTM Performance Shares) (Details) - USD ($)
$ in Millions

3 Months Ended

9 Months Ended

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2012

Sep. 30, 2011

Accrued Expense

Accrued expense at the beginning of period

$ 187.9

Accrued expense at the end of the period

$ 144.7

WTM Incentive Plan and WTM Phantom Share Plans | Performance Share [Member]

Target Performance Share activity

Beginning of period (in shares)

118,450

150,064

163,184

Shares paid or expired (in shares)

^[1]

(68,357)

(51,131)

New grants (in shares)

2,500

38,432

37,675

Assumed forfeitures and cancellations

^[2]

1,359

548

(336)

Ending of period (in shares)

119,591

150,064

119,591

150,064

Accrued Expense

Accrued expense at the beginning of period

$ 32.7

$ 56.5

$ 66.1

$ 29.4

Payments and deferrals

^[1]

0.0

(48.4)

0.0

Assumed forfeitures and cancelations

^[2]

(0.4)

0.0

0.4

(0.6)

Expense recognized

6.6

(1.0)

20.8

26.7

Accrued expense at the end of the period

38.9

$ 55.5

38.9

$ 55.5

Additional compensation cost that would be recognized if all outstanding performance shares vested

$ 26.6

Performance cycle 2009-2011 | Performance Share [Member]

Accrued Expense

Shares issued during the period related to performance shares earned

9,577

Performance cycle 2009-2011 | WTM Incentive Plan and WTM Phantom Share Plans | Performance Share [Member]

Accrued Expense

Percentage of payout for minimum growth target percentage

147.00%

Percentage of payout for maximum growth target percentage

155.00%

[1]	(1) WTM performance share payments in 2012 for the 2009-2011 performance cycle ranged from147% to 155% of target. There were no payments made in 2011 for the 2008-2010 performance cycle; those performance shares did not meet the threshold performance goals and expired.
[2]	(2) Amounts include changes in assumed forfeitures, as required under GAAP.

Employee Share-Based Incentive Compensation Plans (WTM Performance Shares Granted Under the WTM Incentive Plan) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Share-based compensation arrangement by share-based payment award
Accrued incentive compensation	$ 144.7	$ 187.9
W T M Incentive Plan [Member] \| Performance Share [Member]
Share-based compensation arrangement by share-based payment award
Share-based Compensation Arrangement by Share-based Payment Award Equity Instruments Other than Options Nonvested, Number before Forfeitures	117,667
Incentive Compensation Payable before Forfeitures	$ 37.3
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Assumed Forfeitures in Period	(2,941)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Assumed Forfeitures in Period Amount	$ 1.0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	114,726
Accrued incentive compensation	$ 36.3
W T M Incentive Plan [Member] \| Performance Share [Member] \| Range of Performance Cycle from 2010 to 2012 [Member]
Share-based compensation arrangement by share-based payment award
Share-based Compensation Arrangement by Share-based Payment Award Equity Instruments Other than Options Nonvested, Number before Forfeitures	42,320
Incentive Compensation Payable before Forfeitures	$ 19.0
W T M Incentive Plan [Member] \| Performance Share [Member] \| Range of Performance Cycle from 2011 to 2013 [Member]
Share-based compensation arrangement by share-based payment award
Share-based Compensation Arrangement by Share-based Payment Award Equity Instruments Other than Options Nonvested, Number before Forfeitures	37,255
Incentive Compensation Payable before Forfeitures	$ 12.9
W T M Incentive Plan [Member] \| Performance Share [Member] \| Range Of Performance Cycle From 2012 To 2014 [Member]
Share-based compensation arrangement by share-based payment award
Share-based Compensation Arrangement by Share-based Payment Award Equity Instruments Other than Options Nonvested, Number before Forfeitures	38,092
Incentive Compensation Payable before Forfeitures	$ 5.4

Employee Share-Based Incentive Compensation Plans (WTM Phantom Performance Shares Granted Under WTM Phantom Shares Plan) (Details) - USD ($)
$ in Millions

9 Months Ended

Sep. 30, 2012

Dec. 31, 2011

Share-based compensation arrangement by share-based payment award

Accrued incentive compensation

$ 144.7

$ 187.9

Range of Performance Cycle from 2010 to 2012 [Member] | W T M Phantom Share Plans [Member]

Share-based compensation arrangement by share-based payment award

Share-based Compensation Arrangement by Share-based Payment Award Equity Instruments Other than Options Nonvested, Number before Forfeitures

4,990

Incentive Compensation Payable before Forfeitures

$ 2.7

Range of Performance Cycle from 2011 to 2013 [Member] | W T M Phantom Share Plans [Member]

Share-based compensation arrangement by share-based payment award

Share-based Compensation Arrangement by Share-based Payment Award Equity Instruments Other than Options Nonvested, Number before Forfeitures

^[1]

Incentive Compensation Payable before Forfeitures

^[1]

$ 0.0

Range Of Performance Cycle From 2012 To 2014 [Member] | W T M Phantom Share Plans [Member]

Share-based compensation arrangement by share-based payment award

Share-based Compensation Arrangement by Share-based Payment Award Equity Instruments Other than Options Nonvested, Number before Forfeitures

^[1]

Incentive Compensation Payable before Forfeitures

^[1]

$ 0.0

Performance Share [Member] | W T M Phantom Share Plans [Member]

Share-based compensation arrangement by share-based payment award

Share-based Compensation Arrangement by Share-based Payment Award Equity Instruments Other than Options Nonvested, Number before Forfeitures

4,990

Incentive Compensation Payable before Forfeitures

$ 2.7

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Assumed Forfeitures in Period

(125)

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Assumed Forfeitures in Period Amount

$ 0.1

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number

4,865

Accrued incentive compensation

$ 2.6

[1]	(1) All performance shares for the 2011–2013 and 2012–2014 performance cycles were granted fromthe WTM Incentive Plan

Employee Share-Based Incentive Compensation Plans (WTM Restricted Shares) (Details) $ in Millions	3 Months Ended					9 Months Ended
	Sep. 30, 2012 USD ($) shares	Mar. 31, 2012 USD ($) Installment shares	Sep. 30, 2011 USD ($) shares	Mar. 31, 2011 USD ($) shares	Mar. 31, 2010 shares	Sep. 30, 2012 USD ($) shares	Sep. 30, 2011 USD ($) shares
Restricted Share Cliff Vesting in January 2015 [Member]
Target Performance Share activity
Issued (in shares)		25,460				2,500
Restricted Share Cliff Vesting in July 2015 [Member]
Target Performance Share activity
Issued (in shares)						1,200
Restricted Stock [Member]
Target Performance Share activity
Beginning of period (in shares)	93,460	72,000	73,500	46,250		72,000	46,250
Issued (in shares)	3,700		0			32,160	27,250
Vested (in shares)	0		0			(7,000)	0
Assumed forfeitures and cancellations	(1,065)		0			(1,065)	0
Ending of period (in shares)	96,095		73,500			96,095	73,500
Unamortized grant date fair value
Unamortized grant date fair value, beginning balance \| $	$ 21.5	$ 13.3	$ 18.9	$ 14.1		$ 13.3	$ 14.1
Issued \| $	2.0		0.0			15.7	9.9
Assumed forfeitures and cancelations \| $	(0.2)		0.0			(0.2)	0.0
Expense recognized \| $	(3.2)		(2.8)			(8.7)	(7.9)
Unamortized grant date fair value, ending balance \| $	$ 20.1		$ 16.1			$ 20.1	$ 16.1
Restricted Share Vesting Beginning in February 2014 [Member]
Target Performance Share activity
Issued (in shares)						3,000
Unamortized grant date fair value
Number of restricted shares installments \| Installment		2
Restricted Share Cliff Vesting in January 2014 [Member]
Target Performance Share activity
Issued (in shares)				27,000		250
Restricted Share Vested in December 2012 [Member]
Target Performance Share activity
Issued (in shares)					19,750

Employee Share-Based Incentive Compensation Plans (WTM Non-Qualified Options) (Details) - Non-Qualified Options $ / shares in Units, $ in Millions	1 Months Ended		9 Months Ended
	May 31, 2010 USD ($) Year	Jan. 31, 2007 Year $ / shares shares	Sep. 30, 2012 USD ($)	May 26, 2010 $ / shares shares
Before Amendments [Member]
Share-based compensation arrangement by share-based payment award
Granted (in shares) \| shares		200,000
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Date \| Year		7
Vesting period (in years)		5 years
Initial exercise price (in dollars per share) \| $ / shares		$ 650
Annual percentage increase in exercise price		5.00%
Grant Amendments [Member]
Share-based compensation arrangement by share-based payment award
Extension of contractual term (in years) \| Year	3
Exercise price (in dollar per share) \| $ / shares				$ 742
Number of shares extinguished \| shares				75,000
Threshold for in-the-money potential \| $	$ 100.0
Limit on value of in-the-money options over $100 million (as a percent)	50.00%
Expense recognized \| $			$ 0.1

Employee Share-Based Incentive Compensation Plans (OneBeason Peformance Shares) (Details) - USD ($)
$ in Millions

3 Months Ended

9 Months Ended

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2012

Sep. 30, 2011

Expense Amortized

Accrued expense at the beginning of period

$ 187.9

Accrued expense at the end of the period

$ 144.7

One Beacon Long Term Incentive Plan [Member] | Performance Share [Member]

Target options outstanding

Beginning of period (in shares)

560,577

671,727

642,667

1,464,295

Shares paid or expired (in shares)

^[1],[2]

(258,901)

(936,150)

New grants (in shares)

181,290

194,900

Assumed forfeitures and cancellations

^[3]

3,354

(19,583)

(7,833)

(70,901)

Ending of period (in shares)

557,223

652,144

557,223

652,144

Expense Amortized

Accrued expense at the beginning of period

$ 3.1

$ 10.0

$ 9.7

$ 18.5

Payments and deferrals

^[1],[2]

0.0

(7.8)

(10.5)

Assumed forfeitures and cancelations

^[3]

0.0

0.1

0.0

(0.2)

Expense recognized

(2.2)

(0.5)

(1.0)

1.8

Accrued expense at the end of the period

0.9

$ 9.6

0.9

$ 9.6

Additional compensation cost that would be recognized if all outstanding performance shares vested

$ 1.7

Performance cycle 2009-2011 | One Beacon Long Term Incentive Plan [Member] | Performance Share [Member]

Expense Amortized

Percentage of payout for minimum growth target percentage

138.60%

One Beacon Long Term Incentive Plan [Member] | Performance Share [Member]

Expense Amortized

Performance Share Target Vesting Percentage

100.00%

Range of Performance Cycle from 2008 to 2010 [Member] | One Beacon Long Term Incentive Plan [Member] | Performance Share [Member]

Expense Amortized

Percentage of payout for minimum growth target percentage

68.50%

[1]	(1) OneBeacon performance share payments in 2012 for the 2009-2011 performance cycle were at 138.6% of target. OneBeacon performance shares payments in 2011 for the 2008-2010 performance cycle were at 68.5% of target. Amounts include deposits into OneBeacon’s deferred compensation plan.
[2]	(2) OneBeacon performance share payments also include accelerated payments resulting from the OneBeacon Personal Lines and Commercial Lines Transactions. The accelerated OneBeacon performance shares payments for the 2009-2011 and 2010-2012 performance cycles were on a pro rata basis and at a performance factor of 100%.
[3]	(3) Amounts include changes in assumed forfeitures, as required under GAAP.

Employee Share-Based Incentive Compensation Plans (OneBeacon Performance Shares Outstanding) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010
Share-based compensation arrangement by share-based payment award
Accrued incentive compensation	$ 144.7		$ 187.9
Non-Qualified Options \| One Beacon Long Term Incentive Plan [Member]
Share-based compensation arrangement by share-based payment award
Expected life (in years)	5 years 6 months
Performance Share [Member] \| One Beacon Long Term Incentive Plan [Member]
Share-based compensation arrangement by share-based payment award
Share-based Compensation Arrangement by Share-based Payment Award Equity Instruments Other than Options Nonvested, Number before Forfeitures	571,511
Incentive Compensation Payable before Forfeitures	$ 0.9
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Assumed Forfeitures in Period	(14,288)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Assumed Forfeitures in Period Amount	$ 0.0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	557,223	560,577	642,667	652,144	671,727	1,464,295
Accrued incentive compensation	$ 0.9	$ 3.1	$ 9.7	$ 9.6	$ 10.0	$ 18.5
Performance Share [Member] \| One Beacon Long Term Incentive Plan [Member] \| Range of Performance Cycle from 2010 to 2012 [Member]
Share-based compensation arrangement by share-based payment award
Share-based Compensation Arrangement by Share-based Payment Award Equity Instruments Other than Options Nonvested, Number before Forfeitures	238,658
Incentive Compensation Payable before Forfeitures	$ 0.0
Performance Share [Member] \| One Beacon Long Term Incentive Plan [Member] \| Range of Performance Cycle from 2011 to 2013 [Member]
Share-based compensation arrangement by share-based payment award
Share-based Compensation Arrangement by Share-based Payment Award Equity Instruments Other than Options Nonvested, Number before Forfeitures	151,563
Incentive Compensation Payable before Forfeitures	$ 0.4
Performance Share [Member] \| One Beacon Long Term Incentive Plan [Member] \| Range Of Performance Cycle From 2012 To 2014 [Member]
Share-based compensation arrangement by share-based payment award
Share-based Compensation Arrangement by Share-based Payment Award Equity Instruments Other than Options Nonvested, Number before Forfeitures	181,290
Incentive Compensation Payable before Forfeitures	$ 0.5

Employee Share-Based Incentive Compensation Plans (OneBeacon Restsricted Shares) (Details) - One Beacon Restricted Stock [Member] $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	May 31, 2011 Year shares	Sep. 30, 2012 USD ($) shares	Mar. 31, 2012 USD ($) shares	Sep. 30, 2011 USD ($) shares	Sep. 30, 2012 USD ($) shares	Sep. 30, 2011 USD ($) shares	Mar. 01, 2012 Installment	May 25, 2011 Installment
Target Performance Share activity
Beginning of period (in shares)		930,000	630,000	630,000	630,000	630,000
Issued (in shares)		0		0	300,000	0
Shares issued during the period related to performance shares earned		0		0	0	0
Assumed forfeitures and cancellations		0		0	0	0
Ending of period (in shares)		930,000		630,000	930,000	630,000
Unamortized grant date fair value
Unamortized grant date fair value, beginning balance \| $		$ 11.2	$ 7.7	$ 8.5	$ 7.7	$ 8.6
Issued \| $		0.0		0.0	4.6	0.0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value \| $		0.0		0.0	0.0	0.0
Assumed forfeitures and cancelations \| $		0.0		0.0	0.0	0.0
Expense recognized \| $		(0.8)		(0.4)	(1.9)	(0.5)
Unamortized grant date fair value, ending balance \| $		$ 10.4		$ 8.1	$ 10.4	$ 8.1
One Beacon Long Term Incentive Plan [Member]
Target Performance Share activity
Issued (in shares)			300,000
Unamortized grant date fair value
Number of Installments in which the Shares Vest \| Installment							2
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Reduction in Grant, Total	35,000
Chief Executive Officer [Member] \| One Beacon Long Term Incentive Plan [Member]
Target Performance Share activity
Issued (in shares)	630,000
Unamortized grant date fair value
Number of Installments in which the Shares Vest \| Installment								4
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Reduction in Grant, Total	35,000
Years Performance Shares will be Forfeited \| Year	5

Employee Share-Based Incentive Compensation Plans (OneBeacon - Non-Qualified Options) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Nov. 30, 2006	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Nov. 16, 2010	May 27, 2008	Mar. 31, 2008
Unamortized grant date fair value
Accrued expense at the beginning of period				$ 187.9
Accrued expense at the end of the period		$ 144.7		$ 144.7
Non-Qualified Options \| One Beacon Long Term Incentive Plan [Member]
Share-based compensation arrangement by share-based payment award
Granted (in shares)	1,420,000
Target Performance Share activity
Opening balance - outstanding Options (in shares)		0	750,130	740,870	768,652
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross		0	0	0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period		0	(9,260)	0	(27,782)
Share-based Compensation Arrangement by Share-based Payment Award, Options Vested and Expirations in Period		0	0	(740,870)	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period		0	0	0	0
Ending balance - outstanding Options (in shares)		0	740,870	0	740,870
Unamortized grant date fair value
Expected volatility (as a percent)				30.00%
Risk-free rate (as a percent)				4.60%
Forfeiture (as a percent)				5.00%
Expected dividend yield (as a percent)				3.40%
Expected life (in years)				5 years 6 months
Initial exercise price (in dollars per share)				$ 30.00
Amended exercise price of option (in dollars per share)						$ 25.47	$ 27.97
OneBeacon special dividend (in dollars per share)						$ 2.50		$ 2.03
Grant Amendments [Member] \| Non-Qualified Options
Unamortized grant date fair value
Expense recognized				$ 0.1
Grant Amendments [Member] \| OneBeacon \| Non-Qualified Options
Unamortized grant date fair value
Expense recognized		$ 0.1		$ 0.4

Employee Share-Based Incentive Compensation Plans (OneBeacon - Restricted Stock Units) (Details) - One Beacon Long Term Incentive Plan [Member] - One Beacon Restricted Stock [Member]	1 Months Ended
	Mar. 31, 2008 shares
Share-based compensation arrangement by share-based payment award
New grants (in shares)	116,270
Percentage of Growth in Book Value Per Share Condition for Vesting	4.00%

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior notes	$ 676.6	$ 677.5
SIG Preference Shares	250.0	250.0
OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior notes	269.8	269.8
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
SIG Preference Shares	257.5	217.5
Fair Value \| OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior notes	276.3	277.4
Fair Value \| SIG Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior notes	442.9	418.6
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
SIG Preference Shares	250.0	250.0
Carrying Value \| OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior notes	269.8	269.8
Carrying Value \| SIG Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior notes	$ 399.4	$ 399.3

Discontinued Operations (Details) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
Discontinued Operations (Details) $ in Millions	Oct. 31, 2011 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2012 USD ($)	Sep. 30, 2011 USD ($)	Jun. 30, 2012 USD ($)	Mar. 31, 2012 USD ($)	Feb. 22, 2012 Entity	Jan. 02, 2012 USD ($)	Dec. 31, 2011 USD ($)	Jun. 30, 2011 USD ($)	Mar. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)
Discontinued Operations
Gain (loss) on sale of discontinued operation, net of tax		$ (91.0)	$ (18.2)	$ (91.0)	$ (18.2)
Assets held for sale
Fixed maturity investments, at fair value		4,912.4		4,912.4						$ 6,221.9
Cash		549.2		549.2						705.4
Reinsurance recoverable on unpaid losses		356.8	2,581.2	356.8	2,581.2		$ 2,369.4			2,507.3		$ 2,193.0	$ 2,344.0
Reinsurance recoverable on paid losses		14.8		14.8						30.5
Insurance premiums receivable		678.1		678.1						489.2
Deferred acquisition costs		211.3		211.3					$ 5.6	187.0
Deferred Income Tax Assets		555.0		555.0						536.9
Other assets		626.5		626.5						681.9
Total assets held for sale		13,468.8		13,468.8						14,064.0
Liabilities held for sale
Loss and loss adjustment expense reserves		3,059.8	5,882.0	3,059.8	5,882.0	$ 5,329.8				5,702.3	$ 5,642.4		$ 5,736.8
Unearned insurance premiums		1,067.1		1,067.1						846.9
Ceded reinsurance payable		138.6		138.6						134.6
Other liabilities		461.8		461.8						527.8
Total liabilities		9,090.4		9,090.4						9,396.1
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		(15.8)	(12.0)	(24.5)	(7.8)
Esurance
Discontinued Operations
Gain (loss) on sale of discontinued operation, net of tax	$ 677.5
AutoOne
Discontinued Operations
Number of insurance companies sold \| Entity								2
Segment, Discontinued Operations [Member]
Discontinued Operations
Gain (loss) on sale of discontinued operation, net of tax		(91.0)	(18.2)	(91.0)	18.2
Assets held for sale
Fixed maturity investments, at fair value		377.3		377.3						111.8
Cash		0.0		0.0						5.5
Reinsurance recoverable on unpaid losses		1,956.6		1,956.6						0.0
Reinsurance recoverable on paid losses		17.6		17.6						0.0
Insurance premiums receivable		13.6		13.6						8.8
Deferred acquisition costs		0.0		0.0						2.2
Deferred Income Tax Assets		6.1		6.1						1.9
Other assets		17.0		17.0						2.4
Total assets held for sale		2,388.2		2,388.2						132.6
Liabilities held for sale
Loss and loss adjustment expense reserves		2,212.9		2,212.9						64.7
Unearned insurance premiums		0.6		0.6						34.1
Ceded reinsurance payable		19.5		19.5						0.0
Other liabilities		155.2		155.2						8.8
Total liabilities		2,388.2		2,388.2						107.6
Net assets held for sale		0.0		0.0						$ 25.0
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent		(106.8)	(30.2)	(115.5)	(26.0)
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		(15.8)	$ (12.0)	(24.5)	$ (7.8)
Segment, Discontinued Operations [Member] \| AutoOne
Discontinued Operations
Gain (loss) on sale of discontinued operation, net of tax		0.1		$ 0.5
Loss attributable to change in discount rate [Member]
Liabilities held for sale
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest		(9.0)
OneBeacon Runoff [Member]
Discontinued Operations
Gain (loss) on sale of discontinued operation, net of tax		(91.5)
Liabilities held for sale
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent		$ (100.5)

(Income (Loss) from Discontinued Operations) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Revenues
Earned insurance premiums	$ 536.8	$ 491.1	$ 1,545.3	$ 1,433.5
Net investment income	37.6	42.8	119.8	138.1
Net realized and unrealized investment gains (losses)	72.7	2.9	123.2	36.4
Other revenue	50.3	(35.0)	81.0	(28.3)
Revenues	697.4	501.8	1,869.3	1,579.7
Expenses
Loss and loss adjustment expenses	308.1	280.2	821.7	920.4
Insurance and reinsurance acquisition expenses	107.6	107.0	326.2	296.6
Other underwriting expenses	76.6	64.3	228.4	203.9
General and administrative expenses	58.7	36.2	146.3	120.4
Total expenses	562.3	500.5	1,555.7	1,580.1
Income (loss) from discontinued operations	(15.8)	(12.0)	(24.5)	(7.8)
Gain (loss) on sale of discontinued operation, net of tax	(91.0)	(18.2)	(91.0)	(18.2)
Segment, Discontinued Operations [Member]
Revenues
Earned insurance premiums	(0.4)	233.3	10.0	701.9
Net investment income	0.0	3.8	0.0	11.8
Net realized and unrealized investment gains (losses)	0.0	(6.4)	0.0	1.4
Other revenue	0.0	17.5	0.0	54.0
Revenues	(0.4)	248.2	10.0	769.1
Expenses
Loss and loss adjustment expenses	27.7	177.4	48.4	512.3
Insurance and reinsurance acquisition expenses	(0.8)	51.4	(1.3)	154.1
Other underwriting expenses	(1.1)	35.0	1.1	83.9
General and administrative expenses	0.0	1.7	0.0	37.5
Total expenses	25.8	265.5	48.2	787.8
Pre-tax (loss) income	(26.2)	(17.3)	(38.2)	(18.7)
Income tax benefit	10.4	5.3	13.7	10.9
Income (loss) from discontinued operations	(15.8)	(12.0)	(24.5)	(7.8)
Gain (loss) on sale of discontinued operation, net of tax	(91.0)	(18.2)	(91.0)	18.2
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	$ (106.8)	$ (30.2)	$ (115.5)	$ (26.0)

Discontinued Operations (Earnings Per Share) (Details) - USD ($)
$ / shares in Units, $ in Millions

3 Months Ended

9 Months Ended

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2012

Sep. 30, 2011

Discontinued Operations

Net income (loss) from continuing operations attributable to White Mountains’ common shareholders

$ 125.9

$ 14.3

$ 254.6

$ (6.3)

Basic and diluted earnings (loss) per share numerators (in millions):

Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest

(15.8)

(12.0)

(24.5)

(7.8)

Income (Loss) Allocated to Participating Unvested Restricted Common Shares

(1.8)

(0.1)

(3.3)

0.1

Net income attributable to White Mountains' common shareholders, net of restricted common share amounts

$ 19.1

$ (15.8)

$ 139.2

$ (32.3)

Basic earnings per share denominators (in thousands):

Total average common shares outstanding during the period

6,590,400

7,919,300

6,885,900

7,970,000

Average unvested restricted common shares

^[1],[2]

(96,500)

(73,500)

(89,500)

(68,000)

Basic earnings (loss) per share denominator

6,493,900

7,845,800

6,796,400

7,902,000

Diluted earnings per share denominator (in thousands):

Total average common shares outstanding during the period

6,590,400

7,919,300

6,885,900

7,970,000

Average unvested restricted common shares

^[1],[2]

(96,500)

(73,500)

(89,500)

(68,000)

Weighted Average Number Diluted Shares Outstanding Adjustment

^[2]

Diluted earnings (loss) per share denominator

6,493,900

7,845,800

6,796,400

7,902,000

Segment, Discontinued Operations [Member]

Discontinued Operations

Net income (loss) from continuing operations attributable to White Mountains’ common shareholders

$ (106.8)

$ (30.2)

$ (115.5)

$ (26.0)

Basic and diluted earnings (loss) per share numerators (in millions):

Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest

(15.8)

(12.0)

(24.5)

(7.8)

Income (Loss) Allocated to Participating Unvested Restricted Common Shares

1.5

0.3

1.5

0.2

Net income attributable to White Mountains' common shareholders, net of restricted common share amounts

^[3]

$ (105.3)

$ (29.9)

$ (114.0)

$ (25.8)

Basic earnings per share denominators (in thousands):

Total average common shares outstanding during the period

6,590,400

7,919,300

6,885,900

7,970,000

Average unvested restricted common shares

^[4]

(96,500)

(73,500)

(89,500)

(68,000)

Basic earnings (loss) per share denominator

6,796,400

7,902,000

Diluted earnings per share denominator (in thousands):

Total average common shares outstanding during the period

6,590,400

7,919,300

6,885,900

7,970,000

Average unvested restricted common shares

^[4]

(96,500)

(73,500)

(89,500)

(68,000)

Weighted Average Number Diluted Shares Outstanding Adjustment

Diluted earnings (loss) per share denominator

6,493,900

7,845,800

6,796,400

7,902,000

Basic and diluted earnings per share (in dollars per share):

$ (16.21)

$ (3.81)

$ (16.77)

$ (3.26)

[1]	(2) Restricted shares outstanding vest either in equal annual installments or upon a stated date (see Note 12).
[2]	(3) The diluted earnings (loss) per share denominator for the three and nine months ended September 30, 2012 and 2011 do not include common shares issuable upon exercise of the Non-Qualified Options as they are anti-dilutive to the calculation.
[3]	(2) Net loss attributable to White Mountains’ common shareholders, net of restricted share amounts, is equal to undistributed loss for the three and nine months ended September 30, 2012 and 2011.
[4]	(1) Restricted shares issued by White Mountains contain dividend participation features, and therefore, are considered participating securities.

Discontinued Operations Reinsurance (Details) $ in Millions	3 Months Ended		9 Months Ended
Discontinued Operations Reinsurance (Details) $ in Millions	Sep. 30, 2012 USD ($) Contract	Sep. 30, 2011 USD ($)	Sep. 30, 2012 USD ($) Contract	Sep. 30, 2011 USD ($)	Dec. 31, 2011 USD ($)	May 31, 2001 USD ($)
Reinsurance [Line Items]
Reinsurance recoverable on paid losses	$ 14.8		$ 14.8		$ 30.5
Purchase accounting adjustments	153.0		153.0
Amount of held for sale to be reinsured at closing	36.7		36.7
Gain (loss) on sale of discontinued operation, net of tax	(91.0)	$ (18.2)	(91.0)	$ (18.2)
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(15.8)	(12.0)	$ (24.5)	(7.8)
OneBeacon Runoff [Member]
Reinsurance [Line Items]
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	(100.5)
Gain (loss) on sale of discontinued operation, net of tax	$ (91.5)
OneBeacon
Reinsurance [Line Items]
Number of Contracts Seller Caused One Beacon to Purchase Prior to Acquisition \| Contract	2		2
Reinsurance Recoverables	$ 1,449.2		$ 1,449.2
Reinsurance recoverable on paid losses	2.0		2.0
GRC Cover \| OneBeacon
Reinsurance [Line Items]
Reinsurance Recoverable Cover under Reinsurance Contract			570.0
NICO Cover \| OneBeacon
Reinsurance [Line Items]
Reinsurance Recoverable Cover under Reinsurance Contract			2,500.0
General Reinsurance Corporation [Member] \| GRC Cover \| OneBeacon
Reinsurance [Line Items]
Adverse Loss Reserve Development on Losses Occurring in Years 2000 and Prior						$ 400.0
Loss Reserves Ceded at Acquisition						$ 170.0
Segment, Discontinued Operations [Member]
Reinsurance [Line Items]
Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent	(106.8)	(30.2)	(115.5)	(26.0)
Reinsurance recoverable on paid losses	17.6		17.6		$ 0.0
Reinsurance Recoverables, Gross of Purchase Accounting Adjustments	2,110.0		2,110.0
Gain (loss) on sale of discontinued operation, net of tax	(91.0)	(18.2)	(91.0)	18.2
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(15.8)	$ (12.0)	$ (24.5)	$ (7.8)
Loss attributable to change in discount rate [Member]
Reinsurance [Line Items]
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(9.0)
Loss attributable to prior year reserve devolopment [Member]
Reinsurance [Line Items]
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ (6.5)

Contingencies (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended		12 Months Ended
Contingencies (Details) - USD ($) $ in Millions	Jun. 30, 2007	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Note 15. Contingencies [Abstract]
Gain on sale of business in discontinued operations				$ 700.0
Proceeds from Divestiture of Interest in Subsidiaries and Affiliates		$ 9.8	$ 0.0	1,010.0
Disposal Group Including Discontinued Operation Book Value				$ 308.0
Total amount in dispute with Allstate		20.0
DAC amount in dispute with Allstate, Pre-tax		24.7
DAC amount in dispute with Allstate, after-tax		16.0
Extra contractual obligation in dispute with Allstate, pre-tax		5.2
Extra contractual obligation in dispute with Allstate, after-tax		$ 3.4
Proceeds from Sale, Maturity and Collection of Investments	$ 32.0

Subsequent Event (Details) $ in Millions	12 Months Ended
Subsequent Event (Details) $ in Millions	Sep. 30, 2012 USD ($) Months	Oct. 16, 2012 USD ($)
Subsequent Event [Line Items]
Hagerty written premiums number of months \| Months	12
Significant Acquisitions and Disposals, Gain (Loss) on Sale or Disposal, Net of Tax		$ 15
Hagerty Insurance Agency [Member]
Subsequent Event [Line Items]
Direct Premiums Written	$ 179
Hagerty percentage of direct written premiums	16.00%

Label	Element	Value
Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents	us-gaap_DisposalGroupIncludingDiscontinuedOperationCashAndCashEquivalents	$ 4,700,000
Disposal Group, Including Discontinued Operation, Cash and Cash Equivalents	us-gaap_DisposalGroupIncludingDiscontinuedOperationCashAndCashEquivalents	0
Liability for Unpaid Claims and Claims Adjustment Expense, Net	us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet	2,960,400,000
Liability for Unpaid Claims and Claims Adjustment Expense, Net	us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet	$ 3,449,400,000
Performance Share [Member] \| W T M Incentive and Phantom Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber	119,591

- Definition

+ References + Details

- Definition

Liability as of the balance sheet date for amounts representing estimated cost of settling unpaid claims under the terms of the underlying insurance policies, less estimated reinsurance recoveries on such claims. This includes an estimate for claims which have been incurred but not reported. Claim adjustment expenses represent the costs estimated to be incurred in the settlement of unpaid claims.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 13
-Subparagraph a
-Article 7

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 60
-Paragraph 17, 18, 19, 20
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 94-5
-Paragraph 11
-Subparagraph b
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 01-5
-Paragraph 10
-Subparagraph a
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Financial Reporting Release (FRR)
-Number 403
-Paragraph 04
-Subparagraph b

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 113
-Paragraph 21, 22, 23, 24, 25
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details