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CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2011	Dec. 31, 2010
Assets
Fixed maturity investments, at fair value	$ 5,287.7	$ 5,786.1
Short-term investments, at amortized cost (which approximates fair value)	772.8	975.3
Common equity securities, at fair value	669.8	667.0
Convertible fixed maturity investments, at fair value	140.5	143.0
Other long-term investments	328.8	372.1
Total investments	7,199.6	7,943.5
Cash (restricted: $393.3 and $286.7)	557.7	395.0
Reinsurance recoverable on unpaid losses	2,581.2	2,344.0
Reinsurance recoverable on paid losses	30.9	63.1
Insurance and reinsurance premiums receivable	644.8	532.5
Funds held by ceding companies	131.6	118.7
Investments in unconsolidated affiliates	458.6	389.7
Deferred acquisition costs	202.9	176.1
Deferred tax asset	431.7	431.9
Ceded unearned insurance and reinsurance premiums	104.4	184.0
Accrued investment income	58.3	63.3
Accounts receivable on unsettled investment sales	20.3	39.5
Other assets	760.2	730.0
Assets held for sale	1,399.5	1,122.8
Total assets	14,581.7	14,534.1
Liabilities
Loss and loss adjustment expense reserves	5,882.0	5,736.8
Unearned insurance and reinsurance premiums	976.4	938.7
Debt	669.0	818.8
Deferred tax liability	360.6	373.2
Accrued incentive compensation	169.9	157.4
Ceded reinsurance payable	188.3	221.1
Funds held under reinsurance treaties	39.3	85.8
Accounts payable on unsettled investment purchases	57.1	22.3
Other liabilities	1,310.6	1,167.7
Liabilities held for sale	909.4	751.5
Total liabilities	10,562.6	10,273.3
White Mountains' common shareholders' equity
White Mountains' common shares at $1 par value per share - authorized 50,000,000 shares; issued and outstanding 7,630,717 and 8,194,925 shares	7.6	8.2
Paid-in surplus	1,262.7	1,350.8
Retained earnings	2,004.0	2,175.6
Accumulated other comprehensive income, after-tax:
Equity in unrealized gains from investments in unconsolidated affiliates	135.7	58.5
Net unrealized foreign currency translation gains	35.7	61.4
Other	(1.0)	(1.5)
Total White Mountains' common shareholders' equity	3,444.7	3,653.0
Noncontrolling interests
Noncontrolling interest - OneBeacon Ltd.	269.8	295.0
Noncontrolling interest - Sirius Group Preference Shares	250.0	250.0
Noncontrolling interest - consolidated limited partnerships and A.W.G Dewar	54.6	62.8
Total noncontrolling interests	574.4	607.8
Total equity	4,019.1	4,260.8
Total liabilities and equity	$ 14,581.7	$ 14,534.1

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Dec. 31, 2009
CONSOLIDATED BALANCE SHEETS
Cash restricted (in dollars)	$ 393.3	$ 286.7	$ 273.1	$ 217.1
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	7,630,717	8,194,925
Common shares, outstanding shares	7,630,717	8,194,925

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Revenues:
Earned insurance and reinsurance premiums	$ 490.6	$ 498.1	$ 1,436.7	$ 1,772.9
Net investment income	42.8	48.9	138.1	157.4
Net realized and unrealized investment gains	1.7	11.6	78.3	104.7
Other revenue	(33.8)	(7.6)	(68.6)	(21.1)
Total revenues	501.3	551.0	1,584.5	2,013.9
Expenses:
Loss and loss adjustment expenses	277.1	253.4	914.0	1,175.9
Insurance and reinsurance acquisition expenses	107.0	102.1	296.2	370.9
Other underwriting expenses	67.0	75.0	211.5	245.9
General and administrative expenses	36.2	32.1	120.4	119.5
Interest expense on debt	12.8	13.2	38.8	44.2
Total expenses	500.1	475.8	1,580.9	1,956.4
Pre-tax income (loss) from continuing operations	1.2	75.2	3.6	57.5
Income tax (expense) benefit	0.6	(11.7)	(1.9)	(10.3)
Net income (loss) from continuing operations	1.8	63.5	1.7	47.2
Loss from sale of discontinued operations, net of tax	(18.2)		(18.2)
Net (loss) income from discontinued operations, net of tax	(11.9)	3.6	(10.7)	1.2
(Loss) income before equity in earnings of unconsolidated affiliates	(28.3)	67.1	(27.2)	48.4
Equity in earnings of unconsolidated affiliates	1.5	7.9	16.1	1.6
Net (loss) income	(26.8)	75.0	(11.1)	50.0
Net income (loss) attributable to noncontrolling interests	11.0	(24.3)	(21.2)	(36.4)
Net (loss) income attributable to White Mountains' common shareholders	(15.8)	50.7	(32.3)	13.6
Comprehensive income (loss), net of tax:
Change in equity in net unrealized gains from investments in unconsolidated affiliates	55.1	43.1	77.2	126.4
Change in foreign currency translation and other	(81.8)	126.9	(25.3)	45.9
Comprehensive (loss) income	(42.5)	220.7	19.6	185.9
Comprehensive income attributable to noncontrolling interests	0.0		0.0
Comprehensive (loss) income attributable to White Mountains' common shareholders	$ (42.5)	$ 220.7	$ 19.6	$ 185.9
Basic income (loss) per share
Continuing operations (in dollars per share)	$ 1.81	$ 5.58	$ (0.43)	$ 1.44
Discontinued operations (in dollars per share)	(3.81)	0.43	(3.63)	0.13
Diluted income (loss) per share
Continuing operations (in dollars per share)	1.81	5.58	(0.43)	1.44
Discontinued operations (in dollars per share)	$ (3.81)	$ 0.43	(3.63)	0.13
Dividends declared and paid per White Mountains' common share (in dollars per share)			$ 1.00	$ 1.00

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions	Total	White Mountains' 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, 2009		$ 3,657.4	$ 1,445.0	$ 2,215.9	$ (3.5)	$ 684.1
Increase (Decrease) in Stockholders' Equity
Cumulative effect adjustment - ASU 2009-17 \| ASU 2009-17		(0.4)		(0.4)		(22.8)
Tax basis change due to intercompany transfer		(10.4)		(4.4)	(6.0)
Net (loss) income	$ 50.0	13.6		13.6		36.4
Other comprehensive income, after-tax		172.3			172.3
Dividends declared on common shares	(8.8)	(8.8)		(8.8)
Dividends to noncontrolling interests						(80.5)
Repurchases and retirements of common shares		(178.2)	(88.2)	(90.0)
Issuances of common shares		0.8	0.8
Net distributions to noncontrolling interests						(13.5)
Amortization of restricted share and option awards		21.5	21.5			0.1
Balances at Sep. 30, 2010		3,667.8	1,379.1	2,125.9	162.8	603.8
Balances at Dec. 31, 2010	4,260.8	3,653.0	1,359.0	2,175.6	118.4	607.8
Increase (Decrease) in Stockholders' Equity
Net (loss) income	(11.1)	(32.3)		(32.3)		21.2
Other comprehensive income, after-tax		52.0			52.0
Dividends declared on common shares	(8.0)	(8.0)		(8.0)
Dividends to noncontrolling interests						(47.2)
Repurchases and retirements of common shares		(229.8)	(98.5)	(131.3)
Issuances of common shares		0.9	0.9
Net distributions to noncontrolling interests						(7.7)
Amortization of restricted share and option awards		8.9	8.9			0.3
Balances at Sep. 30, 2011	$ 4,019.1	$ 3,444.7	$ 1,270.3	$ 2,004.0	$ 170.4	$ 574.4

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Cash flows from operations:
Net (loss) income	$ (26.8)	$ 75.0	$ (11.1)	$ 50.0
Charges (credits) to reconcile net loss to net cash used for operations:
Net realized and unrealized investment gains	(1.7)	(11.6)	(78.3)	(104.7)
Net loss (income) from discontinued operations	11.9	(3.6)	10.7	(1.2)
Net loss on sale of discontinued operation - AutoOne	18.2		18.2
Other operating items:
Net change in loss and loss adjustment expense reserves			244.5	(237.4)
Net change in reinsurance recoverable on paid and unpaid losses			(209.2)	255.7
Net change in unearned insurance and reinsurance premiums			86.4	39.5
Net change in funds held by ceding companies			(17.2)	14.5
Net change in deferred acquisition costs			(31.2)	36.1
Net change in ceded unearned premiums			76.5	(157.1)
Net change in funds held under reinsurance treaties			(46.0)	(15.1)
Net change in insurance and reinsurance premiums receivable			(85.4)	(100.7)
Net change in ceded reinsurance payable			(76.1)	198.7
Net change in other assets and liabilities, net			141.2	(26.5)
Net cash provided from (used for) operations - continuing operations			23.0	(48.2)
Net cash provided from operations - discontinued operations			17.5	27.2
Net cash provided from (used for) operations			40.5	(21.0)
Cash flows from investing activities:
Net change in short-term investments			112.6	139.3
Sales of fixed maturity and convertible fixed maturity investments			2,905.7	1,625.4
Maturities, calls and paydowns of fixed maturity and convertible fixed maturity investments			1,015.3	1,426.0
Sales of common equity securities			125.4	110.2
Distributions and redemptions of other long-term investments			90.0	26.5
Purchases of other long-term investments			(30.6)	(71.0)
Contribution to discontinued operations			(97.1)	(16.8)
Purchases of common equity securities			(189.0)	(211.0)
Purchases of fixed maturity and convertible fixed maturity investments			(3,497.6)	(2,663.8)
Purchases of consolidated and unconsolidated affiliates, net of cash acquired				(4.9)
Sales of consolidated and unconsolidated affiliates				166.6
Net change in unsettled investment purchases and sales			54.0	(18.7)
Net acquisitions of property and equipment			(3.3)	(3.2)
Net cash provided from investing activities - continuing operations			485.4	504.6
Net cash provided from (used for) investing activities - discontinued operations			173.7	(21.7)
Net cash provided from investing activities			659.1	482.9
Cash flows from financing activities:
Repayment of debt			(161.6)	(14.0)
Repurchase of debt				(197.3)
Cash dividends paid to the Company's common shareholders			(8.0)	(8.8)
Cash dividends paid to OneBeacon Ltd.'s noncontrolling common shareholders			(37.9)	(71.2)
Cash dividends paid on Sirius Group Preference Shares			(9.4)	(9.4)
Common shares repurchased			(229.7)	(178.2)
OneBeacon Ltd. common shares repurchased and retired				(10.5)
Proceeds from issuances of common shares			0.9	0.8
Net cash used for financing activities - continuing operations			(445.7)	(488.6)
Net cash provided from (used for) financing activities - discontinued operations			0.0
Net cash used for financing activities			(445.7)	(488.6)
Effect of exchange rate changes on cash			(2.0)	6.0
Net change in cash during the period			251.9	(20.7)
Net change in cash from discontinued operations			(191.2)	(5.5)
Cash balances at beginning of period (excludes restricted cash balances of $286.7 and $217.1 and AutoOne cash of $4.7 and $3.9)			103.7	120.0	$ 120.0
Cash balances at end of period (excludes restricted cash balances of $393.3 and $273.1 and AutoOne cash of $0 and $4.4)	$ 164.4	$ 93.8	164.4	93.8	$ 103.7
Supplemental cash flows information:
Interest paid			(38.5)	(49.6)
Net income tax payments to national governments			$ (6.4)	$ (10.6)

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) $ in Millions	Sep. 30, 2011 USD ($)
CONSOLIDATED STATEMENTS OF CASH FLOWS
AutoOne cash included in assets held for sale	$ 5.5

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2011

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

Note 1. 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 (formerly White Mountains Re) 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”) and the business that Esurance Insurance cedes to Sirius Group. Esurance has been presented as discontinued operations and assets and liabilities held for sale in the financial statements. Prior year amounts have been reclassified to conform to the current year’s presentation. (See Note 14 for discontinued operations and assets and liabilities held for sale).

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, 2011 and December 31, 2010, White Mountains owned 75.5% and 76.0% of OneBeacon Ltd.’s outstanding common shares. As discussed further in Note 2, OneBeacon entered into a definitive agreement on August 30, 2011 to sell the AutoOne business. Accordingly, effective for September 30, 2011, AutoOne has been presented as discontinued operations and assets and liabilities 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.

The Sirius Group segment (previously defined as the White Mountains Re segment) consists of Sirius International Insurance Group, Ltd. (formerly White Mountains Re 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, casualty, and agriculture and certain other exposures on a worldwide basis through its subsidiaries, Sirius International Insurance Corporation (“Sirius International”, formerly WMRe Sirius) and Sirius America Insurance Company (“Sirius America”, formerly WMRe America). Sirius Group also specializes in the acquisition and management of run-off insurance and reinsurance companies both in the United States and internationally through its White Mountains Re Solutions division. Sirius Group also includes Scandinavian Reinsurance Company, Ltd. (“Scandinavian Re”) and Central National Insurance Company of Omaha (“Central National”), which was acquired during the first quarter of 2010 (see Note 2), both of which are in run-off.

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’ investment in common shares and warrants to purchase common shares of Symetra Financial Corporation (“Symetra”), the consolidated results of Tuckerman Capital, LP fund (“Tuckerman Fund I”), White Mountains’ variable annuity reinsurance business, White Mountains Life Reinsurance (Bermuda) Ltd. (“WM Life Re”), which is in run-off, as well as other entities not included in other segments. The Other Operations segment also included White Mountains’ investment in Lightyear Delos Acquisition Corporation (“Delos”) prior to its disposition in December 2010.

White Mountains’ discontinued operations consist of Esurance Insurance, AFI, the business that Esurance Insurance ceded to Sirius Group and AutoOne. Esurance Insurance writes personal auto insurance directly to customers in 30 states through its website and over the phone and also sells other lines of personal insurance for unaffiliated insurance companies. Esurance Insurance also writes personal auto policies through select online agents and provides other insurance products through partnerships with industry leading online providers. Esurance Insurance earns commissions and fees by referring to unaffiliated insurance companies those shoppers that it cannot underwrite because of pricing or underwriting eligibility. AFI is one of the largest independent personal insurance agencies in the United States. AFI sells 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 that are of a normal recurring nature. 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 2010 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 2010 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 subsidiaries and are presented separately as a component of equity on the balance sheet.

The percentage of the noncontrolling ownership interests in OneBeacon Ltd. at September 30, 2011 and December 31, 2010 was 24.5% and 24.0%. The increase in the noncontrolling ownership percentage during the first nine months of 2011 was the result of the issuance of 630,000 restricted common shares of OneBeacon Ltd. to its CEO in May 2011 (see Note 12).

On May 24, 2007, Sirius International Group, Ltd. (“Sirius International Group” formerly known as White Mountains Re Group, Ltd), an intermediate holding company of Sirius Group, issued 250,000 non-cumulative perpetual preference shares with a $1,000 per share liquidation preference (the “Sirius Group Preference Shares”). Proceeds of $245.7 million, net of $4.3 million of issuance costs and commissions, were received from the issuance. The Sirius Group Preference Shares are included in noncontrolling interests on the balance sheet.

At September 30, 2011 and December 31, 2010, the noncontrolling equity interest in limited partnerships that are consolidated with White Mountains (Tuckerman Fund I, the Prospector Offshore Fund and the Prospector Turtle Fund) was $51.8 million and $59.7 million. At September 30, 2011 and December 31, 2010, the noncontrolling equity interest in A.W.G. Dewar Inc, a subsidiary of OneBeacon, was $2.2 million and $3.1 million.

Recently Adopted Changes in Accounting Principles

Disclosures about Fair Value Measurements

White Mountains adopted Accounting Standards Update (“ASU”) 2010-06, Improving Disclosures about Fair Value Measurements (included in Accounting Standards Codification (“ASC”) 820-10), effective March 31, 2010. The ASU clarifies existing disclosure requirements for fair value measurements and requires the disclosure of the amounts and nature of transfers in and out of Level 1 and Level 2 measurements; purchase, sale, issuance and settlement activity for Level 3 measurements presented on a gross rather than a net basis; fair value measurements by Level presented on a more disaggregated basis, by asset or liability class; and more detailed disclosures about inputs and valuation techniques for Level 2 and Level 3 measurements for interim and annual reporting periods. White Mountains has expanded its fair value disclosures to meet the requirements of the ASU effective for the period ended March 31, 2010 (see Note 5).

Transfers of Financial Assets and Amendments to FIN 46R

On June 12, 2009, the FASB issued ASU 2009-16, Accounting for Transfers of Financial Assets, an amendment of FASB Statement No. 140 (included in ASC 860) and ASU 2009-17, Amendments to FIN46(R) (included in ASC 810). Both ASU 2009-16 and ASU 2009-17 became effective as of the beginning of the first annual reporting period that began after November 15, 2009. White Mountains adopted the new guidance on January 1, 2010.

ASU 2009-16 eliminates the concept of a qualifying special-purpose entity (“QSPE”). Under the new guidance, the appropriateness of de-recognition of assets held by an entity formerly considered a QSPE is evaluated based on whether or not the transferor has surrendered control of the transferred assets. The evaluation must consider any continuing involvement by the transferor. White Mountains did not have any entities that were considered a QSPE under guidance prior to the amendments to ASC 860 and there was no effect resulting from adoption.

ASU 2009-17 amends ASC 810-10 to clarify the application of consolidation accounting for entities for which the controlling financial interest might not be solely indentified through voting rights. Under the new guidance a variable interest represents a controlling financial interest in a variable interest entity (“VIE”) when it has both of the following: (1) the power to direct the activities of a variable interest entity that most significantly impact the entity’s economic performance and (2) the obligation to absorb losses of the entity that could potentially be significant to the VIE or the right to receive benefits from the entity that could potentially be significant to the VIE. A reporting entity must assess whether it has an implicit financial responsibility to ensure that a VIE operates as designed when determining if it has the power to direct the activities of the VIE that most significantly affect the entity’s economic performance. ASC 810-10 as amended requires ongoing reassessments of whether a reporting entity is the primary beneficiary of a VIE.

Upon adoption, White Mountains determined that its ownership interest in Tuckerman Fund II did not meet the criteria for consolidation under the revised guidance for variable interest entities and, accordingly, effective January 1, 2010, White Mountains deconsolidated its investment in Tuckerman Fund II. Upon deconsolidation, White Mountains made the fair value election for its investment in Tuckerman Fund II and recognized an adjustment to decrease opening retained earnings by $0.4 million.

Recently Issued Accounting Pronouncements

Goodwill Impairment

On September 15, 2011, the FASB issued ASU 2011-08, Testing Goodwill for Impairment (ASC 350). The ASU amends the guidance that requires an entity to test goodwill for impairment on at least an annual basis using a two-step quantitative test. The new guidance permits an entity to first assess facts and circumstances to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If the entity determines on the basis of this assessment that it is not more likely than not that the fair value of the reporting unit is less than its carrying amount, then performance of the two-step quantitative test is not required. ASU 2011-08 is effective for annual and interim goodwill impairment tests performed for fiscal years beginning after December 15, 2011. Early adoption is permitted. White Mountains expects that adoption will have no material effect upon its financial position, results of operations or cash flows.

Comprehensive Income

On June 16, 2011, the FASB issued ASU 2011-05, Presentation of Comprehensive Income (ASC 220). The ASU requires presentation of the components of net income, the total of other comprehensive income and total comprehensive income to be presented on a single statement. The option of presenting other comprehensive income in the statement of changes in equity has been eliminated by the ASU. ASU 2011-05 is effective for fiscal years and interim periods within those fiscal years ending after December 15, 2011. White Mountains already presents comprehensive income in accordance with the requirements of the ASU, so there will be no effect upon adoption.

Fair Value Measurements and Disclosures

On May 12, 2011, the FASB issued ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRS (ASC 820). 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. ASU 2011-04 is effective for interim and annual periods beginning after December 15, 2011. White Mountains is currently evaluating the effect the adoption of ASU 2011-04 will have on its financial position and results of operations.

Policy Acquisition Costs

On October 13, 2010, the FASB issued 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.

ASU 2010-26 is effective for interim periods and annual fiscal years beginning after December 15, 2011 and may be applied prospectively or retrospectively. White Mountains expects that adoption will not have a material effect upon its financial position, results of operations or cash flows.

Significant Transactions

9 Months Ended

Sep. 30, 2011

Significant Transactions

Significant Transactions

Note 2. Significant Transactions

Sale of Esurance

On October 7, 2011, White Mountains completed its sale of Esurance Insurance and AFI to The Allstate Corporation (see Note 15).

Self Tender Offer

On September 21, 2011, White Mountains completed a “modified Dutch auction” self-tender offer whereby White Mountains repurchased 327,872 of its common shares at $415 per share. The total cost of the tender offer was $136.5 million, including $0.4 million of fees and expenses.

Sale of AutoOne

On August 30, 2011, OneBeacon entered into a definitive agreement (the “Purchase Agreement”) to sell the AutoOne business 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 will transfer to the buyer AutoOne Insurance Company (“AOIC”) and AutoOne Select Insurance Company (“AOSIC”), which will contain the assets, liabilities (including loss reserves and unearned premiums), and the equity capital of the business, and will transfer substantially all of the AutoOne infrastructure including staff, systems and office space. The transaction is expected to close in the fourth quarter of 2011, subject to regulatory approvals. As a result of entering into the Purchase Agreement, AutoOne is now reported as discontinued operations. See Note 14.

During the three months ended September 30, 2011, OneBeacon recorded an after-tax charge of $18.2 million reflecting the estimated loss on sale of the AutoOne business.

OneBeacon Personal Lines Sale

In July 2010, OneBeacon completed the sale of its traditional personal lines business (the “Personal Lines Transaction”) to Tower Group, Inc. (“Tower”) for consideration of $166.6 million. The Personal Lines Transaction included two insurance companies, York Insurance Company of Maine (“York”) and Massachusetts Homeland Insurance Company (“MHIC”), through which the majority of the traditional personal lines business was written on a direct basis. Subsequent to the transaction, OneBeacon cedes to Tower, on a 100% quota share basis, traditional personal lines business not directly written by York and MHIC; and OneBeacon assumes, on a 100% quota share basis, non-traditional personal lines business written directly by York. The Personal Lines Transaction also included two attorneys-in-fact managing the reciprocal insurance exchanges (“reciprocals”) that wrote the traditional personal lines business in New York and New Jersey, the surplus notes issued by the New York and New Jersey reciprocals, and the remaining renewal rights to certain other traditional personal lines insurance policies. The sale of the two attorneys-in-fact and the transfer of the surplus notes triggered deconsolidation of the reciprocals by White Mountains. OneBeacon and Tower also entered into a Transition Services Agreement (“TSA”), pursuant to which OneBeacon provides certain services to Tower during a three-year term.

Acquisition of Central National

On February 26, 2010, Sirius Group acquired Central National for $5 million in cash. Central National ceased writing business in 1989 and was operated under the control of the Nebraska Department of Insurance since 1990. The transaction resulted in a gain of $12.8 million recorded in other revenues.

Loss and Loss Adjustment Expense Reserves

9 Months Ended

Sep. 30, 2011

Loss and Loss Adjustment Expense Reserves

Loss and Loss Adjustment Expense Reserves

Note 3. 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, 2011 and 2010:

	Three Months Ended September 30,						Nine Months Ended September 30,
Millions	2011			2010			2011			2010
Gross beginning balance	$	5,642.4		$	6,198.1		$	5,736.8		$	6,379.2
Less beginning reinsurance recoverable on unpaid losses	(2,193.0		)	(2,748.3		)	(2,344.0		)	(2,771.5		)
Net loss and LAE reserves	3,449.4			3,449.8			3,392.8			3,607.7

Less: Beginning net loss and LAE reserves for AutoOne (1)	(58.6		)	(81.7		)	(68.2		)	(95.8		)

Loss and LAE reserves acquired — Central National	—			—			—			17.6
Loss and LAE reserves sold — OneBeacon Personal Lines (2)	—			—			—			(231.0		)

Loss and LAE incurred relating to:
Current year losses	307.8			284.7			972.2			1,244.9
Prior year losses	(30.7		)	(31.3		)	(58.2		)	(69.0		)
Total incurred losses and LAE	277.1			253.4			914.0			1,175.9

Accretion of fair value adjustment to loss and LAE reserves	2.1			2.1			6.2			6.3
Foreign currency translation adjustment to loss and LAE reserves	(25.5		)	39.9			5.7			6.7

Loss and LAE paid relating to:
Current year losses	(112.8		)	(156.3		)	(237.9		)	(403.9		)
Prior year losses	(230.9		)	(211.8		)	(711.8		)	(788.1		)
Total loss and LAE payments	(343.7		)	(368.1		)	(949.7		)	(1,192.0		)

Plus: Ending net loss and LAE reserves for AutoOne (1)	—			82.9			—			82.9

Net ending balance	3,300.8			3,378.3			3,300.8			3,378.3
Plus ending reinsurance recoverable on unpaid losses	2,581.2			2,592.1			2,581.2			2,592.1
Gross ending balance	$	5,882.0		$	5,970.4		$	5,882.0		$	5,970.4

(1)	Adjustment is to present loss and LAE reserve activities from continuing operations. At September 30, 2011, loss and LAE reserves for AutoOne have been reclassified as liabilities held for sale. Loss and LAE reserve balances for AutoOne prior to September 30, 2011 were not reclassified. See Note 14.
(2)	In the second quarter of 2010, $231.0 of net loss and LAE reserves related to the Personal Lines Transaction were reclassified to liabilities held for sale. The Personal Lines Transaction closed in July 2010.

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 $30.7 million and $58.2 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 $9.8 million and $25.0 million. The favorable loss reserve development was primarily due to lower than expected severity on losses 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.

Loss and LAE incurred relating to prior year losses for the three and nine months ended September 30, 2010

During the three and nine months ended September 30, 2010, White Mountains experienced $31.3 million and $69.0 million of net favorable loss reserve development.

For the three and nine months ended September 30, 2010, OneBeacon had net favorable loss reserve development of $17.8 million and $42.1 million. The favorable loss reserve development was primarily due to lower than expected severity on losses related to professional liability lines, commercial package business and other general liability lines.

For the three and nine months ended September 30, 2010, Sirius Group had net favorable loss reserve development of $13.5 million and $26.9 million. The favorable loss reserve development at Sirius Group was primarily due to short-tailed lines of business, primarily property, accident and health, and aviation.

Fair value adjustment to loss and LAE reserves

In connection with purchase accounting for the acquisitions of Scandinavian Re and Stockbridge Insurance Company (“Stockbridge”), 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.

Sirius Group recognized $2.1 million and $6.2 million for the three and nine months ended September 30, 2011, and $2.1 million and $6.3 million for the three and nine months ended September 30, 2010. As of September 30, 2011, the pre-tax un-accreted adjustment was $14.9 million.

- Definition

Disclosure of accounting policy for the various components of the reserve for future policy benefits and guaranteed minimum benefits, and for claims and claims adjustment expenses; the significant assumptions for estimating claims losses; causes of significant variances from prior periods (such as catastrophes, asbestos and environmental claims reserve losses); and reconciliations of beginning to ending reserve balances.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 7
-Section 03
-Paragraph 13

Reference 2: 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 3: 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 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437

Reference 5: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6482852&loc=d3e14931-158439

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14754-158437

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.13(a)(1),(b))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Third Party Reinsurance

9 Months Ended

Sep. 30, 2011

Third Party Reinsurance

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, 2011, OneBeacon had $13.7 million of reinsurance recoverables on paid losses and $2,405.7 million (gross of $166.6 million in purchase accounting adjustments) that will become recoverable if claims are paid in accordance with current reserve estimates. The collectability of balances due from OneBeacon’s reinsurers is critical to OneBeacon’s financial strength because reinsurance contracts do not relieve OneBeacon of its primary obligation to its policyholders. 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.

The following table provides a listing of OneBeacon’s top reinsurers, excluding industry pools and associations, 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, 2011		% of Total		A.M. Best Rating(1)
National Indemnity Company and General Reinsurance Corporation (2)	$	1,565.2	65	%		A++
Hanover Insurance Company	110.1		5	%		A
Tokio Marine and Nichido Fire (3)	55.8		2	%		A++
Tower Insurance Company	53.7		2	%		A-
Munich Reinsurance America	31.5		1	%		A+

(1)	A.M. Best ratings as detailed above are: “A++” (Superior, which is the highest of fifteen ratings), “A+” (Superior, which is the second highest of fifteen ratings), “A” (Excellent, which is the third highest of fifteen ratings), and “A-” (Excellent, which is the fourth highest of fifteen ratings).
(2)	Includes $198.3 of Third Party Recoverables (as defined below), which NICO (as defined below) would pay under the terms of the NICO Cover (as defined below) if they are unable to collect from third party reinsurers.
(3)	Includes $29.3 of reinsurance recoverables from various third party reinsurers that are guaranteed by Tokio Marine and Nichido Fire under the terms of a 100% quota share reinsurance agreement between Houston General Insurance Company and Tokio Marine and Nichido Fire.

Immediately prior to White Mountains’ acquisition of OneBeacon, the seller caused OneBeacon to purchase two reinsurance contracts from subsidiaries of Berkshire Hathaway Inc. (“Berkshire”): a full risk-transfer cover from 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 (the “GRC Cover”) from General Reinsurance Corporation (“GRC”) for up to $570.0 million, comprised of $400.0 million of adverse loss reserve development on losses occurring in years 2000 and prior and $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.

Under the terms of the NICO Cover, NICO receives the economic benefit of reinsurance recoverables (“Third Party Recoverables”) from certain of OneBeacon’s third party reinsurers in existence at the time the NICO Cover was executed. As a result, the Third Party Recoverables serve to protect the $2.5 billion limit of NICO coverage for the benefit of OneBeacon. White Mountains estimates that on an incurred basis, net of Third Party Recoverables, as of September 30, 2011 it has used approximately $2.3 billion of the coverage provided by NICO. Through September 30, 2011, $1.4 billion of these incurred losses have been paid by NICO. Since entering into the NICO Cover, approximately 8% ($187.7 million), of the $2.3 billion of utilized coverage from NICO related to uncollectible Third Party Recoverables. To the extent that actual experience differs from White Mountains’ estimate of ultimate A&E losses and Third Party Recoverables, future losses could utilize some or all of the protection remaining under the NICO Cover.

Pursuant to the GRC Cover, OneBeacon is not entitled to recover losses to the full contract limit if such losses are reimbursed by GRC more quickly than anticipated at the time the contract was signed. OneBeacon intends to only seek reimbursement from GRC for claims which result in payment patterns similar to those supporting its recoverables recorded pursuant to the GRC Cover. The economic cost of not submitting certain other eligible claims to GRC is primarily the investment spread between the rate credited by GRC and the rate achieved by OneBeacon on its own investments. This cost, if any, is expected to be nominal. During the three and nine months ended September 30, 2011, $13.6 million and $60.7 million was collected under the GRC Cover.

During the third quarter of 2011, OneBeacon completed a new ground-up study of its legacy asbestos and environmental exposures. The previous study was based on experience through 2007. Reasonable estimates of potential adverse scenarios continue to be within the $2.5 billion reinsurance cover issued by NICO. The point estimate of incurred losses ceded to NICO increased from $2.2 billion to $2.3 billion.

Effective May 1, 2011, OneBeacon renewed its property catastrophe reinsurance program through April 30, 2012. The program provides coverage for OneBeacon’s property business as well as certain acts of terrorism. Under the program, the first $50.0 million of losses resulting from any single catastrophe are retained by OneBeacon. The next $175.0 million of losses resulting from the catastrophe are reinsured with OneBeacon co-participating in the losses. OneBeacon retains 26% of the losses from $50.0 million up to $100.0 million and 10% of the losses from $100.0 million up to $175.0 million. Any loss above $225.0 million is retained by OneBeacon. 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.

OneBeacon had entered into a 30% quota share agreement with a group of reinsurers that ran from January 1, 2009 through December 31, 2009, and had renewed the agreement effective January 1, 2010 through July 1, 2010, the closing date of the Personal Lines Transaction. Through June 30, 2010, OneBeacon ceded $25.6 million of written premiums from its Northeast homeowners business written through OneBeacon Insurance Company (“OBIC”) and its subsidiary companies, along with Adirondack Insurance Exchange (“Adirondack Insurance”) and New Jersey Skylands Insurance Agency (“NJSIA”) in New York and New Jersey, respectively.

Sirius Group

At September 30, 2011, Sirius Group had $17.2 million of reinsurance recoverables on paid losses and $342.1 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 critical 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, 2011		% of Total		A.M. Best Rating (1)		% Collateralized
General Reinsurance Corporation	$	43.3	12	%		A++	2	%
Olympus (2)	40.8		11	%		NR-5	100	%
Swiss Re Group	40.0		11	%		A	4	%
Lloyds of London(3)	31.3		9	%		A	6	%
Michigan Catastrophic Claims Association	14.6		4	%		N/A(4)	—	%

(1)	A.M. Best ratings as detailed above are: “NR-5” (Not formally followed), “A++” (Superior, which is the highest of fifteen ratings), and “A” (Excellent, which is the third highest of fifteen ratings).
(2)	Non-U.S. insurance entity. Balances are fully collateralized through funds held, letters of credit or trust agreements.
(3)	Represents the total of reinsurance recoverables due to Sirius Group from all Lloyds Syndicates.
(4)	Michigan Catastrophic Claims Association (“MCCA”) is a non-profit unincorporated association of 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 pursuant to its acquisition of Stockbridge.

- 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 Statement of Financial Accounting Standard (FAS)
-Number 113
-Paragraph 27
-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 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 7
-Section 03
-Paragraph 13

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Statement of Position (SOP)
-Number 92-5
-Paragraph 19
-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 SEC
-Name Regulation S-X (SX)
-Number 210
-Article 7
-Section 03
-Paragraph 6

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 50
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-URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6811-158387

Reference 6: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 944
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-URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6816-158387

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27374-158547

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=6588590&loc=d3e27703-158548

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6485557&loc=d3e21549-158491

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 55
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=6588590&loc=d3e27795-158548

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.6,13)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 113
-Paragraph 120
-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

9 Months Ended

Sep. 30, 2011

Investment Securities

Investment Securities

Note 5. 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 fixed maturity investments, convertible fixed maturities 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 pre-tax in 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 accreted or amortized 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 cost, which approximated fair value as of September 30, 2011 and December 31, 2010.

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, 2011 and 2010 consisted of the following:

	Three Months Ended September 30,						Nine Months Ended September 30,
Millions	2011			2010			2011			2010
Investment income:
Fixed maturity investments	$	38.5		$	46.9		$	127.0		$	149.9
Short-term investments	.9			.8			3.2			3.7
Common equity securities	3.6			2.7			10.1			7.1
Convertible fixed maturity investments	1.3			.4			3.9			4.4
Other long-term investments	1.2			1.1			1.9			1.6
Interest on funds held under reinsurance treaties	.2			(.5		)	(.6		)	(2.2		)
Total investment income	45.7			51.4			145.5			164.5
Less third-party investment expenses	(2.9		)	(2.5		)	(7.4		)	(7.1		)
Net investment income, pre-tax	$	42.8		$	48.9		$	138.1		$	157.4

Net Realized and Unrealized Investment Gains and Losses

	Three Months Ended September 30,						Nine Months Ended September 30,
Millions	2011			2010			2011			2010
Net realized investment gains (losses), pre-tax	$	37.1		$	31.4		$	109.6		$	93.7
Net unrealized investment gains (losses), pre-tax	(35.4		)	(19.8		)	(31.3		)	11.0
Net realized and unrealized investment gains (losses), pre-tax	1.7			11.6			78.3			104.7
Income taxes attributable to realized and unrealized investment gains (losses)	(1.1		)	(22.7		)	(23.7		)	(24.5		)
Net realized and unrealized investment gains (losses), after-tax	$	.6		$	(11.1	)	$	54.6		$	80.2

Net realized investment gains (losses)

Net realized investment gains (losses) for the three and nine months ended September 30, 2011 and 2010 consisted of the following:

	Three Months Ended September 30,						Nine Months Ended September 30,
Millions	2011			2010			2011			2010
Fixed maturity investments	$	14.0		$	34.7		$	33.6		$	68.1
Short-term investments	—			—			—			—
Common equity securities	23.1			(13.7		)	41.0			6.7
Convertible fixed maturity investments	(.7		)	6.2			6.3			19.9
Other long-term investments	.7			4.2			28.7			(1.0		)
Net realized investment gains (losses), pre-tax	37.1			31.4			109.6			93.7
Income taxes attributable to realized investment gains (losses)	(8.0		)	(4.9		)	(31.7		)	(20.5		)
Net realized investment gains (losses), after-tax	$	29.1		$	26.5		$	77.9		$	73.2

Net unrealized investment gains (losses)

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

	Three Months Ended September 30, 2011									Nine Months Ended 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 maturities	$	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 gains (losses), pre-tax	(110.0		)	74.6			(35.4		)	(110.3		)	79.0			(31.3		)
Income taxes attributable to unrealized investment gains (losses)	26.4			(19.5		)	6.9			28.5			(20.5		)	8.0
Net unrealized investment gains (losses), after-tax	$	(83.6	)	$	55.1		$	(28.5	)	$	(81.8	)	$	58.5		$	(23.3	)

	Three Months Ended September 30, 2010									Nine Months Ended September 30, 2010
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 maturities	$	3.3		$	(81.2	)	$	(77.9	)	$	36.4		$	(53.6	)	$	(17.2	)
Short-term investments	—			1.4			1.4			—			.6			.6
Common equity securities	64.3			(10.8		)	53.5			31.8			(9.7		)	22.1
Convertible fixed maturity investments	2.8			—			2.8			(8.3		)	—			(8.3		)
Other long-term investments	9.0			(8.6		)	.4			20.5			(6.7		)	13.8
Net unrealized investment gains (losses), pre-tax	79.4			(99.2		)	(19.8		)	80.4			(69.4		)	11.0
Income taxes attributable to unrealized investment gains (losses)	(28.8		)	11.0			(17.8		)	(22.4		)	18.4			(4.0		)
Net unrealized investment gains (losses), after-tax	$	50.6		$	(88.2	)	$	(37.6	)	$	58.0		$	(51.0	)	$	7.0

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, 2011 and 2010:

	Three Months Ended September 30,					Nine Months Ended September 30,
Millions	2011			2010		2011			2010
Fixed maturities	$	(13.5	)	$	3.3	$	(14.9	)	$	9.5
Common equity securities	(17.5		)	2.5		(17.0		)	(20.0		)
Convertible fixed maturities	—			—		—			—
Other long-term investments	(3.2		)	8.5		(6.5		)	37.4
Total unrealized investment gains (losses), pre-tax - Level 3 investments	$	(34.2	)	$	14.3	$	(38.4	)	$	26.9

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, 2011 and December 31, 2010, were as follows:

	September 30, 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	$	347.1	$	5.8	$	(.2	)	$	.4		$	353.1
Debt securities issued by corporations	1,990.0		76.6		(11.9		)	(.8		)	2,053.9
Municipal obligations	2.4		—		—			—			2.4
Mortgage-backed and asset-backed securities	2,200.8		29.8		(4.9		)	14.9			2,240.6
Foreign government, agency and provincial obligations	653.0		14.1		(.2		)	(.9		)	666.0
Preferred stocks	82.3		3.3		(11.0		)	—			74.6
Total fixed maturity investments(1)	$	5,275.6	$	129.6	$	(28.2	)	$	13.6		$	5,390.6

(1) Carrying value includes $102.9 that is classified as assets held for sale relating to AutoOne discontinued operations.

	December 31, 2010
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency gains (losses)			Carrying value
U.S. Government and agency obligations	$	385.9	$	13.6	$	(.8	)	$	—		$	398.7
Debt securities issued by corporations	2,149.2		87.9		(21.1		)	(37.9		)	2,178.1
Municipal obligations	3.3		.1		(.1		)	—			3.3
Mortgage-backed and asset-backed securities	2,082.0		18.2		(15.6		)	(12.9		)	2,071.7
Foreign government, agency and provincial obligations	1,053.6		7.7		(6.6		)	(8.3		)	1,046.4
Preferred stocks	81.9		6.1		—			(.1		)	87.9
Total fixed maturity investments	$	5,755.9	$	133.6	$	(44.2	)	$	(59.2	)	$	5,786.1

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, 2011 and December 31, 2010, were as follows:

September 30, 2011

Millions

Cost or
amortized
cost

Gross
unrealized
gains

Gross
unrealized
losses

Net foreign
currency
gains (losses)

Carrying
value

Common equity securities

661.0

35.4

(26.6

)

—

669.8

Convertible fixed maturities

143.7

4.4

(7.6

)

—

140.5

Other long-term investments

290.2

56.2

(15.2

)

(2.4

)

328.8

	December 31, 2010
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency gains (losses)			Carrying value
Common equity securities	$	561.2	$	105.5	$	(1.5	)	$	1.8		$	667.0
Convertible fixed maturities	$	126.9	$	16.2	$	(.1	)	$	—		$	143.0
Other long-term investments	$	329.5	$	62.4	$	(13.0	)	$	(6.8	)	$	372.1

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, 2011, White Mountains held investments in 17 hedge funds and 33 private equity funds. The decrease in the fair value of hedge funds and private equity funds is due to net redemptions during the period. The largest investment in a single fund was $31.4 million at September 30, 2011. The following table summarizes investments in hedge funds and private equity interests by investment objective and sector at September 30, 2011 and December 31, 2010:

	September 30, 2011				December 31, 2010
Millions	Fair Value		Unfunded Commitments		Fair Value		Unfunded Commitments
Hedge funds
Long/short equity	$	49.0	$	—	$	50.4	$	—
Long/short credit & distressed	32.3		—		34.1		—
Long diversified strategies	22.0		—		24.0		—
Long/short equity REIT	14.7		—		25.2		—
Long/short equity activist	11.7		—		16.9		—
Long bank loan	.5		—		5.1		—
Total hedge funds	130.2				155.7		—

Private equity funds
Distressed residential real estate	31.4		—		49.2		—
Energy infrastructure & services	29.5		9.9		24.2		10.8
Multi-sector	28.0		8.2		26.0		10.6
Manufacturing/Industrial	17.0		—		17.9		—
Private equity secondaries	11.3		4.0		10.4		4.4
Real estate	10.2		3.3		9.1		4.6
International multi-sector, Europe	8.0		4.7		10.5		5.3
International multi-sector, Asia	3.6		2.7		4.9		2.7
Insurance	3.6		41.3		3.9		41.3
Venture capital	2.5		.5		2.2		1.0
Healthcare	2.3		7.0		1.5		8.0
Total private equity funds	147.4		81.6		159.8		88.7

Total hedge and private equity funds included in other long-term investments	$	277.6	$	81.6	$	315.5	$	88.7

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, 2011 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	$	—	$	—	$	—	$	6.0	$	6.0
Quarterly	26.1		29.7		19.6		—		75.4
Semi-annual	—		5.1		—		14.7		19.8
Annual	21.9		—		6.6		.5		29.0
Total	$	48.0	$	34.8	$	26.2	$	21.2	$	130.2

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, 2011, distributions of $3.2 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, 2011.

White Mountains has also submitted redemption requests for certain of its investments in active hedge funds. At September 30, 2011 redemptions of $2.0 million are outstanding. The date at which such remittances will be received is not determinable at September 30, 2011. 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, 2011, 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	$	47.3	$	—	$	83.1	$	17.0	$	147.4

Fair value measurements at September 30, 2011

White Mountains’ invested assets measured at fair value include fixed maturity securities, common and preferred equity securities, convertible fixed maturity securities 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 maturities, primarily U.S. Treasury securities, publicly-traded common equities and short-term investments, which include U.S. Treasury Bills. Investments valued using Level 2 inputs consist of fixed maturities, including corporate debt, state and other government debt, convertible fixed maturity securities and mortgage-backed and asset-backed securities. Fair value estimates for investments classified as Level 3 measurements include investments in hedge funds, private equity funds and certain investments in fixed maturities and common equity securities. Fair value measurements for securities for which observable inputs are unavailable are estimated using industry standard pricing models and observable inputs such as benchmark interest rates, matrix pricing, market comparables, broker quotes, issuer spreads, bids, offers, credit ratings, prepayment speeds and other relevant inputs. In circumstances where quoted prices or observable inputs are adjusted to reflect management’s best estimate of fair value, such fair value measurements are considered a lower level measurement in the fair value hierarchy.

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 each hedge fund’s and private equity fund’s audited annual financial statements 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 $66.1 million and $77.8 million of investment-related liabilities recorded at fair value and included in other liabilities as of September 30, 2011 and December 31, 2010. 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, 2011 and December 31, 2010, by level. The fair value measurements for derivative assets associated with White Mountains’ variable annuity reinsurance business are presented in Note 8.

	September 30, 2011
Millions	Fair value		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs
Fixed maturities:
US Government and agency obligations	$	353.1	$	343.5	$	9.6	$	—

Debt securities issued by corporations:
Consumer	719.0		—		719.0		—
Industrial	425.3		—		425.3		—
Financials	243.4		5.7		212.2		25.5
Communications	211.0		—		211.0		—
Energy	118.0		—		118.0		—
Basic materials	160.1		—		160.1		—
Utilities	148.3		—		148.3		—
Technology	25.3		—		25.3		—
Diversified	3.5		—		3.5		—
Total debt securities issued by corporations:	2,053.9		5.7		2,022.7		25.5

Municipal obligations	2.4		—		2.4		—
Mortgage-backed and asset-backed securities	2,240.6		—		2,108.7		131.9
Foreign government, agency and provincial obligations	666.0		64.5		601.5		—
Preferred stocks	74.6		—		15.1		59.5
Total fixed maturities(2)	5,390.6		413.7		4,760.0		216.9

Short-term investments	772.8		759.0		13.8		—

Common equity securities:
Financials	191.6		159.4		.5		31.7
Consumer	166.0		164.8		1.2		—
Basic materials	108.4		107.2		1.2		—
Energy	57.5		57.5		—		—
Utilities	40.7		40.7		—		—
Technology	28.6		27.6		1.0		—
Other	77.0		25.3		51.3		.4
Total common equity securities	669.8		582.5		55.2		32.1

Convertible fixed maturity investments	140.5		—		140.5		—
Other long-term investments(1)	292.2		—		—		292.2
Total investments	$	7,265.9	$	1,755.2	$	4,969.5	$	541.2

(1) Excludes carrying value of $36.6 associated with other long-term investment limited partnerships accounted for using the equity method.

(2) Carrying value includes $102.9 that is classified as assets held for sale relating to AutoOne discontinued operations.

	December 31, 2010
Millions	Fair value		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs

Fixed maturities:
US Government and agency obligations	$	398.7	$	388.9	$	9.8	$	—

Debt securities issued by corporations:
Consumer	769.0		—		769.0		—
Industrial	511.3		—		511.3		—
Financials	265.8		6.3		259.5		—
Communications	226.3		—		226.3		—
Basic materials	125.3		—		125.3		—
Utilities	106.7		—		106.7		—
Energy	151.5		—		151.5		—
Technology	22.1		—		22.1		—
Total debt securities issued by corporations:	2,178.0		6.3		2,171.7		—

Municipal obligations	3.3		—		3.3
Mortgage-backed and asset-backed securities	2,071.7		—		2,014.7		57.0
Foreign government, agency and provincial obligations	1,046.5		82.6		963.9		—
Preferred stocks	87.9		—		16.5		71.4
Total fixed maturities	5,786.1		477.8		5,179.9		128.4

Short-term investments	975.3		878.7		96.6		—

Common equity securities:
Financials	221.6		152.6		1.2		67.8
Consumer	123.3		122.5		.8		—
Basic materials	98.8		97.1		1.7		—
Energy	60.2		60.2		—		—
Utilities	47.6		44.6		—		3.0
Technology	31.8		30.4		1.4		—
Other	83.7		30.5		52.8		.4
Total common equity securities	667.0		537.9		57.9		71.2

Convertible fixed maturity investments	143.0		—		143.0		—
Other long-term investments(1)	330.2		—		—		330.2
Total investments	$	7,901.6	$	1,894.4	$	5,477.4	$	529.8

(1) Excludes carrying value of $41.9 associated with other long-term investment limited partnerships 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, 2011 and December 31, 2010:

Millions	September 30, 2011		December 31, 2010
AAA	$	—	$	—
AA	217.4		210.0
A	765.0		833.7
BBB	1,059.8		1,109.1
BB	5.5		24.5
Other	6.2		.7
Debt securities issued by corporations	$	2,053.9	$	2,178.0

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, fixed rate and structurally senior, with more than 20 points of subordination on average for fixed rate CMBS and more than 55 points of subordination on average for floating rate CMBS as of September 30, 2011. 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 any 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, 2011, on average approximately 2% 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, 2011. White Mountains’ investments in hedge funds and private equity funds contain negligible amounts of sub-prime mortgage-backed securities at September 30, 2011. 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 a sub-prime risk 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 of moderate average life and structurally senior. White Mountains does not own any collateralized debt obligations, including residential mortgage-backed collateralized debt obligations.

	September 30, 2011						December 31, 2010
Millions	Fair Value		Level 2		Level 3		Fair Value		Level 2		Level 3
Mortgage-backed securities:
Agency:
GNMA	$	1,268.0	$	1,136.1	$	131.9	$	1,143.6	$	1,102.7	$	40.9
FNMA	268.9		268.9		—		234.9		234.9		—
FHLMC	56.6		56.6		—		39.1		39.1		—
Total Agency(1)	1,593.5		1,461.6		131.9		1,417.6		1,376.7		40.9
Non-agency:
Residential	68.0		68.0		—		90.6		74.5		16.1
Commercial	243.5		243.5		—		87.0		87.0		—
Total Non-agency	311.5		311.5		—		177.6		161.5		16.1

Total mortgage-backed securities	1,905.0		1,773.1		131.9		1,595.2		1,538.2		57.0
Other asset-backed securities:
Credit card receivables	77.5		77.5		—		248.3		248.3		—
Vehicle receivables	235.5		235.5		—		228.1		228.1		—
Other	22.6		22.6		—		.1		.1		—
Total other asset-backed securities	335.6		335.6		—		476.5		476.5		—
Total mortgage and asset-backed securities	$	2,240.6	$	2,108.7	$	131.9	$	2,071.7	$	2,014.7	$	57.0

(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, 2011 are as follows:

			Security Issuance Year
Millions	Fair Value		2003		2005		2006		2007		2009		2010		2011
Non-agency RMBS	$	68.0	$	3.7	$	—	$	24.3	$	29.5	$	—	$	10.5	$	—
Non-agency CMBS	243.5		2.4		14.7		—		17.1		11.3		2.2		195.8
Total	$	311.5	$	6.1	$	14.7	$	24.3	$	46.6	$	11.3	$	12.7	$	195.8

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, 2011:

Millions	Fair Value		Super Senior (1)		Senior (2)		Subordinate(3)
Prime	$	49.9	$	23.2	$	26.7	$	—
Non-prime	18.1		17.2		.9		—
Sub-prime	—		—		—		—
Total	$	68.0	$	40.4	$	27.6	$	—

(1)	At issuance, Super Senior were rated AAA by Standard & Poor’s or Aaa by Moody’s and were senior to other AAA or Aaa bonds.
(2)	At issuance, Senior were rated AAA by Standard & Poor’s or Aaa by Moody’s and were senior to non-AAA or non-Aaa bonds.
(3)	At issuance, Subordinate were not rated AAA by Standard & Poor’s or Aaa by Moody’s 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, 2011:

Millions	Fair Value		Super Senior (1)		Senior(2)		Subordinate(3)
Fixed rate CMBS	$	201.8	$	24.3	$	177.5	$	—
Floating rate CMBS	41.7		31.8		9.9		—
Total	$	243.5	$	56.1	$	187.4	$	—

(1)	At issuance, Super Senior were rated AAA by Standard & Poor’s or Aaa by Moody’s and were senior to other AAA or Aaa bonds.
(2)	At issuance, Senior were rated AAA by Standard & Poor’s or Aaa by Moody’s and were senior to non-AAA or non-Aaa bonds.
(3)	At issuance, Subordinate were not rated AAA by Standard & Poor’s or Aaa by Moody’s 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 maturities, common equity securities, convertible fixed maturities and other long-term investments at September 30, 2011 are comprised 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 table summarizes the changes in White Mountains’ fair value measurements by level for the nine months ended September 30, 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, 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 and other revenue	.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 - Nine-month period ended September 30, 2011

During the first nine months of 2011, seven securities which had been classified as Level 3 measurements in the prior period 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 in the prior period was priced with unobservable inputs during the current period and represents the “Transfers in” of $1 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 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.

- Definition

Tabular disclosure of investments in certain debt and equity securities (and certain other trading assets) which include all debt and equity securities (other than those equity securities accounted for under the equity or cost methods of accounting) with readily determinable fair values. Other trading assets include assets that are carried on the balance sheet at fair value and held for trading purposes. A debt security represents a creditor relationship with an enterprise that is in the form of a security. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities (and other trading assets).

+ References

Reference 1: 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.

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

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-Name Accounting Standards Codification
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Debt Security
-URI http://asc.fasb.org/extlink&oid=6509901
-Topic 320

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Equity Security
-URI http://asc.fasb.org/extlink&oid=6511694
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+ Details

Debt

9 Months Ended

Sep. 30, 2011

Debt

Debt

Note 6. Debt

White Mountains’ debt outstanding as of September 30, 2011 and December 31, 2010 consisted of the following:

Millions	September 30, 2011			December 31, 2010
OBH Senior Notes, at face value	$	269.9		$	419.9
Unamortized original issue discount	(.2		)	(.3		)
OBH Senior Notes, carrying value	269.7			419.6

Sirius Group Senior Notes, at face value	400.0			400.0
Unamortized original issue discount	(.7		)	(.8		)
Sirius Group Senior Notes, carrying value	399.3			399.2

WTM Bank Facility	—			—
Total debt	$	669.0		$	818.8

OBH Senior Notes

On April 20, 2011, through a cash tender offer, OneBeacon U.S. Holdings, Inc. (“OBH”) purchased and retired $150.0 million aggregate principal amount of OBH Senior Notes for $161.6 million, which resulted in a $12.0 million loss, including transaction fees.

On June 1, 2010, through a cash tender offer, OBH purchased and retired $156.4 million aggregate principal amount of OBH Senior Notes for an aggregate purchase price of $165.4 million, which resulted in a $9.6 million loss, including transaction fees.

During 2010, in addition to the cash tender offer, OBH repurchased and retired $29.7 million of outstanding OBH Senior Notes for $30.8 million, which resulted in a $1.2 million loss and OBIC purchased $1.1 million of outstanding OBH Senior Notes for $1.1 million.

Bank Facility

On August 12, 2011 White Mountains entered into a new 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. The WTM Bank Facility replaces the previous revolving credit facility which had a total commitment of $475.0 million. As of September 30, 2011, the WTM Bank Facility was undrawn. During the third quarter of 2011, White Mountains recorded $2.2 million of interest expense on the WTM Bank Facility, primarily related to costs associated with entering into the new facility.

Debt Covenants

At September 30, 2011, White Mountains was in compliance with all debt covenants.

- 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

Sep. 30, 2011

Income Taxes

Income Taxes

Note 7. 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, Germany, Gibraltar, Luxembourg, the Netherlands, Singapore, Sweden, Switzerland, the United Kingdom and the United States.

White Mountains’ effective tax rate for the three and nine months of 2011 was not meaningful as pre-tax income was near break-even ($1.2 million and $3.6 million). The effective tax rate differed from the U.S. statutory rate of 35% due to income generated in jurisdictions other than the United States.

White Mountains’ income tax expense for the three months and nine months ended September 30, 2010 represented effective tax rates of 15.6% and 17.9%. The effective tax rate for the three and nine months ended September 30, 2010 was lower than the U.S. statutory rate of 35% due to income generated in jurisdictions other than the United States and recognition of a tax benefit related to the Personal Lines Transaction, partially offset by an increase in the valuation allowance for the insurance reciprocals.

In arriving at the effective tax rate for the three and nine months ended September 30, 2011 and 2010, White Mountains forecasted the change in unrealized investment gains (losses) and realized investment gains (losses) for the years ending December 31, 2011 and 2010 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. In determining whether a valuation allowance, or change therein, is warranted, White Mountains considers factors such as prior earnings history, expected future earnings, carry-back and carry-forward periods and strategies that if executed would result in the realization of a deferred tax asset. As of September 30, 2011, the net U.S. deferred tax assets were $362.6 million which includes $88.2 million recorded as assets held for sale. 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’ valuation allowance on deferred tax assets and tax expense. Utilization of the deferred tax asset is dependent on future profitability and generation of net capital gains.

White Mountains classifies all interest and penalties on unrecognized tax benefits as part of income tax expense. 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 and Esurance. On January 5, 2011, White Mountains received a revised 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 $18.7 million. White Mountains disagrees with the proposed adjustments 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 12 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 on income tax returns for 2007, 2008 and 2009 for certain U.S. subsidiaries of OneBeacon.

On October 26, 2011, Sirius Re Holdings, Inc. (formerly White Mountains Re Holdings, Inc.) received and signed the IRS Revenue Agent’s Report for 2006 - 2007, which contains no proposed adjustments by the Internal Revenue Service.

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.

- 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 SEC
-Name Regulation S-X (SX)
-Number 210
-Section 08
-Paragraph h
-Article 4

Reference 2: 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 3: 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.

Reference 4: http://www.xbrl.org/2003/role/presentationRef
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
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-Paragraph 1
-Subparagraph (SX 210.4-08.(h))
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 740
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 740
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-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319

+ Details

Variable Annuity Reinsurance

9 Months Ended

Sep. 30, 2011

Variable Annuity Reinsurance

Variable Annuity Reinsurance

Note 8. 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, 2011 and December 31, 2010, the total guarantee value was approximately ¥234.5 billion (approximately $3.0 billion at exchange rates on that date) and ¥237.4 billion (approximately $2.9 billion at exchange rates on that date). The collective account values of the underlying variable annuities were approximately 78% and 82% of the guarantee value at September 30, 2011 and December 31, 2010. The following table summarizes the pre-tax operating results of WM Life Re for the three and nine months ended September 30, 2011 and 2010:

	Three Months Ended September 30,						Nine Months Ended September 30,
Millions	2011			2010			2011			2010
Fees, included in other revenues	$	8.4		$	7.7		$	24.3		$	22.3
Change in fair value of variable annuity liability, included in other revenues	(164.4		)	(53.5		)	(148.0		)	(204.7		)
Change in fair value of derivatives, included in other revenues	148.9			(15.7		)	105.4			114.7
Foreign exchange, included in other revenues	14.8			10.4			17.1			16.0
Other investment income and gains (losses)	.5			(.2		)	(.1		)	(.7		)
Total revenues	8.2			(51.3		)	(1.3		)	(52.4		)
Change in fair value of variable annuity death benefit liabilities, included in other expenses	(5.6		)	.3			(3.1		)	(5.8		)
Death benefit claims paid, included in other expenses	(.7		)	(.6		)	(2.4		)	(1.4		)
General and administrative expenses	(1.1		)	(1.4		)	(3.2		)	(5.0		)
Pre-tax income (loss)	$	.8		$	(53.0	)	$	(10.0	)	$	(64.6	)

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

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

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

(1)	Comprises over-the-counter instruments.
(2)	Comprises 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)	Comprises 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 $419.7 at September 30, 2011 posted as collateral to its reinsurance counterparties.

The following summarizes realized and unrealized derivative gains (losses) recognized in other revenues for the three and nine months ended September 30, 2011 and 2010 and the carrying values, included in other assets, at September 30, 2011 and December 31, 2010, by type of instrument:

	Three Months Ended					Nine Months Ended					Carrying Value
	September 30,					September 30,					September 30,		December 31,
Millions	2011		2010			2011		2010			2011		2010
Fixed income/Interest rate	$	29.8	$	(25.5	)	$	17.3	$	(1.9	)	$	50.3	$	43.9
Foreign exchange	63.0		33.0			32.8		99.6			212.0		225.3
Equity	56.1		(23.2		)	55.3		17.0			91.5		78.3
Total	$	148.9	$	(15.7	)	$	105.4	$	114.7		$	353.8	$	347.5

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, 2011		December 31, 2010
Short-term investments	$	72.2	$	52.4
Fixed maturity securities	58.1		48.6
Total	$	130.3	$	101.0

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 provided (held) by WM Life Re and net exposure to credit losses on OTC derivative instruments recorded within other assets:

Millions	September 30, 2011			December 31, 2010
OTC derivative instruments(1)	$	363.4		$	351.5
Collateral held	(130.3		)	(101.0		)
Collateral provided	22.6			25.3
Net exposure to credit losses on fair value of OTC instruments	$	255.7		$	275.8

(1)	Value of OTC derivative instruments as of September 30, 2011 and December 31, 2010 excludes adjustments for counterparty credit risk of $(9.6) and $(4.0) included in fair value under GAAP.

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

Millions	Uncollateralized balance as of September 30, 2011		S&P Rating(1)
Royal Bank of Scotland	$	86.5		A
Bank of America	49.7			A
Citigroup (3)	46.7			A
Barclays	32.2			A+
Nomura	15.6			BBB+
JP Morgan	14.7			A+
BNP Paribas	7.5			AA
Goldman Sachs(2)	2.8			A
Total	$	255.7

(1)

Standard & Poor’s (“S&P”) ratings as detailed above are: “AA” (Very Strong, which is the third highest of twenty-one creditworthiness ratings), “A+” (which is the fifth highest of twenty-one creditworthiness ratings), “A” (which is the sixth highest of twenty-one creditworthiness ratings) and “BBB+” (Adequate, which is the eighth highest of twenty-one 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 comprises the following:

Millions	September 30, 2011		December 31, 2010
Cash	$	393.3	$	291.1
Short-term investments	14.5		31.6
Fixed maturity investments	11.9		3.3
Total	$	419.7	$	326.0

Earnings (Loss) Per Share

9 Months Ended

Sep. 30, 2011

Earnings (Loss) Per Share

Earnings (Loss) Per Share

Note 9. 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, 2011 and 2010 (see Note 14 for earnings per share amounts for discontinued operations):

	Three Months Ended September 30,						Nine Months Ended September 30,
	2011			2010			2011			2010
Basic and diluted earnings per share numerators (in millions):
Net income (loss) attributable to White Mountains’ common shareholders	$	(15.8	)	$	50.7		$	(32.3	)	$	13.6
Less: net (income) loss from discontinued operations	30.1			(3.6		)	28.9			(1.2		)
Net income (loss) attributable to White Mountains’ common shareholders from continuing operations	14.3			47.1			(3.4		)	12.4
Dividends declared and paid	—			—			(8.0		)	(8.8		)
Undistributed earnings (loss)	$	14.3		$	47.1		$	(11.4	)	$	3.6
Basic earnings per share denominators (in thousands):
Average common shares outstanding during the period	7,845			8,332			7,902			8,547
Average unvested restricted shares (1)	74			99			68			97
Basic earnings (loss) per share denominator	7,919			8,431			7,970			8,644
Diluted earnings per share denominator (in thousands):
Average common shares outstanding during the period	7,845			8,332			7,902			8,547
Average unvested restricted shares (1)	74			99			68			97
Average outstanding dilutive options to acquire common shares (2)	—			—			—			1
Diluted earnings (loss) per share denominator	7,919			8,431			7,970			8,645
Basic earnings per share (in dollars):
Net income (loss) attributable to White Mountains’ common shareholders	$	1.81		$	5.58		$	(0.43	)	$	1.44
Dividends declared and paid	—			—			(1.00		)	(1.00		)
Undistributed earnings (loss) per share	$	1.81		$	5.58		$	(1.43	)	$	0.44
Diluted earnings per share (in dollars)
Net income (loss) attributable to White Mountains’ common shareholders	$	1.81		$	5.58		$	(0.43	)	$	1.44
Dividends declared and paid	—			—			(1.00		)	(1.00		)
Undistributed earnings (loss) per share	$	1.81		$	5.58		$	(1.43	)	$	0.44

(1)	Restricted shares outstanding vest either in equal annual installments or upon a stated date (see Note 12).
(2)	The diluted earnings (loss) per share denominator for the three and nine months ended September 30, 2011 and for the three months ended September 30, 2010 does 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 Information

Segment Information

Note 10. Segment Information

White Mountains has determined that its reportable segments are OneBeacon, Sirius Group and Other Operations. As a result of the Esurance Sale, the results of operations for Esurance have been classified as discontinued operations and are now presented, net of related income taxes, in the statement of comprehensive income. In addition, the OneBeacon segment has been presented excluding the results of operations of AutoOne, which has been classified as discontinued operations. Prior year amounts have been reclassified to conform to the current period’s presentation (See Note 14).

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

							Other
Millions	OneBeacon			Sirius Group			Operations			Total
Three months ended September 30, 2011
Earned insurance and reinsurance premiums	$	258.6		$	232.0		$	—		$	490.6
Net investment income	16.1			22.1			4.6			42.8
Net realized and unrealized investment gains (losses)	(47.4		)	64.7			(15.6		)	1.7
Other revenue	.1			(28.1		)	(5.8		)	(33.8		)
Total revenues	227.4			290.7			(16.8		)	501.3
Losses and loss adjustment expenses	146.6			130.5			—			277.1
Insurance and reinsurance acquisition expenses	58.6			48.4			—			107.0
Other underwriting expenses	38.7			28.3			—			67.0
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	250.5			221.1			28.5			500.1
Pre-tax income (loss)	$	(23.1	)	$	69.6		$	(45.3	)	$	1.2

						Other
Millions	OneBeacon		Sirius Group			Operations			Total
Three months ended September 30, 2010
Earned insurance and reinsurance premiums	$	293.6	$	204.5		$	—		$	498.1
Net investment income	21.6		23.0			4.3			48.9
Net realized and unrealized investment gains (losses)	51.6		(51.8		)	11.8			11.6
Other revenue	12.7		43.3			(63.6		)	(7.6		)
Total revenues	379.5		219.0			(47.5		)	551.0
Losses and loss adjustment expenses	155.2		98.2			—			253.4
Insurance and reinsurance acquisition expenses	64.3		37.8			—			102.1
Other underwriting expenses	50.5		24.5			—			75.0
General and administrative expenses	2.1		4.8			25.2			32.1
Interest expense on debt	6.4		6.7			.1			13.2
Total expenses	278.5		172.0			25.3			475.8
Pre-tax income (loss)	$	101.0	$	47.0		$	(72.8	)	$	75.2

							Other
Millions	OneBeacon			Sirius Group			Operations			Total
Nine months ended September 30, 2011
Earned insurance and reinsurance premiums	$	751.2		$	685.5		$	—		$	1,436.7
Net investment income	55.8			68.3			14.0			138.1
Net realized and unrealized investment gains (losses)	(13.3		)	102.6			(11.0		)	78.3
Other revenue	(10.6		)	(55.7		)	(2.3		)	(68.6		)
Total revenues	783.1			800.7			.7			1,584.5
Losses and loss adjustment expenses	414.9			499.1			—			914.0
Insurance and reinsurance acquisition expenses	161.1			135.1			—			296.2
Other underwriting expenses	132.1			79.4			—			211.5
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	731.9			756.5			92.5			1,580.9
Pre-tax income (loss)	$	51.2		$	44.2		$	(91.8	)	$	3.6

					Other
Millions	OneBeacon		Sirius Group		Operations			Total
Nine months ended September 30, 2010
Earned insurance and reinsurance premiums	$	1,134.7	$	638.2	$	—		$	1,772.9
Net investment income	74.9		71.3		11.2			157.4
Net realized and unrealized investment gains (losses)	79.6		13.7		11.4			104.7
Other revenue	1.9		36.4		(59.4		)	(21.1		)
Total revenues	1,291.1		759.6		(36.8		)	2,013.9
Losses and loss adjustment expenses	719.3		456.6		—			1,175.9
Insurance and reinsurance acquisition expenses	248.3		122.6		—			370.9
Other underwriting expenses	176.6		69.3		—			245.9
General and administrative expenses	9.4		23.2		86.9			119.5
Interest expense on debt	23.4		20.1		.7			44.2
Total expenses	1,177.0		691.8		87.6			1,956.4
Pre-tax income (loss)	$	114.1	$	67.8	$	(124.4	)	$	57.5

- 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 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.

Reference 2: 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 3: 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 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9054-108599

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e9031-108599

Reference 6: 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 7: 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 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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-Paragraph 30
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8906-108599

Reference 9: 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 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 29
-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8864-108599

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8380-108599

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8595-108599

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=6534315&loc=d3e8933-108599

+ Details

Investments in Unconsolidated Affiliates

9 Months Ended

Sep. 30, 2011

Investments in Unconsolidated Affiliates

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, 2011		December 31, 2010
Symetra common shares	$	449.0	$	350.4
Symetra warrants	7.7		37.1
Total investment in Symetra	456.7		387.5

Pentelia Capital Management	1.9		2.2
Total investments in unconsolidated affiliates	$	458.6	$	389.7

Symetra

At September 30, 2011 and December 31, 2010, White Mountains owned 17.4 million common shares of 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 and accounts for its Symetra warrants as derivatives with changes in fair value recognized as a gain or loss 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, 2011 were a risk free rate of 0.37%, volatility of 31.64%, an expected life of 2.83 years, a strike price of $11.49 per share and a share price of $8.15 per share.

In January 2010, Symetra completed an initial public offering at a price of $12.00 per share, with 25.3 million shares sold by Symetra and 9.7 million shares sold by existing shareholders. White Mountains did not sell any of its shares in the offering. As a result of the offering, White Mountains’ fully converted ownership in Symetra decreased to approximately 20% during the first quarter of 2010. The issuance of the new Symetra shares at a price below its adjusted book value per share diluted White Mountains’ investment in Symetra’s common shares, resulting in a $16.0 million decrease to White Mountains’ carrying value in Symetra.

The following table summarizes amounts recorded by White Mountains relating to its investment in Symetra for the three months ended September 30, 2011 and 2010:

	Three Months Ended September 30, 2011									Three Months Ended September 30, 2010
	Common									Common
Millions	Shares			Warrants			Total			Shares			Warrants			Total
Carrying value of investment in Symetra as of June 30	$	388.5		$	32.5		$	421.0		$	344.9		$	27.6		$	372.5
Equity in earnings of Symetra (1)	1.6			—			1.6			8.3		(4)	—			8.3
Net unrealized gains from Symetra’s fixed maturity portfolio (2)	59.9			—			59.9			46.9			—			46.9
Dividends received	(1.0		)	—			(1.0		)	(.9		)	—			(.9		)
(Decrease) increase in value of warrants	—			(24.8		)	(24.8		)	—			(10.7		)	(10.7		)
Carrying value of investment in Symetra as September 30 (3)	$	449.0		$	7.7		$	456.7		$	399.2		$	16.9		$	416.1

(1)	Equity in earnings excludes tax expense of $0.1 and $0.7.
(2)	Net unrealized gains excludes tax expense of $4.8 and $3.8.
(3)	Includes White Mountains’ equity in net unrealized gains from Symetra’s fixed maturity portfolio of $147.7 and $120.7 as of September 30, 2011 and 2010, which exclude tax expense of $12.3 and $9.8.
(4)	Includes a $0.1 loss from the dilutive effect of Symetra’s quarterly dividend and the issuance of restricted shares by Symetra.

The following table summarizes amounts recorded by White Mountains relating to its investment in Symetra for the nine months ended September 30, 2011 and 2010:

	Nine Months Ended									Nine Months Ended
	September 30, 2011									September 30, 2010
	Common									Common
Millions	Shares			Warrants			Total			Shares			Warrants			Total
Carrying value of investment in Symetra as of December 31	$	350.4		$	37.1		$	387.5		$	269.2		$	38.5		$	307.7
Equity in earnings of Symetra (1)	17.5			—			17.5			2.1		(4)	—			2.1
Net unrealized gains from Symetra’s fixed maturity portfolio (2)	84.0			—			84.0			129.7		(5)	—			129.7
Dividends received	(2.9		)	—			(2.9		)	(1.8		)	—			(1.8		)
(Decrease) increase in value of warrants	—			(29.4		)	(29.4		)	—			(21.6		)	(21.6		)
Carrying value of investment in Symetra as September 30 (3)	$	449.0		$	7.7		$	456.7		$	399.2		$	16.9		$	416.1

(1)	Equity in earnings excludes tax expense of $1.4 and $0.7.
(2)	Net unrealized gains excludes tax expense of $6.8 and $3.8.
(3)	Includes White Mountains’ equity in net unrealized gains from Symetra’s fixed maturity portfolio of $147.7 and $120.7 as of September 30, 2011 and 2010, which excludes tax expense of $24.2 and $9.8.
(4)	Includes a $17.9 loss from the dilutive effect of Symetra’s initial public offering and a $0.7 loss from the dilutive effect of Symetra’s quarterly dividend and issuance of restricted shares by Symetra.
(5)	Includes a $1.9 gain from the effect of Symetra’s initial public offering.

During the three and nine months ended September 30, 2011, White Mountains received cash dividends from Symetra of $1.0 million and $2.9 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, 2011, White Mountains also received cash dividends from Symetra of $0.6 million and $1.6 million on its investment in Symetra warrants that was recorded in net investment income.

The aggregate value of White Mountains’ investment in common shares of Symetra was $141.8 million based upon the quoted market price of $8.15 at September 30, 2011. White Mountains believes that the difference in the market value and the carrying value of Symetra’s common shares is temporary.

- Definition

The entire disclosure for equity investment, or group of investments, for which combined disclosure is appropriate, including: (a) the name of each investee and percentage of ownership of common stock, (b) accounting policies for investments in common stock, (c) difference between the amount at which the investment is carried and the amount of underlying equity in net assets and the accounting treatment of the difference, (d) the total fair value of each identified investment for which a market value is available, (e) summarized information as to assets, liabilities, and results of operations of the investees (for investments in unconsolidated subsidiaries, common stock of joint ventures, or other investments using the equity method), and (f) material effects of possible conversions, exercises, or contingent issuances of the investee. Other disclosures include (a) the names of any investee in which the investor owns 20 percent or more of the voting stock and investment is not accounted for using the equity method, and the reasons why not, and (b) the names of any investee in which the investor owns less than 20 percent of the voting stock and the investment is accounted for using the equity method, and the reasons why it is.

+ References + Details

Employee Share-Based Incentive Compensation Plans

9 Months Ended

Sep. 30, 2011

Employee Share-Based Incentive Compensation Plans

Employee Share-Based Incentive Compensation Plans

Note 12. 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, 2011 and 2010 for WTM performance shares granted under the WTM Incentive Plan and phantom WTM performance shares granted under subsidiary plans (“WTM Phantom Share Plans”):

	Three Months Ended September 30,								Nine Months Ended September 30,
	2011				2010				2011					2010
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	150,064	$	56.5		163,220		$	20.2	163,184		$	29.4		172,454		$	12.2
Shares expired (1)	—	—			—		—		(51,131	)	—			(49,127	)	—
New grants	—	—			—		—		37,675		—			47,880		—
Assumed forfeitures and cancellations (2)	—	—			(36	)	—		336		(.6		)	(8,023	)	—
Expense recognized	—	(1.0		)	—		3.0		—		26.7			—		11.0
Ending September 30,	150,064	$	55.5		163,184		$	23.2	150,064		$	55.5		163,184		$	23.2

(1) There were no payments made in 2011 and 2010 for the 2008-2010 and 2007-2009 performance cycles; those performance shares did not meet the threshold performance goals and expired.

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

If 100% of the outstanding WTM performance shares had vested on September 30, 2011, the total additional compensation cost to be recognized would have been $23.5 million, based on accrual factors at September 30, 2011 (common share price and payout assumptions).

Performance Shares granted under the WTM Incentive Plan

The following table summarizes WTM performance shares outstanding and accrued expense for WTM performance shares awarded under the WTM Incentive Plan at September 30, 2011 for each performance cycle:

	Target WTM
	Performance
	Shares		Accrued
Millions, except share amounts	Outstanding		Expense
Performance cycle:
2009 – 2011	60,410		$	38.1
2010 – 2012	42,890		7.9
2011 – 2013	37,675		4.5
Sub-total	140,975		50.5
Assumed forfeitures	(3,524	)	(1.3		)
Total at September 30, 2011	137,451		$	49.2

Phantom Performance Shares granted under WTM Phantom Share Plans

The following table summarizes WTM phantom performance shares outstanding and accrued expense for grants made under WTM Phantom Share Plans at September 30, 2011 for each performance cycle:

	Target WTM
	Phantom
	Performance
	Shares		Accrued
Millions, except share amounts	Outstanding		Expense
Performance cycle:
2009 – 2011	7,947		$	5.2
2010 – 2012	4,990		1.2
2011 – 2013(1)	—		—
Sub-total	12,937		6.4
Assumed forfeitures	(324	)	(.1		)
Total at September 30, 2011	12,613		$	6.3

(1) All performance shares for the 2011-2013 performance cycle were granted from the WTM Incentive Plan

Restricted Shares

At September 30, 2011 and 2010, the Company had 73,500 and 98,750 unvested restricted shares outstanding. The following outlines the unrecognized compensation cost associated with the outstanding restricted share awards for the three and nine months ended September 30, 2011 and 2010:

	Three Months Ended September 30,								Nine Months Ended September 30,
	2011				2010				2011				2010
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	73,500	$	18.9		98,750	$	20.9		46,250	$	14.1		91,900		$	23.7
Issued	—	—			—	—			27,250	9.9			19,750		6.7
Vested	—	—			—	—			—	—			(12,650	)	—
Forfeited	—	—			—	—			—	—			(250	)	(.1		)
Modified(1)	—	—			—	—			—	—			—		(3.3		)
Expense recognized	—	(2.8		)	—	(3.3		)	—	(7.9		)	—		(9.4		)
Non-vested at September 30	73,500	$	16.1		98,750	$	17.6		73,500	$	16.1		98,750		$	17.6

(1) During the first quarter of 2007, White Mountains issued 15,000 restricted shares to the Company’s Chairman and CEO in connection with his hiring that would vest in the event of a change in control of the Company before January 20, 2012. During 2010, the Compensation Committee modified the vesting terms so that the 15,000 restricted shares time vest in three equal annual installments beginning on January 20, 2013.

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. As of September 30, 2011, $16.1 million 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 (the “original grant”) that vest 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 (the “Escalator”). The fair value of the Non-Qualified Options was $27.2 million at the grant date. The fair value of the Non-Qualified Options at the grant date was estimated using a closed-form option model using an expected volatility assumption of 29.7%, a risk-free interest rate assumption of 1.1% (or 4.7% less the Escalator), a forfeiture assumption of 0%, an expected dividend rate assumption of 1.4% and a term assumption of seven years.

At the 2010 Annual General Meeting of Members held on May 26, 2010 (the “modification date”), the Company’s shareholders approved the following amendments to the Non-Qualified Options (the “amended grant”): (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 million to 50% of the amount in excess of $100 million. The fair value of the amended grant was $4.4 million at the modification date, while the fair value of the original grant as of the modification date was $3.5 million. The fair value of the amended grant was estimated using a closed-form option model using an expected volatility assumption of 34.0%, a risk-free interest rate assumption of 2.43%, a forfeiture assumption of 0%, an expected dividend rate assumption of 0.32% and a term assumption of 6.67 years. The fair value of the original grant as of the modification date was estimated using a closed-form option model using an expected volatility assumption of 41.0%, a risk-free interest rate assumption of 1.57%, a forfeiture assumption of 0%, an expected dividend rate assumption of 0.32% and a term assumption of 3.67 years.

Prior to the modification, $18.2 million of the original grant fair value had been amortized into income. In connection with the modification, White Mountains recognized $8.7 million of the remaining $9.0 million of unamortized option expense related to the original grant. As of the first quarter in 2011, the Non-Qualified Options have been fully amortized.

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 compared to $10.1 million and $11.5 million of expense in the three and nine months ended September 30, 2010.

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, 2011 and 2010 for OneBeacon performance shares granted under the OneBeacon Incentive Plan:

	Three Months Ended September 30,										Nine Months Ended September 30,
	2011					2010					2011					2010
	Target					Target					Target					Target
	Performance					Performance					Performance					Performance
	Shares		Accrued			Shares		Accrued			Shares		Accrued			Shares		Accrued
Millions, except share amounts	Outstanding		Expense			Outstanding		Expense			Outstanding		Expense			Outstanding		Expense
Beginning of period	671,727		$	10.0		1,770,423		$	15.2		1,464,295		$	18.5		2,224,215		$	15.1
Payments and deferrals (1)(2)	—		—			(199,774	)	(2.2		)	(936,150	)	(10.5		)	(882,118	)	(4.5		)
New awards	—		—			14,618		—			194,900		—			293,478		—
Forfeitures and cancellations	(19,583	)	.1			(20,438	)	(.3		)	(70,901	)	(.2		)	(70,746	)	(.7		)
Expense recognized	—		(.5		)	—		1.7			—		1.8			—		4.5
Ending September 30,	652,144		$	9.6		1,564,829		$	14.4		652,144		$	9.6		1,564,829		$	14.4

(1) OneBeacon performance share payments in 2011 for the 2008-2010 performance cycle were at 68.5% of target. OneBeacon performance shares payments in 2010 for the 2007-2009 performance cycle were at 14.2% 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%.

If 100% of the outstanding OneBeacon performance shares had been vested on September 30, 2011, the total additional compensation cost to be recognized would have been $3.7 million, based on accrual factors at September 30, 2011 (common share price and payout assumptions).

The following table summarizes OneBeacon performance shares outstanding awarded under the OneBeacon Incentive Plan at September 30, 2011 for each performance cycle:

	Target OneBeacon
	Performance
	Shares		Accrued
Millions, except share amounts	Outstanding		Expense
Performance cycle:
2008 – 2010	259,102		$	7.2
2009 – 2011	251,557		1.9
2010 – 2012	151,563		.6
Sub-total	662,222		9.7
Assumed forfeitures	(10,078	)	(.1		)
Total at September 30, 2011	652,144		$	9.6

OneBeacon 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, 2011 and 2010:

	Three Months Ended September 30,								Nine Months Ended September 30,
	2011				2010				2011				2010
Millions, except share amounts	Target Options Outstanding		Expense Amortized		Target Options Outstanding		Expense Amortized		Target Options Outstanding		Expense Amortized		Target Options Outstanding		Expense Amortized
Beginning of period	750,130		$	4.8	879,783		$	4.1	768,652		$	4.5	1,015,610		$	3.6
New awards	—		—		—		—		—		—		—		—
Forfeitures and cancellations	(9,260	)	—		—		—		(27,782	)	—		(37,044	)	—
Vested and expired (1)	—		—		(43,218	)	—		—		—		(142,001	)	—
Exercised	—		—		—		—		—		—		—		—
Expense recognized	—		.1		—		.2		—		.4		—		.7
Ending September 30,	740,870		$	4.9	836,565		$	4.3	740,870		$	4.9	836,565		$	4.3

(1) During the three and nine months ended September 30, 2010, as a result of the Commercial Lines Transaction and the Personal Lines Transaction, 43,218 and 142,001 options vested that were unexercised and expired.

The options vest in equal installments on each of the third, fourth and fifth anniversaries of their issuance and expire 5.5 years from the date of issuance. 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 modification is being recognized ratably over the remaining period.

OneBeacon Restricted Shares

On May 25, 2011, OneBeacon issued 630,000 restricted shares to its CEO that vest one-fourth on each of February 22, 2014, 2015, 2016 and 2017. 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 next 5 years will be reduced by a similar number of shares. The restricted shares contain dividend participation features, and therefore, are considered participating securities. As of September 30, 2011, there were 630,000 unvested restricted shares outstanding. For the three and nine months ended September 30, 2011, OneBeacon recognized $0.4 million and $0.5 million, respectively of expense. As of September 30, 2011, $8.1 million is expected to be recognized ratably over the remaining vesting period.

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 RSUs to actively employed option holders. The RSUs vest one-third on each of 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. Upon vesting, the RSUs are mandatorily deferred into one of OneBeacon’s non-qualified deferred compensation plans and will be paid out in 2012 in cash or shares at the discretion of the OB Compensation Committee. The performance goal for the first and second tranches was attained. The performance goal for the third tranche will be assessed at December 31, 2011. The expense associated with the RSUs is being recognized over the vesting period. OneBeacon recognized no expense for the three months and nine months ended September 30, 2011. For the three and nine months ended September 30, 2010, OneBeacon recognized no expense for the three months ended September 30, 2010 and $0.2 million of expense for the nine months ended September 30, 2010. As of September 30, 2011, there were 22,773 RSUs outstanding.

- 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 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 2: 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.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 14

Reference 4: 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 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 7: 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 8: 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

+ Details

Fair Value of Financial Instruments

9 Months Ended

Sep. 30, 2011

Fair Value of Financial Instruments

Fair Value of Financial Instruments

Note 13. 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 Sirius Group 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, 2011 and December 31, 2010:

September 30, 2011

December 31, 2010

Millions

Fair
Value

Carrying
Value

Fair
Value

Carrying
Value

OBH Senior Notes

276.6

269.7

435.1

419.6

Sirius Group Senior Notes

403.7

399.3

390.9

399.2

Sirius Group Preference Shares

220.0

250.0

212.5

250.0

- 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 Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44A, 44B
-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 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 15C, 15D
-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 FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 15A
-Subparagraph a-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 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 15B
-Subparagraph a, 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 FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 107
-Paragraph 3, 10, 14, 15
-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 157
-Paragraph 32, 33, 34
-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 159
-Paragraph 17-22, 27, 28
-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 Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 11: 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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-Name Accounting Standards Codification
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-SubTopic 10
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-Paragraph 30
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Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
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-Paragraph 16
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Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19296-110258

+ Details

Discontinued Operations

9 Months Ended

Sep. 30, 2011

Discontinued Operations

Discontinued Operations

Note 14. Discontinued Operations

Esurance

On October 7, 2011, White Mountains completed the sale of Esurance Insurance and AFI to The Allstate Corporation (see Note 15). 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. Effective for the nine months ended September 30, 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. The assets and liabilities of the Esurance Disposal Group have been presented in the balance sheet as held for sale. Prior year amounts have been reclassified to conform to the current period’s presentation.

The amounts reflected within discontinued operations differ from amounts previously presented within the Esurance segment. The segment results of operations for Esurance reported in previous periods included investment income and realized and unrealized investment gains and losses allocated to Esurance related to capital that was used by Esurance but contained within Sirius Group’s legal entities. These allocations do not have separately identifiable cash flows and have therefore been excluded from amounts classified in discontinued operations and are now included in the Sirius Group segment. For the three and nine month periods ended September 30, 2011, $0.9 million and $(2.4) million of net investment income and realized and unrealized investment gains and losses that had been previously included in the Esurance segment were excluded from net income (loss) from discontinued operations. For the three and nine month periods ended September 30, 2010, $0.9 million and $3.7 million of net investment income and realized and unrealized investment gains and losses that had been previously included in the Esurance segment were excluded from net income (loss) from discontinued operations.

AutoOne

On August 30, 2011, OneBeacon entered into an agreement to sell the AutoOne business to Interboro. AutoOne operates as a division within OneBeacon, offering products and services to automobile assigned risk markets. The transaction includes the sale of two insurance entities, AOIC and AOSIC, through which substantially all of the AutoOne business is written on a direct basis. For the nine months ended September 30, 2011, 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. Prior year results of operations have been reclassified to conform to the current period’s presentation.

The AutoOne disposal group excludes investing and financing activities from amounts classified as discontinued operations. OneBeacon’s investing and financing operations are conducted on an overall consolidated level and accordingly, there were no separately identifiable cash investing or financing cash flows associated with AutoOne. Prior to the sale of AutoOne, OneBeacon will ensure that the AutoOne legal entities hold an agreed upon level of invested assets and capital. The assets and liabilities associated with the AutoOne business as of September 30, 2011 have been presented in the balance sheet as held for sale sheet assuming the investing and financing steps required to effect the sale were completed as of the current balance sheet date. The prior year balance sheet has not been reclassified to conform to the current period’s presentation because the assets and liabilities associated with AutoOne in the prior year would not provide a meaningful comparison to the assets and liabilities presented as held for sale at September 30, 2011.

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

Millions	September 30, 2011		December 31, 2010
Assets held for sale
Fixed maturity investments, at fair value	$	585.0	$	593.8
Short-term investments, at amortized cost (which approximates fair value)	224.9		131.0
Common equity securities, at fair value	—		43.0
Convertible fixed maturity investments, at fair value	—		17.2
Other long-term investments	—		4.0
Total investments	809.9		789.0
Cash	235.7		39.8
Reinsurance recoverable on paid and unpaid losses	34.6		34.4
Insurance premiums receivable	128.2		102.9
Deferred acquisition costs	42.8		34.7
Deferred tax asset	88.2		67.8
Other assets	60.1		54.2
Total assets held for sale	$	1,399.5	$	1,122.8
Liabilities held for sale
Loss and loss adjustment expense reserves	$	514.9	$	450.4
Unearned insurance premiums	258.3		201.6
Accrued incentive compensation	31.5		19.1
Other liabilities	104.7		80.4
Total liabilities held for sale	909.4		751.5
Net assets held for sale	$	490.1	$	371.3

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

	Three Months Ended September 30,						Nine Months Ended September 30,
Millions, except per share amounts	2011			2010			2011			2010
Revenues
Earned insurance premiums	$	233.8		$	234.6		$	698.7		$	683.6
Net investment income	3.8			5.8			11.8			15.4
Net realized and unrealized investment gains (losses)	(6.4		)	10.4			1.4			17.0
Other revenue	17.5			15.3			52.4			44.7
Total revenues	248.7			266.1			764.3			760.7
Expenses
Loss and loss adjustment expenses	180.5			172.7			518.7			508.0
Insurance and reinsurance acquisition expenses	51.4			50.8			154.5			142.2
Other underwriting expenses	32.3			21.4			76.3			66.9
General and administrative expenses	1.7			12.1			37.5			36.5
Total expenses	265.9			257.0			787.0			753.6
Pre-tax income (loss)	(17.2		)	9.1			(22.7		)	7.1
Income tax (expense) benefit	5.3			(5.5		)	12.0			(5.9		)
Income (loss) from discontinued operations	(11.9		)	3.6			(10.7		)	1.2
Loss from sale of AutoOne, net of tax	(18.2		)	—			(18.2		)	—
Net income (loss) from discontinued operations	$	(30.1	)	$	3.6		$	(28.9	)	$	1.2

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 computation of earnings (loss) per share for discontinued operations for the three and nine months ended September 30, 2011 and 2010:

	Three Months Ended September 30,					Nine Months Ended September 30,
	2011			2010		2011			2010
Basic and diluted earnings (loss) per share numerators (in millions):
Net income (loss)	$	(30.1	)	$	3.6	$	(28.9	)	$	1.2
Basic earnings (loss) per share denominators (in thousands):
Average common shares outstanding during the period	7,845			8,332		7,902			8,547
Average unvested restricted shares	74			99		68			97
Basic earnings (loss) per share denominator	7,919			8,431		7,970			8,644
Diluted earnings (loss) per share denominator (in thousands):
Average common shares outstanding during the period	7,845			8,332		7,902			8,547
Average unvested restricted shares	74			99		68			97
Average outstanding dilutive options to acquire common shares	—			—		—			1
Diluted earnings (loss) per share denominator	7,919			8,431		7,970			8,645
Basic and diluted earnings (loss) per share (in dollars):	$	(3.81	)	$	0.43	$	(3.63	)	$	0.13

- 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 144
-Paragraph 43-48
-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 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6391110&loc=d3e2941-110230

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 1
-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 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1510-107760

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 5
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
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-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6390789&loc=d3e2443-110228

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
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-URI http://asc.fasb.org/extlink&oid=6360339&loc=d3e1436-107760

+ Details

Subsequent Event

9 Months Ended

Sep. 30, 2011

Subsequent Event

Subsequent Event

Note 15. Subsequent Event

Sale of Esurance

On October 7, 2011, White Mountains completed the sale of Esurance Insurance and AFI to The Allstate Corporation for a cash payment of $1.01 billion, which was equal to $700 million plus the estimated pro forma tangible book value at closing of the legal entities sold of approximately $310 million. The final purchase price is subject to true-up of estimated tangible book value of the entities sold through the date of the closing. As a result of the transaction, the Esurance Disposal Group is reported as discontinued operations.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2011

Summary of Significant Accounting Policies

Disclosures about Fair Value Measurements

Transfers of Financial Assets and Amendments to FIN 46R

Goodwill Impairment

Comprehensive Income

Fair Value Measurements and Disclosures

Policy Acquisition Costs

- Definition

Disclosure of accounting policy for transfers and servicing financial assets, including securitization transactions as well as repurchase and resale agreements. This disclosure may include how the entity (1) determines whether a transaction is accounted for as a sale; (2) accounts for a sale transaction, including the initial and subsequent accounting for any interests that the entity obtains or continues to hold in the transaction, how such interests are valued, and the significant assumptions used in the valuation; (3) accounts for a transaction that does not qualify for sale treatment (that is, a financing); and (4) accounts for its servicing assets and liabilities ("servicing"), including how such servicing is measured initially and subsequently, and the methodology and significant assumptions used to value such servicing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Interpretation (FIN)
-Number 41
-Paragraph 3
-Subparagraph a, b, 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 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 140
-Paragraph 17
-Subparagraph 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 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 140
-Paragraph 9-15, 17
-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 FASB
-Name Accounting Standards Codification
-Topic 310
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+ Details

Loss and Loss Adjustment Expense Reserves (Tables)

9 Months Ended

Sep. 30, 2011

Loss and Loss Adjustment Expense Reserves

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

	Three Months Ended September 30,						Nine Months Ended September 30,
Millions	2011			2010			2011			2010
Gross beginning balance	$	5,642.4		$	6,198.1		$	5,736.8		$	6,379.2
Less beginning reinsurance recoverable on unpaid losses	(2,193.0		)	(2,748.3		)	(2,344.0		)	(2,771.5		)
Net loss and LAE reserves	3,449.4			3,449.8			3,392.8			3,607.7

Less: Beginning net loss and LAE reserves for AutoOne (1)	(58.6		)	(81.7		)	(68.2		)	(95.8		)

Loss and LAE reserves acquired — Central National	—			—			—			17.6
Loss and LAE reserves sold — OneBeacon Personal Lines (2)	—			—			—			(231.0		)

Loss and LAE incurred relating to:
Current year losses	307.8			284.7			972.2			1,244.9
Prior year losses	(30.7		)	(31.3		)	(58.2		)	(69.0		)
Total incurred losses and LAE	277.1			253.4			914.0			1,175.9

Accretion of fair value adjustment to loss and LAE reserves	2.1			2.1			6.2			6.3
Foreign currency translation adjustment to loss and LAE reserves	(25.5		)	39.9			5.7			6.7

Loss and LAE paid relating to:
Current year losses	(112.8		)	(156.3		)	(237.9		)	(403.9		)
Prior year losses	(230.9		)	(211.8		)	(711.8		)	(788.1		)
Total loss and LAE payments	(343.7		)	(368.1		)	(949.7		)	(1,192.0		)

Plus: Ending net loss and LAE reserves for AutoOne (1)	—			82.9			—			82.9

Net ending balance	3,300.8			3,378.3			3,300.8			3,378.3
Plus ending reinsurance recoverable on unpaid losses	2,581.2			2,592.1			2,581.2			2,592.1
Gross ending balance	$	5,882.0		$	5,970.4		$	5,882.0		$	5,970.4

(1)	Adjustment is to present loss and LAE reserve activities from continuing operations. At September 30, 2011, loss and LAE reserves for AutoOne have been reclassified as liabilities held for sale. Loss and LAE reserve balances for AutoOne prior to September 30, 2011 were not reclassified. See Note 14.
(2)	In the second quarter of 2010, $231.0 of net loss and LAE reserves related to the Personal Lines Transaction were reclassified to liabilities held for sale. The Personal Lines Transaction closed in July 2010.

Third Party Reinsurance (Tables)

9 Months Ended

Sep. 30, 2011

Third Party Reinsurance

Listing of OneBeacon's top reinsurers

Top Reinsurers (Millions)	Balance at September 30, 2011		% of Total		A.M. Best Rating(1)
National Indemnity Company and General Reinsurance Corporation (2)	$	1,565.2	65	%		A++
Hanover Insurance Company	110.1		5	%		A
Tokio Marine and Nichido Fire (3)	55.8		2	%		A++
Tower Insurance Company	53.7		2	%		A-
Munich Reinsurance America	31.5		1	%		A+

(1)	A.M. Best ratings as detailed above are: “A++” (Superior, which is the highest of fifteen ratings), “A+” (Superior, which is the second highest of fifteen ratings), “A” (Excellent, which is the third highest of fifteen ratings), and “A-” (Excellent, which is the fourth highest of fifteen ratings).
(2)	Includes $198.3 of Third Party Recoverables (as defined below), which NICO (as defined below) would pay under the terms of the NICO Cover (as defined below) if they are unable to collect from third party reinsurers.
(3)	Includes $29.3 of reinsurance recoverables from various third party reinsurers that are guaranteed by Tokio Marine and Nichido Fire under the terms of a 100% quota share reinsurance agreement between Houston General Insurance Company and Tokio Marine and Nichido Fire.

Listing of Sirius Group's top reinsurers

Top Reinsurers (Millions)	Balance at September 30, 2011		% of Total		A.M. Best Rating (1)		% Collateralized
General Reinsurance Corporation	$	43.3	12	%		A++	2	%
Olympus (2)	40.8		11	%		NR-5	100	%
Swiss Re Group	40.0		11	%		A	4	%
Lloyds of London(3)	31.3		9	%		A	6	%
Michigan Catastrophic Claims Association	14.6		4	%		N/A(4)	—	%

(1)	A.M. Best ratings as detailed above are: “NR-5” (Not formally followed), “A++” (Superior, which is the highest of fifteen ratings), and “A” (Excellent, which is the third highest of fifteen ratings).
(2)	Non-U.S. insurance entity. Balances are fully collateralized through funds held, letters of credit or trust agreements.
(3)	Represents the total of reinsurance recoverables due to Sirius Group from all Lloyds Syndicates.
(4)	Michigan Catastrophic Claims Association (“MCCA”) is a non-profit unincorporated association of 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 pursuant to its acquisition of Stockbridge.

Investment Securities (Tables)

9 Months Ended

Sep. 30, 2011

Investment Securities

Net investment income

	Three Months Ended September 30,						Nine Months Ended September 30,
Millions	2011			2010			2011			2010
Investment income:
Fixed maturity investments	$	38.5		$	46.9		$	127.0		$	149.9
Short-term investments	.9			.8			3.2			3.7
Common equity securities	3.6			2.7			10.1			7.1
Convertible fixed maturity investments	1.3			.4			3.9			4.4
Other long-term investments	1.2			1.1			1.9			1.6
Interest on funds held under reinsurance treaties	.2			(.5		)	(.6		)	(2.2		)
Total investment income	45.7			51.4			145.5			164.5
Less third-party investment expenses	(2.9		)	(2.5		)	(7.4		)	(7.1		)
Net investment income, pre-tax	$	42.8		$	48.9		$	138.1		$	157.4

Schedule of Net Realized and Unrealized Investment Gains and Losses

	Three Months Ended September 30,						Nine Months Ended September 30,
Millions	2011			2010			2011			2010
Net realized investment gains (losses), pre-tax	$	37.1		$	31.4		$	109.6		$	93.7
Net unrealized investment gains (losses), pre-tax	(35.4		)	(19.8		)	(31.3		)	11.0
Net realized and unrealized investment gains (losses), pre-tax	1.7			11.6			78.3			104.7
Income taxes attributable to realized and unrealized investment gains (losses)	(1.1		)	(22.7		)	(23.7		)	(24.5		)
Net realized and unrealized investment gains (losses), after-tax	$	.6		$	(11.1	)	$	54.6		$	80.2

Net realized investment gains (losses)

	Three Months Ended September 30,						Nine Months Ended September 30,
Millions	2011			2010			2011			2010
Fixed maturity investments	$	14.0		$	34.7		$	33.6		$	68.1
Short-term investments	—			—			—			—
Common equity securities	23.1			(13.7		)	41.0			6.7
Convertible fixed maturity investments	(.7		)	6.2			6.3			19.9
Other long-term investments	.7			4.2			28.7			(1.0		)
Net realized investment gains (losses), pre-tax	37.1			31.4			109.6			93.7
Income taxes attributable to realized investment gains (losses)	(8.0		)	(4.9		)	(31.7		)	(20.5		)
Net realized investment gains (losses), after-tax	$	29.1		$	26.5		$	77.9		$	73.2

Net unrealized investment gains (losses)

	Three Months Ended September 30, 2011									Nine Months Ended 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 maturities	$	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 gains (losses), pre-tax	(110.0		)	74.6			(35.4		)	(110.3		)	79.0			(31.3		)
Income taxes attributable to unrealized investment gains (losses)	26.4			(19.5		)	6.9			28.5			(20.5		)	8.0
Net unrealized investment gains (losses), after-tax	$	(83.6	)	$	55.1		$	(28.5	)	$	(81.8	)	$	58.5		$	(23.3	)

	Three Months Ended September 30, 2010									Nine Months Ended September 30, 2010
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 maturities	$	3.3		$	(81.2	)	$	(77.9	)	$	36.4		$	(53.6	)	$	(17.2	)
Short-term investments	—			1.4			1.4			—			.6			.6
Common equity securities	64.3			(10.8		)	53.5			31.8			(9.7		)	22.1
Convertible fixed maturity investments	2.8			—			2.8			(8.3		)	—			(8.3		)
Other long-term investments	9.0			(8.6		)	.4			20.5			(6.7		)	13.8
Net unrealized investment gains (losses), pre-tax	79.4			(99.2		)	(19.8		)	80.4			(69.4		)	11.0
Income taxes attributable to unrealized investment gains (losses)	(28.8		)	11.0			(17.8		)	(22.4		)	18.4			(4.0		)
Net unrealized investment gains (losses), after-tax	$	50.6		$	(88.2	)	$	(37.6	)	$	58.0		$	(51.0	)	$	7.0

Net unrealized investment gains (losses) for Level 3 investments

	Three Months Ended September 30,					Nine Months Ended September 30,
Millions	2011			2010		2011			2010
Fixed maturities	$	(13.5	)	$	3.3	$	(14.9	)	$	9.5
Common equity securities	(17.5		)	2.5		(17.0		)	(20.0		)
Convertible fixed maturities	—			—		—			—
Other long-term investments	(3.2		)	8.5		(6.5		)	37.4
Total unrealized investment gains (losses), pre-tax - Level 3 investments	$	(34.2	)	$	14.3	$	(38.4	)	$	26.9

Investment holdings, fixed maturity investments

	September 30, 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	$	347.1	$	5.8	$	(.2	)	$	.4		$	353.1
Debt securities issued by corporations	1,990.0		76.6		(11.9		)	(.8		)	2,053.9
Municipal obligations	2.4		—		—			—			2.4
Mortgage-backed and asset-backed securities	2,200.8		29.8		(4.9		)	14.9			2,240.6
Foreign government, agency and provincial obligations	653.0		14.1		(.2		)	(.9		)	666.0
Preferred stocks	82.3		3.3		(11.0		)	—			74.6
Total fixed maturity investments(1)	$	5,275.6	$	129.6	$	(28.2	)	$	13.6		$	5,390.6

(1) Carrying value includes $102.9 that is classified as assets held for sale relating to AutoOne discontinued operations.

	December 31, 2010
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency gains (losses)			Carrying value
U.S. Government and agency obligations	$	385.9	$	13.6	$	(.8	)	$	—		$	398.7
Debt securities issued by corporations	2,149.2		87.9		(21.1		)	(37.9		)	2,178.1
Municipal obligations	3.3		.1		(.1		)	—			3.3
Mortgage-backed and asset-backed securities	2,082.0		18.2		(15.6		)	(12.9		)	2,071.7
Foreign government, agency and provincial obligations	1,053.6		7.7		(6.6		)	(8.3		)	1,046.4
Preferred stocks	81.9		6.1		—			(.1		)	87.9
Total fixed maturity investments	$	5,755.9	$	133.6	$	(44.2	)	$	(59.2	)	$	5,786.1

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

September 30, 2011

Millions

Cost or
amortized
cost

Gross
unrealized
gains

Gross
unrealized
losses

Net foreign
currency
gains (losses)

Carrying
value

Common equity securities

661.0

35.4

(26.6

)

—

669.8

Convertible fixed maturities

143.7

4.4

(7.6

)

—

140.5

Other long-term investments

290.2

56.2

(15.2

)

(2.4

)

328.8

	December 31, 2010
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency gains (losses)			Carrying value
Common equity securities	$	561.2	$	105.5	$	(1.5	)	$	1.8		$	667.0
Convertible fixed maturities	$	126.9	$	16.2	$	(.1	)	$	—		$	143.0
Other long-term investments	$	329.5	$	62.4	$	(13.0	)	$	(6.8	)	$	372.1

Other long-term investments

	September 30, 2011				December 31, 2010
Millions	Fair Value		Unfunded Commitments		Fair Value		Unfunded Commitments
Hedge funds
Long/short equity	$	49.0	$	—	$	50.4	$	—
Long/short credit & distressed	32.3		—		34.1		—
Long diversified strategies	22.0		—		24.0		—
Long/short equity REIT	14.7		—		25.2		—
Long/short equity activist	11.7		—		16.9		—
Long bank loan	.5		—		5.1		—
Total hedge funds	130.2				155.7		—

Private equity funds
Distressed residential real estate	31.4		—		49.2		—
Energy infrastructure & services	29.5		9.9		24.2		10.8
Multi-sector	28.0		8.2		26.0		10.6
Manufacturing/Industrial	17.0		—		17.9		—
Private equity secondaries	11.3		4.0		10.4		4.4
Real estate	10.2		3.3		9.1		4.6
International multi-sector, Europe	8.0		4.7		10.5		5.3
International multi-sector, Asia	3.6		2.7		4.9		2.7
Insurance	3.6		41.3		3.9		41.3
Venture capital	2.5		.5		2.2		1.0
Healthcare	2.3		7.0		1.5		8.0
Total private equity funds	147.4		81.6		159.8		88.7

Total hedge and private equity funds included in other long-term investments	$	277.6	$	81.6	$	315.5	$	88.7

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	$	—	$	—	$	—	$	6.0	$	6.0
Quarterly	26.1		29.7		19.6		—		75.4
Semi-annual	—		5.1		—		14.7		19.8
Annual	21.9		—		6.6		.5		29.0
Total	$	48.0	$	34.8	$	26.2	$	21.2	$	130.2

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

Millions		1-3 years			3 – 5 years			5 – 10 years			>10 years			Total
Private Equity Funds — expected lock-up period remaining		$	47.3		$	—		$	83.1		$	17.0		$	147.4

Fair value measurements by level, investment securities

	September 30, 2011
Millions	Fair value		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs
Fixed maturities:
US Government and agency obligations	$	353.1	$	343.5	$	9.6	$	—

Debt securities issued by corporations:
Consumer	719.0		—		719.0		—
Industrial	425.3		—		425.3		—
Financials	243.4		5.7		212.2		25.5
Communications	211.0		—		211.0		—
Energy	118.0		—		118.0		—
Basic materials	160.1		—		160.1		—
Utilities	148.3		—		148.3		—
Technology	25.3		—		25.3		—
Diversified	3.5		—		3.5		—
Total debt securities issued by corporations:	2,053.9		5.7		2,022.7		25.5

Municipal obligations	2.4		—		2.4		—
Mortgage-backed and asset-backed securities	2,240.6		—		2,108.7		131.9
Foreign government, agency and provincial obligations	666.0		64.5		601.5		—
Preferred stocks	74.6		—		15.1		59.5
Total fixed maturities(2)	5,390.6		413.7		4,760.0		216.9

Short-term investments	772.8		759.0		13.8		—

Common equity securities:
Financials	191.6		159.4		.5		31.7
Consumer	166.0		164.8		1.2		—
Basic materials	108.4		107.2		1.2		—
Energy	57.5		57.5		—		—
Utilities	40.7		40.7		—		—
Technology	28.6		27.6		1.0		—
Other	77.0		25.3		51.3		.4
Total common equity securities	669.8		582.5		55.2		32.1

Convertible fixed maturity investments	140.5		—		140.5		—
Other long-term investments(1)	292.2		—		—		292.2
Total investments	$	7,265.9	$	1,755.2	$	4,969.5	$	541.2

(1) Excludes carrying value of $36.6 associated with other long-term investment limited partnerships accounted for using the equity method.

(2) Carrying value includes $102.9 that is classified as assets held for sale relating to AutoOne discontinued operations.

	December 31, 2010
Millions	Fair value		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs

Fixed maturities:
US Government and agency obligations	$	398.7	$	388.9	$	9.8	$	—

Debt securities issued by corporations:
Consumer	769.0		—		769.0		—
Industrial	511.3		—		511.3		—
Financials	265.8		6.3		259.5		—
Communications	226.3		—		226.3		—
Basic materials	125.3		—		125.3		—
Utilities	106.7		—		106.7		—
Energy	151.5		—		151.5		—
Technology	22.1		—		22.1		—
Total debt securities issued by corporations:	2,178.0		6.3		2,171.7		—

Municipal obligations	3.3		—		3.3
Mortgage-backed and asset-backed securities	2,071.7		—		2,014.7		57.0
Foreign government, agency and provincial obligations	1,046.5		82.6		963.9		—
Preferred stocks	87.9		—		16.5		71.4
Total fixed maturities	5,786.1		477.8		5,179.9		128.4

Short-term investments	975.3		878.7		96.6		—

Common equity securities:
Financials	221.6		152.6		1.2		67.8
Consumer	123.3		122.5		.8		—
Basic materials	98.8		97.1		1.7		—
Energy	60.2		60.2		—		—
Utilities	47.6		44.6		—		3.0
Technology	31.8		30.4		1.4		—
Other	83.7		30.5		52.8		.4
Total common equity securities	667.0		537.9		57.9		71.2

Convertible fixed maturity investments	143.0		—		143.0		—
Other long-term investments(1)	330.2		—		—		330.2
Total investments	$	7,901.6	$	1,894.4	$	5,477.4	$	529.8

(1) Excludes carrying value of $41.9 associated with other long-term investment limited partnerships accounted for using the equity method.

Debt securities issued by corporations, credit ratings

Millions	September 30, 2011		December 31, 2010
AAA	$	—	$	—
AA	217.4		210.0
A	765.0		833.7
BBB	1,059.8		1,109.1
BB	5.5		24.5
Other	6.2		.7
Debt securities issued by corporations	$	2,053.9	$	2,178.0

Mortgage-backed, asset-backed securities

	September 30, 2011						December 31, 2010
Millions	Fair Value		Level 2		Level 3		Fair Value		Level 2		Level 3
Mortgage-backed securities:
Agency:
GNMA	$	1,268.0	$	1,136.1	$	131.9	$	1,143.6	$	1,102.7	$	40.9
FNMA	268.9		268.9		—		234.9		234.9		—
FHLMC	56.6		56.6		—		39.1		39.1		—
Total Agency(1)	1,593.5		1,461.6		131.9		1,417.6		1,376.7		40.9
Non-agency:
Residential	68.0		68.0		—		90.6		74.5		16.1
Commercial	243.5		243.5		—		87.0		87.0		—
Total Non-agency	311.5		311.5		—		177.6		161.5		16.1

Total mortgage-backed securities	1,905.0		1,773.1		131.9		1,595.2		1,538.2		57.0
Other asset-backed securities:
Credit card receivables	77.5		77.5		—		248.3		248.3		—
Vehicle receivables	235.5		235.5		—		228.1		228.1		—
Other	22.6		22.6		—		.1		.1		—
Total other asset-backed securities	335.6		335.6		—		476.5		476.5		—
Total mortgage and asset-backed securities	$	2,240.6	$	2,108.7	$	131.9	$	2,071.7	$	2,014.7	$	57.0

(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).

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

			Security Issuance Year
Millions	Fair Value		2003		2005		2006		2007		2009		2010		2011
Non-agency RMBS	$	68.0	$	3.7	$	—	$	24.3	$	29.5	$	—	$	10.5	$	—
Non-agency CMBS	243.5		2.4		14.7		—		17.1		11.3		2.2		195.8
Total	$	311.5	$	6.1	$	14.7	$	24.3	$	46.6	$	11.3	$	12.7	$	195.8

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

Millions	Fair Value		Super Senior (1)		Senior (2)		Subordinate(3)
Prime	$	49.9	$	23.2	$	26.7	$	—
Non-prime	18.1		17.2		.9		—
Sub-prime	—		—		—		—
Total	$	68.0	$	40.4	$	27.6	$	—

(1)	At issuance, Super Senior were rated AAA by Standard & Poor’s or Aaa by Moody’s and were senior to other AAA or Aaa bonds.
(2)	At issuance, Senior were rated AAA by Standard & Poor’s or Aaa by Moody’s and were senior to non-AAA or non-Aaa bonds.
(3)	At issuance, Subordinate were not rated AAA by Standard & Poor’s or Aaa by Moody’s and were junior to AAA or Aaa bonds.

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

Millions	Fair Value		Super Senior (1)		Senior(2)		Subordinate(3)
Fixed rate CMBS	$	201.8	$	24.3	$	177.5	$	—
Floating rate CMBS	41.7		31.8		9.9		—
Total	$	243.5	$	56.1	$	187.4	$	—

(1)	At issuance, Super Senior were rated AAA by Standard & Poor’s or Aaa by Moody’s and were senior to other AAA or Aaa bonds.
(2)	At issuance, Senior were rated AAA by Standard & Poor’s or Aaa by Moody’s and were senior to non-AAA or non-Aaa bonds.
(3)	At issuance, Subordinate were not rated AAA by Standard & Poor’s or Aaa by Moody’s and were junior to AAA or Aaa bonds.

Roll forward of fair value investments by level

							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 and other revenue	.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.

Debt (Tables)

9 Months Ended

Sep. 30, 2011

Debt

Schedule of debt outstanding

Millions	September 30, 2011			December 31, 2010
OBH Senior Notes, at face value	$	269.9		$	419.9
Unamortized original issue discount	(.2		)	(.3		)
OBH Senior Notes, carrying value	269.7			419.6

Sirius Group Senior Notes, at face value	400.0			400.0
Unamortized original issue discount	(.7		)	(.8		)
Sirius Group Senior Notes, carrying value	399.3			399.2

WTM Bank Facility	—			—
Total debt	$	669.0		$	818.8

- 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 SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 22
-Article 5

Reference 2: 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 3: 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 4: 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 5: 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 6: 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 7: 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 8: 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 9: 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 10: 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 11: 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

+ Details

Variable Annuity Reinsurance (Tables)

9 Months Ended

Sep. 30, 2011

Variable Annuity Reinsurance

Pre-tax operating results of WM Life Re

	Three Months Ended September 30,						Nine Months Ended September 30,
Millions	2011			2010			2011			2010
Fees, included in other revenues	$	8.4		$	7.7		$	24.3		$	22.3
Change in fair value of variable annuity liability, included in other revenues	(164.4		)	(53.5		)	(148.0		)	(204.7		)
Change in fair value of derivatives, included in other revenues	148.9			(15.7		)	105.4			114.7
Foreign exchange, included in other revenues	14.8			10.4			17.1			16.0
Other investment income and gains (losses)	.5			(.2		)	(.1		)	(.7		)
Total revenues	8.2			(51.3		)	(1.3		)	(52.4		)
Change in fair value of variable annuity death benefit liabilities, included in other expenses	(5.6		)	.3			(3.1		)	(5.8		)
Death benefit claims paid, included in other expenses	(.7		)	(.6		)	(2.4		)	(1.4		)
General and administrative expenses	(1.1		)	(1.4		)	(3.2		)	(5.0		)
Pre-tax income (loss)	$	.8		$	(53.0	)	$	(10.0	)	$	(64.6	)

Changes in White Mountains' variable annuity reinsurance liabilities and derivative instruments

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

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

(1)	Comprises over-the-counter instruments.
(2)	Comprises 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)	Comprises 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 $419.7 at September 30, 2011 posted as collateral to its reinsurance counterparties.

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

Three Months Ended				Nine Months Ended					Carrying Value
	September 30,					September 30,					September 30,		December 31,
Millions	2011		2010			2011		2010			2011		2010
Fixed income/Interest rate	$	29.8	$	(25.5	)	$	17.3	$	(1.9	)	$	50.3	$	43.9
Foreign exchange	63.0		33.0			32.8		99.6			212.0		225.3
Equity	56.1		(23.2		)	55.3		17.0			91.5		78.3
Total	$	148.9	$	(15.7	)	$	105.4	$	114.7		$	353.8	$	347.5

Summary of collateral provided to WM Life Re from counterparties

Millions	September 30, 2011		December 31, 2010
Short-term investments	$	72.2	$	52.4
Fixed maturity securities	58.1		48.6
Total	$	130.3	$	101.0

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

Millions	September 30, 2011			December 31, 2010
OTC derivative instruments(1)	$	363.4		$	351.5
Collateral held	(130.3		)	(101.0		)
Collateral provided	22.6			25.3
Net exposure to credit losses on fair value of OTC instruments	$	255.7		$	275.8

(1)	Value of OTC derivative instruments as of September 30, 2011 and December 31, 2010 excludes adjustments for counterparty credit risk of $(9.6) and $(4.0) included in fair value under GAAP.

Summary of uncollateralized amounts due under WM Life Re's OTC derivative contracts

Millions	Uncollateralized balance as of September 30, 2011		S&P Rating(1)
Royal Bank of Scotland	$	86.5		A
Bank of America	49.7			A
Citigroup (3)	46.7			A
Barclays	32.2			A+
Nomura	15.6			BBB+
JP Morgan	14.7			A+
BNP Paribas	7.5			AA
Goldman Sachs(2)	2.8			A
Total	$	255.7

(1)

(2)

Collateral provided (held) calculated under master netting agreement.

Summary of additional collateral posted for variable reinsurance counterparties

Millions	September 30, 2011		December 31, 2010
Cash	$	393.3	$	291.1
Short-term investments	14.5		31.6
Fixed maturity investments	11.9		3.3
Total	$	419.7	$	326.0

Earnings (Loss) Per Share (Tables)

9 Months Ended

Sep. 30, 2011

Earnings (Loss) Per Share

Computation of earnings per share

	Three Months Ended September 30,						Nine Months Ended September 30,
	2011			2010			2011			2010
Basic and diluted earnings per share numerators (in millions):
Net income (loss) attributable to White Mountains’ common shareholders	$	(15.8	)	$	50.7		$	(32.3	)	$	13.6
Less: net (income) loss from discontinued operations	30.1			(3.6		)	28.9			(1.2		)
Net income (loss) attributable to White Mountains’ common shareholders from continuing operations	14.3			47.1			(3.4		)	12.4
Dividends declared and paid	—			—			(8.0		)	(8.8		)
Undistributed earnings (loss)	$	14.3		$	47.1		$	(11.4	)	$	3.6
Basic earnings per share denominators (in thousands):
Average common shares outstanding during the period	7,845			8,332			7,902			8,547
Average unvested restricted shares (1)	74			99			68			97
Basic earnings (loss) per share denominator	7,919			8,431			7,970			8,644
Diluted earnings per share denominator (in thousands):
Average common shares outstanding during the period	7,845			8,332			7,902			8,547
Average unvested restricted shares (1)	74			99			68			97
Average outstanding dilutive options to acquire common shares (2)	—			—			—			1
Diluted earnings (loss) per share denominator	7,919			8,431			7,970			8,645
Basic earnings per share (in dollars):
Net income (loss) attributable to White Mountains’ common shareholders	$	1.81		$	5.58		$	(0.43	)	$	1.44
Dividends declared and paid	—			—			(1.00		)	(1.00		)
Undistributed earnings (loss) per share	$	1.81		$	5.58		$	(1.43	)	$	0.44
Diluted earnings per share (in dollars)
Net income (loss) attributable to White Mountains’ common shareholders	$	1.81		$	5.58		$	(0.43	)	$	1.44
Dividends declared and paid	—			—			(1.00		)	(1.00		)
Undistributed earnings (loss) per share	$	1.81		$	5.58		$	(1.43	)	$	0.44

(1)	Restricted shares outstanding vest either in equal annual installments or upon a stated date (see Note 12).
(2)	The diluted earnings (loss) per share denominator for the three and nine months ended September 30, 2011 and for the three months ended September 30, 2010 does not include common shares issuable upon exercise of the Non-Qualified Options as they are anti-dilutive to the calculation.

Segment Information (Tables)

9 Months Ended

Sep. 30, 2011

Segment Information

Financial information for White Mountains' segments

							Other
Millions	OneBeacon			Sirius Group			Operations			Total
Three months ended September 30, 2011
Earned insurance and reinsurance premiums	$	258.6		$	232.0		$	—		$	490.6
Net investment income	16.1			22.1			4.6			42.8
Net realized and unrealized investment gains (losses)	(47.4		)	64.7			(15.6		)	1.7
Other revenue	.1			(28.1		)	(5.8		)	(33.8		)
Total revenues	227.4			290.7			(16.8		)	501.3
Losses and loss adjustment expenses	146.6			130.5			—			277.1
Insurance and reinsurance acquisition expenses	58.6			48.4			—			107.0
Other underwriting expenses	38.7			28.3			—			67.0
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	250.5			221.1			28.5			500.1
Pre-tax income (loss)	$	(23.1	)	$	69.6		$	(45.3	)	$	1.2

						Other
Millions	OneBeacon		Sirius Group			Operations			Total
Three months ended September 30, 2010
Earned insurance and reinsurance premiums	$	293.6	$	204.5		$	—		$	498.1
Net investment income	21.6		23.0			4.3			48.9
Net realized and unrealized investment gains (losses)	51.6		(51.8		)	11.8			11.6
Other revenue	12.7		43.3			(63.6		)	(7.6		)
Total revenues	379.5		219.0			(47.5		)	551.0
Losses and loss adjustment expenses	155.2		98.2			—			253.4
Insurance and reinsurance acquisition expenses	64.3		37.8			—			102.1
Other underwriting expenses	50.5		24.5			—			75.0
General and administrative expenses	2.1		4.8			25.2			32.1
Interest expense on debt	6.4		6.7			.1			13.2
Total expenses	278.5		172.0			25.3			475.8
Pre-tax income (loss)	$	101.0	$	47.0		$	(72.8	)	$	75.2

							Other
Millions	OneBeacon			Sirius Group			Operations			Total
Nine months ended September 30, 2011
Earned insurance and reinsurance premiums	$	751.2		$	685.5		$	—		$	1,436.7
Net investment income	55.8			68.3			14.0			138.1
Net realized and unrealized investment gains (losses)	(13.3		)	102.6			(11.0		)	78.3
Other revenue	(10.6		)	(55.7		)	(2.3		)	(68.6		)
Total revenues	783.1			800.7			.7			1,584.5
Losses and loss adjustment expenses	414.9			499.1			—			914.0
Insurance and reinsurance acquisition expenses	161.1			135.1			—			296.2
Other underwriting expenses	132.1			79.4			—			211.5
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	731.9			756.5			92.5			1,580.9
Pre-tax income (loss)	$	51.2		$	44.2		$	(91.8	)	$	3.6

					Other
Millions	OneBeacon		Sirius Group		Operations			Total
Nine months ended September 30, 2010
Earned insurance and reinsurance premiums	$	1,134.7	$	638.2	$	—		$	1,772.9
Net investment income	74.9		71.3		11.2			157.4
Net realized and unrealized investment gains (losses)	79.6		13.7		11.4			104.7
Other revenue	1.9		36.4		(59.4		)	(21.1		)
Total revenues	1,291.1		759.6		(36.8		)	2,013.9
Losses and loss adjustment expenses	719.3		456.6		—			1,175.9
Insurance and reinsurance acquisition expenses	248.3		122.6		—			370.9
Other underwriting expenses	176.6		69.3		—			245.9
General and administrative expenses	9.4		23.2		86.9			119.5
Interest expense on debt	23.4		20.1		.7			44.2
Total expenses	1,177.0		691.8		87.6			1,956.4
Pre-tax income (loss)	$	114.1	$	67.8	$	(124.4	)	$	57.5

- 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, 2011

Investments in Unconsolidated Affiliates

Schedule of investments in unconsolidated affiliates

Millions	September 30, 2011		December 31, 2010
Symetra common shares	$	449.0	$	350.4
Symetra warrants	7.7		37.1
Total investment in Symetra	456.7		387.5

Pentelia Capital Management	1.9		2.2
Total investments in unconsolidated affiliates	$	458.6	$	389.7

Schedule of changes in unconsolidated affiliates

	Three Months Ended September 30, 2011									Three Months Ended September 30, 2010
	Common									Common
Millions	Shares			Warrants			Total			Shares			Warrants			Total
Carrying value of investment in Symetra as of June 30	$	388.5		$	32.5		$	421.0		$	344.9		$	27.6		$	372.5
Equity in earnings of Symetra (1)	1.6			—			1.6			8.3		(4)	—			8.3
Net unrealized gains from Symetra’s fixed maturity portfolio (2)	59.9			—			59.9			46.9			—			46.9
Dividends received	(1.0		)	—			(1.0		)	(.9		)	—			(.9		)
(Decrease) increase in value of warrants	—			(24.8		)	(24.8		)	—			(10.7		)	(10.7		)
Carrying value of investment in Symetra as September 30 (3)	$	449.0		$	7.7		$	456.7		$	399.2		$	16.9		$	416.1

(1)	Equity in earnings excludes tax expense of $0.1 and $0.7.
(2)	Net unrealized gains excludes tax expense of $4.8 and $3.8.
(3)	Includes White Mountains’ equity in net unrealized gains from Symetra’s fixed maturity portfolio of $147.7 and $120.7 as of September 30, 2011 and 2010, which exclude tax expense of $12.3 and $9.8.
(4)	Includes a $0.1 loss from the dilutive effect of Symetra’s quarterly dividend and the issuance of restricted shares by Symetra.

The following table summarizes amounts recorded by White Mountains relating to its investment in Symetra for the nine months ended September 30, 2011 and 2010:

	Nine Months Ended									Nine Months Ended
	September 30, 2011									September 30, 2010
	Common									Common
Millions	Shares			Warrants			Total			Shares			Warrants			Total
Carrying value of investment in Symetra as of December 31	$	350.4		$	37.1		$	387.5		$	269.2		$	38.5		$	307.7
Equity in earnings of Symetra (1)	17.5			—			17.5			2.1		(4)	—			2.1
Net unrealized gains from Symetra’s fixed maturity portfolio (2)	84.0			—			84.0			129.7		(5)	—			129.7
Dividends received	(2.9		)	—			(2.9		)	(1.8		)	—			(1.8		)
(Decrease) increase in value of warrants	—			(29.4		)	(29.4		)	—			(21.6		)	(21.6		)
Carrying value of investment in Symetra as September 30 (3)	$	449.0		$	7.7		$	456.7		$	399.2		$	16.9		$	416.1

(1)	Equity in earnings excludes tax expense of $1.4 and $0.7.
(2)	Net unrealized gains excludes tax expense of $6.8 and $3.8.
(3)	Includes White Mountains’ equity in net unrealized gains from Symetra’s fixed maturity portfolio of $147.7 and $120.7 as of September 30, 2011 and 2010, which excludes tax expense of $24.2 and $9.8.
(4)	Includes a $17.9 loss from the dilutive effect of Symetra’s initial public offering and a $0.7 loss from the dilutive effect of Symetra’s quarterly dividend and issuance of restricted shares by Symetra.
(5)	Includes a $1.9 gain from the effect of Symetra’s initial public offering.

Employee Share-Based Incentive Compensation Plans (Tables)

9 Months Ended

Sep. 30, 2011

Employee Share-Based Incentive Compensation Plans

Summary of performance share activity

	Three Months Ended September 30,								Nine Months Ended September 30,
	2011				2010				2011					2010
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	150,064	$	56.5		163,220		$	20.2	163,184		$	29.4		172,454		$	12.2
Shares expired (1)	—	—			—		—		(51,131	)	—			(49,127	)	—
New grants	—	—			—		—		37,675		—			47,880		—
Assumed forfeitures and cancellations (2)	—	—			(36	)	—		336		(.6		)	(8,023	)	—
Expense recognized	—	(1.0		)	—		3.0		—		26.7			—		11.0
Ending September 30,	150,064	$	55.5		163,184		$	23.2	150,064		$	55.5		163,184		$	23.2

(1) There were no payments made in 2011 and 2010 for the 2008-2010 and 2007-2009 performance cycles; those performance shares did not meet the threshold performance goals and expired.

(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

	Target WTM
	Performance
	Shares		Accrued
Millions, except share amounts	Outstanding		Expense
Performance cycle:
2009 – 2011	60,410		$	38.1
2010 – 2012	42,890		7.9
2011 – 2013	37,675		4.5
Sub-total	140,975		50.5
Assumed forfeitures	(3,524	)	(1.3		)
Total at September 30, 2011	137,451		$	49.2

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

	Target WTM
	Phantom
	Performance
	Shares		Accrued
Millions, except share amounts	Outstanding		Expense
Performance cycle:
2009 – 2011	7,947		$	5.2
2010 – 2012	4,990		1.2
2011 – 2013(1)	—		—
Sub-total	12,937		6.4
Assumed forfeitures	(324	)	(.1		)
Total at September 30, 2011	12,613		$	6.3

(1) All performance shares for the 2011-2013 performance cycle were granted from the WTM Incentive Plan

Summary of restricted share activity

	Three Months Ended September 30,								Nine Months Ended September 30,
	2011				2010				2011				2010
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	73,500	$	18.9		98,750	$	20.9		46,250	$	14.1		91,900		$	23.7
Issued	—	—			—	—			27,250	9.9			19,750		6.7
Vested	—	—			—	—			—	—			(12,650	)	—
Forfeited	—	—			—	—			—	—			(250	)	(.1		)
Modified(1)	—	—			—	—			—	—			—		(3.3		)
Expense recognized	—	(2.8		)	—	(3.3		)	—	(7.9		)	—		(9.4		)
Non-vested at September 30	73,500	$	16.1		98,750	$	17.6		73,500	$	16.1		98,750		$	17.6

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

	Three Months Ended September 30,										Nine Months Ended September 30,
	2011					2010					2011					2010
	Target					Target					Target					Target
	Performance					Performance					Performance					Performance
	Shares		Accrued			Shares		Accrued			Shares		Accrued			Shares		Accrued
Millions, except share amounts	Outstanding		Expense			Outstanding		Expense			Outstanding		Expense			Outstanding		Expense
Beginning of period	671,727		$	10.0		1,770,423		$	15.2		1,464,295		$	18.5		2,224,215		$	15.1
Payments and deferrals (1)(2)	—		—			(199,774	)	(2.2		)	(936,150	)	(10.5		)	(882,118	)	(4.5		)
New awards	—		—			14,618		—			194,900		—			293,478		—
Forfeitures and cancellations	(19,583	)	.1			(20,438	)	(.3		)	(70,901	)	(.2		)	(70,746	)	(.7		)
Expense recognized	—		(.5		)	—		1.7			—		1.8			—		4.5
Ending September 30,	652,144		$	9.6		1,564,829		$	14.4		652,144		$	9.6		1,564,829		$	14.4

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

	Target OneBeacon
	Performance
	Shares		Accrued
Millions, except share amounts	Outstanding		Expense
Performance cycle:
2008 – 2010	259,102		$	7.2
2009 – 2011	251,557		1.9
2010 – 2012	151,563		.6
Sub-total	662,222		9.7
Assumed forfeitures	(10,078	)	(.1		)
Total at September 30, 2011	652,144		$	9.6

Summary of OneBeacon option activity

	Three Months Ended September 30,								Nine Months Ended September 30,
	2011				2010				2011				2010
Millions, except share amounts	Target Options Outstanding		Expense Amortized		Target Options Outstanding		Expense Amortized		Target Options Outstanding		Expense Amortized		Target Options Outstanding		Expense Amortized
Beginning of period	750,130		$	4.8	879,783		$	4.1	768,652		$	4.5	1,015,610		$	3.6
New awards	—		—		—		—		—		—		—		—
Forfeitures and cancellations	(9,260	)	—		—		—		(27,782	)	—		(37,044	)	—
Vested and expired (1)	—		—		(43,218	)	—		—		—		(142,001	)	—
Exercised	—		—		—		—		—		—		—		—
Expense recognized	—		.1		—		.2		—		.4		—		.7
Ending September 30,	740,870		$	4.9	836,565		$	4.3	740,870		$	4.9	836,565		$	4.3

Fair Value of Financial Instruments (Tables)

9 Months Ended

Sep. 30, 2011

Fair Value of Financial Instruments

Summary of the fair value and carrying value of financial instruments

September 30, 2011

December 31, 2010

Millions

Fair
Value

Carrying
Value

Fair
Value

Carrying
Value

OBH Senior Notes

276.6

269.7

435.1

419.6

Sirius Group Senior Notes

403.7

399.3

390.9

399.2

Sirius Group Preference Shares

220.0

250.0

212.5

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 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.

Reference 2: 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 3: 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 4: 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 5: 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 6: 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 7: http://www.xbrl.org/2003/role/presentationRef
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Reference 12: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6447952&loc=d3e13220-108610

+ Details

Discontinued Operations (Tables)

9 Months Ended

Sep. 30, 2011

Discontinued Operations

Schedule of discontinued operations balance sheet

Millions	September 30, 2011		December 31, 2010
Assets held for sale
Fixed maturity investments, at fair value	$	585.0	$	593.8
Short-term investments, at amortized cost (which approximates fair value)	224.9		131.0
Common equity securities, at fair value	—		43.0
Convertible fixed maturity investments, at fair value	—		17.2
Other long-term investments	—		4.0
Total investments	809.9		789.0
Cash	235.7		39.8
Reinsurance recoverable on paid and unpaid losses	34.6		34.4
Insurance premiums receivable	128.2		102.9
Deferred acquisition costs	42.8		34.7
Deferred tax asset	88.2		67.8
Other assets	60.1		54.2
Total assets held for sale	$	1,399.5	$	1,122.8
Liabilities held for sale
Loss and loss adjustment expense reserves	$	514.9	$	450.4
Unearned insurance premiums	258.3		201.6
Accrued incentive compensation	31.5		19.1
Other liabilities	104.7		80.4
Total liabilities held for sale	909.4		751.5
Net assets held for sale	$	490.1	$	371.3

Schedule of discontinued operations income statement

	Three Months Ended September 30,						Nine Months Ended September 30,
Millions, except per share amounts	2011			2010			2011			2010
Revenues
Earned insurance premiums	$	233.8		$	234.6		$	698.7		$	683.6
Net investment income	3.8			5.8			11.8			15.4
Net realized and unrealized investment gains (losses)	(6.4		)	10.4			1.4			17.0
Other revenue	17.5			15.3			52.4			44.7
Total revenues	248.7			266.1			764.3			760.7
Expenses
Loss and loss adjustment expenses	180.5			172.7			518.7			508.0
Insurance and reinsurance acquisition expenses	51.4			50.8			154.5			142.2
Other underwriting expenses	32.3			21.4			76.3			66.9
General and administrative expenses	1.7			12.1			37.5			36.5
Total expenses	265.9			257.0			787.0			753.6
Pre-tax income (loss)	(17.2		)	9.1			(22.7		)	7.1
Income tax (expense) benefit	5.3			(5.5		)	12.0			(5.9		)
Income (loss) from discontinued operations	(11.9		)	3.6			(10.7		)	1.2
Loss from sale of AutoOne, net of tax	(18.2		)	—			(18.2		)	—
Net income (loss) from discontinued operations	$	(30.1	)	$	3.6		$	(28.9	)	$	1.2

Discontinued operations, computation of earnings per share

	Three Months Ended September 30,					Nine Months Ended September 30,
	2011			2010		2011			2010
Basic and diluted earnings (loss) per share numerators (in millions):
Net income (loss)	$	(30.1	)	$	3.6	$	(28.9	)	$	1.2
Basic earnings (loss) per share denominators (in thousands):
Average common shares outstanding during the period	7,845			8,332		7,902			8,547
Average unvested restricted shares	74			99		68			97
Basic earnings (loss) per share denominator	7,919			8,431		7,970			8,644
Diluted earnings (loss) per share denominator (in thousands):
Average common shares outstanding during the period	7,845			8,332		7,902			8,547
Average unvested restricted shares	74			99		68			97
Average outstanding dilutive options to acquire common shares	—			—		—			1
Diluted earnings (loss) per share denominator	7,919			8,431		7,970			8,645
Basic and diluted earnings (loss) per share (in dollars):	$	(3.81	)	$	0.43	$	(3.63	)	$	0.13

Summary of Significant Accounting Policies (Details) $ / shares in Units, $ in Millions	1 Months Ended
	May 31, 2007 USD ($) shares	Sep. 30, 2011 USD ($) state	May 25, 2011 shares	Dec. 31, 2010 USD ($)	May 24, 2007 USD ($) $ / shares
Basis of Presentation
Number of states in which Esurance insurance directly writes insurance \| state		30
Noncontrolling equity interest		$ 54.6		$ 62.8
OneBeacon Restricted Stock \| Chairman and CEO \| OneBeacon Long-Term Incentive Plan
Basis of Presentation
Issuance of restricted common shares (in shares) \| shares			630,000
OneBeacon Ltd.
Basis of Presentation
Ownership percentage of OneBeacon Ltd.'s outstanding common shares (as a percent)		75.50%		76.00%
Noncontrolling ownership percentage in OneBeacon Ltd (as a percent)		24.50%		24.00%
Sirius Group \| Non-cumulative perpetual preference shares
Basis of Presentation
Non-cumulative perpetual preference shares issued (in shares) \| shares	250,000
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
Tuckerman Fund I, the Prospector Offshore Fund and the Prospector Turtle Fund
Basis of Presentation
Noncontrolling equity interest		$ 51.8		$ 59.7
A.W.G. Dewar Inc
Basis of Presentation
Noncontrolling equity interest		$ 2.2		$ 3.1

Summary of Significant Accounting Policies (Details 2) $ in Millions	9 Months Ended
	Sep. 30, 2011 USD ($)
Cumulative-Effect Adjustment, Deconsolidation of Variable Interest Entity \| Tuckerman Fund II
New Accounting Pronouncements or Change in Accounting Principle
Decrease in opening retained earnings	$ 0.4

- Definition

Amount of the cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 154
-Paragraph 2, 17, 18
-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 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=6801783&loc=d3e22499-107794

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6801783&loc=d3e22580-107794

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Indirect Effects of a Change in Accounting Principle
-URI http://asc.fasb.org/extlink&oid=6515603

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Accounting Change
-URI http://asc.fasb.org/extlink&oid=6503790

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Change in Accounting Principle
-URI http://asc.fasb.org/extlink&oid=6507316

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Direct Effects of a Change in Accounting Principle
-URI http://asc.fasb.org/extlink&oid=6510796

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6801783&loc=d3e22583-107794

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Retrospective Application
-URI http://asc.fasb.org/extlink&oid=6523989

+ Details

Significant Transactions (Details) - Tender Offer $ / shares in Units, $ in Millions	1 Months Ended
	Sep. 30, 2011 USD ($) $ / shares shares
Significant Transactions
Shares purchased under tender offer (in shares) \| shares	327,872
Value of shares purchased under tender offer (in dollars per share) \| $ / shares	$ 415
Value of shares purchased under tender offer	$ 136.5
Fees and expenses related to the tender offer	$ 0.4

Significant Transactions (Details 2) $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
Significant Transactions (Details 2) $ in Millions	Jul. 31, 2010 USD ($) company attorney year	Sep. 30, 2011 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2010 USD ($)
Significant Transactions
Consideration from sale of business				$ 166.6
Net loss on sale of discontinued operation - AutoOne		$ 18.2	$ 18.2
OneBeacon Personal Lines
Significant Transactions
Consideration from sale of business	$ 166.6
Number of insurance companies sold \| company	2
Ceded share of traditional personal lines business (as a percent)		100.00%	100.00%
Assumed risk, non-traditional personal lines business written by York (as a percent)		100.00%	100.00%
Number of attorneys-in-fact sold \| attorney	2
Period to provide certain services to Tower (in years) \| year	3
AutoOne
Significant Transactions
Net loss on sale of discontinued operation - AutoOne		$ 18.2	$ 18.2

Significant Transactions (Details 3) - Central National - USD ($) $ in Millions	1 Months Ended
	Feb. 28, 2010	Feb. 26, 2010
Business acquisition
Cash to be paid on acquisition		$ 5.0
Gain on acquisition	$ 12.8

- Definition

In a business combination in which the amount of net identifiable assets acquired and liabilities assumed exceeds the aggregate consideration transferred or to be transferred (as defined), this element represents the amount of gain recognized by the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141R
-Paragraph 68
-Subparagraph o(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 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141R
-Paragraph 36, 37, 38
-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 FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6571-128477

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6527-128477

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 25
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6387-128476

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 25
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6393-128476

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 25
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6396-128476

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (f)(1)
-URI http://asc.fasb.org/extlink&oid=6911361&loc=d3e6927-128479

+ Details

Loss and Loss Adjustment Expense Reserves (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Loss and Loss Adjustment Expense Reserves
Gross beginning balance	$ 5,642.4	$ 6,198.1	$ 5,736.8	$ 6,379.2
Less beginning reinsurance recoverable on unpaid losses	(2,193.0)	(2,748.3)	(2,344.0)	(2,771.5)
Net loss and LAE reserves	3,449.4	3,449.8	3,392.8	3,607.7
Loss and LAE reserves acquired - Central National				17.6
Loss and LAE reserves sold - One Beacon Personal Lines				(231.0)
Loss and LAE incurred relating to Current year losses	307.8	284.7	972.2	1,244.9
Loss and LAE incurred relating to Prior year losses	(30.7)	(31.3)	(58.2)	(69.0)
Total incurred losses and LAE	277.1	253.4	914.0	1,175.9
Accretion of fair value adjustment to loss and LAE reserves	2.1	2.1	6.2	6.3
Foreign currency translation adjustment to loss and LAE reserves	(25.5)	39.9	5.7	6.7
Loss and LAE paid relating to Current year losses	(112.8)	(156.3)	(237.9)	(403.9)
Loss and LAE paid relating to Prior year losses	(230.9)	(211.8)	(711.8)	(788.1)
Total loss and LAE payments	(343.7)	(368.1)	(949.7)	(1,192.0)
Net ending balance	3,300.8	3,378.3	3,300.8	3,378.3
Plus ending reinsurance recoverable on unpaid losses	(2,581.2)	(2,592.1)	(2,581.2)	(2,592.1)
Gross ending balance	5,882.0	5,970.4	5,882.0	5,970.4
Net favorable loss reserve development	30.7	31.3	58.2	69.0
Pre-tax un-accreted adjustment			14.9
OneBeacon Segment
Loss and Loss Adjustment Expense Reserves
Loss and LAE incurred relating to Prior year losses	(9.8)	(17.8)	(25.0)	(42.1)
Net favorable loss reserve development	9.8	17.8	25.0	42.1
AutoOne
Loss and Loss Adjustment Expense Reserves
Net loss and LAE reserves	58.6	68.2	81.7	95.8
Net ending balance		82.9		82.9
Sirius Group.
Loss and Loss Adjustment Expense Reserves
Loss and LAE incurred relating to Prior year losses	(20.9)	(13.5)	(33.2)	(26.9)
Total incurred losses and LAE	130.5	98.2	499.1	456.6
Plus ending reinsurance recoverable on unpaid losses	(342.1)		(342.1)
Net favorable loss reserve development	$ 20.9	$ 13.5	$ 33.2	$ 26.9

Third Party Reinsurance (Details) $ in Millions	1 Months Ended	3 Months Ended	6 Months Ended	9 Months Ended	121 Months Ended
Third Party Reinsurance (Details) $ in Millions	May 31, 2001 USD ($) contract	Sep. 30, 2011 USD ($) rating	Jun. 30, 2010 USD ($)	Sep. 30, 2011 USD ($) rating	Jun. 30, 2011 USD ($)	Dec. 31, 2010 USD ($)	Sep. 30, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2007 USD ($)
Third party reinsurance
Reinsurance recoverable on paid losses		$ 30.9		$ 30.9		$ 63.1
Reinsurance recoverable on unpaid losses		$ 2,581.2	$ 2,748.3	$ 2,581.2	$ 2,193.0	$ 2,344.0	$ 2,592.1	$ 2,771.5
Number of ratings in A.M. Best ratings \| rating		15		15
OneBeacon
Third party reinsurance
Reinsurance recoverable on paid losses		$ 13.7		$ 13.7
Reinsurance recoverable on unpaid losses		2,405.7		2,405.7
Purchase accounting adjustments		$ 166.6		$ 166.6
Number of reinsurance contracts the seller caused OneBeacon to purchase immediately prior to the entity's acquisition of OneBeacon \| contract	2
OneBeacon \| Northeast homeowners business
Third party reinsurance
The percentage ceded under quota share reinsurance agreement (as a percent)				30.00%
Premiums ceded under quota share agreement			$ 25.6
OneBeacon \| Property catastrophe reinsurance program
Third party reinsurance
Maximum amount of loss on a single catastrophe retained, first layer				$ 50.0
Amount of loss on a single catastrophe reinsured, second layer				$ 175.0
First retention percentage of loss on a single catastrophe reinsured, second layer (as a percent)		26.00%		26.00%
Amount of loss on a single catastrophe reinsured, first retention slab for second layer, low end of range				$ 50.0
Amount of loss on a single catastrophe reinsured, first retention slab for second layer, high end of range				$ 100.0
Second retention percentage of loss on a single catastrophe reinsured, second layer (as a percent)		10.00%		10.00%
Amount of loss on a single catastrophe reinsured, second retention slab for second layer, low end of range				$ 100.0
Amount of loss on a single catastrophe reinsured, second retention slab for second layer, high end of range				175.0
Minimum amount of loss on a single catastrophe retained, third layer				$ 225.0
OneBeacon \| National Indemnity Company and General Reinsurance Corporation
Third party reinsurance
Percentage of total paid and unpaid reinsurance recoverables (as a percent)		65.00%		65.00%
Reinsurance recoverables		$ 1,565.2		$ 1,565.2
OneBeacon \| National Indemnity Company \| NICO Cover
Third party reinsurance
Third party recoverables which reinsurer would pay if they are unable to collect from third party reinsurers		198.3		198.3
Maximum cover under reinsurance contract		2,500.0		2,500.0
Utilized coverage from NICO					2,300.0
Reinsurance receivables paid by the reinsurer					$ 1,400.0
Percentage of utilized coverage from NICO that relates to uncollectible Third Party Recoverables (as a percent)					8.00%
Utilized coverage from NICO that relates to uncollectible Third Party Recoverables					$ 187.7
Ceded estimated incurred losses		2,300.0		2,300.0					$ 2,200.0
OneBeacon \| General Reinsurance Corporation \| GRC Cover
Third party reinsurance
Maximum cover under reinsurance contract	$ 570.0
Adverse loss reserve development on losses occurring in years 2000 and prior	400.0
Reserves ceded as of the date of the OneBeacon acquisition	$ 170.0
Reinsurance receivables paid by the reinsurer		$ 13.6		$ 60.7
OneBeacon \| Tower Insurance Company
Third party reinsurance
Percentage of total paid and unpaid reinsurance recoverables (as a percent)		2.00%		2.00%
Reinsurance recoverables		$ 53.7		$ 53.7
OneBeacon \| Tokio Marine and Nichido Fire
Third party reinsurance
Percentage of total paid and unpaid reinsurance recoverables (as a percent)		2.00%		2.00%
Reinsurance recoverables		$ 55.8		$ 55.8
Reinsurance recoverable from various third party reinsurers, guaranteed by the third party reinsurer under reinsurance agreement		$ 29.3		$ 29.3
The percentage ceded under quota share reinsurance agreement (as a percent)		100.00%		100.00%
OneBeacon \| Hanover Insurance Company
Third party reinsurance
Percentage of total paid and unpaid reinsurance recoverables (as a percent)		5.00%		5.00%
Reinsurance recoverables		$ 110.1		$ 110.1
OneBeacon \| Munich Reinsurance America
Third party reinsurance
Percentage of total paid and unpaid reinsurance recoverables (as a percent)		1.00%		1.00%
Reinsurance recoverables		$ 31.5		$ 31.5
Sirius Group.
Third party reinsurance
Reinsurance recoverable on paid losses		17.2		17.2
Reinsurance recoverable on unpaid losses		$ 342.1		$ 342.1
Sirius Group. \| General Reinsurance Corporation
Third party reinsurance
Percentage of total paid and unpaid reinsurance recoverables (as a percent)		12.00%		12.00%
Reinsurance recoverables		$ 43.3		$ 43.3
Percentage collateralized (as a percent)		2.00%		2.00%
Sirius Group. \| Lloyds of London
Third party reinsurance
Percentage of total paid and unpaid reinsurance recoverables (as a percent)		9.00%		9.00%
Reinsurance recoverables		$ 31.3		$ 31.3
Percentage collateralized (as a percent)		6.00%		6.00%
Sirius Group. \| Olympus
Third party reinsurance
Percentage of total paid and unpaid reinsurance recoverables (as a percent)		11.00%		11.00%
Reinsurance recoverables		$ 40.8		$ 40.8
Percentage collateralized (as a percent)		100.00%		100.00%
Sirius Group. \| Swiss Re Group
Third party reinsurance
Percentage of total paid and unpaid reinsurance recoverables (as a percent)		11.00%		11.00%
Reinsurance recoverables		$ 40.0		$ 40.0
Percentage collateralized (as a percent)		4.00%		4.00%
Sirius Group. \| Michigan Catastrophic Claims Association
Third party reinsurance
Percentage of total paid and unpaid reinsurance recoverables (as a percent)		4.00%		4.00%
Reinsurance recoverables		$ 14.6		$ 14.6

Investment Securities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Investment Securities (Details) - USD ($) $ in Millions	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Investment income
Total investment income	$ 45.7	$ 51.4	$ 145.5	$ 164.5
Third-party investment expenses	(2.9)	(2.5)	(7.4)	(7.1)
Net investment income, pre-tax	42.8	48.9	138.1	157.4
Fixed maturity investments
Investment income
Total investment income	38.5	46.9	127.0	149.9
Short-term investments
Investment income
Total investment income	0.9	0.8	3.2	3.7
Equity security investments
Investment income
Total investment income	3.6	2.7	10.1	7.1
Convertible fixed maturity investments
Investment income
Total investment income	1.3	0.4	3.9	4.4
Other long-term investments.
Investment income
Total investment income	1.2	1.1	1.9	1.6
Interest on funds held under reinsurance treaties
Investment income
Total investment income	$ 0.2	$ (0.5)	$ (0.6)	$ (2.2)

Investment Securities (Details 2) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Investment Securities (Details 2) - USD ($) $ in Millions	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Net Realized and Unrealized Investment Gains and Losses
Net realized investment gains (losses), pre-tax	$ 37.1	$ 31.4	$ 109.6	$ 93.7
Net unrealized investment gains (losses), pre-tax	(35.4)	(19.8)	(31.3)	11.0
Net realized and unrealized investment gains (losses), pre-tax	1.7	11.6	78.3	104.7
Income taxes attributable to realized and unrealized investment gains (losses)	(1.1)	(22.7)	(23.7)	(24.5)
Net realized and unrealized investment gains (losses), after-tax	0.6	(11.1)	54.6	80.2
Net realized investment gains (losses)
Net realized investment gains (losses), pre-tax	37.1	31.4	109.6	93.7
Income taxes attributable to realized investment gains (losses)	(8.0)	(4.9)	(31.7)	(20.5)
Net realized investment gains (losses), after-tax	29.1	26.5	77.9	73.2
Net unrealized investment gains (losses)
Net unrealized gains (losses), pre-tax	(110.0)	79.4	(110.3)	80.4
Income taxes attributable to unrealized investment gains (losses)	26.4	(28.8)	28.5	(22.4)
Net unrealized investment gains (losses), after-tax	(83.6)	50.6	(81.8)	58.0
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	74.6	(99.2)	79.0	(69.4)
Income taxes attributable to unrealized investment gains, net foreign exchange gains (losses)	(19.5)	11.0	(20.5)	18.4
Net unrealized investment gains (losses), net foreign exchange gains (losses), after tax	55.1	(88.2)	58.5	(51.0)
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings	(35.4)	(19.8)	(31.3)	11.0
Income taxes attributable to unrealized investment gains (losses), total changes in fair value reflected in earnings	6.9	(17.8)	8.0	(4.0)
Net unrealized investment gains (losses) after-tax, total changes in fair value reflected in earnings	(28.5)	(37.6)	(23.3)	7.0
Fixed maturity investments
Net Realized and Unrealized Investment Gains and Losses
Net realized investment gains (losses), pre-tax	14.0	34.7	33.6	68.1
Net unrealized investment gains (losses), pre-tax	71.0	(77.9)	90.3	(17.2)
Net realized investment gains (losses)
Net realized investment gains (losses), pre-tax	14.0	34.7	33.6	68.1
Net unrealized investment gains (losses)
Net unrealized gains (losses), pre-tax	3.5	3.3	12.6	36.4
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	67.5	(81.2)	77.7	(53.6)
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings	71.0	(77.9)	90.3	(17.2)
Short-term investments
Net Realized and Unrealized Investment Gains and Losses
Net unrealized investment gains (losses), pre-tax	(0.5)	1.4	(1.5)	0.6
Net unrealized investment gains (losses)
Net unrealized gains (losses), pre-tax	(0.1)		(0.1)
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	(0.4)	1.4	(1.4)	0.6
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings	(0.5)	1.4	(1.5)	0.6
Common Equity Securities
Net Realized and Unrealized Investment Gains and Losses
Net realized investment gains (losses), pre-tax	23.1	(13.7)	41.0	6.7
Net unrealized investment gains (losses), pre-tax	(101.9)	53.5	(96.9)	22.1
Net realized investment gains (losses)
Net realized investment gains (losses), pre-tax	23.1	(13.7)	41.0	6.7
Net unrealized investment gains (losses)
Net unrealized gains (losses), pre-tax	(101.0)	64.3	(95.1)	31.8
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	(0.9)	(10.8)	(1.8)	(9.7)
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings	(101.9)	53.5	(96.9)	22.1
Convertible fixed maturity investments
Net Realized and Unrealized Investment Gains and Losses
Net realized investment gains (losses), pre-tax	(0.7)	6.2	6.3	19.9
Net unrealized investment gains (losses), pre-tax	(11.2)	2.8	(19.3)	(8.3)
Net realized investment gains (losses)
Net realized investment gains (losses), pre-tax	(0.7)	6.2	6.3	19.9
Net unrealized investment gains (losses)
Net unrealized gains (losses), pre-tax	(11.2)	2.8	(19.3)	(8.3)
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings	(11.2)	2.8	(19.3)	(8.3)
Other long-term investments.
Net Realized and Unrealized Investment Gains and Losses
Net realized investment gains (losses), pre-tax	0.7	4.2	28.7	(1.0)
Net unrealized investment gains (losses), pre-tax	7.2	0.4	(3.9)	13.8
Net realized investment gains (losses)
Net realized investment gains (losses), pre-tax	0.7	4.2	28.7	(1.0)
Net unrealized investment gains (losses)
Net unrealized gains (losses), pre-tax	(1.2)	9.0	(8.4)	20.5
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	8.4	(8.6)	4.5	(6.7)
Net unrealized investment gains (losses) pre-tax, total changes in fair value reflected in earnings	$ 7.2	$ 0.4	$ (3.9)	$ 13.8

Investment Securities (Details 3) - Level 3 Inputs - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	$ (34.2)	$ 14.3	$ (38.4)	$ 26.9
Fixed maturity investments
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	(13.5)	3.3	(14.9)	9.5
Common Equity Securities
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	(17.5)	2.5	(17.0)	(20.0)
Other long-term investments.
Investment securities
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	$ (3.2)	$ 8.5	$ (6.5)	$ 37.4

Investment Securities (Details 4) - USD ($) $ in Millions	Sep. 30, 2011	Dec. 31, 2010
Investment securities
Cost or amortized cost	$ 5,275.6	$ 5,755.9
Gross unrealized gains	129.6	133.6
Gross unrealized losses	(28.2)	(44.2)
Net foreign currency gains (losses)	13.6	(59.2)
Fixed maturity investments, at fair value	5,287.7	5,786.1
Fixed maturity investments, at fair value	5,390.6
Carrying value, common equity securities	669.8	667.0
Carrying value, other long-term investments	328.8	372.1
Carrying value, convertible fixed securities	140.5	143.0
AutoOne investments that are reclassified to assets held for sale	102.9
U.S. Government and agency obligations
Investment securities
Cost or amortized cost	347.1	385.9
Gross unrealized gains	5.8	13.6
Gross unrealized losses	(0.2)	(0.8)
Net foreign currency gains (losses)	0.4
Fixed maturity investments, at fair value	353.1	398.7
Debt securities issued by corporations
Investment securities
Cost or amortized cost	1,990.0	2,149.2
Gross unrealized gains	76.6	87.9
Gross unrealized losses	(11.9)	(21.1)
Net foreign currency gains (losses)	(0.8)	(37.9)
Fixed maturity investments, at fair value	2,053.9	2,178.1
Municipal obligations
Investment securities
Cost or amortized cost	2.4	3.3
Gross unrealized gains		0.1
Gross unrealized losses		(0.1)
Fixed maturity investments, at fair value	2.4	3.3
Mortgage-backed and asset-backed securities
Investment securities
Cost or amortized cost	2,200.8	2,082.0
Gross unrealized gains	29.8	18.2
Gross unrealized losses	(4.9)	(15.6)
Net foreign currency gains (losses)	14.9	(12.9)
Fixed maturity investments, at fair value	2,240.6	2,071.7
Foreign government, agency and provincial obligations
Investment securities
Cost or amortized cost	653.0	1,053.6
Gross unrealized gains	14.1	7.7
Gross unrealized losses	(0.2)	(6.6)
Net foreign currency gains (losses)	(0.9)	(8.3)
Fixed maturity investments, at fair value	666.0	1,046.4
Non-cumulative perpetual preference shares
Investment securities
Cost or amortized cost	82.3	81.9
Gross unrealized gains	3.3	6.1
Gross unrealized losses	(11.0)
Net foreign currency gains (losses)		(0.1)
Fixed maturity investments, at fair value	74.6	87.9
Equity security investments
Investment securities
Cost or amortized cost	661.0	561.2
Gross unrealized gains	35.4	105.5
Gross unrealized losses	(26.6)	(1.5)
Net foreign currency gains (losses)		1.8
Carrying value, common equity securities	669.8	667.0
Convertible fixed maturity investments
Investment securities
Cost or amortized cost	143.7	126.9
Gross unrealized gains	4.4	16.2
Gross unrealized losses	(7.6)	(0.1)
Carrying value, convertible fixed securities	140.5	143.0
Other long-term investments
Investment securities
Cost or amortized cost	290.2	329.5
Gross unrealized gains	56.2	62.4
Gross unrealized losses	(15.2)	(13.0)
Net foreign currency gains (losses)	(2.4)	(6.8)
Carrying value, other long-term investments	$ 328.8	$ 372.1

Investment Securities (Details 5) $ in Millions	Sep. 30, 2011 USD ($) investment	Dec. 31, 2010 USD ($)
Hedge and private equity funds included in other long-term investments
Other long-term investments
Largest single fund investment	$ 31.4
Other long-term investments	277.6	$ 315.5
Unfunded Commitments	$ 81.6	88.7
Hedge funds
Other long-term investments
Number of limited partnership and limited liability corporation investments \| investment	17
Other long-term investments	$ 130.2	155.7
Distributions outstanding	3.2
Redemption requests	2.0
Hedge funds \| 30-59 days notice
Other long-term investments
Other long-term investments	48.0
Hedge funds \| 60-89 days notice
Other long-term investments
Other long-term investments	34.8
Hedge funds \| 90-119 days notice
Other long-term investments
Other long-term investments	26.2
Hedge funds \| 120+ days notice
Other long-term investments
Other long-term investments	21.2
Hedge funds \| Monthly
Other long-term investments
Other long-term investments	6.0
Hedge funds \| Monthly \| 120+ days notice
Other long-term investments
Other long-term investments	6.0
Hedge funds \| Quarterly
Other long-term investments
Other long-term investments	75.4
Hedge funds \| Quarterly \| 30-59 days notice
Other long-term investments
Other long-term investments	26.1
Hedge funds \| Quarterly \| 60-89 days notice
Other long-term investments
Other long-term investments	29.7
Hedge funds \| Quarterly \| 90-119 days notice
Other long-term investments
Other long-term investments	19.6
Hedge funds \| Semi-annual
Other long-term investments
Other long-term investments	19.8
Hedge funds \| Semi-annual \| 60-89 days notice
Other long-term investments
Other long-term investments	5.1
Hedge funds \| Semi-annual \| 120+ days notice
Other long-term investments
Other long-term investments	14.7
Hedge funds \| Annual
Other long-term investments
Other long-term investments	29.0
Hedge funds \| Annual \| 30-59 days notice
Other long-term investments
Other long-term investments	21.9
Hedge funds \| Annual \| 90-119 days notice
Other long-term investments
Other long-term investments	6.6
Hedge funds \| Annual \| 120+ days notice
Other long-term investments
Other long-term investments	0.5
Long/short equity
Other long-term investments
Other long-term investments	49.0	50.4
Long/short credit & distressed
Other long-term investments
Other long-term investments	32.3	34.1
Long diversified strategies
Other long-term investments
Other long-term investments	22.0	24.0
Long/short equity REIT
Other long-term investments
Other long-term investments	14.7	25.2
Long/short equity activist
Other long-term investments
Other long-term investments	11.7	16.9
Long bank loan
Other long-term investments
Other long-term investments	$ 0.5	5.1
Private equity funds
Other long-term investments
Number of limited partnership and limited liability corporation investments \| investment	33
Other long-term investments	$ 147.4	159.8
Unfunded Commitments	81.6	88.7
Private equity funds \| 1-3 years
Other long-term investments
Other long-term investments	47.3
Private equity funds \| 5-10 years
Other long-term investments
Other long-term investments	83.1
Private equity funds \| >10 years
Other long-term investments
Other long-term investments	17.0
Distressed residential real estate
Other long-term investments
Other long-term investments	31.4	49.2
Energy infrastructure and services
Other long-term investments
Other long-term investments	29.5	24.2
Unfunded Commitments	9.9	10.8
Multi-sector
Other long-term investments
Other long-term investments	28.0	26.0
Unfunded Commitments	8.2	10.6
Manufacturing/Industrial
Other long-term investments
Other long-term investments	17.0	17.9
Private equity secondaries
Other long-term investments
Other long-term investments	11.3	10.4
Unfunded Commitments	4.0	4.4
Real estate
Other long-term investments
Other long-term investments	10.2	9.1
Unfunded Commitments	3.3	4.6
International multi-sector, Europe
Other long-term investments
Other long-term investments	8.0	10.5
Unfunded Commitments	4.7	5.3
International multi-sector, Asia
Other long-term investments
Other long-term investments	3.6	4.9
Unfunded Commitments	2.7	2.7
Insurance
Other long-term investments
Other long-term investments	3.6	3.9
Unfunded Commitments	41.3	41.3
Venture capital fund
Other long-term investments
Other long-term investments	2.5	2.2
Unfunded Commitments	0.5	1.0
Healthcare
Other long-term investments
Other long-term investments	2.3	1.5
Unfunded Commitments	$ 7.0	$ 8.0

Investment Securities (Details 6) - USD ($) $ in Millions	Sep. 30, 2011	Dec. 31, 2010
Investment Securities
Fair value, investment-related liabilities	$ 66.1	$ 77.8
Fair Value
Investment securities
Fair value investments	7,265.9	7,901.6
Level 1 Inputs
Investment securities
Fair value investments	1,755.2	1,894.4
Level 2 Inputs
Investment securities
Fair value investments	4,969.5	5,477.4
Fixed maturity investments \| Level 3 Inputs
Investment securities
Fair value investments	216.9	128.4
Debt securities issued by corporations
Investment securities
Fair value investments	2,053.9	2,178.0
Mortgage-backed and asset-backed securities \| Fair Value
Investment securities
Fair value investments	2,240.6	2,071.7
Mortgage-backed and asset-backed securities \| Level 2 Inputs
Investment securities
Fair value investments	2,108.7	2,014.7
Mortgage-backed and asset-backed securities \| Level 3 Inputs
Investment securities
Fair value investments	131.9	57.0
Common Equity Securities \| Level 3 Inputs
Investment securities
Fair value investments	32.1	71.2
Other long-term investments. \| Level 3 Inputs
Investment securities
Fair value investments	292.2	330.2
Carrying value of investment accounted for using the equity method	36.6	41.9
Fair value measured on a recurring basis \| Fair Value
Investment securities
Fair value investments	7,265.9	7,901.6
Fair value measured on a recurring basis \| Level 1 Inputs
Investment securities
Fair value investments	1,755.2	1,894.4
Fair value measured on a recurring basis \| Level 2 Inputs
Investment securities
Fair value investments	4,969.5	5,477.4
Fair value measured on a recurring basis \| Level 3 Inputs
Investment securities
Fair value investments	541.2	529.8
Fair value measured on a recurring basis \| Fixed maturity investments \| Fair Value
Investment securities
Fair value investments	5,390.6	5,786.1
Fair value measured on a recurring basis \| Fixed maturity investments \| Level 1 Inputs
Investment securities
Fair value investments	413.7	477.8
Fair value measured on a recurring basis \| Fixed maturity investments \| Level 2 Inputs
Investment securities
Fair value investments	4,760.0	5,179.9
Fair value measured on a recurring basis \| Fixed maturity investments \| Level 3 Inputs
Investment securities
Fair value investments	216.9	128.4
Fair value measured on a recurring basis \| U.S. Government and agency obligations \| Fair Value
Investment securities
Fair value investments	353.1	398.7
Fair value measured on a recurring basis \| U.S. Government and agency obligations \| Level 1 Inputs
Investment securities
Fair value investments	343.5	388.9
Fair value measured on a recurring basis \| U.S. Government and agency obligations \| Level 2 Inputs
Investment securities
Fair value investments	9.6	9.8
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Fair Value
Investment securities
Fair value investments	2,053.9	2,178.0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Level 1 Inputs
Investment securities
Fair value investments	5.7	6.3
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Level 2 Inputs
Investment securities
Fair value investments	2,022.7	2,171.7
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Level 3 Inputs
Investment securities
Fair value investments	25.5
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Consumer \| Fair Value
Investment securities
Fair value investments	719.0	769.0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Consumer \| Level 2 Inputs
Investment securities
Fair value investments	719.0	769.0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Industrial \| Fair Value
Investment securities
Fair value investments	425.3	511.3
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Industrial \| Level 2 Inputs
Investment securities
Fair value investments	425.3	511.3
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Financials \| Fair Value
Investment securities
Fair value investments	243.4	265.8
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Financials \| Level 1 Inputs
Investment securities
Fair value investments	5.7	6.3
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Financials \| Level 2 Inputs
Investment securities
Fair value investments	212.2	259.5
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Financials \| Level 3 Inputs
Investment securities
Fair value investments	25.5
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Communications \| Fair Value
Investment securities
Fair value investments	211.0	226.3
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Communications \| Level 2 Inputs
Investment securities
Fair value investments	211.0	226.3
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Energy \| Fair Value
Investment securities
Fair value investments	118.0	151.5
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Energy \| Level 2 Inputs
Investment securities
Fair value investments	118.0	151.5
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Basic materials \| Fair Value
Investment securities
Fair value investments	160.1	125.3
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Basic materials \| Level 2 Inputs
Investment securities
Fair value investments	160.1	125.3
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Utilities \| Fair Value
Investment securities
Fair value investments	148.3	106.7
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Utilities \| Level 2 Inputs
Investment securities
Fair value investments	148.3	106.7
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Technology \| Fair Value
Investment securities
Fair value investments	25.3	22.1
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Technology \| Level 2 Inputs
Investment securities
Fair value investments	25.3	22.1
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Diversified \| Fair Value
Investment securities
Fair value investments	3.5
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Diversified \| Level 2 Inputs
Investment securities
Fair value investments	3.5
Fair value measured on a recurring basis \| Municipal obligations \| Fair Value
Investment securities
Fair value investments	2.4	3.3
Fair value measured on a recurring basis \| Municipal obligations \| Level 2 Inputs
Investment securities
Fair value investments	2.4	3.3
Fair value measured on a recurring basis \| Mortgage-backed and asset-backed securities \| Fair Value
Investment securities
Fair value investments	2,240.6	2,071.7
Fair value measured on a recurring basis \| Mortgage-backed and asset-backed securities \| Level 2 Inputs
Investment securities
Fair value investments	2,108.7	2,014.7
Fair value measured on a recurring basis \| Mortgage-backed and asset-backed securities \| Level 3 Inputs
Investment securities
Fair value investments	131.9	57.0
Fair value measured on a recurring basis \| Foreign government, agency and provincial obligations. \| Fair Value
Investment securities
Fair value investments	666.0	1,046.5
Fair value measured on a recurring basis \| Foreign government, agency and provincial obligations. \| Level 1 Inputs
Investment securities
Fair value investments	64.5	82.6
Fair value measured on a recurring basis \| Foreign government, agency and provincial obligations. \| Level 2 Inputs
Investment securities
Fair value investments	601.5	963.9
Fair value measured on a recurring basis \| Non-cumulative perpetual preference shares \| Fair Value
Investment securities
Fair value investments	74.6	87.9
Fair value measured on a recurring basis \| Non-cumulative perpetual preference shares \| Level 2 Inputs
Investment securities
Fair value investments	15.1	16.5
Fair value measured on a recurring basis \| Non-cumulative perpetual preference shares \| Level 3 Inputs
Investment securities
Fair value investments	59.5	71.4
Fair value measured on a recurring basis \| Common Equity Securities \| Fair Value
Investment securities
Fair value investments	669.8	667.0
Fair value measured on a recurring basis \| Common Equity Securities \| Level 1 Inputs
Investment securities
Fair value investments	582.5	537.9
Fair value measured on a recurring basis \| Common Equity Securities \| Level 2 Inputs
Investment securities
Fair value investments	55.2	57.9
Fair value measured on a recurring basis \| Common Equity Securities \| Level 3 Inputs
Investment securities
Fair value investments	32.1	71.2
Fair value measured on a recurring basis \| Common Equity Securities \| Consumer \| Fair Value
Investment securities
Fair value investments	166.0	123.3
Fair value measured on a recurring basis \| Common Equity Securities \| Consumer \| Level 1 Inputs
Investment securities
Fair value investments	164.8	122.5
Fair value measured on a recurring basis \| Common Equity Securities \| Consumer \| Level 2 Inputs
Investment securities
Fair value investments	1.2	0.8
Fair value measured on a recurring basis \| Common Equity Securities \| Financials \| Fair Value
Investment securities
Fair value investments	191.6	221.6
Fair value measured on a recurring basis \| Common Equity Securities \| Financials \| Level 1 Inputs
Investment securities
Fair value investments	159.4	152.6
Fair value measured on a recurring basis \| Common Equity Securities \| Financials \| Level 2 Inputs
Investment securities
Fair value investments	0.5	1.2
Fair value measured on a recurring basis \| Common Equity Securities \| Financials \| Level 3 Inputs
Investment securities
Fair value investments	31.7	67.8
Fair value measured on a recurring basis \| Common Equity Securities \| Energy \| Fair Value
Investment securities
Fair value investments	57.5	60.2
Fair value measured on a recurring basis \| Common Equity Securities \| Energy \| Level 1 Inputs
Investment securities
Fair value investments	57.5	60.2
Fair value measured on a recurring basis \| Common Equity Securities \| Basic materials \| Fair Value
Investment securities
Fair value investments	108.4	98.8
Fair value measured on a recurring basis \| Common Equity Securities \| Basic materials \| Level 1 Inputs
Investment securities
Fair value investments	107.2	97.1
Fair value measured on a recurring basis \| Common Equity Securities \| Basic materials \| Level 2 Inputs
Investment securities
Fair value investments	1.2	1.7
Fair value measured on a recurring basis \| Common Equity Securities \| Utilities \| Fair Value
Investment securities
Fair value investments	40.7	47.6
Fair value measured on a recurring basis \| Common Equity Securities \| Utilities \| Level 1 Inputs
Investment securities
Fair value investments	40.7	44.6
Fair value measured on a recurring basis \| Common Equity Securities \| Utilities \| Level 3 Inputs
Investment securities
Fair value investments		3.0
Fair value measured on a recurring basis \| Common Equity Securities \| Technology \| Fair Value
Investment securities
Fair value investments	28.6	31.8
Fair value measured on a recurring basis \| Common Equity Securities \| Technology \| Level 1 Inputs
Investment securities
Fair value investments	27.6	30.4
Fair value measured on a recurring basis \| Common Equity Securities \| Technology \| Level 2 Inputs
Investment securities
Fair value investments	1.0	1.4
Fair value measured on a recurring basis \| Common Equity Securities \| Other: \| Fair Value
Investment securities
Fair value investments	77.0	83.7
Fair value measured on a recurring basis \| Common Equity Securities \| Other: \| Level 1 Inputs
Investment securities
Fair value investments	25.3	30.5
Fair value measured on a recurring basis \| Common Equity Securities \| Other: \| Level 2 Inputs
Investment securities
Fair value investments	51.3	52.8
Fair value measured on a recurring basis \| Common Equity Securities \| Other: \| Level 3 Inputs
Investment securities
Fair value investments	0.4	0.4
Fair value measured on a recurring basis \| Short-term investments \| Fair Value
Investment securities
Fair value investments	772.8	975.3
Fair value measured on a recurring basis \| Short-term investments \| Level 1 Inputs
Investment securities
Fair value investments	759.0	878.7
Fair value measured on a recurring basis \| Short-term investments \| Level 2 Inputs
Investment securities
Fair value investments	13.8	96.6
Fair value measured on a recurring basis \| Convertible fixed maturity investments \| Fair Value
Investment securities
Fair value investments	140.5	143.0
Fair value measured on a recurring basis \| Convertible fixed maturity investments \| Level 2 Inputs
Investment securities
Fair value investments	140.5	143.0
Fair value measured on a recurring basis \| Other long-term investments. \| Fair Value
Investment securities
Fair value investments	292.2	330.2
Fair value measured on a recurring basis \| Other long-term investments. \| Level 3 Inputs
Investment securities
Fair value investments	292.2	330.2
Carrying value of investment accounted for using the equity method	$ 36.6	$ 41.9

Investment Securities (Details 7) - Debt securities issued by corporations - USD ($) $ in Millions	Sep. 30, 2011	Dec. 31, 2010
Investment securities
Fair value investments	$ 2,053.9	$ 2,178.0
AA
Investment securities
Fair value investments	217.4	210.0
A
Investment securities
Fair value investments	765.0	833.7
BBB
Investment securities
Fair value investments	1,059.8	1,109.1
BB
Investment securities
Fair value investments	5.5	24.5
Other rating
Investment securities
Fair value investments	$ 6.2	$ 0.7

- 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 (Details 8) $ in Millions	9 Months Ended
Investment Securities (Details 8) $ in Millions	Sep. 30, 2011 USD ($)	Dec. 31, 2010 USD ($)
Super Senior
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	$ 40.4
Super Senior \| Prime
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	23.2
Super Senior \| Non-prime
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	17.2
Senior
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	27.6
Senior \| Prime
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	26.7
Senior \| Non-prime
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	0.9
Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	7,265.9	$ 7,901.6
Fair Value \| Prime
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	49.9
Fair Value \| Non-prime
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	18.1
Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	4,969.5	5,477.4
Mortgage-backed and asset-backed securities \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	2,240.6	2,071.7
Mortgage-backed and asset-backed securities \| Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	2,108.7	2,014.7
Mortgage-backed and asset-backed securities \| Level 3 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	131.9	57.0
Mortgage-backed securities \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	1,905.0	1,595.2
Mortgage-backed securities \| Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	1,773.1	1,538.2
Mortgage-backed securities \| Level 3 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	131.9	57.0
Agency mortgage-backed securities \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	1,593.5	1,417.6
Agency mortgage-backed securities \| Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	1,461.6	1,376.7
Agency mortgage-backed securities \| Level 3 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	131.9	40.9
GNMA \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	1,268.0	1,143.6
GNMA \| Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	1,136.1	1,102.7
GNMA \| Level 3 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	131.9	40.9
FNMA \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	268.9	234.9
FNMA \| Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	268.9	234.9
FHLMC \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	56.6	39.1
FHLMC \| Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	56.6	39.1
Non-agency mortgage-backed securities \| 2003
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	6.1
Non-agency mortgage-backed securities \| 2005
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	14.7
Non-agency mortgage-backed securities \| 2006
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	24.3
Non-agency mortgage-backed securities \| 2007
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	46.6
Non-agency mortgage-backed securities \| 2009
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	11.3
Non-agency mortgage-backed securities \| 2010
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	12.7
Non-agency mortgage-backed securities \| 2011
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	195.8
Non-agency mortgage-backed securities \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	311.5	177.6
Non-agency mortgage-backed securities \| Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	311.5	161.5
Non-agency mortgage-backed securities \| Level 3 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments		16.1
Non-agency residential mortgage-backed securities (RMBS) \| 2003
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	3.7
Non-agency residential mortgage-backed securities (RMBS) \| 2006
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	24.3
Non-agency residential mortgage-backed securities (RMBS) \| 2007
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	29.5
Non-agency residential mortgage-backed securities (RMBS) \| 2010
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	10.5
Non-agency residential mortgage-backed securities (RMBS) \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	68.0	90.6
Non-agency residential mortgage-backed securities (RMBS) \| Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	$ 68.0	74.5
Non-agency residential mortgage-backed securities (RMBS) \| Level 3 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments		16.1
Non-agency commercial mortgage-backed securities (CMBS)
Mortgage-backed, Asset-backed Securities Abstract
Percentage of underlying loans reported as non-performing (as a percent)	2.00%
Non-agency commercial mortgage-backed securities (CMBS) \| Super Senior
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	$ 56.1
Non-agency commercial mortgage-backed securities (CMBS) \| Senior
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	187.4
Non-agency commercial mortgage-backed securities (CMBS) \| 2003
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	2.4
Non-agency commercial mortgage-backed securities (CMBS) \| 2005
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	14.7
Non-agency commercial mortgage-backed securities (CMBS) \| 2007
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	17.1
Non-agency commercial mortgage-backed securities (CMBS) \| 2009
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	11.3
Non-agency commercial mortgage-backed securities (CMBS) \| 2010
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	2.2
Non-agency commercial mortgage-backed securities (CMBS) \| 2011
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	195.8
Non-agency commercial mortgage-backed securities (CMBS) \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	243.5	87.0
Non-agency commercial mortgage-backed securities (CMBS) \| Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	$ 243.5	87.0
Fixed Rate CMBS
Mortgage-backed, Asset-backed Securities Abstract
Average basis points of subordination (as a percent)	20
Fixed Rate CMBS \| Super Senior
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	$ 24.3
Fixed Rate CMBS \| Senior
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	177.5
Fixed Rate CMBS \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	$ 201.8
Floating Rate CMBS
Mortgage-backed, Asset-backed Securities Abstract
Average basis points of subordination (as a percent)	55
Floating Rate CMBS \| Super Senior
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	$ 31.8
Floating Rate CMBS \| Senior
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	9.9
Floating Rate CMBS \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	41.7
Other asset-backed securities \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	335.6	476.5
Other asset-backed securities \| Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	335.6	476.5
Credit card receivables \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	77.5	248.3
Credit card receivables \| Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	77.5	248.3
Vehicle receivables \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	235.5	228.1
Vehicle receivables \| Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	235.5	228.1
Other \| Fair Value
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	22.6	0.1
Other \| Level 2 Inputs
Mortgage-backed, Asset-backed Securities Abstract
Fair value investments	$ 22.6	$ 0.1

Investment Securities (Details 9) $ in Millions	9 Months Ended
Investment Securities (Details 9) $ in Millions	Sep. 30, 2011 USD ($) security	Dec. 31, 2010 USD ($)
Level 1 Inputs
Investment securities
Fair value investments	$ 1,755.2	$ 1,894.4
Total realized and unrealized gains (losses)	(50.5)
Foreign currency gains (losses) through OCI and other revenue	0.3
Amortization/Accretion	2.4
Purchases	6,690.7
Sales	(6,782.1)
Level 2 Inputs
Investment securities
Fair value investments	4,969.5	5,477.4
Total realized and unrealized gains (losses)	115.9
Foreign currency gains (losses) through OCI and other revenue	(84.4)
Amortization/Accretion	(40.7)
Purchases	3,987.4
Sales	(4,596.9)
Transfers in	111.8
Transfers out	(1.0)
Securities of level 3 measurements recategorized as level 2 measurements	$ 111.8
Number of securities with unobservable inputs \| security	1
Level 3 Inputs
Investment securities
Number of securities with unobservable inputs \| security	7
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
Fair Value
Investment securities
Fair value investments	7,265.9	7,901.6
Total realized and unrealized gains (losses)	72.4
Foreign currency gains (losses) through OCI and other revenue	(91.9)
Amortization/Accretion	(38.4)
Purchases	10,938.5
Sales	(11,516.3)
Transfers in	112.8
Transfers out	(112.8)
Fixed maturity investments \| Level 3 Inputs
Investment securities
Fair value investments	216.9	128.4
Total realized and unrealized gains (losses)	(10.6)
Foreign currency gains (losses) through OCI and other revenue	(4.4)
Amortization/Accretion	(0.1)
Purchases	212.8
Sales	1.6
Transfers in	1.0
Transfers out	(111.8)
Common Equity Securities \| Level 3 Inputs
Investment securities
Fair value investments	32.1	71.2
Total realized and unrealized gains (losses)	(4.9)
Foreign currency gains (losses) through OCI and other revenue	1.6
Purchases	19.7
Sales	(55.5)
Other long-term investments. \| Level 3 Inputs
Investment securities
Fair value investments	292.2	330.2
Total realized and unrealized gains (losses)	22.5
Foreign currency gains (losses) through OCI and other revenue	(5.0)
Purchases	27.9
Sales	(83.4)
Carrying value of investment accounted for using the equity method	$ 36.6	$ 41.9

Debt (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended	9 Months Ended	12 Months Ended
Debt (Details) - USD ($) $ in Millions	Apr. 30, 2011	Jun. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Aug. 12, 2011
Debt Instrument
Total debt			$ 669.0		$ 818.8
Aggregate purchase price of senior notes purchased and retired				$ 197.3
OBH Senior Notes \| Tender offer.
Debt Instrument
Aggregate principal amount of senior notes purchased and retired	$ 150.0	$ 156.4
Aggregate purchase price of senior notes purchased and retired	161.6	165.4
Loss on retirement of debt	$ 12.0	$ 9.6
OBH Senior Notes \| Additional repurchase and retirement of debt
Debt Instrument
Aggregate principal amount of senior notes purchased and retired					29.7
Aggregate purchase price of senior notes purchased and retired					30.8
Loss on retirement of debt					1.2
OBH Senior Notes \| Repurchase and retirement of debt
Debt Instrument
Aggregate principal amount of senior notes purchased and retired					1.1
Aggregate purchase price of senior notes purchased and retired					1.1
OBH Senior Notes \| OneBeacon U.S. Holdings, Inc. ("OBH")
Debt Instrument
Debt instrument at face value			269.9		419.9
Unamortized original issue discount			(0.2)		(0.3)
Total debt			269.7		419.6
Sirius Group Senior Notes
Debt Instrument
Debt instrument at face value			400.0		400.0
Unamortized original issue discount			(0.7)		(0.8)
Total debt			399.3		$ 399.2
WTM Bank Facility
Debt Instrument
Total commitment under revolving credit facility			375.0
Interest expense			$ 2.2
Previous revolving credit facility
Debt Instrument
Total commitment under revolving credit facility						$ 475.0

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Income Taxes (Details) - USD ($) $ in Millions	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Jan. 05, 2011
Income Taxes
Effective tax rates (as a percent)		15.60%		17.90%
U.S. statutory rate (as a percent)	35.00%	35.00%		35.00%
Pre-tax (loss)	$ 1.2	$ 75.2	$ 3.6	$ 57.5
Deferred tax assets held for sale	88.2		88.2
U.S. deferred tax asset, net	$ 362.6		$ 362.6
Estimated total assessment					$ 18.7

Variable Annuity Reinsurance (Details) $ in Millions, ¥ in Billions	3 Months Ended		9 Months Ended
	Sep. 30, 2011 USD ($)	Sep. 30, 2010 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2010 USD ($)	Sep. 30, 2011 USD ($) rating	Sep. 30, 2011 JPY (¥) rating	Dec. 31, 2010 USD ($)	Dec. 31, 2010 JPY (¥)
Pre-tax operating results of WM Life Re
Total revenues	$ 501.3	$ 551.0	$ 1,584.5	$ 2,013.9
General and administrative expenses	(36.2)	(32.1)	(120.4)	(119.5)
Pre-tax income (loss) from continuing operations	1.2	75.2	3.6	57.5
Credit risk on derivative instruments
Number of creditworthiness ratings \| rating					21	21
Fixed income/Interest rate
Pre-tax operating results of WM Life Re
Change in fair value of derivatives, included in other revenues	29.8	(25.5)	17.3	(1.9)
Changes in derivative instruments
Balance of assets, at the beginning of the period			43.9
Realized and unrealized gains (losses)	29.8	(25.5)	17.3	(1.9)
Balance of assets, at the end of the period	50.3		50.3
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized derivative gains (losses) recognized in other revenues	29.8	(25.5)	17.3	(1.9)
Carrying Value	50.3		43.9		$ 50.3		$ 43.9
Foreign exchange
Pre-tax operating results of WM Life Re
Change in fair value of derivatives, included in other revenues	63.0	33.0	32.8	99.6
Changes in derivative instruments
Balance of assets, at the beginning of the period			225.3
Realized and unrealized gains (losses)	63.0	33.0	32.8	99.6
Balance of assets, at the end of the period	212.0		212.0
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized derivative gains (losses) recognized in other revenues	63.0	33.0	32.8	99.6
Carrying Value	212.0		225.3		212.0		225.3
Equity
Pre-tax operating results of WM Life Re
Change in fair value of derivatives, included in other revenues	56.1	(23.2)	55.3	17.0
Changes in derivative instruments
Balance of assets, at the beginning of the period			78.3
Realized and unrealized gains (losses)	56.1	(23.2)	55.3	17.0
Balance of assets, at the end of the period	91.5		91.5
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized derivative gains (losses) recognized in other revenues	56.1	(23.2)	55.3	17.0
Carrying Value	91.5		78.3		91.5		78.3
Level 1 Inputs
Pre-tax operating results of WM Life Re
Change in fair value of derivatives, included in other revenues	27.6		10.8
Changes in derivative instruments
Balance of assets, at the beginning of the period	(11.9)
Realized and unrealized gains (losses)	27.6		10.8
Sales/settlements	(15.7)		(10.8)
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized derivative gains (losses) recognized in other revenues	27.6		10.8
Carrying Value	(11.9)
Level 2 Inputs
Pre-tax operating results of WM Life Re
Change in fair value of derivatives, included in other revenues	75.7		67.5
Changes in derivative instruments
Balance of assets, at the beginning of the period	48.2		72.2
Realized and unrealized gains (losses)	75.7		67.5
Sales/settlements	(48.4)		(64.2)
Balance of assets, at the end of the period	75.5		75.5
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized derivative gains (losses) recognized in other revenues	75.7		67.5
Carrying Value	48.2		72.2		75.5		72.2
Level 3 Inputs
Pre-tax operating results of WM Life Re
Change in fair value of derivatives, included in other revenues	45.6		27.1
Changes in derivative instruments
Balance of assets, at the beginning of the period	232.7		275.3
Purchases			5.0
Realized and unrealized gains (losses)	45.6		27.1
Sales/settlements			(29.1)
Balance of assets, at the end of the period	278.3		278.3
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized derivative gains (losses) recognized in other revenues	45.6		27.1
Carrying Value	232.7		275.3		278.3		275.3
Fair Value
Pre-tax operating results of WM Life Re
Change in fair value of derivatives, included in other revenues	148.9		105.4
Changes in derivative instruments
Balance of assets, at the beginning of the period	269.0		347.5
Purchases			5.0
Realized and unrealized gains (losses)	148.9		105.4
Sales/settlements	(64.1)		(104.1)
Balance of assets, at the end of the period	353.8		353.8
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized derivative gains (losses) recognized in other revenues	148.9		105.4
Carrying Value	269.0		347.5		353.8		347.5
Variable annuity reinsurance.
Variable annuity reinsurance
Total guarantee value					$ 3,000.0	¥ 234.5	$ 2,900.0	¥ 237.4
Collective account values of underlying variable annuities as a percentage of the guarantee value (as a percent)					78.00%	78.00%	82.00%	82.00%
Variable annuity reinsurance. \| Level 3 Inputs
Changes in variable annuity liabilities
Balance of liabilities, at the beginning of the period	(591.3)		(610.2)
Realized and unrealized gains (losses)	(170.0)		(151.1)
Balance of liabilities, at the end of the period	(761.3)		(761.3)
WM Life Re
Pre-tax operating results of WM Life Re
Fees, included in other revenues	8.4	7.7	24.3	22.3
Change in fair value of derivatives, included in other revenues	148.9	(15.7)	105.4	114.7
Foreign exchange, included in other revenues	14.8	10.4	17.1	16.0
Other investment income and gains (losses)	0.5	(0.2)	(0.1)	(0.7)
Total revenues	8.2	(51.3)	(1.3)	(52.4)
Death benefit claims paid, included in other expenses	(0.7)	(0.6)	(2.4)	(1.4)
General and administrative expenses	(1.1)	(1.4)	(3.2)	(5.0)
Pre-tax income (loss) from continuing operations	0.8	(53.0)	(10.0)	(64.6)
Changes in derivative instruments
Realized and unrealized gains (losses)	148.9	(15.7)	105.4	114.7
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized derivative gains (losses) recognized in other revenues	148.9	(15.7)	105.4	114.7
Credit risk on derivative instruments
OTC derivative instruments					$ 363.4		$ 351.5
Collateral held					(130.3)		(101.0)
Collateral provided					22.6		25.3
Net exposure to credit losses on fair value of OTC instruments					255.7		275.8
Additional collateral					419.7		326.0
Adjustments for counterparty credit risk					(9.6)		(4.0)
WM Life Re \| Citigroup
Credit risk on derivative instruments
Net exposure to credit losses on fair value of OTC instruments					46.7
WM Life Re \| Royal Bank of Scotland
Credit risk on derivative instruments
Net exposure to credit losses on fair value of OTC instruments					86.5
WM Life Re \| Bank of America
Credit risk on derivative instruments
Net exposure to credit losses on fair value of OTC instruments					49.7
WM Life Re \| Barclays
Credit risk on derivative instruments
Net exposure to credit losses on fair value of OTC instruments					32.2
WM Life Re \| Nomura
Credit risk on derivative instruments
Net exposure to credit losses on fair value of OTC instruments					15.6
WM Life Re \| JP Morgan
Credit risk on derivative instruments
Net exposure to credit losses on fair value of OTC instruments					14.7
WM Life Re \| BNP Paribas
Credit risk on derivative instruments
Net exposure to credit losses on fair value of OTC instruments					7.5
WM Life Re \| Goldman Sachs
Credit risk on derivative instruments
Net exposure to credit losses on fair value of OTC instruments					2.8
WM Life Re \| Cash.
Credit risk on derivative instruments
Additional collateral					393.3		291.1
WM Life Re \| Fixed maturity investments
Credit risk on derivative instruments
Collateral held					(58.1)		(48.6)
Additional collateral					11.9		3.3
WM Life Re \| Short-term investments
Credit risk on derivative instruments
Collateral held					(72.2)		(52.4)
Additional collateral					$ 14.5		$ 31.6
WM Life Re \| Variable annuity reinsurance.
Pre-tax operating results of WM Life Re
Change in fair value of variable annuity liability, included in other revenues	(164.4)	(53.5)	(148.0)	(204.7)
Change in fair value of variable annuity death benefit liabilities, included in other expenses	$ (5.6)	$ 0.3	$ (3.1)	$ (5.8)

Earnings (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Basic and diluted earnings per share numerators (in millions):
Net income (loss) attributable to White Mountains' common shareholders	$ (15.8)	$ 50.7	$ (32.3)	$ 13.6
Less: net (income) loss from discontinued operations	30.1	(3.6)	28.9	(1.2)
Net income (loss) attributable to White Mountains' common shareholders from continuing operations	14.3	47.1	(3.4)	12.4
Dividends declared on common shares			(8.0)	(8.8)
Undistributed earnings (loss)	$ 14.3	$ 47.1	$ (11.4)	$ 3.6
Basic earnings per share denominators (in thousands):
Average common shares outstanding during the period (in shares)	7,845	8,332	7,902	8,547
Average unvested restricted shares (in shares)	74	99	68	97
Basic earnings (loss) per share denominator (in shares)	7,919	8,431	7,970	8,644
Diluted earnings per share denominator (in thousands):
Average common shares outstanding during the period (in shares)	7,845	8,332	7,902	8,547
Average unvested restricted shares (in shares)	74	99	68	97
Average outstanding dilutive options to acquire common shares (in shares)				1
Diluted earnings (loss) per share denominator (in shares)	7,919	8,431	7,970	8,645
Basic earnings per share (in dollars):
Net income (loss) from continuing operations attributable to White Mountains' common shareholders (in dollars per share)	$ 1.81	$ 5.58	$ (0.43)	$ 1.44
Dividends declared and paid (in dollars per share)			(1.00)	(1.00)
Undistributed earnings (loss) per share (in dollars per share)	1.81	5.58	(1.43)	0.44
Diluted earnings per share (in dollars)
Net income from continuing operations attributable to White Mountains' common shareholders (in dollars per share)	1.81	5.58	(0.43)	1.44
Dividends declared and paid (in dollars per share)			(1.00)	(1.00)
Undistributed earnings (loss) per share (in dollars per share)	$ 1.81	$ 5.58	$ (1.43)	$ 0.44

Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Segment Information (Details) - USD ($) $ in Millions	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Segment reporting information
Earned insurance and reinsurance premiums	$ 490.6	$ 498.1	$ 1,436.7	$ 1,772.9
Net investment income	42.8	48.9	138.1	157.4
Net realized and unrealized investment gains (losses)	1.7	11.6	78.3	104.7
Other revenue	(33.8)	(7.6)	(68.6)	(21.1)
Total revenues	501.3	551.0	1,584.5	2,013.9
Loss and loss adjustment expenses	277.1	253.4	914.0	1,175.9
Insurance and reinsurance acquisition expenses	107.0	102.1	296.2	370.9
Other underwriting expenses	67.0	75.0	211.5	245.9
General and administrative expenses	36.2	32.1	120.4	119.5
Interest expense on debt	12.8	13.2	38.8	44.2
Total expenses	500.1	475.8	1,580.9	1,956.4
Pre-tax income (loss) from continuing operations	1.2	75.2	3.6	57.5
OneBeacon
Segment reporting information
Earned insurance and reinsurance premiums	258.6	293.6	751.2	1,134.7
Net investment income	16.1	21.6	55.8	74.9
Net realized and unrealized investment gains (losses)	(47.4)	51.6	(13.3)	79.6
Other revenue	0.1	12.7	(10.6)	1.9
Total revenues	227.4	379.5	783.1	1,291.1
Loss and loss adjustment expenses	146.6	155.2	414.9	719.3
Insurance and reinsurance acquisition expenses	58.6	64.3	161.1	248.3
Other underwriting expenses	38.7	50.5	132.1	176.6
General and administrative expenses	2.5	2.1	7.4	9.4
Interest expense on debt	4.1	6.4	16.4	23.4
Total expenses	250.5	278.5	731.9	1,177.0
Pre-tax income (loss) from continuing operations	(23.1)	101.0	51.2	114.1
Sirius Group.
Segment reporting information
Earned insurance and reinsurance premiums	232.0	204.5	685.5	638.2
Net investment income	22.1	23.0	68.3	71.3
Net realized and unrealized investment gains (losses)	64.7	(51.8)	102.6	13.7
Other revenue	(28.1)	43.3	(55.7)	36.4
Total revenues	290.7	219.0	800.7	759.6
Loss and loss adjustment expenses	130.5	98.2	499.1	456.6
Insurance and reinsurance acquisition expenses	48.4	37.8	135.1	122.6
Other underwriting expenses	28.3	24.5	79.4	69.3
General and administrative expenses	7.4	4.8	23.3	23.2
Interest expense on debt	6.5	6.7	19.6	20.1
Total expenses	221.1	172.0	756.5	691.8
Pre-tax income (loss) from continuing operations	69.6	47.0	44.2	67.8
Other Operations
Segment reporting information
Net investment income	4.6	4.3	14.0	11.2
Net realized and unrealized investment gains (losses)	(15.6)	11.8	(11.0)	11.4
Other revenue	(5.8)	(63.6)	(2.3)	(59.4)
Total revenues	(16.8)	(47.5)	0.7	(36.8)
General and administrative expenses	26.3	25.2	89.7	86.9
Interest expense on debt	2.2	0.1	2.8	0.7
Total expenses	28.5	25.3	92.5	87.6
Pre-tax income (loss) from continuing operations	$ (45.3)	$ (72.8)	$ (91.8)	$ (124.4)

Investments in Unconsolidated Affiliates (Details) - USD ($) $ in Millions	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Dec. 31, 2009
Investments in unconsolidated affiliates
Total investments in unconsolidated affiliates	$ 458.6		$ 389.7
Symetra
Investments in unconsolidated affiliates
Total investments in unconsolidated affiliates	456.7	$ 421.0	387.5	$ 416.1	$ 372.5	$ 307.7
Symetra \| Common shareholders' equity
Investments in unconsolidated affiliates
Total investments in unconsolidated affiliates	449.0	388.5	350.4	399.2	344.9	269.2
Symetra \| Warrants
Investments in unconsolidated affiliates
Total investments in unconsolidated affiliates	7.7	$ 32.5	37.1	$ 16.9	$ 27.6	$ 38.5
Pentelia Capital Management
Investments in unconsolidated affiliates
Total investments in unconsolidated affiliates	$ 1.9		$ 2.2

Investments in Unconsolidated Affiliates (Details 2) - Symetra - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	3 Months Ended	9 Months Ended
	Jan. 31, 2010	Mar. 31, 2010	Sep. 30, 2011	Dec. 31, 2010
Investments in unconsolidated affiliates
Ownership interest after initial public offering (as a percent)		20.00%
Decrease in carrying value of Symetra from dilution		$ 16.0
Common shareholders' equity
Investments in unconsolidated affiliates
Investments in unconsolidated affiliates (in shares)			17.4	17.4
Additional common shares (in shares)			9.5	9.5
Warrants
Investments in unconsolidated affiliates
Risk free interest rate (as a percent)			0.37%
Volatility rate (as a percent)			31.64%
Expected life (in years)			2.83Y
Strike price (in dollars per share)			$ 11.49
Share price (in dollars per share)			$ 8.15
Initial public offering
Investments in unconsolidated affiliates
Initial public offering issue price (in dollars per share)	$ 12.00
Sale of Symetra common shares by Symetra (in shares)	25.3
Sale of Symetra common shares by existing shareholders (in shares)	9.7

Investments in Unconsolidated Affiliates (Details 3) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Changes in carrying value of investment in Symetra
Carrying value at the beginning of the period			$ 389.7
Equity in earnings of Symetra	$ (1.5)	$ (7.9)	(16.1)	$ (1.6)
Carrying value at the end of the period	458.6		458.6
Symetra
Changes in carrying value of investment in Symetra
Carrying value at the beginning of the period	421.0	372.5	387.5	307.7
Equity in earnings of Symetra	1.6	8.3	17.5	2.1
Net unrealized gains from investee's fixed maturity portfolio	59.9	46.9	84.0	129.7
Dividends received	(1.0)	(0.9)	(2.9)	(1.8)
(Decrease) increase in value of warrants	(24.8)	(10.7)	(29.4)	(21.6)
Carrying value at the end of the period	456.7	416.1	456.7	416.1
Tax on net unrealized gains from investee's fixed maturity portfolio	4.8	3.8	6.8	3.8
Aggregate value of White Mountains common shares of Symetra at quoted market price	$ 141.8		$ 141.8
Quoted market price (in dollars per share)	$ 8.15		$ 8.15
Symetra \| Common shareholders' equity
Changes in carrying value of investment in Symetra
Carrying value at the beginning of the period	$ 388.5	344.9	$ 350.4	269.2
Equity in earnings of Symetra	1.6	8.3	17.5	2.1
Net unrealized gains from investee's fixed maturity portfolio	59.9	46.9	84.0	129.7
Dividends received	(1.0)	(0.9)	(2.9)	(1.8)
Carrying value at the end of the period	449.0	399.2	449.0	399.2
Tax on equity in earnings	0.1	0.7	1.4	0.7
Tax on net unrealized gains from investee's fixed maturity portfolio	4.8	3.8	6.8	3.8
Equity in net unrealized gains	147.7	120.7	147.7	120.7
Tax on equity in net unrealized gains	12.3	9.8	24.2	9.8
Loss from dilutive effect resulting from public offering				17.9
Loss from dilutive effect resulting from dividend and issuance of restricted shares		0.1		0.7
Gain from dilutive effect resulting from public offering				1.9
Symetra \| Warrants
Changes in carrying value of investment in Symetra
Carrying value at the beginning of the period	32.5	27.6	37.1	38.5
(Decrease) increase in value of warrants	(24.8)	(10.7)	(29.4)	(21.6)
Carrying value at the end of the period	7.7	$ 16.9	7.7	$ 16.9
Cash dividends received on warrants	$ 0.6		$ 1.6

Employee Share-Based Incentive Compensation Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Expense Amortized
Accrued expense at the beginning of period			$ 157.4
Accrued expense at the end of the period	$ 169.9		169.9
Non-Qualified Options
Expense Amortized
Expense recognized		$ 10.1	$ 0.1	$ 11.5
WTM Incentive Plan and WTM Phantom Share Plans \| Performance shares
Share-based compensation arrangement by share-based payment award
Vesting period (in years)			3Y
Target Performance Share activity
Beginning of period (in shares)	150,064	163,220	163,184	172,454
Shares expired (in shares)			(51,131)	(49,127)
New grants (in shares)			37,675	47,880
Cancellations and change in assumed forfeitures (in shares)		(36)	336	(8,023)
Ending of period (in shares)	150,064	163,184	150,064	163,184
Expense Amortized
Accrued expense at the beginning of period	$ 56.5	$ 20.2	$ 29.4	$ 12.2
Assumed forfeitures and cancellations			(0.6)
Expense recognized	(1.0)	3.0	26.7	11.0
Accrued expense at the end of the period	$ 55.5	$ 23.2	$ 55.5	$ 23.2
Target vesting percentage of performance shares (as a percent)	100.00%		100.00%
Additional compensation cost that would be recognized if all outstanding performance shares vested	$ 23.5		$ 23.5
OneBeacon Long-Term Incentive Plan \| Performance shares
Target Performance Share activity
Beginning of period (in shares)	671,727	1,770,423	1,464,295	2,224,215
Shares expired (in shares)		(199,774)	(936,150)	(882,118)
New grants (in shares)		14,618	194,900	293,478
Cancellations and change in assumed forfeitures (in shares)	(19,583)	(20,438)	(70,901)	(70,746)
Ending of period (in shares)	652,144	1,564,829	652,144	1,564,829
Expense Amortized
Accrued expense at the beginning of period	$ 10.0	$ 15.2	$ 18.5	$ 15.1
Payments and deferrals		(2.2)	(10.5)	(4.5)
Assumed forfeitures and cancellations	0.1	(0.3)	(0.2)	(0.7)
Expense recognized	(0.5)	1.7	1.8	4.5
Accrued expense at the end of the period	$ 9.6	14.4	$ 9.6	14.4
Percentage of target achieved by former employees as a result of the Commercial Lines and Personal Lines Transactions (as a percent)			100.00%
Target vesting percentage of performance shares (as a percent)	100.00%		100.00%
Additional compensation cost that would be recognized if all outstanding performance shares vested	$ 3.7		$ 3.7
OneBeacon Long-Term Incentive Plan \| Performance shares \| Performance cycle 2007-2009
Expense Amortized
Percentage of target achieved by former employees as a result of the Commercial Lines and Personal Lines Transactions (as a percent)			14.20%
OneBeacon Long-Term Incentive Plan \| Performance shares \| Performance cycle 2008-2010
Expense Amortized
Percentage of target achieved by former employees as a result of the Commercial Lines and Personal Lines Transactions (as a percent)			68.50%
OneBeacon Long-Term Incentive Plan \| Non-Qualified Options
Share-based compensation arrangement by share-based payment award
Vesting period (in years)			Third, fourth and fifth anniversaries
Expense Amortized
Accrued expense at the beginning of period	4.8	4.1	$ 4.5	3.6
Expense recognized	0.1	0.2	0.4	0.7
Accrued expense at the end of the period	$ 4.9	$ 4.3	$ 4.9	$ 4.3

Employee Share-Based Incentive Compensation Plans (Details 2) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Dec. 31, 2009
Share-based compensation arrangement by share-based payment award
Accrued incentive compensation	$ 169.9		$ 157.4
WTM Incentive Plan \| Performance shares
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding (in shares)	140,975
Accrued Expense	$ 50.5
Assumed forfeitures (in shares)	(3,524)
Assumed forfeitures	$ (1.3)
Target WTM Performance Shares Outstanding	137,451
Accrued incentive compensation	$ 49.2
WTM Incentive Plan \| Performance cycle 2009-2011 \| Performance shares
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding (in shares)	60,410
Accrued Expense	$ 38.1
WTM Incentive Plan \| Performance cycle 2010-2012 \| Performance shares
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding (in shares)	42,890
Accrued Expense	$ 7.9
WTM Incentive Plan \| Performance cycle 2011-2013 \| Performance shares
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding (in shares)	37,675
Accrued Expense	$ 4.5
WTM Phantom Share Plans \| Performance shares
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding (in shares)	12,937
Accrued Expense	$ 6.4
Assumed forfeitures (in shares)	(324)
Assumed forfeitures	$ (0.1)
Target WTM Performance Shares Outstanding	12,613
Accrued incentive compensation	$ 6.3
WTM Phantom Share Plans \| Performance cycle 2009-2011 \| Performance shares
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding (in shares)	7,947
Accrued Expense	$ 5.2
WTM Phantom Share Plans \| Performance cycle 2010-2012 \| Performance shares
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding (in shares)	4,990
Accrued Expense	$ 1.2
OneBeacon Long-Term Incentive Plan \| Performance shares
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding (in shares)	662,222
Accrued Expense	$ 9.7
Assumed forfeitures (in shares)	(10,078)
Assumed forfeitures	$ (0.1)
Target WTM Performance Shares Outstanding	652,144	671,727	1,464,295	1,564,829	1,770,423	2,224,215
Accrued incentive compensation	$ 9.6	$ 10.0	$ 18.5	$ 14.4	$ 15.2	$ 15.1
OneBeacon Long-Term Incentive Plan \| Performance cycle 2008-2010 \| Performance shares
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding (in shares)	259,102
Accrued Expense	$ 7.2
OneBeacon Long-Term Incentive Plan \| Performance cycle 2009-2011 \| Performance shares
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding (in shares)	251,557
Accrued Expense	$ 1.9
OneBeacon Long-Term Incentive Plan \| Performance cycle 2010-2012 \| Performance shares
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding (in shares)	151,563
Accrued Expense	$ 0.6

Employee Share-Based Incentive Compensation Plans (Details 3) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2011 USD ($) shares	Jun. 30, 2011 USD ($) shares	Mar. 31, 2011 USD ($) shares	Sep. 30, 2010 USD ($) shares	Mar. 31, 2010 USD ($) shares	Mar. 31, 2007 shares	Sep. 30, 2011 USD ($) shares	Sep. 30, 2010 USD ($) shares	Dec. 31, 2010 installment
WTM Restricted Stock
Activity in plan
Beginning of period (in shares)	73,500		46,250	98,750	91,900		46,250	91,900
Issued (in shares)							27,250	19,750
Vested (in shares)		(250)	(27,000)					(12,650)
Cancellations and change in assumed forfeitures (in shares)								(250)
Ending of period (in shares)	73,500	73,500		98,750			73,500	98,750
Unamortized grant date fair value
Unamortized grant date fair value, beginning balance \| $	$ 18.9		$ 14.1	$ 20.9	$ 23.7		$ 14.1	$ 23.7
Issued \| $							9.9	6.7
Forfeited \| $								(0.1)
Modified \| $								(3.3)
Expense recognized \| $	(2.8)			(3.3)			(7.9)	(9.4)
Unamortized grant date fair value, ending balance \| $	$ 16.1	$ 18.9		$ 17.6			$ 16.1	$ 17.6
Number of installments in which the shares vest \| installment									3
Issued (in shares)							27,250	19,750
WTM Restricted Stock \| Chairman and CEO
Activity in plan
Issued (in shares)						15,000
Unamortized grant date fair value
Issued (in shares)						15,000
Restricted shares that will vest in December, 2012
Activity in plan
Issued (in shares)					19,750
Unamortized grant date fair value
Issued (in shares)					19,750

Employee Share-Based Incentive Compensation Plans (Details 4) - Non-Qualified Options $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended	9 Months Ended
	May 31, 2010 USD ($) year	Jan. 31, 2007 USD ($) year $ / shares shares	Sep. 30, 2010 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2010 USD ($)	May 26, 2010 USD ($) $ / shares shares
Assumptions of stock-based compensation awards
Expense recognized			$ 10.1	$ 0.1	$ 11.5
Before amendments
Share-based compensation arrangement by share-based payment award
Stock-based awards, contractual term (in years)		7
Vesting period (in years)		5Y
Initial exercise price (in dollars per share) \| $ / shares		$ 650
Fair value		$ 27.2				$ 3.5
Unamortized amount at modification date						9.0
Annual percentage increase in exercise price (as a percent)		5.00%
Assumptions of stock-based compensation awards
Expected volatility (as a percent)	41.00%	29.70%
Risk-free rate (as a percent)	1.57%	1.10%
Risk-free rate less the Escalator (as a percent)		4.70%
Forfeiture (as a percent)	0.00%	0.00%
Expected dividend yield (as a percent)	0.32%	1.40%
Expected life (in years) \| year	3.67	7
Expense recognized	$ 8.7
Granted (in shares) \| shares		200,000
Amended Grant
Share-based compensation arrangement by share-based payment award
Fair value						4.4
Amount amortized into income prior to the modification						$ 18.2
Assumptions of stock-based compensation awards
Expected volatility (as a percent)	34.00%
Risk-free rate (as a percent)	2.43%
Forfeiture (as a percent)	0.00%
Expected dividend yield (as a percent)	0.32%
Expected life (in years) \| year	6.67
Extension of contractual term (in years) \| year	3
Exercise price (in dollars per share) \| $ / shares						$ 742
Number of shares extinguished (in shares) \| 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%

Employee Share-Based Incentive Compensation Plans (Details 5) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended
	Nov. 30, 2006 $ / shares shares	Sep. 30, 2011 USD ($) shares	Sep. 30, 2010 USD ($) $ / shares shares	Jun. 30, 2010 USD ($) shares	Sep. 30, 2011 USD ($) year shares	Sep. 30, 2010 USD ($) $ / shares shares	Nov. 16, 2010 $ / shares	May 27, 2008 $ / shares	Mar. 31, 2008 $ / shares
Expense Amortized
Accrued expense at the beginning of period					$ 157.4
Accrued expense at the end of the period		$ 169.9			169.9
Non-Qualified Options
Expense Amortized
Expense recognized			$ 10.1		$ 0.1	$ 11.5
OneBeacon Long-Term Incentive Plan \| Non-Qualified Options
Share-based compensation arrangement by share-based payment award
Granted (in shares) \| shares	1,420,000
Target options outstanding
Opening balance - outstanding Options (in shares) \| shares		750,130	879,783	1,015,610	768,652	1,015,610
Forfeitures and cancellations (in shares) \| shares		(9,260)			(27,782)	(37,044)
Vested and expired (in shares) \| shares			(43,218)			(142,001)
Ending balance - outstanding Options (in shares) \| shares		740,870	836,565	879,783	740,870	836,565
Expense Amortized
Accrued expense at the beginning of period		$ 4.8	$ 4.1	$ 3.6	$ 4.5	$ 3.6
Expense recognized		0.1	0.2		0.4	0.7
Accrued expense at the end of the period		$ 4.9	$ 4.3	$ 4.1	$ 4.9	$ 4.3
Options vesting period (in years)					Third, fourth and fifth anniversaries
Expiration period of award (in years)				5.5
Assumptions of stock-based compensation awards
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) \| year					5.5
Initial exercise price (in dollars per share) \| $ / shares	$ 30.00
Amended exercise price of option (in dollars per share) \| $ / shares							$ 25.47	$ 27.97
OneBeacon special dividend (in dollars per share) \| $ / shares			$ 2.50			$ 2.50			$ 2.03

Employee Share-Based Incentive Compensation Plans (Details 6) - OneBeacon Long-Term Incentive Plan $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	May 31, 2011 year shares	Sep. 30, 2011 USD ($) shares	Sep. 30, 2010 USD ($) shares	Mar. 31, 2008 shares	Sep. 30, 2011 USD ($) shares	Sep. 30, 2010 USD ($) shares	Jun. 30, 2011 shares	May 25, 2011 shares	Dec. 31, 2010 shares	Jun. 30, 2010 shares	Dec. 31, 2009 shares
Restricted Stock Units, RSU
Share-based compensation arrangement by share-based payment award
Expense recognized \| $						$ 0.2
New grants (in shares)				116,270
Proportion of award vests on each of Nov 9, 2009, 2010 and 2011 (as a percent)				33.00%
Minimum percentage of growth in book value per share for vesting each tranche of units (as a percent)				4.00%
Outstanding (in shares)		22,773			22,773
OneBeacon Restricted Stock
Share-based compensation arrangement by share-based payment award
Expense not yet recognized \| $		$ 8.1			$ 8.1
OneBeacon Restricted Stock \| Chairman and CEO
Share-based compensation arrangement by share-based payment award
One Beacon Restricted shares issued (in shares)								630,000
Total number of performance share grants to be reduced (in shares)	35,000
Numerator value of the ratio in which restricted shares vest (as a percent)	1
Denominator value of the ratio in which restricted shares vest (as a percent)	4
Period in which performance share awards will be reduced by a similar number of shares (in years) \| year	5
Expense recognized \| $		$ 0.4			$ 0.5
Outstanding (in shares)		630,000			630,000
Performance shares
Share-based compensation arrangement by share-based payment award
Forfeiture of performance shares granted for the 2011 - 2013 performance cycle (in shares)		19,583	20,438		70,901	70,746
Expense recognized \| $		$ (0.5)	$ 1.7		$ 1.8	$ 4.5
New grants (in shares)			14,618		194,900	293,478
Outstanding (in shares)		652,144	1,564,829		652,144	1,564,829	671,727		1,464,295	1,770,423	2,224,215

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2011	Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior Notes	$ 669.0	$ 818.8
Preference Shares	250.0	250.0
Carrying Value \| OneBeacon U.S. Holdings, Inc. ("OBH")
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior Notes	269.7	419.6
Carrying Value \| Sirius Group
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior Notes	399.3	399.2
Preference Shares	250.0	250.0
Fair Value \| OneBeacon U.S. Holdings, Inc. ("OBH")
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior Notes	276.6	435.1
Fair Value \| Sirius Group
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior Notes	403.7	390.9
Preference Shares	$ 220.0	$ 212.5

Discontinued Operations (Details) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
Discontinued Operations (Details) $ in Millions	Aug. 31, 2011 count	Sep. 30, 2011 USD ($)	Sep. 30, 2010 USD ($)	Sep. 30, 2011 USD ($)	Sep. 30, 2010 USD ($)	Jun. 30, 2011 USD ($)	Dec. 31, 2010 USD ($)	Jun. 30, 2010 USD ($)	Dec. 31, 2009 USD ($)
Assets held for sale
Fixed maturity investments, at fair value		$ 5,287.7		$ 5,287.7			$ 5,786.1
Short-term investments, at amortized cost (which approximates fair value)		772.8		772.8			975.3
Common equity securities, at fair value		669.8		669.8			667.0
Convertible fixed maturity investments, at fair value		140.5		140.5			143.0
Other long-term investments		328.8		328.8			372.1
Total investments		7,199.6		7,199.6			7,943.5
Cash		557.7		557.7			395.0
Insurance premiums receivable		644.8		644.8			532.5
Deferred acquisition costs		202.9		202.9			176.1
Deferred tax asset		431.7		431.7			431.9
Other assets		760.2		760.2			730.0
Total assets		14,581.7		14,581.7			14,534.1
Liabilities held for sale
Loss and loss adjustment expense reserves		5,882.0	$ 5,970.4	5,882.0	$ 5,970.4	$ 5,642.4	5,736.8	$ 6,198.1	$ 6,379.2
Unearned insurance premiums		976.4		976.4			938.7
Accrued incentive compensation		169.9		169.9			157.4
Other liabilities		1,310.6		1,310.6			1,167.7
Total liabilities		10,562.6		10,562.6			10,273.3
Businesses classified as discontinued operations
Assets held for sale
Fixed maturity investments, at fair value		585.0		585.0			593.8
Short-term investments, at amortized cost (which approximates fair value)		224.9		224.9			131.0
Common equity securities, at fair value							43.0
Convertible fixed maturity investments, at fair value							17.2
Other long-term investments							4.0
Total investments		809.9		809.9			789.0
Cash		235.7		235.7			39.8
Reinsurance recoverable on paid and unpaid losses		34.6		34.6			34.4
Insurance premiums receivable		128.2		128.2			102.9
Deferred acquisition costs		42.8		42.8			34.7
Deferred tax asset		88.2		88.2			67.8
Other assets		60.1		60.1			54.2
Total assets		1,399.5		1,399.5			1,122.8
Liabilities held for sale
Loss and loss adjustment expense reserves		514.9		514.9			450.4
Unearned insurance premiums		258.3		258.3			201.6
Accrued incentive compensation		31.5		31.5			19.1
Other liabilities		104.7		104.7			80.4
Total liabilities		909.4		909.4			751.5
Net assets held for sale		490.1		490.1			$ 371.3
Sirius Group.
Discontinued Operations
Investment income and realized and unrealized investment gains and losses previously included in the Esurance segment excluded from net income (loss) from discontinued operations		$ 0.9	$ 0.9	$ (2.4)	$ 3.7
OneBeacon Segment \| AutoOne
Discontinued Operations
Number of insurance entities (AOIC and AOSIC) sold under the agreement to sell the AutoOne business to Interboro (in counts) \| count	2

Discontinued Operations (Details 2) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Discontinued Operations (Details 2) - USD ($) $ in Millions	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Revenues
Earned insurance premiums	$ 490.6	$ 498.1	$ 1,436.7	$ 1,772.9
Net investment income	42.8	48.9	138.1	157.4
Net realized and unrealized investment gains (losses)	1.7	11.6	78.3	104.7
Other revenue	(33.8)	(7.6)	(68.6)	(21.1)
Total revenues	501.3	551.0	1,584.5	2,013.9
Expenses
Loss and loss adjustment expenses	277.1	253.4	914.0	1,175.9
Insurance and reinsurance acquisition expenses	107.0	102.1	296.2	370.9
Other underwriting expenses	67.0	75.0	211.5	245.9
General and administrative expenses	36.2	32.1	120.4	119.5
Total expenses	500.1	475.8	1,580.9	1,956.4
Income tax (expense) benefit	(0.6)	11.7	1.9	10.3
Income (loss) from discontinued operations	(11.9)	3.6	(10.7)	1.2
Loss from sale of discontinued operations, net of tax	(18.2)		(18.2)
Net income (loss) from discontinued operations, net of tax	30.1	(3.6)	28.9	(1.2)
AutoOne
Expenses
Loss from sale of discontinued operations, net of tax	(18.2)		(18.2)
Businesses classified as discontinued operations
Revenues
Earned insurance premiums	233.8	234.6	698.7	683.6
Net investment income	3.8	5.8	11.8	15.4
Net realized and unrealized investment gains (losses)	(6.4)	10.4	1.4	17.0
Other revenue	17.5	15.3	52.4	44.7
Total revenues	248.7	266.1	764.3	760.7
Expenses
Loss and loss adjustment expenses	180.5	172.7	518.7	508.0
Insurance and reinsurance acquisition expenses	51.4	50.8	154.5	142.2
Other underwriting expenses	32.3	21.4	76.3	66.9
General and administrative expenses	1.7	12.1	37.5	36.5
Total expenses	265.9	257.0	787.0	753.6
Pre-tax income (loss)	(17.2)	9.1	(22.7)	7.1
Income tax (expense) benefit	5.3	(5.5)	12.0	(5.9)
Income (loss) from discontinued operations	(11.9)	3.6	(10.7)	1.2
Net income (loss) from discontinued operations, net of tax	(30.1)	$ 3.6	(28.9)	$ 1.2
Businesses classified as discontinued operations \| AutoOne
Expenses
Loss from sale of discontinued operations, net of tax	$ (18.2)		$ (18.2)

Discontinued Operations (Details 3) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Basic and diluted earnings per share numerators (in millions):
Net income (loss)	$ (15.8)	$ 50.7	$ (32.3)	$ 13.6
Basic earnings per share denominators (in thousands):
Average common shares outstanding during the period (in shares)	7,845	8,332	7,902	8,547
Average unvested restricted shares (in shares)	74	99	68	97
Basic earnings (loss) per share denominator (in shares)	7,919	8,431	7,970	8,644
Diluted earnings per share denominator (in thousands):
Average common shares outstanding during the period (in shares)	7,845	8,332	7,902	8,547
Average unvested restricted shares (in shares)	74	99	68	97
Average outstanding dilutive options to acquire common shares (in shares)				1
Diluted earnings (loss) per share denominator (in shares)	7,919	8,431	7,970	8,645
Businesses classified as discontinued operations
Basic and diluted earnings per share numerators (in millions):
Net income (loss)	$ (30.1)	$ 3.6	$ (28.9)	$ 1.2
Basic earnings per share denominators (in thousands):
Average common shares outstanding during the period (in shares)	7,845	8,332	7,902	8,547
Average unvested restricted shares (in shares)	74	99	68	97
Basic earnings (loss) per share denominator (in shares)	7,919	8,431	7,970	8,644
Diluted earnings per share denominator (in thousands):
Average common shares outstanding during the period (in shares)	7,845	8,332	7,902	8,547
Average unvested restricted shares (in shares)	74	99	68	97
Average outstanding dilutive options to acquire common shares (in shares)				1
Diluted earnings (loss) per share denominator (in shares)	7,919	8,431	7,970	8,645
Basic and diluted earnings (loss) per share (in dollars):	$ (3.81)	$ 0.43	$ (3.63)	$ 0.13

Subsequent Event (Details) - Subsequent Sale - Esurance Disposal - USD ($) $ in Millions	1 Months Ended
	Oct. 31, 2011	Oct. 07, 2011
Subsequent Event
Consideration received on sale of business	$ 1,010
Consideration received in excess of tangible book value		$ 700
Estimated pro forma tangible book value at closing of the legal entities sold		$ 310

Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2011	Oct. 28, 2011
Document and Entity Information
Entity Registrant Name	WHITE MOUNTAINS INSURANCE GROUP LTD
Entity Central Index Key	0000776867
Document Type	10-Q
Document Period End Date	Sep. 30, 2011
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		7,630,717
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	Q3

Label

Element

Value

Cash and Cash Equivalents at Carrying Value Discontinued Operations

wtm_CashAndCashEquivalentsAtCarryingValueDiscontinuedOperations

$ 4,700,000

Cash and Cash Equivalents at Carrying Value Discontinued Operations

wtm_CashAndCashEquivalentsAtCarryingValueDiscontinuedOperations

3,900,000

Cash and Cash Equivalents at Carrying Value Discontinued Operations

wtm_CashAndCashEquivalentsAtCarryingValueDiscontinuedOperations

^[1]

Cash and Cash Equivalents at Carrying Value Discontinued Operations

wtm_CashAndCashEquivalentsAtCarryingValueDiscontinuedOperations

$ 4,400,000

[1]	AutoOne cash of $5.5 is included in assets held for sale at September 30, 2011.