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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2013	Apr. 29, 2013
Document and Entity Information [Abstract]
Entity Registrant Name	WHITE MOUNTAINS INSURANCE GROUP LTD
Entity Central Index Key	0000776867
Document Type	10-Q
Document Period End Date	Mar. 31, 2013
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		6,176,210
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q1
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No

CONSOLIDATED BALANCE SHEET - USD ($) $ in Millions	Mar. 31, 2013	Dec. 31, 2012
Assets
Fixed maturity investments, at fair value	$ 4,854.4	$ 5,196.2
Short-term investments, at amortized cost (which approximates fair value)	654.4	630.6
Common equity securities, at fair value	1,073.2	1,029.7
Convertible fixed maturity investments, at fair value	95.6	127.4
Other long-term investments	295.2	294.2
Total investments	6,972.8	7,278.1
Cash (restricted: $188.5 and $249.8)	411.5	462.4
Reinsurance recoverable on unpaid losses	410.8	429.1
Reinsurance recoverable on paid losses	15.6	17.9
Insurance and reinsurance premiums receivable	717.6	556.3
Funds held by ceding companies	110.6	127.4
Investments in unconsolidated affiliates	383.6	387.9
Deferred acquisition costs	190.4	195.3
Deferred tax asset	539.1	569.6
Ceded unearned insurance and reinsurance premiums	144.1	91.8
Accrued investment income	44.7	45.9
Accounts receivable on unsettled investment sales	99.0	3.9
Other assets	416.5	503.0
Assets held for sale	2,155.2	2,226.8
Total assets	12,611.5	12,895.4
Liabilities
Loss and loss adjustment expense reserves	3,100.6	3,168.9
Unearned insurance and reinsurance premiums	1,064.9	924.1
Variable annuity benefit guarantee	251.6	441.5
Debt	676.2	751.2
Deferred tax liability	337.1	341.3
Accrued incentive compensation	100.8	159.0
Ceded reinsurance payable	175.7	116.5
Funds held under reinsurance treaties	67.3	43.7
Accounts payable on unsettled investment purchases	25.7	11.4
Other liabilities	374.4	452.8
Liabilities held for sale	2,155.2	2,226.8
Total liabilities	8,329.5	8,637.2
White Mountains’ common shareholders’ equity
White Mountains’ common shares at $1 par value per share - authorized 50,000,000 shares; issued and outstanding 6,176,210 and 6,290,964 shares	6.2	6.3
Paid-in surplus	1,031.1	1,050.9
Retained earnings	2,601.4	2,542.7
Accumulated other comprehensive income, after tax:
Equity in net unrealized gains from investments in unconsolidated affiliates	49.7	57.7
Net unrealized foreign currency translation gains	82.0	85.7
Pension liability and other	(11.5)	(11.5)
Total White Mountains’ common shareholders’ equity	3,758.9	3,731.8
Non-controlling interests
Non-controlling interest - OneBeacon Ltd.	263.5	251.4
Non-controlling interest - SIG Preference Shares	250.0	250.0
Non-controlling interest - HG Global	16.6	16.6
Non-controlling interest - BAM	(53.8)	(36.0)
Non-controlling interest - other	46.8	44.4
Total non-controlling interests	523.1	526.4
Total equity	4,282.0	4,258.2
Total liabilities and equity	$ 12,611.5	$ 12,895.4

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2013	Dec. 31, 2012
Cash (in dollars)	$ 188.5	$ 249.8
Common shares, par value per share (in dollars per share)	$ 1.00	$ 1.00
Common shares, authorized shares	50,000,000	50,000,000
Common shares, issued shares	6,176,210	6,290,964
Common shares, outstanding shares	6,176,210	6,290,964

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Revenues:
Earned insurance and reinsurance premiums	$ 495.4	$ 498.0
Net investment income	28.5	41.8
Net realized and unrealized investment gains	75.2	58.6
Other revenue	28.3	31.2
Total revenues	627.4	629.6
Expenses:
Loss and loss adjustment expenses	244.3	249.8
Insurance and reinsurance acquisition expenses	98.2	109.1
Other underwriting expenses	79.1	73.5
General and administrative expenses	43.8	45.5
Interest expense on debt	10.2	10.9
Total expenses	475.6	488.8
Pre-tax income from continuing operations	151.8	140.8
Income tax expense	(41.6)	(31.1)
Net income from continuing operations	110.2	109.7
Net income (loss) from discontinued operations, net of tax	0.5	(9.3)
Income before equity in earnings of unconsolidated affiliates	110.7	100.4
Equity in earnings of unconsolidated affiliates, net of tax	9.2	10.2
Net income	119.9	110.6
Net loss (income) attributable to non-controlling interests	0.5	(16.8)
Net income attributable to White Mountains’ common shareholders	120.4	93.8
Other comprehensive income, net of tax:
Change in equity in net unrealized losses from investments in unconsolidated affiliates	(8.0)	(1.2)
Change in foreign currency translation and other	(3.7)	23.5
Comprehensive income	108.7	116.1
Comprehensive income attributable to non-controlling interests	0.0	0.0
Comprehensive income attributable to White Mountains’ common shareholders	$ 108.7	$ 116.1
Income (loss) per share attributable to White Mountains’ common shareholders
Continuing operations	$ 19.10	$ 13.86
Discontinued operations	0.07	(1.25)
Total consolidated operations	19.17	12.61
Diluted income (loss) per share
Continuing operations	19.10	13.86
Discontinued operations	0.07	(1.25)
Total consolidated operations	19.17	12.61
Dividends declared per White Mountains’ common share	$ 1	$ 1

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions	Total	Common shares and paid-in surplus White Mountains	Retained earnings White Mountains	Accum. Other comprehensive income (loss),after-tax White Mountains	White Mountains excluding noncontrolling interest White Mountains	Non-controlling interest	Total Equity includes Noncontrolling Interest
Balances at Dec. 31, 2011		$ 1,261.3	$ 2,789.7	$ 36.7	$ 4,087.7	$ 580.2	$ 4,667.9
Increase (Decrease) in Shareholders' Equity
Net income	$ 110.6	0.0	93.8	0.0	93.8	16.8	110.6
Net change in unrealized losses from investments in unconsolidated affiliates	(1.2)	0.0	0.0	(1.2)	(1.2)	0.0	(1.2)
Change in foreign currency translation and other	23.5	0.0	0.0	23.5	23.5	0.0	23.5
Net change in pension liability and other accumulated comprehensive items		0.0	0.0	0.0	0.0	0.0	0.0
Total comprehensive income	116.1	0.0	93.8	22.3	116.1	16.8	132.9
Dividends declared on common shares		0.0	(6.6)	0.0	(6.6)	0.0	(6.6)
Dividends to noncontrolling interests		0.0	0.0	0.0	0.0	(5.0)	(5.0)
Repurchases and retirements of common shares	(485.8)	(162.6)	(323.2)	0.0	(485.8)	0.0	(485.8)
Issuances of common shares		4.6	0.0	0.0	4.6	0.0	4.6
Net distributions to noncontrolling interests		0.0	0.0	0.0	0.0	(1.5)	(1.5)
Amortization of restricted share and option awards		2.8	0.0	0.0	2.8	0.2	3.0
Balances at Mar. 31, 2012		1,106.1	2,553.7	59.0	3,718.8	590.7	4,309.5
Balances at Dec. 31, 2012	4,258.2	1,057.2	2,542.7	131.9	3,731.8	526.4	4,258.2
Increase (Decrease) in Shareholders' Equity
Net income	119.9	0.0	120.4	0.0	120.4	(0.5)	119.9
Net change in unrealized losses from investments in unconsolidated affiliates	(8.0)	0.0	0.0	(8.0)	(8.0)	0.0	(8.0)
Change in foreign currency translation and other	(3.7)	0.0	0.0	(3.7)	(3.7)	0.0	(3.7)
Net change in pension liability and other accumulated comprehensive items		0.0	0.0	0.0	0.0	0.0	0.0
Total comprehensive income	108.7	0.0	120.4	(11.7)	108.7	(0.5)	108.2
Dividends declared on common shares		0.0	(6.2)	0.0	(6.2)	0.0	(6.2)
Dividends to noncontrolling interests		0.0	0.0	0.0	0.0	(5.2)	(5.2)
Repurchases and retirements of common shares	(79.0)	(23.5)	(55.5)	0.0	(79.0)	0.0	(79.0)
Issuances of common shares		0.0	0.0	0.0	0.0	0.0	0.0
Net distributions to noncontrolling interests		0.0	0.0	0.0	0.0	2.2	2.2
Amortization of restricted share and option awards		3.6	0.0	0.0	3.6	0.2	3.8
Balances at Mar. 31, 2013	$ 4,282.0	$ 1,037.3	$ 2,601.4	$ 120.2	$ 3,758.9	$ 523.1	$ 4,282.0

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Cash flows from operations:
Net income	$ 119.9	$ 110.6
Charges (credits) to reconcile net income to net cash (used for) provided from operations:
Net realized and unrealized investment gains	(75.2)	(58.6)
Deferred income tax expense	25.8	26.3
Net (income) loss from discontinued operations	(0.5)	9.3
Gain on sale of subsidiary - Essentia	(23.0)	0.0
Excess of FV of aquired net assets over cost - American Fuji	(6.9)	0.0
Undistributed equity in earnings from unconsolidated affiliates, net of tax	(9.2)	(10.2)
Other operating items:
Net change in loss and loss adjustment expense reserves	(86.2)	(172.0)
Net change in reinsurance recoverable on paid and unpaid losses	20.1	43.7
Net change in unearned insurance and reinsurance premiums	146.1	215.3
Net change in variable annuity benefit guarantee liabilities	(189.9)	(220.0)
Net change in variable annuity benefit derivative instruments	22.5	116.1
Net change in deferred acquisition costs	4.5	(10.0)
Net change in funds held by ceding companies	25.2	(0.6)
Net change in ceded unearned premiums	(52.4)	(54.4)
Net change in funds held under reinsurance treaties	23.7	1.3
Net change in insurance and reinsurance premiums receivable	(179.7)	(242.1)
Net change in ceded reinsurance payable	75.7	51.2
Net change in other assets and liabilities, net	(24.7)	(78.1)
Net cash used for operations - continuing operations	(184.2)	(272.2)
Net cash used for operations - discontinued operations	(40.7)	(61.1)
Net cash used for operations	(224.9)	(333.3)
Cash flows from investing activities:
Net change in short-term investments	26.3	(88.1)
Sales of fixed maturity and convertible fixed maturity investments	1,962.9	2,450.2
Maturities, calls and paydowns of fixed maturity and convertible fixed maturity investments	176.3	194.9
Sales of common equity securities	181.9	22.2
Distributions and redemptions of other long-term investments	20.9	11.1
Sales of consolidated and unconsolidated affiliates, net of cash sold	31.3	0.0
Funding of operational cash flows for discontinued operations	(40.7)	(61.1)
Purchases of other long-term investments	(17.4)	(6.1)
Purchases of common equity securities	(143.3)	(98.7)
Purchases of fixed maturity and convertible fixed maturity investments	(1,742.5)	(1,737.1)
Purchases of consolidated and unconsolidated affiliates, net of cash acquired	(9.2)	0.0
Net change in unsettled investment purchases and sales	(80.8)	67.1
Net acquisitions of property and equipment	(3.5)	(0.6)
Net cash provided from investing activities - continuing operations	362.2	753.8
Net cash provided from investing activities - discontinued operations	40.7	61.1
Net cash provided from investing activities	402.9	814.9
Cash flows from financing activities:
Draw down of revolving line of credit	80.0	0.0
Repayment of revolving line of credit	(155.0)	0.0
Payments on capital lease obligation	(1.8)	(1.2)
Cash dividends paid to the Company’s common shareholders	(6.2)	0.0
Cash dividends paid to OneBeacon Ltd.’s non-controlling common shareholders	(5.0)	(5.0)
Common shares repurchased	(79.0)	(485.8)
Net cash used for financing activities - continuing operations	(167.0)	(492.0)
Net cash (used for) provided from financing activities - discontinued operations	0.0	0.0
Net cash used for financing activities	(167.0)	(492.0)
Effect of exchange rate changes on cash	(0.6)	(1.7)
Net change in cash during the period	10.4	(12.1)
Cash reclassified from assets held for sale (cash sold of $0 and $3.5)	0.0	5.5
Cash balances at beginning of period (excludes restricted cash balances of $249.8 and $453.5)	212.6	251.9	$ 251.9
Cash balances at end of period (excludes restricted cash balances of $188.5 and $360.1)	223.0	245.3	$ 212.6
Supplemental cash flows information:
Interest paid	(12.9)	(12.8)
Net income tax payments to national governments	$ (2.2)	$ (8.7)

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Cash Reclassified to Assets Held-for-sale	$ 0.0	$ 3.5
Restricted cash balances, beginning of period	249.8	453.5
Restricted cash balances, end of period	$ 188.5	$ 360.1

Summary of Significant Accounting Policies	3 Months Ended
Summary of Significant Accounting Policies	Mar. 31, 2013
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation These interim consolidated financial statements include the accounts of White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”) and its subsidiaries (collectively, with the Company, “White Mountains”) and have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”). The Company is an exempted Bermuda limited liability company whose principal businesses are conducted through its property and casualty insurance and reinsurance subsidiaries and affiliates. The Company’s headquarters is located at 14 Wesley Street, Hamilton, Bermuda HM 11, its principal executive office is located at 80 South Main Street, Hanover, New Hampshire 03755-2053 and its registered office is located at Clarendon House, 2 Church Street, Hamilton, Bermuda HM 11. White Mountains’ reportable segments are OneBeacon, Sirius Group, HG Global/BAM and Other Operations. The OneBeacon segment consists of OneBeacon Insurance Group, Ltd. (“OneBeacon Ltd.”), an exempted Bermuda limited liability company that owns a family of U.S.-based property and casualty insurance companies (collectively, “OneBeacon”). 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 both March 31, 2013 and December 31, 2012, White Mountains owned 75.2% of OneBeacon Ltd.’s outstanding common shares. As discussed further in Note 2, OneBeacon entered into a definitive agreement to sell its runoff business in October 2012 (the “Runoff Transaction”) and sold its AutoOne Insurance business (“AutoOne”) in February 2012. Accordingly, the runoff business and AutoOne are presented as discontinued operations. Assets and liabilities associated with the runoff business as of March 31, 2013 and December 31, 2012 have been presented as held for sale in the financial statements. Prior year income statement and cash flow amounts have been reclassified to conform to the current year's presentation. (See Note 15 for discontinued operations). The Sirius Group segment consists of Sirius International Insurance Group, Ltd., an exempted Bermuda limited liability company, and its subsidiaries (collectively, “Sirius Group”). Sirius Group provides insurance and reinsurance products for property, accident and health, aviation and space, trade credit, marine, agriculture and certain other exposures on a worldwide basis through its subsidiaries, Sirius International Insurance Corporation (“Sirius International”), Sirius America Insurance Company (“Sirius America”) and Lloyds Syndicate 1945 (“Syndicate 1945”). Sirius Group also specializes in the acquisition and management of runoff insurance and reinsurance companies both in the United States and internationally through its White Mountains Solutions division (“WM Solutions”). The HG Global/BAM segment consists of White Mountains' investment in HG Global Ltd. (“HG Global”) and the consolidated results of Build America Mutual Assurance Company (“BAM”). During the third quarter of 2012, White Mountains capitalized HG Global with approximately $600 million to fund the start-up of BAM. BAM is a municipal bond insurer domiciled in New York that was established to provide insurance on bonds issued to support essential U.S. public purposes such as schools, utilities, core governmental functions and existing transportation facilities. HG Global, together with its subsidiaries, provided the initial capitalization of BAM through the purchase of $503 million of surplus notes issued by BAM (the “BAM Surplus Notes”). HG Global, through its wholly-owned subsidiary, HG Re Ltd. (“HG Re”), also provides 15%-of-par, first loss reinsurance protection for policies underwritten by BAM. As of March 31, 2013 and December 31, 2012, White Mountains owned 97.3% of HG Global's preferred equity and 88.7% of its common equity. White Mountains does not have an ownership interest in BAM, which is a mutual insurance company owned by its members. However, GAAP requires White Mountains to consolidate BAM's results in its financial statements. BAM's results are attributed to non-controlling interests. White Mountains’ Other Operations segment consists of the Company and its intermediate holding companies, its wholly-owned investment management subsidiary, White Mountains Advisors LLC (“WM Advisors”), White Mountains’ variable annuity reinsurance business, White Mountains Life Reinsurance (Bermuda) Ltd. (“WM Life Re”), which is in runoff, as well as various other entities not included in other segments. Prior to 2012, the Other Operations segment also included the consolidated results of the Tuckerman Capital, LP fund (“Tuckerman Fund I”). On December 31, 2011, Tuckerman Fund I was dissolved and all of the net assets of the fund were distributed to the owners of the fund, of which White Mountains owned approximately 94%. In conjunction with the dissolution, White Mountains received a portion of the shares of Hamer, LLC (“Hamer”) and Bri-Mar Manufacturing, LLC (“Bri-Mar”), two small manufacturing companies. Prior to the dissolution, Tuckerman Fund I was consolidated within White Mountains' financial statements. The consolidated results of Hamer and Bri-Mar are included in the Other Operations segment from January 1, 2012 through September 30, 2012, from which point these companies were no longer consolidated by White Mountains. White Mountains' discontinued operations consist of OneBeacon's runoff business and AutoOne. The OneBeacon runoff business included assets and liabilities that were principally related to non-specialty commercial lines and certain other runoff business that it no longer writes, including nearly all of its asbestos and environmental reserves. AutoOne was formed by OneBeacon in 2001 to provide products and services to automobile assigned risk markets primarily in New York and New Jersey. All significant intercompany transactions have been eliminated in consolidation. These interim financial statements include all adjustments considered necessary by management to fairly present the financial position, results of operations and cash flows of White Mountains. These interim financial statements may not be indicative of financial results for the full year and should be read in conjunction with the Company’s 2012 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. Certain amounts in the prior period financial statements have been reclassified to conform to the current presentation. Refer to the Company’s 2012 Annual Report on Form 10-K for a complete discussion regarding White Mountains’ significant accounting policies. Non-controlling Interests Non-controlling interests consist of the ownership interests of non-controlling shareholders in consolidated subsidiaries and are presented separately on the balance sheet. The percentage of the non-controlling shareholders' ownership interest in OneBeacon Ltd. at both March 31, 2013 and December 31, 2012 was 24.8%. In July 2012, HG Global was capitalized with $594.5 million from White Mountains and $14.5 million from certain management members of BAM, the latter of which is included in non-controlling interest. Upon closing, certain BAM management members also received additional common and preferred shares of HG Global that resulted in a $2.2 million allocation of the carrying value of White Mountains' investment in HG Global to the non-controlling interest, which was recorded as an adjustment to paid-in surplus in White Mountains' consolidated statement of changes in equity. White Mountains is required to consolidate BAM in its GAAP financial statements. However, since BAM is a mutual insurance company that is owned by its members, BAM's results do not affect White Mountains' common shareholders' equity as they are attributable to non-controlling interests. For the three months ended March 31, 2013, BAM reported $20.1 million in losses that have been allocated to non-controlling interest. In May 2007, Sirius International Group, Ltd. (“SIG”), an intermediate holding company of Sirius Group, issued $250 million non-cumulative perpetual preference shares, with a $1,000 per share liquidation preference (the “SIG Preference Shares”), and received $245.7 million of proceeds, net of $4.3 million of issuance costs and commissions. SIG Preference Shares and dividends thereon are included in non-controlling interest on the balance sheet and on the statement of income and comprehensive income. At March 31, 2013 and December 31, 2012, the non-controlling equity interest in White Mountains' consolidated limited partnerships was $44.1 million and $41.5 million. At March 31, 2013 and December 31, 2012, the non-controlling equity interest in A.W.G. Dewar Inc, a subsidiary of OneBeacon, was $2.5 million and $2.8 million. At both March 31, 2013 and December 31, 2012, the non-controlling equity interest in Passage2Health Limited, a subsidiary of Sirius Group, was $0.2 million. Recently Adopted Changes in Accounting Principles Policy Acquisition Costs On January 1, 2012, White Mountains adopted ASU 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts (ASC 944). The new standard changes the types of policy acquisition costs that are eligible for deferral. Specifically, the new guidance limits deferrable costs to those that are incremental direct costs of contract acquisition and certain costs related to acquisition activities performed by the insurer, such as underwriting, policy issuance and processing, medical and inspection costs and sales force contract selling. The ASU defines incremental direct costs as those costs that result directly from and were essential to the contract acquisition and would not have been incurred absent the acquisition. Accordingly, under the new guidance, deferrable acquisition costs are limited to costs related to successful contract acquisitions. Acquisition costs that are not eligible for deferral are to be charged to expense in the period incurred. White Mountains adopted ASU 2010-26 prospectively. Upon adoption, certain acquisition costs, primarily a portion of the profit sharing commissions associated with OneBeacon's collector car and boat business, no longer met the criteria for deferral. During the year ended December 31, 2012, White Mountains recognized $5.6 million of expense related to such previously deferrable acquisition costs that, if White Mountains had adopted ASU 2010-26 retrospectively, would have been recognized during 2011. Fair Value Measurements On January 1, 2012, White Mountains adopted ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRS. The ASU clarifies existing guidance with respect to the concepts of highest and best use and valuation premise and measuring instruments classified within a reporting entity’s shareholders’ equity. The ASU also clarifies disclosure requirements, requiring disclosure of quantitative information about unobservable inputs used in Level 3 fair value measurements. The ASU also amends existing guidance. In circumstances where a reporting entity manages a portfolio of financial assets and liabilities based on the net market and counterparty credit risk exposures, the ASU permits determination of the fair value of those instruments to be based on the net risk exposure. In addition, the ASU permits the application of premiums or discounts to be applied in a fair value measurement to the extent that market participants would consider them in valuing the financial instruments. The ASU also expands the required disclosures for Level 3 measurements, requiring that reporting entities provide a narrative description of the sensitivity of Level 3 fair value measurements to changes in unobservable inputs and the interrelationships between those inputs, if any. As a result of adopting ASU 2011-04, White Mountains expanded its fair value disclosures. (See Note 5). Recently Issued Accounting Pronouncements Offsetting Assets and Liabilities Effective January 1, 2013, White Mountains adopted ASU 2011-11, Disclosures about Offsetting Assets and Liabilities (ASC 210) and ASU 2013-01, Clarifying the Scope of Disclosures about Offsetting Assets and Liabilities. The new guidance expands the required disclosures in circumstances where either balances have been offset or the right of offset exists to make it easier for financial statement users to evaluate the effect or potential effect of netting arrangements on a reporting entity’s financial position. White Mountains is party to master netting arrangements in connection with derivative instruments held by WM Life Re and Sirius International. As a result of adoption, White Mountains has expanded its disclosures to present the gross amounts of assets and liabilities subject to master netting arrangements along with any related collateral amounts.

Significant Transactions	3 Months Ended
Significant Transactions	Mar. 31, 2013
Significant Transactions Disclosure
Significant Transactions	Significant Transactions Sale of Essentia Insurance Company Effective January 1, 2013, OneBeacon completed the sale of Essentia Insurance Company (“Essentia”), an indirect wholly-owned subsidiary which wrote the collector car and boat business, to Markel Corporation. Concurrently therewith, OneBeacon and Hagerty Insurance Agency (“Hagerty”) terminated their underwriting arrangement with respect to the collector car and boat business. OneBeacon recognized a pre-tax gain on sale of $23.0 million ($15.0 million after tax) in the first quarter of 2013. The business associated with this agreement generated net written premiums of $35.3 million, or 11.7% of consolidated net written premiums, for the three months ended March 31, 2012. WM Solutions In the third quarter of 2013, WM Solutions acquired American Fuji Fire (“American Fuji”), an AIG runoff subsidiary. The transaction resulted in a gain of $6.9 million recorded in other revenues. Sale of OneBeacon Runoff Business On October 17, 2012, one of OneBeacon’s indirect wholly-owned subsdiaries, OneBeacon Insurance Group LLC, entered into a definitive agreement with Trebuchet US Holdings, Inc. (“Trebuchet”), a wholly-owned subsidiary of Armour Group Holdings Limited (together with Trebuchet, “Armour”), to sell its runoff business. Pursuant to the terms of the agreement, at closing OneBeacon will transfer to Trebuchet all of the issued and outstanding shares of common stock of certain legal entities that will contain the assets, liabilities (including gross and ceded loss reserves) and capital supporting the runoff business as well as certain elements of the runoff business infrastructure, including staff and office space. The transaction is subject to regulatory approvals (see Note 15). Sale of AutoOne On February 22, 2012, OneBeacon completed the sale of AutoOne to Interboro Holdings, Inc. (“Interboro”). OneBeacon formed AutoOne in 2001 to provide products and services to automobile assigned risk markets primarily in New York and New Jersey. OneBeacon transferred to the buyer AutoOne Insurance Company (“AOIC”) and AutoOne Select Insurance Company (“AOSIC”), which contained the assets, liabilities (including loss reserves and unearned premiums), and the capital of the AutoOne business, and transferred substantially all of the AutoOne infrastructure including systems and office space as well as certain staff. As a result of the sale, AutoOne is reported as discontinued operations (see Note 15). Common Shares Repurchased and Retired During the past several years, White Mountains' board of directors has authorized the Company to repurchase its common shares, from time to time, subject to market conditions. The repurchase authorizations do not have a stated expiration date. As of March 31, 2013, White Mountains may repurchase an additional 545,496 shares under these board authorizations. In addition, from time to time White Mountains has also repurchased its common shares through tender offers that were separately approved by its board of directors. During the three months ended March 31, 2013, the Company repurchased 140,224 common shares for $79.0 million at an average share price of $564, which were comprised of 140,000 common shares repurchased under the board authorization and 224 common shares repurchased pursuant to employee benefit plans. Shares repurchased pursuant to employee benefit plans do not fall under the board authorizations referred to above. During the three months ended March 31, 2012, the Company repurchased 977,019 common shares for $485.8 million at an average share price of $497, which were comprised of (1) 157,629 common shares repurchased under the board authorization for $76.0 million at an average share price of $482; (2) 816,829 common shares repurchased through a fixed-price tender offer for $408.6 million at a share price of $500; and (3) 2,561 common shares repurchased to satisfy employee income tax withholding, pursuant to employee benefit plans.

Loss and Loss Adjustment Expense Reserves

3 Months Ended

Mar. 31, 2013

Insurance Loss Reserves [Abstract]

Loss and Loss Adjustment Expense Reserves

The following table summarizes the loss and loss adjustment expense (“LAE”) reserve activities of White Mountains’ insurance and reinsurance subsidiaries for the three months ended March 31, 2013 and 2012:



	Three Months Ended
	March 31,
Millions	2013			2012
Gross beginning balance	$	3,168.9		$	5,702.3
Less beginning reinsurance recoverable on unpaid losses	(429.1		)	(2,507.3		)
Net loss and LAE reserves	2,739.8			3,195.0

Less: Beginning net loss and LAE reserves for OneBeacon's runoff business⁽¹⁾	—			(383.3		)

Loss and LAE reserves acquired - American Fuji	21.3			—

Loss and LAE incurred relating to:
Current year losses	242.9			257.4
Prior year losses	1.4			(7.6		)
Total incurred losses and LAE	244.3			249.8

Accretion of fair value adjustment to loss and LAE reserves	1.2			7.1
Foreign currency translation adjustment to loss and LAE reserves	(9.6		)	11.8

Loss and LAE paid relating to:
Current year losses	(36.6		)	(44.5		)
Prior year losses	(270.6		)	(322.9		)
Total loss and LAE payments	(307.2		)	(367.4		)

Plus: Ending net loss and LAE reserves for OneBeacon's runoff business⁽¹⁾	—			332.4

Net ending balance	2,689.8			3,045.4
Plus ending reinsurance recoverable on unpaid losses	410.8			2,465.4
Gross ending balance	$	3,100.6		$	5,510.8

⁽¹⁾ Loss and LAE reserve balances for OneBeacon's run-off business prior to September 30, 2012 were not classified as held for sale. Adjustment is to present loss and LAE reserve activities from continuing operations.

Loss and LAE incurred relating to prior year losses for the three months ended March 31, 2013

During the three months ended March 31, 2013, White Mountains experienced $1.4 million of net unfavorable loss reserve development. OneBeacon had net favorable loss reserve development of $2.9 million primarily driven by medical facilities and managed care errors and omissions lines in its healthcare business, which is included in OneBeacon's Professional Insurance underwriting unit. Sirius Group had net unfavorable loss reserve development of $4.3 million primarily due to a late reported agricultural claim related to the 2012 U.S. drought.

Loss and LAE incurred relating to prior year losses for the three months ended March 31, 2012

During the three months ended March 31, 2012, White Mountains experienced $7.6 million of net favorable loss reserve development. OneBeacon had net favorable loss reserve development of $1.9 million, primarily due to lower than expected severity on non-catastrophe losses related to professional liability lines, multiple peril liability lines and other general liability lines. Sirius Group had net favorable loss reserve development of $5.7 million included reductions for the 2011 Japan earthquake and tsunami of $8.1 million, partially offset by increases to asbestos and environmental reserves and reserves for other prior period catastrophe losses.

Fair value adjustment to loss and LAE reserves

In connection with purchase accounting for acquisitions, White Mountains is required to adjust loss and LAE reserves and the related reinsurance recoverables to fair value on their respective acquired balance sheets. The net reduction to loss and LAE reserves is being recognized through an income statement charge ratably with and over the period the claims are settled.

White Mountains recognized $1.2 million of such charges, recorded as loss and LAE for the three months ended March 31, 2013, and $7.1 million for the three months ended March 31, 2012. Accretion of fair value adjustment to losses and LAE reserves increased by $5.0 million in the first quarter of 2012 due to the acceleration of the amortization of the purchase accounting established for the acquisition of Scandinavian Re. This acceleration was a result of a final settlement and commutation of Scandinavian Re's multi-year retrocessional Casualty Aggregate Stop Loss Agreement with St. Paul Fire & Marine Insurance Company (“St Paul”). As of March 31, 2013, the remaining pre-tax un-accreted adjustment was $4.5 million.

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
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-URI http://asc.fasb.org/extlink&oid=6482852&loc=d3e14931-158439

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

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

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

+ Details

Third Party Reinsurance

3 Months Ended

Mar. 31, 2013

Reinsurance Disclosures [Abstract]

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 March 31, 2013, OneBeacon had $2.4 million and $105.8 million of reinsurance recoverables on paid and unpaid losses. Reinsurance contracts do not relieve OneBeacon of its 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. As of March 31, 2013, greater than 90% of reinsurance recoverables on paid and unpaid losses are from reinsurers with an A.M. Best Company ("A.M. Best") rating of A (Excellent, which is the third highest of 16 financial strength ratings) or better. The largest recoverable from an individual reinsurer was $11.0 million with Hannover Ruckversich, which has an A.M. Best rating of A+ (Superior, which is the second highest of 16 financial strength ratings). The reinsurance balances associated with the runoff business are included in discontinued operations (see Note 15).

Sirius Group

At March 31, 2013, Sirius Group had $13.2 million of reinsurance recoverables on paid losses and $305.0 million of reinsurance recoverables on unpaid losses that will become recoverable if claims are paid in accordance with current reserve estimates. Because retrocessional reinsurance contracts do not relieve Sirius Group of its obligation to its insureds, the collectability of balances due from Sirius Group's reinsurers is critical to its financial strength. Sirius Group monitors the financial strength and ratings of retrocessionaires on an ongoing basis.

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



Top Reinsurers (Millions)	Balance at March 31, 2013		% of Total		A.M. Best Rating⁽¹⁾	% Collateralized
Berkshire Hathaway	$	56.9	18	%	A++	—	%
Swiss Re Group	34.8		11	%	A+	—	%
Olympus Reinsurance Company⁽²⁾	24.9		8	%	NR-5	100	%
Lloyds of London⁽³⁾	17.0		5	%	A	9	%
Michigan Catastrophic Claims Association⁽⁴⁾	14.7		5	%	N/A	—	%

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

⁽²⁾Non-U.S. insurance entity. The balance is 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, established by the State of Michigan with the power to issue and collect assessments, to which every insurance company that sells automobile coverage in Michigan is required to be a member. A.M. Best does not rate MCCA. Sirius Group acquired its recoverable from MCCA in the acquisition of Stockbridge Insurance Company. As part of the acquisition, Sirius Group obtained $25.0 of reinsurance protection from the seller (currently rated A+ by A.M. Best) for unfavorable loss reserve development, including uncollectible reinsurance.

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6816-158387

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
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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 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.

Reference 10: 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 11: 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 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 6
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Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 13
-Article 7

+ Details

Investment Securities

3 Months Ended

Mar. 31, 2013

Investments, Debt and Equity Securities [Abstract]

Investment Securities

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

Realized investment gains and losses resulting from sales of investment securities are accounted for using the specific identification method. Premiums and discounts on all fixed maturity investments are amortized or accreted to income over the anticipated life of the investment. Short-term investments consist of money market funds, certificates of deposit and other securities which, at the time of purchase, mature or become available for use within one year. Short-term investments are carried at amortized or accreted cost, which approximated fair value as of March 31, 2013 and December 31, 2012.

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 months ended March 31, 2013 and 2012 consisted of the following:



	Three Months Ended
	March 31,
Millions	2013			2012
Investment income:
Fixed maturity investments	$	26.0		$	36.7
Short-term investments	.8			1.0
Common equity securities	4.7			4.4
Convertible fixed maturity investments	.8			1.9
Other long-term investments	.7			.8
Interest on funds held under reinsurance treaties	—			—
Total investment income	33.0			44.8
Less third-party investment expenses	(4.5		)	(3.0		)
Net investment income, pre-tax	$	28.5		$	41.8

Net Realized and Unrealized Investment Gains and Losses

The following table summarizes net realized and unrealized investment gains (losses) for the three months ended March 31, 2013 and 2012:



	Three Months Ended									Three Months Ended
	March 31, 2013									March 31, 2012
Millions	Net realized and unrealized gains (losses)			Net foreign exchange gains (losses)			Total net realized and unrealized gains (losses) reflected in earnings			Net realized and unrealized gains (losses)			Net foreign currency gains (losses)			Total net realized and unrealized gains (losses) reflected in earnings
Fixed maturity investments	$	(8.0	)	$	(10.0	)	$	(18.0	)	$	30.7		$	(21.4	)	$	9.3
Short-term investments	—			.1			.1			—			(.3		)	(.3		)
Common equity securities	84.5			(.2		)	84.3			36.6			—			36.6
Convertible fixed maturity investments	1.6			(.2		)	1.4			6.2			—			6.2
Other long-term investments	6.5			.5			7.0			10.2			(3.4		)	6.8
Forward Contracts	.4			—			.4			—			—			—
Net realized and unrealized investment gains (losses), pre-tax	85.0			(9.8		)	75.2			83.7			(25.1		)	58.6
Income tax expense attributable to net realized and unrealized investment (losses) gains	(15.9		)	2.2			(13.7		)	(20.6		)	6.6			(14.0		)
Net realized and unrealized investment gains (losses), after tax	$	69.1		$	(7.6	)	$	61.5		$	63.1		$	(18.5	)	$	44.6

The following table summarizes the amount of total pre-tax gains included in earnings attributable to unrealized investment gains for Level 3 investments for the three months ended March 31, 2013 and 2012:



	Three Months Ended
	March 31,
Millions	2013			2012
Fixed maturity investments	$	.2		$	7.8
Common equity securities	(.1		)	.5
Other long-term investments	6.4			7.2
Total unrealized investment gains, pre-tax - Level 3 investments	$	6.5		$	15.5

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 March 31, 2013 and December 31, 2012 were as follows:



	March 31, 2013
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency gains (losses)			Carrying value
U.S. Government and agency obligations	$	435.9	$	.9	$	(.1	)	$	(1.2	)	$	435.5
Debt securities issued by corporations	2,361.2		75.7		(2.6		)	(24.6		)	2,409.7
Municipal obligations	5.3		—		(.1		)	—			5.2
Mortgage-backed and asset-backed securities	1,698.7		12.6		(1.9		)	(2.1		)	1,707.3
Foreign government, agency and provincial obligations	516.4		5.4		(6.3		)	(9.4		)	506.1
Preferred stocks	79.9		7.7		—			(.1		)	87.5
Total fixed maturity investments including assets held for sale	$	5,097.4	$	102.3	$	(11.0	)	$	(37.4	)	$	5,151.3
Fixed maturity investments reclassified to assets held for sale related to the Runoff Transaction											(296.9		)
Total fixed maturity investments											$	4,854.4



	December 31, 2012
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency gains (losses)			Carrying value
U.S. Government and agency obligations	$	440.4	$	1.0	$	(.1	)	$	(1.2	)	$	440.1
Debt securities issued by corporations	2,321.4		88.3		(1.6		)	(23.0		)	2,385.1
Municipal obligations	5.3		—		(.1		)	—			5.2
Mortgage-backed and asset-backed securities	2,081.0		25.1		(1.1		)	(9.4		)	2,095.6
Foreign government, agency and provincial obligations	526.6		6.9		(3.0		)	(8.6		)	521.9
Preferred stocks	79.9		6.7		—			(.2		)	86.4
Total fixed maturity investments including assets held for sale	$	5,454.6	$	128.0	$	(5.9	)	$	(42.4	)	$	5,534.3
Fixed maturity investments reclassified to assets held for sale related to the Runoff Transaction											(338.1		)
Total fixed maturity investments											$	5,196.2

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 March 31, 2013 and December 31, 2012 were as follows:



	March 31, 2013
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency losses			Carrying value
Common equity securities	$	876.8	$	201.7	$	(5.2	)	$	(.1	)	$	1,073.2
Convertible fixed maturity investments	$	91.2	$	5.9	$	(1.3	)	$	(.2	)	$	95.6
Other long-term investments	$	254.5	$	57.0	$	(10.3	)	$	(6.0	)	$	295.2



	December 31, 2012
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency losses			Carrying value
Common equity securities	$	895.2	$	143.4	$	(8.8	)	$	(.1	)	$	1,029.7
Convertible fixed maturity investments	$	121.7	$	6.1	$	(.4	)	$	—		$	127.4
Other long-term investments	$	257.2	$	65.9	$	(22.8	)	$	(6.1	)	$	294.2

Hedge Funds and Private Equity Funds

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 March 31, 2013, White Mountains held investments in 15 hedge funds and 38 private equity funds. The largest investment in a single fund was $16.7 million at March 31, 2013. The following table summarizes investments in hedge funds and private equity interests by investment objective and sector at March 31, 2013 and December 31, 2012:



	March 31, 2013				December 31, 2012
Millions	Fair Value		Unfunded Commitments		Fair Value		Unfunded Commitments
Hedge funds
Long/short equity	$	60.0	$	—	$	60.3	$	—
Long/short credit & distressed	24.5		—		22.7		—
Long diversified strategies	1.7		—		1.7		—
Long/short equity REIT	16.7		—		16.0		—
Long/short equity activist	14.5		—		13.6		—
Long bank loan	.3		—		.3		—
Total hedge funds	117.7		—		114.6		—

Private equity funds
Multi-sector	25.9		8.9		23.3		5.4
Energy infrastructure & services	35.0		14.8		36.3		15.6
Distressed residential real estate	14.6		—		15.8		—
Real estate	10.9		3.3		11.6		3.3
Private equity secondaries	10.6		3.1		10.5		3.1
International multi-sector, Europe	4.2		5.0		5.1		5.0
Manufacturing/Industrial	9.0		28.7		9.9		29.1
Healthcare	4.2		5.0		4.3		5.4
International multi-sector, Asia	—		2.7		.4		2.7
Insurance	2.5		41.3		3.0		41.3
Aerospace/Defense/Government	3.0		21.8		2.8		22.2
Venture capital	2.2		.3		2.2		.3
Total private equity funds	122.1		134.9		125.2		133.4

Total hedge and private equity funds included in other long-term investments⁽¹⁾	$	239.8	$	134.9	$	239.8	$	133.4

⁽¹⁾Excludes carrying value of $35.0 and $34.9 at January 1, 2013 and March 31, 2013 associated with hedge funds and private equity funds accounted for using the equity method.

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 March 31, 2013 fair value of hedge funds subject to restrictions on redemption frequency and advance notice period requirements for investments in active hedge funds:



	Notice Period
Millions Redemption frequency	30-59 days notice		60-89 days notice		90-119 days notice		120+ days notice		Total
Monthly	$	—	$	—	$	—	$	6.8	$	6.8
Quarterly	27.9		31.2		9.0		9.6		77.7
Semi-annual	—		22.7		—		—		22.7
Annual	1.7		—		8.5		.3		10.5
Total	$	29.6	$	53.9	$	17.5	$	16.7	$	117.7

Certain of the hedge fund investments in which White Mountains is invested are no longer active and are in the process of disposing of their underlying investments. Distributions from such funds are remitted to investors as the fund’s underlying investments are liquidated. At March 31, 2013, distributions of $2.6 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 March 31, 2013.

White Mountains has also submitted redemption requests for certain of its investments in active hedge funds. At March 31, 2013, redemptions of $7.1 million are outstanding and are subject to market fluctuations. The majority of such remittances are expected to be received in the second quarter of 2013. Redemptions are recorded as receivables when the investment is 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 March 31, 2013, 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	$21.6	$34.0	$57.4	$9.1	$122.1

Fair value measurements at March 31, 2013

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

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

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

In addition to the investments described above, White Mountains has $79.4 million and $79.7 million of investment-related liabilities recorded at fair value and included in other liabilities as of March 31, 2013 and December 31, 2012. 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 March 31, 2013 and December 31, 2012, by level:



	March 31, 2013
Millions	Fair value		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs
Fixed maturity investments:
U.S. Government and agency obligations	$	435.5	$	364.6	$	70.9	$	—

Debt securities issued by corporations:
Consumer	735.5		—		735.5		—
Financials	378.4		—		378.4		—
Communications	331.6		—		331.6		—
Industrial	308.0		—		308.0		—
Basic Materials	211.6		—		211.6		—
Utilities	202.3		—		202.3		—
Energy	183.2		—		183.2		—
Technology	53.0		—		53.0		—
Other	6.1		—		6.1		—
Total debt securities issued by corporations:	2,409.7		—		2,409.7		—

Mortgage-backed and asset-backed securities	1,707.3		—		1,677.2		30.1
Foreign government, agency and provincial obligations	506.1		48.5		457.6		—
Preferred stocks	87.5		—		16.6		70.9
Municipal obligations	5.2		—		5.2		—
Total fixed maturity investments ⁽¹⁾	5,151.3		413.1		4,637.2		101.0

Short-term investments	654.4		654.4		—		—

Common equity securities:
Financials	320.1		283.3		—		36.8
Consumer	305.8		305.8		—		—
Energy	86.2		86.2		—		—
Basic materials	77.6		77.6		—		—
Technology	76.9		76.9		—		—
Communications	39.9		39.9		—		—
Utilities	39.7		39.6		.1		—
Other	127.0		64.0		63.0		—
Total common equity securities	1,073.2		973.3		63.1		36.8

Convertible fixed maturity investments	95.6		—		95.6		—
Other long-term investments ⁽²⁾	260.5		—		—		260.5
Total investments	$	7,235.0	$	2,040.8	$	4,795.9	$	398.3

⁽¹⁾Carrying value includes $296.9 that is classified as assets held for sale relating to discontinued operations.

⁽²⁾Excludes carrying value of $34.9 associated with other long-term investment limited partnerships accounted for using the equity method and $(0.2) related to forward contracts.



	December 31, 2012
Millions	Fair value		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs
Fixed maturity investments:
U.S. Government and agency obligations	$	440.1	$	369.1	$	71.0	$	—

Debt securities issued by corporations:
Consumer	727.1		—		727.1		—
Financials	401.4		1.0		400.4		—
Industrial	330.8		—		330.8		—
Communications	276.1		—		276.1		—
Utilities	204.2		—		204.2		—
Basic materials	189.1		—		189.1		—
Energy	181.5		—		181.5		—
Technology	54.0		—		54.0		—
Other	20.9		—		20.9		—
Total debt securities issued by corporations:	2,385.1		1.0		2,384.1		—

Mortgage-backed and asset-backed securities	2,095.6		—		2,073.5		22.1
Foreign government, agency and provincial obligations	521.9		52.1		469.8		—
Preferred stocks	86.4		—		15.6		70.8
Municipal obligations	5.2		—		5.2		—
Total fixed maturity investments ⁽¹⁾	5,534.3		422.2		5,019.2		92.9

Short-term investments	630.6		630.6		—		—

Common equity securities:
Financials	324.5		286.3		.9		37.3
Consumer	255.6		255.6		—		—
Basic materials	103.3		103.3		—		—
Energy	101.0		101.0		—		—
Technology	55.0		55.0		—		—
Utilities	43.6		43.4		.2		—
Communications	35.2		35.2		—		—
Other	111.5		53.1		58.4		—
Total common equity securities	1,029.7		932.9		59.5		37.3

Convertible fixed maturity investments	127.4		—		127.4		—
Other long-term investments ⁽²⁾	259.3		—		—		259.3
Total investments	$	7,581.3	$	1,985.7	$	5,206.1	$	389.5

⁽¹⁾Carrying value includes $338.1 that is classified as assets held for sale relating to discontinued operations.

⁽²⁾Excludes carrying value of $35.0 associated with other long-term investment limited partnerships accounted for using the equity method and $(0.1) related to currency forward contracts.

Debt securities issued by corporations

The following table summarizes the ratings of the corporate debt securities held in White Mountains’ investment portfolio as of March 31, 2013 and December 31, 2012:



	Fair Value at
Millions	March 31, 2013		December 31, 2012
AAA	$	—	$	—
AA	164.4		193.4
A	1,132.3		1,061.0
BBB	1,099.4		1,116.9
BB	7.0		7.0
Other	8.0		6.8
Debt securities issued by corporations ⁽¹⁾	$	2,411.1	$	2,385.1

⁽¹⁾Credit ratings are assigned based on the following hierarchy: 1) Standard and Poor's Financial Services LLC ("Standard & Poor’s") and 2) Moody’s Investor Service ("Moody's").

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-term and structurally senior, with more than 25 points of subordination on average for fixed rate CMBS and more than 30 points of subordination on average for floating rate CMBS as of March 31, 2013. In general, subordination represents the percentage principal loss on the underlying collateral that would be absorbed by other securities lower in the capital structure before the more senior security incurs a loss. White Mountains believes these levels of protection will mitigate the risk of loss tied to the refinancing challenges facing the commercial real estate market. As of March 31, 2013, on average less than 1% 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 March 31, 2013. White Mountains’ investments in hedge funds and private equity funds contain negligible amounts of sub-prime mortgage-backed securities at March 31, 2013. White Mountains considers sub-prime mortgage-backed securities as those that have underlying loan pools that exhibit weak credit characteristics, or those that are issued from dedicated sub-prime shelves or dedicated second-lien shelf registrations (i.e., White Mountains considers investments backed primarily by second-liens to be sub-prime risks regardless of credit scores or other metrics).

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

The following table summarizes mortgage and asset-backed securities as of March 31, 2013 and December 31, 2012:



	March 31, 2013						December 31, 2012
Millions	Fair Value		Level 2		Level 3		Fair Value		Level 2		Level 3
Mortgage-backed securities:
Agency:
GNMA	$	805.5	$	805.5	$	—	$	1,013.4	$	1,013.4	$	—
FNMA	140.2		140.2		—		74.6		74.6		—
FHLMC	55.6		55.6		—		55.8		55.8		—
Total Agency⁽¹⁾	1,001.3		1,001.3		—		1,143.8		1,143.8		—
Non-agency:
Residential	55.6		55.6		—		160.6		160.6		—
Commercial	284.9		276.9		8.0		334.1		334.1		—
Total Non-agency	340.5		332.5		8.0		494.7		494.7		—

Total mortgage-backed securities	1,341.8		1,333.8		8.0		1,638.5		1,638.5		—
Other asset-backed securities:
Credit card receivables	132.3		110.2		22.1		173.5		151.4		22.1
Vehicle receivables	210.3		210.3		—		265.1		265.1		—
Other	22.9		22.9		—		18.5		18.5		—
Total other asset-backed securities	365.5		343.4		22.1		457.1		435.0		22.1
Total mortgage and asset-backed securities	$	1,707.3	$	1,677.2	$	30.1	$	2,095.6	$	2,073.5	$	22.1

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

Non-agency Mortgage-backed Securities

The security issuance years of White Mountains’ investments in non-agency RMBS and non-agency CMBS securities as of March 31, 2013 are as follows:



			Security Issuance Year
Millions	Fair Value		2005		2006		2007		2008		2010		2011		2012		2013
Non-agency RMBS	$	55.6	$	34.9	$	11.0	$	4.8	$	—	$	4.9	$	—	$	—	$	—
Non-agency CMBS	284.9		—		8.7		15.0		35.0		12.9		39.8		122.5		51.0
Total	$	340.5	$	34.9	$	19.7	$	19.8	$	35.0	$	17.8	$	39.8	$	122.5	$	51.0

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 March 31, 2013:



Millions	Fair Value		Super Senior ⁽¹⁾		Senior ⁽²⁾		Subordinate ⁽³⁾
Prime	$	55.6	$	4.9	$	50.7	$	—
Non-prime	—		—		—		—
Sub-prime	—		—		—		—
Total	$	55.6	$	4.9	$	50.7	$	—

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

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

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

Non-agency Commercial Mortgage-backed Securities

The amount of fixed and floating rate securities and their tranche levels of White Mountains’ non-agency CMBS securities are as follows as of March 31, 2013:



Millions	Fair Value		Super Senior ⁽¹⁾		Senior ⁽²⁾		Subordinate ⁽³⁾
Fixed rate CMBS	$	206.5	$	128.0	$	60.7	$	17.8
Floating rate CMBS	78.4		14.9		36.4		27.1
Total	$	284.9	$	142.9	$	97.1	$	44.9

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

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

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

Rollforward of Fair Value Measurements by Level

White Mountains uses quoted market prices where available as the inputs to estimate fair value for its investments in active markets. Such measurements are considered to be either Level 1 or Level 2 measurements, depending on whether the quoted market price inputs are for identical securities (Level 1) or similar securities (Level 2). Level 3 measurements for fixed maturity investments, common equity securities, convertible fixed maturity investments and other long-term investments at March 31, 2013 and 2012 consist of securities for which the estimated fair value has not been determined based upon quoted market price inputs for identical or similar securities.

The following tables summarize the changes in White Mountains’ fair value measurements by level for the three months ended March 31, 2013 and 2012:



							Level 3 Investments
Millions	Level 1 ⁽³⁾ Investments			Level 2 Investments			Fixed Maturities		Common equity securities			Convertible fixed maturities		Other long-term investments			Total
Balance at January 1, 2013	$	1,355.1		$	5,206.1		$	92.9	$	37.3		$	—	$	259.3		$	6,950.7		⁽¹⁾⁽²⁾
Total realized and unrealized gains (losses)	80.1			(10.8		)	.1		(.1		)	—		5.8			75.1
Foreign currency losses through OCI	(.4		)	(4.8		)	—		—			—		(.4		)	(5.6		)
Amortization/Accretion	(.4		)	(14.0		)	—		—			—		—			(14.4		)
Purchases	318.6			1,445.8			8.0		—			—		18.9			1,791.3
Sales	(382.3		)	(1,828.3		)	—		—			—		(23.1		)	(2,233.7		)
Net change in investments related to purchases and sales of consolidated affiliates	14.5			2.7			—		—			—		—			17.2
Transfers in	1.2			—			—		—			—		—			1.2
Transfers out	—			(.8		)	—		(.4		)	—		—			(1.2		)
Balance at March 31, 2013	$	1,386.4		$	4,795.9		$	101.0	$	36.8		$	—	$	260.5		$	6,580.6		⁽¹⁾⁽²⁾

⁽¹⁾Excludes carrying value of $35.0 and $34.9 at January 1, 2013 and March 31, 2013 associated with other long-term investments accounted for using the equity method and $(0.1) and $(0.2) at January 1, 2013 and March 31, 2013 related to forward contracts.

⁽²⁾Carrying value includes $338.1 and $296.9 at January 1, 2013 and March 31, 2013 that is classified as assets held for sale relating to discontinued operations.

⁽³⁾Excludes carrying value of $630.6 and $654.4 at January 1, 2013 and March 31, 2013 and realized and unrealized gain for the period of $0.1 associated with short-term investments classified as level 1.



							Level 3 Investments
Millions	Level 1⁽³⁾ Investments			Level 2 Investments			Fixed Maturities			Common equity securities		Convertible fixed maturities		Other long-term investments				Total
Balance at January 1, 2012	$	1,033.1		$	6,088.2		$	78.9		$	32.3	$	—	$	268.3		⁽¹⁾	$	7,500.8		⁽¹⁾⁽²⁾
Total realized and unrealized gains	34.7			10.1			7.1			.5		—		6.5				58.9
Foreign currency gains through OCI	.7			50.4			.7			—		—		2.7				54.5
Amortization/Accretion	(.3		)	(12.5		)	(1.1		)	—		—						(13.9		)
Purchases	166.6			1,708.2			97.7			—		—		5.7				1,978.2
Sales	(129.0		)	(2,729.4		)	(4.1		)	—		—		(9.7		)		(2,872.2		)
Transfers in	—			—			—			—		—		—				—
Transfers out	—			—			—			—		—		—				—
Balance at March 31, 2012	$	1,105.8		$	5,115.0		$	179.2		$	32.8	$	—	$	273.5		⁽¹⁾	$	6,706.3		⁽¹⁾⁽²⁾

⁽¹⁾Excludes carrying value of $33.0 and $33.2 at March 31, 2012 and January 1, 2012 associated with other long-term investment limited partnerships accounted for using the equity method.

⁽²⁾Carrying value includes $111.8 that is classified as assets held for sale relating to discontinued operations.

⁽³⁾Excludes carrying value of $877.5 and $846.0 at March 31, 2012 and January 1, 2012 and realized and unrealized loss for the period of $0.3 associated with short-term investments classified as level 1.

Fair Value Measurements — transfers between levels - Three-month period ended March 31, 2013 and 2012

During the first three months of 2013 and 2012, no fixed income securities classified as Level 3 measurements in the prior period was recategorized as Level 2 measurements because quoted market prices for similar securities that were considered reliable and could be validated against an alternative source were available at March 31, 2013.

Significant Unobservable Inputs

The following summarizes significant unobservable inputs used in estimating the fair value of investment securities classified within Level 3 other than hedge funds and private equity funds at March 31, 2013. The fair value of investments in hedge funds and private equity funds, which are classified within Level 3, are estimated using the net asset value of the funds.

($ in Millions)

March 31, 2013

Description

Fair Value

Rating⁽²⁾

Valuation Technique(s)

Unobservable Input

Preferred Stock⁽¹⁾

$70.9

Discounted cash flow

Discount yield

7.4

Asset-backed securities

$8.0

BBB-

Broker pricing

Broker quote

$22.1

AA+

Broker pricing

Broker quote

Private equity securities

$36.8

Multiple of GAAP book value

Book value multiple

1.0

⁽¹⁾As of March 31, 2013 asset type consists of one security.

⁽²⁾Credit ratings are assigned based on the following hierarchy: 1) Standard and Poor's Financial Services LLC (“Standard & Poor’s”) and 2) Moody’s Investor Service (“Moody's”).

- Definition

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

+ References

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

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

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

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

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

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

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

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27161-111563

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

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

+ Details

Debt

3 Months Ended

Mar. 31, 2013

Debt Disclosure [Abstract]

Debt

White Mountains’ debt outstanding as of March 31, 2013 and December 31, 2012 consisted of the following:



Millions	March 31, 2013			December 31, 2012
2012 OBH Senior Notes, at face value	$	275.0		$	275.0
Unamortized original issue discount	(.3		)	(.3		)
2012 OBH Senior Notes, carrying value	274.7			274.7
SIG Senior Notes, at face value	400.0			400.0
Unamortized original issue discount	(.6		)	(.6		)
SIG Senior Notes, carrying value	399.4			399.4
WTM Bank Facility	—			75.0
Old Lyme Note	2.1			2.1
Total debt	$	676.2		$	751.2

WTM Bank Facility

White Mountains has a revolving credit facility with a total commitment of $375.0 million (the “WTM Bank Facility”) with a syndicate of lenders administered by Bank of America, N.A. that has a maturity date of August 12, 2015.

In December 2012, White Mountains borrowed $150.0 million under the WTM Bank Facility at a blended interest rate of 3.53%. White Mountains repaid $75.0 million in December 2012 and the remaining balance of $75.0 million in January 2013. As of March 31, 2013, the WTM Bank Facility was undrawn.

The WTM Bank Facility contains various affirmative, negative and financial covenants which White Mountains considers to be customary for such borrowings, including certain minimum net worth and maximum debt to capitalization standards. Failure to meet one or more of these covenants could result in an event of default, which ultimately could eliminate availability under these facilities and result in acceleration of principal repayment on any amounts outstanding.

Debt Covenants

At March 31, 2013, White Mountains was in compliance with all of the covenants under the WTM Bank Facility, the 2012 OBH Senior Notes and the SIG Senior Notes.

- 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	3 Months Ended
Income Taxes	Mar. 31, 2013
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company and its Bermuda domiciled subsidiaries are not subject to Bermuda income tax under current Bermuda law. In the event there is a change in the current law such that taxes are imposed, the Company and its Bermuda domiciled subsidiaries would be exempt from such tax until March 31, 2035, pursuant to the Bermuda Exempted Undertakings Tax Protection Act of 1966. The Company has subsidiaries and branches that operate in various other jurisdictions around the world that are subject to tax in the jurisdictions in which they operate. The jurisdictions in which the Company's subsidiaries and branches are subject to tax are Australia, Belgium, Canada, Germany, Gibraltar, Luxembourg, the Netherlands, Singapore, Sweden, Switzerland, the United Kingdom and the United States. White Mountains' income tax expense for the three months ended March 31, 2013 and 2012, represented an effective tax rate of 27.4% and 22.1%, which was lower than the U.S. statutory rate of 35% primarily due to income generated in jurisdictions other than the United States. In arriving at the effective tax rate for the three months ended March 31, 2013 and 2012, White Mountains forecasted all income and expense items including the change in unrealized investment gains (losses) and realized investment gains (losses) for the years ending December 31, 2013 and 2012. White Mountains records a valuation allowance against deferred tax assets if it becomes more likely than not that all or a portion of a deferred tax asset will not be realized. Changes in valuation allowances from period to period are included in income tax expense in the period of change. In determining whether or not a valuation allowance, or change therein, is warranted, White Mountains considers factors such as prior earnings history, expected future earnings, carryback and carryforward periods and strategies that if executed would result in the realization of a deferred tax asset. During the next twelve months, it is possible that certain planning strategies or projected earnings in certain subsidiaries may not be feasible to utilize the entire deferred tax asset, which could result in material changes to White Mountains’ deferred tax assets and 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. On January 5, 2011, White Mountains received Form 4549-A (Income Tax Discrepancy Adjustments) from the IRS relating to the examination of tax years 2005 and 2006. The estimated total assessment, including interest and utilization of alternative minimum and foreign tax credit carryovers, is $18.7 million. White Mountains disagrees with the adjustments proposed by the IRS and is defending its position. Although the timing of the resolution of these issues is uncertain, it is reasonably possible that the resolution could occur within the next twelve months. An estimate of the range of potential outcomes cannot be made at this time. When ultimately settled, White Mountains does not expect the resolution of this examination to result in a material change to its financial position. On July 28, 2011, the IRS commenced an examination of the income tax returns for 2007, 2008 and 2009 for certain U.S. subsidiaries of OneBeacon. On April 5, 2013, White Mountains received Form 4549-A (Income Tax Discrepancy Adjustments) from the IRS relating to the examination of tax years 2007, 2008 and 2009. The estimated total assessment, including interest, utilization of alternative minimum and foreign tax credit carryovers and capital loss carrybacks, is $87.0 million. However, $80.6 million of the proposed adjustments relate to items for which the expense deduction has been disallowed in a year being examined, but ultimate deductibility is highly certain to occur in a later period. Because of the impact of deferred tax accounting, other than interest and penalties, the disallowance of these deductions in the exam period would not affect the effective tax rate, but would accelerate the payment of cash to the taxing authority. White Mountains disagrees with the adjustments proposed by the IRS and is defending its position. Although the timing of the resolution of these issues is uncertain, it is reasonably possible that the resolution could occur within the next twelve months. An estimate of the range of potential outcomes cannot be made at this time. When ultimately settled, White Mountains does not expect the resolution of this examination to result in a material change to its financial position. On December 15, 2011, the IRS commenced an examination of the income tax returns for 2010 for certain U.S. subsidiaries of Answer Financial Inc. On March 26, 2013, White Mountains received Form 4549 (Income Tax Examination Changes) from the IRS relating to the examination year 2010. The adjustments on such Form 4549 were not significant.

- Definition

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

+ References

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

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

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

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

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

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

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

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

+ Details

Derivatives

3 Months Ended

Mar. 31, 2013

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivatives

Variable Annuity Reinsurance

White Mountains has entered into agreements to reinsure death and living benefit guarantees associated with certain variable annuities in Japan. At March 31, 2013 and December 31, 2012, the total guarantee value was approximately ¥228.5 billion (approximately $2.4 billion at exchange rates on that date) and ¥230.0 billion (approximately $2.7 billion at exchange rates on that date), respectively. The collective account values of the underlying variable annuities were approximately 94% and 87% of the guarantee value at March 31, 2013 and December 31, 2012, respectively.

The following table summarizes the pre-tax operating results of WM Life Re for the three months ended March 31, 2013 and 2012



	Three Months Ended
	March 31,
Millions	2013			2012
Fees, included in other revenues	$	6.8		$	8.0
Change in fair value of variable annuity liability, included in other revenues	184.3			211.2
Change in fair value of derivatives, included in other revenues	(181.8		)	(206.5		)
Foreign exchange, included in other revenues	(14.6		)	(23.0		)
Other investment income and gains (losses)	(4.0		)	(2.1		)
Total revenues	(9.3		)	(12.4		)
Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses	5.6			8.8
Death benefit claims paid, included in general and administrative expenses	(1.1		)	(1.8		)
General and administrative expenses	(1.7		)	(1.3		)
Pre-tax loss	$	(6.5	)	$	(6.7	)

The following summarizes realized and unrealized derivative gains (losses) recognized in other revenues for the three months ended March 31, 2013 and 2012 and the carrying values, included in other assets, at March 31, 2013 and December 31, 2012 by type of instrument:



							Carrying Value
	Three Months Ended						As of
	March 31,						March 31, 2013			December 31, 2012
Millions	2013			2012			March 31, 2013			December 31, 2012
Fixed income/interest rate	$	(30.9	)	$	(79.0	)	$	(16.2	)	$	27.1
Foreign exchange	(53.6		)	(55.0		)	74.1			52.8
Equity	(97.3		)	(72.5		)	17.9			18.4
Total	$	(181.8	)	$	(206.5	)	$	75.8		$	98.3

The following tables summarize the changes in White Mountains’ variable annuity reinsurance liabilities and derivative instruments for the three months ended March 31, 2013 and 2012:



	Three Months Ended March 31, 2013
	Variable Annuity (Liabilities)				Derivative Instruments
Millions	Level 3				Level 3 ⁽¹⁾			Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total
Beginning of period	$	(441.5	)		$	140.5		$	(20.5	)	$	(21.7	)	$	98.3
Purchases	—				36.1			—			—			36.1
Realized and unrealized gains (losses)	189.9			⁽⁴⁾	(49.2		)	(85.5		)	(47.1		)	(181.8		)
Transfers in	—				—			—			—			—
Sales/settlements	—				—			63.1			60.1			123.2
End of period	$	(251.6	)		$	127.4		$	(42.9	)	$	(8.7	)	$	75.8



	Three Months Ended March 31, 2012
	Variable Annuity (Liabilities)				Derivative Instruments
Millions	Level 3				Level 3 ⁽¹⁾			Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total
Beginning of period	$	(768.5	)		$	247.1		$	39.2		$	4.1		$	290.4
Purchases	—				6.1			—			—			6.1
Realized and unrealized gains (losses)	220.0			⁽⁴⁾	(60.3		)	(98.2		)	(48.0		)	(206.5		)
Transfers in	—				—			—			—			—
Sales/settlements	—				(9.1		)	58.9			34.5			84.3
End of period	$	(548.5	)		$	183.8		$	(.1	)	$	(9.4	)	$	174.3

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

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

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

⁽⁴⁾ Includes $5.6 and $8.8 for the three months ended March 31, 2013 and 2012, respectively, related to the increase in the fair value of variable annuity death benefit liabilities, which are included in other general and administrative expenses.

The U.S. dollar strengthened significantly against the Japanese Yen during the first quarter of 2013, which contributed to the decrease in the variable annuity liability during the quarter.

In addition to derivative instruments, WM Life Re held cash, short-term and fixed maturity investments posted as collateral to its variable annuity reinsurance counterparties. The total collateral comprises the following:



Millions	March 31, 2013		December 31, 2012		March 31, 2012
Cash	$	188.5	$	249.8	$	360.1
Short-term investments	15.6		5.1		1.5
Fixed maturity investments	25.7		138.7		29.3
Total	$	229.8	$	393.6	$	390.9

Collateral in the form of fixed maturity securities consists of Government of Japan Bonds, 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.

All of White Mountains’ variable annuity reinsurance liabilities were classified as Level 3 measurements at March 31, 2013 and 2012. The fair value of White Mountains’ variable annuity reinsurance liabilities are estimated using actuarial and capital market assumptions related to the projected discounted cash flows over the term of the reinsurance agreement. Actuarial assumptions regarding future policyholder behavior, including surrender and lapse rates, are generally unobservable inputs and significantly impact the fair value estimates. Market conditions including, but not limited to, changes in interest rates, equity indices, market volatility and foreign currency exchange rates as well as the variations in actuarial assumptions regarding policyholder behavior may result in significant fluctuations in the fair value estimates. Generally, the liabilities associated with these guarantees increase with declines in the equity markets, interest rates and currencies against the Japanese yen, as well as with increases in market volatilities. White Mountains uses derivative instruments, including put options, interest rate swaps, total return swaps on bond and equity indices and forwards and futures contracts on major equity indices, currency pairs and government bonds, to mitigate the risks associated with changes in the fair value of the reinsured variable annuity guarantees. The types of inputs used to estimate the fair value of these derivative instruments, with the exception of actuarial assumptions regarding policyholder behavior and risk margins, are generally the same as those used to estimate the fair value of variable annuity liabilities.

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



($ in Millions)	March 31, 2013
Description	Fair Value		Valuation Technique(s)	Unobservable Input	Range				Weighted Average
Variable annuity benefit guarantee liabilities	$	251.6	Discounted cash flows	Surrenders
				1 year	0.3	%	-	3.0%	0.7	%
				2 year	0.2	%	-	3.0%	0.8	%
				3 and more years	0.1	%	-	3.0%	0.7	%
				Mortality	0.0	%	-	5.3%	0.9	%
				Foreign exchange volatilities
				1 year	11.2	%	-	13.3%	12.2	%
				2 year	11.7	%	-	14.0%	12.6	%
				3 and more years	12.3	%	-	14.6%	13.2	%
				Index volatilities
				1 year	11.9	%	-	17.9%	13.3	%
				2 year	16.5	%	-	20.7%	18.0	%
				3 and more years	18.6	%	-	22.3%	20.9	%
Foreign exchange options	$	74.2	Counterparty valuations, adjusted for unwind quote discount	Adjustment to counterparty valuations	(0.1	)%	-	(3.2)%	(2.1	)%
Foreign exchange options			Counterparty valuations, adjusted for unwind quote discount	Adjustment to counterparty valuations
Equity index options	$	53.2	Counterparty valuations, adjusted for unwind quote discount	Adjustment to counterparty valuations	(1.7	)%	-	(3.0)%	(2.5	)%
Equity index options			Counterparty valuations, adjusted for unwind quote discount	Adjustment to counterparty valuations

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. The OTC derivative contracts are subject to restrictions on liquidation of the instruments and distribution of proceeds under collateral agreements.

In the case of exchange traded instruments, WM Life Re has exposure to credit risk for amounts uncollateralized by margin balances. 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 amounts offset under master netting agreements:



	March 31, 2013								December 31, 2012
Millions	Gross asset amounts before offsets⁽¹⁾		Gross liability amounts offset under master netting arrangements			Net amounts recognized in Other Assets			Gross asset amounts before offsets⁽¹⁾		Gross liability amounts offset under master netting arrangements			Net amounts recognized in Other Assets
Interest rate contracts
OTC	$	—	$	(15.6	)	$	(15.6	)	$	52.6	$	(26.9	)	$	25.7
Exchange traded	1.0		(1.6		)	(.6		)	1.6		(.2		)	1.4
Foreign exchange contracts
OTC	89.6		(15.5		)	74.1			87.8		(34.4		)	53.4
Exchange traded	.6		(.6		)	—			.8		(1.4		)	(.6		)
Equity contracts
OTC	53.2		(27.2		)	26.0			63.6		(22.9		)	40.7
Exchange traded	.4		(8.5		)	(8.1		)	.1		(22.4		)	(22.3		)
Total⁽²⁾	$	144.8	$	(69.0	)	$	75.8		$	206.5	$	(108.2	)	$	98.3

⁽¹⁾Amount equal to fair value of instrument as recognized in other assets.

⁽²⁾ All derivative instruments held by WM Life Re are subject to master netting arrangements.

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



	March 31, 2013
Millions	Net amount of assets reflected in Balance Sheet			Collateral provided - Financial Instruments		Collateral held - Financial Instruments		Collateral provided - Cash		Collateral held - Cash		Net amount of exposure after effect of collateral held		Standard & Poor's Rating⁽¹⁾
Bank of America	$	60.0		$	—	$	—	$	—	$	10.8	$	49.2	A
Barclays	6.5			—		—		—		—		6.5		A	+
JP Morgan	3.1			—		—		31.3		—		34.4		A	+
Royal Bank of Scotland	26.4			—		—		—		—		26.4		A
Nomura	(6.2		)	25.6		—		8.2		—		27.6		BBB	+
Goldman Sachs	—			—		—		—		—		—		A	-
Citigroup - OTC	(5.3		)	—		—		25.3		—		20.0		A
Citigroup - Exchange Traded	(8.7		)	—		—		24.7		—		16.0		A
Total	$	75.8		$	25.6	$	—	$	89.5	$	10.8	$	180.1



	December 31, 2012
Millions	Net amount of assets reflected in Balance Sheet			Collateral provided - Financial Instruments		Collateral held - Financial Instruments		Collateral provided - Cash		Collateral held - Cash		Net amount of exposure after effect of collateral held		Standard & Poor's Rating⁽¹⁾
Bank of America	$	78.5		$	—	$	—	$	—	$	30.6	$	47.9	A
Barclays	11.6			—		—		—		—		11.6		A	+
JP Morgan	(22.8		)	—		—		55.6		—		32.8		A	+
Royal Bank of Scotland	33.6			—		—		—		—		33.6		A
Nomura	(0.9		)	28.1		—		1.7		—		28.9		BBB	+
Goldman Sachs	(0.1		)	—		—		3.2		—		3.1		A	-
Citigroup - OTC	19.9			—		—		30.8		—		50.7		A
Citigroup - Exchange Traded	(21.5		)	—		—		35.0		—		13.5		A
Total	$	98.3		$	28.1	$	—	$	126.3	$	30.6	$	222.1

⁽¹⁾Standard & Poor’s (“S&P”) ratings as detailed above are: “A+” (Strong, which is the fifth highest of twenty-one creditworthiness ratings), “A” (Strong, which is the sixth highest of twenty-one creditworthiness ratings), “A-” (Strong, which is the seventh highest of twenty-one creditworthiness ratings) and “BBB+” (Adequate, which is the eighth highest of twenty-one creditworthiness ratings).

Forward Contracts

Beginning in September 2012, White Mountains entered into forward contracts to assist in maintaining currency positions within pre-defined ranges at Sirius Group. White Mountains monitors its exposure to foreign currency and adjusts its forward positions within the risk guidelines and ranges established by senior management for each currency, as necessary. While White Mountains actively manages its forward positions, mismatches between movements in foreign currency rates and its forward contracts may result in currency positions being outside the pre-defined ranges and/or foreign currency losses. At March 31, 2013, White Mountains held approximately $79.3 million (SEK 517.5 million) total gross notional value of foreign currency forward contracts.

All of White Mountains' forward contracts are traded over-the-counter. The fair value of the contracts has been estimated using OTC quotes for similar instruments and accordingly, the measurements have been classified as Level 2 measurements at March 31, 2013.

The following tables summarize the changes in White Mountains' forward contracts for the three months ended March 31, 2013:



Millions	March 31, 2013
Beginning of period	$	(.1	)
Purchases	—
Net realized and unrealized gains	.4
Sales/settlements	(.5		)
End of period	$	(.2	)

The following summarizes realized and unrealized derivative gains (losses) recognized in net realized and unrealized investment gains for the three months ended March 31, 2013 and the carrying values, included in other long-term investments, at March 31, 2013 by type of currency:



	March 31, 2013
Millions	Gains (Losses)			Carrying Value
USD	$	(.3	)	$	(.3	)
SEK	—			—
EUR	—			—
GBP	.7			.1
Total	$	.4		$	(.2	)

All of White Mountains' forward contracts are over the counter instruments subject to master netting agreements. The following summarizes amounts offset under master netting agreements:



	March 31, 2013								December 31, 2012
Millions	Gross asset amounts before offsets⁽¹⁾		Gross liability amounts offset under master netting arrangements			Net amounts recognized in Other assets			Gross asset amounts before offsets⁽¹⁾		Gross liability amounts offset under master netting arrangements			Net amounts recognized in Other assets
USD	$	.1	$	(.4	)	$	(.3	)	$	—	$	—		$	—
EUR	—		—			—			—		(.1		)	(.1		)
GBP	.2		(.1		)	.1			—		—			—
Total	$	.3	$	(.5	)	$	(.2	)	$	—	$	(.1	)	$	(.1	)

⁽¹⁾Amount equal to fair value of instrument as recognized in other assets.

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



	March 31, 2013						December 31, 2012
Millions	Notional Amount		Carrying Value			Standard & Poor's Rating⁽¹⁾	Notional Amount		Carrying Value
Barclays	24.7		.1			A+	7.7		(.1		)
Deutsche Bank	13.8		(.2		)	A+	11.1		—
Goldman Sachs	1.1		—			A-	.4		—
HSBC	.1		—			AA-	10.1		—
JP Morgan	22.1		.1			A+	1.9		—
Royal Bank of Canada	17.5		(.2		)	AA-	—		—
Total	$	79.3	$	(.2	)		$	31.2	$	(.1	)

⁽¹⁾Standard & Poor's (“S&P”) ratings as detailed above are: “AA-” (Very Strong, which is the sixth highest of twenty-one creditworthiness ratings), “A+” (Strong, which is the seventh highest of twenty-one creditworthiness ratings) and “A” (Strong, which is the eighth highest of twenty-one creditworthiness ratings).

Municipal Bond Guarantee

3 Months Ended

Mar. 31, 2013

Guarantees [Abstract]

Municipal Bond Guarantee Insurance

In 2012, HG Global was capitalized with $594.5 million from White Mountains and $14.5 million from non-controlling interests to fund BAM, a newly formed mutual municipal bond insurer. As of March 31, 2013, White Mountains owned 97.3% of HG Global's preferred equity and 88.7% of its common equity. HG Global, together with its subsidiaries, provided the initial capitalization of BAM through the purchase of $503.0 million of BAM surplus notes. Through HG Re, which had statutory capital of $417.7 million at March 31, 2013, HG Global provides first loss reinsurance protection for policies underwritten by BAM of up to 15% of par outstanding, on a per policy basis. HG Re’s obligations to BAM are collateralized in trusts, and there is an aggregate loss limit that is equal to the total assets in the collateral trusts at any point in time. For the three months ended March 31, 2013, HG Global had pre-tax income of $9.9 million, which included $10.1 million of interest income on the BAM surplus notes. For the three months ended March 31, 2013, BAM had a pre-tax loss of $18.4 million that was recorded in net loss attributable to non-controlling interests, which included $10.1 million of interest expense on the BAM surplus notes.

All of the contracts issued by BAM are accounted for as insurance contracts under ASC 944-605, Financial Guarantee Insurance Contracts. Premiums are received upfront and an unearned premium revenue liability, equal to the amount of the cash received, is established at contract inception. Premium revenues are recognized in revenue over the period of the contracts in proportion to the amount of insurance protection provided using a constant rate. The constant rate is calculated based on the relationship between the par outstanding in a given reporting period compared with the sum of each of the par amounts outstanding for all periods.

The following table provides a schedule of BAM's insured obligations:



	March 31, 2013		December 31, 2012
Contracts issued and outstanding	105		3
Remaining weighted average contract period (in years)	13.1		10.4
Contractual debt service outstanding (in millions):
Principal	$	698.6	$	25.8
Interest	$	497.6	$	8.9
Unearned premium revenue	$	2.0	$	.1

Earnings Per Share

3 Months Ended

Mar. 31, 2013

Earnings Per Share [Abstract]

Earnings Per Share

Basic earnings 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 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 per share from continuing operations for the three months ended March 31, 2013 and 2012 (see Note 15 for earnings per share amounts for discontinued operations):



	Three Months Ended
	March 31,
	2013			2012
Basic and diluted earnings per share numerators (in millions):
Net income from continuing operations attributable to White Mountains’ common shareholders	$	119.9		$	103.1
Allocation of income for unvested restricted common shares	(1.5		)	(1.1		)
Dividends declared on participating restricted common shares ⁽¹⁾	(.1		)	(.1		)
Total allocation to restricted common shares	(1.6		)	(1.2		)
Net income attributable to White Mountains’ common shareholders, net of restricted common share amounts	$	118.3		$	101.9
Undistributed net earnings (in millions):
Net income attributable to White Mountains’ common shareholders, net of restricted common share amounts	$	118.3		$	101.9
Dividends declared on participating restricted common shares⁽¹⁾	(6.1		)	(6.5		)
Total undistributed net earnings, net of restricted common share amounts	$	112.2		$	95.4
Basic earnings per share denominators (in thousands):
Total average common shares outstanding during the period	6,273.5			7,431.7
Average unvested restricted shares ⁽²⁾	(79.0		)	(78.3		)
Basic earnings per share denominator	6,194.5			7,353.4
Diluted earnings per share denominator (in thousands):
Total average common shares outstanding during the period	6,273.5			7,431.7
Average unvested restricted common shares⁽²⁾	(79.0		)	(78.3		)
Average outstanding dilutive options to acquire common shares⁽³⁾	—			—
Diluted earnings per share denominator	6,194.5			7,353.4
Basic earnings per share (in dollars):
Net income attributable to White Mountains’ common shareholders	$	19.10		$	13.86
Dividends declared	(1.00		)	(1.00		)
Undistributed earnings	$	18.10		$	12.86
Diluted earnings per share (in dollars)
Net income attributable to White Mountains’ common shareholders	$	19.10		$	13.86
Dividends declared	(1.00		)	(1.00		)
Undistributed earnings	$	18.10		$	12.86

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

⁽²⁾Restricted shares outstanding vest either in equal annual installments or upon a stated date (see Note 13).

⁽³⁾The diluted earnings per share denominator for the three months ended March 31, 2013 and 2012 do not include common shares issuable upon exercise of the Non-Qualified Options as they are anti-dilutive to the calculation.

Segment Information

3 Months Ended

Mar. 31, 2013

Segment Reporting [Abstract]

Segment Informartion

Segment Information

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

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

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



					HG Global/BAM
Millions	OneBeacon		Sirius Group		HG			BAM			Other Operations			Total
Three Months Ended March 31, 2013
Earned insurance and reinsurance premiums	$	286.5	$	208.9	$	—		$	—		$	—		$	495.4
Net investment income	9.4		13.1		.3			1.1			4.6			28.5
Net investment income - surplus note income	—		—		10.1			(10.1		)	—			—
Net realized and unrealized investment gains (losses)	28.4		13.1		(.2		)	(1.1		)	35.0			75.2
Other revenue	24.0		10.5		—			.1			(6.3		)	28.3
Total revenues	348.3		245.6		10.2			(10.0		)	33.3			627.4
Losses and loss adjustment expenses	148.9		95.4		—			—			—			244.3
Insurance and reinsurance acquisition expenses	54.8		43.3		—			.1			—			98.2
Other underwriting expenses	49.3		29.7		—			.1			—			79.1
General and administrative expenses	4.0		9.5		.3			8.2			21.8			43.8
Interest expense on debt	3.2		6.6		—			—			.4			10.2
Total expenses	260.2		184.5		.3			8.4			22.2			475.6
Pre-tax income (loss)	$	88.1	$	61.1	$	9.9		$	(18.4	)	$	11.1		$	151.8



Millions	OneBeacon		Sirius Group		Other Operations		Total
Three Months Ended March 31, 2012
Earned insurance and reinsurance premiums	$	271.8	$	226.2	$	—	$	498.0
Net investment income	14.7		17.1		10.0		41.8
Net realized and unrealized investment gains	29.8		13.7		15.1		58.6
Other revenue	.1		18.3		12.8		31.2
Total revenues	316.4		275.3		37.9		629.6
Losses and loss adjustment expenses	136.4		113.4		—		249.8
Insurance and reinsurance acquisition expenses	58.1		51.0		—		109.1
Other underwriting expenses	47.5		26.0		—		73.5
General and administrative expenses	2.7		18.9		23.9		45.5
Interest expense on debt	4.1		6.5		.3		10.9
Total expenses	248.8		215.8		24.2		488.8
Pre-tax income	$	67.6	$	59.5	$	13.7	$	140.8

- Definition

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

+ References

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

+ Details

Investments in Unconsolidated Affiliates

3 Months Ended

Mar. 31, 2013

Equity Method Investments and Joint Ventures [Abstract]

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	March 31, 2013		December 31, 2012
Symetra common shares	$	296.8	$	288.4
Unrealized gains from Symetra's fixed maturity portfolio	54.1		62.8
Carrying value of Symetra common shares	350.9		351.2
Symetra warrants	26.6		30.3
Total investment in Symetra	377.5		381.5
Hamer	3.8		4.0
Bri-Mar	1.8		1.9
Pentelia Capital Management	.5		.5
Total investments in unconsolidated affiliates	$	383.6	$	387.9

Symetra

At March 31, 2013 and December 31, 2012, White Mountains owned 17.4 million common shares of Symetra Financial Corporation (“Symetra”) and warrants to acquire an additional 9.5 million common shares. White Mountains accounts for its investment in common shares of Symetra using the equity method. At December 31, 2011, due to the prolonged low interest rate environment in which life insurance companies currently operate, White Mountains concluded that its investment in Symetra common shares was other-than-temporarily impaired and wrote down the GAAP book value of the investment to its estimated fair value of $261.0 million, or $15 per share at December 31, 2011. White Mountains recorded $45.9 million of after-tax equity in losses of unconsolidated affiliates and $136.6 million of after-tax equity in net unrealized losses of unconsolidated affiliates.

Under the equity method, the GAAP carrying value of White Mountains’ investment in Symetra common shares is normally equal to the percentage of Symetra’s GAAP book value represented by White Mountains’ common share ownership, which was 15% at March 31, 2013. As a result of recording the write-down, White Mountains’ carrying value of its investment in Symetra differs from the carrying value by applying its ownership share against Symetra’s GAAP equity as normally done under the equity method. The pre-tax basis difference of $195.8 million as of December 31, 2011 is being amortized over a 30 year period pro rata based on estimated future cash flows associated with Symetra’s underlying assets and liabilities to which the basis difference has been attributed. White Mountains continues to record its equity in Symetra’s earnings and net unrealized gains (losses). In addition, White Mountains recognizes the amortization of the basis difference through equity in earnings of unconsolidated affiliates and equity in net unrealized gains (losses) from investments in unconsolidated affiliates consistent with the original attribution of the writedown between equity in earnings and equity in net unrealized gains (losses). For the three months ended March 31, 2013, White Mountains recognized after-tax amortization of $0.7 million through equity in earnings of unconsolidated affiliates and $2.5 million through equity in net unrealized gains from investments in unconsolidated affiliates. At March 31, 2013, the pre-tax unamortized basis difference was $175.7 million.

White Mountains accounts for its Symetra warrants as derivatives with changes in fair value recognized through the income statement as a gain or loss recognized through other revenues. White Mountains uses a Black Scholes valuation model to determine the fair value of the Symetra warrants. The major assumptions used in valuing the Symetra warrants at March 31, 2013 were a risk free rate of 0.17%, volatility of 29.1%, an expected life of 1.33 years, a strike price of $11.49 per share and a share price of $13.41 per share.

The following table summarizes amounts recorded by White Mountains relating to its investment in Symetra for the three months ended March 31, 2013 and 2012:



	Three Months Ended									Three Months Ended
	March 31, 2013									March 31, 2012
Millions	Common Shares			Warrants			Total			Common Shares			Warrants		Total
Carrying value of investment in Symetra as of January 1	$	351.2		$	30.3		$	381.5		$	261.0		$	12.6	$	273.6
Equity in earnings ⁽¹⁾⁽²⁾	9.8			—			9.8			10.9			—		10.9
Equity in net unrealized gains from Symetra’s fixed maturity portfolio⁽³⁾	(8.7		)	—			(8.7		)	(1.2		)	—		(1.2		)
Dividends received	(1.4		)	—			(1.4		)	(1.2		)	—		(1.2		)
(Decrease) increase in value of warrants	—			(3.7		)	(3.7		)	—			11.1		11.1
Carrying value of investment in Symetra as March 31 ⁽⁴⁾⁽⁵⁾	$	350.9		$	26.6		$	377.5		$	269.5		$	23.7	$	293.2

⁽¹⁾Equity in earnings excludes tax expense of $0.8 and $0.7.

⁽²⁾Equity in earnings includes $0.7 and $1.1 increase relating to the pre-tax amortization of Symetra common share impairment from March 31, 2013 and 2012.

⁽³⁾Net unrealized gains includes $2.7 and $3.2 increase relating to the pre-tax amortization of Symetra common share impairment from March 31, 2013 and 2012.

⁽⁴⁾Includes White Mountains’ equity in net unrealized gains from Symetra’s fixed maturity portfolio of $(8.7) and $(1.2) as of March 31, 2013 and 2012, which exclude tax benefit of $0.7 and $0.0.

⁽⁵⁾The aggregate value of White Mountains’ investment in common shares of Symetra was $233.3 based upon the quoted market price of $13.41 per share at

March 31, 2013.

During the three months ended March 31, 2013, White Mountains received cash dividends from Symetra of $1.4 million on its common share investment that was recorded as a reduction of White Mountains’ investment in Symetra. During the three months ended March 31, 2013, White Mountains also received cash dividends of $0.8 million from Symetra on its investment in Symetra warrants that was recorded in net investment income.

Hamer and Bri-Mar

White Mountains received equity interests in Hamer and Bri-Mar, two small manufacturing companies distributed to White Mountains in connection with the dissolution of the Tuckerman Capital, LP fund. Effective October 1, 2012, these investments are accounted for under the equity method. For the three months ended March 31, 2013, White Mountains recorded equity in earnings of $0.3 million for Hamer. Bri-Mar did not have any earnings for the three months ended March 31, 2013. As of March 31, 2013, White Mountains' investments in Hamer and Bri-Mar was $3.8 million and $1.8 million, respectively.

- Definition

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

+ References + Details

Employee Share-Based Incentive Compensation Plans

3 Months Ended

Mar. 31, 2013

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

Employee Share-Based Incentive Compensation Plans

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

Share-Based Compensation Based on White Mountains Common Shares

WTM Performance Shares

Performance shares are conditional grants of a specified maximum number of common shares or an equivalent amount of cash. Performance share awards vest, subject to the attainment of performance goals, at the end of a three-year period and are valued based on the market value of common shares at the time awards are paid. The following table summarizes performance share activity for the three months ended March 31, 2013 and 2012 for performance shares granted under the WTM Incentive Plan and phantom performance shares granted under the Sirius Group Performance Plan (the “WTM Phantom Share Plan”):



	Three Months Ended March 31,
	2013					2012
Millions, except share amounts	Target Performance Shares Outstanding		Accrued Expense			Target Performance Shares Outstanding		Accrued Expense
Beginning of period	119,357		$	29.4		150,064		$	66.1
Shares paid ⁽¹⁾	(47,310	)	(11.0		)	(68,357	)	(48.4		)
New grants	46,920		—			35,932		—
Assumed forfeitures and cancellations ⁽²⁾	9		.1			811		1.0
Expense recognized	—		10.1			—		8.7
Ending March 31,	118,976		$	28.6		118,450		$	27.4

⁽¹⁾WTM performance share payments in 2013 for the 2010-2012 performance cycle ranged from 33% to 98% of target. WTM performance share payments in 2012 for the 2009-2011 performance cycle ranged from 147% to 155% of target.

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

For the 2009-2011 performance cycle, the Company issued common shares for 9,577 performance shares earned and all other performance shares earned were settled in cash. For the 2010-2012 performance cycle, the Company settled all performance shares earned in cash.

If the outstanding WTM performance shares had vested on March 31, 2013, the total additional compensation cost to be recognized would have been $44.4 million, based on accrual factors at March 31, 2013 (common share price and payout assumptions).

Performance Shares granted under the WTM Incentive Plan

The following table summarizes performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan at March 31, 2013 for each performance cycle:



Millions, except share amounts	Target Performance Shares Outstanding		Accrued Expense
Performance cycle:
2013 – 2015	46,920		$	2.2
2012 – 2014	37,977		11.4
2011 – 2013	37,130		15.8
Sub-total	122,027		29.4
Assumed forfeitures	(3,051	)	(.8		)
Total at March 31, 2013	118,976		$	28.6

Restricted Shares

The following outlines the unrecognized compensation cost associated with the outstanding restricted share awards for the three months ended March 31, 2013 and 2012:



	Three Months Ended March 31,
	2013				2012
Millions, except share amounts	Restricted Shares	Unamortized Issue Date Fair Value			Restricted Shares		Unamortized Issue Date Fair Value
Non-vested,
Beginning of period	69,910	$	16.8		72,000		$	13.3
Issued	25,470	14.3			28,460		13.7
Vested	—	—			(7,000	)	—
Forfeited	—	—			—		—
Expense recognized	—	(2.9		)	—		(2.5		)
Non-vested at March 31,	95,380	$	28.2		93,460		$	24.5

During the first quarter of 2013, White Mountains issued 25,470 restricted shares that vest on January 1, 2016. During the first quarter of 2012, White Mountains issued 25,460 restricted shares that vest on January 1, 2015 and 3,000 restricted shares that vest in two equal annual installments beginning in February 2014. The unrecognized compensation cost at March 31, 2013 is expected to be recognized ratably over the remaining vesting periods.

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 include OneBeacon performance shares and restricted shares.

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 months ended March 31, 2013 and 2012 for OneBeacon performance shares granted under the OneBeacon Incentive Plan:



	Three Months Ended March 31,
	2013				2012
Millions, except share amounts	Target Performance Shares Outstanding		Accrued Expense		Target Performance Shares Outstanding		Accrued Expense
Beginning of period	563,190		$	1.2	642,667		$	9.7
Shares paid or expired⁽¹⁾	(238,658	)	—		(249,733	)	(7.5		)
New awards	179,000		—		181,290		—
Assumed forfeitures and cancellations⁽²⁾	(13,665	)	—		(4,479	)	—
Expense recognized	—		.4		—		1.0
Ending March 31,	489,867		$	1.6	569,745		$	3.2

⁽¹⁾ There were no payments made in 2013 for the 2010-2012 performance cycle; those performance shares did not meet the threshold performance goals and expired. OneBeacon performance share payments in 2012 for the 2009-2011 performance cycle were at 138.6% of target. Amounts include deposits into OneBeacon’s deferred compensation plan.

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

If the outstanding OneBeacon performance shares had been vested on March 31, 2013, the total additional compensation cost to be recognized would have been $1.4 million, based on accrual factors at March 31, 2013 (common share price and payout assumptions).

The following table summarizes OneBeacon performance shares outstanding awarded under the OneBeacon Incentive Plan at March 31, 2013 for each performance cycle:



Millions, except share amounts	Target OneBeacon Performance Shares Outstanding		Accrued Expense
Performance cycle:
2013 – 2015	179,000		$	.2
2012 – 2014	181,290		1.1
2011 – 2013	142,138		.3
Sub-total	502,428		1.6
Assumed forfeitures	(12,561	)	—
Total at March 31, 2013	489,867		$	1.6

OneBeacon Restricted Shares

The following summarizes the unrecognized compensation cost associated with the outstanding OneBeacon restricted share awards for the three months ended March 31, 2013 and 2012:



	Three Months Ended March 31,
	2013					2012
Millions, except share amounts	Restricted Shares		Unamortized Issue Date Fair Value			Restricted Shares	Unamortized Issue Date Fair Value
Non-vested,
Beginning of period	927,000		$	9.6		630,000	$	7.7
Issued	—		—			300,000	4.6
Vested	(9,000	)	—			—	—
Forfeited	—		—			—	—
Expense recognized	—		(.8		)	—	(.4		)
Non-vested at March 31,	918,000		$	8.8		930,000	$	11.9

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

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

The unrecognized compensation cost at March 31, 2013 is expected to be recognized ratably over the remaining vesting periods.

- Definition

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

+ References

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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 5: http://www.xbrl.org/2003/role/presentationRef
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-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5444-113901

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

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

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

+ Details

Fair Value of Financial Instruments

3 Months Ended

Mar. 31, 2013

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

White Mountains accounts for its financial instruments at fair value with the exception of 1) the OBH Senior Notes and the SIG Senior Notes, which are recorded as debt liabilities at face value less unamortized original issue discount, and 2) the SIG Preference Shares, which are recorded as non-controlling interest at face value.

The following table summarizes the fair value and book value of financial instruments as of March 31, 2013 and December 31, 2012:



	March 31, 2013				December 31, 2012
Millions	Fair Value		Book Value		Fair Value		Book Value
2012 OBH Senior Notes	$	287.8	$	274.7	$	282.4	$	274.7
SIG Senior Notes	454.0		399.4		441.9		399.4
SIG Preference Shares	262.5		250.0		257.5		250.0

The fair value estimate for the 2012 OBH Senior Notes has been determined using quoted market prices. The 2012 OBH Senior Notes are considered a Level 2 measurement based upon the volume and frequency of observable transactions. The fair value estimates for the SIG Senior Notes and the SIG Preference Shares have been determined based on indicative broker quotes and are considered to be Level 3 measurements.

- Definition

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

+ References

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+ Details

Discontinued Operations

3 Months Ended

Mar. 31, 2013

Discontinued Operations and Disposal Groups [Abstract]

Discontinued Operations

AutoOne

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

Runoff Transaction

On October 17, 2012, OneBeacon entered into an agreement to sell its runoff business to Armour. During three months ended March 31, 2013 and 2012, the results of operations for the runoff business have been classified as discontinued operations and are presented, net of related income taxes, in the statement of comprehensive income. Prior year results of operations have been reclassified to conform to the current period’s presentation. The assets and liabilities associated with the runoff business as of March 31, 2013 and December 31, 2012 have been presented in the balance sheet as held for sale. The amounts classified as discontinued operations exclude investing and financing activities that are conducted on an overall consolidated level and, accordingly, there were no separately identifiable investments associated with the runoff business.

During the three months ended March 31, 2013 and 2012, OneBeacon recorded $0.5 million in income and a $9.4 million loss from operations related to the Runoff Transaction.

Loss and LAE reserve development

OneBeacon experienced $0.2 million of favorable loss reserve development and $12.4 million of unfavorable loss reserve development in the runoff business during the three months ended March 31, 2013 and 2012. The unfavorable development in 2012 was primarily driven by case incurred development on a small number of claims related to multiple peril liability lines and general liability lines and also the impact of an adverse court ruling in Mississippi regarding a disputed assessment from an involuntary pool for hurricane Katrina claims.

Reinsurance

Included in the assets held for sale are reinsurance recoverables from two reinsurance contracts with subsidiaries of Berkshire Hathaway Inc. that OneBeacon was required to purchase in connection with White Mountains' acquisition of OneBeacon in 2001 (the "OneBeacon Acquisition"): a reinsurance contract with National Indemnity Company (“NICO”) for up to $2.5 billion in old asbestos and environmental (“A&E”) claims and certain other exposures (the “NICO Cover”) and an adverse loss reserve development cover from General Reinsurance Corporation (“GRC”) for up to $570.0 million, comprised of $400.0 million of adverse loss reserve development occurring in years 2000 and prior (the “GRC Cover”) in addition to $170.0 million of reserves ceded as of the date of the OneBeacon Acquisition. The NICO Cover and GRC Cover, which were contingent on and occurred contemporaneously with the OneBeacon Acquisition, were put in place in lieu of a seller guarantee of loss and LAE reserves and are therefore accounted for under GAAP as a seller guarantee. As of March 31, 2013 and December 31, 2012, the total reinsurance recoverables on paid and unpaid losses of $1,381.0 million and $1,401.9 million related to both the NICO cover and the GRC cover have been included in assets held for sale. Both NICO and GRC have an A.M Best rating of A++, Superior, which is the highest of sixteen ratings.

The total reinsurance recoverables on paid and unpaid losses in assets held for sale were $14.1 million and $1,960.9 million as of March 31, 2012. The reinsurance recoverable on unpaid amount is gross of $146.8 million in purchase accounting adjustments that will become recoverable if claims are paid in accordance with current reserve estimates.

Net Assets Held for Sale

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



Millions	March 31, 2013		December 31, 2012
Assets held for sale
Fixed maturity investments, at fair value	$	296.9	$	338.1
Cash	—		—
Reinsurance recoverable on unpaid losses	1,814.1		1,840.8
Reinsurance recoverable on paid losses	14.1		15.6
Insurance premiums receivable	9.9		11.0
Deferred acquisition costs	—		—
Deferred tax asset	4.2		5.1
Other assets	16.0		16.2
Total assets held for sale	$	2,155.2	$	2,226.8
Liabilities held for sale
Loss and loss adjustment expense reserves	$	1,980.2	$	2,052.6
Unearned insurance premiums	.5		.5
Ceded reinsurance payable	23.5		21.9
Other liabilities	151.0		151.8
Total liabilities held for sale	2,155.2		2,226.8
Net assets held for sale	$	—	$	—

Net Income (Loss) from Discontinued Operations

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



	Three Months Ended March 31,
Millions	2013			2012
Revenues
Earned insurance premiums	$	.9		$	8.8
Net investment income	—			—
Net realized and unrealized investment gains (losses)	—			—
Other revenue	—			—
Total revenues	.9			8.8
Expenses
Loss and loss adjustment expenses	—			19.6
Insurance and reinsurance acquisition expenses	.1			.3
Other underwriting expenses	.1			1.5
General and administrative expenses	—			—
Total expenses	.2			21.4
Pre-tax income (loss)	.7			(12.6		)
Income tax (expense) benefit	(.2		)	3.3
Income (loss) from discontinued operations	.5			(9.3		)
Loss from sale of discontinued operations	—			—
Net income (loss) from discontinued operations	$	.5		$	(9.3	)

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 computation of earnings (loss) per share for discontinued operations for the three months ended March 31, 2013 and 2012:



	Three Months Ended March 31,
	2013			2012
Basic and diluted earnings (loss) per share numerators (in millions):
Net income (loss) attributable to White Mountains’ common shareholders	$	.5		$	(9.3	)
Allocation of income for participating unvested restricted common shares ⁽¹⁾	—			.1
Net income (loss) attributable to White Mountains’ common shareholders, net of restricted common share amounts⁽²⁾	$	.5		$	(9.2	)
Basic earnings (loss) per share denominators (in thousands):
Total average common shares outstanding during the period	6,273.5			7,431.7
Average unvested restricted common shares⁽³⁾	(79.0		)	(78.3		)
Basic earnings (loss) per share denominator	6,194.5			7,353.4
Diluted earnings (loss) per share denominator (in thousands):
Total average common shares outstanding during the period	6,273.5			7,431.7
Average unvested restricted common shares⁽³⁾	(79.0		)	(78.3		)
Average outstanding dilutive options to acquire common shares⁽⁴⁾	—			—
Diluted earnings (loss) per share denominator	6,194.5			7,353.4
Basic and diluted earnings (loss) per share (in dollars):	$	.07		$	(1.25	)

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

⁽²⁾Net earnings (loss) attributable to White Mountains’ common shareholders, net of restricted share amounts, is equal to undistributed earnings (loss) for the three months ended March 31, 2013 and 2012.

⁽³⁾ Restricted common shares outstanding vest either in equal annual installments or upon a stated date (see Note 13).

⁽⁴⁾The diluted earnings per share denominator for the three months ended March 31, 2013 and 2012 do not include common shares issuable upon exercise of the Non-Qualified Options as they are anti-dilutive to the calculation.

- Definition

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

+ References

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+ Details

Contingencies	3 Months Ended
Contingencies	Mar. 31, 2013
Commitments and Contingencies Disclosure [Abstract]
Contingencies	Contingencies Esurance On October 7, 2011, the Company completed the sale of its Esurance and Answer Financial subsidiaries (the “Transferred Subsidiaries”) to Allstate pursuant a Stock Purchase Agreement dated as of May 17, 2011 (filed as an exhibit to the Company's current report on Form 8-K on May 18, 2011, the “Agreement”). The Company has certain contingencies under the Agreement as follows: (i) the final purchase price payable by Allstate under the Agreement, which is based upon the book value of the Transferred Subsidiaries at the closing date, is subject to a true-up process that has not yet been concluded, (ii) subject to specified thresholds and limits, the Company generally indemnifies Allstate for breaches of its representations and warranties in the Agreement for a period of eighteen months (although longer for specified representations and warranties) from the closing, (iii) the Company indemnifies Allstate for breaches of certain covenants in the Agreement, including certain agreements by the Company not to engage in certain competing business activities for two years after the closing and not to solicit certain employees of the Transferred Subsidiaries for three years after the closing, and (iv) subject to specified thresholds and limits, the Company indemnifies Allstate for specified matters related to the pre-closing period, including (a) specified litigation matters, (b) losses of the Transferred Subsidiaries arising from extra-contractual claims and claims in excess of policy limits (“ECO/EPL losses”), (c) certain corporate reorganizations effected to remove entities from the Transferred Subsidiaries that were not being sold in the transaction, and (d) certain tax matters, including certain net operating losses being less than stated levels. In addition, the Company retains 90% of positive or negative development in the loss reserves of the Transferred Subsidiaries as of the closing date (net of ECO/EPL losses). Legal Contingencies White Mountains, and the insurance and reinsurance industry in general, are routinely subject to claims related litigation and arbitration in the normal course of business, as well as litigation and arbitration that do not arise from, or are directly related to, claims activity. White Mountains' estimates of the costs of settling matters routinely encountered in claims activity are reflected in the reserves for unpaid loss and LAE. See Note 3. White Mountains considers the requirements of ASC 450 when evaluating its exposure to non-claims related litigation and arbitration. ASC 450 requires that accruals be established for litigation and arbitration if it is probable that a loss has been incurred and it can be reasonably estimated. ASC 450 also requires that litigation and arbitration be disclosed if it is probable that a loss has been incurred or if there is a reasonable possibility that a loss may have been incurred. Although the ultimate outcome of claims and non-claims related litigation and arbitration, and the amount or range of potential loss at any particular time, is often inherently uncertain, management does not believe that the ultimate outcome of such claims and non-claims related litigation and arbitration will have a material adverse effect on White Mountains' financial condition, results of operations or cash flows. The following summarizes significant ongoing non-claims related litigation or arbitration as of March 31, 2013: Esurance Sale In 2011, the Company sold its Esurance and Answer Financial businesses (the “Transferred Companies”) to The Allstate Corporation (“Allstate”) for a purchase price of approximately $1.01 billion. The purchase price consisted of $700 million plus the tangible book value of the Transferred Companies at the closing, which was estimated to be $308 million. Following closing, Allstate was required to prepare a final closing statement, including an audited balance sheet for the Transferred Companies as of the closing date. The Company is disputing Allstate's calculation of tangible book value in the closing statement. The amount in dispute is approximately $20 million, after tax. The dispute principally relates to (i) the elimination of $24.7 million (pre-tax) of deferred acquisition costs ($16.0 million, after tax) and (ii) the inclusion of a liability equal to the costs associated with an Esurance extra-contractual (“ECO”) matter settled in April 2012 of $5.2 million ($3.4 million, after tax). Per the agreement governing the sale of the Transferred Companies (the “Sale Agreement”), disputes over the closing statement are to be arbitrated by an independent accountant. The Company believes this final closing statement was required to be prepared and audited no later than January 5, 2012. Allstate did not deliver the final closing statement to the Company until June 6, 2012, with an audit report dated June 1, 2012. As a result, in addition to the substantive disputes over the final closing statement, the Company also believes that Allstate's failure to have the final closing statement prepared and audited by the required date constituted a breach of Allstate's obligations under the Sale Agreement. The Company brought suit in the United States District Court for the Southern District of New York in connection with such breach. The court concluded that the Company's breach claim should also be arbitrated by the independent accountant under the Sale Agreement. That process is expected to be completed in the fourth quarter of 2013. Tribune Company In June 2011, Deutsche Bank Trust Company Americas, Law Debenture Company of New York and Wilmington Trust Company (collectively referred to as “Plaintiffs”), in their capacity as trustees for certain senior notes issued by the Tribune Company (“Tribune”), filed lawsuits in various jurisdictions (the “Noteholder Actions”) against numerous defendants including OneBeacon, OBIC-sponsored benefit plans and other affiliates of White Mountains in their capacity as former shareholders of Tribune seeking recovery of the proceeds from the sale of common stock of Tribune in connection with Tribune's leveraged buyout in 2007 (the “LBO”). Tribune filed for bankruptcy in 2008 in the Delaware bankruptcy court (the “Bankruptcy Court”). The Bankruptcy Court granted Plaintiffs permission to commence these LBO-related actions. Plaintiffs seek recovery of the proceeds received by the former Tribune shareholders on a theory of constructive fraudulent transfer asserting that Tribune purchased or repurchased its common shares without receiving fair consideration at a time when it was, or as a result of the purchases of shares, was rendered, insolvent. OneBeacon has entered into a joint defense agreement with other affiliates of White Mountains that are defendants in the action. Certain subsidiaries of White Mountains received approximately $39 million for Tribune common stock tendered in connection with the LBO. In December 2011, the Judicial Panel on Multidistrict Litigation granted a motion to consolidate all of the Noteholder Actions for pretrial matters and transfer all such proceedings to the United States District Court for the Southern District of New York. In addition, OneBeacon, OBIC-sponsored benefit plans and other affiliates of White Mountains in their capacity as former shareholders of Tribune, along with thousands of former Tribune shareholders, have been named as defendants in an adversary proceeding brought by the Official Committee of Unsecured Creditors of the Tribune Company, on behalf of the Tribune Company, which seeks to avoid the repurchase of shares by Tribune in the LBO on a theory of intentional fraudulent transfer (the “Committee Action”). The Committee Action has since been consolidated with the Noteholder Actions. In September 2012, a case management order was entered in the consolidated cases, setting forth, among other things, a briefing schedule for an omnibus motion to dismiss in the Noteholder Actions. The court is expected to hear oral argument on that motion in the second quarter of 2013. Discovery and other motion practice (other than motions to amend the complaints) in the Committee Action and the Noteholder Actions is stayed until further order of the court. Ace American Insurance Company A subsidiary of OneBeacon, OneBeacon U.S. Holdings, Inc. (“OBH”), was sued in Federal Court in the Eastern District of Pennsylvania on August 17, 2012 by Ace American Insurance Company (“Ace”). The complaint alleged that OBH, through a professional recruiting firm, improperly hired a group of Ace employees from Ace's surety division. The complaint sought injunctive relief and unspecified damages. After court-ordered expedited discovery was completed, the claims for injunctive relief were resolved pursuant to a confidential agreement. After the claims against OBH for injunctive relief were resolved, Ace filed a Demand for Arbitration against five of the former Ace surety employees hired by OneBeacon, alleging breach of their duty of loyalty to Ace and misappropriation of Ace trade secrets. On March 6, 2013, Ace also filed an Amended Complaint in the Federal Court action, naming OneBeacon Insurance Group, Ltd., OneBeacon Insurance Group, LLC and OneBeacon Services, LLC as additional defendants. The only remaining claim is for damages and trial is scheduled for June 2013. OneBeacon believes that Ace's damages claim against all of the OneBeacon companies and the claims against the individual employees are without merit and intends to vigorously defend both claims.

- Definition

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

+ References

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-Number 14
-Paragraph 3
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 5
-Paragraph 9, 10, 11, 12
-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

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2013
Accounting Policies [Abstract]
Noncontrolling Interests	Non-controlling Interests Non-controlling interests consist of the ownership interests of non-controlling shareholders in consolidated subsidiaries and are presented separately on the balance sheet. The percentage of the non-controlling shareholders' ownership interest in OneBeacon Ltd. at both March 31, 2013 and December 31, 2012 was 24.8%. In July 2012, HG Global was capitalized with $594.5 million from White Mountains and $14.5 million from certain management members of BAM, the latter of which is included in non-controlling interest. Upon closing, certain BAM management members also received additional common and preferred shares of HG Global that resulted in a $2.2 million allocation of the carrying value of White Mountains' investment in HG Global to the non-controlling interest, which was recorded as an adjustment to paid-in surplus in White Mountains' consolidated statement of changes in equity. White Mountains is required to consolidate BAM in its GAAP financial statements. However, since BAM is a mutual insurance company that is owned by its members, BAM's results do not affect White Mountains' common shareholders' equity as they are attributable to non-controlling interests. For the three months ended March 31, 2013, BAM reported $20.1 million in losses that have been allocated to non-controlling interest. In May 2007, Sirius International Group, Ltd. (“SIG”), an intermediate holding company of Sirius Group, issued $250 million non-cumulative perpetual preference shares, with a $1,000 per share liquidation preference (the “SIG Preference Shares”), and received $245.7 million of proceeds, net of $4.3 million of issuance costs and commissions. SIG Preference Shares and dividends thereon are included in non-controlling interest on the balance sheet and on the statement of income and comprehensive income. At March 31, 2013 and December 31, 2012, the non-controlling equity interest in White Mountains' consolidated limited partnerships was $44.1 million and $41.5 million. At March 31, 2013 and December 31, 2012, the non-controlling equity interest in A.W.G. Dewar Inc, a subsidiary of OneBeacon, was $2.5 million and $2.8 million. At both March 31, 2013 and December 31, 2012, the non-controlling equity interest in Passage2Health Limited, a subsidiary of Sirius Group, was $0.2 million.
Policy Acquisition Costs	Policy Acquisition Costs On January 1, 2012, White Mountains adopted ASU 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts (ASC 944). The new standard changes the types of policy acquisition costs that are eligible for deferral. Specifically, the new guidance limits deferrable costs to those that are incremental direct costs of contract acquisition and certain costs related to acquisition activities performed by the insurer, such as underwriting, policy issuance and processing, medical and inspection costs and sales force contract selling. The ASU defines incremental direct costs as those costs that result directly from and were essential to the contract acquisition and would not have been incurred absent the acquisition. Accordingly, under the new guidance, deferrable acquisition costs are limited to costs related to successful contract acquisitions. Acquisition costs that are not eligible for deferral are to be charged to expense in the period incurred. White Mountains adopted ASU 2010-26 prospectively. Upon adoption, certain acquisition costs, primarily a portion of the profit sharing commissions associated with OneBeacon's collector car and boat business, no longer met the criteria for deferral. During the year ended December 31, 2012, White Mountains recognized $5.6 million of expense related to such previously deferrable acquisition costs that, if White Mountains had adopted ASU 2010-26 retrospectively, would have been recognized during 2011.
Fair Value Measurements	Fair Value Measurements On January 1, 2012, White Mountains adopted ASU 2011-04, Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRS. The ASU clarifies existing guidance with respect to the concepts of highest and best use and valuation premise and measuring instruments classified within a reporting entity’s shareholders’ equity. The ASU also clarifies disclosure requirements, requiring disclosure of quantitative information about unobservable inputs used in Level 3 fair value measurements. The ASU also amends existing guidance. In circumstances where a reporting entity manages a portfolio of financial assets and liabilities based on the net market and counterparty credit risk exposures, the ASU permits determination of the fair value of those instruments to be based on the net risk exposure. In addition, the ASU permits the application of premiums or discounts to be applied in a fair value measurement to the extent that market participants would consider them in valuing the financial instruments. The ASU also expands the required disclosures for Level 3 measurements, requiring that reporting entities provide a narrative description of the sensitivity of Level 3 fair value measurements to changes in unobservable inputs and the interrelationships between those inputs, if any. As a result of adopting ASU 2011-04, White Mountains expanded its fair value disclosures. (See Note 5).
Offsetting Assets and Liabilities	Offsetting Assets and Liabilities Effective January 1, 2013, White Mountains adopted ASU 2011-11, Disclosures about Offsetting Assets and Liabilities (ASC 210) and ASU 2013-01, Clarifying the Scope of Disclosures about Offsetting Assets and Liabilities. The new guidance expands the required disclosures in circumstances where either balances have been offset or the right of offset exists to make it easier for financial statement users to evaluate the effect or potential effect of netting arrangements on a reporting entity’s financial position. White Mountains is party to master netting arrangements in connection with derivative instruments held by WM Life Re and Sirius International. As a result of adoption, White Mountains has expanded its disclosures to present the gross amounts of assets and liabilities subject to master netting arrangements along with any related collateral amounts.

Loss and Loss Adjustment Expense Reserves (Tables)

3 Months Ended

Mar. 31, 2013

Insurance Loss Reserves [Abstract]

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



	Three Months Ended
	March 31,
Millions	2013			2012
Gross beginning balance	$	3,168.9		$	5,702.3
Less beginning reinsurance recoverable on unpaid losses	(429.1		)	(2,507.3		)
Net loss and LAE reserves	2,739.8			3,195.0

Less: Beginning net loss and LAE reserves for OneBeacon's runoff business⁽¹⁾	—			(383.3		)

Loss and LAE reserves acquired - American Fuji	21.3			—

Loss and LAE incurred relating to:
Current year losses	242.9			257.4
Prior year losses	1.4			(7.6		)
Total incurred losses and LAE	244.3			249.8

Accretion of fair value adjustment to loss and LAE reserves	1.2			7.1
Foreign currency translation adjustment to loss and LAE reserves	(9.6		)	11.8

Loss and LAE paid relating to:
Current year losses	(36.6		)	(44.5		)
Prior year losses	(270.6		)	(322.9		)
Total loss and LAE payments	(307.2		)	(367.4		)

Plus: Ending net loss and LAE reserves for OneBeacon's runoff business⁽¹⁾	—			332.4

Net ending balance	2,689.8			3,045.4
Plus ending reinsurance recoverable on unpaid losses	410.8			2,465.4
Gross ending balance	$	3,100.6		$	5,510.8

Third Party Reinsurance (Tables)

3 Months Ended

Mar. 31, 2013

Reinsurance Disclosures [Abstract]

Listing of Sirius's top reinsurers

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



Top Reinsurers (Millions)	Balance at March 31, 2013		% of Total		A.M. Best Rating⁽¹⁾	% Collateralized
Berkshire Hathaway	$	56.9	18	%	A++	—	%
Swiss Re Group	34.8		11	%	A+	—	%
Olympus Reinsurance Company⁽²⁾	24.9		8	%	NR-5	100	%
Lloyds of London⁽³⁾	17.0		5	%	A	9	%
Michigan Catastrophic Claims Association⁽⁴⁾	14.7		5	%	N/A	—	%

⁽²⁾Non-U.S. insurance entity. The balance is 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.

Investment Securities (Tables)

3 Months Ended

Mar. 31, 2013

Investments, Debt and Equity Securities [Abstract]

Pre-tax net investment income

Pre-tax net investment income for the three months ended March 31, 2013 and 2012 consisted of the following:



	Three Months Ended
	March 31,
Millions	2013			2012
Investment income:
Fixed maturity investments	$	26.0		$	36.7
Short-term investments	.8			1.0
Common equity securities	4.7			4.4
Convertible fixed maturity investments	.8			1.9
Other long-term investments	.7			.8
Interest on funds held under reinsurance treaties	—			—
Total investment income	33.0			44.8
Less third-party investment expenses	(4.5		)	(3.0		)
Net investment income, pre-tax	$	28.5		$	41.8

Schedule of realized and unrealized gain (loss) on investments

The following table summarizes net realized and unrealized investment gains (losses) for the three months ended March 31, 2013 and 2012:



	Three Months Ended									Three Months Ended
	March 31, 2013									March 31, 2012
Millions	Net realized and unrealized gains (losses)			Net foreign exchange gains (losses)			Total net realized and unrealized gains (losses) reflected in earnings			Net realized and unrealized gains (losses)			Net foreign currency gains (losses)			Total net realized and unrealized gains (losses) reflected in earnings
Fixed maturity investments	$	(8.0	)	$	(10.0	)	$	(18.0	)	$	30.7		$	(21.4	)	$	9.3
Short-term investments	—			.1			.1			—			(.3		)	(.3		)
Common equity securities	84.5			(.2		)	84.3			36.6			—			36.6
Convertible fixed maturity investments	1.6			(.2		)	1.4			6.2			—			6.2
Other long-term investments	6.5			.5			7.0			10.2			(3.4		)	6.8
Forward Contracts	.4			—			.4			—			—			—
Net realized and unrealized investment gains (losses), pre-tax	85.0			(9.8		)	75.2			83.7			(25.1		)	58.6
Income tax expense attributable to net realized and unrealized investment (losses) gains	(15.9		)	2.2			(13.7		)	(20.6		)	6.6			(14.0		)
Net realized and unrealized investment gains (losses), after tax	$	69.1		$	(7.6	)	$	61.5		$	63.1		$	(18.5	)	$	44.6

Net unrealized investment gains (losses) for Level 3 investments



	Three Months Ended
	March 31,
Millions	2013			2012
Fixed maturity investments	$	.2		$	7.8
Common equity securities	(.1		)	.5
Other long-term investments	6.4			7.2
Total unrealized investment gains, pre-tax - Level 3 investments	$	6.5		$	15.5

Investment holdings, fixed maturity investments



	March 31, 2013
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency gains (losses)			Carrying value
U.S. Government and agency obligations	$	435.9	$	.9	$	(.1	)	$	(1.2	)	$	435.5
Debt securities issued by corporations	2,361.2		75.7		(2.6		)	(24.6		)	2,409.7
Municipal obligations	5.3		—		(.1		)	—			5.2
Mortgage-backed and asset-backed securities	1,698.7		12.6		(1.9		)	(2.1		)	1,707.3
Foreign government, agency and provincial obligations	516.4		5.4		(6.3		)	(9.4		)	506.1
Preferred stocks	79.9		7.7		—			(.1		)	87.5
Total fixed maturity investments including assets held for sale	$	5,097.4	$	102.3	$	(11.0	)	$	(37.4	)	$	5,151.3
Fixed maturity investments reclassified to assets held for sale related to the Runoff Transaction											(296.9		)
Total fixed maturity investments											$	4,854.4



	December 31, 2012
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency gains (losses)			Carrying value
U.S. Government and agency obligations	$	440.4	$	1.0	$	(.1	)	$	(1.2	)	$	440.1
Debt securities issued by corporations	2,321.4		88.3		(1.6		)	(23.0		)	2,385.1
Municipal obligations	5.3		—		(.1		)	—			5.2
Mortgage-backed and asset-backed securities	2,081.0		25.1		(1.1		)	(9.4		)	2,095.6
Foreign government, agency and provincial obligations	526.6		6.9		(3.0		)	(8.6		)	521.9
Preferred stocks	79.9		6.7		—			(.2		)	86.4
Total fixed maturity investments including assets held for sale	$	5,454.6	$	128.0	$	(5.9	)	$	(42.4	)	$	5,534.3
Fixed maturity investments reclassified to assets held for sale related to the Runoff Transaction											(338.1		)
Total fixed maturity investments											$	5,196.2

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



	March 31, 2013
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency losses			Carrying value
Common equity securities	$	876.8	$	201.7	$	(5.2	)	$	(.1	)	$	1,073.2
Convertible fixed maturity investments	$	91.2	$	5.9	$	(1.3	)	$	(.2	)	$	95.6
Other long-term investments	$	254.5	$	57.0	$	(10.3	)	$	(6.0	)	$	295.2



	December 31, 2012
Millions	Cost or amortized cost		Gross unrealized gains		Gross unrealized losses			Net foreign currency losses			Carrying value
Common equity securities	$	895.2	$	143.4	$	(8.8	)	$	(.1	)	$	1,029.7
Convertible fixed maturity investments	$	121.7	$	6.1	$	(.4	)	$	—		$	127.4
Other long-term investments	$	257.2	$	65.9	$	(22.8	)	$	(6.1	)	$	294.2

Other long-term investments

The following table summarizes investments in hedge funds and private equity interests by investment objective and sector at March 31, 2013 and December 31, 2012:



	March 31, 2013				December 31, 2012
Millions	Fair Value		Unfunded Commitments		Fair Value		Unfunded Commitments
Hedge funds
Long/short equity	$	60.0	$	—	$	60.3	$	—
Long/short credit & distressed	24.5		—		22.7		—
Long diversified strategies	1.7		—		1.7		—
Long/short equity REIT	16.7		—		16.0		—
Long/short equity activist	14.5		—		13.6		—
Long bank loan	.3		—		.3		—
Total hedge funds	117.7		—		114.6		—

Private equity funds
Multi-sector	25.9		8.9		23.3		5.4
Energy infrastructure & services	35.0		14.8		36.3		15.6
Distressed residential real estate	14.6		—		15.8		—
Real estate	10.9		3.3		11.6		3.3
Private equity secondaries	10.6		3.1		10.5		3.1
International multi-sector, Europe	4.2		5.0		5.1		5.0
Manufacturing/Industrial	9.0		28.7		9.9		29.1
Healthcare	4.2		5.0		4.3		5.4
International multi-sector, Asia	—		2.7		.4		2.7
Insurance	2.5		41.3		3.0		41.3
Aerospace/Defense/Government	3.0		21.8		2.8		22.2
Venture capital	2.2		.3		2.2		.3
Total private equity funds	122.1		134.9		125.2		133.4

Total hedge and private equity funds included in other long-term investments⁽¹⁾	$	239.8	$	134.9	$	239.8	$	133.4

⁽¹⁾Excludes carrying value of $35.0 and $34.9 at January 1, 2013 and March 31, 2013 associated with hedge funds and private equity funds accounted for using the equity method.

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

The following summarizes the March 31, 2013 fair value of hedge funds subject to restrictions on redemption frequency and advance notice period requirements for investments in active hedge funds:



	Notice Period
Millions Redemption frequency	30-59 days notice		60-89 days notice		90-119 days notice		120+ days notice		Total
Monthly	$	—	$	—	$	—	$	6.8	$	6.8
Quarterly	27.9		31.2		9.0		9.6		77.7
Semi-annual	—		22.7		—		—		22.7
Annual	1.7		—		8.5		.3		10.5
Total	$	29.6	$	53.9	$	17.5	$	16.7	$	117.7

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

At March 31, 2013, 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	$21.6	$34.0	$57.4	$9.1	$122.1

Fair value measurements by level, investment securities

The following tables summarize White Mountains’ fair value measurements for investments at March 31, 2013 and December 31, 2012, by level:



	March 31, 2013
Millions	Fair value		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs
Fixed maturity investments:
U.S. Government and agency obligations	$	435.5	$	364.6	$	70.9	$	—

Debt securities issued by corporations:
Consumer	735.5		—		735.5		—
Financials	378.4		—		378.4		—
Communications	331.6		—		331.6		—
Industrial	308.0		—		308.0		—
Basic Materials	211.6		—		211.6		—
Utilities	202.3		—		202.3		—
Energy	183.2		—		183.2		—
Technology	53.0		—		53.0		—
Other	6.1		—		6.1		—
Total debt securities issued by corporations:	2,409.7		—		2,409.7		—

Mortgage-backed and asset-backed securities	1,707.3		—		1,677.2		30.1
Foreign government, agency and provincial obligations	506.1		48.5		457.6		—
Preferred stocks	87.5		—		16.6		70.9
Municipal obligations	5.2		—		5.2		—
Total fixed maturity investments ⁽¹⁾	5,151.3		413.1		4,637.2		101.0

Short-term investments	654.4		654.4		—		—

Common equity securities:
Financials	320.1		283.3		—		36.8
Consumer	305.8		305.8		—		—
Energy	86.2		86.2		—		—
Basic materials	77.6		77.6		—		—
Technology	76.9		76.9		—		—
Communications	39.9		39.9		—		—
Utilities	39.7		39.6		.1		—
Other	127.0		64.0		63.0		—
Total common equity securities	1,073.2		973.3		63.1		36.8

Convertible fixed maturity investments	95.6		—		95.6		—
Other long-term investments ⁽²⁾	260.5		—		—		260.5
Total investments	$	7,235.0	$	2,040.8	$	4,795.9	$	398.3

⁽¹⁾Carrying value includes $296.9 that is classified as assets held for sale relating to discontinued operations.

⁽²⁾Excludes carrying value of $34.9 associated with other long-term investment limited partnerships accounted for using the equity method and $(0.2) related to forward contracts.



	December 31, 2012
Millions	Fair value		Level 1 Inputs		Level 2 Inputs		Level 3 Inputs
Fixed maturity investments:
U.S. Government and agency obligations	$	440.1	$	369.1	$	71.0	$	—

Debt securities issued by corporations:
Consumer	727.1		—		727.1		—
Financials	401.4		1.0		400.4		—
Industrial	330.8		—		330.8		—
Communications	276.1		—		276.1		—
Utilities	204.2		—		204.2		—
Basic materials	189.1		—		189.1		—
Energy	181.5		—		181.5		—
Technology	54.0		—		54.0		—
Other	20.9		—		20.9		—
Total debt securities issued by corporations:	2,385.1		1.0		2,384.1		—

Mortgage-backed and asset-backed securities	2,095.6		—		2,073.5		22.1
Foreign government, agency and provincial obligations	521.9		52.1		469.8		—
Preferred stocks	86.4		—		15.6		70.8
Municipal obligations	5.2		—		5.2		—
Total fixed maturity investments ⁽¹⁾	5,534.3		422.2		5,019.2		92.9

Short-term investments	630.6		630.6		—		—

Common equity securities:
Financials	324.5		286.3		.9		37.3
Consumer	255.6		255.6		—		—
Basic materials	103.3		103.3		—		—
Energy	101.0		101.0		—		—
Technology	55.0		55.0		—		—
Utilities	43.6		43.4		.2		—
Communications	35.2		35.2		—		—
Other	111.5		53.1		58.4		—
Total common equity securities	1,029.7		932.9		59.5		37.3

Convertible fixed maturity investments	127.4		—		127.4		—
Other long-term investments ⁽²⁾	259.3		—		—		259.3
Total investments	$	7,581.3	$	1,985.7	$	5,206.1	$	389.5

⁽¹⁾Carrying value includes $338.1 that is classified as assets held for sale relating to discontinued operations.

⁽²⁾Excludes carrying value of $35.0 associated with other long-term investment limited partnerships accounted for using the equity method and $(0.1) related to currency forward contracts.

Debt securities issued by corporations, credit ratings

The following table summarizes the ratings of the corporate debt securities held in White Mountains’ investment portfolio as of March 31, 2013 and December 31, 2012:



	Fair Value at
Millions	March 31, 2013		December 31, 2012
AAA	$	—	$	—
AA	164.4		193.4
A	1,132.3		1,061.0
BBB	1,099.4		1,116.9
BB	7.0		7.0
Other	8.0		6.8
Debt securities issued by corporations ⁽¹⁾	$	2,411.1	$	2,385.1

⁽¹⁾Credit ratings are assigned based on the following hierarchy: 1) Standard and Poor's Financial Services LLC ("Standard & Poor’s") and 2) Moody’s Investor Service ("Moody's").

Mortgage-backed, asset-backed securities

The following table summarizes mortgage and asset-backed securities as of March 31, 2013 and December 31, 2012:



	March 31, 2013						December 31, 2012
Millions	Fair Value		Level 2		Level 3		Fair Value		Level 2		Level 3
Mortgage-backed securities:
Agency:
GNMA	$	805.5	$	805.5	$	—	$	1,013.4	$	1,013.4	$	—
FNMA	140.2		140.2		—		74.6		74.6		—
FHLMC	55.6		55.6		—		55.8		55.8		—
Total Agency⁽¹⁾	1,001.3		1,001.3		—		1,143.8		1,143.8		—
Non-agency:
Residential	55.6		55.6		—		160.6		160.6		—
Commercial	284.9		276.9		8.0		334.1		334.1		—
Total Non-agency	340.5		332.5		8.0		494.7		494.7		—

Total mortgage-backed securities	1,341.8		1,333.8		8.0		1,638.5		1,638.5		—
Other asset-backed securities:
Credit card receivables	132.3		110.2		22.1		173.5		151.4		22.1
Vehicle receivables	210.3		210.3		—		265.1		265.1		—
Other	22.9		22.9		—		18.5		18.5		—
Total other asset-backed securities	365.5		343.4		22.1		457.1		435.0		22.1
Total mortgage and asset-backed securities	$	1,707.3	$	1,677.2	$	30.1	$	2,095.6	$	2,073.5	$	22.1

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

The security issuance years of White Mountains’ investments in non-agency RMBS and non-agency CMBS securities as of March 31, 2013 are as follows:



			Security Issuance Year
Millions	Fair Value		2005		2006		2007		2008		2010		2011		2012		2013
Non-agency RMBS	$	55.6	$	34.9	$	11.0	$	4.8	$	—	$	4.9	$	—	$	—	$	—
Non-agency CMBS	284.9		—		8.7		15.0		35.0		12.9		39.8		122.5		51.0
Total	$	340.5	$	34.9	$	19.7	$	19.8	$	35.0	$	17.8	$	39.8	$	122.5	$	51.0

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

The classification of the underlying collateral quality and the tranche levels of White Mountains’ non-agency RMBS securities are as follows as of March 31, 2013:



Millions	Fair Value		Super Senior ⁽¹⁾		Senior ⁽²⁾		Subordinate ⁽³⁾
Prime	$	55.6	$	4.9	$	50.7	$	—
Non-prime	—		—		—		—
Sub-prime	—		—		—		—
Total	$	55.6	$	4.9	$	50.7	$	—

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

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

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

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

The amount of fixed and floating rate securities and their tranche levels of White Mountains’ non-agency CMBS securities are as follows as of March 31, 2013:



Millions	Fair Value		Super Senior ⁽¹⁾		Senior ⁽²⁾		Subordinate ⁽³⁾
Fixed rate CMBS	$	206.5	$	128.0	$	60.7	$	17.8
Floating rate CMBS	78.4		14.9		36.4		27.1
Total	$	284.9	$	142.9	$	97.1	$	44.9

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

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

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

Rollforward of fair value investments by level

The following tables summarize the changes in White Mountains’ fair value measurements by level for the three months ended March 31, 2013 and 2012:



							Level 3 Investments
Millions	Level 1 ⁽³⁾ Investments			Level 2 Investments			Fixed Maturities		Common equity securities			Convertible fixed maturities		Other long-term investments			Total
Balance at January 1, 2013	$	1,355.1		$	5,206.1		$	92.9	$	37.3		$	—	$	259.3		$	6,950.7		⁽¹⁾⁽²⁾
Total realized and unrealized gains (losses)	80.1			(10.8		)	.1		(.1		)	—		5.8			75.1
Foreign currency losses through OCI	(.4		)	(4.8		)	—		—			—		(.4		)	(5.6		)
Amortization/Accretion	(.4		)	(14.0		)	—		—			—		—			(14.4		)
Purchases	318.6			1,445.8			8.0		—			—		18.9			1,791.3
Sales	(382.3		)	(1,828.3		)	—		—			—		(23.1		)	(2,233.7		)
Net change in investments related to purchases and sales of consolidated affiliates	14.5			2.7			—		—			—		—			17.2
Transfers in	1.2			—			—		—			—		—			1.2
Transfers out	—			(.8		)	—		(.4		)	—		—			(1.2		)
Balance at March 31, 2013	$	1,386.4		$	4,795.9		$	101.0	$	36.8		$	—	$	260.5		$	6,580.6		⁽¹⁾⁽²⁾

⁽²⁾Carrying value includes $338.1 and $296.9 at January 1, 2013 and March 31, 2013 that is classified as assets held for sale relating to discontinued operations.



							Level 3 Investments
Millions	Level 1⁽³⁾ Investments			Level 2 Investments			Fixed Maturities			Common equity securities		Convertible fixed maturities		Other long-term investments				Total
Balance at January 1, 2012	$	1,033.1		$	6,088.2		$	78.9		$	32.3	$	—	$	268.3		⁽¹⁾	$	7,500.8		⁽¹⁾⁽²⁾
Total realized and unrealized gains	34.7			10.1			7.1			.5		—		6.5				58.9
Foreign currency gains through OCI	.7			50.4			.7			—		—		2.7				54.5
Amortization/Accretion	(.3		)	(12.5		)	(1.1		)	—		—						(13.9		)
Purchases	166.6			1,708.2			97.7			—		—		5.7				1,978.2
Sales	(129.0		)	(2,729.4		)	(4.1		)	—		—		(9.7		)		(2,872.2		)
Transfers in	—			—			—			—		—		—				—
Transfers out	—			—			—			—		—		—				—
Balance at March 31, 2012	$	1,105.8		$	5,115.0		$	179.2		$	32.8	$	—	$	273.5		⁽¹⁾	$	6,706.3		⁽¹⁾⁽²⁾

⁽¹⁾Excludes carrying value of $33.0 and $33.2 at March 31, 2012 and January 1, 2012 associated with other long-term investment limited partnerships accounted for using the equity method.

⁽²⁾Carrying value includes $111.8 that is classified as assets held for sale relating to discontinued operations.

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

($ in Millions)

March 31, 2013

Description

Fair Value

Rating⁽²⁾

Valuation Technique(s)

Unobservable Input

Preferred Stock⁽¹⁾

$70.9

Discounted cash flow

Discount yield

7.4

Asset-backed securities

$8.0

BBB-

Broker pricing

Broker quote

$22.1

AA+

Broker pricing

Broker quote

Private equity securities

$36.8

Multiple of GAAP book value

Book value multiple

1.0

⁽¹⁾As of March 31, 2013 asset type consists of one security.

⁽²⁾Credit ratings are assigned based on the following hierarchy: 1) Standard and Poor's Financial Services LLC (“Standard & Poor’s”) and 2) Moody’s Investor Service (“Moody's”).

Debt (Tables)

3 Months Ended

Mar. 31, 2013

Debt Disclosure [Abstract]

Schedule of debt outstanding

White Mountains’ debt outstanding as of March 31, 2013 and December 31, 2012 consisted of the following:



Millions	March 31, 2013			December 31, 2012
2012 OBH Senior Notes, at face value	$	275.0		$	275.0
Unamortized original issue discount	(.3		)	(.3		)
2012 OBH Senior Notes, carrying value	274.7			274.7
SIG Senior Notes, at face value	400.0			400.0
Unamortized original issue discount	(.6		)	(.6		)
SIG Senior Notes, carrying value	399.4			399.4
WTM Bank Facility	—			75.0
Old Lyme Note	2.1			2.1
Total debt	$	676.2		$	751.2

- Definition

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

+ References

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

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

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

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

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

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

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

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

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

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

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

+ Details

Derivatives (Tables)

3 Months Ended

Mar. 31, 2013

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Pre-tax operating results of WM Life Re

The following table summarizes the pre-tax operating results of WM Life Re for the three months ended March 31, 2013 and 2012



	Three Months Ended
	March 31,
Millions	2013			2012
Fees, included in other revenues	$	6.8		$	8.0
Change in fair value of variable annuity liability, included in other revenues	184.3			211.2
Change in fair value of derivatives, included in other revenues	(181.8		)	(206.5		)
Foreign exchange, included in other revenues	(14.6		)	(23.0		)
Other investment income and gains (losses)	(4.0		)	(2.1		)
Total revenues	(9.3		)	(12.4		)
Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses	5.6			8.8
Death benefit claims paid, included in general and administrative expenses	(1.1		)	(1.8		)
General and administrative expenses	(1.7		)	(1.3		)
Pre-tax loss	$	(6.5	)	$	(6.7	)

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



							Carrying Value
	Three Months Ended						As of
	March 31,						March 31, 2013			December 31, 2012
Millions	2013			2012			March 31, 2013			December 31, 2012
Fixed income/interest rate	$	(30.9	)	$	(79.0	)	$	(16.2	)	$	27.1
Foreign exchange	(53.6		)	(55.0		)	74.1			52.8
Equity	(97.3		)	(72.5		)	17.9			18.4
Total	$	(181.8	)	$	(206.5	)	$	75.8		$	98.3

Fair Value of Assets and Liabilities Measured on Recurring and Non-recurring Basis Table

The following tables summarize the changes in White Mountains’ variable annuity reinsurance liabilities and derivative instruments for the three months ended March 31, 2013 and 2012:



	Three Months Ended March 31, 2013
	Variable Annuity (Liabilities)				Derivative Instruments
Millions	Level 3				Level 3 ⁽¹⁾			Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total
Beginning of period	$	(441.5	)		$	140.5		$	(20.5	)	$	(21.7	)	$	98.3
Purchases	—				36.1			—			—			36.1
Realized and unrealized gains (losses)	189.9			⁽⁴⁾	(49.2		)	(85.5		)	(47.1		)	(181.8		)
Transfers in	—				—			—			—			—
Sales/settlements	—				—			63.1			60.1			123.2
End of period	$	(251.6	)		$	127.4		$	(42.9	)	$	(8.7	)	$	75.8



	Three Months Ended March 31, 2012
	Variable Annuity (Liabilities)				Derivative Instruments
Millions	Level 3				Level 3 ⁽¹⁾			Level 2 ⁽¹⁾⁽²⁾			Level 1 ⁽³⁾			Total
Beginning of period	$	(768.5	)		$	247.1		$	39.2		$	4.1		$	290.4
Purchases	—				6.1			—			—			6.1
Realized and unrealized gains (losses)	220.0			⁽⁴⁾	(60.3		)	(98.2		)	(48.0		)	(206.5		)
Transfers in	—				—			—			—			—
Sales/settlements	—				(9.1		)	58.9			34.5			84.3
End of period	$	(548.5	)		$	183.8		$	(.1	)	$	(9.4	)	$	174.3

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

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

The following tables summarize the changes in White Mountains' forward contracts for the three months ended March 31, 2013:



Millions	March 31, 2013
Beginning of period	$	(.1	)
Purchases	—
Net realized and unrealized gains	.4
Sales/settlements	(.5		)
End of period	$	(.2	)

Summary of additional collateral posted for variable reinsurance counterparties



Millions	March 31, 2013		December 31, 2012		March 31, 2012
Cash	$	188.5	$	249.8	$	360.1
Short-term investments	15.6		5.1		1.5
Fixed maturity investments	25.7		138.7		29.3
Total	$	229.8	$	393.6	$	390.9

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



($ in Millions)	March 31, 2013
Description	Fair Value		Valuation Technique(s)	Unobservable Input	Range				Weighted Average
Variable annuity benefit guarantee liabilities	$	251.6	Discounted cash flows	Surrenders
				1 year	0.3	%	-	3.0%	0.7	%
				2 year	0.2	%	-	3.0%	0.8	%
				3 and more years	0.1	%	-	3.0%	0.7	%
				Mortality	0.0	%	-	5.3%	0.9	%
				Foreign exchange volatilities
				1 year	11.2	%	-	13.3%	12.2	%
				2 year	11.7	%	-	14.0%	12.6	%
				3 and more years	12.3	%	-	14.6%	13.2	%
				Index volatilities
				1 year	11.9	%	-	17.9%	13.3	%
				2 year	16.5	%	-	20.7%	18.0	%
				3 and more years	18.6	%	-	22.3%	20.9	%
Foreign exchange options	$	74.2	Counterparty valuations, adjusted for unwind quote discount	Adjustment to counterparty valuations	(0.1	)%	-	(3.2)%	(2.1	)%
Foreign exchange options			Counterparty valuations, adjusted for unwind quote discount	Adjustment to counterparty valuations
Equity index options	$	53.2	Counterparty valuations, adjusted for unwind quote discount	Adjustment to counterparty valuations	(1.7	)%	-	(3.0)%	(2.5	)%
Equity index options			Counterparty valuations, adjusted for unwind quote discount	Adjustment to counterparty valuations

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

The following summarizes amounts offset under master netting agreements:



	March 31, 2013								December 31, 2012
Millions	Gross asset amounts before offsets⁽¹⁾		Gross liability amounts offset under master netting arrangements			Net amounts recognized in Other Assets			Gross asset amounts before offsets⁽¹⁾		Gross liability amounts offset under master netting arrangements			Net amounts recognized in Other Assets
Interest rate contracts
OTC	$	—	$	(15.6	)	$	(15.6	)	$	52.6	$	(26.9	)	$	25.7
Exchange traded	1.0		(1.6		)	(.6		)	1.6		(.2		)	1.4
Foreign exchange contracts
OTC	89.6		(15.5		)	74.1			87.8		(34.4		)	53.4
Exchange traded	.6		(.6		)	—			.8		(1.4		)	(.6		)
Equity contracts
OTC	53.2		(27.2		)	26.0			63.6		(22.9		)	40.7
Exchange traded	.4		(8.5		)	(8.1		)	.1		(22.4		)	(22.3		)
Total⁽²⁾	$	144.8	$	(69.0	)	$	75.8		$	206.5	$	(108.2	)	$	98.3

⁽¹⁾Amount equal to fair value of instrument as recognized in other assets.

⁽²⁾ All derivative instruments held by WM Life Re are subject to master netting arrangements.

Schedule of Uncollateralized Amounts Due



	March 31, 2013
Millions	Net amount of assets reflected in Balance Sheet			Collateral provided - Financial Instruments		Collateral held - Financial Instruments		Collateral provided - Cash		Collateral held - Cash		Net amount of exposure after effect of collateral held		Standard & Poor's Rating⁽¹⁾
Bank of America	$	60.0		$	—	$	—	$	—	$	10.8	$	49.2	A
Barclays	6.5			—		—		—		—		6.5		A	+
JP Morgan	3.1			—		—		31.3		—		34.4		A	+
Royal Bank of Scotland	26.4			—		—		—		—		26.4		A
Nomura	(6.2		)	25.6		—		8.2		—		27.6		BBB	+
Goldman Sachs	—			—		—		—		—		—		A	-
Citigroup - OTC	(5.3		)	—		—		25.3		—		20.0		A
Citigroup - Exchange Traded	(8.7		)	—		—		24.7		—		16.0		A
Total	$	75.8		$	25.6	$	—	$	89.5	$	10.8	$	180.1



	December 31, 2012
Millions	Net amount of assets reflected in Balance Sheet			Collateral provided - Financial Instruments		Collateral held - Financial Instruments		Collateral provided - Cash		Collateral held - Cash		Net amount of exposure after effect of collateral held		Standard & Poor's Rating⁽¹⁾
Bank of America	$	78.5		$	—	$	—	$	—	$	30.6	$	47.9	A
Barclays	11.6			—		—		—		—		11.6		A	+
JP Morgan	(22.8		)	—		—		55.6		—		32.8		A	+
Royal Bank of Scotland	33.6			—		—		—		—		33.6		A
Nomura	(0.9		)	28.1		—		1.7		—		28.9		BBB	+
Goldman Sachs	(0.1		)	—		—		3.2		—		3.1		A	-
Citigroup - OTC	19.9			—		—		30.8		—		50.7		A
Citigroup - Exchange Traded	(21.5		)	—		—		35.0		—		13.5		A
Total	$	98.3		$	28.1	$	—	$	126.3	$	30.6	$	222.1

The following summarizes amounts offset under master netting agreements:



	March 31, 2013								December 31, 2012
Millions	Gross asset amounts before offsets⁽¹⁾		Gross liability amounts offset under master netting arrangements			Net amounts recognized in Other assets			Gross asset amounts before offsets⁽¹⁾		Gross liability amounts offset under master netting arrangements			Net amounts recognized in Other assets
USD	$	.1	$	(.4	)	$	(.3	)	$	—	$	—		$	—
EUR	—		—			—			—		(.1		)	(.1		)
GBP	.2		(.1		)	.1			—		—			—
Total	$	.3	$	(.5	)	$	(.2	)	$	—	$	(.1	)	$	(.1	)

⁽¹⁾Amount equal to fair value of instrument as recognized in other assets.

Unrealized derivative gains and losses



	March 31, 2013
Millions	Gains (Losses)			Carrying Value
USD	$	(.3	)	$	(.3	)
SEK	—			—
EUR	—			—
GBP	.7			.1
Total	$	.4		$	(.2	)

Schedule of uncollateralized amounts due

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



	March 31, 2013						December 31, 2012
Millions	Notional Amount		Carrying Value			Standard & Poor's Rating⁽¹⁾	Notional Amount		Carrying Value
Barclays	24.7		.1			A+	7.7		(.1		)
Deutsche Bank	13.8		(.2		)	A+	11.1		—
Goldman Sachs	1.1		—			A-	.4		—
HSBC	.1		—			AA-	10.1		—
JP Morgan	22.1		.1			A+	1.9		—
Royal Bank of Canada	17.5		(.2		)	AA-	—		—
Total	$	79.3	$	(.2	)		$	31.2	$	(.1	)

Municipal Bond Guarantee (Tables)

3 Months Ended

Mar. 31, 2013

Schedule of insured obligations [Abstract]

Schedule of Municipal Guarantee Insured Obligations [Table Text Block]

The following table provides a schedule of BAM's insured obligations:



	March 31, 2013		December 31, 2012
Contracts issued and outstanding	105		3
Remaining weighted average contract period (in years)	13.1		10.4
Contractual debt service outstanding (in millions):
Principal	$	698.6	$	25.8
Interest	$	497.6	$	8.9
Unearned premium revenue	$	2.0	$	.1

Earnings Per Share (Tables)

3 Months Ended

Mar. 31, 2013

Earnings Per Share [Abstract]

Computation of earnings per share

The following table outlines the Company’s computation of earnings per share from continuing operations for the three months ended March 31, 2013 and 2012 (see Note 15 for earnings per share amounts for discontinued operations):



	Three Months Ended
	March 31,
	2013			2012
Basic and diluted earnings per share numerators (in millions):
Net income from continuing operations attributable to White Mountains’ common shareholders	$	119.9		$	103.1
Allocation of income for unvested restricted common shares	(1.5		)	(1.1		)
Dividends declared on participating restricted common shares ⁽¹⁾	(.1		)	(.1		)
Total allocation to restricted common shares	(1.6		)	(1.2		)
Net income attributable to White Mountains’ common shareholders, net of restricted common share amounts	$	118.3		$	101.9
Undistributed net earnings (in millions):
Net income attributable to White Mountains’ common shareholders, net of restricted common share amounts	$	118.3		$	101.9
Dividends declared on participating restricted common shares⁽¹⁾	(6.1		)	(6.5		)
Total undistributed net earnings, net of restricted common share amounts	$	112.2		$	95.4
Basic earnings per share denominators (in thousands):
Total average common shares outstanding during the period	6,273.5			7,431.7
Average unvested restricted shares ⁽²⁾	(79.0		)	(78.3		)
Basic earnings per share denominator	6,194.5			7,353.4
Diluted earnings per share denominator (in thousands):
Total average common shares outstanding during the period	6,273.5			7,431.7
Average unvested restricted common shares⁽²⁾	(79.0		)	(78.3		)
Average outstanding dilutive options to acquire common shares⁽³⁾	—			—
Diluted earnings per share denominator	6,194.5			7,353.4
Basic earnings per share (in dollars):
Net income attributable to White Mountains’ common shareholders	$	19.10		$	13.86
Dividends declared	(1.00		)	(1.00		)
Undistributed earnings	$	18.10		$	12.86
Diluted earnings per share (in dollars)
Net income attributable to White Mountains’ common shareholders	$	19.10		$	13.86
Dividends declared	(1.00		)	(1.00		)
Undistributed earnings	$	18.10		$	12.86

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

⁽²⁾Restricted shares outstanding vest either in equal annual installments or upon a stated date (see Note 13).

Segment Information (Tables)

3 Months Ended

Mar. 31, 2013

Segment Reporting [Abstract]

Financial information for White Mountains' segments

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



					HG Global/BAM
Millions	OneBeacon		Sirius Group		HG			BAM			Other Operations			Total
Three Months Ended March 31, 2013
Earned insurance and reinsurance premiums	$	286.5	$	208.9	$	—		$	—		$	—		$	495.4
Net investment income	9.4		13.1		.3			1.1			4.6			28.5
Net investment income - surplus note income	—		—		10.1			(10.1		)	—			—
Net realized and unrealized investment gains (losses)	28.4		13.1		(.2		)	(1.1		)	35.0			75.2
Other revenue	24.0		10.5		—			.1			(6.3		)	28.3
Total revenues	348.3		245.6		10.2			(10.0		)	33.3			627.4
Losses and loss adjustment expenses	148.9		95.4		—			—			—			244.3
Insurance and reinsurance acquisition expenses	54.8		43.3		—			.1			—			98.2
Other underwriting expenses	49.3		29.7		—			.1			—			79.1
General and administrative expenses	4.0		9.5		.3			8.2			21.8			43.8
Interest expense on debt	3.2		6.6		—			—			.4			10.2
Total expenses	260.2		184.5		.3			8.4			22.2			475.6
Pre-tax income (loss)	$	88.1	$	61.1	$	9.9		$	(18.4	)	$	11.1		$	151.8



Millions	OneBeacon		Sirius Group		Other Operations		Total
Three Months Ended March 31, 2012
Earned insurance and reinsurance premiums	$	271.8	$	226.2	$	—	$	498.0
Net investment income	14.7		17.1		10.0		41.8
Net realized and unrealized investment gains	29.8		13.7		15.1		58.6
Other revenue	.1		18.3		12.8		31.2
Total revenues	316.4		275.3		37.9		629.6
Losses and loss adjustment expenses	136.4		113.4		—		249.8
Insurance and reinsurance acquisition expenses	58.1		51.0		—		109.1
Other underwriting expenses	47.5		26.0		—		73.5
General and administrative expenses	2.7		18.9		23.9		45.5
Interest expense on debt	4.1		6.5		.3		10.9
Total expenses	248.8		215.8		24.2		488.8
Pre-tax income	$	67.6	$	59.5	$	13.7	$	140.8

- 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)

3 Months Ended

Mar. 31, 2013

Equity Method Investments and Joint Ventures [Abstract]

Investments in and Advances to Affiliates



Millions	March 31, 2013		December 31, 2012
Symetra common shares	$	296.8	$	288.4
Unrealized gains from Symetra's fixed maturity portfolio	54.1		62.8
Carrying value of Symetra common shares	350.9		351.2
Symetra warrants	26.6		30.3
Total investment in Symetra	377.5		381.5
Hamer	3.8		4.0
Bri-Mar	1.8		1.9
Pentelia Capital Management	.5		.5
Total investments in unconsolidated affiliates	$	383.6	$	387.9

Schedule of Changes in Investments in Unconsolidated Affiliates

The following table summarizes amounts recorded by White Mountains relating to its investment in Symetra for the three months ended March 31, 2013 and 2012:



	Three Months Ended									Three Months Ended
	March 31, 2013									March 31, 2012
Millions	Common Shares			Warrants			Total			Common Shares			Warrants		Total
Carrying value of investment in Symetra as of January 1	$	351.2		$	30.3		$	381.5		$	261.0		$	12.6	$	273.6
Equity in earnings ⁽¹⁾⁽²⁾	9.8			—			9.8			10.9			—		10.9
Equity in net unrealized gains from Symetra’s fixed maturity portfolio⁽³⁾	(8.7		)	—			(8.7		)	(1.2		)	—		(1.2		)
Dividends received	(1.4		)	—			(1.4		)	(1.2		)	—		(1.2		)
(Decrease) increase in value of warrants	—			(3.7		)	(3.7		)	—			11.1		11.1
Carrying value of investment in Symetra as March 31 ⁽⁴⁾⁽⁵⁾	$	350.9		$	26.6		$	377.5		$	269.5		$	23.7	$	293.2

⁽¹⁾Equity in earnings excludes tax expense of $0.8 and $0.7.

⁽²⁾Equity in earnings includes $0.7 and $1.1 increase relating to the pre-tax amortization of Symetra common share impairment from March 31, 2013 and 2012.

⁽³⁾Net unrealized gains includes $2.7 and $3.2 increase relating to the pre-tax amortization of Symetra common share impairment from March 31, 2013 and 2012.

⁽⁵⁾The aggregate value of White Mountains’ investment in common shares of Symetra was $233.3 based upon the quoted market price of $13.41 per share at

March 31, 2013.

Employee Share-Based Incentive Compensation Plans (Tables)

3 Months Ended

Mar. 31, 2013

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

Summary of performance share activity

The following table summarizes performance share activity for the three months ended March 31, 2013 and 2012 for performance shares granted under the WTM Incentive Plan and phantom performance shares granted under the Sirius Group Performance Plan (the “WTM Phantom Share Plan”):



	Three Months Ended March 31,
	2013					2012
Millions, except share amounts	Target Performance Shares Outstanding		Accrued Expense			Target Performance Shares Outstanding		Accrued Expense
Beginning of period	119,357		$	29.4		150,064		$	66.1
Shares paid ⁽¹⁾	(47,310	)	(11.0		)	(68,357	)	(48.4		)
New grants	46,920		—			35,932		—
Assumed forfeitures and cancellations ⁽²⁾	9		.1			811		1.0
Expense recognized	—		10.1			—		8.7
Ending March 31,	118,976		$	28.6		118,450		$	27.4

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

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

The following table summarizes performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan at March 31, 2013 for each performance cycle:



Millions, except share amounts	Target Performance Shares Outstanding		Accrued Expense
Performance cycle:
2013 – 2015	46,920		$	2.2
2012 – 2014	37,977		11.4
2011 – 2013	37,130		15.8
Sub-total	122,027		29.4
Assumed forfeitures	(3,051	)	(.8		)
Total at March 31, 2013	118,976		$	28.6

Summary of restricted share activity

The following outlines the unrecognized compensation cost associated with the outstanding restricted share awards for the three months ended March 31, 2013 and 2012:



	Three Months Ended March 31,
	2013				2012
Millions, except share amounts	Restricted Shares	Unamortized Issue Date Fair Value			Restricted Shares		Unamortized Issue Date Fair Value
Non-vested,
Beginning of period	69,910	$	16.8		72,000		$	13.3
Issued	25,470	14.3			28,460		13.7
Vested	—	—			(7,000	)	—
Forfeited	—	—			—		—
Expense recognized	—	(2.9		)	—		(2.5		)
Non-vested at March 31,	95,380	$	28.2		93,460		$	24.5

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

The following table summarizes performance share activity for the three months ended March 31, 2013 and 2012 for OneBeacon performance shares granted under the OneBeacon Incentive Plan:



	Three Months Ended March 31,
	2013				2012
Millions, except share amounts	Target Performance Shares Outstanding		Accrued Expense		Target Performance Shares Outstanding		Accrued Expense
Beginning of period	563,190		$	1.2	642,667		$	9.7
Shares paid or expired⁽¹⁾	(238,658	)	—		(249,733	)	(7.5		)
New awards	179,000		—		181,290		—
Assumed forfeitures and cancellations⁽²⁾	(13,665	)	—		(4,479	)	—
Expense recognized	—		.4		—		1.0
Ending March 31,	489,867		$	1.6	569,745		$	3.2

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

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

The following table summarizes OneBeacon performance shares outstanding awarded under the OneBeacon Incentive Plan at March 31, 2013 for each performance cycle:



Millions, except share amounts	Target OneBeacon Performance Shares Outstanding		Accrued Expense
Performance cycle:
2013 – 2015	179,000		$	.2
2012 – 2014	181,290		1.1
2011 – 2013	142,138		.3
Sub-total	502,428		1.6
Assumed forfeitures	(12,561	)	—
Total at March 31, 2013	489,867		$	1.6

Summary of OneBeacon restricted shares activity

The following summarizes the unrecognized compensation cost associated with the outstanding OneBeacon restricted share awards for the three months ended March 31, 2013 and 2012:



	Three Months Ended March 31,
	2013					2012
Millions, except share amounts	Restricted Shares		Unamortized Issue Date Fair Value			Restricted Shares	Unamortized Issue Date Fair Value
Non-vested,
Beginning of period	927,000		$	9.6		630,000	$	7.7
Issued	—		—			300,000	4.6
Vested	(9,000	)	—			—	—
Forfeited	—		—			—	—
Expense recognized	—		(.8		)	—	(.4		)
Non-vested at March 31,	918,000		$	8.8		930,000	$	11.9

Fair Value of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2013

Fair Value Disclosures [Abstract]

Summary of the fair value and carrying value of financial instruments

The following table summarizes the fair value and book value of financial instruments as of March 31, 2013 and December 31, 2012:



	March 31, 2013				December 31, 2012
Millions	Fair Value		Book Value		Fair Value		Book Value
2012 OBH Senior Notes	$	287.8	$	274.7	$	282.4	$	274.7
SIG Senior Notes	454.0		399.4		441.9		399.4
SIG Preference Shares	262.5		250.0		257.5		250.0

- Definition

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

+ References

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

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

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

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

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

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

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

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

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

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

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

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

+ Details

Discontinued Operations (Tables)

3 Months Ended

Mar. 31, 2013

Discontinued Operations and Disposal Groups [Abstract]

Schedule of discontinued operations balance sheet

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



Millions	March 31, 2013		December 31, 2012
Assets held for sale
Fixed maturity investments, at fair value	$	296.9	$	338.1
Cash	—		—
Reinsurance recoverable on unpaid losses	1,814.1		1,840.8
Reinsurance recoverable on paid losses	14.1		15.6
Insurance premiums receivable	9.9		11.0
Deferred acquisition costs	—		—
Deferred tax asset	4.2		5.1
Other assets	16.0		16.2
Total assets held for sale	$	2,155.2	$	2,226.8
Liabilities held for sale
Loss and loss adjustment expense reserves	$	1,980.2	$	2,052.6
Unearned insurance premiums	.5		.5
Ceded reinsurance payable	23.5		21.9
Other liabilities	151.0		151.8
Total liabilities held for sale	2,155.2		2,226.8
Net assets held for sale	$	—	$	—

Schedule of discontinued operations income statement

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



	Three Months Ended March 31,
Millions	2013			2012
Revenues
Earned insurance premiums	$	.9		$	8.8
Net investment income	—			—
Net realized and unrealized investment gains (losses)	—			—
Other revenue	—			—
Total revenues	.9			8.8
Expenses
Loss and loss adjustment expenses	—			19.6
Insurance and reinsurance acquisition expenses	.1			.3
Other underwriting expenses	.1			1.5
General and administrative expenses	—			—
Total expenses	.2			21.4
Pre-tax income (loss)	.7			(12.6		)
Income tax (expense) benefit	(.2		)	3.3
Income (loss) from discontinued operations	.5			(9.3		)
Loss from sale of discontinued operations	—			—
Net income (loss) from discontinued operations	$	.5		$	(9.3	)

Discontinued operations, computation of earnings per share

The following table outlines the computation of earnings (loss) per share for discontinued operations for the three months ended March 31, 2013 and 2012:



	Three Months Ended March 31,
	2013			2012
Basic and diluted earnings (loss) per share numerators (in millions):
Net income (loss) attributable to White Mountains’ common shareholders	$	.5		$	(9.3	)
Allocation of income for participating unvested restricted common shares ⁽¹⁾	—			.1
Net income (loss) attributable to White Mountains’ common shareholders, net of restricted common share amounts⁽²⁾	$	.5		$	(9.2	)
Basic earnings (loss) per share denominators (in thousands):
Total average common shares outstanding during the period	6,273.5			7,431.7
Average unvested restricted common shares⁽³⁾	(79.0		)	(78.3		)
Basic earnings (loss) per share denominator	6,194.5			7,353.4
Diluted earnings (loss) per share denominator (in thousands):
Total average common shares outstanding during the period	6,273.5			7,431.7
Average unvested restricted common shares⁽³⁾	(79.0		)	(78.3		)
Average outstanding dilutive options to acquire common shares⁽⁴⁾	—			—
Diluted earnings (loss) per share denominator	6,194.5			7,353.4
Basic and diluted earnings (loss) per share (in dollars):	$	.07		$	(1.25	)

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

⁽³⁾ Restricted common shares outstanding vest either in equal annual installments or upon a stated date (see Note 13).

Summary of Significant Accounting Policies (Basis of Presentation) (Details) $ / shares in Units, $ in Millions	1 Months Ended			3 Months Ended			12 Months Ended
	Jul. 31, 2012 USD ($)	Dec. 31, 2011 company	May 31, 2007 USD ($) shares	Mar. 31, 2013 USD ($)	Sep. 30, 2012 USD ($)	Mar. 31, 2012 USD ($)	Dec. 31, 2012 USD ($)	May 24, 2007 USD ($) $ / shares
Basis of Presentation
Percentage of par value of policy reinsured				15.00%
Number of small manufacturing companies owned by the Tuckerman Fund I from whom the entity received shares \| company		2
Net loss (income) attributable to non-controlling interests				$ 0.5		$ (16.8)
OneBeacon Ltd.
Basis of Presentation
Ownership percentage in outstanding common shares				75.20%			75.20%
Noncontrolling equity percentage in OneBeacon Ltd.				24.80%
White Mountains
Basis of Presentation
Funds to Capitalize HG Global					$ 600.0		$ 594.5
Funds to Capitalized HG Global	$ 594.5
HG Global
Basis of Presentation
Surplus Notes							503.0
White Mountains Consolidated Limited Partnership
Basis of Presentation
Noncontrolling interest - other				$ 44.1			41.5
A W G Dewar Inc
Basis of Presentation
Noncontrolling interest - other				2.5			2.8
Passage 2 Health Limited
Basis of Presentation
Noncontrolling interest - other				$ 0.2			$ 0.2
Preferred Stock \| Sirius International Group Ltd
Basis of Presentation
Non-cumulative perpetual preference shares issued \| shares			250,000,000
Non-cumulative perpetual preference shares per share liquidation preference (in dollars per share) \| $ / shares								$ 1,000
Proceeds from non-cumulative perpetual preference shares			$ 245.7
Non-cumulative perpetual preference shares issuance cost and commission								$ 4.3
Preferred Stock \| HG Global
Basis of Presentation
Ownership interest (as a percent)				97.30%			97.30%
Common Stock \| HG Global
Basis of Presentation
Percentage of par value of policy reinsured				15.00%
Ownership interest (as a percent)				88.70%			88.70%
Common shares and paid-in surplus \| HG Global
Basis of Presentation
Fair Value of Net Assets Acquired							$ 2.2
Non-controlling interest \| Build America Mutual
Basis of Presentation
Net loss (income) attributable to non-controlling interests				$ 20.1
Tuckerman Fund I \| Common Stock
Basis of Presentation
Ownership interest in VIE (as a percent)		94.00%
BAM Management \| HG Global
Basis of Presentation
Funds to Capitalize HG Global	$ 14.5

Summary of Significant Accounting Policies (Recently Adopted Changes in Accounting Principles) (Details) - USD ($) $ in Millions	Mar. 31, 2013	Dec. 31, 2012	Jan. 02, 2012
New Accounting Pronouncement, Early Adoption [Line Items]
Deferred acquisition costs	$ 190.4	$ 195.3
Accounting Standards Update 2010-26 [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Deferred acquisition costs			$ 5.6

- Definition

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

+ References

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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6481648&loc=d3e11198-158413

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

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

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 97
-Paragraph 22
-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 120
-Paragraph 5, 6
-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 AICPA
-Name Statement of Position (SOP)
-Number 95-1
-Paragraph 19-23
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 7
-Article 7

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

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 16
-Article 12

+ Details

Significant Transactions (Details) - USD ($) $ in Millions	3 Months Ended
Significant Transactions (Details) - USD ($) $ in Millions	Mar. 31, 2013	Mar. 31, 2012
Significant Transactions
Gain on sale of subsidiary - Essentia	$ 23.0	$ 0.0
Excess of FV of aquired net assets over cost - American Fuji	6.9	$ 0.0
OneBeacon \| Essentia
Significant Transactions
Gain on sale of subsidiary - Essentia	23.0
Gain on sale of Essentia, after tax	15.0
Premiums written	$ 35.3
Premiums written, percentage	11.70%

- Definition

Net of tax amount of gain (loss) classified as extraordinary item, including amount attributable to noncontrolling interests.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Extraordinary Items
-URI http://asc.fasb.org/extlink&oid=6512381

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.15)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.16)
-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 20
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6904752&loc=d3e14428-107780

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 20
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=6904752&loc=d3e14571-107780

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 20
-Section 45
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=18498875&loc=d3e38679-109324

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 15
-Article 7

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
-Paragraph 38
-Subparagraph b(3)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Research Bulletin (ARB)
-Number 51
-Paragraph 29
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 17
-Article 5

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher AICPA
-Name Accounting Principles Board Opinion (APB)
-Number 30
-Paragraph 11, 20, 24
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 109
-Paragraph 35
-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

Significant Transactions (Share Repurchases) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Significant Transactions
Additional authorized repurchase of common shares	545,496
Common shares repurchased and retired during the period	140,224	977,019
Value of common shares repurchased and retired during the period	$ 79.0	$ 485.8
Average price per share	$ 564	$ 497
Common Stock
Significant Transactions
Common shares repurchased and retired during the period	140,000
Stock repurchased and retired during period, pursuant of employee benefit Plans, shares	224
Combination One \| Tender Offer
Significant Transactions
Common shares repurchased and retired during the period		157,629
Value of common shares repurchased and retired during the period		$ 76.0
Average price per share		$ 482
Combination Two \| Tender Offer
Significant Transactions
Common shares repurchased and retired during the period		816,829
Value of common shares repurchased and retired during the period		$ 408.6
Average price per share		$ 500
Combination Three
Significant Transactions
Common shares repurchased and retired during the period		2,561

Loss and Loss Adjustment Expense Reserves Details (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Loss and Loss Adjustment, Expense Reserves [Line Items]
Net favorable and unfavorable loss reserve development	$ 1.4	$ (7.6)
Liability For Unpaid Claims And Claims Adjustment Expense Incurred Claims Prior Years Due To 2011 Japan Earthquake		8.1
Accretion of fair value adjustment to net loss and LAE reserves	1.2	7.1
Adjustment to loss and loss adjustment expense reserves, before tax	4.5
One Beacon
Loss and Loss Adjustment, Expense Reserves [Line Items]
Net favorable and unfavorable loss reserve development	(2.9)	(1.9)
Sirius
Loss and Loss Adjustment, Expense Reserves [Line Items]
Net favorable and unfavorable loss reserve development	$ 4.3	(5.7)
Scandinavian Reinsurance Company [Member]
Loss and Loss Adjustment, Expense Reserves [Line Items]
Accretion of fair value adjustment to net loss and LAE reserves increase		$ 5.0

Loss and Loss Adjustment Expense Reserves (Loss and Loss Adjustment Expense) (Details) - USD ($)
$ in Millions

3 Months Ended

Mar. 31, 2013

Mar. 31, 2012

Mar. 31, 2013

Mar. 31, 2012

Loss and Loss Adjustment Expense Reserve

Gross beginning balance

$ 3,168.9

$ 5,702.3

Less beginning reinsurance recoverable on unpaid losses

(429.1)

(2,507.3)

Net loss and LAE reserves

2,739.8

3,195.0

Loss and LAE reserves acquired - American Fuji

21.3

0.0

Loss and LAE incurred relating to current year losses

242.9

257.4

Net favorable and unfavorable loss reserve development

1.4

(7.6)

Total incurred losses and LAE

244.3

249.8

Accretion of fair value adjustment to net loss and LAE reserves

1.2

7.1

Foreign currency translation adjustment to net loss and LAE reserves

(9.6)

11.8

Current year losses

(36.6)

(44.5)

Prior year losses

(270.6)

(322.9)

Total loss and LAE payments

(307.2)

(367.4)

Net loss and LAE reserves

2,689.8

3,045.4

Plus ending reinsurance recoverable on unpaid losses

429.1

2,507.3

$ 410.8

$ 2,465.4

Gross ending balance

3,100.6

5,510.8

OneBeacon Runoff

Loss and Loss Adjustment Expense Reserve

Net loss and LAE reserves

^[1]

0.0

383.3

Net loss and LAE reserves

^[1]

$ 0.0

$ 332.4

[1]	Loss and LAE reserve balances for OneBeacon's run-off business prior to September 30, 2012 were not classified as held for sale. Adjustment is to present loss and LAE reserve activities from continuing operations.

Third Party Reinsurance (One Beacon) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2013 USD ($) Rating	Dec. 31, 2012 USD ($)	Mar. 31, 2012 USD ($)	Dec. 31, 2011 USD ($)
Reinsurance [Line Items]
Reinsurance recoverable on paid losses	$ 15.6	$ 17.9
Reinsurance recoverable on unpaid losses	410.8	$ 429.1	$ 2,465.4	$ 2,507.3
OneBeacon
Reinsurance [Line Items]
Reinsurance recoverable on paid losses	2.4
Reinsurance recoverable on unpaid losses	$ 105.8
Reinsurance Recoverables on Unpaid Losses	90.00%
Number of ratings in A.M. Best ratings \| Rating	16
Largest Recoverable from reinsurer	$ 11.0

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

3 Months Ended

Mar. 31, 2013

USD ($)

Rating

Dec. 31, 2012

USD ($)

Mar. 31, 2012

USD ($)

Dec. 31, 2011

USD ($)

Reinsurance [Line Items]

Reinsurance recoverable on paid losses

$ 15.6

$ 17.9

Reinsurance recoverable on unpaid losses

410.8

$ 429.1

$ 2,465.4

$ 2,507.3

OneBeacon

Reinsurance [Line Items]

Reinsurance recoverable on paid losses

2.4

Reinsurance recoverable on unpaid losses

$ 105.8

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

Sirius

Reinsurance [Line Items]

Reinsurance recoverable on paid losses

$ 13.2

Reinsurance recoverable on unpaid losses

$ 305.0

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

Seller Note From Acquisition

$ 25.0

Berkshire Hathaway [Member] | Sirius

Reinsurance [Line Items]

Reinsurance recoverables

$ 56.9

Percentage of total paid and unpaid reinsurance recoverables

18.00%

Percentage Collateralized

0.00%

Swiss Re Group | Sirius

Reinsurance [Line Items]

Reinsurance recoverables

$ 34.8

Percentage of total paid and unpaid reinsurance recoverables

11.00%

Percentage Collateralized

0.00%

Olympus | Sirius

Reinsurance [Line Items]

Reinsurance recoverables

^[1]

$ 24.9

Percentage of total paid and unpaid reinsurance recoverables

^[1]

8.00%

Percentage Collateralized

^[1]

100.00%

Lloyds of London | Sirius

Reinsurance [Line Items]

Reinsurance recoverables

^[2]

$ 17.0

Percentage of total paid and unpaid reinsurance recoverables

^[2]

5.00%

Percentage Collateralized

^[2]

9.00%

Michigan Catastrophic Claims Association | Sirius

Reinsurance [Line Items]

Reinsurance recoverables

^[3]

$ 14.7

Percentage of total paid and unpaid reinsurance recoverables

^[3]

5.00%

Percentage Collateralized

^[3]

0.00%

[1]	Non-U.S. insurance entity. The balance is fully collateralized through funds held, letters of credit or trust agreements.
[2]	Represents the total of reinsurance recoverables due to Sirius Group from all Lloyds Syndicates.
[3]	Michigan Catastrophic Claims Association (“MCCA”) is a non-profit unincorporated association, established by the State of Michigan with the power to issue and collect assessments, to which every insurance company that sells automobile coverage in Michigan is required to be a member. A.M. Best does not rate MCCA. Sirius Group acquired its recoverable from MCCA in the acquisition of Stockbridge Insurance Company. As part of the acquisition, Sirius Group obtained $25.0 of reinsurance protection from the seller (currently rated A+ by A.M. Best) for unfavorable loss reserve development, including uncollectible reinsurance.

Investment Securities (Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Investment income
Total investment income	$ 33.0	$ 44.8
Third-party investment expenses	(4.5)	(3.0)
Net investment income	28.5	41.8
Fixed maturity investments.
Investment income
Total investment income	26.0	36.7
Short-term investments
Investment income
Total investment income	0.8	1.0
Common Stock
Investment income
Total investment income	4.7	4.4
Convertible fixed maturity investments
Investment income
Total investment income	0.8	1.9
Other long-term investments
Investment income
Total investment income	0.7	0.8
Interest on funds held under reinsurance treaties
Investment income
Total investment income	$ 0.0	$ 0.0

Investment Securities (Net Unrealized Investment Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Investment securities
Net realized and unrealized gain (loss) on trading securities	$ 85.0	$ 83.7
Trading securities, tax on realized and unrealized holding gain (loss) on investments	(15.9)	(20.6)
Trading securities realized and unrealized holding gain (loss) on investments after tax	69.1	63.1
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	(9.8)	(25.1)
Trading securities, unrealized foreign currency transaction gain (loss) tax	2.2	6.6
Trading securities, unrealized foreign currency gain (loss) net of tax	(7.6)	(18.5)
Net unrealized gain (loss) and foreign currency gain (loss) on trading securities	75.2	58.6
Net realized and unrealized gain (loss) and foreign currency gain (loss) on trading securities tax	(13.7)	(14.0)
Net realized and unrealized gain (loss) and foreign currency gain (loss) on trading securities net of tax	61.5	44.6
Fixed maturity investments.
Investment securities
Net realized and unrealized gain (loss) on trading securities	(8.0)	30.7
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	(10.0)	(21.4)
Net unrealized gain (loss) and foreign currency gain (loss) on trading securities	(18.0)	9.3
Short-term investments
Investment securities
Net realized and unrealized gain (loss) on trading securities	0.0	0.0
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	0.1	(0.3)
Net unrealized gain (loss) and foreign currency gain (loss) on trading securities	0.1	(0.3)
Common equity securities
Investment securities
Net realized and unrealized gain (loss) on trading securities	84.5	36.6
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	(0.2)	0.0
Net unrealized gain (loss) and foreign currency gain (loss) on trading securities	84.3	36.6
Convertible Debt Securities
Investment securities
Net realized and unrealized gain (loss) on trading securities	1.6	6.2
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	(0.2)	0.0
Net unrealized gain (loss) and foreign currency gain (loss) on trading securities	1.4	6.2
Other long-term investments
Investment securities
Net realized and unrealized gain (loss) on trading securities	6.5	10.2
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	0.5	(3.4)
Net unrealized gain (loss) and foreign currency gain (loss) on trading securities	7.0	6.8
Forward Contracts
Investment securities
Net realized and unrealized gain (loss) on trading securities	0.4	0.0
Net unrealized investment gains (losses), net foreign exchange gains (losses), pre-tax	0.0	0.0
Net unrealized gain (loss) and foreign currency gain (loss) on trading securities	$ 0.4	$ 0.0

Investment Securities (Investment gains (losses) for Level 3) (Details) - Level 3 Inputs - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2011
Investment securities
Unrealized gains (losses) on investments	$ 6.5	$ 15.5
Fixed maturity investments.
Investment securities
Unrealized gains (losses) on investments	0.2		$ 7.8
Common equity securities
Investment securities
Unrealized gains (losses) on investments	(0.1)		0.5
Other long-term investments
Investment securities
Unrealized gains (losses) on investments	$ 6.4		$ 7.2

Investment Securities (Investment Holdings) (Details) - USD ($) $ in Millions	Mar. 31, 2013	Dec. 31, 2012
Investment securities
Fixed maturity investments, at fair value	$ 4,854.4	$ 5,196.2
Fixed maturity investments reclassified to assets held for sale		(338.1)
U.S. Government and agency obligations
Investment securities
Cost or amortized cost	435.9	440.4
Gross unrealized gains	0.9	1.0
Gross unrealized losses	(0.1)	(0.1)
Net foreign currency gains (losses)	(1.2)	(1.2)
Fixed maturity investments, at fair value	435.5	440.1
Debt securities issued by corporations
Investment securities
Cost or amortized cost	2,361.2	2,321.4
Gross unrealized gains	75.7	88.3
Gross unrealized losses	(2.6)	(1.6)
Net foreign currency gains (losses)	(24.6)	(23.0)
Fixed maturity investments, at fair value	2,409.7	2,385.1
Municipal obligations
Investment securities
Cost or amortized cost	5.3	5.3
Gross unrealized gains	0.0	0.0
Gross unrealized losses	(0.1)	(0.1)
Net foreign currency gains (losses)	0.0	0.0
Fixed maturity investments, at fair value	5.2	5.2
Mortgage-backed and asset-backed securities
Investment securities
Cost or amortized cost	1,698.7	2,081.0
Gross unrealized gains	12.6	25.1
Gross unrealized losses	(1.9)	(1.1)
Net foreign currency gains (losses)	(2.1)	(9.4)
Fixed maturity investments, at fair value	1,707.3	2,095.6
Foreign government, agency and provincial obligations
Investment securities
Cost or amortized cost	516.4	526.6
Gross unrealized gains	5.4	6.9
Gross unrealized losses	(6.3)	(3.0)
Net foreign currency gains (losses)	(9.4)	(8.6)
Fixed maturity investments, at fair value	506.1	521.9
Non-cumulative perpetual preference shares
Investment securities
Cost or amortized cost	79.9	79.9
Gross unrealized gains	7.7	6.7
Gross unrealized losses	0.0	0.0
Net foreign currency gains (losses)	(0.1)	(0.2)
Fixed maturity investments, at fair value	87.5	86.4
Common Stock
Investment securities
Cost or amortized cost	876.8	895.2
Gross unrealized gains	201.7	143.4
Gross unrealized losses	(5.2)	(8.8)
Net foreign currency gains (losses)	(0.1)	(0.1)
Convertible fixed maturity investments
Investment securities
Cost or amortized cost	91.2	121.7
Gross unrealized gains	5.9	6.1
Gross unrealized losses	(1.3)	(0.4)
Net foreign currency gains (losses)	(0.2)	0.0
Other long-term investments.
Investment securities
Cost or amortized cost	254.5	257.2
Gross unrealized gains	57.0	65.9
Gross unrealized losses	(10.3)	(22.8)
Net foreign currency gains (losses)	(6.0)	(6.1)
Fixed Income Investments
Investment securities
Cost or amortized cost	5,097.4	5,454.6
Gross unrealized gains	102.3	128.0
Gross unrealized losses	(11.0)	(5.9)
Net foreign currency gains (losses)	(37.4)	(42.4)
Total fixed maturity investments including assets held for sale	5,151.3	5,534.3
OneBeacon Runoff
Investment securities
Fixed maturity investments reclassified to assets held for sale	$ (296.9)	$ (338.1)

Investment Securities (The Cost or Amortized Cost, Gross Unrealized Investment Gains and Losses) (Details) - USD ($) $ in Millions	Mar. 31, 2013	Dec. 31, 2012
Investment securities
Common equity securities, at fair value	$ 1,073.2	$ 1,029.7
Convertible fixed maturity investments, at fair value	95.6	127.4
Other long-term investments	295.2	294.2
Common shareholders' equity.
Investment securities
Cost or amortized cost	876.8	895.2
Gross unrealized gains	201.7	143.4
Trading Securities, Gross Unrealized Loss	5.2	8.8
Net foreign currency gains (losses)	(0.1)	(0.1)
Common equity securities, at fair value	1,073.2	1,029.7
Convertible Debt Securities
Investment securities
Cost or amortized cost	91.2	121.7
Gross unrealized gains	5.9	6.1
Trading Securities, Gross Unrealized Loss	1.3	0.4
Net foreign currency gains (losses)	(0.2)	0.0
Convertible fixed maturity investments, at fair value	95.6	127.4
Other long-term investments.
Investment securities
Cost or amortized cost	254.5	257.2
Gross unrealized gains	57.0	65.9
Trading Securities, Gross Unrealized Loss	10.3	22.8
Net foreign currency gains (losses)	(6.0)	(6.1)
Other long-term investments	$ 295.2	$ 294.2

Investment Securities (Other long-term investments) (Details) $ in Millions	Mar. 31, 2013 USD ($) fund
Hedge and private equity funds included in other long-term investments
Investment securities
Largest single fund investment \| $	$ 16.7
Hedge funds
Investment securities
Number of investments	15
Private equity funds
Investment securities
Number of investments	38

Investment Securities (Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency) (Details) - USD ($)
$ in Millions

Mar. 31, 2013

Dec. 31, 2012

Mar. 31, 2012

Dec. 31, 2011

Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) - Hedge funds $ in Millions	Mar. 31, 2013 USD ($)
Investment securities
Other long-term investments	$ 117.7
Distributions from inactive hedge funds	2.6
Redemption requests	7.1
Monthly
Investment securities
Other long-term investments	6.8
Quarterly
Investment securities
Other long-term investments	77.7
Semi-annual
Investment securities
Other long-term investments	22.7
Annual
Investment securities
Other long-term investments	10.5
30-59 days notice
Investment securities
Other long-term investments	29.6
30-59 days notice \| Monthly
Investment securities
Other long-term investments	0.0
30-59 days notice \| Quarterly
Investment securities
Other long-term investments	27.9
30-59 days notice \| Semi-annual
Investment securities
Other long-term investments	0.0
30-59 days notice \| Annual
Investment securities
Other long-term investments	1.7
60-89 days notice
Investment securities
Other long-term investments	53.9
60-89 days notice \| Monthly
Investment securities
Other long-term investments	0.0
60-89 days notice \| Quarterly
Investment securities
Other long-term investments	31.2
60-89 days notice \| Semi-annual
Investment securities
Other long-term investments	22.7
60-89 days notice \| Annual
Investment securities
Other long-term investments	0.0
90-119 days notice
Investment securities
Other long-term investments	17.5
90-119 days notice \| Monthly
Investment securities
Other long-term investments	0.0
90-119 days notice \| Quarterly
Investment securities
Other long-term investments	9.0
90-119 days notice \| Semi-annual
Investment securities
Other long-term investments	0.0
90-119 days notice \| Annual
Investment securities
Other long-term investments	8.5
120+ days notice
Investment securities
Other long-term investments	16.7
120+ days notice \| Monthly
Investment securities
Other long-term investments	6.8
120+ days notice \| Quarterly
Investment securities
Other long-term investments	9.6
120+ days notice \| Semi-annual
Investment securities
Other long-term investments	0.0
120+ days notice \| Annual
Investment securities
Other long-term investments	$ 0.3

Investment Securities (Investments In Private Equity Funds Subject to Lock-Up Periods) (Details) - Private equity funds $ in Millions	Mar. 31, 2013 USD ($)
Investment securities
Other long-term investments	$ 122.1
1-3 years
Investment securities
Other long-term investments	21.6
3-5 years
Investment securities
Other long-term investments	34.0
5-10 years
Investment securities
Other long-term investments	57.4
Greater than 10 years
Investment securities
Other long-term investments	$ 9.1

Debt (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
Debt (Details) - USD ($) $ in Millions	Dec. 31, 2012	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Jan. 31, 2013	Aug. 12, 2011
Debt Instrument
Total debt	$ 751.2	$ 676.2		$ 751.2
Proceeds from lines of credit		80.0	$ 0.0
Repayments of debt		155.0	$ 0.0
2012 OBH Senior Notes
Debt Instrument
Debt instrument at face value	275.0	275.0		275.0
Unamortized original issue discount	(0.3)	(0.3)		(0.3)
Total debt	274.7	274.7		274.7
SIG Senior Notes
Debt Instrument
Debt instrument at face value	400.0	400.0		400.0
Unamortized original issue discount	(0.6)	(0.6)		(0.6)
Total debt	399.4	399.4		399.4
WTM Bank Facility
Debt Instrument
Total debt	$ 75.0	0.0		75.0	$ 75.0
Total commitment under revolving credit facility						$ 375.0
Proceeds from lines of credit				$ 150.0
Interest rate	3.53%			3.53%
Repayments of debt	$ 75.0
Old Lyme
Debt Instrument
Total debt	$ 2.1	$ 2.1		$ 2.1

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
Income Taxes (Details) - USD ($) $ in Millions	Mar. 31, 2013	Mar. 31, 2012	Jul. 28, 2011
Income Tax Contingency [Line Items]
Effective tax rates (as a percent)	27.40%	22.10%
U.S. statutory rate (as a percent)	35.00%	35.00%
Foreign tax credit carryforwards	$ 18.7
Tax Assessment Year 2007 to 2009 \| Internal Revenue Service (IRS)
Income Tax Contingency [Line Items]
Total tax assessment			$ 87.0
Tax assessments related to disallowed deductions			$ 80.6

Derivatives (Details) ¥ in Billions, $ in Billions	Mar. 31, 2013 JPY (¥)	Mar. 31, 2013 USD ($)	Dec. 31, 2012 JPY (¥)	Dec. 31, 2012 USD ($)
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Total guarantee value	¥ 228.5	$ 2.4	¥ 230.0	$ 2.7
Collective account values of underlying variable annuities as a percentage of the guarantee value	94.00%	94.00%	87.00%	87.00%

Derivatives (Pre-Tax Operating Results of WM Life Re) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Pre-tax operating results of WM Life Re
Total revenues	$ 627.4	$ 629.6
General and administrative expenses	(43.8)	(45.5)
Pre-tax income from continuing operations	151.8	140.8
White Mountains Life Re
Pre-tax operating results of WM Life Re
Fees, included in other revenues	6.8	8.0
Change in fair value of variable annuity liability, included in other revenues	184.3	211.2
Realized and unrealized (losses) gains	(181.8)	(206.5)
Foreign exchange, included in other revenues	(14.6)	(23.0)
Other investment income and gains (losses)	(4.0)	(2.1)
Total revenues	(9.3)	(12.4)
Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses	5.6	8.8
Death benefit claims paid, included in general and administrative expenses	(1.1)	(1.8)
General and administrative expenses	(1.7)	(1.3)
Pre-tax income from continuing operations	$ (6.5)	$ (6.7)

Derivatives Additional Collateral (Details) - White Mountains Life Re - USD ($) $ in Millions	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Credit risk on derivative instruments
Collateral cash and investments	$ 229.8	$ 393.6	$ 390.9
Cash
Credit risk on derivative instruments
Derivative collateral right to reclaim	188.5	249.8	360.1
Short-term investments
Credit risk on derivative instruments
Derivative collateral right to reclaim	15.6	5.1	1.5
Fixed maturity investments.
Credit risk on derivative instruments
Derivative collateral right to reclaim	$ 25.7	$ 138.7	$ 29.3

Derivatives (Level 3 Derivative Instruments) (Details) - White Mountains Life Re $ in Millions	3 Months Ended
	Mar. 31, 2013 USD ($)
Variable annuity benefit guarantee liabilities
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value Liabilities	$ 251.6
Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Mortality (as a percent)	0.00%
Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Mortality (as a percent)	5.30%
Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Mortality (as a percent)	0.90%
Foreign Exchange Options
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value Liabilities	$ 74.2
Foreign Exchange Options \| Black-Scholes option pricing model \| Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	(0.10%)
Foreign Exchange Options \| Black-Scholes option pricing model \| Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	(3.20%)
Foreign Exchange Options \| Black-Scholes option pricing model \| Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	(2.10%)
Equity Index Options
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value Liabilities	$ 53.2
Equity Index Options \| Black-Scholes option pricing model \| Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Expected equity dividends (as a percent)	(1.70%)
Equity Index Options \| Black-Scholes option pricing model \| Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Expected equity dividends (as a percent)	(3.00%)
Equity Index Options \| Black-Scholes option pricing model \| Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Expected equity dividends (as a percent)	(2.50%)
Year One \| Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	0.30%
Foreign exchange volatilities (as a percent)	11.20%
Index volatilities (as a percent)	11.90%
Year One \| Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	3.00%
Foreign exchange volatilities (as a percent)	13.30%
Index volatilities (as a percent)	17.90%
Year One \| Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	0.70%
Foreign exchange volatilities (as a percent)	12.20%
Index volatilities (as a percent)	13.30%
Year Two \| Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	0.20%
Foreign exchange volatilities (as a percent)	11.70%
Index volatilities (as a percent)	16.50%
Year Two \| Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	3.00%
Foreign exchange volatilities (as a percent)	14.00%
Index volatilities (as a percent)	20.70%
Year Two \| Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	0.80%
Foreign exchange volatilities (as a percent)	12.60%
Index volatilities (as a percent)	18.00%
Year Three and Thereafter \| Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	0.10%
Foreign exchange volatilities (as a percent)	12.30%
Index volatilities (as a percent)	18.60%
Year Three and Thereafter \| Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	3.00%
Foreign exchange volatilities (as a percent)	14.60%
Index volatilities (as a percent)	22.30%
Year Three and Thereafter \| Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	0.70%
Foreign exchange volatilities (as a percent)	13.20%
Index volatilities (as a percent)	20.90%

Derivatives Forward Contracts (Details) - Forward Contracts kr in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2013 USD ($)	Mar. 31, 2013 SEK (kr)	Mar. 31, 2013 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount		kr 517.5	$ 79.3
Changes in derivative instruments
Beginning balance	$ (0.1)
Purchases	0.0
Realized and unrealized gains (losses)	0.4
Sales/settlements	(0.5)
Ending balance	$ (0.2)

Derivatives (Unrealized and Realized Derivative Gains (Losses) Forward Contracts) (Details) - Forward Contracts - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Realized and unrealized gains (losses)	$ 0.4
Derivative, fair value, net	(0.2)	$ (0.1)
United States of America, Dollars
Derivative [Line Items]
Realized and unrealized gains (losses)	(0.3)
Derivative, fair value, net	(0.3)
Sweden, Kronor
Derivative [Line Items]
Realized and unrealized gains (losses)	0.0
Derivative, fair value, net	0.0
Euro Member Countries, Euro
Derivative [Line Items]
Realized and unrealized gains (losses)	0.0
Derivative, fair value, net	0.0
United Kingdom, Pounds
Derivative [Line Items]
Realized and unrealized gains (losses)	0.7
Derivative, fair value, net	$ 0.1

Municipal Bond Guarantee (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
Municipal Bond Guarantee (Details) - USD ($) $ in Millions	Jul. 31, 2012	Mar. 31, 2013	Sep. 30, 2012	Dec. 31, 2012
Guarantor Obligations [Line Items]
Municipal bond contract		105		3
Insured Financial Obligations with Credit Deterioration, Remaining Weighted Average Contract Period		13 years 1 month 6 days		10 years 4 months 24 days
Municipal bond outstanding principal		$ 698.6		$ 25.8
Municipal bond outstanding interest		$ 497.6		8.9
Percentage of par value of policy reinsured		15.00%
Financial Guarantee Insurance Contracts, Unearned Premium Revenue		$ 2.0		0.1
White Mountains
Guarantor Obligations [Line Items]
Funds to Capitalize HG Global			$ 600.0	594.5
Funds to Capitalized HG Global	$ 594.5
HG Global
Guarantor Obligations [Line Items]
Surplus Notes				$ 503.0
Income (Loss) from Continuing Operations before Income Taxes, Foreign		9.9
Interest income (expense), surplus notes		$ 10.1
HG Global \| Preferred Stock
Guarantor Obligations [Line Items]
Ownership interest (as a percent)		97.30%		97.30%
HG Global \| Common Stock
Guarantor Obligations [Line Items]
Ownership interest (as a percent)		88.70%		88.70%
Percentage of par value of policy reinsured		15.00%
Build America Mutual
Guarantor Obligations [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Foreign		$ 18.4
Non-controlling interest
Guarantor Obligations [Line Items]
Funds to Capitalize HG Global				$ 14.5
BAM
Guarantor Obligations [Line Items]
Interest income (expense), surplus notes		$ 10.1
HG Global
Guarantor Obligations [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance				$ 417.7

Segment Information (Details) - USD ($) $ in Millions	3 Months Ended
Segment Information (Details) - USD ($) $ in Millions	Mar. 31, 2013	Mar. 31, 2012
Segment reporting information
Earned insurance premiums	$ 495.4	$ 498.0
Net investment income	28.5	41.8
Net investment income - surplus note income	0.0
Net realized and unrealized investment gains (losses)	75.2	58.6
Other revenue	28.3	31.2
Total revenues	627.4	629.6
Losses and loss adjustment expenses	244.3	249.8
Insurance and reinsurance acquisition expenses	98.2	109.1
Other underwriting expenses	79.1	73.5
General and administrative expenses	43.8	45.5
Interest expense on debt	10.2	10.9
Total expenses	475.6	488.8
Pre-tax income (loss)	151.8	140.8
OneBeacon
Segment reporting information
Earned insurance premiums	286.5	271.8
Net investment income	9.4	14.7
Net investment income - surplus note income	0.0
Net realized and unrealized investment gains (losses)	28.4	29.8
Other revenue	24.0	0.1
Total revenues	348.3	316.4
Losses and loss adjustment expenses	148.9	136.4
Insurance and reinsurance acquisition expenses	54.8	58.1
Other underwriting expenses	49.3	47.5
General and administrative expenses	4.0	2.7
Interest expense on debt	3.2	4.1
Total expenses	260.2	248.8
Pre-tax income (loss)	88.1	67.6
Sirius
Segment reporting information
Earned insurance premiums	208.9	226.2
Net investment income	13.1	17.1
Net investment income - surplus note income	0.0
Net realized and unrealized investment gains (losses)	13.1	13.7
Other revenue	10.5	18.3
Total revenues	245.6	275.3
Losses and loss adjustment expenses	95.4	113.4
Insurance and reinsurance acquisition expenses	43.3	51.0
Other underwriting expenses	29.7	26.0
General and administrative expenses	9.5	18.9
Interest expense on debt	6.6	6.5
Total expenses	184.5	215.8
Pre-tax income (loss)	61.1	59.5
HG Global
Segment reporting information
Earned insurance premiums	0.0
Net investment income	0.3
Net investment income - surplus note income	10.1
Net realized and unrealized investment gains (losses)	(0.2)
Other revenue	0.0
Total revenues	10.2
Losses and loss adjustment expenses	0.0
Insurance and reinsurance acquisition expenses	0.0
Other underwriting expenses	0.0
General and administrative expenses	0.3
Interest expense on debt	0.0
Total expenses	0.3
Pre-tax income (loss)	9.9
BAM
Segment reporting information
Earned insurance premiums	0.0
Net investment income	1.1
Net investment income - surplus note income	(10.1)
Net realized and unrealized investment gains (losses)	(1.1)
Other revenue	0.1
Total revenues	(10.0)
Losses and loss adjustment expenses	0.0
Insurance and reinsurance acquisition expenses	0.1
Other underwriting expenses	0.1
General and administrative expenses	8.2
Interest expense on debt	0.0
Total expenses	8.4
Pre-tax income (loss)	(18.4)
Other Operations
Segment reporting information
Earned insurance premiums	0.0	0.0
Net investment income	4.6	10.0
Net investment income - surplus note income	0.0
Net realized and unrealized investment gains (losses)	35.0	15.1
Other revenue	(6.3)	12.8
Total revenues	33.3	37.9
Losses and loss adjustment expenses	0.0	0.0
Insurance and reinsurance acquisition expenses	0.0	0.0
Other underwriting expenses	0.0	0.0
General and administrative expenses	21.8	23.9
Interest expense on debt	0.4	0.3
Total expenses	22.2	24.2
Pre-tax income (loss)	$ 11.1	$ 13.7

Employee Share-Based Incentive Compensation Plans (WTM - Performance Shares Granted Under the WTM Incentive Plan) (Details) - USD ($) $ in Millions	Mar. 31, 2013	Dec. 31, 2012
Share-based compensation arrangement by share-based payment award
Total Accrued Expense	$ 100.8	$ 159.0
W T M Incentive Plan \| Performance Share
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	122,027
Accrued Expense	$ 29.4
Target Performance Shares Outstanding, Assumed forfeitures	(3,051)
Accrued Expense, Assumed forfeitures	(0.8)
Total Target Performance Shares Outstanding	118,976
Total Accrued Expense	$ 28.6
W T M Incentive Plan \| Performance Share \| Performance Cycle 2013 to 2015
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	46,920
Accrued Expense	$ 2.2
W T M Incentive Plan \| Performance Share \| Performance Cycle 2012 To 2014
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	37,977
Accrued Expense	$ 11.4
W T M Incentive Plan \| Performance Share \| Performance Cycle 2011 to 2013
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	37,130
Accrued Expense	$ 15.8

Employee Share-Based Incentive Compensation Plans (WTM - Restricted Shares) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2013 USD ($) shares	Mar. 31, 2012 USD ($) Installment shares
Restricted Share Cliff Vesting in January 2016 [Member]
Target Performance Share activity
Issued (in shares)	25,470
Restricted Share Cliff Vesting in January 2015
Target Performance Share activity
Issued (in shares)		25,460
Restricted Share Vesting Beginning in February 2014
Target Performance Share activity
Issued (in shares)		3,000
Unamortized grant date fair value
Number of restricted shares installments \| Installment		2
W T M Incentive Plan \| Restricted Stock
Target Performance Share activity
Beginning of period (in shares)	69,910	72,000
Issued (in shares)	25,470	28,460
Vested (in shares)	0	(7,000)
Assumed forfeitures and cancellations	0	0
Ending of period (in shares)	95,380	93,460
Unamortized grant date fair value
Unamortized grant date fair value, beginning balance \| $	$ 16.8	$ 13.3
Issued \| $	14.3	13.7
Assumed forfeitures and cancellations \| $	0.0	0.0
Expense recognized \| $	(2.9)	(2.5)
Unamortized grant date fair value, ending balance \| $	$ 28.2	$ 24.5

Employee Share-Based Incentive Compensation Plans (OneBeacon - Restricted Shares) (Details) - One Beacon Long Term Incentive Plan - One Beacon Restricted Stock $ in Millions	1 Months Ended	3 Months Ended
	May 31, 2011 shares	Mar. 31, 2013 USD ($) shares	Mar. 31, 2012 USD ($) shares	Mar. 01, 2012 Installment	May 25, 2011 Installment
Target Performance Share activity
Beginning of period (in shares)		927,000	630,000
Issued (in shares)		0	300,000
Shares issued during the period related to performance shares earned		(9,000)	0
Assumed forfeitures and cancellations		0	0
Ending of period (in shares)		918,000	930,000
Unamortized grant date fair value
Unamortized grant date fair value, beginning balance \| $		$ 9.6	$ 7.7
Issued \| $		0.0	4.6
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value \| $		0.0	0.0
Assumed forfeitures and cancellations \| $		0.0	0.0
Expense recognized \| $		(0.8)	(0.4)
Unamortized grant date fair value, ending balance \| $		$ 8.8	$ 11.9
Number of Installments in which the Shares Vest \| Installment				2
Chief Executive Officer
Target Performance Share activity
Issued (in shares)	630,000
Unamortized grant date fair value
Number of Installments in which the Shares Vest \| Installment					4
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Reduction in Grant, Total	35,000
Years Performance Shares will be Forfeited	5 years

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior notes	$ 676.2	$ 751.2
SIG Preference Shares	250.0	250.0
2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior notes	274.7	274.7
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
SIG Preference Shares	262.5	257.5
Fair Value \| 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior notes	287.8	282.4
Fair Value \| SIG Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior notes	454.0	441.9
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions
SIG Preference Shares	250.0	250.0
Carrying Value \| 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior notes	274.7	274.7
Carrying Value \| SIG Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Senior notes	$ 399.4	$ 399.4

Discontinued Operations (Details) $ in Millions	3 Months Ended
Discontinued Operations (Details) $ in Millions	Mar. 31, 2013 USD ($) Contract	Mar. 31, 2012 USD ($)	Dec. 31, 2012 USD ($)	Feb. 22, 2012 Entity	May 31, 2001 USD ($)
Reinsurance [Line Items]
Net income (loss) from discontinued operations, net of tax	$ 0.5	$ (9.3)
Net favorable and unfavorable loss reserve development	1.4	(7.6)
Reinsurance recoverable on paid losses	15.6		$ 17.9
Segment, Discontinued Operations
Reinsurance [Line Items]
Loss from sale of discontinued operations	0.0	0.0
Net income (loss) from discontinued operations, net of tax	0.5	(9.3)
Reinsurance recoverable on paid losses	$ 14.1		15.6
Segment, Discontinued Operations \| OneBeacon Runoff
Reinsurance [Line Items]
Number of contracts seller caused one beacon to purchase prior to acquisition \| Contract	2
Reinsurance recoverables	$ 1,381.0		$ 1,401.9
Reinsurance recoverable on paid losses	14.1
Reinsurance recoverables, gross of purchase accounting adjustments	1,960.9
Purchase accounting adjustments	146.8
Segment, Discontinued Operations \| GRC Cover \| OneBeacon Runoff
Reinsurance [Line Items]
Reinsurance recoverable cover under reinsurance contract	570.0
Segment, Discontinued Operations \| NICO Cover \| OneBeacon Runoff
Reinsurance [Line Items]
Reinsurance recoverable cover under reinsurance contract	2,500.0
Segment, Discontinued Operations \| General Reinsurance Corporation \| GRC Cover \| OneBeacon Runoff
Reinsurance [Line Items]
Adverse loss reserve development on losses occurring in years 2000 and prior					$ 400.0
Loss reserves ceded at acquisition					$ 170.0
OneBeacon Runoff \| Segment, Discontinued Operations
Reinsurance [Line Items]
Net income (loss) from discontinued operations, net of tax	0.5	(9.4)
AutoOne
Reinsurance [Line Items]
Number of insurance companies sold \| Entity				2
OneBeacon Runoff \| Segment, Discontinued Operations
Reinsurance [Line Items]
Net favorable and unfavorable loss reserve development	$ 0.2	$ (12.4)

Discontinued Operations (Net Assets Held for Sale) (Details) - USD ($) $ in Millions	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Assets held for sale
Fixed maturity investments, at fair value	$ 4,854.4	$ 5,196.2
Cash	411.5	462.4
Reinsurance recoverable on unpaid losses	410.8	429.1	$ 2,465.4	$ 2,507.3
Reinsurance recoverable on paid losses	15.6	17.9
Insurance premiums receivable	717.6	556.3
Deferred acquisition costs	190.4	195.3
Deferred tax asset	539.1	569.6
Other assets	416.5	503.0
Total assets	12,611.5	12,895.4
Liabilities held for sale
Loss and loss adjustment expense reserves	3,100.6	3,168.9	$ 5,510.8	$ 5,702.3
Unearned insurance premiums	1,064.9	924.1
Ceded reinsurance payable	175.7	116.5
Other liabilities	374.4	452.8
Total liabilities	8,329.5	8,637.2
Segment, Discontinued Operations
Assets held for sale
Fixed maturity investments, at fair value	296.9	338.1
Cash	0.0	0.0
Reinsurance recoverable on unpaid losses	1,814.1	1,840.8
Reinsurance recoverable on paid losses	14.1	15.6
Insurance premiums receivable	9.9	11.0
Deferred acquisition costs	0.0	0.0
Deferred tax asset	4.2	5.1
Other assets	16.0	16.2
Total assets	2,155.2	2,226.8
Liabilities held for sale
Loss and loss adjustment expense reserves	1,980.2	2,052.6
Unearned insurance premiums	0.5	0.5
Ceded reinsurance payable	23.5	21.9
Other liabilities	151.0	151.8
Total liabilities	2,155.2	2,226.8
Net assets held for sale	$ 0.0	$ 0.0

(Income (Loss) from Discontinued Operations) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Revenues
Earned insurance premiums	$ 495.4	$ 498.0
Net investment income	28.5	41.8
Net realized and unrealized investment gains (losses)	75.2	58.6
Other revenue	28.3	31.2
Total revenues	627.4	629.6
Expenses
Loss and loss adjustment expenses	244.3	249.8
Insurance and reinsurance acquisition expenses	98.2	109.1
Other underwriting expenses	79.1	73.5
General and administrative expenses	43.8	45.5
Total expenses	475.6	488.8
Income (loss) from discontinued operations	0.5	(9.3)
Segment, Discontinued Operations
Revenues
Earned insurance premiums	0.9	8.8
Net investment income	0.0	0.0
Net realized and unrealized investment gains (losses)	0.0	0.0
Other revenue	0.0	0.0
Total revenues	0.9	8.8
Expenses
Loss and loss adjustment expenses	0.0	19.6
Insurance and reinsurance acquisition expenses	0.1	0.3
Other underwriting expenses	0.1	1.5
General and administrative expenses	0.0	0.0
Total expenses	0.2	21.4
Pre-tax income (loss)	0.7	(12.6)
Income tax (expense) benefit	(0.2)	3.3
Income (loss) from discontinued operations	0.5	(9.3)
Loss from sale of discontinued operations	0.0	0.0
Net income (loss) from discontinued operations	$ 0.5	$ (9.3)

Contingencies (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
Contingencies (Details) - USD ($) $ in Millions	Jun. 30, 2007	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 30, 2011
Loss Contingencies [Line Items]
Sales of consolidated and unconsolidated affiliates, net of cash sold		$ 31.3	$ 0.0
Proceeds from Sale, Maturity and Collection of Investments	$ 39.0
Esurance
Loss Contingencies [Line Items]
Warranty agreement period		18 months
Covenant breach agreement period		2 years
Non-soliciation agreement period		3 years
Percentage of fluctuation in loss reserves of transferred subsidiaries retained					90.00%
Sales of consolidated and unconsolidated affiliates, net of cash sold				$ 1,010.0
Gain on sale of business in discontinued operations				700.0
Disposal Group Including Discontinued Operation Book Value				$ 308.0
Total amount in dispute with Allstate						$ 20.0
DAC amount in dispute with Allstate, Pre-tax						24.7
DAC amount in dispute with Allstate, after-tax						16.0
Extra contractual obligation in dispute with Allstate, pre-tax						5.2
Extra contractual obligation in dispute with Allstate, after-tax						$ 3.4