White Mountains Insurance (WTM) 10-K 28 Feb 14 2013 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2013	Feb. 28, 2014	Jun. 30, 2013
Document and Entity Information [Abstract]	'	'	'
Entity Registrant Name	'WHITE MOUNTAINS INSURANCE GROUP LTD	'	'
Entity Central Index Key	'0000776867	'	'
Document Type	'10-K	'	'
Document Period End Date	31-Dec-13	'	'
Amendment Flag	'false	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Well-known Seasoned Issuer	'Yes	'	'
Entity Voluntary Filers	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Entity Public Float	'	'	$3,324,933,214
Entity Common Stock, Shares Outstanding	'	6,179,986	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Assets	'	'
Fixed maturity investments, at fair value	$5,030.50	$5,196.20
Short-term investments, at amortized cost (which approximates fair value)	635.9	630.6
Common equity securities, at fair value	1,156.80	1,029.70
Convertible fixed maturity investments, at fair value	80.5	127.4
Other long-term investments	288.9	294.2
Total investments	7,192.60	7,278.10
Cash (restricted $56.1 and $249.8)	382.8	462.4
Reinsurance recoverable on unpaid losses	428.1	429.1
Reinsurance recoverable on paid losses	25.4	17.9
Insurance and reinsurance premiums receivable	518.9	556.3
Funds held by ceding companies	106.3	127.4
Investments in unconsolidated affiliates	321.4	387.9
Deferred acquisition costs	174.7	195.3
Deferred tax asset	512.1	569.6
Ceded unearned insurance and reinsurance premiums	92.4	91.8
Accrued investment income	39.3	45.9
Accounts receivable on unsettled investment sales	12.1	3.9
Other assets	458.1	503
Assets held for sale	1,880.10	2,226.80
Total assets	12,144.30	12,895.40
Liabilities	'	'
Loss and loss adjustment expense reserves	3,079.30	3,168.90
Unearned insurance and reinsurance premiums	901.4	924.1
Variable annuity benefit guarantee	52.8	441.5
Debt	676.4	751.2
Deferred tax liability	356.2	341.3
Accrued incentive compensation	218.3	159
Ceded reinsurance payable	71.9	116.5
Funds held under insurance and reinsurance contracts	127.1	43.7
Accounts payable on unsettled investment purchases	20.5	11.4
Other liabilities	362.9	452.8
Liabilities held for sale	1,880.10	2,226.80
Total liabilities	7,746.90	8,637.20
White Mountains’ common shareholders’ equity	'	'
White Mountains’ common shares at $1 par value per share—authorized 50,000,000 shares; issued and outstanding 6,176,739 and 6,290,964 shares	6.2	6.3
Paid-in surplus	1,044.90	1,050.90
Retained earnings	2,802.30	2,542.70
Accumulated other comprehensive income (loss), after-tax:	'	'
Equity in net unrealized (losses) gains from investments in Symetra common shares	-40.4	57.7
Net unrealized foreign currency translation gains	88.4	85.7
Pension liability and other	4.1	-11.5
Total White Mountains’ common shareholders’ equity	3,905.50	3,731.80
Non-controlling interests	'	'
Total non-controlling interests	491.9	526.4
Total equity	4,397.40	4,258.20
Total liabilities and equity	12,144.30	12,895.40
OneBeacon	'	'
Non-controlling interests	'	'
Total non-controlling interests	273.7	251.4
Sirius Group	'	'
Non-controlling interests	'	'
Total non-controlling interests	250	250
HG Global	'	'
Non-controlling interests	'	'
Total non-controlling interests	16.6	16.6
BAM	'	'
Non-controlling interests	'	'
Total non-controlling interests	-97.6	-36
Other Noncontrolling Interest	'	'
Non-controlling interests	'	'
Total non-controlling interests	$49.20	$44.40

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, except Share data, unless otherwise specified
Cash restricted (in dollars)	$56.10	$249.80
Common shares, par value per share (in dollars per share)	$1	$1
Common shares, authorized shares	50,000,000	50,000,000
Common shares, issued shares	6,176,739	6,290,964
Common shares, outstanding shares	6,176,739	6,290,964

CONSOLIDATED_STATEMENTS_OF_OPE

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (USD $)	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues	'	'	'
Earned insurance and reinsurance premiums	$1,987.30	$2,063.60	$1,924.50
Net investment income	110.9	153.6	184.5
Net realized and unrealized investment gains	161.7	118.2	74.1
Other revenue	57.5	100.3	-10
Total revenues	2,317.40	2,435.70	2,173.10
Expenses	'	'	'
Loss and loss adjustment expenses	1,040.50	1,193.90	1,174.30
Insurance and reinsurance acquisition expenses	376.9	430.2	402.2
Other underwriting expenses	331.3	321.8	268.1
General and administrative expenses	181.3	182.2	175.3
Interest expense on debt	42.5	44.8	55.2
Total expenses	1,972.50	2,172.90	2,075.10
Pre-tax income	344.9	262.8	98
Income tax (expense) benefit	-76.6	15.7	110
Net income from continuing operations	268.3	278.5	208
Gain (loss) on sale of discontinued operations, net of tax	46.6	-91	658.3
Net loss from discontinued operations, net of tax	-42.1	-24	-36.7
Income before equity in earnings of unconsolidated affiliates	272.8	163.5	829.6
Equity in earnings (losses) of unconsolidated affiliates, net of tax	36.6	29.9	-20.2
Net income	309.4	193.4	809.4
Net loss (income) attributable to non-controlling interests	12.4	14	-41.5
Net income attributable to White Mountains’ common shareholders	321.8	207.4	767.9
Other comprehensive income, net of tax:	'	'	'
Change in equity in net unrealized (losses) gains from investments in Symetra common shares, net of tax	-98.1	57.7	-58.5
Change in foreign currency translation, net of tax	2.7	39.6	-15.2
Net change in pension liability and other, net of tax	20.8	-2.9	-10.8
Comprehensive income	247.2	301.8	683.4
Comprehensive (income) loss attributable to non-controlling interests	-5.2	0.8	2.8
Comprehensive income attributable to White Mountains’ common shareholders	$242	$302.60	$686.20
Basic earnings (loss) per share	'	'	'
Continuing operations	$51.15	$47.41	$18.56
Discontinued operations	$0.74	($16.91)	$78.88
Total consolidated operations	$51.89	$30.50	$97.44
Diluted earnings (loss) per share	'	'	'
Continuing operations	$51.15	$47.41	$18.56
Discontinued operations	$0.74	($16.91)	$78.88
Total consolidated operations	$51.89	$30.50	$97.44
Dividends declared and paid per White Mountains’ common share	$1	$1	$1

CONSOLIDATED_STATEMENTS_OF_CHA

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (USD $)	Total	Common shares and paid-in surplus	Retained earnings	AOCI, after-tax	Total	Non-controlling Interests	Total Equity includes Noncontrolling Interest [Member]
In Millions, unless otherwise specified
Beginning balance at Dec. 31, 2010	'	$1,359	$2,175.60	$118.40	$3,653	$607.80	$4,260.80
Increase (Decrease) in Shareholders' Equity	'	'	'	'	'	'	'
Net income	809.4	0	767.9	0	767.9	41.5	809.4
Net change in unrealized gains (losses) on investments in unconsolidated affiliates, after tax	-58.5	0	0	-58.5	-58.5	0	-58.5
Change in foreign currency translation, net of tax	-15.2	0	0	-15.2	-15.2	0	-15.2
Net change in pension liability and other accumulated comprehensive items	-10.8	0	0	-8	-8	-2.8	-10.8
Comprehensive income	683.4	0	767.9	-81.7	686.2	38.7	724.9
Dividends declared on common shares	'	0	-8	0	-8	0	-8
Dividends/distributions to non-controlling interests	'	0	0	0	0	-61.5	-61.5
Issuances of common shares	'	0.9	0	0	0.9	0	0.9
Repurchases and retirements of common shares	-253	-107.2	-145.8	0	-253	0	-253
Contribution or Distribution to/ from Non-Controlling Interests	'	0	0	0	0	-8.6	-8.6
Amortization of restricted share and option awards	'	12	0	0	12	0.4	12.4
Non-controlling interest attributable to intercompany sale of subsidiary	'	-3.4	0	0	-3.4	3.4	0
Ending balance at Dec. 31, 2011	'	1,261.30	2,789.70	36.7	4,087.70	580.2	4,667.90
Increase (Decrease) in Shareholders' Equity	'	'	'	'	'	'	'
Net income	193.4	0	207.4	0	207.4	-14	193.4
Net change in unrealized gains (losses) on investments in unconsolidated affiliates, after tax	57.7	0	0	57.7	57.7	0	57.7
Change in foreign currency translation, net of tax	39.6	0	0	39.6	39.6	0	39.6
Net change in pension liability and other accumulated comprehensive items	-2.9	0	0	-2.1	-2.1	-0.8	-2.9
Comprehensive income	301.8	0	207.4	95.2	302.6	-14.8	287.8
Dividends declared on common shares	'	0	-6.6	0	-6.6	0	-6.6
Dividends/distributions to non-controlling interests	'	0	0	0	0	-39.1	-39.1
Issuances of common shares	'	5.8	0	0	5.8	0	5.8
Repurchases and retirements of common shares	-669.1	-221.3	-447.8	0	-669.1	0	-669.1
Contribution or Distribution to/ from Non-Controlling Interests	'	0	0	0	0	1.6	1.6
Amortization of restricted share and option awards	'	13.6	0	0	13.6	0.8	14.4
Deconsolidation of Hamer and Bri-Mar	'	0	0	0	0	-4.5	-4.5
Allocation of fair value of net assets acquired to non-controlling interests	'	-2.2	0	0	-2.2	2.2	0
Ending balance at Dec. 31, 2012	3,731.80	1,057.20	2,542.70	131.9	3,731.80	526.4	4,258.20
Increase (Decrease) in Shareholders' Equity	'	'	'	'	'	'	'
Net income	309.4	0	321.8	0	321.8	-12.4	309.4
Net change in unrealized gains (losses) on investments in unconsolidated affiliates, after tax	-98.1	0	0	-98.1	-98.1	0	-98.1
Change in foreign currency translation, net of tax	2.7	0	0	2.7	2.7	0	2.7
Net change in pension liability and other accumulated comprehensive items	20.8	0	0	15.6	15.6	5.2	20.8
Comprehensive income	247.2	0	321.8	-79.8	242	-7.2	234.8
Dividends declared on common shares	'	0	-6.2	0	-6.2	0	-6.2
Dividends/distributions to non-controlling interests	'	0	0	0	0	-39.7	-39.7
Issuances of common shares	'	1	0	0	1	0	1
Repurchases and retirements of common shares	-79.8	-23.8	-56	0	-79.8	0	-79.8
Contribution or Distribution to/ from Non-Controlling Interests	'	0	0	0	0	11.5	11.5
Amortization of restricted share and option awards	'	16.7	0	0	16.7	0.9	17.6
Ending balance at Dec. 31, 2013	$3,905.50	$1,051.10	$2,802.30	$52.10	$3,905.50	$491.90	$4,397.40

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operations:	'	'	'
Net income	$309,400,000	$193,400,000	$809,400,000
Charges (credits) to reconcile net income to net cash (used for) provided from operations:	'	'	'
Net realized and unrealized investment gains	-161,700,000	-118,200,000	-74,100,000
Net (gain) loss on sale of consolidated and unconsolidated affiliates	-21,300,000	0	0
Excess of fair value of acquired net assets over cost	-15,200,000	-34,200,000	-7,200,000
Deferred income tax expense (benefit)	39,700,000	-16,800,000	-71,000,000
Undistributed equity in (earnings) loss from unconsolidated affiliates, after-tax	-36,600,000	-29,900,000	20,200,000
Net loss from discontinued operations	42,100,000	24,000,000	36,700,000
Net (gain) loss on sale of other discontinued operations	-46,600,000	91,000,000	-658,300,000
Other operating items:	'	'	'
Net change in loss and loss adjustment expense reserves	-164,600,000	-172,200,000	-23,400,000
Net change in reinsurance recoverable on paid and unpaid losses	25,000,000	42,400,000	66,000,000
Net change in unearned insurance and reinsurance premiums	-12,500,000	63,100,000	67,000,000
Net change in ceded reinsurance premiums payable	-28,100,000	3,800,000	39,500,000
Net change in ceded unearned insurance and reinsurance premiums	1,400,000	0	-8,600,000
Net change in insurance and reinsurance premiums receivable	12,700,000	-79,200,000	-42,400,000
Net change in variable annuity benefit guarantee liabilities	-388,700,000	-327,100,000	158,300,000
Net change in variable annuity benefit derivative instruments	29,100,000	192,100,000	57,100,000
Net change in deferred acquisition costs	17,100,000	-5,700,000	-15,300,000
Net change in funds held by ceding companies	14,400,000	-17,700,000	11,600,000
Net change in funds held under reinsurance treaties	98,800,000	10,600,000	-42,400,000
Net change in restricted cash	193,700,000	203,700,000	-166,800,000
Net change in other assets and liabilities, net	63,200,000	-52,700,000	-62,200,000
Net cash (used for) provided from continuing operations	-28,700,000	-29,600,000	94,100,000
Net cash used for discontinued operations	-72,300,000	-196,200,000	-208,600,000
Net cash used for operations	-101,000,000	-225,800,000	-114,500,000
Cash flows from investing activities:	'	'	'
Net change in short-term investments	34,800,000	145,300,000	174,500,000
Sales of fixed maturity and convertible fixed maturity investments	3,879,800,000	6,040,000,000	3,481,900,000
Maturities, calls and paydowns of fixed maturity and convertible fixed maturity investments	465,800,000	678,400,000	1,163,600,000
Sales of common equity securities	521,100,000	192,400,000	237,800,000
Distributions and redemptions of other long-term investments	58,100,000	86,700,000	150,700,000
Sales of unconsolidated affiliates, net of cash sold and held in escrow	32,400,000	24,800,000	1,010,600,000
Contributions to other long-term investments	-36,300,000	-96,700,000	-65,800,000
Funding of operational cash flows for discontinued operations	-72,300,000	-196,200,000	-171,800,000
Purchases of common equity securities	-432,200,000	-365,200,000	-297,800,000
Purchases of fixed maturity and convertible fixed maturity investments	-4,132,000,000	-5,810,100,000	-5,200,600,000
Purchases of consolidated and unconsolidated affiliates (net of cash acquired of $28.5, $9.0 and $2.0)	15,900,000	-41,300,000	-3,200,000
Net change in unsettled investment purchases and sales	7,500,000	-22,400,000	47,000,000
Net acquisitions of property and equipment	-13,100,000	-2,300,000	-5,500,000
Net cash provided from investing activities — continuing operations	329,500,000	633,400,000	521,400,000
Net cash provided from investing activities — discontinued operations	72,300,000	196,200,000	278,200,000
Net cash provided from investing activities	401,800,000	829,600,000	799,600,000
Cash flows from financing activities:	'	'	'
Draw down of revolving line of credit	200,000,000	150,000,000	0
Repayment of revolving line of credit	-275,000,000	-75,000,000	0
Repurchase of debt	0	-275,900,000	-161,600,000
Issuance of debt, net of debt issuance costs	0	271,900,000	0
Change in capital lease obligation	-5,700,000	-4,900,000	23,100,000
Cash dividends paid to the Company’s common shareholders	-6,200,000	-6,600,000	-8,000,000
Cash dividends paid to OneBeacon Ltd.’s non-controlling common shareholders	-19,900,000	-19,800,000	-42,800,000
Cash dividends paid on SIG Preference Shares	-18,800,000	-18,800,000	-18,800,000
Common shares repurchased	-79,800,000	-669,100,000	-253,000,000
Proceeds from issuances of common shares	0	0	900,000
Capital contributions from non-controlling interest of consolidated LPs	1,600,000	0	0
Redemptions paid to non-controlling interest of consolidated LPs	-700,000	0	0
Purchase of interest rate cap	-9,900,000	0	0
Collateral provided by interest rate cap counterparties	10,800,000	0	0
Capital contributions from BAM members	17,100,000	0	0
Net cash used for financing activities — continuing operations	-186,500,000	-648,200,000	-460,200,000
Net cash (used for) provided from financing activities — discontinued operations	0	0	0
Net cash used for financing activities	-186,500,000	-648,200,000	-460,200,000
Effect of exchange rate changes on cash	-200,000	3,100,000	-1,500,000
Net change in cash during the period	114,100,000	-41,300,000	223,400,000
Cash reclassified to assets held for sale (net of cash sold of $0, $3.5, and $0)	0	2,000,000	-5,500,000
Cash balance at beginning of year (excludes restricted cash balances of $249.8, $453.5 and $286.7 and AutoOne cash of $0, $0 and $4.7)	212,600,000	251,900,000	103,600,000
Cash balance at end of year (excludes restricted cash balances of $56.1, $249.8, and $453.5)	326,700,000	212,600,000	251,900,000
Discontinued Operations	'	'	'
Charges (credits) to reconcile net income to net cash (used for) provided from operations:	'	'	'
Net realized and unrealized investment gains	0	0	-700,000
Net loss from discontinued operations	42,100,000	24,000,000	36,700,000
Net (gain) loss on sale of other discontinued operations	-46,600,000	91,000,000	-658,300,000
Cash flows from financing activities:	'	'	'
Net change in cash during the period	$0	$0	($69,600,000)

CONSOLIDATED_STATEMENTS_OF_CAS1

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2009
Cash restricted end of period	$56.10	$249.80	$453.50	'
AutoOne Cash, end of period	'	0	4.7	3.9
Cash reclassified to assets held-for-sale	0	3.5	0	'
Cash Acquired from Acquisition	$28.50	$9	$2	'

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Summary of Significant Accounting Policies	'
	Summary of Significant Accounting Policies
	Basis of Presentation
	The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the accounts of White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”), its subsidiaries (collectively with the Company, “White Mountains”) and other entities required to be consolidated under GAAP. The Company is an exempted Bermuda limited liability company whose principal businesses are conducted through its 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 property and casualty insurance companies (collectively “OneBeacon”). OneBeacon is a specialty property and casualty insurance writer that offers a wide range of insurance products in the United States primarily through independent agencies, regional and national brokers, wholesalers and managing general agencies. During the third quarter of 2013, OneBeacon formed Split Rock Insurance, Ltd. (“Split Rock”), a Bermuda-based reinsurance company. As of both December 31, 2013 and 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 December 31, 2013 and 2012 have been presented as held for sale in the financial statements. (See Note 21 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 primary subsidiaries, Sirius International Insurance Corporation (“Sirius International”), Sirius America Insurance Company (“Sirius America”) and Lloyd’s 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 both December 31, 2013 and 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., which is in runoff, and its U.S.-based service provider, White Mountains Financial Services LLC (collectively, “WM Life Re”), as well as various other entities not included in other segments. For 2011, the Other Operations segment also included the consolidated results of the Tuckerman Capital, LP fund (“Tuckerman Fund I”). On December 31, 2011, Tuckerman Fund I 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 are no longer consolidated by White Mountains.
	White Mountains’ discontinued operations consist of Esurance Holdings, Inc. and its subsidiaries (“Esurance Insurance”), Answer Financial Inc. and its subsidiaries (“AFI”), the Runoff Transaction and AutoOne.  Esurance Insurance wrote personal auto insurance directly to customers in 30 states through its website and over the phone and also sold other lines of personal insurance for unaffiliated insurance companies.  Esurance Insurance also wrote personal auto policies through select online agents and provided other insurance products through partnerships with industry leading online providers.  Esurance Insurance earned commissions and fees by referring to unaffiliated insurance companies those shoppers that it could not underwrite because of pricing or underwriting eligibility.  AFI sold insurance online and through call centers for both Esurance Insurance and unaffiliated companies utilizing a comparison quoting platform.  The OneBeacon runoff business included assets, liabilities and capital that was 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 (the “Runoff Business”). 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. 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.
	Significant Accounting Policies
	Investment Securities
	At December 31, 2013, White Mountains’ invested assets consisted of securities and other investments held for general investment purposes.  White Mountains’ portfolio of fixed maturity investments and common equity securities held for general investment purposes are classified as trading and are reported at fair value as of the balance sheet date.  Changes in unrealized gains and losses are reported pre-tax in revenues. Realized investment gains and losses are accounted for using the specific identification method and are reported pre-tax in revenues. Premiums and discounts on all fixed maturity investments are accreted to income over the anticipated life of the investment.
	White Mountains’ invested assets that are measured at fair value include fixed maturity securities, common and preferred equity securities, convertible fixed maturity securities and other long-term investments, such as interests in hedge funds and private equities. In determining its estimates of fair value, White Mountains uses a variety of valuation approaches and inputs. Whenever possible, White Mountains estimates fair value using valuation methods that maximize the use of quoted prices and other observable inputs.
	As of December 31, 2013 and 2012, approximately 95% of the investment portfolio recorded at fair value was priced based upon quoted market prices or other observable inputs. Investments valued using Level 1 inputs include fixed maturities, primarily investments in U.S. Treasuries, common equities and short-term investments, which include U.S. Treasury Bills. Investments valued using Level 2 inputs comprise fixed maturities including corporate debt, state and other governmental debt, convertible fixed maturity securities and mortgage and asset-backed securities. Fair value estimates for investments that trade infrequently and have few or no observable market prices are classified as Level 3 measurements. Level 3 fair value estimates based upon unobservable inputs include White Mountains’ investments in hedge funds and private equity funds, as well as investments in certain debt securities, including asset-backed securities, where quoted market prices are unavailable. White Mountains determines when transfers between levels have occurred as of the beginning of the period. 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, 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 a review of the pricing services’ quality control processes and procedures on at least an annual basis, comparison of market prices to prices obtained from a 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 million from the expected price based on these procedures are considered outliers. Prices that have not changed from period to period and prices that have trended unusually compared to market conditions are also 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.  During the past year, approximately thirty-five securities fell outside White Mountains’ expected results, thereby triggering the challenge with the pricing service. 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, including asset-backed 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 prospectively over the remaining economic life.
	Short-term investments consist of money market funds, certificates of deposit and other securities which, at the time of purchase, mature or become available for use within one year.  Short-term investments are carried at amortized cost, which approximated fair value as of December 31, 2013 and 2012.
	Other Long-term Investments
	White Mountains’ other long-term investments consist primarily of hedge funds, private equity funds and other investments in limited partnerships. White Mountains has taken the fair value option for most of its investments in hedge funds, private equity funds and other limited partnership investments. For the investments for which White Mountains has taken the fair value option, changes in fair value are reported in revenues on a pre-tax basis. For those hedge fund and private equity investments for which White Mountains has not made the fair value election, White Mountains accounts for its interests under the equity method.
	Derivative Financial Instruments
	White Mountains holds a variety of derivative financial instruments for both risk management and investment purposes. White Mountains recognizes all derivatives as either assets or liabilities, measured at fair value, in the consolidated balance sheets. Changes in the fair value of derivative instruments are recognized in current period pre-tax income.
	Warrants
	At December 31, 2012, White Mountains held warrants to purchase 9.49 million common shares of Symetra which were included as investments in unconsolidated affiliates. The Symetra warrants held by White Mountains were entitled to dividends declared to common shareholders. On June 20, 2013, White Mountains exercised its warrants in a cashless transaction and received 2.65 million common shares of Symetra in exchange for the warrants.
	White Mountains also holds warrants that it has received in the restructuring (e.g., securities received from bankruptcy proceedings) of certain of its common equity and/or fixed maturity investments. White Mountains accounts for its investments in warrants as derivatives.
	Derivatives—Variable Annuity Reinsurance
	White Mountains has entered into agreements to reinsure death and living benefit guarantees associated with certain variable annuities in Japan through its wholly owned subsidiary, WM Life Re. The accounting for benefit guarantees differs depending on whether or not the guarantee is classified as a derivative or an insurance liability.
	Guaranteed minimum accumulation benefits (“GMABs”) are paid to an annuitant for any shortfall between accumulated account value at the end of the accumulation period and the annuitant’s total deposit, less any withdrawal payments made to the annuitant during the accumulation period. GMABs meet the definition of a derivative for accounting purposes. Therefore, GMABs are carried at fair value, with changes thereon recognized in income in the period of the change. The liability for the reinsured GMAB contracts has been determined using internal valuation models that use assumptions for interest rates, equity markets, foreign exchange rates and market volatilities at the valuation date, as well as annuitant-related actuarial assumptions, including surrender and mortality rates.
	If an annuitant dies during the accumulation period of an annuity contract, guaranteed minimum death benefits (“GMDBs”) are paid to the annuitant’s beneficiary for shortfalls between accumulated account value at the time of an annuitant’s death and the annuitant’s total deposit, less any living benefit payments or withdrawal payments previously made to the annuitant. White Mountains has elected to measure its GMDB liabilities at fair value.
	The valuation of these liabilities involves significant judgment and is subject to change based upon changes in capital market assumptions and emerging surrender and mortality experience of the underlying contracts in force.
	WM Life Re has entered into derivative contracts that are designed to economically hedge against changes in the fair value of living and death benefit liabilities associated with its variable annuity reinsurance arrangements. The derivatives include futures and over-the-counter option contracts on interest rates, major bond and equity indices, and foreign currencies. All WM Life Re’s derivative instruments are recorded as assets or liabilities at fair value on the balance sheet within other assets. These derivative financial instruments do not meet the criteria for hedge accounting treatment, and accordingly, changes in fair value are recognized in the current period as gains or losses in the income statement within other revenues.
	WM Life Re includes the effect of counterparty credit risk when determining the fair value of its derivative contracts and its GMAB and GMDB liabilities.
	Cash
	Cash includes amounts on hand and demand deposits with banks and other financial institutions. Amounts presented in the statement of cash flows are shown net of balances acquired and sold in the purchase or sale of the Company’s consolidated subsidiaries and exclude changes in amounts of restricted cash (See Note 8).
	Insurance and Reinsurance Operations
	White Mountains accounts for insurance and reinsurance policies that it writes in accordance with ASC 944. Premiums written are recognized as revenues and are earned ratably over the term of the related policy or reinsurance treaty. Unearned premiums represent the portion of premiums written that are applicable to future insurance or reinsurance coverage provided by policies or treaties in force.  White Mountains charges fees on certain of its insurance policies. Refundable fees are classified with premiums and recognized in earnings over the policy term. Fees that represent a reimbursement of expenses, such as installment fees, are recorded as a reduction of underwriting expenses.
	Deferred acquisition costs represent commissions, premium taxes, brokerage expenses and other costs which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent they relate to successful contract acquisitions over the applicable premium recognition period as insurance and reinsurance acquisition expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income. This limitation is referred to as a premium deficiency. A premium deficiency is recognized if the sum of expected loss and loss adjustment expenses (“LAE”), expected dividends to policyholders, unamortized acquisition costs, and maintenance costs exceeds related unearned premiums and anticipated investment income. A premium deficiency is recognized by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs then a liability is accrued for the excess deficiency.
	Losses and LAE are charged against income as incurred. Unpaid insurance losses and LAE are based on estimates (generally determined by claims adjusters, legal counsel and actuarial staff) of the ultimate costs of settling claims, including the effects of inflation and other societal and economic factors. Unpaid reinsurance losses and LAE are based primarily on reports received from ceding companies and actuarial projections. Unpaid loss and LAE reserves represent management’s best estimate of ultimate losses and LAE, net of estimated salvage and subrogation recoveries, if applicable. Such estimates are regularly reviewed and updated and any adjustments resulting there from are reflected in current operations. The process of estimating loss and LAE involves a considerable degree of judgment by management and the ultimate amount of expense to be incurred could be considerably greater than or less than the amounts currently reflected in the financial statements.
	OneBeacon discounts certain of its long-term workers compensation loss and LAE reserves when such liabilities constitute unpaid but settled claims under which the payment pattern and ultimate costs are fixed and determinable on an individual claim basis. OneBeacon discounts these reserves using an average discount rate which is determined based on the various assumptions including consideration of when the claims will be settled (3.5% at both December 31, 2013 and 2012). As of December 31, 2013, the discount on OneBeacon’s workers compensation loss and LAE reserves amounted to $3.0 million (excluding $61.7 million which relates to reserves classified as held for sale). As of December 31, 2012, the discount on OneBeacon’s workers compensation loss and LAE reserves amounted to $4.6 million, (excluding $77.9 million on reserves classified as discontinued operations).
	White Mountains’ insurance and reinsurance subsidiaries enter into ceded reinsurance contracts from time to time to protect their businesses from losses due to concentration of risk, to manage their operating leverage ratios and to limit losses arising from catastrophic events. Such reinsurance contracts are executed through excess of loss treaties and catastrophe contracts under which the reinsurer indemnifies White Mountains for a specified part or all of certain types of losses over stipulated amounts arising from any one occurrence or event. White Mountains has also entered into quota share treaties with reinsurers under which all risks meeting prescribed criteria are covered on a pro-rata basis. The amount of each risk ceded by White Mountains is subject to maximum limits which vary by line of business and type of coverage.
	Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured policies. The collectability of reinsurance recoverables is subject to the solvency of the reinsurers. White Mountains is selective in regard to its reinsurers, principally placing reinsurance with those reinsurers with a strong financial condition, industry ratings and underwriting ability. Management monitors the financial condition and ratings of its reinsurers on an ongoing basis.
	Reinsurance premiums, commissions, expense reimbursements and reserves related to reinsured business are accounted for on a basis consistent with those used in accounting for the original policies issued and the terms of the reinsurance contracts. Premiums ceded to other companies are reported as a reduction of premiums written. Expense allowances received in connection with reinsurance ceded have been accounted for as a reduction of the related policy acquisition costs and are deferred and amortized accordingly. Funds held by ceding companies represent amounts due to White Mountains in connection with certain assumed reinsurance agreements in which the ceding company retains a portion of the premium to provide security against future loss payments. The funds held by ceding companies are generally invested by the ceding company and a contractually agreed interest amount is credited to the Company and recognized as investment income. Funds held under insurance and reinsurance contracts represent contractual payments due to White Mountains that have been retained to secure such obligations. Such amounts are recorded as liabilities in the consolidated financial statements.
	Accruals for contingent commission liabilities are established for reinsurance contracts that provide for the stated commission percentage to increase or decrease based on the loss experience of the contract. Changes in the estimated liability for such arrangements are recorded as contingent commissions. Accruals for contingent commission liabilities are determined through the review of the contracts that have these adjustable features and are estimated based on expected loss and LAE.
	Municipal Bond Insurance
	All of the contracts issued by BAM are accounted for as insurance contracts under ASC 944-605, Financial Guarantee Insurance Contracts. Premiums are generally 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.
	Deferred acquisition costs represent commissions, premium taxes, excise taxes and other costs which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent they relate to successful contract acquisitions over the applicable premium recognition period as acquisition expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income.
	Mandatory Shared Market Mechanisms
	As a condition to its licenses to do business in certain states, White Mountains’ insurance operations must participate in various mandatory shared market mechanisms commonly referred to as “residual” or “involuntary” markets. These markets generally consist of risks considered to be undesirable from a standard or routine underwriting perspective. Each state dictates the levels of insurance coverage that are mandatorily assigned to participating insurers within these markets. The total amount of such business an insurer must accept in a particular state is generally based on that insurer’s market share of voluntary business written within that state. In certain cases, White Mountains is obligated to write business from shared market mechanisms at a future date based on its historical market share of all voluntary policies written within that state. Involuntary business generated from mandatory shared market mechanisms is accounted for as direct insurance business or as assumed reinsurance depending upon the structure of the mechanism.
	OneBeacon’s market assignments are typically required to be written in the current period, however, in certain cases OneBeacon is required to accept policy assignments at a future date. Anticipated losses associated with future market assignments are recognized when the amount of such anticipated losses is determined to be probable and can be reasonably estimated.
	Insurance-related Assessments
	Under existing guaranty fund laws in all states, insurers licensed to do business in those states can be assessed for certain obligations of insolvent insurance companies to policyholders and claimants. White Mountains records guaranty fund assessments when it is probable that an assessment will be made and the amount can be reasonably estimated.
	Deferred Software Costs
	White Mountains capitalizes costs related to computer software developed for internal use during the application development stage of software development projects. These costs generally consist of certain external, payroll and payroll-related costs. White Mountains begins amortization of these costs once the project is completed and ready for its intended use. Amortization is on a straight-line basis and over a useful life of three to five years. At December 31, 2013 and 2012, White Mountains had unamortized deferred software costs of $23.8 million and $17.1 million.
	Federal and Foreign Income Taxes
	A significant portion of White Mountains’ subsidiaries file consolidated tax returns in the United States. Income earned or losses generated by companies outside the United States are generally subject to an overall effective tax rate lower than that imposed by the United States.
	Deferred tax assets and liabilities are recorded when a difference between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts for tax purposes exists, and for other temporary differences. The deferred tax asset or liability is recorded based on tax rates expected to be in effect when the difference reverses. The deferred tax asset is recognized when it is more likely than not that it will be realized.
	Foreign Currency Exchange
	The U.S. dollar is the functional currency for all of White Mountains’ businesses except for Sirius International, the Canadian reinsurance operations of Sirius America and certain other smaller international activities.  White Mountains also invests in securities denominated in foreign currencies. Assets and liabilities recorded in these foreign currencies are translated into U.S. dollars at exchange rates in effect at the balance sheet date, and revenues and expenses are converted using the average exchange rates for the period. Net foreign exchange gains and losses arising from the translation are generally reported in shareholders’ equity, in accumulated other comprehensive income or loss.
	Assets and liabilities relating to foreign operations are translated into the functional currency using current exchange rates; revenues and expenses are translated into the functional currency using the weighted average exchange rate for the period.  The resulting exchange gains and losses are reported as a component of net income in the period in which they arise. As of December 31, 2013 and 2012, White Mountains had unrealized foreign currency translation gains of $88.4 million and $85.7 million recorded in accumulated other comprehensive income on its consolidated balance sheet.
	The following rates of exchange for the U.S. dollar have been used for the most significant operations:
	Currency	Opening Rate	Closing Rate	Opening Rate	Closing Rate
		2013	2013	2012	2012
	Swedish kronor	6.4973	6.4339	6.8645	6.4973
British pound	0.6154	0.6044	0.6434	0.6154
Canadian dollar	0.9955	1.0625	1.0193	0.9955
Non-controlling Interest
Non-controlling interests consist of the ownership interests of non-controlling shareholders in consolidated subsidiaries, and are presented separately on the balance sheet. The portion of comprehensive income attributable to non-controlling interests is presented net of related income taxes in the statement of operations and comprehensive income. The percentage of the non-controlling shareholders’ ownership interest in OneBeacon Ltd. at both December 31, 2013 and 2012 was 24.8%.
In 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 years ended December 31, 2013 and 2012, BAM reported $78.6 million and $36.3 million in pre-tax losses that have been allocated to non-controlling interest.
On May 24, 2007, Sirius International Group, Ltd. (“SIG”), an intermediate holding company of Sirius Group, issued $250.0 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. These shares were issued in an offering that was exempt from the registration requirements of the Securities Act of 1933. Holders of the SIG Preference Shares receive dividends on a non-cumulative basis when and if declared by SIG. The holders of the SIG Preference Shares have the right to elect two directors to SIG’s board in the event of non-payment of dividends for six quarterly dividend periods. The right ceases upon the payment of dividends for four quarterly periods or the redemption of the SIG Preference Shares. In addition, SIG may not declare or pay dividends on its common shares (other than stock dividends and dividends paid for purposes of any employee benefit plans of SIG and its subsidiaries) unless it is current on its most recent dividend period. The dividend rate is fixed at an annual rate of 7.506% until June 30, 2017 and dividends are paid on a semi-annual basis. After June 30, 2017, the dividend rate will be paid at a floating annual rate, equal to the greater of (1) the 3 month LIBOR plus 320 bps or (2) 7.506% and dividends will be paid on a quarterly basis. The SIG Preference Shares are redeemable solely at the discretion of SIG on or after June 30, 2017 at their liquidation preference of $1,000 per share, plus any declared but unpaid dividends. In July 2013, SIG executed a 5-year forward LIBOR cap (the “Interest Rate Cap”) for the period from June 2017 to June 2022 to protect against a significant increase in interest rates during that 5-year period. The Interest Rate Cap fixes the annual dividend rate on the SIG Preference Shares from June 2017 to June 2022 at 8.30%. The Interest Rate Cap is recorded in other assets at fair value. Changes in fair value are recorded in other revenue.
Prior to June 30, 2017, SIG may elect to redeem the SIG Preference Shares at an amount equal to the greater of (1) the aggregate liquidation preference of the shares to be redeemed and (2) the sum of the present values of the aggregate liquidation preference of the shares to be redeemed and the remaining scheduled dividend payments on the shares to be redeemed (excluding June 30, 2017), discounted to the redemption date on a semi-annual basis at a rate equal to the rate on a comparable treasury issue plus 45 basis points. In the event of liquidation of SIG, the holders of the SIG Preference Shares would have preference over the common shareholders and would receive a distribution equal to the liquidation preference per share, subject to availability of funds. SIG Preference Shares and dividends thereon are included in non-controlling interest on the balance sheet and as non-controlling interest expense on the statement of income and comprehensive income.
At December 31, 2013 and 2012, the non-controlling equity interest in White Mountains’ consolidated limited partnerships was $46.1 million and $41.5 million. At December 31, 2013 and 2012, the non-controlling equity interest in A.W.G. Dewar Inc, a subsidiary of OneBeacon, was $3.1 million and $2.8 million. On September 30, 2013, Sirius Group purchased the remaining 25.0% ownership in one of its subsidiaries, Passage2Health Limited. At December 31, 2012, the non-controlling equity interest in Passage2Health Limited was $0.2 million.
Variable Interest Entities
White Mountains consolidates a variable interest entity (“VIE”) when it has both the power to direct the activities of the VIE that most significantly impact its economic performance and either the obligation to absorb losses or the right to receive returns from the VIE that could potentially be significant to the VIE (See Note 17).
Recently Adopted Changes in Accounting Principles
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.
Policy Acquisition Costs
On January 1, 2012, White Mountains adopted ASU 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts (ASC 944). The new standard changes the types of policy acquisition costs that are eligible for deferral. Specifically, the new guidance limits deferrable costs to those that are incremental direct costs of contract acquisition and certain costs related to acquisition activities performed by the insurer, such as underwriting, policy issuance and processing, medical and inspection costs and sales force contract selling. The ASU defines incremental direct costs as those costs that result directly from and were essential to the contract acquisition and would not have been incurred absent the acquisition. Accordingly, under the new guidance, deferrable acquisition costs are limited to costs related to successful contract acquisitions. Acquisition costs that are not eligible for deferral are to be charged to expense in the period incurred.
White Mountains adopted ASU 2010-26 prospectively. Upon adoption, certain acquisition costs, primarily a portion of the profit sharing commissions associated with OneBeacon’s collector car and boats business, no longer 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.  (See Note 5).
Comprehensive Income
For fiscal periods beginning after December 15, 2011, ASU 2011-05, Comprehensive Income (ASC 220) became effective, which requires all components of comprehensive income to be reported in a continuous financial statement or in consecutive statements displaying the components of net income and the components of other comprehensive income. Since White Mountains presents comprehensive income in a continuous financial statement, adoption of ASU 2011-05 had no effect on White Mountains’ financial statement presentation.
Recent Accounting Pronouncements
Qualified Affordable Housing Projects
On January 15, 2014, the FASB issued ASU 2014-01, Accounting for Investments in Qualified Affordable Housing Projects ("QAHP") (ASC 323). The new guidance eases the requirements for an investor to elect to account for its investment in a QAHP using the effective yield method. Prior to the issuance of the new guidance, investors had to have a letter of credit guaranteeing the availability of the tax credit allocable to the investor, had to demonstrate that the projected yield based solely on the cash flows from the guaranteed tax credits was positive and had to be a limited partner in the QAHP for both legal and tax purposes. Under the new guidance, the letter of credit requirement has been eliminated and instead, the investor must simply be able to demonstrate that the tax credit allocable to the investor will be available. Investments in QAHP not meeting the criteria in the new guidance would be accounted for under the equity method or the cost method. The election to use the effective yield method is considered an accounting policy decision that should be applied consistently to all QAHP investments. The new guidance is effective for annual and interim reporting periods beginning after December 15, 2014. The guidance should be applied retrospectively, with early adoption permitted. White Mountains holds an investment in a QAHP which is accounted for under the equity method and is still in the process of assessing the potential effect of adoption.
Unrecognized Tax Benefits
On July 18, 2013, the FASB issued ASU 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists (ASC 740). The new ASU requires balance sheet presentation of an unrecognized tax benefit as a reduction of a deferred tax asset for a net operating loss (“NOL”) carryforward or tax credit carryforward rather than as a liability. The exception is in circumstances where a carryforward is not available to settle the additional taxes that might arise upon disallowance of the tax position under the tax law of the applicable jurisdiction. Prior to the issuance of ASU 2013-11, the guidance for unrecognized tax benefits under ASC 740 did not provide explicit guidance on whether an entity should present an unrecognized tax benefit as a liability or as a reduction of NOL carryforwards or other tax credits. In circumstances where an NOL carryforward is not available to offset settlement of any additional taxes arising from a disallowed tax position, the unrecognized tax benefit should be presented as a liability. The new guidance becomes effective for fiscal periods beginning on or after December 15, 2013 and should be applied prospectively to all unrecognized tax benefits that exist at the effective date. Retrospective adoption is allowed. White Mountains will adopt ASU 2013-11 effective January 1, 2014. White Mountains is still in the process of assessing the effect of adoption, but believes adoption may result in a reclassification between taxes payable and deferred tax assets.

Significant_Transactions

Significant Transactions	12 Months Ended
	Dec. 31, 2013
Significant Transactions [Abstract]	'
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 cars and boats business, to Markel Corporation. Concurrently therewith, OneBeacon and Hagerty Insurance Agency (“Hagerty”) terminated their underwriting arrangement with respect to the collector cars and boats 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 $179.7 million and $166.6 million for December 31, 2012 and 2011, or 8.0% of White Mountains’ net written premiums for both periods.
	Formation of HG Global and BAM
	In 2012, White Mountains capitalized HG Global with $594.5 million to fund BAM, a newly formed mutual municipal bond insurer. As of December 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. HG Global provides first loss reinsurance protection for policies underwritten by BAM of up to 15% of par outstanding on a per policy basis through HG Re, which had statutory capital of $436.9 million and $412.0 million at December 31, 2013 and 2012. 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.
	Sale of OneBeacon Runoff Business
	On October 17, 2012, one of OneBeacon’s indirect wholly-owned subsidiaries, OneBeacon Insurance Group LLC, entered into a definitive agreement (as amended, the “Runoff SPA”) with Trebuchet US Holdings, Inc. (“Trebuchet”), a wholly-owned subsidiary of Armour Group Holdings Limited (together with Trebuchet, “Armour”), to sell the Runoff Business (the “Runoff Transaction”). Pursuant to the terms of the Runoff SPA, 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 and is expected to close in mid-2014 (see Note 21).
	WM Solutions
	On October 15, 2013, WM Solutions acquired Empire Insurance Company (“Empire”), a runoff insurance subsidiary of Leucadia National Corporation. The transaction resulted in a gain of $7.3 million recorded in other revenue.
	In the first quarter of 2013, WM Solutions acquired Ashmere Insurance Company (“Ashmere”, formerly known as American Fuji Fire and Marine Insurance Company), an American International Group, Inc. (“AIG”) runoff subsidiary. The transaction resulted in a gain of $6.9 million recorded in other revenue.
	On December 3, 2012, WM Solutions acquired four runoff entities including Physicians Insurance Company of Ohio (“PICO”) and Citation Insurance Company (“Citation”) from PICO Holdings and two AIG runoff subsidiaries, Woodridge Insurance Company (“Woodridge”, formerly known as American General Indemnity Company) and Oakwood Insurance Company (“Oakwood”, formerly known as American General Property Insurance Company). The transactions resulted in a gain of $14.5 million recorded in other revenue.
	On December 30, 2011, WM Solutions acquired the runoff loss reserve portfolio of Old Lyme, a Bermuda-based reinsurer in runoff, for $6.0 million in cash and a purchase note for $2.1 million (see Note 6).  The transaction resulted in a gain of $7.2 million recorded in other revenue.
	Sale of AutoOne
	On August 30, 2011, OneBeacon entered into a definitive agreement (the “Purchase Agreement”) to sell the AutoOne business to Interboro Holdings, Inc. (“Interboro”). 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 21).
	Sale of Esurance
	On October 7, 2011, White Mountains completed the sale of Esurance Insurance and AFI to The Allstate Corporation (“Allstate”) for $700.0 million in excess of tangible book value.  White Mountains recorded a gain on the sale of $677.5 million in discontinued operations (see Note 21). The transaction is subject to a true-up of the estimated tangible book value of the entities sold through the date of closing and certain other contingencies (see Note 20).

Reserves_for_Unpaid_Losses_and

Reserves for Unpaid Losses and Loss Adjustment Expenses	12 Months Ended
	Dec. 31, 2013
Insurance Loss Reserves [Abstract]	'
Reserves for Unpaid Losses and Loss Adjustment Expenses	'
	Reserves for Unpaid Losses and Loss Adjustment Expenses
	Insurance
	White Mountains’ insurance subsidiaries establish loss and LAE reserves that are estimates of amounts needed to pay claims and related expenses in the future for insured events that have already occurred. The process of estimating reserves involves a considerable degree of judgment by management and, as of any given date, is inherently uncertain.
	Loss and LAE reserves are typically comprised of (1) case reserves for claims reported and (2) reserves for losses that have occurred but for which claims have not yet been reported, referred to as incurred but not reported (“IBNR”) reserves, which include a provision for expected future development on case reserves. Case reserves are estimated based on the experience and knowledge of claims staff regarding the nature and potential cost of each claim and are adjusted as additional information becomes known or payments are made. IBNR reserves are derived by subtracting paid loss and LAE and case reserves from estimates of ultimate loss and LAE. Actuaries estimate ultimate loss and LAE using various generally accepted actuarial methods applied to known losses and other relevant information. Like case reserves, IBNR reserves are adjusted as additional information becomes known or payments are made.
	Ultimate loss and LAE are generally determined by extrapolation of claim emergence and settlement patterns observed in the past that can reasonably be expected to persist into the future. In forecasting ultimate loss and LAE with respect to any line of business, past experience with respect to that line of business is the primary resource, but cannot be relied upon in isolation. White Mountains’ own experience, particularly claims development experience, such as trends in case reserves, payments on and closings of claims, as well as changes in business mix and coverage limits, is the most important information for estimating its reserves. External data, available from organizations such as statistical bureaus, consulting firms and reinsurance companies, is sometimes used to supplement or corroborate White Mountains’ own experience, and can be especially useful for estimating costs of new business. For some lines of business, such as “long-tail” coverages discussed below, claims data reported in the most recent accident year is often too limited to provide a meaningful basis for analysis due to the typical delay in reporting of claims. For this type of business, White Mountains uses a selected loss ratio method for the initial accident year or years. This is a standard and accepted actuarial reserve estimation method in these circumstances in which the loss ratio is selected based upon information used in pricing policies for that line of business, as well as any publicly available industry data, such as industry pricing, experience and trends, for that line of business.
	Uncertainties in estimating ultimate loss and LAE are magnified by the time lag between when a claim actually occurs and when it is reported and settled. This time lag is sometimes referred to as the “claim-tail”. The claim-tail for most property coverages is typically short (usually a few days up to a few months). The claim-tail for liability/casualty coverages, such as automobile liability, general liability, products liability, multiple peril coverage, and workers compensation, can be especially long as claims are often reported and ultimately paid or settled years, even decades, after the related loss events occur. During the long claims reporting and settlement period, additional facts regarding coverages written in prior accident years, as well as about actual claims and trends may become known and, as a result, White Mountains may adjust its reserves. If management determines that an adjustment is appropriate, the adjustment is booked in the accounting period in which such determination is made in accordance with GAAP. Accordingly, should reserves need to be increased or decreased in the future from amounts currently established, future results of operations would be negatively or positively impacted, as applicable.
	In determining ultimate loss and LAE, the cost to indemnify claimants, provide needed legal defense and other services for insureds and administer the investigation and adjustment of claims are considered. These claim costs are influenced by many factors that change over time, such as expanded coverage definitions as a result of new court decisions, inflation in costs to repair or replace damaged property, inflation in the cost of medical services and legislated changes in statutory benefits, as well as by the particular, unique facts that pertain to each claim. As a result, the rate at which claims arose in the past and the costs to settle them may not always be representative of what will occur in the future. The factors influencing changes in claim costs are often difficult to isolate or quantify and developments in paid and incurred losses from historical trends are frequently subject to multiple and conflicting interpretations. Changes in coverage terms or claims handling practices may also cause future experience and/or development patterns to vary from the past. A key objective of actuaries in developing estimates of ultimate loss and LAE, and resulting IBNR reserves, is to identify aberrations and systemic changes occurring within historical experience and accurately adjust for them so that the future can be projected reliably. Because of the factors previously discussed, this process requires the use of informed judgment and is inherently uncertain.
	White Mountains’ actuaries use several generally accepted actuarial methods to evaluate its loss reserves, each of which has its own strengths and weaknesses. Management places more or less reliance on a particular method based on the facts and circumstances at the time the reserve estimates are made. These methods generally fall into one of the following categories or are hybrids of one or more of the following categories:
	•	Historical paid loss development methods:  These methods use historical loss payments over discrete periods of time to estimate future losses. Historical paid loss development methods assume that the ratio of losses paid in one period to losses paid in an earlier period will remain constant. These methods necessarily assume that factors that have affected paid losses in the past, such as inflation or the effects of litigation, will remain constant in the future. Because historical paid loss development methods do not use case reserves to estimate ultimate losses, they can be more reliable than the other methods discussed below that look to case reserves (such as actuarial methods that use incurred losses) in situations where there are significant changes in how case reserves are established by a company’s claims adjusters. However, historical paid loss development methods are more leveraged, meaning that small changes in payments have a larger impact on estimates of ultimate losses, than actuarial methods that use incurred losses because cumulative loss payments take much longer to equal the expected ultimate losses than cumulative incurred amounts. In addition, and for similar reasons, historical paid loss development methods are often slow to react to situations when new or different factors arise than those that have affected paid losses in the past.
	•	Historical incurred loss development methods:  These methods, like historical paid loss development methods, assume that the ratio of losses in one period to losses in an earlier period will remain constant in the future. However, instead of using paid losses, these methods use incurred losses (i.e., the sum of cumulative historical loss payments plus outstanding case reserves) over discrete periods of time to estimate future losses. Historical incurred loss development methods can be preferable to historical paid loss development methods because they explicitly take into account open cases and the claims adjusters’ evaluations of the cost to settle all known claims. However, historical incurred loss development methods necessarily assume that case reserving practices are consistently applied over time. Therefore, when there have been significant changes in how case reserves are established, using incurred loss data to project ultimate losses can be less reliable than other methods.
	•	Expected loss ratio methods:  These methods are based on the assumption that ultimate losses vary proportionately with premiums. Expected loss ratios are typically developed based upon the information used in pricing, and are multiplied by the total amount of premiums written to calculate ultimate losses. Expected loss ratio methods are useful for estimating ultimate losses in the early years of long-tailed lines of business, when little or no paid or incurred loss information is available.
	•	Adjusted historical paid and incurred loss development methods:  These methods take traditional historical paid and incurred loss development methods and adjust them for the estimated impact of changes from the past in factors such as inflation, the speed of claim payments or the adequacy of case reserves. Adjusted historical paid and incurred loss development methods are often more reliable methods of predicting ultimate losses in periods of significant change, provided the actuaries can develop methods to reasonably quantify the impact of changes.
	White Mountains performs an actuarial review of its recorded reserves each quarter. White Mountains’ actuaries compare the previous quarter’s estimates of paid loss and LAE, case reserves and IBNR to amounts indicated by actual experience. Differences between previous estimates and actual experience are evaluated to determine whether a given actuarial method for estimating loss and LAE should be relied upon to a greater or lesser extent than it had been in the past. While some variance is expected each quarter due to the inherent uncertainty in loss and LAE, persistent or large variances would indicate that prior assumptions and/or reliance on certain reserving methods may need to be revised going forward.
	The actuarial analysis is a primary consideration for management in determining its best estimate of loss and LAE reserves. In making its best estimate, management also considers other qualitative factors that may lead to a difference between its best estimate of loss and LAE reserves and the actuarial point estimate. Typically, these factors exist when management and the company’s actuaries conclude that there is insufficient historical incurred and paid loss information or that trends included in the historical incurred and paid loss information are unlikely to repeat in the future. These factors may include, among others, changes in the techniques used to assess underwriting risk, more accurate and detailed levels of data submitted with reinsurance applications, the uncertainty of the current reinsurance pricing environment, the level of inflation in loss costs, changes in ceding company reserving practices, and legal and regulatory developments.
	Reinsurance
	Sirius Group establishes loss and LAE reserves that are estimates of future amounts needed to pay claims and related expenses for events that have already occurred. Sirius Group also obtains reinsurance whereby another reinsurer contractually agrees to indemnify White Mountains for all or a portion of the reinsurance risks underwritten by White Mountains. Such arrangements, where one reinsurer provides reinsurance to another reinsurer, are usually referred to as “retrocessional reinsurance” arrangements. White Mountains establishes estimates of amounts recoverable from retrocessional reinsurance in a manner consistent with the loss and LAE liability associated with reinsurance contracts offered to its customers (the “ceding companies”), net of an allowance for uncollectible amounts. Net reinsurance loss reserves represent loss and LAE reserves reduced by retrocessional reinsurance recoverable on unpaid losses.
	The estimation of net reinsurance loss and LAE reserves is subject to the same risk as the estimation of insurance loss and LAE reserves. In addition to those risk factors which give rise to inherent uncertainties in establishing insurance loss and LAE reserves, the inherent uncertainties of estimating such reserves are even greater for the reinsurer, due primarily to: (1) the claim-tail for reinsurers being further extended because claims are first reported to the original primary insurance company and then through one or more intermediaries or reinsurers, (2) the diversity of loss development patterns among different types of reinsurance treaties or facultative contracts, (3) the necessary reliance on the ceding companies for information regarding reported claims and (4) the differing reserving practices among ceding companies.
	As with insurance reserves, the process of estimating reinsurance reserves involves a considerable degree of judgment by management and, as of any given date, is inherently uncertain. Based on the above, such uncertainty may be larger relative to the reserves for a company that principally writes reinsurance compared to an insurance company, and certainty may take a longer time to emerge.
	Upon notification of a loss from an insured (typically a ceding company), Sirius Group establishes case reserves, including LAE reserves, based upon Sirius Group’s share of the amount of reserves established by the insured and Sirius Group’s independent evaluation of the loss. In cases where available information indicates that reserves established by a ceding company are inadequate, Sirius Group establishes case reserves or IBNR in excess of its share of the reserves established by the ceding company.  Also, in certain instances, Sirius Group may decide not to establish case reserves or IBNR, when the information available indicates that reserves established by ceding companies are not adequately supported. In addition, specific claim information reported by insureds or obtained through claim audits can alert management to emerging trends such as changing legal interpretations of coverage and liability, claims from unexpected sources or classes of business, and significant changes in the frequency or severity of individual claims where customary. Generally, ceding company audits are not customary outside the United States. This information is often used to supplement estimates of IBNR.
	Although loss and LAE reserves are initially determined based on underwriting and pricing analyses, Sirius Group regularly reviews the adequacy of its recorded reserves by using a variety of generally accepted actuarial methods, including historical incurred and paid loss development methods. If actual loss activity differs substantially from expectations, an adjustment to recorded reserves may be warranted. As time passes, loss reserve estimates for a given year will rely more on actual loss activity and historical patterns than on initial assumptions based on pricing indications.
	The actuarial methods described above are used to calculate a point estimate of loss and LAE reserves for each company within Sirius Group. These point estimates are then aggregated to produce an actuarial point estimate for the entire segment. Once a point estimate is established, Sirius Group’s actuaries estimate loss reserve ranges to measure the sensitivity of the actuarial assumptions used to set the point estimates. These ranges are calculated from historical variations in loss ratios, payment and reporting patterns by class and type of business.
	Loss and Loss Adjustment Expense Reserve Summary
	The following table summarizes the loss and LAE reserve activities of White Mountains’ insurance and reinsurance subsidiaries for the years ended December 31, 2013, 2012 and 2011:
			Year Ended December 31,
	Millions		2013			2012			2011
	Gross beginning balance		$	3,168.90		$	5,702.30		$	5,736.80
	Less beginning reinsurance recoverable on unpaid losses		(429.1		)	(2,507.3		)	(2,344.0		)
	Net loss and LAE reserves		2,739.80			3,195.00			3,392.80
	Less: Beginning net loss and LAE reserves for AutoOne and		—			(383.3		)	(619.6		)
	the Runoff Transaction(1)
	Loss and LAE reserves acquired(2)		37.7			17			21
	Losses and LAE incurred relating to:
	Current year losses		1,088.90			1,235.80			1,251.00
	Prior year losses		(48.4		)	(41.9		)	(76.7		)
	Total incurred losses and LAE		1,040.50			1,193.90			1,174.30
	Accretion of fair value adjustment to net loss and LAE reserves		1.7			10.6			8.3
	Foreign currency translation adjustment to net loss and LAE reserves		0.3			12.9			0.1
	Loss and LAE paid relating to:
	Current year losses		(336.2		)	(404.7		)	(387.9		)
	Prior year losses		(832.6		)	(901.6		)	(777.3		)
	Total loss and LAE payments		(1,168.8		)	(1,306.3		)	(1,165.2		)
	Plus: Ending net loss and LAE reserves for AutoOne and		—			—			383.3
	the Runoff Transaction(1)
	Net ending balance		2,651.20			2,739.80			3,195.00
	Plus ending reinsurance recoverable on unpaid losses		428.1			429.1			2,507.30
	Gross ending balance		$	3,079.30		$	3,168.90		$	5,702.30
	(1)	Loss and LAE reserve balances from OneBeacon’s Runoff Business prior to December 31, 2012 and AutoOne prior to December 31, 2011 were not classified as held for sale. Adjustment is to present loss and LAE reserve activities for continuing operations.
	(2)	Loss and LAE reserves acquired relate to WM Solutions purchases of Empire and Ashmere in 2013, PICO, Citation, Woodridge and Oakwood in 2012 and Old Lyme in 2011.
	Loss and LAE development —2013
	During the year ended December 31, 2013, White Mountains experienced $48.4 million of net favorable loss reserve development, which related entirely to Sirius Group. Sirius Group’s net favorable loss reserve development included $23.9 million of favorable loss reserve development on prior years’ catastrophe losses. Other major reductions in loss reserve estimates recognized included property ($16.6 million), aviation/space ($10.1 million), and accident and health ($9.2 million) lines, partially offset by an $11.8 million increase in asbestos loss reserves.
	During 2013, OneBeacon experienced no net loss and LAE reserve development on prior accident year reserves. OneBeacon experienced unfavorable development primarily related to property, general liability and accident and health lines, which was offset by favorable development in its other liability and ocean marine lines.
	Loss and LAE development —2012
	During the year ended December 31, 2012, White Mountains experienced $41.9 million of net favorable loss reserve development, which consisted of $7.4 million of net favorable loss reserve development at OneBeacon and $34.5 million of net favorable loss reserve development at Sirius Group.
	During 2012, OneBeacon experienced $7.4 million of net favorable loss and LAE reserve development on prior accident year reserves. The favorable reserve development at OneBeacon was primarily from workers' compensation, multiple peril liability and general liability lines. This favorable development was offset somewhat by adverse development on excess property claims.
	In 2012, Sirius Group had net favorable loss reserve development of $34.5 million. The major reductions in loss reserve estimates at Sirius Group were recognized in casualty runoff ($31.5 million), property ($28.4 million), marine/energy ($11.6 million), trade credit ($6.8 million) and aviation/space ($5.3 million) lines, partially offset by a $46.4 million increase in asbestos loss reserves and a $4.3 million increase in accident and health.
	Loss and LAE development —2011
	During the year ended December 31, 2011, White Mountains experienced $76.7 million of net favorable loss reserve development, which consisted of $29.8 million of net favorable loss and LAE reserve development on prior accident year loss reserves at OneBeacon and $46.9 million of net favorable loss reserve development at Sirius Group.
	OneBeacon’s net favorable loss and LAE reserve development was primarily due to lower than expected severity on losses related to professional liability lines, multiple peril liability lines and other general liability lines. With respect to the favorable loss reserve development in specialty insurance operations, at December 31, 2010, management had revised its expectations downward for future loss emergence in the professional liability business, which had initially been based on market analysis when this business was initiated in 2002 and 2003. However, during 2011, losses continued to be significantly lower than these revised expectations. As a result, management lowered its selected reserves on the earliest years which affected more recent years as total loss expectations for those years are based in part on prior years’ results. The impact of this revised estimate was a decrease to professional liability reserves of $11.5 million.
	During 2010, management began separately reviewing loss reserves for some business which had been previously managed as a part of OneBeacon’s former commercial lines underwriting unit. As of December 31, 2010, the reserves for these businesses had been selected based on expected emergence that was based on the historic loss development of former commercial lines underwriting unit. However, during 2011 the actual emerged experience for these businesses was
	significantly lower than the expected emergence. As a result of this favorable emergence, management lowered the loss
	reserves for these businesses by $(14.0) million during 2011.
	In addition to the development described for the lines of business above, OneBeacon also recorded a $4.3 million net decrease in reserves in other lines of business as a result of its review of loss reserves at December 31, 2011.
	The net favorable loss reserve development at Sirius Group was primarily attributable to $41.2 million of favorable development on property lines including, $(13.1) million of loss reserve reductions for the 2010 Chile earthquake, partially offset by asbestos and environmental increases of $12.3 million.
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 $1.7 million, $10.6 million and $8.3 million of such charges, recorded as loss and LAE during 2013, 2012 and 2011. As of December 31, 2013, the pre-tax un-accreted adjustment was $4.7 million.
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity
White Mountains’ reserves include provisions made for claims that assert damages from asbestos and environmental related exposures. Asbestos claims relate primarily to injuries asserted by those who came in contact with asbestos or products containing asbestos. Environmental claims relate primarily to pollution and related clean-up cost obligations, particularly as mandated by U.S. federal and state environmental protection agencies. In addition to the factors described above regarding the reserving process, White Mountains estimates its A&E reserves based upon, among other factors, facts surrounding reported cases and exposures to claims, such as policy limits and deductibles, current law, past and projected claim activity and past settlement values for similar claims, as well as analysis of industry studies and events, such as recent settlements and asbestos-related bankruptcies. The cost of administering A&E claims, which is an important factor in estimating loss reserves, tends to be higher than in the case of non-A&E claims due to the higher legal costs typically associated with A&E claims.
Substantially all of OneBeacon's reserves for unpaid loss and LAE for asbestos and environmental exposures relates to discontinued operations (see Note 21). As of December 31, 2013, the remaining unpaid loss and LAE loss reserves for asbestos and environmental exposures related to continuing operations is less than $1.0 million on both a gross and net basis at December 31, 2013.
Sirius Group's A&E exposure is primarily from reinsurance contracts written between 1974 through 1985 by acquired companies, mainly MONY Reinsurance Company and Christiania General Insurance Company. The exposures are mostly higher layer excess of loss treaty and facultative coverages with relatively low limits exposed for each claim. In 2013 and 2012, Sirius Group increased its net A&E exposure through incoming runoff portfolios acquired by White Mountains Solutions. These acquisitions added $13.0 million in net asbestos reserves and $1.0 million in net environmental reserves in 2013, and $11.0 million in net asbestos reserves and $0.7 million in net environmental reserves in 2012. The acquisition of companies having modest portfolios of A&E exposure has been typical of several prior White Mountains Solutions transactions and is likely to be an element of at least some future acquisitions. However, the acquisition of new A&E liabilities is undertaken only after careful due diligence and utilizing conservative reserving assumptions in relation to industry benchmarks. In the case of the portfolios acquired during 2013 and 2012, the exposures arise almost entirely from old assumed reinsurance contracts having small limits of liability.
Sirius Group recorded $11.8 million, $46.4 million and $10.3 million of asbestos-related incurred losses and LAE on its already existing asbestos reserves in 2013, 2012 and 2011.  The 2013 incurred losses were primarily the result of management’s monitoring of a variety of metrics including actual paid and reported claims activity as compared to the most recent in-depth analysis performed in 2012, net paid and reported survival ratios, peer comparisons, and industry benchmarks. In 2012, the increase in net asbestos losses included $14.0 million in response to Sirius Group’s quarterly monitoring of newly reported claims and $33.0 million as a result of an in-depth analysis of all treaty and facultative contracts likely to have asbestos exposure which examined total expected asbestos losses and LAE from a variety of information sources, including previous asbestos studies, reported client data and external benchmarking scenarios.  The 2011 incurred losses were primarily the result of management's monitoring of a variety of metrics including actual paid and reported claims activity, net survival ratios, peer comparisons, and industry benchmarks.
Sirius Group recorded an increase of $0.8 million and $2.0 million of environmental losses in 2013 and 2011, and a decrease of $0.5 million of environmental losses in 2012 on its already existing reserves.
Sirius Group’s net reserves for A&E losses were $193.9 million and $189.4 million at December 31, 2013 and 2012, respectively. Sirius Group’s A&E three-year net paid survival ratio was approximately 8.0 years and 9.0 years at December 31, 2013 and 2012.
White Mountains’ reserves for A&E losses at December 31, 2013 represent management’s best estimate of its ultimate liability based on information currently available. However, as case law expands, and medical and clean-up costs increase and industry settlement practices change, White Mountains may be subject to asbestos and environmental losses beyond currently estimated amounts. White Mountains cannot reasonably estimate at the present time loss reserve additions arising from any such future adverse developments and cannot be sure that allocated loss reserves, plus the remaining capacity under the NICO Cover and other reinsurance contracts, will be sufficient to cover additional liability arising from any such adverse developments.
Sirius Group
Net A&E Loss Reserve Activity		Year Ended December 31,
		2013						2012						2011
Millions		Gross			Net			Gross			Net			Gross			Net
Asbestos:
Beginning balance		$	208.2		$	174.2		$	185.1		$	146.2		$	191.9		$	151.5
Losses and LAE acquired		13			13			11			11			—			—
Incurred losses and LAE		12.1			11.8			46.8			46.4			13.6			10.3
Paid losses and LAE		(25.9		)	(20.3		)	(34.7		)	(29.4		)	(20.4		)	(15.6		)
Ending balance		207.4			178.7			208.2			174.2			185.1			146.2
Environmental:
Beginning balance		20.4			15.2			22.1			16.5			22.4			18.1
Losses and LAE acquired		1			1			0.7			0.7			—			—
Incurred losses and LAE		0.8			0.8			(.1		)	(.5		)	2.9			2
Paid losses and LAE		(1.8		)	(1.8		)	(2.3		)	(1.5		)	(3.2		)	(3.6		)
Ending balance		20.4			15.2			20.4			15.2			22.1			16.5
Total asbestos and environmental:
Beginning balance		228.6			189.4			207.2			162.7			214.3			169.6
Losses and LAE acquired		14			14			11.7			11.7			—			—
Incurred losses and LAE		12.9			12.6			46.7			45.9			16.5			12.3
Paid losses and LAE		(27.7		)	(22.1		)	(37.0		)	(30.9		)	(23.6		)	(19.2		)
Ending balance		$	227.8		$	193.9		$	228.6		$	189.4		$	207.2		$	162.7

Third_Party_Reinsurance

Third Party Reinsurance	12 Months Ended
	Dec. 31, 2013
Reinsurance Disclosures [Abstract]	'
Third-Party Reinsurance	'
	Third-Party Reinsurance
	In the normal course of business, White Mountains’ insurance and reinsurance subsidiaries 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. The effects of reinsurance on White Mountains’ insurance and reinsurance subsidiaries’ written and earned premiums and on losses and LAE were as follows (see Note 9 for balances related to White Mountains financial guarantee business):
		Year Ended December 31, 2013
	Millions	OneBeacon			Sirius Group			Total
	Written premiums:
	Direct	$	1,103.10		$	177.3		$	1,280.40
	Assumed	59.8			943.1			1,002.90
	Gross written premiums	1,162.90			1,120.40			2,283.30
	Ceded	(74.3		)	(243.8		)	(318.1		)
	Net written premiums	$	1,088.60		$	876.6		$	1,965.20
	Earned premiums:
	Direct	$	1,043.30		$	174		$	1,217.30
	Assumed	148.5			938.6			1,087.10
	Gross earned premiums	1,191.80			1,112.60			2,304.40
	Ceded	(71.4		)	(246.2		)	(317.6		)
	Net earned premiums	$	1,120.40		$	866.4		$	1,986.80
	Losses and LAE:
	Direct	$	584.9		$	98.1		$	683
	Assumed	76.3			455.5			531.8
	Gross losses and LAE	661.2			553.6			1,214.80
	Ceded	(39.1		)	(135.2		)	(174.3		)
	Net losses and LAE	$	622.1		$	418.4		$	1,040.50
		Year Ended December 31, 2012
	Millions	OneBeacon			Sirius Group			Total
	Written premiums:
	Direct	$	1,204.00		$	186.1		$	1,390.10
	Assumed	55.2			992.7			1,047.90
	Gross written premiums	1,259.20			1,178.80			2,438.00
	Ceded	(80.0		)	(231.1		)	(311.1		)
	Net written premiums	$	1,179.20		$	947.7		$	2,126.90
	Earned premiums:
	Direct	$	1,158.30		$	169.9		$	1,328.20
	Assumed	52.8			988.3			1,041.10
	Gross earned premiums	1,211.10			1,158.20			2,369.30
	Ceded	(79.1		)	(226.6		)	(305.7		)
	Net earned premiums	$	1,132.00		$	931.6		$	2,063.60
	Losses and LAE:
	Direct	$	687.5		$	96.9		$	784.4
	Assumed	29.6			523.9			553.5
	Gross losses and LAE	717.1			620.8			1,337.90
	Ceded	(67.1		)	(76.9		)	(144.0		)
	Net losses and LAE	$	650		$	543.9		$	1,193.90
		Year Ended December 31, 2011
	Millions	OneBeacon			Sirius Group			Total
	Written premiums:
	Direct	$	1,079.20		$	139.5		$	1,218.70
	Assumed	49.1			988.6			1,037.70
	Gross written premiums	1,128.30			1,128.10			2,256.40
	Ceded	(65.6		)	(212.4		)	(278.0		)
	Net written premiums	$	1,062.70		$	915.7		$	1,978.40
	Earned premiums:
	Direct	$	1,035.90		$	128.5		$	1,164.40
	Assumed	42.3			989.8			1,032.10
	Gross earned premiums	1,078.20			1,118.30			2,196.50
	Ceded	(66.0		)	(206.0		)	(272.0		)
	Net earned premiums	$	1,012.20		$	912.3		$	1,924.50
	Losses and LAE:
	Direct	$	551.8		$	80		$	631.8
	Assumed	9.2			627.8			637
	Gross losses and LAE	561			707.8			1,268.80
	Ceded	(12.7		)	(81.8		)	(94.5		)
	Net losses and LAE	$	548.3		$	626		$	1,174.30
	OneBeacon
In the normal course of business, OneBeacon purchases reinsurance from high-quality, highly rated, third-party reinsurers in order to minimize loss from large losses or catastrophic events.
The timing and size of catastrophe losses are unpredictable and the level of losses experienced in any year could be material to OneBeacon’s operating results and financial position. Examples of catastrophes include losses caused by earthquakes, wildfires, hurricanes and other types of storms and terrorist acts. The extent of losses caused by catastrophes is a function of the amount and type of insured exposure in the area affected by the event as well as the severity of the event. OneBeacon uses models (primarily AIR Worldwide (“AIR”) Classic/2 version 15.0) to estimate the potential losses from catastrophes. OneBeacon uses this model output in conjunction with other data to manage its exposure to catastrophe losses through individual risk selection and by limiting its concentration of insurance written in catastrophe-prone areas such as coastal regions. In addition, OneBeacon imposes wind deductibles on existing coastal windstorm exposures.
Since the terrorist attacks of September 11, 2001, OneBeacon has sought to mitigate the risk associated with any future terrorist attacks by limiting the aggregate insured value of policies in geographic areas with exposure to losses from terrorist attacks. This is accomplished by either limiting the total insured values exposed, or, where applicable, through the use of terrorism exclusions.
In December 2007, the U.S. government extended the Terrorism Risk Insurance Program Reauthorization Act (the “Terrorism Act” or “TRIPRA”) until December 31, 2014. The Terrorism Act established a federal “backstop” for commercial property and casualty losses, including workers compensation, resulting from acts of terrorism by or on behalf of any foreign person or foreign interest. As extended, the law now also covers domestic acts of terrorism. The law limits the industry’s aggregate liability by requiring the federal government to share 85% of certified losses once a company meets a specific retention or deductible as determined by its prior year’s direct written premiums and limits the aggregate liability to be paid by the government and industry without further action by Congress at $100.0 billion. In exchange for this “backstop,” primary insurers are required to make coverage available to commercial insureds for losses from acts of terrorism as specified in the Terrorism Act. The following types of coverage are excluded from the program: commercial automobile, burglary and theft, surety, farmowners multi-peril and all professional liability coverage except directors and officers coverage.
OneBeacon estimates its individual retention level for commercial policies subject to the Terrorism Act to be approximately $100.0 million in 2014. The federal government will pay 85% of covered terrorism losses that exceed OneBeacon’s or the industry’s retention levels in 2014, up to a total of $100.0 billion.
OneBeacon seeks to further reduce its potential loss from catastrophe exposures through the purchase of catastrophe reinsurance. Effective May 1, 2013, OneBeacon renewed its property catastrophe reinsurance program through April 30, 2014. The program provides coverage for OneBeacon’s property business as well as certain acts of terrorism. Under the program, the first $20.0 million of losses resulting from any single catastrophe are retained and $117.0 million of the next $130.0 million of losses resulting from the catastrophe are reinsured in three layers. OneBeacon retains 50% of losses from $20.0 million to $30.0 million, 10% of losses from $30.0 million to $70.0 million, and 5% of losses from $70.0 million to $150.0 million. Thus, for a $150.0 million loss, OneBeacon would retain $33.0 million. Losses above $150.0 million are not covered by the property catastrophe program. In the event of a catastrophe, OneBeacon’s property catastrophe reinsurance program is reinstated for the remainder of the original contract term by paying a reinstatement premium that is based on the percentage of coverage reinstated and the original property catastrophe coverage premium. This $150.0 million limit was reduced from the $180.0 million limit that OneBeacon’s previous catastrophe reinsurance program provided, as a result of lower catastrophe exposure as a specialty-focused company.
OneBeacon’s property catastrophe reinsurance program does not cover property losses resulting from any nuclear events or biological, chemical or radiological terrorist attacks or losses resulting from acts of terrorism as defined under the Terrorism Act, committed by an individual or individuals acting on behalf of any foreign person or foreign interest, as well as domestic acts of terrorism. Such losses are subject to coverage provided to insurance companies by TRIPRA.
OneBeacon purchases property-per-risk reinsurance coverage to reduce large loss volatility. The property-per-risk reinsurance program reinsures losses in excess of $10.0 million up to $100.0 million on certain risks. Individual risk facultative reinsurance is purchased above $100.0 million. OneBeacon retains 5% for losses in excess of $20.0 million up to $40.0 million and 10% of losses in excess of $40.0 million. The property-per-risk treaty also provides one limit of reinsurance protection for losses in excess of $10.0 million up to $100.0 million for acts of foreign terrorism. However, any nuclear events, or biological, chemical or radiological terrorist attacks are not covered.
OneBeacon also maintains a casualty reinsurance program that provides protection for individual policies involving general liability, automobile liability, professional liability or umbrella liability. OneBeacon's healthcare professional liability treaty covers losses in excess of $5.0 million up to $20.0 million in two layers. The first layer, $5.0 million excess of $5.0 million, has a 10% co-participation. All other casualty business is covered in a separate treaty covering losses in excess of $5.0 million up to $21.0 million. This treaty has a 10.0% co-participation in the first layer ($6.0 million in excess of $5.0 million) as well as a $3.0 million aggregate deductible, and a 5% co-participation in the second layer ($10.0 million in excess of $11.0 million). OneBeacon also purchases a treaty to protect against large workers compensation losses that covers 100% of the loss in excess of $1.0 million up to $10.0 million per occurrence. Additionally, for casualty and/or workers compensation catastrophe losses, OneBeacon maintains a dedicated clash treaty that covers up to $60.0 million in excess of a $10.0 million retention.
OneBeacon purchases a per-occurrence treaty for inland and ocean marine business that protects against large occurrences, whether a single large claim or a catastrophe. The marine treaty attaches at $2.0 million per occurrence. The first layer of the marine treaty is $5.0 million in excess of $2.0 million, with annual aggregate deductibles of $1.5 million for individual ocean marine large claims, $1.5 million for individual inland marine large claims and $5.0 million for catastrophe losses. OneBeacon retains 60% of the loss from $2.0 million up to $7.0 million. Catastrophe coverage is provided up to $60.0 million. Retained catastrophe losses are subject to the corporate catastrophe treaty. Individual risk losses from inland marine exceeding $20.0 million are subject to the corporate property per risk treaty. Reinstatement premiums are paid in full or in part depending on the layer and the occurrence if the coverage is attached. OneBeacon also purchases reinsurance for its surety underwriting operating segment which covers 100% of losses in excess of $5.0 million up to $30.0 million per bond and up to $60.0 million in aggregate.
At December 31, 2013, OneBeacon had $9.7 million and $80.2 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.
The following table summarizes Standard & Poor’s Financial Services LLC (“Standard & Poor’s”) ratings for OneBeacon’s reinsurers. The reinsurance balances associated with the Runoff Business are included in discontinued operations (see Note 21).
Standard & Poor’s Rating(1)	Balance at December 31, 2013			% of Total
AA	$	26.4		30	%
A	56.1			62	%
BBB+, Not rated and other	7.4			8	%
Total	$	89.9		100	%
(1)  Standard & Poor’s ratings as detailed above are: “AA” (Very strong), “A” (Strong) and “BBB+” (Adequate).
Sirius Group
Sirius Group's reinsurance protection primarily consists of pro-rata and excess of loss protections to cover A&H, aviation, trade credit, and certain property exposures. Sirius Group's core proportional property reinsurance programs provide protection for parts of the non-proportional treaty accounts written in Europe, the Americas, Asia, the Middle East, and Australia.  These reinsurance protections are designed to increase underwriting capacity where appropriate, and to reduce exposure both to large catastrophe losses and to a frequency of smaller loss events.  Attachment points and coverage limits vary by region around the world. In addition to its proportional reinsurance, Sirius Group also purchases excess of loss reinsurance protection for $15.0 million in excess of a retention of $5.0 million for the facultative and direct property portfolios written by the Stockholm, Hamburg and London branches (excluding business written in the United States).  Syndicate 1945 has a reinsurance cover of $10.0 million in excess of $5.0 million for the facultative and direct property portfolio. An additional $15.0 million of reinsurance protection in excess of the $20.0 million coverage is in place for the facultative and direct property portfolios written by the Hamburg and Stockholm branches. At January 1, 2014, an additional $2.5 million of second loss coverage was purchased for the facultative and direct property portfolios written by the Hamburg, Stockholm and London branches in excess of a retention of $2.5 million. Sirius Group also has $5.0 million of protection in excess of a retention of $5.0 million for the London branch and Syndicate 1945 for facultative and direct U.S.-catastrophe exposed business, which was renewed through June 30, 2014.
Sirius Group has in place excess of loss retrocessional coverage for its non-U.S. and non-Japan earthquake-related exposures. This cover was renewed for one year at April 1, 2013, providing $40.0 million of reinsurance protection in excess of Sirius Group's retention of $35.0 million and a further $15.8 million of partially placed coverage in excess of $75.0 million.
In addition, Sirius Group periodically purchases industry loss warranty (“ILW”) contracts to augment its overall retrocessional program. A European windstorm and flood ILW totaling $7.5 million in coverage and attaching at a market event level of €5.0 billion or greater ($6.9 billion based on the December 31, 2013 EUR to USD exchange rate) was purchased in October 2013 and remains in force throughout 2014. Two additional ILWs were purchased at January 1, 2014, in force through March 31, 2014, totaling $10.0 million in coverage for European windstorm and flood attaching at a market event level of $7.5 billion.
Sirius Group's aviation reinsurance program is intended to reduce exposure to a frequency of small losses, a single large loss, or a combination of both.  For the proportional and facultative aviation portfolios, reinsurance protection purchases are generally for coverage on losses from events that cause a market loss in excess of $150.0 million up to a full policy limit of $2.25 billion. This program is in effect through November 2014. For the non-proportional aviation portfolio, reinsurance protection includes a 15% quota share treaty. In addition, the non-proportional portfolio is protected by ILWs with a limit of $30.5 million. The ILWs attach at industry loss levels between $350.0 million and $1.0 billion.
For the marine yacht portfolio written by the London branch and Syndicate 1945, reinsurance coverage is in place for $9.8 million in excess of a retention of $0.3 million.
For accident and health, Sirius Group has excess of loss protection covering personal accident and life of €10.0 million ($13.8 million based on the December 31, 2013 EUR to USD exchange rate) of protection in excess of a €5.0 million ($6.9 million based on the December 31, 2013 EUR to USD exchange rate) retention for the Stockholm, Hamburg, Liege and Singapore branches. In addition, the Sirius America’s direct insurance portfolio includes quota share reinsurance of various percentages.
For 2013, Sirius Group ceded 20% and 50% of its trade credit and bond business, respectively, under a quota share retrocession, which supported growth in this line.  The treaty was renewed for 2014 at the same cession percentages.
For 2013, Sirius Group also ceded 30% of the direct contingency business written in the London branch and Syndicate 1945 on a proportional basis. The treaty was renewed at January 1, 2014.
Almost all of Sirius Group's excess of loss reinsurance protections, excluding ILWs which tend to cover only one loss event, include provisions that reinstate coverage at a cost of 100% or more of the original reinsurance premium.
At December 31, 2013, Sirius Group had $15.7 million of reinsurance recoverables on paid losses and $347.9 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 gross and net recoverable amounts by the reinsurer’s Standard & Poor’s rating and the percentage of total recoverables.
Rating(1)	Gross			Collateral			Net			% of Net Total
AAA	$	62.9		$	—		$	62.9		19	%
AA	60.6			4.5			56.1			17	%
A	127.5			1.6			125.9			39	%
BBB+	21			—			21			7	%
BBB or lower	16.6			—			16.6			5	%
Not rated	75			31.5			43.5			13	%
Total	$	363.6		$	37.6		$	326		100	%
(1) Standard & Poor’s ratings as detailed above are: “AAA” (Extremely strong), “AA” (Very strong), “A” (Strong), and “BBB+” and “BBB” (Adequate).

Investment_Securities

Investment Securities	12 Months Ended
	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]	'
Investment Securities	'
	Investment Securities
	Net Investment Income
	White Mountains’ net investment income is comprised primarily of interest income associated with White Mountains’ fixed maturity investments, dividend income from its equity investments and interest income from its short-term investments.
	Pre-tax net investment income for 2013, 2012 and 2011 consisted of the following:
			Year Ended December 31,
	Millions		2013				2012				2011
	Investment income:
	Fixed maturity investments		$	100.5			$	132			$	166.2
	Short-term investments		3.4				3.1				4.5
	Common equity securities		20.5				22.2				15.4
	Convertible fixed maturity investments		2.9				6				5.5
	Other long-term investments		3				3.1				4.2
	Interest on funds held under reinsurance treaties		0.3				0.6				(.4		)
	Total investment income		130.6				167				195.4
	Third-party investment expenses		(19.7		)		(13.4		)		(10.9		)
	Net investment income, pre-tax		$	110.9			$	153.6			$	184.5
	Net Realized and Unrealized Investment Gains and Losses
	Net realized and unrealized investment gains and losses consisted of the following:
			Year Ended December 31,
	Millions		2013				2012				2011
	Net realized investment gains, pre-tax		$	104.5			$	68.1			$	68.3
	Net unrealized investment gains, pre-tax		57.2				50.1				5.8
	Net realized and unrealized investment gains, pre-tax		161.7				118.2				74.1
	Income tax expense attributable to net realized and		(21.9		)		(26.8		)		(18.1		)
	unrealized investment gains
	Net realized and unrealized investment gains, after tax		$	139.8			$	91.4			$	56
	Net realized investment gains (losses)
	Net realized investment gains (losses) for 2013, 2012 and 2011 consisted of the following:
			Year ended December 31, 2013
	Millions		Net realized gains (losses)				Net				Total
							foreign				changes in
							exchange				fair value
							gains				reflected in
							(losses)				earnings
	Fixed maturity investments		$	8.6			$	(15.0	)		$	(6.4	)
	Short-term investments		0.1				—				0.1
	Common equity securities		104.5				(3.7		)		100.8
	Convertible fixed maturity investments		1				—				1
	Other long-term investments		7.5				1.4				8.9
	Forward contracts		0.1				—				0.1
	Net realized investment gains (losses), pre-tax		121.8				(17.3		)		104.5
	Income taxes attributable to realized		(30.0		)		5.5				(24.5		)
	investment gains (losses)
	Net realized investment gains (losses), after-tax		$	91.8			$	(11.8	)		$	80
			Year ended December 31, 2012
	Millions		Net realized gains (losses)				Net				Total
							foreign				changes in
							exchange				fair value
							gains				reflected in
							(losses)				earnings
	Fixed maturity investments		$	82.5			$	(2.5	)		$	80
	Short-term investments		—				(4.3		)		(4.3		)
	Common equity securities		1.3				—				1.3
	Convertible fixed maturity investments		(8.2		)		(1.8		)		(10.0		)
	Other long-term investments		1.4				—				1.4
	Forward contracts		(.3		)		—				(.3		)
	Net realized investment gains (losses), pre-tax		76.7				(8.6		)		68.1
	Income taxes attributable to realized		(23.8		)		2.2				(21.6		)
	investment gains (losses)
	Net realized investment gains (losses), after-tax		$	52.9			$	(6.4	)		$	46.5
			Year ended December 31, 2011
	Millions		Net realized gains (losses)				Net				Total
							foreign				changes in
exchange							fair value
gains							reflected in
(losses)							earnings
Fixed maturity investments		$	49.4			$	(38.3	)		$	11.1
Short-term investments		—				(9.9		)		(9.9		)
Common equity securities		34.6				—				34.6
Convertible fixed maturity investments		(2.2		)		—				(2.2		)
Other long-term investments		35.2				(0.5		)		34.7
Net realized investment gains (losses), pre-tax		117				(48.7		)		68.3
Income taxes attributable to realized		(37.0		)		12.8				(24.2		)
investment gains (losses)
Net realized investment gains (losses), after-tax		$	80			$	(35.9	)		$	44.1
Net unrealized investment gains (losses)
The following table summarizes net unrealized investment gains (losses) and changes in the carrying value of investments measured at fair value:
		Year ended December 31, 2013
Millions		Net				Net				Total net unrealized
		unrealized				foreign				gains (losses)
		gains				exchange				reflected in
		(losses)				gains				earnings
						(losses)
Fixed maturity investments		$	(93.9	)		$	15.3			$	(78.6	)
Short-term investments		0.1				—				0.1
Common equity securities		119.2				(0.4		)		118.8
Convertible fixed maturity investments		3.2				—				3.2
Other long-term investments		10.3				3.4				13.7
Forward contracts		—				—				—
Net unrealized investment gains (losses), pre-tax		38.9				18.3				57.2
Income taxes attributable to unrealized		8.2				(5.6		)		2.6
investment gains (losses)
Net unrealized investment gains (losses), after-tax		$	47.1			$	12.7			$	59.8
		Year ended December 31, 2012
Millions		Net				Net				Total net unrealized
		unrealized				foreign				gains (losses)
		gains				exchange				reflected in
		(losses)				gains				earnings
						(losses)
Fixed maturity investments		$	18.5			$	(45.9	)		$	(27.4	)
Short-term investments		—				0.1				0.1
Common equity securities		65.9				(.1		)		65.8
Convertible fixed maturity investments		1.1				—				1.1
Other long-term investments		13.2				(2.7		)		10.5
Net unrealized investment gains (losses), pre-tax		98.7				(48.6		)		50.1
Income taxes attributable to unrealized		(17.9		)		12.7				(5.2		)
investment gains (losses)
Net unrealized investment gains (losses), after-tax		$	80.8			$	(35.9	)		$	44.9
		Year ended December 31, 2011
Millions		Net				Net				Total net unrealized
		unrealized				foreign				gains (losses)
		gains				exchange				reflected in
		(losses)				gains				earnings
						(losses)
Fixed maturity investments		$	7.6			$	68.9			$	76.5
Short-term investments		—				(1.1		)		(1.1		)
Common equity securities		(40.6		)		(1.8		)		(42.4		)
Convertible fixed maturity investments		(11.5		)		—				(11.5		)
Other long-term investments		(19.1		)		3.4				(15.7		)
Net unrealized investment gains (losses), pre-tax		(63.6		)		69.4				5.8
Income taxes attributable to unrealized		24				(17.9		)		6.1
investment gains (losses)
Net unrealized investment gains (losses), after-tax		$	(39.6	)		$	51.5			$	11.9
White Mountains recognized gross realized investment gains of $221.4 million, $162.2 million and $191.6 million and gross realized investment losses of $116.9 million, $94.1 million and $123.3 million on sales of investment securities during 2013, 2012 and 2011. As of December 31, 2013 and 2012, White Mountains reported $20.5 million and $11.4 million in accounts payable on unsettled investment purchases and $12.1 million and $3.9 million in accounts receivable on unsettled investment sales.
The following table summarizes the amount of total gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments for the years ended December 31, 2013, 2012 and 2011.
		Year Ended December 31,
Millions		2013				2012				2011
Fixed maturity investments		$	(2.3	)		$	7.7			$	(12.2	)
Common equity securities		0.9				3				(16.6		)
Convertible fixed maturity investments		—				—				—
Other long-term investments		11.2				7				(16.8		)
Total net unrealized investment gains (losses), pre-tax - Level 3 investments		$	9.8			$	17.7			$	(45.6	)
The components of White Mountains’ net realized and unrealized investment gains (losses), after-tax, as recorded on the statements of operations and comprehensive income were as follows:
		Year Ended December 31,
Millions		2013				2012				2011
Net change in pre-tax unrealized gains (losses) on investments in		$	(106.4	)		$	62.8			$	(63.6	)
unconsolidated affiliates
Income taxes		8.3				(5.1		)		5.1
Net change in unrealized gains (losses) on investments in		(98.1		)		57.7				(58.5		)
unconsolidated affiliates, after tax
Net realized and unrealized foreign currency gains (losses) on		11.3				95.5				(41.7		)
investments through OCI
Total investments gains (losses) through accumulated other		(86.8		)		153.2				(100.2		)
comprehensive income
Net realized and unrealized investment gains, after-tax		139.8				$	91.4			$	56
Total investment gains (losses) recorded during the period, after-tax		$	53			$	244.6			$	(44.2	)
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 December 31, 2013 and 2012, were as follows:
		31-Dec-13
Millions		Cost or				Gross				Gross				Net foreign				Carrying
		amortized				unrealized				unrealized				currency				value
		cost				gains				losses				losses
US Government and agency obligations		$	365.5			$	0.5			$	(1.0	)		$	(2.5	)		$	362.5
Debt securities issued by corporations		2,330.70				44				(13.2		)		(14.3		)		2,347.20
Municipal obligations		18.3				—				(.4		)		—				17.9
Mortgage-backed and asset-backed securities		2,027.30				2.4				(9.9		)		(5.3		)		2,014.50
Foreign government, agency and provincial		444.2				3.7				(3.2		)		(4.8		)		439.9
obligations
Preferred stocks		79.9				5.1				—				(.2		)		84.8
Total fixed maturity investments including		$	5,265.90			$	55.7			$	(27.7	)		$	(27.1	)		$	5,266.80
assets held for sale
Fixed maturity investments reclassified to																		(236.3		)
assets held for sale (1)
Total fixed maturity investments																		$	5,030.50
(1)	Assets held for sale related to discontinued operations. See Note 21.
		31-Dec-12
Millions		Cost or				Gross				Gross				Net foreign				Carrying
		amortized				unrealized				unrealized				currency				value
		cost				gains				losses				gains (losses)
US Government and agency obligations		$	440.4			$	1			$	(.1	)		$	(1.2	)		$	440.1
Debt securities issued by corporations		2,321.40				88.3				(1.6		)		(23.0		)		2,385.10
Municipal obligations		5.3				—				(0.1		)		—				5.2
Mortgage-backed and asset-backed securities		2,081.00				25.1				(1.1		)		(9.4		)		2,095.60
Foreign government, agency and provincial		526.6				6.9				(3.0		)		(8.6		)		521.9
obligations
Preferred stocks		79.9				6.7				—				(.2		)		86.4
Total fixed maturity investments including		$	5,454.60			$	128			$	(5.9	)		$	(42.4	)		$	5,534.30
assets held for sale
Fixed maturity investments reclassified to																		(338.1		)
assets held for sale (1)
Total fixed maturity investments																		$	5,196.20
(1)	Assets held for sale related to discontinued operations. See Note 21.
The weighted average duration of White Mountains’ fixed income portfolio at December 31, 2013 was approximately 2.1 years, including short-term investments, and approximately 2.4 years excluding short-term investments.
The cost or amortized cost and carrying value of White Mountains’ fixed maturity investments and convertible fixed maturity investments at December 31, 2013 is presented below by contractual maturity. Actual maturities could differ from contractual maturities because borrowers may have the right to call or prepay certain obligations with or without call or prepayment penalties.
		31-Dec-13
Millions		Cost or				Carrying
		amortized cost				value
Due in one year or less		$	491.2			$	490.7
Due after one year through five years		2,376.70				2,389.30
Due after five years through ten years		321				322.2
Due after ten years		41.5				45.8
Mortgage-backed and asset-backed securities		2,027.30				2,014.50
Preferred stocks		79.9				84.8
Total		$	5,337.60			$	5,347.30
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 maturity investments and other long-term investments as of December 31, 2013 and 2012 were as follows:
		31-Dec-13
Millions		Cost or				Gross unrealized				Gross unrealized				Net foreign				Carrying
		amortized cost				gains				losses				currency losses				value
Common equity securities		$	890.2			$	271			$	(3.6	)		$	(.8	)		$	1,156.80
Convertible fixed maturity investments		$	71.7			$	9.9			$	(.9	)		$	(.2	)		$	80.5
Other long-term investments		$	238.3			$	79.6			$	(26.6	)		$	(2.4	)		$	288.9
		31-Dec-12
Millions		Cost or				Gross unrealized				Gross unrealized				Net foreign				Carrying
		amortized cost				gains				losses				currency losses				value
Common equity securities		$	895.2			$	143.4			$	(8.8	)		$	(.1	)		$	1,029.70
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
Proceeds from the sales and maturities of investments, excluding short-term investments, totaled $4,924.8 million, $6,997.5 million and $5,034.0 million for the years ended December 31, 2013, 2012 and 2011.
Investments Held on Deposit or as Collateral
As of December 31, 2013 and 2012, investments of $170.4 million and $169.9 million, respectively, were held in trusts required to be maintained in relation to various reinsurance agreements. White Mountains’ consolidated insurance and reinsurance operations are required to maintain deposits with certain insurance regulatory agencies in order to maintain their insurance licenses. The fair value of such deposits which are included within total investments totaled $290.7 million and $319.3 million as of December 31, 2013 and 2012.
As of December 31, 2013 and 2012, OneBeacon held unrestricted collateral from its customers, which is included in cash and invested assets, relating to its surety business of $63.3 million and $5.9 million. The obligation to return these funds is included in funds held under insurance and reinsurance contracts in the consolidated balance sheets.
As of December 31, 2013 and 2012, White Mountains held $23.2 million and $138.7 million of restricted collateral in the form of fixed maturities and $2.0 million and $5.1 million of restricted collateral in the form of short-term investments associated with variable annuity reinsurance and interest rate cap agreements. See Note 8.
Fair value measurements at December 31, 2013
White Mountains used quoted market prices or other observable inputs to determine fair value for the 95% of its investment portfolio. Investments valued using Level 1 inputs include fixed maturity investments, primarily investments in U.S. Treasuries, common equities and short-term investments, which include U.S. Treasury Bills. Investments valued using Level 2 inputs consist of fixed maturity investments including corporate debt, state and other governmental debt, convertible fixed maturity securities and mortgage and asset-backed securities. Fair value estimates for investments that trade infrequently and have few or no observable market prices are classified as Level 3 measurements. Level 3 fair value estimates based upon unobservable inputs include White Mountains’ investments in hedge funds and private equity funds, as well as investments in certain debt securities where quoted market prices are unavailable. White Mountains uses brokers and outside pricing services to assist in determining fair values. For investments in active markets, White Mountains uses the quoted market prices provided by outside pricing services to determine fair value. The outside pricing services used by White Mountains have indicated that if no observable inputs are available for a security, they will not provide a price. In those circumstances, White Mountains estimates the fair value using industry standard pricing models and observable inputs such as benchmark interest rates, 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 value of White Mountains’ investments in hedge funds and private equity funds has 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 $86.3 million and $79.7 million of investment-related liabilities recorded at fair value and included in other liabilities as of December 31, 2013 and 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 December 31, 2013 and 2012 by level. The fair value measurements for derivative assets associated with White Mountains’ variable annuity business are presented in Note 8.
		31-Dec-13
Millions		Fair value				Level 1 Inputs				Level 2 Inputs				Level 3 Inputs
Fixed maturity investments:
U.S. Government and agency obligations		$	362.5			$	295.8			$	66.7			$	—
Debt securities issued by corporations:
Consumer		754.4				—				754.4				—
Financials		434.4				—				434.4				—
Industrial		281.1				—				281.1				—
Communications		265				—				265				—
Utilities		173.6				—				173.6				—
Energy		159.7				—				159.7				—
Basic Materials		149.1				—				149.1				—
Technology		91.2				—				91.2				—
Other		38.7				—				38.7				—
Total debt securities issued by corporations:		2,347.20				—				2,347.20				—
Mortgage-backed and asset-backed securities		2,014.50				—				1,992.50				22
Foreign government, agency and provincial obligations		439.9				44.5				395.4				—
Preferred stocks		84.8				—				13.8				71
Municipal obligations		17.9				—				17.9				—
Total fixed maturity investments (1)		5,266.80				340.3				4,833.50				93
Short-term investments		635.9				621.5				14.4				—
Common equity securities:
Financials		360.4				314.3				—				46.1
Consumer		308.2				308.2				—				—
Industrial		105.4				105.4				—				—
Energy		78.6				78.6				—				—
Technology		60.6				60.6				—				—
Communications		57.1				57.1				—				—
Basic materials		53.4				53.4				—				—
Utilities		34.3				34.3				—				—
Other		98.8				24.5				74.3				—
Total common equity securities		1,156.80				1,036.40				74.3				46.1
Convertible fixed maturity investments		80.5				—				74.4				6.1
Other long-term investments (2)		262.4				—				—				262.4
Total investments		$	7,402.40			$	1,998.20			$	4,996.60			$	407.6
(1)	Carrying value includes $236.3 that is classified as assets held for sale relating to discontinued operations.
(2)	Excludes carrying value of $26.6 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) related to currency forward contracts.
		31-Dec-12
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			$	—
Debt securities issued by corporations:
Consumer		727.1				—				727.1				—
Financials		401.4				1				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				—				54				—
Other		20.9				—				20.9				—
Total debt securities issued by corporations:		2,385.10				1				2,384.10				—
Mortgage-backed and asset-backed securities		2,095.60				—				2,073.50				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)		5,534.30				422.2				5,019.20				92.9
Short-term investments		630.6				630.6				—				—
Common equity securities:
Financials		324.5				286.3				0.9				37.3
Consumer		255.6				255.6				—				—
Basic materials		103.3				103.3				—				—
Energy		101				101				—				—
Technology		55				55				—				—
Utilities		43.6				43.4				0.2				—
Industrial		41.9				41.9				—				—
Communications		35.2				35.2				—				—
Other		69.6				11.2				58.4				—
Total common equity securities		1,029.70				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		$	7,581.30			$	1,985.70			$	5,206.10			$	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 $(.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 December 31, 2013 and 2012:
		Fair Value at
		December 31,
Millions		2013				2012
AAA		$	—			$	—
AA		228.8				193.4
A		1,039.50				1,061.00
BBB		1,075.50				1,116.90
BB		—				7
Other		3.4				6.8
Debt securities issued by corporations(1)		$	2,347.20			$	2,385.10
(1)	Credit ratings are assigned based on the following hierarchy: 1) Standard & Poor’s and 2) 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 both fixed rate CMBS and floating rate CMBS as of December 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.  As of December 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. White Mountains’ investments in hedge funds and private equity funds contain negligible amounts of sub-prime mortgage-backed securities at December 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. White Mountains does not own any collateralized debt obligations, with the exception of $41.8 million of non-agency residential mortgage resecuritization tranches, each a senior tranche in its own right and each collateralized by a single earlier vintage Super Senior or Senior non-agency residential mortgage backed security.
		December 31, 2013												December 31, 2012
Millions		Fair Value				Level 2				Level 3				Fair Value				Level 2				Level 3
Mortgage-backed securities:
Agency:
GNMA		$	512.3			$	512.3			$	—			$	1,013.40			$	1,013.40			$	—
FNMA		81.2				81.2				—				74.6				74.6				—
FHLMC		91.3				91.3				—				55.8				55.8				—
Total Agency(1)		684.8				684.8				—				1,143.80				1,143.80				—
Non-agency:
Residential		125.7				125.7				—				160.6				160.6				—
Commercial		282.3				282.3				—				334.1				334.1				—
Total Non-agency		408				408				—				494.7				494.7				—
Total mortgage-backed securities		1,092.80				1,092.80				—				1,638.50				1,638.50				—
Asset-backed securities:
Credit card receivables		311.4				289.4				22				173.5				151.4				22.1
Vehicle receivables		365				365				—				233.2				233.2				—
Other		245.3				245.3				—				50.4				50.4				—
Total asset-backed securities		921.7				899.7				22				457.1				435				22.1
Total mortgage and asset-backed securities		$	2,014.50			$	1,992.50			$	22			$	2,095.60			$	2,073.50			$	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 December 31, 2013 are as follows:
									Security Issuance Year
Millions		Fair Value				2004			2005				2006				2007				2008				2009			2010		2011		2012		2013
Non-agency RMBS		$	125.7			$	11.9		$	33.4			$	10.8			$	2.1			$	—			$	—		$	33.4	$	—	$	—	$	34.1
Non-agency CMBS		282.3				—			—				8.6				5.7				28.1				—			11.5		31.9		113.8		82.7
Total		$	408			$	11.9		$	33.4			$	19.4			$	7.8			$	28.1			$	—		$	44.9	$	31.9	$	113.8	$	116.8
Non-agency Residential Mortgage-backed Securities
The classification of the underlying collateral quality and the tranche levels of White Mountains’ non-agency RMBS securities are as follows as of December 31, 2013:
Millions		Fair Value				Super Senior(1)				Senior(2)				Subordinate(3)
Prime		$	96.1			$	24.1			$	72			$	—
Non-prime		21.9				—				21.9				—
Sub-prime		7.7				7.7				—				—
Total		$	125.7			$	31.8			$	93.9			$	—
(1)	At issuance, Super Senior, or in the case of resecuritization, the underlying securities, were rated “AAA” by Standard & Poor’s, “Aaa” by Moody’s or “AAA” by Fitch Ratings (“Fitch”) and were senior to other “AAA” or “Aaa” bonds.
(2)	At issuance, Senior, or in the case of resecuritization, the underlying securities, 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 December 31, 2013:
Millions		Fair Value				Super Senior(1)				Senior(2)				Subordinate(3)
Fixed rate CMBS		$	189			$	117.2			$	54.4			$	17.4
Floating rate CMBS		93.3				5.7				28				59.6
Total		$	282.3			$	122.9			$	82.4			$	77
(1)	At issuance, Super Senior, or in the case of resecuritization, the underlying securities, 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, or in the case of resecuritization, the underlying securities, 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.
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 December 31, 2013, White Mountains held investments in 15 hedge funds and 39 private equity funds.  The largest investment in a single fund was $18.3 million at December 31, 2013 and $16.0 million at December 31, 2012. The following table summarizes investments in hedge funds and private equity interests by investment objective and sector at December 31, 2013 and 2012:
		31-Dec-13								December 31, 2012
Millions		Fair Value				Unfunded				Fair Value				Unfunded
						Commitments								Commitments
Hedge funds
Long/short equity		$	62.6			$	—			$	60.3			$	—
Long/short credit & distressed		22.8				—				22.7				—
Long/short equity REIT		18.3				—				16				—
Long/short equity activist		16.8				—				13.6				—
Long bank loan		0.2				—				0.3				—
Long diversified strategies		0.1				—				1.7				—
Total hedge funds		120.8				—				114.6				—
Private equity funds
Energy infrastructure & services		45.9				13.1				36.3				15.6
Multi-sector		23.8				6.5				23.3				5.4
Manufacturing/Industrial		11.2				15.5				9.9				15.1
Private equity secondaries		9.5				3.1				10.5				3.1
Real estate		8.2				3.3				11.6				3.3
Aerospace/Defense/Government		5.8				19.2				2.8				22.2
Healthcare		5.6				2.8				4.3				5.4
International multi-sector, Europe		3.9				2.8				5.1				5
Insurance		2.3				41.3				3				41.3
Venture capital		1.6				0.3				2.2				0.3
Distressed residential real estate		0.4				—				15.8				—
International multi-sector, Asia		—				2.7				0.4				2.7
Total private equity funds		118.2				110.6				125.2				119.4
Total hedge and private equity funds included		$	239			$	110.6			$	239.8			$	119.4
in other long-term investments
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 December 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		30-59 days				60-89 days				90-119 days				120+ days				Total
Redemption frequency		notice				notice				notice				notice
Monthly		$	—			$	—			$	—			$	5.8			$	5.8
Quarterly		29.1				30.2				11.8				8.6				79.7
Semi-annual		—				25.4				—				—				25.4
Annual		0.1				—				9.6				0.2				9.9
Total		$	29.2			$	55.6			$	21.4			$	14.6			$	120.8
Certain of the hedge fund and private equity 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 December 31, 2013, distributions of $3.0 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 December 31, 2013.
White Mountains has also submitted redemption requests for certain of its investments in active hedge funds.  At December 31, 2013, redemptions of $2.1 million are outstanding and are subject to market fluctuations. The date at which such
redemptions will be received is not determinable at December 31, 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 December 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		$	6.9			$	30.8			$	67.6			$	12.9			$	118.2
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 December 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 years ended December 31, 2013 and 2012:
										Level 3 Investments
Millions		Level 1				Level 2				Fixed				Common				Convertible				Other long-term				Total
		Investments				Investments				maturity investments				equity				fixed				investments
														securities				maturity investments
Balance at January 1, 2013		$	1,355.10			$	5,206.10			$	92.9			$	37.3			$	—			$	259.3		(1)	$	6,950.70		(1)(2)(3)
Total realized and unrealized gains (losses)		221.9				(56.9		)		(2.7		)		1				—				18.7				182			(4)
Foreign currency gains (losses) in OCI		(.3		)		12.5				0.3				—				—				(.9		)		11.6
Amortization/Accretion		(1.0		)		(51.2		)		—				—				—				—				(52.2		)
Purchases		862.1				3,689.60				37.9				8.8				—				37.1				4,635.50
Sales		(1,078.9		)		(3,842.8		)		(6.3		)		—				—				(51.8		)		(4,979.8		)
Net change in investments		16				2.7				—				—				—				—				18.7
related to purchases and
sales of consolidated
affiliates
Transfers in		1.8				119.4				90.3				—				6.1				—				217.6
Transfers out		—				(97.2		)		(119.4		)		(1.0		)		—				—				(217.6		)
Balance at		$	1,376.70			$	4,982.20			$	93			$	46.1			$	6.1			$	262.4		(1)	$	6,766.50		(1)(2)(3)
December 31, 2013
(1)	Excludes carrying value of $26.6 and $35.0 at December 31, 2013 and January 1, 2013 associated with other long-term investments accounted for using the equity method and $(.1) at December 31, 2013 related to currency forward contracts.
(2)	Carrying value includes $236.3 and $338.1 at December 31, 2013 and January 1, 2013 that is classified as assets held for sale relating to discontinued operations.
(3)	Excludes carrying value of $635.9 and $630.6 at December 31, 2013 and January 1, 2013 classified as short-term investments.
(4)	Excludes $20.6 of realized and unrealized losses associated with the Prospector Funds consolidation of investment-related liabilities and $.2 of realized and unrealized gains associated with short-term investments.
										Level 3 Investments
Millions		Level 1				Level 2				Fixed				Common				Convertible				Other long-term				Total
		Investments				Investments				maturity investments				equity				fixed				investments
														securities				maturity investments
Balance at January 1, 2012		$	1,033.10			$	6,088.20			$	78.9			$	32.3			$	—			$	268.3		(1)	$	7,500.80		(1)(2)(3)
Total realized and unrealized (losses) gains		52				53.6				8.7				12.4				—				(3.3		)		123.4
Foreign currency gains (losses) in OCI		4.4				81.9				0.8				0.2				—				3.7				91
Amortization/Accretion		(.8		)		(48.0		)		(.8		)		—				—				—				(49.6		)
Purchases		1,216.90				4,927.10				144.4				3.1				—				39.4				6,330.90
Sales		(950.5		)		(5,937.0		)		(99.4		)		(10.1		)		—				(48.8		)		(7,045.8		)
Transfers in		—				62.4				22.1				—				—				—				84.5
Transfers out		—				(22.1		)		(61.8		)		(.6		)		—				—				(84.5		)
Balance at		$	1,355.10			$	5,206.10			$	92.9			$	37.3			$	—			$	259.3		(1)	$	6,950.70		(1)(2)(3)
December 31, 2012
(1)	Excludes carrying value of $35.0 and $33.0 at December 31, 2012 and January 1, 2012 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) at December 31, 2012 related to currency forward contracts.
(2)	Carrying value includes $338.1 and $111.8 at December 31, 2012 and January 1, 2012 that is classified as assets held for sale relating to AutoOne discontinued operations.
(3)	Excludes carrying value of $630.6 and $846.0 at December 31, 2012 and January 1, 2012 classified as short-term investments.
Fair Value Measurements — transfers between levels
During 2013, three fixed maturity securities classified as Level 3 measurements in the prior period were recategorized as Level 2 measurements because quoted market prices for similar securities that were considered reliable and could be validated against an alternative source were available at December 31, 2013.  These measurements comprise “Transfers out” of Level 3 and “Transfers in” to Level 2 of $119.4 million for the period ended December 31, 2013. Included in these transfers is one asset-backed fixed maturity security classified within Level 2 as of June 30, 2013 that was recategorized to Level 3 as of September 30, 2013. The security represents “Transfers out” of Level 2 and “Transfer in” to Level 3 of $90.3 million as of September 30, 2013. As of September 30, 2013, the estimated fair value for this security determined using the industry standard pricing models was $1.3 million less than the estimated fair value based upon quoted prices provided by a third party pricing vendor. As of December 31, 2013, reliable quoted market prices provided by a third party pricing vendor were available for the security and the security was transferred back to Level 2.
During 2012, two fixed maturity securities classified as Level 3 measurements in the prior period were recategorized as Level 2 measurements because quoted market prices for similar securities that were considered reliable and could be validated against an alternative source were available at December 31, 2012. These measurements comprise “Transfers out” of Level 3 and “Transfers in” to Level 2 of $61.8 million for the period ended December 31, 2012. For the year-ended December 31, 2012, “Transfers out” of Level 2 and “Transfers in” to Level 3 fixed maturity investments of $22.1 million consists of one
asset-backed security for which the estimated fair value was determined using a single broker quote.
Significant Unobservable Inputs
The following summarizes significant unobservable inputs used in estimating the fair value of investment securities classified within Level 3 other than hedge funds and private equities at December 31, 2013. The fair value of investments in hedge funds and private equity funds, which are classified within Level 3, are estimated using the net asset value of the funds.
($ in Millions)		December 31, 2013
Description		Fair Value	Rating(2)	Valuation Technique(s)	Unobservable Input
Preferred Stock(1)		$71.00	NR	Discounted cash flow	Discount yield	-	7.40%
Private equity security		$35.60	NR	Multiple of GAAP book value	Book value multiple	-	1
Private equity security		$10.50	NR	Share price of recent transaction	Average share price	-	$1.10
Convertible preferred		$6.10	NR	Share price of recent transaction	Share price of	-	$6.10
securities					recent transaction
Asset-backed securities (1)		$22.00	AA+	Broker pricing	Broker quote
(1)	As of December 31, 2013 each asset type consists of one security.
(2)	Credit ratings are assigned based on the following hierarchy: 1) Standard & Poor’s and 2) Moody’s.

Debt

Debt	12 Months Ended
	Dec. 31, 2013
Debt Disclosure [Abstract]	'
Debt	'
	Debt
	White Mountains’ debt outstanding as of December 31, 2013 and 2012 consisted of the following:
			December 31,
	Millions		2013			2012
	2012 OBH Senior Notes, at face value		$	275		$	275
	Unamortized original issue discount		(.3		)	(.3		)
	2012 OBH Senior Notes, carrying value		274.7			274.7
	SIG Senior Notes, at face value		400			400
	Unamortized original issue discount		(.4		)	(.6		)
	SIG Senior Notes, carrying value		399.6			399.4
	WTM Bank Facility		—			—
	Previous WTM Bank Facility		—			75
	Old Lyme Note		2.1			2.1
	Total debt		$	676.4		$	751.2
	A schedule of contractual repayments of White Mountains’ debt as of December 31, 2013, follows:
	Millions	December 31,
		2013
	Due in one year or less	$	—
	Due in two to three years	2.1
	Due in four to five years	400
	Due after five years	275
	Total	$	677.1
	OBH Senior Notes
	In November 2012, OneBeacon U.S. Holdings, Inc. (“OBH”), an intermediate holding company of OneBeacon, issued $275.0 million face value of senior unsecured notes (“2012 OBH Senior Notes”) through a public offering, at an issue price of 99.9% and received $272.9 million of proceeds. The 2012 OBH Senior Notes bear an annual interest rate of 4.6% payable semi-annually in arrears on May 9 and November 9, until maturity on November 9, 2022, and are fully and unconditionally guaranteed as to the payment of principal and interest by OneBeacon Ltd. OBH incurred $2.8 million in expenses related to the issuance of the 2012 OBH Senior Notes (including $1.8 million in underwriting fees), which have been deferred and are being recognized into interest expense over the life of the 2012 OBH Senior Notes. Taking into effect the amortization of the original issue discount and all underwriting and issuance expenses, the 2012 OBH Senior Notes have an effective yield to maturity of approximately 4.7% per annum.
	In May 2003, OBH issued $700.0 million face value of senior unsecured notes (the “2003 OBH Senior Notes”) through a public offering, at an issue price of 99.7% and received $693.4 million of proceeds. The 2003 OBH Senior Notes had an annual interest rate of 5.875%, payable semi-annually in arrears on May 15 and November 15, until maturity in May 2013. White Mountains fully and unconditionally guaranteed the payment of principal and interest on the 2003 OBH Senior Notes for a fee equal to 25 basis points per annum on the outstanding principal amount of the 2003 OBH Senior Notes. OBH incurred $7.3 million in expenses related to the issuance of the 2003 OBH Senior Notes (including $4.5 million in underwriting fees), which were recognized into interest expense over the life of the 2003 OBH Senior Notes. Taking into effect the amortization of the original issue discount and all underwriting and issuance expenses, the 2003 OBH Senior Notes had an effective yield to maturity of approximately 6.0% per annum.
	In December 2012, the proceeds from the 2012 OBH Senior Notes were utilized to repurchase the remaining $269.8 million of 2003 OBH Senior Notes for $275.9 million, which resulted in a $6.3 million loss, including transaction fees and the write-off of the remaining $0.2 million in unamortized deferred costs and original issue discount at the time of repurchase.
	On April 6, 2011, through a cash tender offer, OBH purchased and retired $150.0 million aggregate principal amount of 2003 OBH Senior Notes for $161.6 million, which resulted in a $12.0 million loss, including transaction fees.
	OBH recorded $13.0 million, $16.9 million and $20.5 million in interest expense on the OBH Senior Notes for the years ended December 31, 2013, 2012 and 2011.
	SIG Senior Notes
	In March 2007, SIG issued $400.0 million face value of senior unsecured notes (“SIG Senior Notes”) at an issue price of 99.715% for net proceeds of $392.0 million after taking into effect both deferrable and non-deferrable issuance costs, including the interest rate lock agreement described below. The SIG Senior Notes were issued in an offering that was exempt from the registration requirements of the Securities Act of 1933. The SIG Senior Notes bear an annual interest rate of 6.375%, payable semi-annually in arrears on March 20 and September 20, until maturity in March 2017.
	SIG incurred $3.6 million in expenses related to the issuance of the SIG Senior Notes (including $2.6 million in underwriting fees), which have been deferred and are being recognized into interest expense over the life of the SIG Senior Notes.
	In anticipation of the issuance of the SIG Senior Notes, SIG entered into an interest rate lock agreement to hedge its interest rate exposure from the date of the agreement until the pricing of the SIG Senior Notes. The agreement was terminated on March 15, 2007 with a loss of $2.4 million, which was recorded in other comprehensive income. The loss is being reclassified from accumulated other comprehensive income over the life of the SIG Senior Notes using the interest method and is included in interest expense. At December 31, 2013, the unamortized balance of the loss remaining in accumulated other comprehensive income was $1.0 million.
	Taking into effect the amortization of the original issue discount and all underwriting and issuance expenses, including the interest rate lock agreement, the SIG Senior Notes yield an effective rate of approximately 6.5% per annum. White Mountains recorded $26.2 million of interest expense, inclusive of amortization of issuance costs and the interest rate lock agreement, on the SIG Senior Notes for each of the years ended December 31, 2013, 2012 and 2011.
	WTM Bank Facility
	On August 14, 2013, White Mountains entered into a revolving credit facility with a syndicate of lenders administered by Wells Fargo Bank, N.A. which has a total commitment of $425.0 million (the “WTM Bank Facility”) and has a maturity date of August 14, 2018 (the “WTM Bank Facility”). The WTM Bank Facility replaced White Mountains’ previous revolving credit facility administered by Bank of America, N.A. which had a total commitment of $375.0 million (the “Previous WTM Bank Facility”).  During 2013, White Mountains borrowed and repaid a total of $50.0 million under the WTM Bank Facility at a blended interest rate of 3.65%. As of December 31, 2013, the WTM Bank Facility was undrawn. White Mountains recorded $0.3 million of interest expense on the WTM Bank Facility for the year ended December 31, 2013.
	During 2013, White Mountains also borrowed and repaid a total of $150.0 million under the Previous WTM Bank Facility at a blended interest rate of 2.83%. White Mountains recorded $2.9 million, $1.7 million and $3.1 million of interest expense on the Previous WTM Bank Facility for the years ended December 31, 2013, 2012 and 2011.
	In December 2012, White Mountains borrowed $150.0 million under the Previous 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.
	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.
	Old Lyme Note
	On December 31, 2011 Sirius Group acquired the runoff loss reserve portfolio of Old Lyme (see Note 2).  As part of the acquisition, Sirius Group entered into a five-year $2.1 million purchase note.  The principal amount of the purchase note is subject to upward adjustments for favorable loss reserve development (up to 50% of $6.0 million) and downward adjustments for any adverse loss reserve development.
	Sierra Note
	In connection with its acquisition of the Sierra Insurance Group Companies (“Sierra Group”) on March 31, 2004, Sirius Group entered into a $62.0 million purchase note (the “Sierra Note”), $58.0 million of which may be adjusted over its six-year term to reflect favorable or adverse loss reserve development on the acquired reserve portfolio and runoff of remaining policies in force (mainly workers compensation business), as well as certain other balance sheet protections. Since inception the principal of the Sierra Note had been reduced by $29.0 million as a result of adverse development on the acquired reserves and runoff of unearned premium, which includes $5.2 million and $22.8 million of adverse development which occurred during 2008 and 2005 and $1.9 million and $9.1 million of favorable development in 2010 and 2007. Interest accrued on the unpaid balance of the Sierra Note at a rate of 4.0% per annum, compounded quarterly, and was payable at its maturity.
	On October 31, 2008, White Mountains transferred its interest in the Sierra Group to Berkshire Hathaway Inc. (“Berkshire”). White Mountains was still obligated to repay the Sierra Note, but Berkshire provided White Mountains an indemnity, whereby Berkshire reimbursed White Mountains all amounts due under the Sierra Note at its maturity, as adjusted for future reserve development, except for the portion of interest on the Sierra Note that accrued from its issue date through December 31, 2007, plus interest on this accrued amount through the date of repayment.
	The Sierra Note matured on March 31, 2010.  However, the final amount due was in dispute with respect to the amount of loss reserve development.  On September 15, 2010, White Mountains paid Sierra the undisputed amounts owed of $42.8 million on the Sierra Note which consisted of $33.0 million for the principal repayment and $9.8 million for accrued interest.  Berkshire reimbursed White Mountains $36.7 million, which consisted of the $33.0 million principal balance and $3.7 million for accrued interest.
	During the fourth quarter of 2011, the dispute was settled through arbitration.  White Mountains paid additional interest accrued on the Sierra Note and recognized $5.5 million of interest expense.
	Debt Covenants
	At December 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.
	Interest
	Total interest expense incurred by White Mountains for its indebtedness was $42.5 million, $44.8 million and $55.2 million in 2013, 2012 and 2011. Total interest paid by White Mountains for its indebtedness was $42.6 million, $44.6 million, and $59.0 million in 2013, 2012 and 2011.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 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.
	The total income tax benefit (expense) for the years ended December 31, 2013, 2012 and 2011 consisted of the following:
			Year Ended December 31,
	Millions		2013			2012			2011
	Current tax (expense) benefit:
	U.S. federal		$	(19.0	)	$	8.2		$	36.3
	State		(1.4		)	(3.4		)	(2.4		)
	Non-U.S.		(16.5		)	(5.9		)	5.1
	Total current tax (expense) benefit		(36.9		)	(1.1		)	39
	Deferred tax (expense) benefit:
	U.S. federal		(24.4		)	(55.5		)	(43.7		)
	State		—			—			—
	Non-U.S.		(15.3		)	72.3			114.7
	Total deferred tax (expense) benefit		(39.7		)	16.8			71
	Total income tax (expense) benefit		$	(76.6	)	$	15.7		$	110
	Effective Rate Reconciliation
	A reconciliation of taxes calculated using the 35% U.S. statutory rate (the tax rate at which the majority of White Mountains’ worldwide operations are taxed) to the income tax (expense) benefit on pre-tax income follows:
			Year Ended December 31,
	Millions		2013			2012			2011
	Tax (expense) benefit at the U.S. statutory rate		$	(120.7	)	$	(92.0	)	$	(34.3	)
	Differences in taxes resulting from:
	Non-U.S. earnings, net of foreign taxes		82.9			43			6.2
	Change in valuation allowance		(33.6		)	(14.1		)	128.2
	Tax reserve adjustments		(10.2		)	(1.3		)	4.3
	Purchase of subsidiaries		5.3			5.1			—
	Tax exempt interest and dividends		3.2			3.1			2.9
	Withholding tax		(1.7		)	(2.9		)	0.2
	Tax rate change enacted in Sweden		—			65.4			—
	Tax rate change enacted in Luxembourg		—			7.2			1.2
	Other, net		(1.8		)	2.2			1.3
	Total income tax (expense) benefit on pre-tax income		$	(76.6	)	$	15.7		$	110
	In 2012, new tax legislation was enacted in Sweden, which was effective January 1, 2013, that reduces the corporate tax rate from 26.3% to 22.0%. This resulted in a reduction of $65.4 million in Sirius Group’s net deferred tax liabilities in Sweden.
	The non-U.S. component of pre-tax income was $294.3 million, $250.0 million and $65.4 million for the years ended December 31, 2013, 2012 and 2011.
	Tax Payments and Receipts
	Net income tax payments to (receipts from) national governments (primarily the United States) totaled $13.9 million, $17.5 million, and $12.5 million for the years ended December 31, 2013, 2012 and 2011.
	Deferred Tax Inventory
	Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts for tax purposes.
	An outline of the significant components of White Mountains’ deferred tax assets and liabilities follows:
			December 31,
	Millions		2013			2012
	Deferred income tax assets related to:
	Non-U.S. net operating loss carryforwards		$	520.6		$	511.9
	U.S. federal net operating and capital loss carryforwards		148.6			164.8
	Loss reserve discount		74.9			88.6
	Incentive compensation		53.9			36.8
	Unearned premiums		38.9			45.5
	Runoff Transaction		24.2			49.3
	Tax credit carryforwards		23.1			17
	Deferred compensation		10.3			10.4
	Fixed assets		4.9			2.8
	Accrued interest		1.1			8
	Pension and benefit accruals		—			10.3
	Other items		6.9			5.7
	Total gross deferred income tax assets		907.4			951.1
	Less: valuation allowances		(289.8		)	(254.0		)
	Total net deferred income tax assets		617.6			697.1
	Deferred income tax liabilities related to:
	Safety reserve		357.2			326.7
	Net unrealized investment gains		44.6			54.2
	Deferred acquisition costs		33			49.8
	Purchase accounting		7.2			9.5
	Members surplus contributions		5.4			0.1
Pension and benefit accruals		3.4			—
Investment basis difference		3			21
Other items		7.9			7.5
Total deferred income tax liabilities		461.7			468.8
Net deferred tax asset		$	155.9		$	228.3
White Mountains’ deferred tax assets are net of U.S. federal, state, and non-U.S. valuation allowances and, to the extent they relate to non-U.S. jurisdictions, they are shown at year-end exchange rates.
Of the $155.9 million net deferred tax asset at December 31, 2013, $193.1 million relates to net deferred tax assets in U.S. subsidiaries, $315.7 million relates to net deferred tax assets in Luxembourg subsidiaries, $3.3 million relates to net deferred tax assets in United Kingdom subsidiaries and $356.2 million relates to net deferred tax liabilities in Sweden subsidiaries.
Valuation Allowance
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.  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.
Of the $289.8 million valuation allowance at December 31, 2013, $195.8 million relates to deferred tax assets on net operating losses in Luxembourg subsidiaries (discussed under “Net Operating Loss and Capital Loss Carryforwards”), $93.7 million relates to deferred tax assets on U.S. losses and other federal deferred tax benefits, and $0.3 million relates to net operating losses in the Netherlands subsidiaries. Of the $254.0 million valuation allowance at December 31, 2012, $192.0 million relates to deferred tax assets on net operating losses in Luxembourg subsidiaries and $62.0 million relates to deferred tax assets on U.S. losses and other federal deferred tax benefits.
Luxembourg
During 2013, White Mountains recorded a net tax expense of $1.4 million which consisted of a tax benefit of $16.7 million from the release of valuation allowances against deferred tax assets and a tax expense of $18.1 million to establish valuation allowances against deferred tax assets related to additional net operating loss carryforwards at certain Luxembourg-domiciled subsidiaries.
During the fourth quarter of 2012, White Mountains recorded net tax benefits of $41.3 million from the net release of valuation allowances against deferred tax assets in Luxembourg-domiciled subsidiaries.  These companies had built up substantial deferred tax assets due to net operating loss carryforwards.  The loss carryforwards primarily relate to tax deductible write downs in 2007 and 2008 of investments in U.S. subsidiaries. There were partial valuation allowances on these deferred tax assets in periods prior to the fourth quarter of 2012 because the companies did not expect sufficient future taxable income to utilize them.
During the fourth quarter of 2012, Sirius Group undertook a series of reorganizations to optimize operational and capital efficiency.  As part of the reorganizations, investments and outstanding internal debt instruments were contributed to Luxembourg-domiciled subsidiaries with net operating loss carryforwards. One of the companies, S.I. Holdings (Luxembourg) S.à r.l., (“SI Holdings”) (formerly OneBeacon Holdings (Luxembourg) S.à r.l.), was acquired from OneBeacon on January 24, 2012.  As the plan for the Sirius Group to acquire SI Holdings and contribute the notes was in place on December 31, 2011, and this was a transaction between entities under common control, White Mountains accounted for the tax effects of the transaction as if it had occurred in 2011. An investment portfolio was contributed to SI Holdings in January 2013, pursuant to a plan in place on December 31, 2012, that will generate income utilizing the deferred tax asset over an extended period of time. The deferred tax assets for the remaining net operating loss carryforwards at the companies are offset by a valuation allowance as no additional taxable income is expected.
United States
During 2013, White Mountains recorded tax expense of $16.6 million to establish a valuation allowance against deferred tax assets of Guilford Holdings, Inc. and subsidiaries (“Guilford”), as White Mountains management does not anticipate sufficient taxable income to utilize the deferred tax assets.  Guilford consists of service companies that are included in the Other Operations segment.
During the fourth quarter 2012, White Mountains recorded tax expense of $3.9 million to establish a valuation allowance against deferred tax assets related to foreign tax credit carryforwards at Sirius Re Holdings, Inc. and subsidiaries (“SRHI”) that expire in 2016 and 2017. SRHI is no longer expected to generate sufficient taxable income to utilize these credits. SRHI has an additional $5.2 million of foreign tax credits that expire in 2018-2022 that are still expected to be utilized.
During 2013, White Mountains recorded tax expense of $21.3 million to establish valuation allowances against deferred tax assets of BAM as it is uncertain if these companies will have sufficient taxable income to utilize their deferred tax assets. Also during 2013, BAM has income in other comprehensive income that is available to offset its loss from continuing operations, as a result, BAM recorded a tax benefit of $5.4 million in continuing operations, with an offsetting tax expense in other comprehensive income. However, since BAM is a mutual insurance company that is owned by its members, its results do not affect White Mountains’ common shareholders’ equity as they are attributable to non-controlling interests.
During 2013, Houston General Insurance Exchange (“Houston General Insurance”) recorded tax benefit of $6.0 million to reduce a valuation allowance primarily due to the restructuring of a surplus note. Houston General Insurance is a reciprocal which is included in the Company’s consolidated results as a variable interest entity. See Note 17.
Net Operating Loss and Capital Loss Carryforwards
Net operating loss and capital loss carryforwards as of December 31, 2013, the expiration dates and the deferred tax assets thereon are as follows:
		31-Dec-13
Millions		United States			Luxembourg			Sweden			Netherlands			UK		Total
2013		$	—		$	—		$	—		$	—		$	—	$	—
2014 - 2018		—			—			—			0.5			—		0.5
2019 - 2023		11.2			—			—			0.6			—		11.8
2024 - 2033		429.8			—			—			—			—		429.8
No expiration date		—			1,750.00			62.3			—			15.6		1,827.90
Total		$	441		$	1,750.00		$	62.3		$	1.1		$	15.6	$	2,270.00
Gross deferred tax asset		$	148.6		$	511.3		$	5.8		$	0.3		$	3.2	$	669.2
Valuation allowance		(58.3		)	(195.7		)	—			(.3		)	—		(254.3		)
Net deferred tax asset		$	90.3		$	315.6		$	5.8		$	—		$	3.2	$	414.9
White Mountains expects to utilize net operating loss carryforwards in Luxembourg of $1,284.1 million but does not expect to utilize the remainder as they belong to companies that are not expected to have sufficient income in the future.  These losses primarily relate to tax deductible write-downs in 2007 and 2008 of investments in U.S. subsidiaries held by Luxembourg subsidiaries.  Included in the U.S. net operating loss carryforwards are losses of $18.2 million subject to an annual limitation on utilization under Internal Revenue Code Section 382.  At December 31, 2013, there are U.S. foreign tax credit carryforwards available of $11.6 million, which begin to expire in 2016.  As discussed above, a deferred tax valuation allowance of $3.9 million is established against these credits. At December 31, 2013, there are U.S. alternative minimum tax credit carryforwards of $11.5 million which do not expire.
Uncertain Tax Positions
Recognition of the benefit of a given tax position is based upon whether a company determines that it is more likely than not that a tax position will be sustained upon examination based upon the technical merits of the position. In evaluating the more-likely-than-not recognition threshold, White Mountains must presume that the tax position will be subject to examination by a taxing authority with full knowledge of all relevant information. If the recognition threshold is met, then the tax position is measured at the largest amount of benefit that is more than 50% likely of being realized upon ultimate settlement.
A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows:
Millions		Permanent			Temporary			Interest and			Total
		Differences(1)			Differences(2)			Penalties(3)
Balance at January 1, 2011		$	14.5		$	75.1		$	6.2		$	95.8
Changes in prior year tax positions		(.9		)	0.1			2			1.2
Tax positions taken during the current year		—			(20.4		)	—			(20.4		)
Lapse in statute of limitations		(3.4		)	(5.7		)	(1.4		)	(10.5		)
Settlements with tax authorities		(.6		)	—			—			(.6		)
Balance at December 31, 2011		9.6			49.1			6.8			65.5
Changes in prior year tax positions		0.5			—			1.4			1.9
Tax positions taken during the current year		—			(20.2		)	—			(20.2		)
Settlements with tax authorities		(.4		)	—			(.2		)	(.6		)
Balance at December 31, 2012		9.7			28.9			8			46.6
Changes in prior year tax positions		0.6			(7.1		)	1.7			(4.8		)
Tax positions taken during the current year		7.9			0.7			—			8.6
Settlements with tax authorities		—			—			(.4		)	(.4		)
Balance at December 31, 2013		$	18.2		$	22.5		$	9.3		$	50
(1)	Represents the amount of unrecognized tax benefits that, if recognized, would impact the effective tax rate.
(2)	Represents the amount of unrecognized tax benefits that, if recognized would create a temporary difference between the reported amount of an item in the Company’s Consolidated Balance Sheet and its tax basis.
(3)	Net of tax benefit.
If White Mountains determines in the future that its reserves for unrecognized tax benefits on permanent differences and interest and penalties are not needed, the reversal of $27.5 million of such reserves at December 31, 2013 would be recorded as an income tax benefit and would impact the effective tax rate. If White Mountains determines in the future that its reserves for unrecognized tax benefits on temporary differences are not needed, the reversal of $22.5 million of such reserves at December 31, 2013 would not impact the effective tax rate due to deferred tax accounting but would accelerate the payment of cash to the taxing authority. The vast majority of White Mountains’ reserves for unrecognized tax benefits on temporary differences relate to deductions for loss reserves where the timing of the deductions is uncertain. The Company expects that the gross amount of unrecognized tax benefits will decrease by $5.2 million within the next twelve months due to the Company’s resolution of its 2005 and 2006 IRS examination for certain subsidiaries of OneBeacon.
White Mountains classifies all interest and penalties on unrecognized tax benefits as part of income tax expense. During the years ended December 31, 2013, 2012 and 2011, White Mountains recognized $1.3 million, $1.2 million, $0.6 million in interest expense, net of any tax benefit. The balance of accrued interest at December 31, 2013 and 2012 is $9.3 million and $8.0 million, net of any tax benefit.
Tax Examinations
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 concluded an examination of income tax returns for 2005 and 2006 for certain U.S. subsidiaries of OneBeacon. On February 14, 2014, White Mountains received Form 870-AD (Offer to Waive Restrictions on Assessment and Collection Tax Deficiency and to Accept Over Assessment) from the IRS Appeals Office relating to the examination of tax years 2005 and 2006. All disputed items have been agreed to and resolved with the Joint Committee. The total assessment, including interest, is $3.3 million. However, $2.7 million of the 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 the deduction in the exam period will not affect the effective tax rate. As the receipt of the Form 870-AD described above represents formal settlement, White Mountains expects to record a tax benefit of approximately $5.0 million in the first quarter of 2014 relating to the settlement of the IRS examination for tax years 2005 and 2006.
On July 28, 2011, the IRS commenced an examination of the income tax returns 2007, 2008 and 2009 for certain U.S. subsidiaries of OneBeacon. On July 17, 2013, White Mountains received a revised 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 $68.3 million. However, $60.2 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 the deduction 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 September 2, 2013, the IRS commenced an examination of the income tax returns 2010, 2011 and 2012 for certain U.S. subsidiaries of OneBeacon. White Mountains does not expect the resolution of this examination to result in a material change to its financial position, results of operations and cash flows.

Derivatives

Derivatives	12 Months Ended
	Dec. 31, 2013
Derivative [Line Items]	'
Derivatives	'
	Derivatives
Variable Annuity Reinsurance	'
Derivative [Line Items]	'
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 December 31, 2013, the total guarantee value was approximately ¥203.6 billion (approximately $1.9 billion at exchange rates on that date).  The collective account values of the underlying variable annuities were approximately 104% of the guarantee value at December 31, 2013.
	The following table summarizes the pre-tax operating results of WM Life Re for the years ended December 31, 2013, 2012 and 2011:
			Year Ended December 31,
	Millions		2013				2012			2011
	Fees, included in other revenue		$	25			$	31.8		$	32.5
	Change in fair value of variable annuity liability, included in other revenue		378.5				312.8			(156.5		)
	Change in fair value of derivatives, included in other revenue		(402.0		)		(339.0		)	92.9
	Foreign exchange, included in other revenue		(14.5		)		(30.3		)	15.1
	Other investment income and (losses) gains		(7.1		)		2.5			(.9		)
	Total revenues		(20.1		)		(22.2		)	(16.9		)
	Change in fair value of variable annuity death benefit liabilities, included in		10.2				14.2			(1.8		)
	general and administrative expenses
	Death benefit claims paid, included in general and administrative expenses		(1.9		)		(5.7		)	(3.8		)
	General and administrative expenses		(4.9		)		(5.2		)	(4.7		)
	Pre-tax loss		$	(16.7	)		$	(18.9	)	$	(27.2	)
	During 2013, the ratio of annuitants’ aggregate account values to the aggregate guarantee value provided by WM Life Re increased, and as a result, annuitants have been surrendering their policies at higher rates than WM Life Re has observed in the past. In response to this trend, WM Life Re adjusted the projected surrender assumptions used in the valuation of its variable annuity reinsurance liability upward. For the year ended December 31, 2013, the change in the fair value of the variable annuity liability included $6.5 million of gains associated with changes in projected surrender assumptions. There was no change in projected surrender assumptions in 2012. For the year ended December 31, 2011, the change in the fair value of the variable annuity liability included $7.2 million of losses associated with changes in projected surrender assumptions.
	All of White Mountains’ variable annuity reinsurance liabilities were classified as Level 3 measurements at December 31, 2013.
	The following summarizes realized and unrealized gains (losses) recognized in other revenues for the years ended December 31, 2013, 2012 and 2011 and the carrying values at December 31, 2013 and 2012 by type of derivative instrument:
														Carrying Value
			Year Ended December 31,											December 31,
	Millions		2013				2012			2011				2013				2012
	Fixed income/interest rate		$	(108.7	)		$	(149.5	)	$	8.9			$	(9.7	)		$	27.1
	Foreign exchange		(96.7		)		(102.3		)	29.5				58				52.8
	Equity		(196.6		)		(87.2		)	54.5				20.9				18.4
	Total		$	(402.0	)		$	(339.0	)	$	92.9			$	69.2			$	98.3
	The following table summarizes the changes in White Mountains’ variable annuity reinsurance liabilities and derivative instruments for the year ended December 31, 2013, 2012 and 2011:
			Variable Annuity				Derivative Instruments
			(Liabilities)
	Millions		Level 3				Level 3(1)			Level 2(1)(2)				Level 1(3)				Total(4)
	Balance at January 1, 2013		$	(441.5	)		$	140.5		$	(20.5	)		$	(21.7	)		$	98.3
	Purchases		—				59.4			—				—				59.4
	Realized and unrealized gains (losses)		388.7			(5)	(136.5		)	(196.1		)		(69.4		)		(402.0		)
	Transfers in (out)		—				—			—				—				—
	Sales/settlements		—				—			221.3				92.2				313.5
	Balance at December 31, 2013		$	(52.8	)		$	63.4		$	4.7			$	1.1			$	69.2
			Variable Annuity				Derivative Instruments
			(Liabilities)
	Millions		Level 3				Level 3(1)			Level 2(1)(2)				Level 1(3)				Total(4)
	Balance at January 1, 2012		$	(768.5	)		$	247.1		$	39.2			$	4.1			$	290.4
	Purchases		—				6.1			—				—				6.1
	Realized and unrealized (losses) gains		327			(5)	(84.0		)	(186.9		)		(68.1		)		(339.0		)
	Transfers in (out)		—				—			—				—				—
	Sales/settlements		—				(28.7		)	127.2				42.3				140.8
	Balance at December 31, 2012		$	(441.5	)		$	140.5		$	(20.5	)		$	(21.7	)		$	98.3
			Variable Annuity				Derivative Instruments
			(Liabilities)
	Millions		Level 3				Level 3(1)			Level 2(1)(2)				Level 1(3)				Total(4)
	Balance at January 1, 2011		$	(610.2	)		$	275.3		$	72.2			$	—			$	347.5
	Purchases		—				5			—				—				5
	Realized and unrealized (losses) gains		(158.3		)	(5)	14.5			67.7				10.7				92.9
	Transfers in (out)		—				—			—				—				—
	Sales/settlements		—				(47.7		)	(100.7		)		(6.6		)		(155.0		)
	Balance at December 31, 2011		$	(768.5	)		$	247.1		$	39.2			$	4.1			$	290.4
	(1)	Consists of over-the-counter instruments.
	(2)	Consists of interest rate swaps, total return swaps, foreign currency forward contracts, and bond forwards. Fair value measurement based upon bid/ask pricing quotes for similar instruments that are actively traded, where available.  Swaps for which an active market does not exist have been priced using observable inputs including the swap curve and the underlying bond index.
	(3)	Consists of exchange traded equity index, foreign currency and interest rate futures. Fair value measurements based upon quoted prices for identical instruments that are actively traded.
	(4)	In addition to derivative instruments, WM Life Re held cash, short-term and fixed maturity investments of $81.3, $393.6 and $485.3 at December 31, 2013, 2012 and 2011 posted as collateral to its reinsurance counterparties.
	(5)	Includes $10.2, $14.2, $(1.8) for December 31, 2013, 2012 and 2011 related to the change in the fair value of variable annuity death benefit liabilities, which are included in general and administrative expenses.
	In addition, WM Life Re held cash and short-term investments posted as collateral to its variable annuity reinsurance and derivatives counterparties. The total collateral includes the following:
			December 31,
	Millions		2013				2012
	Cash		$	56.1			$	249.8
Short-term investments		2				5.1
Fixed maturity investments		23.2				138.7
Total		$	81.3			$	393.6
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 December 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. 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)		December 31, 2013
Description		Fair				Valuation		Unobservable Input	Range					Weighted Average
		Value				Technique(s)
Variable annuity benefit guarantee liabilities		$	52.8			Discounted cash flows		Surrenders
								0-1 year	0.3	%	-	30.00%		21	%
								1-2 years	0.2	%	-	32.00%		15.8	%
								2-3 years	0.1	%	-	14.00%		6.2	%
								Mortality	0	%	-	5.30%		1	%
								Foreign exchange volatilities
								0-1 year	11.6	%	-	14.00%		12.5	%
								1-2 years	12.9	%	-	15.00%		13.7	%
								2-3 years	13.5	%	-	16.30%		14.3	%
								Index volatilities
								0-1 year	16.4	%	-	19.50%		17.9	%
								1-2 years	17.6	%	-	20.10%		19.4	%
								2-3 years	18.9	%	-	21.90%		21.9	%
Foreign Exchange Options		$	32.6			Counterparty valuations, adjusted for unwind quote discount		Adjustment to counterparty valuations	(1.2	)%	-	8.00%		2.4	%
Equity Index Options		$	30.8			Counterparty valuations, adjusted for unwind quote discount		Adjustment to counterparty valuations	0.50%		-	9.70%		3.4	%
WM Life Re enters into both over-the-counter (“OTC”) and exchange traded derivative instruments to economically hedge the liability from the variable annuity benefit guarantee.  In the case of OTC derivatives, WM Life Re has exposure to credit risk for amounts that are uncollateralized by counterparties. WM Life Re’s internal risk management guidelines establish net counterparty exposure thresholds that take into account OTC counterparties’ credit ratings. 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:
		December 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		$	2.4			$	(11.7	)	$	(9.3	)		$	52.6			$	(26.9	)	$	25.7
Exchange traded		1				(1.6		)	(.6		)		1.6				(.2		)	1.4
Foreign exchange contracts
OTC		67.8				(12.0		)	55.8				87.8				(34.4		)	53.4
Exchange traded		2.3				—			2.3				0.8				(1.4		)	(.6		)
Equity contracts
OTC		30.7				(9.2		)	21.5				63.6				(22.9		)	40.7
Exchange traded		1.8				(2.3		)	(.5		)		0.1				(22.4		)	(22.3		)
Total(2)		$	106			$	(36.8	)	$	69.2			$	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:
		31-Dec-13
Millions		Net amount of assets reflected in Balance Sheet				Collateral provided to counterparty - Cash			Collateral provided to counter-party - Financial Instruments				Net amount of exposure after effect of collateral provided				Excess collateral provided to counter-party- Cash			Excess collateral provided - Financial Instruments			Counter-party collateral held by WM Life Re - Cash		Net amount of exposure to counter-party		Standard
																											& Poor's
																											Rating(1)
JP Morgan		$	9.1			$	—		$	—			$	9.1			$	22		$	—		$	—	$	31.1	A	+
Bank of America		27.2				—			—				27.2				—			—			—		27.2		A
Nomura		(.4		)		—			0.4				—				—			22.8			0.8		22		BBB	+
Citigroup - OTC		19.4				—			—				19.4				2.3			—			—		21.7		A
Citigroup - Exchange Traded		1.2				—			—				1.2				19.8			—			—		21		A
Royal Bank of Scotland		11.3				—			—				11.3				—			—			—		11.3		A	-
Barclays		1.4				—			—				1.4				—			—			—		1.4		A
Total		$	69.2			$	—		$	0.4			$	69.6			$	44.1		$	22.8		$	0.8	$	135.7
		31-Dec-12
Millions		Net amount of assets reflected in Balance Sheet				Collateral provided to counter-party - Cash			Collateral provided to counter-party - Financial Instruments				Net amount of exposure after effect of collateral provided				Excess collateral provided to counter-party- Cash			Excess collateral provided - Financial Instruments			Counter-party collateral held by WM Life Re- Cash		Net amount of exposure to counter-party		Standard
																											& Poor's
																											Rating(1)
Citigroup - OTC		$	19.9			$	—		$	—			$	19.9			$	30.8		$	—		$	—	$	50.7	A
Bank of America		78.5				—			—				78.5				—			—			30.6		47.9		A
Royal Bank of Scotland		33.6				—			—				33.6				—			—			—		33.6		A
JP Morgan		(22.8		)		22.8			—				—				32.8			—			—		32.8		A	+
Nomura		(.9		)		0.9			—				—				0.8			28			—		28.8		BBB	+
Citigroup - Exchange Traded		(21.5		)		21.5			—				—				13.6			—			—		13.6		A
Barclays		11.6				—			—				11.6				—			—			—		11.6		A	+
Goldman Sachs		(.1		)		0.1			—				—				3.1			—			—		3.1		A	-
Total		$	98.3			$	45.3		$	—			$	143.6			$	81.1		$	28		$	30.6	$	222.1
(1)	Standard & Poor’s ratings as detailed above are:  “A+” (Strong, which is the fifth highest of twenty-one creditworthiness ratings),“A” (which is the sixth highest of twenty-one creditworthiness ratings), “A-” (which is the seventh highest of twenty-one creditworthiness ratings), and BBB+ (which is the eighth highest of twenty-one creditworthiness ratings).
Forward contracts	'
Derivative [Line Items]	'
Derivatives	'
	Forward Contracts
	White Mountains is exposed to foreign currency risk related to Sirius International as its functional currency is the Swedish krona (SEK). In addition, Sirius International holds net assets denominated in euros (EUR), British pound sterling (GBP), and U.S. Dollars (USD). Beginning in September 2012, White Mountains entered into forward contracts through a twelve month trial program with a third-party currency specialist manager to determine whether purchasing external forward currency contracts would improve the management of foreign currency exposure 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 December 31, 2013, White Mountains held approximately $20.4 million (SEK 131.3 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 December 31, 2013.
	The following tables summarize the changes in White Mountains’ forward contracts for the year ended December 31, 2013 and 2012:
	Millions		December 31, 2013				December 31, 2012
	Beginning of period		$	(.1	)		$	—
	Purchases		—				—
	Realized and unrealized losses		(.1		)		(.3		)
	Sales/settlements		0.1				0.2
	End of period		$	(.1	)		$	(.1	)
	The following summarizes realized and unrealized derivative gains (losses) recognized in net realized and unrealized investment gains and the carrying values, included in other long-term investments, at December 31, 2013 and 2012 by type of currency:
			December 31, 2013							December 31, 2012
	Millions		Gains (Losses)				Carrying Value			Gains (Losses)				Carrying Value
	USD		$	(.2	)		$	—		$	(.2	)		$	—
	SEK		—				—			—				—
	EUR		0.1				(.1		)	(.1		)		(.1		)
	GBP		—				—			—				—
	Total		$	(.1	)		$	(.1	)	$	(.3	)		$	(.1	)
	All of White Mountains’ forward contracts are subject to master netting agreements. The following summarizes amounts offset under master netting agreements:
			December 31, 2013											December 31, 2012
	Millions		Gross asset				Gross liability amounts offset under master netting arrangements			Net amounts recognized in investments				Gross asset				Gross liability amounts offset under master netting arrangements			Net amounts recognized in investments
			amounts before											amounts before
			offsets(1)											offsets(1)
	USD		$	—			$	—		$	—			$	—			$	—		$	—
	EUR		—				(.1		)	(.1		)		—				(.1		)	(.1		)
	GBP		—				—			—				—				—			—
	Total		$	—			$	(.1	)	$	(.1	)		$	—			$	(.1	)	$	(.1	)
	(1)	Amount equal to fair value of instrument as recognized in investments.
	White Mountains does not hold or provide any collateral for the forward contracts.  The following table summarizes the notional amounts and the uncollateralized balances associated with forward currency contracts by counterparty:
			31-Dec-13									31-Dec-12
	Millions		Notional Amount				Carrying Value			Standard & Poor's		Notional Amount				Carrying Value
										Rating(1)
	Barclays Bank Plc		$	5.8			$	—		A		$	7.7			$	(.1	)
	Deutsche Bank		7.7				—			A		11.1				—
	Goldman Sachs		2.1				—			A-		0.4				—
	HSBC		3.3				(.1		)	AA-		10.1				—
	JP Morgan		1.3				—			A+		1.9				—
	Royal Bank of Canada		0.2				—			AA-		—				—
	Total		$	20.4			$	(.1	)			$	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).
Interest Rate Cap	'
Derivative [Line Items]	'
Derivatives	'
	Interest Rate Cap
	In May 2007, SIG issued the SIG Preference Shares, with an initial fixed annual dividend rate of 7.506%. In June 2017, the fixed rate will move to a floating rate equal to the greater of (i) 7.506% or (ii) 3 month LIBOR plus 320 bps. In July 2013, SIG executed an interest rate cap for the period from June 2017 to June 2022 to protect against a significant increase in interest rates during that 5-year period (the “Interest Rate Cap”). The Interest Rate Cap economically fixes the annual dividend rate on the SIG Preference Shares from June 2017 to June 2022 at 8.30%. The cost of the Interest Rate Cap was an upfront premium of 395 bps of the $250.0 million notional value, or approximately $9.9 million for the full notional amount.
	The Interest Rate Cap does not qualify for hedge accounting. It is recorded in other assets at fair value. Changes in fair value are recognized as unrealized gains or losses and are presented within other revenues. Collateral held is recorded within short-term investments with an equal amount recognized as a liability to return collateral. The fair value of the interest rate cap has been estimated using a single broker quote and accordingly, has been classified as a Level 3 measurement at December 31, 2013.
	The following table summarizes the change in the fair value of the Interest Rate Cap for the year ended December 31, 2013:
	Millions		December 31,
			2013
	Beginning of period		$	—
	Purchases		9.9
	Net realized and unrealized gains		1.2
	Sales/settlements		—
	End of period		$	11.1
	White Mountains does not provide any collateral to the interest rate counterparties. Under the terms of the Interest Rate Cap, White Mountains holds collateral in respect of future amounts due. White Mountains’ liability to return that collateral is based on the amounts provided by the counterparties and investment earnings thereon. The following table summarizes the Interest Rate Cap collateral balances held by White Mountains and ratings by counterparty:
			31-Dec-13
	Millions		Collateral Balances Held				Standard & Poor’s
							Rating(1)
	Barclays Bank Plc		$	7.5			A
	Nordea Bank Finland Plc		3.3				AA-
	Total		$	10.8
	(1)	Standard & Poor’s ratings as detailed above are: “A” (Strong, which is the sixth highest of twenty-one creditworthiness ratings) and “AA-” (Very Strong, which is the fourth highest of twenty-one creditworthiness ratings).
weather derivatives [Member]	'
Derivative [Line Items]	'
Derivatives	'
	Weather Derivatives
	For the year ended December 31, 2013, Sirius Group recognized $0.6 million of net gains on its weather and weather contingent derivatives portfolio. The fair values of the assumed contracts are subject to change in the near-term and reflect management’s best estimate based on various factors including, but not limited to, observed and forecasted weather conditions, changes in interest or foreign currency exchange rates and other market factors. Estimating the fair value of derivative instruments that do not have quoted market prices requires management’s judgment in determining amounts that could reasonably be expected to be received from or paid to a third party to settle the contracts. Such amounts could be materially different from the amounts that might be realized in an actual transaction to settle the contract with a third party. Because of the significance of the unobservable inputs used to estimate the fair value of Sirius Group’s weather risk contracts, the fair value measurements of the contracts are deemed to be Level 3 measurements in the fair value hierarchy.

Municipal_Bond_Guarantee_Insur

Municipal Bond Guarantee Insurance (Notes)	12 Months Ended
	Dec. 31, 2013
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]	'
Financial Guarantee Insurance Contracts [Text Block]	'
	Note 9. 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 December 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. HG Global provides first loss reinsurance protection for policies underwritten by BAM of up to 15% of par outstanding on a per policy basis through HG Re, which had statutory capital of $436.9 million at December 31, 2013. 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. At December 31, 2013 and 2012, HG Global had pre-tax income of $38.1 million and $14.2 million, which included $40.2 million and $18.4 million of interest income on the BAM surplus notes. At December 31, 2013 and 2012, BAM had a pre-tax loss of $78.6 million and $36.3 million that was recorded in net loss attributable to non-controlling interests, which included $40.2 million and $18.4 million of interest expense on the BAM surplus notes. As of December 31, 2013, HG Global has accrued $58.6 million of interest receivable on the BAM surplus notes.
	The following table provides a schedule of BAM’s insured obligations:
		31-Dec-13		31-Dec-12
	Contracts issued and outstanding	218		3
	Remaining weighted average contract period (in years)	13.8		10.4
	Contractual debt service outstanding (in millions):
	Principal	$	4,703.70	$	25.8
	Interest	$	3,264.40	$	8.9
	Gross unearned insurance premiums	$	13.2	$	0.1

Earnings_Per_Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2013
Earnings Per Share [Abstract]	'
Earnings per share	'
	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 years ended December 31, 2013, 2012 and 2011 (see Note 21 for earnings per share amounts for discontinued operations):
			Year Ended December 31,
			2013			2012			2011
	Basic and diluted earnings per share numerators (in millions):
	Net income from continuing operations attributable to		$	317.3		$	322.4		$	146.3
	White Mountains’ common shareholders
	Allocation of income for unvested restricted common shares		(4.7		)	(4.3		)	(1.2		)
	Dividends declared on participating restricted common shares(1)		(.1		)	(.1		)	(.1		)
	Total allocation to restricted common shares		(4.8		)	(4.4		)	(1.3		)
	Net income attributable to White Mountains’ common shareholders,		$	312.5		$	318		$	145
	net of restricted share amounts
	Undistributed net earnings (in millions):
	Net income attributable to White Mountains’ common shareholders,		$	312.5		$	318		$	145
	net of restricted common share amounts
	Dividends declared net of restricted common share amounts(1)		(6.1		)	(6.5		)	(7.9		)
	Total undistributed net earnings, net of restricted common share amounts		$	306.4		$	311.5		$	137.1
	Basic earnings per share denominators (in thousands):
	Total average common shares outstanding during the period		6,200.40			6,799.80			7,881.00
	Average unvested restricted common shares(2)		(91.4		)	(91.1		)	(69.4		)
	Basic earnings per share denominator		6,109.00			6,708.70			7,811.60
	Diluted earnings per share denominator (in thousands):
	Total average common shares outstanding during the period		6,200.40			6,799.80			7,881.00
	Average unvested restricted common shares(2)		(91.4		)	(91.1		)	(69.4		)
	Average outstanding dilutive options to acquire common shares(3)		—			—			—
	Diluted earnings per share denominator		6,109.00			6,708.70			7,811.60
	Basic earnings per share (in dollars):
	Net income attributable to White Mountains’ common shareholders		$	51.15		$	47.41		$	18.56
	Dividends declared and paid		(1.00		)	(1.00		)	(1.00		)
	Undistributed earnings		$	50.15		$	46.41		$	17.56
	Diluted earnings per share (in dollars)
	Net income attributable to White Mountains’ common shareholders		$	51.15		$	47.41		$	18.56
	Dividends declared and paid		(1.00		)	(1.00		)	(1.00		)
	Undistributed earnings		$	50.15		$	46.41		$	17.56
	(1)	Restricted shares issued by White Mountains receive dividends, and therefore, are considered participating securities.
	(2)	Restricted common shares outstanding vest either in equal annual installments or upon a stated date (see Note 12).
	(3)	The diluted earnings per share denominator for the years ended December 31, 2013, 2012 and 2011 do not include the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding as they are anti-dilutive to the calculation.

Retirement_and_Postretirement_

Retirement and Postretirement Plans	12 Months Ended
	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]	'
Retirement and Postretirement Plans	'
	Retirement and Postretirement Plans
	OneBeacon sponsors qualified and non-qualified, non-contributory, defined benefit pension plans covering substantially all employees who were employed as of December 31, 2001 and former employees who had met the eligibility requirements, as well as retirees. Current plans include the OneBeacon qualified pension plan (the “Qualified Plan”) and the OneBeacon non-qualified pension plan (the “Non-qualified Plan”) (collectively the “Plans”). The Plans were frozen and curtailed in 2002 and, as a result, the projected benefit obligation is equal to the accumulated benefit obligation.
	The benefits for the Plans are based primarily on years of service and employees’ compensation through December 31, 2002. OneBeacon’s funding policy is consistent with the funding requirements of U.S. federal laws and regulations.
	The following tables set forth the obligations and funded status, assumptions, plan assets and cash flows associated with the Plans at December 31, 2013 and 2012:
			Pension Benefits
			December 31,
	Millions		2013				2012
	Change in projected benefit obligation:
	Projected benefit obligation at beginning of year		$	119.5			$	113
	Service cost		0.8				0.7
	Interest cost		4.2				4.7
	Settlement gain		—				(.7		)
	Special termination benefit cost		0.3				0.6
	Assumption changes		(13.0		)		11.2
	Actuarial gain		(.5		)		(.2		)
	Benefits and expenses paid with plan assets		(6.2		)		(7.5		)
	Benefits paid directly by OneBeacon		(2.2		)		(2.3		)
	Projected benefit obligation at end of year		$	102.9			$	119.5
	Change in plan assets:
	Fair value of plan assets at beginning of year		$	124.7			$	120.8
	Actual return on plan assets		24.3				11.4
	Benefits and expenses paid		(6.2		)		(7.5		)
	Fair value of plan assets at end of year		$	142.8			$	124.7
	Funded status at end of year		$	39.9			$	5.2
	The funded status of the consolidated pension plans at December 31, 2013 was $39.9 million, which represents an over-funding of $64.1 million related to the Qualified Plan and an under-funding of $24.2 million related to the Non-qualified Plan. The Non-qualified Plan, which is unfunded, does not hold any assets. OneBeacon has set aside $16.2 million in an irrevocable rabbi trust for the benefit of Non-qualified Plan participants. Assets held in the rabbi trust are not reflected in the funded status of the consolidated pension plans as presented.
	Amounts recognized in the financial statements as of December 31, 2013 and 2012 consist of:
			December 31,
	Millions		2013				2012
	Net assets of the Qualified Plan recorded in other assets		$	64.1			$	32.8
	Net liabilities of the Non-qualified Plan recorded in other liabilities		(24.2		)		(27.6		)
	Net amount accrued in the financial statements		$	39.9			$	5.2
	Information for the Non-qualified Plan, which had accumulated benefit obligations in excess of plan assets, was as follows:
			December 31,
	Millions		2013				2012
	Projected benefit obligation		$	24.2			$	27.6
	Accumulated benefit obligation		$	24.2			$	27.6
	Fair value of plan assets		$	—			$	—
	Information for the Qualified Plan, which had accumulated benefit obligations less than plan assets, was as follows:
			December 31,
	Millions		2013				2012
	Projected benefit obligation		$	78.7			$	91.9
	Accumulated benefit obligation		$	78.7			$	91.9
	Fair value of plan net assets(1)		$	142.8			$	124.7
	(1)	Includes receivables related to securities sold, interest and dividends as well as payables related to securities purchased.
	The amounts recognized in accumulated other comprehensive income (loss) on a pre-tax basis and before non-controlling interest for the years ended December 31, 2013 and 2012 were as follows:
			December 31,
	Millions		2013				2012
	Accumulated other comprehensive loss beginning balance		$	(21.2	)		$	(16.7	)
	Increase (decrease) in accumulated other comprehensive income (loss):
	Amortization of net actuarial losses recognized during the year		0.9				0.8
	Net actuarial gains (losses) occurring during the year(1)		30.8				(5.9		)
	Other adjustments		—				0.6
	Accumulated other comprehensive income (loss) ending balance		$	10.5			$	(21.2	)
	(1)	Net actuarial gains (losses) resulted from investment returns and demographic experience different than assumed, as well as changes in assumptions in estimating the projected benefit obligation in the years ended December 31, 2013 and 2012.
	During 2013, OneBeacon expects $0.3 million will be amortized from accumulated other comprehensive income into net periodic benefit cost. The components of net periodic benefit (income) cost for the years ended December 31, 2013, 2012 and 2011 were as follows:
			Year Ended December 31,
	Millions		2013				2012			2011
	Service cost		$	0.8			$	0.7		$	0.8
	Interest cost		4.2				4.7			5.2
	Expected return on plan assets		(7.1		)		(6.9		)	(7.6		)
	Amortization of unrecognized loss		0.9				0.8			0.5
	Net periodic pension income before settlements, curtailments and		(1.2		)		(.7		)	(1.1		)
	special termination benefits
Settlement loss		—				0.6			0.5
Special termination benefits expense(1)		0.3				0.6			0.8
Total net periodic benefit (income) cost		$	(.9	)		$	0.5		$	0.2
(1)	Special termination benefits represent additional payments made from the Qualified Plan to certain vested participants when their employment was terminated due to a reduction in force.
Assumptions
The weighted average discount rate assumptions used to determine benefit obligations was 4.66% and 3.64% at December 31, 2013 and 2012. The weighted average assumptions used to determine net periodic benefit cost included a 3.64% discount rate and 5.75% expected long-term rate of return on plan assets for the year ended December 31, 2013.  The weighted average assumptions used to determine net periodic benefit cost included a 4.38% discount rate and 5.75% expected long-term rate of return on plan assets for the year ended December 31, 2012.
OneBeacon’s discount rate assumptions used to account for the Plans reflect the rates at which the benefit obligations could be effectively settled. In addition to consideration of published yields for high quality long-term corporate bonds, U.S. Treasuries and insurance company annuity contract pricing, consideration was given to cash flow matching analyses.
OneBeacon performed an analysis of expected long-term rates of return based on the allocation of its Qualified Plan assets at December 31, 2012 and 2011 to develop expected rates of return for 2013 and 2012 for each significant asset class or economic indicator. A range of returns was developed based both on forecasts and on broad market historical benchmarks for expected return, correlation, and volatility for each asset class.
Plan Assets
The majority of the Qualified Plans’ assets are managed by Prospector Partners, LLC (“Prospector”), a related party (see Note 19). The investment policy places an emphasis on preserving invested assets through a diversified portfolio of high-quality income producing investments and equity investments.
The investment management process integrates the risks and returns available in the investment markets with the risks and returns available to the Qualified Plan in establishing the proper allocation of invested assets. The asset classes may include fixed maturity, equity, convertible fixed maturities, and cash and short-term investments. Fixed maturity and convertible fixed maturities may include bonds, convertible fixed maturities and convertible preferred stocks of companies from diversified industries. Equity securities primarily include investments in large-cap and mid-cap companies primarily located in the United States. Cash and short-term investments include registered investment companies and common/collective trust funds.
The factors examined in establishing the appropriate investment mix include the outlook for risk and return in the various investment markets and sectors and the long-term need for capital growth.
The Qualified Plan’s investments are stated at fair value. Many factors are considered in arriving at fair market value. In general, fixed maturity investments such as corporate bonds and government securities are valued based on yields currently available on comparable securities of issuers with similar credit ratings. Shares of common and preferred stock are valued at quoted market prices when available.  Convertible fixed maturities are valued based on quoted market prices, analysis of listed markets and use of sensitivity analyses. Registered investment companies are valued at the net asset value as reported by the fund at year-end.
The fair value of the Qualified Plan’s assets and their related inputs at December 31, 2013 and 2012 by asset category were as follows:
		31-Dec-13												31-Dec-12
Millions		Fair				Level 1			Level 2			Level 3		Fair		Level 1		Level 2		Level 3
		Value				Inputs			Inputs			Inputs		Value		Inputs		Inputs		Inputs
Fixed maturity investments		$	—			$	—		$	—		$	—	$	1.9	$	—	$	1.9	$	—
Common equity securities		103.3				103.3			—			—		79.5		79.5		—		—
Convertible fixed maturity investments		29.9				—			29.9			—		34.5		—		34.5		—
Cash and short-term investments		8.9				8.8			0.1			—		8.1		8.1		—		—
Total		$	142.1			$	112.1		$	30		$	—	$	124	$	87.6	$	36.4	$	—
There were no transfers between Levels 1, 2 or 3 during the years ended December 31, 2013 and 2012.
The Qualified Plan’s asset allocations at December 31, 2013 and 2012, by asset category were as follows:
		Plan Assets at
		December 31,
Asset Category		2013			2012
Fixed maturity investments		—	%		1.5	%
Common equity securities		72.7			64.2
Convertible fixed maturity investments		21.1			27.8
Cash and short-term investments		6.2			6.5
Total		100	%		100	%
As described above, the Qualified Plan’s investment securities are exposed to various risks such as interest rate, market, and credit risks. Market prices of common equity securities, in general, are subject to fluctuations which would cause the amount to be realized upon sale or exercise of the instruments to differ significantly from the current reported value. The fluctuations may result from perceived changes in the underlying economic characteristics of the investee, the relative price of alternative investments, general market conditions and supply and demand imbalances for a particular security. Increases and decreases in prevailing interest rates generally translate into decreases and increases in fair values of fixed maturity and convertible fixed maturity investments, respectively. Additionally, fair values of interest rate sensitive instruments may be affected by the creditworthiness of the issuer, prepayment options, relative values of alternative investments, the liquidity of the instrument and other general market conditions.
Cash Flows
OneBeacon does not expect to make a contribution to its Qualified Plan in 2013. OneBeacon anticipates contributing $2.2 million to the Non-qualified Plan, for which OneBeacon has assets held in a rabbi trust.
The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid:
Millions		Expected Benefit Payments
2014		$	5.1
2015		5.4
2016		5.6
2017		5.8
2018		6.1
2019-2023		33.9
Other Benefit Plans
OneBeacon sponsors a defined contribution plan, the OneBeacon 401(k) Savings and Employee Stock Ownership Plan (“KSOP”), covering the majority of its employees. The contributory plan provides qualifying employees with matching contributions of 50% up to the first six percent of salary (subject to U.S. federal limits on allowable contributions in a given year). Total expense for matching contributions to the plan was $2.3 million, $2.8 million and $3.0 million in 2013, 2012 and 2011.
The employee stock ownership component of the KSOP provides all of its participants with an annual base contribution in common shares equal to 3% of their salary, up to the applicable Social Security wage base ($113,700 for 2013). Additionally, those participants not otherwise eligible to receive certain other OneBeacon benefits can earn a variable contribution of up to 6% of their salary, subject to the applicable IRS annual covered compensation limits ($255,000 for 2013) and contingent upon OneBeacon’s performance.  White Mountains recorded $6.3 million, $4.8 million and $6.3 million in compensation expense to pay benefits and allocate common shares to participant’s accounts for the years ended 2013, 2012 and 2011.
OneBeacon had a post-employment benefit liability, which primarily relates to disability coverage for former employees, of $5.8 million and $7.1 million at December 31, 2013 and 2012.
Sirius Group sponsors an employee savings plan (defined contribution plan) covering the majority of its U.S. employees. The contributory plan provides qualifying employees with matching contributions of 100% up to the first 2% and 50% of the next 4% of salary (subject to U.S. federal limits on allowable contributions in a given year). Total expense for matching contributions to the plan was $0.6 million, $0.6 million and $0.7 million in 2013, 2012 and 2011. Additionally, all participants in the plan can earn a variable contribution of up to 7% of their salary, subject to the applicable IRS annual covered compensation limits ($255,000 for 2013) and contingent upon Sirius Group’s performance. Total expense for variable contributions to the plan was $0.7 million, $0.4 million and $0.3 million in 2013, 2012 and 2011.
Sirius Group funds other governmental pension plans and other employee savings plans in various countries for its global employees. As of December 31, 2013 and 2012, the projected benefit obligation of Sirius Group’s other governmental pension plans was $13.1 million and $12.4 million, and the funded status was $1.0 million and $1.7 million. The expense for those plans totaled $9.7 million, $7.5 million and $9.6 million in 2013, 2012 and 2011.

Employee_ShareBased_Incentive_

Employee Share-Based Incentive Compensation Plans	12 Months Ended
	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Employee Share-Based Incentive Compensation Plans	'
	Employee Share-Based Incentive Compensation Plans
	White Mountains’ share-based incentive compensation plans are designed to incentivize key employees and service providers to maximize shareholder value over long periods of time. White Mountains believes that this is best pursued by utilizing a pay-for-performance program that closely aligns the financial interests of management with those of its shareholders. White Mountains accomplishes this by emphasizing highly variable long-term compensation that is contingent on performance over a number of years rather than entitlements. White Mountains expenses all its share-based compensation. As a result, White Mountains’ calculation of its owners’ returns includes the expense of all outstanding share-based compensation awards.
	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 White Mountains. The WTM Incentive Plan was adopted by the Board, was approved by the Company’s sole shareholder in 1985 and was subsequently amended by its shareholders in 1995, 2001, 2003, 2005, 2010 and 2013. Share-based incentive awards that may be granted under the plan include performance shares, restricted shares, performance units, incentive stock options and non-qualified stock options (“Non-Qualified Options”). Performance shares are conditional grants of a specified maximum number of common shares or an equivalent amount of cash. Awards generally vest at the end of a three-year period, are subject to the attainment of pre-specified performance goals, and are valued based on the market value of common shares at the time awards are paid. Performance shares earned under the WTM Incentive Plan are typically paid in cash but may be paid in common shares or by deferral into certain non-qualified compensation plans of White Mountains. Compensation expense is recognized on a pro rata basis over the vesting period of the awards.
	The OneBeacon Long-Term Incentive Plan (the “OneBeacon Incentive Plan”) provides for grants to key employees of OneBeacon various types of share-based incentive awards, including performance shares, restricted shares, restricted stock units and Non-Qualified Options.
	The Sirius Group Performance Plan provides for granting phantom White Mountains performance shares (the “WTM Phantom Share Plan”) to certain key employees of Sirius Group. Beginning with the 2011-2013 performance cycle, employees of Sirius Group were granted performance shares from the WTM Incentive Plan.  The performance goals for full payment of performance shares issued under these plans are identical to those of the WTM Incentive Plan. Performance shares earned under the WTM Phantom Share Plan are typically paid in cash but could be paid in common shares or by deferral into certain non-qualified compensation plans of White Mountains. Compensation expense is recognized on a pro rata basis over the vesting period of the awards.
	White Mountains offers certain types of share-based compensation under qualified retirement plans. The defined contribution plans of OneBeacon and Sirius Group (the “401(k) Plans”) offer its U.S.-domiciled participants the ability to invest their balances in several different investment options, including the Company’s or OneBeacon’s common shares.
	OneBeacon’s KSOP is an employer-funded benefit plan that provides all of its participants with an annual base contribution in common shares equal to 3% of their salary, up to the applicable Social Security wage base ($113,700 for 2013). Additionally, those participants not otherwise eligible to receive certain other OneBeacon benefits can earn a variable contribution of up to 6% of their salary, subject to the applicable IRS annual covered compensation limits ($255,000 for 2013) and contingent upon OneBeacon’s performance.
	Performance Shares
	Performance shares are designed to reward company-wide performance. The level of payout ranges from zero to two times the number of shares initially granted, depending on White Mountains’ financial performance. Performance shares become payable at the conclusion of a performance cycle (typically three years) if pre-defined financial targets are met.
	The principal performance measure used for determining performance share payouts is after-tax growth in White Mountains’ intrinsic business value per share. The Compensation Committee historically has considered the growth in intrinsic business value per share to be based equally on the growth of economic value per share and growth in adjusted book value per share, both inclusive of dividends. Economic value is calculated by adjusting the GAAP book value per share for differences between the GAAP carrying values of certain assets and liabilities and White Mountains’ estimate of their underlying economic values (for example, the time value discount in loss reserves).
	The following summarizes performance share activity for the years ended December 31, 2013, 2012 and 2011 for performance shares granted under the WTM Incentive Plan and the WTM Phantom Share Plan:
			Year Ended December 31,
			2013							2012							2011
	Millions, except share amounts		Target			Accrued				Target			Accrued				Target			Accrued
			Performance			Expense				Performance			Expense				Performance			Expense
			Shares							Shares							Shares
			Outstanding							Outstanding							Outstanding
	Beginning of period		119,357			$	29.4			150,064			$	66.1			163,184			$	29.4
	Shares paid or expired(1)		(47,310	)		(11.0		)		(68,357	)		(58.3		)		(51,131	)		—
	New grants		47,170			—				38,432			—				37,675			—
	Assumed forfeitures and cancellations(2)		3			(.6		)		(782	)		0.6				336			(.9		)
	Expense recognized		—			42.4				—			21				—			37.6
	Ending December 31,		119,220			$	60.2			119,357			$	29.4			150,064			$	66.1
	(1)	WTM performance shares 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. At December 31, 2012, White Mountains paid $9.9 as a partial payment for the 2010-2012 performance cycle. There were no payments made in 2011 for the 2008-2010 performance cycle; those performance shares did not meet the threshold performance goal and expired.
	(2)	Amounts include changes in assumed forfeitures, as required under GAAP.
	For the 2009-2011 performance cycle, the Company issued common shares for 9,577 performance shares earned and all other performance shares earned were settled in cash.
	If all outstanding performance shares had vested on December 31, 2013, the total additional compensation cost to be recognized would have been $33.8 million, based on accrual factors at December 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 December 31, 2013 for each performance cycle:
	Millions, except share amounts		Target WTM			Accrued Expense
			Performance Shares
			Outstanding
	Performance cycle:
	2013 – 2015		47,170			$	12.1
	2012 – 2014		37,977			21.4
	2011 – 2013		37,130			28.2
	Sub-total		122,277			61.7
	Assumed forfeitures		(3,057	)		(1.5		)
	Total at December 31, 2013		119,220			$	60.2
	The targeted performance goal for full payment of outstanding performance shares granted under the WTM Incentive Plan to non-investment personnel for the 2013-2015 performance cycles is an 8% growth in intrinsic business value per share. Growth of 2% or less would result in no payout and growth of 14% or more would result in a payout of 200%.
	The targeted performance goal for full payment of outstanding performance shares granted under the WTM Incentive Plan to non-investment personnel for the 2012-2014 performance cycles is an 8% growth in intrinsic business value per share. Growth of 2% or less would result in no payout and growth of 14% or more would result in a payout of 200%.
	The targeted performance goal for full payment of outstanding performance shares granted under the WTM Incentive Plan to non-investment personnel for the 2011-2013 performance cycles is a 10% growth in intrinsic business value per share. Growth of 3% or less would result in no payout and growth of 17% or more would result in a payout of 200%.
	For investment personnel, the targeted performance goal for full payment of outstanding performance shares granted under the WTM Incentive Plan is based one-third on growth in intrinsic business value per share (as described above), one-third on achieving a total return on invested assets as measured against metrics based on U.S. Treasury Note returns and one-third on achieving a total return on invested assets as measured against metrics based on the Barclays U.S. Intermediate Aggregate Index returns.
	For Prospector Partners, the targeted performance goal for full payment of outstanding performance shares granted under the WTM Incentive Plan is based equally on growth in intrinsic business value per share (as described above) and achieving a total return on invested assets as measured against metrics based on U.S. Treasury Note returns.
	Restricted Shares
	The following outlines the unrecognized compensation cost associated with the outstanding restricted share awards under the WTM Incentive Plan for the years ended December 31, 2013, 2012 and 2011:
			Year Ended December 31,
			2013						2012						2011
	Millions, except share amounts		Restricted		Unamortized				Restricted		Unamortized				Restricted		Unamortized
			Shares		Issue Date Fair				Shares		Issue Date Fair				Shares		Issue Date Fair
					Value						Value						Value
	Non-vested,
	Beginning of period		69,910		$	16.8			72,000		$	13.3			46,250		$	14.1
	Issued		25,720		14.4				32,160		15.7				27,250		9.9
	Vested(1)		(1,500	)	—				(32,945	)	—				(1,500	)	—
	Forfeited		—		—				(1,305	)	(.2		)		—		—
	Expense recognized		—		(14.2		)		—		(12.0		)		—		(10.7		)
	Non-vested at December 31,		94,130		$	17			69,910		$	16.8			72,000		$	13.3
	(1)	During 2012, the Compensation Committee accelerated the vesting date for an installment of 5,000 restricted shares from January 20, 2013 to December 31, 2012.
	During 2013, White Mountains issued 25,720 restricted shares that vest on January 1, 2016. During 2012, White Mountains issued 27,960 restricted shares that vest on January 1, 2015, 3,000 restricted shares that vest in two equal annual installments beginning on February 22, 2014 and 1,200 restricted shares that vest on July 16, 2015. During 2011, White Mountains issued 27,250 restricted shares that vest on January 1, 2014.  The unrecognized compensation cost at December 31, 2013 is expected to be recognized ratably over the remaining vesting periods.
	Stock Options
	Non-Qualified Options
The Company’s Chairman and CEO holds 125,000 Non-Qualified Options, which are exercisable at $742 per common share and expire on January 20, 2017. The potential in-the-money value of the Non-Qualified Options in excess of $100 million is limited to 50% of the excess amount. The Non-Qualified Options were fully amortized as of the first quarter in 2011. For the year ended December 31, 2011, White Mountains recognized $0.1 million of amortization expense.
Share-Based Compensation Based on OneBeacon Ltd. Common Shares
OneBeacon Performance Shares
The following summarizes activity for the years ended December 31, 2013, 2012 and 2011 for OneBeacon performance shares granted under the OneBeacon Incentive Plan:
		Year Ended December 31,
		2013							2012							2011
Millions, except share amounts		Target			Accrued				Target			Accrued				Target			Accrued
		Performance			Expense				Performance			Expense				Performance			Expense
		Shares							Shares							Shares
		Outstanding							Outstanding							Outstanding
Beginning of period		563,190			$	1.2			642,667			$	9.7			1,464,295			$	18.5
Payments and deferrals(1)		(238,658	)		—				(258,901	)		(7.7		)		(936,150	)		(10.5		)
New awards		179,000			—				181,290			—				194,900			—
Forfeitures and cancellations(2)		(10,111	)		(0.1		)		(1,866	)		—				(80,378	)		(0.5		)
Expense recognized		—			2.9				—			(0.8		)		—			2.2
End of period		493,421			$	4			563,190			$	1.2			642,667			$	9.7
(1)	No payments were made in 2013 for the 2010-2012 OneBeacon performance cycle as the performance factor was zero. OneBeacon performance share payments in 2012 for the 2009-2011 performance cycle were at 138.6% of target. OneBeacon performance shares payments in 2011 for the 2008-2010 performance cycle were at 68.5% of target. Amounts include deposits into OneBeacon’s deferred compensation plan.
(2)	Amounts include changes in assumed forfeitures, as required under GAAP.
The following summarizes OneBeacon performance shares outstanding awarded under the OneBeacon Incentive Plan at December 31, 2013 for each performance cycle:
Millions, except share amounts		Target			Accrued
		OneBeacon			Expense
		Performance
		Shares
		Outstanding
Performance cycle:
2013 – 2015		179,000			$	1
2012 – 2014		181,290			2.1
2011 – 2013		142,138			1
Sub-total		502,428			4.1
Assumed forfeitures		(9,007	)		(.1		)
Total at December 31, 2013		493,421			$	4
If the outstanding OneBeacon performance shares had been vested on December 31, 2013, the total additional compensation cost to be recognized would have been $2.9 million, based on December 31, 2013 accrual factors (common share price and payout assumptions).
The targeted performance goal for full payment of the outstanding OneBeacon performance shares granted during 2013 is growth in book value per share of 13%. At a growth in book value per share of 6% or less, no performance shares would be earned and at a growth in book value per share of 20% or more, 200% of performance shares would be earned.
The targeted performance goal for full payment of the outstanding OneBeacon performance shares granted during 2012 is growth in book value per share of 10%. At a growth in book value per share of 3% or less, no performance shares would be earned and at a growth in book value per share of 17% or more, 200% of performance shares would be earned.
The targeted performance goal for full payment of the outstanding OneBeacon performance shares granted during 2011 is growth in book value per share of 11%. At a growth in book value per share of 4% or less, no performance shares would be earned and at a growth in book value per share of 18% or more, 200% of performance shares would be earned.
OneBeacon Restricted Shares
The following table summarizes the unrecognized compensation cost associated with the outstanding OneBeacon restricted stock awards for the years ended December 31, 2013, 2012 and 2011.
		Year Ended December 31,
		2013							2012							2011
Millions, except share amounts		Restricted Shares			Unamortized Issue Date Fair Value				Restricted Shares			Unamortized Issue Date Fair Value				Restricted Shares			Unamortized Issue Date Fair Value
Non-vested,
Beginning of period		927,000			$	9.6			630,000			$	7.7			—			$	—
Issued		—			—				300,000			4.5				630,000			8.6
Vested		(9,000	)		—				(667	)		—				—			—
Forfeited		(3,000	)		—				(2,333	)		—				—			—
Expense recognized		—			(3.1		)		—			(2.6		)		—			(.9		)
End of period		915,000			$	6.5			927,000			$	9.6			630,000			$	7.7
On March 1, 2012, OneBeacon issued 300,000 restricted shares to key employees that vest in two equal 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, 2015, 2016 and 2017.  Concurrently with the grant of the restricted shares, 35,000 OneBeacon performance shares issued to OneBeacon’s CEO for the 2011-2013 performance share cycle were forfeited and performance share awards to OneBeacon’s CEO for the subsequent 5 years have been or will also be reduced by 35,000 shares.  The restricted shares contain dividend participation features, and therefore, are considered participating securities.  The unrecognized compensation cost associated with outstanding restricted share awards at December 31, 2013 is expected to be recognized ratably over the remaining vesting periods.
Share-based Compensation Under Qualified Retirement Plans
Contributions to the KSOP with respect to the years ended 2013, 2012 and 2011 were made with either the Company’s or OneBeacon Ltd.’s common shares, dependent on the employer.  The variable contribution amounts for eligible participants of the KSOP constituted approximately 4%, 3% and 2% of salary for the years ended 2013, 2012 and 2011. White Mountains recorded $6.3 million, $4.8 million and $6.3 million in compensation expense to pay benefits and allocate common shares to participant’s accounts for the years ended 2013, 2012 and 2011. As of December 31, 2013 and 2012, the plans owned 3% or less of either of the Company’s or OneBeacon Ltd.’s total common shares outstanding.  All White Mountains common shares held by the KSOP are considered outstanding for earnings (loss) per share computations.

Common_Shareholders_Equity

Common Shareholders' Equity	12 Months Ended
	Dec. 31, 2013
Stockholders' Equity Note [Abstract]	'
Common Shareholder's Equity	'
	Common Shareholders’ Equity
	Common Shares Repurchased and Retired
	In 2006, White Mountains’ Board of Directors authorized the Company to repurchase up to 1,000,000 of its common shares, from time to time, subject to market conditions.  In 2010 and 2012, White Mountains’ Board of Directors authorized the Company to repurchase an additional 600,000 and 1,000,000, respectively, of its common shares, for a total authorization of 2,600,000 shares. Shares may be repurchased on the open market or through privately negotiated transactions. The repurchase authorizations do not have a stated expiration date. As of December 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. Shares repurchased pursuant to employee benefit plans do not fall under the board authorizations referred to above.
	During 2013, the Company repurchased 141,535 common shares for $79.8 million at an average share price of $564, which were comprised of 140,000 common shares repurchased in a private transaction under the board authorization for $78.9 million at an average share price of $564 and 1,535 common shares repurchased pursuant to employee benefit plans.
	During 2012, the Company repurchased 1,329,640 common shares for $669.1 million at an average share price of $503, which were comprised of (1) 502,801 common shares repurchased under the board authorization for $256.0 million at an average share price of $508; (2) 816,829 common shares repurchased through a fixed-price tender offer for $408.6 million at a share price of $500; and (3) 10,010 common shares repurchased pursuant to employee benefit plans.
	During 2011, the Company repurchased 646,502 common shares for $253.0 million at an average share price of $390, which were comprised of (1) 313,967 common shares repurchased under the board authorization for $114.0 million at an average share price of $364; (2) 332,346 common shares repurchased through two “modified Dutch auction” self-tender offers for $138.8 million at an average share price of $418; and (3) 189 common shares repurchased pursuant to employee benefit plans.
	Common Shares Issued
	During 2013, the Company issued a total of 27,310 common shares, which consisted of 25,720 restricted shares issued to key management personnel and 1,590 shares issued to directors of the Company. During 2012, the Company issued a total of 44,054 common shares, which consisted of 32,160 restricted shares and 700 shares issued to key management personnel, 9,577 shares issued in satisfaction of performance shares and 1,617 shares issued to directors of the Company. During 2011, the Company issued a total of 29,432 common shares, which consisted of 27,250 restricted shares issued to key management personnel and 2,182 shares issued to directors of the Company.
	Dividends on Common Shares
	For the years ended December 31, 2013, 2012 and 2011, the Company declared and paid cash dividends totaling $6.2 million, $6.6 million, and $8.0 million (or $1.00 per common share).

Statutory_Capital_and_Surplus

Statutory Capital and Surplus	12 Months Ended
	Dec. 31, 2013
Insurance [Abstract]	'
Statutory Capital and Surplus	'
	Statutory Capital and Surplus
	White Mountains’ insurance and reinsurance operations are subject to regulation and supervision in each of the jurisdictions where they are domiciled and licensed to conduct business. Generally, regulatory authorities have broad supervisory and administrative powers over such matters as licenses, standards of solvency, premium rates, policy forms, investments, security deposits, methods of accounting, form and content of financial statements, reserves for unpaid loss and LAE, reinsurance, minimum capital and surplus requirements, dividends and other distributions to shareholders, periodic examinations and annual and other report filings. In general, such regulation is for the protection of policyholders rather than shareholders.  In addition, the NAIC uses risk-based capital (“RBC”) standards for property and casualty insurers as a means of monitoring certain aspects affecting the overall financial condition of insurance companies. At December 31, 2013, White Mountains’ active insurance and reinsurance operating subsidiaries exceeded their respective RBC requirements.
	The Insurance Act 1978 of Bermuda and related regulations, as amended (“Insurance Act”), regulates the insurance business of Split Rock. Under the Insurance Act, Split Rock is required to maintain available statutory capital and surplus at a level equal to or in excess of its enhanced capital requirement which is established by reference to either a Bermuda Solvency Capital Requirement (“BSCR”) model or an approved internal capital model. At December 31, 2013, Split Rock Insurance Ltd. met Bermuda’s statutory capital and surplus requirements.
	OneBeacon’s combined statutory surplus (including U.S. statutory surplus and Bermuda statutory capital and surplus for Split Rock) was $1.0 billion and $0.9 billion as of December 31, 2013 and 2012. OneBeacon’s combined U.S. statutory surplus was $0.9 billion as of both December 31, 2013 and 2012. OneBeacon’s combined U.S. statutory net income for the years ended December 31, 2013, 2012 and 2011 was $100.1 million, $82.0 million and $119.6 million. The minimum policyholders' surplus necessary to satisfy OneBeacon's regulatory requirements was $164.7 million at December 31, 2013, which equals the authorized control level of the NAIC risk-based capital of OneBeacon’s primary top tier regulated operating subsidiary.
	Split Rock’s statutory capital and surplus was $96.4 million as of December 31, 2013.
	The principal differences between OneBeacon’s combined U.S. statutory amounts and Split Rock, and the amounts reported in accordance with GAAP include deferred acquisition costs, deferred taxes, and market value adjustments for debt securities. OneBeacon's insurance subsidiaries' statutory policyholders' surplus at December 31, 2013 was in excess of the minimum requirements of relevant state and Bermuda insurance regulations.
	Sirius International is subject to regulation and supervision in Sweden by the Financial Supervisory Authority (“FSA”). Sirius International’s total regulatory capital at December 31, 2013 was $2.5 billion.  In accordance with FSA regulations, Sirius International holds restricted equity of $1.7 billion as a component of Swedish regulatory capital. This restricted equity cannot be paid as dividends. The minimum regulatory capital held by Sirius International necessary to satisfy the requirements established by the FSA was $132.4 million at December 31, 2013.
	Sirius America’s policyholders’ surplus, as reported to regulatory authorities as of December 31, 2013 and 2012, was $548.4 million and $528.3 million. Sirius America’s statutory net income for the years ended December 31, 2013, 2012 and 2011 was $55.9 million, $26.2 million and $101.4 million The principal differences between Sirius America’s statutory amounts and the amounts reported in accordance with GAAP include deferred acquisition costs, deferred taxes, gains recognized under retroactive reinsurance contracts and market value adjustments for debt securities. The minimum policyholders’ surplus necessary to satisfy Sirius America’s regulatory requirements was $113.9 million at December 31, 2013, which equals the authorized control level of the NAIC risk-based capital based on Sirius America’s policyholders’ surplus.
	Central National’s policyholders’ surplus, as reported to regulatory authorities as of December 31, 2013 and 2012, was $9.3 million and $11.2 million. Central National’s statutory net (loss) income for the years ended December 31, 2013 and 2012 was $(0.5) million and $1.7 million. The minimum policyholders’ surplus necessary to satisfy Central National’s regulatory requirements was $1.5 million at December 31, 2013, which equals the authorized control level of the NAIC risk-based capital based on Central National’s policyholders’ surplus.
	Woodridge’s policyholders' surplus, as reported to regulatory authorities as of December 31, 2013 and 2012, was $8.4 million and $8.6 million. Woodridge’s statutory net (loss) income for the years ended December 31, 2013 and 2012 was $(0.1) million and $0.1 million. The minimum policyholders' surplus necessary to satisfy Woodridge’s regulatory requirements was $0 million at December 31, 2013, which equals the authorized control level of the NAIC risk-based capital based on Woodridge’s policyholders' surplus.
	Oakwood's policyholders' surplus, as reported to regulatory authorities as of December 31, 2013 and 2012, was $20.7 million and $24.5 million. Oakwood’s statutory net (loss) income for the years ended December 31, 2013 and 2012 was $(0.9) million and $3.9 million. The minimum policyholders' surplus necessary to satisfy Oakwood’s regulatory requirements was $2.2 million at December 31, 2013, which equals the authorized control level of the NAIC risk-based capital based on Oakwood’s policyholders' surplus. PICO’s policyholders’ surplus, as reported to regulatory authorities as of December 31, 2012, was $6.3 million. In 2013, the net assets of PICO were transferred to Oakwood and PICO was subsequently dissolved.
	Citation’s policyholders' surplus, as reported to regulatory authorities as of December 31, 2013 and 2012, was $11.9 million and $13.1 million. Citation’s statutory net loss for the years ended December 31, 2013 and 2012 was $0.3 million and $4.2 million. The minimum policyholders' surplus necessary to satisfy Citation’s regulatory requirements was $0.1 million at December 31, 2013, which equals the authorized control level of the NAIC risk-based capital based on Citation’s policyholders' surplus.
	Ashmere’s policyholders' surplus, as reported to regulatory authorities as of December 31, 2013, was $12.7 million. Ashmere’s statutory net loss for the year ended December 31, 2013 was $0.4 million. The minimum policyholders' surplus necessary to satisfy Ashmere’s regulatory requirements was $4.6 million at December 31, 2013, which equals the authorized control level of the NAIC risk-based capital based on Ashmere’s policyholders' surplus.
	Empire’s policyholders' surplus, as reported to regulatory authorities as of December 31, 2013, was $10.7 million. Empire’s statutory net loss for the year ended December 31, 2013 was $10.4 million. The minimum policyholders' surplus necessary to satisfy Empire’s regulatory requirements was $1.4 million at December 31, 2013, which equals the authorized control level of the NAIC risk-based capital based on Empire’s policyholders' surplus.
	White Shoals Re Ltd. (“White Shoals Re”) is also subject to regulation and supervision by the Bermuda Monetary Authority (“BMA”). Generally, the BMA has broad supervisory and administrative powers over such matters as licenses, standards of solvency, investments, methods of accounting, form and content of financial statements, minimum capital and surplus requirements, and annual and other report filings. In general, such regulation is for the protection of policyholders rather than shareholders. As of December 31, 2013, White Shoals Re had statutory capital and surplus of $14.6 million. The minimum regulatory capital held by White Shoals Re necessary to satisfy the requirements established by the BMA was $6.2 million at December 31, 2013.
	WM Life Re is subject to regulation and supervision by the BMA. As of December 31, 2013, WM Life Re had statutory capital and surplus of $85.9 million. The minimum regulatory capital held by WM Life Re necessary to satisfy the requirements established by the BMA was $0.7 million at December 31, 2013.
	HG Re is a Special Purpose Insurer under Bermuda insurance regulations and is subject to regulation and supervision by the BMA. As of December 31, 2013, HG Re had statutory capital of $436.9 million. As a Special Purpose Insurer, HG Re does not have minimum regulatory capital requirements.
	BAM is domiciled in New York and is subject to regulation by the New York State Department of Financial Services (“NYDFS”). New York financial guarantee insurance law establishes single risk and aggregate limits with respect to insured obligations insured by financial guarantee insurers. BAM’s members’ surplus, as reported to regulatory authorities as of December 31, 2013 was $469.0 million, which exceeds the minimum members’ surplus necessary for BAM to maintain its New York State financial guarantee insurance license of $66.0 million.
	Dividend Capacity
	There are no restrictions under Bermuda law or the law of any other jurisdiction on the payment of dividends from retained earnings by White Mountains. However, under the insurance laws of the states and jurisdictions under which White Mountains' insurance and reinsurance operating subsidiaries are domiciled, an insurer is restricted with respect to the timing and the amount of dividends it may pay without prior approval by regulatory authorities. At December 31, 2013, White Mountains’ top tier insurance and reinsurance subsidiaries have approximately $2.8 billion of GAAP shareholders’ equity (net of $246 million of non-controlling interest at OneBeacon), $0.8 billion of which can be distributed to White Mountains without prior regulatory approval. As a result, at December 31, 2013, $2.0 billion of White Mountains’ GAAP shareholders' equity held in its insurance and reinsurance subsidiaries was not available for the payment of dividends without prior regulatory approval, and approximately $755 million of White Mountains’ retained earnings is unrestricted with respect to the payment of dividends to White Mountains’ common shareholders. When determining whether to make distributions from its insurance and reinsurance operating subsidiaries, White Mountains also considers factors such as internal capital targets and rating agency capital requirements. Accordingly, there can be no assurance regarding the amount of such dividends that may be paid by such subsidiaries in the future.
	Following is a description of the dividend capacity of White Mountains’ insurance and reinsurance operating subsidiaries:
	OneBeacon:
	Generally, OneBeacon's top tier regulated insurance operating subsidiaries have the ability to pay dividends during any twelve-month period without the prior approval of regulatory authorities in an amount set by formula based on the greater of prior year statutory net income or 10% of prior year end statutory surplus, subject to the availability of unassigned funds. OneBeacon Insurance Company (“OBIC”), OneBeacon's primary top tier regulated U.S. insurance operating subsidiary, has the ability to pay $86.6 million of dividends during 2014 (based on its 2013 statutory surplus of $866.2 million) without prior approval of regulatory authorities, subject to the availability of unassigned funds. The amount of dividends available to be paid by OBIC in any given year is also subject to cash flow and earnings generated by OBIC’s business, which now just comprises the Runoff Business, as well as to dividends received from its subsidiaries, including Atlantic Specialty Insurance Company (“ASIC”), the lead U.S. insurance operating subsidiary for the Ongoing Business. At December 31, 2013, OBIC had $0.6 billion of unassigned funds and $0.9 billion of statutory surplus.
	As disclosed in Note 21 - “Discontinued Operations”, during the fourth quarter of 2012, OneBeacon executed various intercompany reinsurance agreements which, along with other internal capital transactions among its regulated U.S. insurance operating subsidiaries, resulted in ASIC becoming the lead insurance company for the ongoing specialty business and OBIC becoming the lead insurance company for the Runoff Business. Notwithstanding these restructuring transactions, OneBeacon continues to manage its statutory capital on a combined basis. Although OBIC remains the primary top tier regulated U.S. insurance operating subsidiary and maintains sufficient statutory capital to support the Runoff Business, the majority of the group's statutory capital is now included in ASIC, which is currently a subsidiary of OBIC, to support the ongoing specialty business. Prior to the closing of the Runoff Transaction and subject to regulatory approval, OBIC will distribute ASIC to its immediate parent, OneBeacon LLC.
	ASIC has the ability to pay dividends during any twelve-month period without the prior approval of regulatory authorities in an amount set by formula based on the lesser of net investment income, as defined by statute, or 10% of statutory surplus, in both cases as most recently reported to regulatory authorities, subject to the availability of earned surplus and subject to dividends paid in prior periods. ASIC has the ability to pay $23.9 million of dividends during 2014 without prior approval of regulatory authorities, subject to the availability of earned surplus. Given the changes in structure noted above, and in order for ASIC to pay dividends consistent with being the lead insurance company for the Ongoing Business, ASIC may require prior approval by regulatory authorities in order to make additional distributions until it builds up a historical net investment income stream and earned surplus balance under its new structure. At December 31, 2013, ASIC had $94.6 million of earned surplus and $0.7 billion of statutory surplus. During 2013, ASIC paid a $190.0 million extraordinary return of capital to OBIC, which, in turn, distributed the $190.0 million to its immediate parent. During 2013, OneBeacon also contributed $35.0 million to OBIC.
	Split Rock has the ability to declare or pay dividends during any twelve-month period without the prior approval of Bermuda regulatory authorities on condition that any such declaration or payment of dividends does not cause a breach of any of its regulatory solvency and liquidity requirements. If Split Rock fails to meet its regulatory solvency or liquidity requirements on the last day of any financial year, it is prohibited from declaring or paying any dividends during the next financial year without the approval of the BMA.
	In addition, under the Companies Act 1981 of Bermuda (the “Companies Act”), Split Rock is prohibited from declaring or paying a dividend or making a distribution out of contributed surplus if there are reasonable grounds for believing that after such payment is made, Split Rock would be unable to pay its liabilities as they become due or the realizable value of its assets would be less than its liabilities.
	During 2014, Split Rock has the ability to make capital distributions without the prior approval of regulatory authorities, subject to meeting all appropriate liquidity and solvency requirements, of up to $20.3 million, which is equal to 15% of its December 31, 2013 statutory capital, excluding earned surplus. During 2013, OneBeacon contributed $135.1 million to Split Rock. Split Rock did not pay any dividends in 2013.
	During 2013, OneBeacon's unregulated insurance operating subsidiaries paid $17.3 million of dividends to their immediate parent.  At December 31, 2013, OneBeacon's unregulated insurance operating subsidiaries had $57.9 million of net unrestricted cash, short-term investments and fixed maturity investments.
	During 2013, OneBeacon Ltd. paid $80.2 million of regular quarterly dividends to its common shareholders. White Mountains received $60.3 million of these dividends.
	At December 31, 2013, OneBeacon Ltd. and its intermediate holding companies held $217.5 million of net unrestricted cash, short-term investments and fixed maturity investments and $89.8 million of common equity securities and convertible fixed maturity investments outside of its regulated and unregulated insurance operating subsidiaries.
	Sirius Group:
	Subject to certain limitations under Swedish law, Sirius International is permitted to transfer a portion of its pre-tax income to its Swedish parent companies to minimize taxes (referred to as a group contribution). In 2013, Sirius International transferred $101.9 million of its 2012 pre-tax income to its Swedish parent companies as a group contribution.
	Sirius International has the ability to pay dividends subject to the availability of unrestricted statutory surplus. Historically, Sirius International has allocated the majority of its pre-tax income, after group contributions to its Swedish parent companies, to the Safety Reserve (see “Safety Reserve” on next page). At December 31, 2013, Sirius International had $587.0 million (based on the December 31, 2013 SEK to USD exchange rate) of unrestricted statutory surplus, which is available for distribution in 2014. The amount of dividends available to be paid by Sirius International in any given year is also subject to cash flow and earnings generated by Sirius International’s business, as well as to dividends received from its subsidiaries, including Sirius America. During 2013, Sirius International distributed $326.4 million of dividends to its immediate parent, $75.0 million of which had been declared and accrued in December 2012.
	Sirius America has the ability to pay dividends during any twelve-month period without the prior approval of regulatory authorities in an amount set by formula based on the lesser of net investment income, as defined by statute, or 10% of statutory surplus, in both cases as most recently reported to regulatory authorities, subject to the availability of earned surplus and subject to dividends paid in prior periods. Based upon 2013 statutory net investment income and dividends paid in 2013, Sirius America has no ability to pay any dividends during 2014 without prior approval of regulatory authorities.  At December 31, 2013, Sirius America had $548.4 million of statutory surplus and $33.0 million of earned surplus.  In 2013, Sirius America paid $75.0 million of dividends to its immediate parent.
	During 2013, Sirius Group distributed $250.0 million to its immediate parent, $75.0 million of which had been declared and accrued in December 2012.
	At December 31, 2013, Sirius Group and its intermediate holding companies held $67.0 million of net unrestricted cash, short-term investments and fixed maturity investments and $20.3 million of other long-term investments outside of its regulated and unregulated insurance and reinsurance operating subsidiaries.
	Capital Maintenance
	There is a capital maintenance agreement between Sirius International and Sirius America which obligates Sirius International to make contributions to Sirius America's surplus in order for Sirius America to maintain surplus equal to at least 125% of the company action level risk based capital as defined in the NAIC Property/Casualty Risk-Based Capital Report. The agreement provides for a maximum contribution to Sirius America of $200.0 million.  Sirius International also provides Sirius America with accident year stop loss reinsurance, which protects Sirius America's accident year loss and allocated loss adjustment expense ratio in excess of 70%, with a limit of $90.0 million.
	Safety Reserve
	Subject to certain limitations under Swedish law, Sirius International is permitted to transfer pre-tax amounts into an untaxed reserve referred to as a safety reserve. At December 31, 2013, Sirius International’s safety reserve amounted to SEK 10.4 billion or $1.6 billion at the December 31, 2013 exchange rate of 6.43 USD to SEK. Under GAAP, an amount equal to the safety reserve, net of a related deferred tax liability established at the Swedish tax rate of 22.0%, is classified as shareholder’s equity. Generally, this deferred tax liability is only required to be paid by Sirius International if it fails to maintain prescribed levels of premium writings and loss reserves in future years. As a result of the indefinite deferral of these taxes, Swedish regulatory authorities apply no taxes to the safety reserve when calculating solvency capital under Swedish insurance regulations. Accordingly, under local statutory requirements, an amount equal to the deferred tax liability on Sirius International’s safety reserve ($357.2 million at December 31, 2013) is included in solvency capital. Access to the safety reserve is restricted to coverage of reinsurance losses. Access for any other purpose requires the approval of Swedish regulatory authorities. Similar to the approach taken by Swedish regulatory authorities, most major rating agencies generally include the $1.6 billion balance of the safety reserve, without any provision for deferred taxes, in Sirius International’s capital when assessing Sirius International’s financial strength.
	HG Global/BAM:
	At December 31, 2013, HG Global has $613.0 million face value of preferred shares outstanding, of which White Mountains owned 97.3%. Holders of the HG Global preferred shares receive cumulative dividends at a fixed annual rate of 6.0% on a quarterly basis, when and if declared by HG Global. HG Global did not declare or pay any preferred dividends in 2013. As of December 31, 2013, HG Global has accrued $55.2 million of dividends payable to holders of its preferred shares, $53.7 million of which is payable to White Mountains and eliminated in consolidation.
	HG Re is a Special Purpose Insurer subject to regulation and supervision by the BMA, but does not require regulatory approval to pay dividends. However, HG Re’s dividend capacity is limited by amounts held in the collateral trusts pursuant to the first loss reinsurance treaty (“FLRT”) with BAM. As of December 31, 2013, HG Re had statutory capital of $436.9 million, of which $35.0 million primarily relates to accrued interest on the BAM Surplus Notes held by HG Re, and $400.0 million was held as collateral in the supplemental trust pursuant to the FLRT with BAM.
	Interest on the BAM Surplus Notes is payable quarterly at a fixed annual rate of 8.0%. Interest and principal payments on the BAM Surplus Notes are subject to approval of the NYDFS. BAM did not pay any interest on the BAM Surplus Notes in 2013 or 2012.
	Other Operations:
	During 2013, WM Advisors did not pay any dividends to its immediate parent. At December 31, 2013, WM Advisors held $17.3 million of net unrestricted cash and short-term investments.
	At December 31, 2013, the Company and its intermediate holding companies held $231.0 million of net unrestricted cash, short-term investments and fixed maturity investments, $490.2 million of common equity securities and $139.2 million of other long-term investments included in its Other Operations segment. During 2013, White Mountains paid a $6.2 million common share dividend.

Segment_Information

Segment Information	12 Months Ended
	Dec. 31, 2013
Segment Reporting [Abstract]	'
Segment Information	'
	NOTE 15. Segment Information
	White Mountains has determined that its reportable segments are OneBeacon, Sirius Group, HG Global/BAM and Other Operations. As a result of the Esurance Sale, the AutoOne Sale and the Runoff Business sale, the results of operations for Esurance, AutoOne and the Runoff Business have been classified as discontinued operations and are now presented, net of related income taxes, as such in the statement of comprehensive income. Prior year amounts have been reclassified to conform to the current period’s presentation (see Note 21).
	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.
	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.
	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.
	The HG Global/BAM segment consists of White Mountains’ investment in HG Global and the consolidated results 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 BAM Surplus Notes. HG Global also provides 15%-of-par, first loss reinsurance protection for policies underwritten by BAM. BAM's results are attributed to non-controlling interests.
	Other Operations consists of the Company, the Company’s intermediate holding companies, WM Advisors and WM Life Re as well as and various other entities not included in other 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 Global			BAM(1)				Other			Total
															Operations
	Year Ended December 31, 2013
	Earned insurance and reinsurance premiums		$	1,120.40		$	866.4	$	0.4		$	0.1			$	—		$	1,987.30
	Net investment income		41.1			48.8		1			4.7				15.3			110.9
	Net investment income (loss) - surplus note		—			—		40.2			(40.2		)		—			—
	interest
	Net realized and unrealized investment		49.4			26.7		(2.0		)	(9.3		)		96.9			161.7
	gains (losses)
	Other revenue		31.2			16.8		—			0.4				9.1			57.5
	Total revenues		1,242.10			958.7		39.6			(44.3		)		121.3			2,317.40
	Losses and LAE		622.1			418.4		—			—				—			1,040.50
	Insurance and reinsurance acquisition expenses		208.9			166.5		0.1			1.4				—			376.9
	Other underwriting expenses		204.8			126.1		—			0.4				—			331.3
	General and administrative expenses		12			32.2		1.4			32.5				103.2			181.3
	Interest expense on debt		13			26.3		—			—				3.2			42.5
	Total expenses		1,060.80			769.5		1.5			34.3				106.4			1,972.50
	Pre-tax income (loss)		$	181.3		$	189.2	$	38.1		$	(78.6	)		$	14.9		$	344.9
								HG Global/BAM
	Millions		OneBeacon			Sirius Group		HG Global			BAM(1)				Other			Total
															Operations
	Year Ended December 31, 2012
	Earned insurance and reinsurance premiums		$	1,132.00		$	931.6	$	—		$	—			$	—		$	2,063.60
	Net investment income		53.6			65		0.3			1.9				32.8			153.6
	Net investment income (loss) - surplus note		—			—		18.4			(18.4		)		—			—
	interest
	Net realized and unrealized investment gains		55.7			17.3		—			—				45.2			118.2
	Other (loss) revenue		(.5		)	70.6		—			—				30.2			100.3
	Total revenues		1,240.80			1,084.50		18.7			(16.5		)		108.2			2,435.70
	Losses and LAE		650			543.9		—			—				—			1,193.90
	Insurance and reinsurance acquisition expenses		249.4			180.8		—			—				—			430.2
	Other underwriting expenses		205.2			116.4		—			0.2				—			321.8
	General and administrative expenses		13.4			45.9		4.5			19.6				98.8			182.2
	Interest expense on debt		16.9			26.2		—			—				1.7			44.8
	Total expenses		1,134.90			913.2		4.5			19.8				100.5			2,172.90
	Pre-tax income (loss)		$	105.9		$	171.3	$	14.2		$	(36.3	)		$	7.7		$	262.8
	Millions		OneBeacon			Sirius Group		Other			Total
								Operations
	Year Ended December 31, 2011
	Earned insurance and reinsurance premiums		$	1,012.20		$	912.3	$	—		$	1,924.50
	Net investment income		71.4			89.9		23.2			184.5
	Net realized and unrealized investment gains		10.6			53.2		10.3			74.1
	Other (loss) revenue		(12.4		)	4.1		(1.7		)	(10.0		)
	Total revenues		1,081.80			1,059.50		31.8			2,173.10
	Losses and LAE		548.3			626		—			1,174.30
	Insurance and reinsurance acquisition expenses		221.2			181		—			402.2
	Other underwriting expenses		162.3			105.8		—			268.1
	General and administrative expenses		9.8			34.1		131.4			175.3
	Interest expense on debt		20.5			31.6		3.1			55.2
	Total expenses		962.1			978.5		134.5			2,075.10
	Pre-tax income (loss)		$	119.7		$	81	$	(102.7	)	$	98
								HG Global/BAM
	Selected Balance Sheet Data		OneBeacon			Sirius Group		HG Global			BAM					Other			Total
	Millions															Operations
December 31, 2013:
Total investments		$	2,364.90		$	3,251.40	$	107.9		$	468.6				$	999.8		$	7,192.60
Reinsurance recoverable on paid and unpaid losses		89.9			363.6		—			—					—			453.5
Assets held for sale		1,880.10			—		—			—					—			1,880.10
Total assets		5,191.30			5,124.10		675			(77.9		)	(2	)	1,231.80			12,144.30
Loss and LAE reserves		1,054.30			2,025.00		—			—					—			3,079.30
Liabilities held for sale		1,880.10			—		—			—					—			1,880.10
Total liabilities		4,083.90			3,414.50		68.9			19.7					159.9			7,746.90
Total White Mountains’ common shareholders’		830.6			1,459.60		589.5			—					1,025.80			3,905.50
equity
Non-controlling interest		276.8			250		16.6			(97.6		)			46.1			491.9
December 31, 2012:
Total investments		$	2,291.50		$	3,534.30	$	101.5		$	472.4				$	878.4		$	7,278.10
Reinsurance recoverable on paid and unpaid losses		110.7			336.3		—			—					—			447
Assets held for sale		2,226.80			—		—			—					—			2,226.80
Total assets		5,382.30			5,962.00		623.6			(28.6		)	(2	)	956.1			12,895.40
Loss and LAE reserves		1,000.00			2,168.90		—			—					—			3,168.90
Liabilities held for sale		2,226.80			—		—			—					—			2,226.80
Total liabilities		4,365.00			4,123.20		0.9			7.4					140.7			8,637.20
Total White Mountains’ common shareholders’		763.1			1,559.70		606.2			—					802.8			3,731.80
equity
Non-controlling interest		254.2			279.1		16.6			(36.0		)			12.5			526.4
(1)	BAM manages its affairs on a statutory accounting basis. BAM’s statutory surplus includes surplus notes and is not reduced by accruals of interest expense on the surplus notes. BAM’s statutory surplus is reduced only after a payment of principal or interest has been approved by the New York Department of Financial Services.
(2)	BAM total assets reflect the elimination of $503.0 in surplus notes issued to HG Global and its subsidiaries, and $58.6 and $18.4 in accrued interest related to those surplus notes as of December 31, 2013 and 2012.

Investments_in_Unconsolidated_

Investments in Unconsolidated Affiliates	12 Months Ended
	Dec. 31, 2013
Equity Method Investments and Joint Ventures [Abstract]	'
Investments in Unconsolidated Affiliates	'
	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.
			December 31,
	Millions		2013			2012
	Symetra common shares		$	360.9		$	288.4
	Unrealized (losses) gains from Symetra’s fixed maturity portfolio		(43.6		)	62.8
	Carrying value of Symetra common shares		317.3			351.2
	Symetra warrants		—			30.3
	Total investment in Symetra		317.3			381.5
	Hamer(1)		4.1			4
	Bri-Mar(1)		—			1.9
	Pentelia Capital Management		—			0.5
	Total investments in unconsolidated affiliates		$	321.4		$	387.9
	(1) As of October 1, 2012, Hamer and Bri-Mar are no longer consolidated and are accounted for as investments in unconsolidated affiliates.
	Symetra
	At December 31, 2013 and 2012, White Mountains owned 20.05 million and 17.40 million common shares of Symetra, which represented 17.03% and 14.60% of Symetra’s common share ownership. At December 31, 2012, White Mountains also owned warrants to acquire an additional 9.49 million common shares of Symetra. White Mountains accounts for its investment in common shares of Symetra using the equity method. White Mountains accounted for its Symetra warrants as derivatives with changes in fair value recognized as a gain or loss through other revenue in the income statement.  White Mountains used a Black Scholes valuation model to determine the fair value of the Symetra warrants.
	In January 2010, Symetra completed an initial public offering at a price of $12.00 per share, with 25.3 million shares sold by Symetra and 9.7 million shares sold by existing shareholders. White Mountains did not sell any of its shares in the offering. As a result of the offering, White Mountains’ fully converted ownership in Symetra decreased from 24% to approximately 20% during the first quarter of 2010. The issuance of the new Symetra shares at a price below its adjusted book value per share diluted White Mountains’ investment in Symetra’s common shares, resulting in a $16.0 million decrease to White Mountains’ carrying value in Symetra.
	On June 20, 2013, White Mountains exercised its warrants in a cashless transaction and received 2.65 million common shares of Symetra in exchange for the warrants. In addition, Symetra repurchased 6.6 million of its common shares at an average price of $13.44 during the second quarter of 2013. The net effect of Symetra’s share repurchases and the warrant exercises resulted in a basis difference between the GAAP carrying value of White Mountains’ investment in Symetra common shares and the amount derived by multiplying the percentage of White Mountains’ common share ownership by Symetra’s total GAAP equity. This basis difference totaled $19.3 million, of which $0.4 million is attributable to equity in earnings of unconsolidated affiliates and $18.9 million is attributable to equity in net unrealized gains of unconsolidated affiliates.
	During the three and six months ended June 30, 2013, White Mountains recognized a $14.5 million and $10.8 million increase in the value of the warrants through other revenues based on the final Black Scholes valuation that was agreed upon between Symetra and White Mountains. The major assumptions used in valuing the Symetra warrants at June 20, 2013 were a risk free rate of a 0.34%, volatility of 26.5%, an expected life of 1.11 years, a strike price of $11.49 per share and a share price of $15.53 per share. During the six months ended June 30, 2013, White Mountains also received dividends of $1.5 million from Symetra on its investment in Symetra warrants that were recorded in net investment income.
	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.  This impairment also resulted in a basis difference between the GAAP carrying value of White Mountains’ investment in Symetra common shares and the amount derived by multiplying the percentage of White Mountains common share ownership by Symetra’s total GAAP equity. 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 GAAP, a decline in the fair value of an investment is considered to be other-than-temporary when the fair value of the investment is not expected to recover to its GAAP carrying value in the near term.  Declines in the fair value of an investment that are considered to be other-than-temporary are recognized as a write-down to the GAAP carrying value of the investment.  The GAAP fair value of an investment is the price that would be paid by a market participant to acquire it in the investment’s principal (or most advantageous) market. For investments that are publicly traded, quoted market prices generally provide the best measurement of GAAP fair value. However, a decline in the quoted market price of an investment below its GAAP carrying value is not necessarily indicative of a loss in value that is other-than-temporary, and in circumstances where the characteristics of the investment being measured are not the same as those for which quoted market prices are available, unadjusted quoted market prices do not represent GAAP fair value. White Mountains’ investment in Symetra common shares is different than the shares that are traded on the public stock exchange, principally due to the size of its position and its representation on Symetra’s Board of Directors. In circumstances like this, GAAP requires that fair value be determined giving consideration to multiple valuation techniques. Management considered three different valuation techniques to determine the GAAP fair value of White Mountains’ investment in Symetra common shares at December 31, 2011.
	Valuation techniques based on actuarial appraisal
	When determining the value of life insurance holding companies that are acquisition targets, market participants commonly utilize an approach that values the company as the sum of (A) adjusted statutory net worth of any regulated life insurance companies (i.e. statutory surplus plus asset valuation reserve) plus the GAAP net assets of any non-life businesses, less holding company debt and (B) the present value of future earnings related to business in force as of the valuation date plus the present value of future earnings related to business written after the valuation date. Part A of the calculation can be performed using observable inputs from the statutory and GAAP financial statements. Part B of the calculation requires a large number of actuarial calculations including assumptions such as discount rates, mortality, persistency and future investment results that, while based on historical data and are supportable, are nonetheless judgmental and largely unobservable. For Symetra, part A was approximately $15 per share as of December 31, 2011. Symetra management provided White Mountains with an actuarial appraisal that demonstrates that part B would be a meaningful positive value in most reasonable scenarios. When determining the GAAP fair value of White Mountains’ investment in Symetra common shares at December 31, 2011, management ascribed the greatest weight to part A, as it is observable and less subjective.
	Valuation techniques based on multiples from recent transactions
	White Mountains uses growth in adjusted book value to assess Symetra’s financial performance. Adjusted book value excludes unrealized gains and losses from Symetra’s fixed maturity investment portfolio. Life insurance industry analysts and market participants commonly use multiples of adjusted book value per share to determine relative values of companies in the life insurance industry. Applying this approach to Symetra at December 31, 2011, utilizing multiples which were observed in a recently announced transaction within the life insurance industry provides an estimated fair value range from $16 to $30 per share. However, the range of fair value estimates generated by applying the adjusted book value per share multiple and market premium observed in the recently announced transaction is wide, and there have been no other significant acquisitions of life insurance companies in 2011. Therefore, management did not ascribe significant weight to valuations determined using the adjusted book value per share multiple or market price premium observed in recent acquisition activity when determining the GAAP fair value of White Mountains’ investment in Symetra common shares at December 31, 2011.
	Valuation techniques based on quoted market prices
	White Mountains’ representation on Symetra’s Board of Directors gives it the ability to exercise significant influence over Symetra’s operations and policies. Generally, market participants are willing to pay a premium to obtain the ability to exert influence over the operations and policies of an investee, which is not reflected in the quoted market price of Symetra’s common shares. There is no reliable means to calculate the value of this premium for an investment in a life insurance company. The actuarial appraisals used by market participants described above implicitly consider the ability to influence an investee’s operations and policies in the actuarial assumptions underlying projected future earnings, but the value associated with the ability to exert influence is not explicitly calculated separately from other components of value. As a result, management did not ascribe significant weight to valuations based on quoted market prices when determining the GAAP fair value of White Mountains’ investment in Symetra common shares at December 31, 2011, as the premium associated with the ability to exert influence over the operations and policies of Symetra is unobservable and highly subjective.
	After considering these valuation techniques, management determined that the best estimate of the GAAP fair value of White Mountains’ investment in Symetra’s common shares at December 31, 2011 was $15 per share. Given the scarcity of relevant observable inputs and the wide range of estimates developed under the approaches used, the estimated GAAP fair value of White Mountains’ investment in Symetra’s common shares involved a significant degree of judgment, is very subjective in nature and, accordingly, is considered a Level 3 fair value measurement.
	As a result of the various basis adjustments, 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 differences are being amortized over a 30-year period with a weighted average 29 years remaining. The amortization is based on estimated future cash flows associated with Symetra’s underlying assets and liabilities to which the basis differences have 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 differences 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 basis differences between equity in earnings and equity in net unrealized gains (losses). For the year ended December 31, 2013, White Mountains recognized after-tax amortization of $2.7 million through equity in earnings of unconsolidated affiliates and $10.8 million through equity in net unrealized gains from investments in unconsolidated affiliates. At December 31, 2013, the pre-tax unamortized basis difference was $183.7 million. Management does not believe that the investment in Symetra’s common shares is other-than-temporarily impaired at December 31, 2013.
	During 2013, White Mountains received cash dividends from Symetra of $6.4 million on its common share investment which is accounted for as a reduction of White Mountains’ investment in Symetra in accordance with equity accounting.
	The following table summarizes amounts recorded by White Mountains relating to its investment in Symetra:
	Millions		Common			Warrants			Total
			shares
	Carrying value of investment in Symetra as of December 31, 2010		$	350.4		$	37.1		$	387.5
	Equity in earnings(1)(8)		28.2			—			28.2
	Impairment of equity in earnings of Symetra(3)		(50.0		)	—			(50.0		)
	Equity in net unrealized gains from Symetra’s fixed maturity portfolio(7)		85			—			85
	Impairment of net unrealized gains from Symetra’s fixed maturity portfolio(4)		(148.6		)	—			(148.6		)
	Dividends received		(4.0		)	—			(4.0		)
	Decrease in value of warrants		—			(24.5		)	(24.5		)
	Carrying value of investment in Symetra as of December 31, 2011(2)		261			12.6			273.6
	Equity in earnings(1)(5)(8)		32.3			—			32.3
	Equity in net unrealized gains from Symetra’s fixed maturity portfolio(6)(7)		62.8			—			62.8
	Dividends received		(4.9		)	—			(4.9		)
	Increase in value of warrants		—			17.7			17.7
	Carrying value of investment in Symetra as of December 31, 2012(2)		351.2			30.3			381.5
	Equity in earnings(1)(5)(8)		37.8			—			37.8
	Equity in net unrealized losses from Symetra’s fixed maturity portfolio(6)(7)		(106.4		)	—			(106.4		)
	Dividends received		(6.4		)	—			(6.4		)
	Increase in value of warrants		—			10.8			10.8
	Exercise of warrants		41.1			(41.1		)	—
	Carrying value of investment in Symetra as of December 31, 2013(2)(9)		$	317.3		$	—		$	317.3
	(1)	Equity in earnings for the years end December 31, 2013, 2012 and 2011 excludes tax expense of $2.8, $2.6, and $2.3
	(2)	Includes White Mountains’ equity in net unrealized (losses) gains from Symetra’s fixed maturity portfolio of $(43.6), $62.8, and $0 as of December 31, 2013, 2012 and 2011, which excludes tax benefit (expense) of $3.2, $(5.1) and $0
	(3)	Impairment of equity in earnings of Symetra excludes tax benefit of $4.1
	(4)	Impairment of net unrealized gains from Symetra’s fixed maturity portfolio excludes tax benefit $12.0
	(5)	Equity in earnings for the years ended December 31, 2013 and 2012 includes $3.0 and $3.5 increases relating to the pre-tax amortization of the Symetra common share basis difference.
	(6)	Net unrealized gains for the years ended December 31, 2013 and 2012 includes $11.8 and $13.1 increases relating to the pre-tax amortization of the Symetra common share basis difference.
	(7)	Net unrealized (losses) gains from Symetra’s fixed maturity portfolio excludes tax benefit (expense) of $8.3, $(5.1) and $(6.9) for the years ended December 31, 2013, 2012 and 2011.
	(8)	Equity in earnings for the years end December 31, 2013, 2012 and 2011 includes $.2, $1.3, and $1.0 loss from the dilutive effect of Symetra’s yearly dividend and the issuance of restricted shares by Symetra
	(9)	The aggregate value of White Mountains’ investment in common shares of Symetra was $380.1 based upon the quoted market price of $18.96 per share at December 31, 2013.
	The following table summarizes financial information for Symetra as of December 31, 2013 and 2012:
			December 31,
Millions		2013			2012
Symetra balance sheet data:
Total investments		$	27,901.10		$	27,556.40
Separate account assets		978.4			807.7
Total assets		30,129.50			29,460.90
Policyholder liabilities		25,328.80			23,735.20
Long-term debt		449.5			449.4
Separate account liabilities		978.4			807.7
Total liabilities		27,187.60			25,830.80
Common shareholders’ equity		2,941.90			3,630.10
The following table summarizes financial information for Symetra for the years ended December 31, 2013, 2012 and 2011:
		Years ended December 31,
Millions		2013			2012			2011
Symetra income statement data:
Net premiums earned		$	627.2		$	605		$	540.5
Net investment income		1,285.00			1,275.20			1,270.90
Total revenues(1)		2,103.90			2,101.20			1,999.30
Policy benefits		1,394.90			1,371.80			1,307.30
Total expenses(1)		1,865.30			1,831.10			1,726.10
Net income(1)		220.7			205.4			195.8
Comprehensive net income		(777.6		)	549.3			785.5
(1)	Amounts for the years ended December 31, 2011 have been restated for the effect of Symetra’s adoption of ASU 2010-26.
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 (see Note 16). Effective October 1, 2012, these investments are accounted for under the equity method. For the years ended December 31, 2013 and 2012, White Mountains recorded equity in earnings of $0.9 million and $0.4 million for Hamer.  For December 31, 2013, White Mountains also received $0.8 million of cash dividends from Hamer. As of December 31, 2013, White Mountains’ investments in Hamer was $4.1 million.
On October 10, 2013, White Mountains sold its interest in Bri-Mar under an asset purchase agreement. For the year ended December 31, 2013, White Mountains recorded $1.1 million of cash proceeds from the sale and a $1.7 million loss on sale. Prior to the sale, White Mountains recorded equity in earnings of $0.9 million for Bri-Mar for the nine months ended September 31, 2013. Bri-Mar did not have any equity in earnings for December 31, 2012.
Pentelia
White Mountains obtained an equity interest of 33% in Pentelia Capital Management (“PCM”) for $1.6 million in April 2007. This investment is accounted for under the equity method. During the years ended December 31, 2013, 2012 and 2011, White Mountains recorded $0.1 million, $(1.3) million and $(0.2) million of equity in earnings in PCM.  During the year ended December 31, 2013, White Mountains received $.4 million of cash dividends from PCM which liquidated White Mountains equity interest. As of December 31, 2012, White Mountains investment in PCM was $0.5 million.

Variable_Interest_Entities

Variable Interest Entities	12 Months Ended
	Dec. 31, 2013
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]	'
Variable Interest Entities	'
	Variable Interest Entities
	BAM
	BAM is a newly formed mutual insurance company. As a mutual company BAM is owned by its members and a portion of each member’s policy payments represents a contribution to member’s surplus. During 2012, White Mountains capitalized HG Global to fund BAM through the purchase of $503.0 million of BAM Surplus Notes. The equity at risk funded by BAM’s members is not sufficient to fund its operations without the additional subordinated financial support provided by the BAM Surplus Notes and accordingly, BAM is considered to be a variable interest entity (“VIE”).
	BAM and HG Global, through its wholly-owned subsidiary, HG Re, entered into a first loss reinsurance treaty (“FLRT”), under which HG Re will provide first loss protection up to 15% of par outstanding on each bond insured by BAM in exchange for 60% of the premium, net of a ceding commission, charged by BAM.  HG Re's obligations under the FLRT are satisfied by the assets in two collateral trusts: a Regulation 114 Trust and a Supplemental Trust.  Losses required to be reimbursed to BAM by HG Re are subject to an aggregate limit equal to the assets held in the collateral trusts at any point in time. In addition, HG Global has the right to designate two directors for election to BAM’s board of directors. White Mountains is required to consolidate the results of BAM. Since BAM is owned by its members, its equity and results of operations are included in non-controlling interests (see Note 9).
	Reciprocals
	Reciprocals are policyholder-owned insurance carriers organized as unincorporated associations. Each policyholder insured by the reciprocal shares risk with the other policyholders. Policyholders share profits and losses in the same proportion as the amount of insurance purchased but are not subject to assessment for net losses of the reciprocal.
	In 2004, OneBeacon formed Houston General Management Company to provide management services for a fee to a reciprocal, Houston General Insurance Exchange (“HGIE”). During 2004, OneBeacon contributed $2.0 million of capital to HGIE and in 2005, contributed one of its subsidiaries, Houston General Insurance Company (“HGIC”) with assets of $149.4 million and liabilities of $127.6 million, to HGIE. Subsequent to the contribution of HGIC, HGIE issued a surplus note for $23.7 million to OneBeacon. During 2013, HGIE repaid $19.0 million of the interest owed on the surplus note, as well as $1.0 million of the outstanding principal balance. Subsequent to this payment, the surplus note was amended such that the remaining balance was reduced to $4.0 million. The principal and interest on the remaining surplus note is repayable to OneBeacon only with regulatory approval. The obligation to repay principal on the note is subordinated to all other liabilities including obligations to policyholders and claimants for benefits under insurance policies. OneBeacon has no ownership interest in the reciprocal.
	OneBeacon has determined that HGIE qualifies as a VIE. Furthermore, OneBeacon has determined that it is the primary beneficiary as it has both the power to direct the activities of the VIE that most significantly impact the entity's economic performance and the obligation to absorb losses or receive benefits of the entity that could potentially be significant to the VIE as a result of the management services provided to the reciprocal and the funds loaned to it. Accordingly, OneBeacon consolidates HGIE.
	At December 31, 2013 and 2012, consolidated amounts related to HGIE included total assets of $2.6 million and $22.6 million and total liabilities of $4.2 million and $43.8 million. At December 31, 2013, the net amount of capital at risk is equal to the surplus note of $4.0 million less the accumulated losses of $1.6 million which includes accrued interest on the surplus note of $0.1 million that eliminates in consolidation.
	Prospector Funds
	White Mountains has determined that the Prospector Offshore Fund, Ltd. and Prospector Turtle Fund, Ltd. (collectively, the “Prospector Funds”) are VIEs for which White Mountains is the primary beneficiary and is required to consolidate. At December 31, 2013 and 2012, White Mountains consolidated total assets of $249.2 million and $238.6 million and total liabilities of $90.6 million and $94.4 million of the Prospector Funds. In addition, at December 31, 2013 and 2012, White Mountains recorded non-controlling interest of $46.2 million and $41.5 million in the Prospector Funds. For the years ended December 31, 2013, 2012 and 2011, White Mountains recorded $14.5 million, $9.3 million, and $(1.0) million of income (loss) and $4.0 million, $2.7 million and $(0.2) million of non-controlling interest income (loss) related to the Prospector Funds. At December 31, 2013, the net amount of capital at risk is equal to White Mountains’ investment in the Funds of $112.5 million, which represents White Mountains’ ownership interest of 71.7% in the Prospector Offshore Fund and 68.9% in the Prospector Turtle Fund.
	Tuckerman Fund I
	On December 31, 2011, the Tuckerman Capital, LP fund (“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 and Bri-Mar, two small manufacturing companies that were owned by the Tuckerman Fund I. The consolidated results of Hamer and Bri-Mar are included in the Other Operations segment from January 1, 2012 through September 30, 2012, at which point the results of these companies were no longer consolidated by White Mountains.
	Prior to the dissolution, White Mountains had determined that Tuckerman Fund I was a VIE for which White Mountains was the primary beneficiary and was required to consolidate Tuckerman Fund I. At December 31, 2011, White Mountains consolidated assets of $17.6 million, liabilities of $9.9 million, non-controlling interests of $3.5 million and $2.2 million of non-controlling interest expense related to the companies distributed by Tuckerman Fund I.

Fair_Value_of_Financial_Instru

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Fair Value of Financial Instruments	'
	Fair Value of Financial Instruments
	White Mountains accounts for its financial instruments at fair value with the exception of the OBH Senior Notes and the SIG Senior Notes, which are recorded as debt liabilities at face value less unamortized original issue discount, and the SIG Preference Shares, which are recorded as non-controlling interest at face value.
	The following table summarizes the fair value and carrying value of financial instruments as of December 31, 2013 and 2012:
		31-Dec-13				31-Dec-12
	Millions	Fair		Carrying		Fair		Carrying
		Value		Value		Value		Value
	2012 OBH Senior Notes	$	269.8	$	274.7	$	282.4	$	274.7
	SIG Senior Notes	438.1		399.6		441.9		399.4
	SIG Preference Shares	260		250		257.5		250
	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.

Transactions_with_Related_Pers

Transactions with Related Persons	12 Months Ended
	Dec. 31, 2013
Related Party Transactions [Abstract]	'
Transactions with Related Persons	'
	Transactions with Related Persons
	Prospector
	Mr. John Gillespie, a director of White Mountains, is the founder and Managing Member of Prospector.  Prospector serves as a discretionary adviser with respect to specified assets, primarily equity securities, managed by WM Advisors on behalf of White Mountains and other clients of WM Advisors.
	Pursuant to an investment management agreement with WM Advisors (the “WMA Agreement”), Prospector charges WM Advisors fees based on the following schedule: 100 basis points on the first $200.0 million of assets under management; 50 basis points on the next $200.0 million and 25 basis points on amounts over $400.0 million. At December 31, 2013, Prospector managed a total of $461.0 million of assets for White Mountains (excluding OneBeacon and Symetra) under this arrangement.  Prospector has a separate investment management agreement with Symetra that began on July 1, 2010.  Until that date, Symetra was a party to the WMA Agreement and subject to the above fee schedule.
	Prospector has separate investment management agreements with OneBeacon (the “OneBeacon Agreements”) pursuant to which Prospector supervises and directs specified assets, primarily equity securities, including assets in OneBeacon’s defined benefit and defined contribution plans (the “ERISA Assets”).  All assets managed under the OneBeacon Agreements are subject to a single fee schedule that is substantially similar to the terms of the WMA Agreement fee schedule.  At December 31, 2013, Prospector managed $556.8 million of assets for OneBeacon under this arrangement, including $215.6 million of ERISA Assets.
	During 2013, 2012 and 2011, Prospector earned $6.5 million, $6.4 million, and $6.0 million in total fees pursuant to the WMA Agreement and the OneBeacon Agreements.
	Prospector also advises White Mountains on matters including capital management, asset allocation, private equity investments and mergers and acquisitions. Pursuant to a Consulting Agreement for those services, Prospector was granted 6,250 performance shares for the 2014-2016 cycle, 7,000 performance shares for the 2013-2015 cycle and 7,750 performance shares for the 2012-2014 cycle. In accordance with the terms of the WTM Incentive Plan, performance against target governing the performance shares will be confirmed by the Compensation Committee of the Board following the end of each performance cycle and the number of performance shares actually awarded at that time will range from 0% to 200% of the target number granted.  Based on the Company’s performance, Prospector received 131.5% of the 8,500 performance shares granted for the 2011-2013 performance cycle for a total payout of $6.5 million.  Unless and until the Consulting Agreement has been terminated, and subject to the approval of the Compensation Committee, at the beginning of each performance cycle Prospector is to be granted performance shares with a value of approximately $4.5 million.  The Compensation Committee establishes the performance target for such performance shares.
	Pursuant to a revenue sharing agreement, Prospector has agreed to pay White Mountains 6% of the revenues in excess of $500,000 of certain of Prospector’s funds in return for White Mountains having made a founding investment in 1997.  During 2013, 2012 and 2011, White Mountains earned $0.9 million, $0.5 million, and $0.2 million under this arrangement.
	At December 31, 2013, White Mountains had $108.4 million invested in limited partnership investment interests managed by Prospector (the “Funds”).  This total includes $14.9 million of OneBeacon assets.  Under the limited partnership agreements, Prospector serves as general partner and general manager of the Funds and is paid management and incentive performance fees by White Mountains and OneBeacon.  For the year ended December 31, 2013, 2012 and 2011, White Mountains and OneBeacon incurred $1.3 million, $1.1 million and $1.1 million in management fees and $3.2 million, $1.3 million and $0 in incentive fees.  In addition, Messrs. Barrette, Davis, Gillespie and Waters, each a director of the Company, and Mr. Campbell, an executive officer of the Company, owned limited partnership investment interests managed by Prospector as of such date.
	Oakum Bay Capital
	Mr. Kernan Oberting, a Managing Director of White Mountains Capital, founded Oakum Bay Capital (“OBC”). OBC serves as the general manager and owns general partnership interests in KVO Capital Partners (“KCP”) and the Trimarc Capital Fund (“TCF”) hedge funds.
	In connection with Mr. Oberting commencing employment with White Mountains Capital, on July 16, 2012, White Mountains purchased $2 million of preferred stock and received 7.5% of the common equity of OBC. After giving effect to the White Mountains’ investment, Mr. Oberting and his family beneficially owned 67.5% of the common equity of OBC. During 2013, Mr. Oberting and his family assigned all of their common equity interests to unaffiliated OBC management with effect from January 1, 2013.
	In September 2013, White Mountains exchanged its preferred stock and common equity interest in OBC for $500,000 in cash and a portion of OBC’s revenue for the next ten years.
	As of December 31, 2013, White Mountains investment in TCF was $8.6 million. Mr. Oberting is a limited partner in KCP and TCF. Mr. Barrette had a limited partnership investment in KCP that was redeemed in full in September 2012.
	For the years ended December 31, 2013 and 2012, White Mountains paid investment management fees of $0.1 million and $0.1 million to OBC.
	Other Relationships and Transactions
	WMA provides investment advisory and management services to Symetra.  At December 31, 2013 and 2012, WMA had $27.8 billion and $27.4 billion of assets under management from Symetra.  During 2013, 2012 and 2011, WMA earned $16.5 million, $15.9 million and $15.2 million in fees from Symetra.
	On March 15, 2013, the Company repurchased 140,000 WTM common shares from the estate of John J. Byrne, a beneficial owner of the Company. The price per share was $563.57, the market price at the time the agreement was reached.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	Commitments and Contingencies
	White Mountains leases certain office space under non-cancellable operating leases that expired on various dates through 2021. Rental expense for all of White Mountains’ locations was $20.2 million, $18.8 million and $22.8 million for the years ended December 31, 2013, 2012 and 2011. White Mountains also has various other lease obligations that are immaterial in the aggregate.  White Mountains’ future annual minimum rental payments required under non-cancellable leases, which are primarily for office space, are $15.3 million, $13.9 million, $12.6 million, and $27.7 million for 2014, 2015, 2016 and 2017 and thereafter, respectively.
	White Mountains also has future binding commitments to fund certain other-long term investments. These commitments, which total $115.9 million, do not have fixed funding dates.
	Capital Lease
	OBIC sold the majority of its fixed assets and capitalized software to OneBeacon Services LLC (“OB Services”) at a cost equal to book value with no gain or loss recorded on the sale. Subsequent to purchasing the fixed assets and capitalized software from OBIC, OB Services entered into lease financing arrangements with US Bancorp and Fifth Third whereby OB Services sold its furniture and equipment and its capitalized software, respectively, to US Bancorp and Fifth Third. The assets were sold at a cost equal to net book value. OB Services then leased the fixed assets back from US Bancorp for a lease term of five years and leased the capitalized software back from Fifth Third for a lease term of four years. OB Services received cash proceeds of $23.1 million as a result of entering into the sale-leaseback transactions. At the end of the lease terms, OB Services will be obligated to purchase the leased assets for a nominal fee, after which all rights, title and interest would transfer to OB Services. In accordance with ASC 840, OBIC recorded the sale of the assets with no gain or loss recognized while OB Services has recorded a capital lease obligation and a capital lease asset. As of December 31, 2013 and 2012, OB Services had a capital lease obligation of $12.5 million and $18.2 million, respectively, included within other liabilities and a capital lease asset of $10.9 million and $16.1 million included within other assets. The underlying assets will continue to be depreciated over their respective useful lives. OB Services’ future annual minimum rental payments are $5.3 million for each of the years ended December 31, 2014 and 2015 and $1.9 million for the year ended December 31, 2016.
	Assigned Risks
	As a condition of its license to do business in certain states, White Mountains’ insurance operations are required to participate in mandatory shared market mechanisms. Each state dictates the types of insurance and the level of coverage that must be provided. The total amount of business an insurer is required to accept is based on its market share of voluntary business in the state. In certain cases, White Mountains is obligated to write business from mandatory shared market mechanisms at some time in the future based on the market share of voluntary policies it is currently writing. Underwriting results related to assigned risk plans are typically adverse and are not subject to the predictability associated with White Mountains’ voluntarily written business.
	Under existing guaranty fund laws in all states, insurers licensed to do business in those states can be assessed for certain obligations of insolvent insurance companies to policyholders and claimants. White Mountains accrues any significant insolvencies when the loss is probable and the assessment amount can be reasonably estimated. The actual amount of such assessments will depend upon the final outcome of rehabilitation proceedings and will be paid over several years. At December 31, 2013, the reserve for such assessments totaled $13.0 million.
	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 it 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 December 31, 2013:
	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) 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, (ii) the Company indemnifies Allstate for breaches of certain covenants in the Agreement, including certain agreements by the Company not to solicit certain employees of the Transferred Subsidiaries for three years after the closing, and (iii) 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).
	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, OneBeacon-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”) and emerged from bankruptcy at the end of 2012 in a Chapter 11 reorganization.  During the bankruptcy proceedings, the Bankruptcy Court granted Plaintiffs permission to commence these LBO-related actions, and in 2011, the Judicial Panel on Multidistrict Litigation granted a motion to consolidate the actions for pretrial matters and transferred all such proceedings to the United States District Court for the Southern District of New York. 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.
	The Court granted an omnibus motion to dismiss the Noteholder Actions in September 2013 and Plaintiffs have filed a notice of appeal.
	In addition, OneBeacon, OneBeacon-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 (the “Committee”), 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”). Tribune emerged from bankruptcy in 2012, and a litigation trustee replaced the Committee as plaintiff in the Committee Action. This matter was consolidated for pretrial matters with the Noteholder Actions in the United States District Court for the Southern District of New York and was stayed pending the motion to dismiss in the Noteholder Action. The Committee Action will proceed upon the lifting of the stay and a scheduling order from the court.

Discontinued_Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2013
Discontinued Operations and Disposal Groups [Abstract]	'
Discontinued operations	'
	Discontinued Operations
	Esurance
	On October 7, 2011, White Mountains completed the sale of Esurance Insurance and AFI to Allstate (see Note 2).  As a result of the transaction, Esurance Insurance, AFI and the business Esurance Insurance cedes to Sirius Group (collectively, “the Esurance Disposal Group”) are reported as discontinued operations.  White Mountains recognized a gain of $677.5 million on the Esurance Sale which is recorded net of tax in discontinued operations.  Effective as of December 31, 2011, the results of operations for the Esurance Disposal Group have been classified as discontinued operations and are presented, net of related income taxes, in the statement of comprehensive income.
	AutoOne
	On February 22, 2012, OneBeacon completed the sale of the AutoOne business to Interboro. AutoOne operated as a division within OneBeacon that offered products and services to automobile assigned risk markets. The transaction included the sale of two insurance entities, AOIC and AOSIC, through which substantially all of the AutoOne business was written on a direct basis. The results of operations for the AutoOne business have been classified as discontinued operations and are presented, net of related income taxes, in the statement of comprehensive income.
	During 2012, OneBeacon and Interboro finalized the post-closing adjustments to the closing balance sheet resulting in OneBeacon recording a net gain of $0.5 million after tax. This after-tax net gain is included in loss from sale of discontinued operations in the statements of comprehensive income (loss) for the year ended December 31, 2012. During 2011, OneBeacon recorded an after-tax loss of $19.2 million in loss from sale of discontinued operations for the estimated loss on sale of AutoOne.
	Runoff Transaction
	In October 2012, OneBeacon entered into an agreement to sell the Runoff Business to Armour. During 2012, the results of operations for the Runoff Business were 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 December 31, 2013 and 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.
	The Pennsylvania Insurance Department (“PID”) is required to conduct an examination of the Runoff Business as part of its regulatory review of the Runoff Transaction. Pursuant to this examination, the PID required a third party actuarial review to provide an independent actuarial assessment of the loss reserves associated with the Runoff Business, which is a normal requirement associated with such examinations. The independent actuarial review was completed in September 2013, at which time the PID posted the summary review to its website. The independent actuarial review produced a range of total statutory net loss and LAE reserves of $215 million to $668 million as of March 31, 2013, compared to the OneBeacon’s recorded statutory net loss and LAE reserves of $166 million as of March 31, 2013. Since March 31, 2013, OneBeacon increased the Runoff Business loss and LAE reserves by $78.9 million.
	During the fourth quarter of 2013, and as part of its annual actuarial certification process, OneBeacon completed a comprehensive actuarial analysis of the non-A&E loss and LAE reserves associated with the Runoff Business. In addition to OneBeacon’s internal actuaries taking into account the differing assumptions, methods, and analyses produced by the independent actuarial review and other factors, management considered other sources of information, including runoff claims staffing models and related costs. For A&E reserve estimates associated with the Runoff Business, OneBeacon primarily relies on the internal study of its legacy A&E exposures completed in 2011 and on subsequent monitoring of quarterly A&E activity, including the comparison of that activity against what was assumed in that most recent study.
	As a result of the comprehensive actuarial analysis conducted by OneBeacon during the fourth quarter of 2013, OneBeacon recorded $71.5 million of unfavorable prior year non-A&E loss and LAE development related to the Runoff Business. The increase in loss reserves was concentrated in the workers compensation, personal auto liability and excess liability lines of business. In addition, OneBeacon increased its estimate of adjusting and other expenses, a component of LAE reserves. OneBeacon has not revised its estimate of net ultimate A&E payments.
	Workers compensation unpaid loss reserves increased by $36.6 million due to changes in how OneBeacon evaluates various estimated settlement rates, mortality and medical inflation assumptions. These three key assumptions, which were previously evaluated implicitly as part of overall case incurred activity, were separately analyzed and then explicitly reviewed under varying assumptions and an array of resulting reserve estimates, to generate an actuarial indication which management selected for its best estimate. For personal auto liability, a $16.9 million loss provision was recorded based on a ground-up analysis of unlimited medical automobile no-fault claims from the 1970s and 1980s, which produced a range of estimates at varying medical inflation rates. The remaining $5.4 million loss reserve increase was driven by adverse prior year loss development recorded on a few large excess liability claims. Finally, OneBeacon recorded a provision to increase its LAE reserves by $12.6 million for adjusting and other expenses due to a change in assumptions of staff efficiency associated with handling and settling runoff claims.
	For the full year 2013, the OneBeacon recorded $78.9 million loss and LAE provision for the Runoff Business, which includes a $7.4 million of increase in loss and LAE reserves recorded in the second quarter of 2013. The $78.9 million loss and LAE adverse development recorded in 2013 was partially offset by other revenue of $7.8 million associated with a settlement award in the second quarter of 2013 in the Safeco v. American International Group, Inc. (“AIG”) class action related to AIG's alleged underreporting of workers' compensation premiums to the National Workers' Compensation Reinsurance Pool.
	As of December 31, 2013, the recorded net unpaid loss and LAE reserves associated with the Runoff Business totaled $188.4 million. Management believes that the recorded net loss and LAE reserves reflect a reasonable provision for expected future loss and LAE payments and represent management’s best estimate within a range of reasonable estimates.
	The $71.5 million ($46.5 million after-tax) increase in Runoff Business loss and LAE reserves was recorded in the fourth quarter of 2013 as a component of discontinued operations and offset by an equal after-tax amount which decreased the estimated ultimate loss on sale of the Runoff Business. The terms of the Runoff SPA prescribe that the buyer has assumed the risk that loss and LAE reserves develop unfavorably from September 30, 2012 onward, resulting in the offset.
	During the fourth quarter of 2013, OneBeacon also increased the estimated pre-tax transaction costs associated with the Runoff Transaction, which was partially offset by the accretion of interest on the original sales price and, coupled with the $46.5 million after tax provision for loss and LAE, resulted in a $46.6 million after-tax reduction in the ultimate loss from discontinued operations. This reduction in the ultimate loss on sale was essentially offset by a $46.6 million after-tax gain on sale that was also recorded in OneBeacon’s fourth quarter and full year results. The estimated ultimate loss on sale of the Runoff Business is $69.0 million, pre-tax ($44.9 million after-tax).
	Although the Runoff SPA stipulates the amount of reserves and surplus to be transferred to Armour at closing, the PID may require additional reserves and/or surplus as a closing condition. In that event, and to respond to such a closing condition, the Runoff SPA provides that OneBeacon would invest in surplus notes issued by the transferring companies, subject to certain limits on the amount of surplus notes issued. OneBeacon believes that the transferred reserves and surplus plus the funding requirements/limitations agreed to in the Runoff SPA cover the full range of claim projections produced in the independent actuarial review. Currently, OneBeacon expects to provide financing by way of surplus notes in an amount that falls within the provisions of the Runoff SPA.
	In October 2013, OneBeacon and Armour amended the Runoff SPA to extend the date by which either party may terminate the Runoff SPA to July 31, 2014.  If the required regulatory approval to close the Runoff Transaction has not been obtained on or prior to July 31, 2014, either OneBeacon or Armour may unilaterally extend the termination date of the Runoff SPA by up to 90 days. OneBeacon expects the Runoff Transaction to close in mid-2014.
	Results of Discontinued Operations
	Loss from discontinued operations, net of tax, for the year ended December 31, 2013 was $42.1 million. During 2013, OneBeacon recognized a $71.5 million pre-tax ($46.5 million after tax) increase in Runoff Business loss and LAE reserves which was offset by an equal after tax amount which decreased the estimated ultimate loss on sale of the Runoff Transaction. The terms of the Runoff SPA prescribe that the buyer has assumed the risk that loss and LAE reserves develop unfavorably from September 30, 2012 onward, resulting in the offset. OneBeacon also increased the estimated pre-tax transaction costs associated with the Runoff Transaction which was partially offset by the accretion of interest on the original purchase price. The estimated ultimate loss on sale of the Runoff Business is $69.0 million pre-tax, ($44.9 million after-tax).
	During 2013, the results of discontinued operations included other revenue that was primarily associated with a settlement award in the Safeco Insurance Company of America v. AIG class action related to AIG’s alleged underreporting of workers’ compensation premiums to the National Workers’ Compensation Reinsurance Pool. OneBeacon increased loss reserves by approximately the same amount of the benefit resulting from the class action settlement award.
	For the year ended December 31, 2012, White Mountains recorded a $91.5 million after-tax loss on sale and a $24.0 million loss from operations which included a $9.0 million after-tax loss related to a reduction in the workers compensation loss reserve discount rate on reserves being transferred as part of the sale. OneBeacon also recognized $6.5 million of after-tax underwriting losses primarily related to unfavorable loss reserve development. 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.
	Loss and LAE reserve development. During 2013, OneBeacon experienced $78.9 million of net unfavorable loss reserve development from the Runoff Business, primarily related to workers compensation, personal auto liability and excess liability lines, as well as the estimate of adjusting and other expenses.
	During 2012, OneBeacon experienced $40.0 million of net unfavorable loss reserve development from the Runoff Business. The net unfavorable loss reserve development was primarily related to case incurred development on multiple peril liability and general liability claims and the impact of an adverse court ruling in Mississippi regarding a disputed assessment from an involuntary pool for hurricane Katrina claims. In addition, there was a change in the workers' compensation tabular discount rate from 4.5% to 3.5% that resulted in a charge of $15.2 million.
	During 2011, OneBeacon experienced $26.7 million of net unfavorable loss reserve development from the Runoff Business. The net unfavorable loss reserve development resulted from a detailed review of runoff expenses, principally unallocated loss adjustment expenses (“ULAE”), completed during the fourth quarter of 2011. Specifically, OneBeacon completed a detailed review of loss and defense and cost containment expenses (allocated LAE or “ALAE”) and other adjusting expenses (ULAE) during the fourth quarter of 2011. The analysis considered costs, based on current non-staff expenses and staffing projections for the Runoff Business, as OneBeacon continued efforts to segregate its claims operations between ongoing claims and runoff claims. The analysis also factored in the revised definition of runoff claims to include the non-specialty commercial lines business that was exited via the renewal rights agreement sale beginning with January 1, 2010 effective dates.
	Reinsurance. Included in the assets held for sale are reinsurance recoverables from two reinsurance contracts with subsidiaries of Berkshire Hathaway Inc. that OneBeacon was required to purchase in connection with White Mountains’ acquisition of OneBeacon in 2001: a reinsurance contract with National Indemnity Company (“NICO”) for up to $2.5 billion in old asbestos and environmental (“A&E”) claims and certain other exposures (the “NICO Cover”) and an adverse loss reserve development cover from General Reinsurance Corporation (“GRC”) for up to $570.0 million, comprised of $400.0 million of adverse loss reserve development occurring in years 2000 and prior in addition to $170.0 million of reserves ceded as of the date of the OneBeacon Acquisition (the “GRC Cover”) . 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 December 31, 2013, the total reinsurance recoverable on paid and unpaid losses of $1,243.7 million related to both the NICO cover and the GRC cover has been included in assets held for sale. Both NICO and GRC have an A.M Best rating of A++, Superior, which is the highest of sixteen ratings.
	The total reinsurance recoverables on paid and unpaid losses in assets held for sale were $10.7 million and $1,741.6 million as of December 31, 2013. The reinsurance recoverable on unpaid amount is gross of $136.9 million in purchase accounting adjustments that will become recoverable if claims are paid in accordance with current reserve estimates.
	Asbestos and environmental loss and LAE reserve activity. OneBeacon's reserves include provisions made for claims that assert damages from A&E related exposures. Substantially all of these reserves have been reclassified to liabilities held for sale as of December 31, 2013, as they relate to the Runoff Business. Asbestos claims relate primarily to injuries asserted by those who came in contact with asbestos or products containing asbestos. Environmental claims relate primarily to pollution and related clean-up obligations, particularly as mandated by Federal and state environmental protection agencies. In addition to the factors regarding the reserving process, OneBeacon estimates its A&E reserves based upon, among other factors, facts surrounding reported cases and exposures to claims, such as policy limits and deductibles, current law, past and projected claim activity and past settlement values for similar claims, as well as analysis of industry studies and events, such as recent settlements and asbestos-related bankruptcies. The cost of administering A&E claims, which is an important factor in estimating loss reserves, tends to be higher than in the case of non-A&E claims due to the higher legal costs typically associated with A&E claims.
	OneBeacon's reserves for A&E losses at December 31, 2013 represent management's best estimate of its ultimate liability based on information currently available. However, significant uncertainties, including but not limited to case law developments, medical and cleanup cost increases and industry settlement practices, limit OneBeacon's ability to accurately estimate ultimate liability and OneBeacon may be subject to A&E losses beyond currently estimated amounts. In addition, OneBeacon remains liable for risks reinsured in the event that a reinsurer does not honor its obligations under reinsurance contracts. OneBeacon cannot reasonably estimate at the present time loss reserve additions arising from any such future adverse loss reserve developments and cannot be sure that allocated loss reserves, plus the remaining capacity under the NICO Cover and other reinsurance contracts, will be sufficient to cover additional liability arising from any such adverse loss reserve developments.
	The following tables summarize reported A&E loss and LAE reserve activities (gross and net of reinsurance) for OneBeacon for the years ended December 31, 2013, 2012 and 2011, respectively.
	Net A&E Loss		Year Ended December 31,
	Reserve Activity		2013									2012									2011
						Pre-NICO									Pre-NICO									Pre-NICO
	Millions		Gross			Net(1)			Net(2)			Gross			Net(1)			Net(2)			Gross			Net(1)			Net(2)
	Asbestos:
	Beginning balance		$	929.4		$	602.5		$	2.4		$	1,074.30		$	681.2		$	2.2		$	904		$	647.3		$	6.4
	Incurred losses and LAE		—			—			—			(.3		)	(.5		)	(.5		)	256.8			32.2			(4.0		)
	Paid losses and LAE		(84.3		)	(79.3		)	(.5		)	(144.6		)	(78.2		)	0.7			(86.5		)	1.7			(.2		)
	Ending balance		845.1			523.2			1.9			929.4			602.5			2.4			1,074.30			681.2			2.2
	Environmental:
	Beginning balance		233			125.4			6.4			279.8			151.6			9			119			93.8			9.2
	Incurred losses and LAE		—			—			—			(.9		)	(.5		)	(.5		)	231.8			62.2			10
	Paid losses and LAE		(64.3		)	(33.0		)	(2.6		)	(45.9		)	(25.7		)	(2.1		)	(71.0		)	(4.4		)	(10.2		)
	Ending balance		168.7			92.4			3.8			233			125.4			6.4			279.8			151.6			9
	Total asbestos and environmental:
	Beginning balance		1,162.40			727.9			8.8			1,354.10			832.8			11.2			1,023.00			741.1			15.6
	Incurred losses and LAE		—			—			—			(1.2		)	(1.0		)	(1.0		)	488.6			94.4			6
	Paid losses and LAE		(148.6		)	(112.3		)	(3.1		)	(190.5		)	(103.9		)	(1.4		)	(157.5		)	(2.7		)	(10.4		)
	Ending balance		$	1,013.80		$	615.6		$	5.7		$	1,162.40		$	727.9		$	8.8		$	1,354.10		$	832.8		$	11.2
	(1)	Represents A&E reserve activity, net of third-party reinsurance, but prior to the NICO Cover.
	(2)	Includes NICO cover.
	Net Assets Held for Sale
	The following summarizes the assets and liabilities associated with the businesses classified as held for sale:
			December 31,
	Millions		2013			2012
	Assets held for sale
	Fixed maturity investments, at fair value		$	236.3		$	338.1
	Cash		—			—
	Reinsurance recoverable on unpaid losses		1,604.70			1,840.80
	Reinsurance recoverable on paid losses		10.7			15.6
	Insurance premiums receivable		9.1			11
	Deferred acquisition costs		—			—
	Deferred tax asset		3.3			5.1
Other assets		16			16.2
Total assets held for sale		$	1,880.10		$	2,226.80
Liabilities held for sale
Loss and loss adjustment expense reserves		$	1,793.10		$	2,052.60
Unearned insurance premiums		0.2			0.5
Ceded reinsurance payable		12.3			21.9
Other liabilities		74.5			151.8
Total liabilities held for sale		1,880.10			2,226.80
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:
		Year Ended December 31,
Millions, except per share amounts		2013			2012			2011
Revenues
Earned insurance premiums		$	0.8		$	10.6		$	731.2
Net investment income		—			—			12
Net realized and unrealized investment gains		—			—			0.7
Other revenue		10.8			—			55.1
Total revenues		11.6			10.6			799
Expenses
Loss and loss adjustment expenses		78.9			48.4			574.9
Insurance and reinsurance acquisition expenses		—			(2.1		)	157
Other underwriting expenses		(.2		)	1.7			91.4
General and administrative expenses		—			—			38.3
Total expenses		78.7			48			861.6
Pre-tax loss		(67.1		)	(37.4		)	(62.6		)
Income tax benefit		25			13.4			25.9
Loss from discontinued operations		(42.1		)	(24.0		)	(36.7		)
Gain (loss) on sale of discontinued operations, net of tax		46.6			(91.0		)	658.3
Net income (loss) from discontinued operations		$	4.5		$	(115.0	)	$	621.6
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 years ended December 31, 2013, 2012 and 2011:
		Year Ended December 31,
		2013			2012			2011
Basic and diluted earnings (loss) per share numerators (in millions):
Net income (loss) attributable to White Mountains’ common shareholders		$	4.5		$	(115.0	)	$	621.6
Allocation of income for participating unvested restricted common shares (1)		—			1.5			(5.4		)
Net income (loss) attributable to White Mountains’ common shareholders, net of		$	4.5		$	(113.5	)	$	616.2
restricted common share amounts (3)
Basic earnings (loss) per share denominators (in thousands):
Total average common shares outstanding during the period		6,200.40			6,799.80			7,881.00
Average unvested restricted common shares (1)		(91.4		)	(91.1		)	(69.4		)
Basic earnings (loss) per share denominator		6,109.00			6,708.70			7,811.60
Diluted earnings (loss) per share denominator (in thousands):
Total average common shares outstanding during the period		6,200.40			6,799.80			7,881.00
Average unvested restricted common shares (1)		(91.4		)	(91.1		)	(69.4		)
Average outstanding dilutive options to acquire common shares (2)		—			—			—
Diluted earnings (loss) per share denominator		6,109.00			6,708.70			7,811.60
Basic and diluted earnings (loss) per share (in dollars):		$	0.74		$	(16.91	)	$	78.88
(1)	Restricted common shares outstanding vest either in equal annual installments or upon a stated date (see Note 12).
(2)	The diluted earnings per share denominator for the years ended December 31, 2013, 2012 and 2011 do not include the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding as they are anti-dilutive to the calculation.
(3)	Net income (loss) attributable to White Mountains’ common shareholders, net of restricted share amounts, is equal to undistributed earnings (loss) for the years ended December 31, 2013, 2012 and 2011.

Subsequent_Event_Notes

Subsequent Event (Notes)	12 Months Ended
	Dec. 31, 2013
Subsequent Events [Abstract]	'
Subsequent Event	'
	Subsequent Events
	Wobi
	On February 19, 2014, White Mountains acquired 54% of the outstanding common shares of Wobi Insurance Agency Ltd. (“Wobi”), an Israeli online personal lines price comparison business, for NIS 14.4 million (approximately $4.1 million based upon the foreign exchange spot rate at the date of acquisition).  In addition to the common shares, White Mountains also purchased NIS 12.7 million (approximately $3.6 million based upon the foreign exchange spot rate at the date of acquisition) of newly-issued convertible preferred shares of Wobi.
	Star & Shield
	On January 31, 2014, White Mountains acquired certain assets and liabilities of Star & Shield Holdings LLC, including Star & Shield Risk Management LLC, the attorney-in-fact for Star & Shield Insurance Exchange (“SSIE”), for a purchase price of $1.8 million. SSIE is a Florida-domiciled reciprocal insurance exchange providing private passenger auto insurance to members of the public safety community and their families. In connection with the acquisition, White Mountains also purchased $12.0 million of surplus notes issued by SSIE.

Selected_Quarterly_Financial_D

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]	'
Selected Quartely Financial Data	'
	SELECTED QUARTERLY FINANCIAL DATA
	(Unaudited)
	Selected quarterly financial data for 2013 and 2012 is shown in the following table. The quarterly financial data includes, in the opinion of management, all recurring adjustments necessary for a fair presentation of the results of operations for the interim periods. As a result of the Esurance Sale, AutoOne Sale and the Runoff Business sale, the results of operations for Esurance, AutoOne and the Runoff Business have been classified as discontinued operations and are now presented, net of related income taxes, as such in the statement of comprehensive income. Prior year amounts have been reclassified to conform to the current period’s presentation (see Note 21).
		2013 Three Months Ended											2012 Three Months Ended
	Millions, except per share amounts	Dec. 31			Sept. 30			June 30		Mar. 31			Dec. 31			Sept. 30			June 30			Mar. 31
	Revenues	$	626.6		$	574.1		$	489.3	$	627.4		$	566.4		$	697.4		$	542.3		$	629.7
	Expenses	492.4			518.8			485.7		475.6			617.2			562.3			504.7			488.8
	Pre-tax income (loss)	134.2			55.3			3.6		151.8			(50.8		)	135.1			37.6			140.9
	Tax benefit (expense)	(27.4		)	(8.2		)	0.6		(41.6		)	101			(47.8		)	(6.4		)	(31.1		)
	Income (loss) from continuing operations	106.8			47.1			4.2		110.2			50.2			87.3			31.2			109.8
	Income (loss) from discontinued operations, net of tax	(.3		)	0.4			3.9		0.5			0.5			(106.8		)	0.5			(9.2		)
	Non-controlling interest in consolidated subsidiaries	(.3		)	1.1			11.1		0.5			12			30.9			(12.1		)	(16.8		)
	Equity in (loss) earnings of unconsolidated affiliates	11.7			8.6			7.1		9.2			5.5			7.7			6.5			10.2
	Income (loss) attributable to White Mountains’ common shareholders	$	117.9		$	57.2		$	26.3	$	120.4		$	68.2		$	19.1		$	26.1		$	94
	Income (loss) attributable to White Mountains’ common shareholders:
	Basic
	Continuing operations	$	19.14		$	9.2		$	3.62	$	19.1		$	10.36		$	19.11		$	3.85		$	13.85
	Discontinued operations	(.05		)	0.06			0.64		0.07			0.07			(16.21		)	0.07			(1.24		)
	Total consolidated operations	$	19.09		$	9.26		$	4.26	$	19.17		$	10.43		$	2.9		$	3.92		$	12.61
	Diluted
	Continuing operations	$	19.14		$	9.2		$	3.62	$	19.1		$	10.36		$	19.11		$	3.85		$	13.85
	Discontinued operations	(.05		)	0.06			0.64		0.07			0.07			(16.21		)	0.07			(1.24		)
	Total consolidated operations	$	19.09		$	9.26		$	4.26	$	19.17		$	10.43		$	2.9		$	3.92		$	12.61
	Adjusted book value per share	$	642.27		$	621.56		$	604.75	$	606.2		$	587.63		$	573.66		$	564.77		$	565.38

SCHEDULE_I_SUMMARY_OF_INVESTME

SCHEDULE I SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES	12 Months Ended
	Dec. 31, 2013
Summary of Investments, Other than Investments in Related Parties [Abstract]	'
SCHEDULE I SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES	'
	WHITE MOUNTAINS INSURANCE GROUP, LTD.
	SUMMARY OF INVESTMENTS—OTHER THAN
	INVESTMENTS IN RELATED PARTIES
	At December 31, 2013
	Millions		Cost		Carrying		Fair
					Value (1)		Value
	Fixed maturity investments:
	Bonds:
	U.S. Government and government agencies and authorities		$	365.5	$	362.5	$	362.5
	Debt securities issued by corporations		2,330.70		2,347.20		2,347.20
	Mortgage-backed and asset-backed securities		2,027.30		2,014.50		2,014.50
	States, municipalities and political subdivisions		18.3		17.9		17.9
	Foreign governments		444.2		439.9		439.9
	Redeemable preferred stocks		79.9		84.8		84.8
	Total fixed maturity investments(1)		5,265.90		5,266.80		5,266.80
	Short-term investments		635.9		635.9		635.9
	Common equity securities:
	Banks, trust and insurance companies		274.2		360.4		360.4
	Public utilities		32.1		34.3		34.3
	Industrial, miscellaneous and other		583.9		762.1		762.1
	Total common equity securities		890.2		1,156.80		1,156.80
	Convertible fixed maturity investments		71.7		80.5		80.5
	Other long-term investments		238.3		288.9		288.9
	Total investments(1)		$	7,102.00	$	7,428.90	$	7,428.90
	(1)	Carrying value and fair value includes $236.3 classified as assets held for sale relating to discontinued operations. See Note 21 - “Discontinued Operations”.
	Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes.

SCHEDULE_II_CONDENSED_FINANCIA

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT	12 Months Ended
	Dec. 31, 2013
Condensed Financial Information of Parent Company Only Disclosure [Abstract]	'
SCHEDULE II CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT	'
	CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT
	CONDENSED BALANCE SHEETS
			December 31,
	Millions		2013			2012
	Assets:
	Cash		$	0.2		$	0.5
	Fixed maturity investments, at fair value		31.8			39
	Short-term investments, at amortized cost		1.4			8.9
	Receivable due from subsidiary		—			96.6
	Other assets		0.4			1
	Investments in consolidated and unconsolidated affiliates		3,919.10			3,664.60
	Total assets		$	3,952.90		$	3,810.60
	Liabilities:
	Revolving line of credit		$	—		$	75
	Payable to subsidiary		47			—
	Other liabilities		0.4			3.8
	Total liabilities		47.4			78.8
	White Mountains’ common shareholders’ equity		3,905.50			3,731.80
	Total liabilities and equity		$	3,952.90		$	3,810.60
	CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS)
			Year Ended December 31,
	Millions		2013			2012			2011
	Revenues (including realized gains and losses)		$	1.2		$	20.8		$	6.4
	Expenses		39			32.4			51.7
	Pre-tax loss		(37.8		)	(11.6		)	(45.3		)
	Income tax (expense) benefit		(.1		)	(.3		)	6.5
	Net loss		(37.9		)	(11.9		)	(38.8		)
	Equity in earnings from consolidated and unconsolidated affiliates		359.7			219.3			806.7
	Net income attributable to White Mountains’ common shareholders		321.8			207.4			767.9
	Other comprehensive (loss) income items, after-tax		(79.8		)	95.2			(81.7		)
	Comprehensive income attributable to White Mountains’ common		$	242		$	302.6		$	686.2
	shareholders
	Computation of net income available to common shareholders:
	Net income available to common shareholders		$	321.8		$	207.4		$	767.9
	Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes.
	SCHEDULE II
	(continued)
	CONDENSED STATEMENTS OF CASH FLOWS
			Year Ended December 31,
	Millions		2013			2012			2011
	Net income attributable to White Mountains’ common shareholders		$	321.8		$	207.4		$	767.9
	Charges (credits) to reconcile net income to net cash from operations:
	Net realized and unrealized (gains) losses on sales of investments		(.2		)	(11.0		)	(3.1		)
	Undistributed current earnings from subsidiaries		(359.7		)	(219.3		)	(806.7		)
	Other non-cash reconciling items including restricted share and option amortization		15.6			22.1			7.2
	Net change in other assets and liabilities, net		(2.9		)	(10.0		)	6.5
	Net cash used for operations		(25.4		)	(10.8		)	(28.2		)
	Cash flows from investing activities:
	Net decrease in short-term investments(4)		7.5			63.3			267.3
	Purchases of investment securities(1)(4)		(26.2		)	(706.2		)	(237.3		)
	Sales and maturities of investment securities(3)		61.1			2,009.70			59
	Issuance of debt from (to) subsidiaries(2)		153.9			(121.0		)	—
	Repayment of debt (to) from subsidiaries(4)		(10.3		)	28.5			192.5
	Contributions to subsidiaries(3)		—			(663.0		)	—
	Distributions from subsidiaries(1)		0.1			—			7.2
	Net cash provided from investing activities		186.1			611.3			288.7
	Cash flows from financing activities:
	Draw down of revolving line of credit(5)		200			150			—
	Repayment of revolving line of credit(2)(5)		(275.0		)	(75.0		)	—
	Proceeds from issuances of common shares		—			—			0.9
	Repurchases and retirement of common shares(2)(3)		(79.8		)	(669.1		)	(253.0		)
	Dividends paid on common shares		(6.2		)	(6.6		)	(8.0		)
	Net cash used for financing activities		(161.0		)	(600.7		)	(260.1		)
Net (decrease) increase in cash during the year		(.3		)	(.2		)	0.4
Cash balance at beginning of year		0.5			0.7			0.3
Cash balance at end of year		$	0.2		$	0.5		$	0.7
Supplemental cash flow information:
Interest paid		$	3.7		$	2		$	12.4
(1)	During 2013, the Company received a distribution of $28.0 from its direct wholly-owned subsidiary Lone Tree Holdings, Ltd. The distribution included $27.9 of fixed maturities and $.1 of cash. Purchases of investment securities excludes the non-cash distribution of $27.9.
(2)	During 2013, the Company used cash proceeds received from the issuance of debt to repurchase $79.8 of its common shares and repay $75.0 of its revolving line of credit.
(3)	During 2012, the Company sold the majority of its fixed maturity investments and used the proceeds to (a) contribute $663.0 to its subsidiaries, the majority of which was used to fund HG Global and (b) repurchase 1,329,640 of its common shares for $669.1.
(4)	In November 2011, Lone Tree Insurance Group Ltd., a direct wholly-owned subsidiary of the Registrant, was liquidated into the Registrant. Significant non-cash balances that were transferred to the Registrant as part of the liquidation included fixed maturity investments of $1,146.9, short-term investments of $284.7 and a payable to subsidiary of $417.5.
(5)	The WTM Bank Facility presented in Note 6 - “Debt” is a direct obligation of the Registrant.
Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes.

SCHEDULE_III_SUPPLEMENTARY_INS

SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION	12 Months Ended
	Dec. 31, 2013
Supplementary Insurance Information [Abstract]	'
SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION	'
	WHITE MOUNTAINS INSURANCE GROUP, LTD.
	SUPPLEMENTARY INSURANCE INFORMATION
	(Millions)
	Column A		Column B		Column C		Column D		Column E		Column F		Column G			Column H		Column I		Column J		Column K
	Segment		Deferred		Future policy		Unearned		Other policy		Premiums		Net			Benefits,		Amortization		Other		Premiums
			acquisition		benefits, losses, claims		premiums		claims and		earned		investment			claims,		of deferred		operating		written
			costs		and loss				benefits				income (1)			losses, and		policy		expenses
					expenses				payable							settlement		acquisition
																expenses		costs
	Years ended:
	31-Dec-13
	OneBeacon(2)		$	103.7	$	1,054.30	$	544.9	$	—	$	1,120.40	$	41.1		$	622.1	$	208.9	$	204.8	$	1,088.60
	Sirius Group		69.3		2,025.00		343.3		—		866.4		30.3			418.4		166.5		126.1		876.6
	HG Global/BAM		1.7		—		13.2		—		0.5		5.7			—		1.5		0.4		13.6
	Other operations		—		—		—		—		—		0.1			—		—		—		—
	31-Dec-12
	OneBeacon(2)		$	123.9	$	1,000.00	$	573.8	$	—	$	1,132.00	$	53.6		$	650	$	249.4	$	205.2	$	1,179.20
	Sirius Group		71.4		2,168.90		350.2		—		931.6		65			543.9		180.8		116.4		947.7
	HG Global/BAM		—		—		—		—		—		2.2			—		—		0.2		—
	Other operations		—		—		—		—		—		0.5			—		—		—		—
	31-Dec-11
	OneBeacon(2)		$	123.5	$	3,358.60	$	528	$	—	$	1,012.20	$	71.4		$	548.3	$	221.2	$	162.3	$	1,062.70
	Sirius Group		63.5		2,343.70		319		—		912.3		89.9			626		181		105.8		915.7
	Other operations		—		—		—		—		—		(.1		)	—		—		—		—
	(1)	The amounts shown exclude net investment income relating to non-insurance operations of $33.7, $32.3 and $23.3 for the twelve months ended December 31, 2013, 2012 and 2011, respectively.
	(2)	The amounts shown excludes balances reclassified to held for sale in the consolidated balance sheets related to the Runoff Transaction as of December 31, 2013 and 2012 and to AutoOne as of December 31, 2011. See Note 21 - “Discontinued Operations”.
	Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes.

SCHEDULE_IV_REINSURANCE

SCHEDULE IV REINSURANCE	12 Months Ended
	Dec. 31, 2013
Supplemental Schedule of Reinsurance Premiums for Insurance Companies [Abstract]	'
SCHEDULE IV REINSURANCE	'
	WHITE MOUNTAINS INSURANCE GROUP, LTD.
	REINSURANCE
	(Millions)
	Column A		Column B		Column C			Column D		Column E		Column F
	Premiums earned		Gross amount		Ceded to other			Assumed from		Net amount		Percentage of
					companies			other companies				amount assumed
												to net
	Years ended:
	31-Dec-13
	OneBeacon (1)		$	1,043.30	$	(71.4	)	$	148.5	$	1,120.40	13.3	%
	Sirius Group		174		(246.2		)	938.6		866.4		108.3	%
	31-Dec-12
	OneBeacon(1)		$	1,158.30	$	(79.1	)	$	52.8	$	1,132.00	4.7	%
	Sirius Group		169.9		(226.6		)	988.3		931.6		106.1	%
	31-Dec-11
	OneBeacon(1)		$	1,035.90	$	(66.0	)	$	42.3	$	1,012.20	4.2	%
	Sirius Group		128.5		(206.0		)	989.8		912.3		108.5	%
	-1	The amounts shown excludes balances reclassified to held for sale in the consolidated balance sheets related to the Runoff Transaction as of December 31, 2013 and 2012 and to AutoOne as of December 31, 2011. See Note 21 - “Discontinued Operations”.
	Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes.

SCHEDULE_V_VALUATION_AND_QUALI

SCHEDULE V VALUATION AND QUALIFYING ACCOUNTS	12 Months Ended
	Dec. 31, 2013
Valuation and Qualifying Accounts [Abstract]	'
SCHEDULE V VALUATION AND QUALIFYING ACCOUNTS	'
	WHITE MOUNTAINS INSURANCE GROUP, LTD.
	VALUATION AND QUALIFYING ACCOUNTS
	Column A		Column B		Column C						Column D			Column E
					Additions (subtractions)
	Millions		Balance at beginning of		Charged to costs			Charged to other			Deductions described (1)			Balance at end of
			period		and expenses			accounts						period
	Years ended:
	31-Dec-13
	Reinsurance recoverable on paid losses:
	Allowance for reinsurance balances		$	35.5	$	(.6	)	$	—		$	(11.2	)	$	23.7
	Property and casualty insurance and reinsurance premiums receivable:
	Allowance for uncollectible accounts		4.4		1			—			(1.4		)	4
	31-Dec-12
	Reinsurance recoverable on paid losses:
	Allowance for reinsurance balances		$	34.4	$	(.6	)	$	—		$	1.7		$	35.5
	Property and casualty insurance and reinsurance premiums receivable:
	Allowance for uncollectible accounts		3.4		1.1			—			(.1		)	4.4
	31-Dec-11
	Reinsurance recoverable on paid losses:
	Allowance for reinsurance balances		$	29.4	$	8.5		$	—		$	(3.5	)	$	34.4
	Property and casualty insurance and reinsurance premiums receivable:
	Allowance for uncollectible accounts		3.9		—			(.5		)	—			3.4
	(1)	Represents net collections (charge-offs) of balances receivable and foreign currency translation.
	Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes.

SCHEDULE_VI_SUPPLEMENTAL_INFOR

SCHEDULE VI SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS	12 Months Ended
	Dec. 31, 2013
Supplemental Information for Property, Casualty Insurance Underwriters [Abstract]	'
SCHEDULE VI SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS	'
	WHITE MOUNTAINS INSURANCE GROUP, LTD.
	SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS
	(Millions)
	Column A		Column B		Column C		Column D			Column E		Column F		Column G		Column H					Column I		Column J		Column K
			Deferred acquisition		Reserves		Discount, if any, deducted in			Unearned		Earned		Net investment		Claims and Claims					Amortization		Paid		Premiums
			costs(4)		for Unpaid		Column C			Premiums		Premiums		income		Adjustment Expenses					of deferred		Claims and		written
					Claims and											Incurred Related to					policy acquisition(4)		Claims Adjustment
					Claims Adjustment																costs		Expenses
	Affiliation with				Expenses											(1) Current		(2) Prior
	registrant															Year		Year
	OneBeacon(3):
	2013		$	103.7	$	1,054.30	$	3	(1)	$	544.9	$	1,120.40	$	41.1	$	622.1	$	—		$	208.9	$	540.7	$	1,088.60
	2012		123.9		1,000.00		4.6		(1)	573.8		1,132.00		53.6		657.4		(7.4		)	249.4		565.1		1,179.20
	2011		123.5		3,358.60		271.6		(1)	528		1,012.20		71.4		578.1		(29.8		)	221.2		523.2		1,062.70
	Sirius Group:
	2013		$	69.3	$	2,025.00	$	1.7	(2)	$	343.3	$	866.4	$	30.3	$	466.8	$	(48.4	)	$	166.5	$	628.1	$	876.6
	2012		71.4		2,168.90		2.4		(2)	350.2		931.6		65		578.4		(34.5		)	180.8		741.2		947.7
	2011		63.5		2,343.70		12.8		(2)	319		912.3		89.9		672.9		(46.9		)	181		642		915.7
	(1)	The amounts shown represent OneBeacon’s discount on its long-term workers compensation loss and LAE reserves, as such liabilities constitute unpaid but settled claims under which the payment pattern and ultimate costs are fixed and determinable on an individual basis. OneBeacon discounts these reserves using a discount rate which is determined based on the facts and circumstances applicable at the time the claims are settled (3.5%, 3.5% and 5.0% at December 31, 2013, 2012 and 2011). Also the amounts shown include unamortized fair value adjustments to reserves for unpaid claims and claims adjustment expenses made in purchase accounting as a result of White Mountains’ purchase of OneBeacon for the years ended December 31, 2013, 2012 and 2011.
	(2)	The amount shown represents unamortized fair value adjustments to reserves for unpaid claims and claims adjustment expenses made in purchase accounting as a result of White Mountains’ purchase of Sirius International during 2004.
	(3)	The amounts shown excludes balances reclassified to held for sale in the consolidated balance sheets related to the Runoff Transaction as of December 31, 2013 and 2012 and to AutoOne as of December 31, 2011. See Note 21 - “Discontinued Operations”.
	(4)	In 2012, the Company adopted ASU 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts (ASC 944). See Note 1 - “Summary of Significant Accounting Policies”.
	Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Investment securities	'
	Investment Securities
	At December 31, 2013, White Mountains’ invested assets consisted of securities and other investments held for general investment purposes.  White Mountains’ portfolio of fixed maturity investments and common equity securities held for general investment purposes are classified as trading and are reported at fair value as of the balance sheet date.  Changes in unrealized gains and losses are reported pre-tax in revenues. Realized investment gains and losses are accounted for using the specific identification method and are reported pre-tax in revenues. Premiums and discounts on all fixed maturity investments are accreted to income over the anticipated life of the investment.
	White Mountains’ invested assets that are measured at fair value include fixed maturity securities, common and preferred equity securities, convertible fixed maturity securities and other long-term investments, such as interests in hedge funds and private equities. In determining its estimates of fair value, White Mountains uses a variety of valuation approaches and inputs. Whenever possible, White Mountains estimates fair value using valuation methods that maximize the use of quoted prices and other observable inputs.
	As of December 31, 2013 and 2012, approximately 95% of the investment portfolio recorded at fair value was priced based upon quoted market prices or other observable inputs. Investments valued using Level 1 inputs include fixed maturities, primarily investments in U.S. Treasuries, common equities and short-term investments, which include U.S. Treasury Bills. Investments valued using Level 2 inputs comprise fixed maturities including corporate debt, state and other governmental debt, convertible fixed maturity securities and mortgage and asset-backed securities. Fair value estimates for investments that trade infrequently and have few or no observable market prices are classified as Level 3 measurements. Level 3 fair value estimates based upon unobservable inputs include White Mountains’ investments in hedge funds and private equity funds, as well as investments in certain debt securities, including asset-backed securities, where quoted market prices are unavailable. White Mountains determines when transfers between levels have occurred as of the beginning of the period. 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, 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 a review of the pricing services’ quality control processes and procedures on at least an annual basis, comparison of market prices to prices obtained from a 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 million from the expected price based on these procedures are considered outliers. Prices that have not changed from period to period and prices that have trended unusually compared to market conditions are also 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.  During the past year, approximately thirty-five securities fell outside White Mountains’ expected results, thereby triggering the challenge with the pricing service. 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, including asset-backed 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 prospectively over the remaining economic life.
	Short-term investments consist of money market funds, certificates of deposit and other securities which, at the time of purchase, mature or become available for use within one year.  Short-term investments are carried at amortized cost, which approximated fair value as of December 31, 2013 and 2012.
Other long-term investments	'
	Other Long-term Investments
	White Mountains’ other long-term investments consist primarily of hedge funds, private equity funds and other investments in limited partnerships. White Mountains has taken the fair value option for most of its investments in hedge funds, private equity funds and other limited partnership investments. For the investments for which White Mountains has taken the fair value option, changes in fair value are reported in revenues on a pre-tax basis. For those hedge fund and private equity investments for which White Mountains has not made the fair value election, White Mountains accounts for its interests under the equity method.
Derivative financial instruments	'
	Derivative Financial Instruments
	White Mountains holds a variety of derivative financial instruments for both risk management and investment purposes. White Mountains recognizes all derivatives as either assets or liabilities, measured at fair value, in the consolidated balance sheets. Changes in the fair value of derivative instruments are recognized in current period pre-tax income.
Warrants	'
	Warrants
	At December 31, 2012, White Mountains held warrants to purchase 9.49 million common shares of Symetra which were included as investments in unconsolidated affiliates. The Symetra warrants held by White Mountains were entitled to dividends declared to common shareholders. On June 20, 2013, White Mountains exercised its warrants in a cashless transaction and received 2.65 million common shares of Symetra in exchange for the warrants.
	White Mountains also holds warrants that it has received in the restructuring (e.g., securities received from bankruptcy proceedings) of certain of its common equity and/or fixed maturity investments. White Mountains accounts for its investments in warrants as derivatives.
Derivatives - Variable annuity reinsurance	'
	Derivatives—Variable Annuity Reinsurance
	White Mountains has entered into agreements to reinsure death and living benefit guarantees associated with certain variable annuities in Japan through its wholly owned subsidiary, WM Life Re. The accounting for benefit guarantees differs depending on whether or not the guarantee is classified as a derivative or an insurance liability.
	Guaranteed minimum accumulation benefits (“GMABs”) are paid to an annuitant for any shortfall between accumulated account value at the end of the accumulation period and the annuitant’s total deposit, less any withdrawal payments made to the annuitant during the accumulation period. GMABs meet the definition of a derivative for accounting purposes. Therefore, GMABs are carried at fair value, with changes thereon recognized in income in the period of the change. The liability for the reinsured GMAB contracts has been determined using internal valuation models that use assumptions for interest rates, equity markets, foreign exchange rates and market volatilities at the valuation date, as well as annuitant-related actuarial assumptions, including surrender and mortality rates.
	If an annuitant dies during the accumulation period of an annuity contract, guaranteed minimum death benefits (“GMDBs”) are paid to the annuitant’s beneficiary for shortfalls between accumulated account value at the time of an annuitant’s death and the annuitant’s total deposit, less any living benefit payments or withdrawal payments previously made to the annuitant. White Mountains has elected to measure its GMDB liabilities at fair value.
	The valuation of these liabilities involves significant judgment and is subject to change based upon changes in capital market assumptions and emerging surrender and mortality experience of the underlying contracts in force.
	WM Life Re has entered into derivative contracts that are designed to economically hedge against changes in the fair value of living and death benefit liabilities associated with its variable annuity reinsurance arrangements. The derivatives include futures and over-the-counter option contracts on interest rates, major bond and equity indices, and foreign currencies. All WM Life Re’s derivative instruments are recorded as assets or liabilities at fair value on the balance sheet within other assets. These derivative financial instruments do not meet the criteria for hedge accounting treatment, and accordingly, changes in fair value are recognized in the current period as gains or losses in the income statement within other revenues.
	WM Life Re includes the effect of counterparty credit risk when determining the fair value of its derivative contracts and its GMAB and GMDB liabilities.
Cash	'
	Cash
	Cash includes amounts on hand and demand deposits with banks and other financial institutions. Amounts presented in the statement of cash flows are shown net of balances acquired and sold in the purchase or sale of the Company’s consolidated subsidiaries and exclude changes in amounts of restricted cash (See Note 8).
Insurance and reinsurance operations	'
	Insurance and Reinsurance Operations
	White Mountains accounts for insurance and reinsurance policies that it writes in accordance with ASC 944. Premiums written are recognized as revenues and are earned ratably over the term of the related policy or reinsurance treaty. Unearned premiums represent the portion of premiums written that are applicable to future insurance or reinsurance coverage provided by policies or treaties in force.  White Mountains charges fees on certain of its insurance policies. Refundable fees are classified with premiums and recognized in earnings over the policy term. Fees that represent a reimbursement of expenses, such as installment fees, are recorded as a reduction of underwriting expenses.
	Deferred acquisition costs represent commissions, premium taxes, brokerage expenses and other costs which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent they relate to successful contract acquisitions over the applicable premium recognition period as insurance and reinsurance acquisition expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income. This limitation is referred to as a premium deficiency. A premium deficiency is recognized if the sum of expected loss and loss adjustment expenses (“LAE”), expected dividends to policyholders, unamortized acquisition costs, and maintenance costs exceeds related unearned premiums and anticipated investment income. A premium deficiency is recognized by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs then a liability is accrued for the excess deficiency.
	Losses and LAE are charged against income as incurred. Unpaid insurance losses and LAE are based on estimates (generally determined by claims adjusters, legal counsel and actuarial staff) of the ultimate costs of settling claims, including the effects of inflation and other societal and economic factors. Unpaid reinsurance losses and LAE are based primarily on reports received from ceding companies and actuarial projections. Unpaid loss and LAE reserves represent management’s best estimate of ultimate losses and LAE, net of estimated salvage and subrogation recoveries, if applicable. Such estimates are regularly reviewed and updated and any adjustments resulting there from are reflected in current operations. The process of estimating loss and LAE involves a considerable degree of judgment by management and the ultimate amount of expense to be incurred could be considerably greater than or less than the amounts currently reflected in the financial statements.
	OneBeacon discounts certain of its long-term workers compensation loss and LAE reserves when such liabilities constitute unpaid but settled claims under which the payment pattern and ultimate costs are fixed and determinable on an individual claim basis. OneBeacon discounts these reserves using an average discount rate which is determined based on the various assumptions including consideration of when the claims will be settled (3.5% at both December 31, 2013 and 2012). As of December 31, 2013, the discount on OneBeacon’s workers compensation loss and LAE reserves amounted to $3.0 million (excluding $61.7 million which relates to reserves classified as held for sale). As of December 31, 2012, the discount on OneBeacon’s workers compensation loss and LAE reserves amounted to $4.6 million, (excluding $77.9 million on reserves classified as discontinued operations).
	White Mountains’ insurance and reinsurance subsidiaries enter into ceded reinsurance contracts from time to time to protect their businesses from losses due to concentration of risk, to manage their operating leverage ratios and to limit losses arising from catastrophic events. Such reinsurance contracts are executed through excess of loss treaties and catastrophe contracts under which the reinsurer indemnifies White Mountains for a specified part or all of certain types of losses over stipulated amounts arising from any one occurrence or event. White Mountains has also entered into quota share treaties with reinsurers under which all risks meeting prescribed criteria are covered on a pro-rata basis. The amount of each risk ceded by White Mountains is subject to maximum limits which vary by line of business and type of coverage.
	Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured policies. The collectability of reinsurance recoverables is subject to the solvency of the reinsurers. White Mountains is selective in regard to its reinsurers, principally placing reinsurance with those reinsurers with a strong financial condition, industry ratings and underwriting ability. Management monitors the financial condition and ratings of its reinsurers on an ongoing basis.
	Reinsurance premiums, commissions, expense reimbursements and reserves related to reinsured business are accounted for on a basis consistent with those used in accounting for the original policies issued and the terms of the reinsurance contracts. Premiums ceded to other companies are reported as a reduction of premiums written. Expense allowances received in connection with reinsurance ceded have been accounted for as a reduction of the related policy acquisition costs and are deferred and amortized accordingly. Funds held by ceding companies represent amounts due to White Mountains in connection with certain assumed reinsurance agreements in which the ceding company retains a portion of the premium to provide security against future loss payments. The funds held by ceding companies are generally invested by the ceding company and a contractually agreed interest amount is credited to the Company and recognized as investment income. Funds held under insurance and reinsurance contracts represent contractual payments due to White Mountains that have been retained to secure such obligations. Such amounts are recorded as liabilities in the consolidated financial statements.
	Accruals for contingent commission liabilities are established for reinsurance contracts that provide for the stated commission percentage to increase or decrease based on the loss experience of the contract. Changes in the estimated liability for such arrangements are recorded as contingent commissions. Accruals for contingent commission liabilities are determined through the review of the contracts that have these adjustable features and are estimated based on expected loss and LAE.
Municipal Bond Insurance	'
	Municipal Bond Insurance
	All of the contracts issued by BAM are accounted for as insurance contracts under ASC 944-605, Financial Guarantee Insurance Contracts. Premiums are generally 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.
	Deferred acquisition costs represent commissions, premium taxes, excise taxes and other costs which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent they relate to successful contract acquisitions over the applicable premium recognition period as acquisition expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income.
Mandatory Shared Market Mechanisms	'
	Mandatory Shared Market Mechanisms
	As a condition to its licenses to do business in certain states, White Mountains’ insurance operations must participate in various mandatory shared market mechanisms commonly referred to as “residual” or “involuntary” markets. These markets generally consist of risks considered to be undesirable from a standard or routine underwriting perspective. Each state dictates the levels of insurance coverage that are mandatorily assigned to participating insurers within these markets. The total amount of such business an insurer must accept in a particular state is generally based on that insurer’s market share of voluntary business written within that state. In certain cases, White Mountains is obligated to write business from shared market mechanisms at a future date based on its historical market share of all voluntary policies written within that state. Involuntary business generated from mandatory shared market mechanisms is accounted for as direct insurance business or as assumed reinsurance depending upon the structure of the mechanism.
	OneBeacon’s market assignments are typically required to be written in the current period, however, in certain cases OneBeacon is required to accept policy assignments at a future date. Anticipated losses associated with future market assignments are recognized when the amount of such anticipated losses is determined to be probable and can be reasonably estimated.
Insurance-Related Assessments	'
	Insurance-related Assessments
	Under existing guaranty fund laws in all states, insurers licensed to do business in those states can be assessed for certain obligations of insolvent insurance companies to policyholders and claimants. White Mountains records guaranty fund assessments when it is probable that an assessment will be made and the amount can be reasonably estimated.
Deferred Software Costs	'
	Deferred Software Costs
	White Mountains capitalizes costs related to computer software developed for internal use during the application development stage of software development projects. These costs generally consist of certain external, payroll and payroll-related costs. White Mountains begins amortization of these costs once the project is completed and ready for its intended use. Amortization is on a straight-line basis and over a useful life of three to five years. At December 31, 2013 and 2012, White Mountains had unamortized deferred software costs of $23.8 million and $17.1 million.
Federal and foreign income taxes	'
	Federal and Foreign Income Taxes
	A significant portion of White Mountains’ subsidiaries file consolidated tax returns in the United States. Income earned or losses generated by companies outside the United States are generally subject to an overall effective tax rate lower than that imposed by the United States.
	Deferred tax assets and liabilities are recorded when a difference between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts for tax purposes exists, and for other temporary differences. The deferred tax asset or liability is recorded based on tax rates expected to be in effect when the difference reverses. The deferred tax asset is recognized when it is more likely than not that it will be realized.
Foreign currency exchange	'
	Foreign Currency Exchange
	The U.S. dollar is the functional currency for all of White Mountains’ businesses except for Sirius International, the Canadian reinsurance operations of Sirius America and certain other smaller international activities.  White Mountains also invests in securities denominated in foreign currencies. Assets and liabilities recorded in these foreign currencies are translated into U.S. dollars at exchange rates in effect at the balance sheet date, and revenues and expenses are converted using the average exchange rates for the period. Net foreign exchange gains and losses arising from the translation are generally reported in shareholders’ equity, in accumulated other comprehensive income or loss.
	Assets and liabilities relating to foreign operations are translated into the functional currency using current exchange rates; revenues and expenses are translated into the functional currency using the weighted average exchange rate for the period.  The resulting exchange gains and losses are reported as a component of net income in the period in which they arise. As of December 31, 2013 and 2012, White Mountains had unrealized foreign currency translation gains of $88.4 million and $85.7 million recorded in accumulated other comprehensive income on its consolidated balance sheet.
	The following rates of exchange for the U.S. dollar have been used for the most significant operations:
	Currency	Opening Rate	Closing Rate	Opening Rate	Closing Rate
		2013	2013	2012	2012
	Swedish kronor	6.4973	6.4339	6.8645	6.4973
	British pound	0.6154	0.6044	0.6434	0.6154
	Canadian dollar	0.9955	1.0625	1.0193	0.9955
Noncontrolling Interest	'
	Non-controlling Interest
	Non-controlling interests consist of the ownership interests of non-controlling shareholders in consolidated subsidiaries, and are presented separately on the balance sheet. The portion of comprehensive income attributable to non-controlling interests is presented net of related income taxes in the statement of operations and comprehensive income. The percentage of the non-controlling shareholders’ ownership interest in OneBeacon Ltd. at both December 31, 2013 and 2012 was 24.8%.
	In 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 years ended December 31, 2013 and 2012, BAM reported $78.6 million and $36.3 million in pre-tax losses that have been allocated to non-controlling interest.
	On May 24, 2007, Sirius International Group, Ltd. (“SIG”), an intermediate holding company of Sirius Group, issued $250.0 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. These shares were issued in an offering that was exempt from the registration requirements of the Securities Act of 1933. Holders of the SIG Preference Shares receive dividends on a non-cumulative basis when and if declared by SIG. The holders of the SIG Preference Shares have the right to elect two directors to SIG’s board in the event of non-payment of dividends for six quarterly dividend periods. The right ceases upon the payment of dividends for four quarterly periods or the redemption of the SIG Preference Shares. In addition, SIG may not declare or pay dividends on its common shares (other than stock dividends and dividends paid for purposes of any employee benefit plans of SIG and its subsidiaries) unless it is current on its most recent dividend period. The dividend rate is fixed at an annual rate of 7.506% until June 30, 2017 and dividends are paid on a semi-annual basis. After June 30, 2017, the dividend rate will be paid at a floating annual rate, equal to the greater of (1) the 3 month LIBOR plus 320 bps or (2) 7.506% and dividends will be paid on a quarterly basis. The SIG Preference Shares are redeemable solely at the discretion of SIG on or after June 30, 2017 at their liquidation preference of $1,000 per share, plus any declared but unpaid dividends. In July 2013, SIG executed a 5-year forward LIBOR cap (the “Interest Rate Cap”) for the period from June 2017 to June 2022 to protect against a significant increase in interest rates during that 5-year period. The Interest Rate Cap fixes the annual dividend rate on the SIG Preference Shares from June 2017 to June 2022 at 8.30%. The Interest Rate Cap is recorded in other assets at fair value. Changes in fair value are recorded in other revenue.
	Prior to June 30, 2017, SIG may elect to redeem the SIG Preference Shares at an amount equal to the greater of (1) the aggregate liquidation preference of the shares to be redeemed and (2) the sum of the present values of the aggregate liquidation preference of the shares to be redeemed and the remaining scheduled dividend payments on the shares to be redeemed (excluding June 30, 2017), discounted to the redemption date on a semi-annual basis at a rate equal to the rate on a comparable treasury issue plus 45 basis points. In the event of liquidation of SIG, the holders of the SIG Preference Shares would have preference over the common shareholders and would receive a distribution equal to the liquidation preference per share, subject to availability of funds. SIG Preference Shares and dividends thereon are included in non-controlling interest on the balance sheet and as non-controlling interest expense on the statement of income and comprehensive income.
	At December 31, 2013 and 2012, the non-controlling equity interest in White Mountains’ consolidated limited partnerships was $46.1 million and $41.5 million. At December 31, 2013 and 2012, the non-controlling equity interest in A.W.G. Dewar Inc, a subsidiary of OneBeacon, was $3.1 million and $2.8 million. On September 30, 2013, Sirius Group purchased the remaining 25.0% ownership in one of its subsidiaries, Passage2Health Limited. At December 31, 2012, the non-controlling equity interest in Passage2Health Limited was $0.2 million.
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.
Policy Acquisition Costs	'
	Policy Acquisition Costs
	On January 1, 2012, White Mountains adopted ASU 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts (ASC 944). The new standard changes the types of policy acquisition costs that are eligible for deferral. Specifically, the new guidance limits deferrable costs to those that are incremental direct costs of contract acquisition and certain costs related to acquisition activities performed by the insurer, such as underwriting, policy issuance and processing, medical and inspection costs and sales force contract selling. The ASU defines incremental direct costs as those costs that result directly from and were essential to the contract acquisition and would not have been incurred absent the acquisition. Accordingly, under the new guidance, deferrable acquisition costs are limited to costs related to successful contract acquisitions. Acquisition costs that are not eligible for deferral are to be charged to expense in the period incurred.
	White Mountains adopted ASU 2010-26 prospectively. Upon adoption, certain acquisition costs, primarily a portion of the profit sharing commissions associated with OneBeacon’s collector car and boats business, no longer 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.  (See Note 5).
Comprehensive Income	'
	Comprehensive Income
	For fiscal periods beginning after December 15, 2011, ASU 2011-05, Comprehensive Income (ASC 220) became effective, which requires all components of comprehensive income to be reported in a continuous financial statement or in consecutive statements displaying the components of net income and the components of other comprehensive income. Since White Mountains presents comprehensive income in a continuous financial statement, adoption of ASU 2011-05 had no effect on White Mountains’ financial statement presentation.
Variable Interest Entities	'
	Variable Interest Entities
	White Mountains consolidates a variable interest entity (“VIE”) when it has both the power to direct the activities of the VIE that most significantly impact its economic performance and either the obligation to absorb losses or the right to receive returns from the VIE that could potentially be significant to the VIE (See Note 17).

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2013
Accounting Policies [Abstract]	'
Schedule of rates of exchange for the U.S. dollar that have been used for the most significant operations	'
	The following rates of exchange for the U.S. dollar have been used for the most significant operations:
	Currency	Opening Rate	Closing Rate	Opening Rate	Closing Rate
		2013	2013	2012	2012
	Swedish kronor	6.4973	6.4339	6.8645	6.4973
	British pound	0.6154	0.6044	0.6434	0.6154
	Canadian dollar	0.9955	1.0625	1.0193	0.9955

Reserves_for_Unpaid_Losses_and1

Reserves for Unpaid Losses and Loss Adjustment Expenses (Tables)	12 Months Ended
	Dec. 31, 2013
Insurance Loss Reserves [Abstract]	'
Loss and LAE reserve activities	'
	The following table summarizes the loss and LAE reserve activities of White Mountains’ insurance and reinsurance subsidiaries for the years ended December 31, 2013, 2012 and 2011:
			Year Ended December 31,
	Millions		2013			2012			2011
	Gross beginning balance		$	3,168.90		$	5,702.30		$	5,736.80
	Less beginning reinsurance recoverable on unpaid losses		(429.1		)	(2,507.3		)	(2,344.0		)
	Net loss and LAE reserves		2,739.80			3,195.00			3,392.80
	Less: Beginning net loss and LAE reserves for AutoOne and		—			(383.3		)	(619.6		)
	the Runoff Transaction(1)
	Loss and LAE reserves acquired(2)		37.7			17			21
	Losses and LAE incurred relating to:
	Current year losses		1,088.90			1,235.80			1,251.00
	Prior year losses		(48.4		)	(41.9		)	(76.7		)
	Total incurred losses and LAE		1,040.50			1,193.90			1,174.30
	Accretion of fair value adjustment to net loss and LAE reserves		1.7			10.6			8.3
	Foreign currency translation adjustment to net loss and LAE reserves		0.3			12.9			0.1
	Loss and LAE paid relating to:
	Current year losses		(336.2		)	(404.7		)	(387.9		)
	Prior year losses		(832.6		)	(901.6		)	(777.3		)
	Total loss and LAE payments		(1,168.8		)	(1,306.3		)	(1,165.2		)
	Plus: Ending net loss and LAE reserves for AutoOne and		—			—			383.3
	the Runoff Transaction(1)
	Net ending balance		2,651.20			2,739.80			3,195.00
	Plus ending reinsurance recoverable on unpaid losses		428.1			429.1			2,507.30
	Gross ending balance		$	3,079.30		$	3,168.90		$	5,702.30
	(1)	Loss and LAE reserve balances from OneBeacon’s Runoff Business prior to December 31, 2012 and AutoOne prior to December 31, 2011 were not classified as held for sale. Adjustment is to present loss and LAE reserve activities for continuing operations.
	(2)	Loss and LAE reserves acquired relate to WM Solutions purchases of Empire and Ashmere in 2013, PICO, Citation, Woodridge and Oakwood in 2012 and Old Lyme in 2011.
Schedule of asbestos and environmental loss and LAE reserve activities	'
	Sirius Group
	Net A&E Loss Reserve Activity		Year Ended December 31,
			2013						2012						2011
	Millions		Gross			Net			Gross			Net			Gross			Net
	Asbestos:
	Beginning balance		$	208.2		$	174.2		$	185.1		$	146.2		$	191.9		$	151.5
	Losses and LAE acquired		13			13			11			11			—			—
	Incurred losses and LAE		12.1			11.8			46.8			46.4			13.6			10.3
	Paid losses and LAE		(25.9		)	(20.3		)	(34.7		)	(29.4		)	(20.4		)	(15.6		)
	Ending balance		207.4			178.7			208.2			174.2			185.1			146.2
	Environmental:
	Beginning balance		20.4			15.2			22.1			16.5			22.4			18.1
	Losses and LAE acquired		1			1			0.7			0.7			—			—
	Incurred losses and LAE		0.8			0.8			(.1		)	(.5		)	2.9			2
	Paid losses and LAE		(1.8		)	(1.8		)	(2.3		)	(1.5		)	(3.2		)	(3.6		)
	Ending balance		20.4			15.2			20.4			15.2			22.1			16.5
	Total asbestos and environmental:
	Beginning balance		228.6			189.4			207.2			162.7			214.3			169.6
	Losses and LAE acquired		14			14			11.7			11.7			—			—
	Incurred losses and LAE		12.9			12.6			46.7			45.9			16.5			12.3
	Paid losses and LAE		(27.7		)	(22.1		)	(37.0		)	(30.9		)	(23.6		)	(19.2		)
	Ending balance		$	227.8		$	193.9		$	228.6		$	189.4		$	207.2		$	162.7
	The following tables summarize reported A&E loss and LAE reserve activities (gross and net of reinsurance) for OneBeacon for the years ended December 31, 2013, 2012 and 2011, respectively.
	Net A&E Loss		Year Ended December 31,
	Reserve Activity		2013									2012									2011
						Pre-NICO									Pre-NICO									Pre-NICO
	Millions		Gross			Net(1)			Net(2)			Gross			Net(1)			Net(2)			Gross			Net(1)			Net(2)
	Asbestos:
	Beginning balance		$	929.4		$	602.5		$	2.4		$	1,074.30		$	681.2		$	2.2		$	904		$	647.3		$	6.4
	Incurred losses and LAE		—			—			—			(.3		)	(.5		)	(.5		)	256.8			32.2			(4.0		)
	Paid losses and LAE		(84.3		)	(79.3		)	(.5		)	(144.6		)	(78.2		)	0.7			(86.5		)	1.7			(.2		)
	Ending balance		845.1			523.2			1.9			929.4			602.5			2.4			1,074.30			681.2			2.2
	Environmental:
	Beginning balance		233			125.4			6.4			279.8			151.6			9			119			93.8			9.2
	Incurred losses and LAE		—			—			—			(.9		)	(.5		)	(.5		)	231.8			62.2			10
	Paid losses and LAE		(64.3		)	(33.0		)	(2.6		)	(45.9		)	(25.7		)	(2.1		)	(71.0		)	(4.4		)	(10.2		)
	Ending balance		168.7			92.4			3.8			233			125.4			6.4			279.8			151.6			9
	Total asbestos and environmental:
	Beginning balance		1,162.40			727.9			8.8			1,354.10			832.8			11.2			1,023.00			741.1			15.6
	Incurred losses and LAE		—			—			—			(1.2		)	(1.0		)	(1.0		)	488.6			94.4			6
	Paid losses and LAE		(148.6		)	(112.3		)	(3.1		)	(190.5		)	(103.9		)	(1.4		)	(157.5		)	(2.7		)	(10.4		)
	Ending balance		$	1,013.80		$	615.6		$	5.7		$	1,162.40		$	727.9		$	8.8		$	1,354.10		$	832.8		$	11.2
	(1)	Represents A&E reserve activity, net of third-party reinsurance, but prior to the NICO Cover.
	(2)	Includes NICO cover

Third_Party_Reinsurance_Tables

Third Party Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2013
Ceded Credit Risk [Line Items]	'
Schedule of direct assumed and ceded amounts	'
	The effects of reinsurance on White Mountains’ insurance and reinsurance subsidiaries’ written and earned premiums and on losses and LAE were as follows (see Note 9 for balances related to White Mountains financial guarantee business):
		Year Ended December 31, 2013
	Millions	OneBeacon			Sirius Group			Total
	Written premiums:
	Direct	$	1,103.10		$	177.3		$	1,280.40
	Assumed	59.8			943.1			1,002.90
	Gross written premiums	1,162.90			1,120.40			2,283.30
	Ceded	(74.3		)	(243.8		)	(318.1		)
	Net written premiums	$	1,088.60		$	876.6		$	1,965.20
	Earned premiums:
	Direct	$	1,043.30		$	174		$	1,217.30
	Assumed	148.5			938.6			1,087.10
	Gross earned premiums	1,191.80			1,112.60			2,304.40
	Ceded	(71.4		)	(246.2		)	(317.6		)
	Net earned premiums	$	1,120.40		$	866.4		$	1,986.80
	Losses and LAE:
	Direct	$	584.9		$	98.1		$	683
	Assumed	76.3			455.5			531.8
	Gross losses and LAE	661.2			553.6			1,214.80
	Ceded	(39.1		)	(135.2		)	(174.3		)
	Net losses and LAE	$	622.1		$	418.4		$	1,040.50
		Year Ended December 31, 2012
	Millions	OneBeacon			Sirius Group			Total
	Written premiums:
	Direct	$	1,204.00		$	186.1		$	1,390.10
	Assumed	55.2			992.7			1,047.90
	Gross written premiums	1,259.20			1,178.80			2,438.00
	Ceded	(80.0		)	(231.1		)	(311.1		)
	Net written premiums	$	1,179.20		$	947.7		$	2,126.90
	Earned premiums:
	Direct	$	1,158.30		$	169.9		$	1,328.20
	Assumed	52.8			988.3			1,041.10
	Gross earned premiums	1,211.10			1,158.20			2,369.30
	Ceded	(79.1		)	(226.6		)	(305.7		)
	Net earned premiums	$	1,132.00		$	931.6		$	2,063.60
	Losses and LAE:
	Direct	$	687.5		$	96.9		$	784.4
	Assumed	29.6			523.9			553.5
	Gross losses and LAE	717.1			620.8			1,337.90
	Ceded	(67.1		)	(76.9		)	(144.0		)
	Net losses and LAE	$	650		$	543.9		$	1,193.90
		Year Ended December 31, 2011
	Millions	OneBeacon			Sirius Group			Total
	Written premiums:
	Direct	$	1,079.20		$	139.5		$	1,218.70
	Assumed	49.1			988.6			1,037.70
	Gross written premiums	1,128.30			1,128.10			2,256.40
	Ceded	(65.6		)	(212.4		)	(278.0		)
	Net written premiums	$	1,062.70		$	915.7		$	1,978.40
	Earned premiums:
	Direct	$	1,035.90		$	128.5		$	1,164.40
	Assumed	42.3			989.8			1,032.10
	Gross earned premiums	1,078.20			1,118.30			2,196.50
	Ceded	(66.0		)	(206.0		)	(272.0		)
	Net earned premiums	$	1,012.20		$	912.3		$	1,924.50
	Losses and LAE:
	Direct	$	551.8		$	80		$	631.8
	Assumed	9.2			627.8			637
	Gross losses and LAE	561			707.8			1,268.80
	Ceded	(12.7		)	(81.8		)	(94.5		)
	Net losses and LAE	$	548.3		$	626		$	1,174.30
OneBeacon	'
Ceded Credit Risk [Line Items]	'
Ceded Credit Risk	'
	The reinsurance balances associated with the Runoff Business are included in discontinued operations (see Note 21).
	Standard & Poor’s Rating(1)	Balance at December 31, 2013			% of Total
	AA	$	26.4		30	%
	A	56.1			62	%
	BBB+, Not rated and other	7.4			8	%
	Total	$	89.9		100	%
	(1)  Standard & Poor’s ratings as detailed above are: “AA” (Very strong), “A” (Strong) and “BBB+” (Adequate).
Sirius Group	'
Ceded Credit Risk [Line Items]	'
Ceded Credit Risk	'
	The following table provides a listing of Sirius Group’s gross and net recoverable amounts by the reinsurer’s Standard & Poor’s rating and the percentage of total recoverables.
	Rating(1)	Gross			Collateral			Net			% of Net Total
	AAA	$	62.9		$	—		$	62.9		19	%
	AA	60.6			4.5			56.1			17	%
	A	127.5			1.6			125.9			39	%
	BBB+	21			—			21			7	%
	BBB or lower	16.6			—			16.6			5	%
	Not rated	75			31.5			43.5			13	%
	Total	$	363.6		$	37.6		$	326		100	%
	(1) Standard & Poor’s ratings as detailed above are: “AAA” (Extremely strong), “AA” (Very strong), “A” (Strong), and “BBB+” and “BBB” (Adequate).

Investment_Securities_Tables

Investment Securities (Tables)	12 Months Ended
	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]	'
Pre-tax net investment income	'
	Pre-tax net investment income for 2013, 2012 and 2011 consisted of the following:
			Year Ended December 31,
	Millions		2013				2012				2011
	Investment income:
	Fixed maturity investments		$	100.5			$	132			$	166.2
	Short-term investments		3.4				3.1				4.5
	Common equity securities		20.5				22.2				15.4
	Convertible fixed maturity investments		2.9				6				5.5
	Other long-term investments		3				3.1				4.2
	Interest on funds held under reinsurance treaties		0.3				0.6				(.4		)
	Total investment income		130.6				167				195.4
	Third-party investment expenses		(19.7		)		(13.4		)		(10.9		)
	Net investment income, pre-tax		$	110.9			$	153.6			$	184.5
Net Realized and Unrealized Investment Gains and Losses	'
	Net Realized and Unrealized Investment Gains and Losses
	Net realized and unrealized investment gains and losses consisted of the following:
			Year Ended December 31,
	Millions		2013				2012				2011
	Net realized investment gains, pre-tax		$	104.5			$	68.1			$	68.3
	Net unrealized investment gains, pre-tax		57.2				50.1				5.8
	Net realized and unrealized investment gains, pre-tax		161.7				118.2				74.1
	Income tax expense attributable to net realized and		(21.9		)		(26.8		)		(18.1		)
	unrealized investment gains
	Net realized and unrealized investment gains, after tax		$	139.8			$	91.4			$	56
Net unrealized investment gains (losses) for Level 3 investments	'
	The following table summarizes the amount of total gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments for the years ended December 31, 2013, 2012 and 2011.
			Year Ended December 31,
	Millions		2013				2012				2011
	Fixed maturity investments		$	(2.3	)		$	7.7			$	(12.2	)
	Common equity securities		0.9				3				(16.6		)
	Convertible fixed maturity investments		—				—				—
	Other long-term investments		11.2				7				(16.8		)
	Total net unrealized investment gains (losses), pre-tax - Level 3 investments		$	9.8			$	17.7			$	(45.6	)
Net realized and unrealized investment gains, after-tax, as recorded on the statements of operations and comprehensive income (losses)	'
	The components of White Mountains’ net realized and unrealized investment gains (losses), after-tax, as recorded on the statements of operations and comprehensive income were as follows:
			Year Ended December 31,
	Millions		2013				2012				2011
	Net change in pre-tax unrealized gains (losses) on investments in		$	(106.4	)		$	62.8			$	(63.6	)
	unconsolidated affiliates
	Income taxes		8.3				(5.1		)		5.1
	Net change in unrealized gains (losses) on investments in		(98.1		)		57.7				(58.5		)
	unconsolidated affiliates, after tax
	Net realized and unrealized foreign currency gains (losses) on		11.3				95.5				(41.7		)
	investments through OCI
	Total investments gains (losses) through accumulated other		(86.8		)		153.2				(100.2		)
	comprehensive income
	Net realized and unrealized investment gains, after-tax		139.8				$	91.4			$	56
	Total investment gains (losses) recorded during the period, after-tax		$	53			$	244.6			$	(44.2	)
Realized Gain (Loss) on Investments	'
	Net realized investment gains (losses)
	Net realized investment gains (losses) for 2013, 2012 and 2011 consisted of the following:
			Year ended December 31, 2013
	Millions		Net realized gains (losses)				Net				Total
							foreign				changes in
							exchange				fair value
							gains				reflected in
							(losses)				earnings
	Fixed maturity investments		$	8.6			$	(15.0	)		$	(6.4	)
	Short-term investments		0.1				—				0.1
	Common equity securities		104.5				(3.7		)		100.8
	Convertible fixed maturity investments		1				—				1
	Other long-term investments		7.5				1.4				8.9
	Forward contracts		0.1				—				0.1
	Net realized investment gains (losses), pre-tax		121.8				(17.3		)		104.5
	Income taxes attributable to realized		(30.0		)		5.5				(24.5		)
	investment gains (losses)
	Net realized investment gains (losses), after-tax		$	91.8			$	(11.8	)		$	80
			Year ended December 31, 2012
	Millions		Net realized gains (losses)				Net				Total
							foreign				changes in
							exchange				fair value
							gains				reflected in
							(losses)				earnings
	Fixed maturity investments		$	82.5			$	(2.5	)		$	80
	Short-term investments		—				(4.3		)		(4.3		)
	Common equity securities		1.3				—				1.3
	Convertible fixed maturity investments		(8.2		)		(1.8		)		(10.0		)
	Other long-term investments		1.4				—				1.4
	Forward contracts		(.3		)		—				(.3		)
	Net realized investment gains (losses), pre-tax		76.7				(8.6		)		68.1
	Income taxes attributable to realized		(23.8		)		2.2				(21.6		)
	investment gains (losses)
	Net realized investment gains (losses), after-tax		$	52.9			$	(6.4	)		$	46.5
			Year ended December 31, 2011
	Millions		Net realized gains (losses)				Net				Total
							foreign				changes in
							exchange				fair value
							gains				reflected in
							(losses)				earnings
	Fixed maturity investments		$	49.4			$	(38.3	)		$	11.1
	Short-term investments		—				(9.9		)		(9.9		)
	Common equity securities		34.6				—				34.6
	Convertible fixed maturity investments		(2.2		)		—				(2.2		)
	Other long-term investments		35.2				(0.5		)		34.7
	Net realized investment gains (losses), pre-tax		117				(48.7		)		68.3
	Income taxes attributable to realized		(37.0		)		12.8				(24.2		)
	investment gains (losses)
	Net realized investment gains (losses), after-tax		$	80			$	(35.9	)		$	44.1
Unrealized Gain (Loss) on Investments	'
	Net unrealized investment gains (losses)
	The following table summarizes net unrealized investment gains (losses) and changes in the carrying value of investments measured at fair value:
			Year ended December 31, 2013
	Millions		Net				Net				Total net unrealized
			unrealized				foreign				gains (losses)
			gains				exchange				reflected in
			(losses)				gains				earnings
							(losses)
	Fixed maturity investments		$	(93.9	)		$	15.3			$	(78.6	)
	Short-term investments		0.1				—				0.1
	Common equity securities		119.2				(0.4		)		118.8
	Convertible fixed maturity investments		3.2				—				3.2
	Other long-term investments		10.3				3.4				13.7
	Forward contracts		—				—				—
	Net unrealized investment gains (losses), pre-tax		38.9				18.3				57.2
	Income taxes attributable to unrealized		8.2				(5.6		)		2.6
	investment gains (losses)
	Net unrealized investment gains (losses), after-tax		$	47.1			$	12.7			$	59.8
			Year ended December 31, 2012
	Millions		Net				Net				Total net unrealized
			unrealized				foreign				gains (losses)
			gains				exchange				reflected in
			(losses)				gains				earnings
							(losses)
	Fixed maturity investments		$	18.5			$	(45.9	)		$	(27.4	)
	Short-term investments		—				0.1				0.1
	Common equity securities		65.9				(.1		)		65.8
	Convertible fixed maturity investments		1.1				—				1.1
	Other long-term investments		13.2				(2.7		)		10.5
	Net unrealized investment gains (losses), pre-tax		98.7				(48.6		)		50.1
	Income taxes attributable to unrealized		(17.9		)		12.7				(5.2		)
	investment gains (losses)
	Net unrealized investment gains (losses), after-tax		$	80.8			$	(35.9	)		$	44.9
			Year ended December 31, 2011
	Millions		Net				Net				Total net unrealized
			unrealized				foreign				gains (losses)
			gains				exchange				reflected in
			(losses)				gains				earnings
							(losses)
	Fixed maturity investments		$	7.6			$	68.9			$	76.5
	Short-term investments		—				(1.1		)		(1.1		)
	Common equity securities		(40.6		)		(1.8		)		(42.4		)
	Convertible fixed maturity investments		(11.5		)		—				(11.5		)
	Other long-term investments		(19.1		)		3.4				(15.7		)
	Net unrealized investment gains (losses), pre-tax		(63.6		)		69.4				5.8
	Income taxes attributable to unrealized		24				(17.9		)		6.1
	investment gains (losses)
	Net unrealized investment gains (losses), after-tax		$	(39.6	)		$	51.5			$	11.9
Investment holdings, fixed maturity investments	'
	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 December 31, 2013 and 2012, were as follows:
			31-Dec-13
	Millions		Cost or				Gross				Gross				Net foreign				Carrying
			amortized				unrealized				unrealized				currency				value
			cost				gains				losses				losses
	US Government and agency obligations		$	365.5			$	0.5			$	(1.0	)		$	(2.5	)		$	362.5
	Debt securities issued by corporations		2,330.70				44				(13.2		)		(14.3		)		2,347.20
	Municipal obligations		18.3				—				(.4		)		—				17.9
	Mortgage-backed and asset-backed securities		2,027.30				2.4				(9.9		)		(5.3		)		2,014.50
	Foreign government, agency and provincial		444.2				3.7				(3.2		)		(4.8		)		439.9
	obligations
	Preferred stocks		79.9				5.1				—				(.2		)		84.8
	Total fixed maturity investments including		$	5,265.90			$	55.7			$	(27.7	)		$	(27.1	)		$	5,266.80
	assets held for sale
	Fixed maturity investments reclassified to																		(236.3		)
	assets held for sale (1)
	Total fixed maturity investments																		$	5,030.50
	(1)	Assets held for sale related to discontinued operations. See Note 21.
			31-Dec-12
	Millions		Cost or				Gross				Gross				Net foreign				Carrying
			amortized				unrealized				unrealized				currency				value
			cost				gains				losses				gains (losses)
	US Government and agency obligations		$	440.4			$	1			$	(.1	)		$	(1.2	)		$	440.1
	Debt securities issued by corporations		2,321.40				88.3				(1.6		)		(23.0		)		2,385.10
	Municipal obligations		5.3				—				(0.1		)		—				5.2
	Mortgage-backed and asset-backed securities		2,081.00				25.1				(1.1		)		(9.4		)		2,095.60
	Foreign government, agency and provincial		526.6				6.9				(3.0		)		(8.6		)		521.9
	obligations
	Preferred stocks		79.9				6.7				—				(.2		)		86.4
	Total fixed maturity investments including		$	5,454.60			$	128			$	(5.9	)		$	(42.4	)		$	5,534.30
	assets held for sale
	Fixed maturity investments reclassified to																		(338.1		)
	assets held for sale (1)
	Total fixed maturity investments																		$	5,196.20
	(1)	Assets held for sale related to discontinued operations. See Note 21.
Schedule of contractual maturities of fixed maturities	'
	The cost or amortized cost and carrying value of White Mountains’ fixed maturity investments and convertible fixed maturity investments at December 31, 2013 is presented below by contractual maturity. Actual maturities could differ from contractual maturities because borrowers may have the right to call or prepay certain obligations with or without call or prepayment penalties.
			31-Dec-13
	Millions		Cost or				Carrying
			amortized cost				value
	Due in one year or less		$	491.2			$	490.7
	Due after one year through five years		2,376.70				2,389.30
	Due after five years through ten years		321				322.2
	Due after ten years		41.5				45.8
	Mortgage-backed and asset-backed securities		2,027.30				2,014.50
	Preferred stocks		79.9				84.8
	Total		$	5,337.60			$	5,347.30
Investment holdings, equity securities, convertible fixed maturities and other long-term investments	'
	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 maturity investments and other long-term investments as of December 31, 2013 and 2012 were as follows:
			31-Dec-13
	Millions		Cost or				Gross unrealized				Gross unrealized				Net foreign				Carrying
			amortized cost				gains				losses				currency losses				value
	Common equity securities		$	890.2			$	271			$	(3.6	)		$	(.8	)		$	1,156.80
	Convertible fixed maturity investments		$	71.7			$	9.9			$	(.9	)		$	(.2	)		$	80.5
	Other long-term investments		$	238.3			$	79.6			$	(26.6	)		$	(2.4	)		$	288.9
			31-Dec-12
	Millions		Cost or				Gross unrealized				Gross unrealized				Net foreign				Carrying
			amortized cost				gains				losses				currency losses				value
	Common equity securities		$	895.2			$	143.4			$	(8.8	)		$	(.1	)		$	1,029.70
	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
Fair value measurements by level, investment securities	'
	The following tables summarize White Mountains’ fair value measurements for investments at December 31, 2013 and 2012 by level. The fair value measurements for derivative assets associated with White Mountains’ variable annuity business are presented in Note 8.
			31-Dec-13
	Millions		Fair value				Level 1 Inputs				Level 2 Inputs				Level 3 Inputs
	Fixed maturity investments:
	U.S. Government and agency obligations		$	362.5			$	295.8			$	66.7			$	—
	Debt securities issued by corporations:
	Consumer		754.4				—				754.4				—
	Financials		434.4				—				434.4				—
	Industrial		281.1				—				281.1				—
	Communications		265				—				265				—
	Utilities		173.6				—				173.6				—
	Energy		159.7				—				159.7				—
	Basic Materials		149.1				—				149.1				—
	Technology		91.2				—				91.2				—
	Other		38.7				—				38.7				—
	Total debt securities issued by corporations:		2,347.20				—				2,347.20				—
	Mortgage-backed and asset-backed securities		2,014.50				—				1,992.50				22
	Foreign government, agency and provincial obligations		439.9				44.5				395.4				—
	Preferred stocks		84.8				—				13.8				71
	Municipal obligations		17.9				—				17.9				—
	Total fixed maturity investments (1)		5,266.80				340.3				4,833.50				93
	Short-term investments		635.9				621.5				14.4				—
	Common equity securities:
	Financials		360.4				314.3				—				46.1
	Consumer		308.2				308.2				—				—
	Industrial		105.4				105.4				—				—
	Energy		78.6				78.6				—				—
	Technology		60.6				60.6				—				—
	Communications		57.1				57.1				—				—
	Basic materials		53.4				53.4				—				—
	Utilities		34.3				34.3				—				—
	Other		98.8				24.5				74.3				—
	Total common equity securities		1,156.80				1,036.40				74.3				46.1
	Convertible fixed maturity investments		80.5				—				74.4				6.1
	Other long-term investments (2)		262.4				—				—				262.4
	Total investments		$	7,402.40			$	1,998.20			$	4,996.60			$	407.6
	(1)	Carrying value includes $236.3 that is classified as assets held for sale relating to discontinued operations.
	(2)	Excludes carrying value of $26.6 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) related to currency forward contracts.
			31-Dec-12
	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			$	—
	Debt securities issued by corporations:
	Consumer		727.1				—				727.1				—
	Financials		401.4				1				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				—				54				—
	Other		20.9				—				20.9				—
	Total debt securities issued by corporations:		2,385.10				1				2,384.10				—
	Mortgage-backed and asset-backed securities		2,095.60				—				2,073.50				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)		5,534.30				422.2				5,019.20				92.9
	Short-term investments		630.6				630.6				—				—
	Common equity securities:
	Financials		324.5				286.3				0.9				37.3
	Consumer		255.6				255.6				—				—
	Basic materials		103.3				103.3				—				—
Energy		101				101				—				—
Technology		55				55				—				—
Utilities		43.6				43.4				0.2				—
Industrial		41.9				41.9				—				—
Communications		35.2				35.2				—				—
Other		69.6				11.2				58.4				—
Total common equity securities		1,029.70				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		$	7,581.30			$	1,985.70			$	5,206.10			$	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 $(.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 December 31, 2013 and 2012:
			Fair Value at
			December 31,
	Millions		2013				2012
	AAA		$	—			$	—
	AA		228.8				193.4
	A		1,039.50				1,061.00
	BBB		1,075.50				1,116.90
	BB		—				7
	Other		3.4				6.8
	Debt securities issued by corporations(1)		$	2,347.20			$	2,385.10
	(1)	Credit ratings are assigned based on the following hierarchy: 1) Standard & Poor’s and 2) Moody’s.
Mortgage-backed, asset-backed securities	'
			December 31, 2013												December 31, 2012
	Millions		Fair Value				Level 2				Level 3				Fair Value				Level 2				Level 3
	Mortgage-backed securities:
	Agency:
	GNMA		$	512.3			$	512.3			$	—			$	1,013.40			$	1,013.40			$	—
	FNMA		81.2				81.2				—				74.6				74.6				—
	FHLMC		91.3				91.3				—				55.8				55.8				—
	Total Agency(1)		684.8				684.8				—				1,143.80				1,143.80				—
	Non-agency:
	Residential		125.7				125.7				—				160.6				160.6				—
	Commercial		282.3				282.3				—				334.1				334.1				—
	Total Non-agency		408				408				—				494.7				494.7				—
	Total mortgage-backed securities		1,092.80				1,092.80				—				1,638.50				1,638.50				—
	Asset-backed securities:
	Credit card receivables		311.4				289.4				22				173.5				151.4				22.1
	Vehicle receivables		365				365				—				233.2				233.2				—
	Other		245.3				245.3				—				50.4				50.4				—
	Total asset-backed securities		921.7				899.7				22				457.1				435				22.1
	Total mortgage and asset-backed securities		$	2,014.50			$	1,992.50			$	22			$	2,095.60			$	2,073.50			$	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).
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 December 31, 2013 are as follows:
										Security Issuance Year
	Millions		Fair Value				2004			2005				2006				2007				2008				2009			2010		2011		2012		2013
	Non-agency RMBS		$	125.7			$	11.9		$	33.4			$	10.8			$	2.1			$	—			$	—		$	33.4	$	—	$	—	$	34.1
	Non-agency CMBS		282.3				—			—				8.6				5.7				28.1				—			11.5		31.9		113.8		82.7
	Total		$	408			$	11.9		$	33.4			$	19.4			$	7.8			$	28.1			$	—		$	44.9	$	31.9	$	113.8	$	116.8
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 December 31, 2013:
	Millions		Fair Value				Super Senior(1)				Senior(2)				Subordinate(3)
	Prime		$	96.1			$	24.1			$	72			$	—
	Non-prime		21.9				—				21.9				—
	Sub-prime		7.7				7.7				—				—
	Total		$	125.7			$	31.8			$	93.9			$	—
	(1)	At issuance, Super Senior, or in the case of resecuritization, the underlying securities, were rated “AAA” by Standard & Poor’s, “Aaa” by Moody’s or “AAA” by Fitch Ratings (“Fitch”) and were senior to other “AAA” or “Aaa” bonds.
	(2)	At issuance, Senior, or in the case of resecuritization, the underlying securities, 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 December 31, 2013:
	Millions		Fair Value				Super Senior(1)				Senior(2)				Subordinate(3)
	Fixed rate CMBS		$	189			$	117.2			$	54.4			$	17.4
	Floating rate CMBS		93.3				5.7				28				59.6
	Total		$	282.3			$	122.9			$	82.4			$	77
Other long-term investments	'
	The following table summarizes investments in hedge funds and private equity interests by investment objective and sector at December 31, 2013 and 2012:
			31-Dec-13								December 31, 2012
	Millions		Fair Value				Unfunded				Fair Value				Unfunded
							Commitments								Commitments
	Hedge funds
	Long/short equity		$	62.6			$	—			$	60.3			$	—
	Long/short credit & distressed		22.8				—				22.7				—
	Long/short equity REIT		18.3				—				16				—
	Long/short equity activist		16.8				—				13.6				—
	Long bank loan		0.2				—				0.3				—
	Long diversified strategies		0.1				—				1.7				—
	Total hedge funds		120.8				—				114.6				—
	Private equity funds
	Energy infrastructure & services		45.9				13.1				36.3				15.6
	Multi-sector		23.8				6.5				23.3				5.4
	Manufacturing/Industrial		11.2				15.5				9.9				15.1
	Private equity secondaries		9.5				3.1				10.5				3.1
	Real estate		8.2				3.3				11.6				3.3
	Aerospace/Defense/Government		5.8				19.2				2.8				22.2
	Healthcare		5.6				2.8				4.3				5.4
	International multi-sector, Europe		3.9				2.8				5.1				5
	Insurance		2.3				41.3				3				41.3
	Venture capital		1.6				0.3				2.2				0.3
	Distressed residential real estate		0.4				—				15.8				—
	International multi-sector, Asia		—				2.7				0.4				2.7
	Total private equity funds		118.2				110.6				125.2				119.4
	Total hedge and private equity funds included		$	239			$	110.6			$	239.8			$	119.4
	in other long-term investments
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 December 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		30-59 days				60-89 days				90-119 days				120+ days				Total
	Redemption frequency		notice				notice				notice				notice
	Monthly		$	—			$	—			$	—			$	5.8			$	5.8
	Quarterly		29.1				30.2				11.8				8.6				79.7
	Semi-annual		—				25.4				—				—				25.4
	Annual		0.1				—				9.6				0.2				9.9
	Total		$	29.2			$	55.6			$	21.4			$	14.6			$	120.8
Fair Value of private equity funds subject to lock-up periods	'
	At December 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		$	6.9			$	30.8			$	67.6			$	12.9			$	118.2
Rollforward of fair value investments by level	'
	The following tables summarize the changes in White Mountains’ fair value measurements by level for the years ended December 31, 2013 and 2012:
											Level 3 Investments
	Millions		Level 1				Level 2				Fixed				Common				Convertible				Other long-term				Total
			Investments				Investments				maturity investments				equity				fixed				investments
															securities				maturity investments
	Balance at January 1, 2013		$	1,355.10			$	5,206.10			$	92.9			$	37.3			$	—			$	259.3		(1)	$	6,950.70		(1)(2)(3)
	Total realized and unrealized gains (losses)		221.9				(56.9		)		(2.7		)		1				—				18.7				182			(4)
	Foreign currency gains (losses) in OCI		(.3		)		12.5				0.3				—				—				(.9		)		11.6
	Amortization/Accretion		(1.0		)		(51.2		)		—				—				—				—				(52.2		)
	Purchases		862.1				3,689.60				37.9				8.8				—				37.1				4,635.50
	Sales		(1,078.9		)		(3,842.8		)		(6.3		)		—				—				(51.8		)		(4,979.8		)
	Net change in investments		16				2.7				—				—				—				—				18.7
	related to purchases and
	sales of consolidated
	affiliates
	Transfers in		1.8				119.4				90.3				—				6.1				—				217.6
	Transfers out		—				(97.2		)		(119.4		)		(1.0		)		—				—				(217.6		)
	Balance at		$	1,376.70			$	4,982.20			$	93			$	46.1			$	6.1			$	262.4		(1)	$	6,766.50		(1)(2)(3)
	December 31, 2013
	(1)	Excludes carrying value of $26.6 and $35.0 at December 31, 2013 and January 1, 2013 associated with other long-term investments accounted for using the equity method and $(.1) at December 31, 2013 related to currency forward contracts.
	(2)	Carrying value includes $236.3 and $338.1 at December 31, 2013 and January 1, 2013 that is classified as assets held for sale relating to discontinued operations.
	(3)	Excludes carrying value of $635.9 and $630.6 at December 31, 2013 and January 1, 2013 classified as short-term investments.
	(4)	Excludes $20.6 of realized and unrealized losses associated with the Prospector Funds consolidation of investment-related liabilities and $.2 of realized and unrealized gains associated with short-term investments.
											Level 3 Investments
	Millions		Level 1				Level 2				Fixed				Common				Convertible				Other long-term				Total
			Investments				Investments				maturity investments				equity				fixed				investments
															securities				maturity investments
	Balance at January 1, 2012		$	1,033.10			$	6,088.20			$	78.9			$	32.3			$	—			$	268.3		(1)	$	7,500.80		(1)(2)(3)
	Total realized and unrealized (losses) gains		52				53.6				8.7				12.4				—				(3.3		)		123.4
	Foreign currency gains (losses) in OCI		4.4				81.9				0.8				0.2				—				3.7				91
	Amortization/Accretion		(.8		)		(48.0		)		(.8		)		—				—				—				(49.6		)
	Purchases		1,216.90				4,927.10				144.4				3.1				—				39.4				6,330.90
	Sales		(950.5		)		(5,937.0		)		(99.4		)		(10.1		)		—				(48.8		)		(7,045.8		)
	Transfers in		—				62.4				22.1				—				—				—				84.5
	Transfers out		—				(22.1		)		(61.8		)		(.6		)		—				—				(84.5		)
	Balance at		$	1,355.10			$	5,206.10			$	92.9			$	37.3			$	—			$	259.3		(1)	$	6,950.70		(1)(2)(3)
	December 31, 2012
	(1)	Excludes carrying value of $35.0 and $33.0 at December 31, 2012 and January 1, 2012 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) at December 31, 2012 related to currency forward contracts.
	(2)	Carrying value includes $338.1 and $111.8 at December 31, 2012 and January 1, 2012 that is classified as assets held for sale relating to AutoOne discontinued operations.
	(3)	Excludes carrying value of $630.6 and $846.0 at December 31, 2012 and January 1, 2012 classified as short-term investments.
Schedule of significant unobservable inputs used in estimating the fair value of investment securities	'
	The fair value of investments in hedge funds and private equity funds, which are classified within Level 3, are estimated using the net asset value of the funds.
	($ in Millions)		December 31, 2013
	Description		Fair Value	Rating(2)	Valuation Technique(s)	Unobservable Input
	Preferred Stock(1)		$71.00	NR	Discounted cash flow	Discount yield	-	7.40%
	Private equity security		$35.60	NR	Multiple of GAAP book value	Book value multiple	-	1
	Private equity security		$10.50	NR	Share price of recent transaction	Average share price	-	$1.10
	Convertible preferred		$6.10	NR	Share price of recent transaction	Share price of	-	$6.10
	securities					recent transaction
	Asset-backed securities (1)		$22.00	AA+	Broker pricing	Broker quote
	(1)	As of December 31, 2013 each asset type consists of one security.
	(2)	Credit ratings are assigned based on the following hierarchy: 1) Standard & Poor’s and 2) Moody’s.

Debt_Tables

Debt (Tables)	12 Months Ended
	Dec. 31, 2013
Debt Disclosure [Abstract]	'
Schedule of debt outstanding	'
	White Mountains’ debt outstanding as of December 31, 2013 and 2012 consisted of the following:
			December 31,
	Millions		2013			2012
	2012 OBH Senior Notes, at face value		$	275		$	275
	Unamortized original issue discount		(.3		)	(.3		)
	2012 OBH Senior Notes, carrying value		274.7			274.7
	SIG Senior Notes, at face value		400			400
	Unamortized original issue discount		(.4		)	(.6		)
	SIG Senior Notes, carrying value		399.6			399.4
	WTM Bank Facility		—			—
	Previous WTM Bank Facility		—			75
	Old Lyme Note		2.1			2.1
	Total debt		$	676.4		$	751.2
Schedule of contractual repayments of debt	'
	A schedule of contractual repayments of White Mountains’ debt as of December 31, 2013, follows:
	Millions	December 31,
		2013
	Due in one year or less	$	—
	Due in two to three years	2.1
	Due in four to five years	400
	Due after five years	275
	Total	$	677.1

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Schedule of total income tax benefit (expense)	'
	The total income tax benefit (expense) for the years ended December 31, 2013, 2012 and 2011 consisted of the following:
			Year Ended December 31,
	Millions		2013			2012			2011
	Current tax (expense) benefit:
	U.S. federal		$	(19.0	)	$	8.2		$	36.3
	State		(1.4		)	(3.4		)	(2.4		)
	Non-U.S.		(16.5		)	(5.9		)	5.1
	Total current tax (expense) benefit		(36.9		)	(1.1		)	39
	Deferred tax (expense) benefit:
	U.S. federal		(24.4		)	(55.5		)	(43.7		)
	State		—			—			—
	Non-U.S.		(15.3		)	72.3			114.7
	Total deferred tax (expense) benefit		(39.7		)	16.8			71
	Total income tax (expense) benefit		$	(76.6	)	$	15.7		$	110
Reconciliation of the U.S. federal statutory income tax rate and actual effective tax rate on pre-tax income	'
	A reconciliation of taxes calculated using the 35% U.S. statutory rate (the tax rate at which the majority of White Mountains’ worldwide operations are taxed) to the income tax (expense) benefit on pre-tax income follows:
			Year Ended December 31,
	Millions		2013			2012			2011
	Tax (expense) benefit at the U.S. statutory rate		$	(120.7	)	$	(92.0	)	$	(34.3	)
	Differences in taxes resulting from:
	Non-U.S. earnings, net of foreign taxes		82.9			43			6.2
	Change in valuation allowance		(33.6		)	(14.1		)	128.2
	Tax reserve adjustments		(10.2		)	(1.3		)	4.3
	Purchase of subsidiaries		5.3			5.1			—
	Tax exempt interest and dividends		3.2			3.1			2.9
	Withholding tax		(1.7		)	(2.9		)	0.2
	Tax rate change enacted in Sweden		—			65.4			—
	Tax rate change enacted in Luxembourg		—			7.2			1.2
	Other, net		(1.8		)	2.2			1.3
	Total income tax (expense) benefit on pre-tax income		$	(76.6	)	$	15.7		$	110
Schedule of components of deferred income tax assets and liabilities	'
	An outline of the significant components of White Mountains’ deferred tax assets and liabilities follows:
			December 31,
	Millions		2013			2012
	Deferred income tax assets related to:
	Non-U.S. net operating loss carryforwards		$	520.6		$	511.9
	U.S. federal net operating and capital loss carryforwards		148.6			164.8
	Loss reserve discount		74.9			88.6
	Incentive compensation		53.9			36.8
	Unearned premiums		38.9			45.5
	Runoff Transaction		24.2			49.3
	Tax credit carryforwards		23.1			17
	Deferred compensation		10.3			10.4
	Fixed assets		4.9			2.8
	Accrued interest		1.1			8
	Pension and benefit accruals		—			10.3
	Other items		6.9			5.7
	Total gross deferred income tax assets		907.4			951.1
	Less: valuation allowances		(289.8		)	(254.0		)
	Total net deferred income tax assets		617.6			697.1
	Deferred income tax liabilities related to:
	Safety reserve		357.2			326.7
	Net unrealized investment gains		44.6			54.2
	Deferred acquisition costs		33			49.8
	Purchase accounting		7.2			9.5
	Members surplus contributions		5.4			0.1
	Pension and benefit accruals		3.4			—
	Investment basis difference		3			21
	Other items		7.9			7.5
	Total deferred income tax liabilities		461.7			468.8
	Net deferred tax asset		$	155.9		$	228.3
Schedule of net operating and capital loss carryforwards by expiration dates and the deferred tax assets thereon	'
	Net operating loss and capital loss carryforwards as of December 31, 2013, the expiration dates and the deferred tax assets thereon are as follows:
			31-Dec-13
	Millions		United States			Luxembourg			Sweden			Netherlands			UK		Total
	2013		$	—		$	—		$	—		$	—		$	—	$	—
	2014 - 2018		—			—			—			0.5			—		0.5
	2019 - 2023		11.2			—			—			0.6			—		11.8
	2024 - 2033		429.8			—			—			—			—		429.8
	No expiration date		—			1,750.00			62.3			—			15.6		1,827.90
	Total		$	441		$	1,750.00		$	62.3		$	1.1		$	15.6	$	2,270.00
	Gross deferred tax asset		$	148.6		$	511.3		$	5.8		$	0.3		$	3.2	$	669.2
	Valuation allowance		(58.3		)	(195.7		)	—			(.3		)	—		(254.3		)
	Net deferred tax asset		$	90.3		$	315.6		$	5.8		$	—		$	3.2	$	414.9
Reconciliation of changes in the amount of unrecognized tax benefits	'
	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows:
	Millions		Permanent			Temporary			Interest and			Total
			Differences(1)			Differences(2)			Penalties(3)
	Balance at January 1, 2011		$	14.5		$	75.1		$	6.2		$	95.8
	Changes in prior year tax positions		(.9		)	0.1			2			1.2
	Tax positions taken during the current year		—			(20.4		)	—			(20.4		)
	Lapse in statute of limitations		(3.4		)	(5.7		)	(1.4		)	(10.5		)
	Settlements with tax authorities		(.6		)	—			—			(.6		)
	Balance at December 31, 2011		9.6			49.1			6.8			65.5
	Changes in prior year tax positions		0.5			—			1.4			1.9
	Tax positions taken during the current year		—			(20.2		)	—			(20.2		)
	Settlements with tax authorities		(.4		)	—			(.2		)	(.6		)
	Balance at December 31, 2012		9.7			28.9			8			46.6
	Changes in prior year tax positions		0.6			(7.1		)	1.7			(4.8		)
	Tax positions taken during the current year		7.9			0.7			—			8.6
	Settlements with tax authorities		—			—			(.4		)	(.4		)
	Balance at December 31, 2013		$	18.2		$	22.5		$	9.3		$	50
	(1)	Represents the amount of unrecognized tax benefits that, if recognized, would impact the effective tax rate.
	(2)	Represents the amount of unrecognized tax benefits that, if recognized would create a temporary difference between the reported amount of an item in the Company’s Consolidated Balance Sheet and its tax basis.
	(3)	Net of tax benefit.

Derivatives_Tables

Derivatives (Tables)	12 Months Ended
	Dec. 31, 2013
Forward contracts	'
Derivative [Line Items]	'
Fair Value of Assets and Liabilities Measured on Recurring and Non-recurring Basis Table [Text Block]	'
	The following tables summarize the changes in White Mountains’ forward contracts for the year ended December 31, 2013 and 2012:
	Millions		December 31, 2013				December 31, 2012
	Beginning of period		$	(.1	)		$	—
	Purchases		—				—
	Realized and unrealized losses		(.1		)		(.3		)
	Sales/settlements		0.1				0.2
	End of period		$	(.1	)		$	(.1	)
Offestting Assets and Liabilities	'
	The following summarizes amounts offset under master netting agreements:
			December 31, 2013											December 31, 2012
	Millions		Gross asset				Gross liability amounts offset under master netting arrangements			Net amounts recognized in investments				Gross asset				Gross liability amounts offset under master netting arrangements			Net amounts recognized in investments
			amounts before											amounts before
			offsets(1)											offsets(1)
	USD		$	—			$	—		$	—			$	—			$	—		$	—
	EUR		—				(.1		)	(.1		)		—				(.1		)	(.1		)
	GBP		—				—			—				—				—			—
	Total		$	—			$	(.1	)	$	(.1	)		$	—			$	(.1	)	$	(.1	)
	(1)	Amount equal to fair value of instrument as recognized in investments.
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value	'
	The following summarizes realized and unrealized derivative gains (losses) recognized in net realized and unrealized investment gains and the carrying values, included in other long-term investments, at December 31, 2013 and 2012 by type of currency:
			December 31, 2013							December 31, 2012
	Millions		Gains (Losses)				Carrying Value			Gains (Losses)				Carrying Value
	USD		$	(.2	)		$	—		$	(.2	)		$	—
	SEK		—				—			—				—
	EUR		0.1				(.1		)	(.1		)		(.1		)
	GBP		—				—			—				—
	Total		$	(.1	)		$	(.1	)	$	(.3	)		$	(.1	)
Schedule of Derivative Instruments [Table Text Block]	'
	The following table summarizes the notional amounts and the uncollateralized balances associated with forward currency contracts by counterparty:
			31-Dec-13									31-Dec-12
	Millions		Notional Amount				Carrying Value			Standard & Poor's		Notional Amount				Carrying Value
										Rating(1)
	Barclays Bank Plc		$	5.8			$	—		A		$	7.7			$	(.1	)
	Deutsche Bank		7.7				—			A		11.1				—
	Goldman Sachs		2.1				—			A-		0.4				—
	HSBC		3.3				(.1		)	AA-		10.1				—
	JP Morgan		1.3				—			A+		1.9				—
	Royal Bank of Canada		0.2				—			AA-		—				—
	Total		$	20.4			$	(.1	)			$	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).
Variable Annuity Reinsurance	'
Derivative [Line Items]	'
Pre-tax operating results	'
	The following table summarizes the pre-tax operating results of WM Life Re for the years ended December 31, 2013, 2012 and 2011:
			Year Ended December 31,
	Millions		2013				2012			2011
	Fees, included in other revenue		$	25			$	31.8		$	32.5
	Change in fair value of variable annuity liability, included in other revenue		378.5				312.8			(156.5		)
	Change in fair value of derivatives, included in other revenue		(402.0		)		(339.0		)	92.9
	Foreign exchange, included in other revenue		(14.5		)		(30.3		)	15.1
	Other investment income and (losses) gains		(7.1		)		2.5			(.9		)
	Total revenues		(20.1		)		(22.2		)	(16.9		)
	Change in fair value of variable annuity death benefit liabilities, included in		10.2				14.2			(1.8		)
	general and administrative expenses
	Death benefit claims paid, included in general and administrative expenses		(1.9		)		(5.7		)	(3.8		)
	General and administrative expenses		(4.9		)		(5.2		)	(4.7		)
	Pre-tax loss		$	(16.7	)		$	(18.9	)	$	(27.2	)
Fair Value of Assets and Liabilities Measured on Recurring and Non-recurring Basis Table [Text Block]	'
	The following table summarizes the changes in White Mountains’ variable annuity reinsurance liabilities and derivative instruments for the year ended December 31, 2013, 2012 and 2011:
			Variable Annuity				Derivative Instruments
			(Liabilities)
	Millions		Level 3				Level 3(1)			Level 2(1)(2)				Level 1(3)				Total(4)
	Balance at January 1, 2013		$	(441.5	)		$	140.5		$	(20.5	)		$	(21.7	)		$	98.3
	Purchases		—				59.4			—				—				59.4
	Realized and unrealized gains (losses)		388.7			(5)	(136.5		)	(196.1		)		(69.4		)		(402.0		)
	Transfers in (out)		—				—			—				—				—
	Sales/settlements		—				—			221.3				92.2				313.5
	Balance at December 31, 2013		$	(52.8	)		$	63.4		$	4.7			$	1.1			$	69.2
			Variable Annuity				Derivative Instruments
			(Liabilities)
	Millions		Level 3				Level 3(1)			Level 2(1)(2)				Level 1(3)				Total(4)
	Balance at January 1, 2012		$	(768.5	)		$	247.1		$	39.2			$	4.1			$	290.4
	Purchases		—				6.1			—				—				6.1
	Realized and unrealized (losses) gains		327			(5)	(84.0		)	(186.9		)		(68.1		)		(339.0		)
	Transfers in (out)		—				—			—				—				—
	Sales/settlements		—				(28.7		)	127.2				42.3				140.8
	Balance at December 31, 2012		$	(441.5	)		$	140.5		$	(20.5	)		$	(21.7	)		$	98.3
			Variable Annuity				Derivative Instruments
			(Liabilities)
	Millions		Level 3				Level 3(1)			Level 2(1)(2)				Level 1(3)				Total(4)
	Balance at January 1, 2011		$	(610.2	)		$	275.3		$	72.2			$	—			$	347.5
	Purchases		—				5			—				—				5
	Realized and unrealized (losses) gains		(158.3		)	(5)	14.5			67.7				10.7				92.9
	Transfers in (out)		—				—			—				—				—
	Sales/settlements		—				(47.7		)	(100.7		)		(6.6		)		(155.0		)
	Balance at December 31, 2011		$	(768.5	)		$	247.1		$	39.2			$	4.1			$	290.4
	(1)	Consists of over-the-counter instruments.
	(2)	Consists of interest rate swaps, total return swaps, foreign currency forward contracts, and bond forwards. Fair value measurement based upon bid/ask pricing quotes for similar instruments that are actively traded, where available.  Swaps for which an active market does not exist have been priced using observable inputs including the swap curve and the underlying bond index.
	(3)	Consists of exchange traded equity index, foreign currency and interest rate futures. Fair value measurements based upon quoted prices for identical instruments that are actively traded.
	(4)	In addition to derivative instruments, WM Life Re held cash, short-term and fixed maturity investments of $81.3, $393.6 and $485.3 at December 31, 2013, 2012 and 2011 posted as collateral to its reinsurance counterparties.
	(5)	Includes $10.2, $14.2, $(1.8) for December 31, 2013, 2012 and 2011 related to the change in the fair value of variable annuity death benefit liabilities, which are included in general and administrative expenses.
Schedule of collateral [Table Text Block]	'
	In addition, WM Life Re held cash and short-term investments posted as collateral to its variable annuity reinsurance and derivatives counterparties. The total collateral includes the following:
			December 31,
	Millions		2013				2012
	Cash		$	56.1			$	249.8
	Short-term investments		2				5.1
	Fixed maturity investments		23.2				138.7
	Total		$	81.3			$	393.6
Schedule of significant unobservable inputs associated with the fair value estimates for variable annuity reinsurance liabilities and derivative instruments	'
	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)		December 31, 2013
	Description		Fair				Valuation		Unobservable Input	Range					Weighted Average
			Value				Technique(s)
	Variable annuity benefit guarantee liabilities		$	52.8			Discounted cash flows		Surrenders
									0-1 year	0.3	%	-	30.00%		21	%
									1-2 years	0.2	%	-	32.00%		15.8	%
									2-3 years	0.1	%	-	14.00%		6.2	%
									Mortality	0	%	-	5.30%		1	%
									Foreign exchange volatilities
									0-1 year	11.6	%	-	14.00%		12.5	%
									1-2 years	12.9	%	-	15.00%		13.7	%
									2-3 years	13.5	%	-	16.30%		14.3	%
									Index volatilities
									0-1 year	16.4	%	-	19.50%		17.9	%
									1-2 years	17.6	%	-	20.10%		19.4	%
									2-3 years	18.9	%	-	21.90%		21.9	%
	Foreign Exchange Options		$	32.6			Counterparty valuations, adjusted for unwind quote discount		Adjustment to counterparty valuations	(1.2	)%	-	8.00%		2.4	%
	Equity Index Options		$	30.8			Counterparty valuations, adjusted for unwind quote discount		Adjustment to counterparty valuations	0.50%		-	9.70%		3.4	%
Offestting Assets and Liabilities	'
	The following summarizes amounts offset under master netting agreements:
			December 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		$	2.4			$	(11.7	)	$	(9.3	)		$	52.6			$	(26.9	)	$	25.7
	Exchange traded		1				(1.6		)	(.6		)		1.6				(.2		)	1.4
	Foreign exchange contracts
	OTC		67.8				(12.0		)	55.8				87.8				(34.4		)	53.4
	Exchange traded		2.3				—			2.3				0.8				(1.4		)	(.6		)
	Equity contracts
	OTC		30.7				(9.2		)	21.5				63.6				(22.9		)	40.7
	Exchange traded		1.8				(2.3		)	(.5		)		0.1				(22.4		)	(22.3		)
	Total(2)		$	106			$	(36.8	)	$	69.2			$	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.
Offsetting Assets	'
	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:
			31-Dec-13
	Millions		Net amount of assets reflected in Balance Sheet				Collateral provided to counterparty - Cash			Collateral provided to counter-party - Financial Instruments				Net amount of exposure after effect of collateral provided				Excess collateral provided to counter-party- Cash			Excess collateral provided - Financial Instruments			Counter-party collateral held by WM Life Re - Cash		Net amount of exposure to counter-party		Standard
																												& Poor's
																												Rating(1)
	JP Morgan		$	9.1			$	—		$	—			$	9.1			$	22		$	—		$	—	$	31.1	A	+
	Bank of America		27.2				—			—				27.2				—			—			—		27.2		A
	Nomura		(.4		)		—			0.4				—				—			22.8			0.8		22		BBB	+
	Citigroup - OTC		19.4				—			—				19.4				2.3			—			—		21.7		A
	Citigroup - Exchange Traded		1.2				—			—				1.2				19.8			—			—		21		A
	Royal Bank of Scotland		11.3				—			—				11.3				—			—			—		11.3		A	-
	Barclays		1.4				—			—				1.4				—			—			—		1.4		A
	Total		$	69.2			$	—		$	0.4			$	69.6			$	44.1		$	22.8		$	0.8	$	135.7
			31-Dec-12
	Millions		Net amount of assets reflected in Balance Sheet				Collateral provided to counter-party - Cash			Collateral provided to counter-party - Financial Instruments				Net amount of exposure after effect of collateral provided				Excess collateral provided to counter-party- Cash			Excess collateral provided - Financial Instruments			Counter-party collateral held by WM Life Re- Cash		Net amount of exposure to counter-party		Standard
																												& Poor's
																												Rating(1)
	Citigroup - OTC		$	19.9			$	—		$	—			$	19.9			$	30.8		$	—		$	—	$	50.7	A
	Bank of America		78.5				—			—				78.5				—			—			30.6		47.9		A
	Royal Bank of Scotland		33.6				—			—				33.6				—			—			—		33.6		A
	JP Morgan		(22.8		)		22.8			—				—				32.8			—			—		32.8		A	+
	Nomura		(.9		)		0.9			—				—				0.8			28			—		28.8		BBB	+
	Citigroup - Exchange Traded		(21.5		)		21.5			—				—				13.6			—			—		13.6		A
	Barclays		11.6				—			—				11.6				—			—			—		11.6		A	+
	Goldman Sachs		(.1		)		0.1			—				—				3.1			—			—		3.1		A	-
	Total		$	98.3			$	45.3		$	—			$	143.6			$	81.1		$	28		$	30.6	$	222.1
	(1)	Standard & Poor’s ratings as detailed above are:  “A+” (Strong, which is the fifth highest of twenty-one creditworthiness ratings),“A” (which is the sixth highest of twenty-one creditworthiness ratings), “A-” (which is the seventh highest of twenty-one creditworthiness ratings), and BBB+ (which is the eighth highest of twenty-one creditworthiness ratings).
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values, by the type of instrument	'
	The following summarizes realized and unrealized gains (losses) recognized in other revenues for the years ended December 31, 2013, 2012 and 2011 and the carrying values at December 31, 2013 and 2012 by type of derivative instrument:
														Carrying Value
			Year Ended December 31,											December 31,
	Millions		2013				2012			2011				2013				2012
	Fixed income/interest rate		$	(108.7	)		$	(149.5	)	$	8.9			$	(9.7	)		$	27.1
	Foreign exchange		(96.7		)		(102.3		)	29.5				58				52.8
	Equity		(196.6		)		(87.2		)	54.5				20.9				18.4
	Total		$	(402.0	)		$	(339.0	)	$	92.9			$	69.2			$	98.3
Interest Rate Cap	'
Derivative [Line Items]	'
Fair Value of Assets and Liabilities Measured on Recurring and Non-recurring Basis Table	'
	The following table summarizes the change in the fair value of the Interest Rate Cap for the year ended December 31, 2013:
	Millions		December 31,
			2013
	Beginning of period		$	—
	Purchases		9.9
	Net realized and unrealized gains		1.2
	Sales/settlements		—
	End of period		$	11.1
Assets Held under Reinsurance Counterparty Trust Agreement [Table Text Block]	'
	The following table summarizes the Interest Rate Cap collateral balances held by White Mountains and ratings by counterparty:
			31-Dec-13
	Millions		Collateral Balances Held				Standard & Poor’s
							Rating(1)
	Barclays Bank Plc		$	7.5			A
	Nordea Bank Finland Plc		3.3				AA-
	Total		$	10.8
	(1)	Standard & Poor’s ratings as detailed above are: “A” (Strong, which is the sixth highest of twenty-one creditworthiness ratings) and “AA-” (Very Strong, which is the fourth highest of twenty-one creditworthiness ratings).

Municipal_Bond_Guarantee_Insur1

Municipal Bond Guarantee Insurance (Tables)	12 Months Ended
	Dec. 31, 2013
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]	'
Schedule of Municipal Guarantee Insured Obligations [Table Text Block]	'
	The following table provides a schedule of BAM’s insured obligations:
		31-Dec-13		31-Dec-12
	Contracts issued and outstanding	218		3
	Remaining weighted average contract period (in years)	13.8		10.4
	Contractual debt service outstanding (in millions):
	Principal	$	4,703.70	$	25.8
	Interest	$	3,264.40	$	8.9
	Gross unearned insurance premiums	$	13.2	$	0.1

Earnings_Per_Share_Tables

Earnings Per Share (Tables)	12 Months Ended
	Dec. 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 years ended December 31, 2013, 2012 and 2011 (see Note 21 for earnings per share amounts for discontinued operations):
			Year Ended December 31,
			2013			2012			2011
	Basic and diluted earnings per share numerators (in millions):
	Net income from continuing operations attributable to		$	317.3		$	322.4		$	146.3
	White Mountains’ common shareholders
	Allocation of income for unvested restricted common shares		(4.7		)	(4.3		)	(1.2		)
	Dividends declared on participating restricted common shares(1)		(.1		)	(.1		)	(.1		)
	Total allocation to restricted common shares		(4.8		)	(4.4		)	(1.3		)
	Net income attributable to White Mountains’ common shareholders,		$	312.5		$	318		$	145
	net of restricted share amounts
	Undistributed net earnings (in millions):
	Net income attributable to White Mountains’ common shareholders,		$	312.5		$	318		$	145
	net of restricted common share amounts
	Dividends declared net of restricted common share amounts(1)		(6.1		)	(6.5		)	(7.9		)
	Total undistributed net earnings, net of restricted common share amounts		$	306.4		$	311.5		$	137.1
	Basic earnings per share denominators (in thousands):
	Total average common shares outstanding during the period		6,200.40			6,799.80			7,881.00
	Average unvested restricted common shares(2)		(91.4		)	(91.1		)	(69.4		)
	Basic earnings per share denominator		6,109.00			6,708.70			7,811.60
	Diluted earnings per share denominator (in thousands):
	Total average common shares outstanding during the period		6,200.40			6,799.80			7,881.00
	Average unvested restricted common shares(2)		(91.4		)	(91.1		)	(69.4		)
	Average outstanding dilutive options to acquire common shares(3)		—			—			—
	Diluted earnings per share denominator		6,109.00			6,708.70			7,811.60
	Basic earnings per share (in dollars):
	Net income attributable to White Mountains’ common shareholders		$	51.15		$	47.41		$	18.56
	Dividends declared and paid		(1.00		)	(1.00		)	(1.00		)
	Undistributed earnings		$	50.15		$	46.41		$	17.56
	Diluted earnings per share (in dollars)
	Net income attributable to White Mountains’ common shareholders		$	51.15		$	47.41		$	18.56
	Dividends declared and paid		(1.00		)	(1.00		)	(1.00		)
	Undistributed earnings		$	50.15		$	46.41		$	17.56
	(1)	Restricted shares issued by White Mountains receive dividends, and therefore, are considered participating securities.
	(2)	Restricted common shares outstanding vest either in equal annual installments or upon a stated date (see Note 12).
	(3)	The diluted earnings per share denominator for the years ended December 31, 2013, 2012 and 2011 do not include the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding as they are anti-dilutive to the calculation.

Retirement_and_Postretirement_1

Retirement and Postretirement Plans (Tables)	12 Months Ended
	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]	'
Schedule of changes in projected benefit obligations and fair value of plan assets and funded status of plan assets	'
	The following tables set forth the obligations and funded status, assumptions, plan assets and cash flows associated with the Plans at December 31, 2013 and 2012:
			Pension Benefits
			December 31,
	Millions		2013				2012
	Change in projected benefit obligation:
	Projected benefit obligation at beginning of year		$	119.5			$	113
	Service cost		0.8				0.7
	Interest cost		4.2				4.7
	Settlement gain		—				(.7		)
	Special termination benefit cost		0.3				0.6
	Assumption changes		(13.0		)		11.2
	Actuarial gain		(.5		)		(.2		)
	Benefits and expenses paid with plan assets		(6.2		)		(7.5		)
	Benefits paid directly by OneBeacon		(2.2		)		(2.3		)
	Projected benefit obligation at end of year		$	102.9			$	119.5
	Change in plan assets:
	Fair value of plan assets at beginning of year		$	124.7			$	120.8
	Actual return on plan assets		24.3				11.4
	Benefits and expenses paid		(6.2		)		(7.5		)
	Fair value of plan assets at end of year		$	142.8			$	124.7
	Funded status at end of year		$	39.9			$	5.2
Schedule of amounts recorded in financial statements	'
	Amounts recognized in the financial statements as of December 31, 2013 and 2012 consist of:
			December 31,
	Millions		2013				2012
	Net assets of the Qualified Plan recorded in other assets		$	64.1			$	32.8
	Net liabilities of the Non-qualified Plan recorded in other liabilities		(24.2		)		(27.6		)
	Net amount accrued in the financial statements		$	39.9			$	5.2
Information for the Non-qualified Plan, which has accumulated benefit obligations in excess of plan assets	'
	Information for the Non-qualified Plan, which had accumulated benefit obligations in excess of plan assets, was as follows:
			December 31,
	Millions		2013				2012
	Projected benefit obligation		$	24.2			$	27.6
	Accumulated benefit obligation		$	24.2			$	27.6
	Fair value of plan assets		$	—			$	—
Information for the Qualified Plan, which had accumulated benefit obligations less than plan assets	'
	Information for the Qualified Plan, which had accumulated benefit obligations less than plan assets, was as follows:
			December 31,
	Millions		2013				2012
	Projected benefit obligation		$	78.7			$	91.9
	Accumulated benefit obligation		$	78.7			$	91.9
	Fair value of plan net assets(1)		$	142.8			$	124.7
	(1)	Includes receivables related to securities sold, interest and dividends as well as payables related to securities purchased.
Schedule of amounts recognized in accumulated other comprehensive income (loss) on a pre-tax basis and before noncontrolling interest	'
	The amounts recognized in accumulated other comprehensive income (loss) on a pre-tax basis and before non-controlling interest for the years ended December 31, 2013 and 2012 were as follows:
			December 31,
	Millions		2013				2012
	Accumulated other comprehensive loss beginning balance		$	(21.2	)		$	(16.7	)
	Increase (decrease) in accumulated other comprehensive income (loss):
	Amortization of net actuarial losses recognized during the year		0.9				0.8
	Net actuarial gains (losses) occurring during the year(1)		30.8				(5.9		)
	Other adjustments		—				0.6
	Accumulated other comprehensive income (loss) ending balance		$	10.5			$	(21.2	)
	(1)	Net actuarial gains (losses) resulted from investment returns and demographic experience different than assumed, as well as changes in assumptions in estimating the projected benefit obligation in the years ended December 31, 2013 and 2012.
Schedule of components of net periodic benefit cost (income)	'
	The components of net periodic benefit (income) cost for the years ended December 31, 2013, 2012 and 2011 were as follows:
			Year Ended December 31,
	Millions		2013				2012			2011
	Service cost		$	0.8			$	0.7		$	0.8
	Interest cost		4.2				4.7			5.2
	Expected return on plan assets		(7.1		)		(6.9		)	(7.6		)
	Amortization of unrecognized loss		0.9				0.8			0.5
	Net periodic pension income before settlements, curtailments and		(1.2		)		(.7		)	(1.1		)
	special termination benefits
	Settlement loss		—				0.6			0.5
	Special termination benefits expense(1)		0.3				0.6			0.8
	Total net periodic benefit (income) cost		$	(.9	)		$	0.5		$	0.2
	(1)	Special termination benefits represent additional payments made from the Qualified Plan to certain vested participants when their employment was terminated due to a reduction in force.
Schedule of fair value of the Plan assets and their related inputs	'
	The fair value of the Qualified Plan’s assets and their related inputs at December 31, 2013 and 2012 by asset category were as follows:
			31-Dec-13												31-Dec-12
	Millions		Fair				Level 1			Level 2			Level 3		Fair		Level 1		Level 2		Level 3
			Value				Inputs			Inputs			Inputs		Value		Inputs		Inputs		Inputs
	Fixed maturity investments		$	—			$	—		$	—		$	—	$	1.9	$	—	$	1.9	$	—
	Common equity securities		103.3				103.3			—			—		79.5		79.5		—		—
	Convertible fixed maturity investments		29.9				—			29.9			—		34.5		—		34.5		—
	Cash and short-term investments		8.9				8.8			0.1			—		8.1		8.1		—		—
	Total		$	142.1			$	112.1		$	30		$	—	$	124	$	87.6	$	36.4	$	—
	There were no transfers between Levels 1, 2 or 3 during the years ended December 31, 2013 and 2012.
	The Qualified Plan’s asset allocations at December 31, 2013 and 2012, by asset category were as follows:
			Plan Assets at
			December 31,
	Asset Category		2013			2012
	Fixed maturity investments		—	%		1.5	%
	Common equity securities		72.7			64.2
	Convertible fixed maturity investments		21.1			27.8
	Cash and short-term investments		6.2			6.5
	Total		100	%		100	%
Schedule of expected future benefit payments	'
	The following benefit payments, which reflect expected future service, as appropriate, are expected to be paid:
	Millions		Expected Benefit Payments
	2014		$	5.1
	2015		5.4
	2016		5.6
	2017		5.8
	2018		6.1
	2019-2023		33.9

Employee_ShareBased_Incentive_1

Employee Share-Based Incentive Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2013
White Mountains	'
Share-based compensation arrangement by share-based payment award	'
Summary of performance share activity	'
	The following summarizes performance share activity for the years ended December 31, 2013, 2012 and 2011 for performance shares granted under the WTM Incentive Plan and the WTM Phantom Share Plan:
			Year Ended December 31,
			2013							2012							2011
	Millions, except share amounts		Target			Accrued				Target			Accrued				Target			Accrued
			Performance			Expense				Performance			Expense				Performance			Expense
			Shares							Shares							Shares
			Outstanding							Outstanding							Outstanding
	Beginning of period		119,357			$	29.4			150,064			$	66.1			163,184			$	29.4
	Shares paid or expired(1)		(47,310	)		(11.0		)		(68,357	)		(58.3		)		(51,131	)		—
	New grants		47,170			—				38,432			—				37,675			—
	Assumed forfeitures and cancellations(2)		3			(.6		)		(782	)		0.6				336			(.9		)
	Expense recognized		—			42.4				—			21				—			37.6
	Ending December 31,		119,220			$	60.2			119,357			$	29.4			150,064			$	66.1
	(1)	WTM performance shares 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. At December 31, 2012, White Mountains paid $9.9 as a partial payment for the 2010-2012 performance cycle. There were no payments made in 2011 for the 2008-2010 performance cycle; those performance shares did not meet the threshold performance goal and expired.
	(2)	Amounts include changes in assumed forfeitures, as required under GAAP.
Summary of performance shares outstanding and accrued expense for performance shares awarded under an Incentive Plan	'
	The following table summarizes performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan at December 31, 2013 for each performance cycle:
	Millions, except share amounts		Target WTM			Accrued Expense
			Performance Shares
			Outstanding
	Performance cycle:
	2013 – 2015		47,170			$	12.1
	2012 – 2014		37,977			21.4
	2011 – 2013		37,130			28.2
	Sub-total		122,277			61.7
	Assumed forfeitures		(3,057	)		(1.5		)
	Total at December 31, 2013		119,220			$	60.2
Summary of restricted share activity	'
	The following outlines the unrecognized compensation cost associated with the outstanding restricted share awards under the WTM Incentive Plan for the years ended December 31, 2013, 2012 and 2011:
			Year Ended December 31,
			2013						2012						2011
	Millions, except share amounts		Restricted		Unamortized				Restricted		Unamortized				Restricted		Unamortized
			Shares		Issue Date Fair				Shares		Issue Date Fair				Shares		Issue Date Fair
					Value						Value						Value
	Non-vested,
	Beginning of period		69,910		$	16.8			72,000		$	13.3			46,250		$	14.1
	Issued		25,720		14.4				32,160		15.7				27,250		9.9
	Vested(1)		(1,500	)	—				(32,945	)	—				(1,500	)	—
	Forfeited		—		—				(1,305	)	(.2		)		—		—
	Expense recognized		—		(14.2		)		—		(12.0		)		—		(10.7		)
	Non-vested at December 31,		94,130		$	17			69,910		$	16.8			72,000		$	13.3
	(1)	During 2012, the Compensation Committee accelerated the vesting date for an installment of 5,000 restricted shares from January 20, 2013 to December 31, 2012.
OneBeacon	'
Share-based compensation arrangement by share-based payment award	'
Summary of performance share activity	'
	The following summarizes activity for the years ended December 31, 2013, 2012 and 2011 for OneBeacon performance shares granted under the OneBeacon Incentive Plan:
			Year Ended December 31,
			2013							2012							2011
	Millions, except share amounts		Target			Accrued				Target			Accrued				Target			Accrued
			Performance			Expense				Performance			Expense				Performance			Expense
			Shares							Shares							Shares
			Outstanding							Outstanding							Outstanding
	Beginning of period		563,190			$	1.2			642,667			$	9.7			1,464,295			$	18.5
	Payments and deferrals(1)		(238,658	)		—				(258,901	)		(7.7		)		(936,150	)		(10.5		)
	New awards		179,000			—				181,290			—				194,900			—
	Forfeitures and cancellations(2)		(10,111	)		(0.1		)		(1,866	)		—				(80,378	)		(0.5		)
	Expense recognized		—			2.9				—			(0.8		)		—			2.2
	End of period		493,421			$	4			563,190			$	1.2			642,667			$	9.7
	(1)	No payments were made in 2013 for the 2010-2012 OneBeacon performance cycle as the performance factor was zero. OneBeacon performance share payments in 2012 for the 2009-2011 performance cycle were at 138.6% of target. OneBeacon performance shares payments in 2011 for the 2008-2010 performance cycle were at 68.5% of target. Amounts include deposits into OneBeacon’s deferred compensation plan.
	(2)	Amounts include changes in assumed forfeitures, as required under GAAP.
Summary of performance shares outstanding and accrued expense for performance shares awarded under an Incentive Plan	'
	The following summarizes OneBeacon performance shares outstanding awarded under the OneBeacon Incentive Plan at December 31, 2013 for each performance cycle:
	Millions, except share amounts		Target			Accrued
			OneBeacon			Expense
			Performance
			Shares
			Outstanding
	Performance cycle:
	2013 – 2015		179,000			$	1
	2012 – 2014		181,290			2.1
	2011 – 2013		142,138			1
	Sub-total		502,428			4.1
	Assumed forfeitures		(9,007	)		(.1		)
	Total at December 31, 2013		493,421			$	4
Summary of restricted share activity	'
	The following table summarizes the unrecognized compensation cost associated with the outstanding OneBeacon restricted stock awards for the years ended December 31, 2013, 2012 and 2011.
			Year Ended December 31,
			2013							2012							2011
	Millions, except share amounts		Restricted Shares			Unamortized Issue Date Fair Value				Restricted Shares			Unamortized Issue Date Fair Value				Restricted Shares			Unamortized Issue Date Fair Value
	Non-vested,
	Beginning of period		927,000			$	9.6			630,000			$	7.7			—			$	—
	Issued		—			—				300,000			4.5				630,000			8.6
	Vested		(9,000	)		—				(667	)		—				—			—
	Forfeited		(3,000	)		—				(2,333	)		—				—			—
	Expense recognized		—			(3.1		)		—			(2.6		)		—			(.9		)
	End of period		915,000			$	6.5			927,000			$	9.6			630,000			$	7.7

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2013
Segment Reporting [Abstract]	'
Financial information for White Mountains' segments	'
	Financial information for White Mountains’ segments follows:
								HG Global/BAM
	Millions		OneBeacon			Sirius Group		HG Global			BAM(1)				Other			Total
															Operations
	Year Ended December 31, 2013
	Earned insurance and reinsurance premiums		$	1,120.40		$	866.4	$	0.4		$	0.1			$	—		$	1,987.30
	Net investment income		41.1			48.8		1			4.7				15.3			110.9
	Net investment income (loss) - surplus note		—			—		40.2			(40.2		)		—			—
	interest
	Net realized and unrealized investment		49.4			26.7		(2.0		)	(9.3		)		96.9			161.7
	gains (losses)
	Other revenue		31.2			16.8		—			0.4				9.1			57.5
	Total revenues		1,242.10			958.7		39.6			(44.3		)		121.3			2,317.40
	Losses and LAE		622.1			418.4		—			—				—			1,040.50
	Insurance and reinsurance acquisition expenses		208.9			166.5		0.1			1.4				—			376.9
	Other underwriting expenses		204.8			126.1		—			0.4				—			331.3
	General and administrative expenses		12			32.2		1.4			32.5				103.2			181.3
	Interest expense on debt		13			26.3		—			—				3.2			42.5
	Total expenses		1,060.80			769.5		1.5			34.3				106.4			1,972.50
	Pre-tax income (loss)		$	181.3		$	189.2	$	38.1		$	(78.6	)		$	14.9		$	344.9
								HG Global/BAM
	Millions		OneBeacon			Sirius Group		HG Global			BAM(1)				Other			Total
															Operations
	Year Ended December 31, 2012
	Earned insurance and reinsurance premiums		$	1,132.00		$	931.6	$	—		$	—			$	—		$	2,063.60
	Net investment income		53.6			65		0.3			1.9				32.8			153.6
	Net investment income (loss) - surplus note		—			—		18.4			(18.4		)		—			—
	interest
	Net realized and unrealized investment gains		55.7			17.3		—			—				45.2			118.2
	Other (loss) revenue		(.5		)	70.6		—			—				30.2			100.3
	Total revenues		1,240.80			1,084.50		18.7			(16.5		)		108.2			2,435.70
	Losses and LAE		650			543.9		—			—				—			1,193.90
	Insurance and reinsurance acquisition expenses		249.4			180.8		—			—				—			430.2
	Other underwriting expenses		205.2			116.4		—			0.2				—			321.8
	General and administrative expenses		13.4			45.9		4.5			19.6				98.8			182.2
	Interest expense on debt		16.9			26.2		—			—				1.7			44.8
	Total expenses		1,134.90			913.2		4.5			19.8				100.5			2,172.90
	Pre-tax income (loss)		$	105.9		$	171.3	$	14.2		$	(36.3	)		$	7.7		$	262.8
	Millions		OneBeacon			Sirius Group		Other			Total
								Operations
	Year Ended December 31, 2011
	Earned insurance and reinsurance premiums		$	1,012.20		$	912.3	$	—		$	1,924.50
	Net investment income		71.4			89.9		23.2			184.5
	Net realized and unrealized investment gains		10.6			53.2		10.3			74.1
	Other (loss) revenue		(12.4		)	4.1		(1.7		)	(10.0		)
	Total revenues		1,081.80			1,059.50		31.8			2,173.10
	Losses and LAE		548.3			626		—			1,174.30
	Insurance and reinsurance acquisition expenses		221.2			181		—			402.2
	Other underwriting expenses		162.3			105.8		—			268.1
	General and administrative expenses		9.8			34.1		131.4			175.3
	Interest expense on debt		20.5			31.6		3.1			55.2
	Total expenses		962.1			978.5		134.5			2,075.10
	Pre-tax income (loss)		$	119.7		$	81	$	(102.7	)	$	98
								HG Global/BAM
	Selected Balance Sheet Data		OneBeacon			Sirius Group		HG Global			BAM					Other			Total
	Millions															Operations
	December 31, 2013:
	Total investments		$	2,364.90		$	3,251.40	$	107.9		$	468.6				$	999.8		$	7,192.60
	Reinsurance recoverable on paid and unpaid losses		89.9			363.6		—			—					—			453.5
	Assets held for sale		1,880.10			—		—			—					—			1,880.10
	Total assets		5,191.30			5,124.10		675			(77.9		)	(2	)	1,231.80			12,144.30
	Loss and LAE reserves		1,054.30			2,025.00		—			—					—			3,079.30
	Liabilities held for sale		1,880.10			—		—			—					—			1,880.10
Total liabilities		4,083.90			3,414.50		68.9			19.7					159.9			7,746.90
Total White Mountains’ common shareholders’		830.6			1,459.60		589.5			—					1,025.80			3,905.50
equity
Non-controlling interest		276.8			250		16.6			(97.6		)			46.1			491.9
December 31, 2012:
Total investments		$	2,291.50		$	3,534.30	$	101.5		$	472.4				$	878.4		$	7,278.10
Reinsurance recoverable on paid and unpaid losses		110.7			336.3		—			—					—			447
Assets held for sale		2,226.80			—		—			—					—			2,226.80
Total assets		5,382.30			5,962.00		623.6			(28.6		)	(2	)	956.1			12,895.40
Loss and LAE reserves		1,000.00			2,168.90		—			—					—			3,168.90
Liabilities held for sale		2,226.80			—		—			—					—			2,226.80
Total liabilities		4,365.00			4,123.20		0.9			7.4					140.7			8,637.20
Total White Mountains’ common shareholders’		763.1			1,559.70		606.2			—					802.8			3,731.80
equity
Non-controlling interest		254.2			279.1		16.6			(36.0		)			12.5			526.4
Schedule of selected balance sheet data by segment	'
								HG Global/BAM
	Selected Balance Sheet Data		OneBeacon			Sirius Group		HG Global			BAM					Other			Total
	Millions															Operations
	December 31, 2013:
	Total investments		$	2,364.90		$	3,251.40	$	107.9		$	468.6				$	999.8		$	7,192.60
	Reinsurance recoverable on paid and unpaid losses		89.9			363.6		—			—					—			453.5
	Assets held for sale		1,880.10			—		—			—					—			1,880.10
	Total assets		5,191.30			5,124.10		675			(77.9		)	(2	)	1,231.80			12,144.30
	Loss and LAE reserves		1,054.30			2,025.00		—			—					—			3,079.30
	Liabilities held for sale		1,880.10			—		—			—					—			1,880.10
	Total liabilities		4,083.90			3,414.50		68.9			19.7					159.9			7,746.90
	Total White Mountains’ common shareholders’		830.6			1,459.60		589.5			—					1,025.80			3,905.50
	equity
	Non-controlling interest		276.8			250		16.6			(97.6		)			46.1			491.9
	December 31, 2012:
	Total investments		$	2,291.50		$	3,534.30	$	101.5		$	472.4				$	878.4		$	7,278.10
	Reinsurance recoverable on paid and unpaid losses		110.7			336.3		—			—					—			447
	Assets held for sale		2,226.80			—		—			—					—			2,226.80
	Total assets		5,382.30			5,962.00		623.6			(28.6		)	(2	)	956.1			12,895.40
	Loss and LAE reserves		1,000.00			2,168.90		—			—					—			3,168.90
	Liabilities held for sale		2,226.80			—		—			—					—			2,226.80
	Total liabilities		4,365.00			4,123.20		0.9			7.4					140.7			8,637.20
	Total White Mountains’ common shareholders’		763.1			1,559.70		606.2			—					802.8			3,731.80
	equity
	Non-controlling interest		254.2			279.1		16.6			(36.0		)			12.5			526.4
	(1)	BAM manages its affairs on a statutory accounting basis. BAM’s statutory surplus includes surplus notes and is not reduced by accruals of interest expense on the surplus notes. BAM’s statutory surplus is reduced only after a payment of principal or interest has been approved by the New York Department of Financial Services.
	(2)	BAM total assets reflect the elimination of $503.0 in surplus notes issued to HG Global and its subsidiaries, and $58.6 and $18.4 in accrued interest related to those surplus notes as of December 31, 2013 and 2012.

Investments_in_Unconsolidated_1

Investments in Unconsolidated Affiliates (Tables)	12 Months Ended
	Dec. 31, 2013
Investments in unconsolidated affiliates	'
Schedule of 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.
			December 31,
	Millions		2013			2012
	Symetra common shares		$	360.9		$	288.4
	Unrealized (losses) gains from Symetra’s fixed maturity portfolio		(43.6		)	62.8
	Carrying value of Symetra common shares		317.3			351.2
	Symetra warrants		—			30.3
	Total investment in Symetra		317.3			381.5
	Hamer(1)		4.1			4
	Bri-Mar(1)		—			1.9
	Pentelia Capital Management		—			0.5
	Total investments in unconsolidated affiliates		$	321.4		$	387.9
	(1) As of October 1, 2012, Hamer and Bri-Mar are no longer consolidated and are accounted for as investments in unconsolidated affiliates.
Schedule of changes in unconsolidated affiliates	'
	The following table summarizes amounts recorded by White Mountains relating to its investment in Symetra:
	Millions		Common			Warrants			Total
			shares
	Carrying value of investment in Symetra as of December 31, 2010		$	350.4		$	37.1		$	387.5
	Equity in earnings(1)(8)		28.2			—			28.2
	Impairment of equity in earnings of Symetra(3)		(50.0		)	—			(50.0		)
	Equity in net unrealized gains from Symetra’s fixed maturity portfolio(7)		85			—			85
	Impairment of net unrealized gains from Symetra’s fixed maturity portfolio(4)		(148.6		)	—			(148.6		)
	Dividends received		(4.0		)	—			(4.0		)
	Decrease in value of warrants		—			(24.5		)	(24.5		)
	Carrying value of investment in Symetra as of December 31, 2011(2)		261			12.6			273.6
	Equity in earnings(1)(5)(8)		32.3			—			32.3
	Equity in net unrealized gains from Symetra’s fixed maturity portfolio(6)(7)		62.8			—			62.8
	Dividends received		(4.9		)	—			(4.9		)
	Increase in value of warrants		—			17.7			17.7
	Carrying value of investment in Symetra as of December 31, 2012(2)		351.2			30.3			381.5
	Equity in earnings(1)(5)(8)		37.8			—			37.8
	Equity in net unrealized losses from Symetra’s fixed maturity portfolio(6)(7)		(106.4		)	—			(106.4		)
	Dividends received		(6.4		)	—			(6.4		)
	Increase in value of warrants		—			10.8			10.8
	Exercise of warrants		41.1			(41.1		)	—
	Carrying value of investment in Symetra as of December 31, 2013(2)(9)		$	317.3		$	—		$	317.3
	(1)	Equity in earnings for the years end December 31, 2013, 2012 and 2011 excludes tax expense of $2.8, $2.6, and $2.3
	(2)	Includes White Mountains’ equity in net unrealized (losses) gains from Symetra’s fixed maturity portfolio of $(43.6), $62.8, and $0 as of December 31, 2013, 2012 and 2011, which excludes tax benefit (expense) of $3.2, $(5.1) and $0
	(3)	Impairment of equity in earnings of Symetra excludes tax benefit of $4.1
	(4)	Impairment of net unrealized gains from Symetra’s fixed maturity portfolio excludes tax benefit $12.0
	(5)	Equity in earnings for the years ended December 31, 2013 and 2012 includes $3.0 and $3.5 increases relating to the pre-tax amortization of the Symetra common share basis difference.
	(6)	Net unrealized gains for the years ended December 31, 2013 and 2012 includes $11.8 and $13.1 increases relating to the pre-tax amortization of the Symetra common share basis difference.
	(7)	Net unrealized (losses) gains from Symetra’s fixed maturity portfolio excludes tax benefit (expense) of $8.3, $(5.1) and $(6.9) for the years ended December 31, 2013, 2012 and 2011.
	(8)	Equity in earnings for the years end December 31, 2013, 2012 and 2011 includes $.2, $1.3, and $1.0 loss from the dilutive effect of Symetra’s yearly dividend and the issuance of restricted shares by Symetra
	(9)	The aggregate value of White Mountains’ investment in common shares of Symetra was $380.1 based upon the quoted market price of $18.96 per share at December 31, 2013.
Symetra	'
Investments in unconsolidated affiliates	'
Summarized statement of financial position of Symetra	'
	The following table summarizes financial information for Symetra as of December 31, 2013 and 2012:
			December 31,
	Millions		2013			2012
	Symetra balance sheet data:
	Total investments		$	27,901.10		$	27,556.40
	Separate account assets		978.4			807.7
	Total assets		30,129.50			29,460.90
	Policyholder liabilities		25,328.80			23,735.20
	Long-term debt		449.5			449.4
	Separate account liabilities		978.4			807.7
	Total liabilities		27,187.60			25,830.80
	Common shareholders’ equity		2,941.90			3,630.10
	The following table summarizes financial information for Symetra for the years ended December 31, 2013, 2012 and 2011:
			Years ended December 31,
	Millions		2013			2012			2011
	Symetra income statement data:
	Net premiums earned		$	627.2		$	605		$	540.5
	Net investment income		1,285.00			1,275.20			1,270.90
	Total revenues(1)		2,103.90			2,101.20			1,999.30
	Policy benefits		1,394.90			1,371.80			1,307.30
	Total expenses(1)		1,865.30			1,831.10			1,726.10
	Net income(1)		220.7			205.4			195.8
	Comprehensive net income		(777.6		)	549.3			785.5
	(1)	Amounts for the years ended December 31, 2011 have been restated for the effect of Symetra’s adoption of ASU 2010-26.

Fair_Value_of_Financial_Instru1

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 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 carrying value of financial instruments as of December 31, 2013 and 2012:
		31-Dec-13				31-Dec-12
	Millions	Fair		Carrying		Fair		Carrying
		Value		Value		Value		Value
	2012 OBH Senior Notes	$	269.8	$	274.7	$	282.4	$	274.7
	SIG Senior Notes	438.1		399.6		441.9		399.4
	SIG Preference Shares	260		250		257.5		250

Discontinued_Operations_Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2013
Discontinued Operations and Disposal Groups [Abstract]	'
Schedule of asbestos and environmental loss and LAE reserve activities	'
	Sirius Group
	Net A&E Loss Reserve Activity		Year Ended December 31,
			2013						2012						2011
	Millions		Gross			Net			Gross			Net			Gross			Net
	Asbestos:
	Beginning balance		$	208.2		$	174.2		$	185.1		$	146.2		$	191.9		$	151.5
	Losses and LAE acquired		13			13			11			11			—			—
	Incurred losses and LAE		12.1			11.8			46.8			46.4			13.6			10.3
	Paid losses and LAE		(25.9		)	(20.3		)	(34.7		)	(29.4		)	(20.4		)	(15.6		)
	Ending balance		207.4			178.7			208.2			174.2			185.1			146.2
	Environmental:
	Beginning balance		20.4			15.2			22.1			16.5			22.4			18.1
	Losses and LAE acquired		1			1			0.7			0.7			—			—
	Incurred losses and LAE		0.8			0.8			(.1		)	(.5		)	2.9			2
	Paid losses and LAE		(1.8		)	(1.8		)	(2.3		)	(1.5		)	(3.2		)	(3.6		)
	Ending balance		20.4			15.2			20.4			15.2			22.1			16.5
	Total asbestos and environmental:
	Beginning balance		228.6			189.4			207.2			162.7			214.3			169.6
	Losses and LAE acquired		14			14			11.7			11.7			—			—
	Incurred losses and LAE		12.9			12.6			46.7			45.9			16.5			12.3
	Paid losses and LAE		(27.7		)	(22.1		)	(37.0		)	(30.9		)	(23.6		)	(19.2		)
	Ending balance		$	227.8		$	193.9		$	228.6		$	189.4		$	207.2		$	162.7
	The following tables summarize reported A&E loss and LAE reserve activities (gross and net of reinsurance) for OneBeacon for the years ended December 31, 2013, 2012 and 2011, respectively.
	Net A&E Loss		Year Ended December 31,
	Reserve Activity		2013									2012									2011
						Pre-NICO									Pre-NICO									Pre-NICO
	Millions		Gross			Net(1)			Net(2)			Gross			Net(1)			Net(2)			Gross			Net(1)			Net(2)
	Asbestos:
	Beginning balance		$	929.4		$	602.5		$	2.4		$	1,074.30		$	681.2		$	2.2		$	904		$	647.3		$	6.4
	Incurred losses and LAE		—			—			—			(.3		)	(.5		)	(.5		)	256.8			32.2			(4.0		)
	Paid losses and LAE		(84.3		)	(79.3		)	(.5		)	(144.6		)	(78.2		)	0.7			(86.5		)	1.7			(.2		)
	Ending balance		845.1			523.2			1.9			929.4			602.5			2.4			1,074.30			681.2			2.2
	Environmental:
	Beginning balance		233			125.4			6.4			279.8			151.6			9			119			93.8			9.2
	Incurred losses and LAE		—			—			—			(.9		)	(.5		)	(.5		)	231.8			62.2			10
	Paid losses and LAE		(64.3		)	(33.0		)	(2.6		)	(45.9		)	(25.7		)	(2.1		)	(71.0		)	(4.4		)	(10.2		)
	Ending balance		168.7			92.4			3.8			233			125.4			6.4			279.8			151.6			9
	Total asbestos and environmental:
	Beginning balance		1,162.40			727.9			8.8			1,354.10			832.8			11.2			1,023.00			741.1			15.6
	Incurred losses and LAE		—			—			—			(1.2		)	(1.0		)	(1.0		)	488.6			94.4			6
	Paid losses and LAE		(148.6		)	(112.3		)	(3.1		)	(190.5		)	(103.9		)	(1.4		)	(157.5		)	(2.7		)	(10.4		)
	Ending balance		$	1,013.80		$	615.6		$	5.7		$	1,162.40		$	727.9		$	8.8		$	1,354.10		$	832.8		$	11.2
	(1)	Represents A&E reserve activity, net of third-party reinsurance, but prior to the NICO Cover.
	(2)	Includes NICO cover
Schedule of discontinued operations balance sheet and income statement	'
	The following summarizes the assets and liabilities associated with the businesses classified as held for sale:
			December 31,
	Millions		2013			2012
	Assets held for sale
	Fixed maturity investments, at fair value		$	236.3		$	338.1
	Cash		—			—
	Reinsurance recoverable on unpaid losses		1,604.70			1,840.80
	Reinsurance recoverable on paid losses		10.7			15.6
	Insurance premiums receivable		9.1			11
	Deferred acquisition costs		—			—
	Deferred tax asset		3.3			5.1
	Other assets		16			16.2
	Total assets held for sale		$	1,880.10		$	2,226.80
	Liabilities held for sale
	Loss and loss adjustment expense reserves		$	1,793.10		$	2,052.60
	Unearned insurance premiums		0.2			0.5
	Ceded reinsurance payable		12.3			21.9
	Other liabilities		74.5			151.8
	Total liabilities held for sale		1,880.10			2,226.80
	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:
			Year Ended December 31,
	Millions, except per share amounts		2013			2012			2011
	Revenues
	Earned insurance premiums		$	0.8		$	10.6		$	731.2
	Net investment income		—			—			12
	Net realized and unrealized investment gains		—			—			0.7
	Other revenue		10.8			—			55.1
	Total revenues		11.6			10.6			799
	Expenses
	Loss and loss adjustment expenses		78.9			48.4			574.9
	Insurance and reinsurance acquisition expenses		—			(2.1		)	157
	Other underwriting expenses		(.2		)	1.7			91.4
	General and administrative expenses		—			—			38.3
	Total expenses		78.7			48			861.6
	Pre-tax loss		(67.1		)	(37.4		)	(62.6		)
	Income tax benefit		25			13.4			25.9
	Loss from discontinued operations		(42.1		)	(24.0		)	(36.7		)
	Gain (loss) on sale of discontinued operations, net of tax		46.6			(91.0		)	658.3
	Net income (loss) from discontinued operations		$	4.5		$	(115.0	)	$	621.6
Discontinued operations, computation of earnings per share	'
	The following table outlines the computation of earnings (loss) per share for discontinued operations for the years ended December 31, 2013, 2012 and 2011:
			Year Ended December 31,
			2013			2012			2011
	Basic and diluted earnings (loss) per share numerators (in millions):
	Net income (loss) attributable to White Mountains’ common shareholders		$	4.5		$	(115.0	)	$	621.6
	Allocation of income for participating unvested restricted common shares (1)		—			1.5			(5.4		)
	Net income (loss) attributable to White Mountains’ common shareholders, net of		$	4.5		$	(113.5	)	$	616.2
	restricted common share amounts (3)
	Basic earnings (loss) per share denominators (in thousands):
	Total average common shares outstanding during the period		6,200.40			6,799.80			7,881.00
	Average unvested restricted common shares (1)		(91.4		)	(91.1		)	(69.4		)
	Basic earnings (loss) per share denominator		6,109.00			6,708.70			7,811.60
	Diluted earnings (loss) per share denominator (in thousands):
	Total average common shares outstanding during the period		6,200.40			6,799.80			7,881.00
	Average unvested restricted common shares (1)		(91.4		)	(91.1		)	(69.4		)
	Average outstanding dilutive options to acquire common shares (2)		—			—			—
	Diluted earnings (loss) per share denominator		6,109.00			6,708.70			7,811.60
	Basic and diluted earnings (loss) per share (in dollars):		$	0.74		$	(16.91	)	$	78.88
	(1)	Restricted common shares outstanding vest either in equal annual installments or upon a stated date (see Note 12).
	(2)	The diluted earnings per share denominator for the years ended December 31, 2013, 2012 and 2011 do not include the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding as they are anti-dilutive to the calculation.
	(3)	Net income (loss) attributable to White Mountains’ common shareholders, net of restricted share amounts, is equal to undistributed earnings (loss) for the years ended December 31, 2013, 2012 and 2011.

Selected_Quarterly_Financial_D1

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]	'
Schedule of Quarterly Financial Information	'
	Selected quarterly financial data for 2013 and 2012 is shown in the following table. The quarterly financial data includes, in the opinion of management, all recurring adjustments necessary for a fair presentation of the results of operations for the interim periods. As a result of the Esurance Sale, AutoOne Sale and the Runoff Business sale, the results of operations for Esurance, AutoOne and the Runoff Business have been classified as discontinued operations and are now presented, net of related income taxes, as such in the statement of comprehensive income. Prior year amounts have been reclassified to conform to the current period’s presentation (see Note 21).
		2013 Three Months Ended											2012 Three Months Ended
	Millions, except per share amounts	Dec. 31			Sept. 30			June 30		Mar. 31			Dec. 31			Sept. 30			June 30			Mar. 31
	Revenues	$	626.6		$	574.1		$	489.3	$	627.4		$	566.4		$	697.4		$	542.3		$	629.7
	Expenses	492.4			518.8			485.7		475.6			617.2			562.3			504.7			488.8
	Pre-tax income (loss)	134.2			55.3			3.6		151.8			(50.8		)	135.1			37.6			140.9
	Tax benefit (expense)	(27.4		)	(8.2		)	0.6		(41.6		)	101			(47.8		)	(6.4		)	(31.1		)
	Income (loss) from continuing operations	106.8			47.1			4.2		110.2			50.2			87.3			31.2			109.8
	Income (loss) from discontinued operations, net of tax	(.3		)	0.4			3.9		0.5			0.5			(106.8		)	0.5			(9.2		)
	Non-controlling interest in consolidated subsidiaries	(.3		)	1.1			11.1		0.5			12			30.9			(12.1		)	(16.8		)
	Equity in (loss) earnings of unconsolidated affiliates	11.7			8.6			7.1		9.2			5.5			7.7			6.5			10.2
	Income (loss) attributable to White Mountains’ common shareholders	$	117.9		$	57.2		$	26.3	$	120.4		$	68.2		$	19.1		$	26.1		$	94
	Income (loss) attributable to White Mountains’ common shareholders:
	Basic
	Continuing operations	$	19.14		$	9.2		$	3.62	$	19.1		$	10.36		$	19.11		$	3.85		$	13.85
	Discontinued operations	(.05		)	0.06			0.64		0.07			0.07			(16.21		)	0.07			(1.24		)
	Total consolidated operations	$	19.09		$	9.26		$	4.26	$	19.17		$	10.43		$	2.9		$	3.92		$	12.61
	Diluted
	Continuing operations	$	19.14		$	9.2		$	3.62	$	19.1		$	10.36		$	19.11		$	3.85		$	13.85
	Discontinued operations	(.05		)	0.06			0.64		0.07			0.07			(16.21		)	0.07			(1.24		)
	Total consolidated operations	$	19.09		$	9.26		$	4.26	$	19.17		$	10.43		$	2.9		$	3.92		$	12.61
	Adjusted book value per share	$	642.27		$	621.56		$	604.75	$	606.2		$	587.63		$	573.66		$	564.77		$	565.38

Summary_of_Significant_Account3

Summary of Significant Accounting Policies (Basis of Presentation) (Details) (USD $)

1 Months Ended

12 Months Ended

3 Months Ended

1 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2011

company

state

OneBeacon Ltd.

OneBeacon Ltd.

HG Global

HG Global

HG Global

Redeemable preferred stocks

Redeemable preferred stocks

Common Stock

Common Stock

Tuckerman Fund I

Tuckerman Fund I

HG Global

HG Global

HG Global

HG Global

Common Stock

Common Stock

Basis of Presentation

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Capital contributions

'

'

'

'

'

$600

'

'

'

'

'

'

'

'

BAM Surplus notes

'

'

'

'

'

'

$503

$503

'

'

'

'

'

'

Ownership interest (as a percent)

'

'

'

75.20%

75.20%

'

97.30%

'

97.30%

97.30%

88.70%

88.70%

'

'

Percentage of par value of policy reinsured

'

'

15.00%

'

'

'

15.00%

'

'

'

'

'

'

'

Ownership interest in VIE (as a percent)

'

'

'

'

'

'

'

'

'

'

'

'

94.00%

94.00%

Number of manufacturing companies

2

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of states

'

30

'

'

'

'

'

'

'

'

'

'

'

'

Workers compensation discount percent

'

3.50%

3.50%

'

'

'

'

'

'

'

'

'

'

'

Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners

'

'

'

24.80%

24.80%

'

'

'

'

'

'

'

'

'

Summary_of_Significant_Account4

Summary of Significant Accounting Policies (Investment Securities) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
	security
Accounting Policies [Abstract]	'
Percentage of investments recorded at fair value	95.00%
Minimum percentage of variation expected	5.00%
Minimum variation expected	$1
Securities outside variance threshold	35

Summary_of_Significant_Account5

Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Warrants) (Details) (Symetra)	Jun. 20, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Symetra	'	'
New Accounting Pronouncements or Change in Accounting Principle [Line Items]	'	'
Investments in unconsolidated affiliates on conversion of warrants	2.65	9.49

Summary_of_Significant_Account6

Summary of Significant Accounting Policies (Insurance and Reinsurance Operations) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Workers compensation discount percent	3.50%	3.50%
Workers compensation discount amount	$3	$4.60
OneBeacon Runoff	'	'
Workers compensation discount amount	$61.70	$77.90

Summary_of_Significant_Account7

Summary of Significant Accounting Policies (Deferred Softward Costs) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2013
In Millions, unless otherwise specified			Minimum	Maximum
			Software and Software Development Costs	Software and Software Development Costs
Useful lives	'	'	'3 years	'5 years
Deferred software costs	$23.80	$17.10	'	'

Summary_of_Significant_Account8

Summary of Significant Accounting Policies (Foreign Currency Exchange) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Millions, unless otherwise specified
Significant Transactions	'	'	'
Net unrealized foreign currency translation gains	88.4	85.7	'
SEK	'	'	'
Significant Transactions	'	'	'
Foreign currency exchange rate	6.4339	6.4973	6.8645
GBP	'	'	'
Significant Transactions	'	'	'
Foreign currency exchange rate	0.6044	0.6154	0.6434
Canada, Dollars	'	'	'
Significant Transactions	'	'	'
Foreign currency exchange rate	1.0625	0.9955	1.0193

Summary_of_Significant_Account9

Summary of Significant Accounting Policies (Noncontrolling Interest) (Details) (USD $)

3 Months Ended

12 Months Ended

12 Months Ended

3 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

61 Months Ended

1 Months Ended

In Millions, except Share data, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Sep. 30, 2012

Dec. 31, 2013

31-May-07

24-May-07

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Jun. 30, 2022

31-May-07

31-May-07

31-May-07

31-May-07

White Mountains Consolidated Limited Partnership

White Mountains Consolidated Limited Partnership

A W G Dewar Inc

A W G Dewar Inc

Passage 2 Health Limited

Passage 2 Health Limited

OneBeacon Ltd.

OneBeacon Ltd.

White Mountains

HG Global

HG Global

Preferred stocks

Preferred stocks

BAM Management

Common shares and paid-in surplus

Non-controlling Interests

BAM

BAM

Interest Rate Cap

Interest Rate Cap

Interest Rate Cap

Scenario, 1 [Member]

Scenario, 1 [Member]

Scenario, 2 [Member]

Sirius Internation Group Ltd

Sirius Internation Group Ltd

Non-controlling Interests

Non-controlling Interests

Sirius Internation Group Ltd

Sirius Internation Group Ltd

Preferred stocks

Preferred stocks

Interest Rate Cap

Preferred stocks

Period

Sirius Internation Group Ltd

Sirius Internation Group Ltd

Preferred stocks

Sirius Internation Group Ltd

quarter

Sirius Internation Group Ltd

Noncontrolling Interest [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

25.00%

'

24.80%

24.80%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Capital contributions

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$594.50

$600

'

'

'

$14.50

'

'

'

'

'

'

'

'

'

'

Fair Value of Net Assets Acquired

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2.2

-2.2

'

'

'

'

'

'

'

'

Pre-tax loss

134.2

55.3

3.6

151.8

-50.8

135.1

37.6

140.9

344.9

262.8

98

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-78.6

[1]

-36.3

[1]

'

'

'

'

'

'

Non-cumulative perpetual preference shares issued

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

250,000,000

'

'

'

'

'

'

'

'

250,000,000

'

'

'

Non-cumulative perpetual preference shares per share liquidation preference (in dollars per share)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$1,000

'

'

'

'

'

'

'

'

'

'

'

Percentage of investments recorded at fair value

'

'

'

'

'

'

'

'

95.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Proceeds from non-cumulative perpetual preference shares

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

245.7

'

'

'

'

'

'

'

'

'

'

'

'

Non-cumulative perpetual preference shares issuance cost and commission

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4.3

'

'

'

'

'

'

'

'

'

'

'

'

years of interest rate cap

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'5 years

'5 years

'

'

'

'

Derivative, Cap Interest Rate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

8.30%

'

'

'

'

'

Preferred Stock Redemption Basis Spread on Treasury Issue Rate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

45.00%

'

'

'

'

'

'

'

'

'

'

'

'

Right to elect directors on board number

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2

'

'

'

'

'

'

'

'

'

'

'

'

Period for non payment of dividend which give right to elect directors on board

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6

'

'

'

'

'

'

'

'

'

'

'

'

Minimum required payment period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4

'

'

'

'

'

'

'

'

'

'

'

'

Preferred stock dividend rate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6.00%

'

'

'

'

'

'

'

'

'

7.51%

'

'

7.51%

Preference shares reference rate for dividend

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'3 month LIBOR

'

Preference shares floating rate of dividend amount in excess of libor

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3.20%

'

'

Noncontrolling interest—consolidated limited partnerships

'

'

'

'

'

'

'

'

'

'

'

$46.10

$41.50

$3.10

$2.80

'

$0.20

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

[1]

BAM manages its affairs on a statutory accounting basis. BAM’s statutory surplus includes surplus notes and is not reduced by accruals of interest expense on the surplus notes. BAM’s statutory surplus is reduced only after a payment of principal or interest has been approved by the New York Department of Financial Services.

Recovered_Sheet1

Summary of Significant Accounting Policies (Recently Adopted in Accounting Principles) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2012
Accounting Policies [Abstract]	'
Deferred policy acquisition costs, amortization expense	$5.60

Significant_Transactions_Sale_

Significant Transactions Sale of Essentia (Details) (USD $)	12 Months Ended			3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
				Essentia	Underwriting Agreement [Member]	Underwriting Agreement [Member]
				OneBeacon	Essentia	Essentia
					OneBeacon	OneBeacon
Unusual or Infrequent Item [Line Items]	'	'	'	'	'	'
Gain (Loss) on Disposition of Stock in Subsidiary	$21.30	$0	$0	$23	'	'
Gain (Loss) on Disposition of Stock in Subsidiary, After Tax	'	'	'	15	'	'
Premiums Written, Net	'	'	'	'	$179.70	$166.60
Premiums written, percentage of total	'	'	'	'	8.00%	8.00%

Significant_Transactions_Forma

Significant Transactions (Formation of HG and BAM) (Details) (USD $)

Dec. 31, 2012

Dec. 31, 2012

Sep. 30, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

In Millions, unless otherwise specified

White Mountains

HG Global

HG Global

HG Global

HG Global

HG Global

HG Global

HG Global

HG Re

HG Re

HG Global

Total

Total

Redeemable preferred stocks

Redeemable preferred stocks

Significant Transactions

'

'

'

'

'

'

'

'

'

'

'

'

Capital contributions

'

$594.50

$600

'

'

'

'

'

'

'

'

'

Ownership interest (as a percent)

'

'

'

97.30%

'

88.70%

88.70%

97.30%

97.30%

'

'

'

Surplus notes

'

'

'

503

503

'

'

'

'

'

'

'

Statutory capital and surplus

'

'

'

'

'

'

'

'

'

$436.90

$412

'

Percentage of par value of policy reinsured

15.00%

'

'

15.00%

'

'

'

'

'

'

'

15.00%

Significant_Transactions_WM_So

Significant Transactions (WM Solutions) (Details) (WM Solutions, USD $)	3 Months Ended	0 Months Ended	3 Months Ended	1 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 03, 2012	Mar. 31, 2013	Dec. 31, 2011	Dec. 31, 2011	Dec. 30, 2011
	Empire [Member]	Runoff Entities [Member]	American Fuji [Member]	Old Lyme	Old Lyme	Old Lyme
Business Acquisition [Line Items]	'	'	'	'	'	'
Cash to be paid on acquisition	'	'	'	'	$6	'
Cash purchase price of note	'	'	'	'	'	2.1
Gain recognized	$7.30	$14.50	$6.90	$7.20	'	'

Significant_Transactions_Sale_1

Significant Transactions (Sale of Esurance) (Details) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Oct. 31, 2011	Dec. 31, 2011
				Esurance	Esurance
Significant Transactions	'	'	'	'	'
Gain (Loss) on Disposition of Business	'	'	'	'	$700
Gain (loss) on sale of discontinued operations, net of tax	$46.60	($91)	$658.30	$677.50	'

Reserves_for_Unpaid_Losses_and2

Reserves for Unpaid Losses and Loss Adjustment Expenses (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Loss and LAE incurred relating prior year losses	($48.40)	($41.90)	($76.70)	'
Increase (decrease) in reserves	1,040.50	1,193.90	1,174.30	'
Accretion of fair value adjustment to net loss and LAE reserves	1.7	10.6	8.3	'
Un-accreted fair value, adjustment to loss and loss adjustment expense reserves, before tax	4.7	'	'	'
Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Loss and LAE incurred relating prior year losses	-23.9	-34.5	-46.9	'
Liability for asbestos and environmental claims, gross	227.8	228.6	207.2	214.3
Liability for asbestos and environmental claims	193.9	189.4	162.7	169.6
Asbestos and Environmental Loss Three Year Survival Ratio Period	'8 years	'9 years	'	'
Liability for asbestos claims, net, period increase (decrease)	11.8	46.4	10.3	'
Liabilty for environmental claims, net, period increase (decrease)	0.8	-0.5	2	'
OneBeacon	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Loss and LAE incurred relating prior year losses	'	-7.4	-29.8	'
Liability for asbestos and environmental claims, gross	1	'	'	'
Chile Earthquake Loss Cover | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Increase (decrease) in reserves	'	'	-13.1	'
Asbestos | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Liability for asbestos and environmental claims, gross	207.4	208.2	185.1	191.9
Liability for asbestos and environmental claims	178.7	174.2	146.2	151.5
Environmental | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Liability for asbestos and environmental claims, gross	20.4	20.4	22.1	22.4
Liability for asbestos and environmental claims	15.2	15.2	16.5	18.1
WM Solutions | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Liability for asbestos claims, net, period increase (decrease)	13	11	'	'
Liabilty for environmental claims, net, period increase (decrease)	1	0.7	'	'
Accident and Health Insurance Product Line [Member] | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Loss and LAE incurred relating prior year losses	-9.2	'	'	'
Asbestos [Member] | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Loss and LAE incurred relating prior year losses	11.8	46.4	'	'
Casualty Runoff [Member] | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Loss and LAE incurred relating prior year losses	'	-31.5	'	'
Aviation Space [Member] | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Loss and LAE incurred relating prior year losses	-10.1	-5.3	'	'
Property [Member] | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Loss and LAE incurred relating prior year losses	-16.6	-28.4	'	'
Property Insurance Product Line [Member] | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Increase (decrease) in reserves	'	'	-41.2	'
asbestos and environmental [Member] | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Increase (decrease) in reserves	'	'	12.3	'
Marine Energy [Member] | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Loss and LAE incurred relating prior year losses	'	-11.6	'	'
Trade Credit [Member] | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Loss and LAE incurred relating prior year losses	'	-6.8	'	'
Accident and Health | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Loss and LAE incurred relating prior year losses	'	4.3	'	'
Professional Liability | OneBeacon	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Increase (decrease) in reserves	'	'	-11.5	'
Property and Casualty, Commercial Insurance Product Line [Member] | OneBeacon	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Increase (decrease) in reserves	'	'	-14	'
Other Lines of Business [Member] | OneBeacon	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Increase (decrease) in reserves	'	'	-4.3	'
Quarterly Monitoring [Member] | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Liability for asbestos claims, net, period increase (decrease)	'	14	'	'
In-depth Analysis [Member] | Sirius Group	'	'	'	'
Asbestos and Environmental Loss and Loss Adjustment Expense Reserve Activity	'	'	'	'
Liability for asbestos claims, net, period increase (decrease)	'	$33	'	'

Reserves_for_Unpaid_Losses_and3

Reserves for Unpaid Losses and Loss Adjustment Expenses (Reserve Summary) (Details) (USD $)

12 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

AutoOne

AutoOne

AutoOne

AutoOne

WM Solutions

WM Solutions

WM Solutions

Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]

'

'

'

'

'

'

'

'

'

'

Gross beginning balance

$3,168.90

$5,702.30

$5,736.80

'

'

'

'

'

'

'

Less beginning reinsurance recoverable on unpaid losses

-429.1

-2,507.30

-2,344

'

'

'

'

'

'

'

Net loss and LAE reserves

2,739.80

3,195

3,392.80

0

[1]

0

[1]

-383.3

[1]

-619.6

[1]

'

'

'

Loss and LAE reserves acquired

'

'

'

'

'

'

'

37.7

[2]

17

[2]

21

[2]

Loss and LAE incurred relating to current year losses

1,088.90

1,235.80

1,251

'

'

'

'

'

'

'

Loss and LAE incurred relating prior year losses

-48.4

-41.9

-76.7

'

'

'

'

'

'

'

Total incurred losses and LAE

1,040.50

1,193.90

1,174.30

'

'

'

'

'

'

'

Accretion of fair value adjustment to net loss and LAE reserves

1.7

10.6

8.3

'

'

'

'

'

'

'

Foreign currency translation adjustment to net loss and LAE reserves

0.3

12.9

0.1

'

'

'

'

'

'

'

Loss and LAE paid relating to current year losses

-336.2

-404.7

-387.9

'

'

'

'

'

'

'

Loss and LAE paid relating to prior year losses

-832.6

-901.6

-777.3

'

'

'

'

'

'

'

Total loss and LAE payments

-1,168.80

-1,306.30

-1,165.20

'

'

'

'

'

'

'

Net loss and LAE reserves

2,651.20

2,739.80

3,195

0

[1]

0

[1]

-383.3

[1]

-619.6

[1]

'

'

'

Plus ending reinsurance recoverable on unpaid losses

428.1

429.1

2,507.30

'

'

'

'

'

'

'

Gross ending balance

$3,079.30

$3,168.90

$5,702.30

'

'

'

'

'

'

'

[1]

Loss and LAE reserve balances from OneBeacon’s Runoff Business prior to December 31, 2012 and AutoOne prior to December 31, 2011 were not classified as held for sale. Adjustment is to present loss and LAE reserve activities for continuing operations.

[2]

Loss and LAE reserves acquired relate to WM Solutions purchases of Empire and Ashmere in 2013, PICO, Citation, Woodridge and Oakwood in 2012 and Old Lyme in 2011.

Reserves_for_Unpaid_Losses_and4

Reserves for Unpaid Losses and Loss Adjustment Expenses (LAE Reserve Activity) (Details) (Sirius Group, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Gross	'	'	'
Beginning balance	$228.60	$207.20	$214.30
Losses and LAE acquired	14	11.7	0
Incurred losses and LAE	12.9	46.7	16.5
Paid losses and LAE	-27.7	-37	-23.6
Ending balance	227.8	228.6	207.2
Net	'	'	'
Beginning balance	189.4	162.7	169.6
Losses and LAE acquired Central National	14	11.7	0
Incurred losses and LAE	12.6	45.9	12.3
Liability for unpaid claims and claims adjustment expense	-22.1	-30.9	-19.2
Ending balance	193.9	189.4	162.7
Asbestos	'	'	'
Gross	'	'	'
Beginning balance	208.2	185.1	191.9
Losses and LAE acquired	13	11	0
Incurred losses and LAE	12.1	46.8	13.6
Paid losses and LAE	-25.9	-34.7	-20.4
Ending balance	207.4	208.2	185.1
Net	'	'	'
Beginning balance	174.2	146.2	151.5
Losses and LAE acquired Central National	13	11	0
Incurred losses and LAE	11.8	46.4	10.3
Liability for unpaid claims and claims adjustment expense	-20.3	-29.4	-15.6
Ending balance	178.7	174.2	146.2
Environmental	'	'	'
Gross	'	'	'
Beginning balance	20.4	22.1	22.4
Losses and LAE acquired	1	0.7	0
Incurred losses and LAE	0.8	-0.1	2.9
Paid losses and LAE	-1.8	-2.3	-3.2
Ending balance	20.4	20.4	22.1
Net	'	'	'
Beginning balance	15.2	16.5	18.1
Losses and LAE acquired Central National	1	0.7	0
Incurred losses and LAE	0.8	-0.5	2
Liability for unpaid claims and claims adjustment expense	-1.8	-1.5	-3.6
Ending balance	$15.20	$15.20	$16.50

Third_Party_Reinsurance_Writte

Third Party Reinsurance (Written and Earned Premiums) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Earned premiums:	'		'		'
Net earned premiums	$1,987.30		$2,063.60		$1,924.50
Losses and LAE:	'		'		'
Total incurred losses and LAE	1,040.50		1,193.90		1,174.30
OneBeacon	'		'		'
Written premiums:	'		'		'
Direct	1,103.10		1,204		1,079.20
Assumed	59.8		55.2		49.1
Gross written premiums	1,162.90		1,259.20		1,128.30
Ceded	-74.3		-80		-65.6
Net written premiums	1,088.60		1,179.20		1,062.70
Earned premiums:	'		'		'
Gross amount	1,043.30	[1]	1,158.30	[1]	1,035.90	[1]
Assumed from other companies	148.5	[1]	52.8	[1]	42.3	[1]
Gross earned premiums	1,191.80		1,211.10		1,078.20
Ceded	-71.4	[1]	-79.1	[1]	-66	[1]
Net earned premiums	1,120.40	[1]	1,132	[1]	1,012.20	[1]
Losses and LAE:	'		'		'
Direct	584.9		687.5		551.8
Policyholder Benefits and Claims Incurred, Assumed	76.3		29.6		9.2
Gross losses and LAE	661.2		717.1		561
Ceded	-39.1		-67.1		-12.7
Total incurred losses and LAE	622.1		650		548.3
Sirius Group	'		'		'
Written premiums:	'		'		'
Direct	177.3		186.1		139.5
Assumed	943.1		992.7		988.6
Gross written premiums	1,120.40		1,178.80		1,128.10
Ceded	-243.8		-231.1		-212.4
Net written premiums	876.6		947.7		915.7
Earned premiums:	'		'		'
Gross amount	174		169.9		128.5
Assumed from other companies	938.6		988.3		989.8
Gross earned premiums	1,112.60		1,158.20		1,118.30
Ceded	-246.2		-226.6		-206
Net earned premiums	866.4		931.6		912.3
Losses and LAE:	'		'		'
Direct	98.1		96.9		80
Policyholder Benefits and Claims Incurred, Assumed	455.5		523.9		627.8
Gross losses and LAE	553.6		620.8		707.8
Ceded	-135.2		-76.9		-81.8
Total incurred losses and LAE	418.4		543.9		626
OneBeacon and Sirius Group	'		'		'
Written premiums:	'		'		'
Direct	1,280.40		1,390.10		1,218.70
Assumed	1,002.90		1,047.90		1,037.70
Gross written premiums	2,283.30		2,438		2,256.40
Ceded	-318.1		-311.1		-278
Net written premiums	1,965.20		2,126.90		1,978.40
Earned premiums:	'		'		'
Gross amount	1,217.30		1,328.20		1,164.40
Assumed from other companies	1,087.10		1,041.10		1,032.10
Gross earned premiums	2,304.40		2,369.30		2,196.50
Ceded	-317.6		-305.7		-272
Net earned premiums	1,986.80		2,063.60		1,924.50
Losses and LAE:	'		'		'
Direct	683		784.4		631.8
Policyholder Benefits and Claims Incurred, Assumed	531.8		553.5		637
Gross losses and LAE	1,214.80		1,337.90		1,268.80
Ceded	-174.3		-144		-94.5
Total incurred losses and LAE	$1,040.50		$1,193.90		$1,174.30
[1]	The amounts shown excludes balances reclassified to held for sale in the consolidated balance sheets related to the Runoff Transaction as of December 31, 2013 and 2012 and to AutoOne as of December 31, 2011. See Note 21 - “Discontinued Operations”.

ThirdParty_Reinsurance_OneBeac

Third-Party Reinsurance (OneBeacon) (Details) (USD $)

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

In Millions, unless otherwise specified

OneBeacon

OneBeacon

Casualty Reinsurance Program

Property Per-Risk, Acts of Terrorism

Property Per-Risk, Acts of Terrorism

Property Per-Risk, Acts of Terrorism

Property Per-Risk, Acts of Terrorism

Property Per-Risk, Acts of Terrorism

Property Catastrophe Reinsurance

Property Catastrophe Reinsurance

Property Catastrophe Reinsurance

Property Catastrophe Reinsurance

Property Catastrophe Reinsurance

Property Per Risk Reinsurance Program

Property Per Risk Reinsurance Program

Property Per Risk Reinsurance Program

Layer One

Layer One

Layer One

Layer One

Layer One

Layer Two

Layer Two

Layer Two

Layer Two

Layer Two

Layer Three

Layer Three

Layer Three

Inland and Ocean Marine

Inland and Ocean Marine

Inland and Ocean Marine

Inland and Ocean Marine

Inland and Ocean Marine

Inland and Ocean Marine

Inland and Ocean Marine

Catastrophic Losses [Member]

Surety Underwriting

Surety Underwriting

Surety Underwriting

Health Insurance Product Line

Health Insurance Product Line

Health Insurance Product Line

Property, Liability and Casualty Insurance Product Line

Property, Liability and Casualty Insurance Product Line

Property, Liability and Casualty Insurance Product Line

Property, Liability and Casualty Insurance Product Line

Property, Liability and Casualty Insurance Product Line

Workers compensation

Workers compensation

Workers compensation

AA

A

BBB

OneBeacon

OneBeacon

OneBeacon

Maximum

OneBeacon

OneBeacon

OneBeacon

Minimum

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

Property Catastrophe Reinsurance

Property Catastrophe Reinsurance

Property Catastrophe Reinsurance

Property Per Risk Reinsurance Program

Property Per Risk Reinsurance Program

Property Catastrophe Reinsurance

Property Catastrophe Reinsurance

Property Catastrophe Reinsurance

Property Per Risk Reinsurance Program

Property Per Risk Reinsurance Program

Property Catastrophe Reinsurance

Property Catastrophe Reinsurance

Property Catastrophe Reinsurance

Marine Treaty Per Occurrence

Marine Treaty

Layer One

Layer One

Layer One

Layer One

Layer One

Layer One

Insurance Per Bond

Insurance Per Bond

Insurance Per Bond

Casualty Reinsurance Program

Casualty Reinsurance Program

Layer One

Casualty Reinsurance Program

Casualty Reinsurance Program

Layer One

Layer Two

Layer Two

Casualty Reinsurance Program

Casualty Reinsurance Program

Casualty Reinsurance Program

OneBeacon

OneBeacon

OneBeacon

OneBeacon

Maximum

Minimum

OneBeacon

Maximum

Maximum

Maximum

Minimum

OneBeacon

Minimum

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

Marine Treaty

Marine Treaty

Marine Treaty

Property Per Risk Treaty

Catastrophic Losses [Member]

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

Casualty Reinsurance Program

OneBeacon

OneBeacon

Casualty Reinsurance Program

Casualty Reinsurance Program

Casualty Reinsurance Program

OneBeacon

OneBeacon

OneBeacon

OneBeacon

Maximum

Maximum

Minimum

Maximum

Minimum

Minimum

Maximum

Minimum

OneBeacon

OneBeacon

OneBeacon

OneBeacon

OneBeacon

Maximum

Minimum

Maximum

Minimum

OneBeacon

Maximum

Minimum

OneBeacon

OneBeacon

Maximum

Minimum

Maximum

Minimum

Maximum

Effects of Reinsurance [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance recoverable on paid and unpaid losses

'

'

'

'

$89.90

[1]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$26.40

[1]

$56.10

[1]

$7.40

[1]

Reinsurance recoverables, percentage of total

'

'

'

'

100.00%

[1]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

30.00%

[1]

62.00%

[1]

8.00%

[1]

Percentage of certified losses required to be shared by federal government subject to terrorism risk insurance act

'

'

'

'

85.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance retention policy, amount retained

'

'

'

'

'

'

10

100

'

100,000

'

'

'

20

33

150

180

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2

'

'

'

'

20

2

'

'

'

'

'

'

5

'

'

5

'

11

'

'

'

'

'

'

Annual Aggregate Deductible to Reinsurance Retention Policy

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1.5

5

'

'

'

'

'

'

'

'

'

3

'

'

'

'

'

'

'

Reinsurance Retention Policy Excess Retention Amount Reinsured Net Of Participation

'

'

'

'

'

'

'

'

'

'

'

'

117

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance retention policy, excess retention, amount reinsured

'

'

'

'

'

'

60

'

'

'

100

10

130

'

'

'

'

'

100

10

'

20

30

40

20

'

70

30

'

40

'

150

70

'

60

'

7

2

'

5

'

60

30

5

20

5

5

21

5

6

'

10

'

10

1

'

'

'

Property Catastrophe Reinsurance Treaty Second Layer Co-Partipation Percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

10.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Property Catastrophe Reinsurance Treaty First Layer Co-Partipation Percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

60.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance Retention Policy, Excess Retention, Percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

50.00%

'

'

'

'

10.00%

'

'

'

'

5.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance Retention Policy, Reinsured Risk, Percentage

'

'

'

'

'

'

'

'

85.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100.00%

'

'

'

'

10.00%

'

'

10.00%

'

5.00%

100.00%

'

'

'

'

'

Reinsurance recoverable on paid losses

'

'

'

'

'

9.7

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance recoverable on unpaid losses

$428.10

$429.10

$2,507.30

$2,344

'

$80.20

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

[1]

Standard & Poor’s ratings as detailed above are: “AA” (Very strong), “A” (Strong) and “BBB+” (Adequate).

Third_Party_Reinsurance_Sirius

Third Party Reinsurance (Sirius Group) (Details)

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Feb. 28, 2014

Feb. 28, 2014

Dec. 31, 2013

USD ($)

USD ($)

USD ($)

USD ($)

Sirius Group

Sirius Group

OneBeacon

OneBeacon

AAA

AA

AA

A

A

BBB

BBB

BBB or lower

Not Rated [Member]

Faculative and Direct Property Portfolios

Faculative and Direct Property Portfolios

Faculative and Direct U.S. Catastophe Exposed Business

Non U.S and Non Japan Earthquake Related Exposure

Non U.S and Non Japan Earth Quake Related Exposure Partial Coverage

ILW

ILW

Aviation Reinsurance

Aviation Reinsurance

Aviation Reinsurance

Marine Yacht Portfolio, London Branch and Syndicate 1945

Accident and Health

Accident and Health

Subsequent Event

Subsequent Event

Hamburg and Stockholm [Member]

USD ($)

USD ($)

USD ($)

USD ($)

Sirius Group

Sirius Group

OneBeacon

Sirius Group

OneBeacon

Sirius Group

OneBeacon

Sirius Group

Sirius Group

Sirius Group

Lloyds Syndicate 1945 [Member]

Lloyds Syndicate 1945 [Member]

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Minimum

Maximum

Sirius Group

Sirius Group

Sirius Group

Faculative and Direct Property Portfolios

ILW

Faculative and Direct Property Portfolios

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

EUR (€)

USD ($)

Sirius Group

Sirius Group

USD ($)

USD ($)

EUR (€)

Lloyds Syndicate 1945 [Member]

Sirius Group

Lloyds Syndicate 1945 [Member]

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

Reinsurance Retention Policy [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance retention policy, amount retained

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$5,000,000

$5,000,000

$5,000,000

$35,000,000

$75,000,000

$7,500,000

'

'

$150,000,000

$2,250,000,000

$300,000

$6,900,000

€ 5,000,000

$2,500,000

'

$20,000,000

Reinsurance retention level, event policy

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6,900,000,000

5,000,000,000

'

'

'

'

'

'

'

7,500,000,000

'

Percentage of quota share reinsurance agreement

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

15.00%

'

'

'

'

'

'

'

'

Percentage of trade credit business ceded under quota share retrocession

'

'

'

'

20.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of bond business ceded under renewed quota share retrocession

'

'

'

'

50.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aviation reinsurance program cover in first event industry loss warranties

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

350,000,000

1,000,000,000

'

'

'

'

'

'

Reinsurance retention policy, excess retention, amount reinsured

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

15,000,000

10,000,000

5,000,000

40,000,000

15,800,000

'

'

30,500,000

'

'

9,800,000

13,800,000

10,000,000

2,500,000

10,000,000

15,000,000

Direct contingency business ceded

'

'

'

'

30.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of property catastrophe reinsurance treaty reinstatement premiums

'

'

'

'

100.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance recoverable on paid losses

'

'

'

'

15,700,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance recoverable on unpaid losses

428,100,000

429,100,000

2,507,300,000

2,344,000,000

347,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance recoverables, gross

453,500,000

447,000,000

'

'

363,600,000

[1]

336,300,000

89,900,000

110,700,000

62,900,000

[1]

60,600,000

[1]

'

127,500,000

[1]

'

21,000,000

[1]

'

16,600,000

[1]

75,000,000

[1]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance Recoverables, Collateral

'

'

'

'

37,600,000

[1]

'

'

'

0

[1]

4,500,000

[1]

'

1,600,000

[1]

'

0

[1]

'

0

[1]

31,500,000

[1]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance recoverable on paid and unpaid losses

'

'

'

'

$326,000,000

[1]

'

$89,900,000

[2]

'

$62,900,000

[1]

$56,100,000

[1]

$26,400,000

[2]

$125,900,000

[1]

$56,100,000

[2]

$21,000,000

[1]

$7,400,000

[2]

$16,600,000

[1]

$43,500,000

[1]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance recoverables, percentage of total

'

'

'

'

100.00%

[1]

'

100.00%

[2]

'

19.00%

[1]

17.00%

[1]

30.00%

[2]

39.00%

[1]

62.00%

[2]

7.00%

[1]

8.00%

[2]

5.00%

[1]

13.00%

[1]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

[1]

Standard & Poor’s ratings as detailed above are: “AAA” (Extremely strong), “AA” (Very strong), “A” (Strong), and “BBB+” and “BBB” (Adequate).

[2]

Standard & Poor’s ratings as detailed above are: “AA” (Very strong), “A” (Strong) and “BBB+” (Adequate).

Investment_Securities_Net_Inve

Investment Securities (Net Investment Income) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investment income:	'	'	'
Total investment income	$130.60	$167	$195.40
Third-party investment expenses	-19.7	-13.4	-10.9
Net investment income, pre-tax	110.9	153.6	184.5
Fixed maturity investments	'	'	'
Investment income:	'	'	'
Total investment income	100.5	132	166.2
Short-term investments	'	'	'
Investment income:	'	'	'
Total investment income	3.4	3.1	4.5
Common Stock	'	'	'
Investment income:	'	'	'
Total investment income	20.5	22.2	15.4
Convertible fixed maturity investments	'	'	'
Investment income:	'	'	'
Total investment income	2.9	6	5.5
Other long-term investments	'	'	'
Investment income:	'	'	'
Total investment income	3	3.1	4.2
Interest on funds held under reinsurance treaties	'	'	'
Investment income:	'	'	'
Total investment income	$0.30	$0.60	($0.40)

Investment_Securities_Net_Real

Investment Securities (Net Realized and Unrealized Investement Gains and Losses) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investments, Debt and Equity Securities [Abstract]	'	'	'
Net realized investment gains, pre-tax	$104.50	$68.10	$68.30
Net unrealized investment gains, pre-tax	57.2	50.1	5.8
Net realized and unrealized investment gains, pre-tax	161.7	118.2	74.1
Income tax expense attributable to net realized and unrealized investment gains	-21.9	-26.8	-18.1
Net realized and unrealized investment gains, after tax	$139.80	$91.40	$56

Investment_Securities_Investme

Investment Securities Investment Securities (Net Realized Investment Gain (losses) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investment securities	'	'	'
Trading Securities, Realized Gain (Loss)	$121.80	$76.70	$117
Foreign Currency Transaction Gain (Loss), Realized	-17.3	-8.6	-48.7
Net realized investment gains, pre-tax	104.5	68.1	68.3
Trading securities, Tax on Realized Holding Gain (Loss) on Investments	-30	-23.8	-37
Trading Securities, Tax on Realized Foreign Currency Transaction Gain (Loss) Tax	5.5	2.2	12.8
Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	-24.5	-21.6	-24.2
Trading Securities Realized Holding Gain (Loss) on Investments after Tax	91.8	52.9	80
Trading Securities, Realized Foreign Currency Gain (Loss) Net of Tax	-11.8	-6.4	-35.9
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	80	46.5	44.1
Fixed maturity investments	'	'	'
Investment securities	'	'	'
Trading Securities, Realized Gain (Loss)	8.6	82.5	49.4
Foreign Currency Transaction Gain (Loss), Realized	-15	-2.5	-38.3
Net realized investment gains, pre-tax	-6.4	80	11.1
Short-term investments	'	'	'
Investment securities	'	'	'
Trading Securities, Realized Gain (Loss)	0.1	0	0
Foreign Currency Transaction Gain (Loss), Realized	0	-4.3	-9.9
Net realized investment gains, pre-tax	0.1	-4.3	-9.9
Common equity securities	'	'	'
Investment securities	'	'	'
Trading Securities, Realized Gain (Loss)	104.5	1.3	34.6
Foreign Currency Transaction Gain (Loss), Realized	-3.7	0	0
Net realized investment gains, pre-tax	100.8	1.3	34.6
Convertible fixed maturity investments	'	'	'
Investment securities	'	'	'
Trading Securities, Realized Gain (Loss)	1	-8.2	-2.2
Foreign Currency Transaction Gain (Loss), Realized	0	-1.8	0
Net realized investment gains, pre-tax	1	-10	-2.2
Other long-term investments	'	'	'
Investment securities	'	'	'
Trading Securities, Realized Gain (Loss)	7.5	1.4	35.2
Foreign Currency Transaction Gain (Loss), Realized	1.4	0	-0.5
Net realized investment gains, pre-tax	8.9	1.4	34.7
Forward contracts	'	'	'
Investment securities	'	'	'
Trading Securities, Realized Gain (Loss)	0.1	-0.3	'
Foreign Currency Transaction Gain (Loss), Realized	0	0	'
Net realized investment gains, pre-tax	$0.10	($0.30)	'

Investment_Securities_Investme1

Investment Securities Investment Securities (Net Unrealized Investment Gains (Losses)) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investment securities	'	'	'
Trading Securities, Change in Unrealized Holding Gain (Loss)	$38.90	$98.70	($63.60)
Foreign Currency Transaction Gain (Loss), Unrealized	18.3	-48.6	69.4
Net unrealized investment gains, pre-tax	57.2	50.1	5.8
Trading Securities, Tax on Unrealized Holding Gain (Loss) on Investments	8.2	-17.9	24
Trading Securities, Unrealized Foreign Currency Transaction Gain (Loss) Tax	-5.6	12.7	-17.9
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Tax	2.6	-5.2	6.1
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax	47.1	80.8	-39.6
Trading Securities, Unrealized Foreign Currency Gain (Loss) Net of Tax	12.7	-35.9	51.5
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	59.8	44.9	11.9
Fixed maturity investments	'	'	'
Investment securities	'	'	'
Trading Securities, Change in Unrealized Holding Gain (Loss)	-93.9	18.5	7.6
Foreign Currency Transaction Gain (Loss), Unrealized	15.3	-45.9	68.9
Net unrealized investment gains, pre-tax	-78.6	-27.4	76.5
Short-term investments	'	'	'
Investment securities	'	'	'
Trading Securities, Change in Unrealized Holding Gain (Loss)	0.1	0	0
Foreign Currency Transaction Gain (Loss), Unrealized	0	0.1	-1.1
Net unrealized investment gains, pre-tax	0.1	0.1	-1.1
Common equity securities	'	'	'
Investment securities	'	'	'
Trading Securities, Change in Unrealized Holding Gain (Loss)	119.2	65.9	-40.6
Foreign Currency Transaction Gain (Loss), Unrealized	-0.4	-0.1	-1.8
Net unrealized investment gains, pre-tax	118.8	65.8	-42.4
Convertible fixed maturity investments	'	'	'
Investment securities	'	'	'
Trading Securities, Change in Unrealized Holding Gain (Loss)	3.2	1.1	-11.5
Foreign Currency Transaction Gain (Loss), Unrealized	0	0	0
Net unrealized investment gains, pre-tax	3.2	1.1	-11.5
Other long-term investments	'	'	'
Investment securities	'	'	'
Trading Securities, Change in Unrealized Holding Gain (Loss)	10.3	13.2	-19.1
Foreign Currency Transaction Gain (Loss), Unrealized	3.4	-2.7	3.4
Net unrealized investment gains, pre-tax	13.7	10.5	-15.7
Forward contracts	'	'	'
Investment securities	'	'	'
Trading Securities, Change in Unrealized Holding Gain (Loss)	0	'	'
Foreign Currency Transaction Gain (Loss), Unrealized	0	'	'
Net unrealized investment gains, pre-tax	$0	'	'

Investment_Securities_Investme2

Investment Securities (Investment Gains (Losses) For Level 3) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investment securities	'	'	'
Realized gains	$221.40	$162.20	$191.60
Realized losses	116.9	94.1	123.3
Accounts payable on unsettled investment purchases	20.5	11.4	'
Accounts receivable on unsettled investment sales	12.1	3.9	'
Level 3 Inputs	'	'	'
Investment securities	'	'	'
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	9.8	17.7	-45.6
Fixed maturity investments | Level 3 Inputs	'	'	'
Investment securities	'	'	'
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	-2.3	7.7	-12.2
Common equity securities | Level 3 Inputs	'	'	'
Investment securities	'	'	'
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	0.9	3	-16.6
Convertible fixed maturity investments | Level 3 Inputs	'	'	'
Investment securities	'	'	'
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	0	0	0
Other long-term investments | Level 3 Inputs	'	'	'
Investment securities	'	'	'
Total pre-tax gains (losses) included in earnings attributable to unrealized investment gains (losses) for Level 3 investments	$11.20	$7	($16.80)

Investment_Securities_Net_Real1

Investment Securities (Net Realized and Unrealized Gains (Losses) After Tax) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investments, Debt and Equity Securities [Abstract]	'	'	'
Net change in pre-tax unrealized gains (losses) on investments in unconsolidated affiliates	($106.40)	$62.80	($63.60)
Income taxes	8.3	-5.1	5.1
Net change in unrealized gains (losses) on investments in unconsolidated affiliates, after tax	-98.1	57.7	-58.5
Net realized and unrealized foreign currency gains (losses) on investments through OCI	11.3	95.5	-41.7
Total investments gains (losses) through accumulated other comprehensive income	-86.8	153.2	-100.2
Net Realized and Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	139.8	91.4	56
Total investment gains (losses) recorded during the period, after-tax	$53	$244.60	($44.20)

Investment_Securities_Investme3

Investment Securities (Investment Holdings) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Investment securities	'		'
Fixed maturity investments, at fair value	$5,030.50		$5,196.20
Including Short Term Fixed	'		'
Investment securities	'		'
Duration of Fixed Maturities	'		'2 years 1 month 6 days
US Government and agency obligations	'		'
Investment securities	'		'
Trading Securities, Cost	365.5		440.4
Net foreign currency losses	-2.5		-1.2
Fixed maturity investments, at fair value	362.5		440.1
Trading Securities, Unrealized Holding Gain	0.5		1
Trading Securities, Unrealized Holding Loss	-1		-0.1
Debt securities issued by corporations	'		'
Investment securities	'		'
Trading Securities, Cost	2,330.70		2,321.40
Net foreign currency losses	-14.3		-23
Fixed maturity investments, at fair value	2,347.20		2,385.10
Trading Securities, Unrealized Holding Gain	44		88.3
Trading Securities, Unrealized Holding Loss	-13.2		-1.6
Municipal obligations	'		'
Investment securities	'		'
Trading Securities, Cost	18.3		5.3
Net foreign currency losses	0		0
Fixed maturity investments, at fair value	17.9		5.2
Trading Securities, Unrealized Holding Gain	0		0
Trading Securities, Unrealized Holding Loss	-0.4		-0.1
Mortgage-backed and asset-backed securities	'		'
Investment securities	'		'
Trading Securities, Cost	2,027.30		2,081
Net foreign currency losses	-5.3		-9.4
Fixed maturity investments, at fair value	2,014.50		2,095.60
Trading Securities, Unrealized Holding Gain	2.4		25.1
Trading Securities, Unrealized Holding Loss	-9.9		-1.1
Foreign government, agency and provincial obligations	'		'
Investment securities	'		'
Trading Securities, Cost	444.2		526.6
Net foreign currency losses	-4.8		-8.6
Fixed maturity investments, at fair value	439.9		521.9
Trading Securities, Unrealized Holding Gain	3.7		6.9
Trading Securities, Unrealized Holding Loss	-3.2		-3
Preferred stocks	'		'
Investment securities	'		'
Trading Securities, Cost	79.9		79.9
Net foreign currency losses	-0.2		-0.2
Fixed maturity investments, at fair value	84.8		86.4
Trading Securities, Unrealized Holding Gain	5.1		6.7
Trading Securities, Unrealized Holding Loss	0		0
Fixed Income Investments [Member]	'		'
Investment securities	'		'
Trading Securities, Cost	5,265.90		5,454.60
Net foreign currency losses	-27.1		-42.4
Total fixed maturity investments including assets held for sale	5,266.80		5,534.30
Trading Securities, Unrealized Holding Gain	55.7		128
Trading Securities, Unrealized Holding Loss	-27.7		-5.9
Excluding Short Term Investments	'		'
Investment securities	'		'
Duration of Fixed Maturities	'		'2 years 4 months 24 days
OneBeacon Runoff	'		'
Investment securities	'		'
Fixed maturity investments reclassified to assets held for sale (1)	($236.30)	[1]	($338.10)	[1]
[1]	Assets held for sale related to discontinued operations. See Note 21.

Investment_Securities_Cost_and

Investment Securities (Cost and Amortized Cost Maturity Schedule) (Details) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Trading Securities by Maturity Cost or Amortized Cost	'
Cost or amortized cost	$5,337.60
Trading Securities by Maturity, Fair Value	'
Trading Securities	5,347.30
Fixed Maturities and Convertible Fixed Maturities Excluding A B S M B S and Preferred Stock	'
Trading Securities by Maturity Cost or Amortized Cost	'
Due in one year or less	491.2
Due after one year through five years	2,376.70
Due after five years through ten years	321
Due after ten years	41.5
Trading Securities by Maturity, Fair Value	'
Due in one year or less	490.7
Due after one year through five years	2,389.30
Due after five years through ten years	322.2
Due after ten years	45.8
Mortgage-backed and asset-backed securities	'
Trading Securities by Maturity Cost or Amortized Cost	'
Trading Securities, Maturities without Single Maturity Date, Amortized Cost	2,027.30
Trading Securities by Maturity, Fair Value	'
Trading Securities, Maturities without Single Maturity Date, Carrying Value	2,014.50
Preferred stocks	'
Trading Securities by Maturity Cost or Amortized Cost	'
Trading Securities, Maturities without Single Maturity Date, Amortized Cost	79.9
Trading Securities by Maturity, Fair Value	'
Trading Securities, Maturities without Single Maturity Date, Carrying Value	$84.80

Investment_Securities_Cost_or_

Investment Securities (Cost or Amortized Cost, Gross Unrealized Investment Gains and Losses) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Investment securities	'	'	'
Sales and maturities of investment securities	$4,924.80	$6,997.50	$5,034
Fixed maturity investments, at fair value	5,030.50	5,196.20	'
Common Stock	'	'	'
Investment securities	'	'	'
Trading Securities, Cost	890.2	895.2	'
Net foreign currency losses	-0.8	-0.1	'
Fixed maturity investments, at fair value	1,156.80	1,029.70	'
Trading Securities, Unrealized Holding Gain	271	143.4	'
Trading Securities, Unrealized Holding Loss	-3.6	-8.8	'
Convertible fixed maturity investments	'	'	'
Investment securities	'	'	'
Trading Securities, Cost	71.7	121.7	'
Net foreign currency losses	-0.2	0	'
Fixed maturity investments, at fair value	80.5	127.4	'
Trading Securities, Unrealized Holding Gain	9.9	6.1	'
Trading Securities, Unrealized Holding Loss	-0.9	-0.4	'
Other long-term investments	'	'	'
Investment securities	'	'	'
Trading Securities, Cost	238.3	257.2	'
Net foreign currency losses	-2.4	-6.1	'
Fixed maturity investments, at fair value	288.9	294.2	'
Trading Securities, Unrealized Holding Gain	79.6	65.9	'
Trading Securities, Unrealized Holding Loss	($26.60)	($22.80)	'

Investment_Securities_Investme4

Investment Securities (Investments Held on Deposit or as Collateral) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Investment securities	'	'
Investments held in trusts	$170.40	$169.90
Assets held by insurance regulators	290.7	319.3
Surety Product Line [Member] | OneBeacon	'	'
Investment securities	'	'
Assets Held in Collateral	63.3	5.9
Fixed maturity investments | White Mountains Life Re	'	'
Investment securities	'	'
Derivative Collateral Right to Reclaim	23.2	138.7
Short-term investments | White Mountains Life Re	'	'
Investment securities	'	'
Derivative Collateral Right to Reclaim	$2	$5.10

Investment_Securities_Fair_Val

Investment Securities (Fair Value Measurement by Level) (Details) (USD $)

12 Months Ended

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Debt securities issued by corporations

Debt securities issued by corporations

Discontinued Operations

Discontinued Operations

Discontinued Operations

Fair value

Fair value

Fair value

Fair value

Fair value

Level 1

Level 1

Level 1

Level 2

Level 2

Level 2

Level 2

Level 2

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Fair value measured on a recurring basis

Banks, trust and insurance companies

Mortgage-backed and asset-backed securities

Mortgage-backed and asset-backed securities

Mortgage-backed and asset-backed securities

Mortgage-backed and asset-backed securities

Mortgage-backed and asset-backed securities

Mortgage-backed and asset-backed securities

Fixed maturity investments

Fixed maturity investments

Fixed maturity investments

Common equity securities

Common equity securities

Common equity securities

Convertible fixed maturity investments

Convertible fixed maturity investments

Convertible fixed maturity investments

Other long-term investments

Other long-term investments

Other long-term investments

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Fair value

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 1

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 2

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Level 3

Fair value measured on a recurring basis

US Government and agency obligations

US Government and agency obligations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Mortgage-backed and asset-backed securities

Mortgage-backed and asset-backed securities

Foreign government, agency and provincial obligations

Foreign government, agency and provincial obligations

Preferred stocks

Preferred stocks

Municipal obligations

Municipal obligations

Fixed maturity investments

Fixed maturity investments

Short-term investments

Short-term investments

Short-term investments

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Convertible fixed maturity investments

Convertible fixed maturity investments

Other long-term investments

Other long-term investments

US Government and agency obligations

US Government and agency obligations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Mortgage-backed and asset-backed securities

Mortgage-backed and asset-backed securities

Foreign government, agency and provincial obligations

Foreign government, agency and provincial obligations

Preferred stocks

Preferred stocks

Municipal obligations

Municipal obligations

Fixed maturity investments

Fixed maturity investments

Short-term investments

Short-term investments

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Convertible fixed maturity investments

Convertible fixed maturity investments

Other long-term investments

Other long-term investments

US Government and agency obligations

US Government and agency obligations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Mortgage-backed and asset-backed securities

Mortgage-backed and asset-backed securities

Foreign government, agency and provincial obligations

Foreign government, agency and provincial obligations

Preferred stocks

Preferred stocks

Municipal obligations

Municipal obligations

Fixed maturity investments

Fixed maturity investments

Short-term investments

Short-term investments

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Convertible fixed maturity investments

Convertible fixed maturity investments

Other long-term investments

Other long-term investments

Forward contracts

Forward contracts

US Government and agency obligations

US Government and agency obligations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Debt securities issued by corporations

Mortgage-backed and asset-backed securities

Mortgage-backed and asset-backed securities

Foreign government, agency and provincial obligations

Foreign government, agency and provincial obligations

Preferred stocks

Preferred stocks

Municipal obligations

Municipal obligations

Fixed maturity investments

Fixed maturity investments

Short-term investments

Short-term investments

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Common equity securities

Convertible fixed maturity investments

Convertible fixed maturity investments

Other long-term investments

Other long-term investments

Other long-term investments

Fair value

Financials

Financials

Consumer

Consumer

Industrial

Industrial

Communications

Communications

Utilities

Utilities

Energy

Energy

Basic Materials

Basic Materials

Technology

Technology

Other

Other

Financials

Consumer

Consumer

Industrial

Industrial

Communications

Communications

Utilities

Utilities

Energy

Energy

Basic Materials

Basic Materials

Technology

Technology

Other

Other

Financials

Financials

Consumer

Consumer

Industrial

Industrial

Communications

Communications

Utilities

Utilities

Energy

Energy

Basic Materials

Basic Materials

Technology

Technology

Other

Other

Financials

Financials

Consumer

Consumer

Industrial

Industrial

Communications

Communications

Utilities

Utilities

Energy

Energy

Basic Materials

Basic Materials

Technology

Technology

Other

Other

Financials

Financials

Consumer

Consumer

Industrial

Industrial

Communications

Communications

Utilities

Utilities

Energy

Energy

Basic Materials

Basic Materials

Technology

Technology

Other

Other

Financials

Financials

Consumer

Consumer

Industrial

Industrial

Communications

Communications

Utilities

Utilities

Energy

Energy

Basic Materials

Basic Materials

Technology

Technology

Other

Other

Financials

Financials

Consumer

Consumer

Industrial

Industrial

Communications

Communications

Utilities

Utilities

Energy

Energy

Basic Materials

Basic Materials

Technology

Technology

Other

Other

Financials

Financials

Consumer

Consumer

Industrial

Industrial

Communications

Communications

Utilities

Utilities

Energy

Energy

Basic Materials

Basic Materials

Technology

Technology

Other

Other

Common equity securities

Financials

Investment securities

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Percentage of investments recorded at fair value

95.00%

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Maximum percentage of price difference provided by pricing services

5.00%

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Maximum price difference provided by pricing services

$1,000,000

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'

Fair value investments

'

'

2,347,200,000

[1]

2,385,100,000

[1]

'

'

'

6,766,500,000

[2],[3],[4]

6,950,700,000

[2],[3],[4],[5],[6],[7]

7,500,800,000

[5],[6],[7]

2,014,500,000

2,095,600,000

1,376,700,000

1,355,100,000

1,033,100,000

4,982,200,000

5,206,100,000

6,088,200,000

1,992,500,000

2,073,500,000

22,000,000

22,100,000

93,000,000

92,900,000

78,900,000

46,100,000

37,300,000

32,300,000

6,100,000

0

0

262,400,000

[2]

259,300,000

[2],[6]

268,300,000

[6]

7,402,400,000

7,581,300,000

362,500,000

440,100,000

2,347,200,000

2,385,100,000

434,400,000

401,400,000

754,400,000

727,100,000

281,100,000

330,800,000

265,000,000

276,100,000

173,600,000

204,200,000

159,700,000

181,500,000

149,100,000

189,100,000

91,200,000

54,000,000

38,700,000

20,900,000

2,014,500,000

2,095,600,000

439,900,000

521,900,000

84,800,000

86,400,000

17,900,000

5,200,000

5,266,800,000

[8]

5,534,300,000

[9]

635,900,000

630,600,000

0

324,500,000

308,200,000

255,600,000

105,400,000

41,900,000

57,100,000

35,200,000

34,300,000

43,600,000

78,600,000

101,000,000

53,400,000

103,300,000

60,600,000

55,000,000

98,800,000

69,600,000

1,156,800,000

1,029,700,000

80,500,000

127,400,000

262,400,000

[10]

259,300,000

[11]

1,998,200,000

1,985,700,000

295,800,000

369,100,000

0

1,000,000

0

1,000,000

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

44,500,000

52,100,000

0

0

0

0

340,300,000

[8]

422,200,000

[9]

621,500,000

630,600,000

314,300,000

286,300,000

308,200,000

255,600,000

105,400,000

41,900,000

57,100,000

35,200,000

34,300,000

43,400,000

78,600,000

101,000,000

53,400,000

103,300,000

60,600,000

55,000,000

24,500,000

11,200,000

1,036,400,000

932,900,000

0

0

0

[10]

0

[11]

4,996,600,000

5,206,100,000

66,700,000

71,000,000

2,347,200,000

2,384,100,000

434,400,000

400,400,000

754,400,000

727,100,000

281,100,000

330,800,000

265,000,000

276,100,000

173,600,000

204,200,000

159,700,000

181,500,000

149,100,000

189,100,000

91,200,000

54,000,000

38,700,000

20,900,000

1,992,500,000

2,073,500,000

395,400,000

469,800,000

13,800,000

15,600,000

17,900,000

5,200,000

4,833,500,000

[8]

5,019,200,000

[9]

14,400,000

0

0

900,000

0

0

0

0

0

0

0

200,000

0

0

0

0

0

0

74,300,000

58,400,000

74,300,000

59,500,000

74,400,000

127,400,000

0

[10]

0

[11]

'

'

407,600,000

389,500,000

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

22,000,000

22,100,000

0

0

71,000,000

70,800,000

0

0

93,000,000

[8]

92,900,000

[9]

0

0

46,100,000

37,300,000

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

46,100,000

37,300,000

6,100,000

0

262,400,000

[10]

259,300,000

[11]

'

360,400,000

Investments reclassified to assets held for sale

'

'

'

'

236,300,000

338,100,000

111,800,000

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'

Carrying value of investment accounted for using the equity method

'

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'

'

'

26,600,000

35,000,000

33,000,000

'

Change in fair value of derivatives, included in other revenue

'

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'

'

-100,000

0

'

'

'

'

'

'

'

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Fair value, investment-related liabilities

$86,300,000

$79,700,000

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[1]

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

[2]

Excludes carrying value of $26.6 and $35.0 at December 31, 2013 and January 1, 2013 associated with other long-term investments accounted for using the equity method and $(.1) at December 31, 2013 related to currency forward contracts.

[3]

Excludes carrying value of $635.9 and $630.6 at December 31, 2013 and January 1, 2013 classified as short-term investments.

[4]

Carrying value includes $236.3 and $338.1 at December 31, 2013 and January 1, 2013 that is classified as assets held for sale relating to discontinued operations.

[5]

Carrying value includes $338.1 and $111.8 at December 31, 2012 and January 1, 2012 that is classified as assets held for sale relating to AutoOne discontinued operations.

[6]

Excludes carrying value of $35.0 and $33.0 at December 31, 2012 and January 1, 2012 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) at December 31, 2012 related to currency forward contracts.

[7]

Excludes carrying value of $630.6 and $846.0 at December 31, 2012 and January 1, 2012 classified as short-term investments.

[8]

Carrying value includes $236.3 that is classified as assets held for sale relating to discontinued operations.

[9]

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

[10]

Excludes carrying value of $26.6 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) related to currency forward contracts.

[11]

Excludes carrying value of $35.0 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) related to currency forward contracts.

Investment_Securities_Debt_Sec

Investment Securities (Debt Securities Issued By Corporation) (Details) (Debt securities issued by corporations, USD $)	Dec. 31, 2013		Dec. 31, 2012
Investment securities	'		'
Fair value investments	$2,347,200,000	[1]	$2,385,100,000	[1]
Other Standard Poors Rating [Member]	'		'
Investment securities	'		'
Fair value investments	3,400,000		6,800,000
Standard & Poor's, BB Rating [Member]	'		'
Investment securities	'		'
Fair value investments	0		7,000,000
BBB	'		'
Investment securities	'		'
Fair value investments	1,075,500,000		1,116,900,000
A	'		'
Investment securities	'		'
Fair value investments	1,039,500,000		1,061,000,000
AA	'		'
Investment securities	'		'
Fair value investments	228,800,000		193,400,000
AAA	'		'
Investment securities	'		'
Fair value investments	$0		$0
[1]	Credit ratings are assigned based on the following hierarchy: 1) Standard & Poor’s and 2) Moody’s

Investment_Securities_Mortgage

Investment Securities (Mortgage-backed, Asset-backed Securities) (Details)	12 Months Ended
	Dec. 31, 2013
Fixed rate CMBS	'
Investment securities	'
Average basis points of subordination (as a percent)	0.25
Maximum | Commercial	'
Investment securities	'
Percentage of underlying loans reported as non-performing	1.00%

Investment_Securities_Mortgage1

Investment Securities (Mortgage-backed Asset Securities) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Level 2 Inputs	'		'		'
Investment securities	'		'		'
Fair value investments	$4,982,200,000		$5,206,100,000		$6,088,200,000
Level 2 Inputs | GNMA	'		'		'
Investment securities	'		'		'
Fair value investments	512,300,000		1,013,400,000		'
Level 2 Inputs | FNMA	'		'		'
Investment securities	'		'		'
Fair value investments	81,200,000		74,600,000		'
Level 2 Inputs | FHLMC	'		'		'
Investment securities	'		'		'
Fair value investments	91,300,000		55,800,000		'
Level 2 Inputs | Total Agency	'		'		'
Investment securities	'		'		'
Fair value investments	684,800,000	[1]	1,143,800,000	[1]	'
Level 2 Inputs | Residential	'		'		'
Investment securities	'		'		'
Fair value investments	125,700,000		160,600,000		'
Level 2 Inputs | Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	282,300,000		334,100,000		'
Level 2 Inputs | Total Non-agency	'		'		'
Investment securities	'		'		'
Fair value investments	408,000,000		494,700,000		'
Level 2 Inputs | Total mortgage-backed securities	'		'		'
Investment securities	'		'		'
Fair value investments	1,092,800,000		1,638,500,000		'
Level 2 Inputs | Credit card receivables	'		'		'
Investment securities	'		'		'
Fair value investments	289,400,000		151,400,000		'
Level 2 Inputs | Vehicle receivables	'		'		'
Investment securities	'		'		'
Fair value investments	365,000,000		233,200,000		'
Level 2 Inputs | Other	'		'		'
Investment securities	'		'		'
Fair value investments	245,300,000		50,400,000		'
Level 2 Inputs | Total asset-backed securities	'		'		'
Investment securities	'		'		'
Fair value investments	899,700,000		435,000,000		'
Level 2 Inputs | Total mortgage and asset- backed securities	'		'		'
Investment securities	'		'		'
Fair value investments	1,992,500,000		2,073,500,000		'
Level 3 Inputs | GNMA	'		'		'
Investment securities	'		'		'
Fair value investments	0		0		'
Level 3 Inputs | FNMA	'		'		'
Investment securities	'		'		'
Fair value investments	0		0		'
Level 3 Inputs | FHLMC	'		'		'
Investment securities	'		'		'
Fair value investments	0		0		'
Level 3 Inputs | Total Agency	'		'		'
Investment securities	'		'		'
Fair value investments	0	[1]	0	[1]	'
Level 3 Inputs | Residential	'		'		'
Investment securities	'		'		'
Fair value investments	0		0		'
Level 3 Inputs | Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	0		0		'
Level 3 Inputs | Total Non-agency	'		'		'
Investment securities	'		'		'
Fair value investments	0		0		'
Level 3 Inputs | Total mortgage-backed securities	'		'		'
Investment securities	'		'		'
Fair value investments	0		0		'
Level 3 Inputs | Credit card receivables	'		'		'
Investment securities	'		'		'
Fair value investments	22,000,000		22,100,000		'
Level 3 Inputs | Vehicle receivables	'		'		'
Investment securities	'		'		'
Fair value investments	0		0		'
Level 3 Inputs | Other	'		'		'
Investment securities	'		'		'
Fair value investments	0		0		'
Level 3 Inputs | Total asset-backed securities	'		'		'
Investment securities	'		'		'
Fair value investments	22,000,000		22,100,000		'
Level 3 Inputs | Total mortgage and asset- backed securities	'		'		'
Investment securities	'		'		'
Fair value investments	22,000,000		22,100,000		'
Fair value	'		'		'
Investment securities	'		'		'
Fair value investments	6,766,500,000	[2],[3],[4]	6,950,700,000	[2],[3],[4],[5],[6],[7]	7,500,800,000	[5],[6],[7]
Fair value | GNMA	'		'		'
Investment securities	'		'		'
Fair value investments	512,300,000		1,013,400,000		'
Fair value | FNMA	'		'		'
Investment securities	'		'		'
Fair value investments	81,200,000		74,600,000		'
Fair value | FHLMC	'		'		'
Investment securities	'		'		'
Fair value investments	91,300,000		55,800,000		'
Fair value | Total Agency	'		'		'
Investment securities	'		'		'
Fair value investments	684,800,000	[1]	1,143,800,000	[1]	'
Fair value | Residential	'		'		'
Investment securities	'		'		'
Fair value investments	125,700,000		160,600,000		'
Fair value | Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	282,300,000		334,100,000		'
Fair value | Total Non-agency	'		'		'
Investment securities	'		'		'
Fair value investments	408,000,000		494,700,000		'
Fair value | Total mortgage-backed securities	'		'		'
Investment securities	'		'		'
Fair value investments	1,092,800,000		1,638,500,000		'
Fair value | Credit card receivables	'		'		'
Investment securities	'		'		'
Fair value investments	311,400,000		173,500,000		'
Fair value | Vehicle receivables	'		'		'
Investment securities	'		'		'
Fair value investments	365,000,000		233,200,000		'
Fair value | Other	'		'		'
Investment securities	'		'		'
Fair value investments	245,300,000		50,400,000		'
Fair value | Total asset-backed securities	'		'		'
Investment securities	'		'		'
Fair value investments	921,700,000		457,100,000		'
Fair value | Total mortgage and asset- backed securities	'		'		'
Investment securities	'		'		'
Fair value investments	2,014,500,000		2,095,600,000		'
Fair value | Non-Agency Residential Mortgage	'		'		'
Investment securities	'		'		'
Fair value investments	$0		'		'
[1]	Represents publicly traded mortgage-backed securities which carry the full faith and credit guaranty of the U.S. government (i.e., GNMA) or are guaranteed by a government sponsored entity (i.e., FNMA, FHLMC).
[2]	Excludes carrying value of $26.6 and $35.0 at December 31, 2013 and January 1, 2013 associated with other long-term investments accounted for using the equity method and $(.1) at December 31, 2013 related to currency forward contracts.
[3]	Excludes carrying value of $635.9 and $630.6 at December 31, 2013 and January 1, 2013 classified as short-term investments.
[4]	Carrying value includes $236.3 and $338.1 at December 31, 2013 and January 1, 2013 that is classified as assets held for sale relating to discontinued operations.
[5]	Carrying value includes $338.1 and $111.8 at December 31, 2012 and January 1, 2012 that is classified as assets held for sale relating to AutoOne discontinued operations.
[6]	Excludes carrying value of $35.0 and $33.0 at December 31, 2012 and January 1, 2012 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) at December 31, 2012 related to currency forward contracts.
[7]	Excludes carrying value of $630.6 and $846.0 at December 31, 2012 and January 1, 2012 classified as short-term investments.

Investment_Securities_Nonagenc

Investment Securities (Non-agency Mortgage-backed Securities) (Details) (Fair value, USD $)	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Investment securities	'		'		'
Fair value investments	$6,766,500,000	[1],[2],[3]	$6,950,700,000	[1],[2],[3],[4],[5],[6]	$7,500,800,000	[4],[5],[6]
Residential	'		'		'
Investment securities	'		'		'
Fair value investments	125,700,000		160,600,000		'
Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	282,300,000		334,100,000		'
Total Non-agency	'		'		'
Investment securities	'		'		'
Fair value investments	408,000,000		494,700,000		'
Securities Issued in 2004 [Member] | Residential	'		'		'
Investment securities	'		'		'
Fair value investments	11,900,000		'		'
Securities Issued in 2004 [Member] | Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	0		'		'
Securities Issued in 2004 [Member] | Total Non-agency	'		'		'
Investment securities	'		'		'
Fair value investments	11,900,000		'		'
2005 | Residential	'		'		'
Investment securities	'		'		'
Fair value investments	33,400,000		'		'
2005 | Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	0		'		'
2005 | Total Non-agency	'		'		'
Investment securities	'		'		'
Fair value investments	33,400,000		'		'
2006 | Residential	'		'		'
Investment securities	'		'		'
Fair value investments	10,800,000		'		'
2006 | Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	8,600,000		'		'
2006 | Total Non-agency	'		'		'
Investment securities	'		'		'
Fair value investments	19,400,000		'		'
2007 | Residential	'		'		'
Investment securities	'		'		'
Fair value investments	2,100,000		'		'
2007 | Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	5,700,000		'		'
2007 | Total Non-agency	'		'		'
Investment securities	'		'		'
Fair value investments	7,800,000		'		'
2008 | Residential	'		'		'
Investment securities	'		'		'
Fair value investments	0		'		'
2008 | Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	28,100,000		'		'
2008 | Total Non-agency	'		'		'
Investment securities	'		'		'
Fair value investments	28,100,000		'		'
2010 | Residential	'		'		'
Investment securities	'		'		'
Fair value investments	33,400,000		'		'
2010 | Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	11,500,000		'		'
2010 | Total Non-agency	'		'		'
Investment securities	'		'		'
Fair value investments	44,900,000		'		'
2011 | Residential	'		'		'
Investment securities	'		'		'
Fair value investments	0		'		'
2011 | Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	31,900,000		'		'
2011 | Total Non-agency	'		'		'
Investment securities	'		'		'
Fair value investments	31,900,000		'		'
2012 | Residential	'		'		'
Investment securities	'		'		'
Fair value investments	0		'		'
2012 | Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	113,800,000		'		'
2012 | Total Non-agency	'		'		'
Investment securities	'		'		'
Fair value investments	113,800,000		'		'
Securities Issued in 2013 [Member] | Residential	'		'		'
Investment securities	'		'		'
Fair value investments	34,100,000		'		'
Securities Issued in 2013 [Member] | Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	82,700,000		'		'
Securities Issued in 2013 [Member] | Total Non-agency	'		'		'
Investment securities	'		'		'
Fair value investments	$116,800,000		'		'
[1]	Excludes carrying value of $26.6 and $35.0 at December 31, 2013 and January 1, 2013 associated with other long-term investments accounted for using the equity method and $(.1) at December 31, 2013 related to currency forward contracts.
[2]	Excludes carrying value of $635.9 and $630.6 at December 31, 2013 and January 1, 2013 classified as short-term investments.
[3]	Carrying value includes $236.3 and $338.1 at December 31, 2013 and January 1, 2013 that is classified as assets held for sale relating to discontinued operations.
[4]	Carrying value includes $338.1 and $111.8 at December 31, 2012 and January 1, 2012 that is classified as assets held for sale relating to AutoOne discontinued operations.
[5]	Excludes carrying value of $35.0 and $33.0 at December 31, 2012 and January 1, 2012 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) at December 31, 2012 related to currency forward contracts.
[6]	Excludes carrying value of $630.6 and $846.0 at December 31, 2012 and January 1, 2012 classified as short-term investments.

Investment_Securities_Nonagenc1

Investment Securities (Non-agency Residential Mortgage-backed Securities) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Fair value	'		'		'
Investment securities	'		'		'
Fair value investments	$6,766,500,000	[1],[2],[3]	$6,950,700,000	[1],[2],[3],[4],[5],[6]	$7,500,800,000	[4],[5],[6]
Residential | Fair value	'		'		'
Investment securities	'		'		'
Fair value investments	125,700,000		160,600,000		'
Residential | Prime | Fair value	'		'		'
Investment securities	'		'		'
Fair value investments	96,100,000		'		'
Residential | Non-prime | Fair value	'		'		'
Investment securities	'		'		'
Fair value investments	21,900,000		'		'
Residential | Sub-prime | Fair value	'		'		'
Investment securities	'		'		'
Fair value investments	7,700,000		'		'
Residential | Super Senior	'		'		'
Investment securities	'		'		'
Fair value investments	31,800,000	[7]	'		'
Residential | Super Senior | Prime	'		'		'
Investment securities	'		'		'
Fair value investments	24,100,000	[7]	'		'
Residential | Super Senior | Non-prime	'		'		'
Investment securities	'		'		'
Fair value investments	0	[7]	'		'
Residential | Super Senior | Sub-prime	'		'		'
Investment securities	'		'		'
Fair value investments	7,700,000	[7]	'		'
Residential | Senior	'		'		'
Investment securities	'		'		'
Fair value investments	93,900,000	[8]	'		'
Residential | Senior | Prime	'		'		'
Investment securities	'		'		'
Fair value investments	72,000,000	[8]	'		'
Residential | Senior | Non-prime	'		'		'
Investment securities	'		'		'
Fair value investments	21,900,000	[8]	'		'
Residential | Senior | Sub-prime	'		'		'
Investment securities	'		'		'
Fair value investments	0	[8]	'		'
Residential | Subordinate	'		'		'
Investment securities	'		'		'
Fair value investments	0	[9]	'		'
Residential | Subordinate | Prime	'		'		'
Investment securities	'		'		'
Fair value investments	0	[9]	'		'
Residential | Subordinate | Non-prime	'		'		'
Investment securities	'		'		'
Fair value investments	0	[9]	'		'
Residential | Subordinate | Sub-prime	'		'		'
Investment securities	'		'		'
Fair value investments	$0	[9]	'		'
[1]	Excludes carrying value of $26.6 and $35.0 at December 31, 2013 and January 1, 2013 associated with other long-term investments accounted for using the equity method and $(.1) at December 31, 2013 related to currency forward contracts.
[2]	Excludes carrying value of $635.9 and $630.6 at December 31, 2013 and January 1, 2013 classified as short-term investments.
[3]	Carrying value includes $236.3 and $338.1 at December 31, 2013 and January 1, 2013 that is classified as assets held for sale relating to discontinued operations.
[4]	Carrying value includes $338.1 and $111.8 at December 31, 2012 and January 1, 2012 that is classified as assets held for sale relating to AutoOne discontinued operations.
[5]	Excludes carrying value of $35.0 and $33.0 at December 31, 2012 and January 1, 2012 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) at December 31, 2012 related to currency forward contracts.
[6]	Excludes carrying value of $630.6 and $846.0 at December 31, 2012 and January 1, 2012 classified as short-term investments.
[7]	At issuance, Super Senior, or in the case of resecuritization, the underlying securities, were rated “AAA” by Standard & Poor’s, “Aaa” by Moody’s or “AAA” by Fitch Ratings (“Fitch”) and were senior to other “AAA” or “Aaa” bonds.
[8]	At issuance, Senior, or in the case of resecuritization, the underlying securities, 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.
[9]	At issuance, Subordinate were not rated “AAA” by Standard & Poor’s, “Aaa” by Moody’s or “AAA” by Fitch and were junior to “AAA” or “Aaa” bonds.

Investment_Securities_Nonagenc2

Investment Securities (Non-agency Commercial Mortgage-backed Securities) (Details) (Fair value, USD $)	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Investment securities	'		'		'
Fair value investments	$6,766,500,000	[1],[2],[3]	$6,950,700,000	[1],[2],[3],[4],[5],[6]	$7,500,800,000	[4],[5],[6]
Fixed rate CMBS	'		'		'
Investment securities	'		'		'
Fair value investments	189,000,000		'		'
Fixed rate CMBS | Super Senior	'		'		'
Investment securities	'		'		'
Fair value investments	117,200,000	[7]	'		'
Fixed rate CMBS | Senior	'		'		'
Investment securities	'		'		'
Fair value investments	54,400,000	[8]	'		'
Fixed rate CMBS | Subordinate	'		'		'
Investment securities	'		'		'
Fair value investments	17,400,000	[9]	'		'
Floating rate CMBS	'		'		'
Investment securities	'		'		'
Fair value investments	93,300,000		'		'
Floating rate CMBS | Super Senior	'		'		'
Investment securities	'		'		'
Fair value investments	5,700,000	[7]	'		'
Floating rate CMBS | Senior	'		'		'
Investment securities	'		'		'
Fair value investments	28,000,000	[8]	'		'
Floating rate CMBS | Subordinate	'		'		'
Investment securities	'		'		'
Fair value investments	59,600,000	[9]	'		'
Commercial	'		'		'
Investment securities	'		'		'
Fair value investments	282,300,000		334,100,000		'
Commercial | Super Senior	'		'		'
Investment securities	'		'		'
Fair value investments	122,900,000	[7]	'		'
Commercial | Senior	'		'		'
Investment securities	'		'		'
Fair value investments	82,400,000	[8]	'		'
Commercial | Subordinate	'		'		'
Investment securities	'		'		'
Fair value investments	$77,000,000	[9]	'		'
[1]	Excludes carrying value of $26.6 and $35.0 at December 31, 2013 and January 1, 2013 associated with other long-term investments accounted for using the equity method and $(.1) at December 31, 2013 related to currency forward contracts.
[2]	Excludes carrying value of $635.9 and $630.6 at December 31, 2013 and January 1, 2013 classified as short-term investments.
[3]	Carrying value includes $236.3 and $338.1 at December 31, 2013 and January 1, 2013 that is classified as assets held for sale relating to discontinued operations.
[4]	Carrying value includes $338.1 and $111.8 at December 31, 2012 and January 1, 2012 that is classified as assets held for sale relating to AutoOne discontinued operations.
[5]	Excludes carrying value of $35.0 and $33.0 at December 31, 2012 and January 1, 2012 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) at December 31, 2012 related to currency forward contracts.
[6]	Excludes carrying value of $630.6 and $846.0 at December 31, 2012 and January 1, 2012 classified as short-term investments.
[7]	At issuance, Super Senior, or in the case of resecuritization, the underlying securities, were rated “AAA” by Standard & Poor’s, “Aaa” by Moody’s or “AAA” by Fitch and were senior to other “AAA” or “Aaa” bonds.
[8]	At issuance, Senior, or in the case of resecuritization, the underlying securities, 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.
[9]	At issuance, Subordinate were not rated “AAA” by Standard & Poor’s, “Aaa” by Moody’s or “AAA” by Fitch and were junior to “AAA” or “Aaa” bonds.

Investment_Securities_Other_Lo

Investment Securities (Other Long-Term Investments) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Hedge funds	'	'
Investment securities	'	'
Number of Investments Held	15	'
Trading Securities, Other	$120.80	'
Private equity funds	'	'
Investment securities	'	'
Number of Investments Held	39	'
Trading Securities, Other	118.2	'
Total hedge and private equity funds included in other long-term investments	'	'
Investment securities	'	'
Other Long-term Investments Largest Single Investment	18.3	16
Trading Securities, Other	$239	$239.80

Investment_Securities_Fair_Val1

Investment Securities (Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Private equity funds	'	'
Investment securities	'	'
Trading Securities, Other	$118.20	'
Hedge funds	'	'
Investment securities	'	'
Trading Securities, Other	120.8	'
Total hedge and private equity funds included in other long-term investments	'	'
Investment securities	'	'
Trading Securities, Other	239	239.8
Fair value unfunded commitments	110.6	119.4
Other Long-term Investments Largest Single Investment	18.3	16
Private equity funds | Private equity funds	'	'
Investment securities	'	'
Trading Securities, Other	118.2	125.2
Fair value unfunded commitments	110.6	119.4
Private equity funds | Multi-sector	'	'
Investment securities	'	'
Trading Securities, Other	23.8	23.3
Fair value unfunded commitments	6.5	5.4
Private equity funds | Energy infrastructure & services	'	'
Investment securities	'	'
Trading Securities, Other	45.9	36.3
Fair value unfunded commitments	13.1	15.6
Private equity funds | Distressed residential real estate	'	'
Investment securities	'	'
Trading Securities, Other	0.4	15.8
Fair value unfunded commitments	0	0
Private equity funds | Real estate	'	'
Investment securities	'	'
Trading Securities, Other	8.2	11.6
Fair value unfunded commitments	3.3	3.3
Private equity funds | Private equity secondaries	'	'
Investment securities	'	'
Trading Securities, Other	9.5	10.5
Fair value unfunded commitments	3.1	3.1
Private equity funds | International multi-sector, Europe	'	'
Investment securities	'	'
Trading Securities, Other	3.9	5.1
Fair value unfunded commitments	2.8	5
Private equity funds | Manufacturing/Industrial	'	'
Investment securities	'	'
Trading Securities, Other	11.2	9.9
Fair value unfunded commitments	15.5	15.1
Private equity funds | Healthcare	'	'
Investment securities	'	'
Trading Securities, Other	5.6	4.3
Fair value unfunded commitments	2.8	5.4
Private equity funds | International multi-sector, Asia	'	'
Investment securities	'	'
Trading Securities, Other	0	0.4
Fair value unfunded commitments	2.7	2.7
Private equity funds | Insurance	'	'
Investment securities	'	'
Trading Securities, Other	2.3	3
Fair value unfunded commitments	41.3	41.3
Private equity funds | Aerospace/Defense/Government	'	'
Investment securities	'	'
Trading Securities, Other	5.8	2.8
Fair value unfunded commitments	19.2	22.2
Private equity funds | Venture capital	'	'
Investment securities	'	'
Trading Securities, Other	1.6	2.2
Fair value unfunded commitments	0.3	0.3
Hedge funds | Hedge funds	'	'
Investment securities	'	'
Trading Securities, Other	120.8	114.6
Fair value unfunded commitments	0	0
Hedge funds | Long/short equity	'	'
Investment securities	'	'
Trading Securities, Other	62.6	60.3
Fair value unfunded commitments	0	0
Hedge funds | Long/short credit & distressed	'	'
Investment securities	'	'
Trading Securities, Other	22.8	22.7
Fair value unfunded commitments	0	0
Hedge funds | Long diversified strategies	'	'
Investment securities	'	'
Trading Securities, Other	0.1	1.7
Fair value unfunded commitments	0	0
Hedge funds | Long/short equity REIT	'	'
Investment securities	'	'
Trading Securities, Other	18.3	16
Fair value unfunded commitments	0	0
Hedge funds | Long/short equity activist	'	'
Investment securities	'	'
Trading Securities, Other	16.8	13.6
Fair value unfunded commitments	0	0
Hedge funds | Long bank loan	'	'
Investment securities	'	'
Trading Securities, Other	0.2	0.3
Fair value unfunded commitments	$0	$0

Investment_Securities_Restrict

Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) (Hedge funds, USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Investment securities	'
Trading Securities, Other	$120.80
Distributions from inactive hedge funds	3
Investments entities that calculate net asset value per share redemption request	2.1
Monthly	'
Investment securities	'
Trading Securities, Other	5.8
Quarterly	'
Investment securities	'
Trading Securities, Other	79.7
Semi-annual	'
Investment securities	'
Trading Securities, Other	25.4
Annual	'
Investment securities	'
Trading Securities, Other	9.9
30-59 days notice	'
Investment securities	'
Trading Securities, Other	29.2
30-59 days notice | Monthly	'
Investment securities	'
Trading Securities, Other	0
30-59 days notice | Quarterly	'
Investment securities	'
Trading Securities, Other	29.1
30-59 days notice | Semi-annual	'
Investment securities	'
Trading Securities, Other	0
30-59 days notice | Annual	'
Investment securities	'
Trading Securities, Other	0.1
60-89 days notice	'
Investment securities	'
Trading Securities, Other	55.6
60-89 days notice | Monthly	'
Investment securities	'
Trading Securities, Other	0
60-89 days notice | Quarterly	'
Investment securities	'
Trading Securities, Other	30.2
60-89 days notice | Semi-annual	'
Investment securities	'
Trading Securities, Other	25.4
60-89 days notice | Annual	'
Investment securities	'
Trading Securities, Other	0
90-119 days notice	'
Investment securities	'
Trading Securities, Other	21.4
90-119 days notice | Monthly	'
Investment securities	'
Trading Securities, Other	0
90-119 days notice | Quarterly	'
Investment securities	'
Trading Securities, Other	11.8
90-119 days notice | Semi-annual	'
Investment securities	'
Trading Securities, Other	0
90-119 days notice | Annual	'
Investment securities	'
Trading Securities, Other	9.6
120 days notice	'
Investment securities	'
Trading Securities, Other	14.6
120 days notice | Monthly	'
Investment securities	'
Trading Securities, Other	5.8
120 days notice | Quarterly	'
Investment securities	'
Trading Securities, Other	8.6
120 days notice | Semi-annual	'
Investment securities	'
Trading Securities, Other	0
120 days notice | Annual	'
Investment securities	'
Trading Securities, Other	$0.20

Investment_Securities_Investme5

Investment Securities (Investments In Private Equity Funds Subject to Lock-Up Periods) (Details) (Private equity funds, USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Investment securities	'
Trading Securities, Other	$118.20
1-3 years	'
Investment securities	'
Trading Securities, Other	6.9
3 – 5 years	'
Investment securities	'
Trading Securities, Other	30.8
5 – 10 years	'
Investment securities	'
Trading Securities, Other	67.6
10 years	'
Investment securities	'
Trading Securities, Other	$12.90

Investment_Securities_Rollforw

Investment Securities (Rollforward of Fair Value Measurements by Level) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Investment securities	'		'		'
Net realized and unrealized investment gains	$161,700,000		$118,200,000		$74,100,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Sales	-4,924,800,000		-6,997,500,000		-5,034,000,000
Discontinued Operations	'		'		'
Investment securities	'		'		'
Net realized and unrealized investment gains	0		0		700,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fixed maturity investments reclassified to assets held for sale (1)	-236,300,000		-338,100,000		-111,800,000
Level 1 Inputs	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	1,355,100,000		1,033,100,000		'
Total realized and unrealized gains (losses)	221,900,000		52,000,000		'
Foreign currency gains (losses) through OCI	-300,000		4,400,000		'
Amortization/Accretion	-1,000,000		-800,000		'
Purchases	862,100,000		1,216,900,000		'
Sales	-1,078,900,000		-950,500,000		'
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates	16,000,000		'		'
Transfers in	1,800,000		0		'
Transfers out	0		0		'
Fair value investments	1,376,700,000		1,355,100,000		'
Level 1 Inputs | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	1,998,200,000		1,985,700,000		'
Level 1 Inputs | Fixed maturity investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	340,300,000	[1]	422,200,000	[2]	'
Level 1 Inputs | Convertible fixed maturity investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	0		0		'
Level 1 Inputs | Other long-term investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	0	[3]	0	[4]	'
Level 1 Inputs | Short-term investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	621,500,000		630,600,000		'
Level 2 Inputs	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	5,206,100,000		6,088,200,000		'
Total realized and unrealized gains (losses)	-56,900,000		53,600,000		'
Foreign currency gains (losses) through OCI	12,500,000		81,900,000		'
Amortization/Accretion	-51,200,000		-48,000,000		'
Purchases	3,689,600,000		4,927,100,000		'
Sales	-3,842,800,000		-5,937,000,000		'
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates	2,700,000		'		'
Transfers in	119,400,000		62,400,000		'
Transfers out	-97,200,000		-22,100,000		'
Fair value investments	4,982,200,000		5,206,100,000		'
Level 2 Inputs | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	4,996,600,000		5,206,100,000		'
Level 2 Inputs | Fixed maturity investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	4,833,500,000	[1]	5,019,200,000	[2]	'
Level 2 Inputs | Convertible fixed maturity investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	74,400,000		127,400,000		'
Level 2 Inputs | Other long-term investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	0	[3]	0	[4]	'
Level 2 Inputs | Forward contracts | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Change in fair value of derivatives, included in other revenue	-100,000		0		'
Level 2 Inputs | Short-term investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	14,400,000		0		'
Level 3 Inputs | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	407,600,000		389,500,000		'
Level 3 Inputs | Fixed maturity investments	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	92,900,000		78,900,000		'
Total realized and unrealized gains (losses)	-2,700,000		8,700,000		'
Foreign currency gains (losses) through OCI	300,000		800,000		'
Amortization/Accretion	0		-800,000		'
Purchases	37,900,000		144,400,000		'
Sales	-6,300,000		-99,400,000		'
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates	0		'		'
Transfers in	90,300,000		22,100,000		'
Transfers out	-119,400,000		-61,800,000		'
Fair value investments	93,000,000		92,900,000		'
Number of investments	3		'		'
Level 3 Inputs | Fixed maturity investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	93,000,000	[1]	92,900,000	[2]	'
Level 3 Inputs | Common equity securities	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	37,300,000		32,300,000		'
Total realized and unrealized gains (losses)	1,000,000		12,400,000		'
Foreign currency gains (losses) through OCI	0		200,000		'
Amortization/Accretion	0		0		'
Purchases	8,800,000		3,100,000		'
Sales	0		-10,100,000		'
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates	0		'		'
Transfers in	0		0		'
Transfers out	-1,000,000		-600,000		'
Fair value investments	46,100,000		37,300,000		'
Level 3 Inputs | Convertible fixed maturity investments	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	0		0		'
Total realized and unrealized gains (losses)	0		0		'
Foreign currency gains (losses) through OCI	0		0		'
Amortization/Accretion	0		0		'
Purchases	0		0		'
Sales	0		0		'
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates	0		'		'
Transfers in	6,100,000		0		'
Transfers out	0		0		'
Fair value investments	6,100,000		0		'
Level 3 Inputs | Convertible fixed maturity investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	6,100,000		0		'
Level 3 Inputs | Other long-term investments	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	259,300,000	[5],[6]	268,300,000	[5]	'
Total realized and unrealized gains (losses)	18,700,000		-3,300,000		'
Foreign currency gains (losses) through OCI	-900,000		3,700,000		'
Amortization/Accretion	0		0		'
Purchases	37,100,000		39,400,000		'
Sales	-51,800,000		-48,800,000		'
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates	0		'		'
Transfers in	0		0		'
Transfers out	0		0		'
Fair value investments	262,400,000	[6]	259,300,000	[5],[6]	'
Level 3 Inputs | Other long-term investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	262,400,000	[3]	259,300,000	[4]	'
Carrying value of investment accounted for using the equity method	26,600,000		35,000,000		33,000,000
Level 3 Inputs | Short-term investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	0		0		'
Fair value	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	6,950,700,000	[10],[5],[6],[7],[8],[9]	7,500,800,000	[5],[7],[8]	'
Total realized and unrealized gains (losses)	182,000,000	[11]	123,400,000		'
Foreign currency gains (losses) through OCI	11,600,000		91,000,000		'
Amortization/Accretion	-52,200,000		49,600,000		'
Purchases	4,635,500,000		6,330,900,000		'
Sales	-4,979,800,000		7,045,800,000		'
Net change in investments related to purchases and sales of consolidated/unconsolidated affiliates	18,700,000		'		'
Transfers in	217,600,000		84,500,000		'
Transfers out	-217,600,000		84,500,000		'
Fair value investments	6,766,500,000	[10],[6],[9]	6,950,700,000	[10],[5],[6],[7],[8],[9]	'
Fair value | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	7,402,400,000		7,581,300,000		'
Fair value | Fixed maturity investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	5,266,800,000	[1]	5,534,300,000	[2]	'
Fair value | Convertible fixed maturity investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	80,500,000		127,400,000		'
Fair value | Other long-term investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	262,400,000	[3]	259,300,000	[4]	'
Fair value | Short-term investments | Fair value measured on a recurring basis	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Fair value investments	635,900,000		630,600,000		0
Prospector	'		'		'
Investment securities	'		'		'
Net realized and unrealized investment gains	0		'		'
Less than market price [Member] | Level 3 Inputs | Fixed maturity investments	'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'		'		'
Transfers in	$1,300,000		'		'
[1]	Carrying value includes $236.3 that is classified as assets held for sale relating to discontinued operations.
[2]	Carrying value includes $338.1 that is classified as assets held for sale relating to discontinued operations.
[3]	Excludes carrying value of $26.6 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) related to currency forward contracts.
[4]	Excludes carrying value of $35.0 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) related to currency forward contracts.
[5]	Excludes carrying value of $35.0 and $33.0 at December 31, 2012 and January 1, 2012 associated with other long-term investment limited partnerships accounted for using the equity method and $(.1) at December 31, 2012 related to currency forward contracts.
[6]	Excludes carrying value of $26.6 and $35.0 at December 31, 2013 and January 1, 2013 associated with other long-term investments accounted for using the equity method and $(.1) at December 31, 2013 related to currency forward contracts.
[7]	Carrying value includes $338.1 and $111.8 at December 31, 2012 and January 1, 2012 that is classified as assets held for sale relating to AutoOne discontinued operations.
[8]	Excludes carrying value of $630.6 and $846.0 at December 31, 2012 and January 1, 2012 classified as short-term investments.
[9]	Excludes carrying value of $635.9 and $630.6 at December 31, 2013 and January 1, 2013 classified as short-term investments.
[10]	Carrying value includes $236.3 and $338.1 at December 31, 2013 and January 1, 2013 that is classified as assets held for sale relating to discontinued operations.
[11]	Excludes $20.6 of realized and unrealized losses associated with the Prospector Funds consolidation of investment-related liabilities and $.2 of realized and unrealized gains associated with short-term investments.

Investment_Securities_Signific

Investment Securities (Significant Unobservable Inputs) (Details) (USD $)

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Investment

Standard & Poor's, AA+ Rating [Member]

Standard Poors NR Rating [Member]

Standard Poors NR Rating [Member]

Standard Poors NR Rating [Member]

Standard Poors NR Rating [Member]

Standard Poors NR Rating [Member]

Standard Poors NR Rating [Member]

Agency CMBS

Redeemable preferred stocks

Redeemable preferred stocks

Redeemable preferred stocks

Private equity funds

Private equity funds

Private equity securities

Broker Pricing

Discounted cash flows

Discount Yield

Multiple of GAAP book value

Multiple of GAAP book value

Market Approach Valuation Technique [Member]

Market Approach Valuation Technique [Member]

Quantitative information for Level 3 Fair Value Measurements Assets

'

'

'

'

'

'

'

'

Fair value Assets

'

$22,000,000

[1],[2]

$71,000,000

[2]

'

'

$35,600,000

[2]

$10,500,000

[2]

$6,100,000

[2]

Share Price of Recent Transaction Used As Unobservable Input

'

'

'

'

'

'

'

6.1

Average Share Price Used As Unobservable Input

'

'

'

'

'

'

$1.10

'

Book Value Multiple to Calculate Fair Value

'

'

'

'

100.00%

'

'

'

Discount Yield (as a percent)

'

'

'

7.40%

'

'

'

'

Number of Investments with Significant Unobseravble Inputs

1

'

'

'

'

'

'

'

[1]

As of December 31, 2013 each asset type consists of one security.

[2]

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

Debt_Debt_Outstanding_Details

Debt (Debt Outstanding) (Details) (USD $)

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Mar. 31, 2007

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Jan. 31, 2013

Dec. 31, 2012

In Millions, unless otherwise specified

2012 OBH Senior Notes

2012 OBH Senior Notes

SIG Senior Notes

SIG Senior Notes

SIG Senior Notes

WTM Bank Facility

WTM Bank Facility

Old Lyme

Old Lyme

Old Lyme

Prior W T M Bank Facility

Prior W T M Bank Facility

Prior W T M Bank Facility

Debt Instrument

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt instrument at face value

'

'

$275

$275

$400

$400

$400

'

'

'

'

'

'

'

'

Unamortized original issue discount

'

'

-0.3

-0.3

-0.4

-0.6

'

'

'

'

'

'

'

'

'

Debt

$676.40

$751.20

$274.70

$274.70

$399.60

$399.40

'

$0

$0

$2.10

$2.10

$2.10

$0

$75

$75

Debt_Schedule_of_Contractual_R

Debt (Schedule of Contractual Repayments) (Details) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Debt Disclosure [Abstract]	'
Due in one year or less	$0
Due in two to three years	2.1
Due in four to five years	400
Due after five years	275
Total	$677.10

Debt_Narrative_Details

Debt (Narrative) (Details) (USD $)

12 Months Ended

1 Months Ended

12 Months Ended

3 Months Ended

12 Months Ended

9 Months Ended

12 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

3 Months Ended

1 Months Ended

3 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Mar. 31, 2007

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Aug. 12, 2011

Sep. 30, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Jan. 31, 2013

Aug. 12, 2011

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Nov. 30, 2012

Dec. 31, 2013

31-May-03

Dec. 31, 2012

Dec. 31, 2011

Apr. 30, 2011

Dec. 31, 2012

Sep. 30, 2010

Mar. 31, 2004

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2008

Dec. 31, 2007

Dec. 31, 2005

Sep. 15, 2010

2012 OBH Senior Notes

2012 OBH Senior Notes

SIG Senior Notes

SIG Senior Notes

SIG Senior Notes

SIG Senior Notes

WTM Bank Facility

WTM Bank Facility

WTM Bank Facility

WTM Bank Facility

Prior W T M Bank Facility

Prior W T M Bank Facility

Prior W T M Bank Facility

Prior W T M Bank Facility

Prior W T M Bank Facility

Prior W T M Bank Facility

Old Lyme

Old Lyme

Old Lyme

One Beacon US Holdings Inc.

One Beacon US Holdings Inc.

One Beacon US Holdings Inc.

One Beacon US Holdings Inc.

One Beacon US Holdings Inc.

One Beacon US Holdings Inc.

One Beacon US Holdings Inc.

Sirius Internation Group Ltd

Sirius Internation Group Ltd

Sirius Internation Group Ltd

Sirius Internation Group Ltd

Sirius Internation Group Ltd

Sirius Internation Group Ltd

Sirius Internation Group Ltd

Sirius Internation Group Ltd

2012 OBH Senior Notes

2012 OBH Senior Notes

2003 OBH Senior Notes

2003 OBH Senior Notes

2003 OBH Senior Notes

Senior Notes

Senior Notes

Sierra Note

Sierra Note

Sierra Note

Sierra Note

Sierra Note

Sierra Note

Sierra Note

Sierra Note

2003 OBH Senior Notes

2003 OBH Senior Notes

Debt Instrument

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt instrument at face value

'

'

'

$275

$275

$400

$400

$400

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$275

'

$700

'

'

'

'

'

$62

'

'

'

'

'

'

Debt

676.4

751.2

'

274.7

274.7

'

399.6

399.4

'

0

0

0

'

'

0

75

'

75

'

2.1

2.1

2.1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of par value at which debt was issued

'

'

'

'

'

99.72%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

99.90%

'

99.70%

'

'

'

'

'

'

'

'

'

'

'

'

Issuance of debt, net of debt issuance costs

0

271.9

0

'

'

392

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

272.9

'

693.4

'

'

'

'

'

'

'

'

'

'

'

'

Debt issue costs

'

'

'

'

'

3.6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2.8

'

7.3

'

'

'

'

'

'

'

'

'

'

'

'

Underwriting discount

'

'

'

'

'

2.6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1.8

'

4.5

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate (as a percent)

'

'

'

'

'

6.38%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4.60%

'

5.88%

'

'

'

'

'

4.00%

'

'

'

'

'

'

Effective yield (as a percent)

'

'

'

'

'

6.50%

'

'

'

3.65%

3.65%

'

'

'

2.83%

3.53%

'

'

'

'

'

'

4.70%

'

6.00%

'

'

'

'

'

'

'

'

'

'

'

'

Interest expense on debt

42.5

44.8

55.2

'

'

'

26.2

26.2

26.2

'

0.3

'

'

'

2.9

1.7

3.1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5.5

'

'

'

'

'

Debt Instrument, Repurchase Amount

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

269.8

'

'

'

'

'

'

'

'

Guarantee fee basis points per annum on outstanding principal amount of debt (as a percent)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2.50%

'

'

'

'

'

'

'

'

'

'

'

'

Expenses related to issuance, including underwriting fees

'

'

'

'

'

3.6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2.8

'

7.3

'

'

'

'

'

'

'

'

'

'

'

'

Repayments of lines of credit

'

'

'

'

'

'

'

'

'

50

'

'

'

150

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Aggregate principal amount of senior notes purchased and retired

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

150

'

'

'

'

'

'

'

'

'

Aggregate purchase price of senior notes purchased and retired

0

275.9

161.6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

161.6

275.9

'

'

'

'

'

'

'

'

Loss on retirement of debt

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-12

-6.3

'

'

'

'

'

'

'

'

Interest Expense

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

13

'

16.9

20.5

'

'

'

'

'

'

'

'

'

'

Write off of deferred issuance costs

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.2

'

'

'

'

'

'

'

'

Loss from interest rate hedge recorded in other comprehensive income

'

'

'

'

'

-2.4

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unamortized loss remaining in accumulated other comprehensive income

'

'

'

'

'

'

1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total commitment under revolving credit facility

'

'

'

'

'

'

'

'

'

'

'

'

425

'

'

'

'

'

375

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Draw down of revolving line of credit

200

150

0

'

'

'

'

'

'

50

'

'

'

150

'

150

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

50.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Principal amount of purchase note

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt Instrument Term (in years)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'5 years

'

'

'

'

'

'

'

'

'

'

'6 years

'

'

'

'

'

'

Amount of debt available for adjustment

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

58

'

'

'

'

'

'

Interest Paid

42.6

44.6

59

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

9.8

'

'

'

'

'

'

'

Increase (decrease) in the principal of the note issued

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-29

'

1.9

-5.2

9.1

-22.8

'

Undisputed amounts, principal and interest

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

42.8

Repayments of debt, principal

275

75

0

'

'

'

'

'

'

'

'

'

'

'

'

75

'

'

'

'

'

'

'

'

'

'

'

'

'

33

'

'

'

'

'

'

'

Reimbursement of debt repayment by Berkshire

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

36.7

'

'

'

'

'

'

'

Reimbursement of debt repayment by Berkshire, principal portion

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

33

'

'

'

'

'

'

'

Reimbursement of debt prepayment by Berkshire, accrued interest portion

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$3.70

'

'

'

'

'

'

'

Income_Taxes_Income_Tax_Benefi

Income Taxes (Income Tax Benefit (Expense) (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current tax (expense) benefit:	'	'	'	'	'	'	'	'	'	'	'
U.S. federal	'	'	'	'	'	'	'	'	$19	($8.20)	($36.30)
State	'	'	'	'	'	'	'	'	1.4	3.4	2.4
Non-U.S.	'	'	'	'	'	'	'	'	16.5	5.9	-5.1
Total current tax (expense) benefit	'	'	'	'	'	'	'	'	36.9	1.1	-39
Deferred tax (expense) benefit:	'	'	'	'	'	'	'	'	'	'	'
U.S. federal	'	'	'	'	'	'	'	'	24.4	55.5	43.7
State	'	'	'	'	'	'	'	'	0	0	0
Non-U.S.	'	'	'	'	'	'	'	'	15.3	-72.3	-114.7
Total deferred tax (expense) benefit	'	'	'	'	'	'	'	'	39.7	-16.8	-71
Total income tax (expense) benefit	$27.40	$8.20	($0.60)	$41.60	($101)	$47.80	$6.40	$31.10	$76.60	($15.70)	($110)

Income_Taxes_Effective_Rate_Re

Income Taxes (Effective Rate Reconciliation) (Details) (USD $)

3 Months Ended

12 Months Ended

2 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Jan. 02, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Non-US

Non-US

Non-US

SWEDEN

SWEDEN

SWEDEN

Luxembourg

Luxembourg

Luxembourg

Luxembourg

Sirius Group

Sirius Group

Business Acquisition [Member]

Business Acquisition [Member]

Business Acquisition [Member]

SWEDEN

SWEDEN

Income Tax Contingency [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

U.S. statutory rate (as a percent)

'

'

'

'

35.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Tax (expense) benefit at the U.S. statutory rate

'

'

'

'

'

'

'

'

($120,700,000)

($92,000,000)

($34,300,000)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Differences in taxes resulting from:

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Non-U.S. earnings, net of foreign taxes

'

'

'

'

'

'

'

'

82,900,000

43,000,000

6,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Change in valuation allowance

'

'

'

'

'

'

'

'

-33,600,000

-14,100,000

128,200,000

'

'

'

'

'

'

-41,300,000

-1,400,000

'

'

'

'

'

'

'

Effective Income Tax Rate Reconciliation, Tax Contingency, Amount

'

'

'

'

'

'

'

'

-10,200,000

-1,300,000

4,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Tax exempt interest and dividends

'

'

'

'

'

'

'

'

-3,200,000

-3,100,000

-2,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Effective Income Tax Rate Reconciliation, Deduction, Other, Amount

'

'

'

'

'

'

'

'

1,700,000

2,900,000

-200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Tax rate change enacted

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

65,400,000

0

'

0

7,200,000

1,200,000

'

'

'

'

'

Other, net

'

'

'

'

'

'

'

'

-1,800,000

2,200,000

1,300,000

'

'

'

'

'

'

'

'

'

'

'

'

5,300,000

5,100,000

0

Income tax (expense) benefit

-27,400,000

-8,200,000

600,000

-41,600,000

101,000,000

-47,800,000

-6,400,000

-31,100,000

-76,600,000

15,700,000

110,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Effective income tax

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

22.00%

26.30%

'

'

'

Increase (Decrease) in Deferred Income Taxes

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

65,400,000

'

'

'

'

Pre-tax loss

134,200,000

55,300,000

3,600,000

151,800,000

-50,800,000

135,100,000

37,600,000

140,900,000

344,900,000

262,800,000

98,000,000

294,300,000

250,000,000

65,400,000

'

'

'

'

'

'

'

'

'

'

'

'

Tax Payments and Receipts

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income tax payments to (receipts from) national governments, total

'

'

'

'

'

'

'

'

$13,900,000

$17,500,000

$12,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Income_Taxes_Deferred_Tax_Inve

Income Taxes (Deferred Tax Inventory) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Contingency [Line Items]	'	'	'
Valuation allowance	$33,600,000	$14,100,000	($128,200,000)
Deferred income tax assets related to:	'	'	'
Non-U.S. net operating loss carryforwards	520,600,000	511,900,000	'
U.S. federal net operating and capital loss carryforwards	148,600,000	164,800,000	'
Loss reserve discount	74,900,000	88,600,000	'
Incentive compensation	10,300,000	10,400,000	'
Unearned premiums	38,900,000	45,500,000	'
Tax credit carryforwards	23,100,000	17,000,000	'
Fixed assets	4,900,000	2,800,000	'
Accrued interest	1,100,000	8,000,000	'
Pension and benefit accruals	0	10,300,000	'
Other items	6,900,000	5,700,000	'
Total gross deferred income tax assets	907,400,000	951,100,000	'
Less: valuation allowances	-289,800,000	-254,000,000	'
Total net deferred income tax assets	617,600,000	697,100,000	'
Deferred income tax liabilities related to:	'	'	'
Net unrealized investment gains	44,600,000	54,200,000	'
Investment basis difference	3,000,000	21,000,000	'
Deferred acquisition costs	33,000,000	49,800,000	'
Other items	7,900,000	7,500,000	'
Total deferred income tax liabilities	461,700,000	468,800,000	'
Net deferred tax asset	155,900,000	228,300,000	'
OneBeacon Runoff	'	'	'
Deferred income tax assets related to:	'	'	'
Runoff Transaction	24,200,000	49,300,000	'
Safety Reserve [Member]	'	'	'
Deferred income tax liabilities related to:	'	'	'
Deferred Tax Liabilities, Gross, Noncurrent	357,200,000	326,700,000	'
Purchase Accounting [Member]	'	'	'
Deferred income tax liabilities related to:	'	'	'
Deferred Tax Liabilities, Gross, Noncurrent	7,200,000	9,500,000	'
Members Surplus Contributions [Member]	'	'	'
Deferred income tax liabilities related to:	'	'	'
Deferred Tax Liabilities, Gross, Noncurrent	5,400,000	100,000	'
Other Pension Plan, Postretirement or Supplemental Plans, Defined Benefit [Member]	'	'	'
Deferred income tax liabilities related to:	'	'	'
Deferred Tax Liabilities, Gross, Noncurrent	3,400,000	0	'
Incentive Compensation [Member]	'	'	'
Deferred income tax assets related to:	'	'	'
Incentive compensation	53,900,000	36,800,000	'
UNITED STATES	'	'	'
Deferred income tax liabilities related to:	'	'	'
Net deferred tax asset	193,100,000	'	'
Luxembourg	'	'	'
Deferred income tax liabilities related to:	'	'	'
Net deferred tax asset	315,700,000	'	'
UNITED KINGDOM	'	'	'
Deferred income tax liabilities related to:	'	'	'
Net deferred tax asset	3,300,000	'	'
SWEDEN	'	'	'
Deferred income tax liabilities related to:	'	'	'
Total deferred income tax liabilities	$356,200,000	'	'

Income_Taxes_Valuation_Allowan

Income Taxes (Valuation Allowance) (Details) (USD $)

3 Months Ended

12 Months Ended

2 Months Ended

12 Months Ended

3 Months Ended

3 Months Ended

12 Months Ended

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Net operating losses in Luxembourg subsidiaries

Net operating losses in Luxembourg subsidiaries

U.S. losses and other federal deferred tax benefits

U.S. losses and other federal deferred tax benefits

Net Operating Losses in Netherlands Subsidiaries [Member] [Member]

Luxembourg

Luxembourg

Luxembourg

Luxembourg

Sirius Re Holdings Inc.

Sirius Re Holdings Inc.

Guilford Holdings, Inc.

BAM

BAM

Houston General Insurance [Member]

Tax benefit

Tax Expense [Member]

UNITED STATES

Valuation Allowance [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Valuation allowance

$289,800,000

'

'

'

$254,000,000

'

'

'

$289,800,000

$254,000,000

'

$195,800,000

$192,000,000

$93,700,000

$62,000,000

$300,000

'

'

'

'

'

'

'

'

'

'

Change in valuation allowance

'

'

'

'

'

'

'

'

-33,600,000

-14,100,000

128,200,000

'

'

'

'

'

-41,300,000

-1,400,000

-16,700,000

-18,100,000

-3,900,000

'

-16,600,000

'

-21,300,000

-6

Income Tax Expense (Benefit)

27,400,000

8,200,000

-600,000

41,600,000

-101,000,000

47,800,000

6,400,000

31,100,000

76,600,000

-15,700,000

-110,000,000

'

'

'

'

'

'

'

'

'

'

'

'

5,400,000

'

'

Foreign tax credit carryforwards, subject to expiration

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$5,200,000

'

'

'

'

Income_Taxes_Net_Operating_and

Income Taxes (Net Operating and Capital Loss Carryforwards) (Details) (USD $)

12 Months Ended

3 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

UNITED STATES

Sirius Re Holdings Inc.

Sirius Re Holdings Inc.

Expected to be utilized [Member]

Subject to annual limitations [Member]

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Operating and Capital Loss Carryforward

Luxembourg

UNITED STATES

UNITED STATES

Luxembourg

SWEDEN

UNITED KINGDOM

NETHERLANDS

2013 [Member]

2013 [Member]

2013 [Member]

2013 [Member]

2013 [Member]

2013 [Member]

2014-2018 [Member]

2014-2018 [Member]

2014-2018 [Member]

2014-2018 [Member]

2014-2018 [Member]

2014-2018 [Member]

2019-2013 [Member]

2019-2013 [Member]

2019-2013 [Member]

2019-2013 [Member]

2019-2013 [Member]

2019-2013 [Member]

2024-2033 [Member]

2024-2033 [Member]

2024-2033 [Member]

2024-2033 [Member]

2024-2033 [Member]

2024-2033 [Member]

No expiration date [Member]

No expiration date [Member]

No expiration date [Member]

No expiration date [Member]

No expiration date [Member]

No expiration date [Member]

UNITED STATES

Luxembourg

SWEDEN

UNITED KINGDOM

NETHERLANDS

UNITED STATES

Luxembourg

SWEDEN

UNITED KINGDOM

NETHERLANDS

UNITED STATES

Luxembourg

SWEDEN

UNITED KINGDOM

NETHERLANDS

UNITED STATES

Luxembourg

SWEDEN

UNITED KINGDOM

NETHERLANDS

UNITED STATES

Luxembourg

SWEDEN

UNITED KINGDOM

NETHERLANDS

Summary of net operating loss and capital loss carryforwards, the expiration dates and the deferred tax assets thereon

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Operating Loss Carryforwards

'

'

'

'

'

'

$1,284,100,000

$18,200,000

$2,270,000,000

$441,000,000

$1,750,000,000

$62,300,000

$15,600,000

$1,100,000

$0

$0

$0

$0

$0

$0

$500,000

$0

$0

$0

$0

$500,000

$11,800,000

$11,200,000

$0

$0

$0

$600,000

$429,800,000

$429,800,000

$0

$0

$0

$0

$1,827,900,000

$0

$1,750,000,000

$62,300,000

$15,600,000

$0

Net deferred tax assets

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Gross deferred tax asset

'

'

'

'

'

'

'

'

669,200,000

148,600,000

511,300,000

5,800,000

3,200,000

300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Valuation allowance

'

'

'

'

'

'

'

'

-254,300,000

-58,300,000

-195,700,000

0

0

-300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total net deferred income tax assets

617,600,000

697,100,000

'

'

'

'

'

'

414,900,000

90,300,000

315,600,000

5,800,000

3,200,000

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Foreign tax credit carryforwards, subject to expiration

'

'

'

11,600,000

'

5,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Valuation allowance

33,600,000

14,100,000

-128,200,000

'

3,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Alternative minimum tax credit carryforwards, not subject to expiration

$11,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Income_Taxes_ASC_74010_Details

Income Taxes (ASC 740-10) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Mar. 31, 2014
Income Tax Contingency [Line Items]	'		'		'		'
Percentage of likelihood for realization of benefit upon ultimate settlement	'		50.00%		'		'
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns	'		'		'		'
Balance at beginning	$46.60		$65.50		$95.80		'
Changes in prior year tax positions	-4.8		1.9		1.2		'
Tax positions taken during the current year	8.6		'		'		'
Lapse in statute of limitations	'		'		-10.5		'
Settlements with tax authorities	-0.4		-0.6		-0.6		'
Tax positions taken during the current year	'		-20.2		-20.4		'
Balance at year end	50		46.6		65.5		'
Unrecognized tax benefit recognition including interest and penalties, if recognized, would effect income tax expense	27.5		'		'		5
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Estimated Range of Change, Upper Bound	5.2		'		'		'
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	1.3		1.2		0.6		'
Permanent Differences [Member]	'		'		'		'
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns	'		'		'		'
Balance at beginning	9.7	[1]	9.6	[1]	14.5	[1]	'
Changes in prior year tax positions	0.6	[1]	0.5	[1]	-0.9	[1]	'
Tax positions taken during the current year	7.9	[1]	'		'		'
Lapse in statute of limitations	'		'		-3.4	[1]	'
Settlements with tax authorities	0	[1]	-0.4	[1]	-0.6	[1]	'
Tax positions taken during the current year	'		0	[1]	0	[1]	'
Balance at year end	18.2	[1]	9.7	[1]	9.6	[1]	'
Temporary Differences [Member]	'		'		'		'
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns	'		'		'		'
Balance at beginning	28.9	[2]	49.1	[2]	75.1	[2]	'
Changes in prior year tax positions	-7.1	[2]	0	[2]	0.1	[2]	'
Tax positions taken during the current year	0.7	[2]	'		'		'
Lapse in statute of limitations	'		'		-5.7	[2]	'
Settlements with tax authorities	0	[2]	0	[2]	0	[2]	'
Tax positions taken during the current year	'		-20.2	[2]	-20.4	[2]	'
Balance at year end	22.5	[2]	28.9	[2]	49.1	[2]	'
Interest and Penalties Net of Tax Benefit [Member]	'		'		'		'
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns	'		'		'		'
Balance at beginning	8	[3]	6.8	[3]	6.2	[3]	'
Changes in prior year tax positions	1.7	[3]	1.4	[3]	2	[3]	'
Tax positions taken during the current year	0	[3]	'		'		'
Lapse in statute of limitations	'		'		-1.4	[3]	'
Settlements with tax authorities	-0.4	[3]	-0.2	[3]	0	[3]	'
Tax positions taken during the current year	'		0	[3]	0	[3]	'
Balance at year end	$9.30	[3]	$8	[3]	$6.80	[3]	'
[1]	Represents the amount of unrecognized tax benefits that, if recognized, would impact the effective tax rate.
[2]	Represents the amount of unrecognized tax benefits that, if recognized would create a temporary difference between the reported amount of an item in the Company’s Consolidated Balance Sheet and its tax basis.
[3]	Net of tax benefit.

Income_Taxes_Tax_Examinations_

Income Taxes (Tax Examinations) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Income Tax Examination [Line Items]	'	'
Unrecognized tax benefit recognition including interest and penalties, if recognized, would effect income tax expense	$5	$27.50
Tax Assessment Year 2007 to 2009 [Member] | IRS	'	'
Income Tax Examination [Line Items]	'	'
Tax Examination	'	68.3
Tax Assessment Year 2007 to 2009 [Member] | Assessment related to temporary differences [Member] | IRS	'	'
Income Tax Examination [Line Items]	'	'
Tax Examination	'	60.2
Tax Assessment Year 2005 to 2006 [Member] | IRS	'	'
Income Tax Examination [Line Items]	'	'
Tax Examination	'	3.3
Tax Assessment Year 2005 to 2006 [Member] | Assessment related to temporary differences [Member] | IRS	'	'
Income Tax Examination [Line Items]	'	'
Tax Examination	'	$2.70

Derivatives_Details

Derivatives (Details)	Dec. 31, 2013	Dec. 31, 2013
In Billions, unless otherwise specified	USD ($)	JPY (¥)
Derivative Instruments and Hedging Activities Disclosure [Abstract]	'	'
Notional amount	$1.90	¥ 203.6
Collective account values of underlying variable annuities as a percentage of the guarantee value	104.00%	104.00%

Derivatives_PreTax_Operating_R

Derivatives (Pre-Tax Operating Results of WM Life Re) (Details) (USD $)

3 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Pre-tax operating results of WM Life Re

'

'

'

'

'

'

'

'

'

'

'

Total revenues

$626.60

$574.10

$489.30

$627.40

$566.40

$697.40

$542.30

$629.70

$2,317.40

$2,435.70

$2,173.10

General and administrative expenses

'

'

'

'

'

'

'

'

-181.3

-182.2

-175.3

Pre-tax income

134.2

55.3

3.6

151.8

-50.8

135.1

37.6

140.9

344.9

262.8

98

White Mountains Life Re

'

'

'

'

'

'

'

'

'

'

'

Pre-tax operating results of WM Life Re

'

'

'

'

'

'

'

'

'

'

'

Fees, included in other revenue

'

'

'

'

'

'

'

'

25

31.8

32.5

Change in Fair Value of Variable Annuity Liability, included in other revenues

'

'

'

'

'

'

'

'

378.5

312.8

-156.5

Change in fair value of derivatives, included in other revenue

'

'

'

'

'

'

'

'

-402

-339

92.9

Foreign exchange, included in other revenue

'

'

'

'

'

'

'

'

-14.5

-30.3

15.1

Other investment income and (losses) gains

'

'

'

'

'

'

'

'

-7.1

2.5

-0.9

Total revenues

'

'

'

'

'

'

'

'

-20.1

-22.2

-16.9

Change in fair value of variable annuity death benefit liabilities, included in general and administrative expenses

'

'

'

'

'

'

'

'

10.2

14.2

-1.8

Death benefit claims paid, included in general and administrative expenses

'

'

'

'

'

'

'

'

-1.9

-5.7

-3.8

General and administrative expenses

'

'

'

'

'

'

'

'

-4.9

-5.2

-4.7

Pre-tax income

'

'

'

'

'

'

'

'

-16.7

-18.9

-27.2

Level 3 | White Mountains Life Re

'

'

'

'

'

'

'

'

'

'

'

Pre-tax operating results of WM Life Re

'

'

'

'

'

'

'

'

'

'

'

Change in fair value of derivatives, included in other revenue

'

'

'

'

'

'

'

'

136.5

[1]

84

[1]

-14.5

[1]

Level 3 | Projected Surrender Assumption [Member] | White Mountains Life Re

'

'

'

'

'

'

'

'

'

'

'

Pre-tax operating results of WM Life Re

'

'

'

'

'

'

'

'

'

'

'

Change in fair value of derivatives, included in other revenue

'

'

'

'

'

'

'

'

$6.50

'

$7.20

[1]

Consists of over-the-counter instruments.

Derivatives_Realized_and_Unrea

Derivatives (Realized and Unrealized Gains (Losses)) (Details) (White Mountains Life Re, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Variable Annuity Reinsurance [Line Items]	'		'		'		'
Change in fair value of variable annuity death benefit liabilities, included in general and administrative expenses	$10.20		$14.20		($1.80)		'
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments	'		'		'		'
Change in fair value of derivatives, included in other revenue	-402		-339		92.9		'
Derivative, Fair Value, Net	69.2		98.3		'		'
Fixed income/interest rate	'		'		'		'
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments	'		'		'		'
Change in fair value of derivatives, included in other revenue	-108.7		-149.5		8.9		'
Derivative, Fair Value, Net	-9.7		27.1		'		'
Foreign exchange	'		'		'		'
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments	'		'		'		'
Change in fair value of derivatives, included in other revenue	-96.7		-102.3		29.5		'
Derivative, Fair Value, Net	58		52.8		'		'
Equity	'		'		'		'
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments	'		'		'		'
Change in fair value of derivatives, included in other revenue	-196.6		-87.2		54.5		'
Derivative, Fair Value, Net	20.9		18.4		'		'
Level 3	'		'		'		'
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments	'		'		'		'
Change in fair value of derivatives, included in other revenue	136.5	[1]	84	[1]	-14.5	[1]	'
Derivative, Fair Value, Net	63.4	[1]	140.5	[1]	247.1	[1]	275.3	[1]
Level 3 | Projected Surrender Assumption [Member]	'		'		'		'
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments	'		'		'		'
Change in fair value of derivatives, included in other revenue	$6.50		'		$7.20		'
[1]	Consists of over-the-counter instruments.

Derivatives_Variable_Annuity_R

Derivatives (Variable Annuity Reinsurance Liabilities and Derivative Instruments) (Details) (White Mountains Life Re, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Changes in derivative instruments	'		'		'
Beginning of period	$98.30		'		'
Realized and unrealized gains (losses)	402		339		-92.9
Ending balance	69.2		98.3		'
Level 3	'		'		'
Changes in variable annuity (liabilities)	'		'		'
Beginning balance	-441.5		-768.5		-610.2
Purchases	0		0		0
Realized and unrealized gains (losses)	-388.7	[1]	-327	[1]	158.3	[1]
Transfers in (out)	0		0		0
Sales/settlements	'		0		0
Ending balance	-52.8		-441.5		-768.5
Changes in derivative instruments	'		'		'
Beginning of period	140.5	[2]	247.1	[2]	275.3	[2]
Purchases	59.4	[2]	6.1	[2]	5	[2]
Realized and unrealized gains (losses)	-136.5	[2]	-84	[2]	14.5	[2]
Transfers in (out)	0	[2]	0	[2]	0	[2]
Sales/settlements	'	[2]	-28.7	[2]	-47.7	[2]
Ending balance	63.4	[2]	140.5	[2]	247.1	[2]
Level 2	'		'		'
Changes in derivative instruments	'		'		'
Beginning of period	-20.5	[2],[3]	39.2	[2],[3]	72.2	[2],[3]
Purchases	0	[2],[3]	0	[2],[3]	0	[2],[3]
Realized and unrealized gains (losses)	-196.1	[2],[3]	-186.9	[2],[3]	67.7	[2],[3]
Transfers in (out)	0	[2],[3]	0	[2],[3]	0	[2],[3]
Sales/settlements	221.3	[2],[3]	127.2	[2],[3]	-100.7	[2],[3]
Ending balance	4.7	[2],[3]	-20.5	[2],[3]	39.2	[2],[3]
Level 1	'		'		'
Changes in derivative instruments	'		'		'
Beginning of period	-21.7	[4]	4.1	[4]	0	[4]
Purchases	0	[4]	0	[4]	0	[4]
Realized and unrealized gains (losses)	-69.4	[4]	-68.1	[4]	10.7	[4]
Transfers in (out)	0	[4]	0	[4]	0	[4]
Sales/settlements	92.2	[4]	42.3	[4]	-6.6	[4]
Ending balance	1.1	[4]	-21.7	[4]	4.1	[4]
Fair value	'		'		'
Changes in derivative instruments	'		'		'
Beginning of period	98.3	[5]	290.4	[5]	347.5	[5]
Purchases	59.4	[5]	6.1	[5]	5	[5]
Realized and unrealized gains (losses)	-402	[5]	-339	[5]	92.9	[5]
Transfers in (out)	0	[5]	0	[5]	0	[5]
Sales/settlements	313.5	[5]	140.8	[5]	-155	[5]
Ending balance	$69.20	[5]	$98.30	[5]	$290.40	[5]
[1]	Includes $10.2, $14.2, $(1.8) for December 31, 2013, 2012 and 2011 related to the change in the fair value of variable annuity death benefit liabilities, which are included in general and administrative expenses.
[2]	Consists of over-the-counter instruments.
[3]	Consists of interest rate swaps, total return swaps, foreign currency forward contracts, and bond forwards. Fair value measurement based upon bid/ask pricing quotes for similar instruments that are actively traded, where available. Swaps for which an active market does not exist have been priced using observable inputs including the swap curve and the underlying bond index.
[4]	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.
[5]	In addition to derivative instruments, WM Life Re held cash, short-term and fixed maturity investments of $81.3, $393.6 and $485.3 at December 31, 2013, 2012 and 2011 posted as collateral to its reinsurance counterparties.

Derivatives_Additional_Collate

Derivatives (Additional Collateral) (Details) (White Mountains Life Re, USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Millions, unless otherwise specified
Credit risk on derivative instruments	'	'	'
Collateral Cash and Investments	$81.30	$393.60	$485.30
Cash	'	'	'
Credit risk on derivative instruments	'	'	'
Derivative Collateral Right to Reclaim	56.1	249.8	'
Short-term investments	'	'	'
Credit risk on derivative instruments	'	'	'
Derivative Collateral Right to Reclaim	2	5.1	'
Fixed maturity investments	'	'	'
Credit risk on derivative instruments	'	'	'
Derivative Collateral Right to Reclaim	$23.20	$138.70	'

Derivatives_Level_3_Derivative

Derivatives (Level 3 Derivative Instruments) (Details) (White Mountains Life Re, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
Equity Index Options	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Fair value Liabilities	30.8
Equity Index Options | Black-Scholes option pricing model | Minimum	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Adjustment to counterparty valuations	0.50%
Equity Index Options | Black-Scholes option pricing model | Maximum	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Adjustment to counterparty valuations	9.70%
Equity Index Options | Black-Scholes option pricing model | Weighted Average	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Adjustment to counterparty valuations	3.40%
Variable annuity benefit guarantee liabilities	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Fair value Liabilities	52.8
Variable annuity benefit guarantee liabilities | Discounted cash flows | Minimum	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Mortality	0.00%
Variable annuity benefit guarantee liabilities | Discounted cash flows | Maximum	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Mortality	5.30%
Variable annuity benefit guarantee liabilities | Discounted cash flows | Weighted Average	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Mortality	1.00%
Foreign Exchange Options	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Fair value Liabilities	32.6
Foreign Exchange Options | Black-Scholes option pricing model | Minimum	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Foreign exchange volatilities	-1.20%
Foreign Exchange Options | Black-Scholes option pricing model | Maximum	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Foreign exchange volatilities	8.00%
Foreign Exchange Options | Black-Scholes option pricing model | Weighted Average	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Foreign exchange volatilities	2.40%
Year Three and Thereafter [Member] | Variable annuity benefit guarantee liabilities | Discounted cash flows | Minimum	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Surrenders	0.10%
Foreign exchange volatilities	13.50%
Index volatilities	18.90%
Year Three and Thereafter [Member] | Variable annuity benefit guarantee liabilities | Discounted cash flows | Maximum	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Surrenders	14.00%
Foreign exchange volatilities	16.30%
Index volatilities	21.90%
Year Three and Thereafter [Member] | Variable annuity benefit guarantee liabilities | Discounted cash flows | Weighted Average	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Surrenders	6.20%
Foreign exchange volatilities	14.30%
Index volatilities	21.90%
Year Two [Member] | Variable annuity benefit guarantee liabilities | Discounted cash flows | Minimum	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Surrenders	0.20%
Foreign exchange volatilities	12.90%
Index volatilities	17.60%
Year Two [Member] | Variable annuity benefit guarantee liabilities | Discounted cash flows | Maximum	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Surrenders	32.00%
Foreign exchange volatilities	15.00%
Index volatilities	20.10%
Year Two [Member] | Variable annuity benefit guarantee liabilities | Discounted cash flows | Weighted Average	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Surrenders	15.80%
Foreign exchange volatilities	13.70%
Index volatilities	19.40%
Year One [Member] | Variable annuity benefit guarantee liabilities | Discounted cash flows | Minimum	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Surrenders	0.30%
Foreign exchange volatilities	11.60%
Index volatilities	16.40%
Year One [Member] | Variable annuity benefit guarantee liabilities | Discounted cash flows | Maximum	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Surrenders	30.00%
Foreign exchange volatilities	14.00%
Index volatilities	19.50%
Year One [Member] | Variable annuity benefit guarantee liabilities | Discounted cash flows | Weighted Average	'
Quantitative information for Level 3 Fair Value Measurements Liabilities	'
Surrenders	21.00%
Foreign exchange volatilities	12.50%
Index volatilities	17.90%

Derivatives_Derivatives_Gross_

Derivatives Derivatives (Gross Asset (Gross liability) Amounts Offset Under Master Netting Agreements) (Details) (White Mountains Life Re, USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Derivative [Line Items]	'		'
Derivative Asset	$106	[1]	$206.50	[1],[2]
Derivative Liability	-36.8	[1]	-108.2	[1]
Net amounts recognized in Other Assets	69.2	[1]	98.3	[1]
Interest Rate Contract | Over the Counter [Member]	'		'
Derivative [Line Items]	'		'
Derivative Asset	2.4		52.6	[2]
Derivative Liability	-11.7		-26.9
Net amounts recognized in Other Assets	-9.3		25.7
Interest Rate Contract | Exchange Traded [Member]	'		'
Derivative [Line Items]	'		'
Derivative Asset	1		1.6	[2]
Derivative Liability	-1.6		-0.2
Net amounts recognized in Other Assets	-0.6		1.4
Foreign Exchange Contract | Over the Counter [Member]	'		'
Derivative [Line Items]	'		'
Derivative Asset	67.8		87.8	[2]
Derivative Liability	-12		-34.4
Net amounts recognized in Other Assets	55.8		53.4
Foreign Exchange Contract | Exchange Traded [Member]	'		'
Derivative [Line Items]	'		'
Derivative Asset	2.3		0.8	[2]
Derivative Liability	0		-1.4
Net amounts recognized in Other Assets	2.3		-0.6
Equity Contract | Over the Counter [Member]	'		'
Derivative [Line Items]	'		'
Derivative Asset	30.7		63.6	[2]
Derivative Liability	-9.2		-22.9
Net amounts recognized in Other Assets	21.5		40.7
Equity Contract | Exchange Traded [Member]	'		'
Derivative [Line Items]	'		'
Derivative Asset	1.8		0.1	[2]
Derivative Liability	-2.3		-22.4
Net amounts recognized in Other Assets	($0.50)		($22.30)
[1]	All derivative instruments held by WM Life Re are subject to master netting arrangements.
[2]	Amount equal to fair value of instrument as recognized in other assets.

Derivatives_Uncollateralized_A

Derivatives (Uncollateralized Amounts Due Under WM Life Re's OTC Derivative Contracts) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
White Mountains Life Re	'		'
Variable Annuity Reinsurance [Line Items]	'		'
Net amounts recognized in Other Assets	$69.20	[1]	$98.30	[1]
Credit risk on derivative instruments	'		'
Net exposure on fair value of OTC instruments	135.7		222.1
Derivative, Collateral, Right to Reclaim Cash	0		45.3
Derivative, Collateral, Right to Reclaim Securities	0.4		0
Derivative Asset, Fair Value, Amount Offset Against Collateral	69.6		143.6
Excess collateral provided to counterparty in cash	44.1		81.1
Excess collateral providedto counterparty in financial instruments	22.8		28
Derivative, Collateral, Obligation to Return Cash	0.8		30.6
Forward contracts	'		'
Variable Annuity Reinsurance [Line Items]	'		'
Net amounts recognized in Other Assets	-0.1		-0.1
Credit risk on derivative instruments	'		'
S&P Credit Ratings	21		'
A | Citigroup OTC [Member] | White Mountains Life Re	'		'
Variable Annuity Reinsurance [Line Items]	'		'
Net amounts recognized in Other Assets	19.4		19.9
Credit risk on derivative instruments	'		'
Net exposure on fair value of OTC instruments	21.7		50.7
Derivative, Collateral, Right to Reclaim Cash	0		0
Derivative, Collateral, Right to Reclaim Securities	0		0
Derivative Asset, Fair Value, Amount Offset Against Collateral	19.4		19.9
Excess collateral provided to counterparty in cash	2.3		30.8
Excess collateral providedto counterparty in financial instruments	0		0
Derivative, Collateral, Obligation to Return Cash	0		0
A | Royal Bank of Scotland [Member] | White Mountains Life Re	'		'
Variable Annuity Reinsurance [Line Items]	'		'
Net amounts recognized in Other Assets	11.3		33.6
Credit risk on derivative instruments	'		'
Net exposure on fair value of OTC instruments	11.3		33.6
Derivative, Collateral, Right to Reclaim Cash	0		0
Derivative, Collateral, Right to Reclaim Securities	0		0
Derivative Asset, Fair Value, Amount Offset Against Collateral	11.3		33.6
Excess collateral provided to counterparty in cash	0		0
Excess collateral providedto counterparty in financial instruments	0		0
Derivative, Collateral, Obligation to Return Cash	0		0
A | Barclays [Member] | White Mountains Life Re	'		'
Variable Annuity Reinsurance [Line Items]	'		'
Net amounts recognized in Other Assets	1.4		'
Credit risk on derivative instruments	'		'
Net exposure on fair value of OTC instruments	1.4		'
Derivative, Collateral, Right to Reclaim Cash	0		'
Derivative, Collateral, Right to Reclaim Securities	0		'
Derivative Asset, Fair Value, Amount Offset Against Collateral	1.4		'
Excess collateral provided to counterparty in cash	0		'
Excess collateral providedto counterparty in financial instruments	0		'
Derivative, Collateral, Obligation to Return Cash	0		'
A | Bank of America [Member] | White Mountains Life Re	'		'
Variable Annuity Reinsurance [Line Items]	'		'
Net amounts recognized in Other Assets	27.2		78.5
Credit risk on derivative instruments	'		'
Net exposure on fair value of OTC instruments	27.2		47.9
Derivative, Collateral, Right to Reclaim Cash	0		0
Derivative, Collateral, Right to Reclaim Securities	0		0
Derivative Asset, Fair Value, Amount Offset Against Collateral	27.2		78.5
Excess collateral provided to counterparty in cash	0		0
Excess collateral providedto counterparty in financial instruments	0		0
Derivative, Collateral, Obligation to Return Cash	0		30.6
A | Citigroup Exchange Traded [Member] | White Mountains Life Re	'		'
Variable Annuity Reinsurance [Line Items]	'		'
Net amounts recognized in Other Assets	1.2		-21.5
Credit risk on derivative instruments	'		'
Net exposure on fair value of OTC instruments	21		13.6
Derivative, Collateral, Right to Reclaim Cash	0		21.5
Derivative, Collateral, Right to Reclaim Securities	0		0
Derivative Asset, Fair Value, Amount Offset Against Collateral	1.2		0
Excess collateral provided to counterparty in cash	19.8		13.6
Excess collateral providedto counterparty in financial instruments	0		0
Derivative, Collateral, Obligation to Return Cash	0		0
BBB | Nomura [Member] | White Mountains Life Re	'		'
Variable Annuity Reinsurance [Line Items]	'		'
Net amounts recognized in Other Assets	-0.4		-0.9
Credit risk on derivative instruments	'		'
Net exposure on fair value of OTC instruments	22		28.8
Derivative, Collateral, Right to Reclaim Cash	0		0.9
Derivative, Collateral, Right to Reclaim Securities	0.4		0
Derivative Asset, Fair Value, Amount Offset Against Collateral	0		0
Excess collateral provided to counterparty in cash	0		0.8
Excess collateral providedto counterparty in financial instruments	22.8		28
Derivative, Collateral, Obligation to Return Cash	0.8		0
Standard & Poor's, A+ Rating [Member] | J P Morgan Chase [Member] | White Mountains Life Re	'		'
Variable Annuity Reinsurance [Line Items]	'		'
Net amounts recognized in Other Assets	9.1		-22.8
Credit risk on derivative instruments	'		'
Net exposure on fair value of OTC instruments	31.1		32.8
Derivative, Collateral, Right to Reclaim Cash	0		22.8
Derivative, Collateral, Right to Reclaim Securities	0		0
Derivative Asset, Fair Value, Amount Offset Against Collateral	9.1		0
Excess collateral provided to counterparty in cash	22		32.8
Excess collateral providedto counterparty in financial instruments	0		0
Derivative, Collateral, Obligation to Return Cash	0		0
Standard & Poor's, A+ Rating [Member] | Barclays [Member] | White Mountains Life Re	'		'
Variable Annuity Reinsurance [Line Items]	'		'
Net amounts recognized in Other Assets	'		11.6
Credit risk on derivative instruments	'		'
Net exposure on fair value of OTC instruments	'		11.6
Derivative, Collateral, Right to Reclaim Cash	'		0
Derivative, Collateral, Right to Reclaim Securities	'		0
Derivative Asset, Fair Value, Amount Offset Against Collateral	'		11.6
Excess collateral provided to counterparty in cash	'		0
Excess collateral providedto counterparty in financial instruments	'		0
Derivative, Collateral, Obligation to Return Cash	'		0
Standard & Poor's, A- Rating [Member] | Goldman Sachs [Member] | White Mountains Life Re	'		'
Variable Annuity Reinsurance [Line Items]	'		'
Net amounts recognized in Other Assets	'		-0.1
Credit risk on derivative instruments	'		'
Net exposure on fair value of OTC instruments	'		3.1
Derivative, Collateral, Right to Reclaim Cash	'		0.1
Derivative, Collateral, Right to Reclaim Securities	'		0
Derivative Asset, Fair Value, Amount Offset Against Collateral	'		0
Excess collateral provided to counterparty in cash	'		3.1
Excess collateral providedto counterparty in financial instruments	'		0
Derivative, Collateral, Obligation to Return Cash	'		$0
[1]	All derivative instruments held by WM Life Re are subject to master netting arrangements.

Derivatives_Forward_Contracts_

Derivatives (Forward Contracts) (Details)	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013
In Millions, unless otherwise specified	USD ($)	JPY (¥)	Forward contracts	Forward contracts	Forward contracts
			USD ($)	USD ($)	SEK
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'	'
Notional amount	$1,900	¥ 203,600	$20.40	$31.20	131.3
Changes in derivative instruments	'	'	'	'	'
Beginning of period	'	'	-0.1	0	'
Purchases	'	'	0	0	'
Realized and unrealized gains (losses)	'	'	0.1	0.3	'
Sales/settlements	'	'	0.1	0.2	'
Ending balance	'	'	($0.10)	($0.10)	'

Derivatives_Derivatives_Unreal

Derivatives Derivatives (Unrealized and Realized Derivative Gains (Losses) Forward Contracts) (Details) (Forward contracts, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]	'	'	'
Change in fair value of derivatives, included in other revenue	($0.10)	($0.30)	'
Derivative, Fair Value, Net	-0.1	-0.1	0
GBP	'	'	'
Derivative [Line Items]	'	'	'
Change in fair value of derivatives, included in other revenue	0	0	'
Derivative, Fair Value, Net	0	0	'
Euro Member Countries, Euro	'	'	'
Derivative [Line Items]	'	'	'
Change in fair value of derivatives, included in other revenue	0.1	-0.1	'
Derivative, Fair Value, Net	-0.1	-0.1	'
SEK	'	'	'
Derivative [Line Items]	'	'	'
Change in fair value of derivatives, included in other revenue	0	0	'
Derivative, Fair Value, Net	0	0	'
United States of America, Dollars	'	'	'
Derivative [Line Items]	'	'	'
Change in fair value of derivatives, included in other revenue	-0.2	-0.2	'
Derivative, Fair Value, Net	$0	$0	'

Derivatives_Derivatives_Forwar

Derivatives Derivatives (Forward Contract Netting) (Details) (Forward contracts, USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Derivative [Line Items]	'	'
Derivative Asset	$0	$0	[1]
Derivative Liability	-0.1	-0.1
Net amounts recognized in Other Assets	-0.1	-0.1
United States of America, Dollars	'	'
Derivative [Line Items]	'	'
Derivative Asset	0	0	[1]
Derivative Liability	0	0
Net amounts recognized in Other Assets	0	0
Euro Member Countries, Euro	'	'
Derivative [Line Items]	'	'
Derivative Asset	0	0	[1]
Derivative Liability	-0.1	-0.1
Net amounts recognized in Other Assets	-0.1	-0.1
GBP	'	'
Derivative [Line Items]	'	'
Derivative Asset	0	0	[1]
Derivative Liability	0	0
Net amounts recognized in Other Assets	$0	$0
[1]	Amount equal to fair value of instrument as recognized in investments.

Derivatives_Derivatives_Forwar1

Derivatives Derivatives (Forward Contracts Collateral) (Details)

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

In Millions, unless otherwise specified

USD ($)

JPY (¥)

Forward contracts

Forward contracts

Forward contracts

Barclays [Member]

Barclays [Member]

Deutsche Bank [Member]

Deutsche Bank [Member]

Goldman Sachs [Member]

Goldman Sachs [Member]

HSBC Bank plc [Member]

HSBC Bank plc [Member]

J P Morgan Chase [Member]

J P Morgan Chase [Member]

Royal Bank of Canada [Member]

Royal Bank of Canada [Member]

USD ($)

SEK

USD ($)

A

A

A

A

Standard & Poor's, A- Rating [Member]

Standard & Poor's, A- Rating [Member]

Standard & Poor's, AA- Rating [Member]

Standard & Poor's, AA- Rating [Member]

Standard & Poor's, A+ Rating [Member]

Standard & Poor's, A+ Rating [Member]

Standard & Poor's, AA- Rating [Member]

Standard & Poor's, AA- Rating [Member]

Forward contracts

Forward contracts

Forward contracts

Forward contracts

Forward contracts

Forward contracts

Forward contracts

Forward contracts

Forward contracts

Forward contracts

Forward contracts

Forward contracts

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

USD ($)

Derivative [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Notional amount

$1,900

¥ 203,600

$20.40

131.3

$31.20

$5.80

$7.70

$7.70

$11.10

$2.10

$0.40

$3.30

$10.10

$1.30

$1.90

$0.20

$0

Uncollaterailized Balance of Forward Currency Derivatives

'

'

($0.10)

[1]

'

($0.10)

$0

[1]

($0.10)

$0

[1]

$0

$0

[1]

$0

($0.10)

[1]

$0

$0

[1]

$0

$0

[1]

$0

[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).

Derivatives_Derivatives_Intere

Derivatives Derivatives (Interest Rate Cap) (Details) (USD $)

1 Months Ended

12 Months Ended

61 Months Ended

1 Months Ended

1 Months Ended

In Millions, except Share data, unless otherwise specified

31-May-07

Dec. 31, 2013

Dec. 31, 2013

Jun. 30, 2022

31-May-07

Dec. 31, 2013

Dec. 31, 2013

31-May-07

31-May-07

Preferred stocks

Interest Rate Cap

Interest Rate Cap

Interest Rate Cap

Interest Rate Cap

Standard & Poor's, AA- Rating [Member]

A

Scenario, 1 [Member]

Scenario, 1 [Member]

Sirius Internation Group Ltd

Rating

Sirius Internation Group Ltd

Sirius Internation Group Ltd

Preferred stocks

Nordea Bank Finland [Member]

Barclays [Member]

Preferred stocks

Interest Rate Cap

Sirius Internation Group Ltd

Interest Rate Cap

Interest Rate Cap

Sirius Internation Group Ltd

Preferred stocks

Sirius Internation Group Ltd

Derivative [Line Items]

'

'

'

'

'

'

'

'

'

Preferred stock dividend rate

'

'

'

'

7.51%

'

'

'

'

Preference shares reference rate for dividend

'

'

'

'

'

'

'

'

'3 month LIBOR

Preference shares floating rate of dividend amount in excess of libor

'

'

'

'

'

'

'

3.20%

'

Derivative, Cap Interest Rate

'

'

8.30%

'

'

'

'

'

'

basis points

'

'

3.95%

'

'

'

'

'

'

years of interest rate cap

'

'

'5 years

'5 years

'

'

'

'

'

Non-cumulative perpetual preference shares issued

250,000,000

'

'

'

250,000,000

'

'

'

'

Derivative, Cost of Hedge

'

'

$9.90

'

'

'

'

'

'

Beginning of period

'

0

'

'

'

'

'

'

'

Purchases

'

9.9

'

'

'

'

'

'

'

Realized and unrealized gains (losses)

'

1.2

'

'

'

'

'

'

'

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

'

0

'

'

'

'

'

'

'

Ending balance

'

11.1

'

'

'

'

'

'

'

Derivative Collateral Right to Reclaim

'

$10.80

[1]

'

'

'

$3.30

[1]

$7.50

[1]

'

'

S&P Credit Ratings

'

21

'

'

'

'

'

'

'

[1]

Standard & Poor’s ratings as detailed above are: “A” (Strong, which is the sixth highest of twenty-one creditworthiness ratings) and “AA-” (Very Strong, which is the fourth highest of twenty-one creditworthiness ratings).

Derivatives_Derivatives_Weathe

Derivatives Derivatives (Weather) (Details) (weather derivatives [Member], Sirius Group, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
weather derivatives [Member] | Sirius Group	'
Derivative [Line Items]	'
Realized and unrealized gains (losses)	$0.60

Municipal_Bond_Guarantee_Insur2

Municipal Bond Guarantee Insurance (Details) (USD $)

3 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Percentage of par value of policy reinsured

'

'

'

'

15.00%

'

'

'

'

15.00%

'

Pre-tax loss

$134.20

$55.30

$3.60

$151.80

($50.80)

$135.10

$37.60

$140.90

$344.90

$262.80

$98

Net investment income (loss) - surplus note interest

'

'

'

'

'

'

'

'

0

0

'

BAM

'

'

'

'

'

'

'

'

'

'

'

Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Statutory capital and surplus

469

'

'

'

'

'

'

'

469

'

'

Municipal bond contract

218

'

'

'

3

'

'

'

218

3

'

Insured Financial Obligations with Credit Deterioration, Remaining Weighted Average Contract Period

'

'

'

'

'

'

'

'

'13 years 9 months 21 days

'10 years 4 months 24 days

'

Municipal bond outstanding principal

4,703.70

'

'

'

25.8

'

'

'

4,703.70

25.8

'

Municipal bond outstanding interest

3,264.40

'

'

'

8.9

'

'

'

3,264.40

8.9

'

Financial Guarantee Insurance Contracts, Unearned Premium Revenue

13.2

'

'

'

0.1

'

'

'

13.2

0.1

'

White Mountains

'

'

'

'

'

'

'

'

'

'

'

Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Capital contributions

'

'

'

'

'

'

'

'

'

594.5

'

HG Global

'

'

'

'

'

'

'

'

'

'

'

Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Capital contributions

'

'

'

'

'

600

'

'

'

'

'

Ownership interest (as a percent)

97.30%

'

'

'

'

'

'

'

97.30%

'

'

Surplus notes

503

'

'

'

503

'

'

'

503

503

'

Percentage of par value of policy reinsured

15.00%

'

'

'

'

'

'

'

15.00%

'

'

BAM Management

'

'

'

'

'

'

'

'

'

'

'

Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Capital contributions

'

'

'

'

'

'

'

'

'

14.5

'

Preferred stocks | HG Global

'

'

'

'

'

'

'

'

'

'

'

Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Ownership interest (as a percent)

97.30%

'

'

'

97.30%

'

'

'

97.30%

97.30%

'

Common Stock | HG Global

'

'

'

'

'

'

'

'

'

'

'

Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Ownership interest (as a percent)

88.70%

'

'

'

88.70%

'

'

'

88.70%

88.70%

'

BAM

'

'

'

'

'

'

'

'

'

'

'

Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Surplus notes

503

'

'

'

'

'

'

'

503

'

'

Interest income (expense), surplus notes

'

'

'

'

'

'

'

'

-40.2

[1]

-18.4

[1]

'

HG Re

'

'

'

'

'

'

'

'

'

'

'

Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Statutory capital and surplus

436.9

'

'

'

412

'

'

'

436.9

412

'

HG Global

'

'

'

'

'

'

'

'

'

'

'

Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Percentage of par value of policy reinsured

15.00%

'

'

'

'

'

'

'

15.00%

'

'

Pre-tax loss

'

'

'

'

'

'

'

'

38.1

14.2

'

Net investment income (loss) - surplus note interest

'

'

'

'

'

'

'

'

40.2

18.4

'

Non-controlling Interests | BAM

'

'

'

'

'

'

'

'

'

'

'

Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Pre-tax loss

'

'

'

'

'

'

'

'

-78.6

[1]

-36.3

[1]

'

Surplus Note | HG Global

'

'

'

'

'

'

'

'

'

'

'

Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]

'

'

'

'

'

'

'

'

'

'

'

Interest Receivable

$58.60

'

'

'

'

'

'

'

$58.60

'

'

[1]

BAM manages its affairs on a statutory accounting basis. BAM’s statutory surplus includes surplus notes and is not reduced by accruals of interest expense on the surplus notes. BAM’s statutory surplus is reduced only after a payment of principal or interest has been approved by the New York Department of Financial Services.

Earnings_Per_Share_Details

Earnings Per Share (Details) (USD $)

3 Months Ended

12 Months Ended

In Millions, except Share data, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Earnings Per Share [Abstract]

'

'

'

'

'

'

'

'

'

'

'

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

'

'

'

'

'

'

'

'

$317.30

$322.40

$146.30

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

'

'

'

'

'

'

'

'

'

'

'

Allocation of income for unvested restricted common shares

'

'

'

'

'

'

'

'

-4.7

-4.3

-1.2

Dividends declared on participating restricted common shares(1)

'

'

'

'

'

'

'

'

-0.1

[1]

-0.1

[1]

-0.1

[1]

Total allocation to restricted common shares

'

'

'

'

'

'

'

'

-4.8

-4.4

-1.3

Net income attributable to White Mountains’ common shareholders, net of restricted share amounts

'

'

'

'

'

'

'

'

312.5

318

145

Undistributed net earnings (in millions):

'

'

'

'

'

'

'

'

'

'

'

Net income attributable to White Mountains’ common shareholders, net of restricted share amounts

'

'

'

'

'

'

'

'

312.5

318

145

Dividends declared net of restricted common share amounts(1)

'

'

'

'

'

'

'

'

-6.1

[1]

-6.5

[1]

-7.9

[1]

Total undistributed net earnings, net of restricted common share amounts

'

'

'

'

'

'

'

'

$306.40

$311.50

$137.10

Basic earnings per share denominators (in thousands):

'

'

'

'

'

'

'

'

'

'

'

Total average common shares outstanding during the period

'

'

'

'

'

'

'

'

6,200,400

6,799,800

7,881,000

Average unvested restricted common shares

'

'

'

'

'

'

'

'

-91,400

[2]

-91,100

[2]

-69,400

[2]

Basic earnings per share denominator

'

'

'

'

'

'

'

'

6,109,000

6,708,700

7,811,600

Diluted earnings per share denominator (in thousands):

'

'

'

'

'

'

'

'

'

'

'

Total average common shares outstanding during the period

'

'

'

'

'

'

'

'

6,200,400

6,799,800

7,881,000

Average unvested restricted common shares

'

'

'

'

'

'

'

'

-91,400

[2]

-91,100

[2]

-69,400

[2]

Average outstanding dilutive options to acquire common shares

'

'

'

'

'

'

'

'

0

[3]

0

[3]

0

[3]

Diluted earnings (loss) per share denominator

'

'

'

'

'

'

'

'

6,109,000

6,708,700

7,811,600

Basic earnings per share (in dollars):

'

'

'

'

'

'

'

'

'

'

'

Net income attributable to White Mountains’ common shareholders

$19.14

$9.20

$3.62

$19.10

$10.36

$19.11

$3.85

$13.85

$51.15

$47.41

$18.56

Dividends declared and paid

'

'

'

'

'

'

'

'

($1)

($1)

($1)

Undistributed earnings

'

'

'

'

'

'

'

'

$50.15

$46.41

$17.56

Diluted earnings per share (in dollars)

'

'

'

'

'

'

'

'

'

'

'

Net income attributable to White Mountains’ common shareholders

$19.14

$9.20

$3.62

$19.10

$10.36

$19.11

$3.85

$13.85

$51.15

$47.41

$18.56

Dividends declared and paid

'

'

'

'

'

'

'

'

($1)

($1)

($1)

Undistributed earnings

'

'

'

'

'

'

'

'

$50.15

$46.41

$17.56

Incremental common shares attributable to share-based payment arrangements

'

'

'

'

'

'

'

'

125,000

'

'

[1]

Restricted shares issued by White Mountains receive dividends, and therefore, are considered participating securities

[2]

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

[3]

The diluted earnings per share denominator for the years ended December 31, 2013, 2012 and 2011 do not include the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding as they are anti-dilutive to the calculation.

Retirement_and_Postretirement_2

Retirement and Postretirement Plans (Benefit Obligations) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Change in projected benefit obligation:	'		'		'
Projected benefit obligation at beginning of year	$119.50		$113		'
Service cost	0.8		0.7		0.8
Interest cost	4.2		4.7		5.2
Settlement gain	0		-0.7		'
Special termination benefit cost	0.3	[1]	0.6	[1]	0.8	[1]
Assumption changes	-13		11.2		'
Actuarial gain	-0.5		-0.2		'
Benefits and expenses paid with plan assets	6.2		7.5		'
Benefits paid directly by OneBeacon	2.2		2.3		'
Projected benefit obligation at end of year	102.9		119.5		113
Change in plan assets:	'		'		'
Fair value of plan assets at beginning of year	124.7		120.8		'
Actual return on plan assets	24.3		11.4		'
Benefits and expenses paid with plan assets	6.2		7.5		'
Fair value of plan assets at end of year	142.8		124.7		120.8
Funded status at end of year	39.9		5.2		'
Amounts recognized in the financial statements	'		'		'
Net assets of the Qualified Plan recorded in other assets	64.1		32.8		'
Net liabilities of the Non-qualified Plan recorded in other liabilities	-24.2		-27.6		'
Defined Benefit Plan, Amounts Recognized in Balance Sheet	39.9		5.2		'
Qualified Plan	'		'		'
Change in plan assets:	'		'		'
Fair value of plan assets at end of year	142.1		124		'
Amounts recognized in the financial statements	'		'		'
Net assets of the Qualified Plan recorded in other assets	64.1		'		'
Non-qualified Plan	'		'		'
Amounts recognized in the financial statements	'		'		'
Net liabilities of the Non-qualified Plan recorded in other liabilities	-24.2		'		'
Non-qualified Plan | OneBeacon Ltd.	'		'		'
Change in plan assets:	'		'		'
Amount set aside in irrevocable rabbi trust	$16.20		'		'
[1]	Special termination benefits represent additional payments made from the Qualified Plan to certain vested participants when their employment was terminated due to a reduction in force.

Retirement_and_Postretirement_3

Retirement and Postretirement Plans (Qualifed, Non-qualified, and Accumulated Benefit Obligations) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Amounts recognized in accumulated other comprehensive income (loss) on a pre-tax basis noncontrolling interest	'		'
Accumulated other comprehensive loss beginning balance	($21.20)		($16.70)
Increase (decrease) in accumulated other comprehensive income (loss):	'		'
Amortization of net actuarial losses recognized during the year	0.9		0.8
Net actuarial (losses) gains occurring during the year	30.8	[1]	-5.9	[1]
Other adjustments	0		0.6
Accumulated other comprehensive income (loss) ending balance	10.5		-21.2
OneBeacon Ltd.	'		'
Increase (decrease) in accumulated other comprehensive income (loss):	'		'
Amount expected to be amortized from accumulated other comprehensive income (loss) into net periodic benefit cost during 2012	'		0.3
Qualified Plan	'		'
Information for the Qualified Plan, which had accumulated benefit obligations less than plan assets	'		'
Projected benefit obligation	78.7		91.9
Accumulated benefit obligation	78.7		91.9
Fair value of plan net assets	142.8	[2]	124.7	[2]
Non-qualified Plan	'		'
Information for the Non-qualified Plan, which had accumulated benefit obligations in excess of plan assets	'		'
Projected benefit obligation	24.2		27.6
Accumulated benefit obligation	24.2		27.6
Fair value of plan assets	$0		$0
[1]	Net actuarial gains (losses) resulted from investment returns and demographic experience different than assumed, as well as changes in assumptions in estimating the projected benefit obligation in the years ended December 31, 2013 and 2012.
[2]	Includes receivables related to securities sold, interest and dividends as well as payables related to securities purchased.

Retirement_and_Postretirement_4

Retirement and Postretirement Plans (Periodic Benefit Cost) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Components of net periodic benefit cost (income)	'		'		'
Service cost	$0.80		$0.70		$0.80
Interest cost	4.2		4.7		5.2
Expected return on plan assets	-7.1		-6.9		-7.6
Amortization of unrecognized loss	0.9		0.8		0.5
Net periodic pension income before settlements, curtailments and special termination benefits	-1.2		-0.7		-1.1
Settlement loss	0		0.6		0.5
Special termination benefits expense	0.3	[1]	0.6	[1]	0.8	[1]
Total net periodic benefit (income) cost	($0.90)		$0.50		$0.20
Pension Plan, Defined Benefit [Member]	'		'		'
Defined Benefit Plan Disclosure [Line Items]	'		'		'
Discount Yield (as a percent)	4.66%		3.64%		'
Weighted average discount rate assumptions used to determine benefit obligations	'		'		'
Discount rate (as a percent)	3.64%		'		'
Pension Costs [Member]	'		'		'
Weighted average discount rate assumptions used to determine benefit obligations	'		'		'
Discount rate (as a percent)	'		4.38%		'
Long-Duration Contracts, Assumptions by Product and Guarantee, Estimated Average Investment Yield	5.75%		5.75%		'
[1]	Special termination benefits represent additional payments made from the Qualified Plan to certain vested participants when their employment was terminated due to a reduction in force.

Retirement_and_Postretirement_5

Retirement and Postretirement Plans (Qualified Plan's Assets) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Millions, unless otherwise specified
Plan Assets	'	'	'
Fair value	$142.80	$124.70	$120.80
Qualified Plan	'	'	'
Plan Assets	'	'	'
Fair value	142.1	124	'
Asset allocations (as a percent)	100.00%	100.00%	'
Qualified Plan | Level 1 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	112.1	87.6	'
Qualified Plan | Level 2 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	30	36.4	'
Qualified Plan | Level 3 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	0	0	'
Qualified Plan | Fixed maturity investments	'	'	'
Plan Assets	'	'	'
Fair value	0	1.9	'
Asset allocations (as a percent)	0.00%	1.50%	'
Qualified Plan | Fixed maturity investments | Level 1 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	0	0	'
Qualified Plan | Fixed maturity investments | Level 2 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	0	1.9	'
Qualified Plan | Fixed maturity investments | Level 3 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	0	0	'
Qualified Plan | Common equity securities	'	'	'
Plan Assets	'	'	'
Fair value	103.3	79.5	'
Asset allocations (as a percent)	72.70%	64.20%	'
Qualified Plan | Common equity securities | Level 1 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	103.3	79.5	'
Qualified Plan | Common equity securities | Level 2 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	0	0	'
Qualified Plan | Common equity securities | Level 3 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	0	0	'
Qualified Plan | Convertible fixed maturity investments	'	'	'
Plan Assets	'	'	'
Fair value	29.9	34.5	'
Asset allocations (as a percent)	21.10%	27.80%	'
Qualified Plan | Convertible fixed maturity investments | Level 1 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	0	0	'
Qualified Plan | Convertible fixed maturity investments | Level 2 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	29.9	34.5	'
Qualified Plan | Convertible fixed maturity investments | Level 3 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	0	0	'
Qualified Plan | Cash	'	'	'
Plan Assets	'	'	'
Fair value	8.9	8.1	'
Asset allocations (as a percent)	6.20%	6.50%	'
Qualified Plan | Cash | Level 1 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	8.8	8.1	'
Qualified Plan | Cash | Level 2 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	0.1	0	'
Qualified Plan | Cash | Level 3 Inputs	'	'	'
Plan Assets	'	'	'
Fair value	$0	$0	'

Retirement_and_Postretirement_6

Retirement and Postretirement Plans Retirement and Postretirment Plans (Assumptions) (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Pension Plan, Defined Benefit [Member]	'	'
Discount Yield (as a percent)	4.66%	3.64%
Discount rate (as a percent)	3.64%	'
Pension Costs [Member]	'	'
Discount rate (as a percent)	'	4.38%
Long-Duration Contracts, Assumptions by Product and Guarantee, Estimated Average Investment Yield	5.75%	5.75%

Retirement_and_Postretirement_7

Retirement and Postretirement Plans (Cash Flow) (Details) (USD $)

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2014

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

OneBeacon Ltd.

OneBeacon Ltd.

OneBeacon

OneBeacon

Sirius Group

Sirius Group

Sirius Group

Government Pension Plans [Member]

Government Pension Plans [Member]

Government Pension Plans [Member]

Defined Contribution Plan [Member]

Defined Contribution Plan [Member]

Defined Contribution Plan [Member]

Combination One [Member]

Combination Two [Member]

Maximum

Maximum

Minimum

One Beacon Employee Stock Ownership Plan

One Beacon Employee Stock Ownership Plan

One Beacon Employee Stock Ownership Plan

One Beacon Employee Stock Ownership Plan

One Beacon Employee Stock Ownership Plan

One Beacon Employee Stock Ownership Plan

IRS

IRS

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Defined Contribution Plan [Member]

Defined Contribution Plan [Member]

Sirius Group

Defined Contribution Plan [Member]

Defined Contribution Plan [Member]

OneBeacon

OneBeacon

OneBeacon

OneBeacon

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Expected Benefit Payments

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2014

'

'

'

'

$5,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2015

'

'

'

'

5,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2016

'

'

'

'

5,600,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2017

'

'

'

'

5,800,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2018

'

'

'

'

6,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2019-2023

'

'

'

'

33,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Employee savings plan

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Defined Contribution Plan, Employer Matching Contribution, Percent of Match

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100.00%

50.00%

'

'

'

50.00%

'

'

'

'

Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2.00%

4.00%

'

'

'

'

'

'

6.00%

'

'

'

'

Defined Contribution Plan, Cost Recognized

'

'

'

'

'

'

'

700,000

400,000

300,000

9,700,000

7,500,000

9,600,000

600,000

600,000

700,000

'

'

'

'

'

6,300,000

4,800,000

6,300,000

2,300,000

2,800,000

3,000,000

'

'

Anticipated contribution to plan

'

'

'

2,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Annual base contribution provided to participants expressed as percentage of salary

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3.00%

'

'

'

'

'

'

'

Social security wage base amount maximum

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

113,700

'

'

'

'

'

'

'

Variable contribution provided to participants (as percentage)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6.00%

'

'

'

'

'

'

'

Employer matching contribution variable contributions

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

7.00%

'

'

'

'

'

'

'

'

'

'

Deferred Benefit Plan Compensation Limits

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

255,000

255,000

Defined Benefit Plan, Benefit Obligation

102,900,000

119,500,000

113,000,000

'

'

'

'

'

'

'

13,100,000

12,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Funded status at end of year

39,900,000

5,200,000

'

'

'

'

'

'

'

'

1,000,000

1,700,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Post-employment benefit liability

'

'

'

'

'

$5,800,000

$7,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Employee_ShareBased_Incentive_2

Employee Share-Based Incentive Compensation Plans (WTM Performance Shares) (Details) (USD $)	12 Months Ended			12 Months Ended
	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2013
	One Beacon Employee Stock Ownership Plan	Performance Shares [Member]	Performance Shares [Member]	Performance Cycle From 2010 to 2012	W T M Incentive and Phantom Plan [Member]	Performance Cycle From 2010 to 2012	Performance Cycle From 2009 to 2011	Performance Cycle From 2009 to 2011	IRS
		White Mountains	W T M Incentive and Phantom Plan [Member]	W T M Incentive and Phantom Plan [Member]	Performance Shares [Member]	Performance Shares [Member]	Performance Shares [Member]	Performance Shares [Member]	OneBeacon
		multiplier				W T M Incentive and Phantom Plan [Member]		W T M Incentive and Phantom Plan [Member]
Share-based compensation arrangement by share-based payment award	'	'	'	'	'	'	'	'	'
Vesting period (in years)	'	'	'	'	'3 years	'	'	'	'
Annual base contribution provided to participants expressed as percentage of salary	3.00%	'	'	'	'	'	'	'	'
Social security wage base amount maximum	$113,700	'	'	'	'	'	'	'	'
Variable contribution provided to participants (as percentage)	6.00%	'	'	'	'	'	'	'	'
Deferred Benefit Plan Compensation Limits	'	'	'	'	'	'	'	'	255,000
Multiplier for determining payout, low end of range	'	0	'	'	'	'	'	'	'
Multiplier for determining payout, high end of range	'	2	'	'	'	'	'	'	'
Performance cycle period	'	'3 years	'	'	'	'	'	'	'
Performance goal percentage for minimum payout	'	'	'	'	'	33.00%	'	147.00%	'
Payout for maximum growth target percentage	'	'	'	'	'	98.00%	'	155.00%	'
Partial Payout for 2010 - 2012 cycle	'	'	'	9.9	'	'	'	'	'
Vested (in shares)	'	'	'	'	'	'	9,577	'	'
Unamortized grant date fair value	'	'	$33,800,000	'	'	'	'	'	'

Employee_ShareBased_Incentive_3

Employee Share-Based Incentive Compensation Plans (WTM Performance Shares Granted Under the WTM Incentive Plan) (Details) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Sep. 30, 2012
Target Performance Share activity	'		'		'		'
Assumed forfeitures and cancellations (in shares)	'		'		0		'
Accrued Expense	'		'		'		'
Accrued expense at the end of the period	$218.30		$159		'		'
W T M Incentive Plan	'		'		'		'
Target Performance Share activity	'		'		'		'
Beginning of period (in shares)	'		'		46,250		'
Assumed forfeitures and cancellations (in shares)	'		'		0		'
Ending of period (in shares)	'		'		72,000		'
Accrued Expense	'		'		'		'
Assumed forfeitures and cancellations	'		'		0		'
Expense recognized	'		'		10.7		'
Vested (in shares)	'		'		-1,500	[1]	'
W T M Incentive Plan | Performance Shares [Member]	'		'		'		'
Share-based compensation arrangement by share-based payment award	'		'		'		'
Options nonvested, number before forfeitures (in shares)	122,277		'		'		'
Incentive compensation payable before forfeitures	61.7		'		'		'
Target Performance Share activity	'		'		'		'
Ending of period (in shares)	119,220		'		'		'
Accrued Expense	'		'		'		'
Accrued expense at the end of the period	60.2		'		'		'
forfeitures	-3,057		'		'		'
Assumed forfeitures in period amount	-1.5		'		'		'
W T M Incentive and Phantom Plan [Member] | Performance Shares [Member]	'		'		'		'
Target Performance Share activity	'		'		'		'
Beginning of period (in shares)	119,357		150,064		163,184		119,357
Shares paid or expired (in shares)	-47,310	[2]	-68,357	[2]	-51,131	[2]	'
Assumed forfeitures and cancellations (in shares)	-3	[3]	-782	[3]	-336	[3]	'
New grants (in shares)	47,170		38,432		37,675		'
Ending of period (in shares)	119,220		119,357		150,064		119,357
Accrued Expense	'		'		'		'
Accrued expense at the beginning of period	29.4		66.1		29.4		29.4
Payments and deferrals	-11	[2]	-58.3	[2]	0	[2]	'
Assumed forfeitures and cancellations	-0.6	[3]	0.6	[3]	-0.9	[3]	'
Expense recognized	42.4		21		37.6		'
Accrued expense at the end of the period	60.2		29.4		66.1		29.4
Performance Cycle From 2011 to 2013 | W T M Incentive Plan | Performance Shares [Member]	'		'		'		'
Share-based compensation arrangement by share-based payment award	'		'		'		'
Targeted performance goal for personnel expressed as percentage of growth in intrinsic business value per share	10.00%		'		'		'
Options nonvested, number before forfeitures (in shares)	37,130		'		'		'
Incentive compensation payable before forfeitures	28.2		'		'		'
Accrued Expense	'		'		'		'
Share-based Compensation Arrangement by Share-based Payment Award, Payout for Maximum Growth Target Percentage	200.00%		'		'		'
Performance Cycle From 2013 to 2015 | W T M Incentive Plan | Performance Shares [Member]	'		'		'		'
Share-based compensation arrangement by share-based payment award	'		'		'		'
Targeted performance goal for personnel expressed as percentage of growth in intrinsic business value per share	8.00%		'		'		'
Options nonvested, number before forfeitures (in shares)	47,170		'		'		'
Incentive compensation payable before forfeitures	12.1		'		'		'
Accrued Expense	'		'		'		'
Share-based Compensation Arrangement by Share-based Payment Award, Payout for Maximum Growth Target Percentage	200.00%		'		'		'
Performance Cycle From 2012 to 2014 | W T M Incentive Plan | Performance Shares [Member]	'		'		'		'
Share-based compensation arrangement by share-based payment award	'		'		'		'
Targeted performance goal for personnel expressed as percentage of growth in intrinsic business value per share	8.00%		'		'		'
Options nonvested, number before forfeitures (in shares)	37,977		'		'		'
Incentive compensation payable before forfeitures	$21.40		'		'		'
Accrued Expense	'		'		'		'
Share-based Compensation Arrangement by Share-based Payment Award, Payout for Maximum Growth Target Percentage	200.00%		'		'		'
Performance Cycle From 2011 to 2013 | Minimum | W T M Incentive Plan | Performance Shares [Member]	'		'		'		'
Share-based compensation arrangement by share-based payment award	'		'		'		'
Performance goal percentage for minimum payout	3.00%		'		'		'
Performance Cycle From 2011 to 2013 | Maximum | W T M Incentive Plan | Performance Shares [Member]	'		'		'		'
Share-based compensation arrangement by share-based payment award	'		'		'		'
Performance goal percentage for minimum payout	17.00%		'		'		'
Performance Cycle From 2012 to 2014 | Minimum | W T M Incentive Plan | Performance Shares [Member]	'		'		'		'
Share-based compensation arrangement by share-based payment award	'		'		'		'
Performance goal percentage for minimum payout	2.00%		'		'		'
Performance Cycle From 2012 to 2014 | Maximum | W T M Incentive Plan | Performance Shares [Member]	'		'		'		'
Share-based compensation arrangement by share-based payment award	'		'		'		'
Performance goal percentage for minimum payout	14.00%		'		'		'
Performance Cycle From 2013 to 2015 | Minimum | W T M Incentive Plan | Performance Shares [Member]	'		'		'		'
Share-based compensation arrangement by share-based payment award	'		'		'		'
Performance goal percentage for minimum payout	2.00%		'		'		'
Performance Cycle From 2013 to 2015 | Maximum | W T M Incentive Plan | Performance Shares [Member]	'		'		'		'
Share-based compensation arrangement by share-based payment award	'		'		'		'
Performance goal percentage for minimum payout	14.00%		'		'		'
[1]	During 2012, the Compensation Committee accelerated the vesting date for an installment of 5,000 restricted shares from January 20, 2013 to December 31, 2012.
[2]	WTM performance shares 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. At December 31, 2012, White Mountains paid $9.9 as a partial payment for the 2010-2012 performance cycle. There were no payments made in 2011 for the 2008-2010 performance cycle; those performance shares did not meet the threshold performance goal and expired.
[3]	Amounts include changes in assumed forfeitures, as required under GAAP.

Employee_ShareBased_Incentive_4

Employee Share-Based Incentive Compensation Plans (WTM Restricted Shares) (Details) (USD $)

12 Months Ended

In Millions, except Share data, unless otherwise specified

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Restricted Share Cliff Vesting in January 2016 [Member]

Restricted Share Cliff Vesting in January 2015 [Member]

Restricted Share Vesting Beginning in February 2014 [Member]

Restricted Share Cliff Vesting in July 2015 [Member]

Restricted Share Cliff Vesting in January 2014 [Member]

W T M Incentive Plan

W T M Incentive Plan

W T M Incentive Plan

Restricted Share Vested in December 2012 [Member]

Installment

Restricted Stock

Restricted Stock

Restricted Stock

Target Performance Share activity

'

'

'

'

'

'

'

'

'

'

Beginning of period (in shares)

'

'

'

'

'

'

46,250

69,910

72,000

'

Issued (in shares)

'

25,720

27,960

3,000

1,200

27,250

27,250

25,720

32,160

'

Vested (in shares)

'

'

'

'

'

'

-1,500

[1]

-1,500

[1]

-32,945

[1]

'

Assumed forfeitures and cancellations (in shares)

0

'

'

'

'

'

0

0

-1,305

'

Ending of period (in shares)

'

'

'

'

'

'

72,000

94,130

69,910

'

Unamortized grant date fair value

'

'

'

'

'

'

'

'

'

'

Beginning balance

'

'

'

'

'

'

$14.10

$16.80

$13.30

'

Issued

'

'

'

'

'

'

9.9

14.4

15.7

'

Assumed forfeitures and cancellations

'

'

'

'

'

'

0

0

-0.2

'

Expense recognized

'

'

'

'

'

'

-10.7

-14.2

-12

'

Ending balance

'

'

'

'

'

'

$13.30

$17

$16.80

'

Number of restricted shares installments

'

'

'

2

'

'

'

'

'

5,000

[1]

During 2012, the Compensation Committee accelerated the vesting date for an installment of 5,000 restricted shares from January 20, 2013 to December 31, 2012.

Employee_ShareBased_Incentive_5

Employee Share-Based Incentive Compensation Plans (WTM Non-Qualified and Qualified Options) (Details) (Non-Qualified Options, USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2011
Non-Qualified Options	'	'
Share-based compensation arrangement by share-based payment award	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	125,000	'
Exercise price (in dollar per share)	$742	'
Threshold for in-the-money potential	$100	'
Limit on value of in-the-money options over $100 million (as a percent)	50.00%	'
Expense recognized	'	$0.10

Employee_ShareBased_Incentive_6

Employee Share-Based Incentive Compensation Plans (OneBeason Peformance Shares) (Details) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Target options outstanding	'		'		'
Assumed forfeitures and cancellations (in shares)	'		'		0
Expense Amortized	'		'		'
Accrued expense at the end of the period	$218.30		$159		'
One Beacon Insurance Company | Performance Shares [Member] | Long Term Incentive Plan	'		'		'
Target options outstanding	'		'		'
Beginning of period (in shares)	563,190		642,667		1,464,295
Shares paid or expired (in shares)	-238,658	[1]	-258,901	[1]	-936,150	[1]
New grants (in shares)	179,000		181,290		194,900
Assumed forfeitures and cancellations (in shares)	-10,111	[2]	-1,866	[2]	-80,378	[2]
Ending of period (in shares)	493,421		563,190		642,667
Expense Amortized	'		'		'
Accrued expense at the beginning of period	1.2		9.7		18.5
Payments and deferrals	0	[1]	-7.7	[1]	-10.5	[1]
Assumed forfeitures and cancellations	-0.1	[2]	0	[2]	-0.5	[2]
Expense recognized	2.9		-0.8		2.2
Accrued expense at the end of the period	$4		$1.20		$9.70
Range of Performance Cycle from 2008 to 2010 | Long Term Incentive Plan	'		'		'
Expense Amortized	'		'		'
Percentage of payout for minimum growth target percentage	'		'		68.50%
Performance Cycle From 2009 to 2011 | Long Term Incentive Plan	'		'		'
Expense Amortized	'		'		'
Percentage of payout for minimum growth target percentage	'		138.60%		'
[1]	No payments were made in 2013 for the 2010-2012 OneBeacon performance cycle as the performance factor was zero. OneBeacon performance share payments in 2012 for the 2009-2011 performance cycle were at 138.6% of target. OneBeacon performance shares payments in 2011 for the 2008-2010 performance cycle were at 68.5% of target. Amounts include deposits into OneBeacon’s deferred compensation plan.
[2]	Amounts include changes in assumed forfeitures, as required under GAAP.

Employee_ShareBased_Incentive_7

Employee Share-Based Incentive Compensation Plans (OneBeacon Performance Shares Outstanding) (Details) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based compensation arrangement by share-based payment award	'	'	'
Accrued incentive compensation	$218.30	159	'
OneBeacon | Performance Shares [Member] | Long Term Incentive Plan	'	'	'
Share-based compensation arrangement by share-based payment award	'	'	'
Options nonvested, number before forfeitures (in shares)	502,428	'	'
Incentive compensation payable before forfeitures	4.1	'	'
forfeitures	-9,007	'	'
Assumed forfeitures in period amount	-0.1	'	'
Shares outstanding (in shares)	493,421	'	'
Accrued incentive compensation	4	'	'
Unamortized grant date fair value	2.9	'	'
Targeted performance goal for personnel expressed as percentage of growth in intrinsic business value per share	13.00%	10.00%	11.00%
Performance Cycle From 2011 to 2013 | OneBeacon | Performance Shares [Member] | Long Term Incentive Plan	'	'	'
Share-based compensation arrangement by share-based payment award	'	'	'
Options nonvested, number before forfeitures (in shares)	142,138	'	'
Incentive compensation payable before forfeitures	1	'	'
Performance Cycle From 2012 to 2014 | OneBeacon | Performance Shares [Member] | Long Term Incentive Plan	'	'	'
Share-based compensation arrangement by share-based payment award	'	'	'
Options nonvested, number before forfeitures (in shares)	181,290	'	'
Incentive compensation payable before forfeitures	2.1	'	'
Performance Cycle From 2013 to 2015 | OneBeacon | Performance Shares [Member] | Long Term Incentive Plan	'	'	'
Share-based compensation arrangement by share-based payment award	'	'	'
Options nonvested, number before forfeitures (in shares)	179,000	'	'
Incentive compensation payable before forfeitures	$1	'	'
Minimum | OneBeacon | Performance Shares [Member] | Long Term Incentive Plan	'	'	'
Share-based compensation arrangement by share-based payment award	'	'	'
Performance goal percentage for minimum payout	6.00%	3.00%	4.00%
Maximum | OneBeacon | Performance Shares [Member] | Long Term Incentive Plan	'	'	'
Share-based compensation arrangement by share-based payment award	'	'	'
Performance goal percentage for minimum payout	20.00%	17.00%	18.00%
Percentage of performance shares earned	200.00%	200.00%	200.00%

Employee_ShareBased_Incentive_8

Employee Share-Based Incentive Compensation Plans (OneBeacon Restsricted Shares) (Details) (USD $)	12 Months Ended		1 Months Ended	12 Months Ended			0 Months Ended	1 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2013	31-May-11	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 01, 2012	31-May-11	25-May-11
		Restricted Stock	Restricted Stock	Restricted Stock	Restricted Stock	Restricted Stock	Restricted Stock	Restricted Stock	Restricted Stock
			One Beacon Insurance Company	One Beacon Insurance Company	One Beacon Insurance Company	One Beacon Insurance Company	One Beacon Insurance Company	One Beacon Insurance Company	One Beacon Insurance Company
			Long Term Incentive Plan	Long Term Incentive Plan	Long Term Incentive Plan	Long Term Incentive Plan	Long Term Incentive Plan	Long Term Incentive Plan	Long Term Incentive Plan
							Chief Executive Officer	Chief Executive Officer	Chief Executive Officer
							Installment		Installment
Target Performance Share activity	'	'	'	'	'	'	'	'	'
Beginning of period (in shares)	'	'	'	927,000	630,000	0	'	'	'
Issued (in shares)	'	'	'	0	300,000	630,000	300,000	630,000	'
Vested (in shares)	'	'	'	-9,000	-667	0	'	'	'
Assumed forfeitures and cancellations (in shares)	0	'	'	-3,000	-2,333	'	'	'	'
Ending of period (in shares)	'	'	'	915,000	927,000	630,000	'	'	'
Beginning balance	'	'	'	$9.60	$7.70	$0	'	'	'
Issued	'	'	'	0	4.5	8.6	'	'	'
Vested	'	0	'	'	'	0	'	'	'
Assumed forfeitures and cancellations	'	'	'	0	0	0	'	'	'
Expense recognized	'	'	'	-3.1	-2.6	-0.9	'	'	'
Ending balance	'	'	'	$6.50	$9.60	$7.70	'	'	'
Number of installments in which the shares vest	'	'	'	'	'	'	2	'	4
Forfeited shares	'	'	35,000	'	'	'	'	35,000	'
Years performance shares will be forfeited	'	'	'	'	'	'	'	'5 years	'

Employee_ShareBased_Incentive_9

Employee Share-Based Incentive Compensation Plans (Under Qualified Retirement Plans) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Qualified Plan	'	'	'
Share-based compensation arrangement by share-based payment award	'	'	'
Eligible contribution percentage	4.00%	3.00%	2.00%
Percentage of common shares outstanding	3.00%	3.00%	'
One Beacon Employee Stock Ownership Plan	'	'	'
Share-based compensation arrangement by share-based payment award	'	'	'
Defined Contribution Plan, Cost Recognized	6.3	4.8	6.3

Common_Shareholders_Equity_Det

Common Shareholders' Equity (Details) (USD $)

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

In Millions, except Share data, unless otherwise specified

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Nov. 17, 2006

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2012

Dec. 31, 2012

Common Stock

Common Stock

Common Stock

Restricted Stock

Restricted Stock

Restricted Stock

Performance Shares [Member]

Common Stock

Common Stock

Common Stock

Combination Two [Member]

Combination Two [Member]

General Board Authorization [Member]

General Board Authorization [Member]

General Board Authorization [Member]

General Board Authorization [Member]

Other Pension Plan, Postretirement or Supplemental Plans, Defined Benefit [Member]

Other Pension Plan, Postretirement or Supplemental Plans, Defined Benefit [Member]

Other Pension Plan, Postretirement or Supplemental Plans, Defined Benefit [Member]

Tender Offer [Member]

Tender Offer [Member]

STO

Common Stock

Combination Three [Member]

Combination Three [Member]

Combination Three [Member]

Combination Two [Member]

Combination Two [Member]

Common Stock

Common Shares Repurchased and Retired [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Authorized repurchase of common shares

'

2,600,000

'

1,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Additional authorized repurchase of common shares

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

545,496

1,000,000

'

600,000

'

'

'

'

'

Common shares repurchased and retired during the period

'

1,329,640

'

'

'

'

'

'

'

'

'

141,535

1,329,640

646,502

'

332,346

140,000

502,801

313,967

'

'

'

'

'

816,829

Number of Modified Dutch Auction

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2

'

'

'

'

'

'

'

'

'

'

Value of common shares repurchased and retired during the period

$79.80

$669.10

$253

'

$79.80

$669.10

$253

'

'

'

'

'

'

'

$138.80

'

$78.90

$256

$114

'

'

'

'

$408.60

'

Value of each common share repurchased and retired during the period (in dollars per share)

$564

$503

$390

'

'

'

'

'

'

'

'

'

'

'

$417.55

'

$564

$508

$364

'

$1,535

$10,010

$189

$500

'

Stock Issued During Period, Shares, New Issues

27,310

44,054

29,432

'

'

'

'

25,720

700

'

9,577

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common shares, issued shares

6,176,739

6,290,964

'

'

'

'

'

'

32,160

27,250

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common Shares Issued [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares issued to directors (in shares)

1,590

1,617

2,182

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Dividends, Common Stock [Abstract]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Cash dividends declared and paid

$6.20

$6.60

$8

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Dividends delared and paid (in dollars per share)

$1

$1

$1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Statutory_Capital_and_Surplus_

Statutory Capital and Surplus (Details) (USD $)

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Jan. 02, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Split Rock [Member]

Sirius Group

Sirius Group

OneBeacon

OneBeacon

OneBeacon

Other Operations

Other Operations

Regulated Operation

Regulated Operation

Unregulated Operation

OneBeacon

Sirius International

Sirius International

Sirius International

Sirius International

Sirius International

HG Global

HG Re

BAM

Subsidiaries

One Beacon Insurance Company

One Beacon Insurance Company

Split Rock [Member]

White Mountains

Atlantic Speciality Insurance Company (ASIC) [Member]

Atlantic Speciality Insurance Company (ASIC) [Member]

Atlantic Speciality Insurance Company (ASIC) [Member]

Sirius America

Sirius America

Sirius America

Sirius America

Central National

Central National

Woodridge

Woodridge

Oakwood

Oakwood

PICO Holdings

Citation

Citation

Ashmere [Member]

Empire [Member]

White Shoals Reinsurance Company

White Mountains Life Re

White Mountains Advisors LLC

Surplus Note

SWEDEN

SWEDEN

Preferred stocks

Preferred stocks

SEK

SEK

SEK

SEK

Common Stock [Member]

Common Equities [Member]

Retained earnings

Retained earnings

Retained earnings

Retained earnings

Retained earnings

U.S and Bermuda [Member]

U.S and Bermuda [Member]

UNITED STATES

OneBeacon

OneBeacon

OneBeacon

Sirius Group

Sirius Group

Regulated Operation

Regulated Operation

Regulated Operation

Regulated Operation

Regulated Operation

Sirius Group

Sirius Group

Sirius Group

Regulated Operation

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Sirius Group

Sirius Group

BAM

Sirius Group

Sirius Group

HG Global

White Mountains

Sirius International

OneBeacon

Other Operations

Split Rock [Member]

OneBeacon

OneBeacon

OneBeacon

Sirius Group

Sirius Group

OneBeacon

OneBeacon

OneBeacon

Sirius Group

HG Global

Sirius Group

Statutory Accounting Practices [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Statutory capital and surplus

'

'

$96,400,000

'

'

$866,200,000

'

'

'

'

'

$900,000,000

'

'

'

'

$2,500,000,000

'

'

'

$436,900,000

$469,000,000

'

'

'

'

'

'

'

$700,000,000

$548,400,000

$528,300,000

'

'

$9,300,000

$11,200,000

$8,400,000

$8,600,000

$20,700,000

$24,500,000

'

$11,900,000

$13,100,000

$12,700,000

$10,700,000

$14,600,000

$85,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$1,000,000,000

$900,000,000

$900,000,000

Payments of Capital Distribution

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

190,000,000

'

'

'

190,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Proceeds from Contributions from Affiliates

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

35,000,000

'

135,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Statutory net income (loss)

'

'

'

'

'

100,100,000

82,000,000

119,600,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

55,900,000

26,200,000

101,400,000

'

-500,000

1,700,000

-100,000

100,000

-900,000

3,900,000

'

-300,000

-4,200,000

-400,000

-10,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Restricted equity

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,700,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Surplus required

'

'

'

'

'

164,700,000

'

'

'

'

'

'

'

'

'

'

132,400,000

'

'

'

'

66,000,000

'

'

'

'

'

'

'

'

113,900,000

'

'

'

1,500,000

'

0

'

2,200,000

'

6,300,000

100,000

'

4,600,000

1,400,000

6,200,000

700,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stockholders' Equity Attributable to Parent

3,905,500,000

3,731,800,000

'

1,459,600,000

1,559,700,000

830,600,000

763,100,000

'

1,025,800,000

802,800,000

'

'

'

'

'

'

'

'

'

'

'

'

2,800,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2,802,300,000

2,542,700,000

2,789,700,000

2,175,600,000

'

'

'

'

Amount available for dividend distributions without prior approval from regulatory authorities

800,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

86,600,000

'

'

'

'

23,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

755,000,000

'

'

'

20,300,000

'

'

'

Statutory Accounting Practices, Statutory Capital, Percent

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

15.00%

'

'

'

Dividends available, net of noncontrolling interest

'

'

'

'

'

'

'

'

'

'

'

'

'

246,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of prior year statutory surplus that may be paid as dividends without prior approval of regulatory authorities

'

'

'

'

'

'

'

'

'

'

10.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

10.00%

'

'

10.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unassigned funds

'

'

'

'

'

'

'

'

'

'

'

600,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Cash Dividends Paid to Parent Company

'

'

'

250,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Cash dividends declared to parent company by consolidated subsidiaries

'

'

'

'

75,000,000

'

'

'

'

'

'

'

'

'

'

'

'

75,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Distributions made

6,200,000

'

'

'

'

'

80,200,000

'

'

'

'

'

17,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

60,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net unrestricted cash, short-term investments and fixed maturity investments

'

'

'

67,000,000

'

217,500,000

'

'

231,000,000

'

'

'

57,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

17,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Trading Securities

5,347,300,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

89,800,000

490,200,000

'

'

'

'

'

'

'

'

Pre-tax income transferred to parent company

'

'

'

'

'

'

'

'

'

'

'

'

'

'

101,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unrestricted statutory surplus available for distribution

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

587,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Cash Dividends Paid to Parent Company by Consolidated Subsidiaries

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

326,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

75,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Equity held in insurance and reinsurance subsidiaries

'

2,000,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Statutory accounting practices earned surplus

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

94,600,000

33,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Exchange rate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6.43

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6.4339

6.4973

6.8645

'

'

'

'

'

'

'

'

'

'

'

Effective income tax

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

22.00%

26.30%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Other long-term investments

288,900,000

294,200,000

'

20,300,000

'

'

'

'

139,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Safety Reserve

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amount of safety reserve

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,600,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

10,400,000,000

'

'

'

'

'

'

'

'

'

'

Deferred Tax Liabilities, Safety Reserve

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

357,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Statutory capital and surplus required, percent

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

125.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Maximum contributions per bankruptcy agreement

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

200,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ratio limitation

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

70.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Expense limitation

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

90,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Preferred stock, value

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

613,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ownership interest (as a percent)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

97.30%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Preferred stock dividend rate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Dividends Payable

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

55,200,000

53,700,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Accrued interest on surplus notes

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

35,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Collateral Held in Supplement Trust

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$400,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate (as a percent)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

8.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Segment_Information_Details

Segment Information (Details) (USD $)

3 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Segment reporting information

'

'

'

'

'

'

'

'

'

'

'

Earned insurance and reinsurance premiums

'

'

'

'

'

'

'

'

$1,987.30

$2,063.60

$1,924.50

Net investment income

'

'

'

'

'

'

'

'

110.9

153.6

184.5

Net investment income (loss) - surplus note interest

'

'

'

'

'

'

'

'

0

0

'

Net realized and unrealized investment gains

'

'

'

'

'

'

'

'

161.7

118.2

74.1

Other revenue

'

'

'

'

'

'

'

'

57.5

100.3

-10

Total revenues

626.6

574.1

489.3

627.4

566.4

697.4

542.3

629.7

2,317.40

2,435.70

2,173.10

Loss and loss adjustment expenses

'

'

'

'

'

'

'

'

1,040.50

1,193.90

1,174.30

Insurance and reinsurance acquisition expenses

'

'

'

'

'

'

'

'

376.9

430.2

402.2

Other underwriting expenses

'

'

'

'

'

'

'

'

331.3

321.8

268.1

General and administrative expenses

'

'

'

'

'

'

'

'

181.3

182.2

175.3

Interest expense on debt

'

'

'

'

'

'

'

'

42.5

44.8

55.2

Total expenses

492.4

518.8

485.7

475.6

617.2

562.3

504.7

488.8

1,972.50

2,172.90

2,075.10

Pre-tax income

134.2

55.3

3.6

151.8

-50.8

135.1

37.6

140.9

344.9

262.8

98

Percentage of par value of policy reinsured

'

'

'

'

15.00%

'

'

'

'

15.00%

'

Sirius Group Segment [Member]

'

'

'

'

'

'

'

'

'

'

'

Segment reporting information

'

'

'

'

'

'

'

'

'

'

'

Earned insurance and reinsurance premiums

'

'

'

'

'

'

'

'

866.4

931.6

912.3

Pre-tax income

'

'

'

'

'

'

'

'

'

171.3

'

OneBeacon

'

'

'

'

'

'

'

'

'

'

'

Segment reporting information

'

'

'

'

'

'

'

'

'

'

'

Earned insurance and reinsurance premiums

'

'

'

'

'

'

'

'

1,120.40

[1]

1,132

[1]

1,012.20

[1]

Net investment income

'

'

'

'

'

'

'

'

41.1

53.6

71.4

Net investment income (loss) - surplus note interest

'

'

'

'

'

'

'

'

0

0

'

Net realized and unrealized investment gains

'

'

'

'

'

'

'

'

49.4

55.7

10.6

Other revenue

'

'

'

'

'

'

'

'

31.2

-0.5

-12.4

Total revenues

'

'

'

'

'

'

'

'

1,242.10

1,240.80

1,081.80

Loss and loss adjustment expenses

'

'

'

'

'

'

'

'

622.1

650

548.3

Insurance and reinsurance acquisition expenses

'

'

'

'

'

'

'

'

208.9

249.4

221.2

Other underwriting expenses

'

'

'

'

'

'

'

'

204.8

205.2

162.3

General and administrative expenses

'

'

'

'

'

'

'

'

12

13.4

9.8

Interest expense on debt

'

'

'

'

'

'

'

'

13

16.9

20.5

Total expenses

'

'

'

'

'

'

'

'

1,060.80

1,134.90

962.1

Pre-tax income

'

'

'

'

'

'

'

'

181.3

105.9

119.7

Sirius Group

'

'

'

'

'

'

'

'

'

'

'

Segment reporting information

'

'

'

'

'

'

'

'

'

'

'

Earned insurance and reinsurance premiums

'

'

'

'

'

'

'

'

866.4

931.6

912.3

Net investment income

'

'

'

'

'

'

'

'

48.8

65

89.9

Net investment income (loss) - surplus note interest

'

'

'

'

'

'

'

'

0

0

'

Net realized and unrealized investment gains

'

'

'

'

'

'

'

'

26.7

17.3

53.2

Other revenue

'

'

'

'

'

'

'

'

16.8

70.6

4.1

Total revenues

'

'

'

'

'

'

'

'

958.7

1,084.50

1,059.50

Loss and loss adjustment expenses

'

'

'

'

'

'

'

'

418.4

543.9

626

Insurance and reinsurance acquisition expenses

'

'

'

'

'

'

'

'

166.5

180.8

181

Other underwriting expenses

'

'

'

'

'

'

'

'

126.1

116.4

105.8

General and administrative expenses

'

'

'

'

'

'

'

'

32.2

45.9

34.1

Interest expense on debt

'

'

'

'

'

'

'

'

26.3

26.2

31.6

Total expenses

'

'

'

'

'

'

'

'

769.5

913.2

978.5

Pre-tax income

'

'

'

'

'

'

'

'

189.2

'

81

BAM

'

'

'

'

'

'

'

'

'

'

'

Segment reporting information

'

'

'

'

'

'

'

'

'

'

'

Earned insurance and reinsurance premiums

'

'

'

'

'

'

'

'

0.1

[2]

0

'

Net investment income

'

'

'

'

'

'

'

'

4.7

[2]

1.9

[2]

'

Interest income (expense), surplus notes

'

'

'

'

'

'

'

'

-40.2

[2]

-18.4

[2]

'

Net realized and unrealized investment gains

'

'

'

'

'

'

'

'

-9.3

[2]

0

[2]

'

Other revenue

'

'

'

'

'

'

'

'

0.4

[2]

0

[2]

'

Total revenues

'

'

'

'

'

'

'

'

-44.3

[2]

-16.5

[2]

'

Loss and loss adjustment expenses

'

'

'

'

'

'

'

'

0

[2]

0

[2]

'

Insurance and reinsurance acquisition expenses

'

'

'

'

'

'

'

'

1.4

[2]

0

[2]

'

Other underwriting expenses

'

'

'

'

'

'

'

'

0.4

[2]

0.2

[2]

'

General and administrative expenses

'

'

'

'

'

'

'

'

32.5

[2]

19.6

[2]

'

Interest expense on debt

'

'

'

'

'

'

'

'

0

[2]

0

[2]

'

Total expenses

'

'

'

'

'

'

'

'

34.3

[2]

19.8

[2]

'

HG Global

'

'

'

'

'

'

'

'

'

'

'

Segment reporting information

'

'

'

'

'

'

'

'

'

'

'

Earned insurance and reinsurance premiums

'

'

'

'

'

'

'

'

0.4

0

'

Net investment income

'

'

'

'

'

'

'

'

1

0.3

'

Net investment income (loss) - surplus note interest

'

'

'

'

'

'

'

'

40.2

18.4

'

Net realized and unrealized investment gains

'

'

'

'

'

'

'

'

-2

0

'

Other revenue

'

'

'

'

'

'

'

'

0

0

'

Total revenues

'

'

'

'

'

'

'

'

39.6

18.7

'

Loss and loss adjustment expenses

'

'

'

'

'

'

'

'

0

0

'

Insurance and reinsurance acquisition expenses

'

'

'

'

'

'

'

'

0.1

0

'

Other underwriting expenses

'

'

'

'

'

'

'

'

0

0

'

General and administrative expenses

'

'

'

'

'

'

'

'

1.4

4.5

'

Interest expense on debt

'

'

'

'

'

'

'

'

0

0

'

Total expenses

'

'

'

'

'

'

'

'

1.5

4.5

'

Pre-tax income

'

'

'

'

'

'

'

'

38.1

14.2

'

Percentage of par value of policy reinsured

15.00%

'

'

'

'

'

'

'

15.00%

'

'

Other Operations

'

'

'

'

'

'

'

'

'

'

'

Segment reporting information

'

'

'

'

'

'

'

'

'

'

'

Earned insurance and reinsurance premiums

'

'

'

'

'

'

'

'

0

0

0

Net investment income

'

'

'

'

'

'

'

'

15.3

32.8

23.2

Net investment income (loss) - surplus note interest

'

'

'

'

'

'

'

'

0

0

'

Net realized and unrealized investment gains

'

'

'

'

'

'

'

'

96.9

45.2

10.3

Other revenue

'

'

'

'

'

'

'

'

9.1

30.2

-1.7

Total revenues

'

'

'

'

'

'

'

'

121.3

108.2

31.8

Loss and loss adjustment expenses

'

'

'

'

'

'

'

'

0

0

0

Insurance and reinsurance acquisition expenses

'

'

'

'

'

'

'

'

0

0

0

Other underwriting expenses

'

'

'

'

'

'

'

'

0

0

0

General and administrative expenses

'

'

'

'

'

'

'

'

103.2

98.8

131.4

Interest expense on debt

'

'

'

'

'

'

'

'

3.2

1.7

3.1

Total expenses

'

'

'

'

'

'

'

'

106.4

100.5

134.5

Pre-tax income

'

'

'

'

'

'

'

'

14.9

7.7

-102.7

Non-controlling Interests | BAM

'

'

'

'

'

'

'

'

'

'

'

Segment reporting information

'

'

'

'

'

'

'

'

'

'

'

Pre-tax income

'

'

'

'

'

'

'

'

($78.60)

[2]

($36.30)

[2]

'

[1]

The amounts shown excludes balances reclassified to held for sale in the consolidated balance sheets related to the Runoff Transaction as of December 31, 2013 and 2012 and to AutoOne as of December 31, 2011. See Note 21 - “Discontinued Operations”.

[2]

BAM manages its affairs on a statutory accounting basis. BAM’s statutory surplus includes surplus notes and is not reduced by accruals of interest expense on the surplus notes. BAM’s statutory surplus is reduced only after a payment of principal or interest has been approved by the New York Department of Financial Services.

Segment_Information_Assets_Det

Segment Information (Assets) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
In Millions, unless otherwise specified
Segment reporting information	'		'		'	'
Total investments	$7,192.60		$7,278.10		'	'
Reinsurance recoverables, gross	453.5		447		'	'
Assets held for sale	1,880.10		2,226.80		'	'
Assets	12,144.30		12,895.40		'	'
Loss and loss adjustment expense reserves	3,079.30		3,168.90		5,702.30	5,736.80
Liabilities held for sale	1,880.10		2,226.80		'	'
Liabilities	7,746.90		8,637.20		'	'
Total non-controlling interests	491.9		526.4		'	'
White Mountains’ common shareholders’ equity	3,905.50		3,731.80		'	'
OneBeacon	'		'		'	'
Segment reporting information	'		'		'	'
Total investments	2,364.90		2,291.50		'	'
Reinsurance recoverables, gross	89.9		110.7		'	'
Assets held for sale	1,880.10		2,226.80		'	'
Assets	5,191.30		5,382.30		'	'
Loss and loss adjustment expense reserves	1,054.30		1,000		'	'
Liabilities held for sale	1,880.10		2,226.80		'	'
Liabilities	4,083.90		4,365		'	'
Total non-controlling interests	276.8		254.2		'	'
White Mountains’ common shareholders’ equity	830.6		763.1		'	'
Sirius Group	'		'		'	'
Segment reporting information	'		'		'	'
Total investments	3,251.40		3,534.30		'	'
Reinsurance recoverables, gross	363.6	[1]	336.3		'	'
Assets held for sale	0		0		'	'
Assets	5,124.10		5,962		'	'
Loss and loss adjustment expense reserves	2,025		2,168.90		'	'
Liabilities held for sale	0		0		'	'
Liabilities	3,414.50		4,123.20		'	'
Total non-controlling interests	250		279.1		'	'
White Mountains’ common shareholders’ equity	1,459.60		1,559.70		'	'
HG Global	'		'		'	'
Segment reporting information	'		'		'	'
Total investments	107.9		101.5		'	'
Reinsurance recoverables, gross	0		0		'	'
Assets held for sale	0		0		'	'
Assets	675		623.6		'	'
Loss and loss adjustment expense reserves	0		0		'	'
Liabilities held for sale	0		0		'	'
Liabilities	68.9		0.9		'	'
Total non-controlling interests	16.6		16.6		'	'
White Mountains’ common shareholders’ equity	589.5		606.2		'	'
BAM	'		'		'	'
Segment reporting information	'		'		'	'
Surplus notes	503		'		'	'
Total investments	468.6		472.4		'	'
Reinsurance recoverables, gross	0		0		'	'
Assets held for sale	0		0		'	'
Assets	-77.9	[2]	-28.6	[2]	'	'
Loss and loss adjustment expense reserves	0		0		'	'
Liabilities held for sale	0		0		'	'
Liabilities	19.7		7.4		'	'
Total non-controlling interests	-97.6		-36		'	'
White Mountains’ common shareholders’ equity	0		0		'	'
Accrued interest on surplus notes	58.6		18.4		'	'
Other Operations	'		'		'	'
Segment reporting information	'		'		'	'
Total investments	999.8		878.4		'	'
Reinsurance recoverables, gross	0		0		'	'
Assets held for sale	0		0		'	'
Assets	1,231.80		956.1		'	'
Loss and loss adjustment expense reserves	0		0		'	'
Liabilities held for sale	0		0		'	'
Liabilities	159.9		140.7		'	'
Total non-controlling interests	46.1		12.5		'	'
White Mountains’ common shareholders’ equity	$1,025.80		$802.80		'	'
[1]	Standard & Poor’s ratings as detailed above are: “AAA” (Extremely strong), “AA” (Very strong), “A” (Strong), and “BBB+” and “BBB” (Adequate).
[2]	BAM total assets reflect the elimination of $503.0 in surplus notes issued to HG Global and its subsidiaries, and $58.6 and $18.4 in accrued interest related to those surplus notes as of December 31, 2013 and 2012.

Investments_in_Unconsolidated_2

Investments in Unconsolidated Affiliates (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
In Millions, unless otherwise specified
Investments in unconsolidated affiliates	'		'		'		'
Investments in unconsolidated affiliates	$321.40		$387.90		'		'
Symetra	'		'		'		'
Investments in unconsolidated affiliates	'		'		'		'
Unrealized (losses) gains from Symetra’s fixed maturity portfolio	-43.6		62.8		'		'
Investments in unconsolidated affiliates	317.3	[1],[2]	381.5	[3]	273.6	[3]	387.5
Symetra | Common Stock	'		'		'		'
Investments in unconsolidated affiliates	'		'		'		'
Symetra common shares	360.9		288.4		'		'
Investments in unconsolidated affiliates	317.3	[1],[2]	351.2	[3]	261	[3]	350.4
Symetra | Warrants	'		'		'		'
Investments in unconsolidated affiliates	'		'		'		'
Investments in unconsolidated affiliates	0	[1],[2]	30.3	[3]	12.6	[3]	37.1
Hamer, LLC	'		'		'		'
Investments in unconsolidated affiliates	'		'		'		'
Investments in unconsolidated affiliates	4.1	[4]	4	[4]	'		'
Bri-Mar Manufacturing, LLC	'		'		'		'
Investments in unconsolidated affiliates	'		'		'		'
Investments in unconsolidated affiliates	0	[4]	1.9	[4]	'		'
Pentelia Capital Management	'		'		'		'
Investments in unconsolidated affiliates	'		'		'		'
Investments in unconsolidated affiliates	$0		$0.50		'		'
[1]	Equity in earnings for the years end December 31, 2013, 2012 and 2011 excludes tax expense of $2.8, $2.6, and $2.3
[2]	The aggregate value of White Mountains’ investment in common shares of Symetra was $380.1 based upon the quoted market price of $18.96 per share at December 31, 2013.
[3]	Includes White Mountains’ equity in net unrealized (losses) gains from Symetra’s fixed maturity portfolio of $(43.6), $62.8, and $0 as of December 31, 2013, 2012 and 2011, which excludes tax benefit (expense) of $3.2, $(5.1) and $0
[4]	As of October 1, 2012, Hamer and Bri-Mar are no longer consolidated and are accounted for as investments in unconsolidated affiliates.

Investments_in_Unconsolidated_3

Investments in Unconsolidated Affiliates (Symetra Narrative) (Details) (USD $)

12 Months Ended

12 Months Ended

3 Months Ended

6 Months Ended

12 Months Ended

1 Months Ended

3 Months Ended

6 Months Ended

In Millions, except Share data, unless otherwise specified

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Jun. 20, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Jun. 30, 2013

Jun. 20, 2013

Jun. 20, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Jan. 31, 2010

Mar. 31, 2010

Dec. 31, 2011

Dec. 31, 2011

Jun. 20, 2013

Jun. 20, 2013

Jun. 20, 2013

Dec. 31, 2011

Symetra

Symetra

Symetra

Symetra

Common Stock

Common Stock

Common Stock

Warrants

Warrants

Warrants

Warrants

Warrants

Warrants

IPO

IPO

Minimum

Maximum

Symetra

equity in earnings of unconsolidated affiliates [Member]

Net unrealized gains (losses) of unconsolidated affiliates [Member]

Best Estimate [Member]

technique

Symetra

Symetra

Symetra

Symetra

Symetra

Symetra

Symetra

Symetra

Symetra

Symetra

Symetra

Common Stock

Symetra

Symetra

Symetra

Investments in unconsolidated affiliates

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares of symetra financial corporation owned (in shares)

'

'

'

20,050,000

17,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Price per share

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$12

'

'

'

'

'

'

'

Investments in unconsolidated affiliates on conversion of warrants

'

'

'

'

9,490,000

'

2,650,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Non-cumulative perpetual preference shares issued

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

25,300,000

'

'

'

'

'

'

'

Number of shares sold in transaction by existing shareholders

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

9,700,000

'

'

'

'

'

'

'

Ownership percentage before transaction

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

24.00%

'

'

'

'

'

'

Ownership percentage after transaction

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

20.00%

'

'

'

'

'

'

Decrease in carrying value of wymetra from dilution

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$16

'

'

'

'

'

'

'

Fair value of investment

'

'

'

'

'

261

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Estimated fair value of investment per share

'

'

'

'

'

$15

'

'

'

'

'

'

'

'

'

'

'

'

$16

$30

'

'

'

$15

After-tax equity in losses of unconsolidated affiliates

'

'

'

'

'

45.9

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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

'

'

'

'

'

136.6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ownership interest (as a percent)

'

'

'

17.03%

14.60%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of valuation techniques

'

'

'

'

'

3

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Term of amortization (in years)

'

'

'

'

'

'30 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Weight Average Years Remaining

'

'

'

'29 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

After tax amortization through equity in earnings

'

'

'

2.7

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

After tax amortization through equity in net unrealized losses

'

'

'

10.8

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Equity Method Investment, Difference Between Carrying Amount and Underlying Equity

'

'

'

183.7

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Risk free interest rate (as a percent)

'

'

'

'

'

'

'

'

'

'

'

'

0.34%

'

'

'

'

'

'

'

'

'

'

'

Volatility rate (as a percent)

'

'

'

'

'

'

'

'

'

'

'

'

26.50%

'

'

'

'

'

'

'

'

'

'

'

Per share price, class of warrant (in dollars per share)

'

'

'

'

'

'

'

$18.96

'

'

'

'

$15.53

'

'

'

'

'

'

'

'

'

'

'

Cash dividends received on warrants

'

'

'

'

'

'

'

'

'

'

'

'

1.5

'

'

'

'

'

'

'

'

'

'

'

Fair Value Assumptions, Expected Term

'

'

'

'

'

'

'

'

'

'

'

'

'1 year 1 month 10 days

'

'

'

'

'

'

'

'

'

'

'

Class of Warrant or Right, Exercise Price of Warrants or Rights

'

'

'

'

'

'

'

'

'

'

'

'

11.49

'

'

'

'

'

'

'

'

'

'

'

Common shares repurchased and retired during the period

'

1,329,640

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6,600,000

'

'

'

Treasury Stock Acquired, Average Cost Per Share

$564

$503

$390

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$13.44

'

'

'

Unamortized basis difference

'

'

'

'

'

'

19.3

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.4

18.9

'

Gain (Loss) on Warrants

'

'

'

10.8

17.7

-24.5

'

0

0

0

14.5

10.8

'

10.8

17.7

-24.5

'

'

'

'

'

'

'

'

Dividends received

'

'

'

($6.40)

($4.90)

($4)

'

($6.40)

($4.90)

($4)

'

'

'

$0

$0

$0

'

'

'

'

'

'

'

'

Investments_in_Unconsolidated_4

Investments in Unconsolidated Affiliates (Investments in Symetra) (Details) (USD $)

3 Months Ended

12 Months Ended

3 Months Ended

6 Months Ended

12 Months Ended

12 Months Ended

In Millions, except Per Share data, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Jun. 30, 2013

Jun. 20, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Jun. 20, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Symetra

Symetra

Symetra

Common Stock

Common Stock

Common Stock

Common Stock

Common Stock

Common Stock

Warrants

Warrants

Warrants

Warrants

Warrants

Warrants

equity in earnings of unconsolidated affiliates [Member]

equity in earnings of unconsolidated affiliates [Member]

equity in earnings of unconsolidated affiliates [Member]

Net unrealized gains (losses) of unconsolidated affiliates [Member]

Net unrealized gains (losses) of unconsolidated affiliates [Member]

Net unrealized gains (losses) of unconsolidated affiliates [Member]

Net unrealized gains (losses) of unconsolidated affiliates [Member]

Net unrealized gains (losses) of unconsolidated affiliates [Member]

Net unrealized gains (losses) of unconsolidated affiliates [Member]

impairment of equity in earnings [Member]

impairment of net unrealized gains (losses) [Member]

impairment of net unrealized gains (losses) [Member]

impairment of net unrealized gains (losses) [Member]

Amortization of common share basis difference [Member]

Amortization of common share basis difference [Member]

Symetra

Symetra

Symetra

White Mountains

White Mountains

White Mountains

Symetra

Symetra

Symetra

Symetra

Common Stock

Common Stock

Common Stock

Common Stock

Common Stock

Common Stock

Common Stock

Common Stock

Common Stock

equity in earnings of unconsolidated affiliates [Member]

Net unrealized gains (losses) of unconsolidated affiliates [Member]

Net unrealized gains (losses) of unconsolidated affiliates [Member]

Net unrealized gains (losses) of unconsolidated affiliates [Member]

Common Stock

Common Stock

Symetra

Symetra

Symetra

Symetra

Symetra

Symetra

White Mountains

White Mountains

White Mountains

Common Stock

Common Stock

Common Stock

Common Stock

Symetra

Symetra

Symetra

Symetra

Symetra

Symetra

Changes in carrying value of investment in Symetra

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Carrying value at the beginning of the period

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$387.90

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$387.90

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$381.50

[1]

$273.60

[1]

$387.50

$351.20

[1]

$261

[1]

$350.40

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$30.30

[1]

$12.60

[1]

$37.10

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Equity in earnings (losses) of unconsolidated affiliates, net of tax

11.7

8.6

7.1

9.2

5.5

7.7

6.5

10.2

36.6

29.9

-20.2

37.8

32.3

[2],[3],[4]

28.2

[2],[3]

37.8

32.3

[2],[3],[4]

28.2

[2],[3]

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0

0

[2],[3],[4]

0

[2],[3]

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3

3.5

Impairment of equity in earnings of Symetra

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0

[5]

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-50

[6]

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-148.6

[5]

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Net change in pre-tax unrealized gains (losses) on investments in unconsolidated affiliates

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-106.4

62.8

-63.6

-106.4

[7],[8]

62.8

[7],[8]

85

[7]

-106.4

[7],[8]

62.8

[7],[8]

85

[7]

-43.6

62.8

0

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0

[7],[8]

0

[7],[8]

0

[7]

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11.8

13.1

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Dividends received

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-6.4

-4.9

-4

-6.4

-4.9

-4

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0

0

0

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Increase (decrease) in value of warrants

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10.8

17.7

-24.5

0

0

0

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14.5

10.8

10.8

17.7

-24.5

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Carrying value at the end of the period

321.4

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387.9

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321.4

387.9

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317.3

[2],[9]

381.5

[1]

273.6

[1]

317.3

[2],[9]

351.2

[1]

261

[1]

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0

[2],[9]

30.3

[1]

12.6

[1]

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Unrealized (losses) gains from Symetra’s fixed maturity portfolio

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-43.6

62.8

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Income Tax Expense (Benefit)

27.4

8.2

-0.6

41.6

-101

47.8

6.4

31.1

76.6

-15.7

-110

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2.8

2.6

2.3

-8.3

5.1

6.9

-3.2

5.1

0

-4.1

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-12

'

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Loss from dilutive effect resulting from dividend and issuance of restricted shares

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0.2

1.3

1

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

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136.6

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

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380.1

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Share Price

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$18.96

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$15.53

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Exercise of warrants

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$0

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$41.10

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($41.10)

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[1]

Includes White Mountains’ equity in net unrealized (losses) gains from Symetra’s fixed maturity portfolio of $(43.6), $62.8, and $0 as of December 31, 2013, 2012 and 2011, which excludes tax benefit (expense) of $3.2, $(5.1) and $0

[2]

Equity in earnings for the years end December 31, 2013, 2012 and 2011 excludes tax expense of $2.8, $2.6, and $2.3

[3]

Equity in earnings for the years end December 31, 2013, 2012 and 2011 includes $.2, $1.3, and $1.0 loss from the dilutive effect of Symetra’s yearly dividend and the issuance of restricted shares by Symetra

[4]

Equity in earnings for the years ended December 31, 2013 and 2012 includes $3.0 and $3.5 increases relating to the pre-tax amortization of the Symetra common share basis difference.

[5]

Impairment of net unrealized gains from Symetra’s fixed maturity portfolio excludes tax benefit $12.0

[6]

Impairment of equity in earnings of Symetra excludes tax benefit of $4.1

[7]

Net unrealized (losses) gains from Symetra’s fixed maturity portfolio excludes tax benefit (expense) of $8.3, $(5.1) and $(6.9) for the years ended December 31, 2013, 2012 and 2011.

[8]

Net unrealized gains for the years ended December 31, 2013 and 2012 includes $11.8 and $13.1 increases relating to the pre-tax amortization of the Symetra common share basis difference.

[9]

The aggregate value of White Mountains’ investment in common shares of Symetra was $380.1 based upon the quoted market price of $18.96 per share at December 31, 2013.

Investments_in_Unconsolidated_5

Investments in Unconsolidated Affiliates (Financial Information) (Details) (USD $)

3 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

9 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Apr. 30, 2007

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Sep. 30, 2013

Dec. 31, 2013

Dec. 31, 2012

Symetra

Symetra

Symetra

Symetra

Pentelia Capital Management

Pentelia Capital Management

Pentelia Capital Management

Pentelia Capital Management

Hamer, LLC

Hamer, LLC

Bri-Mar Manufacturing, LLC

Bri-Mar Manufacturing, LLC

Bri-Mar Manufacturing, LLC

Symetra balance sheet data; [Abstract]

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'

Total investments

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'

$27,901.10

$27,556.40

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Separate account assets

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'

978.4

807.7

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Total assets

'

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30,129.50

29,460.90

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'

'

Policyholder liabilities

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25,328.80

23,735.20

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Long-term debt

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449.5

449.4

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Separate account liabilities

'

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'

'

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'

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'

978.4

807.7

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'

Total liabilities

'

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'

'

'

'

'

'

'

27,187.60

25,830.80

'

'

'

'

'

'

'

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'

'

Common shareholders’ equity

'

'

'

'

'

'

'

'

'

'

'

2,941.90

3,630.10

'

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'

Symetra income statement data: [Abstract]

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Net premiums earned

'

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627.2

605

540.5

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Net investment income

'

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1,285

1,275.20

1,270.90

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'

'

Total revenues

'

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'

'

'

'

'

'

'

'

2,103.90

[1]

2,101.20

[1]

1,999.30

[1]

'

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'

'

'

'

'

'

Policy benefits

'

'

'

'

'

'

'

'

'

'

'

1,394.90

1,371.80

1,307.30

'

'

'

'

'

'

'

'

'

'

Total expenses

'

'

'

'

'

'

'

'

'

'

'

1,865.30

[1]

1,831.10

[1]

1,726.10

[1]

'

'

'

'

'

'

'

'

'

'

Net income

'

'

'

'

'

'

'

'

'

'

'

220.7

[1]

205.4

[1]

195.8

[1]

'

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'

'

'

'

'

'

'

'

Comprehensive net income

'

'

'

'

'

'

'

'

'

'

'

-777.6

549.3

785.5

'

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'

'

'

'

'

'

Ownership interest (as a percent)

'

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'

'

'

'

'

'

'

'

'

17.03%

14.60%

'

'

33.00%

'

'

'

'

'

'

'

'

Payments to acquire investment

'

'

'

'

'

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'

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'

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'

'

'

'

'

1.6

'

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'

'

'

'

'

Equity in earnings (losses) of unconsolidated affiliates, net of tax

11.7

8.6

7.1

9.2

5.5

7.7

6.5

10.2

36.6

29.9

-20.2

37.8

32.3

[2],[3],[4]

28.2

[2],[3]

'

'

0.1

-1.3

-0.2

0.9

0.4

0.9

'

'

Dividends received

'

'

'

'

'

'

'

'

'

'

'

-6.4

-4.9

-4

'

'

-0.4

'

'

-0.8

'

'

'

'

Investments in unconsolidated affiliates

321.4

'

'

'

387.9

'

'

'

321.4

387.9

'

317.3

[2],[5]

381.5

[6]

273.6

[6]

387.5

'

0

0.5

'

4.1

[7]

4

[7]

'

0

[7]

1.9

[7]

Proceeds from Sale of Equity Method Investments

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1.1

'

Equity Method Investment, Realized Gain (Loss) on Disposal

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$1.70

'

[1]

Amounts for the years ended December 31, 2011 have been restated for the effect of Symetra’s adoption of ASU 2010-26.

[2]

Equity in earnings for the years end December 31, 2013, 2012 and 2011 excludes tax expense of $2.8, $2.6, and $2.3

[3]

Equity in earnings for the years end December 31, 2013, 2012 and 2011 includes $.2, $1.3, and $1.0 loss from the dilutive effect of Symetra’s yearly dividend and the issuance of restricted shares by Symetra

[4]

Equity in earnings for the years ended December 31, 2013 and 2012 includes $3.0 and $3.5 increases relating to the pre-tax amortization of the Symetra common share basis difference.

[5]

The aggregate value of White Mountains’ investment in common shares of Symetra was $380.1 based upon the quoted market price of $18.96 per share at December 31, 2013.

[6]

Includes White Mountains’ equity in net unrealized (losses) gains from Symetra’s fixed maturity portfolio of $(43.6), $62.8, and $0 as of December 31, 2013, 2012 and 2011, which excludes tax benefit (expense) of $3.2, $(5.1) and $0

[7]

As of October 1, 2012, Hamer and Bri-Mar are no longer consolidated and are accounted for as investments in unconsolidated affiliates.

Variable_Interest_Entities_Det

Variable Interest Entities (Details) (USD $)

1 Months Ended

3 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2011

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2004

Dec. 31, 2012

Dec. 31, 2005

Dec. 31, 2013

Dec. 31, 2011

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2011

Dec. 31, 2005

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

company

HG Global

HG Global

Prospector Turtle Fund [Member]

Prospector

Prospector

Prospector

Houston General Insurance [Member]

Houston General Insurance [Member]

Houston General Insurance [Member]

Houston General Insurance [Member]

Prospector Offshore Fund Ltd [Member]

Tuckerman Fund I

Entities Owned by Tuckerman Fund I

Common Stock

Common Stock

Common Stock

Houston General Insurance Company

BAM

BAM

HG Global

HG Global

Surplus Note

First Loss Reinsurance Treaty [Member]

First Loss Reinsurance Treaty [Member]

First Loss Reinsurance Treaty [Member]

Amendment [Member]

company

BAM

Tuckerman Fund I

Tuckerman Fund I

Houston General Insurance [Member]

HG Global

BAM

HG Global

Houston General Insurance [Member]

trust

Variable Interest Entity [Line Items]

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'

Issuance of notes

'

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'

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'

'

'

'

'

'

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'

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'

'

'

'

'

'

'

'

'

'

$503

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of par value of policy reinsured

'

'

'

'

'

15.00%

'

'

'

'

15.00%

'

15.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

15.00%

'

'

15.00%

'

'

'

Percentage of Premiums

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

60.00%

'

'

Number of Trust

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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'

'

'

'

'

'

2

'

Right to elect directors on board number

'

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'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2

'

'

'

'

'

'

'

'

Proceeds from Contributions from Parent

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total assets related to consolidated VIE's

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

249.2

238.6

'

2.6

'

22.6

'

'

17.6

'

'

'

'

149.4

'

'

'

'

'

'

'

'

'

Total liabilities related to consolidated VIE's

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

90.6

94.4

'

4.2

'

43.8

'

'

9.9

'

'

'

'

127.6

'

'

'

'

'

'

'

'

'

Surplus notes

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4

'

'

23.7

'

'

'

'

'

'

'

'

'

503

503

'

'

'

'

4

Interest Paid

'

'

'

'

'

'

'

'

'

42.6

44.6

59

'

'

'

'

'

'

19

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Repayments of debt, principal

'

'

'

'

'

'

'

'

'

275

75

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1

'

'

'

'

Accumulated losses

'

2,802.30

'

'

'

2,542.70

'

'

'

2,802.30

2,542.70

'

'

'

'

'

'

'

1.6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Accrued interest on surplus notes

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Noncontrolling interest in VIE

'

491.9

'

'

'

526.4

'

'

'

491.9

526.4

'

16.6

16.6

'

46.2

41.5

'

'

'

'

'

'

3.5

'

'

'

'

'

-36

-97.6

16.6

16.6

'

'

'

'

'

Net Income (Loss) Attributable to Parent

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

14.5

9.3

-1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Non-controlling interest in consolidated subsidiaries

'

0.3

-1.1

-11.1

-0.5

-12

-30.9

12.1

16.8

-12.4

-14

41.5

'

'

'

4

2.7

-0.2

'

'

'

'

'

2.2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Ownership interest in VIE (as a percent)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

68.90%

'

'

'

'

'

'

'

71.70%

'

'

'

94.00%

94.00%

'

'

'

'

'

'

'

'

'

'

Number of small manufacturing companies owned by the Tuckerman Fund I from whom the entity received shares

2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2

'

'

'

'

'

'

'

'

'

'

'

'

'

Captial at risk, investment in the fund

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$112.50

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Transactions_with_Related_Pers1

Transactions with Related Persons (Details) (USD $)

12 Months Ended

3 Months Ended

12 Months Ended

12 Months Ended

9 Months Ended

12 Months Ended

3 Months Ended

0 Months Ended

12 Months Ended

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Mar. 31, 2013

Mar. 15, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Sep. 30, 2013

Jul. 16, 2012

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Mar. 31, 2014

Mar. 31, 2014

Jul. 16, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Beneficial Owner

Beneficial Owner

Prospector

Prospector

Prospector

OneBeacon

White Mountains Advisors LLC

White Mountains Advisors LLC

White Mountains Advisors LLC

White Mountains Advisors LLC

Oakum Bay Capital

Oakum Bay Capital

Oakum Bay Capital

Performance Cycle From 2012 to 2014

Performance Cycle From 2013 to 2015

First Threshold Limit

Second Threshold Limit

Third Threshold Limit

Maximum

Minimum

Range Of Performance Cycle From 2014-2016

Performance Cycle From 2011 to 2013

Preferred Equity Securities

revenue sharing agreement

revenue sharing agreement

revenue sharing agreement

Trimarc Capital Fund

Trimarc Capital Fund

Trimarc Capital Fund

Prospector

Symetra

Symetra

Symetra

Prospector

Director

Prospector

Prospector

White Mountains Advisors LLC

White Mountains Advisors LLC

White Mountains Advisors LLC

Prospector

Prospector

Prospector

Prospector

Oakum Bay Capital

Prospector

Prospector

Prospector

Oakum Bay Capital

Oakum Bay Capital

Hedge funds

Prospector

Prospector

Prospector

Oakum Bay Capital

Related Party Transaction [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

basis points

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100.00%

50.00%

25.00%

'

'

'

'

'

'

'

'

'

'

'

Assets under management

'

'

'

'

'

'

'

'

$556,800,000

$27,800,000,000

$27,400,000,000

'

$461,000,000

'

'

'

'

'

$200,000,000

$200,000,000

$400,000,000

'

'

'

'

'

'

'

'

'

'

'

ERISA Assets

'

'

'

'

'

'

'

'

215,600,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Asset Management Fees

'

'

'

'

'

6,500,000

6,400,000

6,000,000

'

16,500,000

15,900,000

15,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of target number granted actually received by prospector

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

131.50%

'

'

'

'

'

'

'

Number of performance shares granted

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

7,750

7,000

'

'

'

'

'

6,250

8,500

'

'

'

'

'

'

'

Target number of performance shares granted (as a percent)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

200.00%

0.00%

'

'

'

'

'

'

'

'

'

Per share price, class of warrant (in dollars per share)

'

'

'

'

$563.57

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Payment made with respect to the performance shares granted to the related party

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6,500,000

'

'

'

'

'

'

'

Performance shares granted at the beginning of each performance cycle

'

'

'

'

'

'

4,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of fees in excess of $500,000 revenue chargeable

'

'

'

'

'

6.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amount of revenue over which 6% of fees chargeable

'

'

'

'

'

'

500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Fees from Revenue Sharing Agreement with Related Party

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

900,000

500,000

200,000

'

'

'

Invested in limited partnership investment interests

'

'

'

'

'

108,400,000

'

'

14,900,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Management Fees, Base Revenue

'

'

'

'

'

1,300,000

1,100,000

1,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Incentive fees incurred

'

'

'

'

'

3,200,000

1,300,000

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Management fees

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100,000

100,000

'

Purchases

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2,000,000

'

'

'

'

'

'

Ownerhsip percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

7.50%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Related party ownerhship percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

67.50%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Sales of common equity securities

521,100,000

192,400,000

237,800,000

'

'

'

'

'

'

'

'

'

'

500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of years to receive portion of revenue

'

'

'

'

'

'

'

'

'

'

'

'

'

'10 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares purchased

'

'

'

140,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Trading Securities, Other

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$8,600,000

Fair_Value_of_Financial_Instru2

Fair Value of Financial Instruments (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Fair Value, Balance Sheet Grouping, Financial Statement Captions	'	'
Senior notes	$676.40	$751.20
2012 OBH Senior Notes	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions	'	'
Senior notes	274.7	274.7
Fair value | 2012 OBH Senior Notes	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions	'	'
Senior notes	269.8	282.4
Fair value | SIG Senior Notes	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions	'	'
Senior notes	438.1	441.9
Fair value | SIG Preference Shares	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions	'	'
Senior notes	260	257.5
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	399.6	399.4
Carrying Value | SIG Preference Shares	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions	'	'
Senior notes	$250	$250

Commitments_and_Contingencies_

Commitments and Contingencies (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Loss Contingencies [Line Items]	'	'	'
Rent expense	$20.20	$18.80	$22.80
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]	'	'	'
Capital lease payments due in two years	13.9	'	'
Capital lease payments due in three years	12.6	'	'
Capital Lease payments due in four years and thereafter	27.7	'	'
Commitments to fund other-long term investments	115.9	'	'
Capital Leases, Future Minimum Payments Due, Next Twelve Months	15.3	'	'
Reserve for probable liability from mandatory shared market mechanisms	13	'	'
OB Services	'	'	'
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]	'	'	'
Capital lease payments due in two years	5.3	'	'
Capital lease payments due in three years	1.9	'	'
Cash proceeds received a result of entering into the sale-leaseback transactions	'	23.1	'
Capital lease obligation	12.5	18.2	'
Capital lease asset	10.9	16.1	'
Capital Leases, Future Minimum Payments Due, Next Twelve Months	$5.30	'	'
Furniture and equipment | OB Services	'	'	'
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]	'	'	'
Capital lease term (in years)	'	'5 years	'
Capitalized software | OB Services	'	'	'
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]	'	'	'
Capital lease term (in years)	'	'4 years	'

Commitments_and_Contingencies_1

Commitments and Contingencies (Legal Contingencies) (Details) (USD $)	12 Months Ended				12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jun. 30, 2007	Dec. 31, 2011
				Tribune Company Litigation	Esurance
Legal Contingency [Abstract]	'	'	'	'	'
Sales of unconsolidated affiliates, net of cash sold and held in escrow	$32.40	$24.80	$1,010.60	'	'
Gain (Loss) on Disposition of Business	'	'	'	'	700
Period for which company has indemnified Allstate for breaches of representations and warranties (in months)	'	'18 months	'	'	'
Period for which the entity has agreed not to solicit certain employees of transferred subsidiaries (in years)	'	'3 years	'	'	'
Percentage of positive or negative development in the loss reserves of the Transferred Subsidiaries retained	90.00%	'	'	'	'
Proceeds in connection with Tribune leveraged buyout	'	'	'	$39	'

Discontinued_Operations_Detail

Discontinued Operations (Details) (USD $)

3 Months Ended

12 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

3 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

3 Months Ended

In Millions, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Oct. 31, 2011

Dec. 31, 2012

Dec. 31, 2011

Feb. 22, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Jun. 30, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Mar. 31, 2013

Dec. 31, 2012

Mar. 31, 2013

Dec. 31, 2012

Mar. 31, 2013

Mar. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

31-May-01

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Jun. 30, 2013

Discontinued Operations

Discontinued Operations

Discontinued Operations

Esurance

AutoOne

AutoOne

AutoOne

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

Minimum

Minimum

Maximum

Maximum

Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense, Cause [Domain]

N I C O Cover [Member]

G R C Cover [Member]

General Reinsurance Corporation

Workers compensation

Personal Auto Liability [Member]

Property and Casualty, Personal Insurance Product Line [Member]

Workers compensation loss reserves [Member]

Insurance Claims [Member]

Change in Assumption of Liability [Member]

Safeco v. American International Group, Inc. [Member]

Discontinued Operations

Discontinued Operations

Discontinued Operations

Contract

Discontinued Operations

Discontinued Operations

Discontinued Operations

Discontinued Operations

Discontinued Operations

Discontinued Operations

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

G R C Cover [Member]

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

OneBeacon Runoff

Entity

Rating

Rating

Discontinued Operations

Discontinued Operations

Discontinued Operations

Discontinued Operations

Discontinued Operations

OneBeacon Runoff

Discontinued Operations

Discontinued Operations

Discontinued Operations

Discontinued Operations

Discontinued Operations

Discontinued Operations

Discontinued Operations

Reinsurance Retention Policy [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

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

'

'

'

'

'

'

'

'

$46.60

($91)

$658.30

'

$46.60

($91)

$658.30

$677.50

$0.50

($19.20)

'

'

'

'

'

$44.90

$91.50

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of insurance companies sold

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Loss and loss adjustment expense reserves

3,079.30

'

'

'

3,168.90

'

'

'

3,079.30

3,168.90

5,702.30

5,736.80

1,793.10

2,052.60

'

'

'

'

'

'

'

188.4

'

188.4

'

'

166

'

215

'

668

78.9

'

'

'

'

'

'

'

'

'

'

Net income (loss) from discontinued operations

'

'

'

'

'

'

'

'

'

'

'

'

4.5

-115

621.6

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Loss and LAE incurred relating prior year losses

'

'

'

'

'

'

'

'

48.4

41.9

76.7

'

'

'

'

'

'

'

'

'

'

71.5

'

-6.5

-40

-26.7

'

'

'

'

'

'

'

'

'

'

-16.9

-78.9

'

-5.4

-12.6

'

Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

36.6

'

'

'

'

'

'

Loss and loss adjustment expenses

'

'

'

'

'

'

'

'

1,040.50

1,193.90

1,174.30

'

78.9

48.4

574.9

'

'

'

'

'

'

'

7.4

78.9

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Other revenue

'

'

'

'

'

'

'

'

57.5

100.3

-10

'

10.8

0

55.1

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

7.8

liability for unpaid claims and claims adjustment expenses, incurred claims, prior years, after-tax

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

46.5

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net loss from discontinued operations, net of tax

-0.3

0.4

3.9

0.5

0.5

-106.8

0.5

-9.2

-42.1

-24

-36.7

'

-42.1

-24

-36.7

'

'

'

'

'

'

46.6

'

'

24

'

'

'

'

'

'

'

'

'

'

'

'

'

9

'

'

'

Maximum Number of Days to Extend the Termination Date

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'90 days

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

69

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of contracts seller caused One Beacon to purchase prior to acquisition

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance recoverables, gross

453.5

'

'

'

447

'

'

'

453.5

447

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2,500

570

'

'

'

'

'

'

'

'

Workers compensation discount percent

'

'

'

'

'

'

'

'

3.50%

3.50%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3.50%

'

4.50%

'

'

'

'

'

'

'

'

'

'

'

'

Workers compensation discount amount

3

'

'

'

4.6

'

'

'

3

4.6

'

'

'

'

'

'

'

'

'

61.7

77.9

'

'

'

15.2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Adverse loss reserve development

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

400

'

'

'

'

'

'

'

Loss reserves ceded at acquisition

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

170

'

'

'

'

'

'

'

Reinsurance recoverable on paid and unpaid losses

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,243.70

'

1,243.70

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

AM Best Rating System Number Of Ratings

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

16

'

16

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance recoverable on paid losses

25.4

'

'

'

17.9

'

'

'

25.4

17.9

'

'

'

15.6

'

'

'

'

'

'

'

10.7

'

10.7

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Reinsurance recoverables

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,741.60

'

1,741.60

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Purchase accounting adjustments

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$136.90

'

$136.90

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Discontinued_Operations_Discon

Discontinued Operations Discontinued Operations (Asbestos and environmental loss and LAE reserve activity) (Details) (OneBeacon Runoff, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Gross	'		'		'
Beginning balance	$1,162.40		$1,354.10		$1,023
Incurred losses and LAE	0		-1.2		488.6
Paid losses and LAE	-148.6		-190.5		-157.5
Ending balance	1,013.80		1,162.40		1,354.10
Beginning balance	727.9	[1]	832.8	[1]	741.1	[1]
Incurred losses and LAE	0	[1]	-1	[1]	94.4	[1]
Paid losses and LAE	-112.3	[1]	-103.9	[1]	-2.7	[1]
Ending balance	615.6	[1]	727.9	[1]	832.8	[1]
Beginning balance	8.8	[2]	11.2	[2]	15.6	[2]
Incurred losses and LAE	0	[2]	-1	[2]	6	[2]
Liability for unpaid claims and claims adjustment expense	-3.1	[2]	-1.4	[2]	-10.4	[2]
Ending balance	5.7	[2]	8.8	[2]	11.2	[2]
Asbestos	'		'		'
Gross	'		'		'
Beginning balance	929.4		1,074.30		904
Incurred losses and LAE	0		-0.3		256.8
Paid losses and LAE	-84.3		-144.6		-86.5
Ending balance	845.1		929.4		1,074.30
Beginning balance	602.5	[1]	681.2	[1]	647.3	[1]
Incurred losses and LAE	0	[1]	-0.5	[1]	32.2	[1]
Paid losses and LAE	-79.3	[1]	-78.2	[1]	1.7	[1]
Ending balance	523.2	[1]	602.5	[1]	681.2	[1]
Beginning balance	2.4	[2]	2.2	[2]	6.4	[2]
Incurred losses and LAE	0	[2]	-0.5	[2]	-4	[2]
Liability for unpaid claims and claims adjustment expense	-0.5	[2]	0.7	[2]	-0.2	[2]
Ending balance	1.9	[2]	2.4	[2]	2.2	[2]
Environmental	'		'		'
Gross	'		'		'
Beginning balance	233		279.8		119
Incurred losses and LAE	0		-0.9		231.8
Paid losses and LAE	-64.3		-45.9		-71
Ending balance	168.7		233		279.8
Beginning balance	125.4	[1]	151.6	[1]	93.8	[1]
Incurred losses and LAE	0	[1]	-0.5	[1]	62.2	[1]
Paid losses and LAE	-33	[1]	-25.7	[1]	-4.4	[1]
Ending balance	92.4	[1]	125.4	[1]	151.6	[1]
Beginning balance	6.4	[2]	9	[2]	9.2	[2]
Incurred losses and LAE	0	[2]	-0.5	[2]	10	[2]
Liability for unpaid claims and claims adjustment expense	-2.6	[2]	-2.1	[2]	-10.2	[2]
Ending balance	$3.80	[2]	$6.40	[2]	$9	[2]
[1]	Represents A&E reserve activity, net of third-party reinsurance, but prior to the NICO Cover.
[2]	Includes NICO cover

Discontinued_Operations_Assets

Discontinued Operations (Assets and Liabilities Classified as Held for Sale) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
In Millions, unless otherwise specified
Assets held for sale	'	'	'	'
Fixed maturity investments, at fair value	$5,030.50	$5,196.20	'	'
Cash	382.8	462.4	'	'
Insurance and reinsurance premiums receivable	518.9	556.3	'	'
Deferred acquisition costs	174.7	195.3	'	'
Deferred tax asset	155.9	228.3	'	'
Other assets	458.1	503	'	'
Total assets	12,144.30	12,895.40	'	'
Liabilities held for sale	'	'	'	'
Loss and loss adjustment expense reserves	3,079.30	3,168.90	5,702.30	5,736.80
Unearned insurance premiums	901.4	924.1	'	'
Ceded reinsurance payable	71.9	116.5	'	'
Other liabilities	362.9	452.8	'	'
Total liabilities	7,746.90	8,637.20	'	'
Reinsurance recoverable on unpaid losses	428.1	429.1	'	'
Reinsurance recoverable on paid losses	25.4	17.9	'	'
Discontinued Operations	'	'	'	'
Assets held for sale	'	'	'	'
Fixed maturity investments, at fair value	236.3	338.1	'	'
Cash	0	0	'	'
Insurance and reinsurance premiums receivable	9.1	11	'	'
Deferred acquisition costs	0	0	'	'
Deferred tax asset	3.3	5.1	'	'
Other assets	16	16.2	'	'
Total assets	1,880.10	2,226.80	'	'
Liabilities held for sale	'	'	'	'
Loss and loss adjustment expense reserves	1,793.10	2,052.60	'	'
Unearned insurance premiums	0.2	0.5	'	'
Ceded reinsurance payable	12.3	21.9	'	'
Other liabilities	74.5	151.8	'	'
Total liabilities	1,880.10	2,226.80	'	'
Net assets held for sale	0	0	'	'
Reinsurance recoverable on unpaid losses	1,604.70	1,840.80	'	'
Reinsurance recoverable on paid losses	'	$15.60	'	'

Discontinued_Operations_Loss_f

Discontinued Operations (Loss from Discontinued Operations) (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues	'	'	'	'	'	'	'	'	'	'	'
Earned insurance premiums	'	'	'	'	'	'	'	'	$1,987.30	$2,063.60	$1,924.50
Net investment income	'	'	'	'	'	'	'	'	110.9	153.6	184.5
Net realized and unrealized investment gains	'	'	'	'	'	'	'	'	161.7	118.2	74.1
Other revenue	'	'	'	'	'	'	'	'	57.5	100.3	-10
Revenues (including realized gains and losses)	626.6	574.1	489.3	627.4	566.4	697.4	542.3	629.7	2,317.40	2,435.70	2,173.10
Expenses	'	'	'	'	'	'	'	'	'	'	'
Loss and loss adjustment expenses	'	'	'	'	'	'	'	'	1,040.50	1,193.90	1,174.30
Insurance and reinsurance acquisition expenses	'	'	'	'	'	'	'	'	376.9	430.2	402.2
Other underwriting expenses	'	'	'	'	'	'	'	'	331.3	321.8	268.1
General and administrative expenses	'	'	'	'	'	'	'	'	181.3	182.2	175.3
Total expenses	492.4	518.8	485.7	475.6	617.2	562.3	504.7	488.8	1,972.50	2,172.90	2,075.10
Net loss from discontinued operations, net of tax	-0.3	0.4	3.9	0.5	0.5	-106.8	0.5	-9.2	-42.1	-24	-36.7
Gain (loss) on sale of discontinued operations, net of tax	'	'	'	'	'	'	'	'	46.6	-91	658.3
Discontinued Operations	'	'	'	'	'	'	'	'	'	'	'
Revenues	'	'	'	'	'	'	'	'	'	'	'
Earned insurance premiums	'	'	'	'	'	'	'	'	0.8	10.6	731.2
Net investment income	'	'	'	'	'	'	'	'	0	0	12
Net realized and unrealized investment gains	'	'	'	'	'	'	'	'	0	0	0.7
Other revenue	'	'	'	'	'	'	'	'	10.8	0	55.1
Revenues (including realized gains and losses)	'	'	'	'	'	'	'	'	11.6	10.6	799
Expenses	'	'	'	'	'	'	'	'	'	'	'
Loss and loss adjustment expenses	'	'	'	'	'	'	'	'	78.9	48.4	574.9
Insurance and reinsurance acquisition expenses	'	'	'	'	'	'	'	'	0	-2.1	157
Other underwriting expenses	'	'	'	'	'	'	'	'	-0.2	1.7	91.4
General and administrative expenses	'	'	'	'	'	'	'	'	0	0	38.3
Total expenses	'	'	'	'	'	'	'	'	78.7	48	861.6
Loss from discontinued operations	'	'	'	'	'	'	'	'	-67.1	-37.4	-62.6
Income tax benefit	'	'	'	'	'	'	'	'	-25	-13.4	-25.9
Net loss from discontinued operations, net of tax	'	'	'	'	'	'	'	'	-42.1	-24	-36.7
Gain (loss) on sale of discontinued operations, net of tax	'	'	'	'	'	'	'	'	46.6	-91	658.3
Net income (loss) from discontinued operations	'	'	'	'	'	'	'	'	$4.50	($115)	$621.60

Discontinued_Operations_Earnin

Discontinued Operations (Earnings Per Share) (Details) (USD $)

3 Months Ended

12 Months Ended

9 Months Ended

12 Months Ended

In Millions, except Share data, unless otherwise specified

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Sep. 30, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Discontinued Operations

Discontinued Operations

Discontinued Operations

Discontinued Operations

Discontinued Operations

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income (loss) from discontinued operations

'

'

'

'

'

'

'

'

'

'

'

'

$4.50

($115)

$621.60

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

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Allocation of income for participating unvested restricted common shares

'

'

'

'

'

'

'

'

-4.7

-4.3

-1.2

'

0

[1]

1.5

[1]

-5.4

[1]

Net income attributable to White Mountains’ common shareholders

$117.90

$57.20

$26.30

$120.40

$68.20

$19.10

$26.10

$94

$321.80

$207.40

$767.90

'

$4.50

($113.50)

$616.20

Basic earnings (loss) per share denominators (in thousands):

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total average common shares outstanding during the period

'

'

'

'

'

'

'

'

6,200,400

6,799,800

7,881,000

'

6,200,400

6,799,800

7,881,000

Average unvested restricted common shares

'

'

'

'

'

'

'

'

-91,400

[1]

-91,100

[1]

-69,400

[1]

'

-91,400

[1]

-91,100

[1]

-69,400

[1]

Basic earnings (loss) per share denominator

'

'

'

'

'

'

'

'

6,109,000

6,708,700

7,811,600

'

6,109,000

6,708,700

7,811,600

Diluted earnings (loss) per share denominator (in thousands):

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total average common shares outstanding during the period

'

'

'

'

'

'

'

'

6,200,400

6,799,800

7,881,000

'

6,200,400

6,799,800

7,881,000

Average unvested restricted common shares

'

'

'

'

'

'

'

'

-91,400

[1]

-91,100

[1]

-69,400

[1]

'

-91,400

[1]

-91,100

[1]

-69,400

[1]

Average outstanding dilutive options to acquire common shares

'

'

'

'

'

'

'

'

0

[2]

0

[2]

0

[2]

'

0

[2]

0

[2]

0

[2]

Diluted earnings (loss) per share denominator

'

'

'

'

'

'

'

'

6,109,000

6,708,700

7,811,600

'

6,109,000

6,708,700

7,811,600

Basic and diluted earnings (loss) per share (in dollars):

'

'

'

'

'

'

'

'

'

'

'

'

$0.74

($16.91)

$78.88

Incremental common shares attributable to share-based payment arrangements

'

'

'

'

'

'

'

'

125,000

'

'

125,000

'

'

'

[1]

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

[2]

The diluted earnings per share denominator for the years ended December 31, 2013, 2012 and 2011 do not include the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding as they are anti-dilutive to the calculation.

Subsequent_Event_Subsequent_Ev

Subsequent Event Subsequent Events (Details)	12 Months Ended				1 Months Ended		2 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Feb. 19, 2014	Jan. 31, 2014	Jan. 31, 2013	Feb. 19, 2014	Feb. 19, 2014	Feb. 19, 2014	Feb. 19, 2014
	USD ($)	USD ($)	USD ($)	Subsequent Event	Subsequent Event	Subsequent Event	Subsequent Event	Subsequent Event	Subsequent Event	Subsequent Event
				WOBI	Star & Shield LLC	Star & Shield LLC	Common Stock	Common Stock	Preferred stocks	Preferred stocks
					USD ($)	USD ($)	Israel, New Shekels	United States of America, Dollars	Israel, New Shekels	United States of America, Dollars
							WOBI	WOBI	WOBI	WOBI
							ILS	USD ($)	ILS	USD ($)
Subsequent Event [Line Items]	'	'	'	'	'	'	'	'	'	'
Ownership interest (as a percent)	'	'	'	54.00%	'	'	'	'	'	'
Purchases of common equity securities	$432.20	$365.20	$297.80	'	'	'	14.4	$4.10	12.7	$3.60
Payments to acquire interest in subsidiaries and affiliates	'	'	'	'	1.8	'	'	'	'	'
Purchase of Surplus Notes	'	'	'	'	'	$12	'	'	'	'

Selected_Quarterly_Financial_D2

Selected Quarterly Financial Data (Unaudited) (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information Disclosure [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Revenues (including realized gains and losses)	$626.60	$574.10	$489.30	$627.40	$566.40	$697.40	$542.30	$629.70	$2,317.40	$2,435.70	$2,173.10
Total expenses	492.4	518.8	485.7	475.6	617.2	562.3	504.7	488.8	1,972.50	2,172.90	2,075.10
Pre-tax loss	134.2	55.3	3.6	151.8	-50.8	135.1	37.6	140.9	344.9	262.8	98
Tax benefit (expense)	-27.4	-8.2	0.6	-41.6	101	-47.8	-6.4	-31.1	-76.6	15.7	110
Net income from continuing operations	106.8	47.1	4.2	110.2	50.2	87.3	31.2	109.8	268.3	278.5	208
Net loss from discontinued operations, net of tax	-0.3	0.4	3.9	0.5	0.5	-106.8	0.5	-9.2	-42.1	-24	-36.7
Non-controlling interest in consolidated subsidiaries	-0.3	1.1	11.1	0.5	12	30.9	-12.1	-16.8	12.4	14	-41.5
Equity in earnings (losses) of unconsolidated affiliates, net of tax	11.7	8.6	7.1	9.2	5.5	7.7	6.5	10.2	36.6	29.9	-20.2
Net income attributable to White Mountains’ common shareholders	$117.90	$57.20	$26.30	$120.40	$68.20	$19.10	$26.10	$94	$321.80	$207.40	$767.90
Basic earnings (loss) per share	'	'	'	'	'	'	'	'	'	'	'
Continuing operations	$19.14	$9.20	$3.62	$19.10	$10.36	$19.11	$3.85	$13.85	$51.15	$47.41	$18.56
Discontinued operations	($0.05)	$0.06	$0.64	$0.07	$0.07	($16.21)	$0.07	($1.24)	$0.74	($16.91)	$78.88
Total consolidated operations	$19.09	$9.26	$4.26	$19.17	$10.43	$2.90	$3.92	$12.61	$51.89	$30.50	$97.44
Diluted earnings (loss) per share	'	'	'	'	'	'	'	'	'	'	'
Continuing operations	$19.14	$9.20	$3.62	$19.10	$10.36	$19.11	$3.85	$13.85	$51.15	$47.41	$18.56
Discontinued operations	($0.05)	$0.06	$0.64	$0.07	$0.07	($16.21)	$0.07	($1.24)	$0.74	($16.91)	$78.88
Total consolidated operations	$19.09	$9.26	$4.26	$19.17	$10.43	$2.90	$3.92	$12.61	$51.89	$30.50	$97.44
Adjusted book value per share	$642.27	$621.56	$604.75	$606.20	$587.63	$573.66	$564.77	$565.38	'	'	'

SCHEDULE_I_SUMMARY_OF_INVESTME1

SCHEDULE I SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
In Millions, unless otherwise specified
Summary of investments other than investments in related parties	'		'	'
Cost	$7,102	[1]	'	'
Carrying Value	7,428.90	[1]	'	'
Fair Value	7,428.90	[1]	'	'
Fixed maturity investments	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	5,265.90	[1]	'	'
Carrying Value	5,266.80	[1]	'	'
Fair Value	5,266.80	[1]	'	'
US Government and agency obligations	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	365.5		'	'
Carrying Value	362.5		'	'
Fair Value	362.5		'	'
Debt securities issued by corporations	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	2,330.70		'	'
Carrying Value	2,347.20		'	'
Fair Value	2,347.20		'	'
Mortgage-backed and asset-backed securities	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	2,027.30		'	'
Carrying Value	2,014.50		'	'
Fair Value	2,014.50		'	'
Municipal obligations	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	18.3		'	'
Carrying Value	17.9		'	'
Fair Value	17.9		'	'
Foreign government, agency and provincial obligations	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	444.2		'	'
Carrying Value	439.9		'	'
Fair Value	439.9		'	'
Redeemable preferred stocks	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	79.9		'	'
Carrying Value	84.8		'	'
Fair Value	84.8		'	'
Short-term investments	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	635.9		'	'
Carrying Value	635.9		'	'
Fair Value	635.9		'	'
Common equity securities	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	890.2		'	'
Carrying Value	1,156.80		'	'
Fair Value	1,156.80		'	'
Banks, trust and insurance companies	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	274.2		'	'
Carrying Value	360.4		'	'
Fair Value	360.4		'	'
Public utilities	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	32.1		'	'
Carrying Value	34.3		'	'
Fair Value	34.3		'	'
Industrial, miscellaneous and other	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	583.9		'	'
Carrying Value	762.1		'	'
Fair Value	762.1		'	'
Convertible fixed maturity investments	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	71.7		'	'
Carrying Value	80.5		'	'
Fair Value	80.5		'	'
Other long-term investments	'		'	'
Summary of investments other than investments in related parties	'		'	'
Cost	238.3		'	'
Carrying Value	288.9		'	'
Fair Value	288.9		'	'
Discontinued Operations	'		'	'
Summary of investments other than investments in related parties	'		'	'
Investments reclassified to assets held for sale	$236.30		$338.10	$111.80
[1]	Carrying value and fair value includes $236.3 classified as assets held for sale relating to discontinued operations. See Note 21 - “Discontinued Operations”.

SCHEDULE_II_CONDENSED_FINANCIA1

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Assets	'	'
Cash	$382.80	$462.40
Fixed maturity investments, at fair value	5,030.50	5,196.20
Common equity securities, at fair value	1,156.80	1,029.70
Short-term investments, at amortized cost	635.9	630.6
Other assets	458.1	503
Total assets	12,144.30	12,895.40
Liabilities	'	'
Debt	676.4	751.2
Other liabilities	362.9	452.8
Total liabilities	7,746.90	8,637.20
White Mountains’ common shareholders’ equity	4,397.40	4,258.20
Total liabilities and equity	12,144.30	12,895.40
White Mountains Insurance Group Ltd.	'	'
Assets	'	'
Cash	0.2	0.5
Fixed maturity investments, at fair value	31.8	39
Short-term investments, at amortized cost	1.4	8.9
Receivable due from subsidiary	0	96.6
Other assets	0.4	1
Investments in consolidated and unconsolidated affiliates	3,919.10	3,664.60
Total assets	3,952.90	3,810.60
Liabilities	'	'
Debt	0	75
Payable to subsidiary	47	0
Other liabilities	0.4	3.8
Total liabilities	47.4	78.8
White Mountains’ common shareholders’ equity	3,905.50	3,731.80
Total liabilities and equity	$3,952.90	$3,810.60

SCHEDULE_II_CONDENSED_FINANCIA2

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT (Details 2) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT	'	'	'	'	'	'	'	'	'	'	'
Revenues (including realized gains and losses)	$626.60	$574.10	$489.30	$627.40	$566.40	$697.40	$542.30	$629.70	$2,317.40	$2,435.70	$2,173.10
Expenses	492.4	518.8	485.7	475.6	617.2	562.3	504.7	488.8	1,972.50	2,172.90	2,075.10
Pre-tax loss	134.2	55.3	3.6	151.8	-50.8	135.1	37.6	140.9	344.9	262.8	98
Income tax (expense) benefit	-27.4	-8.2	0.6	-41.6	101	-47.8	-6.4	-31.1	-76.6	15.7	110
Net income from continuing operations	106.8	47.1	4.2	110.2	50.2	87.3	31.2	109.8	268.3	278.5	208
Net income attributable to White Mountains’ common shareholders	117.9	57.2	26.3	120.4	68.2	19.1	26.1	94	321.8	207.4	767.9
Comprehensive income attributable to White Mountains’ common shareholders	'	'	'	'	'	'	'	'	242	302.6	686.2
Computation of net income (loss) available to common shareholders:	'	'	'	'	'	'	'	'	'	'	'
Net income attributable to White Mountains’ common shareholders	117.9	57.2	26.3	120.4	68.2	19.1	26.1	94	321.8	207.4	767.9
White Mountains Insurance Group Ltd.	'	'	'	'	'	'	'	'	'	'	'
CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT	'	'	'	'	'	'	'	'	'	'	'
Revenues (including realized gains and losses)	'	'	'	'	'	'	'	'	1.2	20.8	6.4
Expenses	'	'	'	'	'	'	'	'	39	32.4	51.7
Pre-tax loss	'	'	'	'	'	'	'	'	-37.8	-11.6	-45.3
Income tax (expense) benefit	'	'	'	'	'	'	'	'	-0.1	-0.3	6.5
Net income from continuing operations	'	'	'	'	'	'	'	'	-37.9	-11.9	-38.8
Equity in earnings (losses) from consolidated and unconsolidated affiliates	'	'	'	'	'	'	'	'	359.7	219.3	806.7
Net income attributable to White Mountains’ common shareholders	'	'	'	'	'	'	'	'	321.8	207.4	767.9
Other comprehensive income (loss), after-tax	'	'	'	'	'	'	'	'	-79.8	95.2	-81.7
Comprehensive income attributable to White Mountains’ common shareholders	'	'	'	'	'	'	'	'	242	302.6	686.2
Computation of net income (loss) available to common shareholders:	'	'	'	'	'	'	'	'	'	'	'
Net income attributable to White Mountains’ common shareholders	'	'	'	'	'	'	'	'	$321.80	$207.40	$767.90

SCHEDULE_II_CONDENSED_FINANCIA3

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT (Details 3) (USD $)

3 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

Dec. 31, 2013

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Nov. 30, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2010

Dec. 31, 2013

Nov. 30, 2011

Nov. 30, 2011

Dec. 31, 2013

Dec. 31, 2013

Lone Tree Insurance Group Ltd

Lone Tree Insurance Group Ltd

White Mountains Insurance Group Ltd.

White Mountains Insurance Group Ltd.

White Mountains Insurance Group Ltd.

White Mountains Insurance Group Ltd.

Fixed maturity investments

Fixed maturity investments

Short-term investments

Cash

Revolving Credit Facility [Member]

Lone Tree Insurance Group Ltd

Lone Tree Insurance Group Ltd

Lone Tree Insurance Group Ltd

Lone Tree Insurance Group Ltd

White Mountains Insurance Group Ltd.

CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net income attributable to White Mountains’ common shareholders

$117,900,000

$57,200,000

$26,300,000

$120,400,000

$68,200,000

$19,100,000

$26,100,000

$94,000,000

$321,800,000

$207,400,000

$767,900,000

'

'

'

$321,800,000

$207,400,000

$767,900,000

'

'

'

'

'

'

Charges (credits) to reconcile net income to net cash (used for) provided from operations:

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net realized and unrealized investment gains

'

'

'

'

'

'

'

'

-161,700,000

-118,200,000

-74,100,000

'

'

'

-200,000

-11,000,000

-3,100,000

'

'

'

'

'

'

Undistributed current earnings from subsidiaries

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-359,700,000

-219,300,000

-806,700,000

'

'

'

'

'

'

Other non-cash reconciling items including restricted share and option amortization

'

'

'

'

'

'

'

'

'

'

'

'

'

'

15,600,000

22,100,000

7,200,000

'

'

'

'

'

'

Net change in other assets and liabilities, net

'

'

'

'

'

'

'

'

63,200,000

-52,700,000

-62,200,000

'

'

'

-2,900,000

-10,000,000

6,500,000

'

'

'

'

'

'

Net cash used for operations

'

'

'

'

'

'

'

'

-101,000,000

-225,800,000

-114,500,000

'

'

'

-25,400,000

-10,800,000

-28,200,000

'

'

'

'

'

'

Cash flows from investing activities:

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Net decrease in short-term investments

'

'

'

'

'

'

'

'

34,800,000

145,300,000

174,500,000

'

'

'

7,500,000

[1]

63,300,000

[1]

267,300,000

[1]

'

'

'

'

'

'

Purchases of investment securities

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-26,200,000

[1],[2]

-706,200,000

[1],[2]

-237,300,000

[1],[2]

'

'

'

'

'

'

Sales and maturities of investment securities

'

'

'

'

'

'

'

'

4,924,800,000

6,997,500,000

5,034,000,000

'

'

'

61,100,000

[3]

2,009,700,000

[3]

59,000,000

[3]

'

'

'

'

'

'

Issuance of debt (to) from subsidiaries

'

'

'

'

'

'

'

'

'

'

'

'

'

'

153,900,000

[4]

-121,000,000

[4]

0

[4]

'

'

'

'

'

'

Repayment of debt (to) from subsidiaries

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-10,300,000

[1]

28,500,000

[1]

192,500,000

[1]

'

'

'

'

'

'

Payments to subsidiaries

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

[3]

-663,000,000

[3]

0

[3]

'

'

'

'

'

'

Distributions from subsidiaries

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100,000

[2]

0

[2]

7,200,000

[2]

'

'

'

'

'

'

Net cash provided from investing activities

'

'

'

'

'

'

'

'

401,800,000

829,600,000

799,600,000

'

'

'

186,100,000

611,300,000

288,700,000

'

'

'

'

'

'

Cash flows from financing activities:

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Draw down of revolving line of credit

'

'

'

'

'

'

'

'

200,000,000

150,000,000

0

'

'

'

200,000,000

[5]

150,000,000

[5]

0

[5]

'

'

'

'

'

'

Repayment of revolving line of credit

'

'

'

'

'

'

'

'

-275,000,000

-75,000,000

0

'

'

'

-275,000,000

[4],[5]

-75,000,000

[4],[5]

0

[4],[5]

'

'

'

'

'

-75,000,000

Proceeds from issuances of common shares

'

'

'

'

'

'

'

'

0

0

900,000

'

'

'

0

0

900,000

'

'

'

'

'

'

Repurchases and retirement of common shares

'

'

'

'

'

'

'

'

-79,800,000

-669,100,000

-253,000,000

'

'

'

-79,800,000

[3],[4]

-669,100,000

[3],[4]

-253,000,000

[3],[4]

'

'

'

'

'

'

Dividends paid on common shares

'

'

'

'

'

'

'

'

-6,200,000

-6,600,000

-8,000,000

'

'

'

-6,200,000

-6,600,000

-8,000,000

'

'

'

'

'

'

Net cash used for financing activities

'

'

'

'

'

'

'

'

-186,500,000

-648,200,000

-460,200,000

'

'

'

-161,000,000

-600,700,000

-260,100,000

'

'

'

'

'

'

Net change in cash during the period

'

'

'

'

'

'

'

'

114,100,000

-41,300,000

223,400,000

'

'

'

-300,000

-200,000

400,000

'

'

'

'

'

'

Cash balance at beginning of year

326,700,000

'

'

'

212,600,000

'

'

'

326,700,000

212,600,000

251,900,000

103,600,000

'

'

200,000

500,000

700,000

300,000

'

'

'

'

'

Cash balance at end of year

326,700,000

'

'

'

212,600,000

'

'

'

326,700,000

212,600,000

251,900,000

103,600,000

'

'

200,000

500,000

700,000

300,000

'

'

'

'

'

Cash dividends received on warrants

'

'

'

'

'

'

'

'

'

'

'

'

0

'

'

'

'

'

0

'

'

0

'

Interest Paid

'

'

'

'

'

'

'

'

42,600,000

44,600,000

59,000,000

'

'

'

3,700,000

2,000,000

12,400,000

'

'

'

'

'

'

Noncash distribution received

'

'

'

'

'

'

'

'

'

'

'

'

0

'

'

'

'

'

'

'

'

'

'

Common shares repurchased and retired during the period

'

'

'

'

'

'

'

'

'

1,329,640

'

'

'

'

'

'

'

'

'

'

'

'

'

Noncash investments acquired

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

284.7

'

'

Noncash payables acquired

'

'

'

'

'

'

'

'

'

'

'

'

'

$417.50

'

'

'

'

'

'

'

'

'

[1]

In November 2011, Lone Tree Insurance Group Ltd., a direct wholly-owned subsidiary of the Registrant, was liquidated into the Registrant. Significant non-cash balances that were transferred to the Registrant as part of the liquidation included fixed maturity investments of $1,146.9, short-term investments of $284.7 and a payable to subsidiary of $417.5.

[2]

During 2013, the Company received a distribution of $28.0 from its direct wholly-owned subsidiary Lone Tree Holdings, Ltd. The distribution included $27.9 of fixed maturities and $.1 of cash. Purchases of investment securities excludes the non-cash distribution of $27.9.

[3]

During 2012, the Company sold the majority of its fixed maturity investments and used the proceeds to (a) contribute $663.0 to its subsidiaries, the majority of which was used to fund HG Global and (b) repurchase 1,329,640 of its common shares for $669.1.

[4]

During 2013, the Company used cash proceeds received from the issuance of debt to repurchase $79.8 of its common shares and repay $75.0 of its revolving line of credit.

[5]

The WTM Bank Facility presented in Note 6 - “Debt” is a direct obligation of the Registrant.

SCHEDULE_III_SUPPLEMENTARY_INS1

SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
SUPPLEMENTARY INSURANCE INFORMATION	'		'		'
Net investment income	$110.90		$153.60		$184.50
OneBeacon	'		'		'
SUPPLEMENTARY INSURANCE INFORMATION	'		'		'
Deferred acquisition costs	103.7	[1]	123.9	[1]	123.5	[1]
Future policy benefits, losses, claims and loss expenses	1,054.30	[1]	1,000	[1]	3,358.60	[1]
Unearned premiums	544.9	[1]	573.8	[1]	528	[1]
Other policy claims and benefits payable	0	[1]	0	[1]	0	[1]
Premiums earned	1,120.40	[1]	1,132	[1]	1,012.20	[1]
Net investment income	41.1	[1],[2]	53.6	[1],[2]	71.4	[1],[2]
Benefits, claims, losses, and settlement expenses	622.1	[1]	650	[1]	548.3	[1]
Amortization of deferred policy acquisition costs	208.9	[1]	249.4	[1]	221.2	[1]
Other operating expenses	204.8	[1]	205.2	[1]	162.3	[1]
Premiums written	1,088.60	[1]	1,179.20	[1]	1,062.70	[1]
Net investment income	41.1		53.6		71.4
Sirius Group	'		'		'
SUPPLEMENTARY INSURANCE INFORMATION	'		'		'
Deferred acquisition costs	69.3		71.4		63.5
Future policy benefits, losses, claims and loss expenses	2,025		2,168.90		2,343.70
Unearned premiums	343.3		350.2		319
Other policy claims and benefits payable	0		0		0
Premiums earned	866.4		931.6		912.3
Net investment income	30.3	[2]	65	[2]	89.9	[2]
Benefits, claims, losses, and settlement expenses	418.4		543.9		626
Amortization of deferred policy acquisition costs	166.5		180.8		181
Other operating expenses	126.1		116.4		105.8
Premiums written	876.6		947.7		915.7
HG Global-BAM	'		'		'
SUPPLEMENTARY INSURANCE INFORMATION	'		'		'
Deferred acquisition costs	1.7		0		'
Future policy benefits, losses, claims and loss expenses	0		0		'
Unearned premiums	13.2		0		'
Other policy claims and benefits payable	0		0		'
Premiums earned	0.5		0		'
Net investment income	5.7	[2]	2.2	[2]	'
Benefits, claims, losses, and settlement expenses	0		0		'
Amortization of deferred policy acquisition costs	1.5		0		'
Other operating expenses	0.4		0.2		'
Premiums written	13.6		0		'
Other Operations	'		'		'
SUPPLEMENTARY INSURANCE INFORMATION	'		'		'
Deferred acquisition costs	0		0		0
Future policy benefits, losses, claims and loss expenses	0		0		0
Unearned premiums	0		0		0
Other policy claims and benefits payable	0		0		0
Premiums earned	0		0		0
Net investment income	0.1	[2]	0.5	[2]	-0.1	[2]
Benefits, claims, losses, and settlement expenses	0		0		0
Amortization of deferred policy acquisition costs	0		0		0
Other operating expenses	0		0		0
Premiums written	0		0		0
Net investment income	15.3		32.8		23.2
Non-insurance [Member] | Operating Segments	'		'		'
SUPPLEMENTARY INSURANCE INFORMATION	'		'		'
Net investment income	$33.70		$32.30		$23.30
[1]	The amounts shown excludes balances reclassified to held for sale in the consolidated balance sheets related to the Runoff Transaction as of December 31, 2013 and 2012 and to AutoOne as of December 31, 2011. See Note 21 - “Discontinued Operations”.
[2]	The amounts shown exclude net investment income relating to non-insurance operations of $33.7, $32.3 and $23.3 for the twelve months ended December 31, 2013, 2012 and 2011, respectively.

SCHEDULE_IV_REINSURANCE_Detail

SCHEDULE IV REINSURANCE (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Premiums earned	'		'		'
Net earned premiums	$1,987.30		$2,063.60		$1,924.50
OneBeacon	'		'		'
Premiums earned	'		'		'
Gross amount	1,043.30	[1]	1,158.30	[1]	1,035.90	[1]
Ceded to other companies	-71.4	[1]	-79.1	[1]	-66	[1]
Assumed from other companies	148.5	[1]	52.8	[1]	42.3	[1]
Net earned premiums	1,120.40	[1]	1,132	[1]	1,012.20	[1]
Percentage of amount assumed to net	13.30%	[1]	4.70%	[1]	4.20%	[1]
Sirius Group	'		'		'
Premiums earned	'		'		'
Gross amount	174		169.9		128.5
Ceded to other companies	-246.2		-226.6		-206
Assumed from other companies	938.6		988.3		989.8
Net earned premiums	$866.40		$931.60		$912.30
Percentage of amount assumed to net	108.30%		106.10%		108.50%
[1]	The amounts shown excludes balances reclassified to held for sale in the consolidated balance sheets related to the Runoff Transaction as of December 31, 2013 and 2012 and to AutoOne as of December 31, 2011. See Note 21 - “Discontinued Operations”.

SCHEDULE_V_VALUATION_AND_QUALI1

SCHEDULE V VALUATION AND QUALIFYING ACCOUNTS (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Reinsurance recoverable on paid losses: Allowance for reinsurance balances	'		'		'
VALUATION AND QUALIFYING ACCOUNTS	'		'		'
Balance at beginning of period	$35.50		$34.40		$29.40
Charged to costs and expenses	-0.6		-0.6		8.5
Charged to other accounts	0		0		0
Deductions described	-11.2	[1]	1.7	[1]	-3.5	[1]
Balance at end of period	23.7		35.5		34.4
Property and casualty insurance and reinsurance premiums receivable: Allowance for uncollectible accounts	'		'		'
VALUATION AND QUALIFYING ACCOUNTS	'		'		'
Balance at beginning of period	4.4		3.4		3.9
Charged to costs and expenses	1		1.1		0
Charged to other accounts	0		0		-0.5
Deductions described	-1.4	[1]	-0.1	[1]	0	[1]
Balance at end of period	$4		$4.40		$3.40
[1]	Represents net collections (charge-offs) of balances receivable and foreign currency translation.

SCHEDULE_VI_SUPPLEMENTAL_INFOR1

SCHEDULE VI SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS	'		'		'
Rate at which reserves are discounted (as a percent)	3.50%		3.50%		5.00%
OneBeacon	'		'		'
SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS	'		'		'
Deferred acquisition costs(4)	$103.70	[1]	$123.90	[1]	$123.50	[1]
Reserves for Unpaid Claims and Claims Adjustment Expenses	1,054.30	[1]	1,000	[1]	3,358.60	[1]
Discount, if any, deducted in Column C	3	[1],[2]	4.6	[1],[2]	271.6	[1],[2]
Unearned Premiums	544.9	[1]	573.8	[1]	528	[1]
Earned Premiums	1,120.40	[1]	1,132	[1]	1,012.20	[1]
Net investment income	41.1	[1]	53.6	[1]	71.4	[1]
Claims and ClaimsAdjustment ExpensesIncurred Related to, Current Year	622.1	[1]	657.4	[1]	578.1	[1]
Claims and ClaimsAdjustment ExpensesIncurred Related to, Prior Year	0	[1]	-7.4	[1]	-29.8	[1]
Amortization of deferred policy acquisition(4) costs	208.9	[1],[3]	249.4	[1],[3]	221.2	[1],[3]
Paid Claims and Claims Adjustment Expenses	540.7	[1]	565.1	[1]	523.2	[1]
Premiums written	1,088.60	[1]	1,179.20	[1]	1,062.70	[1]
Sirius Group	'		'		'
SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS	'		'		'
Deferred acquisition costs(4)	69.3		71.4		63.5
Reserves for Unpaid Claims and Claims Adjustment Expenses	2,025		2,168.90		2,343.70
Discount, if any, deducted in Column C	1.7	[4]	2.4	[4]	12.8	[4]
Unearned Premiums	343.3		350.2		319
Earned Premiums	866.4		931.6		912.3
Net investment income	30.3		65		89.9
Claims and ClaimsAdjustment ExpensesIncurred Related to, Current Year	466.8		578.4		672.9
Claims and ClaimsAdjustment ExpensesIncurred Related to, Prior Year	-48.4		-34.5		-46.9
Amortization of deferred policy acquisition(4) costs	166.5	[3]	180.8	[3]	181	[3]
Paid Claims and Claims Adjustment Expenses	628.1		741.2		642
Premiums written	$876.60		$947.70		$915.70
[1]	The amounts shown excludes balances reclassified to held for sale in the consolidated balance sheets related to the Runoff Transaction as of December 31, 2013 and 2012 and to AutoOne as of December 31, 2011. See Note 21 - “Discontinued Operations”.
[2]	The amounts shown represent OneBeacon’s discount on its long-term workers compensation loss and LAE reserves, as such liabilities constitute unpaid but settled claims under which the payment pattern and ultimate costs are fixed and determinable on an individual basis. OneBeacon discounts these reserves using a discount rate which is determined based on the facts and circumstances applicable at the time the claims are settled (3.5%, 3.5% and 5.0% at December 31, 2013, 2012 and 2011). Also the amounts shown include unamortized fair value adjustments to reserves for unpaid claims and claims adjustment expenses made in purchase accounting as a result of White Mountains’ purchase of OneBeacon for the years ended December 31, 2013, 2012 and 2011.
[3]	) In 2012, the Company adopted ASU 2010-26, Accounting for Costs Associated with Acquiring or Renewing Insurance Contracts (ASC 944). See Note 1 - “Summary of Significant Accounting Policies”.
[4]	The amount shown represents unamortized fair value adjustments to reserves for unpaid claims and claims adjustment expenses made in purchase accounting as a result of White Mountains’ purchase of Sirius International during 2004.