White Mountains Insurance (WTM) 10-Q 2 May 16 2016 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2016	May. 02, 2016
Document and Entity Information [Abstract]
Entity Registrant Name	WHITE MOUNTAINS INSURANCE GROUP LTD
Entity Central Index Key	776,867
Document Type	10-Q
Document Period End Date	Mar. 31, 2016
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		5,064,039
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q1

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Assets
Fixed maturity investments, at fair value	$ 2,613.2	$ 2,639.7
Short-term investments, at amortized cost (which approximates fair value)	261.7	211.3
Common equity securities, at fair value	443	1,113.9
Other long-term investments	321.8	315.8
Total investments	3,639.7	4,280.7
Cash	178.8	179.3
Reinsurance recoverable on unpaid losses	150.9	186.5
Reinsurance recoverable on paid losses	16.6	7.5
Insurance premiums receivable	234.3	223.3
Deferred acquisition costs	109.8	107.6
Deferred tax asset	133.6	112.8
Ceded unearned insurance premiums	36.3	29.5
Accrued investment income	13.4	14
Accounts receivable on unsettled investment sales	4.5	41.9
Goodwill and intangible assets	371.5	375.7
Other assets	286.9	316.8
Assets held for sale	5,215.5	4,407
Total assets	10,391.8	10,282.6
Liabilities
Loss and loss adjustment expense reserves	1,349.6	1,395.8
Unearned insurance premiums	626.5	612.6
Debt	532.6	440.5
Deferred Tax Liability, Net of Valuation Allowance	7.1	7
Accrued incentive compensation	114.2	141.7
Ceded reinsurance payable	31.8	30.5
Funds held under insurance contracts	134.9	137.8
Accounts payable on unsettled investment purchases	6.9	0
Other liabilities	229.8	264.7
Total liabilities held for sale	3,121.1	2,884
Total liabilities	6,154.5	5,914.6
White Mountains’s common shareholders’ equity
White Mountains’ common shares	5.4	5.6
Paid-in surplus	933.5	972.6
Retained earnings	2,959.6	3,084.9
Accumulated other comprehensive loss, after tax:
Net unrealized foreign currency translation losses	(108.3)	(145.6)
Pension liability and other	(4.3)	(4.3)
Total White Mountains’s common shareholders’ equity	3,785.9	3,913.2
Non-controlling interests
Non-controlling interests	451.4	454.8
Total equity	4,237.3	4,368
Total liabilities and equity	10,391.8	10,282.6
OneBeacon [Member]
Non-controlling interests
Non-controlling interests	$ 243.4	$ 245.6

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Cash	$ 8.4	$ 5.8
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	5,415,462	5,623,735
Common shares, outstanding shares	5,415,462	5,623,735

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE (LOSS) INCOME - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Revenues:
Earned insurance premiums	$ 282.1	$ 289.3
Net investment income	17.9	12.6
Net realized and unrealized investment gains	29.5	25
Other revenue	97.6	64.9
Total revenues	427.1	391.8
Expenses:
Loss and loss adjustment expenses	161.1	167.9
Insurance and Reinsurance Acquisition Expenses	52.7	53
Other Underwriting Expense	55.4	56
General and administrative expenses	140.5	110.1
Interest expense	5.9	4.3
Total expenses	415.6	391.3
Pre-tax income from continuing operations	11.5	0.5
Income tax benefit (expense)	8.7	(4.6)
Net income (loss) from continuing operations	20.2	(4.1)
Net gain on sale of discontinued operations	0	8
Net (loss) income from discontinued operations, net of tax	(0.9)	65.8
Income before equity in earnings of unconsolidated affiliates	19.3	69.7
Equity in earnings of unconsolidated affiliates, net of tax	0	7.3
Net income	19.3	77
Net (income) loss attributable to non-controlling interests	(6.3)	7.3
Net income attributable to White Mountains’s common shareholders	13	84.3
Other comprehensive (loss) income, net of tax:
Change in equity in net unrealized gains from investments in Symetra common shares, net of tax	0	28.9
Change in foreign currency translation, pension liability and other, net of tax	0.1	0
Comprehensive income	50.3	25.6
Other comprehensive (loss) income attributable to non-controlling interests	0	0
Comprehensive income attributable to White Mountains’s common shareholders	$ 50.3	$ 25.6
Basic income per share
Continuing operations	$ 2.51	$ 1.76
Discontinued operations	(0.17)	12.33
Total consolidated operations	2.34	14.09
Diluted income per share
Continuing operations	2.51	1.76
Discontinued operations	(0.17)	12.33
Total consolidated operations	2.34	14.09
Dividends declared per White Mountains’s common share	$ 1	$ 1
Sirius Group
Revenues:
Net realized and unrealized investment gains	$ 4.1	$ 0.3
Other comprehensive (loss) income, net of tax:
Accumulated Other Comprehensive Income Loss Net Of Tax Other Period Increase Decrease	$ 37.2	$ (87.6)

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions	Total	Common shares and paid-in surplus	Retained earnings	AOCI, after tax	Total	Non-controlling interest	Total Equity	Foreign Currency Gain (Loss)Common shares and paid-in surplus	Foreign Currency Gain (Loss)Retained earnings	Foreign Currency Gain (Loss)AOCI, after tax	Foreign Currency Gain (Loss)Total	Foreign Currency Gain (Loss)Non-controlling interest	Foreign Currency Gain (Loss)Total Equity	Pension liability and other accumulated comprehensive itemsCommon shares and paid-in surplus	Pension liability and other accumulated comprehensive itemsRetained earnings	Pension liability and other accumulated comprehensive itemsAOCI, after tax	Pension liability and other accumulated comprehensive itemsTotal	Pension liability and other accumulated comprehensive itemsNon-controlling interest	Pension liability and other accumulated comprehensive itemsTotal Equity
Balances at Dec. 31, 2014		$ 1,034.7	$ 3,010.5	$ (49.5)	$ 3,995.7	$ 542.7	$ 4,538.4
Increase (Decrease) in Shareholders' Equity
Net income	$ 77	0	84.3	0	84.3	(7.3)	77
Net change in unrealized gains (losses) from investments in unconsolidated affiliates	28.9	0	0	28.9	28.9	0	28.9
Net change in foreign currency translation	0							$ 0	$ 0	$ (87.8)	$ (87.8)	$ 0	$ (87.8)
Other Comprehensive Income (Loss), Net of Tax														$ 0	$ 0	$ 0.2	$ 0.2	$ 0	$ 0.2
Total comprehensive income (loss)	25.6	0	84.3	(58.7)	25.6	(7.3)	18.3
Dividends declared on common shares		0	(6)	0	(6)	0	(6)
Dividends to non-controlling interests	0.7	0	0	0	0	(7)	(7)
Repurchases and retirements of common shares		(3)	(8)	0	(11)	0	(11)
Acquisition from non-controlling interests		4.6	0	0	4.6	(4.6)	0
Noncontrolling Interest, Period Increase (Decrease)		0	0	0	0	5.2	5.2
Amortization of restricted share awards		2.4	0	0	2.4	(0.5)	1.9
Balances at Mar. 31, 2015		1,038.7	3,080.8	(108.2)	4,011.3	528.5	4,539.8
Balances at Dec. 31, 2015	4,368	978.2	3,084.9	(149.9)	3,913.2	454.8	4,368
Increase (Decrease) in Shareholders' Equity
Net income	19.3	0	13	0	13	6.3	19.3
Net change in unrealized gains (losses) from investments in unconsolidated affiliates	0
Net change in foreign currency translation	0.1							$ 0	$ 0	$ 37.3	$ 37.3	$ 0	$ 37.3
Total comprehensive income (loss)	50.3	0	13	37.3	50.3	6.3	56.6
Dividends declared on common shares		0	(5.4)	0	(5.4)	0	(5.4)
Dividends to non-controlling interests	0	0	0	0	0	(6.2)	(6.2)
Repurchases and retirements of common shares		(39.8)	(132.9)	0	(172.7)	0	(172.7)
Acquisition from non-controlling interests		(2.7)	0	0	(2.7)	(8.8)	(11.5)
Issuance of shares to non-controlling interests		0	0	0	0	0.3	0.3
Noncontrolling Interest, Period Increase (Decrease)		0	0	0	0	4.8	4.8
Amortization of restricted share awards		3.2	0	0	3.2	0.2	3.4
Balances at Mar. 31, 2016	$ 4,237.3	$ 938.9	$ 2,959.6	$ (112.6)	$ 3,785.9	$ 451.4	$ 4,237.3

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operations:
Net income	$ 19.3	$ 77
Charges (credits) to reconcile net income to net cash used for operations:
Net realized and unrealized investment gains	(29.5)	(25)
Deferred income tax expense (benefit)	5.3	(0.3)
Net loss (income) from discontinued operations	0.9	(65.8)
Net gain on sale of discontinued operations	0	(8)
Amortization and depreciation	17.4	15.3
Undistributed equity in earnings from unconsolidated affiliates, net of tax	0	(7.3)
Other operating items:
Net change in loss and loss adjustment expense reserves	(46.2)	(39.4)
Net change in reinsurance recoverable on paid and unpaid losses	26.5	13.9
Net change in unearned insurance premiums	13.9	7.6
Net change in variable annuity benefit guarantee liabilities	(0.4)	(0.4)
Net change in variable annuity benefit guarantee derivative instruments	7	9.4
Net change in deferred acquisition costs	(2.2)	(3)
Net change in funds held by ceding entities	0	19.7
Net change in ceded unearned premiums	(6.8)	(1.5)
Net change in funds held under insurance treaties	(2.8)	12
Net change in insurance premiums receivable	(11)	(18.3)
Net change in ceded reinsurance payable	1.3	5.2
Net change in restricted cash	(2.6)	(5.3)
Net change in other assets and liabilities, net	(31.8)	(29.2)
Net cash used for operations - continuing operations	(41.7)	(43.4)
Net cash used for operations	(92.4)	(57.7)
Cash flows from investing activities:
Net change in short-term investments	(50.4)	(75.6)
Sales of fixed maturity and convertible investments	202.3	344.7
Maturities, calls and paydowns of fixed maturity and convertible investments	155.9	35.9
Sales of common equity securities	767.5	59.9
Distributions and redemptions of other long-term investments	3	3.4
Net change in cash during the period	0	7.9
Purchases of other long-term investments	(10.9)	(6.5)
Purchases of common equity securities	(86.1)	(38.8)
Purchases of fixed maturity and convertible investments	(315.2)	(398.7)
Purchases of consolidated and unconsolidated subsidiaries, net of cash acquired	(8.1)	(2.4)
Net change in unsettled investment purchases and sales	44.3	74
Net acquisitions of property and equipment	(2.7)	(4)
Net cash provided from (used for) investing activities - continuing operations	139.8	(0.2)
Net cash provided from investing activities	174.8	35.8
Cash flows from financing activities:
Draw down of debt and revolving line of credit	107	4.5
Repayment of debt and revolving line of credit	(15.1)	(1.3)
Payments on capital lease obligation	(0.5)	(1.3)
Cash dividends paid to the Company’s common shareholders	(5.4)	(6)
Cash dividends paid to OneBeacon Ltd.’s non-controlling common shareholders	(4.7)	(4.9)
Common shares repurchased	(166.9)	(4.3)
OneBeacon Ltd. common shares repurchased and retired	(11.5)	(1.7)
Distribution to non-controlling interest shareholders	0	(0.7)
Distributions from (contributions to) discontinued operations	(3)	(3)
Payment of contingent consideration	(7.8)	0
Capital contributions from BAM members	6.7	4.6
Net cash used for financing activities - continuing operations	(101.2)	(14.1)
Net cash used for financing activities	(98.8)	(12.3)
Effect of Exchange Rate on Cash and Cash Equivalents	0	0
Net change in cash during the period - continuing operations	(3.1)	(57.7)
Cash balances at beginning of period	173.5	238
Cash balances at end of period	170.4	180.3
Supplemental cash flows information:
Interest paid	(1.6)	0
Net income tax refund from (payment to) national governments	13.5	(8)
Discontinued Operations [Member]
Charges (credits) to reconcile net income to net cash used for operations:
Net realized and unrealized investment gains	8.8	(78.4)
Net loss (income) from discontinued operations	1.8	(86.3)
Net gain on sale of discontinued operations	0.9	(65.9)
Other operating items:
Net cash used for operations - discontinued operations	(50.7)	(14.3)
Cash flows from investing activities:
Net change in cash during the period	(9.1)	15
Net cash (used for) provided from investing activities - discontinued operations	35	36
Cash flows from financing activities:
Net cash provided from financing activities - discontinued operations	2.4	1.8
Cash balances at beginning of period	143.9	111.5
Cash balances at end of period	134.8	126.5
Supplemental cash flows information:
Net income tax refund from (payment to) national governments	36.4	7
Symetra
Cash flows from investing activities:
Sales of common equity securities	658
Symetra | Discontinued Operations [Member]
Cash flows from investing activities:
Sales of common equity securities	(559.8)	0
Sirius Group
Charges (credits) to reconcile net income to net cash used for operations:
Net realized and unrealized investment gains	(4.1)	(0.3)
Sirius Group | Discontinued Operations [Member]
Charges (credits) to reconcile net income to net cash used for operations:
Net realized and unrealized investment gains	8.8	(78.4)
Net loss (income) from discontinued operations	1.8	(86.3)
Net gain on sale of discontinued operations	$ 0.9	$ (65.9)

CONSOLIDATED STATEMENTS OF CAS7

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash and Cash Equivalents, at Carrying Value	$ 170.4	$ 180.3
Restricted cash balances	8.4	29
Effect of Exchange Rate on Cash and Cash Equivalents, Discontinued Operations	4.2	(8.5)
Discontinued Operations [Member]
Cash and Cash Equivalents, at Carrying Value	$ 134.8	$ 126.5

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation These interim 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’s reportable segments are OneBeacon, HG Global/BAM and Other Operations. As discussed further in Note 2 , on April 18, 2016, White Mountains completed its sale of Sirius International Insurance Group, Ltd., and its subsidiaries (collectively, “Sirius Group”) to CM International Holding PTE Ltd. (“CMI”), the Singapore-based investment arm of China Minsheng Investment Corp., Ltd. (See Note 2 - “Significant Transactions”). Accordingly, for the quarter ended March 31, 2016, Sirius Group has been presented as discontinued operations in the statement of comprehensive income and its assets and liabilities have been classified as held of sale in the balance sheet. Prior year amounts have been reclassified to conform to the current period’s presentation. (See Note 17 - “Discontinued 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 through independent agencies, regional and national brokers, wholesalers and managing general agencies. As of March 31, 2016 and December 31, 2015 , White Mountains owned 76.1% and 75.5% of OneBeacon Ltd.’s outstanding common shares. The HG Global/BAM segment consists of HG Global Ltd. (“HG Global”) and the consolidated results of Build America Mutual Assurance Company (“BAM”). BAM is a municipal bond insurer domiciled in New York that was established in 2012 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 $503.0 million of surplus notes issued by BAM (the “BAM Surplus Notes”). HG Global, through its wholly-owned subsidiary, HG Re Ltd. (“HG Re”), also provides 15% -of-par, first loss reinsurance protection for policies underwritten by BAM. As of March 31, 2016 and December 31, 2015 , White Mountains owned 96.9% of HG Global’s preferred equity and 88.4% 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’s 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’s variable annuity reinsurance business, White Mountains Life Reinsurance (Bermuda) Ltd. (“Life Re Bermuda”), which is in runoff with all of its contracts maturing by June 30, 2016, and its U.S.-based service provider, White Mountains Financial Services LLC (collectively, “WM Life Re”), and White Mountains’s ownership positions in Tranzact Holdings, LLC, QL Holdings, LLC (together with its subsidiaries “MediaAlpha”) and Wobi Insurance Agency Ltd. (“Wobi”). The Other Operations segment also includes Star & Shield Services LLC, Star & Shield Risk Management LLC (“SSRM”), and Star & Shield Claims Services LLC (collectively “Star & Shield”). Star & Shield provides management services for a fee to Star & Shield Insurance Exchange (“SSIE”), a reciprocal that is owned by its members, who are policyholders. As of March 31, 2016 , White Mountains holds $21.0 million of surplus notes issued by SSIE (the “SSIE Surplus Notes”) but does not have an ownership interest in SSIE. However, because SSRM’s role as the attorney-in-fact to SSIE gives it the power to direct the significant economic activities of SSIE, White Mountains is required to consolidate SSIE in its GAAP financial statements. SSIE’s results do not affect White Mountains’s common shareholders’ equity as they are attributable to non-controlling interests. All significant intercompany transactions have been eliminated in consolidation. Certain amounts in the prior period financial statements have been reclassified to conform to the current presentation. These interim financial statements include all adjustments considered necessary by management to fairly present the financial position, results of operations and cash flows of White Mountains. These interim financial statements may not be indicative of financial results for the full year and should be read in conjunction with the Company’s 2015 Annual Report on Form 10-K. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Refer to the Company’s 2015 Annual Report on Form 10-K for a complete discussion regarding White Mountains’s significant accounting policies. Recently Adopted Changes in Accounting Principles Business Combinations - Measurement Period Adjustments Effective January 1, 2016, White Mountains adopted ASU 2015-16, Simplifying the Accounting for Measurement-Period Adjustments, which requires adjustments to provisional amounts recorded in connection with a business combination that are identified during the measurement period to be recorded in the reporting period in which the adjustment amounts are determined, rather than as retroactive adjustments to prior periods. White Mountains has not recognized any adjustments to estimated purchase accounting amounts for the year to date period ended March 31, 2016 and accordingly, there was no effect to White Mountains’s financial statements upon adoption. Fair Value Measurements On January 1, 2016, White Mountains adopted ASU 2015-07, Fair Value Measurement - Disclosures for Investments in Certain Entities that Calculate Net Asset Value per Share (or Its Equivalent) (ASC 820), which eliminates the requirement to disclose the fair value hierarchy level for investments for which fair value is measured at net asset value using the practical expedient in ASC 820. White Mountains measures the fair value of its investments in hedge funds and private equity funds using this practical expedient. Upon adoption, these fair value measurements are no longer classified within the fair value hierarchy. Prior year amounts have been modified to conform to the current year’s disclosures. Amendments to Consolidation Analysis On January 1, 2016, White Mountains adopted ASU 2015-02, Amendments to the Consolidation Analysis (ASC 810) which amends the guidance for determining whether an entity is a variable interest entity (“VIE”). ASU 2015-02 eliminates the separate consolidation guidance for limited partnerships and, with it, the presumption that a general partner should consolidate a limited partnership. In addition, ASU 2015-02 changes the guidance for determining if fee arrangements qualify as variable interests and the effect fee arrangements have on the determination of the primary beneficiary. Adoption of ASU 2015-02 did not affect the consolidation analysis for any of White Mountains’s investments. Share-Based Compensation Awards On January 1, 2016, White Mountains adopted ASU 2014-12, Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period (ASC 718) . The new guidance requires that a performance target that affects vesting and that can be achieved after the requisite service period be treated as a performance condition. Compensation cost is to be recognized in the period when it becomes probable the performance target will be achieved in an amount equal to the compensation cost attributable to the periods for which service has been rendered. Adoption did not have a significant effect on White Mountains’s financial position, results of operations, cash flows, presentation or disclosures. Debt Issuance Costs On January 1, 2016, White Mountains adopted ASU 2015-03, Imputation of Interest (ASC 835), which requires debt issuance costs to be presented as a deduction from the carrying amount of the related debt, consistent with the treatment required for debt discounts. The new guidance requires amortization of debt issuance costs to be classified within interest expense and also requires disclosure to the debt’s effective interest rate. White Mountains has applied the guidance retrospectively and as a result has reclassified $1.9 million of unamortized debt issuance costs from other assets to debt as of December 31, 2015, reflecting these amounts as a reduction from the related debt, and has modified its disclosures to include the required effective interest rate on its debt. As of March 31, 2016, the unamortized debt issuance costs included in debt is $3.8 million . Recently Issued Accounting Pronouncements Short-Duration Contracts On May 21, 2015, the FASB issued ASU 2015-09, Disclosures about Short Duration Contracts (ASC 944), which requires expanded footnote disclosures about loss and loss adjustment expense (“LAE”) reserves. Under the new guidance, some disclosures currently presented outside of White Mountains’s financial statements, such as loss development tables and a reconciliation of loss development data to the loss and LAE reserves reflected on the balance sheet, will become part of the financial statement footnotes. In addition, the loss development tables required to be presented under the new ASU must be presented on a disaggregated basis by accident year rather than by reporting year as currently presented. Some of the expanded disclosures are new requirements, such as the disclosure of reserves for losses incurred but not reported (“IBNR”) plus expected development on reported claims, which must be presented by accident year on a disaggregated basis. The new guidance also requires new disclosures about claim frequency data together with descriptions of the approach used to measure that data. Qualitative descriptions of methodologies and assumptions used to develop IBNR estimates must be presented together with the amounts of IBNR to which they relate, along with a discussion of any significant changes in methodology and assumptions and the related effect upon the loss reserves. The new guidance will be effective for annual periods beginning after December 15, 2015 and interim periods within annual periods beginning after December 15, 2016 with retrospective restatement of prior periods required. White Mountains will modify its financial statement footnote disclosures to conform to the requirements of ASU 2015-09 upon adoption, including revisions to prior year’s disclosures. Stock Compensation On March 30, 2016, the Board issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting (ASC 718) which is intended to simplify certain aspects of the accounting for share-based compensation. The new guidance provides an accounting policy election to account for forfeitures by either applying an assumption, as required under existing guidance, or by recognizing forfeitures when they actually occur. The new guidance is effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods with early adoption permitted. White Mountains does not expect a significant effect upon adoption. Leases On February 25, 2016, the FASB issued ASU 2016-02, Leases (ASC 842). The new guidance requires lessees to recognize lease assets and liabilities on the balance sheet for both operating and financing leases, with the exception of leases with an original term of 12 months or less. Under existing guidance recognition of lease assets and liabilities is not required for operating leases. The lease assets and liabilities to be recognized are both measured initially based on the present value of the lease payments. Under the new guidance, a sale-leaseback transaction must meet the recognition criteria under ASC 606, Revenues in order to be accounted for as sale. The new guidance is effective for White Mountains for years beginning after December 15, 2018, including interim periods therein. White Mountains is evaluating the expected impact of this new guidance and available adoption methods. Financial Instruments - Recognition and Measurement On January 5, 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities (ASC 825-10). The new guidance requires all equity securities with readily determinable fair values to be measured at fair value with changes therein recognized through current period earnings. In addition, the new ASU requires a qualitative assessment for equity investments without readily determinable fair values to identify impairment, and for impaired equity security investments to be measured at fair value. ASU 2016-01 is effective for fiscal years beginning after December 15, 2017, with early adoption permitted. White Mountains has taken the fair value election for its portfolio of equity security investments and, accordingly, does not expect the adoption of ASU 2016-01 to have a significant impact on its financial statements. Revenue Recognition On May 28, 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (ASC 606), which modifies the guidance for revenue recognition. The scope of the new ASU excludes insurance contracts but is applicable to certain fee arrangements, such as third party investment management fees charged by White Mountains Advisors as well as commissions and other non-insurance revenues. In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (ASC 606) , which delayed the effective date of ASU 2014-09 to annual and interim reporting periods beginning after December 15, 2017. White Mountains is in the process of evaluating the new guidance and has not yet determined the potential effect of adoption on its financial position, results of operations, or cash flows.

Significant Transactions

Significant Transactions	3 Months Ended
	Mar. 31, 2016
Significant Transactions [Abstract]
Significant Transactions	Significant Transactions Sale of Sirius Group On April 18, 2016, White Mountains completed the sale of Sirius Group to CMI for approximately $2.6 billion . $ 161.8 million of this amount was used to purchase certain assets to be retained by White Mountains out of Sirius Group, including shares of OneBeacon. The amount paid at closing was based on an estimate of Sirius Group’s closing date tangible common shareholder’s equity. The purchase price will be adjusted upon determination of Sirius Group’s actual closing date tangible common shareholder’s equity. Sirius Group’s results are reported as discontinued operations and assets and liabilities held for sale within White Mountains’s GAAP financial statements. Assets held for sale does not include White Mountains’s investment in OneBeacon and certain other investments were held in the Sirius Group legal entities as of March 31, 2016 and December 31, 2015. The value of these investments, net of related tax effects, is approximately $161.8 million and $ 686.2 million , of which $0 and $ 528.6 million was Symetra’s common shares, as of March 31, 2016 and December 31, 2015. In connection with the transaction, White Mountains caused Sirius Group to purchase several industry loss warranty contracts to mitigate the potential impact of major events on Sirius Group’s balance sheet pending the close of the sale to CMI (the “ILW Covers”). The cost and potential economic benefit provided by the coverage under the ILW Covers inure to White Mountains. The majority of the contracts expire in May or June 2016. The following summarizes the ILW Covers: Scope Limit Industry Loss Trigger United States first event $75.0 million $40.0 billion United States first event $22.5 million $50.0 billion United States second event $45.0 million $15.0 billion Japan first event (1) $25.0 million $12.5 billion (1) ILW cover expired on March 31, 2016. Symetra On February 1, 2016, White Mountains sold its investment in Symetra for proceeds of $ 658.0 million , or $32.00 per share. (See Note 14 - “Investments in Unconsolidated Affiliates”) . OneBeacon Crop Business On July 31, 2015, OneBeacon exited its multiple peril crop insurance (“MPCI”) and its related crop-hail business (collectively, “Crop Business”) as its exclusive managing general agency, Climate Crop Insurance Agency (“CCIA”), exited the business through a sale of the agency to an affiliate of AmTrust. As a result of the transaction, OneBeacon and CCIA agreed to an early termination of the existing five-year agreement. In connection with the termination of the agreement, OneBeacon received a payment of $ 3.0 million . Also related to the transaction, OneBeacon withdrew its 2016 Plan of Operations, which previously authorized it to write MPCI for the 2016 Reinsurance Year, and affiliates of AmTrust agreed to reinsure the Company’s remaining net Crop Business exposure for the 2015 Reinsurance Year under a related 100% quota share reinsurance agreement which, coupled with other transfer and assignment agreements as well as communications with policyholders and agents, had the effect of assumption reinsurance. As a result of this transaction, the Company has no material net exposure related to the Crop Business. Tranzact On October 10, 2014, White Mountains acquired majority ownership of Tranzact, a provider of comprehensive direct-to-consumer customer acquisition solutions for leading insurance carriers. White Mountains acquired 63.2% of Tranzact for a purchase price of $177.7 million , representing an enterprise value of $281.2 million . Immediately following the closing, Tranzact completed a recapitalization that allowed for the return of $44.2 million to White Mountains. As of the acquisition date, White Mountains recognized total assets acquired related to Tranzact of $332.8 million , including $41.4 million of tangible assets, $145.1 million of goodwill, and $146.3 million of other intangible assets, and total liabilities assumed of $108.7 million at their estimated fair values. The liabilities assumed include a contingent consideration liability of $ 7.4 million associated with a prior acquisition by Tranzact. The contingent consideration is payable if earnings before interest expense, taxes, depreciation and amortization (“EBITDA”) of the acquiree exceed amounts defined in the purchase agreement. On September 1, 2015, Tranzact acquired 100.0% of the outstanding share capital of TruBridge, Inc. and TruBroker, LLC (collectively “TruBridge”) for a purchase price of $ 31.0 million . The purchase price is subject to an adjustment linked to the amount of marketing expense reimbursements expected to be received in 2016 and 2017. As of the acquisition date, Tranzact recognized total assets acquired of $ 54.5 million , which includes $ 18.7 million of goodwill and $ 28.1 million of other intangible assets, and total liabilities assumed of $ 4.3 million at their estimated fair values. On November 6, 2015, Tranzact acquired the domain name CancerInsurance.com for a purchase price of $ 3.1 million , which is included in other intangible assets. The purchase price included cash of $ 1.1 million and a liability of $ 2.0 million for contingent consideration that is payable if EBITDA exceeds amounts defined in the purchase agreement between November 6, 2016 and May 6, 2018. The maximum amount of the contingent consideration is $ 6.8 million . MediaAlpha On March 14, 2014, White Mountains acquired 60% of the outstanding Class A common units of MediaAlpha. MediaAlpha is a California-based advertising technology company that develops programmatic platforms that bring transparency and efficiency to the buying and selling of insurance and other vertical-specific performance media (clicks, calls and leads). MediaAlpha’s exchange technology and sophisticated analytical tools facilitate transparent, real-time transactions between advertisers (buyers of advertising inventory) and publishers (sellers of advertising inventory). MediaAlpha works with over 200 advertisers and 200 publishers across a number of insurance (auto, motorcycle, home, renter, health, and life) and non-insurance (travel, education) verticals. White Mountains paid an initial purchase price of $28.1 million. The purchase price was subject to adjustment equal to 62.5% of the 2015 gross profit in excess of the 2013 gross profit. On February 26, 2016, White Mountains paid $ 7.8 million in settlement of the final purchase adjustment. After adjustment for the estimated contingent purchase price adjustment, White Mountains recognized total assets acquired related to MediaAlpha of $70.1 million , including $18.3 million of goodwill and $38.5 million of other intangible assets, and total liabilities assumed of $10.0 million , reflecting acquisition date fair values. On January 15, 2016, MediaAlpha acquired certain assets from Oversee.net for a purchase price of $ 3.9 million . The majority of assets acquired, which are included in other intangible assets, consist of customer relationships, a customer contract, a non-compete agreement from the seller, domain names and technology. Wobi On February 19, 2014, White Mountains acquired 54% of the outstanding common shares of Wobi for NIS 14.4 million (approximately $4.1 million based upon the foreign exchange spot rate at the date of acquisition). During 2014, in addition to the common shares, White Mountains also purchased NIS 31.5 million (approximately $9.0 million based upon the foreign exchange spot rate at the dates of acquisition) of newly-issued convertible preferred shares of Wobi. Wobi is the only price comparison/aggregation business in Israel, with an insurance carrier panel that represents 85% of the premiums written in the Israeli insurance market. Wobi sells four insurance lines of business, primarily personal auto, and operates as an agency, charging upfront commissions on all insurance policy sales. Wobi also offers a pension products comparison service for Israeli customers and is paid transaction fees when customers use the service to connect to companies that sell those pension products. As of the acquisition date, White Mountains recognized total assets acquired related to Wobi of $13.4 million , including $5.5 million of goodwill and $2.9 million of other intangible assets; and total liabilities assumed of $0.7 million at their estimated fair values. During 2015, White Mountains purchased NIS 91.4 million (approximately $ 23.8 million based upon the foreign exchange spot rate at the dates of acquisition) of convertible preferred shares of Wobi. For both periods, March 31, 2016 and December 31, 2016, White Mountains’s ownership share was 96.1% on a fully converted basis. During 2015, Wobi acquired Tnuva Finansit Ltd. (“Cashboard”) in two transactions for a total of NIS 35.9 million (approximately $8.9 million based upon the foreign exchange spot rate at the dates of acquisition). The acquisition of Cashboard accelerated Wobi’s development of its pension products comparison service. As of the acquisition date, Wobi recognized total assets acquired of $5.5 million , including $0.3 million of goodwill and $2.8 million of other intangible assets; and total liabilities assumed of $1.2 million at their estimated acquisition date fair values. Star & Shield On January 31, 2014, White Mountains acquired certain assets and liabilities of Star & Shield Holdings LLC, including SSRM, the attorney-in-fact for SSIE, for a purchase price of $1.8 million . White Mountains owns $21.0 million of surplus notes issued by SSIE. Principal and interest on the surplus notes are payable to White Mountains only with approval from the Florida Office of Insurance Regulation. SSIE is a Florida-domiciled reciprocal insurance exchange providing private passenger auto insurance to the public safety community and their families. SSIE is a variable interest entity (“VIE”). As a result of SSRM’s role as the attorney-in-fact to SSIE and the investment in SSIE’s Surplus Notes, White Mountains is required to consolidate SSIE. At March 31, 2016 and December 31, 2015, consolidated amounts included total assets of $13.3 million and $14.2 million and total liabilities of $29.4 million and $30.3 million , respectively, of SSIE. The surplus notes purchased by White Mountains and the corresponding liability included in SSIE’s liabilities are eliminated in consolidation. For the three months ended March 31, 2016 and 2015, SSIE had pre-tax losses of $0.1 million and $1.1 million that were recorded in net loss attributable to non-controlling interests. 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. During the first quarter of 2015, OneBeacon recognized in other revenues a $ 3.7 million negative adjustment to the pre-tax gain on sale of Essentia in connection with an assessment from the Michigan Catastrophic Claims Association payable to Markel Corporation pursuant to the indemnification provisions in the stock purchase agreement governing the sale of Essentia.

Loss and Loss Adjustment Expens

Loss and Loss Adjustment Expense Reserves	3 Months Ended
	Mar. 31, 2016
Insurance Loss Reserves [Abstract]
Loss and Loss Adjustment Expense Reserves	Loss and Loss Adjustment Expense Reserves The following table summarizes the loss and loss adjustment expense (“LAE”) reserve activities of White Mountains’s insurance and reinsurance subsidiaries for the three months ended March 31, 2016 and 2015 : Three Months Ended March 31, Millions 2016 2015 Gross beginning balance $ 1,395.8 $ 1,350.0 Less beginning reinsurance recoverable on unpaid losses (186.5 ) (161.7 ) Net loss and LAE reserves 1,209.3 1,188.3 Loss and LAE incurred relating to: Current year losses 161.2 169.8 Prior year losses (0.1 ) (1.9 ) Total incurred losses and LAE 161.1 167.9 Loss and LAE paid relating to: Current year losses (23.1 ) (23.3 ) Prior year losses (148.6 ) (164.0 ) Total loss and LAE payments (171.7 ) (187.3 ) Net ending balance 1,198.7 1,168.9 Plus ending reinsurance recoverable on unpaid losses 150.9 141.7 Gross ending balance $ 1,349.6 $ 1,310.6 Loss and LAE incurred relating to prior year losses for the three months ended March 31, 2016 For the three months ended March 31, 2016 , White Mountains experienced net favorable loss reserve development of $0.1 million . During the three months ended March 31, 2016 , OneBeacon experienced no net loss and LAE reserve development on prior accident year reserves, as favorable development from several businesses, including Technology and Accident, was offset by unfavorable development primarily in Healthcare. For the three months ended March 31, 2016 , SSIE had net favorable loss reserve development of $0.1 million . Loss and LAE incurred relating to prior year losses for the three months ended March 31, 2015 For the three months ended March 31, 2015 , White Mountains experienced net favorable loss reserve development of $1.9 million . For the three months ended March 31, 2015 , OneBeacon had net favorable loss reserve development of $1.8 million primarily attributable to favorable development from Crop resulting from the 2014 crop year and favorable development in several other businesses, including Ocean Marine, Technology, Government Risks, Surety and Specialty Property. This favorable development was mostly offset by unfavorable development in Entertainment driven by several claims and by losses within the Inland Marine business driven by a few large claims. For the three months ended March 31, 2015 , SSIE had net favorable loss reserve development of $0.1 million .

Third Party Reinsurance

Third Party Reinsurance	3 Months Ended
	Mar. 31, 2016
Reinsurance Disclosures [Abstract]
Third Party Reinsurance	Third Party Reinsurance In the normal course of business, White Mountains’s insurance subsidiaries may seek to limit losses that may arise from catastrophes or other events by reinsuring with third party reinsurers. White Mountains remains liable for risks reinsured in the event that the reinsurer does not honor its obligations under reinsurance contracts. OneBeacon At March 31, 2016 , OneBeacon had $16.6 million and $150.4 million of reinsurance recoverables on paid and unpaid losses. At December 31, 2015 , OneBeacon had $7.5 million and $186.0 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 and ratings of its reinsurers on an ongoing basis. Uncollectible amounts related to the ongoing specialty business historically have not been significant. In the first quarter of 2016, OneBeacon entered into a 50% quota share reinsurance agreement related to its Financial Institutions business.

Investment Securities

Investment Securities	3 Months Ended
	Mar. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Investment Securities	Investment Securities White Mountains’s invested assets consist of investment securities and other long-term investments held for general investment purposes. The portfolio of investment securities includes fixed maturity investments, short-term investments, common equity securities, and other-long term investments which are all classified as trading securities. Trading securities are reported at fair value as of the balance sheet date. Realized and unrealized investment gains and losses on trading securities are reported in pre-tax revenues. White Mountains’s investments in fixed maturity investments are generally valued using industry standard pricing models. Key inputs include benchmark yields, benchmark securities, reported trades, issuer spreads, bids, offers, credit ratings and prepayment speeds. Income on mortgage-backed and asset-backed securities is recognized using an effective yield based on anticipated prepayments and the estimated economic life of the securities. When actual prepayments differ significantly from anticipated prepayments, the estimated economic life is recalculated and the remaining unamortized premium or discount is amortized prospectively over the remaining economic life. Realized investment gains and losses resulting from sales of investment securities are accounted for using the specific identification method. Premiums and discounts on all fixed maturity investments are amortized or accreted to income over the anticipated life of the investment. Short-term investments consist of money market funds, certificates of deposit and other securities which, at the time of purchase, mature or become available for use within one year. Short-term investments are carried at amortized or accreted cost, which approximated fair value as of March 31, 2016 and December 31, 2015 . Other long-term investments consist primarily of hedge funds, private equity funds, direct investments in privately held common and convertible securities and the OneBeacon surplus notes. Net Investment Income White Mountains’s net investment income is comprised primarily of interest income associated with White Mountains’s fixed maturity investments, dividend income from its equity investments and interest income from its short-term investments. Pre-tax net investment income for the three months ended March 31, 2016 and 2015 consisted of the following: Three Months Ended March 31, Millions 2016 2015 Investment income: Fixed maturity investments $ 14.5 $ 12.5 Short-term investments .2 — Common equity securities 1.2 2.2 Other long-term investments 2.8 (.1 ) Total investment income 18.7 14.6 Third-party investment expenses (.8 ) (2.0 ) Net investment income, pre-tax $ 17.9 $ 12.6 Net Realized and Unrealized Investment Gains (Losses) Net realized and unrealized investment gains (losses) consisted of the following: Three Months Ended March 31, Millions 2016 2015 Net realized investment gains, pre-tax $ 256.8 $ 14.8 Net unrealized investment (losses) gains, pre-tax (227.3 ) 10.2 Net realized and unrealized investment gains, pre-tax 29.5 25.0 Income tax expense attributable to net realized and unrealized investment gains (8.5 ) (7.1 ) Net realized and unrealized investment gains, after tax $ 21.0 $ 17.9 Net realized investment gains (losses) Net realized investment gains (losses) for the three months ended March 31, 2016 and 2015 consisted of the following: Three Months Ended Three Months Ended March 31, 2016 March 31, 2015 Millions Net Net Total net realized Net Net Total net realized Fixed maturity investments $ (1.1 ) $ — $ (1.1 ) $ .5 $ — $ .5 Short-term investments — — — — — — Common equity securities 257.6 — 257.6 22.0 .5 22.5 Other long-term investments .3 — .3 (8.2 ) — (8.2 ) Net realized investment gains, pre-tax 256.8 — 256.8 14.3 .5 14.8 Income tax expense attributable to net realized investment gains (42.9 ) — (42.9 ) (4.5 ) — (4.5 ) Net realized investment gains, after tax $ 213.9 $ — $ 213.9 $ 9.8 $ .5 $ 10.3 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: Three Months Ended Three Months Ended March 31, 2016 March 31, 2015 Millions Net unrealized gains (losses) Net gains Total net unrealized gains (losses) reflected in earnings Net unrealized gains (losses) Net Total net unrealized gains (losses) reflected in earnings Fixed maturity investments $ 21.7 $ — $ 21.7 $ 11.4 $ — $ 11.4 Short-term investments — — — — — — Common equity securities (249.8 ) 2.4 (247.4 ) (2.8 ) (4.0 ) (6.8 ) Other long-term investments (2.0 ) .4 (1.6 ) 6.6 (1.0 ) 5.6 Net unrealized investment (losses) gains, pre-tax (230.1 ) 2.8 (227.3 ) 15.2 (5.0 ) 10.2 Income tax benefit (expense) 34.4 — 34.4 (2.6 ) — (2.6 ) Net unrealized investment $ (195.7 ) $ 2.8 $ (192.9 ) $ 12.6 $ (5.0 ) $ 7.6 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 three months ended March 31, 2016 and 2015 : Three Months Ended March 31, Millions 2016 2015 Fixed maturity investments $ .5 $ .2 Common equity securities — (1.8 ) Other long-term investments 1.1 5.7 Total unrealized investment gains, pre-tax - Level 3 investments $ 1.6 $ 4.1 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’s fixed maturity investments as of March 31, 2016 and December 31, 2015 were as follows: March 31, 2016 Millions Cost or amortized cost Gross unrealized gains Gross unrealized losses Net foreign currency gains (losses) Carrying value U.S. Government and agency obligations $ 88.4 $ .4 $ — $ — $ 88.8 Debt securities issued by corporations 899.0 12.5 (1.1 ) — 910.4 Municipal obligations 264.3 4.6 (.2 ) — 268.7 Mortgage-backed and asset-backed securities 1,259.9 5.1 (4.1 ) — 1,260.9 Foreign government, agency and provincial obligations 1.0 .2 — — 1.2 Preferred stocks 78.3 4.9 — — 83.2 Total fixed maturity investments $ 2,590.9 $ 27.7 $ (5.4 ) $ — $ 2,613.2 December 31, 2015 Millions Cost or amortized cost Gross unrealized gains Gross unrealized losses Net foreign currency gains (losses) Carrying value U.S. Government and agency obligations $ 160.4 $ — $ (.4 ) $ — $ 160.0 Debt securities issued by corporations 1,001.0 4.3 (5.3 ) — 1,000.0 Municipal obligations 227.8 2.2 (1.2 ) — 228.8 Mortgage-backed and asset-backed securities 1,170.6 2.0 (5.6 ) — 1,167.0 Foreign government, agency and provincial obligations 1.0 .2 — — 1.2 Preferred stocks 78.3 4.4 — — 82.7 Total fixed maturity investments $ 2,639.1 $ 13.1 $ (12.5 ) $ — $ 2,639.7 The cost or amortized cost, gross unrealized investment gains and losses, net foreign currency gains and losses, and carrying values of White Mountains’s common equity securities and other long-term investments as of March 31, 2016 and December 31, 2015 were as follows: March 31, 2016 Millions Cost or amortized cost Gross unrealized gains Gross unrealized losses Net foreign Carrying value Common equity securities $ 399.0 $ 52.9 $ (8.9 ) $ — $ 443.0 Other long-term investments $ 312.3 $ 32.7 $ (21.3 ) $ (1.9 ) $ 321.8 December 31, 2015 Millions Cost or Gross Gross Net foreign Carrying value Common equity securities $ 822.5 $ 302.8 $ (11.4 ) $ — $ 1,113.9 Other long-term investments $ 304.5 $ 32.0 $ (18.4 ) $ (2.3 ) $ 315.8 Other Long-term Investments Other long-term investments consist of the following as of March 31, 2016 and December 31, 2015 : Carrying Value at Millions March 31, 2016 December 31, 2015 Hedge funds and private equity funds, at fair value (1) $ 131.3 $ 127.8 Private equity securities and limited liability companies, at fair value (1) 84.7 82.1 Surplus notes investments, at fair value (1) 51.8 51.5 Private convertible preferred securities (1) 32.9 32.7 Tax advantaged federal affordable housing development fund (2) 14.1 14.7 Partnership investments accounted for under the equity method 3.7 3.8 Other 3.3 3.2 Total other-long term investments $ 321.8 $ 315.8 (1) See Fair Value Measurements by Level table. (2) Fund accounted for using the proportional amortization method. 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. As of March 31, 2016 , White Mountains held investments in 5 hedge funds and 23 private equity funds. The largest investment in a single fund was $22.8 million as of March 31, 2016 . The following table summarizes investments in hedge funds and private equity funds by investment objective and sector as of March 31, 2016 and December 31, 2015 : March 31, 2016 December 31, 2015 Millions Fair Value Unfunded Commitments Fair Value Unfunded Commitments Hedge funds Long/short equity REIT $ 20.2 $ — $ 20.6 $ — Long/short banks and financial 12.6 — 12.8 — Other 3.6 — 3.6 — Total hedge funds 36.4 — 37.0 — Private equity funds Aerospace/Defense/Government 27.9 22.1 19.8 30.3 Manufacturing/Industrial 25.8 2.1 24.9 2.5 Energy infrastructure & services 18.0 3.3 20.7 3.4 Multi-sector 13.0 2.1 14.8 2.1 Private equity secondaries 3.9 2.1 4.4 2.1 Healthcare 3.8 .4 3.8 .4 Insurance 2.0 41.3 2.0 41.3 Real estate .5 .1 .4 .1 Total private equity funds 94.9 73.5 90.8 82.2 Total hedge funds and private equity funds included in other long-term investments $ 131.3 $ 73.5 $ 127.8 $ 82.2 Redemption of investments in certain hedge funds is subject to restrictions including lock-up periods where no redemptions or withdrawals are allowed, restrictions on redemption frequency and advance notice periods for redemptions. Amounts requested for redemptions remain subject to market fluctuations until the redemption effective date, which generally falls at the end of the defined redemption period. The following summarizes the March 31, 2016 fair value of hedge funds subject to restrictions on redemption frequency and advance notice period requirements for investments in active hedge funds: Notice Period Millions Redemption frequency 30-59 days notice 60-89 days notice 90-119 days notice Total Monthly $ — $ — $ — $ — Quarterly 13.7 — — 13.7 Semi-annual — 20.2 — 20.2 Annual — — 2.5 2.5 Total $ 13.7 $ 20.2 $ 2.5 $ 36.4 Certain of White Mountains’s hedge fund investments 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. As of March 31, 2016 , distributions of $1.1 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 as of March 31, 2016 . White Mountains has also submitted redemption requests for certain of its investments in active hedge funds. As of March 31, 2016 , redemptions of $2.5 million are outstanding that would be subject to market fluctuations. The date at which such redemptions will be received is not determinable as of March 31, 2016 . 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. As of March 31, 2016 , 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 $29.2 $3.9 $61.8 $— $94.9 OneBeacon Surplus Notes In the fourth quarter of 2014, in conjunction with the Runoff Transaction, OneBeacon provided financing in the form of surplus notes having a par value of $101.0 million , which had a fair value of $51.8 million and $ 51.5 million as of March 31, 2016 and December 31, 2015, respectively. The surplus notes, issued by one of the transferred entities, Bedivere (“Issuer”), were in the form of both seller priority and pari passu notes. The internal valuation model used to estimate the fair value is based on discounted expected cash flows using information as of the measurement date. The estimated fair value of the surplus notes is sensitive to changes in treasury rates and public debt credit spreads, as well as changes in estimates with respect to other variables including a discount to reflect the private nature of the notes (and the related lack of liquidity), the credit quality of the notes and the timing, amount, and likelihood of interest and principal payments on the notes, which are subject to regulatory approval and therefore may vary from the contractual terms. An interest payment of $2.4 million was received in the three months ended March 31, 2016. OneBeacon has assumed for valuation purposes that subsequent interest payments will begin in year five (2020) and principal repayments begin on a graduated basis in year ten (2025) for the seller priority note and year fifteen (2030) for the pari passu note. Although these variables involve considerable judgment, the Company does not currently expect any resulting changes in the estimated value of the surplus notes to be material to its financial position. Below is a table illustrating the valuation adjustments taken to arrive at estimated fair value of the surplus notes as of March 31, 2016 and December 31, 2015: Type of Surplus Note Total as of March 31, 2016 Total as of December 31, 2015 Millions Seller Priority Pari Passu Par Value $ 57.9 $ 43.1 $ 101.0 $ 101.0 Fair value adjustments to reflect: Current market rates on public debt and contract-based repayments (1) (.5 ) (14.2 ) (14.7 ) (15.1 ) Regulatory approval (2) (11.4 ) (13.0 ) (24.4 ) (24.2 ) Liquidity adjustment (3) (7.8 ) (2.3 ) (10.1 ) (10.2 ) Total adjustments (19.7 ) (29.5 ) (49.2 ) (49.5 ) Fair value $ 38.2 $ 13.6 $ 51.8 $ 51.5 (1) Represents the value of the surplus notes, at current market yields on comparable publicly traded debt, and assuming issuer is allowed to make principal and interest payments when its financial capacity is available, as measured by statutory capital in excess of a 250% RBC score. (2) Represents anticipated timing of securing regulatory approvals for interest and principal payments to reflect graduated changes in Issuer’s statutory surplus. T he monetary impact of the anticipated timing is measured based on credit spreads of public securities with roughly equivalent percentages of discounted payments missed. ( 3) Represents impact of liquidity spread to account for OneBeacon’s sole ownership of the surplus notes, lack of a trading market and ongoing regulatory approval risk. Fair value measurements as of March 31, 2016 Fair value measurements are categorized into a hierarchy that distinguishes between inputs based on market data from independent sources (“observable inputs”) and a reporting entity’s internal assumptions based upon the best information available when external market data is limited or unavailable (“unobservable inputs”). Quoted prices in active markets for identical assets or liabilities have the highest priority (“Level 1”), followed by observable inputs other than quoted prices, including prices for similar but not identical assets or liabilities (“Level 2”) and unobservable inputs, including the reporting entity’s estimates of the assumptions that market participants would use, having the lowest priority (“Level 3”). White Mountains used quoted market prices or other observable inputs to determine fair value for 89% of its investment portfolio as of March 31, 2016. Investments valued using Level 1 inputs include fixed maturity investments, primarily investments in U.S. Treasuries, common equity securities and short-term investments, which include U.S. Treasury Bills. Investments valued using Level 2 inputs are primarily comprised of fixed maturity investments, which have been disaggregated into classes, including debt securities issued by corporations, municipal obligations, mortgage and asset-backed securities, foreign government, agency and provincial obligations and preferred stocks. Fair value estimates for investments that trade infrequently and have few or no observable market prices are classified as Level 3 measurements. Investments valued using Level 2 inputs also include certain ETFs that track U.S. stock indices such as the S&P 500 but are traded on foreign exchanges and that management values using the fund’s published NAV to account for the difference in market close times. Level 3 fair value estimates based upon unobservable inputs include White Mountains’s investments in surplus notes, as well as certain investments in fixed maturity investments, common equity securities and other long-term investments where quoted market prices are unavailable or are not considered reasonable. Transfers between levels are based on investments held 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 White Mountains uses have indicated that they will only provide prices where observable inputs are available. In circumstances where quoted market prices are unavailable or are not considered reasonable, White Mountains estimates the fair value using industry standard pricing models and observable inputs such as benchmark yields, reported trades, broker-dealer quotes, issuer spreads, benchmark securities, bids, offers, prepayment speeds, reference data including research publications and other relevant inputs. Given that many fixed maturity investments do not trade on a daily basis, the outside pricing services evaluate a wide range of fixed maturity investments by regularly drawing parallels from recent trades and quotes of comparable securities with similar features. The characteristics used to identify comparable fixed maturity investments vary by asset type and take into account market convention. White Mountains’s process to assess the reasonableness of the market prices obtained from the outside pricing sources covers substantially all of its fixed maturity investments and includes, but is not limited to, evaluation of model pricing methodologies, 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. Also considered outliers are prices that haven’t changed from period to period and prices that have trended unusually compared to market conditions. In circumstances where the results of White Mountains’s review process does 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 valuation process above is generally applicable to all of White Mountains’s fixed maturity investments. The techniques and inputs specific to asset classes within White Mountains’s fixed maturity investments for Level 2 securities that use observable inputs are as follow: Debt securities issued by corporations: The fair value of debt securities issued by corporations is determined from an evaluated pricing model that uses information from market sources and integrates relative credit information, observed market movements, and sector news. Key inputs include benchmark yields, reported trades, broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including sector, coupon, credit quality ratings, duration, credit enhancements, early redemption features and market research publications. Mortgage and asset-backed securities: The fair value of mortgage and asset-backed securities is determined from an evaluated pricing model that uses information from market sources and leveraging similar securities. Key inputs include benchmark yields, reported trades, underlying tranche cash flow data, collateral performance, plus new issue data, as well as broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including issuer, vintage, loan type, collateral attributes, prepayment speeds, default rates, recovery rates, cash flow stress testing, credit quality ratings and market research publications. Municipal obligations: The fair value of municipal obligations is determined from a pricing model that uses information from market makers, brokers-dealers, buy-side firms, and analysts along with general market information. Key inputs include benchmark yields, reported trades, issuer financial statements, material event notices and new issue data, as well as broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including type, coupon, credit quality ratings, duration, credit enhancements, geographic location and market research publications. Foreign government, agency and provincial obligations: The fair value of foreign government, agency and provincial obligations is determined from an evaluated pricing model that uses feeds from data sources in each respective country, including active market makers and inter-dealer brokers. Key inputs include benchmark yields, reported trades, broker-dealer quotes, two-sided markets, benchmark securities, bids, offers, local exchange prices, foreign exchange rates and reference data including coupon, credit quality ratings, duration and market research publications. Preferred stocks: The fair value of preferred stocks is determined from an evaluated pricing model that calculates the appropriate spread over a comparable security for each issue. Key inputs include exchange prices (underlying and common stock of same issuer), benchmark yields, reported trades, broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including sector, coupon, credit quality ratings, duration, credit enhancements, early redemption features and market research publications. Level 3 valuations are generated from techniques that use assumptions not observable in the market. These unobservable assumptions reflect White Mountains’s assumptions that market participants would use in valuing the investment. Generally, certain securities may start out as Level 3 when they are originally issued but as observable inputs become available in the market, they may be reclassified to Level 2. 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 hedge funds and private equity funds 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. The fair value of White Mountains’s investments in hedge funds and private equity funds has been determined using net asset value. Fair Value Measurements by Level The following tables summarize White Mountains’s fair value measurements for investments as of March 31, 2016 and December 31, 2015 by level. The major security types were based on the legal form of the securities. White Mountains has disaggregated its fixed maturity investments based on the issuing entity type, which impacts credit quality, with debt securities issued by U.S. government entities carrying minimal credit risk, while the credit and other risks associated with other issuers, such as corporations, foreign governments, municipalities or entities issuing mortgage-backed or asset-backed securities vary depending on the nature of the issuing entity type. White Mountains further disaggregates debt securities issued by corporations and equity securities by industry sector because investors often reference commonly used benchmarks and their subsectors to monitor risk and performance. Accordingly, White Mountains has further disaggregated these asset classes into subclasses based on the similar sectors and industry classifications it uses to evaluate investment risk and performance against commonly used benchmarks, such as the Barclays Intermediate Aggregate and S&P 500 indices. March 31, 2016 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 88.8 $ 72.3 $ 16.5 $ — Debt securities issued by corporations: Consumer 242.1 — 242.1 — Financials 155.5 — 155.5 — Industrial 135.1 — 135.1 — Health Care 124.7 — 124.7 — Energy 69.3 — 69.3 — Utilities 57.2 — 57.2 — Technology 57.1 — 57.1 — Communications 43.3 — 43.3 — Materials 26.1 — 26.1 — Other — — — — Total debt securities issued by corporations 910.4 — 910.4 — Mortgage-backed and asset-backed securities 1,260.9 — 1,260.9 — Municipal obligations 268.7 — 268.7 — Foreign government, agency and provincial obligations 1.2 .6 .6 — Preferred stocks 83.2 — 12.7 70.5 Total fixed maturity investments 2,613.2 72.9 2,469.8 70.5 Short-term investments 261.7 261.7 — — Common equity securities: Exchange traded funds (1) 130.5 109.0 21.5 — Consumer 73.1 73.1 — Technology 47.8 47.8 — — Health Care 39.0 39.0 — — Communications 34.9 34.9 — — Industrial 30.0 30.0 — — Financials 12.9 12.9 — — Other 74.8 — 74.8 — Total common equity securities 443.0 346.7 96.3 — Other long-term investments (2)(3) 172.7 — — 172.7 Total investments $ 3,490.6 $ 681.3 $ 2,566.1 $ 243.2 (1) ETFs traded on foreign exchanges are priced using the fund's published NAV to account for the difference in market close times and are therefore designated a level 2 measurement. (2) Excludes carrying value of $3.7 associated with other long-term investment limited partnerships accounted for using the equity method. Excludes carrying value of $14.1 associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method. (3) Excludes carrying value of $131.3 associated with hedge funds and private equity funds for which fair value is measured at net asset value using the practical expedient. December 31, 2015 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 160.0 $ 133.4 $ 26.6 $ — Debt securities issued by corporations: Consumer 253.3 — 253.3 — Financials 175.9 — 175.9 — Health Care 151.3 — 151.3 — Industrial 135.6 — 135.6 — Energy 82.0 — 82.0 — Utilities 61.5 — 61.5 — Technology 60.0 — 60.0 — Communications 49.2 — 49.2 — Materials 31.2 — 31.2 — Other — — — — Total debt securities issued by corporations 1,000.0 — 1,000.0 — Mortgage-backed and asset-backed securities 1,167.0 — 1,167.0 — Municipal obligations 228.8 — 228.8 — Foreign government, agency and provincial obligations 1.2 .6 .6 — Preferred stocks 82.7 — 12.7 70.0 Total fixed maturity investments 2,639.7 134.0 2,435.7 70.0 Short-term investments 211.3 211.3 — — Common equity securities: Exchange traded funds (1) 141.8 120.5 21.3 — Financials 694.7 694.7 — — Consumer 70.0 70.0 — — Communications 43.7 43.7 — — Health Care 35.7 35.7 — — Technology 27.0 27.0 — — Industrial 26.6 26.6 — — Other 74.4 — 74.4 — Total common equity securities 1,113.9 1,018.2 95.7 — Other long-term investments (2)(3) 169.5 — — 169.5 Total investments $ 4,134.4 $ 1,363.5 $ 2,531.4 $ 239.5 (1) ETFs traded on foreign exchanges are priced using the fund's published NAV to account for the difference in market close times and are therefore designated a level 2 measurement. (2) Excludes carrying value of $3.8 associated with other long-term investment limited partnerships accounted for using the equity method. Excludes carrying value of $14.7 associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method. (3) Excludes carrying value of $127.8 associated with hedge funds and private equity funds for which fair value is measured at net asset value using the practical expedient. Debt securities issued by corporations The following table summarizes the ratings of debt securities issued by corporations held in White Mountains’s investment portfolio as of March 31, 2016 and December 31, 2015 : Fair Value at Millions March 31, 2016 December 31, 2015 AAA $ 9.4 $ — AA 107.4 95.2 A 364.2 397.7 BBB 429.4 507.1 Other — — Debt securities issued by corporations (1) $ 910.4 $ 1,000.0 (1) Credit ratings are assigned based on the following hierarchy: 1) Standard & Poor’s and 2) Moody’s. Mortgage-backed and Asset-backed Securities White Mountains purchases commercial mortgage-backed securities (“CMBS”) and residential mortgage-backed securities (“RMBS”) with the goal of maximizing risk adjusted returns in the context of a diversified portfolio. 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’s review of the characteristics of their underlying mortgage loan pools, such as credit scores and financial ratios. White Mountains’s non-agency RMBS 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 $36.0 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. March 31, 2016 December 31, 2015 Millions Fair Value Level 2 Level 3 Fair Value Level 2 Level 3 Mortgage-backed securities: Agency: GNMA $ 275.0 $ 275.0 $ — $ 265.5 $ 265.5 $ — FNMA 45.0 45.0 — 42.2 42.2 — FHLMC 22.1 22.1 — 22.8 22.8 — Total Agency (1) 342.1 342.1 — 330.5 330.5 — Non-agency: Residential 132.3 132.3 — 133.2 133.2 — Commercial 128.8 128.8 — 140.4 140.4 — Total Non-agency 261.1 261.1 — 273.6 273.6 — Total mortgage-backed securities 603.2 603.2 — 604.1 604.1 — Other asset-backed securities: Credit card receivables 281.6 281.6 — 217.7 217.7 — Vehicle receivables 290.8 290.8 — 269.7 269.7 — Other 85.3 85.3 — 75.5 75.5 — Total other asset-backed securities 657.7 657.7 — 562.9 562.9 — Total mortgage and asset-backed securities $ 1,260.9 $ 1,260.9 $ — $ 1,167.0 $ 1,167.0 $ — (1) Represents publicly traded mortgage-backed securities which carry the full faith and credit guaranty of the U.S. government (i.e., GNMA) or are guaranteed by a government sponsored entity (i.e., FNMA, FHLMC). Non-agency Mortgage-backed Securities The security issuance years of White Mountains’s investments in non-agency RMBS and non-agency CMBS securities as of March 31, 2016 are as follows: Security Issuance Year Mill

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	3 Months Ended
	Mar. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets White Mountains has recognized goodwill and other identifiable intangible assets at the acquisition date fair values in connection with its purchases of subsidiaries. On January 15, 2016, MediaAlpha acquired certain assets from Oversee.net for a purchase price of $3.9 million . The majority of assets acquired, which are included in other intangible assets, consists of customer relationships, a customer contract, a non-compete agreement from the seller, domain names and technology. During 2015, Wobi acquired Cashboard in two transactions for a total of NIS 35.9 million (approximately $8.9 million based upon the foreign exchange spot rate at the dates of acquisition), representing a controlling financial interest. As of the acquisition date, Wobi recognized total assets acquired of $5.5 million , including $0.3 million of goodwill and $2.8 million of other intangible assets, and total liabilities assumed of $1.2 million at their estimated fair values. The following table shows the change in goodwill and other intangible assets: Three Months Ended March 31, Millions 2016 2015 Goodwill Other intangible assets Goodwill Other intangible assets Beginning balance $ 187.9 $ 187.8 $ 168.9 $ 182.3 Acquisitions of businesses — — .3 2.8 Acquisitions of intangible assets — 3.9 — — Amortization, including foreign currency translation — (8.1 ) — (6.9 ) Ending balance $ 187.9 $ 183.6 $ 169.2 $ 178.2

Debt

Debt	3 Months Ended
	Mar. 31, 2016
Debt Disclosure [Abstract]
Debt	Debt White Mountains’s debt outstanding as of March 31, 2016 and December 31, 2015 consisted of the following: Millions March 31, Effective Rate (1) December 31, Effective Rate (1) WTM Bank Facility $ 150.0 N/A $ 50.0 N/A OBH Senior Notes, at face value 275.0 4.7% 275.0 4.7% Unamortized original issue discount and debt issuance costs (2.1 ) (2.1 ) OBH Senior Notes, carrying value 272.9 272.9 OneBeacon Bank Facility — N/A — N/A Tranzact Bank Facility 94.1 6.0% 104.7 5.6% Unamortized issuance cost (1.6 ) (1.8 ) Tranzact Bank Facility, carrying value 92.5 102.9 MediaAlpha Bank Facility 17.5 6.4% 15.0 5.5% Unamortized issuance cost (.3 ) (.3 ) MediaAlpha Bank Facility, carrying value 17.2 14.7 Total debt $ 532.6 $ 440.5 (1) Effective rate considers the effect of the debt issuance costs. 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 and has a maturity date of August 14, 2018 (the “WTM Bank Facility”). During the three months ended March 31, 2016 , White Mountains borrowed $100.0 million under the WTM Bank Facility at a blended interest rate of 3.90% . As of March 31, 2016 , the WTM Bank Facility had an outstanding balance of $150.0 million . 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. OneBeacon Bank Facility On September 29, 2015, OneBeacon Ltd. and OneBeacon U.S. Holdings, Inc. (“OBH”), as co-borrowers and co-guarantors, entered into a revolving credit facility administered by U.S. Bank N.A. with BMO Harris Bank N.A. as an additional lender, which has a total commitment of $65.0 million and has a maturity date of September 29, 2019 (the “OneBeacon Bank Facility”). As of March 31, 2016, the OneBeacon Bank Facility was undrawn. The OneBeacon 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. Tranzact Bank Facility On October 10, 2014, Tranzact entered into a secured credit facility with a syndicate of lenders administered by the PrivateBank and Trust Company that has a maturity date of October 10, 2019 (the “Tranzact Bank Facility”). During 2015, Tranzact amended the Tranzact Bank Facility, which now has a total commitment of $116.0 million , consisting of a $101.0 million term loan facility and a $15.0 million revolving loan facility. The amendment increased the term loan facility by $31.0 million , the proceeds of which were used by Tranzact to finance the acquisition of TruBridge. During the three months ended March 31, 2016 , Tranzact also borrowed $4.5 million and repaid $12.5 million under the revolving loan facility. During the three months ended March 31, 2016 , Tranzact repaid a total of $2.6 million under the term loan portion. As of March 31, 2016 , the total amount outstanding under the Tranzact Bank Facility was $94.1 million . Tranzact has entered into an interest rate swap agreement to effectively fix the rate it pays on $70.0 million of the $101.0 million term loan. (See Note 9 - “Derivatives“ ) The Tranzact Bank Facility, which is secured by intellectual property and the common stock of Tranzact’s subsidiaries, contains various affirmative, negative and financial covenants which White Mountains considers to be customary for such borrowings, including a minimum fixed charge coverage ratio and a maximum leverage ratio. MediaAlpha Bank Facility On July 23, 2015, MediaAlpha entered into a secured credit facility with Opus Bank, which has a total commitment of $20.0 million and has a maturity date of July 23, 2019 (the “MediaAlpha Bank Facility”). The MediaAlpha Bank Facility consists of a $15.0 million term loan facility, which was fully drawn as of March 31, 2016 , and a revolving loan facility for an additional $5.0 million , which has an outstanding balance of $2.5 million as of March 31, 2016 . During the three months ended March 31, 2016 , MediaAlpha borrowed $2.5 million under the revolving loan facility. The MediaAlpha Bank Facility carries a variable interest rate that is based on the Prime Rate, as published by the Wall Street Journal. The MediaAlpha Bank Facility is secured by intellectual property and the common stock of MediaAlpha’s subsidiaries, and contains various affirmative, negative and financial covenants that White Mountains considers to be customary for such borrowings, including a maximum leverage ratio. Compliance At March 31, 2016 , White Mountains was in compliance with all of the covenants under all of its debt facilities.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2016
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 consolidated subsidiaries and branches are subject to tax are Barbados, Germany, Gibraltar, Israel, Luxembourg, the Netherlands, Peru, Sweden, Switzerland, the United Kingdom and the United States. White Mountains’s income tax benefit related to pre-tax income from continuing operations for the three months ended March 31, 2016, represented a net effective tax rate of (75.7)% . As noted below, the effective tax rate for the three months ended March 31, 2016 was impacted by a $12.8 million tax benefit on the settlement of the 2007-2009 IRS exam. Without the tax benefit on the settlement of the 2007-2009 IRS exam there would have been tax expense, which would have resulted in a net effective tax rate that is approximately the same as the U.S. statutory rate of 35% . White Mountains’s effective tax rate for the three months ended March 31, 2015 was not meaningful as pre-tax income was near break-even. In arriving at the effective tax rate for the three months ended March 31, 2016 and 2015 , White Mountains forecasted all income and expense items including the change in unrealized investment gains (losses) and realized investment gains (losses) for the years ending December 31, 2016 and 2015. 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’s deferred tax assets and tax expense. With few exceptions, White Mountains is no longer subject to U.S. federal, state or non-U.S. income tax examinations by tax authorities for years before 2010. On January 19, 2016, White Mountains received Form 870-AD (Offer to Waive Restrictions on Assessment and Collection Tax Deficiency and to Accept Overassessment) from the IRS Appeals Office relating to the examination of tax years 2007, 2008 and 2009 for certain U.S. Subsidiaries of OneBeacon. All disputed items have now been agreed to and resolved with the Joint Committee on Taxation. As the receipt of the Form 870-AD described above represents formal settlement, OneBeacon recorded a tax benefit of $12.8 million in the first quarter of 2016 related to tax years 2007, 2008 and 2009. On September 5, 2013, the IRS commenced an examination of the income tax returns for 2010, 2011 and 2012 for certain U.S. subsidiaries of OneBeacon. On March 22, 2016, White Mountains received Form 4549-A (Income Tax Discrepancy Adjustments) from the IRS relating to the examination of tax years 2010, 2011 and 2012. The estimated total overpayment is $6.0 million . However, $4.7 million of the adjustments relate to items for which the expense deduction has been disallowed in an earlier period, but deductibility will occur in a year being examined. Because of the impact of deferred tax accounting, other than interest and penalties, the allowance of the deduction in the exam period would not affect the effective tax rate. 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. On December 18, 2014, the IRS commenced an examination of the 2012 income tax return for Guilford Holdings, Inc. and subsidiaries. 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	3 Months Ended
	Mar. 31, 2016
Derivatives	Derivatives
Variable Annuity
Derivatives	Variable Annuity Reinsurance White Mountains has entered into agreements to reinsure death and living benefit guarantees associated with certain variable annuities in Japan. At March 31, 2016 and December 31, 2015 , the total guarantee value was approximately ¥ 21.2 billion ( $188.9 million at exchange rates on that date) and ¥50.7 billion (approximately $421.1 million at exchange rates on that date), respectively. The collective account values of the underlying variable annuities were approximately 107% and 109% of the guarantee value at March 31, 2016 and December 31, 2015 . During the second quarter of 2015, the variable annuity contracts reinsured by WM Life Re began to mature and will fully runoff by June 30, 2016. The following table summarizes the pre-tax operating results of WM Life Re for the three months ended March 31, 2016 and 2015 . Three Months Ended March 31, Millions 2016 2015 Fees, included in other revenue $ 1.0 $ 3.0 Change in fair value of variable annuity liability, included in other revenue (.4 ) .4 Change in fair value of derivatives, included in other revenue (1.7 ) (5.5 ) Foreign exchange, included in other revenue .9 (1.1 ) Other investment income and (losses) gains — — Total revenue (.2 ) (3.2 ) Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses — — Death benefit claims paid, included in general and administrative expenses (.1 ) — General and administrative expenses (.8 ) (1.4 ) Pre-tax income (loss) $ (1.1 ) $ (4.6 ) The following summarizes realized and unrealized derivative gains (losses) recognized in other revenue for the three months ended March 31, 2016 and 2015 and the carrying values, included in other assets, at March 31, 2016 and December 31, 2015 by type of instrument: Gains (losses) Carrying Value Three Months Ended As of March 31, March 31, December 31, 2015 Millions 2016 2015 Fixed income/interest rate $ 1.8 $ 9.3 $ (.4 ) $ .5 Foreign exchange (4.2 ) (12.1 ) 12.5 14.8 Equity .7 (2.7 ) 1.0 4.8 Total $ (1.7 ) $ (5.5 ) $ 13.1 $ 20.1 The following tables summarize the changes in White Mountains’s variable annuity reinsurance liabilities and derivative instruments for the three months ended March 31, 2016 and 2015 : Three Months Ended March 31, 2016 Variable Annuity Assets (Liabilities) Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ .3 $ 2.7 $ 16.5 $ .9 $ 20.1 Purchases — — — — — Realized and unrealized gains (losses) (.4 ) 1.2 1.1 (4.0 ) (1.7 ) Transfers in — — — — — Sales/settlements — (1.3 ) (7.3 ) 3.3 (5.3 ) End of period $ (.1 ) $ 2.6 $ 10.3 $ .2 $ 13.1 Three Months Ended March 31, 2015 Variable Annuity Assets Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ .7 $ 18.9 $ 33.8 $ 3.7 $ 56.4 Purchases — — — — — Realized and unrealized gains (losses) .4 (.6 ) (6.5 ) 1.6 (5.5 ) Transfers in — — — — — Sales/settlements — (1.3 ) 3.9 (6.5 ) (3.9 ) End of period $ 1.1 $ 17.0 $ 31.2 $ (1.2 ) $ 47.0 (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. In addition to derivative instruments, WM Life Re held cash and fixed maturity investments posted as collateral to its variable annuity reinsurance counterparties. The total collateral includes the following: Millions March 31, 2016 December 31, 2015 March 31, 2015 Cash $ 8.4 $ 5.8 $ 29.0 Fixed maturity investments — — 4.5 Total $ 8.4 $ 5.8 $ 33.5 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’s variable annuity reinsurance liabilities were classified as Level 3 measurements at March 31, 2016 and 2015 . The fair value of White Mountains’s variable annuity reinsurance liabilities are estimated using actuarial and capital market assumptions related to the projected discounted cash flows over the term of the reinsurance agreement. Actuarial assumptions regarding future policyholder behavior, including surrender and lapse rates, are generally unobservable inputs and significantly impact the fair value estimates. Market conditions including, but not limited to, changes in interest rates, equity indices, market volatility and foreign currency exchange rates as well as the variations in actuarial assumptions regarding policyholder behavior may result in significant fluctuations in the fair value estimates. Generally, the liabilities associated with these guarantees increase with declines in the equity markets, interest rates and currencies against the Japanese yen, as well as with increases in market volatilities. White Mountains uses derivative instruments, including put options, interest rate swaps, total return swaps on bond and equity indices and forwards and futures contracts on major equity indices, currency pairs and government bonds, to mitigate the risks associated with changes in the fair value of the reinsured variable annuity guarantees. The types of inputs used to estimate the fair value of these derivative instruments, with the exception of actuarial assumptions regarding policyholder behavior and risk margins, are generally the same as those used to estimate the fair value of variable annuity liabilities. The following summarizes quantitative information about significant unobservable inputs associated with the fair value estimates for variable annuity reinsurance liabilities and derivative instruments that have been classified as Level 3 measurements: ($ in Millions) March 31, 2016 Description Fair Value Valuation Technique(s) Unobservable Input Range Weighted Average Variable annuity benefit guarantee liabilities $ (.1 ) Discounted cash flows Surrenders 0-1 year 0.1 % - 40.0% 40.0 % Mortality 0.0 % - 6.4% 1.1 % Foreign exchange volatilities 0-1 year 12.0 % - 18.4% 13.5 % Index volatilities 0-1 year 25.5 % - 28.8% 26.2 % Foreign exchange options $ 1.1 Counterparty valuations, adjusted for unwind quote discount Adjustment to counterparty valuations (4.3 )% - (7.3)% (5.9 )% Equity index options $ 1.5 Counterparty valuations, adjusted for unwind quote discount Adjustment to counterparty valuations (0.6 )% - (5.7)% (5.6 )% WM Life Re enters into both over-the-counter (“OTC”) and exchange traded derivative instruments to economically hedge the liability from the variable annuity benefit guarantee. In the case of OTC derivatives, WM Life Re has exposure to credit risk for amounts that are uncollateralized by counterparties. WM Life Re’s internal risk management guidelines establish net counterparty exposure thresholds that take into account OTC counterparties’ credit ratings. The OTC derivative contracts are subject to restrictions on liquidation of the instruments and distribution of proceeds under collateral agreements. In the case of exchange traded instruments, WM Life Re has exposure to credit risk for amounts uncollateralized by margin balances. WM Life Re has entered into master netting agreements with certain of its counterparties whereby the collateral provided (held) is calculated on a net basis. The following summarizes amounts offset under master netting agreements: March 31, 2016 December 31, 2015 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 $ 2.2 $ (2.5 ) $ (.3 ) $ 2.4 $ (2.1 ) $ .3 Exchange traded — — — .1 (.1 ) — Foreign exchange contracts OTC 12.7 — 12.7 15.0 — 15.0 Exchange traded — (.1 ) (.1 ) .1 (.3 ) (.2 ) Equity contracts OTC 1.5 (.9 ) .6 4.4 (.6 ) 3.8 Exchange traded .3 (.1 ) .2 1.2 — 1.2 Total (2) $ 16.7 $ (3.6 ) $ 13.1 $ 23.2 $ (3.1 ) $ 20.1 (1) Amount equal to fair value of instrument as recognized in other assets (2) All derivative instruments held by WM Life Re are subject to master netting arrangements. The following summarizes the value, collateral held or provided by WM Life Re and net exposure to credit losses on OTC and exchange traded derivative instruments by counterparty recorded within other assets: March 31, 2016 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 WMLife Re - Cash Net amount of exposure to counter-party Standard & Poor's Rating (1) Bank of America $ 1.4 $ — $ — $ 1.4 $ — $ — $ — $ 1.4 A JP Morgan 6.5 — — 6.5 — — 5.4 1.1 A + Citigroup - OTC 5.0 — — 5.0 — — .5 4.5 A Citigroup - Exchange Traded .2 — — .2 7.9 — — 8.1 A Total $ 13.1 $ — $ — $ 13.1 $ 7.9 $ — $ 5.9 $ 15.1 December 31, 2015 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 WMLife Re- Cash Net amount of exposure to counter-party Standard & Poor's Rating (1) Bank of America $ .7 $ — $ — $ .7 $ — $ — $ — $ .7 A JP Morgan 8.5 — — 8.5 — — 5.5 3.0 A + Citigroup - OTC 9.9 — — 9.9 — — 1.4 8.5 A Citigroup - Exchange Traded 1.0 — — 1.0 5.8 — — 6.8 A Total $ 20.1 $ — $ — $ 20.1 $ 5.8 $ — $ 6.9 $ 19.0 (1) Standard & Poor’s ratings as detailed above are: “A+” (Strong, which is the fifth highest of twenty-three creditworthiness ratings), “A” (Strong, which is the sixth highest of twenty-three creditworthiness ratings), “A-” (Strong, which is the seventh highest of twenty-three creditworthiness ratings) and “BBB+” (Adequate, which is the eighth highest of twenty-three creditworthiness ratings).
Tranzact Interest Rate Swap
Derivatives	Tranzact Interest Rate Swap Tranzact has a $101.0 million term loan facility that carries a variable rate equal to the U.S. dollar LIBOR rate, plus an applicable margin. At March 31, 2016 , the variable interest rate on the term loan was 4.94% , including a margin over LIBOR of 4.50% . Effective October 10, 2014, to effectively fix the rate it pays on this term loan, Tranzact entered into an interest rate swap agreement with an initial notional amount of $70.0 million . The notional amount decreases over the term of the swap by amounts equivalent to scheduled principal repayments made on Tranzact’s term loan. Under the terms of the swap agreement, Tranzact pays a fixed rate of 1.34% and receives a variable rate, which is reset monthly, based on the then-current U.S. dollar LIBOR rate. The variable rate received by Tranzact under the swap agreement was 0.15% at inception and 0.439% at March 31, 2016. The total current effective rate on Tranzact’s debt was 6.28% at March 31, 2016 . The swap is measured at fair value with changes therein recognized within other revenues and is accounted for as a non-hedge derivative instrument. As of March 31, 2016 , the estimated fair value of the swap was $(0.8) million . There are no collateral arrangements associated with the swap.

Municipal Bond Guarantee

Municipal Bond Guarantee	3 Months Ended
	Mar. 31, 2016
Guarantees [Abstract]
Municipal Bond Guarantee Insurance	Municipal Bond Guarantee Insurance In 2012, HG Global was capitalized with $594.5 million from White Mountains and $14.5 million from non-controlling interests to fund BAM, a newly formed mutual municipal bond insurer. As of March 31, 2016 , White Mountains owned 96.9% of HG Global’s preferred equity and 88.4% of its common equity. HG Global, together with its subsidiaries, provided the initial capitalization of BAM through the purchase of $503.0 million of BAM Surplus Notes. Through HG Re, which had statutory capital of $467.2 million at March 31, 2016 , HG Global provides first loss reinsurance protection for policies underwritten by BAM of up to 15% of par outstanding, on a per policy basis. HG Re’s obligations to BAM are collateralized in trusts, and there is an aggregate loss limit that is equal to the total assets in the collateral trusts at any point in time. For the three months ended March 31, 2016 , HG Global had pre-tax income of $7.3 million , which included $4.5 million of interest income on the BAM Surplus Notes. For the three months ended March 31, 2015 , HG Global had pre-tax income of $5.5 million , which included $4.0 million of interest income on the BAM Surplus Notes. For the three months ended March 31, 2016 and 2015, White Mountains reported pre-tax losses of $7.6 million and $8.8 million on BAM that were recorded in net loss attributable to non-controlling interests, which included $4.5 million and $4.0 million of interest expense on the BAM Surplus Notes. Effective January 1, 2014, HG Global and BAM agreed to change the interest rate on the BAM Surplus Notes for the five years ending December 31, 2018 from a fixed rate of 8% to a variable rate equal to the one -year U.S. treasury rate plus 300 basis points, set annually, which is 3.54% and 3.15% for 2016 and 2015. Prior to the end of 2018, BAM has the option to extend the variable rate period for an additional three years. At the end of the variable rate period, the interest rate will be fixed at the higher of the then current variable rate or 8% . BAM is required to seek regulatory approval to pay interest and principal on its surplus notes only when adequate capital resources have accumulated beyond BAM’s initial capitalization and a level that continues to support its outstanding obligations, business plan and ratings. All of the contracts issued by BAM are accounted for as insurance contracts under ASC 944-605, Financial Guarantee Insurance Contracts. Premiums are received upfront and an unearned premium revenue liability, equal to the amount of the cash received, is established at contract inception. Premium revenues are recognized in revenue over the period of the contracts in proportion to the amount of insurance protection provided using a constant rate. The constant rate is calculated based on the relationship between the par outstanding in a given reporting period compared with the sum of each of the par amounts outstanding for all periods. The following table provides a schedule of BAM’s insured obligations: March 31, 2016 December 31, 2015 Contracts outstanding 3,422 3,103.0 Remaining weighted average contract period outstanding (in years) 12.7 12.8 Contractual debt service outstanding (in millions): Principal $ 24,641.6 $ 22,556.0 Interest 12,711.9 11,984.4 Total debt service outstanding $ 37,353.5 $ 34,540.4 Gross unearned insurance premiums $ 55.8 $ 50.2

Earnings Per Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2016
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 three months ended March 31, 2016 and 2015 . (See Note 17 - “Discontinued Operations” ). Three Months Ended March 31, 2016 2015 Basic and diluted earnings per share numerators (in millions): Net income from continuing operations attributable to White Mountains’s common shareholders $ 13.9 $ 10.5 Allocation of income for unvested restricted common shares (.1 ) (.1 ) Dividends declared on participating restricted common shares (1) (.1 ) (.1 ) Total allocation to restricted common shares (.2 ) (.2 ) Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ 13.7 $ 10.3 Undistributed net earnings (in millions): Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ 13.7 $ 10.3 Dividends declared net of restricted common share amounts (1) (5.9 ) (5.9 ) Total undistributed net earnings, net of restricted common share amounts $ 7.8 $ 4.4 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 5,539.6 5,978.4 Average unvested restricted shares (2) (54.0 ) (58.8 ) Basic earnings per share denominator 5,485.6 5,919.6 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 5,540.5 5,978.4 Average unvested restricted common shares (2) (54.0 ) (58.8 ) Average outstanding dilutive options to acquire common shares (3) — — Diluted earnings per share denominator 5,486.5 5,919.6 Basic earnings per share (in dollars): Net income attributable to White Mountains’s common shareholders $ 2.51 $ 1.76 Dividends declared and paid (1.00 ) (1.00 ) Undistributed earnings $ 1.51 $ .76 Diluted earnings per share (in dollars): Net income attributable to White Mountains’s common shareholders $ 2.51 $ 1.76 Dividends declared and paid (1.00 ) (1.00 ) Undistributed earnings $ 1.51 $ .76 (1) Restricted shares issued by White Mountains receive dividends, and therefore, are considered participating securities. (2) Restricted shares outstanding vest either in equal annual installments or upon a stated date. (See Note 15 - “Employee Share-Based Compensation Plans”) . (3) The diluted earnings per share denominator for the three months ended March 31, 2016 includes the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding, which results in 882 incremental shares outstanding over the period. The incremental shares had an effect on diluted earning per share of less than $0.01 . The diluted earnings per share denominator for the three months ended March 31, 2015 does not include the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding as they were anti-dilutive to the calculation.

Non-controlling Interest

Non-controlling Interest	3 Months Ended
	Mar. 31, 2016
Noncontrolling Interest [Abstract]
Non-controlling Interests	The following table details the balance of non-controlling interests included in White Mountains’s total equity and the related percentage of each consolidated entity’s total equity owned by non-controlling shareholders as of March 31, 2016 and December 31, 2015: March 31, 2016 December 31, 2015 $ in millions Non-controlling Percentage Non-controlling Equity Non-controlling Percentage Non-controlling Equity OneBeacon Ltd. 23.9 % $ 243.4 24.5 % $ 245.6 SIG Preference Shares 100.0 250.0 100.0 250.0 Other, excluding mutuals and reciprocals HG Global 3.1 17.2 3.1 17.1 MediaAlpha 40.0 14.2 40.0 14.4 Tranzact 36.8 79.7 36.8 79.4 Wobi 3.9 .5 3.9 .6 Dewar 30.1 3.2 19.0 3.7 Total other, excluding mutuals and reciprocals 114.8 115.2 Mutuals and reciprocals BAM 100.0 (140.7 ) 100.0 (140.0 ) SSIE 100.0 (16.1 ) 100.0 (16.0 ) Total non-controlling interests $ 451.4 $ 454.8

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2016
Segment Reporting [Abstract]
Segment Informartion	Segment Information White Mountains has determined that its reportable segments are OneBeacon, HG Global/BAM and Other Operations. As a result of the Sirius Group sale, the results of operations for Sirius Group have been classified as discontinued operations and are now presented, net of related income taxes, as such in the statement of operations and comprehensive income. Prior year amounts have been reclassified to conform to the current period’s presentation (See Note 17). White Mountains has made its segment determination based on consideration of the following criteria: (i) the nature of the business activities of each of the Company’s subsidiaries and affiliates; (ii) the manner in which the Company’s subsidiaries and affiliates are organized; (iii) the existence of primary managers responsible for specific subsidiaries and affiliates; and (iv) the organization of information provided to the chief operating decision makers and the Board of Directors. Significant intercompany transactions among White Mountains’s segments have been eliminated herein. Financial information for White Mountains’s segments follows: HG Global/BAM Millions OneBeacon HG BAM (1) Other Operations Total Three Months Ended March 31, 2016 Earned insurance premiums $ 278.6 $ .9 $ .3 $ 2.3 $ 282.1 Net investment income 14.4 .5 1.6 1.4 17.9 Net investment income (loss) - surplus note interest — 4.5 (4.5 ) — — Net realized and unrealized investment gains 16.6 2.1 4.9 5.9 29.5 Other revenue .9 — .1 96.6 (2) 97.6 Total revenues 310.5 8.0 2.4 106.2 427.1 Losses and LAE 158.8 — — 2.3 161.1 Insurance acquisition expenses 51.0 .2 .7 .8 52.7 Other underwriting expenses 55.3 — .1 — 55.4 General and administrative expenses 3.6 .5 9.2 119.1 (3) 132.4 Amortization of intangible assets .3 — — 7.8 8.1 Interest expense 3.3 — — 2.6 5.9 Total expenses 272.3 .7 10.0 132.6 415.6 Pre-tax (loss) income $ 38.2 $ 7.3 $ (7.6 ) $ (26.4 ) $ 11.5 HG Global/BAM Millions OneBeacon HG BAM (1) Other Operations Total Three Months Ended March 31, 2015 Earned insurance premiums $ 286.6 $ .5 $ .2 $ 2.0 $ 289.3 Net investment income 10.5 .4 1.0 .7 12.6 Net investment income (loss) - surplus note interest — 4.0 (4.0 ) — — Net realized and unrealized investment losses 14.2 1.1 3.0 6.7 25.0 Other (loss) revenue (3.1 ) — .1 67.9 (2) 64.9 Total revenues 308.2 6.0 .3 77.3 391.8 Losses and LAE 165.9 — — 2.0 167.9 Insurance acquisition expenses 51.0 .1 .8 1.1 53.0 Other underwriting expenses 55.9 — .1 — 56.0 General and administrative expenses 3.8 .4 8.2 90.8 (3) 103.2 Amortization of intangible assets .3 — — 6.6 6.9 Interest expense 3.2 — — 1.1 4.3 Total expenses 280.1 .5 9.1 101.6 391.3 Pre-tax income (loss) $ 28.1 $ 5.5 $ (8.8 ) $ (24.3 ) $ .5 (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) Includes $ 57.8 from Tranzact and $ 32.7 from MediaAlpha for the quarter ended March 31, 2016. and $ 37.5 from Tranzact and $ 29.7 from MediaAlpha for the year ended March 31, 2015. (3) Includes $ 48.4 from Tranzact and $ 30.5 from MediaAlpha for the quarter ended March 31, 2016, and $ 34.9 from Tranzact and $ 27.7 from MediaAlpha for the year ended March 31, 2015.

Investments in Unconsolidated A

Investments in Unconsolidated Affiliates	3 Months Ended
	Mar. 31, 2016
Equity Method Investments and Joint Ventures [Abstract]
Investments in Unconsolidated Affiliates	Investments in Unconsolidated Affiliates White Mountains’s 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. Symetra In August 2015, Symetra announced it had entered into a definitive merger agreement with Sumitomo Life pursuant to which Sumitomo Life would acquire all of the outstanding shares of Symetra. Following the announcement and Symetra shareholders’ November 5, 2015 meeting to approve the transaction, White Mountains relinquished its representation on Symetra’s board of directors. As a result, White Mountains changed its accounting for Symetra common shares from the equity method to fair value as of December 31, 2015. During the fourth quarter of 2015, White Mountains recognized $ 258.8 million ($ 241.1 million after tax) of unrealized investment gains through net income, representing the difference between the carrying value of Symetra common shares under the equity method at the date of change and fair value at December 31, 2015. On February 1, 2016, Symetra closed its definitive merger agreement with Sumitomo Life and White Mountains received proceeds of $ 658.0 million , or $ 32.00 per common share. White Mountains recognized $4.7 million in pre-tax net investment gains associated with Symetra in the first quarter of 2016. During the three months ended March 31, 2015, White Mountains received cash dividends from Symetra of $2.2 million , which were accounted for as a reduction of White Mountains’s investment in Symetra in accordance with equity method accounting. As of December 31, 2011, 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 or $15 per share. This impairment, as well as the effect of Symetra capital transactions, resulted in a basis difference between the GAAP carrying value of White Mountains’s investment in Symetra common shares under the equity method and the amount derived by multiplying the percentage of White Mountains common share ownership by Symetra’s total GAAP equity. As of March 31, 2015, the pre-tax unamortized basis difference was $165.7 million , of which $35.1 million is attributable to equity in earnings of unconsolidated affiliates and $130.6 million is attributable to equity in net unrealized gains of unconsolidated affiliates. The pre-tax basis difference was amortized over a 30 -year period, based on estimated future cash flows associated with Symetra’s underlying assets and liabilities to which the basis differences was attributed. White Mountains recognized the amortization of the basis difference through equity in earnings of unconsolidated affiliates and equity in net unrealized gains (losses) from investments in unconsolidated affiliates consistent with the original attribution of the basis differences between equity in earnings and equity in net unrealized gains (losses). For the three months ended March 31, 2015, White Mountains recognized after-tax amortization of $0.7 million through equity in earnings of unconsolidated affiliates and $2.8 million through equity in net unrealized gains from investments in unconsolidated affiliates. The following table summarizes amounts recorded by White Mountains under the equity method relating to its investment in Symetra for the three months ended March 31, 2015: Three Months Ended Millions March 31, 2015 Equity method carrying value of investment in Symetra as of December 31, 2014 $ 411.4 Equity in earnings (1)(2) 7.2 Equity in net unrealized gains from Symetra’s fixed maturity portfolio (3) 30.9 Dividends received (2.2 ) Equity method carrying value of investment in Symetra as of March 31, 2015 (4) $ 447.3 (1) Equity in earnings excludes tax expense of $0.4 . (2) Equity in earnings includes $0.7 increase relating to the pre-tax amortization of the Symetra common share basis difference. (3) Net unrealized gains includes $2.9 increase relating to the pre-tax amortization of the Symetra common share basis difference. (4) Includes White Mountains’s equity in net unrealized gains from Symetra’s fixed maturity portfolio of $68.4 as of March 31, 2015, which excludes tax expense of $4.6 . Hamer On May 27, 2015, White Mountains sold its interest in Hamer LLC, which resulted in a gain of $20.0 million recorded in other revenue. White Mountains recorded equity in earnings relating to Hamer of $0.5 million for the three months ended March 31, 2015.

Employee Share-Based Incentive

Employee Share-Based Incentive Compensation Plans	3 Months Ended
	Mar. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Employee Share-Based Incentive Compensation Plans	Employee Share-Based Incentive Compensation Plans White Mountains’s 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. White Mountains’s share-based compensation incentive awards consist of performance shares, restricted shares and stock options. Share-Based Compensation Based on White Mountains Common Shares WTM Performance Shares Performance shares are conditional grants of a specified maximum number of common shares or an equivalent amount of cash. 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. The following table summarizes performance share activity for the three months ended March 31, 2016 and 2015 for performance shares granted under the WTM Incentive Plan: Three Months Ended March 31, 2016 2015 Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Beginning of period 96,211 $ 58.2 113,198 $ 44.4 Shares paid or expired (1) — — (34,001 ) (24.9 ) New grants 16,215 — 29,078 — Assumed forfeitures and cancellations (2) (1,186 ) (.6 ) 123 .5 Expense recognized — 14.2 — 5.7 End of period (3) 111,240 $ 71.8 108,398 $ 25.7 (1) WTM performance share payments in 2016 for the 2013-2015 performance cycle, which were paid in April 2016, ranged from 140% to 142% of target. WTM performance share payments in 2015 for the 2012-2014 performance cycle ranged from 88% to 131.5% of target. (2) Amounts include changes in assumed forfeitures, as required under GAAP. (3) Outstanding performance share awards as of March 31, 2016 and 2015 both exclude 7,998 performance share awards, net of assumed forfeitures, granted to employees of Sirius Group, which is accounted for as discontinued operations. For the 2012-2014 performance cycle, all performance shares earned were settled in cash. If the outstanding WTM performance shares had vested on March 31, 2016 , the total additional compensation cost to be recognized would have been $35.2 million , based on accrual factors at March 31, 2016 (common share price and payout assumptions). Performance Shares granted under the WTM Incentive Plan The following table summarizes performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan at March 31, 2016 for each performance cycle: Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Performance cycle: 2016 – 2018 16,215 $ 1.0 2015 – 2017 29,428 12.8 2014 – 2016 32,157 18.7 2013 – 2015 36,293 41.1 Sub-total 114,093 73.6 Assumed forfeitures (2,853 ) (1.8 ) Total at March 31, 2016 111,240 $ 71.8 Restricted Shares The following table summarizes the unrecognized compensation cost associated with the outstanding restricted share awards for the three months ended March 31, 2016 and 2015 : Three Months Ended March 31, 2016 2015 Millions, except share amounts Restricted Unamortized Restricted Unamortized Non-vested, Beginning of period 70,675 $ 15.7 83,314 $ 14.3 Issued 21,215 16.3 22,890 15.2 Vested (24,620 ) — (35,079 ) — Forfeited (800 ) .2 — — Expense recognized — (3.0 ) — (3.0 ) End of period (1) 66,470 $ 29.2 71,125 $ 26.5 (1) Outstanding restricted share awards as of March 31, 2016 and 2015 include 2,512 and 3,572 restricted shares issued to employees of Sirius Group, which is accounted for as discontinued operations. During the first three months of 2016, White Mountains issued 21,215 restricted shares that vest on January 1, 2019. During the first three months of 2015, White Mountains issued 22,890 restricted shares that vest on January 1, 2018. The unrecognized compensation cost at March 31, 2016 is expected to be recognized ratably over the remaining vesting periods. Share-Based Compensation Based on OneBeacon Ltd. Common Shares The OneBeacon Long-Term Incentive Plan (the “OneBeacon Incentive Plan”) provides for grants to key employees of OneBeacon various types of share-based and non share-based incentive awards. OneBeacon’s share-based incentive awards include OneBeacon performance shares and restricted shares. OneBeacon Performance Shares OneBeacon performance shares are conditional grants of a specified maximum number of common shares or an equivalent amount of cash. OneBeacon performance share awards 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 OneBeacon Ltd. common shares at the time awards are paid. The following table summarizes performance share activity for the three months ended March 31, 2016 and 2015 for OneBeacon performance shares granted under the OneBeacon Incentive Plan: Three Months Ended March 31, 2016 2015 Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Beginning of period 449,435 $ 1.4 517,470 $ 3.4 Shares paid or expired (1) (167,300 ) (.7 ) (181,290 ) (1.5 ) New grants 163,150 — 154,887 — Assumed forfeitures and cancellations (2) (4,079 ) — (28,920 ) — Expense recognized — .4 — .2 End of period 441,206 $ 1.1 462,147 $ 2.1 (1) OneBeacon performance share payments in 2016 for the 2013-2015 performance cycle were at 24.3% of target. OneBeacon performance share payments in 2015 for the 2012-2014 performance cycle were at 45.7% of target. (2) Amounts include changes in assumed forfeitures, as required under GAAP. If the outstanding OneBeacon performance shares had been vested on March 31, 2016 , the total additional compensation cost to be recognized would have been $3.1 million , based on accrual factors at March 31, 2016 (common share price, accumulated dividends and payout assumptions). The following table summarizes OneBeacon performance shares outstanding awarded under the OneBeacon Incentive Plan at March 31, 2016 for each performance cycle: Millions, except share amounts Target Accrued Expense Performance cycle: 2016 – 2018 163,150 $ .1 2015 – 2017 146,659 .8 2014 – 2016 142,710 .2 Sub-total 452,519 1.1 Assumed forfeitures (11,313 ) — Total at March 31, 2016 441,206 $ 1.1 OneBeacon Restricted Shares The following table summarizes the unrecognized compensation cost associated with the outstanding OneBeacon restricted stock awards for the three months ended March 31, 2016 and 2015 : Three Months Ended March 31, 2016 2015 Millions, except share amounts Restricted Unamortized Restricted Unamortized Non-vested, Beginning of period 382,722 $ 2.5 612,500 $ 3.5 Issued 170,650 2.3 75,950 1.1 Vested (157,500 ) — (296,000 ) — Forfeited — — (1,500 ) — Expense recognized — (.5 ) — (.6 ) End of period 395,872 $ 4.3 390,950 $ 4.0 On February 24, 2016, OneBeacon issued 170,650 restricted shares, of which 92,500 restricted shares vest on February 24, 2018 and 78,150 vest on January 1, 2019. On February 24, 2015, OneBeacon issued 75,950 restricted shares that vest on January 1, 2018. On May 25, 2011, OneBeacon issued 630,000 restricted shares to its CEO that vest in four equal annual installments. The first installment vested on February 22, 2014. Concurrently with the grant of the restricted shares, 35,000 OneBeacon performance shares issued to OneBeacon’s CEO for the 2011-2013 performance share cycle were forfeited and performance share awards to OneBeacon’s CEO for the subsequent five years have been or will also be reduced by 35,000 shares. The unrecognized compensation cost at March 31, 2016 is expected to be recognized ratably over the remaining vesting periods. OneBeacon Restricted Stock Units During the first quarter of 2016, the OneBeacon Compensation Committee awarded to certain employees 222,449 restricted stock units (“RSUs”) that are scheduled to vest on January 1, 2019 and will be paid out in cash or shares at the discretion of the OneBeacon Compensation Committee. During the first quarter of 2015, the OneBeacon Compensation Committee awarded to certain employees 207,848 RSU that are scheduled to vest on January 1, 2018, of which, net of forfeiture assumptions, 198,928 were outstanding as of March 31, 2016. For the three months ended March 31, 2016 and 2015, the expense associated with the RSUs was $0.4 million and $0.1 million .

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2016
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, the Tranzact Bank Facility and MediaAlpha Bank Facility, which are recorded as debt at face value less unamortized original issue discount. The following table summarizes the fair value and carrying value of these financial instruments as of March 31, 2016 and December 31, 2015 : March 31, 2016 December 31, 2015 Millions Fair Value Carrying Value Fair Value Carrying Value OBH Senior Notes $ 278.0 $ 272.9 $ 276.4 $ 272.9 Tranzact Bank Facility 92.8 92.4 102.8 102.9 MediaAlpha Bank Facility 15.1 17.2 15.0 14.7 The fair value estimate for the OBH Senior Notes has been determined using quoted market prices. The OBH Senior Notes are considered a Level 2 measurement based on the closing market price at the end of the first quarter of 2016. The fair value estimate for the Tranzact Bank Facility and MediaAlpha Bank Facility have been determined based on a discounted cash flows approach and is considered to be a Level 3 measurement.

Discontinued Operations

Discontinued Operations	3 Months Ended
	Mar. 31, 2016
Discontinued Operations and Disposal Groups [Abstract]
Discontinued Operations	Discontinued Operations Sirius Group On April 18, 2016, White Mountains completed the sale of Sirius Group to CMI for approximately $2.6 billion . $161.8 million of this amount was used to purchase certain assets to be retained by White Mountains out of Sirius Group, including shares of OneBeacon. The amount paid at closing was based on an estimate of Sirius Group’s closing date tangible common shareholder’s equity. The purchase price will be adjusted upon determination of Sirius Group’s actual closing date tangible common shareholder’s equity. As of March 31, 2016, Sirius Group’s results are reported as discontinued operations and assets and liabilities held for sale within White Mountains’s GAAP financial statements. Assets held for sale does not include White Mountains’s investment in OneBeacon and certain other investments that are in the Sirius Group legal entities as of March 31, 2016. As of March 31, 2016 and December 31, 2015, the value of these investments, net of related tax effects, is $161.8 million and $686.2 million , of which $528.6 million as of December 31, 2015 is related to Symetra. Net income (loss) from discontinued operations does not include White Mountains’s net investment income and realized and unrealized investment gains and losses associated with these investments. For the three months ended March 31, 2016, $4.1 million of net investment income and realized and unrealized investment gains and losses, net of related tax effects, that are included in the Sirius Group legal entities have been excluded from net income (loss) from discontinued operations. For the three months ended March 31, 2015, $0.3 million of net investment income and realized and unrealized investment gains and losses, net of related tax effects, that had been previously included in the Sirius Group legal entities have been excluded from net income (loss) from discontinued operations. OneBeacon Runoff The loss from discontinued operations, net of tax, of $0.1 million for the three months ended March 31, 2015, was the result of post-closing expenses incurred in connection with the Runoff Business, which was completed in December of 2014. Esurance For the three months ended March 31, 2015, White Mountains recorded a net gain from the sale of discontinued operations of $8.0 million , which primarily related to an installment payment from Allstate for the favorable development on loss reserves. (See Note 18 - “Contingencies” ). Summary of Reclassified Balances and Related Items Net Assets Held for Sale The following summarizes the assets and liabilities associated with the business classified as held for sale, which all relate to Sirius Group: Millions March 31, 2016 December 31, 2015 Assets held for sale Fixed maturity investments, at fair value $ 2,758.3 $ 2,374.0 Short-term 534.5 352.0 Common equities 214.3 174.4 Other 61.3 72.2 Total investments 3,568.4 2,972.6 Cash 134.8 143.9 Reinsurance recoverable on unpaid losses 286.2 283.1 Reinsurance recoverable on paid losses 11.1 10.2 Insurance premiums receivable 483.3 323.6 Deferred acquisition costs 91.6 74.6 Deferred tax asset 291.2 303.1 Ceded unearned insurance and reinsurance premiums 134.7 87.7 Accounts receivable on unsettled investment sales 9.8 29.0 Goodwill and intangible assets 10.2 10.2 Other assets 194.2 169.0 Total assets held for sale $ 5,215.5 $ 4,407.0 Liabilities held for sale Loss and loss adjustment expense reserves $ 1,649.5 $ 1,644.4 Unearned insurance premiums 501.3 342.2 Debt 403.6 403.5 Deferred tax liability 278.5 263.6 Accrued incentive compensation 43.1 63.2 Ceded reinsurance payable 132.4 67.1 Funds held under reinsurance treaties 57.0 52.9 Accounts payable on unsettled investment purchases 5.4 — Other liabilities 50.3 47.1 Total liabilities held for sale 3,121.1 2,884.0 Net assets held for sale $ 2,094.4 $ 1,523.0 Net Income from Discontinued Operations The following summarizes the results of operations, including related income taxes associated with the business classified as discontinued operations. The results of Sirius Group up to but not including the closing date of the transaction inures to White Mountains. Three Months Ended Three Months Ended March 31, 2016 March 31, 2015 Millions Sirius Group Other Disc Ops Total Sirius Group Other Disc Ops Total Revenues Earned insurance premiums $ 202.4 $ — $ 202.4 $ 205.0 $ — $ 205.0 Net investment income 12.2 — 12.2 9.0 — 9.0 Net realized and unrealized (losses) gains (8.8 ) — (8.8 ) 78.4 — 78.4 Other revenue (4.1 ) — (4.1 ) (27.4 ) — (27.4 ) Total revenues 201.7 — 201.7 265.0 — 265.0 Expenses Loss and loss adjustment expenses 113.7 — 113.7 97.5 — 97.5 Insurance and reinsurance acquisition expenses 48.4 — 48.4 42.6 — 42.6 Other underwriting expenses 26.7 — 26.7 25.5 — 25.5 General and administrative expenses 8.1 — 8.1 6.3 — 6.3 Interest expense 6.6 — 6.6 6.8 — 6.8 Total expenses 203.5 — 203.5 178.7 — 178.7 Pre-tax (loss) income (1.8 ) — (1.8 ) 86.3 — 86.3 Income tax benefit (expense) .9 — .9 (20.4 ) — (20.4 ) Net (loss) income from discontinued operations (.9 ) — (.9 ) 65.9 — 65.9 Net losses from sales of discontinued operations - OneBeacon — — — — (.1 ) (.1 ) Net gain from sales of discontinued operations - Esurance — — — — 8.0 8.0 Total (loss) income from discontinued operations $ (.9 ) $ — $ (.9 ) $ 65.9 $ 7.9 $ 73.8 Change in foreign currency translation and other from discontinued operations $ 37.2 $ — $ 37.2 $ (87.6 ) $ — $ (87.6 ) Comprehensive income (loss) from discontinued operations $ 36.3 $ — $ 36.3 $ (21.7 ) $ 7.9 $ (13.8 ) Net Change in Cash from Discontinued Operations The following summarizes the net change in cash, including income tax (payment to) refund from national governments and interest paid associated with the business classified as discontinued operations: Three Months Ended March 31, (Millions) 2016 2015 Net cash provided from operations $ (50.7 ) $ (14.3 ) Net cash provided from investing activities 35.0 36.0 Net cash used for financing activities 2.4 1.8 Effect of exchange rate changes on cash 4.2 (8.5 ) Net change in cash during the period (9.1 ) 15.0 Cash balances at beginning of period 143.9 111.5 Cash balances at end of period $ 134.8 $ 126.5 Supplemental cash flows information: Interest paid $ — $ (12.8 ) Net income tax payment to national governments $ (36.4 ) $ (7.0 ) 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 computation of earnings per share for discontinued operations for the three months ended March 31, 2016 and 2015 : Three Months Ended March 31, 2016 2015 Basic and diluted earnings per share numerators (in millions): Net income attributable to White Mountains’s common shareholders $ (.9 ) $ 73.8 Allocation of income for participating unvested restricted common shares (1) — (.7 ) Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts (2) $ (.9 ) $ 73.1 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 5,539.6 5,978.4 Average unvested restricted common shares (3) (54.0 ) (58.8 ) Basic earnings per share denominator 5,485.6 5,919.6 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 5,540.5 5,978.4 Average unvested restricted common shares (3) (54.0 ) (58.8 ) Average outstanding dilutive options to acquire common shares (4) — — Diluted earnings per share denominator 5,486.5 5,919.6 Basic and diluted earnings per share (in dollars): $ (.17 ) $ 12.33 (1) Restricted shares issued by White Mountains contain dividend participation features, and therefore, are considered participating securities. (2) Net earnings attributable to White Mountains’s common shareholders, net of restricted share amounts, is equal to undistributed earnings for the three months ended March 31, 2016 and 2015 . (3) Restricted common shares outstanding vest either in equal annual installments or upon a stated date. (See Note 15 - “Employee Share-Based Compensation Plans” ). (4) The diluted earnings per share denominator for the three months ended March 31, 2016 includes the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding, which results in 882 incremental shares outstanding over the period. The incremental shares had an effect on diluted earning per share of less than $0.01 per share. The diluted earnings per share denominator for the three months ended March 31, 2015 does 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. Fair Value of Financial Instruments The SIG Senior Notes are recorded as debt at face value less unamortized original issue discount, and the SIG Preference Shares are recorded as non-controlling interest at face value. The following table summarizes the fair value and carrying value of these financial instruments as of March 31, 2016 and December 31, 2015 : March 31, 2016 December 31, 2015 Millions Fair Value Carrying Value Fair Value Carrying Value SIG Senior Notes $ 409.0 $ 399.9 $ 410.0 $ 399.8 SIG Preference Shares 247.5 250.0 255.0 250.0 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. Interest Rate Cap In May 2007, Sirius International Group, Ltd. (“SIG”), an intermediate holding company of Sirius Group, 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% and (ii) 3 -month LIBOR plus 320 basis points. In July 2013, SIG executed 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 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 basis points 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 within other revenue. 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 March 31, 2016 . The following tables summarize the changes in the fair value of the Interest Rate Cap for the three months ended March 31, 2016 and 2015: Three Months Ended March 31, Millions 2016 2015 Beginning of period $ 1.9 $ 4.1 Net realized and unrealized losses (.8 ) (1.0 ) End of period $ 1.1 $ 3.1 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’s 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: March 31, 2016 Millions Collateral Balances Held Standard & Poor’s Rating (1) Barclays Bank Plc $ .7 A- Nordea Bank Finland Plc .4 AA- Total $ 1.1 (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).

Contingencies

Contingencies	3 Months Ended
	Mar. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Contingencies	Contingencies Legal Contingencies White Mountains, and the insurance and reinsurance industry in general, are routinely subject to claims related litigation and arbitration in the normal course of business, as well as litigation and arbitration that do not arise from, or are directly related to, claims activity. White Mountains’s 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 - “Loss and Loss Adjustment Expense Reserves”) . White Mountains considers the requirements of ASC 450 when evaluating its exposure to non-claims related litigation and arbitration. ASC 450 requires that accruals be established for litigation and arbitration if it is probable that a loss has been incurred and it can be reasonably estimated. ASC 450 also requires that litigation and arbitration be disclosed if it is probable that a loss has been incurred or if there is a reasonable possibility that a loss may have been incurred. Although the ultimate outcome of claims and non-claims related litigation and arbitration, and the amount or range of potential loss at any particular time, is often inherently uncertain, management does not believe that the ultimate outcome of such claims and non-claims related litigation and arbitration will have a material adverse effect on White Mountains’s financial condition, results of operations or cash flows. The following summarizes significant legal contingencies, ongoing non-claims related litigation or arbitration as of March 31, 2016 : Esurance On October 7, 2011, the Company completed the sale of its Esurance and Answer Financial subsidiaries (the “Transferred Subsidiaries”) to The Allstate Corporation (“Allstate”) pursuant to 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”). Subject to specified thresholds and limits, the Company remains contingently liable to 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 retained 90% of positive or negative development in the loss reserves of the Transferred Subsidiaries as of the closing date (net of ECO/EPL losses) through December 31, 2014 (the “Reserve Settlement”). White Mountains recorded a net gain from the sale of discontinued operations of $8.0 million in the first quarter of 2015 and an additional $ 10.3 million in the third quarter of 2015 related to the final settlement with Allstate for favorable development on loss reserves transferred in the sale of Esurance and Answer Financial. Since the closing of the transaction, White Mountains received a net amount of $ 28.3 million from Allstate, primarily related to the favorable development on loss reserves. 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”). 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. OneBeacon received approximately $32.0 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 the plaintiffs appealed. On March 29, 2016, a three judge panel of the U.S. Second Circuit Court of Appeals affirmed the dismissal of the Noteholders Action. The plaintiffs may now accept the decision, ask the three judge panel to reconsider, file a motion for a rehearing en banc or seek a writ of certiorari to the U.S. Supreme Court. 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. An omnibus motion to dismiss the shareholder defendants in the Committee Action was filed in May 2014. No amount has been accrued in connection with this matter as of March 31, 2016, as the amount of loss, if any, cannot be reasonably estimated.

OneBeacon Pension Plan

OneBeacon Pension Plan	3 Months Ended
	Mar. 31, 2016
Compensation Related Costs [Abstract]
OneBeacon Pension Plan	OneBeacon Pension Plan OneBeacon previously sponsored the OneBeacon qualified pension plan (the “Qualified Plan”). During the three months ended March 31, 2016, the Qualified Plan finalized its termination by purchasing group annuity contracts from the Principal Financial Group and making lump sum distributions to Qualified Plan participants electing such payments, which eliminated the remaining Qualified Plan liability. As a result of these transactions, OneBeacon recognized a pre-tax pension settlement charge of $0.3 million and no longer has a projected benefit obligation with respect to the Qualified Plan as of March 31, 2016. OneBeacon continues to hold $55.4 million of excess invested assets, of which it expects to transfer the majority of the assets to a new trust that will fund future contributions to a defined contribution qualified replacement plan during 2016. A portion of the assets will be left in the trust in order to wind-down potential post-termination obligations of the Qualified Plan, as approved by way of a March 2016 private letter ruling from the IRS. These invested assets are included in other assets and are accounted for at fair value. The annuity purchase is subject to a final true-up, anticipated in the second quarter of 2016, to the extent actual experience is different than expected up until OneBeacon ceases administrating claims payments on June 1, 2016. OneBeacon continues to sponsor a non-qualified, non-contributory, defined benefit pension plan (“Non-qualified Plan”)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. The Non-qualified Plan was frozen and curtailed in 2002, resulting in the pension benefit obligation being equal to the accumulated benefit obligation. The benefits are based primarily on years of service and employees’ compensation through December 31, 2002. OneBeacon’s funding policy is generally to contribute amounts to satisfy actual disbursements for the calendar year.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2016
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Subsequent Events Sirius Group Sale On April 18, 2016, White Mountains completed the sale of Sirius Group to CMI for approximately $ 2.6 billion . $161.8 million of this amount was used to purchase certain assets to be retained by White Mountains out of Sirius Group, including shares of OneBeacon. The amount paid at closing was based on an estimate of Sirius Group’s closing date tangible common shareholder’s equity. The purchase price will be adjusted upon determination of Sirius Group’s actual closing date tangible common shareholder’s equity. Share Repurchases During April 2016, White Mountains repurchased and retired 356,423 of its common shares for $ 287 million at an average share price of $ 806.52 , which included 325,000 common shares repurchased from Franklin Mutual Advisers for $ 807.00 per share, the market price at the time the agreement was reached.

Summary of Significant Accoun28

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2016
Accounting Policies [Abstract]
Recently Adopted Changes in Accounting Principles and Recently Issued Accounting Pronouncements	Recently Adopted Changes in Accounting Principles Business Combinations - Measurement Period Adjustments Effective January 1, 2016, White Mountains adopted ASU 2015-16, Simplifying the Accounting for Measurement-Period Adjustments, which requires adjustments to provisional amounts recorded in connection with a business combination that are identified during the measurement period to be recorded in the reporting period in which the adjustment amounts are determined, rather than as retroactive adjustments to prior periods. White Mountains has not recognized any adjustments to estimated purchase accounting amounts for the year to date period ended March 31, 2016 and accordingly, there was no effect to White Mountains’s financial statements upon adoption. Fair Value Measurements On January 1, 2016, White Mountains adopted ASU 2015-07, Fair Value Measurement - Disclosures for Investments in Certain Entities that Calculate Net Asset Value per Share (or Its Equivalent) (ASC 820), which eliminates the requirement to disclose the fair value hierarchy level for investments for which fair value is measured at net asset value using the practical expedient in ASC 820. White Mountains measures the fair value of its investments in hedge funds and private equity funds using this practical expedient. Upon adoption, these fair value measurements are no longer classified within the fair value hierarchy. Prior year amounts have been modified to conform to the current year’s disclosures. Amendments to Consolidation Analysis On January 1, 2016, White Mountains adopted ASU 2015-02, Amendments to the Consolidation Analysis (ASC 810) which amends the guidance for determining whether an entity is a variable interest entity (“VIE”). ASU 2015-02 eliminates the separate consolidation guidance for limited partnerships and, with it, the presumption that a general partner should consolidate a limited partnership. In addition, ASU 2015-02 changes the guidance for determining if fee arrangements qualify as variable interests and the effect fee arrangements have on the determination of the primary beneficiary. Adoption of ASU 2015-02 did not affect the consolidation analysis for any of White Mountains’s investments. Share-Based Compensation Awards On January 1, 2016, White Mountains adopted ASU 2014-12, Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period (ASC 718) . The new guidance requires that a performance target that affects vesting and that can be achieved after the requisite service period be treated as a performance condition. Compensation cost is to be recognized in the period when it becomes probable the performance target will be achieved in an amount equal to the compensation cost attributable to the periods for which service has been rendered. Adoption did not have a significant effect on White Mountains’s financial position, results of operations, cash flows, presentation or disclosures. Debt Issuance Costs On January 1, 2016, White Mountains adopted ASU 2015-03, Imputation of Interest (ASC 835), which requires debt issuance costs to be presented as a deduction from the carrying amount of the related debt, consistent with the treatment required for debt discounts. The new guidance requires amortization of debt issuance costs to be classified within interest expense and also requires disclosure to the debt’s effective interest rate. White Mountains has applied the guidance retrospectively and as a result has reclassified $1.9 million of unamortized debt issuance costs from other assets to debt as of December 31, 2015, reflecting these amounts as a reduction from the related debt, and has modified its disclosures to include the required effective interest rate on its debt. As of March 31, 2016, the unamortized debt issuance costs included in debt is $3.8 million . Recently Issued Accounting Pronouncements Short-Duration Contracts On May 21, 2015, the FASB issued ASU 2015-09, Disclosures about Short Duration Contracts (ASC 944), which requires expanded footnote disclosures about loss and loss adjustment expense (“LAE”) reserves. Under the new guidance, some disclosures currently presented outside of White Mountains’s financial statements, such as loss development tables and a reconciliation of loss development data to the loss and LAE reserves reflected on the balance sheet, will become part of the financial statement footnotes. In addition, the loss development tables required to be presented under the new ASU must be presented on a disaggregated basis by accident year rather than by reporting year as currently presented. Some of the expanded disclosures are new requirements, such as the disclosure of reserves for losses incurred but not reported (“IBNR”) plus expected development on reported claims, which must be presented by accident year on a disaggregated basis. The new guidance also requires new disclosures about claim frequency data together with descriptions of the approach used to measure that data. Qualitative descriptions of methodologies and assumptions used to develop IBNR estimates must be presented together with the amounts of IBNR to which they relate, along with a discussion of any significant changes in methodology and assumptions and the related effect upon the loss reserves. The new guidance will be effective for annual periods beginning after December 15, 2015 and interim periods within annual periods beginning after December 15, 2016 with retrospective restatement of prior periods required. White Mountains will modify its financial statement footnote disclosures to conform to the requirements of ASU 2015-09 upon adoption, including revisions to prior year’s disclosures. Stock Compensation On March 30, 2016, the Board issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting (ASC 718) which is intended to simplify certain aspects of the accounting for share-based compensation. The new guidance provides an accounting policy election to account for forfeitures by either applying an assumption, as required under existing guidance, or by recognizing forfeitures when they actually occur. The new guidance is effective for annual periods beginning after December 15, 2016, and interim periods within those annual periods with early adoption permitted. White Mountains does not expect a significant effect upon adoption. Leases On February 25, 2016, the FASB issued ASU 2016-02, Leases (ASC 842). The new guidance requires lessees to recognize lease assets and liabilities on the balance sheet for both operating and financing leases, with the exception of leases with an original term of 12 months or less. Under existing guidance recognition of lease assets and liabilities is not required for operating leases. The lease assets and liabilities to be recognized are both measured initially based on the present value of the lease payments. Under the new guidance, a sale-leaseback transaction must meet the recognition criteria under ASC 606, Revenues in order to be accounted for as sale. The new guidance is effective for White Mountains for years beginning after December 15, 2018, including interim periods therein. White Mountains is evaluating the expected impact of this new guidance and available adoption methods. Financial Instruments - Recognition and Measurement On January 5, 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities (ASC 825-10). The new guidance requires all equity securities with readily determinable fair values to be measured at fair value with changes therein recognized through current period earnings. In addition, the new ASU requires a qualitative assessment for equity investments without readily determinable fair values to identify impairment, and for impaired equity security investments to be measured at fair value. ASU 2016-01 is effective for fiscal years beginning after December 15, 2017, with early adoption permitted. White Mountains has taken the fair value election for its portfolio of equity security investments and, accordingly, does not expect the adoption of ASU 2016-01 to have a significant impact on its financial statements. Revenue Recognition On May 28, 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (ASC 606), which modifies the guidance for revenue recognition. The scope of the new ASU excludes insurance contracts but is applicable to certain fee arrangements, such as third party investment management fees charged by White Mountains Advisors as well as commissions and other non-insurance revenues. In August 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (ASC 606) , which delayed the effective date of ASU 2014-09 to annual and interim reporting periods beginning after December 15, 2017. White Mountains is in the process of evaluating the new guidance and has not yet determined the potential effect of adoption on its financial position, results of operations, or cash flows.

Significant Transactions Signif

Significant Transactions Significant Transactions (Tables)	3 Months Ended
	Mar. 31, 2016
Insurance [Abstract]
Industry Loss Warranty	The following summarizes the ILW Covers: Scope Limit Industry Loss Trigger United States first event $75.0 million $40.0 billion United States first event $22.5 million $50.0 billion United States second event $45.0 million $15.0 billion Japan first event (1) $25.0 million $12.5 billion (1) ILW cover expired on March 31, 2016.

Loss and Loss Adjustment Expe30

Loss and Loss Adjustment Expense Reserves (Tables)	3 Months Ended
	Mar. 31, 2016
Insurance Loss Reserves [Abstract]
Loss and loss adjustment expense ("LAE") reserve activities	The following table summarizes the loss and loss adjustment expense (“LAE”) reserve activities of White Mountains’s insurance and reinsurance subsidiaries for the three months ended March 31, 2016 and 2015 : Three Months Ended March 31, Millions 2016 2015 Gross beginning balance $ 1,395.8 $ 1,350.0 Less beginning reinsurance recoverable on unpaid losses (186.5 ) (161.7 ) Net loss and LAE reserves 1,209.3 1,188.3 Loss and LAE incurred relating to: Current year losses 161.2 169.8 Prior year losses (0.1 ) (1.9 ) Total incurred losses and LAE 161.1 167.9 Loss and LAE paid relating to: Current year losses (23.1 ) (23.3 ) Prior year losses (148.6 ) (164.0 ) Total loss and LAE payments (171.7 ) (187.3 ) Net ending balance 1,198.7 1,168.9 Plus ending reinsurance recoverable on unpaid losses 150.9 141.7 Gross ending balance $ 1,349.6 $ 1,310.6

Investment Securities (Tables)

Investment Securities (Tables)	3 Months Ended
	Mar. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Par Value to Fair Value Reconciliation of Surplus Notes [Table Text Block]	Below is a table illustrating the valuation adjustments taken to arrive at estimated fair value of the surplus notes as of March 31, 2016 and December 31, 2015: Type of Surplus Note Total as of March 31, 2016 Total as of December 31, 2015 Millions Seller Priority Pari Passu Par Value $ 57.9 $ 43.1 $ 101.0 $ 101.0 Fair value adjustments to reflect: Current market rates on public debt and contract-based repayments (1) (.5 ) (14.2 ) (14.7 ) (15.1 ) Regulatory approval (2) (11.4 ) (13.0 ) (24.4 ) (24.2 ) Liquidity adjustment (3) (7.8 ) (2.3 ) (10.1 ) (10.2 ) Total adjustments (19.7 ) (29.5 ) (49.2 ) (49.5 ) Fair value $ 38.2 $ 13.6 $ 51.8 $ 51.5 (1) Represents the value of the surplus notes, at current market yields on comparable publicly traded debt, and assuming issuer is allowed to make principal and interest payments when its financial capacity is available, as measured by statutory capital in excess of a 250% RBC score. (2) Represents anticipated timing of securing regulatory approvals for interest and principal payments to reflect graduated changes in Issuer’s statutory surplus. T he monetary impact of the anticipated timing is measured based on credit spreads of public securities with roughly equivalent percentages of discounted payments missed. ( 3) Represents impact of liquidity spread to account for OneBeacon’s sole ownership of the surplus notes, lack of a trading market and ongoing regulatory approval risk.
Pre-tax net investment income	Pre-tax net investment income for the three months ended March 31, 2016 and 2015 consisted of the following: Three Months Ended March 31, Millions 2016 2015 Investment income: Fixed maturity investments $ 14.5 $ 12.5 Short-term investments .2 — Common equity securities 1.2 2.2 Other long-term investments 2.8 (.1 ) Total investment income 18.7 14.6 Third-party investment expenses (.8 ) (2.0 ) Net investment income, pre-tax $ 17.9 $ 12.6
Schedule of Realized and Unrealized Gain (Loss) on Investments	Net realized and unrealized investment gains (losses) consisted of the following: Three Months Ended March 31, Millions 2016 2015 Net realized investment gains, pre-tax $ 256.8 $ 14.8 Net unrealized investment (losses) gains, pre-tax (227.3 ) 10.2 Net realized and unrealized investment gains, pre-tax 29.5 25.0 Income tax expense attributable to net realized and unrealized investment gains (8.5 ) (7.1 ) Net realized and unrealized investment gains, after tax $ 21.0 $ 17.9
Realized Gain (Loss) on Investments	Net realized investment gains (losses) for the three months ended March 31, 2016 and 2015 consisted of the following: Three Months Ended Three Months Ended March 31, 2016 March 31, 2015 Millions Net Net Total net realized Net Net Total net realized Fixed maturity investments $ (1.1 ) $ — $ (1.1 ) $ .5 $ — $ .5 Short-term investments — — — — — — Common equity securities 257.6 — 257.6 22.0 .5 22.5 Other long-term investments .3 — .3 (8.2 ) — (8.2 ) Net realized investment gains, pre-tax 256.8 — 256.8 14.3 .5 14.8 Income tax expense attributable to net realized investment gains (42.9 ) — (42.9 ) (4.5 ) — (4.5 ) Net realized investment gains, after tax $ 213.9 $ — $ 213.9 $ 9.8 $ .5 $ 10.3
Schedule of unrealized gain (loss) on investments	The following table summarizes net unrealized investment gains (losses) and changes in the carrying value of investments measured at fair value: Three Months Ended Three Months Ended March 31, 2016 March 31, 2015 Millions Net unrealized gains (losses) Net gains Total net unrealized gains (losses) reflected in earnings Net unrealized gains (losses) Net Total net unrealized gains (losses) reflected in earnings Fixed maturity investments $ 21.7 $ — $ 21.7 $ 11.4 $ — $ 11.4 Short-term investments — — — — — — Common equity securities (249.8 ) 2.4 (247.4 ) (2.8 ) (4.0 ) (6.8 ) Other long-term investments (2.0 ) .4 (1.6 ) 6.6 (1.0 ) 5.6 Net unrealized investment (losses) gains, pre-tax (230.1 ) 2.8 (227.3 ) 15.2 (5.0 ) 10.2 Income tax benefit (expense) 34.4 — 34.4 (2.6 ) — (2.6 ) Net unrealized investment $ (195.7 ) $ 2.8 $ (192.9 ) $ 12.6 $ (5.0 ) $ 7.6
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 three months ended March 31, 2016 and 2015 : Three Months Ended March 31, Millions 2016 2015 Fixed maturity investments $ .5 $ .2 Common equity securities — (1.8 ) Other long-term investments 1.1 5.7 Total unrealized investment gains, pre-tax - Level 3 investments $ 1.6 $ 4.1
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’s fixed maturity investments as of March 31, 2016 and December 31, 2015 were as follows: March 31, 2016 Millions Cost or amortized cost Gross unrealized gains Gross unrealized losses Net foreign currency gains (losses) Carrying value U.S. Government and agency obligations $ 88.4 $ .4 $ — $ — $ 88.8 Debt securities issued by corporations 899.0 12.5 (1.1 ) — 910.4 Municipal obligations 264.3 4.6 (.2 ) — 268.7 Mortgage-backed and asset-backed securities 1,259.9 5.1 (4.1 ) — 1,260.9 Foreign government, agency and provincial obligations 1.0 .2 — — 1.2 Preferred stocks 78.3 4.9 — — 83.2 Total fixed maturity investments $ 2,590.9 $ 27.7 $ (5.4 ) $ — $ 2,613.2 December 31, 2015 Millions Cost or amortized cost Gross unrealized gains Gross unrealized losses Net foreign currency gains (losses) Carrying value U.S. Government and agency obligations $ 160.4 $ — $ (.4 ) $ — $ 160.0 Debt securities issued by corporations 1,001.0 4.3 (5.3 ) — 1,000.0 Municipal obligations 227.8 2.2 (1.2 ) — 228.8 Mortgage-backed and asset-backed securities 1,170.6 2.0 (5.6 ) — 1,167.0 Foreign government, agency and provincial obligations 1.0 .2 — — 1.2 Preferred stocks 78.3 4.4 — — 82.7 Total fixed maturity investments $ 2,639.1 $ 13.1 $ (12.5 ) $ — $ 2,639.7 The cost or amortized cost, gross unrealized investment gains and losses, net foreign currency gains and losses, and carrying values of White Mountains’s common equity securities and other long-term investments as of March 31, 2016 and December 31, 2015 were as follows: March 31, 2016 Millions Cost or amortized cost Gross unrealized gains Gross unrealized losses Net foreign Carrying value Common equity securities $ 399.0 $ 52.9 $ (8.9 ) $ — $ 443.0 Other long-term investments $ 312.3 $ 32.7 $ (21.3 ) $ (1.9 ) $ 321.8 December 31, 2015 Millions Cost or Gross Gross Net foreign Carrying value Common equity securities $ 822.5 $ 302.8 $ (11.4 ) $ — $ 1,113.9 Other long-term investments $ 304.5 $ 32.0 $ (18.4 ) $ (2.3 ) $ 315.8 Other Long-term Investments Other long-term investments consist of the following as of March 31, 2016 and December 31, 2015 : Carrying Value at Millions March 31, 2016 December 31, 2015 Hedge funds and private equity funds, at fair value (1) $ 131.3 $ 127.8 Private equity securities and limited liability companies, at fair value (1) 84.7 82.1 Surplus notes investments, at fair value (1) 51.8 51.5 Private convertible preferred securities (1) 32.9 32.7 Tax advantaged federal affordable housing development fund (2) 14.1 14.7 Partnership investments accounted for under the equity method 3.7 3.8 Other 3.3 3.2 Total other-long term investments $ 321.8 $ 315.8 (1) See Fair Value Measurements by Level table. (2) Fund accounted for using the proportional amortization method.
Other long-term investments	The following table summarizes investments in hedge funds and private equity funds by investment objective and sector as of March 31, 2016 and December 31, 2015 : March 31, 2016 December 31, 2015 Millions Fair Value Unfunded Commitments Fair Value Unfunded Commitments Hedge funds Long/short equity REIT $ 20.2 $ — $ 20.6 $ — Long/short banks and financial 12.6 — 12.8 — Other 3.6 — 3.6 — Total hedge funds 36.4 — 37.0 — Private equity funds Aerospace/Defense/Government 27.9 22.1 19.8 30.3 Manufacturing/Industrial 25.8 2.1 24.9 2.5 Energy infrastructure & services 18.0 3.3 20.7 3.4 Multi-sector 13.0 2.1 14.8 2.1 Private equity secondaries 3.9 2.1 4.4 2.1 Healthcare 3.8 .4 3.8 .4 Insurance 2.0 41.3 2.0 41.3 Real estate .5 .1 .4 .1 Total private equity funds 94.9 73.5 90.8 82.2 Total hedge funds and private equity funds included in other long-term investments $ 131.3 $ 73.5 $ 127.8 $ 82.2
Fair value of hedge funds subject to restrictions on redemption frequency and advance notice period requirements for investments in active hedge funds	The following summarizes the March 31, 2016 fair value of hedge funds subject to restrictions on redemption frequency and advance notice period requirements for investments in active hedge funds: Notice Period Millions Redemption frequency 30-59 days notice 60-89 days notice 90-119 days notice Total Monthly $ — $ — $ — $ — Quarterly 13.7 — — 13.7 Semi-annual — 20.2 — 20.2 Annual — — 2.5 2.5 Total $ 13.7 $ 20.2 $ 2.5 $ 36.4
Fair Value of private equity funds subject to lock-up periods	As of March 31, 2016 , 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 $29.2 $3.9 $61.8 $— $94.9
Fair value measurements by level, investment securities	The following tables summarize White Mountains’s fair value measurements for investments as of March 31, 2016 and December 31, 2015 by level. The major security types were based on the legal form of the securities. White Mountains has disaggregated its fixed maturity investments based on the issuing entity type, which impacts credit quality, with debt securities issued by U.S. government entities carrying minimal credit risk, while the credit and other risks associated with other issuers, such as corporations, foreign governments, municipalities or entities issuing mortgage-backed or asset-backed securities vary depending on the nature of the issuing entity type. White Mountains further disaggregates debt securities issued by corporations and equity securities by industry sector because investors often reference commonly used benchmarks and their subsectors to monitor risk and performance. Accordingly, White Mountains has further disaggregated these asset classes into subclasses based on the similar sectors and industry classifications it uses to evaluate investment risk and performance against commonly used benchmarks, such as the Barclays Intermediate Aggregate and S&P 500 indices. March 31, 2016 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 88.8 $ 72.3 $ 16.5 $ — Debt securities issued by corporations: Consumer 242.1 — 242.1 — Financials 155.5 — 155.5 — Industrial 135.1 — 135.1 — Health Care 124.7 — 124.7 — Energy 69.3 — 69.3 — Utilities 57.2 — 57.2 — Technology 57.1 — 57.1 — Communications 43.3 — 43.3 — Materials 26.1 — 26.1 — Other — — — — Total debt securities issued by corporations 910.4 — 910.4 — Mortgage-backed and asset-backed securities 1,260.9 — 1,260.9 — Municipal obligations 268.7 — 268.7 — Foreign government, agency and provincial obligations 1.2 .6 .6 — Preferred stocks 83.2 — 12.7 70.5 Total fixed maturity investments 2,613.2 72.9 2,469.8 70.5 Short-term investments 261.7 261.7 — — Common equity securities: Exchange traded funds (1) 130.5 109.0 21.5 — Consumer 73.1 73.1 — Technology 47.8 47.8 — — Health Care 39.0 39.0 — — Communications 34.9 34.9 — — Industrial 30.0 30.0 — — Financials 12.9 12.9 — — Other 74.8 — 74.8 — Total common equity securities 443.0 346.7 96.3 — Other long-term investments (2)(3) 172.7 — — 172.7 Total investments $ 3,490.6 $ 681.3 $ 2,566.1 $ 243.2 (1) ETFs traded on foreign exchanges are priced using the fund's published NAV to account for the difference in market close times and are therefore designated a level 2 measurement. (2) Excludes carrying value of $3.7 associated with other long-term investment limited partnerships accounted for using the equity method. Excludes carrying value of $14.1 associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method. (3) Excludes carrying value of $131.3 associated with hedge funds and private equity funds for which fair value is measured at net asset value using the practical expedient. December 31, 2015 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 160.0 $ 133.4 $ 26.6 $ — Debt securities issued by corporations: Consumer 253.3 — 253.3 — Financials 175.9 — 175.9 — Health Care 151.3 — 151.3 — Industrial 135.6 — 135.6 — Energy 82.0 — 82.0 — Utilities 61.5 — 61.5 — Technology 60.0 — 60.0 — Communications 49.2 — 49.2 — Materials 31.2 — 31.2 — Other — — — — Total debt securities issued by corporations 1,000.0 — 1,000.0 — Mortgage-backed and asset-backed securities 1,167.0 — 1,167.0 — Municipal obligations 228.8 — 228.8 — Foreign government, agency and provincial obligations 1.2 .6 .6 — Preferred stocks 82.7 — 12.7 70.0 Total fixed maturity investments 2,639.7 134.0 2,435.7 70.0 Short-term investments 211.3 211.3 — — Common equity securities: Exchange traded funds (1) 141.8 120.5 21.3 — Financials 694.7 694.7 — — Consumer 70.0 70.0 — — Communications 43.7 43.7 — — Health Care 35.7 35.7 — — Technology 27.0 27.0 — — Industrial 26.6 26.6 — — Other 74.4 — 74.4 — Total common equity securities 1,113.9 1,018.2 95.7 — Other long-term investments (2)(3) 169.5 — — 169.5 Total investments $ 4,134.4 $ 1,363.5 $ 2,531.4 $ 239.5 (1) ETFs traded on foreign exchanges are priced using the fund's published NAV to account for the difference in market close times and are therefore designated a level 2 measurement. (2) Excludes carrying value of $3.8 associated with other long-term investment limited partnerships accounted for using the equity method. Excludes carrying value of $14.7 associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method. (3) Excludes carrying value of $127.8 associated with hedge funds and private equity funds for which fair value is measured at net asset value using the practical expedient.
Debt securities issued by corporations, credit ratings	The following table summarizes the ratings of debt securities issued by corporations held in White Mountains’s investment portfolio as of March 31, 2016 and December 31, 2015 : Fair Value at Millions March 31, 2016 December 31, 2015 AAA $ 9.4 $ — AA 107.4 95.2 A 364.2 397.7 BBB 429.4 507.1 Other — — Debt securities issued by corporations (1) $ 910.4 $ 1,000.0 (1) Credit ratings are assigned based on the following hierarchy: 1) Standard & Poor’s and 2) Moody’s.
Mortgage-backed, asset-backed securities	March 31, 2016 December 31, 2015 Millions Fair Value Level 2 Level 3 Fair Value Level 2 Level 3 Mortgage-backed securities: Agency: GNMA $ 275.0 $ 275.0 $ — $ 265.5 $ 265.5 $ — FNMA 45.0 45.0 — 42.2 42.2 — FHLMC 22.1 22.1 — 22.8 22.8 — Total Agency (1) 342.1 342.1 — 330.5 330.5 — Non-agency: Residential 132.3 132.3 — 133.2 133.2 — Commercial 128.8 128.8 — 140.4 140.4 — Total Non-agency 261.1 261.1 — 273.6 273.6 — Total mortgage-backed securities 603.2 603.2 — 604.1 604.1 — Other asset-backed securities: Credit card receivables 281.6 281.6 — 217.7 217.7 — Vehicle receivables 290.8 290.8 — 269.7 269.7 — Other 85.3 85.3 — 75.5 75.5 — Total other asset-backed securities 657.7 657.7 — 562.9 562.9 — Total mortgage and asset-backed securities $ 1,260.9 $ 1,260.9 $ — $ 1,167.0 $ 1,167.0 $ — (1) Represents publicly traded mortgage-backed securities which carry the full faith and credit guaranty of the U.S. government (i.e., GNMA) or are guaranteed by a government sponsored entity (i.e., FNMA, FHLMC).
Schedule of security issuance years of investments in non-agency RMBS and non-agency CMBS securities	The security issuance years of White Mountains’s investments in non-agency RMBS and non-agency CMBS securities as of March 31, 2016 are as follows: Security Issuance Year Millions Fair Value 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Non-agency RMBS $ 132.3 $ 23.3 $ 8.1 $ 3.6 $ — $ 3.4 $ — $ 13.1 $ 12.6 $ 9.3 $ 13.2 $ 45.7 $ — Non-agency CMBS 128.8 — — — — — — 5.2 — 18.3 15.4 44.8 45.1 Total $ 261.1 $ 23.3 $ 8.1 $ 3.6 $ — $ 3.4 $ — $ 18.3 $ 12.6 $ 27.6 $ 28.6 $ 90.5 $ 45.1
Non-agency residential mortgage securities, collateral quality and tranche levels	The classification of the underlying collateral quality and the tranche levels of White Mountains’s non-agency RMBS securities are as follows as of March 31, 2016 : Millions Fair Value Super Senior (1) Senior (2) Subordinate (3) Prime $ 124.8 $ 63.1 $ 61.7 $ — Non-prime 7.5 — 7.5 — Sub-prime — — — — Total $ 132.3 $ 63.1 $ 69.2 $ — (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.
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’s non-agency CMBS securities are as follows as of March 31, 2016 : Millions Fair Value Super Senior (1) Senior (2) Subordinate (3) Fixed rate CMBS $ 96.1 $ 8.8 $ 46.0 $ 41.3 Floating rate CMBS 32.7 — — 32.7 Total $ 128.8 $ 8.8 $ 46.0 $ 74.0 (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.
Rollforward of fair value investments by level	The following tables summarize the changes in White Mountains’s fair value measurements by level for the three months ended March 31, 2016 and 2015 : Level 3 Investments Millions Level 1 investments Level 2 investments Fixed maturity investments Common equity securities Other long-term investments Hedge Funds and Private Equity Funds measured at NAV (3) Total Balance at January 1, 2016 $ 1,152.2 $ 2,531.4 $ 70.0 $ — $ 169.5 $ 127.8 $ 4,050.9 (1)(2) Total realized and unrealized gains (losses) 11.3 19.1 .5 — 1.1 (2.4 ) 29.6 Amortization/Accretion — (4.2 ) — — — — (4.2 ) Purchases 109.0 292.4 — — 2.1 8.9 412.4 Sales (852.9 ) (272.6 ) — — — (3.0 ) (1,128.5 ) Transfers in — — — — — — — Transfers out — — — — — — — Balance at March 31, 2016 $ 419.6 $ 2,566.1 $ 70.5 $ — $ 172.7 $ 131.3 $ 3,360.2 (1)(2) (1) Excludes carrying value of $3.8 and $3.7 at January 1, 2016 and March 31, 2016 associated with other long-term investments accounted for using the equity method. Excludes carrying value of $14.7 and $14.1 January 1, 2016 and March 31, 2016 associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method. (2) Excludes carrying value of $ 211.3 and $ 261.7 at January 1, 2016 and March 31, 2016 associated with short-term investments. (3) Investments for which fair value is measured at net asset value using the practical expedient are no longer classified within the fair value hierarchy. See Note 1. Level 3 Investments Millions Level 1 investments Level 2 investments Fixed maturity investments Common equity securities Other long-term investments Hedge Funds and Private Equity Funds measured at NAV (4) Total Balance at January 1, 2015 $ 550.6 $ 2,372.9 $ 76.4 $ 39.5 $ 110.6 $ 193.6 $ 3,343.6 (1)(2) Total realized and unrealized gains (losses) 10.0 16.9 .2 1.8 (6.2 ) 3.2 25.9 (3) Amortization/Accretion — (4.6 ) — — — — (4.6 ) Purchases 94.1 317.4 29.7 — 1.4 5.2 447.8 Sales (117.7 ) (326.9 ) — (9.3 ) (3.0 ) (.5 ) (457.4 ) Transfers in — 5.2 — — — — 5.2 Transfers out — — (5.2 ) — — — (5.2 ) Balance at March 31, 2015 $ 537.0 $ 2,380.9 $ 101.1 $ 32.0 $ 102.8 $ 201.5 $ 3,355.3 (1)(2) (1) Excludes carrying value of $ 5.2 and $3.8 at January 1, 2015 and March 31, 2015 associated with other long-term investment limited partnerships accounted for using the equity method. Excludes carrying value of $16.8 and $16.2 at January 1, 2015 and March 31, 2015 associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method. (2) Excludes carrying value of $376.8 and $ 453.7 at January 1, 2015 and March 31, 2015 associated with short-term investments. (3) Excludes $0.8 realized and unrealized losses associated with the Prospector Offshore Fund consolidation of investment-related liabilities. (4) Investments for which fair value is measured at net asset value using the practical expedient are no longer classified within the fair value hierarchy. See Note 1.
Schedule of significant unobservable inputs used in estimating the fair value of investment securities	The following summarizes significant unobservable inputs used in estimating the fair value of investment securities classified within Level 3 as of March 31, 2016 and December 31, 2015 . The fair value of investments in hedge funds and private equity funds are estimated using the net asset value of the funds. Description March 31, 2016 $ in millions, except share price Rating (2) Valuation Technique(s) Fair (3) Unobservable Input Preferred Stock (1) NR Discounted cash flow $70.5 Discount yield - 8.07% Private equity security (1) NR Share price of most recent transaction $21.0 Share price - $1.00 Private equity security (1) NR Share price of most recent transaction $33.8 Share price - $1.03 Private equity security (1) NR Share price of most recent transaction $3.2 Share price - $2.52 Convertible preferred security (1) NR Multiple of EBITDA $5.9 EBITDA multiple - 6.00 Convertible preferred security (1) NR Share price of most recent transaction $27.0 Share price - $3.83 Private equity security (1) NR Option pricing method $10.0 Time until expiration - 4 years Volatility/Standard deviation - 60.0% Risk free rate - 1.15% Surplus notes: NR - Seller priority Discounted cash flow $38.2 Discount rate (4) - 12.5% Timing of interest payments (6) - 5 years Timing of principal payments (6) - 10 years - Pari passu Discounted cash flow $13.6 Discount rate (5) - 22.5% Timing of interest payments (6) - 5 years Timing of principal payments (6) - 15 years (1) As of March 31, 2016 , each asset type consists of one security. (2) Credit ratings are assigned based on the following hierarchy: 1) Standard and Poor's and 2) Moody’s. (3) Includes the unrealized gains and losses associated with foreign currency; foreign currency effects based on observable inputs. (4) Stochastic modeling supporting the fair value estimation indicates that the average percentage of discounted payments missed on the seller priority note is roughly equivalent to that of a conventional debt security with a credit rating of ‘B’. The corresponding credit spread increased by an additional 250 bps to reflect both a liquidity discount for a private debt instrument and regulatory payment approval uncertainty, was added to the treasury rate to determine the discount rate for the seller priority note. (5) Stochastic modeling supporting the fair value estimation indicates that the average percentage of discounted payments missed on the pari passu note is roughly equivalent to that of a conventional debt security with a credit rating of ‘CCC’. The corresponding credit spread increased by an additional 250 bps to reflect both a liquidity discount for a private debt instrument and regulatory payment approval uncertainty, was added to the treasury rate to determine the discount rate for the seller priority note. (6) OneBeacon has assumed for valuation purposes that subsequent interest payments will begin in year five (2020) and principal repayments begin on a graduated basis in year ten (2025) for the seller priority note and year fifteen (2030) for the pari passu note. Description December 31, 2015 $ in millions, except share price Rating (2) Valuation Technique(s) Fair (3) Unobservable Input Preferred Stock (1) NR Par value (8) $70.0 Issuer’s intent to call - $70.0 Private equity security (1) NR Share price of most recent transaction $21.0 Share price - $1.00 Private equity security (1) NR Share price of most recent transaction $33.8 Share price - $1.03 Convertible preferred security (1) NR Multiple of EBITDA $5.7 EBITDA multiple - 6.00 Convertible preferred security (1) NR Share price of most recent transaction $27.0 Share price - $3.83 Private equity security (1) NR Option pricing method $9.6 Time until expiration - 4 years Volatility/Standard deviation - 60.0% Risk free rate - 1.15% Surplus notes (7) : NR - Seller priority Discounted cash flow $38.0 Discount rate (4) - 13.0% Timing of interest payments (6) - 5 years Timing of principal payments (6) - 10 years - Pari passu Discounted cash flow $13.5 Discount rate (5) - 22.4% Timing of interest payments (6) - 5 years Timing of principal payments (6) - 15 years (1) As of December 31, 2015 each asset type consists of one security. (2) Credit ratings are assigned based on the following hierarchy: 1) Standard and Poor's and 2) Moody’s. (3) Includes the unrealized gains and losses associated with foreign currency; foreign currency effects based on observable inputs. (4) Stochastic modeling supporting the fair value estimation indicates that the average percentage of discounted payments missed on the seller priority note is roughly equivalent to that of a conventional debt security with a credit rating of ‘B’. The corresponding credit spread increased by an additional 250 bps to reflect both a liquidity discount for a private debt instrument and regulatory payment approval uncertainty, was added to the treasury rate to determine the discount rate for the seller priority note. (5) Stochastic modeling supporting the fair value estimation indicates that the average percentage of discounted payments missed on the pari passu note is roughly equivalent to that of a conventional debt security with a credit rating of ‘CCC’. The corresponding credit spread increased by an additional 250 bps to reflect both a liquidity discount for a private debt instrument and regulatory payment approval uncertainty, was added to the treasury rate to determine the discount rate for the seller priority note. (6) For estimated value purposes, the assumption has been made that interest payouts begin in year five and that principal repayments being on a graduated basis in year ten for the seller priority notes and year fifteen for the pari passu note. (7) The decrease in the fair value of the surplus notes during the twelve months ended December 31, 2015 was primarily due to widening of non-investment grade credit spreads. (8) Valuation based on the issuer’s intent as of December 31, 2015 to call the security in the near term.

Goodwill and Other Intangible32

Goodwill and Other Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Intangible Assets and Goodwill	The following table shows the change in goodwill and other intangible assets: Three Months Ended March 31, Millions 2016 2015 Goodwill Other intangible assets Goodwill Other intangible assets Beginning balance $ 187.9 $ 187.8 $ 168.9 $ 182.3 Acquisitions of businesses — — .3 2.8 Acquisitions of intangible assets — 3.9 — — Amortization, including foreign currency translation — (8.1 ) — (6.9 ) Ending balance $ 187.9 $ 183.6 $ 169.2 $ 178.2

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2016
Debt Disclosure [Abstract]
Schedule of debt outstanding	White Mountains’s debt outstanding as of March 31, 2016 and December 31, 2015 consisted of the following: Millions March 31, Effective Rate (1) December 31, Effective Rate (1) WTM Bank Facility $ 150.0 N/A $ 50.0 N/A OBH Senior Notes, at face value 275.0 4.7% 275.0 4.7% Unamortized original issue discount and debt issuance costs (2.1 ) (2.1 ) OBH Senior Notes, carrying value 272.9 272.9 OneBeacon Bank Facility — N/A — N/A Tranzact Bank Facility 94.1 6.0% 104.7 5.6% Unamortized issuance cost (1.6 ) (1.8 ) Tranzact Bank Facility, carrying value 92.5 102.9 MediaAlpha Bank Facility 17.5 6.4% 15.0 5.5% Unamortized issuance cost (.3 ) (.3 ) MediaAlpha Bank Facility, carrying value 17.2 14.7 Total debt $ 532.6 $ 440.5 (1) Effective rate considers the effect of the debt issuance costs.

Derivatives (Tables)

Derivatives (Tables) - Variable Annuity	3 Months Ended
	Mar. 31, 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Pre-tax operating results of WM Life Re	The following table summarizes the pre-tax operating results of WM Life Re for the three months ended March 31, 2016 and 2015 . Three Months Ended March 31, Millions 2016 2015 Fees, included in other revenue $ 1.0 $ 3.0 Change in fair value of variable annuity liability, included in other revenue (.4 ) .4 Change in fair value of derivatives, included in other revenue (1.7 ) (5.5 ) Foreign exchange, included in other revenue .9 (1.1 ) Other investment income and (losses) gains — — Total revenue (.2 ) (3.2 ) Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses — — Death benefit claims paid, included in general and administrative expenses (.1 ) — General and administrative expenses (.8 ) (1.4 ) Pre-tax income (loss) $ (1.1 ) $ (4.6 )
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values, by the type of instrument	The following summarizes realized and unrealized derivative gains (losses) recognized in other revenue for the three months ended March 31, 2016 and 2015 and the carrying values, included in other assets, at March 31, 2016 and December 31, 2015 by type of instrument: Gains (losses) Carrying Value Three Months Ended As of March 31, March 31, December 31, 2015 Millions 2016 2015 Fixed income/interest rate $ 1.8 $ 9.3 $ (.4 ) $ .5 Foreign exchange (4.2 ) (12.1 ) 12.5 14.8 Equity .7 (2.7 ) 1.0 4.8 Total $ (1.7 ) $ (5.5 ) $ 13.1 $ 20.1
Fair Value of Assets and Liabilities Measured on Recurring and Non-recurring Basis Table	The following tables summarize the changes in White Mountains’s variable annuity reinsurance liabilities and derivative instruments for the three months ended March 31, 2016 and 2015 : Three Months Ended March 31, 2016 Variable Annuity Assets (Liabilities) Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ .3 $ 2.7 $ 16.5 $ .9 $ 20.1 Purchases — — — — — Realized and unrealized gains (losses) (.4 ) 1.2 1.1 (4.0 ) (1.7 ) Transfers in — — — — — Sales/settlements — (1.3 ) (7.3 ) 3.3 (5.3 ) End of period $ (.1 ) $ 2.6 $ 10.3 $ .2 $ 13.1 Three Months Ended March 31, 2015 Variable Annuity Assets Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ .7 $ 18.9 $ 33.8 $ 3.7 $ 56.4 Purchases — — — — — Realized and unrealized gains (losses) .4 (.6 ) (6.5 ) 1.6 (5.5 ) Transfers in — — — — — Sales/settlements — (1.3 ) 3.9 (6.5 ) (3.9 ) End of period $ 1.1 $ 17.0 $ 31.2 $ (1.2 ) $ 47.0 (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.
Assets Held under Reinsurance Counterparty Trust Agreement	The total collateral includes the following: Millions March 31, 2016 December 31, 2015 March 31, 2015 Cash $ 8.4 $ 5.8 $ 29.0 Fixed maturity investments — — 4.5 Total $ 8.4 $ 5.8 $ 33.5
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) March 31, 2016 Description Fair Value Valuation Technique(s) Unobservable Input Range Weighted Average Variable annuity benefit guarantee liabilities $ (.1 ) Discounted cash flows Surrenders 0-1 year 0.1 % - 40.0% 40.0 % Mortality 0.0 % - 6.4% 1.1 % Foreign exchange volatilities 0-1 year 12.0 % - 18.4% 13.5 % Index volatilities 0-1 year 25.5 % - 28.8% 26.2 % Foreign exchange options $ 1.1 Counterparty valuations, adjusted for unwind quote discount Adjustment to counterparty valuations (4.3 )% - (7.3)% (5.9 )% Equity index options $ 1.5 Counterparty valuations, adjusted for unwind quote discount Adjustment to counterparty valuations (0.6 )% - (5.7)% (5.6 )%
Exchange traded and OTC derivative instruments	The following summarizes amounts offset under master netting agreements: March 31, 2016 December 31, 2015 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 $ 2.2 $ (2.5 ) $ (.3 ) $ 2.4 $ (2.1 ) $ .3 Exchange traded — — — .1 (.1 ) — Foreign exchange contracts OTC 12.7 — 12.7 15.0 — 15.0 Exchange traded — (.1 ) (.1 ) .1 (.3 ) (.2 ) Equity contracts OTC 1.5 (.9 ) .6 4.4 (.6 ) 3.8 Exchange traded .3 (.1 ) .2 1.2 — 1.2 Total (2) $ 16.7 $ (3.6 ) $ 13.1 $ 23.2 $ (3.1 ) $ 20.1 (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.
Net exposure to collateral	The following summarizes the value, collateral held or provided by WM Life Re and net exposure to credit losses on OTC and exchange traded derivative instruments by counterparty recorded within other assets: March 31, 2016 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 WMLife Re - Cash Net amount of exposure to counter-party Standard & Poor's Rating (1) Bank of America $ 1.4 $ — $ — $ 1.4 $ — $ — $ — $ 1.4 A JP Morgan 6.5 — — 6.5 — — 5.4 1.1 A + Citigroup - OTC 5.0 — — 5.0 — — .5 4.5 A Citigroup - Exchange Traded .2 — — .2 7.9 — — 8.1 A Total $ 13.1 $ — $ — $ 13.1 $ 7.9 $ — $ 5.9 $ 15.1 December 31, 2015 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 WMLife Re- Cash Net amount of exposure to counter-party Standard & Poor's Rating (1) Bank of America $ .7 $ — $ — $ .7 $ — $ — $ — $ .7 A JP Morgan 8.5 — — 8.5 — — 5.5 3.0 A + Citigroup - OTC 9.9 — — 9.9 — — 1.4 8.5 A Citigroup - Exchange Traded 1.0 — — 1.0 5.8 — — 6.8 A Total $ 20.1 $ — $ — $ 20.1 $ 5.8 $ — $ 6.9 $ 19.0 (1) Standard & Poor’s ratings as detailed above are: “A+” (Strong, which is the fifth highest of twenty-three creditworthiness ratings), “A” (Strong, which is the sixth highest of twenty-three creditworthiness ratings), “A-” (Strong, which is the seventh highest of twenty-three creditworthiness ratings) and “BBB+” (Adequate, which is the eighth highest of twenty-three creditworthiness ratings).

Municipal Bond Guarantee (Table

Municipal Bond Guarantee (Tables)	3 Months Ended
	Mar. 31, 2016
Guarantees [Abstract]
Schedule of Municipal Bond Guarantee Insured Obligations	The following table provides a schedule of BAM’s insured obligations: March 31, 2016 December 31, 2015 Contracts outstanding 3,422 3,103.0 Remaining weighted average contract period outstanding (in years) 12.7 12.8 Contractual debt service outstanding (in millions): Principal $ 24,641.6 $ 22,556.0 Interest 12,711.9 11,984.4 Total debt service outstanding $ 37,353.5 $ 34,540.4 Gross unearned insurance premiums $ 55.8 $ 50.2

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2016
Earnings Per Share [Abstract]
Computation of earnings per share	The following table outlines the Company’s computation of earnings per share from continuing operations for the three months ended March 31, 2016 and 2015 . (See Note 17 - “Discontinued Operations” ). Three Months Ended March 31, 2016 2015 Basic and diluted earnings per share numerators (in millions): Net income from continuing operations attributable to White Mountains’s common shareholders $ 13.9 $ 10.5 Allocation of income for unvested restricted common shares (.1 ) (.1 ) Dividends declared on participating restricted common shares (1) (.1 ) (.1 ) Total allocation to restricted common shares (.2 ) (.2 ) Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ 13.7 $ 10.3 Undistributed net earnings (in millions): Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ 13.7 $ 10.3 Dividends declared net of restricted common share amounts (1) (5.9 ) (5.9 ) Total undistributed net earnings, net of restricted common share amounts $ 7.8 $ 4.4 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 5,539.6 5,978.4 Average unvested restricted shares (2) (54.0 ) (58.8 ) Basic earnings per share denominator 5,485.6 5,919.6 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 5,540.5 5,978.4 Average unvested restricted common shares (2) (54.0 ) (58.8 ) Average outstanding dilutive options to acquire common shares (3) — — Diluted earnings per share denominator 5,486.5 5,919.6 Basic earnings per share (in dollars): Net income attributable to White Mountains’s common shareholders $ 2.51 $ 1.76 Dividends declared and paid (1.00 ) (1.00 ) Undistributed earnings $ 1.51 $ .76 Diluted earnings per share (in dollars): Net income attributable to White Mountains’s common shareholders $ 2.51 $ 1.76 Dividends declared and paid (1.00 ) (1.00 ) Undistributed earnings $ 1.51 $ .76 (1) Restricted shares issued by White Mountains receive dividends, and therefore, are considered participating securities. (2) Restricted shares outstanding vest either in equal annual installments or upon a stated date. (See Note 15 - “Employee Share-Based Compensation Plans”) . (3) The diluted earnings per share denominator for the three months ended March 31, 2016 includes the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding, which results in 882 incremental shares outstanding over the period. The incremental shares had an effect on diluted earning per share of less than $0.01 . The diluted earnings per share denominator for the three months ended March 31, 2015 does not include the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding as they were anti-dilutive to the calculation.

Non-controlling Interest (Table

Non-controlling Interest (Tables)	3 Months Ended
	Mar. 31, 2016
Noncontrolling Interest [Abstract]
Noncontrolling Interest Disclosure	The following table details the balance of non-controlling interests included in White Mountains’s total equity and the related percentage of each consolidated entity’s total equity owned by non-controlling shareholders as of March 31, 2016 and December 31, 2015: March 31, 2016 December 31, 2015 $ in millions Non-controlling Percentage Non-controlling Equity Non-controlling Percentage Non-controlling Equity OneBeacon Ltd. 23.9 % $ 243.4 24.5 % $ 245.6 SIG Preference Shares 100.0 250.0 100.0 250.0 Other, excluding mutuals and reciprocals HG Global 3.1 17.2 3.1 17.1 MediaAlpha 40.0 14.2 40.0 14.4 Tranzact 36.8 79.7 36.8 79.4 Wobi 3.9 .5 3.9 .6 Dewar 30.1 3.2 19.0 3.7 Total other, excluding mutuals and reciprocals 114.8 115.2 Mutuals and reciprocals BAM 100.0 (140.7 ) 100.0 (140.0 ) SSIE 100.0 (16.1 ) 100.0 (16.0 ) Total non-controlling interests $ 451.4 $ 454.8

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2016
Segment Reporting [Abstract]
Financial information for White Mountains' segments	Significant intercompany transactions among White Mountains’s segments have been eliminated herein. Financial information for White Mountains’s segments follows: HG Global/BAM Millions OneBeacon HG BAM (1) Other Operations Total Three Months Ended March 31, 2016 Earned insurance premiums $ 278.6 $ .9 $ .3 $ 2.3 $ 282.1 Net investment income 14.4 .5 1.6 1.4 17.9 Net investment income (loss) - surplus note interest — 4.5 (4.5 ) — — Net realized and unrealized investment gains 16.6 2.1 4.9 5.9 29.5 Other revenue .9 — .1 96.6 (2) 97.6 Total revenues 310.5 8.0 2.4 106.2 427.1 Losses and LAE 158.8 — — 2.3 161.1 Insurance acquisition expenses 51.0 .2 .7 .8 52.7 Other underwriting expenses 55.3 — .1 — 55.4 General and administrative expenses 3.6 .5 9.2 119.1 (3) 132.4 Amortization of intangible assets .3 — — 7.8 8.1 Interest expense 3.3 — — 2.6 5.9 Total expenses 272.3 .7 10.0 132.6 415.6 Pre-tax (loss) income $ 38.2 $ 7.3 $ (7.6 ) $ (26.4 ) $ 11.5 HG Global/BAM Millions OneBeacon HG BAM (1) Other Operations Total Three Months Ended March 31, 2015 Earned insurance premiums $ 286.6 $ .5 $ .2 $ 2.0 $ 289.3 Net investment income 10.5 .4 1.0 .7 12.6 Net investment income (loss) - surplus note interest — 4.0 (4.0 ) — — Net realized and unrealized investment losses 14.2 1.1 3.0 6.7 25.0 Other (loss) revenue (3.1 ) — .1 67.9 (2) 64.9 Total revenues 308.2 6.0 .3 77.3 391.8 Losses and LAE 165.9 — — 2.0 167.9 Insurance acquisition expenses 51.0 .1 .8 1.1 53.0 Other underwriting expenses 55.9 — .1 — 56.0 General and administrative expenses 3.8 .4 8.2 90.8 (3) 103.2 Amortization of intangible assets .3 — — 6.6 6.9 Interest expense 3.2 — — 1.1 4.3 Total expenses 280.1 .5 9.1 101.6 391.3 Pre-tax income (loss) $ 28.1 $ 5.5 $ (8.8 ) $ (24.3 ) $ .5 (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) Includes $ 57.8 from Tranzact and $ 32.7 from MediaAlpha for the quarter ended March 31, 2016. and $ 37.5 from Tranzact and $ 29.7 from MediaAlpha for the year ended March 31, 2015. (3) Includes $ 48.4 from Tranzact and $ 30.5 from MediaAlpha for the quarter ended March 31, 2016, and $ 34.9 from Tranzact and $ 27.7 from MediaAlpha for the year ended March 31, 2015.

Investments in Unconsolidated39

Investments in Unconsolidated Affiliates (Tables)	3 Months Ended
	Mar. 31, 2016
Equity Method Investments and Joint Ventures [Abstract]
Schedule of Changes in Investments in Unconsolidated Affiliates	The following table summarizes amounts recorded by White Mountains under the equity method relating to its investment in Symetra for the three months ended March 31, 2015: Three Months Ended Millions March 31, 2015 Equity method carrying value of investment in Symetra as of December 31, 2014 $ 411.4 Equity in earnings (1)(2) 7.2 Equity in net unrealized gains from Symetra’s fixed maturity portfolio (3) 30.9 Dividends received (2.2 ) Equity method carrying value of investment in Symetra as of March 31, 2015 (4) $ 447.3 (1) Equity in earnings excludes tax expense of $0.4 . (2) Equity in earnings includes $0.7 increase relating to the pre-tax amortization of the Symetra common share basis difference. (3) Net unrealized gains includes $2.9 increase relating to the pre-tax amortization of the Symetra common share basis difference. (4) Includes White Mountains’s equity in net unrealized gains from Symetra’s fixed maturity portfolio of $68.4 as of March 31, 2015, which excludes tax expense of $4.6 .

Employee Share-Based Incentiv40

Employee Share-Based Incentive Compensation Plans (Tables)	3 Months Ended
	Mar. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of performance share activity	The following table summarizes performance share activity for the three months ended March 31, 2016 and 2015 for performance shares granted under the WTM Incentive Plan: Three Months Ended March 31, 2016 2015 Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Beginning of period 96,211 $ 58.2 113,198 $ 44.4 Shares paid or expired (1) — — (34,001 ) (24.9 ) New grants 16,215 — 29,078 — Assumed forfeitures and cancellations (2) (1,186 ) (.6 ) 123 .5 Expense recognized — 14.2 — 5.7 End of period (3) 111,240 $ 71.8 108,398 $ 25.7 (1) WTM performance share payments in 2016 for the 2013-2015 performance cycle, which were paid in April 2016, ranged from 140% to 142% of target. WTM performance share payments in 2015 for the 2012-2014 performance cycle ranged from 88% to 131.5% of target. (2) Amounts include changes in assumed forfeitures, as required under GAAP. (3) Outstanding performance share awards as of March 31, 2016 and 2015 both exclude 7,998 performance share awards, net of assumed forfeitures, granted to employees of Sirius Group, which is accounted for as discontinued operations.
Summary of performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan	The following table summarizes performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan at March 31, 2016 for each performance cycle: Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Performance cycle: 2016 – 2018 16,215 $ 1.0 2015 – 2017 29,428 12.8 2014 – 2016 32,157 18.7 2013 – 2015 36,293 41.1 Sub-total 114,093 73.6 Assumed forfeitures (2,853 ) (1.8 ) Total at March 31, 2016 111,240 $ 71.8
Summary of restricted share activity	The following table summarizes the unrecognized compensation cost associated with the outstanding restricted share awards for the three months ended March 31, 2016 and 2015 : Three Months Ended March 31, 2016 2015 Millions, except share amounts Restricted Unamortized Restricted Unamortized Non-vested, Beginning of period 70,675 $ 15.7 83,314 $ 14.3 Issued 21,215 16.3 22,890 15.2 Vested (24,620 ) — (35,079 ) — Forfeited (800 ) .2 — — Expense recognized — (3.0 ) — (3.0 ) End of period (1) 66,470 $ 29.2 71,125 $ 26.5 (1) Outstanding restricted share awards as of March 31, 2016 and 2015 include 2,512 and 3,572 restricted shares issued to employees of Sirius Group, which is accounted for as discontinued operations.
Summary of performance share activity for OneBeacon performance shares granted under OneBeacon Incentive Plan	The following table summarizes performance share activity for the three months ended March 31, 2016 and 2015 for OneBeacon performance shares granted under the OneBeacon Incentive Plan: Three Months Ended March 31, 2016 2015 Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Beginning of period 449,435 $ 1.4 517,470 $ 3.4 Shares paid or expired (1) (167,300 ) (.7 ) (181,290 ) (1.5 ) New grants 163,150 — 154,887 — Assumed forfeitures and cancellations (2) (4,079 ) — (28,920 ) — Expense recognized — .4 — .2 End of period 441,206 $ 1.1 462,147 $ 2.1 (1) OneBeacon performance share payments in 2016 for the 2013-2015 performance cycle were at 24.3% of target. OneBeacon performance share payments in 2015 for the 2012-2014 performance cycle were at 45.7% of target. (2) Amounts include changes in assumed forfeitures, as required under GAAP.
Summary of OneBeacon performance shares outstanding and accrued expense for OneBeacon performance shares awarded under the OneBeacon Incentive Plan	The following table summarizes OneBeacon performance shares outstanding awarded under the OneBeacon Incentive Plan at March 31, 2016 for each performance cycle: Millions, except share amounts Target Accrued Expense Performance cycle: 2016 – 2018 163,150 $ .1 2015 – 2017 146,659 .8 2014 – 2016 142,710 .2 Sub-total 452,519 1.1 Assumed forfeitures (11,313 ) — Total at March 31, 2016 441,206 $ 1.1
Summary of OneBeacon restricted shares activity	The following table summarizes the unrecognized compensation cost associated with the outstanding OneBeacon restricted stock awards for the three months ended March 31, 2016 and 2015 : Three Months Ended March 31, 2016 2015 Millions, except share amounts Restricted Unamortized Restricted Unamortized Non-vested, Beginning of period 382,722 $ 2.5 612,500 $ 3.5 Issued 170,650 2.3 75,950 1.1 Vested (157,500 ) — (296,000 ) — Forfeited — — (1,500 ) — Expense recognized — (.5 ) — (.6 ) End of period 395,872 $ 4.3 390,950 $ 4.0

Fair Value of Financial Instr41

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2016
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 these financial instruments as of March 31, 2016 and December 31, 2015 : March 31, 2016 December 31, 2015 Millions Fair Value Carrying Value Fair Value Carrying Value OBH Senior Notes $ 278.0 $ 272.9 $ 276.4 $ 272.9 Tranzact Bank Facility 92.8 92.4 102.8 102.9 MediaAlpha Bank Facility 15.1 17.2 15.0 14.7

Discontinued Operations (Tables

Discontinued Operations (Tables)	3 Months Ended
	Mar. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Schedule of Disposal Groups, Including Discontinued Operations, Income Statement, Balance Sheet And Additional Disclosures	Summary of Reclassified Balances and Related Items Net Assets Held for Sale The following summarizes the assets and liabilities associated with the business classified as held for sale, which all relate to Sirius Group: Millions March 31, 2016 December 31, 2015 Assets held for sale Fixed maturity investments, at fair value $ 2,758.3 $ 2,374.0 Short-term 534.5 352.0 Common equities 214.3 174.4 Other 61.3 72.2 Total investments 3,568.4 2,972.6 Cash 134.8 143.9 Reinsurance recoverable on unpaid losses 286.2 283.1 Reinsurance recoverable on paid losses 11.1 10.2 Insurance premiums receivable 483.3 323.6 Deferred acquisition costs 91.6 74.6 Deferred tax asset 291.2 303.1 Ceded unearned insurance and reinsurance premiums 134.7 87.7 Accounts receivable on unsettled investment sales 9.8 29.0 Goodwill and intangible assets 10.2 10.2 Other assets 194.2 169.0 Total assets held for sale $ 5,215.5 $ 4,407.0 Liabilities held for sale Loss and loss adjustment expense reserves $ 1,649.5 $ 1,644.4 Unearned insurance premiums 501.3 342.2 Debt 403.6 403.5 Deferred tax liability 278.5 263.6 Accrued incentive compensation 43.1 63.2 Ceded reinsurance payable 132.4 67.1 Funds held under reinsurance treaties 57.0 52.9 Accounts payable on unsettled investment purchases 5.4 — Other liabilities 50.3 47.1 Total liabilities held for sale 3,121.1 2,884.0 Net assets held for sale $ 2,094.4 $ 1,523.0 Net Income from Discontinued Operations The following summarizes the results of operations, including related income taxes associated with the business classified as discontinued operations. The results of Sirius Group up to but not including the closing date of the transaction inures to White Mountains. Three Months Ended Three Months Ended March 31, 2016 March 31, 2015 Millions Sirius Group Other Disc Ops Total Sirius Group Other Disc Ops Total Revenues Earned insurance premiums $ 202.4 $ — $ 202.4 $ 205.0 $ — $ 205.0 Net investment income 12.2 — 12.2 9.0 — 9.0 Net realized and unrealized (losses) gains (8.8 ) — (8.8 ) 78.4 — 78.4 Other revenue (4.1 ) — (4.1 ) (27.4 ) — (27.4 ) Total revenues 201.7 — 201.7 265.0 — 265.0 Expenses Loss and loss adjustment expenses 113.7 — 113.7 97.5 — 97.5 Insurance and reinsurance acquisition expenses 48.4 — 48.4 42.6 — 42.6 Other underwriting expenses 26.7 — 26.7 25.5 — 25.5 General and administrative expenses 8.1 — 8.1 6.3 — 6.3 Interest expense 6.6 — 6.6 6.8 — 6.8 Total expenses 203.5 — 203.5 178.7 — 178.7 Pre-tax (loss) income (1.8 ) — (1.8 ) 86.3 — 86.3 Income tax benefit (expense) .9 — .9 (20.4 ) — (20.4 ) Net (loss) income from discontinued operations (.9 ) — (.9 ) 65.9 — 65.9 Net losses from sales of discontinued operations - OneBeacon — — — — (.1 ) (.1 ) Net gain from sales of discontinued operations - Esurance — — — — 8.0 8.0 Total (loss) income from discontinued operations $ (.9 ) $ — $ (.9 ) $ 65.9 $ 7.9 $ 73.8 Change in foreign currency translation and other from discontinued operations $ 37.2 $ — $ 37.2 $ (87.6 ) $ — $ (87.6 ) Comprehensive income (loss) from discontinued operations $ 36.3 $ — $ 36.3 $ (21.7 ) $ 7.9 $ (13.8 ) Net Change in Cash from Discontinued Operations The following summarizes the net change in cash, including income tax (payment to) refund from national governments and interest paid associated with the business classified as discontinued operations: Three Months Ended March 31, (Millions) 2016 2015 Net cash provided from operations $ (50.7 ) $ (14.3 ) Net cash provided from investing activities 35.0 36.0 Net cash used for financing activities 2.4 1.8 Effect of exchange rate changes on cash 4.2 (8.5 ) Net change in cash during the period (9.1 ) 15.0 Cash balances at beginning of period 143.9 111.5 Cash balances at end of period $ 134.8 $ 126.5 Supplemental cash flows information: Interest paid $ — $ (12.8 ) Net income tax payment to national governments $ (36.4 ) $ (7.0 ) 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 computation of earnings per share for discontinued operations for the three months ended March 31, 2016 and 2015 : Three Months Ended March 31, 2016 2015 Basic and diluted earnings per share numerators (in millions): Net income attributable to White Mountains’s common shareholders $ (.9 ) $ 73.8 Allocation of income for participating unvested restricted common shares (1) — (.7 ) Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts (2) $ (.9 ) $ 73.1 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 5,539.6 5,978.4 Average unvested restricted common shares (3) (54.0 ) (58.8 ) Basic earnings per share denominator 5,485.6 5,919.6 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 5,540.5 5,978.4 Average unvested restricted common shares (3) (54.0 ) (58.8 ) Average outstanding dilutive options to acquire common shares (4) — — Diluted earnings per share denominator 5,486.5 5,919.6 Basic and diluted earnings per share (in dollars): $ (.17 ) $ 12.33 (1) Restricted shares issued by White Mountains contain dividend participation features, and therefore, are considered participating securities. (2) Net earnings attributable to White Mountains’s common shareholders, net of restricted share amounts, is equal to undistributed earnings for the three months ended March 31, 2016 and 2015 . (3) Restricted common shares outstanding vest either in equal annual installments or upon a stated date. (See Note 15 - “Employee Share-Based Compensation Plans” ). (4) The diluted earnings per share denominator for the three months ended March 31, 2016 includes the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding, which results in 882 incremental shares outstanding over the period. The incremental shares had an effect on diluted earning per share of less than $0.01 per share. The diluted earnings per share denominator for the three months ended March 31, 2015 does 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.
Summary of the fair value and carrying value of financial instruments	The following table summarizes the fair value and carrying value of these financial instruments as of March 31, 2016 and December 31, 2015 : March 31, 2016 December 31, 2015 Millions Fair Value Carrying Value Fair Value Carrying Value OBH Senior Notes $ 278.0 $ 272.9 $ 276.4 $ 272.9 Tranzact Bank Facility 92.8 92.4 102.8 102.9 MediaAlpha Bank Facility 15.1 17.2 15.0 14.7
Interest Rate Cap [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair Value of Assets and Liabilities Measured on Recurring and Non-recurring Basis Table	The following tables summarize the changes in the fair value of the Interest Rate Cap for the three months ended March 31, 2016 and 2015: Three Months Ended March 31, Millions 2016 2015 Beginning of period $ 1.9 $ 4.1 Net realized and unrealized losses (.8 ) (1.0 ) End of period $ 1.1 $ 3.1
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Summary of the fair value and carrying value of financial instruments	The following table summarizes the fair value and carrying value of these financial instruments as of March 31, 2016 and December 31, 2015 : March 31, 2016 December 31, 2015 Millions Fair Value Carrying Value Fair Value Carrying Value SIG Senior Notes $ 409.0 $ 399.9 $ 410.0 $ 399.8 SIG Preference Shares 247.5 250.0 255.0 250.0
Sirius Group | Interest Rate Cap [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Schedule of collateral [Table Text Block]	The following table summarizes the Interest Rate Cap collateral balances held by White Mountains and ratings by counterparty: March 31, 2016 Millions Collateral Balances Held Standard & Poor’s Rating (1) Barclays Bank Plc $ .7 A- Nordea Bank Finland Plc .4 AA- Total $ 1.1 (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).

Summary of Significant Accoun43

Summary of Significant Accounting Policies (Basis of Presentation) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Jul. 31, 2012
Basis of Presentation
Debt Issuance Cost	$ 3.8
Net investment income	17.9	$ 12.6
Income Tax Expense (Benefit)	(8.7)	4.6
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 7.3
OneBeacon Ltd.
Basis of Presentation
Ownership interest (as a percent)	76.10%		75.50%
HG Global
Basis of Presentation
Surplus Notes				$ 503
Percentage of par value of policy reinsured	15.00%
Noncontrolling equity percentage	3.10%		3.10%
Star & Shield Insurance Exchange
Basis of Presentation
Surplus Notes	$ 21
Noncontrolling equity percentage	100.00%		100.00%
OneBeacon [Member]
Basis of Presentation
Debt Issuance Cost			$ 1.9
Noncontrolling equity percentage	23.90%		24.50%
Preferred Stock | HG Global
Basis of Presentation
Ownership interest (as a percent)	96.90%
Noncontrolling equity percentage	96.90%		96.90%
Common Stock | HG Global
Basis of Presentation
Ownership interest (as a percent)	88.40%
Noncontrolling equity percentage	88.40%		88.40%

Significant Transactions (Detai

Significant Transactions (Details) $ / shares in Units, ₪ in Millions, $ in Millions

Feb. 01, 2016USD ($)

Nov. 06, 2015USD ($)

Sep. 30, 2015USD ($)

Jan. 31, 2014USD ($)

Oct. 31, 2011USD ($)

Feb. 23, 2015ILS (₪)

Feb. 23, 2015USD ($)

Feb. 19, 2014ILS (₪)

Feb. 19, 2014USD ($)

Jun. 30, 2016USD ($)

Mar. 31, 2016USD ($)$ / shares

Mar. 31, 2016USD ($)$ / shares

Jun. 30, 2015ILS (₪)

Jun. 30, 2015USD ($)

Mar. 31, 2015USD ($)

Dec. 31, 2014USD ($)

Mar. 31, 2014USD ($)

Dec. 31, 2015USD ($)

Sep. 01, 2015USD ($)

Oct. 10, 2014USD ($)

Mar. 14, 2014USD ($)

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Other Investments

$ (10.9)

$ (6.5)

Investments

3,639.7

$ 3,639.7

$ 4,280.7

Sales of common equity securities

767.5

59.9

Loss and loss adjustment expenses

161.1

167.9

Payments to Acquire Businesses and Interest in Affiliates

8.1

2.4

Payment of contingent consideration

(7.8)

0

Assets

10,391.8

10,391.8

10,282.6

Goodwill

187.9

187.9

169.2

$ 168.9

187.9

Intangible Assets, Net (Excluding Goodwill)

183.6

183.6

178.2

182.3

187.8

Goodwill and intangible assets

371.5

371.5

375.7

Liabilities

6,154.5

6,154.5

5,914.6

Net Income (Loss) Attributable to Noncontrolling Interest

(6.3)

7.3

Cancerinsurance.com [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Interest in Subsidiaries and Affiliates

$ 3.1

Cash

1.1

Business Combination, Contingent Consideration, Liability

6.8

Liabilities

$ 2

Tranzact [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Interest in Subsidiaries and Affiliates

$ 177.7

Enterprise Value of Subsidiary

$ 281.2

Proceeds from Contributions from Affiliates

$ 44.2

Business Combination, Contingent Consideration, Liability

$ 7.4

Ownership interest (as a percent)

63.20%

Assets

$ 332.8

Tangible Assets

41.4

Goodwill

145.1

Intangible Assets, Net (Excluding Goodwill)

146.3

Liabilities

$ 108.7

TruBridge [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Interest in Subsidiaries and Affiliates

$ 31

Ownership interest (as a percent)

100.00%

Assets

$ 54.5

Goodwill

18.7

Intangible Assets, Net (Excluding Goodwill)

28.1

Liabilities

$ 4.3

Star & Shield Insurance Exchange

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Purchase of Surplus Notes

21

21

Assets

13.3

13.3

14.2

Liabilities

29.4

29.4

30.3

MediaAlpha [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Businesses and Interest in Affiliates

$ 28.1

Percentage of gross profit

62.50%

Payment of contingent consideration

$ 7.8

Assets

$ 70.1

Goodwill

18.3

Goodwill and intangible assets

38.5

Liabilities

$ 10

WOBI

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Percentage of Business in the Insurance Market

85.00%

Goodwill

$ 5.5

Liabilities

$ 0.7

Star & Shield LLC [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Businesses and Interest in Affiliates

$ 1.8

Lowfares.com [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Businesses and Interest in Affiliates

$ 3.9

OneBeacon [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Percentage of Quota Share Reinsurance Agreement

50.00%

Common Class A | MediaAlpha [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Ownership interest (as a percent)

60.00%

Common Stock | WOBI

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Ownership interest (as a percent)

54.00%

96.10%

96.10%

Non-controlling interest | Star & Shield Insurance Exchange

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Net Income (Loss) Attributable to Noncontrolling Interest

$ (0.1)

(1.1)

Israel, New Shekels | Common Stock | WOBI

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Additional Interest in Subsidiaries | ₪

₪ 91.4

Israel, New Shekels | Preferred Stock [Member] | WOBI

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Businesses and Interest in Affiliates | ₪

₪ 31.5

Israel, New Shekels | Common Stock | Cashboard [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Businesses and Interest in Affiliates | ₪

₪ 35.9

Israel, New Shekels | Common Stock | WOBI

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Businesses and Interest in Affiliates | ₪

₪ 14.4

United States of America, Dollars | Common Stock | WOBI

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Additional Interest in Subsidiaries

$ 23.8

United States of America, Dollars | Preferred Stock [Member] | WOBI

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Businesses and Interest in Affiliates

$ 9

United States of America, Dollars | Common Stock | Cashboard [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Businesses and Interest in Affiliates

$ 8.9

United States of America, Dollars | Common Stock | WOBI

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Businesses and Interest in Affiliates

4.1

Lowfares.com [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Payments to Acquire Businesses and Interest in Affiliates

3.9

Cashboard [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Assets

5.5

Goodwill

0.3

Intangible Assets, Net (Excluding Goodwill)

2.8

Liabilities

$ 1.2

WOBI

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Assets

13.4

Intangible Assets, Net (Excluding Goodwill)

$ 2.9

Sirius Group

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Proceeds from Divestiture of Interest in Subsidiaries and Affiliates

$ 2,600

Payments to Acquire Other Investments

161.8

Investments

$ 161.8

$ 161.8

686.2

Essentia [Member] | OneBeacon [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Gain (Loss) from Adjustments to Prior Period Extraordinary Items

$ 3.7

Crop insurance [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Proceeds related from termination of agreement

3

Percentage of Quota Share Reinsurance Agreement

100.00%

Symetra

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Sales of common equity securities

$ 658

Expected [Member] | Symetra

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Dividends Payable, Amount Per Share | $ / shares

$ 32

$ 32

Symetra

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Sales of common equity securities

$ 658

Symetra | Sirius Group

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Investments

$ 528.6

UNITED STATES

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Industry Loss Warranty Limit on Contract

45

Industry Loss Trigger on Industry Loss Warranty

15,000

JAPAN

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Industry Loss Warranty Limit on Contract

25

Industry Loss Trigger on Industry Loss Warranty

12,500

Combination One [Member] | UNITED STATES

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Industry Loss Warranty Limit on Contract

75

Industry Loss Trigger on Industry Loss Warranty

40,000

Combination Two [Member] | UNITED STATES

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Industry Loss Warranty Limit on Contract

22.5

Industry Loss Trigger on Industry Loss Warranty

$ 50,000

Subsequent Event [Member]

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Proceeds from Divestiture of Interest in Subsidiaries and Affiliates

2,600

Payments to Acquire Other Investments

161.8

Subsequent Event [Member] | Sirius Group

Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]

Proceeds from Divestiture of Interest in Subsidiaries and Affiliates

2,592

Payments to Acquire Other Investments

$ 161.8

Loss and Loss Adjustment Expe45

Loss and Loss Adjustment Expense Reserves (Loss and Loss Adjustment Expense) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Insurance Loss Reserves [Abstract]
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 7.3
Gross beginning balance	1,395.8	1,350
Less beginning reinsurance recoverable on unpaid losses	(186.5)	(161.7)
Net loss and LAE reserves	1,209.3	1,188.3
Loss and LAE incurred relating to current year losses	161.2	169.8
Net (favorable) and unfavorable loss reserve development	(0.1)	(1.9)
Total incurred losses and LAE	161.1	167.9
Current year losses	(23.1)	(23.3)
Prior year losses	(148.6)	(164)
Total loss and LAE payments	(171.7)	(187.3)
Net ending balance	1,198.7	1,168.9
Plus ending reinsurance recoverable on unpaid losses	150.9	141.7
Gross ending balance	$ 1,349.6	$ 1,310.6

Loss and Loss Adjustment Expe46

Loss and Loss Adjustment Expense Reserves (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Loss and Loss Adjustment, Expense Reserves [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 7.3
Net (favorable) and unfavorable loss reserve development	(0.1)	(1.9)
Star & Shield Insurance Exchange
Loss and Loss Adjustment, Expense Reserves [Line Items]
Net (favorable) and unfavorable loss reserve development	$ 0.1	0.1
OneBeacon [Member]
Loss and Loss Adjustment, Expense Reserves [Line Items]
Net (favorable) and unfavorable loss reserve development		$ 1.8
OneBeacon [Member]
Loss and Loss Adjustment, Expense Reserves [Line Items]
Percentage of Quota Share Reinsurance Agreement	50.00%

Third Party Reinsurance (Narrat

Third Party Reinsurance (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Reinsurance Retention Policy [Line Items]
Reinsurance recoverable on paid losses	$ 16.6	$ 7.5
Reinsurance recoverable on unpaid losses	150.9	186.5
OneBeacon [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance recoverable on paid losses	16.6	7.5
Reinsurance recoverable on unpaid losses	$ 150.4	$ 186
OneBeacon [Member]
Reinsurance Retention Policy [Line Items]
Percentage of Quota Share Reinsurance Agreement	50.00%

Investment Securities (Net Inve

Investment Securities (Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 7.3
Investment income
Total investment income	18.7	14.6
Third-party investment expenses	(0.8)	(2)
Net investment income, pre-tax	17.9	12.6
Fixed maturity investments.
Investment income
Total investment income	14.5	12.5
Short-term investments
Investment income
Total investment income	0.2	0
Common Stock
Investment income
Total investment income	1.2	2.2
Other long-term investments
Investment income
Total investment income	$ 2.8	$ (0.1)

Investment Securities (Net Real

Investment Securities (Net Realized and Unrealized Investment Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 7.3
Net realized investment gains, pre-tax	256.8	14.8
Net unrealized investment (losses) gains, pre-tax	(227.3)	10.2
Net realized and unrealized investment gains, pre-tax	29.5	25
Income tax expense attributable to net realized and unrealized investment gains	(8.5)	(7.1)
Net realized and unrealized investment gains, after tax	21	17.9
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	(1.1)	0.5
Net unrealized investment (losses) gains, pre-tax	21.7	11.4
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	0	0
Net unrealized investment (losses) gains, pre-tax	0	0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	257.6	22.5
Net unrealized investment (losses) gains, pre-tax	(247.4)	(6.8)
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	0.3	(8.2)
Net unrealized investment (losses) gains, pre-tax	$ (1.6)	$ 5.6

Investment Securities (Net Re50

Investment Securities (Net Realized Investment Gains (Losses)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	$ 256.8	$ 14.3
Trading securities, Tax on Realized Holding Gain (Loss) on Investments	(42.9)	(4.5)
Trading securities realized holding gain (loss) on investments after tax	213.9	9.8
Foreign Currency Transaction Gain (Loss), Realized	0	0.5
Trading Securities, Tax on Realized Foreign Currency Transaction Gain (Loss) Tax	0	0
Trading securities, realized foreign currency gain (loss) net of tax	0	0.5
Net realized investment gains, pre-tax	256.8	14.8
Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(42.9)	(4.5)
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	213.9	10.3
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	(1.1)	0.5
Foreign Currency Transaction Gain (Loss), Realized	0	0
Net realized investment gains, pre-tax	(1.1)	0.5
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	0	0
Foreign Currency Transaction Gain (Loss), Realized	0	0
Net realized investment gains, pre-tax	0	0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	257.6	22
Foreign Currency Transaction Gain (Loss), Realized	0	0.5
Net realized investment gains, pre-tax	257.6	22.5
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	0.3	(8.2)
Foreign Currency Transaction Gain (Loss), Realized	0	0
Net realized investment gains, pre-tax	$ 0.3	$ (8.2)

Investment Securities (Net Unre

Investment Securities (Net Unrealized Investment Gains (Losses)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	$ (230.1)	$ 15.2
Trading Securities, Tax on Unrealized Holding Gain (Loss) on Investments	34.4	(2.6)
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax	(195.7)	12.6
Foreign Currency Transaction Gain (Loss), Unrealized	2.8	(5)
Trading Securities, Unrealized Foreign Currency Transaction Gain (Loss) Tax	0	0
Trading Securities, Unrealized Foreign Currency Gain (Loss) Net of Tax	2.8	(5)
Net unrealized investment (losses) gains, pre-tax	(227.3)	10.2
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Tax	34.4	(2.6)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	(192.9)	7.6
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	21.7	11.4
Foreign Currency Transaction Gain (Loss), Unrealized	0	0
Net unrealized investment (losses) gains, pre-tax	21.7	11.4
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	0	0
Foreign Currency Transaction Gain (Loss), Unrealized	0	0
Net unrealized investment (losses) gains, pre-tax	0	0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	(249.8)	(2.8)
Foreign Currency Transaction Gain (Loss), Unrealized	2.4	(4)
Net unrealized investment (losses) gains, pre-tax	(247.4)	(6.8)
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	(2)	6.6
Foreign Currency Transaction Gain (Loss), Unrealized	0.4	(1)
Net unrealized investment (losses) gains, pre-tax	$ (1.6)	$ 5.6

Investment Securities (Investme

Investment Securities (Investment gains (losses) for Level 3) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 7.3
Unrealized gains (losses) on investments	(230.1)	15.2
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	21.7	11.4
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	(249.8)	(2.8)
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	(2)	6.6
Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	1.6	4.1
Level 3 Inputs | Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	0.5	0.2
Level 3 Inputs | Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	0	(1.8)
Level 3 Inputs | Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	$ 1.1	$ 5.7

Investment Securities (Invest53

Investment Securities (Investment Holdings Fixed Maturity Table) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity investments, at fair value	$ 2,613.2	$ 2,639.7
U.S. Government and agency obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	88.4	160.4
Trading Securities, Unrealized Holding Gain	0.4	0
Trading Securities, Unrealized Holding Loss	0	(0.4)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	88.8	160
Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	899	1,001
Trading Securities, Unrealized Holding Gain	12.5	4.3
Trading Securities, Unrealized Holding Loss	(1.1)	(5.3)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	910.4	1,000
Municipal obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	264.3	227.8
Trading Securities, Unrealized Holding Gain	4.6	2.2
Trading Securities, Unrealized Holding Loss	(0.2)	(1.2)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	268.7	228.8
Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	1,259.9	1,170.6
Trading Securities, Unrealized Holding Gain	5.1	2
Trading Securities, Unrealized Holding Loss	(4.1)	(5.6)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	1,260.9	1,167
Foreign government, agency and provincial obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	1	1
Trading Securities, Unrealized Holding Gain	0.2	0.2
Trading Securities, Unrealized Holding Loss	0	0
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	1.2	1.2
Preferred Stock
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	78.3	78.3
Trading Securities, Unrealized Holding Gain	4.9	4.4
Trading Securities, Unrealized Holding Loss	0	0
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	83.2	82.7
Fixed Income Investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	2,590.9	2,639.1
Trading Securities, Unrealized Holding Gain	27.7	13.1
Trading Securities, Unrealized Holding Loss	(5.4)	(12.5)
Net foreign currency gains (losses)	0	0
Total fixed maturity investments including assets held for sale	$ 2,613.2	$ 2,639.7

Investment Securities (Invest54

Investment Securities (Investment Holding Common Equities/ Other Investments) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity investments, at fair value	$ 2,613.2	$ 2,639.7
Common Stock
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	399	822.5
Trading Securities, Unrealized Holding Gain	52.9	302.8
Trading Securities, Unrealized Holding Loss	(8.9)	(11.4)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	443	1,113.9
Other long-term investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	312.3	304.5
Trading Securities, Unrealized Holding Gain	32.7	32
Trading Securities, Unrealized Holding Loss	(21.3)	(18.4)
Net foreign currency gains (losses)	(1.9)	(2.3)
Fixed maturity investments, at fair value	$ 321.8	$ 315.8

Investment Securities (Other lo

Investment Securities (Other long-term investments) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Payments to Acquire Other Investments	$ 10,900	$ 6,500
Other Investments	321,800		$ 315,800
Hedge and private equity funds included in other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	131,300		127,800
Limited liability companies and private equity securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	84,700		82,100
Surplus Note
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	51,800		51,500
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	32,900		32,700
Affordable Housing Development Fund [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	14,100	$ 16,200	14,700	$ 16,800
Partnership investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	3,700		3,800
Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	3,300		3,200
Hedge Funds Equity R E I T [Member] | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	20,200		20,600
Unfunded Commitments	$ 0		$ 0

Investment Securities (Hedge Fu

Investment Securities (Hedge Funds and Private Equity Funds) (Details) $ in Millions	Mar. 31, 2016USD ($)fund	Dec. 31, 2015USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments | $	$ 321.8	$ 315.8
Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of investments | fund	5
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of investments | fund	23
Hedge and private equity funds included in other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Largest single fund investment | $	$ 22.8

Investment Securities (Fair Val

Investment Securities (Fair Value of Hedge Funds and Private Equity Funds) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	$ 36.4
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	94.9
Hedge and private equity funds included in other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	131.3	$ 127.8
Unfunded Commitments	73.5	82.2
Private equity funds | Private Equity Energy Infrastructure and Services
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	18	20.7
Unfunded Commitments	3.3	3.4
Private equity funds | Private Equity Multi Sector
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	13	14.8
Unfunded Commitments	2.1	2.1
Private equity funds | Private Equity Secondaries
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	3.9	4.4
Unfunded Commitments	2.1	2.1
Private equity funds | Private Equity Healthcare
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	3.8	3.8
Unfunded Commitments	0.4	0.4
Private equity funds | Private Equity Insurance
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	2	2
Unfunded Commitments	41.3	41.3
Private equity funds | Aerospace Defense Government
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	27.9	19.8
Unfunded Commitments	22.1	30.3
Private equity funds | Industrial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	25.8	24.9
Unfunded Commitments	2.1	2.5
Private equity funds | Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	94.9	90.8
Unfunded Commitments	73.5	82.2
Private equity funds | Real Estate Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0.5	0.4
Unfunded Commitments	0.1	0.1
Hedge funds | Hedge Fund, Long/ Short Equity Banks and Financial [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	12.6	12.8
Unfunded Commitments	0	0
Hedge funds | Hedge Funds Equity R E I T [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	20.2	20.6
Unfunded Commitments	0	0
Hedge funds | Hedge Funds, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	3.6	3.6
Unfunded Commitments	0	0
Hedge funds | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	36.4	37
Unfunded Commitments	$ 0	$ 0

Investment Securities (Restrict

Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) - Hedge funds $ in Millions	Mar. 31, 2016USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Distributions from Inactive Hedge Funds	$ 1.1
Other long-term investments	36.4
Redemption requests	2.5
30-59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	13.7
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Notice Period60 To89 Days [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	20.2
Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Notice Period90 To119 Days [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	2.5
Monthly
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0
Monthly | 30-59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0
Monthly | Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Notice Period60 To89 Days [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0
Monthly | Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Notice Period90 To119 Days [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0
Quarterly
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	13.7
Quarterly | 30-59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	13.7
Quarterly | Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Notice Period60 To89 Days [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0
Quarterly | Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Notice Period90 To119 Days [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0
Semi-annual
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	20.2
Semi-annual | 30-59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0
Semi-annual | Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Notice Period60 To89 Days [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	20.2
Semi-annual | Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Notice Period90 To119 Days [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0
Annual
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	2.5
Annual | 30-59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0
Annual | Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Notice Period60 To89 Days [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0
Annual | Fair Value Investments Entities that Calculate Net Asset Value Per Share Investment Redemption Notice Period90 To119 Days [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	$ 2.5

Investment Securities (Invest59

Investment Securities (Investments In Private Equity Funds Subject to Lock-Up Periods) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interest	$ 6.3	$ (7.3)
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	94.9
1-3 years | Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	29.2
3-5 years | Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	3.9
5-10 years | Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	61.8
Greater than 10 years | Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	$ 0

Investment Securities OneBeacon

Investment Securities OneBeacon Surplus Notes (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 23, 2014
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 7.3
Interest Paid	1.6	$ 0
OneBeacon [Member]
Assets, Fair Value Adjustment	(49.2)		$ (49.5)
OneBeacon [Member] | Par Value [Member]
Surplus Notes	101		101	$ 101
OneBeacon [Member] | Fair Value [Member]
Surplus Notes	51.8		51.5
OneBeacon [Member] | Current market rates on repayments [Member]
Assets, Fair Value Adjustment	(14.7)		(15.1)
OneBeacon [Member] | Regulatory Approval [Member]
Assets, Fair Value Adjustment	(24.4)		(24.2)
OneBeacon [Member] | Liquidity Adjustment [Member]
Assets, Fair Value Adjustment	(10.1)		$ (10.2)
Seller Priority Surplus Note [Member] | OneBeacon [Member]
Assets, Fair Value Adjustment	(19.7)
Seller Priority Surplus Note [Member] | OneBeacon [Member] | Par Value [Member]
Surplus Notes	57.9
Seller Priority Surplus Note [Member] | OneBeacon [Member] | Fair Value [Member]
Surplus Notes	38.2
Seller Priority Surplus Note [Member] | OneBeacon [Member] | Current market rates on repayments [Member]
Assets, Fair Value Adjustment	(0.5)
Seller Priority Surplus Note [Member] | OneBeacon [Member] | Regulatory Approval [Member]
Assets, Fair Value Adjustment	(11.4)
Seller Priority Surplus Note [Member] | OneBeacon [Member] | Liquidity Adjustment [Member]
Assets, Fair Value Adjustment	(7.8)
Surplus Note
Interest Paid	2.4
Pari Passu Surplus Note [Member] | OneBeacon [Member]
Assets, Fair Value Adjustment	(29.5)
Pari Passu Surplus Note [Member] | OneBeacon [Member] | Par Value [Member]
Surplus Notes	43.1
Pari Passu Surplus Note [Member] | OneBeacon [Member] | Fair Value [Member]
Surplus Notes	13.6
Pari Passu Surplus Note [Member] | OneBeacon [Member] | Current market rates on repayments [Member]
Assets, Fair Value Adjustment	(14.2)
Pari Passu Surplus Note [Member] | OneBeacon [Member] | Regulatory Approval [Member]
Assets, Fair Value Adjustment	(13)
Pari Passu Surplus Note [Member] | OneBeacon [Member] | Liquidity Adjustment [Member]
Assets, Fair Value Adjustment	$ (2.3)
Surplus Note
RBC Score			250.00%

Investment Securities (Fair V61

Investment Securities (Fair Value Measurements) (Details) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2016USD ($)
Investments, Debt and Equity Securities [Abstract]
Percentage of Investments Recorded at Fair Value	89.00%
Maximum percentage of price difference provided by pricing services	5.00%
Maximum price difference provided by pricing services	$ 1

Investment Securities (Fair V62

Investment Securities (Fair Value Measurement by Level) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,360,200	$ 4,050,900	$ 3,355,300	$ 3,343,600
Other Investments	321,800	315,800
Short-term investments, at amortized cost (which approximates fair value)	261,700	211,300
Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	419,600	1,152,200	537,000	550,600
Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,566,100	2,531,400	2,380,900	2,372,900
Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	910,400	1,000,000
Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,260,900	1,167,000
Mortgage-backed and asset-backed securities | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,260,900	1,167,000
Mortgage-backed and asset-backed securities | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fixed maturity investments. | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	70,500	70,000	101,100	76,400
Common equity securities | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0	32,000	39,500
Other long-term investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	172,700	169,500	102,800	110,600
Hedge and private equity funds included in other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	131,300	127,800
Hedge and private equity funds included in other long-term investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	131,300	127,800	201,500	193,600
Fair value measured on a recurring basis
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	3,490,600	4,134,400
Fair value measured on a recurring basis | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	681,300	1,363,500
Fair value measured on a recurring basis | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,566,100	2,531,400
Fair value measured on a recurring basis | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	243,200	239,500
Fair value measured on a recurring basis | U.S. Government and agency obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	88,800	160,000
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	72,300	133,400
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	16,500	26,600
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	910,400	1,000,000
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	910,400	1,000,000
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	242,100	253,300
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	242,100	253,300
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	135,100	135,600
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	135,100	135,600
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	155,500	175,900
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	155,500	175,900
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	43,300	49,200
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	43,300	49,200
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications [Member] | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	124,700	151,300
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	124,700	151,300
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care [Member] | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	69,300	82,000
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	69,300	82,000
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	57,100	60,000
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	57,100	60,000
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	57,200	61,500
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	57,200	61,500
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	26,100	31,200
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	26,100	31,200
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Other:
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Other: | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Other: | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Other: | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,260,900	1,167,000
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,260,900	1,167,000
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Municipal obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	268,700	228,800
Fair value measured on a recurring basis | Municipal obligations | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Municipal obligations | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	268,700	228,800
Fair value measured on a recurring basis | Municipal obligations | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,200	1,200
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	600	600
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	600	600
Fair value measured on a recurring basis | Foreign government, agency and provincial obligations | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Preferred Stock
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	83,200	82,700
Fair value measured on a recurring basis | Preferred Stock | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Preferred Stock | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	12,700	12,700
Fair value measured on a recurring basis | Preferred Stock | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	70,500	70,000
Fair value measured on a recurring basis | Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,613,200	2,639,700
Fair value measured on a recurring basis | Fixed maturity investments. | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	72,900	134,000
Fair value measured on a recurring basis | Fixed maturity investments. | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,469,800	2,435,700
Fair value measured on a recurring basis | Fixed maturity investments. | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	70,500	70,000
Fair value measured on a recurring basis | Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	261,700	211,300
Fair value measured on a recurring basis | Short-term investments | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	261,700	211,300
Short-term investments, at amortized cost (which approximates fair value)		211,300	453,700	376,800
Fair value measured on a recurring basis | Short-term investments | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Short-term investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Consumer
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	73,100	70,000
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	73,100	70,000
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments		0
Fair value measured on a recurring basis | Common equity securities | Consumer | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Industrial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	30,000	26,600
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	30,000	26,600
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Industrial | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Financials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	12,900	694,700
Fair value measured on a recurring basis | Common equity securities | Financials | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	12,900	694,700
Fair value measured on a recurring basis | Common equity securities | Financials | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Financials | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Communications [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	34,900	43,700
Fair value measured on a recurring basis | Common equity securities | Communications [Member] | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	34,900	43,700
Fair value measured on a recurring basis | Common equity securities | Communications [Member] | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Communications [Member] | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Health Care [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	39,000	35,700
Fair value measured on a recurring basis | Common equity securities | Health Care [Member] | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	39,000	35,700
Fair value measured on a recurring basis | Common equity securities | Health Care [Member] | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Health Care [Member] | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Technology
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	47,800	27,000
Fair value measured on a recurring basis | Common equity securities | Technology | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	47,800	27,000
Fair value measured on a recurring basis | Common equity securities | Technology | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Technology | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	130,500	141,800
Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	109,000	120,500
Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	21,500	21,300
Fair value measured on a recurring basis | Common equity securities | Exchange Traded Funds [Member] | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Other:
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	74,800	74,400
Fair value measured on a recurring basis | Common equity securities | Other: | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Other: | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	74,800	74,400
Fair value measured on a recurring basis | Common equity securities | Other: | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	443,000	1,113,900
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	346,700	1,018,200
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	96,300	95,700
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	172,700	169,500
Fair value measured on a recurring basis | Other long-term investments | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Other long-term investments | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Other long-term investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	172,700	169,500
Carrying value of investment accounted for using the equity method	3,700	3,800	3,800	5,200
Affordable Housing Development Fund [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	14,100	14,700	$ 16,200	$ 16,800
Affordable Housing Development Fund [Member] | Fair value measured on a recurring basis | Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	$ 14,100	$ 14,700

Investment Securities (Debt sec

Investment Securities (Debt securities issued by corporation) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,360.2	$ 4,050.9	$ 3,355.3	$ 3,343.6
Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	910.4	1,000
AAA | Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	9.4	0
AA | Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	107.4	95.2
A | Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	364.2	397.7
BBB | Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	429.4	507.1
Other | Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 0	$ 0

Investment Securities (Mortgage

Investment Securities (Mortgage-backed, Asset-backed Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,360.2	$ 4,050.9	$ 3,355.3	$ 3,343.6
Non-Agency Residential Mortgage [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	36
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 128.8	$ 140.4

Investment Securities (Mortga65

Investment Securities (Mortgage-backed Asset Securities Table) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,360.2	$ 4,050.9	$ 3,355.3	$ 3,343.6
Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	96.1
Government National Mortgage Association Certificates and Obligations (GNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	275	265.5
Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	45	42.2
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	22.1	22.8
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	342.1	330.5
Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	132.3	133.2
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	128.8	140.4
Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	261.1	273.6
Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	603.2	604.1
Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	281.6	217.7
Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	290.8	269.7
Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	85.3	75.5
Asset-backed Securities, Securitized Loans and Receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	657.7	562.9
Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,260.9	1,167
Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,566.1	2,531.4	$ 2,380.9	$ 2,372.9
Level 2 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	275	265.5
Level 2 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	45	42.2
Level 2 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	22.1	22.8
Level 2 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	342.1	330.5
Level 2 Inputs | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	132.3	133.2
Level 2 Inputs | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	128.8	140.4
Level 2 Inputs | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	261.1	273.6
Level 2 Inputs | Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	603.2	604.1
Level 2 Inputs | Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	281.6	217.7
Level 2 Inputs | Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	290.8	269.7
Level 2 Inputs | Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	85.3	75.5
Level 2 Inputs | Asset-backed Securities, Securitized Loans and Receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	657.7	562.9
Level 2 Inputs | Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,260.9	1,167
Level 3 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Level 3 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Level 3 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Level 3 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Level 3 Inputs | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Level 3 Inputs | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Level 3 Inputs | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Level 3 Inputs | Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Level 3 Inputs | Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Level 3 Inputs | Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Level 3 Inputs | Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Level 3 Inputs | Asset-backed Securities, Securitized Loans and Receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Level 3 Inputs | Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 0	$ 0
Maximum | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Loans and Leases Receivable, Ratio of Nonperforming Loans to All Loans	1.00%

Investment Securities (Non-agen

Investment Securities (Non-agency Mortgage-backed Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,360.2	$ 4,050.9	$ 3,355.3	$ 3,343.6
Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	96.1
Commercial Mortgage Backed Securities Floating Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	32.7
Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	132.3	133.2
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	128.8	140.4
Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	261.1	$ 273.6
Securities Issued in 2004 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	23.3
Securities Issued in 2004 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued in 2004 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	23.3
Securities Issued in 2005 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	8.1
Securities Issued in 2005 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued in 2005 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	8.1
Securities Issued In 2006 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	3.6
Securities Issued In 2006 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued In 2006 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	3.6
Securities Issued In 2007 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued In 2007 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued In 2007 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued In 2008 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	3.4
Securities Issued In 2008 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued In 2008 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	3.4
Securities Issued In 2009 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued In 2009 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued In 2009 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued In 2010 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	13.1
Securities Issued In 2010 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	5.2
Securities Issued In 2010 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	18.3
Securities Issued In 2011 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	12.6
Securities Issued In 2011 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued In 2011 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	12.6
Securities Issued in 2012 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	9.3
Securities Issued in 2012 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	18.3
Securities Issued in 2012 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	27.6
Securities Issued in 2013 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	13.2
Securities Issued in 2013 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	15.4
Securities Issued in 2013 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	28.6
Securities Issued in 2014 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	45.7
Securities Issued in 2014 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	44.8
Securities Issued in 2014 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	90.5
Securities Issued in 2015 [Member] | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued in 2015 [Member] | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	45.1
Securities Issued in 2015 [Member] | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	45.1
Subordinate | Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	41.3
Subordinate | Commercial Mortgage Backed Securities Floating Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	32.7
Subordinate | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Subordinate | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	74
Super Senior | Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	8.8
Super Senior | Commercial Mortgage Backed Securities Floating Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Super Senior | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	63.1
Super Senior | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	8.8
Senior | Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	46
Senior | Commercial Mortgage Backed Securities Floating Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Senior | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	69.2
Senior | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 46

Investment Securities (Non-ag67

Investment Securities (Non-agency Residential Mortgage-backed Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,360.2	$ 4,050.9	$ 3,355.3	$ 3,343.6
Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	132.3	$ 133.2
Residential Mortgage Backed Securities | Super Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	63.1
Residential Mortgage Backed Securities | Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	69.2
Residential Mortgage Backed Securities | Subordinate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Prime | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	124.8
Prime | Residential Mortgage Backed Securities | Super Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	63.1
Prime | Residential Mortgage Backed Securities | Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	61.7
Prime | Residential Mortgage Backed Securities | Subordinate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Non-prime | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	7.5
Non-prime | Residential Mortgage Backed Securities | Super Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Non-prime | Residential Mortgage Backed Securities | Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	7.5
Non-prime | Residential Mortgage Backed Securities | Subordinate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Sub-prime | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Sub-prime | Residential Mortgage Backed Securities | Super Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Sub-prime | Residential Mortgage Backed Securities | Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Sub-prime | Residential Mortgage Backed Securities | Subordinate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 0

Investment Securities (Non-ag68

Investment Securities (Non-agency Commercial Mortgage-backed Securities) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Mar. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,360.2	$ 4,050.9	$ 3,355.3	$ 3,343.6
Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Average Basis Points of Subordination	25
Fair value investments	$ 96.1
Commercial Mortgage Backed Securities Fixed Rate [Member] | Super Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	8.8
Commercial Mortgage Backed Securities Fixed Rate [Member] | Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	46
Commercial Mortgage Backed Securities Fixed Rate [Member] | Subordinate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	41.3
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	128.8	$ 140.4
Commercial Mortgage Backed Securities | Super Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	8.8
Commercial Mortgage Backed Securities | Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	46
Commercial Mortgage Backed Securities | Subordinate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 74

Rollforward of Fair Value Measu

Rollforward of Fair Value Measurements by Level (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	$ 4,050,900	$ 3,343,600
Total realized and unrealized gains (losses)	(29,600)	(25,900)
Amortization/Accretion	(4,200)	(4,600)
Purchases	(412,400)	447,800
Sales	(1,128,500)	(457,400)
Transfers in	0	5,200
Transfers out	0	(5,200)
Balance at March 31, 2016	3,360,200	3,355,300
Other Investments	321,800		$ 315,800
Net realized and unrealized investment gains, after tax	21,000	17,900
Net realized and unrealized investment gains	29,500	25,000
Short-term investments, at amortized cost (which approximates fair value)	$ 261,700		211,300
Maximum Percentage Differences Between Prices Provided by Pricing Services Considered Outliers	(5.00%)
Maximum price difference provided by pricing services	$ 1,000
Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	1,152,200	550,600
Total realized and unrealized gains (losses)	(11,300)	10,000
Amortization/Accretion	0	0
Purchases	(109,000)	94,100
Sales	(852,900)	117,700
Transfers in	0	0
Transfers out	0	0
Balance at March 31, 2016	419,600	537,000
Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	2,531,400	2,372,900
Total realized and unrealized gains (losses)	(19,100)	16,900
Amortization/Accretion	(4,200)	(4,600)
Purchases	(292,400)	317,400
Sales	(272,600)	326,900
Transfers in	0	5,200
Transfers out	0	0
Balance at March 31, 2016	2,566,100	2,380,900
Fixed maturity investments. | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	70,000	76,400
Total realized and unrealized gains (losses)	(500)	200
Amortization/Accretion	0	0
Purchases	0	29,700
Sales	0	0
Transfers in	0	0
Transfers out	0	(5,200)
Balance at March 31, 2016	70,500	101,100
Common equity securities | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	0	39,500
Total realized and unrealized gains (losses)	0	1,800
Amortization/Accretion	0	0
Purchases	0	0
Sales	0	9,300
Transfers in	0	0
Transfers out	0	0
Balance at March 31, 2016	0	32,000
Other long-term investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	169,500	110,600
Total realized and unrealized gains (losses)	(1,100)	(6,200)
Amortization/Accretion	0	0
Purchases	(2,100)	1,400
Sales	0	3,000
Transfers in	0	0
Transfers out	0	0
Balance at March 31, 2016	172,700	102,800
Hedge and private equity funds included in other long-term investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	127,800	193,600
Total realized and unrealized gains (losses)	2,400	3,200
Amortization/Accretion	0	0
Purchases	(8,900)	5,200
Sales	(3,000)	500
Transfers in	0	0
Transfers out	0	0
Balance at March 31, 2016	131,300	201,500
Fair value measured on a recurring basis
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	4,134,400
Balance at March 31, 2016	3,490,600
Fair value measured on a recurring basis | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	1,363,500
Balance at March 31, 2016	681,300
Fair value measured on a recurring basis | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	2,531,400
Balance at March 31, 2016	2,566,100
Fair value measured on a recurring basis | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	239,500
Balance at March 31, 2016	243,200
Fair value measured on a recurring basis | Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	2,639,700
Balance at March 31, 2016	2,613,200
Fair value measured on a recurring basis | Fixed maturity investments. | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	134,000
Balance at March 31, 2016	72,900
Fair value measured on a recurring basis | Fixed maturity investments. | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	2,435,700
Balance at March 31, 2016	2,469,800
Fair value measured on a recurring basis | Fixed maturity investments. | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	70,000
Balance at March 31, 2016	70,500
Fair value measured on a recurring basis | Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	169,500
Balance at March 31, 2016	172,700
Fair value measured on a recurring basis | Other long-term investments | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	0
Balance at March 31, 2016	0
Fair value measured on a recurring basis | Other long-term investments | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	0
Balance at March 31, 2016	0
Fair value measured on a recurring basis | Other long-term investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	169,500
Balance at March 31, 2016	172,700
Carrying value of investment accounted for using the equity method	3,700	3,800	3,800	$ 5,200
Fair value measured on a recurring basis | Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	211,300
Balance at March 31, 2016	261,700
Fair value measured on a recurring basis | Short-term investments | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	211,300
Balance at March 31, 2016	261,700
Short-term investments, at amortized cost (which approximates fair value)		453,700	211,300	376,800
Fair value measured on a recurring basis | Short-term investments | Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	0
Balance at March 31, 2016	0
Fair value measured on a recurring basis | Short-term investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016	0
Balance at March 31, 2016	0
Discontinued Operations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized and unrealized investment gains	(8,800)	78,400
Prospector Offshore Fund Ltd [Member] | Fair value measured on a recurring basis | Investment related liabilities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized and unrealized investment gains		800
Affordable Housing Development Fund [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	14,100	$ 16,200	14,700	$ 16,800
Affordable Housing Development Fund [Member] | Fair value measured on a recurring basis | Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	$ 14,100		$ 14,700

Investment Securities (Signific

Investment Securities (Significant Unobservable Inputs) (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016USD ($)Investment	Mar. 31, 2015USD ($)	Dec. 31, 2015USD ($)inputInvestment
Quantitative information for Level 3 Fair Value Measurements Assets
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 7.3
Number of Investments with Significant Unobseravble Inputs | Investment	1		1
NR | Preferred Stock | Par Value [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure			$ 70
NR | Preferred Stock | Issuer's intent to call [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value Measurements, Valuation Techniques			70
NR | Convertible Preferred Stock [Member] | Multiple of EBITA [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs | input			0
Fair Value Measurements, Valuation Techniques			6
NR | Convertible Preferred Stock [Member] | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure			$ 5.7
NR | Seller Priority Surplus Note [Member] | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 38.2		$ 38
Timing of interest payments	5 years		5 years
Timing of principal payments	10 years		10 years
Fair Value Measurements, Valuation Techniques	0.125		0.13
NR | Pari Passu Surplus Note [Member] | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 13.6		$ 13.5
Timing of interest payments	5 years		5 years
Timing of principal payments	15 years		15 years
Fair Value Measurements, Valuation Techniques	.225		0.224
MSA [Member] | NR | Preferred Stock | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 70.5
Fair Value Measurements, Valuation Techniques	.0807
PassportCard [Member] | NR | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 21		$ 21
PassportCard [Member] | NR | Private equity funds | Average Share Price [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value Measurements, Valuation Techniques	1		1
Compare.com [Member] | NR | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 33.8
Compare.com [Member] | NR | Private equity funds | Average Share Price [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value Measurements, Valuation Techniques	1.03
Compare.com [Member] | NR | Private equity funds | Recent Transaction Two [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure			$ 33.8
Fair Value Measurements, Valuation Techniques			1.03
OneTitle [Member] | NR | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 3.2
OneTitle [Member] | NR | Private equity funds | Average Share Price [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value Measurements, Valuation Techniques	2.521
Galvanic [Member] | NR | Convertible Preferred Stock [Member] | Multiple of EBITA [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value Measurements, Valuation Techniques	6
Galvanic [Member] | NR | Convertible Preferred Stock [Member] | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 5.9
Captricity [Member] | NR | Convertible Preferred Stock [Member] | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 27		$ 27
Fair Value Measurements, Valuation Techniques	3.83		3.83
durchblicker.at [Member] | NR | Private equity funds
Quantitative information for Level 3 Fair Value Measurements Assets
Time Until Expiration of Security	4 years		4 years
Volatility Rate	60.00%		60.00%
Risk Free Rate	1.15%		1.15%
durchblicker.at [Member] | NR | Private equity funds | Option pricing method [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 10		$ 9.6
Standard & Poor's, B Rating [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Basis points	2.50%		2.50%
Standard & Poor's, CCC Rating [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Basis points	2.50%		2.50%

Goodwill and Other Intangible71

Goodwill and Other Intangible Assets (Details) ₪ in Millions, $ in Millions	2 Months Ended		3 Months Ended
	Feb. 23, 2015ILS (₪)	Feb. 23, 2015USD ($)	Mar. 31, 2016USD ($)	Mar. 31, 2016USD ($)	Mar. 31, 2015USD ($)	Dec. 31, 2015USD ($)	Sep. 01, 2015USD ($)	Dec. 31, 2014USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Businesses and Interest in Affiliates			$ 8.1		$ 2.4
Assets			10,391.8	$ 10,391.8		$ 10,282.6
Goodwill			187.9	187.9	169.2	187.9		$ 168.9
Intangible Assets, Net (Excluding Goodwill)			183.6	183.6	$ 178.2	187.8		$ 182.3
Liabilities			$ 6,154.5	6,154.5		$ 5,914.6
Lowfares.com [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Businesses and Interest in Affiliates				$ 3.9
TruBridge [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Ownership interest (as a percent)							100.00%
Assets							$ 54.5
Goodwill							18.7
Intangible Assets, Net (Excluding Goodwill)							28.1
Liabilities							$ 4.3
Common Stock | Israel, New Shekels | Cashboard [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Businesses and Interest in Affiliates | ₪	₪ 35.9
Common Stock | United States of America, Dollars | Cashboard [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Businesses and Interest in Affiliates		$ 8.9
Cashboard [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Assets		5.5
Goodwill		0.3
Intangible Assets, Net (Excluding Goodwill)		2.8
Liabilities		$ 1.2

Goodwill and Other Intangible72

Goodwill and Other Intangible Assets - Goodwill Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 187.9	$ 169.2	$ 187.9	$ 168.9
Intangible Assets, Net (Excluding Goodwill)	183.6	178.2	$ 187.8	$ 182.3
Goodwill, Acquired During Period	0	0.3
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	3.9	2.8
Amortization of Intangible Assets	$ (8.1)	$ (6.9)

Debt (Details)

Debt (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Jul. 23, 2015	Oct. 10, 2014	Aug. 14, 2013
Debt Instrument
Total debt	$ 532.6		$ 440.5
Repayments of Debt	15.1	$ 1.3
Draw down of debt and revolving line of credit	107	$ 4.5
WTM Bank Facility
Debt Instrument
Total debt	150
Total commitment under revolving credit facility						$ 425
Proceeds from Issuance of Debt	$ 100
Debt, Weighted Average Interest Rate	3.90%
OB Bank Facility [Member]
Debt Instrument
Total commitment under revolving credit facility	$ 65
OneBeacon [Member] | OneBeacon Bank Facility [Member]
Debt Instrument
Long-term Line of Credit	0
OneBeacon [Member] | 2012 OBH Senior Notes
Debt Instrument
Debt instrument at face value	275		275
Unamortized original issue discount	(2.1)		(2.1)
Total debt	$ 272.9		$ 272.9
Debt Instrument, Interest Rate, Effective Percentage	4.70%		4.70%
White Mountains | WTM Bank Facility
Debt Instrument
Total debt	$ 150		$ 50
Tranzact [Member] | OneBeacon Bank Facility [Member]
Debt Instrument
Long-term Line of Credit			0
Tranzact [Member] | Tranzact Bank Facility [Member]
Debt Instrument
Long-term Line of Credit	$ 94.1		$ 104.7
Debt Instrument, Interest Rate, Effective Percentage	5.96%		5.60%
Unamortized Debt Issuance Expense	$ (1.6)		$ (1.8)
Line of Credit Facility, Fair Value of Amount Outstanding	92.5		102.9
Total commitment under revolving credit facility	116
Notional amount	101				$ 70
Line of Credit Facility, Remaining Borrowing Capacity	15
MediaAlpha [Member] | MediaAlpha Bank Facility [Member]
Debt Instrument
Total debt	2.5
Long-term Line of Credit	$ 17.5		$ 15
Debt Instrument, Interest Rate, Effective Percentage	6.40%		5.50%
Unamortized Debt Issuance Expense	$ (0.3)		$ (0.3)
Line of Credit Facility, Fair Value of Amount Outstanding	17.2		$ 14.7
Total commitment under revolving credit facility				$ 20
Notional amount	15
Proceeds from Issuance of Debt	2.5
Line of Credit Facility, Remaining Borrowing Capacity	5
Revolving Credit Facility [Member] | Tranzact [Member] | Tranzact Bank Facility [Member]
Debt Instrument
Proceeds from Issuance of Debt	4.5
Repayments of Debt	12.5
Term Loan [Member] | Tranzact [Member] | Tranzact Bank Facility [Member]
Debt Instrument
Repayments of Debt	2.6
TruBridge [Member] | Tranzact [Member] | Tranzact Bank Facility [Member]
Debt Instrument
Notional amount	$ 31

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Jun. 30, 2014
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Percent	(75.70%)
U.S. statutory rate (as a percent)	35.00%		35.00%
Income Tax Expense (Benefit)	$ (8.7)	$ 4.6
Equity in earnings of unconsolidated affiliates, net of tax	0	$ 7.3
Tax Assessment Year 2007 to 2009 [Member]
Income Tax Contingency [Line Items]
Income Tax Expense (Benefit)	12.8
Tax Years 2007, 2008, 2009 [Member] | OneBeacon [Member]
Income Tax Contingency [Line Items]
Income Tax Expense (Benefit)	12.8
Proceeds from Income Tax Refunds	6
Income Tax Credits and Adjustments	$ 4.7

Derivatives (Details)

Derivatives (Details) ¥ in Billions, $ in Billions	Mar. 31, 2016USD ($)	Mar. 31, 2016JPY (¥)	Dec. 31, 2015USD ($)	Dec. 31, 2015JPY (¥)
Collective account values of underlying variable annuities as a percentage of the guarantee value			113.00%	113.00%
White Mountains Life Re
Notional amount	$ 0.2	¥ 21.2	$ 0.4	¥ 50.7
Collective account values of underlying variable annuities as a percentage of the guarantee value	107.00%	107.00%	109.00%	109.00%

Derivatives Pre-Tax Operating R

Derivatives Pre-Tax Operating Results of WM Life Re (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pre-tax operating results of WM Life Re
Total revenues	$ 427.1	$ 391.8
General and administrative expenses	(140.5)	(110.1)
Pre-tax income from continuing operations	11.5	0.5
White Mountains Life Re
Pre-tax operating results of WM Life Re
Fees, included in other revenue	1	3
Change in fair value of variable annuity liability, included in other revenue	(0.4)	0.4
Realized and unrealized gains (losses)	(1.7)	(5.5)
Foreign exchange, included in other revenue	0.9	(1.1)
Other investment income and (losses) gains	0	0
Total revenues	(0.2)	(3.2)
Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses	0	0
Death benefit claims paid, included in general and administrative expenses	(0.1)	0
General and administrative expenses	(0.8)	(1.4)
Pre-tax income from continuing operations	$ (1.1)	$ (4.6)

Derivatives Realized and Unreal

Derivatives Realized and Unrealized Gains (Losses) (Details) - White Mountains Life Re - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	$ (1.7)	$ (5.5)
Derivative, fair value, net	13.1	47	$ 20.1	$ 56.4
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0
Derivative Transfers In (Out), Net	0	0
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements	5.3	3.9
Fixed income/interest rate
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	1.8	9.3
Derivative, fair value, net	(0.4)		0.5
Foreign exchange
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	(4.2)	(12.1)
Derivative, fair value, net	12.5		14.8
Equity
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	0.7	(2.7)
Derivative, fair value, net	1		4.8
Level 2 Inputs
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	1.1	(6.5)
Derivative, fair value, net	10.3	31.2	16.5	33.8
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0
Derivative Transfers In (Out), Net	0	0
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements	7.3	(3.9)
Level 1 Inputs
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	(4)	1.6
Derivative, fair value, net	0.2	(1.2)	0.9	3.7
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0
Derivative Transfers In (Out), Net	0	0
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements	(3.3)	6.5
Fair Value, Inputs, Level 3 [Member] | Variable Annuity
Variable Annuity Reinsurance [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	(0.1)	1.1	0.3	0.7
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	(0.4)	0.4
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers	0	0
Fair Value Measurement with Unobservable Inputs, Reconciliation, Recurring Basis, Liability Sales or Settlements	0	0
Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	1.2	(0.6)
Derivative, fair value, net	2.6	17	$ 2.7	$ 18.9
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0
Derivative Transfers In (Out), Net	0	0
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements	$ 1.3	$ 1.3

Derivatives Variable Annuity Re

Derivatives Variable Annuity Reinsurance Liabilities and Derivative Instruments (Details) $ in Millions, ¥ in Billions	3 Months Ended
	Mar. 31, 2016USD ($)	Mar. 31, 2015USD ($)	Mar. 31, 2016JPY (¥)	Dec. 31, 2015USD ($)	Dec. 31, 2015JPY (¥)
Changes in derivative instruments
Collective account values of underlying variable annuities as a percentage of the guarantee value				113.00%	113.00%
White Mountains Life Re
Variable Annuity Reinsurance [Line Items]
Notional amount	$ 200		¥ 21.2	$ 400	¥ 50.7
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0
Changes in derivative instruments
Beginning of period	20.1	$ 56.4
Purchases		0
Realized and unrealized gains (losses)	(1.7)	(5.5)
Transfers in	0	0
Sales/settlements	(5.3)	(3.9)
End of period	13.1	47
Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses	$ 0	0
Collective account values of underlying variable annuities as a percentage of the guarantee value	107.00%		107.00%	109.00%	109.00%
White Mountains Life Re | Level 2 Inputs
Variable Annuity Reinsurance [Line Items]
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	$ 0
Changes in derivative instruments
Beginning of period	16.5	33.8
Purchases		0
Realized and unrealized gains (losses)	1.1	(6.5)
Transfers in	0	0
Sales/settlements	(7.3)	3.9
End of period	10.3	31.2
White Mountains Life Re | Level 1 Inputs
Variable Annuity Reinsurance [Line Items]
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0
Changes in derivative instruments
Beginning of period	0.9	3.7
Purchases		0
Realized and unrealized gains (losses)	(4)	1.6
Transfers in	0	0
Sales/settlements	3.3	(6.5)
End of period	0.2	(1.2)
Variable Annuity | White Mountains Life Re | Level 3 Inputs
Variable Annuity Reinsurance [Line Items]
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0
Changes in derivative instruments
Beginning balance	0.3	0.7
Realized and unrealized gains (losses)	(0.4)	0.4
Transfers in	0	0
Sales/settlements	0	0
Ending balance	(0.1)	1.1
Purchases		0
Derivative [Member] | White Mountains Life Re | Level 3 Inputs
Variable Annuity Reinsurance [Line Items]
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0
Changes in derivative instruments
Beginning of period	2.7	18.9
Purchases		0
Realized and unrealized gains (losses)	1.2	(0.6)
Transfers in	0	0
Sales/settlements	(1.3)	(1.3)
End of period	$ 2.6	$ 17

Derivatives Additional Collater

Derivatives Additional Collateral (Details) - White Mountains Life Re - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Credit risk on derivative instruments
Collateral cash and investments	$ 8.4	$ 5.8	$ 33.5
Cash
Credit risk on derivative instruments
Derivative collateral right to reclaim	8.4	5.8	29
Fixed maturity investments.
Credit risk on derivative instruments
Derivative collateral right to reclaim	$ 0	$ 0	$ 4.5

Derivatives (Level 3 Derivative

Derivatives (Level 3 Derivative Instruments) (Details) - White Mountains Life Re $ in Millions	3 Months Ended
	Mar. 31, 2016USD ($)
Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value Liabilities	$ (0.1)
Variable annuity benefit guarantee liabilities | Discounted cash flows | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Mortality (as a percent)	0.00%
Variable annuity benefit guarantee liabilities | Discounted cash flows | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Mortality (as a percent)	6.40%
Variable annuity benefit guarantee liabilities | Discounted cash flows | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Mortality (as a percent)	1.10%
Foreign Exchange Option [Member] | Counterparty valuations
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value Liabilities	$ (1.1)
Foreign Exchange Option [Member] | Counterparty valuations | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	(4.30%)
Foreign Exchange Option [Member] | Counterparty valuations | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	(7.30%)
Foreign Exchange Option [Member] | Counterparty valuations | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	(5.90%)
Equity Index Options | Counterparty valuations
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value Liabilities	$ (1.5)
Equity Index Options | Counterparty valuations | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Expected equity dividends (as a percent)	(0.60%)
Equity Index Options | Counterparty valuations | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Expected equity dividends (as a percent)	(5.70%)
Equity Index Options | Counterparty valuations | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Expected equity dividends (as a percent)	(5.60%)
Year One | Variable annuity benefit guarantee liabilities | Discounted cash flows | Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	0.10%
Foreign exchange volatilities (as a percent)	12.00%
Index volatilities (as a percent)	25.50%
Year One | Variable annuity benefit guarantee liabilities | Discounted cash flows | Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	40.00%
Foreign exchange volatilities (as a percent)	18.40%
Index volatilities (as a percent)	28.80%
Year One | Variable annuity benefit guarantee liabilities | Discounted cash flows | Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	40.00%
Foreign exchange volatilities (as a percent)	13.50%
Index volatilities (as a percent)	26.20%

Derivatives (Value, Collateral

Derivatives (Value, Collateral (held) provided by WM Life Re and Net Exposure to Credit Losses on OTC Derivative Instruments) (Details) - White Mountains Life Re - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Offsetting Liabilities [Line Items]
Derivative Assets	$ 16.7	$ 23.2
Derivative Liabilities	(3.6)	(3.1)
Net amounts recognized in Other assets	13.1	20.1
Over The Counter | Fixed income/interest rate
Offsetting Liabilities [Line Items]
Derivative Assets	2.2	2.4
Derivative Liabilities	(2.5)	(2.1)
Net amounts recognized in Other assets	(0.3)	0.3
Over The Counter | Foreign exchange
Offsetting Liabilities [Line Items]
Derivative Assets	12.7	15
Derivative Liabilities	0	0
Net amounts recognized in Other assets	12.7	15
Over The Counter | Equity
Offsetting Liabilities [Line Items]
Derivative Assets	1.5	4.4
Derivative Liabilities	(0.9)	(0.6)
Net amounts recognized in Other assets	0.6	3.8
Exchange Traded | Fixed income/interest rate
Offsetting Liabilities [Line Items]
Derivative Assets	0	0.1
Derivative Liabilities	0	(0.1)
Net amounts recognized in Other assets	0	0
Exchange Traded | Foreign exchange
Offsetting Liabilities [Line Items]
Derivative Assets	0	0.1
Derivative Liabilities	(0.1)	(0.3)
Net amounts recognized in Other assets	(0.1)	(0.2)
Exchange Traded | Equity
Offsetting Liabilities [Line Items]
Derivative Assets	0.3	1.2
Derivative Liabilities	(0.1)	0
Net amounts recognized in Other assets	$ 0.2	$ 1.2

Derivatives (Uncollateralized A

Derivatives (Uncollateralized Amounts Due Under WM Life Re's OTC Derivative Contracts) (Details) - White Mountains Life Re $ in Thousands	Mar. 31, 2016USD ($)Rating	Dec. 31, 2015USD ($)
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	$ 13,100	$ 20,100
Collertal provided to counterparty in cash	0	0
Collateral provided to counterparty in financial instruments	0	0
Net amount of exposure after effect of collateral	13,100	20,100
Excess collateral provided to counterparty in cash	7,900	5,800
Derivative, Collateral, Right to Reclaim Securities	0	0
Counter-party collateral held by WMLife Re - Cash	5,900	6,900
Net amount of exposure to counter-party	$ 15,100	19,000
S and P Credit Ratings | Rating	23
Standard & Poor's, A Rating [Member] | Bank of America [Member]
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	$ 1,400	700
Collertal provided to counterparty in cash	0	0
Collateral provided to counterparty in financial instruments	0	0
Net amount of exposure after effect of collateral	1,400	700
Excess collateral provided to counterparty in cash	0	0
Derivative, Collateral, Right to Reclaim Securities	0	0
Counter-party collateral held by WMLife Re - Cash	0	0
Net amount of exposure to counter-party	1,400	700
Standard & Poor's, A Rating [Member] | Citigroup - OTC
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	5,000	9,900
Collertal provided to counterparty in cash	0	0
Collateral provided to counterparty in financial instruments	0	0
Net amount of exposure after effect of collateral	5,000	9,900
Excess collateral provided to counterparty in cash	0	0
Derivative, Collateral, Right to Reclaim Securities	0	0
Counter-party collateral held by WMLife Re - Cash	500	1,400
Net amount of exposure to counter-party	4,500	8,500
Standard & Poor's, A Rating [Member] | Citigroup Exchange Traded [Member]
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	200	1,000
Collertal provided to counterparty in cash	0	0
Collateral provided to counterparty in financial instruments	0	0
Net amount of exposure after effect of collateral	200	1,000
Excess collateral provided to counterparty in cash	7,900	5,800
Derivative, Collateral, Right to Reclaim Securities	0	0
Counter-party collateral held by WMLife Re - Cash	0	0
Net amount of exposure to counter-party	8,100	6,800
Standard & Poor's, A plus | JP Morgan
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	6,500	8,500
Collertal provided to counterparty in cash	0	0
Collateral provided to counterparty in financial instruments	0	0
Net amount of exposure after effect of collateral	6,500	8,500
Excess collateral provided to counterparty in cash	0	0
Derivative, Collateral, Right to Reclaim Securities	0	0
Counter-party collateral held by WMLife Re - Cash	5,400	5,500
Net amount of exposure to counter-party	$ 1,100	$ 3,000

Derivatives (Tranzact Interest

Derivatives (Tranzact Interest Rate Swap) (Details) - Tranzact [Member] - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Oct. 10, 2014
Tranzact Bank Facility [Member]
Derivative [Line Items]
Line of Credit Facility, Fair Value of Amount Outstanding	$ 92.5	$ 102.9
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate	4.9385%
Notional amount	$ 101		$ 70
Debt Instrument, Interest Rate, Effective Percentage	5.96%	5.60%
Minimum | Tranzact Bank Facility [Member]
Derivative [Line Items]
LIBOR rate	4.50%
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Fixed Interest Rate	1.34%
Derivative, Variable Interest Rate	0.4385%		0.1518%
Debt Instrument, Interest Rate, Effective Percentage	6.28%
Derivative, fair value, net	$ (0.8)

Municipal Bond Guarantee (Detai

Municipal Bond Guarantee (Details) $ in Millions	1 Months Ended	3 Months Ended		12 Months Ended
	Jul. 31, 2012USD ($)	Mar. 31, 2016USD ($)yrContract	Mar. 31, 2015USD ($)	Dec. 31, 2015USD ($)Contract
Guarantor Obligations [Line Items]
Pre-tax (loss) income		$ 11.5	$ 0.5
Net investment income (loss) - surplus note interest		$ 0	0
BAM
Guarantor Obligations [Line Items]
Municipal bond contract | Contract		3,422		3,103
Insured Financial Obligations, Remaining Weighted Average Contract Period		12 years 8 months		12 years 10 months
Municipal bond outstanding principal		$ 24,641.6		$ 22,556
Municipal bond outstanding interest		12,711.9		11,984.4
Municipal bond debt service outstanding		37,353.5		34,540.4
Financial Guarantee Insurance Contracts, Unearned Premium Revenue		$ 55.8		$ 50.2
Year of U.S. Treasury Rate | yr		1
HG Global
Guarantor Obligations [Line Items]
Partners Capital Contribution	$ 594.5
Surplus Notes	503
Income (Loss) from Continuing Operations before Income Taxes, Domestic		$ 7.3
HG Global | Preferred Stock
Guarantor Obligations [Line Items]
Ownership interest (as a percent)		96.90%
HG Global | Common Stock
Guarantor Obligations [Line Items]
Ownership interest (as a percent)		88.40%
Build America Mutual
Guarantor Obligations [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Domestic		$ (7.6)	(8.8)
HG Re
Guarantor Obligations [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		467.2
HG Global
Guarantor Obligations [Line Items]
Pre-tax (loss) income		7.3
Net investment income (loss) - surplus note interest		$ 4.5
HG Global | HG Global
Guarantor Obligations [Line Items]
Pre-tax (loss) income			5.5
Net investment income (loss) - surplus note interest			4
BAM Management
Guarantor Obligations [Line Items]
Partners Capital Contribution	$ 14.5
Surplus Note | BAM
Guarantor Obligations [Line Items]
Basis points		3.00%
Interest Income, Other		$ 4.5
Derivative, Fixed Interest Rate		3.54%		3.15%
Surplus Note | Build America Mutual
Guarantor Obligations [Line Items]
Interest income (expense), surplus notes		$ 4.5	$ 4
Combination One [Member] | Surplus Note | BAM
Guarantor Obligations [Line Items]
Number of years of change in interest rate | yr		5
Combination Two [Member] | Surplus Note | BAM
Guarantor Obligations [Line Items]
Number of years of change in interest rate | yr		3
Financial Guarantee [Member]
Guarantor Obligations [Line Items]
Percentage of par value of policy reinsured		15.00%
Fixed interest rate [Member] | Surplus Note | BAM
Guarantor Obligations [Line Items]
Derivative, Fixed Interest Rate		8.00%

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Jun. 30, 2014
Basic and diluted earnings per share numerators (in millions):
Net income (loss) attributable to White Mountains’ common shareholders	$ 13.9	$ 10.5
Allocation of income for unvested restricted common shares	(0.1)	(0.1)
Dividends declared on participating restricted common shares	(0.1)	(0.1)
Total allocation to restricted common shares	(0.2)	(0.2)
Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts	13.7	10.3
Undistributed net earnings (in millions):
Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts	13.7	10.3
Dividends declared net of restricted common share amounts	(5.9)	(5.9)
Total undistributed net earnings, net of restricted common share amounts	$ 7.8	$ 4.4
Basic earnings per share denominators
Total average common shares outstanding during the period	5,539,600	5,978,400
Average unvested restricted common shares	(54,000)	(58,800)
Basic earnings per share denominator	5,485,600	5,919,600
Diluted earnings per share denominator
Total average common shares outstanding during the period	5,539,600	5,978,400
Average unvested restricted common shares	(54,000)	(58,800)
Average outstanding dilutive options to acquire common shares	5,540,500	5,978,400
Diluted earnings (loss) per share denominator	5,486,500	5,919,600
Basic earnings per share (in dollars):
Continuing operations	$ 2.51	$ 1.76
Dividends declared	(0.01)
Undistributed earnings (loss) (in dollars per share)	1.51	0.76
Earnings Per Share, Diluted [Abstract]
Continuing operations	2.51	1.76
Dividends declared	(1)	(1)
Undistributed earnings (loss) (in dollars per share)	$ 1.51	$ 0.76
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	882	125,000
Discontinued Operations [Member]
Basic and diluted earnings per share numerators (in millions):
Allocation of income for unvested restricted common shares	$ 0	$ (0.7)
Basic earnings per share denominators
Total average common shares outstanding during the period	5,540,500	5,978,400
Average unvested restricted common shares	(54,000)	(58,800)
Basic earnings per share denominator	5,485,600	5,919,600
Diluted earnings per share denominator
Total average common shares outstanding during the period	5,540,500	5,978,400
Average unvested restricted common shares	(54,000)	(58,800)
Average outstanding dilutive options to acquire common shares	0	0
Diluted earnings (loss) per share denominator	5,486,500	5,919,600
Earnings Per Share, Diluted [Abstract]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements			125,000
Employee Stock Option [Member]
Earnings Per Share, Diluted [Abstract]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	125,000

Non-controlling Interest (Detai

Non-controlling Interest (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 451.4	$ 454.8
Total Non-Controlling Excluding Reciprocals [Member]
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 114.8	$ 115.2
OneBeacon [Member]
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	23.90%	24.50%
Total non-controlling interests	$ 243.4	$ 245.6
SIG Preference Shares
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ 250	$ 250
HG Global
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.10%	3.10%
Total non-controlling interests	$ 17.2	$ 17.1
MediaAlpha [Member]
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	40.00%	40.00%
Total non-controlling interests	$ 14.2	$ 14.4
Tranzact [Member]
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	36.80%	36.80%
Total non-controlling interests	$ 79.7	$ 79.4
WOBI
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.90%	3.90%
Total non-controlling interests	$ 0.5	$ 0.6
AWG Dewar
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	30.10%	19.00%
Total non-controlling interests	$ 3.2	$ 3.7
Build America Mutual
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ (140.7)	$ (140)
Star & Shield Insurance Exchange
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ (16.1)	$ (16)

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Segment reporting information
Earned insurance premiums	$ 282.1	$ 289.3
Net investment income	17.9	12.6
Net investment income (loss) - surplus note interest	0	0
Net realized and unrealized investment gains (losses)	29.5	25
Other revenue	97.6	64.9
Total revenues	427.1	391.8
Losses and LAE	161.1	167.9
Insurance and Reinsurance Acquisition Expenses	52.7	53
Other Underwriting Expense	55.4	56
General and administrative expenses	140.5	110.1
Amortization of Intangible Assets	8.1	6.9
Interest expense	5.9	4.3
Total expenses	415.6	391.3
Pre-tax (loss) income	11.5	0.5
OneBeacon [Member]
Segment reporting information
Earned insurance premiums	278.6	286.6
Net investment income	14.4	10.5
Net investment income (loss) - surplus note interest	0	0
Net realized and unrealized investment gains (losses)	16.6	14.2
Other revenue	0.9	(3.1)
Total revenues	310.5	308.2
Losses and LAE	158.8	165.9
Insurance and Reinsurance Acquisition Expenses	51	51
Other Underwriting Expense	55.3	55.9
Interest expense	3.3	3.2
Total expenses	272.3	280.1
Pre-tax (loss) income	38.2	28.1
HG Global
Segment reporting information
Earned insurance premiums	0.9	0.5
Net investment income	0.5	0.4
Net investment income (loss) - surplus note interest	4.5
Net realized and unrealized investment gains (losses)	2.1	1.1
Other revenue	0	0
Total revenues	8	6
Losses and LAE	0	0
Insurance and Reinsurance Acquisition Expenses	0.2	0.1
Other Underwriting Expense	0	0
Interest expense	0	0
Total expenses	0.7	0.5
Pre-tax (loss) income	7.3
BAM
Segment reporting information
Earned insurance premiums	0.3	0.2
Net investment income	1.6	1
Net investment income (loss) - surplus note interest	(4.5)	(4)
Net realized and unrealized investment gains (losses)	4.9	3
Other revenue	0.1	0.1
Total revenues	2.4	0.3
Losses and LAE	0	0
Insurance and Reinsurance Acquisition Expenses	0.7	0.8
Other Underwriting Expense	0.1	0.1
Interest expense	0	0
Total expenses	10	9.1
Pre-tax (loss) income	(7.6)	(8.8)
Other Operations
Segment reporting information
Earned insurance premiums	2.3	2
Net investment income	1.4	0.7
Net investment income (loss) - surplus note interest	0	0
Net realized and unrealized investment gains (losses)	5.9	6.7
Other revenue	96.6	67.9
Total revenues	106.2	77.3
Losses and LAE	2.3	2
Insurance and Reinsurance Acquisition Expenses	0.8	1.1
Other Underwriting Expense	0	0
Interest expense	2.6	1.1
Total expenses	132.6	101.6
Pre-tax (loss) income	(26.4)	(24.3)
Segment Reconciling Items [Member]
Segment reporting information
General and administrative expenses	132.4	103.2
Segment Reconciling Items [Member] | OneBeacon [Member]
Segment reporting information
General and administrative expenses	3.6	3.8
Segment Reconciling Items [Member] | HG Global
Segment reporting information
General and administrative expenses	0.5	0.4
Segment Reconciling Items [Member] | BAM
Segment reporting information
General and administrative expenses	9.2	8.2
Segment Reconciling Items [Member] | Other Operations
Segment reporting information
General and administrative expenses	119.1	90.8
General and Administrative Expense [Member]
Segment reporting information
Amortization of Intangible Assets	8.1	6.9
General and Administrative Expense [Member] | OneBeacon [Member]
Segment reporting information
Amortization of Intangible Assets	0.3	0.3
General and Administrative Expense [Member] | HG Global
Segment reporting information
Amortization of Intangible Assets	0	0
General and Administrative Expense [Member] | BAM
Segment reporting information
Amortization of Intangible Assets	0	0
General and Administrative Expense [Member] | Other Operations
Segment reporting information
Amortization of Intangible Assets	7.8	6.6
Tranzact [Member] | Other Operations
Segment reporting information
Other revenue	57.8	37.5
General and administrative expenses	48.4	34.9
MediaAlpha [Member] | Other Operations
Segment reporting information
Other revenue	32.7	29.7
General and administrative expenses	$ 30.5	$ 27.7

Investments in Unconsolidated88

Investments in Unconsolidated Affiliates (Investment in Unconsolidated Affiliates Table) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2014
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 7.3
Symetra | Common Stock
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax		7.2
Total investments in unconsolidated affiliates		447.3	$ 411.4
Hamer, LLC [Member]
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax		$ 0.5

Investments in Unconsolidated89

Investments in Unconsolidated Affiliates (Symetra) (Details) - USD ($)	Feb. 01, 2016	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax		$ 0		$ 7,300,000
Unrealized gains (losses) on investments		(230,100,000)		15,200,000
Revenues		427,100,000		391,800,000
Total expenses		415,600,000		391,300,000
Pre-tax (loss) income		11,500,000		500,000
Net income		19,300,000		77,000,000
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax		(195,700,000)		12,600,000
Sales of common equity securities		$ 767,500,000		59,900,000
Common shares, par value per share (in dollars per share)		$ 1	$ 1
Net realized and unrealized investment gains		$ 29,500,000		$ 25,000,000
Symetra
Investments in unconsolidated affiliates
Unrealized gains (losses) on investments			$ 258,800,000
Term of amortization (in years)				30 years
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity				$ 165,700,000
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax			$ 241,100,000
Sales of common equity securities	$ 658,000,000
Common shares, par value per share (in dollars per share)	$ 32
Net realized and unrealized investment gains		$ 4,700,000
Common Stock | Symetra
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax				7,200,000
Proceeds from Equity Method Investment, Dividends or Distributions				2,200,000
equity in earnings of unconsolidated affiliates | Symetra
Investments in unconsolidated affiliates
After tax amortization through equity in earnings				700,000
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity				35,100,000
Net unrealized gains (losses) of unconsolidated affiliates | Symetra
Investments in unconsolidated affiliates
After tax amortization through equity in net unrealized losses				2,800,000
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity				130,600,000
Expected [Member] | Symetra
Investments in unconsolidated affiliates
Dividends Payable, Amount Per Share		$ 32
Amortization of common share basis difference | Common Stock | Symetra
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax		$ 2,015		$ 700,000

Investments in Unconsolidated90

Investments in Unconsolidated Affiliates (Investments in Symetra Table Rollforward) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Changes in carrying value of investment in Symetra
Equity in earnings	$ 0	$ 7,300,000
Income Tax Expense (Benefit)	(8,700,000)	4,600,000
Symetra | Common Stock
Changes in carrying value of investment in Symetra
Carrying value at the beginning of the period		411,400,000
Equity in earnings		7,200,000
Equity in net unrealized gains (losses) from Symetra's fixed maturity portfolio		30,900,000
Dividends received		(2,200,000)
Carrying value at the end of the period		447,300,000
White Mountains | Common Stock
Changes in carrying value of investment in Symetra
Equity in net unrealized gains (losses) from Symetra's fixed maturity portfolio		68,400,000
equity in earnings of unconsolidated affiliates | Symetra | Common Stock
Changes in carrying value of investment in Symetra
Income Tax Expense (Benefit)		400,000
Net unrealized gains (losses) of unconsolidated affiliates | White Mountains | Common Stock
Changes in carrying value of investment in Symetra
Income Tax Expense (Benefit)		(4,600,000)
Amortization of common share basis difference | Symetra | Common Stock
Changes in carrying value of investment in Symetra
Equity in earnings	$ 2,015	700,000
impairment of net unrealized gains (losses) | Net unrealized gains (losses) of unconsolidated affiliates | Symetra | Common Stock
Changes in carrying value of investment in Symetra
Equity in net unrealized gains (losses) from Symetra's fixed maturity portfolio		$ 2,900,000

Investments in Unconsolidated91

Investments in Unconsolidated Affiliates Hamer (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Jun. 30, 2015	Mar. 31, 2015
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Realized Gain (Loss) on Disposal		$ 20
Equity in earnings of unconsolidated affiliates, net of tax	$ 0		$ 7.3
Hamer, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax			$ 0.5

Employee Share-Based Incentiv92

Employee Share-Based Incentive Compensation Plans (WTM - Performance Shares) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Share-based compensation arrangement by share-based payment award
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 7.3
Accrued Expense
Accrued expense at the beginning of period	141.7
Accrued expense at the end of the period	$ 114.2		$ 141.7
Performance Share | W T M Incentive Plan | Performance Cycle 2013 to 2015
Accrued Expense
Percentage of target payout - minimum actual	140.00%
Percentage of target payout - maximum actual	142.00%
Performance Share | W T M Incentive Plan | Range Of Performance Cycle From 2012 To 2014 [Member]
Accrued Expense
Percentage of target payout - minimum actual			88.00%
Percentage of target payout - maximum actual			131.50%
White Mountains | Performance Share | W T M Incentive Plan
Target Performance Share Activity
Beginning of period (in shares)	96,211	113,198	113,198
Shares paid or expired (in shares)	0	(34,001)
New grants (in shares)	16,215	29,078
Assumed forfeitures and cancellations	1,186	123
Ending of period (in shares)	111,240	108,398	96,211
Accrued Expense
Accrued expense at the beginning of period	$ 58.2	$ 44.4	$ 44.4
Payments and deferrals	0	(24.9)
Assumed forfeitures and cancellations	0.6	0.5
Expense recognized	14.2	5.7
Accrued expense at the end of the period	$ 71.8	$ 25.7	$ 58.2
Vesting Period	3 years
Additional compensation cost that would be recognized if all outstanding performance shares vested	$ 35.2
Sirius Group | Performance Share | W T M Incentive Plan
Target Performance Share Activity
Ending of period (in shares)	7,998

Employee Share-Based Incentiv93

Employee Share-Based Incentive Compensation Plans (WTM - Performance Shares Granted Under the WTM Incentive Plan) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Share-based compensation arrangement by share-based payment award
Total Accrued Expense	$ 114.2	$ 141.7
White Mountains | Performance Share | W T M Incentive Plan
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	114,093
Accrued Expense	$ 73.6
Target Performance Shares Outstanding, Assumed forfeitures	(2,853)
Accrued Expense, Assumed forfeitures	(1.8)
Total Target Performance Shares Outstanding	111,240	96,211	108,398	113,198
Total Accrued Expense	$ 71.8	$ 58.2	$ 25.7	$ 44.4
White Mountains | Performance Share | W T M Incentive Plan | Performance Cycle 2016 to 2018
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	16,215
Accrued Expense	$ 1
White Mountains | Performance Share | W T M Incentive Plan | Performance Cycle 2015 to 2017
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	29,428
Accrued Expense	$ 12.8
White Mountains | Performance Share | W T M Incentive Plan | Performance Cycle 2014 to 2016
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	32,157
Accrued Expense	$ 18.7
White Mountains | Performance Share | W T M Incentive Plan | Performance Cycle 2013 to 2015
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	36,293
Accrued Expense	$ 41.1

Employee Share-Based Incentiv94

Employee Share-Based Incentive Compensation Plans (WTM - Restricted Shares) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Share-based compensation arrangement by share-based payment award
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 7.3
White Mountains | W T M Incentive Plan | Restricted Share Cliff Vesting in January 2019 [Member]
Target Restricted Share Activity
Issued (in shares)	21,215
White Mountains | W T M Incentive Plan | Restricted Share Cliff Vesting in January 2018
Target Restricted Share Activity
Issued (in shares)		22,890
White Mountains | W T M Incentive Plan | Restricted Stock
Target Restricted Share Activity
Beginning of period (in shares)	70,675	83,314
Issued (in shares)	21,215	22,890
Vested (in shares)	(24,620)	(35,079)
Assumed forfeitures and cancellations	(800)	0
Ending of period (in shares)	66,470	71,125
Unamortized grant date fair value
Unamortized grant date fair value, beginning balance	$ 15.7	$ 14.3
Issued	16.3	15.2
Assumed forfeitures and cancellations	0.2	0
Expense recognized	(3)	(3)
Unamortized grant date fair value, ending balance	$ 29.2	$ 26.5
Sirius Group | W T M Incentive Plan | Restricted Stock
Target Restricted Share Activity
Ending of period (in shares)	2,512	3,572

Employee Share-Based Incentiv95

Employee Share-Based Incentive Compensation Plans (OneBeason - Peformance Shares) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Share-based compensation arrangement by share-based payment award
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 7.3
Expense Amortized
Accrued expense at the beginning of period	141.7
Accrued expense at the end of the period	$ 114.2		$ 141.7
OneBeacon [Member] | Performance Share | One Beacon Long Term Incentive Plan
Share-based compensation arrangement by share-based payment award
Vesting Period		3 years
OneBeacon [Member] | One Beacon Long Term Incentive Plan | Performance Cycle 2013 to 2015
Expense Amortized
Percentage of target payout - minimum actual	24.30%
OneBeacon [Member] | One Beacon Long Term Incentive Plan | Range Of Performance Cycle From 2012 To 2014 [Member]
Expense Amortized
Percentage of target payout - minimum actual		45.70%
OneBeacon [Member] | One Beacon Long Term Incentive Plan | Performance Share
Target Performance Shares Outstanding
Beginning of period (in shares)	449,435	517,470	517,470
Shares paid or expired (in shares)	(167,300)	(181,290)
New grants (in shares)	163,150	154,887
Assumed forfeitures and cancellations	(4,079)	(28,920)
Ending of period (in shares)	441,206	462,147	449,435
Expense Amortized
Accrued expense at the beginning of period	$ 1.4	$ 3.4	$ 3.4
Payments and deferrals	(0.7)	(1.5)
Assumed forfeitures and cancellations	0	0
Expense recognized	0.4	0.2
Accrued expense at the end of the period	1.1	$ 2.1	$ 1.4
Additional compensation cost that would be recognized if all outstanding performance shares vested	$ 3.1

Employee Share-Based Incentiv96

Employee Share-Based Incentive Compensation Plans (OneBeacon - Performance Shares Outstanding) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Share-based compensation arrangement by share-based payment award
Accrued incentive compensation	$ 114.2	$ 141.7
OneBeacon [Member] | Performance Share | One Beacon Long Term Incentive Plan
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	452,519
Incentive Compensation Payable before Forfeitures	$ 1.1
Target Performance Shares Outstanding, Assumed forfeitures	(11,313)
Accrued Expense, Assumed forfeitures	0
Total Target Performance Shares Outstanding	441,206	449,435	462,147	517,470
Accrued incentive compensation	$ 1.1	$ 1.4	$ 2.1	$ 3.4
OneBeacon [Member] | Performance Share | One Beacon Long Term Incentive Plan | Performance Cycle 2016 to 2018
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	163,150
Incentive Compensation Payable before Forfeitures	$ 0.1
OneBeacon [Member] | Performance Share | One Beacon Long Term Incentive Plan | Performance Cycle 2015 to 2017
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	146,659
Incentive Compensation Payable before Forfeitures	$ 0.8
OneBeacon [Member] | Performance Share | One Beacon Long Term Incentive Plan | Performance Cycle 2014 to 2016
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	142,710
Incentive Compensation Payable before Forfeitures	$ 0.2

Employee Share-Based Incentiv97

Employee Share-Based Incentive Compensation Plans (OneBeacon - Restricted Shares) (Details) $ in Millions	1 Months Ended	3 Months Ended
	May. 31, 2011shares	Mar. 31, 2016USD ($)shares	Mar. 31, 2015USD ($)shares	May. 25, 2011Installment
Share-based compensation arrangement by share-based payment award
Equity in earnings of unconsolidated affiliates, net of tax | $		$ 0	$ 7.3
OneBeacon [Member] | One Beacon Long Term Incentive Plan | Restricted Stock
Target Restricted Share Activity
Beginning of period (in shares)		382,722	612,500
Issued (in shares)		170,650	75,950
Vested (in shares)		(157,500)	(296,000)
Assumed forfeitures and cancellations		0	(1,500)
Ending of period (in shares)		395,872	390,950
Unamortized grant date fair value
Unamortized grant date fair value, beginning balance | $		$ 2.5	$ 3.5
Issued | $		2.3	1.1
Assumed forfeitures and cancellations | $		0	0
Expense recognized | $		(0.5)	(0.6)
Unamortized grant date fair value, ending balance | $		$ 4.3	$ 4
OneBeacon [Member] | One Beacon Long Term Incentive Plan | Restricted Stock | Chief Executive Officer
Target Restricted Share Activity
Issued (in shares)	630,000
Unamortized grant date fair value
Number of Installments in which the Shares Vest | Installment				4
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Reduction in the next five years	35,000
OneBeacon [Member] | One Beacon Long Term Incentive Plan | Performance Share
Target Restricted Share Activity
Beginning of period (in shares)		449,435	517,470
Assumed forfeitures and cancellations		(4,079)	(28,920)
Ending of period (in shares)		441,206	462,147
Unamortized grant date fair value
Assumed forfeitures and cancellations | $		$ 0	$ 0
Expense recognized | $		(0.4)	$ (0.2)
Unamortized grant date fair value, ending balance | $		$ 3.1
OneBeacon [Member] | One Beacon Long Term Incentive Plan | Performance Share | Chief Executive Officer
Unamortized grant date fair value
Annual reduction in performance shares	35,000
Years Performance Shares will be Forfeited	5 years
OneBeacon [Member] | One Beacon Long Term Incentive Plan | Restricted Stock Units (RSUs) [Member]
Target Restricted Share Activity
Issued (in shares)		222,449	207,848
Ending of period (in shares)		198,928
Unamortized grant date fair value
Expense recognized | $		$ (0.4)	$ (0.1)
Restricted Share Vesting in February 2018 [Member] | OneBeacon [Member] | One Beacon Long Term Incentive Plan | Restricted Stock
Target Restricted Share Activity
Issued (in shares)		92,500
Restricted Share Vesting in February 2019 [Member] | OneBeacon [Member] | One Beacon Long Term Incentive Plan | Restricted Stock
Target Restricted Share Activity
Issued (in shares)		78,150

Employee Share-Based Incentiv98

Employee Share-Based Incentive Compensation Plans (OneBeacon - Restricted Stock Units) (Details) - Restricted Stock Units (RSUs) [Member] - OneBeacon [Member] - One Beacon Long Term Incentive Plan - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Share-based compensation arrangement by share-based payment award
Issued (in shares)	222,449	207,848
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	198,928
Expense recognized	$ 0.4	$ 0.1

Fair Value of Financial Instr99

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	$ 532.6	$ 440.5
OneBeacon [Member] | 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	272.9	272.9
OneBeacon [Member] | Book Value | 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	272.9	272.9
OneBeacon [Member] | Estimate of Fair Value Measurement [Member] | 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	278	276.4
Tranzact [Member] | Tranzact Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Long-term Line of Credit	94.1	104.7
Tranzact [Member] | Book Value | Tranzact Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	92.4	102.9
Tranzact [Member] | Estimate of Fair Value Measurement [Member] | Tranzact Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	92.8	102.8
MediaAlpha [Member] | MediaAlpha Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	2.5
Long-term Line of Credit	17.5	15
MediaAlpha [Member] | Book Value | MediaAlpha Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	17.2	14.7
MediaAlpha [Member] | Estimate of Fair Value Measurement [Member] | MediaAlpha Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	$ 15.1	$ 15

Discontinued Operations (Detail

Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended	54 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Mar. 31, 2015	Jun. 30, 2014	Sep. 30, 2015	Mar. 31, 2016	Dec. 31, 2015
Discontinued Operations [Line Items}
Payments to Acquire Other Investments		$ 10.9	$ 6.5
Investments		3,639.7				$ 3,639.7	$ 4,280.7
Net realized and unrealized investment gains		29.5	25
Net gain on sale of discontinued operations		0	8
Net (loss) income from discontinued operations, net of tax		(0.9)	65.8
Net Realized and Unrealized Gain (Loss) on Trading Securities		29.5	25
Sirius Group
Discontinued Operations [Line Items}
Proceeds from Divestiture of Interest in Subsidiaries and Affiliates	$ 2,600
Payments to Acquire Other Investments	$ (161.8)
Investments		161.8				161.8	686.2
Net realized and unrealized investment gains		4.1	0.3
Symetra | Sirius Group
Discontinued Operations [Line Items}
Investments							$ 528.6
Discontinued Operations [Member]
Discontinued Operations [Line Items}
Net realized and unrealized investment gains		(8.8)	78.4
Net loss from discontinued operations, net of tax		(0.9)	73.8
Net gain on sale of discontinued operations		(0.9)	65.9	$ 2.7
Discontinued Operations [Member] | Sirius Group
Discontinued Operations [Line Items}
Net realized and unrealized investment gains		(8.8)	78.4
Net loss from discontinued operations, net of tax		(0.9)	65.9
Net gain on sale of discontinued operations		(0.9)	65.9
Discontinued Operations [Member] | OneBeacon Runoff [Member]
Discontinued Operations [Line Items}
Net loss from discontinued operations, net of tax			(0.1)
Net gain on sale of discontinued operations		0	(0.1)
Discontinued Operations [Member] | Esurance
Discontinued Operations [Line Items}
Net gain on sale of discontinued operations		$ 0	$ 8		$ 10.3	$ 28.3

Discontinued Operations - Finan

Discontinued Operations - Financial Statement Disclosures (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended	54 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Jun. 30, 2014	Sep. 30, 2015	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disposal Group, Including Discontinued Operation, Assets [Abstract]
Fixed maturity investments, at fair value	$ 2,613.2				$ 2,613.2	$ 2,639.7
Short-term	261.7				261.7	211.3
Common equities	443				443	1,113.9
Other	321.8				321.8	315.8
Total investments	3,639.7				3,639.7	4,280.7
Cash	178.8				178.8	179.3
Reinsurance recoverable on unpaid losses	150.9				150.9	186.5
Reinsurance recoverable on paid losses	16.6				16.6	7.5
Insurance premiums receivable	234.3				234.3	223.3
Deferred acquisition costs	109.8				109.8	107.6
Deferred tax asset	133.6				133.6	112.8
Ceded unearned insurance premiums	36.3				36.3	29.5
Accounts receivable on unsettled investment sales	4.5				4.5	41.9
Goodwill and intangible assets	371.5				371.5	375.7
Other assets	286.9				286.9	316.8
Assets held for sale	5,215.5				5,215.5	4,407
Loss and loss adjustment expense reserves	1,349.6	$ 1,310.6			1,349.6	1,395.8	$ 1,350
Unearned insurance premiums	626.5				626.5	612.6
Debt	532.6				532.6	440.5
Accrued incentive compensation	114.2				114.2	141.7
Ceded reinsurance payable	31.8				31.8	30.5
Funds held under insurance contracts	134.9				134.9	137.8
Accounts payable on unsettled investment purchases	6.9				6.9	0
Other liabilities	229.8				229.8	264.7
Total liabilities held for sale	3,121.1				3,121.1	2,884
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Earned insurance premiums	282.1	289.3
Net investment income	17.9	12.6
Net realized and unrealized investment gains	29.5	25
Other revenue	97.6	64.9
Total revenues	427.1	391.8
Loss and loss adjustment expenses	161.1	167.9
Insurance and Reinsurance Acquisition Expenses	52.7	53
Other Underwriting Expense	55.4	56
General and administrative expenses	140.5	110.1
Interest expense	5.9	4.3
Total expenses	415.6	391.3
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	(0.9)	65.8
Net gain on sale of discontinued operations	0	8
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	0.1	0
Comprehensive (loss) income	50.3	25.6
Net Cash Provided by (Used in) Discontinued Operations [Abstract]
Net change in cash during the period	0	7.9
Cash balances at beginning of period	173.5	238		$ 238
Cash balances at end of period	170.4	180.3			170.4
Net income tax refund from national governments	(13.5)	8
Sirius Group
Disposal Group, Including Discontinued Operation, Assets [Abstract]
Total investments	161.8				161.8	686.2
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net realized and unrealized investment gains	4.1	0.3
Discontinued Operations [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Earned insurance premiums	202.4	205
Net investment income	12.2	9
Net realized and unrealized investment gains	(8.8)	78.4
Other revenue	(4.1)	(27.4)
Total revenues	201.7	265
Loss and loss adjustment expenses	113.7	97.5
Insurance and Reinsurance Acquisition Expenses	48.4	42.6
Other Underwriting Expense	26.7	25.5
General and administrative expenses	8.1	6.3
Interest expense	6.6	6.8
Total expenses	203.5	178.7
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	(1.8)	86.3
Discontinued Operation, Tax Effect of Discontinued Operation	0.9	(20.4)
Net gain on sale of discontinued operations	(0.9)	65.9	$ 2.7
Net loss from discontinued operations, net of tax	(0.9)	73.8
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	37.2	(87.6)
Comprehensive (loss) income	36.3	(13.8)
Net Cash Provided by (Used in) Discontinued Operations [Abstract]
Net cash used for operations - discontinued operations	(50.7)	(14.3)
Net cash (used for) provided from investing activities - discontinued operations	35	36
Net cash provided from financing activities - discontinued operations	2.4	1.8
Effect of exchange rate changes on cash	4.2	(8.5)
Net change in cash during the period	(9.1)	15
Cash balances at beginning of period	143.9	111.5		111.5
Cash balances at end of period	134.8	126.5			134.8
Interest paid	0	(12.8)
Net income tax refund from national governments	(36.4)	(7)
Discontinued Operations [Member] | Discontinued Operations, Held-for-sale [Member]
Disposal Group, Including Discontinued Operation, Assets [Abstract]
Fixed maturity investments, at fair value	2,758.3				2,758.3	2,374
Short-term	534.5				534.5	352
Common equities	214.3				214.3	174.4
Other	61.3				61.3	72.2
Total investments	3,568.4				3,568.4	2,972.6
Cash	134.8				134.8	143.9
Reinsurance recoverable on unpaid losses	286.2				286.2	283.1
Reinsurance recoverable on paid losses	11.1				11.1	10.2
Insurance premiums receivable	483.3				483.3	323.6
Deferred acquisition costs	91.6				91.6	74.6
Deferred tax asset	291.2				291.2	303.1
Ceded unearned insurance premiums	134.7				134.7	87.7
Goodwill and intangible assets	10.2				10.2	10.2
Other assets	194.2				194.2	169
Assets held for sale	5,215.5				5,215.5	4,407
Loss and loss adjustment expense reserves	1,649.5				1,649.5	1,644.4
Unearned insurance premiums	501.3				501.3	342.2
Debt	403.6				403.6	403.5
Deferred tax liability	278.5				278.5	263.6
Accrued incentive compensation	43.1				43.1	63.2
Ceded reinsurance payable	132.4				132.4	67.1
Funds held under insurance contracts	57				57	52.9
Other liabilities	50.3				50.3	47.1
Total liabilities held for sale	3,121.1				3,121.1	2,884
Discontinued Operations [Member] | Sirius Group
Disposal Group, Including Discontinued Operation, Assets [Abstract]
Accounts receivable on unsettled investment sales	9.8				9.8	29
Accounts payable on unsettled investment purchases	5.4				5.4	0
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Earned insurance premiums	202.4	205
Net investment income	12.2	9
Net realized and unrealized investment gains	(8.8)	78.4
Other revenue	(4.1)	(27.4)
Total revenues	201.7	265
Loss and loss adjustment expenses	113.7	97.5
Insurance and Reinsurance Acquisition Expenses	48.4	42.6
Other Underwriting Expense	26.7	25.5
General and administrative expenses	8.1	6.3
Interest expense	6.6	6.8
Total expenses	203.5	178.7
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	(1.8)	86.3
Discontinued Operation, Tax Effect of Discontinued Operation	0.9	(20.4)
Net gain on sale of discontinued operations	(0.9)	65.9
Net loss from discontinued operations, net of tax	(0.9)	65.9
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	37.2	(87.6)
Comprehensive (loss) income	36.3	(21.7)
Net Cash Provided by (Used in) Discontinued Operations [Abstract]
Net Assets	2,094.4				2,094.4	$ 1,523
Discontinued Operations [Member] | Other Discontinued Operations [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Earned insurance premiums	0	0
Net investment income	0	0
Net realized and unrealized investment gains	0	0
Other revenue	0	0
Total revenues	0	0
Loss and loss adjustment expenses	0	0
Insurance and Reinsurance Acquisition Expenses	0	0
Other Underwriting Expense	0	0
General and administrative expenses	0	0
Interest expense	0	0
Total expenses	0	0
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	0	0
Discontinued Operation, Tax Effect of Discontinued Operation	0	0
Net gain on sale of discontinued operations	0	0
Net loss from discontinued operations, net of tax	0	7.9
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	0	0
Comprehensive (loss) income	0	7.9
Discontinued Operations [Member] | OneBeacon Runoff [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations	0	(0.1)
Net loss from discontinued operations, net of tax		(0.1)
Discontinued Operations [Member] | Esurance
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations	$ 0	$ 8		$ 10.3	$ 28.3

Discontinued Operations - EPS (

Discontinued Operations - EPS (Details) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Jun. 30, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 7,300,000
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	882	125,000
Incremental Dilutive Effect per Share of Share-based Payment Arrangements	$ 0.01
Income (Loss) Allocated to Participating Unvested Restricted Common Shares	$ 100,000	$ 100,000
Net Income (Loss) Available to Common Stockholders, Basic	$ 13,000,000	$ 84,300,000
Total average common shares outstanding during the period	5,539,600	5,978,400
Average unvested restricted common shares	(54,000)	(58,800)
Basic earnings per share denominator	5,485,600	5,919,600
Average outstanding dilutive options to acquire common shares	5,540,500	5,978,400
Diluted earnings (loss) per share denominator	5,486,500	5,919,600
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements			125,000
Net loss from discontinued operations, net of tax	$ (900,000)	$ 73,800,000
Income (Loss) Allocated to Participating Unvested Restricted Common Shares	0	700,000
Net Income (Loss) Available to Common Stockholders, Basic	$ (900,000)	$ 73,100,000
Total average common shares outstanding during the period	5,540,500	5,978,400
Average unvested restricted common shares	(54,000)	(58,800)
Basic earnings per share denominator	5,485,600	5,919,600
Average outstanding dilutive options to acquire common shares	0	0
Diluted earnings (loss) per share denominator	5,486,500	5,919,600
Earnings Per Share, Basic and Diluted	$ (0.17)	$ 12.33
Common Stock [Member] | Symetra
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax		$ 7,200,000
Amortization of common share basis difference | Common Stock [Member] | Symetra
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax	$ 2,015	$ 700,000
Employee Stock Option [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	125,000

Discontinued Operations - Fair

Discontinued Operations - Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	$ 532.6	$ 440.5
Estimate of Fair Value Measurement [Member] | SIG Senior Notes | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	409	410
Estimate of Fair Value Measurement [Member] | SIG Preference Shares | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	247.5	255
Book Value | SIG Senior Notes | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	399.9	399.8
Book Value | SIG Preference Shares | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	$ 250	$ 250

Discontinued Operations - Inter

Discontinued Operations - Interest Rate Cap (Details) $ in Millions	1 Months Ended		3 Months Ended			12 Months Ended
	Jul. 31, 2013USD ($)shares	May. 31, 2007	Mar. 31, 2016USD ($)Rating	Mar. 31, 2015USD ($)	Sep. 30, 2013	Dec. 31, 2015USD ($)
Preferred Stock [Member] | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Preferred Stock, Dividend Rate, Percentage		7.506%
Interest Rate Cap [Member] | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
S and P Credit Ratings | Rating			21
Derivative collateral right to reclaim			$ 1.1
Years of interest rate cap					5 years
Derivative, Cap Interest Rate	8.30%
Derivative, Cost of Hedge	$ 9.9
Beginning of period			1.9	$ 4.1		$ 4.1
Realized and unrealized gains (losses)			(0.8)	(1)
End of period			1.1	$ 3.1		$ 1.9
Interest Rate Cap [Member] | Preferred Stock [Member] | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale of Stock, Number of Shares Issued in Transaction | shares	250,000,000
Sirius Group Ltd [Member] | Preferred Stock [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Term of LIBOR loan		3 months
Basis points		3.20%
Sirius Group Ltd [Member] | Interest Rate Cap [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Basis points	3.95%
Barclays [Member] | Standard & Poor's, A Rating [Member] | Interest Rate Cap [Member] | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Derivative collateral right to reclaim			0.7
Nordea Bank Finland [Member] | Standard & Poor's, AA- Rating [Member] | Interest Rate Cap [Member] | Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Derivative collateral right to reclaim			$ 0.4

Contingencies (Details)

Contingencies (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended	54 Months Ended
	Jun. 30, 2007	Mar. 31, 2016	Mar. 31, 2015	Jun. 30, 2014	Sep. 30, 2015	Mar. 31, 2016	Oct. 07, 2011
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		$ 0	$ 8
Esurance
Loss Contingencies [Line Items]
Percentage of fluctuation in loss reserves of transferred subsidiaries retained							90.00%
Tribune Company Litigation | Pending Litigation | OneBeacon [Member]
Loss Contingencies [Line Items]
Proceeds from Sale, Maturity and Collection of Investments	$ 32
Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		(0.9)	65.9	$ 2.7
Esurance | Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		0	8		$ 10.3	$ 28.3
OneBeacon Runoff [Member] | Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		0	(0.1)
Sirius Group | Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		$ (0.9)	$ 65.9

OneBeacon Pension Plan (Details

OneBeacon Pension Plan (Details) - Pension Plan [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2016
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		$ 55.4
Defined Benefit Pension Plan Liabilities, Current	$ 0.3

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Mar. 31, 2015
Subsequent Event [Line Items]
Other Underwriting Expense		$ 55.4	$ 56
Payments to Acquire Other Investments		10.9	$ 6.5
Subsequent Event [Member]
Subsequent Event [Line Items]
Proceeds from Divestiture of Interest in Subsidiaries and Affiliates	$ 2,600
Payments to Acquire Other Investments	(161.8)
Stock Repurchased and Retired During Period, Value	$ 287
Treasury Stock Acquired, Average Cost Per Share	$ 807
UNITED STATES
Subsequent Event [Line Items]
Stop Loss Limitation		45
Industry Loss Trigger on Industry Loss Warranty		15,000
UNITED STATES | Combination One [Member]
Subsequent Event [Line Items]
Stop Loss Limitation		75
Industry Loss Trigger on Industry Loss Warranty		40,000
UNITED STATES | Combination Two [Member]
Subsequent Event [Line Items]
Stop Loss Limitation		22.5
Industry Loss Trigger on Industry Loss Warranty		50,000
JAPAN
Subsequent Event [Line Items]
Stop Loss Limitation		25
Industry Loss Trigger on Industry Loss Warranty		$ 12,500
Common Stock [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Stock Repurchased and Retired During Period, Shares	356,423
Franklin Mutual Advisers [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Stock Repurchased and Retired During Period, Shares	325,000
Treasury Stock Acquired, Average Cost Per Share	$ 807