White Mountains Insurance (WTM) 10-Q 3 Aug 16 2016 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2016	Jul. 31, 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	Jun. 30, 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		4,930,938
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q2

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Assets
Fixed maturity investments, at fair value	$ 4,362.8	$ 2,630.2
Short-term investments, at amortized cost (which approximates fair value)	421.8	211.2
Common equity securities, at fair value	407.5	1,113.9
Other long-term investments	329.2	315.8
Total investments	5,521.3	4,271.1
Cash	135	173
Reinsurance recoverable on unpaid losses	162.8	186
Reinsurance recoverable on paid losses	20.7	7.5
Insurance premiums receivable	240.4	220.3
Deferred acquisition costs	113.9	107.6
Deferred tax asset	122.2	112.8
Ceded unearned insurance premiums	34.5	29.5
Accrued investment income	16	13.9
Accounts receivable on unsettled investment sales	21.5	41.9
Goodwill and intangible assets	53.3	55.4
Other assets	239.4	273.2
Assets held for sale	384.6	4,790.4
Total assets	7,065.6	10,282.6
Liabilities
Loss and loss adjustment expense reserves	1,376.6	1,389.8
Unearned insurance premiums	619.7	610.5
Debt	289.8	337.6
Accrued incentive compensation	106.3	140.7
Ceded reinsurance payable	23.9	29.9
Funds held under insurance contracts	140.9	137.8
Accounts payable on unsettled investment purchases	69.9	0
Other liabilities	188.5	199.9
Total liabilities held for sale	150.6	3,068.4
Total liabilities	2,966.2	5,914.6
White Mountains’s common shareholders’ equity
White Mountains’ common shares	5	5.6
Paid-in surplus	868.1	972.6
Retained earnings	3,006.6	3,084.9
Accumulated other comprehensive loss, after tax:
Net unrealized foreign currency translation losses	(0.7)	(145.6)
Pension liability and other	(3.8)	(4.3)
Total White Mountains’s common shareholders’ equity	3,875.2	3,913.2
Non-controlling interests
Non-controlling interests	224.2	454.8
Total equity	4,099.4	4,368
Total liabilities and equity	7,065.6	10,282.6
OneBeacon [Member]
Non-controlling interests
Non-controlling interests	$ 244.8	$ 245.6

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Cash	$ 0	$ 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	4,963,921	5,623,735
Common shares, outstanding shares	4,963,921	5,623,735

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE (LOSS) INCOME - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenues:
Earned insurance premiums	$ 274.7	$ 321.8	$ 556.8	$ 611.1
Net investment income	19.2	13.2	37.1	25.8
Net realized and unrealized investment gains (losses)	28.1	(15)	57.6	10
Other revenue	36.2	48.7	76	76.1
Total revenues	358.2	368.7	727.5	723
Expenses:
Loss and loss adjustment expenses	182	196.2	343.1	364.1
Insurance and Reinsurance Acquisition Expenses	50.1	57.8	102.8	110.8
Other Underwriting Expense	51	53	106.4	109
General and administrative expenses	73.1	63.4	160.2	134.3
Interest expense	4.1	3.4	8.6	6.9
Total expenses	360.3	373.8	721.1	725.1
Pre-tax (loss) income from continuing operations	(2.1)	(5.1)	6.4	(2.1)
Income tax benefit (expense)	6	2.2	15.7	(2.4)
Net income (loss) from continuing operations	3.9	(2.9)	22.1	(4.5)
Net gain on sale of discontinued operations	366.6	(0.1)	366.6	7.9
Net (loss) income from discontinued operations, net of tax	(8)	(0.4)	(6.9)	62.9
Income (loss) before equity in earnings of unconsolidated affiliates	362.5	(3.4)	381.8	66.3
Equity in earnings of unconsolidated affiliates, net of tax	0	6.8	0	14.1
Net income	362.5	3.4	381.8	80.4
Net (income) loss attributable to non-controlling interests	(21.4)	0.9	(27.7)	8.2
Net income attributable to White Mountains’s common shareholders	341.1	4.3	354.1	88.6
Other comprehensive (loss) income, net of tax:
Change in equity in net unrealized gains from investments in Symetra common shares, net of tax	0	(61.8)	0	(32.9)
Change in foreign currency translation, pension liability and other, net of tax	0	0.2	0.1	0.2
Comprehensive income (loss)	449.2	(13.3)	499.5	12.3
Other comprehensive (loss) income attributable to non-controlling interests	0	0	0	0
Comprehensive income (loss) attributable to White Mountains’s common shareholders	$ 449.2	$ (13.3)	$ 499.5	$ 12.3
Basic income per share
Continuing operations	$ (3.44)	$ 0.80	$ (1.07)	$ 2.96
Discontinued operations	70.37	(0.08)	67.64	11.84
Total consolidated operations	66.93	0.72	66.57	14.80
Diluted income per share
Continuing operations	(3.43)	0.80	(1.06)	2.96
Discontinued operations	70.22	(0.08)	67.56	11.84
Total consolidated operations	66.79	0.72	66.50	14.80
Dividends declared per White Mountains’s common share	$ 0	$ 0	$ 1	$ 1
Sirius Group
Revenues:
Net realized and unrealized investment gains (losses)	$ 0.4	$ 2.4	$ 3.7	$ 2.7
Expenses:
Net gain on sale of discontinued operations			366.6
Other comprehensive (loss) income, net of tax:
Accumulated Other Comprehensive Income Loss Net Of Tax Other Period Increase Decrease	(5.2)	44	32	(43.6)
Sale of Sirius Group [Member]
Other comprehensive (loss) income, net of tax:
Accumulated Other Comprehensive Income Loss Net Of Tax Other Period Increase Decrease	$ 113.3	$ 0	$ 113.3	$ 0

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	Prospector Turtle FundCommon shares and paid-in surplus	Prospector Turtle FundRetained earnings	Prospector Turtle FundAOCI, after tax	Prospector Turtle FundTotal	Prospector Turtle FundNon-controlling interest	Prospector Turtle FundTotal Equity	Sale of Sirius Group [Member]Common shares and paid-in surplus	Sale of Sirius Group [Member]Retained earnings	Sale of Sirius Group [Member]AOCI, after tax	Sale of Sirius Group [Member]Total	Sale of Sirius Group [Member]Non-controlling interest	Sale of Sirius Group [Member]Total Equity	Sale of Sirius Group [Member]Foreign Currency Gain (Loss)Common shares and paid-in surplus	Sale of Sirius Group [Member]Foreign Currency Gain (Loss)Retained earnings	Sale of Sirius Group [Member]Foreign Currency Gain (Loss)AOCI, after tax	Sale of Sirius Group [Member]Foreign Currency Gain (Loss)Total	Sale of Sirius Group [Member]Foreign Currency Gain (Loss)Non-controlling interest	Sale of Sirius Group [Member]Foreign Currency Gain (Loss)Total 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	$ 80.4	0	88.6	0	88.6	(8.2)	80.4
Net change in unrealized gains (losses) from investments in unconsolidated affiliates	(32.9)	0	0	(32.9)	(32.9)	0	(32.9)
Net change in foreign currency translation	0.2							$ 0	$ 0	$ (43.8)	$ (43.8)	$ (0.1)	$ (43.9)
Net change in pension liability and other accumulated comprehensive items														$ 0	$ 0	$ 0.4	$ 0.4	$ 0.1	$ 0.5
Total comprehensive income (loss)	12.3	0	88.6	(76.3)	12.3	(8.2)	4.1
Dividends declared on common shares		0	(6)	0	(6)	0	(6)
Dividends to non-controlling interests	1	0	0	0	0	(21.9)	(21.9)
Repurchases and retirements of common shares		(8.8)	(23.9)	0	(32.7)	0	(32.7)
Issuances of common shares		0.9	0	0	0.9	0	0.9
Acquisition from non-controlling interests		(2.2)	0	0	(2.2)	(2.7)	(4.9)													$ 0	$ 0	$ 0	$ 0	$ (31.5)	$ (31.5)
Net contributions from non-controlling interests		0	0	0	0	5.8	5.8
Amortization of restricted share awards		6.6	0	0	6.6	(0.3)	6.3
Balances at Jun. 30, 2015		1,031.2	3,069.2	(125.8)	3,974.6	483.9	4,458.5
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	381.8	0	354.1	0	354.1	27.7	381.8
Net change in unrealized gains (losses) from investments in unconsolidated affiliates	0
Net change in foreign currency translation	0.1							$ 0	$ 0	$ 32	$ 32	$ 0	$ 32																			$ 0	$ 0	$ 113.3	$ 113.3	$ 0	$ 113.3
Net change in pension liability and other accumulated comprehensive items														$ 0	$ 0	$ 0.1	$ 0.1	$ 0	$ 0.1
Total comprehensive income (loss)	499.5	0	354.1	145.4	499.5	27.7	527.2
Dividends declared on common shares		0	(5.4)	0	(5.4)	0	(5.4)
Dividends to non-controlling interests	0.7	0	0	0	0	(12.1)	(12.1)
Repurchases and retirements of common shares		(120.4)	(427)	0	(547.4)	0	(547.4)
Issuances of common shares		9.1	0	0	9.1	0	9.1
Noncontrolling Interest, Decrease from Deconsolidation																										$ 0	$ 0	$ 0	$ 0	$ 250	$ 250
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
Net contributions from non-controlling interests		0	0	0	0	11.9	11.9
Amortization of restricted share awards		8.9	0	0	8.9	0.4	9.3
Balances at Jun. 30, 2016	$ 4,099.4	$ 873.1	$ 3,006.6	$ (4.5)	$ 3,875.2	$ 224.2	$ 4,099.4

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Cash Reclassified from Assets Held-for-sale	$ 0.6	$ 2.7	$ 0.6	$ 2.7	$ 1.2	$ 2.1
Cash flows from operations:
Net income	362.5	3.4	381.8	80.4
Charges (credits) to reconcile net income to net cash used for operations:
Net realized and unrealized investment gains	(28.1)	15	(57.6)	(10)
Deferred income tax expense (benefit)			12.8	(6.3)
Net loss (income) from discontinued operations			6.9	(62.9)
Net gain on sale of discontinued operations	(366.6)	0.1	(366.6)	(7.9)
Net gain on sale of unconsolidated subsidiaries			0	(16.1)
Amortization and depreciation			22.5	20.9
Undistributed equity in earnings from unconsolidated affiliates, net of tax	0	(6.8)	0	(14.1)
Other operating items:
Net change in loss and loss adjustment expense reserves			(13.5)	7
Net change in reinsurance recoverable on paid and unpaid losses			10	5.8
Net change in unearned insurance premiums			8.9	39
Net change in deferred acquisition costs			(6.3)	(10)
Net change in funds held by ceding entities			0	(12.2)
Net change in ceded unearned premiums			(5)	(25.4)
Net change in funds held under insurance treaties			3.2	21.6
Net change in insurance premiums receivable			(19.5)	(52.5)
Net change in ceded reinsurance payable			(6.8)	34.6
Net change in restricted cash			5.8	2.8
Net change in other assets and liabilities, net			(120.7)	(17.5)
Net cash used for operations - continuing operations			(144.1)	(22.8)
Net cash used for operations			(187.2)	(35.7)
Cash flows from investing activities:
Net change in short-term investments			(207.7)	(49.7)
Sales of fixed maturity and convertible investments			1,453.5	680.8
Maturities, calls and paydowns of fixed maturity and convertible investments			316.5	136.7
Sales of common equity securities			851.3	306.8
Distributions and redemptions of other long-term investments			10.1	49.1
Sales of consolidated and unconsolidated subsidiaries, net of cash sold			2,248.5	24
Purchases of other long-term investments			(13.3)	(28.6)
Purchases of common equity securities			(141.4)	(275.1)
Purchases of fixed maturity and convertible investments			(3,467)	(953.6)
Purchases of consolidated and unconsolidated subsidiaries, net of cash acquired			(8.1)	(2.4)
Net change in unsettled investment purchases and sales			90.3	56.2
Net acquisitions of property and equipment			(3.7)	54.9
Net cash provided from investing activities - continuing operations			719.3	6.4
Net cash provided from investing activities			948.9	65.7
Cash flows from financing activities:
Draw down of debt and revolving line of credit			102.5	15
Repayment of debt and revolving line of credit			(150.5)	(15)
Proceeds from Issuance of Common Stock			3.7	0
Payments on capital lease obligation			(1)	(2.8)
Cash dividends paid to the Company’s common shareholders			(5.4)	(6)
Cash dividends paid to OneBeacon Ltd.’s non-controlling common shareholders			(9.5)	(9.9)
Common shares repurchased			(541.5)	(17.1)
OneBeacon Ltd. common shares repurchased and retired			(11.5)	(1.6)
Distribution to non-controlling interest shareholders			(0.7)	(1)
Contributions to discontinued operations			(3)	(6.1)
Acquisition of additional shares from non-controlling interest			0	(9.1)
Payments of contingent consideration related to purchases of consolidated subsidiaries			(7.8)	0
Capital contributions from BAM members			16.7	11.5
Net cash used for financing activities - continuing operations			(608)	(42.1)
Net cash used for financing activities			(599)	(44.1)
Effect of Exchange Rate on Cash and Cash Equivalents			0	0
Net change in cash during the period - continuing operations			(32.8)	(58.5)
Cash balances at beginning of period			167.2	232.9	232.9
Cash balances at end of period	135	173.8	135	173.8	167.2
Supplemental cash flows information:
Interest paid			(0.5)	(73.3)
Net income tax refund from national governments			13.5	7.5
Discontinued Operations [Member]
Charges (credits) to reconcile net income to net cash used for operations:
Net realized and unrealized investment gains	(7.3)	46.1	1.5	(32.3)
Net loss (income) from discontinued operations	9.1	0.9	7.9	(82.8)
Net gain on sale of discontinued operations	8	0.4	6.9	(62.9)
Other operating items:
Net cash used for operations - discontinued operations			(43.1)	(12.9)
Cash flows from investing activities:
Sales of common equity securities			(409.7)	7.3
Net change in cash during the period			195.5	42.3
Net cash provided from investing activities - discontinued operations			229.6	59.3
Cash flows from financing activities:
Net cash provided from (used for) financing activities - discontinued operations			9	(2)
Cash balances at beginning of period			148.9	114.5	114.5
Cash balances at end of period	$ 1.3	$ 156.8	1.3	156.8	$ 148.9
Supplemental cash flows information:
Net income tax refund from national governments			$ 31.8	$ 24.6

CONSOLIDATED STATEMENTS OF CAS7

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Cash and Cash Equivalents, at Carrying Value	$ 135	$ 173.8
Restricted cash balances	0	29
Effect of Exchange Rate on Cash and Cash Equivalents, Discontinued Operations	0	(2.1)
Discontinued Operations [Member]
Cash and Cash Equivalents, at Carrying Value	$ 1.3	$ 156.8

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 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 26 Reid 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 - “Significant Transactions” , 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” ). On June 9, 2016, White Mountains entered into an agreement to sell Tranzact Holdings, LLC (“Tranzact”) to an affiliate of Clayton, Dubilier & Rice, LLC, which was completed on July 21, 2016. Accordingly, for the quarter and six months ended June 30, 2016 , Sirius Group and Tranzact have been presented as discontinued operations in the statement of operations and comprehensive income. Prior year amounts have been reclassified to conform to the current period’s presentation. The assets and liabilities of Tranzact are classified as held for sale in the balance sheet as of June 30, 2016 and December 31, 2015. The assets and liabilities of Sirius Group are classified as held for sale in the balance sheet as of December 31, 2015. (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 June 30, 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 June 30, 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 completed its 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 QL Holdings, LLC (together with its subsidiaries “MediaAlpha”) and Wobi Insurance Agency Ltd. (“Wobi”). The Other Operations segment also includes Abiaka Holdings, LLC, 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. White Mountains holds 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 state 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 June 30, 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 June 30, 2016, the unamortized debt issuance costs included in debt is $2.0 million . Recently Issued Accounting Pronouncements Short-Duration Contracts In May 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. Credit Losses In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments (ASC 326), which establishes new guidance for the recognition of credit losses for financial assets measured at amortized cost. The new ASU, which applies to financial assets that have the contractual right to receive cash, including reinsurance receivables, requires reporting entities to estimate the credit losses expected over the life of a credit exposure using historical information, current information and reasonable and supportable forecasts that affect the collectability of the financial asset. ASU 2016-13 is effective for annual periods beginning after January 1, 2020, including interim periods. White Mountains is evaluating the expected impact of this new guidance. Stock Compensation In March 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 In February 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 In January 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 In May 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	6 Months Ended
	Jun. 30, 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. White Mountains recorded $366.6 million of gain from sale of Sirius Group in discontinued operations and $113.3 million in other comprehensive income from discontinued operations for a total increase to book value of $479.9 million in the second quarter of 2016. Through April 18, 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 do not include White Mountains’s investment in OneBeacon and certain other investments that were held in the Sirius Group legal entities as of December 31, 2015. The value of these investments, net of related tax effects, was approximately $ 686.2 million , of which $ 528.6 million was Symetra common shares, as of December 31, 2015. As part of the sale of Sirius Group, White Mountains purchased Ashmere Insurance Company (“Ashmere”), a subsidiary formerly owned by Sirius Group. Ashmere is currently under an agreement to be sold and the completion of the sale is pending regulatory approval. As of June 30, 2016, Ashmere's assets and liabilities are presented as held for sale. The transactions to purchase of the investments in OneBeacon and the other investments held by Sirius Group prior to the closing are presented in the statement of cash flows as net settlement of investment cash flows with discontinued operations. 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 contracts have expired. 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 $25.0 million $12.5 billion Symetra On February 1, 2016, White Mountains sold its investment in Symetra Financial Corporation (“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 White Mountains acquired 63.2% of Tranzact for a purchase price of $177.7 million in October 2014. Immediately following the closing, Tranzact completed a recapitalization that resulted in the return of $44.2 million to White Mountains. On June 9, 2016, White Mountains entered into an agreement to sell Tranzact to an affiliate of Clayton, Dubilier & Rice, LLC. As a result, Tranzact’s results are reported as discontinued operations and assets and liabilities held for sale within White Mountains’s GAAP financial statements. On July 21, 2016, White Mountains completed the sale of Tranzact and received net proceeds of $221.3 million . (See Note 17 - “Discontinued Operations”) . 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 80% 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. During the three and six months ended June 30, 2016, White Mountains purchased NIS 16.4 million (approximately $ 4.4 million based upon the foreign exchange spot rate at the dates of acquisition) of convertible preferred shares of Wobi, increasing its ownership share to 96.5% 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 . SSIE is a Florida-domiciled reciprocal insurance exchange providing private passenger auto insurance to the public safety community and their families. White Mountains invested $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 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. In response to the significant increases in both frequency and severity of accidents in the private passenger automobile insurance market in the State of Florida, SSIE voluntarily ceased writing new policies effective July 1, 2016 and will voluntarily cease renewing policies at a future date, subject to regulatory approval. As a result, in June 2016, White Mountains wrote down its investment in SSIE surplus notes to its estimated net realizable value of $1.0 million . White Mountains consolidates the issuer of the surplus notes, Star & Shield Insurance Exchange and, accordingly the impact of the write down is eliminated in pre-tax income. However, the write down resulted in a $ 20.0 million decrease to net income attributable to White Mountains's common shareholders and a corresponding increase to net income attributable to non-controlling interests. At June 30, 2016 and December 31, 2015 , consolidated amounts included total assets of $12.3 million and $14.2 million and total liabilities of $8.5 million and $30.3 million , respectively, of SSIE. For the three months ended June 30, 2016 and 2015, SSIE had pre-tax gain of $20.0 million and pre-tax loss of $0.8 million that were recorded in net gain (loss) attributable to non-controlling interests. For the six months ended June 30, 2016 and 2015, SSIE had pre-tax income of $19.9 million and pre-tax loss of $1.9 million that were recorded in net gain (loss) attributable to non-controlling interests. The decrease in total liabilities and increase in pre-tax income in the current year is due to the $ 20.0 million write down of the surplus notes at SSIE.

Loss and Loss Adjustment Expens

Loss and Loss Adjustment Expense Reserves	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2016 and 2015 : Three Months Ended Six Months Ended June 30, June 30, Millions 2016 2015 2016 2015 Gross beginning balance $ 1,343.8 $ 1,304.0 $ 1,389.8 $ 1,342.2 Less beginning reinsurance recoverable on unpaid losses (150.4 ) (141.6 ) (186.0 ) (161.6 ) Net loss and LAE reserves 1,193.4 1,162.4 1,203.8 1,180.6 SSIE reserves held for sale at beginning of the period (1) 5.3 6.5 5.5 7.7 Loss and LAE incurred relating to: Current year losses 166.7 196.5 327.9 366.3 Prior year losses 15.3 (.3 ) 15.2 (2.2 ) Total incurred losses and LAE 182.0 196.2 343.1 364.1 Loss and LAE paid relating to: Current year losses (38.1 ) (43.9 ) (61.2 ) (67.2 ) Prior year losses (123.5 ) (111.4 ) (272.1 ) (275.4 ) Total loss and LAE payments (161.6 ) (155.3 ) (333.3 ) (342.6 ) SSIE reserves held for sale at end of the period (1) (5.3 ) (6.1 ) (5.3 ) (6.1 ) Net ending balance 1,213.8 1,203.7 1,213.8 1,203.7 Plus ending reinsurance recoverable on unpaid losses 162.8 147.1 162.8 147.1 Gross ending balance $ 1,376.6 $ 1,350.8 $ 1,376.6 $ 1,350.8 (1) See Note 17 - “Discontinued Operations” . Loss and LAE incurred relating to prior year losses for the three and six months ended June 30, 2016 For the three and six months ended June 30, 2016 , White Mountains experienced net unfavorable loss reserve development of $15.3 million and $15.2 million . During both the three and six months ended June 30, 2016 , OneBeacon experienced net unfavorable loss reserve development of $15.4 million on prior accident year reserves. During both the three and six months ended June 30, 2016, the net unfavorable development was primarily related to OneBeacon's Healthcare business and Programs business, partially offset by favorable loss reserve development in its financial services, property, technology and accident businesses. During the second quarter of 2016, OneBeacon recognized $ 20.0 million of unfavorable loss reserve development and also increased the current accident year provision related to its Healthcare business. Paid and incurred activity in the second quarter for extended care facilities coverage within OneBeacon's Healthcare business increased above expectations and above what was experienced in the first quarter of 2016. Extended care facilities coverage provides liability insurance for assisted living, memory care and continuing care facilities, among others. In addition, there were two large claims from the managed care errors and omissions coverage within OneBeacon's Healthcare business that contributed to the adverse loss reserve development. For the three and six months ended June 30, 2016 , SSIE had net favorable loss reserve development of $0.1 million and $0.2 million . Loss and LAE incurred relating to prior year losses for the three and six months ended June 30, 2015 For the three and six months ended June 30, 2015 , White Mountains experienced net favorable loss reserve development of $0.3 million and $2.2 million . During the three months ended June 30, 2015, OneBeacon experienced no net loss and LAE reserve development on prior accident year reserves. For the six months ended June 30, 2015, OneBeacon had net favorable loss reserve development of $1.8 million . For the three and six months ended June 30, 2015 , SSIE had net favorable loss reserve development of $ 0.3 million and $ 0.4 million.

Third Party Reinsurance

Third Party Reinsurance	6 Months Ended
	Jun. 30, 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 June 30, 2016 , OneBeacon had $20.7 million and $162.8 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. Effective May 1, 2016, OneBeacon renewed its property catastrophe reinsurance program through April 30, 2017. The program provides coverage for OneBeacon's property business as well as certain acts of terrorism. Under the program, the first $ 20.0 million of losses resulting from any single catastrophe are retained, with 100.0% of the next $ 110.0 million of losses resulting from the catastrophe being reinsured. Any part of a catastrophe loss in excess of $ 130.0 million would be retained in full. In the event of a catastrophe, OneBeacon's property catastrophe reinsurance program is reinstated for the remainder of the original contract term by paying a reinstatement premium that is based on the percentage of coverage reinstated and the original property catastrophe coverage premium.

Investment Securities

Investment Securities	6 Months Ended
	Jun. 30, 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 fixed maturity investments are generally valued using industry standard pricing methodologies. 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 June 30, 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 and six months ended June 30, 2016 and 2015 consisted of the following: Three Months Ended Six Months Ended June 30, June 30, Millions 2016 2015 2016 2015 Investment income: Fixed maturity investments $ 17.9 $ 12.4 $ 32.5 $ 24.8 Short-term investments .5 .1 .6 .1 Common equity securities .9 2.1 2.0 4.3 Other long-term investments .6 .9 3.4 .9 Total investment income 19.9 15.5 38.5 30.1 Third-party investment expenses (.7 ) (2.3 ) (1.4 ) (4.3 ) Net investment income, pre-tax $ 19.2 $ 13.2 $ 37.1 $ 25.8 Net Realized and Unrealized Investment Gains (Losses) Net realized and unrealized investment gains (losses) consisted of the following: Three Months Ended Six Months Ended June 30, June 30, Millions 2016 2015 2016 2015 Net realized investment gains, pre-tax $ 2.7 $ 42.3 $ 259.5 $ 57.1 Net unrealized investment gains (losses), pre-tax 25.4 (57.3 ) (201.9 ) (47.1 ) Net realized and unrealized investment gains (losses), pre-tax 28.1 (15.0 ) 57.6 10.0 Income tax (expense) benefit attributable to net realized and unrealized investment gains (losses) (9.9 ) 4.5 (18.4 ) (2.6 ) Net realized and unrealized investment gains (losses), after tax $ 18.2 $ (10.5 ) $ 39.2 $ 7.4 Net realized investment gains (losses) Net realized investment gains (losses) for the three and six months ended June 30, 2016 and 2015 consisted of the following: Three Months Ended Three Months Ended June 30, 2016 June 30, 2015 Millions Net Net Total net realized Net Net Total net realized Fixed maturity investments $ 1.8 $ — $ 1.8 $ 1.6 $ — $ 1.6 Short-term investments .1 — .1 — — — Common equity securities 3.8 — 3.8 25.5 (.1 ) 25.4 Other long-term investments (3.0 ) — (3.0 ) 15.3 — 15.3 Net realized investment gains (losses), pre-tax 2.7 — 2.7 42.4 (.1 ) 42.3 Income tax expense attributable to net realized investment gains (losses) (.4 ) — (.4 ) (12.7 ) — (12.7 ) Net realized investment gains (losses), after tax $ 2.3 $ — $ 2.3 $ 29.7 $ (.1 ) $ 29.6 Six Months Ended Six Months Ended June 30, 2016 June 30, 2015 Millions Net Net Total net realized Net Net Total net realized Fixed maturity investments $ .7 $ — $ .7 $ 2.1 $ — $ 2.1 Short-term investments .2 — .2 — — — Common equity securities 261.4 — 261.4 47.5 .4 47.9 Other long-term investments (2.8 ) — (2.8 ) 7.1 — 7.1 Net realized investment gains, pre-tax 259.5 — 259.5 56.7 .4 57.1 Income tax expense attributable to net realized investment gains (43.3 ) — (43.3 ) (17.2 ) — (17.2 ) Net realized investment gains, after tax $ 216.2 $ — $ 216.2 $ 39.5 $ .4 $ 39.9 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 June 30, 2016 June 30, 2015 Millions Net unrealized gains (losses) Net losses Total net unrealized gains (losses) reflected in earnings Net unrealized losses Net Total net unrealized losses reflected in earnings Fixed maturity investments $ 20.7 $ — $ 20.7 $ (13.4 ) $ — $ (13.4 ) Short-term investments — — — — — — Common equity securities (10.6 ) — (10.6 ) (22.6 ) 1.6 (21.0 ) Other long-term investments 15.5 (.2 ) 15.3 (23.1 ) .2 (22.9 ) Net unrealized investment gains (losses), pre-tax 25.6 (.2 ) 25.4 (59.1 ) 1.8 (57.3 ) Income tax (expense) benefit (9.5 ) — (9.5 ) 17.3 (.1 ) 17.2 Net unrealized investment $ 16.1 $ (.2 ) $ 15.9 $ (41.8 ) $ 1.7 $ (40.1 ) Six Months Ended Six Months Ended June 30, 2016 June 30, 2015 Millions Net unrealized gains (losses) Net gains Total net unrealized gains (losses) reflected in earnings Net unrealized losses Net Total net unrealized losses reflected in earnings Fixed maturity investments $ 42.4 $ — $ 42.4 $ (2.0 ) $ — $ (2.0 ) Short-term investments — — — — — — Common equity securities (260.4 ) 2.4 (258.0 ) (25.3 ) (2.4 ) (27.7 ) Other long-term investments 13.5 .2 13.7 (16.6 ) (.8 ) (17.4 ) Net unrealized investment (losses) gains, pre-tax (204.5 ) 2.6 (201.9 ) (43.9 ) (3.2 ) (47.1 ) Income tax benefit (expense) 24.9 — 24.9 14.7 (.1 ) 14.6 Net unrealized investment $ (179.6 ) $ 2.6 $ (177.0 ) $ (29.2 ) $ (3.3 ) $ (32.5 ) 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 and six months ended June 30, 2016 and 2015 : Three Months Ended Six Months Ended June 30, June 30, Millions 2016 2015 2016 2015 Fixed maturity investments $ .8 $ (.2 ) $ 1.3 $ — Common equity securities — 4.7 — 2.9 Other long-term investments 11.8 (5.5 ) 12.9 .2 Total unrealized investment gains (losses), pre-tax - Level 3 investments $ 12.6 $ (1.0 ) $ 14.2 $ 3.1 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 June 30, 2016 and December 31, 2015 were as follows: June 30, 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 $ 261.2 $ .7 $ — $ — $ 261.9 Debt securities issued by corporations 1,046.9 19.3 (.1 ) — 1,066.1 Municipal obligations 294.8 8.2 (.1 ) — 302.9 Mortgage and asset-backed securities 2,646.8 10.4 (2.0 ) — 2,655.2 Foreign government, agency and provincial obligations 1.0 .2 — — 1.2 Preferred stocks 78.3 6.4 — — 84.7 Total fixed maturity investments $ 4,329.0 $ 45.2 $ (2.2 ) $ — $ 4,372.0 Less: fixed maturity investments reclassified to assets held for sale related to SSIE 9.2 Total fixed maturity investments $ 4,362.8 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 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 Less: fixed maturity investments reclassified to assets held for sale related to SSIE 9.5 Total fixed maturity investments $ 2,630.2 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 June 30, 2016 and December 31, 2015 were as follows: June 30, 2016 Millions Cost or amortized cost Gross unrealized gains Gross unrealized losses Net foreign Carrying value Common equity securities $ 374.1 $ 43.5 $ (10.1 ) $ — $ 407.5 Other long-term investments $ 305.0 $ 36.7 $ (10.3 ) $ (2.2 ) $ 329.2 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 June 30, 2016 and December 31, 2015 : Carrying Value at Millions June 30, 2016 December 31, 2015 Hedge funds and private equity funds, at fair value (1) $ 127.8 $ 127.8 Private equity securities and limited liability companies, at fair value (1) 84.3 82.1 Surplus notes investments, at fair value (1) 62.8 51.5 Private convertible preferred securities (1) 34.1 32.7 Tax advantaged federal affordable housing development fund (2) 13.4 14.7 Partnership investments accounted for under the equity method 3.5 3.8 Other 3.3 3.2 Total other-long term investments $ 329.2 $ 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 June 30, 2016 , White Mountains held investments in 5 hedge funds and 24 private equity funds. The largest investment in a single fund was $21.5 million as of June 30, 2016 . The following table summarizes investments in hedge funds and private equity funds by investment objective and sector as of June 30, 2016 and December 31, 2015 : June 30, 2016 December 31, 2015 Millions Fair Value Unfunded Commitments Fair Value Unfunded Commitments Hedge funds Long/short equity REIT $ 20.5 $ — $ 20.6 $ — Long/short banks and financial 13.6 — 12.8 — Other 3.5 — 3.6 — Total hedge funds 37.6 — 37.0 — Private equity funds Aerospace/Defense/Government 25.9 23.5 19.8 30.3 Manufacturing/Industrial 24.8 20.2 24.9 2.5 Energy infrastructure & services 19.1 3.2 20.7 3.4 Multi-sector 11.1 2.1 14.8 2.1 Private equity secondaries 3.8 2.1 4.4 2.1 Healthcare 3.5 .4 3.8 .4 Insurance 1.7 41.3 2.0 41.3 Real estate .3 .1 .4 .1 Direct lending/Mezzanine debt — 37.5 — — Total private equity funds 90.2 130.4 90.8 82.2 Total hedge funds and private equity funds included in other long-term investments $ 127.8 $ 130.4 $ 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 June 30, 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 14.6 — — 14.6 Semi-annual — 20.5 — 20.5 Annual — — 2.5 2.5 Total $ 14.6 $ 20.5 $ 2.5 $ 37.6 Certain of White Mountains’s investments in hedge funds 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 June 30, 2016 , the fair value of hedge funds in liquidation was $1.0 million . 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 June 30, 2016 . White Mountains has also submitted redemption requests for certain of its investments in active hedge funds. As of June 30, 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 June 30, 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 June 30, 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 $27.1 $3.5 $59.6 $— $90.2 OneBeacon Surplus Notes In the fourth quarter of 2014, in conjunction with OneBeacon's sale of its runoff business to an affiliate of Armour Group Holdings Limited (the "OneBeacon Runoff Transaction"), OneBeacon provided financing in the form of surplus notes with a par value of $101.0 million , which had a fair value of $62.8 million and $ 51.5 million as of June 30, 2016 and December 31, 2015, respectively. Subsequent to closing, the surplus notes are included in OneBeacon’s investment portfolio, classified within other long-term investments. The internal valuation model used to estimate the fair value is based on discounted expected cash flows. The estimated fair value of the surplus notes is sensitive to changes in U.S. treasury rates and public corporate 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 based on the financial performance of the Issuer relative to expectations, 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 six months ended June 30, 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 June 30, 2016 and December 31, 2015: Type of Surplus Note Total as of June 30, 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) 2.7 (8.4 ) (5.7 ) (15.1 ) Regulatory approval (2) (7.4 ) (12.5 ) (19.9 ) (24.2 ) Liquidity adjustment (3) (9.0 ) (3.6 ) (12.6 ) (10.2 ) Total adjustments (13.7 ) (24.5 ) (38.2 ) (49.5 ) Fair value (4) $ 44.2 $ 18.6 $ 62.8 $ 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 publicly traded debt 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. (4) The increase in the fair value of the surplus notes during the six months ended June 30, 2016 was driven primarily by the narrowing of non-investment grade credit spreads as well as the time value of money benefit generated by moving six months closer to modeled cash receipts, partially offset by the impact of an interest payment received in the first quarter of 2016. Fair value measurements as of June 30, 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 91% of its investment portfolio as of June 30, 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 methodologies and observable inputs such as benchmark yields, reported trades, broker-dealer quotes, issuer spreads, benchmark securities, bids, offers, credit ratings, 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 pricing methodologies, and review of the pricing services’ quality control processes and procedures on at least an annual basis, comparison of market prices to prices obtained from alternate 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 periodic and audited annual financial statements of hedge funds and private equity funds and discussing each fund’s pricing with the fund manager throughout the year. 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 June 30, 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 common 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 U.S. Intermediate Aggregate and S&P 500 indices. June 30, 2016 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 261.9 $ 252.3 $ 9.6 $ — Debt securities issued by corporations: Consumer 333.5 — 333.5 — Health Care 157.3 — 157.3 — Financials 154.8 — 154.8 — Industrial 139.0 — 139.0 — Utilities 94.3 — 94.3 — Energy 60.6 — 60.6 — Technology 57.3 — 57.3 — Communications 43.3 — 43.3 — Materials 26.0 — 26.0 — Total debt securities issued by corporations 1,066.1 — 1,066.1 — Mortgage and asset-backed securities 2,655.2 2,573.2 82.0 Municipal obligations 302.9 — 302.9 — Foreign government, agency and provincial obligations 1.2 .6 .6 — Preferred stocks 84.7 — 13.5 71.2 Total fixed maturity investments (4) 4,372.0 252.9 3,965.9 153.2 Short-term investments (4) 422.1 422.1 — — Common equity securities: Consumer 152.8 152.8 — — Exchange traded funds (1) 87.5 65.6 21.9 — Health Care 36.4 36.4 — — Communications 32.7 32.7 — — Technology 24.8 24.8 — — Other 73.3 — 73.3 — Total common equity securities 407.5 312.3 95.2 — Other long-term investments (2)(3) 184.5 — — 184.5 Total investments (4) $ 5,386.1 $ 987.3 $ 4,061.1 $ 337.7 (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 $3.5 associated with other long-term investment limited partnerships accounted for using the equity method. Excludes carrying value of $13.4 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. (4) Includes carrying value of $9.2 in fixed maturity investments and $0.3 in short-term investments that are classified as assets held for sale related to SSIE. 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 — Total debt securities issued by corporations 1,000.0 — 1,000.0 — Mortgage 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 (4) 2,639.7 134.0 2,435.7 70.0 Short-term investments (4) 211.3 211.3 — — Common equity securities: Financials 694.7 694.7 — — Exchange traded funds (1) 141.8 120.5 21.3 — 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) $ 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. (4) Includes carrying value of $9.5 in fixed maturity investments and $0.1 in short-term investments that are classified as assets held for sale related to SSIE. 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 June 30, 2016 and December 31, 2015 : Fair Value at Millions June 30, 2016 December 31, 2015 AAA $ — $ — AA 125.7 95.2 A 376.6 397.7 BBB 563.8 507.1 Other — — Debt securities issued by corporations (1) $ 1,066.1 $ 1,000.0 (1) Credit ratings are assigned based on the following hiera

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	6 Months Ended
	Jun. 30, 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 June 30, Millions 2016 2015 Goodwill Other intangible assets Goodwill Other intangible assets Beginning balance $ 24.1 $ 32.2 $ 24.1 $ 39.0 Amounts held for sale at beginning of the period (1) — .3 — .7 Amortization, including foreign currency translation — (3.3 ) — (2.7 ) Amounts held for sale at end of the period (1) — — — (.6 ) Ending balance $ 24.1 $ 29.2 $ 24.1 $ 36.4 Six Months Ended June 30, Millions 2016 2015 Goodwill Other intangible assets Goodwill Other intangible assets Beginning balance $ 24.1 $ 31.3 $ 23.8 $ 38.7 Amounts held for sale at beginning of the period (1) — .4 — .8 Acquisitions of businesses — — .3 2.8 Acquisitions of intangible assets — 3.9 — — Amortization, including foreign currency translation — (6.4 ) — (5.3 ) Amounts held for sale at end of the period (1) — — — (.6 ) Ending balance $ 24.1 $ 29.2 $ 24.1 $ 36.4 (1) See Note 17 - “Discontinued Operations” .

Debt

Debt	6 Months Ended
	Jun. 30, 2016
Debt Disclosure [Abstract]
Debt	Debt White Mountains’s debt outstanding as of June 30, 2016 and December 31, 2015 consisted of the following: Millions June 30, Effective Rate (1) December 31, Effective Rate (1) WTM Bank Facility $ — N/A $ 50.0 3.9% OBH Senior Notes, at face value 275.0 4.7% 275.0 4.7% Unamortized original issue discount and debt issuance costs (2.0 ) (2.1 ) OBH Senior Notes, carrying value 273.0 272.9 OneBeacon Bank Facility — N/A — N/A MediaAlpha Bank Facility 17.0 5.9% 15.0 5.5% Unamortized issuance cost (.2 ) (.3 ) MediaAlpha Bank Facility, carrying value 16.8 14.7 Total debt $ 289.8 $ 337.6 (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 June 30, 2016 , White Mountains repaid $150.0 million under the WTM Bank Facility. During the six months ended June 30, 2016 , White Mountains borrowed an additional $100.0 million and repaid $150.0 million under the WTM Bank Facility at a blended interest rate of 3.90% . As of June 30, 2016 , the WTM Bank Facility was undrawn. The WTM Bank Facility contains various affirmative, negative and financial covenants which White Mountains considers to be customary for such borrowings, including certain minimum net worth and maximum debt to capitalization standards. OBH Senior Notes In November 2012, OneBeacon U.S. Holdings, Inc. (“OBH”) issued $275.0 million face value of senior unsecured notes (“OBH Senior Notes”) through a public offering, at an issue price of 99.9% and received $272.9 million of proceeds. The OBH Senior Notes bear an annual interest rate of 4.6% payable semi-annually in arrears on May 9 and November 9, until maturity on November 9, 2022, and are fully and unconditionally guaranteed as to the payment of principal and interest by OneBeacon Ltd. Taking into effect the amortization of the original issue discount and all underwriting and issuance expenses, the OBH Senior Notes have an effective yield to maturity of approximately 4.7% per annum. The OBH Senior Notes were issued under indentures that contain restrictive covenants which, among other things, limit the ability of OneBeacon Ltd., OBH, and their respective subsidiaries to create liens and enter into sale and leaseback transactions and limits the ability of OneBeacon Ltd. and OBH to consolidate, merge or transfer its properties and assets. The indentures do not contain any financial ratios or specified levels of net worth or liquidity to which the OneBeacon Ltd. or OBH must adhere. In addition, a failure by OneBeacon Ltd. or OBH or their respective subsidiaries to pay principal and interest on covered debt, where such failure results in the acceleration of at least $75.0 million of the principal amount of covered debt, could trigger the acceleration of the OBH Senior Notes. 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. and also including BMO Harris Bank N.A., which has a total commitment of $65.0 million and has a maturity date of September 29, 2019 (the “OneBeacon Bank Facility”). As of June 30, 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. 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 and a revolving loan facility for $5.0 million , which had an outstanding balance of $2.0 million as of June 30, 2016 . During the six months ended June 30, 2016 , MediaAlpha borrowed $2.5 million and repaid $0.5 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, plus a spread of 1.5% as of June 30, 2016. 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 June 30, 2016 , White Mountains was in compliance with all of the covenants under all of its debt instruments.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 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, Gibraltar, Israel, Luxembourg, the Netherlands, the United Kingdom and the United States. White Mountains’s income tax benefit related to pre-tax income from continuing operations for the three and six months ended June 30, 2016 was different from the U.S. statutory rate of 35% primarily due to tax benefits recorded for the settlements of tax examinations. White Mountains’s effective tax rate for the three and six months ended June 30, 2016 was not meaningful as pre-tax income was near break-even. The rate for the three months ended June 30, 2016 was impacted by a $ 3.5 million favorable settlement of the 2010-2012 IRS exam and the rate for the six months ended June 30, 2016 was impacted by a $ 12.8 million favorable settlement of the 2007-2009 IRS exam, as further described below. White Mountains’s income tax benefit for the three months ended June 30, 2015 represented an effective tax rate of 43.1% . The effective tax rate for the three months ended June 30, 2015 was higher than the U.S. statutory rate of 35% primarily due to changes in forecasted earnings by jurisdiction used in determining interim tax expense. White Mountains’s effective tax rate for the six months ended June 30, 2015 was not meaningful as pre-tax income was near break-even. In arriving at the effective tax rate for the three and six months ended June 30, 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 May 27, 2016, White Mountains received the Closing Letter (Letter 1156) from the IRS Revenue Agent relating to the examination of tax years 2010, 2011 and 2012 for certain U.S. Subsidiaries of OneBeacon. All disputed items have now been agreed to and resolved. As the receipt of the Closing Letter described above represents formal settlement, White Mountains recorded a tax benefit of $ 3.5 million in the second quarter of 2016 related to tax years 2010, 2011 and 2012. On June 22, 2016, White Mountains received the Closing Letter (Letter 1156) from the IRS Revenue Agent relating to the examination of tax year 2012 for Guilford Holdings, Inc. and subsidiaries. All disputed items have now been agreed to and resolved. As the receipt of the Closing Letter described above represents formal settlement, White Mountains recorded an increase to net operating loss carryforwards of $ 1.7 million related to tax year 2012.

Derivatives

Derivatives	6 Months Ended
	Jun. 30, 2016
Derivatives	Derivatives
Variable Annuity
Derivatives	Variable Annuity Reinsurance White Mountains entered into agreements to reinsure death and living benefit guarantees associated with certain variable annuities in Japan. During the second quarter of 2015, the variable annuity contracts reinsured by WM Life Re began to mature and were fully runoff by June 30, 2016. At December 31, 2015 , the total guarantee value was approximately ¥50.7 billion (approximately $0.4 billion at exchange rates on that date), respectively. The collective account values of the underlying variable annuities were approximately 109% of the guarantee value at December 31, 2015 . The following table summarizes the pre-tax operating results of WM Life Re for the three and six months ended June 30, 2016 and 2015 . Three Months Ended Six Months Ended June 30, June 30, Millions 2016 2015 2016 2015 Fees, included in other revenue $ .3 $ 2.6 $ 1.2 $ 5.6 Change in fair value of variable annuity liability, included in other revenue .1 .7 (.3 ) 1.1 Change in fair value of derivatives, included in other revenue (.3 ) (2.3 ) (2.0 ) (7.8 ) Foreign exchange, included in other revenue .4 — 1.3 (1.2 ) Other investment income and (losses) gains — (.1 ) — (.2 ) Total revenue .5 .9 .2 (2.5 ) 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 (.2 ) (.1 ) (.3 ) — General and administrative expenses (1.2 ) (.9 ) (1.9 ) (2.3 ) Pre-tax income (loss) $ (.9 ) $ (.1 ) $ (2.0 ) $ (4.8 ) The following summarizes realized and unrealized derivative gains (losses) recognized in other revenue for the three and six months ended June 30, 2016 and 2015 and the carrying values, included in other assets, at June 30, 2016 and December 31, 2015 by type of instrument: Gains (losses) Carrying Value Three Months Ended Six Months Ended As of June 30, June 30, June 30, December 31, 2015 Millions 2016 2015 2016 2015 Fixed income/interest rate $ — $ (5.9 ) $ 1.8 $ 3.4 $ — $ .5 Foreign exchange (.6 ) 9.2 (4.8 ) (2.9 ) — 14.8 Equity .3 (5.6 ) 1.0 (8.3 ) — 4.8 Total $ (.3 ) $ (2.3 ) $ (2.0 ) $ (7.8 ) $ — $ 20.1 The following tables summarize the changes in White Mountains’s variable annuity reinsurance liabilities and derivative instruments for the three and six months ended June 30, 2016 and 2015 : Three Months Ended June 30, 2016 Variable Annuity Assets (Liabilities) Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ (.1 ) $ 2.6 $ 10.3 $ .2 $ 13.1 Purchases — — — — — Realized and unrealized gains (losses) .1 1.7 (1.8 ) (.2 ) (.3 ) Transfers in — — — — — Sales/settlements — (4.3 ) (8.5 ) — (12.8 ) End of period $ — $ — $ — $ — $ — Six Months Ended June 30, 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) (.3 ) 2.9 (.7 ) (4.2 ) (2.0 ) Transfers in — — — — — Sales/settlements — (5.6 ) (15.8 ) 3.3 (18.1 ) End of period $ — $ — $ — $ — $ — Three Months Ended June 30, 2015 Variable Annuity Assets Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ 1.1 $ 17.0 $ 31.2 $ (1.2 ) $ 47.0 Purchases — — — — — Realized and unrealized gains (losses) .7 (8.3 ) .6 5.4 (2.3 ) Transfers in — — — — — Sales/settlements — (.4 ) .7 (9.3 ) (9.0 ) End of period $ 1.8 $ 8.3 $ 32.5 $ (5.1 ) $ 35.7 Six Months Ended June 30, 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) 1.1 (9.0 ) (5.9 ) 7.1 (7.8 ) Transfers in — — — — — Sales/settlements — (1.6 ) 4.6 (15.9 ) (12.9 ) End of period $ 1.8 $ 8.3 $ 32.5 $ (5.1 ) $ 35.7 (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 June 30, 2016 December 31, 2015 June 30, 2015 Cash $ — $ 5.8 $ 20.9 Fixed maturity investments — — 4.4 Total $ — $ 5.8 $ 25.3 Collateral in the form of fixed maturity securities consisted of Government of Japan Bonds, recorded at fair value. Collateral in the form of short-term investments consisted of money-market instruments, carried at amortized cost, which approximated fair value. All of White Mountains’s variable annuity reinsurance liabilities were classified as Level 3 measurements. The fair value of White Mountains’s variable annuity reinsurance liabilities were 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, were generally unobservable inputs and significantly impacted the fair value estimates. Generally, the liabilities associated with these guarantees increased with declines in the equity markets, interest rates and currencies against the Japanese yen, as well as with increases in market volatilities. White Mountains used derivative instruments 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, were generally the same as those used to estimate the fair value of variable annuity liabilities. There were no open derivatives instruments remaining as of June 30, 2016. WM Life Re entered 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 had exposure to credit risk for amounts that were uncollateralized by counterparties. WM Life Re’s internal risk management guidelines established net counterparty exposure thresholds that took into account OTC counterparties’ credit ratings. The OTC derivative contracts were 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 had exposure to credit risk for amounts uncollateralized by margin balances. WM Life Re had master netting agreements with certain of its counterparties whereby the collateral provided (held) was calculated on a net basis. The following summarizes amounts offset under master netting agreements: June 30, 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 $ — $ — $ — $ 2.4 $ (2.1 ) $ .3 Exchange traded — — — .1 (.1 ) — Foreign exchange contracts OTC — — — 15.0 — 15.0 Exchange traded — — — .1 (.3 ) (.2 ) Equity contracts OTC — — — 4.4 (.6 ) 3.8 Exchange traded — — — 1.2 — 1.2 Total (2) $ — $ — $ — $ 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 were subject to master netting arrangements. There were no open derivative instruments as of June 30, 2016 and no exposure to credit losses on OTC and exchanged traded derivatives as of that date. 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 as of December 31, 2015: 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 WM Life Re- Cash Net amount of exposure to counter-party Standard & Poor's Rating (1) JP Morgan $ 8.5 $ — $ — $ 8.5 $ — $ — $ 5.5 $ 3.0 A + Bank of America .7 — — .7 — — — .7 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

Municipal Bond Guarantee	6 Months Ended
	Jun. 30, 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 June 30, 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 $471.5 million at June 30, 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 and six months ended June 30, 2016 , HG Global had pre-tax income of $5.9 million and $13.2 million , which included $4.4 million and $8.9 million of interest income on the BAM Surplus Notes. For the three and six months ended June 30, 2015 , HG Global had pre-tax income of $3.1 million and $8.6 million , which included $3.9 million and $7.9 million of interest income on the BAM Surplus Notes. For the three and six months ended June 30, 2016 , White Mountains reported pre-tax losses of $9.0 million and $16.6 million on BAM that were recorded in net loss attributable to non-controlling interests, which included $4.4 million and $8.9 million of interest expense on the BAM Surplus Notes. For the three and six months ended June 30, 2015 , White Mountains reported pre-tax losses of $14.1 million and $22.9 million on BAM that were recorded in net loss attributable to non-controlling interests, which included $3.9 million and $7.9 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: June 30, 2016 December 31, 2015 Contracts outstanding 3,910 3,103 Remaining weighted average contract period outstanding (in years) 10.9 12.8 Contractual debt service outstanding (in millions): Principal $ 27,780.2 $ 22,556.0 Interest 14,074.2 11,984.4 Total debt service outstanding $ 41,854.4 $ 34,540.4 Gross unearned insurance premiums $ 63.3 $ 50.2 The following table is a schedule of BAM’s future premium revenues as of June 30, 2016 : Millions June 30, 2016 July 1, 2016 - December 31, 2016 $ 2.9 January 1, 2017 - March 31, 2017 1.4 April 1, 2017 - June 30, 2017 1.4 July 1, 2017 - September 30, 2017 1.4 October 1, 2017 - December 31, 2017 1.4 5.6 2018 5.3 2019 5.1 2020 4.8 2022 and thereafter 39.6 Total $ 63.3

Earnings Per Share

Earnings Per Share	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2016 and 2015 . (See Note 17 - “Discontinued Operations” ). Three Months Ended Six Months Ended June 30, June 30, 2016 2015 2016 2015 Basic and diluted earnings per share numerators (in millions): Net income (loss) from continuing operations attributable to White Mountains’s common shareholders $ (17.5 ) $ 4.8 $ (5.6 ) $ 17.8 Allocation of income for unvested restricted common shares .2 (.1 ) .1 (.2 ) Dividends declared on participating restricted common shares (1) — — (.1 ) (.1 ) Total allocation to restricted common shares .2 (.1 ) — (.3 ) Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ (17.3 ) $ 4.7 $ (5.6 ) $ 17.5 Undistributed net earnings (in millions): Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ (17.3 ) $ 4.7 $ (5.6 ) $ 17.5 Dividends declared net of restricted common share amounts (1) — — (5.9 ) (5.9 ) Total undistributed net earnings, net of restricted common share amounts $ (17.3 ) $ 4.7 $ (11.5 ) $ 11.6 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 5,096.1 5,985.7 5,317.8 5,982.1 Average unvested restricted shares (2) (66.5 ) (71.4 ) (60.2 ) (65.2 ) Basic earnings per share denominator 5,029.6 5,914.3 5,257.6 5,916.9 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period (3) 5,107.0 5,985.7 5,324.3 5,982.1 Average unvested restricted common shares (2) (66.5 ) (71.4 ) (60.2 ) (65.2 ) Diluted earnings per share denominator (3) 5,040.5 5,914.3 5,264.1 5,916.9 Basic earnings per share (in dollars): Net income attributable to White Mountains’s common shareholders $ (3.44 ) $ .80 $ (1.07 ) $ 2.96 Dividends declared and paid — — (1.00 ) (1.00 ) Undistributed earnings $ (3.44 ) $ .80 $ (2.07 ) $ 1.96 Diluted earnings per share (in dollars): Net income attributable to White Mountains’s common shareholders $ (3.43 ) $ .80 $ (1.06 ) $ 2.96 Dividends declared and paid — — (1.00 ) (1.00 ) Undistributed earnings $ (3.43 ) $ .80 $ (2.06 ) $ 1.96 (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 and six months ended June 30, 2016 includes the impact of 120,000 common shares issuable upon exercise of the non-qualified options outstanding, which results in 10,863 and 6,194 incremental shares outstanding over the periods.

Non-controlling Interest

Non-controlling Interest	6 Months Ended
	Jun. 30, 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 June 30, 2016 and December 31, 2015 : June 30, 2016 December 31, 2015 $ in millions Non-controlling Percentage Non-controlling Equity Non-controlling Percentage Non-controlling Equity OneBeacon Ltd. 23.9 % $ 244.8 24.5 % $ 245.6 SIG Preference Shares N/A — 100.0 250.0 Other, excluding mutuals and reciprocals HG Global 3.1 17.0 3.1 17.1 MediaAlpha 40.0 13.2 40.0 14.4 Tranzact 36.8 79.2 36.8 79.4 Wobi 3.5 .5 3.9 .6 Dewar 18.8 3.7 18.6 3.7 Total other, excluding mutuals and reciprocals 113.6 115.2 Mutuals and reciprocals BAM 100.0 (138.0 ) 100.0 (140.0 ) SSIE 100.0 3.8 100.0 (16.0 ) Total mutuals and reciprocals (134.2 ) (156.0 ) Total non-controlling interests $ 224.2 $ 454.8

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 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 - “Held for Sale and Discontinued Operations” ). White Mountains has made its segment determination based on consideration of the following criteria: (i) the nature of the business activities of each of the Company’s subsidiaries and affiliates; (ii) the manner in which the Company’s subsidiaries and affiliates are organized; (iii) the existence of primary managers responsible for specific subsidiaries and affiliates; and (iv) the organization of information provided to the chief operating decision makers and the Board of Directors. Significant intercompany transactions among White Mountains’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 June 30, 2016 Earned insurance premiums $ 271.4 $ 1.0 $ .4 $ 1.9 $ 274.7 Net investment income 12.1 .5 1.8 4.8 19.2 Net investment income (loss) - surplus note interest — 4.4 (4.4 ) — — Net realized and unrealized investment gains (losses) 24.7 .5 3.2 (.3 ) 28.1 Other revenue .8 — .3 35.1 (2) 36.2 Total revenues 309.0 6.4 1.3 41.5 358.2 Losses and LAE 179.7 — — 2.3 182.0 Insurance acquisition expenses 48.7 .2 .6 .6 50.1 Other underwriting expenses 50.9 — .1 — 51.0 General and administrative expenses 3.2 .3 9.6 56.7 (3) 69.8 Amortization of intangible assets .3 — — 3.0 3.3 Interest expense 3.2 — — .9 4.1 Total expenses 286.0 .5 10.3 63.5 360.3 Pre-tax income (loss) $ 23.0 $ 5.9 $ (9.0 ) $ (22.0 ) $ (2.1 ) HG Global/BAM Millions OneBeacon HG BAM (1) Other Operations Total Six Months Ended June 30, 2016 Earned insurance premiums $ 550.0 $ 1.9 $ .7 $ 4.2 $ 556.8 Net investment income 26.5 1.0 3.4 6.2 37.1 Net investment income (loss) - surplus note interest — 8.9 (8.9 ) — — Net realized and unrealized investment gains 41.3 2.6 8.1 5.6 57.6 Other revenue 1.7 — .4 73.9 (2) 76.0 Total revenues 619.5 14.4 3.7 89.9 727.5 Losses and LAE 338.5 — — 4.6 343.1 Insurance acquisition expenses 99.7 .4 1.3 1.4 102.8 Other underwriting expenses 106.2 — .2 — 106.4 General and administrative expenses 6.8 .8 18.8 127.4 (3) 153.8 Amortization of intangible assets .6 — — 5.8 6.4 Interest expense 6.5 — — 2.1 8.6 Total expenses 558.3 1.2 20.3 141.3 721.1 Pre-tax income (loss) $ 61.2 $ 13.2 $ (16.6 ) $ (51.4 ) $ 6.4 HG Global/BAM Millions OneBeacon HG BAM (1) Other Operations Total Three Months Ended June 30, 2015 Earned insurance premiums $ 319.3 $ .6 $ .1 $ 1.8 $ 321.8 Net investment income 10.1 .5 .8 1.8 13.2 Net investment income (loss) - surplus note interest — 3.9 (3.9 ) — — Net realized and unrealized investment (losses) gains (14.0 ) (1.4 ) (1.9 ) 2.3 (15.0 ) Other (loss) revenue (1.2 ) — .2 49.7 (2) 48.7 Total revenues 314.2 3.6 (4.7 ) 55.6 368.7 Losses and LAE 194.5 — — 1.7 196.2 Insurance acquisition expenses 56.4 .1 .6 .7 57.8 Other underwriting expenses 52.9 — .1 — 53.0 General and administrative expenses 3.8 .4 8.7 47.8 (3) 60.7 Amortization of intangible assets .4 — — 2.3 2.7 Interest expense 3.3 — — .1 3.4 Total expenses 311.3 .5 9.4 52.6 373.8 Pre-tax income (loss) $ 2.9 $ 3.1 $ (14.1 ) $ 3.0 $ (5.1 ) HG Global/BAM Millions OneBeacon HG BAM (1) Other Operations Total Six Months Ended June 30, 2015 Earned insurance premiums $ 605.9 $ 1.1 $ .3 $ 3.8 $ 611.1 Net investment income 20.6 .9 1.8 2.5 25.8 Net investment income (loss) - surplus note interest — 7.9 (7.9 ) — — Net realized and unrealized investment gains (losses) .2 (.3 ) 1.1 9.0 10.0 Other (loss) revenue (4.3 ) — .3 80.1 (2) 76.1 Total revenues 622.4 9.6 (4.4 ) 95.4 723.0 Losses and LAE 360.4 — — 3.7 364.1 Insurance acquisition expenses 107.4 .2 1.4 1.8 110.8 Other underwriting expenses 108.8 — .2 — 109.0 General and administrative expenses 7.6 .8 16.9 103.7 (3) 129.0 Amortization of intangible assets .7 — — 4.6 5.3 Interest expense 6.5 — — .4 6.9 Total expenses 591.4 1.0 18.5 114.2 725.1 Pre-tax income (loss) $ 31.0 $ 8.6 $ (22.9 ) $ (18.8 ) $ (2.1 ) (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 $ 28.1 and $ 60.8 from MediaAlpha for the three months and six months ended June 30, 2016 , and $ 23.2 and $ 52.9 from MediaAlpha for the three months and six months ended June 30, 2015 . (3) Includes $ 26.0 and $ 56.5 from MediaAlpha for the three months and six months ended June 30, 2016 , and $ 21.9 and $ 49.6 from MediaAlpha for the three months and six months ended June 30, 2015 .

Investments in Unconsolidated A

Investments in Unconsolidated Affiliates	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2015 , White Mountains received cash dividends from Symetra of $2.2 million and $4.4 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 June 30, 2015, the pre-tax unamortized basis difference was $164.1 million , of which $33.0 million is attributable to equity in earnings of unconsolidated affiliates and $131.1 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 and six months ended June 30, 2015, White Mountains recognized after-tax amortization of $0.7 million and $1.4 million and through equity in earnings of unconsolidated affiliates and $2.7 million and $5.5 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 and six months ended June 30, 2015: Three Months Ended Six Months Ended Millions June 30, 2015 June 30, 2015 Equity method carrying value of investment in Symetra at the beginning of the period $ 447.3 $ 411.4 Equity in earnings (1)(2) 6.1 13.3 Equity in net unrealized losses from Symetra’s fixed maturity portfolio (3) (66.4 ) (35.5 ) Dividends received (2.2 ) (4.4 ) Distribution from Prospector Offshore Fund 12.4 12.4 Equity method carrying value of investment in Symetra at the end of the period (4) $ 397.2 $ 397.2 (1) For the three and six months ended June 30, 2015 , equity in earnings excludes tax expense of $0.4 and $0.8 . (2) For the three and six months ended June 30, 2015 , equity in earnings includes $0.7 and $1.4 increase relating to the pre-tax amortization of the Symetra common share basis difference. (3) For the three and six months ended June 30, 2015 , net unrealized gains includes $2.8 and $5.7 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 $2.0 as of June 30, 2015 , which excludes tax expense of $0.0 . 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. Prior to the sale, White Mountains recorded equity in earnings of $1.1 million and $1.6 million for the three and six months ended June 30, 2015.

Employee Share-Based Incentive

Employee Share-Based Incentive Compensation Plans	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2016 and 2015 for performance shares granted under the WTM Incentive Plan: Three Months Ended June 30, Six Months Ended June 30, 2016 2015 2016 2015 Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Beginning of period 111,387 $ 71.3 108,545 $ 25.7 96,358 $ 57.7 113,295 $ 44.4 Shares paid or expired (1) (36,294 ) (41.3 ) — — (36,294 ) (41.3 ) (34,001 ) (24.9 ) New grants — — 750 — 16,215 — 29,878 — Forfeitures and cancellations (2) 908 .9 (19 ) — (278 ) .3 104 .5 Expense recognized — 1.3 — 3.1 — 15.5 — 8.8 End of period (3) 76,001 $ 32.2 109,276 $ 28.8 76,001 $ 32.2 109,276 $ 28.8 (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 June 30, 2016 and 2015 both exclude 4,428 and 7,851 performance share awards, net of assumed forfeitures, granted to employees of Sirius Group, which is accounted for as discontinued operations. For performance shares earned in the 2013-2015 performance cycle, the Company issued 5,000 common shares and settled the remainder in cash. For the 2012-2014 performance cycle, all performance shares earned were settled in cash. If all the outstanding WTM performance shares had vested on June 30, 2016 , the total additional compensation cost to be recognized would have been $27.2 million , based on accrual factors at June 30, 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 June 30, 2016 for each performance cycle: Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Performance cycle: 2016 – 2018 16,215 $ 2.2 2015 – 2017 29,478 12.7 2014 – 2016 32,256 18.2 Sub-total 77,949 33.1 Assumed forfeitures (1,948 ) (.9 ) Total at June 30, 2016 76,001 $ 32.2 Restricted Shares The following table summarizes the unrecognized compensation cost associated with the outstanding restricted share awards for the three and six months ended June 30, 2016 and 2015 : Three Months Ended June 30, Six Months Ended June 30, 2016 2015 2016 2015 Millions, except share amounts Restricted Unamortized Restricted Unamortized Restricted Shares Unamortized Issue Date Fair Value Restricted Shares Unamortized Issue Date Fair Value Non-vested, Beginning of period 66,470 $ 29.2 71,125 $ 26.5 70,675 $ 15.7 83,314 $ 14.3 Issued — — 750 .5 21,215 16.3 23,640 15.7 Vested — — — — (24,620 ) — (35,079 ) — Forfeited — — — — (800 ) .2 — — Expense recognized (1) — (5.0 ) — (3.8 ) — (8.0 ) — (6.8 ) End of period (2) 66,470 $ 24.2 71,875 $ 23.2 66,470 $ 24.2 71,875 $ 23.2 (1) In connection with the sale of Sirius Group in the second quarter of 2016, White Mountains recognized $ 1.4 from accelerating the amortization of the issue date fair value for shares issued to Sirius Group employees, who no longer have a service obligation to the Company. (2) Outstanding restricted share awards as of June 30, 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 six months of 2016, White Mountains issued 21,215 restricted shares that vest on January 1, 2019. During the first six months of 2015, White Mountains issued 23,640 restricted shares that vest on January 1, 2018. The unrecognized compensation cost at June 30, 2016 is expected to be recognized ratably over the remaining vesting periods. Stock Options Non-Qualified Options As of December 31, 2015 and June 30, 2016, the Company’s Chairman and CEO held 125,000 and 120,000 Non-Qualified Options, which are exercisable at a fixed price of $742 per common share and expire on January 20, 2017. The potential in-the-money value of the Non-Qualified Options in excess of $100 million is limited to 50% of the excess amount. The Non-Qualified Options were fully amortized as of the first quarter in 2011. On May 5, 2016, the Company’s Chairman and CEO exercised 5,000 Non-Qualified Options at $742 per common share. 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 and six months ended June 30, 2016 and 2015 for OneBeacon performance shares granted under the OneBeacon Incentive Plan: Three Months Ended June 30, Six Months Ended June 30, 2016 2015 2016 2015 Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Beginning of period 441,206 $ 1.1 462,147 $ 2.1 449,435 $ 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 — (.1 ) — .3 — .3 — .5 End of period 441,206 $ 1.0 462,147 $ 2.4 441,206 $ 1.0 462,147 $ 2.4 (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 June 30, 2016 , the total additional compensation cost to be recognized would have been $2.5 million , based on accrual factors at June 30, 2016 (common share price, accumulated dividends and payout assumptions). The following table summarizes OneBeacon performance shares outstanding awarded under the OneBeacon Incentive Plan at June 30, 2016 for each performance cycle: Millions, except share amounts Target Accrued Expense Performance cycle: 2016 – 2018 163,150 $ .4 2015 – 2017 146,659 .6 2014 – 2016 142,710 — Sub-total 452,519 1.0 Assumed forfeitures (11,313 ) — Total at June 30, 2016 441,206 $ 1.0 OneBeacon Restricted Shares The following table summarizes the unrecognized compensation cost associated with the outstanding OneBeacon restricted stock awards for the three and six months ended June 30, 2016 and 2015 : Three Months Ended June 30, Six Months Ended June 30, 2016 2015 2016 2015 Millions, except share amounts Restricted Unamortized Restricted Unamortized Restricted Unamortized Restricted Unamortized Non-vested, Beginning of period 395,872 $ 4.3 390,950 $ 4.0 382,722 $ 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 — (.8 ) — (.5 ) — (1.3 ) — (1.1 ) End of period 395,872 $ 3.5 390,950 $ 3.5 395,872 $ 3.5 390,950 $ 3.5 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 were reduced by 35,000 shares. The unrecognized compensation cost at June 30, 2016 is expected to be recognized ratably over the remaining vesting periods. OneBeacon Restricted Stock Units During the first six months of 2016, the OneBeacon Compensation Committee awarded to certain employees 227,788 restricted stock units (“RSUs”) that are scheduled to vest on December 31, 2018, of which, net of forfeiture assumptions, 215,698 were outstanding as of June 30, 2016. During the first six months of 2015, the OneBeacon Compensation Committee awarded to certain employees 207,848 RSU that are scheduled to vest on December 31, 2017, of which, net of forfeiture assumptions, 185,004 were outstanding as of June 30, 2016. The RSUs will be paid out in cash or shares at the discretion of the OneBeacon Compensation Committee. For the three and six months ended June 30, 2016 , the expense associated with the RSUs was $0.5 million and $0.9 million . For the three and six months ended June 30, 2015, the expense associated with the RSUs was $0.3 million and $0.4 million .

Fair Value of Financial Instrum

Fair Value of Financial Instruments	6 Months Ended
	Jun. 30, 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 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 June 30, 2016 and December 31, 2015 : June 30, 2016 December 31, 2015 Millions Fair Value Carrying Value Fair Value Carrying Value OBH Senior Notes $ 279.7 $ 273.0 $ 276.4 $ 272.9 MediaAlpha Bank Facility 17.0 16.8 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 MediaAlpha Bank Facility has been determined based on a discounted cash flows approach and is considered to be a Level 3 measurement.

Discontinued Operations

Discontinued Operations	6 Months Ended
	Jun. 30, 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. White Mountains recorded $ 366.6 million of gain from sale of Sirius in discontinued operations in the statement of operations and $ 113.3 million in other comprehensive income from discontinued operations for a total increase to book value of $ 479.9 million in the second quarter of 2016. For the stub period ended April 18, 2016, Sirius Group reported a $ 3.4 million net loss from discontinued operations in the statement of operations and $ 5.2 million of other comprehensive loss from discontinued operations. For the six months ended June 30, 2016, White Mountains recorded a $ 4.3 million net loss from discontinued operations from Sirius Group and $ 32.0 million of other comprehensive income. Through April 18, 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 did not include White Mountains’s investment in OneBeacon and certain other investments that are in the Sirius Group legal entities. As of December 31, 2015, the value of these investments, net of related tax effects, was $686.2 million , of which $528.6 million 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 and six months ended June 30, 2016, $0.4 million and $3.7 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 and six months ended June 30, 2015, $2.4 million and $2.7 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. As part of the sale of Sirius Group, White Mountains purchased Ashmere, a subsidiary formerly owned by Sirius Group. Ashmere is currently under an agreement to be sold and the completion of the sale is pending on regulatory approval. As of June 30, 2016, Ashmere's assets and liabilities are presented as held for sale. Tranzact On June 9, 2016, White Mountains announced that it had entered into a definitive agreement for the sale of Tranzact to an affiliate of Clayton, Dubilier & Rice, LLC. On July 21, 2016, White Mountains completed the sale of Tranzact and received net proceeds of $ 221.3 million . As of June 30, 2016 and December 31, 2015, Tranzact’s results are reported as discontinued operations and assets and liabilities held for sale within White Mountains’s GAAP financial statements. Net loss from discontinued operations related to Tranzact was $ 0.5 million and $ 2.5 million for the three and six months ended June 30, 2016 and $ 6.5 million and $ 4.0 million for the three and six months ended June 30, 2015. Star & Shield SSIE voluntarily ceased writing new policies effective July 1, 2016 and will voluntarily cease renewing policies at a future date, subject to regulatory approval. White Mountains is pursuing a sale of Star & Shield and its investment in SSIE surplus notes as of June 30, 2016 and as a result White Mountains has presented Star & Shield's and SSIE's assets and liabilities as held for sale. OneBeacon Runoff For both the three and six months ended June 30, 2015, the gain from the sale of discontinued operations relating to the Runoff Business was $0.3 million . The gain related to an adjustment to the estimated loss on sale, which included the final settlement of certain post-closing items. For the three and six months ended June 30, 2015, the net loss from discontinued operations relating to the Runoff Business, net of tax, was $0.2 million and $0.3 million . The Runoff Business was completed in December of 2014. Esurance For the three months June 30, 2015, White Mountains recorded a net loss from the sale of discontinued operations of $0.3 million , which related to a tax payment to Allstate pursuant to the Esurance sale. For the six months June 30, 2015, White Mountains recorded a net gain from the sale of discontinued operations of $7.6 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 business classified as held for sale. At December 31, 2015, amounts presented relate to Sirius Group, Tranzact, Abiaka and SSIE. At June 30, 2016, the amounts presented relate to Tranzact, Abiaka, SSIE and Ashmere, a subsidiary formerly owned by Sirius Group. Millions June 30, 2016 December 31, 2015 Assets held for sale Fixed maturity investments, at fair value $ 14.4 $ 2,383.5 Short-term investments, at amortized cost (which approximates fair value) 4.2 352.1 Common equity securities, at fair value — 174.4 Other long-term investments — 72.2 Total investments 18.6 2,982.2 Cash 1.9 150.2 Reinsurance recoverable on unpaid losses .4 283.6 Reinsurance recoverable on paid losses — 10.2 Insurance and reinsurance premiums receivable 2.4 326.6 Deferred acquisition costs — 74.6 Deferred tax asset — 303.1 Ceded unearned insurance and reinsurance premiums — 87.7 Accounts receivable on unsettled investment sales — 29.0 Goodwill and intangible assets 315.1 330.5 Other assets 46.2 212.7 Total assets held for sale $ 384.6 $ 4,790.4 Liabilities held for sale Loss and loss adjustment expense reserves $ 5.7 $ 1,650.4 Unearned insurance and reinsurance premiums 1.8 344.3 Debt 96.9 506.4 Deferred tax liability 8.7 270.6 Accrued incentive compensation 1.0 64.2 Ceded reinsurance payable (.2 ) 67.7 Funds held under reinsurance treaties — 52.9 Accounts payable on unsettled investment purchases — — Other liabilities 36.7 111.9 Total liabilities held for sale 150.6 3,068.4 Net assets held for sale $ 234.0 $ 1,722.0 Net Income from Discontinued Operations The following summarizes the results of operations, including related income taxes associated with the business classified as discontinued operations. For the three and six months ended June 30, 2016, the amounts presented relate to Sirius Group and Tranzact. For the three and six months ended June 30, 2015, the amounts presented relate to the sales of Sirius Group, Tranzact, Esurance, and the OneBeacon's runoff business. The results of discontinued operations from Sirius Group up to the closing date of the transaction inure to White Mountains. Three Months Ended Three Months Ended June 30, 2016 June 30, 2015 Millions Sirius Group Other Disc Ops Total Sirius Group Other Disc Ops Total Revenues Earned insurance premiums $ 37.7 $ — $ 37.7 $ 215.5 $ — $ 215.5 Net investment income 2.2 — 2.2 9.1 — 9.1 Net realized and unrealized gains (losses) 7.3 — 7.3 (46.1 ) — (46.1 ) Other revenue 4.7 47.0 51.7 5.4 34.7 40.1 Total revenues 51.9 47.0 98.9 183.9 34.7 218.6 Expenses Loss and loss adjustment expenses 41.2 — 41.2 92.1 — 92.1 Insurance and reinsurance acquisition expenses 10.6 — 10.6 47.5 — 47.5 Other underwriting expenses 4.2 — 4.2 27.7 — 27.7 General and administrative expenses .2 49.2 49.4 6.7 38.0 44.7 Interest expense 1.3 1.3 2.6 6.6 .9 7.5 Total expenses 57.5 50.5 108.0 180.6 38.9 219.5 Pre-tax (loss) income (5.6 ) (3.5 ) (9.1 ) 3.3 (4.2 ) (.9 ) Income tax benefit (expense) 2.2 (1.1 ) 1.1 .5 — .5 Net (loss) income from discontinued operations (3.4 ) (4.6 ) (8.0 ) 3.8 (4.2 ) (.4 ) Net gain from sales of discontinued operations - Sirius 366.6 — 366.6 — — — Net gain from sales of discontinued operations - OneBeacon — — — — .3 .3 Net loss from sale of discontinued operations - Esurance — — — — (.4 ) (.4 ) Total income (loss) from discontinued operations $ 363.2 $ (4.6 ) $ 358.6 $ 3.8 $ (4.3 ) $ (.5 ) Change in foreign currency translation and other from discontinued operations (5.2 ) — (5.2 ) 44.0 — 44.0 Change in foreign currency translation and other 113.3 — 113.3 — — — Comprehensive income (loss) from discontinued operations $ 471.3 $ (4.6 ) $ 466.7 $ 47.8 $ (4.3 ) $ 43.5 Six Months Ended Six Months Ended June 30, 2016 June 30, 2015 Millions Sirius Group Other Disc Ops Total Sirius Group Other Disc Ops Total Revenues Earned insurance premiums $ 240.1 $ — $ 240.1 $ 420.5 $ — $ 420.5 Net investment income 14.4 — 14.4 18.1 — 18.1 Net realized and unrealized (losses) gains (1.5 ) — (1.5 ) 32.3 — 32.3 Other revenue .6 104.8 105.4 (22.0 ) 72.1 50.1 Total revenues 253.6 104.8 358.4 448.9 72.1 521.0 Expenses Loss and loss adjustment expenses 154.9 — 154.9 189.6 — 189.6 Insurance and reinsurance acquisition expenses 59.0 — 59.0 90.1 — 90.1 Other underwriting expenses 30.9 — 30.9 53.2 — 53.2 General and administrative expenses 8.3 102.6 110.9 13.0 77.2 90.2 Interest expense 7.9 2.7 10.6 13.4 1.7 15.1 Total expenses 261.0 105.3 366.3 359.3 78.9 438.2 Pre-tax (loss) income (7.4 ) (.5 ) (7.9 ) 89.6 (6.8 ) 82.8 Income tax benefit (expense) 3.1 (2.1 ) 1.0 (19.9 ) — (19.9 ) Net (loss) income from discontinued operations (4.3 ) (2.6 ) (6.9 ) 69.7 (6.8 ) 62.9 Net gain from sales of discontinued operations - Sirius 366.6 — 366.6 — — — Net gain from sales of discontinued operations - OneBeacon — — — — .3 .3 Net gain from sales of discontinued operations - Esurance — — — — 7.6 7.6 Total income (loss) from discontinued operations $ 362.3 $ (2.6 ) $ 359.7 $ 69.7 $ 1.1 $ 70.8 Change in foreign currency translation and other from discontinued operations 32.0 — 32.0 (43.6 ) — (43.6 ) Change in foreign currency translation and other from sale of Sirius Group 113.3 — 113.3 — — — Comprehensive income (loss) from discontinued operations $ 507.6 $ (2.6 ) $ 505.0 $ 26.1 $ 1.1 $ 27.2 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: Six Months Ended June 30, (Millions) 2016 2015 Net cash used for operations $ (43.1 ) $ (12.9 ) Net cash provided from investing activities 229.6 59.3 Net cash provided from (used for) financing activities 9.0 (2.0 ) Effect of exchange rate changes on cash — (2.1 ) Net change in cash during the period 195.5 42.3 Cash balances at beginning of period 148.9 114.5 Cash balances at end of period $ 344.4 $ 156.8 Supplemental cash flows information: Interest paid $ (1.4 ) $ (14.5 ) Net income tax payment to national governments $ (31.8 ) $ (24.6 ) 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 and six months ended June 30, 2016 and 2015 : Three Months Ended Six Months Ended June 30, June 30, 2016 2015 2016 2015 Basic and diluted earnings per share numerators (in millions): Net income attributable to White Mountains’s common shareholders $ 358.6 $ (.5 ) $ 359.7 $ 70.8 Allocation of income for participating unvested restricted common shares (1) (4.7 ) — (4.1 ) (.8 ) Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts (2) $ 353.9 $ (.5 ) $ 355.6 $ 70.0 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 5,096.1 5,985.7 5,317.8 5,982.1 Average unvested restricted common shares (3) (66.5 ) (71.4 ) (60.2 ) (65.2 ) Basic earnings per share denominator 5,029.6 5,914.3 5,257.6 5,916.9 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period (4) 5,107.0 5,985.7 5,324.0 5,982.1 Average unvested restricted common shares (3) (66.5 ) (71.4 ) (60.2 ) (65.2 ) Diluted earnings per share denominator (4) 5,040.5 5,914.3 5,263.8 5,916.9 Basic earnings per share (in dollars): $ 70.37 $ (.08 ) $ 67.64 $ 11.84 Diluted earnings per share (in dollars): $ 70.22 $ (.08 ) $ 67.56 $ 11.84 (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 and six months ended June 30, 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 and six months ended June 30, 2016 includes the impact of 120,000 common shares issuable upon exercise of the non-qualified options outstanding, which results in 10,863 and 6,194 incremental shares outstanding over the periods.

Contingencies

Contingencies	6 Months Ended
	Jun. 30, 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 June 30, 2016 : Sale of Sirius Group On April 18, 2016, the Company completed the sale of Sirius Group to CMI pursuant a Stock Purchase Agreement dated as of July 24, 2015 (filed as an exhibit to the Company’s current report on Form 8-K on July 27, 2015, the (“Agreement”)). White Mountains has provided indemnification to CMI for certain representations and warranties made in the Agreement. Additionally, the final purchase price payable by CMI under the Agreement, which is based upon the tangible book value of Sirius Group at the closing date, is subject to a true-up process expected to be completed in the third quarter of 2016. Sale of 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. 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”). For the three months June 30, 2015, White Mountains recorded a net loss from the sale of discontinued operations of $0.3 million , which related to a tax payment to Allstate pursuant to the Esurance sale. For the six months ended June 30, 2015, White Mountains recorded a net gain from the sale of discontinued operations of $7.6 million 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. On July 22, 2016, the Plaintiff's petition to the Second Circuit for reconsideration or for a rehearing en banc was denied in full. The Plaintiffs have 90 days in which to file for a writ of certiorari, seeking review in the United States 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 June 30, 2016 , as the amount of loss, if any, cannot be reasonably estimated.

OneBeacon Pension Plan

OneBeacon Pension Plan	6 Months Ended
	Jun. 30, 2016
Compensation Related Costs [Abstract]
OneBeacon Pension Plan	Note 19. OneBeacon Pension Plan OneBeacon previously sponsored the OneBeacon qualified pension plan (the “Qualified Plan”). In the first quarter of 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 an estimated 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 June 30, 2016 . During the three months ended June 30, 2016, OneBeacon recognized a true-up to the estimate of less than a $ 0.1 million gain. The final true-up is anticipated to occur in the second half of 2016. During the second quarter of 2016, OneBeacon ceased administratively paying claims. OneBeacon transferred $ 42.4 million of excess invested assets from the Qualified Plan into the trust supporting the OneBeacon 401(k) Savings and Employee Stock Ownership Plan (“KSOP”), which is the Qualified Replacement Plan (“QRP”). OneBeacon will transfer additional assets upon the final true-up, with approximately $ 12.0 million of excess invested assets to be held in trust in order to wind-down potential post-termination obligations of that plan, as approved by way of a March 2016 private letter ruling from the IRS. The invested assets related to both the former Qualified Plan and the QRP are included in other assets and are accounted for at fair value. OneBeacon continues to sponsor a non-qualified, non-contributory, defined benefit pension plan (“Non-qualified Plan”)covering certain 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	6 Months Ended
	Jun. 30, 2016
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Note 20. Subsequent Events On July 21, 2016, White Mountains closed its previously announced sale of Tranzact Holdings, LLC to an affiliate of Clayton, Dubilier & Rice, LLC. White Mountains received net proceeds of $221.3 million from the sale.

Summary of Significant Accoun28

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 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 June 30, 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 June 30, 2016, the unamortized debt issuance costs included in debt is $2.0 million . Recently Issued Accounting Pronouncements Short-Duration Contracts In May 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. Credit Losses In June 2016, the FASB issued ASU 2016-13, Measurement of Credit Losses on Financial Instruments (ASC 326), which establishes new guidance for the recognition of credit losses for financial assets measured at amortized cost. The new ASU, which applies to financial assets that have the contractual right to receive cash, including reinsurance receivables, requires reporting entities to estimate the credit losses expected over the life of a credit exposure using historical information, current information and reasonable and supportable forecasts that affect the collectability of the financial asset. ASU 2016-13 is effective for annual periods beginning after January 1, 2020, including interim periods. White Mountains is evaluating the expected impact of this new guidance. Stock Compensation In March 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 In February 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 In January 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 In May 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)	6 Months Ended
	Jun. 30, 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 $25.0 million $12.5 billion

Loss and Loss Adjustment Expe30

Loss and Loss Adjustment Expense Reserves (Tables)	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2016 and 2015 : Three Months Ended Six Months Ended June 30, June 30, Millions 2016 2015 2016 2015 Gross beginning balance $ 1,343.8 $ 1,304.0 $ 1,389.8 $ 1,342.2 Less beginning reinsurance recoverable on unpaid losses (150.4 ) (141.6 ) (186.0 ) (161.6 ) Net loss and LAE reserves 1,193.4 1,162.4 1,203.8 1,180.6 SSIE reserves held for sale at beginning of the period (1) 5.3 6.5 5.5 7.7 Loss and LAE incurred relating to: Current year losses 166.7 196.5 327.9 366.3 Prior year losses 15.3 (.3 ) 15.2 (2.2 ) Total incurred losses and LAE 182.0 196.2 343.1 364.1 Loss and LAE paid relating to: Current year losses (38.1 ) (43.9 ) (61.2 ) (67.2 ) Prior year losses (123.5 ) (111.4 ) (272.1 ) (275.4 ) Total loss and LAE payments (161.6 ) (155.3 ) (333.3 ) (342.6 ) SSIE reserves held for sale at end of the period (1) (5.3 ) (6.1 ) (5.3 ) (6.1 ) Net ending balance 1,213.8 1,203.7 1,213.8 1,203.7 Plus ending reinsurance recoverable on unpaid losses 162.8 147.1 162.8 147.1 Gross ending balance $ 1,376.6 $ 1,350.8 $ 1,376.6 $ 1,350.8 (1) See Note 17 - “Discontinued Operations” .

Investment Securities (Tables)

Investment Securities (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2016 and December 31, 2015: Type of Surplus Note Total as of June 30, 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) 2.7 (8.4 ) (5.7 ) (15.1 ) Regulatory approval (2) (7.4 ) (12.5 ) (19.9 ) (24.2 ) Liquidity adjustment (3) (9.0 ) (3.6 ) (12.6 ) (10.2 ) Total adjustments (13.7 ) (24.5 ) (38.2 ) (49.5 ) Fair value (4) $ 44.2 $ 18.6 $ 62.8 $ 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 publicly traded debt 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. (4) The increase in the fair value of the surplus notes during the six months ended June 30, 2016 was driven primarily by the narrowing of non-investment grade credit spreads as well as the time value of money benefit generated by moving six months closer to modeled cash receipts, partially offset by the impact of an interest payment received in the first quarter of 2016.
Pre-tax net investment income	Pre-tax net investment income for the three and six months ended June 30, 2016 and 2015 consisted of the following: Three Months Ended Six Months Ended June 30, June 30, Millions 2016 2015 2016 2015 Investment income: Fixed maturity investments $ 17.9 $ 12.4 $ 32.5 $ 24.8 Short-term investments .5 .1 .6 .1 Common equity securities .9 2.1 2.0 4.3 Other long-term investments .6 .9 3.4 .9 Total investment income 19.9 15.5 38.5 30.1 Third-party investment expenses (.7 ) (2.3 ) (1.4 ) (4.3 ) Net investment income, pre-tax $ 19.2 $ 13.2 $ 37.1 $ 25.8
Schedule of Realized and Unrealized Gain (Loss) on Investments	Net realized and unrealized investment gains (losses) consisted of the following: Three Months Ended Six Months Ended June 30, June 30, Millions 2016 2015 2016 2015 Net realized investment gains, pre-tax $ 2.7 $ 42.3 $ 259.5 $ 57.1 Net unrealized investment gains (losses), pre-tax 25.4 (57.3 ) (201.9 ) (47.1 ) Net realized and unrealized investment gains (losses), pre-tax 28.1 (15.0 ) 57.6 10.0 Income tax (expense) benefit attributable to net realized and unrealized investment gains (losses) (9.9 ) 4.5 (18.4 ) (2.6 ) Net realized and unrealized investment gains (losses), after tax $ 18.2 $ (10.5 ) $ 39.2 $ 7.4
Realized Gain (Loss) on Investments	Net realized investment gains (losses) for the three and six months ended June 30, 2016 and 2015 consisted of the following: Three Months Ended Three Months Ended June 30, 2016 June 30, 2015 Millions Net Net Total net realized Net Net Total net realized Fixed maturity investments $ 1.8 $ — $ 1.8 $ 1.6 $ — $ 1.6 Short-term investments .1 — .1 — — — Common equity securities 3.8 — 3.8 25.5 (.1 ) 25.4 Other long-term investments (3.0 ) — (3.0 ) 15.3 — 15.3 Net realized investment gains (losses), pre-tax 2.7 — 2.7 42.4 (.1 ) 42.3 Income tax expense attributable to net realized investment gains (losses) (.4 ) — (.4 ) (12.7 ) — (12.7 ) Net realized investment gains (losses), after tax $ 2.3 $ — $ 2.3 $ 29.7 $ (.1 ) $ 29.6 Six Months Ended Six Months Ended June 30, 2016 June 30, 2015 Millions Net Net Total net realized Net Net Total net realized Fixed maturity investments $ .7 $ — $ .7 $ 2.1 $ — $ 2.1 Short-term investments .2 — .2 — — — Common equity securities 261.4 — 261.4 47.5 .4 47.9 Other long-term investments (2.8 ) — (2.8 ) 7.1 — 7.1 Net realized investment gains, pre-tax 259.5 — 259.5 56.7 .4 57.1 Income tax expense attributable to net realized investment gains (43.3 ) — (43.3 ) (17.2 ) — (17.2 ) Net realized investment gains, after tax $ 216.2 $ — $ 216.2 $ 39.5 $ .4 $ 39.9
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 June 30, 2016 June 30, 2015 Millions Net unrealized gains (losses) Net losses Total net unrealized gains (losses) reflected in earnings Net unrealized losses Net Total net unrealized losses reflected in earnings Fixed maturity investments $ 20.7 $ — $ 20.7 $ (13.4 ) $ — $ (13.4 ) Short-term investments — — — — — — Common equity securities (10.6 ) — (10.6 ) (22.6 ) 1.6 (21.0 ) Other long-term investments 15.5 (.2 ) 15.3 (23.1 ) .2 (22.9 ) Net unrealized investment gains (losses), pre-tax 25.6 (.2 ) 25.4 (59.1 ) 1.8 (57.3 ) Income tax (expense) benefit (9.5 ) — (9.5 ) 17.3 (.1 ) 17.2 Net unrealized investment $ 16.1 $ (.2 ) $ 15.9 $ (41.8 ) $ 1.7 $ (40.1 ) Six Months Ended Six Months Ended June 30, 2016 June 30, 2015 Millions Net unrealized gains (losses) Net gains Total net unrealized gains (losses) reflected in earnings Net unrealized losses Net Total net unrealized losses reflected in earnings Fixed maturity investments $ 42.4 $ — $ 42.4 $ (2.0 ) $ — $ (2.0 ) Short-term investments — — — — — — Common equity securities (260.4 ) 2.4 (258.0 ) (25.3 ) (2.4 ) (27.7 ) Other long-term investments 13.5 .2 13.7 (16.6 ) (.8 ) (17.4 ) Net unrealized investment (losses) gains, pre-tax (204.5 ) 2.6 (201.9 ) (43.9 ) (3.2 ) (47.1 ) Income tax benefit (expense) 24.9 — 24.9 14.7 (.1 ) 14.6 Net unrealized investment $ (179.6 ) $ 2.6 $ (177.0 ) $ (29.2 ) $ (3.3 ) $ (32.5 )
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 and six months ended June 30, 2016 and 2015 : Three Months Ended Six Months Ended June 30, June 30, Millions 2016 2015 2016 2015 Fixed maturity investments $ .8 $ (.2 ) $ 1.3 $ — Common equity securities — 4.7 — 2.9 Other long-term investments 11.8 (5.5 ) 12.9 .2 Total unrealized investment gains (losses), pre-tax - Level 3 investments $ 12.6 $ (1.0 ) $ 14.2 $ 3.1
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 June 30, 2016 and December 31, 2015 were as follows: June 30, 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 $ 261.2 $ .7 $ — $ — $ 261.9 Debt securities issued by corporations 1,046.9 19.3 (.1 ) — 1,066.1 Municipal obligations 294.8 8.2 (.1 ) — 302.9 Mortgage and asset-backed securities 2,646.8 10.4 (2.0 ) — 2,655.2 Foreign government, agency and provincial obligations 1.0 .2 — — 1.2 Preferred stocks 78.3 6.4 — — 84.7 Total fixed maturity investments $ 4,329.0 $ 45.2 $ (2.2 ) $ — $ 4,372.0 Less: fixed maturity investments reclassified to assets held for sale related to SSIE 9.2 Total fixed maturity investments $ 4,362.8 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 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 Less: fixed maturity investments reclassified to assets held for sale related to SSIE 9.5 Total fixed maturity investments $ 2,630.2 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 June 30, 2016 and December 31, 2015 were as follows: June 30, 2016 Millions Cost or amortized cost Gross unrealized gains Gross unrealized losses Net foreign Carrying value Common equity securities $ 374.1 $ 43.5 $ (10.1 ) $ — $ 407.5 Other long-term investments $ 305.0 $ 36.7 $ (10.3 ) $ (2.2 ) $ 329.2 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 June 30, 2016 and December 31, 2015 : Carrying Value at Millions June 30, 2016 December 31, 2015 Hedge funds and private equity funds, at fair value (1) $ 127.8 $ 127.8 Private equity securities and limited liability companies, at fair value (1) 84.3 82.1 Surplus notes investments, at fair value (1) 62.8 51.5 Private convertible preferred securities (1) 34.1 32.7 Tax advantaged federal affordable housing development fund (2) 13.4 14.7 Partnership investments accounted for under the equity method 3.5 3.8 Other 3.3 3.2 Total other-long term investments $ 329.2 $ 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 June 30, 2016 and December 31, 2015 : June 30, 2016 December 31, 2015 Millions Fair Value Unfunded Commitments Fair Value Unfunded Commitments Hedge funds Long/short equity REIT $ 20.5 $ — $ 20.6 $ — Long/short banks and financial 13.6 — 12.8 — Other 3.5 — 3.6 — Total hedge funds 37.6 — 37.0 — Private equity funds Aerospace/Defense/Government 25.9 23.5 19.8 30.3 Manufacturing/Industrial 24.8 20.2 24.9 2.5 Energy infrastructure & services 19.1 3.2 20.7 3.4 Multi-sector 11.1 2.1 14.8 2.1 Private equity secondaries 3.8 2.1 4.4 2.1 Healthcare 3.5 .4 3.8 .4 Insurance 1.7 41.3 2.0 41.3 Real estate .3 .1 .4 .1 Direct lending/Mezzanine debt — 37.5 — — Total private equity funds 90.2 130.4 90.8 82.2 Total hedge funds and private equity funds included in other long-term investments $ 127.8 $ 130.4 $ 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 June 30, 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 14.6 — — 14.6 Semi-annual — 20.5 — 20.5 Annual — — 2.5 2.5 Total $ 14.6 $ 20.5 $ 2.5 $ 37.6
Fair Value of private equity funds subject to lock-up periods	As of June 30, 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 $27.1 $3.5 $59.6 $— $90.2
Fair value measurements by level, investment securities	The following tables summarize White Mountains’s fair value measurements for investments as of June 30, 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 common 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 U.S. Intermediate Aggregate and S&P 500 indices. June 30, 2016 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 261.9 $ 252.3 $ 9.6 $ — Debt securities issued by corporations: Consumer 333.5 — 333.5 — Health Care 157.3 — 157.3 — Financials 154.8 — 154.8 — Industrial 139.0 — 139.0 — Utilities 94.3 — 94.3 — Energy 60.6 — 60.6 — Technology 57.3 — 57.3 — Communications 43.3 — 43.3 — Materials 26.0 — 26.0 — Total debt securities issued by corporations 1,066.1 — 1,066.1 — Mortgage and asset-backed securities 2,655.2 2,573.2 82.0 Municipal obligations 302.9 — 302.9 — Foreign government, agency and provincial obligations 1.2 .6 .6 — Preferred stocks 84.7 — 13.5 71.2 Total fixed maturity investments (4) 4,372.0 252.9 3,965.9 153.2 Short-term investments (4) 422.1 422.1 — — Common equity securities: Consumer 152.8 152.8 — — Exchange traded funds (1) 87.5 65.6 21.9 — Health Care 36.4 36.4 — — Communications 32.7 32.7 — — Technology 24.8 24.8 — — Other 73.3 — 73.3 — Total common equity securities 407.5 312.3 95.2 — Other long-term investments (2)(3) 184.5 — — 184.5 Total investments (4) $ 5,386.1 $ 987.3 $ 4,061.1 $ 337.7 (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 $3.5 associated with other long-term investment limited partnerships accounted for using the equity method. Excludes carrying value of $13.4 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. (4) Includes carrying value of $9.2 in fixed maturity investments and $0.3 in short-term investments that are classified as assets held for sale related to SSIE. 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 — Total debt securities issued by corporations 1,000.0 — 1,000.0 — Mortgage 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 (4) 2,639.7 134.0 2,435.7 70.0 Short-term investments (4) 211.3 211.3 — — Common equity securities: Financials 694.7 694.7 — — Exchange traded funds (1) 141.8 120.5 21.3 — 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) $ 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. (4) Includes carrying value of $9.5 in fixed maturity investments and $0.1 in short-term investments that are classified as assets held for sale related to SSIE.
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 June 30, 2016 and December 31, 2015 : Fair Value at Millions June 30, 2016 December 31, 2015 AAA $ — $ — AA 125.7 95.2 A 376.6 397.7 BBB 563.8 507.1 Other — — Debt securities issued by corporations (1) $ 1,066.1 $ 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	June 30, 2016 December 31, 2015 Millions Fair Value Level 2 Level 3 Fair Value Level 2 Level 3 Mortgage-backed securities: Agency: GNMA $ 284.7 $ 284.7 $ — $ 265.5 $ 265.5 $ — FNMA 203.5 152.5 51.0 42.2 42.2 — FHLMC 37.5 37.5 — 22.8 22.8 — Total Agency (1) 525.7 474.7 51.0 330.5 330.5 — Non-agency: Residential 194.3 194.3 — 133.2 133.2 — Commercial 104.5 104.5 — 140.4 140.4 — Total Non-agency 298.8 298.8 — 273.6 273.6 — Total mortgage-backed securities 824.5 773.5 51.0 604.1 604.1 — Other asset-backed securities: Credit card receivables 689.1 658.1 31.0 217.7 217.7 — Vehicle receivables 977.4 977.4 — 269.7 269.7 — Other 164.2 164.2 — 75.5 75.5 — Total other asset-backed securities 1,830.7 1,799.7 31.0 562.9 562.9 — Total mortgage and asset-backed securities $ 2,655.2 $ 2,573.2 $ 82.0 $ 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 June 30, 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 $ 194.3 $ 21.9 $ 6.4 $ 3.4 $ — $ 3.2 $ — $ 10.8 $ 11.8 $ 6.9 $ 12.3 $ 65.3 $ 52.3 Non-agency CMBS 104.5 — — — — — — 5.0 — 18.4 11.6 23.4 46.1 Total $ 298.8 $ 21.9 $ 6.4 $ 3.4 $ — $ 3.2 $ — $ 15.8 $ 11.8 $ 25.3 $ 23.9 $ 88.7 $ 98.4
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 June 30, 2016 : Millions Fair Value Super Senior (1) Senior (2) Subordinate (3) Prime $ 187.4 $ 133.6 $ 53.8 $ — Non-prime 6.9 — 6.9 — Sub-prime — — — — Total $ 194.3 $ 133.6 $ 60.7 $ — (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 June 30, 2016 : Millions Fair Value Super Senior (1) Senior (2) Subordinate (3) Fixed rate CMBS $ 93.2 $ 8.9 $ 46.1 $ 38.2 Floating rate CMBS 11.3 — — 11.3 Total $ 104.5 $ 8.9 $ 46.1 $ 49.5 (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 six months ended June 30, 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)(4) Total realized and unrealized gains (losses) 7.1 38.3 1.3 — 12.9 (2.0 ) 57.6 Amortization/Accretion .1 (8.1 ) — — — — (8.0 ) Purchases 1,449.7 2,076.9 84.7 — 2.1 9.1 3,622.5 Sales (2,043.9 ) (577.4 ) (2.8 ) — — (7.1 ) (2,631.2 ) Transfers in — — — — — — — Transfers out — — — — — — — Balance at June 30, 2016 $ 565.2 $ 4,061.1 $ 153.2 $ — $ 184.5 $ 127.8 $ 5,091.8 (1)(2)(4) (1) Excludes carrying value of $3.8 and $3.5 at January 1, 2016 and June 30, 2016 associated with other long-term investments accounted for using the equity method. Excludes carrying value of $14.7 and $13.4 at January 1, 2016 and June 30, 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 $ 422.1 at January 1, 2016 and June 30, 2016 associated with short-term investments, of which $0.1 and $0.3 is classified as held for sale at January 1, 2016 and June 30, 2016 . (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 - “Summary of Significant Accounting Policies” ). (4) Includes carrying value of $9.5 and $ 9.2 of fixed maturity investments at January 1, 2016 and June 30, 2016 that is classified as assets held for sale related to SSIE. 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 $ 126.9 $ 177.3 $ 3,343.6 (1)(2)(5) Total realized and unrealized gains (losses) 9.0 5.9 — 6.6 (6.8 ) (3.6 ) 11.1 (3) Amortization/Accretion — (9.9 ) — — — — (9.9 ) Purchases 495.4 734.3 35.3 — 22.5 6.2 1,293.7 Sales (604.2 ) (616.0 ) — (13.1 ) (2.3 ) (23.3 ) (1,258.9 ) Transfers in — 34.9 — — — — 34.9 Transfers out — — (34.9 ) — — — (34.9 ) Balance at June 30, 2015 $ 450.8 $ 2,522.1 $ 76.8 $ 33.0 $ 140.3 $ 156.6 $ 3,379.6 (1)(2)(5) (1) Excludes carrying value of $ 5.2 and $3.9 at January 1, 2015 and June 30, 2015 associated with other long-term investment limited partnerships accounted for using the equity method. Excludes carrying value of $16.8 and $15.8 at January 1, 2015 and June 30, 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 $ 401.3 at January 1, 2015 and June 30, 2015 associated with short-term investments of which $1.9 and $1.1 is classified as held for sale at January 1, 2015 and June 30, 2015 . (3) Excludes $0.9 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 - “Summary of Significant Accounting Policies” ). (5) Includes carrying value of $10.1 and $9.1 of fixed maturity investments at January 1, 2015 and June 30, 2015 that is classified as assets held for sale related to SSIE.
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 June 30, 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 June 30, 2016 $ in millions, except share price Rating (2) Valuation Technique(s) Fair (3) Unobservable Input Preferred Stock (1) NR Discounted cash flow $71.2 Discount yield - 7.04% Asset-backed securities (1) AAA Broker pricing $31.0 Broker quote Agency residential mortgage-backed securities (1) (7) AA+ Discounted cash flow $51.0 Prepayment - 15 CPR Discount spread/Treasury - 95 bps 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 $7.1 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 $9.7 Time until expiration - 4 years Volatility/Standard deviation - 60.0% Risk free rate - 1.15% Surplus notes: NR - Seller priority Discounted cash flow $44.2 Discount rate (4) - 10.6% Timing of interest payments (6) - 5 years Timing of principal payments (6) - 10 years - Pari passu Discounted cash flow $18.6 Discount rate (5) - 18.0% Timing of interest payments (6) - 5 years Timing of principal payments (6) - 15 years (1) As of June 30, 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. (7) Conditional prepayment rate (“CPR”) is an annualized percentage of the existing mortgage pool that is expected to be prepaid in a year. The assumed prepayment rate is a significant unobservable input used to estimate the fair value of investments in mortgage-backed securities. Generally for bonds priced at a premium, increases in prepayment speeds will result in a lower fair value, while decreases in prepayment speed may result in a higher fair value, with the inverse for bonds priced at a discount. Description December 31, 2015 $ in millions, except share price Rating (2) Valuation Technique(s) Fair (3) Unobservable Input Preferred Stock (1)(7) NR Par value (7) $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: 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) 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)	6 Months Ended
	Jun. 30, 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 June 30, Millions 2016 2015 Goodwill Other intangible assets Goodwill Other intangible assets Beginning balance $ 24.1 $ 32.2 $ 24.1 $ 39.0 Amounts held for sale at beginning of the period (1) — .3 — .7 Amortization, including foreign currency translation — (3.3 ) — (2.7 ) Amounts held for sale at end of the period (1) — — — (.6 ) Ending balance $ 24.1 $ 29.2 $ 24.1 $ 36.4 Six Months Ended June 30, Millions 2016 2015 Goodwill Other intangible assets Goodwill Other intangible assets Beginning balance $ 24.1 $ 31.3 $ 23.8 $ 38.7 Amounts held for sale at beginning of the period (1) — .4 — .8 Acquisitions of businesses — — .3 2.8 Acquisitions of intangible assets — 3.9 — — Amortization, including foreign currency translation — (6.4 ) — (5.3 ) Amounts held for sale at end of the period (1) — — — (.6 ) Ending balance $ 24.1 $ 29.2 $ 24.1 $ 36.4 (1) See Note 17 - “Discontinued Operations” .

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2016
Debt Disclosure [Abstract]
Schedule of debt outstanding	White Mountains’s debt outstanding as of June 30, 2016 and December 31, 2015 consisted of the following: Millions June 30, Effective Rate (1) December 31, Effective Rate (1) WTM Bank Facility $ — N/A $ 50.0 3.9% OBH Senior Notes, at face value 275.0 4.7% 275.0 4.7% Unamortized original issue discount and debt issuance costs (2.0 ) (2.1 ) OBH Senior Notes, carrying value 273.0 272.9 OneBeacon Bank Facility — N/A — N/A MediaAlpha Bank Facility 17.0 5.9% 15.0 5.5% Unamortized issuance cost (.2 ) (.3 ) MediaAlpha Bank Facility, carrying value 16.8 14.7 Total debt $ 289.8 $ 337.6 (1) Effective rate considers the effect of the debt issuance costs.

Derivatives (Tables)

Derivatives (Tables) - Variable Annuity	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2016 and 2015 . Three Months Ended Six Months Ended June 30, June 30, Millions 2016 2015 2016 2015 Fees, included in other revenue $ .3 $ 2.6 $ 1.2 $ 5.6 Change in fair value of variable annuity liability, included in other revenue .1 .7 (.3 ) 1.1 Change in fair value of derivatives, included in other revenue (.3 ) (2.3 ) (2.0 ) (7.8 ) Foreign exchange, included in other revenue .4 — 1.3 (1.2 ) Other investment income and (losses) gains — (.1 ) — (.2 ) Total revenue .5 .9 .2 (2.5 ) 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 (.2 ) (.1 ) (.3 ) — General and administrative expenses (1.2 ) (.9 ) (1.9 ) (2.3 ) Pre-tax income (loss) $ (.9 ) $ (.1 ) $ (2.0 ) $ (4.8 )
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 and six months ended June 30, 2016 and 2015 and the carrying values, included in other assets, at June 30, 2016 and December 31, 2015 by type of instrument: Gains (losses) Carrying Value Three Months Ended Six Months Ended As of June 30, June 30, June 30, December 31, 2015 Millions 2016 2015 2016 2015 Fixed income/interest rate $ — $ (5.9 ) $ 1.8 $ 3.4 $ — $ .5 Foreign exchange (.6 ) 9.2 (4.8 ) (2.9 ) — 14.8 Equity .3 (5.6 ) 1.0 (8.3 ) — 4.8 Total $ (.3 ) $ (2.3 ) $ (2.0 ) $ (7.8 ) $ — $ 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 and six months ended June 30, 2016 and 2015 : Three Months Ended June 30, 2016 Variable Annuity Assets (Liabilities) Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ (.1 ) $ 2.6 $ 10.3 $ .2 $ 13.1 Purchases — — — — — Realized and unrealized gains (losses) .1 1.7 (1.8 ) (.2 ) (.3 ) Transfers in — — — — — Sales/settlements — (4.3 ) (8.5 ) — (12.8 ) End of period $ — $ — $ — $ — $ — Six Months Ended June 30, 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) (.3 ) 2.9 (.7 ) (4.2 ) (2.0 ) Transfers in — — — — — Sales/settlements — (5.6 ) (15.8 ) 3.3 (18.1 ) End of period $ — $ — $ — $ — $ — Three Months Ended June 30, 2015 Variable Annuity Assets Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ 1.1 $ 17.0 $ 31.2 $ (1.2 ) $ 47.0 Purchases — — — — — Realized and unrealized gains (losses) .7 (8.3 ) .6 5.4 (2.3 ) Transfers in — — — — — Sales/settlements — (.4 ) .7 (9.3 ) (9.0 ) End of period $ 1.8 $ 8.3 $ 32.5 $ (5.1 ) $ 35.7 Six Months Ended June 30, 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) 1.1 (9.0 ) (5.9 ) 7.1 (7.8 ) Transfers in — — — — — Sales/settlements — (1.6 ) 4.6 (15.9 ) (12.9 ) End of period $ 1.8 $ 8.3 $ 32.5 $ (5.1 ) $ 35.7 (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 June 30, 2016 December 31, 2015 June 30, 2015 Cash $ — $ 5.8 $ 20.9 Fixed maturity investments — — 4.4 Total $ — $ 5.8 $ 25.3
Exchange traded and OTC derivative instruments	The following summarizes amounts offset under master netting agreements: June 30, 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 $ — $ — $ — $ 2.4 $ (2.1 ) $ .3 Exchange traded — — — .1 (.1 ) — Foreign exchange contracts OTC — — — 15.0 — 15.0 Exchange traded — — — .1 (.3 ) (.2 ) Equity contracts OTC — — — 4.4 (.6 ) 3.8 Exchange traded — — — 1.2 — 1.2 Total (2) $ — $ — $ — $ 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 were 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 as of December 31, 2015: 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 WM Life Re- Cash Net amount of exposure to counter-party Standard & Poor's Rating (1) JP Morgan $ 8.5 $ — $ — $ 8.5 $ — $ — $ 5.5 $ 3.0 A + Bank of America .7 — — .7 — — — .7 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)	6 Months Ended
	Jun. 30, 2016
Guarantees [Abstract]
Schedule of Municipal Bond Guarantee Insured Obligations	The following table provides a schedule of BAM’s insured obligations: June 30, 2016 December 31, 2015 Contracts outstanding 3,910 3,103 Remaining weighted average contract period outstanding (in years) 10.9 12.8 Contractual debt service outstanding (in millions): Principal $ 27,780.2 $ 22,556.0 Interest 14,074.2 11,984.4 Total debt service outstanding $ 41,854.4 $ 34,540.4 Gross unearned insurance premiums $ 63.3 $ 50.2
Financial Guarantee Insurance Contracts, Premium Received over Contract Period [Table Text Block]	The following table is a schedule of BAM’s future premium revenues as of June 30, 2016 : Millions June 30, 2016 July 1, 2016 - December 31, 2016 $ 2.9 January 1, 2017 - March 31, 2017 1.4 April 1, 2017 - June 30, 2017 1.4 July 1, 2017 - September 30, 2017 1.4 October 1, 2017 - December 31, 2017 1.4 5.6 2018 5.3 2019 5.1 2020 4.8 2022 and thereafter 39.6 Total $ 63.3

Earnings Per Share (Tables)

Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2016 and 2015 . (See Note 17 - “Discontinued Operations” ). Three Months Ended Six Months Ended June 30, June 30, 2016 2015 2016 2015 Basic and diluted earnings per share numerators (in millions): Net income (loss) from continuing operations attributable to White Mountains’s common shareholders $ (17.5 ) $ 4.8 $ (5.6 ) $ 17.8 Allocation of income for unvested restricted common shares .2 (.1 ) .1 (.2 ) Dividends declared on participating restricted common shares (1) — — (.1 ) (.1 ) Total allocation to restricted common shares .2 (.1 ) — (.3 ) Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ (17.3 ) $ 4.7 $ (5.6 ) $ 17.5 Undistributed net earnings (in millions): Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ (17.3 ) $ 4.7 $ (5.6 ) $ 17.5 Dividends declared net of restricted common share amounts (1) — — (5.9 ) (5.9 ) Total undistributed net earnings, net of restricted common share amounts $ (17.3 ) $ 4.7 $ (11.5 ) $ 11.6 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 5,096.1 5,985.7 5,317.8 5,982.1 Average unvested restricted shares (2) (66.5 ) (71.4 ) (60.2 ) (65.2 ) Basic earnings per share denominator 5,029.6 5,914.3 5,257.6 5,916.9 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period (3) 5,107.0 5,985.7 5,324.3 5,982.1 Average unvested restricted common shares (2) (66.5 ) (71.4 ) (60.2 ) (65.2 ) Diluted earnings per share denominator (3) 5,040.5 5,914.3 5,264.1 5,916.9 Basic earnings per share (in dollars): Net income attributable to White Mountains’s common shareholders $ (3.44 ) $ .80 $ (1.07 ) $ 2.96 Dividends declared and paid — — (1.00 ) (1.00 ) Undistributed earnings $ (3.44 ) $ .80 $ (2.07 ) $ 1.96 Diluted earnings per share (in dollars): Net income attributable to White Mountains’s common shareholders $ (3.43 ) $ .80 $ (1.06 ) $ 2.96 Dividends declared and paid — — (1.00 ) (1.00 ) Undistributed earnings $ (3.43 ) $ .80 $ (2.06 ) $ 1.96 (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 and six months ended June 30, 2016 includes the impact of 120,000 common shares issuable upon exercise of the non-qualified options outstanding, which results in 10,863 and 6,194 incremental shares outstanding over the periods.

Non-controlling Interest (Table

Non-controlling Interest (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2016 and December 31, 2015 : June 30, 2016 December 31, 2015 $ in millions Non-controlling Percentage Non-controlling Equity Non-controlling Percentage Non-controlling Equity OneBeacon Ltd. 23.9 % $ 244.8 24.5 % $ 245.6 SIG Preference Shares N/A — 100.0 250.0 Other, excluding mutuals and reciprocals HG Global 3.1 17.0 3.1 17.1 MediaAlpha 40.0 13.2 40.0 14.4 Tranzact 36.8 79.2 36.8 79.4 Wobi 3.5 .5 3.9 .6 Dewar 18.8 3.7 18.6 3.7 Total other, excluding mutuals and reciprocals 113.6 115.2 Mutuals and reciprocals BAM 100.0 (138.0 ) 100.0 (140.0 ) SSIE 100.0 3.8 100.0 (16.0 ) Total mutuals and reciprocals (134.2 ) (156.0 ) Total non-controlling interests $ 224.2 $ 454.8

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2016 Earned insurance premiums $ 271.4 $ 1.0 $ .4 $ 1.9 $ 274.7 Net investment income 12.1 .5 1.8 4.8 19.2 Net investment income (loss) - surplus note interest — 4.4 (4.4 ) — — Net realized and unrealized investment gains (losses) 24.7 .5 3.2 (.3 ) 28.1 Other revenue .8 — .3 35.1 (2) 36.2 Total revenues 309.0 6.4 1.3 41.5 358.2 Losses and LAE 179.7 — — 2.3 182.0 Insurance acquisition expenses 48.7 .2 .6 .6 50.1 Other underwriting expenses 50.9 — .1 — 51.0 General and administrative expenses 3.2 .3 9.6 56.7 (3) 69.8 Amortization of intangible assets .3 — — 3.0 3.3 Interest expense 3.2 — — .9 4.1 Total expenses 286.0 .5 10.3 63.5 360.3 Pre-tax income (loss) $ 23.0 $ 5.9 $ (9.0 ) $ (22.0 ) $ (2.1 ) HG Global/BAM Millions OneBeacon HG BAM (1) Other Operations Total Six Months Ended June 30, 2016 Earned insurance premiums $ 550.0 $ 1.9 $ .7 $ 4.2 $ 556.8 Net investment income 26.5 1.0 3.4 6.2 37.1 Net investment income (loss) - surplus note interest — 8.9 (8.9 ) — — Net realized and unrealized investment gains 41.3 2.6 8.1 5.6 57.6 Other revenue 1.7 — .4 73.9 (2) 76.0 Total revenues 619.5 14.4 3.7 89.9 727.5 Losses and LAE 338.5 — — 4.6 343.1 Insurance acquisition expenses 99.7 .4 1.3 1.4 102.8 Other underwriting expenses 106.2 — .2 — 106.4 General and administrative expenses 6.8 .8 18.8 127.4 (3) 153.8 Amortization of intangible assets .6 — — 5.8 6.4 Interest expense 6.5 — — 2.1 8.6 Total expenses 558.3 1.2 20.3 141.3 721.1 Pre-tax income (loss) $ 61.2 $ 13.2 $ (16.6 ) $ (51.4 ) $ 6.4 HG Global/BAM Millions OneBeacon HG BAM (1) Other Operations Total Three Months Ended June 30, 2015 Earned insurance premiums $ 319.3 $ .6 $ .1 $ 1.8 $ 321.8 Net investment income 10.1 .5 .8 1.8 13.2 Net investment income (loss) - surplus note interest — 3.9 (3.9 ) — — Net realized and unrealized investment (losses) gains (14.0 ) (1.4 ) (1.9 ) 2.3 (15.0 ) Other (loss) revenue (1.2 ) — .2 49.7 (2) 48.7 Total revenues 314.2 3.6 (4.7 ) 55.6 368.7 Losses and LAE 194.5 — — 1.7 196.2 Insurance acquisition expenses 56.4 .1 .6 .7 57.8 Other underwriting expenses 52.9 — .1 — 53.0 General and administrative expenses 3.8 .4 8.7 47.8 (3) 60.7 Amortization of intangible assets .4 — — 2.3 2.7 Interest expense 3.3 — — .1 3.4 Total expenses 311.3 .5 9.4 52.6 373.8 Pre-tax income (loss) $ 2.9 $ 3.1 $ (14.1 ) $ 3.0 $ (5.1 ) HG Global/BAM Millions OneBeacon HG BAM (1) Other Operations Total Six Months Ended June 30, 2015 Earned insurance premiums $ 605.9 $ 1.1 $ .3 $ 3.8 $ 611.1 Net investment income 20.6 .9 1.8 2.5 25.8 Net investment income (loss) - surplus note interest — 7.9 (7.9 ) — — Net realized and unrealized investment gains (losses) .2 (.3 ) 1.1 9.0 10.0 Other (loss) revenue (4.3 ) — .3 80.1 (2) 76.1 Total revenues 622.4 9.6 (4.4 ) 95.4 723.0 Losses and LAE 360.4 — — 3.7 364.1 Insurance acquisition expenses 107.4 .2 1.4 1.8 110.8 Other underwriting expenses 108.8 — .2 — 109.0 General and administrative expenses 7.6 .8 16.9 103.7 (3) 129.0 Amortization of intangible assets .7 — — 4.6 5.3 Interest expense 6.5 — — .4 6.9 Total expenses 591.4 1.0 18.5 114.2 725.1 Pre-tax income (loss) $ 31.0 $ 8.6 $ (22.9 ) $ (18.8 ) $ (2.1 ) (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 $ 28.1 and $ 60.8 from MediaAlpha for the three months and six months ended June 30, 2016 , and $ 23.2 and $ 52.9 from MediaAlpha for the three months and six months ended June 30, 2015 . (3) Includes $ 26.0 and $ 56.5 from MediaAlpha for the three months and six months ended June 30, 2016 , and $ 21.9 and $ 49.6 from MediaAlpha for the three months and six months ended June 30, 2015 .

Investments in Unconsolidated39

Investments in Unconsolidated Affiliates (Tables)	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2015: Three Months Ended Six Months Ended Millions June 30, 2015 June 30, 2015 Equity method carrying value of investment in Symetra at the beginning of the period $ 447.3 $ 411.4 Equity in earnings (1)(2) 6.1 13.3 Equity in net unrealized losses from Symetra’s fixed maturity portfolio (3) (66.4 ) (35.5 ) Dividends received (2.2 ) (4.4 ) Distribution from Prospector Offshore Fund 12.4 12.4 Equity method carrying value of investment in Symetra at the end of the period (4) $ 397.2 $ 397.2 (1) For the three and six months ended June 30, 2015 , equity in earnings excludes tax expense of $0.4 and $0.8 . (2) For the three and six months ended June 30, 2015 , equity in earnings includes $0.7 and $1.4 increase relating to the pre-tax amortization of the Symetra common share basis difference. (3) For the three and six months ended June 30, 2015 , net unrealized gains includes $2.8 and $5.7 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 $2.0 as of June 30, 2015 , which excludes tax expense of $0.0 .

Employee Share-Based Incentiv40

Employee Share-Based Incentive Compensation Plans (Tables)	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2016 and 2015 for performance shares granted under the WTM Incentive Plan: Three Months Ended June 30, Six Months Ended June 30, 2016 2015 2016 2015 Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Beginning of period 111,387 $ 71.3 108,545 $ 25.7 96,358 $ 57.7 113,295 $ 44.4 Shares paid or expired (1) (36,294 ) (41.3 ) — — (36,294 ) (41.3 ) (34,001 ) (24.9 ) New grants — — 750 — 16,215 — 29,878 — Forfeitures and cancellations (2) 908 .9 (19 ) — (278 ) .3 104 .5 Expense recognized — 1.3 — 3.1 — 15.5 — 8.8 End of period (3) 76,001 $ 32.2 109,276 $ 28.8 76,001 $ 32.2 109,276 $ 28.8 (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 June 30, 2016 and 2015 both exclude 4,428 and 7,851 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 June 30, 2016 for each performance cycle: Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Performance cycle: 2016 – 2018 16,215 $ 2.2 2015 – 2017 29,478 12.7 2014 – 2016 32,256 18.2 Sub-total 77,949 33.1 Assumed forfeitures (1,948 ) (.9 ) Total at June 30, 2016 76,001 $ 32.2
Summary of restricted share activity	The following table summarizes the unrecognized compensation cost associated with the outstanding restricted share awards for the three and six months ended June 30, 2016 and 2015 : Three Months Ended June 30, Six Months Ended June 30, 2016 2015 2016 2015 Millions, except share amounts Restricted Unamortized Restricted Unamortized Restricted Shares Unamortized Issue Date Fair Value Restricted Shares Unamortized Issue Date Fair Value Non-vested, Beginning of period 66,470 $ 29.2 71,125 $ 26.5 70,675 $ 15.7 83,314 $ 14.3 Issued — — 750 .5 21,215 16.3 23,640 15.7 Vested — — — — (24,620 ) — (35,079 ) — Forfeited — — — — (800 ) .2 — — Expense recognized (1) — (5.0 ) — (3.8 ) — (8.0 ) — (6.8 ) End of period (2) 66,470 $ 24.2 71,875 $ 23.2 66,470 $ 24.2 71,875 $ 23.2 (1) In connection with the sale of Sirius Group in the second quarter of 2016, White Mountains recognized $ 1.4 from accelerating the amortization of the issue date fair value for shares issued to Sirius Group employees, who no longer have a service obligation to the Company. (2) Outstanding restricted share awards as of June 30, 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 and six months ended June 30, 2016 and 2015 for OneBeacon performance shares granted under the OneBeacon Incentive Plan: Three Months Ended June 30, Six Months Ended June 30, 2016 2015 2016 2015 Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Target Performance Shares Outstanding Accrued Expense Beginning of period 441,206 $ 1.1 462,147 $ 2.1 449,435 $ 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 — (.1 ) — .3 — .3 — .5 End of period 441,206 $ 1.0 462,147 $ 2.4 441,206 $ 1.0 462,147 $ 2.4 (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 June 30, 2016 for each performance cycle: Millions, except share amounts Target Accrued Expense Performance cycle: 2016 – 2018 163,150 $ .4 2015 – 2017 146,659 .6 2014 – 2016 142,710 — Sub-total 452,519 1.0 Assumed forfeitures (11,313 ) — Total at June 30, 2016 441,206 $ 1.0
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 and six months ended June 30, 2016 and 2015 : Three Months Ended June 30, Six Months Ended June 30, 2016 2015 2016 2015 Millions, except share amounts Restricted Unamortized Restricted Unamortized Restricted Unamortized Restricted Unamortized Non-vested, Beginning of period 395,872 $ 4.3 390,950 $ 4.0 382,722 $ 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 — (.8 ) — (.5 ) — (1.3 ) — (1.1 ) End of period 395,872 $ 3.5 390,950 $ 3.5 395,872 $ 3.5 390,950 $ 3.5

Fair Value of Financial Instr41

Fair Value of Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2016 and December 31, 2015 : June 30, 2016 December 31, 2015 Millions Fair Value Carrying Value Fair Value Carrying Value OBH Senior Notes $ 279.7 $ 273.0 $ 276.4 $ 272.9 MediaAlpha Bank Facility 17.0 16.8 15.0 14.7

Discontinued Operations (Tables

Discontinued Operations (Tables)	6 Months Ended
	Jun. 30, 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 business classified as held for sale. At December 31, 2015, amounts presented relate to Sirius Group, Tranzact, Abiaka and SSIE. At June 30, 2016, the amounts presented relate to Tranzact, Abiaka, SSIE and Ashmere, a subsidiary formerly owned by Sirius Group. Millions June 30, 2016 December 31, 2015 Assets held for sale Fixed maturity investments, at fair value $ 14.4 $ 2,383.5 Short-term investments, at amortized cost (which approximates fair value) 4.2 352.1 Common equity securities, at fair value — 174.4 Other long-term investments — 72.2 Total investments 18.6 2,982.2 Cash 1.9 150.2 Reinsurance recoverable on unpaid losses .4 283.6 Reinsurance recoverable on paid losses — 10.2 Insurance and reinsurance premiums receivable 2.4 326.6 Deferred acquisition costs — 74.6 Deferred tax asset — 303.1 Ceded unearned insurance and reinsurance premiums — 87.7 Accounts receivable on unsettled investment sales — 29.0 Goodwill and intangible assets 315.1 330.5 Other assets 46.2 212.7 Total assets held for sale $ 384.6 $ 4,790.4 Liabilities held for sale Loss and loss adjustment expense reserves $ 5.7 $ 1,650.4 Unearned insurance and reinsurance premiums 1.8 344.3 Debt 96.9 506.4 Deferred tax liability 8.7 270.6 Accrued incentive compensation 1.0 64.2 Ceded reinsurance payable (.2 ) 67.7 Funds held under reinsurance treaties — 52.9 Accounts payable on unsettled investment purchases — — Other liabilities 36.7 111.9 Total liabilities held for sale 150.6 3,068.4 Net assets held for sale $ 234.0 $ 1,722.0 Net Income from Discontinued Operations The following summarizes the results of operations, including related income taxes associated with the business classified as discontinued operations. For the three and six months ended June 30, 2016, the amounts presented relate to Sirius Group and Tranzact. For the three and six months ended June 30, 2015, the amounts presented relate to the sales of Sirius Group, Tranzact, Esurance, and the OneBeacon's runoff business. The results of discontinued operations from Sirius Group up to the closing date of the transaction inure to White Mountains. Three Months Ended Three Months Ended June 30, 2016 June 30, 2015 Millions Sirius Group Other Disc Ops Total Sirius Group Other Disc Ops Total Revenues Earned insurance premiums $ 37.7 $ — $ 37.7 $ 215.5 $ — $ 215.5 Net investment income 2.2 — 2.2 9.1 — 9.1 Net realized and unrealized gains (losses) 7.3 — 7.3 (46.1 ) — (46.1 ) Other revenue 4.7 47.0 51.7 5.4 34.7 40.1 Total revenues 51.9 47.0 98.9 183.9 34.7 218.6 Expenses Loss and loss adjustment expenses 41.2 — 41.2 92.1 — 92.1 Insurance and reinsurance acquisition expenses 10.6 — 10.6 47.5 — 47.5 Other underwriting expenses 4.2 — 4.2 27.7 — 27.7 General and administrative expenses .2 49.2 49.4 6.7 38.0 44.7 Interest expense 1.3 1.3 2.6 6.6 .9 7.5 Total expenses 57.5 50.5 108.0 180.6 38.9 219.5 Pre-tax (loss) income (5.6 ) (3.5 ) (9.1 ) 3.3 (4.2 ) (.9 ) Income tax benefit (expense) 2.2 (1.1 ) 1.1 .5 — .5 Net (loss) income from discontinued operations (3.4 ) (4.6 ) (8.0 ) 3.8 (4.2 ) (.4 ) Net gain from sales of discontinued operations - Sirius 366.6 — 366.6 — — — Net gain from sales of discontinued operations - OneBeacon — — — — .3 .3 Net loss from sale of discontinued operations - Esurance — — — — (.4 ) (.4 ) Total income (loss) from discontinued operations $ 363.2 $ (4.6 ) $ 358.6 $ 3.8 $ (4.3 ) $ (.5 ) Change in foreign currency translation and other from discontinued operations (5.2 ) — (5.2 ) 44.0 — 44.0 Change in foreign currency translation and other 113.3 — 113.3 — — — Comprehensive income (loss) from discontinued operations $ 471.3 $ (4.6 ) $ 466.7 $ 47.8 $ (4.3 ) $ 43.5 Six Months Ended Six Months Ended June 30, 2016 June 30, 2015 Millions Sirius Group Other Disc Ops Total Sirius Group Other Disc Ops Total Revenues Earned insurance premiums $ 240.1 $ — $ 240.1 $ 420.5 $ — $ 420.5 Net investment income 14.4 — 14.4 18.1 — 18.1 Net realized and unrealized (losses) gains (1.5 ) — (1.5 ) 32.3 — 32.3 Other revenue .6 104.8 105.4 (22.0 ) 72.1 50.1 Total revenues 253.6 104.8 358.4 448.9 72.1 521.0 Expenses Loss and loss adjustment expenses 154.9 — 154.9 189.6 — 189.6 Insurance and reinsurance acquisition expenses 59.0 — 59.0 90.1 — 90.1 Other underwriting expenses 30.9 — 30.9 53.2 — 53.2 General and administrative expenses 8.3 102.6 110.9 13.0 77.2 90.2 Interest expense 7.9 2.7 10.6 13.4 1.7 15.1 Total expenses 261.0 105.3 366.3 359.3 78.9 438.2 Pre-tax (loss) income (7.4 ) (.5 ) (7.9 ) 89.6 (6.8 ) 82.8 Income tax benefit (expense) 3.1 (2.1 ) 1.0 (19.9 ) — (19.9 ) Net (loss) income from discontinued operations (4.3 ) (2.6 ) (6.9 ) 69.7 (6.8 ) 62.9 Net gain from sales of discontinued operations - Sirius 366.6 — 366.6 — — — Net gain from sales of discontinued operations - OneBeacon — — — — .3 .3 Net gain from sales of discontinued operations - Esurance — — — — 7.6 7.6 Total income (loss) from discontinued operations $ 362.3 $ (2.6 ) $ 359.7 $ 69.7 $ 1.1 $ 70.8 Change in foreign currency translation and other from discontinued operations 32.0 — 32.0 (43.6 ) — (43.6 ) Change in foreign currency translation and other from sale of Sirius Group 113.3 — 113.3 — — — Comprehensive income (loss) from discontinued operations $ 507.6 $ (2.6 ) $ 505.0 $ 26.1 $ 1.1 $ 27.2 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: Six Months Ended June 30, (Millions) 2016 2015 Net cash used for operations $ (43.1 ) $ (12.9 ) Net cash provided from investing activities 229.6 59.3 Net cash provided from (used for) financing activities 9.0 (2.0 ) Effect of exchange rate changes on cash — (2.1 ) Net change in cash during the period 195.5 42.3 Cash balances at beginning of period 148.9 114.5 Cash balances at end of period $ 344.4 $ 156.8 Supplemental cash flows information: Interest paid $ (1.4 ) $ (14.5 ) Net income tax payment to national governments $ (31.8 ) $ (24.6 ) 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 and six months ended June 30, 2016 and 2015 : Three Months Ended Six Months Ended June 30, June 30, 2016 2015 2016 2015 Basic and diluted earnings per share numerators (in millions): Net income attributable to White Mountains’s common shareholders $ 358.6 $ (.5 ) $ 359.7 $ 70.8 Allocation of income for participating unvested restricted common shares (1) (4.7 ) — (4.1 ) (.8 ) Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts (2) $ 353.9 $ (.5 ) $ 355.6 $ 70.0 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 5,096.1 5,985.7 5,317.8 5,982.1 Average unvested restricted common shares (3) (66.5 ) (71.4 ) (60.2 ) (65.2 ) Basic earnings per share denominator 5,029.6 5,914.3 5,257.6 5,916.9 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period (4) 5,107.0 5,985.7 5,324.0 5,982.1 Average unvested restricted common shares (3) (66.5 ) (71.4 ) (60.2 ) (65.2 ) Diluted earnings per share denominator (4) 5,040.5 5,914.3 5,263.8 5,916.9 Basic earnings per share (in dollars): $ 70.37 $ (.08 ) $ 67.64 $ 11.84 Diluted earnings per share (in dollars): $ 70.22 $ (.08 ) $ 67.56 $ 11.84 (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 and six months ended June 30, 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 and six months ended June 30, 2016 includes the impact of 120,000 common shares issuable upon exercise of the non-qualified options outstanding, which results in 10,863 and 6,194 incremental shares outstanding over the periods.
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 June 30, 2016 and December 31, 2015 : June 30, 2016 December 31, 2015 Millions Fair Value Carrying Value Fair Value Carrying Value OBH Senior Notes $ 279.7 $ 273.0 $ 276.4 $ 272.9 MediaAlpha Bank Facility 17.0 16.8 15.0 14.7

Summary of Significant Accoun43

Summary of Significant Accounting Policies (Basis of Presentation) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Jul. 31, 2012
Basis of Presentation
Debt Issuance Cost			$ 2
Net investment income	$ 19.2	$ 13.2	37.1	$ 25.8
Income Tax Expense (Benefit)	(6)	(2.2)	(15.7)	2.4
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 6.8	$ 0	$ 14.1
OneBeacon Ltd.
Basis of Presentation
Ownership interest (as a percent)	76.10%		76.10%		75.50%
HG Global
Basis of Presentation
Surplus Notes						$ 503
Percentage of par value of policy reinsured	15.00%		15.00%
Noncontrolling equity percentage	3.10%		3.10%		3.10%
Star & Shield Insurance Exchange
Basis of Presentation
Surplus Notes	$ 1		$ 1
Noncontrolling equity percentage	100.00%		100.00%		100.00%
OneBeacon [Member]
Basis of Presentation
Debt Issuance Cost					$ 1.9
Noncontrolling equity percentage	23.90%		23.90%		24.50%
Preferred Stock | HG Global
Basis of Presentation
Ownership interest (as a percent)	96.90%		96.90%
Noncontrolling equity percentage	96.90%		96.90%		96.90%
Common Stock | HG Global
Basis of Presentation
Ownership interest (as a percent)	88.40%		88.40%
Noncontrolling equity percentage	88.40%		88.40%		88.40%

Significant Transactions (Detai

Significant Transactions (Details) $ / shares in Units, ₪ in Millions, $ in Millions	Apr. 18, 2016USD ($)	Feb. 01, 2016USD ($)	Jan. 31, 2014USD ($)	Oct. 31, 2011USD ($)	Feb. 23, 2015ILS (₪)	Feb. 23, 2015USD ($)	Feb. 19, 2014ILS (₪)	Feb. 19, 2014USD ($)	Jun. 30, 2016ILS (₪)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)$ / shares	Mar. 31, 2016USD ($)$ / shares	Jun. 30, 2015USD ($)	Dec. 31, 2014USD ($)	Jun. 30, 2016ILS (₪)	Jun. 30, 2016USD ($)	Jun. 30, 2015USD ($)	Dec. 31, 2015USD ($)	Mar. 31, 2015USD ($)	Oct. 10, 2014	Mar. 31, 2014USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Other Investments																$ 13.3	$ 28.6
Investments										$ 5,521.3						5,521.3		$ 4,271.1
Sales of common equity securities																851.3	306.8
Loss and loss adjustment expenses										182			$ 196.2			343.1	364.1
Payments to Acquire Businesses and Interest in Affiliates																8.1	2.4
Other Income										36.2			48.7			76	76.1
Assets										7,065.6						7,065.6		10,282.6
Goodwill										24.1	$ 24.1	$ 24.1	24.1	$ 23.8		24.1	24.1	24.1	$ 24.1
Intangible Assets, Net (Excluding Goodwill)										29.2	32.2	$ 32.2	36.4	38.7		29.2	36.4	31.3	$ 39
Goodwill and intangible assets										53.3						53.3		55.4
Liabilities										2,966.2						2,966.2		5,914.6
Net Income (Loss) Attributable to Noncontrolling Interest										(21.4)			0.9			(27.7)	8.2
Net gain on sale of discontinued operations										366.6			(0.1)			366.6	7.9
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
Proceeds from Contributions from Affiliates														$ 44.2
Ownership interest (as a percent)																				63.20%
Star & Shield Insurance Exchange
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase of Surplus Notes																					$ 21
Surplus Notes										1						1
Other Income																(20)
Assets										12.3						12.3		14.2
Liabilities										$ 8.5						8.5		30.3
Net Income (Loss) Attributable to Noncontrolling Interest																$ 19.9	(1.9)
WOBI
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of Business in the Insurance Market															80.00%	80.00%
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
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%	54.00%		96.50%						96.50%
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										$ 20			(0.8)
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 | ₪									₪ 16.4						₪ 16.4
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										4.4						$ 4.4
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
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
Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Increase of Book Value																479.9
Payments to Acquire Other Investments	$ 161.8									161.8
Investments																		686.2
Net gain on sale of discontinued operations																366.6
Accumulated Other Comprehensive Income Loss Net Of Tax Other Period Increase Decrease										(5.2)			44			32	(43.6)
Sale of Sirius Group [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Accumulated Other Comprehensive Income Loss Net Of Tax Other Period Increase Decrease										$ 113.3			$ 0			$ 113.3	$ 0
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%	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

Loss and Loss Adjustment Expe45

Loss and Loss Adjustment Expense Reserves (Loss and Loss Adjustment Expense) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 6.8	$ 0	$ 14.1
Gross beginning balance	1,343.8	1,304	1,389.8	1,342.2	$ 1,342.2
Less beginning reinsurance recoverable on unpaid losses	(150.4)	(141.6)	(186)	(161.6)	(161.6)
Net loss and LAE reserves	1,193.4	1,162.4	1,203.8	1,180.6	1,180.6
Loss and LAE incurred relating to current year losses	166.7	196.5	327.9	366.3
Net (favorable) and unfavorable loss reserve development	15.3	(0.3)	15.2	(2.2)
Total incurred losses and LAE	182	196.2	343.1	364.1
Current year losses	(38.1)	(43.9)	(61.2)	(67.2)
Prior year losses	(123.5)	(111.4)	(272.1)	(275.4)
Total loss and LAE payments	(161.6)	(155.3)	(333.3)	(342.6)
Net ending balance	1,213.8	1,203.7	1,213.8	1,203.7	1,203.8
Plus ending reinsurance recoverable on unpaid losses	162.8	147.1	162.8	147.1	186
Gross ending balance	1,376.6	1,350.8	1,376.6	1,350.8	$ 1,389.8
Star & Shield Insurance Exchange
Net ending balance	5.3	6.1	5.3	6.1
Star & Shield Insurance Exchange
Liability for Unpaid Claims and Claims Adjustment Expense, Consolidated Claims Current Year	5.3	6.5	5.5	7.7
Net (favorable) and unfavorable loss reserve development	$ (0.1)	$ (0.3)	$ (0.2)	$ (0.4)

Loss and Loss Adjustment Expe46

Loss and Loss Adjustment Expense Reserves (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Loss and Loss Adjustment, Expense Reserves [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax	$ 0		$ 6.8	$ 0	$ 14.1
Net (favorable) and unfavorable loss reserve development	15.3		(0.3)	15.2	(2.2)
Loss and LAE incurred relating to current year losses	166.7		196.5	327.9	366.3
Star & Shield Insurance Exchange
Loss and Loss Adjustment, Expense Reserves [Line Items]
Net (favorable) and unfavorable loss reserve development	(0.1)		$ (0.3)	(0.2)	(0.4)
OneBeacon [Member]
Loss and Loss Adjustment, Expense Reserves [Line Items]
Net (favorable) and unfavorable loss reserve development	15.4				$ 1.8
Loss and LAE incurred relating to current year losses	$ 20
OneBeacon [Member]
Loss and Loss Adjustment, Expense Reserves [Line Items]
Percentage of Quota Share Reinsurance Agreement		50.00%
Net (favorable) and unfavorable loss reserve development				$ 15.4

Third Party Reinsurance (Narrat

Third Party Reinsurance (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Reinsurance Retention Policy [Line Items]
Reinsurance recoverable on paid losses		$ 20.7	$ 7.5
Reinsurance recoverable on unpaid losses		162.8	186
OneBeacon [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance recoverable on paid losses		20.7	7.5
Reinsurance recoverable on unpaid losses		$ 162.8	$ 186
OneBeacon [Member]
Reinsurance Retention Policy [Line Items]
Percentage of Quota Share Reinsurance Agreement	50.00%
Property Catastrophe Program [Member] | OneBeacon [Member]
Reinsurance Retention Policy [Line Items]
Percentage of par value of policy reinsured		100.00%
Reinsurance Retention Policy Excess Retention Amount Reinsured Net Of Participation		$ 110
Property Catastrophe Program [Member] | Minimum | OneBeacon [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Amount Retained		20
Property Catastrophe Program [Member] | Maximum [Member] | OneBeacon [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Excess Retention, Amount Reinsured		$ 130

Investment Securities (Net Inve

Investment Securities (Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 6.8	$ 0	$ 14.1
Investment income
Total investment income	19.9	15.5	38.5	30.1
Third-party investment expenses	(0.7)	(2.3)	(1.4)	(4.3)
Net investment income, pre-tax	19.2	13.2	37.1	25.8
Fixed maturity investments.
Investment income
Total investment income	17.9	12.4	32.5	24.8
Short-term investments
Investment income
Total investment income	0.5	0.1	0.6	0.1
Common Stock
Investment income
Total investment income	0.9	2.1	2	4.3
Other long-term investments
Investment income
Total investment income	$ 0.6	$ 0.9	$ 3.4	$ 0.9

Investment Securities (Net Real

Investment Securities (Net Realized and Unrealized Investment Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 6.8	$ 0	$ 14.1
Net realized investment gains, pre-tax	2.7	42.3	259.5	57.1
Net unrealized investment gains (losses), pre-tax	25.4	(57.3)	(201.9)	(47.1)
Net realized and unrealized investment gains (losses), pre-tax	28.1	(15)	57.6	10
Income tax (expense) benefit attributable to net realized and unrealized investment gains (losses)	(9.9)	4.5	(18.4)	(2.6)
Net realized and unrealized investment gains (losses), after tax	18.2	(10.5)	39.2	7.4
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	1.8	1.6	0.7	2.1
Net unrealized investment gains (losses), pre-tax	20.7	(13.4)	42.4	(2)
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	0.1	0	0.2	0
Net unrealized investment gains (losses), pre-tax	0	0	0	0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	3.8	25.4	261.4	47.9
Net unrealized investment gains (losses), pre-tax	(10.6)	(21)	(258)	(27.7)
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized investment gains, pre-tax	(3)	15.3	(2.8)	7.1
Net unrealized investment gains (losses), pre-tax	$ 15.3	$ (22.9)	$ 13.7	$ (17.4)

Investment Securities (Net Re50

Investment Securities (Net Realized Investment Gains (Losses)) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	$ 2.7	$ 42.4	$ 259.5	$ 56.7
Trading securities, Tax on Realized Holding Gain (Loss) on Investments	(0.4)	(12.7)	(43.3)	(17.2)
Trading securities realized holding gain (loss) on investments after tax	2.3	29.7	216.2	39.5
Foreign Currency Transaction Gain (Loss), Realized	0	(0.1)	0	0.4
Trading Securities, Tax on Realized Foreign Currency Transaction Gain (Loss) Tax	0	0	0	0
Trading securities, realized foreign currency gain (loss) net of tax	0	(0.1)	0	0.4
Net realized investment gains, pre-tax	2.7	42.3	259.5	57.1
Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(0.4)	(12.7)	(43.3)	(17.2)
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	2.3	29.6	216.2	39.9
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	1.8	1.6	0.7	2.1
Foreign Currency Transaction Gain (Loss), Realized	0	0	0	0
Net realized investment gains, pre-tax	1.8	1.6	0.7	2.1
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	0.1	0	0.2	0
Foreign Currency Transaction Gain (Loss), Realized	0	0	0	0
Net realized investment gains, pre-tax	0.1	0	0.2	0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	3.8	25.5	261.4	47.5
Foreign Currency Transaction Gain (Loss), Realized	0	(0.1)	0	0.4
Net realized investment gains, pre-tax	3.8	25.4	261.4	47.9
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	(3)	15.3	(2.8)	7.1
Foreign Currency Transaction Gain (Loss), Realized	0	0	0	0
Net realized investment gains, pre-tax	$ (3)	$ 15.3	$ (2.8)	$ 7.1

Investment Securities (Net Unre

Investment Securities (Net Unrealized Investment Gains (Losses)) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	$ 25.6	$ (59.1)	$ (204.5)	$ (43.9)
Trading Securities, Tax on Unrealized Holding Gain (Loss) on Investments	(9.5)	17.3	24.9	14.7
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax	16.1	(41.8)	(179.6)	(29.2)
Foreign Currency Transaction Gain (Loss), Unrealized	(0.2)	1.8	2.6	(3.2)
Trading Securities, Unrealized Foreign Currency Transaction Gain (Loss) Tax	0	(0.1)	0	(0.1)
Trading Securities, Unrealized Foreign Currency Gain (Loss) Net of Tax	(0.2)	1.7	2.6	(3.3)
Net unrealized investment gains (losses), pre-tax	25.4	(57.3)	(201.9)	(47.1)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Tax	(9.5)	17.2	24.9	14.6
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	15.9	(40.1)	(177)	(32.5)
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	20.7	(13.4)	42.4	(2)
Foreign Currency Transaction Gain (Loss), Unrealized	0	0	0	0
Net unrealized investment gains (losses), pre-tax	20.7	(13.4)	42.4	(2)
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	0	0	0	0
Foreign Currency Transaction Gain (Loss), Unrealized	0	0	0	0
Net unrealized investment gains (losses), pre-tax	0	0	0	0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	(10.6)	(22.6)	(260.4)	(25.3)
Foreign Currency Transaction Gain (Loss), Unrealized	0	1.6	2.4	(2.4)
Net unrealized investment gains (losses), pre-tax	(10.6)	(21)	(258)	(27.7)
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	15.5	(23.1)	13.5	(16.6)
Foreign Currency Transaction Gain (Loss), Unrealized	(0.2)	0.2	0.2	(0.8)
Net unrealized investment gains (losses), pre-tax	$ 15.3	$ (22.9)	$ 13.7	$ (17.4)

Investment Securities (Investme

Investment Securities (Investment gains (losses) for Level 3) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 6.8	$ 0	$ 14.1
Unrealized gains (losses) on investments	25.6	(59.1)	(204.5)	(43.9)
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	20.7	(13.4)	42.4	(2)
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	(10.6)	(22.6)	(260.4)	(25.3)
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	15.5	(23.1)	13.5	(16.6)
Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	12.6	(1)	14.2	3.1
Level 3 Inputs | Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	0.8	(0.2)	1.3	0
Level 3 Inputs | Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	0	4.7	0	2.9
Level 3 Inputs | Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	$ 11.8	$ (5.5)	$ 12.9	$ 0.2

Investment Securities (Invest53

Investment Securities (Investment Holdings Fixed Maturity Table) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity investments, at fair value	$ 4,362.8	$ 2,630.2
U.S. Government and agency obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	261.2	160.4
Trading Securities, Unrealized Holding Gain	0.7	0
Trading Securities, Unrealized Holding Loss	0	(0.4)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	261.9	160
Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	1,046.9	1,001
Trading Securities, Unrealized Holding Gain	19.3	4.3
Trading Securities, Unrealized Holding Loss	(0.1)	(5.3)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	1,066.1	1,000
Municipal obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	294.8	227.8
Trading Securities, Unrealized Holding Gain	8.2	2.2
Trading Securities, Unrealized Holding Loss	(0.1)	(1.2)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	302.9	228.8
Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	2,646.8	1,170.6
Trading Securities, Unrealized Holding Gain	10.4	2
Trading Securities, Unrealized Holding Loss	(2)	(5.6)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	2,655.2	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	6.4	4.4
Trading Securities, Unrealized Holding Loss	0	0
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	84.7	82.7
Fixed Income Investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	4,329	2,639.1
Trading Securities, Unrealized Holding Gain	45.2	13.1
Trading Securities, Unrealized Holding Loss	(2.2)	(12.5)
Net foreign currency gains (losses)	0	0
Total fixed maturity investments including assets held for sale	4,372	2,639.7
Star & Shield Insurance Exchange
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities Debt Reclassified to Assets Held-for-sale	$ 9.2	$ 9.5	$ 9.1	$ 10.1

Investment Securities (Invest54

Investment Securities (Investment Holding Common Equities/ Other Investments) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity investments, at fair value	$ 4,362.8	$ 2,630.2
Common Stock
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	374.1	822.5
Trading Securities, Unrealized Holding Gain	43.5	302.8
Trading Securities, Unrealized Holding Loss	(10.1)	(11.4)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	407.5	1,113.9
Other long-term investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	305	304.5
Trading Securities, Unrealized Holding Gain	36.7	32
Trading Securities, Unrealized Holding Loss	(10.3)	(18.4)
Net foreign currency gains (losses)	(2.2)	(2.3)
Fixed maturity investments, at fair value	$ 329.2	$ 315.8

Investment Securities (Other lo

Investment Securities (Other long-term investments) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Payments to Acquire Other Investments	$ 13,300	$ 28,600
Other Investments	329,200		$ 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	127,800		127,800
Limited liability companies and private equity securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	84,300		82,100
Surplus Note
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	62,800		51,500
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	34,100		32,700
Affordable Housing Development Fund [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	13,400	$ 15,800	14,700	$ 16,800
Partnership investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	3,500		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	20,500		20,600
Unfunded Commitments	$ 0		$ 0

Investment Securities (Hedge Fu

Investment Securities (Hedge Funds and Private Equity Funds) (Details) $ in Millions	Jun. 30, 2016USD ($)fund	Dec. 31, 2015USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments | $	$ 329.2	$ 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	24
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 | $	$ 21.5

Investment Securities (Fair Val

Investment Securities (Fair Value of Hedge Funds and Private Equity Funds) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	$ 37.6
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	90.2
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	127.8	$ 127.8
Unfunded Commitments	130.4	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	19.1	20.7
Unfunded Commitments	3.2	3.4
Private equity funds | Private Equity Multi Sector
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	11.1	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	3.8	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	3.5	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	1.7	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	25.9	19.8
Unfunded Commitments	23.5	30.3
Private equity funds | Industrial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	24.8	24.9
Unfunded Commitments	20.2	2.5
Private equity funds | Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	90.2	90.8
Unfunded Commitments	130.4	82.2
Private equity funds | Real Estate Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0.3	0.4
Unfunded Commitments	0.1	0.1
Private equity funds | Venture Capital Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0	0
Unfunded Commitments	37.5	0
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	13.6	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	20.5	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	3.5	3.6
Unfunded Commitments	0	0
Hedge funds | Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	37.6	37
Unfunded Commitments	$ 0	$ 0

Investment Securities (Restrict

Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) - Hedge funds $ in Millions	Jun. 30, 2016USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Distributions from Inactive Hedge Funds	$ 1
Other long-term investments	37.6
Redemption requests	2.5
30-59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	14.6
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	20.5
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	14.6
Quarterly | 30-59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	14.6
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	20.5
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	20.5
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		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interest	$ 21.4	$ (0.9)	$ 27.7	$ (8.2)
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	90.2		90.2
1-3 years | Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	27.1		27.1
3-5 years | Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	3.5		3.5
5-10 years | Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	59.6		59.6
Greater than 10 years | Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	$ 0		$ 0

Investment Securities OneBeacon

Investment Securities OneBeacon Surplus Notes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 23, 2014
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 6.8	$ 0	$ 14.1
Interest Paid			0.5	$ 73.3
OneBeacon [Member]
Assets, Fair Value Adjustment			(38.2)		$ (49.5)
OneBeacon [Member] | Par Value [Member]
Surplus Notes	101		101		101	$ 101
OneBeacon [Member] | Fair Value [Member]
Surplus Notes	62.8		62.8		51.5
OneBeacon [Member] | Current market rates on repayments [Member]
Assets, Fair Value Adjustment			(5.7)		(15.1)
OneBeacon [Member] | Regulatory Approval [Member]
Assets, Fair Value Adjustment			(19.9)		(24.2)
OneBeacon [Member] | Liquidity Adjustment [Member]
Assets, Fair Value Adjustment			(12.6)		$ (10.2)
Seller Priority Surplus Note [Member] | OneBeacon [Member]
Assets, Fair Value Adjustment			(13.7)
Seller Priority Surplus Note [Member] | OneBeacon [Member] | Par Value [Member]
Surplus Notes	57.9		57.9
Seller Priority Surplus Note [Member] | OneBeacon [Member] | Fair Value [Member]
Surplus Notes	44.2		44.2
Seller Priority Surplus Note [Member] | OneBeacon [Member] | Current market rates on repayments [Member]
Assets, Fair Value Adjustment			2.7
Seller Priority Surplus Note [Member] | OneBeacon [Member] | Regulatory Approval [Member]
Assets, Fair Value Adjustment			(7.4)
Seller Priority Surplus Note [Member] | OneBeacon [Member] | Liquidity Adjustment [Member]
Assets, Fair Value Adjustment			(9)
Surplus Note
Interest Paid			2.4
Pari Passu Surplus Note [Member] | OneBeacon [Member]
Assets, Fair Value Adjustment			(24.5)
Pari Passu Surplus Note [Member] | OneBeacon [Member] | Par Value [Member]
Surplus Notes	43.1		43.1
Pari Passu Surplus Note [Member] | OneBeacon [Member] | Fair Value [Member]
Surplus Notes	$ 18.6		18.6
Pari Passu Surplus Note [Member] | OneBeacon [Member] | Current market rates on repayments [Member]
Assets, Fair Value Adjustment			(8.4)
Pari Passu Surplus Note [Member] | OneBeacon [Member] | Regulatory Approval [Member]
Assets, Fair Value Adjustment			(12.5)
Pari Passu Surplus Note [Member] | OneBeacon [Member] | Liquidity Adjustment [Member]
Assets, Fair Value Adjustment			$ (3.6)
Surplus Note
RBC Score			250.00%		250.00%

Investment Securities (Fair V61

Investment Securities (Fair Value Measurements) (Details) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2016USD ($)
Investments, Debt and Equity Securities [Abstract]
Maximum percentage of price difference provided by pricing services	5.00%
Maximum price difference provided by pricing services	$ 1

Investment Securities (Fair V62

Investment Securities (Fair Value Measurement by Level) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Percentage of Investments Recorded at Fair Value			91.00%
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 6,800	$ 0	$ 14,100
Fair value investments	5,091,800	3,379,600	5,091,800	3,379,600	$ 4,050,900	$ 3,343,600
Other Investments	329,200		329,200		315,800
Short-term investments, at amortized cost (which approximates fair value)	421,800		421,800		211,200
Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	565,200	450,800	565,200	450,800	1,152,200	550,600
Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	4,061,100	2,522,100	4,061,100	2,522,100	2,531,400	2,372,900
Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,066,100		1,066,100		1,000,000
Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,655,200		2,655,200		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	2,573,200		2,573,200		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	82,000		82,000		0
Fixed maturity investments. | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	153,200	76,800	153,200	76,800	70,000	76,400
Common equity securities | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	33,000	0	33,000	0	39,500
Other long-term investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	184,500	140,300	184,500	140,300	169,500	126,900
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	127,800		127,800		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	127,800	156,600	127,800	156,600	127,800	177,300
Fair value measured on a recurring basis
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	5,386,100		5,386,100		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	987,300		987,300		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	4,061,100		4,061,100		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	337,700		337,700		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	261,900		261,900		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	252,300		252,300		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	9,600		9,600		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		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	1,066,100		1,066,100		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		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	1,066,100		1,066,100		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		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	333,500		333,500		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		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	333,500		333,500		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		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	139,000		139,000		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		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	139,000		139,000		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		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	154,800		154,800		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		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	154,800		154,800		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		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		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		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		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		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	157,300		157,300		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		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	157,300		157,300		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		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	60,600		60,600		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		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	60,600		60,600		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		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	57,300		57,300		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		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	57,300		57,300		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		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	94,300		94,300		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		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	94,300		94,300		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		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	26,000		26,000		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		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	26,000		26,000		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		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	2,655,200		2,655,200		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
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	2,573,200		2,573,200		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	82,000		82,000		0
Fair value measured on a recurring basis | Municipal obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	302,900		302,900		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		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	302,900		302,900		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		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		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		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		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		0
Fair value measured on a recurring basis | Preferred Stock
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	84,700		84,700		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		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	13,500		13,500		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	71,200		71,200		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	4,372,000		4,372,000		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	252,900		252,900		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	3,965,900		3,965,900		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	153,200		153,200		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	422,100		422,100		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	422,100		422,100		211,300
Short-term investments, at amortized cost (which approximates fair value)		401,300		401,300	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]
Fair value investments	0		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		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	152,800		152,800		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	152,800		152,800		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		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					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					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
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
Fair value measured on a recurring basis | Common equity securities | Financials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments					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					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
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
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	32,700		32,700		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	32,700		32,700		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		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		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	36,400		36,400		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	36,400		36,400		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		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		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	24,800		24,800		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	24,800		24,800		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		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		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	87,500		87,500		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	65,600		65,600		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	21,900		21,900		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		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	73,300		73,300		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		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	73,300		73,300		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		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	407,500		407,500		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	312,300		312,300		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	95,200		95,200		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		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	184,500		184,500		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		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		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	184,500		184,500		169,500
Carrying value of investment accounted for using the equity method	3,500	3,900	3,500	3,900	3,800	5,200
Affordable Housing Development Fund [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	13,400	15,800	13,400	15,800	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	13,400		13,400		14,700
Star & Shield Insurance Exchange
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities Debt Reclassified to Assets Held-for-sale	9,200	$ 9,100	9,200	$ 9,100	9,500	$ 10,100
Star & Shield Insurance Exchange | Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities Debt Reclassified to Assets Held-for-sale	$ 300		$ 300		$ 100
Surplus Note
Schedule of Trading Securities and Other Trading Assets [Line Items]
RBC Score			250.00%		250.00%

Investment Securities (Debt sec

Investment Securities (Debt securities issued by corporation) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 5,091.8	$ 4,050.9	$ 3,379.6	$ 3,343.6
Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,066.1	1,000
AAA | Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
AA | Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	125.7	95.2
A | Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	376.6	397.7
BBB | Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	563.8	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	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 5,091.8	$ 4,050.9	$ 3,379.6	$ 3,343.6
Non-Agency Residential Mortgage [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	31.2
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 104.5	$ 140.4

Investment Securities (Mortga65

Investment Securities (Mortgage-backed Asset Securities Table) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 5,091.8	$ 4,050.9	$ 3,379.6	$ 3,343.6
Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	93.2
Government National Mortgage Association Certificates and Obligations (GNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	284.7	265.5
Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	203.5	42.2
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	37.5	22.8
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	525.7	330.5
Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	194.3	133.2
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	104.5	140.4
Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	298.8	273.6
Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	824.5	604.1
Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	689.1	217.7
Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	977.4	269.7
Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	164.2	75.5
Asset-backed Securities, Securitized Loans and Receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,830.7	562.9
Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,655.2	1,167
Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	4,061.1	2,531.4	$ 2,522.1	$ 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	284.7	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	152.5	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	37.5	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	474.7	330.5
Level 2 Inputs | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	194.3	133.2
Level 2 Inputs | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	104.5	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	298.8	273.6
Level 2 Inputs | Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	773.5	604.1
Level 2 Inputs | Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	658.1	217.7
Level 2 Inputs | Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	977.4	269.7
Level 2 Inputs | Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	164.2	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	1,799.7	562.9
Level 2 Inputs | Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,573.2	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	51	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	51	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	51	0
Level 3 Inputs | Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	31	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	31	0
Level 3 Inputs | Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 82	$ 0

Investment Securities (Non-agen

Investment Securities (Non-agency Mortgage-backed Securities) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 5,091.8	$ 4,050.9	$ 3,379.6	$ 3,343.6
Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	93.2
Commercial Mortgage Backed Securities Floating Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	11.3
Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	194.3	133.2
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	104.5	140.4
Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	298.8	$ 273.6
Securities Issued in 2004 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	21.9
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	21.9
Securities Issued in 2005 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	6.4
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	6.4
Securities Issued In 2006 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	3.4
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	3.4
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	3.2
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	3.2
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	10.8
Securities Issued In 2010 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	5
Securities Issued In 2010 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	15.8
Securities Issued In 2011 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	11.8
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	11.8
Securities Issued in 2012 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	6.9
Securities Issued in 2012 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	18.4
Securities Issued in 2012 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	25.3
Securities Issued in 2013 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	12.3
Securities Issued in 2013 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	11.6
Securities Issued in 2013 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	23.9
Securities Issued in 2014 | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	65.3
Securities Issued in 2014 | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	23.4
Securities Issued in 2014 | Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	88.7
Securities Issued in 2015 [Member] | Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	52.3
Securities Issued in 2015 [Member] | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	46.1
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	98.4
Subordinate | Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	38.2
Subordinate | Commercial Mortgage Backed Securities Floating Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	11.3
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	49.5
Super Senior | Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	8.9
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	133.6
Super Senior | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	8.9
Senior | Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	46.1
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	60.7
Senior | Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 46.1

Investment Securities (Non-ag67

Investment Securities (Non-agency Residential Mortgage-backed Securities) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 5,091.8	$ 4,050.9	$ 3,379.6	$ 3,343.6
Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	194.3	$ 133.2
Residential Mortgage Backed Securities | Super Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	133.6
Residential Mortgage Backed Securities | Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	60.7
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	187.4
Prime | Residential Mortgage Backed Securities | Super Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	133.6
Prime | Residential Mortgage Backed Securities | Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	53.8
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	6.9
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	6.9
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	12 Months Ended
	Dec. 31, 2015USD ($)	Jun. 30, 2016USD ($)	Jun. 30, 2015USD ($)	Dec. 31, 2014USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 4,050.9	$ 5,091.8	$ 3,379.6	$ 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	30
Fair value investments		93.2
Commercial Mortgage Backed Securities Fixed Rate [Member] | Super Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments		8.9
Commercial Mortgage Backed Securities Fixed Rate [Member] | Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments		46.1
Commercial Mortgage Backed Securities Fixed Rate [Member] | Subordinate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments		38.2
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 140.4	104.5
Commercial Mortgage Backed Securities | Super Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments		8.9
Commercial Mortgage Backed Securities | Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments		46.1
Commercial Mortgage Backed Securities | Subordinate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments		$ 49.5

Rollforward of Fair Value Measu

Rollforward of Fair Value Measurements by Level (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 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)			57,600	11,100
Amortization/Accretion			(8,000)	(9,900)
Purchases			3,622,500	1,293,700
Sales			(2,631,200)	(1,258,900)
Transfers in			0	34,900
Transfers out			0	(34,900)
Balance at June 30, 2016	$ 5,091,800	$ 3,379,600	5,091,800	3,379,600
Other Investments	329,200		329,200		$ 315,800
Net realized and unrealized investment gains (losses), after tax	18,200	(10,500)	39,200	7,400
Net realized and unrealized investment gains (losses)	28,100	(15,000)	57,600	10,000
Short-term investments, at amortized cost (which approximates fair value)	421,800		$ 421,800		211,200
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)			7,100	9,000
Amortization/Accretion			100	0
Purchases			1,449,700	495,400
Sales			(2,043,900)	(604,200)
Transfers in			0	0
Transfers out			0	0
Balance at June 30, 2016	565,200	450,800	565,200	450,800
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)			38,300	5,900
Amortization/Accretion			(8,100)	(9,900)
Purchases			2,076,900	734,300
Sales			(577,400)	(616,000)
Transfers in			0	34,900
Transfers out			0	0
Balance at June 30, 2016	4,061,100	2,522,100	4,061,100	2,522,100
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)			1,300	0
Amortization/Accretion			0	0
Purchases			84,700	35,300
Sales			(2,800)
Transfers in			0	0
Transfers out			0	(34,900)
Balance at June 30, 2016	153,200	76,800	153,200	76,800
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	6,600
Amortization/Accretion			0	0
Purchases			0	0
Sales			0	(13,100)
Transfers in			0	0
Transfers out			0	0
Balance at June 30, 2016	0	33,000	0	33,000
Other long-term investments | Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016			169,500	126,900
Total realized and unrealized gains (losses)			12,900	(6,800)
Amortization/Accretion			0	0
Purchases			2,100	22,500
Sales			0	(2,300)
Transfers in			0	0
Transfers out			0	0
Balance at June 30, 2016	184,500	140,300	184,500	140,300
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	177,300
Total realized and unrealized gains (losses)			(2,000)	(3,600)
Amortization/Accretion			0	0
Purchases			9,100	6,200
Sales			(7,100)	(23,300)
Transfers in			0	0
Transfers out			0	0
Balance at June 30, 2016	127,800	156,600	127,800	156,600
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 June 30, 2016	5,386,100		5,386,100
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 June 30, 2016	987,300		987,300
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 June 30, 2016	4,061,100		4,061,100
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 June 30, 2016	337,700		337,700
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 June 30, 2016	4,372,000		4,372,000
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 June 30, 2016	252,900		252,900
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 June 30, 2016	3,965,900		3,965,900
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 June 30, 2016	153,200		153,200
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 June 30, 2016	184,500		184,500
Fair value measured on a recurring basis | Other long-term investments | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2016			0
Balance at June 30, 2016	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]
Balance at January 1, 2016			0
Balance at June 30, 2016	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]
Balance at January 1, 2016			169,500
Balance at June 30, 2016	184,500		184,500
Carrying value of investment accounted for using the equity method	3,500	3,900	3,500	3,900	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 June 30, 2016	422,100		422,100
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 June 30, 2016	422,100		422,100
Short-term investments, at amortized cost (which approximates fair value)		401,300		401,300	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 June 30, 2016	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]
Balance at January 1, 2016			0
Balance at June 30, 2016	0		0
Discontinued Operations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized and unrealized investment gains (losses)	7,300	(46,100)	(1,500)	32,300
Star & Shield Insurance Exchange | Fair value measured on a recurring basis | Short-term investments | Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Short-term investments, at amortized cost (which approximates fair value)	300	1,100	300	1,100	100	1,900
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 (losses)				900
Affordable Housing Development Fund [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	13,400	15,800	13,400	15,800	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	13,400		13,400		14,700
Star & Shield Insurance Exchange
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities Debt Reclassified to Assets Held-for-sale	$ 9,200	$ 9,100	$ 9,200	$ 9,100	$ 9,500	$ 10,100

Investment Securities (Signific

Investment Securities (Significant Unobservable Inputs) (Details) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016USD ($)Investment	Jun. 30, 2015USD ($)	Jun. 30, 2016USD ($)Investment	Jun. 30, 2015USD ($)	Dec. 31, 2015USD ($)inputInvestment
Quantitative information for Level 3 Fair Value Measurements Assets
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 6.8	$ 0	$ 14.1
Number of Investments with Significant Unobseravble Inputs | Investment	1		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	$ 44.2		$ 44.2		$ 38
Timing of interest payments			5 years		5 years
Timing of principal payments			10 years		10 years
Fair Value Measurements, Valuation Techniques			0.106		0.13
NR | Pari Passu Surplus Note [Member] | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	18.6		$ 18.6		$ 13.5
Timing of interest payments			5 years		5 years
Timing of principal payments			15 years		15 years
Fair Value Measurements, Valuation Techniques			0.18		0.224
AAA | Mortgage-backed and asset-backed securities | Broker Pricing [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	31		$ 31
Standard & Poor's, AA+ Rating [Member] | Residential Mortgage Backed Securities | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	51		$ 51
Conditional Prepayment Rate			1.50%
MSA [Member] | NR | Preferred Stock | Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	71.2		$ 71.2
Fair Value Measurements, Valuation Techniques			0.0704
PassportCard [Member] | NR | Private equity funds | Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	21		$ 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		$ 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		$ 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	7.1		$ 7.1
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		$ 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%		60.00%
Risk Free Rate	1.15%		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	$ 9.7		$ 9.7		$ 9.6
Standard & Poor's, B Rating [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Basis points			2.50%
Standard & Poor's, CCC Rating [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Basis points					2.50%

Goodwill and Other Intangible71

Goodwill and Other Intangible Assets (Details) ₪ in Millions, $ in Millions	2 Months Ended		3 Months Ended	6 Months Ended
	Feb. 23, 2015ILS (₪)	Feb. 23, 2015USD ($)	Mar. 31, 2016USD ($)	Jun. 30, 2016USD ($)	Jun. 30, 2015USD ($)	Dec. 31, 2015USD ($)	Mar. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Businesses and Interest in Affiliates				$ 8.1	$ 2.4
Assets				7,065.6		$ 10,282.6
Goodwill			$ 24.1	24.1	24.1	24.1	$ 24.1	$ 23.8
Intangible Assets, Net (Excluding Goodwill)			32.2	29.2	$ 36.4	31.3	$ 39	$ 38.7
Liabilities				$ 2,966.2		$ 5,914.6
Lowfares.com [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Businesses and Interest in Affiliates			$ 3.9
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		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 24.1	$ 24.1	$ 24.1	$ 24.1	$ 24.1	$ 24.1	$ 24.1	$ 23.8
Intangible Assets, Net (Excluding Goodwill)	29.2	36.4	29.2	36.4	32.2	31.3	39	38.7
Disposal Group, Including Discontinued Operation, Intangible Assets		(0.6)		(0.6)	$ 0.3	$ 0.4	$ 0.7	$ 0.8
Goodwill, Acquired During Period				0.3
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill			0	2.8
Finite-lived Intangible Assets Acquired			3.9
Amortization of Intangible Assets	$ (3.3)	$ (2.7)	$ (6.4)	$ (5.3)

Debt (Details)

Debt (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended
	Nov. 30, 2012	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2012	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Jul. 23, 2015	Aug. 14, 2013
Debt Instrument
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements		10,863			6,194
Total debt		$ 289.8			$ 289.8		$ 337.6
Repayments of Debt					150.5	$ 15
Draw down of debt and revolving line of credit					102.5	$ 15
MediaAlpha Bank Facility [Member]
Debt Instrument
Repayments of Debt					0.5
Proceeds from Issuance of Debt					$ 2.5
Debt Instrument, Basis Spread on Variable Rate					1.50%
WTM Bank Facility
Debt Instrument
Debt Instrument, Interest Rate, Effective Percentage							3.90%
Total commitment under revolving credit facility									$ 425
Debt, Weighted Average Interest Rate		3.90%			3.90%
Repayments of Debt		$ 150			$ 150
Proceeds from Issuance of Debt			$ 100	$ 275
OB Bank Facility [Member]
Debt Instrument
Total commitment under revolving credit facility		65			65
One Beacon Holdings Inc [Member] | 2012 OBH Senior Notes
Debt Instrument
Debt Instrument, Interest Rate, Effective Percentage	4.70%
Proceeds from Issuance of Debt	$ 272.9
Debt Instrument, Interest Rate, Stated Percentage	4.60%
Debt Instrument, Issue Price as Percentage of Par Value	99.90%
OneBeacon [Member] | OneBeacon Bank Facility [Member]
Debt Instrument
Long-term Line of Credit		0			0
OneBeacon [Member] | 2012 OBH Senior Notes
Debt Instrument
Debt instrument at face value		275			275		$ 275
Unamortized original issue discount		(2)			(2)		(2.1)
Total debt		$ 273			$ 273		$ 272.9
Debt Instrument, Interest Rate, Effective Percentage		4.70%			4.70%		4.70%
White Mountains | WTM Bank Facility
Debt Instrument
Total debt		$ 0			$ 0		$ 50
Tranzact [Member] | OneBeacon Bank Facility [Member]
Debt Instrument
Long-term Line of Credit							0
MediaAlpha [Member] | MediaAlpha Bank Facility [Member]
Debt Instrument
Total debt		2			2
Long-term Line of Credit		$ 17			$ 17		$ 15
Debt Instrument, Interest Rate, Effective Percentage		5.90%			5.90%		5.50%
Unamortized Debt Issuance Expense		$ (0.2)			$ (0.2)		$ (0.3)
Line of Credit Facility, Fair Value of Amount Outstanding		16.8			16.8		$ 14.7
Total commitment under revolving credit facility								$ 20
Notional amount		15			15
Line of Credit Facility, Remaining Borrowing Capacity		$ 5			$ 5

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Tax Contingency [Line Items]
U.S. statutory rate (as a percent)				35.00%
Income Tax Expense (Benefit)	$ (6)		$ (2.2)	$ (15.7)	$ 2.4
Effective Income Tax Rate Reconciliation, Percent			43.10%
Equity in earnings of unconsolidated affiliates, net of tax	0		$ 6.8	0	$ 14.1
Tax Year 2012 [Member]
Income Tax Contingency [Line Items]
Operating Loss Carryforwards	1.7			1.7
Tax Assessment Year 2010 to 2012 [Member]
Income Tax Contingency [Line Items]
Income Tax Expense (Benefit)	$ 3.5
Tax Assessment Year 2007 to 2009 [Member]
Income Tax Contingency [Line Items]
Income Tax Expense (Benefit)		$ 12.8		$ 12.8

Derivatives (Details)

Derivatives (Details) ¥ in Billions, $ in Billions	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	$ 0.4	¥ 50.7
Collective account values of underlying variable annuities as a percentage of the guarantee value	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		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Variable Annuity Reinsurance [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 6.8	$ 0	$ 14.1
Pre-tax operating results of WM Life Re
Total revenues	358.2	368.7	727.5	723
General and administrative expenses	(73.1)	(63.4)	(160.2)	(134.3)
Pre-tax (loss) income from continuing operations	(2.1)	(5.1)	6.4	(2.1)
White Mountains Life Re
Pre-tax operating results of WM Life Re
Fees, included in other revenue	0.3	2.6	1.2	5.6
Change in fair value of variable annuity liability, included in other revenue	0.1	0.7	(0.3)	1.1
Realized and unrealized gains (losses)	(0.3)	(2.3)	(2)	(7.8)
Foreign exchange, included in other revenue	0.4	0	1.3	(1.2)
Other investment income and (losses) gains	0	(0.1)	0	(0.2)
Total revenues	0.5	0.9	0.2	(2.5)
Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses	0	0	0	0
Death benefit claims paid, included in general and administrative expenses	(0.2)	(0.1)	(0.3)	0
General and administrative expenses	(1.2)	(0.9)	(1.9)	(2.3)
Pre-tax (loss) income from continuing operations	$ (0.9)	$ (0.1)	$ (2)	$ (4.8)

Derivatives Realized and Unreal

Derivatives Realized and Unrealized Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Variable Annuity Reinsurance [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 6.8	$ 0	$ 14.1
White Mountains Life Re
Variable Annuity Reinsurance [Line Items]
Derivative, Fair Value, Amount Offset Against Collateral, Net	0		0			$ 20.1
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	(0.3)	(2.3)	(2)	(7.8)
Derivative, fair value, net	0	35.7	0	35.7	$ 13.1	20.1	$ 47	$ 56.4
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0		0
Derivative Transfers In (Out), Net	0	0	0	0
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements	12.8	9	18.1	12.9
Fixed income/interest rate | White Mountains Life Re
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	0	(5.9)	1.8	3.4
Derivative, fair value, net	0		0			0.5
Foreign exchange | White Mountains Life Re
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	(0.6)	9.2	(4.8)	(2.9)
Derivative, fair value, net	0		0			14.8
Equity | White Mountains Life Re
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	0.3	(5.6)	1	(8.3)
Derivative, fair value, net	0		0			4.8
Level 2 Inputs | White Mountains Life Re
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	(1.8)	0.6	(0.7)	(5.9)
Derivative, fair value, net	0	32.5	0	32.5	10.3	16.5	31.2	33.8
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0		0
Derivative Transfers In (Out), Net	0	0	0	0
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements	8.5	(0.7)	15.8	(4.6)
Level 1 Inputs | White Mountains Life Re
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	(0.2)	5.4	(4.2)	7.1
Derivative, fair value, net	0	(5.1)	0	(5.1)	0.2	0.9	(1.2)	3.7
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0		0
Derivative Transfers In (Out), Net	0	0	0	0
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements		9.3	(3.3)	15.9
Fair Value, Inputs, Level 3 [Member] | Variable Annuity | White Mountains Life Re
Variable Annuity Reinsurance [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	0	(1.8)	0	(1.8)	(0.1)	(0.3)	(1.1)	(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		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	0.1	0.7	(0.3)	1.1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers	0	0	0	0
Fair Value Measurement with Unobservable Inputs, Reconciliation, Recurring Basis, Liability Sales or Settlements	0	0	0	0
Fair Value, Inputs, Level 3 [Member] | Derivative [Member] | White Mountains Life Re
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	1.7	(8.3)	2.9	(9)
Derivative, fair value, net	0	8.3	0	8.3	$ 2.6	$ 2.7	$ 17	$ 18.9
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0		0
Derivative Transfers In (Out), Net	0	0	0	0
Fair Value Derivatives Measured on Recurring Basis, Asset Sales and Settlements	$ 4.3	$ 0.4	$ 5.6	$ 1.6

Derivatives Variable Annuity Re

Derivatives Variable Annuity Reinsurance Liabilities and Derivative Instruments (Details) $ in Millions, ¥ in Billions	3 Months Ended		6 Months Ended
	Jun. 30, 2016USD ($)	Jun. 30, 2015USD ($)	Jun. 30, 2016USD ($)	Jun. 30, 2015USD ($)	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					$ 400	¥ 50.7
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	$ 0		$ 0
Changes in derivative instruments
Beginning of period	13.1	$ 47	20.1	$ 56.4
Purchases		0		0
Realized and unrealized gains (losses)	(0.3)	(2.3)	(2)	(7.8)
Transfers in	0	0	0	0
Sales/settlements	(12.8)	(9)	(18.1)	(12.9)
End of period	0	35.7	0	35.7
Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses	0	0	0	0
Collective account values of underlying variable annuities as a percentage of the guarantee value					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		0
Changes in derivative instruments
Beginning of period	10.3	31.2	16.5	33.8
Purchases		0		0
Realized and unrealized gains (losses)	(1.8)	0.6	(0.7)	(5.9)
Transfers in	0	0	0	0
Sales/settlements	(8.5)	0.7	(15.8)	4.6
End of period	0	32.5	0	32.5
White Mountains Life Re | Level 1 Inputs
Variable Annuity Reinsurance [Line Items]
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0		0
Changes in derivative instruments
Beginning of period	0.2	(1.2)	0.9	3.7
Purchases		0		0
Realized and unrealized gains (losses)	(0.2)	5.4	(4.2)	7.1
Transfers in	0	0	0	0
Sales/settlements		(9.3)	3.3	(15.9)
End of period	0	(5.1)	0	(5.1)
Variable Annuity | White Mountains Life Re | Level 3 Inputs
Variable Annuity Reinsurance [Line Items]
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0		0
Changes in derivative instruments
Beginning balance	(0.1)	(1.1)	(0.3)	(0.7)
Realized and unrealized gains (losses)	0.1	0.7	(0.3)	1.1
Transfers in	0	0	0	0
Sales/settlements	0	0	0	0
Ending balance	0	(1.8)	0	(1.8)
Purchases		0		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		0
Changes in derivative instruments
Beginning of period	2.6	17	2.7	18.9
Purchases		0		0
Realized and unrealized gains (losses)	1.7	(8.3)	2.9	(9)
Transfers in	0	0	0	0
Sales/settlements	(4.3)	(0.4)	(5.6)	(1.6)
End of period	$ 0	$ 8.3	$ 0	$ 8.3

Derivatives Additional Collater

Derivatives Additional Collateral (Details) - White Mountains Life Re - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Credit risk on derivative instruments
Collateral cash and investments	$ 0	$ 5.8	$ 25.3
Cash
Credit risk on derivative instruments
Derivative collateral right to reclaim	0	5.8	20.9
Fixed maturity investments.
Credit risk on derivative instruments
Derivative collateral right to reclaim	$ 0	$ 0	$ 4.4

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	Jun. 30, 2016	Dec. 31, 2015
Offsetting Liabilities [Line Items]
Derivative Assets	$ 0	$ 23.2
Derivative Liabilities	0	(3.1)
Net amounts recognized in Other assets	0	20.1
Over The Counter | Fixed income/interest rate
Offsetting Liabilities [Line Items]
Derivative Assets	0	2.4
Derivative Liabilities	0	(2.1)
Net amounts recognized in Other assets	0	0.3
Over The Counter | Foreign exchange
Offsetting Liabilities [Line Items]
Derivative Assets	0	15
Derivative Liabilities	0	0
Net amounts recognized in Other assets	0	15
Over The Counter | Equity
Offsetting Liabilities [Line Items]
Derivative Assets	0	4.4
Derivative Liabilities	0	(0.6)
Net amounts recognized in Other assets	0	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	(0.3)
Net amounts recognized in Other assets	0	(0.2)
Exchange Traded | Equity
Offsetting Liabilities [Line Items]
Derivative Assets	0	1.2
Derivative Liabilities	0	0
Net amounts recognized in Other assets	$ 0	$ 1.2

Derivatives (Uncollateralized A

Derivatives (Uncollateralized Amounts Due Under WM Life Re's OTC Derivative Contracts) (Details) - White Mountains Life Re $ in Thousands	Jun. 30, 2016USD ($)Rating	Dec. 31, 2015USD ($)
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	$ 0	$ 20,100
Collertal provided to counterparty in cash		0
Collateral provided to counterparty in financial instruments		0
Net amount of exposure after effect of collateral		20,100
Excess collateral provided to counterparty in cash		5,800
Derivative, Collateral, Right to Reclaim Securities		0
Counter-party collateral held by WMLife Re - Cash		6,900
Net amount of exposure to counter-party		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		700
Collertal provided to counterparty in cash		0
Collateral provided to counterparty in financial instruments		0
Net amount of exposure after effect of collateral		700
Excess collateral provided to counterparty in cash		0
Derivative, Collateral, Right to Reclaim Securities		0
Counter-party collateral held by WMLife Re - Cash		0
Net amount of exposure to counter-party		700
Standard & Poor's, A Rating [Member] | Citigroup - OTC
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments		9,900
Collertal provided to counterparty in cash		0
Collateral provided to counterparty in financial instruments		0
Net amount of exposure after effect of collateral		9,900
Excess collateral provided to counterparty in cash		0
Derivative, Collateral, Right to Reclaim Securities		0
Counter-party collateral held by WMLife Re - Cash		1,400
Net amount of exposure to counter-party		8,500
Standard & Poor's, A Rating [Member] | Citigroup Exchange Traded [Member]
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments		1,000
Collertal provided to counterparty in cash		0
Collateral provided to counterparty in financial instruments		0
Net amount of exposure after effect of collateral		1,000
Excess collateral provided to counterparty in cash		5,800
Derivative, Collateral, Right to Reclaim Securities		0
Counter-party collateral held by WMLife Re - Cash		0
Net amount of exposure to counter-party		6,800
Standard & Poor's, A plus | JP Morgan
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments		8,500
Collertal provided to counterparty in cash		0
Collateral provided to counterparty in financial instruments		0
Net amount of exposure after effect of collateral		8,500
Excess collateral provided to counterparty in cash		0
Derivative, Collateral, Right to Reclaim Securities		0
Counter-party collateral held by WMLife Re - Cash		5,500
Net amount of exposure to counter-party		$ 3,000

Municipal Bond Guarantee (Detai

Municipal Bond Guarantee (Details) $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended		12 Months Ended
	Jul. 31, 2012USD ($)	Jun. 30, 2016USD ($)Contract	Mar. 31, 2016	Jun. 30, 2015USD ($)	Jun. 30, 2016USD ($)yrContract	Jun. 30, 2015USD ($)	Dec. 31, 2015USD ($)Contract
Guarantor Obligations [Line Items]
Pre-tax (loss) income		$ (2.1)		$ (5.1)	$ 6.4	$ (2.1)
Net investment income (loss) - surplus note interest		$ 0		0	$ 0	0
BAM
Guarantor Obligations [Line Items]
Municipal bond contract | Contract		3,910			3,910		3,103
Insured Financial Obligations, Remaining Weighted Average Contract Period					10 years 10 months 20 days		12 years 10 months
Municipal bond outstanding principal		$ 27,780.2			$ 27,780.2		$ 22,556
Municipal bond outstanding interest		14,074.2			14,074.2		11,984.4
Municipal bond debt service outstanding		41,854.4			41,854.4		34,540.4
Financial Guarantee Insurance Contracts, Unearned Premium Revenue		4.8			$ 4.8
Year of U.S. Treasury Rate | yr					1
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Remainder of Fiscal Year		2.9			$ 2.9
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Next Twelve Months		1.4			1.4
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Two		5.6			5.6
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Three		5.3			5.3
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Six Through Ten		5.1			5.1
Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Year Six Through Ten		39.6			39.6
Financial Guarantee Insurance Contracts, Unearned Premium Revenue		63.3			63.3		$ 50.2
HG Global
Guarantor Obligations [Line Items]
Partners Capital Contribution	$ 594.5
Surplus Notes	503
Income (Loss) from Continuing Operations before Income Taxes, Domestic		$ 5.9			$ 13.2
HG Global | Preferred Stock
Guarantor Obligations [Line Items]
Ownership interest (as a percent)		96.90%			96.90%
HG Global | Common Stock
Guarantor Obligations [Line Items]
Ownership interest (as a percent)		88.40%			88.40%
Build America Mutual
Guarantor Obligations [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Domestic		$ (9)		(14.1)	$ (16.6)	(22.9)
HG Re
Guarantor Obligations [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		471.5			471.5
HG Global
Guarantor Obligations [Line Items]
Pre-tax (loss) income		5.9		3.1	13.2	8.6
Net investment income (loss) - surplus note interest		4.4		3.9	8.9	7.9
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		$ 4.4			$ 8.9
Derivative, Fixed Interest Rate		3.54%			3.54%		3.15%
Surplus Note | Build America Mutual
Guarantor Obligations [Line Items]
Interest expense		$ 4.4		$ 3.9	$ 8.9	$ 7.9
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%			8.00%

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Basic and diluted earnings per share numerators (in millions):
Net income (loss) attributable to White Mountains’ common shareholders	$ (17.5)	$ 4.8	$ (5.6)	$ 17.8
Allocation of income for unvested restricted common shares	0.2	(0.1)	0.1	(0.2)
Dividends declared on participating restricted common shares	0	0	(0.1)	(0.1)
Total allocation to restricted common shares	0.2	(0.1)	0	(0.3)
Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts	(17.3)	4.7	(5.6)	17.5
Undistributed net earnings (in millions):
Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts	(17.3)	4.7	(5.6)	17.5
Dividends declared net of restricted common share amounts	0	0	(5.9)	(5.9)
Total undistributed net earnings, net of restricted common share amounts	$ (17.3)	$ 4.7	$ (11.5)	$ 11.6
Basic earnings per share denominators
Total average common shares outstanding during the period	5,096,100	5,985,700	5,317,800	5,982,100
Average unvested restricted common shares	(66,500)	(71,400)	(60,200)	(65,200)
Basic earnings per share denominator	5,029,600	5,914,300	5,257,600	5,916,900
Diluted earnings per share denominator
Total average common shares outstanding during the period	5,096,100	5,985,700	5,317,800	5,982,100
Average unvested restricted common shares	(66,500)	(71,400)	(60,200)	(65,200)
Average outstanding dilutive options to acquire common shares	5,107,000	5,985,700	5,324,300	5,982,100
Diluted earnings (loss) per share denominator	5,040,500	5,914,300	5,264,100	5,916,900
Basic earnings per share (in dollars):
Continuing operations	$ (3.44)	$ 0.80	$ (1.07)	$ 2.96
Undistributed earnings (loss) (in dollars per share)	(3.44)	0.80	(2.07)	1.96
Earnings Per Share, Diluted [Abstract]
Continuing operations	(3.43)	0.80	(1.06)	2.96
Dividends declared	0	0	(1)	(1)
Undistributed earnings (loss) (in dollars per share)	$ (3.43)	$ 0.80	$ (2.06)	$ 1.96
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	10,863		6,194
Discontinued Operations [Member]
Basic and diluted earnings per share numerators (in millions):
Allocation of income for unvested restricted common shares	$ 4.7	$ 0	$ (4.1)	$ 0.8
Basic earnings per share denominators
Total average common shares outstanding during the period	5,107,000	5,985,700	5,324,000	5,982,100
Average unvested restricted common shares	(66,500)	(71,400)	(60,200)	(65,200)
Basic earnings per share denominator	5,029,600	5,914,300	5,257,600	5,916,900
Diluted earnings per share denominator
Total average common shares outstanding during the period	5,107,000	5,985,700	5,324,000	5,982,100
Average unvested restricted common shares	(66,500)	(71,400)	(60,200)	(65,200)
Diluted earnings (loss) per share denominator	5,040,500	5,914,300	5,263,800	5,916,900
Employee Stock Option [Member]
Earnings Per Share, Diluted [Abstract]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	120,000		120,000

Non-controlling Interest (Detai

Non-controlling Interest (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 224.2	$ 454.8
Total Non-Controlling Excluding Reciprocals [Member]
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 113.6	$ 115.2
OneBeacon [Member]
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	23.90%	24.50%
Total non-controlling interests	$ 244.8	$ 245.6
SIG Preference Shares
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage		100.00%
Total non-controlling interests	$ 0	$ 250
HG Global
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.10%	3.10%
Total non-controlling interests	$ 17	$ 17.1
MediaAlpha [Member]
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	40.00%	40.00%
Total non-controlling interests	$ 13.2	$ 14.4
Tranzact [Member]
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	36.80%	36.80%
Total non-controlling interests	$ 79.2	$ 79.4
WOBI
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.50%	3.90%
Total non-controlling interests	$ 0.5	$ 0.6
AWG Dewar
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	18.80%	18.60%
Total non-controlling interests	$ 3.7	$ 3.7
Build America Mutual
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ (138)	$ (140)
Star & Shield Insurance Exchange
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ 3.8	$ (16)
Star & Shield Insurance Exchange | Total mutual and reciprocals [Member]
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ (134.2)	$ (156)

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment reporting information
Premiums Earned, Net	$ 274.7	$ 321.8	$ 556.8	$ 611.1
Net investment income	19.2	13.2	37.1	25.8
Net investment income (loss) - surplus note interest	0	0	0	0
Net realized and unrealized investment gains (losses)	28.1	(15)	57.6	10
Other Income	36.2	48.7	76	76.1
Total revenues	358.2	368.7	727.5	723
Loss and loss adjustment expenses	182	196.2	343.1	364.1
Insurance and Reinsurance Acquisition Expenses	50.1	57.8	102.8	110.8
Other Underwriting Expense	51	53	106.4	109
General and administrative expenses	73.1	63.4	160.2	134.3
Amortization of Intangible Assets	3.3	2.7	6.4	5.3
Interest expense	4.1	3.4	8.6	6.9
Total expenses	360.3	373.8	721.1	725.1
Pre-tax (loss) income	(2.1)	(5.1)	6.4	(2.1)
OneBeacon [Member]
Segment reporting information
Premiums Earned, Net	271.4	319.3	550	605.9
Net investment income	12.1	10.1	26.5	20.6
Net investment income (loss) - surplus note interest	0	0	0	0
Net realized and unrealized investment gains (losses)	24.7	(14)	41.3	0.2
Other Income	0.8	(1.2)	1.7	(4.3)
Total revenues	309	314.2	619.5	622.4
Loss and loss adjustment expenses	179.7	194.5	338.5	360.4
Insurance and Reinsurance Acquisition Expenses	48.7	56.4	99.7	107.4
Other Underwriting Expense	50.9	52.9	106.2	108.8
Interest expense	3.2	3.3	6.5	6.5
Total expenses	286	311.3	558.3	591.4
Pre-tax (loss) income	23	2.9	61.2	31
HG Global
Segment reporting information
Premiums Earned, Net	1	0.6	1.9	1.1
Net investment income	0.5	0.5	1	0.9
Net investment income (loss) - surplus note interest	4.4	3.9	8.9	7.9
Net realized and unrealized investment gains (losses)	0.5	(1.4)	2.6	(0.3)
Other Income	0	0	0	0
Total revenues	6.4	3.6	14.4	9.6
Loss and loss adjustment expenses	0	0	0	0
Insurance and Reinsurance Acquisition Expenses	0.2	0.1	0.4	0.2
Other Underwriting Expense	0	0	0	0
Interest expense	0	0	0	0
Total expenses	0.5	0.5	1.2	1
Pre-tax (loss) income	5.9	3.1	13.2	8.6
BAM
Segment reporting information
Premiums Earned, Net	0.4	0.1	0.7	0.3
Net investment income	1.8	0.8	3.4	1.8
Net investment income (loss) - surplus note interest	(4.4)	(3.9)	(8.9)	(7.9)
Net realized and unrealized investment gains (losses)	3.2	(1.9)	8.1	1.1
Other Income	0.3	0.2	0.4	0.3
Total revenues	1.3	(4.7)	3.7	(4.4)
Loss and loss adjustment expenses	0	0	0	0
Insurance and Reinsurance Acquisition Expenses	0.6	0.6	1.3	1.4
Other Underwriting Expense	0.1	0.1	0.2	0.2
Interest expense	0	0	0	0
Total expenses	10.3	9.4	20.3	18.5
Pre-tax (loss) income	(9)	(14.1)	(16.6)	(22.9)
Other Operations
Segment reporting information
Premiums Earned, Net	1.9	1.8	4.2	3.8
Net investment income	4.8	1.8	6.2	2.5
Net investment income (loss) - surplus note interest	0	0	0	0
Net realized and unrealized investment gains (losses)	(0.3)	2.3	5.6	9
Other Income	35.1	49.7	73.9	80.1
Total revenues	41.5	55.6	89.9	95.4
Loss and loss adjustment expenses	2.3	1.7	4.6	3.7
Insurance and Reinsurance Acquisition Expenses	0.6	0.7	1.4	1.8
Other Underwriting Expense	0	0	0	0
Interest expense	0.9	0.1	2.1	0.4
Total expenses	63.5	52.6	141.3	114.2
Pre-tax (loss) income	(22)	3	(51.4)	(18.8)
Segment Reconciling Items [Member]
Segment reporting information
General and administrative expenses	69.8	60.7	153.8	129
Segment Reconciling Items [Member] | OneBeacon [Member]
Segment reporting information
General and administrative expenses	3.2	3.8	6.8	7.6
Segment Reconciling Items [Member] | HG Global
Segment reporting information
General and administrative expenses	0.3	0.4	0.8	0.8
Segment Reconciling Items [Member] | BAM
Segment reporting information
General and administrative expenses	9.6	8.7	18.8	16.9
Segment Reconciling Items [Member] | Other Operations
Segment reporting information
General and administrative expenses	56.7	47.8	127.4	103.7
General and Administrative Expense [Member]
Segment reporting information
Amortization of Intangible Assets	3.3	2.7	6.4	5.3
General and Administrative Expense [Member] | OneBeacon [Member]
Segment reporting information
Amortization of Intangible Assets	0.3	0.4	0.6	0.7
General and Administrative Expense [Member] | HG Global
Segment reporting information
Amortization of Intangible Assets	0	0	0	0
General and Administrative Expense [Member] | BAM
Segment reporting information
Amortization of Intangible Assets	0	0	0	0
General and Administrative Expense [Member] | Other Operations
Segment reporting information
Amortization of Intangible Assets	3	2.3	5.8	4.6
Star & Shield Insurance Exchange
Segment reporting information
Other Income			(20)
MediaAlpha [Member] | Other Operations
Segment reporting information
Other Income	28.1	23.2	0	0
General and administrative expenses	$ 26	$ 21.9	$ 56.5	$ 49.6

Investments in Unconsolidated86

Investments in Unconsolidated Affiliates (Investment in Unconsolidated Affiliates Table) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 6.8	$ 0	$ 14.1
Symetra | Common Stock
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax		6.1		13.3
Hamer, LLC [Member]
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax		$ 1.1		$ 1.6

Investments in Unconsolidated87

Investments in Unconsolidated Affiliates (Symetra) (Details) - USD ($)	Feb. 01, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2016	Jun. 30, 2015	Nov. 05, 2015	Dec. 31, 2015	Dec. 31, 2011
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax		$ 0			$ 6,800,000		$ 0	$ 14,100,000
Unrealized gains (losses) on investments		25,600,000			(59,100,000)		(204,500,000)	(43,900,000)
Revenues		358,200,000			368,700,000		727,500,000	723,000,000
Total expenses		360,300,000			373,800,000		721,100,000	725,100,000
Pre-tax (loss) income		(2,100,000)			(5,100,000)		6,400,000	(2,100,000)
Net income		362,500,000			3,400,000		381,800,000	80,400,000
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax		$ 16,100,000			(41,800,000)		(179,600,000)	(29,200,000)
Sales of common equity securities							$ 851,300,000	306,800,000
Common shares, par value per share (in dollars per share)		$ 1		$ 1			$ 1			$ 1
Net realized and unrealized investment gains (losses)		$ 28,100,000			(15,000,000)		$ 57,600,000	$ 10,000,000
Symetra
Investments in unconsolidated affiliates
Unrealized gains (losses) on investments				$ 258,800,000
Equity Method Investments Fair Value Per Share											$ 15
Term of amortization (in years)								30 years
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity					164,100,000			$ 164,100,000
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 (losses)			$ 4,700,000
Common Stock | Symetra
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax					6,100,000			13,300,000
Proceeds from Equity Method Investment, Dividends or Distributions					2,200,000	$ 2,200,000		4,400,000	$ 4,400,000
equity in earnings of unconsolidated affiliates | Symetra
Investments in unconsolidated affiliates
After tax amortization through equity in earnings					700,000			1,400,000
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity					33,000,000			33,000,000
Net unrealized gains (losses) of unconsolidated affiliates | Symetra
Investments in unconsolidated affiliates
After tax amortization through equity in net unrealized losses					2,700,000			5,500,000
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity					131,100,000			$ 131,100,000
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					$ 700,000					$ 1,400,000

Investments in Unconsolidated88

Investments in Unconsolidated Affiliates (Investments in Symetra Table Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		10 Months Ended	12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2016	Jun. 30, 2015	Nov. 05, 2015	Dec. 31, 2015
Changes in carrying value of investment in Symetra
Equity in earnings	$ 0	$ 6.8		$ 0	$ 14.1
Income Tax Expense (Benefit)	$ (6)	(2.2)		$ (15.7)	2.4
Symetra | Common Stock
Changes in carrying value of investment in Symetra
Carrying value at the beginning of the period		447.3	$ 411.4		411.4	$ 411.4	$ 411.4
Equity in earnings		6.1			13.3
Equity in net unrealized gains (losses) from Symetra's fixed maturity portfolio		(66.4)			(35.5)
Dividends received		(2.2)	(2.2)		(4.4)	$ (4.4)
Carrying value of a distribution		12.4			12.4
Carrying value at the end of the period		397.2	$ 447.3		$ 397.2
White Mountains | Common Stock
Changes in carrying value of investment in Symetra
Equity in net unrealized gains (losses) from Symetra's fixed maturity portfolio		2
equity in earnings of unconsolidated affiliates | Symetra | Common Stock
Changes in carrying value of investment in Symetra
Income Tax Expense (Benefit)		0.4					0.8
Net unrealized gains (losses) of unconsolidated affiliates | White Mountains | Common Stock
Changes in carrying value of investment in Symetra
Income Tax Expense (Benefit)		0
Amortization of common share basis difference | Symetra | Common Stock
Changes in carrying value of investment in Symetra
Equity in earnings		0.7					1.4
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		$ 2.8					$ 5.7

Investments in Unconsolidated89

Investments in Unconsolidated Affiliates Hamer (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 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	6.8	$ 0	$ 14.1
Hamer, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax		$ 1.1		$ 1.6

Employee Share-Based Incentiv90

Employee Share-Based Incentive Compensation Plans (WTM - Performance Shares) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Share-based compensation arrangement by share-based payment award
Common shares, issued shares	4,963,921		4,963,921		5,623,735
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 6.8	$ 0	$ 14.1
Accrued Expense
Accrued expense at the beginning of period			140.7
Accrued expense at the end of the period	$ 106.3		$ 106.3		$ 140.7
Performance Share | W T M Incentive Plan | Performance Cycle 2013 to 2015
Share-based compensation arrangement by share-based payment award
Common shares, issued shares	5,000		5,000
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)	111,387	108,545	96,358	113,295	113,295
Shares paid or expired (in shares)	(36,294)	0	(36,294)	(34,001)
New grants (in shares)	0	750	16,215	29,878
Assumed forfeitures and cancellations	908	(19)	(278)	104
Ending of period (in shares)	76,001	109,276	76,001	109,276	96,358
Accrued Expense
Accrued expense at the beginning of period	$ 71.3	$ 25.7	$ 57.7	$ 44.4	$ 44.4
Payments and deferrals	(41.3)	0	(41.3)	(24.9)
Assumed forfeitures and cancellations	0.9	0	0.3	0.5
Expense recognized	1.3	3.1	15.5	8.8
Accrued expense at the end of the period	32.2	$ 28.8	$ 32.2	$ 28.8	$ 57.7
Vesting Period			3 years
Additional compensation cost that would be recognized if all outstanding performance shares vested	$ 27.2		$ 27.2
Sirius Group | Performance Share | W T M Incentive Plan
Target Performance Share Activity
Ending of period (in shares)	4,428	7,851	4,428	7,851

Employee Share-Based Incentiv91

Employee Share-Based Incentive Compensation Plans (WTM - Performance Shares Granted Under the WTM Incentive Plan) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Share-based compensation arrangement by share-based payment award
Total Accrued Expense	$ 106.3		$ 140.7
White Mountains | Performance Share | W T M Incentive Plan
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	77,949
Accrued Expense	$ 33.1
Target Performance Shares Outstanding, Assumed forfeitures	(1,948)
Accrued Expense, Assumed forfeitures	(0.9)
Total Target Performance Shares Outstanding	76,001	111,387	96,358	109,276	108,545	113,295
Total Accrued Expense	$ 32.2	$ 71.3	$ 57.7	$ 28.8	$ 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	$ 2.2
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	29,478
Accrued Expense	$ 12.7
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	32,256
Accrued Expense	$ 18.2

Employee Share-Based Incentiv92

Employee Share-Based Incentive Compensation Plans (WTM - Restricted Shares) (Details) - USD ($) $ / shares in Units, $ in Millions	May 05, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Share-based compensation arrangement by share-based payment award
Equity in earnings of unconsolidated affiliates, net of tax		$ 0	$ 6.8	$ 0	$ 14.1
Non-Qualified Options [Member]
Share-based compensation arrangement by share-based payment award
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value		$ 100		$ 100
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage				50.00%
Share-based Compensation Arrangement by Share-based Payment Award, Number Exercised	5,000
Target Restricted Share Activity
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number		120,000		120,000		125,000
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Exercise Price	$ 742					$ 742
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)					23,640
White Mountains | W T M Incentive Plan | Restricted Stock
Target Restricted Share Activity
Beginning of period (in shares)		66,470	71,125	70,675	83,314	83,314
Issued (in shares)		0	750	21,215	23,640
Vested (in shares)		0	0	(24,620)	(35,079)
Assumed forfeitures and cancellations		0	0	(800)	0
Ending of period (in shares)		66,470	71,875	66,470	71,875	70,675
Unamortized grant date fair value
Unamortized grant date fair value, beginning balance		$ 29.2	$ 26.5	$ 15.7	$ 14.3	$ 14.3
Issued		0	0.5	16.3	15.7
Assumed forfeitures and cancellations		0	0	0.2	0
Expense recognized		(5)	(3.8)	(8)	(6.8)
Unamortized grant date fair value, ending balance		$ 24.2	$ 23.2	$ 24.2	$ 23.2	$ 15.7
Sirius Group | W T M Incentive Plan | Restricted Stock
Target Restricted Share Activity
Ending of period (in shares)		2,512	3,572	2,512	3,572
Unamortized grant date fair value
Expense recognized		$ 1.4

Employee Share-Based Incentiv93

Employee Share-Based Incentive Compensation Plans (OneBeason - Peformance Shares) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Share-based compensation arrangement by share-based payment award
Equity in earnings of unconsolidated affiliates, net of tax	$ 0	$ 6.8	$ 0	$ 14.1
Expense Amortized
Accrued expense at the beginning of period			140.7
Accrued expense at the end of the period	$ 106.3		$ 106.3		$ 140.7
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)	441,206	462,147	449,435	517,470	517,470
Shares paid or expired (in shares)	0	0	(167,300)	(181,290)
New grants (in shares)	0	0	163,150	154,887
Assumed forfeitures and cancellations	0	0	(4,079)	28,920
Ending of period (in shares)	441,206	462,147	441,206	462,147	449,435
Expense Amortized
Accrued expense at the beginning of period	$ 1.1	$ 2.1	$ 1.4	$ 3.4	$ 3.4
Payments and deferrals	0	0	(0.7)	(1.5)
Assumed forfeitures and cancellations	0	0	0	0
Expense recognized	(0.1)	0.3	0.3	0.5
Accrued expense at the end of the period	1	$ 2.4	1	$ 2.4	$ 1.4
Additional compensation cost that would be recognized if all outstanding performance shares vested	$ 2.5		$ 2.5

Employee Share-Based Incentiv94

Employee Share-Based Incentive Compensation Plans (OneBeacon - Performance Shares Outstanding) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014
Share-based compensation arrangement by share-based payment award
Accrued incentive compensation	$ 106.3		$ 140.7
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
Target Performance Shares Outstanding, Assumed forfeitures	(11,313)
Accrued Expense, Assumed forfeitures	0
Total Target Performance Shares Outstanding	441,206	441,206	449,435	462,147	462,147	517,470
Accrued incentive compensation	$ 1	$ 1.1	$ 1.4	$ 2.4	$ 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	$ 0.4
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	$ 0.6
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

Employee Share-Based Incentiv95

Employee Share-Based Incentive Compensation Plans (OneBeacon - Restricted Shares) (Details) $ in Millions	Feb. 24, 2016shares	Feb. 24, 2015shares	May 31, 2011shares	Jun. 30, 2016USD ($)shares	Jun. 30, 2015USD ($)shares	Jun. 30, 2016USD ($)shares	Jun. 30, 2015USD ($)shares	Dec. 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	$ 6.8	$ 0	$ 14.1
OneBeacon [Member] | One Beacon Long Term Incentive Plan | Restricted Stock
Target Restricted Share Activity
Beginning of period (in shares)				395,872	390,950	382,722	612,500	612,500
Issued (in shares)	170,650	75,950		0	0	170,650	75,950
Vested (in shares)				0	0	(157,500)	(296,000)
Assumed forfeitures and cancellations				0	0	0	(1,500)
Ending of period (in shares)				395,872	390,950	395,872	390,950	382,722
Unamortized grant date fair value
Unamortized grant date fair value, beginning balance | $				$ 4.3	$ 4	$ 2.5	$ 3.5	$ 3.5
Issued | $				0	0	2.3	1.1
Vested | $						0
Assumed forfeitures and cancellations | $				0	0	0	0
Expense recognized | $				(0.8)	(0.5)	(1.3)	(1.1)
Unamortized grant date fair value, ending balance | $				$ 3.5	$ 3.5	$ 3.5	$ 3.5	$ 2.5
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)				441,206	462,147	449,435	517,470	517,470
Assumed forfeitures and cancellations				0	0	(4,079)	28,920
Ending of period (in shares)				441,206	462,147	441,206	462,147	449,435
Unamortized grant date fair value
Assumed forfeitures and cancellations | $				$ 0	$ 0	$ 0	$ 0
Expense recognized | $				0.1	$ (0.3)	(0.3)	$ (0.5)
Unamortized grant date fair value, ending balance | $				$ 2.5		$ 2.5
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)						227,788	207,848
Ending of period (in shares)				215,698	185,004	215,698	185,004
Unamortized grant date fair value
Expense recognized | $				$ (0.5)	$ (0.3)	$ (0.9)	$ (0.4)
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 Incentiv96

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		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Share-based compensation arrangement by share-based payment award
Issued (in shares)			227,788	207,848
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	215,698	185,004	215,698	185,004
Expense recognized	$ 0.5	$ 0.3	$ 0.9	$ 0.4

Fair Value of Financial Instr97

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	$ 289.8	$ 337.6
OneBeacon [Member] | 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	273	272.9
OneBeacon [Member] | Book Value | 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	273	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	279.7	276.4
MediaAlpha [Member] | MediaAlpha Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	2
Long-term Line of Credit	17	15
MediaAlpha [Member] | Book Value | MediaAlpha Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	16.8	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	$ 17	$ 15

Discontinued Operations (Detail

Discontinued Operations (Details) - USD ($) $ in Millions	Apr. 18, 2016	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Discontinued Operations [Line Items}
Sales of consolidated and unconsolidated subsidiaries, net of cash sold						$ 2,248.5	$ 24
Payments to Acquire Other Investments						13.3	28.6
Investments			$ 5,521.3			5,521.3		$ 4,271.1
Net realized and unrealized investment gains (losses)			28.1		$ (15)	57.6	10
Net gain on sale of discontinued operations			366.6		(0.1)	366.6	7.9
Net (loss) income from discontinued operations, net of tax			(8)		(0.4)	(6.9)	62.9
Net Realized and Unrealized Gain (Loss) on Trading Securities			28.1		(15)	57.6	10
Sirius Group
Discontinued Operations [Line Items}
Sales of consolidated and unconsolidated subsidiaries, net of cash sold	$ 2,600		2,600
Payments to Acquire Other Investments	$ 161.8		161.8
Investments								686.2
Net realized and unrealized investment gains (losses)			0.4		2.4	3.7	2.7
Net gain on sale of discontinued operations						366.6
Accumulated Other Comprehensive Income Loss Net Of Tax Other Period Increase Decrease			(5.2)		44	32	(43.6)
Increase of Book Value						479.9
Sale of Sirius Group [Member]
Discontinued Operations [Line Items}
Accumulated Other Comprehensive Income Loss Net Of Tax Other Period Increase Decrease			113.3		0	113.3	0
Symetra | Sirius Group
Discontinued Operations [Line Items}
Investments								$ 528.6
Discontinued Operations [Member]
Discontinued Operations [Line Items}
Net realized and unrealized investment gains (losses)			7.3		(46.1)	(1.5)	32.3
Net gain on sale of discontinued operations			(8)		(0.4)	(6.9)	62.9
Discontinued Operations [Member] | Sirius Group
Discontinued Operations [Line Items}
Net realized and unrealized investment gains (losses)			7.3		(46.1)	(1.5)	32.3
Net gain on sale of discontinued operations			(3.4)		3.8	(4.3)	69.7
Net (loss) income from discontinued operations, net of tax			(3.4)			(4.3)
Discontinued Operations [Member] | Tranzact [Member]
Discontinued Operations [Line Items}
Net (loss) income from discontinued operations, net of tax			$ (0.5)		(6.5)	(2.5)	(4)
Discontinued Operations [Member] | OneBeacon Runoff [Member]
Discontinued Operations [Line Items}
Net gain on sale of discontinued operations					0.3		0.3
Discontinued Operations [Member] | Esurance
Discontinued Operations [Line Items}
Net gain on sale of discontinued operations				$ 10.3	$ (0.3)	$ 28.3	$ 7.6
Sale of Tranzact [Member]
Discontinued Operations [Line Items}
Sales of consolidated and unconsolidated subsidiaries, net of cash sold		$ 221.3
Sale of Tranzact [Member] | Tranzact [Member]
Discontinued Operations [Line Items}
Sales of consolidated and unconsolidated subsidiaries, net of cash sold		$ 221.3

Discontinued Operations - Finan

Discontinued Operations - Financial Statement Disclosures (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Disposal Group, Including Discontinued Operation, Assets [Abstract]
Fixed maturity investments, at fair value	$ 4,362.8				$ 4,362.8		$ 2,630.2
Short-term investments, at amortized cost (which approximates fair value)	421.8				421.8		211.2
Common equity securities, at fair value	407.5				407.5		1,113.9
Other long-term investments	329.2				329.2		315.8
Total investments	5,521.3				5,521.3		4,271.1
Cash	135				135		173
Reinsurance recoverable on unpaid losses	162.8				162.8		186
Reinsurance recoverable on paid losses	20.7				20.7		7.5
Insurance premiums receivable	240.4				240.4		220.3
Deferred acquisition costs	113.9				113.9		107.6
Deferred tax asset	122.2				122.2		112.8
Ceded unearned insurance premiums	34.5				34.5		29.5
Accounts receivable on unsettled investment sales	21.5				21.5		41.9
Goodwill and intangible assets	53.3				53.3		55.4
Other assets	239.4				239.4		273.2
Assets held for sale	384.6				384.6		4,790.4
Loss and loss adjustment expense reserves	1,376.6	$ 1,343.8		$ 1,350.8	1,376.6	$ 1,350.8	1,389.8	$ 1,304	$ 1,342.2
Unearned insurance premiums	619.7				619.7		610.5
Debt	289.8				289.8		337.6
Accrued incentive compensation	106.3				106.3		140.7
Ceded reinsurance payable	23.9				23.9		29.9
Funds held under insurance contracts	140.9				140.9		137.8
Accounts payable on unsettled investment purchases	69.9				69.9		0
Other liabilities	188.5				188.5		199.9
Total liabilities held for sale	150.6				150.6		3,068.4
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Earned insurance premiums	274.7			321.8	556.8	611.1
Net investment income	19.2			13.2	37.1	25.8
Net realized and unrealized investment gains (losses)	28.1			(15)	57.6	10
Other revenue	36.2			48.7	76	76.1
Total revenues	358.2			368.7	727.5	723
Loss and loss adjustment expenses	182			196.2	343.1	364.1
Insurance and Reinsurance Acquisition Expenses	50.1			57.8	102.8	110.8
Other Underwriting Expense	51			53	106.4	109
General and administrative expenses	73.1			63.4	160.2	134.3
Interest expense	4.1			3.4	8.6	6.9
Total expenses	360.3			373.8	721.1	725.1
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax					(6.9)	62.9
Net gain on sale of discontinued operations	366.6			(0.1)	366.6	7.9
Net Cash Provided by (Used in) Discontinued Operations [Abstract]
Cash balances at beginning of period		167.2	$ 173.8		167.2	232.9
Cash balances at end of period	135			173.8	135	173.8
Net income tax refund from national governments					(13.5)	(7.5)
Net change in foreign currency translation	0			0.2	0.1	0.2
Total comprehensive income (loss)	449.2			(13.3)	499.5	12.3
Sirius Group
Disposal Group, Including Discontinued Operation, Assets [Abstract]
Total investments							686.2
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net realized and unrealized investment gains (losses)	0.4			2.4	3.7	2.7
Net gain on sale of discontinued operations					366.6
Discontinued Operations [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Earned insurance premiums	37.7			215.5	240.1	420.5
Net investment income	2.2			9.1	14.4	18.1
Net realized and unrealized investment gains (losses)	7.3			(46.1)	(1.5)	32.3
Other revenue	51.7			40.1	105.4	50.1
Total revenues	98.9			218.6	358.4	521
Loss and loss adjustment expenses	41.2			92.1	154.9	189.6
Insurance and Reinsurance Acquisition Expenses	10.6			47.5	59	90.1
Other Underwriting Expense	4.2			27.7	30.9	53.2
General and administrative expenses	49.4			44.7	110.9	90.2
Interest expense	2.6			7.5	10.6	15.1
Total expenses	108			219.5	366.3	438.2
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	(9.1)			(0.9)	(7.9)	82.8
Discontinued Operation, Tax Effect of Discontinued Operation	1.1			0.5	1	(19.9)
Net gain on sale of discontinued operations	(8)			(0.4)	(6.9)	62.9
Net loss from discontinued operations, net of tax	358.6			(0.5)	359.7	70.8
Net Cash Provided by (Used in) Discontinued Operations [Abstract]
Net cash used for operations - discontinued operations					(43.1)	(12.9)
Net cash provided from investing activities - discontinued operations					229.6	59.3
Net cash provided from (used for) financing activities - discontinued operations					9	(2)
Effect of exchange rate changes on cash					0	(2.1)
Net change in cash during the period					195.5	42.3
Cash balances at beginning of period		$ 148.9	156.8		148.9	114.5
Cash balances at end of period	1.3			156.8	1.3	156.8
Interest paid					(1.4)	(14.5)
Net income tax refund from national governments					(31.8)	(24.6)
Net change in foreign currency translation	(5.2)			44		(43.6)
Total comprehensive income (loss)	466.7			43.5	505	27.2
Discontinued Operations [Member] | Net gain (loss) from sale of discontinued operations [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations	366.6				366.6
Discontinued Operations [Member] | Discontinued Operations, Held-for-sale [Member]
Disposal Group, Including Discontinued Operation, Assets [Abstract]
Fixed maturity investments, at fair value	14.4				14.4		2,383.5
Short-term investments, at amortized cost (which approximates fair value)	4.2				4.2		352.1
Common equity securities, at fair value	0				0		174.4
Other long-term investments	0				0		72.2
Total investments	18.6				18.6		2,982.2
Cash	1.9				1.9		150.2
Reinsurance recoverable on unpaid losses	0.4				0.4		283.6
Reinsurance recoverable on paid losses	0				0		10.2
Insurance premiums receivable	2.4				2.4		326.6
Deferred acquisition costs	0				0		74.6
Deferred tax asset	0				0		303.1
Ceded unearned insurance premiums	0				0		87.7
Goodwill and intangible assets	315.1				315.1		330.5
Other assets	46.2				46.2		212.7
Assets held for sale	384.6				384.6		4,790.4
Loss and loss adjustment expense reserves	5.7				5.7		1,650.4
Unearned insurance premiums	1.8				1.8		344.3
Debt	96.9				96.9		506.4
Deferred tax liability	8.7				8.7		270.6
Accrued incentive compensation	1				1		64.2
Ceded reinsurance payable	(0.2)				(0.2)		67.7
Funds held under insurance contracts	0				0		52.9
Other liabilities	36.7				36.7		111.9
Total liabilities held for sale	150.6				150.6		3,068.4
Discontinued Operations [Member] | Sirius Group
Disposal Group, Including Discontinued Operation, Assets [Abstract]
Accounts receivable on unsettled investment sales	0				0		29
Accounts payable on unsettled investment purchases	0				0		0
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Earned insurance premiums	37.7			215.5	240.1	420.5
Net investment income	2.2			9.1	14.4	18.1
Net realized and unrealized investment gains (losses)	7.3			(46.1)	(1.5)	32.3
Other revenue	4.7			5.4	0.6	(22)
Total revenues	51.9			183.9	253.6	448.9
Loss and loss adjustment expenses	41.2			92.1	154.9	189.6
Insurance and Reinsurance Acquisition Expenses	10.6			47.5	59	90.1
Other Underwriting Expense	4.2			27.7	30.9	53.2
General and administrative expenses	0.2			6.7	8.3	13
Interest expense	1.3			6.6	7.9	13.4
Total expenses	57.5			180.6	261	359.3
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	(5.6)			3.3	(7.4)	89.6
Discontinued Operation, Tax Effect of Discontinued Operation	2.2			0.5	3.1	(19.9)
Net gain on sale of discontinued operations	(3.4)			3.8	(4.3)	69.7
Net loss from discontinued operations, net of tax	363.2			3.8	362.3	69.7
Net Cash Provided by (Used in) Discontinued Operations [Abstract]
Net Assets	234				234		$ 1,722
Net change in foreign currency translation	(5.2)			44	32	(43.6)
Total comprehensive income (loss)	471.3			47.8	507.6	26.1
Discontinued Operations [Member] | Sirius Group | Net gain (loss) from sale of discontinued operations [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations	366.6				366.6
Discontinued Operations [Member] | Other Discontinued Operations [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Earned insurance premiums	0			0	0	0
Net investment income	0			0	0	0
Net realized and unrealized investment gains (losses)	0			0	0	0
Other revenue	47			34.7	104.8	72.1
Total revenues	47			34.7	104.8	72.1
Loss and loss adjustment expenses	0			0	0	0
Insurance and Reinsurance Acquisition Expenses	0			0	0	0
Other Underwriting Expense	0			0	0	0
General and administrative expenses	49.2			38	102.6	77.2
Interest expense	1.3			0.9	2.7	1.7
Total expenses	50.5			38.9	105.3	78.9
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	(3.5)			(4.2)	(0.5)	(6.8)
Discontinued Operation, Tax Effect of Discontinued Operation	(1.1)			0	(2.1)	0
Net gain on sale of discontinued operations	(4.6)			(4.2)	(2.6)	(6.8)
Net loss from discontinued operations, net of tax	(4.6)			(4.3)	(2.6)	1.1
Net Cash Provided by (Used in) Discontinued Operations [Abstract]
Total comprehensive income (loss)	(4.6)			(4.3)	(2.6)	1.1
Discontinued Operations [Member] | Sale of Sirius Group [Member]
Net Cash Provided by (Used in) Discontinued Operations [Abstract]
Net change in foreign currency translation	113.3			0	113.3
Discontinued Operations [Member] | OneBeacon Runoff [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations				0.3		0.3
Net loss from discontinued operations, net of tax				(0.2)		(0.3)
Discontinued Operations [Member] | OneBeacon Runoff [Member] | Net gain (loss) from sale of discontinued operations [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations	0			0.3		0.3
Discontinued Operations [Member] | Esurance
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations			$ 10.3	(0.3)	$ 28.3	7.6
Discontinued Operations [Member] | Esurance | Net gain (loss) from sale of discontinued operations [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations	$ 0			$ (0.4)		$ 7.6

Discontinued Operations - EPS (

Discontinued Operations - EPS (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
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	$ 6.8	$ 0	$ 14.1
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	10,863		6,194
Income (Loss) Allocated to Participating Unvested Restricted Common Shares	$ (0.2)	0.1	$ (0.1)	0.2
Net Income (Loss) Available to Common Stockholders, Basic	$ 341.1	$ 4.3	$ 354.1	$ 88.6
Total average common shares outstanding during the period	5,096,100	5,985,700	5,317,800	5,982,100
Average unvested restricted common shares	(66,500)	(71,400)	(60,200)	(65,200)
Basic earnings per share denominator	5,029,600	5,914,300	5,257,600	5,916,900
Average outstanding dilutive options to acquire common shares	5,107,000	5,985,700	5,324,300	5,982,100
Diluted earnings (loss) per share denominator	5,040,500	5,914,300	5,264,100	5,916,900
Earnings Per Share, Diluted	$ 66.79	$ 0.72	$ 66.50	$ 14.80
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net loss from discontinued operations, net of tax	$ 358.6	$ (0.5)	$ 359.7	$ 70.8
Income (Loss) Allocated to Participating Unvested Restricted Common Shares	(4.7)	0	4.1	(0.8)
Net Income (Loss) Available to Common Stockholders, Basic	$ 353.9	$ (0.5)	$ 355.6	$ 70
Total average common shares outstanding during the period	5,107,000	5,985,700	5,324,000	5,982,100
Average unvested restricted common shares	(66,500)	(71,400)	(60,200)	(65,200)
Basic earnings per share denominator	5,029,600	5,914,300	5,257,600	5,916,900
Diluted earnings (loss) per share denominator	5,040,500	5,914,300	5,263,800	5,916,900
Earnings Per Share, Basic and Diluted	$ 70.37	$ (0.08)	$ 67.64	$ 11.84
Earnings Per Share, Diluted	$ 70.22	$ (0.08)	$ 67.56	$ 11.84
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		$ 6.1		$ 13.3
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		$ 0.7			$ 1.4
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	120,000		120,000

Discontinued Operations - Fair

Discontinued Operations - Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	$ 289.8	$ 337.6

Contingencies (Details)

Contingencies (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended
	Jun. 30, 2007	Jun. 30, 2016	Sep. 30, 2015	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Oct. 07, 2011
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		$ 366.6		$ (0.1)	$ 366.6	$ 7.9
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		(8)		(0.4)	(6.9)	62.9
Esurance | Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations			$ 10.3	(0.3)	28.3	7.6
OneBeacon Runoff [Member] | Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations				0.3		0.3
Sirius Group
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations					366.6
Sirius Group | Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		$ (3.4)		$ 3.8	$ (4.3)	$ 69.7

OneBeacon Pension Plan (Details

OneBeacon Pension Plan (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Defined Contribution Plan Disclosure [Line Items]
Other Income	$ 36.2	$ 48.7	$ 76	$ 76.1
Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Pension Plan Liabilities, Current			0.3
Defined Benefit Plan, Assets for Plan Benefits	42.4		42.4
Transfer of assets	12		12
OneBeacon [Member]
Defined Contribution Plan Disclosure [Line Items]
Other Income	0.8	$ (1.2)	$ 1.7	$ (4.3)
OneBeacon [Member] | Pension Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Other Income	$ 0.1

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Jun. 30, 2015
Subsequent Event [Line Items]
Sales of consolidated and unconsolidated subsidiaries, net of cash sold		$ 2,248.5	$ 24
Sale of Tranzact [Member]
Subsequent Event [Line Items]
Sales of consolidated and unconsolidated subsidiaries, net of cash sold	$ 221.3