White Mountains Insurance (WTM) 10-Q2 Nov 152015 Q3 Quarterly reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2015	Nov. 02, 2015
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	Sep. 30, 2015
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		5,686,165
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	Q3

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Assets
Fixed maturity investments, at fair value	$ 2,602.2	$ 2,422
Short-term investments, at amortized cost (which approximates fair value)	325	376.8
Common equity securities, at fair value	482.1	611.7
Convertible fixed maturity and preferred investments, at fair value	5.6	13.9
Other long-term investments	294.6	318
Total investments	3,709.5	3,742.4
Cash (restricted: $16.8 and $23.7)	200	261.7
Reinsurance recoverable on unpaid losses	214.6	161.7
Reinsurance recoverable on paid losses	22.6	12.2
Insurance premiums receivable	273.3	241.1
Funds held by ceding entities	4.6	37.1
Investments in unconsolidated affiliates	392.6	414.4
Deferred acquisition costs	110.8	107.2
Deferred tax asset	133.9	114.6
Ceded unearned insurance premiums	41.4	17.8
Accrued investment income	13.7	14.3
Accounts receivable on unsettled investment sales	11.5	37.8
Goodwill and intangible assets	381.7	351.2
Other assets	307.7	311.6
Assets held for sale	4,528.1	4,630.6
Total assets	10,346	10,455.7
Liabilities
Loss and loss adjustment expense reserves	1,433.3	1,350
Unearned insurance premiums	671.3	616.7
Debt	383.3	343.1
Accrued incentive compensation	121	108.1
Ceded reinsurance payable	46.8	34.2
Funds held under insurance contracts	100.3	81
Accounts payable on unsettled investment purchases	46	0.5
Other liabilities	304.9	278.4
Total liabilities held for sale	3,032.8	3,105.3
Total liabilities	6,139.7	5,917.3
White Mountains’s common shareholders’ equity
White Mountains’ common shares	5.7	6
Paid-in surplus	992.3	1,028.7
Retained earnings	2,888.3	3,010.5
Accumulated other comprehensive income (loss), after tax:
Equity in net unrealized gains from investment in Symetra common shares	5.5	34.9
Net unrealized foreign currency translation losses	(142.4)	(79.8)
Pension liability and other	(3.9)	(4.6)
Total White Mountains’s common shareholders’ equity	3,745.5	3,995.7
Non-controlling interests
Total non-controlling interests	460.8	542.7
Total equity	4,206.3	4,538.4
Total liabilities and equity	10,346	10,455.7
OneBeacon
Non-controlling interests
Total non-controlling interests	246.9	258.4
Sirius Group
Non-controlling interests
Total non-controlling interests	250	250
Mutuals and reciprocals
Non-controlling interests
Total non-controlling interests	(149.4)	(134.3)
Other Noncontrolling Interest
Non-controlling interests
Total non-controlling interests	$ 113.3	$ 168.6

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Cash	$ 16.8	$ 23.7
Common shares, par value per share (in dollars per share)	$ 1	$ 1
Common shares, authorized shares	50,000,000	50,000,000
Common shares, issued shares	5,745,002	5,986,214
Common shares, outstanding shares	5,745,002	5,986,214

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE (LOSS) INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Revenues:
Earned insurance premiums	$ 284.9	$ 307.2	$ 896	$ 879.1
Net investment income	16.8	13.8	42.6	44.7
Net realized and unrealized investment (losses) gains	(43.9)	(27.5)	(33.9)	64.4
Other revenue	76.9	29.7	225.4	60.3
Total revenues	334.7	323.2	1,130.1	1,048.5
Expenses:
Loss and loss adjustment expenses	170	185.5	534.1	527.3
Insurance and Reinsurance Acquisition Expenses	55.3	55.2	166.1	153
Other Underwriting Expense	56.5	51.3	165.5	152.6
General and administrative expenses	142.6	63	354.1	168.3
Interest expense	4.9	3.7	13.5	10.6
Total expenses	429.3	358.7	1,233.3	1,011.8
Pre-tax (loss) income from continuing operations	(94.6)	(35.5)	(103.2)	36.7
Income tax benefit (expense)	1.6	4.7	(0.8)	(11.4)
Net (loss) income from continuing operations	(93)	(30.8)	(104)	25.3
Net gain on sale of discontinued operations	10.3	7	18.2	9.7
Net income from discontinued operations, net of tax	3.9	56.9	73.3	166.8
(Loss) Income before equity in earnings of unconsolidated affiliates	(78.8)	33.1	(12.5)	201.8
Equity in earnings of unconsolidated affiliates, net of tax	3.9	7	18	33.3
Net income	(74.9)	40.1	5.5	235.1
Net loss attributable to non-controlling interests	16	11.2	24.2	7.2
Net (loss) income attributable to White Mountains’s common shareholders	(58.9)	51.3	29.7	242.3
Other comprehensive (loss) income, net of tax:
Change in equity in net unrealized gains (losses) from investments in Symetra common shares, net of tax	3.5	(9.9)	(29.4)	59.5
Change in foreign currency translation, pension liability and other	0	(0.2)	0.3	(0.1)
Comprehensive (loss) income	(73.8)	(22.9)	(61.5)	201.8
Other comprehensive (loss) income attributable to non-controlling interests	(0.1)	0.1	(0.1)	0.1
Comprehensive (loss) income attributable to White Mountains’s common shareholders	$ (73.9)	$ (22.8)	$ (61.6)	$ 201.9
Basic income per share
Continuing operations	$ (12.42)	$ (2.07)	$ (10.40)	$ 10.70
Discontinued operations	2.41	10.49	15.37	28.74
Total consolidated operations	(10.01)	8.42	4.97	39.44
Diluted income per share
Continuing operations	(12.42)	(2.07)	(10.40)	10.70
Discontinued operations	2.41	10.49	15.37	28.74
Total consolidated operations	(10.01)	8.42	4.97	39.44
Dividends declared per White Mountains’s common share	$ 1	$ 1	$ 1	$ 1
Sirius Group
Other comprehensive (loss) income, net of tax:
Accumulated Other Comprehensive Income Loss Net Of Tax Other Period Increase Decrease	$ (18.4)	$ (64.1)	$ (62.1)	$ (99.9)

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) [Member]Common shares and paid-in surplus	Foreign Currency Gain (Loss) [Member]Retained earnings	Foreign Currency Gain (Loss) [Member]AOCI, after tax	Foreign Currency Gain (Loss) [Member]Total	Foreign Currency Gain (Loss) [Member]Non-controlling interest	Foreign Currency Gain (Loss) [Member]Total Equity	Pension liability and other accumulated comprehensive items [Member]Common shares and paid-in surplus	Pension liability and other accumulated comprehensive items [Member]Retained earnings	Pension liability and other accumulated comprehensive items [Member]AOCI, after tax	Pension liability and other accumulated comprehensive items [Member]Total	Pension liability and other accumulated comprehensive items [Member]Non-controlling interest	Pension liability and other accumulated comprehensive items [Member]Total Equity
Balances at Dec. 31, 2013		$ 1,051.1	$ 2,801.8	$ 52.1	$ 3,905	$ 491.8	$ 4,396.8
Increase (Decrease) in Shareholders' Equity
Net income	$ 235.1	0	242.3	0	242.3	(7.2)	235.1
Net change in unrealized gains (losses) from investments in unconsolidated affiliates	59.5	0	0	59.5	59.5	0	59.5
Other Comprehensive Income (Loss), Net of Tax								$ 0	$ 0	$ (100.3)	$ (100.3)	$ (0.1)	$ (100.4)	$ 0	$ 0	$ 0.4	$ 0.4	$ 0	$ 0.4
Total comprehensive income (loss)	201.8	0	242.3	(40.4)	201.9	(7.3)	194.6
Dividends declared on common shares		0	(6.2)	0	(6.2)	0	(6.2)
Dividends to non-controlling interests	0	0	0	0	0	(26)	(26)
Repurchases and retirements of common shares		(29.6)	(77.3)	0	(106.9)	0	(106.9)
Issuances of common shares		2.9	0	0	2.9	0	2.9
Noncontrolling Interest, Period Increase (Decrease)		0	0	0	0	29.4	29.4
Amortization of restricted share awards		12.5	0	0	12.5	0.6	13.1
Balances at Sep. 30, 2014		1,036.9	2,960.6	11.7	4,009.2	488.5	4,497.7
Balances at Dec. 31, 2014	4,538.4	1,034.7	3,010.5	(49.5)	3,995.7	542.7	4,538.4
Increase (Decrease) in Shareholders' Equity
Net income	5.5	0	29.7	0	29.7	(24.2)	5.5
Net change in unrealized gains (losses) from investments in unconsolidated affiliates	(29.4)	0	0	(29.4)	(29.4)	0	(29.4)
Other Comprehensive Income (Loss), Net of Tax								$ 0	$ 0	$ (62.6)	$ (62.6)	$ 0	$ (62.6)	$ 0	$ 0	$ 0.7	$ 0.7	$ 0.1	$ 0.8
Total comprehensive income (loss)	(61.5)	0	29.7	(91.3)	(61.6)	(24.1)	(85.7)
Dividends declared on common shares		0	(6)	0	(6)	0	(6)
Dividends to non-controlling interests	9.1	0	0	0	0	(35.4)	(35.4)
Repurchases and retirements of common shares		(46)	(145.9)	0	(191.9)	0	(191.9)
Issuances of common shares		0.9	0	0	0.9	0	0.9
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests		0	0	0	0	(31.5)	(31.5)
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Changes, Additional Interest Issued to Parent		(2.2)	0	0	(2.2)	(2.7)	(4.9)
Noncontrolling Interest, Period Increase (Decrease)		0	0	0	0	12.1	12.1
Amortization of restricted share awards		10.6	0	0	10.6	(0.3)	10.3
Balances at Sep. 30, 2015	$ 4,206.3	$ 998	$ 2,888.3	$ (140.8)	$ 3,745.5	$ 460.8	$ 4,206.3

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operations:
Net income	$ 5.5	$ 235.1
Charges (credits) to reconcile net income to net cash used for operations:
Net realized and unrealized investment losses (gains)	33.9	(64.4)
Deferred income tax (benefit) expense	(20.2)	5.8
Net income from discontinued operations	(73.3)	(166.8)
Net gain on sale of discontinued operations	(18.2)	(9.7)
Gain on sale of subsidiaries - Hamer and Essentia	(16.1)	0
Amortization and depreciation	46.8	27.6
Undistributed equity in earnings from unconsolidated affiliates, net of tax	(18)	(33.3)
Other operating items:
Net change in loss and loss adjustment expense reserves	83.3	101.7
Net change in reinsurance recoverable on paid and unpaid losses	(63.3)	(23.4)
Net change in unearned insurance premiums	54.6	90.8
Net change in variable annuity benefit guarantee liabilities	(1.7)	(41.1)
Net change in variable annuity benefit guarantee derivative instruments	19.4	3.9
Net change in deferred acquisition costs	(3.6)	(19.7)
Net change in funds held by ceding entities	32.5	(33.3)
Net change in ceded unearned premiums	(23.4)	(0.4)
Net change in funds held under insurance treaties	19.3	13.5
Net change in insurance premiums receivable	(32)	(50.4)
Net change in ceded reinsurance payable	12.6	3.3
Net change in restricted cash	6.9	32.3
Net change in other assets and liabilities, net	35.6	2
Net cash provided from operations - continuing operations	80.6	73.5
Net cash provided from operations	87.3	123.3
Cash flows from investing activities:
Net change in short-term investments	26.6	(104.2)
Sales of fixed maturity and convertible fixed maturity investments	865	1,734.7
Maturities, calls and paydowns of fixed maturity and convertible fixed maturity investments	249.5	241.6
Sales of common equity securities	370.6	312.8
Distributions and redemptions of other long-term investments	56.6	26.2
Sales of consolidated and unconsolidated affiliates, net of cash sold	24	0
Net change in cash during the period	17.5	(27.6)
Purchases of other long-term investments	(30.5)	(26.8)
Purchases of common equity securities	(329.4)	(141.9)
Purchases of fixed maturity and convertible fixed maturity investments	(1,300.2)	(1,822.6)
Purchases of consolidated and unconsolidated affiliates, net of cash acquired	(33.3)	(32.2)
Net change in unsettled investment purchases and sales	71.8	9.3
Net dispositions (acquisitions) of property and equipment	37	(3.3)
Net cash provided from investing activities - continuing operations	25.2	166
Net cash provided from investing activities	60.9	213.5
Cash flows from financing activities:
Draw down of debt and revolving line of credit	134	40
Repayment of debt and revolving line of credit	(92.9)	(40.2)
Payments on capital lease obligation	(3.5)	(4)
Cash dividends paid to the Company’s common shareholders	(6)	(6.2)
Cash dividends paid to OneBeacon Ltd.’s non-controlling common shareholders	(14.8)	(14.8)
Common shares repurchased	(168.6)	(100.6)
OneBeacon Ltd. common shares repurchased and retired	(1.8)	(1.8)
Proceeds from Partnership Contribution	0	2.5
Distribution to non-controlling interest shareholders	(9.1)	0
Proceeds from (Payments for) Other Financing Activities	0	(4.9)
Distributions from contributions to discontinued operations	(9.1)	40.8
Payments to Acquire Additional Interest in Subsidiaries	(9.1)	0
Capital contributions from BAM members	20.3	11.6
Net cash used for financing activities - continuing operations	(160.6)	(77.6)
Net cash used for financing activities	(163)	(133.2)
Effect of exchange rate changes on cash (excludes ($4.1) and ($10.6) related to discontinued operations)	0	0
Net change in cash during the period - continuing operations	(54.8)	161.9
Cash balances at beginning of period	238	233.5
Cash balances at end of period	183.2	395.4
Supplemental cash flows information:
Interest paid	(8.9)	(6.4)
Net income tax refund from national governments	8	0.3
Discontinued Operations [Member]
Charges (credits) to reconcile net income to net cash used for operations:
Net realized and unrealized investment losses (gains)	(31.4)	(134.1)
Net income from discontinued operations	(95.5)	(218.6)
Net gain on sale of discontinued operations	(73.3)	(166.8)
Other operating items:
Net cash provided from operations - discontinued operations	6.7	49.8
Cash flows from investing activities:
Net change in cash during the period	35.9	31.1
Net cash provided from investing activities - discontinued operations	35.7	47.5
Cash flows from financing activities:
Net cash used for financing activities - discontinued operations	(2.4)	(55.6)
Cash balances at beginning of period	111.5	93.2
Cash balances at end of period	147.4	124.3
Supplemental cash flows information:
Net income tax refund from national governments	$ 30.3	$ (7.5)

CONSOLIDATED STATEMENTS OF CAS7

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Cash and Cash Equivalents, at Carrying Value	$ 183.2	$ 238	$ 395.4	$ 233.5
Restricted cash balances	16.8	23.7	23.8	56.1
Discontinued Operations [Member]
Cash and Cash Equivalents, at Carrying Value	$ 147.4	$ 111.5	$ 124.3	$ 93.2

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
Summary of Significant Accounting Policies	Sep. 30, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation These interim consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the accounts of White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”), its subsidiaries (collectively, with the Company, “White Mountains”) and other entities required to be consolidated under GAAP. The Company is an exempted Bermuda limited liability company whose principal businesses are conducted through its insurance and reinsurance subsidiaries and affiliates. The Company’s headquarters is located at 14 Wesley Street, Hamilton, Bermuda HM 11, its principal executive office is located at 80 South Main Street, Hanover, New Hampshire 03755-2053 and its registered office is located at Clarendon House, 2 Church Street, Hamilton, Bermuda HM 11. White Mountains’s reportable segments are OneBeacon, HG Global/BAM and Other Operations. During the third quarter of 2015, White Mountains signed a definitive agreement to sell Sirius International Insurance Group, Ltd, an exempted Bermuda limited liability company, and its subsidiaries (collectively, “Sirius Group”) to CM International Holding PTE Ltd., the Singapore-based investment arm of China Minsheng Investment Corp., Ltd. (“CMI”). (See Note 2 - “Significant Transactions”). Accordingly, effective for September 30, 2015, Sirius Group has been presented as discontinued operations and assets and liabilities held for sale in the financial statements. Prior year amounts have been reclassified to conform to the current year’s presentation. (See Note 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. During the third quarter of 2013, OneBeacon formed Split Rock Insurance, Ltd. (“Split Rock”), a Bermuda-based reinsurance company. As of September 30, 2015 and December 31, 2014 , White Mountains owned 75.3% of OneBeacon Ltd.’s outstanding common shares for both periods. In December 2014, OneBeacon completed the sale of its runoff business (the “Runoff Transaction”). Accordingly, OneBeacon’s runoff business is presented as discontinued operations. In the second quarter of 2015, OneBeacon completed the sale of its building in Canton, MA for $58.0 million . The building was presented as held for sale at December 31, 2014. (See Note 17 - “Discontinued Operations”) . 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 September 30, 2015 and December 31, 2014 , White Mountains owned 96.9% of HG Global's preferred equity and 88.4% of its common equity. White Mountains does not have an ownership interest in BAM, which is a mutual insurance company owned by its members. However, GAAP requires White Mountains to consolidate BAM's results in its financial statements. BAM's results are attributed to non-controlling interests. White Mountains’s Other Operations segment consists of the Company and its intermediate holding companies, its wholly-owned investment management subsidiary, White Mountains Advisors LLC (“WM Advisors”), White Mountains’s variable annuity reinsurance business, White Mountains Life Reinsurance (Bermuda) Ltd. (“Life Re Bermuda”), which is in runoff with all of its contracts maturing by June 30, 2016, and its U.S.-based service provider, White Mountains Financial Services LLC (collectively, “WM Life Re”), and White Mountains’s ownership positions in Tranzact Holdings, LLC, Wobi Insurance Agency Ltd. (“Wobi”) and QL Holdings, LLC (together with its subsidiaries “MediaAlpha”). The Other Operations segment also includes Star & Shield Services LLC, Star & Shield Risk Management LLC (“SSRM”), and Star & Shield Claims Services LLC (collectively “Star & Shield”). Star & Shield provides management services for a fee to Star & Shield Insurance Exchange (“SSIE”), a reciprocal that is owned by its members, who are policyholders. As of September 30, 2015 , White Mountains holds $20.0 million of surplus notes issued by SSIE (the “SSIE Surplus Notes”) but does not have an ownership interest in SSIE. However, 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 its GAAP financial statements. SSIE’s results do not affect White Mountains’s common shareholders’ equity as they are attributable to non-controlling interests. All significant intercompany transactions have been eliminated in consolidation. Certain amounts in the prior period financial statements have been reclassified to conform to the current presentation. These interim financial statements include all adjustments considered necessary by management to fairly present the financial position, results of operations and cash flows of White Mountains. These interim financial statements may not be indicative of financial results for the full year and should be read in conjunction with the Company’s 2014 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 2014 Annual Report on Form 10-K for a complete discussion regarding White Mountains’s significant accounting policies. Recently Adopted Changes in Accounting Principles Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity On April 10, 2014, the FASB issued ASU 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity (ASC 205 and ASC 360) to reduce diversity in practice for reporting discontinued operations. ASU 2014-08 limits discontinued operations treatment to disposals that have a major effect on a reporting entity’s operations and financial results to be reported as discontinued operations. The revised guidance also requires expanded disclosure in the financial statements for discontinued operations as well as for disposals of significant components of an entity that do not qualify for discontinued operations presentation. As discussed further in Note 2, White Mountains has entered into an agreement to sell Sirius Group, which has been classified as discontinued operations in accordance with ASU 2014-08. Qualified Affordable Housing Projects Effective January 1, 2015, White Mountains adopted ASU 2014-01, Accounting for Investments in Qualified Affordable Housing Projects ( “ QAHP ” ) (ASC 323). ASU 2014-01 allows investors in QAHP to make a policy election to use the proportional amortization method. Under the proportional amortization method, the investor amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits received and recognizes the investment results, net of the related tax benefits, as a component of income tax expense. Prior to adoption, White Mountains accounted for its QAHP investment under the equity method and recognized its share of its QAHP investment's losses in investment income. White Mountains made the policy election to account for its investment in its QAHP investment using the proportional amortization method, applied retrospectively. Under the proportional amortization method, the cumulative loss recognized through December 31, 2014 and December 31, 2013 was $0.9 million and $0.5 million . The retrospective adoption resulted in an increase of $0.4 million and $1.3 million to net investment income and a net increase of $0.6 million and $1.8 million to income tax expense for the three and nine months ended September 30, 2014. Footnote disclosures for prior year amounts have been amended to be consistent with the restated amounts described above. Pushdown Accounting ASU 2014-17, Pushdown Accounting, a consensus of the FASB Emerging Issues Task Force (ASC 805) became effective upon its issuance on November 18, 2014 . The new guidance, which is applicable prospectively, gives an acquired non-public company the option to apply pushdown accounting in its separate company financial statements in the period in which it is acquired in a change of control transaction. Once pushdown accounting has been applied, the election is irreversible. Acquired entities that chose not to apply pushdown accounting at the time of acquisition, may apply pushdown accounting in a subsequent period as a change in accounting principle under ASC 250, Accounting Changes and Error Corrections . White Mountains has not had any acquisitions for which it has elected to apply pushdown accounting since ASU 2014-17 became effective. Unrecognized Tax Benefits Effective January 1, 2014, White Mountains adopted ASU 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists (ASC 740). The new ASU requires balance sheet presentation of an unrecognized tax benefit as a reduction of a deferred tax asset for a net operating loss (“NOL”) carryforward or tax credit carryforward rather than as a liability. The exception is in circumstances where a carryforward is not available to settle the additional taxes that might arise upon disallowance of the tax position under the tax law of the applicable jurisdiction. Prior to the issuance of ASU 2013-11, the guidance for unrecognized tax benefits under ASC 740 did not provide explicit guidance on whether an entity should present an unrecognized tax benefit as a liability or as a reduction of NOL carryforwards or other tax credits. In circumstances where an NOL carryforward is not available to offset settlement of any additional taxes arising from a disallowed tax position, the unrecognized tax benefit should be presented as a liability. The new guidance became effective for White Mountains on January 1, 2014. Adoption did not have any impact on White Mountains's financial condition, results of operations or cash flows or financial statement presentation. Recently Issued Accounting Pronouncements Business Combinations - Measurement Period Adjustments On September 25, 2015, the FASB issued ASU 2015-16, Simplifying the Accounting for Measurement-Period Adjustments. At the date of an acquisition, fair value of certain assets and liabilities may not be accurately determinable and are therefore recognized at the acquirer's best estimate. Such amounts may be updated as additional information becomes available in periods subsequent to the acquisition for up to one year. Prior to the issuance of this new ASU, subsequent adjustments had to be pushed back to the acquisition date, which required retroactive adjustments to prior period amounts. Under the new guidance, adjustments to provisional amounts that are identified during the measurement period are to be recorded in the reporting period in which the adjustment amounts are determined. ASU 2015-16 is effective for fiscal years beginning after December 15, 2015 and is applied prospectively to adjustments to estimated purchase accounting amounts that occur after the effective date. Early application is permitted. White Mountains has not recognized any adjustments to estimated purchase accounting amounts for the year to date period ended September 30, 2015. Short-Duration Contracts On May 21, 2015, the FASB issued ASU 2015-09, Disclosures about Short Duration Contracts (ASC 944) which requires expanded footnote disclosures about loss and loss adjustment expense (“LAE”) reserves. Under the new guidance, some disclosures currently presented outside of White Mountains’s financial statements, such as loss development tables and a reconciliation of loss development data to the loss and LAE reserves reflected on the balance sheet, will become part of the financial statement footnotes. In addition, the loss development tables required to be presented under the new ASU must be presented on a disaggregated basis by accident year rather than by reporting year as currently presented. Some of the expanded disclosures are new requirements, such as the disclosure of reserves for losses incurred but not reported (“IBNR”) plus expected development on reported claims, which must be presented by accident year on a disaggregated basis. The new guidance also requires new disclosures about claim frequency data together with descriptions of the approach used to measure that data. Qualitative descriptions of methodologies and assumptions used to develop IBNR estimates must be presented together with the disaggregated 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. Fair Value Measurements On May 1, 2015, the FASB issued 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 and has classified those measurements within Level 3 of the fair value hierarchy. The new guidance is effective for fiscal years beginning after December 15, 2015 and interim periods within those fiscal years. Debt Issuance Costs On April 7, 2015, the FASB issued ASU 2015-03, Imputation of Interest (ASC 835) which requires debt issuance costs related to a recognized debt liability to be presented as a deduction from the carrying amount of the related debt, consistent with the treatment required for debt discounts. On August 18, 2015, the FASB issued ASU 2015-15, Imputation of Interest (ASC 835) which addresses the presentation and subsequent measurement of debt issuance costs related to line-of-credit arrangements. ASU 2015-03 and ASU 2-15-15 are effective for annual and interim reporting periods beginning after December 15, 2015. White Mountains does not expect ASU 2015-03 or ASU 2015-15 to impact its financial position, results of operations, cash flows, presentation and disclosures. Amendments to Consolidation Analysis On February 18, 2015, the FASB issued 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. ASU 2015-02 is effective for annual and interim reporting periods beginning after December 15, 2015 and must be applied retrospectively. White Mountains does not expect ASU 2015-02 to affect the consolidation analysis for any of its existing investments. Share-Based Compensation Awards On June 19, 2014, the FASB issued 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 is intended to eliminate diversity in practice for employee share-based awards containing performance targets that could be achieved after the requisite service period. Some reporting entities account for performance targets that can be achieved after the requisite service period as performance conditions that affect the vesting of the award while other reporting entities treat those performance targets as non-vesting conditions that affect the grant-date fair value of the award. The updated 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 should be recognized in the period it becomes probable that the performance target will be achieved and should represent the compensation cost attributable to the periods for which service has been rendered. The new guidance is effective for annual and interim reporting periods beginning after December 15, 2015. White Mountains does not expect adoption to have a significant effect on its financial position, results of operations, cash flows, presentation or disclosures. Revenue Recognition On May 28, 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (ASC 606) , which modifies the guidance for revenue recognition. The scope of the new ASU excludes insurance contracts but is applicable to certain fee arrangements, such as third-party investment management fees charged by White Mountains Advisors, which were $2.0 million and $5.9 million for the three and nine months ended September 30, 2015 and $3.2 million and $9.2 million for the three and nine months ended September 30, 2014. 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. On August 12, 2015, the FASB issued ASU 2015-14, which defers the effective date of ASU 2014-09 to annual and interim reporting periods beginning after December 15, 2017.

Significant Transactions

Significant Transactions	9 Months Ended
Significant Transactions	Sep. 30, 2015
Significant Transactions [Abstract]
Significant Transactions	Significant Transactions Sale of Sirius Group On July 27, 2015, White Mountains entered into an agreement to sell Sirius Group to CM International Holding PTE Ltd., the Singapore-based investment arm of CMI. The purchase price will be paid in cash in an amount equal to 127.3% of Sirius Group’s closing date tangible common shareholder’s equity, plus $10.0 million . White Mountains has the option to replenish Sirius’s tangible common shareholder’s equity to its December 31, 2014 level should it be below that level at closing. The transaction is expected to close in the first quarter of 2016 and is subject to regulatory approvals and other customary closing conditions. As a result of the transaction, Sirius Group’s results are reported as discontinued operations and assets and liabilities held for sale within White Mountains’s GAAP financial statements. Assets held for sale does not include White Mountains's investment in Symetra and certain other investments that are in the Sirius Group legal entities as of September 30, 2015 but will be retained by White Mountains subsequent to the sale. As part of the transaction, White Mountains will transfer assets at closing equal to the value of the investments to be retained. The value of these investments, net of related tax effects, is approximately $510.8 million as of September 30, 2015. In connection with the transaction, White Mountains caused Sirius Group to purchase several industry loss warranty contracts purchased to mitigate the potential impact of major events on Sirius Group's balance sheet pending the close of the sale to CMI (the “ILW Covers”). The cost and potential economic benefit provided by the coverage under the ILW Covers inure to White Mountains. The majority of the contracts expire in May or June 2016. The following summarizes the ILW Covers: Scope Limit Industry Loss Trigger United States first event $75.0 million $40.0 billion United States first event $22.5 million $50.0 billion United States second event $45.0 million $15.0 billion Japan first event $25.0 million $12.5 billion Symetra During the third quarter of 2015, Symetra Financial Corporation (“Symetra”) announced that it entered into a definitive merger agreement with Sumitomo Life Insurance Company (“Sumitomo Life”) pursuant to which Sumitomo Life will acquire all of the outstanding shares of Symetra. White Mountains expects to receive $32.00 per share in cash at closing. White Mountains also received a special dividend of $.50 per share as part of the transaction that was paid in the third quarter of 2015. The transaction is expected to close in the first quarter of 2016 and is subject to regulatory approval and other customary closing conditions. 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. OneBeacon has withdrawn its 2016 Plan of Operations and AmTrust will reinsure OneBeacon’s remaining net Crop Business exposure for the 2015 reinsurance year. As a result of this transaction, OneBeacon has no material net exposure related to the Crop Business. For the three months ended September 30, 2015, OneBeacon recorded ceded written premiums of $35.9 million , ceded earned premiums of $16.8 million , ceded loss and loss adjustment expenses of $15.1 million , ceded insurance acquisition expenses of $2.8 million as a result of this transaction. OneBeacon also received a payment of $3.0 million in connection with the termination of its agreement with CCIA, which has been recorded in other revenue. PassportCard On April 2, 2015, White Mountains closed on its 50 / 50 joint venture with DavidShield Life Insurance Agency (2000) Ltd. (“DavidShield”) for the development, marketing and distribution of PassportCard travel insurance (“PassportCard”), with White Mountains and DavidShield each contributing $21.0 million of assets to the newly formed entity, PassportCard Limited (formerly PPCI Global Limited). OneTitle On April 22, 2015, White Mountains agreed to provide up to $13.0 million to OneTitle National Guaranty Company, Inc. (“OneTitle”) and will take a minority stake in the company. OneTitle is a licensed New York title insurance underwriter that works directly with attorneys, lenders, developers and homeowners. The transaction will close subject to regulatory approval. Tranzact On October 10, 2014, White Mountains acquired majority ownership of Tranzact, a leading provider of end-to-end, performance-driven customer acquisition solutions to the insurance sector. White Mountains acquired 63.2% of Tranzact for a purchase price of $177.7 million , representing an enterprise value of $281.2 million . Immediately following the closing, Tranzact completed a recapitalization that allowed for the return of $44.2 million in capital to White Mountains. As of the acquisition date, White Mountains recognized total assets acquired related to Tranzact of $332.8 million , including $41.4 million of tangible assets, $145.1 million of goodwill, and $146.3 million of other intangible assets; and total liabilities assumed of $108.7 million at their estimated fair values. On September 1, 2015, Tranzact acquired 100.0% of the outstanding share capital of TruBridge, Inc. and TruBroker, LLC (collectively “TruBridge”) for a purchase price of $31.0 million , representing an enterprise value of $50.2 million . The purchase price is subject to an adjustment linked to the amount of marketing expense reimbursements expected to be received in 2016 and 2017. As of the acquisition date, Tranzact recognized total assets acquired of $53.8 million , which includes $20.1 million of goodwill and $28.1 million of other intangible assets, and total liabilities assumed of $3.6 million at their estimated fair values. At September 30, 2015, Tranzact recognized $9.7 million for the purchase price adjustment. durchblicker.at In July 2014, White Mountains acquired 45% of the outstanding common shares of durchblicker.at, Austria's first independent price comparison portal for insurance, gas/electricity and financial services, for EUR 8.5 million (approximately $11.7 million based upon the foreign exchange spot rate at the date of acquisition). MediaAlpha On March 14, 2014, White Mountains acquired 60% of the outstanding Class A common units of MediaAlpha. MediaAlpha is a California-based advertising technology company offering a transparent online exchange and sophisticated analytical tools that facilitate transactions between buyers (advertisers) and sellers (publishers) of insurance media (clicks, leads, and calls). Its exchange operates in four verticals: auto, home, health and life. White Mountains paid an initial purchase price of $28.1 million. The purchase price is subject to adjustment equal to 62.5% of the 2015 gross profit in excess of the 2013 gross profit. As of September 30, 2015 and December 31, 2014, White Mountains has recognized a $7.9 million liability for the contingent purchase price adjustment. After adjustment for the estimated contingent purchase price adjustment, White Mountains recognized total assets acquired related to MediaAlpha of $70.1 million , including $18.3 million of goodwill and $38.5 million of other intangible assets, and total liabilities assumed of $10.0 million , reflecting acquisition date fair values. 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 $8.5 million ) of newly-issued convertible preferred shares of Wobi. Wobi is the only price comparison/aggregation business in Israel, with an insurance carrier panel that represents 85% of the premiums written in the Israeli insurance market. Wobi sells four insurance lines of business, primarily personal auto, and operates as an agency, charging upfront commissions on all insurance policy sales. Wobi also offers a pension products comparison service for Israeli customers and is paid transaction fees when customers use the service to connect to companies that sell those pension products. As of the acquisition date, White Mountains recognized total assets acquired related to Wobi of $13.4 million , including $5.5 million of goodwill and $2.9 million of other intangible assets; and total liabilities assumed of $0.7 million at their estimated fair values. During the second quarter of 2015, White Mountains increased its ownership interest in Wobi through the purchase of shares from a non-controlling interest shareholder for NIS 35.0 million (approximately $ 9.1 million ) and newly-issued convertible preferred shares for NIS 25.0 million (approximately $ 6.6 million ). As of September 30, 2015, White Mountains’s ownership share was 95.3% on a fully converted basis. On February 23, 2015, Wobi acquired 56.2% of the outstanding share capital of Tnuva Finansit Ltd. (“Cashboard”) for NIS 9.5 million (approximately $2.4 million ). 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 fair values. During the second quarter of 2015, Wobi purchased newly issued common shares of Cashboard for NIS 10.0 million (approximately $2.6 million ), which increased its ownership interest in Cashboard to 68.3% . Star & Shield On January 31, 2014, White Mountains acquired certain assets and liabilities of Star & Shield Holdings LLC, including SSRM, the attorney-in-fact for SSIE, for a purchase price of $1.8 million . White Mountains owns $20.0 million of surplus notes issued by SSIE. Principal and interest on the surplus notes are payable to White Mountains only with approval from the Florida Office of Insurance Regulation. SSIE is a Florida-domiciled reciprocal insurance exchange providing private passenger auto insurance to the public safety community and their families. SSIE is a variable interest entity (“VIE”). As a result of SSRM’s role as the attorney-in-fact to SSIE and the investment in SSIE’s Surplus Notes, White Mountains is required to consolidate SSIE. At September 30, 2015 and December 31, 2014, consolidated amounts included total assets of $16.3 million and $13.5 million and total liabilities of $31.5 million and $25.9 million , respectively of SSIE. The surplus notes purchased by White Mountains and the corresponding liability included in SSIE's liabilities are eliminated in consolidation. For the three months ended September 30, 2015 and 2014, SSIE had pre-tax losses of $0.9 million and $1.4 million that were recorded in net loss attributable to non-controlling interests. For the nine months ended September 30, 2015 and 2014, SSIE had pre-tax losses of $2.8 million and $11.1 million that were recorded in net loss attributable to non-controlling interests.

Loss and Loss Adjustment Expens

Loss and Loss Adjustment Expense Reserves	9 Months Ended
Loss and Loss Adjustment Expense Reserves	Sep. 30, 2015
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 subsidiaries for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Gross beginning balance $ 1,357.0 $ 1,137.8 $ 1,350.0 $ 1,054.3 Less beginning reinsurance recoverable on unpaid losses (147.2 ) (92.1 ) (161.7 ) (80.2 ) Net loss and LAE reserves 1,209.8 1,045.7 1,188.3 974.1 Loss and LAE reserves consolidated — SSIE — — — 13.6 Loss and LAE incurred relating to: Current year losses 170.4 178.4 536.7 511.0 Prior year losses (0.4 ) 7.1 (2.6 ) 16.3 Total incurred losses and LAE 170.0 185.5 534.1 527.3 Loss and LAE paid relating to: Current year losses (53.0 ) (55.9 ) (120.2 ) (116.5 ) Prior year losses (108.1 ) (107.3 ) (383.5 ) (330.5 ) Total loss and LAE payments (161.1 ) (163.2 ) (503.7 ) (447.0 ) Net ending balance 1,218.7 1,068.0 1,218.7 1,068.0 Plus ending reinsurance recoverable on unpaid losses 214.6 101.5 214.6 101.5 Gross ending balance $ 1,433.3 $ 1,169.5 $ 1,433.3 $ 1,169.5 Loss and LAE incurred relating to prior year losses for the three and nine months ended September 30, 2015 For the three and nine months ended September 30, 2015 , White Mountains experienced net favorable loss reserve development of $0.4 million and $2.6 million . During the three months ended September 30, 2015 , OneBeacon experienced no net loss and LAE reserve development. For the nine months ended September 30, 2015 , OneBeacon had net favorable loss reserve development of $1.8 million . For the three and nine months ended September 30, 2015 , SSIE had net favorable loss reserve development of $0.4 million and $0.8 million . Loss and LAE incurred relating to prior year losses for the three and nine months ended September 30, 2014 For the three and nine months ended September 30, 2014 , White Mountains experienced net unfavorable loss reserve development of $7.1 million and $16.3 million . For the three and nine months ended September 30, 2014 , OneBeacon had net unfavorable loss reserve development of $7.3 million and $14.3 million primarily related to a few large losses in OneBeacon Other Professional Lines and Management Liability, as well as OneBeacon Entertainment, OneBeacon Government Risks and OneBeacon Accident Group, partially offset by favorable loss reserve development in OneBeacon Specialty Property. For both the three and nine months ended September 30, 2014 , SSIE had net favorable loss reserve development of $0.2 million and net unfavorable loss reserve development of $2.0 million .

Third Party Reinsurance

Third Party Reinsurance	9 Months Ended
Third Party Reinsurance	Sep. 30, 2015
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 September 30, 2015 , OneBeacon had $22.6 million and $214.2 million of reinsurance recoverables on paid and unpaid losses. At December 31, 2014 , OneBeacon had $12.2 million and $161.6 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. Except as discussed below, there have been no material changes to OneBeacon's reinsurance coverage as discussed in Note 4 —“Reinsurance” in White Mountains’s 2014 Annual Report on Form 10-K. Effective January 1, 2015, OneBeacon purchased an aggregate stop loss on its multiple peril crop insurance (“MPCI”) portfolio, providing 52.0% coverage in excess of a 98.0% loss ratio on premiums covered by the contract and a separate aggregate stop loss providing 80% coverage in excess of a 100% loss ratio on its crop-hail portfolio. OneBeacon also purchased a new quota share contract on 30% of its MPCI portfolio. On July 31, 2015, OneBeacon reinsured 100% of its net retained losses for both its MPCI and crop-hail business by entering into a quota share reinsurance agreement with an insurance operating affiliate of AmTrust for the remaining net exposure to the 2015 Crop reinsurance year, which coupled with other transfer and assignment agreements as well as communications with policyholders and agents, had the effect of assumption reinsurance. (See Note 2 -“Significant Transactions”) . Effective May 1, 2015, OneBeacon renewed its property catastrophe reinsurance program through April 30, 2016. The program provides coverage for OneBeacon's property business as well as certain acts of terrorism. Under the program, the first $20.0 million of losses resulting from any single catastrophe are retained, and 95.0% of the next $10.0 million of losses and 100.0% of the next $100.0 million of losses resulting from the catastrophe are reinsured. The part of the 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. Also effective May 1, 2015, OneBeacon lowered its retention on its property-per-risk reinsurance program from $5.0 million to $3.0 million . Effective June 1, 2015, OneBeacon lowered its retentions on certain casualty and healthcare treaties from $5.0 million to $3.0 million .

Investment Securities

Investment Securities	9 Months Ended
Investment Securities	Sep. 30, 2015
Investments, Debt and Equity Securities [Abstract]
Investment Securities	Investment Securities White Mountains’s invested assets consist of 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 convertible fixed maturity and preferred 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. 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 September 30, 2015 and December 31, 2014 . Other long-term investments consist primarily of hedge funds, private equity funds, surplus note investments, private equity securities and limited liability companies and other investments in limited partnerships. Net Investment Income Pre-tax net investment income for the three and nine months ended September 30, 2015 and 2014 consisted of the following: Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Investment income: Fixed maturity investments $ 13.7 $ 12.7 $ 38.5 $ 38.4 Short-term investments — .1 .1 .2 Common equity securities 1.4 3.3 5.7 11.9 Convertible fixed maturity and preferred investments .1 1.0 .4 1.5 Other long-term investments 1.9 .2 2.5 2.2 Total investment income 17.1 17.3 47.2 54.2 External investment expenses (.3 ) (3.5 ) (4.6 ) (9.5 ) Net investment income, pre-tax $ 16.8 $ 13.8 $ 42.6 $ 44.7 Net Realized and Unrealized Investment Gains and Losses Net realized and unrealized investment gains and losses for the three and nine months ended September 30, 2015 and 2014 consisted of the following: Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Net realized investment (losses) gains, pre-tax $ (7.4 ) $ 57.9 $ 49.7 $ 97.0 Net unrealized investment (losses), pre-tax (36.5 ) (85.4 ) (83.6 ) (32.6 ) Net realized and unrealized investment (losses) gains, pre-tax (43.9 ) (27.5 ) (33.9 ) 64.4 Income tax benefit (expense) attributable to net realized and unrealized investment gains (losses) 9.4 5.6 6.9 (12.2 ) Net realized and unrealized investment (losses) gains, after tax $ (34.5 ) $ (21.9 ) $ (27.0 ) $ 52.2 Net realized investment gains (losses) Net realized investment gains (losses) for the three and nine months ended September 30, 2015 and 2014 consisted of the following: Three Months Ended Three Months Ended September 30, 2015 September 30, 2014 Millions Net Net Total net realized Net Net Total net realized Fixed maturity investments $ (.1 ) $ — $ (.1 ) $ 2.3 $ (.1 ) $ 2.2 Short-term investments — — — — — — Common equity securities (5.9 ) — (5.9 ) 51.4 — 51.4 Convertible fixed maturity and preferred investments — — — 1.6 — 1.6 Other long-term investments (1.4 ) — (1.4 ) 2.7 — 2.7 Net realized investment (losses) gains, pre-tax (7.4 ) — (7.4 ) 58.0 (.1 ) 57.9 Income tax benefit (expense) attributable to net realized investment gains 1.5 — 1.5 (7.0 ) — (7.0 ) Net realized investment (losses) gains, after tax $ (5.9 ) $ — $ (5.9 ) $ 51.0 $ (.1 ) $ 50.9 Nine Months Ended Nine Months Ended September 30, 2015 September 30, 2014 Millions Net Net Total net realized Net Net Total net realized Fixed maturity investments $ 2.0 $ — $ 2.0 $ 4.7 $ (.1 ) $ 4.6 Short-term investments — — — — — — Common equity securities 41.6 .4 42.0 83.2 — 83.2 Convertible fixed maturity and preferred investments (4.3 ) — (4.3 ) 6.5 — 6.5 Other long-term investments 10.0 — 10.0 2.7 — 2.7 Net realized investment gains (losses), pre-tax 49.3 .4 49.7 97.1 (.1 ) 97.0 Income tax (expense) attributable to net realized investment gains (losses) (15.7 ) — (15.7 ) (13.3 ) — (13.3 ) Net realized investment gains (losses), after tax $ 33.6 $ .4 $ 34.0 $ 83.8 $ (.1 ) $ 83.7 Net unrealized investment gains (losses) The following table summarizes net unrealized investment gains (losses) for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended Three Months Ended September 30, 2015 September 30, 2014 Millions Net unrealized gains (losses) Net Total net unrealized gains (losses) reflected in earnings Net unrealized (losses) Net Total net unrealized (losses) reflected in earnings Fixed maturity investments $ 3.3 $ — $ 3.3 $ (10.0 ) $ — $ (10.0 ) Short-term investments — — — — — — Common equity securities (30.6 ) (.2 ) (30.8 ) (63.9 ) (5.3 ) (69.2 ) Convertible fixed maturity and preferred investments 1.1 — 1.1 (3.4 ) — (3.4 ) Other long-term investments (10.1 ) — (10.1 ) (2.8 ) — (2.8 ) Net unrealized investment (losses), pre-tax (36.3 ) (.2 ) (36.5 ) (80.1 ) (5.3 ) (85.4 ) Income tax benefit 7.9 — 7.9 12.6 — 12.6 Net unrealized investment $ (28.4 ) $ (.2 ) $ (28.6 ) $ (67.5 ) $ (5.3 ) $ (72.8 ) Nine Months Ended Nine Months Ended September 30, 2015 September 30, 2014 Millions Net unrealized gains (losses) Net Total net unrealized gains (losses) reflected in earnings Net unrealized gains (losses) Net Total net unrealized gains (losses) reflected in earnings Fixed maturity investments $ 1.3 $ — $ 1.3 $ 12.3 $ — $ 12.3 Short-term investments — — — — — — Common equity securities (56.0 ) (2.5 ) (58.5 ) (43.2 ) (5.3 ) (48.5 ) Convertible fixed maturity and preferred investments 2.0 — 2.0 (5.1 ) — (5.1 ) Other long-term investments (27.6 ) (.8 ) (28.4 ) 8.7 — 8.7 Net unrealized investment (losses), pre-tax (80.3 ) (3.3 ) (83.6 ) (27.3 ) (5.3 ) (32.6 ) Income tax benefit attributable to net unrealized investment losses 22.6 — 22.6 1.1 — 1.1 Net unrealized investment (losses), after tax $ (57.7 ) $ (3.3 ) $ (61.0 ) $ (26.2 ) $ (5.3 ) $ (31.5 ) The following table summarizes the amount of total pre-tax unrealized investment (losses) gains included in earnings for Level 3 investments for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Fixed maturity investments $ (1.0 ) $ 2.1 $ (.9 ) $ 2.7 Common equity securities 1.1 1.0 4.0 3.8 Convertible fixed maturity and preferred investments 1.1 .1 1.8 3.3 Other long-term investments (10.0 ) (3.5 ) (28.1 ) (5.7 ) Total unrealized investment (losses) gains, pre-tax - Level 3 investments $ (8.8 ) $ (.3 ) $ (23.2 ) $ 4.1 Investment Holdings The cost or amortized cost, gross unrealized investment gains and losses, net foreign currency gains and losses, and carrying values of White Mountains’s fixed maturity investments as of September 30, 2015 and December 31, 2014 were as follows: September 30, 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 $ 99.6 $ .2 $ — $ — $ 99.8 Debt securities issued by corporations 998.6 8.7 (1.5 ) — 1,005.8 Municipal obligations 145.8 1.8 (.8 ) — 146.8 Mortgage-backed and asset-backed securities 1,261.2 6.4 (2.2 ) — 1,265.4 Foreign government, agency and provincial obligations 1.0 .3 — — 1.3 Preferred stocks 78.3 4.8 — — 83.1 Total fixed maturity investments $ 2,584.5 $ 22.2 $ (4.5 ) $ — $ 2,602.2 December 31, 2014 Millions Cost or amortized cost Gross unrealized gains Gross unrealized losses Net foreign currency gains (losses) Carrying value U.S. Government and agency obligations $ 105.4 $ .1 $ (.3 ) $ — $ 105.2 Debt securities issued by corporations 1,162.0 13.1 (3.4 ) — 1,171.7 Municipal obligations 81.0 1.4 (.2 ) — 82.2 Mortgage-backed and asset-backed securities 967.5 2.8 (2.4 ) — 967.9 Foreign government, agency and provincial obligations 11.5 .3 (1.0 ) — 10.8 Preferred stocks 78.3 5.9 — — 84.2 Total fixed maturity investments $ 2,405.7 $ 23.6 $ (7.3 ) $ — $ 2,422.0 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, convertible fixed maturity and preferred investments and other long-term investments as of September 30, 2015 and December 31, 2014 were as follows: September 30, 2015 Millions Cost or amortized cost Gross unrealized gains Gross unrealized losses Net foreign Carrying value Common equity securities $ 453.0 $ 52.0 $ (22.9 ) $ — $ 482.1 Convertible fixed maturity and preferred investments $ 3.1 $ 2.5 $ — $ — $ 5.6 Other long-term investments $ 271.9 $ 37.7 $ (12.9 ) $ (2.1 ) $ 294.6 December 31, 2014 Millions Cost or Gross Gross Net foreign Carrying value Common equity securities $ 495.3 $ 127.4 $ (3.6 ) $ (7.4 ) $ 611.7 Convertible fixed maturity and preferred investments $ 13.4 $ .8 $ (.3 ) $ — $ 13.9 Other long-term investments $ 273.3 $ 52.5 $ (6.5 ) $ (1.3 ) $ 318.0 Other Long-term Investments Other long-term investments consist of the following as of September 30, 2015 and December 31, 2014 : Carrying Value at Millions September 30, 2015 December 31, 2014 Hedge funds and private equity funds, at fair value (1) $ 148.6 $ 178.5 Surplus notes investments, at fair value (1)(4) 58.0 65.1 Private equity securities and limited liability companies, at fair value (1)(2) 65.3 45.3 Tax advantaged federal affordable housing development fund (3) 15.2 16.8 Partnership investments accounted for under the equity method 3.9 5.1 Other (1) 3.6 7.2 Total other-long term investments $ 294.6 $ 318.0 (1) See Fair Value Measurements by Level table. (2) On April 2, 2015, White Mountains invested $21.0 in PassportCard. White Mountains has chosen to take the fair value election for its investment. (3) Fund accounted for using the proportional amortization method. (4) The decrease in the fair value of the surplus notes during the nine months ended September 30, 2015 was primarily due to widening of non- investment grade credit spreads. 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 September 30, 2015 , White Mountains held investments in 10 hedge funds and 22 private equity funds. The largest investment in a single fund was $22.3 million as of September 30, 2015 . The following table summarizes investments in hedge funds and private equity funds by investment objective and sector as of September 30, 2015 and December 31, 2014 : September 30, 2015 December 31, 2014 Millions Fair Value Unfunded Commitments Fair Value Unfunded Commitments Hedge funds Long/short equity REIT $ 20.0 $ — $ 20.4 $ — Long/short credit & distressed 8.1 — 8.4 — Long/short equity banks and financial 15.4 — 29.9 — Other 12.1 — 15.7 — Total hedge funds 55.6 — 74.4 — Private equity funds Energy infrastructure & services 26.3 4.0 33.1 4.8 Manufacturing/Industrial 23.5 2.5 23.2 7.3 Multi-sector 14.9 2.1 14.5 2.2 Aerospace/Defense/Government 17.1 33.6 20.7 5.1 Healthcare 3.9 .4 3.1 1.4 Private equity secondaries 4.5 2.1 5.7 2.1 Insurance 2.0 41.3 2.1 41.3 Real estate .8 .1 1.7 .1 Total private equity funds 93.0 86.1 104.1 64.3 Total hedge funds and private equity funds included in other long-term investments $ 148.6 $ 86.1 $ 178.5 $ 64.3 Redemption of investments in certain hedge funds is subject to restrictions including lock-up periods where no redemptions or withdrawals are allowed, restrictions on redemption frequency and advance notice periods for redemptions. Amounts requested for redemptions remain subject to market fluctuations until the redemption effective date, which generally falls at the end of the defined redemption period. The following summarizes the September 30, 2015 fair value of hedge funds subject to restrictions on redemption frequency and advance notice period requirements for investments in active hedge funds: Notice Period Millions Redemption frequency 30-59 days notice 60-89 days notice 90-119 days notice 120+ days notice Total Monthly $ — $ — $ — $ — $ — Quarterly 16.4 8.1 — 8.4 32.9 Semi-annual — 20.0 — — 20.0 Annual — — 2.7 — 2.7 Total $ 16.4 $ 28.1 $ 2.7 $ 8.4 $ 55.6 Certain of the hedge fund investments in which White Mountains is invested are no longer active and are in the process of disposing of their underlying investments. Distributions from such funds are remitted to investors as the fund’s underlying investments are liquidated. As of September 30, 2015 , distributions of $1.0 million were outstanding from these investments. The actual amount of the final distribution remittances remain subject to market fluctuations. The date at which such remittances will be received is not determinable as of September 30, 2015 . White Mountains has also submitted redemption requests for certain of its investments in active hedge funds. As of September 30, 2015 , redemptions of $22.1 million are outstanding and are subject to market fluctuations. The date at which such redemptions will be received is not determinable as of September 30, 2015 . 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 September 30, 2015 , 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 $25.8 $11.1 $56.1 $— $93.0 Fair value measurements as of September 30, 2015 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”). 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 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, hedge funds and private equity funds, as well as certain investments in fixed maturity investments, common equity securities, and convertible fixed and preferred maturity investments where quoted market prices are unavailable or are not considered reasonable. White Mountains determines when transfers between levels have occurred as of the beginning of the period. White Mountains uses brokers and outside pricing services to assist in determining fair values. For investments in active markets, White Mountains uses the quoted market prices provided by outside pricing services to determine fair value. The outside pricing services White Mountains uses have indicated that they will only provide prices where observable inputs are available. In circumstances where quoted market prices are unavailable or are not considered reasonable, White Mountains estimates the fair value using industry standard pricing models and observable inputs such as benchmark yields, reported trades, broker-dealer quotes, issuer spreads, benchmark securities, bids, offers, prepayment speeds, reference data including research publications and other relevant inputs. Given that many fixed maturity investments do not trade on a daily basis, the outside pricing services evaluate a wide range of fixed maturity investments by regularly drawing parallels from recent trades and quotes of comparable securities with similar features. The characteristics used to identify comparable fixed maturity investments vary by asset type and take into account market convention. White Mountains's process to assess the reasonableness of the market prices obtained from the outside pricing sources covers substantially all of its fixed maturity investments and includes, but is not limited to, evaluation of model pricing methodologies, review of the pricing services' quality control processes and procedures on at least an annual basis, comparison of market prices to prices obtained from different independent pricing vendors on at least a semi-annual basis, monthly analytical reviews of certain prices and review of assumptions utilized by the pricing service for selected measurements on an ad hoc basis throughout the year. White Mountains also performs back-testing of selected purchases and sales activity to determine whether there are any significant differences between the market price used to value the security prior to purchase or sale and the actual purchase or 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. Municipal obligations: The fair value of municipal obligations is determined from an evaluated 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. 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. Foreign government obligations: The fair value of foreign government obligations is determined from an evaluated pricing model that uses feeds from data sources in each respective country, including active market makers and inter-dealer brokers. Key inputs include benchmark yields, reported trades, broker-dealer quotes, two-sided markets, benchmark securities, bids, offers, local exchange prices, foreign exchange rates and reference data including coupon, credit quality ratings, duration and market research publications. Preferred stocks: The fair value of preferred stocks is determined from an evaluated pricing model that calculates the appropriate spread over a comparable security for each issue. Key inputs include exchange prices (underlying and common stock of same issuer), benchmark yields, reported trades, broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including sector, coupon, credit quality ratings, duration, credit enhancements, early redemption features and market research publications. Level 3 valuations are generated from techniques that use assumptions not observable in the market. These unobservable assumptions reflect White Mountains’s assumptions that market participants would use in valuing the investment. Generally, certain securities may start out as Level 3 when they are originally issued but as observable inputs become available in the market, they may be reclassified to Level 2. White Mountains employs a number of procedures to assess the reasonableness of the fair value measurements for its other long-term investments, including obtaining and reviewing the audited annual financial statements of hedge funds and private equity funds and periodically discussing each fund’s pricing with the fund manager. However, since the fund managers do not provide sufficient information to evaluate the pricing inputs and methods for each underlying investment, the inputs are considered to be unobservable. Accordingly, the fair values of White Mountains’s investments in hedge funds and private equity funds have been classified as Level 3 measurements. The fair value of White Mountains’s investments in hedge funds and private equity funds has been determined using net asset value. Prior to the liquidation of the Prospector Offshore Fund, in addition to the investments described above, White Mountains had $31.6 million of investment-related liabilities recorded at fair value and included in other liabilities as of December 31, 2014 . These liabilities relate to securities that have been sold short by limited partnerships in which White Mountains has investments and was required to consolidate under GAAP. These liabilities have a Level 1 designation. Fair Value Measurements by Level The following tables summarize White Mountains’s fair value measurements for investments as of September 30, 2015 and December 31, 2014 , by major security type and class by level. The major security types were based on the legal form of the securities, with a separate break-out for convertible fixed maturity investments as they may react similar to either debt securities or equity securities, depending on prevailing market conditions. 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 asset-backed securities vary depending on the nature of the issuing entity type. White Mountains further disaggregates debt securities issued by corporations and equity securities by industry sector because investors often reference commonly used benchmarks and their subsectors to monitor risk and performance. Accordingly, White Mountains has further disaggregated these asset classes into subclasses based on the similar sectors and industry classifications it uses to evaluate investment risk and performance against commonly used benchmarks, such as the Barclays Intermediate Aggregate and S&P 500 indices: September 30, 2015 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 99.8 $ 61.8 $ 38.0 $ — Debt securities issued by corporations: Consumer 223.1 — 223.1 — Financials 201.3 — 201.3 — Health Care 177.2 — 177.2 — Industrial 132.8 — 132.8 — Communications 52.7 — 52.7 — Energy 57.8 — 57.8 — Utilities 62.5 — 62.5 — Technology 64.7 — 64.7 — Materials 31.4 — 31.4 — Other 2.3 — 2.3 — Total debt securities issued by corporations 1,005.8 — 1,005.8 — Municipal obligations 146.8 — 146.8 — Mortgage-backed and asset-backed securities 1,265.4 — 1,265.4 — Foreign government, agency and provincial obligations 1.3 .6 .7 — Preferred stocks 83.1 — 12.8 70.3 Total fixed maturity investments 2,602.2 62.4 2,469.5 70.3 Short-term investments 325.0 325.0 — — Common equity securities: Exchange traded funds (1) 172.6 152.6 20.0 — Financials 63.2 29.0 — 34.2 Consumer 56.5 56.5 — — Health Care 34.5 34.5 — — Industrial 25.2 25.2 — — Technology 22.0 22.0 — — Communications 36.0 36.0 — — Energy — — — — Materials — — — — Utilities — — — — Other 72.1 — 72.1 — Total common equity securities 482.1 355.8 92.1 34.2 Convertible fixed maturity and preferred investments 5.6 — — 5.6 Other long-term investments (2) 275.5 — — 275.5 Total investments $ 3,690.4 $ 743.2 $ 2,561.6 $ 385.6 (1) ETF's 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 $3.9 associated with other long-term investment limited partnerships accounted for using the equity method. Excludes carrying value of $15.2 associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method. December 31, 2014 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 105.2 $ 51.2 $ 54.0 $ — Debt securities issued by corporations: Consumer 259.2 — 259.2 — Financials 254.7 — 254.7 — Health Care 181.8 — 181.8 — Industrial 107.3 — 102.0 5.3 Communications 71.5 — 71.5 — Energy 65.6 — 65.6 — Utilities 84.1 — 84.1 — Technology 88.3 — 88.3 — Materials 51.7 — 51.7 — Other 7.5 — 7.5 — Total debt securities issued by corporations 1,171.7 — 1,166.4 5.3 Mortgage-backed and asset-backed securities 967.9 — 967.9 — Foreign government, agency and provincial obligations 10.8 .6 10.2 — Preferred stocks 84.2 — 13.1 71.1 Municipal obligations 82.2 — 82.2 — Total fixed maturity investments 2,422.0 51.8 2,293.8 76.4 Short-term investments 376.8 376.3 .5 — Common equity securities: Financials 180.7 141.2 — 39.5 Consumer 116.0 115.9 .1 — Health Care 74.4 74.4 — — Industrial 57.1 57.1 — — Technology 44.8 44.8 — — Communications 28.5 28.5 — — Energy 18.1 18.1 — — Materials 12.0 12.0 — — Utilities 4.9 4.9 — — Other 75.2 1.9 73.3 — Total common equity securities 611.7 498.8 73.4 39.5 Convertible fixed maturity and preferred investments 13.9 — 5.7 8.2 Other long-term investments (1) 296.0 — — 296.0 Total investments $ 3,720.4 $ 926.9 $ 2,373.4 $ 420.1 (1) Excludes carrying value of $5.2 associated with other long-term investment limited partnerships accounted for using the equity method. Excludes carrying value of $16.8 associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method. Debt securities issued by corporations The following table summarizes the ratings of the corporate debt securities held in White Mountains’s investment portfolio as of September 30, 2015 and December 31, 2014 : Fair Value at Millions September 30, 2015 December 31, 2014 AAA $ — $ — AA 112.3 144.9 A 439.7 594.9 BBB 453.8 426.5 BB — — Other — 5.4 Debt securities issued by corporations (1) $ 1,005.8 $ 1,171.7 (1) Credit ratings are assigned based on the following hierarchy: 1) Standard and Poor's Financial Services LLC (“Standard & Poor’s”) and 2) Moody’s Investor Service (“Moody's”). Mortgage-backed, Asset-backed Securities White Mountains purchases commercial and residential mortgage-backed securities with the goal of maximizing risk adjusted returns in the context of a diversified portfolio. White Mountains categorizes mortgage-backed securities as “non-prime” (also called “Alt A” or “A-”) if they are backed by collateral that has overall credit quality between prime and sub-prime based on White Mountains’s review of the characteristics of their underlying mortgage loan pools, such as credit scores and financial ratios. White Mountains considers sub-prime mortgage-backed securities as those that have underlying loan pools that exhibit weak credit characteristics, or those that are issued from dedicated sub-prime shelves or dedicated second-lien shelf registrations (i.e., White Mountains considers investments backed primarily by second-liens to be sub-prime risks regardless of credit scores or other metrics). The following table summarizes mortgage and asset-backed securities as of September 30, 2015 and December 31, 2014 : September 30, 2015 December 31, 2014 Millions Fair Value Level 2 Level 3 Fair Value Level 2 Level 3 Mortgage-backed securities: Agency: GNMA $ 293.9 $ 293.9 $ — $ 308.7 $ 308.7 $ — FNMA 41.6 41.6 — 33.4 33.4 — FHLMC 24.8 24.8 — 28.9 28.9 — Total Agency (1) 360.3 360.3 — 371.0 371.0 — Non-agency: Residential 123.7 123.7 — 71.0 71.0 — Commercial 133.7 133.7 — 109.3 109.3 — Total Non-agency 257.4 257.4 — 180.3 180.3 — Total mortgage-backed securities 617.7 617.7 — 551.3 551.3 — Other asset-backed securities: Credit card receivables 293.3 293.3 — 218.1 218.1 — Vehicle receivables 276.4 276.4 — 152.8 152.8 — Other 78.0 78.0 — 45.7 45.7 — Total other asset-backed securities 647.7 647.7 — 416.6 416.6 — Total mortgage and asset-backed securities $ 1,265.4 $ 1,265.4 $ — $ 967.9 $ 967.9 $ — (1) Represents publicly traded mortgage-backed securities which carry the full faith and credit guaranty of the U.S. government (i.e., GNMA) or are guaranteed by a government sponsored entity (i.e., FNMA, FHLMC). Non-agency Mortgage-backed Securities The security issuance years of White Mountains’s investments in non-agency residential mortgage-backed securities ("RMBS") and non-agency commercial mortgage-backed securities (“CMBS”) as of September 30, 2015 are as follows: Security Issuance Year Millions Fair Value 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Non-agency RMBS $ 123.7 $ 18.3 $ 2.9 $ 4.0 $ — $ 4.2 $ — $ 17.1 $ 14.6 $ 13.4 $ 14.7 $ 34.5 $ — Non-agency CMBS 133.7 — — — — — — 5.7 — 8.6 18.4 55.6 45.4 Total $ 257.4 $ 18.3 $ 2.9 $ 4.0 $ — $ 4.2 $ — $ 22.8 $ 14.6 $ 22.0 $ 33.1 $ 90.1 $ 45.4 Non-agency Residential Mort

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	9 Months Ended
Goodwill and Other Intangible Assets	Sep. 30, 2015
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 February 23, 2015, Wobi acquired 56.2% of the outstanding share capital of Tnuva Finansit Ltd. (“Cashboard”) for NIS 9.5 million (approximately $2.4 million based upon the foreign exchange spot rate at the date 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. On September 1, 2015, Tranzact acquired 100.0% of the outstanding share capital of TruBridge for a purchase price of $31.0 million , representing an enterprise value of $50.2 million . As of the acquisition date, Tranzact recognized total assets acquired of $53.8 million , which includes $20.1 million of goodwill and $28.1 million of other intangible assets, and total liabilities assumed of $3.6 million at their estimated fair values. The following table shows the change in goodwill and other intangible assets: Three Months Ended September 30, Millions 2015 2014 Goodwill Other intangible assets Goodwill Other intangible assets Beginning balance $ 169.2 $ 171.2 $ 23.8 $ 44.6 Acquisitions of businesses 20.1 28.1 — — Dispositions of businesses — — — — Amortization, including foreign currency translation — (6.9 ) — (2.6 ) Ending balance $ 189.3 $ 192.4 $ 23.8 $ 42.0 Nine Months Ended September 30, Millions 2015 2014 Goodwill Other intangible assets Goodwill Other intangible assets Beginning balance $ 168.9 $ 182.3 $ — $ 5.1 Acquisitions of businesses 20.4 30.9 23.8 42.4 Dispositions of businesses — — — — Amortization, including foreign currency translation — (20.8 ) — (5.5 ) Ending balance $ 189.3 $ 192.4 $ 23.8 $ 42.0

Debt

Debt	9 Months Ended
Debt	Sep. 30, 2015
Debt Disclosure [Abstract]
Debt	Debt White Mountains’s debt outstanding as of September 30, 2015 and December 31, 2014 consisted of the following: Millions September 30, December 31, 2012 OBH Senior Notes, at face value $ 275.0 $ 275.0 Unamortized original issue discount (.2 ) (.3 ) 2012 OBH Senior Notes, carrying value 274.8 274.7 WTM Bank Facility — — OneBeacon Bank Facility — — Tranzact Bank Facility 95.8 68.7 Unamortized issuance cost (2.0 ) (1.3 ) Tranzact Bank Facility, carrying value 93.8 67.4 MediaAlpha Bank Facility 15.0 — Unamortized issuance cost (.3 ) — MediaAlpha Bank Facility, carrying value 14.7 — Other debt — 1.0 Total debt $ 383.3 $ 343.1 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 September 30, 2015 , White Mountains borrowed and repaid a total of $60.0 million under the WTM Bank Facility at a blended interest rate of 3.65% . As of September 30, 2015 , 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. 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 September 30, 2015, the OneBeacon Bank Facility was undrawn. The OneBeacon Bank Facility contains various affirmative, negative and financial covenants which White Mountains considers to be customary for such borrowings, including certain minimum net worth and maximum debt to capitalization standards. Tranzact Bank Facility On October 10, 2014, Tranzact entered into a secured credit facility with a syndicate of lenders administered by the PrivateBank and Trust Company that has a maturity date of October 10, 2019 (the “Tranzact Bank Facility”). During the third quarter of 2015, Tranzact amended the Tranzact Bank Facility, which now has a total commitment of $116.0 million , consisting of a $101.0 million term loan facility and a $15.0 million revolving facility. The amendment increased the term loan facility by $31.0 million , the proceeds of which were used by Tranzact to finance the acquisition of TruBridge. During the nine months ended September 30, 2015 , Tranzact also borrowed and repaid $13.0 million under the revolving facility. During the three and nine months ended September 30, 2015 , Tranzact repaid a total of $1.3 million and $3.9 million under the term loan portion. As of September 30, 2015 , the total amount outstanding under the Tranzact Bank Facility was $95.8 million . Tranzact has entered into an interest rate swap agreement to effectively fix the rate it pays on $70.0 million of the $101.0 million term loan. (See Note 9 - “Derivatives“ ) The Tranzact Bank Facility, which is secured by intellectual property and the common stock of Tranzact and its subsidiaries, contains various affirmative, negative and financial covenants which White Mountains considers to be customary for such borrowings, including a minimum fixed charge coverage ratio and a maximum leverage ratio. MediaAlpha Bank Facility On July 23, 2015, MediaAlpha entered into a credit facility with Opus Bank, which has a total commitment of $20.0 million and has a maturity date of July 23, 2019 (the “MediaAlpha Bank Facility”). The MediaAlpha Bank Facility consists of a $15.0 million term loan facility, which was fully drawn as of September 30, 2015, and a revolving credit facility for an additional $5 million , which was undrawn as of September 30, 2015. 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. The MediaAlpha Bank Facility carries a variable interest rate that is based on the U.S. dollar LIBOR rate. Debt At September 30, 2015 , White Mountains was in compliance with all of the covenants under all of its debt facilities.

Income Taxes

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2015
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 Australia, Belgium, Canada, Denmark, Germany, Gibraltar, Israel, Luxembourg, Malaysia, the Netherlands, Peru, Singapore, Sweden, Switzerland, the United Kingdom and the United States. White Mountains’s income tax benefit from continuing operations for the third quarter of 2015 was near zero and White Mountains’s income tax benefit from continuing operations for the third quarter of 2014 represented an effective tax rate of 13.0% . White Mountains’s income tax expense from continuing operations for the first nine months of 2015 was near zero and White Mountains's income tax expense from continuing operations for the first nine months of 2014 represented an effective tax rate 31.0% . The effective tax rates for the nine months ended September 30, 2015 and the three and nine months ended 2014 were lower than the U.S. statutory rate of 35% due to income generated in jurisdictions with lower tax rates than the United States. In arriving at the effective tax rate for the three and nine months ended September 30, 2015 and 2014 , 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, 2015 and 2014. 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. White Mountains is no longer subject to U.S. federal or state tax examinations by tax authorities for years before 2007. With few exceptions, White Mountains is no longer subject to non-U.S. income tax examinations by tax authorities for years before 2005. On July 28, 2011, the IRS commenced an examination of the income tax returns for 2007, 2008 and 2009 for certain U.S. subsidiaries of OneBeacon. On September 1, 2015, OneBeacon received a revised Form 4549-A (Income Tax Discrepancy Adjustments) from the IRS Appeals Office relating to the examination of tax years 2007, 2008 and 2009. The estimated total overpayment, including interest, utilization of alternative minimum and foreign tax credit carryovers and capital loss carrybacks, is $4.0 million . However, $2.7 million of the proposed overpayment relates to items for which the expense deduction was disallowed in an earlier year and is being allowed in a year being examined. White Mountains agrees with the adjustments proposed by the IRS and is awaiting final review by the Joint Committee on Taxation. Although the timing of the resolution of these issues is uncertain, it is reasonably possible that the resolution could occur within the next twelve months. When ultimately settled, White Mountains does not expect the resolution of this examination to result in a material adverse change to its financial position results of operations and cash flows. On September 5, 2013, the IRS commenced an examination of the income tax returns for 2010, 2011 and 2012 for certain U.S. subsidiaries of OneBeacon. White Mountains does not expect the resolution of this examination to result in a material change to its financial position, results of operations and cash flows. On December 18, 2014, the IRS commenced an examination of the 2012 income tax return for Guilford Holdings, Inc. and subsidiaries. White Mountains does not expect the resolution of this examination to result in a material change to its financial position, results of operations and cash flows.

Derivatives

Derivatives	9 Months Ended
Derivatives	Sep. 30, 2015
Derivatives	Derivatives
Variable Annuity
Derivatives	Variable Annuity Reinsurance White Mountains has entered into agreements to reinsure death and living benefit guarantees associated with certain variable annuities in Japan. At September 30, 2015 and December 31, 2014 , the total guarantee value was approximately ¥ 76.3 billion (approximately $637.2 million at exchange rates on that date) and ¥134.2 billion (approximately $1.1 billion at exchange rates on that date), respectively. The collective account values of the underlying variable annuities were approximately 107% and 113% of the guarantee value at September 30, 2015 and December 31, 2014 . During the second quarter of 2015, the variable annuity contracts reinsured by WM Life Re began to mature. WMLife Re is in runoff, and all of its contracts will mature by June 30, 2016. The following table summarizes the pre-tax operating results of WM Life Re for the three and nine months ended September 30, 2015 and 2014 . Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Fees, included in other revenue $ 2.1 $ 4.5 $ 7.7 $ 15.0 Change in fair value of variable annuity liability, included in other revenue (2.8 ) 19.9 (1.7 ) 40.5 Change in fair value of derivatives, included in other revenue 1.5 (23.8 ) (6.3 ) (56.5 ) Foreign exchange, included in other revenue .4 (1.7 ) (.8 ) (1.2 ) Other investment income and (losses) gains (.2 ) (.9 ) (.3 ) (.4 ) Total revenue 1.0 (2.0 ) (1.4 ) (2.6 ) Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses — .2 — .6 Death benefit claims paid, included in general and administrative expenses — — — (.1 ) General and administrative expenses (.8 ) (.9 ) (3.1 ) (3.3 ) Pre-tax income (loss) $ .2 $ (2.7 ) $ (4.5 ) $ (5.4 ) The following summarizes realized and unrealized derivative gains (losses) recognized in other revenue for the three and nine months ended September 30, 2015 and 2014 and the carrying values, included in other assets, at September 30, 2015 and December 31, 2014 by type of instrument: Gains (losses) Carrying Value Three Months Ended Nine Months Ended As of September 30, September 30, September 30, December 31, 2014 Millions 2015 2014 2015 2014 Fixed income/interest rate $ 2.6 $ (8.4 ) $ 6.0 $ (20.4 ) $ — $ (1.7 ) Foreign exchange (3.1 ) (.4 ) (6.0 ) (13.3 ) 27.9 44.1 Equity 2.0 (15.0 ) (6.3 ) (22.8 ) 9.1 14.0 Total $ 1.5 $ (23.8 ) $ (6.3 ) $ (56.5 ) $ 37.0 $ 56.4 The following tables summarize the changes in White Mountains’s variable annuity reinsurance liabilities and derivative instruments for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended September 30, 2015 Variable Annuity Assets Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ 1.8 $ 8.3 $ 32.5 $ (5.1 ) $ 35.7 Purchases — — — — — Realized and unrealized gains (losses) (2.8 ) 3.4 3.2 (5.1 ) 1.5 Transfers in — — — — — Sales/settlements — (.5 ) (7.8 ) 8.1 (.2 ) End of period $ (1.0 ) $ 11.2 $ 27.9 $ (2.1 ) $ 37.0 Nine Months Ended September 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) (1.7 ) (5.5 ) (2.7 ) 1.9 (6.3 ) Transfers in — — — — — Sales/settlements — (2.2 ) (3.2 ) (7.7 ) (13.1 ) End of period $ (1.0 ) $ 11.2 $ 27.9 $ (2.1 ) $ 37.0 Three Months Ended September 30, 2014 Variable Annuity Assets Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ (31.8 ) $ 53.3 $ 22.3 $ (.8 ) $ 74.8 Purchases — — — — — Realized and unrealized gains (losses) 20.1 (17.4 ) (19.8 ) 13.4 (23.8 ) Transfers in — — — — — Sales/settlements — — 22.5 (8.2 ) 14.3 End of period $ (11.7 ) $ 35.9 $ 25.0 $ 4.4 $ 65.3 Nine Months Ended September 30, 2014 Variable Annuity (Liabilities) Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ (52.8 ) $ 63.4 $ 4.7 $ 1.1 $ 69.2 Purchases — — — — — Realized and unrealized gains (losses) 41.1 (27.5 ) (42.1 ) 13.1 (56.5 ) Transfers in — — — — — Sales/settlements — — 62.4 (9.8 ) 52.6 End of period $ (11.7 ) $ 35.9 $ 25.0 $ 4.4 $ 65.3 (1) Consists of over-the-counter instruments. (2) Consists of interest rate swaps, total return swaps, foreign currency forward contracts, and bond forwards. Fair value measurement based upon bid/ask pricing quotes for similar instruments that are actively traded, where available. Swaps for which an active market does not exist have been priced using observable inputs including the swap curve and the underlying bond index. (3) Consists of exchange traded equity index, foreign currency and interest rate futures. Fair value measurements based upon quoted prices for identical instruments that are actively traded. 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 September 30, 2015 December 31, 2014 September 30, 2014 Cash $ 16.8 $ 23.7 $ 23.8 Fixed maturity investments — 9.5 10.4 Total $ 16.8 $ 33.2 $ 34.2 Collateral in the form of fixed maturity securities consists of Government of Japan Bonds, which are recorded at fair value. Collateral in the form of short-term investments consists of money-market instruments, carried at amortized cost, which approximates fair value. All of White Mountains’s variable annuity reinsurance liabilities were classified as Level 3 measurements at September 30, 2015 and 2014 . The fair value of White Mountains’s variable annuity reinsurance liabilities are estimated using actuarial and capital market assumptions related to the projected discounted cash flows over the term of the reinsurance agreement. Actuarial assumptions regarding future policyholder behavior, including surrender and lapse rates, are generally unobservable inputs and significantly impact the fair value estimates. Market conditions including, but not limited to, changes in interest rates, equity indices, market volatility and foreign currency exchange rates as well as the variations in actuarial assumptions regarding policyholder behavior may result in significant fluctuations in the fair value estimates. Generally, the liabilities associated with these guarantees increase with declines in the equity markets, interest rates and currencies against the Japanese yen, as well as with increases in market volatilities. White Mountains uses derivative instruments, including put options, interest rate swaps, total return swaps on bond and equity indices and forwards and futures contracts on major equity indices, currency pairs and government bonds, to mitigate the risks associated with changes in the fair value of the reinsured variable annuity guarantees. The types of inputs used to estimate the fair value of these derivative instruments, with the exception of actuarial assumptions regarding policyholder behavior and risk margins, are generally the same as those used to estimate the fair value of variable annuity liabilities. The following summarizes quantitative information about significant unobservable inputs associated with the fair value estimates for variable annuity reinsurance liabilities and derivative instruments that have been classified as Level 3 measurements: ($ in Millions) September 30, 2015 Description Fair Value Valuation Technique(s) Unobservable Input Range Weighted Average Variable annuity benefit guarantee liabilities $ 1.0 Discounted cash flows Surrenders 0-1 year 0.1 % - 40.0% 40.0 % Mortality 0.0 % - 6.4% 1.0 % Foreign exchange volatilities 0-1 year 11.6 % - 18.6% 12.5 % Index volatilities 0-1 year 26.2 % - 29.9% 28.2 % Foreign exchange options $ 2.6 Counterparty valuations, adjusted for unwind quote discount Adjustment to counterparty valuations 0.5 % - 11.6% 3.7 % Equity index options $ 8.6 Counterparty valuations, adjusted for unwind quote discount Adjustment to counterparty valuations (0.7 )% - 6.5% 2.0 % WM Life Re enters into both over-the-counter (“OTC”) and exchange traded derivative instruments to economically hedge the liability from the variable annuity benefit guarantee. In the case of OTC derivatives, WM Life Re has exposure to credit risk for amounts that are uncollateralized by counterparties. WM Life Re’s internal risk management guidelines establish net counterparty exposure thresholds that take into account OTC counterparties’ credit ratings. The OTC derivative contracts are subject to restrictions on liquidation of the instruments and distribution of proceeds under collateral agreements. In the case of exchange traded instruments, WM Life Re has exposure to credit risk for amounts uncollateralized by margin balances. WM Life Re has entered into master netting agreements with certain of its counterparties whereby the collateral provided (held) is calculated on a net basis. The following summarizes amounts offset under master netting agreements: September 30, 2015 December 31, 2014 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 $ .5 $ (.8 ) $ (0.3 ) $ 1.0 $ (5.4 ) $ (4.4 ) Exchange traded .3 (.1 ) .2 2.8 (.1 ) 2.7 Foreign exchange contracts OTC 27.9 — 27.9 45.5 — 45.5 Exchange traded .1 (.1 ) — — (1.4 ) (1.4 ) Equity contracts OTC 11.5 — 11.5 11.7 (.2 ) 11.5 Exchange traded — (2.3 ) (2.3 ) 3.4 (.9 ) 2.5 Total (2) $ 40.3 $ (3.3 ) $ 37.0 $ 64.4 $ (8.0 ) $ 56.4 (1) Amount equal to fair value of instrument as recognized in other assets (2) All derivative instruments held by WM Life Re are subject to master netting arrangements. The following summarizes the value, collateral held or provided by WM Life Re and net exposure to credit losses on OTC and exchange traded derivative instruments by counterparty recorded within other assets: September 30, 2015 Millions Net amount of assets reflected in Balance Sheet Collateral provided to counterparty - Cash Collateral provided to counter-party - Financial Instruments Net amount of exposure after effect of collateral provided Excess collateral provided to counter-party- Cash Excess collateral provided - Financial Instruments Counter-party collateral held by WMLife Re - Cash Net amount of exposure to counter-party Standard & Poor's Rating (1) Bank of America $ 3.2 $ — $ — $ 3.2 $ — $ — $ — $ 3.2 A Barclays — — — — — — — — A - JP Morgan 15.9 — — 15.9 — — 5.9 10.0 A + Royal Bank of Scotland 1.5 — — 1.5 — — — 1.5 BBB + Nomura (.1 ) .1 — — 1.4 — — 1.4 BBB + Citigroup - OTC 18.6 — — 18.6 — — 5.3 13.3 A Citigroup - Exchange Traded (2.1 ) 2.1 — — 12.8 — — 12.8 A Total $ 37.0 $ 2.2 $ — $ 39.2 $ 14.2 $ — $ 11.2 $ 42.2 December 31, 2014 Millions Net amount of assets reflected in Balance Sheet Collateral provided to counter-party - Cash Collateral provided to counter-party - Financial Instruments Net amount of exposure after effect of collateral provided Excess collateral provided to counter-party- Cash Excess collateral provided - Financial Instruments Counter-party collateral held by WMLife Re- Cash Net amount of exposure to counter-party Standard & Poor's Rating (1) Bank of America $ 5.6 $ — $ — $ 5.6 $ — $ — $ — $ 5.6 A Barclays .1 — — .1 — — — .1 A JP Morgan 24.3 — — 24.3 — — 8.8 15.5 A + Royal Bank of Scotland 4.0 — — 4.0 — — — 4.0 A - Nomura (3.5 ) 3.5 — — 1.7 9.5 — 11.2 BBB + Citigroup - OTC 22.2 — — 22.2 — — 1.1 21.1 A Citigroup - Exchange Traded 3.7 — — 3.7 16.0 — — 19.7 A Total $ 56.4 $ 3.5 $ — $ 59.9 $ 17.7 $ 9.5 $ 9.9 $ 77.2 (1) Standard & Poor’s ratings as detailed above are: “A+” (Strong, which is the fifth highest of twenty-three creditworthiness ratings), “A” (Strong, which is the sixth highest of twenty-three creditworthiness ratings), “A-” (Strong, which is the seventh highest of twenty-three creditworthiness ratings) and “BBB+” (Adequate, which is the eighth highest of twenty-three creditworthiness ratings).
Tranzact Interest Rate Swap
Derivatives	Tranzact Interest Rate Swap Tranzact has a $101.0 million term loan facility that carries a variable rate equal to the U.S. dollar LIBOR rate, plus an applicable margin. At September 30, 2015 , the variable interest rate on the term loan was 4.70% , including a margin over LIBOR of 4.50% . Effective October 10, 2014, to effectively fix the rate it pays on this term loan, Tranzact entered into an interest rate swap agreement with an initial notional amount of $70.0 million . The notional amount decreases over the term of the swap by amounts equivalent to scheduled principal repayments made on Tranzact’s term loan. Under the terms of the swap agreement, Tranzact pays a fixed rate of 1.34% and receives a variable rate, which is reset monthly, based on the then-current U.S. dollar LIBOR rate. The variable rate received by Tranzact under the swap agreement was 0.15% at inception and 0.20% at September 30, 2015. The total current effective rate on Tranzact's debt was 6.04% at September 30, 2015 . The swap is measured at fair value with changes therein recognized within other revenues and is accounted for as a non-hedge derivative instrument. As of September 30, 2015 , the estimated fair value of the swap was $(0.8) million . There are no collateral arrangements associated with the swap.

Municipal Bond Guarantee

Municipal Bond Guarantee	9 Months Ended
Municipal Bond Guarantee	Sep. 30, 2015
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 September 30, 2015 , 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 $458.3 million at September 30, 2015 , 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 nine months ended September 30, 2015 , HG Global had pre-tax income of $5.2 million and $13.8 million , which included $4.0 million and $11.9 million of interest income on the BAM Surplus Notes. For the three and nine months ended September 30, 2014 , HG Global had pre-tax income of $3.8 million and $13.4 million , which included $3.9 million and $11.8 million of interest income on the BAM Surplus Notes. For the three and nine months ended September 30, 2015 , White Mountains reported pre-tax losses of $10.6 million and $33.5 million on BAM that were recorded in net loss attributable to non-controlling interests, which included $4.0 million and $11.9 million of interest expense on the BAM Surplus Notes. For the three and nine months ended September 30, 2014 , White Mountains reported pre-tax losses of $13.1 million and $29.7 million on BAM that were recorded in net loss attributable to non-controlling interests, which included $3.9 million and $11.8 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 3.15% and 3.13% for 2015 and 2014. 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: September 30, 2015 December 31, 2014 Contracts outstanding 2,733 1,750 Remaining weighted average contract period outstanding (in years) 12.7 12.8 Contractual debt service outstanding (in millions): Par $ 19,841.0 $ 12,362.5 Interest 10,574.3 7,086.9 Total debt service outstanding $ 30,415.3 $ 19,449.4 Gross unearned insurance premiums $ 43.2 $ 27.6

Earnings Per Share

Earnings Per Share	9 Months Ended
Earnings Per Share	Sep. 30, 2015
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share White Mountains calculates earnings per share on the two-class method and accordingly, the net income allocable to common shareholders, undistributed net earnings and weighted average number of common shares outstanding exclude amounts associated with restricted shares that are considered participating securities. Diluted earnings per share amounts are based on the weighted average number of common shares, net of the effect of unvested restricted shares and potentially dilutive common shares outstanding. For periods where White Mountains has recognized a net loss, unvested restricted shares are excluded from the calculation of basic and diluted earnings per share because they would be anti-dilutive. The following table outlines the Company’s computation of earnings per share from continuing operations for the three and nine months ended September 30, 2015 and 2014 . (See Note 17 - “Discontinued Operations” ). Three Months Ended Nine Months Ended September 30, September 30, 2015 2014 2015 2014 Basic and diluted earnings per share numerators (in millions): Net income from continuing operations attributable to White Mountains’s common shareholders $ (73.1 ) $ (12.6 ) $ (61.8 ) $ 65.8 Allocation of income for unvested restricted common shares — — — (.8 ) Dividends declared on participating restricted common shares (1) — — (.1 ) (.1 ) Total allocation to restricted common shares — — (.1 ) (.9 ) Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ (73.1 ) $ (12.6 ) $ (61.9 ) $ 64.9 Undistributed net earnings (in millions): Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ (73.1 ) $ (12.6 ) $ (61.9 ) $ 64.9 Dividends declared net of restricted common share amounts (1) — — (5.9 ) (6.1 ) Total undistributed net earnings, net of restricted common share amounts $ (73.1 ) $ (12.6 ) $ (67.8 ) $ 58.8 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 5,890.1 6,091.4 5,951.1 6,140.9 Average unvested restricted shares (2) — — — (77.7 ) Basic earnings per share denominator 5,890.1 6,091.4 5,951.1 6,063.2 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 5,890.1 6,091.4 5,951.1 6,140.9 Average unvested restricted common shares (2) — — — (77.7 ) Average outstanding dilutive options to acquire common shares (3) — — — — Diluted earnings per share denominator 5,890.1 6,091.4 5,951.1 6,063.2 Basic earnings per share (in dollars): Net income attributable to White Mountains’s common shareholders $ (12.42 ) $ (2.07 ) $ (10.40 ) $ 10.70 Dividends declared and paid — — (1.00 ) (1.00 ) Undistributed earnings $ (12.42 ) $ (2.07 ) $ (11.40 ) $ 9.70 Diluted earnings per share (in dollars): Net income attributable to White Mountains’s common shareholders $ (12.42 ) $ (2.07 ) $ (10.40 ) $ 10.70 Dividends declared and paid — — (1.00 ) (1.00 ) Undistributed earnings $ (12.42 ) $ (2.07 ) $ (11.40 ) $ 9.70 (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 nine months ended September 30, 2015 and 2014 does not include the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding as they are anti-dilutive to the calculation.

Non-controlling Interest

Non-controlling Interest	9 Months Ended
Non-controlling Interest	Sep. 30, 2015
Noncontrolling Interest [Abstract]
Noncontrolling Interest Disclosure [Text Block]	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 September 30, 2015 and December 31, 2014: September 30, 2015 December 31, 2014 $ in millions Non-controlling Percentage Non-controlling Equity Non-controlling Percentage Non-controlling Equity OneBeacon Ltd. 24.7 % $ 246.9 24.7 % $ 258.4 SIG Preference Shares 100.0 250.0 100.0 250.0 Other, excluding mutuals and reciprocals HG Global 3.1 17.3 3.1 17.9 MediaAlpha 40.0 15.1 40.0 22.6 Tranzact 36.8 75.6 36.8 88.2 Wobi 4.7 1.8 36.7 5.4 Dewar 32.2 3.5 18.0 3.4 Prospector Offshore Fund — — 23.4 31.1 Total other, excluding mutuals and reciprocals 113.3 168.6 Mutuals and reciprocals BAM 100.0 (134.2 ) 100.0 (121.9 ) SSIE 100.0 (15.2 ) 100.0 (12.4 ) Total non-controlling interests $ 460.8 $ 542.7

Segment Information

Segment Information	9 Months Ended
Segment Information	Sep. 30, 2015
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 sale, the results of operations for Sirius Group have been classified as discontinued operations and are now presented, net of related income taxes, as such in the statement of operations and comprehensive income. Prior year amounts have been reclassified to conform to the current period’s presentation (See Note 17). White Mountains has made its segment determination based on consideration of the following criteria: (i) the nature of the business activities of each of the Company’s subsidiaries and affiliates; (ii) the manner in which the Company’s subsidiaries and affiliates are organized; (iii) the existence of primary managers responsible for specific subsidiaries and affiliates; and (iv) the organization of information provided to the chief operating decision makers and the Board of Directors. Significant intercompany transactions among White Mountains’s segments have been eliminated herein. Financial information for White Mountains’s segments follows: HG Global/BAM Millions OneBeacon HG BAM Other Operations Total Three Months Ended September 30, 2015 Earned insurance premiums $ 281.4 $ .6 $ .3 $ 2.6 $ 284.9 Net investment income 12.4 .5 1.1 2.8 16.8 Net investment income (loss) - surplus note interest — 4.0 (4.0 ) — — Net realized and unrealized investment (losses) gains (29.9 ) .6 1.7 (16.3 ) (43.9 ) Other revenue 3.9 — .2 72.8 76.9 Total revenues 267.8 5.7 (.7 ) 61.9 334.7 Losses and LAE 167.5 — — 2.5 170.0 Insurance acquisition expenses 53.8 .1 .4 1.0 55.3 Other underwriting expenses 56.4 — .1 — 56.5 General and administrative expenses 3.7 .4 9.4 129.1 142.6 Interest expense 3.2 — — 1.7 4.9 Total expenses 284.6 .5 9.9 134.3 429.3 Pre-tax (loss) income $ (16.8 ) $ 5.2 $ (10.6 ) $ (72.4 ) $ (94.6 ) HG Global/BAM Millions OneBeacon HG BAM Other Operations Total Nine Months Ended September 30, 2015 Earned insurance premiums $ 887.3 $ 1.7 $ .6 $ 6.4 $ 896.0 Net investment income 33.0 1.4 2.9 5.3 42.6 Net investment income (loss) - surplus note interest — 11.9 (11.9 ) — — Net realized and unrealized investment (losses) gains (29.7 ) .3 2.8 (7.3 ) (33.9 ) Other (loss) revenue (.4 ) — .5 225.3 225.4 Total revenues 890.2 15.3 (5.1 ) 229.7 1,130.1 Losses and LAE 527.9 — — 6.2 534.1 Insurance acquisition expenses 161.2 .3 1.8 2.8 166.1 Other underwriting expenses 165.2 — .3 — 165.5 General and administrative expenses 12.0 1.2 26.3 314.6 354.1 Interest expense 9.7 — — 3.8 13.5 Total expenses 876.0 1.5 28.4 327.4 1,233.3 Pre-tax income (loss) $ 14.2 $ 13.8 $ (33.5 ) $ (97.7 ) $ (103.2 ) HG Global/BAM Millions OneBeacon HG BAM Other Operations Total Three Months Ended September 30, 2014 Earned insurance premiums $ 305.4 $ .4 $ .1 $ 1.3 $ 307.2 Net investment income 10.8 .4 1.4 1.2 13.8 Net investment income (loss) - surplus note interest — 3.9 (3.9 ) — — Net realized and unrealized investment losses (16.0 ) (.5 ) (1.4 ) (9.6 ) (27.5 ) Other revenue 1.3 — .2 28.2 29.7 Total revenues 301.5 4.2 (3.6 ) 21.1 323.2 Losses and LAE 185.2 — — .3 185.5 Insurance acquisition expenses 54.6 — .5 .1 55.2 Other underwriting expenses 51.2 — .1 — 51.3 General and administrative expenses 2.4 .4 8.9 51.3 63.0 Interest expense 3.2 — — .5 3.7 Total expenses 296.6 .4 9.5 52.2 358.7 Pre-tax income (loss) $ 4.9 $ 3.8 $ (13.1 ) $ (31.1 ) $ (35.5 ) HG Global/BAM Millions OneBeacon HG BAM Other Operations Total Nine Months Ended September 30, 2014 Earned insurance premiums $ 872.8 $ .9 $ .3 $ 5.1 $ 879.1 Net investment income 33.4 1.0 4.2 6.1 44.7 Net investment income (loss) - surplus note interest — 11.8 (11.8 ) — — Net realized and unrealized investment gains 24.8 1.1 5.4 33.1 64.4 Other revenue (loss) 3.3 — .5 56.5 60.3 Total revenues 934.3 14.8 (1.4 ) 100.8 1,048.5 Losses and LAE 520.7 — — 6.6 527.3 Insurance acquisition expenses 150.9 .2 1.4 .5 153.0 Other underwriting expenses 152.3 — .3 — 152.6 General and administrative expenses 9.3 1.2 26.6 131.2 168.3 Interest expense 9.7 — — .9 10.6 Total expenses 842.9 1.4 28.3 139.2 1,011.8 Pre-tax income (loss) $ 91.4 $ 13.4 $ (29.7 ) $ (38.4 ) $ 36.7

Investments in Unconsolidated A

Investments in Unconsolidated Affiliates	9 Months Ended
Investments in Unconsolidated Affiliates	Sep. 30, 2015
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. Millions September 30, December 31, Symetra common shares $ 386.9 $ 373.8 Unrealized gains from Symetra’s fixed maturity portfolio 5.7 37.6 Carrying value of Symetra common shares 392.6 411.4 Hamer — 3.0 Total investments in unconsolidated affiliates $ 392.6 $ 414.4 Symetra During the third quarter of 2015, Symetra announced that it entered into a definitive merger agreement with Sumitomo Life pursuant to which Sumitomo Life will acquire all of the outstanding shares of Symetra. White Mountains expects to receive $32.00 per share in cash at closing. White Mountains also received a special dividend of $.50 per share as part of the transaction that was paid in the third quarter of 2015. The transaction is expected to close in the first quarter of 2016 and is subject to regulatory approval and other customary closing conditions. For the nine months ended September 30, 2015, Symetra reported total revenues of $1,605.9 million , total benefits and expenses of $1,543.6 million , pre-tax income of $62.3 million and net income of $89.6 million . For the nine months ended September 30, 2014, Symetra reported total revenues of $1,601.6 million , total benefits and expenses of $1,387.0 million , pre-tax income of $214.6 million and net income of $186.8 million . On June 30, 2015, pursuant to the redemption of White Mountains's investments in the Prospector Funds, 513,500 common shares of Symetra were distributed to White Mountains. At September 30, 2015 and December 31, 2014 , White Mountains owned 20,562,379 and 20,048,879 common shares of Symetra, a 17.70% and 17.31% common share ownership. White Mountains accounts for its investment in common shares of Symetra using the equity method. During the three and nine months ended September 30, 2015 , White Mountains received cash dividends from Symetra of $12.5 million and $16.9 million , which included a special dividend of $10.3 million . The dividends were recorded as a reduction of White Mountains’s investment in Symetra. During the three and nine months ended September 30, 2014, White Mountains received cash dividends from Symetra of $2.0 million and $6.0 million . 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 $261.0 million or $15 per share. This impairment, as well as the effect of Symetra capital transactions, has resulted in a basis difference between the GAAP carrying value of White Mountains’s investment in Symetra common shares and the amount derived by multiplying the percentage of White Mountains common share ownership by Symetra’s total GAAP equity. As of September 30, 2015 , the pre-tax unamortized basis difference was $160.8 million , of which $32.6 million is attributable to equity in earnings of unconsolidated affiliates and $128.2 million is attributable to equity in net unrealized gains of unconsolidated affiliates. As of December 31, 2014, the pre-tax unamortized basis difference was $170.4 million , of which $36.4 million is attributable to equity in earnings of unconsolidated affiliates and $134.0 million is attributable to equity in net unrealized gains of unconsolidated affiliates. The pre-tax basis difference is being amortized over a 30 -year period with a weighted average of 28 -years remaining. The amortization is based on estimated future cash flows associated with Symetra’s underlying assets and liabilities to which the basis differences have been attributed. White Mountains continues to record its equity in Symetra's earnings and net unrealized gains (losses). In addition, White Mountains recognizes the amortization of the basis 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 nine months ended September 30, 2015 , White Mountains recognized after-tax amortization of $0.6 million and $2.0 million through equity in earnings of unconsolidated affiliates and $2.6 million and $8.1 million through equity in net unrealized gains from investments in unconsolidated affiliates. For the three and nine months ended September 30, 2014, White Mountains recognized after-tax amortization of $0.7 million and $2.1 million through equity in earnings of unconsolidated affiliates and $2.9 million and $8.7 million through equity in net unrealized gains from investments in unconsolidated affiliates. The following table summarizes amounts recorded by White Mountains relating to its investment in Symetra for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Carrying value of investment in Symetra at beginning of period $ 397.2 $ 415.5 $ 411.4 $ 317.3 Equity in earnings (1)(2) 4.2 7.0 17.5 34.5 Equity in net unrealized gains (losses) from Symetra’s fixed maturity portfolio (3) 3.7 (10.7 ) (31.8 ) 64.0 Dividends received (12.5 ) (2.0 ) (16.9 ) (6.0 ) Distribution from Prospector Offshore Fund — — 12.4 — Carrying value of investment in Symetra at end of period (4)(5) $ 392.6 $ 409.8 $ 392.6 $ 409.8 (1) For the three months ended September 30, 2015 and 2014 , equity in earnings excludes tax expense of $0.3 and $0.5 . For the nine months ended September 30, 2015 and 2014 , equity in earnings excludes tax expense of $1.1 and $2.4 . (2) For the three months ended September 30, 2015 and 2014 , equity in earnings includes $0.7 and $0.7 increase relating to the pre-tax amortization of the Symetra common share basis difference. For the nine months ended September 30, 2015 and 2014 , equity in earnings includes $2.1 and $2.2 increase relating to the pre-tax amortization of the Symetra common share basis difference. (3) For the three months ended September 30, 2015 and 2014 , net unrealized gains includes $2.9 and $3.1 increase relating to the pre-tax amortization of the Symetra common share basis difference. For the nine months ended September 30, 2015 and 2014 , net unrealized gains includes $8.6 and $9.4 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 $5.7 and $20.5 as of September 30, 2015 and 2014 , which excludes tax expense of $0.2 and $1.4 . (5) The aggregate value of White Mountains’s investment in common shares of Symetra was $650.6 based upon the quoted market price of $ 31.64 per share at September 30, 2015 . 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 and $0.4 million and $0.8 million for the three and six months ended June 30, 2014.

Employee Share-Based Incentive

Employee Share-Based Incentive Compensation Plans	9 Months Ended
Employee Share-Based Incentive Compensation Plans	Sep. 30, 2015
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 nine months ended September 30, 2015 and 2014 for performance shares granted under the WTM Incentive Plan: Three Months Ended September 30, Nine Months Ended September 30, 2015 2014 2015 2014 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 109,129 $ 28.8 116,259 $ 46.3 113,198 $ 44.4 108,605 $ 54.9 Shares paid or expired (1) (8,958 ) (5.5 ) — — (42,958 ) (30.7 ) (33,730 ) (24.1 ) New grants — — — — 29,828 — 41,580 — Assumed forfeitures and cancellations (2) (3,960 ) (.8 ) — (.2 ) (3,857 ) (.3 ) (196 ) — Expense recognized — 30.0 — 6.3 — 39.1 — 21.6 End of period (3) 96,211 $ 52.5 116,259 $ 52.4 96,211 $ 52.5 116,259 $ 52.4 (1) WTM performance share payments in 2015 for the 2012-2014 performance cycle ranged from 91% to 145.5% of target. WTM performance share payments in 2014 for the 2011-2013 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 September 30, 2015 and 2014 exclude 7,997 and 11,278 performance share awards, net of assumed forfeitures, granted to employees of Sirius Group, which is accounted for as discontinued operations. For the 2012-2014 performance cycle, all performance shares earned were settled in cash. For the 2011-2013 performance cycle, the Company issued common shares for 1,425 performance shares earned and all other performance shares earned were settled in cash. If the outstanding WTM performance shares had vested on September 30, 2015 , the total additional compensation cost to be recognized would have been $30.2 million , based on accrual factors at September 30, 2015 (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 September 30, 2015 for each performance cycle: Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Performance cycle: 2015 – 2017 29,828 $ 6.3 2014 – 2016 32,557 12.3 2013 – 2015 36,293 35.4 Sub-total 98,678 54.0 Assumed forfeitures (2,467 ) (1.5 ) Total at September 30, 2015 96,211 $ 52.5 Restricted Shares The following table summarizes the unrecognized compensation cost associated with the outstanding restricted share awards for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended September 30, Nine Months Ended September 30, 2015 2014 2015 2014 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 68,303 $ 21.9 79,011 $ 20.5 80,050 $ 13.7 90,341 $ 16.4 Issued — — — — 22,078 14.7 20,400 11.8 Vested (1,200 ) — — — (35,025 ) — (31,730 ) — Forfeited — — — — — — — — Expense recognized — (3.5 ) — (3.2 ) — (10.0 ) — (10.9 ) End of period (1) 67,103 $ 18.4 79,011 $ 17.3 67,103 $ 18.4 79,011 $ 17.3 (1) Outstanding restricted share awards as of September 30, 2015 and 2014 exclude 3,571 and 2,314 restricted shares issued to employees of Sirius Group, which is accounted for as discontinued operations. During the first nine months of 2015, White Mountains issued 22,078 restricted shares that vest on January 1, 2018. During the first nine months of 2014, White Mountains issued 20,400 restricted shares that vest on January 1, 2017. The unrecognized compensation cost at September 30, 2015 is expected to be recognized ratably over the remaining vesting periods. Share-Based Compensation Based on OneBeacon Ltd. Common Shares The OneBeacon Long-Term Incentive Plan (the “OneBeacon Incentive Plan”) provides for grants to key employees of OneBeacon various types of share-based and non share-based incentive awards. OneBeacon’s share-based incentive awards include OneBeacon performance shares and restricted shares. OneBeacon Performance Shares OneBeacon performance shares are conditional grants of a specified maximum number of common shares or an equivalent amount of cash. OneBeacon performance share awards generally vest at the end of a three -year period, are subject to the attainment of pre-specified performance goals, and are valued based on the market value of OneBeacon Ltd. common shares at the time awards are paid. The following table summarizes performance share activity for the three and nine months ended September 30, 2015 and 2014 for OneBeacon performance shares granted under the OneBeacon Incentive Plan: Three Months Ended September 30, Nine Months Ended September 30, 2015 2014 2015 2014 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 462,147 $ 2.4 512,938 $ 4.4 517,470 $ 3.4 493,421 $ 4.0 Shares paid or expired (1) — — — — (181,290 ) (1.5 ) (142,138 ) (1.0 ) New grants — — — — 154,887 — 165,800 — Assumed forfeitures and cancellations (2) — — — — (28,920 ) — (4,145 ) — Expense recognized — (.3 ) — 1.1 — .2 — 2.5 End of period 462,147 $ 2.1 512,938 $ 5.5 462,147 $ 2.1 512,938 $ 5.5 (1) OneBeacon performance share payments in 2015 for the 2012-2014 performance cycle were at 45.7% of target. OneBeacon performance share payments in 2014 for the 2011-2013 performance cycle were at 37.1% of target. (2) Amounts include changes in assumed forfeitures, as required under GAAP. If the outstanding OneBeacon performance shares had been vested on September 30, 2015 , the total additional compensation cost to be recognized would have been $2.0 million , based on accrual factors at September 30, 2015 (common share price, accumulated dividends and payout assumptions). The following table summarizes OneBeacon performance shares outstanding awarded under the OneBeacon Incentive Plan at September 30, 2015 for each performance cycle: Millions, except share amounts Target Accrued Expense Performance cycle: 2015 – 2017 154,887 $ .5 2014 – 2016 151,810 .3 2013 – 2015 167,300 1.3 Sub-total 473,997 2.1 Assumed forfeitures (11,850 ) — Total at September 30, 2015 462,147 $ 2.1 OneBeacon Restricted Shares The following table summarizes the unrecognized compensation cost associated with the outstanding OneBeacon restricted stock awards for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended September 30, Nine Months Ended September 30, 2015 2014 2015 2014 Millions, except share amounts Restricted Unamortized Restricted Unamortized Restricted Unamortized Restricted Unamortized Non-vested, Beginning of period 390,950 $ 3.5 612,500 $ 4.9 612,500 $ 3.5 915,000 $ 6.5 Issued — — — — 75,950 1.1 — — Vested — — — — (296,000 ) — (300,000 ) — Forfeited — — — — (1,500 ) — (2,500 ) — Expense recognized — (.5 ) — (.7 ) — (1.6 ) — (2.3 ) End of period 390,950 $ 3.0 612,500 $ 4.2 390,950 $ 3.0 612,500 $ 4.2 On February 24, 2015, OneBeacon issued 75,950 restricted shares that vest on January 1, 2018. On March 1, 2012, OneBeacon issued 300,000 restricted shares that vest in two equal annual installments. The first installment vested on February 28, 2014. On May 25, 2011, OneBeacon issued 630,000 restricted shares to its CEO that vest in four equal annual installments. The first installment vested on February 22, 2014. Concurrently with the grant of the restricted shares, 35,000 OneBeacon performance shares issued to OneBeacon’s CEO for the 2011-2013 performance share cycle were forfeited and performance share awards to OneBeacon’s CEO for the subsequent five years have been or will also be reduced by 35,000 shares. The unrecognized compensation cost at September 30, 2015 is expected to be recognized ratably over the remaining vesting periods. OneBeacon Restricted Stock Units During the first nine months of 2015, the OneBeacon Compensation Committee awarded to certain employees 214,430 restricted stock units (“RSUs”), of which, net of forfeiture assumptions, 204,179 were outstanding as of September 30, 2015. The RSUs are scheduled to vest on January 1, 2018 and will be paid out in cash or shares at the discretion of the OneBeacon Compensation Committee. For the three and nine months ended September 30, 2015 , the expense associated with the RSUs was $0.2 million and $0.6 million .

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
Fair Value of Financial Instruments	Sep. 30, 2015
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments White Mountains accounts for its financial instruments at fair value with the exception of the OBH Senior Notes and the Tranzact 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 September 30, 2015 and December 31, 2014 : September 30, 2015 December 31, 2014 Millions Fair Value Carrying Value Fair Value Carrying Value 2012 OBH Senior Notes $ 279.8 $ 274.8 $ 286.0 $ 274.7 Tranzact Bank Facility 94.6 93.8 68.7 67.4 The fair value estimate for the 2012 OBH Senior Notes has been determined using quoted market prices. The 2012 OBH Senior Notes are considered a Level 2 measurement based upon the volume and frequency of observable transactions. The fair value estimate for the Tranzact Bank Facility has been determined based on a discounted cash flows approach and is considered to be a Level 3 measurement. The MediaAlpha Bank Facility is a recently issued variable rate instrument. As a result it is considered a Level 2 measurement. As of September 30, 2015, the carrying value of the amount drawn on the MediaAlpha Debt Facility approximates fair value.

Discontinued Operations

Discontinued Operations	9 Months Ended
Discontinued Operations	Sep. 30, 2015
Discontinued Operations and Disposal Groups [Abstract]
Disposal Groups, Including Discontinued Operations, Disclosure	Note 17. Discontinued Operations Sirius On July 27, 2015, White Mountains entered into an agreement to sell Sirius Group to CM International Holding PTE Ltd., the Singapore-based investment arm of CMI. The results of operations for Sirius Group have been classified as discontinued operations in the statement of operations and comprehensive income and the assets and liabilities of Sirius Group have been presented in the balance sheet as held for sale. Prior year amounts have been reclassified to conform to the current period’s presentation. The amounts reflected within discontinued operations differ from amounts previously presented within the Sirius Group segment. The segment results of operations for Sirius Group reported in previous periods included investment income and realized and unrealized investment gains and losses from certain investments that are to be retained by White Mountains after the completion of the sale. For the three and nine month periods of September 30, 2015, $5.5 million and $1.4 million of net investment income and realized and unrealized investment gains and losses that had been previously included in the Sirius Group segment were excluded from net income (loss) from discontinued operations. For the three and nine months ended September 30, 2014, $0.9 million and $ 1.8 million of net investment income and realized and unrealized investment gains and losses that had been previously included in the Sirius segment were excluded from net income (loss) from discontinued operations. OneBeacon Runoff In December 2014, OneBeacon completed the sale of its runoff business (the “Runoff Transaction”). The results of operations for the Runoff Business have been classified as discontinued operations and are presented, net of related income taxes, in the statement of operations and comprehensive income. The amounts classified as discontinued operations exclude investing and financing activities that are conducted on an overall consolidated level and, accordingly, there were no separately identifiable investments associated with the Runoff Business. During the second quarter of 2014, OneBeacon amended the Runoff SPA, primarily to increase the cap on seller financing by $6.7 million to $80.9 million , as well as to extend the termination date to December 31, 2014. Consistent with the proposed closing balance sheet, pro forma as of June 30, 2014, OneBeacon expected to provide seller financing at closing in the form of surplus notes with an estimated par value of $80.9 million (the “OBIC Surplus Notes”). As a result, OneBeacon recorded an increase of $8.2 million ( $5.3 million after-tax) in the estimated loss on sale of the Runoff Business during the second quarter of 2014 to reflect the estimated difference between the fair value and par value of the surplus notes upon issuance. Additionally, during the second quarter of 2014, OneBeacon's expectation of the treatment under the Runoff SPA of the $7.4 million reserve charge recorded during the second quarter of 2013 changed. Previously, OneBeacon expected that the Runoff SPA would be amended to provide for the transfer of $7.4 million of additional assets to support the reserve charge. As previously noted, the Runoff SPA was instead revised to increase the cap on seller financing. As a result, the $7.4 million reserve charge ( $4.8 million after-tax) was recorded as a reduction to the estimated loss on sale during the second quarter of 2014. During the third quarter of 2014, OneBeacon updated its estimated loss on sale to reflect the change in the valuation of the surplus notes expected to be issued in conjunction with the closing of the Runoff Transaction. The change in the valuation estimate resulted in a loss of $10.3 million ( $6.7 million after-tax), which was a result of widening credit spreads during the quarter, as well as an increase to the estimated discount rate related to the private nature of the notes and the related lack of liquidity. In the second quarter of 2015, OneBeacon also completed the sale of its building in Canton, MA for $58.0 million . The building was presented as held for sale at December 31, 2014. Esurance White Mountains recognized $10.3 million and $18.2 million of net income from discontinued operations in the third quarter and first nine months of 2015 related to the final settlement with The Allstate Corporation for favorable development on loss reserves transferred in the sale of Esurance and Answer Financial. (See Note 18 - “Contingencies” ) For the nine months ended September, 2014, White Mountains recorded a net gain from the sale of discontinued operations of $3.2 million , which primarily related to an installment payment from Allstate for the favorable development on loss reserves. Fireman's Fund During the third quarter of 2014, White Mountains recorded a gain in discontinued operations of $14.0 million from a payment received from Allianz, the purchaser of White Mountains's former subsidiary Fireman’s Fund Insurance Company (“FFIC”), related to the utilization of alternative minimum tax credits associated with the tax loss on the sale of FFIC in 1991. Summary of Reclassified Balances and Related Items Net Assets Held for Sale The following summarizes the assets and liabilities associated with the business classified as held for sale, which all relate to Sirius Group with the exception of the building held by OneBeacon at December 31, 2014: Millions September 30, 2015 December 31, 2014 Assets held for sale Fixed maturity investments $ 2,394.3 $ 2,362.3 Short-term investments 360.5 494.9 Common equity securities 164.3 189.9 Convertible fixed maturity and preferred investments — 6.6 Other long-term investments 82.1 89.0 Total investments 3,001.2 3,142.7 Cash 147.4 111.5 Reinsurance recoverable on unpaid losses 276.5 322.2 Reinsurance recoverable on paid losses 11.0 11.4 Reinsurance premiums receivable 416.6 306.6 Funds held by ceding entities 81.1 91.9 Deferred acquisition costs 82.7 69.9 Deferred tax asset 309.6 341.5 Ceded unearned reinsurance premiums 118.4 76.2 Goodwill and intangible assets 10.2 15.2 Other assets 73.4 83.4 Other assets - OneBeacon building — 58.1 Total assets held for sale $ 4,528.1 $ 4,630.6 Liabilities held for sale Loss and loss adjustment expense reserves $ 1,662.9 $ 1,809.8 Unearned insurance premiums 429.4 338.6 Debt 403.5 403.5 Deferred tax liability 257.8 282.8 Accrued incentive compensation 55.5 76.5 Ceded reinsurance payable 131.4 71.5 Funds held under reinsurance treaties 45.1 57.9 Other liabilities 47.2 64.7 Total liabilities held for sale $ 3,032.8 $ 3,105.3 Net Income from Discontinued Operations The following summarizes the results of operations, including related income taxes associated with the business classified as discontinued operations. The results of Sirius Group through the closing date of the transaction inures to White Mountains. Three Months Ended Three Months Ended September 30, 2015 September 30, 2014 Millions Sirius Group Other Disc Ops Total Sirius Group Other Disc Ops Total Revenues Earned insurance premiums $ 202.8 $ — $ 202.8 $ 231.4 $ .3 $ 231.7 Net investment income 10.5 — 10.5 9.7 — 9.7 Net realized and unrealized (losses) gains (.9 ) — (.9 ) 48.3 — 48.3 Other revenue 1.8 (.1 ) 1.7 (22.8 ) — — Total revenues 214.2 (.1 ) 214.2 266.6 .3 266.9 Expenses Loss and loss adjustment expenses 121.7 — 121.7 103.6 — 103.6 Insurance and reinsurance acquisition expenses 45.4 — 45.4 50.1 .1 50.2 Other underwriting expenses 24.8 — 24.8 29.7 .8 30.5 General and administrative expenses 9.4 — 9.4 6.3 — 6.3 Interest expense 6.6 — 6.6 6.6 — 6.6 Total expenses 207.9 — 207.9 196.3 .9 197.2 Pre-tax income (loss) 6.3 (.1 ) 6.2 70.3 (.6 ) 69.7 Income tax (expense) benefit (2.3 ) — (2.3 ) (13.1 ) .3 (12.8 ) Net income (loss) from discontinued operations 4.0 (.1 ) 3.9 57.2 (.3 ) 56.9 Net gain from sales of discontinued operations - FFIC — — — — 14.0 14.0 Net losses from sales of discontinued operations - OneBeacon — — — — (7.0 ) (7.0 ) Net gain from sales of discontinued operations - Esurance — 10.3 10.3 — — — Total income from discontinued operations $ 4.0 $ 10.2 $ 14.2 $ 57.2 $ 6.7 $ 63.9 Change in foreign currency translation and other from discontinued operations $ (18.4 ) $ — $ (18.4 ) $ (64.1 ) $ — $ (64.1 ) Comprehensive income from discontinued operations $ (14.4 ) $ 10.2 $ (4.2 ) $ (6.9 ) $ 6.7 $ (.2 ) Nine Months Ended Nine Months Ended September 30, 2015 September 30, 2014 Millions Sirius Group Other Disc Ops Total Sirius Group Other Disc Ops Total Revenues Earned insurance premiums $ 623.3 $ — $ 623.3 $ 656.5 $ .1 $ 656.6 Net investment income 28.6 — 28.6 30.0 — 30.0 Net realized and unrealized gains 31.4 — 31.4 134.1 — 134.1 Other revenue (20.2 ) (.4 ) (20.6 ) (47.3 ) — (47.3 ) Total revenues 663.1 (.4 ) 662.7 773.3 .1 773.4 Expenses Loss and loss adjustment expenses 311.3 — 311.3 273.8 (.7 ) $ 273.1 Insurance and reinsurance acquisition expenses 135.5 — 135.5 146.3 .1 $ 146.4 Other underwriting expenses 78.0 — 78.0 91.7 2.2 $ 93.9 General and administrative expenses 22.4 — 22.4 21.6 — $ 21.6 Interest expense 20.0 — 20.0 19.8 — $ 19.8 Total expenses 567.2 — 567.2 553.2 1.6 554.8 Pre-tax income (loss) 95.9 (.4 ) 95.5 220.1 (1.5 ) 218.6 Income tax (expense) benefit (22.2 ) — (22.2 ) (52.4 ) .6 $ (51.8 ) Net income (loss) from discontinued operations 73.7 (.4 ) 73.3 167.7 (.9 ) 166.8 Net gain from sales of discontinued operations - FFIC — — — — 14.0 $ 14.0 Net losses from sales of discontinued operations - OneBeacon — .3 .3 — (7.5 ) $ (7.5 ) Net gain from sales of discontinued operations - Esurance — 17.9 17.9 — 3.2 $ 3.2 Total income from discontinued operations $ 73.7 $ 17.8 $ 91.5 $ 167.7 $ 8.8 $ 176.5 Change in foreign currency translation and other from discontinued operations $ (62.1 ) $ — $ (62.1 ) $ (99.9 ) $ — $ (99.9 ) Comprehensive income from discontinued operations $ 11.6 $ 17.8 $ 29.4 $ 67.8 $ 8.8 $ 76.6 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: Nine Months Ended September 30, (Millions) 2015 2014 Net cash provided from operations $ 6.7 $ 49.8 Net cash provided from investing activities 35.7 47.5 Net cash used for financing activities (2.4 ) (55.6 ) Effect of exchange rate changes on cash (4.1 ) (10.6 ) Net change in cash during the period 35.9 31.1 Cash balances at beginning of period 111.5 93.2 Cash balances at end of period $ 147.4 $ 124.3 Supplemental cash flows information: Interest paid $ (25.5 ) $ (34.9 ) Net income tax (payment to) refund from national governments $ (30.3 ) $ 7.5 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 nine months ended September 30, 2015 and 2014 : Three Months Ended Nine Months Ended September 30, September 30, 2015 2014 2015 2014 Basic and diluted earnings per share numerators (in millions): Net income attributable to White Mountains’s common shareholders $ 14.2 $ 63.9 $ 91.5 $ 176.5 Allocation of income for participating unvested restricted common shares (1) (.2 ) (.9 ) (1.0 ) (2.2 ) Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts (2) $ 14.0 $ 63.0 $ 90.5 $ 174.3 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 5,890.1 6,091.4 5,951.1 6,140.9 Average unvested restricted common shares (3) (70.9 ) (81.3 ) (67.1 ) (77.7 ) Basic earnings per share denominator 5,819.2 6,010.1 5,884.0 6,063.2 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 5,890.1 6,091.4 5,951.1 6,140.9 Average unvested restricted common shares (3) (70.9 ) (81.3 ) (67.1 ) (77.7 ) Average outstanding dilutive options to acquire common shares (4) — — — — Diluted earnings per share denominator 5,819.2 6,010.1 5,884.0 6,063.2 Basic and diluted earnings per share (in dollars): $ 2.41 $ 10.49 $ 15.37 $ 28.74 (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 nine months ended September 30, 2015 and 2014 . (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 nine months ended September 30, 2015 and 2014 does not include the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding as they are anti-dilutive to the calculation. Fair Value of Financial Instruments The SIG Senior Notes are recorded as debt at face value less unamortized original issue discount, and the SIG Preference Shares are recorded as non-controlling interest at face value. The following table summarizes the fair value and carrying value of these financial instruments as of September 30, 2015 and December 31, 2014 : September 30, 2015 December 31, 2014 Millions Fair Value Carrying Value Fair Value Carrying Value SIG Senior Notes $ 423.6 $ 399.8 $ 437.8 $ 399.7 SIG Preference Shares 252.5 250.0 260.0 250.0 The fair value estimates for the SIG Senior Notes and the SIG Preference Shares have been determined based on indicative broker quotes and are considered to be Level 3 measurements. Interest Rate Cap In May 2007, Sirius International Group, Ltd. (“SIG”), an intermediate holding company of Sirius Group, issued the SIG Preference Shares, with an initial fixed annual dividend rate of 7.506% . In June 2017, the fixed rate will move to a floating rate equal to the greater of (i) 7.506% and (ii) 3 -month LIBOR plus 320 basis points. In July 2013, SIG executed the Interest Rate Cap for the period from June 2017 to June 2022 to protect against a significant increase in interest rates during that 5 -year period. The Interest Rate Cap economically fixes the annual dividend rate on the SIG Preference Shares from June 2017 to June 2022 at 8.30% . The cost of the Interest Rate Cap was an upfront premium of 395 basis points of the $250.0 million notional value, or approximately $9.9 million for the full notional amount. The Interest Rate Cap does not qualify for hedge accounting. It is recorded in other assets at fair value. Changes in fair value are recognized within other revenue. Collateral held is recorded within short-term investments with an equal amount recognized as a liability to return collateral. The fair value of the Interest Rate Cap has been estimated using a single broker quote and accordingly, has been classified as a Level 3 measurement at September 30, 2015 . The following tables summarize the changes in the fair value of the Interest Rate Cap for the three and nine months ended September 30, 2015 and 2014: Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Beginning of period $ 3.3 $ 6.2 $ 4.1 $ 11.1 Net realized and unrealized losses (1.1 ) (.8 ) (1.9 ) (5.7 ) End of period $ 2.2 $ 5.4 $ 2.2 $ 5.4 Sirius Group does not provide any collateral to the interest rate counterparties. Under the terms of the Interest Rate Cap, Sirius Group holds collateral in respect of future amounts due. Sirius Group’s liability to return that collateral is based on the amounts provided by the counterparty and investment earnings thereon. Foreign Currency Swap On April 28, 2015, Sirius Group executed two foreign currency swaps, each with a notional amount of $50.0 million , maturing on March 20, 2017. Under the first swap, Sirius Group pays Swedish krona and receives U.S. dollars. Under the second swap, White Mountains pays Euros and receives U.S. dollars. The swaps, which were executed as part of Sirius Group's management of overall foreign currency exposure at Sirius Group, have not been designated or accounted for under hedge accounting. At September 30, 2015, the fair value of the swaps of $(2.3) million was recorded within other assets. Changes in fair value are recognized as unrealized gains or losses and are presented within other revenues. Sirius Group does not provide or hold any collateral associated with the swaps. Stand By Letter of Credit Facilities On November 25, 2014, Sirius International entered into two stand by letter of credit facility agreements totaling $200.0 million to provide capital support for its Lloyds Syndicate 1945. One letter of credit is a $125.0 million facility from Nordea Bank Finland plc (the “Nordea facility”), $100.0 million of which is issued on an unsecured basis. The second letter of credit is a $75.0 million facility with Lloyds Bank plc (the “Lloyds Bank facility”), $25.0 million of which is issued on an unsecured basis. The Nordea facility and the Lloyds Bank facility are renewable annually. The unsecured portions of the Nordea facility and the Lloyds Bank facility are subject to various affirmative, negative and financial covenants that Sirius Group considers to be customary for such borrowings, including certain minimum net worth and maximum debt to capitalization standards. Sirius International has other secured letter of credit and trust arrangements with various financial institutions to support its insurance operations. At September 30, 2015 , Sirius Group was in compliance with all of the covenants under all of its debt and unsecured letter of credit facilities.

Contingencies

Contingencies	9 Months Ended
Contingencies	Sep. 30, 2015
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 September 30, 2015 : Esurance On October 7, 2011, the Company completed the sale of its Esurance and Answer Financial subsidiaries (the “Transferred Subsidiaries”) to The Allstate Corporation (“Allstate”) pursuant to a Stock Purchase Agreement dated as of May 17, 2011 (filed as an exhibit to the Company’s current report on Form 8-K on May 18, 2011, the “Agreement”). Subject to specified thresholds and limits, the Company remains contingently liable to Allstate for specified matters related to the pre-closing period, including (a) specified litigation matters, (b) losses of the Transferred Subsidiaries arising from extra-contractual claims and claims in excess of policy limits (“ECO/EPL losses”), (c) certain corporate reorganizations effected to remove entities from the Transferred Subsidiaries that were not being sold in the transaction, and (d) certain tax matters, including certain net operating losses being less than stated levels. In addition, the Company retained 90% of positive or negative development in the loss reserves of the Transferred Subsidiaries as of the closing date (net of ECO/EPL losses) through December 31, 2014 (the “Reserve Settlement”). White Mountains recognized $10.3 million and $18.2 million of net income from discontinued operations in the third quarter and first nine months 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 through September 30, 2015, White Mountains has received a net amount of $28.3 million from Allstate, primarily related to the favorable development on loss reserves. Runoff Transaction Subsequent to the closing of the Runoff Transaction, on January 22, 2015, three holders of insurance policies issued by the companies OneBeacon sold to Armour filed a Petition for Review with the Commonwealth Court of Pennsylvania (“Commonwealth Court”) requesting that the Commonwealth Court vacate the Pennsylvania Insurance Department’s (“PID”) orders approving the Runoff Transaction and denying their right to intervene in the PID’s regulatory review of the Runoff Transaction. White Mountains believes the claims made by the petitioners are without merit and has intervened in the proceedings before the Commonwealth Court to vigorously defend the propriety of the PID’s orders in their entirety. White Mountains believes that the possibility is remote that these proceedings could result in an adverse outcome or have a material financial impact on the Company’s results of operations or financial position in the future. 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 and Sirius Group, which is now included in discontinued operations, received $6.1 million for Tribune common stock tendered in connection with the LBO. The Court granted an omnibus motion to dismiss the Noteholder Actions in September 2013 and Plaintiffs appeal is pending. 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, 2015, as the amount of loss, if any, cannot be reasonably estimated.

Pension Plan (Notes)

Pension Plan (Notes)	9 Months Ended
Pension Plan (Notes)	Sep. 30, 2015
Compensation Related Costs [Abstract]
Pension and Other Postretirement Benefits Disclosure [Text Block]	Note 19. OneBeacon Pension Plan OneBeacon sponsors qualified and non-qualified, non-contributory, defined benefit pension plans covering substantially all employees who were employed as of December 31, 2001 and former employees who had met the eligibility requirements, as well as retirees. Current plans include the OneBeacon qualified pension plan (the “Qualified Plan”) and the OneBeacon nonqualified pension plan (the “Non-qualified Plan”) (collectively the “Plans”). OneBeacon's Plans were frozen and curtailed in 2002. The benefits for the Plans are based primarily on years of service and employees’ compensation through December 31, 2002. OneBeacon’s funding policy is consistent with the funding requirements of U.S. federal laws and regulations. In April 2014, OneBeacon voted to terminate the Qualified Plan as of June 30, 2014 and applied for a determination letter from the Internal Revenue Service (“IRS”) with respect to the Qualified Plan's tax qualified status at termination and received a favorable determination letter from the IRS on July 23, 2015. OneBeacon currently anticipates the majority of plan assets to be distributed within 12 months of the receipt of the favorable determination letter by way of annuity contract purchases and/or lump sum payments to Plan participants. The purchase of annuities is also subject to the availability of such contracts, with creditworthy insurance companies, at negotiated market terms deemed acceptable to the Plan Sponsor. OneBeacon reserves the right to revoke the termination and does not expect the impact of the termination to be material on OneBeacon's financial position.

Summary of Significant Accoun27

Summary of Significant Accounting Policies (Policies)	9 Months Ended
Summary of Significant Accounting Policies (Policies)	Sep. 30, 2015
Accounting Policies [Abstract]
Recently Adopted Changes in Accounting Principles and Recently Issued Accounting Pronouncements	Recently Adopted Changes in Accounting Principles Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity On April 10, 2014, the FASB issued ASU 2014-08, Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity (ASC 205 and ASC 360) to reduce diversity in practice for reporting discontinued operations. ASU 2014-08 limits discontinued operations treatment to disposals that have a major effect on a reporting entity’s operations and financial results to be reported as discontinued operations. The revised guidance also requires expanded disclosure in the financial statements for discontinued operations as well as for disposals of significant components of an entity that do not qualify for discontinued operations presentation. As discussed further in Note 2, White Mountains has entered into an agreement to sell Sirius Group, which has been classified as discontinued operations in accordance with ASU 2014-08. Qualified Affordable Housing Projects Effective January 1, 2015, White Mountains adopted ASU 2014-01, Accounting for Investments in Qualified Affordable Housing Projects ( “ QAHP ” ) (ASC 323). ASU 2014-01 allows investors in QAHP to make a policy election to use the proportional amortization method. Under the proportional amortization method, the investor amortizes the initial cost of the investment in proportion to the tax credits and other tax benefits received and recognizes the investment results, net of the related tax benefits, as a component of income tax expense. Prior to adoption, White Mountains accounted for its QAHP investment under the equity method and recognized its share of its QAHP investment's losses in investment income. White Mountains made the policy election to account for its investment in its QAHP investment using the proportional amortization method, applied retrospectively. Under the proportional amortization method, the cumulative loss recognized through December 31, 2014 and December 31, 2013 was $0.9 million and $0.5 million . The retrospective adoption resulted in an increase of $0.4 million and $1.3 million to net investment income and a net increase of $0.6 million and $1.8 million to income tax expense for the three and nine months ended September 30, 2014. Footnote disclosures for prior year amounts have been amended to be consistent with the restated amounts described above. Pushdown Accounting ASU 2014-17, Pushdown Accounting, a consensus of the FASB Emerging Issues Task Force (ASC 805) became effective upon its issuance on November 18, 2014 . The new guidance, which is applicable prospectively, gives an acquired non-public company the option to apply pushdown accounting in its separate company financial statements in the period in which it is acquired in a change of control transaction. Once pushdown accounting has been applied, the election is irreversible. Acquired entities that chose not to apply pushdown accounting at the time of acquisition, may apply pushdown accounting in a subsequent period as a change in accounting principle under ASC 250, Accounting Changes and Error Corrections . White Mountains has not had any acquisitions for which it has elected to apply pushdown accounting since ASU 2014-17 became effective. Unrecognized Tax Benefits Effective January 1, 2014, White Mountains adopted ASU 2013-11, Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists (ASC 740). The new ASU requires balance sheet presentation of an unrecognized tax benefit as a reduction of a deferred tax asset for a net operating loss (“NOL”) carryforward or tax credit carryforward rather than as a liability. The exception is in circumstances where a carryforward is not available to settle the additional taxes that might arise upon disallowance of the tax position under the tax law of the applicable jurisdiction. Prior to the issuance of ASU 2013-11, the guidance for unrecognized tax benefits under ASC 740 did not provide explicit guidance on whether an entity should present an unrecognized tax benefit as a liability or as a reduction of NOL carryforwards or other tax credits. In circumstances where an NOL carryforward is not available to offset settlement of any additional taxes arising from a disallowed tax position, the unrecognized tax benefit should be presented as a liability. The new guidance became effective for White Mountains on January 1, 2014. Adoption did not have any impact on White Mountains's financial condition, results of operations or cash flows or financial statement presentation. Recently Issued Accounting Pronouncements Business Combinations - Measurement Period Adjustments On September 25, 2015, the FASB issued ASU 2015-16, Simplifying the Accounting for Measurement-Period Adjustments. At the date of an acquisition, fair value of certain assets and liabilities may not be accurately determinable and are therefore recognized at the acquirer's best estimate. Such amounts may be updated as additional information becomes available in periods subsequent to the acquisition for up to one year. Prior to the issuance of this new ASU, subsequent adjustments had to be pushed back to the acquisition date, which required retroactive adjustments to prior period amounts. Under the new guidance, adjustments to provisional amounts that are identified during the measurement period are to be recorded in the reporting period in which the adjustment amounts are determined. ASU 2015-16 is effective for fiscal years beginning after December 15, 2015 and is applied prospectively to adjustments to estimated purchase accounting amounts that occur after the effective date. Early application is permitted. White Mountains has not recognized any adjustments to estimated purchase accounting amounts for the year to date period ended September 30, 2015. Short-Duration Contracts On May 21, 2015, the FASB issued ASU 2015-09, Disclosures about Short Duration Contracts (ASC 944) which requires expanded footnote disclosures about loss and loss adjustment expense (“LAE”) reserves. Under the new guidance, some disclosures currently presented outside of White Mountains’s financial statements, such as loss development tables and a reconciliation of loss development data to the loss and LAE reserves reflected on the balance sheet, will become part of the financial statement footnotes. In addition, the loss development tables required to be presented under the new ASU must be presented on a disaggregated basis by accident year rather than by reporting year as currently presented. Some of the expanded disclosures are new requirements, such as the disclosure of reserves for losses incurred but not reported (“IBNR”) plus expected development on reported claims, which must be presented by accident year on a disaggregated basis. The new guidance also requires new disclosures about claim frequency data together with descriptions of the approach used to measure that data. Qualitative descriptions of methodologies and assumptions used to develop IBNR estimates must be presented together with the disaggregated 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. Fair Value Measurements On May 1, 2015, the FASB issued 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 and has classified those measurements within Level 3 of the fair value hierarchy. The new guidance is effective for fiscal years beginning after December 15, 2015 and interim periods within those fiscal years. Debt Issuance Costs On April 7, 2015, the FASB issued ASU 2015-03, Imputation of Interest (ASC 835) which requires debt issuance costs related to a recognized debt liability to be presented as a deduction from the carrying amount of the related debt, consistent with the treatment required for debt discounts. On August 18, 2015, the FASB issued ASU 2015-15, Imputation of Interest (ASC 835) which addresses the presentation and subsequent measurement of debt issuance costs related to line-of-credit arrangements. ASU 2015-03 and ASU 2-15-15 are effective for annual and interim reporting periods beginning after December 15, 2015. White Mountains does not expect ASU 2015-03 or ASU 2015-15 to impact its financial position, results of operations, cash flows, presentation and disclosures. Amendments to Consolidation Analysis On February 18, 2015, the FASB issued 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. ASU 2015-02 is effective for annual and interim reporting periods beginning after December 15, 2015 and must be applied retrospectively. White Mountains does not expect ASU 2015-02 to affect the consolidation analysis for any of its existing investments. Share-Based Compensation Awards On June 19, 2014, the FASB issued 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 is intended to eliminate diversity in practice for employee share-based awards containing performance targets that could be achieved after the requisite service period. Some reporting entities account for performance targets that can be achieved after the requisite service period as performance conditions that affect the vesting of the award while other reporting entities treat those performance targets as non-vesting conditions that affect the grant-date fair value of the award. The updated 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 should be recognized in the period it becomes probable that the performance target will be achieved and should represent the compensation cost attributable to the periods for which service has been rendered. The new guidance is effective for annual and interim reporting periods beginning after December 15, 2015. White Mountains does not expect adoption to have a significant effect on its financial position, results of operations, cash flows, presentation or disclosures. Revenue Recognition On May 28, 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (ASC 606) , which modifies the guidance for revenue recognition. The scope of the new ASU excludes insurance contracts but is applicable to certain fee arrangements, such as third-party investment management fees charged by White Mountains Advisors, which were $2.0 million and $5.9 million for the three and nine months ended September 30, 2015 and $3.2 million and $9.2 million for the three and nine months ended September 30, 2014. 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. On August 12, 2015, the FASB issued ASU 2015-14, which defers the effective date of ASU 2014-09 to annual and interim reporting periods beginning after December 15, 2017.

Loss and Loss Adjustment Expe28

Loss and Loss Adjustment Expense Reserves (Tables)	9 Months Ended
Loss and Loss Adjustment Expense Reserves (Tables)	Sep. 30, 2015
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 subsidiaries for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Gross beginning balance $ 1,357.0 $ 1,137.8 $ 1,350.0 $ 1,054.3 Less beginning reinsurance recoverable on unpaid losses (147.2 ) (92.1 ) (161.7 ) (80.2 ) Net loss and LAE reserves 1,209.8 1,045.7 1,188.3 974.1 Loss and LAE reserves consolidated — SSIE — — — 13.6 Loss and LAE incurred relating to: Current year losses 170.4 178.4 536.7 511.0 Prior year losses (0.4 ) 7.1 (2.6 ) 16.3 Total incurred losses and LAE 170.0 185.5 534.1 527.3 Loss and LAE paid relating to: Current year losses (53.0 ) (55.9 ) (120.2 ) (116.5 ) Prior year losses (108.1 ) (107.3 ) (383.5 ) (330.5 ) Total loss and LAE payments (161.1 ) (163.2 ) (503.7 ) (447.0 ) Net ending balance 1,218.7 1,068.0 1,218.7 1,068.0 Plus ending reinsurance recoverable on unpaid losses 214.6 101.5 214.6 101.5 Gross ending balance $ 1,433.3 $ 1,169.5 $ 1,433.3 $ 1,169.5

Investment Securities (Tables)

Investment Securities (Tables)	9 Months Ended
Investment Securities (Tables)	Sep. 30, 2015
Investments, Debt and Equity Securities [Abstract]
Pre-tax net investment income	Pre-tax net investment income for the three and nine months ended September 30, 2015 and 2014 consisted of the following: Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Investment income: Fixed maturity investments $ 13.7 $ 12.7 $ 38.5 $ 38.4 Short-term investments — .1 .1 .2 Common equity securities 1.4 3.3 5.7 11.9 Convertible fixed maturity and preferred investments .1 1.0 .4 1.5 Other long-term investments 1.9 .2 2.5 2.2 Total investment income 17.1 17.3 47.2 54.2 External investment expenses (.3 ) (3.5 ) (4.6 ) (9.5 ) Net investment income, pre-tax $ 16.8 $ 13.8 $ 42.6 $ 44.7
Schedule of Realized and Unrealized Gain (Loss) on Investments	Net realized and unrealized investment gains and losses for the three and nine months ended September 30, 2015 and 2014 consisted of the following: Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Net realized investment (losses) gains, pre-tax $ (7.4 ) $ 57.9 $ 49.7 $ 97.0 Net unrealized investment (losses), pre-tax (36.5 ) (85.4 ) (83.6 ) (32.6 ) Net realized and unrealized investment (losses) gains, pre-tax (43.9 ) (27.5 ) (33.9 ) 64.4 Income tax benefit (expense) attributable to net realized and unrealized investment gains (losses) 9.4 5.6 6.9 (12.2 ) Net realized and unrealized investment (losses) gains, after tax $ (34.5 ) $ (21.9 ) $ (27.0 ) $ 52.2
Realized Gain (Loss) on Investments	Net realized investment gains (losses) for the three and nine months ended September 30, 2015 and 2014 consisted of the following: Three Months Ended Three Months Ended September 30, 2015 September 30, 2014 Millions Net Net Total net realized Net Net Total net realized Fixed maturity investments $ (.1 ) $ — $ (.1 ) $ 2.3 $ (.1 ) $ 2.2 Short-term investments — — — — — — Common equity securities (5.9 ) — (5.9 ) 51.4 — 51.4 Convertible fixed maturity and preferred investments — — — 1.6 — 1.6 Other long-term investments (1.4 ) — (1.4 ) 2.7 — 2.7 Net realized investment (losses) gains, pre-tax (7.4 ) — (7.4 ) 58.0 (.1 ) 57.9 Income tax benefit (expense) attributable to net realized investment gains 1.5 — 1.5 (7.0 ) — (7.0 ) Net realized investment (losses) gains, after tax $ (5.9 ) $ — $ (5.9 ) $ 51.0 $ (.1 ) $ 50.9 Nine Months Ended Nine Months Ended September 30, 2015 September 30, 2014 Millions Net Net Total net realized Net Net Total net realized Fixed maturity investments $ 2.0 $ — $ 2.0 $ 4.7 $ (.1 ) $ 4.6 Short-term investments — — — — — — Common equity securities 41.6 .4 42.0 83.2 — 83.2 Convertible fixed maturity and preferred investments (4.3 ) — (4.3 ) 6.5 — 6.5 Other long-term investments 10.0 — 10.0 2.7 — 2.7 Net realized investment gains (losses), pre-tax 49.3 .4 49.7 97.1 (.1 ) 97.0 Income tax (expense) attributable to net realized investment gains (losses) (15.7 ) — (15.7 ) (13.3 ) — (13.3 ) Net realized investment gains (losses), after tax $ 33.6 $ .4 $ 34.0 $ 83.8 $ (.1 ) $ 83.7
Schedule of unrealized gain (loss) on investments	The following table summarizes net unrealized investment gains (losses) for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended Three Months Ended September 30, 2015 September 30, 2014 Millions Net unrealized gains (losses) Net Total net unrealized gains (losses) reflected in earnings Net unrealized (losses) Net Total net unrealized (losses) reflected in earnings Fixed maturity investments $ 3.3 $ — $ 3.3 $ (10.0 ) $ — $ (10.0 ) Short-term investments — — — — — — Common equity securities (30.6 ) (.2 ) (30.8 ) (63.9 ) (5.3 ) (69.2 ) Convertible fixed maturity and preferred investments 1.1 — 1.1 (3.4 ) — (3.4 ) Other long-term investments (10.1 ) — (10.1 ) (2.8 ) — (2.8 ) Net unrealized investment (losses), pre-tax (36.3 ) (.2 ) (36.5 ) (80.1 ) (5.3 ) (85.4 ) Income tax benefit 7.9 — 7.9 12.6 — 12.6 Net unrealized investment $ (28.4 ) $ (.2 ) $ (28.6 ) $ (67.5 ) $ (5.3 ) $ (72.8 ) Nine Months Ended Nine Months Ended September 30, 2015 September 30, 2014 Millions Net unrealized gains (losses) Net Total net unrealized gains (losses) reflected in earnings Net unrealized gains (losses) Net Total net unrealized gains (losses) reflected in earnings Fixed maturity investments $ 1.3 $ — $ 1.3 $ 12.3 $ — $ 12.3 Short-term investments — — — — — — Common equity securities (56.0 ) (2.5 ) (58.5 ) (43.2 ) (5.3 ) (48.5 ) Convertible fixed maturity and preferred investments 2.0 — 2.0 (5.1 ) — (5.1 ) Other long-term investments (27.6 ) (.8 ) (28.4 ) 8.7 — 8.7 Net unrealized investment (losses), pre-tax (80.3 ) (3.3 ) (83.6 ) (27.3 ) (5.3 ) (32.6 ) Income tax benefit attributable to net unrealized investment losses 22.6 — 22.6 1.1 — 1.1 Net unrealized investment (losses), after tax $ (57.7 ) $ (3.3 ) $ (61.0 ) $ (26.2 ) $ (5.3 ) $ (31.5 )
Net unrealized investment gains (losses) for Level 3 investments	The following table summarizes the amount of total pre-tax unrealized investment (losses) gains included in earnings for Level 3 investments for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Fixed maturity investments $ (1.0 ) $ 2.1 $ (.9 ) $ 2.7 Common equity securities 1.1 1.0 4.0 3.8 Convertible fixed maturity and preferred investments 1.1 .1 1.8 3.3 Other long-term investments (10.0 ) (3.5 ) (28.1 ) (5.7 ) Total unrealized investment (losses) gains, pre-tax - Level 3 investments $ (8.8 ) $ (.3 ) $ (23.2 ) $ 4.1
Investment holdings, equity securities, convertible fixed maturities and other long-term investments	The cost or amortized cost, gross unrealized investment gains and losses, net foreign currency gains and losses, and carrying values of White Mountains’s fixed maturity investments as of September 30, 2015 and December 31, 2014 were as follows: September 30, 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 $ 99.6 $ .2 $ — $ — $ 99.8 Debt securities issued by corporations 998.6 8.7 (1.5 ) — 1,005.8 Municipal obligations 145.8 1.8 (.8 ) — 146.8 Mortgage-backed and asset-backed securities 1,261.2 6.4 (2.2 ) — 1,265.4 Foreign government, agency and provincial obligations 1.0 .3 — — 1.3 Preferred stocks 78.3 4.8 — — 83.1 Total fixed maturity investments $ 2,584.5 $ 22.2 $ (4.5 ) $ — $ 2,602.2 December 31, 2014 Millions Cost or amortized cost Gross unrealized gains Gross unrealized losses Net foreign currency gains (losses) Carrying value U.S. Government and agency obligations $ 105.4 $ .1 $ (.3 ) $ — $ 105.2 Debt securities issued by corporations 1,162.0 13.1 (3.4 ) — 1,171.7 Municipal obligations 81.0 1.4 (.2 ) — 82.2 Mortgage-backed and asset-backed securities 967.5 2.8 (2.4 ) — 967.9 Foreign government, agency and provincial obligations 11.5 .3 (1.0 ) — 10.8 Preferred stocks 78.3 5.9 — — 84.2 Total fixed maturity investments $ 2,405.7 $ 23.6 $ (7.3 ) $ — $ 2,422.0 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, convertible fixed maturity and preferred investments and other long-term investments as of September 30, 2015 and December 31, 2014 were as follows: September 30, 2015 Millions Cost or amortized cost Gross unrealized gains Gross unrealized losses Net foreign Carrying value Common equity securities $ 453.0 $ 52.0 $ (22.9 ) $ — $ 482.1 Convertible fixed maturity and preferred investments $ 3.1 $ 2.5 $ — $ — $ 5.6 Other long-term investments $ 271.9 $ 37.7 $ (12.9 ) $ (2.1 ) $ 294.6 December 31, 2014 Millions Cost or Gross Gross Net foreign Carrying value Common equity securities $ 495.3 $ 127.4 $ (3.6 ) $ (7.4 ) $ 611.7 Convertible fixed maturity and preferred investments $ 13.4 $ .8 $ (.3 ) $ — $ 13.9 Other long-term investments $ 273.3 $ 52.5 $ (6.5 ) $ (1.3 ) $ 318.0 Other Long-term Investments Other long-term investments consist of the following as of September 30, 2015 and December 31, 2014 : Carrying Value at Millions September 30, 2015 December 31, 2014 Hedge funds and private equity funds, at fair value (1) $ 148.6 $ 178.5 Surplus notes investments, at fair value (1)(4) 58.0 65.1 Private equity securities and limited liability companies, at fair value (1)(2) 65.3 45.3 Tax advantaged federal affordable housing development fund (3) 15.2 16.8 Partnership investments accounted for under the equity method 3.9 5.1 Other (1) 3.6 7.2 Total other-long term investments $ 294.6 $ 318.0 (1) See Fair Value Measurements by Level table. (2) On April 2, 2015, White Mountains invested $21.0 in PassportCard. White Mountains has chosen to take the fair value election for its investment. (3) Fund accounted for using the proportional amortization method. (4) The decrease in the fair value of the surplus notes during the nine months ended September 30, 2015 was primarily due to widening of non- investment grade credit spreads.
Other long-term investments	The following table summarizes investments in hedge funds and private equity funds by investment objective and sector as of September 30, 2015 and December 31, 2014 : September 30, 2015 December 31, 2014 Millions Fair Value Unfunded Commitments Fair Value Unfunded Commitments Hedge funds Long/short equity REIT $ 20.0 $ — $ 20.4 $ — Long/short credit & distressed 8.1 — 8.4 — Long/short equity banks and financial 15.4 — 29.9 — Other 12.1 — 15.7 — Total hedge funds 55.6 — 74.4 — Private equity funds Energy infrastructure & services 26.3 4.0 33.1 4.8 Manufacturing/Industrial 23.5 2.5 23.2 7.3 Multi-sector 14.9 2.1 14.5 2.2 Aerospace/Defense/Government 17.1 33.6 20.7 5.1 Healthcare 3.9 .4 3.1 1.4 Private equity secondaries 4.5 2.1 5.7 2.1 Insurance 2.0 41.3 2.1 41.3 Real estate .8 .1 1.7 .1 Total private equity funds 93.0 86.1 104.1 64.3 Total hedge funds and private equity funds included in other long-term investments $ 148.6 $ 86.1 $ 178.5 $ 64.3
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 September 30, 2015 fair value of hedge funds subject to restrictions on redemption frequency and advance notice period requirements for investments in active hedge funds: Notice Period Millions Redemption frequency 30-59 days notice 60-89 days notice 90-119 days notice 120+ days notice Total Monthly $ — $ — $ — $ — $ — Quarterly 16.4 8.1 — 8.4 32.9 Semi-annual — 20.0 — — 20.0 Annual — — 2.7 — 2.7 Total $ 16.4 $ 28.1 $ 2.7 $ 8.4 $ 55.6
Fair Value of private equity funds subject to lock-up periods	As of September 30, 2015 , 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 $25.8 $11.1 $56.1 $— $93.0
Fair value measurements by level, investment securities	The following tables summarize White Mountains’s fair value measurements for investments as of September 30, 2015 and December 31, 2014 , by major security type and class by level. The major security types were based on the legal form of the securities, with a separate break-out for convertible fixed maturity investments as they may react similar to either debt securities or equity securities, depending on prevailing market conditions. 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 asset-backed securities vary depending on the nature of the issuing entity type. White Mountains further disaggregates debt securities issued by corporations and equity securities by industry sector because investors often reference commonly used benchmarks and their subsectors to monitor risk and performance. Accordingly, White Mountains has further disaggregated these asset classes into subclasses based on the similar sectors and industry classifications it uses to evaluate investment risk and performance against commonly used benchmarks, such as the Barclays Intermediate Aggregate and S&P 500 indices: September 30, 2015 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 99.8 $ 61.8 $ 38.0 $ — Debt securities issued by corporations: Consumer 223.1 — 223.1 — Financials 201.3 — 201.3 — Health Care 177.2 — 177.2 — Industrial 132.8 — 132.8 — Communications 52.7 — 52.7 — Energy 57.8 — 57.8 — Utilities 62.5 — 62.5 — Technology 64.7 — 64.7 — Materials 31.4 — 31.4 — Other 2.3 — 2.3 — Total debt securities issued by corporations 1,005.8 — 1,005.8 — Municipal obligations 146.8 — 146.8 — Mortgage-backed and asset-backed securities 1,265.4 — 1,265.4 — Foreign government, agency and provincial obligations 1.3 .6 .7 — Preferred stocks 83.1 — 12.8 70.3 Total fixed maturity investments 2,602.2 62.4 2,469.5 70.3 Short-term investments 325.0 325.0 — — Common equity securities: Exchange traded funds (1) 172.6 152.6 20.0 — Financials 63.2 29.0 — 34.2 Consumer 56.5 56.5 — — Health Care 34.5 34.5 — — Industrial 25.2 25.2 — — Technology 22.0 22.0 — — Communications 36.0 36.0 — — Energy — — — — Materials — — — — Utilities — — — — Other 72.1 — 72.1 — Total common equity securities 482.1 355.8 92.1 34.2 Convertible fixed maturity and preferred investments 5.6 — — 5.6 Other long-term investments (2) 275.5 — — 275.5 Total investments $ 3,690.4 $ 743.2 $ 2,561.6 $ 385.6 (1) ETF's 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 $3.9 associated with other long-term investment limited partnerships accounted for using the equity method. Excludes carrying value of $15.2 associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method. December 31, 2014 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 105.2 $ 51.2 $ 54.0 $ — Debt securities issued by corporations: Consumer 259.2 — 259.2 — Financials 254.7 — 254.7 — Health Care 181.8 — 181.8 — Industrial 107.3 — 102.0 5.3 Communications 71.5 — 71.5 — Energy 65.6 — 65.6 — Utilities 84.1 — 84.1 — Technology 88.3 — 88.3 — Materials 51.7 — 51.7 — Other 7.5 — 7.5 — Total debt securities issued by corporations 1,171.7 — 1,166.4 5.3 Mortgage-backed and asset-backed securities 967.9 — 967.9 — Foreign government, agency and provincial obligations 10.8 .6 10.2 — Preferred stocks 84.2 — 13.1 71.1 Municipal obligations 82.2 — 82.2 — Total fixed maturity investments 2,422.0 51.8 2,293.8 76.4 Short-term investments 376.8 376.3 .5 — Common equity securities: Financials 180.7 141.2 — 39.5 Consumer 116.0 115.9 .1 — Health Care 74.4 74.4 — — Industrial 57.1 57.1 — — Technology 44.8 44.8 — — Communications 28.5 28.5 — — Energy 18.1 18.1 — — Materials 12.0 12.0 — — Utilities 4.9 4.9 — — Other 75.2 1.9 73.3 — Total common equity securities 611.7 498.8 73.4 39.5 Convertible fixed maturity and preferred investments 13.9 — 5.7 8.2 Other long-term investments (1) 296.0 — — 296.0 Total investments $ 3,720.4 $ 926.9 $ 2,373.4 $ 420.1 (1) Excludes carrying value of $5.2 associated with other long-term investment limited partnerships accounted for using the equity method. Excludes carrying value of $16.8 associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method.
Debt securities issued by corporations, credit ratings	The following table summarizes the ratings of the corporate debt securities held in White Mountains’s investment portfolio as of September 30, 2015 and December 31, 2014 : Fair Value at Millions September 30, 2015 December 31, 2014 AAA $ — $ — AA 112.3 144.9 A 439.7 594.9 BBB 453.8 426.5 BB — — Other — 5.4 Debt securities issued by corporations (1) $ 1,005.8 $ 1,171.7 (1) Credit ratings are assigned based on the following hierarchy: 1) Standard and Poor's Financial Services LLC (“Standard & Poor’s”) and 2) Moody’s Investor Service (“Moody's”).
Mortgage-backed, asset-backed securities	The following table summarizes mortgage and asset-backed securities as of September 30, 2015 and December 31, 2014 : September 30, 2015 December 31, 2014 Millions Fair Value Level 2 Level 3 Fair Value Level 2 Level 3 Mortgage-backed securities: Agency: GNMA $ 293.9 $ 293.9 $ — $ 308.7 $ 308.7 $ — FNMA 41.6 41.6 — 33.4 33.4 — FHLMC 24.8 24.8 — 28.9 28.9 — Total Agency (1) 360.3 360.3 — 371.0 371.0 — Non-agency: Residential 123.7 123.7 — 71.0 71.0 — Commercial 133.7 133.7 — 109.3 109.3 — Total Non-agency 257.4 257.4 — 180.3 180.3 — Total mortgage-backed securities 617.7 617.7 — 551.3 551.3 — Other asset-backed securities: Credit card receivables 293.3 293.3 — 218.1 218.1 — Vehicle receivables 276.4 276.4 — 152.8 152.8 — Other 78.0 78.0 — 45.7 45.7 — Total other asset-backed securities 647.7 647.7 — 416.6 416.6 — Total mortgage and asset-backed securities $ 1,265.4 $ 1,265.4 $ — $ 967.9 $ 967.9 $ — (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 residential mortgage-backed securities ("RMBS") and non-agency commercial mortgage-backed securities (“CMBS”) as of September 30, 2015 are as follows: Security Issuance Year Millions Fair Value 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Non-agency RMBS $ 123.7 $ 18.3 $ 2.9 $ 4.0 $ — $ 4.2 $ — $ 17.1 $ 14.6 $ 13.4 $ 14.7 $ 34.5 $ — Non-agency CMBS 133.7 — — — — — — 5.7 — 8.6 18.4 55.6 45.4 Total $ 257.4 $ 18.3 $ 2.9 $ 4.0 $ — $ 4.2 $ — $ 22.8 $ 14.6 $ 22.0 $ 33.1 $ 90.1 $ 45.4
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 September 30, 2015 : Millions Fair Value Super Senior (1) Senior (2) Subordinate (3) Prime $ 123.7 $ 35.1 $ 88.6 $ — Non-prime — — — — Sub-prime — — — — Total $ 123.7 $ 35.1 $ 88.6 $ — (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” securities. (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” securities. (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” securities.
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 September 30, 2015 : Millions Fair Value Super Senior (1) Senior (2) Subordinate (3) Fixed rate CMBS $ 93.2 $ 9.6 $ 41.4 $ 42.2 Floating rate CMBS 40.5 — — 40.5 Total $ 133.7 $ 9.6 $ 41.4 $ 82.7 (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 Ratings (“Fitch”) and were senior to other “AAA” or “Aaa” securities. (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” securities. (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” securities.
Rollforward of fair value investments by level	The following tables summarize the changes in White Mountains’s fair value measurements by level for the three months ended September 30, 2015 and 2014 : Level 3 Investments Millions Level 1 investments Level 2 investments Fixed maturity investments Common equity securities Convertible fixed maturity and preferred investments Other long-term investments Total Balance at January 1, 2015 $ 550.6 $ 2,372.9 $ 76.4 $ 39.5 $ 8.2 $ 296.0 $ 3,343.6 (1)(2) Total realized and unrealized (losses) gains (19.5 ) .6 (.9 ) 7.7 (2.6 ) (18.0 ) (32.7 ) (3) Amortization/Accretion — (15.2 ) — — — — (15.2 ) Purchases 550.0 1,056.0 35.3 — — 30.7 1,672.0 Sales (618.2 ) (894.4 ) — (9.4 ) — (18.9 ) (1,540.9 ) Effect of redemption of Prospector hedge funds (43.5 ) — — (3.6 ) — (14.3 ) (61.4 ) Transfers in — 41.7 — — — — 41.7 Transfers out (1.2 ) — (40.5 ) — — — (41.7 ) Balance at September 30, 2015 $ 418.2 $ 2,561.6 $ 70.3 $ 34.2 $ 5.6 $ 275.5 $ 3,365.4 (1)(2) (1) Excludes carrying value of $5.2 and $3.9 at January 1, 2015 and September 30, 2015 associated with other long-term investments accounted for using the equity method. Excludes carrying value of $16.8 and $15.2 at January 1, 2015 and September 30, 2015 million 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 $ 325.0 at January 1, 2015 and September 30, 2015 associated with short-term investments. (3) Excludes $0.8 realized and unrealized losses associated with the Prospector Offshore Fund consolidation of investment-related liabilities. Level 3 Investments Millions Level 1 investments Level 2 investments Fixed maturity investments Common equity securities Convertible fixed maturity and preferred investments Other long-term investments Total Balance at January 1, 2014 $ 997.2 $ 2,575.4 $ 81.8 $ 45.4 $ 6.1 $ 183.1 $ 3,889.0 (1)(2)(3) Total realized and unrealized gains (losses) 30.7 12.5 2.7 3.7 3.3 (3.2 ) 49.7 (4) Amortization/Accretion .1 (14.3 ) (.1 ) — — — (14.3 ) Purchases 661.2 1,265.3 45.5 — 1.5 42.7 2,016.2 Sales (926.2 ) (1,392.5 ) — (10.9 ) — (11.1 ) (2,340.7 ) Net change in investments consolidated affiliates 3.4 7.4 — — — — 10.8 Transfers in — 42.1 — — — — 42.1 Transfers out (.2 ) — (41.9 ) — — — (42.1 ) Balance at September 30, 2014 $ 766.2 $ 2,495.9 $ 88.0 $ 38.2 $ 10.9 $ 211.5 $ 3,610.7 (1)(2)(3) (1) Excludes carrying value of $ 6.8 and $5.1 at January 1, 2014 and September 30, 2014 associated with other long-term investment limited partnerships accounted for using the equity method. Excludes carrying value of $19.1 and $17.3 at January 1, 2014 and September 30, 2014 associated with a tax advantaged federal affordable housing development fund accounted for using the proportional amortization method. (2) Carrying value includes $236.3 and 203.9 at January 1, 2014 and September 30, 2014 that is classified as assets held for sale relating to discontinued operations. (3) Excludes carrying value of $310.4 and $ 402.7 at January 1, 2014 and September 30, 2014 associated with short-term investments. (4) Excludes $0.5 realized and unrealized gains associated with the Prospector Offshore Fund and Prospector Turtle Fund consolidation of investment-related liabilities.
Schedule of significant unobservable inputs used in estimating the fair value of investment securities	The following summarizes significant unobservable inputs used in estimating the fair value of investment securities classified within Level 3 other than hedge funds and private equity funds as of September 30, 2015 and December 31, 2014 . The fair value of investments in hedge funds and private equity funds, which are classified within Level 3, are estimated using the net asset value of the funds. ($ in millions) September 30, 2015 December 31, 2014 Description Rating (2) Valuation Technique(s) Fair (7) Unobservable Input Fair (7) Unobservable Input Preferred Stock (1) NR Discounted cash flow $70.3 Discount yield - 8.4% $71.1 Discount yield - 7.1% Private equity security (1)(9) NR Share price of pending transaction (9) $34.2 Share price - $17.16 $39.5 Multiple of GAAP book value (9) - 1.10 Private equity security (1) NR Share price of most recent transaction $21.0 Share price - $1.00 N/A N/A - N/A Private equity security (1) NR Share price of most recent transaction $20.1 Share price - $1.06 $20.1 Share price - $1.06 Private equity security (1) NR Share price of most recent transaction $9.6 Share price - $290.96 $10.4 Share price - $290.96 Convertible preferred security (1) NR Multiple of EBITDA $5.6 EBITDA multiple - 6.00 $3.8 EBITDA multiple - 6.00 Convertible preferred security (1) NR Share price of most recent transaction N/A N/A N/A $4.5 Share price - $0.71 Debt security issued by corporation (1) NR Discounted cash flow N/A N/A N/A $5.3 Illiquidity discount (3) - 10% Surplus notes (8) : NR - Seller priority Discounted cash flow $41.0 Discount rate (4) - 11.6% $44.0 Discount rate (4) - 9.3% Timing of interest payments (5) - 5 years Timing of interest payments (5) - 5 years Timing of principal payments (5) - 10 years Timing of principal payments (5) - 10 years - Pari passu Discounted cash flow $17.0 Discount rate (5) - 18.3% $21.1 Discount rate (5) - 13.5% Timing of interest payments (6) - 5 years Timing of interest payments (6) - 5 years Timing of principal payments (6) - 15 years Timing of principal payments (6) - 10 years (1) As of September 30, 2015 , consists of 1 security. (2) Credit ratings are assigned based on the following hierarchy: 1) Standard and Poor's and 2) Moody’s. (3) Judgmentally determined based on the Company’s limited trading ability of the issuer. (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 pari passu 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 principal repayments begin on a graduated basis in year ten for the seller priority note and year fifteen for the pari passu note. (7) Includes the unrealized gains and losses associated with foreign currency; foreign currency effects based on observable inputs. (8) The decrease in the fair value of the surplus notes during the nine months ended September 30, 2015 was primarily due to widening of non-investment grade credit spreads. (9) As of December 31, 2014, the valuation technique for the private equity security was a multiple of GAAP book value. As of September 30, 2015, the valuation technique was the estimated share price from a pending transaction that is expected to close in the fourth quarter of 2015.

Goodwill and Other Intangible30

Goodwill and Other Intangible Assets (Tables)	9 Months Ended
Goodwill and Other Intangible Assets (Tables)	Sep. 30, 2015
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 September 30, Millions 2015 2014 Goodwill Other intangible assets Goodwill Other intangible assets Beginning balance $ 169.2 $ 171.2 $ 23.8 $ 44.6 Acquisitions of businesses 20.1 28.1 — — Dispositions of businesses — — — — Amortization, including foreign currency translation — (6.9 ) — (2.6 ) Ending balance $ 189.3 $ 192.4 $ 23.8 $ 42.0 Nine Months Ended September 30, Millions 2015 2014 Goodwill Other intangible assets Goodwill Other intangible assets Beginning balance $ 168.9 $ 182.3 $ — $ 5.1 Acquisitions of businesses 20.4 30.9 23.8 42.4 Dispositions of businesses — — — — Amortization, including foreign currency translation — (20.8 ) — (5.5 ) Ending balance $ 189.3 $ 192.4 $ 23.8 $ 42.0

Debt (Tables)

Debt (Tables)	9 Months Ended
Debt (Tables)	Sep. 30, 2015
Debt Disclosure [Abstract]
Schedule of debt outstanding	White Mountains’s debt outstanding as of September 30, 2015 and December 31, 2014 consisted of the following: Millions September 30, December 31, 2012 OBH Senior Notes, at face value $ 275.0 $ 275.0 Unamortized original issue discount (.2 ) (.3 ) 2012 OBH Senior Notes, carrying value 274.8 274.7 WTM Bank Facility — — OneBeacon Bank Facility — — Tranzact Bank Facility 95.8 68.7 Unamortized issuance cost (2.0 ) (1.3 ) Tranzact Bank Facility, carrying value 93.8 67.4 MediaAlpha Bank Facility 15.0 — Unamortized issuance cost (.3 ) — MediaAlpha Bank Facility, carrying value 14.7 — Other debt — 1.0 Total debt $ 383.3 $ 343.1

Derivatives (Tables)

Derivatives (Tables) - Variable Annuity	9 Months Ended
Derivatives (Tables) - Variable Annuity	Sep. 30, 2015
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 nine months ended September 30, 2015 and 2014 . Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Fees, included in other revenue $ 2.1 $ 4.5 $ 7.7 $ 15.0 Change in fair value of variable annuity liability, included in other revenue (2.8 ) 19.9 (1.7 ) 40.5 Change in fair value of derivatives, included in other revenue 1.5 (23.8 ) (6.3 ) (56.5 ) Foreign exchange, included in other revenue .4 (1.7 ) (.8 ) (1.2 ) Other investment income and (losses) gains (.2 ) (.9 ) (.3 ) (.4 ) Total revenue 1.0 (2.0 ) (1.4 ) (2.6 ) Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses — .2 — .6 Death benefit claims paid, included in general and administrative expenses — — — (.1 ) General and administrative expenses (.8 ) (.9 ) (3.1 ) (3.3 ) Pre-tax income (loss) $ .2 $ (2.7 ) $ (4.5 ) $ (5.4 )
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 nine months ended September 30, 2015 and 2014 and the carrying values, included in other assets, at September 30, 2015 and December 31, 2014 by type of instrument: Gains (losses) Carrying Value Three Months Ended Nine Months Ended As of September 30, September 30, September 30, December 31, 2014 Millions 2015 2014 2015 2014 Fixed income/interest rate $ 2.6 $ (8.4 ) $ 6.0 $ (20.4 ) $ — $ (1.7 ) Foreign exchange (3.1 ) (.4 ) (6.0 ) (13.3 ) 27.9 44.1 Equity 2.0 (15.0 ) (6.3 ) (22.8 ) 9.1 14.0 Total $ 1.5 $ (23.8 ) $ (6.3 ) $ (56.5 ) $ 37.0 $ 56.4
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 nine months ended September 30, 2015 and 2014 : Three Months Ended September 30, 2015 Variable Annuity Assets Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ 1.8 $ 8.3 $ 32.5 $ (5.1 ) $ 35.7 Purchases — — — — — Realized and unrealized gains (losses) (2.8 ) 3.4 3.2 (5.1 ) 1.5 Transfers in — — — — — Sales/settlements — (.5 ) (7.8 ) 8.1 (.2 ) End of period $ (1.0 ) $ 11.2 $ 27.9 $ (2.1 ) $ 37.0 Nine Months Ended September 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) (1.7 ) (5.5 ) (2.7 ) 1.9 (6.3 ) Transfers in — — — — — Sales/settlements — (2.2 ) (3.2 ) (7.7 ) (13.1 ) End of period $ (1.0 ) $ 11.2 $ 27.9 $ (2.1 ) $ 37.0 Three Months Ended September 30, 2014 Variable Annuity Assets Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ (31.8 ) $ 53.3 $ 22.3 $ (.8 ) $ 74.8 Purchases — — — — — Realized and unrealized gains (losses) 20.1 (17.4 ) (19.8 ) 13.4 (23.8 ) Transfers in — — — — — Sales/settlements — — 22.5 (8.2 ) 14.3 End of period $ (11.7 ) $ 35.9 $ 25.0 $ 4.4 $ 65.3 Nine Months Ended September 30, 2014 Variable Annuity (Liabilities) Derivative Instruments Millions Level 3 Level 3 (1) Level 2 (1)(2) Level 1 (3) Total Beginning of period $ (52.8 ) $ 63.4 $ 4.7 $ 1.1 $ 69.2 Purchases — — — — — Realized and unrealized gains (losses) 41.1 (27.5 ) (42.1 ) 13.1 (56.5 ) Transfers in — — — — — Sales/settlements — — 62.4 (9.8 ) 52.6 End of period $ (11.7 ) $ 35.9 $ 25.0 $ 4.4 $ 65.3 (1) Consists of over-the-counter instruments. (2) Consists of interest rate swaps, total return swaps, foreign currency forward contracts, and bond forwards. Fair value measurement based upon bid/ask pricing quotes for similar instruments that are actively traded, where available. Swaps for which an active market does not exist have been priced using observable inputs including the swap curve and the underlying bond index. (3) Consists of exchange traded equity index, foreign currency and interest rate futures. Fair value measurements based upon quoted prices for identical instruments that are actively traded.
Assets Held under Reinsurance Counterparty Trust Agreement	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 September 30, 2015 December 31, 2014 September 30, 2014 Cash $ 16.8 $ 23.7 $ 23.8 Fixed maturity investments — 9.5 10.4 Total $ 16.8 $ 33.2 $ 34.2
Schedule of significant unobservable inputs associated with the fair value estimates for variable annuity reinsurance liabilities and derivative instruments	The following summarizes quantitative information about significant unobservable inputs associated with the fair value estimates for variable annuity reinsurance liabilities and derivative instruments that have been classified as Level 3 measurements: ($ in Millions) September 30, 2015 Description Fair Value Valuation Technique(s) Unobservable Input Range Weighted Average Variable annuity benefit guarantee liabilities $ 1.0 Discounted cash flows Surrenders 0-1 year 0.1 % - 40.0% 40.0 % Mortality 0.0 % - 6.4% 1.0 % Foreign exchange volatilities 0-1 year 11.6 % - 18.6% 12.5 % Index volatilities 0-1 year 26.2 % - 29.9% 28.2 % Foreign exchange options $ 2.6 Counterparty valuations, adjusted for unwind quote discount Adjustment to counterparty valuations 0.5 % - 11.6% 3.7 % Equity index options $ 8.6 Counterparty valuations, adjusted for unwind quote discount Adjustment to counterparty valuations (0.7 )% - 6.5% 2.0 %
Exchange traded and OTC derivative instruments	The following summarizes amounts offset under master netting agreements: September 30, 2015 December 31, 2014 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 $ .5 $ (.8 ) $ (0.3 ) $ 1.0 $ (5.4 ) $ (4.4 ) Exchange traded .3 (.1 ) .2 2.8 (.1 ) 2.7 Foreign exchange contracts OTC 27.9 — 27.9 45.5 — 45.5 Exchange traded .1 (.1 ) — — (1.4 ) (1.4 ) Equity contracts OTC 11.5 — 11.5 11.7 (.2 ) 11.5 Exchange traded — (2.3 ) (2.3 ) 3.4 (.9 ) 2.5 Total (2) $ 40.3 $ (3.3 ) $ 37.0 $ 64.4 $ (8.0 ) $ 56.4 (1) Amount equal to fair value of instrument as recognized in other assets (2) All derivative instruments held by WM Life Re are subject to master netting arrangements.
Net exposure to collateral	The following summarizes the value, collateral held or provided by WM Life Re and net exposure to credit losses on OTC and exchange traded derivative instruments by counterparty recorded within other assets: September 30, 2015 Millions Net amount of assets reflected in Balance Sheet Collateral provided to counterparty - Cash Collateral provided to counter-party - Financial Instruments Net amount of exposure after effect of collateral provided Excess collateral provided to counter-party- Cash Excess collateral provided - Financial Instruments Counter-party collateral held by WMLife Re - Cash Net amount of exposure to counter-party Standard & Poor's Rating (1) Bank of America $ 3.2 $ — $ — $ 3.2 $ — $ — $ — $ 3.2 A Barclays — — — — — — — — A - JP Morgan 15.9 — — 15.9 — — 5.9 10.0 A + Royal Bank of Scotland 1.5 — — 1.5 — — — 1.5 BBB + Nomura (.1 ) .1 — — 1.4 — — 1.4 BBB + Citigroup - OTC 18.6 — — 18.6 — — 5.3 13.3 A Citigroup - Exchange Traded (2.1 ) 2.1 — — 12.8 — — 12.8 A Total $ 37.0 $ 2.2 $ — $ 39.2 $ 14.2 $ — $ 11.2 $ 42.2 December 31, 2014 Millions Net amount of assets reflected in Balance Sheet Collateral provided to counter-party - Cash Collateral provided to counter-party - Financial Instruments Net amount of exposure after effect of collateral provided Excess collateral provided to counter-party- Cash Excess collateral provided - Financial Instruments Counter-party collateral held by WMLife Re- Cash Net amount of exposure to counter-party Standard & Poor's Rating (1) Bank of America $ 5.6 $ — $ — $ 5.6 $ — $ — $ — $ 5.6 A Barclays .1 — — .1 — — — .1 A JP Morgan 24.3 — — 24.3 — — 8.8 15.5 A + Royal Bank of Scotland 4.0 — — 4.0 — — — 4.0 A - Nomura (3.5 ) 3.5 — — 1.7 9.5 — 11.2 BBB + Citigroup - OTC 22.2 — — 22.2 — — 1.1 21.1 A Citigroup - Exchange Traded 3.7 — — 3.7 16.0 — — 19.7 A Total $ 56.4 $ 3.5 $ — $ 59.9 $ 17.7 $ 9.5 $ 9.9 $ 77.2 (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)	9 Months Ended
Municipal Bond Guarantee (Tables)	Sep. 30, 2015
Guarantees [Abstract]
Schedule of Municipal Bond Guarantee Insured Obligations	The following table provides a schedule of BAM’s insured obligations: September 30, 2015 December 31, 2014 Contracts outstanding 2,733 1,750 Remaining weighted average contract period outstanding (in years) 12.7 12.8 Contractual debt service outstanding (in millions): Par $ 19,841.0 $ 12,362.5 Interest 10,574.3 7,086.9 Total debt service outstanding $ 30,415.3 $ 19,449.4 Gross unearned insurance premiums $ 43.2 $ 27.6

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
Earnings Per Share (Tables)	Sep. 30, 2015
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 nine months ended September 30, 2015 and 2014 . (See Note 17 - “Discontinued Operations” ). Three Months Ended Nine Months Ended September 30, September 30, 2015 2014 2015 2014 Basic and diluted earnings per share numerators (in millions): Net income from continuing operations attributable to White Mountains’s common shareholders $ (73.1 ) $ (12.6 ) $ (61.8 ) $ 65.8 Allocation of income for unvested restricted common shares — — — (.8 ) Dividends declared on participating restricted common shares (1) — — (.1 ) (.1 ) Total allocation to restricted common shares — — (.1 ) (.9 ) Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ (73.1 ) $ (12.6 ) $ (61.9 ) $ 64.9 Undistributed net earnings (in millions): Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ (73.1 ) $ (12.6 ) $ (61.9 ) $ 64.9 Dividends declared net of restricted common share amounts (1) — — (5.9 ) (6.1 ) Total undistributed net earnings, net of restricted common share amounts $ (73.1 ) $ (12.6 ) $ (67.8 ) $ 58.8 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 5,890.1 6,091.4 5,951.1 6,140.9 Average unvested restricted shares (2) — — — (77.7 ) Basic earnings per share denominator 5,890.1 6,091.4 5,951.1 6,063.2 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 5,890.1 6,091.4 5,951.1 6,140.9 Average unvested restricted common shares (2) — — — (77.7 ) Average outstanding dilutive options to acquire common shares (3) — — — — Diluted earnings per share denominator 5,890.1 6,091.4 5,951.1 6,063.2 Basic earnings per share (in dollars): Net income attributable to White Mountains’s common shareholders $ (12.42 ) $ (2.07 ) $ (10.40 ) $ 10.70 Dividends declared and paid — — (1.00 ) (1.00 ) Undistributed earnings $ (12.42 ) $ (2.07 ) $ (11.40 ) $ 9.70 Diluted earnings per share (in dollars): Net income attributable to White Mountains’s common shareholders $ (12.42 ) $ (2.07 ) $ (10.40 ) $ 10.70 Dividends declared and paid — — (1.00 ) (1.00 ) Undistributed earnings $ (12.42 ) $ (2.07 ) $ (11.40 ) $ 9.70 (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 nine months ended September 30, 2015 and 2014 does not include the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding as they are anti-dilutive to the calculation.

Non-controlling Interest (Table

Non-controlling Interest (Tables)	9 Months Ended
Non-controlling Interest (Tables)	Sep. 30, 2015
Noncontrolling Interest [Line Items]
Noncontrolling Interest Disclosure [Text Block]	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 September 30, 2015 and December 31, 2014: September 30, 2015 December 31, 2014 $ in millions Non-controlling Percentage Non-controlling Equity Non-controlling Percentage Non-controlling Equity OneBeacon Ltd. 24.7 % $ 246.9 24.7 % $ 258.4 SIG Preference Shares 100.0 250.0 100.0 250.0 Other, excluding mutuals and reciprocals HG Global 3.1 17.3 3.1 17.9 MediaAlpha 40.0 15.1 40.0 22.6 Tranzact 36.8 75.6 36.8 88.2 Wobi 4.7 1.8 36.7 5.4 Dewar 32.2 3.5 18.0 3.4 Prospector Offshore Fund — — 23.4 31.1 Total other, excluding mutuals and reciprocals 113.3 168.6 Mutuals and reciprocals BAM 100.0 (134.2 ) 100.0 (121.9 ) SSIE 100.0 (15.2 ) 100.0 (12.4 ) Total non-controlling interests $ 460.8 $ 542.7

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
Segment Information (Tables)	Sep. 30, 2015
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 Other Operations Total Three Months Ended September 30, 2015 Earned insurance premiums $ 281.4 $ .6 $ .3 $ 2.6 $ 284.9 Net investment income 12.4 .5 1.1 2.8 16.8 Net investment income (loss) - surplus note interest — 4.0 (4.0 ) — — Net realized and unrealized investment (losses) gains (29.9 ) .6 1.7 (16.3 ) (43.9 ) Other revenue 3.9 — .2 72.8 76.9 Total revenues 267.8 5.7 (.7 ) 61.9 334.7 Losses and LAE 167.5 — — 2.5 170.0 Insurance acquisition expenses 53.8 .1 .4 1.0 55.3 Other underwriting expenses 56.4 — .1 — 56.5 General and administrative expenses 3.7 .4 9.4 129.1 142.6 Interest expense 3.2 — — 1.7 4.9 Total expenses 284.6 .5 9.9 134.3 429.3 Pre-tax (loss) income $ (16.8 ) $ 5.2 $ (10.6 ) $ (72.4 ) $ (94.6 ) HG Global/BAM Millions OneBeacon HG BAM Other Operations Total Nine Months Ended September 30, 2015 Earned insurance premiums $ 887.3 $ 1.7 $ .6 $ 6.4 $ 896.0 Net investment income 33.0 1.4 2.9 5.3 42.6 Net investment income (loss) - surplus note interest — 11.9 (11.9 ) — — Net realized and unrealized investment (losses) gains (29.7 ) .3 2.8 (7.3 ) (33.9 ) Other (loss) revenue (.4 ) — .5 225.3 225.4 Total revenues 890.2 15.3 (5.1 ) 229.7 1,130.1 Losses and LAE 527.9 — — 6.2 534.1 Insurance acquisition expenses 161.2 .3 1.8 2.8 166.1 Other underwriting expenses 165.2 — .3 — 165.5 General and administrative expenses 12.0 1.2 26.3 314.6 354.1 Interest expense 9.7 — — 3.8 13.5 Total expenses 876.0 1.5 28.4 327.4 1,233.3 Pre-tax income (loss) $ 14.2 $ 13.8 $ (33.5 ) $ (97.7 ) $ (103.2 ) HG Global/BAM Millions OneBeacon HG BAM Other Operations Total Three Months Ended September 30, 2014 Earned insurance premiums $ 305.4 $ .4 $ .1 $ 1.3 $ 307.2 Net investment income 10.8 .4 1.4 1.2 13.8 Net investment income (loss) - surplus note interest — 3.9 (3.9 ) — — Net realized and unrealized investment losses (16.0 ) (.5 ) (1.4 ) (9.6 ) (27.5 ) Other revenue 1.3 — .2 28.2 29.7 Total revenues 301.5 4.2 (3.6 ) 21.1 323.2 Losses and LAE 185.2 — — .3 185.5 Insurance acquisition expenses 54.6 — .5 .1 55.2 Other underwriting expenses 51.2 — .1 — 51.3 General and administrative expenses 2.4 .4 8.9 51.3 63.0 Interest expense 3.2 — — .5 3.7 Total expenses 296.6 .4 9.5 52.2 358.7 Pre-tax income (loss) $ 4.9 $ 3.8 $ (13.1 ) $ (31.1 ) $ (35.5 ) HG Global/BAM Millions OneBeacon HG BAM Other Operations Total Nine Months Ended September 30, 2014 Earned insurance premiums $ 872.8 $ .9 $ .3 $ 5.1 $ 879.1 Net investment income 33.4 1.0 4.2 6.1 44.7 Net investment income (loss) - surplus note interest — 11.8 (11.8 ) — — Net realized and unrealized investment gains 24.8 1.1 5.4 33.1 64.4 Other revenue (loss) 3.3 — .5 56.5 60.3 Total revenues 934.3 14.8 (1.4 ) 100.8 1,048.5 Losses and LAE 520.7 — — 6.6 527.3 Insurance acquisition expenses 150.9 .2 1.4 .5 153.0 Other underwriting expenses 152.3 — .3 — 152.6 General and administrative expenses 9.3 1.2 26.6 131.2 168.3 Interest expense 9.7 — — .9 10.6 Total expenses 842.9 1.4 28.3 139.2 1,011.8 Pre-tax income (loss) $ 91.4 $ 13.4 $ (29.7 ) $ (38.4 ) $ 36.7

Investments in Unconsolidated37

Investments in Unconsolidated Affiliates (Tables)	9 Months Ended
Investments in Unconsolidated Affiliates (Tables)	Sep. 30, 2015
Equity Method Investments and Joint Ventures [Abstract]
Investments in and Advances to 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. Millions September 30, December 31, Symetra common shares $ 386.9 $ 373.8 Unrealized gains from Symetra’s fixed maturity portfolio 5.7 37.6 Carrying value of Symetra common shares 392.6 411.4 Hamer — 3.0 Total investments in unconsolidated affiliates $ 392.6 $ 414.4
Schedule of Changes in Investments in Unconsolidated Affiliates	The following table summarizes amounts recorded by White Mountains relating to its investment in Symetra for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Carrying value of investment in Symetra at beginning of period $ 397.2 $ 415.5 $ 411.4 $ 317.3 Equity in earnings (1)(2) 4.2 7.0 17.5 34.5 Equity in net unrealized gains (losses) from Symetra’s fixed maturity portfolio (3) 3.7 (10.7 ) (31.8 ) 64.0 Dividends received (12.5 ) (2.0 ) (16.9 ) (6.0 ) Distribution from Prospector Offshore Fund — — 12.4 — Carrying value of investment in Symetra at end of period (4)(5) $ 392.6 $ 409.8 $ 392.6 $ 409.8 (1) For the three months ended September 30, 2015 and 2014 , equity in earnings excludes tax expense of $0.3 and $0.5 . For the nine months ended September 30, 2015 and 2014 , equity in earnings excludes tax expense of $1.1 and $2.4 . (2) For the three months ended September 30, 2015 and 2014 , equity in earnings includes $0.7 and $0.7 increase relating to the pre-tax amortization of the Symetra common share basis difference. For the nine months ended September 30, 2015 and 2014 , equity in earnings includes $2.1 and $2.2 increase relating to the pre-tax amortization of the Symetra common share basis difference. (3) For the three months ended September 30, 2015 and 2014 , net unrealized gains includes $2.9 and $3.1 increase relating to the pre-tax amortization of the Symetra common share basis difference. For the nine months ended September 30, 2015 and 2014 , net unrealized gains includes $8.6 and $9.4 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 $5.7 and $20.5 as of September 30, 2015 and 2014 , which excludes tax expense of $0.2 and $1.4 . (5) The aggregate value of White Mountains’s investment in common shares of Symetra was $650.6 based upon the quoted market price of $ 31.64 per share at September 30, 2015 .

Employee Share-Based Incentiv38

Employee Share-Based Incentive Compensation Plans (Tables)	9 Months Ended
Employee Share-Based Incentive Compensation Plans (Tables)	Sep. 30, 2015
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 nine months ended September 30, 2015 and 2014 for performance shares granted under the WTM Incentive Plan: Three Months Ended September 30, Nine Months Ended September 30, 2015 2014 2015 2014 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 109,129 $ 28.8 116,259 $ 46.3 113,198 $ 44.4 108,605 $ 54.9 Shares paid or expired (1) (8,958 ) (5.5 ) — — (42,958 ) (30.7 ) (33,730 ) (24.1 ) New grants — — — — 29,828 — 41,580 — Assumed forfeitures and cancellations (2) (3,960 ) (.8 ) — (.2 ) (3,857 ) (.3 ) (196 ) — Expense recognized — 30.0 — 6.3 — 39.1 — 21.6 End of period (3) 96,211 $ 52.5 116,259 $ 52.4 96,211 $ 52.5 116,259 $ 52.4 (1) WTM performance share payments in 2015 for the 2012-2014 performance cycle ranged from 91% to 145.5% of target. WTM performance share payments in 2014 for the 2011-2013 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 September 30, 2015 and 2014 exclude 7,997 and 11,278 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 September 30, 2015 for each performance cycle: Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Performance cycle: 2015 – 2017 29,828 $ 6.3 2014 – 2016 32,557 12.3 2013 – 2015 36,293 35.4 Sub-total 98,678 54.0 Assumed forfeitures (2,467 ) (1.5 ) Total at September 30, 2015 96,211 $ 52.5
Summary of restricted share activity	The following table summarizes the unrecognized compensation cost associated with the outstanding restricted share awards for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended September 30, Nine Months Ended September 30, 2015 2014 2015 2014 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 68,303 $ 21.9 79,011 $ 20.5 80,050 $ 13.7 90,341 $ 16.4 Issued — — — — 22,078 14.7 20,400 11.8 Vested (1,200 ) — — — (35,025 ) — (31,730 ) — Forfeited — — — — — — — — Expense recognized — (3.5 ) — (3.2 ) — (10.0 ) — (10.9 ) End of period (1) 67,103 $ 18.4 79,011 $ 17.3 67,103 $ 18.4 79,011 $ 17.3 (1) Outstanding restricted share awards as of September 30, 2015 and 2014 exclude 3,571 and 2,314 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 nine months ended September 30, 2015 and 2014 for OneBeacon performance shares granted under the OneBeacon Incentive Plan: Three Months Ended September 30, Nine Months Ended September 30, 2015 2014 2015 2014 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 462,147 $ 2.4 512,938 $ 4.4 517,470 $ 3.4 493,421 $ 4.0 Shares paid or expired (1) — — — — (181,290 ) (1.5 ) (142,138 ) (1.0 ) New grants — — — — 154,887 — 165,800 — Assumed forfeitures and cancellations (2) — — — — (28,920 ) — (4,145 ) — Expense recognized — (.3 ) — 1.1 — .2 — 2.5 End of period 462,147 $ 2.1 512,938 $ 5.5 462,147 $ 2.1 512,938 $ 5.5 (1) OneBeacon performance share payments in 2015 for the 2012-2014 performance cycle were at 45.7% of target. OneBeacon performance share payments in 2014 for the 2011-2013 performance cycle were at 37.1% 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 September 30, 2015 for each performance cycle: Millions, except share amounts Target Accrued Expense Performance cycle: 2015 – 2017 154,887 $ .5 2014 – 2016 151,810 .3 2013 – 2015 167,300 1.3 Sub-total 473,997 2.1 Assumed forfeitures (11,850 ) — Total at September 30, 2015 462,147 $ 2.1
Summary of OneBeacon restricted shares activity	The following table summarizes the unrecognized compensation cost associated with the outstanding OneBeacon restricted stock awards for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended September 30, Nine Months Ended September 30, 2015 2014 2015 2014 Millions, except share amounts Restricted Unamortized Restricted Unamortized Restricted Unamortized Restricted Unamortized Non-vested, Beginning of period 390,950 $ 3.5 612,500 $ 4.9 612,500 $ 3.5 915,000 $ 6.5 Issued — — — — 75,950 1.1 — — Vested — — — — (296,000 ) — (300,000 ) — Forfeited — — — — (1,500 ) — (2,500 ) — Expense recognized — (.5 ) — (.7 ) — (1.6 ) — (2.3 ) End of period 390,950 $ 3.0 612,500 $ 4.2 390,950 $ 3.0 612,500 $ 4.2

Fair Value of Financial Instr39

Fair Value of Financial Instruments (Tables)	9 Months Ended
Fair Value of Financial Instruments (Tables)	Sep. 30, 2015
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 September 30, 2015 and December 31, 2014 : September 30, 2015 December 31, 2014 Millions Fair Value Carrying Value Fair Value Carrying Value 2012 OBH Senior Notes $ 279.8 $ 274.8 $ 286.0 $ 274.7 Tranzact Bank Facility 94.6 93.8 68.7 67.4

Discontinued Operations (Tables

Discontinued Operations (Tables)	9 Months Ended
Discontinued Operations (Tables)	Sep. 30, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Summary of the fair value and carrying value of financial instruments	The following table summarizes the fair value and carrying value of these financial instruments as of September 30, 2015 and December 31, 2014 : September 30, 2015 December 31, 2014 Millions Fair Value Carrying Value Fair Value Carrying Value 2012 OBH Senior Notes $ 279.8 $ 274.8 $ 286.0 $ 274.7 Tranzact Bank Facility 94.6 93.8 68.7 67.4
Schedule of Disposal Groups, Including Discontinued Operations, Income Statement, Balance Sheet And Additional Disclosures	Summary of Reclassified Balances and Related Items Net Assets Held for Sale The following summarizes the assets and liabilities associated with the business classified as held for sale, which all relate to Sirius Group with the exception of the building held by OneBeacon at December 31, 2014: Millions September 30, 2015 December 31, 2014 Assets held for sale Fixed maturity investments $ 2,394.3 $ 2,362.3 Short-term investments 360.5 494.9 Common equity securities 164.3 189.9 Convertible fixed maturity and preferred investments — 6.6 Other long-term investments 82.1 89.0 Total investments 3,001.2 3,142.7 Cash 147.4 111.5 Reinsurance recoverable on unpaid losses 276.5 322.2 Reinsurance recoverable on paid losses 11.0 11.4 Reinsurance premiums receivable 416.6 306.6 Funds held by ceding entities 81.1 91.9 Deferred acquisition costs 82.7 69.9 Deferred tax asset 309.6 341.5 Ceded unearned reinsurance premiums 118.4 76.2 Goodwill and intangible assets 10.2 15.2 Other assets 73.4 83.4 Other assets - OneBeacon building — 58.1 Total assets held for sale $ 4,528.1 $ 4,630.6 Liabilities held for sale Loss and loss adjustment expense reserves $ 1,662.9 $ 1,809.8 Unearned insurance premiums 429.4 338.6 Debt 403.5 403.5 Deferred tax liability 257.8 282.8 Accrued incentive compensation 55.5 76.5 Ceded reinsurance payable 131.4 71.5 Funds held under reinsurance treaties 45.1 57.9 Other liabilities 47.2 64.7 Total liabilities held for sale $ 3,032.8 $ 3,105.3 Net Income from Discontinued Operations The following summarizes the results of operations, including related income taxes associated with the business classified as discontinued operations. The results of Sirius Group through the closing date of the transaction inures to White Mountains. Three Months Ended Three Months Ended September 30, 2015 September 30, 2014 Millions Sirius Group Other Disc Ops Total Sirius Group Other Disc Ops Total Revenues Earned insurance premiums $ 202.8 $ — $ 202.8 $ 231.4 $ .3 $ 231.7 Net investment income 10.5 — 10.5 9.7 — 9.7 Net realized and unrealized (losses) gains (.9 ) — (.9 ) 48.3 — 48.3 Other revenue 1.8 (.1 ) 1.7 (22.8 ) — — Total revenues 214.2 (.1 ) 214.2 266.6 .3 266.9 Expenses Loss and loss adjustment expenses 121.7 — 121.7 103.6 — 103.6 Insurance and reinsurance acquisition expenses 45.4 — 45.4 50.1 .1 50.2 Other underwriting expenses 24.8 — 24.8 29.7 .8 30.5 General and administrative expenses 9.4 — 9.4 6.3 — 6.3 Interest expense 6.6 — 6.6 6.6 — 6.6 Total expenses 207.9 — 207.9 196.3 .9 197.2 Pre-tax income (loss) 6.3 (.1 ) 6.2 70.3 (.6 ) 69.7 Income tax (expense) benefit (2.3 ) — (2.3 ) (13.1 ) .3 (12.8 ) Net income (loss) from discontinued operations 4.0 (.1 ) 3.9 57.2 (.3 ) 56.9 Net gain from sales of discontinued operations - FFIC — — — — 14.0 14.0 Net losses from sales of discontinued operations - OneBeacon — — — — (7.0 ) (7.0 ) Net gain from sales of discontinued operations - Esurance — 10.3 10.3 — — — Total income from discontinued operations $ 4.0 $ 10.2 $ 14.2 $ 57.2 $ 6.7 $ 63.9 Change in foreign currency translation and other from discontinued operations $ (18.4 ) $ — $ (18.4 ) $ (64.1 ) $ — $ (64.1 ) Comprehensive income from discontinued operations $ (14.4 ) $ 10.2 $ (4.2 ) $ (6.9 ) $ 6.7 $ (.2 ) Nine Months Ended Nine Months Ended September 30, 2015 September 30, 2014 Millions Sirius Group Other Disc Ops Total Sirius Group Other Disc Ops Total Revenues Earned insurance premiums $ 623.3 $ — $ 623.3 $ 656.5 $ .1 $ 656.6 Net investment income 28.6 — 28.6 30.0 — 30.0 Net realized and unrealized gains 31.4 — 31.4 134.1 — 134.1 Other revenue (20.2 ) (.4 ) (20.6 ) (47.3 ) — (47.3 ) Total revenues 663.1 (.4 ) 662.7 773.3 .1 773.4 Expenses Loss and loss adjustment expenses 311.3 — 311.3 273.8 (.7 ) $ 273.1 Insurance and reinsurance acquisition expenses 135.5 — 135.5 146.3 .1 $ 146.4 Other underwriting expenses 78.0 — 78.0 91.7 2.2 $ 93.9 General and administrative expenses 22.4 — 22.4 21.6 — $ 21.6 Interest expense 20.0 — 20.0 19.8 — $ 19.8 Total expenses 567.2 — 567.2 553.2 1.6 554.8 Pre-tax income (loss) 95.9 (.4 ) 95.5 220.1 (1.5 ) 218.6 Income tax (expense) benefit (22.2 ) — (22.2 ) (52.4 ) .6 $ (51.8 ) Net income (loss) from discontinued operations 73.7 (.4 ) 73.3 167.7 (.9 ) 166.8 Net gain from sales of discontinued operations - FFIC — — — — 14.0 $ 14.0 Net losses from sales of discontinued operations - OneBeacon — .3 .3 — (7.5 ) $ (7.5 ) Net gain from sales of discontinued operations - Esurance — 17.9 17.9 — 3.2 $ 3.2 Total income from discontinued operations $ 73.7 $ 17.8 $ 91.5 $ 167.7 $ 8.8 $ 176.5 Change in foreign currency translation and other from discontinued operations $ (62.1 ) $ — $ (62.1 ) $ (99.9 ) $ — $ (99.9 ) Comprehensive income from discontinued operations $ 11.6 $ 17.8 $ 29.4 $ 67.8 $ 8.8 $ 76.6 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: Nine Months Ended September 30, (Millions) 2015 2014 Net cash provided from operations $ 6.7 $ 49.8 Net cash provided from investing activities 35.7 47.5 Net cash used for financing activities (2.4 ) (55.6 ) Effect of exchange rate changes on cash (4.1 ) (10.6 ) Net change in cash during the period 35.9 31.1 Cash balances at beginning of period 111.5 93.2 Cash balances at end of period $ 147.4 $ 124.3 Supplemental cash flows information: Interest paid $ (25.5 ) $ (34.9 ) Net income tax (payment to) refund from national governments $ (30.3 ) $ 7.5 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 nine months ended September 30, 2015 and 2014 : Three Months Ended Nine Months Ended September 30, September 30, 2015 2014 2015 2014 Basic and diluted earnings per share numerators (in millions): Net income attributable to White Mountains’s common shareholders $ 14.2 $ 63.9 $ 91.5 $ 176.5 Allocation of income for participating unvested restricted common shares (1) (.2 ) (.9 ) (1.0 ) (2.2 ) Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts (2) $ 14.0 $ 63.0 $ 90.5 $ 174.3 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 5,890.1 6,091.4 5,951.1 6,140.9 Average unvested restricted common shares (3) (70.9 ) (81.3 ) (67.1 ) (77.7 ) Basic earnings per share denominator 5,819.2 6,010.1 5,884.0 6,063.2 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 5,890.1 6,091.4 5,951.1 6,140.9 Average unvested restricted common shares (3) (70.9 ) (81.3 ) (67.1 ) (77.7 ) Average outstanding dilutive options to acquire common shares (4) — — — — Diluted earnings per share denominator 5,819.2 6,010.1 5,884.0 6,063.2 Basic and diluted earnings per share (in dollars): $ 2.41 $ 10.49 $ 15.37 $ 28.74 (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 nine months ended September 30, 2015 and 2014 . (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 nine months ended September 30, 2015 and 2014 does not include the impact of 125,000 common shares issuable upon exercise of the non-qualified options outstanding as they are anti-dilutive to the calculation.
Interest Rate Cap [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Fair Value of Assets and Liabilities Measured on Recurring and Non-recurring Basis Table	The following tables summarize the changes in the fair value of the Interest Rate Cap for the three and nine months ended September 30, 2015 and 2014: Three Months Ended Nine Months Ended September 30, September 30, Millions 2015 2014 2015 2014 Beginning of period $ 3.3 $ 6.2 $ 4.1 $ 11.1 Net realized and unrealized losses (1.1 ) (.8 ) (1.9 ) (5.7 ) End of period $ 2.2 $ 5.4 $ 2.2 $ 5.4
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Summary of the fair value and carrying value of financial instruments	The following table summarizes the fair value and carrying value of these financial instruments as of September 30, 2015 and December 31, 2014 : September 30, 2015 December 31, 2014 Millions Fair Value Carrying Value Fair Value Carrying Value SIG Senior Notes $ 423.6 $ 399.8 $ 437.8 $ 399.7 SIG Preference Shares 252.5 250.0 260.0 250.0

Summary of Significant Accoun41

Summary of Significant Accounting Policies (Basis of Presentation) (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Jun. 30, 2014	Jul. 31, 2012
Basis of Presentation
Net investment income	$ 16.8		$ 13.8	$ 42.6	$ 44.7
Income Tax Expense (Benefit)	$ (1.6)		(4.7)	$ 0.8	11.4
OneBeacon Ltd.
Basis of Presentation
Cumulative Effect on Retained Earnings, Net of Tax						$ 0.9	$ 0.5
Ownership interest (as a percent)	75.30%			75.30%		75.30%
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	$ 20			$ 20
Noncontrolling equity percentage	100.00%			100.00%		100.00%
White Mountains Advisors L L C [Member]
Basis of Presentation
Investment Advisory, Management and Administrative Fees	$ 2		3.2	$ 5.9	9.2
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%
Accounting Standards Update 2014-01 [Member] \| Restatement Adjustment [Member] \| OneBeacon Ltd.
Basis of Presentation
Net investment income			0.4		1.3
Income Tax Expense (Benefit)			$ 0.6		$ 1.8
OneBeacon Runoff [Member]
Basis of Presentation
Proceeds from Sale of Buildings		$ 58
Surplus Notes								$ 80.9

Significant Transactions (Detai

Significant Transactions (Details) $ / shares in Units, ₪ in Millions, $ in Millions	1 Months Ended			2 Months Ended				3 Months Ended						9 Months Ended
	Sep. 30, 2015USD ($)$ / shares	Jan. 31, 2014USD ($)	Oct. 31, 2011USD ($)	Feb. 23, 2015ILS (₪)	Feb. 23, 2015USD ($)	Feb. 19, 2014ILS (₪)business	Feb. 19, 2014USD ($)business	Sep. 30, 2015USD ($)$ / shares	Jun. 30, 2015ILS (₪)	Jun. 30, 2015USD ($)	Dec. 31, 2014USD ($)	Sep. 30, 2014USD ($)	Mar. 31, 2014USD ($)	Sep. 30, 2015USD ($)$ / shares	Sep. 30, 2014USD ($)	Sep. 01, 2015USD ($)	Jul. 27, 2015USD ($)	Oct. 10, 2014USD ($)	Jul. 01, 2014	Jun. 30, 2014USD ($)	Mar. 14, 2014USD ($)	Dec. 31, 2013USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Investments	$ 3,709.5							$ 3,709.5			$ 3,742.4			$ 3,709.5
Loss and loss adjustment expenses								170				$ 185.5		534.1	$ 527.3
Payments to Acquire Businesses and Interest in Affiliates														33.3	32.2
Assets	10,346							10,346			10,455.7			10,346
Goodwill	189.3							189.3		$ 169.2	168.9	23.8		189.3	23.8					$ 23.8		$ 0
Intangible Assets, Net (Excluding Goodwill)	192.4							192.4		$ 171.2	182.3	42		192.4	42					$ 44.6		$ 5.1
Goodwill and intangible assets	381.7							381.7			351.2			381.7
Liabilities	6,139.7							6,139.7			5,917.3			6,139.7
Payments to Acquire Additional Interest in Subsidiaries														9.1	0
Net Income (Loss) Attributable to Noncontrolling Interest								16				11.2		24.2	7.2
QuoteLab
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Combination, Contingent Consideration, Liability											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
Enterprise Value of Subsidiary																		$ 281.2
Proceeds from Contributions from Affiliates											44.2
Ownership interest (as a percent)																		63.20%
Assets																		$ 332.8
Tangible Assets																		41.4
Goodwill																		145.1
Intangible Assets, Net (Excluding Goodwill)																		146.3
Liabilities																		$ 108.7
TruBridge [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Enterprise Value of Subsidiary																$ 50.2
PPCI Global Ltd. [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share										50
Payments to Acquire Interest in Subsidiaries and Affiliates										$ 21
OneTitle [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Agreed Upon Commitment of Contributed Capital										13
Star & Shield Insurance Exchange
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase of Surplus Notes	20							20						20
Assets	16.3							16.3			13.5			16.3
Liabilities	$ 31.5							$ 31.5			$ 25.9			$ 31.5
MediaAlpha
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Combination, Contingent Consideration, Liability										$ 7.9
Payments to Acquire Businesses and Interest in Affiliates													$ 28.1
Percentage of gross profit																					62.50%
Assets																					$ 70.1
Goodwill																					18.3
Goodwill and intangible assets																					38.5
Liabilities																					$ 10
WOBI
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Premiums Written, Percentage of Total						85.00%	85.00%
Number of lines of business \| business						4	4
Goodwill							$ 5.5
Liabilities							$ 0.7
Star & Shield LLC [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Businesses and Interest in Affiliates		$ 1.8
Common Class A \| durchblicker.at [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest (as a percent)																			45.00%
Common Class A \| MediaAlpha
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest (as a percent)																					60.00%
Common Stock \| TruBridge [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest (as a percent)																100.00%
Common Stock \| Cashboard [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest (as a percent)					56.20%					68.30%
Common Stock \| WOBI
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest (as a percent)	95.30%						54.00%	95.30%						95.30%
Non-controlling interest \| Star & Shield Insurance Exchange
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interest								$ (0.9)				1.4		$ (2.8)	$ 11.1
Common Stock \| TruBridge [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Businesses and Interest in Affiliates	$ 31
Euro Member Countries, Euro \| Common Stock \| durchblicker.at [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Businesses and Interest in Affiliates												8.5
Israel, New Shekels
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Interest in Subsidiaries and Affiliates \| ₪									₪ 10
Israel, New Shekels \| Convertible Preferred Stock [Member] \| WOBI
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Additional Interest in Subsidiaries \| ₪									25
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 \| ₪									₪ 35
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 \| ₪				₪ 9.5
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
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Interest in Subsidiaries and Affiliates										$ 2.6
United States of America, Dollars \| Convertible Preferred Stock [Member] \| WOBI
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Additional Interest in Subsidiaries										6.6
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										$ 9.1
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							$ 8.5
United States of America, Dollars \| Common Stock \| durchblicker.at [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Businesses and Interest in Affiliates												$ 11.7
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					$ 2.4
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 Businesses and Interest in Affiliates							4.1
TruBridge [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets																$ 53.8
Goodwill																20.1
Intangible Assets, Net (Excluding Goodwill)																28.1
Liabilities																$ 3.6
Goodwill, Purchase Accounting Adjustments														9.7
Cashboard [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets					5.5
Goodwill					0.3
Intangible Assets, Net (Excluding Goodwill)					2.8
Liabilities					$ 1.2
WOBI
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets							13.4
Intangible Assets, Net (Excluding Goodwill)							$ 2.9
Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of common shareholder's equity																	127.30%
Investments	510.8							510.8						510.8
Sale of Sirius [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Additional cash that will be paid as part of the purchase price																	$ 10
Crop insurance [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ceded Premiums Written								35.9
Ceded Premiums Earned								16.8
Loss and loss adjustment expenses								15.1
Ceded insurance Acquisition Expenses								2.8
Proceeds related from termination of agreement	$ 3							$ 3						$ 3
Symetra
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest (as a percent)	17.70%							17.70%			17.31%			17.70%
Dividends \| $ / shares								$ 0.50
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						$ 32

Loss and Loss Adjustment Expe43

Loss and Loss Adjustment Expense Reserves (Loss and Loss Adjustment Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Loss and Loss Adjustment Expense Reserve
Gross beginning balance	$ 1,357	$ 1,137.8	$ 1,350	$ 1,054.3
Less beginning reinsurance recoverable on unpaid losses	(147.2)	(92.1)	(161.7)	(80.2)
Net loss and LAE reserves	1,209.8	1,045.7	1,188.3	974.1
Loss and LAE incurred relating to current year losses	170.4	178.4	536.7	511
Net (favorable) and unfavorable loss reserve development	(0.4)	7.1	(2.6)	16.3
Total incurred losses and LAE	170	185.5	534.1	527.3
Current year losses	(53)	(55.9)	(120.2)	(116.5)
Prior year losses	(108.1)	(107.3)	(383.5)	(330.5)
Total loss and LAE payments	(161.1)	(163.2)	(503.7)	(447)
Net ending balance	1,218.7	1,068	1,218.7	1,068
Plus ending reinsurance recoverable on unpaid losses	214.6	101.5	214.6	101.5
Gross ending balance	1,433.3	1,169.5	1,433.3	1,169.5
Star & Shield Insurance Exchange
Loss and Loss Adjustment Expense Reserve
Loss and LAE reserves consolidated — SSIE	0	0	0	13.6
Net (favorable) and unfavorable loss reserve development	$ (0.4)	$ (0.2)	$ (0.8)	$ 2

Loss and Loss Adjustment Expe44

Loss and Loss Adjustment Expense Reserves Details (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Loss and Loss Adjustment, Expense Reserves [Line Items]
Net (favorable) and unfavorable loss reserve development	$ (0.4)	$ 7.1	$ (2.6)	$ 16.3
Star & Shield Insurance Exchange
Loss and Loss Adjustment, Expense Reserves [Line Items]
Net (favorable) and unfavorable loss reserve development	$ (0.4)	(0.2)	(0.8)	2
OneBeacon
Loss and Loss Adjustment, Expense Reserves [Line Items]
Net (favorable) and unfavorable loss reserve development		$ 7.3	$ (1.8)	$ 14.3

Third Party Reinsurance (One Be

Third Party Reinsurance (One Beacon) (Details) - USD ($) $ in Millions	4 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015	Dec. 31, 2014
Reinsurance Retention Policy [Line Items]
Reinsurance recoverable on paid losses	$ 22.6	$ 22.6	$ 12.2
Reinsurance recoverable on unpaid losses	214.6	214.6	161.7
OneBeacon
Reinsurance Retention Policy [Line Items]
Reinsurance recoverable on paid losses	22.6	22.6	12.2
Reinsurance recoverable on unpaid losses	214.2	$ 214.2	$ 161.6
Crop insurance [Member] \| OneBeacon
Reinsurance Retention Policy [Line Items]
Percentage of par value of policy reinsured		52.00%
Reinsurance Retention Policy, Loss Ratio Reinsured risk, Percentage		98.00%
Percentage of Quota Share Reinsurance Agreement		30.00%
Crop-hail insurance [Member] \| OneBeacon
Reinsurance Retention Policy [Line Items]
Percentage of par value of policy reinsured		80.00%
Reinsurance Retention Policy, Loss Ratio Reinsured risk, Percentage		100.00%
Crop-hail and multiple peril crop insurance [Member] \| OneBeacon
Reinsurance Retention Policy [Line Items]
Percentage of par value of policy reinsured		100.00%
OneBeacon
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Excess Retention, Amount Reinsured		$ 130
Reinsurance Retention Policy, Amount Retained		$ 20
OneBeacon \| Combination One
Reinsurance Retention Policy [Line Items]
Percentage of par value of policy reinsured		95.00%
Reinsurance Retention Policy Excess Retention Amount Reinsured Net Of Participation		$ 10
OneBeacon \| Minimum \| Property [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Amount Retained		3
OneBeacon \| Minimum \| Health Care [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Amount Retained	3
OneBeacon \| Maximum \| Property [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Amount Retained		$ 5
OneBeacon \| Maximum \| Health Care [Member]
Reinsurance Retention Policy [Line Items]
Reinsurance Retention Policy, Amount Retained	$ 5
OneBeacon \| Combination Two
Reinsurance Retention Policy [Line Items]
Percentage of par value of policy reinsured		100.00%
Reinsurance Retention Policy Excess Retention Amount Reinsured Net Of Participation		$ 100

Investment Securities (Net Inve

Investment Securities (Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Investment income
Total investment income	$ 17.1	$ 17.3	$ 47.2	$ 54.2
External investment expenses	(0.3)	(3.5)	(4.6)	(9.5)
Net investment income, pre-tax	16.8	13.8	42.6	44.7
Fixed maturity investments.
Investment income
Total investment income	13.7	12.7	38.5	38.4
Short-term investments
Investment income
Total investment income	0	0.1	0.1	0.2
Common Stock
Investment income
Total investment income	1.4	3.3	5.7	11.9
Convertible fixed maturity investments
Investment income
Total investment income	0.1	1	0.4	1.5
Other long-term investments
Investment income
Total investment income	$ 1.9	$ 0.2	$ 2.5	$ 2.2

Investment Securities (Net Real

Investment Securities (Net Realized and Unrealized Investment Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	$ (7.4)	$ 58	$ 49.3	$ 97.1
Trading Securities, Realized Gain (Loss), Total	(7.4)	57.9	49.7	97
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(36.5)	(85.4)	(83.6)	(32.6)
Net Realized and Unrealized Gain (Loss) on Trading Securities	(43.9)	(27.5)	(33.9)	64.4
Income tax benefit (expense) attributable to net realized and unrealized investment gains (losses)	9.4	5.6	6.9	(12.2)
Realized and unrealized gain	(34.5)	(21.9)	(27)	52.2
Foreign Currency Transaction Gain (Loss), Realized	0	(0.1)	0.4	(0.1)
Trading securities, Tax on Realized Holding Gain (Loss) on Investments	1.5	(7)	(15.7)	(13.3)
Trading Securities, Tax on Realized Foreign Currency Transaction Gain (Loss) Tax	0	0	0	0
Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	1.5	(7)	(15.7)	(13.3)
Trading Securities Realized Holding Gain (Loss) on Investments after Tax	(5.9)	51	33.6	83.8
Trading Securities, Realized Foreign Currency Gain (Loss) Net of Tax	0	(0.1)	0.4	(0.1)
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	(5.9)	50.9	34	83.7
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	(0.1)	2.3	2	4.7
Trading Securities, Realized Gain (Loss), Total	(0.1)	2.2	2	4.6
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	3.3	(10)	1.3	12.3
Foreign Currency Transaction Gain (Loss), Realized	0	(0.1)	0	(0.1)
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	0	0	0	0
Trading Securities, Realized Gain (Loss), Total	0	0	0	0
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	0	0	0	0
Foreign Currency Transaction Gain (Loss), Realized	0	0	0	0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	(5.9)	51.4	41.6	83.2
Trading Securities, Realized Gain (Loss), Total	(5.9)	51.4	42	83.2
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(30.8)	(69.2)	(58.5)	(48.5)
Foreign Currency Transaction Gain (Loss), Realized	0	0	0.4	0
Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	0	1.6	(4.3)	6.5
Trading Securities, Realized Gain (Loss), Total	0	1.6	(4.3)	6.5
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	1.1	(3.4)	2	(5.1)
Foreign Currency Transaction Gain (Loss), Realized	0	0	0	0
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	(1.4)	2.7	10	2.7
Trading Securities, Realized Gain (Loss), Total	(1.4)	2.7	10	2.7
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(10.1)	(2.8)	(28.4)	8.7
Foreign Currency Transaction Gain (Loss), Realized	$ 0	$ 0	$ 0	$ 0

Investment Securities (Net Re48

Investment Securities (Net Realized Investment Gains (Losses)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	$ (7.4)	$ 58	$ 49.3	$ 97.1
Trading securities, Tax on Realized Holding Gain (Loss) on Investments	1.5	(7)	(15.7)	(13.3)
Trading securities realized holding gain (loss) on investments after tax	(5.9)	51	33.6	83.8
Foreign Currency Transaction Gain (Loss), Realized	0	(0.1)	0.4	(0.1)
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)	0.4	(0.1)
Trading Securities, Realized Gain (Loss), Total	(7.4)	57.9	49.7	97
Tax on Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	1.5	(7)	(15.7)	(13.3)
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	(5.9)	50.9	34	83.7
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	(0.1)	2.3	2	4.7
Foreign Currency Transaction Gain (Loss), Realized	0	(0.1)	0	(0.1)
Trading Securities, Realized Gain (Loss), Total	(0.1)	2.2	2	4.6
Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	0	0	0	0
Foreign Currency Transaction Gain (Loss), Realized	0	0	0	0
Trading Securities, Realized Gain (Loss), Total	0	0	0	0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	(5.9)	51.4	41.6	83.2
Foreign Currency Transaction Gain (Loss), Realized	0	0	0.4	0
Trading Securities, Realized Gain (Loss), Total	(5.9)	51.4	42	83.2
Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	0	1.6	(4.3)	6.5
Foreign Currency Transaction Gain (Loss), Realized	0	0	0	0
Trading Securities, Realized Gain (Loss), Total	0	1.6	(4.3)	6.5
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities, Realized Gain (Loss)	(1.4)	2.7	10	2.7
Foreign Currency Transaction Gain (Loss), Realized	0	0	0	0
Trading Securities, Realized Gain (Loss), Total	$ (1.4)	$ 2.7	$ 10	$ 2.7

Investment Securities (Net Unre

Investment Securities (Net Unrealized Investment Gains (Losses)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	$ (36.3)	$ (80.1)	$ (80.3)	$ (27.3)
Trading Securities, Tax on Unrealized Holding Gain (Loss) on Investments	7.9	12.6	22.6	1.1
Trading Securities Unrealized Holding Gain (Loss) on Investments after Tax	(28.4)	(67.5)	(57.7)	(26.2)
Foreign Currency Transaction Gain (Loss), Unrealized	(0.2)	(5.3)	(3.3)	(5.3)
Trading Securities, Unrealized Foreign Currency Transaction Gain (Loss) Tax	0	0	0	0
Trading Securities, Unrealized Foreign Currency Gain (Loss) Net of Tax	(0.2)	(5.3)	(3.3)	(5.3)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(36.5)	(85.4)	(83.6)	(32.6)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Tax	7.9	12.6	22.6	1.1
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	(28.6)	(72.8)	(61)	(31.5)
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	3.3	(10)	1.3	12.3
Foreign Currency Transaction Gain (Loss), Unrealized	0	0	0	0
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	3.3	(10)	1.3	12.3
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 Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	0	0	0	0
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	(30.6)	(63.9)	(56)	(43.2)
Foreign Currency Transaction Gain (Loss), Unrealized	(0.2)	(5.3)	(2.5)	(5.3)
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(30.8)	(69.2)	(58.5)	(48.5)
Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	1.1	(3.4)	2	(5.1)
Foreign Currency Transaction Gain (Loss), Unrealized	0	0	0	0
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	1.1	(3.4)	2	(5.1)
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	(10.1)	(2.8)	(27.6)	8.7
Foreign Currency Transaction Gain (Loss), Unrealized	0	0	(0.8)	0
Net Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	$ (10.1)	$ (2.8)	$ (28.4)	$ 8.7

Investment Securities (Investme

Investment Securities (Investment gains (losses) for Level 3) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	$ (36.3)	$ (80.1)	$ (80.3)	$ (27.3)
Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	3.3	(10)	1.3	12.3
Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	(30.6)	(63.9)	(56)	(43.2)
Convertible Debt Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	1.1	(3.4)	2	(5.1)
Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	(10.1)	(2.8)	(27.6)	8.7
Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	(8.8)	(0.3)	(23.2)	4.1
Level 3 Inputs \| Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	(1)	2.1	(0.9)	2.7
Level 3 Inputs \| Common equity securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	1.1	1	4	3.8
Level 3 Inputs \| Convertible Debt Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	1.1	0.1	1.8	3.3
Level 3 Inputs \| Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unrealized gains (losses) on investments	$ (10)	$ (3.5)	$ (28.1)	$ (5.7)

Investment Securities (Invest51

Investment Securities (Investment Holdings Fixed Maturity Table) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity investments, at fair value	$ 2,602.2	$ 2,422
U.S. Government and agency obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	99.6	105.4
Trading Securities, Unrealized Holding Gain	0.2	0.1
Trading Securities, Unrealized Holding Loss	0	(0.3)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	99.8	105.2
Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	998.6	1,162
Trading Securities, Unrealized Holding Gain	8.7	13.1
Trading Securities, Unrealized Holding Loss	(1.5)	(3.4)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	1,005.8	1,171.7
Municipal obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	145.8	81
Trading Securities, Unrealized Holding Gain	1.8	1.4
Trading Securities, Unrealized Holding Loss	(0.8)	(0.2)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	146.8	82.2
Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	1,261.2	967.5
Trading Securities, Unrealized Holding Gain	6.4	2.8
Trading Securities, Unrealized Holding Loss	(2.2)	(2.4)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	1,265.4	967.9
Foreign government, agency and provincial obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	1	11.5
Trading Securities, Unrealized Holding Gain	0.3	0.3
Trading Securities, Unrealized Holding Loss	0	(1)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	1.3	10.8
Preferred Stock
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	78.3	78.3
Trading Securities, Unrealized Holding Gain	4.8	5.9
Trading Securities, Unrealized Holding Loss	0	0
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	83.1	84.2
Fixed Income Investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	2,584.5	2,405.7
Trading Securities, Unrealized Holding Gain	22.2	23.6
Trading Securities, Unrealized Holding Loss	(4.5)	(7.3)
Net foreign currency gains (losses)	0	0
Total fixed maturity investments including assets held for sale	$ 2,602.2	$ 2,422

Investment Securities (Invest52

Investment Securities (Investment Holding Common Equities/ Other Investments) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity investments, at fair value	$ 2,602.2	$ 2,422
Common Stock
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	453	495.3
Trading Securities, Unrealized Holding Gain	52	127.4
Trading Securities, Unrealized Holding Loss	(22.9)	(3.6)
Net foreign currency gains (losses)	0	(7.4)
Fixed maturity investments, at fair value	482.1	611.7
Convertible Debt Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	3.1	13.4
Trading Securities, Unrealized Holding Gain	2.5	0.8
Trading Securities, Unrealized Holding Loss	0	(0.3)
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	5.6	13.9
Other long-term investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or amortized cost	271.9	273.3
Trading Securities, Unrealized Holding Gain	37.7	52.5
Trading Securities, Unrealized Holding Loss	(12.9)	(6.5)
Net foreign currency gains (losses)	(2.1)	(1.3)
Fixed maturity investments, at fair value	$ 294.6	$ 318

Investment Securities (Other lo

Investment Securities (Other long-term investments) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Payments to Acquire Other Investments		$ 30.5	$ 26.8
Other Investments		294.6		$ 318
Partnership investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments		3.9		5.1
Hedge and private equity funds included in other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments		148.6		178.5
Surplus Note
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments		58		65.1
Limited Liability Companies and Private Equity Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments		65.3		45.3
Affordable Housing Development Fund [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments		15.2	$ 17.3	16.8	$ 19.1
Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments		3.6		7.2
PassportCard [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Payments to Acquire Other Investments	$ 21
Hedge Funds, Equity Long (Short) [Member] \| Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unfunded Commitments		0		0
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		20.4
Unfunded Commitments		$ 0		$ 0

Investment Securities (Hedge Fu

Investment Securities (Hedge Funds and Private Equity Funds) (Details) $ in Millions	Sep. 30, 2015USD ($)fund	Jun. 30, 2015USD ($)	Dec. 31, 2014USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	$ 294.6		$ 318
Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of investments \| fund	10
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of investments \| fund	22
Hedge and private equity funds included in other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Largest single fund investment		$ 22.3

Investment Securities (Fair Val

Investment Securities (Fair Value of Hedge Funds and Private Equity Funds) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	$ 55.6
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	93
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	148.6	$ 178.5
Unfunded Commitments	86.1	64.3
Private equity funds \| Private Equity Multi Sector
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	14.9	14.5
Unfunded Commitments	2.1	2.2
Private equity funds \| Private Equity Energy Infrastructure and Services
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	26.3	33.1
Unfunded Commitments	4	4.8
Private equity funds \| Real Estate Funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	0.8	1.7
Unfunded Commitments	0.1	0.1
Private equity funds \| Private Equity Secondaries
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	4.5	5.7
Unfunded Commitments	2.1	2.1
Private equity funds \| Private Equity Funds Manufacturing and Industrial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	23.5	23.2
Unfunded Commitments	2.5	7.3
Private equity funds \| Private Equity Healthcare
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	3.9	3.1
Unfunded Commitments	0.4	1.4
Private equity funds \| Private Equity Insurance
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	2	2.1
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	17.1	20.7
Unfunded Commitments	33.6	5.1
Private equity funds \| Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	93	104.1
Unfunded Commitments	86.1	64.3
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	15.4	29.9
Hedge funds \| Hedge Funds, Equity Long (Short) [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
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	20.4
Unfunded Commitments	0	0
Hedge funds \| Hedge Funds, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	12.1	15.7
Hedge funds \| Hedge Funds Bank Loan [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Unfunded Commitments	0	0
Hedge funds \| Hedge Funds Credit and Distressed
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	8.1	8.4
Unfunded Commitments	0	0
Hedge funds \| Hedge funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	55.6	74.4
Unfunded Commitments	$ 0	$ 0

Investment Securities (Restrict

Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) - Hedge funds $ in Millions	Sep. 30, 2015USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Distributions from Inactive Hedge Funds	$ 1
Other long-term investments	55.6
Redemption requests	22.1
30-59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	16.4
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	28.1
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	2.7
120+ days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	8.4
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
Monthly \| 120+ days notice
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	32.9
Quarterly \| 30-59 days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	16.4
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	8.1
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
Quarterly \| 120+ days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	8.4
Semi-annual
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	20
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
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
Semi-annual \| 120+ days notice
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	2.7
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	2.7
Annual \| 120+ days notice
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	$ 0

Investment Securities (Invest57

Investment Securities (Investments In Private Equity Funds Subject to Lock-Up Periods) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interest	$ (16)	$ (11.2)	$ (24.2)	$ (7.2)
Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	93		93
1-3 years \| Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	25.8		25.8
3-5 years \| Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	11.1		11.1
5-10 years \| Private equity funds
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other long-term investments	56.1		56.1
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 (Fair V58

Investment Securities (Fair Value Measurements) (Details) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
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
Fair value, investment-related liabilities		$ 31.6

Investment Securities (Fair V59

Investment Securities (Fair Value Measurement by Level) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,365.4	$ 3,343.6	$ 3,610.7	$ 3,889
Other Investments	294.6	318
Short-term investments, at amortized cost (which approximates fair value)	325	376.8
Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	418.2	550.6	766.2	997.2
Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,561.6	2,372.9	2,495.9	2,575.4
Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,005.8	1,171.7
Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,265.4	967.9
Mortgage-backed and asset-backed securities \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,265.4	967.9
Mortgage-backed and asset-backed securities \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fixed maturity investments. \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	70.3	76.4	88	81.8
Common equity securities \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	34.2	39.5	38.2	45.4
Convertible fixed maturity investments \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	5.6	8.2	10.9	6.1
Other long-term investments \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	275.5	296	211.5	183.1
Fair value measured on a recurring basis
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	3,690.4	3,720.4
Fair value measured on a recurring basis \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	743.2	926.9
Fair value measured on a recurring basis \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,561.6	2,373.4
Fair value measured on a recurring basis \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	385.6	420.1
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	99.8	105.2
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	61.8	51.2
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	38	54
Fair value measured on a recurring basis \| U.S. Government and agency obligations \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,005.8	1,171.7
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,005.8	1,166.4
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	5.3
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	223.1	259.2
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Consumer \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Consumer \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	223.1	259.2
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Consumer \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Industrial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	132.8	107.3
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Industrial \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Industrial \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	132.8	102
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	5.3
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	201.3	254.7
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Financials \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Financials \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	201.3	254.7
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Financials \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Communications [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	52.7	71.5
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Communications [Member] \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Communications [Member] \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	52.7	71.5
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Communications [Member] \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Health Care [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	177.2	181.8
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Health Care [Member] \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Health Care [Member] \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	177.2	181.8
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Health Care [Member] \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Energy
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	57.8	65.6
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Energy \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Energy \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	57.8	65.6
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
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	64.7	88.3
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Technology \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Technology \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	64.7	88.3
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Technology \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Utilities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	62.5	84.1
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Utilities \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Utilities \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	62.5	84.1
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Utilities \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Materials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	31.4	51.7
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Materials \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Materials \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	31.4	51.7
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Materials \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Other:
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2.3	7.5
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Other: \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Other: \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2.3	7.5
Fair value measured on a recurring basis \| Debt securities issued by corporations \| Other: \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Municipal obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	146.8	967.9
Fair value measured on a recurring basis \| Municipal obligations \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Municipal obligations \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	146.8	967.9
Fair value measured on a recurring basis \| Municipal obligations \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,265.4	10.8
Fair value measured on a recurring basis \| Mortgage-backed and asset-backed securities \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0.6
Fair value measured on a recurring basis \| Mortgage-backed and asset-backed securities \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,265.4	10.2
Fair value measured on a recurring basis \| Mortgage-backed and asset-backed securities \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Foreign government, agency and provincial obligations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1.3	84.2
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	0.6	0
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	0.7	13.1
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	71.1
Fair value measured on a recurring basis \| Preferred Stock
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	83.1	82.2
Fair value measured on a recurring basis \| Preferred Stock \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Preferred Stock \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	12.8	82.2
Fair value measured on a recurring basis \| Preferred Stock \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	70.3	0
Fair value measured on a recurring basis \| Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,602.2	2,422
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	62.4	51.8
Fair value measured on a recurring basis \| Fixed maturity investments. \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,469.5	2,293.8
Fair value measured on a recurring basis \| Fixed maturity investments. \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	70.3	76.4
Fair value measured on a recurring basis \| Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	325	376.8
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	325	376.3
Short-term investments, at amortized cost (which approximates fair value)	325	376.8	402.7	310.4
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	0.5
Fair value measured on a recurring basis \| Short-term investments \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Consumer
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	56.5	116
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	56.5	115.9
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	0.1
Fair value measured on a recurring basis \| Common equity securities \| Consumer \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Industrial
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	25.2	57.1
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	25.2	57.1
Fair value measured on a recurring basis \| Common equity securities \| Industrial \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Industrial \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Financials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	63.2	180.7
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	29	141.2
Fair value measured on a recurring basis \| Common equity securities \| Financials \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Financials \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	34.2	39.5
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	36	28.5
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	36	28.5
Fair value measured on a recurring basis \| Common equity securities \| Communications [Member] \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Communications [Member] \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Health Care [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	34.5	74.4
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	34.5	74.4
Fair value measured on a recurring basis \| Common equity securities \| Health Care [Member] \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Health Care [Member] \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Energy
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	18.1
Fair value measured on a recurring basis \| Common equity securities \| Energy \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	18.1
Fair value measured on a recurring basis \| Common equity securities \| Energy \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Energy \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Technology
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	22	44.8
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	22	44.8
Fair value measured on a recurring basis \| Common equity securities \| Technology \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Technology \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Utilities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	4.9
Fair value measured on a recurring basis \| Common equity securities \| Utilities \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	4.9
Fair value measured on a recurring basis \| Common equity securities \| Utilities \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Utilities \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Materials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	12
Fair value measured on a recurring basis \| Common equity securities \| Materials \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	12
Fair value measured on a recurring basis \| Common equity securities \| Materials \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Materials \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Other:
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	72.1	75.2
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	1.9
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	72.1	73.3
Fair value measured on a recurring basis \| Common equity securities \| Other: \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Common equity securities \| Exchange Traded Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	172.6
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	152.6
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	20
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
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	482.1	611.7
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	355.8	498.8
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	92.1	73.4
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	34.2	39.5
Fair value measured on a recurring basis \| Convertible fixed maturity investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	5.6	13.9
Fair value measured on a recurring basis \| Convertible fixed maturity investments \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Convertible fixed maturity investments \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	5.7
Fair value measured on a recurring basis \| Convertible fixed maturity investments \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	5.6	8.2
Fair value measured on a recurring basis \| Other long-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	275.5	296
Carrying value of investment accounted for using the equity method	3.9
Fair value measured on a recurring basis \| Other long-term investments \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Other long-term investments \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis \| Other long-term investments \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	275.5	296
Carrying value of investment accounted for using the equity method		5.2	5.1	6.8
Discontinued Operations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fixed maturity investments reclassified to assets held for sale			203.9	236.3
Affordable Housing Development Fund [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	15.2	16.8	$ 17.3	$ 19.1
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	$ 15.2	$ 16.8

Investment Securities (Debt sec

Investment Securities (Debt securities issued by corporation) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,365.4	$ 3,343.6	$ 3,610.7	$ 3,889
Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,005.8	1,171.7
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	112.3	144.9
A \| Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	439.7	594.9
BBB \| Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	453.8	426.5
BB \| Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0	0
Other \| Debt securities issued by corporations
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 0	$ 5.4

Investment Securities (Mortgage

Investment Securities (Mortgage-backed, Asset-backed Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,365.4	$ 3,343.6	$ 3,610.7	$ 3,889
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 133.7	$ 109.3

Investment Securities (Mortga62

Investment Securities (Mortgage-backed Asset Securities Table) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,365.4		$ 3,343.6	$ 3,610.7	$ 3,889
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	293.9		308.7
Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	41.6		33.4
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	24.8		28.9
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	360.3		371
Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	123.7		71
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	133.7		109.3
Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	257.4		180.3
Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	617.7		551.3
Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	293.3		218.1
Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	276.4		152.8
Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	78		45.7
Asset-backed Securities, Securitized Loans and Receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	647.7		416.6
Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,265.4		967.9
Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2,561.6		2,372.9	$ 2,495.9	$ 2,575.4
Level 2 Inputs \| Government National Mortgage Association Certificates and Obligations (GNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	293.9		308.7
Level 2 Inputs \| Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	41.6		33.4
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	24.8		28.9
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	360.3		371
Level 2 Inputs \| Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	123.7		71
Level 2 Inputs \| Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	133.7		109.3
Level 2 Inputs \| Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	257.4		180.3
Level 2 Inputs \| Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	617.7		551.3
Level 2 Inputs \| Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	293.3		218.1
Level 2 Inputs \| Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	276.4		152.8
Level 2 Inputs \| Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	78		45.7
Level 2 Inputs \| Asset-backed Securities, Securitized Loans and Receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	647.7		416.6
Level 2 Inputs \| Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	1,265.4		967.9
Level 3 Inputs \| Government National Mortgage Association Certificates and Obligations (GNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0		0
Level 3 Inputs \| Federal National Mortgage Association Certificates and Obligations (FNMA)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0		0
Level 3 Inputs \| Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0		0
Level 3 Inputs \| Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0		0
Level 3 Inputs \| Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0		0
Level 3 Inputs \| Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0		0
Level 3 Inputs \| Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0		0
Level 3 Inputs \| Collateralized Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0		0
Level 3 Inputs \| Collateralized Credit Card Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0		0
Level 3 Inputs \| Collateralized Auto Loans
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0		0
Level 3 Inputs \| Collateralized Securities, Other
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0		0
Level 3 Inputs \| Asset-backed Securities, Securitized Loans and Receivables
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0		0
Level 3 Inputs \| Mortgage-backed and asset-backed securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 0		$ 0
Maximum \| Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Loans and Leases Receivable, Ratio of Nonperforming Loans to All Loans		1.00%

Investment Securities (Non-agen

Investment Securities (Non-agency Mortgage-backed Securities) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,365.4	$ 3,343.6	$ 3,610.7	$ 3,889
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	40.5
Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	123.7	71
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	133.7	109.3
Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	257.4	$ 180.3
Securities Issued in 2004 \| Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	18.3
Securities Issued in 2004 \| Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued in 2004 \| Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	18.3
Securities Issued in 2005 \| Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	2.9
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	2.9
Securities Issued In 2006 \| Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	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	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	4.2
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	4.2
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	17.1
Securities Issued In 2010 \| Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	5.7
Securities Issued In 2010 \| Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	22.8
Securities Issued In 2011 \| Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	14.6
Securities Issued In 2011 \| Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued In 2011 \| Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	14.6
Securities Issued in 2012 \| Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	13.4
Securities Issued in 2012 \| Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	8.6
Securities Issued in 2012 \| Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	22
Securities Issued in 2013 \| Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	14.7
Securities Issued in 2013 \| Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	18.4
Securities Issued in 2013 \| Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	33.1
Securities Issued in 2014 \| Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	34.5
Securities Issued in 2014 \| Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	55.6
Securities Issued in 2014 \| Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	90.1
Securities Issued in 2015 [Member] \| Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	0
Securities Issued in 2015 [Member] \| Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	45.4
Securities Issued in 2015 [Member] \| Mortgage-backed Securities, Issued by Private Enterprises
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	45.4
Subordinate \| Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	42.2
Subordinate \| Commercial Mortgage Backed Securities Floating Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	40.5
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	82.7
Super Senior \| Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	9.6
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	35.1
Super Senior \| Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	9.6
Senior \| Commercial Mortgage Backed Securities Fixed Rate [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	41.4
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	88.6
Senior \| Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 41.4
Non-Agency Commercial Mortgage Backed Securities [Member] [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Basis points	2.50%

Investment Securities (Non-ag64

Investment Securities (Non-agency Residential Mortgage-backed Securities) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,365.4	$ 3,343.6	$ 3,610.7	$ 3,889
Non-Agency Residential Mortgage [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	44
Residential Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	123.7	$ 71
Residential Mortgage Backed Securities \| Super Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	35.1
Residential Mortgage Backed Securities \| Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	88.6
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	123.7
Prime \| Residential Mortgage Backed Securities \| Super Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	35.1
Prime \| Residential Mortgage Backed Securities \| Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	88.6
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	0
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	0
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-ag65

Investment Securities (Non-agency Commercial Mortgage-backed Securities) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 3,365.4	$ 3,343.6	$ 3,610.7	$ 3,889
Commercial Mortgage Backed Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	133.7	$ 109.3
Commercial Mortgage Backed Securities \| Super Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	9.6
Commercial Mortgage Backed Securities \| Senior
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	41.4
Commercial Mortgage Backed Securities \| Subordinate
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair value investments	$ 82.7
Non-Agency Commercial Mortgage Backed Securities [Member] [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Basis points	2.50%

Rollforward of Fair Value Measu

Rollforward of Fair Value Measurements by Level (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015USD ($)	Sep. 30, 2014USD ($)	Sep. 30, 2015USD ($)	Sep. 30, 2014USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			$ 3,343.6	$ 3,889
Total realized and unrealized (losses) gains			(32.7)	49.7
Amortization/Accretion			(15.2)	(14.3)
Purchases			1,672	2,016.2
Sales			(1,540.9)	(2,340.7)
Net change in investments related to (sales) purchases of consolidated affiliates				10.8
Fair Value, Assets Measured on Recurring Basis, Other			(61.4)
Transfers in			41.7	42.1
Transfers out			(41.7)	(42.1)
Balance at September 30, 2015	$ 3,365.4	$ 3,610.7	3,365.4	3,610.7
Other Investments	294.6		294.6		$ 318
Realized and unrealized gain	(34.5)	(21.9)	(27)	52.2
Net realized and unrealized investment (losses) gains	(43.9)	(27.5)	(33.9)	64.4
Short-term investments, at amortized cost (which approximates fair value)	325		$ 325		376.8
Maximum Percentage Differences Between Prices Provided by Pricing Services Considered Outliers			(5.00%)
Maximum price difference provided by pricing services			$ 1
Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			550.6	997.2
Total realized and unrealized (losses) gains			(19.5)	30.7
Amortization/Accretion			0	0.1
Purchases			550	661.2
Sales			(618.2)	(926.2)
Net change in investments related to (sales) purchases of consolidated affiliates				3.4
Fair Value, Assets Measured on Recurring Basis, Other			(43.5)
Transfers in			0	0
Transfers out			(1.2)	(0.2)
Balance at September 30, 2015	418.2	766.2	418.2	766.2
Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			2,372.9	2,575.4
Total realized and unrealized (losses) gains			0.6	12.5
Amortization/Accretion			(15.2)	(14.3)
Purchases			1,056	1,265.3
Sales			(894.4)	(1,392.5)
Net change in investments related to (sales) purchases of consolidated affiliates				7.4
Fair Value, Assets Measured on Recurring Basis, Other			0
Transfers in			41.7	42.1
Transfers out			0	0
Balance at September 30, 2015	2,561.6	2,495.9	2,561.6	2,495.9
Fixed maturity investments. \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			76.4	81.8
Total realized and unrealized (losses) gains			(0.9)	2.7
Amortization/Accretion			0	(0.1)
Purchases			35.3	45.5
Sales			0	0
Net change in investments related to (sales) purchases of consolidated affiliates				0
Fair Value, Assets Measured on Recurring Basis, Other			0
Transfers in			0	0
Transfers out			(40.5)	(41.9)
Balance at September 30, 2015	70.3	$ 88	70.3	$ 88
Number of Investments		6		6
Common equity securities \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			39.5	$ 45.4
Total realized and unrealized (losses) gains			7.7	3.7
Amortization/Accretion			0	0
Purchases			0	0
Sales			(9.4)	(10.9)
Net change in investments related to (sales) purchases of consolidated affiliates				0
Fair Value, Assets Measured on Recurring Basis, Other			(3.6)
Transfers in			0	0
Transfers out			0	0
Balance at September 30, 2015	34.2	$ 38.2	34.2	38.2
Convertible Debt Securities \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			8.2	6.1
Total realized and unrealized (losses) gains			(2.6)	3.3
Amortization/Accretion			0	0
Purchases			0	1.5
Sales			0	0
Net change in investments related to (sales) purchases of consolidated affiliates				0
Fair Value, Assets Measured on Recurring Basis, Other			0
Transfers in			0	0
Transfers out			0	0
Balance at September 30, 2015	5.6	10.9	5.6	10.9
Other long-term investments \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			296	183.1
Total realized and unrealized (losses) gains			(18)	(3.2)
Amortization/Accretion			0	0
Purchases			30.7	42.7
Sales			(18.9)	(11.1)
Net change in investments related to (sales) purchases of consolidated affiliates				0
Fair Value, Assets Measured on Recurring Basis, Other			(14.3)
Transfers in			0	0
Transfers out			0	0
Balance at September 30, 2015	275.5	211.5	275.5	211.5
Fair value measured on a recurring basis
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			3,720.4
Balance at September 30, 2015	3,690.4		3,690.4
Fair value measured on a recurring basis \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			926.9
Balance at September 30, 2015	743.2		743.2
Fair value measured on a recurring basis \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			2,373.4
Balance at September 30, 2015	2,561.6		2,561.6
Fair value measured on a recurring basis \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			420.1
Balance at September 30, 2015	385.6		385.6
Fair value measured on a recurring basis \| Fixed maturity investments.
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			2,422
Balance at September 30, 2015	2,602.2		2,602.2
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, 2015			51.8
Balance at September 30, 2015	62.4		62.4
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, 2015			2,293.8
Balance at September 30, 2015	2,469.5		2,469.5
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, 2015			76.4
Balance at September 30, 2015	70.3		70.3
Fair value measured on a recurring basis \| Convertible Debt Securities
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			13.9
Balance at September 30, 2015	5.6		5.6
Fair value measured on a recurring basis \| Convertible Debt Securities \| Level 1 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			0
Balance at September 30, 2015	0		0
Fair value measured on a recurring basis \| Convertible Debt Securities \| Level 2 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			5.7
Balance at September 30, 2015	0		0
Fair value measured on a recurring basis \| Convertible Debt Securities \| Level 3 Inputs
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			8.2
Balance at September 30, 2015	5.6		5.6
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, 2015			296
Balance at September 30, 2015	275.5		275.5
Carrying value of investment accounted for using the equity method	3.9		3.9
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, 2015			0
Balance at September 30, 2015	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, 2015			0
Balance at September 30, 2015	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, 2015			296
Balance at September 30, 2015	275.5		275.5
Carrying value of investment accounted for using the equity method		5.1		5.1	5.2	$ 6.8
Fair value measured on a recurring basis \| Short-term investments
Schedule of Trading Securities and Other Trading Assets [Line Items]
Balance at January 1, 2015			376.8
Balance at September 30, 2015	325		325
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, 2015			376.3
Balance at September 30, 2015	325		325
Short-term investments, at amortized cost (which approximates fair value)	325	402.7	325	402.7	376.8	310.4
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, 2015			0.5
Balance at September 30, 2015	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, 2015			0
Balance at September 30, 2015	0		0
Discontinued Operations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net realized and unrealized investment (losses) gains	(0.9)	48.3	31.4	134.1
Fixed maturity investments reclassified to assets held for sale		203.9		203.9		236.3
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 (losses) gains			0.8	0.5
Affordable Housing Development Fund [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Other Investments	15.2	$ 17.3	15.2	$ 17.3	16.8	$ 19.1
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	$ 15.2		$ 15.2		$ 16.8

Investment Securities (Signific

Investment Securities (Significant Unobservable Inputs) (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2015USD ($)Investment	Dec. 31, 2014USD ($)	Jun. 30, 2015input
Quantitative information for Level 3 Fair Value Measurements Assets
Number of Investments with Significant Unobseravble Inputs \| Investment	1
Conditional Prepayment Rate	12.00%
Discount Yield [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value Inputs, Discount Rate
NR \| Preferred Stock \| Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 70,300,000	$ 71,100,000
NR \| Preferred Stock \| Discount Yield [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Fair Value Inputs, Discount Rate	8.40%	7.10%
NR \| Convertible Preferred Stock [Member] \| Multiple of EBITA [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Unobservable Inputs \| input			0
Assets, Fair Value Disclosure	$ 5,600,000	$ 3,800,000
Share Price of Most Recent Transaction	6	6
NR \| Convertible Preferred Stock [Member] \| Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure		4,500,000
Share Price of Most Recent Transaction		0.71
NR \| Seller Priority Surplus Note [Member] \| Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 41,000,000	$ 44,000,000
Fair Value Inputs, Discount Rate	11.60%	9.30%
Timing of interest payments	5 years	5 years
Timing of principal payments	10 years	10 years
NR \| Pari Passu Surplus Note [Member] \| Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 17,000,000	$ 21,100,000
Fair Value Inputs, Discount Rate	18.30%	13.50%
Timing of interest payments	5 years	5 years
Timing of principal payments	15 years	10 years
CompareNow [Member] \| NR \| Private equity funds \| Average Share Price
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price of Most Recent Transaction	$ 1.06
Ironshore [Member] \| NR \| Private equity funds \| Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	34,200,000	$ 39,500,000
Ironshore [Member] \| NR \| Private equity funds \| Multiple of GAAP book value [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price of Most Recent Transaction		1.10
Ironshore [Member] \| NR \| Private equity funds \| Average Share Price
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price of Most Recent Transaction	17.16
durchblicker.at [Member] \| NR \| Private equity funds \| Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	9,600,000	10,400,000
Share Price of Most Recent Transaction	290.96	290.96
Centrus [Member] \| NR \| Debt securities issued by corporations \| Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure		$ 5,300,000
Fair Value Inputs, Discount Rate		10.00%
PassportCard [Member] \| NR \| Private equity funds \| Average Share Price
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price of Most Recent Transaction	$ 1
Minimum \| discount spread [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Basis points	0.45%
Minimum \| Default Rate [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Constant Default Rate	2.50%
Maximum \| discount spread [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Basis points	1.80%
Maximum \| Default Rate [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Constant Default Rate	8.75%
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%
PassportCard [Member] \| NR \| Private equity funds \| Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 21,000,000
CompareNow [Member] \| NR \| Private equity funds \| Recent transaction [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, Fair Value Disclosure	$ 20,100,000	$ 20,100,000
CompareNow [Member] \| NR \| Private equity funds \| Average Share Price
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price of Most Recent Transaction		$ 1.06

Goodwill and Other Intangible68

Goodwill and Other Intangible Assets (Details) ₪ in Millions, $ in Millions	1 Months Ended	2 Months Ended		9 Months Ended
	Sep. 30, 2015USD ($)	Feb. 23, 2015ILS (₪)	Feb. 23, 2015USD ($)	Sep. 30, 2015USD ($)	Sep. 30, 2014USD ($)	Sep. 01, 2015USD ($)	Jun. 30, 2015USD ($)	Dec. 31, 2014USD ($)	Jun. 30, 2014USD ($)	Dec. 31, 2013USD ($)
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Businesses and Interest in Affiliates				$ 33.3	$ 32.2
Assets	$ 10,346			10,346				$ 10,455.7
Goodwill	189.3			189.3	23.8		$ 169.2	168.9	$ 23.8	$ 0
Intangible Assets, Net (Excluding Goodwill)	192.4			192.4	$ 42		$ 171.2	182.3	$ 44.6	$ 5.1
Liabilities	6,139.7			$ 6,139.7				$ 5,917.3
TruBridge [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Enterprise Value of Subsidiary						$ 50.2
TruBridge [Member] \| Common Stock
Acquired Finite-Lived Intangible Assets [Line Items]
Ownership interest (as a percent)						100.00%
Cashboard [Member] \| Common Stock
Acquired Finite-Lived Intangible Assets [Line Items]
Ownership interest (as a percent)			56.20%				68.30%
Common Stock \| TruBridge [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Businesses and Interest in Affiliates	$ 31
Common Stock \| Israel, New Shekels \| Cashboard [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Businesses and Interest in Affiliates \| ₪		₪ 9.5
Common Stock \| United States of America, Dollars \| Cashboard [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Businesses and Interest in Affiliates			$ 2.4
TruBridge [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Assets						$ 53.8
Goodwill						20.1
Intangible Assets, Net (Excluding Goodwill)						28.1
Liabilities						$ 3.6
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 Intangible69

Goodwill and Other Intangible Assets - Goodwill Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Acquired Finite-Lived Intangible Assets [Line Items]
Goodwill	$ 189.3	$ 23.8	$ 189.3	$ 23.8	$ 169.2	$ 168.9	$ 23.8	$ 0
Intangible Assets, Net (Excluding Goodwill)	192.4	42	192.4	42	$ 171.2	$ 182.3	$ 44.6	$ 5.1
Goodwill, Acquired During Period	20.1	0	20.4	23.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	28.1	0	30.9	42.4
Disposition of Goodwill through disposition of business	0	0	0	0
Amortization of Intangible Assets	$ (6.9)	$ (2.6)	$ (20.8)	$ (5.5)

Debt (Details)

Debt (Details) - USD ($)	3 Months Ended	9 Months Ended
Debt (Details) - USD ($)	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Jul. 23, 2015	Dec. 31, 2014	Nov. 25, 2014	Oct. 10, 2014	Aug. 14, 2013
Debt Instrument
Total debt	$ 383,300,000	$ 383,300,000			$ 343,100,000
Repayments of Debt		92,900,000	$ 40,200,000
Draw down of debt and revolving line of credit		$ 134,000,000	$ 40,000,000
WTM Bank Facility
Debt Instrument
Total commitment under revolving credit facility								$ 425,000,000
Proceeds from Issuance of Debt	$ 60,000,000
Debt, Weighted Average Interest Rate	3.65%	3.65%
Repayments of Debt	$ 60,000,000
OB Bank Facility [Member]
Debt Instrument
Total commitment under revolving credit facility	65,000,000	$ 65,000,000
Other Debt [Member]
Debt Instrument
Total debt	0	0			1,000,000
OneBeacon \| 2012 OBH Senior Notes
Debt Instrument
Debt instrument at face value	275,000,000	275,000,000			275,000,000
Unamortized original issue discount	(200,000)	(200,000)			(300,000)
Total debt	274,800,000	274,800,000			274,700,000
White Mountains \| WTM Bank Facility
Debt Instrument
Total debt	0	0			0
Tranzact [Member] \| Tranzact Bank Facility [Member]
Debt Instrument
Long-term Line of Credit	95,800,000	95,800,000			68,700,000
Unamortized Debt Issuance Expense	(2,000,000)	(2,000,000)			(1,300,000)
Line of Credit Facility, Fair Value of Amount Outstanding	93,800,000	93,800,000			67,400,000
Total commitment under revolving credit facility	116,000,000	116,000,000
Notional amount	101,000,000	101,000,000					$ 70,000,000
Line of Credit Facility, Remaining Borrowing Capacity	15,000,000	15,000,000
Proceeds from Long-term Lines of Credit		13,000,000
Repayments of Debt	1,300,000	3,900,000
MediaAlpha \| MediaAlpha Bank Facility [Member]
Debt Instrument
Long-term Line of Credit	15,000,000	15,000,000			0
Unamortized Debt Issuance Expense	(300,000)	(300,000)			0
Line of Credit Facility, Fair Value of Amount Outstanding	14,700,000	14,700,000			$ 0
Total commitment under revolving credit facility				$ 20,000,000
Notional amount	15,000,000	15,000,000
Line of Credit Facility, Remaining Borrowing Capacity	5,000,000	5,000,000
Nordea Bank Finland
Debt Instrument
Total commitment under revolving credit facility						$ 125,000,000
Lloyds Bank plc [Member]
Debt Instrument
Total commitment under revolving credit facility						75,000,000
Unsecured Debt [Member] \| Nordea Bank Finland
Debt Instrument
Total commitment under revolving credit facility						100,000,000
Unsecured Debt [Member] \| Lloyds Bank plc [Member]
Debt Instrument
Total commitment under revolving credit facility						$ 25,000,000
TruBridge [Member] \| Tranzact [Member] \| Tranzact Bank Facility [Member]
Debt Instrument
Notional amount	$ 31,000,000	$ 31,000,000

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
Income Taxes (Details) - USD ($) $ in Millions	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jul. 17, 2013
Income Tax Contingency [Line Items]
Effective tax rates (as a percent)		13.00%			31.00%
U.S. statutory rate (as a percent)			35.00%	35.00%
Income Tax Expense (Benefit)	$ (1.6)	$ (4.7)		$ 0.8	$ 11.4
Tax Assessment Year 2007 to 2009 \| Internal Revenue Service (IRS)
Income Tax Contingency [Line Items]
Total tax assessment						$ 4
Tax assessments related to disallowed deductions						$ 2.7

Derivatives (Details)

Derivatives (Details) ¥ in Billions, $ in Billions	Sep. 30, 2015USD ($)	Sep. 30, 2015JPY (¥)	Dec. 31, 2014USD ($)	Dec. 31, 2014JPY (¥)
Collective account values of underlying variable annuities as a percentage of the guarantee value			113.00%	113.00%
White Mountains Life Re
Notional amount	$ 0.6	¥ 76.3	$ 1.1	¥ 134.2
Collective account values of underlying variable annuities as a percentage of the guarantee value	107.00%	107.00%

Derivatives Pre-Tax Operating R

Derivatives Pre-Tax Operating Results of WM Life Re (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pre-tax operating results of WM Life Re
Total revenues	$ 334.7	$ 323.2	$ 1,130.1	$ 1,048.5
General and administrative expenses	(142.6)	(63)	(354.1)	(168.3)
Pre-tax (loss) income from continuing operations	(94.6)	(35.5)	(103.2)	36.7
White Mountains Life Re
Pre-tax operating results of WM Life Re
Fees, included in other revenue	2.1	4.5	7.7	15
Change in fair value of variable annuity liability, included in other revenue	(2.8)	19.9	(1.7)	40.5
Realized and unrealized gains (losses)	1.5	(23.8)	(6.3)	(56.5)
Foreign exchange, included in other revenue	0.4	(1.7)	(0.8)	(1.2)
Other investment income and (losses) gains	(0.2)	(0.9)	(0.3)	(0.4)
Total revenues	1	(2)	(1.4)	(2.6)
Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses	0	0.2	0	0.6
Death benefit claims paid, included in general and administrative expenses	0	0	0	(0.1)
General and administrative expenses	(0.8)	(0.9)	(3.1)	(3.3)
Pre-tax (loss) income from continuing operations	$ 0.2	$ (2.7)	$ (4.5)	$ (5.4)

Derivatives Realized and Unreal

Derivatives Realized and Unrealized Gains (Losses) (Details) - White Mountains Life Re - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	$ 1.5	$ (23.8)	$ (6.3)	$ (56.5)
Derivative, fair value, net	37	65.3	37	65.3	$ 35.7	$ 56.4	$ 74.8	$ 69.2
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	0.2	(14.3)	13.1	(52.6)
Fixed income/interest rate
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	2.6	(8.4)	6	(20.4)
Derivative, fair value, net	0		0			(1.7)
Foreign exchange
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	(3.1)	(0.4)	(6)	(13.3)
Derivative, fair value, net	27.9		27.9			44.1
Equity
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	2	(15)	(6.3)	(22.8)
Derivative, fair value, net	9.1		9.1			14
Level 2 Inputs
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	3.2	(19.8)	(2.7)	(42.1)
Derivative, fair value, net	27.9	25	27.9	25	32.5	33.8	22.3	4.7
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	7.8	(22.5)	3.2	(62.4)
Level 1 Inputs
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	(5.1)	13.4	1.9	13.1
Derivative, fair value, net	(2.1)	4.4	(2.1)	4.4	(5.1)	3.7	(0.8)	1.1
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	(8.1)	8.2	7.7	9.8
Fair Value, Inputs, Level 3 [Member] \| Variable Annuity
Variable Annuity Reinsurance [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	(1)	(11.7)	(1)	(11.7)	1.8	0.7	(31.8)	(52.8)
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	(2.8)	20.1	(1.7)	41.1
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]
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized gains (losses)	3.4	(17.4)	(5.5)	(27.5)
Derivative, fair value, net	11.2	35.9	11.2	35.9	$ 8.3	$ 18.9	$ 53.3	$ 63.4
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	$ 0.5	$ 0	$ 2.2	$ 0

Derivatives Variable Annuity Re

Derivatives Variable Annuity Reinsurance Liabilities and Derivative Instruments (Details) $ in Millions, ¥ in Billions	3 Months Ended		9 Months Ended
	Sep. 30, 2015USD ($)	Sep. 30, 2014USD ($)	Sep. 30, 2015USD ($)	Sep. 30, 2014USD ($)	Sep. 30, 2015JPY (¥)	Dec. 31, 2014USD ($)	Dec. 31, 2014JPY (¥)
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	$ 600		$ 600		¥ 76.3	$ 1,100	¥ 134.2
Fair Value Derivatives Measured on Recurring Basis, Asset Purchases	0		0
Changes in derivative instruments
Beginning of period	35.7	$ 74.8	56.4	$ 69.2
Purchases		0		0
Realized and unrealized gains (losses)	1.5	(23.8)	(6.3)	(56.5)
Transfers in	0	0	0	0
Sales/settlements	(0.2)	14.3	(13.1)	52.6
End of period	37	65.3	37	65.3
Change in fair value of variable annuity death benefit liabilities, included in other general and administrative expenses	$ 0	0.2	$ 0	0.6
Collective account values of underlying variable annuities as a percentage of the guarantee value	107.00%		107.00%		107.00%
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	32.5	22.3	33.8	4.7
Purchases		0		0
Realized and unrealized gains (losses)	3.2	(19.8)	(2.7)	(42.1)
Transfers in	0	0	0	0
Sales/settlements	(7.8)	22.5	(3.2)	62.4
End of period	27.9	25	27.9	25
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	(5.1)	(0.8)	3.7	1.1
Purchases		0		0
Realized and unrealized gains (losses)	(5.1)	13.4	1.9	13.1
Transfers in	0	0	0	0
Sales/settlements	8.1	(8.2)	(7.7)	(9.8)
End of period	(2.1)	4.4	(2.1)	4.4
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	1.8	(31.8)	0.7	(52.8)
Realized and unrealized gains (losses)	(2.8)	20.1	(1.7)	41.1
Transfers in	0	0	0	0
Sales/settlements	0	0	0	0
Ending balance	(1)	(11.7)	(1)	(11.7)
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	8.3	53.3	18.9	63.4
Purchases		0		0
Realized and unrealized gains (losses)	3.4	(17.4)	(5.5)	(27.5)
Transfers in	0	0	0	0
Sales/settlements	(0.5)	0	(2.2)	0
End of period	$ 11.2	$ 35.9	$ 11.2	$ 35.9

Derivatives Additional Collater

Derivatives Additional Collateral (Details) - White Mountains Life Re - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Credit risk on derivative instruments
Collateral cash and investments	$ 16.8	$ 33.2	$ 34.2
Cash
Credit risk on derivative instruments
Derivative collateral right to reclaim	16.8	23.7	23.8
Fixed maturity investments.
Credit risk on derivative instruments
Derivative collateral right to reclaim	$ 0	$ 9.5	$ 10.4

Derivatives (Level 3 Derivative

Derivatives (Level 3 Derivative Instruments) (Details) - White Mountains Life Re $ in Millions	9 Months Ended
	Sep. 30, 2015USD ($)
Discounted cash flows
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value Liabilities	$ 1
Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Mortality (as a percent)	0.00%
Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Mortality (as a percent)	6.40%
Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Mortality (as a percent)	1.00%
Foreign Exchange Option [Member] \| Counterparty valuations
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value Liabilities	$ 2.6
Foreign Exchange Option [Member] \| Counterparty valuations \| Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	0.50%
Foreign Exchange Option [Member] \| Counterparty valuations \| Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	11.60%
Foreign Exchange Option [Member] \| Counterparty valuations \| Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Foreign exchange volatilities (as a percent)	3.70%
Equity Index Options \| Counterparty valuations
Quantitative information for Level 3 Fair Value Measurements Liabilities
Fair value Liabilities	$ 8.6
Equity Index Options \| Counterparty valuations \| Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Expected equity dividends (as a percent)	(0.70%)
Equity Index Options \| Counterparty valuations \| Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Expected equity dividends (as a percent)	6.50%
Equity Index Options \| Counterparty valuations \| Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Expected equity dividends (as a percent)	2.00%
Year One \| Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Minimum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	0.10%
Foreign exchange volatilities (as a percent)	11.60%
Index volatilities (as a percent)	26.20%
Year One \| Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Maximum
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	40.00%
Foreign exchange volatilities (as a percent)	18.60%
Index volatilities (as a percent)	29.90%
Year One \| Variable annuity benefit guarantee liabilities \| Discounted cash flows \| Weighted Average
Quantitative information for Level 3 Fair Value Measurements Liabilities
Surrenders (as a percent)	40.00%
Foreign exchange volatilities (as a percent)	12.50%
Index volatilities (as a percent)	28.20%

Derivatives (Value, Collateral

Derivatives (Value, Collateral (held) provided by WM Life Re and Net Exposure to Credit Losses on OTC Derivative Instruments) (Details) - White Mountains Life Re - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Offsetting Liabilities [Line Items]
Derivative Assets	$ 40.3	$ 64.4
Derivative Liabilities	(3.3)	(8)
Net amounts recognized in Other assets	37	56.4
Over The Counter \| Fixed income/interest rate
Offsetting Liabilities [Line Items]
Derivative Assets	0.5	1
Derivative Liabilities	(0.8)	(5.4)
Net amounts recognized in Other assets	(0.3)	(4.4)
Over The Counter \| Foreign exchange
Offsetting Liabilities [Line Items]
Derivative Assets	27.9	45.5
Derivative Liabilities	0	0
Net amounts recognized in Other assets	27.9	45.5
Over The Counter \| Equity
Offsetting Liabilities [Line Items]
Derivative Assets	11.5	11.7
Derivative Liabilities	0	(0.2)
Net amounts recognized in Other assets	11.5	11.5
Exchange Traded \| Fixed income/interest rate
Offsetting Liabilities [Line Items]
Derivative Assets	0.3	2.8
Derivative Liabilities	(0.1)	(0.1)
Net amounts recognized in Other assets	0.2	2.7
Exchange Traded \| Foreign exchange
Offsetting Liabilities [Line Items]
Derivative Assets	0.1	0
Derivative Liabilities	(0.1)	(1.4)
Net amounts recognized in Other assets	0	(1.4)
Exchange Traded \| Equity
Offsetting Liabilities [Line Items]
Derivative Assets	0	3.4
Derivative Liabilities	(2.3)	(0.9)
Net amounts recognized in Other assets	$ (2.3)	$ 2.5

Derivatives (Uncollateralized A

Derivatives (Uncollateralized Amounts Due Under WM Life Re's OTC Derivative Contracts) (Details) - White Mountains Life Re $ in Thousands	Sep. 30, 2015USD ($)Rating	Dec. 31, 2014USD ($)
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	$ 37,000	$ 56,400
Collertal provided to counterparty in cash	2,200	3,500
Collateral provided to counterparty in financial instruments	0	0
Net amount of exposure after effect of collateral	39,200	59,900
Excess collateral provided to counterparty in cash	14,200	17,700
Derivative, Collateral, Right to Reclaim Securities	0	9,500
Counter-party collateral held by WMLife Re - Cash	11,200	9,900
Net amount of exposure to counter-party	$ 42,200	77,200
S and P Credit Ratings \| Rating	23
Standard & Poor's, A Rating \| Bank of America [Member]
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	$ 3,200	5,600
Collertal provided to counterparty in cash	0	0
Collateral provided to counterparty in financial instruments	0	0
Net amount of exposure after effect of collateral	3,200	5,600
Excess collateral provided to counterparty in cash	0	0
Derivative, Collateral, Right to Reclaim Securities	0	0
Counter-party collateral held by WMLife Re - Cash	0	0
Net amount of exposure to counter-party	3,200	5,600
Standard & Poor's, A Rating \| Barclays
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	0	100
Collertal provided to counterparty in cash	0	0
Collateral provided to counterparty in financial instruments	0	0
Net amount of exposure after effect of collateral	0	100
Excess collateral provided to counterparty in cash	0	0
Derivative, Collateral, Right to Reclaim Securities	0	0
Counter-party collateral held by WMLife Re - Cash	0	0
Net amount of exposure to counter-party	0	100
Standard & Poor's, A Rating \| Royal Bank of Scotland
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments		4,000
Collertal provided to counterparty in cash		0
Collateral provided to counterparty in financial instruments		0
Net amount of exposure after effect of collateral		4,000
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		4,000
Standard & Poor's, A Rating \| Citigroup - OTC
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	18,600	22,200
Collertal provided to counterparty in cash	0	0
Collateral provided to counterparty in financial instruments	0	0
Net amount of exposure after effect of collateral	18,600	22,200
Excess collateral provided to counterparty in cash	0	0
Derivative, Collateral, Right to Reclaim Securities	0	0
Counter-party collateral held by WMLife Re - Cash	5,300	1,100
Net amount of exposure to counter-party	13,300	21,100
Standard & Poor's, A Rating \| Citigroup Exchange Traded [Member]
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	(2,100)	3,700
Collertal provided to counterparty in cash	2,100	0
Collateral provided to counterparty in financial instruments	0	0
Net amount of exposure after effect of collateral	0	3,700
Excess collateral provided to counterparty in cash	12,800	16,000
Derivative, Collateral, Right to Reclaim Securities	0	0
Counter-party collateral held by WMLife Re - Cash	0	0
Net amount of exposure to counter-party	12,800	19,700
Standard & Poor's, A plus \| JP Morgan
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	15,900	24,300
Collertal provided to counterparty in cash	0	0
Collateral provided to counterparty in financial instruments	0	0
Net amount of exposure after effect of collateral	15,900	24,300
Excess collateral provided to counterparty in cash	0	0
Derivative, Collateral, Right to Reclaim Securities	0	0
Counter-party collateral held by WMLife Re - Cash	5,900	8,800
Net amount of exposure to counter-party	10,000	15,500
Standard & Poor's, BBB plus Rating \| Royal Bank of Scotland
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	1,500
Collertal provided to counterparty in cash	0
Collateral provided to counterparty in financial instruments	0
Net amount of exposure after effect of collateral	1,500
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	1,500
Standard & Poor's, BBB plus Rating \| Nomura [Member]
Credit risk on derivative instruments
Excess collateral provided - Financial Instruments	(100)	(3,500)
Collertal provided to counterparty in cash	100	3,500
Collateral provided to counterparty in financial instruments	0	0
Net amount of exposure after effect of collateral	0	0
Excess collateral provided to counterparty in cash	1,400	1,700
Derivative, Collateral, Right to Reclaim Securities	0	9,500
Counter-party collateral held by WMLife Re - Cash	0	0
Net amount of exposure to counter-party	$ 1,400	$ 11,200

Derivatives (Tranzact Interest

Derivatives (Tranzact Interest Rate Swap) (Details) - Tranzact [Member] - USD ($) $ in Millions	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Oct. 10, 2014
Tranzact Bank Facility [Member]
Derivative [Line Items]
Line of Credit Facility, Fair Value of Amount Outstanding	$ 93.8		$ 67.4
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate		4.697%
Notional amount	$ 101			$ 70
Minimum \| Tranzact Bank Facility [Member]
Derivative [Line Items]
LIBOR rate		4.50%
Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, Fixed Interest Rate		1.34%
Derivative, Variable Interest Rate		0.198%		0.1518%
Debt Instrument, Interest Rate, Effective Percentage		6.04%
Derivative, fair value, net		$ (0.8)

Municipal Bond Guarantee (Detai

Municipal Bond Guarantee (Details) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended	9 Months Ended		12 Months Ended
Municipal Bond Guarantee (Details) $ in Millions	Jul. 31, 2012USD ($)	Sep. 30, 2015USD ($)Contract	Sep. 30, 2014USD ($)	Jun. 30, 2015	Sep. 30, 2015USD ($)Contractyr	Sep. 30, 2014USD ($)	Dec. 31, 2014USD ($)Contract
Guarantor Obligations [Line Items]
Pre-tax (loss) income		$ (94.6)	$ (35.5)		$ (103.2)	$ 36.7
Net investment income (loss) - surplus note interest		$ 0	0		$ 0	0
BAM
Guarantor Obligations [Line Items]
Municipal bond contract \| Contract		2,733			2,733		1,750
Insured Financial Obligations, Remaining Weighted Average Contract Period					12 years 8 months		12 years 10 months
Municipal bond outstanding principal		$ 19,841			$ 19,841		$ 12,362.5
Municipal bond outstanding interest		10,574.3			10,574.3		7,086.9
Municipal bond debt service outstanding		30,415.3			30,415.3		19,449.4
Financial Guarantee Insurance Contracts, Unearned Premium Revenue		43.2			$ 43.2		$ 27.6
Year of U.S. Treasury Rate \| yr					1
HG Global
Guarantor Obligations [Line Items]
Partners Capital Contribution	$ 594.5
Surplus Notes	503
Income (Loss) from Continuing Operations before Income Taxes, Domestic		$ 5.2			$ 13.8
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		$ (10.6)	(13.1)		$ (33.5)	(29.7)
HG Re
Guarantor Obligations [Line Items]
Statutory Accounting Practices, Statutory Capital and Surplus, Balance		458.3			458.3
HG Global
Guarantor Obligations [Line Items]
Pre-tax (loss) income		5.2			13.8
Net investment income (loss) - surplus note interest		4			11.9
HG Global \| HG Global
Guarantor Obligations [Line Items]
Pre-tax (loss) income			3.8			13.4
Net investment income (loss) - surplus note interest			3.9			11.8
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			$ 11.9
Derivative, Fixed Interest Rate		3.15%			3.15%		3.13%
Surplus Note \| Build America Mutual
Guarantor Obligations [Line Items]
Interest income (expense), surplus notes		$ 4	$ 3.9		$ 11.9	$ 11.8
Combination One \| Surplus Note \| BAM
Guarantor Obligations [Line Items]
Number of years of change in interest rate \| yr					5
Combination Two \| 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	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Basic and diluted earnings per share numerators (in millions):
Net income (loss) attributable to White Mountains’ common shareholders	$ (73.1)	$ (12.6)		$ (61.8)	$ 65.8
Allocation of income for unvested restricted common shares	0	0		0	(0.8)
Dividends declared on participating restricted common shares	0	0		(0.1)	(0.1)
Total allocation to restricted common shares	0	0		(0.1)	(0.9)
Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts	(73.1)	(12.6)		(61.9)	64.9
Undistributed net earnings (in millions):
Net income attributable to White Mountains’s common shareholders, net of restricted common share amounts	(73.1)	(12.6)		(61.9)	64.9
Dividends declared net of restricted common share amounts	0	0		(5.9)	(6.1)
Total undistributed net earnings, net of restricted common share amounts	$ (73.1)	$ (12.6)		$ (67.8)	$ 58.8
Basic earnings per share denominators
Total average common shares outstanding during the period	5,890,100	6,091,400		5,951,100	6,140,900
Average unvested restricted common shares	0	0		0	(77,700)
Basic earnings per share denominator	5,890,100	6,091,400		5,951,100	6,063,200
Diluted earnings per share denominator
Total average common shares outstanding during the period	5,890,100	6,091,400		5,951,100	6,140,900
Average unvested restricted common shares	0	0		0	(77,700)
Average outstanding dilutive options to acquire common shares	0	0		0	0
Diluted earnings (loss) per share denominator	5,890,100	6,091,400		5,951,100	6,063,200
Basic earnings per share (in dollars):
Continuing operations	$ (12.42)	$ (2.07)		$ (10.40)	$ 10.70
Dividends declared	(1)	(1)		(1)	(1)
Undistributed earnings (loss) (in dollars per share)	(12.42)	(2.07)		(11.40)	9.70
Earnings Per Share, Diluted [Abstract]
Continuing operations	(12.42)	(2.07)		(10.40)	10.70
Dividends declared	(1)	(1)		(1)	(1)
Undistributed earnings (loss) (in dollars per share)	$ (12.42)	$ (2.07)		$ (11.40)	$ 9.70
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	125,000	125,000		125,000	125,000
Discontinued Operations [Member]
Basic and diluted earnings per share numerators (in millions):
Allocation of income for unvested restricted common shares	$ 0.2	$ (0.9)		$ (1)	$ 2.2
Basic earnings per share denominators
Total average common shares outstanding during the period	5,890,100	6,091,400		5,951,100	6,140,900
Average unvested restricted common shares	(70,900)	(81,300)		(67,100)	(77,700)
Basic earnings per share denominator	5,819,200	6,010,100		5,884,000	6,063,200
Diluted earnings per share denominator
Total average common shares outstanding during the period	5,890,100	6,091,400		5,951,100	6,140,900
Average unvested restricted common shares	(70,900)	(81,300)		(67,100)	(77,700)
Average outstanding dilutive options to acquire common shares	0	0		0	0
Diluted earnings (loss) per share denominator	5,819,200	6,010,100		5,884,000	6,063,200
Earnings Per Share, Diluted [Abstract]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements			125,000

Non-controlling Interest (Detai

Non-controlling Interest (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 460.8	$ 542.7
Total Non-Controlling Excluding Reciprocals [Member]
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 113.3	$ 168.6
OneBeacon
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	24.70%	24.70%
Total non-controlling interests	$ 246.9	$ 258.4
SIG Preference Shares
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ 250	$ 250
HG Global
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.10%	3.10%
Total non-controlling interests	$ 17.3	$ 17.9
MediaAlpha
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	40.00%	40.00%
Total non-controlling interests	$ 15.1	$ 22.6
Tranzact [Member]
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	36.80%	36.80%
Total non-controlling interests	$ 75.6	$ 88.2
WOBI
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	4.70%	36.70%
Total non-controlling interests	$ 1.8	$ 5.4
Prospector Offshore Fund Ltd [Member]
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	0.00%	23.40%
Total non-controlling interests	$ 0	$ 31.1
A W G Dewar Inc [Member]
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	32.20%	18.00%
Total non-controlling interests	$ 3.5	$ 3.4
Build America Mutual
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ (134.2)	$ (121.9)
Star & Shield Insurance Exchange
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ (15.2)	$ (12.4)

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Segment Information (Details) - USD ($) $ in Millions	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment reporting information
Earned insurance premiums	$ 284.9	$ 307.2	$ 896	$ 879.1
Net investment income	16.8	13.8	42.6	44.7
Net investment income (loss) - surplus note interest	0	0	0	0
Net realized and unrealized investment gains (losses)	(43.9)	(27.5)	(33.9)	64.4
Other revenue	76.9	29.7	225.4	60.3
Total revenues	334.7	323.2	1,130.1	1,048.5
Losses and LAE	170	185.5	534.1	527.3
Insurance and Reinsurance Acquisition Expenses	55.3	55.2	166.1	153
Other Underwriting Expense	56.5	51.3	165.5	152.6
General and administrative expenses	142.6	63	354.1	168.3
Interest expense	4.9	3.7	13.5	10.6
Total expenses	429.3	358.7	1,233.3	1,011.8
Pre-tax (loss) income	(94.6)	(35.5)	(103.2)	36.7
OneBeacon
Segment reporting information
Earned insurance premiums	281.4	305.4	887.3	872.8
Net investment income	12.4	10.8	33	33.4
Net investment income (loss) - surplus note interest	0	0	0	0
Net realized and unrealized investment gains (losses)	(29.9)	(16)	(29.7)	24.8
Other revenue	3.9	1.3	(0.4)	3.3
Total revenues	267.8	301.5	890.2	934.3
Losses and LAE	167.5	185.2	527.9	520.7
Insurance and Reinsurance Acquisition Expenses	53.8	54.6	161.2	150.9
Other Underwriting Expense	56.4	51.2	165.2	152.3
General and administrative expenses	3.7	2.4	12	9.3
Interest expense	3.2	3.2	9.7	9.7
Total expenses	284.6	296.6	876	842.9
Pre-tax (loss) income	(16.8)	4.9	14.2	91.4
HG Global
Segment reporting information
Earned insurance premiums	0.6	0.4	1.7	0.9
Net investment income	0.5	0.4	1.4	1
Net investment income (loss) - surplus note interest	4		11.9
Net realized and unrealized investment gains (losses)	0.6	(0.5)	0.3	1.1
Other revenue	0	0	0	0
Total revenues	5.7	4.2	15.3	14.8
Losses and LAE	0	0	0	0
Insurance and Reinsurance Acquisition Expenses	0.1	0	0.3	0.2
Other Underwriting Expense	0	0	0	0
General and administrative expenses	0.4	0.4	1.2	1.2
Interest expense	0	0	0	0
Total expenses	0.5	0.4	1.5	1.4
Pre-tax (loss) income	5.2		13.8
BAM
Segment reporting information
Earned insurance premiums	0.3	0.1	0.6	0.3
Net investment income	1.1	1.4	2.9	4.2
Net investment income (loss) - surplus note interest	(4)	(3.9)	(11.9)	(11.8)
Net realized and unrealized investment gains (losses)	1.7	(1.4)	2.8	5.4
Other revenue	0.2	0.2	0.5	0.5
Total revenues	(0.7)	(3.6)	(5.1)	(1.4)
Losses and LAE	0	0	0	0
Insurance and Reinsurance Acquisition Expenses	0.4	0.5	1.8	1.4
Other Underwriting Expense	0.1	0.1	0.3	0.3
General and administrative expenses	9.4	8.9	26.3	26.6
Interest expense	0	0	0	0
Total expenses	9.9	9.5	28.4	28.3
Pre-tax (loss) income	(10.6)	(13.1)	(33.5)	(29.7)
Other Operations
Segment reporting information
Earned insurance premiums	2.6	1.3	6.4	5.1
Net investment income	2.8	1.2	5.3	6.1
Net investment income (loss) - surplus note interest	0	0	0	0
Net realized and unrealized investment gains (losses)	(16.3)	(9.6)	(7.3)	33.1
Other revenue	72.8	28.2	225.3	56.5
Total revenues	61.9	21.1	229.7	100.8
Losses and LAE	2.5	0.3	6.2	6.6
Insurance and Reinsurance Acquisition Expenses	1	0.1	2.8	0.5
Other Underwriting Expense	0	0	0	0
General and administrative expenses	129.1	51.3	314.6	131.2
Interest expense	1.7	0.5	3.8	0.9
Total expenses	134.3	52.2	327.4	139.2
Pre-tax (loss) income	$ (72.4)	$ (31.1)	$ (97.7)	$ (38.4)

Investments in Unconsolidated85

Investments in Unconsolidated Affiliates (Investment in Unconsolidated Affiliates Table) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended		9 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax	$ 3.9		$ 7				$ 18	$ 33.3
Total investments in unconsolidated affiliates	392.6						392.6		$ 414.4
Symetra
Investments in unconsolidated affiliates
Equity in Unrealized Gains (Losses) from Investments in Unconsolidated Affiliates	5.7						5.7		37.6
Symetra \| Common Stock
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax	4.2		7				17.5	34.5
Symetra Common Shares excluding unrealized gains (losses)	386.9						386.9		373.8
Total investments in unconsolidated affiliates	392.6	$ 397.2	$ 409.8	$ 415.5	$ 397.2	$ 415.5	392.6	$ 409.8	411.4	$ 317.3
Hamer, LLC [Member]
Investments in unconsolidated affiliates
Equity in earnings of unconsolidated affiliates, net of tax		$ 1.1		$ 0.4	$ 1.6	$ 0.8
Total investments in unconsolidated affiliates	$ 0						$ 0		$ 3

Investments in Unconsolidated86

Investments in Unconsolidated Affiliates (Symetra) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2011
Investments in unconsolidated affiliates
Revenues	$ 334.7	$ 323.2	$ 1,130.1	$ 1,048.5
Total expenses	429.3	358.7	1,233.3	1,011.8
Pre-tax (loss) income	(94.6)	(35.5)	(103.2)	36.7
Net income	$ (74.9)	40.1	5.5	235.1
Symetra
Investments in unconsolidated affiliates
Dividends	$ 0.50
Revenues			$ 1,605.9	1,601.6
Stock Repurchased and Retired During Period, Value	513,500
Shares of Symetra Financial Corporation owned (in shares)	20,562,379		20,562,379			20,048,879
Ownership interest (as a percent)	17.70%		17.70%			17.31%
Equity Method Investments Fair Value Per Share							$ 15
Term of amortization (in years)					30 years
Weight Average Years Remaining			28 years
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	$ 160.8		$ 160.8			$ 170.4
Total expenses			1,543.6	1,387
Pre-tax (loss) income			62.3	214.6
Net income			89.6	186.8
Common Stock \| Symetra
Investments in unconsolidated affiliates
Proceeds from Equity Method Investment, Dividends or Distributions	$ 12.5	2	$ 16.9	6
Fair value of investment							$ 261
Share Price	$ 31.64		$ 31.64
equity in earnings of unconsolidated affiliates \| Symetra
Investments in unconsolidated affiliates
After tax amortization through equity in earnings	$ 0.6	0.7	$ 2	2.1
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	32.6		32.6			36.4
Net unrealized gains (losses) of unconsolidated affiliates \| Symetra
Investments in unconsolidated affiliates
After tax amortization through equity in net unrealized losses	2.6	$ 2.9	8.1	$ 8.7
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	$ 128.2		$ 128.2			$ 134
Expected [Member] \| Symetra
Investments in unconsolidated affiliates
Dividends Payable, Amount Per Share	$ 32		$ 32
Special Dividend [Member] \| Common Stock \| Symetra
Investments in unconsolidated affiliates
Proceeds from Equity Method Investment, Dividends or Distributions	$ (10.3)

Investments in Unconsolidated87

Investments in Unconsolidated Affiliates (Investments in Symetra Table Rollforward) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Changes in carrying value of investment in Symetra
Carrying value at the beginning of the period			$ 414.4		$ 414.4
Equity in earnings	$ 3.9	$ 7			18	$ 33.3
Carrying value at the end of the period	392.6				392.6
Income Tax Expense (Benefit)	$ (1.6)	(4.7)			$ 0.8	11.4
Symetra \| Common Stock
Investments in unconsolidated affiliates
Share Price	$ 31.64				$ 31.64
Changes in carrying value of investment in Symetra
Carrying value at the beginning of the period	$ 397.2	415.5	411.4	$ 317.3	$ 411.4	317.3
Equity in earnings	4.2	7			17.5	34.5
Equity in net unrealized gains (losses) from Symetra's fixed maturity portfolio	3.7	(10.7)			(31.8)	64
Dividends received	(12.5)	(2)			(16.9)	(6)
Carrying value at the end of the period	392.6	409.8	$ 397.2	$ 415.5	392.6	409.8
Aggregate value of White Mountains common shares of Symetra at quoted market price	650.6				650.6
Number of Shares Distributed	0	0			12.4	0
White Mountains \| Common Stock
Changes in carrying value of investment in Symetra
Equity in net unrealized gains (losses) from Symetra's fixed maturity portfolio					5.7	20.5
equity in earnings of unconsolidated affiliates \| Symetra \| Common Stock
Changes in carrying value of investment in Symetra
Income Tax Expense (Benefit)	0.3	0.5			1.1	2.4
Net unrealized gains (losses) of unconsolidated affiliates \| White Mountains \| Common Stock
Changes in carrying value of investment in Symetra
Income Tax Expense (Benefit)					0.2	1.4
Amortization of common share basis difference \| Symetra \| Common Stock
Changes in carrying value of investment in Symetra
Equity in earnings	0.7	0.7			2.1	2.2
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	$ 2.9	$ 3.1			$ 8.6	$ 9.4

Investments in Unconsolidated88

Investments in Unconsolidated Affiliates Hamer (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended		9 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
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	$ 3.9		$ 7				$ 18	$ 33.3
Hamer, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity in earnings of unconsolidated affiliates, net of tax		$ 1.1		$ 0.4	$ 1.6	$ 0.8

Employee Share-Based Incentiv89

Employee Share-Based Incentive Compensation Plans (WTM - Performance Shares) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Accrued Expense
Accrued expense at the beginning of period			$ 108.1
Accrued expense at the end of the period	$ 121		$ 121		$ 108.1
Performance Share \| Range Of Performance Cycle From 2012 To 2014 [Member]
Accrued Expense
Vested (in shares)					1,425
Performance Share \| W T M Incentive Plan \| Range Of Performance Cycle From 2012 To 2014 [Member]
Accrued Expense
Percentage of target payout - minimum actual			91.00%
Percentage of target payout - maximum actual			145.50%
Performance Share \| W T M Incentive Plan \| Performance Cycle 2011 to 2013
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)	109,129	116,259	113,198	108,605	108,605
Shares paid or expired (in shares)	(8,958)	0	(42,958)	(33,730)
New grants (in shares)	0	0	29,828	41,580
Assumed forfeitures and cancellations	(3,960)	0	(3,857)	(196)
Ending of period (in shares)	96,211	116,259	96,211	116,259	113,198
Accrued Expense
Accrued expense at the beginning of period	$ 28.8	$ 46.3	$ 44.4	$ 54.9	$ 54.9
Payments and deferrals	(5.5)	0	(30.7)	(24.1)
Assumed forfeitures and cancellations	(0.8)	(0.2)	(0.3)	0
Expense recognized	30	6.3	39.1	21.6
Accrued expense at the end of the period	52.5	$ 52.4	$ 52.5	$ 52.4	$ 44.4
Vesting Period			3 years
Additional compensation cost that would be recognized if all outstanding performance shares vested	$ 30.2		$ 30.2
Sirius Group \| Performance Share \| W T M Incentive Plan
Target Performance Share Activity
Ending of period (in shares)	7,997	11,278	7,997	11,278

Employee Share-Based Incentiv90

Employee Share-Based Incentive Compensation Plans (WTM - Performance Shares Granted Under the WTM Incentive Plan) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Share-based compensation arrangement by share-based payment award
Total Accrued Expense	$ 121		$ 108.1
White Mountains \| Performance Share \| W T M Incentive Plan
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	98,678
Accrued Expense	$ 54
Target Performance Shares Outstanding, Assumed forfeitures	(2,467)
Accrued Expense, Assumed forfeitures	(1.5)
Total Target Performance Shares Outstanding	96,211	109,129	113,198	116,259	116,259	108,605
Total Accrued Expense	$ 52.5	$ 28.8	$ 44.4	$ 52.4	$ 46.3	$ 54.9
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	29,828
Accrued Expense	$ 6.3
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	32,557
Accrued Expense	$ 12.3
White Mountains \| Performance Share \| W T M Incentive Plan \| Performance Cycle 2013 to 2015
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	36,293
Accrued Expense	$ 35.4

Employee Share-Based Incentiv91

Employee Share-Based Incentive Compensation Plans (WTM - Restricted Shares) (Details) - W T M Incentive Plan - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
White Mountains \| Restricted Share Cliff Vesting in January 2018
Target Restricted Share Activity
Issued (in shares)			22,078
White Mountains \| Restricted Share Cliff Vesting in January 2017
Target Restricted Share Activity
Issued (in shares)			20,400
White Mountains \| Restricted Stock
Target Restricted Share Activity
Beginning of period (in shares)	68,303	79,011	80,050	90,341	90,341
Issued (in shares)	0	0	22,078	20,400
Vested (in shares)	(1,200)	0	(35,025)	(31,730)
Assumed forfeitures and cancellations	0	0	0	0
Ending of period (in shares)	67,103	79,011	67,103	79,011	80,050
Unamortized grant date fair value
Unamortized grant date fair value, beginning balance	$ 21.9	$ 20.5	$ 13.7	$ 16.4	$ 16.4
Issued	0	0	14.7	11.8
Assumed forfeitures and cancellations	0	0	0	0
Expense recognized	(3.5)	(3.2)	(10)	(10.9)
Unamortized grant date fair value, ending balance	$ 18.4	$ 17.3	$ 18.4	$ 17.3	$ 13.7
Sirius Group \| Restricted Stock
Target Restricted Share Activity
Ending of period (in shares)	3,571	2,314	3,571	2,314

Employee Share-Based Incentiv92

Employee Share-Based Incentive Compensation Plans (OneBeason - Peformance Shares) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Expense Amortized
Accrued expense at the beginning of period			$ 108.1
Accrued expense at the end of the period	$ 121		$ 121		$ 108.1
OneBeacon \| Performance Share \| One Beacon Long Term Incentive Plan
Share-based compensation arrangement by share-based payment award
Vesting Period			3 years
OneBeacon \| 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 \| One Beacon Long Term Incentive Plan \| Performance Cycle 2011 to 2013
Expense Amortized
Percentage of target payout - minimum actual			37.10%
OneBeacon \| One Beacon Long Term Incentive Plan \| Performance Share
Target Performance Shares Outstanding
Beginning of period (in shares)	462,147	512,938	517,470	493,421	493,421
Shares paid or expired (in shares)	0	0	(181,290)	(142,138)
New grants (in shares)	0	0	154,887	165,800
Assumed forfeitures and cancellations	0	0	(28,920)	(4,145)
Ending of period (in shares)	462,147	512,938	462,147	512,938	517,470
Expense Amortized
Accrued expense at the beginning of period	$ 2.4	$ 4.4	$ 3.4	$ 4	$ 4
Payments and deferrals	0	0	(1.5)	(1)
Assumed forfeitures and cancellations	0	0	0	0
Expense recognized	(0.3)	1.1	0.2	2.5
Accrued expense at the end of the period	2.1	$ 5.5	2.1	$ 5.5	$ 3.4
Additional compensation cost that would be recognized if all outstanding performance shares vested	$ 2		$ 2

Employee Share-Based Incentiv93

Employee Share-Based Incentive Compensation Plans (OneBeacon - Performance Shares Outstanding) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Share-based compensation arrangement by share-based payment award
Accrued incentive compensation	$ 121		$ 108.1
OneBeacon \| Performance Share \| One Beacon Long Term Incentive Plan
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	473,997
Incentive Compensation Payable before Forfeitures	$ 2.1
Target Performance Shares Outstanding, Assumed forfeitures	(11,850)
Accrued Expense, Assumed forfeitures	0
Total Target Performance Shares Outstanding	462,147	462,147	517,470	512,938	512,938	493,421
Accrued incentive compensation	$ 2.1	$ 2.4	$ 3.4	$ 5.5	$ 4.4	$ 4
OneBeacon \| 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	154,887
Incentive Compensation Payable before Forfeitures	$ 0.5
OneBeacon \| 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	151,810
Incentive Compensation Payable before Forfeitures	$ 0.3
OneBeacon \| Performance Share \| One Beacon Long Term Incentive Plan \| Performance Cycle 2013 to 2015
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	167,300
Incentive Compensation Payable before Forfeitures	$ 1.3

Employee Share-Based Incentiv94

Employee Share-Based Incentive Compensation Plans (OneBeacon - Restricted Shares) (Details) - OneBeacon - One Beacon Long Term Incentive Plan $ in Millions	Feb. 24, 2015shares	Mar. 01, 2012shares	May. 31, 2011shares	Sep. 30, 2015USD ($)shares	Sep. 30, 2014USD ($)shares	Sep. 30, 2015USD ($)shares	Sep. 30, 2014USD ($)shares	Dec. 31, 2014USD ($)shares	Feb. 28, 2012Installment	May. 25, 2011Installment
Restricted Stock
Target Restricted Share Activity
Beginning of period (in shares)				390,950	612,500	612,500	915,000	915,000
Issued (in shares)	75,950	300,000		0	0	75,950	0
Vested (in shares)				0	0	(296,000)	(300,000)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value \| $						$ 0
Assumed forfeitures and cancellations				0	0	(1,500)	(2,500)
Ending of period (in shares)				390,950	612,500	390,950	612,500	612,500
Unamortized grant date fair value
Unamortized grant date fair value, beginning balance \| $				$ 3.5	$ 4.9	$ 3.5	$ 6.5	$ 6.5
Issued \| $				0	0	1.1	0
Assumed forfeitures and cancellations \| $				0	0	0	0
Expense recognized \| $				(0.5)	(0.7)	(1.6)	(2.3)
Unamortized grant date fair value, ending balance \| $				$ 3	$ 4.2	$ 3	$ 4.2	$ 3.5
Number of Installments in which the Shares Vest \| Installment									2
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
Performance Share
Target Restricted Share Activity
Beginning of period (in shares)				462,147	512,938	517,470	493,421	493,421
Assumed forfeitures and cancellations				0	0	(28,920)	(4,145)
Ending of period (in shares)				462,147	512,938	462,147	512,938	517,470
Unamortized grant date fair value
Assumed forfeitures and cancellations \| $				$ 0	$ 0	$ 0	$ 0
Expense recognized \| $				(0.3)	$ 1.1	0.2	$ 2.5
Unamortized grant date fair value, ending balance \| $				$ 2		$ 2
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

Employee Share-Based Incentiv95

Employee Share-Based Incentive Compensation Plans (OneBeacon - Restricted Stock Units) (Details) - Restricted Stock Units (RSUs) [Member] - OneBeacon - One Beacon Long Term Incentive Plan $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2015USD ($)shares	Sep. 30, 2015USD ($)shares
Share-based compensation arrangement by share-based payment award
Issued (in shares)		214,430
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	204,179	204,179
Expense recognized \| $	$ 0.2	$ 0.6

Fair Value of Financial Instr96

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	$ 383.3	$ 343.1
OneBeacon \| 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	274.8	274.7
OneBeacon \| Book Value \| 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	274.8	274.7
OneBeacon \| Estimate of Fair Value Measurement [Member] \| 2012 OBH Senior Notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Debt	279.8	286
Tranzact [Member] \| Tranzact Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Long-term Line of Credit	95.8	68.7
Tranzact [Member] \| Book Value \| Tranzact Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Long-term Line of Credit	93.8	67.4
Tranzact [Member] \| Estimate of Fair Value Measurement [Member] \| Tranzact Bank Facility [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions
Long-term Line of Credit	$ 94.6	$ 68.7

Discontinued Operations (Detail

Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended		48 Months Ended
Discontinued Operations (Details) - USD ($) $ in Millions	Sep. 30, 2015	Jun. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015
Discontinued Operations [Line Items}
Net gain on sale of discontinued operations	$ 10.3		$ 7		$ 18.2	$ 9.7
Net income from discontinued operations, net of tax	3.9		56.9		73.3	166.8
Net Realized and Unrealized Gain (Loss) on Trading Securities	(43.9)		(27.5)		(33.9)	64.4
Sirius Group
Discontinued Operations [Line Items}
Investment Income, Net	5.5		0.9		1.4	1.8
Net Realized and Unrealized Gain (Loss) on Trading Securities	5.5		0.9		1.4	1.8
OneBeacon Runoff [Member]
Discontinued Operations [Line Items}
Change in seller financing				$ 6.7
Amount of Seller Financing				80.9
Surplus Notes				80.9
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax	10.3		10.3	8.2	18.2		$ 28.3
Net gain on sale of discontinued operations			6.7	5.3
Reserve charge under the SPA, before tax				7.4
Transfer of assets				7.4
Reserve Charge After-Tax				$ 4.8
Proceeds from Sale of Buildings		$ 58
Esurance
Discontinued Operations [Line Items}
Net gain on sale of discontinued operations						$ 3.2
Net income from discontinued operations, net of tax	$ 10.3				$ 18.2
Fireman's Fund Insurance Company [Member]
Discontinued Operations [Line Items}
Net gain on sale of discontinued operations			$ 14

Discontinued Operations - Finan

Discontinued Operations - Financial Statement Disclosures (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Disposal Group, Including Discontinued Operation, Assets [Abstract]
Fixed maturity investments	$ 2,602.2			$ 2,602.2			$ 2,422
Short-term investments	325			325			376.8
Common equity securities	482.1			482.1			611.7
Convertible fixed maturity and preferred investments	5.6			5.6			13.9
Other long-term investments	294.6			294.6			318
Total investments	3,709.5			3,709.5			3,742.4
Cash	200			200			261.7
Reinsurance recoverable on unpaid losses	214.6			214.6			161.7
Reinsurance recoverable on paid losses	22.6			22.6			12.2
Insurance premiums receivable	273.3			273.3			241.1
Funds held by ceding entities	4.6			4.6			37.1
Deferred acquisition costs	110.8			110.8			107.2
Deferred tax asset	133.9			133.9			114.6
Ceded unearned insurance premiums	41.4			41.4			17.8
Goodwill and intangible assets	381.7			381.7			351.2
Other assets	307.7			307.7			311.6
Assets held for sale	4,528.1			4,528.1			4,630.6
Loss and loss adjustment expense reserves	1,433.3	$ 1,169.5	$ 1,137.8	1,433.3	$ 1,169.5	$ 1,357	1,350	$ 1,054.3
Unearned insurance premiums	671.3			671.3			616.7
Debt	383.3			383.3			343.1
Accrued incentive compensation	121			121			108.1
Ceded reinsurance payable	46.8			46.8			34.2
Funds held under insurance contracts	100.3			100.3			81
Other liabilities	304.9			304.9			278.4
Total liabilities held for sale	3,032.8			3,032.8			3,105.3
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Earned insurance premiums	284.9	307.2		896	879.1
Net investment income	16.8	13.8		42.6	44.7
Net realized and unrealized investment (losses) gains	(43.9)	(27.5)		(33.9)	64.4
Other revenue	76.9	29.7		225.4	60.3
Total revenues	334.7	323.2		1,130.1	1,048.5
Loss and loss adjustment expenses	170	185.5		534.1	527.3
Insurance and Reinsurance Acquisition Expenses	55.3	55.2		166.1	153
Other Underwriting Expense	56.5	51.3		165.5	152.6
General and administrative expenses	142.6	63		354.1	168.3
Interest expense	4.9	3.7		13.5	10.6
Total expenses	429.3	358.7		1,233.3	1,011.8
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax				73.3	166.8
Net gain on sale of discontinued operations	10.3	7		18.2	9.7
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	0	(0.2)		0.3	(0.1)
Comprehensive (loss) income	(73.8)	(22.9)		(61.5)	201.8
Net Cash Provided by (Used in) Discontinued Operations [Abstract]
Net change in cash during the period				17.5	(27.6)
Cash balances at beginning of period				238	233.5
Cash balances at end of period	183.2	395.4		183.2	395.4
Net income tax refund from national governments				(8)	(0.3)
Sirius Group
Disposal Group, Including Discontinued Operation, Assets [Abstract]
Total investments	510.8			510.8
Fireman's Fund Insurance Company [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations		14
OneBeacon Runoff [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations		6.7	5.3
Esurance
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations					3.2
Discontinued Operations [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Earned insurance premiums	202.8	231.7		623.3	656.6
Net investment income	10.5	9.7		28.6	30
Net realized and unrealized investment (losses) gains	(0.9)	48.3		31.4	134.1
Other revenue	1.7	0		(20.6)	(47.3)
Total revenues	214.2	266.9		662.7	773.4
Loss and loss adjustment expenses	121.7	103.6		311.3	273.1
Insurance and Reinsurance Acquisition Expenses	45.4	50.2		135.5	146.4
Other Underwriting Expense	24.8	30.5		78	93.9
General and administrative expenses	9.4	6.3		22.4	21.6
Interest expense	6.6	6.6		20	19.8
Total expenses	207.9	197.2		567.2	554.8
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	6.2	69.7		95.5	218.6
Discontinued Operation, Tax Effect of Discontinued Operation	(2.3)	(12.8)		(22.2)	(51.8)
Net gain on sale of discontinued operations	3.9	56.9	$ 2.7	73.3	166.8
Net loss from discontinued operations, net of tax	14.2	63.9		91.5	176.5
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(18.4)	(64.1)		(62.1)	(99.9)
Comprehensive (loss) income	(4.2)	(0.2)		29.4	76.6
Net Cash Provided by (Used in) Discontinued Operations [Abstract]
Net cash provided from operations - discontinued operations				6.7	49.8
Net cash provided from investing activities - discontinued operations				35.7	47.5
Net cash used for financing activities - discontinued operations				(2.4)	(55.6)
Effect of exchange rate changes on cash				(4.1)	(10.6)
Net change in cash during the period				35.9	31.1
Cash balances at beginning of period				111.5	93.2
Cash balances at end of period	147.4	124.3		147.4	124.3
Interest paid				(25.5)	(34.9)
Net income tax refund from national governments				(30.3)	7.5
Discontinued Operations [Member] \| Discontinued Operations, Held-for-sale [Member]
Disposal Group, Including Discontinued Operation, Assets [Abstract]
Fixed maturity investments	2,394.3			2,394.3			2,362.3
Short-term investments	360.5			360.5			494.9
Common equity securities	164.3			164.3			189.9
Convertible fixed maturity and preferred investments	0			0			6.6
Other long-term investments	82.1			82.1			89
Total investments	3,001.2			3,001.2			3,142.7
Cash	147.4			147.4			111.5
Reinsurance recoverable on unpaid losses	276.5			276.5			322.2
Reinsurance recoverable on paid losses	11			11			11.4
Insurance premiums receivable	416.6			416.6			306.6
Funds held by ceding entities	81.1			81.1			91.9
Deferred acquisition costs	82.7			82.7			69.9
Deferred tax asset	309.6			309.6			341.5
Ceded unearned insurance premiums	118.4			118.4			76.2
Goodwill and intangible assets	10.2			10.2			15.2
Other assets	73.4			73.4			83.4
Assets held for sale	4,528.1			4,528.1			4,630.6
Loss and loss adjustment expense reserves	1,662.9			1,662.9			1,809.8
Unearned insurance premiums	429.4			429.4			338.6
Debt	403.5			403.5			403.5
Deferred tax liability	257.8			257.8			282.8
Accrued incentive compensation	55.5			55.5			76.5
Ceded reinsurance payable	131.4			131.4			71.5
Funds held under insurance contracts	45.1			45.1			57.9
Other liabilities	47.2			47.2			64.7
Total liabilities held for sale	3,032.8			3,032.8			3,105.3
Discontinued Operations [Member] \| Sirius Group
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Earned insurance premiums	202.8	231.4		623.3	656.5
Net investment income	10.5	9.7		28.6	30
Net realized and unrealized investment (losses) gains	(0.9)	48.3		31.4	134.1
Other revenue	1.8	(22.8)		(20.2)	(47.3)
Total revenues	214.2	266.6		663.1	773.3
Loss and loss adjustment expenses	121.7	103.6		311.3	273.8
Insurance and Reinsurance Acquisition Expenses	45.4	50.1		135.5	146.3
Other Underwriting Expense	24.8	29.7		78	91.7
General and administrative expenses	9.4	6.3		22.4	21.6
Interest expense	6.6	6.6		20	19.8
Total expenses	207.9	196.3		567.2	553.2
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	6.3	70.3		95.9	220.1
Discontinued Operation, Tax Effect of Discontinued Operation	(2.3)	(13.1)		(22.2)	(52.4)
Net gain on sale of discontinued operations	4	57.2		73.7	167.7
Net loss from discontinued operations, net of tax	4	57.2		73.7	167.7
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(18.4)	(64.1)		(62.1)	(99.9)
Comprehensive (loss) income	(14.4)	(6.9)		11.6	67.8
Discontinued Operations [Member] \| Other Discontinued Operations [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Earned insurance premiums	0	0.3		0	0.1
Net investment income	0	0		0	0
Net realized and unrealized investment (losses) gains	0	0		0	0
Other revenue	(0.1)	0		(0.4)	0
Total revenues	(0.1)	0.3		(0.4)	0.1
Loss and loss adjustment expenses	0	0		0	(0.7)
Insurance and Reinsurance Acquisition Expenses	0	0.1		0	0.1
Other Underwriting Expense	0	0.8		0	2.2
General and administrative expenses	0	0		0	0
Interest expense	0	0		0	0
Total expenses	0	0.9		0	1.6
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax	(0.1)	(0.6)		(0.4)	(1.5)
Discontinued Operation, Tax Effect of Discontinued Operation	0	0.3		0	0.6
Net gain on sale of discontinued operations	(0.1)	(0.3)		(0.4)	(0.9)
Net loss from discontinued operations, net of tax	10.2	6.7		17.8	8.8
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	0	0		0	0
Comprehensive (loss) income	10.2	6.7		17.8	8.8
Discontinued Operations [Member] \| OneBeacon \| Discontinued Operations, Held-for-sale [Member]
Disposal Group, Including Discontinued Operation, Assets [Abstract]
Other assets	0			0			$ 58.1
Discontinued Operations [Member] \| Fireman's Fund Insurance Company [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations	0	14		0	14
Discontinued Operations [Member] \| OneBeacon Runoff [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations	0	(7)		0.3	(7.5)
Discontinued Operations [Member] \| Esurance
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Net gain on sale of discontinued operations	$ 10.3	$ 0		$ 17.9	$ 3.2

Discontinued Operations - EPS (

Discontinued Operations - EPS (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	125,000	125,000		125,000	125,000
Income (Loss) Allocated to Participating Unvested Restricted Common Shares	$ 0	$ 0		$ 0	$ 0.8
Net Income (Loss) Available to Common Stockholders, Basic	$ (58.9)	$ 51.3		$ 29.7	$ 242.3
Total average common shares outstanding during the period	5,890,100	6,091,400		5,951,100	6,140,900
Average unvested restricted common shares	0	0		0	(77,700)
Basic earnings per share denominator	5,890,100	6,091,400		5,951,100	6,063,200
Average outstanding dilutive options to acquire common shares	0	0		0	0
Diluted earnings (loss) per share denominator	5,890,100	6,091,400		5,951,100	6,063,200
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements			125,000
Net loss from discontinued operations, net of tax	$ 14.2	$ 63.9		$ 91.5	$ 176.5
Income (Loss) Allocated to Participating Unvested Restricted Common Shares	(0.2)	0.9		1	(2.2)
Net Income (Loss) Available to Common Stockholders, Basic	$ 14	$ 63		$ 90.5	$ 174.3
Total average common shares outstanding during the period	5,890,100	6,091,400		5,951,100	6,140,900
Average unvested restricted common shares	(70,900)	(81,300)		(67,100)	(77,700)
Basic earnings per share denominator	5,819,200	6,010,100		5,884,000	6,063,200
Average outstanding dilutive options to acquire common shares	0	0		0	0
Diluted earnings (loss) per share denominator	5,819,200	6,010,100		5,884,000	6,063,200
Earnings Per Share, Basic and Diluted	$ 2.41	$ 10.49		$ 15.37	$ 28.74

Discontinued Operations - Fair

Discontinued Operations - Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	$ 383.3	$ 343.1
Estimate of Fair Value Measurement [Member] \| SIG Senior Notes \| Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	423.6	437.8
Estimate of Fair Value Measurement [Member] \| SIG Preference Shares \| Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	252.5	260
Book Value \| SIG Senior Notes \| Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	399.8	399.7
Book Value \| SIG Preference Shares \| Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt	$ 250	$ 250

Discontinued Operations - Inter

Discontinued Operations - Interest Rate Cap (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended			6 Months Ended	9 Months Ended
	Jul. 31, 2013	May. 31, 2007	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Jun. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Preferred Stock [Member] \| Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Preferred Stock, Dividend Rate, Percentage		7.506%
Interest Rate Cap [Member] \| Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Years of interest rate cap					5 years
Derivative, Cap Interest Rate	8.30%
Derivative, Cost of Hedge	$ 9.9
Beginning of period			$ 3.3	$ 6.2		$ 4.1	$ 4.1	$ 11.1
Realized and unrealized gains (losses)			(1.1)	(0.8)			(1.9)	(5.7)
End of period			$ 2.2	$ 5.4		$ 3.3	$ 2.2	$ 5.4
Interest Rate Cap [Member] \| Preferred Stock [Member] \| Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale of Stock, Number of Shares Issued in Transaction	250,000,000
Sirius Group Ltd [Member] \| Preferred Stock [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Term of LIBOR loan		3 months
Basis points		3.20%
Sirius Group Ltd [Member] \| Interest Rate Cap [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Basis points	3.95%

Discontinued Operations - Forei

Discontinued Operations - Foreign Currency Swap and LOCs (Details) ¥ in Billions	Sep. 30, 2015USD ($)	Apr. 28, 2015USD ($)	Apr. 28, 2015JPY (¥)	Nov. 25, 2014USD ($)
Currency Swap [Member] \| Sirius Group
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Derivative, fair value, net	$ (2,300,000)
Currency Swap [Member] \| Sirius Group \| Euro Member Countries, Euro
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Notional amount \| ¥			¥ 0.1
Currency Swap [Member] \| Sirius Group \| Sweden, Kronor
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Notional amount		$ 50,000,000
Letter of Credit [Member] \| Sirius International [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
number of Credit Lines				2
Line of Credit Facility, Fair Value of Amount Outstanding				$ 200,000,000
Nordea Bank Finland
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total commitment under revolving credit facility				125,000,000
Lloyds Bank plc [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total commitment under revolving credit facility				75,000,000
Unsecured Debt [Member] \| Nordea Bank Finland
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total commitment under revolving credit facility				100,000,000
Unsecured Debt [Member] \| Lloyds Bank plc [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total commitment under revolving credit facility				$ 25,000,000

Contingencies (Details)

Contingencies (Details) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended		48 Months Ended
Contingencies (Details) $ in Millions	Jun. 30, 2007USD ($)	Sep. 30, 2015USD ($)	Sep. 30, 2014USD ($)	Jun. 30, 2014USD ($)	Sep. 30, 2015USD ($)	Sep. 30, 2014USD ($)	Sep. 30, 2015USD ($)	Jan. 22, 2015	Oct. 07, 2011
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		$ 10.3	$ 7		$ 18.2	$ 9.7
Esurance
Loss Contingencies [Line Items]
Percentage of fluctuation in loss reserves of transferred subsidiaries retained									90.00%
Tribune Company Litigation \| Pending Litigation \| OneBeacon
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		3.9	56.9	$ 2.7	73.3	166.8
OneBeacon Runoff [Member]
Loss Contingencies [Line Items]
Discontinued Operation, Gain (Loss) from Disposal of Discontinued Operation, before Income Tax		10.3	10.3	8.2	18.2		$ 28.3
Net gain on sale of discontinued operations			6.7	$ 5.3
Number of insurance holders								3
OneBeacon Runoff [Member] \| Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		0	(7)		0.3	(7.5)
Sirius Group \| Tribune Company Litigation \| Pending Litigation
Loss Contingencies [Line Items]
Proceeds from Sale, Maturity and Collection of Investments	$ 6.1
Sirius Group \| Discontinued Operations [Member]
Loss Contingencies [Line Items]
Net gain on sale of discontinued operations		$ 4	$ 57.2		$ 73.7	$ 167.7

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Subsequent Events (Details) - USD ($) $ in Millions	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Subsequent Event [Line Items]
Other Underwriting Expense	$ 56.5	$ 51.3	$ 165.5	$ 152.6
UNITED STATES \| Sale of Sirius [Member]
Subsequent Event [Line Items]
Stop Loss Limitation			45
Industry Loss Trigger on Industry Loss Warranty			15,000
UNITED STATES \| Combination One \| Sale of Sirius [Member]
Subsequent Event [Line Items]
Stop Loss Limitation			75
Industry Loss Trigger on Industry Loss Warranty			40,000
UNITED STATES \| Combination Two \| Sale of Sirius [Member]
Subsequent Event [Line Items]
Stop Loss Limitation			22.5
Industry Loss Trigger on Industry Loss Warranty			50,000
JAPAN \| Sale of Sirius [Member]
Subsequent Event [Line Items]
Stop Loss Limitation			25
Industry Loss Trigger on Industry Loss Warranty			$ 12,500

Pension Plan (Details)

Pension Plan (Details)	9 Months Ended
Pension Plan (Details)	Sep. 30, 2015
Compensation Related Costs [Abstract]
Months of Plan Assets to be Distributed	12 months