White Mountains Insurance (WTM) 10-Q 8 May 20 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2020	May 06, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity File Number	1-8993
Entity Registrant Name	WHITE MOUNTAINS INSURANCE GROUP, LTD
Entity Incorporation, State or Country Code	D0
Entity Tax Identification Number	94-2708455
Entity Address, Address Line One	23 South Main Street,
Entity Address, Postal Zip Code	03755-2053
Entity Address, City or Town	Hanover,
Entity Address, State or Province	NH
City Area Code	603
Local Phone Number	640-2200
Title of 12(b) Security	Common Shares, par value $1.00
Trading Symbol	WTM
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		3,105,038
Entity Central Index Key	0000776867
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Assets
Goodwill and other intangible assets	$ 646.8	$ 654.7
Total assets	3,739.7	3,983.2
Liabilities
Debt	294.7	283.5
Total liabilities	780.6	838.5
White Mountains’s common shareholders’ equity
White Mountains’s common shares at $1 par value per share—authorized 50,000,000 shares; issued and outstanding 3,135,005 and 3,185,353 shares and paid-in surplus	589.3	596.3
Retained earnings	2,498	2,672.4
Accumulated other comprehensive loss, after tax:
Accumulated Other Comprehensive Income (Loss), Net of Tax	(10.6)	(7.2)
Total White Mountains’s common shareholders’ equity	3,076.7	3,261.5
Non-controlling interests
Non-controlling interests	(117.6)	(116.8)
Total equity	2,959.1	3,144.7
Total liabilities and equity	3,739.7	3,983.2
HG Global-BAM
Assets
Fixed maturity investments, at fair value	818.2	799.3
Short-term investments, at fair value	24.5	46.3
Total investments	842.7	845.6
Cash	10.5	24.2
Insurance premiums receivable	6.8	6.7
Deferred acquisition costs	23.3	22.1
Accrued investment income	5.5	5.4
Other assets	15.4	20
Total assets	904.2	924
Liabilities
Unearned insurance premiums	202.7	198.4
Accrued incentive compensation	9.7	21.7
Other liabilities	26.4	26.7
Total liabilities	238.8	246.8
NSM Holding Co LLC
Assets
Cash	89.7	89.7
Accounts Receivable, after Allowance for Credit Loss	71.5	70.8
Goodwill and other intangible assets	615.2	623
Other assets	46.5	41.7
Total assets	822.9	825.2
Liabilities
Debt	218.4	219.2
Premiums payable	110.8	102.3
Contingent consideration earnout liabilities	13.4	20.6
Other liabilities	61.1	59
Total liabilities	403.7	401.1
Non-controlling interests
Non-controlling interests	15	14.9
Kudu investments
Assets
Short-term investments, at fair value	0.1	0.1
Other long-term investments	262.7	266.5
Total investments	262.8	266.6
Cash	7.7	5.8
Accrued investment income	5.6	5.8
Goodwill and other intangible assets	9.5	9.6
Other assets	2.8	2.7
Total assets	288.4	290.5
Liabilities
Debt	65.7	53.6
Other liabilities	1.4	3.4
Total liabilities	67.1	57
Non-controlling interests
Non-controlling interests	2	2.2
Other Segment
Assets
Fixed maturity investments, at fair value	394.1	406.5
Short-term investments, at fair value	113	154.8
Common equity securities, at fair value	523.7	683.9
Other long-term investments	542.9	589.8
Total investments	1,573.7	1,835
Cash	28.5	41.3
Accrued investment income	7.3	5.7
Accounts receivable on unsettled investment sales	58.1	5.1
Goodwill and other intangible assets	22.1	22.1
Other assets	31.5	31.3
Assets held for sale	3	3
Total assets	1,724.2	1,943.5
Liabilities
Debt	10.6	10.7
Accrued incentive compensation	11.7	55.1
Accounts payable on unsettled investment purchases	1	0
Other liabilities	47.7	67.8
Total liabilities	$ 71	$ 133.6

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
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	3,135,005	3,185,353
Common shares, outstanding shares	3,135,005	3,185,353
NSM Holding Co LLC
Cash	$ 64.9	$ 56.3

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenues:
Net investment income	$ 22.9	$ 16
Net realized and unrealized investment gains	(156.7)	245.6
Total revenues	(59.2)	433.6
Expenses:
Total expenses	106.8	151.9
Pre-Tax and Net Income [Abstract]
Pre-tax (loss) income from continuing operations	(166)	281.7
Income tax benefit (expense)	25.5	(10.2)
Net (loss) income from continuing operations	(140.5)	271.5
Net gain from sale of discontinued operations, net of tax	0.9	0.7
Net income (loss)	(139.6)	272.2
Net loss attributable to non-controlling interests	10.8	12.2
Net (loss) income attributable to White Mountains’s common shareholders	(128.8)	284.4
HG Global-BAM
Revenues:
Earned insurance premiums	5.4	4.2
Net investment income	5.5	5.3
Net realized and unrealized investment gains	6.1	11.8
Commission revenues	0	0
Other revenue	0.5	0.6
Total revenues	17.5	21.9
Expenses:
Deferred Policy Acquisition Costs, Amortization Expense	1.7	1.3
Cost of sales		0
General and administrative expenses	14.7	14.4
Cost of sales	0
Amortization of other intangible assets	0	0
Interest expense	0
Total expenses	16.4	15.7
Pre-Tax and Net Income [Abstract]
Pre-tax (loss) income from continuing operations	1.1	6.2
NSM Holding Co LLC
Revenues:
Earned insurance premiums	0
Net investment income	0
Net realized and unrealized investment gains	0
Commission revenues	53	43.3
Other revenue	12	6
Total revenues	65	49.3
Expenses:
Deferred Policy Acquisition Costs, Amortization Expense	0
General and administrative expenses	39.6	25.3
Broker commission expenses	18.3	15.5
Change in fair value of contingent consideration earnout liabilities	(0.6)	1.3
Cost of sales	0
Amortization of other intangible assets	4.8	5
Interest expense	4.3	3.7
Total expenses	66.4	50.8
Pre-Tax and Net Income [Abstract]
Pre-tax (loss) income from continuing operations	(1.4)	(1.5)
Kudu investments
Revenues:
Earned insurance premiums	0
Net investment income	7.3	0
Net realized and unrealized investment gains	(24.8)	0
Commission revenues	0
Other revenue	0.1
Total revenues	(17.4)	0
Expenses:
Deferred Policy Acquisition Costs, Amortization Expense	0
General and administrative expenses	2.5	0
Cost of sales	0
Amortization of other intangible assets	0.1	0
Interest expense	1.4	0
Total expenses	4	0
Pre-Tax and Net Income [Abstract]
Pre-tax (loss) income from continuing operations	(21.4)
MediaAlpha
Revenues:
Earned insurance premiums		0
Net investment income		0
Net realized and unrealized investment gains		0
Commission revenues	0	48.8
Other revenue	0	0
Total revenues	0	48.8
Expenses:
Deferred Policy Acquisition Costs, Amortization Expense		0
General and administrative expenses	0	12.5
Cost of sales	0	40.6
Amortization of other intangible assets	0	1.6
Interest expense	0	0.2
Total expenses	0	54.9
Pre-Tax and Net Income [Abstract]
Pre-tax (loss) income from continuing operations		(6.1)
Other Segment
Revenues:
Earned insurance premiums	0	0
Net investment income	10.1	10.7
Net realized and unrealized investment gains	(138)	119.1
Realized gain and unrealized investment gain from the MediaAlpha Transaction		182.2
Commission revenues	2.1	1.3
Other revenue	1.5	0.3
Total revenues	(124.3)	313.6
Expenses:
Deferred Policy Acquisition Costs, Amortization Expense	0	0
General and administrative expenses	17.5	29.4
Cost of sales	2	1.1
Amortization of other intangible assets	0.2	0
Interest expense	0.3	0
Total expenses	20	30.5
Pre-Tax and Net Income [Abstract]
Pre-tax (loss) income from continuing operations	(144.3)	283.1
Discontinued Operations
Pre-Tax and Net Income [Abstract]
Net (loss) income attributable to White Mountains’s common shareholders	$ (128.8)	$ 284.4

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income (loss) attributable to White Mountains’s common shareholders	$ (128.8)	$ 284.4
Other comprehensive loss, net of tax	(3.4)	(0.3)
Comprehensive (loss) income	(132.2)	284.1
Comprehensive loss attributable to non-controlling interests	0	0
Comprehensive (loss) income attributable to White Mountains’s common shareholders	$ (132.2)	$ 284.1
Basic (loss) earnings per share
Continuing operations (in usd per share)	$ (40.82)	$ 89.42
Discontinued operations (in usd per share)	0.28	0.22
Total consolidated operations (in usd per share)	(40.54)	89.64
Diluted (loss) earnings per share
Continuing operations (in usd per share)	(40.82)	89.42
Discontinued operations (in usd per share)	0.28	0.22
Total consolidated operations (in usd per share)	(40.54)	89.64
Dividends declared per White Mountains’s common share	$ 1	$ 1

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Unaudited) - 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)AOCI, after tax	Foreign Currency Gain (Loss)Total	Foreign Currency Gain (Loss)Non-controlling interest	Foreign Currency Gain (Loss)Total Equity	BAMNon-controlling interest	BAMTotal Equity	MediaAlphaNon-controlling interest	MediaAlphaTotal Equity
Members Capital Contribution	$ (7.9)
Beginning Balances at Dec. 31, 2018		$ 584	$ 2,264.9	$ (5.8)	$ 2,843.1	$ (124.9)	$ 2,718.2
Increase (Decrease) in Shareholders' Equity
Net (loss) income	272.2		284.4		284.4	(12.2)	272.2
Net change in foreign currency translation and other								$ (0.3)	$ (0.3)	$ 0	$ (0.3)
Total comprehensive loss	284.1		284.4	0.3	284.1	(12.2)	271.9
Dividends declared on common shares			(3.2)		(3.2)		(3.2)
Dividends to non-controlling interests						(0.5)	(0.5)
Repurchases and retirements of common shares		(1)	(3.8)		(4.8)		(4.8)
Capital contributions from BAM members, net of tax												$ (6.8)	$ (6.8)
Net contributions from other non-controlling interests						0.7	0.7
Amortization of restricted share awards		2.5			2.5		2.5
Recognition of equity-based units of subsidiary		0.3			0.3	0	0.3
Effect of deconsolidation of MediaAlpha														$ (13.8)	$ (13.8)
Acquisition of non-controlling interests						0.2	0.2
Ending Balances at Mar. 31, 2019		585.8	2,542.3	(6.1)	3,122	(143.7)	2,978.3
Members Capital Contribution	(10)
Beginning Balances at Dec. 31, 2019	3,144.7	596.3	2,672.4	(7.2)	3,261.5	(116.8)	3,144.7
Increase (Decrease) in Shareholders' Equity
Net (loss) income	(139.6)		(128.8)		(128.8)	(10.8)	(139.6)
Net change in foreign currency translation and other				(3.4)					$ (3.4)	$ 0	$ (3.4)
Total comprehensive loss	(132.2)		(128.8)	(3.4)	(132.2)	(10.8)	(143)
Dividends declared on common shares			(3.2)		(3.2)		(3.2)
Dividends to non-controlling interests						(0.5)	(0.5)
Repurchases and retirements of common shares		(12.1)	(42.4)		54.5		(54.5)
Capital contributions from BAM members, net of tax												$ 10	$ 10
Net contributions from other non-controlling interests						0.5	0.5
Amortization of restricted share awards		5.1			5.1		5.1
Ending Balances at Mar. 31, 2020	$ 2,959.1	$ 589.3	$ 2,498	$ (10.6)	$ 3,076.7	$ (117.6)	$ 2,959.1

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operations:
Net (loss) income	$ (139.6)	$ 272.2
Adjustments to reconcile net income to net cash used for operations:
Net realized and unrealized investment losses (gains)	156.7	(245.6)
Realized gain from the MediaAlpha Transaction	0	(66.2)
Deferred income tax (benefit) expense	(27.9)	7.5
Net gain from sale of discontinued operations, net of tax	(0.9)	(0.7)
Amortization of restricted share and option awards	5.1	2.8
Amortization and depreciation	7.1	8.3
Other operating items:
Net change in Premiums and Commissions Receivable	(0.7)	(7.9)
Net change in Premiums Payable	8.5	16.2
Net change in unearned insurance premiums	4.3	3.6
Net change in deferred acquisition costs	(1.2)	(0.6)
Net change in restricted cash	8.6	10.8
Investments in asset management firms - Kudu	(21)	0
Net change in other assets and liabilities, net	(58.8)	(41.5)
Net cash used for operations	(59.8)	(41.1)
Cash flows from investing activities:
Net change in short-term investments	63.9	(55.3)
Sales of fixed maturity and convertible investments	116.1	93
Maturities, calls and paydowns of fixed maturity and convertible investments	58.9	25.6
Sales of common equity securities	40.3	136.5
Distributions and redemptions of other long-term investments and settlements of forward contracts	64.1	(1.9)
Purchases of other long-term investments	(10.9)	(60.6)
Purchases of common equity securities	(20.9)	(4.6)
Purchases of fixed maturity and convertible investments	(180.1)	(152.3)
Purchases of consolidated subsidiaries, net of cash acquired of $0.4	0	(9.6)
Other investing activities, net	(50.9)	(17.4)
Net cash provided from (used for) investing activities	80.5	(42.8)
Cash flows from financing activities:
Draw down of debt and revolving line of credit	12	106.5
Repayment of debt and revolving line of credit	(1)	(14.8)
Cash dividends paid to the Company’s common shareholders	(3.2)	(3.2)
Common shares repurchased	(47.8)	0
Distribution to non-controlling interest shareholders	(0.7)	(27.6)
Payments on contingent consideration earnout liability	(6.4)	0
Repurchase of shares from non-controlling interest shareholders	0	(21.1)
Proceeds from issuance of shares to non-controlling interest shareholders	0	62.7
Capital contributions to non-controlling interest shareholders	0.4	0.7
Capital contributions from BAM members	10	7.9
Fidus Re premium payment	(0.8)	(0.7)
Restricted share statutory withholding tax payments	(6.7)	(4.9)
Net cash (used for) provided from financing activities	(44.2)	105.5
Effect of exchange rate changes on cash	(1.1)	0.3
Net change in cash during the period - continuing operations, including the effect of exchange rate changes	(24.6)	21.9
Cash balances at beginning of period	161	110.3
Cash balances at end of period	136.4	132.2
Supplemental cash flows information:
Interest paid	(5.2)	(3.7)
Net income tax refunds	$ 0	$ 0

CONSOLIDATED STATEMENTS OF CA_2

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Cash balance	$ 136.4	$ 132.2	$ 161	$ 110.3
Cash acquired from acquisition	0	0.4
Discontinued Operations
Cash balance	$ 64.9	$ 60.8	$ 56.3	$ 50

Basis of Presentation and Signi

Basis of Presentation and Significant Accouting Policies	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation and Significant Accouting Policies	Basis of Presentation and Significant Accounting Policies Basis of Presentation The Company is an exempted Bermuda limited liability company whose principal businesses are conducted through its subsidiaries and other affiliates. The Company’s headquarters is located at 26 Reid Street, Hamilton, Bermuda HM 11, its principal executive office is located at 23 South Main Street, Hanover, New Hampshire 03755-2053 and its registered office is located at Clarendon House, 2 Church Street, Hamilton, Bermuda HM 11. The Company’s website is located at www.whitemountains.com. The information contained on White Mountains’s website is not incorporated by reference into, and is not a part of, this report. The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the accounts of White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”), its subsidiaries (collectively with the Company, “White Mountains”) and other entities required to be consolidated under GAAP. Consolidation Principles Under GAAP, the Company is required to consolidate any entity in which it holds a controlling financial interest. A controlling financial interest is usually in the form of an investment representing the majority of the subsidiary’s voting interests. However, a controlling financial interest may also arise from a financial interest in a variable interest entity (“VIE”) through arrangements that do not involve ownership of voting interests. The Company consolidates a VIE if it determines that it is the primary beneficiary. The primary beneficiary is defined as the entity who holds a variable interest that gives it both the power to direct the VIE’s activities that most significantly impact its economic performance and the obligation to absorb losses of, or the right to receive returns from, the VIE that could potentially be significant to the VIE. Intercompany transactions have been eliminated in consolidation. These interim financial statements include all adjustments considered necessary by management to fairly state the financial position, results of operations and cash flows of White Mountains. These interim financial statements may not be indicative of financial results for the full year and should be read in conjunction with the Company’s 2019 Annual Report on Form 10-K. Business Combinations White Mountains accounts for purchases of businesses using the acquisition method, which requires the measurement of assets acquired, including goodwill and other intangible assets, and liabilities assumed, including contingent liabilities, at their estimated fair values as of the acquisition date. The acquisition date fair values represent management’s best estimates and are based upon established valuation techniques, reasonable assumptions and, where appropriate, valuations performed by independent third parties. In circumstances where additional information is required in order to determine the acquisition date fair value of balance sheet amounts, provisional amounts may be recorded as of the acquisition date and may be subject to subsequent adjustment throughout the measurement period, which is up to one year from the acquisition date. Measurement period adjustments are recognized in the period in which they are determined. The results of operations and cash flows of businesses acquired are included in the consolidated financial statements from the date of acquisition. White Mountains accounts for purchases of other intangible assets that do not meet the definition of a business as asset acquisitions. Asset acquisitions are recognized at the amount of consideration paid, which is deemed to equal fair value. Use of Estimates 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. Reportable Segments White Mountains has determined its reportable segments based on the nature of the underlying businesses, the manner in which the Company’s subsidiaries and affiliates are organized and managed and the organization of the financial information provided to the chief operating decision maker to assess performance and make decisions regarding allocation of resources. As of March 31, 2020, White Mountains’s reportable segments were HG Global/BAM, NSM, Kudu and Other Operations. As a result of the MediaAlpha Transaction, White Mountains no longer consolidated MediaAlpha, and consequently it was no longer a reportable segment. See Note 13 — “Segment Information” . The HG Global/BAM segment consists of HG Global Ltd. and its wholly-owned subsidiaries (“HG Global”) and the consolidated results of Build America Mutual Assurance Company (“BAM”) (collectively, “HG Global/BAM”). BAM is the first and only mutual municipal bond insurance company in the United States. By insuring the timely payment of principal and interest, BAM provides market access to, and lowers interest expense for, issuers of municipal bonds used to finance essential public purposes such as schools, utilities and transportation facilities. BAM is owned by and operated for the benefit of its members, the municipalities that purchase BAM’s insurance for their debt issuances. HG Global was established to fund the startup of BAM and, through its wholly-owned subsidiary, HG Re Ltd. (“HG Re”), to provide up to 15% -of-par, first loss reinsurance protection for policies underwritten by BAM. HG Global, together with its subsidiaries, funded the initial capitalization of BAM through the purchase of $503.0 million of surplus notes issued by BAM, consisting of $203.0 million of Series A Notes and $300.0 million of Series B Notes (the “BAM Surplus Notes”). As of March 31, 2020 and December 31, 2019, 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. However, White Mountains is required to consolidate BAM’s results in its financial statements because BAM is a VIE for which White Mountains is the primary beneficiary. BAM’s results are attributed to non-controlling interests. The NSM segment consists of NSM Insurance HoldCo, LLC and its subsidiaries (collectively, “NSM”). NSM is a full-service managing general underwriting agency (“MGU”) and program administrator for specialty property and casualty insurance. The company places insurance in niche sectors such as specialty transportation, real estate, social services and pet health insurance. On behalf of its insurance carrier partners, NSM manages all aspects of the placement process, including product development, marketing, underwriting, policy issuance and claims. NSM earns commissions based on the volume and profitability of the insurance that it places. NSM does not take insurance risk. As of March 31, 2020 and December 31, 2019, White Mountains owned 96.4% of the basic units outstanding of NSM ( 88.4% on a fully diluted, fully converted basis). See Note 2 — “Significant Transactions ”. The Kudu segment consists of Kudu Investment Management, LLC and its subsidiaries (collectively “Kudu”), a capital solutions provider for asset management firms. Kudu provides capital solutions for boutique asset managers for a variety of purposes including generational ownership transfers, management buyouts, acquisition and growth finance and legacy partner liquidity. Kudu also provides strategic assistance to investees from time to time. Kudu’s capital solutions typically are structured as minority preferred equity stakes with distribution rights, typically tied to gross revenues and designed to generate immediate strong, stable cash yields. On April 4, 2019, White Mountains acquired the ownership interests in Kudu held by certain funds managed by Oaktree Capital Management, L.P. (“Oaktree”) for cash consideration of $81.4 million . In addition, White Mountains assumed all of Oaktree’s unfunded capital commitments to Kudu, increasing White Mountains’s total capital commitment to $250.0 million (the “Kudu Transaction”). As a result of the Kudu Transaction, White Mountains’s basic unit ownership of Kudu increased from 49.5% to 99.1% ( 42.7% to 85.4% on a fully diluted, fully converted basis), and White Mountains began consolidating Kudu in its financial statements during the second quarter of 2019. During the fourth quarter of 2019, White Mountains increased its total capital commitment to Kudu by an additional $100.0 million to $350.0 million and, Kudu obtained a committed $125.0 million credit facility. See Note 2 — “Significant Transactions” . The Other Operations segment consists of the Company and its wholly-owned subsidiary, White Mountains Capital, Inc., its other intermediate holding companies, its wholly-owned investment management subsidiary, White Mountains Advisors LLC (“WM Advisors”), investment assets managed by WM Advisors, its interests in MediaAlpha (for periods after the MediaAlpha Transaction), PassportCard Limited (“PassportCard”) and DavidShield Life Insurance Agency (2000) Ltd. (“DavidShield”) (collectively, “PassportCard/ DavidShield”), Elementum Holdings LP (“Elementum”) and Kudu (for periods prior to the Kudu Transaction), and certain other consolidated and unconsolidated entities and certain other strategic investments. The MediaAlpha segment consisted of QL Holdings LLC and its wholly-owned subsidiary QuoteLab, LLC (collectively “MediaAlpha”). MediaAlpha is a marketing technology company that enables the programmatic buying and selling of vertical-specific, performance-based media between advertisers (buyers of advertising inventory) and publishers (sellers of advertising inventory). On February 26, 2019, MediaAlpha completed the sale of a significant minority stake to Insignia Capital Group in connection with a recapitalization and cash distribution to existing equityholders (the “MediaAlpha Transaction”). White Mountains deconsolidated MediaAlpha as a result of the MediaAlpha Transaction and no longer reports it as a segment. White Mountains’s consolidated statement of comprehensive income and its segment disclosures include MediaAlpha’s results of operations through the date of the MediaAlpha Transaction. See Note 2 — “Significant Transactions” . Discontinued Operations and Assets Held for Sale White Mountains has classified its Guilford, Connecticut property, which consists of an office building and adjacent land, as held for sale as of March 31, 2020 and December 31, 2019. The property has been measured at its estimated fair value, net of disposal costs. See Note 17 — “Held for Sale and Discontinued Operations” . Derivatives From time to time, White Mountains holds derivative financial instruments for risk management purposes. White Mountains recognizes all derivatives as either assets or liabilities, measured at fair value, on the consolidated balance sheet. Changes in the fair value of derivative instruments that meet the criteria for hedge accounting are recognized in other comprehensive income and reclassified into current period pre-tax income when the hedged items are recognized therein. Changes in the fair value of derivative instruments that do not meet the criteria for hedge accounting are recognized in current period pre-tax income. As of March 31, 2020 and December 31, 2019, NSM holds an interest rate swap derivative instrument that meets the criteria for hedge accounting. See Note 7 — “Derivatives” . Reinsurance Contracts Accounted for as Deposits Reinsurance contracts that do not meet the risk transfer requirements necessary to be accounted for as reinsurance are accounted for using the deposit method under GAAP. BAM entered into a reinsurance contract agreement with Fidus Reinsurance Ltd. (“Fidus Re”) during the quarter ended June 30, 2018, which is accounted for using the deposit method. See Note 8 — “Municipal Bond Guarantee Insurance” . The nonrefundable consideration paid by BAM to Fidus Re is charged to financing expense within general and administrative expenses. Restricted Cash Cash includes amounts on hand and demand deposits with banks and other financial institutions. Cash balances that are not immediately available for general corporate purposes, including fiduciary accounts, are classified as restricted. Restricted amounts included within cash are disclosed parenthetically on the balance sheet. Amounts presented in the statement of cash flows are shown net of balances acquired and sold in the purchase or sale of White Mountains’s consolidated subsidiaries. Changes in restricted cash balances are presented as a separate caption within the operations, investing and financing activities sections of the statement of cash flows. Significant Accounting Policies Refer to the Notes to Consolidated Financial Statements in the Company’s 2019 Annual Report on Form 10-K for a complete discussion regarding White Mountains’s significant accounting policies. Recently Adopted Changes in Accounting Principles Income Taxes On January 1, 2020, White Mountains adopted ASU 2019-12, Simplifying the Accounting for Income Taxes (ASC 740), which removes exceptions to standard guidance. Under the new guidance non-income-based taxes, such as franchise taxes, will be reported within pre-tax income rather than being included in income taxes. In addition, the new guidance eliminates the exception to the incremental approach for interperiod tax allocation, which previously allowed consideration of the tax effects of items such as discontinued operations and items recognized through other comprehensive income. For periods subsequent to the adoption of ASU 2019-12, White Mountains records both the tax expense related to BAM’s members surplus contributions (“MSC”) and the related valuation allowance on such taxes through the non-controlling interest equity. Prior to the adoption of ASU 2019-12, White Mountains recorded the tax expense related to BAM’s MSC directly to non-controlling interest equity, while the valuation allowance on such taxes was recorded through the income statement. Goodwill On January 1, 2020, White Mountains adopted ASU 2017-04, Simplifying the Test for Goodwill Impairment (ASC 350), which changes the guidance on goodwill impairment testing. Under the new guidance, the qualitative assessment of the recoverability of goodwill remains the same. However, the second step that requires a quantitative review of the estimated fair value of the individual assets and liabilities compared to the carrying value of the goodwill is no longer required if the qualitative assessment is sufficient to indicate that there is no impairment. White Mountains did not recognize an impairment in goodwill during the quarter ended March 31, 2020 and accordingly, adoption of ASU 2017-04 had no impact on White Mountains’s financial statements. Credit Losses On January 1, 2020, White Mountains adopted ASU 2016-13, Measurement of Credit Losses on Financial Instruments (ASC 326), which establishes new guidance for the recognition of credit losses for financial assets measured at amortized cost. The new ASU requires reporting entities to estimate the credit losses expected over the life of a credit exposure using historical information, current information and reasonable and supportable forecasts that affect the collectability of the financial asset. White Mountains measures its portfolio of investment securities at fair value with changes therein recognized through current period earnings and, accordingly, adoption of ASU 2016-13 had no impact on White Mountains’s financial statements Leases On January 1, 2019, White Mountains adopted ASU 2016-02, Leases (ASC 842), which requires lessees to recognize lease assets and liabilities on the balance sheet for both operating and financing leases, with the exception of leases with an original term of 12 months or less. White Mountains elected the optional transition method that permits prospective adoption with recognition of a cumulative effect adjustment to the opening balance of retained earnings. As a result, White Mountains has presented comparative periods prior to adoption in accordance with previous lease accounting guidance. White Mountains also elected all available practical expedients permitted under ASC 842, which allowed White Mountains to carryforward its historical lease classification and not reassess leases for the definition of a lease under the new guidance. As of January 1, 2019, White Mountains recognized $23.2 million for both the lease right-of-use assets and lease liabilities. As of March 31, 2020, White Mountains recognized $22.9 million and $ 23.2 million of lease right-of-use assets and lease liabilities. Adoption of ASU 2016-02 did not result in an adjustment to opening retained earnings. Premium Amortization on Callable Debt Securities On January 1, 2019, White Mountains adopted ASU 2017-08, Premium Amortization on Purchased Callable Debt Securities

Significant Transactions

Significant Transactions	3 Months Ended
	Mar. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Significant Transactions	Significant Transactions Acquisitions Elementum On May 31, 2019, White Mountains acquired a 30.0% limited partnership interest in Elementum, a third-party registered investment adviser specializing in natural catastrophe insurance-linked securities (“ILS”), for $55.1 million (the “Elementum Transaction”). Elementum manages separate accounts and pooled investment vehicles across various ILS sectors, including catastrophe bonds, collateralized reinsurance investments and industry loss warranties, on behalf of third-party clients. As part of the Elementum Transaction, White Mountains also committed to invest $50.0 million in ILS funds managed by Elementum. As of March 31, 2020, White Mountains had $46.2 million invested into four Elementum-managed funds. White Mountains has elected to use the fair value option for its investments in Elementum and the ILS funds managed by Elementum. Both the investment in Elementum and the investments in ILS funds managed by Elementum are included within other long-term investments. NSM On May 11, 2018, White Mountains acquired a 95.0% basic units ownership interest in NSM ( 83.6% on a fully diluted, fully converted basis). White Mountains paid $274.2 million of cash consideration for its equity interest in NSM, and NSM borrowed $100.0 million in new debt as part of the transaction. On May 18, 2018, NSM acquired 100% of Fresh Insurance Services Group Limited (“Fresh Insurance”). Fresh Insurance is an insurance broker that offers non-standard personal lines products in the United Kingdom. NSM paid $ 49.6 million of upfront cash consideration for Fresh Insurance. NSM borrowed $51.0 million to fund the transaction. During the three months ended March 31, 2019, NSM paid a purchase price adjustment of an additional $0.7 million of consideration. The purchase price is subject to additional adjustments based upon growth in EBITDA during two earnout periods, one which ended in February 2020 and one ending in February 2022. On December 3, 2018, NSM acquired all the net assets of KBK Insurance Group, Inc. (“KBK”), a specialized MGU focused on the towing and transportation space. NSM paid $60.0 million of upfront cash consideration for KBK. White Mountains contributed $29.0 million to NSM and NSM borrowed $30.1 million to fund the transaction. As of December 31, 2018, White Mountains had recognized $59.4 million of goodwill and other intangible assets, reflecting acquisition date fair values. During the three months ended March 31, 2019, NSM recorded a purchase price adjustment of $5.9 million relating to the fair value of the contingent consideration earnout liability in connection with the acquisition, which was not previously determined. As of March 31, 2019, White Mountains determined that the relative values of goodwill and other intangible assets recorded in connection with the KBK transaction were $32.6 million and $32.7 million , reflecting acquisition date fair value. The purchase price is subject to additional adjustments based upon growth in EBITDA during three earn out periods, one which ended in December 2019, one ending in December 2020 and one ending in December 2021. On April 1, 2019, NSM acquired 100% of Embrace Pet Insurance (“Embrace”), a nationwide provider of pet health insurance for dogs and cats. NSM paid $71.5 million , of cash consideration, net of cash acquired, for Embrace. White Mountains contributed $58.2 million to NSM and NSM borrowed $20.4 million to fund the transaction. White Mountains recognized $52.2 million of goodwill and $15.4 million of other intangible assets, reflecting acquisition date fair values. On June 28, 2019, NSM acquired the renewal rights on its U.S. collector car business (the “Renewal Rights”) from American International Group, Inc. (“AIG”) for $82.5 million . The acquisition satisfied NSM’s contingent obligation to acquire the Renewal Rights from AIG. White Mountains contributed $59.1 million to NSM and NSM borrowed $22.5 million to fund the transaction. White Mountains recognized $82.5 million of other intangible assets, reflecting acquisition date fair values. See Note 4 — “Goodwill and Other Intangible Assets” . As of March 31, 2020 and December 31, 2019, NSM recorded total contingent consideration earnout liabilities of $ 13.4 million and $20.6 million . The contingent consideration earnout liabilities primarily related to the Fresh Insurance and KBK acquisitions are subject to adjustments based upon EBITDA, EBITDA projections, and present value factors for acquired entities. For the three months ended March 31, 2020 and 2019, NSM recognized pre-tax (income) expense of $(0.6) million and $1.3 million for the change in the fair value of its contingent consideration earnout liabilities. Any future adjustments to contingent consideration earnout liabilities under the agreements will also be recognized through pre-tax income. For the three months ended March 31, 2020, NSM paid $6.4 million related to KBK’s contingent consideration earnout liabilities. There were no payments for the three months ended March 31, 2019. Kudu On February 5, 2018, White Mountains entered into an agreement to fund up to $125.0 million in Kudu in exchange for a 49.5% basic units ownership interest in Kudu ( 42.7% on a fully diluted, fully converted basis). On April 4, 2019, White Mountains acquired the ownership interests in Kudu held by certain funds managed by Oaktree for cash consideration of $81.4 million . In addition, White Mountains assumed all of Oaktree’s unfunded capital commitments to Kudu, increasing White Mountains’s total capital commitment to $250.0 million . White Mountains recognized total assets acquired of $155.5 million , including $7.6 million of goodwill and $2.2 million of other intangible assets, total liabilities assumed of $0.8 million and non-controlling interest of $1.5 million . As a result of the Kudu Transaction, White Mountains’s basic unit ownership of Kudu increased from 49.5% to 99.1% ( 42.7% to 85.4% on a fully diluted, fully converted basis), and White Mountains began consolidating Kudu as a reportable segment in its financial statements during the second quarter of 2019. White Mountains’s consolidated financial statements and its segment disclosures include Kudu’s results from April 4, 2019, the date of the Kudu Transaction. For periods prior to the Kudu Transaction, White Mountains determined that Kudu was a VIE, but White Mountains was not the primary beneficiary. In those periods, White Mountains elected to use the fair value option. During the fourth quarter of 2019, White Mountains increased its total capital commitment to Kudu by $100.0 million to $350.0 million , of which $122.5 million and $129.0 million was undrawn as of March 31, 2020 and December 31, 2019. During the fourth quarter of 2019, Kudu obtained a committed $125.0 million credit facility, of which $56.0 million and $68.0 million was undrawn as of March 31, 2020 and December 31, 2019. See Note 5 — “Debt” . Dispositions MediaAlpha On February 26, 2019, MediaAlpha completed the MediaAlpha Transaction. White Mountains received net cash proceeds of $89.3 million from the MediaAlpha Transaction. White Mountains recognized a realized gain of $ 67.5 million and reduced its ownership interest to 48.3% of the basic units outstanding of MediaAlpha ( 42.0% on a fully diluted, fully converted basis) as a result of the MediaAlpha Transaction. White Mountains’s remaining ownership interest in MediaAlpha no longer meets the criteria for a controlling ownership interest and, accordingly, White Mountains deconsolidated MediaAlpha on February 26, 2019. White Mountains’s consolidated statement of operations and comprehensive income and its segment disclosures include MediaAlpha’s results of operations for the period from January 1, 2019 through February 26, 2019. Upon deconsolidation, White Mountains’s investment in MediaAlpha met the criteria to be accounted for under the equity method or under the fair value option. See Note 14 — “Equity-Method Eligible Investments” . White Mountains elected the fair value option and the investment in MediaAlpha was initially measured at its estimated fair value of $114.7 million as of the transaction date, with the change in fair value of $114.7 million recognized as an unrealized investment gain. White Mountains recognized a total of $ 182.2 million of realized gain and unrealized investment gain on the MediaAlpha Transaction.

Investment Securities

Investment Securities	3 Months Ended
	Mar. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Investment Securities	Investment Securities White Mountains’s portfolio of investment securities held for general investment purposes consists of fixed maturity investments, short-term investments, common equity securities and other long-term investments, which are classified as trading securities. Trading securities are reported at fair value as of the balance sheet date. Net realized and unrealized investment gains (losses) on trading securities are reported in pre-tax revenues. White Mountains’s fixed maturity investments are generally valued using industry standard pricing methodologies. Key inputs include benchmark yields, benchmark securities, reported trades, issuer spreads, bids, offers, credit ratings and prepayment speeds. Income on mortgage 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 (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 interest-bearing money market funds, certificates of deposit and other securities, which at the time of purchase, mature or become available for use within one year. Short-term investments are carried at amortized or accreted cost, which approximated fair value as of March 31, 2020 and December 31, 2019. Other long-term investments consist primarily of unconsolidated entities, including Kudu’s non-controlling equity interests in the form of revenue and earnings participation contracts (“Participation Contracts”), private equity funds, hedge funds, ILS funds and private debt instruments. Net Investment Income White Mountains’s net investment income is comprised primarily of interest income associated with White Mountains’s fixed maturity investments and short-term investments and dividend income from its common equity securities and other long-term investments. The following table presents pre-tax net investment income for the three months ended March 31, 2020 and 2019 : Three Months Ended March 31, Millions 2020 2019 Fixed maturity investments $ 8.1 $ 8.1 Short-term investments .8 1.3 Common equity securities 3.8 5.4 Other long-term investments 10.5 1.6 Total investment income 23.2 16.4 Third-party investment expenses (.3 ) (.4 ) Net investment income, pre-tax $ 22.9 $ 16.0 Net Realized and Unrealized Investment Gains (Losses) The following table presents net realized and unrealized investment gains (losses) for the three months ended March 31, 2020 and 2019 : Three Months Ended Three Months Ended March 31, 2020 March 31, 2019 Millions Total Net Realized and Unrealized Gains (Losses) Reflected in Earnings Total Net Realized and Fixed maturity investments $ 2.2 $ 21.1 Short-term investments .4 — Common equity securities (140.8 ) 111.3 Other long-term investments (1) (2) (18.5 ) 113.2 Net realized and unrealized investment (losses) gains, pre-tax (156.7 ) 245.6 Income tax benefit (expense) attributable to net realized and unrealized investment (losses) gains 25.5 (52.2 ) Net realized and unrealized investment (losses) gains, after-tax $ (131.2 ) $ 193.4 (1) For the three months ended March 31, 2019, excludes $67.5 of realized gain and includes $114.7 of unrealized investment gain associated with the MediaAlpha Transaction, which are both recorded in a separate line item in the statement of operations titled Realized gain and unrealized investment gain from the MediaAlpha Transaction. See Note 2 — “Significant Transactions”. (2) For the three months ended March 31, 2020 and March 31, 2019, includes $0.4 and $0.3 of realized and unrealized investment losses related to foreign currency exchange. The following table presents total gains (losses) included in earnings attributable to net unrealized investment gains (losses) for Level 3 investments for the three months ended March 31, 2020 and 2019 : Three Months Ended March 31, Millions 2020 2019 Other long-term investments $ (9.4 ) $ 114.0 Total net unrealized investment (losses) gains, pre-tax - Level 3 investments $ (9.4 ) $ 114.0 Investment Holdings The following tables present the cost or amortized cost, gross unrealized investment gains (losses) and carrying values of White Mountains’s fixed maturity investments as of March 31, 2020 and December 31, 2019 : March 31, 2020 Millions Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Carrying Value U.S. Government and agency obligations $ 217.5 $ 6.4 $ — $ 223.9 Debt securities issued by corporations 486.2 9.2 (8.7 ) 486.7 Municipal obligations 255.2 14.8 — 270.0 Mortgage and asset-backed securities 225.7 6.2 (.2 ) 231.7 Total fixed maturity investments $ 1,184.6 $ 36.6 $ (8.9 ) $ 1,212.3 December 31, 2019 Millions Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Carrying Value U.S. Government and agency obligations $ 231.7 $ 1.0 $ (.2 ) $ 232.5 Debt securities issued by corporations 454.9 12.5 (.2 ) 467.2 Municipal obligations 284.7 12.5 (.1 ) 297.1 Mortgage and asset-backed securities 206.6 2.7 (.3 ) 209.0 Total fixed maturity investments $ 1,177.9 $ 28.7 $ (.8 ) $ 1,205.8 The following tables present the cost or amortized cost, gross unrealized investment gains (losses), net foreign currency losses, and carrying values of White Mountains’s common equity securities and other long-term investments as of March 31, 2020 and December 31, 2019 : March 31, 2020 Millions Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Net Foreign Currency Losses Carrying Value Common equity securities $ 544.8 $ 11.3 $ (32.4 ) $ — $ 523.7 Other long-term investments $ 610.1 $ 265.7 $ (67.6 ) $ (2.6 ) $ 805.6 December 31, 2019 Millions Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Net Foreign Carrying Value Common equity securities $ 553.3 $ 130.6 $ — $ — $ 683.9 Other long-term investments $ 667.4 $ 255.2 $ (64.1 ) $ (2.2 ) $ 856.3 Other Long-Term Investments The following table presents the carrying values of White Mountains’s other long-term investments as of March 31, 2020 and December 31, 2019 : Carrying Value at Millions March 31, 2020 December 31, 2019 Kudu’s Participation Contracts (1) $ 262.7 $ 266.5 MediaAlpha (1) 210.0 180.0 PassportCard/DavidShield (1) 80.0 90.0 Elementum (1) 55.1 55.1 Other unconsolidated entities (1)(2) 24.8 31.2 Total unconsolidated entities (1) 632.6 622.8 Private equity funds and hedge funds 98.5 161.1 Insurance-linked securities funds 46.2 41.2 Private debt investments 25.8 28.7 Other 2.5 2.5 Total other long-term investments $ 805.6 $ 856.3 (1) See Fair Value Measurements by Level table. (2) Includes White Mountains’s non-controlling equity interests in certain private common equity securities, limited liability companies and convertible preferred securities. Private Equity Funds and Hedge Funds White Mountains invests in private equity funds and hedge funds, which are included in other long-term investments. The fair value of these investments is generally estimated using the net asset value (“NAV”) of the funds. As of March 31, 2020 , White Mountains held investments in thirteen private equity funds. The largest investment in a single private equity fund or hedge fund was $21.1 million as of March 31, 2020 and $54.6 million as of December 31, 2019 . In the first quarter of 2020, White Mountains submitted a notice to redeem its sole hedge fund having a fair value of $45.6 million, which was recorded in accounts receivable on unsettled investment sales as of March 31, 2020. The bulk of the redemption proceeds, subject to customary audit holdbacks, were received in April 2020 and the remaining balance is expected to be received in April 2021. The following table presents investments and unfunded commitments in private equity funds and hedge funds by investment objective and sector as of March 31, 2020 and December 31, 2019 : March 31, 2020 December 31, 2019 Millions Fair Value Unfunded Commitments Fair Value Unfunded Commitments Private equity funds Manufacturing/Industrial $ 44.5 $ 4.0 $ 57.7 $ 4.1 Aerospace/Defense/Government 37.5 23.3 33.8 23.3 Financial services 16.5 25.9 15.0 22.8 Total private equity funds 98.5 53.2 106.5 50.2 Hedge funds Long/short banks and financials — — 54.6 — Total hedge funds — — 54.6 — Total private equity funds and hedge funds included in other long-term investments $ 98.5 $ 53.2 $ 161.1 $ 50.2 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 have the option to extend the lock-up period. The following table presents investments in private equity funds that were subject to lock-up periods as of March 31, 2020 : Millions 1 – 3 years 3 – 5 years 5 – 10 years >10 years Total Private equity funds — expected lock-up period remaining $4.7 $39.3 $43.3 $11.2 $98.5 Investors in private equity funds are generally subject to indemnification obligations outside of the capital commitment period and prior to the winding up of the fund. As of March 31, 2020 and December 31, 2019, White Mountains is not aware of any indemnification claims relating to its investments in private equity funds. Redemption of investments in most 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. Insurance-Linked Securities Funds White Mountains’s other long-term investments include ILS funds. The fair value of these investments is generally estimated using the NAV of the funds. As of March 31, 2020, White Mountains held investments in four ILS funds with a fair value of $46.2 million and $5.2 million of unfunded commitments. Investments in ILS funds are generally subject to restrictions, including lock-up periods where no redemptions or withdrawals are allowed, non-renewal clauses, restrictions on redemption frequency and advance notice periods for redemptions. From time to time, natural catastrophe, liquidity, market or other events will occur that make the determination of fair value for underlying investments in an ILS fund less certain due to the potential for loss development. In such circumstances, the impacted investments may be subject to additional lock-up provisions. As of March 31, 2020, White Mountains holds one ILS fund subject to a lock-up period that expires on June 1, 2020. White Mountains’s ILS funds are subject to monthly and annual restrictions on redemptions and advance redemption notice period requirements that range between 30 and 90 days. 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. In the first quarter of 2020, White Mountains invested in an ILS fund that requires shareholders to make additional capital commitments annually equal to their existing capital commitment, unless a non-renewal notice is provided on or before September 15 of each calendar year. The notice of non-renewal constitutes a redemption request. Fund proceeds become available on the last calendar day of month when the last underlying fund investment has fully matured or been commuted, which is typically three years from the initial investment in the fund. Fair Value Measurements as of March 31, 2020 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”). As of March 31, 2020 and December 31, 2019, White Mountains used quoted market prices or other observable inputs to determine fair value for approximately 70% and 71% of the investment portfolio. Fair Value Measurements by Level The following tables present White Mountains’s fair value measurements for investments as of March 31, 2020 and December 31, 2019 by level. The major security types were based on the legal form of the securities. White Mountains has disaggregated its fixed maturity investments based on the issuing entity type, which impacts credit quality, with debt securities issued by U.S. government entities carrying minimal credit risk, while the credit and other risks associated with other issuers, such as corporations, foreign governments, municipalities or entities issuing mortgage and asset-backed securities vary depending on the nature of the issuing entity type. White Mountains further disaggregates debt securities issued by corporations and common equity securities by industry sector because investors often reference commonly used benchmarks and their subsectors to monitor risk and performance. Accordingly, White Mountains has further disaggregated these asset classes into subclasses based on the similar sectors and industry classifications it uses to evaluate investment risk and performance against commonly used benchmarks, such as the Bloomberg Barclays U.S. Intermediate Aggregate and S&P 500 indices. March 31, 2020 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 223.9 $ 223.9 $ — $ — Debt securities issued by corporations: Financials 151.3 — 151.3 — Industrial 63.4 — 63.4 — Healthcare 52.8 — 52.8 — Technology 52.7 — 52.7 — Consumer 47.5 — 47.5 — Energy 38.2 — 38.2 — Utilities 30.4 — 30.4 — Communications 29.1 — 29.1 — Materials 21.3 — 21.3 — Total debt securities issued by corporations 486.7 — 486.7 — Municipal obligations 270.0 — 270.0 — Mortgage and asset-backed securities 231.7 — 231.7 — Total fixed maturity investments 1,212.3 223.9 988.4 — Short-term investments (1) 137.6 130.9 6.7 — Common equity securities: Exchange traded funds (2) 415.6 403.7 11.9 — Other (3) 108.1 18.0 90.0 .1 Total common equity securities 523.7 421.7 101.9 .1 Other long-term investments 660.9 — — 660.9 Other long-term investments — NAV (4) 144.7 — — — Total investments $ 2,679.2 $ 776.5 $ 1,097.0 $ 661.0 (1) Short-term investments are measured at amortized cost, which approximates fair value. (2) ETFs traded on foreign exchanges are priced using the fund’s published NAV to account for the difference in market close times and are therefore designated a Level 2 measurement. (3) Primarily consists of two investments in unit trusts that predominantly invest in international equities and an open-end mutual fund that invests in domestic large-cap companies. (4) Consists of private equity funds and ILS funds for which fair value is measured at NAV using the practical expedient. Investments for which fair value is measured at NAV are not classified within the fair value hierarchy. December 31, 2019 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 232.5 $ 232.5 $ — $ — Debt securities issued by corporations: Financials 144.8 — 144.8 — Industrial 59.0 — 59.0 — Healthcare 52.6 — 52.6 — Consumer 50.9 — 50.9 — Energy 44.9 — 44.9 — Technology 41.2 — 41.2 — Communications 31.3 — 31.3 — Utilities 25.0 — 25.0 — Materials 17.5 — 17.5 — Total debt securities issued by corporations 467.2 — 467.2 — Municipal obligations 297.1 — 297.1 — Mortgage and asset-backed securities 209.0 — 209.0 — Total fixed maturity investments 1,205.8 232.5 973.3 — Short-term investments (1) 201.2 189.4 11.8 — Common equity securities: Exchange traded funds (2) 536.4 521.6 14.8 — Other (3) 147.5 25.9 121.5 .1 Total common equity securities 683.9 547.5 136.3 .1 Other long-term investments 654.0 — — 654.0 Other long-term investments — NAV (4) 202.3 — — — Total investments $ 2,947.2 $ 969.4 $ 1,121.4 $ 654.1 (1) Short-term investments are measured at amortized cost, which approximates fair value. (2) ETFs traded on foreign exchanges are priced using the fund’s published NAV to account for the difference in market close times and are therefore designated a Level 2 measurement. (3) Primarily consists of two investments in unit trusts that predominantly invest in international equities and an open-end mutual fund that invests in domestic large-cap companies. (4) Consists of private equity funds, one hedge fund and ILS funds for which fair value is measured at NAV using the practical expedient. Investments for which fair value is measured at NAV are not classified within the fair value hierarchy. Debt Securities Issued by Corporations The following table presents the ratings of debt securities issued by corporations held in White Mountains’s investment portfolio as of March 31, 2020 and December 31, 2019 : Fair Value at Millions March 31, 2020 December 31, 2019 AAA $ 11.3 $ 9.5 AA 63.6 73.9 A 304.7 288.5 BBB 106.1 95.3 BB 1.0 — Debt securities issued by corporations (1) $ 486.7 $ 467.2 (1) Credit ratings are based upon issuer credit ratings provided by Standard & Poor’s Financial Services LLC (“Standard & Poor’s”), or if unrated by Standard & Poor’s, long-term obligation ratings provided by Moody’s Investor Service, Inc. Mortgage and Asset-backed Securities The following table presents the fair value of White Mountains’s mortgage and asset-backed securities as of March 31, 2020 and December 31, 2019 : March 31, 2020 December 31, 2019 Millions Fair Value Level 2 Level 3 Fair Value Level 2 Level 3 Mortgage-backed securities: Agency: FNMA $ 90.6 $ 90.6 $ — $ 88.6 $ 88.6 $ — FHLMC 72.1 72.1 — 60.5 60.5 — GNMA 45.7 45.7 — 30.8 30.8 — Total agency (1) 208.4 208.4 — 179.9 179.9 — Total mortgage-backed securities 208.4 208.4 — 179.9 179.9 — Other asset-backed securities: Vehicle receivables 12.2 12.2 — 15.1 15.1 — Credit card receivables 11.1 11.1 — 14.0 14.0 — Total other asset-backed securities 23.3 23.3 — 29.1 29.1 — Total mortgage and asset-backed securities $ 231.7 $ 231.7 $ — $ 209.0 $ 209.0 $ — (1) Represents publicly traded mortgage-backed securities which carry the full faith and credit guaranty of the U.S. Government (i.e., GNMA) or are guaranteed by a government sponsored entity (i.e., FNMA, FHLMC). Rollforward of Fair Value Measurements by Level White Mountains uses quoted market prices where available as the inputs to estimate fair value for its investments in active markets. Such measurements are considered to be either Level 1 or Level 2 measurements, depending on whether the quoted market price inputs are for identical securities (Level 1) or similar securities (Level 2). Level 3 measurements for fixed maturity investments, common equity securities and other long-term investments as of March 31, 2020 and 2019 consist of securities for which the estimated fair value has not been determined based upon quoted market price inputs for identical or similar securities. The following tables present the changes in White Mountains’s fair value measurements by level for the three months ended March 31, 2020 and 2019 : Level 3 Investments Other Long-term Investments Measured at NAV (2) Millions Level 1 Investments Level 2 Investments Common Equity Securities Other Long-term Investments Total Balance at December 31, 2019 $ 780.0 $ 1,109.6 $ .1 $ 654.0 $ 202.3 $ 2,746.0 (1) Net realized and unrealized (losses) (98.7 ) (39.9 ) — (9.7 ) (8.8 ) (157.1 ) (3) Amortization/Accretion — (.8 ) — — — (.8 ) Purchases 74.2 126.8 — 24.7 7.2 232.9 Sales (109.9 ) (105.4 ) — (8.1 ) (56.0 ) (279.4 ) Transfers in — — — — — — Transfers out — — — — — — Balance at March 31, 2020 $ 645.6 $ 1,090.3 $ .1 $ 660.9 $ 144.7 $ 2,541.6 (1) (1) Excludes carrying value of $ 137.6 million and $ 201.2 as of March 31, 2020 and December 31, 2019 classified as short-term investments. (2) Includes private equity funds, hedge funds, ILS funds and unconsolidated entities for which fair value is measured at NAV using the practical expedient are no longer classified within the fair value hierarchy. See Note 1 — “Basis of Presentation and Significant Accounting Policies” . (3) Excludes realized and unrealized gains associated with short-term investments of $0.4 for the three months ended March 31, 2020. Level 3 Investments Other Long-term Investments Measured at NAV (3) Millions Level 1 Investments Level 2 Investments Other Long-term Investments Total Balance at December 31, 2018 $ 842.6 $ 1,160.5 $ 138.7 $ 186.9 $ 2,328.7 (1) Net realized and unrealized gains (losses) 91.7 40.7 114.0 (.8 ) 245.6 (2) Amortization/Accretion .1 (.4 ) — — (.3 ) Purchases 14.6 142.3 11.5 49.2 217.6 Sales (149.7 ) (105.4 ) — (1.9 ) (257.0 ) Transfers in — — 10.9 — 10.9 Transfers out — — — (10.9 ) (10.9 ) Balance at March 31, 2019 $ 799.3 $ 1,237.7 $ 275.1 $ 222.5 $ 2,534.6 (1) (1) Excludes carrying value of $ 269.8 and $ 214.2 as of March 31, 2019 and December 31, 2018 classified as short-term investments. (2) Includes $114.7 unrealized investment gain associated with the MediaAlpha Transaction, which is recorded in a separate line item in the statement of operations titled Realized gain and unrealized investment gain from the MediaAlpha Transaction. See Note 2 — “Significant Transactions”. (3) Includes private equity funds, hedge funds and unconsolidated entities for which fair value is measured at NAV using the practical expedient are no longer classified within the fair value hierarchy. See Note 1 — “Basis of Presentation and Significant Accounting Policies” . Fair Value Measurements — Transfers Between Levels - Three-months ended March 31, 2020 and 2019 Transfers between levels are recorded using the fair value measurement as of the end of the quarterly period in which the event or change in circumstance giving rise to the transfer occurred. During the first three months of 2020 and 2019, there were no fixed maturity investments or other long-term investments classified as Level 3 measurements in the prior period that were transferred to Level 2 measurements. During the first three months of 2020 and 2019, there were no fixed maturity investments or other long-term investments classified as Level 2 measurements in the prior period that were transferred to Level 3 measurements. Significant Unobservable Inputs The following tables present significant unobservable inputs used in estimating the fair value of other long-term investments, other than private equity funds, hedge funds and ILS funds, classified within Level 3 as of March 31, 2020 and December 31, 2019 . The fair value of investments in private equity funds, hedge funds and ILS funds are generally estimated using the NAV of the funds. $ in Millions March 31, 2020 Description Valuation Technique(s) Fair Value (2) Unobservable Inputs Discount Rate (2) Terminal Cash Flow Exit Multiple (x) or Terminal Revenue Growth Rate (%) (3) Kudu’s Participation Contracts (1) Discounted cash flow $262.7 18% - 24% 6x - 12x MediaAlpha Discounted cash flow $210.0 15% 4% PassportCard/DavidShield Discounted cash flow $80.0 25% 4% Elementum Holdings, L.P. Discounted cash flow $55.1 20% 4% Private debt instruments Discounted cash flow $25.8 7% - 15% N/A All other Discounted cash flow $13.6 25% 4% Noblr, Inc. Share price of recent transaction $8.7 Share price: $2.17 Zillion Insurance Services, Inc. Recent transaction $2.5 Transaction price: $2.5 Compare.com Estimated net realizable value $2.5 Net realizable value: $2.5 (1) In the first quarter of 2020, Kudu deployed $21.0 million in Creation Investments Capital Management. (2) Includes the net unrealized investment gains (losses) associated with foreign currency; foreign currency effects based on observable inputs. (3) Increases (decreases) to the discount rates in isolation would result in lower (higher) fair value measurements, while increases (decreases) to the terminal cash flow exit multiples or terminal revenue growth rates in isolation would result in higher (lower) fair value measurements. $ in Millions December 31, 2019 Description Valuation Technique(s) Fair Value (1) Unobservable Inputs Discount Rate (2) Terminal Cash Flow Exit Multiple (x) or Terminal Revenue Growth Rate (%) (2) Kudu’s Participation Contracts Discounted cash flow $266.5 15% - 22% 6x - 12x MediaAlpha Discounted cash flow $180.0 15% 4% PassportCard/DavidShield Discounted cash flow $90.0 22% 4% Elementum Holdings, L.P. Discounted cash flow $55.1 20% 4% Private debt instruments Discounted cash flow $23.7 4% - 9% N/A All other Discounted cash flow $23.7 25% - 32% 4% Noblr, Inc. Share price of recent transaction $5.0 Share price: $2.17 Zillion Insurance Services, Inc. Recent transaction $2.5 Transaction price: $2.5 Compare.com Estimated net realizable value $2.5 Net realizable value: $2.5 (1) Includes the net unrealized investment gains (losses) associated with foreign currency; foreign currency effects based on observable inputs. (2) Increases (decreases) to the discount rates in isolation would result in lower (higher) fair value measurements, while increases (decreases) to the terminal cash flow exit multiples or terminal revenue growth rates in isolation would result in higher (lower) fair value measurements.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	3 Months Ended
	Mar. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets White Mountains accounts for purchases of businesses using the acquisition method. Under the acquisition method, White Mountains recognizes and measures the assets acquired, liabilities assumed and any noncontrolling interest in the acquired entities at their acquisition date fair values. The estimated acquisition date fair values, generally consisting of intangible assets and liabilities for contingent consideration, may be recorded at provisional amounts in circumstances where the information necessary to complete the acquisition accounting is not available at the reporting date. Any such provisional amounts are finalized as measurement period adjustments within one year of the acquisition date. The following table presents the acquisition date fair values, accumulated amortization and net carrying values for other intangible assets and goodwill, by company as of March 31, 2020 and December 31, 2019 : $ in Millions Weighted Average Economic Life (in years) March 31, 2020 December 31, 2019 Acquisition Date Fair Value Accumulated Amortization Net Carrying Value Acquisition Date Fair Value Accumulated Amortization Impairments Net Carrying Value Goodwill: NSM (1) N/A $ 379.1 $ — $ 379.1 $ 381.6 $ — $ — $ 381.6 Kudu N/A 7.6 — 7.6 7.6 — — 7.6 Other Operations N/A 5.7 — 5.7 13.1 — 7.6 5.5 Total goodwill 392.4 — 392.4 402.3 — 7.6 394.7 Other intangible assets: NSM (1) Customer relationships 9 120.1 23.5 96.6 121.7 19.8 1.4 100.5 Trade names 19 61.2 5.8 55.4 61.9 5.3 .4 56.2 Information technology platform 5 3.1 1.3 1.8 3.9 1.4 .6 1.9 Renewal rights 12 82.5 1.0 81.5 82.5 .7 — 81.8 Other 3 1.7 .9 .8 1.7 .7 — 1.0 Subtotal 268.6 32.5 236.1 271.7 27.9 2.4 241.4 Kudu Trade names 7 2.2 .3 1.9 2.2 .2 — 2.0 Other Operations Trade names 10 1.0 .1 .9 1.7 .5 .2 1.0 Customer relationships 11 7.2 .5 6.7 7.2 .4 — 6.8 Information technology platform 5 — — — .5 .3 .2 — Insurance Licenses N/A 8.6 — 8.6 8.6 — — 8.6 Other 5 .2 — .2 .2 — — .2 Subtotal 17.0 .6 16.4 18.2 1.2 .4 16.6 Total other intangible assets 287.8 33.4 254.4 292.1 29.3 2.8 260.0 Total goodwill and other intangible assets $ 680.2 $ 33.4 646.8 $ 694.4 $ 29.3 10.4 654.7 Goodwill and other intangible assets attributed to non-controlling interests (23.5 ) (23.4 ) Goodwill and other intangible assets included in White Mountains’s common shareholders’ equity $ 623.3 $ 631.3 (1) As of March 31, 2020 , NSM’s goodwill and intangible assets included $(2.5) and $ (0.5) of the effect of foreign currency translation. As of December 31, 2019, NSM’s goodwill and intangible assets included $ 1.4 and $0.7 of the effect of foreign currency translation. The goodwill recognized for the entities shown above is attributed to expected future cash flows. The acquisition date fair values of other intangible assets with finite lives are estimated using income approach techniques, which use future expected cash flows to develop a discounted present value amount. The multi-period-excess-earnings method estimates fair value using the present value of the incremental after-tax cash flows attributable solely to the other intangible asset over its remaining life. This approach was used to estimate the fair value of other intangible assets associated with trade names, customer relationships and contracts and information technology. The relief-from-royalty method was used to estimate fair value for other intangible assets that relate to rights that could be obtained via a license from a third-party owner. Under this method, the fair value is estimated using the present value of license fees avoided by owning rather than leasing the asset. This technique was used to estimate the fair value of domain names, certain trademarks and brand names. The with-or-without method estimates the fair value of an other intangible asset that provides an incremental benefit. Under this method, the fair value of the other intangible asset is calculated by comparing the value of the entity with and without the other intangible asset. This approach was used to estimate the fair value of favorable lease terms. The following table presents a summary of the acquisition date fair values of goodwill and other intangible assets for acquisitions completed from January 1, 2019 through March 31, 2020 : $ in Millions Acquisition of subsidiary/ asset Goodwill and Other intangible asset (1) Acquisition Date Embrace (2) $ 67.6 April 1, 2019 Renewal Rights (3) 82.5 June 28, 2019 Total NSM segment $ 150.1 Kudu Transaction $ 9.8 April 4, 2019 Other Operations $ 22.6 Various (1) Acquisition date fair values include the effect of adjustments during the measurement period and excludes the effect of foreign currency translation subsequent to the acquisition date. (2) Exclude $3.4 of software classified within other assets. (3) NSM’s purchase of the Renewal Rights from AIG was an asset acquisition. On an annual basis beginning no later than the interim period included in the one-year anniversary of an acquisition, White Mountains evaluates goodwill for potential impairment. Between annual evaluations, White Mountains considers changes in circumstances or events subsequent to the most recent evaluation that may indicate that an impairment may exist and, if necessary will perform an interim review for potential impairment. There were no impairments recognized during the three month periods ended March 31, 2020 and 2019 and no events or changes in circumstances that would indicate the existence of an impairment of goodwill or other intangible asset for any acquired entity. The following tables presents the change in goodwill and other intangible assets for the three months ended March 31, 2020 and 2019: Three Months Ended March 31, 2020 2019 Millions Goodwill Other Intangible Assets Total Goodwill and Other Intangible Assets Goodwill Other Intangible Assets Total Goodwill and Other Intangible Assets Beginning balance $ 394.7 $ 260.0 654.7 $ 379.9 $ 157.6 $ 537.5 Deconsolidation of MediaAlpha — — — (18.3 ) (23.5 ) (41.8 ) Attribution of acquisition date fair value estimates between goodwill and other intangible assets — — — (26.8 ) 26.8 — Acquisitions of businesses — — — 13.4 — 13.4 Foreign currency translation (2.5 ) (.5 ) (3.0 ) 1.2 .3 1.5 Adjustments to reflect acquisition date fair value .2 — .2 .3 5.9 6.2 Amortization — (5.1 ) (5.1 ) — (6.6 ) (6.6 ) Ending balance $ 392.4 $ 254.4 $ 646.8 $ 349.7 $ 160.5 $ 510.2

Debt

Debt	3 Months Ended
	Mar. 31, 2020
Debt Disclosure [Abstract]
Debt	Debt The following table presents White Mountains’s debt outstanding as of March 31, 2020 and December 31, 2019: Millions March 31, Effective Rate (1) December 31, Effective Rate (1) NSM Bank Facility $ 220.7 6.8% $ 221.3 7.5% Unamortized issuance cost (3.6 ) (3.9 ) NSM Bank Facility, carrying value 217.1 217.4 Other NSM debt 1.3 2.2% 1.8 3.0% Kudu Bank Facility 69.0 9.1% 57.0 8.3% Unamortized issuance cost (3.3 ) (3.4 ) Kudu Bank Facility, carrying value 65.7 53.6 Other Operations debt 11.0 8.2% 11.1 8.3% Unamortized issuance cost (.4 ) (.4 ) Other Operations, carrying value 10.6 10.7 Total debt $ 294.7 $ 283.5 (1) Effective rate considers the effect of the debt issuance costs. NSM Bank Facility On May 11, 2018, NSM entered into a secured credit facility (the “NSM Bank Facility”) with Ares Capital Corporation in order to refinance NSM’s existing debt and to fund the acquisitions of subsidiaries. The NSM Bank Facility is comprised of term loans totaling $224.0 million and a revolving credit loan commitment of $10.0 million , under which NSM initially borrowed $2.0 million . The term loans under the NSM Bank Facility mature on May 11, 2024, and the revolving loan under the NSM Bank Facility matures on May 11, 2023. During the three months ended March 31, 2020 and 2019, NSM repaid $0.6 million and $0.5 million on the term loans and had no repayments on the revolving credit loan. During the three months ended March 31, 2020 , NSM did not make any borrowings on the term loans or revolving credit loans. During the three months ended March 31, 2019, NSM borrowed $6.5 million on the revolving credit loan. As of March 31, 2020 , the term loans had an outstanding balance of $220.7 million and the revolving credit loan was undrawn. Interest on the NSM Bank Facility accrues at a floating interest rate equal to the three-month LIBOR or the Prime Rate, as published by the Wall Street Journal plus, in each case, an applicable margin. The margin over LIBOR may vary between 4.25% and 4.75% , and the margin over the Prime Rate may vary between 3.25% and 3.75% , in each case, depending on the consolidated total leverage ratio of the borrower. On June 15, 2018, NSM entered into an interest rate swap agreement to hedge its exposure to interest rate risk on $151.0 million of its variable rate term loans. Under the terms of the swap agreement, NSM pays a fixed rate of 2.97% and receives a variable rate, which is reset monthly, based on then-current LIBOR. As of March 31, 2020 , the variable rate received by NSM under the swap agreement was 1.58% . As of March 31, 2020 , the interest rate, including the effect of the swap, for the outstanding term loans of $148.4 million that are hedged by the swap was 7.47% . The effective interest on the outstanding term loans of $72.3 million that are unhedged was 6.25% . The effective interest rate on the total outstanding term loans under the NSM Bank Facility of $220.7 million was 6.34% , excluding the effect of debt issuance costs. See Note 7 — “Derivatives” . The NSM Bank Facility is secured by all property of the loan parties and contains various affirmative, negative and financial covenants that White Mountains considers to be customary for such borrowings, including a maximum consolidated total leverage ratio covenant. Other NSM Debt NSM also has a secured term loan related to its U.K.-based operations. As of March 31, 2020, the secured term loan had an outstanding balance of $1.6 million and a maturity date of May 11, 2026. Kudu Bank Facility On December 23, 2019, Kudu entered into a secured credit facility (the “Kudu Bank Facility”) with Monroe Capital Management Advisors, LLC to provide funding for distributions to unitholders and fund new investments and related transaction expenses. The Kudu Bank Facility has a maximum borrowing capacity of $125.0 million , which is comprised of a revolving credit loan commitment of $5.0 million , an initial term loan of $57.0 million and a delayed-draw term loan of $63.0 million . The term loans and revolving credit loans, under the Kudu Bank Facility, mature in 2025. During the three months ended March 31, 2020 , Kudu borrowed $12.0 million in term loans under the Kudu Bank Facility and made no repayments. As of March 31, 2020, the term loans had an outstanding balance of $69.0 million and the revolving credit loan was undrawn. Interest on the Kudu Bank Facility accrues at a floating interest rate equal to the greater of the one-month LIBOR and 1.0% or the Prime Rate plus 1% , plus in each case, an applicable margin. The margin over LIBOR may vary between 5.50% and 6.25% and the margin over the Base Rate may vary between 4.50% and 5.25% , depending on the consolidated total leverage ratio of the borrower. The Kudu Bank Facility is secured by all property of the loan parties and contains various affirmative, negative and financial covenants that White Mountains considers to be customary for such borrowings, including a maximum consolidated total leverage ratio covenant. Other Operations Debt As of March 31, 2020, debt in White Mountains’s Other Operations segment consisted of a secured credit facility that had a maximum borrowing capacity of $16.3 million , which is comprised of a term loan of $11.3 million , a delayed-draw term loan of $3.0 million and a revolving credit loan commitment of $2.0 million , all with a maturity date of March 12, 2024. As of March 31, 2020, the term loans had an outstanding balance of $11.0 million and the revolving credit loan was undrawn. Compliance At March 31, 2020 , White Mountains was in compliance with the covenants under all of its debt instruments.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2020
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 and taxes are imposed, the Company and its Bermuda domiciled subsidiaries would be exempt from such tax until March 31, 2035, pursuant to the Bermuda Exempted Undertakings Tax Protection Act of 1966. The Company has subsidiaries and branches that operate in various other jurisdictions around the world that are subject to tax in the jurisdictions in which they operate. The jurisdictions in which the Company’s subsidiaries and branches are subject to tax are Barbados, Ireland, Israel, Luxembourg, the United Kingdom and the United States. In the first quarter of 2020, White Mountains adopted ASU 2019-12, Simplifying the Accounting for Income Taxes (ASC 740) (“ASU 2019-12”). For periods subsequent to the adoption of ASU 2019-12, White Mountains records both the tax expense related to BAM’s MSC and the related valuation allowance on such taxes through the non-controlling interest equity. Prior to the adoption of ASU 2019-12, White Mountains recorded the tax expense related to BAM’s MSC directly to non-controlling interest equity, while the valuation allowance on such taxes was recorded through the income statement. White Mountains’s income tax benefit related to pre-tax loss from continuing operations for the three months ended March 31, 2020 represented an effective tax rate of 15.4% . The effective tax rate was different from the U.S. statutory rate of 21.0% , due to income generated in jurisdictions with lower tax rates than the United States and state income taxes. White Mountains’s income tax expense related to pre-tax income from continuing operations for the three months ended March 31, 2019 represented an effective tax rate of 3.6% . The effective tax rate was different from the U.S. statutory rate of 21.0% , primarily due to a release of a full valuation allowance on net deferred tax assets at U.S. consolidated group Guilford Holdings, Inc. and subsidiaries (“Guilford”). Guilford includes Kudu, White Mountains’s investment in MediaAlpha, various service companies and certain other entities and investments that are included in the Other Operations segment. The effective rate was also different due to withholding taxes and a tax benefit recorded at BAM. For BAM, MSC and the related taxes thereon were recorded directly to non-controlling interest equity, while the valuation allowance on such taxes was recorded through the income statement. For the three months ended March 31, 2019, BAM recorded a tax benefit of $1.1 million associated with the valuation allowance on taxes related to MSC that is included in the effective tax rate. In arriving at the effective tax rate for the three months ended March 31, 2020 and 2019, 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, 2020 and 2019. 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. With few exceptions, White Mountains is no longer subject to U.S. federal, state, or non-U.S. income tax examinations by tax authorities for years before 2013.

Derivatives

Derivatives	3 Months Ended
	Mar. 31, 2020
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivatives	Derivatives
Interest Rate Swap
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivatives	NSM Interest Rate Swap On May 11, 2018, NSM entered into the NSM Bank Facility. Interest on the NSM Bank Facility accrues at a floating interest rate equal to the three month LIBOR or the Prime Rate, as published by the Wall Street Journal plus, in each case, an applicable margin. The margin over LIBOR may vary between 4.25% and 4.75% , and the margin over the Prime Rate may vary between 3.25% and 3.75% , in each case, depending on the consolidated total leverage ratio of the borrower. On June 15, 2018, NSM entered into an interest rate swap agreement to hedge its exposure to interest rate risk on $151.0 million of its variable rate term loans. Under the terms of the swap agreement, NSM pays a fixed rate of 2.97% and receives a variable rate, which is reset monthly, based on the then-current LIBOR. As of March 31, 2020, the variable rate received by NSM under the swap agreement was 1.58% . Over the term of the swap, the notional amount decreases in accordance with the principal repayments NSM expects to make on its term loans. As of March 31, 2020, the interest rate, including the effect of the swap, for the outstanding term loans of $148.4 million that are hedged by the swap was 7.47% , excluding the effect of debt issuance costs. NSM’s obligations under the swap are secured by the same collateral securing the NSM Bank Facility on a pari passu basis. NSM does not currently hold any collateral deposits from or provide any collateral deposits to the swap counterparty. NSM evaluated the effectiveness of the swap to hedge its interest rate risk associated with its variable rate debt and concluded at the swap inception date that the swap was highly effective in hedging that risk. NSM evaluates the effectiveness of the hedging relationship on an ongoing basis. For the three months ended March 31, 2020 and 2019, White Mountains recognized net interest expense of $0.5 million and $0.2 million for the periodic net settlement payments on the swap. As of March 31, 2020 and December 31, 2019, the estimated fair value of the swap and the accrual of the periodic net settlement payments recorded in other liabilities was $9.8 million and $6.6 million . There was no ineffectiveness in the hedge for the three month periods ended March 31, 2020 or March 31, 2019. For the three months ended March 31, 2020 and 2019, the $(3.2) million and $(1.9) million change in the fair value of the swap is included within White Mountains’s accumulated other comprehensive income (loss).

Municipal Bond Guarantee

Municipal Bond Guarantee	3 Months Ended
	Mar. 31, 2020
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 the initial capitalization of BAM, a newly formed mutual municipal bond insurer. As of March 31, 2020 , 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. At inception, BAM and HG Re also entered into a first loss reinsurance treaty (“FLRT”). HG Re provides first loss reinsurance protection up to 15% -of-par outstanding on each municipal bond insured by BAM. For capital appreciation bonds, par is adjusted to the estimated equivalent par value for current interest paying bonds. In return, BAM cedes 60% of the risk premium charged for insuring the municipal bond, net of a ceding commission. HG Re’s obligations under the FLRT are limited to the assets in two collateral trusts: a Regulation 114 Trust and a supplemental collateral trust (the “Supplemental Trust” and, together with the Regulation 114 Trust, the “Collateral Trusts”). Losses required to be reimbursed under the FLRT are subject to an aggregate limit equal to the assets held in the Collateral Trusts at any point in time. At inception, the Supplemental Trust contained the original $300.0 million of Series B Notes and $100.0 million of cash and fixed income securities. During 2017, in order to further support BAM’s long-term capital position and business prospects, HG Global agreed to contribute the original $203.0 million of Series A Notes into the Supplemental Trust. At the same time HG Global and BAM also changed the payment terms of the Series B Notes, so that payments reduce principal and accrued interest on a pro rata basis, consistent with the payment terms on the Series A Notes. The terms of the Series B Notes had previously stipulated that payments would first reduce interest owed, then reduce principal owed once all accrued interest had been paid. The New York State Department of Financial Services (“NYDFS”) approved the change during 2017. In connection with the contribution and change in payment terms of the Series B Notes, the Series A Notes were merged into the Series B Notes. On a monthly basis, BAM deposits cash equal to ceded premiums, net of ceding commissions, due to HG Re under the FLRT directly into the Regulation 114 Trust. The Regulation 114 Trust target balance is equal to gross ceded unearned premiums and unpaid ceded loss and LAE expenses, if any. If, at the end of any quarter, the Regulation 114 Trust balance is below the target balance, funds will be withdrawn from the Supplemental Trust and deposited into the Regulation 114 Trust in an amount equal to the shortfall. If, at the end of any quarter, the Regulation 114 Trust balance is above 102% of the target balance, funds will be withdrawn from the Regulation 114 Trust and deposited into the Supplemental Trust. The Supplemental Trust target balance is $603.0 million , less the amount of cash and securities in the Regulation 114 Trust in excess of its target balance (the “Supplemental Trust Target Balance”). If, at the end of any quarter, the Supplemental Trust balance exceeds the Supplemental Trust Target Balance, such excess may be distributed to HG Re. The distribution will be made first as an assignment of accrued interest on the BAM Surplus Notes and second in cash and/or fixed income securities. As the BAM Surplus Notes are repaid over time, the BAM Surplus Notes will be replaced in the Supplemental Trust by cash and fixed income securities. 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 8.0% to a variable rate equal to the one -year U.S. treasury rate plus 300 basis points, set annually. In 2018, BAM exercised its option to extend the variable rate period for an additional three years. The variable rate was 5.7% for 2019 and is 4.6% for 2020. In January 2020, HG Global and BAM agreed to amend the BAM Surplus Notes to extend the end of the variable interest rate period until December 31, 2024. At the end of the variable rate period, the interest rate will be fixed at the higher of the then current variable rate or 8.0% . BAM is required to seek regulatory approval to pay interest and principal on the BAM Surplus Notes only to the extent that its remaining qualified statutory capital and other capital resources continue to support its outstanding obligations, its business plan and its “AA/stable” rating from Standard & Poor’s. No payment of principal or interest on the BAM Surplus Notes may be made without the approval of the NYDFS. Under GAAP, if the terms of a debt instrument are amended, unless there is a greater than 10% change in the expected discounted future cash flows of such instrument, a change in the instrument’s carrying value is not permitted. White Mountains has determined that the impact of the changes to the terms of the BAM Surplus Notes on the expected discounted future cash flows was not greater than 10% . Also in January 2020, HG Global and BAM agreed to extend the initial 10 -year term of the FLRT to the end of 2022 and to enter into an excess of loss reinsurance agreement (the “XOLT”). Under the XOLT, HG Re provides last dollar protection for exposures on municipal bonds insured by BAM in excess of NYDFS single issuer limits. The XOLT is subject to an aggregate limit equal to the lesser of $75.0 million or the assets held in the Supplemental Trust at any point in time. At inception, BAM ceded exposure on one covered risk to HG Re under the XOLT. Additional cessions under the XOLT are subject to approval by HG Re. In connection with the actions described in the preceding paragraphs, in January 2020, BAM made a $65.0 million special cash payment of principal and interest on the BAM Surplus Notes. Of this payment, $47.9 million was a repayment of principal held in the Supplemental Trust, $0.9 million was a payment of accrued interest held inside the Supplemental Trust and $16.2 million was a payment of accrued interest held outside the Supplemental Trust. As of March 31, 2020 and December 31, 2019 , the collateral trusts held assets of $792.7 million and $786.7 million , which included $409.7 million and $457.6 million of BAM Surplus Notes. As of March 31, 2020 and December 31, 2019 , HG Global has accrued $150.4 million and $162.7 million of interest receivable on the BAM Surplus Notes. The following table presents a schedule of BAM’s insured obligations as of March 31, 2020 and December 31, 2019 : March 31, 2020 December 31, 2019 Contracts outstanding 9,312 8,987 Remaining weighted average contract period outstanding (in years) 10.6 10.7 Contractual debt service outstanding (in millions): Principal $ 64,481.2 $ 62,250.5 Interest 32,449.1 31,799.7 Total debt service outstanding $ 96,930.3 $ 94,050.2 Gross unearned insurance premiums (in millions) $ 202.7 $ 198.4 The following table presents a schedule of BAM’s future premium revenues as of March 31, 2020 : Millions March 31, 2020 April 1, 2020 - December 31, 2020 $ 14.3 January 1, 2021 - March 31, 2021 4.6 April 1, 2021 - June 30, 2021 4.5 July 1, 2021 - September 30, 2021 4.5 October 1, 2021 - December 31, 2021 4.4 Total 2021 18.0 2022 16.9 2023 15.9 2024 14.8 2025 13.8 2026 and thereafter 109.0 Total gross unearned insurance premiums $ 202.7 The following table presents a schedule of net written premiums and net earned premiums included in White Mountains’s HG Global/BAM segment for the three months ended March 31, 2020 and 2019 : Three Months Ended March 31, Millions 2020 2019 Written premiums: Direct $ 9.7 $ 7.9 Assumed — — Gross written premiums $ 9.7 $ 7.9 Earned premiums: Direct $ 4.5 $ 3.7 Assumed .9 .5 Gross earned premiums $ 5.4 $ 4.2 In April 2018, BAM entered into a collateralized financial guarantee excess of loss reinsurance agreement with Fidus Re, Ltd. (“Fidus Re”), a Bermuda based special purpose insurer created solely to provide reinsurance protection to BAM. Fidus Re was capitalized by the issuance of $100.0 million of insurance linked securities. The proceeds from issuance were placed in a collateral trust supporting Fidus Re’s obligations to BAM. The insurance linked securities were issued by Fidus Re with an initial term of twelve years and are callable five years after the date of issuance. Fidus Re reinsures 90% of aggregate losses exceeding $165.0 million on a portion of BAM’s financial guarantee portfolio up to a total reimbursement of $100.0 million . The aggregate loss limit under the agreement is $276.1 million . The agreement is accounted for using deposit accounting and any related financing expenses are recorded in general and administrative expenses as the agreement does not meet the risk transfer requirements necessary to be accounted for as reinsurance. In September 2019, BAM entered into facultative quota share reinsurance agreements under which it assumed a portfolio of municipal bond guarantee contracts with a par value of $1.1 billion . In November 2018, BAM entered into a 100% quota share facultative quota share reinsurance agreement under which it assumed a portfolio of municipal bond guarantee contracts with a par value of $2.2 billion . None of the contracts assumed were non-performing and no loss reserves have been established for any of the contracts, either as of the transaction dates or as of March 31, 2020. The agreement, which covers future claims exposure only, meets the risk transfer criteria under ASC 944-20, Insurance Activities

Investments in Unconsolidated E

Investments in Unconsolidated Entities	3 Months Ended
	Mar. 31, 2020
Equity Method Investments and Joint Ventures [Abstract]
Investments in Unconsolidated Entities	The following table presents the carrying values of White Mountains’s equity method eligible investments recorded within other long-term investments as of March 31, 2020 and December 31, 2019: Millions March 31, 2020 December 31, 2019 Equity method eligible investments, at fair value $ 718.0 $ 761.7 Other (1) 87.6 94.6 Total other long-term investments $ 805.6 $ 856.3 (1) Consists of other long-term investments that are not equity method eligible. The following table presents White Mountains’s significant equity method eligible investments as of March 31, 2020 and December 31, 2019: Basic Ownership Interest Investee March 31, 2020 December 31, 2019 Instrument Held PassportCard/DavidShield 50.0% 50.0% Common shares MediaAlpha 48.3% 48.3% Units durchblicker 45.0% 45.0% Common shares Elementum 30.0% 30.0% Limited partnership interest Compare.com 18.4% 18.4% Common shares Tuckerman Capital Funds 16.1 - 61.3% 17.5 - 62.4% Limited and general partnership interests Enlightenment Capital Funds 9.6 - 36.5% 10.0 - 38.4% Limited and general partnership interests JAM Partners L.P. — 11.1% Limited partnership interest Kudu Participation Contracts 3.2 - 30.0% 3.2 - 30.0% Revenue and earnings participation contracts As a result of the MediaAlpha Transaction, White Mountains reduced its ownership interest in MediaAlpha to 48.3% of the basic units outstanding ( 42.0% on a fully diluted, fully converted basis). White Mountains’s remaining ownership interest in MediaAlpha no longer meets the criteria for a controlling ownership interest and, accordingly, White Mountains deconsolidated MediaAlpha as of February 26, 2019. Upon deconsolidation, White Mountains’s investment in MediaAlpha met the criteria to be accounted for under the equity method or under the fair value option. White Mountains elected the fair value option and the investment in MediaAlpha was initially measured at its estimated fair value of $114.7 million as of March 31, 2019, with the change in fair value of $114.7 million recognized as an unrealized investment gain. For the twelve months ended December 31, 2019, White Mountains recognized $180.0 million in unrealized investment gains associated with its investment in MediaAlpha including changes in the fair value of White Mountains’s investment in MediaAlpha subsequent to the MediaAlpha Transaction. For the three months ended March 31, 2020, White Mountains recognized $30.0 million in unrealized investment gains associated with its investment in MediaAlpha. White Mountains’s consolidated statement of comprehensive income and its segment disclosures include MediaAlpha’s results of operations for the period from January 1, 2019 through February 26, 2019. See Note 2 — “Significant Transactions”. For the period from February 26, 2019 to March 31, 2019, MediaAlpha’s total revenues, total expenses, and pre-tax income were $33.5 million , $32.5 million , and $1.1 million . The following tables present summarized financial information for MediaAlpha: Millions March 31, 2020 December 31, 2019 Balance sheet data: Total assets $ 108.4 $ 106.9 Total liabilities $ 137.5 $ 144.6 Three Months Ended March 31, Millions 2020 2019 Income statement data: Total revenues $ 119.5 $ 48.8 Total expenses 109.5 54.9 Net income (loss) $ 10.0 $ (6.1 )

Earnings Per Share

Earnings Per Share	3 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
Earnings Per Share	Earnings Per Share White Mountains calculates earnings per share using the two-class method, which allocates earnings between common shares and unvested restricted common shares. Both classes of shares participate equally in dividends and earnings on a per share basis. Basic earnings per share amounts are based on the weighted average number of common shares outstanding adjusted for unvested restricted common shares. The following table presents the Company’s computation of earnings per share from continuing operations for the three months ended March 31, 2020 and 2019 . See Note 17 — “Held for Sale and Discontinued Operations” . Three Months Ended March 31, 2020 2019 Basic and diluted earnings per share numerators (in millions): Net (loss) income attributable to White Mountains’s common shareholders $ (128.8 ) $ 284.4 Less: total income from discontinued operations, net of tax .9 .7 Net (loss) income from continuing operations attributable to White Mountains’s common shareholders $ (129.7 ) $ 283.7 Allocation of losses (earnings) to participating restricted common shares (1) 1.3 (2.9 ) Basic and diluted (losses) earnings per share numerators $ (128.4 ) $ 280.8 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,178.0 3,172.2 Average unvested restricted common shares (2) (33.8 ) (32.5 ) Basic (losses) earnings per share denominator 3,144.2 3,139.7 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,178.0 3,172.2 Average unvested restricted common shares (2) (33.8 ) (32.5 ) Diluted (losses) earnings per share denominator 3,144.2 3,139.7 Basic and diluted earnings per share (in dollars) - continuing operations: Distributed earnings - dividends declared and paid $ 1.00 $ 1.00 Undistributed (losses) earnings (41.82 ) 88.42 Basic and diluted (losses) earnings per share $ (40.82 ) $ 89.42 (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 10 — “Employee Share-Based Incentive Compensation Plans”. The following table presents the undistributed net earnings (losses) from continuing operations for the three months ended March 31, 2020 and 2019 . See Note 17 — “Held for Sale and Discontinued Operations” . Three Months Ended March 31, Millions 2020 2019 Undistributed net earnings - continuing operations: Net (loss) income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ (128.4 ) $ 280.8 Dividends declared, net of restricted common share amounts (1) (3.1 ) (3.2 ) Total undistributed net (losses) earnings, net of restricted common share amounts $ (131.5 ) $ 277.6 (1) Restricted shares issued by White Mountains receive dividends, and therefore, are considered participating securities.

Employee Share-Based Incentive

Employee Share-Based Incentive Compensation Plans	3 Months Ended
	Mar. 31, 2020
Share-based Payment Arrangement [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 of White Mountains. As of March 31, 2020 , White Mountains’s share-based compensation incentive awards consist of performance shares and restricted shares. Performance Shares Performance shares are designed to reward employees for meeting company-wide performance targets. 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 service period, are subject to the attainment of pre-specified performance goals, and are valued based on the market value of common shares at the time awards are paid. Performance shares earned under the WTM Incentive Plan are typically paid in cash but may be paid in common shares. Compensation expense is recognized for the vested portion of the awards over the related service periods. The level of payout ranges from zero to two times the number of shares initially granted, depending on White Mountains’s financial performance. Performance shares become payable at the conclusion of a performance cycle (typically 3 years ) if pre-defined financial targets are met. The performance measures used for determining performance share payouts are growth in White Mountains’s adjusted book value per share and intrinsic value per share. Intrinsic value per share is generally calculated by adjusting adjusted book value per share for differences between the adjusted book value of certain assets and liabilities and White Mountains’s estimate of their underlying intrinsic values. The following table presents the performance share activity for the three months ended March 31, 2020 and 2019 for performance shares granted under the WTM Incentive Plan: Three Months Ended March 31, 2020 2019 Millions, except share amounts Target Performance Accrued Expense Target Performance Accrued Expense Beginning of period 42,473 $ 43.7 40,616 $ 31.7 Shares paid (1) (14,070 ) (27.7 ) (13,715 ) (18.1 ) New grants 14,055 — 13,700 — Forfeitures and cancellations (2) — .4 1 .2 Expense recognized — (6.6 ) — 9.3 End of period 42,458 $ 9.8 40,602 $ 23.1 (1) WTM performance share payments in 2020 for the 2017-2019 performance cycle, which were paid in cash in March 2020, ranged from 174% to 180% of target. WTM performance share payments in 2019 for the 2016-2018 performance cycle, which were paid in cash in March 2019, ranged from 139% to 166% of target. (2) Amounts include changes in assumed forfeitures, as required under GAAP. During the three months ended March 31, 2020 , White Mountains granted 14,055 performance shares for the 2020-2022 performance cycle. During the three months ended March 31, 2019 , White Mountains granted 13,700 performance shares for the 2019-2021 performance cycle. For performance shares earned in the 2017-2019 and 2016-2018 performance cycles, all performance shares earned were settled in cash. If all the outstanding WTM performance shares had vested on March 31, 2020 , the total additional compensation cost to be recognized would have been $18.5 million , based on accrual factors (common share price and payout assumptions) as of March 31, 2020 . The following table presents performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan as of March 31, 2020 for each performance cycle: Three Months Ended March 31, 2020 Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Performance cycle: 2018 – 2020 13,450 $ 5.1 2019 – 2021 15,600 3.8 2020 – 2022 14,055 1.1 Sub-total 43,105 10.0 Assumed forfeitures (647 ) (.2 ) March 31, 2020 42,458 $ 9.8 Restricted Shares Restricted shares are grants of a specified number of common shares that generally vest at the end of a three-year service period. The following table presents the unrecognized compensation cost associated with the outstanding restricted share awards for the three months ended March 31, 2020 and 2019 : Three Months Ended March 31, 2020 2019 Millions, except share amounts Restricted Unamortized Fair Value Restricted Unamortized Non-vested, Beginning of period 43,395 $ 16.7 41,510 $ 12.5 Issued 14,055 15.1 13,700 12.8 Vested (14,345 ) — (13,715 ) — Forfeited — — — — Expense recognized — (5.2 ) — (2.5 ) End of period 43,105 $ 26.6 41,495 $ 22.8 During the three months ended March 31, 2020 , White Mountains issued 14,055 restricted shares that vest on January 1, 2023. During the three months ended March 31, 2019 , White Mountains issued 13,700 restricted shares that vest on January 1, 2022. The unamortized issue date fair value as of March 31, 2020

Leases

Leases	3 Months Ended
	Mar. 31, 2020
Leases [Abstract]
Leases	Leases White Mountains has entered into lease agreements, primarily for office space. These leases are classified as operating leases, with lease expense recognized on a straight-line basis over the term of the lease. Lease incentives, such as free rent or landlord reimbursements for leasehold improvements, are recognized at lease inception and amortized on a straight-line basis over the term of the lease. Lease expense and the amortization of leasehold improvements are recognized within general and administrative expenses. Lease payments related to options to extend or renew the lease term are excluded from the calculation of lease liabilities unless White Mountains is reasonably certain of exercising those options. On January 1, 2019, White Mountains adopted ASU 2016-02, Leases (ASC 842). See Note 1 — “Basis of Presentation and Significant Accounting Policies” — Basis of Presentation and Significant Accounting Policies . Prior to adoption of ASU 2016-02, White Mountains recognized lease expense for operating leases on a straight-line basis, but did not recognize lease assets or liabilities on its consolidated balance sheet. Upon adoption on January 1, 2019, White Mountains recognized lease right-of-use (“ROU”) assets of $23.2 million and lease liabilities of $23.2 million . As of March 31, 2020 and December 31, 2019, the ROU asset was $22.9 million and $22.6 million and lease liabilities were $ 23.2 million and $22.8 million . The following table summarizes net lease expense recognized in White Mountains’s consolidated statement of operations for the three months ended March 31, 2020 and 2019: Millions Lease Cost Three Months Ended March 31, 2020 Three Months Ended March 31, 2019 Lease cost $ 2.0 $ 1.7 Less: sublease income .1 .1 Net lease cost $ 1.9 $ 1.6 The following table presents the contractual maturities of the lease liabilities associated with White Mountains’s operating lease agreements as of March 31, 2020 : Millions As of March 31, 2020 Remainder of 2020 $ 4.6 2021 5.4 2022 5.0 2023 4.2 2024 3.1 Thereafter 3.4 Total undiscounted lease payments 25.7 Less: present value adjustment 2.5 Operating lease liability $ 23.2 The following tables present lease related assets and liabilities by reportable segment as of March 31, 2020 and December 31, 2019: As of March 31, 2020 Millions HG/BAM NSM Kudu Other Operations Total Weighted Average Incremental Borrowing Rate (1) ROU lease asset $ 10.0 $ 6.2 $ 2.2 $ 4.5 $ 22.9 4.7% Lease liability $ 10.0 $ 6.2 $ 2.2 $ 4.8 $ 23.2 (1) The present value of the remaining lease payments was determined by discounting the lease payments using the incremental borrowing rate. As of December 31, 2019 Millions HG/BAM NSM Kudu Other Operations Total Weighted Average Incremental Borrowing Rate (1) ROU lease asset $ 10.4 $ 4.8 $ 2.3 $ 5.1 $ 22.6 4.6% Lease liability $ 10.4 $ 4.8 $ 2.3 $ 5.3 $ 22.8 (1) The present value of the remaining lease payments was determined by discounting the lease payments using the incremental borrowing rate.

Non-controlling Interests

Non-controlling Interests	3 Months Ended
	Mar. 31, 2020
Noncontrolling Interest [Abstract]
Non-controlling Interests	Non-controlling Interests Non-controlling interests consist of the ownership interests of non-controlling shareholders in consolidated entities and are presented separately on the balance sheet. The following table presents the balance of non-controlling interests included in White Mountains’s total equity and the related percentage of each consolidated entity’s total equity owned by non-controlling shareholders as of March 31, 2020 and December 31, 2019 : March 31, 2020 December 31, 2019 $ in Millions Non-controlling Percentage Non-controlling Equity Non-controlling Percentage Non-controlling Equity Non-controlling interests, excluding BAM HG Global 3.1 % $ 14.0 3.1 % $ 14.4 NSM 3.6 15.0 3.6 14.9 Other NSM 13.4 (.1 ) 13.4 (.1 ) Kudu .9 2.0 .9 2.2 Other Operations various (1.6 ) various (1.5 ) Total, excluding BAM 29.3 29.9 BAM 100.0 (146.9 ) 100.0 (146.7 ) Total non-controlling interests $ (117.6 ) $ (116.8 )

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2020
Segment Reporting [Abstract]
Segment Informartion	Segment Information As of March 31, 2020, White Mountains conducted its operations through four segments: (1) HG Global/BAM, (2) NSM, (3) Kudu and (4) Other Operations. In addition, MediaAlpha was consolidated as a reportable segment until the date of the MediaAlpha Transaction. As a result of the Kudu Transaction, White Mountains began consolidating Kudu in its financial statements in the second quarter of 2019. See Note 2 — “Significant Transactions” . As a result of the MediaAlpha Transaction, White Mountains no longer consolidated MediaAlpha, and consequently it was no longer a reportable segment. White Mountains’s segment disclosures for the three months ended March 31, 2019 include MediaAlpha’s results of operations for the period from January 1, 2019 to February 26, 2019, the date of the MediaAlpha Transaction. See Note 2 — “Significant Transactions” . 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. The following tables present the financial information for White Mountains’s segments for the three months ended March 31, 2020 and 2019: Millions HG Global/ BAM NSM Kudu Other Operations Total Three Months Ended March 31, 2020 Earned insurance premiums $ 5.4 $ — $ — $ — $ 5.4 Net investment income 5.5 — 7.3 10.1 22.9 Net realized and unrealized investment gains (loss) 6.1 — (24.8 ) (138.0 ) (156.7 ) Advertising and commission revenues — 53.0 — 2.1 55.1 Other revenue .5 12.0 .1 1.5 14.1 Total revenues 17.5 65.0 (17.4 ) (124.3 ) (59.2 ) Insurance acquisition expenses 1.7 — — — 1.7 Cost of sales — — — 2.0 2.0 General and administrative expenses 14.7 39.6 2.5 17.5 74.3 Broker commission expense — 18.3 — — 18.3 Change in fair value of contingent consideration — (.6 ) — — (.6 ) Amortization of other intangible assets — 4.8 .1 .2 5.1 Interest expense — 4.3 1.4 .3 6.0 Total expenses 16.4 66.4 4.0 20.0 106.8 Pre-tax income (loss) $ 1.1 $ (1.4 ) $ (21.4 ) $ (144.3 ) $ (166.0 ) Millions HG Global/BAM NSM MediaAlpha Other Operations Total Three Months Ended March 31, 2019 Earned insurance premiums $ 4.2 $ — $ — $ — $ 4.2 Net investment income 5.3 — — 10.7 16.0 Net realized and unrealized investment gains 11.8 — — 119.1 130.9 Realized and unrealized gains from the MediaAlpha Transaction — — — 182.2 182.2 Advertising and commission revenues (1) — 43.3 48.8 1.3 93.4 Other revenue .6 6.0 — .3 6.9 Total revenues 21.9 49.3 48.8 313.6 433.6 Insurance acquisition expenses 1.3 — — — 1.3 Cost of sales — — 40.6 1.1 41.7 General and administrative expenses 14.4 25.3 12.5 29.4 81.6 Broker commission expense — 15.5 — — 15.5 Change in fair value of contingent consideration — 1.3 — — 1.3 Amortization of other intangible assets — 5.0 1.6 — 6.6 Interest expense — 3.7 .2 — 3.9 Total expenses 15.7 50.8 54.9 30.5 151.9 Pre-tax income (loss) $ 6.2 $ (1.5 ) $ (6.1 ) $ 283.1 $ 281.7 (1) MediaAlpha’s results are from January 1, 2019 to February 26, 2019, the date of the MediaAlpha Transaction. In compliance with ASC 606, Revenues from Contracts with Customers, the following tables present White Mountains’s total revenues by revenue source for the three months ended March 31, 2020 and 2019: Millions HG Global/BAM NSM Kudu Other Operations Total Three Months Ended March 31, 2020 Commission and other revenue Specialty Transportation $ — $ 20.3 $ — $ — $ 20.3 Real Estate — 11.3 — — 11.3 Social Services — 6.3 — — 6.3 Pet — 11.8 — — 11.8 United Kingdom — 10.0 — — 10.0 Other — 5.3 — 1.4 6.7 Total commission and other revenue — 65.0 — 1.4 66.4 Product revenues — — — 2.1 — Revenues from contracts with customers — 65.0 — 3.5 68.5 Other revenues (1) 17.5 — (17.4 ) (127.8 ) (127.7 ) Total revenues $ 17.5 $ 65.0 $ (17.4 ) $ (124.3 ) $ (59.2 ) (1) Other revenues consist of premiums, investment income, investment gains and losses and other revenues outside the scope of ASC 606, Revenues from Contracts with Customers. Millions HG Global/BAM NSM MediaAlpha (2) Other Operations Total Three Months Ended March 31, 2019 Commission and other revenue Specialty Transportation $ — $ 17.9 $ — $ — $ 17.9 Real Estate — 9.0 — — 9.0 Social Services — 5.8 — — 5.8 United Kingdom — 12.1 — — 12.1 Other — 4.5 — 1.3 5.8 Total commission and other revenue — 49.3 — 1.3 50.6 Advertising revenues — — 48.8 — 48.8 Revenues from contracts with customers — 49.3 48.8 1.3 99.4 Other revenues (1) 21.9 — — 312.3 334.2 Total revenues $ 21.9 $ 49.3 $ 48.8 $ 313.6 $ 433.6 (1) Other revenues consist of premiums, investment income, investment gains and losses and other revenues outside the scope of ASC 606, Revenues from Contracts with Customers. (2) MediaAlpha’s results are from January 1, 2019 to February 26, 2019, the date of the MediaAlpha Transaction.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments White Mountains records its financial instruments at fair value with the exception of debt obligations, which are recorded as debt at face value less unamortized original issue discount. The following table presents the fair value and carrying value of this financial instrument as of March 31, 2020 and December 31, 2019 : March 31, 2020 December 31, 2019 Millions Fair Value Carrying Value Fair Value Carrying Value NSM Bank Facility $ 208.7 $ 217.1 $ 221.2 $ 217.4 Other NSM debt $ 1.6 $ 1.3 $ 1.7 $ 1.8 Kudu Bank Facility $ 63.4 $ 65.7 $ 53.6 (1) $ 53.6 Other Operations debt $ 11.3 $ 10.6 $ 11.3 $ 10.7 (1) White Mountains measured the fair value of the Kudu Bank Facility debt at the carrying value as a result of the debt being acquired on December 23, 2019. See Note 5 — “Debt” .

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Contingencies Legal Contingencies White Mountains is subject to litigation and arbitration in the normal course of business. White Mountains considers the requirements of ASC 450 when evaluating its exposure to 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. White Mountains does not have any current litigation that may have a material adverse effect on White Mountains’s financial condition, results of operations or cash flows. The following description presents significant legal contingencies, ongoing non-claims related litigation or arbitration as of March 31, 2020: Esurance On October 7, 2011, the Company completed the sale of its Esurance Holdings, Inc. and its subsidiaries and Answer Financial Inc. and its subsidiaries (collectively, “Esurance”) to The Allstate Corporation (“Allstate”) pursuant to a Stock Purchase Agreement dated as of May 17, 2011. Subject to specified thresholds and limits, the Company remains contingently liable to Allstate for specified matters related to the pre-closing period, including (a) losses of Esurance arising from extra-contractual claims and claims in excess of policy limits, (b) certain corporate reorganizations effected to remove entities from Esurance that were not being sold in the transaction, and (c) certain tax matters, including certain net operating losses being less than stated levels. Sirius Group Tax Contingency A subsidiary of Sirius Group, which was sold by White Mountains in 2016, has been denied interest deductions by the Swedish Tax Authority (“STA”) for tax years 2013-2016. In October 2018, the Swedish Administrative Court ruled against Sirius Group on its appeal of the Swedish Tax Agency’s denial of certain interest deductions relating to periods prior to the sale of Sirius Group to CMI. In connection with the sale, White Mountains indemnified Sirius Group against the loss of certain tax attributes, including those related to these interest deductions. As of March 31, 2020 and December 31, 2019 , White Mountains reported a liability of $15.5 million and $16.5 million , reflecting the value of these interest deductions. For the three months ended March 31, 2020 and 2019, the decreases in the liability of $1.0 million and $0.7 million is related to foreign currency translation and included within net gain on sale of discontinued operations. Sirius Group has appealed the decision to the Swedish Administrative Court of Appeal.

Held for Sale and Discontinued

Held for Sale and Discontinued Operations	3 Months Ended
	Mar. 31, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Held for Sale and Discontinued Operations	Held for Sale and Discontinued Operations Sirius Group As of March 31, 2020 and December 31, 2019, White Mountains recorded a liability of $15.5 million and $16.5 million , related to the Sirius Group tax contingency. For the three months ended March 31, 2020 and 2019, the decreases in the liability of $ 0.9 million and $0.7 million , is related to foreign currency translation and included within net gain on sale of discontinued operations. See Note 16 — “Commitments and Contingencies” . Other As of December 31, 2017, White Mountains has classified its Guilford, Connecticut property, which consists of an office building and adjacent land, as held for sale. The property has been measured at its estimated fair value net of costs of disposal, of $3.0 million as of March 31, 2020 and December 31, 2019
Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Held for Sale and Discontinued Operations	Earnings Per Share from Discontinued Operations White Mountains calculates earnings per share using the two-class method, which allocates earnings between common and unvested restricted common shares. Both classes of shares participate equally in earnings on a per share basis. Basic earnings per share amounts are based on the weighted average number of common shares outstanding adjusted for unvested restricted common shares. Diluted earnings per share amounts are also impacted by the net effect of potentially dilutive common shares outstanding. The following table presents the Company’s computation of earnings per share for discontinued operations for the three months ended March 31, 2020 and 2019 : Three Months Ended March 31, 2020 2019 Basic and diluted earnings per share numerators (in millions): Net (loss) income attributable to White Mountains’s common shareholders $ (128.8 ) $ 284.4 Less: total (loss) income from continuing operations, net of tax (129.7 ) 283.7 Net income from discontinued operations attributable to White Mountains’s common shareholders $ .9 $ .7 Allocation of earnings to participating restricted common shares (1) — — Basic and diluted earnings per share numerators (2) $ .9 $ .7 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,178.0 3,172.2 Average unvested restricted common shares (3) (33.8 ) (32.5 ) Basic earnings per share denominator 3,144.2 3,139.7 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,178.0 3,172.2 Average unvested restricted common shares (3) (33.8 ) (32.5 ) Diluted earnings per share denominator 3,144.2 3,139.7 Basic and diluted earnings per share (in dollars) - discontinued operations: $ .28 $ .22 (1) Restricted shares issued by White Mountains contain dividend participation features, and therefore, are considered participating securities. (2) Net earnings attributable to White Mountains’s common shareholders, net of restricted share amounts, is equal to undistributed earnings for the three months ended March 31, 2020 and 2019 . (3) Restricted common shares outstanding vest either in equal annual installments or upon a stated date. See Note 10 — “Employee Share-Based Incentive Compensation Plans” .

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	Note 18. Subsequent Events COVID-19 On January 30, 2020, the spread of novel coronavirus (“COVID-19”) was declared a Public Health Emergency of International Concern by the World Health Organization (“WHO”). Subsequently, on March 11, 2020, the WHO characterized the COVID-19 outbreak as a pandemic. White Mountains continues to monitor the impact of the COVID-19 pandemic, but at the date of this report it is too early to determine the full impact this may have on the global financial markets, the overall economy and on White Mountains’s businesses, results of operations and financial condition. Kingsbridge On April 7, 2020, NSM acquired 100% of Kingsbridge Group Limited (“Kingsbridge”), a leading provider of commercial lines insurance and consulting services to the U.K.’s contractor and freelancer markets. The transaction valued Kingsbridge at approximately £ 120 million . The transaction consideration consisted of approximately £ 103 million in upfront cash plus additional target earn-out consideration of approximately £ 17 million that is contingent on Kingsbridge achieving certain EBITDA growth objectives through January 2022. Actual earnout consideration could be more or less than the target amount. White Mountains contributed $ 79.9 million (approximately £ 64.9 million based upon the foreign exchange spot rate at the date of acquisition) to NSM and NSM borrowed £ 42.5 million

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accouting Policies (Policies)	3 Months Ended
	Mar. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The Company is an exempted Bermuda limited liability company whose principal businesses are conducted through its subsidiaries and other affiliates. The Company’s headquarters is located at 26 Reid Street, Hamilton, Bermuda HM 11, its principal executive office is located at 23 South Main Street, Hanover, New Hampshire 03755-2053 and its registered office is located at Clarendon House, 2 Church Street, Hamilton, Bermuda HM 11. The Company’s website is located at www.whitemountains.com. The information contained on White Mountains’s website is not incorporated by reference into, and is not a part of, this report. The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) and include the accounts of White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”), its subsidiaries (collectively with the Company, “White Mountains”) and other entities required to be consolidated under GAAP. Consolidation Principles Under GAAP, the Company is required to consolidate any entity in which it holds a controlling financial interest. A controlling financial interest is usually in the form of an investment representing the majority of the subsidiary’s voting interests. However, a controlling financial interest may also arise from a financial interest in a variable interest entity (“VIE”) through arrangements that do not involve ownership of voting interests. The Company consolidates a VIE if it determines that it is the primary beneficiary. The primary beneficiary is defined as the entity who holds a variable interest that gives it both the power to direct the VIE’s activities that most significantly impact its economic performance and the obligation to absorb losses of, or the right to receive returns from, the VIE that could potentially be significant to the VIE. Intercompany transactions have been eliminated in consolidation. These interim financial statements include all adjustments considered necessary by management to fairly state the financial position, results of operations and cash flows of White Mountains. These interim financial statements may not be indicative of financial results for the full year and should be read in conjunction with the Company’s 2019 Annual Report on Form 10-K.
Business Combinations	Business Combinations
Use of Estimates	Use of Estimates 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.
Reportable Segments	Reportable Segments White Mountains has determined its reportable segments based on the nature of the underlying businesses, the manner in which the Company’s subsidiaries and affiliates are organized and managed and the organization of the financial information provided to the chief operating decision maker to assess performance and make decisions regarding allocation of resources. As of March 31, 2020, White Mountains’s reportable segments were HG Global/BAM, NSM, Kudu and Other Operations. As a result of the MediaAlpha Transaction, White Mountains no longer consolidated MediaAlpha, and consequently it was no longer a reportable segment. See Note 13 — “Segment Information” . The HG Global/BAM segment consists of HG Global Ltd. and its wholly-owned subsidiaries (“HG Global”) and the consolidated results of Build America Mutual Assurance Company (“BAM”) (collectively, “HG Global/BAM”). BAM is the first and only mutual municipal bond insurance company in the United States. By insuring the timely payment of principal and interest, BAM provides market access to, and lowers interest expense for, issuers of municipal bonds used to finance essential public purposes such as schools, utilities and transportation facilities. BAM is owned by and operated for the benefit of its members, the municipalities that purchase BAM’s insurance for their debt issuances. HG Global was established to fund the startup of BAM and, through its wholly-owned subsidiary, HG Re Ltd. (“HG Re”), to provide up to 15% -of-par, first loss reinsurance protection for policies underwritten by BAM. HG Global, together with its subsidiaries, funded the initial capitalization of BAM through the purchase of $503.0 million of surplus notes issued by BAM, consisting of $203.0 million of Series A Notes and $300.0 million of Series B Notes (the “BAM Surplus Notes”). As of March 31, 2020 and December 31, 2019, 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. However, White Mountains is required to consolidate BAM’s results in its financial statements because BAM is a VIE for which White Mountains is the primary beneficiary. BAM’s results are attributed to non-controlling interests. The NSM segment consists of NSM Insurance HoldCo, LLC and its subsidiaries (collectively, “NSM”). NSM is a full-service managing general underwriting agency (“MGU”) and program administrator for specialty property and casualty insurance. The company places insurance in niche sectors such as specialty transportation, real estate, social services and pet health insurance. On behalf of its insurance carrier partners, NSM manages all aspects of the placement process, including product development, marketing, underwriting, policy issuance and claims. NSM earns commissions based on the volume and profitability of the insurance that it places. NSM does not take insurance risk. As of March 31, 2020 and December 31, 2019, White Mountains owned 96.4% of the basic units outstanding of NSM ( 88.4% on a fully diluted, fully converted basis). See Note 2 — “Significant Transactions ”. The Kudu segment consists of Kudu Investment Management, LLC and its subsidiaries (collectively “Kudu”), a capital solutions provider for asset management firms. Kudu provides capital solutions for boutique asset managers for a variety of purposes including generational ownership transfers, management buyouts, acquisition and growth finance and legacy partner liquidity. Kudu also provides strategic assistance to investees from time to time. Kudu’s capital solutions typically are structured as minority preferred equity stakes with distribution rights, typically tied to gross revenues and designed to generate immediate strong, stable cash yields. On April 4, 2019, White Mountains acquired the ownership interests in Kudu held by certain funds managed by Oaktree Capital Management, L.P. (“Oaktree”) for cash consideration of $81.4 million . In addition, White Mountains assumed all of Oaktree’s unfunded capital commitments to Kudu, increasing White Mountains’s total capital commitment to $250.0 million (the “Kudu Transaction”). As a result of the Kudu Transaction, White Mountains’s basic unit ownership of Kudu increased from 49.5% to 99.1% ( 42.7% to 85.4% on a fully diluted, fully converted basis), and White Mountains began consolidating Kudu in its financial statements during the second quarter of 2019. During the fourth quarter of 2019, White Mountains increased its total capital commitment to Kudu by an additional $100.0 million to $350.0 million and, Kudu obtained a committed $125.0 million credit facility. See Note 2 — “Significant Transactions” . The Other Operations segment consists of the Company and its wholly-owned subsidiary, White Mountains Capital, Inc., its other intermediate holding companies, its wholly-owned investment management subsidiary, White Mountains Advisors LLC (“WM Advisors”), investment assets managed by WM Advisors, its interests in MediaAlpha (for periods after the MediaAlpha Transaction), PassportCard Limited (“PassportCard”) and DavidShield Life Insurance Agency (2000) Ltd. (“DavidShield”) (collectively, “PassportCard/ DavidShield”), Elementum Holdings LP (“Elementum”) and Kudu (for periods prior to the Kudu Transaction), and certain other consolidated and unconsolidated entities and certain other strategic investments. The MediaAlpha segment consisted of QL Holdings LLC and its wholly-owned subsidiary QuoteLab, LLC (collectively “MediaAlpha”). MediaAlpha is a marketing technology company that enables the programmatic buying and selling of vertical-specific, performance-based media between advertisers (buyers of advertising inventory) and publishers (sellers of advertising inventory). On February 26, 2019, MediaAlpha completed the sale of a significant minority stake to Insignia Capital Group in connection with a recapitalization and cash distribution to existing equityholders (the “MediaAlpha Transaction”). White Mountains deconsolidated MediaAlpha as a result of the MediaAlpha Transaction and no longer reports it as a segment. White Mountains’s consolidated statement of comprehensive income and its segment disclosures include MediaAlpha’s results of operations through the date of the MediaAlpha Transaction. See Note 2 — “Significant Transactions” .
Discontinued Operations and Assets and Liabilities Held for Sale	Discontinued Operations and Assets Held for Sale White Mountains has classified its Guilford, Connecticut property, which consists of an office building and adjacent land, as held for sale as of March 31, 2020
Reinsurance Contracts Accounted For As Deposits	Reinsurance Contracts Accounted for as Deposits Reinsurance contracts that do not meet the risk transfer requirements necessary to be accounted for as reinsurance are accounted for using the deposit method under GAAP. BAM entered into a reinsurance contract agreement with Fidus Reinsurance Ltd. (“Fidus Re”) during the quarter ended June 30, 2018, which is accounted for using the deposit method. See Note 8 — “Municipal Bond Guarantee Insurance”
Restricted Cash	Restricted Cash
Recently Adopted Changes in Accounting Principles and Recently Issued Accounting Pronouncements	Recently Adopted Changes in Accounting Principles Income Taxes On January 1, 2020, White Mountains adopted ASU 2019-12, Simplifying the Accounting for Income Taxes (ASC 740), which removes exceptions to standard guidance. Under the new guidance non-income-based taxes, such as franchise taxes, will be reported within pre-tax income rather than being included in income taxes. In addition, the new guidance eliminates the exception to the incremental approach for interperiod tax allocation, which previously allowed consideration of the tax effects of items such as discontinued operations and items recognized through other comprehensive income. For periods subsequent to the adoption of ASU 2019-12, White Mountains records both the tax expense related to BAM’s members surplus contributions (“MSC”) and the related valuation allowance on such taxes through the non-controlling interest equity. Prior to the adoption of ASU 2019-12, White Mountains recorded the tax expense related to BAM’s MSC directly to non-controlling interest equity, while the valuation allowance on such taxes was recorded through the income statement. Goodwill On January 1, 2020, White Mountains adopted ASU 2017-04, Simplifying the Test for Goodwill Impairment (ASC 350), which changes the guidance on goodwill impairment testing. Under the new guidance, the qualitative assessment of the recoverability of goodwill remains the same. However, the second step that requires a quantitative review of the estimated fair value of the individual assets and liabilities compared to the carrying value of the goodwill is no longer required if the qualitative assessment is sufficient to indicate that there is no impairment. White Mountains did not recognize an impairment in goodwill during the quarter ended March 31, 2020 and accordingly, adoption of ASU 2017-04 had no impact on White Mountains’s financial statements. Credit Losses On January 1, 2020, White Mountains adopted ASU 2016-13, Measurement of Credit Losses on Financial Instruments (ASC 326), which establishes new guidance for the recognition of credit losses for financial assets measured at amortized cost. The new ASU requires reporting entities to estimate the credit losses expected over the life of a credit exposure using historical information, current information and reasonable and supportable forecasts that affect the collectability of the financial asset. White Mountains measures its portfolio of investment securities at fair value with changes therein recognized through current period earnings and, accordingly, adoption of ASU 2016-13 had no impact on White Mountains’s financial statements Leases On January 1, 2019, White Mountains adopted ASU 2016-02, Leases (ASC 842), which requires lessees to recognize lease assets and liabilities on the balance sheet for both operating and financing leases, with the exception of leases with an original term of 12 months or less. White Mountains elected the optional transition method that permits prospective adoption with recognition of a cumulative effect adjustment to the opening balance of retained earnings. As a result, White Mountains has presented comparative periods prior to adoption in accordance with previous lease accounting guidance. White Mountains also elected all available practical expedients permitted under ASC 842, which allowed White Mountains to carryforward its historical lease classification and not reassess leases for the definition of a lease under the new guidance. As of January 1, 2019, White Mountains recognized $23.2 million for both the lease right-of-use assets and lease liabilities. As of March 31, 2020, White Mountains recognized $22.9 million and $ 23.2 million of lease right-of-use assets and lease liabilities. Adoption of ASU 2016-02 did not result in an adjustment to opening retained earnings. Premium Amortization on Callable Debt Securities On January 1, 2019, White Mountains adopted ASU 2017-08, Premium Amortization on Purchased Callable Debt Securities

Investment Securities (Tables)

Investment Securities (Tables)	3 Months Ended
	Mar. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Pre-tax net investment income	The following table presents pre-tax net investment income for the three months ended March 31, 2020 and 2019 : Three Months Ended March 31, Millions 2020 2019 Fixed maturity investments $ 8.1 $ 8.1 Short-term investments .8 1.3 Common equity securities 3.8 5.4 Other long-term investments 10.5 1.6 Total investment income 23.2 16.4 Third-party investment expenses (.3 ) (.4 ) Net investment income, pre-tax $ 22.9 $ 16.0
Schedule of realized gain (loss) on investments	The following table presents net realized and unrealized investment gains (losses) for the three months ended March 31, 2020 and 2019 : Three Months Ended Three Months Ended March 31, 2020 March 31, 2019 Millions Total Net Realized and Unrealized Gains (Losses) Reflected in Earnings Total Net Realized and Fixed maturity investments $ 2.2 $ 21.1 Short-term investments .4 — Common equity securities (140.8 ) 111.3 Other long-term investments (1) (2) (18.5 ) 113.2 Net realized and unrealized investment (losses) gains, pre-tax (156.7 ) 245.6 Income tax benefit (expense) attributable to net realized and unrealized investment (losses) gains 25.5 (52.2 ) Net realized and unrealized investment (losses) gains, after-tax $ (131.2 ) $ 193.4
Schedule of unrealized gain (loss) on investments	The following table presents net realized and unrealized investment gains (losses) for the three months ended March 31, 2020 and 2019 : Three Months Ended Three Months Ended March 31, 2020 March 31, 2019 Millions Total Net Realized and Unrealized Gains (Losses) Reflected in Earnings Total Net Realized and Fixed maturity investments $ 2.2 $ 21.1 Short-term investments .4 — Common equity securities (140.8 ) 111.3 Other long-term investments (1) (2) (18.5 ) 113.2 Net realized and unrealized investment (losses) gains, pre-tax (156.7 ) 245.6 Income tax benefit (expense) attributable to net realized and unrealized investment (losses) gains 25.5 (52.2 ) Net realized and unrealized investment (losses) gains, after-tax $ (131.2 ) $ 193.4 (1) For the three months ended March 31, 2019, excludes $67.5 of realized gain and includes $114.7 of unrealized investment gain associated with the MediaAlpha Transaction, which are both recorded in a separate line item in the statement of operations titled Realized gain and unrealized investment gain from the MediaAlpha Transaction. See Note 2 — “Significant Transactions”. (2) For the three months ended March 31, 2020 and March 31, 2019, includes $0.4 and $0.3 of realized and unrealized investment losses related to foreign currency exchange.
Net unrealized investment gains (losses) for Level 3 investments	The following table presents total gains (losses) included in earnings attributable to net unrealized investment gains (losses) for Level 3 investments for the three months ended March 31, 2020 and 2019 : Three Months Ended March 31, Millions 2020 2019 Other long-term investments $ (9.4 ) $ 114.0 Total net unrealized investment (losses) gains, pre-tax - Level 3 investments $ (9.4 ) $ 114.0
Investment holdings, equity securities, convertible fixed maturities and other long-term investments	The following tables present the cost or amortized cost, gross unrealized investment gains (losses) and carrying values of White Mountains’s fixed maturity investments as of March 31, 2020 and December 31, 2019 : March 31, 2020 Millions Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Carrying Value U.S. Government and agency obligations $ 217.5 $ 6.4 $ — $ 223.9 Debt securities issued by corporations 486.2 9.2 (8.7 ) 486.7 Municipal obligations 255.2 14.8 — 270.0 Mortgage and asset-backed securities 225.7 6.2 (.2 ) 231.7 Total fixed maturity investments $ 1,184.6 $ 36.6 $ (8.9 ) $ 1,212.3 December 31, 2019 Millions Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Carrying Value U.S. Government and agency obligations $ 231.7 $ 1.0 $ (.2 ) $ 232.5 Debt securities issued by corporations 454.9 12.5 (.2 ) 467.2 Municipal obligations 284.7 12.5 (.1 ) 297.1 Mortgage and asset-backed securities 206.6 2.7 (.3 ) 209.0 Total fixed maturity investments $ 1,177.9 $ 28.7 $ (.8 ) $ 1,205.8 The following tables present the cost or amortized cost, gross unrealized investment gains (losses), net foreign currency losses, and carrying values of White Mountains’s common equity securities and other long-term investments as of March 31, 2020 and December 31, 2019 : March 31, 2020 Millions Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Net Foreign Currency Losses Carrying Value Common equity securities $ 544.8 $ 11.3 $ (32.4 ) $ — $ 523.7 Other long-term investments $ 610.1 $ 265.7 $ (67.6 ) $ (2.6 ) $ 805.6 December 31, 2019 Millions Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Net Foreign Carrying Value Common equity securities $ 553.3 $ 130.6 $ — $ — $ 683.9 Other long-term investments $ 667.4 $ 255.2 $ (64.1 ) $ (2.2 ) $ 856.3 Other Long-Term Investments The following table presents the carrying values of White Mountains’s other long-term investments as of March 31, 2020 and December 31, 2019 : Carrying Value at Millions March 31, 2020 December 31, 2019 Kudu’s Participation Contracts (1) $ 262.7 $ 266.5 MediaAlpha (1) 210.0 180.0 PassportCard/DavidShield (1) 80.0 90.0 Elementum (1) 55.1 55.1 Other unconsolidated entities (1)(2) 24.8 31.2 Total unconsolidated entities (1) 632.6 622.8 Private equity funds and hedge funds 98.5 161.1 Insurance-linked securities funds 46.2 41.2 Private debt investments 25.8 28.7 Other 2.5 2.5 Total other long-term investments $ 805.6 $ 856.3
Other long-term investments	The following table presents investments and unfunded commitments in private equity funds and hedge funds by investment objective and sector as of March 31, 2020 and December 31, 2019 : March 31, 2020 December 31, 2019 Millions Fair Value Unfunded Commitments Fair Value Unfunded Commitments Private equity funds Manufacturing/Industrial $ 44.5 $ 4.0 $ 57.7 $ 4.1 Aerospace/Defense/Government 37.5 23.3 33.8 23.3 Financial services 16.5 25.9 15.0 22.8 Total private equity funds 98.5 53.2 106.5 50.2 Hedge funds Long/short banks and financials — — 54.6 — Total hedge funds — — 54.6 — Total private equity funds and hedge funds included in other long-term investments $ 98.5 $ 53.2 $ 161.1 $ 50.2
Fair Value of private equity funds subject to lock-up periods	The following table presents investments in private equity funds that were subject to lock-up periods as of March 31, 2020 : Millions 1 – 3 years 3 – 5 years 5 – 10 years >10 years Total Private equity funds — expected lock-up period remaining $4.7 $39.3 $43.3 $11.2 $98.5
Fair value measurements by level, investment securities	The following tables present White Mountains’s fair value measurements for investments as of March 31, 2020 and December 31, 2019 by level. The major security types were based on the legal form of the securities. White Mountains has disaggregated its fixed maturity investments based on the issuing entity type, which impacts credit quality, with debt securities issued by U.S. government entities carrying minimal credit risk, while the credit and other risks associated with other issuers, such as corporations, foreign governments, municipalities or entities issuing mortgage and asset-backed securities vary depending on the nature of the issuing entity type. White Mountains further disaggregates debt securities issued by corporations and common equity securities by industry sector because investors often reference commonly used benchmarks and their subsectors to monitor risk and performance. Accordingly, White Mountains has further disaggregated these asset classes into subclasses based on the similar sectors and industry classifications it uses to evaluate investment risk and performance against commonly used benchmarks, such as the Bloomberg Barclays U.S. Intermediate Aggregate and S&P 500 indices. March 31, 2020 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 223.9 $ 223.9 $ — $ — Debt securities issued by corporations: Financials 151.3 — 151.3 — Industrial 63.4 — 63.4 — Healthcare 52.8 — 52.8 — Technology 52.7 — 52.7 — Consumer 47.5 — 47.5 — Energy 38.2 — 38.2 — Utilities 30.4 — 30.4 — Communications 29.1 — 29.1 — Materials 21.3 — 21.3 — Total debt securities issued by corporations 486.7 — 486.7 — Municipal obligations 270.0 — 270.0 — Mortgage and asset-backed securities 231.7 — 231.7 — Total fixed maturity investments 1,212.3 223.9 988.4 — Short-term investments (1) 137.6 130.9 6.7 — Common equity securities: Exchange traded funds (2) 415.6 403.7 11.9 — Other (3) 108.1 18.0 90.0 .1 Total common equity securities 523.7 421.7 101.9 .1 Other long-term investments 660.9 — — 660.9 Other long-term investments — NAV (4) 144.7 — — — Total investments $ 2,679.2 $ 776.5 $ 1,097.0 $ 661.0 (1) Short-term investments are measured at amortized cost, which approximates fair value. (2) ETFs traded on foreign exchanges are priced using the fund’s published NAV to account for the difference in market close times and are therefore designated a Level 2 measurement. (3) Primarily consists of two investments in unit trusts that predominantly invest in international equities and an open-end mutual fund that invests in domestic large-cap companies. (4) Consists of private equity funds and ILS funds for which fair value is measured at NAV using the practical expedient. Investments for which fair value is measured at NAV are not classified within the fair value hierarchy. December 31, 2019 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 232.5 $ 232.5 $ — $ — Debt securities issued by corporations: Financials 144.8 — 144.8 — Industrial 59.0 — 59.0 — Healthcare 52.6 — 52.6 — Consumer 50.9 — 50.9 — Energy 44.9 — 44.9 — Technology 41.2 — 41.2 — Communications 31.3 — 31.3 — Utilities 25.0 — 25.0 — Materials 17.5 — 17.5 — Total debt securities issued by corporations 467.2 — 467.2 — Municipal obligations 297.1 — 297.1 — Mortgage and asset-backed securities 209.0 — 209.0 — Total fixed maturity investments 1,205.8 232.5 973.3 — Short-term investments (1) 201.2 189.4 11.8 — Common equity securities: Exchange traded funds (2) 536.4 521.6 14.8 — Other (3) 147.5 25.9 121.5 .1 Total common equity securities 683.9 547.5 136.3 .1 Other long-term investments 654.0 — — 654.0 Other long-term investments — NAV (4) 202.3 — — — Total investments $ 2,947.2 $ 969.4 $ 1,121.4 $ 654.1 (1) Short-term investments are measured at amortized cost, which approximates fair value. (2) ETFs traded on foreign exchanges are priced using the fund’s published NAV to account for the difference in market close times and are therefore designated a Level 2 measurement. (3) Primarily consists of two investments in unit trusts that predominantly invest in international equities and an open-end mutual fund that invests in domestic large-cap companies. (4) Consists of private equity funds, one hedge fund and ILS funds for which fair value is measured at NAV using the practical expedient. Investments for which fair value is measured at NAV are not classified within the fair value hierarchy.
Debt securities issued by corporations, credit ratings	The following table presents the ratings of debt securities issued by corporations held in White Mountains’s investment portfolio as of March 31, 2020 and December 31, 2019 : Fair Value at Millions March 31, 2020 December 31, 2019 AAA $ 11.3 $ 9.5 AA 63.6 73.9 A 304.7 288.5 BBB 106.1 95.3 BB 1.0 — Debt securities issued by corporations (1) $ 486.7 $ 467.2 (1) Credit ratings are based upon issuer credit ratings provided by Standard & Poor’s Financial Services LLC (“Standard & Poor’s”), or if unrated by Standard & Poor’s, long-term obligation ratings provided by Moody’s Investor Service, Inc.
Mortgage-backed, asset-backed securities	The following table presents the fair value of White Mountains’s mortgage and asset-backed securities as of March 31, 2020 and December 31, 2019 : March 31, 2020 December 31, 2019 Millions Fair Value Level 2 Level 3 Fair Value Level 2 Level 3 Mortgage-backed securities: Agency: FNMA $ 90.6 $ 90.6 $ — $ 88.6 $ 88.6 $ — FHLMC 72.1 72.1 — 60.5 60.5 — GNMA 45.7 45.7 — 30.8 30.8 — Total agency (1) 208.4 208.4 — 179.9 179.9 — Total mortgage-backed securities 208.4 208.4 — 179.9 179.9 — Other asset-backed securities: Vehicle receivables 12.2 12.2 — 15.1 15.1 — Credit card receivables 11.1 11.1 — 14.0 14.0 — Total other asset-backed securities 23.3 23.3 — 29.1 29.1 — Total mortgage and asset-backed securities $ 231.7 $ 231.7 $ — $ 209.0 $ 209.0 $ — (1) Represents publicly traded mortgage-backed securities which carry the full faith and credit guaranty of the U.S. Government (i.e., GNMA) or are guaranteed by a government sponsored entity (i.e., FNMA, FHLMC).
Rollforward of fair value investments by level	The following tables present the changes in White Mountains’s fair value measurements by level for the three months ended March 31, 2020 and 2019 : Level 3 Investments Other Long-term Investments Measured at NAV (2) Millions Level 1 Investments Level 2 Investments Common Equity Securities Other Long-term Investments Total Balance at December 31, 2019 $ 780.0 $ 1,109.6 $ .1 $ 654.0 $ 202.3 $ 2,746.0 (1) Net realized and unrealized (losses) (98.7 ) (39.9 ) — (9.7 ) (8.8 ) (157.1 ) (3) Amortization/Accretion — (.8 ) — — — (.8 ) Purchases 74.2 126.8 — 24.7 7.2 232.9 Sales (109.9 ) (105.4 ) — (8.1 ) (56.0 ) (279.4 ) Transfers in — — — — — — Transfers out — — — — — — Balance at March 31, 2020 $ 645.6 $ 1,090.3 $ .1 $ 660.9 $ 144.7 $ 2,541.6 (1) (1) Excludes carrying value of $ 137.6 million and $ 201.2 as of March 31, 2020 and December 31, 2019 classified as short-term investments. (2) Includes private equity funds, hedge funds, ILS funds and unconsolidated entities for which fair value is measured at NAV using the practical expedient are no longer classified within the fair value hierarchy. See Note 1 — “Basis of Presentation and Significant Accounting Policies” . (3) Excludes realized and unrealized gains associated with short-term investments of $0.4 for the three months ended March 31, 2020. Level 3 Investments Other Long-term Investments Measured at NAV (3) Millions Level 1 Investments Level 2 Investments Other Long-term Investments Total Balance at December 31, 2018 $ 842.6 $ 1,160.5 $ 138.7 $ 186.9 $ 2,328.7 (1) Net realized and unrealized gains (losses) 91.7 40.7 114.0 (.8 ) 245.6 (2) Amortization/Accretion .1 (.4 ) — — (.3 ) Purchases 14.6 142.3 11.5 49.2 217.6 Sales (149.7 ) (105.4 ) — (1.9 ) (257.0 ) Transfers in — — 10.9 — 10.9 Transfers out — — — (10.9 ) (10.9 ) Balance at March 31, 2019 $ 799.3 $ 1,237.7 $ 275.1 $ 222.5 $ 2,534.6 (1) (1) Excludes carrying value of $ 269.8 and $ 214.2 as of March 31, 2019 and December 31, 2018 classified as short-term investments. (2) Includes $114.7 unrealized investment gain associated with the MediaAlpha Transaction, which is recorded in a separate line item in the statement of operations titled Realized gain and unrealized investment gain from the MediaAlpha Transaction. See Note 2 — “Significant Transactions”. (3) Includes private equity funds, hedge funds and unconsolidated entities for which fair value is measured at NAV using the practical expedient are no longer classified within the fair value hierarchy. See Note 1 — “Basis of Presentation and Significant Accounting Policies” .
Schedule of significant unobservable inputs used in estimating the fair value of investment securities	The following tables present significant unobservable inputs used in estimating the fair value of other long-term investments, other than private equity funds, hedge funds and ILS funds, classified within Level 3 as of March 31, 2020 and December 31, 2019 . The fair value of investments in private equity funds, hedge funds and ILS funds are generally estimated using the NAV of the funds. $ in Millions March 31, 2020 Description Valuation Technique(s) Fair Value (2) Unobservable Inputs Discount Rate (2) Terminal Cash Flow Exit Multiple (x) or Terminal Revenue Growth Rate (%) (3) Kudu’s Participation Contracts (1) Discounted cash flow $262.7 18% - 24% 6x - 12x MediaAlpha Discounted cash flow $210.0 15% 4% PassportCard/DavidShield Discounted cash flow $80.0 25% 4% Elementum Holdings, L.P. Discounted cash flow $55.1 20% 4% Private debt instruments Discounted cash flow $25.8 7% - 15% N/A All other Discounted cash flow $13.6 25% 4% Noblr, Inc. Share price of recent transaction $8.7 Share price: $2.17 Zillion Insurance Services, Inc. Recent transaction $2.5 Transaction price: $2.5 Compare.com Estimated net realizable value $2.5 Net realizable value: $2.5 (1) In the first quarter of 2020, Kudu deployed $21.0 million in Creation Investments Capital Management. (2) Includes the net unrealized investment gains (losses) associated with foreign currency; foreign currency effects based on observable inputs. (3) Increases (decreases) to the discount rates in isolation would result in lower (higher) fair value measurements, while increases (decreases) to the terminal cash flow exit multiples or terminal revenue growth rates in isolation would result in higher (lower) fair value measurements. $ in Millions December 31, 2019 Description Valuation Technique(s) Fair Value (1) Unobservable Inputs Discount Rate (2) Terminal Cash Flow Exit Multiple (x) or Terminal Revenue Growth Rate (%) (2) Kudu’s Participation Contracts Discounted cash flow $266.5 15% - 22% 6x - 12x MediaAlpha Discounted cash flow $180.0 15% 4% PassportCard/DavidShield Discounted cash flow $90.0 22% 4% Elementum Holdings, L.P. Discounted cash flow $55.1 20% 4% Private debt instruments Discounted cash flow $23.7 4% - 9% N/A All other Discounted cash flow $23.7 25% - 32% 4% Noblr, Inc. Share price of recent transaction $5.0 Share price: $2.17 Zillion Insurance Services, Inc. Recent transaction $2.5 Transaction price: $2.5 Compare.com Estimated net realizable value $2.5 Net realizable value: $2.5 (1) Includes the net unrealized investment gains (losses) associated with foreign currency; foreign currency effects based on observable inputs. (2) Increases (decreases) to the discount rates in isolation would result in lower (higher) fair value measurements, while increases (decreases) to the terminal cash flow exit multiples or terminal revenue growth rates in isolation would result in higher (lower) fair value measurements.

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	3 Months Ended
	Mar. 31, 2020
Acquired Finite-Lived Intangible Assets [Line Items]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	January 1, 2019 through March 31, 2020 : $ in Millions Acquisition of subsidiary/ asset Goodwill and Other intangible asset (1) Acquisition Date Embrace (2) $ 67.6 April 1, 2019 Renewal Rights (3) 82.5 June 28, 2019 Total NSM segment $ 150.1 Kudu Transaction $ 9.8 April 4, 2019 Other Operations $ 22.6 Various (1)
Schedule of Intangible Assets and Goodwill	The following tables presents the change in goodwill and other intangible assets for the three months ended March 31, 2020 and 2019: Three Months Ended March 31, 2020 2019 Millions Goodwill Other Intangible Assets Total Goodwill and Other Intangible Assets Goodwill Other Intangible Assets Total Goodwill and Other Intangible Assets Beginning balance $ 394.7 $ 260.0 654.7 $ 379.9 $ 157.6 $ 537.5 Deconsolidation of MediaAlpha — — — (18.3 ) (23.5 ) (41.8 ) Attribution of acquisition date fair value estimates between goodwill and other intangible assets — — — (26.8 ) 26.8 — Acquisitions of businesses — — — 13.4 — 13.4 Foreign currency translation (2.5 ) (.5 ) (3.0 ) 1.2 .3 1.5 Adjustments to reflect acquisition date fair value .2 — .2 .3 5.9 6.2 Amortization — (5.1 ) (5.1 ) — (6.6 ) (6.6 ) Ending balance $ 392.4 $ 254.4 $ 646.8 $ 349.7 $ 160.5 $ 510.2
Weighted Average [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Schedule of Intangible Assets and Goodwill	The following table presents the acquisition date fair values, accumulated amortization and net carrying values for other intangible assets and goodwill, by company as of March 31, 2020 and December 31, 2019 : $ in Millions Weighted Average Economic Life (in years) March 31, 2020 December 31, 2019 Acquisition Date Fair Value Accumulated Amortization Net Carrying Value Acquisition Date Fair Value Accumulated Amortization Impairments Net Carrying Value Goodwill: NSM (1) N/A $ 379.1 $ — $ 379.1 $ 381.6 $ — $ — $ 381.6 Kudu N/A 7.6 — 7.6 7.6 — — 7.6 Other Operations N/A 5.7 — 5.7 13.1 — 7.6 5.5 Total goodwill 392.4 — 392.4 402.3 — 7.6 394.7 Other intangible assets: NSM (1) Customer relationships 9 120.1 23.5 96.6 121.7 19.8 1.4 100.5 Trade names 19 61.2 5.8 55.4 61.9 5.3 .4 56.2 Information technology platform 5 3.1 1.3 1.8 3.9 1.4 .6 1.9 Renewal rights 12 82.5 1.0 81.5 82.5 .7 — 81.8 Other 3 1.7 .9 .8 1.7 .7 — 1.0 Subtotal 268.6 32.5 236.1 271.7 27.9 2.4 241.4 Kudu Trade names 7 2.2 .3 1.9 2.2 .2 — 2.0 Other Operations Trade names 10 1.0 .1 .9 1.7 .5 .2 1.0 Customer relationships 11 7.2 .5 6.7 7.2 .4 — 6.8 Information technology platform 5 — — — .5 .3 .2 — Insurance Licenses N/A 8.6 — 8.6 8.6 — — 8.6 Other 5 .2 — .2 .2 — — .2 Subtotal 17.0 .6 16.4 18.2 1.2 .4 16.6 Total other intangible assets 287.8 33.4 254.4 292.1 29.3 2.8 260.0 Total goodwill and other intangible assets $ 680.2 $ 33.4 646.8 $ 694.4 $ 29.3 10.4 654.7 Goodwill and other intangible assets attributed to non-controlling interests (23.5 ) (23.4 ) Goodwill and other intangible assets included in White Mountains’s common shareholders’ equity $ 623.3 $ 631.3 (1) As of March 31, 2020 , NSM’s goodwill and intangible assets included $(2.5) and $ (0.5) of the effect of foreign currency translation. As of December 31, 2019, NSM’s goodwill and intangible assets included $ 1.4 and $0.7 of the effect of foreign currency translation.

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2020
Debt Disclosure [Abstract]
Schedule of debt outstanding	The following table presents White Mountains’s debt outstanding as of March 31, 2020 and December 31, 2019: Millions March 31, Effective Rate (1) December 31, Effective Rate (1) NSM Bank Facility $ 220.7 6.8% $ 221.3 7.5% Unamortized issuance cost (3.6 ) (3.9 ) NSM Bank Facility, carrying value 217.1 217.4 Other NSM debt 1.3 2.2% 1.8 3.0% Kudu Bank Facility 69.0 9.1% 57.0 8.3% Unamortized issuance cost (3.3 ) (3.4 ) Kudu Bank Facility, carrying value 65.7 53.6 Other Operations debt 11.0 8.2% 11.1 8.3% Unamortized issuance cost (.4 ) (.4 ) Other Operations, carrying value 10.6 10.7 Total debt $ 294.7 $ 283.5 (1) Effective rate considers the effect of the debt issuance costs.

Municipal Bond Guarantee (Table

Municipal Bond Guarantee (Tables)	3 Months Ended
	Mar. 31, 2020
Guarantees [Abstract]
Schedule of Municipal Bond Guarantee Insured Obligations	The following table presents a schedule of BAM’s insured obligations as of March 31, 2020 and December 31, 2019 : March 31, 2020 December 31, 2019 Contracts outstanding 9,312 8,987 Remaining weighted average contract period outstanding (in years) 10.6 10.7 Contractual debt service outstanding (in millions): Principal $ 64,481.2 $ 62,250.5 Interest 32,449.1 31,799.7 Total debt service outstanding $ 96,930.3 $ 94,050.2 Gross unearned insurance premiums (in millions) $ 202.7 $ 198.4
Financial Guarantee Insurance Contracts, Premium Received over Contract Period	The following table presents a schedule of BAM’s future premium revenues as of March 31, 2020 : Millions March 31, 2020 April 1, 2020 - December 31, 2020 $ 14.3 January 1, 2021 - March 31, 2021 4.6 April 1, 2021 - June 30, 2021 4.5 July 1, 2021 - September 30, 2021 4.5 October 1, 2021 - December 31, 2021 4.4 Total 2021 18.0 2022 16.9 2023 15.9 2024 14.8 2025 13.8 2026 and thereafter 109.0 Total gross unearned insurance premiums $ 202.7
Schedule of Net Written Premiums	The following table presents a schedule of net written premiums and net earned premiums included in White Mountains’s HG Global/BAM segment for the three months ended March 31, 2020 and 2019 : Three Months Ended March 31, Millions 2020 2019 Written premiums: Direct $ 9.7 $ 7.9 Assumed — — Gross written premiums $ 9.7 $ 7.9 Earned premiums: Direct $ 4.5 $ 3.7 Assumed .9 .5 Gross earned premiums $ 5.4 $ 4.2

Investments in Unconsolidated_2

Investments in Unconsolidated Entities (Tables)	3 Months Ended
	Mar. 31, 2020
Schedule of Equity Method Investments [Line Items]
Investments in and Advances to Affiliates	The following table presents the carrying values of White Mountains’s equity method eligible investments recorded within other long-term investments as of March 31, 2020 and December 31, 2019: Millions March 31, 2020 December 31, 2019 Equity method eligible investments, at fair value $ 718.0 $ 761.7 Other (1) 87.6 94.6 Total other long-term investments $ 805.6 $ 856.3 (1) Consists of other long-term investments that are not equity method eligible.
Affiliated Entity
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	The following table presents White Mountains’s significant equity method eligible investments as of March 31, 2020 and December 31, 2019: Basic Ownership Interest Investee March 31, 2020 December 31, 2019 Instrument Held PassportCard/DavidShield 50.0% 50.0% Common shares MediaAlpha 48.3% 48.3% Units durchblicker 45.0% 45.0% Common shares Elementum 30.0% 30.0% Limited partnership interest Compare.com 18.4% 18.4% Common shares Tuckerman Capital Funds 16.1 - 61.3% 17.5 - 62.4% Limited and general partnership interests Enlightenment Capital Funds 9.6 - 36.5% 10.0 - 38.4% Limited and general partnership interests JAM Partners L.P. — 11.1% Limited partnership interest Kudu Participation Contracts 3.2 - 30.0% 3.2 - 30.0% Revenue and earnings participation contracts
MediaAlpha
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	The following tables present summarized financial information for MediaAlpha: Millions March 31, 2020 December 31, 2019 Balance sheet data: Total assets $ 108.4 $ 106.9 Total liabilities $ 137.5 $ 144.6 Three Months Ended March 31, Millions 2020 2019 Income statement data: Total revenues $ 119.5 $ 48.8 Total expenses 109.5 54.9 Net income (loss) $ 10.0 $ (6.1 )

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
Computation of earnings per share	The following table presents the Company’s computation of earnings per share from continuing operations for the three months ended March 31, 2020 and 2019 . See Note 17 — “Held for Sale and Discontinued Operations” . Three Months Ended March 31, 2020 2019 Basic and diluted earnings per share numerators (in millions): Net (loss) income attributable to White Mountains’s common shareholders $ (128.8 ) $ 284.4 Less: total income from discontinued operations, net of tax .9 .7 Net (loss) income from continuing operations attributable to White Mountains’s common shareholders $ (129.7 ) $ 283.7 Allocation of losses (earnings) to participating restricted common shares (1) 1.3 (2.9 ) Basic and diluted (losses) earnings per share numerators $ (128.4 ) $ 280.8 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,178.0 3,172.2 Average unvested restricted common shares (2) (33.8 ) (32.5 ) Basic (losses) earnings per share denominator 3,144.2 3,139.7 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,178.0 3,172.2 Average unvested restricted common shares (2) (33.8 ) (32.5 ) Diluted (losses) earnings per share denominator 3,144.2 3,139.7 Basic and diluted earnings per share (in dollars) - continuing operations: Distributed earnings - dividends declared and paid $ 1.00 $ 1.00 Undistributed (losses) earnings (41.82 ) 88.42 Basic and diluted (losses) earnings per share $ (40.82 ) $ 89.42 (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 10 — “Employee Share-Based Incentive Compensation Plans”.
Disposal Groups, Including Discontinued Operations	The following table presents the undistributed net earnings (losses) from continuing operations for the three months ended March 31, 2020 and 2019 . See Note 17 — “Held for Sale and Discontinued Operations” . Three Months Ended March 31, Millions 2020 2019 Undistributed net earnings - continuing operations: Net (loss) income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ (128.4 ) $ 280.8 Dividends declared, net of restricted common share amounts (1) (3.1 ) (3.2 ) Total undistributed net (losses) earnings, net of restricted common share amounts $ (131.5 ) $ 277.6 (1) Restricted shares issued by White Mountains receive dividends, and therefore, are considered participating securities. three months ended March 31, 2020 and 2019 : Three Months Ended March 31, 2020 2019 Basic and diluted earnings per share numerators (in millions): Net (loss) income attributable to White Mountains’s common shareholders $ (128.8 ) $ 284.4 Less: total (loss) income from continuing operations, net of tax (129.7 ) 283.7 Net income from discontinued operations attributable to White Mountains’s common shareholders $ .9 $ .7 Allocation of earnings to participating restricted common shares (1) — — Basic and diluted earnings per share numerators (2) $ .9 $ .7 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,178.0 3,172.2 Average unvested restricted common shares (3) (33.8 ) (32.5 ) Basic earnings per share denominator 3,144.2 3,139.7 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,178.0 3,172.2 Average unvested restricted common shares (3) (33.8 ) (32.5 ) Diluted earnings per share denominator 3,144.2 3,139.7 Basic and diluted earnings per share (in dollars) - discontinued operations: $ .28 $ .22 (1) Restricted shares issued by White Mountains contain dividend participation features, and therefore, are considered participating securities. (2) Net earnings attributable to White Mountains’s common shareholders, net of restricted share amounts, is equal to undistributed earnings for the three months ended March 31, 2020 and 2019 . (3) Restricted common shares outstanding vest either in equal annual installments or upon a stated date. See Note 10 — “Employee Share-Based Incentive Compensation Plans” .

Employee Share-Based Incentiv_2

Employee Share-Based Incentive Compensation Plans (Tables) - White Mountains	3 Months Ended
	Mar. 31, 2020
Share-based compensation arrangement by share-based payment award
Summary of performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan	Performance shares are designed to reward employees for meeting company-wide performance targets. 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 service period, are subject to the attainment of pre-specified performance goals, and are valued based on the market value of common shares at the time awards are paid. Performance shares earned under the WTM Incentive Plan are typically paid in cash but may be paid in common shares. Compensation expense is recognized for the vested portion of the awards over the related service periods. The level of payout ranges from zero to two times the number of shares initially granted, depending on White Mountains’s financial performance. Performance shares become payable at the conclusion of a performance cycle (typically 3 years ) if pre-defined financial targets are met. The performance measures used for determining performance share payouts are growth in White Mountains’s adjusted book value per share and intrinsic value per share. Intrinsic value per share is generally calculated by adjusting adjusted book value per share for differences between the adjusted book value of certain assets and liabilities and White Mountains’s estimate of their underlying intrinsic values. The following table presents the performance share activity for the three months ended March 31, 2020 and 2019 for performance shares granted under the WTM Incentive Plan: Three Months Ended March 31, 2020 2019 Millions, except share amounts Target Performance Accrued Expense Target Performance Accrued Expense Beginning of period 42,473 $ 43.7 40,616 $ 31.7 Shares paid (1) (14,070 ) (27.7 ) (13,715 ) (18.1 ) New grants 14,055 — 13,700 — Forfeitures and cancellations (2) — .4 1 .2 Expense recognized — (6.6 ) — 9.3 End of period 42,458 $ 9.8 40,602 $ 23.1 (1) WTM performance share payments in 2020 for the 2017-2019 performance cycle, which were paid in cash in March 2020, ranged from 174% to 180% of target. WTM performance share payments in 2019 for the 2016-2018 performance cycle, which were paid in cash in March 2019, ranged from 139% to 166% of target. (2) Amounts include changes in assumed forfeitures, as required under GAAP.
Share-based Compensation, Performance Shares Award Outstanding Activity	The following table presents performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan as of March 31, 2020 for each performance cycle: Three Months Ended March 31, 2020 Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Performance cycle: 2018 – 2020 13,450 $ 5.1 2019 – 2021 15,600 3.8 2020 – 2022 14,055 1.1 Sub-total 43,105 10.0 Assumed forfeitures (647 ) (.2 ) March 31, 2020 42,458 $ 9.8
Summary of restricted shares activity	The following table presents the unrecognized compensation cost associated with the outstanding restricted share awards for the three months ended March 31, 2020 and 2019 : Three Months Ended March 31, 2020 2019 Millions, except share amounts Restricted Unamortized Fair Value Restricted Unamortized Non-vested, Beginning of period 43,395 $ 16.7 41,510 $ 12.5 Issued 14,055 15.1 13,700 12.8 Vested (14,345 ) — (13,715 ) — Forfeited — — — — Expense recognized — (5.2 ) — (2.5 ) End of period 43,105 $ 26.6 41,495 $ 22.8

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2020
Leases [Abstract]
Lease, Cost	The following table summarizes net lease expense recognized in White Mountains’s consolidated statement of operations for the three months ended March 31, 2020 and 2019: Millions Lease Cost Three Months Ended March 31, 2020 Three Months Ended March 31, 2019 Lease cost $ 2.0 $ 1.7 Less: sublease income .1 .1 Net lease cost $ 1.9 $ 1.6
Lessee, Operating Lease, Liability, Maturity	The following table presents the contractual maturities of the lease liabilities associated with White Mountains’s operating lease agreements as of March 31, 2020 : Millions As of March 31, 2020 Remainder of 2020 $ 4.6 2021 5.4 2022 5.0 2023 4.2 2024 3.1 Thereafter 3.4 Total undiscounted lease payments 25.7 Less: present value adjustment 2.5 Operating lease liability $ 23.2
Schedule of Right-of-Use Assets and Lease Liabilities	The following tables present lease related assets and liabilities by reportable segment as of March 31, 2020 and December 31, 2019: As of March 31, 2020 Millions HG/BAM NSM Kudu Other Operations Total Weighted Average Incremental Borrowing Rate (1) ROU lease asset $ 10.0 $ 6.2 $ 2.2 $ 4.5 $ 22.9 4.7% Lease liability $ 10.0 $ 6.2 $ 2.2 $ 4.8 $ 23.2 (1) The present value of the remaining lease payments was determined by discounting the lease payments using the incremental borrowing rate. As of December 31, 2019 Millions HG/BAM NSM Kudu Other Operations Total Weighted Average Incremental Borrowing Rate (1) ROU lease asset $ 10.4 $ 4.8 $ 2.3 $ 5.1 $ 22.6 4.6% Lease liability $ 10.4 $ 4.8 $ 2.3 $ 5.3 $ 22.8 (1) The present value of the remaining lease payments was determined by discounting the lease payments using the incremental borrowing rate.

Non-controlling Interests (Tabl

Non-controlling Interests (Tables)	3 Months Ended
	Mar. 31, 2020
Noncontrolling Interest [Abstract]
Non-controlling Interests	The following table presents the balance of non-controlling interests included in White Mountains’s total equity and the related percentage of each consolidated entity’s total equity owned by non-controlling shareholders as of March 31, 2020 and December 31, 2019 : March 31, 2020 December 31, 2019 $ in Millions Non-controlling Percentage Non-controlling Equity Non-controlling Percentage Non-controlling Equity Non-controlling interests, excluding BAM HG Global 3.1 % $ 14.0 3.1 % $ 14.4 NSM 3.6 15.0 3.6 14.9 Other NSM 13.4 (.1 ) 13.4 (.1 ) Kudu .9 2.0 .9 2.2 Other Operations various (1.6 ) various (1.5 ) Total, excluding BAM 29.3 29.9 BAM 100.0 (146.9 ) 100.0 (146.7 ) Total non-controlling interests $ (117.6 ) $ (116.8 )

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2020
Segment Reporting [Abstract]
Financial information for White Mountains' segments	in. The following tables present the financial information for White Mountains’s segments for the three months ended March 31, 2020 and 2019: Millions HG Global/ BAM NSM Kudu Other Operations Total Three Months Ended March 31, 2020 Earned insurance premiums $ 5.4 $ — $ — $ — $ 5.4 Net investment income 5.5 — 7.3 10.1 22.9 Net realized and unrealized investment gains (loss) 6.1 — (24.8 ) (138.0 ) (156.7 ) Advertising and commission revenues — 53.0 — 2.1 55.1 Other revenue .5 12.0 .1 1.5 14.1 Total revenues 17.5 65.0 (17.4 ) (124.3 ) (59.2 ) Insurance acquisition expenses 1.7 — — — 1.7 Cost of sales — — — 2.0 2.0 General and administrative expenses 14.7 39.6 2.5 17.5 74.3 Broker commission expense — 18.3 — — 18.3 Change in fair value of contingent consideration — (.6 ) — — (.6 ) Amortization of other intangible assets — 4.8 .1 .2 5.1 Interest expense — 4.3 1.4 .3 6.0 Total expenses 16.4 66.4 4.0 20.0 106.8 Pre-tax income (loss) $ 1.1 $ (1.4 ) $ (21.4 ) $ (144.3 ) $ (166.0 ) Millions HG Global/BAM NSM MediaAlpha Other Operations Total Three Months Ended March 31, 2019 Earned insurance premiums $ 4.2 $ — $ — $ — $ 4.2 Net investment income 5.3 — — 10.7 16.0 Net realized and unrealized investment gains 11.8 — — 119.1 130.9 Realized and unrealized gains from the MediaAlpha Transaction — — — 182.2 182.2 Advertising and commission revenues (1) — 43.3 48.8 1.3 93.4 Other revenue .6 6.0 — .3 6.9 Total revenues 21.9 49.3 48.8 313.6 433.6 Insurance acquisition expenses 1.3 — — — 1.3 Cost of sales — — 40.6 1.1 41.7 General and administrative expenses 14.4 25.3 12.5 29.4 81.6 Broker commission expense — 15.5 — — 15.5 Change in fair value of contingent consideration — 1.3 — — 1.3 Amortization of other intangible assets — 5.0 1.6 — 6.6 Interest expense — 3.7 .2 — 3.9 Total expenses 15.7 50.8 54.9 30.5 151.9 Pre-tax income (loss) $ 6.2 $ (1.5 ) $ (6.1 ) $ 283.1 $ 281.7 (1) MediaAlpha’s results are from January 1, 2019 to February 26, 2019, the date of the MediaAlpha Transaction.
Reconciliation of Revenue from Segments to Consolidated	In compliance with ASC 606, Revenues from Contracts with Customers, the following tables present White Mountains’s total revenues by revenue source for the three months ended March 31, 2020 and 2019: Millions HG Global/BAM NSM Kudu Other Operations Total Three Months Ended March 31, 2020 Commission and other revenue Specialty Transportation $ — $ 20.3 $ — $ — $ 20.3 Real Estate — 11.3 — — 11.3 Social Services — 6.3 — — 6.3 Pet — 11.8 — — 11.8 United Kingdom — 10.0 — — 10.0 Other — 5.3 — 1.4 6.7 Total commission and other revenue — 65.0 — 1.4 66.4 Product revenues — — — 2.1 — Revenues from contracts with customers — 65.0 — 3.5 68.5 Other revenues (1) 17.5 — (17.4 ) (127.8 ) (127.7 ) Total revenues $ 17.5 $ 65.0 $ (17.4 ) $ (124.3 ) $ (59.2 ) (1) Other revenues consist of premiums, investment income, investment gains and losses and other revenues outside the scope of ASC 606, Revenues from Contracts with Customers. Millions HG Global/BAM NSM MediaAlpha (2) Other Operations Total Three Months Ended March 31, 2019 Commission and other revenue Specialty Transportation $ — $ 17.9 $ — $ — $ 17.9 Real Estate — 9.0 — — 9.0 Social Services — 5.8 — — 5.8 United Kingdom — 12.1 — — 12.1 Other — 4.5 — 1.3 5.8 Total commission and other revenue — 49.3 — 1.3 50.6 Advertising revenues — — 48.8 — 48.8 Revenues from contracts with customers — 49.3 48.8 1.3 99.4 Other revenues (1) 21.9 — — 312.3 334.2 Total revenues $ 21.9 $ 49.3 $ 48.8 $ 313.6 $ 433.6 (1) Other revenues consist of premiums, investment income, investment gains and losses and other revenues outside the scope of ASC 606, Revenues from Contracts with Customers. (2) MediaAlpha’s results are from January 1, 2019 to February 26, 2019, the date of the MediaAlpha Transaction.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2020
Fair Value Disclosures [Abstract]
Summary of the fair value and carrying value of financial instruments	The following table presents the fair value and carrying value of this financial instrument as of March 31, 2020 and December 31, 2019 : March 31, 2020 December 31, 2019 Millions Fair Value Carrying Value Fair Value Carrying Value NSM Bank Facility $ 208.7 $ 217.1 $ 221.2 $ 217.4 Other NSM debt $ 1.6 $ 1.3 $ 1.7 $ 1.8 Kudu Bank Facility $ 63.4 $ 65.7 $ 53.6 (1) $ 53.6 Other Operations debt $ 11.3 $ 10.6 $ 11.3 $ 10.7 (1) White Mountains measured the fair value of the Kudu Bank Facility debt at the carrying value as a result of the debt being acquired on December 23, 2019. See Note 5 — “Debt” .

Held for Sale and Discontinue_2

Held for Sale and Discontinued Operations (Tables)	3 Months Ended
	Mar. 31, 2020
Discontinued Operations and Disposal Groups [Abstract]
Disposal Groups, Including Discontinued Operations	The following table presents the undistributed net earnings (losses) from continuing operations for the three months ended March 31, 2020 and 2019 . See Note 17 — “Held for Sale and Discontinued Operations” . Three Months Ended March 31, Millions 2020 2019 Undistributed net earnings - continuing operations: Net (loss) income attributable to White Mountains’s common shareholders, net of restricted common share amounts $ (128.4 ) $ 280.8 Dividends declared, net of restricted common share amounts (1) (3.1 ) (3.2 ) Total undistributed net (losses) earnings, net of restricted common share amounts $ (131.5 ) $ 277.6 (1) Restricted shares issued by White Mountains receive dividends, and therefore, are considered participating securities. three months ended March 31, 2020 and 2019 : Three Months Ended March 31, 2020 2019 Basic and diluted earnings per share numerators (in millions): Net (loss) income attributable to White Mountains’s common shareholders $ (128.8 ) $ 284.4 Less: total (loss) income from continuing operations, net of tax (129.7 ) 283.7 Net income from discontinued operations attributable to White Mountains’s common shareholders $ .9 $ .7 Allocation of earnings to participating restricted common shares (1) — — Basic and diluted earnings per share numerators (2) $ .9 $ .7 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,178.0 3,172.2 Average unvested restricted common shares (3) (33.8 ) (32.5 ) Basic earnings per share denominator 3,144.2 3,139.7 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,178.0 3,172.2 Average unvested restricted common shares (3) (33.8 ) (32.5 ) Diluted earnings per share denominator 3,144.2 3,139.7 Basic and diluted earnings per share (in dollars) - discontinued operations: $ .28 $ .22 (1) Restricted shares issued by White Mountains contain dividend participation features, and therefore, are considered participating securities. (2) Net earnings attributable to White Mountains’s common shareholders, net of restricted share amounts, is equal to undistributed earnings for the three months ended March 31, 2020 and 2019 . (3) Restricted common shares outstanding vest either in equal annual installments or upon a stated date. See Note 10 — “Employee Share-Based Incentive Compensation Plans” .

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accouting Policies (Basis of Presentation) (Details) - USD ($) $ in Millions	Apr. 04, 2019	Dec. 31, 2019	Mar. 31, 2020	Apr. 03, 2019	Jan. 01, 2019	May 11, 2018	Feb. 05, 2018	Dec. 31, 2017	Jul. 31, 2012
Basis of Presentation
Ownership interest (as a percent)		50.00%	50.00%
ROU lease asset		$ 22.6	$ 22.9
Operating lease liability		$ 22.8	$ 23.2
Payments to acquire business, net	$ 81.4
HG Global
Basis of Presentation
Percentage of par value of policy reinsured			15.00%
Surplus notes									$ 503
Preferred Stock | HG Global
Basis of Presentation
Ownership interest (as a percent)		96.90%	96.90%
Common Stock | HG Global
Basis of Presentation
Ownership interest (as a percent)		88.40%	88.40%
NSM Insurance HoldCo, LLC
Basis of Presentation
Ownership interest (as a percent)			96.40%			95.00%
Fully diluted ownership interest (as a percent)			88.40%			83.60%
Kudu investments
Basis of Presentation
Ownership interest (as a percent)	99.10%	49.50%		49.50%			49.50%
Fully diluted ownership interest (as a percent)	85.40%	42.70%		42.70%			42.70%
Unfunded Capital Commitment	$ 250	$ 129	$ 122.5	$ 250
Increase (Decrease) in Capital Commitment		100
Funded Capital Commitment		350
Accounting Standards Update 2016-02
Basis of Presentation
ROU lease asset		22.6	22.9		$ 23.2
Operating lease liability		22.8	$ 23.2		$ 23.2
Series A BAM Surplus Note | HG Global
Basis of Presentation
Surplus notes								$ 203	203
Series B BAM Surplus Note | HG Global
Basis of Presentation
Surplus notes									$ 300
Kudu Debt [Member] | Delayed Draw Term Loans [Member] | Kudu
Basis of Presentation
Total commitment under revolving credit facility		$ 125

Significant Transactions (Detai

Significant Transactions (Details)	Jun. 28, 2019USD ($)	Apr. 04, 2019USD ($)	Apr. 01, 2019USD ($)	Feb. 26, 2019USD ($)	Dec. 03, 2018USD ($)	May 11, 2018USD ($)	Mar. 31, 2020USD ($)earnout_period	Dec. 31, 2019USD ($)	Mar. 31, 2019USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2019USD ($)	May 31, 2019USD ($)	Apr. 03, 2019USD ($)	May 18, 2018USD ($)	Feb. 05, 2018USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest (as a percent)							50.00%	50.00%			50.00%
Commitment to Fund															$ 125,000,000
Payments to Acquire Businesses and Interest in Affiliates							$ 0		$ 9,600,000
Payments to acquire business, net		$ 81,400,000
Goodwill							392,400,000	$ 394,700,000			$ 394,700,000
NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Change in fair value of contingent consideration earnout liabilities							(600,000)		1,300,000	$ 2,600,000
Payment for contingent consideration liability							6,400,000
Contingent consideration earnout liabilities							13,400,000	20,600,000			20,600,000
White Mountains
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other Investments							805,600,000	$ 856,300,000			856,300,000
MediaAlpha
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest (as a percent)				48.30%
Fully diluted ownership interest (as a percent)				42.00%
Proceeds from dividends received				$ 89,300,000
Net gain from sale of discontinued operations, net of tax									67,500,000
Assets, fair value				$ 114,700,000					114,700,000
Unrealized investment gain							30,000,000		114,700,000		$ 180,000,000
Total realized and unrealized gain on sale of minority stake							$ 182,200,000
Elementum Holdings, L.P.
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest (as a percent)							30.00%	30.00%			30.00%	30.00%
Other Investments												$ 55,100,000
Insurance-Linked Securities Funds
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Commitment to Fund												$ 50,000,000
Elementum Funds
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Equity method investment, aggregate cost							$ 46,200,000
NSM Insurance HoldCo, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest (as a percent)						95.00%	96.40%
Payments to Acquire Businesses and Interest in Affiliates						$ 274,200,000
Number of earnout periods | earnout_period							2
Fully diluted ownership interest (as a percent)						83.60%	88.40%
Fresh Insurance Services Group Limited
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest (as a percent)														100.00%
Equity method investment, aggregate cost														$ 49,600,000
Purchase price adjustment									700,000
Proceeds from borrowings					$ 51,000,000
Fresh Insurance Services Group Limited | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Purchase price adjustment									5,900,000
KBK Insurance Group, Inc. & KBK Premium Services, Inc.
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Businesses and Interest in Affiliates					60,000,000
Goodwill and intangible assets acquired					59,400,000				32,600,000
Stock Issued During Period, Value, Acquisitions					29,000,000
Proceeds from borrowings					$ 30,100,000
Intangible assets acquired									32,700,000
AIG Collector Car Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Businesses and Interest in Affiliates	$ 82,500,000
Intangible assets acquired	82,500,000
AIG Collector Car Business | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from borrowings	22,500,000
AIG Collector Car Business | White Mountains
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stock Issued During Period, Value, Acquisitions	$ 59,100,000
Kudu investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest (as a percent)		99.10%						49.50%			49.50%		49.50%		49.50%
Assets acquired		$ 155,500,000
Liabilities acquired		800,000
Noncontrolling interest acquired		$ 1,500,000
Fully diluted ownership interest (as a percent)		85.40%						42.70%			42.70%		42.70%		42.70%
Unfunded capital commitment		$ 250,000,000					$ 122,500,000	$ 129,000,000			$ 129,000,000		$ 250,000,000
Goodwill		7,600,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles		$ 2,200,000
Increase (Decrease) in Capital Commitment								100,000,000
Funded Capital Commitment								350,000,000			350,000,000
NSM Bank Facility | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long-term line of credit						$ 100,000,000
NSM Bank Facility | Term Loan | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Long-term line of credit						$ 224,000,000	220,700,000	221,300,000			221,300,000
Proceeds from borrowings									$ 6,500,000
Kudu Debt [Member] | Delayed Draw Term Loans [Member] | Kudu
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total commitment under revolving credit facility								125,000,000			125,000,000
Line of Credit Facility, Remaining Borrowing Capacity							$ 56,000,000	$ 68,000,000			$ 68,000,000
Embrace Pet Insurance
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill and intangible assets acquired			$ 67,600,000
Intangible assets acquired			15,400,000
Goodwill			52,200,000
Embrace Pet Insurance | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stock Issued During Period, Value, Acquisitions			58,200,000
Proceeds from borrowings			$ 20,400,000
Percentage of voting interests acquired			100.00%
Payments to acquire businesses, gross			$ 71,500,000

Investment Securities (Net Inve

Investment Securities (Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Investment income
Total investment income	$ 23.2	$ 16.4
Third-party investment expenses	(0.3)	(0.4)
Net investment income, pre-tax	22.9	16
Fixed maturity investments
Investment income
Total investment income	8.1	8.1
Short-term investments
Investment income
Total investment income	0.8	1.3
Common Stock
Investment income
Total investment income	3.8	5.4
Other long-term investments
Investment income
Total investment income	$ 10.5	$ 1.6

Investment Securities (Net Real

Investment Securities (Net Realized and Unrealized Investment Gains (Losses)) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Net Realized and Unrealized investment (losses) gains, pre-tax	$ (156,700,000)	$ 245,600,000
Tax on Net Realized and Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities	(25,500,000)	52,200,000
Net Realized and Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	(131,200,000)	193,400,000
MediaAlpha
Debt and Equity Securities, FV-NI [Line Items]
Trading securities, net realized gains		67,500,000
Unrealized investment gain	30,000,000	114,700,000	$ 180,000,000
Foreign Currency Gain (Loss)
Debt and Equity Securities, FV-NI [Line Items]
Net Realized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	$ 400,000	$ 300,000

Investment Securities (Net Unre

Investment Securities (Net Unrealized Investment Gains (Losses)) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Net Realized and Unrealized Gain (Loss) and Foreign Currency Gain (Loss) on Trading Securities Net of Tax	$ (131,200,000)	$ 193,400,000
Fixed maturity investments
Debt and Equity Securities, FV-NI [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	2,200,000	21,100,000
Short-term investments
Debt and Equity Securities, FV-NI [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	400,000	0
Common equity securities
Debt and Equity Securities, FV-NI [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	(140,800,000)	111,300,000
Other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	(18,500,000)	113,200,000
MediaAlpha
Debt and Equity Securities, FV-NI [Line Items]
Unrealized investment gain	$ 30,000,000	$ 114,700,000	$ 180,000,000

Investment Securities (Investme

Investment Securities (Investment gains (losses) for Level 3) (Details) - Level 3 Inputs - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Unrealized gains (losses) on investments	$ (9.4)	$ 114
Other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Unrealized gains (losses) on investments	$ (9.4)	$ 114

Investment Securities (Invest_2

Investment Securities (Investment Holdings Fixed Maturity Table) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
U.S. Government and agency obligations
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	$ 217.5	$ 231.7
Trading Securities, Unrealized Holding Gain	6.4	1
Trading Securities, Unrealized Holding Loss	0	(0.2)
Fixed maturity investments, at fair value	223.9	232.5
Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	486.2	454.9
Trading Securities, Unrealized Holding Gain	9.2	12.5
Trading Securities, Unrealized Holding Loss	(8.7)	(0.2)
Fixed maturity investments, at fair value	486.7	467.2
Municipal obligations
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	255.2	284.7
Trading Securities, Unrealized Holding Gain	14.8	12.5
Trading Securities, Unrealized Holding Loss	0	(0.1)
Fixed maturity investments, at fair value	270	297.1
Mortgage-backed and asset-backed securities
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	225.7	206.6
Trading Securities, Unrealized Holding Gain	6.2	2.7
Trading Securities, Unrealized Holding Loss	(0.2)	(0.3)
Fixed maturity investments, at fair value	231.7	209
Fixed Income Investments
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	1,184.6	1,177.9
Trading Securities, Unrealized Holding Gain	36.6	28.7
Trading Securities, Unrealized Holding Loss	(8.9)	(0.8)
Total fixed maturity investments including assets held for sale	$ 1,212.3	$ 1,205.8

Investment Securities (Invest_3

Investment Securities (Investment Holding Common Equities/ Other Investments) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Common Stock
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	$ 544.8	$ 553.3
Trading Securities, Unrealized Holding Gain	11.3	130.6
Trading Securities, Unrealized Holding Loss	(32.4)	0
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	523.7	683.9
Other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	610.1	667.4
Trading Securities, Unrealized Holding Gain	265.7	255.2
Trading Securities, Unrealized Holding Loss	(67.6)	(64.1)
Net foreign currency gains (losses)	(2.6)	(2.2)
Fixed maturity investments, at fair value	$ 805.6	$ 856.3

Investment Securities (Other lo

Investment Securities (Other long-term investments) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Kudu investments
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	$ 262.7	$ 266.5
MediaAlpha
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	210	180
DavidShield & PassportCard
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	80	90
Elementum Holdings, L.P.
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	55.1	55.1
Other unconsolidated entities
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	24.8	31.2
Total unconsolidated entities
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	632.6	622.8
Hedge and private equity funds included in other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	98.5	161.1
Insurance-linked securities funds
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	46.2	41.2
Private Debt Instrument
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	25.8	28.7
Other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	2.5	2.5
White Mountains
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	$ 805.6	$ 856.3

Investment Securities (Hedge Fu

Investment Securities (Hedge Funds and Private Equity Funds) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020USD ($)fund	Dec. 31, 2019USD ($)
Private equity security
Debt and Equity Securities, FV-NI [Line Items]
Number of investments | fund	13
Fair Value	$ 98.5
Hedge and private equity funds included in other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Largest single fund investment	21.1	$ 54.6
Hedge funds | Hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	0	$ 54.6
Transfer from investments	$ 45.6

Investment Securities (Fair Val

Investment Securities (Fair Value of Hedge Funds and Private Equity Funds) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Private equity security
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 98.5
Hedge and private equity funds included in other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments	98.5	$ 161.1
Unfunded Commitments	53.2	50.2
Hedge funds | Hedge Fund, Long/ Short Equity Banks and Financial
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	0	54.6
Unfunded Commitments	0	0
Hedge funds | Hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	0	54.6
Unfunded Commitments	0	0
Private equity security | Manufacturing/Industrial
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	44.5	57.7
Unfunded Commitments	4	4.1
Private equity security | Aerospace/Defense/Government
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	37.5	33.8
Unfunded Commitments	23.3	23.3
Private equity security | Financial services
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	16.5	15
Unfunded Commitments	25.9	22.8
Private equity security | Private equity security
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	98.5	106.5
Unfunded Commitments	$ 53.2	$ 50.2

Investment Securities (Invest_4

Investment Securities (Investments In Private Equity Funds Subject to Lock-Up Periods) (Details) - Private equity security $ in Millions	Mar. 31, 2020USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 98.5
1-3 years
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	4.7
3-5 years
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	39.3
5-10 years
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	43.3
Greater than 10 years
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 11.2

Investment Securities (Restrict

Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) - Hedge funds - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Hedge funds
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 0	$ 54.6
Hedge Fund, Long/ Short Equity Banks and Financial
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 0	$ 54.6

Investment Securities (Insuranc

Investment Securities (Insurance-Linked Securities Funds) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 2,541.6	$ 2,746	$ 2,534.6	$ 2,328.7
Minimum
Debt and Equity Securities, FV-NI [Line Items]
Redemptions and advanced redemption notice period	30 days
Maximum
Debt and Equity Securities, FV-NI [Line Items]
Redemptions and advanced redemption notice period	90 days
Insurance-Linked Securities Funds
Debt and Equity Securities, FV-NI [Line Items]
Number of Investments	4
Fair value investments	$ 46.2
Unfunded Capital Commitment	$ 5.2

Investment Securities (Fair V_2

Investment Securities (Fair Value Measurements) (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Percentage of investments recorded at fair value	70.00%	71.00%

Investment Securities (Fair V_3

Investment Securities (Fair Value Measurement by Level) (Details) $ in Millions	Mar. 31, 2020USD ($)Investment	Dec. 31, 2019USD ($)Investment	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 2,541.6	$ 2,746	$ 2,534.6	$ 2,328.7
Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	645.6	780	799.3	842.6
Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 1,090.3	$ 1,109.6	1,237.7	1,160.5
Common Stock
Debt and Equity Securities, FV-NI [Line Items]
Number of Investments | Investment	2	2
Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 486.7	$ 467.2
Mortgage-backed and asset-backed securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	231.7	209
Mortgage-backed and asset-backed securities | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	231.7	209
Mortgage-backed and asset-backed securities | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Short-term investments
Debt and Equity Securities, FV-NI [Line Items]
Short-term investments, at fair value	137.6	201.2	269.8	214.2
Common equity securities | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0.1	0.1
Other long-term investments | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	660.9	654	$ 275.1	$ 138.7
Fair value measured on a recurring basis
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	2,679.2	2,947.2
Fair value measured on a recurring basis | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	776.5	969.4
Fair value measured on a recurring basis | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	1,097	1,121.4
Fair value measured on a recurring basis | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	661	654.1
Fair value measured on a recurring basis | U.S. Government and agency obligations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	223.9	232.5
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	223.9	232.5
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | U.S. Government and agency obligations | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	486.7	467.2
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	486.7	467.2
Fair value measured on a recurring basis | Debt securities issued by corporations | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	151.3	144.8
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	151.3	144.8
Fair value measured on a recurring basis | Debt securities issued by corporations | Financials | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments		0
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	52.8	52.6
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	52.8	52.6
Fair value measured on a recurring basis | Debt securities issued by corporations | Health Care | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	63.4	59
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	63.4	59
Fair value measured on a recurring basis | Debt securities issued by corporations | Industrial | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	52.7	41.2
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	52.7	41.2
Fair value measured on a recurring basis | Debt securities issued by corporations | Technology | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	38.2	44.9
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	38.2	44.9
Fair value measured on a recurring basis | Debt securities issued by corporations | Energy | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	47.5	50.9
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	47.5	50.9
Fair value measured on a recurring basis | Debt securities issued by corporations | Consumer | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	29.1	31.3
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	29.1	31.3
Fair value measured on a recurring basis | Debt securities issued by corporations | Communications | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	30.4	25
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	30.4	25
Fair value measured on a recurring basis | Debt securities issued by corporations | Utilities | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	21.3	17.5
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	21.3	17.5
Fair value measured on a recurring basis | Debt securities issued by corporations | Materials | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	231.7	209
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	231.7	209
Fair value measured on a recurring basis | Mortgage-backed and asset-backed securities | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Municipal obligations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	270	297.1
Fair value measured on a recurring basis | Municipal obligations | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Municipal obligations | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	270	297.1
Fair value measured on a recurring basis | Municipal obligations | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Fixed maturity investments
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	1,212.3	1,205.8
Fair value measured on a recurring basis | Fixed maturity investments | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	223.9	232.5
Fair value measured on a recurring basis | Fixed maturity investments | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	988.4	973.3
Fair value measured on a recurring basis | Fixed maturity investments | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Short-term investments
Debt and Equity Securities, FV-NI [Line Items]
Short-term investments, at fair value	137.6	201.2
Fair value measured on a recurring basis | Short-term investments | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Short-term investments, at fair value	130.9	189.4
Fair value measured on a recurring basis | Short-term investments | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Short-term investments, at fair value	6.7	11.8
Fair value measured on a recurring basis | Short-term investments | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Short-term investments, at fair value	0	0
Fair value measured on a recurring basis | Common equity securities | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	421.7
Fair value measured on a recurring basis | Common equity securities | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	101.9
Fair value measured on a recurring basis | Common equity securities | Exchange traded funds
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	415.6	536.4
Fair value measured on a recurring basis | Common equity securities | Exchange traded funds | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	403.7	521.6
Fair value measured on a recurring basis | Common equity securities | Exchange traded funds | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	11.9	14.8
Fair value measured on a recurring basis | Common equity securities | Exchange traded funds | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Common equity securities | Other
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	108.1	147.5
Fair value measured on a recurring basis | Common equity securities | Other | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	18	25.9
Fair value measured on a recurring basis | Common equity securities | Other | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	90	121.5
Fair value measured on a recurring basis | Common equity securities | Other | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0.1	0.1
Fair value measured on a recurring basis | Common equity securities | Common equity securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	523.7	683.9
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments		547.5
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments		136.3
Fair value measured on a recurring basis | Common equity securities | Common equity securities | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0.1	0.1
Fair value measured on a recurring basis | Other long-term investments | Other Long-Term Investment NAV [Member]
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	144.7	202.3
Fair value measured on a recurring basis | Other long-term investments | Other Long-Term Investment NAV [Member] | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0
Fair value measured on a recurring basis | Other long-term investments | Other Long-Term Investment NAV [Member] | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0
Fair value measured on a recurring basis | Other long-term investments | Other Long-Term Investment NAV [Member] | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0
Fair value measured on a recurring basis | Other long-term investments | Other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	660.9	654
Fair value measured on a recurring basis | Other long-term investments | Other long-term investments | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0
Fair value measured on a recurring basis | Other long-term investments | Other long-term investments | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Fair value measured on a recurring basis | Other long-term investments | Other long-term investments | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 660.9	$ 654

Investment Securities (Debt sec

Investment Securities (Debt securities issued by corporation) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 2,541.6	$ 2,746	$ 2,534.6	$ 2,328.7
Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	486.7	467.2
Fair value investments	486.7	467.2
AAA | Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	11.3	9.5
AA | Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	63.6	73.9
A | Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	304.7	288.5
BBB | Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	106.1	95.3
BB | Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 1	$ 0

Investment Securities (Mortgage

Investment Securities (Mortgage-backed Asset Securities Table) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 2,541.6	$ 2,746	$ 2,534.6	$ 2,328.7
Federal National Mortgage Association Certificates and Obligations (FNMA)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	90.6	88.6
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	72.1	60.5
Government National Mortgage Association Certificates and Obligations (GNMA)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	45.7	30.8
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	208.4	179.9
Collateralized Mortgage Backed Securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	208.4	179.9
Collateralized Auto Loans
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	12.2	15.1
Collateralized Credit Card Securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	11.1	14
Asset-backed Securities, Securitized Loans and Receivables
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	23.3	29.1
Mortgage-backed and asset-backed securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	231.7	209
Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	1,090.3	1,109.6	$ 1,237.7	$ 1,160.5
Level 2 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	90.6	88.6
Level 2 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	72.1	60.5
Level 2 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	45.7	30.8
Level 2 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	208.4	179.9
Level 2 Inputs | Collateralized Mortgage Backed Securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	208.4	179.9
Level 2 Inputs | Collateralized Auto Loans
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	12.2	15.1
Level 2 Inputs | Collateralized Credit Card Securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	11.1	14
Level 2 Inputs | Asset-backed Securities, Securitized Loans and Receivables
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	23.3	29.1
Level 2 Inputs | Mortgage-backed and asset-backed securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	231.7	209
Level 3 Inputs | Federal National Mortgage Association Certificates and Obligations (FNMA)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Level 3 Inputs | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Level 3 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Level 3 Inputs | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Level 3 Inputs | Collateralized Mortgage Backed Securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Level 3 Inputs | Collateralized Auto Loans
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Level 3 Inputs | Collateralized Credit Card Securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Level 3 Inputs | Asset-backed Securities, Securitized Loans and Receivables
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	0	0
Level 3 Inputs | Mortgage-backed and asset-backed securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 0	$ 0

Investment Securities (Rollforw

Investment Securities (Rollforward of Fair Value Measurements by Level) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance	$ 2,746,000,000	$ 2,328,700,000	$ 2,328,700,000
Net realized and unrealized (losses)	(157,100,000)	245,600,000
Amortization/Accretion	(800,000)	(300,000)
Purchases	232,900,000	217,600,000
Sales	(279,400,000)	(257,000,000)
Transfers in	0	10,900,000
Transfers out	0	(10,900,000)
Ending balance	2,541,600,000	2,534,600,000	2,746,000,000
Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance	780,000,000	842,600,000	842,600,000
Net realized and unrealized (losses)	(98,700,000)	91,700,000
Amortization/Accretion	0	100,000
Purchases	74,200,000	14,600,000
Sales	(109,900,000)	(149,700,000)
Transfers in	0	0
Transfers out	0	0
Ending balance	645,600,000	799,300,000	780,000,000
Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance	1,109,600,000	1,160,500,000	1,160,500,000
Net realized and unrealized (losses)	(39,900,000)	40,700,000
Amortization/Accretion	(800,000)	(400,000)
Purchases	126,800,000	142,300,000
Sales	(105,400,000)	(105,400,000)
Transfers in	0	0
Transfers out	0	0
Ending balance	1,090,300,000	1,237,700,000	1,109,600,000
Common equity securities | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance	100,000
Net realized and unrealized (losses)	0
Amortization/Accretion	0
Purchases	0
Sales	0
Transfers in	0
Transfers out	0
Ending balance	100,000		100,000
Other long-term investments | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance	654,000,000	138,700,000	138,700,000
Net realized and unrealized (losses)	(9,700,000)	114,000,000
Amortization/Accretion	0	0
Purchases	24,700,000	11,500,000
Sales	(8,100,000)
Transfers in	0	10,900,000
Transfers out	0	0
Ending balance	660,900,000	275,100,000	654,000,000
Hedge and private equity funds included in other long-term investments | NAV
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance	202,300,000	186,900,000	186,900,000
Net realized and unrealized (losses)	(8,800,000)	(800,000)
Amortization/Accretion	0	0
Purchases	7,200,000	49,200,000
Sales	(56,000,000)	(1,900,000)
Transfers in	0	0
Transfers out	0	(10,900,000)
Ending balance	144,700,000	222,500,000	202,300,000
Short-term investments
Debt and Equity Securities, FV-NI [Line Items]
Short-term investments, at fair value	137,600,000	269,800,000	201,200,000	$ 214,200,000
Realized and unrealized losses	(400,000)
Fair value measured on a recurring basis
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance	2,947,200,000
Ending balance	2,679,200,000		2,947,200,000
Fair value measured on a recurring basis | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance	969,400,000
Ending balance	776,500,000		969,400,000
Fair value measured on a recurring basis | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance	1,121,400,000
Ending balance	1,097,000,000		1,121,400,000
Fair value measured on a recurring basis | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance	654,100,000
Ending balance	661,000,000		654,100,000
Fair value measured on a recurring basis | Common equity securities | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Ending balance	421,700,000
Fair value measured on a recurring basis | Common equity securities | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Ending balance	101,900,000
Fair value measured on a recurring basis | Short-term investments
Debt and Equity Securities, FV-NI [Line Items]
Short-term investments, at fair value	137,600,000		201,200,000
Fair value measured on a recurring basis | Short-term investments | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Short-term investments, at fair value	130,900,000		189,400,000
Fair value measured on a recurring basis | Short-term investments | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Short-term investments, at fair value	6,700,000		11,800,000
Fair value measured on a recurring basis | Short-term investments | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Short-term investments, at fair value	0		0
MediaAlpha
Debt and Equity Securities, FV-NI [Line Items]
Unrealized investment gain	$ 30,000,000	$ 114,700,000	$ 180,000,000

Investment Securities (Signific

Investment Securities (Significant Unobservable Inputs) (Details) - NR $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020USD ($)$ / shares	Dec. 31, 2019USD ($)$ / shares
Kudu Investments | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 21
MediaAlpha | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 210	$ 180
MediaAlpha | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	15.00%	15.00%
MediaAlpha | Long-term revenue growth
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal Revenue Growth Rate	4.00%	4.00%
DavidShield & PassportCard | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 80	$ 90
DavidShield & PassportCard | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	25.00%	22.00%
DavidShield & PassportCard | Revenue exit multiple
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal Revenue Growth Rate	4.00%	4.00%
Equity Securities, FV-NI, Measurement Input	1	1
Private Debt Instrument | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 25.8	$ 23.7
Private Debt Instrument | Minimum | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	7.00%	4.00%
Private Debt Instrument | Maximum | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	15.00%	9.00%
Kudu Investments | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 262.7	$ 266.5
Kudu Investments | Minimum | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	18.00%	15.00%
Kudu Investments | Minimum | Long-term revenue growth
Quantitative information for Level 3 Fair Value Measurements Assets
Measurement input	6	6
Kudu Investments | Maximum | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	24.00%	22.00%
Kudu Investments | Maximum | Long-term revenue growth
Quantitative information for Level 3 Fair Value Measurements Assets
Measurement input	12	12
Elementum Holdings, L.P. | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 55.1	$ 55.1
Elementum Holdings, L.P. | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	20.00%	20.00%
Terminal Revenue Growth Rate	4.00%	4.00%
Other | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 13.6	$ 23.7
Other | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate	25.00%
Terminal Revenue Growth Rate	4.00%	4.00%
Other | Minimum | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		25.00%
Other | Minimum | Revenue exit multiple
Quantitative information for Level 3 Fair Value Measurements Assets
Equity Securities, FV-NI, Measurement Input	2	2
Other | Maximum | Discount rate
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		32.00%
Other | Maximum | Revenue exit multiple
Quantitative information for Level 3 Fair Value Measurements Assets
Equity Securities, FV-NI, Measurement Input	4	4
Noblr Inc [Member] | Recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 8.7	$ 5
Noblr Inc [Member] | Recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price | $ / shares	$ 2.17	$ 2.17
Compare.com | Estimated Net Realizable Value
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 2.5	$ 2.5
Compare.com | Revenue exit multiple
Quantitative information for Level 3 Fair Value Measurements Assets
Equity Securities, FV-NI, Measurement Input		3
Compare.com | Estimated Net Realizable Value
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	2.5	$ 2.5
Zillion Insurance Services [Member] | Recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	2.5	2.5
Zillion Insurance Services [Member] | Recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 2.5	$ 2.5

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Fair Value of Goodwill and Other Intangible Assets (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Mar. 31, 2020	Jun. 28, 2019	Apr. 04, 2019	Apr. 01, 2019	Mar. 12, 2019
Goodwill [Line Items]
Goodwill, acquisition date fair value		$ 402.3	$ 392.4
Goodwill, Impairment Loss		7.6
Goodwill and other intangible assets		654.7	646.8
Goodwill		394.7	392.4
Renewal Rights
Goodwill [Line Items]
Goodwill and intangible assets acquired				$ 82.5
NSM Holding Co LLC
Goodwill [Line Items]
Goodwill, acquisition date fair value		381.6	379.1
Goodwill and intangible assets acquired			150.1
Goodwill		381.6	379.1
Kudu investments
Goodwill [Line Items]
Goodwill, acquisition date fair value		7.6	7.6
Goodwill		7.6	7.6
Other [Member]
Goodwill [Line Items]
Goodwill, acquisition date fair value		13.1	5.7
Goodwill, Impairment Loss		7.6
Goodwill		$ 5.5	$ 5.7
Embrace Pet Insurance
Goodwill [Line Items]
Capitalized Computer Software, Additions	$ 3.4
Goodwill and intangible assets acquired						$ 67.6
Goodwill						$ 52.2
Kudu
Goodwill [Line Items]
Goodwill and intangible assets acquired					$ 9.8
Other Operations
Goodwill [Line Items]
Goodwill and intangible assets acquired							$ 22.6

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Schedule of Goodwill and Other Intangible Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill, acquisition date fair value	$ 392.4		$ 402.3
Goodwill, Impairment Loss			7.6
Goodwill	392.4		394.7
Other intangible assets, acquisition date fair value	680.2		694.4
Other intangible assets, accumulated amortization	33.4		29.3
Impairment of Intangible Assets, Finite-lived			10.4
Goodwill and intangible assets, net carrying value	646.8		654.7
NSM Holding Co LLC
Goodwill [Line Items]
Goodwill, acquisition date fair value	379.1		381.6
Goodwill	379.1		381.6
Other intangible assets, acquisition date fair value	268.6		271.7
Other intangible assets, accumulated amortization	32.5		27.9
Impairment of Intangible Assets, Finite-lived			2.4
Other intangible assets, net carrying value	236.1		241.4
Amortization of Intangible Assets	(4.8)	$ (5)
Kudu investments
Goodwill [Line Items]
Goodwill, acquisition date fair value	7.6		7.6
Goodwill	7.6		7.6
Amortization of Intangible Assets	(0.1)	0
MediaAlpha
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	17		18.2
Other intangible assets, accumulated amortization	0.6		1.2
Impairment of Intangible Assets, Finite-lived			0.4
Other intangible assets, net carrying value	16.4
Goodwill and intangible assets, net carrying value			16.6
Amortization of Intangible Assets	0	(1.6)
Other
Goodwill [Line Items]
Goodwill, acquisition date fair value	5.7		13.1
Goodwill, Impairment Loss			7.6
Goodwill	5.7		5.5
Customer relationships | NSM Holding Co LLC
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	120.1		121.7
Other intangible assets, accumulated amortization	23.5		19.8
Impairment of Intangible Assets, Finite-lived			1.4
Other intangible assets, net carrying value	$ 96.6		100.5
Acquired finite-lived intangible assets, weighted average useful life	9 years
Customer relationships | MediaAlpha
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	$ 7.2		7.2
Other intangible assets, accumulated amortization	0.5		0.4
Impairment of Intangible Assets, Finite-lived			0
Other intangible assets, net carrying value	$ 6.7
Goodwill and intangible assets, net carrying value			6.8
Customer relationships | Other
Goodwill [Line Items]
Acquired finite-lived intangible assets, weighted average useful life	11 years
Trade names | NSM Holding Co LLC
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	$ 61.2		61.9
Other intangible assets, accumulated amortization	5.8		5.3
Impairment of Intangible Assets, Finite-lived			0.4
Other intangible assets, net carrying value	$ 55.4		56.2
Acquired finite-lived intangible assets, weighted average useful life	19 years
Trade names | Kudu investments
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	$ 2.2		2.2
Other intangible assets, accumulated amortization	0.3		0.2
Impairment of Intangible Assets, Finite-lived			0
Other intangible assets, net carrying value	$ 1.9		2
Acquired finite-lived intangible assets, weighted average useful life	7 years
Trade names | MediaAlpha
Goodwill [Line Items]
Other intangible assets, acquisition date fair value			1.7
Other intangible assets, accumulated amortization			0.5
Impairment of Intangible Assets, Finite-lived			0.2
Goodwill and intangible assets, net carrying value			1
Trade names | Other
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	$ 1
Other intangible assets, accumulated amortization	0.1
Other intangible assets, net carrying value	$ 0.9
Acquired finite-lived intangible assets, weighted average useful life	10 years
Information technology | NSM Holding Co LLC
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	$ 3.1		3.9
Other intangible assets, accumulated amortization	1.3		1.4
Impairment of Intangible Assets, Finite-lived			0.6
Other intangible assets, net carrying value	$ 1.8		1.9
Acquired finite-lived intangible assets, weighted average useful life	5 years
Information technology | MediaAlpha
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	$ 0		0.5
Other intangible assets, accumulated amortization	0		0.3
Impairment of Intangible Assets, Finite-lived			0.2
Other intangible assets, net carrying value	$ 0
Goodwill and intangible assets, net carrying value			0
Information technology | Other
Goodwill [Line Items]
Acquired finite-lived intangible assets, weighted average useful life	5 years
Other | NSM Holding Co LLC
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	$ 1.7		1.7
Other intangible assets, accumulated amortization	0.9		0.7
Impairment of Intangible Assets, Finite-lived			0
Other intangible assets, net carrying value	$ 0.8		1
Acquired finite-lived intangible assets, weighted average useful life	3 years
Other | MediaAlpha
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	$ 0.2		0.2
Other intangible assets, accumulated amortization	0		0
Impairment of Intangible Assets, Finite-lived			0
Other intangible assets, net carrying value	$ 0.2
Goodwill and intangible assets, net carrying value			0.2
Other | Other
Goodwill [Line Items]
Acquired finite-lived intangible assets, weighted average useful life	5 years
Renewal Rights | NSM Holding Co LLC
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	$ 82.5		82.5
Other intangible assets, accumulated amortization	1		0.7
Impairment of Intangible Assets, Finite-lived			0
Other intangible assets, net carrying value	$ 81.5		81.8
Acquired finite-lived intangible assets, weighted average useful life	12 years
Other Intangible Assets
Goodwill [Line Items]
Foreign currency translation	$ (0.5)	0.3
Measurement Period Adjustments	0	5.9
Intangible Assets, Net (Excluding Goodwill)	254.4	160.5	260	$ 157.6
Other intangible assets, acquisition date fair value	287.8		292.1
Other intangible assets, accumulated amortization	33.4		29.3
Impairment of Intangible Assets, Finite-lived			2.8
Other intangible assets, net carrying value	254.4
Goodwill and intangible assets, net carrying value			260
Deconsolidation of Business	0	(23.5)
Adjustments to reflect acquisition date fair value	0	26.8
Amortization of Intangible Assets	(5.1)	(6.6)
Acquisitions of businesses	0	0
Licensing Agreements [Member] | MediaAlpha
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	8.6		8.6
Other intangible assets, accumulated amortization	0		0
Impairment of Intangible Assets, Finite-lived			0
Other intangible assets, net carrying value	8.6
Goodwill and intangible assets, net carrying value			8.6
Non-controlling interest
Goodwill [Line Items]
Goodwill and intangible assets, net carrying value	(23.5)		(23.4)
Total
Goodwill [Line Items]
Goodwill and intangible assets, net carrying value	623.3		631.3
Goodwill
Goodwill [Line Items]
Measurement Period Adjustments	0.2	0.3
Goodwill	392.4	349.7	394.7	379.9
Deconsolidation of Business	0	(18.3)
Adjustments to reflect acquisition date fair value	0	(26.8)
Goodwill, Acquired During Period	0	13.4
Foreign currency translation	(2.5)	1.2
Intangible Asset and Goodwill
Goodwill [Line Items]
Foreign currency translation	(3)	1.5
Measurement Period Adjustments	0.2	6.2
Goodwill and intangible assets, acquisition date fair value	646.8	510.2	654.7	$ 537.5
Deconsolidation of Business	0	(41.8)
Amortization of Intangible Assets	(5.1)	(6.6)
Acquisitions of businesses	0	$ 13.4
Other Intangible Assets | NSM Holding Co LLC
Goodwill [Line Items]
Foreign currency translation			0.7
NSM Holding Co LLC
Goodwill [Line Items]
Goodwill and intangible assets, net carrying value	615.2		623
NSM Holding Co LLC | Goodwill
Goodwill [Line Items]
Foreign currency translation	$ (2.5)		$ 1.4

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets - Schedule of Goodwill and Other Intangible Assets Footnotes (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Goodwill
Acquired Finite-Lived Intangible Assets [Line Items]
Foreign currency translation	$ (2.5)	$ 1.2
NSM Holding Co LLC | Goodwill
Acquired Finite-Lived Intangible Assets [Line Items]
Foreign currency translation	(2.5)		$ 1.4
NSM Holding Co LLC | Finite-Lived Intangible Assets [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Foreign currency translation	$ (0.5)
NSM Holding Co LLC | Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Foreign currency translation			$ 0.7

Debt - Narrative (Details)

Debt - Narrative (Details) - USD ($) $ in Millions	Apr. 01, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 23, 2019	Jun. 15, 2018	May 11, 2018
Debt Instrument
Fair value investments		$ 2,541.6	$ 2,534.6	$ 2,328.7	$ 2,746
Total debt		294.7			283.5
Repayments of debt		1	14.8
Other Operations
Debt Instrument
Total commitment under revolving credit facility		16.3
NSM Holding Co LLC
Debt Instrument
Total debt		218.4			219.2
NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total debt		217.1			217.4
Face amount								$ 100
Kudu | Kudu Bank Facility [Member]
Debt Instrument
Total commitment under revolving credit facility						$ 125
Kudu | Kudu Debt [Member]
Debt Instrument
Total debt		65.7			53.6
Term Loan | Other Operations
Debt Instrument
Total commitment under revolving credit facility		11.3
Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total debt		220.7
Face amount		$ 220.7			$ 221.3			224
Effective percentage		6.80%			7.50%
Unamortized issuance cost		$ (3.6)			$ (3.9)
Repayments of debt		0.6	0.5
Proceeds from borrowings			$ 6.5
Term Loan | NSM Holding Co LLC | Other NSM
Debt Instrument
Total debt		1.3			$ 1.8
Face amount		$ 1.6
Effective percentage		2.20%			3.00%
Term Loan | Kudu | Kudu Bank Facility [Member]
Debt Instrument
Face amount		$ 69			$ 57
Total commitment under revolving credit facility						57
Proceeds from Issuance of Long-term Debt		$ 12
Term Loan | Kudu | Kudu Debt [Member]
Debt Instrument
Effective percentage		9.10%			8.30%
Unamortized issuance cost		$ (3.3)			$ (3.4)
Term Loan | Other | Other
Debt Instrument
Total debt		10.6			10.7
Face amount		$ 11			$ 11.1
Effective percentage		8.20%			8.30%
Unamortized issuance cost		$ (0.4)			$ (0.4)
Delayed Draw Term Loans [Member] | Other Operations
Debt Instrument
Total commitment under revolving credit facility		3
Delayed Draw Term Loans [Member] | Kudu | Kudu Bank Facility [Member]
Debt Instrument
Total commitment under revolving credit facility						63
Delayed Draw Term Loans [Member] | Kudu | Kudu Debt [Member]
Debt Instrument
Total commitment under revolving credit facility					125
Revolving Credit Facility | Other Operations
Debt Instrument
Total commitment under revolving credit facility		$ 2
Revolving Credit Facility | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total commitment under revolving credit facility								10
Borrowings under facility								$ 2
Revolving Credit Facility | Kudu | Kudu Bank Facility [Member]
Debt Instrument
Total commitment under revolving credit facility						$ 5
Interest Rate Swap | NSM Holding Co LLC
Debt Instrument
Derivative, fixed interest rate							2.97%
Derivative, variable interest rate		1.58%
Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total debt		$ 148.4
Total commitment under revolving credit facility							$ 151
Hedged Liability, Fair Value Hedge							$ 151
Derivative, fixed interest rate		2.97%
Debt, weighted average interest rate, all-in		6.34%
London Interbank Offered Rate (LIBOR) | Line of Credit [Member] | Kudu | Kudu Bank Facility [Member]
Debt Instrument
Basis spread on variable rate		1.00%
London Interbank Offered Rate (LIBOR) | Minimum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Basis spread on variable rate		4.25%		4.25%
London Interbank Offered Rate (LIBOR) | Minimum | Line of Credit [Member] | Kudu | Kudu Bank Facility [Member]
Debt Instrument
Basis spread on variable rate		5.50%
London Interbank Offered Rate (LIBOR) | Maximum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Basis spread on variable rate		4.75%		4.75%
London Interbank Offered Rate (LIBOR) | Maximum | Line of Credit [Member] | Kudu | Kudu Bank Facility [Member]
Debt Instrument
Basis spread on variable rate		6.25%
Prime Rate | Line of Credit [Member] | Kudu | Kudu Bank Facility [Member]
Debt Instrument
Basis spread on variable rate		1.00%
Prime Rate | Minimum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Basis spread on variable rate		3.25%		3.25%
Prime Rate | Minimum | Line of Credit [Member] | Kudu | Kudu Bank Facility [Member]
Debt Instrument
Basis spread on variable rate		4.50%
Prime Rate | Maximum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Basis spread on variable rate		3.75%		3.75%
Prime Rate | Maximum | Line of Credit [Member] | Kudu | Kudu Bank Facility [Member]
Debt Instrument
Basis spread on variable rate		5.25%
Designated as Hedging Instrument | Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total debt		$ 148.4
Debt, weighted average interest rate, all-in		7.47%
Not Designated as Hedging Instrument | Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total debt		$ 72.3
Effective percentage		6.25%
Embrace | NSM Holding Co LLC
Debt Instrument
Proceeds from borrowings	$ 20.4
Carrying Value | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total debt		$ 217.1			217.4
Debt securities issued by corporations
Debt Instrument
Fair value investments		486.7			467.2
Debt securities issued by corporations | AAA
Debt Instrument
Fair value investments		11.3			9.5
Debt securities issued by corporations | AA
Debt Instrument
Fair value investments		63.6			73.9
Debt securities issued by corporations | Standard & Poor's, A Rating [Member]
Debt Instrument
Fair value investments		304.7			288.5
Debt securities issued by corporations | BBB
Debt Instrument
Fair value investments		106.1			95.3
Debt securities issued by corporations | BB
Debt Instrument
Fair value investments		$ 1			$ 0

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Tax Contingency [Line Items]
Effective income tax rate reconciliation, percent	15.40%	3.60%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	21.00%
Income tax expense (benefit)	$ (25.5)	$ 10.2
Continuing Operations | BAM
Income Tax Contingency [Line Items]
Income tax expense (benefit)		$ 1.1

Derivatives - NSM Interest Rate

Derivatives - NSM Interest Rate Swap (Details) - USD ($) $ in Millions	3 Months Ended		8 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Jun. 15, 2018
Derivative [Line Items]
Debt	$ 294.7			$ 283.5
NSM Holding Co LLC
Derivative [Line Items]
Debt	218.4			219.2
NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Debt	217.1			217.4
Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Debt	$ 220.7
Interest Rate Swap | NSM Holding Co LLC
Derivative [Line Items]
Derivative, fixed interest rate					2.97%
Derivative, variable interest rate	1.58%
Interest expense, net	$ 0.5	$ 0.2
Derivative, fair value, net	9.8			$ 6.6
Change in fair value of derivative	$ (3.2)	$ (1.9)
Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Total commitment under revolving credit facility					$ 151
Derivative, fixed interest rate	2.97%
Debt	$ 148.4
Debt, weighted average interest rate, all-in	6.34%
Margin over London Interbank Offered Rate (LIBOR) | Minimum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Basis spread on variable rate	4.25%		4.25%
Margin over London Interbank Offered Rate (LIBOR) | Maximum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Basis spread on variable rate	4.75%		4.75%
Margin over Prime Rate | Minimum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Basis spread on variable rate	3.25%		3.25%
Margin over Prime Rate | Maximum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Basis spread on variable rate	3.75%		3.75%
Designated as Hedging Instrument | Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Debt	$ 148.4
Debt, weighted average interest rate, all-in	7.47%

Municipal Bond Guarantee - Narr

Municipal Bond Guarantee - Narrative (Details) $ in Millions

1 Months Ended

3 Months Ended

12 Months Ended

Jan. 31, 2020USD ($)

Apr. 30, 2018USD ($)

Mar. 31, 2020USD ($)Contract

Mar. 31, 2019USD ($)

Dec. 31, 2018USD ($)

Mar. 31, 2018yr

Dec. 31, 2019USD ($)Contract

Dec. 31, 2012USD ($)

Dec. 31, 2024

Dec. 31, 2020

Sep. 30, 2019USD ($)

Dec. 31, 2017USD ($)

Jul. 31, 2012USD ($)

Guarantor Obligations [Line Items]

Ownership interest (as a percent)

50.00%

50.00%

Repayments of debt

$ 1

$ 14.8

Interest paid

$ 5.2

$ 3.7

HG Global

Guarantor Obligations [Line Items]

Partners capital contribution

$ 594.5

Surplus notes

$ 503

Cash and Fixed Income Securities

100

Percent over a target trust balance

102.00%

Supplement Trust Target

$ 603

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%

BAM

Guarantor Obligations [Line Items]

Percentage of risk premium ceded

60.00%

Year of U.S. Treasury rate | yr

1

Contracts outstanding | Contract

9,312

8,987

Remaining weighted average contract period outstanding (in years)

10 years 7 months 6 days

10 years 8 months 12 days

Municipal bond outstanding principal

$ 64,481.2

$ 62,250.5

$ 1,100

Municipal bond outstanding interest

32,449.1

31,799.7

Municipal bond debt service outstanding

96,930.3

94,050.2

April 1, 2020 - December 31, 2020

14.3

2021

18

2022

16.9

2023

15.9

2024

14.8

2025

13.8

2026 and thereafter

109

Total gross unearned insurance premiums

202.7

198.4

HG Global

Guarantor Obligations [Line Items]

Collateral held in supplement trust

792.7

786.7

Interest receivable

$ 150.4

162.7

HG Re

Guarantor Obligations [Line Items]

Percentage of par value of policy reinsured

15.00%

BAM

Guarantor Obligations [Line Items]

Surplus notes

$ 409.7

$ 457.6

BAM Management

Guarantor Obligations [Line Items]

Partners capital contribution

$ 14.5

Supplemental Trust [Member] | BAM

Guarantor Obligations [Line Items]

Repayments of Unsecured Debt

47.9

Accrued Interest Payment on Surplus Notes

$ 0.9

Surplus Note | BAM

Guarantor Obligations [Line Items]

Derivative, fixed interest rate (as a percent)

10.00%

Repayments of Unsecured Debt

$ 65

Accrued Interest Payment on Surplus Notes

$ 16.2

Combination One | Surplus Note | BAM

Guarantor Obligations [Line Items]

Number of years of change in interest rate | yr

5

US Treasury Rate | Surplus Note | BAM

Guarantor Obligations [Line Items]

Basis spread on variable rate

3.00%

Fixed interest rate | Surplus Note | BAM

Guarantor Obligations [Line Items]

Derivative, fixed interest rate (as a percent)

8.00%

8.00%

First Quarter, year two | BAM

Guarantor Obligations [Line Items]

2021

$ 4.6

Second Quarter, year two | BAM

Guarantor Obligations [Line Items]

2021

4.5

Third Quarter, year two | BAM

Guarantor Obligations [Line Items]

2021

4.5

Fourth Quarter, year two | BAM

Guarantor Obligations [Line Items]

2021

$ 4.4

Series A BAM Surplus Note | HG Global

Guarantor Obligations [Line Items]

Surplus notes

$ 203

203

Series B BAM Surplus Note | HG Global

Guarantor Obligations [Line Items]

Surplus notes

$ 300

BAM | Fidus Re Ltd.

Guarantor Obligations [Line Items]

Losses above retention, percentage of liability

90.00%

BAM | HG Global

Guarantor Obligations [Line Items]

Term of Agreement

10 years

Fidus Re Ltd. | BAM

Guarantor Obligations [Line Items]

Secured Debt

$ 100

Collateralized financial guarantee, term

12 years

Collateral financial guarantee, callable term

5 years

Aggregate losses on ceded business

$ 165

Premium receivable, Premium expected to be collected

100

Percentage of Quota Share Reinsurance Agreement

100.00%

Direct written premiums

$ 2,200

Maximum | BAM | HG Global

Guarantor Obligations [Line Items]

Aggregate losses on ceded business

$ 75

Maximum | Fidus Re Ltd. | BAM

Guarantor Obligations [Line Items]

Aggregate losses on ceded business

$ 276.1

Scenario, Forecast | Surplus Note | BAM

Guarantor Obligations [Line Items]

Derivative, fixed interest rate (as a percent)

5.70%

4.60%

Municipal Bond Guarantee - Sche

Municipal Bond Guarantee - Schedule of Net Written Premiums (Details) - HG/BAM - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Direct written premiums	$ 9.7	$ 7.9
Assumed written premiums	0	0
Gross written premiums	9.7	7.9
Direct premiums earned	4.5	3.7
Assumed premiums earned	0.9	0.5
Gross earned premiums	$ 5.4	$ 4.2

Investments in Unconsolidated_3

Investments in Unconsolidated Entities (Details) - White Mountains - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Investments in unconsolidated affiliates
Other Investments	$ 805.6	$ 856.3
Equity method eligible private equity securities, at fair value
Investments in unconsolidated affiliates
Other Investments	718	761.7
Other unconsolidated investments
Investments in unconsolidated affiliates
Other Investments	$ 87.6	$ 94.6

Investments in Unconsolidated_4

Investments in Unconsolidated Entities - White Mountain's Investments (Details)	Mar. 31, 2020	Dec. 31, 2019	May 31, 2019
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	50.00%	50.00%
MediaAlpha
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	48.30%	48.30%
durchblicker
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	45.00%	45.00%
Elementum Holdings, L.P.
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	30.00%	30.00%	30.00%
Compare.com
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	18.40%	18.40%
JAM Partners L.P.
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)		11.10%
Minimum | Tuckerman Capital Funds
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	16.10%	17.50%
Minimum | Enlightenment Capital Funds
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	9.60%	10.00%
Minimum | Kudu Investments
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	3.20%	3.20%
Maximum | Tuckerman Capital Funds
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	61.30%	62.40%
Maximum | Enlightenment Capital Funds
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	36.50%	38.40%
Maximum | Kudu Investments
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)	30.00%	30.00%

Investments in Unconsolidated_5

Investments in Unconsolidated Entities - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Feb. 26, 2019
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)		50.00%		50.00%
Total revenues		$ (59,200,000)	$ 433,600,000
Total assets		3,739,700,000		$ 3,983,200,000
Total liabilities		780,600,000		838,500,000
MediaAlpha
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)					48.30%
Fully diluted ownership interest (as a percent)					42.00%
Assets, fair value	$ 114,700,000		114,700,000		$ 114,700,000
Unrealized investment gain		30,000,000	114,700,000	180,000,000
MediaAlpha
Schedule of Equity Method Investments [Line Items]
Total revenues		0	48,800,000
MediaAlpha | MediaAlpha
Schedule of Equity Method Investments [Line Items]
Total revenues	33,500,000
Expenses	32,500,000
Pre-tax income	$ 1,100,000
MediaAlpha
Schedule of Equity Method Investments [Line Items]
Total revenues		119,500,000	48,800,000
Expenses		109,500,000	54,900,000
Total assets		108,400,000		106,900,000
Total liabilities		137,500,000		$ 144,600,000
Net Income (Loss) Attributable to Parent		$ 10,000,000	$ (6,100,000)

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Basic and diluted earnings per share numerators (in millions):
Net (loss) income attributable to White Mountains’s common shareholders	$ (128.8)	$ 284.4
Less: total income (loss) from discontinued operations	0.9	0.7
Net (loss) income from continuing operations attributable to White Mountains’s common shareholders	(129.7)	283.7
Basic and diluted (losses) earnings per share numerators	$ (128.4)	$ 280.8
Basic earnings per share denominators (in thousands):
Total average common shares outstanding during the period	3,178,000	3,172,200
Average unvested restricted common shares	(33,800)	(32,500)
Basic (losses) earnings per share denominator	3,144,200	3,139,700
Diluted earnings per share denominator (in thousands):
Total average common shares outstanding during the period	3,178,000	3,172,200
Average unvested restricted common shares	(33,800)	(32,500)
Diluted (losses) earnings per share denominator	3,144,200	3,139,700
Basic earnings per share (in dollars) - continuing operations:
Distributed earnings - dividends declared and paid	$ 1	$ 1
Undistributed (losses) earnings	(41.82)	88.42
Basic and diluted (losses) earnings per share	$ (40.82)	$ 89.42

Earnings Per Share - Undistribu

Earnings Per Share - Undistributed Net Earnings (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net (loss) income attributable to White Mountains’s common shareholders, net of restricted common share amounts	$ (128.4)	$ 280.8
Dividends declared net of restricted common share amounts	(3.1)	(3.2)
Total undistributed net (losses) earnings, net of restricted common share amounts	$ (131.5)	$ 277.6

Employee Share-Based Incentiv_3

Employee Share-Based Incentive Compensation Plans (Performance Shares) (Details) - Performance Share $ in Millions	3 Months Ended
	Mar. 31, 2020USD ($)multipliershares	Mar. 31, 2019USD ($)shares
W T M Incentive Plan | Performance Cycle 2016 to 2018
Accrued Expense
Percentage of target payout - minimum actual		139.00%
Percentage of target payout - maximum actual		166.00%
W T M Incentive Plan | Performance Cycle 2018 to 2020
Accrued Expense
Percentage of target payout - minimum actual	174.00%
Percentage of target payout - maximum actual	180.00%
White Mountains
Share-based compensation arrangement by share-based payment award
Share-based Compensation Arrangement by Share-based Payment Award, Multiplier for Determining Payout, Low End of Range | multiplier	0
Accrued Expense
Share-based Compensation Arrangement by Share-based Payment Award, Multiplier for Determining Payout, High End of Range | multiplier	2
Share-based Compensation Arrangement by Share-based Payment Award, Performance Cycle Period	3 years
White Mountains | W T M Incentive Plan
Share-based compensation arrangement by share-based payment award
Vesting Period	3 years
Target Performance Share Activity
Beginning of period (in shares) | shares	42,473	40,616
Shares paid or expired (in shares) | shares	(14,070)	(13,715)
New grants (in shares) | shares	14,055	13,700
Assumed forfeitures and cancellations | shares	0	1
Ending of period (in shares) | shares	42,458	40,602
Accrued Expense
Accrued expense at the beginning of period	$ 43.7	$ 31.7
Payments and deferrals	(27.7)	(18.1)
Assumed forfeitures and cancellations	0.4	0.2
Expense recognized	(6.6)	9.3
Accrued expense at the end of the period	9.8	$ 23.1
Additional compensation cost that would be recognized if all outstanding performance shares vested	$ 18.5

Employee Share-Based Incentiv_4

Employee Share-Based Incentive Compensation Plans (Performance Shares Granted Under the WTM Incentive Plan) (Details) - Performance Share - W T M Incentive Plan - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Performance Cycle 2018 to 2020
Share-based compensation arrangement by share-based payment award
Percentage of target payout - minimum actual	174.00%
Percentage of target payout - maximum actual	180.00%
Performance Cycle 2016 to 2018
Share-based compensation arrangement by share-based payment award
Percentage of target payout - minimum actual		139.00%
Percentage of target payout - maximum actual		166.00%
White Mountains
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	43,105
Accrued Expense	$ 10
Target Performance Shares Outstanding, Assumed forfeitures	(647)
Accrued Expense, Assumed forfeitures	(0.2)
Total Target Performance Shares Outstanding	42,458	40,602	42,473	40,616
Total Accrued Expense	$ 9.8	$ 23.1	$ 43.7	$ 31.7
White Mountains | Performance Cycle 2018 to 2020
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	13,450
Accrued Expense	$ 5.1
White Mountains | Performance Cycle 2019 to 2021
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	15,600
Accrued Expense	$ 3.8
White Mountains | Performance Cycle 2020 to 2022
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	14,055
Accrued Expense	$ 1.1

Employee Share-Based Incentiv_5

Employee Share-Based Incentive Compensation Plans (Restricted Shares) (Details) - White Mountains - W T M Incentive Plan - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Restricted Stock
Target Restricted Share Activity
Beginning of period (in shares)	43,395	41,510
Issued (in shares)	14,055	13,700
Vested (in shares)	(14,345)	(13,715)
Assumed forfeitures and cancellations	0	0
Ending of period (in shares)	43,105	41,495
Unamortized grant date fair value
Unamortized grant date fair value, beginning balance	$ 16.7	$ 12.5
Issued	15.1	12.8
Assumed forfeitures and cancellations	0	0
Expense recognized	(5.2)	(2.5)
Unamortized grant date fair value, ending balance	$ 26.6	$ 22.8
Restricted Share Cliff Vesting in January 2022
Unamortized grant date fair value
Target Performance Shares Outstanding	14,055
Restricted Share Cliff Vesting in January 2021
Unamortized grant date fair value
Target Performance Shares Outstanding		13,700

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
ROU lease asset	$ 22.9	$ 22.6
Operating lease liability	23.2	22.8
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
ROU lease asset	22.9	22.6	$ 23.2
Operating lease liability	$ 23.2	$ 22.8	$ 23.2

Leases - Schedule of Lease Cost

Leases - Schedule of Lease Cost (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Leases [Abstract]
Lease cost	$ 2	$ 1.7
Less: sublease income	0.1	0.1
Net lease cost	$ 1.9	$ 1.6

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Payments on Operating Leases (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Remainder of 2019	$ 4.6
2020	5.4
2021	5
2022	4.2
2023	3.1
Thereafter	3.4
Total undiscounted lease payments	25.7
Less: present value adjustment	2.5
Operating lease liability	$ 23.2	$ 22.8

Leases - Schedule of Right-of-U

Leases - Schedule of Right-of-Use Assets and Lease Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
ROU lease asset	$ 22.9	$ 22.6
Lease liability	$ 23.2	$ 22.8
Operating lease, weighted average incremental borrowing rate, percent	4.70%	4.60%
HG/BAM
Lessee, Lease, Description [Line Items]
ROU lease asset	$ 10	$ 10.4
Lease liability	10	10.4
NSM Holding Co LLC
Lessee, Lease, Description [Line Items]
ROU lease asset	6.2	4.8
Lease liability	6.2	4.8
Kudu investments
Lessee, Lease, Description [Line Items]
ROU lease asset	2.2	2.3
Lease liability	2.2	2.3
Other
Lessee, Lease, Description [Line Items]
ROU lease asset	4.5	5.1
Lease liability	$ 4.8	$ 5.3

Non-controlling Interests (Deta

Non-controlling Interests (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ (117.6)	$ (116.8)
Total Non-Controlling Excluding Reciprocals
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 29.3	$ 29.9
HG Global
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.10%	3.10%
Total non-controlling interests	$ 14	$ 14.4
NSM Holding Co LLC
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.60%	3.60%
Total non-controlling interests	$ 15	$ 14.9
Other NSM
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	13.40%	13.40%
Total non-controlling interests	$ (0.1)	$ (0.1)
Kudu Investment Management, LLC
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	0.90%	0.90%
Total non-controlling interests	$ 2	$ 2.2
Other Operations
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ (1.6)	$ (1.5)
Build America Mutual
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ (146.9)	$ (146.7)

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		5 Months Ended
	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2018
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		$ 68.5	$ 99.4
Net investment income		22.9	16
Net realized and unrealized investment gains		(156.7)	245.6
Total revenues		(59.2)	433.6
Total expenses		106.8	151.9
Pre-tax income (loss)		(166)	281.7
Other Revenue		(127.7)	334.2
Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
Total revenues		(17.4)
Other Revenue		(17.4)
Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		3.5	1.3
Total revenues		(124.3)	313.6
Other Revenue		(127.8)	312.3
Kudu investments
Segment reporting information
Earned insurance premiums		0
Net investment income		7.3	0
Net realized and unrealized investment gains		(24.8)	0
Commission revenues		0
Other revenue		0.1
Total revenues		(17.4)	0
Insurance acquisition expenses		0
Cost of sales		0
General and administrative expenses		2.5	0
Amortization		0.1	0
Interest expense		1.4	0
Total expenses		4	0
Pre-tax income (loss)		(21.4)
HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0	0
Earned insurance premiums		5.4	4.2
Net investment income		5.5	5.3
Net realized and unrealized investment gains		6.1	11.8
Commission revenues		0	0
Other revenue		0.5	0.6
Total revenues		17.5	21.9
Insurance acquisition expenses		1.7	1.3
Cost of sales			0
Cost of sales		0
General and administrative expenses		14.7	14.4
Amortization		0	0
Interest expense		0
Total expenses		16.4	15.7
Pre-tax income (loss)		1.1	6.2
Other Revenue		17.5	21.9
NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		65	49.3
Earned insurance premiums		0
Net investment income		0
Net realized and unrealized investment gains		0
Commission revenues		53	43.3
Other revenue		12	6
Total revenues		65	49.3
Insurance acquisition expenses		0
Cost of sales		0
General and administrative expenses		39.6	25.3
Broker commission expenses		18.3	15.5
Change in fair value of contingent consideration earnout liabilities		(0.6)	1.3
Amortization		4.8	5
Interest expense		4.3	3.7
Total expenses		66.4	50.8
Pre-tax income (loss)		(1.4)	(1.5)
Other Revenue		0	0
MediaAlpha
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax			48.8
Earned insurance premiums			0
Net investment income			0
Net realized and unrealized investment gains			0
Commission revenues		0	48.8
Other revenue		0	0
Total revenues		0	48.8
Insurance acquisition expenses			0
Cost of sales		0	40.6
General and administrative expenses		0	12.5
Amortization		0	1.6
Interest expense		0	0.2
Total expenses		0	54.9
Pre-tax income (loss)			(6.1)
Other Revenue			0
Other Segment
Segment reporting information
Earned insurance premiums		0	0
Net investment income		10.1	10.7
Net realized and unrealized investment gains		(138)	119.1
Realized gain and unrealized investment gain from the MediaAlpha Transaction			182.2
Commission revenues		2.1	1.3
Other revenue		1.5	0.3
Total revenues		(124.3)	313.6
Insurance acquisition expenses		0	0
Cost of sales		2	1.1
General and administrative expenses		17.5	29.4
Amortization		0.2	0
Interest expense		0.3	0
Total expenses		20	30.5
Pre-tax income (loss)		(144.3)	283.1
Total
Segment reporting information
Earned insurance premiums		5.4	4.2
Net investment income		22.9	16
Net realized and unrealized investment gains		(156.7)	130.9
Realized gain and unrealized investment gain from the MediaAlpha Transaction			182.2
Commission revenues		55.1	93.4
Other revenue		14.1	6.9
Total revenues		(59.2)	433.6
Insurance acquisition expenses		1.7	1.3
Cost of sales			41.7
Cost of sales		2	81.6
General and administrative expenses		74.3	15.5
Broker commission expenses		18.3	1.3
Change in fair value of contingent consideration earnout liabilities		(0.6)	6.6
Amortization		5.1	3.9
Interest expense		6
Total expenses		106.8	151.9
Pre-tax income (loss)		(166)	281.7
Kudu investments | Kudu investments
Segment reporting information
Other revenue			0
NSM Holding Co LLC
Segment reporting information
Change in fair value of contingent consideration earnout liabilities		(0.6)	1.3	$ 2.6
MediaAlpha | MediaAlpha
Segment reporting information
Total revenues	$ 33.5
Commission and Other Revenue [Member]
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		66.4	50.6
Commission and Other Revenue [Member] | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
Commission and Other Revenue [Member] | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		1.4	1.3
Commission and Other Revenue [Member] | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0	0
Commission and Other Revenue [Member] | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		65	49.3
Commission and Other Revenue [Member] | MediaAlpha
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax			0
Real Estate [Member]
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		11.3	9
Real Estate [Member] | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
Real Estate [Member] | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0	0
Real Estate [Member] | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0	0
Real Estate [Member] | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		11.3	9
Real Estate [Member] | MediaAlpha
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax			0
Social Services [Member]
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		6.3	5.8
Social Services [Member] | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
Social Services [Member] | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0	0
Social Services [Member] | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0	0
Social Services [Member] | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		6.3	5.8
Social Services [Member] | MediaAlpha
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax			0
Other
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		6.7	5.8
Other | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
Other | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		1.4	1.3
Other | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0	0
Other | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		5.3	4.5
Other | MediaAlpha
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax			0
Product [Member]
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
Product [Member] | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
Product [Member] | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		2.1
Product [Member] | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
Product [Member] | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
Pet [Member]
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		11.8
Pet [Member] | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
Pet [Member] | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
Pet [Member] | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
Pet [Member] | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		11.8
Advertising [Member]
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax			48.8
Advertising [Member] | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax			0
Advertising [Member] | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax			0
Advertising [Member] | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax			0
Advertising [Member] | MediaAlpha
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax			48.8
Specialty Transportation [Member]
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		20.3	17.9
Specialty Transportation [Member] | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
Specialty Transportation [Member] | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0	0
Specialty Transportation [Member] | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0	0
Specialty Transportation [Member] | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		20.3	17.9
Specialty Transportation [Member] | MediaAlpha
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax			0
UNITED KINGDOM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		10	12.1
UNITED KINGDOM | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0
UNITED KINGDOM | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0	0
UNITED KINGDOM | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		0	0
UNITED KINGDOM | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax		$ 10	12.1
UNITED KINGDOM | MediaAlpha
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax			$ 0

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Balance Sheet Grouping, Financial Statement Captions
Carrying value	$ 294.7	$ 283.5
NSM Holding Co LLC
Balance Sheet Grouping, Financial Statement Captions
Carrying value	218.4	219.2
NSM Holding Co LLC | NSM Bank Facility
Balance Sheet Grouping, Financial Statement Captions
Carrying value	217.1	217.4
NSM Holding Co LLC | Carrying Value | NSM Bank Facility
Balance Sheet Grouping, Financial Statement Captions
Carrying value	217.1	217.4
NSM Holding Co LLC | Estimate of Fair Value Measurement | NSM Bank Facility
Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	208.7	221.2
NSM Holding Co LLC | Estimate of Fair Value Measurement | Other NSM
Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	1.6	1.7
Kudu | Kudu Debt [Member]
Balance Sheet Grouping, Financial Statement Captions
Carrying value	65.7	53.6
Kudu | Estimate of Fair Value Measurement | Kudu Debt [Member]
Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	63.4	53.6
Other Operations | Carrying Value
Balance Sheet Grouping, Financial Statement Captions
Carrying value		10.7
Other Operations | Estimate of Fair Value Measurement
Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	11.3	11.3
Term Loan | NSM Holding Co LLC | NSM Bank Facility
Balance Sheet Grouping, Financial Statement Captions
Carrying value	220.7
Term Loan | NSM Holding Co LLC | Other NSM
Balance Sheet Grouping, Financial Statement Captions
Carrying value	$ 1.3	$ 1.8

Commitments and Contingencies (

Commitments and Contingencies (Details) - Sirius Group - Swedish Tax Authority - Sirius Group - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Loss Contingencies [Line Items]
Contingent liability	$ 15.5		$ 16.5
Change in contingent liability	$ (1)	$ (0.7)

Held for Sale and Discontinue_3

Held for Sale and Discontinued Operations - (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Discontinued Operations [Line Items}
Net gain from sale of discontinued operations, net of tax	$ 0.9	$ 0.7
Connecticut | Discontinued Operations, Held-for-sale
Discontinued Operations [Line Items}
Assets held for sale	3		$ 3
Sirius Group | Swedish Tax Authority | Sirius Group
Discontinued Operations [Line Items}
Contingent liability	$ 15.5		$ 16.5

Held for Sale and Discontinue_4

Held for Sale and Discontinued Operations - EPS (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Basic and diluted earnings per share numerators (in millions):
Net (loss) income attributable to White Mountains’s common shareholders	$ (128.8)	$ 284.4
Less: total (loss) income from continuing operations, net of tax	(129.7)	283.7
Net income from discontinued operations attributable to White Mountains’s common shareholders	0.9	0.7
Allocation of income for participating unvested restricted common shares	1.3	(2.9)
Basic and diluted (losses) earnings per share numerators	$ (128.4)	$ 280.8
Basic earnings per share denominators (in thousands):
Total average common shares outstanding during the period	3,178,000	3,172,200
Average unvested restricted common shares	(33,800)	(32,500)
Basic (losses) earnings per share denominator	3,144,200	3,139,700
Diluted earnings per share denominator (in thousands):
Total average common shares outstanding during the period	3,178,000	3,172,200
Average unvested restricted common shares	(33,800)	(32,500)
Diluted earnings per share denominator	3,144,200	3,139,700
Earnings Per Share, Basic and Diluted	$ (40.54)	$ 89.64
Discontinued Operations
Basic and diluted earnings per share numerators (in millions):
Net (loss) income attributable to White Mountains’s common shareholders	$ (128.8)	$ 284.4
Less: total (loss) income from continuing operations, net of tax	(129.7)	283.7
Net income from discontinued operations attributable to White Mountains’s common shareholders	0.9	0.7
Allocation of income for participating unvested restricted common shares	0	0
Basic and diluted (losses) earnings per share numerators	$ 0.9	$ 0.7
Basic earnings per share denominators (in thousands):
Total average common shares outstanding during the period	3,178,000	3,172,200
Average unvested restricted common shares	(33,800)	(32,500)
Basic (losses) earnings per share denominator	3,144,200	3,139,700
Diluted earnings per share denominator (in thousands):
Total average common shares outstanding during the period	3,178,000	3,172,200
Average unvested restricted common shares	(33,800)	(32,500)
Diluted earnings per share denominator	3,144,200	3,139,700
Earnings Per Share, Basic and Diluted	$ 0.28	$ 0.22

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Mar. 31, 2019	Apr. 07, 2020	Dec. 31, 2019
Subsequent Event [Line Items]
Ownership interest (as a percent)		50.00%			50.00%
Payments to Acquire Businesses and Interest in Affiliates		$ 0	$ 9.6
Subsequent Event
Subsequent Event [Line Items]
Ownership interest (as a percent)				100.00%
United Kingdom, Pounds | Subsequent Event
Subsequent Event [Line Items]
Business Combination, Step Acquisition, Equity Interest in Acquiree, Fair Value	$ 120
Payments to Acquire Businesses and Interest in Affiliates	103
Contingent consideration				$ 17
Stock Issued During Period, Value, Acquisitions	64.9
Proceeds from borrowings	42.5
United States of America, Dollars | Subsequent Event
Subsequent Event [Line Items]
Stock Issued During Period, Value, Acquisitions	$ 79.9