White Mountains Insurance (WTM) 10-Q 7 Aug 20 2019 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Aug. 05, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 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, Suite 3B
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		3,101,761
Entity Central Index Key	0000776867
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Assets
Goodwill and other intangible assets	$ 759.9	$ 654.7
Total assets	4,000.3	3,983.2
Liabilities
Debt	349.8	283.5
Total liabilities	937	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 3,101,761 and 3,185,353 shares and paid-in surplus	587	596.3
Retained earnings	2,589.3	2,672.4
Accumulated other comprehensive loss, after tax:
Accumulated Other Comprehensive Income (Loss), Net of Tax	(10.3)	(7.2)
Total White Mountains’s common shareholders’ equity	3,166	3,261.5
Non-controlling interests
Non-controlling interests	(102.7)	(116.8)
Total equity	3,063.3	3,144.7
Total liabilities and equity	4,000.3	3,983.2
HG Global-BAM
Assets
Fixed maturity investments, at fair value	821.7	799.3
Short-term investments, at fair value	54.7	46.3
Total investments	876.4	845.6
Cash	32	24.2
Insurance premiums receivable	7.3	6.7
Deferred acquisition costs	25	22.1
Accrued investment income	5.2	5.4
Accounts receivable on unsettled investment sales	0	3.9
Other assets	14.6	16.1
Total assets	960.5	924
Liabilities
Unearned insurance premiums	218.6	198.4
Accrued incentive compensation	14.1	21.7
Accounts payable on unsettled investment purchases	3	0
Other liabilities	27.3	26.7
Total liabilities	263	246.8
NSM Holding Co LLC
Assets
Cash	140.5	89.7
Accounts Receivable, after Allowance for Credit Loss	76.7	70.8
Goodwill and other intangible assets	728.6	623
Other assets	55.1	41.7
Total assets	1,000.9	825.2
Liabilities
Debt	268.4	219.2
Premiums payable	139.7	102.3
Contingent consideration earnout liabilities	11.7	20.6
Other liabilities	81.1	59
Total liabilities	500.9	401.1
Kudu investments
Assets
Short-term investments, at fair value	0.1	0.1
Other long-term investments	315.6	266.5
Total investments	315.7	266.6
Cash	5.9	5.8
Accrued investment income	5.6	5.8
Goodwill and other intangible assets	9.4	9.6
Other assets	2.7	2.7
Total assets	339.3	290.5
Liabilities
Debt	70.8	53.6
Other liabilities	6.5	3.4
Total liabilities	77.3	57
Other Segment
Assets
Fixed maturity investments, at fair value	369.9	406.5
Short-term investments, at fair value	62.8	154.8
Common equity securities, at fair value	567.2	683.9
Other long-term investments	582.5	589.8
Total investments	1,582.4	1,835
Cash	32.9	41.3
Accrued investment income	4	5.7
Accounts receivable on unsettled investment sales	23.4	5.1
Goodwill and other intangible assets	21.9	22.1
Other assets	32	31.3
Assets held for sale	3	3
Total assets	1,699.6	1,943.5
Liabilities
Debt	10.6	10.7
Accrued incentive compensation	18.9	55.1
Other liabilities	66.3	67.8
Total liabilities	$ 95.8	$ 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	3,101,761	3,185,353
Common shares, outstanding shares	3,101,761	3,185,353
NSM Holding Co LLC
Cash	$ 96.3	$ 56.3

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues:
Net investment income	$ 19.6	$ 21	$ 42.5	$ 37
Net realized and unrealized investment gains			(3.8)	280.8
Total revenues	259.6	129	200.4	562.6
Expenses:
Total expenses	126.9	113.2	233.7	265.1
Pre-Tax and Net Income [Abstract]
Pre-tax income (loss) from continuing operations	132.7	15.8	(33.3)	297.5
Income tax (expense) benefit	(24.1)	0.1	1.4	(10.1)
Net income (loss) from continuing operations	108.6	15.9	(31.9)	287.4
Net (loss) income from sale of discontinued operations, net of tax	(1)	0	(0.1)	0.7
Net income (loss)	107.6	15.9	(32)	288.1
Net loss attributable to non-controlling interests	7.8	4.6	18.6	16.8
Net income (loss) attributable to White Mountains’s common shareholders	115.4	20.5	(13.4)	304.9
HG Global-BAM
Revenues:
Earned insurance premiums	5.6	4.3	11	8.5
Net investment income	4.9	5.4	10.4	10.7
Net realized and unrealized investment gains	14.4	11.5	20.5	23.3
Advertising and commission revenues	0	0	0
Other revenue	1.2	0.4	1.7	1
Total revenues	26.1	21.6	43.6	43.5
Expenses:
Deferred Policy Acquisition Costs, Amortization Expense	2.1	1.4	3.8	2.7
Other underwriting expenses	0.2	0.1	0.2	0.2
Cost of sales	0	0	0
General and administrative expenses	12.5	12.3	27.2	26.6
Amortization of other intangible assets	0	0	0
Interest expense	0		0
Total expenses	14.8	13.8	31.2	29.5
Pre-Tax and Net Income [Abstract]
Pre-tax income (loss) from continuing operations	11.3	7.8	12.4	14
NSM Holding Co LLC
Revenues:
Earned insurance premiums	0		0
Net investment income	0		0
Net realized and unrealized investment gains	0		0
Advertising and commission revenues	63	54.9	116	98.2
Other revenue	13.1	11.2	25.1	17.2
Total revenues	76.1	66.1	141.1	115.4
Expenses:
Deferred Policy Acquisition Costs, Amortization Expense	0
Other underwriting expenses	0		0
Cost of sales	0		0
General and administrative expenses	48.5	32.8	88.1	58.1
Broker commission expenses	21	18.1	39.3	33.6
Change in fair value of contingent consideration earnout liabilities	(1.7)	6.3	(2.3)	7.6
Amortization of other intangible assets	6.3	4.1	11.1	9.1
Interest expense	5.7	4.1	10	7.8
Total expenses	79.8	65.4	146.2	116.2
Pre-Tax and Net Income [Abstract]
Pre-tax income (loss) from continuing operations	(3.7)	0.7	(5.1)	(0.8)
Kudu investments
Revenues:
Earned insurance premiums	0		0
Net investment income	5.6	4	12.9	4
Net realized and unrealized investment gains	16.5	0.4	(8.3)	0.4
Advertising and commission revenues	0		0
Other revenue	0	0	0.1	0
Total revenues	22.1	4.4	4.7	4.4
Expenses:
Deferred Policy Acquisition Costs, Amortization Expense	0		0
Other underwriting expenses	0		0
Cost of sales	0		0
General and administrative expenses	2.8	2.2	5.3	2.2
Amortization of other intangible assets	0.1	0	0.2	0
Interest expense	1.5	0	2.9	0
Total expenses	4.4	2.2	8.4	2.2
Pre-Tax and Net Income [Abstract]
Pre-tax income (loss) from continuing operations	17.7		(3.7)	2.2
MediaAlpha
Revenues:
Advertising and commission revenues	0	0	0	48.8
Total revenues	0	0	0	48.8
Expenses:
Cost of sales	0	0	0	40.6
General and administrative expenses	0	0	0	12.5
Amortization of other intangible assets	0	0	0	1.6
Interest expense	0	0	0	0.2
Total expenses	0	0	0	54.9
Pre-Tax and Net Income [Abstract]
Pre-tax income (loss) from continuing operations				(6.1)
Other Segment
Revenues:
Earned insurance premiums	0	0	0
Net investment income	9.1	11.6	19.2	22.3
Net realized and unrealized investment gains	122	23.3	(16)	142.4
Realized gain and unrealized investment gain from the MediaAlpha Transaction		0	0	182.2
Advertising and commission revenues	1.9	1.3	4	2.6
Other revenue	2.3	0.7	3.8	1
Total revenues	135.3	36.9	11	350.5
Expenses:
Deferred Policy Acquisition Costs, Amortization Expense	0	0	0
Other underwriting expenses	0		0
Cost of sales	2.2	1.6	4.2	2.7
General and administrative expenses	25.3	30.1	42.8	59.5
Amortization of other intangible assets	0.2	0.1	0.4	0.1
Interest expense	0.2	0	0.5	0
Total expenses	27.9	31.8	47.9	62.3
Pre-Tax and Net Income [Abstract]
Pre-tax income (loss) from continuing operations	$ 107.4	$ 5.1	$ (36.9)	$ 288.2

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income (loss) attributable to White Mountains’s common shareholders	$ 115.4	$ 20.5	$ (13.4)	$ 304.9
Other comprehensive income (loss), net of tax	0.5	(3.1)	(2.9)	(3.4)
Comprehensive income (loss)	115.9	17.4	(16.3)	301.5
Other Comprehensive (income) loss attributable to non-controlling interests	(0.2)	0.2	(0.2)	0.2
Comprehensive income (loss) attributable to White Mountains’s common shareholders	$ 115.7	$ 17.6	$ (16.5)	$ 301.7
Basic earnings (loss) per share
Continuing operations (in usd per share)	$ 37.46	$ 6.44	$ (4.25)	$ 95.71
Discontinued operations (in usd per share)	(0.32)	0	(0.03)	0.22
Total consolidated operations (in usd per share)	37.14	6.44	(4.28)	95.93
Diluted earnings (loss) per share
Continuing operations (in usd per share)	37.46	6.44	(4.25)	95.71
Discontinued operations (in usd per share)	(0.32)	0	(0.03)	0.22
Total consolidated operations (in usd per share)	37.14	6.44	(4.28)	95.93
Dividends declared per White Mountains’s common share	$ 0	$ 0	$ 1	$ 1

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Unaudited) - USD ($) shares in Millions, $ 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	$ (19.9)
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	288.1		304.9		304.9	(16.8)	288.1
Net change in foreign currency translation and other								$ 3.2	$ 3.2	$ 0.2	$ 3.4
Total comprehensive loss	301.5		(304.9)	3.2	(301.7)	17	(284.7)
Dividends declared on common shares			(3.2)		$ (3.2)		(3.2)
Dividends to non-controlling interests						$ (1)	$ (1)
Stock Issued During Period, Shares, New Issues		2.2			2.2	0	2.2
Repurchases and retirements of common shares		$ (1.1)	(3.8)		$ (4.9)		$ (4.9)
Capital contributions from BAM members, net of tax												$ 17	$ 17
Net contributions and dilution from non-controlling interests						$ 1.5	1.5
Amortization of restricted share awards		5.1			5.1		5.1
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						1.8	1.8
Ending Balances at Jun. 30, 2019		590.5	2,562.8	(9)	3,144.3	(136.4)	3,007.9
Beginning Balances at Mar. 31, 2019		$ 585.8	2,542.3	(6.1)	3,122	(143.7)	2,978.3
Increase (Decrease) in Shareholders' Equity
Net (loss) income	15.9		20.5		20.5	(4.6)	15.9
Net change in foreign currency translation and other								$ 2.9	2.9	0.2	3.1
Total comprehensive loss	17.4		(20.5)	2.9	$ (17.6)	4.8	(12.8)
Dividends to non-controlling interests						$ (0.5)	$ (0.5)
Stock Issued During Period, Shares, New Issues		2.2			2.2	0	2.2
Repurchases and retirements of common shares		$ (0.1)	0		$ (0.1)		$ (0.1)
Capital contributions from BAM members, net of tax												10.2	10.2
Net contributions and dilution from non-controlling interests						$ 0.8	0.8
Amortization of restricted share awards		2.6			2.6		2.6
Acquisition of non-controlling interests						1.6	1.6
Ending Balances at Jun. 30, 2019		590.5	2,562.8	(9)	3,144.3	(136.4)	3,007.9
Members Capital Contribution	(31.5)
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	(32)		(13.4)		(13.4)	(18.6)	(32)
Net change in foreign currency translation and other				(3.1)					(3.1)	0.1	(3)
Total comprehensive loss	(16.3)		(13.4)	(3.1)	(16.5)	(18.5)	(35)
Dividends declared on common shares			(3.2)		$ (3.2)		(3.2)
Dividends to non-controlling interests						$ (1.4)	$ (1.4)
Stock Issued During Period, Shares, New Issues		1.3			1.3	0	1.3
Repurchases and retirements of common shares		$ (18.6)	(66.5)		$ (85.1)		$ (85.1)
Capital contributions from BAM members, net of tax												31.5	31.5
Net contributions and dilution from non-controlling interests		(0.7)			(0.7)	$ 2.5	1.8
Amortization of restricted share awards		8.7			8.7		8.7
Ending Balances at Jun. 30, 2020	3,063.3	587	2,589.3	(10.3)	3,166	(102.7)	3,063.3
Beginning Balances at Mar. 31, 2020		$ 589.3	2,498	(10.6)	3,076.7	(117.6)	2,959.1
Increase (Decrease) in Shareholders' Equity
Net (loss) income	107.6		115.4		115.4	(7.8)	107.6
Net change in foreign currency translation and other				0.3					$ 0.3	$ 0.1	$ 0.4
Total comprehensive loss	115.9		115.4	0.3	115.7	(7.7)	108
Dividends declared on common shares			0		$ 0		0
Dividends to non-controlling interests						$ (0.9)	$ (0.9)
Stock Issued During Period, Shares, New Issues		1.3			1.3	0	1.3
Repurchases and retirements of common shares		$ (6.5)	(24.1)		$ (30.6)		$ (30.6)
Capital contributions from BAM members, net of tax												$ 21.5	$ 21.5
Net contributions and dilution from non-controlling interests		(0.7)			(0.7)	$ 2	1.3
Amortization of restricted share awards		3.6			3.6		3.6
Ending Balances at Jun. 30, 2020	$ 3,063.3	$ 587	$ 2,589.3	$ (10.3)	$ 3,166	$ (102.7)	$ 3,063.3

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operations:
Net (loss) income	$ (32)	$ 288.1
Adjustments to reconcile net income to net cash used for operations:
Net realized and unrealized investment losses (gains)	3.8	(280.8)
Realized gain from the MediaAlpha Transaction	0	(67.5)
Deferred income tax (benefit) expense	(2.7)	4
Net gain from sale of discontinued operations, net of tax	0.1	(0.7)
Amortization of restricted share and option awards	8.7	5.4
Amortization and depreciation	17.4	12
Other operating items:
Net change in Premiums and Commissions Receivable	(3)	(13.6)
Net change in Premiums Payable	28.1	41.5
Net change in unearned insurance premiums	20.2	11.8
Net change in deferred acquisition costs	(2.9)	(1.5)
Net change in restricted cash	40	38.8
Investments in Kudu Participation Contracts	(57.4)	0
Net change in other assets and liabilities, net	(59.2)	(35.7)
Net cash (used for) provided from operations	(38.9)	1.8
Cash flows from investing activities:
Net change in short-term investments	84	30.9
Sales of fixed maturity and convertible investments	244.2	241.5
Maturities, calls and paydowns of fixed maturity and convertible investments	93.7	61.5
Sales of common equity securities	108	360.1
Distributions and redemptions of other long-term investments and settlements of forward contracts	64.1	3.8
Purchases of other long-term investments	(42.3)	(169.1)
Purchases of common equity securities	(33.7)	(4.7)
Purchases of fixed maturity and convertible investments	(293.4)	(297.4)
Purchases of consolidated subsidiaries, net of cash acquired of $11.9 and $12.8	(120.3)	(243.4)
Other investing activities, net	(15.3)	(95.8)
Net cash provided from (used for) investing activities	89	(112.6)
Cash flows from financing activities:
Draw down of debt and revolving line of credit	69.4	149.4
Repayment of debt and revolving line of credit	(1.1)	(21.7)
Cash dividends paid to the Company’s common shareholders	(3.2)	(3.2)
Common shares repurchased	(78.5)	0
Distribution to non-controlling interest shareholders	(1.2)	(27.6)
Payments on contingent consideration earnout liabilities	(6.4)	(2.6)
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	2.2	1.6
Capital contributions from BAM members	31.5	19.9
Fidus Re premium payment	(1.6)	(1.5)
Other financing activities, net	(9.8)	(4.9)
Net cash provided from financing activities	1.3	151
Effect of exchange rate changes on cash	(1.1)	(0.2)
Net change in cash during the period - continuing operations, including the effect of exchange rate changes	50.3	40
Cash balances at beginning of period	161	110.3
Cash balances at end of period	211.3	150.3
Supplemental cash flows information:
Interest paid	(6.7)	(7.3)
Net income tax refunds	$ 0	$ (0.2)

CONSOLIDATED STATEMENTS OF CA_2

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Cash Flows [Abstract]
Restricted cash balance		$ 60.8	$ 96.3	$ 56.3	$ 50
Cash acquired from acquisition	$ 11.9	$ 12.8

Basis of Presentation and Signi

Basis of Presentation and Significant Accouting Policies	6 Months Ended
	Jun. 30, 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 June 30, 2020, White Mountains’s reportable segments were HG Global/BAM, NSM, Kudu and Other Operations. 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 consequently it was no longer a reportable 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” and 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 June 30, 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 June 30, 2020 and December 31, 2019, White Mountains owned 96.6% and 96.4% of the basic units outstanding of NSM ( 89.6% and 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. It operates a transparent and efficient online customer acquisition technology platform that facilitates real-time transactions between buyers and sellers of consumer referrals (e.g., clicks, calls and leads), primarily in the property & casualty, health and life insurance verticals. 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 June 30, 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 June 30, 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 the deposit method, ceded premiums paid are not recognized through income but rather treated as a deposit. BAM entered into a ceded 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. Cash and Restricted Cash Cash includes amounts on hand and demand deposits with banks and other financial institutions. Amounts presented in the statement of cash flows are shown net of balances acquired and sold in the purchase or sale of the Company’s consolidated subsidiaries. Cash balances that are not immediately available for general corporate purposes, including fiduciary accounts held by NSM on behalf of insurance carriers, are classified as restricted. Restricted amounts included within cash are disclosed parenthetically on the balance sheet. 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, are 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 changed the guidance on goodwill impairment testing. Under the new guidance, the qualitative assessment of the recoverability of goodwill remains the same, but the second step of the two-step quantitative test, which required calculation of the implied fair value of goodwill, has been eliminated. Instead, an impairment charge is recognized when the carrying value of a reporting unit exceeds its fair value. Any excess of carrying value over fair value is written down as an impairment. White Mountains did not recognize an impairment of goodwill during the three and six months ended June 30, 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 June 30, 2020 , White Mountains recognized $34.0 million and $ 34.2 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	6 Months Ended
	Jun. 30, 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 June 30, 2020 , White Mountains had $52.1 million invested into four Elementum-managed funds. White Mountains has elected 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 unit 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”), 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 six months ended June 30, 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. NSM did not make any payments related to the first Fresh Insurance earnout period. 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 value. The relative fair values of goodwill and of other intangible assets recognized in connection with the acquisition of KBK had not yet been finalized as of December 31, 2018. As of March 31, 2019, White Mountains determined that the relative values of goodwill and other intangible assets from the KBK transaction were $32.6 million and $32.7 million , reflecting acquisition date fair values, and recorded a liability of $5.9 million relating to the fair value of contingent consideration earnouts made in connection with the acquisition. The purchase price is subject to adjustments based upon growth in EBITDA during three earnout periods, one which ended in December 2019, one ending in December 2020 and one ending in December 2021. In the first quarter of 2020, NSM paid $6.4 million related to the first KBK earnout period. 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” . 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. NSM paid £ 107.2 million (approximately $132 million based upon the foreign exchange spot rate at the date of acquisition) of upfront cash consideration for Kingsbridge. White Mountains contributed $80.3 million to NSM and NSM borrowed £ 42.5 million (approximately $52.4 million based upon the foreign exchange spot rate at the date of acquisition) to fund the transaction. As of June 30, 2020, White Mountains had recognized $ 125.1 million of goodwill and other intangible assets, reflecting acquisition date fair value. The relative fair values of other intangible assets recognized in connection with the acquisition of Kingsbridge had not yet been finalized as of June 30, 2020. The purchase price is subject to adjustment based upon growth in EBITDA during an earnout period ending in January 2022. In connection with the Kingsbridge acquisition, NSM expects to record a contingent consideration earnout liability in the third quarter of 2020. As of June 30, 2020 and December 31, 2019, NSM recorded total contingent consideration earnout liabilities of $ 11.7 million and $20.6 million . The contingent consideration earnout liabilities 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 and six months ended June 30, 2020 , NSM recognized pre-tax income of $1.7 million and $2.3 million for the change in the fair value of its contingent consideration earnout liabilities. For the three and six months ended June 30, 2019 , NSM recognized pre-tax expense of $6.3 million and $7.6 million for the change in the fair value of its contingent consideration earnout liabilities. Any future adjustments to contingent consideration earnout liabilities will be recognized through pre-tax income. For the three months ended June 30, 2020 , NSM made no payments related to its contingent consideration earnout liabilities. For the six months ended June 30, 2020, NSM paid $6.4 million related to KBK’s contingent consideration earnout liabilities. For both the three and six months ended June 30, 2019 , NSM paid $2.6 million related to its U.K. vertical’s contingent consideration earnout liabilities. 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 $94.5 million and $129.0 million was undrawn as of June 30, 2020 and December 31, 2019. During the fourth quarter of 2019, Kudu obtained a committed $125.0 million credit facility, of which $51.0 million and $68.0 million was undrawn as of June 30, 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 of the basic units outstanding of MediaAlpha from 61.0% to 48.3% ( 58.9% to 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 and unrealized investment gains on the MediaAlpha Transaction. Other Transactions PassportCard/DavidShield On May 7, 2020, White Mountains made an additional $15.0 million investment in PassportCard/DavidShield to support operations and to continue global expansion through the ongoing COVID-19 pandemic. The transaction increased White Mountains’s ownership interest from 50.0% to 53.8% in both PassportCard and DavidShield, but had no impact on the governance structure of the companies, including White Mountains’s board representation or other investor rights. The governance structures for both PassportCard and DavidShield were designed to give White Mountains and its co-investor equal power to make the decisions that most significantly impact the operations of PassportCard and DavidShield.

Investment Securities

Investment Securities	6 Months Ended
	Jun. 30, 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 June 30, 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 and six months ended June 30, 2020 and 2019 : Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Fixed maturity investments $ 7.3 $ 8.3 $ 15.4 $ 16.4 Short-term investments .1 1.3 .9 2.6 Common equity securities 2.2 2.9 6.0 8.3 Other long-term investments 10.3 8.8 20.8 10.4 Total investment income 19.9 21.3 43.1 37.7 Third-party investment expenses (.3 ) (.3 ) (.6 ) (.7 ) Net investment income, pre-tax $ 19.6 $ 21.0 $ 42.5 $ 37.0 Net Realized and Unrealized Investment Gains (Losses) The following table presents net realized and unrealized investment gains (losses) for the three and six months ended June 30, 2020 and 2019 : Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Fixed maturity investments $ 30.0 $ 16.9 $ 32.2 $ 38.0 Short-term investments — .3 .4 .3 Common equity securities 98.3 27.8 (42.5 ) 139.1 Other long-term investments (1) (2) 24.6 $ (9.8 ) 6.1 103.4 Net realized and unrealized investment gains (losses) 152.9 35.2 (3.8 ) 280.8 Less: net gains (losses) on investment securities sold during the period 2.2 .2 (6.5 ) 12.4 Net realized and unrealized investment gains on investment securities held at the end of the period $ 150.7 $ 35.0 $ 2.7 $ 268.4 (1) For the six months ended June 30, 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 June 30, 2020 and 2019, includes $0.4 and $0.3 of realized and unrealized investment gains related to foreign currency exchange. For the six months ended June 30, 2020 and 2019, there were no realized and unrealized investment gains 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 and six months ended June 30, 2020 and 2019 for investments still held at the end of the period: Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Other long-term investments $ 25.3 $ (14.0 ) $ 15.9 $ 100.0 Total net unrealized investment gains (losses), pre-tax - Level 3 investments $ 25.3 $ (14.0 ) $ 15.9 $ 100.0 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 June 30, 2020 and December 31, 2019 : June 30, 2020 Millions Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Carrying Value U.S. Government and agency obligations $ 195.5 $ 4.9 $ — $ 200.4 Debt securities issued by corporations 480.2 26.1 (.5 ) 505.8 Municipal obligations 248.3 16.7 (.2 ) 264.8 Mortgage and asset-backed securities 213.2 7.4 — 220.6 Total fixed maturity investments $ 1,137.2 $ 55.1 $ (.7 ) $ 1,191.6 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 June 30, 2020 and December 31, 2019 : June 30, 2020 Millions Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Net Foreign Currency Losses Carrying Value Common equity securities $ 502.8 $ 69.3 $ (4.9 ) $ — $ 567.2 Other long-term investments $ 677.9 $ 289.6 $ (67.1 ) $ (2.3 ) $ 898.1 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 June 30, 2020 and December 31, 2019 : Carrying Value at Millions June 30, 2020 December 31, 2019 Kudu’s Participation Contracts (1) $ 315.6 $ 266.5 MediaAlpha (1) 225.0 180.0 PassportCard/DavidShield (1) 95.0 90.0 Elementum Holdings L.P. (1) 55.1 55.1 Other unconsolidated entities (1)(2) 31.9 33.7 Total unconsolidated entities (1) 722.6 625.3 Private equity funds and hedge funds 105.9 161.1 Insurance-linked securities funds 52.1 41.2 Private debt investments (3) 17.5 28.7 Total other long-term investments $ 898.1 $ 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 and Simple Agreement for Future Equity (“SAFE”) investments. (3) Includes $4.6 and $5.0 in private debt investments carried at fair value as of June 30. 2020 and amortized cost as of December 31, 2019. 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 June 30, 2020 , White Mountains held investments in thirteen private equity funds. The largest investment in a single private equity fund or hedge fund was $23.1 million as of June 30, 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. 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 June 30, 2020 and December 31, 2019 : June 30, 2020 December 31, 2019 Millions Fair Value Unfunded Commitments Fair Value Unfunded Commitments Private equity funds Aerospace/Defense/Government $ 44.8 $ 15.7 $ 33.8 $ 23.3 Manufacturing/Industrial 43.8 4.0 57.7 4.1 Financial services 17.3 24.7 15.0 22.8 Total private equity funds 105.9 44.4 106.5 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 $ 105.9 $ 44.4 $ 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 June 30, 2020 : Millions 1 – 3 years 3 – 5 years 5 – 10 years >10 years Total Private equity funds — expected lock-up period remaining $4.7 $40.4 $56.7 $4.1 $105.9 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 June 30, 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 June 30, 2020, White Mountains held investments in four ILS funds with a fair value of $52.1 million . 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. 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 redemption 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 the 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 June 30, 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 June 30, 2020 and December 31, 2019, White Mountains used quoted market prices or other observable inputs to determine fair value for approximately 68% 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 June 30, 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. June 30, 2020 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 200.4 $ 200.4 $ — $ — Debt securities issued by corporations: Financials 151.9 — 151.9 — Industrial 61.1 — 61.1 — Technology 57.6 — 57.6 — Consumer 55.6 — 55.6 — Healthcare 43.3 — 43.3 — Communications 40.9 — 40.9 — Energy 34.3 — 34.3 — Materials 32.1 — 32.1 — Utilities 29.0 — 29.0 — Total debt securities issued by corporations 505.8 — 505.8 — Municipal obligations 264.8 — 264.8 — Mortgage and asset-backed securities 220.6 — 220.6 — Total fixed maturity investments 1,191.6 200.4 991.2 — Short-term investments (1) 117.6 114.5 3.1 — Common equity securities: Exchange traded funds 442.4 442.4 — — Other (2) 124.8 22.3 102.4 .1 Total common equity securities 567.2 464.7 102.4 .1 Other long-term investments 740.1 — — 740.1 Other long-term investments — NAV (3) 158.0 — — — Total investments $ 2,774.5 $ 779.6 $ 1,096.7 $ 740.2 (1) Short-term investments are measured at amortized cost, which approximates fair value. (2) 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. (3) 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 credit ratings of debt securities issued by corporations held in White Mountains’s investment portfolio as of June 30, 2020 and December 31, 2019 : Fair Value at Millions June 30, 2020 December 31, 2019 AAA $ 8.3 $ 9.5 AA 53.6 73.9 A 314.1 288.5 BBB 128.1 95.3 BB 1.7 — Debt securities issued by corporations (1) $ 505.8 $ 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 June 30, 2020 and December 31, 2019 : June 30, 2020 December 31, 2019 Millions Fair Value Level 2 Level 3 Fair Value Level 2 Level 3 Mortgage-backed securities: Agency: FNMA $ 87.4 $ 87.4 $ — $ 88.6 $ 88.6 $ — FHLMC 68.1 68.1 — 60.5 60.5 — GNMA 42.2 42.2 — 30.8 30.8 — Total agency (1) 197.7 197.7 — 179.9 179.9 — Total mortgage-backed securities 197.7 197.7 — 179.9 179.9 — Other asset-backed securities: Vehicle receivables 11.5 11.5 — 15.1 15.1 — Credit card receivables 11.4 11.4 — 14.0 14.0 — Total other asset-backed securities 22.9 22.9 — 29.1 29.1 — Total mortgage and asset-backed securities $ 220.6 $ 220.6 $ — $ 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 June 30, 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 June 30, 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) gains (13.9 ) 3.6 — 15.6 (9.5 ) (4.2 ) (3) Amortization/Accretion — (1.9 ) — — — (1.9 ) Purchases 113.0 214.2 — 78.6 21.2 427.0 Sales (214.0 ) (231.9 ) — (8.1 ) (56.0 ) (510.0 ) Transfers in — — — — — — Transfers out — — — — — — Balance at June 30, 2020 $ 665.1 $ 1,093.6 $ .1 $ 740.1 $ 158.0 $ 2,656.9 (1) (1) Excludes carrying value of $ 117.6 and $ 201.2 as of June 30, 2020 and December 31, 2019 classified as short-term investments. (2) Includes private equity funds, hedge funds and ILS funds 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 six months ended June 30, 2020. Level 3 Investments Other Long-term Investments Measured at NAV (3,5) 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 115.2 62.0 100.0 3.4 280.6 (2, 4) Amortization/Accretion .1 (.7 ) — — (.6 ) Purchases 70.1 232.0 136.7 102.5 541.3 Sales (343.5 ) (319.7 ) — (3.8 ) (667.0 ) Transfers in — — 82.6 — 82.6 Transfers out — — — (82.6 ) (82.6 ) Balance at June 30, 2019 $ 684.5 $ 1,134.1 $ 458.0 $ 206.4 $ 2,483.0 (1) (1) Excludes carrying value of $ 187.1 and $ 214.2 as of June 30, 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 ILS funds 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” . (4) Excludes realized and unrealized losses associated with short-term investments of $0.2 for the six months ended June 30, 2019. (5) Transfer includes $71.7 associated with the Kudu Transaction. See Note 2 — “Significant Transactions”. Fair Value Measurements — Transfers Between Levels - Six-months ended June 30, 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 six 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 six 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 June 30, 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 June 30, 2020 Description Valuation Technique(s) Fair Value (5) Unobservable Inputs Discount Rate (2)(6) Terminal Cash Flow Exit Multiple (x) or Terminal Revenue Growth Rate (%) (6) Kudu’s Participation Contracts (1)(2) Discounted cash flow $315.6 18% - 23% 6x - 12x MediaAlpha Discounted cash flow $225.0 14% 4% PassportCard/DavidShield (3) Discounted cash flow $95.0 23% 4% Elementum Holdings, L.P. Discounted cash flow $55.1 19% 4% Private debt instruments Discounted cash flow $17.5 6% - 12% N/A All other Discounted cash flow $15.7 24% 4% Noblr, Inc. Share price of recent transaction $8.7 Share price: $2.17 Zillion Insurance Services, Inc. (4) Recent transaction $5.0 Transaction price: $5.0 Compare.com Estimated net realizable value $2.5 Net realizable value: $2.5 (1) During the six months ended June 30, 2020, Kudu deployed a total of $57.4 in new Kudu Participation Contracts, including Creation Investments Capital Management and Sequoia Financial Group. (2) Since Kudu’s Participation Contracts are not subject to corporate taxes within Kudu Investment Management, LLC, pre-tax discount rates are applied to pre-tax cash flows in determining fair values. (3) During the three months ended June 30, 2020, White Mountains made an additional $15.0 investment in PassportCard/DavidShield. See Note 2 - “Significant Transactions” . (4) During the three months ended June 30, 2020, White Mountains made an additional $2.5 investment in Zillion Insurance Services, Inc. (5) Includes the net unrealized investment gains (losses) associated with foreign currency; foreign currency effects based on observable inputs. (6) 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	6 Months Ended
	Jun. 30, 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 acquisition date fair values of certain assets and liabilities, 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 June 30, 2020 and December 31, 2019 : $ in Millions Weighted Average Economic Life (in years) June 30, 2020 December 31, 2019 Acquisition Date Fair Value Accumulated Amortization Impairments Net Carrying Value Acquisition Date Fair Value Accumulated Amortization Impairments Net Carrying Value Goodwill: NSM (1) N/A $ 504.9 $ — $ — $ 504.9 $ 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 518.2 — — 518.2 402.3 — 7.6 394.7 Other intangible assets: NSM (1) Customer 9 120.1 26.9 3.5 89.7 121.7 19.8 1.4 100.5 Trade names 19 61.2 6.6 1.0 53.6 61.9 5.3 .4 56.2 Information technology platform 0 3.1 1.4 1.7 — 3.9 1.4 .6 1.9 Renewal rights 12 82.5 2.8 — 79.7 82.5 .7 — 81.8 Other 3 1.7 1.0 — .7 1.7 .7 — 1.0 Subtotal 268.6 38.7 6.2 223.7 271.7 27.9 2.4 241.4 Kudu Trade names 7 2.2 .4 — 1.8 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 .6 — 6.6 7.2 .4 — 6.8 Information 5 — — — — .5 .3 .2 — Insurance Licenses N/A 8.6 — — 8.6 8.6 — — 8.6 Other 5 .2 .1 — .1 .2 — — .2 Subtotal 17.0 .8 — 16.2 18.2 1.2 .4 16.6 Total other intangible assets 287.8 39.9 6.2 241.7 292.1 29.3 2.8 260.0 Total goodwill and other intangible assets $ 806.0 $ 39.9 $ 6.2 759.9 $ 694.4 $ 29.3 10.4 654.7 Goodwill and other intangible assets attributed to non-controlling interests (25.9 ) (23.4 ) Goodwill and other intangible assets included in White Mountains’s common shareholders’ equity $ 734.0 $ 631.3 (1) As of June 30, 2020 , NSM’s goodwill and intangible assets included $ (1.8) and $ (0.4) 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 on the previous page 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 June 30, 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 Kingsbridge (4) 125.1 April 7, 2020 Total NSM segment $ 275.2 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) Excludes $3.4 of software classified within other assets. (3) NSM’s purchase of the Renewal Rights from AIG was an asset acquisition. (4) The determination of the relative fair values of goodwill and other intangible assets had not yet been finalized as of June 30, 2020. On an annual basis beginning no later than the interim period included in the one-year anniversary of an acquisition, White Mountains evaluates goodwill and other intangible assets 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. During the three months ended June 30, 2020 , White Mountains recognized impairments of other intangible assets of $6.2 million . The impairments related to NSM’s write-off of intangible assets in its U.K. vertical. The impairments related to lower premium volumes, including due to the impact of the COVID-19 pandemic, and certain reorganization initiatives in the U.K. vertical. There were no other impairments of other intangible assets and no impairments of goodwill for the three and six months ended June 30, 2020 and 2019. The following tables present the change in goodwill and other intangible assets for the three and six months ended June 30, 2020 and 2019: Three Months Ended June 30, 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 $ 392.4 $ 254.4 $ 646.8 $ 349.7 $ 160.5 $ 510.2 Acquisitions of businesses 125.1 (1) — 125.1 80.4 (2) — 80.4 Acquisition of renewal rights — — — — 82.5 82.5 Foreign currency translation .7 .1 .8 (1.2 ) .2 (1.0 ) Adjustments to reflect acquisition date fair value — — — (.3 ) — (.3 ) Impairments — (6.2 ) (6.2 ) — — — Amortization — (6.6 ) (6.6 ) — (4.2 ) (4.2 ) Ending balance $ 518.2 $ 241.7 $ 759.9 $ 428.6 $ 239.0 $ 667.6 (1) The relative fair values of goodwill and other intangible assets recognized in connection with the acquisition of Kingsbridge had not yet been finalized at June 30, 2020. (2) The relative fair values of goodwill and other intangible assets recognized in connection with the acquisition of Embrace and the Kudu Transaction had not yet been finalized at June 30, 2019. Six Months Ended June 30, 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 125.1 (1) — 125.1 93.8 (2) — 93.8 Acquisition of renewal rights — — — — 82.5 82.5 Foreign currency translation (1.8 ) (.4 ) (2.2 ) — .5 .5 Adjustments to reflect acquisition date fair value .2 — .2 — 5.9 5.9 Impairments — (6.2 ) (6.2 ) — — — Amortization — (11.7 ) (11.7 ) — (10.8 ) (10.8 ) Ending balance $ 518.2 $ 241.7 $ 759.9 $ 428.6 $ 239.0 $ 667.6 (1) The relative fair values of goodwill and other intangible assets recognized in connection with the acquisition of Kingsbridge had not yet been finalized at June 30, 2020. (2) The relative fair values of goodwill and other intangible assets recognized in connection with the acquisitions of Embrace, Other Operations and the Kudu Transaction had not yet been finalized at June 30, 2019.

Debt

Debt	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Debt	Debt The following table presents White Mountains’s debt outstanding as of June 30, 2020 and December 31, 2019: Millions June 30, Effective Rate (1) December 31, Effective Rate (1) NSM Bank Facility $ 273.4 7.2% $ 221.3 7.5% Unamortized issuance cost (6.4 ) (3.9 ) NSM Bank Facility, carrying value 267.0 217.4 Other NSM debt, carrying value 1.4 3.2% 1.8 3.0% Kudu Bank Facility 74.0 8.1% 57.0 8.3% Unamortized issuance cost (3.2 ) (3.4 ) Kudu Bank Facility, carrying value 70.8 53.6 Other Operations debt 10.9 9.3% 11.1 8.3% Unamortized issuance cost (.3 ) (.4 ) Other Operations, carrying value 10.6 10.7 Total debt $ 349.8 $ 283.5 (1) Effective rate considers the effect of the debt issuance costs. NSM Bank Facility On April 7, 2020, NSM amended its secured credit facility (the “NSM Bank Facility”) with Ares Capital Corporation in connection with the acquisition of Kingsbridge. Under the amendment, the total commitment increased from $234.0 million , comprised of term loans of $224.0 million and a revolving credit loan commitment of $10.0 million , to $291.4 million, comprised of term loans of $276.4 million , including £42.5 million (approximately $52.4 million based upon the foreign exchange spot rate as of June 30, 2020) in a GBP term loan, and a revolving credit loan commitment of $15.0 million . The term loans under the NSM Bank Facility mature on May 11, 2026, and the revolving loan matures on November 11, 2025. Under GAAP, if the terms of a debt instrument are amended, unless there is greater than 10% change in the expected discounted future cash flows of such instrument, the instrument’s carrying value does not change. White Mountains has determined that the impact of the changes to the terms of the NSM Bank Facility on the expected discounted future cash flows was less than 10% . Interest on the NSM Bank Facility accrues at a floating interest rate equal to the three-month LIBOR plus an applicable margin. In connection with the amendment, the reference rates for USD denominated borrowings increased. The USD-LIBOR rate floor increased from 1.0% to 1.25% and the margin over USD-LIBOR increased from a range of 4.25% to 4.75% to a range of 5.50% to 6.00% . For GBP denominated borrowings, the GBP-LIBOR rate floor is 1.25% and the margin over GBP-LIBOR ranges from 6.0% to 6.5% . The margins over the reference interest rates vary within the range depending on the consolidated total leverage ratio of NSM. As of June 30, 2020 and December 31, 2019, the weighted average interest rate on the NSM Bank Facility was 7.21% and 6.60% . The following table presents the change in debt under the NSM Bank Facility for the three and six months ended June 30, 2020 and 2019: NSM Bank Facility Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Beginning balance $ 220.7 $ 186.4 $ 221.3 $ 180.4 Term loans Borrowings (1) 52.4 42.9 52.4 42.9 Repayments — (.5 ) (.6 ) (1.0 ) Foreign currency translation .3 — .3 — Revolving credit loan Borrowings — — — 6.5 Repayments — (6.5 ) — (6.5 ) Ending balance 273.4 222.3 273.4 222.3 (1) Borrowings for both the three and six months ended June 30, 2020 included $52.4 for the funding of the acquisition of Kingsbridge. Borrowings for the three and six months ended June 30, 2019 , included $20.4 and $22.5 for the funding of the acquisitions of Embrace and the Renewal Rights. As of June 30, 2020 , the term loans had an outstanding balance of $273.4 million , including £42.5 million (approximately $52.4 million based upon the foreign exchange spot rate as of June 30, 2020) in a GBP term loan, and the revolving credit loan was undrawn. 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 USD denominated 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 USD-LIBOR. As of June 30, 2020 , the variable rate received by NSM under the swap agreement was 0.17% . As of June 30, 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 8.72% . See Note 7 — “Derivatives” . For the six months ended June 30, 2020, the weighted average effective interest rate on the outstanding term loans of $148.4 million that are hedged by the swap, excluding the effect of the swap, was 6.67% . The weighted average effective interest rate on the outstanding term loans of $125.0 million that are unhedged was 6.90% . The effective interest rate on the total outstanding term loans under the NSM Bank Facility of $273.4 million was 6.78% , excluding the effect of debt issuance costs. On June 4, 2020, NSM entered into an interest rate cap agreement to limit its exposure to the risk of interest rate increases on the GBP denominated term loan. The notional amount of the interest rate cap is £42.5 million (approximately $52.4 million based upon the foreign exchange spot rate as of June 30, 2020) and the termination date is June 4, 2022. Under the terms of the interest rate cap agreement, if the current GBP-LIBOR at the measurement date exceeds 1.25% , NSM will receive payments from the counterparty equal to the then-current GBP-LIBOR rate, less the 1.25% cap rate. 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. vertical. As of June 30, 2020 , the secured term loan had an outstanding balance of $1.6 million and a maturity date of December 31, 2022. 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. As of June 30, 2020, the Kudu Bank Facility has a maximum borrowing capacity of $124.0 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 $62.0 million . The term loans and revolving credit loans, under the Kudu Bank Facility, mature in 2025. During the three and six months ended June 30, 2020 , Kudu borrowed $5.0 million and $ 17.0 million in term loans under the Kudu Bank Facility and made no repayments. As of June 30, 2020 , the term loans had an outstanding balance of $74.0 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 USD-LIBOR and 1.0% or the Prime Rate plus 1.0% , plus in each case, an applicable margin. The margin over USD-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 June 30, 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 June 30, 2020 , the term loans had an outstanding balance of $10.9 million and the revolving credit loan was undrawn. Compliance At June 30, 2020 , White Mountains was in compliance with the covenants under all of its debt instruments.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 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 (expense) benefit related to pre-tax income (loss) from continuing operations for the three and six months ended June 30, 2020 represented an effective tax rate of 18.2% and 4.2% . 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 benefit (expense) related to pre-tax income (loss) from continuing operations for the three and six months ended June 30, 2019 represented an effective tax rate of (0.6)% and 3.4% . 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 and a tax benefit recorded at BAM. Also, the effective tax rate for the six months ended June 30, 2019 was different from the U.S. statutory rate of 21.0% due to the release of a full valuation allowance on the net deferred tax assets of the U.S. consolidated group Guilford Holdings, Inc. and subsidiaries (“Guilford”). Guilford includes Kudu, its investment in MediaAlpha, various service companies and certain other entities and investments that are included in the Other Operations segment. For BAM, member surplus contributions (“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 and six months ended June 30, 2019, BAM recorded a tax benefit of $1.9 million and $3.0 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 and six months ended June 30, 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	6 Months Ended
	Jun. 30, 2020
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivatives	Derivatives NSM Interest Rate Swap 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 USD denominated variable rate term loans under the NSM Bank Facility. 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 USD-LIBOR. As of June 30, 2020 , the variable rate received by NSM under the swap agreement was 0.17% . 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 June 30, 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 8.72% , 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 and six months ended June 30, 2020 , White Mountains recognized net interest expense of $0.7 million and $1.2 million for the periodic net settlement payments on the swap. For the three and six months ended June 30, 2019, White Mountains recognized net interest expense of $0.2 million and $0.4 million . As of June 30, 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 $9.4 million and $6.6 million . There was no ineffectiveness in the hedge for the three and six month periods ended June 30, 2020 and June 30, 2019 . For the three and six months ended June 30, 2020 , the $0.4 million and $(2.8) million change in the fair value of the swap is included within White Mountains’s accumulated other comprehensive income (loss). For the three and six months ended June 30, 2019 , the $(2.4) million and $(4.3) million change in the fair value of the swap is included within White Mountains’s accumulated other comprehensive income (loss). NSM Interest Rate Cap On June 4, 2020, NSM entered into an interest rate cap agreement to limit its exposure to the risk of interest rate increases on the GBP denominated term loan under the NSM Bank Facility. The notional amount of the interest rate cap is £42.5 million (approximately $52.4 million based upon the foreign exchange spot rate as of June 30, 2020) and the termination date is June 4, 2022. NSM paid an initial premium of approximately $0.1 million . Under the terms of the interest rate cap agreement, if the current GBP-LIBOR at the measurement date exceeds 1.25% , NSM will receive payments from the counterparty equal to the then-current GBP-LIBOR rate, less the 1.25% cap rate. As of June 30, 2020, the GBP-LIBOR rate was 0.14% . NSM accounts for the interest rate cap as a derivative at fair value, with changes in fair value recognized in current period earnings within interest expense. For the three months ended June 30, 2020, White Mountains recognized a negligible change in fair value on the interest rate cap within interest expense. As of June 30, 2020, the estimated fair value of the cap recorded in other assets was less than $0.1 million

Municipal Bond Guarantee

Municipal Bond Guarantee	6 Months Ended
	Jun. 30, 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 June 30, 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 greater than 10% change in the expected discounted future cash flows of such instrument, the instrument’s carrying value does not change. 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 less 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. 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 June 30, 2020 and December 31, 2019 , the Collateral Trusts held assets of $811.8 million and $786.7 million , which included $409.7 million and $457.6 million of BAM Surplus Notes and $4.7 million and $7.5 million of interest receivable on the BAM Surplus Notes. As of June 30, 2020 and December 31, 2019, total interest receivable on the BAM Surplus Notes was $155.0 million and $162.7 million . The following table presents a schedule of BAM’s insured obligations as of June 30, 2020 and December 31, 2019 : June 30, 2020 December 31, 2019 Contracts outstanding 9,992 8,987 Remaining weighted average contract period outstanding (in years) 10.6 10.7 Contractual debt service outstanding (in millions): Principal $ 67,591.5 $ 62,250.5 Interest 33,775.8 31,799.7 Total debt service outstanding $ 101,367.3 $ 94,050.2 Gross unearned insurance premiums (in millions) $ 218.6 $ 198.4 The following table presents a schedule of BAM’s future premium revenues as of June 30, 2020 : Millions June 30, 2020 July 1, 2020 - December 31, 2020 $ 10.2 January 1, 2021 - March 31, 2021 5.0 April 1, 2021 - June 30, 2021 4.9 July 1, 2021 - September 30, 2021 4.9 October 1, 2021 - December 31, 2021 4.8 Total 2021 19.6 2022 18.5 2023 17.3 2024 16.2 2025 15.0 2026 and thereafter 121.8 Total gross unearned insurance premiums $ 218.6 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 and six months ended June 30, 2020 and 2019 : Three Months Ended June 30, Six Months Ended June 30, Millions 2020 2019 2020 2019 Written premiums: Direct $ 21.3 $ 12.5 $ 31.0 $ 20.4 Assumed 0.2 — 0.2 — Gross written premiums $ 21.5 $ 12.5 $ 31.2 $ 20.4 Earned premiums: Direct $ 4.7 $ 3.8 $ 9.2 $ 7.5 Assumed 0.9 .5 1.8 1.0 Gross earned premiums $ 5.6 $ 4.3 $ 11.0 $ 8.5 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 June 30, 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	6 Months Ended
	Jun. 30, 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 June 30, 2020 and December 31, 2019: Millions June 30, 2020 December 31, 2019 Equity method eligible investments, at fair value $ 815.3 $ 761.7 Other, at fair value (1) 82.8 94.6 Total other long-term investments $ 898.1 $ 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 June 30, 2020 and December 31, 2019: Basic Ownership Interest Investee June 30, 2020 December 31, 2019 Instrument Held PassportCard/DavidShield (1) 53.8% 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 Tuckerman Capital Funds 14.3 - 62.3% 17.5 - 62.4% Limited and general partnership interests Enlightenment Capital Funds 9.4 - 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 - 35.0% 3.2 - 30.0% Revenue and earnings participation contracts (1) During the three months ending June 30, 2020, White Mountains made an additional $15 investment in PassportCard/DavidShield. See Note 2 — “Significant Transactions” . As a result of the MediaAlpha Transaction, White Mountains reduced its ownership interest of the basic units outstanding of MediaAlpha from 61.0% to 48.3% ( 58.9% to 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 and six months ended June 30, 2020 , White Mountains recognized $15.0 million and $45.0 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 June 30, 2019, MediaAlpha was considered a significant subsidiary. For the period from February 26, 2019 to June 30, 2019, MediaAlpha’s total revenues, total expenses, and net income were $122.7 million , $115.8 million , and $6.9 million . The following tables present summarized financial information for White Mountains’s combined equity-method eligible investees, including MediaAlpha, Tuckerman IV Fund, L.P., and certain Kudu Participation Contracts, which are considered significant subsidiaries for the six months ending June 30, 2020: Millions June 30, 2020 December 31, 2019 Balance sheet data (1) : Total assets $ 420.5 $ 457.0 Total liabilities $ 200.2 $ 199.0 (1) Financial data for Tuckerman IV Fund, L.P. and Kudu Participation Contracts is reported on a one-quarter lag. Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Income statement data (1) : Total revenues $ 118.7 $ 93.7 $ 307.2 $ 178.4 Total expenses $ 131.9 $ 83.6 $ 273.8 $ 171.1 Net income (loss) $ (21.8 ) $ 10.1 $ 21.8 $ 7.3 (1) Financial data for Tuckerman IV Fund, L.P. and Kudu Participation Contracts is reported on a one-quarter lag.

Earnings Per Share

Earnings Per Share	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2020 and 2019 . See Note 17 — “Held for Sale and Discontinued Operations” . Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Basic and diluted earnings per share numerators (in millions): Net income (loss) attributable to White Mountains’s common shareholders $ 115.4 $ 20.5 $ (13.4 ) $ 304.9 Less: total (loss) income from discontinued operations, net of tax (1.0 ) — (.1 ) .7 Net income (loss) from continuing operations attributable to White Mountains’s common shareholders $ 116.4 $ 20.5 $ (13.3 ) $ 304.2 Allocation of (earnings) losses to participating restricted common shares (1) (1.6 ) (.3 ) .1 (3.6 ) Basic and diluted earnings (losses) per share numerators $ 114.8 $ 20.2 $ (13.2 ) $ 300.6 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,107.5 3,183.5 3,142.8 3,177.8 Average unvested restricted common shares (2) (43.1 ) (42.8 ) (38.5 ) (37.6 ) Basic earnings (losses) per share denominator 3,064.4 3,140.7 3,104.3 3,140.2 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,107.5 3,183.5 3,142.8 3,177.8 Average unvested restricted common shares (2) (43.1 ) (42.8 ) (38.5 ) (37.6 ) Diluted earnings (losses) per share denominator 3,064.4 3,140.7 3,104.3 3,140.2 Basic and diluted earnings per share (in dollars) - continuing operations: Distributed earnings - dividends declared and paid $ — $ — $ 1.00 $ 1.00 Undistributed earnings (losses) 37.46 6.44 (5.25 ) 94.71 Basic and diluted earnings (losses) per share $ 37.46 $ 6.44 $ (4.25 ) $ 95.71 (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 and six months ended June 30, 2020 and 2019 . See Note 17 — “Held for Sale and Discontinued Operations” . Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Undistributed net earnings - continuing operations: Net income (loss) attributable to White Mountains’s common shareholders, net of restricted common share amounts $ 114.8 $ 20.2 $ (13.2 ) $ 300.6 Dividends declared, net of restricted common share amounts (1) — — (3.1 ) (3.2 ) Total undistributed net earnings (losses), net of restricted common share amounts $ 114.8 $ 20.2 $ (16.3 ) $ 297.4 (1) Restricted shares issued by White Mountains receive dividends, and are therefore considered participating securities.

Employee Share-Based Incentive

Employee Share-Based Incentive Compensation Plans	6 Months Ended
	Jun. 30, 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 June 30, 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 and six months ended June 30, 2020 and 2019 for performance shares granted under the WTM Incentive Plan: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Millions, except share amounts Target Performance Accrued Expense Target Performance Accrued Expense Target Performance Shares Outstanding Accrued Expense Target Performance Accrued Expense Beginning of period 42,458 $ 9.8 40,602 $ 23.1 42,473 $ 43.7 40,616 $ 31.7 Shares paid (1) — — — — (14,070 ) (27.7 ) (13,715 ) (18.1 ) New grants — — 1,900 — 14,055 — 15,600 — Forfeitures and cancellations (2) — — (29 ) (.2 ) — .4 (28 ) — Expense recognized — 6.0 — 7.9 — (.6 ) — 17.2 End of period 42,458 $ 15.8 42,473 $ 30.8 42,458 $ 15.8 42,473 $ 30.8 (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 six months ended June 30, 2020, White Mountains granted 14,055 performance shares for the 2020-2022 performance cycle. During the three and six months ended June 30, 2019, White Mountains granted 1,900 and 15,600 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 June 30, 2020 , the total additional compensation cost to be recognized would have been $17.3 million , based on accrual factors (common share price and payout assumptions) as of June 30, 2020 . The following table presents performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan as of June 30, 2020 for each performance cycle: Six Months Ended June 30, 2020 Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Performance cycle: 2018 – 2020 13,450 $ 8.0 2019 – 2021 15,600 5.9 2020 – 2022 14,055 2.1 Sub-total 43,105 16.0 Assumed forfeitures (647 ) (.2 ) June 30, 2020 42,458 $ 15.8 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 and six months ended June 30, 2020 and 2019 : Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Millions, except share amounts Restricted Unamortized Fair Value Restricted Unamortized Restricted Unamortized Issue Date Restricted Unamortized Issue Date Non-vested, Beginning of period 43,105 $ 26.6 41,495 $ 22.8 43,395 $ 16.7 41,510 $ 12.5 Issued — — 1,900 1.7 14,055 15.1 15,600 14.5 Vested — — — — (14,345 ) — (13,715 ) — Forfeited — — — — — — — — Expense recognized — (3.6 ) — (2.6 ) — (8.8 ) — (5.1 ) End of period 43,105 $ 23.0 43,395 $ 21.9 43,105 $ 23.0 43,395 $ 21.9 During the three and six months ended June 30, 2020 , White Mountains issued 14,055 restricted shares that vest on January 1, 2023. During the three and six months ended June 30, 2019, White Mountains issued 1,900 and 15,600 restricted shares that vest on January 1, 2022. The unamortized issue date fair value as of June 30, 2020

Leases

Leases	6 Months Ended
	Jun. 30, 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 June 30, 2020 and December 31, 2019, the ROU asset was $34.0 million and $22.6 million and lease liabilities were $ 34.2 million and $22.8 million . The following table summarizes net lease expense recognized in White Mountains’s consolidated statement of operations for the three and six months ended June 30, 2020 and 2019: Millions Three Months Ended June 30, Six Months Ended June 30, Lease Cost 2020 2019 2020 2019 Lease cost $ 2.1 $ 1.8 $ 4.1 $ 3.5 Less: sublease income .1 .1 .2 .2 Net lease cost $ 2.0 $ 1.7 $ 3.9 $ 3.3 The following table presents the contractual maturities of the lease liabilities associated with White Mountains’s operating lease agreements as of June 30, 2020 : Millions As of June 30, 2020 Remainder of 2020 $ 3.1 2021 6.8 2022 6.3 2023 6.1 2024 5.2 Thereafter 14.1 Total undiscounted lease payments 41.6 Less: present value adjustment 7.4 Operating lease liability $ 34.2 The following tables present lease related assets and liabilities by reportable segment as of June 30, 2020 and December 31, 2019: As of June 30, 2020 Millions HG/BAM NSM Kudu Other Operations Total Weighted Average Incremental Borrowing Rate (1) ROU lease asset $ 9.8 $ 16.8 $ 2.2 $ 5.2 $ 34.0 4.8% Lease liability $ 9.8 $ 16.8 $ 2.2 $ 5.4 $ 34.2 (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	6 Months Ended
	Jun. 30, 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 June 30, 2020 and December 31, 2019 : June 30, 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 % $ 14.7 3.1 % $ 14.4 NSM 3.4 % 16.7 3.6 % 14.9 Other NSM 13.4 % (.1 ) 13.4 % (.1 ) Kudu .8 % 2.4 .9 % 2.2 Other Operations various (1.8 ) various (1.5 ) Total, excluding BAM 31.9 29.9 BAM 100.0 % (134.6 ) 100.0 % (146.7 ) Total non-controlling interests $ (102.7 ) $ (116.8 )

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 2020
Segment Reporting [Abstract]
Segment Informartion	Segment Information As of June 30, 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 and six months ended June 30, 2020 and 2019: Millions HG Global/ BAM NSM Kudu Other Operations Total Three Months Ended June 30, 2020 Earned insurance premiums $ 5.6 $ — $ — $ — $ 5.6 Net investment income 4.9 — 5.6 9.1 19.6 Net realized and unrealized investment gains 14.4 — 16.5 122.0 152.9 Advertising and commission revenues — 63.0 — 1.9 64.9 Other revenue 1.2 13.1 — 2.3 16.6 Total revenues 26.1 76.1 22.1 135.3 259.6 Insurance acquisition expenses 2.1 — — — 2.1 Other underwriting expenses .2 — — — .2 Cost of sales — — — 2.2 2.2 General and administrative expenses 12.5 48.5 2.8 25.3 89.1 Broker commission expense — 21.0 — — 21.0 Change in fair value of contingent consideration — (1.7 ) — — (1.7 ) Amortization of other intangible assets — 6.3 .1 .2 6.6 Interest expense — 5.7 1.5 .2 7.4 Total expenses 14.8 79.8 4.4 27.9 126.9 Pre-tax income (loss) $ 11.3 $ (3.7 ) $ 17.7 $ 107.4 $ 132.7 Millions HG Global/ BAM NSM Kudu Other Operations Total Six Months Ended June 30, 2020 Earned insurance premiums $ 11.0 $ — $ — $ — $ 11.0 Net investment income 10.4 — 12.9 19.2 42.5 Net realized and unrealized investment gains (loss) 20.5 — (8.3 ) (16.0 ) (3.8 ) Advertising and commission revenues — 116.0 — 4.0 120.0 Other revenue 1.7 25.1 .1 3.8 30.7 Total revenues 43.6 141.1 4.7 11.0 200.4 Insurance acquisition expenses 3.8 — — — 3.8 Other underwriting expenses .2 — — — .2 Cost of sales — — — 4.2 4.2 General and administrative expenses 27.2 88.1 5.3 42.8 163.4 Broker commission expense — 39.3 — — 39.3 Change in fair value of contingent consideration — (2.3 ) — — (2.3 ) Amortization of other intangible assets — 11.1 .2 .4 11.7 Interest expense — 10.0 2.9 .5 13.4 Total expenses 31.2 146.2 8.4 47.9 233.7 Pre-tax income (loss) $ 12.4 $ (5.1 ) $ (3.7 ) $ (36.9 ) $ (33.3 ) Millions HG Global/BAM NSM Kudu Other Operations Total Three Months Ended June 30, 2019 Earned insurance premiums $ 4.3 $ — $ — $ — $ 4.3 Net investment income 5.4 — 4.0 11.6 21.0 Net realized and unrealized investment gains 11.5 — .4 23.3 35.2 Advertising and commission revenues — 54.9 — 1.3 56.2 Other revenue .4 11.2 — .7 12.3 Total revenues 21.6 66.1 4.4 36.9 129.0 Insurance acquisition expenses 1.4 — — — 1.4 Other underwriting expenses .1 — — — .1 Cost of sales — — — 1.6 1.6 General and administrative expenses 12.3 32.8 2.2 30.1 77.4 Broker commission expense — 18.1 — — 18.1 Change in fair value of contingent consideration — 6.3 — — 6.3 Amortization of other intangible assets — 4.1 — .1 4.2 Interest expense — 4.1 — — 4.1 Total expenses 13.8 65.4 2.2 31.8 113.2 Pre-tax income $ 7.8 $ .7 $ 2.2 $ 5.1 $ 15.8 Millions HG Global/ BAM NSM Kudu (1) MediaAlpha (2) Other Operations Total Six Months Ended June 30, 2019 Earned insurance premiums $ 8.5 $ — $ — $ — $ — $ 8.5 Net investment income 10.7 — 4.0 — 22.3 37.0 Net realized and unrealized investment gains 23.3 — .4 — 142.4 166.1 Realized gain and unrealized investment gain from the MediaAlpha Transaction — — — — 182.2 182.2 Advertising and commission revenues — 98.2 — 48.8 2.6 149.6 Other revenue 1.0 17.2 — — 1.0 19.2 Total revenues 43.5 115.4 4.4 48.8 350.5 562.6 Insurance acquisition expenses 2.7 — — — — 2.7 Other underwriting expenses .2 — — — — .2 Cost of sales — — — 40.6 2.7 43.3 General and administrative expenses 26.6 58.1 2.2 12.5 59.5 158.9 Broker commission expense — 33.6 — — — 33.6 Change in fair value of contingent consideration earnout liabilities — 7.6 — — — 7.6 Amortization of other intangible assets — 9.1 — 1.6 .1 10.8 Interest expense — 7.8 .2 — 8.0 Total expenses 29.5 116.2 2.2 54.9 62.3 265.1 Pre-tax income (loss) $ 14.0 $ (.8 ) $ 2.2 $ (6.1 ) $ 288.2 $ 297.5 (1) Kudu's results are from April 4, 2019, the date White Mountains began consolidating Kudu, to June 30, 2019. (2) 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 June 30, 2020 and 2019: Millions HG Global/BAM NSM Kudu Other Operations Total Three Months Ended June 30, 2020 Commission and other revenue Specialty Transportation $ — $ 23.8 $ — $ — $ 23.8 Real Estate — 15.4 — — 15.4 Social Services — 7.3 — — 7.3 Pet — 13.2 — — 13.2 United Kingdom — 12.4 — — 12.4 Other — 4.0 — 1.8 5.8 Total commission and other revenue — 76.1 — 1.8 77.9 Product revenues — — — 2.3 — Revenues from contracts with customers — 76.1 — 4.1 80.2 Other revenues (1) 26.1 — 22.1 131.2 179.4 Total revenues $ 26.1 $ 76.1 $ 22.1 $ 135.3 $ 259.6 (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. Millions HG Global/BAM NSM Kudu Other Operations Total Six Months Ended June 30, 2020 Commission and other revenue Specialty Transportation $ — $ 44.2 $ — $ — $ 44.2 Real Estate — 26.7 — — 26.7 Social Services — 13.6 — — 13.6 Pet — 25.1 — — 25.1 United Kingdom (2) — 22.4 — — 22.4 Other — 9.1 — 4.0 13.1 Total commission and other revenue — 141.1 — 4.0 145.1 Product revenues — — — 4.4 4.4 Revenues from contracts with customers — 141.1 — 8.4 149.5 Other revenues (1) 43.6 — 4.7 2.6 50.9 Total revenues $ 43.6 $ 141.1 $ 4.7 $ 11.0 $ 200.4 (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) Includes the results of Kingsbridge from April 7, 2020, the date of the Kingsbridge transaction. Millions HG Global/BAM NSM Kudu Other Operations Total Three Months Ended June 30, 2019 Commission and other revenue Specialty Transportation $ — $ 21.7 $ — $ — $ 21.7 Real Estate — 11.5 — — 11.5 Social Services — 6.5 — — 6.5 Pet — 9.5 — — 9.5 United Kingdom — 12.2 — — 12.2 Other — 4.7 — 1.3 6.0 Total commission and other revenue — 66.1 — 1.3 67.4 Products — — — .6 .6 Total revenues from contracts with customers — 66.1 — 1.9 68.0 Other revenues (1) 21.6 — 4.4 35.0 61.0 Total revenues $ 21.6 $ 66.1 $ 4.4 $ 36.9 $ 129.0 (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 Kudu MediaAlpha Other Operations Total Six Months Ended June 30, 2019 Commission and other revenue Specialty Transportation $ — $ 39.6 $ — $ — $ — $ 39.6 Real Estate — 20.5 — — — 20.5 Social Services — 12.3 — — — 12.3 Pet — 9.5 — — — 9.5 United Kingdom — 24.3 — — — 24.3 Other — 9.2 — — 2.6 11.8 Total commission and other revenue — 115.4 — — 2.6 118.0 Advertising revenues — — — 48.8 — 48.8 Revenues from contracts with customers — 115.4 — 48.8 2.6 166.8 Products — — — — .6 0.6 Total revenues from contracts with customers — 115.4 — 48.8 3.2 167.4 Other revenues (1) 43.5 — 4.4 — 347.3 395.2 Total revenues $ 43.5 $ 115.4 $ 4.4 $ 48.8 $ 350.5 $ 562.6 (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.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	6 Months Ended
	Jun. 30, 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 June 30, 2020 and December 31, 2019 : June 30, 2020 December 31, 2019 Millions Fair Value Carrying Value Fair Value Carrying Value NSM Bank Facility $ 272.2 $ 267.0 $ 221.2 $ 217.4 Other NSM debt $ 1.6 $ 1.4 $ 1.7 $ 1.8 Kudu Bank Facility $ 72.8 $ 70.8 $ 53.6 (1) $ 53.6 Other Operations debt $ 9.5 $ 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	6 Months Ended
	Jun. 30, 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 June 30, 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 both June 30, 2020 and December 31, 2019 , White Mountains reported a liability of $16.5 million , reflecting the value of these interest deductions. For the three months ended June 30, 2020 , the change in the liability of $1.0 million was related to foreign currency translation and included within net loss on sale of discontinued operations. For the six months ended June 30, 2020, the liability did not change. For the three months ended June 30, 2019 , there was no change in the liability. For the six months ended June 30, 2019 , the change in the liability of $0.7 million was 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	6 Months Ended
	Jun. 30, 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 both June 30, 2020 and December 31, 2019, White Mountains recorded a liability of $16.5 million , related to the Sirius Group tax contingency. For the three months ended June 30, 2020 , the change in the liability of $1.0 million was related to foreign currency translation and included within net loss on sale of discontinued operations. For the six months ended June 30, 2020, the liability did not change. For the three months ended June 30, 2019 , there was no change in the liability. For the first six months ended June 30, 2019 , the change in the liability of $0.7 million was 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 June 30, 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 and six months ended June 30, 2020 and 2019 : Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Basic and diluted earnings per share numerators (in millions): Net income (loss) attributable to White Mountains’s common shareholders $ 115.4 $ 20.5 $ (13.4 ) $ 304.9 Less: total income (loss) from continuing operations, net of tax 116.4 20.5 (13.3 ) 304.2 Net (loss) income from discontinued operations attributable to White Mountains’s common shareholders $ (1.0 ) $ — $ (.1 ) $ .7 Allocation of earnings to participating restricted common shares (1) — — — — Basic and diluted (losses) earnings per share numerators (2) $ (1.0 ) $ — $ (.1 ) $ .7 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,107.5 3,183.5 3,142.8 3,177.8 Average unvested restricted common shares (3) (43.1 ) (42.8 ) (38.5 ) (37.6 ) Basic earnings per share denominator 3,064.4 3,140.7 3,104.3 3,140.2 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,107.5 3,183.5 3,142.8 3,177.8 Average unvested restricted common shares (3) (43.1 ) (42.8 ) (38.5 ) (37.6 ) Diluted earnings per share denominator 3,064.4 3,140.7 3,104.3 3,140.2 Basic and diluted (losses) earnings per share (in dollars) - discontinued operations: $ (.32 ) $ — $ (.03 ) $ .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 and six months ended June 30, 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	6 Months Ended
	Jun. 30, 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, as the pandemic is ongoing, White Mountains cannot determine the ultimate impact it may have on the global financial markets, the overall economy and on White Mountains’s businesses, results of operations and financial condition.

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accouting Policies (Policies)	6 Months Ended
	Jun. 30, 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 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	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 June 30, 2020, White Mountains’s reportable segments were HG Global/BAM, NSM, Kudu and Other Operations. 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 consequently it was no longer a reportable 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” and 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 June 30, 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 June 30, 2020 and December 31, 2019, White Mountains owned 96.6% and 96.4% of the basic units outstanding of NSM ( 89.6% and 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. It operates a transparent and efficient online customer acquisition technology platform that facilitates real-time transactions between buyers and sellers of consumer referrals (e.g., clicks, calls and leads), primarily in the property & casualty, health and life insurance verticals.
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 June 30, 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 the deposit method, ceded premiums paid are not recognized through income but rather treated as a deposit. BAM entered into a ceded 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 Cash includes amounts on hand and demand deposits with banks and other financial institutions. Amounts presented in the statement of cash flows are shown net of balances acquired and sold in the purchase or sale of the Company’s consolidated subsidiaries.
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, are 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 changed the guidance on goodwill impairment testing. Under the new guidance, the qualitative assessment of the recoverability of goodwill remains the same, but the second step of the two-step quantitative test, which required calculation of the implied fair value of goodwill, has been eliminated. Instead, an impairment charge is recognized when the carrying value of a reporting unit exceeds its fair value. Any excess of carrying value over fair value is written down as an impairment. White Mountains did not recognize an impairment of goodwill during the three and six months ended June 30, 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 June 30, 2020 , White Mountains recognized $34.0 million and $ 34.2 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)	6 Months Ended
	Jun. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Pre-tax net investment income	The following table presents pre-tax net investment income for the three and six months ended June 30, 2020 and 2019 : Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Fixed maturity investments $ 7.3 $ 8.3 $ 15.4 $ 16.4 Short-term investments .1 1.3 .9 2.6 Common equity securities 2.2 2.9 6.0 8.3 Other long-term investments 10.3 8.8 20.8 10.4 Total investment income 19.9 21.3 43.1 37.7 Third-party investment expenses (.3 ) (.3 ) (.6 ) (.7 ) Net investment income, pre-tax $ 19.6 $ 21.0 $ 42.5 $ 37.0
Schedule of realized gain (loss) on investments	The following table presents net realized and unrealized investment gains (losses) for the three and six months ended June 30, 2020 and 2019 : Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Fixed maturity investments $ 30.0 $ 16.9 $ 32.2 $ 38.0 Short-term investments — .3 .4 .3 Common equity securities 98.3 27.8 (42.5 ) 139.1 Other long-term investments (1) (2) 24.6 $ (9.8 ) 6.1 103.4 Net realized and unrealized investment gains (losses) 152.9 35.2 (3.8 ) 280.8 Less: net gains (losses) on investment securities sold during the period 2.2 .2 (6.5 ) 12.4 Net realized and unrealized investment gains on investment securities held at the end of the period $ 150.7 $ 35.0 $ 2.7 $ 268.4
Schedule of unrealized gain (loss) on investments	The following table presents net realized and unrealized investment gains (losses) for the three and six months ended June 30, 2020 and 2019 : Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Fixed maturity investments $ 30.0 $ 16.9 $ 32.2 $ 38.0 Short-term investments — .3 .4 .3 Common equity securities 98.3 27.8 (42.5 ) 139.1 Other long-term investments (1) (2) 24.6 $ (9.8 ) 6.1 103.4 Net realized and unrealized investment gains (losses) 152.9 35.2 (3.8 ) 280.8 Less: net gains (losses) on investment securities sold during the period 2.2 .2 (6.5 ) 12.4 Net realized and unrealized investment gains on investment securities held at the end of the period $ 150.7 $ 35.0 $ 2.7 $ 268.4 (1) For the six months ended June 30, 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 June 30, 2020 and 2019, includes $0.4 and $0.3
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 and six months ended June 30, 2020 and 2019 for investments still held at the end of the period: Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Other long-term investments $ 25.3 $ (14.0 ) $ 15.9 $ 100.0 Total net unrealized investment gains (losses), pre-tax - Level 3 investments $ 25.3 $ (14.0 ) $ 15.9 $ 100.0
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 June 30, 2020 and December 31, 2019 : June 30, 2020 Millions Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Carrying Value U.S. Government and agency obligations $ 195.5 $ 4.9 $ — $ 200.4 Debt securities issued by corporations 480.2 26.1 (.5 ) 505.8 Municipal obligations 248.3 16.7 (.2 ) 264.8 Mortgage and asset-backed securities 213.2 7.4 — 220.6 Total fixed maturity investments $ 1,137.2 $ 55.1 $ (.7 ) $ 1,191.6 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 June 30, 2020 and December 31, 2019 : June 30, 2020 Millions Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Net Foreign Currency Losses Carrying Value Common equity securities $ 502.8 $ 69.3 $ (4.9 ) $ — $ 567.2 Other long-term investments $ 677.9 $ 289.6 $ (67.1 ) $ (2.3 ) $ 898.1 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 June 30, 2020 and December 31, 2019 : Carrying Value at Millions June 30, 2020 December 31, 2019 Kudu’s Participation Contracts (1) $ 315.6 $ 266.5 MediaAlpha (1) 225.0 180.0 PassportCard/DavidShield (1) 95.0 90.0 Elementum Holdings L.P. (1) 55.1 55.1 Other unconsolidated entities (1)(2) 31.9 33.7 Total unconsolidated entities (1) 722.6 625.3 Private equity funds and hedge funds 105.9 161.1 Insurance-linked securities funds 52.1 41.2 Private debt investments (3) 17.5 28.7 Total other long-term investments $ 898.1 $ 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 and Simple Agreement for Future Equity (“SAFE”) investments. (3) Includes $4.6 and $5.0 in private debt investments carried at fair value as of June 30. 2020 and amortized cost as of December 31, 2019.
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 June 30, 2020 and December 31, 2019 : June 30, 2020 December 31, 2019 Millions Fair Value Unfunded Commitments Fair Value Unfunded Commitments Private equity funds Aerospace/Defense/Government $ 44.8 $ 15.7 $ 33.8 $ 23.3 Manufacturing/Industrial 43.8 4.0 57.7 4.1 Financial services 17.3 24.7 15.0 22.8 Total private equity funds 105.9 44.4 106.5 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 $ 105.9 $ 44.4 $ 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 June 30, 2020 : Millions 1 – 3 years 3 – 5 years 5 – 10 years >10 years Total Private equity funds — expected lock-up period remaining $4.7 $40.4 $56.7 $4.1 $105.9
Fair value measurements by level, investment securities	The following tables present White Mountains’s fair value measurements for investments as of June 30, 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. June 30, 2020 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 200.4 $ 200.4 $ — $ — Debt securities issued by corporations: Financials 151.9 — 151.9 — Industrial 61.1 — 61.1 — Technology 57.6 — 57.6 — Consumer 55.6 — 55.6 — Healthcare 43.3 — 43.3 — Communications 40.9 — 40.9 — Energy 34.3 — 34.3 — Materials 32.1 — 32.1 — Utilities 29.0 — 29.0 — Total debt securities issued by corporations 505.8 — 505.8 — Municipal obligations 264.8 — 264.8 — Mortgage and asset-backed securities 220.6 — 220.6 — Total fixed maturity investments 1,191.6 200.4 991.2 — Short-term investments (1) 117.6 114.5 3.1 — Common equity securities: Exchange traded funds 442.4 442.4 — — Other (2) 124.8 22.3 102.4 .1 Total common equity securities 567.2 464.7 102.4 .1 Other long-term investments 740.1 — — 740.1 Other long-term investments — NAV (3) 158.0 — — — Total investments $ 2,774.5 $ 779.6 $ 1,096.7 $ 740.2 (1) Short-term investments are measured at amortized cost, which approximates fair value. (2) 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. (3) 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 credit ratings of debt securities issued by corporations held in White Mountains’s investment portfolio as of June 30, 2020 and December 31, 2019 : Fair Value at Millions June 30, 2020 December 31, 2019 AAA $ 8.3 $ 9.5 AA 53.6 73.9 A 314.1 288.5 BBB 128.1 95.3 BB 1.7 — Debt securities issued by corporations (1) $ 505.8 $ 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 June 30, 2020 and December 31, 2019 : June 30, 2020 December 31, 2019 Millions Fair Value Level 2 Level 3 Fair Value Level 2 Level 3 Mortgage-backed securities: Agency: FNMA $ 87.4 $ 87.4 $ — $ 88.6 $ 88.6 $ — FHLMC 68.1 68.1 — 60.5 60.5 — GNMA 42.2 42.2 — 30.8 30.8 — Total agency (1) 197.7 197.7 — 179.9 179.9 — Total mortgage-backed securities 197.7 197.7 — 179.9 179.9 — Other asset-backed securities: Vehicle receivables 11.5 11.5 — 15.1 15.1 — Credit card receivables 11.4 11.4 — 14.0 14.0 — Total other asset-backed securities 22.9 22.9 — 29.1 29.1 — Total mortgage and asset-backed securities $ 220.6 $ 220.6 $ — $ 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 June 30, 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) gains (13.9 ) 3.6 — 15.6 (9.5 ) (4.2 ) (3) Amortization/Accretion — (1.9 ) — — — (1.9 ) Purchases 113.0 214.2 — 78.6 21.2 427.0 Sales (214.0 ) (231.9 ) — (8.1 ) (56.0 ) (510.0 ) Transfers in — — — — — — Transfers out — — — — — — Balance at June 30, 2020 $ 665.1 $ 1,093.6 $ .1 $ 740.1 $ 158.0 $ 2,656.9 (1) (1) Excludes carrying value of $ 117.6 and $ 201.2 as of June 30, 2020 and December 31, 2019 classified as short-term investments. (2) Includes private equity funds, hedge funds and ILS funds 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 six months ended June 30, 2020. Level 3 Investments Other Long-term Investments Measured at NAV (3,5) 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 115.2 62.0 100.0 3.4 280.6 (2, 4) Amortization/Accretion .1 (.7 ) — — (.6 ) Purchases 70.1 232.0 136.7 102.5 541.3 Sales (343.5 ) (319.7 ) — (3.8 ) (667.0 ) Transfers in — — 82.6 — 82.6 Transfers out — — — (82.6 ) (82.6 ) Balance at June 30, 2019 $ 684.5 $ 1,134.1 $ 458.0 $ 206.4 $ 2,483.0 (1) (1) Excludes carrying value of $ 187.1 and $ 214.2 as of June 30, 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 ILS funds 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” . (4) Excludes realized and unrealized losses associated with short-term investments of $0.2 for the six months ended June 30, 2019. (5) Transfer includes $71.7 associated with the Kudu Transaction. See Note 2 — “Significant Transactions”.
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 June 30, 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 June 30, 2020 Description Valuation Technique(s) Fair Value (5) Unobservable Inputs Discount Rate (2)(6) Terminal Cash Flow Exit Multiple (x) or Terminal Revenue Growth Rate (%) (6) Kudu’s Participation Contracts (1)(2) Discounted cash flow $315.6 18% - 23% 6x - 12x MediaAlpha Discounted cash flow $225.0 14% 4% PassportCard/DavidShield (3) Discounted cash flow $95.0 23% 4% Elementum Holdings, L.P. Discounted cash flow $55.1 19% 4% Private debt instruments Discounted cash flow $17.5 6% - 12% N/A All other Discounted cash flow $15.7 24% 4% Noblr, Inc. Share price of recent transaction $8.7 Share price: $2.17 Zillion Insurance Services, Inc. (4) Recent transaction $5.0 Transaction price: $5.0 Compare.com Estimated net realizable value $2.5 Net realizable value: $2.5 (1) During the six months ended June 30, 2020, Kudu deployed a total of $57.4 in new Kudu Participation Contracts, including Creation Investments Capital Management and Sequoia Financial Group. (2) Since Kudu’s Participation Contracts are not subject to corporate taxes within Kudu Investment Management, LLC, pre-tax discount rates are applied to pre-tax cash flows in determining fair values. (3) During the three months ended June 30, 2020, White Mountains made an additional $15.0 investment in PassportCard/DavidShield. See Note 2 - “Significant Transactions” . (4) During the three months ended June 30, 2020, White Mountains made an additional $2.5 investment in Zillion Insurance Services, Inc. (5) Includes the net unrealized investment gains (losses) associated with foreign currency; foreign currency effects based on observable inputs. (6) 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)	6 Months Ended
	Jun. 30, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	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 June 30, 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 Kingsbridge (4) 125.1 April 7, 2020 Total NSM segment $ 275.2 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) Excludes $3.4 of software classified within other assets. (3) NSM’s purchase of the Renewal Rights from AIG was an asset acquisition. (4) The determination of the relative fair values of goodwill and other intangible assets had not yet been finalized as of June 30, 2020.
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 June 30, 2020 and December 31, 2019 : $ in Millions Weighted Average Economic Life (in years) June 30, 2020 December 31, 2019 Acquisition Date Fair Value Accumulated Amortization Impairments Net Carrying Value Acquisition Date Fair Value Accumulated Amortization Impairments Net Carrying Value Goodwill: NSM (1) N/A $ 504.9 $ — $ — $ 504.9 $ 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 518.2 — — 518.2 402.3 — 7.6 394.7 Other intangible assets: NSM (1) Customer 9 120.1 26.9 3.5 89.7 121.7 19.8 1.4 100.5 Trade names 19 61.2 6.6 1.0 53.6 61.9 5.3 .4 56.2 Information technology platform 0 3.1 1.4 1.7 — 3.9 1.4 .6 1.9 Renewal rights 12 82.5 2.8 — 79.7 82.5 .7 — 81.8 Other 3 1.7 1.0 — .7 1.7 .7 — 1.0 Subtotal 268.6 38.7 6.2 223.7 271.7 27.9 2.4 241.4 Kudu Trade names 7 2.2 .4 — 1.8 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 .6 — 6.6 7.2 .4 — 6.8 Information 5 — — — — .5 .3 .2 — Insurance Licenses N/A 8.6 — — 8.6 8.6 — — 8.6 Other 5 .2 .1 — .1 .2 — — .2 Subtotal 17.0 .8 — 16.2 18.2 1.2 .4 16.6 Total other intangible assets 287.8 39.9 6.2 241.7 292.1 29.3 2.8 260.0 Total goodwill and other intangible assets $ 806.0 $ 39.9 $ 6.2 759.9 $ 694.4 $ 29.3 10.4 654.7 Goodwill and other intangible assets attributed to non-controlling interests (25.9 ) (23.4 ) Goodwill and other intangible assets included in White Mountains’s common shareholders’ equity $ 734.0 $ 631.3 (1) As of June 30, 2020 , NSM’s goodwill and intangible assets included $ (1.8) and $ (0.4) 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 following tables present the change in goodwill and other intangible assets for the three and six months ended June 30, 2020 and 2019: Three Months Ended June 30, 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 $ 392.4 $ 254.4 $ 646.8 $ 349.7 $ 160.5 $ 510.2 Acquisitions of businesses 125.1 (1) — 125.1 80.4 (2) — 80.4 Acquisition of renewal rights — — — — 82.5 82.5 Foreign currency translation .7 .1 .8 (1.2 ) .2 (1.0 ) Adjustments to reflect acquisition date fair value — — — (.3 ) — (.3 ) Impairments — (6.2 ) (6.2 ) — — — Amortization — (6.6 ) (6.6 ) — (4.2 ) (4.2 ) Ending balance $ 518.2 $ 241.7 $ 759.9 $ 428.6 $ 239.0 $ 667.6 (1) The relative fair values of goodwill and other intangible assets recognized in connection with the acquisition of Kingsbridge had not yet been finalized at June 30, 2020. (2) The relative fair values of goodwill and other intangible assets recognized in connection with the acquisition of Embrace and the Kudu Transaction had not yet been finalized at June 30, 2019. Six Months Ended June 30, 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 125.1 (1) — 125.1 93.8 (2) — 93.8 Acquisition of renewal rights — — — — 82.5 82.5 Foreign currency translation (1.8 ) (.4 ) (2.2 ) — .5 .5 Adjustments to reflect acquisition date fair value .2 — .2 — 5.9 5.9 Impairments — (6.2 ) (6.2 ) — — — Amortization — (11.7 ) (11.7 ) — (10.8 ) (10.8 ) Ending balance $ 518.2 $ 241.7 $ 759.9 $ 428.6 $ 239.0 $ 667.6 (1) The relative fair values of goodwill and other intangible assets recognized in connection with the acquisition of Kingsbridge had not yet been finalized at June 30, 2020. (2) The relative fair values of goodwill and other intangible assets recognized in connection with the acquisitions of Embrace, Other Operations and the Kudu Transaction had not yet been finalized at June 30, 2019.

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2020
Debt Instrument
Schedule of debt outstanding	The following table presents White Mountains’s debt outstanding as of June 30, 2020 and December 31, 2019: Millions June 30, Effective Rate (1) December 31, Effective Rate (1) NSM Bank Facility $ 273.4 7.2% $ 221.3 7.5% Unamortized issuance cost (6.4 ) (3.9 ) NSM Bank Facility, carrying value 267.0 217.4 Other NSM debt, carrying value 1.4 3.2% 1.8 3.0% Kudu Bank Facility 74.0 8.1% 57.0 8.3% Unamortized issuance cost (3.2 ) (3.4 ) Kudu Bank Facility, carrying value 70.8 53.6 Other Operations debt 10.9 9.3% 11.1 8.3% Unamortized issuance cost (.3 ) (.4 ) Other Operations, carrying value 10.6 10.7 Total debt $ 349.8 $ 283.5 (1) Effective rate considers the effect of the debt issuance costs.
Term Loan
Debt Instrument
Schedule of debt outstanding	The following table presents the change in debt under the NSM Bank Facility for the three and six months ended June 30, 2020 and 2019: NSM Bank Facility Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Beginning balance $ 220.7 $ 186.4 $ 221.3 $ 180.4 Term loans Borrowings (1) 52.4 42.9 52.4 42.9 Repayments — (.5 ) (.6 ) (1.0 ) Foreign currency translation .3 — .3 — Revolving credit loan Borrowings — — — 6.5 Repayments — (6.5 ) — (6.5 ) Ending balance 273.4 222.3 273.4 222.3 (1) Borrowings for both the three and six months ended June 30, 2020 included $52.4 for the funding of the acquisition of Kingsbridge. Borrowings for the three and six months ended June 30, 2019 , included $20.4 and $22.5 for the funding of the acquisitions of Embrace and the Renewal Rights.

Municipal Bond Guarantee (Table

Municipal Bond Guarantee (Tables)	6 Months Ended
	Jun. 30, 2020
Guarantees [Abstract]
Schedule of Municipal Bond Guarantee Insured Obligations	The following table presents a schedule of BAM’s insured obligations as of June 30, 2020 and December 31, 2019 : June 30, 2020 December 31, 2019 Contracts outstanding 9,992 8,987 Remaining weighted average contract period outstanding (in years) 10.6 10.7 Contractual debt service outstanding (in millions): Principal $ 67,591.5 $ 62,250.5 Interest 33,775.8 31,799.7 Total debt service outstanding $ 101,367.3 $ 94,050.2 Gross unearned insurance premiums (in millions) $ 218.6 $ 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 June 30, 2020 : Millions June 30, 2020 July 1, 2020 - December 31, 2020 $ 10.2 January 1, 2021 - March 31, 2021 5.0 April 1, 2021 - June 30, 2021 4.9 July 1, 2021 - September 30, 2021 4.9 October 1, 2021 - December 31, 2021 4.8 Total 2021 19.6 2022 18.5 2023 17.3 2024 16.2 2025 15.0 2026 and thereafter 121.8 Total gross unearned insurance premiums $ 218.6
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 and six months ended June 30, 2020 and 2019 : Three Months Ended June 30, Six Months Ended June 30, Millions 2020 2019 2020 2019 Written premiums: Direct $ 21.3 $ 12.5 $ 31.0 $ 20.4 Assumed 0.2 — 0.2 — Gross written premiums $ 21.5 $ 12.5 $ 31.2 $ 20.4 Earned premiums: Direct $ 4.7 $ 3.8 $ 9.2 $ 7.5 Assumed 0.9 .5 1.8 1.0 Gross earned premiums $ 5.6 $ 4.3 $ 11.0 $ 8.5

Investments in Unconsolidated_2

Investments in Unconsolidated Entities (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2020 and December 31, 2019: Millions June 30, 2020 December 31, 2019 Equity method eligible investments, at fair value $ 815.3 $ 761.7 Other, at fair value (1) 82.8 94.6 Total other long-term investments $ 898.1 $ 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 June 30, 2020 and December 31, 2019: Basic Ownership Interest Investee June 30, 2020 December 31, 2019 Instrument Held PassportCard/DavidShield (1) 53.8% 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 Tuckerman Capital Funds 14.3 - 62.3% 17.5 - 62.4% Limited and general partnership interests Enlightenment Capital Funds 9.4 - 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 - 35.0% 3.2 - 30.0% Revenue and earnings participation contracts (1) During the three months ending June 30, 2020, White Mountains made an additional $15 investment in PassportCard/DavidShield. See Note 2 — “Significant Transactions” .
MediaAlpha, Kudu and Tuckerman
Schedule of Equity Method Investments [Line Items]
Equity Method Investments	Millions June 30, 2020 December 31, 2019 Balance sheet data (1) : Total assets $ 420.5 $ 457.0 Total liabilities $ 200.2 $ 199.0 (1) Financial data for Tuckerman IV Fund, L.P. and Kudu Participation Contracts is reported on a one-quarter lag. Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Income statement data (1) : Total revenues $ 118.7 $ 93.7 $ 307.2 $ 178.4 Total expenses $ 131.9 $ 83.6 $ 273.8 $ 171.1 Net income (loss) $ (21.8 ) $ 10.1 $ 21.8 $ 7.3

Earnings Per Share (Tables)

Earnings Per Share (Tables)	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2020 and 2019 . See Note 17 — “Held for Sale and Discontinued Operations” . Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Basic and diluted earnings per share numerators (in millions): Net income (loss) attributable to White Mountains’s common shareholders $ 115.4 $ 20.5 $ (13.4 ) $ 304.9 Less: total (loss) income from discontinued operations, net of tax (1.0 ) — (.1 ) .7 Net income (loss) from continuing operations attributable to White Mountains’s common shareholders $ 116.4 $ 20.5 $ (13.3 ) $ 304.2 Allocation of (earnings) losses to participating restricted common shares (1) (1.6 ) (.3 ) .1 (3.6 ) Basic and diluted earnings (losses) per share numerators $ 114.8 $ 20.2 $ (13.2 ) $ 300.6 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,107.5 3,183.5 3,142.8 3,177.8 Average unvested restricted common shares (2) (43.1 ) (42.8 ) (38.5 ) (37.6 ) Basic earnings (losses) per share denominator 3,064.4 3,140.7 3,104.3 3,140.2 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,107.5 3,183.5 3,142.8 3,177.8 Average unvested restricted common shares (2) (43.1 ) (42.8 ) (38.5 ) (37.6 ) Diluted earnings (losses) per share denominator 3,064.4 3,140.7 3,104.3 3,140.2 Basic and diluted earnings per share (in dollars) - continuing operations: Distributed earnings - dividends declared and paid $ — $ — $ 1.00 $ 1.00 Undistributed earnings (losses) 37.46 6.44 (5.25 ) 94.71 Basic and diluted earnings (losses) per share $ 37.46 $ 6.44 $ (4.25 ) $ 95.71 (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 and six months ended June 30, 2020 and 2019 . See Note 17 — “Held for Sale and Discontinued Operations” . Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Undistributed net earnings - continuing operations: Net income (loss) attributable to White Mountains’s common shareholders, net of restricted common share amounts $ 114.8 $ 20.2 $ (13.2 ) $ 300.6 Dividends declared, net of restricted common share amounts (1) — — (3.1 ) (3.2 ) Total undistributed net earnings (losses), net of restricted common share amounts $ 114.8 $ 20.2 $ (16.3 ) $ 297.4 (1) Restricted shares issued by White Mountains receive dividends, and are therefore considered participating securities. three and six months ended June 30, 2020 and 2019 : Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Basic and diluted earnings per share numerators (in millions): Net income (loss) attributable to White Mountains’s common shareholders $ 115.4 $ 20.5 $ (13.4 ) $ 304.9 Less: total income (loss) from continuing operations, net of tax 116.4 20.5 (13.3 ) 304.2 Net (loss) income from discontinued operations attributable to White Mountains’s common shareholders $ (1.0 ) $ — $ (.1 ) $ .7 Allocation of earnings to participating restricted common shares (1) — — — — Basic and diluted (losses) earnings per share numerators (2) $ (1.0 ) $ — $ (.1 ) $ .7 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,107.5 3,183.5 3,142.8 3,177.8 Average unvested restricted common shares (3) (43.1 ) (42.8 ) (38.5 ) (37.6 ) Basic earnings per share denominator 3,064.4 3,140.7 3,104.3 3,140.2 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,107.5 3,183.5 3,142.8 3,177.8 Average unvested restricted common shares (3) (43.1 ) (42.8 ) (38.5 ) (37.6 ) Diluted earnings per share denominator 3,064.4 3,140.7 3,104.3 3,140.2 Basic and diluted (losses) earnings per share (in dollars) - discontinued operations: $ (.32 ) $ — $ (.03 ) $ .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 and six months ended June 30, 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	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2020 and 2019 for performance shares granted under the WTM Incentive Plan: Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Millions, except share amounts Target Performance Accrued Expense Target Performance Accrued Expense Target Performance Shares Outstanding Accrued Expense Target Performance Accrued Expense Beginning of period 42,458 $ 9.8 40,602 $ 23.1 42,473 $ 43.7 40,616 $ 31.7 Shares paid (1) — — — — (14,070 ) (27.7 ) (13,715 ) (18.1 ) New grants — — 1,900 — 14,055 — 15,600 — Forfeitures and cancellations (2) — — (29 ) (.2 ) — .4 (28 ) — Expense recognized — 6.0 — 7.9 — (.6 ) — 17.2 End of period 42,458 $ 15.8 42,473 $ 30.8 42,458 $ 15.8 42,473 $ 30.8 (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 June 30, 2020 for each performance cycle: Six Months Ended June 30, 2020 Millions, except share amounts Target Performance Shares Outstanding Accrued Expense Performance cycle: 2018 – 2020 13,450 $ 8.0 2019 – 2021 15,600 5.9 2020 – 2022 14,055 2.1 Sub-total 43,105 16.0 Assumed forfeitures (647 ) (.2 ) June 30, 2020 42,458 $ 15.8
Summary of restricted shares activity	The following table presents the unrecognized compensation cost associated with the outstanding restricted share awards for the three and six months ended June 30, 2020 and 2019 : Three Months Ended June 30, Six Months Ended June 30, 2020 2019 2020 2019 Millions, except share amounts Restricted Unamortized Fair Value Restricted Unamortized Restricted Unamortized Issue Date Restricted Unamortized Issue Date Non-vested, Beginning of period 43,105 $ 26.6 41,495 $ 22.8 43,395 $ 16.7 41,510 $ 12.5 Issued — — 1,900 1.7 14,055 15.1 15,600 14.5 Vested — — — — (14,345 ) — (13,715 ) — Forfeited — — — — — — — — Expense recognized — (3.6 ) — (2.6 ) — (8.8 ) — (5.1 ) End of period 43,105 $ 23.0 43,395 $ 21.9 43,105 $ 23.0 43,395 $ 21.9

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2020
Leases [Abstract]
Lease, Cost	The following table summarizes net lease expense recognized in White Mountains’s consolidated statement of operations for the three and six months ended June 30, 2020 and 2019: Millions Three Months Ended June 30, Six Months Ended June 30, Lease Cost 2020 2019 2020 2019 Lease cost $ 2.1 $ 1.8 $ 4.1 $ 3.5 Less: sublease income .1 .1 .2 .2 Net lease cost $ 2.0 $ 1.7 $ 3.9 $ 3.3
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 June 30, 2020 : Millions As of June 30, 2020 Remainder of 2020 $ 3.1 2021 6.8 2022 6.3 2023 6.1 2024 5.2 Thereafter 14.1 Total undiscounted lease payments 41.6 Less: present value adjustment 7.4 Operating lease liability $ 34.2
Schedule of Right-of-Use Assets and Lease Liabilities	Millions As of June 30, 2020 Remainder of 2020 $ 3.1 2021 6.8 2022 6.3 2023 6.1 2024 5.2 Thereafter 14.1 Total undiscounted lease payments 41.6 Less: present value adjustment 7.4 Operating lease liability $ 34.2 The following tables present lease related assets and liabilities by reportable segment as of June 30, 2020 and December 31, 2019: As of June 30, 2020 Millions HG/BAM NSM Kudu Other Operations Total Weighted Average Incremental Borrowing Rate (1) ROU lease asset $ 9.8 $ 16.8 $ 2.2 $ 5.2 $ 34.0 4.8% Lease liability $ 9.8 $ 16.8 $ 2.2 $ 5.4 $ 34.2 (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)	6 Months Ended
	Jun. 30, 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 June 30, 2020 and December 31, 2019 : June 30, 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 % $ 14.7 3.1 % $ 14.4 NSM 3.4 % 16.7 3.6 % 14.9 Other NSM 13.4 % (.1 ) 13.4 % (.1 ) Kudu .8 % 2.4 .9 % 2.2 Other Operations various (1.8 ) various (1.5 ) Total, excluding BAM 31.9 29.9 BAM 100.0 % (134.6 ) 100.0 % (146.7 ) Total non-controlling interests $ (102.7 ) $ (116.8 )

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2020 and 2019: Millions HG Global/ BAM NSM Kudu Other Operations Total Three Months Ended June 30, 2020 Earned insurance premiums $ 5.6 $ — $ — $ — $ 5.6 Net investment income 4.9 — 5.6 9.1 19.6 Net realized and unrealized investment gains 14.4 — 16.5 122.0 152.9 Advertising and commission revenues — 63.0 — 1.9 64.9 Other revenue 1.2 13.1 — 2.3 16.6 Total revenues 26.1 76.1 22.1 135.3 259.6 Insurance acquisition expenses 2.1 — — — 2.1 Other underwriting expenses .2 — — — .2 Cost of sales — — — 2.2 2.2 General and administrative expenses 12.5 48.5 2.8 25.3 89.1 Broker commission expense — 21.0 — — 21.0 Change in fair value of contingent consideration — (1.7 ) — — (1.7 ) Amortization of other intangible assets — 6.3 .1 .2 6.6 Interest expense — 5.7 1.5 .2 7.4 Total expenses 14.8 79.8 4.4 27.9 126.9 Pre-tax income (loss) $ 11.3 $ (3.7 ) $ 17.7 $ 107.4 $ 132.7 Millions HG Global/ BAM NSM Kudu Other Operations Total Six Months Ended June 30, 2020 Earned insurance premiums $ 11.0 $ — $ — $ — $ 11.0 Net investment income 10.4 — 12.9 19.2 42.5 Net realized and unrealized investment gains (loss) 20.5 — (8.3 ) (16.0 ) (3.8 ) Advertising and commission revenues — 116.0 — 4.0 120.0 Other revenue 1.7 25.1 .1 3.8 30.7 Total revenues 43.6 141.1 4.7 11.0 200.4 Insurance acquisition expenses 3.8 — — — 3.8 Other underwriting expenses .2 — — — .2 Cost of sales — — — 4.2 4.2 General and administrative expenses 27.2 88.1 5.3 42.8 163.4 Broker commission expense — 39.3 — — 39.3 Change in fair value of contingent consideration — (2.3 ) — — (2.3 ) Amortization of other intangible assets — 11.1 .2 .4 11.7 Interest expense — 10.0 2.9 .5 13.4 Total expenses 31.2 146.2 8.4 47.9 233.7 Pre-tax income (loss) $ 12.4 $ (5.1 ) $ (3.7 ) $ (36.9 ) $ (33.3 ) Millions HG Global/BAM NSM Kudu Other Operations Total Three Months Ended June 30, 2019 Earned insurance premiums $ 4.3 $ — $ — $ — $ 4.3 Net investment income 5.4 — 4.0 11.6 21.0 Net realized and unrealized investment gains 11.5 — .4 23.3 35.2 Advertising and commission revenues — 54.9 — 1.3 56.2 Other revenue .4 11.2 — .7 12.3 Total revenues 21.6 66.1 4.4 36.9 129.0 Insurance acquisition expenses 1.4 — — — 1.4 Other underwriting expenses .1 — — — .1 Cost of sales — — — 1.6 1.6 General and administrative expenses 12.3 32.8 2.2 30.1 77.4 Broker commission expense — 18.1 — — 18.1 Change in fair value of contingent consideration — 6.3 — — 6.3 Amortization of other intangible assets — 4.1 — .1 4.2 Interest expense — 4.1 — — 4.1 Total expenses 13.8 65.4 2.2 31.8 113.2 Pre-tax income $ 7.8 $ .7 $ 2.2 $ 5.1 $ 15.8
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 June 30, 2020 and 2019: Millions HG Global/BAM NSM Kudu Other Operations Total Three Months Ended June 30, 2020 Commission and other revenue Specialty Transportation $ — $ 23.8 $ — $ — $ 23.8 Real Estate — 15.4 — — 15.4 Social Services — 7.3 — — 7.3 Pet — 13.2 — — 13.2 United Kingdom — 12.4 — — 12.4 Other — 4.0 — 1.8 5.8 Total commission and other revenue — 76.1 — 1.8 77.9 Product revenues — — — 2.3 — Revenues from contracts with customers — 76.1 — 4.1 80.2 Other revenues (1) 26.1 — 22.1 131.2 179.4 Total revenues $ 26.1 $ 76.1 $ 22.1 $ 135.3 $ 259.6 (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. Millions HG Global/BAM NSM Kudu Other Operations Total Six Months Ended June 30, 2020 Commission and other revenue Specialty Transportation $ — $ 44.2 $ — $ — $ 44.2 Real Estate — 26.7 — — 26.7 Social Services — 13.6 — — 13.6 Pet — 25.1 — — 25.1 United Kingdom (2) — 22.4 — — 22.4 Other — 9.1 — 4.0 13.1 Total commission and other revenue — 141.1 — 4.0 145.1 Product revenues — — — 4.4 4.4 Revenues from contracts with customers — 141.1 — 8.4 149.5 Other revenues (1) 43.6 — 4.7 2.6 50.9 Total revenues $ 43.6 $ 141.1 $ 4.7 $ 11.0 $ 200.4 (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) Includes the results of Kingsbridge from April 7, 2020, the date of the Kingsbridge transaction. Millions HG Global/BAM NSM Kudu Other Operations Total Three Months Ended June 30, 2019 Commission and other revenue Specialty Transportation $ — $ 21.7 $ — $ — $ 21.7 Real Estate — 11.5 — — 11.5 Social Services — 6.5 — — 6.5 Pet — 9.5 — — 9.5 United Kingdom — 12.2 — — 12.2 Other — 4.7 — 1.3 6.0 Total commission and other revenue — 66.1 — 1.3 67.4 Products — — — .6 .6 Total revenues from contracts with customers — 66.1 — 1.9 68.0 Other revenues (1) 21.6 — 4.4 35.0 61.0 Total revenues $ 21.6 $ 66.1 $ 4.4 $ 36.9 $ 129.0 (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 Kudu MediaAlpha Other Operations Total Six Months Ended June 30, 2019 Commission and other revenue Specialty Transportation $ — $ 39.6 $ — $ — $ — $ 39.6 Real Estate — 20.5 — — — 20.5 Social Services — 12.3 — — — 12.3 Pet — 9.5 — — — 9.5 United Kingdom — 24.3 — — — 24.3 Other — 9.2 — — 2.6 11.8 Total commission and other revenue — 115.4 — — 2.6 118.0 Advertising revenues — — — 48.8 — 48.8 Revenues from contracts with customers — 115.4 — 48.8 2.6 166.8 Products — — — — .6 0.6 Total revenues from contracts with customers — 115.4 — 48.8 3.2 167.4 Other revenues (1) 43.5 — 4.4 — 347.3 395.2 Total revenues $ 43.5 $ 115.4 $ 4.4 $ 48.8 $ 350.5 $ 562.6 (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.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 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 June 30, 2020 and December 31, 2019 : June 30, 2020 December 31, 2019 Millions Fair Value Carrying Value Fair Value Carrying Value NSM Bank Facility $ 272.2 $ 267.0 $ 221.2 $ 217.4 Other NSM debt $ 1.6 $ 1.4 $ 1.7 $ 1.8 Kudu Bank Facility $ 72.8 $ 70.8 $ 53.6 (1) $ 53.6 Other Operations debt $ 9.5 $ 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)	6 Months Ended
	Jun. 30, 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 and six months ended June 30, 2020 and 2019 . See Note 17 — “Held for Sale and Discontinued Operations” . Three Months Ended Six Months Ended June 30, June 30, Millions 2020 2019 2020 2019 Undistributed net earnings - continuing operations: Net income (loss) attributable to White Mountains’s common shareholders, net of restricted common share amounts $ 114.8 $ 20.2 $ (13.2 ) $ 300.6 Dividends declared, net of restricted common share amounts (1) — — (3.1 ) (3.2 ) Total undistributed net earnings (losses), net of restricted common share amounts $ 114.8 $ 20.2 $ (16.3 ) $ 297.4 (1) Restricted shares issued by White Mountains receive dividends, and are therefore considered participating securities. three and six months ended June 30, 2020 and 2019 : Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Basic and diluted earnings per share numerators (in millions): Net income (loss) attributable to White Mountains’s common shareholders $ 115.4 $ 20.5 $ (13.4 ) $ 304.9 Less: total income (loss) from continuing operations, net of tax 116.4 20.5 (13.3 ) 304.2 Net (loss) income from discontinued operations attributable to White Mountains’s common shareholders $ (1.0 ) $ — $ (.1 ) $ .7 Allocation of earnings to participating restricted common shares (1) — — — — Basic and diluted (losses) earnings per share numerators (2) $ (1.0 ) $ — $ (.1 ) $ .7 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,107.5 3,183.5 3,142.8 3,177.8 Average unvested restricted common shares (3) (43.1 ) (42.8 ) (38.5 ) (37.6 ) Basic earnings per share denominator 3,064.4 3,140.7 3,104.3 3,140.2 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,107.5 3,183.5 3,142.8 3,177.8 Average unvested restricted common shares (3) (43.1 ) (42.8 ) (38.5 ) (37.6 ) Diluted earnings per share denominator 3,064.4 3,140.7 3,104.3 3,140.2 Basic and diluted (losses) earnings per share (in dollars) - discontinued operations: $ (.32 ) $ — $ (.03 ) $ .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 and six months ended June 30, 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 ($)	Apr. 04, 2019	Dec. 31, 2019	Jun. 30, 2020	Apr. 07, 2020	Mar. 31, 2020	Apr. 03, 2019	Jan. 01, 2019	Feb. 05, 2018	Dec. 31, 2017	Jul. 31, 2012
Basis of Presentation
Ownership interest (as a percent)		50.00%	53.80%		50.00%
ROU lease asset		$ 22,600,000	$ 34,000,000
Operating lease liability		$ 22,800,000	$ 34,200,000
Payments to acquire business, net	$ 81,400,000
Total commitment under revolving credit facility				$ 291.4	$ 234,000,000
HG Global
Basis of Presentation
Percentage of par value of policy reinsured			15.00%
Surplus notes										$ 503,000,000
Preferred Stock | HG Global
Basis of Presentation
Ownership interest (as a percent)		96.60%	96.90%
Common Stock | HG Global
Basis of Presentation
Ownership interest (as a percent)		89.60%	88.40%		88.40%
NSM Insurance HoldCo, LLC
Basis of Presentation
Ownership interest (as a percent)		96.40%	96.60%
Fully diluted ownership interest (as a percent)		88.40%	89.60%
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	$ 250,000,000	$ 129,000,000	$ 94,500,000			$ 250,000,000
Increase (Decrease) in Capital Commitment		100,000,000
Funded Capital Commitment		350,000,000
Accounting Standards Update 2016-02
Basis of Presentation
ROU lease asset		22,600,000	34,000,000				$ 23,200,000
Operating lease liability		22,800,000	$ 34,200,000				$ 23,200,000
Series A BAM Surplus Note | HG Global
Basis of Presentation
Surplus notes									$ 203,000,000	203,000,000
Series B BAM Surplus Note | HG Global
Basis of Presentation
Surplus notes										$ 300,000,000
Kudu Debt [Member] | Delayed Draw Term Loans [Member] | Kudu
Basis of Presentation
Total commitment under revolving credit facility		$ 125,000,000

Significant Transactions (Detai

Significant Transactions (Details)	May 07, 2020USD ($)	Apr. 07, 2020USD ($)	Jun. 28, 2019USD ($)	Apr. 04, 2019USD ($)	Apr. 01, 2019USD ($)	Feb. 26, 2019USD ($)	Dec. 03, 2018USD ($)	May 18, 2018USD ($)	May 11, 2018USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)earnout_period	Dec. 31, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Dec. 31, 2019USD ($)	May 31, 2019USD ($)	Apr. 03, 2019USD ($)	Dec. 31, 2018USD ($)	Feb. 05, 2018USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment of Intangible Assets, Finite-lived																		$ (10,400,000)
Ownership interest (as a percent)										53.80%	50.00%	50.00%				53.80%		50.00%
Commitment to Fund																						$ 125,000,000
Payments to Acquire Businesses and Interest in Affiliates																$ 120,300,000	$ 243,400,000
Stock Issued During Period, Value, Acquisitions	$ 15,000,000
Payments to Acquire Intangible Assets													$ 82,500,000				82,500,000
Payments to acquire business, net				$ 81,400,000
Goodwill										$ 518,200,000		$ 394,700,000				518,200,000		$ 394,700,000
Total commitment under revolving credit facility		$ 291.4									$ 234,000,000
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										(1,700,000)			6,300,000		$ 2,600,000	2,300,000	7,600,000
Payment for contingent consideration liability													2,600,000			6,400,000	2,600,000
Contingent consideration earnout liabilities										11,700,000		20,600,000				11,700,000		20,600,000
White Mountains
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Other Investments										898,100,000		$ 856,300,000				898,100,000		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%															61.00%
Fully diluted ownership interest (as a percent)						42.00%															58.90%
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										$ 15,000,000				114,700,000		$ 45,000,000	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%	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										$ 52,100,000						$ 52,100,000
NSM Insurance HoldCo, LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Ownership interest (as a percent)										96.60%		96.40%				96.60%		96.40%
Fully diluted ownership interest (as a percent)										89.60%		88.40%				89.60%		88.40%
AIG Collector Car Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Intangible assets acquired			$ 82,500,000
Payments to Acquire Intangible Assets			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]
Payments to Acquire Businesses and Interest in Affiliates			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						$ 94,500,000		$ 129,000,000				$ 94,500,000		$ 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
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt Instrument, Face Amount									$ 100,000,000
NSM Bank Facility | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt Instrument, Face Amount										273,400,000	220,700,000	221,300,000	222,300,000	186,400,000		273,400,000	222,300,000	221,300,000			$ 180,400,000
NSM Bank Facility | Term Loan | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt Instrument, Face Amount		276,400,000								273,400,000	$ 224,000,000	221,300,000				273,400,000		221,300,000
Proceeds from borrowings										52,400,000			42,900,000			52,400,000	42,900,000
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										51,000,000		68,000,000				51,000,000		68,000,000
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%
Payments to Acquire Businesses and Interest in Affiliates							$ 29,000,000		$ 274,200,000
Fully diluted ownership interest (as a percent)									83.60%
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
Proceeds from borrowings							$ 30,100,000
Intangible assets acquired														32,700,000
Contingent consideration earnout liabilities														5,900,000
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
Number of earnout periods | earnout_period											2
Proceeds from borrowings								$ 51,000,000
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]
Payments to Acquire Businesses and Interest in Affiliates					58,200,000
Proceeds from borrowings					$ 20,400,000
Percentage of voting interests acquired					100.00%
Payments to acquire businesses, gross					$ 71,500,000
Embrace Pet Insurance | NSM Bank Facility | Term Loan | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from borrowings													20,400,000
Kingsbridge [Member] | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Businesses and Interest in Affiliates		80,300,000
Goodwill and intangible assets acquired		$ 125,100,000
Percentage of voting interests acquired		100.00%
Kingsbridge [Member] | NSM Bank Facility | Term Loan | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from borrowings										52,400,000
Other Intangible Assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Acquisitions of businesses										0			0			0	26,800,000
Goodwill, Acquired During Period																0	0
Finite Lived Intangible Assets, Foreign Currency Translation Gain (Loss)										100,000			200,000			(400,000)	500,000
Measurement Period Adjustments										0			0			0	5,900,000
Impairment of Intangible Assets, Finite-lived										(6,200,000)						(6,200,000)		(2,800,000)
Intangible Assets, Net (Excluding Goodwill)										241,700,000	$ 254,400,000	260,000,000	239,000,000	160,500,000		241,700,000	239,000,000	260,000,000			157,600,000
Deconsolidation of Business																	(23,500,000)
Amortization										(6,600,000)			(4,200,000)			(11,700,000)	(10,800,000)
Renewal Rights
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Acquisitions of businesses																0
Goodwill and intangible assets acquired			$ 82,500,000
Payments to Acquire Intangible Assets													82,500,000				82,500,000
Intangible Asset and Goodwill
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Acquisitions of businesses										125,100,000			80,400,000			0	0
Goodwill, Acquired During Period																125,100,000	93,800,000
Finite Lived Intangible Assets, Foreign Currency Translation Gain (Loss)										800,000			(1,000,000)			(2,200,000)	500,000
Measurement Period Adjustments										0			(300,000)			200,000	5,900,000
Impairment of Intangible Assets, Finite-lived										(6,200,000)						(6,200,000)
Intangible Assets, Gross (Including Goodwill)										759,900,000	646,800,000	654,700,000	667,600,000	510,200,000		759,900,000	667,600,000	654,700,000			537,500,000
Deconsolidation of Business																	(41,800,000)
Amortization										(6,600,000)			(4,200,000)			(11,700,000)	(10,800,000)
Goodwill
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Acquisitions of businesses																0	(26,800,000)
Goodwill, Acquired During Period										125,100,000			80,400,000			125,100,000	93,800,000
Foreign currency translation										700,000			(1,200,000)			(1,800,000)	0
Measurement Period Adjustments										0			(300,000)			200,000
Goodwill										$ 518,200,000	$ 392,400,000	$ 394,700,000	$ 428,600,000	$ 349,700,000		518,200,000	428,600,000	394,700,000			$ 379,900,000
Deconsolidation of Business																	$ (18,300,000)
Goodwill | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Foreign currency translation																$ (1,800,000)		$ 1,400,000
United Kingdom, Pounds | NSM Bank Facility | Term Loan | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt Instrument, Face Amount		$ 42,500,000
United Kingdom, Pounds | Kingsbridge [Member] | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Businesses and Interest in Affiliates		107,200,000
Proceeds from borrowings		42,500,000
United States of America, Dollars | NSM Bank Facility | Term Loan | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt Instrument, Face Amount		52,400,000
United States of America, Dollars | Kingsbridge [Member] | NSM Holding Co LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments to Acquire Businesses and Interest in Affiliates		132,000,000
Proceeds from borrowings		$ 52,400,000
Measurement Input, Revenue Multiple [Member] | Other [Member] | Maximum | Standard Poors NR Rating
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Equity Securities, FV-NI, Measurement Input										4		4				4		4

Investment Securities (Net Inve

Investment Securities (Net Investment Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Investment income
Total investment income	$ 19.9	$ 21.3	$ 43.1	$ 37.7
Third-party investment expenses	(0.3)	(0.3)	(0.6)	(0.7)
Net investment income, pre-tax	19.6	21	42.5	37
Fixed maturity investments
Investment income
Total investment income	7.3	8.3	15.4	16.4
Short-term investments
Investment income
Total investment income	0.1	1.3	0.9	2.6
Common Stock
Investment income
Total investment income	2.2	2.9	6	8.3
Other long-term investments
Investment income
Total investment income	$ 10.3	$ 8.8	$ 20.8	$ 10.4

Investment Securities (Net Real

Investment Securities (Net Realized and Unrealized Investment Gains (Losses)) (Details) - USD ($)	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Trading Securities, Realized and Unrealized Gain (Loss)	$ 2,200,000	$ 200,000		$ (6,500,000)	$ 12,400,000
MediaAlpha
Debt and Equity Securities, FV-NI [Line Items]
Trading Securities, Realized and Unrealized Gain (Loss)					67,500,000
Unrealized investment gain	15,000,000		$ 114,700,000	$ 45,000,000	$ 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			6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ 152,900,000	$ 35,200,000		$ (3,800,000)	$ 280,800,000
Trading Securities, Realized and Unrealized Gain (Loss)	2,200,000	200,000		(6,500,000)	12,400,000
Fixed maturity investments
Debt and Equity Securities, FV-NI [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	30,000,000	16,900,000		32,200,000	38,000,000
Short-term investments
Debt and Equity Securities, FV-NI [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	0	300,000		400,000	300,000
Common equity securities
Debt and Equity Securities, FV-NI [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	98,300,000	27,800,000		(42,500,000)	139,100,000
Other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	24,600,000	(9,800,000)		6,100,000	103,400,000
MediaAlpha
Debt and Equity Securities, FV-NI [Line Items]
Unrealized investment gain	15,000,000		$ 114,700,000	45,000,000	114,700,000	$ 180,000,000
Trading Securities, Realized and Unrealized Gain (Loss)					67,500,000
Investments Held [Member]
Debt and Equity Securities, FV-NI [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ 150,700,000	$ 35,000,000		$ 2,700,000	$ 268,400,000

Investment Securities (Investme

Investment Securities (Investment gains (losses) for Level 3) (Details) - Level 3 Inputs - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Debt and Equity Securities, FV-NI [Line Items]
Unrealized gains (losses) on investments	$ 25.3	$ (14)	$ 15.9	$ 100
Other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Unrealized gains (losses) on investments	$ 25.3	$ (14)	$ 15.9	$ 100

Investment Securities (Invest_2

Investment Securities (Investment Holdings Fixed Maturity Table) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
U.S. Government and agency obligations
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	$ 195.5	$ 231.7
Trading Securities, Unrealized Holding Gain	4.9	1
Trading Securities, Unrealized Holding Loss	0	(0.2)
Fixed maturity investments, at fair value	200.4	232.5
Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	480.2	454.9
Trading Securities, Unrealized Holding Gain	26.1	12.5
Trading Securities, Unrealized Holding Loss	(0.5)	(0.2)
Fixed maturity investments, at fair value	505.8	467.2
Municipal obligations
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	248.3	284.7
Trading Securities, Unrealized Holding Gain	16.7	12.5
Trading Securities, Unrealized Holding Loss	(0.2)	(0.1)
Fixed maturity investments, at fair value	264.8	297.1
Mortgage-backed and asset-backed securities
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	213.2	206.6
Trading Securities, Unrealized Holding Gain	7.4	2.7
Trading Securities, Unrealized Holding Loss	0	(0.3)
Fixed maturity investments, at fair value	220.6	209
Fixed Income Investments
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	1,137.2	1,177.9
Trading Securities, Unrealized Holding Gain	55.1	28.7
Trading Securities, Unrealized Holding Loss	(0.7)	(0.8)
Total fixed maturity investments including assets held for sale	$ 1,191.6	$ 1,205.8

Investment Securities (Invest_3

Investment Securities (Investment Holding Common Equities/ Other Investments) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Common Stock
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	$ 502.8	$ 553.3
Trading Securities, Unrealized Holding Gain	69.3	130.6
Trading Securities, Unrealized Holding Loss	(4.9)	0
Net foreign currency gains (losses)	0	0
Fixed maturity investments, at fair value	567.2	683.9
Other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Cost or amortized cost	677.9	667.4
Trading Securities, Unrealized Holding Gain	289.6	255.2
Trading Securities, Unrealized Holding Loss	(67.1)	(64.1)
Net foreign currency gains (losses)	(2.3)	(2.2)
Fixed maturity investments, at fair value	$ 898.1	$ 856.3

Investment Securities (Other lo

Investment Securities (Other long-term investments) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Kudu investments
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	$ 315.6	$ 266.5
MediaAlpha
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	225	180
DavidShield & PassportCard
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	95	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	31.9	33.7
Total unconsolidated entities
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	722.6	625.3
Hedge and private equity funds included in other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	105.9	161.1
Insurance-linked securities funds
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	52.1	41.2
Private Debt Instrument
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	17.5	28.7
Noblr [Member]
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	4.6	5
White Mountains
Debt and Equity Securities, FV-NI [Line Items]
Other Investments	$ 898.1	$ 856.3

Investment Securities (Hedge Fu

Investment Securities (Hedge Funds and Private Equity Funds) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020USD ($)	Jun. 30, 2020USD ($)fund	Dec. 31, 2019USD ($)
Private equity security
Debt and Equity Securities, FV-NI [Line Items]
Number of investments | fund		13
Fair Value		$ 105.9
Hedge and private equity funds included in other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Largest single fund investment		23.1	$ 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	Jun. 30, 2020	Dec. 31, 2019
Private equity security
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 105.9
Hedge and private equity funds included in other long-term investments
Debt and Equity Securities, FV-NI [Line Items]
Other long-term investments	105.9	$ 161.1
Unfunded Commitments	44.4	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	43.8	57.7
Unfunded Commitments	4	4.1
Private equity security | Aerospace/Defense/Government
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	44.8	33.8
Unfunded Commitments	15.7	23.3
Private equity security | Financial services
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	17.3	15
Unfunded Commitments	24.7	22.8
Private equity security | Private equity security
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	105.9	106.5
Unfunded Commitments	$ 44.4	$ 50.2

Investment Securities (Invest_4

Investment Securities (Investments In Private Equity Funds Subject to Lock-Up Periods) (Details) - Private equity security $ in Millions	Jun. 30, 2020USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 105.9
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	40.4
5-10 years
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	56.7
Greater than 10 years
Debt and Equity Securities, FV-NI [Line Items]
Fair Value	$ 4.1

Investment Securities (Restrict

Investment Securities (Restrictions on Redemption Frequency and Advance Notice Requirements) (Details) - Hedge funds - USD ($) $ in Millions	Jun. 30, 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	6 Months Ended
	Jun. 30, 2020USD ($)	Dec. 31, 2019USD ($)	Jun. 30, 2019USD ($)	Dec. 31, 2018USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 2,656.9	$ 2,746	$ 2,483	$ 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	$ 52.1

Investment Securities (Fair V_2

Investment Securities (Fair Value Measurements) (Details)	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Percentage of investments recorded at fair value	68.00%	71.00%

Investment Securities (Fair V_3

Investment Securities (Fair Value Measurement by Level) (Details) $ in Millions	Jun. 30, 2020USD ($)Investment	Dec. 31, 2019USD ($)Investment	Jun. 30, 2019USD ($)	Dec. 31, 2018USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 2,656.9	$ 2,746	$ 2,483	$ 2,328.7
Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	665.1	780	684.5	842.6
Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 1,093.6	$ 1,109.6	1,134.1	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	$ 505.8	$ 467.2
Mortgage-backed and asset-backed securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	220.6	209
Mortgage-backed and asset-backed securities | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	220.6	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	117.6	201.2	187.1	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	740.1	654	$ 458	$ 138.7
Fair value measured on a recurring basis
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	2,774.5	2,947.2
Fair value measured on a recurring basis | Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	779.6	969.4
Fair value measured on a recurring basis | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	1,096.7	1,121.4
Fair value measured on a recurring basis | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	740.2	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	200.4	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	200.4	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	505.8	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	505.8	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	151.9	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	151.9	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	43.3	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	43.3	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	61.1	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	61.1	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	57.6	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	57.6	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	34.3	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	34.3	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	55.6	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	55.6	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	40.9	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	40.9	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	29	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	29	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	32.1	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	32.1	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	220.6	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	220.6	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	264.8	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	264.8	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	1,191.6	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	200.4	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	991.2	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	117.6	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	114.5	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	3.1	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	464.7
Fair value measured on a recurring basis | Common equity securities | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	102.4
Fair value measured on a recurring basis | Common equity securities | Exchange traded funds
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	442.4	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	442.4	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	0	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	124.8	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	22.3	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	102.4	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	567.2	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	158	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	740.1	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	$ 740.1	$ 654

Investment Securities (Debt sec

Investment Securities (Debt securities issued by corporation) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 2,656.9	$ 2,746	$ 2,483	$ 2,328.7
Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fixed maturity investments, at fair value	505.8	467.2
Fair value investments	505.8	467.2
AAA | Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	8.3	9.5
AA | Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	53.6	73.9
A | Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	314.1	288.5
BBB | Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	128.1	95.3
BB | Debt securities issued by corporations
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 1.7	$ 0

Investment Securities (Mortgage

Investment Securities (Mortgage-backed Asset Securities Table) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	$ 2,656.9	$ 2,746	$ 2,483	$ 2,328.7
Federal National Mortgage Association Certificates and Obligations (FNMA)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	87.4	88.6
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	68.1	60.5
Government National Mortgage Association Certificates and Obligations (GNMA)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	42.2	30.8
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	197.7	179.9
Collateralized Mortgage Backed Securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	197.7	179.9
Collateralized Auto Loans
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	11.5	15.1
Collateralized Credit Card Securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	11.4	14
Asset-backed Securities, Securitized Loans and Receivables
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	22.9	29.1
Mortgage-backed and asset-backed securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	220.6	209
Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	1,093.6	1,109.6	$ 1,134.1	$ 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	87.4	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	68.1	60.5
Level 2 Inputs | Government National Mortgage Association Certificates and Obligations (GNMA)
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	42.2	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	197.7	179.9
Level 2 Inputs | Collateralized Mortgage Backed Securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	197.7	179.9
Level 2 Inputs | Collateralized Auto Loans
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	11.5	15.1
Level 2 Inputs | Collateralized Credit Card Securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	11.4	14
Level 2 Inputs | Asset-backed Securities, Securitized Loans and Receivables
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	22.9	29.1
Level 2 Inputs | Mortgage-backed and asset-backed securities
Debt and Equity Securities, FV-NI [Line Items]
Fair value investments	220.6	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		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance		$ 2,328,700,000	$ 2,746,000,000	$ 2,328,700,000	$ 2,328,700,000
Net realized and unrealized (losses) gains			(4,200,000)	280,600,000
Amortization/Accretion			(1,900,000)	(600,000)
Purchases			427,000,000	541,300,000
Sales			(510,000,000)	(667,000,000)
Transfers in			0	82,600,000
Transfers out			0	(82,600,000)
Ending balance	$ 2,656,900,000		2,656,900,000	2,483,000,000	2,746,000,000
Level 1 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance		842,600,000	780,000,000	842,600,000	842,600,000
Net realized and unrealized (losses) gains			(13,900,000)	115,200,000
Amortization/Accretion			0	100,000
Purchases			113,000,000	70,100,000
Sales			(214,000,000)	(343,500,000)
Transfers in			0	0
Transfers out			0	0
Ending balance	665,100,000		665,100,000	684,500,000	780,000,000
Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance		1,160,500,000	1,109,600,000	1,160,500,000	1,160,500,000
Net realized and unrealized (losses) gains			3,600,000	62,000,000
Amortization/Accretion			(1,900,000)	(700,000)
Purchases			214,200,000	232,000,000
Sales			(231,900,000)	(319,700,000)
Transfers in			0	0
Transfers out			0	0
Ending balance	1,093,600,000		1,093,600,000	1,134,100,000	1,109,600,000
NAV
Debt and Equity Securities, FV-NI [Line Items]
Transfers out				(71,700,000)
Common equity securities | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance			100,000
Net realized and unrealized (losses) gains			0
Amortization/Accretion			0
Purchases			0
Sales			0
Transfers in			0
Transfers out			0
Ending balance	100,000		100,000		100,000
Other long-term investments | Level 3 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance		138,700,000	654,000,000	138,700,000	138,700,000
Net realized and unrealized (losses) gains			15,600,000	100,000,000
Amortization/Accretion			0	0
Purchases			78,600,000	136,700,000
Sales			(8,100,000)
Transfers in			0	82,600,000
Transfers out			0	0
Ending balance	740,100,000		740,100,000	458,000,000	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		186,900,000	202,300,000	186,900,000	186,900,000
Net realized and unrealized (losses) gains			(9,500,000)	3,400,000
Amortization/Accretion			0	0
Purchases			21,200,000	102,500,000
Sales			(56,000,000)	(3,800,000)
Transfers in			0	0
Transfers out			0	(82,600,000)
Ending balance	158,000,000		158,000,000	206,400,000	202,300,000
Short-term investments
Debt and Equity Securities, FV-NI [Line Items]
Short-term investments, at fair value	117,600,000		117,600,000	187,100,000	201,200,000	$ 214,200,000
Realized and unrealized losses			400,000	(200,000)
Fair value measured on a recurring basis
Debt and Equity Securities, FV-NI [Line Items]
Beginning balance			2,947,200,000
Ending balance	2,774,500,000		2,774,500,000		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	779,600,000		779,600,000		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	1,096,700,000		1,096,700,000		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	740,200,000		740,200,000		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	464,700,000		464,700,000
Fair value measured on a recurring basis | Common equity securities | Level 2 Inputs
Debt and Equity Securities, FV-NI [Line Items]
Ending balance	102,400,000		102,400,000
Fair value measured on a recurring basis | Short-term investments
Debt and Equity Securities, FV-NI [Line Items]
Short-term investments, at fair value	117,600,000		117,600,000		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	114,500,000		114,500,000		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	3,100,000		3,100,000		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		0
MediaAlpha
Debt and Equity Securities, FV-NI [Line Items]
Unrealized investment gain	$ 15,000,000	$ 114,700,000	$ 45,000,000	$ 114,700,000	$ 180,000,000

Investment Securities (Signific

Investment Securities (Significant Unobservable Inputs) (Details) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2020USD ($)$ / shares	Jun. 30, 2020USD ($)$ / shares	Jun. 30, 2019USD ($)	Dec. 31, 2019USD ($)$ / shares
Quantitative information for Level 3 Fair Value Measurements Assets
Increase (Decrease) in Debt Securities, Trading, and Equity Securities, FV-NI		$ 57.4	$ 0
MediaAlpha | Standard Poors NR Rating | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 225	$ 225		$ 180
MediaAlpha | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		14.00%		15.00%
MediaAlpha | Measurement Input, Long-term Revenue Growth Rate [Member] | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal Revenue Growth Rate	4.00%	4.00%		4.00%
DavidShield & PassportCard | Standard Poors NR Rating | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 95	$ 95		$ 90
DavidShield & PassportCard | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		23.00%		22.00%
DavidShield & PassportCard | Measurement Input, Long-term Revenue Growth Rate [Member] | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal Revenue Growth Rate	4.00%	4.00%		4.00%
Private Debt Instrument | Standard Poors NR Rating | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 17.5	$ 17.5		$ 23.7
Private Debt Instrument | Minimum | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		6.00%		4.00%
Private Debt Instrument | Maximum | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		12.00%		9.00%
Kudu Investments | Standard Poors NR Rating | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 315.6	$ 315.6		$ 266.5
Kudu Investments | Minimum | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		18.00%		15.00%
Kudu Investments | Minimum | Terminal Multiple | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal Cash Flow Exit Multiple	6	6		6
Kudu Investments | Maximum | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		23.00%		22.00%
Kudu Investments | Maximum | Terminal Multiple | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal Cash Flow Exit Multiple	12	12		12
Elementum Holdings, L.P. | Standard Poors NR Rating | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 55.1	$ 55.1		$ 55.1
Elementum Holdings, L.P. | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		19.00%		20.00%
Terminal Revenue Growth Rate	4.00%	4.00%		4.00%
Other | Standard Poors NR Rating | Discounted cash flow
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 15.7	$ 15.7		$ 23.7
Other | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate		24.00%
Terminal Revenue Growth Rate	4.00%	4.00%		4.00%
Other | Minimum | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate				25.00%
Other | Minimum | Measurement Input, Revenue Multiple [Member] | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Equity Securities, FV-NI, Measurement Input	2	2		2
Other | Maximum | Discount rate | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate				32.00%
Other | Maximum | Measurement Input, Revenue Multiple [Member] | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Equity Securities, FV-NI, Measurement Input	4	4		4
Noblr Inc [Member] | Standard Poors NR Rating | Recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 8.7	$ 8.7		$ 5
Noblr Inc [Member] | Recent transaction | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Share Price | $ / shares	$ 2.17	$ 2.17		$ 2.17
Compare.com | Standard Poors NR Rating | Estimated Net Realizable Value
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 2.5	$ 2.5		$ 2.5
Compare.com | Estimated Net Realizable Value | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	2.5	2.5		2.5
Zillion Insurance Services [Member] | Standard Poors NR Rating | Recent transaction
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	5	5		2.5
Zillion Insurance Services [Member] | Recent transaction | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	5	5		$ 2.5
Zillion Insurance Services [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Increase (Decrease) in Debt Securities, Trading, and Equity Securities, FV-NI	2.5
Kudu
Quantitative information for Level 3 Fair Value Measurements Assets
Increase (Decrease) in Debt Securities, Trading, and Equity Securities, FV-NI		$ 57.4
Passport/DavidShield [Member]
Quantitative information for Level 3 Fair Value Measurements Assets
Increase (Decrease) in Debt Securities, Trading, and Equity Securities, FV-NI	$ 15

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		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Apr. 07, 2020	Mar. 31, 2020	Jun. 28, 2019	Apr. 04, 2019	Apr. 01, 2019	Mar. 31, 2019	Mar. 12, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill, acquisition date fair value	$ 518.2		$ 518.2		$ 402.3
Goodwill, Impairment Loss					7.6
Goodwill and other intangible assets	759.9		759.9		654.7
Goodwill	518.2		518.2		394.7
Impairment of Intangible Assets, Finite-lived					10.4
Renewal Rights
Goodwill [Line Items]
Goodwill and intangible assets acquired								$ 82.5
Kingsbridge [Member]
Goodwill [Line Items]
Goodwill and intangible assets acquired						$ 125.1
NSM Holding Co LLC
Goodwill [Line Items]
Goodwill, acquisition date fair value	504.9		504.9		381.6
Goodwill and intangible assets acquired	275.2		275.2
Goodwill	504.9		504.9		381.6
Impairment of Intangible Assets, Finite-lived					2.4
NSM Holding Co LLC | Renewal Rights
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived					0
Kudu investments
Goodwill [Line Items]
Goodwill, acquisition date fair value	7.6		7.6		7.6
Goodwill	7.6		7.6		7.6
Other [Member]
Goodwill [Line Items]
Goodwill, acquisition date fair value	5.7		5.7		13.1
Goodwill, Impairment Loss					7.6
Goodwill	5.7		5.7		5.5
Impairment of Intangible Assets, Finite-lived					0.4
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
Goodwill [Line Items]
Goodwill, Foreign Currency Translation Gain (Loss)	0.7	(1.2)	(1.8)	$ 0
Goodwill	518.2	$ 428.6	518.2	$ 428.6	394.7		$ 392.4				$ 349.7		$ 379.9
Other Intangible Assets | NSM Holding Co LLC
Goodwill [Line Items]
Finite Lived Intangible Assets, Foreign Currency Translation Gain (Loss)			(0.4)		0.7
Fresh Insurance Services Group Limited
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			6.2
Fresh Insurance Services Group Limited | NSM Holding Co LLC
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			6.2
Fresh Insurance Services Group Limited | NSM Holding Co LLC | Renewal Rights
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			0
NSM Holding Co LLC
Goodwill [Line Items]
Goodwill and other intangible assets	$ 728.6		728.6		623
NSM Holding Co LLC | Goodwill
Goodwill [Line Items]
Goodwill, Foreign Currency Translation Gain (Loss)			$ (1.8)		$ 1.4

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		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill, acquisition date fair value	$ 518.2		$ 518.2		$ 402.3
Goodwill, Impairment Loss					7.6
Goodwill	518.2		518.2		394.7
Other intangible assets, acquisition date fair value	806		806		694.4
Other intangible assets, accumulated amortization	39.9		39.9		29.3
Impairment of Intangible Assets, Finite-lived					(10.4)
Goodwill and intangible assets, net carrying value	759.9		759.9		654.7
Payments to Acquire Intangible Assets		$ 82.5		$ 82.5
NSM Holding Co LLC
Goodwill [Line Items]
Goodwill, acquisition date fair value	504.9		504.9		381.6
Goodwill	504.9		504.9		381.6
Other intangible assets, acquisition date fair value	268.6		268.6		271.7
Other intangible assets, accumulated amortization	38.7		38.7		27.9
Impairment of Intangible Assets, Finite-lived					(2.4)
Other intangible assets, net carrying value	223.7		223.7		241.4
Amortization of Intangible Assets	(6.3)	(4.1)	(11.1)	(9.1)
Kudu investments
Goodwill [Line Items]
Goodwill, acquisition date fair value	7.6		7.6		7.6
Goodwill	7.6		7.6		7.6
Amortization of Intangible Assets	(0.1)	0	(0.2)	0
Other
Goodwill [Line Items]
Goodwill, acquisition date fair value	5.7		5.7		13.1
Goodwill, Impairment Loss					7.6
Goodwill	5.7		5.7		5.5
Other intangible assets, acquisition date fair value	17		17		18.2
Other intangible assets, accumulated amortization	0.8		0.8		1.2
Impairment of Intangible Assets, Finite-lived					(0.4)
Other intangible assets, net carrying value	16.2		16.2		16.6
Customer relationships | NSM Holding Co LLC
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	120.1		120.1		121.7
Other intangible assets, accumulated amortization	26.9		26.9		19.8
Impairment of Intangible Assets, Finite-lived					(1.4)
Other intangible assets, net carrying value	89.7		$ 89.7		100.5
Acquired finite-lived intangible assets, weighted average useful life			9 years
Customer relationships | Other
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	7.2		$ 7.2		7.2
Other intangible assets, accumulated amortization	0.6		0.6		0.4
Impairment of Intangible Assets, Finite-lived					0
Other intangible assets, net carrying value	6.6		$ 6.6		6.8
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		$ 61.2		61.9
Other intangible assets, accumulated amortization	6.6		6.6		5.3
Impairment of Intangible Assets, Finite-lived					(0.4)
Other intangible assets, net carrying value	53.6		$ 53.6		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		2.2
Other intangible assets, accumulated amortization	0.4		0.4		0.2
Impairment of Intangible Assets, Finite-lived					0
Other intangible assets, net carrying value	1.8		$ 1.8		2
Acquired finite-lived intangible assets, weighted average useful life			7 years
Trade names | Other
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	1		$ 1		1.7
Other intangible assets, accumulated amortization	0.1		0.1		0.5
Impairment of Intangible Assets, Finite-lived					(0.2)
Other intangible assets, net carrying value	0.9		$ 0.9		1
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		$ 3.1		3.9
Other intangible assets, accumulated amortization	1.4		1.4		1.4
Impairment of Intangible Assets, Finite-lived					(0.6)
Other intangible assets, net carrying value	0		0		1.9
Information technology | Other
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	0		0		0.5
Other intangible assets, accumulated amortization	0		0		0.3
Impairment of Intangible Assets, Finite-lived					(0.2)
Other intangible assets, net carrying value	0		$ 0		0
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		1.7
Other intangible assets, accumulated amortization	1		1		0.7
Impairment of Intangible Assets, Finite-lived					0
Other intangible assets, net carrying value	0.7		$ 0.7		1
Acquired finite-lived intangible assets, weighted average useful life			3 years
Other | Other
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	0.2		$ 0.2		0.2
Other intangible assets, accumulated amortization	0.1		0.1		0
Impairment of Intangible Assets, Finite-lived					0
Other intangible assets, net carrying value	0.1		$ 0.1		0.2
Acquired finite-lived intangible assets, weighted average useful life			5 years
Renewal Rights
Goodwill [Line Items]
Acquisitions of businesses			$ 0
Payments to Acquire Intangible Assets		82.5		82.5
Renewal Rights | NSM Holding Co LLC
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	82.5		82.5		82.5
Other intangible assets, accumulated amortization	2.8		2.8		0.7
Impairment of Intangible Assets, Finite-lived					0
Other intangible assets, net carrying value	79.7		$ 79.7		81.8
Acquired finite-lived intangible assets, weighted average useful life			12 years
Other Intangible Assets
Goodwill [Line Items]
Foreign currency translation	0.1	0.2	$ (0.4)	0.5
Measurement Period Adjustments	0	0	0	5.9
Intangible Assets, Net (Excluding Goodwill)	241.7	239	241.7	239	260	$ 254.4	$ 160.5	$ 157.6
Other intangible assets, acquisition date fair value	287.8		287.8		292.1
Other intangible assets, accumulated amortization	39.9		39.9		29.3
Impairment of Intangible Assets, Finite-lived	(6.2)		(6.2)		(2.8)
Other intangible assets, net carrying value	241.7		241.7		260
Deconsolidation of Business				(23.5)
Amortization of Intangible Assets	(6.6)	(4.2)	(11.7)	(10.8)
Goodwill, Acquired During Period			0	0
Acquisitions of businesses	0	0	0	26.8
Licensing Agreements [Member] | Other
Goodwill [Line Items]
Other intangible assets, acquisition date fair value	8.6		8.6		8.6
Other intangible assets, accumulated amortization	0		0		0
Impairment of Intangible Assets, Finite-lived					0
Other intangible assets, net carrying value	8.6		8.6		8.6
Non-controlling interest
Goodwill [Line Items]
Goodwill and intangible assets, net carrying value	(25.9)		(25.9)		(23.4)
Total
Goodwill [Line Items]
Goodwill and intangible assets, net carrying value	734		734		631.3
Goodwill
Goodwill [Line Items]
Measurement Period Adjustments	0	(0.3)	0.2
Goodwill	518.2	428.6	518.2	428.6	394.7	392.4	349.7	379.9
Deconsolidation of Business				(18.3)
Goodwill, Acquired During Period	125.1	80.4	125.1	93.8
Acquisitions of businesses			0	(26.8)
Foreign currency translation	0.7	(1.2)	(1.8)	0
Intangible Asset and Goodwill
Goodwill [Line Items]
Foreign currency translation	0.8	(1)	(2.2)	0.5
Measurement Period Adjustments	0	(0.3)	0.2	5.9
Impairment of Intangible Assets, Finite-lived	(6.2)		(6.2)
Goodwill and intangible assets, acquisition date fair value	759.9	667.6	759.9	667.6	654.7	$ 646.8	$ 510.2	$ 537.5
Deconsolidation of Business				(41.8)
Amortization of Intangible Assets	(6.6)	(4.2)	(11.7)	(10.8)
Goodwill, Acquired During Period			125.1	93.8
Acquisitions of businesses	$ 125.1	$ 80.4	0	$ 0
Other Intangible Assets | NSM Holding Co LLC
Goodwill [Line Items]
Foreign currency translation			(0.4)		$ 0.7
Fresh Insurance Services Group Limited
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			(6.2)
Fresh Insurance Services Group Limited | NSM Holding Co LLC
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			(6.2)
Fresh Insurance Services Group Limited | Customer relationships | NSM Holding Co LLC
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			(3.5)
Fresh Insurance Services Group Limited | Trade names | NSM Holding Co LLC
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			(1)
Fresh Insurance Services Group Limited | Information technology | NSM Holding Co LLC
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			(1.7)
Fresh Insurance Services Group Limited | Other | NSM Holding Co LLC
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			0
Fresh Insurance Services Group Limited | Renewal Rights | NSM Holding Co LLC
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			0
Fresh Insurance Services Group Limited | Other Intangible Assets
Goodwill [Line Items]
Impairment of Intangible Assets, Finite-lived			$ (6.2)

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		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Finite Lived Intangible Assets, Foreign Currency Translation Gain (Loss)	$ 0.1	$ 0.2	$ (0.4)	$ 0.5
Goodwill
Acquired Finite-Lived Intangible Assets [Line Items]
Foreign currency translation	$ 0.7	$ (1.2)	(1.8)	$ 0
NSM Holding Co LLC | Goodwill
Acquired Finite-Lived Intangible Assets [Line Items]
Foreign currency translation			(1.8)		$ 1.4
NSM Holding Co LLC | Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Finite Lived Intangible Assets, Foreign Currency Translation Gain (Loss)			$ (0.4)		$ 0.7

Debt - Narrative (Details)

Debt - Narrative (Details) - USD ($)	Apr. 07, 2020	Apr. 01, 2019	Dec. 03, 2018	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 23, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 15, 2018	May 11, 2018
Debt Instrument
Fair value investments				$ 2,656,900,000		$ 2,483,000,000	$ 2,656,900,000	$ 2,483,000,000	$ 2,746,000,000			$ 2,328,700,000
Total debt				349,800,000			349,800,000		283,500,000
Total commitment under revolving credit facility	$ 291.4				$ 234,000,000
Repayments of debt							(1,100,000)	(21,700,000)
NSM Bank Facility
Debt Instrument
Face amount														$ 100,000,000
Other Operations
Debt Instrument
Total commitment under revolving credit facility				16,300,000			16,300,000
NSM Holding Co LLC
Debt Instrument
Total debt				268,400,000			268,400,000		219,200,000
NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total debt				267,000,000			267,000,000		217,400,000
Face amount				$ 273,400,000	220,700,000	222,300,000	$ 273,400,000	222,300,000	$ 221,300,000		$ 186,400,000	$ 180,400,000
Percentage of discounted future cash flows							10.00%
Debt, weighted average interest rate, all-in				7.21%			7.21%		6.60%
Kudu | Kudu Bank Facility [Member]
Debt Instrument
Total commitment under revolving credit facility										$ 124,000,000
Kudu | Kudu Debt [Member]
Debt Instrument
Total debt				$ 70,800,000			$ 70,800,000		$ 53,600,000
Term Loan | Other Operations
Debt Instrument
Total commitment under revolving credit facility				11,300,000			11,300,000
Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Face amount	276,400,000			$ 273,400,000	224,000,000		$ 273,400,000		$ 221,300,000
Effective percentage				7.20%			7.20%		7.50%
Unamortized issuance cost				$ (6,400,000)			$ (6,400,000)		$ (3,900,000)
Repayments of debt				0		(500,000)	(600,000)	(1,000,000)
Proceeds from borrowings				52,400,000		42,900,000	52,400,000	42,900,000
Debt Instrument, Increase (Decrease), Other, Net				300,000		0	300,000	0
Term Loan | NSM Holding Co LLC | Other NSM
Debt Instrument
Total debt				1,400,000			1,400,000		$ 1,800,000
Face amount				$ 1,600,000			$ 1,600,000
Effective percentage				3.20%			3.20%		3.00%
Term Loan | Kudu | Kudu Bank Facility [Member]
Debt Instrument
Face amount				$ 74,000,000			$ 74,000,000		$ 57,000,000
Total commitment under revolving credit facility										57,000,000
Proceeds from Issuance of Long-term Debt				$ 5,000,000			$ 17,000,000
Term Loan | Kudu | Kudu Debt [Member]
Debt Instrument
Effective percentage				8.10%			8.10%		8.30%
Unamortized issuance cost				$ (3,200,000)			$ (3,200,000)		$ (3,400,000)
Term Loan | Other | Other
Debt Instrument
Total debt				10,600,000			10,600,000		10,700,000
Face amount				$ 10,900,000			$ 10,900,000		$ 11,100,000
Effective percentage				9.30%			9.30%		8.30%
Unamortized issuance cost				$ (300,000)			$ (300,000)		$ (400,000)
Delayed Draw Term Loans [Member] | Other Operations
Debt Instrument
Total commitment under revolving credit facility				3,000,000			3,000,000
Delayed Draw Term Loans [Member] | Kudu | Kudu Bank Facility [Member]
Debt Instrument
Total commitment under revolving credit facility										62,000,000
Delayed Draw Term Loans [Member] | Kudu | Kudu Debt [Member]
Debt Instrument
Total commitment under revolving credit facility									125,000,000
Revolving Credit Facility | Other Operations
Debt Instrument
Total commitment under revolving credit facility				2,000,000			2,000,000
Revolving Credit Facility | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total commitment under revolving credit facility	15,000,000				$ 10,000,000
Repayments of debt				0		(6,500,000)	0	(6,500,000)
Proceeds from borrowings				$ 0		0	$ 0	6,500,000
Revolving Credit Facility | Kudu | Kudu Bank Facility [Member]
Debt Instrument
Total commitment under revolving credit facility										$ 5,000,000
Interest Rate Swap | NSM Holding Co LLC
Debt Instrument
Derivative, fixed interest rate													2.97%
Derivative, variable interest rate				0.17%			0.17%
Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total debt				$ 148,400,000			$ 148,400,000
Total commitment under revolving credit facility													$ 151,000,000
Hedged Liability, Fair Value Hedge													$ 151,000,000
Derivative, fixed interest rate					2.97%
Debt, weighted average interest rate, all-in				6.78%			6.78%
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
Debt Instrument, Interest Rate, Increase (Decrease)							1.00%
Basis spread on variable rate					4.25%		5.50%
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
Debt Instrument, Interest Rate, Increase (Decrease)							1.25%
Basis spread on variable rate					4.75%		6.00%
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 | Line of Credit [Member] | Kudu | Kudu Bank Facility [Member]
Debt Instrument
Basis spread on variable rate							4.50%
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 | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Debt, weighted average interest rate, all-in				6.67%			6.67%
Designated as Hedging Instrument | Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total debt				$ 148,400,000			$ 148,400,000
Debt, weighted average interest rate, all-in				8.72%			8.72%
Not Designated as Hedging Instrument | Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total debt				$ 125,000,000			$ 125,000,000
Effective percentage				6.90%			6.90%
Kingsbridge [Member] | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Proceeds from borrowings				$ 52,400,000
Embrace | NSM Holding Co LLC
Debt Instrument
Proceeds from borrowings		$ 20,400,000
Embrace | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Proceeds from borrowings						$ 20,400,000
KBK Insurance Group, Inc. & KBK Premium Services, Inc.
Debt Instrument
Proceeds from borrowings			$ 30,100,000
Renewal Rights | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Proceeds from borrowings								$ 22,500,000
Carrying Value | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Total debt				267,000,000			$ 267,000,000		217,400,000
Debt securities issued by corporations
Debt Instrument
Fair value investments				505,800,000			505,800,000		467,200,000
Debt securities issued by corporations | AAA
Debt Instrument
Fair value investments				8,300,000			8,300,000		9,500,000
Debt securities issued by corporations | AA
Debt Instrument
Fair value investments				53,600,000			53,600,000		73,900,000
Debt securities issued by corporations | Standard & Poor's, A Rating [Member]
Debt Instrument
Fair value investments				314,100,000			314,100,000		288,500,000
Debt securities issued by corporations | BBB
Debt Instrument
Fair value investments				128,100,000			128,100,000		95,300,000
Debt securities issued by corporations | BB
Debt Instrument
Fair value investments				$ 1,700,000			$ 1,700,000		$ 0
United Kingdom, Pounds | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Face amount	42,500,000
United Kingdom, Pounds | London Interbank Offered Rate (LIBOR) | Minimum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Basis spread on variable rate							6.00%
United Kingdom, Pounds | London Interbank Offered Rate (LIBOR) | Maximum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Debt Instrument, Interest Rate, Increase (Decrease)							1.25%
Basis spread on variable rate							6.50%
Derivative, Cap Interest Rate				1.25%			1.25%
United Kingdom, Pounds | Kingsbridge [Member] | NSM Holding Co LLC
Debt Instrument
Proceeds from borrowings	42,500,000
United States of America, Dollars | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Debt Instrument
Face amount	52,400,000
United States of America, Dollars | Kingsbridge [Member] | NSM Holding Co LLC
Debt Instrument
Proceeds from borrowings	$ 52,400,000

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Tax Contingency [Line Items]
Effective income tax rate reconciliation, percent	18.20%	(0.60%)	4.20%	3.40%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%	21.00%
Income tax expense (benefit)	$ 24.1	$ (0.1)	$ (1.4)	$ 10.1
Continuing Operations | BAM
Income Tax Contingency [Line Items]
Income tax expense (benefit)		$ (1.9)		$ (3)

Derivatives - NSM Interest Rate

Derivatives - NSM Interest Rate Swap and Cap (Details) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jun. 04, 2020	Apr. 07, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 15, 2018	May 11, 2018
Derivative [Line Items]
Total commitment under revolving credit facility		$ 234,000,000					$ 291.4
Debt	$ 349,800,000			$ 349,800,000				$ 283,500,000
NSM Bank Facility
Derivative [Line Items]
Debt Instrument, Face Amount												$ 100,000,000
NSM Holding Co LLC
Derivative [Line Items]
Debt	268,400,000			268,400,000				219,200,000
NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Debt	$ 267,000,000			$ 267,000,000				$ 217,400,000
Debt, weighted average interest rate, all-in	7.21%			7.21%				6.60%
Debt Instrument, Face Amount	$ 273,400,000	220,700,000	$ 222,300,000	$ 273,400,000	$ 222,300,000			$ 221,300,000	$ 186,400,000	$ 180,400,000
Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Debt Instrument, Face Amount	$ 273,400,000	$ 224,000,000		$ 273,400,000			276,400,000	221,300,000
Interest Rate Swap | NSM Holding Co LLC
Derivative [Line Items]
Derivative, fixed interest rate											2.97%
Derivative, variable interest rate	0.17%			0.17%
Interest expense, net	$ 700,000		200,000	$ 1,200,000	400,000
Derivative, fair value, net			9,400,000		9,400,000			$ 6,600,000
Change in fair value of derivative	400,000		$ (2,400,000)	(2,800,000)	$ (4,300,000)
Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Total commitment under revolving credit facility											$ 151,000,000
Derivative, fixed interest rate		2.97%
Debt	$ 148,400,000			$ 148,400,000
Debt, weighted average interest rate, all-in	6.78%			6.78%
Interest Rate Cap | NSM Holding Co LLC
Derivative [Line Items]
Derivative, Cost of Hedge				$ 100,000
Derivative, Cap Interest Rate	1.25%			1.25%
LIBOR rate	0.14%			0.14%
Derivative, fair value, net	$ 100,000			$ 100,000
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%		5.50%
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%		6.00%
Designated as Hedging Instrument | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Debt, weighted average interest rate, all-in	6.67%			6.67%
Designated as Hedging Instrument | Interest Rate Swap | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Debt	$ 148,400,000			$ 148,400,000
Debt, weighted average interest rate, all-in	8.72%			8.72%
United Kingdom, Pounds | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Debt Instrument, Face Amount							42,500,000
United Kingdom, Pounds | Interest Rate Cap | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Debt Instrument, Face Amount						$ 42,500,000
United Kingdom, Pounds | 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				6.00%
United Kingdom, Pounds | Margin over London Interbank Offered Rate (LIBOR) | Maximum | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Derivative, Cap Interest Rate	1.25%			1.25%
Basis spread on variable rate				6.50%
United States of America, Dollars | Term Loan | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Debt Instrument, Face Amount							$ 52,400,000
United States of America, Dollars | Interest Rate Cap | NSM Holding Co LLC | NSM Bank Facility
Derivative [Line Items]
Debt Instrument, Face Amount						$ 52,400,000

Municipal Bond Guarantee - Narr

Municipal Bond Guarantee - Narrative (Details) $ in Millions

1 Months Ended

3 Months Ended

6 Months Ended

12 Months Ended

Jan. 31, 2020USD ($)

Apr. 30, 2018USD ($)

Mar. 31, 2020USD ($)

Dec. 31, 2018USD ($)

Mar. 31, 2018yr

Jun. 30, 2020USD ($)Contract

Jun. 30, 2019USD ($)

Dec. 31, 2019USD ($)Contract

Dec. 31, 2018USD ($)

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%

53.80%

50.00%

Percent change in discounted future cash flows

10.00%

Repayments of debt

$ 1.1

$ 21.7

Interest paid

$ 6.7

$ 7.3

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%

96.60%

HG Global | Common Stock

Guarantor Obligations [Line Items]

Ownership interest (as a percent)

88.40%

88.40%

89.60%

BAM

Guarantor Obligations [Line Items]

Percentage of risk premium ceded

60.00%

Number of years of change in interest rate

3

Year of U.S. Treasury rate | yr

1

Contracts outstanding | Contract

9,992

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

$ 67,591.5

$ 62,250.5

$ 1,100

Municipal bond outstanding interest

33,775.8

31,799.7

Municipal bond debt service outstanding

101,367.3

94,050.2

April 1, 2020 - December 31, 2020

10.2

2021

19.6

2022

18.5

2023

17.3

2024

16.2

2025

15

2026 and thereafter

121.8

Total gross unearned insurance premiums

218.6

198.4

HG Global

Guarantor Obligations [Line Items]

Collateral held in supplement trust

811.8

786.7

Interest receivable

$ 155

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

Interest receivable

$ 4.7

$ 7.5

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)

5.70%

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

$ 5

Second Quarter, year two | BAM

Guarantor Obligations [Line Items]

2021

4.9

Third Quarter, year two | BAM

Guarantor Obligations [Line Items]

2021

4.9

Fourth Quarter, year two | BAM

Guarantor Obligations [Line Items]

2021

$ 4.8

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

Municipal bond outstanding principal

$ 2,200

$ 2,200

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%

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)

4.60%

Scenario, Forecast | Fixed interest rate | Surplus Note | BAM

Guarantor Obligations [Line Items]

Derivative, fixed interest rate (as a percent)

8.00%

Municipal Bond Guarantee - Sche

Municipal Bond Guarantee - Schedule of Net Written Premiums (Details) - HG/BAM - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Direct written premiums	$ 21.3	$ 12.5	$ 31	$ 20.4
Assumed written premiums	0.2	0	0.2	0
Gross written premiums	21.5	12.5	31.2	20.4
Direct premiums earned	4.7	3.8	9.2	7.5
Assumed premiums earned	0.9	0.5	1.8	1
Gross earned premiums	$ 5.6	$ 4.3	$ 11	$ 8.5

Investments in Unconsolidated_3

Investments in Unconsolidated Entities (Details) - White Mountains - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Investments in unconsolidated affiliates
Other Investments	$ 898.1	$ 856.3
Equity method eligible private equity securities, at fair value
Investments in unconsolidated affiliates
Other Investments	815.3	761.7
Other unconsolidated investments
Investments in unconsolidated affiliates
Other Investments	$ 82.8	$ 94.6

Investments in Unconsolidated_4

Investments in Unconsolidated Entities - White Mountain's Investments (Details) - USD ($) $ in Millions	May 07, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	May 31, 2019
Schedule of Equity Method Investments [Line Items]
Stock Issued During Period, Value, Acquisitions	$ 15
Ownership interest (as a percent)		53.80%	50.00%	50.00%
Passport/DavidShield [Member]
Schedule of Equity Method Investments [Line Items]
Stock Issued During Period, Value, Acquisitions		$ 15
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%
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)		14.30%		17.50%
Minimum | Enlightenment Capital Funds
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)		9.40%		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)		62.30%		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)		35.00%		30.00%

Investments in Unconsolidated_5

Investments in Unconsolidated Entities - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended			6 Months Ended		12 Months Ended
	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Mar. 31, 2020	Feb. 26, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)		53.80%			53.80%		50.00%	50.00%
Total revenues		$ 259,600,000	$ 129,000,000		$ 200,400,000	$ 562,600,000
Benefits, Losses and Expenses		126,900,000	113,200,000		233,700,000	265,100,000
Total assets		4,000,300,000			4,000,300,000		$ 3,983,200,000
Total liabilities		937,000,000			937,000,000		838,500,000
Net income (loss) attributable to White Mountains’s common shareholders		115,400,000	20,500,000		(13,400,000)	304,900,000
MediaAlpha
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)									48.30%	61.00%
Fully diluted ownership interest (as a percent)									42.00%	58.90%
Assets, fair value	$ 114,700,000			$ 114,700,000					$ 114,700,000
Unrealized investment gain		15,000,000		$ 114,700,000	45,000,000	114,700,000	180,000,000
MediaAlpha
Schedule of Equity Method Investments [Line Items]
Total revenues		0	0		0	48,800,000
Benefits, Losses and Expenses		0	0		0	54,900,000
MediaAlpha, Kudu and Tuckerman
Schedule of Equity Method Investments [Line Items]
Total revenues		118,700,000	93,700,000		307,200,000	178,400,000
Expenses		131,900,000	83,600,000		273,800,000	171,100,000
Total assets		420,500,000			420,500,000		457,000,000
Total liabilities		200,200,000			200,200,000		$ 199,000,000
Net income (loss) attributable to White Mountains’s common shareholders		$ (21,800,000)	$ 10,100,000		$ 21,800,000	$ 7,300,000
MediaAlpha
Schedule of Equity Method Investments [Line Items]
Ownership interest (as a percent)		48.30%			48.30%		48.30%
Total revenues	122,700,000
Benefits, Losses and Expenses	115,800,000
Net income (loss) attributable to White Mountains’s common shareholders	$ 6,900,000

Earnings Per Share (Details)

Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic and diluted earnings per share numerators (in millions):
Net income (loss) attributable to White Mountains’s common shareholders	$ 115.4	$ 20.5	$ (13.4)	$ 304.9
Less: total income (loss) from discontinued operations	(1)	0	(0.1)	0.7
Net income (loss) from continuing operations attributable to White Mountains’s common shareholders	116.4	20.5	(13.3)	304.2
Allocation of earnings to participating restricted common shares	(1.6)	(0.3)	0.1	(3.6)
Basic and diluted earnings (losses) per share numerators	$ 114.8	$ 20.2	$ (13.2)	$ 300.6
Basic earnings per share denominators (in thousands):
Total average common shares outstanding during the period	3,107,500	3,183,500	3,142,800	3,177,800
Average unvested restricted common shares	(43,100)	(42,800)	(38,500)	(37,600)
Basic earnings (losses) per share denominator	3,064,400	3,140,700	3,104,300	3,140,200
Diluted earnings per share denominator (in thousands):
Total average common shares outstanding during the period	3,107,500	3,183,500	3,142,800	3,177,800
Average unvested restricted common shares	(43,100)	(42,800)	(38,500)	(37,600)
Diluted earnings (losses) per share denominator	3,064,400	3,140,700	3,104,300	3,140,200
Basic earnings per share (in dollars) - continuing operations:
Distributed earnings - dividends declared and paid	$ 0	$ 0	$ 1	$ 1
Undistributed earnings (losses)	37.46	6.44	(5.25)	94.71
Basic and diluted earnings (losses) per share	$ 37.46	$ 6.44	$ (4.25)	$ 95.71

Earnings Per Share - Undistribu

Earnings Per Share - Undistributed Net Earnings (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income (loss) attributable to White Mountains’s common shareholders, net of restricted common share amounts	$ 114.8	$ 20.2	$ (13.2)	$ 300.6
Dividends declared net of restricted common share amounts	0	0	(3.1)	(3.2)
Total undistributed net earnings (losses), net of restricted common share amounts	$ 114.8	$ 20.2	$ (16.3)	$ 297.4

Employee Share-Based Incentiv_3

Employee Share-Based Incentive Compensation Plans (Performance Shares) (Details) - Performance Share $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020USD ($)shares	Mar. 31, 2020USD ($)shares	Jun. 30, 2019USD ($)shares	Jun. 30, 2020USD ($)multipliershares	Jun. 30, 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	42,458	42,473	40,602	42,473	40,616
Shares paid or expired (in shares) | shares	0		0	(14,070)	(13,715)
New grants (in shares) | shares	0		1,900	14,055	15,600
Assumed forfeitures and cancellations | shares	0		(29)	0	(28)
Ending of period (in shares) | shares	42,458	42,458	42,473	42,458	42,473
Accrued Expense
Accrued expense at the beginning of period	$ 9.8	$ 43.7	$ 23.1	$ 43.7	$ 31.7
Payments and deferrals	0		0	(27.7)	(18.1)
Assumed forfeitures and cancellations	0		(0.2)	0.4	0
Expense recognized	6		7.9	(0.6)	17.2
Accrued expense at the end of the period	15.8	$ 9.8	$ 30.8	15.8	$ 30.8
Additional compensation cost that would be recognized if all outstanding performance shares vested	$ 17.3			$ 17.3

Employee Share-Based Incentiv_4

Employee Share-Based Incentive Compensation Plans (Performance Shares Granted Under the WTM Incentive Plan) (Details) - W T M Incentive Plan - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Performance Share | 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 Share | 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 | Restricted Share Cliff Vesting in January 2022 [Member]
Share-based compensation arrangement by share-based payment award
New grants (in shares)		1,900		15,600
White Mountains | Performance Share
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	43,105		43,105
Accrued Expense	$ 16		$ 16
Target Performance Shares Outstanding, Assumed forfeitures	(647)		(647)
Accrued Expense, Assumed forfeitures	(0.2)		(0.2)
Total Target Performance Shares Outstanding	42,458	42,473	42,458	42,473	42,458	42,473	40,602	40,616
Total Accrued Expense	$ 15.8	$ 30.8	$ 15.8	$ 30.8	$ 9.8	$ 43.7	$ 23.1	$ 31.7
New grants (in shares)	0	1,900	14,055	15,600
White Mountains | Performance Share | Performance Cycle 2018 to 2020
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	13,450		13,450
Accrued Expense	$ 8		$ 8
White Mountains | Performance Share | Performance Cycle 2019 to 2021
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	15,600		15,600
Accrued Expense	$ 5.9		$ 5.9
White Mountains | Performance Share | Performance Cycle 2020 to 2022
Share-based compensation arrangement by share-based payment award
Target Performance Shares Outstanding	14,055		14,055
Accrued Expense	$ 2.1		$ 2.1

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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Restricted Stock
Target Restricted Share Activity
Beginning of period (in shares)	43,105	41,495	43,395	41,510
Issued (in shares)	0	1,900	14,055	15,600
Vested (in shares)	0	0	(14,345)	(13,715)
Assumed forfeitures and cancellations	0	0	0	0
Ending of period (in shares)	43,105	43,395	43,105	43,395
Unamortized grant date fair value
Unamortized grant date fair value, beginning balance	$ 26.6	$ 22.8	$ 16.7	$ 12.5
Issued	0	1.7	15.1	14.5
Assumed forfeitures and cancellations	0	0	0	0
Expense recognized	(3.6)	(2.6)	(8.8)	(5.1)
Unamortized grant date fair value, ending balance	$ 23	$ 21.9	$ 23	$ 21.9
Restricted Share Cliff Vesting in January 2022
Unamortized grant date fair value
Target Performance Shares Outstanding	14,055		14,055
Restricted Share Cliff Vesting in January 2022 [Member]
Unamortized grant date fair value
New grants (in shares)		1,900		15,600

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
ROU lease asset	$ 34	$ 22.6
Operating lease liability	34.2	22.8
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
ROU lease asset	34	22.6	$ 23.2
Operating lease liability	$ 34.2	$ 22.8	$ 23.2

Leases - Schedule of Lease Cost

Leases - Schedule of Lease Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Leases [Abstract]
Lease cost	$ 2.1	$ 1.8	$ 4.1	$ 3.5
Less: sublease income	0.1	0.1	0.2	0.2
Net lease cost	$ 2	$ 1.7	$ 3.9	$ 3.3

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Payments on Operating Leases (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Leases [Abstract]
Remainder of 2019	$ 3.1
2020	6.8
2021	6.3
2022	6.1
2023	5.2
Thereafter	14.1
Total undiscounted lease payments	41.6
Less: present value adjustment	7.4
Operating lease liability	$ 34.2	$ 22.8

Leases - Schedule of Right-of-U

Leases - Schedule of Right-of-Use Assets and Lease Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
ROU lease asset	$ 34	$ 22.6
Lease liability	$ 34.2	$ 22.8
Operating lease, weighted average incremental borrowing rate, percent	4.80%	4.60%
HG/BAM
Lessee, Lease, Description [Line Items]
ROU lease asset	$ 9.8	$ 10.4
Lease liability	9.8	10.4
NSM Holding Co LLC
Lessee, Lease, Description [Line Items]
ROU lease asset	16.8	4.8
Lease liability	16.8	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	5.2	5.1
Lease liability	$ 5.4	$ 5.3

Non-controlling Interests (Deta

Non-controlling Interests (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ (102.7)	$ (116.8)
Total Non-Controlling Excluding Reciprocals
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ 31.9	$ 29.9
HG Global
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.10%	3.10%
Total non-controlling interests	$ 14.7	$ 14.4
NSM Holding Co LLC
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	3.40%	3.60%
Total non-controlling interests	$ 16.7	$ 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	0.80%	0.90%
Total non-controlling interests	$ 2.4	$ 2.2
Other Operations
Noncontrolling Interest [Line Items]
Total non-controlling interests	$ (1.8)	$ (1.5)
Build America Mutual
Noncontrolling Interest [Line Items]
Noncontrolling equity percentage	100.00%	100.00%
Total non-controlling interests	$ (134.6)	$ (146.7)

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		5 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2018	Jun. 30, 2020	Jun. 30, 2019
Segment reporting information
Net investment income	$ 19.6	$ 21		$ 42.5	$ 37
Net realized and unrealized investment gains				(3.8)	280.8
Total revenues	259.6	129		200.4	562.6
Total expenses	126.9	113.2		233.7	265.1
Pre-tax income (loss)	132.7	15.8		(33.3)	297.5
Other Revenue	179.4	61		50.9	395.2
Revenues from Contract with Customer and Products, Including Assessed Tax					167.4
Revenue from Contract with Customer, Including Assessed Tax	80.2	68		149.5	166.8
Kudu
Segment reporting information
Earned insurance premiums		0
Commission revenues		0
Total revenues	22.1	4.4		4.7	4.4
Insurance acquisition expenses		0
Cost of sales		0
Amortization		0
Interest expense		0
Total expenses		2.2
Pre-tax income (loss)		2.2
Other Revenue	22.1	4.4		4.7	4.4
Revenues from Contract with Customer and Products, Including Assessed Tax					0
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Other Operations
Segment reporting information
Total revenues	135.3	36.9		11	350.5
Other Revenue	131.2	35		2.6	347.3
Revenues from Contract with Customer and Products, Including Assessed Tax					3.2
Revenue from Contract with Customer, Including Assessed Tax	4.1	1.9		8.4	2.6
Kudu investments
Segment reporting information
Earned insurance premiums	0			0
Net investment income	5.6	4		12.9	4
Net realized and unrealized investment gains	16.5	0.4		(8.3)	0.4
Commission revenues	0			0
Other revenue	0	0		0.1	0
Total revenues	22.1	4.4		4.7	4.4
Insurance acquisition expenses	0			0
Cost of sales	0			0
Cost of sales	0			0
General and administrative expenses	2.8	2.2		5.3	2.2
Amortization	0.1	0		0.2	0
Interest expense	1.5	0		2.9	0
Total expenses	4.4	2.2		8.4	2.2
Pre-tax income (loss)	17.7			(3.7)	2.2
HG Global-BAM
Segment reporting information
Earned insurance premiums	5.6	4.3		11	8.5
Net investment income	4.9	5.4		10.4	10.7
Net realized and unrealized investment gains	14.4	11.5		20.5	23.3
Commission revenues	0	0		0
Other revenue	1.2	0.4		1.7	1
Total revenues	26.1	21.6		43.6	43.5
Insurance acquisition expenses	2.1	1.4		3.8	2.7
Cost of sales	0.2	0.1		0.2	0.2
Cost of sales	0	0		0
General and administrative expenses	12.5	12.3		27.2	26.6
Amortization	0	0		0
Interest expense	0			0
Total expenses	14.8	13.8		31.2	29.5
Pre-tax income (loss)	11.3	7.8		12.4	14
Other Revenue	26.1	21.6		43.6	43.5
Revenues from Contract with Customer and Products, Including Assessed Tax					0
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
NSM Holding Co LLC
Segment reporting information
Earned insurance premiums	0			0
Net investment income	0			0
Net realized and unrealized investment gains	0			0
Commission revenues	63	54.9		116	98.2
Other revenue	13.1	11.2		25.1	17.2
Total revenues	76.1	66.1		141.1	115.4
Insurance acquisition expenses	0
Cost of sales	0			0
Cost of sales	0			0
General and administrative expenses	48.5	32.8		88.1	58.1
Broker commission expenses	21	18.1		39.3	33.6
Change in fair value of contingent consideration earnout liabilities	(1.7)	6.3		(2.3)	7.6
Amortization	6.3	4.1		11.1	9.1
Interest expense	5.7	4.1		10	7.8
Total expenses	79.8	65.4		146.2	116.2
Pre-tax income (loss)	(3.7)	0.7		(5.1)	(0.8)
Other Revenue	0	0		0	0
Revenues from Contract with Customer and Products, Including Assessed Tax					115.4
Revenue from Contract with Customer, Including Assessed Tax	76.1	66.1		141.1	115.4
MediaAlpha
Segment reporting information
Commission revenues	0	0		0	48.8
Total revenues	0	0		0	48.8
Cost of sales	0	0		0	40.6
General and administrative expenses	0	0		0	12.5
Amortization	0	0		0	1.6
Interest expense	0	0		0	0.2
Total expenses	0	0		0	54.9
Pre-tax income (loss)					(6.1)
Other Revenue					0
Revenues from Contract with Customer and Products, Including Assessed Tax					48.8
Revenue from Contract with Customer, Including Assessed Tax					48.8
Other Segment
Segment reporting information
Earned insurance premiums	0	0		0
Net investment income	9.1	11.6		19.2	22.3
Net realized and unrealized investment gains	122	23.3		(16)	142.4
Realized gain and unrealized investment gain from the MediaAlpha Transaction		0		0	182.2
Commission revenues	1.9	1.3		4	2.6
Other revenue	2.3	0.7		3.8	1
Total revenues	135.3	36.9		11	350.5
Insurance acquisition expenses	0	0		0
Cost of sales	0			0
Cost of sales	2.2	1.6		4.2	2.7
General and administrative expenses	25.3	30.1		42.8	59.5
Amortization	0.2	0.1		0.4	0.1
Interest expense	0.2	0		0.5	0
Total expenses	27.9	31.8		47.9	62.3
Pre-tax income (loss)	107.4	5.1		(36.9)	288.2
Total
Segment reporting information
Earned insurance premiums	5.6	4.3		11	8.5
Net investment income	19.6	21		42.5	37
Net realized and unrealized investment gains	152.9	35.2		(3.8)	166.1
Realized gain and unrealized investment gain from the MediaAlpha Transaction					182.2
Commission revenues	64.9	56.2		120	149.6
Other revenue	16.6	12.3		30.7	19.2
Total revenues	259.6	129		200.4	562.6
Insurance acquisition expenses	2.1	1.4		3.8	2.7
Cost of sales	0.2	0.1		0.2	0.2
Cost of sales	2.2	1.6		4.2	43.3
General and administrative expenses	89.1	77.4		163.4	158.9
Broker commission expenses	21	18.1		39.3	33.6
Change in fair value of contingent consideration earnout liabilities	(1.7)	6.3		(2.3)	7.6
Amortization	6.6	4.2		11.7	10.8
Interest expense	7.4	4.1		13.4	8
Total expenses	126.9	113.2		233.7	265.1
Pre-tax income (loss)	132.7	15.8		(33.3)	297.5
NSM Holding Co LLC
Segment reporting information
Change in fair value of contingent consideration earnout liabilities	(1.7)	6.3	$ 2.6	2.3	7.6
Commission and Other Revenue [Member]
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	77.9	67.4		145.1	118
Commission and Other Revenue [Member] | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Commission and Other Revenue [Member] | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	1.8	1.3		4	2.6
Commission and Other Revenue [Member] | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Commission and Other Revenue [Member] | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	76.1	66.1		141.1	115.4
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	15.4	11.5		26.7	20.5
Real Estate [Member] | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Real Estate [Member] | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Real Estate [Member] | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Real Estate [Member] | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	15.4	11.5		26.7	20.5
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	7.3	6.5		13.6	12.3
Social Services [Member] | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Social Services [Member] | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Social Services [Member] | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Social Services [Member] | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	7.3	6.5		13.6	12.3
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	5.8	6		13.1	11.8
Other | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Other | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	1.8	1.3		4	2.6
Other | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Other | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	4	4.7		9.1	9.2
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	0.6		4.4	0.6
Product [Member] | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Product [Member] | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	2.3	0.6		4.4	0.6
Product [Member] | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Product [Member] | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Product [Member] | MediaAlpha
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	13.2	9.5		25.1	9.5
Pet [Member] | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Pet [Member] | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Pet [Member] | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Pet [Member] | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	13.2	9.5		25.1	9.5
Pet [Member] | MediaAlpha
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax					0
Advertising [Member]
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax					48.8
Advertising [Member] | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax					0
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	23.8	21.7		44.2	39.6
Specialty Transportation [Member] | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Specialty Transportation [Member] | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Specialty Transportation [Member] | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
Specialty Transportation [Member] | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	23.8	21.7		44.2	39.6
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	12.4	12.2		22.4	24.3
UNITED KINGDOM | Kudu
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
UNITED KINGDOM | Other Operations
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
UNITED KINGDOM | HG Global-BAM
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	0	0		0	0
UNITED KINGDOM | NSM Holding Co LLC
Segment reporting information
Revenue from Contract with Customer, Including Assessed Tax	$ 12.4	$ 12.2		$ 22.4	24.3
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	Jun. 30, 2020	Dec. 31, 2019
Balance Sheet Grouping, Financial Statement Captions
Carrying value	$ 349.8	$ 283.5
NSM Holding Co LLC
Balance Sheet Grouping, Financial Statement Captions
Carrying value	268.4	219.2
NSM Holding Co LLC | NSM Bank Facility
Balance Sheet Grouping, Financial Statement Captions
Carrying value	267	217.4
NSM Holding Co LLC | Carrying Value | NSM Bank Facility
Balance Sheet Grouping, Financial Statement Captions
Carrying value	267	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	272.2	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	70.8	53.6
Kudu | Estimate of Fair Value Measurement | Kudu Debt [Member]
Balance Sheet Grouping, Financial Statement Captions
Debt Instrument, Fair Value Disclosure	72.8	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	9.5	11.3
Term Loan | NSM Holding Co LLC | Other NSM
Balance Sheet Grouping, Financial Statement Captions
Carrying value	$ 1.4	$ 1.8

Commitments and Contingencies (

Commitments and Contingencies (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Loss Contingencies [Line Items]
Net gain from sale of discontinued operations, net of tax	$ (1)	$ 0	$ (0.1)	$ 0.7
Sirius Group | Swedish Tax Authority | Sirius Group
Loss Contingencies [Line Items]
Contingent liability	16.5		$ 16.5		$ 16.5
Change in contingent liability	$ (1)

Held for Sale and Discontinue_3

Held for Sale and Discontinued Operations - (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Discontinued Operations [Line Items}
Net gain from sale of discontinued operations, net of tax	$ (1)	$ 0	$ (0.1)	$ 0.7
Connecticut | Discontinued Operations, Held-for-sale
Discontinued Operations [Line Items}
Assets held for sale	3		3		$ 3
Sirius Group | Swedish Tax Authority | Sirius Group
Discontinued Operations [Line Items}
Contingent liability	16.5		$ 16.5		$ 16.5
Change in contingent liability	$ (1)

Held for Sale and Discontinue_4

Held for Sale and Discontinued Operations - EPS (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Basic and diluted earnings per share numerators (in millions):
Net income (loss) attributable to White Mountains’s common shareholders	$ 115.4	$ 20.5	$ (13.4)	$ 304.9
Less: total income (loss) from continuing operations, net of tax	116.4	20.5	(13.3)	304.2
Net (loss) income from discontinued operations attributable to White Mountains’s common shareholders	(1)	0	(0.1)	0.7
Basic and diluted earnings (losses) per share numerators	$ 114.8	$ 20.2	$ (13.2)	$ 300.6
Basic earnings per share denominators (in thousands):
Total average common shares outstanding during the period	3,107,500	3,183,500	3,142,800	3,177,800
Average unvested restricted common shares	(43,100)	(42,800)	(38,500)	(37,600)
Basic earnings (losses) per share denominator	3,064,400	3,140,700	3,104,300	3,140,200
Diluted earnings per share denominator (in thousands):
Total average common shares outstanding during the period	3,107,500	3,183,500	3,142,800	3,177,800
Average unvested restricted common shares	(43,100)	(42,800)	(38,500)	(37,600)
Diluted earnings per share denominator	3,064,400	3,140,700	3,104,300	3,140,200
Earnings Per Share, Basic and Diluted	$ 37.14	$ 6.44	$ (4.28)	$ 95.93
Discontinued Operations
Basic and diluted earnings per share numerators (in millions):
Net income (loss) attributable to White Mountains’s common shareholders	$ 115.4	$ 20.5	$ (13.4)	$ 304.9
Less: total income (loss) from continuing operations, net of tax	116.4	20.5	(13.3)	304.2
Net (loss) income from discontinued operations attributable to White Mountains’s common shareholders	(1)	0	(0.1)	0.7
Allocation of income for participating unvested restricted common shares	0	0	0	0
Basic and diluted earnings (losses) per share numerators	$ (1)	$ 0	$ (0.1)	$ 0.7
Basic earnings per share denominators (in thousands):
Total average common shares outstanding during the period	3,107,500	3,183,500	3,142,800	3,177,800
Average unvested restricted common shares	(43,100)	(42,800)	(38,500)	(37,600)
Basic earnings (losses) per share denominator	3,064,400	3,140,700	3,104,300	3,140,200
Diluted earnings per share denominator (in thousands):
Total average common shares outstanding during the period	3,107,500	3,183,500	3,142,800	3,177,800
Average unvested restricted common shares	(43,100)	(42,800)	(38,500)	(37,600)
Diluted earnings per share denominator	3,064,400	3,140,700	3,104,300	3,140,200
Earnings Per Share, Basic and Diluted	$ (0.32)	$ 0	$ (0.03)	$ 0.22