White Mountains Insurance (WTM) 10-K 28 Feb 22 2021 FY Annual report Financial data

Cover Page

Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2021	Feb. 23, 2022	Jun. 30, 2021
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2021
Current Fiscal Year End Date	--12-31
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, City or Town	Hanover,
Entity Address, State or Province	NH
Entity Address, Postal Zip Code	03755-2053
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 Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
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
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 3,482,682,176
Entity Common Stock, Shares Outstanding (in shares)		3,000,849
Documents Incorporated by Reference	Portions of the Registrant’s Definitive Proxy Statement to be filed with the Securities and Exchange Commission (“SEC”) pursuant to Regulation 14A under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), relating to the Registrant’s Annual General Meeting of Members scheduled to be held May 26, 2022 are incorporated by reference into Part III of this Form 10-K. With the exception of the portions of the Proxy Statement specifically incorporated herein by reference, the Proxy Statement is not deemed to be filed as part of this Form 10-K.
Entity Central Index Key	0000776867
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2021
Audit Information [Abstract]
Auditor Name	PricewaterhouseCoopers LLP
Auditor Location	Boston, Massachusetts
Auditor Firm ID	238

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Investments [Abstract]
Other long-term investments	$ 1,377.8	$ 786.8
Total investments	4,265.3	2,939
Total assets	7,000.7	4,831.4
Liabilities
Debt	693	376.4
Total liabilities	3,296	1,013.5
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 3,017,772 and 3,102,011 shares	3	3.1
Paid-in surplus	585.9	592.1
Retained earnings	2,957.5	3,311.2
Accumulated other comprehensive gain (loss), after-tax:
Net unrealized foreign currency translation and interest rate swap gains (losses)	1.7	(0.4)
Total White Mountains’s common shareholders’ equity	3,548.1	3,906
Non-controlling interests	156.6	(88.1)
Total equity	3,704.7	3,817.9
Total liabilities and equity	7,000.7	4,831.4
HG Global-BAM
Investments [Abstract]
Fixed maturity investments, at fair value	934.1	859.5
Short-term investments, at fair value	32.4	60.4
Total investments	966.5	919.9
Cash	19.8	42.8
Insurance premiums receivable	6.9	6.9
Deferred acquisition costs	33.1	27.8
Other assets	18.5	20.4
Total assets	1,044.8	1,017.8
Liabilities
Unearned insurance premiums	266.3	237.5
Accrued incentive compensation	24.7	25.7
Other liabilities	30.9	28.3
Total liabilities	321.9	291.5
Ark
Investments [Abstract]
Fixed maturity investments, at fair value	688.6	0
Short-term investments, at fair value	296.2	0
Common equity securities, at fair value	251.1	0
Other long-term investments	326.2	0
Total investments	1,562.1	0
Cash	67.8	0
Reinsurance recoverables	448.4	0
Cash pre-funded/placed in escrow for Ark Transaction		366.3
Insurance premiums receivable	416	0
Ceded unearned premiums	67.1	0
Deferred acquisition costs	108.2	0
Goodwill and other intangible assets	292.5	0
Other assets	64.9	0
Total assets	3,027	0
Liabilities
Loss and loss adjustment expense reserves	894.7	0
Unearned insurance premiums	495.9	0
Debt	185.9	0
Reinsurance payable	424.1	0
Contingent consideration	28	0
Other liabilities	93.8	0
Total liabilities	2,122.4	0
Accumulated other comprehensive gain (loss), after-tax:
Non-controlling interests	230.7	0
NSM
Investments [Abstract]
Cash	111.5	126.5
Premium and commission receivable	85	76.7
Goodwill and other intangible assets	725.4	736.8
Other assets	55.4	59.6
Total assets	977.3	999.6
Liabilities
Debt	272.1	272.6
Premiums payable	135.9	113.4
Contingent consideration	6.8	14.6
Other liabilities	80.5	91.2
Total liabilities	495.3	491.8
Kudu
Investments [Abstract]
Other long-term investments	669.5	400.6
Cash	21.4	7.8
Accrued investment income	16.9	9.8
Goodwill and other intangible assets	8.9	9.2
Other assets	10.4	2.8
Total assets	727.1	430.2
Liabilities
Debt	218.2	86.3
Other liabilities	42.8	10
Total liabilities	261	96.3
Other Operations
Investments [Abstract]
Fixed maturity investments, at fair value	286.2	347.7
Short-term investments, at fair value	137.3	82.4
Investment in MediaAlpha, at fair value	261.6	802.2
Other long-term investments	382.1	386.2
Total investments	1,067.2	1,618.5
Cash	38.8	34.1
Cash pre-funded/placed in escrow for Ark Transaction	0	646.3
Goodwill and other intangible assets	39.1	36.4
Other assets	63.3	46.2
Assets held for sale	16.1	2.3
Total assets	1,224.5	2,383.8
Liabilities
Debt	16.8	17.5
Accrued incentive compensation	48.5	70.1
Other liabilities	30.1	46.3
Total liabilities	$ 95.4	$ 133.9

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Cash restricted	$ 93.7	$ 78.4
Common shares, par value per share (in dollars per share)	$ 1	$ 1
Common shares, authorized shares (in shares)	50,000,000	50,000,000
Common shares, issued shares (in shares)	3,017,772	3,102,011
Common shares, outstanding shares (in shares)	3,017,772	3,102,011
NSM
Cash restricted	$ 89.2	$ 78.4
Kudu
Cash restricted	$ 4.5	$ 0

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Millions	10 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues:
Earned insurance premiums		$ 664.2	$ 22.8	$ 16.3
Net investment income		82.5	131	79.7
Net realized and unrealized investment gains (losses)		134.2	30.8	253.2
Realized gain (loss) from the 2019 MediaAlpha Transaction				67.5
Commission revenues		267.6	240.8	249.1
Other revenues		176.6	69.3	47.6
Total revenues		944.8	1,180.7	893.4
Expenses:
Insurance acquisition expenses		186.3	7	5.7
Loss and loss adjustment expenses		314.8
Cost of sales		69.3	11.3	48.1
General and administrative expenses		482.9	387.4	328.2
Broker commission expense		80.2	75.3	64.8
Change in fair value of contingent consideration		1	(3.3)	2.1
Amortization of other intangible assets		39.8	28.3	21.8
Loss on assets held for sale		28.7
Interest expense		43.8	29.5	17.6
Total expenses		1,246.8	535.5	488.3
Pre-tax income (loss) from continuing operations		(302)	645.2	405.1
Income tax (expense) benefit		(38.6)	20.5	(29.3)
Net income (loss) from continuing operations		(340.6)	665.7	375.8
Net gain (loss) from sale of discontinued operations, net of tax		18.7	(2.3)	0.8
Net income (loss)		(321.9)	663.4	376.6
Net income (loss) attributable to non-controlling interests		46.5	45.3	37.9
Net income (loss) attributable to White Mountains’s common shareholders		(275.4)	708.7	414.5
MediaAlpha
Revenues:
Net realized and unrealized investment gains (losses) from investment in MediaAlpha		(380.3)	686	180
Total revenues	$ 359.2
Expenses:
Total expenses	336.3
Net income (loss)	$ 22.9
HG Global-BAM
Revenues:
Earned insurance premiums		26.9	22.8	16.3
Net investment income		17.5	19.5	21.6
Net realized and unrealized investment gains (losses)		(22.9)	23.7	27.1
Realized gain (loss) from the 2019 MediaAlpha Transaction				0
Commission revenues		0	0	0
Other revenues		1.5	2.5	1.6
Total revenues		23	68.5	66.6
Expenses:
Insurance acquisition expenses		8.3	7	5.7
Loss and loss adjustment expenses		0
Cost of sales		0	0	0
General and administrative expenses		57.1	56.8	50.9
Broker commission expense		0	0	0
Change in fair value of contingent consideration		0	0	0
Amortization of other intangible assets		0	0	0
Loss on assets held for sale		0
Interest expense		0	0	0
Total expenses		65.4	63.8	56.6
Pre-tax income (loss) from continuing operations		(42.4)	4.7	10
HG Global-BAM | MediaAlpha
Revenues:
Net realized and unrealized investment gains (losses) from investment in MediaAlpha		0	0	0
Ark
Revenues:
Earned insurance premiums		637.3	0	0
Net investment income		2.9	0	0
Net realized and unrealized investment gains (losses)		16.5	0	0
Commission revenues		0
Other revenues		11.8	0	0
Total revenues		668.5	0	0
Expenses:
Insurance acquisition expenses		178	0	0
Loss and loss adjustment expenses		314.8	0	0
Cost of sales		0
General and administrative expenses		115.5	0	0
Broker commission expense		0
Change in fair value of contingent consideration		0
Amortization of other intangible assets		0
Loss on assets held for sale		0
Interest expense		7.3	0	0
Total expenses		615.6	0	0
Pre-tax income (loss) from continuing operations		52.9
Ark | MediaAlpha
Revenues:
Net realized and unrealized investment gains (losses) from investment in MediaAlpha		0
NSM
Revenues:
Earned insurance premiums		0	0	0
Net investment income		0	0	0
Net realized and unrealized investment gains (losses)		0	0	0
Realized gain (loss) from the 2019 MediaAlpha Transaction				0
Commission revenues		258	232.5	193.4
Other revenues		72.4	52.6	39.7
Total revenues		330.4	285.1	233.1
Expenses:
Insurance acquisition expenses		0	0	0
Loss and loss adjustment expenses		0
Cost of sales		0	0	0
General and administrative expenses		190.1	176.9	132.2
Broker commission expense		80.2	75.3	64.8
Change in fair value of contingent consideration		1	(3.3)	2.1
Amortization of other intangible assets		35.2	26.7	19.4
Loss on assets held for sale		28.7	0	0
Interest expense		23.3	22.1	16.7
Total expenses		358.5	297.7	235.2
Pre-tax income (loss) from continuing operations		(28.1)	(12.6)	(2.1)
NSM | MediaAlpha
Revenues:
Net realized and unrealized investment gains (losses) from investment in MediaAlpha		0	0	0
Kudu
Revenues:
Earned insurance premiums		0	0	0
Net investment income		43.9	29.5	14.7
Net realized and unrealized investment gains (losses)		89.9	15.9	6.3
Realized gain (loss) from the 2019 MediaAlpha Transaction				0
Commission revenues		0	0	0
Other revenues		0.2	0.3	0.2
Total revenues		134	45.7	21.2
Expenses:
Insurance acquisition expenses		0	0	0
Loss and loss adjustment expenses		0
Cost of sales		0	0	0
General and administrative expenses		14.5	11.8	10.1
Broker commission expense		0	0	0
Change in fair value of contingent consideration		0	0	0
Amortization of other intangible assets		0.3	0.3	0.2
Loss on assets held for sale		0
Interest expense		11.7	6	0.1
Total expenses		26.5	18.1	10.4
Pre-tax income (loss) from continuing operations		107.5	27.6	10.8
Kudu | MediaAlpha
Revenues:
Net realized and unrealized investment gains (losses) from investment in MediaAlpha		0	0	0
MediaAlpha
Revenues:
Earned insurance premiums				0
Net investment income				0
Net realized and unrealized investment gains (losses)				0
Realized gain (loss) from the 2019 MediaAlpha Transaction				0
Commission revenues		0	0	48.8
Other revenues				0
Total revenues		0	0	48.8
Expenses:
Insurance acquisition expenses				0
Cost of sales		0	0	40.6
General and administrative expenses		0		12.5
Broker commission expense				0
Change in fair value of contingent consideration				0
Amortization of other intangible assets		0	0	1.6
Interest expense		0	0	0.2
Total expenses		0	0	54.9
Pre-tax income (loss) from continuing operations				(6.1)
MediaAlpha | MediaAlpha
Revenues:
Net realized and unrealized investment gains (losses) from investment in MediaAlpha				0
Other Operations
Revenues:
Earned insurance premiums		0	0	0
Net investment income		18.2	82	43.4
Net realized and unrealized investment gains (losses)		50.7	(8.8)	219.8
Net realized and unrealized investment gains (losses) from investment in MediaAlpha		(380.3)	686	180
Realized gain (loss) from the 2019 MediaAlpha Transaction		0	0	67.5
Commission revenues		9.6	8.3	6.9
Other revenues		90.7	13.9	6.1
Total revenues		(211.1)	781.4	523.7
Expenses:
Insurance acquisition expenses		0	0	0
Loss and loss adjustment expenses		0
Cost of sales		69.3	11.3	7.5
General and administrative expenses		105.7	141.9	122.5
Broker commission expense		0	0	0
Change in fair value of contingent consideration		0	0	0
Amortization of other intangible assets		4.3	1.3	0.6
Loss on assets held for sale		0
Interest expense		1.5	1.4	0.6
Total expenses		180.8	155.9	131.2
Pre-tax income (loss) from continuing operations		$ (391.9)	$ 625.5	$ 392.5

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income (loss) attributable to White Mountains’s common shareholders	$ (275.4)	$ 708.7	$ 414.5
Other comprehensive income (loss), net of tax	1.9	7.3	(1.4)
Comprehensive income (loss)	(273.5)	716	413.1
Comprehensive (income) loss attributable to non-controlling interests	0.2	(0.5)	0
Comprehensive income (loss) attributable to White Mountains’s common shareholders	$ (273.3)	$ 715.5	$ 413.1
Basic earnings (loss) per share
Continuing operations (usd per share)	$ (95.53)	$ 227.72	$ 130.02
Discontinued operations (usd per share)	6.07	(0.75)	0.25
Total consolidated operations (usd per share)	(89.46)	226.97	130.27
Diluted earnings (loss) per share
Continuing operations (usd per share)	(95.53)	227.72	130.02
Discontinued operations (usd per share)	6.07	(0.75)	0.25
Total consolidated operations (usd per share)	(89.46)	226.97	130.27
Dividends declared and paid per White Mountains’s common share (usd per share)	$ 1	$ 1	$ 1

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Millions	Total	Total Equity	Common Shares and Paid-in Surplus	Retained Earnings	AOCL, After-tax	Total	Non-controlling Interests
Beginning balance at Dec. 31, 2018		$ 2,718.2	$ 584	$ 2,264.9	$ (5.8)	$ 2,843.1	$ (124.9)
Increase (Decrease) in Shareholders' Equity
Net income (loss)	$ 376.6	376.6		414.5		414.5	(37.9)
Net change in foreign currency translation and other		(1.4)			(1.4)	(1.4)
Comprehensive income (loss)		375.2		414.5	(1.4)	413.1	(37.9)
Dividends declared on common shares		(3.2)		(3.2)		(3.2)
Dividends to non-controlling interests		(2)					(2)
Issuances of common shares		2.2	2.2			2.2
Repurchases and retirements of common shares	(4.9)	(4.9)	(1.1)	(3.8)		(4.9)
BAM member surplus contribution, net of tax		57.6					57.6
Amortization of restricted share awards		10.6	10.6			10.6
Recognition of equity-based compensation expense of subsidiaries		1.5	1.5			1.5
Net contributions and dilution from other non-controlling interests		1.5	(0.9)			(0.9)	2.4
Acquisition of non-controlling interests		1.8					1.8
Deconsolidation of non-controlling interests associated with the MediaAlpha Transaction		(13.8)					(13.8)
Ending balance at Dec. 31, 2019		3,144.7	596.3	2,672.4	(7.2)	3,261.5	(116.8)
Increase (Decrease) in Shareholders' Equity
Net income (loss)	663.4	663.4		708.7		708.7	(45.3)
Net change in foreign currency translation and other		7.3			6.8	6.8	0.5
Comprehensive income (loss)		670.7		708.7	6.8	715.5	(44.8)
Dividends declared on common shares		(3.2)		(3.2)		(3.2)
Dividends to non-controlling interests		(2.1)					(2.1)
Issuances of common shares		1.5	1.5			1.5
Repurchases and retirements of common shares	(85.1)	(85.2)	(18.5)	(66.7)		(85.2)
BAM member surplus contribution, net of tax		68.9					68.9
Amortization of restricted share awards		16.6	16.6			16.6
Recognition of equity-based compensation expense of subsidiaries		2.4	2.3			2.3	0.1
Net contributions and dilution from other non-controlling interests		2.3	(3)			(3)	5.3
Acquisition of non-controlling interests		1.3					1.3
Ending balance at Dec. 31, 2020	3,817.9	3,817.9	595.2	3,311.2	(0.4)	3,906	(88.1)
Increase (Decrease) in Shareholders' Equity
Net income (loss)	(321.9)	(321.9)		(275.4)		(275.4)	(46.5)
Net change in foreign currency translation and other		2.1			2.1	2.1
Comprehensive income (loss)		(319.8)		(275.4)	2.1	(273.3)	(46.5)
Dividends declared on common shares		(3.1)		(3.1)		(3.1)
Dividends to non-controlling interests		(2.3)					(2.3)
Issuances of common shares		1.9	1.9			1.9
Issuances of shares of non-controlling interests		6.5					6.5
Repurchases and retirements of common shares	(107.5)	(107.5)	(18.9)	(88.6)		(107.5)
BAM member surplus contribution, net of tax		62.2					62.2
Amortization of restricted share awards		14.7	14.7			14.7
Recognition of equity-based compensation expense of subsidiaries		3.5	3			3	0.5
Net contributions and dilution from other non-controlling interests		0.4	(7)	13.4		6.4	(6)
Acquisition of non-controlling interests		230.3					230.3
Ending balance at Dec. 31, 2021	$ 3,704.7	$ 3,704.7	$ 588.9	$ 2,957.5	$ 1.7	$ 3,548.1	$ 156.6

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operations:
Net income (loss)	$ (321.9)	$ 663.4	$ 376.6
Adjustments to reconcile net income to net cash used for operations:
Net realized and unrealized investment (gains) losses	(134.2)	(30.8)	(253.2)
Realized (gain) loss from the 2019 MediaAlpha Transaction	0	0	(67.5)
Amortization of restricted share awards	14.7	16.6	10.5
Amortization and depreciation	63.6	43.4	29.8
Deferred income tax expense (benefit)	28.8	(36.2)	24.8
Net (gain) loss from sale of discontinued operations, net of tax	(18.7)	2.3	(0.8)
Other operating items:
Net change in reinsurance recoverables	(15.1)	0	0
Net change in insurance premiums receivable	(179.3)	0	0
Net change in commissions receivable	(7.4)	(3.1)	(26.8)
Net change in ceded unearned premiums	103.1	0	0
Net change in loss and loss adjustment expense reserves	198.7	0	0
Net change in premiums payable	12.8	1.8	25.1
Net change in unearned insurance premiums	198.6	39.1	35.8
Net change in deferred acquisition costs	(41.8)	(5.8)	(3.1)
Net change in reinsurance payable	(104.2)	0	0
Net change in restricted cash	15.3	22.1	6.3
Net change in investments in Kudu Participation Contracts	(178.9)	(118.3)	(118.4)
Net change in other assets and liabilities, net	24.2	30.9	20.4
Net cash provided from (used for) operations	38.6	(60.6)	(120.5)
Cash flows from investing activities:
Net change in short-term investments	54.3	58.7	21.9
Sales of fixed maturity investments	283.6	390	334.3
Maturities, calls and paydowns of fixed maturity investments	199	180.4	119.3
Sales of common equity securities	176.8	787.9	467.2
Distributions and redemptions of other long-term investments and settlements of forward contracts	106.4	69.9	29.4
Purchases of other long-term investments	(218)	(76.8)	(177.7)
Purchases of common equity securities	(203.4)	(33.8)	(29.8)
Purchases of fixed maturity and convertible investments	(1,216.7)	(537.7)	(539.2)
Purchases of consolidated subsidiaries, net of cash acquired of $52.2, $13.4, and $12.8 and including restricted cash of $0.0, $8.4, $0.0	(39.1)	(127.3)	(258)
Release of cash pre-funded/placed in escrow for Ark Transaction	646.3	(646.3)	0
Other investing activities, net	2.5	(0.4)	(27.3)
Net cash provided from (used for) investing activities	(208.3)	64.6	(59.9)
Cash flows from financing activities:
Draw down of debt and revolving lines of credit	436.7	84.6	206.4
Repayment of debt and revolving lines of credit	(154.7)	(4.5)	(22.9)
Cash dividends paid to the Company’s common shareholders	(3.1)	(3.2)	(3.2)
Acquisition of subsidiary shares by non-controlling interest shareholders	6.5	0	0
Common shares repurchased	(100.1)	(78.5)	0
Acquisition of subsidiary shares from non-controlling interest shareholders	(0.4)	(0.5)	(21.1)
Proceeds from issuance of shares to non-controlling interest shareholders	0	0	62.7
Net contributions from non-controlling interest shareholders	1.5	1.7	(26.2)
Contingent considerations related to acquisition of subsidiaries	0	(7)	(7.6)
Capital contributions from BAM members	62.2	68.9	54.6
Fidus Re premium payments	(8.8)	(3)	(3)
Other financing activities, net	(22.2)	(9.5)	(9.2)
Net cash provided from (used for) financing activities	217.6	49	230.5
Effect of exchange rate changes on cash	0.2	(2.8)	0.6
Net change in cash during the period - continuing operations, including the effect of exchange rate changes	48.1	50.2	50.7
Cash balance at beginning of year	211.2	161	110.3
Cash balance at end of year	259.3	211.2	161
MediaAlpha
Adjustments to reconcile net income to net cash used for operations:
Net realized and unrealized investment (gains) losses from MediaAlpha	$ 380.3	$ (686)	$ (180)

CONSOLIDATED STATEMENTS OF CA_2

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Cash Flows [Abstract]
Cash acquired	$ 52.2	$ 13.4	$ 12.8
Restricted cash acquired	0	8.4	0
Cash restricted	93.7	78.4	56.3
Cash held for sale	$ 0.7	$ 0	$ 0

Basis of Presentation and Signi

Basis of Presentation and Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	Basis of Presentation and Significant Accounting Policies Basis of Presentation White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”) 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, Suite 3B, 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 the Company, 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. See Note 18 — “Variable Interest Entities” . Intercompany transactions have been eliminated in consolidation. Certain amounts in the prior period financial statements have been reclassified to conform to the current presentation. 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 December 31, 2021, White Mountains’s reportable segments were HG Global/BAM, Ark, NSM, Kudu and Other Operations. On February 26, 2019, MediaAlpha, Inc. (“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 “2019 MediaAlpha Transaction”). MediaAlpha also repurchased a portion of the holdings of existing equityholders. White Mountains deconsolidated MediaAlpha as a result of the 2019 MediaAlpha Transaction, and consequently it was no longer a reportable segment. White Mountains’s consolidated statement of comprehensive income (loss) and its segment disclosures include MediaAlpha’s results of operations through the date of the 2019 MediaAlpha Transaction. See Note 2 — “ Significant Transactions ” and Note 16 — “ 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 purpose projects, 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 reinsurance 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 (the “BAM Surplus Notes”). As of December 31, 2021 and 2020, 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 Ark segment consists of Ark Insurance Holdings Limited and its subsidiaries (collectively, “Ark”). Ark is a specialty property and casualty insurance and reinsurance company that offers a wide range of niche insurance and reinsurance products, including property, marine & energy, specialty, accident & health and casualty. Ark underwrites select coverages through its two major subsidiaries in the United Kingdom and Bermuda. On January 1, 2021, White Mountains acquired a controlling ownership interest in Ark (the “Ark Transaction”). See Note 2 — “Significant Transactions” . As of December 31, 2021, White Mountains owned 72.0% of Ark on a basic shares outstanding basis (63.0% after taking account of management’s equity incentives). The remaining shares are owned by employees. In the future, management rollover shareholders could earn additional shares in Ark if and to the extent that White Mountains achieves certain multiple of invested capital return thresholds. If fully earned, these additional shares would represent 12.5% of the shares outstanding at closing. NSM is a full-service managing general agent (“MGA”) and program administrator with delegated binding authorities for specialty property and casualty insurance. The company places insurance in niche sectors such as specialty transportation, real estate, social services and pet. On behalf of its insurance carrier partners, NSM typically 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. On May 11, 2018, White Mountains acquired a controlling ownership interest in NSM. See Note 2 — “Significant Transactions” . As of December 31, 2021 and 2020, White Mountains owned 96.5% and 96.6% of the basic units outstanding of NSM (87.3% and 89.6% on a fully diluted, fully converted basis). The Kudu segment consists of Kudu Investment Management, LLC and its subsidiaries (collectively “Kudu”). 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, generally tied to gross revenues and designed to generate immediate strong, stable cash yields. On April 4, 2019, White Mountains acquired a controlling ownership interest in Kudu (the “Kudu Transaction”). See Note 2 — “Significant Transactions” . As of December 31, 2021 and 2020, White Mountains owned 99.3% and 99.3% of the basic units outstanding of Kudu (84.7% and 85.4% on a fully diluted, fully converted basis). The Other Operations segment consists of the Company and its wholly-owned subsidiary, White Mountains Capital, LLC, (“WM Capital”) 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 2019 MediaAlpha Transaction), PassportCard Limited (“PassportCard”) and DavidShield Life Insurance Agency (2000) Ltd. (“DavidShield”) (collectively, “PassportCard/ DavidShield”), Elementum Holdings LP (“Elementum”), Kudu (for periods prior to the Kudu Transaction), certain other consolidated and unconsolidated entities (“Other Operating Businesses”) and certain other assets. 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 customer acquisition technology platform that facilitates real-time transactions between buyers and sellers of consumer referrals (i.e., clicks, calls and leads), primarily in the property & casualty, health and life insurance verticals. MediaAlpha generates revenue by earning a fee for each consumer referral sold on its platform. A transaction becomes payable only on a qualifying consumer action, and is not contingent on the sale of a product to the consumer. MediaAlpha’s core verticals are property & casualty insurance, health insurance and life insurance. White Mountains deconsolidated MediaAlpha as a result of the 2019 MediaAlpha Transaction and stopped reporting it as a segment. Following the 2019 MediaAlpha Transaction, White Mountains’s non-c ontrolling equity interest in MediaAlpha was accounted for at fair value within other long-term investments. See Note 2 — “Significant Transactions” . Held for Sale and Discontinued Operations White Mountains recognizes assets and liabilities classified as held for sale at the lower of carrying value on the date the asset is initially classified as held for sale or fair value less costs to sell. At the time of reclassification to held for sale, White Mountains ceases recognizing depreciation and amortization on assets held for sale. The results of operations of a business that has either been disposed of or are classified as held for sale are reported in discontinued operations if the disposal of the business represents a strategic shift that has (or will have) a major effect on White Mountains operations and financial results. See Note 21 — “Held for Sale and Discontinued Operations” . Significant Accounting Policies Investment Securities As of December 31, 2021 and 2020, White Mountains’s invested assets consisted of securities and other investments held for general investment purposes. White Mountains’s portfolio of fixed maturity investments, common equity securities, its investment in MediaAlpha, and other long-term investments held for general investment purposes are generally classified as trading securities and are reported at fair value as of the balance sheet date. Changes in net unrealized investment gains (losses) are reported pre-tax in revenues. Realized investment gains (losses) are accounted for using the specific identification method and are reported pre-tax in revenues. Premiums and discounts on all fixed maturity investments are amortized and 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 fair value, which approximated amortized or accreted cost as of December 31, 2021 and 2020. White Mountains’s invested assets that are measured at fair value include fixed maturity investments, common equity securities, its investment in MediaAlpha, and other long-term investments, that consists primarily of unconsolidated entities, including non-controlling equity interests in the form of revenue and earnings participation contracts (“Kudu’s Participation Contracts”), a bank loan fund, private equity funds, hedge funds, Lloyd’s trust deposits, insurance-linked securities (“ILS”) funds and private debt instruments. Whenever possible, White Mountains estimates fair value using valuation methods that maximize the use of quoted prices and other observable inputs. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants (an exit price) at a particular measurement date. 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 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”). Assets and liabilities carried at fair value include substantially all of White Mountains’s investment portfolio, and derivative instruments, both exchange-traded and over the counter instruments. Valuation of assets and liabilities measured at fair value require management to make estimates and apply judgment to matters that may carry a significant degree of uncertainty. In determining fair value estimates, White Mountains uses a variety of valuation approaches and inputs. Whenever possible, White Mountains estimates fair value using valuation methods that maximize the use of quoted market prices or other observable inputs. Where appropriate, assets and liabilities measured at fair value have been adjusted for the effect of counterparty credit risk. White Mountains uses outside pricing services and brokers to assist in determining fair values. The outside pricing services White Mountains uses have indicated that they will only provide prices where observable inputs are available. As of December 31, 2021, approximately 68% of the investment portfolio recorded at fair value was priced based upon quoted market prices or other observable inputs. Level 1 Measurements Investments valued using Level 1 inputs include White Mountains’s fixed maturity investments, primarily investments in U.S. Treasuries and short-term investments, which include U.S. Treasury Bills, common equity securities, and its investment in MediaAlpha following the MediaAlpha IPO. For investments in active markets, White Mountains uses the quoted market prices provided by outside pricing services to determine fair value. Level 2 Measurements Investments valued using Level 2 inputs include fixed maturity investments which have been disaggregated into classes, including debt securities issued by corporations, municipal obligations and mortgage and asset-backed securities. Investments valued using Level 2 inputs also include certain passive exchange traded funds (“ETFs”) that track U.S. stock indices such as the S&P 500 Index, but are traded on foreign exchanges, which White Mountains values using the fund manager’s published net asset value per share (“NAV”) to account for the difference in market close times. In circumstances where quoted market prices are unavailable or are not considered reasonable, White Mountains estimates the fair value using industry standard pricing methodologies and observable inputs such as benchmark yields, reported trades, broker-dealer quotes, issuer spreads, benchmark securities, bids, offers, credit ratings, prepayment speeds, reference data including research publications and other relevant inputs. Given that many fixed maturity investments do not trade on a daily basis, the outside pricing services evaluate a wide range of fixed maturity investments by regularly drawing parallels from recent trades and quotes of comparable securities with similar features. The characteristics used to identify comparable fixed maturity investments vary by asset type and take into account market convention. White Mountains’s process to assess the reasonableness of the market prices obtained from the outside pricing sources covers substantially all of its fixed maturity investments and includes, but is not limited to, the evaluation of pricing methodologies and a review of the pricing services’ quality control procedures on at least an annual basis, a comparison of its invested asset prices obtained from alternate independent pricing vendors on at least a semi-annual basis, monthly analytical reviews of certain prices and a review of the underlying assumptions utilized by the pricing services for select measurements on an ad hoc basis throughout the year. White Mountains also performs back-testing of selected investment sales activity to determine whether there are any significant differences between the market price used to value the security prior to sale and the actual sale price of the security on an ad-hoc basis throughout the year. Prices provided by the pricing services that vary by more than $0.5 million and 5% from the expected price based on these assessment procedures are considered outliers, as are prices that have not changed from period to period and prices that have trended unusually compared to market conditions. In circumstances where the results of White Mountains’s review process does not appear to support the market price provided by the pricing services, White Mountains challenges the vendor provided price. If White Mountains cannot gain satisfactory evidence to support the challenged price, White Mountains will rely upon its own internal pricing methodologies to estimate the fair value of the security in question. The valuation process described above is generally applicable to all of White Mountains’s fixed maturity investments. The techniques and inputs specific to asset classes within White Mountains’s fixed maturity investments for Level 2 securities that use observable inputs are as follows: Debt Securities Issued by Corporations The fair value of debt securities issued by corporations is determined from a pricing evaluation technique that uses information from market sources and integrates relative credit information, observed market movements, and sector news. Key inputs include benchmark yields, reported trades, broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including sector, coupon, credit quality ratings, duration, credit enhancements, early redemption features and market research publications. Municipal Obligations The fair value of municipal obligations is determined from a pricing evaluation technique that uses information from market makers, brokers-dealers, buy-side firms, and analysts along with general market information. Key inputs include benchmark yields, reported trades, issuer financial statements, material event notices and new issue data, as well as broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including type, coupon, credit quality ratings, duration, credit enhancements, geographic location and market research publications. Mortgage and Asset-Backed Securities and Collateralized Loan Obligations The fair value of mortgage and asset-backed securities and collateralized loan obligations is determined from a pricing evaluation technique that uses information from market sources and leveraging similar securities. Key inputs include benchmark yields, reported trades, underlying tranche cash flow data, collateral performance, plus new issue data, as well as broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including issuer, vintage, loan type, collateral attributes, prepayment speeds, default rates, recovery rates, cash flow stress testing, credit quality ratings and market research publications. Level 3 Measurements Fair value estimates for investments that trade infrequently and have few or no quoted market prices or other observable inputs are classified as Level 3 measurements. Investments valued using Level 3 fair value estimates are based upon unobservable inputs and include investments in certain fixed maturity investments, common equity securities and other long-term investments where quoted market prices or other observable inputs are unavailable or are not considered reliable or reasonable. Level 3 valuations are generated from techniques that use assumptions not observable in the market. These unobservable inputs reflect White Mountains’s assumptions of what market participants would use in valuing the investment. In certain circumstances, investment securities may start out as Level 3 when they are originally issued, but as observable inputs become available in the market, they may be reclassified to Level 2. Transfers of securities between levels are based on investments held as of the beginning of the period. Other Long-Term Investments As of December 31, 2021, White Mountains owned a portfolio of other long-term investments valued at $1.4 billion, that consisted primarily of unconsolidated entities, including Kudu’s Participation Contracts, a bank loan fund, private equity funds, a hedge fund, Lloyd’s trust deposits, ILS funds and private debt instruments. As of December 31, 2021, $890.6 million of White Mountains’s other long-term investments that consisted primarily of unconsolidated entities, including Kudu’s Participation Contracts and private debt instruments were classified as Level 3 investments in the GAAP fair value hierarchy, were not actively traded in public markets and did not have readily observable market prices. The determination of the fair value of these securities involves significant management judgment, and the use of valuation models and assumptions that are inherently subjective and uncertain. As of December 31, 2021, $482.5 million of White Mountains’s other long-term investments, consisting of a bank loan fund, private equity funds, a hedge fund, Lloyd’s trust deposits and ILS funds, were valued at fair value using NAV as a practical expedient. Investments for which fair value is measured at NAV using the practical expedient are not classified within the fair value hierarchy. White Mountains may use a variety of valuation techniques to determine fair value depending on the nature of the investment, including a discounted cash flow analysis, market multiple approach, cost approach and/or liquidation analysis. On an ongoing basis, White Mountains also considers qualitative changes in facts and circumstances, which may impact the valuation of unconsolidated entities, including economic and market changes in relevant industries, changes to the entity’s capital structure, business strategy and key personnel, and any recent transactions relating to the unconsolidated entity. On a quarterly basis, White Mountains evaluates the most recent qualitative and quantitative information of the business and completes a fair valuation analysis for all Level 3 other long-term investments. Periodically, and at least on an annual basis, White Mountains uses a third-party valuation firm to complete an independent valuation analysis of significant unconsolidated entities. Other Long-term Investments - NAV White Mountains’s portfolio of other long-term investments includes investments in a bank loan fund, private equity funds, hedge funds, Lloyd’s trust deposits and ILS funds, which are valued at fair value using NAV as a practical expedient. White Mountains employs a number of procedures to assess the reasonableness of the fair value measurements for other long-term investments measured at NAV, including obtaining and reviewing periodic and audited annual financial statements as well as periodically discussing each fund’s pricing with the fund manager. However, since the fund managers do not provide sufficient information to evaluate the pricing methods and inputs for each underlying investment, White Mountains considers the valuation inputs to be unobservable. The fair value of White Mountains’s other long-term investments measured at NAV are generally determined using the fund manager’s NAV. In the event that White Mountains believes the fair value differs from the NAV reported by the fund manager due to illiquidity or other factors, White Mountains will adjust the reported NAV to more appropriately represent the fair value of its investment. 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 and the interest reserve account that Kudu maintains under its credit facility, are classified as restricted. 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 its consolidated balance sheet. Changes in the fair value of derivative instruments that meet the criteria for hedge accounting are recognized in other comprehensive income (loss) and reclassified into current period pre-tax income (loss) 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 (loss). As of December 31, 2021 and 2020, White Mountains holds interest rate cap derivative instruments that do not meet the criteria for hedge accounting. As of December 31, 2021 and 2020, White Mountains holds an interest rate swap derivative instrument that meets the criteria for hedge accounting. See Note 9 — “Derivatives” . Municipal Bond Guarantee Insurance All of the contracts issued by BAM are accounted for as insurance contracts under ASC 944-605, Financial Guarantee Insurance Contracts. For capital appreciation bonds, par is adjusted to the estimated equivalent par value for current interest paying bonds. See Note 10 — “Municipal Bond Guarantee Insurance” . Premiums are generally received upfront and an unearned premium revenue liability, equal to the amount of the premium received, is established at contract inception. Premium revenues are recognized in revenue over the period of the contracts in proportion to the amount of insurance protection provided using a constant rate. The constant rate is calculated based on the relationship between the par outstanding in a given reporting period compared with the sum of each of the par amounts outstanding for all periods. Insurance premiums receivable represents amounts due from customers for municipal bond insurance policies. Installment premiums are measured at the present value of contractual premiums, discounted at the risk-free rate, which is set at the inception of the insurance contract. Deferred acquisition costs represent commissions, premium taxes, excise taxes and other costs which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent they relate to successful contract acquisitions over the applicable premium recognition period as acquisition expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income. A premium deficiency is recognized if the sum of expected loss and loss adjustment expenses (“LAE”), expected dividends to policyholders, unamortized acquisition costs, and maintenance costs exceeds related unearned premiums and anticipated investment income. A premium deficiency is recognized by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs then a liability is accrued for the excess deficiency. BAM’s obligation for outstanding contracts consists of the unearned premium reserve and any loss reserves. Loss reserves are recorded only to the extent that the present value of the expected amount of any losses to be paid, net of any expected recoveries, exceeds the associated unearned premium reserve. As of December 31, 2021 and 2020, BAM did not have any loss or loss adjustment expense reserves. Property and Casualty Insurance and Reinsurance Ark writes a diversified portfolio of reinsurance and insurance, including property, marine & energy, specialty, accident & health and casualty, through its Lloyd’s Syndicates 4020 and 3902 (the “Syndicates”) and its wholly-owned subsidiary Group Ark Insurance Limited (“GAIL”). Ark accounts for insurance and reinsurance policies that it writes in accordance with ASC 944, Financial Services - Insurance . Ark’s premiums written comprise premiums on insurance contracts incepted during the year as well as premium adjustments related to prior underwriting years. Insurance premiums are recognized as revenues over the loss exposure or coverage period in proportion to the level of insurance protection provided. In most cases, premiums are earned ratably over the term of the contract with unearned premiums calculated on a monthly pro-rata basis. Catastrophe premiums are earned in proportion to the level of insurance protection provided. Premiums earned are presented net of amounts ceded to reinsurers. Insurance premiums receivable, representing amounts due from insureds, are presented net of an allowance for uncollectible premiums, including expected credit losses. The allowance is based upon Ark’s ongoing review of amounts outstanding, historical loss data, including delinquencies and write-offs, current and forecasted economic conditions and other relevant factors. Credit risk is partially mitigated by Ark’s ability to cancel the policy if the policyholder does not pay the premium. Deferred acquisition costs comprise commission and brokerage fees and taxes which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent they relate to successful contract acquisitions over the applicable premium recognition period as insurance and reinsurance acquisition expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income. A premium deficiency is recognized if the sum of expected loss and LAE, expected dividends to policyholders, unamortized acquisition costs, and maintenance costs exceeds related unearned premiums and anticipated investment income. A premium deficiency is recognized by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs then a liability is accrued for the excess deficiency. Losses and LAE are charged against income as incurred. Unpaid losses and LAE, including estimates for amounts incurred but not reported (“IBNR”) are based on estimates of the ultimate costs of settling claims, including the effects of inflation and other societal and economic factors. Unpaid loss and LAE reserves represent management’s best estimate of ultimate losses and LAE, net of estimated salvage and subrogation recoveries, if applicable. Such estimates are regularly reviewed and updated and any resulting adjustments are reflected in current results of operations. The process of estimating loss and LAE involves a considerable degree of judgment by management and the ultimate amount of expense to be incurred could be considerably greater than or less than the amounts currently reflected in the financial statements. See Note 5 – “Loss and Loss Adjustment Expense Reserves” . As part of its enterprise risk management function, Ark purch

Significant Transactions

Significant Transactions	12 Months Ended
	Dec. 31, 2021
Significant Transactions [Abstract]
Significant Transactions	Significant Transactions MediaAlpha 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. MediaAlpha also repurchased a portion of the holdings of existing equityholders. White Mountains received net cash proceeds of $89.3 million from the 2019 MediaAlpha Transaction. White Mountains recognized a realized gain of $67.5 million and reduced its ownership interest to 48.3% of the basic units outstanding of MediaAlpha (42.0% on a fully diluted, fully converted basis) as a result of the 2019 MediaAlpha Transaction. White Mountains’s remaining ownership interest in MediaAlpha no longer met 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 (loss) 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. White Mountains elected the fair value option and the investment in MediaAlpha was initially measured at its estimated fair value of $114.7 million as of the transaction date, with the change in fair value of $114.7 million recognized as an unrealized investment gain. White Mountains recognized a total of $182.2 million of realized gain and unrealized investment gain on the 2019 MediaAlpha Transaction. On October 30, 2020, MediaAlpha completed the MediaAlpha IPO. In the offering, White Mountains sold 3.6 million shares and received total proceeds of $63.8 million. White Mountains also received $55.0 million of net proceeds related to a dividend recapitalization at MediaAlpha prior to the MediaAlpha IPO. Following the MediaAlpha IPO, White Mountains owned 20.5 million MediaAlpha shares, representing a 35.0% ownership interest (32.3% on a fully-diluted, fully converted basis). At the December 31, 2020 closing price of $39.07 per share, the value of White Mountains’s remaining investment in MediaAlpha was $802.2 million. On March 23, 2021, MediaAlpha completed a secondary offering of 8.05 million shares. In the secondary offering, White Mountains sold 3.6 million shares at $46.00 per share ($44.62 per share net of underwriting fees) for net proceeds of $160.3 million. As of December 31, 2021, White Mountains owned 16.9 million shares, representing a 28.0% basic ownership interest (25.7% fully-diluted/fully-converted basis). At the December 31, 2021 closing price of $15.44 per share, the fair value of White Mountains’s investment in MediaAlpha was $261.6 million. See Note 17 — “Equity-Method Eligible Investments”. Ark O n October 1, 2020, White Mountains entered into a subscription and purchase agreement (the “Ark SPA”) with Ark and certain selling shareholders (collectively with Ark, the “Ark Sellers”). Under the terms of the Ark SPA, White Mountains agreed to contribute $605.4 million of equity capital to Ark, at a pre-money valuation of $300.0 million, and to purchase $40.9 million of shares from the Ark Sellers. White Mountains also agreed to contribute up to an additional $200.0 million of equity capital to Ark in 2021. In accordance with the Ark SPA, in the fourth quarter of 2020 White Mountains pre-funded/placed in escrow a total of $646.3 million in preparation for closing the transaction, including $280.0 million funded directly to Lloyd’s on behalf of Ark under the terms of a credit facility agreement and $366.3 million placed in escrow, which is reflected on the balance sheet within the Other Operations segment as of December 31, 2020. On January 1, 2021, White Mountains completed the Ark Transaction in accordance with the terms of the Ark SPA. As of December 31, 2021, White Mountains owned 72.0% of Ark on a basic shares outstanding basis (63.0% after taking account of management’s equity incentives). The remaining shares are owned by employees. In the future, management rollover shareholders could earn additional shares in Ark if and to the extent that White Mountains achieves certain multiple of invested capital return threshold. If fully earned, these additional shares would represent 12.5% of the shares outstanding at closing. White Mountains recognized total assets acquired related to the Ark Transaction of $2.5 billion, including goodwill and other intangible assets of $292.5 million, and total liabilities of $1.7 billion, including contingent consideration of $22.5 million and non-controlling interest of $220.2 million. Ark incurred transaction costs of $25.3 million in the first quarter of 2021. In the third quarter of 2021, Ark issued $163.3 million of floating rate unsecured subordinated notes (the “Ark 2021 Subordinated Notes”) in three separate transactions. See Note 7 — “Debt” . In connection with the issuance of the Ark 2021 Subordinated Notes, White Mountains and Ark terminated White Mountains’s commitment to provide up to $200.0 million of additional equity capital to Ark in 2021. The following presents additional details of the assets acquired and liabilities assumed as of the January 1, 2021 acquisition date: Millions As of January 1, 2021 Investments $ 594.3 Cash 52.0 (1) Reinsurance recoverables 433.4 Insurance premiums receivable 236.7 Ceded unearned premiums 170.2 Value of in-force business acquired 71.7 Other assets 88.9 Loss and loss adjustment expense reserves (696.0) Unearned insurance premiums (326.1) Debt (46.4) Ceded reinsurance payable (528.3) Other liabilities (25.9) Net tangible assets acquired 24.5 Goodwill 116.8 Other intangible assets - syndicate underwriting capacity 175.7 Deferred tax liability on other intangible assets (33.4) Net assets acquired $ 283.6 (1) Cash excludes the White Mountains cash contribution of $605.4 as part of the Ark Transaction. The values of net tangible assets acquired and the resulting goodwill, other intangible assets and contingent consideration were recorded at fair value using Level 3 inputs. The majority of the tangible assets acquired and liabilities assumed were recorded at their carrying values, as their carrying values approximated their fair values due to their short-term nature. The fair values of goodwill, other intangible assets and the contingent consideration liability were internally estimated primarily based on the income approach. The income approach estimates fair value based on the present value of the cash flows that the assets are expected to generate in the future. White Mountains developed internal estimates for the expected future cash flows and discount rates used in the present value calculations. The value of in-force business acquired represents the estimated profits relating to the unexpired contracts, net of related prepaid reinsurance, at the acquisition date through the expiration date of the contracts. During 2021, Ark recognized $64.2 million of amortization expense on the value of in-force business acquired. The value of the syndicate underwriting capacity intangible asset was estimated using net cash flows attributable to Ark’s rights to write business in the Lloyd’s market. The value of the in-force business acquired and the syndicate underwriting capacity were estimated using a discounted cash flow method. Significant inputs to the valuation models include estimates of growth in premium revenues, investment returns, claim costs, expenses and discount rates based on a weighted average cost of capital. In evaluating the fair value of Ark’s loss and loss adjustment expense reserves, White Mountains determined that the risk-free rate of interest was approximately equal to the risk factor reflecting the uncertainty within the reserves and that no adjustment was necessary. For the year ended December 31, 2021, Ark recognized pre-tax expense of $5.5 million for the change in the fair value of its contingent consideration liabilities. Any future adjustments to contingent consideration liabilities will be recognized through pre-tax income (loss). As of December 31, 2021, Ark recognized total contingent consideration liabilities of $28.0 million. Ark’s segment income and expenses for 2021 are presented in Note 16 — “Segment Information.” NSM On May 18, 2018, NSM acquired 100% of Fresh Insurance, which is an insurance broker that offers non-standard personal lines products in the United Kingdom. NSM paid $49.6 million of upfront cash consideration for Fresh Insurance. NSM borrowed $51.0 million to fund the transaction. During the nine months ended September 30, 2019, NSM paid a purchase price adjustment of an additional $0.7 million of consideration. The purchase price was subject to additional adjustments based upon growth in EBITDA during two earnout periods ending in February 2020 and 2022. NSM did not make any payments related to the first Fresh Insurance earnout period. On April 12, 2021, NSM sold Fresh Insurance’s motor business for net proceeds of £1.1 million ($1.5 million based upon the foreign exchange spot rate as of the transaction date). As of March 31, 2021, the Fresh Insurance motor business was classified as held for sale and NSM recognized a loss of $28.7 million in 2021. See Note 21 — “Held for Sale and Discontinued Operations” . 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 and NSM borrowed $30.1 million to fund the transaction. White Mountains recognized $59.4 million of goodwill and other intangible assets, reflecting acquisition date fair values, for which the relative fair values of goodwill and other intangible assets had not yet been finalized as of December 31, 2018. During 2019, NSM determined that the relative values of goodwill and other intangible assets recorded in connection with the KBK transaction were $32.6 million and $32.7 million, reflecting acquisition date fair values. The purchase price was subject to additional adjustments based upon growth in EBITDA during three earn out periods ending in December 2019, December 2020 and December 2021. During 2019, NSM recorded a purchase price adjustment of $5.9 million relating to the fair value of the contingent consideration liability in connection with the acquisition. During 2021 and 2020, NSM paid $6.7 million and $6.4 million related to the first and second KBK earnout periods. 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 obligation to acquire the Renewal Rights from AIG. See Note 20 — “Commitments and Contingencies” . 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 the acquisition date fair value. 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 for the professional contractor and freelancer markets in the United Kingdom. NSM paid £107.2 million ($132.2 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 ($52.4 million based upon the foreign exchange spot rate at the date of acquisition) to fund the transaction. During 2020, NSM determined that the relative values of goodwill and other intangible assets recorded in connection with the Kingsbridge transaction were $111.5 million and $20.2 million, reflecting acquisition date fair values. The purchase price was subject to adjustment based upon growth in EBITDA during an earnout period ending in January 2022. During 2020, NSM initially recorded a liability relating to the fair value of the Kingsbridge contingent consideration of $4.1 million. During 2021 and 2020, NSM recognized pre-tax income (loss) of $(0.3) million and $4.1 million for the change in fair value of the Kingsbridge contingent consideration liability. As of December 31, 2021, there was no Kingsbridge contingent consideration liability. As of December 31, 2020, the Kingsbridge contingent consideration liability was $0.3 million. On August 6, 2021, NSM acquired 100% of J.C. Taylor Insurance (“J.C. Taylor”), an MGA offering classic and antique collector car insurance. NSM paid $49.6 million of upfront cash consideration for J.C. Taylor. NSM borrowed $35.0 million under its credit facility to fund the acquisition. The remaining balance was funded with cash on hand at NSM. NSM recognized total assets acquired related to the J.C. Taylor transaction of $60.3 million, including goodwill and other intangible assets of $55.7 million, and total liabilities of $10.7 million. During 2021, NSM determined that the relative values of goodwill and other intangible assets recorded in connection with the J.C. Taylor transaction were $28.5 million and $27.2 million, reflecting acquisition date fair values. The contingent consideration liabilities related to NSM’s acquisitions are subject to adjustments based upon EBITDA, EBITDA projections, and present value factors for acquired entities. For the years ended December 31, 2021 and 2020, NSM recognized pre-tax expense (income) of $1.0 million and $(3.3) million for the change in the fair value of its contingent consideration liabilities. Any future adjustments to contingent consideration liabilities under the agreements will be recognized through pre-tax income (loss). As of December 31, 2021 and 2020, NSM recognized total contingent consideration liabilities of $6.8 million and $14.6 million. During 2021 and 2020, NSM paid $8.8 million and $7.0 million of contingent consideration liabilities related to KBK and the U.K. vertical. 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 unit 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 for the period from April 4, 2019 to December 31, 2019. 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. During the fourth quarter of 2021, White Mountains increased its total capital commitment to Kudu by an additional $19.0 million to $369.0 million. As of December 31, 2021, Kudu has fully drawn on the total capital commitment. PassportCard/DavidShield On January 24, 2018, White Mountains acquired a 50.0% ownership interest in DavidShield, its joint venture partner in PassportCard. DavidShield is a managing general agency that is the leading provider of expatriate medical insurance in Israel and uses the same card-based delivery system as PassportCard. As part of the transaction, White Mountains reorganized its equity stake in PassportCard so that White Mountains and its partner in DavidShield would each own 50.0% of both businesses. To facilitate the transaction, White Mountains provided financing to its partner in the form of a non-interest bearing loan that is secured by the partner’s equity in PassportCard and DavidShield. The gross purchase price for the 50.0% interest in DavidShield was $41.8 million, or $28.3 million net of the financing provided for the restructuring. On May 7, 2020, White Mountains made an additional $15.0 million investment in PassportCard/DavidShield to support operations through the ongoing COVID-19 pandemic. The transaction increased White Mountains’s ownership interest from 50.0% to 53.8%, 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	12 Months Ended
	Dec. 31, 2021
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, its investment in MediaAlpha 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 fair value, which approximated amortized cost, as of December 31, 2021 and 2020. Other long-term investments consist primarily of unconsolidated entities, including Kudu’s Participation Contracts, a bank loan fund, private equity funds, hedge funds, Lloyd’s trust deposits, ILS funds and private debt investments. 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, dividend income from common equity securities, distributions from its investment in MediaAlpha and distributions from other long-term investments. The following table presents pre-tax net investment income for the years ended December 31, 2021, 2020 and 2019: Year Ended December 31, Millions 2021 2020 2019 Fixed maturity investments $ 28.8 $ 29.0 $ 32.4 Short-term investments .6 1.1 5.0 Common equity securities .1 6.6 13.5 Investment in MediaAlpha — 59.9 8.0 Other long-term investments 56.3 35.6 22.1 Amount attributable to TPC Providers (1.0) — — Total investment income 84.8 132.2 81.0 Third-party investment expenses (2.3) (1.2) (1.3) Net investment income, pre-tax $ 82.5 $ 131.0 $ 79.7 Net Realized and Unrealized Investment Gains (Losses) The following table presents net realized and unrealized investment gains (losses) for the years ended December 31, 2021, 2020 and 2019: Year Ended December 31, Millions 2021 2020 2019 Realized investment gains (losses) Fixed maturity investments $ 3.9 $ 10.9 $ 4.9 Short-term investments (.1) .4 .2 Common equity securities .4 137.2 85.9 Investment in MediaAlpha 160.3 63.8 — Other long-term investments (7.7) (25.2) 5.6 Net realized investment gains (losses) 156.8 187.1 96.6 Unrealized investment gains (losses) Fixed maturity investments $ (42.2) $ 27.5 $ 38.6 Common equity securities 14.9 (130.6) 109.8 Investment in MediaAlpha (540.6) 622.2 180.0 Other long-term investments 172.7 10.6 8.2 Net unrealized investment gains (losses) (395.2) 529.7 336.6 Net realized and unrealized investment gains (losses), before amount attributable to TPC providers (1) (238.4) 716.8 433.2 Amount attributable to TPC Providers (7.7) — — Net realized and unrealized investment gains (losses) $ (246.1) $ 716.8 $ 433.2 Fixed maturity and short-term investments Net realized and unrealized investment gains (losses) $ (38.4) $ 38.8 $ 43.7 Less: net realized and unrealized gains (losses) on investment (8.4) (8.7) 1.0 Net unrealized investment gains (losses) on investment $ (30.0) $ 47.5 $ 42.7 Common equity securities and investment in MediaAlpha Net realized and unrealized investment gains (losses) on common equity securities $ 15.3 $ 6.6 $ 195.7 Net realized and unrealized investment gains (losses) from investment in MediaAlpha (380.3) 686.0 180.0 Total net realized and unrealized investment gains (losses) (365.0) 692.6 375.7 Less: net realized and unrealized gains (losses) on investment 20.3 38.3 24.0 Net unrealized investment gains (losses) on investment $ (385.3) $ 654.3 $ 351.7 (1) For 2021, 2020 and 2019, includes $(7.7), $4.0 and $(0.3) of realized and unrealized investment gains (losses) related to foreign currency exchange. For the years ended December 31, 2021, 2020 and 2019, all of White Mountains’s net realized and unrealized investment gains (losses) were recorded in the consolidated statements of operations. There were no investment gains (losses) recorded in other comprehensive income. White Mountains recognized gross realized investment gains of $212.3 million, $214.4 million and $104.0 million and gross realized investment losses of $55.5 million, $27.3 million and $7.4 million on sales of investment securities for the years ending December 31, 2021, 2020 and 2019. The following table presents total gains included in earnings attributable to net unrealized investment gains for Level 3 investments for the years ended December 31, 2021, 2020 and 2019 for investments still held at the end of the period: Year Ended December 31, Millions 2021 2020 2019 Other long-term investments (1) $ 98.9 $ 276.0 $ 181.9 Total net unrealized investment gains, pre-tax - Level 3 investments $ 98.9 $ 276.0 $ 181.9 (1) For 2020 and 2019, includes $278.7 and $180.0 of unrealized investment gains from White Mountains’s investment in MediaAlpha. Proceeds from the sales and maturities of investments, excluding short-term investments, totaled $0.8 billion, $1.4 billion and $1.0 billion for the years ended December 31, 2021, 2020 and 2019. 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 December 31, 2021 and 2020. December 31, 2021 Millions Cost or Gross Gross Net Foreign Carrying U.S. Government and agency obligations $ 212.1 $ .5 $ (1.1) $ — $ 211.5 Debt securities issued by corporations 993.3 8.7 (8.7) (.4) 992.9 Municipal obligations 276.4 16.8 (1.3) — 291.9 Mortgage and asset-backed securities 277.2 2.9 (2.5) — 277.6 Collateralized loan obligations 136.5 — (.4) (1.1) 135.0 Total fixed maturity investments $ 1,895.5 $ 28.9 $ (14.0) $ (1.5) $ 1,908.9 December 31, 2020 Millions Cost or Gross Gross Carrying U.S. Government and agency obligations $ 173.2 $ 3.1 $ — $ 176.3 Debt securities issued by corporations 522.8 24.7 (.1) 547.4 Municipal obligations 244.0 21.0 — 265.0 Mortgage and asset-backed securities 211.7 6.8 — 218.5 Total fixed maturity investments $ 1,151.7 $ 55.6 $ (.1) $ 1,207.2 The weighted average duration of White Mountains’s fixed income portfolio was 2.6 years, including short-term investments, and 3.2 years, excluding short-term investments, as of December 31, 2021. The following table presents the cost or amortized cost and carrying value of White Mountains’s fixed maturity investments by contractual maturity as of December 31, 2021. Actual maturities could differ from contractual maturities because borrowers may have the right to call or prepay certain obligations with or without call or prepayment penalties. December 31, 2021 Millions Cost or Amortized Cost Carrying Value Due in one year or less $ 136.7 $ 137.3 Due after one year through five years 866.2 865.0 Due after five years through ten years 365.7 371.5 Due after ten years 113.2 122.5 Mortgage and asset-backed securities and 413.7 412.6 Total fixed maturity investments $ 1,895.5 $ 1,908.9 The following tables present the cost or amortized cost, gross unrealized investment gains (losses), net foreign currency gains (losses), and carrying values of common equity securities, White Mountains’s investment in MediaAlpha and other long-term investments as of December 31, 2021 and 2020: December 31, 2021 Millions Cost or Gross Unrealized Gross Unrealized Losses Net Foreign Carrying Common equity securities $ 236.3 $ 16.1 $ — $ (1.3) $ 251.1 Investment in MediaAlpha $ — $ 261.6 $ — $ — $ 261.6 Other long-term investments $ 1,186.7 $ 239.0 $ (44.1) $ (3.8) $ 1,377.8 December 31, 2020 Millions Cost or Gross Unrealized Gross Unrealized Losses Net Foreign Carrying Investment in MediaAlpha $ — $ 802.2 $ — $ — $ 802.2 Other long-term investments $ 767.4 $ 95.8 $ (78.1) $ 1.7 $ 786.8 Fair Value Measurements As of December 31, 2021 and 2020, White Mountains used quoted market prices or other observable inputs to determine fair value for approximately 68% and 73% of the investment portfolio. See Note 1 — “Basis of Presentation and Significant Accounting Policies”. Fair Value Measurements by Level The following tables present White Mountains’s fair value measurements for investments as of December 31, 2021 and 2020 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, 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 by industry sector because investors often reference commonly used benchmarks and their subsectors to monitor risk and performance. Accordingly, White Mountains has further disaggregated this asset class 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. December 31, 2021 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 211.5 $ 211.5 $ — $ — Debt securities issued by corporations: Financials 264.2 — 264.2 — Consumer 178.1 — 178.1 — Technology 117.9 — 117.9 — Industrial 112.9 — 112.9 — Healthcare 112.8 — 112.8 — Utilities 70.9 — 70.9 — Communications 56.0 — 56.0 — Energy 48.0 — 48.0 — Materials 32.1 — 32.1 — Total debt securities issued by corporations 992.9 — 992.9 — Municipal obligations 291.9 — 291.9 — Mortgage and asset-backed securities 277.6 — 277.6 — Collateralized loan obligations 135.0 — 135.0 — Total fixed maturity investments 1,908.9 211.5 1,697.4 — Short-term investments 465.9 465.9 — — Common equity securities (1) 251.1 — 251.1 — Investment in MediaAlpha 261.6 261.6 — — Other long-term investments 895.3 — 4.7 890.6 Other long-term investments — NAV (2) 482.5 — — — Total other long-term investments 1,377.8 — 4.7 890.6 Total investments $ 4,265.3 $ 939.0 $ 1,953.2 $ 890.6 (1) Consist of investments in listed funds that predominantly invest in international equities. (2) Consists of a bank loan fund, private equity funds, a hedge fund, Lloyd’s trust deposits 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, 2020 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 176.3 $ 176.3 $ — $ — Debt securities issued by corporations: Financials 133.9 — 133.9 — Consumer 81.9 — 81.9 — Industrial 66.9 — 66.9 — Technology 66.7 — 66.7 — Healthcare 51.5 — 51.5 — Communications 44.5 — 44.5 — Energy 35.8 — 35.8 — Materials 33.9 — 33.9 — Utilities 32.3 — 32.3 — Total debt securities issued by corporations 547.4 — 547.4 — Municipal obligations 265.0 — 265.0 — Mortgage and asset-backed securities 218.5 — 218.5 — Total fixed maturity investments 1,207.2 176.3 1,030.9 — Short-term investments 142.8 142.8 — — Investment in MediaAlpha 802.2 802.2 — — Other long-term investments 614.2 — — 614.2 Other long-term investments — NAV (1) 172.6 — — — Total other long-term investments 786.8 — — 614.2 Total investments $ 2,939.0 $ 1,121.3 $ 1,030.9 $ 614.2 (1) 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. Investments Held on Deposit or as Collateral As of December 31, 2021 and 2020, investments of $479.5 million and $432.4 million, were held in trusts required to be maintained in relation to HG Global’s reinsurance agreements with BAM. BAM and one of the Other Operating Businesses are required to maintain deposits with certain insurance regulatory agencies in order to maintain their insurance licenses. The fair value of such deposits, which represent state deposits and are included within the investment portfolio, totaled $4.8 million and $11.9 million as of December 31, 2021 and 2020. Lloyd’s trust deposits are required of Lloyd's syndicates to protect policyholders in non-U.K. markets and are pledged into Lloyd’s trust accounts to provide a portion of the capital needed to support obligations at Lloyd’s. As of December 31, 2021, Ark held Lloyd’s trust deposits with a fair value of $113.8 million. The underwriting capacity of a member of Lloyd’s must be supported by providing a deposit (“Funds at Lloyd’s”) in the form of cash, securities or letters of credit in an amount determined by Lloyd’s. The amount of such deposit is calculated for each member through the completion of an annual capital adequacy exercise. These requirements allow Lloyd’s to evaluate that each member has sufficient assets to meet its underwriting liabilities plus a required solvency margin. As of December 31, 2021, the fair value of Ark’s Funds at Lloyd’s investment deposits totaled $342.8 million. As at December 31, 2021, Ark has $50.0 million of short-term investments pledged as collateral under an uncommitted stand by letter of credit. See Note 7 — “Debt”. 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 December 31, 2021 and 2020: Fair Value at December 31, Millions 2021 2020 AAA $ 12.0 $ 10.6 AA 85.0 57.9 A 490.4 318.3 BBB 396.8 159.6 BB — 1.0 Other 8.7 — Debt securities issued by corporations (1) $ 992.9 $ 547.4 (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 and Collateralized Loan Obligations The following table presents the fair value of White Mountains’s mortgage and asset-backed securities and collateralized loan obligations as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Millions Fair Value Level 2 Level 3 Fair Value Level 2 Level 3 Mortgage-backed securities: Agency: FNMA $ 125.4 $ 125.4 $ — $ 88.7 $ 88.7 $ — FHLMC 90.5 90.5 — 70.1 70.1 — GNMA 40.1 40.1 — 40.6 40.6 — Total agency (1) 256.0 256.0 — 199.4 199.4 — Non-agency: Residential .5 .5 — — — — Total non-agency .5 .5 — — — — Total mortgage-backed securities 256.5 256.5 — 199.4 199.4 — Other asset-backed securities: Credit card receivables 12.3 12.3 — 11.3 11.3 — Vehicle receivables 8.8 8.8 — 7.8 7.8 — Total other asset-backed securities 21.1 21.1 — 19.1 19.1 — Total mortgage and asset-backed securities 277.6 277.6 — 218.5 218.5 — Collateralized loan obligations 135.0 135.0 — — — — Total mortgage and asset-backed securities and $ 412.6 $ 412.6 $ — $ 218.5 $ 218.5 $ — (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). As of December 31, 2021, White Mountains’s investment portfolio included $135.0 million of collateralized loan obligations that are within the senior tranches of their respective fund securitization structures. All of White Mountains’s collateral loan obligations were rated AAA or AA as of December 31, 2021. Investment in MediaAlpha Following the MediaAlpha IPO, White Mountains’s investment in MediaAlpha is accounted for at fair value based on the publicly traded share price of MediaAlpha’s common stock and is presented as a separate line item on the balance sheet. At the December 31, 2021 closing price of $15.44 per share, the fair value of White Mountains’s investment in MediaAlpha was $261.6 million. See Note 2 — “Significant Transactions”. Other Long-Term Investments The following table presents the carrying values of White Mountains’s other long-term investments as of December 31, 2021 and 2020: Fair Value at Millions December 31, 2021 December 31, 2020 Kudu’s Participation Contracts $ 669.5 $ 400.6 PassportCard/DavidShield 120.0 95.0 Elementum Holdings L.P. 45.0 55.1 Other unconsolidated entities (1) 34.4 42.4 Total unconsolidated entities 868.9 593.1 Bank loan fund 163.0 — Private equity funds and hedge funds 153.8 121.2 Lloyd’s trust deposits 113.8 — ILS funds 51.9 51.4 Private debt investments 14.1 21.1 Other 12.3 — Total other long-term investments $ 1,377.8 $ 786.8 (1) Includes White Mountains’s non-controlling equity interests in certain private common equity securities, limited liability companies, convertible preferred securities and Simple Agreement for Future Equity (“SAFE”) investments. 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 December 31, 2021, White Mountains held investments in twelve private equity funds and one hedge fund. The largest investment in a single private equity fund or hedge fund was $31.3 million as of December 31, 2021 and $29.1 million as of December 31, 2020. The following table presents the fair value of investments and unfunded commitments in private equity funds and hedge funds by investment objective and sector as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Millions Fair Value Unfunded Fair Value Unfunded Private equity funds Aerospace/Defense/Government $ 69.8 $ 11.8 $ 69.1 $ 15.3 Financial services 67.7 29.3 23.5 30.4 Real estate 4.3 2.9 — — Manufacturing/Industrial — — 28.6 — Total private equity funds 141.8 44.0 121.2 45.7 Hedge funds European small/mid cap 12.0 — — — Total hedge funds 12.0 — — — Total private equity funds and hedge funds included in other long-term investments $ 153.8 $ 44.0 $ 121.2 $ 45.7 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 December 31, 2021: Millions 1 – 3 years 3 – 5 years 5 – 10 years >10 years Total Private equity funds — expected lock-up period remaining $ .1 $ 13.9 $ 116.3 $ 11.5 $ 141.8 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 December 31, 2021 and 2020, 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. White Mountains’s hedge fund investment is subject to a perpetual two-year restriction on redemption frequency from the initial investment in the fund and a 90-days advanced notice period requirement. Lloyd’s Trust Deposits White Mountains’s other long-term investments include Lloyd’s trust deposits, which consists of non-U.K. deposits and Canadian comingled pooled funds. The Lloyd’s trust deposits invest primarily in short-term government securities, agency securities and corporate bonds held in trusts that are managed by Lloyd's of London. These investments are required of Lloyd's syndicates to protect policyholders in non-U.K. markets and are pledged into Lloyd’s trust accounts to provide a portion of the capital needed to support obligations at Lloyd’s. The fair value of the Lloyd’s trust deposits is generally estimated using the NAV of the funds. As of December 31, 2021, White Mountains held Lloyd’s trust deposits with a fair value of $113.8 million. Bank Loan Fund White Mountains’s other long-term investments include a bank loan fund with a fair value of $163.0 million as of December 31, 2021. The fair value of this investment is estimated using the NAV of the fund. The bank loan fund’s investment objective is to provide, on an unleveraged basis, high current income consistent with preservation of capital and low duration. The bank loan fund primarily invests in a broad portfolio of U.S. dollar-denominated, non-investment grade, floating-rate senior secured loans and may invest in other financial instruments, such as secured and unsecured corporate debt, credit default swaps, reverse repurchase agreements, synthetic indices and cash and cash equivalents. The investment in the bank loan fund is subject to 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. White Mountains may redeem all or a portion of its bank loan fund investment as of any calendar month-end upon 15 calendar days advanced written notice. Insurance-Linked Securities Funds White Mountains’s other long-term investments include ILS fund investments. The fair value of these investments is generally estimated using the NAV of the funds. As of December 31, 2021, White Mountains held investments in ILS funds with a fair value of $51.9 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 ILS funds less certain due to the potential for loss development. In such circumstances, the impacted investments may be subject to additional lock-up provisions. ILS funds are typically 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. One of the ILS funds in White Mountains’s portfolio requires shareholders to provide advance redemption notice on or before September 15 of each calendar year. Amounts requested for redemption in this fund remain subject to market fluctuation until the underlying investment has fully matured or been commuted, which may be up to a period of three years from the start of each calendar year. Rollforward of Level 3 Investments Level 3 measurements as of December 31, 2021 and 2020 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 table presents the changes in White Mountains’s fair value measurements for Level 3 investments for the years ended December 31, 2021 and 2020: Level 3 Investments Millions Other Long-term Common Other Long-term Balance at December 31, 2020 $ 614.2 Balance at December 31, 2019 $ .1 654.0 Net realized and unrealized gains 117.3 Net realized and unrealized gains — 275.6 Amortization/accretion — Amortization/accretion — — Purchases 225.4 Purchases — 151.5 Sales (75.9) Sales (.1) (8.2) Effect of Ark Transaction 9.6 Effect of MediaAlpha IPO (1) — (458.7) Transfers in — Transfers in — — Transfers out — Transfers out — — Balance at December 31, 2021 $ 890.6 Balance at December 31, 2020 $ — $ 614.2 (1) Represents the reclassification of White Mountains’s investment in MediaAlpha from a level 3 measurement to a level 1 measurement in connection with the MediaAlpha IPO. See Note 2 - “Significant Transactions”. Fair Value Measurements — Transfers Between Levels - For Years Ended December 31, 2021 and 2020 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 2021 and 2020, 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 2021 and 2020, 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. During 2020, in connection with the MediaAlpha IPO, White Mountains’s investment in MediaAlpha was reclassified from a Level 3 measurement to a Level 1 measurement. Significant Unobservable Inputs The following tables present significant unobservable inputs used in estimating the fair value of White Mountains’s other long-term investments, classified within Level 3 as of December 31, 2021 and 2020. The tables below exclude $46.7 million and $27.6 million of Level 3 other long-term investments generally valued based on recent or expected transaction prices. The fair value of investments in private equity funds, hedge funds, Lloyd’s trust deposits, bank loans funds and ILS funds are generally estimated using the NAV of the funds. $ in Millions December 31, 2021 Description Valuation Technique(s) (1) Fair Value (2) Unobservable Inputs Discount Rate (6) Terminal Cash Flow Exit Multiple (x) or Terminal Revenue Growth Rate (%) (6) Kudu’s Participation Contracts (3)(4)(5) Discounted cash flow $669.5 18% - 23% 7x - 13x PassportCard/DavidShield Discounted cash flow $120.0 23% 4% Elementum Holdings, L.P. Discounted cash flow $45.0 17% 4% Private debt investments Discounted cash flow $9.4 8% N/A (1) Key inputs to the discounted cash flow analysis generally include projections of future revenue and earnings, discount rates and terminal exit multiples or growth rates. (2) Includes the net unrealized investment gains (losses) associated with foreign currency; foreign currency effects based on observable inputs. (3) 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. The weighted average discount rate and weighted average terminal cash flow exit multiple applied to Kudu’s Participation Contracts is 20% and 10x. (4) In 2021, Kudu deployed a total of $223.4 in new and existing Kudu Participation Contracts, including TIG Advisors, TK Partners, Third Eye Capital Management, Douglass Winthrop Advisors, Granahan Investment Management and Radcliffe Capital Management. (5) As of December 31, 2021, one of Kudu’s Participation Contracts with a total fair value of $78.8 was valued using a probability weighted expected return method, which was based on a discounted cash flow analysis and an expected sale transaction. (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, 2020 Description Valuation Technique(s) (1) Fair Value (2) Unobservable Inputs Discount Rate (6) Terminal Cash Flow Exit Multiple (x) or Terminal Revenue Growth Rate (%) (6) Kudu’s Participation Contracts (3)(4) Discounted cash flow $400.6 18% - 23% 7x - 12x PassportCard/DavidShield (5) Discounted cash flow $95.0 23% 4% Elementum Holdings, L.P. Discounted cash flow $55.1 17% 4% Private debt investments Discounted cash flow $17.1 4% - 8% N/A Other Discounted cash flow $18.8 20% - 24% 4% (1) Key inputs to the discounted cash flow analysis generally include projections of future revenue and earnings, discount rates and terminal exit multiples or growth rates. (2) Includes the net unrealized investment gains (losses) associated with foreign currency; foreign currency effects based on observable inputs. (3) 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. The weighted average discount rate and weighted average terminal cash flow exit multiple applied to Kudu’s Participation Contracts is 20% and 10x. (4) In 2020, Kudu deployed a total of $118.2 in new Kudu Participation Contracts, including Creation Investments Capital, Sequoia Financial Group, Channel Capital and Ranger Investment Management. (5) In 2020, White Mountains made an additional $15.0 investment in PassportCard/DavidShield. See Note 2 — “Significant Transactions” . (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.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets	12 Months Ended
	Dec. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets White Mountains accounts for business combinations using the acquisition method. Under the acquisition method, White Mountains recognizes and measures the assets acquired, liabilities assumed and any non-controlling interest in the acquired entities at their acquisition date fair values. The estimated acquisition date fair values, generally consisting of intangible assets and liabilities for contingent consideration, may be recorded at provisional amounts in circumstances where the information necessary to complete the acquisition accounting is not available at the reporting date. Any such provisional amounts are finalized as measurement period adjustments within one year of the acquisition date. The following table presents the economic lives, acquisition date fair values, accumulated amortization and net carrying values for other intangible assets and goodwill, by company as of December 31, 2021 and 2020: $ in Millions Weighted Average Economic December 31, 2021 December 31, 2020 Acquisition Date Fair Value Accumulated Amortization Impairments and Amounts Allocated to Held for Sale Net Carrying Value Acquisition Date Fair Value Accumulated Amortization Impairments Net Carrying Value Goodwill: Ark N/A $ 116.8 $ — $ — $ 116.8 $ — $ — $ — $ — NSM (1) N/A 533.4 — 30.2 503.2 506.4 — — 506.4 Kudu N/A 7.6 — — 7.6 7.6 — — 7.6 Other Operations N/A 17.9 — — 17.9 11.5 — — 11.5 Total goodwill 675.7 — 30.2 645.5 525.5 — — 525.5 Other intangible Ark Underwriting N/A 175.7 — — 175.7 — — — — NSM (1) Customer 9.0 159.9 57.0 3.5 99.4 136.2 36.7 3.5 96.0 Trade names 18 68.6 11.9 1.0 55.7 65.4 8.3 1.0 56.1 Information 0 3.1 1.4 1.7 — 3.1 1.4 1.7 — Renewal rights 12 82.5 15.8 — 66.7 82.5 4.9 — 77.6 Other 3.3 1.1 .7 — .4 1.7 1.0 — .7 Subtotal 315.2 86.8 6.2 222.2 288.9 52.3 6.2 230.4 Kudu Trade names 7 2.2 .9 — 1.3 2.2 .6 — 1.6 Other Operations Trade names 17.5 8.2 1.5 — 6.7 3.6 .3 — 3.3 Customer 13.0 18.8 4.5 — 14.3 14.2 1.4 — 12.8 Insurance licenses (2) N/A — — — — 8.6 — — 8.6 Other 5.3 .3 .1 — .2 .3 .1 — .2 Subtotal 27.3 6.1 — 21.2 26.7 1.8 24.9 Total other intangible assets 520.4 93.8 6.2 420.4 317.8 54.7 6.2 256.9 Total goodwill and other intangible assets $ 1,196.1 $ 93.8 $ 36.4 1,065.9 $ 843.3 $ 54.7 $ 6.2 782.4 Goodwill and other intangible assets attributed to non-controlling interests (117.6) (28.1) Goodwill and other intangible assets included in White Mountains’s common $ 948.3 $ 754.3 (1) During 2021, NSM’s goodwill and intangible assets includes $(1.5) and $(0.3) of the effect of foreign currency translation. During 2020, NSM’s goodwill and intangible assets includes $13.4 and $1.6 of the effect of foreign currency translation. (2) As of December 31, 2021, White Mountains has classified one of its Other Operating Businesses as held for sale, which includes of $8.6 of insurance licenses. See Note. 21 — “Held for Sale and Discontinued Operations” . Intangible Assets Valuation Methods The goodwill recognized for the entities shown above is attributed to expected future cash flows. The acquisition date fair values of other intangible assets with finite lives are estimated using income approach techniques, which use future expected cash flows to develop a discounted present value amount. The multi-period-excess-earnings method estimates fair value using the present value of the incremental after-tax cash flows attributable solely to the other intangible asset over its remaining life. This approach was used to estimate the fair value of other intangible assets associated with trade names, customer relationships and contracts and information technology. The relief-from-royalty method was used to estimate fair value for other intangible assets that relate to rights that could be obtained via a license from a third-party owner. Under this method, the fair value is estimated using the present value of license fees avoided by owning rather than leasing the asset. This technique was used to estimate the fair value of domain names, certain trademarks and brand names. The with-or-without method estimates the fair value of an other intangible asset that provides an incremental benefit. Under this method, the fair value of the other intangible asset is calculated by comparing the value of the entity with and without the other intangible asset. This approach was used to estimate the fair value of favorable lease terms. On at least 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. The following table presents a summary of the acquisition date fair values of goodwill and other intangible assets for acquisitions completed during 2021 and 2020: $ in Millions Acquisition of Subsidiary/ Asset Goodwill and Other Intangible Assets (1) Acquisition Date Kingsbridge $ 131.7 April 7, 2020 J.C. Taylor 55.7 August 6, 2021 Total NSM segment $ 187.4 Ark $ 292.5 January 1, 2021 Other Operations $ 31.1 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. Goodwill and Other Intangible Asset Rollforward The following table presents the change in goodwill and other intangible assets: December 31, 2021 December 31, 2020 Millions Goodwill Other Intangible Assets Total Goodwill and Other Intangible Assets Goodwill Other Intangible Assets Total Goodwill and Other Intangible Assets Beginning balance $ 525.5 $ 256.9 $ 782.4 $ 394.7 $ 260.0 $ 654.7 Acquisition of businesses (1) 71.5 — 71.5 140.0 — 140.0 Ark Transaction 116.8 175.7 292.5 — — — Attribution of acquisition date fair value estimates between goodwill and other intangible assets (2) (36.5) 36.5 — (23.2) 23.2 — Measurement period adjustments (5) (.1) — (.1) .6 6.6 7.2 Dispositions of businesses — — — — — — Amortization — (39.8) (39.8) — (28.3) (28.3) Impairments (3) — — — — (6.2) (6.2) Assets held for sale (8.6) (8.6) — — — Loss on assets held for sale (4) (30.2) — (30.2) — — — Foreign currency translation (1.5) (.3) (1.8) 13.4 1.6 15.0 Ending balance $ 645.5 $ 420.4 $ 1,065.9 $ 525.5 $ 256.9 $ 782.4 (1) During 2021, amounts include acquisition of J.C. Taylor of $55.7 and acquisitions within Other Operations of $15.8. During 2020, amounts include acquisition of Kingsbridge of $125.1 and acquisitions within Other Operations of $14.9. (2) During 2021, the attribution of acquisition date fair value estimates between goodwill and other intangible assets were $27.2 for the acquisition of J.C. Taylor and $9.3 for acquisitions within Other Operations segment. During 2020, the attribution of acquisition date fair value estimates between goodwill and other intangible assets were $13.6 for the acquisition of Kingsbridge and $9.6 for acquisitions within Other Operations segment. (3) In 2020, impairments relate to NSM’s UK vertical. (4) Relates to the sale of NSM’s Fresh Insurance’s motor business recorded in 2021. This amount excludes $1.5 of net proceeds related to the sale. (5) Measurement period adjustments relate to updated information about acquisition date fair values of assets acquired and liabilities assumed. During 2021, adjustments relate to acquisitions within the Other Operations segment. During 2020, adjustments primarily relate to contingent considerations of $4.1 in connection with the acquisition of Kingsbridge and the remaining amount related to acquisitions within Other Operations segment. During the years ended December 31, 2021 and 2020, White Mountains did not recognize any impairments to goodwill. On April 12, 2021, NSM sold Fresh Insurance’s motor business. During 2021, in connection with the sale, White Mountains recognized a loss of $28.7 million. See Note 21 — “Held for Sale and Discontinued Operations” . During 2020, White Mountains recognized impairments of other intangible assets of $6.2 million related to the UK vertical. The impairments related to lower premium volumes, including due to the impact of the COVID-19 pandemic, and certain reorganization initiatives at the UK vertical. During 2019, White Mountains recognized an impairment of other intangible assets of $2.4 million related to Fresh Insurance and impairments of goodwill and other intangible assets of $7.6 million and $0.4 million, respectively, related to Other Operations. Impairment charges are presented within general and administrative assets expenses for the segments affected on the statement of operations. Amortization of Other Intangible Assets Amortization expense was $39.8 million, $28.3 million and $21.8 million for the years ended December 31, 2021, 2020 and 2019. White Mountains expects to recognize amortization expense in each of the next five years as the following table presents: Millions Amortization Expense 2022 $ 39.4 2023 36.0 2024 32.7 2025 30.5 2026 and years after 106.1 Total (1) $ 244.7 (1) Excludes Ark’s indefinite-lived intangible assets of $175.7.

Loss and Loss Adjustment Expens

Loss and Loss Adjustment Expense Reserves	12 Months Ended
	Dec. 31, 2021
Insurance Loss Reserves [Abstract]
Loss and Loss Adjustment Expense Reserves	Loss and Loss Adjustment Expense Reserves Ark establishes loss and LAE reserves that are estimates of amounts needed to pay claims and related expenses in the future for insured events that have already occurred. The process of estimating reserves involves a considerable degree of judgment by management and, as of any given date, is inherently uncertain. HG Re and BAM do not have any outstanding loss and LAE reserves related to BAM’s municipal bond guarantee business. Loss and LAE reserves are typically comprised of case reserves for claims reported and reserves for losses that have occurred but for which claims have not yet been reported, referred to as IBNR reserves. IBNR reserves include a provision for expected future development on case reserves. Case reserves are estimated based on the experience and knowledge of claims staff regarding the nature and potential cost of each claim and are adjusted as additional information becomes known or payments are made. IBNR reserves are derived by subtracting paid loss and LAE and case reserves from estimates of ultimate loss and LAE. Actuaries estimate ultimate loss and LAE using various generally accepted actuarial methods applied to known losses and other relevant information. Like case reserves, IBNR reserves are adjusted as additional information becomes known or payments are made. Losses and LAE are categorized by the year in which the policy is underwritten (the year of account, or underwriting year) for purposes of Ark’s claims management and estimation of the ultimate loss and LAE reserves. For purposes of Ark’s reporting under GAAP, losses and LAE are categorized by the year in which the claim is incurred (the accident year). Ultimate loss and LAE are generally determined by extrapolation of claim emergence and settlement patterns observed in the past that can reasonably be expected to persist into the future. In forecasting ultimate loss and LAE with respect to any line of business, past experience with respect to that line of business is the primary resource, but cannot be relied upon in isolation. Ark’s own experience, particularly claims development experience, such as trends in case reserves, payments on and closings of claims, as well as changes in business mix and coverage limits, is the most important information for estimating its reserves. External data, available from organizations such as the Lloyd’s Market Association, consulting firms and other insurance and reinsurance companies, is used to supplement or corroborate Ark’s own experience. External data can be especially useful for estimating costs on newer lines of business. Ultimate loss and LAE for major losses and catastrophes are estimated based on the known and expected exposures to the loss event, rather than simply relying on the extrapolation of reported and settled claims. For some lines of business, such as long-tail coverages discussed below, claims data reported in the most recent years of account are often too limited to provide a meaningful basis for analysis due to the typical delay in reporting and settling of claims. For this type of business, Ark uses an expected loss ratio method for the initial years of account. This is a standard and accepted actuarial reserve estimation method in these circumstances in which the loss ratio is selected based upon information used in pricing policies for that line of business, as well as any publicly available industry data, such as industry pricing, experience and trends, for that line of business. Uncertainties in estimating ultimate loss and LAE are magnified by the time lag between when a claim actually occurs and when it is reported and eventually settled. This time lag is sometimes referred to as the “claim-tail”. The claim-tail for reinsurance and insurance obtained through brokers, MGAs and reinsurance intermediaries (collectively the “insurance and reinsurance intermediaries”) is further extended because claims are first reported to either the original primary insurance company or the insurance and reinsurance intermediaries. The claim-tail for most property coverages is typically short (usually a few days up to a few months). Settlements for casualty/liability coverages can extend for long periods of time as claims are often reported and ultimately paid or settled years after the related loss events occur. During the long claims reporting and settlement period, additional facts regarding coverages written in prior years of account, as well as about actual claims and trends, may become known and, as a result, Ark may adjust its reserves. The inherent uncertainties of estimating reserves are increased by the diversity of loss development patterns among different types of reinsurance treaties, facultative contracts or direct insurance contracts, the necessary reliance on the ceding companies and insurance and reinsurance intermediaries for information regarding reported claims and the differing reserving practices among ceding companies and insurance and reinsurance intermediaries. If management determines that an adjustment is appropriate, the adjustment is booked in the accounting period in which such determination is made. Accordingly, should reserves need to be increased or decreased in the future from amounts currently established, future results of operations would be negatively or positively impacted. In determining ultimate loss and LAE, the cost to indemnify claimants, provide needed legal defense and other services for insureds and administer the investigation and adjustment of claims are considered. These claim costs are influenced by many factors that change over time, such as expanded coverage definitions as a result of new court decisions, inflation in costs to repair or replace damaged property, inflation in the cost of medical services, and legislated changes in statutory benefits, as well as by the particular, unique facts that pertain to each claim. As a result, the rate at which claims arose in the past and the costs to settle them may not always be representative of what will occur in the future. The factors influencing changes in claim costs are often difficult to isolate or quantify and developments in paid and incurred losses from historical trends are frequently subject to multiple and conflicting interpretations. Changes in coverage terms or claims handling practices may also cause future experience and/or development patterns to vary from the past. A key objective of actuaries in developing estimates of ultimate loss and LAE and resulting IBNR reserves is to identify aberrations and systemic changes occurring within historical experience and accurately adjust for them so that the future can be projected more reliably. Because of the factors previously discussed, this process requires the use of informed judgment and is inherently uncertain. Ark performs an actuarial review of its recorded loss and LAE reserves each quarter, using several generally accepted actuarial methods to evaluate its loss reserves, each of which has its own strengths and weaknesses. Management places more or less reliance on a particular method based on the facts and circumstances at the time the reserve estimates are made. These methods generally fall into one of the following categories or are hybrids of one or more of the following categories: • Historical paid loss development methods: These methods use historical loss payments over discrete periods of time to estimate future losses. Historical paid loss development methods assume that the ratio of losses paid in one period to losses paid in an earlier period will remain constant. These methods necessarily assume that factors that have affected paid losses in the past, such as inflation or the effects of litigation, will remain constant in the future. Because historical paid loss development methods do not use case reserves to estimate ultimate losses, they can be more reliable than the other methods discussed below that look to case reserves (such as actuarial methods that use incurred losses) in situations where there are significant changes in how case reserves are established by a company’s claims adjusters. However, historical paid loss development methods are more leveraged, meaning that small changes in payments have a larger impact on estimates of ultimate losses, than actuarial methods that use incurred losses because cumulative loss payments take much longer to approach the expected ultimate losses than cumulative incurred amounts. In addition, and for similar reasons, historical paid loss development methods are often slow to react to situations when new or different factors arise than those that have affected paid losses in the past. • Historical incurred loss development methods: These methods, like historical paid loss development methods, assume that the ratio of losses in one period to losses in an earlier period will remain constant in the future. However, instead of using paid losses, these methods use incurred losses (i.e., the sum of cumulative historical loss payments plus outstanding case reserves) over discrete periods of time to estimate future losses. Historical incurred loss development methods can be preferable to historical paid loss development methods because they explicitly take into account open cases and the claims adjusters’ evaluations of the cost to settle all known claims. However, historical incurred loss development methods necessarily assume that case reserving practices are consistently applied over time. Therefore, when there have been significant changes in how case reserves are established, using incurred loss data to project ultimate losses can be less reliable than other methods. • Expected loss ratio methods: These methods are based on the assumption that ultimate losses vary proportionately with premiums. Expected loss ratios are typically developed based upon the information used in pricing, and are multiplied by the total amount of premiums earned to calculate ultimate losses. Expected loss ratio methods are useful for estimating ultimate losses in the early years of long-tailed lines of business, when little or no paid or incurred loss information is available. • Bornhuetter-Ferguson methods: These methods are a blend of the expected loss ratio and loss development methods. The percent of incurred (or paid) loss to ultimate loss implied by the selected development pattern from the incurred (or paid) loss development method is used to determine the percentage of ultimate loss yet to be developed. Inception to date losses are added to losses yet to be developed, yielding an estimate of ultimate for each year of account. • Adjusted historical paid and incurred loss development methods: These methods take traditional historical paid and incurred loss development methods and adjust them for the estimated impact of changes from the past in factors such as inflation, the speed of claim payments or the adequacy of case reserves. Adjusted historical paid and incurred loss development methods are often more reliable methods of predicting ultimate losses in periods of significant change, provided the actuaries can develop methods to reasonably quantify the impact of changes. As part of Ark’s quarterly actuarial review, Ark compares the previous quarter’s projections of incurred, paid and case reserve activity, including amounts incurred but not reported, to actual amounts experienced in the quarter. Differences between previous estimates and actual experience are evaluated to determine whether a given actuarial method for estimating loss and LAE reserves should be relied upon to a greater or lesser extent than it had been in the past. While some variance is expected each quarter due to the inherent uncertainty in estimating loss and LAE reserves, persistent or large variances would indicate that prior assumptions and/or reliance on certain actuarial methods may need to be revised going forward. Upon completion of each quarterly review, Ark selects indicated loss and LAE reserve levels based on the results of the actuarial methods described previously, which are the primary consideration in determining management's best estimate of required loss and LAE reserves. However, in making its best estimate, management also considers other qualitative factors that may lead to a difference between held reserves and the actuarial central estimate of reserves. Typically, these qualitative factors are considered when management and Ark’s actuaries conclude that there is insufficient historical incurred and paid loss information or that trends included in the historical incurred and paid loss information are likely to repeat in the future. Such qualitative factors include, among others, recent entry into new markets or new products, improvements in the claims department that are expected to lessen future ultimate loss costs, legal and regulatory developments, or other uncertainties that may arise. Ark Reserve Estimation by Line of Business The process of establishing loss and LAE reserves, including amounts incurred but not reported, is complex and imprecise as it must consider many variables that are subject to the outcome of future events. As a result, informed subjective estimates and judgments as to the ultimate exposure to losses are an integral component of the loss and LAE reserving process. Ark categorizes and tracks insurance and reinsurance reserves by “reserving class of business” for each underwriting office, London and Bermuda, and then aggregates the reserving classes by line of business, which are summarized herein as property and accident & health, marine & energy, specialty, casualty - active and casualty - runoff. Ark regularly reviews the appropriateness of its loss and LAE reserves at the reserving class of business level, considering a variety of trends that impact the ultimate settlement of claims for the subsets of claims in each particular reserving class. For loss and LAE reserves as of December 31, 2021, Ark considers that the impact of the various reserving factors, as described below, on future paid losses would be similar to the impact of those factors on historical paid losses. The major causes of material uncertainty (i.e., reserving factors) generally will vary for each line of business, as well as for each separately analyzed reserving class of business within the line of business. Also, reserving factors can have offsetting or compounding effects on estimated loss and LAE reserves. In almost all cases, it is impossible to discretely measure the effect of a single reserving factor and construct a meaningful sensitivity expectation. Actual results will likely vary from expectations for each of these assumptions, resulting in an ultimate claim liability that is different from that being estimated currently. Additional causes of material uncertainty exist in most product lines and may impact the types of claims that could occur within a particular line of business or reserving class of business. Examples where reserving factors, within a line of business or reserving class of business, are subject to change include changing types of insured (e.g., type of insured vehicle, size of account, industry insured, jurisdiction), changing underwriting standards, or changing policy provisions (e.g., deductibles, policy limits, endorsements). Following is a detailed description of the reserve factors and consideration for each of the major product lines. Property and Accident & Health Ark’s property and accident & health reserving line of business contains short-tailed reserving classes. As such, reserving for these classes generally involves less uncertainty given the speed of settlement. For property reserving classes, the reserve risk is driven primarily by occasional catastrophe events, though the financial effect of these is mitigated by reinsurance and retrocessional purchases. Ark writes property business on both an insurance and reinsurance basis. The insurance business primarily consists of direct and facultative contracts. However, some business is written through lineslips and MGA binding authorities, which could have a longer tail due to the increased exposure period caused by underlying policies attaching to the binder contract. The reinsurance business can also have a longer tail due to timing delays resulting from attachment points on excess of loss contracts. For accident & health reserving classes, the losses emanate from a wide range of personal accident, sickness, travel and medical insurance risks. The underlying business is a mix of direct and facultative contracts, as well as some MGA and reinsurance contracts, which are typically shorter tail lines. Certain smaller components of the accident & health business can be longer-tailed. The accident & health business is also exposed to occasional catastrophic events though not to the same degree as the property business. Marine & Energy Ark’s marine & energy reserving line of business is underwritten on both an insurance and reinsurance basis and can be broken down into physical damage on marine risks, physical damage on upstream energy platforms, and marine & energy liabilities. The marine reserving classes consist primarily of marine hull, cargo and specie risks. These all generally have some element of transportability, which mitigates the catastrophe risk exposure. For example, having the ability to move out of the path of a hurricane if provided with sufficient notice. The marine reserving classes are generally shorter-tailed. The energy platform reserving classes cover risks that are less transportable and therefore are exposed to catastrophe events similar to property reserving classes. Other energy reserving classes cover construction contracts, which often have considerably protracted exposure periods with the bulk of the risk towards end of the coverage period. This can have the effect of increasing the tail on an otherwise short-tail reserving class. The marine & energy liability reserving classes, which represent a smaller portion of the marine & energy business, are typically longer-tailed compared to physical damage reserving classes. Specialty Ark’s specialty portfolio is comprised of a diverse portfolio of insurance and reinsurance subclasses of business. Certain subclasses of business are exposed to both catastrophe events and man-made loss events, for example terrorism, political violence and space. Although these subclasses have different coverage and exposures, they are all short-tailed in nature and have similar reserving features. Casualty – Active and Casualty – Runoff Ark’s casualty reserving lines of business, which include casualty–active and casualty–runoff, are long-tailed classes of business. Consequently, the ultimate liability may not be known at the date of loss, which results in greater uncertainty when reserving for casualty lines. The casualty–active line of business consists of U.S. reinsurance and insurance risks written on an excess of loss basis. The casualty–runoff line of business consists of international reinsurance risks and U.S. casualty insurance risks written through an MGA binding authority. The losses arising from these lines of business are primarily related to medical malpractice, professional liability and general liability coverages, which are long-tailed lines of business. Casualty policies are generally written on either a claims made or occurrence basis. On a claims made basis, the trigger of loss is based on the date that the loss is reported. On an occurrence basis, the trigger of loss is the date that the loss occurred. Due to delays between loss occurrence and loss reporting, business written on an occurrence basis can be longer-tailed than business written on a claims made basis. There are a number of common reserving factors for casualty lines that can affect the estimated casualty reserves, including: • Changes in claim-handling practices, both in-house and through third-party claims administrators, • Changes in court interpretations of policy provisions, and • Trends in litigation or jury awards. Cumulative Number of Reported Claims Ark counts a claim for each unique combination of individual claimant and loss event. The claim is counted only if, net of any applicable deductibles, a payment has been made or a case reserve has been recorded or is anticipated to be recorded. A claim is still counted if the claim is closed with no payment. Bulk-coded losses are counted as one claim as underlying claim counts are not available. Discounting Ark does not discount loss and LAE reserves. Impact of Third-Party Capital For the years of account prior to the Ark Transaction, a significant proportion of the Syndicates’ underwriting capital was provided by TPC Providers using whole account reinsurance contracts with Ark’s corporate member. The TPC Providers’ participation in the Syndicates for the 2020 and 2019 open years of account is 42.8% and 58.3% of the total net result of the Syndicates. For the years of account subsequent to the Ark Transaction, Ark is no longer using TPC Providers to provide underwriting capital for the Syndicates. A Reinsurance to Close (“RITC”) agreement is generally put in place after the third year of operations for a year of account such that the outstanding loss and LAE reserves, including future development thereon, are reinsured into the next year of account. As a result and in combination with the changing participation provided by TPC Providers, Ark’s participation on outstanding loss and LAE reserves reinsured into the next year of account may change, perhaps significantly. For example, during 2021, an RITC was executed such that the outstanding loss and LAE reserves for claims arising out of the 2018 year of account, for which the TPC Providers’ participation in the total net results of the Syndicates was 57.6%, were reinsured into the 2019 year of account, for which the TPC Providers’ participation in the total net results of the Syndicates is 58.3%. Loss and Loss Adjustment Expense Reserve Summary The following table summarizes the loss and LAE reserve activity of Ark’s insurance and reinsurance subsidiaries for the year ended December 31, 2021: Millions Year Ended Gross beginning balance $ 696.0 Less: beginning reinsurance recoverable on unpaid losses (1) (433.4) Net loss and LAE reserves 262.6 Losses and LAE incurred relating to: Current year losses 336.3 Prior year losses (21.5) Net incurred losses and LAE 314.8 Loss and LAE paid relating to: Current year losses (43.9) Prior year losses (61.6) Net paid losses and LAE (105.5) Change in TPC Providers’ participation (2) (2.2) Foreign currency translation and other adjustments to loss and LAE reserves (3.9) Net ending balance 465.8 Plus: ending reinsurance recoverable on unpaid losses (1) 428.9 Gross ending balance $ 894.7 (1) The beginning reinsurance recoverable on unpaid losses and ending reinsurance recoverable on unpaid losses includes amounts attributable to TPC Providers of $319.2 and $276.8. (2) Amount represents a decrease in net loss and LAE reserves due to a change in the TPC Providers’ participation during 2021, related to the RITC for the 2018 year of account. During the year ended December 31, 2021, Ark experienced $21.5 million of net favorable loss reserve development. Ark’s net favorable loss reserve development was driven primarily by the accident & health ($8.9 million), casualty – ongoing ($3.7 million), specialty ($3.3 million) and casualty – runoff ($3.3 million) reserving lines of business. The favorable loss reserve development in the property and accident & health reserving line of business was driven primarily by positive claims experience within the 2018 and 2019 accident years. The following table summarizes the unpaid loss and LAE reserves, net of reinsurance recoverables on unpaid losses, for each of Ark’s major reserving lines of business as of December 31, 2021: Millions As of Property and Accident & Health $ 175.0 Marine & Energy 99.3 Specialty 85.2 Casualty - Active 37.4 Casualty - Runoff 68.4 Other 0.5 Unpaid loss and LAE reserves, net of reinsurance recoverables on unpaid losses 465.8 Plus: Reinsurance recoverables on unpaid losses (1) Property and Accident & Health 145.2 Marine & Energy 70.2 Specialty 68.9 Casualty - Active 41.4 Casualty - Runoff 103.2 Total Reinsurance recoverables on unpaid losses (1) 428.9 Total unpaid loss and LAE reserves $ 894.7 (1) The reinsurance recoverables on unpaid losses include amounts attributable to TPC Providers of $276.8. The following five tables include one table each for the property and accident & health, marine & energy, specialty, casualty-active and casualty-runoff reserving lines of business, and are presented net of reinsurance, which includes the impact of whole-account quota-share reinsurance arrangements related to TPC Providers. Through the annual RITC process, Ark’s participation on outstanding loss and LAE reserves on prior years of account can fluctuate. Depending on the change in the TPC Providers’ participation from one year of account to the next, the impact could be significant and is reflected in the tables on an accident year basis. The following table summarizes the participation of Ark’s TPC Providers by year of account: 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 TPC Providers’ — % — % 66.2 % 70.0 % 59.6 % 60.0 % 57.6 % 58.3 % 42.8 % — % Each of the five tables includes three sections. The top section of the table presents, for each of the previous 10 accident years (1) cumulative total undiscounted incurred loss and LAE as of each of the previous 10 year-end evaluations, (2) total IBNR plus expected development on reported claims as of December 31, 2021, and (3) the cumulative number of reported claims as of December 31, 2021. The middle section of the table presents cumulative paid loss and LAE for each of the previous 10 accident years as of each of the previous 10 year-end evaluations. Also included in this section is a calculation of the loss and LAE reserves as of December 31, 2021 which is then included in the reconciliation to the consolidated balance sheet presented above. The total unpaid loss and LAE reserves as of December 31, 2021 is calculated as the cumulative incurred loss and LAE from the top section less the cumulative paid loss and LAE from the middle section, plus any outstanding liabilities from accident years prior to 2012. The bottom section of the table is supplementary information about the average historical claims duration as of December 31, 2021. It shows the weighted average annual percentage payout of incurred loss and LAE by accident year as of each age. For example, the first column is calculated as the incremental paid loss and LAE in the first calendar year for each given accident year (e.g. calendar year 2020 for accident year 2020, calendar year 2021 for accident year 2021) divided by the cumulative incurred loss and LAE as of December 31, 2021 for that accident year. The resulting ratios are weighted together using cumulative incurred loss and LAE as of December 31, 2021. Property and Accident & Health $ in Millions Incurred Loss and LAE, Net of Reinsurance For the Years Ended December 31, As of December 31, 2021 Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Total IBNR plus expected development on reported claims Cumulative number of reported claims Unaudited 2012 $ 84.1 $ 68.4 $ 65.1 $ 65.7 $ 60.2 $ 60.0 $ 60.4 $ 60.2 $ 60.2 $ 60.0 $ — 2,710 2013 74.6 66.9 66.6 62.1 61.6 61.7 61.6 61.6 61.6 .4 2,586 2014 34.8 31.3 29.4 28.6 28.6 28.5 28.5 28.5 — 2,963 2015 19.8 17.4 16.2 16.0 15.9 15.9 15.9 .4 2,884 2016 21.7 16.9 17.9 18.0 17.9 18.0 (.3) 3,478 2017 22.6 29.9 37.4 36.7 36.0 3.6 4,610 2018 37.5 44.2 46.3 44.5 1.5 4,270 2019 30.4 27.8 23.4 2.1 4,073 2020 62.9 61.5 15.2 4,532 2021 162.1 70.8 2,860 Total $ 511.5 Property and Accident & Health Millions Cumulative Paid Loss and LAE, Net of Reinsurance For the Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Unaudited 2012 $ 14.2 $ 45.0 $ 53.6 $ 57.3 $ 58.2 $ 58.6 $ 58.7 $ 59.3 $ 59.4 $ 59.5 2013 15.8 40.3 60.0 61.1 61.1 61.3 61.3 61.3 61.2 2014 13.9 25.4 27.6 28.0 28.1 28.2 28.4 28.3 2015 7.0 12.4 13.7 14.9 14.8 15.1 15.3 2016 8.6 13.4 16.8 17.1 17.2 17.5 2017 17.0 26.3 32.1 33.3 30.2 2018 15.8 32.8 40.7 40.7 2019 6.9 17.1 19.1 2020 11.4 34.5 2021 30.8 Total 337.1 All outstanding liabilities before 2012, net of reinsurance .6 Loss and LAE reserves, net of reinsurance $ 175.0 Property and Accident & Health Average Annual Percentage Payout of Incurred Losses and LAE by Age, Net of Reinsurance Unaudited Years 1 2 3 4 5 6 7 8 9 10 31.5% 33.4% 19.2% 5.7% 1.2% 1.4% 0.8% 0.3% —% 0.1% Marine & Energy $ in Millions Incurred Loss and LAE, Net of Reinsurance For the Years Ended December 31, As of December 31, 2021 Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Total IBNR plus expected development on reported claims Cumulative number of reported claims Unaudited 2012 $ 64.7 $ 55.1 $ 46.0 $ 42.8 $ 33.6 $ 32.8 $ 32.6 $ 32.0 $ 32.0 $ 32.1 $ .1 2,428 2013 64.9 50.8 41.9 31.6 31.0 29.9 29.7 29.6 29.9 (.2) 2,641 2014 41.3 27.2 17.4 16.2 14.7 14.3 14.4 14.4 .5 2,581 2015 25.3 15.4 13.6 12.7 12.0 12.0 12.2 .2 3,390 2016 22.3 18.1 16.0 15.1 14.9 15.1 .7 4,117 2017 23.9 18.6 16.9 16.4 16.5 1.1 4,470 2018 24.5 18.9 16.7 17.0 .5 3,487 2019 19.3 17.3 17.2 .6 2,562 2020 24.4 21.7 2.9 1,668 2021 83.7 69.9 1,091 Total $ 259.8 Marine & Energy Millions Cumulative Paid Loss and LAE, Net of Reinsurance For the Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Unaudited 2012 $ 8.1 $ 24.0 $ 27.4 $ 30.2 $ 30.6 $ 31.3 $ 31.7 $ 31.4 $ 31.3 $ 31.0 2013 7.9 22.6 28.1 29.1 29.7 29.9 29.9 29.7 29.9 2014 6.0 12.4 13.5 14.4 14.5 13.7 14.0 13.8 2015 4.0 8.0 9.8 11.3 10.7 10.8 11.2 2016 5.6 10.1 12.8 13.3 13.4 14.0 2017 5.2 11.3 13.1 14.4 14.4 2018 2.7 12.9 14.5 15.2 2019 3.4 10.9 12.9 2020 3.2 12.9 2021 6.4 Total 161.7 All outstanding liabilities before 2012, net of reinsurance 1.2 Loss and LAE reserves, net of reinsurance $ 99.3 Marine & Energy Average Annual Percentage Payout of Incurred Losses and LAE by Age, Net of Reinsurance Unaudited Years 1 2 3 4 5 6 7 8 9 10 19.8% 37.7% 20.2% 5.7% 4.3% 7.2% 0.4% 0.1% (0.4)% 0.2% Specialty $ in Millions Incurred Loss and LAE, Net of Reinsurance For the Years Ended December 31, As of December 31, 2021 Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Total IBNR plus expected development on reported claims Cumulative number of reported claims Unaudited 2012 $ 43.1 $ 36.1 $ 31.8 $ 30.8 $ 26.7 $ 25.8 $ 26.3 $ 26.6 $ 26.8 $ 26.8 $ 2.1 887 2013 48.6 34.9 25.6 17.5 16.9 17.1 16.9 17.3 17.3 1.3 1,122 2014 51.1 51.1 41.9 41.3 41.5 42.9 43.5 43.5 (.3) 1,409 2015 21.3 13.0 10.4 10.1 10.6 10.7 10.8 1.7 1,876 2016 15.9 11.7 8.7 9.2 9.0 9.3 (1.3) 1,941 2017 16.0 11.9 10.9 10.5 10.6 1.5 2,179 2018 12.1 13.9 14.8 13.7 2.4 2,090 2019 16.6 14.6 13.5 2.8 2,315 2020 20.7 19.7 6.2 1,925 2021 67.3 57.4 1,341 Total $ 232.5 Specialty Millions Cumulative Paid Loss and LAE, Net of Reinsurance For the Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Unaudited 2012 $ 16.3 $ 25.2 $ 22.2 $ 22.6 $ 23.2 $ 23.3 $ 24.2 $ 24.4 $ 24.4 $ 24.5 2013 17.1 13.6 15.2 15.8 15.8 16.0 16.0 16.0 16.0 2014 26.8 39.7 40.4 40.8 41.5 42.8 43.6 43.5 2015 4.1 7.2 7.8 8.2 8.2 8.3 8.3 2016 3.2 8.0 9.2 10.0 10.4 10.5 2017 3.3 6.8 8.4 8.5 8.5 2018 2.9 8.1 9.8 10.3 2019 4.9 7.1 7.6 2020 5.4 10.9 2021 5.2 Total 145.3 All outstanding liabilities before 2012, net of reinsurance (2.0) Loss and LAE reserves, net of reinsurance $ 85.2 Specialty Average Annual Percentage Payout of Incurred Losses and LAE by Age, Net of Reinsurance Unaudited Years 1 2 3 4 5 6 7 8 9 10 34.0% 33.8% 7.3% 0.5% 4.6% 4.4% 4.6% 3.1% (3.5)% (1.0)% Casualty - Active $ in Millions Incurred Loss and LAE, Net of Reinsurance For the Years Ended December 31, As of December 31, 2021 Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Total IBNR plus expected development on reported claims Cumulative number of reported claims Unaudited 2012 $ 22.6 $ 21.1 $ 17.7 $ 16.2 $ 10.1 $ 9.9 $ 11.0 $ 11.0 $ 11.3 $ 11.1 $ .8 1,016 2013 23.2 18.8 15.0 8.3 8.1 8.9 8.8 9.0 8.9 1.3 1,134 2014 17.1 13.8 7.5 7.0 8.0 7.8 7.8 7.7 1.2 1,359 2015 12.3 7.7 6.0 7.0 6.5 6.4 6.2 .6 1,247 2016 5.7 5.0 6.3 6.6 7.0 6.9 .1 1,483 2017 7.4 7.8 7.2 6.2 5.9 .7 1,489 2018 8.7 9.0 7.3 7.1 .9 961 2019 8.0 7.4 6.3 1.7 742 2020 7.6 6.2 3.9 420 2021 15.9 14.2 452 Total $ 82.2 Casualty - Active Millions Cumulative Paid Loss and LAE,

Third-Party Reinsurance

Third-Party Reinsurance	12 Months Ended
	Dec. 31, 2021
Reinsurance Disclosures [Abstract]
Third-Party Reinsurance	Third-Party Reinsurance In the normal course of business, Ark may seek to limit losses that may arise from catastrophes or other events by reinsuring certain risks with third-party reinsurers. Ark remains liable for risks reinsured in the event that the reinsurer does not honor its obligations under reinsurance contracts. The following table summarizes the effects of reinsurance on written and earned premiums and on losses and LAE for Ark. Year Ended December 31, 2021 Millions Written premiums: Gross $ 1,058.7 Ceded (199.6) Net written premiums $ 859.1 Earned premiums: Gross $ 886.4 Ceded (249.1) Net earned premiums $ 637.3 Losses and LAE: Gross $ 442.9 Ceded (128.1) Net Losses and LAE $ 314.8 As of December 31, 2021, Ark had $428.9 million and $19.5 million of reinsurance recoverables on unpaid and paid losses. As reinsurance contracts do not relieve Ark of its obligation to its policyholders, Ark seeks to reduce the credit risk associated with reinsurance balances by avoiding over-reliance on specific reinsurers through the application of concentration limits and thresholds. Ark is selective with its reinsurers, placing reinsurance with only those reinsurers having a strong financial condition. Ark monitors the financial strength of its reinsurers on an ongoing basis. As of December 31, 2021, Ark’s reinsurance recoverables of $448.4 million included $276.8 million related to TPC Providers, which are collateralized. The following table provides a listing of Ark’s remaining gross and net reinsurance recoverables, excluding amounts related to TPC Providers, by the reinsurer’s A.M. Best Company, Inc. (“A.M. Best”) rating and the percentage of total recoverables. $ in Millions As of December 31, 2021 A.M. Best Rating (1) Gross Collateral Net % of Total A+ or better $ 120.0 $ 16.9 $ 103.1 77.5 % A - to A 41.5 13.1 28.4 21.3 B++ or lower and not rated 10.1 8.5 1.6 1.2 Total $ 171.6 $ 38.5 $ 133.1 100.0 % (1) A.M. Best ratings as detailed above are: “A+ or better” (Superior) “A- to A” (Excellent), “B++” (Good). See Note 10 — “Municipal Bond Guarantee Insurance” for third-party reinsurance balances related to White Mountains’s financial guarantee business. Reinsurance Contracts Accounted for as Deposits Ark has an aggregate excess of loss contract with SiriusPoint, which is accounted for using the deposit method and recorded within other assets. Ark earns an annual crediting rate of 3.0%, which is recorded within other revenue. During 2021, Ark negotiated a reduction of $31.7 million, including accrued interest, to the aggregate excess of loss contract with SiriusPoint. As of December 31, 2021, the carrying value of Ark’s deposit in SiriusPoint, including accrued interest, was $20.4 million. See Note 10 — “Municipal Bond Guarantee Insurance” for reinsurance contracts accounted for as deposits related to White Mountains’s financial guarantee business.

Debt

Debt	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
Debt	Debt The following table presents White Mountains’s debt outstanding as of December 31, 2021 and 2020: December 31, Effective (1) December 31, Effective (1) $ in Millions 2021 Rate 2020 Rate (1) Ark 2007 Notes Tranche 1 $ 30.0 $ — Ark 2007 Notes Tranche 2 — — Ark 2007 Subordinated Notes, carrying value 30.0 — Ark 2021 Notes Tranche 1 44.2 — Ark 2021 Notes Tranche 2 47.0 — Ark 2021 Notes Tranche 3 70.0 — Unamortized issuance cost (5.3) — Ark 2021 Subordinated Notes, carrying value 155.9 — Total Ark Subordinated Notes, carrying value 185.9 6.9% — NSM Bank Facility 277.6 7.3% (2) 277.4 7.5% (2) Unamortized issuance cost (6.4) (6.1) NSM Bank Facility, carrying value 271.2 271.3 Other NSM debt .9 2.9% 1.3 2.5% Kudu Credit Facility 225.4 4.3% — Unamortized issuance cost (7.2) — Kudu Credit Facility, carrying value 218.2 — Kudu Bank Facility — 89.2 8.3% Unamortized issuance cost — (2.9) Kudu Bank Facility, carrying value — 86.3 Other Operations debt 17.1 7.5% 18.0 7.4% Unamortized issuance cost (.3) (.5) Other Operations debt, carrying value 16.8 17.5 Total debt $ 693.0 $ 376.4 (1) Effective rate includes the effect of the amortization of debt issuance costs. (2) NSM’s effective rate excludes the effect of the interest rate swap on the hedged portion of the debt. The weighted average interest rate for the years ended December 31, 2021 and 2020, excluding the effect of the amortization of debt issuance costs, was 6.5% and 7.0%. The weighted average interest rate for the years ended December 31, 2021 and 2020 on the total NSM Bank Facility including both the effect of the amortization of debt issuance costs and the effect of the interest rate swap and interest rate cap was 8.2% and 8.4%. The following table presents a schedule of contractual repayments of White Mountains’s debt as of December 31, 2021: Millions December 31, 2021 Due in one year or less $ 5.7 Due in two to three years 14.5 Due in four to five years 221.6 Due after five years 470.4 Total $ 712.2 Ark Subordinated Notes In March 2007, GAIL issued $30.0 million face value of floating rate unsecured junior subordinated deferrable interest notes to Alesco Preferred Funding XII Ltd., Alesco Preferred Funding XIII Ltd. and Alesco Preferred Funding XIV Ltd (the “Ark 2007 Notes Tranche 1”) and a €12.0 million floating rate subordinated note to Dekania Europe CDO II plc (the “Ark 2007 Notes Tranche 2”) (together, the “Ark 2007 Subordinated Notes”). The Ark 2007 Notes Tranche 1, which mature in June 2037, accrue interest at a floating rate equal to the three-month U.S. LIBOR plus 4.6%. The Ark 2007 Notes Tranche 2, which matures in June 2027, accrues interest at a floating rate equal to the three-month EURIBOR plus 4.6%. During 2021, Ark repaid €12.0 million ($13.5 million based upon the foreign exchange spot rate at the date of repayment) of the outstanding principal balance on the Ark 2007 Notes Tranche 2. As of December 31, 2021, the Ark 2007 Notes Tranche 1 had an outstanding balance of $30.0 million. In the third quarter of 2021, GAIL issued $163.3 million face value floating rate subordinated notes at par in three separate transactions for proceeds of $157.8 million, net of debt issuance costs. The unsecured subordinated notes (the “Ark 2021 Subordinated Notes”) were issued in private placement offerings that were exempt from the registration requirements of the Securities Act of 1933. On July 13, 2021, Ark issued €39.1 million ($46.3 million based upon the foreign exchange spot rate as of the date of the transaction) face value floating rate unsecured subordinated notes (“Ark 2021 Notes Tranche 1”). The Ark 2021 Notes Tranche 1, which mature in July 2041, accrue interest at a floating rate equal to the three-month EURIBOR plus 5.75%. On August 11, 2021, Ark issued $47.0 million face value floating rate unsecured subordinated notes (“Ark 2021 Notes Tranche 2”). The Ark 2021 Notes Tranche 2, which mature in August 2041, accrue interest at a floating rate equal to the three-month U.S. LIBOR plus 5.75%. On September 8, 2021, Ark issued $70.0 million face value floating rate unsecured subordinated notes (“Ark 2021 Notes Tranche 3”). The Ark 2021 Notes Tranche 3, which mature in September 2041, accrue interest at a floating rate equal to the three-month U.S. LIBOR plus 6.1%. On the ten-year anniversary of the issue dates, the interest rate for the Ark 2021 Subordinated Notes will increase by 1.0% per annum. Ark has the option to redeem, in whole or in part, the Ark 2021 Subordinated Notes ahead of contractual maturity at the outstanding principal amounts plus accrued interest at the ten-year anniversary or any subsequent interest payment date. All payments of principal and interest under the Ark 2021 Subordinated Notes are conditional upon GAIL’s solvency and compliance with the enhanced capital requirements of the Bermuda Monetary Authority (“BMA”). The deferral of payments of principal and interest under these conditions does not constitute a default by Ark and does not give the noteholders any rights to accelerate repayment of the Ark 2021 Subordinated Notes or take any enforcement action under the Ark 2021 Subordinated Notes. If the payments of principal and interest under the Ark 2021 Subordinated Notes become subject to tax withholding on behalf of Bermuda or any political subdivision there, the Ark 2021 Subordinated Notes require the payment of additional amounts such that the amount received by the noteholders is the same as would have been received absent the tax withholding being imposed. The Ark 2021 Notes Tranche 3 require the payment of additional interest of 1.0% per annum upon the occurrence of a Premium Load Event until such event is remedied. Premium Load Events include the failure to meet payment obligations of the Ark 2021 Notes Tranche 3 when due, failure of GAIL to maintain an investment grade credit rating, failure to maintain 120% of GAIL’s Bermuda solvency capital requirement, failure of GAIL to maintain a debt to capital ratio below 40%, late filing of GAIL’s or Ark’s financial information, and making a restricted payment or distribution on GAIL’s common stock or other securities that rank junior or pari passu with the Ark 2021 Notes Tranche 3 when a different Premium Load Event exists or will be caused by the restricted payment. As of December 31, 2021, the Ark 2021 Notes Tranche 1 had an outstanding balance of €39.1 million ($44.2 million based upon the foreign exchange spot rate as of December 31, 2021), the Ark 2021 Notes Tranche 2 had an outstanding balance of $47.0 million, and the Ark 2021 Notes Tranche 3 had an outstanding balance of $70.0 million. Ark Stand By Letter of Credit Facilities In December 2021, Ark entered into two uncommitted secured stand by letter of credit facility agreements to support the continued growth and expansion of its GAIL insurance and reinsurance operations. The stand by letter of credit facility agreements were executed with ING Bank N.V., London Branch (the “ING LOC Facility”) with capacity of $50.0 million on an uncollateralized basis and with Citibank Europe Plc (the “Citibank LOC Facility”) with capacity of $100.0 million on a collateralized basis. As of December 31, 2021, $50.0 million of short-term investments were pledged as collateral under the Citibank LOC Facility. As of December 31, 2021, the ING LOC Facility and the Citibank LOC Facility were undrawn. Ark’s uncommitted secured stand by letter of credit facility agreements contain various representations, warranties and covenants that White Mountains considers to be customary such borrowings. NSM Bank Facility NSM maintains a secured credit facility (the “NSM Bank Facility”) with Ares Capital Corporation. In both 2021 and 2020, NSM amended the terms of the facility. On April 7, 2020, NSM amended the NSM Bank Facility to increase the total commitment from $234.0 million, comprised of term loans of $224.0 million and a revolving credit loan of $10.0 million, to $291.4 million, comprised of term loans of $276.4 million, including £42.5 million ($52.4 million based upon the foreign exchange spot rate as of the date of the transaction) in a GBP term loan, and a revolving credit loan commitment of $15.0 million. In connection with the April 7, 2020 amendment, the reference rates for USD denominated borrowings increased. The USD-LIBOR rate floor increased 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%. On June 2, 2021, NSM amended the NSM Bank Facility to reduce the margin over the reference interest rate for USD LIBOR loans from a range of 5.50% to 6.00% to a range of 4.50% to 5.00%, and reduce the margin over the reference rate for GBP loans from a range of 6.00% to 6.50% to a range of 5.00% to 5.50%. The amendment also increased the revolving credit loan commitment to $40.0 million and added a $50.0 million delayed-draw term loan commitment. The amendment also changed the reference interest rate for the GBP loan from GBP-LIBOR to SONIA. The maturity dates of the term loans and the revolving credit loans were not changed as part of the amendment. The term loans under the NSM Bank Facility mature on May 11, 2026, and the revolving loan matures on November 11, 2025. The reference interest rates under the NSM Bank Facility are generally subject to a 1.25% rate floor. 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 2021 and 2020 amendments to the NSM Bank Facility was less than 10% on the expected discounted future cash flows. The following table presents the change in debt under the NSM Bank Facility for the years ended December 31, 2021, 2020 and 2019: Millions Year Ended December 31, NSM Bank Facility 2021 2020 2019 Beginning balance $ 277.4 $ 221.3 $ 180.4 Term loans Borrowings (1) — 52.4 42.9 Repayments (2.8) (2.0) (2.0) Foreign currency translation (.5) 5.7 — Revolving credit loan Borrowings (2) 35.0 — 6.5 Repayments (31.5) — (6.5) Ending balance $ 277.6 $ 277.4 $ 221.3 (1) Borrowings for the year ended December 31, 2020 included $52.4 for the funding of the acquisition of Kingsbridge. Borrowings for the year ended December 31, 2019 included $20.4 and $22.5 for the funding of the acquisitions of Embrace and the Renewal Rights. (2) Borrowings for the year ended December 31, 2021 included $35.0 for the funding of the acquisition of J.C. Taylor. As of December 31, 2021, the term loans had an outstanding balance of $274.1 million, including £41.9 million ($56.7 million based upon the foreign exchange spot rate as of December 31, 2021) in a GBP term loan, and the revolving credit loan had an outstanding balance of $3.5 million. 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. As of December 31, 2021, $146.1 million of the outstanding term loans were hedged by the swap and $128.0 million of the outstanding term loans were unhedged. The following table presents the NSM weighted average interest rate for the year ended December 31, 2021 and 2020: NSM Weighted Average Interest Rate Year Ended December 31, 2021 2020 Millions Weighted Average Interest Expense (1) Weighted Average Interest rate Weighted Average Interest Expense (1) Weighted Average Interest rate Term loan - hedged $ 146.9 $ 13.2 9.0 % $ 148.4 $ 13.4 9.0 % Term loan - unhedged 129.1 9.4 7.3 % 125.8 8.6 6.8 % Total NSM Facility $ 276.0 $ 22.6 8.2 % $ 274.2 $ 22.0 8.0 % ( 1) Interest expense includes the amortization of debt issuance costs and the effect of the interest rate swap and interest rate cap and excludes $0.7 and $0.1, for the year ended December 31, 2021 and 2020, of interest expense related to the revolving credit loan and Other NSM Debt. 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 December 31, 2021, the secured term loan had an outstanding balance of $1.0 million and a maturity date of December 31, 2022. Kudu Credit Facility and Kudu Bank Facility On December 23, 2019, Kudu entered into a secured credit facility with Monroe Capital Management Advisors, LLC (the “Kudu Bank Facility”). On March 23, 2021, Kudu replaced the Kudu Bank Facility and entered into a secured revolving credit facility (the “Kudu Credit Facility”) with Massachusetts Mutual Life Insurance Company to repay the Kudu Bank Facility, and to fund new investments and related transaction expenses. The maximum borrowing capacity of the Kudu Credit Facility is $300.0 million. The Kudu Credit Facility matures on March 23, 2036. In connection with the replacement of the Kudu Bank Facility, Kudu recognized a total loss of $4.1 million, representing debt issuance costs and prepayment fees, which are included within interest expense for the period ended December 31, 2021. Interest on the Kudu Bank Facility accrues at a floating interest rate equal to the greater of the one-month USD-LIBOR and 0.25%, plus in each case, the applicable spread of 4.30%. The Kudu Credit Facility requires Kudu to maintain an interest reserve account, which is included in restricted cash. As of December 31, 2021, the interest reserve account was $4.5 million. The Kudu Credit Facility requires Kudu to maintain a ratio of outstanding balance to the sum of fair market value of participation contracts and cash held in certain accounts (the “LTV Percentage”) of less than 50% in years 0-3, 40% in years 4-6, 25% in years 7-8, 15% in years 9-10, and 0% thereafter. As of December 31, 2021, Kudu has a 34% LTV Percentage. Kudu may borrow undrawn balances within the initial three-year availability period, subject to customary terms and conditions, to the extent the amount borrowed under the Kudu Credit Facility does not exceed the borrowing base, which is equal to 35% of the fair value of qualifying Kudu Participation Contracts. When considering the fair value of qualifying Kudu Participation Contracts as of December 31, 2021, the available undrawn balance was $8.9 million. The following table presents the change in debt under the Kudu Bank Facility and Kudu Credit Facility for the years ended December 31, 2021, 2020 and 2019: Year Ended December 31, Millions 2021 2020 2019 Kudu Bank Facility Beginning balance $ 89.2 $ 57.0 $ — Term loans Borrowings 3.0 32.2 57.0 Repayments (92.2) — — Ending balance $ — $ 89.2 $ 57.0 Kudu Credit Facility Beginning balance $ — $ — $ — Term loans Borrowings 232.0 — — Repayments (6.6) — — Ending balance $ 225.4 $ — $ — The Kudu Credit Facility is secured by all property of the loan parties and contains various affirmative and negative covenants that White Mountains considers to be customary for such borrowings. Other Operations Debt As of December 31, 2021, debt in White Mountains’s Other Operations segment consisted of three secured credit facilities (collectively, “Other Operations Debt”). The first credit facility has 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. The second credit facility has a maximum borrowing capacity of $15.0 million, which is comprised of a term loan of $9.0 million, a delayed-draw term loan of $4.0 million and a revolving credit loan commitment of $2.0 million, all with a maturity date of July 2, 2025. The third credit facility has a maximum borrowing capacity of $8.0 million, which is comprised of a revolving credit loan commitment, with a maturity date of December 9, 2026. For the year ended December 31, 2021, White Mountains’s Other Operations segment borrowed $3.4 million and had no borrowings in 2020 or 2019. For the year ended December 31, 2021, 2020 and 2019, White Mountains’s Other Operations segment made repayments of $7.7 million, $2.1 million and $0.2 million. As of December 31, 2021 and 2020, the Other Operations Debt had an outstanding balance of $17.1 million and $18.0 million. Compliance As of December 31, 2021, White Mountains was in compliance in all material respects with all of the covenants under all of its debt facilities. Interest Total interest expense incurred by White Mountains for its indebtedness was $43.8 million, $29.5 million and $17.6 million for the years ended December 31, 2021, 2020 and 2019. Total interest paid by White Mountains for its indebtedness was $35.8 million, $27.0 million, and $16.3 million for the years ended December 31, 2021, 2020 and 2019.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company and its Bermuda-domiciled subsidiaries are not subject to Bermuda income tax under current Bermuda law. In the event there is a change in the current law such that taxes are imposed, the Bermuda Exempted Undertakings Tax Protection Act of 1966 states that the Company and its Bermuda-domiciled subsidiaries would be exempt from such tax until March 31, 2035. The Company has subsidiaries and branches that operate in various other jurisdictions around the world and are subject to tax in the jurisdictions in which they operate. As of December 31, 2021, the primary jurisdictions in which the Company’s subsidiaries and branches were subject to tax were Ireland, Israel, Luxembourg, the United Kingdom and the United States. The following table presents the total income tax (expense) benefit for the years ended December 31, 2021, 2020 and 2019: Year Ended December 31, Millions 2021 2020 2019 Current income tax (expense) benefit: U.S. federal $ (3.8) $ (10.4) $ .9 State (2.1) (4.2) (3.7) Non-U.S. (3.9) (1.1) (1.7) Total current income tax (expense) benefit (9.8) (15.7) (4.5) Deferred income tax (expense) benefit: U.S. federal (4.9) 23.2 (14.9) State (5.6) 10.3 (10.4) Non-U.S. (18.3) 2.7 .5 Total deferred income tax (expense) benefit (28.8) 36.2 (24.8) Total income tax (expense) benefit $ (38.6) $ 20.5 $ (29.3) Effective Rate Reconciliation The following table presents a reconciliation of taxes calculated for 2021, 2020 and 2019 using the 21% U.S. federal statutory rate U.S. federal statutory rate (the tax rate at which the majority of White Mountains’s worldwide operations are taxed) to the income tax (expense) benefit on pre-tax income (loss): Year Ended December 31, Millions 2021 2020 2019 Tax (expense) benefit at the U.S. statutory rate $ 63.4 $ (135.5) $ (85.1) Differences in taxes resulting from: Non-U.S. earnings, net of foreign taxes (77.2) 78.4 27.1 Tax rate changes (11.2) 2.7 (5.7) State taxes (6.2) (8.5) (17.5) Member’s surplus contributions (5.6) (4.8) (3.6) Change in valuation allowance (2.4) (29.2) 63.6 Officer compensation (1.5) (1.1) — Withholding tax (.3) (5.0) (1.6) Tax exempt interest and dividends .2 .8 1.1 Reorganization — 130.5 — Tax reserve adjustments — 1.9 (.7) Other, net 2.2 (9.7) (6.9) Total income tax (expense) benefit on pre-tax income (loss) $ (38.6) $ 20.5 $ (29.3) The non-U.S. component of pre-tax (loss) income was $(319.0) million, $327.8 million and $100.4 million for the years ended December 31, 2021, 2020 and 2019. The reorganization benefit resulted from the release of a deferred tax liability following an internal reorganization completed in connection with the MediaAlpha IPO. Tax Payments and Receipts Net income tax (refunds) payments totaled $(0.1) million, $16.2 million, and $3.7 million for the years ended December 31, 2021, 2020 and 2019. Deferred Tax Assets and Liabilities Deferred taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts for tax purposes. The following table presents an outline of the significant components of White Mountains’s U.S. federal, state and non-U.S. deferred tax assets and liabilities: December 31, Millions 2021 2020 Deferred tax assets related to: U.S. federal and state net operating and capital $ 102.8 $ 79.6 Non-U.S. net operating loss carryforwards 47.1 50.5 Incentive compensation 14.6 17.5 Accrued interest 10.8 7.9 Deferred acquisition costs 6.4 5.5 Tax credit carryforwards 4.9 5.5 Other items .7 1.3 Total gross deferred tax assets 187.3 167.8 Less: valuation allowances 92.3 97.4 Total net deferred tax assets 95.0 70.4 Deferred tax liabilities related to: Member’s surplus contributions 60.4 52.9 Purchase accounting 48.5 5.1 Investment basis difference 33.7 11.8 Net unrealized investment gains (losses) 10.7 .3 Deferred underwriting 4.1 — Other items 2.7 2.8 Total deferred tax liabilities 160.1 72.9 Net deferred tax asset (liability) $ (65.1) $ (2.5) White Mountains’s deferred tax assets (liabilities) are net of U.S. federal, state and non-U.S. valuation allowances and, to the extent they relate to non-U.S. jurisdictions, they are shown at year-end exchange rates. Valuation Allowance White Mountains records a valuation allowance against deferred tax assets if it becomes more likely than not that all or a portion of a deferred tax asset will not be realized. Changes in valuation allowances from period to period are included in income tax expense in the period of change. In determining whether or not a valuation allowance, or change therein, is warranted, White Mountains considers factors such as prior earnings history, expected future earnings, carryback and carryforward periods and strategies that if executed would result in the realization of a deferred tax asset. It is possible that certain planning strategies or projected earnings in certain subsidiaries may not be sufficient to utilize the entire deferred tax asset, which could result in material changes to White Mountains’s deferred tax assets and tax expense. Of the $92.3 million valuation allowance as of December 31, 2021, $42.9 million related to deferred tax assets on net operating losses in U.S. subsidiaries and other federal and state deferred tax benefits, $25.2 million related to deferred tax assets on net operating losses and net investment unrealized gains and losses in Luxembourg subsidiaries, $21.9 million related to net operating losses and other deferred tax benefits in Israeli subsidiaries and $2.3 million related to net operating losses and other deferred tax benefits in U.K. subsidiaries. Of the $97.4 million valuation allowance as of December 31, 2020, $46.5 million related to deferred tax assets on net operating losses in U.S. subsidiaries and other federal and state deferred tax benefits, $26.8 million related to deferred tax assets on net operating losses and net investment unrealized gains and losses in Luxembourg subsidiaries, $20.0 million related to net operating losses and other deferred tax benefits in Israeli subsidiaries and $4.1 million related to net operating losses and other deferred tax benefits in U.K. subsidiaries. United States During 2021, White Mountains recorded income tax benefit of $3.6 million to reflect the decrease in the valuation allowance on the net deferred tax assets in certain U.S. operations, consisting of the WM Adams Holdings, Inc. (“WM Adams”) consolidated tax group included within the Other Operations segment, as White Mountains management does not currently anticipate sufficient taxable income to utilize the remaining deferred tax assets. WM Adams includes WM Lincoln Holdings Inc. (“WM Lincoln”), WM Capital, WM Advisors and certain other entities and investments that are included in the Other Operations segment. During 2020, White Mountains recorded income tax expense of $14.9 million to establish a full valuation allowance on the deferred tax assets in certain U.S. operations, consisting of the WM Lincoln consolidated tax group included within the Other Operations segment, as White Mountains management did not currently anticipate sufficient taxable income to utilize the deferred tax assets. WM Lincoln includes WM Capital, WM Advisors and certain other entities and investments that are included in the Other Operations segment. During 2021 and 2020, White Mountains recorded income tax expense of $7.8 million and $4.5 million to reflect the increase in the valuation allowance on net deferred tax assets of BAM. On January 1, 2020, White Mountains adopted 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 changes in valuation allowance on such taxes directly through non-controlling interest equity. Prior to the adoption of ASU 2019-12, White Mountains recorded the tax expense related to BAM’s MSC to non-controlling interest equity, while the change in valuation allowance on such taxes was recorded through the income statement. During 2021 and 2020, BAM had income included in equity due to MSC that was available to offset its loss from continuing operations. In 2021 and 2020, based on the adoption of ASU 2019-12, BAM recorded both the income tax benefit on MSC of $7.5 million and $9.7 million and the offsetting expense in paid-in surplus. During 2021 and 2020, BAM continued to have a full valuation allowance recorded against its net deferred tax assets, as White Mountains management is unsure it will generate sufficient taxable income to utilize the deferred tax assets. During 2021 and 2020, White Mountains recorded income tax (benefit) expense of $(0.8) million and $1.9 million to reflect the decrease or increase of the valuation allowance against a deferred tax asset related to foreign tax credits at White Mountains Catskill Holdings, Inc., as White Mountains management is unsure it will generate sufficient taxable income to utilize the deferred tax asset. During 2021, White Mountains recorded income tax expense of $0.6 million to reflect the establishment of a valuation allowance against deferred tax assets relating to net operating losses at the US branches of the White Mountains U.K. holding companies. Non-U.S. Jurisdictions During 2021, White Mountains recorded income tax benefit of $1.6 million to reflect the decrease of the full valuation allowance against deferred tax assets which primarily relate to losses on the write-down of foreign subsidiaries and the unrealized losses on investments held in Luxembourg-domiciled subsidiaries. During 2020, White Mountains recorded income tax expense of $4.2 million to reflect the increase of the valuation allowance against most of the deferred tax assets which primarily relate to losses on the write-down of foreign subsidiaries and the unrealized losses on investments held in Luxembourg-domiciled subsidiaries. During 2021 and 2020, White Mountains recorded income tax expense of $1.9 million and $2.7 million to establish a full valuation allowance against deferred tax assets at certain Israel-domiciled subsidiaries, as White Mountains management does not currently anticipate sufficient taxable income to utilize the deferred tax assets. During 2021, White Mountains recorded income tax benefit of $1.9 million to reflect the decrease of the valuation allowance against certain deferred tax assets at U.K. subsidiaries, as White Mountains management does not currently anticipate sufficient taxable income to utilize the deferred tax assets. During 2020, White Mountains recorded income tax expense of $1.0 million to reflect the increase of the full valuation allowance against deferred tax assets at certain U.K. subsidiaries, as White Mountains management does not currently anticipate sufficient taxable income to utilize the deferred tax assets. Net Operating Loss and Capital Loss Carryforwards The following table presents net operating loss and capital loss carryforwards as of December 31, 2021, the expiration dates and the deferred tax assets thereon: December 31, 2021 Millions United States Luxembourg United Kingdom Israel Total 2021-2025 $ — $ — $ — $ — $ — 2026-2030 — — — — — 2031-2040 250.7 68.3 — — 319.0 No expiration date 213.8 28.8 6.9 93.3 342.8 Total $ 464.5 $ 97.1 $ 6.9 $ 93.3 $ 661.8 Gross deferred tax asset $ 97.6 $ 24.3 $ 1.4 $ 21.4 $ 144.7 Valuation allowance (83.2) (24.3) (.4) (21.4) (129.3) Net deferred tax asset $ 14.4 $ — $ 1.0 $ — $ 15.4 As of December 31, 2021, there are U.S. foreign tax credit carryforwards available of $4.7 million, which begin to expire in 2028. Uncertain Tax Positions Recognition of the benefit of a given tax position is based upon whether a company determines that it is more likely than not that a tax position will be sustained upon examination based upon the technical merits of the position. In evaluating the more-likely-than-not recognition threshold, White Mountains must presume that the tax position will be subject to examination by a taxing authority with full knowledge of all relevant information. If the recognition threshold is met, then the tax position is measured at the largest amount of benefit that is more than 50% likely of being realized upon ultimate settlement. The following table presents a reconciliation of the beginning and ending amount of unrecognized tax benefits from 2019 to 2021: Millions Permanent Differences (1) Temporary Differences (2) Interest and Penalties (3) Total Balance at December 31, 2018 $ 1.1 $ — $ — $ 1.1 Changes in prior year tax positions 1.3 — — 1.3 Balance at December 31, 2019 2.4 — — 2.4 Changes in prior year tax positions .1 — — .1 Tax positions taken during the current year .1 — — .1 Changes in prior year tax positions (2.6) — — (2.6) Balance at December 31, 2020 — — — — Changes in prior year tax positions — — — — Balance at December 31, 2021 $ — $ — $ — $ — (1) Represents the amount of unrecognized tax benefits that, if recognized, would impact the effective tax rate. (2) Represents the amount of unrecognized tax benefits that, if recognized, would create a temporary difference between the reported amount of an item in White Mountains’s Consolidated Balance Sheet and its tax basis. (3) Net of tax benefit. White Mountains classifies all interest and penalties on unrecognized tax benefits as part of income tax expense. During the years ended December 31, 2021, 2020 and 2019, White Mountains did not recognize any net interest (income) expense. There was no accrued interest as of December 31, 2021 and 2020. Tax Examinations With a few immaterial 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 2016.

Derivatives

Derivatives	12 Months Ended
	Dec. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
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 December 31, 2021, the variable rate received by NSM under the swap agreement was 1.00%. Over the term of the swap, the notional amount decreases in accordance with the principal repayments NSM expects to make on its initial term loans. The interest rate swap is scheduled to mature on June 30, 2024. As of December 31, 2021, $146.1 million of the outstanding term loans were hedged by the swap. For the year ended December 31, 2021, the weighted average effective interest rate on the outstanding term loans that were hedged, including the effect of the amortization of debt issuance costs and the effect of the interest rate swap, was 9.0%. 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 years ended December 31, 2021, 2020 and 2019, White Mountains recognized net interest expense of $2.5 million, $2.5 million and $1.1 million for the periodic net settlement payments on the swap. As of December 31, 2021 and 2020, the estimated fair value of the swap and the accrual of the periodic net settlement payments recorded in other liabilities was $4.8 million and $8.2 million. There was no ineffectiveness in the hedge for the years ended December 31, 2021 and 2020. For the years ended December 31, 2021 and 2020, the $(3.4) million and $(1.6) 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 ($52.4 million based upon the foreign exchange spot rate as of the date of the transaction) and the termination date is June 4, 2022. On August 18, 2020, NSM entered into a separate interest rate cap agreement to extend the term of the original interest rate cap agreement by one year. The second interest rate cap agreement has an effective date of June 15, 2022 and a termination date of June 15, 2023. NSM paid total initial premiums of $0.1 million for the interest rate caps. Under the terms of the interest rate cap agreements, 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 December 31, 2021, the GBP-LIBOR rate was 0.26%.

Municipal Bond Guarantee Insura

Municipal Bond Guarantee Insurance	12 Months Ended
	Dec. 31, 2021
Insurance [Abstract]
Municipal Bond Guarantee Insurance	Municipal Bond Guarantee Insurance HG Global was established to fund the startup of BAM, a mutual municipal bond insurer. HG Global, together with its subsidiaries, provided the initial capitalization of BAM through the purchase of $503.0 million of BAM Surplus Notes. Reinsurance Treaties FLRT BAM is a party to a first loss reinsurance treaty (“FLRT”) with HG Re under which HG Re provides first loss 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 up to 60% of the risk premium charged for insuring the municipal bond, which is net of a ceding commission. The FLRT is a perpetual agreement with terms that can be renegotiated after a specified period of time. During 2021, BAM and HG Re agreed that the terms may be renegotiated at the end of 2024, and each subsequent five-year period thereafter. Fidus Re BAM is party to a collateralized financial guarantee excess of loss reinsurance agreement that serves to increase BAM’s claims paying resources and is provided by Fidus Re. In the second quarter of 2018, Fidus Re was initially capitalized by the issuance of $100.0 million of insurance linked securities (the “Fidus Re 2018 Agreement”). 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 12 years and are callable five years after the date of issuance. Under the Fidus Re 2018 Agreement, Fidus Re reinsures 90% of aggregate losses exceeding $165.0 million on a portion of BAM’s financial guarantee portfolio (the “2018 Covered Portfolio”) up to a total reimbursement of $100.0 million. The Fidus Re 2018 Agreement does not provide coverage for losses in excess of $276.1 million. The 2018 Covered Portfolio consists of approximately 33% of BAM’s portfolio of financial guaranty policies issued through December 31, 2021. In the first quarter of 2021, Fidus Re issued an additional $150.0 million of insurance linked securities (the “Fidus Re 2021 Agreement”) with an initial term of 12 years and are callable five years after the date of issuance. The proceeds from issuance were placed in a collateral trust supporting Fidus Re’s obligations to BAM. Under the Fidus Re 2021 Agreement, Fidus Re reinsures 90% of aggregate losses exceeding $135.0 million on a portion of BAM’s financial guarantee portfolio (the “2021 Covered Portfolio”) up to a total reimbursement of $150.0 million. The Fidus Re 2021 Agreement does not provide coverage for losses in excess of $301.7 million. The 2021 Covered Portfolio consists of approximately 38% of BAM’s portfolio of financial guaranty policies issued through December 31, 2021. The Fidus Re agreements are accounted for using deposit accounting and any related financing expenses are recorded in general and administrative expenses as they do not meet the risk transfer requirements necessary to be accounted for as reinsurance. XOLT In January 2020, BAM entered into an excess of loss reinsurance agreement (the “XOLT”) with HG Re. Under the XOLT, HG Re provides last dollar protection for exposures on municipal bonds insured by BAM in excess of the New York State Department of Financial Services (“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. 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. Collateral Trusts 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. 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, 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 Regulation 114 Trust balance as of December 31, 2021 and 2020 was $250.2 million and $222.8 million. 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. The Supplemental Trust balance as of December 31, 2021 and 2020 was $601.8 million and $604.3 million. As of December 31, 2021 and 2020, the Collateral Trusts held assets of $852.0 million and $827.1 million, which included $481.7 million and $434.5 million of cash and investments, $364.6 million and $388.2 million of BAM Surplus Notes and $5.7 million and $4.4 million of interest receivable on the BAM Surplus Notes. BAM Surplus Notes Through 2024, the interest rate on the BAM Surplus Notes is a variable rate equal to the one-year U.S. Treasury rate plus 300 basis points, set annually. During 2022, the interest rate on the BAM Surplus Notes will be 3.2%. Beginning in 2025, 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. In December 2021, BAM made a $33.8 million cash payment of principal and interest on the BAM Surplus Notes held by HG Global. Of this payment, $23.6 million was a repayment of principal held in the Supplemental Trust, $0.4 million was a payment of accrued interest held inside the Supplemental Trust and $9.8 million was a payment of accrued interest held outside the Supplemental Trust. In December 2020, BAM made a $30.1 million cash payment of principal and interest on the BAM Surplus Notes held by HG Global. Of this payment, $21.5 million was a repayment of principal held in the Supplemental Trust, $0.2 million was a payment of accrued interest held inside the Supplemental Trust and $8.4 million was a payment of accrued interest held outside the Supplemental Trust. In January 2020, BAM made a one-time $65.0 million cash payment of principal and interest on the BAM Surplus Notes held by HG Global. 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 December 31, 2021 and 2020, the principal balance on the BAM Surplus Notes was $364.6 million and $388.2 million and total interest receivable on the BAM Surplus Notes was $157.6 million and $155.7 million. Insured Obligations and Premiums The following table presents a schedule of BAM’s insured obligations as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Contracts outstanding 12,350 10,997 Remaining weighted average contract period (in years) 10.8 10.7 Contractual debt service outstanding (in millions): Principal $ 89,196.5 $ 75,287.7 Interest 41,486.5 36,448.8 Total debt service outstanding $ 130,683.0 $ 111,736.5 Gross unearned insurance premiums $ 266.3 $ 237.5 The following table presents a schedule of BAM’s future premium revenues as of December 31, 2021: Millions December 31, 2021 January 1, 2022 - March 31, 2022 $ 6.4 April 1, 2022 - June 30, 2022 6.4 July 1, 2022 - September 30, 2022 6.3 October 1, 2022 - December 31, 2022 6.1 25.2 2023 23.9 2024 22.2 2025 20.6 2026 19.1 2027 and thereafter 155.3 Total gross unearned insurance premiums $ 266.3 The following table presents a schedule of written premiums and earned premiums included in White Mountains’s HG Global/BAM segment for the years ended December 31, 2021, 2020 and 2019: Millions December 31, 2021 December 31, 2020 December 31, 2019 Written premiums: Direct $ 51.2 $ 61.5 $ 28.1 Assumed 4.6 .2 10.6 Gross written premiums (1) $ 55.8 $ 61.7 $ 38.7 Earned premiums: Direct $ 23.2 $ 19.4 $ 13.6 Assumed 3.7 3.4 2.7 Gross earned premiums (1) $ 26.9 $ 22.8 $ 16.3 (1) There are no ceded premium amounts in the periods presented and Gross earned premium are equivalent to net written premiums and net earned premiums. In the third quarter of 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 the second quarter of 2020, BAM assumed a municipal bond guarantee contract with a par value of $36.9 million through an endorsement to the facultative quota share reinsurance agreement. In the first quarter of 2021, BAM entered into a 100% facultative quota share reinsurance agreement under which it assumed a portfolio of municipal bond guarantee contracts with a par value of $0.8 billion. None of the contracts assumed under these reinsurance agreements were non-performing and no loss reserves have been established for any of the contracts, either as of the transaction dates or as of December 31, 2021. The agreements, which cover future claims exposure only, meet the risk transfer criteria under ASC 944-20, Insurance Activities and accordingly have been accounted for as reinsurance.

Earnings Per Share

Earnings Per Share	12 Months Ended
	Dec. 31, 2021
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 years ended December 31, 2021, 2020 and 2019. See Note 21 — “Held for Sale and Discontinued Operations” . Year Ended December 31, 2021 2020 2019 Basic and diluted earnings per share numerators (in millions): Net income (loss) attributable to White Mountains’s $ (275.4) $ 708.7 $ 414.5 Less: total (loss) income from discontinued operations, net of tax 18.7 (2.3) .8 Net income (loss) from continuing operations attributable to (294.1) 711.0 413.7 Allocation of (earnings) losses to participating restricted common shares (1) 3.5 (9.3) (5.3) Basic and diluted earnings (losses) per share numerators $ (290.6) $ 701.7 $ 408.4 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,079.0 3,122.2 3,181.6 Average unvested restricted common shares (2) (36.5) (40.8) (40.5) Basic earnings (losses) per share denominator 3,042.5 3,081.4 3,141.1 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,079.0 3,122.2 3,181.6 Average unvested restricted common shares (2) (36.5) (40.8) (40.5) Diluted earnings (losses) per share denominator 3,042.5 3,081.4 3,141.1 Basic and diluted earnings per share (in dollars) - continuing operations: Distributed earnings - dividends declared and paid $ 1.00 $ 1.00 $ 1.00 Undistributed earnings (losses) (96.53) 226.72 129.02 Basic and diluted earnings (losses) per share $ (95.53) $ 227.72 $ 130.02 (1) Restricted shares issued by White Mountains receive dividends, and therefore, are considered participating securities. (2) Restricted shares outstanding vest upon a stated date. See Note 12 — “Employee Share-Based Incentive Compensation Plans”. The following table presents the undistributed net earnings (losses) from continuing operations for the years ended December 31, 2021, 2020 and 2019. See Note 21 — “Held for Sale and Discontinued Operations” . Year Ended December 31, Millions 2021 2020 2019 Undistributed net earnings - continuing operations: Net income (loss) attributable to White Mountains’s common shareholders, $ (290.6) $ 701.7 $ 408.4 Dividends declared, net of restricted common share amounts (1) (3.1) (3.1) (3.2) Total undistributed net earnings (losses), net of restricted common share amounts $ (293.7) $ 698.6 $ 405.2 (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	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Employee Share-Based Incentive Compensation Plans	Employee Share-Based Incentive Compensation Plans White Mountains’s share-based incentive compensation plans are designed to incentivize key employees to maximize shareholder value over long periods of time. White Mountains believes that this is best pursued by utilizing a pay-for-performance program that closely aligns the financial interests of management with those of its shareholders. White Mountains accomplishes this by emphasizing highly variable long-term compensation that is contingent on performance over a number of years rather than entitlements. White Mountains expenses all its share-based compensation. As a result, White Mountains’s calculation of its owners’ returns includes the expense of all outstanding share-based compensation awards. Incentive Compensation Plans The WTM Incentive Plan provides for grants of various types of share-based and non-share-based incentive awards to key employees and directors of White Mountains. The WTM Incentive Plan was adopted by the Board, was approved by the Company’s sole shareholder in 1985 and was subsequently amended by its shareholders in 1995, 2001, 2003, 2005, 2010, 2013 and 2019. Share-based incentive awards that may be granted under the plan include performance shares, restricted shares, incentive stock options and non-qualified stock options. 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 The following table presents performance share activity for the years ended December 31, 2021, 2020 and 2019 for performance shares granted under the WTM Incentive Plan: Year Ended December 31, 2021 2020 2019 $ in Millions Target Accrued Target Accrued Target Accrued Beginning of period 42,458 $ 56.3 42,473 $ 43.7 40,616 $ 31.7 Shares paid or expired (1) (14,336) (35.2) (14,070) (27.7) (13,715) (18.1) New grants 13,475 — 14,055 — 15,600 — Forfeitures and cancellations (2) (769) .4 — (.4) (28) (.1) Expense recognized — 20.7 — 40.7 — 30.2 End of period 40,828 $ 42.2 42,458 $ 56.3 42,473 $ 43.7 (1) WTM performance share payments in 2021 for the 2018-2020 performance cycle, which were paid in March 2021 at 200% of target. WTM performance share payments in 2020 for the 2017-2019 performance cycle, which were paid 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 March 2019, ranged from 139% to 166% of target. (2) Amounts include changes in assumed forfeitures, as required under GAAP. During 2021, White Mountains granted 13,475 performance shares for the 2021-2023 performance cycle. During 2020, White Mountains granted 14,055 performance shares for the 2020-2022 performance cycle. During 2019, White Mountains granted 15,600 performance shares for the 2018-2020 performance cycle. For the 2018-2020, 2017-2019 and 2016-2018 performance cycles, all performance shares earned were settled in cash. If the outstanding performance shares had vested on December 31, 2021, the total additional compensation cost to be recognized would have been $12.0 million, based on accrual factors as of December 31, 2021 (common share price and payout assumptions). The following table presents performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan as of December 31, 2021 for each performance cycle: $ in Millions Target Performance Accrued Expense Performance cycle: 2019 – 2021 14,625 $ 25.3 2020 – 2022 13,350 15.4 2021 – 2023 13,475 2.1 Sub-total 41,450 42.8 Assumed forfeitures (622) (.6) Total 40,828 $ 42.2 For the 2021-2023 performance cycle, the targeted performance goal for full payment of outstanding performance shares granted under the WTM Incentive Plan is 8% average growth in adjusted book value per share and intrinsic value per share. Average growth of 3% or less would result in no payout and average growth of 13% or more would result in a payout of 200%. For the 2020-2022 performance cycle, the targeted performance goal for full payment of outstanding performance shares granted under the WTM Incentive Plan is 7% average growth in adjusted book value per share and intrinsic value per share. Average growth of 2% or less would result in no payout and average growth of 12% or more would result in a payout of 200%. For the 2019-2021 performance cycle, the targeted performance goal for full payment of outstanding performance shares granted under the WTM Incentive Plan is 7% average growth in adjusted book value per share and intrinsic value per share. Average growth of 2% or less would result in no payout and average growth of 12% or more would result in a payout of 200%. Restricted Shares Restricted shares are grants of a specified number of common shares that generally vest at the end of a three Year Ended December 31, 2021 2020 2019 $ in Millions Restricted Unamortized Restricted Unamortized Restricted Unamortized Non-vested, Beginning of period 43,105 $ 15.2 43,395 $ 16.7 41,510 $ 12.5 Issued 13,475 16.1 14,055 15.1 15,600 14.5 Vested (17,936) — (14,345) — (13,715) — Forfeited (794) (.8) — — — — Expense recognized — (14.6) — (16.6) — (10.3) End of period 37,850 $ 15.9 43,105 $ 15.2 43,395 $ 16.7

Leases

Leases	12 Months Ended
	Dec. 31, 2021
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. As of December 31, 2021 and 2020, the right-of-use (“ROU”) asset was $42.2 million and $37.6 million and lease liabilities were $45.2 million and $38.3 million. The following table summarizes net lease expense recognized in White Mountains’s consolidated statement of operations for the years ended December 31, 2021 and 2020: Millions Lease Cost December 31, 2021 December 31, 2020 Lease cost $ 9.9 $ 7.7 Less: sublease income .4 .4 Net lease cost $ 9.5 $ 7.3 The following table presents the contractual maturities of the lease liabilities associated with White Mountains’s operating lease agreements as of December 31, 2021: Millions December 31, 2021 2022 $ 10.9 2023 9.9 2024 8.5 2025 6.8 2026 4.3 Thereafter 11.9 Total undiscounted lease payments 52.3 Less: present value adjustment (7.1) Operating lease liability $ 45.2 The following table presents lease related assets and liabilities by reportable segment as of December 31, 2021 and 2020: As of December 31, 2021 $ in Millions HG/BAM Ark NSM Kudu Other Operations Total Weighted Average Incremental Borrowing Rate (1) ROU lease asset $ 7.6 $ 7.0 $ 14.0 $ 6.5 $ 7.1 $ 42.2 5% Lease liability $ 8.1 $ 7.0 $ 15.2 $ 7.1 $ 7.8 $ 45.2 (1) The present value of the remaining lease payments was determined by discounting the lease payments using the incremental borrowing rate. December 31, 2020 $ in Millions HG/BAM NSM Kudu Other Operations Total Weighted Average Incremental Borrowing Rate (1) ROU lease asset $ 10.1 $ 17.1 $ 2.0 $ 8.4 $ 37.6 4.6% Lease liability $ 10.1 $ 17.1 $ 2.0 $ 9.1 $ 38.3 (1) The present value of the remaining lease payments was determined by discounting the lease payments using the incremental borrowing rate.

Common Shareholders_ Equity and

Common Shareholders’ Equity and Non-controlling Interests	12 Months Ended
	Dec. 31, 2021
Stockholders' Equity Note [Abstract]
Common Shareholders’ Equity and Non-controlling Interests	Common Shareholders’ Equity and Non-controlling Interests Common Shares Repurchased and Retired During the past several years, White Mountains’s board of directors authorized the Company to repurchase its common shares, from time to time, subject to market conditions. Shares may be repurchased on the open market or through privately negotiated transactions. The repurchase authorizations do not have a stated expiration date. As of December 31, 2021, White Mountains may repurchase an additional 451,224 shares under these board authorizations. In addition, from time to time White Mountains has also repurchased its common shares through tender offers that were separately authorized by its board of directors. During 2021, the Company repurchased 98,511 common shares for $107.5 million at an average share price of $1,091, which were comprised of 91,293 common shares repurchased under the board authorizations for $100.0 million at an average share price of $1095 and 7,218 common shares repurchased pursuant to employee benefit plans. During 2020, the Company repurchased 99,087 common shares for $85.1 million at an average share price of $859 pursuant to employee benefit plans. During 2019, the Company repurchased 5,679 common shares for $4.9 million at an average share price of $858 pursuant to employee benefit plans. Common Shares Issued During 2021, the Company issued a total of 15,066 common shares, which consisted of 13,475 restricted shares issued to key personnel, 1,591 shares issued to directors of the Company. During 2020, the Company issued a total of 15,745 common shares, which consisted of 14,055 restricted shares issued to key personnel and 1,440 shares issued to directors of the Company and 250 shares issued to MediaAlpha’s management. During 2019, the Company issued a total of 17,917 common shares, which consisted of 15,600 restricted shares issued to key personnel, 2,317 shares issued to directors of the Company. Dividends on Common Shares For the years ended December 31, 2021, 2020 and 2019, the Company declared and paid cash dividends totaling $3.1 million, $3.2 million and $3.2 million (or $1.00 per common share). 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 December 31, 2021 and 2020: December 31, 2021 December 31, 2020 $ in Millions Non-controlling Percentage Non-controlling Equity Non-controlling Percentage Non-controlling Equity Non-controlling interests, excluding BAM HG Global 3.1 % $ 8.9 3.1 % $ 13.5 Ark 28.0 % 230.7 — % — NSM 3.5 % 16.7 3.4 % 17.0 Kudu 2.5 % 12.4 .7 % 2.3 Other various 11.9 various 2.4 Total, excluding BAM 280.6 35.2 BAM 100.0 % (124.0) 100.0 % (123.3) Total non-controlling interests $ 156.6 $ (88.1)

Statutory Capital and Surplus

Statutory Capital and Surplus	12 Months Ended
	Dec. 31, 2021
Insurance [Abstract]
Statutory Capital and Surplus	Statutory Capital and Surplus White Mountains’s insurance operations are subject to regulation and supervision in each of the jurisdictions where they are domiciled and licensed to conduct business. Generally, regulatory authorities have broad supervisory and administrative powers over such matters as licenses, standards of solvency, premium rates, policy forms, investments, security deposits, methods of accounting, form and content of financial statements, minimum capital and surplus requirements, dividends and other distributions to shareholders, periodic examinations and annual and other report filings. In general, such regulation is for the protection of policyholders rather than shareholders. The Insurance Act 1978 of Bermuda and related regulations, as amended (“Insurance Act”), regulates the insurance business of Bermuda-domiciled insurers. Under the Insurance Act, insurers are required to maintain available statutory capital and surplus at a level equal to or in excess of its enhanced capital requirement which is established by reference to either a Bermuda Solvency Capital Requirement (“BSCR”) model or an approved internal capital model. Generally, the Bermuda Monetary Authority (“BMA”) has broad supervisory and administrative powers over such matters as licenses, standards of solvency, investments, methods of accounting, form and content of financial statements, minimum capital and surplus requirements, and annual and other report filings. HG Global/BAM HG Re is a Special Purpose Insurer under Bermuda insurance regulations and is subject to regulation and supervision by the BMA. As of December 31, 2021, HG Re had statutory capital and surplus of $760.0 million. As a Special Purpose Insurer, HG Re has a nominal minimum regulatory capital requirement of $1. BAM is domiciled in New York and is subject to regulation by the NYDFS. New York financial guarantee insurance law establishes single risk and aggregate limits with respect to insured obligations insured by financial guarantee insurers. BAM’s statutory net income (loss) for the years ended December 31, 2021, 2020 and 2019 was $(49.3) million, $(59.3) million and $(38.3) million. BAM’s statutory surplus, as reported to regulatory authorities as of December 31, 2021, was $298.1 million, which exceeds the minimum statutory surplus necessary for BAM to maintain its New York State financial guarantee insurance license of $66.0 million. Ark Syndicates 4020 and 3902 are subject to oversight by the Council of Lloyd’s. Ark Syndicate Management Limited (“ASML”) is authorized by the U.K.’s Prudential Regulation Authority and regulated by the Financial Conduct Authority under the Financial Services and Markets Act 2000. The underwriting capacity of a Member of Lloyd’s must be supported by providing a deposit in the form of cash, securities or letters of credit in an amount determined under the capital adequacy regime of the U.K.’s Prudential Regulation Authority (the “PRA”). This amount is determined by Lloyd’s and is based on each syndicate’s solvency and capital requirement as calculated through its internal model. In addition, if the Funds at Lloyd’s are not sufficient to cover all losses, the Lloyd’s Central Fund provides an additional discretionary level of security for policyholders. As of December 31, 2021, Ark had provided Funds at Lloyd’s of $343.6 million. GAIL is subject to regulation and supervision by the BMA. As of December 31, 2021, GAIL had statutory capital and surplus of $780.3 million. GAIL’s minimum statutory capital and surplus requirement established by the BMA was $288.2 million as of December 31, 2021. Dividend Capacity There are no restrictions under Bermuda law or the law of any other jurisdiction on the payment of dividends from retained earnings by White Mountains, provided that after the payment of any dividend, the Company would continue to be able to pay its liabilities as they become due and the realizable value of the Company’s assets would remain greater that its liabilities. Following is a description of the dividend capacity of White Mountains’s reinsurance and other operating subsidiaries: HG Global/BAM As of December 31, 2021, HG Global had $619.0 million face value of preferred shares outstanding, of which White Mountains owned 96.9%. Holders of the HG Global preferred shares receive cumulative dividends at a fixed annual rate of 6.0% on a quarterly basis, when and if declared by HG Global. During 2021, HG Global declared and paid a $22.0 million preferred dividend, of which $21.3 million was paid to White Mountains. As of December 31, 2021, HG Global had accrued $414.7 million of dividends payable to holders of its preferred shares, of which $400.5 million was payable to White Mountains and eliminated in consolidation. As of December 31, 2021, HG Global and its subsidiaries had $3.1 million of cash outside of HG Re. HG Re is a Special Purpose Insurer subject to regulation and supervision by the BMA, but does not require regulatory approval to pay dividends. However, HG Re’s dividend capacity is limited to amounts held outside of the Collateral Trusts pursuant to the FLRT with BAM. As of December 31, 2021, HG Re had $760.0 million of statutory capital and surplus and $852.0 million of assets held in the Collateral Trusts pursuant to the FLRT with BAM. 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, 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. 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. As of December 31, 2021, the Collateral Trusts held assets of $852.0 million, which included $481.7 million of cash and investments, $364.6 million of BAM Surplus Notes and $5.7 million of interest receivable on the BAM Surplus Notes. As of December 31, 2021, HG Re had $9.4 million of cash and investments and $116.8 million of accrued interest on the BAM Surplus Notes held outside the Collateral Trusts. Through 2024, the interest rate on the BAM Surplus Notes is a variable rate equal to the one-year U.S. Treasury rate plus 300 basis points, set annually. During 2022, the interest rate on the BAM Surplus Notes will be 3.2%. Beginning in 2025, 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, 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. In December 2021, BAM made a $33.8 million cash payment of principal and interest on the BAM Surplus Notes held by HG Global. Of this payment, $23.6 million was a repayment of principal held in the Supplemental Trust, $0.4 million was a payment of accrued interest held in the Supplemental Trust and $9.8 million was a payment of accrued interest held outside the Supplemental Trust. In December 2020, BAM made a $30.1 million cash payment of principal and interest on the BAM Surplus Notes held by HG Global. Of this payment, $21.5 million was a repayment of principal held in the Supplemental Trust, $0.2 million was a payment of accrued interest held in the Supplemental Trust and $8.4 million was a payment of accrued interest held outside the Supplemental Trust. In January 2020, BAM made a one-time $65.0 million cash payment of principal and interest on the BAM Surplus Notes held by HG Global. Of this payment, $47.9 million was a repayment of principal held in the Supplemental Trust, $0.9 million was a payment accrued interest held in the Supplemental Trust and $16.2 million was a payment of accrued interest held outside the Supplemental Trust. Ark During any 12-month period, GAIL, a class 4 licensed Bermuda insurer, has the ability to (i) make capital distributions based on 15%of its total statutory capital per the previous year’s statutory financial statements, or (ii) make dividend payments based on 25% of its total statutory capital and surplus per the previous year’s statutory financial statements, without prior approval of Bermuda regulatory authorities. Accordingly, White Mountains expects GAIL will have the ability to make capital distributions of $113.6 million during 2022, which is equal to 15% of its December 31, 2021 statutory capital of $757.6 million, subject to meeting all appropriate liquidity and solvency requirements and the filing of its December 31, 2021 statutory financial statements. During 2021, GAIL did not pay a dividend to its immediate parent. As of December 31, 2021, Ark and its intermediate holding companies had $4.0 million of net unrestricted cash, short-term investments and fixed maturity investments outside of its regulated and unregulated insurance and reinsurance operating subsidiaries. During 2021, Ark did not pay any dividends to its immediate parent. NSM During 2021, NSM distributed $8.0 million to unitholders, substantially all of which was paid to White Mountains. As of December 31, 2021, NSM had $22.3 million of net unrestricted cash and short-term investments. Kudu During 2021, Kudu distributed $19.4 million to unitholders, substantially all of which was paid to White Mountains. As of December 31, 2021, Kudu had $16.9 million of net unrestricted cash and short-term investments.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2021
Segment Reporting [Abstract]
Segment Information	Segment Information As of December 31, 2021, White Mountains conducted its operations through five segments: (1) HG Global/BAM, (2) Ark, (3) NSM, (4) Kudu and (5) Other Operations. As a result of the Ark Transaction, White Mountains began consolidating Ark in its financial statements as of January 1, 2021. See Note 2 — “Significant Transactions” . As a result of the Kudu Transaction, White Mountains began consolidating Kudu in its financial statements in the second quarter of 2019. White Mountains’s segment disclosures for the year ended December 31, 2019 include Kudu’s results of operations for the period from April 4, 2019, the date of the Kudu Transaction, to December 31, 2019. See Note 2 — “Significant Transactions” . As a result of the 2019 MediaAlpha Transaction, White Mountains no longer consolidated MediaAlpha, and consequently it was no longer a reportable segment. White Mountains’s segment disclosures for the year ended December 31, 2019 include MediaAlpha’s results of operations for the period from January 1, 2019 to February 26, 2019, the date of the 2019 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: Millions HG Global/BAM (1) Ark NSM (3) Kudu Other Total Year Ended December 31, 2021 Earned insurance premiums (2) $ 26.9 $ 637.3 $ — $ — $ — $ 664.2 Net investment income 17.5 2.9 — 43.9 18.2 82.5 Net realized and unrealized investment gains (losses) (22.9) 16.5 — 89.9 50.7 134.2 Net realized and unrealized investment gains (losses) — — — — (380.3) (380.3) Commission revenues (4) — — 258.0 — 9.6 267.6 Other revenues 1.5 11.8 72.4 .2 90.7 176.6 Total revenues 23.0 668.5 330.4 134.0 (211.1) 944.8 Loss and loss adjustment expenses — 314.8 — — — 314.8 Insurance acquisition expenses 8.3 178.0 — — — 186.3 Cost of sales — — — — 69.3 69.3 General and administrative expenses 57.1 115.5 190.1 14.5 105.7 482.9 Broker commission expense — — 80.2 — — 80.2 Change in fair value of contingent — — 1.0 — — 1.0 Amortization of other intangible assets — — 35.2 .3 4.3 39.8 Loss on assets held for sale — — 28.7 — — 28.7 Interest expense — 7.3 23.3 11.7 1.5 43.8 Total expenses 65.4 615.6 358.5 26.5 180.8 1,246.8 Pre-tax income (loss) $ (42.4) $ 52.9 $ (28.1) $ 107.5 $ (391.9) $ (302.0) (1) BAM manages its affairs on a statutory accounting basis. BAM’s statutory surplus includes the BAM Surplus Notes and is not reduced by accruals of interest expense on the BAM Surplus Notes. BAM’s statutory surplus is reduced only after a payment of principal or interest has been approved by the NYDFS. (2) Ark’s earned insurance premiums based on the location of Ark’s underwriting offices in the United Kingdom and Bermuda are $459.3 and $178.0. (3) Includes the results of J.C. Taylor from August 6, 2021, the date of the J.C. Taylor transaction. (4) Approximately 25% of NSM’s commission revenue was associated with one single carrier. Millions HG Global/BAM (1) NSM Kudu Other Total Year Ended December 31, 2020 Earned insurance premiums $ 22.8 $ — $ — $ — $ 22.8 Net investment income 19.5 — 29.5 82.0 131.0 Net realized and unrealized investment gains (losses) 23.7 — 15.9 (8.8) 30.8 Net realized and unrealized investment gains (losses) — — — 686.0 686.0 Commission revenues (2) — 232.5 — 8.3 240.8 Other revenues 2.5 52.6 .3 13.9 69.3 Total revenues 68.5 285.1 45.7 781.4 1,180.7 Insurance acquisition expenses 7.0 — — — 7.0 Cost of sales — — — 11.3 11.3 General and administrative expenses 56.8 176.9 11.8 141.9 387.4 Broker commission expense — 75.3 — — 75.3 Change in fair value of contingent — (3.3) — — (3.3) Amortization of other intangible assets — 26.7 .3 1.3 28.3 Interest expense — 22.1 6.0 1.4 29.5 Total expenses 63.8 297.7 18.1 155.9 535.5 Pre-tax income (loss) $ 4.7 $ (12.6) $ 27.6 $ 625.5 $ 645.2 (1) BAM manages its affairs on a statutory accounting basis. BAM’s statutory surplus includes the BAM Surplus Notes and is not reduced by accruals of interest expense on the BAM Surplus Notes. BAM’s statutory surplus is reduced only after a payment of principal or interest has been approved by the NYDFS. (2) Approximately 19% of NSM’s commission revenue was associated with one single carrier. Millions HG Global/BAM (1) NSM Kudu (2) MediaAlpha (3) Other Total Year Ended December 31, 2019 Earned insurance premiums $ 16.3 $ — $ — $ — $ — $ 16.3 Net investment income 21.6 — 14.7 — 43.4 79.7 Net realized and unrealized 27.1 — 6.3 — 219.8 253.2 Net realized and unrealized investment — — — — 180.0 180.0 Gain from deconsolidation from — — — — 67.5 67.5 Advertising and commission revenues (4) — 193.4 — 48.8 6.9 249.1 Other revenues 1.6 39.7 .2 — 6.1 47.6 Total revenues 66.6 233.1 21.2 48.8 523.7 893.4 Insurance acquisition expenses 5.7 — — — — 5.7 Cost of sales — — — 40.6 7.5 48.1 General and administrative expenses 50.9 132.2 10.1 12.5 122.5 328.2 Broker commission expense — 64.8 — — — 64.8 Change in fair value of contingent — 2.1 — — — 2.1 Amortization of other intangible assets — 19.4 .2 1.6 .6 21.8 Interest expense — 16.7 .1 .2 .6 17.6 Total expenses 56.6 235.2 10.4 54.9 131.2 488.3 Pre-tax income (loss) $ 10.0 $ (2.1) $ 10.8 $ (6.1) $ 392.5 $ 405.1 (1) BAM manages its affairs on a statutory accounting basis. BAM’s statutory surplus includes the BAM Surplus Notes and is not reduced by accruals of interest expense on the BAM Surplus Notes. BAM’s statutory surplus is reduced only after a payment of principal or interest has been approved by the NYDFS. (2) Kudu’s results are from April 4, 2019, the date of the Kudu Transaction, to December 31, 2019. (3) MediaAlpha’s results are from January 1, 2019 to February 26, 2019, the date of the 2019 MediaAlpha Transaction. (4) Approximately 17% of NSM’s commission revenue was associated with one single carrier. Millions HG Global/BAM Ark NSM Kudu Other Held for Sale Total December 31, 2021: Total investments $ 966.5 $ 1,562.1 $ — $ 669.5 $ 1,067.2 $ — $ 4,265.3 Total assets $ 1,044.8 (1) $ 3,027.0 $ 977.3 $ 727.1 $ 1,208.4 (2) $ 16.1 $ 7,000.7 Total liabilities $ 321.9 (2) $ 2,122.4 $ 495.3 $ 261.0 $ 95.4 $ — $ 3,296.0 Total White Mountains’s $ 838.0 (2) $ 673.9 $ 465.3 $ 453.7 $ 1,101.1 (2) $ 16.1 $ 3,548.1 Non-controlling interest $ (115.1) $ 230.7 $ 16.7 $ 12.4 $ 11.9 $ — $ 156.6 December 31, 2020: Total investments $ 919.9 $ — $ — $ 400.6 $ 1,618.5 $ — $ 2,939.0 Total assets $ 1,017.8 (1) $ — $ 999.6 $ 430.2 $ 2,381.5 (2) $ 2.3 $ 4,831.4 Total liabilities $ 291.5 (2) $ — $ 491.8 $ 96.3 $ 133.9 $ — $ 1,013.5 Total White Mountains’s $ 836.1 (2) $ — $ 490.7 $ 331.6 $ 2,245.3 (2) $ 2.3 $ 3,906.0 Non-controlling interest $ (109.8) $ — $ 17.1 $ 2.3 $ 2.3 $ — $ (88.1) (1) As of December 2021 and 2020, total assets in the HG Global/BAM segment reflected the elimination of $364.6 and $388.2 of BAM Surplus Notes issued to HG Global and its subsidiaries, and $157.6 and $155.7 in accrued interest related to the BAM Surplus Notes. (2) HG Global preferred dividends payable to White Mountains’s subsidiaries is eliminated in White Mountains’s consolidated financial statements. For segment reporting, the HG Global preferred dividends payable to White Mountains’s subsidiaries included within the HG Global/BAM segment are eliminated against the offsetting receivable included within the Other Operations segment and therefore added back to White Mountains’s common shareholders’ equity within the HG Global/BAM segment. As of December 31, 2021 and 2020, the HG Global preferred dividends payable to White Mountains’s subsidiaries was $400.5 and $363.9. In compliance with ASC 606, Revenues from Contracts with Customers, the following tables present White Mountains’s total revenues by revenue source: Millions HG Global/BAM Ark NSM Kudu Other Total Year Ended December 31, 2021 Commission and other revenue Specialty Transportation (1) $ — $ — $ 97.2 $ — $ — $ 97.2 Pet — — 76.3 — — 76.3 United Kingdom — — 53.1 — — 53.1 Real Estate — — 34.4 — — 34.4 Social Services — — 33.9 — — 33.9 Other — — 35.5 — 9.6 45.1 Total commission and other revenue — — 330.4 — 9.6 340.0 Products and service revenues — — — — 87.5 87.5 Revenues from contracts with customers — — 330.4 — 97.1 427.5 Other (2) 23.0 668.5 — 134.0 (308.2) 517.3 Total revenues $ 23.0 $ 668.5 $ 330.4 $ 134.0 $ (211.1) $ 944.8 (1) Includes the results of J.C. Taylor from August 6, 2021, the date of the J.C. Taylor transaction. (2) 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 Total Year Ended December 31, 2020 Commission and other revenue Specialty Transportation $ — $ 85.5 $ — $ — $ 85.5 Pet — 55.0 — — 55.0 United Kingdom — 49.4 — — 49.4 Real Estate — 44.9 — — 44.9 Social Services — 28.9 — — 28.9 Other — 21.4 — 8.3 29.7 Total commission and other revenue — 285.1 — 8.3 293.4 Products and service revenues — — — 14.5 14.5 Revenues from contracts with customers — 285.1 — 22.8 307.9 Other (1) 68.5 — 45.7 758.6 872.8 Total revenues $ 68.5 $ 285.1 $ 45.7 $ 781.4 $ 1,180.7 (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 (2) MediaAlpha (3) Other Total Year Ended December 31, 2019 Commission and other revenue Specialty Transportation $ — $ 77.6 $ — $ — $ — $ 77.6 United Kingdom — 45.9 — — — 45.9 Pet — 30.0 — — — 30.0 Real Estate — 34.7 — — — 34.7 Social Services — 25.9 — — — 25.9 Other — 19.0 — — 6.9 25.9 Total commission and other revenue — 233.1 — — 6.9 240.0 Advertising revenues — — — 48.8 — 48.8 Product and service revenues — — — 5.5 5.5 Revenues from contracts with customers — 233.1 — 48.8 12.4 294.3 Other (1) 66.6 — 21.2 — 511.3 599.1 Total revenues $ 66.6 $ 233.1 $ 21.2 $ 48.8 $ 523.7 $ 893.4 (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) Kudu’s results are from April 4, 2019, the date of the Kudu Transaction, to December 31, 2019. (3) MediaAlpha’s results are from January 1, 2019 to February 26, 2019, the date of the 2019 MediaAlpha Transaction.

Equity Method Eligible Investme

Equity Method Eligible Investments	12 Months Ended
	Dec. 31, 2021
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Eligible Investments	Equity Method Eligible Investments White Mountains’s equity method eligible investments include White Mountains’s investment in MediaAlpha, certain other unconsolidated entities, including Kudu’s Participation Contracts, private equity funds and hedge funds in which White Mountains has the ability to exert significant influence over the investee’s operating and financial policies. The following table presents the ownership interests and carrying values of White Mountains’s equity method eligible investments as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Millions Ownership Interest Carrying Value Ownership Interest Carrying Value Kudu Participation Contracts (1) 3.2 - 32.0% $ 669.5 3.2 - 35.0% $ 400.6 Investment in MediaAlpha 28.0 % 261.6 35.0 % 802.2 PassportCard/DavidShield 53.8 % 120.0 53.8 % 95.0 Elementum Holdings, L.P. 29.7 % 45.0 28.9 % 55.1 Other equity method eligible investments, at fair value Under 50.0% 109.3 Under 50.0% 132.2 Other equity method eligible investments, at fair value 50.0% and over 17.8 50.0% and over 15.2 (1) Ownership interest generally references basic ownership interest with the exception of Kudu’s Participation Contracts, which are non-controlling equity interests in the form of revenue and earnings participation contracts. For the years ended December 31, 2021, 2020 and 2019, White Mountains received dividend and income distributions from equity method eligible investments of $56.2 million, $95.0 million and $14.8 million, which were recorded within net investment income in the consolidated statement of operations. As a result of the 2019 MediaAlpha Transaction, 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. 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. Following the MediaAlpha IPO, White Mountains’s investment in MediaAlpha is accounted for at fair value based on the publicly traded share price of MediaAlpha’s common stock and White Mountains presents its investment in MediaAlpha as a separate line item on the balance sheet. See Note 2 — “Significant Transactions”. For the period from February 26, 2019 to December 31, 2019 and for the year ended December 31, 2020, MediaAlpha was considered a significant subsidiary. For the period from February 26, 2019 to December 31, 2019, MediaAlpha’s total revenues, total expenses, and net income were $359.2 million, $336.3 million, and $22.9 million. The following tables present summarized financial information for MediaAlpha as of December 31, 2021 and 2020 for the years ended December 31, 2021, 2020, and 2019: December 31, Millions 2021 2020 Balance sheet data: Total assets $ 289.8 $ 210.3 Total liabilities $ 351.4 $ 315.5 Year Ended December 31, Millions 2021 2020 2019 (1) Income statement data: Total revenues $ 645.3 $ 584.8 $ 408.0 Total expenses $ 653.8 $ 574.2 $ 390.2 Net income (loss) $ (8.5) $ 10.6 $ 17.8 (1) For the year ended December 31, 2019, MediaAlpha recorded out of period adjustments that increased (decreased) total revenues by $0.1, total expenses by $1.2 and net income by $(1.1). The adjustments primarily related to MediaAlpha’s accounting for its equity-based compensation and amortization of other intangible assets. White Mountains has evaluated the impact of the adjustments and concluded that they are not material, individually and in the aggregate, to current or prior period financial statements. The following tables present aggregated summarized financial information for White Mountains’s investments in equity method eligible unconsolidated entities, excluding MediaAlpha: December 31, Millions 2021 2020 Balance sheet data (1) : Total assets $ 1,845.7 $ 1,328.5 Total liabilities $ 373.4 $ 228.7 (1) Financial data for White Mountains’s equity method eligible investees is generally reported on a one-quarter lag. Year Ended December 31, Millions 2021 2020 2019 Income statement data (1) : Total revenues $ 987.4 $ 526.5 $ 344.6 Total expenses $ 418.7 $ 325.9 $ 88.3 Net income (loss) $ 568.7 $ 201.7 $ 255.1 (1) Financial data for White Mountains’s equity method eligible investees is generally reported on a one-quarter lag.

Variable Interest Entities

Variable Interest Entities	12 Months Ended
	Dec. 31, 2021
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Variable Interest Entities	Variable Interest Entities BAM As a mutual insurance company, BAM is owned by its members. BAM charges an insurance premium on each municipal bond insurance policy it writes. A portion of the premium is an MSC and the remainder is a risk premium. In the event of a municipal bond refunding, a portion of the MSC from the original issuance can be reutilized, in effect serving as a credit against the total insurance premium on the refunding of the municipal bond. Issuers of debt insured by BAM are members of BAM so long as any of their BAM-insured debt is outstanding. As members, they have certain interests in BAM, including the right to vote for BAM’s directors and to receive dividends in the future, if declared. The equity at risk funded by BAM’s members is not sufficient to fund its operations without the additional financial support provided by the BAM Surplus Notes and accordingly, BAM is considered to be a VIE. At inception, BAM and HG Re also entered into the FLRT. HG Re provides first loss 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 up to 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 the Regulation 114 Trust and the Supplemental Trust. 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. In addition, under the FLRT, HG Holdings Ltd, a subsidiary of HG Global, has the right to designate two directors for election to BAM’s board of directors. Since BAM is owned by its members, its equity and results of operations are included in non-controlling interests. 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. Elementum On May 31, 2019, White Mountains acquired a 30.0% limited partnership interest in Elementum for $55.1 million. White Mountains has determined that Elementum is a VIE but that White Mountains is not the primary beneficiary. White Mountains’s ownership interest gives White Mountains the ability to exert significant influence over the significant financial and operating activities of Elementum. Accordingly, Elementum meets the criteria to be accounted for under the equity method. White Mountains has taken the fair value option for its investment in Elementum. Changes in the fair value of Elementum are recorded in realized and unrealized investment gains (losses). As of December 31, 2021, White Mountains’s maximum exposure to loss on its investment in Elementum is limited to the carrying value of $45.0 million. PassportCard/DavidShield On January 24, 2018, White Mountains acquired a 50.0% ownership interest in DavidShield, its joint venture partner in PassportCard. As part of the transaction, White Mountains reorganized its equity stake in PassportCard so that White Mountains and its partner in DavidShield would each own 50.0% of both businesses. To facilitate the transaction, White Mountains provided financing to its partner in the form of a non-interest bearing loan that is secured by the partner’s equity in PassportCard/DavidShield. The gross purchase price for the 50.0% interest in DavidShield was $41.8 million, or $28.3 million net of the financing provided for the restructuring. On May 7, 2020, White Mountains made an additional $15.0 million investment in PassportCard/DavidShield to support operations through the ongoing COVID-19 pandemic. The transaction increased White Mountains’s ownership interest from 50.0% to 53.8%, 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 operations. As a result of the transaction, White Mountains’s re-evaluated its accounting treatment for its investment in PassportCard/DavidShield. Because White Mountains does not have the unilateral power to direct the operations of PassportCard or DavidShield, White Mountains does not hold a controlling financial interest and does not consolidate either entity. White Mountains’s ownership interest gives White Mountains the ability to exert significant influence over the significant financial and operating activities of PassportCard/DavidShield. Accordingly, White Mountains’s investment in PassportCard/DavidShield meets the criteria to be accounted for under the equity method. White Mountains has taken the fair value option for its investment in PassportCard/DavidShield. Changes in the fair value of PassportCard/DavidShield are recorded in realized and unrealized investment gains (losses). As of December 31, 2021, White Mountains’s maximum exposure to loss on its equity investment in PassportCard/DavidShield and the non-interest bearing loan to its partner is limited to the total carrying value of $129.4 million. Kudu On April 4, 2019, White Mountains completed the Kudu Transaction for cash consideration of $81.4 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 for the period from April 4, 2019 to December 31, 2019. For periods prior to the Kudu Transaction, White Mountains determined that Kudu was a VIE but that White Mountains was not the primary beneficiary. White Mountains’s ownership interest gave White Mountains the ability to exert significant influence over the significant financial and operating activities of Kudu. Accordingly, for the year ended December 31, 2018, Kudu met the criteria to be accounted for under the equity method. White Mountains took the fair value option for its investment in Kudu, measuring its investment in Kudu at fair value using NAV as a practical expedient with changes therein recorded in realized and unrealized investment gains (losses) for the year ended December 31, 2018.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	12 Months Ended
	Dec. 31, 2021
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. See Note 7 — “Debt” . The following tables presents the fair value and carrying value of these financial instruments as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Millions Fair Value Carrying Value Fair Value Carrying Value Ark 2007 Subordinated Notes $ 27.6 $ 30.0 $ — $ — Ark 2021 Subordinated Notes $ 162.8 $ 155.9 $ — $ — NSM Bank Facility $ 275.8 $ 271.2 $ 279.3 $ 271.3 Other NSM debt $ 1.0 $ .9 $ 1.3 $ 1.3 Kudu Credit Facility $ 246.8 $ 218.2 $ — $ — Kudu Bank Facility $ — $ — $ 89.3 $ 86.3 Other Operations debt $ 17.7 $ 16.8 $ 18.8 $ 17.5 The fair value estimates for the Ark 2007 Subordinated Notes, the Ark 2021 Subordinated Notes, NSM Bank Facility, the Other NSM debt, the Kudu Credit Facility, the Kudu Bank Facility and Other Operations debt have been determined based on a discounted cash flow approach and are considered to be Level 3 measurements.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies White Mountains leases certain office spaces under non-cancellable operating leases that expire on various dates through 2022. Rental expense for all of White Mountains’s locations was $9.9 million, $7.7 million and $7.2 million for the years ended December 31, 2021, 2020 and 2019. White Mountains also has various other lease obligations that are immaterial in the aggregate. White Mountains’s future annual minimum rental payments required under non-cancellable leases, which are primarily for office space, are $10.9 million, $9.9 million, $8.5 million, and $23.0 million for the years ending December 31, 2022, 2023, 2024 and 2025 and thereafter. White Mountains also has future binding commitments to fund certain other long-term investments. These commitments, which totaled $44.0 million as of December 31, 2021, do not have fixed funding dates. Legal Contingencies White Mountains, and the insurance industry in general, is routinely subject to claims related litigation and arbitration in the normal course of business, as well as litigation and arbitration that do not arise from, nor are directly related to, claims activity. White Mountains’s estimates of the costs of settling matters routinely encountered in claims activity are reflected in the reserves for unpaid loss and LAE. See Note 5 — “Losses and Loss Adjustment Expense Reserves” .

Held for Sale and Discontinued

Held for Sale and Discontinued Operations	12 Months Ended
	Dec. 31, 2021
Discontinued Operations and Disposal Groups [Abstract]
Held for Sale and Discontinued Operations	Held for Sale and Discontinued Operations Sirius Group On April 18, 2016, White Mountains completed the sale of Sirius International Insurance Group, Ltd. (“Sirius Group”) to CM International Pte. Ltd. and CM Bermuda Limited (collectively “CMI”). In connection with the sale, White Mountains indemnified Sirius Group against the loss of certain interest deductions claimed by Sirius Group related to periods prior to the sale of Sirius Group to CMI that had been disputed by the Swedish Tax Agency (STA). In late October 2018, the Swedish Administrative Court ruled against Sirius Group on its appeal of the STA’s denial of these interest deductions. As a result, in 2018 White Mountains recorded a loss of $17.3 million within net (loss) gain on sale of discontinued operations reflecting the value of these interest deductions. As of December 31, 2020, White Mountains recorded a liability of $18.7 million, related to the tax indemnification provided in connection with the sale of Sirius Group in 2016. In April 2021, the STA informed the Swedish Administrative Court of Appeal that Sirius Group should prevail in its appeal and that the interest deductions should not be disallowed. In June 2021, the Swedish Administrative Court of Appeal ruled in Sirius Group’s favor. During 2021, White Mountains recorded a gain of $17.6 million in discontinued operations to reverse the liability accrued as of December 31, 2020 and $1.1 million gain related to foreign currency translation. During 2020, White Mountains recorded an increase in the liability of $2.2 million related to foreign currency translation that was included within net loss on sale of discontinued operations. NSM On April 12, 2021, NSM completed the sale of the Fresh Insurance motor business for net proceeds of £1.1 million ($1.5 million based upon the foreign exchange spot rate as of the transaction date). The assets and liabilities included in the transaction, were measured at their estimated fair values, net of disposal and classified as held for sale at March 31, 2021. However, the transaction did not meet the criteria to be classified as discontinued operations. In the first quarter of 2021, NSM recorded a loss of $28.7 million related to the sale. Other As of December 31, 2021, White Mountains classified one of the Other Operating Businesses, which included $16.1 million of insurance licenses, investments and cash, as assets held for sale. As of December 31, 2017, White Mountains classified its Guilford, Connecticut property, which consists of an office building and adjacent land, as held for sale. On August 20, 2020, the office building was sold for $2.3 million. For the year ended December 31, 2020, White Mountains recognized $0.1 million of realized loss on the sale of the office building. As of December 31, 2020, the adjacent land was measured at its estimated fair value, net of costs of disposal, of $0.7 million. On September 17, 2021, the adjacent land was sold for $0.7 million and White Mountains recognized $0.1 million of realized loss within other revenues in the Other Operations segment. As of December 31, 2020, assets held for sale also includes a corporate aircraft. The aircraft was measured at its carrying value of $1.7 million, which is lower than its estimated fair value. On February 12, 2021, the corporate aircraft was sold for $2.1 million and White Mountains recorded $0.5 million of realized gains within other revenues in the Other Operations segment. 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 years ended December 31, 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 Basic and diluted earnings per share numerators (in millions): Net income (loss) attributable to White Mountains’s common shareholders $ (275.4) $ 708.7 $ 414.5 Less: total income (loss) from continuing operations, net of tax (294.1) 711.0 413.7 Net income (loss) from discontinued operations attributable to 18.7 (2.3) .8 Allocation of (earnings) losses to participating restricted common shares (1) (.2) — — Basic and diluted (loss) earnings per share numerators $ 18.5 $ (2.3) $ .8 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,079.0 3,122.2 3,181.6 Average unvested restricted common shares (3) (36.5) (40.8) (40.5) Basic earnings (loss) per share denominator 3,042.5 3,081.4 3,141.1 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,079.0 3,122.2 3,181.6 Average unvested restricted common shares (3) (36.5) (40.8) (40.5) Diluted earnings (loss) per share denominator 3,042.5 3,081.4 3,141.1 Basic (loss) earnings per share (in dollars) - discontinued operations: $ 6.07 $ (.75) $ .25 Diluted (loss) earnings per share (in dollars) - discontinued operations: $ 6.07 $ (.75) $ .25 (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 years ended December 31, 2021, 2020 and 2019. (3) Restricted common shares outstanding vest either in equal annual installments or upon a stated date. See Note 12 — “Employee Share-Based Compensation Plans” .

SCHEDULE I SUMMARY OF INVESTMEN

SCHEDULE I SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES	12 Months Ended
	Dec. 31, 2021
SEC Schedule, 12-15, Insurance Companies, Summary of Investments, Other than Investments in Related Parties [Abstract]
Schedule I - Summary of Investments-Other Than Investments in Related Parties	WHITE MOUNTAINS INSURANCE GROUP, LTD. SUMMARY OF INVESTMENTS—OTHER THAN INVESTMENTS IN RELATED PARTIES At December 31, 2021 Millions Cost Carrying Fair Fixed maturity investments: U.S. Government and agency obligations $ 212.1 $ 211.5 $ 211.5 Debt securities issued by corporations 993.3 992.9 992.9 Municipal obligations 276.4 291.9 291.9 Mortgage and asset-backed securities 277.2 277.6 277.6 Collateralized loan obligations 136.5 135.0 135.0 Total fixed maturity investments 1,895.5 1,908.9 1,908.9 Short-term investments 465.9 465.9 465.9 Investment in MediaAlpha — 261.6 261.6 Common equity securities - Industrial, Miscellaneous, and Other 236.3 251.1 251.1 Other long-term investments 1,186.7 1,377.8 1,377.8 Total investments $ 3,784.4 $ 4,265.3 $ 4,265.3

SCHEDULE II CONDENSED FINANCIAL

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT	12 Months Ended
	Dec. 31, 2021
Condensed Financial Information Disclosure [Abstract]
Schedule II - Condensed Financial Information of the Registrant	CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT CONDENSED BALANCE SHEETS (1) December 31, Millions 2021 2020 Assets: Cash $ .6 $ .7 Fixed maturity investments, at fair value — 10.1 Short-term investments, at amortized cost 6.7 24.3 Other assets 3.0 2.5 Investments in consolidated subsidiaries 3,661.8 3,726.0 Total assets $ 3,672.1 $ 3,763.6 Liabilities: Payable to subsidiary $ 104.9 $ (195.6) Other liabilities (2) 10.1 39.7 Total liabilities 115.0 (155.9) White Mountains’s common shareholders’ equity 3,548.1 3,906.0 Non-controlling interests 9.0 13.5 Total liabilities and equity $ 3,672.1 $ 3,763.6 (1) These condensed unconsolidated financial statements reflect the results of operations, financial condition and cash flows for the Company. Investments in which White Mountains holds a controlling financial interest are accounted for using the equity method. Under the equity method, investments in subsidiaries are recorded on the condensed balance sheets at the amount of the Company’s ownership percentage of the subsidiary’s GAAP book value. The income from subsidiaries is reported on a net of tax basis as equity in earnings from consolidated and unconsolidated subsidiaries on the condensed statements of operations and comprehensive income (loss). Capital contributions to and distributions from consolidated subsidiaries are presented within investing activities on the condensed statements of cash flows. (2) As of December 31, 2020, White Mountains’s other liabilities includes $18.7 related to the Sirius Group tax contingency, which was reversed during 2021. See Note 21 — “Held for Sale and Discontinued Operations ”. Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes. SCHEDULE II (continued) CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) (1) Year Ended December 31, Millions 2021 2020 2019 Revenues (loss) (including realized and unrealized gains and losses) $ (.2) $ (8.7) $ 65.0 Expenses 39.0 61.0 47.1 Pre-tax income (loss) (39.2) (69.7) 17.9 Income tax benefit (expense) — (.3) (.9) Net income (loss) (39.2) (70.0) 17.0 Net gain (loss) from discontinued operations, net of tax (2) 18.7 (2.3) .8 Equity in earnings from consolidated and unconsolidated subsidiaries, (257.4) 782.0 398.5 Net (income) loss attributable to non-controlling interests 2.5 (1.0) (1.8) Net income (loss) attributable to White Mountains’s (275.4) 708.7 414.5 Other comprehensive (loss) income items, net of tax 2.1 6.8 (1.4) Comprehensive income (loss) attributable to White Mountains’s $ (273.3) $ 715.5 $ 413.1 (1) These condensed unconsolidated financial statements reflect the results of operations, financial condition and cash flows for the Company. Investments in which White Mountains holds a controlling financial interest are accounted for using the equity method. Under the equity method, investments in subsidiaries are recorded on the condensed balance sheets at the amount of the Company’s ownership percentage of the subsidiary’s GAAP book value. The income from subsidiaries is reported on a net of tax basis as equity in earnings of subsidiaries on the condensed statements of operations and comprehensive income (loss). Capital contributions to and distributions from subsidiaries are presented within investing activities on the condensed statements of cash flows. (2) During 2021, 2020 and 2019, net gain (loss) from discontinued operations includes $18.7, $(2.3) and $0.8 arising from the tax contingency on the sale of Sirius Group. See Note 21 — “Held for Sale and Discontinued Operations ”. Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes. SCHEDULE II (continued) CONDENSED STATEMENTS OF CASH FLOWS (1) Year Ended December 31, Millions 2021 2020 2019 Net income (loss) attributable to White Mountains’s common shareholders $ (275.4) $ 708.7 $ 414.5 Charges (credits) to reconcile net income to net cash from operations: Net realized and unrealized investment (gains) losses on sales of investments .1 10.1 (61.0) Undistributed earnings from subsidiaries 257.4 (782.0) (398.5) Net (gain) loss from sale of discontinued operations, net of tax (2) (18.7) 2.3 (.8) Other non-cash reconciling items, primarily amortization of restricted share and option awards (3) 14.1 19.0 20.0 Net change in other assets and liabilities (4) (5.7) (2.6) 3.0 Net cash (used for) provided from operations (28.2) (44.5) (22.8) Cash flows from investing activities: Net change in short-term investments (5)(6) 17.7 (127.4) (37.6) Purchases of investment securities — (6.7) (14.8) Sales and maturities of investment securities (6) — 189.7 207.9 Purchases of investment securities from subsidiaries (26.4) — — Sales of investment securities to subsidiaries 36.4 — — Issuance of debt (to) from subsidiaries (7) 94.0 (44.5) (83.5) Repayment of debt to (from) subsidiaries (5) — 92.6 5.0 Net distributions from (contributions to) subsidiaries (5)(8)(9) 17.0 29.1 (46.1) Net cash provided from (used for) investing activities 138.7 132.8 30.9 Cash flows from financing activities: Repurchases and retirement of common shares (100.1) (78.5) — Dividends paid on common shares (3.1) (3.2) (3.2) Payments of restricted shares withholding taxes (7.4) (6.6) (4.9) Net cash used for financing activities (110.6) (88.3) (8.1) Net decrease in cash during the year (.1) — — Cash balance at beginning of year .7 .7 .7 Cash balance at end of year $ .6 $ .7 $ .7 (1) These condensed unconsolidated financial statements reflect the results of operations, financial condition and cash flows for the Company. Investments in which White Mountains holds a controlling financial interest are accounted for using the equity method. Under the equity method, investments in consolidated subsidiaries are recorded on the condensed balance sheets at the amount of the Company’s ownership percentage of the subsidiary’s GAAP book value. The income from consolidated subsidiaries is reported on a net of tax basis as equity in earnings of subsidiaries on the condensed statements of operations and comprehensive income (loss). Capital contributions to and distributions from consolidated subsidiaries are presented within investing activities on the condensed statements of cash flows. (2) During 2021, 2020 and 2019, net gain (loss) from sale of discontinued operations includes $18.7, $(2.3) and $0.8 arising from the tax contingency on the sale of Sirius Group. See Note 21 — “Held for Sale and Discontinued Operations ” (3) For the years ended December 31, 2021, 2020 and 2019, amortization of restricted share awards was $14.7, $16.6 and $10.5. (4) For 2021, 2020 and 2019, net change in other assets and liabilities also included a $6.5, $(4.8), and $(6.6) net change in (receivables) payables to the Company’s subsidiaries. (5) During 2021, the Company’s wholly-owned subsidiary, Bridge Holdings (“Bridge”) repaid $200.0 of outstanding intercompany debt to the Company by transferring shares of its wholly-owned subsidiary, White Mountains Lincoln Holdings, Inc., (“WM Lincoln”), which had carrying value of $212.6. The $12.6 excess of the intercompany debt was a non-cash distribution to the Company. Also as part of the transaction, the Company received a distribution of $18.0 from Bridge, including $17.9 of short-term investments and $0.1 of cash. Subsequent to that transaction, the Company contributed the shares of WM Lincoln, which had a carrying value of $212.6, to its wholly-owned subsidiary White Mountains Adams, Inc. (“WM Adams”). The Company also contributed an additional $42.7 to WM Adams, including $37.1 of short-term investments and $5.6 of cash. (6) During 2020, the Company had non-cash purchases of short-term investments of $169.6. (7) During 2020, the Company had non-cash issuance of debt of $169.6 to Bridge. Proceeds of the debt, which were short-term investments, were transferred to Bridge. (8) During 2019, the Company made cash contributions of $70.5 and $2.0 to Bridge and its wholly-owned subsidiary, White Mountains Investment Bermuda, Ltd (“WMIB”) (9) During 2021, the Company received a distribution of $19.7, including $19.1 of short-term investments and $0.6 of cash, from WMIB. During 2020, the Company received cash distributions of $6.8 and $22.3 from its wholly-owned subsidiary, PSC Holdings, Ltd. and the Company’s subsidiary, HG Global Ltd. During 2019, the Company received cash distributions of $24.4 and $1.9 from WMIB and the Company’s subsidiary, HG Global Ltd. Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes.

SCHEDULE III SUPPLEMENTARY INSU

SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION	12 Months Ended
	Dec. 31, 2021
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Abstract]
Schedule III - Supplementary Insurance Information	WHITE MOUNTAINS INSURANCE GROUP, LTD. SUPPLEMENTARY INSURANCE INFORMATION Column Column Column C Column Column E Column Column Column Column Column Column Millions Segment Deferred Future Unearned Other Policy Premiums Net Benefits, Amortization Other Operating Premiums Years ended: December 31, 2021 HG Global/BAM $ 33.1 $ — $ 266.3 $ — $ 26.9 $ 17.5 $ — $ 8.3 $ .4 $ 55.8 Ark $ 100.8 $ 894.7 $ 495.9 $ — $ 637.3 $ 2.9 $ 314.8 $ 111.3 $ 64.6 $ 859.1 December 31, 2020 HG Global/BAM 27.8 — 237.5 — 22.8 19.5 — 7.0 .4 61.7 December 31, 2019 HG Global/BAM 22.1 — 198.4 — 16.3 21.6 — 5.7 .4 38.7 Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes.

SCHEDULE IV REINSURANCE

SCHEDULE IV REINSURANCE	12 Months Ended
	Dec. 31, 2021
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Abstract]
Schedule IV - Reinsurance	WHITE MOUNTAINS INSURANCE GROUP, LTD. REINSURANCE Column A Column B Column C Column D Column E Column F $ in Millions Premiums Earned Gross Amount Ceded to Other Assumed from Net Amount Percentage of Year ended: December 31, 2021 HG Global/BAM $ 23.2 $ — $ 3.7 $ 26.9 13.8 % Ark 886.4 (249.1) — 637.3 — December 31, 2020 HG Global/BAM 19.4 — 3.4 22.8 14.9 December 31, 2019 HG Global/BAM 13.6 — 2.7 16.3 16.6 Schedules of the Registrant should be read in conjunction with the Consolidated Financial Statements and Notes.

SCHEDULE V VALUATION AND QUALIF

SCHEDULE V VALUATION AND QUALIFYING ACCOUNTS	12 Months Ended
	Dec. 31, 2021
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
SCHEDULE V VALUATION AND QUALIFYING ACCOUNTS	WHITE MOUNTAINS INSURANCE GROUP, LTD. VALUATION AND QUALIFYING ACCOUNTS Column A Column B Column C Column D Column E Additions (subtractions) Millions Balance at beginning of Charged to costs Charged to other Deductions described (1) Balance at end of Years ended: December 31, 2021 Reinsurance recoverable on paid losses: Allowance for reinsurance balances $ .3 $ .4 $ — $ — $ .7 (1) Represents net collections (charge-offs) of balances receivable and foreign currency translation.

SCHEDULE VI SUPPLEMENTAL INFORM

SCHEDULE VI SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS	12 Months Ended
	Dec. 31, 2021
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract]
SCHEDULE VI SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS	WHITE MOUNTAINS INSURANCE GROUP, LTD. SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS (Millions) Column A Column B Column C Column D Column E Column F Column G Column H Column I Column J Column K Deferred acquisition Reserves Discount, if any, deducted in Unearned Earned Net investment Claims and Claims Amortization Paid Premiums Affiliation Current Prior Ark: 2021 100.8 894.7 — 495.9 637.3 2.9 336.3 (21.5) 111.3 105.5 859.1

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation White Mountains Insurance Group, Ltd. (the “Company” or the “Registrant”) 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, Suite 3B, 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.
Consolidation Principles	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. See Note 18 — “Variable Interest Entities” .
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.
Reporting 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 December 31, 2021, White Mountains’s reportable segments were HG Global/BAM, Ark, NSM, Kudu and Other Operations. On February 26, 2019, MediaAlpha, Inc. (“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 “2019 MediaAlpha Transaction”). MediaAlpha also repurchased a portion of the holdings of existing equityholders. White Mountains deconsolidated MediaAlpha as a result of the 2019 MediaAlpha Transaction, and consequently it was no longer a reportable segment. White Mountains’s consolidated statement of comprehensive income (loss) and its segment disclosures include MediaAlpha’s results of operations through the date of the 2019 MediaAlpha Transaction. See Note 2 — “ Significant Transactions ” and Note 16 — “ 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 purpose projects, 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 reinsurance 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 (the “BAM Surplus Notes”). As of December 31, 2021 and 2020, 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 Ark segment consists of Ark Insurance Holdings Limited and its subsidiaries (collectively, “Ark”). Ark is a specialty property and casualty insurance and reinsurance company that offers a wide range of niche insurance and reinsurance products, including property, marine & energy, specialty, accident & health and casualty. Ark underwrites select coverages through its two major subsidiaries in the United Kingdom and Bermuda. On January 1, 2021, White Mountains acquired a controlling ownership interest in Ark (the “Ark Transaction”). See Note 2 — “Significant Transactions” . As of December 31, 2021, White Mountains owned 72.0% of Ark on a basic shares outstanding basis (63.0% after taking account of management’s equity incentives). The remaining shares are owned by employees. In the future, management rollover shareholders could earn additional shares in Ark if and to the extent that White Mountains achieves certain multiple of invested capital return thresholds. If fully earned, these additional shares would represent 12.5% of the shares outstanding at closing. NSM is a full-service managing general agent (“MGA”) and program administrator with delegated binding authorities for specialty property and casualty insurance. The company places insurance in niche sectors such as specialty transportation, real estate, social services and pet. On behalf of its insurance carrier partners, NSM typically 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. On May 11, 2018, White Mountains acquired a controlling ownership interest in NSM. See Note 2 — “Significant Transactions” . As of December 31, 2021 and 2020, White Mountains owned 96.5% and 96.6% of the basic units outstanding of NSM (87.3% and 89.6% on a fully diluted, fully converted basis). The Kudu segment consists of Kudu Investment Management, LLC and its subsidiaries (collectively “Kudu”). 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, generally tied to gross revenues and designed to generate immediate strong, stable cash yields. On April 4, 2019, White Mountains acquired a controlling ownership interest in Kudu (the “Kudu Transaction”). See Note 2 — “Significant Transactions” . As of December 31, 2021 and 2020, White Mountains owned 99.3% and 99.3% of the basic units outstanding of Kudu (84.7% and 85.4% on a fully diluted, fully converted basis). The Other Operations segment consists of the Company and its wholly-owned subsidiary, White Mountains Capital, LLC, (“WM Capital”) 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 2019 MediaAlpha Transaction), PassportCard Limited (“PassportCard”) and DavidShield Life Insurance Agency (2000) Ltd. (“DavidShield”) (collectively, “PassportCard/ DavidShield”), Elementum Holdings LP (“Elementum”), Kudu (for periods prior to the Kudu Transaction), certain other consolidated and unconsolidated entities (“Other Operating Businesses”) and certain other assets. 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 customer acquisition technology platform that facilitates real-time transactions between buyers and sellers of consumer referrals (i.e., clicks, calls and leads), primarily in the property & casualty, health and life insurance verticals. MediaAlpha generates revenue by earning a fee for each consumer referral sold on its platform. A transaction becomes payable only on a qualifying consumer action, and is not contingent on the sale of a product to the consumer. MediaAlpha’s core verticals are property & casualty insurance, health insurance and life insurance. White Mountains deconsolidated MediaAlpha as a result of the 2019 MediaAlpha Transaction and stopped reporting it as a segment. Following the 2019 MediaAlpha Transaction, White Mountains’s non-c ontrolling equity interest in MediaAlpha was accounted for at fair value within other long-term investments. See Note 2 — “Significant Transactions” .
Held for Sale and Discontinued Operations	Held for Sale and Discontinued Operations White Mountains recognizes assets and liabilities classified as held for sale at the lower of carrying value on the date the asset is initially classified as held for sale or fair value less costs to sell. At the time of reclassification to held for sale, White Mountains ceases recognizing depreciation and amortization on assets held for sale. The results of operations of a business that has either been disposed of or are classified as held for sale are reported in discontinued operations if the disposal of the business represents a strategic shift that has (or will have) a major effect on White Mountains operations and financial results. See Note 21 — “Held for Sale and Discontinued Operations” .
Investment Securities	Investment Securities As of December 31, 2021 and 2020, White Mountains’s invested assets consisted of securities and other investments held for general investment purposes. White Mountains’s portfolio of fixed maturity investments, common equity securities, its investment in MediaAlpha, and other long-term investments held for general investment purposes are generally classified as trading securities and are reported at fair value as of the balance sheet date. Changes in net unrealized investment gains (losses) are reported pre-tax in revenues. Realized investment gains (losses) are accounted for using the specific identification method and are reported pre-tax in revenues. Premiums and discounts on all fixed maturity investments are amortized and 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 fair value, which approximated amortized or accreted cost as of December 31, 2021 and 2020. White Mountains’s invested assets that are measured at fair value include fixed maturity investments, common equity securities, its investment in MediaAlpha, and other long-term investments, that consists primarily of unconsolidated entities, including non-controlling equity interests in the form of revenue and earnings participation contracts (“Kudu’s Participation Contracts”), a bank loan fund, private equity funds, hedge funds, Lloyd’s trust deposits, insurance-linked securities (“ILS”) funds and private debt instruments. Whenever possible, White Mountains estimates fair value using valuation methods that maximize the use of quoted prices and other observable inputs. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants (an exit price) at a particular measurement date. 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 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”). Assets and liabilities carried at fair value include substantially all of White Mountains’s investment portfolio, and derivative instruments, both exchange-traded and over the counter instruments. Valuation of assets and liabilities measured at fair value require management to make estimates and apply judgment to matters that may carry a significant degree of uncertainty. In determining fair value estimates, White Mountains uses a variety of valuation approaches and inputs. Whenever possible, White Mountains estimates fair value using valuation methods that maximize the use of quoted market prices or other observable inputs. Where appropriate, assets and liabilities measured at fair value have been adjusted for the effect of counterparty credit risk. White Mountains uses outside pricing services and brokers to assist in determining fair values. The outside pricing services White Mountains uses have indicated that they will only provide prices where observable inputs are available. As of December 31, 2021, approximately 68% of the investment portfolio recorded at fair value was priced based upon quoted market prices or other observable inputs. Level 1 Measurements Investments valued using Level 1 inputs include White Mountains’s fixed maturity investments, primarily investments in U.S. Treasuries and short-term investments, which include U.S. Treasury Bills, common equity securities, and its investment in MediaAlpha following the MediaAlpha IPO. For investments in active markets, White Mountains uses the quoted market prices provided by outside pricing services to determine fair value. Level 2 Measurements Investments valued using Level 2 inputs include fixed maturity investments which have been disaggregated into classes, including debt securities issued by corporations, municipal obligations and mortgage and asset-backed securities. Investments valued using Level 2 inputs also include certain passive exchange traded funds (“ETFs”) that track U.S. stock indices such as the S&P 500 Index, but are traded on foreign exchanges, which White Mountains values using the fund manager’s published net asset value per share (“NAV”) to account for the difference in market close times. In circumstances where quoted market prices are unavailable or are not considered reasonable, White Mountains estimates the fair value using industry standard pricing methodologies and observable inputs such as benchmark yields, reported trades, broker-dealer quotes, issuer spreads, benchmark securities, bids, offers, credit ratings, prepayment speeds, reference data including research publications and other relevant inputs. Given that many fixed maturity investments do not trade on a daily basis, the outside pricing services evaluate a wide range of fixed maturity investments by regularly drawing parallels from recent trades and quotes of comparable securities with similar features. The characteristics used to identify comparable fixed maturity investments vary by asset type and take into account market convention. White Mountains’s process to assess the reasonableness of the market prices obtained from the outside pricing sources covers substantially all of its fixed maturity investments and includes, but is not limited to, the evaluation of pricing methodologies and a review of the pricing services’ quality control procedures on at least an annual basis, a comparison of its invested asset prices obtained from alternate independent pricing vendors on at least a semi-annual basis, monthly analytical reviews of certain prices and a review of the underlying assumptions utilized by the pricing services for select measurements on an ad hoc basis throughout the year. White Mountains also performs back-testing of selected investment sales activity to determine whether there are any significant differences between the market price used to value the security prior to sale and the actual sale price of the security on an ad-hoc basis throughout the year. Prices provided by the pricing services that vary by more than $0.5 million and 5% from the expected price based on these assessment procedures are considered outliers, as are prices that have not changed from period to period and prices that have trended unusually compared to market conditions. In circumstances where the results of White Mountains’s review process does not appear to support the market price provided by the pricing services, White Mountains challenges the vendor provided price. If White Mountains cannot gain satisfactory evidence to support the challenged price, White Mountains will rely upon its own internal pricing methodologies to estimate the fair value of the security in question. The valuation process described above is generally applicable to all of White Mountains’s fixed maturity investments. The techniques and inputs specific to asset classes within White Mountains’s fixed maturity investments for Level 2 securities that use observable inputs are as follows: Debt Securities Issued by Corporations The fair value of debt securities issued by corporations is determined from a pricing evaluation technique that uses information from market sources and integrates relative credit information, observed market movements, and sector news. Key inputs include benchmark yields, reported trades, broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including sector, coupon, credit quality ratings, duration, credit enhancements, early redemption features and market research publications. Municipal Obligations The fair value of municipal obligations is determined from a pricing evaluation technique that uses information from market makers, brokers-dealers, buy-side firms, and analysts along with general market information. Key inputs include benchmark yields, reported trades, issuer financial statements, material event notices and new issue data, as well as broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including type, coupon, credit quality ratings, duration, credit enhancements, geographic location and market research publications. Mortgage and Asset-Backed Securities and Collateralized Loan Obligations The fair value of mortgage and asset-backed securities and collateralized loan obligations is determined from a pricing evaluation technique that uses information from market sources and leveraging similar securities. Key inputs include benchmark yields, reported trades, underlying tranche cash flow data, collateral performance, plus new issue data, as well as broker-dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids, offers, and reference data including issuer, vintage, loan type, collateral attributes, prepayment speeds, default rates, recovery rates, cash flow stress testing, credit quality ratings and market research publications. Level 3 Measurements Fair value estimates for investments that trade infrequently and have few or no quoted market prices or other observable inputs are classified as Level 3 measurements. Investments valued using Level 3 fair value estimates are based upon unobservable inputs and include investments in certain fixed maturity investments, common equity securities and other long-term investments where quoted market prices or other observable inputs are unavailable or are not considered reliable or reasonable. Level 3 valuations are generated from techniques that use assumptions not observable in the market. These unobservable inputs reflect White Mountains’s assumptions of what market participants would use in valuing the investment. In certain circumstances, investment securities may start out as Level 3 when they are originally issued, but as observable inputs become available in the market, they may be reclassified to Level 2. Transfers of securities between levels are based on investments held as of the beginning of the period.
Other Long-Term Investments	Other Long-Term Investments As of December 31, 2021, White Mountains owned a portfolio of other long-term investments valued at $1.4 billion, that consisted primarily of unconsolidated entities, including Kudu’s Participation Contracts, a bank loan fund, private equity funds, a hedge fund, Lloyd’s trust deposits, ILS funds and private debt instruments. As of December 31, 2021, $890.6 million of White Mountains’s other long-term investments that consisted primarily of unconsolidated entities, including Kudu’s Participation Contracts and private debt instruments were classified as Level 3 investments in the GAAP fair value hierarchy, were not actively traded in public markets and did not have readily observable market prices. The determination of the fair value of these securities involves significant management judgment, and the use of valuation models and assumptions that are inherently subjective and uncertain. As of December 31, 2021, $482.5 million of White Mountains’s other long-term investments, consisting of a bank loan fund, private equity funds, a hedge fund, Lloyd’s trust deposits and ILS funds, were valued at fair value using NAV as a practical expedient. Investments for which fair value is measured at NAV using the practical expedient are not classified within the fair value hierarchy. White Mountains may use a variety of valuation techniques to determine fair value depending on the nature of the investment, including a discounted cash flow analysis, market multiple approach, cost approach and/or liquidation analysis. On an ongoing basis, White Mountains also considers qualitative changes in facts and circumstances, which may impact the valuation of unconsolidated entities, including economic and market changes in relevant industries, changes to the entity’s capital structure, business strategy and key personnel, and any recent transactions relating to the unconsolidated entity. On a quarterly basis, White Mountains evaluates the most recent qualitative and quantitative information of the business and completes a fair valuation analysis for all Level 3 other long-term investments. Periodically, and at least on an annual basis, White Mountains uses a third-party valuation firm to complete an independent valuation analysis of significant unconsolidated entities. Other Long-term Investments - NAV White Mountains’s portfolio of other long-term investments includes investments in a bank loan fund, private equity funds, hedge funds, Lloyd’s trust deposits and ILS funds, which are valued at fair value using NAV as a practical expedient. White Mountains employs a number of procedures to assess the reasonableness of the fair value measurements for other long-term investments measured at NAV, including obtaining and reviewing periodic and audited annual financial statements as well as periodically discussing each fund’s pricing with the fund manager. However, since the fund managers do not provide sufficient information to evaluate the pricing methods and inputs for each underlying investment, White Mountains considers the valuation inputs to be unobservable. The fair value of White Mountains’s other long-term investments measured at NAV are generally determined using the fund manager’s NAV. In the event that White Mountains believes the fair value differs from the NAV reported by the fund manager due to illiquidity or other factors, White Mountains will adjust the reported NAV to more appropriately represent the fair value of its investment.
Cash and Restricted Cash	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 and the interest reserve account that Kudu maintains under its credit facility, are classified as restricted.
Derivatives	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 its consolidated balance sheet. Changes in the fair value of derivative instruments that meet the criteria for hedge accounting are recognized in other comprehensive income (loss) and reclassified into current period pre-tax income (loss) 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 (loss). As of December 31, 2021 and 2020, White Mountains holds interest rate cap derivative instruments that do not meet the criteria for hedge accounting. As of December 31, 2021 and 2020, White Mountains holds an interest rate swap derivative instrument that meets the criteria for hedge accounting. See Note 9 — “Derivatives” .
Municipal Bond Guarantee Insurance	Municipal Bond Guarantee Insurance All of the contracts issued by BAM are accounted for as insurance contracts under ASC 944-605, Financial Guarantee Insurance Contracts. For capital appreciation bonds, par is adjusted to the estimated equivalent par value for current interest paying bonds. See Note 10 — “Municipal Bond Guarantee Insurance” . Premiums are generally received upfront and an unearned premium revenue liability, equal to the amount of the premium received, is established at contract inception. Premium revenues are recognized in revenue over the period of the contracts in proportion to the amount of insurance protection provided using a constant rate. The constant rate is calculated based on the relationship between the par outstanding in a given reporting period compared with the sum of each of the par amounts outstanding for all periods. Insurance premiums receivable represents amounts due from customers for municipal bond insurance policies. Installment premiums are measured at the present value of contractual premiums, discounted at the risk-free rate, which is set at the inception of the insurance contract. Deferred acquisition costs represent commissions, premium taxes, excise taxes and other costs which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent they relate to successful contract acquisitions over the applicable premium recognition period as acquisition expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income. A premium deficiency is recognized if the sum of expected loss and loss adjustment expenses (“LAE”), expected dividends to policyholders, unamortized acquisition costs, and maintenance costs exceeds related unearned premiums and anticipated investment income. A premium deficiency is recognized by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs then a liability is accrued for the excess deficiency. BAM’s obligation for outstanding contracts consists of the unearned premium reserve and any loss reserves. Loss reserves are recorded only to the extent that the present value of the expected amount of any losses to be paid, net of any expected recoveries, exceeds the associated unearned premium reserve. As of December 31, 2021 and 2020, BAM did not have any loss or loss adjustment expense reserves.
Property and Casualty Insurance and Reinsurance	Property and Casualty Insurance and Reinsurance Ark writes a diversified portfolio of reinsurance and insurance, including property, marine & energy, specialty, accident & health and casualty, through its Lloyd’s Syndicates 4020 and 3902 (the “Syndicates”) and its wholly-owned subsidiary Group Ark Insurance Limited (“GAIL”). Ark accounts for insurance and reinsurance policies that it writes in accordance with ASC 944, Financial Services - Insurance . Ark’s premiums written comprise premiums on insurance contracts incepted during the year as well as premium adjustments related to prior underwriting years. Insurance premiums are recognized as revenues over the loss exposure or coverage period in proportion to the level of insurance protection provided. In most cases, premiums are earned ratably over the term of the contract with unearned premiums calculated on a monthly pro-rata basis. Catastrophe premiums are earned in proportion to the level of insurance protection provided. Premiums earned are presented net of amounts ceded to reinsurers. Insurance premiums receivable, representing amounts due from insureds, are presented net of an allowance for uncollectible premiums, including expected credit losses. The allowance is based upon Ark’s ongoing review of amounts outstanding, historical loss data, including delinquencies and write-offs, current and forecasted economic conditions and other relevant factors. Credit risk is partially mitigated by Ark’s ability to cancel the policy if the policyholder does not pay the premium. Deferred acquisition costs comprise commission and brokerage fees and taxes which are directly attributable to and vary with the production of business. These costs are deferred and amortized to the extent they relate to successful contract acquisitions over the applicable premium recognition period as insurance and reinsurance acquisition expenses. Deferred acquisition costs are limited to the amount expected to be recovered from future earned premiums and anticipated investment income. A premium deficiency is recognized if the sum of expected loss and LAE, expected dividends to policyholders, unamortized acquisition costs, and maintenance costs exceeds related unearned premiums and anticipated investment income. A premium deficiency is recognized by charging any unamortized acquisition costs to expense to the extent required in order to eliminate the deficiency. If the premium deficiency exceeds unamortized acquisition costs then a liability is accrued for the excess deficiency. Losses and LAE are charged against income as incurred. Unpaid losses and LAE, including estimates for amounts incurred but not reported (“IBNR”) are based on estimates of the ultimate costs of settling claims, including the effects of inflation and other societal and economic factors. Unpaid loss and LAE reserves represent management’s best estimate of ultimate losses and LAE, net of estimated salvage and subrogation recoveries, if applicable. Such estimates are regularly reviewed and updated and any resulting adjustments are reflected in current results of operations. The process of estimating loss and LAE involves a considerable degree of judgment by management and the ultimate amount of expense to be incurred could be considerably greater than or less than the amounts currently reflected in the financial statements. See Note 5 – “Loss and Loss Adjustment Expense Reserves” . As part of its enterprise risk management function, Ark purchases reinsurance for risk mitigation purposes. Ark utilizes reinsurance and retrocession agreements to reduce earnings volatility, protect capital, limit its exposure to risk concentration and accumulation of loss and to manage within its overall internal risk tolerances or those set and agreed by regulators, ratings agencies, and Lloyd’s. Ark also enters into reinsurance and retrocession agreements to reduce its liability on individual risks and enable it to underwrite policies with higher limits where Ark believes this has a broader business benefit. Ark seeks to protect its downside risk from catastrophes and large loss events by purchasing reinsurance, including excess of loss protections, aggregate covers, and industry loss warranties. Ark also considers alternative structures such as collateralized reinsurance, retrocessional reinsurance and catastrophe bonds. The purchase of reinsurance does not discharge Ark from its primary liability for the full value of its policies, and thus the collectability of balances due from Ark’s reinsurers is critical to its financial strength. Ark monitors the financial strength and ratings of its reinsurers on an ongoing basis. See Note 6 – “Third-Party Reinsurance” . For the years of account prior to the Ark Transaction, a significant proportion of the Syndicates’ underwriting capital was provided by third-party insurance and reinsurance groups (“TPC Providers”) using whole account reinsurance contracts with Ark’s corporate member. The TPC Providers’ participation in the Syndicates for the 2020 and 2019 open years of account is 42.8% and 58.3% of the total net result of the Syndicates. For the years of account subsequent to the Ark Transaction, Ark is no longer using TPC Providers to provide underwriting capital for the Syndicates. Captions within results of operations and other comprehensive income are shown net of amounts relating to the TPC Providers share of the Syndicates’ results, including investment results. Reinsurance recoverables represent paid losses and LAE, case reserves and IBNR reserves ceded to reinsurers under reinsurance treaties. Amounts recoverable from reinsurers are estimated in a manner consistent with the associated claim liability. Ark reports its reinsurance recoverables net of an allowance for estimated uncollectible reinsurance, including expected credit losses and coverage disputes. The allowance is based upon Ark’s ongoing review of amounts outstanding, length of collection periods, changes in reinsurer credit standing, disputes, applicable coverage defenses and other relevant factors.
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 two ceded reinsurance agreements with Fidus Re Ltd. (“Fidus Re”), a Bermuda-based special purpose insurer created in 2018 solely to provide reinsurance protection to BAM. The nonrefundable consideration paid by BAM to Fidus Re is charged to financing expense within general and administrative expenses. See Note 10 — “Municipal Bond Guarantee Insurance” . Ark has an aggregate excess of loss contract with SiriusPoint Ltd. (“SiriusPoint”), formerly Third Point Reinsurance Ltd., which is accounted for using the deposit method and recorded within other assets. Ark earns an annual crediting rate of 3.0%, which is recorded within other revenue. See Note 6 — “Third-Party Reinsurance”
Revenue Recognition	Revenue Recognition NSM’s revenues consist primarily of commissions and broker revenues for placement of insurance policies and administrative fees for claims and other services provided to insurance carriers. Commission and broker revenues and service fees are measured based on the contractual rates with insurance carriers, net of any amounts expected to be uncollectible and any amounts associated with expected policy cancellations and adjustments, and are recognized when contractual performance obligations have been fulfilled. NSM’s primary contractual performance obligations are generally satisfied upon the issuance of an insurance policy by the carrier. Where NSM has significant performance obligations beyond the policy issuance date, NSM estimates the relative standalone selling price for the post-issuance services in order to allocate the transaction price using the price charged for the service when sold separately in similar circumstances to similar customers. NSM earns contingent commissions based upon the overall profit and/or volume of the business placed with certain insurance carriers during a calendar year. Contingent commissions are determined after the contractual period has ended. NSM recognizes revenue on contingent commissions when management has determined that it is probable that the contingent commission requirements have been met. NSM’s premiums and commissions receivables consist of insurance premiums receivable from customers and commissions receivable from insurance carriers, net of a provision for amounts estimated to be uncollectible. Deferred revenues associated with unsatisfied performance obligations are recognized within other liabilities. Kudu’s revenues are primarily generated from non-controlling equity interests in revenue and earnings participation contracts with asset management firms. The participation contracts are measured at fair value with the change therein recognized within unrealized investment gains and losses. Distributions from Kudu’s clients are recognized through investment income when Kudu’s right to receive payment has been established and can be reliably measured, which generally occurs on a quarterly basis in accordance with the terms of the underlying participation contracts.
Commission Expense and Cost of Sales	Commission Expense and Cost of Sales NSM’s broker commission expense consists of commissions paid to sub-agents and brokers. Broker commission expense is measured in accordance with contractual terms and recognized when incurred, which is generally at the policy issuance date. MediaAlpha’s cost of sales consisted primarily of revenue sharing payments to publisher partners and traffic acquisition costs to top tier search engines. Cost of sales were measured based on contract terms and recognized when the related revenue transactions are executed. Other Operations’s cost of sales consists of salaries and related expenses, professional services and marketing and advertising expenses directly related to sales generation. These expenses are recognized as incurred.
Goodwill and Other Intangible Assets	Goodwill and Other Intangible Assets Goodwill represents the excess of the amount paid to acquire subsidiaries over the fair value of identifiable net assets at the date of acquisition. Other intangible assets consist primarily of underwriting capacity, customer relationships, renewal rights and trade names. Goodwill and other intangible assets with indefinite lives are not amortized, but rather are evaluated for impairment on an annual basis, or whenever indications of potential impairment exist. In the absence of any indications of potential impairment, the evaluation of goodwill and indefinite-lived intangible assets is performed no later than the interim period in which the anniversary of the acquisition date falls. White Mountains initially evaluates goodwill using a qualitative approach (step zero) to determine whether it is more likely than not that the implied fair value of goodwill is greater than its carrying value. If the results of the qualitative evaluation indicate that it is more likely than not that the carrying value of goodwill exceeds its implied fair value, White Mountains performs the two-step quantitative test for impairment. Other intangible assets with finite lives are measured at their acquisition date fair values, are amortized over their economic lives and presented net of accumulated amortization on the balance sheet. Other intangible assets with finite lives are reviewed for impairment when events occur or there are changes in circumstances indicating that their carrying value may exceed fair value. Impairment exists when the carrying value of other intangible assets exceeds fair value. See Note 4 – “Goodwill and Other Intangible Assets” .
Incentive Compensation	Incentive Compensation 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. Non-share-based awards are recognized over the related service periods based on management’s best estimate of the amounts at which the awards are expected to be paid. Share-based compensation which is typically settled in cash, such as performance shares, is classified as a liability-type award. The compensation cost for liability-classified awards is measured initially at the grant date fair value and remeasured each reporting period until settlement. The compensation cost for equity-classified awards expected to be settled in shares, such as options and restricted shares, is measured at the original grant date fair value of the award. The compensation cost for all awards is recognized for the vested portion of the awards over the related service periods. See Note 12 — “Employee Share-Based Incentive Compensation Plans”.
Income Taxes	Income Taxes White Mountains has subsidiaries and branches that operate in various jurisdictions around the world and are subject to tax in the jurisdictions in which they operate. As of December 31, 2021, the primary jurisdictions in which White Mountains’s subsidiaries and branches were subject to tax were Ireland, Israel, Luxembourg, the United Kingdom and the United States. Income earned or losses generated by companies outside the United States are generally subject to an overall effective tax rate lower than that imposed by the United States. Deferred tax assets and liabilities are recorded when a difference between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts for tax purposes exists, and for other temporary differences. The deferred tax asset or liability is recorded based on tax rates expected to be in effect when the difference reverses. Deferred tax assets represent amounts available to reduce income taxes payable in future periods. 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. See Note 8 – “Income Taxes” .
Leases	Leases Leases consist primarily of operating leases for office space and equipment. Lease assets and liabilities are recognized at the lease commencement date based on the present value of future minimum lease payments over the lease term. Lease assets and liabilities are not recorded for leases with a term at inception of one year or less. Lease expense is included in operating expenses. See Note 13 – “Leases” .
Non-controlling Interests	Non-controlling Interests Non-controlling interests consist of the ownership interests of non-controlling shareholders in consolidated subsidiaries, and are presented separately on the balance sheet. The portion of comprehensive income (loss) attributable to non-controlling interests is presented net of related income taxes in the statement of operations and comprehensive income (loss). See Note 14 — “Common Shareholders’ Equity and Non-controlling Interests”
Foreign Currency Exchange	Foreign Currency Exchange The functional currency for White Mountains’s non-U.S. based subsidiaries are measured, in most instances, using functional currencies other than the U.S. dollar. Net foreign exchange gains and losses arising from the translation of functional currencies are generally reported in shareholders’ equity, in accumulated other comprehensive income or loss. White Mountains also invests in securities denominated in foreign currencies. Assets and liabilities recorded in these foreign currencies are translated into U.S. dollars at exchange rates in effect at the balance sheet date, and revenues and expenses are converted using the weighted average exchange rates for the period. As of December 31, 2021 and 2020, White Mountains had unrealized foreign currency translation gains of $5.1 million and $5.6 million recorded in accumulated other comprehensive income (loss) on its consolidated balance sheet.
Fair Value Measurements	Fair Value Measurements 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). See Note 19 — “Fair Value of Financial Instruments”
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.
Recently Adopted Changes in Accounting Principles	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) (“ASU 2019-12”), 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 eliminated the exception to the incremental approach for inter-period tax allocation, which previously allowed consideration of the tax effect 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 has recorded both the tax expense related to BAM’s member 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) (“ASU 2017-04”), 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 identify any impairment indicators associated with its reporting units and therefore did not recognize an impairment of goodwill during the year ended December 31, 2020, and accordingly, adoption of ASU 2017-04 did not have any 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) (“ASU 2016-13”), 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 did not have any impact on White Mountains’s financial statements.

Significant Transactions (Table

Significant Transactions (Tables)	12 Months Ended
	Dec. 31, 2021
Significant Transactions [Abstract]
Schedule of Recognized Identified Assets Acquired	The following presents additional details of the assets acquired and liabilities assumed as of the January 1, 2021 acquisition date: Millions As of January 1, 2021 Investments $ 594.3 Cash 52.0 (1) Reinsurance recoverables 433.4 Insurance premiums receivable 236.7 Ceded unearned premiums 170.2 Value of in-force business acquired 71.7 Other assets 88.9 Loss and loss adjustment expense reserves (696.0) Unearned insurance premiums (326.1) Debt (46.4) Ceded reinsurance payable (528.3) Other liabilities (25.9) Net tangible assets acquired 24.5 Goodwill 116.8 Other intangible assets - syndicate underwriting capacity 175.7 Deferred tax liability on other intangible assets (33.4) Net assets acquired $ 283.6 (1) Cash excludes the White Mountains cash contribution of $605.4 as part of the Ark Transaction. The following table presents the economic lives, acquisition date fair values, accumulated amortization and net carrying values for other intangible assets and goodwill, by company as of December 31, 2021 and 2020: $ in Millions Weighted Average Economic December 31, 2021 December 31, 2020 Acquisition Date Fair Value Accumulated Amortization Impairments and Amounts Allocated to Held for Sale Net Carrying Value Acquisition Date Fair Value Accumulated Amortization Impairments Net Carrying Value Goodwill: Ark N/A $ 116.8 $ — $ — $ 116.8 $ — $ — $ — $ — NSM (1) N/A 533.4 — 30.2 503.2 506.4 — — 506.4 Kudu N/A 7.6 — — 7.6 7.6 — — 7.6 Other Operations N/A 17.9 — — 17.9 11.5 — — 11.5 Total goodwill 675.7 — 30.2 645.5 525.5 — — 525.5 Other intangible Ark Underwriting N/A 175.7 — — 175.7 — — — — NSM (1) Customer 9.0 159.9 57.0 3.5 99.4 136.2 36.7 3.5 96.0 Trade names 18 68.6 11.9 1.0 55.7 65.4 8.3 1.0 56.1 Information 0 3.1 1.4 1.7 — 3.1 1.4 1.7 — Renewal rights 12 82.5 15.8 — 66.7 82.5 4.9 — 77.6 Other 3.3 1.1 .7 — .4 1.7 1.0 — .7 Subtotal 315.2 86.8 6.2 222.2 288.9 52.3 6.2 230.4 Kudu Trade names 7 2.2 .9 — 1.3 2.2 .6 — 1.6 Other Operations Trade names 17.5 8.2 1.5 — 6.7 3.6 .3 — 3.3 Customer 13.0 18.8 4.5 — 14.3 14.2 1.4 — 12.8 Insurance licenses (2) N/A — — — — 8.6 — — 8.6 Other 5.3 .3 .1 — .2 .3 .1 — .2 Subtotal 27.3 6.1 — 21.2 26.7 1.8 24.9 Total other intangible assets 520.4 93.8 6.2 420.4 317.8 54.7 6.2 256.9 Total goodwill and other intangible assets $ 1,196.1 $ 93.8 $ 36.4 1,065.9 $ 843.3 $ 54.7 $ 6.2 782.4 Goodwill and other intangible assets attributed to non-controlling interests (117.6) (28.1) Goodwill and other intangible assets included in White Mountains’s common $ 948.3 $ 754.3 (1) During 2021, NSM’s goodwill and intangible assets includes $(1.5) and $(0.3) of the effect of foreign currency translation. During 2020, NSM’s goodwill and intangible assets includes $13.4 and $1.6 of the effect of foreign currency translation. (2) As of December 31, 2021, White Mountains has classified one of its Other Operating Businesses as held for sale, which includes of $8.6 of insurance licenses. See Note. 21 — “Held for Sale and Discontinued Operations” . The following table presents a summary of the acquisition date fair values of goodwill and other intangible assets for acquisitions completed during 2021 and 2020: $ in Millions Acquisition of Subsidiary/ Asset Goodwill and Other Intangible Assets (1) Acquisition Date Kingsbridge $ 131.7 April 7, 2020 J.C. Taylor 55.7 August 6, 2021 Total NSM segment $ 187.4 Ark $ 292.5 January 1, 2021 Other Operations $ 31.1 Various

Investment Securities (Tables)

Investment Securities (Tables)	12 Months Ended
	Dec. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Schedule of pre-tax net investment income	The following table presents pre-tax net investment income for the years ended December 31, 2021, 2020 and 2019: Year Ended December 31, Millions 2021 2020 2019 Fixed maturity investments $ 28.8 $ 29.0 $ 32.4 Short-term investments .6 1.1 5.0 Common equity securities .1 6.6 13.5 Investment in MediaAlpha — 59.9 8.0 Other long-term investments 56.3 35.6 22.1 Amount attributable to TPC Providers (1.0) — — Total investment income 84.8 132.2 81.0 Third-party investment expenses (2.3) (1.2) (1.3) Net investment income, pre-tax $ 82.5 $ 131.0 $ 79.7
Schedule of net realized and unrealized investment gains and losses	The following table presents net realized and unrealized investment gains (losses) for the years ended December 31, 2021, 2020 and 2019: Year Ended December 31, Millions 2021 2020 2019 Realized investment gains (losses) Fixed maturity investments $ 3.9 $ 10.9 $ 4.9 Short-term investments (.1) .4 .2 Common equity securities .4 137.2 85.9 Investment in MediaAlpha 160.3 63.8 — Other long-term investments (7.7) (25.2) 5.6 Net realized investment gains (losses) 156.8 187.1 96.6 Unrealized investment gains (losses) Fixed maturity investments $ (42.2) $ 27.5 $ 38.6 Common equity securities 14.9 (130.6) 109.8 Investment in MediaAlpha (540.6) 622.2 180.0 Other long-term investments 172.7 10.6 8.2 Net unrealized investment gains (losses) (395.2) 529.7 336.6 Net realized and unrealized investment gains (losses), before amount attributable to TPC providers (1) (238.4) 716.8 433.2 Amount attributable to TPC Providers (7.7) — — Net realized and unrealized investment gains (losses) $ (246.1) $ 716.8 $ 433.2 Fixed maturity and short-term investments Net realized and unrealized investment gains (losses) $ (38.4) $ 38.8 $ 43.7 Less: net realized and unrealized gains (losses) on investment (8.4) (8.7) 1.0 Net unrealized investment gains (losses) on investment $ (30.0) $ 47.5 $ 42.7 Common equity securities and investment in MediaAlpha Net realized and unrealized investment gains (losses) on common equity securities $ 15.3 $ 6.6 $ 195.7 Net realized and unrealized investment gains (losses) from investment in MediaAlpha (380.3) 686.0 180.0 Total net realized and unrealized investment gains (losses) (365.0) 692.6 375.7 Less: net realized and unrealized gains (losses) on investment 20.3 38.3 24.0 Net unrealized investment gains (losses) on investment $ (385.3) $ 654.3 $ 351.7 (1) For 2021, 2020 and 2019, includes $(7.7), $4.0 and $(0.3) of realized and unrealized investment gains (losses) related to foreign currency exchange.
Schedule of net unrealized investment gains (losses) for Level 3 investments	The following table presents total gains included in earnings attributable to net unrealized investment gains for Level 3 investments for the years ended December 31, 2021, 2020 and 2019 for investments still held at the end of the period: Year Ended December 31, Millions 2021 2020 2019 Other long-term investments (1) $ 98.9 $ 276.0 $ 181.9 Total net unrealized investment gains, pre-tax - Level 3 investments $ 98.9 $ 276.0 $ 181.9 (1) For 2020 and 2019, includes $278.7 and $180.0 of unrealized investment gains from White Mountains’s investment in MediaAlpha.
Schedule of fixed maturity 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 December 31, 2021 and 2020. December 31, 2021 Millions Cost or Gross Gross Net Foreign Carrying U.S. Government and agency obligations $ 212.1 $ .5 $ (1.1) $ — $ 211.5 Debt securities issued by corporations 993.3 8.7 (8.7) (.4) 992.9 Municipal obligations 276.4 16.8 (1.3) — 291.9 Mortgage and asset-backed securities 277.2 2.9 (2.5) — 277.6 Collateralized loan obligations 136.5 — (.4) (1.1) 135.0 Total fixed maturity investments $ 1,895.5 $ 28.9 $ (14.0) $ (1.5) $ 1,908.9 December 31, 2020 Millions Cost or Gross Gross Carrying U.S. Government and agency obligations $ 173.2 $ 3.1 $ — $ 176.3 Debt securities issued by corporations 522.8 24.7 (.1) 547.4 Municipal obligations 244.0 21.0 — 265.0 Mortgage and asset-backed securities 211.7 6.8 — 218.5 Total fixed maturity investments $ 1,151.7 $ 55.6 $ (.1) $ 1,207.2 The following table presents the cost or amortized cost and carrying value of White Mountains’s fixed maturity investments by contractual maturity as of December 31, 2021. Actual maturities could differ from contractual maturities because borrowers may have the right to call or prepay certain obligations with or without call or prepayment penalties. December 31, 2021 Millions Cost or Amortized Cost Carrying Value Due in one year or less $ 136.7 $ 137.3 Due after one year through five years 866.2 865.0 Due after five years through ten years 365.7 371.5 Due after ten years 113.2 122.5 Mortgage and asset-backed securities and 413.7 412.6 Total fixed maturity investments $ 1,895.5 $ 1,908.9
Schedule of equity securities and other long-term investments	The following tables present the cost or amortized cost, gross unrealized investment gains (losses), net foreign currency gains (losses), and carrying values of common equity securities, White Mountains’s investment in MediaAlpha and other long-term investments as of December 31, 2021 and 2020: December 31, 2021 Millions Cost or Gross Unrealized Gross Unrealized Losses Net Foreign Carrying Common equity securities $ 236.3 $ 16.1 $ — $ (1.3) $ 251.1 Investment in MediaAlpha $ — $ 261.6 $ — $ — $ 261.6 Other long-term investments $ 1,186.7 $ 239.0 $ (44.1) $ (3.8) $ 1,377.8 December 31, 2020 Millions Cost or Gross Unrealized Gross Unrealized Losses Net Foreign Carrying Investment in MediaAlpha $ — $ 802.2 $ — $ — $ 802.2 Other long-term investments $ 767.4 $ 95.8 $ (78.1) $ 1.7 $ 786.8
Schedule of fair value measurements for investment securities by level	The following tables present White Mountains’s fair value measurements for investments as of December 31, 2021 and 2020 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, 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 by industry sector because investors often reference commonly used benchmarks and their subsectors to monitor risk and performance. Accordingly, White Mountains has further disaggregated this asset class 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. December 31, 2021 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 211.5 $ 211.5 $ — $ — Debt securities issued by corporations: Financials 264.2 — 264.2 — Consumer 178.1 — 178.1 — Technology 117.9 — 117.9 — Industrial 112.9 — 112.9 — Healthcare 112.8 — 112.8 — Utilities 70.9 — 70.9 — Communications 56.0 — 56.0 — Energy 48.0 — 48.0 — Materials 32.1 — 32.1 — Total debt securities issued by corporations 992.9 — 992.9 — Municipal obligations 291.9 — 291.9 — Mortgage and asset-backed securities 277.6 — 277.6 — Collateralized loan obligations 135.0 — 135.0 — Total fixed maturity investments 1,908.9 211.5 1,697.4 — Short-term investments 465.9 465.9 — — Common equity securities (1) 251.1 — 251.1 — Investment in MediaAlpha 261.6 261.6 — — Other long-term investments 895.3 — 4.7 890.6 Other long-term investments — NAV (2) 482.5 — — — Total other long-term investments 1,377.8 — 4.7 890.6 Total investments $ 4,265.3 $ 939.0 $ 1,953.2 $ 890.6 (1) Consist of investments in listed funds that predominantly invest in international equities. (2) Consists of a bank loan fund, private equity funds, a hedge fund, Lloyd’s trust deposits 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, 2020 Millions Fair Value Level 1 Level 2 Level 3 Fixed maturity investments: U.S. Government and agency obligations $ 176.3 $ 176.3 $ — $ — Debt securities issued by corporations: Financials 133.9 — 133.9 — Consumer 81.9 — 81.9 — Industrial 66.9 — 66.9 — Technology 66.7 — 66.7 — Healthcare 51.5 — 51.5 — Communications 44.5 — 44.5 — Energy 35.8 — 35.8 — Materials 33.9 — 33.9 — Utilities 32.3 — 32.3 — Total debt securities issued by corporations 547.4 — 547.4 — Municipal obligations 265.0 — 265.0 — Mortgage and asset-backed securities 218.5 — 218.5 — Total fixed maturity investments 1,207.2 176.3 1,030.9 — Short-term investments 142.8 142.8 — — Investment in MediaAlpha 802.2 802.2 — — Other long-term investments 614.2 — — 614.2 Other long-term investments — NAV (1) 172.6 — — — Total other long-term investments 786.8 — — 614.2 Total investments $ 2,939.0 $ 1,121.3 $ 1,030.9 $ 614.2 (1) 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.
Schedule of credit ratings of debt securities issued	The following table presents the credit ratings of debt securities issued by corporations held in White Mountains’s investment portfolio as of December 31, 2021 and 2020: Fair Value at December 31, Millions 2021 2020 AAA $ 12.0 $ 10.6 AA 85.0 57.9 A 490.4 318.3 BBB 396.8 159.6 BB — 1.0 Other 8.7 — Debt securities issued by corporations (1) $ 992.9 $ 547.4 (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.
Schedule of mortgage and asset-backed securities	The following table presents the fair value of White Mountains’s mortgage and asset-backed securities and collateralized loan obligations as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Millions Fair Value Level 2 Level 3 Fair Value Level 2 Level 3 Mortgage-backed securities: Agency: FNMA $ 125.4 $ 125.4 $ — $ 88.7 $ 88.7 $ — FHLMC 90.5 90.5 — 70.1 70.1 — GNMA 40.1 40.1 — 40.6 40.6 — Total agency (1) 256.0 256.0 — 199.4 199.4 — Non-agency: Residential .5 .5 — — — — Total non-agency .5 .5 — — — — Total mortgage-backed securities 256.5 256.5 — 199.4 199.4 — Other asset-backed securities: Credit card receivables 12.3 12.3 — 11.3 11.3 — Vehicle receivables 8.8 8.8 — 7.8 7.8 — Total other asset-backed securities 21.1 21.1 — 19.1 19.1 — Total mortgage and asset-backed securities 277.6 277.6 — 218.5 218.5 — Collateralized loan obligations 135.0 135.0 — — — — Total mortgage and asset-backed securities and $ 412.6 $ 412.6 $ — $ 218.5 $ 218.5 $ — (1) Represents publicly traded mortgage-backed securities which carry the full faith and credit guaranty of the U.S. Government (i.e., GNMA) or are guaranteed by a government sponsored entity (i.e., FNMA, FHLMC).
Schedule of carrying values for other long-term investments	The following table presents the carrying values of White Mountains’s other long-term investments as of December 31, 2021 and 2020: Fair Value at Millions December 31, 2021 December 31, 2020 Kudu’s Participation Contracts $ 669.5 $ 400.6 PassportCard/DavidShield 120.0 95.0 Elementum Holdings L.P. 45.0 55.1 Other unconsolidated entities (1) 34.4 42.4 Total unconsolidated entities 868.9 593.1 Bank loan fund 163.0 — Private equity funds and hedge funds 153.8 121.2 Lloyd’s trust deposits 113.8 — ILS funds 51.9 51.4 Private debt investments 14.1 21.1 Other 12.3 — Total other long-term investments $ 1,377.8 $ 786.8 (1) Includes White Mountains’s non-controlling equity interests in certain private common equity securities, limited liability companies, convertible preferred securities and Simple Agreement for Future Equity (“SAFE”) investments.
Schedule of investments and unfunded commitments by investment objective and sector	The following table presents the fair value of investments and unfunded commitments in private equity funds and hedge funds by investment objective and sector as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Millions Fair Value Unfunded Fair Value Unfunded Private equity funds Aerospace/Defense/Government $ 69.8 $ 11.8 $ 69.1 $ 15.3 Financial services 67.7 29.3 23.5 30.4 Real estate 4.3 2.9 — — Manufacturing/Industrial — — 28.6 — Total private equity funds 141.8 44.0 121.2 45.7 Hedge funds European small/mid cap 12.0 — — — Total hedge funds 12.0 — — — Total private equity funds and hedge funds included in other long-term investments $ 153.8 $ 44.0 $ 121.2 $ 45.7
Schedule investments in 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 December 31, 2021: Millions 1 – 3 years 3 – 5 years 5 – 10 years >10 years Total Private equity funds — expected lock-up period remaining $ .1 $ 13.9 $ 116.3 $ 11.5 $ 141.8
Schedule of fair value investments by level	The following table presents the changes in White Mountains’s fair value measurements for Level 3 investments for the years ended December 31, 2021 and 2020: Level 3 Investments Millions Other Long-term Common Other Long-term Balance at December 31, 2020 $ 614.2 Balance at December 31, 2019 $ .1 654.0 Net realized and unrealized gains 117.3 Net realized and unrealized gains — 275.6 Amortization/accretion — Amortization/accretion — — Purchases 225.4 Purchases — 151.5 Sales (75.9) Sales (.1) (8.2) Effect of Ark Transaction 9.6 Effect of MediaAlpha IPO (1) — (458.7) Transfers in — Transfers in — — Transfers out — Transfers out — — Balance at December 31, 2021 $ 890.6 Balance at December 31, 2020 $ — $ 614.2 (1) Represents the reclassification of White Mountains’s investment in MediaAlpha from a level 3 measurement to a level 1 measurement in connection with the MediaAlpha IPO. See Note 2 - “Significant Transactions”.
Schedule of significant unobservable inputs used in estimating the fair value of other long-term investments	The following tables present significant unobservable inputs used in estimating the fair value of White Mountains’s other long-term investments, classified within Level 3 as of December 31, 2021 and 2020. The tables below exclude $46.7 million and $27.6 million of Level 3 other long-term investments generally valued based on recent or expected transaction prices. The fair value of investments in private equity funds, hedge funds, Lloyd’s trust deposits, bank loans funds and ILS funds are generally estimated using the NAV of the funds. $ in Millions December 31, 2021 Description Valuation Technique(s) (1) Fair Value (2) Unobservable Inputs Discount Rate (6) Terminal Cash Flow Exit Multiple (x) or Terminal Revenue Growth Rate (%) (6) Kudu’s Participation Contracts (3)(4)(5) Discounted cash flow $669.5 18% - 23% 7x - 13x PassportCard/DavidShield Discounted cash flow $120.0 23% 4% Elementum Holdings, L.P. Discounted cash flow $45.0 17% 4% Private debt investments Discounted cash flow $9.4 8% N/A (1) Key inputs to the discounted cash flow analysis generally include projections of future revenue and earnings, discount rates and terminal exit multiples or growth rates. (2) Includes the net unrealized investment gains (losses) associated with foreign currency; foreign currency effects based on observable inputs. (3) 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. The weighted average discount rate and weighted average terminal cash flow exit multiple applied to Kudu’s Participation Contracts is 20% and 10x. (4) In 2021, Kudu deployed a total of $223.4 in new and existing Kudu Participation Contracts, including TIG Advisors, TK Partners, Third Eye Capital Management, Douglass Winthrop Advisors, Granahan Investment Management and Radcliffe Capital Management. (5) As of December 31, 2021, one of Kudu’s Participation Contracts with a total fair value of $78.8 was valued using a probability weighted expected return method, which was based on a discounted cash flow analysis and an expected sale transaction. (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, 2020 Description Valuation Technique(s) (1) Fair Value (2) Unobservable Inputs Discount Rate (6) Terminal Cash Flow Exit Multiple (x) or Terminal Revenue Growth Rate (%) (6) Kudu’s Participation Contracts (3)(4) Discounted cash flow $400.6 18% - 23% 7x - 12x PassportCard/DavidShield (5) Discounted cash flow $95.0 23% 4% Elementum Holdings, L.P. Discounted cash flow $55.1 17% 4% Private debt investments Discounted cash flow $17.1 4% - 8% N/A Other Discounted cash flow $18.8 20% - 24% 4% (1) Key inputs to the discounted cash flow analysis generally include projections of future revenue and earnings, discount rates and terminal exit multiples or growth rates. (2) Includes the net unrealized investment gains (losses) associated with foreign currency; foreign currency effects based on observable inputs. (3) 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. The weighted average discount rate and weighted average terminal cash flow exit multiple applied to Kudu’s Participation Contracts is 20% and 10x. (4) In 2020, Kudu deployed a total of $118.2 in new Kudu Participation Contracts, including Creation Investments Capital, Sequoia Financial Group, Channel Capital and Ranger Investment Management. (5) In 2020, White Mountains made an additional $15.0 investment in PassportCard/DavidShield. See Note 2 — “Significant Transactions” . (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.

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Recognized Identified Assets Acquired	The following presents additional details of the assets acquired and liabilities assumed as of the January 1, 2021 acquisition date: Millions As of January 1, 2021 Investments $ 594.3 Cash 52.0 (1) Reinsurance recoverables 433.4 Insurance premiums receivable 236.7 Ceded unearned premiums 170.2 Value of in-force business acquired 71.7 Other assets 88.9 Loss and loss adjustment expense reserves (696.0) Unearned insurance premiums (326.1) Debt (46.4) Ceded reinsurance payable (528.3) Other liabilities (25.9) Net tangible assets acquired 24.5 Goodwill 116.8 Other intangible assets - syndicate underwriting capacity 175.7 Deferred tax liability on other intangible assets (33.4) Net assets acquired $ 283.6 (1) Cash excludes the White Mountains cash contribution of $605.4 as part of the Ark Transaction. The following table presents the economic lives, acquisition date fair values, accumulated amortization and net carrying values for other intangible assets and goodwill, by company as of December 31, 2021 and 2020: $ in Millions Weighted Average Economic December 31, 2021 December 31, 2020 Acquisition Date Fair Value Accumulated Amortization Impairments and Amounts Allocated to Held for Sale Net Carrying Value Acquisition Date Fair Value Accumulated Amortization Impairments Net Carrying Value Goodwill: Ark N/A $ 116.8 $ — $ — $ 116.8 $ — $ — $ — $ — NSM (1) N/A 533.4 — 30.2 503.2 506.4 — — 506.4 Kudu N/A 7.6 — — 7.6 7.6 — — 7.6 Other Operations N/A 17.9 — — 17.9 11.5 — — 11.5 Total goodwill 675.7 — 30.2 645.5 525.5 — — 525.5 Other intangible Ark Underwriting N/A 175.7 — — 175.7 — — — — NSM (1) Customer 9.0 159.9 57.0 3.5 99.4 136.2 36.7 3.5 96.0 Trade names 18 68.6 11.9 1.0 55.7 65.4 8.3 1.0 56.1 Information 0 3.1 1.4 1.7 — 3.1 1.4 1.7 — Renewal rights 12 82.5 15.8 — 66.7 82.5 4.9 — 77.6 Other 3.3 1.1 .7 — .4 1.7 1.0 — .7 Subtotal 315.2 86.8 6.2 222.2 288.9 52.3 6.2 230.4 Kudu Trade names 7 2.2 .9 — 1.3 2.2 .6 — 1.6 Other Operations Trade names 17.5 8.2 1.5 — 6.7 3.6 .3 — 3.3 Customer 13.0 18.8 4.5 — 14.3 14.2 1.4 — 12.8 Insurance licenses (2) N/A — — — — 8.6 — — 8.6 Other 5.3 .3 .1 — .2 .3 .1 — .2 Subtotal 27.3 6.1 — 21.2 26.7 1.8 24.9 Total other intangible assets 520.4 93.8 6.2 420.4 317.8 54.7 6.2 256.9 Total goodwill and other intangible assets $ 1,196.1 $ 93.8 $ 36.4 1,065.9 $ 843.3 $ 54.7 $ 6.2 782.4 Goodwill and other intangible assets attributed to non-controlling interests (117.6) (28.1) Goodwill and other intangible assets included in White Mountains’s common $ 948.3 $ 754.3 (1) During 2021, NSM’s goodwill and intangible assets includes $(1.5) and $(0.3) of the effect of foreign currency translation. During 2020, NSM’s goodwill and intangible assets includes $13.4 and $1.6 of the effect of foreign currency translation. (2) As of December 31, 2021, White Mountains has classified one of its Other Operating Businesses as held for sale, which includes of $8.6 of insurance licenses. See Note. 21 — “Held for Sale and Discontinued Operations” . The following table presents a summary of the acquisition date fair values of goodwill and other intangible assets for acquisitions completed during 2021 and 2020: $ in Millions Acquisition of Subsidiary/ Asset Goodwill and Other Intangible Assets (1) Acquisition Date Kingsbridge $ 131.7 April 7, 2020 J.C. Taylor 55.7 August 6, 2021 Total NSM segment $ 187.4 Ark $ 292.5 January 1, 2021 Other Operations $ 31.1 Various
Schedule of Goodwill and Intangible Assets Rollforward	The following table presents the change in goodwill and other intangible assets: December 31, 2021 December 31, 2020 Millions Goodwill Other Intangible Assets Total Goodwill and Other Intangible Assets Goodwill Other Intangible Assets Total Goodwill and Other Intangible Assets Beginning balance $ 525.5 $ 256.9 $ 782.4 $ 394.7 $ 260.0 $ 654.7 Acquisition of businesses (1) 71.5 — 71.5 140.0 — 140.0 Ark Transaction 116.8 175.7 292.5 — — — Attribution of acquisition date fair value estimates between goodwill and other intangible assets (2) (36.5) 36.5 — (23.2) 23.2 — Measurement period adjustments (5) (.1) — (.1) .6 6.6 7.2 Dispositions of businesses — — — — — — Amortization — (39.8) (39.8) — (28.3) (28.3) Impairments (3) — — — — (6.2) (6.2) Assets held for sale (8.6) (8.6) — — — Loss on assets held for sale (4) (30.2) — (30.2) — — — Foreign currency translation (1.5) (.3) (1.8) 13.4 1.6 15.0 Ending balance $ 645.5 $ 420.4 $ 1,065.9 $ 525.5 $ 256.9 $ 782.4 (1) During 2021, amounts include acquisition of J.C. Taylor of $55.7 and acquisitions within Other Operations of $15.8. During 2020, amounts include acquisition of Kingsbridge of $125.1 and acquisitions within Other Operations of $14.9. (2) During 2021, the attribution of acquisition date fair value estimates between goodwill and other intangible assets were $27.2 for the acquisition of J.C. Taylor and $9.3 for acquisitions within Other Operations segment. During 2020, the attribution of acquisition date fair value estimates between goodwill and other intangible assets were $13.6 for the acquisition of Kingsbridge and $9.6 for acquisitions within Other Operations segment. (3) In 2020, impairments relate to NSM’s UK vertical. (4) Relates to the sale of NSM’s Fresh Insurance’s motor business recorded in 2021. This amount excludes $1.5 of net proceeds related to the sale. (5) Measurement period adjustments relate to updated information about acquisition date fair values of assets acquired and liabilities assumed. During 2021, adjustments relate to acquisitions within the Other Operations segment. During 2020, adjustments primarily relate to contingent considerations of $4.1 in connection with the acquisition of Kingsbridge and the remaining amount related to acquisitions within Other Operations segment.
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	White Mountains expects to recognize amortization expense in each of the next five years as the following table presents: Millions Amortization Expense 2022 $ 39.4 2023 36.0 2024 32.7 2025 30.5 2026 and years after 106.1 Total (1) $ 244.7 (1) Excludes Ark’s indefinite-lived intangible assets of $175.7.

Loss and Loss Adjustment Expe_2

Loss and Loss Adjustment Expense Reserves (Tables)	12 Months Ended
	Dec. 31, 2021
Insurance Loss Reserves [Abstract]
Schedule of Liability for Unpaid Claims and Claims Adjustment Expense	The following table summarizes the loss and LAE reserve activity of Ark’s insurance and reinsurance subsidiaries for the year ended December 31, 2021: Millions Year Ended Gross beginning balance $ 696.0 Less: beginning reinsurance recoverable on unpaid losses (1) (433.4) Net loss and LAE reserves 262.6 Losses and LAE incurred relating to: Current year losses 336.3 Prior year losses (21.5) Net incurred losses and LAE 314.8 Loss and LAE paid relating to: Current year losses (43.9) Prior year losses (61.6) Net paid losses and LAE (105.5) Change in TPC Providers’ participation (2) (2.2) Foreign currency translation and other adjustments to loss and LAE reserves (3.9) Net ending balance 465.8 Plus: ending reinsurance recoverable on unpaid losses (1) 428.9 Gross ending balance $ 894.7 (1) The beginning reinsurance recoverable on unpaid losses and ending reinsurance recoverable on unpaid losses includes amounts attributable to TPC Providers of $319.2 and $276.8. (2) Amount represents a decrease in net loss and LAE reserves due to a change in the TPC Providers’ participation during 2021, related to the RITC for the 2018 year of account. The following table summarizes the unpaid loss and LAE reserves, net of reinsurance recoverables on unpaid losses, for each of Ark’s major reserving lines of business as of December 31, 2021: Millions As of Property and Accident & Health $ 175.0 Marine & Energy 99.3 Specialty 85.2 Casualty - Active 37.4 Casualty - Runoff 68.4 Other 0.5 Unpaid loss and LAE reserves, net of reinsurance recoverables on unpaid losses 465.8 Plus: Reinsurance recoverables on unpaid losses (1) Property and Accident & Health 145.2 Marine & Energy 70.2 Specialty 68.9 Casualty - Active 41.4 Casualty - Runoff 103.2 Total Reinsurance recoverables on unpaid losses (1) 428.9 Total unpaid loss and LAE reserves $ 894.7 (1) The reinsurance recoverables on unpaid losses include amounts attributable to TPC Providers of $276.8.
Schedule of Third Party Participation of LAE Reserves by Year of Account	The following table summarizes the participation of Ark’s TPC Providers by year of account: 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 TPC Providers’ — % — % 66.2 % 70.0 % 59.6 % 60.0 % 57.6 % 58.3 % 42.8 % — %
Short-duration Insurance Contracts, Claims Development	Property and Accident & Health $ in Millions Incurred Loss and LAE, Net of Reinsurance For the Years Ended December 31, As of December 31, 2021 Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Total IBNR plus expected development on reported claims Cumulative number of reported claims Unaudited 2012 $ 84.1 $ 68.4 $ 65.1 $ 65.7 $ 60.2 $ 60.0 $ 60.4 $ 60.2 $ 60.2 $ 60.0 $ — 2,710 2013 74.6 66.9 66.6 62.1 61.6 61.7 61.6 61.6 61.6 .4 2,586 2014 34.8 31.3 29.4 28.6 28.6 28.5 28.5 28.5 — 2,963 2015 19.8 17.4 16.2 16.0 15.9 15.9 15.9 .4 2,884 2016 21.7 16.9 17.9 18.0 17.9 18.0 (.3) 3,478 2017 22.6 29.9 37.4 36.7 36.0 3.6 4,610 2018 37.5 44.2 46.3 44.5 1.5 4,270 2019 30.4 27.8 23.4 2.1 4,073 2020 62.9 61.5 15.2 4,532 2021 162.1 70.8 2,860 Total $ 511.5 Property and Accident & Health Millions Cumulative Paid Loss and LAE, Net of Reinsurance For the Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Unaudited 2012 $ 14.2 $ 45.0 $ 53.6 $ 57.3 $ 58.2 $ 58.6 $ 58.7 $ 59.3 $ 59.4 $ 59.5 2013 15.8 40.3 60.0 61.1 61.1 61.3 61.3 61.3 61.2 2014 13.9 25.4 27.6 28.0 28.1 28.2 28.4 28.3 2015 7.0 12.4 13.7 14.9 14.8 15.1 15.3 2016 8.6 13.4 16.8 17.1 17.2 17.5 2017 17.0 26.3 32.1 33.3 30.2 2018 15.8 32.8 40.7 40.7 2019 6.9 17.1 19.1 2020 11.4 34.5 2021 30.8 Total 337.1 All outstanding liabilities before 2012, net of reinsurance .6 Loss and LAE reserves, net of reinsurance $ 175.0 Marine & Energy $ in Millions Incurred Loss and LAE, Net of Reinsurance For the Years Ended December 31, As of December 31, 2021 Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Total IBNR plus expected development on reported claims Cumulative number of reported claims Unaudited 2012 $ 64.7 $ 55.1 $ 46.0 $ 42.8 $ 33.6 $ 32.8 $ 32.6 $ 32.0 $ 32.0 $ 32.1 $ .1 2,428 2013 64.9 50.8 41.9 31.6 31.0 29.9 29.7 29.6 29.9 (.2) 2,641 2014 41.3 27.2 17.4 16.2 14.7 14.3 14.4 14.4 .5 2,581 2015 25.3 15.4 13.6 12.7 12.0 12.0 12.2 .2 3,390 2016 22.3 18.1 16.0 15.1 14.9 15.1 .7 4,117 2017 23.9 18.6 16.9 16.4 16.5 1.1 4,470 2018 24.5 18.9 16.7 17.0 .5 3,487 2019 19.3 17.3 17.2 .6 2,562 2020 24.4 21.7 2.9 1,668 2021 83.7 69.9 1,091 Total $ 259.8 Marine & Energy Millions Cumulative Paid Loss and LAE, Net of Reinsurance For the Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Unaudited 2012 $ 8.1 $ 24.0 $ 27.4 $ 30.2 $ 30.6 $ 31.3 $ 31.7 $ 31.4 $ 31.3 $ 31.0 2013 7.9 22.6 28.1 29.1 29.7 29.9 29.9 29.7 29.9 2014 6.0 12.4 13.5 14.4 14.5 13.7 14.0 13.8 2015 4.0 8.0 9.8 11.3 10.7 10.8 11.2 2016 5.6 10.1 12.8 13.3 13.4 14.0 2017 5.2 11.3 13.1 14.4 14.4 2018 2.7 12.9 14.5 15.2 2019 3.4 10.9 12.9 2020 3.2 12.9 2021 6.4 Total 161.7 All outstanding liabilities before 2012, net of reinsurance 1.2 Loss and LAE reserves, net of reinsurance $ 99.3 Specialty $ in Millions Incurred Loss and LAE, Net of Reinsurance For the Years Ended December 31, As of December 31, 2021 Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Total IBNR plus expected development on reported claims Cumulative number of reported claims Unaudited 2012 $ 43.1 $ 36.1 $ 31.8 $ 30.8 $ 26.7 $ 25.8 $ 26.3 $ 26.6 $ 26.8 $ 26.8 $ 2.1 887 2013 48.6 34.9 25.6 17.5 16.9 17.1 16.9 17.3 17.3 1.3 1,122 2014 51.1 51.1 41.9 41.3 41.5 42.9 43.5 43.5 (.3) 1,409 2015 21.3 13.0 10.4 10.1 10.6 10.7 10.8 1.7 1,876 2016 15.9 11.7 8.7 9.2 9.0 9.3 (1.3) 1,941 2017 16.0 11.9 10.9 10.5 10.6 1.5 2,179 2018 12.1 13.9 14.8 13.7 2.4 2,090 2019 16.6 14.6 13.5 2.8 2,315 2020 20.7 19.7 6.2 1,925 2021 67.3 57.4 1,341 Total $ 232.5 Specialty Millions Cumulative Paid Loss and LAE, Net of Reinsurance For the Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Unaudited 2012 $ 16.3 $ 25.2 $ 22.2 $ 22.6 $ 23.2 $ 23.3 $ 24.2 $ 24.4 $ 24.4 $ 24.5 2013 17.1 13.6 15.2 15.8 15.8 16.0 16.0 16.0 16.0 2014 26.8 39.7 40.4 40.8 41.5 42.8 43.6 43.5 2015 4.1 7.2 7.8 8.2 8.2 8.3 8.3 2016 3.2 8.0 9.2 10.0 10.4 10.5 2017 3.3 6.8 8.4 8.5 8.5 2018 2.9 8.1 9.8 10.3 2019 4.9 7.1 7.6 2020 5.4 10.9 2021 5.2 Total 145.3 All outstanding liabilities before 2012, net of reinsurance (2.0) Loss and LAE reserves, net of reinsurance $ 85.2 Casualty - Active $ in Millions Incurred Loss and LAE, Net of Reinsurance For the Years Ended December 31, As of December 31, 2021 Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Total IBNR plus expected development on reported claims Cumulative number of reported claims Unaudited 2012 $ 22.6 $ 21.1 $ 17.7 $ 16.2 $ 10.1 $ 9.9 $ 11.0 $ 11.0 $ 11.3 $ 11.1 $ .8 1,016 2013 23.2 18.8 15.0 8.3 8.1 8.9 8.8 9.0 8.9 1.3 1,134 2014 17.1 13.8 7.5 7.0 8.0 7.8 7.8 7.7 1.2 1,359 2015 12.3 7.7 6.0 7.0 6.5 6.4 6.2 .6 1,247 2016 5.7 5.0 6.3 6.6 7.0 6.9 .1 1,483 2017 7.4 7.8 7.2 6.2 5.9 .7 1,489 2018 8.7 9.0 7.3 7.1 .9 961 2019 8.0 7.4 6.3 1.7 742 2020 7.6 6.2 3.9 420 2021 15.9 14.2 452 Total $ 82.2 Casualty - Active Millions Cumulative Paid Loss and LAE, Net of Reinsurance For the Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Unaudited 2012 $ 1.3 $ 3.3 $ 4.8 $ 6.4 $ 7.4 $ 8.0 $ 8.5 $ 9.1 $ 8.9 $ 9.1 2013 1.5 3.6 5.3 5.7 6.3 6.7 7.0 7.0 7.2 2014 1.3 3.5 4.2 4.7 5.2 5.5 5.9 6.0 2015 1.8 2.4 3.2 4.4 4.7 4.9 5.1 2016 .2 1.0 2.3 4.0 4.6 5.3 2017 .8 1.7 2.8 3.4 4.2 2018 .3 1.4 3.5 4.3 2019 .3 1.4 2.3 2020 .5 1.0 2021 .5 Total 45.0 All outstanding liabilities before 2012, net of reinsurance .2 Loss and LAE reserves, net of reinsurance $ 37.4 Casualty - Runoff $ in Millions Incurred Loss and LAE, Net of Reinsurance For the Years Ended December 31, As of December 31, 2021 Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Total IBNR plus expected development on reported claims Cumulative number of reported claims Unaudited 2012 $ 44.3 $ 44.6 $ 37.8 $ 34.4 $ 22.3 $ 21.7 $ 22.3 $ 22.8 $ 22.7 $ 23.1 $ (.2) 1,430 2013 65.7 75.8 70.1 49.2 47.0 49.8 49.8 49.8 49.9 3.1 1,810 2014 46.9 67.5 46.8 46.0 55.9 55.6 56.0 55.0 1.9 1,932 2015 26.9 23.9 26.4 35.7 33.0 33.2 32.0 1.4 2,009 2016 19.1 25.3 38.8 35.4 35.3 34.1 3.8 2,141 2017 17.4 27.2 26.7 28.0 26.7 2.5 1,597 2018 13.5 18.2 20.2 20.0 2.9 1,265 2019 10.8 14.3 15.4 3.7 961 2020 4.2 6.0 3.6 552 2021 1.7 .4 260 Total 263.9 Casualty - Runoff Millions Cumulative Paid Loss and LAE, Net of Reinsurance For the Years Ended December 31, Accident Year 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 Unaudited 2012 $ 3.5 $ 10.4 $ 13.6 $ 16.5 $ 17.8 $ 19.3 $ 20.5 $ 20.8 $ 21.2 $ 21.8 2013 7.2 19.5 35.9 41.0 42.7 44.3 45.0 45.6 46.0 2014 6.5 23.2 29.1 36.5 43.1 47.0 48.7 49.5 2015 4.3 7.9 14.0 20.3 23.9 26.5 28.2 2016 3.8 9.7 16.8 21.8 24.5 26.8 2017 3.1 9.1 14.2 18.3 21.1 2018 3.3 7.2 12.2 14.3 2019 3.2 5.6 7.4 2020 .8 1.3 2021 .5 Total 216.9 All outstanding liabilities before 2012, net of reinsurance 21.4 Loss and LAE reserves, net of reinsurance $ 68.4
Short-duration Insurance Contracts, Schedule of Historical Claims Duration	Property and Accident & Health Average Annual Percentage Payout of Incurred Losses and LAE by Age, Net of Reinsurance Unaudited Years 1 2 3 4 5 6 7 8 9 10 31.5% 33.4% 19.2% 5.7% 1.2% 1.4% 0.8% 0.3% —% 0.1% Marine & Energy Average Annual Percentage Payout of Incurred Losses and LAE by Age, Net of Reinsurance Unaudited Years 1 2 3 4 5 6 7 8 9 10 19.8% 37.7% 20.2% 5.7% 4.3% 7.2% 0.4% 0.1% (0.4)% 0.2% Specialty Average Annual Percentage Payout of Incurred Losses and LAE by Age, Net of Reinsurance Unaudited Years 1 2 3 4 5 6 7 8 9 10 34.0% 33.8% 7.3% 0.5% 4.6% 4.4% 4.6% 3.1% (3.5)% (1.0)% Casualty - Active Average Annual Percentage Payout of Incurred Losses and LAE by Age, Net of Reinsurance Unaudited Years 1 2 3 4 5 6 7 8 9 10 9.1% 14.7% 18.5% 14.2% 9.6% 10.7% 3.9% 3.1% 1.0% 3.1% Casualty - Runoff Average Annual Percentage Payout of Incurred Losses and LAE by Age, Net of Reinsurance Unaudited Years 1 2 3 4 5 6 7 8 9 10 9.4% 15.3% 17.0% 15.9% 9.7% 8.1% 7.0% 3.6% 2.5% 1.7%

Third-Party Reinsurance (Tables

Third-Party Reinsurance (Tables)	12 Months Ended
	Dec. 31, 2021
Reinsurance Disclosures [Abstract]
Effects of Reinsurance	The following table summarizes the effects of reinsurance on written and earned premiums and on losses and LAE for Ark. Year Ended December 31, 2021 Millions Written premiums: Gross $ 1,058.7 Ceded (199.6) Net written premiums $ 859.1 Earned premiums: Gross $ 886.4 Ceded (249.1) Net earned premiums $ 637.3 Losses and LAE: Gross $ 442.9 Ceded (128.1) Net Losses and LAE $ 314.8 $ in Millions As of December 31, 2021 A.M. Best Rating (1) Gross Collateral Net % of Total A+ or better $ 120.0 $ 16.9 $ 103.1 77.5 % A - to A 41.5 13.1 28.4 21.3 B++ or lower and not rated 10.1 8.5 1.6 1.2 Total $ 171.6 $ 38.5 $ 133.1 100.0 % (1) A.M. Best ratings as detailed above are: “A+ or better” (Superior) “A- to A” (Excellent), “B++” (Good).

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
Schedule of debt outstanding	The following table presents White Mountains’s debt outstanding as of December 31, 2021 and 2020: December 31, Effective (1) December 31, Effective (1) $ in Millions 2021 Rate 2020 Rate (1) Ark 2007 Notes Tranche 1 $ 30.0 $ — Ark 2007 Notes Tranche 2 — — Ark 2007 Subordinated Notes, carrying value 30.0 — Ark 2021 Notes Tranche 1 44.2 — Ark 2021 Notes Tranche 2 47.0 — Ark 2021 Notes Tranche 3 70.0 — Unamortized issuance cost (5.3) — Ark 2021 Subordinated Notes, carrying value 155.9 — Total Ark Subordinated Notes, carrying value 185.9 6.9% — NSM Bank Facility 277.6 7.3% (2) 277.4 7.5% (2) Unamortized issuance cost (6.4) (6.1) NSM Bank Facility, carrying value 271.2 271.3 Other NSM debt .9 2.9% 1.3 2.5% Kudu Credit Facility 225.4 4.3% — Unamortized issuance cost (7.2) — Kudu Credit Facility, carrying value 218.2 — Kudu Bank Facility — 89.2 8.3% Unamortized issuance cost — (2.9) Kudu Bank Facility, carrying value — 86.3 Other Operations debt 17.1 7.5% 18.0 7.4% Unamortized issuance cost (.3) (.5) Other Operations debt, carrying value 16.8 17.5 Total debt $ 693.0 $ 376.4 (1) Effective rate includes the effect of the amortization of debt issuance costs. (2) NSM’s effective rate excludes the effect of the interest rate swap on the hedged portion of the debt. The weighted average interest rate for the years ended December 31, 2021 and 2020, excluding the effect of the amortization of debt issuance costs, was 6.5% and 7.0%. The weighted average interest rate for the years ended December 31, 2021 and 2020 on the total NSM Bank Facility including both the effect of the amortization of debt issuance costs and the effect of the interest rate swap and interest rate cap was 8.2% and 8.4%. The following table presents the change in debt under the NSM Bank Facility for the years ended December 31, 2021, 2020 and 2019: Millions Year Ended December 31, NSM Bank Facility 2021 2020 2019 Beginning balance $ 277.4 $ 221.3 $ 180.4 Term loans Borrowings (1) — 52.4 42.9 Repayments (2.8) (2.0) (2.0) Foreign currency translation (.5) 5.7 — Revolving credit loan Borrowings (2) 35.0 — 6.5 Repayments (31.5) — (6.5) Ending balance $ 277.6 $ 277.4 $ 221.3 (1) Borrowings for the year ended December 31, 2020 included $52.4 for the funding of the acquisition of Kingsbridge. Borrowings for the year ended December 31, 2019 included $20.4 and $22.5 for the funding of the acquisitions of Embrace and the Renewal Rights. (2) Borrowings for the year ended December 31, 2021 included $35.0 for the funding of the acquisition of J.C. Taylor. The following table presents the change in debt under the Kudu Bank Facility and Kudu Credit Facility for the years ended December 31, 2021, 2020 and 2019: Year Ended December 31, Millions 2021 2020 2019 Kudu Bank Facility Beginning balance $ 89.2 $ 57.0 $ — Term loans Borrowings 3.0 32.2 57.0 Repayments (92.2) — — Ending balance $ — $ 89.2 $ 57.0 Kudu Credit Facility Beginning balance $ — $ — $ — Term loans Borrowings 232.0 — — Repayments (6.6) — — Ending balance $ 225.4 $ — $ —
Schedule of contractual repayments of debt	The following table presents a schedule of contractual repayments of White Mountains’s debt as of December 31, 2021: Millions December 31, 2021 Due in one year or less $ 5.7 Due in two to three years 14.5 Due in four to five years 221.6 Due after five years 470.4 Total $ 712.2
Schedule of debt	The following table presents the NSM weighted average interest rate for the year ended December 31, 2021 and 2020: NSM Weighted Average Interest Rate Year Ended December 31, 2021 2020 Millions Weighted Average Interest Expense (1) Weighted Average Interest rate Weighted Average Interest Expense (1) Weighted Average Interest rate Term loan - hedged $ 146.9 $ 13.2 9.0 % $ 148.4 $ 13.4 9.0 % Term loan - unhedged 129.1 9.4 7.3 % 125.8 8.6 6.8 % Total NSM Facility $ 276.0 $ 22.6 8.2 % $ 274.2 $ 22.0 8.0 % ( 1) Interest expense includes the amortization of debt issuance costs and the effect of the interest rate swap and interest rate cap and excludes $0.7 and $0.1, for the year ended December 31, 2021 and 2020, of interest expense related to the revolving credit loan and Other NSM Debt.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Schedule of total income tax benefit (expense)	The following table presents the total income tax (expense) benefit for the years ended December 31, 2021, 2020 and 2019: Year Ended December 31, Millions 2021 2020 2019 Current income tax (expense) benefit: U.S. federal $ (3.8) $ (10.4) $ .9 State (2.1) (4.2) (3.7) Non-U.S. (3.9) (1.1) (1.7) Total current income tax (expense) benefit (9.8) (15.7) (4.5) Deferred income tax (expense) benefit: U.S. federal (4.9) 23.2 (14.9) State (5.6) 10.3 (10.4) Non-U.S. (18.3) 2.7 .5 Total deferred income tax (expense) benefit (28.8) 36.2 (24.8) Total income tax (expense) benefit $ (38.6) $ 20.5 $ (29.3)
Schedule of U.S. federal statutory income tax rate and actual effective tax rate on pre-tax income	The following table presents a reconciliation of taxes calculated for 2021, 2020 and 2019 using the 21% U.S. federal statutory rate U.S. federal statutory rate (the tax rate at which the majority of White Mountains’s worldwide operations are taxed) to the income tax (expense) benefit on pre-tax income (loss): Year Ended December 31, Millions 2021 2020 2019 Tax (expense) benefit at the U.S. statutory rate $ 63.4 $ (135.5) $ (85.1) Differences in taxes resulting from: Non-U.S. earnings, net of foreign taxes (77.2) 78.4 27.1 Tax rate changes (11.2) 2.7 (5.7) State taxes (6.2) (8.5) (17.5) Member’s surplus contributions (5.6) (4.8) (3.6) Change in valuation allowance (2.4) (29.2) 63.6 Officer compensation (1.5) (1.1) — Withholding tax (.3) (5.0) (1.6) Tax exempt interest and dividends .2 .8 1.1 Reorganization — 130.5 — Tax reserve adjustments — 1.9 (.7) Other, net 2.2 (9.7) (6.9) Total income tax (expense) benefit on pre-tax income (loss) $ (38.6) $ 20.5 $ (29.3)
Schedule of components of deferred income tax assets and liabilities	The following table presents an outline of the significant components of White Mountains’s U.S. federal, state and non-U.S. deferred tax assets and liabilities: December 31, Millions 2021 2020 Deferred tax assets related to: U.S. federal and state net operating and capital $ 102.8 $ 79.6 Non-U.S. net operating loss carryforwards 47.1 50.5 Incentive compensation 14.6 17.5 Accrued interest 10.8 7.9 Deferred acquisition costs 6.4 5.5 Tax credit carryforwards 4.9 5.5 Other items .7 1.3 Total gross deferred tax assets 187.3 167.8 Less: valuation allowances 92.3 97.4 Total net deferred tax assets 95.0 70.4 Deferred tax liabilities related to: Member’s surplus contributions 60.4 52.9 Purchase accounting 48.5 5.1 Investment basis difference 33.7 11.8 Net unrealized investment gains (losses) 10.7 .3 Deferred underwriting 4.1 — Other items 2.7 2.8 Total deferred tax liabilities 160.1 72.9 Net deferred tax asset (liability) $ (65.1) $ (2.5)
Schedule of net operating and capital loss carryforwards	The following table presents net operating loss and capital loss carryforwards as of December 31, 2021, the expiration dates and the deferred tax assets thereon: December 31, 2021 Millions United States Luxembourg United Kingdom Israel Total 2021-2025 $ — $ — $ — $ — $ — 2026-2030 — — — — — 2031-2040 250.7 68.3 — — 319.0 No expiration date 213.8 28.8 6.9 93.3 342.8 Total $ 464.5 $ 97.1 $ 6.9 $ 93.3 $ 661.8 Gross deferred tax asset $ 97.6 $ 24.3 $ 1.4 $ 21.4 $ 144.7 Valuation allowance (83.2) (24.3) (.4) (21.4) (129.3) Net deferred tax asset $ 14.4 $ — $ 1.0 $ — $ 15.4
Schedule of changes in amount of unrecognized tax benefits	The following table presents a reconciliation of the beginning and ending amount of unrecognized tax benefits from 2019 to 2021: Millions Permanent Differences (1) Temporary Differences (2) Interest and Penalties (3) Total Balance at December 31, 2018 $ 1.1 $ — $ — $ 1.1 Changes in prior year tax positions 1.3 — — 1.3 Balance at December 31, 2019 2.4 — — 2.4 Changes in prior year tax positions .1 — — .1 Tax positions taken during the current year .1 — — .1 Changes in prior year tax positions (2.6) — — (2.6) Balance at December 31, 2020 — — — — Changes in prior year tax positions — — — — Balance at December 31, 2021 $ — $ — $ — $ — (1) Represents the amount of unrecognized tax benefits that, if recognized, would impact the effective tax rate. (2) Represents the amount of unrecognized tax benefits that, if recognized, would create a temporary difference between the reported amount of an item in White Mountains’s Consolidated Balance Sheet and its tax basis. (3) Net of tax benefit.

Municipal Bond Guarantee Insu_2

Municipal Bond Guarantee Insurance (Tables)	12 Months Ended
	Dec. 31, 2021
Insurance [Abstract]
Schedule of Insured Obligations	The following table presents a schedule of BAM’s insured obligations as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Contracts outstanding 12,350 10,997 Remaining weighted average contract period (in years) 10.8 10.7 Contractual debt service outstanding (in millions): Principal $ 89,196.5 $ 75,287.7 Interest 41,486.5 36,448.8 Total debt service outstanding $ 130,683.0 $ 111,736.5 Gross unearned insurance premiums $ 266.3 $ 237.5
Schedule of BAM’s future premium revenues	The following table presents a schedule of BAM’s future premium revenues as of December 31, 2021: Millions December 31, 2021 January 1, 2022 - March 31, 2022 $ 6.4 April 1, 2022 - June 30, 2022 6.4 July 1, 2022 - September 30, 2022 6.3 October 1, 2022 - December 31, 2022 6.1 25.2 2023 23.9 2024 22.2 2025 20.6 2026 19.1 2027 and thereafter 155.3 Total gross unearned insurance premiums $ 266.3
Schedule of Net Written Premiums	The following table presents a schedule of written premiums and earned premiums included in White Mountains’s HG Global/BAM segment for the years ended December 31, 2021, 2020 and 2019: Millions December 31, 2021 December 31, 2020 December 31, 2019 Written premiums: Direct $ 51.2 $ 61.5 $ 28.1 Assumed 4.6 .2 10.6 Gross written premiums (1) $ 55.8 $ 61.7 $ 38.7 Earned premiums: Direct $ 23.2 $ 19.4 $ 13.6 Assumed 3.7 3.4 2.7 Gross earned premiums (1) $ 26.9 $ 22.8 $ 16.3 (1) There are no ceded premium amounts in the periods presented and Gross earned premium are equivalent to net written premiums and net earned premiums.

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Schedule of earnings per share from continuing operations	The following table presents the Company’s computation of earnings per share from continuing operations for the years ended December 31, 2021, 2020 and 2019. See Note 21 — “Held for Sale and Discontinued Operations” . Year Ended December 31, 2021 2020 2019 Basic and diluted earnings per share numerators (in millions): Net income (loss) attributable to White Mountains’s $ (275.4) $ 708.7 $ 414.5 Less: total (loss) income from discontinued operations, net of tax 18.7 (2.3) .8 Net income (loss) from continuing operations attributable to (294.1) 711.0 413.7 Allocation of (earnings) losses to participating restricted common shares (1) 3.5 (9.3) (5.3) Basic and diluted earnings (losses) per share numerators $ (290.6) $ 701.7 $ 408.4 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,079.0 3,122.2 3,181.6 Average unvested restricted common shares (2) (36.5) (40.8) (40.5) Basic earnings (losses) per share denominator 3,042.5 3,081.4 3,141.1 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,079.0 3,122.2 3,181.6 Average unvested restricted common shares (2) (36.5) (40.8) (40.5) Diluted earnings (losses) per share denominator 3,042.5 3,081.4 3,141.1 Basic and diluted earnings per share (in dollars) - continuing operations: Distributed earnings - dividends declared and paid $ 1.00 $ 1.00 $ 1.00 Undistributed earnings (losses) (96.53) 226.72 129.02 Basic and diluted earnings (losses) per share $ (95.53) $ 227.72 $ 130.02 (1) Restricted shares issued by White Mountains receive dividends, and therefore, are considered participating securities. (2) Restricted shares outstanding vest upon a stated date. See Note 12 — “Employee Share-Based Incentive Compensation Plans”.
Schedule of undistributed net earnings (losses) from continuing operations	The following table presents the undistributed net earnings (losses) from continuing operations for the years ended December 31, 2021, 2020 and 2019. See Note 21 — “Held for Sale and Discontinued Operations” . Year Ended December 31, Millions 2021 2020 2019 Undistributed net earnings - continuing operations: Net income (loss) attributable to White Mountains’s common shareholders, $ (290.6) $ 701.7 $ 408.4 Dividends declared, net of restricted common share amounts (1) (3.1) (3.1) (3.2) Total undistributed net earnings (losses), net of restricted common share amounts $ (293.7) $ 698.6 $ 405.2 (1) Restricted shares issued by White Mountains receive dividends, and are therefore considered participating securities.

Employee Share-Based Incentiv_2

Employee Share-Based Incentive Compensation Plans (Tables)	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Schedule of performance share activity	The following table presents performance share activity for the years ended December 31, 2021, 2020 and 2019 for performance shares granted under the WTM Incentive Plan: Year Ended December 31, 2021 2020 2019 $ in Millions Target Accrued Target Accrued Target Accrued Beginning of period 42,458 $ 56.3 42,473 $ 43.7 40,616 $ 31.7 Shares paid or expired (1) (14,336) (35.2) (14,070) (27.7) (13,715) (18.1) New grants 13,475 — 14,055 — 15,600 — Forfeitures and cancellations (2) (769) .4 — (.4) (28) (.1) Expense recognized — 20.7 — 40.7 — 30.2 End of period 40,828 $ 42.2 42,458 $ 56.3 42,473 $ 43.7 (1) WTM performance share payments in 2021 for the 2018-2020 performance cycle, which were paid in March 2021 at 200% of target. WTM performance share payments in 2020 for the 2017-2019 performance cycle, which were paid 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 March 2019, ranged from 139% to 166% of target. (2) Amounts include changes in assumed forfeitures, as required under GAAP.
Schedule of performance shares outstanding and accrued expense for performance shares awarded	The following table presents performance shares outstanding and accrued expense for performance shares awarded under the WTM Incentive Plan as of December 31, 2021 for each performance cycle: $ in Millions Target Performance Accrued Expense Performance cycle: 2019 – 2021 14,625 $ 25.3 2020 – 2022 13,350 15.4 2021 – 2023 13,475 2.1 Sub-total 41,450 42.8 Assumed forfeitures (622) (.6) Total 40,828 $ 42.2
Schedule of unrecognized compensation costs associated with outstanding restricted share awards	The following table presents the unrecognized compensation cost associated with the outstanding restricted share awards under the WTM Incentive Plan for the years ended December 31, 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 $ in Millions Restricted Unamortized Restricted Unamortized Restricted Unamortized Non-vested, Beginning of period 43,105 $ 15.2 43,395 $ 16.7 41,510 $ 12.5 Issued 13,475 16.1 14,055 15.1 15,600 14.5 Vested (17,936) — (14,345) — (13,715) — Forfeited (794) (.8) — — — — Expense recognized — (14.6) — (16.6) — (10.3) End of period 37,850 $ 15.9 43,105 $ 15.2 43,395 $ 16.7

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2021
Leases [Abstract]
Schedule of net lease expense	The following table summarizes net lease expense recognized in White Mountains’s consolidated statement of operations for the years ended December 31, 2021 and 2020: Millions Lease Cost December 31, 2021 December 31, 2020 Lease cost $ 9.9 $ 7.7 Less: sublease income .4 .4 Net lease cost $ 9.5 $ 7.3
Schedule of contractual maturities of lease liabilities	The following table presents the contractual maturities of the lease liabilities associated with White Mountains’s operating lease agreements as of December 31, 2021: Millions December 31, 2021 2022 $ 10.9 2023 9.9 2024 8.5 2025 6.8 2026 4.3 Thereafter 11.9 Total undiscounted lease payments 52.3 Less: present value adjustment (7.1) Operating lease liability $ 45.2
Schedule of lease related assets and liabilities	The following table presents lease related assets and liabilities by reportable segment as of December 31, 2021 and 2020: As of December 31, 2021 $ in Millions HG/BAM Ark NSM Kudu Other Operations Total Weighted Average Incremental Borrowing Rate (1) ROU lease asset $ 7.6 $ 7.0 $ 14.0 $ 6.5 $ 7.1 $ 42.2 5% Lease liability $ 8.1 $ 7.0 $ 15.2 $ 7.1 $ 7.8 $ 45.2 (1) The present value of the remaining lease payments was determined by discounting the lease payments using the incremental borrowing rate. December 31, 2020 $ in Millions HG/BAM NSM Kudu Other Operations Total Weighted Average Incremental Borrowing Rate (1) ROU lease asset $ 10.1 $ 17.1 $ 2.0 $ 8.4 $ 37.6 4.6% Lease liability $ 10.1 $ 17.1 $ 2.0 $ 9.1 $ 38.3 (1) The present value of the remaining lease payments was determined by discounting the lease payments using the incremental borrowing rate.

Common Shareholders_ Equity a_2

Common Shareholders’ Equity and Non-controlling Interests (Tables)	12 Months Ended
	Dec. 31, 2021
Stockholders' Equity Note [Abstract]
Schedule of noncontrolling interest	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 December 31, 2021 and 2020: December 31, 2021 December 31, 2020 $ in Millions Non-controlling Percentage Non-controlling Equity Non-controlling Percentage Non-controlling Equity Non-controlling interests, excluding BAM HG Global 3.1 % $ 8.9 3.1 % $ 13.5 Ark 28.0 % 230.7 — % — NSM 3.5 % 16.7 3.4 % 17.0 Kudu 2.5 % 12.4 .7 % 2.3 Other various 11.9 various 2.4 Total, excluding BAM 280.6 35.2 BAM 100.0 % (124.0) 100.0 % (123.3) Total non-controlling interests $ 156.6 $ (88.1)

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2021
Segment Reporting [Abstract]
Schedule of financial information for segments	The following tables present the financial information for White Mountains’s segments: Millions HG Global/BAM (1) Ark NSM (3) Kudu Other Total Year Ended December 31, 2021 Earned insurance premiums (2) $ 26.9 $ 637.3 $ — $ — $ — $ 664.2 Net investment income 17.5 2.9 — 43.9 18.2 82.5 Net realized and unrealized investment gains (losses) (22.9) 16.5 — 89.9 50.7 134.2 Net realized and unrealized investment gains (losses) — — — — (380.3) (380.3) Commission revenues (4) — — 258.0 — 9.6 267.6 Other revenues 1.5 11.8 72.4 .2 90.7 176.6 Total revenues 23.0 668.5 330.4 134.0 (211.1) 944.8 Loss and loss adjustment expenses — 314.8 — — — 314.8 Insurance acquisition expenses 8.3 178.0 — — — 186.3 Cost of sales — — — — 69.3 69.3 General and administrative expenses 57.1 115.5 190.1 14.5 105.7 482.9 Broker commission expense — — 80.2 — — 80.2 Change in fair value of contingent — — 1.0 — — 1.0 Amortization of other intangible assets — — 35.2 .3 4.3 39.8 Loss on assets held for sale — — 28.7 — — 28.7 Interest expense — 7.3 23.3 11.7 1.5 43.8 Total expenses 65.4 615.6 358.5 26.5 180.8 1,246.8 Pre-tax income (loss) $ (42.4) $ 52.9 $ (28.1) $ 107.5 $ (391.9) $ (302.0) (1) BAM manages its affairs on a statutory accounting basis. BAM’s statutory surplus includes the BAM Surplus Notes and is not reduced by accruals of interest expense on the BAM Surplus Notes. BAM’s statutory surplus is reduced only after a payment of principal or interest has been approved by the NYDFS. (2) Ark’s earned insurance premiums based on the location of Ark’s underwriting offices in the United Kingdom and Bermuda are $459.3 and $178.0. (3) Includes the results of J.C. Taylor from August 6, 2021, the date of the J.C. Taylor transaction. (4) Approximately 25% of NSM’s commission revenue was associated with one single carrier. Millions HG Global/BAM (1) NSM Kudu Other Total Year Ended December 31, 2020 Earned insurance premiums $ 22.8 $ — $ — $ — $ 22.8 Net investment income 19.5 — 29.5 82.0 131.0 Net realized and unrealized investment gains (losses) 23.7 — 15.9 (8.8) 30.8 Net realized and unrealized investment gains (losses) — — — 686.0 686.0 Commission revenues (2) — 232.5 — 8.3 240.8 Other revenues 2.5 52.6 .3 13.9 69.3 Total revenues 68.5 285.1 45.7 781.4 1,180.7 Insurance acquisition expenses 7.0 — — — 7.0 Cost of sales — — — 11.3 11.3 General and administrative expenses 56.8 176.9 11.8 141.9 387.4 Broker commission expense — 75.3 — — 75.3 Change in fair value of contingent — (3.3) — — (3.3) Amortization of other intangible assets — 26.7 .3 1.3 28.3 Interest expense — 22.1 6.0 1.4 29.5 Total expenses 63.8 297.7 18.1 155.9 535.5 Pre-tax income (loss) $ 4.7 $ (12.6) $ 27.6 $ 625.5 $ 645.2 (1) BAM manages its affairs on a statutory accounting basis. BAM’s statutory surplus includes the BAM Surplus Notes and is not reduced by accruals of interest expense on the BAM Surplus Notes. BAM’s statutory surplus is reduced only after a payment of principal or interest has been approved by the NYDFS. (2) Approximately 19% of NSM’s commission revenue was associated with one single carrier. Millions HG Global/BAM (1) NSM Kudu (2) MediaAlpha (3) Other Total Year Ended December 31, 2019 Earned insurance premiums $ 16.3 $ — $ — $ — $ — $ 16.3 Net investment income 21.6 — 14.7 — 43.4 79.7 Net realized and unrealized 27.1 — 6.3 — 219.8 253.2 Net realized and unrealized investment — — — — 180.0 180.0 Gain from deconsolidation from — — — — 67.5 67.5 Advertising and commission revenues (4) — 193.4 — 48.8 6.9 249.1 Other revenues 1.6 39.7 .2 — 6.1 47.6 Total revenues 66.6 233.1 21.2 48.8 523.7 893.4 Insurance acquisition expenses 5.7 — — — — 5.7 Cost of sales — — — 40.6 7.5 48.1 General and administrative expenses 50.9 132.2 10.1 12.5 122.5 328.2 Broker commission expense — 64.8 — — — 64.8 Change in fair value of contingent — 2.1 — — — 2.1 Amortization of other intangible assets — 19.4 .2 1.6 .6 21.8 Interest expense — 16.7 .1 .2 .6 17.6 Total expenses 56.6 235.2 10.4 54.9 131.2 488.3 Pre-tax income (loss) $ 10.0 $ (2.1) $ 10.8 $ (6.1) $ 392.5 $ 405.1 (1) BAM manages its affairs on a statutory accounting basis. BAM’s statutory surplus includes the BAM Surplus Notes and is not reduced by accruals of interest expense on the BAM Surplus Notes. BAM’s statutory surplus is reduced only after a payment of principal or interest has been approved by the NYDFS. (2) Kudu’s results are from April 4, 2019, the date of the Kudu Transaction, to December 31, 2019. (3) MediaAlpha’s results are from January 1, 2019 to February 26, 2019, the date of the 2019 MediaAlpha Transaction. (4) Approximately 17% of NSM’s commission revenue was associated with one single carrier.
Schedule of selected balance sheet data by segment	Millions HG Global/BAM Ark NSM Kudu Other Held for Sale Total December 31, 2021: Total investments $ 966.5 $ 1,562.1 $ — $ 669.5 $ 1,067.2 $ — $ 4,265.3 Total assets $ 1,044.8 (1) $ 3,027.0 $ 977.3 $ 727.1 $ 1,208.4 (2) $ 16.1 $ 7,000.7 Total liabilities $ 321.9 (2) $ 2,122.4 $ 495.3 $ 261.0 $ 95.4 $ — $ 3,296.0 Total White Mountains’s $ 838.0 (2) $ 673.9 $ 465.3 $ 453.7 $ 1,101.1 (2) $ 16.1 $ 3,548.1 Non-controlling interest $ (115.1) $ 230.7 $ 16.7 $ 12.4 $ 11.9 $ — $ 156.6 December 31, 2020: Total investments $ 919.9 $ — $ — $ 400.6 $ 1,618.5 $ — $ 2,939.0 Total assets $ 1,017.8 (1) $ — $ 999.6 $ 430.2 $ 2,381.5 (2) $ 2.3 $ 4,831.4 Total liabilities $ 291.5 (2) $ — $ 491.8 $ 96.3 $ 133.9 $ — $ 1,013.5 Total White Mountains’s $ 836.1 (2) $ — $ 490.7 $ 331.6 $ 2,245.3 (2) $ 2.3 $ 3,906.0 Non-controlling interest $ (109.8) $ — $ 17.1 $ 2.3 $ 2.3 $ — $ (88.1) (1) As of December 2021 and 2020, total assets in the HG Global/BAM segment reflected the elimination of $364.6 and $388.2 of BAM Surplus Notes issued to HG Global and its subsidiaries, and $157.6 and $155.7 in accrued interest related to the BAM Surplus Notes.
Schedule of revenue by revenue source	In compliance with ASC 606, Revenues from Contracts with Customers, the following tables present White Mountains’s total revenues by revenue source: Millions HG Global/BAM Ark NSM Kudu Other Total Year Ended December 31, 2021 Commission and other revenue Specialty Transportation (1) $ — $ — $ 97.2 $ — $ — $ 97.2 Pet — — 76.3 — — 76.3 United Kingdom — — 53.1 — — 53.1 Real Estate — — 34.4 — — 34.4 Social Services — — 33.9 — — 33.9 Other — — 35.5 — 9.6 45.1 Total commission and other revenue — — 330.4 — 9.6 340.0 Products and service revenues — — — — 87.5 87.5 Revenues from contracts with customers — — 330.4 — 97.1 427.5 Other (2) 23.0 668.5 — 134.0 (308.2) 517.3 Total revenues $ 23.0 $ 668.5 $ 330.4 $ 134.0 $ (211.1) $ 944.8 (1) Includes the results of J.C. Taylor from August 6, 2021, the date of the J.C. Taylor transaction. (2) 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 Total Year Ended December 31, 2020 Commission and other revenue Specialty Transportation $ — $ 85.5 $ — $ — $ 85.5 Pet — 55.0 — — 55.0 United Kingdom — 49.4 — — 49.4 Real Estate — 44.9 — — 44.9 Social Services — 28.9 — — 28.9 Other — 21.4 — 8.3 29.7 Total commission and other revenue — 285.1 — 8.3 293.4 Products and service revenues — — — 14.5 14.5 Revenues from contracts with customers — 285.1 — 22.8 307.9 Other (1) 68.5 — 45.7 758.6 872.8 Total revenues $ 68.5 $ 285.1 $ 45.7 $ 781.4 $ 1,180.7 (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 (2) MediaAlpha (3) Other Total Year Ended December 31, 2019 Commission and other revenue Specialty Transportation $ — $ 77.6 $ — $ — $ — $ 77.6 United Kingdom — 45.9 — — — 45.9 Pet — 30.0 — — — 30.0 Real Estate — 34.7 — — — 34.7 Social Services — 25.9 — — — 25.9 Other — 19.0 — — 6.9 25.9 Total commission and other revenue — 233.1 — — 6.9 240.0 Advertising revenues — — — 48.8 — 48.8 Product and service revenues — — — 5.5 5.5 Revenues from contracts with customers — 233.1 — 48.8 12.4 294.3 Other (1) 66.6 — 21.2 — 511.3 599.1 Total revenues $ 66.6 $ 233.1 $ 21.2 $ 48.8 $ 523.7 $ 893.4 (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) Kudu’s results are from April 4, 2019, the date of the Kudu Transaction, to December 31, 2019. (3) MediaAlpha’s results are from January 1, 2019 to February 26, 2019, the date of the 2019 MediaAlpha Transaction.

Equity Method Eligible Invest_2

Equity Method Eligible Investments (Tables)	12 Months Ended
	Dec. 31, 2021
Equity Method Investments and Joint Ventures [Abstract]
Schedule of equity method eligible investments	The following table presents the ownership interests and carrying values of White Mountains’s equity method eligible investments as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Millions Ownership Interest Carrying Value Ownership Interest Carrying Value Kudu Participation Contracts (1) 3.2 - 32.0% $ 669.5 3.2 - 35.0% $ 400.6 Investment in MediaAlpha 28.0 % 261.6 35.0 % 802.2 PassportCard/DavidShield 53.8 % 120.0 53.8 % 95.0 Elementum Holdings, L.P. 29.7 % 45.0 28.9 % 55.1 Other equity method eligible investments, at fair value Under 50.0% 109.3 Under 50.0% 132.2 Other equity method eligible investments, at fair value 50.0% and over 17.8 50.0% and over 15.2
Schedule of significant equity method eligible investments	The following tables present summarized financial information for MediaAlpha as of December 31, 2021 and 2020 for the years ended December 31, 2021, 2020, and 2019: December 31, Millions 2021 2020 Balance sheet data: Total assets $ 289.8 $ 210.3 Total liabilities $ 351.4 $ 315.5 Year Ended December 31, Millions 2021 2020 2019 (1) Income statement data: Total revenues $ 645.3 $ 584.8 $ 408.0 Total expenses $ 653.8 $ 574.2 $ 390.2 Net income (loss) $ (8.5) $ 10.6 $ 17.8 (1) For the year ended December 31, 2019, MediaAlpha recorded out of period adjustments that increased (decreased) total revenues by $0.1, total expenses by $1.2 and net income by $(1.1). The adjustments primarily related to MediaAlpha’s accounting for its equity-based compensation and amortization of other intangible assets. White Mountains has evaluated the impact of the adjustments and concluded that they are not material, individually and in the aggregate, to current or prior period financial statements. The following tables present aggregated summarized financial information for White Mountains’s investments in equity method eligible unconsolidated entities, excluding MediaAlpha: December 31, Millions 2021 2020 Balance sheet data (1) : Total assets $ 1,845.7 $ 1,328.5 Total liabilities $ 373.4 $ 228.7 (1) Financial data for White Mountains’s equity method eligible investees is generally reported on a one-quarter lag. Year Ended December 31, Millions 2021 2020 2019 Income statement data (1) : Total revenues $ 987.4 $ 526.5 $ 344.6 Total expenses $ 418.7 $ 325.9 $ 88.3 Net income (loss) $ 568.7 $ 201.7 $ 255.1 (1) Financial data for White Mountains’s equity method eligible investees is generally reported on a one-quarter lag.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Schedule of the fair value and carrying value of financial instruments	The following tables presents the fair value and carrying value of these financial instruments as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Millions Fair Value Carrying Value Fair Value Carrying Value Ark 2007 Subordinated Notes $ 27.6 $ 30.0 $ — $ — Ark 2021 Subordinated Notes $ 162.8 $ 155.9 $ — $ — NSM Bank Facility $ 275.8 $ 271.2 $ 279.3 $ 271.3 Other NSM debt $ 1.0 $ .9 $ 1.3 $ 1.3 Kudu Credit Facility $ 246.8 $ 218.2 $ — $ — Kudu Bank Facility $ — $ — $ 89.3 $ 86.3 Other Operations debt $ 17.7 $ 16.8 $ 18.8 $ 17.5

Held for Sale and Discontinue_2

Held for Sale and Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2021
Discontinued Operations and Disposal Groups [Abstract]
Schedule of earnings per share for discontinued operations	The following table presents the Company’s computation of earnings per share for discontinued operations for the years ended December 31, 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 Basic and diluted earnings per share numerators (in millions): Net income (loss) attributable to White Mountains’s common shareholders $ (275.4) $ 708.7 $ 414.5 Less: total income (loss) from continuing operations, net of tax (294.1) 711.0 413.7 Net income (loss) from discontinued operations attributable to 18.7 (2.3) .8 Allocation of (earnings) losses to participating restricted common shares (1) (.2) — — Basic and diluted (loss) earnings per share numerators $ 18.5 $ (2.3) $ .8 Basic earnings per share denominators (in thousands): Total average common shares outstanding during the period 3,079.0 3,122.2 3,181.6 Average unvested restricted common shares (3) (36.5) (40.8) (40.5) Basic earnings (loss) per share denominator 3,042.5 3,081.4 3,141.1 Diluted earnings per share denominator (in thousands): Total average common shares outstanding during the period 3,079.0 3,122.2 3,181.6 Average unvested restricted common shares (3) (36.5) (40.8) (40.5) Diluted earnings (loss) per share denominator 3,042.5 3,081.4 3,141.1 Basic (loss) earnings per share (in dollars) - discontinued operations: $ 6.07 $ (.75) $ .25 Diluted (loss) earnings per share (in dollars) - discontinued operations: $ 6.07 $ (.75) $ .25 (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 years ended December 31, 2021, 2020 and 2019. (3) Restricted common shares outstanding vest either in equal annual installments or upon a stated date. See Note 12 — “Employee Share-Based Compensation Plans” .

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Policies - Reportable Segments (Details) - USD ($) $ in Millions	Jan. 01, 2021	Dec. 31, 2021	Dec. 31, 2020	Apr. 04, 2019	Apr. 03, 2019	Feb. 05, 2018	Dec. 31, 2012
Ark
Basis of Presentation
Percent of shares outstanding	12.50%	12.50%
HG Global
Basis of Presentation
Percentage of par value of policy reinsured		15.00%
Surplus notes							$ 503
Ark | Ark
Basis of Presentation
Ownership interest (as a percent)		72.00%
Fully diluted ownership interest (as a percent)		63.00%
Preferred stocks | HG Global
Basis of Presentation
Ownership interest (as a percent)		96.90%	96.90%
Common equity securities | HG Global
Basis of Presentation
Ownership interest (as a percent)		88.40%	88.40%
NSM
Basis of Presentation
Ownership interest (as a percent)		96.50%	96.60%
Fully diluted ownership interest (as a percent)		87.30%	89.60%
Kudu
Basis of Presentation
Ownership interest (as a percent)		99.30%	99.30%	99.10%	49.50%	49.50%
Fully diluted ownership interest (as a percent)		84.70%	85.40%	85.40%	42.70%	42.70%

Basis of Presentation and Sig_4

Basis of Presentation and Significant Accounting Policies - Investment Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Percentage of investments recorded at fair value	68.00%	73.00%
Variance threshold for outliers	$ 0.5
Variance threshold for outliers (as a percent)	5.00%

Basis of Presentation and Sig_5

Basis of Presentation and Significant Accounting Policies - Property and Casualty Insurance and Reinsurance (Details)	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Ark | Amount attributable to TPC Providers
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Percent of underwriting capital provided by third parties	0.00%	42.80%	58.30%	57.60%	60.00%	59.60%	70.00%	66.20%	0.00%	0.00%

Basis of Presentation and Sig_6

Basis of Presentation and Significant Accounting Policies - Fair Value Measurements and Other Long-Term Investments (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	$ 1,377.8	$ 786.8
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	890.6
Fair Value Measured at Net Asset Value Per Share
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other long-term investments	$ 482.5

Basis of Presentation and Sig_7

Basis of Presentation and Significant Accounting Policies - Foreign Currency Exchange (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Net unrealized foreign currency translation gain (losses)	$ 5.1	$ 5.6

Basis of Presentation and Sig_8

Basis of Presentation and Significant Accounting Policies - Municipal Bond Guarantee Insurance (Details)	Dec. 31, 2021
Third Point Re | Ark
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Annual crediting rate	3.00%

Significant Transactions - Medi

Significant Transactions - MediaAlpha (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 23, 2021	Oct. 30, 2020	Feb. 26, 2019	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020
Other Significant Noncash Transactions [Line Items]
Realized gain from transaction				$ 67.5
MediaAlpha
Other Significant Noncash Transactions [Line Items]
Proceeds from dividends received		$ 55
Ownership interest (as a percent)		35.00%			28.00%
Fully diluted ownership interest (as a percent)		32.30%			25.70%
Investment owned (in shares)		20,500,000			16,900,000
Share price (in USD per share)					$ 15.44	$ 39.07
Investment owned, balance					$ 261.6	$ 802.2
MediaAlpha | IPO
Other Significant Noncash Transactions [Line Items]
Sale of stock, number of shares issued in transaction (in shares)		3,600,000
Sale of stock, consideration received in transaction		$ 63.8
MediaAlpha | Secondary Offering
Other Significant Noncash Transactions [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	3,600,000
Sale of stock, consideration received in transaction	$ 160.3
MediaAlpha
Other Significant Noncash Transactions [Line Items]
Proceeds from dividends received			$ 89.3
Realized gain from transaction			$ 67.5
Ownership interest (as a percent)			48.30%
Fully diluted ownership interest (as a percent)			42.00%
Assets, fair value			$ 114.7
Unrealized investment gain			114.7
Total realized and unrealized gain on sale of minority stake			$ 182.2
MediaAlpha | Secondary Offering
Other Significant Noncash Transactions [Line Items]
Sale of stock, number of shares issued in transaction (in shares)	8,050,000
Sale of stock, price per share (in USD per share)	$ 46
Sale of stock, price per share net of underwriting fees (in dollars per share)	$ 44.62

Significant Transactions - Ark

Significant Transactions - Ark (Details) - USD ($) $ in Millions	Jan. 01, 2021	Oct. 01, 2020	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2021
Other Significant Noncash Transactions [Line Items]
Change in fair value of contingent consideration				$ 1	$ (3.3)	$ 2.1
Other Operations
Other Significant Noncash Transactions [Line Items]
Cash pre-funded/placed in escrow for Ark Transaction				0	646.3
Goodwill and other intangible assets				39.1	36.4
Ark
Other Significant Noncash Transactions [Line Items]
Cash pre-funded/placed in escrow for Ark Transaction					366.3
Goodwill and other intangible assets				292.5	0
Contingent consideration				28	0
Change in fair value of contingent consideration				5.5
Ark | In-force Business Acquired
Other Significant Noncash Transactions [Line Items]
Amortization				$ 64.2
Ark | Lloyd
Other Significant Noncash Transactions [Line Items]
Cash pre-funded/placed in escrow for Ark Transaction					$ 280
Ark
Other Significant Noncash Transactions [Line Items]
Merger agreement, equity capital contributed	$ 605.4	$ 605.4
Equity capital, pre money valuation amount		300
Additional equity purchase from shareholders		40.9
Investment, potential additional contribution of equity capital	$ 200	$ 200
Ownership interest after all transactions (as a percent)	72.00%
Ownership interest on fully-diluted basis (as a percent)	63.00%
Percent of shares outstanding	12.50%			12.50%
Assets acquired	$ 2,500
Goodwill and other intangible assets	292.5
Liabilities acquired	1,700
Contingent consideration	22.5
Noncontrolling interest acquired	$ 220.2
Transaction costs			$ 25.3
Ark | Group Ark Insurance Limited | Unsecured Subordinated Debt
Other Significant Noncash Transactions [Line Items]
Notes issued							$ 163.3

Significant Transactions - Sche

Significant Transactions - Schedule of Assets Acquired and Liabilities Assumed, Ark (Details) - USD ($) $ in Millions	Jan. 01, 2021	Oct. 01, 2020	Dec. 31, 2021	Dec. 31, 2020
Other Significant Transactions [Line Items]
Goodwill			$ 645.5	$ 525.5
Ark
Other Significant Transactions [Line Items]
Investments	$ 594.3
Cash	52
Reinsurance recoverables	433.4
Insurance premiums receivable	236.7
Ceded unearned premiums	170.2
Value of in-force business acquired	71.7
Other assets	88.9
Loss and loss adjustment expense reserves	(696)
Unearned insurance premiums	(326.1)
Debt	(46.4)
Ceded reinsurance payable	(528.3)
Other liabilities	(25.9)
Net tangible assets acquired	24.5
Goodwill	116.8
Other intangible assets - syndicate underwriting capacity	175.7
Deferred tax liability on other intangible assets	(33.4)
Net assets acquired	283.6
Merger agreement, equity capital contributed	$ 605.4	$ 605.4

Significant Transactions - NSM

Significant Transactions - NSM (Details) £ in Millions, $ in Millions	Aug. 06, 2021USD ($)	Apr. 12, 2021USD ($)	Apr. 12, 2021GBP (£)	Apr. 07, 2020USD ($)	Apr. 07, 2020GBP (£)	Jun. 28, 2019USD ($)	Apr. 01, 2019USD ($)	Dec. 03, 2018USD ($)	May 18, 2018USD ($)earnout_period	Mar. 31, 2021USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Apr. 07, 2020GBP (£)
Other Significant Noncash Transactions [Line Items]
Purchases of consolidated subsidiaries, net of cash acquired												$ 39.1	$ 127.3	$ 258
Goodwill and intangible assets acquired								$ 59.4
Goodwill												645.5	525.5
Change in fair value of contingent consideration												1	(3.3)	2.1
Contingent consideration payments related to acquisitions of subsidiaries												0	7	7.6
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Fresh Insurance Services Group Limited
Other Significant Noncash Transactions [Line Items]
Proceeds from sale of business		$ 1.5	£ 1.1
Disposal Group, Held-for-sale, Not Discontinued Operations | Fresh Insurance Services Group Limited
Other Significant Noncash Transactions [Line Items]
Loss on sale										$ (28.7)		28.7
Fresh Insurance Services Group Limited
Other Significant Noncash Transactions [Line Items]
Ownership interest (as a percent)									100.00%
Proceeds from borrowings									$ 51
Purchase price adjustment											$ 0.7
Number of earnout periods | earnout_period									2
KBK Insurance Group, Inc. & KBK Premium Services, Inc.
Other Significant Noncash Transactions [Line Items]
Proceeds from borrowings								30.1
Purchases of consolidated subsidiaries, net of cash acquired								60
Goodwill														32.6
Intangible assets acquired														32.7
NSM
Other Significant Noncash Transactions [Line Items]
Purchases of consolidated subsidiaries, net of cash acquired								$ 29
Embrace Pet Insurance
Other Significant Noncash Transactions [Line Items]
Goodwill							$ 52.2
Intangible assets acquired							15.4
J.C. Taylor Insurance
Other Significant Noncash Transactions [Line Items]
Proceeds from borrowings	$ 35
Purchases of consolidated subsidiaries, net of cash acquired	49.6
Goodwill	28.5
Intangible assets acquired	27.2
Assets acquired	60.3
Goodwill and other intangible assets	55.7
Liabilities acquired	$ 10.7
NSM
Other Significant Noncash Transactions [Line Items]
Change in fair value of contingent consideration												1	(3.3)
Contingent consideration												6.8	14.6
Goodwill and other intangible assets												725.4	736.8
NSM | KBK Insurance Group, Inc. & KBK Premium Services, Inc.
Other Significant Noncash Transactions [Line Items]
Contingent consideration payments related to acquisitions of subsidiaries												8.8	7
NSM | Fresh Insurance Services Group Limited
Other Significant Noncash Transactions [Line Items]
Equity method investment, aggregate cost									$ 49.6
NSM | Embrace Pet Insurance
Other Significant Noncash Transactions [Line Items]
Proceeds from borrowings							$ 20.4
Percentage of voting interests acquired							100.00%
Payments to acquire businesses, gross							$ 71.5
Additional investment in acquisition							$ 58.2
NSM | Kingsbridge Group Limited
Other Significant Noncash Transactions [Line Items]
Equity method investment, aggregate cost				$ 132.2											£ 107.2
Proceeds from borrowings				$ 52.4	£ 42.5
Percentage of voting interests acquired				100.00%											100.00%
Additional investment in acquisition				$ 80.3
Acquisitions of businesses													111.5
Finite-lived Intangible Assets Acquired													20.2
Pretax income												(0.3)	4.1
Contingent consideration				$ 4.1									0.3
NSM | J.C. Taylor Insurance
Other Significant Noncash Transactions [Line Items]
Percentage of voting interests acquired	100.00%
KBK Insurance Group, Inc. & KBK Premium Services, Inc.
Other Significant Noncash Transactions [Line Items]
Change in fair value of contingent consideration														$ 5.9
Contingent consideration payments related to acquisitions of subsidiaries												$ 6.7	$ 6.4
AIG Collector Car Business
Other Significant Noncash Transactions [Line Items]
Purchases of consolidated subsidiaries, net of cash acquired						$ 82.5
Intangible assets acquired						82.5
Additional investment in acquisition						59.1
AIG Collector Car Business | NSM
Other Significant Noncash Transactions [Line Items]
Proceeds from borrowings						$ 22.5

Significant Transactions - Kudu

Significant Transactions - Kudu (Details) - USD ($) $ in Millions	Apr. 04, 2019	Dec. 31, 2021	Dec. 31, 2019	Dec. 31, 2020	Apr. 03, 2019	Feb. 05, 2018
Other Significant Noncash Transactions [Line Items]
Goodwill		$ 645.5		$ 525.5
Kudu
Other Significant Noncash Transactions [Line Items]
Equity method investment, aggregate cost						$ 125
Ownership interest (as a percent)	99.10%	99.30%		99.30%	49.50%	49.50%
Fully diluted ownership interest (as a percent)	85.40%	84.70%		85.40%	42.70%	42.70%
Payments to acquire business, net	$ 81.4
Funded capital commitment	250	$ 369	$ 350
Assets acquired	155.5
Goodwill	7.6
Intangible assets acquired	2.2
Liabilities acquired	0.8
Noncontrolling interest acquired	$ 1.5
Increase in capital commitment		$ 19	$ 100

Significant Transactions - Pass

Significant Transactions - PassportCard/DavidShield (Details) - USD ($) $ in Millions	May 07, 2020	Jan. 24, 2018	Dec. 31, 2021	Dec. 31, 2020	May 06, 2020
DavidShield
Other Significant Noncash Transactions [Line Items]
Ownership interest (as a percent)		50.00%
PassportCard
Other Significant Noncash Transactions [Line Items]
Ownership interest (as a percent)		50.00%
PassportCard/DavidShield
Other Significant Noncash Transactions [Line Items]
Ownership interest (as a percent)	53.80%		53.80%	53.80%	50.00%
Payments to acquire businesses, gross		$ 41.8
Payments to acquire business, net		$ 28.3
Additional investment in acquisition	$ 15

Investment Securities - Net Inv

Investment Securities - Net Investment Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Investment income:
Total investment income	$ 84.8	$ 132.2	$ 81
Third-party investment expenses	(2.3)	(1.2)	(1.3)
Net investment income, pre-tax	82.5	131	79.7
Fixed maturity investments
Investment income:
Total investment income	28.8	29	32.4
Short-term investments
Investment income:
Total investment income	0.6	1.1	5
Common equity securities
Investment income:
Total investment income	0.1	6.6	13.5
MediaAlpha
Investment income:
Total investment income	0	59.9	8
Other long-term investments
Investment income:
Total investment income	56.3	35.6	22.1
Amount attributable to TPC Providers
Investment income:
Total investment income	$ (1)	$ 0	$ 0

Investment Securities - Net Rea

Investment Securities - Net Realized and Unrealized Investment Gains and Losses - (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Realized investment gains (losses)	$ 156.8	$ 187.1	$ 96.6
Unrealized investment gains (losses)	(395.2)	529.7	336.6
Gain (loss) on investments related to foreign currency exchange	(7.7)	4	(0.3)
Gross realized investment gains	212.3	214.4	104
Gross realized investment losses	55.5	27.3	7.4
Investments Held
Debt Securities, Available-for-sale [Line Items]
Net realized and unrealized investment gains (losses)	(246.1)	716.8	433.2
Fixed maturity investments
Debt Securities, Available-for-sale [Line Items]
Realized investment gains (losses)	3.9	10.9	4.9
Unrealized investment gains (losses)	(42.2)	27.5	38.6
Short-term investments
Debt Securities, Available-for-sale [Line Items]
Realized investment gains (losses)	(0.1)	0.4	0.2
Common equity securities
Debt Securities, Available-for-sale [Line Items]
Realized investment gains (losses)	0.4	137.2	85.9
Unrealized investment gains (losses)	14.9	(130.6)	109.8
Net realized and unrealized investment gains (losses)	15.3	6.6	195.7
MediaAlpha
Debt Securities, Available-for-sale [Line Items]
Realized investment gains (losses)	160.3	63.8	0
Unrealized investment gains (losses)	(540.6)	622.2	180
Net realized and unrealized investment gains (losses)	(380.3)	686	180
Other long-term investments
Debt Securities, Available-for-sale [Line Items]
Realized investment gains (losses)	(7.7)	(25.2)	5.6
Unrealized investment gains (losses)	172.7	10.6	8.2
Total Investments
Debt Securities, Available-for-sale [Line Items]
Net realized and unrealized investment gains (losses)	(238.4)	716.8	433.2
Amount attributable to TPC Providers
Debt Securities, Available-for-sale [Line Items]
Net realized and unrealized investment gains (losses)	(7.7)	0	0
Fixed maturity and short-term investments
Debt Securities, Available-for-sale [Line Items]
Net realized and unrealized investment gains (losses)	(38.4)	38.8	43.7
Less: net realized and unrealized gains (losses) on investment securities sold during the period	(8.4)	(8.7)	1
Fixed maturity and short-term investments | Investments Held
Debt Securities, Available-for-sale [Line Items]
Net realized and unrealized investment gains (losses)	(30)	47.5	42.7
Common equity securities and investment in MediaAlpha
Debt Securities, Available-for-sale [Line Items]
Net realized and unrealized investment gains (losses)	(365)	692.6	375.7
Less: net realized and unrealized gains (losses) on investment securities sold during the period	20.3	38.3	24
Common equity securities and investment in MediaAlpha | Investments Held
Debt Securities, Available-for-sale [Line Items]
Net realized and unrealized investment gains (losses)	$ (385.3)	$ 654.3	$ 351.7

Investment Securities - Investm

Investment Securities - Investment Gains and Losses For Level 3 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Investment securities
Unrealized investment gains (losses)	$ (395.2)	$ 529.7	$ 336.6
Proceeds from sale and maturity of investments	800	1,400	1,000
Level 3
Investment securities
Unrealized investment gains	98.9	276	181.9
Other long-term investments
Investment securities
Unrealized investment gains (losses)	172.7	10.6	8.2
Other long-term investments | Level 3
Investment securities
Unrealized investment gains	$ 98.9	276	181.9
MediaAlpha
Investment securities
Unrealized investment gains (losses)		$ 278.7	$ 180

Investment Securities - Inves_2

Investment Securities - Investment Holdings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
U.S. Government and agency obligations
Investment securities
Cost or Amortized Cost	$ 212.1	$ 173.2
Gross Unrealized Gains	0.5	3.1
Gross Unrealized Losses	(1.1)	0
Net Foreign Currency Gains (Losses)	0
Carrying Value	211.5	176.3
Debt securities issued by corporations
Investment securities
Cost or Amortized Cost	993.3	522.8
Gross Unrealized Gains	8.7	24.7
Gross Unrealized Losses	(8.7)	(0.1)
Net Foreign Currency Gains (Losses)	(0.4)
Carrying Value	992.9	547.4
Municipal obligations
Investment securities
Cost or Amortized Cost	276.4	244
Gross Unrealized Gains	16.8	21
Gross Unrealized Losses	(1.3)	0
Net Foreign Currency Gains (Losses)	0
Carrying Value	291.9	265
Mortgage and asset-backed securities
Investment securities
Cost or Amortized Cost	277.2	211.7
Gross Unrealized Gains	2.9	6.8
Gross Unrealized Losses	(2.5)	0
Net Foreign Currency Gains (Losses)	0
Carrying Value	277.6	218.5
Collateralized loan obligations
Investment securities
Cost or Amortized Cost	136.5
Gross Unrealized Gains	0
Gross Unrealized Losses	(0.4)
Net Foreign Currency Gains (Losses)	(1.1)
Carrying Value	135
Total fixed maturity investments
Investment securities
Cost or Amortized Cost	1,895.5	1,151.7
Gross Unrealized Gains	28.9	55.6
Gross Unrealized Losses	(14)	(0.1)
Net Foreign Currency Gains (Losses)	(1.5)
Carrying Value	$ 1,908.9	$ 1,207.2
Including short term fixed
Investment securities
Duration of fixed maturities (years)	2 years 7 months 6 days
Excluding short term investments
Investment securities
Duration of fixed maturities (years)	3 years 2 months 12 days

Investment Securities - Cost an

Investment Securities - Cost and Amortized Cost Maturity Schedule (Details) $ in Millions	Dec. 31, 2021USD ($)
Cost or Amortized Cost
Total fixed maturity investments	$ 1,895.5
Carrying Value
Total fixed maturity investments	1,908.9
Fixed Maturities and Convertible Fixed Maturities Excluding Mortgage Backed Securities
Cost or Amortized Cost
Due in one year or less	136.7
Due after one year through five years	866.2
Due after five years through ten years	365.7
Due after ten years	113.2
Carrying Value
Due in one year or less	137.3
Due after one year through five years	865
Due after five years through ten years	371.5
Due after ten years	122.5
Mortgage and asset-backed securities
Cost or Amortized Cost
Mortgage and asset-backed securities and collateralized loan obligations	413.7
Carrying Value
Mortgage and asset-backed securities and collateralized loan obligations	$ 412.6

Investment Securities - Cost or

Investment Securities - Cost or Amortized Cost, Gross Unrealized Investment Gains and Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Common equity securities
Investment securities
Cost or Amortized Cost	$ 236.3
Gross Unrealized Gains	16.1
Gross Unrealized Losses	0
Net Foreign Currency Gains (Losses)	(1.3)
Common equity securities, at fair value	251.1
MediaAlpha
Investment securities
Cost or Amortized Cost	0	$ 0
Gross Unrealized Gains	261.6	802.2
Gross Unrealized Losses	0	0
Net Foreign Currency Gains (Losses)	0	0
Common equity securities, at fair value	261.6	802.2
Other long-term investments
Investment securities
Cost or Amortized Cost	1,186.7	767.4
Gross Unrealized Gains	239	95.8
Gross Unrealized Losses	(44.1)	(78.1)
Net Foreign Currency Gains (Losses)	(3.8)	1.7
Common equity securities, at fair value	$ 1,377.8	$ 786.8

Investment Securities - Inves_3

Investment Securities - Investments Held on Deposit or as Collateral (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Investment securities
Investments held in trusts	$ 479.5	$ 432.4
Assets held by insurance regulators	$ 4.8	$ 11.9
Percentage of investments recorded at fair value	68.00%	73.00%
Lloyds Bank
Investment securities
Investments held in trusts	$ 113.8
Fair value investments	342.8
Short-term investments
Investment securities
Investments pledged as collateral	$ 50

Investment Securities - Fair Va

Investment Securities - Fair Value Measurement by Level (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Investment securities
Other long-term investments	$ 1,377.8	$ 786.8
Debt securities issued by corporations
Investment securities
Fair value investments	992.9	547.4
Mortgage and asset-backed securities
Investment securities
Fair value investments	277.6	218.5
Collateralized loan obligations
Investment securities
Fair value investments	135	0
Level 2 | Mortgage and asset-backed securities
Investment securities
Fair value investments	277.6	218.5
Level 2 | Collateralized loan obligations
Investment securities
Fair value investments	135	0
Level 3
Investment securities
Other long-term investments	890.6
Level 3 | Mortgage and asset-backed securities
Investment securities
Fair value investments	0	0
Level 3 | Collateralized loan obligations
Investment securities
Fair value investments	0	0
Level 3 | Common equity securities
Investment securities
Fair value investments		0	$ 0.1
Level 3 | Other long-term investments
Investment securities
Fair value investments	890.6	614.2	$ 654
Fair value measured on a recurring basis
Investment securities
Fair value investments	4,265.3	2,939
Other long-term investments	1,377.8	786.8
Fair value measured on a recurring basis | MediaAlpha
Investment securities
Other long-term investments	261.6	802.2
Fair value measured on a recurring basis | U.S. Government and agency obligations
Investment securities
Fair value investments	211.5	176.3
Fair value measured on a recurring basis | Debt securities issued by corporations
Investment securities
Fair value investments	992.9	547.4
Fair value measured on a recurring basis | Municipal obligations
Investment securities
Fair value investments	291.9	265
Fair value measured on a recurring basis | Mortgage and asset-backed securities
Investment securities
Fair value investments	277.6	218.5
Fair value measured on a recurring basis | Collateralized loan obligations
Investment securities
Fair value investments	135
Fair value measured on a recurring basis | Fixed maturity investments
Investment securities
Fair value investments	1,908.9	1,207.2
Fair value measured on a recurring basis | Short-term investments
Investment securities
Short-term investments, at fair value	465.9	142.8
Fair value measured on a recurring basis | Common equity securities
Investment securities
Fair value investments	251.1
Fair value measured on a recurring basis | Other long-term investments
Investment securities
Fair value investments	895.3	614.2
Fair value measured on a recurring basis | Other long-term investments — NAV
Investment securities
Fair value investments	482.5	172.6
Fair value measured on a recurring basis | Level 1
Investment securities
Fair value investments	939	1,121.3
Other long-term investments	0	0
Fair value measured on a recurring basis | Level 1 | MediaAlpha
Investment securities
Other long-term investments	261.6	802.2
Fair value measured on a recurring basis | Level 1 | U.S. Government and agency obligations
Investment securities
Fair value investments	211.5	176.3
Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Fair value measured on a recurring basis | Level 1 | Municipal obligations
Investment securities
Fair value investments	0	0
Fair value measured on a recurring basis | Level 1 | Mortgage and asset-backed securities
Investment securities
Fair value investments	0	0
Fair value measured on a recurring basis | Level 1 | Collateralized loan obligations
Investment securities
Fair value investments	0
Fair value measured on a recurring basis | Level 1 | Fixed maturity investments
Investment securities
Fair value investments	211.5	176.3
Fair value measured on a recurring basis | Level 1 | Short-term investments
Investment securities
Short-term investments, at fair value	465.9	142.8
Fair value measured on a recurring basis | Level 1 | Common equity securities
Investment securities
Fair value investments	0
Fair value measured on a recurring basis | Level 1 | Other long-term investments
Investment securities
Fair value investments	0	0
Fair value measured on a recurring basis | Level 1 | Other long-term investments — NAV
Investment securities
Fair value investments	0	0
Fair value measured on a recurring basis | Level 2
Investment securities
Fair value investments	1,953.2	1,030.9
Other long-term investments	4.7	0
Fair value measured on a recurring basis | Level 2 | MediaAlpha
Investment securities
Other long-term investments	0	0
Fair value measured on a recurring basis | Level 2 | U.S. Government and agency obligations
Investment securities
Fair value investments	0	0
Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations
Investment securities
Fair value investments	992.9	547.4
Fair value measured on a recurring basis | Level 2 | Municipal obligations
Investment securities
Fair value investments	291.9	265
Fair value measured on a recurring basis | Level 2 | Mortgage and asset-backed securities
Investment securities
Fair value investments	277.6	218.5
Fair value measured on a recurring basis | Level 2 | Collateralized loan obligations
Investment securities
Fair value investments	135
Fair value measured on a recurring basis | Level 2 | Fixed maturity investments
Investment securities
Fair value investments	1,697.4	1,030.9
Fair value measured on a recurring basis | Level 2 | Short-term investments
Investment securities
Short-term investments, at fair value	0	0
Fair value measured on a recurring basis | Level 2 | Common equity securities
Investment securities
Fair value investments	251.1
Fair value measured on a recurring basis | Level 2 | Other long-term investments
Investment securities
Fair value investments	4.7	0
Fair value measured on a recurring basis | Level 2 | Other long-term investments — NAV
Investment securities
Fair value investments	0	0
Fair value measured on a recurring basis | Level 3
Investment securities
Fair value investments	890.6	614.2
Other long-term investments	890.6	614.2
Fair value measured on a recurring basis | Level 3 | MediaAlpha
Investment securities
Other long-term investments	0	0
Fair value measured on a recurring basis | Level 3 | U.S. Government and agency obligations
Investment securities
Fair value investments	0	0
Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Fair value measured on a recurring basis | Level 3 | Municipal obligations
Investment securities
Fair value investments	0	0
Fair value measured on a recurring basis | Level 3 | Mortgage and asset-backed securities
Investment securities
Fair value investments	0	0
Fair value measured on a recurring basis | Level 3 | Collateralized loan obligations
Investment securities
Fair value investments	0
Fair value measured on a recurring basis | Level 3 | Fixed maturity investments
Investment securities
Fair value investments	0	0
Fair value measured on a recurring basis | Level 3 | Short-term investments
Investment securities
Short-term investments, at fair value	0	0
Fair value measured on a recurring basis | Level 3 | Common equity securities
Investment securities
Fair value investments	0
Fair value measured on a recurring basis | Level 3 | Other long-term investments
Investment securities
Fair value investments	890.6	614.2
Fair value measured on a recurring basis | Level 3 | Other long-term investments — NAV
Investment securities
Fair value investments	0	0
Financials | Fair value measured on a recurring basis | Debt securities issued by corporations
Investment securities
Fair value investments	264.2	133.9
Financials | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Financials | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations
Investment securities
Fair value investments	264.2	133.9
Financials | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Consumer | Fair value measured on a recurring basis | Debt securities issued by corporations
Investment securities
Fair value investments	178.1	81.9
Consumer | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Consumer | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations
Investment securities
Fair value investments	178.1	81.9
Consumer | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Technology | Fair value measured on a recurring basis | Debt securities issued by corporations
Investment securities
Fair value investments	117.9	66.7
Technology | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Technology | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations
Investment securities
Fair value investments	117.9	66.7
Technology | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Industrial | Fair value measured on a recurring basis | Debt securities issued by corporations
Investment securities
Fair value investments	112.9	66.9
Industrial | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Industrial | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations
Investment securities
Fair value investments	112.9	66.9
Industrial | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Healthcare | Fair value measured on a recurring basis | Debt securities issued by corporations
Investment securities
Fair value investments	112.8	51.5
Healthcare | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Healthcare | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations
Investment securities
Fair value investments	112.8	51.5
Healthcare | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Utilities | Fair value measured on a recurring basis | Debt securities issued by corporations
Investment securities
Fair value investments	70.9	32.3
Utilities | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Utilities | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations
Investment securities
Fair value investments	70.9	32.3
Utilities | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Communications | Fair value measured on a recurring basis | Debt securities issued by corporations
Investment securities
Fair value investments	56	44.5
Communications | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Communications | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations
Investment securities
Fair value investments	56	44.5
Communications | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Energy | Fair value measured on a recurring basis | Debt securities issued by corporations
Investment securities
Fair value investments	48	35.8
Energy | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Energy | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations
Investment securities
Fair value investments	48	35.8
Energy | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Materials | Fair value measured on a recurring basis | Debt securities issued by corporations
Investment securities
Fair value investments	32.1	33.9
Materials | Fair value measured on a recurring basis | Level 1 | Debt securities issued by corporations
Investment securities
Fair value investments	0	0
Materials | Fair value measured on a recurring basis | Level 2 | Debt securities issued by corporations
Investment securities
Fair value investments	32.1	33.9
Materials | Fair value measured on a recurring basis | Level 3 | Debt securities issued by corporations
Investment securities
Fair value investments	$ 0	$ 0

Investment Securities - Debt Se

Investment Securities - Debt Securities Issued By Corporation (Details) - Debt securities issued by corporations - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Investment securities
Fair value investments	$ 992.9	$ 547.4
AAA
Investment securities
Fair value investments	12	10.6
AA
Investment securities
Fair value investments	85	57.9
A
Investment securities
Fair value investments	490.4	318.3
BBB
Investment securities
Fair value investments	396.8	159.6
BB
Investment securities
Fair value investments	0	1
Other
Investment securities
Fair value investments	$ 8.7	$ 0

Investment Securities - Mortgag

Investment Securities - Mortgage-backed Asset Securities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Total mortgage-backed securities
Investment securities
Fair value investments	$ 256.5	$ 199.4
Total mortgage-backed securities | Level 2
Investment securities
Fair value investments	256.5	199.4
Total mortgage-backed securities | Level 3
Investment securities
Fair value investments	0	0
Total mortgage-backed securities | FNMA
Investment securities
Fair value investments	125.4	88.7
Total mortgage-backed securities | FNMA | Level 2
Investment securities
Fair value investments	125.4	88.7
Total mortgage-backed securities | FNMA | Level 3
Investment securities
Fair value investments	0	0
Total mortgage-backed securities | FHLMC
Investment securities
Fair value investments	90.5	70.1
Total mortgage-backed securities | FHLMC | Level 2
Investment securities
Fair value investments	90.5	70.1
Total mortgage-backed securities | FHLMC | Level 3
Investment securities
Fair value investments	0	0
Total mortgage-backed securities | GNMA
Investment securities
Fair value investments	40.1	40.6
Total mortgage-backed securities | GNMA | Level 2
Investment securities
Fair value investments	40.1	40.6
Total mortgage-backed securities | GNMA | Level 3
Investment securities
Fair value investments	0	0
Total mortgage-backed securities | Total agency
Investment securities
Fair value investments	256	199.4
Total mortgage-backed securities | Total agency | Level 2
Investment securities
Fair value investments	256	199.4
Total mortgage-backed securities | Total agency | Level 3
Investment securities
Fair value investments	0	0
Total mortgage-backed securities | Non-agency: Residential
Investment securities
Fair value investments	0.5	0
Total mortgage-backed securities | Non-agency: Residential | Level 2
Investment securities
Fair value investments	0.5	0
Total mortgage-backed securities | Non-agency: Residential | Level 3
Investment securities
Fair value investments	0	0
Total mortgage-backed securities | Total non-agency
Investment securities
Fair value investments	0.5	0
Total mortgage-backed securities | Total non-agency | Level 2
Investment securities
Fair value investments	0.5	0
Total mortgage-backed securities | Total non-agency | Level 3
Investment securities
Fair value investments	0	0
Total mortgage-backed securities | Collateralized mortgage obligations
Investment securities
Fair value investments	135
Total other asset-backed securities
Investment securities
Fair value investments	21.1	19.1
Total other asset-backed securities | Level 2
Investment securities
Fair value investments	21.1	19.1
Total other asset-backed securities | Level 3
Investment securities
Fair value investments	0	0
Total other asset-backed securities | Credit card receivables
Investment securities
Fair value investments	12.3	11.3
Total other asset-backed securities | Credit card receivables | Level 2
Investment securities
Fair value investments	12.3	11.3
Total other asset-backed securities | Credit card receivables | Level 3
Investment securities
Fair value investments	0	0
Total other asset-backed securities | Vehicle receivables
Investment securities
Fair value investments	8.8	7.8
Total other asset-backed securities | Vehicle receivables | Level 2
Investment securities
Fair value investments	8.8	7.8
Total other asset-backed securities | Vehicle receivables | Level 3
Investment securities
Fair value investments	0	0
Mortgage and asset-backed securities
Investment securities
Fair value investments	277.6	218.5
Mortgage and asset-backed securities | Level 2
Investment securities
Fair value investments	277.6	218.5
Mortgage and asset-backed securities | Level 3
Investment securities
Fair value investments	0	0
Collateralized loan obligations
Investment securities
Fair value investments	135	0
Collateralized loan obligations | Level 2
Investment securities
Fair value investments	135	0
Collateralized loan obligations | Level 3
Investment securities
Fair value investments	0	0
Total mortgage and asset-backed securities and collateralized loan obligations
Investment securities
Fair value investments	412.6	218.5
Total mortgage and asset-backed securities and collateralized loan obligations | Level 2
Investment securities
Fair value investments	412.6	218.5
Total mortgage and asset-backed securities and collateralized loan obligations | Level 3
Investment securities
Fair value investments	$ 0	$ 0

Investment Securities - Inves_4

Investment Securities - Investment in MediaAlpha (Details) - MediaAlpha - USD ($) $ / shares in Units, $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Investment securities
Share price (in USD per share)	$ 15.44	$ 39.07
Investment owned, balance	$ 261.6	$ 802.2

Investment Securities - Other L

Investment Securities - Other Long-Term Investments (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Investment securities
Other long-term investments	$ 1,377.8	$ 786.8
Kudu
Investment securities
Other long-term investments	669.5	400.6
PassportCard/DavidShield
Investment securities
Other long-term investments	120	95
Elementum Holdings L.P.
Investment securities
Other long-term investments	45	55.1
Other unconsolidated entities
Investment securities
Other long-term investments	34.4	42.4
Total unconsolidated entities
Investment securities
Other long-term investments	868.9	593.1
Bank loan fund
Investment securities
Other long-term investments	163	0
Private equity funds and hedge funds
Investment securities
Other long-term investments	153.8	121.2
Lloyd’s trust deposits
Investment securities
Other long-term investments	113.8	0
ILS funds
Investment securities
Other long-term investments	51.9	51.4
Private debt investments
Investment securities
Other long-term investments	14.1	21.1
Other
Investment securities
Other long-term investments	$ 12.3	$ 0

Investment Securities - Fair _2

Investment Securities - Fair Value of Hedge Funds Subject to Restrictions on Redemption Frequency (Details) $ in Millions	Dec. 31, 2021USD ($)fund	Dec. 31, 2020USD ($)
Total private equity funds and hedge funds included in other long-term investments
Investment securities
Other long-term investments largest single investment	$ 31.3	$ 29.1
Trading security, fair value	153.8	121.2
Fair value unfunded commitments	$ 44	45.7
Private equity funds
Investment securities
Number of investments | fund	12
Trading security, fair value	$ 141.8	121.2
Fair value unfunded commitments	44	45.7
Private equity funds | Aerospace/Defense/Government
Investment securities
Trading security, fair value	69.8	69.1
Fair value unfunded commitments	11.8	15.3
Private equity funds | Financial services
Investment securities
Trading security, fair value	67.7	23.5
Fair value unfunded commitments	29.3	30.4
Private equity funds | Real Estate
Investment securities
Trading security, fair value	4.3	0
Fair value unfunded commitments	2.9	0
Private equity funds | Manufacturing/Industrial
Investment securities
Trading security, fair value	0	28.6
Fair value unfunded commitments	$ 0	0
Hedge funds
Investment securities
Number of investments | fund	1
Trading security, fair value	$ 12	0
Fair value unfunded commitments	0	0
Hedge funds | European small/mid cap
Investment securities
Trading security, fair value	12	0
Fair value unfunded commitments	$ 0	$ 0

Investment Securities - Inves_5

Investment Securities - Investments In Private Equity Funds Subject to Lock-Up Periods (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Investment securities
Investments held in trusts	$ 479.5	$ 432.4
Lloyds Bank
Investment securities
Investments held in trusts	113.8
Fair value investments	342.8
Bank loan fund
Investment securities
Fair value investments	163
ILS funds
Investment securities
Fair value investments	51.9
Short-term investments
Investment securities
Investments pledged as collateral	50
Private equity funds
Investment securities
Trading security, fair value	141.8
1 – 3 years | Private equity funds
Investment securities
Trading security, fair value	0.1
3 – 5 years | Private equity funds
Investment securities
Trading security, fair value	13.9
5 – 10 years | Private equity funds
Investment securities
Trading security, fair value	116.3
>10 years | Private equity funds
Investment securities
Trading security, fair value	$ 11.5
Minimum
Investment securities
Redemptions and advanced redemption notice period	30 days
Maximum
Investment securities
Redemptions and advanced redemption notice period	90 days

Investment Securities - Rollfor

Investment Securities - Rollforward of Fair Value Measurements by Level (Details) - Level 3 - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Other long-term investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 614.2	$ 654
Net realized and unrealized gains	117.3	275.6
Amortization/accretion	0	0
Purchases	225.4	151.5
Sales	(75.9)	(8.2)
Transfers in	0	0
Transfers out	0	0
Ending balance	890.6	614.2
Common equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0	0.1
Net realized and unrealized gains		0
Amortization/accretion		0
Purchases		0
Sales		(0.1)
Transfers in		0
Transfers out		0
Ending balance		0
Ark | Other long-term investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Purchases	$ 9.6
MediaAlpha | Other long-term investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Effect of transfers		(458.7)
MediaAlpha | Common equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Effect of transfers		$ 0

Investment Securities - Signifi

Investment Securities - Significant Unobservable Inputs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Quantitative information for Level 3 Fair Value Measurements Assets
Investments in trading securities	$ 178.9	$ 118.3	$ 118.4
Kudu
Quantitative information for Level 3 Fair Value Measurements Assets
Investments in trading securities		118.2
PassportCard/DavidShield
Quantitative information for Level 3 Fair Value Measurements Assets
Investments in trading securities		15
Other long-term investments | Standard Poors NR Rating | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	46.7	$ 27.6
TIG Advisors LLC, TK Partners LLC, Third Eye Capital Management And Douglass Winthrop Advisors | Kudu
Quantitative information for Level 3 Fair Value Measurements Assets
Investments in trading securities	$ 223.4
Measurement Input, Discount Rate | Kudu's Participation Contracts | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, pretax discount rate	0.20	0.20
Measurement Input, Discount Rate | Kudu's Participation Contracts | Standard Poors NR Rating | Minimum
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate (as a percent)	18.00%	18.00%
Measurement Input, Discount Rate | Kudu's Participation Contracts | Standard Poors NR Rating | Maximum
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate (as a percent)	23.00%	23.00%
Measurement Input, Discount Rate | PassportCard/DavidShield | Standard Poors NR Rating | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate (as a percent)	23.00%	23.00%
Measurement Input, Discount Rate | Elementum Holdings, L.P. | Standard Poors NR Rating | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate (as a percent)	17.00%	17.00%
Measurement Input, Discount Rate | Private debt investments | Standard Poors NR Rating | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate (as a percent)	8.00%
Measurement Input, Discount Rate | Private debt investments | Standard Poors NR Rating | Minimum
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate (as a percent)		4.00%
Measurement Input, Discount Rate | Private debt investments | Standard Poors NR Rating | Maximum
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate (as a percent)		8.00%
Measurement Input, Discount Rate | Other long-term investments | Standard Poors NR Rating | Minimum
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate (as a percent)		20.00%
Measurement Input, Discount Rate | Other long-term investments | Standard Poors NR Rating | Maximum
Quantitative information for Level 3 Fair Value Measurements Assets
Fair value, discount rate (as a percent)		24.00%
Measurement Input, Long-term Revenue Growth Rate | PassportCard/DavidShield | Standard Poors NR Rating | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal revenue growth rate (as a percent)	4.00%	4.00%
Measurement Input, Long-term Revenue Growth Rate | Elementum Holdings, L.P. | Standard Poors NR Rating | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal revenue growth rate (as a percent)	4.00%	4.00%
Measurement Input, Long-term Revenue Growth Rate | Other long-term investments | Standard Poors NR Rating | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Terminal revenue growth rate (as a percent)		4.00%
Terminal Multiple | Kudu's Participation Contracts | Standard Poors NR Rating
Quantitative information for Level 3 Fair Value Measurements Assets
Cash flow exit multiple, pretax	10	10
Terminal Multiple | Kudu's Participation Contracts | Standard Poors NR Rating | Minimum
Quantitative information for Level 3 Fair Value Measurements Assets
Cash flow exit multiple	7	7
Terminal Multiple | Kudu's Participation Contracts | Standard Poors NR Rating | Maximum
Quantitative information for Level 3 Fair Value Measurements Assets
Cash flow exit multiple	13	12
Discounted Cash Flow Valuation Technique | Kudu's Participation Contracts | Standard Poors NR Rating | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 669.5	$ 400.6
Discounted Cash Flow Valuation Technique | PassportCard/DavidShield | Standard Poors NR Rating | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	120	95
Discounted Cash Flow Valuation Technique | Elementum Holdings, L.P. | Standard Poors NR Rating | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	45	55.1
Discounted Cash Flow Valuation Technique | Private debt investments | Standard Poors NR Rating | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	9.4	17.1
Discounted Cash Flow Valuation Technique | Other long-term investments | Standard Poors NR Rating | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value		$ 18.8
Probability Weighted Expected Return Method | Kudu's Participation Contracts | Standard Poors NR Rating | Level 3
Quantitative information for Level 3 Fair Value Measurements Assets
Assets, fair value	$ 78.8

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Summary of Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Line Items]
Goodwill, fair value	$ 675.7	$ 525.5
Goodwill, impairment loss	30.2	0
Goodwill	645.5	525.5
Other intangible assets, fair value	1,196.1	843.3
Other intangible assets, accumulated amortization	93.8	54.7
Other intangible assets, net	244.7
Goodwill and intangible asset impairment	36.4	6.2
Ark
Goodwill [Line Items]
Goodwill, fair value	116.8	0
Goodwill, impairment loss	0	0
Goodwill	116.8	0
NSM
Goodwill [Line Items]
Goodwill, fair value	533.4	506.4
Goodwill, impairment loss	30.2	0
Goodwill	503.2	506.4
Other intangible assets, fair value	315.2	288.9
Other intangible assets, accumulated amortization	86.8	52.3
Impairments and Amounts Allocated to Held for Sale	6.2	6.2
Other intangible assets, net	222.2	230.4
Kudu
Goodwill [Line Items]
Goodwill, fair value	7.6	7.6
Goodwill, impairment loss	0	0
Goodwill	7.6	7.6
Other
Goodwill [Line Items]
Goodwill, fair value	17.9	11.5
Goodwill, impairment loss	0	0
Goodwill	17.9	11.5
Other intangible assets, fair value	27.3	26.7
Other intangible assets, accumulated amortization	6.1	1.8
Impairments and Amounts Allocated to Held for Sale	0
Other intangible assets, net	21.2	24.9
Trade names | Ark
Goodwill [Line Items]
Other intangible assets, fair value	175.7	0
Other intangible assets, accumulated amortization	0	0
Impairments and Amounts Allocated to Held for Sale	0	0
Other intangible assets, net	$ 175.7	0
Trade names | NSM
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life (in years)	18 years
Other intangible assets, fair value	$ 68.6	65.4
Other intangible assets, accumulated amortization	11.9	8.3
Impairments and Amounts Allocated to Held for Sale	1	1
Other intangible assets, net	$ 55.7	56.1
Trade names | Kudu
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life (in years)	7 years
Other intangible assets, fair value	$ 2.2	2.2
Other intangible assets, accumulated amortization	0.9	0.6
Impairments and Amounts Allocated to Held for Sale	0	0
Other intangible assets, net	$ 1.3	1.6
Trade names | Other
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life (in years)	17 years 6 months
Other intangible assets, fair value	$ 8.2	3.6
Other intangible assets, accumulated amortization	1.5	0.3
Impairments and Amounts Allocated to Held for Sale	0	0
Other intangible assets, net	$ 6.7	3.3
Customer relationships | NSM
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life (in years)	9 years
Other intangible assets, fair value	$ 159.9	136.2
Other intangible assets, accumulated amortization	57	36.7
Impairments and Amounts Allocated to Held for Sale	3.5	3.5
Other intangible assets, net	$ 99.4	96
Customer relationships | Other
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life (in years)	13 years
Other intangible assets, fair value	$ 18.8	14.2
Other intangible assets, accumulated amortization	4.5	1.4
Impairments and Amounts Allocated to Held for Sale	0	0
Other intangible assets, net	$ 14.3	12.8
Information technology platform | NSM
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life (in years)	0 years
Other intangible assets, fair value	$ 3.1	3.1
Other intangible assets, accumulated amortization	1.4	1.4
Impairments and Amounts Allocated to Held for Sale	1.7	1.7
Other intangible assets, net	$ 0	0
Renewal rights | NSM
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life (in years)	12 years
Other intangible assets, fair value	$ 82.5	82.5
Other intangible assets, accumulated amortization	15.8	4.9
Impairments and Amounts Allocated to Held for Sale	0	0
Other intangible assets, net	66.7	77.6
Insurance licenses (2) | Other
Goodwill [Line Items]
Other intangible assets, fair value	0	8.6
Other intangible assets, accumulated amortization	0	0
Impairments and Amounts Allocated to Held for Sale	0	0
Other intangible assets, net	0	8.6
Insurance licenses (2) | Other | Disposal Group, Held-for-sale, Not Discontinued Operations
Goodwill [Line Items]
Other intangible assets, net	$ 8.6
Other | NSM
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life (in years)	3 years 3 months 18 days
Other intangible assets, fair value	$ 1.1	1.7
Other intangible assets, accumulated amortization	0.7	1
Impairments and Amounts Allocated to Held for Sale	0	0
Other intangible assets, net	$ 0.4	0.7
Other | Other
Goodwill [Line Items]
Acquired other intangible assets, weighted average useful life (in years)	5 years 3 months 18 days
Other intangible assets, fair value	$ 0.3	0.3
Other intangible assets, accumulated amortization	0.1	0.1
Impairments and Amounts Allocated to Held for Sale	0	0
Other intangible assets, net	0.2	0.2
Total other intangible assets
Goodwill [Line Items]
Other intangible assets, fair value	520.4	317.8
Other intangible assets, accumulated amortization	93.8	54.7
Impairments and Amounts Allocated to Held for Sale	6.2	6.2
Other intangible assets, net	420.4	256.9
Total Equity
Goodwill [Line Items]
Goodwill and other intangible assets	1,065.9	782.4
Non-controlling Interests
Goodwill [Line Items]
Goodwill and other intangible assets	(117.6)	(28.1)
Total
Goodwill [Line Items]
Goodwill and other intangible assets	948.3	754.3
Goodwill
Goodwill [Line Items]
Goodwill, impairment loss	0	0
Goodwill	645.5	525.5	$ 394.7
Goodwill, foreign currency translation gain	(1.5)	13.4
Goodwill | NSM
Goodwill [Line Items]
Goodwill, foreign currency translation gain	(1.5)	13.4
Total other intangible assets
Goodwill [Line Items]
Goodwill, impairment loss	0	6.2
Total other intangible assets | NSM
Goodwill [Line Items]
Goodwill, foreign currency translation gain	$ (0.3)	$ 1.6

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Fair Value of Goodwill and Intangible Assets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Aug. 06, 2021	May 01, 2021	Jan. 01, 2021	Jul. 02, 2020	Apr. 07, 2020	Dec. 03, 2018
Finite-Lived Intangible Assets [Line Items]
Goodwill and intangible assets acquired							$ 59.4
NSM
Finite-Lived Intangible Assets [Line Items]
Goodwill and intangible assets acquired	$ 187.4
Kingsbridge | NSM
Finite-Lived Intangible Assets [Line Items]
Goodwill and intangible assets acquired						$ 131.7
JC Taylor | NSM
Finite-Lived Intangible Assets [Line Items]
Goodwill and intangible assets acquired		$ 55.7
Ark
Finite-Lived Intangible Assets [Line Items]
Goodwill and intangible assets acquired				$ 292.5
Other Operations
Finite-Lived Intangible Assets [Line Items]
Goodwill and intangible assets acquired			$ 31.1		$ 31.1

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets - Schedule of Goodwill and Other Intangible Assets Rollforward (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Acquired Finite-Lived Intangible Assets [Line Items]
Beginning balance	$ 525.5	$ 525.5
Amortization		(39.8)	$ (28.3)	$ (21.8)
Impairments		(30.2)	0
Ending balance		645.5	525.5
J.C. Taylor Insurance
Acquired Finite-Lived Intangible Assets [Line Items]
Attribution of acquisition date fair value estimates between goodwill and other intangible assets		27.2
Kingsbridge Group Limited
Acquired Finite-Lived Intangible Assets [Line Items]
Attribution of acquisition date fair value estimates between goodwill and other intangible assets			13.6
Measurement period adjustments			4.1
Other Operations
Acquired Finite-Lived Intangible Assets [Line Items]
Attribution of acquisition date fair value estimates between goodwill and other intangible assets		9.3	9.6
Fresh Insurance Services Group Limited
Acquired Finite-Lived Intangible Assets [Line Items]
Proceeds from sale of other assets	1.5
Goodwill
Acquired Finite-Lived Intangible Assets [Line Items]
Beginning balance	525.5	525.5	394.7
Acquisition of businesses		71.5	140
Attribution of acquisition date fair value estimates between goodwill and other intangible assets		(36.5)	(23.2)
Measurement period adjustments		(0.1)	0.6
Disposition of businesses		0	0
Amortization		0	0
Impairments		0	0
Assets held for sale			0
Loss on assets held for sale		(30.2)	0
Foreign currency translation		(1.5)	13.4
Ending balance		645.5	525.5	394.7
Goodwill | Ark
Acquired Finite-Lived Intangible Assets [Line Items]
Ark Transaction		116.8	0
Goodwill | J.C. Taylor Insurance
Acquired Finite-Lived Intangible Assets [Line Items]
Acquisition of businesses		55.7
Goodwill | Kingsbridge Group Limited
Acquired Finite-Lived Intangible Assets [Line Items]
Acquisition of businesses			125.1
Goodwill | Other Operations
Acquired Finite-Lived Intangible Assets [Line Items]
Acquisition of businesses			14.9
Goodwill | Other Operations
Acquired Finite-Lived Intangible Assets [Line Items]
Acquisition of businesses		15.8
Total other intangible assets
Acquired Finite-Lived Intangible Assets [Line Items]
Beginning balance	256.9	256.9	260
Acquisition of businesses		0	0
Attribution of acquisition date fair value estimates between goodwill and other intangible assets		36.5	23.2
Measurement period adjustments		0	6.6
Disposition of businesses		0	0
Amortization		(39.8)	(28.3)
Impairments		0	(6.2)
Assets held for sale		(8.6)	0
Loss on assets held for sale		0	0
Foreign currency translation		(0.3)	1.6
Ending balance		420.4	256.9	260
Total other intangible assets | Ark
Acquired Finite-Lived Intangible Assets [Line Items]
Ark Transaction		175.7	0
Total Goodwill and Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Beginning balance	$ 782.4	782.4	654.7
Acquisition of businesses		71.5	140
Attribution of acquisition date fair value estimates between goodwill and other intangible assets		0	0
Measurement period adjustments		(0.1)	7.2
Disposition of businesses		0	0
Amortization		(39.8)	(28.3)
Impairments		0	(6.2)
Assets held for sale		(8.6)	0
Loss on assets held for sale		(30.2)	0
Foreign currency translation		(1.8)	15
Ending balance		1,065.9	782.4	$ 654.7
Total Goodwill and Other Intangible Assets | Ark
Acquired Finite-Lived Intangible Assets [Line Items]
Ark Transaction		$ 292.5	$ 0

Goodwill and Other Intangible_6

Goodwill and Other Intangible Assets - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Goodwill, impairment loss	$ 30.2	$ 0
Amortization of other intangible assets	39.8	28.3	$ 21.8
Fresh Insurance Services Group Limited
Finite-Lived Intangible Assets [Line Items]
Loss on sale	$ 28.7
Impairments of other intangible assets			2.4
UK Vertical
Finite-Lived Intangible Assets [Line Items]
Impairments of other intangible assets		$ 6.2
Other Operations
Finite-Lived Intangible Assets [Line Items]
Impairments of other intangible assets			0.4
Goodwill, impairment loss			$ 7.6

Goodwill and Other Intangible_7

Goodwill and Other Intangible Assets - Amortization Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of other intangible assets	$ 39.8	$ 28.3	$ 21.8
2022	39.4
2023	36
2024	32.7
2025	30.5
2026 and years after	106.1
Total	244.7
Indefinite-lived intangible assets	$ 175.7

Loss and Loss Adjustment Expe_3

Loss and Loss Adjustment Expense Reserves - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Group Ark Insurance Limited
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable loss reserve development	$ (21.5)
Group Ark Insurance Limited | Property and Accident & Health
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable loss reserve development	8.9
Group Ark Insurance Limited | Casualty - Active
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable loss reserve development	3.7
Group Ark Insurance Limited | Specialty
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable loss reserve development	3.3
Group Ark Insurance Limited | Casualty - Runoff
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable loss reserve development	3.3
Group Ark Insurance Limited | All Entities Except TCP Providers
Liability for Claims and Claims Adjustment Expense [Line Items]
Favorable loss reserve development	$ 21.5
Ark | Amount attributable to TPC Providers
Liability for Claims and Claims Adjustment Expense [Line Items]
Percent of underwriting capital provided by third parties	0.00%	42.80%	58.30%	57.60%	60.00%	59.60%	70.00%	66.20%	0.00%	0.00%

Loss and Loss Adjustment Expe_4

Loss and Loss Adjustment Expense Reserves - LAE Reserve Activity (Details) - Group Ark Insurance Limited	12 Months Ended
	Dec. 31, 2021USD ($)
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross beginning balance	$ 696,000,000
Less: beginning reinsurance recoverable on unpaid losses	(433,400,000)
Net loss and LAE reserves	262,600,000
Losses and LAE incurred relating to:
Current Year	336,300,000
Prior Year	(21,500,000)
Net incurred losses and LAE	314,800,000
Loss and LAE paid relating to:
Current year losses	(43,900,000)
Prior year losses	(61,600,000)
Net paid losses and LAE	(105,500,000)
Foreign currency translation and other adjustments to loss and LAE reserves	(3,900,000)
Net ending balance	465,800,000
Plus: ending reinsurance recoverable on unpaid losses	(428,900,000)
Gross ending balance	894,700,000
Amount attributable to TPC Providers
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Less: beginning reinsurance recoverable on unpaid losses	319,200,000
Loss and LAE paid relating to:
Change in TPC Providers’ participation	(2,200,000)
Plus: ending reinsurance recoverable on unpaid losses	$ (276,800,000)

Loss and Loss Adjustment Expe_5

Loss and Loss Adjustment Expense Reserves - Schedule of Ending Liabilities for Unpaid Loss and LAE, Net of Reinsurance (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total Reinsurance recoverables on unpaid losses	$ 428.9
Property and Accident & Health
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Loss and LAE reserves, net of reinsurance	175
Marine & Energy
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Loss and LAE reserves, net of reinsurance	99.3
Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Loss and LAE reserves, net of reinsurance	85.2
Casualty - Active
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Loss and LAE reserves, net of reinsurance	37.4
Casualty - Runoff
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Loss and LAE reserves, net of reinsurance	68.4
Ark
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Unpaid loss and LAE reserves, net of reinsurance recoverables on unpaid losses	465.8
Total Reinsurance recoverables on unpaid losses	428.9
Loss and loss adjustment expense reserves	894.7	$ 0
Ark | Amount attributable to TPC Providers
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Total Reinsurance recoverables on unpaid losses	276.8
Ark | Property and Accident & Health
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Loss and LAE reserves, net of reinsurance	175
Total Reinsurance recoverables on unpaid losses	145.2
Ark | Marine & Energy
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Loss and LAE reserves, net of reinsurance	99.3
Total Reinsurance recoverables on unpaid losses	70.2
Ark | Specialty
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Loss and LAE reserves, net of reinsurance	85.2
Total Reinsurance recoverables on unpaid losses	68.9
Ark | Casualty - Active
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Loss and LAE reserves, net of reinsurance	37.4
Total Reinsurance recoverables on unpaid losses	41.4
Ark | Casualty - Runoff
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Loss and LAE reserves, net of reinsurance	68.4
Total Reinsurance recoverables on unpaid losses	103.2
Ark | Other
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Loss and LAE reserves, net of reinsurance	$ 0.5

Loss and Loss Adjustment Expe_6

Loss and Loss Adjustment Expense Reserves - TPC Participation (Details)	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Ark | Amount attributable to TPC Providers
Liability for Claims and Claims Adjustment Expense [Line Items]
Percent of underwriting capital provided by third parties	0.00%	42.80%	58.30%	57.60%	60.00%	59.60%	70.00%	66.20%	0.00%	0.00%

Loss and Loss Adjustment Expe_7

Loss and Loss Adjustment Expense Reserves - Incurred Loss and Allocated LAE, Net of Reinsurance (Details) $ in Millions	Dec. 31, 2021USD ($)basisPoint	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)
Property and Accident & Health
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 511.5
Marine & Energy
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	259.8
Specialty
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	232.5
Casualty - Active
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	82.2
Casualty - Runoff
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	263.9
2012 | Property and Accident & Health
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	60	$ 60.2	$ 60.2	$ 60.4	$ 60	$ 60.2	$ 65.7	$ 65.1	$ 68.4	$ 84.1
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,710
2012 | Marine & Energy
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 32.1	32	32	32.6	32.8	33.6	42.8	46	55.1	64.7
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.1
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,428
2012 | Specialty
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 26.8	26.8	26.6	26.3	25.8	26.7	30.8	31.8	36.1	43.1
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2.1
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	887
2012 | Casualty - Active
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 11.1	11.3	11	11	9.9	10.1	16.2	17.7	21.1	22.6
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.8
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,016
2012 | Casualty - Runoff
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 23.1	22.7	22.8	22.3	21.7	22.3	34.4	37.8	44.6	$ 44.3
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ (0.2)
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,430
2013 | Property and Accident & Health
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 61.6	61.6	61.6	61.7	61.6	62.1	66.6	66.9	74.6
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.4
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,586
2013 | Marine & Energy
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 29.9	29.6	29.7	29.9	31	31.6	41.9	50.8	64.9
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ (0.2)
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,641
2013 | Specialty
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 17.3	17.3	16.9	17.1	16.9	17.5	25.6	34.9	48.6
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1.3
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,122
2013 | Casualty - Active
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 8.9	9	8.8	8.9	8.1	8.3	15	18.8	23.2
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1.3
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,134
2013 | Casualty - Runoff
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 49.9	49.8	49.8	49.8	47	49.2	70.1	75.8	$ 65.7
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3.1
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,810
2014 | Property and Accident & Health
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 28.5	28.5	28.5	28.6	28.6	29.4	31.3	34.8
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,963
2014 | Marine & Energy
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 14.4	14.4	14.3	14.7	16.2	17.4	27.2	41.3
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.5
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,581
2014 | Specialty
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 43.5	43.5	42.9	41.5	41.3	41.9	51.1	51.1
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ (0.3)
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,409
2014 | Casualty - Active
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 7.7	7.8	7.8	8	7	7.5	13.8	17.1
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1.2
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,359
2014 | Casualty - Runoff
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 55	56	55.6	55.9	46	46.8	67.5	$ 46.9
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1.9
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,932
2015 | Property and Accident & Health
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 15.9	15.9	15.9	16	16.2	17.4	19.8
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.4
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,884
2015 | Marine & Energy
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 12.2	12	12	12.7	13.6	15.4	25.3
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.2
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	3,390
2015 | Specialty
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 10.8	10.7	10.6	10.1	10.4	13	21.3
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1.7
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,876
2015 | Casualty - Active
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 6.2	6.4	6.5	7	6	7.7	12.3
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.6
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,247
2015 | Casualty - Runoff
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 32	33.2	33	35.7	26.4	23.9	$ 26.9
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1.4
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,009
2016 | Property and Accident & Health
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 18	17.9	18	17.9	16.9	21.7
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ (0.3)
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	3,478
2016 | Marine & Energy
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 15.1	14.9	15.1	16	18.1	22.3
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.7
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	4,117
2016 | Specialty
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 9.3	9	9.2	8.7	11.7	15.9
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ (1.3)
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,941
2016 | Casualty - Active
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 6.9	7	6.6	6.3	5	5.7
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.1
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,483
2016 | Casualty - Runoff
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 34.1	35.3	35.4	38.8	25.3	$ 19.1
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3.8
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,141
2017 | Property and Accident & Health
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 36	36.7	37.4	29.9	22.6
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3.6
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	4,610
2017 | Marine & Energy
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 16.5	16.4	16.9	18.6	23.9
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1.1
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	4,470
2017 | Specialty
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 10.6	10.5	10.9	11.9	16
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1.5
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,179
2017 | Casualty - Active
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 5.9	6.2	7.2	7.8	7.4
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.7
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,489
2017 | Casualty - Runoff
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 26.7	28	26.7	27.2	$ 17.4
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2.5
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,597
2018 | Property and Accident & Health
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 44.5	46.3	44.2	37.5
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1.5
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	4,270
2018 | Marine & Energy
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 17	16.7	18.9	24.5
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.5
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	3,487
2018 | Specialty
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 13.7	14.8	13.9	12.1
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2.4
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,090
2018 | Casualty - Active
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 7.1	7.3	9	8.7
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.9
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	961
2018 | Casualty - Runoff
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 20	20.2	18.2	$ 13.5
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2.9
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,265
2019 | Property and Accident & Health
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 23.4	27.8	30.4
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2.1
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	4,073
2019 | Marine & Energy
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 17.2	17.3	19.3
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.6
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,562
2019 | Specialty
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 13.5	14.6	16.6
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2.8
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,315
2019 | Casualty - Active
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 6.3	7.4	8
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 1.7
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	742
2019 | Casualty - Runoff
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 15.4	14.3	$ 10.8
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3.7
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	961
2020 | Property and Accident & Health
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 61.5	62.9
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 15.2
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	4,532
2020 | Marine & Energy
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 21.7	24.4
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 2.9
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,668
2020 | Specialty
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 19.7	20.7
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 6.2
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,925
2020 | Casualty - Active
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 6.2	7.6
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3.9
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	420
2020 | Casualty - Runoff
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 6	$ 4.2
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 3.6
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	552
2021 | Property and Accident & Health
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 162.1
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 70.8
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	2,860
2021 | Marine & Energy
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 83.7
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 69.9
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,091
2021 | Specialty
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 67.3
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 57.4
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	1,341
2021 | Casualty - Active
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 15.9
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 14.2
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	452
2021 | Casualty - Runoff
Claims Development [Line Items]
Incurred Loss and LAE, Net of Reinsurance	$ 1.7
Short-duration Insurance Contracts, Incurred but Not Reported (IBNR) Claims Liability, Net	$ 0.4
Short-duration Insurance Contract, Cumulative Number of Reported Claims | basisPoint	260

Loss and Loss Adjustment Expe_8

Loss and Loss Adjustment Expense Reserves - Cumulative Paid Loss and Allocated LAE, Net of Reinsurance (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property and Accident & Health
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	$ 337.1
All outstanding liabilities before 2012, net of reinsurance	0.6
Loss and LAE reserves, net of reinsurance	175
Property and Accident & Health | 2012
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	59.5	$ 59.4	$ 59.3	$ 58.7	$ 58.6	$ 58.2	$ 57.3	$ 53.6	$ 45	$ 14.2
Property and Accident & Health | 2013
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	61.2	61.3	61.3	61.3	61.1	61.1	60	40.3	15.8
Property and Accident & Health | 2014
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	28.3	28.4	28.2	28.1	28	27.6	25.4	13.9
Property and Accident & Health | 2015
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	15.3	15.1	14.8	14.9	13.7	12.4	7
Property and Accident & Health | 2016
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	17.5	17.2	17.1	16.8	13.4	8.6
Property and Accident & Health | 2017
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	30.2	33.3	32.1	26.3	17
Property and Accident & Health | 2018
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	40.7	40.7	32.8	15.8
Property and Accident & Health | 2019
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	19.1	17.1	6.9
Property and Accident & Health | 2020
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	34.5	11.4
Property and Accident & Health | 2021
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	30.8
Marine & Energy
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	161.7
All outstanding liabilities before 2012, net of reinsurance	1.2
Loss and LAE reserves, net of reinsurance	99.3
Marine & Energy | 2012
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	31	31.3	31.4	31.7	31.3	30.6	30.2	27.4	24	8.1
Marine & Energy | 2013
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	29.9	29.7	29.9	29.9	29.7	29.1	28.1	22.6	7.9
Marine & Energy | 2014
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	13.8	14	13.7	14.5	14.4	13.5	12.4	6
Marine & Energy | 2015
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	11.2	10.8	10.7	11.3	9.8	8	4
Marine & Energy | 2016
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	14	13.4	13.3	12.8	10.1	5.6
Marine & Energy | 2017
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	14.4	14.4	13.1	11.3	5.2
Marine & Energy | 2018
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	15.2	14.5	12.9	2.7
Marine & Energy | 2019
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	12.9	10.9	3.4
Marine & Energy | 2020
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	12.9	3.2
Marine & Energy | 2021
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	6.4
Specialty
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	145.3
All outstanding liabilities before 2012, net of reinsurance	(2)
Loss and LAE reserves, net of reinsurance	85.2
Specialty | 2012
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	24.5	24.4	24.4	24.2	23.3	23.2	22.6	22.2	25.2	16.3
Specialty | 2013
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	16	16	16	16	15.8	15.8	15.2	13.6	17.1
Specialty | 2014
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	43.5	43.6	42.8	41.5	40.8	40.4	39.7	26.8
Specialty | 2015
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	8.3	8.3	8.2	8.2	7.8	7.2	4.1
Specialty | 2016
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	10.5	10.4	10	9.2	8	3.2
Specialty | 2017
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	8.5	8.5	8.4	6.8	3.3
Specialty | 2018
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	10.3	9.8	8.1	2.9
Specialty | 2019
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	7.6	7.1	4.9
Specialty | 2020
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	10.9	5.4
Specialty | 2021
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	5.2
Casualty - Active
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	45
All outstanding liabilities before 2012, net of reinsurance	0.2
Loss and LAE reserves, net of reinsurance	37.4
Casualty - Active | 2012
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	9.1	8.9	9.1	8.5	8	7.4	6.4	4.8	3.3	1.3
Casualty - Active | 2013
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	7.2	7	7	6.7	6.3	5.7	5.3	3.6	1.5
Casualty - Active | 2014
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	6	5.9	5.5	5.2	4.7	4.2	3.5	1.3
Casualty - Active | 2015
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	5.1	4.9	4.7	4.4	3.2	2.4	1.8
Casualty - Active | 2016
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	5.3	4.6	4	2.3	1	0.2
Casualty - Active | 2017
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	4.2	3.4	2.8	1.7	0.8
Casualty - Active | 2018
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	4.3	3.5	1.4	0.3
Casualty - Active | 2019
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	2.3	1.4	0.3
Casualty - Active | 2020
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	1	0.5
Casualty - Active | 2021
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	0.5
Casualty - Runoff
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	216.9
All outstanding liabilities before 2012, net of reinsurance	21.4
Loss and LAE reserves, net of reinsurance	68.4
Casualty - Runoff | 2012
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	21.8	21.2	20.8	20.5	19.3	17.8	16.5	13.6	10.4	$ 3.5
Casualty - Runoff | 2013
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	46	45.6	45	44.3	42.7	41	35.9	19.5	$ 7.2
Casualty - Runoff | 2014
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	49.5	48.7	47	43.1	36.5	29.1	23.2	$ 6.5
Casualty - Runoff | 2015
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	28.2	26.5	23.9	20.3	14	7.9	$ 4.3
Casualty - Runoff | 2016
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	26.8	24.5	21.8	16.8	9.7	$ 3.8
Casualty - Runoff | 2017
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	21.1	18.3	14.2	9.1	$ 3.1
Casualty - Runoff | 2018
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	14.3	12.2	7.2	$ 3.3
Casualty - Runoff | 2019
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	7.4	5.6	$ 3.2
Casualty - Runoff | 2020
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	1.3	$ 0.8
Casualty - Runoff | 2021
Claims Development [Line Items]
Cumulative Paid Loss and LAE, Net of Reinsurance	$ 0.5

Loss and Loss Adjustment Expe_9

Loss and Loss Adjustment Expense Reserves - Average Annual Percentage Payout of Incurred Losses and Allocated LAE by Age, Net of Reinsurance (Details)	Dec. 31, 2021
Property and Accident & Health
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1	31.50%
2	33.40%
3	19.20%
4	5.70%
5	1.20%
6	1.40%
7	0.80%
8	0.30%
9	0.00%
10	0.10%
Marine & Energy
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1	19.80%
2	37.70%
3	20.20%
4	5.70%
5	4.30%
6	7.20%
7	0.40%
8	0.10%
9	0.40%
10	0.20%
Specialty
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1	34.00%
2	33.80%
3	7.30%
4	0.50%
5	4.60%
6	4.40%
7	4.60%
8	3.10%
9	3.50%
10	1.00%
Casualty - Active
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1	9.10%
2	14.70%
3	18.50%
4	14.20%
5	9.60%
6	10.70%
7	3.90%
8	3.10%
9	1.00%
10	3.10%
Casualty - Runoff
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
1	9.40%
2	15.30%
3	17.00%
4	15.90%
5	9.70%
6	8.10%
7	7.00%
8	3.60%
9	2.50%
10	1.70%

Third-Party Reinsurance - Effec

Third-Party Reinsurance - Effects of Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earned premiums:
Net earned premiums	$ 664.2	$ 22.8	$ 16.3
Ark
Written premiums:
Direct	1,058.7
Ceded	(199.6)
Net written premiums	859.1
Earned premiums:
Direct	886.4
Ceded	(249.1)
Net earned premiums	637.3
Losses and LAE:
Gross	442.9
Ceded	(128.1)
Net Losses and LAE	$ 314.8

Third-Party Reinsurance - Narra

Third-Party Reinsurance - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Reinsurance [Line Items]
Total Reinsurance recoverables on unpaid losses	$ 428.9
Reinsurance recoverables on paid losses	19.5
Ark
Reinsurance [Line Items]
Total Reinsurance recoverables on unpaid losses	428.9
Reinsurance recoverables	$ 448.4	$ 0
Ark | Third Point Re
Reinsurance [Line Items]
Annual crediting rate	3.00%
Decrease in investment	$ 31.7
Value of investment	20.4
Amount attributable to TPC Providers
Reinsurance [Line Items]
Total Reinsurance recoverables on unpaid losses	$ 276.8

Third-Party Reinsurance - Remai

Third-Party Reinsurance - Remaining Gross and Net Reinsurance Recoverables (Details) - All Entities Except TCP Providers $ in Millions	Dec. 31, 2021USD ($)
Reinsurance [Line Items]
Gross	$ 171.6
Collateral	38.5
Net	$ 133.1
% of Total	100.00%
A+ or better
Reinsurance [Line Items]
Gross	$ 120
Collateral	16.9
Net	$ 103.1
% of Total	77.50%
A- to A
Reinsurance [Line Items]
Gross	$ 41.5
Collateral	13.1
Net	$ 28.4
% of Total	21.30%
B++ or lower and not rated
Reinsurance [Line Items]
Gross	$ 10.1
Collateral	8.5
Net	$ 1.6
% of Total	1.20%

Debt - Debt Outstanding (Detail

Debt - Debt Outstanding (Details) € in Millions	12 Months Ended
	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2021EUR (€)	Jun. 02, 2021USD ($)	Apr. 07, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Debt Instrument
Total debt	$ 693,000,000	$ 376,400,000
Weighted average interest rate	6.50%	7.00%
Ark Subordinated Notes
Debt Instrument
Unamortized issuance cost	$ (5,300,000)
Ark 2007 Notes Tranche 1 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross	30,000,000
Ark 2007 Notes Tranche 2 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross	0
Ark 2007 Notes | Ark Subordinated Notes
Debt Instrument
Total debt	30,000,000
Ark 2021 Notes Tranche 1
Debt Instrument
Long-term debt, gross | €			€ 39.1
Ark 2021 Notes Tranche 1 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross	44,200,000
Ark 2021 Notes Tranche 2 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross	47,000,000
Ark 2021 Notes Tranche 3 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross	70,000,000
Ark 2021 Notes | Ark Subordinated Notes
Debt Instrument
Total debt	$ 155,900,000
Ark
Debt Instrument
Effective yield (as a percent)	6.90%		6.90%
Ark | Ark Subordinated Notes
Debt Instrument
Total debt	$ 185,900,000
NSM Bank Facility
Debt Instrument
Effective yield (as a percent)	8.20%	8.40%	8.20%
NSM
Debt Instrument
Total debt	$ 272,100,000	$ 272,600,000
NSM | NSM Bank Facility
Debt Instrument
Total debt	277,600,000	277,400,000				$ 221,300,000	$ 180,400,000
Debt instrument at face value	274,100,000
Kudu | Kudu Bank Facility
Debt Instrument
Total debt		86,300,000
Kudu | Kudu Credit Facility
Debt Instrument
Total debt	218,200,000
Other Operations | Other
Debt Instrument
Total debt	$ 16,800,000
Term Loan | Kudu Credit Facility
Debt Instrument
Effective yield (as a percent)	4.30%		4.30%
Term Loan | NSM | NSM Bank Facility
Debt Instrument
Total debt	$ 271,200,000	271,300,000
Unamortized issuance cost	(6,400,000)	(6,100,000)
Debt instrument at face value	$ 277,600,000	$ 277,400,000		$ 50,000,000	$ 276,400,000
Effective yield (as a percent)	7.30%	7.50%	7.30%
Term Loan | NSM | Other NSM
Debt Instrument
Total debt	$ 900,000	$ 1,300,000
Debt instrument at face value	$ 1,000,000
Effective yield (as a percent)	2.90%	2.50%	2.90%
Term Loan | Kudu | Kudu Bank Facility
Debt Instrument
Total debt	$ 0	$ 89,200,000				57,000,000	0
Unamortized issuance cost		(2,900,000)
Debt instrument at face value		$ 89,200,000
Effective yield (as a percent)		8.30%
Term Loan | Kudu | Kudu Credit Facility
Debt Instrument
Total debt	225,400,000	$ 0				$ 0	$ 0
Unamortized issuance cost	(7,200,000)
Debt instrument at face value	225,400,000
Term Loan | Other Operations | Other
Debt Instrument
Total debt		17,500,000
Unamortized issuance cost	(300,000)	(500,000)
Debt instrument at face value	$ 17,100,000	$ 18,000,000
Term Loan | Other Operations | Other Debt
Debt Instrument
Effective yield (as a percent)	7.50%	7.40%	7.50%

Debt - Schedule of Contractual

Debt - Schedule of Contractual Repayments (Details) $ in Millions	Dec. 31, 2021USD ($)
Debt Disclosure [Abstract]
Due in one year or less	$ 5.7
Due in two to three years	14.5
Due in four to five years	221.6
Due after five years	470.4
Total	$ 712.2

Debt - Ark Subordinated Notes N

Debt - Ark Subordinated Notes Narrative (Details)	Sep. 08, 2021USD ($)	Aug. 11, 2021USD ($)	Jul. 13, 2021USD ($)	Mar. 31, 2007USD ($)	Sep. 30, 2021USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2021EUR (€)	Jul. 13, 2021EUR (€)	Dec. 31, 2020USD ($)	Mar. 31, 2007EUR (€)
Debt Instrument
Debt						$ 693,000,000			$ 376,400,000
Unsecured Subordinated Debt | Group Ark Insurance Limited
Debt Instrument
Proceeds from borrowings					$ 157,800,000
Unsecured Subordinated Debt | Ark | Group Ark Insurance Limited
Debt Instrument
Notes issued					$ 163,300,000
Ark 2007 Notes Tranche 1 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross						30,000,000
Ark 2007 Notes Tranche 2 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross						0
Ark 2021 Notes Tranche 1
Debt Instrument
Long-term debt, gross | €							€ 39,100,000
Ark 2021 Notes Tranche 1 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross						44,200,000
Ark 2021 Notes Tranche 1 | Unsecured Subordinated Debt | Group Ark Insurance Limited
Debt Instrument
Notes issued			$ 46,300,000					€ 39,100,000
Ark 2021 Notes Tranche 1 | Unsecured Subordinated Debt | EURIBOR | Group Ark Insurance Limited
Debt Instrument
Basis spread on variable rate			5.75%
Ark 2021 Notes Tranche 2 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross						47,000,000
Ark 2021 Notes Tranche 2 | Unsecured Subordinated Debt | Group Ark Insurance Limited
Debt Instrument
Notes issued		$ 47,000,000
Ark 2021 Notes Tranche 2 | Unsecured Subordinated Debt | United States Dollar London Interbank Offered Rate LIBOR | Group Ark Insurance Limited
Debt Instrument
Basis spread on variable rate		5.75%
Ark 2021 Notes Tranche 3 | Ark Subordinated Notes
Debt Instrument
Long-term debt, gross						70,000,000
Ark 2021 Notes Tranche 3 | Unsecured Subordinated Debt | Group Ark Insurance Limited
Debt Instrument
Notes issued	$ 70,000,000
Additional interest rate	1.00%
Solvency capital requirement	120.00%
Debt to capital requirement	40.00%
Ark 2021 Notes Tranche 3 | Unsecured Subordinated Debt | United States Dollar London Interbank Offered Rate LIBOR | Group Ark Insurance Limited
Debt Instrument
Basis spread on variable rate	6.10%
Ark | Ark 2007 Notes Tranche 1 | Junior Notes
Debt Instrument
Long-term line of credit				$ 30,000,000
Debt						30,000,000
Ark | Ark 2007 Notes Tranche 1 | Junior Notes | United States Dollar London Interbank Offered Rate LIBOR
Debt Instrument
Basis spread on variable rate				4.60%
Ark | Ark 2007 Notes Tranche 2 | Junior Notes
Debt Instrument
Long-term line of credit | €										€ 12,000,000
Debt						$ 13,500,000	€ 12,000,000
Ark | Ark 2007 Notes Tranche 2 | Junior Notes | EURIBOR
Debt Instrument
Basis spread on variable rate				4.60%

Debt - Ark Stand By Letters of

Debt - Ark Stand By Letters of Credit Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2021	Apr. 07, 2020
Debt Instrument
Total commitment under revolving credit facility		$ 291.4
Short-term investments
Debt Instrument
Investments pledged as collateral	$ 50
Uncollateralized | Letter of Credit | Secured Debt | Ark
Debt Instrument
Total commitment under revolving credit facility	50
Collateralized | Letter of Credit | Secured Debt | Ark
Debt Instrument
Total commitment under revolving credit facility	$ 100

Debt - NSM Bank Narrative (Deta

Debt - NSM Bank Narrative (Details) £ in Millions	Jun. 02, 2021USD ($)	Jun. 01, 2021	Apr. 07, 2020USD ($)	Apr. 07, 2020GBP (£)	Apr. 06, 2020USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2021GBP (£)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Jun. 15, 2018USD ($)
Debt Instrument
Total commitment under revolving credit facility			$ 291,400,000
Debt						$ 693,000,000		$ 376,400,000
NSM
Debt Instrument
Debt						272,100,000		272,600,000
NSM Bank Facility | NSM
Debt Instrument
Total commitment under revolving credit facility					$ 234,000,000
Long-term line of credit						$ 274,100,000
Percentage of discounted future cash flows						10.00%	10.00%
Debt						$ 277,600,000		277,400,000	$ 221,300,000	$ 180,400,000
NSM Bank Facility | NSM | Term Loan
Debt Instrument
Total commitment under revolving credit facility					$ 224,000,000
Long-term line of credit	$ 50,000,000		276,400,000			277,600,000		277,400,000
Proceeds from borrowings			$ 52,400,000	£ 42.5		0	£ 41.9	52,400,000	42,900,000
Floor rate			1.25%	1.25%
Debt						271,200,000		271,300,000
NSM Bank Facility | NSM | Term Loan | Interest Rate Swap
Debt Instrument
Total commitment under revolving credit facility											$ 151,000,000
Hedged liability, fair value hedge											$ 151,000,000
Debt						146,100,000
NSM Bank Facility | NSM | Term Loan | Interest Rate Swap | Designated as Hedging Instrument
Debt Instrument
Debt						146,100,000
NSM Bank Facility | NSM | Term Loan | Interest Rate Swap | Not Designated as Hedging Instrument
Debt Instrument
Debt						128,000,000
NSM Bank Facility | NSM | Term Loan | United States Dollar London Interbank Offered Rate LIBOR
Debt Instrument
Floor rate			1.25%	1.25%
NSM Bank Facility | NSM | Term Loan | United States Dollar London Interbank Offered Rate LIBOR | Minimum
Debt Instrument
Basis spread on variable rate	4.50%	5.50%	5.50%	5.50%	4.25%
NSM Bank Facility | NSM | Term Loan | United States Dollar London Interbank Offered Rate LIBOR | Maximum
Debt Instrument
Basis spread on variable rate	5.00%	6.00%	6.00%	6.00%	4.75%
NSM Bank Facility | NSM | Term Loan | British Sterling Pound London Interbank Offered Rate LIBOR | Minimum
Debt Instrument
Basis spread on variable rate	5.00%	6.00%
NSM Bank Facility | NSM | Term Loan | British Sterling Pound London Interbank Offered Rate LIBOR | Maximum
Debt Instrument
Basis spread on variable rate	5.50%	6.50%
NSM Bank Facility | NSM | Term Loan | Foreign Exchange Spot Rate
Debt Instrument
Proceeds from borrowings						56,700,000
NSM Bank Facility | NSM | Revolving Credit Facility
Debt Instrument
Total commitment under revolving credit facility	$ 40,000,000		$ 15,000,000		$ 10,000,000
Proceeds from borrowings						35,000,000		0	$ 6,500,000
Amount outstanding						3,500,000
Other NSM | NSM | Term Loan
Debt Instrument
Long-term line of credit						1,000,000
Debt						$ 900,000		$ 1,300,000

Debt - Kudu Credit Facility and

Debt - Kudu Credit Facility and Bank Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Mar. 23, 2021	Apr. 07, 2020
Debt Instrument
Total commitment under revolving credit facility			$ 291,400,000
Debt covenant, maximum loan to value percent, period one	50.00%
Debt covenant, maximum loan to value percent, period two	40.00%
Debt covenant, maximum loan to value percent, period three	25.00%
Debt covenant, maximum loan to value percent, period four	15.00%
Debt covenant, maximum loan to value percent, period five	0.00%
Debt covenant, maximum loan to value percent	34.00%
Kudu Bank Facility | Kudu
Debt Instrument
Total commitment under revolving credit facility		$ 300,000,000
Kudu Bank Facility | Kudu | Revolving Credit Facility
Debt Instrument
Loss on debt extinguishment	$ 4,100,000
Kudu Bank Facility | Kudu | Line of Credit
Debt Instrument
Interest reserve	$ 4,500,000
Kudu Bank Facility | Kudu | Line of Credit | London Interbank Offered Rate (LIBOR)
Debt Instrument
Basis spread on variable rate	0.25%
Kudu Bank Facility | Kudu | Line of Credit | United States Dollar London Interbank Offered Rate LIBOR
Debt Instrument
Basis spread on variable rate	4.30%
Kudu Bank Facility | Kudu | Term Loan
Debt Instrument
Percentage of borrowing base	35.00%
Undrawn amount on facility	$ 8,900,000

Debt - Other Debt Narrative (De

Debt - Other Debt Narrative (Details)	12 Months Ended
	Dec. 31, 2021USD ($)credit_facility	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Apr. 07, 2020USD ($)
Debt Instrument
Secured credit facilities | credit_facility	3
Total commitment under revolving credit facility				$ 291,400,000
Draw down of debt and revolving lines of credit	$ 436,700,000	$ 84,600,000	$ 206,400,000
Interest expense	43,800,000	29,500,000	17,600,000
Interest paid	35,800,000	27,000,000	16,300,000
First Credit Facility
Debt Instrument
Total commitment under revolving credit facility	16,300,000
First Credit Facility | Term Loan
Debt Instrument
Total commitment under revolving credit facility	11,300,000
First Credit Facility | Delayed Draw Term Loans
Debt Instrument
Total commitment under revolving credit facility	3,000,000
First Credit Facility | Revolving Credit Facility
Debt Instrument
Total commitment under revolving credit facility	2,000,000
Second Credit Facility | Other Operations
Debt Instrument
Total commitment under revolving credit facility	15,000,000
Second Credit Facility | Term Loan
Debt Instrument
Long-term debt, gross		18,000,000
Second Credit Facility | Term Loan | Other Operations
Debt Instrument
Total commitment under revolving credit facility	9,000,000
Second Credit Facility | Delayed Draw Term Loans | Other Operations
Debt Instrument
Total commitment under revolving credit facility	4,000,000
Second Credit Facility | Revolving Credit Facility | Other Operations
Debt Instrument
Total commitment under revolving credit facility	2,000,000
Third Credit Facility | Other Operations
Debt Instrument
Total commitment under revolving credit facility	8,000,000
Third Credit Facility | Term Loan | Other Operations
Debt Instrument
Repayments	7,700,000	2,100,000	$ 200,000
Third Credit Facility | Revolving Credit Facility | Other Operations
Debt Instrument
Draw down of debt and revolving lines of credit	3,400,000
Other | Term Loan | Other Operations
Debt Instrument
Long-term line of credit	$ 17,100,000	$ 18,000,000

Debt - Schedule of the Change i

Debt - Schedule of the Change in Debt under the NSM Bank Facility (Details) £ in Millions, $ in Millions	Apr. 07, 2020USD ($)	Apr. 07, 2020GBP (£)	Apr. 01, 2019USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2021GBP (£)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Debt Instrument
Beginning balance				$ 376.4
Repayment of debt and revolving lines of credit				(154.7)		$ (4.5)	$ (22.9)
Ending balance				693		376.4
NSM
Debt Instrument
Beginning balance				272.6
Ending balance				272.1		272.6
NSM | Embrace Pet Insurance
Debt Instrument
Borrowings			$ 20.4
NSM | NSM Bank Facility
Debt Instrument
Beginning balance				277.4		221.3	180.4
Ending balance				277.6		277.4	221.3
NSM | NSM Bank Facility | Term Loan
Debt Instrument
Beginning balance				271.3
Borrowings	$ 52.4	£ 42.5		0	£ 41.9	52.4	42.9
Repayment of debt and revolving lines of credit				(2.8)		(2)	(2)
Foreign currency translation				(0.5)		5.7	0
Ending balance				271.2		271.3
NSM | NSM Bank Facility | Term Loan | Kingsbridge
Debt Instrument
Borrowings						52.4
NSM | NSM Bank Facility | Term Loan | Embrace Pet Insurance
Debt Instrument
Borrowings							20.4
NSM | NSM Bank Facility | Term Loan | Renewal rights
Debt Instrument
Borrowings							22.5
NSM | NSM Bank Facility | Revolving Credit Facility
Debt Instrument
Borrowings				35		0	6.5
Repayment of debt and revolving lines of credit				(31.5)		$ 0	$ (6.5)
NSM | NSM Bank Facility | Revolving Credit Facility | JC Taylor
Debt Instrument
Borrowings				$ 35

Debt - Schedule of the Change_2

Debt - Schedule of the Change in Debt under the Kudu Facility (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument
Beginning balance	$ 376.4
Repayments	(154.7)	$ (4.5)	$ (22.9)
Ending balance	693	376.4
Kudu Bank Facility | Kudu
Debt Instrument
Beginning balance	86.3
Ending balance		86.3
Kudu Bank Facility | Kudu | Term Loan
Debt Instrument
Beginning balance	89.2	57	0
Borrowings	3	32.2	57
Repayments	(92.2)	0	0
Ending balance	0	89.2	57
Long-term line of credit		89.2
Kudu Credit Facility | Kudu
Debt Instrument
Ending balance	218.2
Kudu Credit Facility | Kudu | Term Loan
Debt Instrument
Beginning balance	0	0	0
Borrowings	232	0	0
Repayments	(6.6)	0	0
Ending balance	225.4	$ 0	$ 0
Long-term line of credit	$ 225.4

Debt - Schedule of Weighted Ave

Debt - Schedule of Weighted Average Interest Rates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument
Interest expense	$ 43.8	$ 29.5	$ 17.6
NSM
Debt Instrument
Weighted Average	276	274.2
Interest expense	$ 22.6	$ 22
Weighted Average Interest rate	8.20%	8.00%
NSM | Other Debt
Debt Instrument
Interest expense	$ 0.7	$ 0.1
NSM | Designated as Hedging Instrument
Debt Instrument
Weighted Average	146.9	148.4
Interest expense	$ 13.2	$ 13.4
Weighted Average Interest rate	9.00%	9.00%
NSM | Not Designated as Hedging Instrument
Debt Instrument
Weighted Average	$ 129.1	$ 125.8
Interest expense	$ 9.4	$ 8.6
Weighted Average Interest rate	7.30%	6.80%

Income Taxes - Income Tax (Bene

Income Taxes - Income Tax (Benefit) Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current income tax (expense) benefit:
U.S. federal	$ (3.8)	$ (10.4)	$ 0.9
State	(2.1)	(4.2)	(3.7)
Non-U.S.	(3.9)	(1.1)	(1.7)
Total current income tax (expense) benefit	(9.8)	(15.7)	(4.5)
Deferred income tax (expense) benefit:
U.S. federal	(4.9)	23.2	(14.9)
State	(5.6)	10.3	(10.4)
Non-U.S.	(18.3)	2.7	0.5
Total deferred income tax (expense) benefit	(28.8)	36.2	(24.8)
Total income tax (expense) benefit	$ (38.6)	$ 20.5	$ (29.3)

Income Taxes - Effective Rate R

Income Taxes - Effective Rate Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Contingency [Line Items]
Tax (expense) benefit at the U.S. statutory rate	$ 63.4	$ (135.5)	$ (85.1)
Differences in taxes resulting from:
Non-U.S. earnings, net of foreign taxes	(77.2)	78.4	27.1
Tax rate changes	(11.2)	2.7	(5.7)
State taxes	(6.2)	(8.5)	(17.5)
Member’s surplus contributions	(5.6)	(4.8)	(3.6)
Change in valuation allowance	(2.4)	(29.2)	63.6
Officer compensation	(1.5)	(1.1)	0
Withholding tax	(0.3)	(5)	(1.6)
Tax exempt interest and dividends	0.2	0.8	1.1
Reorganization	0	130.5	0
Tax reserve adjustments	0	1.9	(0.7)
Other, net	2.2	(9.7)	(6.9)
Total income tax (expense) benefit	(38.6)	20.5	(29.3)
Pre-tax income (loss)	(302)	645.2	405.1
Tax Payments and Receipts
Net income tax payments to US	(0.1)	16.2	3.7
Non-US
Differences in taxes resulting from:
Pre-tax income (loss)	$ (319)	$ 327.8	$ 100.4

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets related to:
U.S. federal and state net operating and capital loss carryforwards	$ 102.8	$ 79.6
Non-U.S. net operating loss carryforwards	47.1	50.5
Incentive compensation	14.6	17.5
Accrued interest	10.8	7.9
Deferred acquisition costs	6.4	5.5
Tax credit carryforwards	4.9	5.5
Other items	0.7	1.3
Total gross deferred tax assets	187.3	167.8
Less: valuation allowances	92.3	97.4
Total net deferred tax assets	95	70.4
Deferred tax liabilities related to:
Member’s surplus contributions	60.4	52.9
Purchase accounting	48.5	5.1
Investment basis difference	33.7	11.8
Net unrealized investment gains (losses)	10.7	0.3
Deferred underwriting	4.1	0
Other items	2.7	2.8
Total deferred tax liabilities	160.1	72.9
Net deferred tax asset (liability)	$ (65.1)	$ (2.5)

Income Taxes - Valuation Allowa

Income Taxes - Valuation Allowance (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Valuation Allowance [Line Items]
Valuation allowance	$ 92.3	$ 97.4
Change in valuation allowance	2.4	29.2	$ (63.6)
Income tax expense (benefit)	38.6	(20.5)	$ 29.3
U.S. losses and other federal deferred tax benefits
Valuation Allowance [Line Items]
Valuation allowance	42.9	46.5
Net operating losses in Luxembourg subsidiaries
Valuation Allowance [Line Items]
Valuation allowance	25.2
Net Operating Losses in Israel Subsidiaries
Valuation Allowance [Line Items]
Valuation allowance	21.9	20
Net Operating Losses in United Kingdom Subsidiaries
Valuation Allowance [Line Items]
Valuation allowance	2.3
Luxembourg | U.S. losses and other federal deferred tax benefits
Valuation Allowance [Line Items]
Change in valuation allowance	(1.6)	4.2
United Kingdom | Net Operating Losses in United Kingdom Subsidiaries
Valuation Allowance [Line Items]
Change in valuation allowance	(1.9)	1
United States | Net Operating Losses in US Branches
Valuation Allowance [Line Items]
Income tax expense (benefit)	0.6
Israel | Net Operating Losses in Israel Subsidiaries
Valuation Allowance [Line Items]
Change in valuation allowance	1.9	2.7
Subsidiaries | Luxembourg | Net operating losses in Luxembourg subsidiaries
Valuation Allowance [Line Items]
Valuation allowance		26.8
Subsidiaries | United Kingdom | Net operating losses in Luxembourg subsidiaries
Valuation Allowance [Line Items]
Valuation allowance		4.1
Guilford Holdings, Inc. | United States
Valuation Allowance [Line Items]
Change in valuation allowance	(3.6)
Income tax expense (benefit)		14.9
BAM | United States
Valuation Allowance [Line Items]
Income tax expense (benefit)	7.8	4.5
BAM | United States | MSC
Valuation Allowance [Line Items]
Income tax expense (benefit)	(7.5)	(9.7)
BAM | United States | Foreign Tax Credits
Valuation Allowance [Line Items]
Income tax expense (benefit)	$ (0.8)	$ 1.9

Income Taxes - Net Operating an

Income Taxes - Net Operating and Capital Loss Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Net deferred tax assets
Total net deferred tax assets	$ 95	$ 70.4
Tax credit carryforwards, foreign	4.7
Operating and Capital Loss Carryforward
Net deferred tax assets
Operating loss carryforwards	661.8
Gross deferred tax asset	144.7
Valuation allowance	(129.3)
Total net deferred tax assets	15.4
Operating and Capital Loss Carryforward | United States
Net deferred tax assets
Operating loss carryforwards	464.5
Gross deferred tax asset	97.6
Valuation allowance	(83.2)
Total net deferred tax assets	14.4
Operating and Capital Loss Carryforward | Luxembourg
Net deferred tax assets
Operating loss carryforwards	97.1
Gross deferred tax asset	24.3
Valuation allowance	(24.3)
Total net deferred tax assets	0
Operating and Capital Loss Carryforward | United Kingdom
Net deferred tax assets
Operating loss carryforwards	6.9
Gross deferred tax asset	1.4
Valuation allowance	(0.4)
Total net deferred tax assets	1
Operating and Capital Loss Carryforward | Israel
Net deferred tax assets
Operating loss carryforwards	93.3
Gross deferred tax asset	21.4
Valuation allowance	(21.4)
Total net deferred tax assets	0
2021-2025 | Operating and Capital Loss Carryforward
Net deferred tax assets
Operating loss carryforwards	0
2021-2025 | Operating and Capital Loss Carryforward | United States
Net deferred tax assets
Operating loss carryforwards	0
2021-2025 | Operating and Capital Loss Carryforward | Luxembourg
Net deferred tax assets
Operating loss carryforwards	0
2021-2025 | Operating and Capital Loss Carryforward | United Kingdom
Net deferred tax assets
Operating loss carryforwards	0
2021-2025 | Operating and Capital Loss Carryforward | Israel
Net deferred tax assets
Operating loss carryforwards	0
2026-2030 | Operating and Capital Loss Carryforward
Net deferred tax assets
Operating loss carryforwards	0
2026-2030 | Operating and Capital Loss Carryforward | United States
Net deferred tax assets
Operating loss carryforwards	0
2026-2030 | Operating and Capital Loss Carryforward | Luxembourg
Net deferred tax assets
Operating loss carryforwards	0
2026-2030 | Operating and Capital Loss Carryforward | United Kingdom
Net deferred tax assets
Operating loss carryforwards	0
2026-2030 | Operating and Capital Loss Carryforward | Israel
Net deferred tax assets
Operating loss carryforwards	0
2031-2040 | Operating and Capital Loss Carryforward
Net deferred tax assets
Operating loss carryforwards	319
2031-2040 | Operating and Capital Loss Carryforward | United States
Net deferred tax assets
Operating loss carryforwards	250.7
2031-2040 | Operating and Capital Loss Carryforward | Luxembourg
Net deferred tax assets
Operating loss carryforwards	68.3
2031-2040 | Operating and Capital Loss Carryforward | United Kingdom
Net deferred tax assets
Operating loss carryforwards	0
2031-2040 | Operating and Capital Loss Carryforward | Israel
Net deferred tax assets
Operating loss carryforwards	0
No expiration date | Operating and Capital Loss Carryforward
Net deferred tax assets
Operating loss carryforwards	342.8
No expiration date | Operating and Capital Loss Carryforward | United States
Net deferred tax assets
Operating loss carryforwards	213.8
No expiration date | Operating and Capital Loss Carryforward | Luxembourg
Net deferred tax assets
Operating loss carryforwards	28.8
No expiration date | Operating and Capital Loss Carryforward | United Kingdom
Net deferred tax assets
Operating loss carryforwards	6.9
No expiration date | Operating and Capital Loss Carryforward | Israel
Net deferred tax assets
Operating loss carryforwards	$ 93.3

Income Taxes - ASC 740-10 (Deta

Income Taxes - ASC 740-10 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Contingency [Line Items]
Percentage of likelihood for realization of benefit upon ultimate settlement	50.00%
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns
Balance at beginning	$ 0	$ 2.4	$ 1.1
Changes in prior year tax positions		0.1	1.3
Tax positions taken during the current year		0.1
Reorganization		(2.6)
Balance at year end	0	0	2.4
Permanent Differences
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns
Balance at beginning	0	2.4	1.1
Changes in prior year tax positions		0.1	1.3
Tax positions taken during the current year		0.1
Reorganization		(2.6)
Balance at year end	0	0	2.4
Temporary Differences
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns
Balance at beginning	0	0	0
Balance at year end	0	0	0
Interest and Penalties Net of Tax Benefit
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns
Balance at beginning	0	0	0
Balance at year end	$ 0	$ 0	$ 0

Derivatives - Narrative (Detail

Derivatives - Narrative (Details)	Aug. 18, 2020	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Jun. 04, 2020USD ($)	Jun. 04, 2020GBP (£)	Apr. 07, 2020USD ($)	Apr. 06, 2020USD ($)	Dec. 31, 2018USD ($)	Jun. 15, 2018USD ($)
Derivative [Line Items]
Total commitment under revolving credit facility							$ 291,400,000
Debt		$ 693,000,000	$ 376,400,000
NSM
Derivative [Line Items]
Debt		$ 272,100,000	$ 272,600,000
Debt, weighted average interest rate		8.20%	8.00%
NSM Bank Facility | NSM
Derivative [Line Items]
Total commitment under revolving credit facility								$ 234,000,000
Debt		$ 277,600,000	$ 277,400,000	$ 221,300,000					$ 180,400,000
NSM Bank Facility | NSM | Term Loan
Derivative [Line Items]
Total commitment under revolving credit facility								$ 224,000,000
Debt		$ 271,200,000	271,300,000
Interest Rate Swap | NSM
Derivative [Line Items]
Fixed interest rate										2.97%
Variable interest rate		1.00%
Net interest expense		$ 2,500,000	2,500,000	$ 1,100,000
Derivative, fair value, net		4,800,000	8,200,000
Change in fair value of derivative instruments		(3,400,000)	(1,600,000)
Interest Rate Swap | NSM Bank Facility | NSM | Term Loan
Derivative [Line Items]
Total commitment under revolving credit facility										$ 151,000,000
Debt		146,100,000
Interest Rate Cap | NSM
Derivative [Line Items]
Derivative, fair value, net		200,000	100,000
Premiums paid		$ 100,000
GBP-LIBOR rate		0.26%
Decrease in fair value of derivative		$ (200,000)	$ (100,000)
Interest Rate Cap | NSM | London Interbank Offered Rate (LIBOR)
Derivative [Line Items]
Derivative, cap interest rate		1.25%
Interest Rate Cap | NSM Bank Facility | NSM
Derivative [Line Items]
Debt instrument extension term (in years)	1 year
Interest Rate Cap | NSM Bank Facility | NSM | United Kingdom, Pounds
Derivative [Line Items]
Notational amount | £						£ 42,500,000
Interest Rate Cap | NSM Bank Facility | NSM | United States of America, Dollars
Derivative [Line Items]
Notational amount					$ 52,400,000
Designated as Hedging Instrument | NSM
Derivative [Line Items]
Debt, weighted average interest rate		9.00%	9.00%
Designated as Hedging Instrument | Interest Rate Swap | NSM Bank Facility | NSM | Term Loan
Derivative [Line Items]
Debt		$ 146,100,000
Debt, weighted average interest rate		9.00%

Municipal Bond Guarantee Insu_3

Municipal Bond Guarantee Insurance - Narrative (Details) - USD ($) $ in Millions	1 Months Ended			3 Months Ended		12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Jan. 31, 2020	Mar. 31, 2021	Jun. 30, 2018	Dec. 31, 2021	Jan. 01, 2025	Dec. 31, 2022	Jun. 30, 2020	Sep. 30, 2019	Dec. 31, 2012
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Percentage of risk premium ceded	60.00%					60.00%
Insurance-linked securities, term				12 years	12 years
Insurance-linked securities, callable term				5 years	5 years
Cash and investments included in collateral trust	$ 481.7					$ 481.7
HG Re
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Percentage of par value of policy reinsured	15.00%					15.00%
Trust balance	$ 250.2	$ 222.8				$ 250.2
HG Global
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Surplus notes											$ 503
Percentage of par value of policy reinsured	15.00%					15.00%
Percent over a target trust balance						102.00%
Supplement trust target	$ 603					$ 603
BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Principal	89,196.5	75,287.7		$ 800		89,196.5				$ 1,100
Additional municipal bond guarantee									$ 36.9
HG Global
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Collateral held in supplement trust	852	827.1				852
Cash and investments included in collateral trust	481.7	434.5				481.7
Interest receivable	157.6	155.7				157.6
BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Surplus notes	364.6	388.2				364.6
Interest receivable	5.7	4.4				5.7
Accrued interest on surplus notes	157.6	155.7				157.6
Supplemental Trust | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Cash repayments on notes	23.6	21.5	$ 47.9
Accrued interest on surplus notes	0.4	0.2	0.9			0.4
Surplus Note | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Cash repayments on notes	33.8	30.1	65
Accrued interest on surplus notes	9.8	8.4	16.2			$ 9.8
BAM | Fidus Re Ltd.
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Losses above retention, percentage of liability				90.00%	90.00%
Fidus Re Ltd. | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Insurance linked securities				$ 150	$ 100
Aggregate loss limit on contracts				135	165
Reimbursement guarantee under contracts				$ 150	100
Percentage of financial guaranty policies covered						38.00%
Percentage of quota share reinsurance agreement				100.00%
Fidus Re Ltd. | BAM | 2018 Covered Portfolio
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Percentage of financial guaranty policies covered						33.00%
Maximum | BAM | HG Global
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Aggregate loss limit on contracts			$ 75
Maximum | Fidus Re Ltd. | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Aggregate loss limit on contracts				$ 301.7	$ 276.1
Series A BAM Surplus Note | HG Global
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Trust balance	$ 601.8	$ 604.3				$ 601.8
Fixed interest rate | Surplus Note | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Interest rate	8.00%					8.00%
Fixed interest rate | Surplus Note | BAM | Forecast
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Interest rate							8.00%
U.S. treasury rate plus | Surplus Note | BAM
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Basis spread on variable rate						3.00%
Effective yield (as a percent)	3.20%					3.20%
U.S. treasury rate plus | Surplus Note | BAM | Forecast
Schedule of Insured Financial Obligations with Credit Deterioration [Line Items]
Effective yield (as a percent)								3.20%

Municipal Bond Guarantee Insu_4

Municipal Bond Guarantee Insurance - Schedule of Municipal Bond Guarantee Insured Obligations (Details) - BAM $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)Contract	Dec. 31, 2020USD ($)Contract	Mar. 31, 2021USD ($)	Sep. 30, 2019USD ($)
Guarantor Obligations [Line Items]
Contracts outstanding | Contract	12,350	10,997
Remaining weighted average contract period (in years)	10 years 9 months 18 days	10 years 8 months 12 days
Principal	$ 89,196.5	$ 75,287.7	$ 800	$ 1,100
Interest	41,486.5	36,448.8
Total debt service outstanding	130,683	111,736.5
Gross unearned insurance premiums	$ 266.3	$ 237.5

Municipal Bond Guarantee - Sche

Municipal Bond Guarantee - Schedule of Municipal Guarantee Insurance Contracts, Premium Received Over Contract Period (Details) - BAM - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Guarantor Obligations [Line Items]
January 1, 2022 - March 31, 2022	$ 6.4
April 1, 2022 - June 30, 2022	6.4
July 1, 2022 - September 30, 2022	6.3
October 1, 2022 - December 31, 2022	6.1
Total 2021	25.2
2023	23.9
2024	22.2
2025	20.6
2026	19.1
2027 and thereafter	155.3
Total gross unearned insurance premiums	$ 266.3	$ 237.5

Municipal Bond Guarantee Insu_5

Municipal Bond Guarantee Insurance - Schedule of Net Written Premiums (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earned premiums:
Net earned premiums	$ 664.2	$ 22.8	$ 16.3
HG/BAM
Written premiums:
Direct	51.2	61.5	28.1
Assumed	4.6	0.2	10.6
Net written premiums	55.8	61.7	38.7
Earned premiums:
Direct	23.2	19.4	13.6
Assumed	3.7	3.4	2.7
Net earned premiums	26.9	22.8	16.3
HG Global-BAM
Earned premiums:
Net earned premiums	$ 26.9	$ 22.8	$ 16.3

Earnings Per Share - Schedule o

Earnings Per Share - Schedule of Earnings Per Share from Continuing Operations (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Basic and diluted earnings per share numerators (in millions):
Net income (loss) attributable to White Mountains’s common shareholders	$ (275.4)	$ 708.7	$ 414.5
Less: total (loss) income from discontinued operations, net of tax	18.7	(2.3)	0.8
Net income (loss) from continuing operations attributable to White Mountains’s common shareholders	(294.1)	711	413.7
Allocation of (earnings) losses to participating restricted common shares	3.5	(9.3)	(5.3)
Basic and diluted earnings (losses) per share numerators	$ (290.6)	$ 701.7	$ 408.4
Basic earnings per share denominators (in thousands):
Total average common shares outstanding during the period (in shares)	3,079,000	3,122,200	3,181,600
Average unvested restricted common shares (in shares)	(36,500)	(40,800)	(40,500)
Basic earnings (losses) per share denominator (in shares)	3,042,500	3,081,400	3,141,100
Diluted earnings per share denominator (in thousands):
Average outstanding dilutive options to acquire common shares (in shares)	3,079,000	3,122,200	3,181,600
Average unvested restricted common shares (in shares)	(36,500)	(40,800)	(40,500)
Diluted earnings (loss) per share denominator (in shares)	3,042,500	3,081,400	3,141,100
Diluted earnings per share (in dollars) - continuing operations:
Dividends declared and paid (usd per share)	$ 1	$ 1	$ 1
Undistributed earnings (losses) (usd per share)	(96.53)	226.72	129.02
Basic and diluted earnings (losses) per share (usd per share)	$ (95.53)	$ 227.72	$ 130.02

Earnings Per Share - Schedule_2

Earnings Per Share - Schedule of Undistributed Net Earnings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net income (loss) attributable to White Mountains’s common shareholders, net of restricted common share amounts	$ (290.6)	$ 701.7	$ 408.4
Dividends declared, net of restricted common share amounts	(3.1)	(3.1)	(3.2)
Total undistributed net earnings (losses), net of restricted common share amounts	$ (293.7)	$ 698.6	$ 405.2

Employee Share-Based Incentiv_3

Employee Share-Based Incentive Compensation Plans - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)multipliershares	Dec. 31, 2020USD ($)shares	Dec. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)
Performance Shares
Share-based compensation arrangement by share-based payment award
Vesting period	3 years
Multiplier for determining payout, low end of range | multiplier	0
Multiplier for determining payout, high end of range | multiplier	2
Performance cycle period	3 years
Unamortized grant date fair value | $	$ 12
Performance Shares | 2021 – 2023
Share-based compensation arrangement by share-based payment award
Targeted performance goal (as a percent)	8.00%
Payout for maximum growth target percentage	200.00%
Performance Shares | 2019 – 2021
Share-based compensation arrangement by share-based payment award
Targeted performance goal (as a percent)	7.00%
Payout for maximum growth target percentage	200.00%
Performance Shares | 2020 – 2022
Share-based compensation arrangement by share-based payment award
Targeted performance goal (as a percent)	7.00%
Payout for maximum growth target percentage	200.00%
Performance Shares | Minimum | 2021 – 2023
Share-based compensation arrangement by share-based payment award
Payout for minimum growth target percentage	3.00%
Performance Shares | Minimum | 2019 – 2021
Share-based compensation arrangement by share-based payment award
Payout for minimum growth target percentage	2.00%
Performance Shares | Minimum | 2020 – 2022
Share-based compensation arrangement by share-based payment award
Payout for minimum growth target percentage	2.00%
Performance Shares | Maximum | 2021 – 2023
Share-based compensation arrangement by share-based payment award
Payout for minimum growth target percentage	13.00%
Performance Shares | Maximum | 2019 – 2021
Share-based compensation arrangement by share-based payment award
Payout for minimum growth target percentage	12.00%
Performance Shares | Maximum | 2020 – 2022
Share-based compensation arrangement by share-based payment award
Payout for minimum growth target percentage	12.00%
Range Of Performance Cycle From 2021 to 2023 | W T M Incentive and Phantom Plan
Share-based compensation arrangement by share-based payment award
Performance shares (in shares)	13,475
Restricted Share Cliff Vesting in January 2023 | W T M Incentive and Phantom Plan
Share-based compensation arrangement by share-based payment award
Performance shares (in shares)		14,055
Restricted Share Cliff Vesting in January 2022 | W T M Incentive and Phantom Plan
Share-based compensation arrangement by share-based payment award
Performance shares (in shares)			15,600
Restricted Stock
Share-based compensation arrangement by share-based payment award
Vesting period	3 years
Performance shares (in shares)	13,475	14,055	15,600
Unamortized grant date fair value | $	$ 15.9	$ 15.2	$ 16.7	$ 12.5
Restricted Share Cliff Vesting in January 2024 | W T M Incentive and Phantom Plan
Share-based compensation arrangement by share-based payment award
Performance shares (in shares)	13,475

Employee Share-Based Incentiv_4

Employee Share-Based Incentive Compensation Plans - Performance Shares (Details) - Performance Shares - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Target Performance Shares Outstanding
Beginning of period (in shares)	42,458	42,473	40,616
Shares paid or expired (in shares)	(14,336)	(14,070)	(13,715)
New grants (in shares)	13,475	14,055	15,600
Forfeitures and cancellations (in shares)	(769)	0	(28)
Expense recognized (in shares)	0	0	0
End of period (in shares)	40,828	42,458	42,473
Accrued Expense
Beginning of period	$ 56.3	$ 43.7	$ 31.7
Shares paid or expired	(35.2)	(27.7)	(18.1)
New grants	0	0	0
Forfeitures and cancellations	0.4	(0.4)	(0.1)
Expense recognized	20.7	40.7	30.2
End of period	$ 42.2	$ 56.3	$ 43.7
Range Of Performance Cycle From 2018 to 2020 | W T M Incentive and Phantom Plan
Accrued Expense
Payout for maximum growth target percentage	200.00%
Range Of Performance Cycle From 2017 to 2019 | W T M Incentive and Phantom Plan
Accrued Expense
Payout for maximum growth target percentage		180.00%
Payout for minimum growth target percentage		174.00%
Range Of Performance Cycle From 2016-2018 | W T M Incentive and Phantom Plan
Accrued Expense
Payout for maximum growth target percentage			166.00%
Payout for minimum growth target percentage			139.00%

Employee Share-Based Incentiv_5

Employee Share-Based Incentive Compensation Plans - Performance Shares Granted (Details) - Performance Shares - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based compensation arrangement by share-based payment award
Number of nonvested options before forfeitures (in shares)	41,450
Incentive compensation payable before forfeitures	$ 42.8
Assumed forfeitures (in shares)	(622)
Assumed forfeitures	$ (0.6)
Shares outstanding (in shares)	40,828	42,458	42,473	40,616
Accrued incentive compensation	$ 42.2	$ 56.3	$ 43.7	$ 31.7
2019 – 2021
Share-based compensation arrangement by share-based payment award
Number of nonvested options before forfeitures (in shares)	14,625
Incentive compensation payable before forfeitures	$ 25.3
2020 – 2022
Share-based compensation arrangement by share-based payment award
Number of nonvested options before forfeitures (in shares)	13,350
Incentive compensation payable before forfeitures	$ 15.4
2021 – 2023
Share-based compensation arrangement by share-based payment award
Number of nonvested options before forfeitures (in shares)	13,475
Incentive compensation payable before forfeitures	$ 2.1

Employee Share-Based Incentiv_6

Employee Share-Based Incentive Compensation Plans - Restricted Shares (Details) - Restricted Stock - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Restricted Shares
Beginning of period (in shares)	43,105	43,395	41,510
Issued (in shares)	13,475	14,055	15,600
Vested (in shares)	(17,936)	(14,345)	(13,715)
Forfeited (in shares)	(794)	0	0
Expense recognized (in shares)	0	0	0
End of period (in shares)	37,850	43,105	43,395
Unamortized Issue Date Fair Value
Beginning of period	$ 15.2	$ 16.7	$ 12.5
Issued	16.1	15.1	14.5
Vested	0	0	0
Forfeited	(0.8)	0	0
Expense recognized	(14.6)	(16.6)	(10.3)
End of period	$ 15.9	$ 15.2	$ 16.7

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Leases [Abstract]
ROU lease asset	$ 42.2	$ 37.6
Operating lease liability	$ 45.2	$ 38.3

Leases - Schedule of Lease Cost

Leases - Schedule of Lease Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Leases [Abstract]
Lease cost	$ 9.9	$ 7.7
Less: sublease income	0.4	0.4
Net lease cost	$ 9.5	$ 7.3

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Payments on Operating Leases (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Leases [Abstract]
2022	$ 10.9
2023	9.9
2024	8.5
2025	6.8
2026	4.3
Thereafter	11.9
Total undiscounted lease payments	52.3
Less: present value adjustment	(7.1)
Operating lease liability	$ 45.2	$ 38.3

Leases - Schedule of Right-of-U

Leases - Schedule of Right-of-Use Assets and Lease Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other assets	Other assets
ROU lease asset	$ 42.2	$ 37.6
Operating Lease, Liability, Statement of Financial Position [Extensible List]	Other liabilities	Other liabilities
Lease liability	$ 45.2	$ 38.3
Weighted Average Incremental Borrowing Rate	5.00%	4.60%
HG/BAM
Lessee, Lease, Description [Line Items]
ROU lease asset	$ 7.6	$ 10.1
Lease liability	8.1	10.1
NSM
Lessee, Lease, Description [Line Items]
ROU lease asset	14	17.1
Lease liability	15.2	17.1
Kudu
Lessee, Lease, Description [Line Items]
ROU lease asset	6.5	2
Lease liability	7.1	2
Other
Lessee, Lease, Description [Line Items]
ROU lease asset	7.1	8.4
Lease liability	7.8	$ 9.1
Ark
Lessee, Lease, Description [Line Items]
ROU lease asset	7
Lease liability	$ 7

Common Shareholders_ Equity a_3

Common Shareholders’ Equity and Non-controlling Interests (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Common Shares Repurchased and Retired
Value of common shares repurchased and retired	$ 107.5	$ 85.1	$ 4.9
Value of each common share repurchased and retired (in usd per share)	$ 1,091	$ 859	$ 858
Common Shares Issued
Stock issued (in shares)	15,066	15,745	17,917
Dividends on Common Shares
Cash dividends declared and paid	$ 3.1	$ 3.2	$ 3.2
Dividends declared and paid (in usd per share)	$ 1
Non-controlling Equity	$ 156.6	$ (88.1)
HG Global
Dividends on Common Shares
Non-controlling Percentage	3.10%	3.10%
Ark
Dividends on Common Shares
Non-controlling Percentage	28.00%	0.00%
NSM
Dividends on Common Shares
Non-controlling Percentage	3.50%	3.40%
Kudu
Dividends on Common Shares
Non-controlling Percentage	2.50%	0.70%
BAM
Dividends on Common Shares
Non-controlling Percentage	100.00%	100.00%
Common equity securities
Common Shares Repurchased and Retired
Common shares repurchased and retired (in shares)	98,511	99,087	5,679
Restricted Stock
Common Shares Issued
Stock issued (in shares)	13,475	14,055	15,600
General Board Authorization
Common Shares Repurchased and Retired
Additional authorized repurchase of common shares (in shares)	451,224
Common shares repurchased and retired (in shares)	91,293
Value of common shares repurchased and retired	$ 100
Value of each common share repurchased and retired (in usd per share)	$ 1,095
Directors | Restricted Stock
Common Shares Issued
Shares issued to directors (in shares)	1,591	1,440	2,317
Repurchased for Employee Benefit Plans
Common Shares Repurchased and Retired
Common shares repurchased and retired (in shares)	7,218
MediaAlpha | Restricted Stock
Common Shares Issued
Stock issued (in shares)		250
HG Global
Dividends on Common Shares
Non-controlling Equity	$ 8.9	$ 13.5
Ark
Dividends on Common Shares
Non-controlling Equity	230.7	0
NSM
Dividends on Common Shares
Non-controlling Equity	16.7	17
Kudu
Dividends on Common Shares
Non-controlling Equity	12.4	2.3
Other
Dividends on Common Shares
Non-controlling Equity	11.9	2.4
BAM
Dividends on Common Shares
Non-controlling Equity	(124)	(123.3)
Total Non-Controlling Excluding Reciprocals
Dividends on Common Shares
Non-controlling Equity	$ 280.6	$ 35.2

Statutory Capital and Surplus (

Statutory Capital and Surplus (Details) - USD ($)	1 Months Ended			12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Jan. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2012
Statutory Accounting Practices [Line Items]
Cash and investments included in collateral trust	$ 481,700,000			$ 481,700,000
Other long-term investments	1,377,800,000	$ 786,800,000		1,377,800,000	$ 786,800,000
Total assets	7,000,700,000	4,831,400,000		7,000,700,000	4,831,400,000
Lloyds Bank
Statutory Accounting Practices [Line Items]
Total assets	343,600,000			343,600,000
HG Global-BAM
Statutory Accounting Practices [Line Items]
Total assets	1,044,800,000	1,017,800,000		1,044,800,000	1,017,800,000
BAM
Statutory Accounting Practices [Line Items]
Surplus notes	364,600,000	388,200,000		364,600,000	388,200,000
Interest receivable	5,700,000	4,400,000		5,700,000	4,400,000
Accrued interest on surplus notes	157,600,000	155,700,000		157,600,000	155,700,000
Ark
Statutory Accounting Practices [Line Items]
Total assets	3,027,000,000	0		3,027,000,000	0
NSM
Statutory Accounting Practices [Line Items]
Distributions made				8,000,000
Kudu
Statutory Accounting Practices [Line Items]
Distributions made				19,400,000
Total assets	727,100,000	430,200,000		727,100,000	430,200,000
Other Operations
Statutory Accounting Practices [Line Items]
Unrestricted cash	453,500,000			453,500,000
Other long-term investments	170,500,000			170,500,000
Total assets	1,208,400,000	2,381,500,000		1,208,400,000	2,381,500,000
HG Global
Statutory Accounting Practices [Line Items]
Collateral held in supplement trust	852,000,000	827,100,000		852,000,000	827,100,000
Cash and investments included in collateral trust	481,700,000	434,500,000		481,700,000	434,500,000
Interest receivable	157,600,000	155,700,000		157,600,000	155,700,000
HG Re | HG Global-BAM
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	760,000,000			760,000,000
Surplus required	1			1
Cash outside of collateral trusts	3,100,000			3,100,000
Collateral held in supplement trust	852,000,000			852,000,000
Cash and investments outside of collateral trusts	9,400,000			9,400,000
Accrued interest held in supplemental trust	116,800,000			116,800,000
BAM | HG Global-BAM
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	298,100,000			298,100,000
Surplus required	66,000,000			66,000,000
Statutory net loss				(49,300,000)	(59,300,000)	$ (38,300,000)
Ark
Statutory Accounting Practices [Line Items]
Other long-term investments	326,200,000	0		326,200,000	0
Total assets	3,027,000,000	0		3,027,000,000	0
Ark | Ark
Statutory Accounting Practices [Line Items]
Statutory capital and surplus	780,300,000			780,300,000
Surplus required	$ 288,200,000			$ 288,200,000
Percent of statutory capital balance	15.00%			15.00%
Percent of statutory capital and surplus balance	25.00%			25.00%
Dividend or capital distributions, maximum				$ 113,600,000
Statutory surplus balance	$ 757,600,000			757,600,000
Unrestricted cash	4,000,000			$ 4,000,000
HG Global
Statutory Accounting Practices [Line Items]
Percent over a target trust balance				102.00%
Supplement trust target	603,000,000			$ 603,000,000
Surplus notes							$ 503,000,000
HG Global | HG Global-BAM
Statutory Accounting Practices [Line Items]
Preferred stock value	$ 619,000,000			$ 619,000,000
Ownership interest (as a percent)	96.90%			96.90%
Preferred stock dividend rate (as a percent)				6.00%
NSM | NSM
Statutory Accounting Practices [Line Items]
Unrestricted cash	$ 22,300,000			$ 22,300,000
Kudu
Statutory Accounting Practices [Line Items]
Unrestricted cash	16,900,000			16,900,000
Surplus Note | BAM
Statutory Accounting Practices [Line Items]
Cash repayments on notes	33,800,000	30,100,000	$ 65,000,000
Accrued interest on surplus notes	$ 9,800,000	8,400,000	16,200,000	$ 9,800,000	8,400,000
Surplus Note | BAM | U.S. treasury rate plus
Statutory Accounting Practices [Line Items]
Basis spread on variable rate				3.00%
Effective yield (as a percent)	3.20%			3.20%
Surplus Note | BAM | Fixed interest rate
Statutory Accounting Practices [Line Items]
Interest rate	8.00%			8.00%
Supplemental Trust | BAM
Statutory Accounting Practices [Line Items]
Cash repayments on notes	$ 23,600,000	21,500,000	47,900,000
Accrued interest on surplus notes	400,000	$ 200,000	$ 900,000	$ 400,000	$ 200,000
Preferred stocks | HG Global
Statutory Accounting Practices [Line Items]
Dividends				22,000,000
Preferred stocks | HG Global | HG Global-BAM
Statutory Accounting Practices [Line Items]
Dividends payable	414,700,000			414,700,000
Preferred stocks | White Mountains | HG Global | HG Global-BAM
Statutory Accounting Practices [Line Items]
Dividends				21,300,000
Dividends payable	400,500,000			400,500,000
Common Equities | Other Operations
Statutory Accounting Practices [Line Items]
Distributions made				3,100,000
Common Equities | MediaAlpha
Statutory Accounting Practices [Line Items]
Common stock	$ 261,600,000			$ 261,600,000

Segment Information - Income St

Segment Information - Income Statement Information (Details) $ in Millions	Feb. 26, 2019USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2021USD ($)segment	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Segment reporting information
Number of operating segments | segment			5
Earned insurance premiums			$ 664.2	$ 22.8	$ 16.3
Net investment income			82.5	131	79.7
Net realized and unrealized investment gains (losses)			134.2	30.8	253.2
Realized gain (loss) from the 2019 MediaAlpha Transaction					67.5
Commission revenues			267.6	240.8	249.1
Other revenues			176.6	69.3	47.6
Total revenues			944.8	1,180.7	893.4
Loss and loss adjustment expenses			314.8
Insurance acquisition expenses			186.3	7	5.7
Cost of sales			69.3	11.3	48.1
General and administrative expenses			482.9	387.4	328.2
Broker commission expense			80.2	75.3	64.8
Change in fair value of contingent consideration			1	(3.3)	2.1
Amortization of other intangible assets			39.8	28.3	21.8
Loss on assets held for sale			28.7
Interest expense			43.8	29.5	17.6
Total expenses			1,246.8	535.5	488.3
Pre-tax income (loss)			(302)	645.2	405.1
MediaAlpha
Segment reporting information
Net realized and unrealized investment gains (losses) from investment in MediaAlpha			(380.3)	686	180
Total revenues		$ 359.2
Total expenses		$ 336.3
HG Global-BAM
Segment reporting information
Earned insurance premiums			26.9	22.8	16.3
Net investment income			17.5	19.5	21.6
Net realized and unrealized investment gains (losses)			(22.9)	23.7	27.1
Realized gain (loss) from the 2019 MediaAlpha Transaction					0
Commission revenues			0	0	0
Other revenues			1.5	2.5	1.6
Total revenues			23	68.5	66.6
Loss and loss adjustment expenses			0
Insurance acquisition expenses			8.3	7	5.7
Cost of sales			0	0	0
General and administrative expenses			57.1	56.8	50.9
Broker commission expense			0	0	0
Change in fair value of contingent consideration			0	0	0
Amortization of other intangible assets			0	0	0
Loss on assets held for sale			0
Interest expense			0	0	0
Total expenses			65.4	63.8	56.6
Pre-tax income (loss)			(42.4)	4.7	10
HG Global-BAM | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains (losses) from investment in MediaAlpha			0	0	0
Ark
Segment reporting information
Earned insurance premiums			637.3	0	0
Net investment income			2.9	0	0
Net realized and unrealized investment gains (losses)			16.5	0	0
Commission revenues			0
Other revenues			11.8	0	0
Total revenues			668.5	0	0
Loss and loss adjustment expenses			314.8	0	0
Insurance acquisition expenses			178	0	0
Cost of sales			0
General and administrative expenses			115.5	0	0
Broker commission expense			0
Change in fair value of contingent consideration			0
Amortization of other intangible assets			0
Loss on assets held for sale			0
Interest expense			7.3	0	0
Total expenses			615.6	0	0
Pre-tax income (loss)			52.9
Ark | United Kingdom
Segment reporting information
Earned insurance premiums			459.3
Ark | BERMUDA
Segment reporting information
Earned insurance premiums			178
Ark | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains (losses) from investment in MediaAlpha			0
NSM
Segment reporting information
Earned insurance premiums			0	0	0
Net investment income			0	0	0
Net realized and unrealized investment gains (losses)			0	0	0
Realized gain (loss) from the 2019 MediaAlpha Transaction					0
Commission revenues			258	232.5	193.4
Other revenues			72.4	52.6	39.7
Total revenues			330.4	285.1	233.1
Loss and loss adjustment expenses			0
Insurance acquisition expenses			0	0	0
Cost of sales			0	0	0
General and administrative expenses			190.1	176.9	132.2
Broker commission expense			80.2	75.3	64.8
Change in fair value of contingent consideration			1	(3.3)	2.1
Amortization of other intangible assets			35.2	26.7	19.4
Loss on assets held for sale			28.7	0	0
Interest expense			23.3	22.1	16.7
Total expenses			358.5	297.7	235.2
Pre-tax income (loss)			$ (28.1)	$ (12.6)	$ (2.1)
Percentage of commission revenue			25.00%	19.00%	17.00%
NSM | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains (losses) from investment in MediaAlpha			$ 0	$ 0	$ 0
Kudu
Segment reporting information
Earned insurance premiums			0	0	0
Net investment income			43.9	29.5	14.7
Net realized and unrealized investment gains (losses)			89.9	15.9	6.3
Realized gain (loss) from the 2019 MediaAlpha Transaction					0
Commission revenues			0	0	0
Other revenues			0.2	0.3	0.2
Total revenues			134	45.7	21.2
Loss and loss adjustment expenses			0
Insurance acquisition expenses			0	0	0
Cost of sales			0	0	0
General and administrative expenses			14.5	11.8	10.1
Broker commission expense			0	0	0
Change in fair value of contingent consideration			0	0	0
Amortization of other intangible assets			0.3	0.3	0.2
Loss on assets held for sale			0
Interest expense			11.7	6	0.1
Total expenses			26.5	18.1	10.4
Pre-tax income (loss)			107.5	27.6	10.8
Kudu | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains (losses) from investment in MediaAlpha			0	0	0
MediaAlpha
Segment reporting information
Earned insurance premiums					0
Net investment income					0
Net realized and unrealized investment gains (losses)					0
Realized gain (loss) from the 2019 MediaAlpha Transaction					0
Commission revenues			0	0	48.8
Other revenues					0
Total revenues			0	0	48.8
Insurance acquisition expenses					0
Cost of sales			0	0	40.6
General and administrative expenses			0		12.5
Broker commission expense					0
Change in fair value of contingent consideration					0
Amortization of other intangible assets			0	0	1.6
Interest expense			0	0	0.2
Total expenses			0	0	54.9
Pre-tax income (loss)					(6.1)
MediaAlpha | MediaAlpha
Segment reporting information
Net realized and unrealized investment gains (losses) from investment in MediaAlpha					0
Other Operations
Segment reporting information
Earned insurance premiums			0	0	0
Net investment income			18.2	82	43.4
Net realized and unrealized investment gains (losses)			50.7	(8.8)	219.8
Net realized and unrealized investment gains (losses) from investment in MediaAlpha			(380.3)	686	180
Realized gain (loss) from the 2019 MediaAlpha Transaction			0	0	67.5
Commission revenues			9.6	8.3	6.9
Other revenues			90.7	13.9	6.1
Total revenues			(211.1)	781.4	523.7
Loss and loss adjustment expenses			0
Insurance acquisition expenses			0	0	0
Cost of sales			69.3	11.3	7.5
General and administrative expenses			105.7	141.9	122.5
Broker commission expense			0	0	0
Change in fair value of contingent consideration			0	0	0
Amortization of other intangible assets			4.3	1.3	0.6
Loss on assets held for sale			0
Interest expense			1.5	1.4	0.6
Total expenses			180.8	155.9	131.2
Pre-tax income (loss)			$ (391.9)	$ 625.5	$ 392.5
MediaAlpha
Segment reporting information
Realized gain (loss) from the 2019 MediaAlpha Transaction	$ 67.5

Segment Information - Assets (D

Segment Information - Assets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2012
Segment reporting information
Total investments	$ 4,265.3	$ 2,939
Total assets	7,000.7	4,831.4
Total liabilities	3,296	1,013.5
Total White Mountains’s common shareholders’ equity	3,548.1	3,906
Non-controlling interests	156.6	(88.1)
Held for Sale
Segment reporting information
Total investments	0	0
Total assets	16.1	2.3
Total liabilities	0	0
Total White Mountains’s common shareholders’ equity	16.1	2.3
Non-controlling interests	0	0
HG Global-BAM
Segment reporting information
Total investments	966.5	919.9
Total assets	1,044.8	1,017.8
Total liabilities	321.9	291.5
Total White Mountains’s common shareholders’ equity	838	836.1
Non-controlling interests	(115.1)	(109.8)
Ark
Segment reporting information
Total investments	1,562.1	0
Total assets	3,027	0
Total liabilities	2,122.4	0
Total White Mountains’s common shareholders’ equity	673.9	0
Non-controlling interests	230.7	0
NSM
Segment reporting information
Total investments	0	0
Total assets	977.3	999.6
Total liabilities	495.3	491.8
Total White Mountains’s common shareholders’ equity	465.3	490.7
Non-controlling interests	16.7	17.1
Kudu
Segment reporting information
Total investments	669.5	400.6
Total assets	727.1	430.2
Total liabilities	261	96.3
Total White Mountains’s common shareholders’ equity	453.7	331.6
Non-controlling interests	12.4	2.3
Other Operations
Segment reporting information
Total investments	1,067.2	1,618.5
Total assets	1,208.4	2,381.5
Total liabilities	95.4	133.9
Total White Mountains’s common shareholders’ equity	1,101.1	2,245.3
Non-controlling interests	11.9	2.3
BAM
Segment reporting information
Surplus notes	364.6	388.2
Accrued interest on surplus notes	157.6	155.7
HG Global
Segment reporting information
Non-controlling interests	8.9	13.5
Surplus notes			$ 503
Preferred Dividends Payable | HG Global
Segment reporting information
Total liabilities	$ 400.5	$ 363.9

Segment Information - Revenue (

Segment Information - Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment reporting information
Revenues from contracts with customers	$ 427.5	$ 307.9	$ 294.3
Other revenues	517.3	872.8	599.1
Total revenues	944.8	1,180.7	893.4
HG Global-BAM
Segment reporting information
Revenues from contracts with customers	0	0	0
Other revenues	23	68.5	66.6
Total revenues	23	68.5	66.6
Ark
Segment reporting information
Revenues from contracts with customers	0
Other revenues	668.5
Total revenues	668.5	0	0
NSM
Segment reporting information
Revenues from contracts with customers	330.4	285.1	233.1
Other revenues	0	0	0
Total revenues	330.4	285.1	233.1
Kudu
Segment reporting information
Revenues from contracts with customers	0	0	0
Other revenues	134	45.7	21.2
Total revenues	134	45.7	21.2
MediaAlpha
Segment reporting information
Revenues from contracts with customers			48.8
Other revenues			0
Total revenues	0	0	48.8
Other Operations
Segment reporting information
Revenues from contracts with customers	97.1	22.8	12.4
Other revenues	(308.2)	758.6	511.3
Total revenues	(211.1)	781.4	523.7
Specialty Transportation
Segment reporting information
Revenues from contracts with customers	97.2	85.5	77.6
Specialty Transportation | HG Global-BAM
Segment reporting information
Revenues from contracts with customers	0	0	0
Specialty Transportation | Ark
Segment reporting information
Revenues from contracts with customers	0
Specialty Transportation | NSM
Segment reporting information
Revenues from contracts with customers	97.2	85.5	77.6
Specialty Transportation | Kudu
Segment reporting information
Revenues from contracts with customers	0	0	0
Specialty Transportation | MediaAlpha
Segment reporting information
Revenues from contracts with customers			0
Specialty Transportation | Other Operations
Segment reporting information
Revenues from contracts with customers	0	0	0
Pet
Segment reporting information
Revenues from contracts with customers	76.3		45.9
Pet | HG Global-BAM
Segment reporting information
Revenues from contracts with customers	0	0	0
Pet | Ark
Segment reporting information
Revenues from contracts with customers	0	55	45.9
Pet | NSM
Segment reporting information
Revenues from contracts with customers	76.3	0	0
Pet | Kudu
Segment reporting information
Revenues from contracts with customers	0	0	0
Pet | Other Operations
Segment reporting information
Revenues from contracts with customers	0	55	0
Real Estate
Segment reporting information
Revenues from contracts with customers	34.4	44.9	34.7
Real Estate | HG Global-BAM
Segment reporting information
Revenues from contracts with customers	0	0	0
Real Estate | Ark
Segment reporting information
Revenues from contracts with customers	0
Real Estate | NSM
Segment reporting information
Revenues from contracts with customers	34.4	44.9	34.7
Real Estate | Kudu
Segment reporting information
Revenues from contracts with customers	0	0	0
Real Estate | MediaAlpha
Segment reporting information
Revenues from contracts with customers			0
Real Estate | Other Operations
Segment reporting information
Revenues from contracts with customers	0	0	0
Social Services
Segment reporting information
Revenues from contracts with customers	33.9	28.9	25.9
Social Services | HG Global-BAM
Segment reporting information
Revenues from contracts with customers	0	0	0
Social Services | Ark
Segment reporting information
Revenues from contracts with customers	0
Social Services | NSM
Segment reporting information
Revenues from contracts with customers	33.9	28.9	25.9
Social Services | Kudu
Segment reporting information
Revenues from contracts with customers	0	0	0
Social Services | MediaAlpha
Segment reporting information
Revenues from contracts with customers			0
Social Services | Other Operations
Segment reporting information
Revenues from contracts with customers	0	0	0
Other
Segment reporting information
Revenues from contracts with customers	45.1	29.7	25.9
Other | HG Global-BAM
Segment reporting information
Revenues from contracts with customers	0	0	0
Other | Ark
Segment reporting information
Revenues from contracts with customers	0
Other | NSM
Segment reporting information
Revenues from contracts with customers	35.5	21.4	19
Other | Kudu
Segment reporting information
Revenues from contracts with customers	0	0	0
Other | MediaAlpha
Segment reporting information
Revenues from contracts with customers			0
Other | Other Operations
Segment reporting information
Revenues from contracts with customers	9.6	8.3	6.9
Total commission and other revenue
Segment reporting information
Revenues from contracts with customers	340	293.4	240
Total commission and other revenue | HG Global-BAM
Segment reporting information
Revenues from contracts with customers	0	0	0
Total commission and other revenue | Ark
Segment reporting information
Revenues from contracts with customers	0
Total commission and other revenue | NSM
Segment reporting information
Revenues from contracts with customers	330.4	285.1	233.1
Total commission and other revenue | Kudu
Segment reporting information
Revenues from contracts with customers	0	0	0
Total commission and other revenue | MediaAlpha
Segment reporting information
Revenues from contracts with customers			0
Total commission and other revenue | Other Operations
Segment reporting information
Revenues from contracts with customers	9.6	8.3	6.9
Advertising revenues
Segment reporting information
Revenues from contracts with customers			48.8
Advertising revenues | HG Global-BAM
Segment reporting information
Revenues from contracts with customers			0
Advertising revenues | NSM
Segment reporting information
Revenues from contracts with customers			0
Advertising revenues | Kudu
Segment reporting information
Revenues from contracts with customers			0
Advertising revenues | MediaAlpha
Segment reporting information
Revenues from contracts with customers			48.8
Advertising revenues | Other Operations
Segment reporting information
Revenues from contracts with customers			0
Products and service revenues
Segment reporting information
Revenues from contracts with customers	87.5	14.5	5.5
Products and service revenues | HG Global-BAM
Segment reporting information
Revenues from contracts with customers	0	0	0
Products and service revenues | Ark
Segment reporting information
Revenues from contracts with customers	0
Products and service revenues | NSM
Segment reporting information
Revenues from contracts with customers	0	0	0
Products and service revenues | Kudu
Segment reporting information
Revenues from contracts with customers	0	0
Products and service revenues | MediaAlpha
Segment reporting information
Revenues from contracts with customers			0
Products and service revenues | Other Operations
Segment reporting information
Revenues from contracts with customers	87.5	14.5	5.5
United Kingdom
Segment reporting information
Revenues from contracts with customers	53.1		30
United Kingdom | HG Global-BAM
Segment reporting information
Revenues from contracts with customers	0	0	0
United Kingdom | Ark
Segment reporting information
Revenues from contracts with customers	0	49.4	30
United Kingdom | NSM
Segment reporting information
Revenues from contracts with customers	53.1	0	0
United Kingdom | Kudu
Segment reporting information
Revenues from contracts with customers	0	0	0
United Kingdom | Other Operations
Segment reporting information
Revenues from contracts with customers	$ 0	$ 49.4	$ 0

Equity Method Eligible Invest_3

Equity Method Eligible Investments - Carrying Value and Ownership Percentages (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	May 07, 2020	May 06, 2020	May 31, 2019
Investments in and Advances to Affiliates [Line Items]
Other long-term investments	$ 1,377.8	$ 786.8
Equity Method Investments
Investments in and Advances to Affiliates [Line Items]
Other long-term investments	17.8	15.2
Kudu's Participation Contracts
Investments in and Advances to Affiliates [Line Items]
Other long-term investments	$ 669.5	$ 400.6
Kudu's Participation Contracts | Minimum
Investments in and Advances to Affiliates [Line Items]
Ownership interest (as a percent)	3.20%	3.20%
Kudu's Participation Contracts | Maximum
Investments in and Advances to Affiliates [Line Items]
Ownership interest (as a percent)	32.00%	35.00%
MediaAlpha
Investments in and Advances to Affiliates [Line Items]
Ownership interest (as a percent)	28.00%	35.00%
Other long-term investments	$ 261.6	$ 802.2
PassportCard/DavidShield
Investments in and Advances to Affiliates [Line Items]
Ownership interest (as a percent)	53.80%	53.80%	53.80%	50.00%
Other long-term investments	$ 120	$ 95
Elementum Holdings, L.P.
Investments in and Advances to Affiliates [Line Items]
Ownership interest (as a percent)	29.70%	28.90%			30.00%
Other long-term investments	$ 45	$ 55.1
Other Investment Sector
Investments in and Advances to Affiliates [Line Items]
Other long-term investments	$ 109.3	$ 132.2

Equity Method Eligible Invest_4

Equity Method Eligible Investments - Narrative (Details) - USD ($) $ in Millions	10 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Total revenues		$ 944.8	$ 1,180.7	$ 893.4
Total expenses		1,246.8	535.5	488.3
Net income (loss)		(321.9)	663.4	376.6
Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Proceeds from dividends received		$ 56.2	$ 95	$ 14.8
MediaAlpha
Schedule of Equity Method Investments [Line Items]
Total revenues	$ 359.2
Total expenses	336.3
Net income (loss)	$ 22.9

Equity Method Eligible Invest_5

Equity Method Eligible Investments - Balance Sheet and Income Statement Tables (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Investments in unconsolidated affiliates
Total assets	$ 7,000.7	$ 4,831.4
Total liabilities	3,296	1,013.5
Total revenues	944.8	1,180.7	$ 893.4
Net income (loss)	(275.4)	708.7	414.5
Total Revenues
Investments in unconsolidated affiliates
Out of period adjustments			0.1
Total Operating Expenses
Investments in unconsolidated affiliates
Out of period adjustments			1.2
Total Net Income (Loss)
Investments in unconsolidated affiliates
Out of period adjustments			(1.1)
White Mountains
Investments in unconsolidated affiliates
Total assets	1,845.7	1,328.5
Total liabilities	373.4	228.7
Total revenues	987.4	526.5	344.6
Total expenses	418.7	325.9	88.3
Net income (loss)	568.7	201.7	255.1
MediaAlpha
Investments in unconsolidated affiliates
Total assets	289.8	210.3
Total liabilities	351.4	315.5
Total revenues	645.3	584.8	408
Total expenses	653.8	574.2	390.2
Net income (loss)	$ (8.5)	$ 10.6	$ 17.8

Variable Interest Entities (Det

Variable Interest Entities (Details) $ in Millions	May 07, 2020USD ($)	Apr. 04, 2019USD ($)	Jan. 24, 2018USD ($)	Dec. 31, 2021USD ($)director	Dec. 31, 2020USD ($)	May 06, 2020	May 31, 2019USD ($)	Apr. 03, 2019	Feb. 05, 2018
Variable Interest Entity [Line Items]
Goodwill				$ 645.5	$ 525.5
BAM
Variable Interest Entity [Line Items]
Number directors to designate for election | director				2
First Loss Reinsurance Treaty | HG Global
Variable Interest Entity [Line Items]
Percentage of par value of policy reinsured				15.00%
First Loss Reinsurance Treaty | BAM
Variable Interest Entity [Line Items]
Percentage of premiums				60.00%
Elementum Holdings, L.P.
Variable Interest Entity [Line Items]
Ownership interest (as a percent)				29.70%	28.90%		30.00%
Other investments				$ 45			$ 55.1
DavidShield
Variable Interest Entity [Line Items]
Ownership interest (as a percent)			50.00%
PassportCard
Variable Interest Entity [Line Items]
Ownership interest (as a percent)			50.00%
PassportCard/DavidShield
Variable Interest Entity [Line Items]
Ownership interest (as a percent)	53.80%			53.80%	53.80%	50.00%
Other investments				$ 129.4
Payments to acquire businesses, gross			$ 41.8
Payments to acquire business			$ 28.3
Additional investment in acquisition	$ 15
Kudu
Variable Interest Entity [Line Items]
Ownership interest (as a percent)		99.10%		99.30%	99.30%			49.50%	49.50%
Payments to acquire business		$ 81.4
Assets acquired		155.5
Goodwill		7.6
Intangible assets acquired		2.2
Liabilities acquired		0.8
Noncontrolling interest acquired		$ 1.5
Fully diluted ownership interest (as a percent)		85.40%		84.70%	85.40%			42.70%	42.70%

Fair Value of Financial Instr_3

Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	$ 693	$ 376.4
Fair value | Ark 2007 Notes
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, fair value	27.6	0
Fair value | Ark 2021 Notes
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, fair value	162.8	0
Fair value | NSM Bank Facility
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, fair value	275.8	279.3
Fair value | Other NSM
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, fair value	1	1.3
Fair value | Kudu Credit Facility
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, fair value	246.8	0
Fair value | Kudu Bank Facility
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, fair value	0	89.3
Fair value | Other Operations
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt, fair value	17.7	18.8
Carrying Value | Ark 2007 Notes
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	30	0
Carrying Value | Ark 2021 Notes
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	155.9	0
Carrying Value | NSM Bank Facility
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	271.2	271.3
Carrying Value | Other NSM
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	0.9	1.3
Carrying Value | Kudu Credit Facility
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	218.2	0
Carrying Value | Kudu Bank Facility
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	0	86.3
Carrying Value | Other Operations
Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt	$ 16.8	$ 17.5

Commitments and Contingencies (

Commitments and Contingencies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Operating lease expense	$ 9.9	$ 7.7	$ 7.2
Due year one	10.9
Due year two	9.9
Due year three	8.5
Due after year three	23
Commitments to fund other-long term investments	$ 44

Held for Sale and Discontinue_3

Held for Sale and Discontinued Operations - Narrative (Details) £ in Millions, $ in Millions	Sep. 17, 2021USD ($)	Apr. 12, 2021USD ($)	Apr. 12, 2021GBP (£)	Feb. 12, 2021USD ($)	Aug. 20, 2020USD ($)	Mar. 31, 2021USD ($)	Dec. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Discontinued Operations
Gain (loss) on sale of discontinued operations							$ 18.7	$ (2.3)	$ 0.8
Total assets							7,000.7	4,831.4
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Corporate Aircraft
Discontinued Operations
Proceeds from sale of property held-for-sale				$ 2.1
Gain on sale of aircraft				$ 0.5
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Connecticut
Discontinued Operations
Proceeds from sale of property held-for-sale					$ 2.3
Realized gain losses on sales of other real estate								(0.1)
Proceeds from sale of land	$ 0.7
Loss on sale of land	$ 0.1
Disposal Group, Held-for-sale, Not Discontinued Operations | Corporate Aircraft
Discontinued Operations
Assets held for sale								1.7
Disposal Group, Held-for-sale, Not Discontinued Operations | Connecticut
Discontinued Operations
Assets held for sale								0.7
Sirius Group
Discontinued Operations
Gain (loss) on sale of discontinued operations										$ 17.3
Sirius Group | Discontinued Operations, Disposed of by Sale
Discontinued Operations
Gain (loss) on sale of discontinued operations							17.6
Discontinued operations, liability								18.7
Increase in discontinued operations liability								$ 2.2
Sirius Group | Discontinued Operations, Disposed of by Sale | Foreign Currency Gain (Loss)
Discontinued Operations
Gain (loss) on sale of discontinued operations							1.1
Fresh Insurance Services Group Limited | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Discontinued Operations
Proceeds from sale of business		$ 1.5	£ 1.1
Fresh Insurance Services Group Limited | Disposal Group, Held-for-sale, Not Discontinued Operations
Discontinued Operations
Loss on sale						$ 28.7	(28.7)
Other Operations | Disposal Group, Held-for-sale, Not Discontinued Operations
Discontinued Operations
Total assets							$ 16.1

Held for Sale and Discontinue_4

Held for Sale and Discontinued Operations - Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Basic and diluted earnings per share numerators (in millions):
Net income (loss) attributable to White Mountains’s common shareholders	$ (275.4)	$ 708.7	$ 414.5
Net income (loss) from continuing operations attributable to White Mountains’s common shareholders	(294.1)	711	413.7
Net income (loss) from discontinued operations attributable to White Mountains’s common shareholders	(18.7)	2.3	(0.8)
Allocation of (earnings) losses to participating restricted common shares	3.5	(9.3)	(5.3)
Basic and diluted earnings (losses) per share numerators	$ (290.6)	$ 701.7	$ 408.4
Basic earnings per share denominators (in thousands):
Total average common shares outstanding during the period (in shares)	3,079,000	3,122,200	3,181,600
Average unvested restricted common shares (in shares)	(36,500)	(40,800)	(40,500)
Basic earnings (losses) per share denominator (in shares)	3,042,500	3,081,400	3,141,100
Diluted earnings per share denominator (in thousands):
Total average common shares outstanding during the period (in shares)	3,079,000	3,122,200	3,181,600
Average unvested restricted common shares (in shares)	(36,500)	(40,800)	(40,500)
Diluted earnings (loss) per share denominator (in shares)	3,042,500	3,081,400	3,141,100
Basic (losses) earnings per share (in usd per share)	$ (89.46)	$ 226.97	$ 130.27
Diluted (losses) earnings per share (in usd per share)	$ (89.46)	$ 226.97	$ 130.27
Discontinued Operations
Basic and diluted earnings per share numerators (in millions):
Net income (loss) attributable to White Mountains’s common shareholders	$ (275.4)	$ 708.7	$ 414.5
Net income (loss) from continuing operations attributable to White Mountains’s common shareholders	(294.1)	711	413.7
Net income (loss) from discontinued operations attributable to White Mountains’s common shareholders	18.7	(2.3)	0.8
Allocation of (earnings) losses to participating restricted common shares	(0.2)	0	0
Basic and diluted earnings (losses) per share numerators	$ 18.5	$ (2.3)	$ 0.8
Basic earnings per share denominators (in thousands):
Total average common shares outstanding during the period (in shares)	3,079,000	3,122,200	3,181,600
Average unvested restricted common shares (in shares)	(36,500)	(40,800)	(40,500)
Basic earnings (losses) per share denominator (in shares)	3,042,500	3,081,400	3,141,100
Diluted earnings per share denominator (in thousands):
Total average common shares outstanding during the period (in shares)	3,079,000	3,122,200	3,181,600
Average unvested restricted common shares (in shares)	(36,500)	(40,800)	(40,500)
Diluted earnings (loss) per share denominator (in shares)	3,042,500	3,081,400	3,141,100
Basic (losses) earnings per share (in usd per share)	$ 6.07	$ (0.75)	$ 0.25
Diluted (losses) earnings per share (in usd per share)	$ 6.07	$ (0.75)	$ 0.25

SCHEDULE I SUMMARY OF INVESTM_2

SCHEDULE I SUMMARY OF INVESTMENTS-OTHER THAN INVESTMENTS IN RELATED PARTIES (Details) $ in Millions	Dec. 31, 2021USD ($)
Summary of investments other than investments in related parties
Cost	$ 3,784.4
Carrying Value	4,265.3
Fair Value	4,265.3
Fixed maturity investments
Summary of investments other than investments in related parties
Cost	1,895.5
Carrying Value	1,908.9
Fair Value	1,908.9
U.S. Government and agency obligations
Summary of investments other than investments in related parties
Cost	212.1
Carrying Value	211.5
Fair Value	211.5
Debt securities issued by corporations
Summary of investments other than investments in related parties
Cost	993.3
Carrying Value	992.9
Fair Value	992.9
Municipal obligations
Summary of investments other than investments in related parties
Cost	276.4
Carrying Value	291.9
Fair Value	291.9
Mortgage and asset-backed securities
Summary of investments other than investments in related parties
Cost	277.2
Carrying Value	277.6
Fair Value	277.6
Collateralized loan obligations
Summary of investments other than investments in related parties
Cost	136.5
Carrying Value	135
Fair Value	135
Short-term investments
Summary of investments other than investments in related parties
Cost	465.9
Carrying Value	465.9
Fair Value	465.9
Investment in MediaAlpha
Summary of investments other than investments in related parties
Cost	0
Carrying Value	261.6
Fair Value	261.6
Common equity securities - Industrial, Miscellaneous, and Other
Summary of investments other than investments in related parties
Cost	236.3
Carrying Value	251.1
Fair Value	251.1
Other long-term investments
Summary of investments other than investments in related parties
Cost	1,186.7
Carrying Value	1,377.8
Fair Value	$ 1,377.8

SCHEDULE II CONDENSED FINANCI_2

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT - Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Assets
Total assets	$ 7,000.7	$ 4,831.4
Liabilities
Total liabilities	3,296	1,013.5
Total White Mountains’s common shareholders’ equity	3,548.1	3,906
Non-controlling interests	156.6	(88.1)
Total liabilities and equity	7,000.7	4,831.4
White Mountains Insurance Group Ltd.
Assets
Cash	0.6	0.7
Fixed maturity investments, at fair value	0	10.1
Short-term investments, at amortized cost	6.7	24.3
Other assets	3	2.5
Investments in consolidated subsidiaries	3,661.8	3,726
Total assets	3,672.1	3,763.6
Liabilities
Payable to subsidiary	104.9	(195.6)
Other liabilities	10.1	39.7
Total liabilities	115	(155.9)
Total White Mountains’s common shareholders’ equity	3,548.1	3,906
Non-controlling interests	9	13.5
Total liabilities and equity	$ 3,672.1	3,763.6
Sirius Group | Swedish Tax Authority | Sirius Group
Liabilities
Loss contingency accrual		$ 18.7

SCHEDULE II CONDENSED FINANCI_3

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT - Statement of Operations and Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT
Revenues (loss) (including realized and unrealized gains and losses)	$ 944.8	$ 1,180.7	$ 893.4
Expenses	1,246.8	535.5	488.3
Pre-tax income (loss)	(302)	645.2	405.1
Income Tax Expense (Benefit)	(38.6)	20.5	(29.3)
Net income (loss) from continuing operations	(340.6)	665.7	375.8
Net income (loss) attributable to non-controlling interests	46.5	45.3	37.9
Net income (loss) attributable to White Mountains’s common shareholders	(275.4)	708.7	414.5
Other comprehensive income (loss), net of tax	1.9	7.3	(1.4)
Comprehensive income (loss) attributable to White Mountains’s common shareholders	(273.3)	715.5	413.1
White Mountains Insurance Group Ltd.
CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT
Revenues (loss) (including realized and unrealized gains and losses)	(0.2)	(8.7)	65
Expenses	39	61	47.1
Pre-tax income (loss)	(39.2)	(69.7)	17.9
Income Tax Expense (Benefit)	0	(0.3)	(0.9)
Net income (loss) from continuing operations	(39.2)	(70)	17
Net income from discontinued operations, net of tax	18.7	(2.3)	0.8
Equity in earnings from consolidated and unconsolidated subsidiaries, net of tax	(257.4)	782	398.5
Net income (loss) attributable to non-controlling interests	2.5	(1)	(1.8)
Net income (loss) attributable to White Mountains’s common shareholders	(275.4)	708.7	414.5
Other comprehensive income (loss), net of tax	2.1	6.8	(1.4)
Comprehensive income (loss) attributable to White Mountains’s common shareholders	(273.3)	715.5	413.1
Swedish Tax Authority | Sirius Group
CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT
Loss contingency accrual, period increase (decrease)	18.7	(2.3)	0.8
Swedish Tax Authority | Sirius Group | White Mountains Insurance Group Ltd.
CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT
Loss contingency accrual, period increase (decrease)	$ 18.7	$ (2.3)	$ 0.8

SCHEDULE II CONDENSED FINANCI_4

SCHEDULE II CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT - Statement of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT
Net income (loss) attributable to White Mountains’s common shareholders	$ (275.4)	$ 708.7	$ 414.5
Adjustments to reconcile net income to net cash used for operations:
Net change in other assets and liabilities, net	24.2	30.9	20.4
Net cash provided from (used for) operations	38.6	(60.6)	(120.5)
Cash flows from investing activities:
Net change in short-term investments	54.3	58.7	21.9
Net cash provided from (used for) investing activities	(208.3)	64.6	(59.9)
Cash flows from financing activities:
Repurchases and retirement of common shares	(100.1)	(78.5)	0
Dividends paid on common shares	(3.1)	(3.2)	(3.2)
Net cash provided from (used for) financing activities	217.6	49	230.5
Net decrease in cash during the year	48.1	50.2	50.7
Cash balance at beginning of year	211.2	161	110.3
Cash balance at end of year	259.3	211.2	161
Amortization of restricted share awards	14.7	16.6	10.5
Net change in (receivables) payables to subsidiaries	6.5	4.8	6.6
White Mountains Insurance Group Ltd.
CONDENSED FINANCIAL INFORMATION OF THE REGISTRANT
Net income (loss) attributable to White Mountains’s common shareholders	(275.4)	708.7	414.5
Adjustments to reconcile net income to net cash used for operations:
Net realized and unrealized investment (gains) losses from MediaAlpha	0.1	10.1	(61)
Undistributed earnings from subsidiaries	257.4	(782)	(398.5)
Net (gain) loss from sale of discontinued operations, net of tax	(18.7)	2.3	(0.8)
Other non-cash reconciling items, primarily amortization of restricted shares and option awards	14.1	19	20
Net change in other assets and liabilities, net	(5.7)	(2.6)	3
Net cash provided from (used for) operations	(28.2)	(44.5)	(22.8)
Cash flows from investing activities:
Net change in short-term investments	17.7	(127.4)	(37.6)
Purchases of investment securities	0	(6.7)	(14.8)
Sales and maturities of investment securities	0	189.7	207.9
Purchases of investment securities from subsidiaries	(26.4)	0	0
Sales of investment securities to subsidiaries	36.4	0	0
Issuance of debt (to) from subsidiaries	94	(44.5)	(83.5)
Repayment of debt to (from) subsidiaries	0	92.6	5
Net distributions from (contributions to) subsidiaries	17	29.1	(46.1)
Net cash provided from (used for) investing activities	138.7	132.8	30.9
Cash flows from financing activities:
Repurchases and retirement of common shares	(100.1)	(78.5)	0
Dividends paid on common shares	(3.1)	(3.2)	(3.2)
Payments of restricted shares withholding taxes	(7.4)	(6.6)	(4.9)
Net cash provided from (used for) financing activities	(110.6)	(88.3)	(8.1)
Net decrease in cash during the year	(0.1)	0	0
Cash balance at beginning of year	0.7	0.7	0.7
Cash balance at end of year	0.6	0.7	0.7
Bridge Holdings, Ltd.
Cash flows from financing activities:
Excess of intercompany debt	12.6
Bridge Holdings, Ltd. | White Mountains Insurance Group Ltd.
Cash flows from investing activities:
Repayment of debt to (from) subsidiaries	200
Net distributions from (contributions to) subsidiaries	18
Cash flows from financing activities:
Proceeds from Contributions from Parent			(70.5)
Bridge Holdings, Ltd. | White Mountains Insurance Group Ltd. | Short-term investments
Cash flows from investing activities:
Net distributions from (contributions to) subsidiaries	17.9
Bridge Holdings, Ltd. | White Mountains Insurance Group Ltd. | Cash
Cash flows from investing activities:
Net distributions from (contributions to) subsidiaries	0.1
HG Global | White Mountains Insurance Group Ltd.
Cash flows from financing activities:
Proceeds from Contributions from Affiliates		22.3	1.9
White Mountains Adams, Inc. | White Mountains Insurance Group Ltd.
Cash flows from investing activities:
Net distributions from (contributions to) subsidiaries	(42.7)
White Mountains Adams, Inc. | White Mountains Insurance Group Ltd. | Short-term investments
Cash flows from investing activities:
Net distributions from (contributions to) subsidiaries	(37.1)
White Mountains Adams, Inc. | White Mountains Insurance Group Ltd. | Cash
Cash flows from investing activities:
Net distributions from (contributions to) subsidiaries	(5.6)
White Mountains Investments Bermuda | White Mountains Insurance Group Ltd.
Cash flows from financing activities:
Proceeds from Contributions from Parent			(2)
Proceeds from Contributions from Affiliates			24.4
PSC Holdings, Ltd | White Mountains Insurance Group Ltd.
Cash flows from financing activities:
Proceeds from Contributions from Affiliates		6.8
Non-cash reconciling item | Guilford Holdings, Inc.
Cash flows from financing activities:
Transfer to investments		169.6
Short-term investments | White Mountains Insurance Group Ltd.
Cash flows from financing activities:
Transfer to investments		169.6
WM Lincoln
Cash flows from financing activities:
Carrying value of stock transferred	212.6
White Mountains Investments Bermuda | White Mountains Insurance Group Ltd.
Cash flows from financing activities:
Proceeds from Contributions from Affiliates	(19.7)
White Mountains Investments Bermuda | White Mountains Insurance Group Ltd. | Short-term investments
Cash flows from financing activities:
Proceeds from Contributions from Affiliates	(19.1)
White Mountains Investments Bermuda | White Mountains Insurance Group Ltd. | Cash
Cash flows from financing activities:
Proceeds from Contributions from Affiliates	(0.6)
Swedish Tax Authority | Sirius Group
Cash flows from financing activities:
Loss contingency accrual, period increase (decrease)	18.7	(2.3)	0.8
Swedish Tax Authority | Sirius Group | White Mountains Insurance Group Ltd.
Cash flows from financing activities:
Loss contingency accrual, period increase (decrease)	$ 18.7	$ (2.3)	$ 0.8

SCHEDULE III SUPPLEMENTARY IN_2

SCHEDULE III SUPPLEMENTARY INSURANCE INFORMATION (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
HG Global-BAM
SUPPLEMENTARY INSURANCE INFORMATION
Deferred Acquisition Costs	$ 33.1	$ 27.8	$ 22.1
Future Policy Benefits, Losses, Claims and Loss Expenses	0	0	0
Unearned Premiums	266.3	237.5	198.4
Other Policy Claims and Benefits Payable	0	0	0
Premiums Earned	26.9	22.8	16.3
Net Investment Income	17.5	19.5	21.6
Benefits, Claims, Losses and Settlement Expenses	0	0	0
Amortization of Deferred Acquisition Costs	8.3	7	5.7
Other Operating Expenses	0.4	0.4	0.4
Premiums Written	55.8	$ 61.7	$ 38.7
Ark
SUPPLEMENTARY INSURANCE INFORMATION
Deferred Acquisition Costs	100.8
Future Policy Benefits, Losses, Claims and Loss Expenses	894.7
Unearned Premiums	495.9
Premiums Earned	637.3
Net Investment Income	2.9
Benefits, Claims, Losses and Settlement Expenses	314.8
Amortization of Deferred Acquisition Costs	111.3
Other Operating Expenses	64.6
Premiums Written	$ 859.1

SCHEDULE IV REINSURANCE (Detail

SCHEDULE IV REINSURANCE (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Premiums earned
Net earned premiums	$ 664.2	$ 22.8	$ 16.3
HG Global/BAM
Premiums earned
Gross Amount	23.2	19.4	13.6
Ceded to Other Companies	0	0	0
Assumed from Other Companies	3.7	3.4	2.7
Net earned premiums	$ 26.9	$ 22.8	$ 16.3
Percentage of Amount Assumed to Net	13.80%	14.90%	16.60%
Ark
Premiums earned
Gross Amount	$ 886.4
Ceded to Other Companies	(249.1)
Assumed from Other Companies	0
Net earned premiums	$ 637.3	$ 0	$ 0
Percentage of Amount Assumed to Net	0.00%

SCHEDULE V VALUATION AND QUAL_2

SCHEDULE V VALUATION AND QUALIFYING ACCOUNTS (Details) - Reinsurance recoverable on paid losses: Allowance for reinsurance balances $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)
VALUATION AND QUALIFYING ACCOUNTS
Balance at beginning of period	$ 0.3
Charged to costs and expenses	0.4
Charged to other accounts	0
Deductions described	0
Balance at end of period	$ 0.7

SCHEDULE VI SUPPLEMENTAL INFO_2

SCHEDULE VI SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS (Details) - Ark $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)
SUPPLEMENTAL INFORMATION FOR PROPERTY AND CASUALTY INSURANCE UNDERWRITERS
Deferred acquisition costs	$ 100.8
Reserves for Unpaid Claims and Claims Adjustment Expenses	894.7
Discount, if any, deducted in Column C	0
Unearned Premiums	495.9
Earned Premiums	637.3
Net investment income	2.9
Current Year	336.3
Prior Year	(21.5)
Amortization of deferred policy acquisition costs	111.3
Paid Claims and Claims Adjustment Expenses	105.5
Premiums written	$ 859.1