Alleghany (Y) 10-K 23 Feb 22 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2021	Feb. 13, 2022	Jun. 30, 2021
Cover [Abstract]
Amendment Flag	false
Document Type	10-K
Document Period End Date	Dec. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Registrant Name	ALLEGHANY CORP /DE
Entity Central Index Key	0000775368
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		13,529,546
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Title of 12(b) Security	Common Stock, $1.00 par value
Security Exchange Name	NYSE
Trading Symbol	Y
Entity File Number	1-9371
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	51-0283071
Entity Address, Address Line One	1411 Broadway, 34th Floor
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10018
City Area Code	212
Local Phone Number	752-1356
Document Annual Report	true
Document Transition Report	false
Entity Public Float			$ 8,961,756,584
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
ICFR Auditor Attestation Flag	true
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive proxy statement relating to the Annual Meeting of Stockholders of Alleghany Corporation to be held on April 22, 2022 to be filed with the Securities and Exchange Commission pursuant to Regulation 14A are incorporated by reference into Part III of this Annual Report on Form 10-K.
Auditor Name	Ernst & Young LLP
Auditor Firm Id	42
Auditor Location	New York

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands		Dec. 31, 2021		Dec. 31, 2020
Investments:
Equity securities		$ 3,683,820		$ 2,718,902
Debt securities, fair value		16,061,560		15,618,470
Short-term investments		1,142,258		714,208
Marketable Securities, Total		20,887,638		19,051,580
Commercial mortgage loans		475,860		670,239
Other invested assets		557,800		465,153
Total investments		21,921,298		20,186,972
Cash		927,966		791,442
Accrued investment income		87,610		88,760
Premium balances receivable		1,458,679		1,145,341
Reinsurance recoverables		2,195,975		1,781,096
Ceded unearned premiums		463,412		311,898
Deferred acquisition costs		586,753		595,117
Property and equipment at cost, net of accumulated depreciation and amortization		304,452		267,872
Goodwill	[1]	753,607		614,163
Intangible assets, net of amortization	[1]	924,406		787,462
Current taxes receivable		0		3,189
Funds held under reinsurance agreements		634,182		794,453
Other assets		2,010,335		1,559,245
Total assets		32,268,675		28,927,010
Liabilities, Redeemable Noncontrolling Interests and Stockholders’ Equity
Loss and loss adjustment expenses		14,357,635	[2]	12,970,626
Unearned premiums		3,179,513		2,984,060
Senior Notes and other debt		2,847,199		2,135,946
Reinsurance payable		322,902		208,384
Current taxes payable		34,297		0
Net deferred tax liabilities		56,958		43,547
Other liabilities		1,965,943		1,594,918
Total liabilities		22,764,447		19,937,481
Redeemable noncontrolling interests		317,346		233,809
Common stock		17,460		17,460
Contributed capital		3,608,905		3,613,454
Accumulated other comprehensive income		141,822		452,402
Treasury stock		(1,934,531)		(1,645,930)
Retained earnings		7,353,226		6,318,334
Total stockholders’ equity attributable to Alleghany stockholders		9,186,882		8,755,720
Total liabilities, redeemable noncontrolling interests and stockholders’ equity		$ 32,268,675		$ 28,927,010
[1]	Goodwill and intangible assets have been reduced by amounts written-down in prior periods, as applicable.
[2]	Includes unallocated LAE, which aggregate t o 1.0 perce nt of gross loss and LAE reserves as of December 31, 2021 . Net loss and LAE reserves by component are shown in the preceding tables, and consolidated gross loss and LAE reserves is presented in the consolidated balance sheets.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands		Dec. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Equity securities, cost		$ 2,552,722	$ 2,051,996
Debt securities, amortized cost		15,727,143	14,898,522
Allowance for credit losses	[1]	$ 502	$ 2,579
Common stock, Shares authorized		22,000,000	22,000,000
Common stock, Shares issued		17,459,961	17,459,961
Treasury stock, shares		3,861,426	3,418,781
[1]	See Note 1(r) for additional information regarding Alleghany’s adoption of new credit loss accounting guidance.

Consolidated Statements of Earn

Consolidated Statements of Earnings and Comprehensive Income - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues
Net premiums earned		$ 7,097,653	$ 6,000,161	$ 5,478,143
Net investment income		540,445	490,856	550,241
Change in the fair value of equity securities		506,769	(110,459)	709,695
Net realized capital gains		67,493	3,098	(6,551)
Change in allowance for credit losses on available for sale securities		2,077	(8,029)
Change in allowance for credit losses on available for sale securities				(19,660)
Product and service revenues		3,789,668	2,521,092	2,328,848
Total revenues		12,004,105	8,896,719	9,040,716
Costs and Expenses
Net loss and loss adjustment expenses		4,834,935	4,339,046	3,686,435
Commissions, brokerage and other underwriting expenses	[1]	2,067,501	1,789,820	1,758,698
Other operating expenses		3,479,528	2,429,262	2,263,326
Corporate administration		57,218	48,581	74,830
Amortization of intangible assets		49,912	44,241	33,834
Interest expense		102,308	88,152	99,957
Total costs and expenses		10,591,402	8,739,102	7,917,080
Earnings (losses) before income taxes		1,412,703	157,617	1,123,636
Income taxes		281,925	30,734	233,435
Net earnings		1,130,778	126,883	890,201
Net earnings attributable to noncontrolling interest		95,886	25,129	32,400
Net earnings attributable to Alleghany stockholders		1,034,892	101,754	857,801
Net earnings		1,130,778	126,883	890,201
Other comprehensive income (loss):
Change in unrealized gains (losses), net of deferred taxes		(253,301)	277,040	402,957
Change in unrealized currency translation adjustment, net of deferred taxes		(4,305)	22,366	2,933
Retirement plans		(463)	14,754	(12,153)
Comprehensive income		820,198	407,935	1,263,554
Comprehensive income attributable to noncontrolling interests		95,886	25,129	32,400
Comprehensive income attributable to Alleghany stockholders		$ 724,312	$ 382,806	$ 1,231,154
Basic earnings per share attributable to Alleghany stockholders		$ 74.70	$ 7.14	$ 59.44
Diluted earnings per share attributable to Alleghany stockholders		$ 74.66	$ 7.04	$ 59.39
Accumulated Net Unrealized Investment Gain Loss
Other comprehensive income (loss):
Less: reclassification for net realized capital gains and change in allowance for credit losses on available for sale securities, net of taxes		$ (52,511)	$ (33,108)	$ (20,384)
[1]	Includes amortization associated with deferred acquisition costs of $ 1,693.1 mil lion, $ 1,457.0 million and $ 1,392.8 million for the years ended December 31, 2021, 2020 and 2019 , respectively.

Consolidated Statements of Ea_2

Consolidated Statements of Earnings and Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Change in unrealized gains (losses), deferred taxes	$ (67,333)	$ 73,643	$ 107,115
Change in unrealized currency translation adjustment, deferred taxes	(1,144)	5,945	780
Accumulated Net Unrealized Investment Gain Loss
Reclassification for net realized capital gains and change in allowance for credit losses on available for sale securities, taxes	$ (13,959)	$ (8,801)	$ (5,419)

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Common StockCumulative Effect, Period of Adoption, Adjustment	Contributed Capital	Contributed CapitalCumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (loss)	Accumulated Other Comprehensive Income (loss)Cumulative Effect, Period of Adoption, Adjustment	Treasury Stock	Treasury StockCumulative Effect, Period of Adoption, Adjustment	Retained Earnings	Retained EarningsCumulative Effect, Period of Adoption, Adjustment
Beginning Balance at Dec. 31, 2018	$ 7,692,710		$ 17,460		$ 3,612,830		$ (202,003)		$ (1,312,939)		$ 5,577,362
Net earnings (losses)	857,801		0		0		0		0		857,801
Other comprehensive income (loss), net of tax:
Retirement plans	(12,153)		0		0		(12,153)		0		0
Change in unrealized appreciation of investments, net	382,573		0		0		382,573		0		0
Change in unrealized currency translation adjustment, net	2,933		0		0		2,933		0		0
Comprehensive income attributable to Alleghany stockholders	1,231,154		0		0		373,353		0		857,801
Treasury stock repurchase	(144,422)		0		0		0		(144,422)		0
Other, net	(2,708)		0		(4,192)		0		1,484		0
Ending Balance at Dec. 31, 2019	8,776,734	$ (3,570)	17,460	$ 0	3,608,638	$ 0	171,350	$ 0	(1,455,877)	$ 0	6,435,163	$ (3,570)
Redeemable noncontrolling interests balance at Dec. 31, 2018	169,762
Redeemable Non-controlling Interests
Net earnings attributable to redeemable noncontrolling interests	32,400
Comprehensive (loss) income attributable to noncontrolling interests	32,400
Other net changes to redeemable noncontrolling interests	2,591
Redeemable noncontrolling interests balance at Dec. 31, 2019	204,753
Net earnings (losses)	101,754		0		0		0		0		101,754
Other comprehensive income (loss), net of tax:
Retirement plans	14,754		0		0		14,754		0		0
Change in unrealized appreciation of investments, net	243,932		0		0		243,932		0		0
Change in unrealized currency translation adjustment, net	22,366		0		0		22,366		0		0
Comprehensive income attributable to Alleghany stockholders	382,806		0		0		281,052		0		101,754
Dividends paid	(215,013)		0		0		0		0		(215,013)
Treasury stock repurchase	(194,762)		0		0		0		(194,762)		0
Other, net	9,525		0		4,816		0		4,709		0
Ending Balance at Dec. 31, 2020	8,755,720		17,460		3,613,454		452,402		(1,645,930)		6,318,334
Redeemable Non-controlling Interests
Net earnings attributable to redeemable noncontrolling interests	25,129
Comprehensive (loss) income attributable to noncontrolling interests	25,129
Other net changes to redeemable noncontrolling interests	3,927
Redeemable noncontrolling interests balance at Dec. 31, 2020	233,809
Net earnings (losses)	1,034,892		0		0		0		0		1,034,892
Other comprehensive income (loss), net of tax:
Retirement plans	(463)		0		0		(463)		0		0
Change in unrealized appreciation of investments, net	(305,812)		0		0		(305,812)		0		0
Change in unrealized currency translation adjustment, net	(4,305)		0		0		(4,305)		0		0
Comprehensive income attributable to Alleghany stockholders	724,312		0		0		(310,580)		0		1,034,892
Treasury stock repurchase	(290,521)		0		0		0		(290,521)		0
Other, net	(2,629)		0		(4,549)		0		1,920		0
Ending Balance at Dec. 31, 2021	9,186,882		$ 17,460		$ 3,608,905		$ 141,822		$ (1,934,531)		$ 7,353,226
Redeemable Non-controlling Interests
Net earnings attributable to redeemable noncontrolling interests	95,886
Comprehensive (loss) income attributable to noncontrolling interests	95,886
Other net changes to redeemable noncontrolling interests	(12,349)
Redeemable noncontrolling interests balance at Dec. 31, 2021	$ 317,346

Consolidated Statements of Ch_2

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - shares	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Stockholders' Equity [Abstract]
Common stock, Shares issued	17,459,961	17,459,961	17,459,961	17,459,961
Treasury stock, shares	3,861,426	3,418,781	3,095,333	2,883,452

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net earnings	$ 1,130,778	$ 126,883	$ 890,201
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization	178,031	160,002	119,513
Change in the fair value of equity securities	(506,769)	110,459	(709,695)
Net realized capital (gains) losses	(67,493)	(3,098)	6,551
Change in allowance for credit losses on available for sale securities	(2,077)	8,029
Change in allowance for credit losses on available for sale securities			19,660
(Increase) decrease in reinsurance recoverables, net of reinsurance payable	(300,361)	(79,149)	259,048
(Increase) decrease in premium balances receivable	(313,338)	(197,331)	(105,368)
(Increase) decrease in ceded unearned premiums	(151,514)	(63,745)	(26,921)
(Increase) decrease in deferred acquisition costs	8,364	(72,540)	(58,031)
(Increase) decrease in funds held under reinsurance agreements	160,271	(38,938)	(11,458)
Increase (decrease) in unearned premiums	195,453	417,890	299,092
Increase (decrease) in loss and loss adjustment expenses	1,387,009	1,042,267	(321,935)
Change in unrealized foreign currency exchange rate losses (gains)	85,778	(99,134)	(18,033)
Other, net	56,101	(274,761)	371,781
Net adjustments	729,455	909,951	(175,796)
Net cash provided by (used in) operating activities	1,860,233	1,036,834	714,405
Cash flows from investing activities
Purchases of debt securities	(6,737,728)	(6,721,073)	(6,726,809)
Purchases of equity securities	(1,092,926)	(1,974,625)	(520,961)
Sales of debt securities	3,582,319	4,042,915	3,645,307
Maturities and redemptions of debt securities	2,240,302	1,664,285	1,166,841
Sales of equity securities	633,111	1,659,234	2,296,371
Net (purchases) sales of short-term investments	(432,422)	208,263	(21,564)
Net (purchases) sales and maturities of commercial mortgage loans	194,379	15,967	(9,674)
(Purchases) sales of property and equipment	(59,651)	(37,519)	(47,572)
Purchases of affiliates and subsidiaries, net of cash acquired	(303,475)	(128,921)	(218,260)
Other, net	(33,039)	(12,973)	(40,218)
Net cash provided by (used in) investing activities	(2,009,130)	(1,284,447)	(476,539)
Cash flows from financing activities
Repayment of senior notes	0	(307,095)	0
Treasury stock acquisitions	(290,521)	(194,762)	(144,422)
Proceeds from issuance of senior notes	493,195	499,335	0
Debt issue costs paid	(5,675)	(4,550)	0
Increase (decrease) in other debt	189,749	85,989	81,738
Cash dividends paid	0	(215,013)	0
Other, net	(82,178)	(27,912)	(40,530)
Net cash provided by (used in) financing activities	304,570	(164,008)	(103,214)
Effect of foreign exchange rate changes on cash	(19,149)	23,965	5,683
Net (decrease) increase in cash	136,524	(387,656)	140,335
Cash at beginning of period	791,442	1,179,098	1,038,763
Cash at end of period	927,966	791,442	1,179,098
Supplemental disclosures of cash flow information
Interest paid	94,540	91,832	97,016
Income taxes paid (refund received)	$ 162,336	$ 90,828	$ 61,786

Summary of Significant Accounti

Summary of Significant Accounting Principles	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Principles	1. Summary of Significant Accounting Principles (a) Principles of Financial Statement Presentation Alleghany Corporation (“Alleghany”), a Delaware corporation, owns and supports certain operating subsidiaries and manages investments, anchored by a core position in property and casualty reinsurance and insurance. Through its wholly-owned subsidiary Transatlantic Holdings, Inc. (“TransRe”), an Alleghany subsidiary since March 2012, Alleghany is engaged in the property and casualty reinsurance business. Through its wholly-owned subsidiary Alleghany Insurance Holdings LLC (“AIHL”), Alleghany is engaged in the property and casualty insurance business. AIHL’s insurance operations are principally conducted by its subsidiaries RSUI Group, Inc. (“RSUI”) and CapSpecialty, Inc. (“CapSpecialty”). RSUI and CapSpecialty have been subsidiaries of AIHL since July 2003 and January 2002, respectively. AIHL Re LLC (“AIHL Re”), a captive reinsurance company which provides reinsurance to Alleghany’s current and former insurance operating subsidiaries and affiliates, has been a subsidiary of Alleghany since its formation in May 2006. Although Alleghany’s primary sources of revenues and earnings are its reinsurance and insurance operations and investments, Alleghany also generates revenues and expenses from a diverse portfolio of non-financial businesses that are owned and supported through its wholly-owned subsidiary Alleghany Capital Corporation (“Alleghany Capital”). Alleghany Capital’s businesses include: • Precision Cutting Technologies, Inc. (“PCT”), a holding company headquartered in Rockford, Illinois, with four operating businesses: (i) Bourn & Koch, Inc., a provider of precision automated machine tool solutions; (ii) Diamond Technology Innovations, Inc., a manufacturer of waterjet orifices and nozzles and a provider of related services; (iii) Coastal Industrial Distributors, LLC, a provider of high-performance solid carbide end mills; and (iv) as of March 2020, Supermill LLC, a manufacturer of high-performance carbide end mills; • R.C. Tway Company, LLC (“Kentucky Trailer”), a manufacturer of custom trailers and truck bodies for the moving and storage industry and other markets, headquartered in Louisville, Kentucky; • IPS-Integrated Project Services, LLC (“IPS”), a global provider of design, engineering, and related services to the biopharmaceutical and life sciences markets, and through its subsidiary, cost and project management services for clients in the data center, technology, and other sectors, headquartered in Blue Bell, Pennsylvania; • Jazwares, LLC (together with its affiliates, “Jazwares”), a global toy company, headquartered in Sunrise, Florida; • WWSC Holdings, LLC (“W&W|AFCO Steel”), a structural steel fabricator and erector, headquartered in Oklahoma City, Oklahoma; • CHECO Holdings, LLC (“Concord”), a hotel management and development company, headquartered in Raleigh, North Carolina; • Wilbert Funeral Services, Inc. (“Wilbert”), a provider of products and services for the funeral and cemetery industries and precast concrete markets, headquartered in Overland Park, Kansas; and • Piedmont Manufacturing Group, LLC (“Piedmont”), a provider of injection molded and thermoformed parts and multi-component assemblies for original equipment manufacturer customers in a range of end-markets, headquartered in Belmont, North Carolina. The results of Piedmont have been included in Alleghany’s consolidated results from its formation and subsequent acquisition of Wilbert, Inc., doing business as Wilbert Plastic Services (“WPS”) on May 10, 2021. On April 1, 2020, Alleghany Capital acquired an additional approximately 55 percent of Wilbert it previously did not own, bringing its equity interest in Wilbert to approximately 100 percent, and as of that date, the results of Wilbert were included in Alleghany’s consolidated results. Prior to April 1, 2020, Wilbert was accounted for under the equity method of accounting and was included in other invested assets. In addition, Alleghany owns certain other holding-company investments. Alleghany’s wholly-owned subsidiary, Alleghany Properties Holdings LLC (“Alleghany Properties”) owns and manages certain properties in the Sacramento, California region. Alleghany’s public equity investments are managed primarily through Alleghany’s wholly-owned subsidiary Roundwood Asset Management LLC. Prior to its December 31, 2020 sale, Stranded Oil Resources Corporation (“SORC”) was a wholly-owned subsidiary. Unless the context otherwise requires, references to “Alleghany” include Alleghany together with its subsidiaries. The accompanying consolidated financial statements include the results of Alleghany and its wholly-owned and majority-owned subsidiaries and have been prepared in accordance with accounting principles generally accepted in the U.S. (“GAAP”). All material inter-company balances and transactions have been eliminated in consolidation. The portion of stockholders’ equity, net earnings and comprehensive income that is not attributable to Alleghany stockholders is presented on the consolidated balance sheets, the consolidated statements of earnings and comprehensive income and the consolidated statements of changes in stockholders’ equity as noncontrolling interests. Because all noncontrolling interests have the option to sell their ownership interests to Alleghany in the future (generally through 2028), the portion of stockholders’ equity that is not attributable to Alleghany stockholders is presented on the consolidated balance sheets and the consolidated statements of changes in stockholders’ equity as redeemable noncontrolling interests for all periods presented. In addition, Alleghany accretes the redeemable noncontrolling interests up to their future estimated redemption value over the period from the date of issuance to the earliest redemption date. The redemption value of the equity interests is generally based on the subsidiary’s earnings in specified periods preceding the applicable redemption date, calculated based on either a specified formula or an independent fair market valua tion. Accretion related to redemption values based on a specified formula are recorded as a component of net earnings attributable to noncontrolling interests, whereas accretion related to redemption values based on an independent fair market valuation are recorded as a component of contributed capital. Accretion may increase or decrease each period, however, the redeemable noncontrolling interest balance may not go below the initial balance established at the acquisition date. The following table presents the components of net earnings attributable to noncontrolling interests for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Accretion of redeemable noncontrolling interests $ 23.5 $ 2.2 $ 8.8 Portion of net earnings attributable to noncontrolling interests 72.4 22.9 23.6 Total $ 95.9 $ 25.1 $ 32.4 In addition, accretion reduced contributed capital by $ 5.3 million, $ 0.0 million and $ 0.0 million for the years ended December 31, 2021, 2020 and 2019, respectively. Such accretion may be adjusted in the first quarter of 2022 as certain significant noncontrolling interest holders have the right to put their respective equity interests to Alleghany Capital. The difference between any actual payouts that may be negotiated and agreed, as compared to the carrying value of such noncontrolling interest holders, will be recorded as accretion and charged to contributed capital. As of December 31, 2021 , the noncontrolling interests outstanding were approximately as follows: Kentucky Trailer - 22 percent; IPS - 18 percent; Jaz wares – 24 percent; W&W|AFCO Steel - 20 percent; and Concord - 15 percent. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions. These estimates and assumptions affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements, as well as the reported amounts of revenues and expenses during the reporting period. Alleghany relies on historical experience and on various other assumptions that it believes to be reasonable under the circumstances to make judgments about the carrying value of assets and liabilities and reported revenues and expenses that are not readily apparent from other sources. Actual results may differ materially from those reported results to the extent that those estimates and assumptions prove to be inaccurate. Changes in estimates are reflected in the consolidated statements of earnings and comprehensive income in the period in which the changes are made. (b) Investments Investments consist of debt securities, equity securities, short-term investments, commercial mortgage loans and other invested assets. Alleghany considers all of its marketable debt securities and short-term investments as available-for-sale (“AFS”). Debt securities consist of securities with an initial fixed maturity of more than one year. Debt securities typically take the form of bonds and redeemable preferred stock. Equity securities generally consist of securities that represent ownership interests in an enterprise. Equity securities typically take the form of common stock or perpetual preferred stock. Mutual funds and exchange-traded securities are also classified as equity securities, including those that invest mostly in debt securities. All marketable equity securities are measured at fair value with changes in fair value recognized in net earnings. Short-term investments include commercial paper, certificates of deposit, money market instruments and any fixed maturity investment with an initial maturity of one year or less. AFS securities are recorded at fair value. Unrealized gains and losses during the year, net of the related tax effect, for AFS securities are excluded from earnings and reflected in comprehensive income, and the cumulative effect is reported as a separate component of stockholders’ equity until realized. Credit losses for AFS securities are recorded through an allowance for credit losses. Changes in the allowance for credit losses are recorded for (or as a reversal of) credit losses on AFS securities. Credit losses on an AFS security cannot exceed the amount by which the fair value of the security is less than its amortized cost. Any portion of a decline in fair value related to a debt security that is believed to arise from factors other than credit is recorded as a component of other comprehensive income rather than charged against earnings. Commercial mortgage loans are carried at unpaid principal balance, less an allowance for credit losses. Credit losses for commercial mortgage loans are recorded through an allowance for credit losses. Estimates of expected credit losses are based on historical experience, current conditions and reasonable and supportable forecasts, and include an ongoing review of amounts outstanding, the creditworthiness of the borrower, value of the real estate collateral and other relevant factors. Amounts deemed to be uncollectible are written off against the allowance. Subsequent reversals in credit loss estimates are recognized in earnings. Interest income on loans is accrued as earned. Other invested assets include invested assets not identified above, primarily related to: (i) equity investments in operating companies where Alleghany has significant influence (an aggregate common stock position held at or above 20 percent is presumed to convey significant influence); (ii) partnership investments (including hedge funds and private equity funds); and (iii) non-marketable equity investments. Equity investments in operating companies where Alleghany has significant influence are accounted for using the equity method. Partnership investments are accounted for at fair value, with changes in fair value recognized in net earnings, or using the equity method where Alleghany has significant influence. Non-marketable equity investments are accounted for at fair value, with changes in fair value recognized in net earnings. Net realized gains and losses on investments are determined in accordance with the specific identification method. Net investment income consists primarily of: (i) interest income from debt securities, short-term investments, commercial mortgage loans, funds withheld by cedants and cash, including any premium amortization or discount accretion; (ii) dividend income from equity securities; and (iii) investment income from other invested assets, which includes results arising from partnership investments, whether accounted for under the equity method or at fair value. Interest income is accrued when earned. Premiums and discounts arising from the purchase of certain debt securities are treated as a yield adjustment over the estimated useful life of the securities, adjusted for anticipated prepayments using the retrospective interest method. Under this method, the effective yield on a security is estimated. Such estimates are based on the prepayment terms of the security, past actual cash flows and assumptions as to future expected cash flow. The future expected cash flow assumptions consider various prepayment assumptions based on historical experience, as well as current market conditions. Periodically, the effective yield is re-estimated to reflect actual prepayments and updated future expected cash flow assumptions. Upon a re-estimation, a security’s book value is restated at the most recently calculated effective yield, assuming that yield had been in effect since the security was purchased. This treatment results in an increase or decrease to net investment income (accretion of premium or amortization of discount) at the new measurement date. With respect to callable debt securities purchased at a premium to par value, the amortization period for that premium is the earliest call date. See Note 4 for additional information regarding investments. (c) Fair value Fair value is defined as the price that would be received upon the sale of an asset or paid to transfer a liability in an orderly transaction between willing, able and knowledgeable market participants at the measurement date. Fair value measurements are not adjusted for transaction costs. In addition, a three-tiered hierarchy for inputs is used in management’s determination of fair value of financial instruments that emphasizes the use of observable inputs over the use of unobservable inputs by requiring that the observable inputs be used when available. Observable inputs are market participant assumptions based on market data obtained from sources independent of the reporting entity. Unobservable inputs are the reporting entity’s own assumptions about market participant assumptions based on the best information available under the circumstances. In assessing the appropriateness of using observable inputs in making its fair value determinations, Alleghany considers whether the market for a particular security is “active” or “inactive” based on all the relevant facts and circumstances. A market may be considered to be inactive if there are relatively few recent transactions or if there is a significant decrease in market volume. Furthermore, Alleghany considers whether observable transactions are “orderly” or not. Alleghany does not consider a transaction to be orderly if there is evidence of a forced liquidation or other distressed condition; as such, little or no weight is given to that transaction as an indicator of fair value. Although Alleghany is responsible for the determination of the fair value of its financial assets and the supporting methodologies and assumptions, it employs third-party valuation service providers to gather, analyze and interpret market information and derive fair values based upon relevant methodologies and assumptions for individual instruments. When those providers are unable to obtain sufficient market observable information upon which to estimate the fair value for a particular security, fair value is determined either by requesting a quote, which is generally non-binding, from brokers who are knowledgeable about these securities or by employing widely accepted valuation models. Valuation service providers typically obtain data about market transactions and other key valuation model inputs from multiple sources and, through the use of widely accepted valuation models, provide a single fair value measurement for individual securities for which a fair value has been requested under the terms of service agreements. The inputs used by the valuation service providers include, but are not limited to, market prices from recently completed transactions and transactions of comparable securities, interest rate yield curves, credit spreads, currency rates and other market observable information, as applicable. The valuation models take into account, among other things, market observable information as of the measurement date as well as the specific attributes of the security being valued including its term, interest rate, credit rating, industry sector and, when applicable, collateral quality and other issue or issuer specific information. When market transactions or other market observable data is limited, the extent to which judgment is applied in determining fair value is greatly increased. The three-tiered hierarchy used in management’s determination of fair value is broken down into three levels based on the reliability and observability of inputs as follows: • Level 1: Valuations are based on unadjusted quoted prices in active markets that Alleghany has the ability to access for identical, unrestricted assets and do not involve any meaningful degree of judgment. An active market is defined as a market where transactions for the financial instrument occur with sufficient frequency and volume to provide pricing information on an ongoing basis. Alleghany’s Level 1 assets include publicly traded common stocks and mutual funds (which are included on the consolidated balance sheet in equity securities) where Alleghany’s valuations are based on quoted market prices. • Level 2: Valuations are based on direct and indirect observable inputs other than quoted market prices included in Level 1. Level 2 inputs include quoted prices for similar assets in active markets and inputs other than quoted prices that are observable for the asset, such as the terms of the security and market-based inputs. Terms of the security include coupon, maturity date and any special provisions that may, for example, enable the investor, at its election, to redeem the security prior to its scheduled maturity date (such provisions may apply to all debt securities except U.S. Government obligations). Market-based inputs include interest rates and yield curves that are observable at commonly quoted intervals and current credit rating(s) of the security. Market-based inputs may also include credit spreads of all debt securities except U.S. Government obligations, and currency rates for certain foreign government obligations and foreign corporate bonds denominated in foreign currencies. Fair values are determined using a market approach that relies on the securities’ relationships to quoted prices for similar assets in active markets, as well as the other inputs described above. In determining the fair values for the vast majority of commercial mortgage-backed securities (“CMBS”) and other asset- backed securities, as well as a small portion of residential mortgage-backed securities (“RMBS”), an income approach is used to corroborate and further support the fair values determined by the market approach. The income approach primarily involves developing a discounted cash flow model using the future projected cash flows of the underlying collateral, and the terms of the security. Level 2 assets generally include short-term investments and most debt securities. Alleghany’s Level 2 liabilities consist of the Senior Notes, as defined in Note 1(n). • Level 3: Valuations are based on techniques that use significant inputs that are unobservable. The valuation of Level 3 assets requires the greatest degree of judgment. These measurements may be made under circumstances in which there is little, if any, market activity for the asset. Alleghany’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment. In making the assessment, Alleghany considers factors specific to the asset. In certain cases, the inputs used to measure fair value may fall into different levels of the fair value hierarchy. In such cases, the level in the fair value hierarchy within which the fair value measurement is classified is determined based on the lowest level input that is significant to the fair value measurement in its entirety. Assets classified as Level 3 principally include other asset-backed securities (primarily, collateralized loan obligations) and, to a lesser extent, U.S. and foreign corporate bonds (including privately issued securities) and commercial mortgage loans. Mortgage-backed and asset-backed securities are initially valued at the transaction price. Subsequently, Alleghany uses widely accepted valuation practices that produce a fair value measurement. The vast majority of fair values are determined using an income approach. The income approach primarily involves developing a discounted cash flow model using the future projected cash flows of the underlying collateral, as well as other inputs described below. A few Level 3 valuations are based entirely on non-binding broker quotes. These securities consist primarily of mortgage-backed and asset-backed securities where reliable pool and loan level collateral information cannot be reasonably obtained, and as such, an income approach is not feasible. Since Level 3 valuations are based on techniques that use significant inputs that are unobservable with little or no market activity, the fair values under the market approach for Level 3 securities are less credible than under the income approach; however, the market approach, where feasible, is used to corroborate the fair values determined by the income approach. The market approach primarily relies on the securities’ relationships to quoted transaction prices for similarly structured instruments. To the extent that transaction prices for similarly structured instruments are not available for a particular security, other market approaches are used to corroborate the fair values determined by the income approach, including option adjusted spread analyses. Unobservable inputs, significant to the measurement and valuation of mortgage-backed and asset-backed securities, are generally used in the income approach, and include assumptions about prepayment speed and collateral performance, including default, delinquency and loss severity rates. Significant changes to any one of these inputs, or combination of inputs, could significantly change the fair value measurement for these securities. The impact of prepayment speeds on fair value is dependent on a number of variables including whether the securities were purchased at a premium or discount. A decrease in interest rates generally increases the assumed rate of prepayments, and an increase in interest rates generally decreases the assumed speed of prepayments. Increased prepayments increase the yield on securities purchased at a discount and reduce the yield on securities purchased at a premium. In a decreasing prepayment environment, yields on securities purchased at a discount are reduced but are increased for securities purchased at a premium. Changes in default assumptions on underlying collateral are generally accompanied by directionally similar changes in other collateral performance factors, but generally result in a directionally opposite change in prepayment assumptions. Alleghany’s Level 3 liabilities consist of the debt of Alleghany Capital’s operating subsidiaries. Alleghany employs specific control processes to determine the reasonableness of the fair values of its financial assets and liabilities. Alleghany’s processes are designed to ensure that the values received or internally estimated are accurately recorded and that the data inputs and the valuation techniques used are appropriate, consistently applied and that the assumptions are reasonable and consistent with the objective of determining fair value. Alleghany assesses the reasonableness of individual security values received from valuation service providers through various analytical techniques. In addition, Alleghany validates the reasonableness of fair values by comparing information obtained from Alleghany’s valuation service providers to other third-party valuation sources for selected securities. Alleghany also validates prices obtained from brokers for selected securities through reviews by those who have relevant expertise and who are independent of those charged with executing investing transactions. In addition to such procedures, Alleghany reviews the reasonableness of its classification of securities within the three-tiered hierarchy to ensure that the classification is consistent with GAAP. See Note 3 for additional information regarding fair value. (d) Cash Cash includes all deposit balances with a bank that are available for immediate withdrawal, whether interest-bearing or non-interest bearing. (e) Premiums and Unearned Premiums Premiums are recognized as revenue on a pro rata basis over the term of an insurance policy. Assumed reinsurance premiums written and earned are based on reports received from ceding companies for pro rata treaty contracts and are generally recorded as written based on contract terms for excess-of-loss treaty contracts. Premiums are earned ratably over the terms of the related coverages. Unearned premiums and ceded unearned premiums represent the portion of gross premiums written and ceded premiums written, respectively, related to the unexpired periods of such coverages. Assumed reinsurance premiums written and earned, along with related costs, for which data has not been reported by the ceding companies, are estimated based on historical patterns and other relevant factors. These estimates may change when actual data for such estimated items becomes available. Premium balances receivable are reported net of an allowance for credit losses. Estimates of expected credit losses are based on historical experience, current conditions and reasonable and supportable forecasts, and include an ongoing review of amounts outstanding, length of collection periods, the creditworthiness of the insured and other relevant factors. Amounts deemed to be uncollectible are written off against the allowance. Subsequent reversals are recognized in earnings. (f) Reinsurance Ceded Reinsurance is used to mitigate the exposure to losses, manage capacity and protect capital resources. Reinsuring loss exposures does not relieve a ceding entity from its obligations to policyholders and cedants. Reinsurance recoverables (including amounts related to incurred but not reported (“IBNR”) claims) and ceded unearned premiums are reported as assets. To minimize exposure to losses related to a reinsurer’s inability to pay, the financial condition of such reinsurer is evaluated initially upon placement of the reinsurance and periodically thereafter. In addition to considering the financial condition of a reinsurer, the collectability of the reinsurance recoverables is evaluated based upon a number of other factors. Such factors include the amounts outstanding, length of collection periods, disputes, any collateral or letters of credit held and other relevant factors. Credit losses for reinsurance recoverables are recorded through an allowance for credit losses. Estimates of expected credit losses are based on historical experience, current conditions and reasonable and supportable forecasts. Amounts deemed to be uncollectible are written off against the allowance. Subsequent reversals in credit loss estimates are recognized in earnings. Ceded premiums written are recorded in accordance with the applicable terms of the various reinsurance contracts and ceded premiums earned are charged against revenue over the period of the various reinsurance contracts. This also generally applies to reinstatement premiums paid to a reinsurer, which arise when contractually-specified ceded loss triggers have been breached. Ceded commissions reduce commissions, brokerage and other underwriting expenses and ceded losses incurred reduce net loss and loss adjustment expenses (“LAE”) incurred over the applicable periods of the various reinsurance contracts with third-party reinsurers. If premiums or commissions are subject to adjustment (for example, retrospectively-rated or experience-rated), the estimated ultimate premium or commission is recognized over the period of the contract. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured business and consistent with the terms of the underlying reinsurance contract. See Note 5 for additional information on reinsurance ceded and reinsurance recoverables. (g) Deferred Acquisition Costs Acquisition costs related to unearned premiums that vary with, and are directly related to, the production of such premiums are deferred. Furthermore, such deferred costs: (i) represent only incremental, direct costs associated with the successful acquisition of a new or renewal insurance or reinsurance contract; (ii) are essential to the contract transaction; (iii) would not have been incurred had the contract transaction not occurred; and (iv) are related directly to the acquisition activities involving underwriting, policy issuance and processing. Acquisition costs principally relate to commissions. To a lesser extent, acquisition costs can include premium taxes and certain qualifying underwriting expenses. For insurance policies written, acquisition costs are generally incurred directly and include commissions, premium taxes and certain qualifying underwriting expenses. For reinsurance contracts written, acquisition costs are generally incurred through brokerage commissions and indirectly through ceding commissions, which are deferred. Deferred acquisition costs are amortized to expense as the related premiums are earned, generally over a period of one year. Deferred acquisition costs are reviewed at least annually to determine their recoverability from future income, including investment income. If any such costs are determined not to be recoverable they are charged to expense. Anticipated net loss and LAE and estimated remaining costs of servicing the contracts are considered when evaluating recoverability of deferred acquisition costs. (h) Property and Equipment Property and equipment is owned primarily by Alleghany Capital’s subsidiaries, and includes buildings, land, leasehold improvements, furniture, fixtures and computer hardware and software, as well as industrial and office machinery and equipment. Property and equipment is carried at cost, net of accumulated depreciation and amortization. Depreciation of buildings and equipment is principally calculated using the straight-line method over the estimated useful life of the respective assets. Estimated useful lives for such assets range from three to 20 years. Amortization of leasehold improvements is principally calculated using the straight-line method over the estimated useful life of the leasehold improvement or the life of the lease, whichever is less. Property and equipment are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable based on estimated, undiscounted future cash flows resulting from the use of the asset and its eventual disposition. When required, impairment losses are recognized based on the excess of the asset’s carrying value over the estimated fair value of the asset. Rental expense on operating leases is recorded on a straight-line basis over the term of the lease, regardless of the timing of actual lease payments. Maintenance and repairs that do not extend the useful lives of property and equipment is charged to expense as incurred. All leases with terms of more than one year are recorded as lease liabilities and corresponding right-of-use assets, and are recorded as a component of other liabilities and other assets , respectively. Lease liabilities represents the present value of expected lease payments over the remaining le

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	2. Goodwill and Intangible Assets The following table presents a rollforward of Alleghany’s goodwill and intangible assets by segment during 2021 and 2020: Goodwill Intangible Assets Alleghany Capital Insurance Reinsurance Total Alleghany Capital Insurance Reinsurance Total ($ in millions) Balance as of December 31, 2019 $ 465.2 $ 49.0 $ 8.8 $ 523.0 $ 542.4 $ 65.4 $ 78.2 $ 686.0 Acquired (1) 92.1 — — 92.1 147.0 — — 147.0 Amortization (2) n/a n/a n/a n/a ( 43.4 ) ( 1.0 ) 0.2 ( 44.2 ) Other increase (decrease) — ( 0.9 ) — ( 0.9 ) — ( 1.3 ) — ( 1.3 ) Balance as of December 31, 2020 557.3 48.1 8.8 614.2 646.0 63.1 78.4 787.5 Acquired (1) 139.4 — — 139.4 189.4 — — 189.4 Amortization (2) n/a n/a n/a n/a ( 48.1 ) ( 0.7 ) ( 1.1 ) ( 49.9 ) Other increase (decrease) — — — — — ( 1.3 ) ( 1.3 ) ( 2.6 ) Balance as of December 31, 2021 $ 696.7 $ 48.1 $ 8.8 $ 753.6 $ 787.3 $ 61.1 $ 76.0 $ 924.4 (1) See description below for a summary of recent material acquisitions impacting goodwill and intangible assets. (2) See table below for additional information regarding amortization and useful lives by major class of intangible asset. On October 14, 2021, IPS acquired the outstanding equity of Anchorbuoy Limited (with its subsidiaries, referred to as "Linesight"), for approximately $ 262.5 million U.S. dollar-equivalent, consisting of: (i) $ 98.6 million of cash from IPS (which includes a $ 97.4 million contribution from Alleghany); (ii) the issuance of certain noncontrolling interests in IPS, which were valued at $ 38.8 million and which increased the aggregate noncontrolling interests in IPS from approximately 15 percent to approximately 18 percent; and (iii) $ 125.1 million of U.S. dollar-equivalent incremental debt, which is denominated in Euro. Headquartered in Dublin, Ireland, Linesight is a global consultancy firm providing cost and project management, project controls, risk, scheduling, and procurement services for clients in the data center, technology and life sciences sectors, as well as other industries. In connection with the acquisition, Alleghany recorded $ 102.1 million of goodwill, $ 124.7 million of finite-lived intangible assets related to customer relationships and $ 15.5 million of indefinite-lived intangible assets related to trade names and trademarks. The acquisition-date consideration transferred and purchase price allocation to the acquired assets and liabilities of Linesight were based on estimated fair values that have not been finalized. As a result, the fair value recorded for these items is a provisional estimate and may be subject to adjustment. Once completed, any adjustment resulting from the valuations may impact the individual amounts recorded for assets acquired and liabilities assumed, as well as the residual goodwill. The acquisition accounting for Linesight is expected to be finalized later in 2022. On May 10, 2021, Piedmont acquired all outstanding equity in WPS for $ 93.4 million, consisting of $ 60.4 million in cash and $ 33.0 million of incremental debt. In connection with the acquisition, Alleghany completed the process of determining the fair value of acquired assets and liabilities in the third quarter of 2021, and recorded $ 17.7 million and $ 36.3 million of goodwill and finite-lived intangible assets, respectively. Finite-lived intangible assets relate primarily to customer relationships. The customer relationship asset is estimated to have a useful life of 18.5 years. On April 1, 2020, Alleghany Capital acquired an additional approximately 55 percent of Wilbert it previously did not own, bringing its equity interest in Wilbert to approximately 100 percent, for $ 121.3 million, consisting of $ 46.3 million in cash and $ 75.0 million of incremental debt. In connection with the acquisition, Alleghany recorded $ 62.9 million of goodwill, $ 21.5 million of finite-lived customer relationship intangible assets, $ 14.9 million of finite-lived license agreements intangible assets and $ 26.2 million of indefinite-lived trade name intangible assets. In connection with the acquisition accounting, Alleghany Capital recorded a $ 16.3 million gain on the remeasurement of its pre-existing approximately 45 percent equity ownership to estimated fair value (the “Wilbert Remeasurement Gain”). See Note 4(e) for information on the Wilbert Remeasurement Gain. On October 1, 2019, Jazwares acquired the outstanding equity of Wicked Cool Toys, LLC (“WCT”), a global toy company based in Bristol, Pennsylvania, for $ 159.0 million. Jazwares funded the acquisition with $ 135.5 million of incremental debt and the issuance of certain noncontrolling interests in Jazwares, which were valued at $ 23.5 million and which increased the aggregate noncontrolling interests in Jazwares from approximately 23 percent to approximately 25 percent. In connection with the acquisition, Alleghany recorded $ 39.1 million of goodwill, $ 83.9 million of finite-lived intangible assets related to license agreements and $ 24.9 million of other finite-lived intangible assets related primarily to customer relationships. In addition to IPS's acquisition of Linesight and Jazwares’ acquisition of WCT, several subsidiaries of Alleghany Capital have made other recent acquisitions, including: • Acquisition made by Kentucky Trailer in 2019 of a controlling interest in a manufacturer of aluminum feed transportation equipment. Specifically, Kentucky Trailer acquired a company based in Birmingham, Alabama in July 2019; • Acquisition made by Jazwares in April 2020 of a controlling interest in a plush toy manufacturer based in Los Angeles, California (“Kelly Toy”); • Acquisitions made by PCT of a manufacturer of a provider of high-performance solid carbide end mills in June 2019 and a manufacturer of high-performance carbide end mills in March 2020; • An acquisition made by IPS in May 2019; and • Several acquisitions made by Wilbert in 2020 and 2021. The following table presents the amount of goodwill and intangible assets, net of accumulated amortization expense, reported on Alleghany’s consolidated balance sheets as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Gross Carrying Accumulated Net Carrying (1) Gross Carrying Accumulated Net Carrying (1) ($ in millions) Alleghany Capital (2)(3) - Goodwill $ 696.7 $ — $ 696.7 $ 557.3 $ — $ 557.3 Alleghany Capital (3) - Intangible assets: Trade name 245.3 5.2 240.1 218.2 2.7 215.5 License agreements 167.1 63.3 103.8 167.1 48.1 119.0 Customer relationships 520.1 100.9 419.2 357.8 72.4 285.4 Other 50.0 25.8 24.2 50.0 23.9 26.1 Total Alleghany Capital intangibles 982.5 195.2 787.3 793.1 147.1 646.0 Total Alleghany Capital goodwill and $ 1,679.2 $ 195.2 $ 1,484.0 $ 1,350.4 $ 147.1 $ 1,203.3 Insurance Segment (2) - Goodwill $ 48.1 $ — $ 48.1 $ 48.1 $ — $ 48.1 Insurance Segment - Intangible assets: Agency relationships 12.5 12.1 0.4 13.8 11.6 2.2 State insurance licenses 25.1 — 25.1 25.1 — 25.1 Trade name 35.5 — 35.5 35.5 — 35.5 Brokerage and reinsurance relationships 33.8 33.8 — 33.8 33.8 — Renewal rights 24.9 24.8 0.1 24.9 24.6 0.3 Other 4.1 4.1 — 4.1 4.1 — Total insurance segment intangibles 135.9 74.8 61.1 137.2 74.1 63.1 Total insurance segment goodwill and $ 184.0 $ 74.8 $ 109.2 $ 185.3 $ 74.1 $ 111.2 Reinsurance Segment (2) - Goodwill $ 8.8 $ — $ 8.8 $ 8.8 $ — $ 8.8 Reinsurance Segment - Intangible assets: Value of business in-force 291.4 291.4 — 291.4 291.4 — Loss and LAE reserves ( 98.8 ) ( 90.9 ) ( 7.9 ) ( 98.8 ) ( 88.6 ) ( 10.2 ) State and foreign insurance licenses 19.0 — 19.0 19.0 — 19.0 Trade name 50.0 — 50.0 50.0 — 50.0 Renewal rights 51.8 40.4 11.4 53.0 35.2 17.8 Leases ( 25.8 ) ( 25.8 ) — ( 25.8 ) ( 23.7 ) ( 2.1 ) Other 15.1 11.6 3.5 15.1 11.2 3.9 Total reinsurance segment intangibles 302.7 226.7 76.0 303.9 225.5 78.4 Total reinsurance segment goodwill and $ 311.5 $ 226.7 $ 84.8 $ 312.7 $ 225.5 $ 87.2 Alleghany consolidated: Goodwill $ 753.6 $ — $ 753.6 $ 614.2 $ — $ 614.2 Intangible assets 1,421.1 496.7 924.4 1,234.2 446.7 787.5 Goodwill and other intangibles assets $ 2,174.7 $ 496.7 $ 1,678.0 $ 1,848.4 $ 446.7 $ 1,401.7 (1) Goodwill and intangible assets have been reduced by amounts written-down in prior periods, as applicable. (2) See N ote 13 for additional information on Alleghany’s segments of business. (3) Represents goodwill and other intangible assets related to the acquisition of: (i) Jazwares on April 15, 2016 and its subsequent acquisitions; (ii) W&W|AFCO Steel on April 28, 2017 and its subsequent acquisition; (iii) Concord on October 1, 2018; (iv) PCT on April 26, 2012 and its subsequent acquisitions; (v) IPS on October 31, 2015 and its subsequent acquisitions; (vi) Kentucky Trailer on August 30, 2013 and its subsequent acquisitions; (vii) Wilbert on April 1, 2020 and its subsequent acquisitions; and (viii) WPS on May 10, 2021. In most instances, trade names and state and foreign insurance licenses generally have an indefinite useful life. The economic useful lives of significant intangible assets are as follows: agency relationships — 15 years; brokerage and reinsurance relationships — 15 years; renewal rights — between 3 and 14 years ; loss and LAE reserves — 15 years; leases — 10 years; license agreements — 8 years; and of customer relationships — betw een 5 and 18.5 years.

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	3. Fair Value of Financial Instruments The following table presents the carrying value and estimated fair value of Alleghany’s consolidated financial instruments as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Carrying Value Fair Value Carrying Value Fair Value ($ in millions) Assets Investments (excluding equity method investments and loans) (1) $ 20,887.7 $ 20,887.7 $ 19,051.9 $ 19,051.9 Liabilities Senior Notes and other debt (2) $ 2,847.2 $ 3,157.9 $ 2,135.9 $ 2,468.7 (1) This table includes debt and equity securities, as well as partnership and non-marketable equity investments accounted for at fair value that are included in other invested assets. This table excludes investments accounted for using the equity method and commercial mortgage loans that are accounted for at unpaid principal balance. The fair value of short-term investments approximates amortized cost. (2) See Note 8 for additional information on the Senior Notes and other debt. The following tables present Alleghany’s financial instruments at fair value and the level of the fair value hierarchy of inputs used as of December 31, 2021 and 2020: Level 1 Level 2 Level 3 Total ($ in millions) As of December 31, 2021 Equity securities: Common stock $ 3,677.1 $ 2.1 $ — $ 3,679.2 Preferred stock — 3.3 1.3 4.6 Total equity securities 3,677.1 5.4 1.3 3,683.8 Debt securities: U.S. Government obligations — 2,050.7 — 2,050.7 Municipal bonds — 2,535.9 — 2,535.9 Foreign government obligations — 854.9 — 854.9 U.S. corporate bonds — 2,807.0 670.3 3,477.3 Foreign corporate bonds — 1,049.7 177.2 1,226.9 Mortgage and asset-backed securities: RMBS (1) — 2,007.1 1.9 2,009.0 CMBS — 905.9 — 905.9 Other asset-backed securities (2) — 1,652.7 1,348.3 3,001.0 Total debt securities — 13,863.9 2,197.7 16,061.6 Short-term investments — 1,142.3 — 1,142.3 Other invested assets — — — — Total investments (excluding equity method investments and loans) $ 3,677.1 $ 15,011.6 $ 2,199.0 $ 20,887.7 Senior Notes and other debt $ — $ 2,377.4 $ 780.5 $ 3,157.9 Level 1 Level 2 Level 3 Total ($ in millions) As of December 31, 2020 Equity securities: Common stock $ 2,711.1 $ 3.5 $ — $ 2,714.6 Preferred stock — 3.0 1.3 4.3 Total equity securities 2,711.1 6.5 1.3 2,718.9 Debt securities: U.S. Government obligations — 1,360.1 — 1,360.1 Municipal bonds — 2,656.8 — 2,656.8 Foreign government obligations — 879.5 — 879.5 U.S. corporate bonds — 2,914.1 631.6 3,545.7 Foreign corporate bonds — 1,133.6 189.5 1,323.1 Mortgage and asset-backed securities: RMBS (1) — 2,608.9 2.5 2,611.4 CMBS — 884.5 5.8 890.3 Other asset-backed securities (2) — 1,448.9 902.7 2,351.6 Total debt securities — 13,886.4 1,732.1 15,618.5 Short-term investments — 714.2 — 714.2 Other invested assets (3) — — 0.3 0.3 Total investments (excluding equity method investments and loans) $ 2,711.1 $ 14,607.1 $ 1,733.7 $ 19,051.9 Senior Notes and other debt $ — $ 1,911.8 $ 556.9 $ 2,468.7 (1) Primarily includes government agency pass-through securities guaranteed by a government agency or government sponsored enterprise, among other types of RMBS. (2) Includes $ 1,320.4 million and $ 878.4 million of collateralized loan obligations as of December 31, 2021 and 2020 , respectively. (3) Includes partnership investments accounted for at fair value and excludes investments accounted for using the equity method. In 2021, Alleghany transferred into Level 3 $ 5.8 million of financial instruments, principally due to a decrease in observable inputs related to the valuation of such assets. Specifically, during 2021 , there was an increase in the weight given to non-binding broker quotes and, as a result, there was a corresponding decrease in quoted prices for similar assets in active markets. All of the $ 5.8 million of transfers related to other asset-backed securities. In 2021, Alleghany transferred out of Level 3 $ 48.2 million of financial instruments, principally due to an increase in observable inputs related to the valuation of such assets. Specifically, during 2021 , there was a decrease in the weight given to non-binding broker quotes and, as a result, there was a corresponding increase in quoted prices for similar assets in active markets. Of the $ 48.2 million of transfers, $ 37.0 million related other asset-backed securities, $ 5.8 million related to CMBS, $ 3.7 million related to U.S. corporate bonds and $ 1.7 million related to foreign government obligations. In 2020, Alleghany transferred out of Level 3 $ 20.7 million of financial instruments, principally due to an increase in observable inputs related to the valuation of such assets. Specifically, during 2020, there was a decrease in the weight given to non-binding broker quotes and, as a result, there was a corresponding increase in quoted prices for similar assets in active markets. Of the $ 20.7 million of transfers, $ 14.5 million related to other asset-backed securities, with the remainder related to foreign corporate bonds. There were no transfers into of Level 3 in 2020. The following tables present reconciliations of the changes during 2021 and 2020 in Level 3 assets measured at fair value: Debt Securities Mortgage and asset - backed Year Ended December 31, 2021 Preferred Foreign Government Obligations U.S. Foreign RMBS CMBS Other Other (1) Total ($ in millions) Balance as of January 1, 2021 $ 1.3 $ — $ 631.6 $ 189.5 $ 2.5 $ 5.8 $ 902.7 $ 0.3 $ 1,733.7 Net realized/unrealized gains (losses) included in: Net earnings (2) — — 0.1 ( 0.1 ) 0.1 — 0.5 0.1 0.7 Other comprehensive income (loss) — — ( 20.4 ) ( 7.2 ) ( 0.1 ) — 8.3 — ( 19.4 ) Purchases — 1.7 151.2 22.7 — — 776.3 — 951.9 Sales — — ( 0.2 ) — — — ( 12.4 ) ( 0.4 ) ( 13.0 ) Issuances — — — — — — — — — Settlements — — ( 88.3 ) ( 27.7 ) ( 0.6 ) — ( 295.9 ) — ( 412.5 ) Transfers into Level 3 — — — — — — 5.8 — 5.8 Transfers out of Level 3 — ( 1.7 ) ( 3.7 ) — — ( 5.8 ) ( 37.0 ) — ( 48.2 ) Balance as of December 31, 2021 $ 1.3 $ — $ 670.3 $ 177.2 $ 1.9 $ — $ 1,348.3 $ — $ 2,199.0 Debt Securities Mortgage and asset - backed Year Ended December 31, 2020 Preferred Foreign Government Obligations U.S. Foreign RMBS CMBS Other Other (1) Total ($ in millions) Balance as of January 1, 2020 $ 2.0 $ — $ 605.0 $ 168.7 $ 1.9 $ 5.8 $ 856.7 $ 0.3 $ 1,640.4 Net realized/unrealized gains (losses) included in: Net earnings (2) ( 0.7 ) — ( 3.8 ) 0.1 — — ( 9.4 ) — ( 13.8 ) Other comprehensive income (loss) — — 22.7 7.3 0.1 0.1 5.3 — 35.5 Purchases — — 56.4 32.0 0.9 — 196.4 — 285.7 Sales — — ( 2.0 ) ( 0.8 ) — — ( 61.7 ) — ( 64.5 ) Issuances — — — — — — — — — Settlements — — ( 46.7 ) ( 11.6 ) ( 0.4 ) ( 0.1 ) ( 70.1 ) — ( 128.9 ) Transfers into Level 3 — — — — — — — — — Transfers out of Level 3 — — — ( 6.2 ) — — ( 14.5 ) — ( 20.7 ) Balance as of December 31, 2020 $ 1.3 $ — $ 631.6 $ 189.5 $ 2.5 $ 5.8 $ 902.7 $ 0.3 $ 1,733.7 (1) Includes partnership and non-marketable equity investments accounted for at fair value. (2) There were no credit losses recorded in net earnings related to Level 3 instruments still held as of December 31, 2021 and 2020 . With respect to changes in Level 3 liabilities during 2021, the increase in senior notes and other debt reflects the impact of Piedmont's WPS acquisition and IPS's Linesight acquisition, as discussed above, partially offset by lower borrowings at other Alleghany Capital subsidiaries due to a decrease in working capital needs. Although Alleghany is responsible for the determination of the fair value of Alleghany’s financial assets and the supporting methodologies and assumptions, it employs third-party valuation service providers to gather, analyze and interpret market information and derive fair values based upon relevant methodologies and assumptions for individual instruments. When those providers are unable to obtain sufficient market observable information upon which to estimate the fair value for a particular security, fair value is determined either by requesting a quote, which is generally non-binding, from brokers who are knowledgeable about these securities or by employing widely accepted valuation models. As of December 31, 2021 and December 31, 2020, the fair value for the vast majority of debt securities included in Level 3 was provided by such third-party valuation service providers, and as such, valuation details on these securities are generally not available to Alleghany. Alleghany employs specific control processes to determine the reasonableness of the fair values of its financial assets and liabilities. Alleghany’s processes are designed to ensure that the values received or internally estimated are accurately recorded and that the data inputs and the valuation techniques used are appropriate, consistently applied and that the assumptions are reasonable and consistent with the objective of determining fair value. Alleghany assesses the reasonableness of individual security values received from valuation service providers through various analytical techniques. In addition, Alleghany validates the reasonableness of fair values by comparing information obtained from Alleghany’s valuation service providers to other third-party valuation sources for selected securities. Alleghany also validates prices obtained from brokers for selected securities through reviews by those who have relevant expertise and who are independent of those charged with executing investing transactions. See Note 1(c) for Alleghany’s accounting policy on fair value.

Investments

Investments	12 Months Ended
	Dec. 31, 2021
Investments [Abstract]
Investments	4. Investments (a) Unrealized Gains and Losses The following tables present the amortized cost and the fair value of AFS securities as of December 31, 2021 and 2020: Amortized Gross Gross Allowance for Credit Losses (2) Fair Value ($ in millions) As of December 31, 2021 Debt securities: U.S. Government obligations $ 2,039.7 $ 27.9 $ ( 16.9 ) $ — $ 2,050.7 Municipal bonds 2,412.7 127.3 ( 4.1 ) — 2,535.9 Foreign government obligations 850.8 12.0 ( 7.9 ) — 854.9 U.S. corporate bonds 3,336.9 159.2 ( 18.3 ) ( 0.5 ) 3,477.3 Foreign corporate bonds 1,216.6 19.9 ( 9.6 ) — 1,226.9 Mortgage and asset-backed securities: RMBS 1,993.6 37.2 ( 21.8 ) — 2,009.0 CMBS 879.8 28.3 ( 2.2 ) — 905.9 Other asset-backed securities (1) 2,997.0 22.0 ( 18.0 ) — 3,001.0 Total debt securities 15,727.1 433.8 ( 98.8 ) ( 0.5 ) 16,061.6 Short-term investments 1,142.3 — — — 1,142.3 Total investments $ 16,869.4 $ 433.8 $ ( 98.8 ) $ ( 0.5 ) $ 17,203.9 Amortized Gross Gross Allowance for Credit Losses (2) Fair Value ($ in millions) As of December 31, 2020 Debt securities: U.S. Government obligations $ 1,317.6 $ 44.0 $ ( 1.5 ) $ — $ 1,360.1 Municipal bonds 2,489.1 168.3 ( 0.6 ) — 2,656.8 Foreign government obligations 846.6 33.4 ( 0.5 ) — 879.5 U.S. corporate bonds 3,262.0 289.7 ( 3.5 ) ( 2.5 ) 3,545.7 Foreign corporate bonds 1,268.3 55.6 ( 0.7 ) ( 0.1 ) 1,323.1 Mortgage and asset-backed securities: RMBS 2,533.6 78.3 ( 0.5 ) — 2,611.4 CMBS 852.6 45.3 ( 7.6 ) — 890.3 Other asset-backed securities (1) 2,328.7 47.6 ( 24.7 ) — 2,351.6 Total debt securities 14,898.5 762.2 ( 39.6 ) ( 2.6 ) 15,618.5 Short-term investments 714.2 — — — 714.2 Total investments $ 15,612.7 $ 762.2 $ ( 39.6 ) $ ( 2.6 ) $ 16,332.7 (1) Includes $ 1,320.4 million and $ 878.4 million of collateralized loan obligations as of December 31, 2021 and 2020 , respectively. (2) See Note 1(r) for additional information regarding Alleghany’s adoption of new credit loss accounting guidance. (b) Contractual Maturity The following table presents the amortized cost and estimated fair value of debt securities by contractual maturity as of December 31, 2021. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. Amortized Cost Fair Value ($ in millions) As of December 31, 2021 Short-term investments due in one year or less $ 1,142.3 $ 1,142.3 Mortgage and asset-backed securities (1) 5,870.4 5,915.9 Debt securities with maturity dates: One year or less 624.2 628.7 Over one through five years 3,714.4 3,772.7 Over five through ten years 3,037.6 3,106.4 Over ten years 2,480.5 2,637.9 Total debt securities $ 15,727.1 $ 16,061.6 (1) Mortgage and asset-backed securities by their nature do not generally have single maturity dates. (c) Net Investment Income The following table presents net investment income for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Interest income $ 397.7 $ 443.1 $ 499.5 Dividend income 79.4 28.0 37.9 Investment expenses ( 26.5 ) ( 28.6 ) ( 28.9 ) Partnerships and other investment results 89.8 48.4 41.7 Total $ 540.4 $ 490.9 $ 550.2 As of December 31, 2021, non-income producing invested assets were immaterial. (d) Change in the Fair Value of Equity Securities The proceeds from sales of equity securities were $ 0.6 billion in 2021 , $ 1.7 billion in 2020 and $ 2.3 billion in 2019. The following table presents changes in the fair value of equity securities for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Change in the fair value of equity securities sold during the period $ 3.2 $ ( 147.4 ) $ 59.1 Change in the fair value of equity securities held at the end of the period 503.6 36.9 650.6 Change in the fair value of equity securities $ 506.8 $ ( 110.5 ) $ 709.7 (e) Realized Gains and Losses The proceeds from sales of debt securities were $ 3.6 billion in 2021 , $ 4.0 billion in 2020 and $ 3.6 billion in 2019. Realized capital gains and losses for 2021, 2020 and 2019 primarily reflect the sale of debt securities, except as noted in the following table. The following table presents the amounts of gross realized capital gains and gross realized capital losses for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Gross realized capital gains $ 84.2 (1) $ 134.6 (2) $ 62.4 Gross realized capital losses ( 16.8 ) ( 131.5 ) (3) ( 68.9 ) (4) Net realized capital gains $ 67.4 $ 3.1 $ ( 6.5 ) (1) Gross realized capital gains in 2021 include a $ 3.1 million realized gain on the remeasurement of fair value of certain outstanding contingent consideration liabilities by Alleghany Capital in connection with its 2018 acquisition of Concord (the "2021 Concord Remeasurement Gain") . (2) Gross realized capital gains in 2020 include (i) a $ 15.0 million realized gain on a partial settlement and remeasurement of fair value of certain outstanding contingent consideration liabilities by Alleghany Capital in connection with its 2018 acquisition of Concord (the “2020 Concord Settlement Gain”); (ii) a gain of $ 16.3 million on April 1, 2020 in connection with Alleghany Capital’s acquisition of an a dditional approximately 55 percent of Wilbert that it did not previously own, and the remeasurement of its pre-existing approximately 45 percent equity ownership to estimated fair value (the “Wilbert Remeasurement Gain”); and (iii) a $ 5.0 million realized gain from a reduction of certain contingent consideration liabilities at the PCT-level in connection with its acquisition of a provider of high-performance solid carbide end mills in June 2019. (3) Gross realized capital losses in 2020 include (i) impairment charges of $ 76.0 million from write-downs of SORC oil field assets prior to SORC’s December 31, 2020 sale; and (ii) a $ 7.1 million realized loss as a result of an early redemption of debt (see Note 8 for additional information on this early redemption). (4) Gross realized capital losses in 2019 include $ 38.4 million from a derivative. Specifically, on July 18, 2019, AIHL purchased an exchange-traded equity derivative index put option (the “Put Option”) for $ 38.4 million to hedge the downside equity market risk on approximately $ 1.0 billion of Alleghany’s equity portfolio. The Put Option did not qualify for hedge accounting. The Put Option expired worthless on December 31, 2019, and the resulting $ 38.4 million decline in value of the Put Option was recorded as a gross realized capital loss. Gross realized capital losses in 2019 also includes a $ 13.6 million loss from the December 2019 sale of a privately held investment accounted for under the equity method. Gross realized loss amounts exclude change in allowance for credit losses on AFS securities, as discussed below. (f) Credit quality for AFS securities Alleghany holds its debt securities as AFS and, as such, these securities are recorded at fair value. Credit losses for AFS securities are recorded through an allowance for credit losses. Changes in the allowance for credit losses are recorded for (or as a reversal of) credit losses on AFS securities. Any portion of a decline in fair value related to a debt security that is believed to arise from factors other than credit is recorded as a component of other comprehensive income rather than charged against earnings. Alleghany continually monitors the difference between amortized cost and the estimated fair value of its debt investments. The analysis of a security’s decline in value is performed in its functional currency. Debt securities in an unrealized loss position are evaluated for credit losses if they meet any of the following criteria: (i) they are trading at a discount of at least 20 percent to amortized cost and have a credit rating below investment grade or are not rated; (ii) there has been a negative credit or news event with respect to the issuer that could indicate the existence of a credit loss; or (iii) Alleghany intends to sell, or it is more likely than not that Alleghany will sell, the debt security before recovery of its amortized cost basis. If Alleghany intends to sell, or it is more likely than not that Alleghany will sell, a debt security before recovery of its amortized cost basis, the total amount of the unrealized loss position is recognized as a credit loss in earnings. To the extent that a debt security that is in an unrealized loss position is not impaired based on the preceding, Alleghany will consider a debt security to be impaired when it believes it to be probable that Alleghany will not be able to collect the entire amortized cost basis. For debt securities in an unrealized loss position as of the end of each quarter, Alleghany develops a best estimate of the present value of expected cash flows. If the results of the cash flow analysis indicate that Alleghany will not recover the full amount of its amortized cost basis in the debt security, Alleghany records a credit loss in earnings equal to the difference between the present value of expected cash flows and the amortized cost basis of the debt security. If applicable, the difference between the total unrealized loss position on the debt security and the total loss recognized in earnings is the non-credit related portion, which is recorded as a component of other comprehensive income. In developing the cash flow analyses for debt securities, Alleghany considers various factors for the different categories of debt securities. For municipal bonds, Alleghany takes into account the taxing power of the issuer, source of revenue, credit risk and enhancements and pre-refunding. For mortgage and asset-backed securities, Alleghany discounts its best estimate of future cash flows at an effective rate equal to the original effective yield of the security or, in the case of floating rate securities, at the current coupon. Alleghany’s models include assumptions about prepayment speeds, default and delinquency rates, underlying collateral (if any), credit ratings, credit enhancements and other observable market data. For corporate bonds, Alleghany reviews business prospects, credit ratings and available information from asset managers and rating agencies for individual securities. Change in allowance for credit losses on AFS securities in 2021 reflects a $ 2.1 million reduction of credit losses on AFS securities primarily from debt security sales. Change in allowance for credit losses on AFS securities in 2020 reflect $ 8.0 million of unrealized losses on debt securities, primarily related to the energy sector and lower-quality corporate bonds in other sectors due to a significant decline in their fair value relative to their amortized costs in the spring of 2020, net of a subsequent reduction of the allowance for credit losses on AFS securities in 2020 arising from the improved bond market conditions and bond sales later in 2020. Change in allowance for credit losses on AFS securities in 2019 reflects $ 19.7 million of unrealized losses on debt securities, primarily related to the deterioration of creditworthiness of the issuers in the domestic energy sector and certain foreign bonds due to a significant decline in fair value. The following table presents a rollforward of Alleghany’s allowance for credit losses on AFS securities for 2021 and 2020: Year Ended December 31, 2021 2020 ($ in millions) Allowance for Credit Losses Beginning balance $ 2.6 $ — Beginning balance - cumulative effect of an accounting change — — Provision for credit losses ( 2.1 ) 8.0 Charge-offs — ( 5.4 ) Recoveries — — Ending balance $ 0.5 $ 2.6 The gross unrealized investment losses for debt securities as of December 31, 2021 were deemed to be temporary, based on, among other factors: (i) the relative magnitude to which the fair value of these investments had been below cost were not indicative of a credit loss; (ii) the absence of compelling evidence that would cause Alleghany to call into question the financial condition or near-term business prospects of the issuer of the security; and (iii) Alleghany’s ability and intent to hold the security for a period of time sufficient to allow for any anticipated recovery. Alleghany’s methodology for assessing credit losses contains inherent risks and uncertainties which could include, but are not limited to, incorrect assumptions about financial condition, liquidity or future prospects, inadequacy of any underlying collateral and unfavorable changes in economic conditions or social trends, interest rates or credit ratings. Alleghany’s consolidated investment portfolio consists mainly of highly rated and liquid debt and equity securities listed on national securities exchanges. The overall credit quality of the debt securities portfolio is measured using the lowest rating of three large, reputable rating agencies. In this regard, the overall weighted-average credit quality rating of Alleghany’s debt securities portfolio as of December 31, 2021 and 2020, was AA-. Although a portion of Alleghany’s debt securities, which consist predominantly of municipal bonds, is insured by third-party financial guaranty insurance companies, the impact of such insurance was not significant to the debt securities’ credit quality rating as of December 31, 2021. The following table presents the ratings of Alleghany’s debt securities as of December 31, 2021: Ratings as of December 31, 2021 AAA / Aaa AA / Aa A BBB / Baa Below (1) Total ($ in millions) U.S. Government obligations $ 1.4 $ 2,049.3 $ — $ — $ — $ 2,050.7 Municipal bonds 219.0 1,756.3 469.2 83.3 8.1 2,535.9 Foreign government obligations 376.5 389.3 87.8 1.1 0.2 854.9 U.S. corporate bonds 13.9 165.6 1,442.9 1,485.1 369.8 3,477.3 Foreign corporate bonds 184.7 69.1 564.1 372.8 36.2 1,226.9 Mortgage and asset-backed securities: RMBS 4.2 1,998.4 — 0.8 5.6 2,009.0 CMBS 324.2 355.4 218.6 7.7 — 905.9 Other asset-backed securities 1,282.1 761.0 477.3 451.6 29.0 3,001.0 Total debt securities $ 2,406.0 $ 7,544.4 $ 3,259.9 $ 2,402.4 $ 448.9 $ 16,061.6 Percentage of debt securities, 15.0 % 47.0 % 20.3 % 14.9 % 2.8 % 100.0 % (1) Consists of $ 140.8 million of securities rated BB / Ba, $ 203.5 million of securities rated B, $ 32.0 million of securities rated CCC, $ 0.5 million of securities rated CC, $ 3.1 million of securities rated below CC and $ 69.0 million of not rated securities. (g) Aging of Gross Unrealized Losses The following tables present gross unrealized losses and related fair values for Alleghany’s AFS securities before an allowance for credit losses, grouped by duration of time in a continuous unrealized loss position, as of December 31, 2021 and 2020: Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross ($ in millions) As of December 31, 2021 Debt securities: U.S. Government obligations $ 1,196.3 $ 11.1 $ 122.1 $ 5.8 $ 1,318.4 $ 16.9 Municipal bonds 267.3 4.0 2.8 0.1 270.1 4.1 Foreign government obligations 350.0 5.3 73.2 2.6 423.2 7.9 U.S. corporate bonds 814.2 12.4 79.3 5.9 893.5 18.3 Foreign corporate bonds 460.6 8.3 34.6 1.3 495.2 9.6 Mortgage and asset-backed securities: RMBS 1,072.8 20.5 50.7 1.3 1,123.5 21.8 CMBS 197.8 0.6 40.9 1.6 238.7 2.2 Other asset-backed securities 1,609.9 13.2 291.5 4.8 1,901.4 18.0 Total temporarily impaired securities $ 5,968.9 $ 75.4 $ 695.1 $ 23.4 $ 6,664.0 $ 98.8 Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross ($ in millions) As of December 31, 2020 Debt securities: U.S. Government obligations $ 255.9 $ 1.5 $ — $ — $ 255.9 $ 1.5 Municipal bonds 36.2 0.6 — — 36.2 0.6 Foreign government obligations 132.8 0.5 — — 132.8 0.5 U.S. corporate bonds 168.5 3.5 2.4 — 170.9 3.5 Foreign corporate bonds 36.4 0.2 19.5 0.5 55.9 0.7 Mortgage and asset-backed securities: RMBS 152.6 0.5 0.4 — 153.0 0.5 CMBS 133.5 7.6 3.8 — 137.3 7.6 Other asset-backed securities 547.9 13.4 533.9 11.3 1,081.8 24.7 Total temporarily impaired securities $ 1,463.8 $ 27.8 $ 560.0 $ 11.8 $ 2,023.8 $ 39.6 As of December 31, 2021 , Alleghany held a total of 1,644 debt securities that were in an unrealized loss position, of which 186 securities were in an unrealized loss position continuously for 12 months or more. The unrealized losses associated with these debt securities consisted of losses related primarily to U.S. corporate bonds, U.S. Government bonds and other asset-backed securities. (h) Statutory Deposits Investments with fair values of approximatel y $ 2.3 b illion as of December 31, 2021, the substantial majority of which were debt securities and equity securities, were deposited with governmental authorities as required by law. (i) Investments in Certain Other Invested Assets In December 2012, TransRe obtained an ownership interest in Pillar Capital Holdings Limited (“Pillar Holdings”), a Bermuda- based insurance asset manager focused on collateralized reinsurance and catastrophe insurance-linked securities. Additionally, TransRe and, to a lesser extent, AIHL invested in limited partnership funds managed by Pillar Holdings (the “Funds”). The objective of the Funds is to create portfolios with attractive risk-reward characteristics and low correlation with other asset classes, using the extensive reinsurance and capital market experience of the principals of Pillar Holdings. Alleghany has concluded that both Pillar Holdings and the Funds (collectively, the “Pillar Investments”) represent variable interest entities and that Alleghany is not the primary beneficiary, as it does not have the ability to direct the activities that most significantly impact each entity’s economic performance. Therefore, the Pillar Investments are not consolidated and are accounted for under the equity method of accounting. Alleghany’s potential maximum loss in the Pillar Investments is limited to its cumulative net investment. As of December 31, 2021 and 2020, Alleghany’s carrying value in the Pillar Investments, as determined under the equity method of accounting, w as $ 156.4 million and $ 173.3 million, respectively, which is reported as a component of other invested assets and is net of returns of capital received from the Pillar Investments. (j) Investments in Commercial Mortgage Loans As of December 31, 2021 and 2020, the carrying value of Alleghany’s commercial mortgage loan portfolio was $ 475.9 million and $ 670.2 million, respectively, representing the unpaid principal balance on the loans, less allowance for credit losses. The estimated fair value of the commercial mortgage loan portfolio approximated carrying value of as December 31, 2021 and 2020 . The commercial mortgage loan portfolio consists primarily of first mortgages on commercial properties in major metropolitan areas in the U.S. The loans earn interest at fixed- and floating-rates, and mature in two to ten years from loan origination. As of December 31, 2021, the vast majority of loans in Alleghany’s portfolio were originated in the 2016 through 2019 years. The principal amounts of the loans were no more than approximately two-thirds of the property’s appraised value at the time the loans were made and the estimated fair value of underlying collateral was approximately double that of the commercial mortgage loan portfolio carrying value as of December 31, 2021 . Fair value estimates of underlying collateral are updated on a rolling basis at least annually, with a portion of the portfolio updated each quarter. As of December 31, 2021 , there was no loan in default or in arrears. The following table presents a rollforward of Alleghany’s allowance for credit losses on commercial mortgage loans for 2021 and 2020: Year Ended December 31, 2021 2020 ($ in millions) Allowance for Credit Losses Beginning balance $ 1.4 $ — Beginning balance - cumulative effect of an accounting change — 0.8 Provision for credit losses ( 1.2 ) 0.6 Charge-offs — — Recoveries — — Ending balance $ 0.2 $ 1.4

Reinsurance Ceded

Reinsurance Ceded	12 Months Ended
	Dec. 31, 2021
Insurance [Abstract]
Reinsurance Ceded	5 . Reinsurance Ceded (a) Overview Alleghany’s reinsurance and insurance subsidiaries reinsure portions of the risks they underwrite in order to reduce the effect of individual or aggregate exposure to losses, manage capacity, protect capital resources, reduce volatility in specific lines of business, improve risk-adjusted portfolio returns and enable them to increase gross premium writings and risk capacity without requiring additional capital. Alleghany’s reinsurance and insurance subsidiaries generally purchase reinsurance and retrocessional coverages from highly-rated third-party reinsurers or on a collateralized basis. If the assuming reinsurers are unable or unwilling to meet the obligations assumed under the applicable reinsurance agreements, Alleghany’s reinsurance and insurance subsidiaries would remain liable for such reinsurance portion not paid by these reinsurers. As such, funds, trust agreements and letters of credit are held to collateralize a portion of Alleghany’s reinsurance recoverables and Alleghany’s reinsurance and insurance subsidiaries reinsure portions of the risks they underwrite or assume with multiple reinsurance programs. (b) Reinsurance Recoverables Amounts recoverable from reinsurers are recognized in a manner consistent with the loss and LAE liabilities associated with the reinsurance placement and presented on the balance sheet as reinsurance recoverables, and are recorded after an allowance for credit losses. Such balances as of December 31, 2021 and 2020 are presented in the table below: As of December 31, 2021 2020 ($ in millions) Reinsurance recoverables on paid losses $ 173.1 $ 85.3 Ceded outstanding loss and LAE 2,026.1 1,703.7 Reinsurance recoverables, before allowance for credit losses 2,199.2 1,789.0 Allowance for credit losses ( 3.2 ) ( 7.9 ) Total $ 2,196.0 $ 1,781.1 The following table presents information regarding concentration of Alleghany’s reinsurance recoverables and the ratings profile of its reinsurers as of December 31, 2021: Reinsurer (1) Rating (2) Amount Percentage ($ in millions) Syndicates at Lloyd's of London A (Excellent) $ 154.5 7.0 % Kane SAC Ltd, Rondout Segregated Account (3) not rated 154.3 7.0 % PartnerRe Ltd A (Excellent) 142.7 6.5 % RenaissanceRe Holdings Ltd A+ (Superior) 135.5 6.2 % Fairfax Financial Holdings Ltd A (Excellent) 124.4 5.7 % Swiss Reinsurance Company A+ (Superior) 99.2 4.5 % Integral Reinsurance Ltd. (3) not rated 97.4 4.4 % Chubb Ltd. A++ (Superior) 79.3 3.6 % W.R. Berkley Corporation A+ (Superior) 77.0 3.5 % SiriusPoint Ltd. A- (Excellent) 73.6 3.3 % All other reinsurers 1,061.3 48.3 % Total reinsurance recoverables, before allowance for credit losses (4) 2,199.2 100.0 % Allowance for credit losses ( 3.2 ) Total $ 2,196.0 Secured reinsurance recoverables (3) $ 967.7 44.0 % (1) Reinsurance recoverables reflect amounts due from one or more reinsurance subsidiaries of the listed company. (2) Represents the A.M. Best Company, Inc. financial strength rating for the applicable reinsurance subsidiary or subsidiaries from which the reinsurance recoverable is due. (3) Represents reinsurance recoverables secured by funds held, trust agreements or letters of credit. (4) Approximately 66 percent of Alleghany’s reinsurance recoverables balance as of December 31, 2021 was due from reinsurers having an A.M. Best Company, Inc. financial strength rating of A (Excellent) or higher, with a majority of the other reinsurance recoverables being secured by funds held, trust agreements or letters of credit. The following table presents a rollforward of Alleghany’s allowance for credit losses on reinsurance recoverables for 2021 and 2020: Year Ended December 31, 2021 2020 ($ in millions) Allowance for Credit Losses Beginning balance $ 7.9 $ — Beginning balance - cumulative effect of an accounting change — 3.3 Provision for credit losses ( 4.7 ) 4.6 Charge-offs — — Recoveries — — Ending balance $ 3.2 $ 7.9 Reinsured loss and LAE ceded included in Alleghany’s consolidated statements of earnings wer e $ 866.6 million, $ 562.7 million and $ 407.7 million for 2021, 2020 and 2019, respectively. (c) Premiums Written and Earned The following table presents property and casualty premiums written and earned for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Gross premiums written – direct $ 2,704.3 $ 2,214.6 $ 1,800.3 Gross premiums written – assumed 5,834.5 5,114.8 4,856.1 Ceded premiums written ( 1,389.4 ) ( 985.0 ) ( 904.7 ) Net premiums written $ 7,149.4 $ 6,344.4 $ 5,751.7 Gross premiums earned – direct $ 3,005.7 $ 2,370.4 $ 2,114.1 Gross premiums earned – assumed 5,364.8 4,582.9 4,268.8 Ceded premiums earned ( 1,272.8 ) ( 953.1 ) ( 904.8 ) Net premiums earned $ 7,097.7 $ 6,000.2 $ 5,478.1 (d) Significant Reinsurance Contracts Alleghany’s reinsurance and insurance subsidiaries reinsure portions of the risks they underwrite or assume with multiple reinsurance programs. A summary of the more significant programs follows. TransRe enters into various retrocession arrangements, including property catastrophe retrocession contracts, to manage the effects of individual or aggregate exposure to losses, reduce volatility in specific lines of business, improve risk-adjusted portfolio returns, strengthen its market position and enhance capital efficiency. These include excess-of-loss and quota share treaties in both traditional rated and collateralized form as well as catastrophe bonds. TransRe’s retrocession protections generally have a one-year term and renewal dates occur throughout the year, with the majority renewing at January 1. The catastrophe bonds, however, have a four-year term, with maturities in 2022 and 2023. RSUI reinsures its property lines of business through a program consisting of surplus share treaties, facultative placements, and per risk and catastrophe excess of loss treaties. RSUI’s catastrophe reinsurance program and property per risk reinsurance program each run on an annual basis from May 1 to the following April 30 and portions expired on April 30, 2021. Both programs were renewed on May 1, 2021 with substantially similar terms as the expired programs. RSUI reinsures certain portions of its casualty lines of business utilizing various quota share treaties and facultative placements. (e) Significant AIHL Re Reinsurance Contracts AIHL Re and CapSpecialty entered into an intercompany reinsurance contract, effective July 1, 2015, pursuant to which AIHL Re provides CapSpecialty with coverage primarily for adverse development on certain net loss and allocated LAE in excess of its carried reserves at June 30, 2015. AIHL Re’s commitments are intended to cover the statutory collateral requirements at CapSpecialty, if and when necessary, and AIHL Re’s obligations are subject to an aggregate limit of $ 50.0 million. In connection with such intercompany reinsurance agreement, Alleghany and AIHL Re entered into a contract whereby Alleghany will guarantee the recoverable balances owed to CapSpecialty from AIHL Re up to $ 50.0 million. The above agreements had no impact on Alleghany’s consolidated results of operations and financial condition. In connection with the December 31, 2017 sale of Pacific Compensation Corporation (“PacificComp”) by AIHL, AIHL Re provides adverse development reinsurance coverage to the acquirer on PacificComp’s pre-acquisition claims, subject to certain terms and conditions. AIHL Re’s obligation, which are guaranteed by Alleghany, are subject to an aggregate limit of $ 150.0 million and a final commutation and settlement as of December 31, 2024.

Liability for Loss and LAE

Liability for Loss and LAE	12 Months Ended
	Dec. 31, 2021
Insurance [Abstract]
Liability for Loss and LAE	6. Liability for Loss and LAE (a) Liability Rollforward The following table presents the activity in the liability for loss and LAE in 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Reserves as of January 1 $ 12,970.6 $ 11,928.4 $ 12,250.3 Less: reinsurance recoverables (1) 1,703.7 1,583.9 1,857.4 Net reserves as of January 1 11,266.9 10,344.5 10,392.9 Other adjustments 0.1 ( 4.0 ) ( 2.3 ) Incurred loss and LAE, net of reinsurance, related to: Current year 5,084.6 4,559.9 3,871.1 Prior years ( 249.7 ) ( 220.8 ) ( 184.7 ) Total incurred loss and LAE, net of reinsurance 4,834.9 4,339.1 3,686.4 Paid loss and LAE, net of reinsurance, related to: (2) Current year 1,032.8 931.7 884.6 Prior years 2,655.9 2,571.8 2,839.9 Total paid loss and LAE, net of reinsurance 3,688.7 3,503.5 3,724.5 Foreign currency exchange rate effect ( 81.7 ) 90.8 ( 8.0 ) Net reserves as of December 31 12,331.5 11,266.9 10,344.5 Reinsurance recoverables as of December 31 (1) 2,026.1 1,703.7 1,583.9 Reserves as of December 31 $ 14,357.6 $ 12,970.6 $ 11,928.4 (1) Reinsurance recoverables in this table include only ceded loss and LAE reserves. (2) Includes paid loss and LAE, net of reinsurance, related to commutations. Gross loss and LAE reserves as of December 31, 2021 increased from December 31, 2020 , primarily reflecting the impact of growing net premiums earned and catastrophe losses incurred in 2021, partially offset by payments on catastrophe losses incurred in prior years and favorable prior accident year loss reserve development. The 2021 catastrophe losses, net of reinsurance, include $ 268.7 million from Hurricane Ida in August and early September 2021, $ 252.8 million, related to Winter Storm Uri and other storms in February 2021, primarily in Texas, $ 125.2 million from severe flooding in Northwestern and Central Europe in July 2021 and $ 18.5 million in December 2021 from the Midwest Tornadoes, primarily in Kentucky. Gross loss and LAE reserves as of December 31, 2020 increased from December 31, 2019 , primarily reflecting the impact 415.2 million related to the COVID-19 global pandemic (the “Pandemic”), $ 114.2 million 92.6 million related to Hurricane Sally and $ 19.1 million related to earthquakes in Puerto Rico. (b) Liability Development The following table presents the (favorable) unfavorable prior accident year loss reserve development for 2021, 2020 and 2019: Year Ended December, 2021 2020 2019 ($ in millions) Reinsurance Segment Property: Catastrophe events (excluding Pandemic) $ ( 35.5 ) (1) $ ( 43.3 ) (2) $ ( 6.8 ) (3) Pandemic 62.6 - - Non-catastrophe ( 50.9 ) (4) ( 33.6 ) (5) ( 39.4 ) (6) Total ( 23.8 ) ( 76.9 ) ( 46.2 ) Casualty & specialty: Catastrophe events (excluding Pandemic) ( 0.4 ) ( 5.9 ) ( 4.4 ) Pandemic ( 48.9 ) — — Non-catastrophe ( 176.5 ) (7) ( 124.1 ) (8) ( 145.2 ) (9) Total ( 225.8 ) ( 130.0 ) ( 149.6 ) Total Reinsurance Segment ( 249.6 ) ( 206.9 ) ( 195.8 ) Insurance Segment RSUI: Casualty 5.0 (10) 1.8 (11) ( 16.3 ) (12) Property and other ( 11.1 ) (13) ( 14.6 ) (14) ( 1.2 ) (15) Total ( 6.1 ) ( 12.8 ) ( 17.5 ) CapSpecialty: Ongoing lines of business 6.1 (16) ( 2.0 ) (17) 26.1 (18) Terminated Program (19) ( 0.1 ) 0.9 3.0 Asbestos-related illness and environmental impairment liability — — ( 0.5 ) Total 6.0 ( 1.1 ) 28.6 Total incurred related to prior years $ ( 249.7 ) $ ( 220.8 ) $ ( 184.7 ) (1) Primarily reflects favorable prior accident year loss reserve development related to catastrophic events in the 2018 accident year, partially offset by unfavorable prior accident year loss reserve development related to Hurricane Laura and Sally in the 2020 accident year. (2) Primarily reflects favorable prior accident year loss reserve development related to Typhoon Hagibis in the 2019 accident year and wildfires in California in the 2017 and 2018 accident years, partially offset by unfavorable prior accident year loss reserve development related to Hurricane Irma in the 2017 accident year and Typhoon Faxai in the 2019 accident year. (3) Primarily reflects favorable prior accident year loss reserve development related to wildfires in California in the 2018 accident year, partially offset by unfavorable prior accident year loss reserve development related to Typhoon Jebi in the 2018 accident year and Hurricane Irma in the 2017 accident year. (4) Primarily reflects favorable prior accident year loss reserve development in the 2020 accident year. (5) Primarily reflects favorable prior accident year loss reserve development in the 2017 accident year. (6) Primarily reflects favorable prior accident year loss reserve development in the 2016 and 2017 accident years, partially offset by unfavorable prior accident year loss reserve development in the 2018 accident year. (7) Primarily reflects favorable prior accident year loss reserve development in the shorter-tailed lines of business in the 2020 accident year and in both the longer- and shorter-tailed lines of business in the 2015 and earlier accident years, partially offset by unfavorable prior accident year loss reserve development in the longer-tailed lines of business in the 2016 to 2018 accident years. (8) Primarily reflects favorable prior accident year loss reserve development in the longer-tailed casualty lines of business in the 2014 and prior accident years and, to a lesser extent, shorter-tailed lines of business in the 2014 and prior accident years, partially offset by unfavorable prior accident year loss reserve development in the marine and aviation lines of business in the 2018 accident year. (9) Primarily reflects favorable prior accident year loss reserve development in the longer-tailed casualty lines of business in the 2014 and prior accident years and, to a lesser extent, shorter-tailed lines of business in the 2014 and prior accident years, partially offset by unfavorable prior accident year loss reserve development in the marine and aviation lines of business in the 2018 accident year. (10) Primarily reflects unfavorable prior accident year loss reserve development in the directors’ and officers’ liability lines of business in the 2012 and 2014 accident years and, to a lesser extent, the general liability and binding authority lines of business in earlier accident years, partially offset by favorable prior accident year loss reserve development in the umbrella/excess lines of business in the 2005 through 2015 accident years. (11) Primarily reflects unfavorable prior accident year loss reserve development in the professional liability lines of business in the 2 017 through 2019 accident years, partially offset by favorable prior accident year loss reserve development in the directors’ and officers’ liability and umbrella/excess lines of business in the 2011 through 2015 accident years. (12) Primarily reflects favorable prior accident year loss reserve development in the directors’ and officers’ liability and umbrella/excess lines of business in the 2011 through 2015 accident years, partially offset by unfavorable prior accident year loss reserve development in the professional liability lines of business in the 2016 through 2018 accident years. (13) Primarily reflects favorable prior accident year loss reserve development related to losses not classified as catastrophes in recent accident years and, to a lesser extent, catastrophes in the 2017, 2018 and 2019 accident years, partially offset by unfavorable prior accident year loss reserve development related to catastrophes in the 2020 accident year. (14) Primarily reflects favorable prior accident year loss reserve development related to U.S. catastrophe losses in the 2018 accident year and, to a lesser extent, favorable prior accident year loss reserve development related to the assumed property reinsurance lines of business from catastrophe losses in the 2019 and 2018 accident years. (15) Primarily reflects favorable prior accident year loss reserve development related to Superstorm Sandy in the 2012 accident year, Hurricanes Florence and Michael in the 2018 accident year and Hurricanes Harvey and Maria in the 2017 accident year, partially offset by unfavorable prior accident year loss reserve development related to assumed property reinsurance lines of business from both catastrophe and non-catastrophe losses in the 2018 accident year. (16) Primarily reflects unfavorable prior accident year loss reserve development in the healthcare, construction liability and other casualty lines of business in the 2015 through 2017 accident years. (17) Primarily reflects favorable prior acciden t year loss reserve development in the surety lines of business in recent accident years. (18) Primarily reflects unfavorable prior accident loss reserve development related to the professional liability and other casualty lines of business in the 2015 through 2018 accident years. (19) Represents certain specialty lines of business written through a program administrator in connection with a terminated program in the 2010 and 2009 accident years and reflects favorable loss emergence compared with loss emergence patterns assumed in earlier periods for such business. (c) Information on Incurred and Paid Loss and LAE Development The following is information about incurred and paid loss and LAE development, net of reinsurance. The information for the years ended December 31, 2012 through 2020 is unaudited and is provided as supplementary information. Information is also included for the portion of unpaid loss and LAE, net of reinsurance recoverables, that relate to IBNR and, for the insurance segment, the cumulative number of reported insurance claims. For the reinsurance segment, reported insurance claim information is generally not received from the cedants, and such information is therefore impracticable to disclose. Reinsurance Segment Property Incurred Loss and LAE, Net of Reinsurance As of Year Ended December 31, December 31, 2021 Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 IBNR ($ in millions) 2012 $ 697.2 $ 579.1 $ 530.3 $ 495.6 $ 478.1 $ 469.4 $ 462.5 $ 460.3 $ 454.9 $ 456.1 $ — 2013 501.2 470.6 444.6 422.1 406.8 403.6 398.1 394.7 394.0 — 2014 496.4 464.8 451.3 435.2 429.8 425.1 419.7 416.2 — 2015 368.8 332.0 320.6 306.3 301.9 297.9 295.5 1.4 2016 684.1 647.2 596.7 587.9 577.8 578.1 2.6 2017 1,174.6 1,179.5 1,148.3 1,127.7 1,114.8 20.2 2018 1,152.7 1,169.4 1,147.8 1,116.8 49.1 2019 988.7 981.5 972.2 56.0 2020 1,207.5 1,253.5 297.1 2021 1,468.1 640.3 Total Incurred Loss and LAE for the 2012 through 2021 accident years $ 8,065.3 Paid Loss and LAE, Net of Reinsurance Year Ended December 31, Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 ($ in millions) 2012 $ 90.3 $ 268.9 $ 377.8 $ 416.7 $ 438.0 $ 448.0 $ 451.2 $ 460.1 $ 461.1 $ 466.6 2013 113.1 277.4 361.0 389.8 396.7 399.7 401.4 403.0 403.9 2014 109.4 297.6 360.0 382.9 394.0 397.3 398.4 399.4 2015 96.0 217.7 278.3 303.1 307.6 308.8 311.9 2016 210.5 429.8 504.8 535.1 552.2 563.9 2017 324.5 818.5 977.9 1,023.0 1,039.9 2018 309.5 811.8 944.2 1,002.3 2019 265.1 645.5 793.2 2020 301.1 732.1 2021 413.5 Cumulative Paid Loss and LAE for the 2012 through 2021 accident years $ 6,126.7 Total incurred loss and LAE for the 2012 through 2021 accident years $ 8,065.3 Cumulative paid loss and LAE for the 2012 through 2021 accident years 6,126.7 Unpaid loss and LAE, net of reinsurance recoverables, for accident years prior to 2012 19.7 Unpaid loss and LAE, net of reinsurance recoverables, as of December 31, 2021 $ 1,958.3 Reinsurance Segment Casualty & specialty – Longer-Tailed Lines of Business (1) Incurred Loss and LAE, Net of Reinsurance As of Year Ended December 31, December 31, 2021 Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 IBNR ($ in millions) 2012 $ 877.5 $ 877.5 $ 875.9 $ 860.8 $ 833.1 $ 829.8 $ 832.4 $ 826.4 $ 819.7 $ 802.3 $ 60.9 2013 798.6 802.2 799.2 777.5 776.7 783.0 767.4 740.5 726.8 100.8 2014 801.8 791.1 794.3 793.9 790.3 784.8 771.7 764.0 126.2 2015 794.8 799.0 797.0 793.7 799.1 799.6 798.2 123.0 2016 776.7 776.8 787.4 807.8 842.2 862.9 126.0 2017 764.4 765.7 783.4 800.1 824.0 180.3 2018 727.3 741.6 752.5 767.4 279.5 2019 759.7 761.6 765.4 415.2 2020 978.1 952.4 729.1 2021 1,239.9 1,124.0 Total Incurred Loss and LAE for the 2012 through 2021 accident years $ 8,503.3 Paid Loss and LAE, Net of Reinsurance Year Ended December 31, Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 ($ in millions) 2012 $ 46.9 $ 106.8 $ 201.1 $ 316.6 $ 435.7 $ 521.3 $ 587.0 $ 624.4 $ 648.7 $ 677.8 2013 22.2 85.1 176.6 296.4 378.0 452.7 494.6 528.5 558.8 2014 29.8 107.5 229.6 342.9 444.7 522.7 580.6 619.2 2015 32.2 100.4 205.0 325.8 455.8 536.5 595.9 2016 34.8 121.8 242.9 370.0 491.1 573.6 2017 34.0 110.6 221.8 347.5 447.9 2018 33.0 104.6 206.7 324.7 2019 29.0 99.7 202.5 2020 47.2 127.6 2021 48.3 Cumulative Paid Loss and LAE for the 2012 through 2021 accident years $ 4,176.3 Total incurred loss and LAE for the 2012 through 2021 accident years $ 8,503.3 Cumulative paid loss and LAE for the 2012 through 2021 accident years 4,176.3 Unpaid loss and LAE, net of reinsurance recoverables, for accident years prior to 2012 793.5 Unpaid loss and LAE, net of reinsurance recoverables, as of December 31, 2021 $ 5,120.5 (1) Represents the following reinsurance lines of business: directors’ and officers’ liability; errors and omissions liability; general liability; and medical malpractice. Reinsurance Segment Casualty & specialty – Shorter-Tailed Lines of Business (1) Incurred Loss and LAE, Net of Reinsurance As of Year Ended December 31, December 31, 2021 Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 IBNR ($ in millions) 2012 $ 1,022.3 $ 1,059.9 $ 1,056.8 $ 1,005.5 $ 983.9 $ 958.9 $ 948.4 $ 941.4 $ 933.9 $ 929.9 $ 6.4 2013 850.8 868.8 838.4 823.4 804.1 790.3 780.7 769.6 764.5 9.2 2014 850.4 833.0 808.8 784.3 772.4 755.0 752.5 740.8 15.2 2015 763.4 768.6 784.0 798.4 776.7 776.2 771.9 17.0 2016 1,118.0 1,124.4 1,111.6 1,100.3 1,092.6 1,085.2 25.7 2017 1,095.9 1,046.3 1,026.9 994.5 989.0 49.0 2018 1,255.4 1,266.1 1,270.7 1,267.3 89.2 2019 1,408.6 1,411.8 1,400.7 159.8 2020 1,408.2 1,335.1 325.8 2021 1,333.1 729.0 Total Incurred Loss and LAE for the 2012 through 2021 accident years $ 10,617.5 Paid Loss and LAE, Net of Reinsurance Year Ended December 31, Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 ($ in millions) 2012 $ 354.8 $ 614.5 $ 740.0 $ 792.7 $ 828.3 $ 846.5 $ 860.2 $ 871.4 $ 876.1 $ 880.3 2013 265.4 523.5 613.3 663.0 685.5 704.9 717.5 723.9 730.7 2014 251.2 421.1 523.3 572.9 604.6 627.8 636.8 647.8 2015 218.5 409.1 518.7 577.7 629.1 653.2 669.5 2016 367.2 685.6 828.7 921.3 973.8 1,002.0 2017 342.8 639.1 793.5 867.6 909.8 2018 397.9 774.4 952.2 1,033.3 2019 462.0 881.3 1,051.3 2020 418.0 810.7 2021 411.4 Cumulative Paid Loss and LAE for the 2012 through 2021 accident years $ 8,146.8 Total incurred loss and LAE for the 2012 through 2021 accident years $ 10,617.5 Cumulative paid loss and LAE for the 2012 through 2021 accident years 8,146.8 Unpaid loss and LAE, net of reinsurance recoverables, for accident years prior to 2012 151.6 Unpaid loss and LAE, net of reinsurance recoverables, as of December 31, 2021 $ 2,622.3 (1) Primarily represents the following reinsurance lines of business: ocean marine and aviation; auto liability; accident & health; mortgage reinsurance; surety; and credit. Insurance Segment RSUI - Property As of Incurred Loss and LAE, Net of Reinsurance Cumulative Year Ended December 31, Number of Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 IBNR Reported (1) ($ in millions) 2012 $ 270.9 $ 262.5 $ 258.6 $ 256.1 $ 235.1 $ 236.1 $ 235.5 $ 228.3 $ 228.4 $ 228.2 $ 0.8 2,313 2013 157.3 157.2 150.4 152.1 152.4 152.5 154.3 154.4 153.5 1.1 2,395 2014 170.7 166.2 155.9 153.7 153.8 153.6 153.4 153.3 1.1 3,094 2015 140.5 136.1 142.6 141.3 140.1 140.2 140.4 1.5 3,004 2016 181.4 170.5 172.9 173.9 175.3 175.1 2.4 3,368 2017 330.7 306.5 304.1 300.0 296.7 10.6 3,696 2018 259.9 265.7 256.7 237.0 9.6 3,071 2019 204.3 200.9 205.1 13.9 3,343 2020 357.2 365.4 40.6 4,257 2021 341.5 80.6 3,193 Total Incurred Loss and LAE for the 2012 through 2021 accident years $ 2,296.2 Paid Loss and LAE, Net of Reinsurance Year Ended December 31, Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 ($ in millions) 2012 $ 62.0 $ 157.5 $ 181.9 $ 193.5 $ 202.4 $ 216.2 $ 216.7 $ 219.2 $ 219.4 $ 222.5 2013 72.7 118.7 134.0 141.1 144.0 148.7 151.5 151.8 152.1 2014 93.2 133.8 145.0 148.8 150.3 151.3 151.6 151.9 2015 70.8 106.9 120.0 129.8 136.5 138.0 138.5 2016 72.0 127.1 147.1 161.2 167.3 169.8 2017 88.6 213.3 253.3 267.3 278.5 2018 62.3 175.1 202.9 216.1 2019 79.8 145.8 167.1 2020 118.8 251.2 2021 137.2 Cumulative Paid Loss and LAE for the 2012 through 2021 accident years $ 1,885.0 Total incurred loss and LAE for the 2012 through 2021 accident years $ 2,296.2 Cumulative paid loss and LAE for the 2012 through 2021 accident years 1,885.0 Unpaid loss and LAE, net of reinsurance recoverables, for accident years prior to 2012 4.3 Unpaid loss and LAE, net of reinsurance recoverables, as of December 31, 2021 $ 415.5 (1) Represents claims reported by insured claimants. Insurance Segment RSUI - Casualty As of Incurred Loss and LAE, Net of Reinsurance Cumulative Year Ended December 31, Number of Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 IBNR Reported (1) ($ in millions) 2012 $ 226.3 $ 226.3 $ 230.3 $ 242.8 $ 238.9 $ 233.8 $ 231.9 $ 221.8 $ 210.2 $ 213.4 $ 12.3 7,726 2013 264.8 264.8 277.6 280.1 279.0 273.5 269.6 261.4 263.7 30.1 8,791 2014 292.0 322.7 321.1 322.4 320.3 310.9 300.3 301.7 29.7 10,293 2015 300.2 300.2 304.2 302.2 291.4 289.8 283.6 54.9 9,489 2016 290.7 293.7 301.3 312.0 317.5 317.8 56.7 9,110 2017 282.5 286.4 299.1 311.1 309.7 79.2 9,073 2018 290.0 301.5 310.0 312.8 95.8 9,441 2019 316.9 332.2 332.2 171.9 8,792 2020 393.9 393.9 291.5 7,690 2021 470.2 430.8 6,909 Total Incurred Loss and LAE for the 2012 through 2021 accident years $ 3,199.0 Paid Loss and LAE, Net of Reinsurance Year Ended December 31, Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 ($ in millions) 2012 $ 6.8 $ 38.4 $ 96.0 $ 125.5 $ 144.0 $ 159.3 $ 166.7 $ 176.1 $ 178.5 $ 180.2 2013 10.1 50.0 103.4 146.2 176.6 191.3 203.9 212.9 222.8 2014 13.0 69.5 130.1 179.1 206.5 234.6 249.1 259.7 2015 9.0 47.3 96.6 129.2 176.5 196.2 207.3 2016 13.7 69.2 123.6 197.8 220.8 239.1 2017 9.4 63.6 115.6 163.1 196.2 2018 13.0 70.4 116.8 165.6 2019 12.9 57.9 104.2 2020 12.6 45.7 2021 10.2 Cumulative Paid Loss and LAE for the 2012 through 2021 accident years $ 1,631.0 Total incurred loss and LAE for the 2012 through 2021 accident years $ 3,199.0 Cumulative paid loss and LAE for the 2012 through 2021 accident years 1,631.0 Unpaid loss and LAE, net of reinsurance recoverables, for accident years prior to 2012 80.4 Unpaid loss and LAE, net of reinsurance recoverables, as of December 31, 2021 $ 1,648.4 (1) Represents claims reported by insured claimants. Insurance Segment CapSpecialty (1) As of Incurred Loss and LAE, Net of Reinsurance Cumulative Year Ended December 31, Number of Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 IBNR Reported (2) ($ in millions) 2012 $ 72.7 $ 71.8 $ 66.2 $ 69.3 $ 69.7 $ 68.7 $ 68.8 $ 69.1 $ 69.1 $ 68.9 $ 0.3 5,269 2013 78.7 81.4 85.2 84.4 87.2 88.6 87.4 87.4 88.1 1.1 5,181 2014 102.8 102.7 101.0 100.2 98.6 97.6 97.7 99.0 1.4 6,050 2015 111.0 111.8 109.2 109.7 112.4 115.2 118.0 3.3 5,666 2016 129.4 132.4 132.7 135.0 133.4 136.7 4.4 6,297 2017 147.3 143.7 157.6 156.2 159.9 9.7 6,561 2018 164.1 173.3 176.5 180.9 22.3 6,848 2019 193.0 188.9 185.4 58.4 6,171 2020 214.9 209.5 116.8 4,917 2021 231.7 183.7 4,616 Total Incurred Loss and LAE for the 2012 through 2021 accident years $ 1,478.1 Paid Loss and LAE, Net of Reinsurance Year Ended December 31, Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 ($ in millions) 2012 $ 18.6 $ 38.6 $ 46.9 $ 57.2 $ 63.3 $ 65.0 $ 66.5 $ 67.7 $ 67.7 $ 68.2 2013 23.4 48.0 62.0 69.6 78.6 84.5 85.3 86.1 86.5 2014 34.0 56.3 71.9 83.1 89.8 93.1 94.2 95.1 2015 30.9 57.4 73.5 88.8 101.1 106.7 110.5 2016 30.3 64.0 86.6 106.1 116.3 123.2 2017 30.1 65.6 95.1 116.1 126.6 2018 31.7 72.4 102.1 130.4 2019 29.8 62.5 88.5 2020 27.8 60.9 2021 26.1 Cumulative Paid Loss and LAE for the 2012 through 2021 accident years $ 916.0 Total incurred loss and LAE for the 2012 through 2021 accident years $ 1,478.1 Cumulative paid loss and LAE for the 2012 through 2021 accident years 916.0 Unpaid loss and LAE, net of reinsurance recoverables, for accident years prior to 2012 4.4 Unpaid loss and LAE, net of reinsurance recoverables, as of December 31, 2021 $ 566.5 (1) The vast majority of the CapSpecialty’s loss and LAE reserves relate to its casualty lines of business. (2) Represents claims reported by insured claimants. Loss and LAE Reserve Summary and Reconciliation to Consolidated Balance Sheet Unpaid loss and LAE as of December 31, 2021 (1) Gross Loss and Reinsurance Net Loss and ($ in millions) Reinsurance Segment: Property $ 2,599.4 $ 641.1 $ 1,958.3 Casualty & specialty - Longer-Tailed Lines of Business 5,264.9 144.4 5,120.5 Casualty & specialty - Shorter-Tailed Lines of Business 2,883.9 261.6 2,622.3 10,748.2 1,047.1 9,701.1 Insurance Segment: RSUI - Property 617.0 201.5 415.5 RSUI - Casualty 2,399.2 750.8 1,648.4 RSUI 3,016.2 952.3 2,063.9 CapSpecialty 669.8 103.3 566.5 3,686.0 1,055.6 2,630.4 Eliminations ( 76.6 ) ( 76.6 ) — Total $ 14,357.6 $ 2,026.1 $ 12,331.5 (1) Includes unallocated LAE, which aggregate t o 1.0 perce nt of gross loss and LAE reserves as of December 31, 2021 . Net loss and LAE reserves by component are shown in the preceding tables, and consolidated gross loss and LAE reserves is presented in the consolidated balance sheets. (d) Supplementary Information on Historical Loss and LAE Duration (Unaudited) The following table presents supplemental information about average historical loss and LAE duration, net of reinsurance, as of December 31, 2021. Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance As of December 31, 2021 Years 1 2 3 4 5 6 7 8 9 10 Reinsurance Segment: Property 28.0 % 40.9 % 16.9 % 6.3 % 2.5 % 1.2 % 0.6 % 0.9 % 0.2 % 1.2 % Casualty & specialty - Longer-Tailed Lines of Business 4.2 % 9.0 % 13.5 % 15.2 % 13.6 % 10.2 % 7.2 % 4.8 % 3.6 % 3.6 % Casualty & specialty - Shorter-Tailed Lines of Business 33.0 % 28.6 % 13.5 % 7.0 % 4.5 % 2.7 % 1.6 % 1.2 % 0.7 % 0.5 % Insurance Segment: RSUI - Property 34.7 % 13.9 % 6.1 % 3.1 % 2.5 % 0.8 % 0.6 % 0.1 % 0.2 % 1.3 % RSUI - Casualty 14.4 % 17.8 % 17.3 % 13.0 % 10.7 % 6.3 % 5.1 % 3.6 % 3.9 % 1.9 % CapSpecialty 19.1 % 21.6 % 15.6 % 13.3 % 8.2 % 4.6 % 1.9 % 1.1 % 0.3 % 0.7 %

Credit Agreements

Credit Agreements	12 Months Ended
	Dec. 31, 2021
Credit Agreement [Abstract]
Credit Agreements	7. Credit Agreements On July 31, 2017 , Alleghany entered into a five-year credit agreement (the “Credit Agreement”) with certain lenders party thereto, which provides for an unsecured revolving credit facility in an aggregate principal amount of up to $ 300.0 million. The credit facility is scheduled to expire on July 31, 2022 , unless earlier terminated. Borrowings under the Credit Agreement will be available for working capital and general corporate purposes, including permitted acquisitions and repurchases of Common Stock. Borrowings under the Credit Agreement bear a floating rate of interest based in part on Alleghany’s credit rating, among other factors. The Credit Agreement contains representations, warranties and covenants customary for bank loan facilities of this nature. There were no borrowings under the Credit Agreement in 2021, 2020 and 2019 and there were no outstanding borrowings under the Credit Agreement as of December 31, 2021. In addition to the Credit Agreement, several of Alleghany Capital’s subsidiaries have credit agreements with third-party financial institutions. Any borrowings under such agreements are not guaranteed by Alleghany or Alleghany Capital. See Note 8(c) for information on the borrowings arising from these credit agreements.

Debt

Debt	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
Debt	8. Debt (a) Alleghany Senior Notes On August 13, 2021, Alleghany completed a public offering of $ 500.0 million aggregate principal amount of its 3.250 % senior notes due on August 15, 2051 (the “2051 Senior Notes”). The 2051 Senior Notes are unsecured and unsubordinated general Interest on the 2051 Senior Notes is payable semi-annually in arrears on February 15 and August 15 of each year, commencing February 15, 2022. The terms of the 2051 Senior Notes permit redemption prior to maturity. The indenture under which the 2051 Senior Notes were issued contains covenants that impose conditions on Alleghany’s ability to create liens on the capital stock of AIHL, TransRe or RSUI. The 2051 Senior Notes were issued at approximately 98.6 percent of par, resulting in proceeds after underwriting discount, commissions and other expenses of $ 487.5 million, and an effective yield of approximately 3.32 percent. Approximately $ 5.7 million of underwriting discount, commissions and other expenses were recorded as deferred charges, which are amortized over the life of the 2051 Senior Notes. Alleghany intends to use the net proceeds of this offering for general corporate purposes, which may include the repayment at maturity of the 4.95 % senior notes due June 27, 2022 (the “2022 Senior Notes”), which are further described below. On May 18, 2020, Alleghany completed a public offering of $ 500.0 million aggregate principal amount of its 3.625 % senior notes due on May 15, 2030 (the “2030 Senior Notes”). The 2030 Senior Notes are unsecured and unsubordinated general obligations of Alleghany. Interest on the 2030 Senior Notes is payable semi-annually in arrears on May 15 and November 15 of each year. The terms of the 2030 Senior Notes permit redemption prior to maturity. The indenture under which the 2030 Senior Notes were issued contains covenants that impose conditions on Alleghany’s ability to create liens on the capital stock of AIHL, TransRe or RSUI. The 2030 Senior Notes were issued at approximately 99.9 percent of par, resulting in proceeds after underwriting discount, commissions and other expenses of $ 494.8 million, and an effective yield of approximately 3.64 percent. Approximately $ 4.6 million of underwriting discount, commissions and other expenses were recorded as deferred charges, which are amortized over the life of the 2030 Senior Notes. On September 9, 2014, Alleghany completed a public offering of $ 300.0 million aggregate principal amount of its 4.90 % senior notes due on September 15, 2044 (the “2044 Senior Notes”). The 2044 Senior Notes are unsecured and unsubordinated general obligations of Alleghany. Interest on the 2044 Senior Notes is payable semi-annually on March 15 and September 15 of each year. The terms of the 2044 Senior Notes permit redemption prior to their maturity. The indenture under which the 2044 Senior Notes were issued contains covenants that impose conditions on Alleghany’s ability to create liens on, or engage in sales of, the capital stock of AIHL, TransRe or RSUI. The 2044 Senior Notes were issued at approximately 99.3 percent of par, resulting in proceeds after underwriting discount, commissions and other expenses of $ 294.3 million and an effective yield of approximately 5.0 percent. On June 26, 2012, Alleghany completed a public offering of $ 400.0 million aggregate principal amount of its 2022 Senior Notes. The 2022 Senior Notes are unsecured and unsubordinated general obligations of Alleghany. Interest on the 2022 Senior Notes is payable semi-annually on June 27 and December 27 of each year. The terms of the 2022 Senior Notes permit redemption prior to their maturity. The indenture under which the 2022 Senior Notes were issued contains covenants that impose conditions on Alleghany’s ability to create liens on, or engage in sales of, the capital stock of AIHL, TransRe or RSUI. The 2022 Senior Notes were issued at approximately 99.9 percent of par, resulting in proceeds after underwriting discount, commissions and other expenses of $ 396.0 million and an effective yield of approximately 5.05 percent. On September 20, 2010, Alleghany completed a public offering of $ 300.0 million aggregate principal amount of its 5.625 % senior notes due on September 15, 2020 (the “2020 Senior Notes”). The 2020 Senior Notes are unsecured and unsubordinated general obligations of Alleghany. Interest on the 2020 Senior Notes is payable semi-annually on March 15 and September 15 of each year. The terms of the 2020 Senior Notes permit redemption prior to their maturity. The indenture under which the 2020 Senior Notes were issued contains covenants that impose conditions on Alleghany’s ability to create liens on, or engage in sales of, the capital stock of AIHL or RSUI. The 2020 Senior Notes were issued at approximately 99.6 percent of par, resulting in proceeds after underwriting discount, commissions and other expenses of $ 298.9 million and an effective yield of approximately 5.67 percent. On January 15, 2020, Alleghany redeemed all of its outstanding 2020 Senior Notes for $ 312.7 million, consisting of the $ 300.0 million aggregate principal amount redeemed, $ 7.1 million of redemption premium and $ 5.6 million of accrued and unpaid interest on the principal amount being redeemed to the date of redemption. As a result of this early extinguishment of debt, Alleghany recorded a realized loss, before tax, of $ 7.1 million in 2020. (b) TransRe Senior Notes On November 23, 2009, TransRe completed a public offering of $ 350.0 million aggregate principal amount of its 8.00 % senior notes due on November 30, 2039 (the “2039 Senior Notes”). The 2039 Senior Notes are unsecured and unsubordinated general obligations of TransRe and are not guaranteed by Alleghany. Interest on the 2039 Senior Notes is payable semi-annually . The terms of the 2039 Senior Notes permit redemption prior to their maturity. The indentures under which the 2039 Senior Notes were issued contain covenants that impose conditions on TransRe’s ability to create liens on, or engage in sales of, the capital stock of certain of its subsidiaries, including Transatlantic Reinsurance Company, TransRe Europe S.A. or Fair American Insurance and Reinsurance Company. (c) Alleghany Capital Operating Subsidiaries The debt associated with Alleghany Capital’s operating subsidiaries totaled $ 780.5 million and $ 556.9 million as of December 31, 2021 and 2020, respectively, and is generally used to support working capital needs and to help finance acquisitions. As of December 31, 2021 , the $ 780.5 million includes: • $ 349.2 million of borrowings by Jazwares under its available credit facilities to support its seasonal peak working capital requirements and borrowings incurred and assumed from its acquisition of WCT in 2019 and its acquisition of Kelly Toy in 2020; • $ 162.9 million of borrowings by IPS under its available credi t facility and term loans, including approximately $ 125 million of U.S. dollar-equivalent Euro based borrowings incurred from its acquisition of Linesight in 2021 ; • $ 83.5 million of borrowings by W&W|AFCO Steel under its available credit facilities; • $ 73.4 million of borrowings by Wilbert under its available credit facility and term loans; • $ 55.3 million of term loans at Kentucky Trailer primarily related to borrowings to finance small acquisitions, including its acquisitions of a controlling interest in two manufacturers of aluminum feed transportation equipment in 2018 and 2019, and borrowings under its available credit facilities; • $ 31.8 million of term loans at Piedmont primarily related to borrowings to finance the acquisition of WPS in 2021; and • $ 24.4 million of term loans at PCT primarily related to borrowings to finance the acquisition of a waterjet orifice and nozzle manufacturer in 2016 and the acquisition of a consumable cutting tool manufacturer in 2019; None of the above liabilities are guaranteed by Alleghany or Alleghany Capital. In December 2019, third-party, floating-rate term loans at Concord were repaid and replaced with approximately $ 33 million of intercompany floating-rate debt funded by the Alleghany parent company. The intercompany debt and related interest expenses are eliminated at the Alleghany consolidated level.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes The following table presents income tax expense (benefit) for 2021, 2020 and 2019: Federal State Foreign Total ($ in millions) Year ended December 31, 2021 Current $ 141.6 $ 16.2 $ 36.3 $ 194.1 Deferred 88.2 ( 0.3 ) ( 0.1 ) 87.8 $ 229.8 $ 15.9 $ 36.2 $ 281.9 Year ended December 31, 2020 Current $ 6.9 $ 9.7 $ 58.3 $ 74.9 Deferred ( 45.8 ) 0.8 0.8 ( 44.2 ) $ ( 38.9 ) $ 10.5 $ 59.1 $ 30.7 Year ended December 31, 2019 Current $ 87.9 $ 12.0 $ 70.8 $ 170.7 Deferred 62.9 0.5 ( 0.7 ) 62.7 $ 150.8 $ 12.5 $ 70.1 $ 233.4 Earnings (losses) before income taxes from domestic operations were $ 1,208.7 million, ($ 21.0 ) million and $ 952.4 million in 2021, 2020 and 2019 , respectively. Earnings before income taxes from foreign operations were $ 204.0 million, $ 178.6 million and $ 171.2 million in 2021, 2020 and 2019, respectively. Foreign tax expense was primarily attributable to the U.K., Canada and France. Alleghany treats taxes due on U.S. inclusions in taxable income related to Global Intangible Low-Taxed Income as a current-period expense when incurred. The following table presents the difference between the federal income tax rate and the effective income tax rate: Year Ended December 31, 2021 2020 2019 Federal income tax rate 21.0 % 21.0 % 21.0 % Foreign tax expense reduced by foreign tax credits 0.6 6.9 0.4 Income subject to dividends-received deduction ( 0.3 ) ( 1.3 ) ( 0.3 ) Tax-exempt interest ( 0.7 ) ( 6.0 ) ( 1.0 ) State taxes, net of federal tax benefit 0.9 4.9 0.9 Prior period adjustment ( 0.1 ) ( 2.6 ) 0.2 Other, net (1) ( 1.4 ) ( 3.4 ) ( 0.4 ) Effective tax rate 20.0 % 19.5 % 20.8 % _____________________________________ (1) For 2021, includes the benefit from non-controlling interests, various general business tax credits, partially offset by disallowed expense deductions primarily related to certain executive compensation paid in 2021. For 2020 , includes various general business credits and tax benefits resulting from corporate acquisitions and dispositions, partially offset by disallowed expense deductions primarily related to certain executive compensation paid in 2020. The higher effective tax rate in 2021 compared with 2020 primarily reflects higher earnings before income taxes and the resulting decrease from the impact of permanent tax benefits, such as tax-exempt interest income and dividends-received deductions, when expressed on an effective tax rate basis. The lower effective tax rate in 2020 compared with 2019 primarily reflects lower earnings before income taxes and the resulting increase from the impact of these permanent tax benefits when expressed on an effective tax rate basis. The following table presents the tax effects of temporary differences that give rise to the deferred tax assets and deferred tax liabilities as of December 31, 2021 and 2020: As of December 31, 2021 2020 ($ in millions) Deferred tax assets: Loss and LAE reserves $ 144.5 $ 132.3 Foreign tax credit carry forward 59.2 74.1 Compensation accruals 99.7 87.5 Unearned premiums 114.1 112.2 Allowance for credit losses on available for sale securities 5.2 5.7 State net operating loss carry forward 13.2 12.5 Other 97.8 98.0 Gross deferred tax assets before valuation allowance 533.7 522.3 Valuation allowance ( 12.9 ) ( 12.5 ) Gross deferred tax assets 520.8 509.8 Deferred tax liabilities: Net unrealized gains on investments 308.4 294.7 Deferred acquisition costs 127.0 128.4 Purchase accounting adjustments 11.2 11.7 Other 131.2 118.5 Gross deferred tax liabilities 577.8 553.3 Net deferred tax (liabilities) assets $ ( 57.0 ) $ ( 43.5 ) Other deferred tax assets include significant amounts of foreign currency exchange losses. Our foreign tax credit carry forwards begin to expire in 2028 . A valuation allowance is provided against deferred tax assets when, in the opinion of management, it is more likely than not that a portion of the deferred tax asset will not be realized. As of December 31, 2021 and 2020 , Alleghany recognized $ 13.2 million and $ 12.5 million, respectively, of deferred tax assets for certain state net operating and capital loss carryovers, and a valuation allowance of $ 12.9 million and $ 12.5 million, respectively, has been established against these deferred tax assets as Alleghany does not currently anticipate it will generate sufficient income in these states to absorb such loss carryovers. Alleghany's income tax return was audited by the Internal Revenue Service for the 2014 through 2017 tax years and those audits were settled with no additional tax due. The following table presents the tax years of Alleghany and TransRe tax returns that remain subject to examination by major tax jurisdictions as of December 31, 2021. Major Tax Jurisdiction Open Tax Years Australia 2016 - 2021 Canada 2017 - 2021 France 2018 - 2021 Germany 2019 - 2021 Hong Kong 2015 - 2021 Japan 2019 - 2021 Luxembourg 2019 - 2021 Singapore 2017 - 2021 Switzerland 2018 - 2021 U.K. 2015 - 2021 U.S. 2018 - 2021 Alleghany believes that, as of December 31, 2021 , it had no material uncertain tax positions. Interest and penalties related to unrecognized tax expenses (benefits) are recognized in income tax expense, when applicable. There were no material liabilities for interest or penalties accrued as of December 31, 2021 .

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2021
Stockholders' Equity Note [Abstract]
Stockholders' Equity	10. Stockholders’ Equity (a) Common Stock Repurchases In June 2018, the Alleghany Board of Directors authorized, upon the completion of the program authorized in 2015, the repurchase of additional shares of Common Stock at such times and at prices as management determines to be advisable, up to an aggregate of $ 400.0 million. In September 2019, the Alleghany Board of Directors authorized, upon the completion of the program authorized in 2018, the repurchase of additional shares of Common Stock at such times and at prices as management determines to be advisable, up to an aggregate of $ 500.0 million. As of December 31, 2021, Alleghany had $ 141.9 million remaining in the aggregate under its share repurchase authorizations. The following table presents the shares of Common Stock that Alleghany repurchased in 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 Shares repurchased 446,596 333,393 215,091 Cost of shares repurchased (in millions) $ 290.5 $ 194.8 $ 144.4 Average price per share repurchased $ 650.52 $ 584.18 $ 671.44 (b) Accumulated Other Comprehensive Income (Loss) The following table presents a reconciliation of the changes during 2021 and 2020 in accumulated other comprehensive income attributable to Alleghany stockholders: Unrealized Unrealized Retirement Total ($ in millions) Balance as of January 1, 2021 $ 564.9 $ ( 99.4 ) $ ( 13.1 ) $ 452.4 Other comprehensive income (loss), net of tax: Other comprehensive loss before reclassifications ( 253.3 ) ( 4.3 ) ( 0.5 ) ( 258.1 ) Reclassifications from accumulated other comprehensive income ( 52.5 ) — — ( 52.5 ) Total ( 305.8 ) ( 4.3 ) ( 0.5 ) ( 310.6 ) Balance as of December 31, 2021 $ 259.1 $ ( 103.7 ) $ ( 13.6 ) $ 141.8 Unrealized Unrealized Retirement (1) Total ($ in millions) Balance as of January 1, 2020 $ 321.0 $ ( 121.8 ) $ ( 27.9 ) $ 171.3 Other comprehensive income (loss), net of tax: Other comprehensive income (loss) before reclassifications 277.0 22.4 ( 0.4 ) 299.0 Reclassifications from accumulated other comprehensive income ( 33.1 ) — 15.2 ( 17.9 ) Total 243.9 22.4 14.8 281.1 Balance as of December 31, 2020 $ 564.9 $ ( 99.4 ) $ ( 13.1 ) $ 452.4 (1) See Note 15 for further information on retirement plan-related reclassifications from accumulated other comprehensive income. The following table presents unrealized appreciation of investment reclassifications out of accumulated other comprehensive income attributable to Alleghany stockholders during 2021 and 2020: Accumulated Other Year Ended December 31, Comprehensive Income Component Line in Consolidated Statement of Earnings 2021 2020 ($ in millions) Unrealized appreciation of investments: Net realized capital gains (1) $ ( 64.4 ) $ ( 49.9 ) Change in allowance for credit losses on available for sale securities ( 2.1 ) 8.0 Income taxes 14.0 8.8 Total reclassifications: Net earnings $ ( 52.5 ) $ ( 33.1 ) (1) For 2021, excludes: the 2021 Concord Remeasurement Gain. For 2020, excludes: (i) the 2020 Concord Settlement Gain; ( ii) $ 76.0 million of impairment charge from a write-down of SORC oil field assets; (iii) the Wilbert Remeasurement Gain; (iv) a $ 7.1 million realized loss as a result of an early redemption of debt; and (v) a $ 5.0 million realized gain resulting from a reduction of certain PCT contingent consideration liabilities. See Note 4(e) for additional information. (c) Regulations and Dividend Restrictions As of December 31, 2021 , approximately $ 7.3 billion of Alleghany’s total equity of $ 9.2 billion was unavailable for dividends or advances to Alleghany from its subsidiaries. The remaining $ 1.9 billion was available for dividends or advances to Alleghany from its subsidiaries, or was retained at the Alleghany parent company-level and, as such, was available to pay dividends to Alleghany’s stockholders as of December 31, 2021. The ability of Alleghany’s reinsurance and insurance subsidiaries to pay dividends or other distributions is subject to the laws and regulations applicable to each subsidiary, as well as each subsidiary’s need to maintain capital requirements adequate to maintain its operations and financial strength ratings issued by independent rating agencies. In the U.S., Alleghany’s reinsurance and insurance subsidiaries are subject to insurance laws and regulations that restrict the amount and timing of dividends they may pay without the prior approval of regulatory authorities. Under the insurance holding company laws and regulations, Alleghany’s reinsurance and insurance subsidiaries may not pay an “extraordinary” dividend or distribution without the approval of state insurance regulators. In general, an “extraordinary” dividend or distribution is defined as a dividend or distribution that, together with other dividends and distributions made within the preceding 12 months, exceeds the lesser (or, in some jurisdictions, the greater) of (i) 10 percent of the statutory surplus of the reinsurer or insurer as of the end of the prior calendar year (or, in certain states, as of the end of the prior quarter) and (ii) the net income during the prior calendar year (or, in certain states, the adjusted statutory net investment income). In addition, certain states where Alleghany’s reinsurance and insurance subsidiaries are domiciled prohibit a domestic insurance company from paying dividends except out of earned surplus. TransRe’s operations are also regulated in various foreign jurisdictions with respect to currency, amount and type of security deposits, amount and type of reserves and amount and type of local investment. Regulations governing constitution of technical reserves and remittance balances in some countries may hinder remittance of profits and repatriation of assets. International operations and assets held abroad may also be adversely affected by political and other developments in foreign countries, including possible tax changes, nationalization and changes in regulatory policy, as well as by consequences of hostilities and unrest. The risks of such occurrences and their overall effect upon TransRe vary from country to country and cannot easily be predicted. The following table presents the dividends paid to Alleghany by its reinsurance and insurance subsidiaries in 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 (1) ($ in millions) TransRe (2) $ 280.0 $ 210.0 $ 301.0 RSUI 150.0 225.0 100.0 Total $ 430.0 $ 435.0 $ 401.0 (1) Includes $ 101.0 million representing the July 1, 2019 carrying value of TransRe’s ownership interest in CapSpecialty, which was transferred to Alleghany. (2) In 2021, 2020 and 2019 , TRC paid cash dividends of $ 290.0 million, $ 245.0 million and $ 220.0 million, respectively, to the TransRe holding company. In addition, in 2019, TRC transferred its ownership interest in CapSpecialty to the TransRe holding company, and consequently, the TransRe holding company recorded a dividend from TRC in the amount of $ 101.0 million. As of December 31, 2021 , a maximum amount of $ 108.6 million was available for dividends by TRC without prior approval of the applicable regulatory authorities. Aside from Alleghany’s reinsurance and insurance subsidiaries, dividends are regularly paid to Alleghany from the subsidiaries of Alleghany Capital, where there are generally no regulatory restrictions on dividends being paid from retained earnings. The statutory net income of Alleghany’s reinsurance and insurance subsidiaries was $ 681.4 million and $ 274.8 million for the years ended December 31, 2021 and 2020, respectively. As of December 31, 2021 and 2020 , the combined statutory capital and surplus of Alleghany’s reinsurance and insurance subsidiaries was $ 7.2 billion and $ 6.8 billion, respectively. As of December 31, 2021, the amount of statutory capital and surplus necessary to satisfy regulatory requirements was not significant in relation to the actual statutory capital and surplus of Alleghany’s reinsurance and insurance companies in the U.S. Aside from Alleghany’s reinsurance and insurance subsidiaries, Alleghany Capital’s subsidiaries pay dividends to Alleghany Capital based primarily on each subsidiary’s need to maintain its operations. The following table presents the dividends paid to Alleghany Capital by its subsidiaries in 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Alleghany Capital Subsidiaries (1) $ 133.3 $ 60.9 $ 82.4 (1) Federal income taxes for most Alleghany Capital subsidiaries are incurred at the Alleghany Capital corporate level. As such, these dividends were arrived at after deducting a provision for estimated income taxes to be paid at the Alleghany Capital-level, as applicable. Income tax provisions are finalized when tax returns are filed in future periods. (d) Special Dividends In February 2020, the Alleghany Board of Directors declared a special dividend of $ 15.00 per share for stockholders of record on March 5, 2020 . On March 16, 2020 Alleghany paid dividends to stockholders totaling $ 215.0 million.

Earnings Per Share of Common St

Earnings Per Share of Common Stock	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Earnings Per Share of Common Stock	11. Earnings Per Share of Common Stock The following table presents a reconciliation of the earnings and share data used in the basic and diluted earnings per share computations for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions, except share amounts) Net earnings available to Alleghany stockholders $ 1,034.9 $ 101.8 $ 857.8 Effect of dilutive securities — ( 1.2 ) — Income available to common stockholders for diluted earnings per share $ 1,034.9 $ 100.6 $ 857.8 Weighted average common shares outstanding applicable to basic earnings per share 13,853,780 14,257,793 14,431,892 Effect of dilutive securities 7,167 25,825 11,584 Adjusted weighted average common shares outstanding applicable to diluted earnings per share 13,860,947 14,283,618 14,443,476 Contingently issuable shares (1) 62,264 34,148 48,468 (1) Contingently issuable shares were potentially available in the periods presented, but were not included in the diluted earnings per share computations because the impact was anti-dilutive to the earnings per share calculation.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	12. Commitments and Contingencies (a) Legal Proceedings Certain of Alleghany’s subsidiaries are parties to pending litigation and claims in connection with the ordinary course of their businesses. Each such subsidiary makes provisions for estimated losses to be incurred in such litigation and claims, including legal costs. In the opinion of management, such provisions are adequate, and management does not believe that any pending litigation will have a material adverse effect on Alleghany’s consolidated results of operations, financial position or cash flows. (b) Leases Alleghany and its subsidiaries lease certain facilities, land, furniture and equipment under long-term, non-cancellable lease agreements that expire at various dates through 2040 . Most of Alleghany’s leases relate to office facilities. Alleghany’s lease agreements do not contain any material restrictive covenants and substantially all are considered to be operating leases. Lease expense was $ 53.7 million, $ 45.4 million and $ 40.0 million in 2021, 2020 and 2019 , respectively. The following table presents Alleghany’s consolidated lease liabilities and right-of-use lease assets related to operating leases as of December 31, 2021: As of Maturity of lease payments, by year ($ in millions) 1 year or less $ 50.3 More than 1 year to 2 years 45.7 More than 2 years to 3 years 42.7 More than 3 years to 4 years 35.4 More than 4 years to 5 years 30.3 More than 5 years 143.3 Total lease payments (1) 347.7 Less: interest (2) ( 79.2 ) Lease liabilities (3) $ 268.5 Right-of-use l ease assets (4) $ 240.5 Prepaid lease assets, net of lease allowances and incentives 28.0 $ 268.5 (1) As of December 31, 2021, the weighted average lease term was approximately 13 y ears. (2) As of December 31, 2021, the weighted average discount rate was approximate ly 5 p ercent. (3) Represents the present val ue of expected lease payments over the remaining lease term and is reported as a component of other liabilities on Alleghany’s consolidated balance sheet. Such lease payments do not include future lease payments arising from certain leases that are yet to commence. Based on current lease contracts that are set to commence in early 2022, Alleghany will be committed to pay additional lease contracts in future years in the amount of approximately $ 30 million. (4) Reported as a component of other assets on Alleghany’s consolidated balance sheet. (c) Asbestos-Related Illness and Environmental Impairment Exposure Loss and LAE include amounts for risks related to asbestos-related illness and environmental impairment. The following table presents such gross and net reserves as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Gross Net Gross Net ($ in millions) TransRe $ 105.0 $ 101.1 $ 108.4 $ 103.6 CapSpecialty 4.5 4.5 4.6 4.6 Total $ 109.5 $ 105.6 $ 113.0 $ 108.2 The reserves carried for such claims, including the IBNR portion, are based upon known facts and current law at the respective balance sheet dates. However, significant uncertainty exists in determining the amount of ultimate liability for asbestos-related illness and environmental impairment losses. This uncertainty is due to, among other reasons, inconsistent and changing court resolutions and judicial interpretations with respect to underlying policy intent and coverage and uncertainties as to the allocation of responsibility for resultant damages, among other reasons. Further, possible future changes in statutes, laws, regulations, theories of liability and other factors could have a material effect on these liabilities and, accordingly, future earnings. (d) The Pandemic The Pandemic has significantly disrupted many aspects of society, as well as financial markets, and has caused widespread global economic dislocation. A negative impact on Alleghany's results of operations arising from the Pandemic began in the first quarter of 2020 and that impact continued throughout 2020 and, to a lesser extent, 2021. Widespread vaccine rollouts in the U.S. occurred in early 2021 and are continuing, however, new variants of the virus have emerged. Alleghany cannot reasonably estimate the duration or severity of the Pandemic, or the extent to which the related disruption may adversely impact its results of operations, financial position and cash flows, or those of its subsidiaries. Adverse impacts from the Pandemic in future periods may include realized and unrealized losses in Alleghany’s investment portfolio and receivables, increased underwriting losses at its reinsurance and insurance segments, and impairment losses on certain subsidiary goodwill and intangible assets. (e) Hotel Development Commitments Commencing in 2020, Alleghany Capital invested in certain hotel development projects. As of December 31, 2021, Alleghany Capital has invested $ 5.4 million in these hotel development projects. The projects are conducted through certain limited liability entities, which are variable interest entities, to which Alleghany is not the primary beneficiary. As of December 31, 2021 , Alleghany guaranteed up to $ 5.3 million of debt of these entities to certain third party lenders, for which Alleghany receives a fee.

Segments of Business

Segments of Business	12 Months Ended
	Dec. 31, 2021
Segment Reporting [Abstract]
Segments of Business	13. Segments of Business (a) Overview Alleghany’s segments are reported in a manner consistent with the way management evaluates the businesses. As such, Alleghany classifies its businesses into three reportable segments – reinsurance, insurance and Alleghany Capital. Reinsurance and insurance underwriting activities are evaluated separately from investment and other activities. Segment accounting policies are described in Note 1. The reinsurance segment consists of property and casualty reinsurance operations conducted by TransRe’s reinsurance operating subsidiaries and is further reported through two major product lines – property and casualty & specialty. TransRe provides property and casualty reinsurance to insurers and other reinsurers through brokers and on a direct basis to ceding companies. TransRe writes a modest amount of property and casualty insurance business, which is included in the reinsurance segment. A significant portion of the premiums earned by TransRe’s operations are generated by offices located in Canada, Europe, Asia, Australia, Africa and those serving Latin America and the Caribbean. Although the majority of the premiums earned by these offices typically relate to the regions where they are located, a significant portion may be derived from other regions of the world, including the U.S. In addition, although a significant portion of the assets and liabilities of these foreign offices generally relate to the countries where the ceding companies and reinsurers are located, most investments are located in the country of domicile of these offices. The insurance segment consists of property and casualty insurance operations conducted in the U.S. by AIHL through its insurance operating subsidiaries RSUI and CapSpecialty. RSUI also writes a modest amount of assumed reinsurance business, which is included in the insurance segment. The Alleghany Capital segment consists of industrial operations, consumer & services operations (formerly non-industrial operations) and corporate operations at the Alleghany Capital level, which include certain hotel development projects. Industrial operations are conducted through PCT, Kentucky Trailer, W&W|AFCO Steel, beginning April 1, 2020, Wilbert, and beginning May 10, 2021, Piedmont. Consumer & services operations are conducted through IPS, Jazwares and Concord. Corporate activities are not classified as a segment. The primary components of corporate activities are Alleghany Properties, activities at the Alleghany parent company and, prior to its December 31, 2020 sale, SORC. Corporate activities also include the elimination of minor activity between segments. In addition, corporate activities include interest expense associated with the senior notes issued by Alleghany, whereas interest expense associated with senior notes issued by TransRe is included in “Total Segments” and interest expense associated with other debt is included in Alleghany Capital. Information related to the senior notes and other debt can be found in Note 8. (b) Results The following tables present segment results for Alleghany’s three reportable segments and for corporate activities for 2021, 2020 and 2019: Reinsurance Segment Insurance Segment Year Ended December 31, 2021 Property Casualty & (1) Total RSUI Cap Total Subtotal Alleghany Total Corporate Consolidated ($ in millions) Gross premiums written $ 1,975.2 $ 4,058.8 $ 6,034.0 $ 2,067.6 $ 475.2 $ 2,542.8 $ 8,576.8 $ — $ 8,576.8 $ ( 38.0 ) $ 8,538.8 Net premiums written 1,550.4 3,837.0 5,387.4 1,354.7 407.3 1,762.0 7,149.4 — 7,149.4 — 7,149.4 Net premiums earned 1,708.8 3,768.3 5,477.1 1,230.7 389.9 1,620.6 7,097.7 — 7,097.7 — 7,097.7 Net loss and LAE 1,444.2 2,347.4 3,791.6 805.5 237.8 1,043.3 4,834.9 — 4,834.9 — 4,834.9 Commissions, brokerage and other underwriting expenses (2) 480.1 1,176.6 1,656.7 261.1 149.7 410.8 2,067.5 — 2,067.5 — 2,067.5 Underwriting (loss) profit (3) $ ( 215.5 ) $ 244.3 $ 28.8 $ 164.1 $ 2.4 $ 166.5 195.3 — 195.3 — 195.3 Net investment income 509.0 ( 0.2 ) 508.8 31.6 540.4 Change in the fair value of equity securities 457.1 — 457.1 49.7 506.8 Net realized capital gains 57.6 7.6 65.2 2.2 67.4 Change in allowance for credit losses on available for sale securities 2.0 — 2.0 0.1 2.1 Product and service revenues 39.3 3,736.4 3,775.7 14.0 3,789.7 Other operating expenses 88.9 3,387.8 3,476.7 2.9 3,479.6 Corporate administration ( 0.1 ) — ( 0.1 ) 57.3 57.2 Amortization of intangible assets 1.8 48.1 49.9 — 49.9 Interest expense 26.9 16.2 43.1 59.2 102.3 Earnings (losses) before income taxes $ 1,142.8 $ 291.7 $ 1,434.5 $ ( 21.8 ) $ 1,412.7 Reinsurance Segment Insurance Segment Year Ended December 31, 2020 Property Casualty & (1) Total RSUI Cap Total Subtotal Alleghany Total Corporate Consolidated ($ in millions) Gross premiums written $ 1,761.7 $ 3,475.6 $ 5,237.3 $ 1,714.4 $ 411.3 $ 2,125.7 $ 7,363.0 $ — $ 7,363.0 $ ( 33.6 ) $ 7,329.4 Net premiums written 1,439.6 3,405.4 4,845.0 1,124.8 374.6 1,499.4 6,344.4 — 6,344.4 — 6,344.4 Net premiums earned 1,379.7 3,265.0 4,644.7 1,008.8 346.7 1,355.5 6,000.2 — 6,000.2 — 6,000.2 Net loss and LAE 1,130.6 2,256.3 3,386.9 738.4 213.8 952.2 4,339.1 — 4,339.1 — 4,339 .1 Commissions, brokerage and other underwriting expenses (2) 424.2 1,000.8 1,425.0 226.1 138.7 364.8 1,789.8 — 1,789.8 — 1,789.8 Underwriting (loss) profit (3) $ ( 175.1 ) $ 7.9 $ ( 167.2 ) $ 44.3 $ ( 5.8 ) $ 38.5 ( 128.7 ) — ( 128.7 ) — ( 128.7 ) Net investment income 465.7 1.9 467.6 23.3 490.9 Change in the fair value of equity securities ( 55.8 ) — ( 55.8 ) ( 54.7 ) ( 110.5 ) Net realized capital gains 37.1 35.5 72.6 ( 69.5 ) 3.1 Change in allowance for credit losses on available for sale securities ( 8.0 ) — ( 8.0 ) — ( 8.0 ) Product and service revenues 34.9 2,477.5 2,512.4 8.7 2,521.1 Other operating expenses 103.6 2,310.0 2,413.6 15.7 2,429.3 Corporate administration ( 0.3 ) — ( 0.3 ) 48.9 48.6 Amortization of intangible assets 0.8 43.4 44.2 — 44.2 Interest expense 27.0 15.5 42.5 45.7 88.2 Earnings (losses) before income taxes $ 214.1 $ 146.0 $ 360.1 $ ( 202.5 ) $ 157.6 Reinsurance Segment Insurance Segment Year Ended December 31, 2019 Property Casualty & (1) Total RSUI Cap Total Subtotal Alleghany Total Corporate Consolidated ($ in millions) Gross premiums written $ 1,700.3 $ 3,245.4 $ 4,945.7 $ 1,366.6 $ 371.8 $ 1,738.4 $ 6,684.1 $ — $ 6,684.1 $ ( 27.7 ) $ 6,656.4 Net premiums written 1,328.8 3,166.2 4,495.0 912.0 344.7 1,256.7 5,751.7 — 5,751.7 — 5,751.7 Net premiums earned 1,280.1 3,046.9 4,327.0 824.2 326.9 1,151.1 5,478.1 — 5,478.1 — 5,478.1 Net loss and LAE 942.6 2,018.5 2,961.1 503.7 221.6 725.3 3,686.4 — 3,686.4 — 3,686.4 Commissions, brokerage and other underwriting expenses (2) 424.2 982.6 1,406.8 219.2 132.7 351.9 1,758.7 — 1,758.7 — 1,758.7 Underwriting (loss) profit (3) $ ( 86.7 ) $ 45.8 $ ( 40.9 ) $ 101.3 $ ( 27.4 ) $ 73.9 33.0 — 33.0 — 33.0 Net investment income 533.2 6.3 539.5 10.7 550.2 Change in the fair value of equity securities 705.8 — 705.8 3.9 709.7 Net realized capital gains 6.0 1.0 7.0 ( 13.5 ) ( 6.5 ) Change in allowance for credit losses on available for sale securities ( 19.7 ) — ( 19.7 ) — ( 19.7 ) Product and service revenues 27.0 2,289.3 2,316.3 12.5 2,328.8 Other operating expenses 103.1 2,132.9 2,236.0 27.3 2,263.3 Corporate administration 4.1 — 4.1 70.7 74.8 Amortization of intangible assets 1.3 32.5 33.8 — 33.8 Interest expense 27.1 20.1 47.2 52.8 100.0 Earnings (losses) before income taxes $ 1,149.7 $ 111.1 $ 1,260.8 $ ( 137.2 ) $ 1,123.6 (1) Primarily consists of the following reinsurance lines of business: directors’ and officers’ liability; errors and omissions liability; general liability; medical malpractice; ocean marine and aviation; auto liability; accident & health; mortgage reinsurance; surety; and credit. (2) Includes amortization associated with deferred acquisition costs of $ 1,693.1 mil lion, $ 1,457.0 million and $ 1,392.8 million for the years ended December 31, 2021, 2020 and 2019 , respectively. (3) Underwriting profit represents net premiums earned less net loss and LAE and commissions, brokerage and other underwriting expenses, all as determined in accordance with GAAP, and does not include net investment income, change in the fair value of equity securities, net realized capital gains, change in allowance for credit losses on available for sale securities, product and service revenues, other operating expenses, corporate administration, amortization of intangible assets or interest expense. Underwriting profit does not replace earnings before income taxes determined in accordance with GAAP as a measure of profitability. Rather, Alleghany believes that underwriting profit enhances the understanding of its reinsurance and insurance segments’ operating results by highlighting net earnings attributable to their underwriting performance. Earnings before income taxes (a GAAP measure) may show a profit despite an underlying underwriting loss. Where underwriting losses persist over extended periods, a reinsurance or an insurance company’s ability to continue as an ongoing concern may be at risk. Therefore, Alleghany views underwriting profit as an important measure in the overall evaluation of performance. (c) Foreign operations Information associated with Alleghany’s foreign operations in its reinsurance segment (representing the vast majority of Alleghany’s foreign operations), is as follows: • Foreign gross premiums written were approximately $ 1.7 billion in each of 2021, 2020 and 2019. • Foreign net premiums earned in 2021, 2020 and 2019 were approximately $ 1.6 billion, $ 1.6 billion and $ 1.5 billion, respectively. The foreign country in which Alleghany generates the largest amount of premium revenues is the U.K. Net premiums earned by operations in the U.K. in 2021, 2020 and 2019 were $ 756.6 million, $ 699.6 million and $ 615.6 million, respectively. • Certain of Alleghany Capital’s subsidiaries earned revenues outside of the U.S., however, substantially all of Alleghany Capital’s consolidated revenues were earned in the U.S. (d) Identifiable assets and equity The following table presents identifiable assets, the portion of identifiable assets related to cash and invested assets, and equity attributable to Alleghany, for Alleghany’s reportable segments and for corporate activities as of December 31, 2021: Identifiable Invested Assets Equity ($ in millions) Reinsurance segment $ 19,048.2 $ 15,208.8 $ 5,398.4 Insurance segment 8,402.7 6,080.2 2,759.1 Subtotal 27,450.9 21,289.0 8,157.5 Alleghany Capital 3,368.0 165.9 1,337.9 Total segments 30,818.9 21,454.9 9,495.4 Corporate activities 1,449.7 1,394.5 ( 308.5 ) Consolidated $ 32,268.6 $ 22,849.4 $ 9,186.9 (e) Alleghany Capital Product and Service Revenues For Alleghany Capital’s industrial and consumer & services operations, product and service revenues consists of the sale of manufactured goods and services. The following table presents product and service revenues for the Alleghany Capital segment for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Industrial (1) $ 1,662.3 $ 1,220.9 $ 1,105.6 Consumer & services (2) 2,074.1 1,256.5 1,183.7 Corporate & other — 0.1 — Alleghany Capital $ 3,736.4 $ 2,477.5 $ 2,289.3 (1) For 2021, 2020 and 2019 , the vast majority of industrial product and service revenues were recognized as goods and services transferred to customers over time. (2) For 2021, 2020 and 2019 , approximately 50 percent, 59 percent and 70 percent, respectively, of consumer & services product and service revenues were recognized as services transferred to customers over time, with the remainder recognized as goods transferred at a point in time. (f) Concentration Significant portions of the reinsurance segment’s gross premiums written are produced by a limited number of brokers. Gross premiums written produced by the reinsurance segment’s three largest brokers were approximately: 30 percent, 23 percent and 10 percent in 2021 ; 27 percent, 19 percent and 14 percent in 2020 ; and 26 percent, 17 percent and 16 percent in 2019. A large whole account quota share treaty accounted for approximately 8 percent in 2021 , 13 percent in 2020 and 14 percent in 2019 of gross premiums written in the reinsurance segme nt. The lower percentage in 2021 reflects TransRe's decision to not renew the large whole account quota share treaty as of December 31, 2021.

Long-Term Compensation Plans

Long-Term Compensation Plans	12 Months Ended
	Dec. 31, 2021
Share-based Payment Arrangement [Abstract]
Long-Term Compensation Plans	14. Long-Term Compensation Plans (a) Alleghany Parent Company-Level As of December 31, 2021, Alleghany had long-term compensation plans for parent company-level employees and directors. Alleghany parent company-level long-term compensation awards to current employees do not include stock options but consist only of restricted stock awards, including restricted stock units and performance share awards of Common Stock. Alleghany parent company-level, long-term compensation awards to non-employee directors consist of annual grants of restricted shares and restricted stock units of Common Stock. Amounts recognized as compensation expense in the consolidated statements of earnings and comprehensive income with respect to long-term compensation awards under plans for Alleghany parent company-level employees and non-employee directors were $ 21.5 million, $ 4.3 million and $ 38.7 million in 2021, 2020 and 2019 , respectively. The amount of related income tax benefit in the consolidated statements of earnings and comprehensive income with respect to these plans was $ 4.5 million, $ 0.9 million and $ 8.1 million in 2021, 2020 and 2019, respectively. In 2021, 2020 and 2019 , $ 2.5 million, $ 5.0 million and $ 2.4 million of Common Stock at fair market value, respectively, and $ 8.4 million, $ 12.8 million and $ 2.2 million of cash, respectively, was paid by Alleghany under these plans for Alleghany parent company-level employees and non-employee directors. As noted above, as of December 31, 2021 and 2020, all outstanding awards were accounted for under the fair-value-based method of accounting. The following is a summary of the Alleghany parent company-level, long-term compensation plans. Director Restricted Stock Plan The annual grant to each non-employee director consists of either restricted shares or restricted stock units of Common Stock, at the director’s election. Awards granted to non-employee directors were not material to Alleghany’s results of operations, financial condition or cash flows for the three years ended December 31, 2021. Alleghany Long-Term Incentive Plans Awards under Alleghany’s long-term compensation plans may include, but are not limited to, cash and/or shares of Common Stock, rights to receive cash and/or shares of Common Stock and options to purchase shares of Common Stock, including options intended to qualify as incentive stock options under the Internal Revenue Code, and options not intended to so qualify. The following types of awards were outstanding as of December 31, 2021: • Performance Share Awards — Depending on the grant date, participants are entitled, at the end of a multi-year award period, to a maximum amount equal to the value of either one and one-half shares or two shares of Common Stock for each performance share issued to them based on market value on the payment date. Payouts are made provided defined levels of performance are achieved. Expenses are recorded based on changes in the fair value of the awards. The fair value is calculated based primarily on the value of Common Stock as of the balance sheet date, the degree to which performance targets have been achieved and the time elapsed with respect to each award period. • Restricted Share Awards — From time to time, Alleghany has awarded to management employees restricted shares or restricted stock units of Common Stock. These awards entitle the participants to a specified maximum amount equal to the value of one share of Common Stock for each restricted share or restricted stock unit issued to them based on the market value on the grant date, subject to certain conditions. The expense is recognized ratably over the performance period, which can be extended under certain circumstances. (b) TransRe Plans TransRe has a Book Value Unit Plan and a Mid-Term Incentive Plan (collectively, the “TransRe Plans”) for the purpose of providing incentives to key employees of TransRe. Under the TransRe Plans, book value units (“BVUs”) and mid-term incentive plan (“MTIP”) awards are issued. BVUs and MTIP awards may only be settled in cash. The fair value of each BVU is calculated as the stockholder’s equity of TransRe, adjusted for certain capital transactions, divided by the adjusted number of BVUs outstanding. Certain BVU grants also have a performance factor which can increase or decrease the number of nominal units based on performance to a specified target. BVUs generally have vesting dates of approximately the fourth anniversary of the date of grant. The fair value of MTIP awards is calculated based on underwriting results compared to specified targets or based on overall results as determined by TransRe’s board of directors. MTIP awards have vesting dates of approximately the second or third anniversary of the date of grant. The BVUs and MTIP awards contain certain restrictions, related to, among other things, forfeiture in the event of termination of employment and transferability. In 2021, 2020 and 2019 , TransRe recorded $ 36.1 million, $ 44.3 million and $ 48.7 million, respectively, in compensation expense and a deferred tax benefit of $ 7.6 million, $ 9.3 million and $ 10.2 million, respectively, related to the TransRe Plans. (c) RSUI Plans RSUI has a Restricted Stock Unit Plan (the “RSU Plan”) and a Book Value Unit Plan (the “BVU Plan”) (collectively the “RSUI Plans”) for the purpose of providing equity-like incentives to key employees of RSUI. Under the RSU Plan, restricted stock units (“RSUs”) were issued. RSUs may only be settled in cash. The fair value of each unit is calculated as the stockholder’s equity of RSUI, adjusted for certain capital transactions and accumulated compensation expense recognized under the RSU Plan, divided by the sum of RSUI common stock outstanding and the original units available under the RSU Plan. The units vest on the fourth anniversary of the date of grant and contain certain restrictions, related to, among other things, forfeiture in the event of termination of employment and transferability. Effective July 1, 2019, no additional units were awarded from the RSU Plan. The BVU Plan was initiated on July 1, 2019. Under the BVU Plan, BVUs are issued. The BVUs may only be settled in cash. The fair value of each BVU is calculated as the stockholder’s equity of RSUI, adjusted for certain capital transactions, divided by the BVUs outstanding. The units vest on the fourth anniversary of the date of grant and contain certain restrictions, related to, among other things, forfeiture in the event of termination of employment and transferability. In 2021, 2020 and 2019 , RSUI recorded $ 37.3 million, $ 29.0 million and $ 37.4 million, respectively, in compensation expense related to the RSUI Plans. During the same periods, a deferred tax benefit of $ 7.8 million, $ 6.1 million and $ 7.8 million, respectively, related to the compensation expense were recorded. (d) Other Subsidiary Plans Long-term incentive plans exist at certain other subsidiaries for the purpose of providing equity-like incentives to key employees. The awards under such plans were not material to Alleghany’s results of operations, financial condition or cash flows for the three years ended December 31, 2021 .

Employee Retirement Benefit Pla

Employee Retirement Benefit Plans	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Employee Retirement Benefit Plans	15. Employee Retirement Benefit Plans (a) Overview Alleghany and certain of its subsidiaries provide a variety of retirement benefits. Alleghany provides supplemental retirement benefits through deferred compensation programs and profit sharing plans for certain of its Alleghany parent company-level officers and employees. In addition, Alleghany’s subsidiaries sponsor both qualified, defined contribution retirement plans for substantially all employees, including executives, and non-qualified plans only for executives, some of which provide for voluntary salary reduction contributions by employees and matching contributions by each respective subsidiary, subject to specified limitations. Alleghany has endorsement split-dollar life insurance policies for its Alleghany parent company-level officers that are effective during employment, as well as retirement. Premiums are paid by Alleghany and death benefits are split between Alleghany and the beneficiaries of the officers. Death benefits for current employees that inure to the beneficiaries are generally equal to four times the annual salary at the time of an officer’s death. After retirement, death benefits that inure to the beneficiaries are generally equal to the annual salary of the officer as of the date of retirement. In addition, Alleghany and TransRe have defined benefit pensions plans for certain of their employees, as further described below. These employee retirement plans are not material to Alleghany’s results of operations, financial condition or cash flows for the three years ended December 31, 2021. Alleghany recognizes on its balance sheet an asset for a plan’s overfunded status or a liability for a plan’s underfunded status, with changes in funded status reported in other comprehensive income, net of tax. In December 2019, the Alleghany Board of Directors authorized the termination of the executive retirement plans at both the Alleghany Parent company-level and at TransRe effective December 24, 2019. Due in large part to this authorization for termination of these plans, other comprehensive losses attributable to retirement plans in the amount of $ 15.4 million was incurred in 2019. In December 2020, approximately $ 57 million of total payments were made to all executive retirement participants and $ 19.2 million of accumulated other comprehensive losses attributable, consisting of $ 15.4 million of other comprehensive losses incurred in 2019 and $ 3.8 million of other comprehensive losses incurred from earlier periods, was reversed out of accumulated other comprehensive losses and reclassified to the consolidated statement of operations as expenses. Of the $ 19.2 million of reclassified expenses in 2020, $ 13.6 million related to Alleghany Parent executive retirement plan participants was recorded as corporate administration expense, and $ 5.6 million related to TransRe executive retirement plan participants was recorded as other operating expense. All of the forgoing amounts are presented before income taxes. (b) Alleghany Parent Company-Level Alleghany had an unfunded, noncontributory defined benefit pension plan for Alleghany parent company-level executives, which was frozen as of December 31, 2013 and terminated in December 2019. Alleghany has a funded, noncontributory defined benefit pension plan for Alleghany parent company-level employees, which was also frozen as of December 31, 2013. As of December 31, 2021 and 2020, the projected benefit obligations of defined benefit pension plans were $ 3.9 million and $ 3.9 million, respectively, and the related fair value of plan assets was $ 3.7 million and $ 3.8 million, respectively. (c) TransRe TransRe had an unfunded, noncontributory defined benefit plan for executives and has a funded noncontributory defined benefit plan for certain of its employees in the U.S. Benefits under TransRe’s defined benefit plans were frozen as of December 31, 2009 and the unfunded, noncontributory defined benefit plan for executives was terminated in December 2019. As of December 31, 2021 and 2020 , the projected benefit obligations of defined benefit pension plans were $ 68.7 million and $ 72.2 million, respectively, and the related fair value of plan assets was $ 60.3 million and $ 63.7 million, respectively.

Quarterly Results of Operations

Quarterly Results of Operations (unaudited)	12 Months Ended
	Dec. 31, 2021
Quarterly Financial Information Disclosure [Abstract]
Quarterly Results of Operations (unaudited)	16. Quarterly Results of Operations (unaudited) Selected quarterly financial data for 2021 and 2020 are presented below: Quarter Ended March 31 June 30 September 30 December 31 ($ in millions, except per share data) 2021 Revenues $ 2,653.7 $ 2,928.7 $ 2,866.6 $ 3,555.0 Net earnings (losses) (1) 230.0 403.7 ( 115.0 ) 516.2 Basic earnings (losses) per share of common stock (1)(2) 16.44 29.00 ( 8.31 ) 37.76 2020 Revenues $ 1,482.9 $ 2,227.4 $ 2,522.9 $ 2,663.5 Net (losses) earnings (1) ( 361.2 ) 177.4 126.5 159.1 Basic (losses) earnings per share of common stock (1)(2) ( 25.19 ) 12.39 8.86 11.28 (1) Attributable to Alleghany stockholders. (2) Earnings per share by quarter may not equal the amount for the full year due to the timing of repurchases of Common Stock, as well as rounding.

Summary of Investments - Other

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]
Summary of Investments - Other Than Investments in Related Parties	Schedule I – Summary of Investments – Ot her Than Investments in Related Parties ALLEGHANY CORPORATION AND SUBSIDIARIES December 31, 2021 Type of Investment Cost Fair Value Amount at ($ in millions) Fixed maturities: Bonds: U.S. Government obligations $ 2,039.7 $ 2,050.7 $ 2,050.7 Municipal bonds 2,412.7 2,535.9 2,535.9 Foreign government obligations 850.8 854.9 854.9 U.S. corporate bonds 3,336.9 3,477.3 3,477.3 Foreign corporate bonds 1,216.6 1,226.9 1,226.9 Mortgage and asset-backed securities: RMBS 1,993.6 2,009.0 2,009.0 CMBS 879.8 905.9 905.9 Other asset-backed securities 2,997.0 3,001.0 3,001.0 Fixed maturities 15,727.1 16,061.6 16,061.6 Equity securities: Common stocks: Public utilities 179.2 189.6 189.6 Banks, trust and insurance companies 353.0 483.2 483.2 Industrial, miscellaneous and all other 2,015.2 3,006.4 3,006.4 Nonredeemable preferred stocks 5.3 4.6 4.6 Equity securities 2,552.7 3,683.8 3,683.8 Commercial mortgage loans 475.9 475.9 475.9 Other invested assets 557.8 557.8 557.8 Short-term investments 1,142.3 1,142.3 1,142.3 Total investments $ 20,455.8 $ 21,921.4 $ 21,921.4

Condensed Financial Information

Condensed Financial Information of Registrant	12 Months Ended
	Dec. 31, 2020
Condensed Financial Information Disclosure [Abstract]
Condensed Financial Information of Registrant	Schedule II – Condensed Finan cial Information of Registrant Condensed Balance Sheets ALLEGHANY CORPORATION December 31, 2021 and 2020 2021 2020 ($ in thousands) Assets Equity securities (cost: 2021 – $ 681,375 ; 2020 – $ 587,418 ) $ 741,620 $ 571,314 Debt securities (amortized cost: 2020 – $ 47,397 ; allowance for credit losses: 2020 – $ 57 ) — 48,753 Short-term investments 452,549 76,259 Other invested assets 165,931 91,873 Cash 21,847 17,243 Property and equipment at cost, net of accumulated depreciation and amortization 3,561 3,707 Other assets 55,581 60,089 Net deferred tax assets 5,240 21,060 Current taxes receivable 4,296 17,649 Investment in subsidiaries 9,843,147 9,361,261 Total assets $ 11,293,772 $ 10,269,208 Liabilities, Redeemable Noncontrolling Interests and Stockholders’ Equity Senior notes $ 1,678,964 $ 1,190,192 Other liabilities 110,580 89,487 Total liabilities 1,789,544 1,279,679 Redeemable noncontrolling interest 317,346 233,809 Stockholders' equity attributable to Alleghany stockholders 9,186,882 8,755,720 Total liabilities, redeemable noncontrolling interest and stockholders’ equity $ 11,293,772 $ 10,269,208 See accompanying Notes to Condensed Financial Statements Condensed Statements of Earnings ALLEGHANY CORPORATION Year ended December 31, 2021 2020 2019 ($ in thousands) Revenues Net investment income $ 32,778 $ 24,448 $ 10,790 Change in the fair value of equity securities 49,715 ( 54,647 ) 3,937 Net realized capital gains 2,322 6,522 ( 13,497 ) Change in allowance for credit losses on available for sale securities 57 ( 57 ) — Product and service revenues 81 771 85 Total revenues 84,953 ( 22,963 ) 1,315 Costs and Expenses Interest expense 60,379 46,811 52,908 Corporate administration 57,301 48,849 70,692 Total costs and expenses 117,680 95,660 123,600 (Losses) before equity in earnings of consolidated subsidiaries and income taxes ( 32,727 ) ( 118,623 ) ( 122,285 ) Equity in earnings of consolidated subsidiaries 1,445,430 276,240 1,245,921 Earnings before income taxes 1,412,703 157,617 1,123,636 Income taxes 281,925 30,734 233,435 Net earnings 1,130,778 126,883 890,201 Net earnings attributable to noncontrolling interest 95,886 25,129 32,400 Net earnings attributable to Alleghany stockholders $ 1,034,892 $ 101,754 $ 857,801 See accompanying Notes to Condensed Financial Statements Condensed Statements of Cash Flows ALLEGHANY CORPORATION Year ended December 31, 2021 2020 2019 ($ in thousands) Cash flows from operating activities Net earnings $ 1,130,778 $ 126,883 $ 890,201 Adjustments to reconcile net earnings to net cash provided by (used in) Equity in undistributed net (earnings) losses of consolidated subsidiaries ( 1,157,344 ) ( 226,590 ) ( 989,486 ) Depreciation and amortization 1,976 4,064 2,249 Change in the fair value of equity securities ( 49,715 ) 54,647 ( 3,937 ) Net realized capital (gains) losses ( 2,322 ) ( 6,522 ) 13,497 Change in allowance for credit losses on available for sale securities ( 57 ) 57 — Increase (decrease) in other liabilities and taxes payable 47,462 ( 56,298 ) 24,593 Net adjustments ( 1,160,000 ) ( 230,642 ) ( 953,084 ) Net cash (used in) provided by operating activities ( 29,222 ) ( 103,759 ) ( 62,883 ) Cash flows from investing activities Purchases of equity securities ( 220,914 ) ( 763,986 ) — Purchases of debt securities — ( 497,058 ) ( 194,706 ) Sales of debt securities 45,786 606,110 1,186 Maturities and redemptions of debt securities 3,049 32,383 13,344 Sales of equity securities 100,324 142,065 64,016 Net (purchase) sale of short-term investments ( 376,290 ) 49,154 162,161 Purchases of property and equipment ( 395 ) ( 9 ) ( 124 ) Other, net ( 64,345 ) ( 8,731 ) ( 33,245 ) Net cash (used in) provided by investing activities ( 512,785 ) ( 440,072 ) 12,632 Cash flows from financing activities Repayment of senior notes — ( 307,095 ) — Treasury stock acquisitions ( 290,521 ) ( 194,762 ) ( 144,422 ) Proceeds from issuance of senior notes 493,195 499,335 — Debt issue costs paid ( 5,675 ) ( 4,550 ) — Cash dividends paid — ( 215,013 ) — Capital contributions to consolidated subsidiaries ( 140,000 ) ( 87,323 ) ( 15,267 ) Distributions from consolidated subsidiaries 488,500 865,000 215,000 Other, net 1,112 4,798 ( 4,707 ) Net cash provided by (used in) financing activities 546,611 560,390 50,604 Net increase (decrease) in cash 4,604 16,559 353 Cash at beginning of period 17,243 684 331 Cash at end of period $ 21,847 $ 17,243 $ 684 Supplemental disclosures of cash flow information Cash paid during the period for: Interest paid $ 52,652 $ 49,036 $ 51,375 Income taxes paid (refunds received) 94,001 17,255 ( 4,189 ) See accompanying Notes to Condensed Financial Statements Notes to Condensed Financial Statements ALLEGHANY CORPORATION 1. Investment in Consolidated Subsidiaries. Reference is made to Note 1 to the Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of this Form 10-K. 2. Adoption of New Accounting Guidance. Reference is made to Note 1 to the Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of this Form 10-K. 3. Income Taxes. Reference is made to Note 9 to the Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of this Form 10-K. 4. Commitments and Contingencies. Reference is made to Note 12 to the Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of this Form 10-K. 5. Stockholders’ Equity. Reference is made to Note 10 to the Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of this Form 10-K with respect to stockholders’ equity and surplus available for dividend payments to Alleghany from its subsidiaries. 6. Senior Notes. Reference is made to Note 8 to the Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of this Form 10-K. 7. Credit Agreement. Reference is made to Note 7 to the Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of this Form 10-K. 8. Long-Term Compensation Plans. Reference is made to Note 14 to the Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of this Form 10-K. 9. Employee Retirement Benefit Plans. Reference is made to Note 15 to the Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of this Form 10-K.

Supplemental Insurance Informat

Supplemental Insurance Information	12 Months Ended
	Dec. 31, 2021
SEC Schedule, 12-16, Insurance Companies, Supplementary Insurance Information [Abstract]
Supplemental Insurance Information	Schedule III – Supplement al Insurance Information ALLEGHANY CORPORATION AND SUBSIDIARIES At December 31, For the Year Ended December 31, Year Segment Deferred Future Unearned Other Premium Net Benefits, Amortization Other Premiums ($ in millions) 2021 Reinsurance $ 434.3 $ 10,748.2 $ 1,848.1 $ — $ 5,477.1 $ 347.8 $ 3,791.6 $ 1,429.3 $ 227.4 $ 5,387.4 2020 Reinsurance $ 460.7 $ 9,814.0 $ 1,873.7 $ — $ 4,644.7 $ 330.2 $ 3,386.9 $ 1,225.3 $ 199.7 $ 4,845.0 2019 Reinsurance $ 406.7 $ 9,323.8 $ 1,668.1 $ — $ 4,327.0 $ 371.9 $ 2,961.1 $ 1,178.7 $ 228.1 $ 4,495.0 2021 Insurance $ 152.5 $ 3,686.0 $ 1,347.8 $ — $ 1,620.6 $ 161.2 $ 1,043.3 $ 263.8 $ 147.0 $ 1,762.0 2020 Insurance $ 134.4 $ 3,226.9 $ 1,124.2 $ — $ 1,355.5 $ 135.5 $ 952.2 $ 231.7 $ 133.1 $ 1,499.4 2019 Insurance $ 115.9 $ 2,670.3 $ 910.1 $ — $ 1,151.1 $ 161.3 $ 725.3 $ 214.1 $ 137.8 $ 1,256.7

Reinsurance

Reinsurance	12 Months Ended
	Dec. 31, 2021
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Abstract]
Reinsurance	Schedule IV – Reinsurance ALLEGHANY CORPORATION AND SUBSIDIARIES Year ended December 31, Year Line of Business Gross Amount Ceded to Other Assumed from Net Amount Percentage of ($ in millions) 2021 Property and casualty $ 3,005.7 $ 1,272.8 $ 5,364.8 $ 7,097.7 75.6 % 2020 Property and casualty $ 2,370.4 $ 953.1 $ 4,582.9 $ 6,000.2 76.4 % 2019 Property and casualty $ 2,114.1 $ 904.8 $ 4,268.8 $ 5,478.1 77.9 %

Valuation and Qualifying Accoun

Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2021
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Valuation and Qualifying Accounts	Schedule V – Valuation and Qualifying Accounts ALLEGHANY CORPORATION AND SUBSIDIARIES Year Description Balance at Charged to Charged to Deductions Balance at ($ in millions) 2021 Allowance for credit losses for reinsurance recoverable $ 7.9 $ — $ — $ 4.7 $ 3.2 Allowance for credit losses for premiums receivable $ 2.2 $ — $ — $ 1.2 $ 1.0 2020 Allowance for uncollectible reinsurance recoverable $ — $ 4.6 $ 3.3 $ — $ 7.9 Allowance for uncollectible premiums receivable $ 0.7 $ 1.1 $ 0.4 $ — $ 2.2 2019 Allowance for uncollectible reinsurance recoverable $ — $ — $ — $ — $ — Allowance for uncollectible premiums receivable $ 0.4 $ 0.9 $ — $ 0.6 $ 0.7

Supplemental Information Concer

Supplemental Information Concerning Insurance Operations	12 Months Ended
	Dec. 31, 2021
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract]
Supplemental Information Concerning Insurance Operations	SCHEDULE VI – Supplemental Informat ion Concerning Insurance Operations ALLEGHANY CORPORATION AND SUBSIDIARIES At December 31, For the Year Ended December 31, Deferred Reserves for Discount if Unearned Earned Net Claims and Claim Amortization Paid Claims Premiums Year Line of Business Costs Expenses Expenses Premiums Premiums Income Current Year Prior Year Costs Expenses Written ($ in millions) 2021 Property and Casualty Insurance $ 586.8 $ 14,357.6 $ — $ 3,179.5 $ 7,097.7 $ 509.0 $ 5,084.6 $ ( 249.7 ) $ 1,693.1 $ 3,688.7 $ 7,149.4 2020 Property and Casualty Insurance $ 595.1 $ 12,970.6 $ — $ 2,984.1 $ 6,000.2 $ 465.7 $ 4,559.9 $ ( 220.8 ) $ 1,457.0 $ 3,503.5 $ 6,344.4 2019 Property and Casualty Insurance $ 522.6 $ 11,928.4 $ — $ 2,566.2 $ 5,478.1 $ 533.2 $ 3,871.1 $ ( 184.7 ) $ 1,392.8 $ 3,724.5 $ 5,751.7

Summary of Significant Accoun_2

Summary of Significant Accounting Principles (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
Principles of Financial Statement Presentation	(a) Principles of Financial Statement Presentation Alleghany Corporation (“Alleghany”), a Delaware corporation, owns and supports certain operating subsidiaries and manages investments, anchored by a core position in property and casualty reinsurance and insurance. Through its wholly-owned subsidiary Transatlantic Holdings, Inc. (“TransRe”), an Alleghany subsidiary since March 2012, Alleghany is engaged in the property and casualty reinsurance business. Through its wholly-owned subsidiary Alleghany Insurance Holdings LLC (“AIHL”), Alleghany is engaged in the property and casualty insurance business. AIHL’s insurance operations are principally conducted by its subsidiaries RSUI Group, Inc. (“RSUI”) and CapSpecialty, Inc. (“CapSpecialty”). RSUI and CapSpecialty have been subsidiaries of AIHL since July 2003 and January 2002, respectively. AIHL Re LLC (“AIHL Re”), a captive reinsurance company which provides reinsurance to Alleghany’s current and former insurance operating subsidiaries and affiliates, has been a subsidiary of Alleghany since its formation in May 2006. Although Alleghany’s primary sources of revenues and earnings are its reinsurance and insurance operations and investments, Alleghany also generates revenues and expenses from a diverse portfolio of non-financial businesses that are owned and supported through its wholly-owned subsidiary Alleghany Capital Corporation (“Alleghany Capital”). Alleghany Capital’s businesses include: • Precision Cutting Technologies, Inc. (“PCT”), a holding company headquartered in Rockford, Illinois, with four operating businesses: (i) Bourn & Koch, Inc., a provider of precision automated machine tool solutions; (ii) Diamond Technology Innovations, Inc., a manufacturer of waterjet orifices and nozzles and a provider of related services; (iii) Coastal Industrial Distributors, LLC, a provider of high-performance solid carbide end mills; and (iv) as of March 2020, Supermill LLC, a manufacturer of high-performance carbide end mills; • R.C. Tway Company, LLC (“Kentucky Trailer”), a manufacturer of custom trailers and truck bodies for the moving and storage industry and other markets, headquartered in Louisville, Kentucky; • IPS-Integrated Project Services, LLC (“IPS”), a global provider of design, engineering, and related services to the biopharmaceutical and life sciences markets, and through its subsidiary, cost and project management services for clients in the data center, technology, and other sectors, headquartered in Blue Bell, Pennsylvania; • Jazwares, LLC (together with its affiliates, “Jazwares”), a global toy company, headquartered in Sunrise, Florida; • WWSC Holdings, LLC (“W&W|AFCO Steel”), a structural steel fabricator and erector, headquartered in Oklahoma City, Oklahoma; • CHECO Holdings, LLC (“Concord”), a hotel management and development company, headquartered in Raleigh, North Carolina; • Wilbert Funeral Services, Inc. (“Wilbert”), a provider of products and services for the funeral and cemetery industries and precast concrete markets, headquartered in Overland Park, Kansas; and • Piedmont Manufacturing Group, LLC (“Piedmont”), a provider of injection molded and thermoformed parts and multi-component assemblies for original equipment manufacturer customers in a range of end-markets, headquartered in Belmont, North Carolina. The results of Piedmont have been included in Alleghany’s consolidated results from its formation and subsequent acquisition of Wilbert, Inc., doing business as Wilbert Plastic Services (“WPS”) on May 10, 2021. On April 1, 2020, Alleghany Capital acquired an additional approximately 55 percent of Wilbert it previously did not own, bringing its equity interest in Wilbert to approximately 100 percent, and as of that date, the results of Wilbert were included in Alleghany’s consolidated results. Prior to April 1, 2020, Wilbert was accounted for under the equity method of accounting and was included in other invested assets. In addition, Alleghany owns certain other holding-company investments. Alleghany’s wholly-owned subsidiary, Alleghany Properties Holdings LLC (“Alleghany Properties”) owns and manages certain properties in the Sacramento, California region. Alleghany’s public equity investments are managed primarily through Alleghany’s wholly-owned subsidiary Roundwood Asset Management LLC. Prior to its December 31, 2020 sale, Stranded Oil Resources Corporation (“SORC”) was a wholly-owned subsidiary. Unless the context otherwise requires, references to “Alleghany” include Alleghany together with its subsidiaries. The accompanying consolidated financial statements include the results of Alleghany and its wholly-owned and majority-owned subsidiaries and have been prepared in accordance with accounting principles generally accepted in the U.S. (“GAAP”). All material inter-company balances and transactions have been eliminated in consolidation. The portion of stockholders’ equity, net earnings and comprehensive income that is not attributable to Alleghany stockholders is presented on the consolidated balance sheets, the consolidated statements of earnings and comprehensive income and the consolidated statements of changes in stockholders’ equity as noncontrolling interests. Because all noncontrolling interests have the option to sell their ownership interests to Alleghany in the future (generally through 2028), the portion of stockholders’ equity that is not attributable to Alleghany stockholders is presented on the consolidated balance sheets and the consolidated statements of changes in stockholders’ equity as redeemable noncontrolling interests for all periods presented. In addition, Alleghany accretes the redeemable noncontrolling interests up to their future estimated redemption value over the period from the date of issuance to the earliest redemption date. The redemption value of the equity interests is generally based on the subsidiary’s earnings in specified periods preceding the applicable redemption date, calculated based on either a specified formula or an independent fair market valua tion. Accretion related to redemption values based on a specified formula are recorded as a component of net earnings attributable to noncontrolling interests, whereas accretion related to redemption values based on an independent fair market valuation are recorded as a component of contributed capital. Accretion may increase or decrease each period, however, the redeemable noncontrolling interest balance may not go below the initial balance established at the acquisition date. The following table presents the components of net earnings attributable to noncontrolling interests for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Accretion of redeemable noncontrolling interests $ 23.5 $ 2.2 $ 8.8 Portion of net earnings attributable to noncontrolling interests 72.4 22.9 23.6 Total $ 95.9 $ 25.1 $ 32.4 In addition, accretion reduced contributed capital by $ 5.3 million, $ 0.0 million and $ 0.0 million for the years ended December 31, 2021, 2020 and 2019, respectively. Such accretion may be adjusted in the first quarter of 2022 as certain significant noncontrolling interest holders have the right to put their respective equity interests to Alleghany Capital. The difference between any actual payouts that may be negotiated and agreed, as compared to the carrying value of such noncontrolling interest holders, will be recorded as accretion and charged to contributed capital. As of December 31, 2021 , the noncontrolling interests outstanding were approximately as follows: Kentucky Trailer - 22 percent; IPS - 18 percent; Jaz wares – 24 percent; W&W|AFCO Steel - 20 percent; and Concord - 15 percent. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions. These estimates and assumptions affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements, as well as the reported amounts of revenues and expenses during the reporting period. Alleghany relies on historical experience and on various other assumptions that it believes to be reasonable under the circumstances to make judgments about the carrying value of assets and liabilities and reported revenues and expenses that are not readily apparent from other sources. Actual results may differ materially from those reported results to the extent that those estimates and assumptions prove to be inaccurate. Changes in estimates are reflected in the consolidated statements of earnings and comprehensive income in the period in which the changes are made.
Investments	(b) Investments Investments consist of debt securities, equity securities, short-term investments, commercial mortgage loans and other invested assets. Alleghany considers all of its marketable debt securities and short-term investments as available-for-sale (“AFS”). Debt securities consist of securities with an initial fixed maturity of more than one year. Debt securities typically take the form of bonds and redeemable preferred stock. Equity securities generally consist of securities that represent ownership interests in an enterprise. Equity securities typically take the form of common stock or perpetual preferred stock. Mutual funds and exchange-traded securities are also classified as equity securities, including those that invest mostly in debt securities. All marketable equity securities are measured at fair value with changes in fair value recognized in net earnings. Short-term investments include commercial paper, certificates of deposit, money market instruments and any fixed maturity investment with an initial maturity of one year or less. AFS securities are recorded at fair value. Unrealized gains and losses during the year, net of the related tax effect, for AFS securities are excluded from earnings and reflected in comprehensive income, and the cumulative effect is reported as a separate component of stockholders’ equity until realized. Credit losses for AFS securities are recorded through an allowance for credit losses. Changes in the allowance for credit losses are recorded for (or as a reversal of) credit losses on AFS securities. Credit losses on an AFS security cannot exceed the amount by which the fair value of the security is less than its amortized cost. Any portion of a decline in fair value related to a debt security that is believed to arise from factors other than credit is recorded as a component of other comprehensive income rather than charged against earnings. Commercial mortgage loans are carried at unpaid principal balance, less an allowance for credit losses. Credit losses for commercial mortgage loans are recorded through an allowance for credit losses. Estimates of expected credit losses are based on historical experience, current conditions and reasonable and supportable forecasts, and include an ongoing review of amounts outstanding, the creditworthiness of the borrower, value of the real estate collateral and other relevant factors. Amounts deemed to be uncollectible are written off against the allowance. Subsequent reversals in credit loss estimates are recognized in earnings. Interest income on loans is accrued as earned. Other invested assets include invested assets not identified above, primarily related to: (i) equity investments in operating companies where Alleghany has significant influence (an aggregate common stock position held at or above 20 percent is presumed to convey significant influence); (ii) partnership investments (including hedge funds and private equity funds); and (iii) non-marketable equity investments. Equity investments in operating companies where Alleghany has significant influence are accounted for using the equity method. Partnership investments are accounted for at fair value, with changes in fair value recognized in net earnings, or using the equity method where Alleghany has significant influence. Non-marketable equity investments are accounted for at fair value, with changes in fair value recognized in net earnings. Net realized gains and losses on investments are determined in accordance with the specific identification method. Net investment income consists primarily of: (i) interest income from debt securities, short-term investments, commercial mortgage loans, funds withheld by cedants and cash, including any premium amortization or discount accretion; (ii) dividend income from equity securities; and (iii) investment income from other invested assets, which includes results arising from partnership investments, whether accounted for under the equity method or at fair value. Interest income is accrued when earned. Premiums and discounts arising from the purchase of certain debt securities are treated as a yield adjustment over the estimated useful life of the securities, adjusted for anticipated prepayments using the retrospective interest method. Under this method, the effective yield on a security is estimated. Such estimates are based on the prepayment terms of the security, past actual cash flows and assumptions as to future expected cash flow. The future expected cash flow assumptions consider various prepayment assumptions based on historical experience, as well as current market conditions. Periodically, the effective yield is re-estimated to reflect actual prepayments and updated future expected cash flow assumptions. Upon a re-estimation, a security’s book value is restated at the most recently calculated effective yield, assuming that yield had been in effect since the security was purchased. This treatment results in an increase or decrease to net investment income (accretion of premium or amortization of discount) at the new measurement date. With respect to callable debt securities purchased at a premium to par value, the amortization period for that premium is the earliest call date. See Note 4 for additional information regarding investments.
Fair value	(c) Fair value Fair value is defined as the price that would be received upon the sale of an asset or paid to transfer a liability in an orderly transaction between willing, able and knowledgeable market participants at the measurement date. Fair value measurements are not adjusted for transaction costs. In addition, a three-tiered hierarchy for inputs is used in management’s determination of fair value of financial instruments that emphasizes the use of observable inputs over the use of unobservable inputs by requiring that the observable inputs be used when available. Observable inputs are market participant assumptions based on market data obtained from sources independent of the reporting entity. Unobservable inputs are the reporting entity’s own assumptions about market participant assumptions based on the best information available under the circumstances. In assessing the appropriateness of using observable inputs in making its fair value determinations, Alleghany considers whether the market for a particular security is “active” or “inactive” based on all the relevant facts and circumstances. A market may be considered to be inactive if there are relatively few recent transactions or if there is a significant decrease in market volume. Furthermore, Alleghany considers whether observable transactions are “orderly” or not. Alleghany does not consider a transaction to be orderly if there is evidence of a forced liquidation or other distressed condition; as such, little or no weight is given to that transaction as an indicator of fair value. Although Alleghany is responsible for the determination of the fair value of its financial assets and the supporting methodologies and assumptions, it employs third-party valuation service providers to gather, analyze and interpret market information and derive fair values based upon relevant methodologies and assumptions for individual instruments. When those providers are unable to obtain sufficient market observable information upon which to estimate the fair value for a particular security, fair value is determined either by requesting a quote, which is generally non-binding, from brokers who are knowledgeable about these securities or by employing widely accepted valuation models. Valuation service providers typically obtain data about market transactions and other key valuation model inputs from multiple sources and, through the use of widely accepted valuation models, provide a single fair value measurement for individual securities for which a fair value has been requested under the terms of service agreements. The inputs used by the valuation service providers include, but are not limited to, market prices from recently completed transactions and transactions of comparable securities, interest rate yield curves, credit spreads, currency rates and other market observable information, as applicable. The valuation models take into account, among other things, market observable information as of the measurement date as well as the specific attributes of the security being valued including its term, interest rate, credit rating, industry sector and, when applicable, collateral quality and other issue or issuer specific information. When market transactions or other market observable data is limited, the extent to which judgment is applied in determining fair value is greatly increased. The three-tiered hierarchy used in management’s determination of fair value is broken down into three levels based on the reliability and observability of inputs as follows: • Level 1: Valuations are based on unadjusted quoted prices in active markets that Alleghany has the ability to access for identical, unrestricted assets and do not involve any meaningful degree of judgment. An active market is defined as a market where transactions for the financial instrument occur with sufficient frequency and volume to provide pricing information on an ongoing basis. Alleghany’s Level 1 assets include publicly traded common stocks and mutual funds (which are included on the consolidated balance sheet in equity securities) where Alleghany’s valuations are based on quoted market prices. • Level 2: Valuations are based on direct and indirect observable inputs other than quoted market prices included in Level 1. Level 2 inputs include quoted prices for similar assets in active markets and inputs other than quoted prices that are observable for the asset, such as the terms of the security and market-based inputs. Terms of the security include coupon, maturity date and any special provisions that may, for example, enable the investor, at its election, to redeem the security prior to its scheduled maturity date (such provisions may apply to all debt securities except U.S. Government obligations). Market-based inputs include interest rates and yield curves that are observable at commonly quoted intervals and current credit rating(s) of the security. Market-based inputs may also include credit spreads of all debt securities except U.S. Government obligations, and currency rates for certain foreign government obligations and foreign corporate bonds denominated in foreign currencies. Fair values are determined using a market approach that relies on the securities’ relationships to quoted prices for similar assets in active markets, as well as the other inputs described above. In determining the fair values for the vast majority of commercial mortgage-backed securities (“CMBS”) and other asset- backed securities, as well as a small portion of residential mortgage-backed securities (“RMBS”), an income approach is used to corroborate and further support the fair values determined by the market approach. The income approach primarily involves developing a discounted cash flow model using the future projected cash flows of the underlying collateral, and the terms of the security. Level 2 assets generally include short-term investments and most debt securities. Alleghany’s Level 2 liabilities consist of the Senior Notes, as defined in Note 1(n). • Level 3: Valuations are based on techniques that use significant inputs that are unobservable. The valuation of Level 3 assets requires the greatest degree of judgment. These measurements may be made under circumstances in which there is little, if any, market activity for the asset. Alleghany’s assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment. In making the assessment, Alleghany considers factors specific to the asset. In certain cases, the inputs used to measure fair value may fall into different levels of the fair value hierarchy. In such cases, the level in the fair value hierarchy within which the fair value measurement is classified is determined based on the lowest level input that is significant to the fair value measurement in its entirety. Assets classified as Level 3 principally include other asset-backed securities (primarily, collateralized loan obligations) and, to a lesser extent, U.S. and foreign corporate bonds (including privately issued securities) and commercial mortgage loans. Mortgage-backed and asset-backed securities are initially valued at the transaction price. Subsequently, Alleghany uses widely accepted valuation practices that produce a fair value measurement. The vast majority of fair values are determined using an income approach. The income approach primarily involves developing a discounted cash flow model using the future projected cash flows of the underlying collateral, as well as other inputs described below. A few Level 3 valuations are based entirely on non-binding broker quotes. These securities consist primarily of mortgage-backed and asset-backed securities where reliable pool and loan level collateral information cannot be reasonably obtained, and as such, an income approach is not feasible. Since Level 3 valuations are based on techniques that use significant inputs that are unobservable with little or no market activity, the fair values under the market approach for Level 3 securities are less credible than under the income approach; however, the market approach, where feasible, is used to corroborate the fair values determined by the income approach. The market approach primarily relies on the securities’ relationships to quoted transaction prices for similarly structured instruments. To the extent that transaction prices for similarly structured instruments are not available for a particular security, other market approaches are used to corroborate the fair values determined by the income approach, including option adjusted spread analyses. Unobservable inputs, significant to the measurement and valuation of mortgage-backed and asset-backed securities, are generally used in the income approach, and include assumptions about prepayment speed and collateral performance, including default, delinquency and loss severity rates. Significant changes to any one of these inputs, or combination of inputs, could significantly change the fair value measurement for these securities. The impact of prepayment speeds on fair value is dependent on a number of variables including whether the securities were purchased at a premium or discount. A decrease in interest rates generally increases the assumed rate of prepayments, and an increase in interest rates generally decreases the assumed speed of prepayments. Increased prepayments increase the yield on securities purchased at a discount and reduce the yield on securities purchased at a premium. In a decreasing prepayment environment, yields on securities purchased at a discount are reduced but are increased for securities purchased at a premium. Changes in default assumptions on underlying collateral are generally accompanied by directionally similar changes in other collateral performance factors, but generally result in a directionally opposite change in prepayment assumptions. Alleghany’s Level 3 liabilities consist of the debt of Alleghany Capital’s operating subsidiaries. Alleghany employs specific control processes to determine the reasonableness of the fair values of its financial assets and liabilities. Alleghany’s processes are designed to ensure that the values received or internally estimated are accurately recorded and that the data inputs and the valuation techniques used are appropriate, consistently applied and that the assumptions are reasonable and consistent with the objective of determining fair value. Alleghany assesses the reasonableness of individual security values received from valuation service providers through various analytical techniques. In addition, Alleghany validates the reasonableness of fair values by comparing information obtained from Alleghany’s valuation service providers to other third-party valuation sources for selected securities. Alleghany also validates prices obtained from brokers for selected securities through reviews by those who have relevant expertise and who are independent of those charged with executing investing transactions. In addition to such procedures, Alleghany reviews the reasonableness of its classification of securities within the three-tiered hierarchy to ensure that the classification is consistent with GAAP. See Note 3 for additional information regarding fair value.
Cash	(d) Cash Cash includes all deposit balances with a bank that are available for immediate withdrawal, whether interest-bearing or non-interest bearing.
Premiums and Unearned Premiums	(e) Premiums and Unearned Premiums Premiums are recognized as revenue on a pro rata basis over the term of an insurance policy. Assumed reinsurance premiums written and earned are based on reports received from ceding companies for pro rata treaty contracts and are generally recorded as written based on contract terms for excess-of-loss treaty contracts. Premiums are earned ratably over the terms of the related coverages. Unearned premiums and ceded unearned premiums represent the portion of gross premiums written and ceded premiums written, respectively, related to the unexpired periods of such coverages. Assumed reinsurance premiums written and earned, along with related costs, for which data has not been reported by the ceding companies, are estimated based on historical patterns and other relevant factors. These estimates may change when actual data for such estimated items becomes available. Premium balances receivable are reported net of an allowance for credit losses. Estimates of expected credit losses are based on historical experience, current conditions and reasonable and supportable forecasts, and include an ongoing review of amounts outstanding, length of collection periods, the creditworthiness of the insured and other relevant factors. Amounts deemed to be uncollectible are written off against the allowance. Subsequent reversals are recognized in earnings.
Reinsurance Ceded	(f) Reinsurance Ceded Reinsurance is used to mitigate the exposure to losses, manage capacity and protect capital resources. Reinsuring loss exposures does not relieve a ceding entity from its obligations to policyholders and cedants. Reinsurance recoverables (including amounts related to incurred but not reported (“IBNR”) claims) and ceded unearned premiums are reported as assets. To minimize exposure to losses related to a reinsurer’s inability to pay, the financial condition of such reinsurer is evaluated initially upon placement of the reinsurance and periodically thereafter. In addition to considering the financial condition of a reinsurer, the collectability of the reinsurance recoverables is evaluated based upon a number of other factors. Such factors include the amounts outstanding, length of collection periods, disputes, any collateral or letters of credit held and other relevant factors. Credit losses for reinsurance recoverables are recorded through an allowance for credit losses. Estimates of expected credit losses are based on historical experience, current conditions and reasonable and supportable forecasts. Amounts deemed to be uncollectible are written off against the allowance. Subsequent reversals in credit loss estimates are recognized in earnings. Ceded premiums written are recorded in accordance with the applicable terms of the various reinsurance contracts and ceded premiums earned are charged against revenue over the period of the various reinsurance contracts. This also generally applies to reinstatement premiums paid to a reinsurer, which arise when contractually-specified ceded loss triggers have been breached. Ceded commissions reduce commissions, brokerage and other underwriting expenses and ceded losses incurred reduce net loss and loss adjustment expenses (“LAE”) incurred over the applicable periods of the various reinsurance contracts with third-party reinsurers. If premiums or commissions are subject to adjustment (for example, retrospectively-rated or experience-rated), the estimated ultimate premium or commission is recognized over the period of the contract. Amounts recoverable from reinsurers are estimated in a manner consistent with the claim liability associated with the reinsured business and consistent with the terms of the underlying reinsurance contract. See Note 5 for additional information on reinsurance ceded and reinsurance recoverables.
Deferred Acquisition Costs	(g) Deferred Acquisition Costs Acquisition costs related to unearned premiums that vary with, and are directly related to, the production of such premiums are deferred. Furthermore, such deferred costs: (i) represent only incremental, direct costs associated with the successful acquisition of a new or renewal insurance or reinsurance contract; (ii) are essential to the contract transaction; (iii) would not have been incurred had the contract transaction not occurred; and (iv) are related directly to the acquisition activities involving underwriting, policy issuance and processing. Acquisition costs principally relate to commissions. To a lesser extent, acquisition costs can include premium taxes and certain qualifying underwriting expenses. For insurance policies written, acquisition costs are generally incurred directly and include commissions, premium taxes and certain qualifying underwriting expenses. For reinsurance contracts written, acquisition costs are generally incurred through brokerage commissions and indirectly through ceding commissions, which are deferred. Deferred acquisition costs are amortized to expense as the related premiums are earned, generally over a period of one year. Deferred acquisition costs are reviewed at least annually to determine their recoverability from future income, including investment income. If any such costs are determined not to be recoverable they are charged to expense. Anticipated net loss and LAE and estimated remaining costs of servicing the contracts are considered when evaluating recoverability of deferred acquisition costs.
Property and Equipment	(h) Property and Equipment Property and equipment is owned primarily by Alleghany Capital’s subsidiaries, and includes buildings, land, leasehold improvements, furniture, fixtures and computer hardware and software, as well as industrial and office machinery and equipment. Property and equipment is carried at cost, net of accumulated depreciation and amortization. Depreciation of buildings and equipment is principally calculated using the straight-line method over the estimated useful life of the respective assets. Estimated useful lives for such assets range from three to 20 years. Amortization of leasehold improvements is principally calculated using the straight-line method over the estimated useful life of the leasehold improvement or the life of the lease, whichever is less. Property and equipment are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable based on estimated, undiscounted future cash flows resulting from the use of the asset and its eventual disposition. When required, impairment losses are recognized based on the excess of the asset’s carrying value over the estimated fair value of the asset. Rental expense on operating leases is recorded on a straight-line basis over the term of the lease, regardless of the timing of actual lease payments. Maintenance and repairs that do not extend the useful lives of property and equipment is charged to expense as incurred. All leases with terms of more than one year are recorded as lease liabilities and corresponding right-of-use assets, and are recorded as a component of other liabilities and other assets , respectively. Lease liabilities represents the present value of expected lease payments over the remaining lease term. Expected lease payments are specified in the lease contract over the stated term, including any options to extend or terminate that Alleghany is reasonably certain to exercise. Expected lease payments also include certain non-lease components, such as office cleanings, security and maintenance services provided by Alleghany’s lessors for certain of its leases. See Note 12(b) for additio nal information on Alleghany’s leases.
Goodwill and Other Intangible Assets	(i) Goodwill and Other Intangible Assets Goodwill and other intangible assets, net of amortization, are recorded as a consequence of business acquisitions. Goodwill represents the excess, if any, of the amount paid to acquire subsidiaries and other businesses over the fair value of their net assets as of the date of acquisition. Other intangible assets are recorded at their fair value as of the acquisition date. A significant amount of judgment is needed to determine the fair value as of the date of acquisition of other intangible assets and the net assets acquired in a business acquisition. The determination of the fair value of other intangible assets and net assets often involves the use of valuation models and other estimates, which involve many assumptions and variables and are inherently subjective. The fair value estimates may include the use of financial projections and discount rates. Other intangible assets that are not deemed to have an indefinite useful life are amortized over their estimated useful lives. Goodwill and intangible assets that have an indefinite useful life are not subject to amortization. Goodwill and other intangible assets deemed to have an indefinite useful life are tested annually for impairment in the fourth quarter. Goodwill and other intangible assets are also tested whenever events and changes in circumstances suggest that the carrying amount may not be recoverable. A significant amount of judgment is required in performing goodwill and other intangible asset impairment tests. These tests may include estimating the fair value of Alleghany’s operating subsidiaries, which include Alleghany Capital’s operating subsidiaries, and other intangible assets. The fair value estimates may include the use of financial projections and discount rates. If it is determined that an asset has been impaired, the asset is written down by the amount of the impairment, with a corresponding charge to net earnings. Subsequent reversal of any impairment charge is not permitted. With respect to goodwill, a qualitative assessment is first made to determine whether it is necessary to perform quantitative testing. This initial assessment includes, among other factors, consideration of: (i) past, current and projected future earnings and equity; (ii) recent trends and market conditions; and (iii) valuation metrics involving similar companies that are publicly traded and acquisitions of similar companies, if available. If this initial qualitative assessment indicates that the fair value of an operating subsidiary may be less than its carrying amount, a second step is taken, involving a comparison between the estimated fair value of the operating subsidiary with its respective carrying amount including goodwill. Under GAAP, fair value refers to the amount for which the entire operating subsidiary may be bought or sold. The methods for estimating the fair value of an operating subsidiary values include asset and liability fair values and other valuation techniques, such as discounted cash flows and multiples of earnings or revenues. All of these methods involve significant estimates and assumptions. If the carrying value exceeds estimated fair value, an impairment charge is recognized for the amount by which the carrying amount of the operating subsidiary exceeds its estimated fair value. Any resulting impairment loss recognized cannot exceed the total amount of goodwill associated with the operating subsidiary. See Note 2 for additional information on goodwill and other intangible assets.
Income Taxes	(j) Income Taxes Alleghany files a consolidated federal income tax return with its subsidiaries. Alleghany’s consolidated federal income tax return includes as part of its taxable income all items of income of non-U.S. subsidiaries that are subject to current U.S. income tax, currently pursuant to provisions of the Internal Revenue Code. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amount of existing assets and liabilities and their respective tax bases and operating loss and tax credit carry-forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. Current tax liabilities or assets are recognized for the estimated taxes payable or refundable on tax returns for the current year. A valuation allowance is provided when it is more likely than not that some portion of the deferred tax assets will not be realized. This determination is based upon a review of all available information, both positive and negative, including Alleghany’s earnings history, the timing, character and amount of future earnings potential, the reversal of taxable temporary differences and the tax planning strategies available. See Note 9 for additional information on income taxes.
Loss Reserves	(k) Loss Reserves The reserves for loss and LAE represent management’s best estimate of the ultimate cost of all reported and unreported losses incurred through the balance sheet date. The reserves for loss and LAE include but are not limited to: (i) reports and individual case estimates received from ceding companies with respect to assumed reinsurance business; (ii) the accumulation of individual estimates for claims reported with respect to direct insurance business; (iii) estimates for IBNR claims based on past experience, modified for current trends and industry data; and (iv) estimates of expenses for investigating and settling claims based on past experience. The methods used to determine such estimates and to establish the resulting reserves are continually reviewed and updated. Any adjustments are reflected in current income. Net loss and LAE consist of the estimated ultimate cost of settling claims incurred within the reporting period (net of related reinsurance recoverable), including IBNR claims, plus changes in estimates of prior period losses. The estimation of the liability for unpaid loss and LAE is inherently difficult and subjective, especially in view of changing legal and economic environments that impact the development of loss reserves, and therefore, quantitative techniques frequently have to be supplemented by subjective considerations and managerial judgment. In addition, trends that have affected development of liabilities in the past may not necessarily occur or affect liability development to the same degree in the future. While the reserving process is difficult for the insurance business, the inherent uncertainties of estimating loss reserves are even greater for the reinsurance business, due primarily to the longer-term nature of most of the business, the diversity of development patterns among different types of reinsurance contracts, the necessary reliance on the ceding companies for information regarding reported claims and differing reserving practices among ceding companies, which may change without notice. TransRe writes a significant amount of non-proportional assumed casualty reinsurance as well as proportional assumed reinsurance of excess liability business. Claims from such classes can exhibit greater volatility over time than most other classes due to their low frequency, high severity nature and loss cost trends that are more difficult to predict. Net loss and LAE also include amounts for risks related to asbestos-related illness and environmental impairment. Each of Alleghany’s reinsurance and insurance subsidiaries establishes reserves on its balance sheet for unpaid loss and LAE related to its property and casualty reinsurance and insurance contracts. As of any balance sheet date, there are claims that have not yet been reported, and some claims may not be reported for many years after the date a loss occurs. As a result of this historical pattern, the liability for unpaid loss and LAE includes significant estimates for IBNR claims. Additionally, reported claims are in various stages of the settlement process. Each claim is settled individually based upon its merits, and certain claims may take years to settle, especially if legal action is involved. As a result, the liabilities for unpaid loss and LAE include significant judgments, assumptions and estimates made by management related to the actual ultimate losses that will arise from the claims. As noted above, as of any balance sheet date, not all claims that have occurred have been reported to Alleghany, and if reported may not have been settled. The time period between the occurrence of a loss and the time it is settled is referred to as the “claim tail.” Reported losses for the shorter-tailed classes, such as property, generally reach the ultimate level of incurred losses in a relatively short period of time and as such, are only relevant for the more recent accident years. Casualty claims can have a very long claim tail, in certain situations extending for many years. In addition, casualty claims are more susceptible to litigation and the legal environment and can be significantly affected by changing contract interpretations, all of which contribute to extending the claim tail. For long-tail casualty lines of business, estimating the ultimate liabilities for unpaid loss and LAE is a more complex process and depends on a number of factors, including the line and volume of the business involved. Alleghany’s loss reserve review processes use actuarial methods that vary by operating subsidiary and line of business and produce point estimates for each class of business. The actuarial methods used include the following methods: • Reported Loss Development Method: a reported loss development pattern is calculated based on historical loss development data, and this pattern is then used to project the latest evaluation of cumulative reported losses for each accident year or underwriting year, as appropriate, to ultimate levels; • Paid Development Method: a paid loss development pattern is calculated based on historical paid loss development data, and this pattern is then used to project the latest evaluation of cumulative paid losses for each accident year or underwriting year, as appropriate, to ultimate levels; • Expected Loss Ratio Method: expected loss ratios are applied to premiums earned, based on historical company experience, or historical insurance industry results when company experience is deemed not to be sufficient; and • Bornhuetter-Ferguson Method: the results from the Expected Loss Ratio Method are essentially blended with either the Reported Loss Development Method or the Paid Development Method. See Note 6 and Note 12(c) for additional information on loss reserves.
Earnings Per Share of Common Stock Attributable to Alleghany Stockholders	(l) Earnings Per Share of Common Stock Attributable to Alleghany Stockholders Basic earnings per share of common stock is based on the average number of shares of outstanding common stock, par value $ 1.00 per share, of Alleghany (“Common Stock”) during the period, retroactively adjusted for stock dividends, where applicable. Diluted earnings per share of Common Stock are based on those shares used to calculate basic earnings per share of Common Stock plus the dilutive effect of stock-based compensation awards, retroactively adjusted for stock dividends, where applicable. See Note 11 for additional information on earnings per share.
Stock-Based Compensation Plans	(m) Stock-Based Compensation Plans The cost resulting from all stock-based compensation transactions is recognized in the financial statements, with fair value as the measurement objective in accounting for stock-based compensation arrangements. The fair value-based measurement method applies in accounting for stock-based compensation transactions with employees. Non-employee directors are treated as employees for accounting purposes. See Note 14 for additional information on Alleghany’s long-term compensation plans, which include stock-based compensation plans.
Senior Notes and Other Debt	(n) Senior Notes and Other Debt Debt consists of senior notes issued by Alleghany (the “Alleghany Senior Notes”), senior notes issued by TransRe (the “TransRe Senior Notes,” and together with the Alleghany Senior Notes, the “Senior Notes”) and other debt. Other debt consists primarily of borrowings at Alleghany Capital’s subsidiaries and is generally used to fund acquisitions and support working capital needs. The Senior Notes and other debt are carried at unpaid principal balance, including any unamortized premium or discount and any unamortized debt issuance costs. See Note 8 for additional information on the Senior Notes and other debt.
Currency Translation	(o) Currency Translation Assets and liabilities denominated in foreign currencies are translated into U.S. dollars at period-end exchange rates. Income and expense accounts are translated at average exchange rates for the year. The resulting unrealized currency translation gain or loss for functional currencies is recorded, net of tax, in accumulated other comprehensive income, a component of stockholders’ equity. Transaction gains and losses on assets and liabilities denominated in foreign currencies are recorded as a component of net realized capital gains during the period in which they occur.
Product and Service Revenues and Other Operating Expenses	(p) Product and Service Revenues and Other Operating Expenses Product and service revenues relate primarily to manufactured products and services sold by Alleghany Capital’s subsidiaries. Products manufactured and sold by Alleghany Capital's subsidiaries primarily include fabricated steel, trailers, machine tools, funeral products and injection molded and thermoformed parts and multi-component assemblies, and products manufactured by third-parties primarily include toys. Services primarily include facility design, construction management, technical services and hotel management and development. Product and service revenues and related operating expenses arising from the sale of manufactured goods and services are generally recognized as the transfer of goods and services to customers takes place. Payment terms for products and services vary by the type of product or service offered. Product and service revenues reflect the payment or payments that are expected to be received from the customers for those goods and services. Other operating expenses consist of the cost of goods and services sold and selling, general and administrative expenses. Other operating expenses also include: (i) advertising and marketing costs; and (ii) finders’ fees, legal and accounting costs and other transaction-related expenses, all of which are recognized as incurred. Product and service revenues and related operating expenses from manufactured products are generally recognized at the time title transfers to the customer, which typically occurs at the point of shipment or delivery to the customer, depending on the terms of the sales arrangement. For certain products, partial payment in the form of a deposit is required before the products are delivered to the customer and such deposits are recorded as a component of other liabilities. For certain manufactured products, customers are provided one or more of the following programs: (i) sales incentives; (ii) support for customer promotions; and (iii) allowances for returns or defective merchandise. Estimates for the cost of these programs are recorded as revenue adjustments that reduce revenue in the period the related sale is recognized. Product and service revenues and related operating expenses from services are generally recognized as the services are performed. Services provided pursuant to a contract are recognized either over the contract period or upon completion of the elements specified in the contract, depending on the terms of the contract. Service revenues related to uncompleted facility construction projects are further recognized as the work progresses, which involve estimates of costs needed to complete the facilities, among other things. The cumulative impact of revisions in total cost estimates are reflected in the period in which these changes become known, including, to the extent required, the increase or reversal of profit recognized in prior periods. External factors, such as weather, changes in customer requirements and other factors outside of Alleghany’s control, may affect the progress and estimated cost of a project’s completion and, therefore, the timing and amount of recognition of revenues and income. Costs incurred on uncompleted contracts in excess of billings are recorded as a component of other assets and billings on uncompleted contracts in excess of costs incurred are recorded as a component of other liabilities. Provisions for estimated losses on uncompleted contracts, if any, are made in the period in which such losses are determined. For certain customer contracts in the technical service and hotel management businesses, construction-related costs and recurring hotel operating expenses that Alleghany Capital subsidiaries control and oversee as a principal are incurred and recognized as other operating expenses but are passed through to the customer and correspondingly recognized as product and service revenues. Accounts receivable arising from product and service revenues are reported as a component of other assets and net of an allowance for credit losses. Such allowance reflects all expected credit losses over the remaining expected life of accounts receivable based on historical experience, current conditions and reasonable and supportable forecasts. In this regard, amounts outstanding, the current business environment, length of collection periods, the creditworthiness of the customer and other relevant factors are reviewed and considered on an ongoing basis. Alleghany Capital’s subsidiaries may obtain collateral held, letters of credit or credit insurance to back certain payment obligations. Amounts deemed to be uncollectible are written off against the allowance. Subsequent reversals in credit loss estimates are permitted and are recognized in earnings. Most Alleghany Capital subsidiaries maintain product inventory assets. Inventories consist primarily of raw materials, work-in-process and finished goods. Inventories are valued using the first-in-first-out method, are stated at the lower of cost or net realizable value, and are reported as a component of other assets.
Reclassification	(q) Reclassification Certain prior year amounts have been reclassified to conform to the 2021 presentation of the financial statements.
Recent Accounting Standards	(r) Recent Accounting Standards Recently Adopted - 2019 In February 2016, the Financial Accounting Standards Board (the “FASB”) issued guidance on leases. Under this guidance, a lessee is required to recognize lease liabilities and corresponding right-of-use assets for leases with terms of more than one year, whereas under the prior guidance, a lessee was only required to recognize assets and liabilities for those leases qualifying as capital leases. This guidance also requires new disclosures about the amount, timing and uncertainty of cash flows arising from leases. The accounting by lessors remains largely unchanged. This guidance became effective in the first quarter of 2019 for public companies, with early adoption permitted. A modified retrospective transition approach was elected for all leases in existence as of, or entered into after, the beginning of the earliest comparative period presented in the financial statements. Alleghany adopted this guidance in the first quarter of 2019, and the implementation did not have a material impact on its results of operations and financial condition. As part of its implementation, Alleghany elected to not separate lease components from non-lease components (such as office cleanings, security and maintenance services provided by Alleghany’s lessors for certain of its leases). Alleghany also elected the package of practical expedients under the transition guidance, which allowed Alleghany to not reevaluate existing lease classifications, among others. As of January 1, 2019, Alleghany’s adoption of this guidance resulted in recognition of an additional right-of-use asset of approximately $ 0.2 billion and a corresponding lease liability of $ 0.2 billion. See Note 12(b) for additional information on Alleghany’s leases. In August 2017, the FASB issued guidance that simplifies the requirements to achieve hedge accounting, better reflects the economic results of hedging in financial statements and improves the alignment between hedge accounting and a company’s risk management activities. This guidance was effective in the first quarter of 2019 for public companies, with early adoption permitted. Alleghany adopted this guidance in the first quarter of 2019 and the implementation did not have a material impact on its results of operations and financial condition. Recently Adopted – 2020 In June 2016, the FASB issued guidance on credit losses. Under this guidance, a company is required to measure all expected credit losses on loans, reinsurance recoverables and other financial assets accounted for at cost or amortized cost, as applicable, over the remaining expected life of such assets. Estimates of expected credit losses are to be based on historical experience, current conditions and reasonable and supportable forecasts. Under former FASB guidance, credit losses on these assets generally required a company to recognize credit losses when it was probable that a loss had been incurred. Credit losses for securities accounted for on an AFS basis are to be measured in a manner similar to GAAP as applied under former guidance and cannot exceed the amount by which the fair value is less than the amortized cost, although the new guidance removes the length of time a security has been in an unrealized loss position as a possible indication of a credit impairment. Credit losses for all financial assets are to be recorded through an allowance for credit losses. Subsequent reversals in credit loss estimates are permitted and are to be recognized in earnings. This guidance also requires new disclosures about the significant estimates and judgments used in estimating credit losses, as well as the credit quality of financial assets. This guidance was effective in the first quarter of 2020 for public companies, with early adoption permitted. Alleghany adopted this guidance in the first quarter of 2020. As of January 1, 2020, Alleghany increased its allowances for credit losses on certain financial assets accounted for at cost or amortized cost by $ 4.5 million and recorded an after-tax cumulative effect reduction in opening retained earnings of $ 3.6 million. The increase in allowances for credit losses primarily relates to reinsurance recoverables and commercial mortgage loans. See Note 5 for further information on Alleghany’s reinsurance recoverables and Note 4(j) for further information on Alleghany’s investments in commercial mortgage loans. The increase in allowances for credit losses also relates to premium balances receivable. Estimates of expected credit losses for all of these assets are based on certain market-based indicators of credit quality, which are updated on an annual basis and re-assessed at least quarterly. Related credit loss expenses are recorded as a component of other operating expenses. As of January 1, 2020, credit losses for Alleghany’s AFS securities are recorded through an allowance for credit losses on the consolidated balance sheets and as a change in allowance for credit losses on AFS securities in the consolidated statements of earnings and comprehensive income. See Note 4(f) for further information on the credit quality for Alleghany’s AFS securities. In January 2017, the FASB issued guidance that simplifies the subsequent measurement of goodwill. Under this guidance, if an initial qualitative assessment indicates that the fair value of an operating subsidiary may be less than its carrying amount, an impairment charge is recognized for the amount by which the carrying amount of the operating subsidiary exceeds its estimated fair value. Any resulting impairment loss recognized cannot exceed the total amount of goodwill associated with the operating subsidiary. This guidance was effective in the first quarter of 2020 for public companies, with early adoption permitted. Alleghany adopted this guidance in the first quarter of 2020 and the implementation did not have a material impact on its results of operations and financial condition. See Note 2 for further information on Alleghany’s goodwill. In August 2018, the FASB issued guidance that changes the financial statement disclosure requirements for measuring fair value. With respect to financial instruments classified as “Level 3” in the fair value disclosure hierarchy, the guidance requires certain additional disclosures for public companies related to amounts included in other comprehensive income and significant unobservable inputs used in the valuation, while removing disclosure requirements related to an entity’s overall valuation processes. The guidance also removes certain disclosure requirements related to transfers between financial instruments classified as “Level 1” and “Level 2” and provides clarification on certain other existing disclosure requirements. This guidance was effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted with respect to any eliminated or modified disclosures. Alleghany adopted this guidance in the first quarter of 2020 and the implementation did not impact its results of operations or financial condition. See Note 3 for further information on the fair value of Alleghany’s financial instruments. In March 2020, the FASB issued guidance to expedite and simplify the accounting associated with the anticipated migration away from the widely-used London Inter-bank Offered Rate and other similar rates as benchmark interest rates (collectively, "LIBOR") after 2021. Under pre-existing GAAP, such modifications made to: (i) loans and certain other contracts would require re-assessments of the accounting for those contacts, such as whether they were extinguished and remeasured from an accounting perspective; and (ii) derivative contracts may cause a change in accounting, such as a possible dedesignation of hedge accounting. This new guidance largely eliminates these requirements as a result of this migration to one or more new benchmark rates and is generally applicable for contract modifications made prior to December 31, 2022. As a consequence, Alleghany will not recognize gains and losses during this benchmark interest rate transition period that would Certain of Alleghany's assets and liabilities bear interest on a LIBOR-based floating rate. Assets primarily include a small portion of Alleghany’s debt securities portfolio and certain of its commercial mortgage loans. Liabilities primarily include certain of Alleghany Capital’s borrowings. In general, the underlying contracts associated with these assets and liabilities contain appropriate LIBOR fallback provisions if LIBOR is no longer available and / or mature before the relevant LIBOR phase-out date. Future Application of Accounting Standards In August 2020, the FASB issued guidance that simplifies the accounting and disclosure requirements for certain financial instruments with characteristics of liabilities and equity, such as convertible debt and convertible preferred stock. This guidance also modifies the accounting for certain contracts involving an entity’s own stock. This guidance is effective in the first quarter of 2022 for public companies, with early adoption permitted. Alleghany will adopt this guidance in the first quarter of 2022 and does not currently believe that the implementation will have a material impact on its results of operations and financial condition. In May 2021, the FASB issued guidance on how issuers should account for modifications or exchanges of freestanding equity-classified written call options that remain equity classified after the modification or exchange. Under this guidance, the issuer will determine the accounting for the modification or exchange based on the economic substance of the modification or exchange (i.e. to issue equity, to issue or modify debt, or other reasons). This guidance is effective in the first quarter of 2022 for all entities, with early adoption permitted when applied as of the beginning of the fiscal year. Alleghany will adopt this guidance in the first quarter of 2022 and does not currently believe that the implementation will have a material impact on its results of operations and financial condition. In October 2021, the FASB issued guidance related to contract assets and liabilities recorded in a business combination. A contract asset is recorded when the amount of goods or services transferred to a customer exceed the amount received or receivable from the customer, and a contract liability is recorded when the amount received or receivable from a customer exceeds the amount of goods or services transferred to the customer. The guidance requires that the acquirer of a business determine and record a customer contract asset and / or liability it would have recorded if the acquirer had entered into the original contract with the customer at the same date and at the same terms as the acquiree using preexisting revenue recognition guidance. Under current guidance, contract assets and liabilities are recorded at acquisition date fair value. As a result of this guidance, the acquisition date recognition and measurement of customer contract assets and liabilities will likely be similar to the acquiree carrying values, and post-acquisition revenue recognition will likely be similar to what the acquiree would have recorded. This guidance is effective for public companies for business acquisitions completed on or after January 1, 2023, with early adoption permitted subject to certain conditions and requirements. Alleghany will adopt this guidance for business acquisitions completed on or after January 1, 2023 and does not currently believe that the implementation will have a material impact on its results of operations and financial condition.

Summary of Significant Accoun_3

Summary of Significant Accounting Principles (Tables)	12 Months Ended
	Dec. 31, 2021
Noncontrolling Interest [Abstract]
Components of Net Earnings Attributable to Noncontrolling Interests	The following table presents the components of net earnings attributable to noncontrolling interests for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Accretion of redeemable noncontrolling interests $ 23.5 $ 2.2 $ 8.8 Portion of net earnings attributable to noncontrolling interests 72.4 22.9 23.6 Total $ 95.9 $ 25.1 $ 32.4

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Rollforward of Goodwill and Intangible Assets	The following table presents a rollforward of Alleghany’s goodwill and intangible assets by segment during 2021 and 2020: Goodwill Intangible Assets Alleghany Capital Insurance Reinsurance Total Alleghany Capital Insurance Reinsurance Total ($ in millions) Balance as of December 31, 2019 $ 465.2 $ 49.0 $ 8.8 $ 523.0 $ 542.4 $ 65.4 $ 78.2 $ 686.0 Acquired (1) 92.1 — — 92.1 147.0 — — 147.0 Amortization (2) n/a n/a n/a n/a ( 43.4 ) ( 1.0 ) 0.2 ( 44.2 ) Other increase (decrease) — ( 0.9 ) — ( 0.9 ) — ( 1.3 ) — ( 1.3 ) Balance as of December 31, 2020 557.3 48.1 8.8 614.2 646.0 63.1 78.4 787.5 Acquired (1) 139.4 — — 139.4 189.4 — — 189.4 Amortization (2) n/a n/a n/a n/a ( 48.1 ) ( 0.7 ) ( 1.1 ) ( 49.9 ) Other increase (decrease) — — — — — ( 1.3 ) ( 1.3 ) ( 2.6 ) Balance as of December 31, 2021 $ 696.7 $ 48.1 $ 8.8 $ 753.6 $ 787.3 $ 61.1 $ 76.0 $ 924.4 (1) See description below for a summary of recent material acquisitions impacting goodwill and intangible assets. (2) See table below for additional information regarding amortization and useful lives by major class of intangible asset.
Schedule of Goodwill and Intangible Assets	The following table presents the amount of goodwill and intangible assets, net of accumulated amortization expense, reported on Alleghany’s consolidated balance sheets as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Gross Carrying Accumulated Net Carrying (1) Gross Carrying Accumulated Net Carrying (1) ($ in millions) Alleghany Capital (2)(3) - Goodwill $ 696.7 $ — $ 696.7 $ 557.3 $ — $ 557.3 Alleghany Capital (3) - Intangible assets: Trade name 245.3 5.2 240.1 218.2 2.7 215.5 License agreements 167.1 63.3 103.8 167.1 48.1 119.0 Customer relationships 520.1 100.9 419.2 357.8 72.4 285.4 Other 50.0 25.8 24.2 50.0 23.9 26.1 Total Alleghany Capital intangibles 982.5 195.2 787.3 793.1 147.1 646.0 Total Alleghany Capital goodwill and $ 1,679.2 $ 195.2 $ 1,484.0 $ 1,350.4 $ 147.1 $ 1,203.3 Insurance Segment (2) - Goodwill $ 48.1 $ — $ 48.1 $ 48.1 $ — $ 48.1 Insurance Segment - Intangible assets: Agency relationships 12.5 12.1 0.4 13.8 11.6 2.2 State insurance licenses 25.1 — 25.1 25.1 — 25.1 Trade name 35.5 — 35.5 35.5 — 35.5 Brokerage and reinsurance relationships 33.8 33.8 — 33.8 33.8 — Renewal rights 24.9 24.8 0.1 24.9 24.6 0.3 Other 4.1 4.1 — 4.1 4.1 — Total insurance segment intangibles 135.9 74.8 61.1 137.2 74.1 63.1 Total insurance segment goodwill and $ 184.0 $ 74.8 $ 109.2 $ 185.3 $ 74.1 $ 111.2 Reinsurance Segment (2) - Goodwill $ 8.8 $ — $ 8.8 $ 8.8 $ — $ 8.8 Reinsurance Segment - Intangible assets: Value of business in-force 291.4 291.4 — 291.4 291.4 — Loss and LAE reserves ( 98.8 ) ( 90.9 ) ( 7.9 ) ( 98.8 ) ( 88.6 ) ( 10.2 ) State and foreign insurance licenses 19.0 — 19.0 19.0 — 19.0 Trade name 50.0 — 50.0 50.0 — 50.0 Renewal rights 51.8 40.4 11.4 53.0 35.2 17.8 Leases ( 25.8 ) ( 25.8 ) — ( 25.8 ) ( 23.7 ) ( 2.1 ) Other 15.1 11.6 3.5 15.1 11.2 3.9 Total reinsurance segment intangibles 302.7 226.7 76.0 303.9 225.5 78.4 Total reinsurance segment goodwill and $ 311.5 $ 226.7 $ 84.8 $ 312.7 $ 225.5 $ 87.2 Alleghany consolidated: Goodwill $ 753.6 $ — $ 753.6 $ 614.2 $ — $ 614.2 Intangible assets 1,421.1 496.7 924.4 1,234.2 446.7 787.5 Goodwill and other intangibles assets $ 2,174.7 $ 496.7 $ 1,678.0 $ 1,848.4 $ 446.7 $ 1,401.7 (1) Goodwill and intangible assets have been reduced by amounts written-down in prior periods, as applicable. (2) See N ote 13 for additional information on Alleghany’s segments of business. (3) Represents goodwill and other intangible assets related to the acquisition of: (i) Jazwares on April 15, 2016 and its subsequent acquisitions; (ii) W&W|AFCO Steel on April 28, 2017 and its subsequent acquisition; (iii) Concord on October 1, 2018; (iv) PCT on April 26, 2012 and its subsequent acquisitions; (v) IPS on October 31, 2015 and its subsequent acquisitions; (vi) Kentucky Trailer on August 30, 2013 and its subsequent acquisitions; (vii) Wilbert on April 1, 2020 and its subsequent acquisitions; and (viii) WPS on May 10, 2021.

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2021
Fair Value Disclosures [Abstract]
Carrying Value and Estimated Fair Value of Consolidated Financial Instruments	The following table presents the carrying value and estimated fair value of Alleghany’s consolidated financial instruments as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Carrying Value Fair Value Carrying Value Fair Value ($ in millions) Assets Investments (excluding equity method investments and loans) (1) $ 20,887.7 $ 20,887.7 $ 19,051.9 $ 19,051.9 Liabilities Senior Notes and other debt (2) $ 2,847.2 $ 3,157.9 $ 2,135.9 $ 2,468.7 (1) This table includes debt and equity securities, as well as partnership and non-marketable equity investments accounted for at fair value that are included in other invested assets. This table excludes investments accounted for using the equity method and commercial mortgage loans that are accounted for at unpaid principal balance. The fair value of short-term investments approximates amortized cost. See Note 8 for additional information on the Senior Notes and other debt.
Financial Instruments at Fair Value and Level of Fair Value Hierarchy of Inputs	The following tables present Alleghany’s financial instruments at fair value and the level of the fair value hierarchy of inputs used as of December 31, 2021 and 2020: Level 1 Level 2 Level 3 Total ($ in millions) As of December 31, 2021 Equity securities: Common stock $ 3,677.1 $ 2.1 $ — $ 3,679.2 Preferred stock — 3.3 1.3 4.6 Total equity securities 3,677.1 5.4 1.3 3,683.8 Debt securities: U.S. Government obligations — 2,050.7 — 2,050.7 Municipal bonds — 2,535.9 — 2,535.9 Foreign government obligations — 854.9 — 854.9 U.S. corporate bonds — 2,807.0 670.3 3,477.3 Foreign corporate bonds — 1,049.7 177.2 1,226.9 Mortgage and asset-backed securities: RMBS (1) — 2,007.1 1.9 2,009.0 CMBS — 905.9 — 905.9 Other asset-backed securities (2) — 1,652.7 1,348.3 3,001.0 Total debt securities — 13,863.9 2,197.7 16,061.6 Short-term investments — 1,142.3 — 1,142.3 Other invested assets — — — — Total investments (excluding equity method investments and loans) $ 3,677.1 $ 15,011.6 $ 2,199.0 $ 20,887.7 Senior Notes and other debt $ — $ 2,377.4 $ 780.5 $ 3,157.9 Level 1 Level 2 Level 3 Total ($ in millions) As of December 31, 2020 Equity securities: Common stock $ 2,711.1 $ 3.5 $ — $ 2,714.6 Preferred stock — 3.0 1.3 4.3 Total equity securities 2,711.1 6.5 1.3 2,718.9 Debt securities: U.S. Government obligations — 1,360.1 — 1,360.1 Municipal bonds — 2,656.8 — 2,656.8 Foreign government obligations — 879.5 — 879.5 U.S. corporate bonds — 2,914.1 631.6 3,545.7 Foreign corporate bonds — 1,133.6 189.5 1,323.1 Mortgage and asset-backed securities: RMBS (1) — 2,608.9 2.5 2,611.4 CMBS — 884.5 5.8 890.3 Other asset-backed securities (2) — 1,448.9 902.7 2,351.6 Total debt securities — 13,886.4 1,732.1 15,618.5 Short-term investments — 714.2 — 714.2 Other invested assets (3) — — 0.3 0.3 Total investments (excluding equity method investments and loans) $ 2,711.1 $ 14,607.1 $ 1,733.7 $ 19,051.9 Senior Notes and other debt $ — $ 1,911.8 $ 556.9 $ 2,468.7 (1) Primarily includes government agency pass-through securities guaranteed by a government agency or government sponsored enterprise, among other types of RMBS. (2) Includes $ 1,320.4 million and $ 878.4 million of collateralized loan obligations as of December 31, 2021 and 2020 , respectively. (3) Includes partnership investments accounted for at fair value and excludes investments accounted for using the equity method.
Reconciliations of Changes in Level Three Assets Measured at Fair Value	The following tables present reconciliations of the changes during 2021 and 2020 in Level 3 assets measured at fair value: Debt Securities Mortgage and asset - backed Year Ended December 31, 2021 Preferred Foreign Government Obligations U.S. Foreign RMBS CMBS Other Other (1) Total ($ in millions) Balance as of January 1, 2021 $ 1.3 $ — $ 631.6 $ 189.5 $ 2.5 $ 5.8 $ 902.7 $ 0.3 $ 1,733.7 Net realized/unrealized gains (losses) included in: Net earnings (2) — — 0.1 ( 0.1 ) 0.1 — 0.5 0.1 0.7 Other comprehensive income (loss) — — ( 20.4 ) ( 7.2 ) ( 0.1 ) — 8.3 — ( 19.4 ) Purchases — 1.7 151.2 22.7 — — 776.3 — 951.9 Sales — — ( 0.2 ) — — — ( 12.4 ) ( 0.4 ) ( 13.0 ) Issuances — — — — — — — — — Settlements — — ( 88.3 ) ( 27.7 ) ( 0.6 ) — ( 295.9 ) — ( 412.5 ) Transfers into Level 3 — — — — — — 5.8 — 5.8 Transfers out of Level 3 — ( 1.7 ) ( 3.7 ) — — ( 5.8 ) ( 37.0 ) — ( 48.2 ) Balance as of December 31, 2021 $ 1.3 $ — $ 670.3 $ 177.2 $ 1.9 $ — $ 1,348.3 $ — $ 2,199.0 Debt Securities Mortgage and asset - backed Year Ended December 31, 2020 Preferred Foreign Government Obligations U.S. Foreign RMBS CMBS Other Other (1) Total ($ in millions) Balance as of January 1, 2020 $ 2.0 $ — $ 605.0 $ 168.7 $ 1.9 $ 5.8 $ 856.7 $ 0.3 $ 1,640.4 Net realized/unrealized gains (losses) included in: Net earnings (2) ( 0.7 ) — ( 3.8 ) 0.1 — — ( 9.4 ) — ( 13.8 ) Other comprehensive income (loss) — — 22.7 7.3 0.1 0.1 5.3 — 35.5 Purchases — — 56.4 32.0 0.9 — 196.4 — 285.7 Sales — — ( 2.0 ) ( 0.8 ) — — ( 61.7 ) — ( 64.5 ) Issuances — — — — — — — — — Settlements — — ( 46.7 ) ( 11.6 ) ( 0.4 ) ( 0.1 ) ( 70.1 ) — ( 128.9 ) Transfers into Level 3 — — — — — — — — — Transfers out of Level 3 — — — ( 6.2 ) — — ( 14.5 ) — ( 20.7 ) Balance as of December 31, 2020 $ 1.3 $ — $ 631.6 $ 189.5 $ 2.5 $ 5.8 $ 902.7 $ 0.3 $ 1,733.7 (1) Includes partnership and non-marketable equity investments accounted for at fair value. (2) There were no credit losses recorded in net earnings related to Level 3 instruments still held as of December 31, 2021 and 2020 .

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2021
Investments [Abstract]
Amortized Cost and Fair Value of Available For Sale Securities	The following tables present the amortized cost and the fair value of AFS securities as of December 31, 2021 and 2020: Amortized Gross Gross Allowance for Credit Losses (2) Fair Value ($ in millions) As of December 31, 2021 Debt securities: U.S. Government obligations $ 2,039.7 $ 27.9 $ ( 16.9 ) $ — $ 2,050.7 Municipal bonds 2,412.7 127.3 ( 4.1 ) — 2,535.9 Foreign government obligations 850.8 12.0 ( 7.9 ) — 854.9 U.S. corporate bonds 3,336.9 159.2 ( 18.3 ) ( 0.5 ) 3,477.3 Foreign corporate bonds 1,216.6 19.9 ( 9.6 ) — 1,226.9 Mortgage and asset-backed securities: RMBS 1,993.6 37.2 ( 21.8 ) — 2,009.0 CMBS 879.8 28.3 ( 2.2 ) — 905.9 Other asset-backed securities (1) 2,997.0 22.0 ( 18.0 ) — 3,001.0 Total debt securities 15,727.1 433.8 ( 98.8 ) ( 0.5 ) 16,061.6 Short-term investments 1,142.3 — — — 1,142.3 Total investments $ 16,869.4 $ 433.8 $ ( 98.8 ) $ ( 0.5 ) $ 17,203.9 Amortized Gross Gross Allowance for Credit Losses (2) Fair Value ($ in millions) As of December 31, 2020 Debt securities: U.S. Government obligations $ 1,317.6 $ 44.0 $ ( 1.5 ) $ — $ 1,360.1 Municipal bonds 2,489.1 168.3 ( 0.6 ) — 2,656.8 Foreign government obligations 846.6 33.4 ( 0.5 ) — 879.5 U.S. corporate bonds 3,262.0 289.7 ( 3.5 ) ( 2.5 ) 3,545.7 Foreign corporate bonds 1,268.3 55.6 ( 0.7 ) ( 0.1 ) 1,323.1 Mortgage and asset-backed securities: RMBS 2,533.6 78.3 ( 0.5 ) — 2,611.4 CMBS 852.6 45.3 ( 7.6 ) — 890.3 Other asset-backed securities (1) 2,328.7 47.6 ( 24.7 ) — 2,351.6 Total debt securities 14,898.5 762.2 ( 39.6 ) ( 2.6 ) 15,618.5 Short-term investments 714.2 — — — 714.2 Total investments $ 15,612.7 $ 762.2 $ ( 39.6 ) $ ( 2.6 ) $ 16,332.7 (1) Includes $ 1,320.4 million and $ 878.4 million of collateralized loan obligations as of December 31, 2021 and 2020 , respectively. (2) See Note 1(r) for additional information regarding Alleghany’s adoption of new credit loss accounting guidance.
Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity	The following table presents the amortized cost and estimated fair value of debt securities by contractual maturity as of December 31, 2021. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. Amortized Cost Fair Value ($ in millions) As of December 31, 2021 Short-term investments due in one year or less $ 1,142.3 $ 1,142.3 Mortgage and asset-backed securities (1) 5,870.4 5,915.9 Debt securities with maturity dates: One year or less 624.2 628.7 Over one through five years 3,714.4 3,772.7 Over five through ten years 3,037.6 3,106.4 Over ten years 2,480.5 2,637.9 Total debt securities $ 15,727.1 $ 16,061.6 (1) Mortgage and asset-backed securities by their nature do not generally have single maturity dates.
Net Investment Income	The following table presents net investment income for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Interest income $ 397.7 $ 443.1 $ 499.5 Dividend income 79.4 28.0 37.9 Investment expenses ( 26.5 ) ( 28.6 ) ( 28.9 ) Partnerships and other investment results 89.8 48.4 41.7 Total $ 540.4 $ 490.9 $ 550.2
Summary of Changes in Fair Value of Equity Securities	The following table presents changes in the fair value of equity securities for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Change in the fair value of equity securities sold during the period $ 3.2 $ ( 147.4 ) $ 59.1 Change in the fair value of equity securities held at the end of the period 503.6 36.9 650.6 Change in the fair value of equity securities $ 506.8 $ ( 110.5 ) $ 709.7
Amounts of Gross Realized Capital Gains and Gross Realized Capital Losses of Available For Sale Securities	The following table presents the amounts of gross realized capital gains and gross realized capital losses for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Gross realized capital gains $ 84.2 (1) $ 134.6 (2) $ 62.4 Gross realized capital losses ( 16.8 ) ( 131.5 ) (3) ( 68.9 ) (4) Net realized capital gains $ 67.4 $ 3.1 $ ( 6.5 ) (1) Gross realized capital gains in 2021 include a $ 3.1 million realized gain on the remeasurement of fair value of certain outstanding contingent consideration liabilities by Alleghany Capital in connection with its 2018 acquisition of Concord (the "2021 Concord Remeasurement Gain") . (2) Gross realized capital gains in 2020 include (i) a $ 15.0 million realized gain on a partial settlement and remeasurement of fair value of certain outstanding contingent consideration liabilities by Alleghany Capital in connection with its 2018 acquisition of Concord (the “2020 Concord Settlement Gain”); (ii) a gain of $ 16.3 million on April 1, 2020 in connection with Alleghany Capital’s acquisition of an a dditional approximately 55 percent of Wilbert that it did not previously own, and the remeasurement of its pre-existing approximately 45 percent equity ownership to estimated fair value (the “Wilbert Remeasurement Gain”); and (iii) a $ 5.0 million realized gain from a reduction of certain contingent consideration liabilities at the PCT-level in connection with its acquisition of a provider of high-performance solid carbide end mills in June 2019. (3) Gross realized capital losses in 2020 include (i) impairment charges of $ 76.0 million from write-downs of SORC oil field assets prior to SORC’s December 31, 2020 sale; and (ii) a $ 7.1 million realized loss as a result of an early redemption of debt (see Note 8 for additional information on this early redemption). (4) Gross realized capital losses in 2019 include $ 38.4 million from a derivative. Specifically, on July 18, 2019, AIHL purchased an exchange-traded equity derivative index put option (the “Put Option”) for $ 38.4 million to hedge the downside equity market risk on approximately $ 1.0 billion of Alleghany’s equity portfolio. The Put Option did not qualify for hedge accounting. The Put Option expired worthless on December 31, 2019, and the resulting $ 38.4 million decline in value of the Put Option was recorded as a gross realized capital loss. Gross realized capital losses in 2019 also includes a $ 13.6 million loss from the December 2019 sale of a privately held investment accounted for under the equity method.
Allowance for Credit Losses on Available for Sale Securities	The following table presents a rollforward of Alleghany’s allowance for credit losses on AFS securities for 2021 and 2020: Year Ended December 31, 2021 2020 ($ in millions) Allowance for Credit Losses Beginning balance $ 2.6 $ — Beginning balance - cumulative effect of an accounting change — — Provision for credit losses ( 2.1 ) 8.0 Charge-offs — ( 5.4 ) Recoveries — — Ending balance $ 0.5 $ 2.6
Summary of Rating of Debt securities	The following table presents the ratings of Alleghany’s debt securities as of December 31, 2021: Ratings as of December 31, 2021 AAA / Aaa AA / Aa A BBB / Baa Below (1) Total ($ in millions) U.S. Government obligations $ 1.4 $ 2,049.3 $ — $ — $ — $ 2,050.7 Municipal bonds 219.0 1,756.3 469.2 83.3 8.1 2,535.9 Foreign government obligations 376.5 389.3 87.8 1.1 0.2 854.9 U.S. corporate bonds 13.9 165.6 1,442.9 1,485.1 369.8 3,477.3 Foreign corporate bonds 184.7 69.1 564.1 372.8 36.2 1,226.9 Mortgage and asset-backed securities: RMBS 4.2 1,998.4 — 0.8 5.6 2,009.0 CMBS 324.2 355.4 218.6 7.7 — 905.9 Other asset-backed securities 1,282.1 761.0 477.3 451.6 29.0 3,001.0 Total debt securities $ 2,406.0 $ 7,544.4 $ 3,259.9 $ 2,402.4 $ 448.9 $ 16,061.6 Percentage of debt securities, 15.0 % 47.0 % 20.3 % 14.9 % 2.8 % 100.0 % (1) Consists of $ 140.8 million of securities rated BB / Ba, $ 203.5 million of securities rated B, $ 32.0 million of securities rated CCC, $ 0.5 million of securities rated CC, $ 3.1 million of securities rated below CC and $ 69.0 million of not rated securities.
Gross Unrealized Losses and Related Fair Values for AFS Securities before an Allowance for Credit Losses Grouped by Duration of Time in Continuous Unrealized Loss Position	The following tables present gross unrealized losses and related fair values for Alleghany’s AFS securities before an allowance for credit losses, grouped by duration of time in a continuous unrealized loss position, as of December 31, 2021 and 2020: Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross ($ in millions) As of December 31, 2021 Debt securities: U.S. Government obligations $ 1,196.3 $ 11.1 $ 122.1 $ 5.8 $ 1,318.4 $ 16.9 Municipal bonds 267.3 4.0 2.8 0.1 270.1 4.1 Foreign government obligations 350.0 5.3 73.2 2.6 423.2 7.9 U.S. corporate bonds 814.2 12.4 79.3 5.9 893.5 18.3 Foreign corporate bonds 460.6 8.3 34.6 1.3 495.2 9.6 Mortgage and asset-backed securities: RMBS 1,072.8 20.5 50.7 1.3 1,123.5 21.8 CMBS 197.8 0.6 40.9 1.6 238.7 2.2 Other asset-backed securities 1,609.9 13.2 291.5 4.8 1,901.4 18.0 Total temporarily impaired securities $ 5,968.9 $ 75.4 $ 695.1 $ 23.4 $ 6,664.0 $ 98.8 Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross ($ in millions) As of December 31, 2020 Debt securities: U.S. Government obligations $ 255.9 $ 1.5 $ — $ — $ 255.9 $ 1.5 Municipal bonds 36.2 0.6 — — 36.2 0.6 Foreign government obligations 132.8 0.5 — — 132.8 0.5 U.S. corporate bonds 168.5 3.5 2.4 — 170.9 3.5 Foreign corporate bonds 36.4 0.2 19.5 0.5 55.9 0.7 Mortgage and asset-backed securities: RMBS 152.6 0.5 0.4 — 153.0 0.5 CMBS 133.5 7.6 3.8 — 137.3 7.6 Other asset-backed securities 547.9 13.4 533.9 11.3 1,081.8 24.7 Total temporarily impaired securities $ 1,463.8 $ 27.8 $ 560.0 $ 11.8 $ 2,023.8 $ 39.6
Allowance for Credit Losses on Commercial Mortgage Loans	The following table presents a rollforward of Alleghany’s allowance for credit losses on commercial mortgage loans for 2021 and 2020: Year Ended December 31, 2021 2020 ($ in millions) Allowance for Credit Losses Beginning balance $ 1.4 $ — Beginning balance - cumulative effect of an accounting change — 0.8 Provision for credit losses ( 1.2 ) 0.6 Charge-offs — — Recoveries — — Ending balance $ 0.2 $ 1.4

Reinsurance Ceded (Tables)

Reinsurance Ceded (Tables)	12 Months Ended
	Dec. 31, 2021
Insurance [Abstract]
Reinsurance Recoverables After Allowance for Credit Losses	Amounts recoverable from reinsurers are recognized in a manner consistent with the loss and LAE liabilities associated with the reinsurance placement and presented on the balance sheet as reinsurance recoverables, and are recorded after an allowance for credit losses. Such balances as of December 31, 2021 and 2020 are presented in the table below: As of December 31, 2021 2020 ($ in millions) Reinsurance recoverables on paid losses $ 173.1 $ 85.3 Ceded outstanding loss and LAE 2,026.1 1,703.7 Reinsurance recoverables, before allowance for credit losses 2,199.2 1,789.0 Allowance for credit losses ( 3.2 ) ( 7.9 ) Total $ 2,196.0 $ 1,781.1
Information Regarding Concentration of Reinsurance Recoverables and Ratings Profile of Our Reinsurers	The following table presents information regarding concentration of Alleghany’s reinsurance recoverables and the ratings profile of its reinsurers as of December 31, 2021: Reinsurer (1) Rating (2) Amount Percentage ($ in millions) Syndicates at Lloyd's of London A (Excellent) $ 154.5 7.0 % Kane SAC Ltd, Rondout Segregated Account (3) not rated 154.3 7.0 % PartnerRe Ltd A (Excellent) 142.7 6.5 % RenaissanceRe Holdings Ltd A+ (Superior) 135.5 6.2 % Fairfax Financial Holdings Ltd A (Excellent) 124.4 5.7 % Swiss Reinsurance Company A+ (Superior) 99.2 4.5 % Integral Reinsurance Ltd. (3) not rated 97.4 4.4 % Chubb Ltd. A++ (Superior) 79.3 3.6 % W.R. Berkley Corporation A+ (Superior) 77.0 3.5 % SiriusPoint Ltd. A- (Excellent) 73.6 3.3 % All other reinsurers 1,061.3 48.3 % Total reinsurance recoverables, before allowance for credit losses (4) 2,199.2 100.0 % Allowance for credit losses ( 3.2 ) Total $ 2,196.0 Secured reinsurance recoverables (3) $ 967.7 44.0 % (1) Reinsurance recoverables reflect amounts due from one or more reinsurance subsidiaries of the listed company. (2) Represents the A.M. Best Company, Inc. financial strength rating for the applicable reinsurance subsidiary or subsidiaries from which the reinsurance recoverable is due. (3) Represents reinsurance recoverables secured by funds held, trust agreements or letters of credit. Approximately 66 percent of Alleghany’s reinsurance recoverables balance as of December 31, 2021 was due from reinsurers having an A.M. Best Company, Inc. financial strength rating of A (Excellent) or higher, with a majority of the other reinsurance recoverables being secured by funds held, trust agreements or letters of credit.
Allowance for Credit Losses on Reinsurance Recoverables	The following table presents a rollforward of Alleghany’s allowance for credit losses on reinsurance recoverables for 2021 and 2020: Year Ended December 31, 2021 2020 ($ in millions) Allowance for Credit Losses Beginning balance $ 7.9 $ — Beginning balance - cumulative effect of an accounting change — 3.3 Provision for credit losses ( 4.7 ) 4.6 Charge-offs — — Recoveries — — Ending balance $ 3.2 $ 7.9
Property and Casualty Premiums Written and Earned	The following table presents property and casualty premiums written and earned for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Gross premiums written – direct $ 2,704.3 $ 2,214.6 $ 1,800.3 Gross premiums written – assumed 5,834.5 5,114.8 4,856.1 Ceded premiums written ( 1,389.4 ) ( 985.0 ) ( 904.7 ) Net premiums written $ 7,149.4 $ 6,344.4 $ 5,751.7 Gross premiums earned – direct $ 3,005.7 $ 2,370.4 $ 2,114.1 Gross premiums earned – assumed 5,364.8 4,582.9 4,268.8 Ceded premiums earned ( 1,272.8 ) ( 953.1 ) ( 904.8 ) Net premiums earned $ 7,097.7 $ 6,000.2 $ 5,478.1

Liability for Loss and LAE (Tab

Liability for Loss and LAE (Tables)	12 Months Ended
	Dec. 31, 2021
Activity in Liability for Loss and Loss Adjustment Expense	The following table presents the activity in the liability for loss and LAE in 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Reserves as of January 1 $ 12,970.6 $ 11,928.4 $ 12,250.3 Less: reinsurance recoverables (1) 1,703.7 1,583.9 1,857.4 Net reserves as of January 1 11,266.9 10,344.5 10,392.9 Other adjustments 0.1 ( 4.0 ) ( 2.3 ) Incurred loss and LAE, net of reinsurance, related to: Current year 5,084.6 4,559.9 3,871.1 Prior years ( 249.7 ) ( 220.8 ) ( 184.7 ) Total incurred loss and LAE, net of reinsurance 4,834.9 4,339.1 3,686.4 Paid loss and LAE, net of reinsurance, related to: (2) Current year 1,032.8 931.7 884.6 Prior years 2,655.9 2,571.8 2,839.9 Total paid loss and LAE, net of reinsurance 3,688.7 3,503.5 3,724.5 Foreign currency exchange rate effect ( 81.7 ) 90.8 ( 8.0 ) Net reserves as of December 31 12,331.5 11,266.9 10,344.5 Reinsurance recoverables as of December 31 (1) 2,026.1 1,703.7 1,583.9 Reserves as of December 31 $ 14,357.6 $ 12,970.6 $ 11,928.4 (1) Reinsurance recoverables in this table include only ceded loss and LAE reserves. Includes paid loss and LAE, net of reinsurance, related to commutations.
(Favorable) Unfavorable Prior Accident Year Loss Reserve Development	The following table presents the (favorable) unfavorable prior accident year loss reserve development for 2021, 2020 and 2019: Year Ended December, 2021 2020 2019 ($ in millions) Reinsurance Segment Property: Catastrophe events (excluding Pandemic) $ ( 35.5 ) (1) $ ( 43.3 ) (2) $ ( 6.8 ) (3) Pandemic 62.6 - - Non-catastrophe ( 50.9 ) (4) ( 33.6 ) (5) ( 39.4 ) (6) Total ( 23.8 ) ( 76.9 ) ( 46.2 ) Casualty & specialty: Catastrophe events (excluding Pandemic) ( 0.4 ) ( 5.9 ) ( 4.4 ) Pandemic ( 48.9 ) — — Non-catastrophe ( 176.5 ) (7) ( 124.1 ) (8) ( 145.2 ) (9) Total ( 225.8 ) ( 130.0 ) ( 149.6 ) Total Reinsurance Segment ( 249.6 ) ( 206.9 ) ( 195.8 ) Insurance Segment RSUI: Casualty 5.0 (10) 1.8 (11) ( 16.3 ) (12) Property and other ( 11.1 ) (13) ( 14.6 ) (14) ( 1.2 ) (15) Total ( 6.1 ) ( 12.8 ) ( 17.5 ) CapSpecialty: Ongoing lines of business 6.1 (16) ( 2.0 ) (17) 26.1 (18) Terminated Program (19) ( 0.1 ) 0.9 3.0 Asbestos-related illness and environmental impairment liability — — ( 0.5 ) Total 6.0 ( 1.1 ) 28.6 Total incurred related to prior years $ ( 249.7 ) $ ( 220.8 ) $ ( 184.7 ) (1) Primarily reflects favorable prior accident year loss reserve development related to catastrophic events in the 2018 accident year, partially offset by unfavorable prior accident year loss reserve development related to Hurricane Laura and Sally in the 2020 accident year. (2) Primarily reflects favorable prior accident year loss reserve development related to Typhoon Hagibis in the 2019 accident year and wildfires in California in the 2017 and 2018 accident years, partially offset by unfavorable prior accident year loss reserve development related to Hurricane Irma in the 2017 accident year and Typhoon Faxai in the 2019 accident year. (3) Primarily reflects favorable prior accident year loss reserve development related to wildfires in California in the 2018 accident year, partially offset by unfavorable prior accident year loss reserve development related to Typhoon Jebi in the 2018 accident year and Hurricane Irma in the 2017 accident year. (4) Primarily reflects favorable prior accident year loss reserve development in the 2020 accident year. (5) Primarily reflects favorable prior accident year loss reserve development in the 2017 accident year. (6) Primarily reflects favorable prior accident year loss reserve development in the 2016 and 2017 accident years, partially offset by unfavorable prior accident year loss reserve development in the 2018 accident year. (7) Primarily reflects favorable prior accident year loss reserve development in the shorter-tailed lines of business in the 2020 accident year and in both the longer- and shorter-tailed lines of business in the 2015 and earlier accident years, partially offset by unfavorable prior accident year loss reserve development in the longer-tailed lines of business in the 2016 to 2018 accident years. (8) Primarily reflects favorable prior accident year loss reserve development in the longer-tailed casualty lines of business in the 2014 and prior accident years and, to a lesser extent, shorter-tailed lines of business in the 2014 and prior accident years, partially offset by unfavorable prior accident year loss reserve development in the marine and aviation lines of business in the 2018 accident year. (9) Primarily reflects favorable prior accident year loss reserve development in the longer-tailed casualty lines of business in the 2014 and prior accident years and, to a lesser extent, shorter-tailed lines of business in the 2014 and prior accident years, partially offset by unfavorable prior accident year loss reserve development in the marine and aviation lines of business in the 2018 accident year. (10) Primarily reflects unfavorable prior accident year loss reserve development in the directors’ and officers’ liability lines of business in the 2012 and 2014 accident years and, to a lesser extent, the general liability and binding authority lines of business in earlier accident years, partially offset by favorable prior accident year loss reserve development in the umbrella/excess lines of business in the 2005 through 2015 accident years. (11) Primarily reflects unfavorable prior accident year loss reserve development in the professional liability lines of business in the 2 017 through 2019 accident years, partially offset by favorable prior accident year loss reserve development in the directors’ and officers’ liability and umbrella/excess lines of business in the 2011 through 2015 accident years. (12) Primarily reflects favorable prior accident year loss reserve development in the directors’ and officers’ liability and umbrella/excess lines of business in the 2011 through 2015 accident years, partially offset by unfavorable prior accident year loss reserve development in the professional liability lines of business in the 2016 through 2018 accident years. (13) Primarily reflects favorable prior accident year loss reserve development related to losses not classified as catastrophes in recent accident years and, to a lesser extent, catastrophes in the 2017, 2018 and 2019 accident years, partially offset by unfavorable prior accident year loss reserve development related to catastrophes in the 2020 accident year. (14) Primarily reflects favorable prior accident year loss reserve development related to U.S. catastrophe losses in the 2018 accident year and, to a lesser extent, favorable prior accident year loss reserve development related to the assumed property reinsurance lines of business from catastrophe losses in the 2019 and 2018 accident years. (15) Primarily reflects favorable prior accident year loss reserve development related to Superstorm Sandy in the 2012 accident year, Hurricanes Florence and Michael in the 2018 accident year and Hurricanes Harvey and Maria in the 2017 accident year, partially offset by unfavorable prior accident year loss reserve development related to assumed property reinsurance lines of business from both catastrophe and non-catastrophe losses in the 2018 accident year. (16) Primarily reflects unfavorable prior accident year loss reserve development in the healthcare, construction liability and other casualty lines of business in the 2015 through 2017 accident years. (17) Primarily reflects favorable prior acciden t year loss reserve development in the surety lines of business in recent accident years. (18) Primarily reflects unfavorable prior accident loss reserve development related to the professional liability and other casualty lines of business in the 2015 through 2018 accident years. (19) Represents certain specialty lines of business written through a program administrator in connection with a terminated program in the 2010 and 2009 accident years and reflects favorable loss emergence compared with loss emergence patterns assumed in earlier periods for such business.
Loss and LAE Reserve Summary and Reconciliation to Consolidated Balance Sheet	Loss and LAE Reserve Summary and Reconciliation to Consolidated Balance Sheet Unpaid loss and LAE as of December 31, 2021 (1) Gross Loss and Reinsurance Net Loss and ($ in millions) Reinsurance Segment: Property $ 2,599.4 $ 641.1 $ 1,958.3 Casualty & specialty - Longer-Tailed Lines of Business 5,264.9 144.4 5,120.5 Casualty & specialty - Shorter-Tailed Lines of Business 2,883.9 261.6 2,622.3 10,748.2 1,047.1 9,701.1 Insurance Segment: RSUI - Property 617.0 201.5 415.5 RSUI - Casualty 2,399.2 750.8 1,648.4 RSUI 3,016.2 952.3 2,063.9 CapSpecialty 669.8 103.3 566.5 3,686.0 1,055.6 2,630.4 Eliminations ( 76.6 ) ( 76.6 ) — Total $ 14,357.6 $ 2,026.1 $ 12,331.5 Includes unallocated LAE, which aggregate t o 1.0 perce nt of gross loss and LAE reserves as of December 31, 2021 . Net loss and LAE reserves by component are shown in the preceding tables, and consolidated gross loss and LAE reserves is presented in the consolidated balance sheets.
Average Historical Loss and LAE Duration	The following table presents supplemental information about average historical loss and LAE duration, net of reinsurance, as of December 31, 2021. Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance As of December 31, 2021 Years 1 2 3 4 5 6 7 8 9 10 Reinsurance Segment: Property 28.0 % 40.9 % 16.9 % 6.3 % 2.5 % 1.2 % 0.6 % 0.9 % 0.2 % 1.2 % Casualty & specialty - Longer-Tailed Lines of Business 4.2 % 9.0 % 13.5 % 15.2 % 13.6 % 10.2 % 7.2 % 4.8 % 3.6 % 3.6 % Casualty & specialty - Shorter-Tailed Lines of Business 33.0 % 28.6 % 13.5 % 7.0 % 4.5 % 2.7 % 1.6 % 1.2 % 0.7 % 0.5 % Insurance Segment: RSUI - Property 34.7 % 13.9 % 6.1 % 3.1 % 2.5 % 0.8 % 0.6 % 0.1 % 0.2 % 1.3 % RSUI - Casualty 14.4 % 17.8 % 17.3 % 13.0 % 10.7 % 6.3 % 5.1 % 3.6 % 3.9 % 1.9 % CapSpecialty 19.1 % 21.6 % 15.6 % 13.3 % 8.2 % 4.6 % 1.9 % 1.1 % 0.3 % 0.7 %
Reinsurance Segment | Property
Supplemental Information About Incurred and Paid Loss and LAE Development and Reconciliation to Consolidated Balance Sheet	Reinsurance Segment Property Incurred Loss and LAE, Net of Reinsurance As of Year Ended December 31, December 31, 2021 Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 IBNR ($ in millions) 2012 $ 697.2 $ 579.1 $ 530.3 $ 495.6 $ 478.1 $ 469.4 $ 462.5 $ 460.3 $ 454.9 $ 456.1 $ — 2013 501.2 470.6 444.6 422.1 406.8 403.6 398.1 394.7 394.0 — 2014 496.4 464.8 451.3 435.2 429.8 425.1 419.7 416.2 — 2015 368.8 332.0 320.6 306.3 301.9 297.9 295.5 1.4 2016 684.1 647.2 596.7 587.9 577.8 578.1 2.6 2017 1,174.6 1,179.5 1,148.3 1,127.7 1,114.8 20.2 2018 1,152.7 1,169.4 1,147.8 1,116.8 49.1 2019 988.7 981.5 972.2 56.0 2020 1,207.5 1,253.5 297.1 2021 1,468.1 640.3 Total Incurred Loss and LAE for the 2012 through 2021 accident years $ 8,065.3 Paid Loss and LAE, Net of Reinsurance Year Ended December 31, Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 ($ in millions) 2012 $ 90.3 $ 268.9 $ 377.8 $ 416.7 $ 438.0 $ 448.0 $ 451.2 $ 460.1 $ 461.1 $ 466.6 2013 113.1 277.4 361.0 389.8 396.7 399.7 401.4 403.0 403.9 2014 109.4 297.6 360.0 382.9 394.0 397.3 398.4 399.4 2015 96.0 217.7 278.3 303.1 307.6 308.8 311.9 2016 210.5 429.8 504.8 535.1 552.2 563.9 2017 324.5 818.5 977.9 1,023.0 1,039.9 2018 309.5 811.8 944.2 1,002.3 2019 265.1 645.5 793.2 2020 301.1 732.1 2021 413.5 Cumulative Paid Loss and LAE for the 2012 through 2021 accident years $ 6,126.7 Total incurred loss and LAE for the 2012 through 2021 accident years $ 8,065.3 Cumulative paid loss and LAE for the 2012 through 2021 accident years 6,126.7 Unpaid loss and LAE, net of reinsurance recoverables, for accident years prior to 2012 19.7 Unpaid loss and LAE, net of reinsurance recoverables, as of December 31, 2021 $ 1,958.3
Reinsurance Segment | Casualty & Other | Longer Tailed Lines of Business
Supplemental Information About Incurred and Paid Loss and LAE Development and Reconciliation to Consolidated Balance Sheet	Reinsurance Segment Casualty & specialty – Longer-Tailed Lines of Business (1) Incurred Loss and LAE, Net of Reinsurance As of Year Ended December 31, December 31, 2021 Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 IBNR ($ in millions) 2012 $ 877.5 $ 877.5 $ 875.9 $ 860.8 $ 833.1 $ 829.8 $ 832.4 $ 826.4 $ 819.7 $ 802.3 $ 60.9 2013 798.6 802.2 799.2 777.5 776.7 783.0 767.4 740.5 726.8 100.8 2014 801.8 791.1 794.3 793.9 790.3 784.8 771.7 764.0 126.2 2015 794.8 799.0 797.0 793.7 799.1 799.6 798.2 123.0 2016 776.7 776.8 787.4 807.8 842.2 862.9 126.0 2017 764.4 765.7 783.4 800.1 824.0 180.3 2018 727.3 741.6 752.5 767.4 279.5 2019 759.7 761.6 765.4 415.2 2020 978.1 952.4 729.1 2021 1,239.9 1,124.0 Total Incurred Loss and LAE for the 2012 through 2021 accident years $ 8,503.3 Paid Loss and LAE, Net of Reinsurance Year Ended December 31, Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 ($ in millions) 2012 $ 46.9 $ 106.8 $ 201.1 $ 316.6 $ 435.7 $ 521.3 $ 587.0 $ 624.4 $ 648.7 $ 677.8 2013 22.2 85.1 176.6 296.4 378.0 452.7 494.6 528.5 558.8 2014 29.8 107.5 229.6 342.9 444.7 522.7 580.6 619.2 2015 32.2 100.4 205.0 325.8 455.8 536.5 595.9 2016 34.8 121.8 242.9 370.0 491.1 573.6 2017 34.0 110.6 221.8 347.5 447.9 2018 33.0 104.6 206.7 324.7 2019 29.0 99.7 202.5 2020 47.2 127.6 2021 48.3 Cumulative Paid Loss and LAE for the 2012 through 2021 accident years $ 4,176.3 Total incurred loss and LAE for the 2012 through 2021 accident years $ 8,503.3 Cumulative paid loss and LAE for the 2012 through 2021 accident years 4,176.3 Unpaid loss and LAE, net of reinsurance recoverables, for accident years prior to 2012 793.5 Unpaid loss and LAE, net of reinsurance recoverables, as of December 31, 2021 $ 5,120.5 Represents the following reinsurance lines of business: directors’ and officers’ liability; errors and omissions liability; general liability; and medical malpractice.
Reinsurance Segment | Casualty & Other | Shorter Tailed Lines Of Business
Supplemental Information About Incurred and Paid Loss and LAE Development and Reconciliation to Consolidated Balance Sheet	Reinsurance Segment Casualty & specialty – Shorter-Tailed Lines of Business (1) Incurred Loss and LAE, Net of Reinsurance As of Year Ended December 31, December 31, 2021 Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 IBNR ($ in millions) 2012 $ 1,022.3 $ 1,059.9 $ 1,056.8 $ 1,005.5 $ 983.9 $ 958.9 $ 948.4 $ 941.4 $ 933.9 $ 929.9 $ 6.4 2013 850.8 868.8 838.4 823.4 804.1 790.3 780.7 769.6 764.5 9.2 2014 850.4 833.0 808.8 784.3 772.4 755.0 752.5 740.8 15.2 2015 763.4 768.6 784.0 798.4 776.7 776.2 771.9 17.0 2016 1,118.0 1,124.4 1,111.6 1,100.3 1,092.6 1,085.2 25.7 2017 1,095.9 1,046.3 1,026.9 994.5 989.0 49.0 2018 1,255.4 1,266.1 1,270.7 1,267.3 89.2 2019 1,408.6 1,411.8 1,400.7 159.8 2020 1,408.2 1,335.1 325.8 2021 1,333.1 729.0 Total Incurred Loss and LAE for the 2012 through 2021 accident years $ 10,617.5 Paid Loss and LAE, Net of Reinsurance Year Ended December 31, Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 ($ in millions) 2012 $ 354.8 $ 614.5 $ 740.0 $ 792.7 $ 828.3 $ 846.5 $ 860.2 $ 871.4 $ 876.1 $ 880.3 2013 265.4 523.5 613.3 663.0 685.5 704.9 717.5 723.9 730.7 2014 251.2 421.1 523.3 572.9 604.6 627.8 636.8 647.8 2015 218.5 409.1 518.7 577.7 629.1 653.2 669.5 2016 367.2 685.6 828.7 921.3 973.8 1,002.0 2017 342.8 639.1 793.5 867.6 909.8 2018 397.9 774.4 952.2 1,033.3 2019 462.0 881.3 1,051.3 2020 418.0 810.7 2021 411.4 Cumulative Paid Loss and LAE for the 2012 through 2021 accident years $ 8,146.8 Total incurred loss and LAE for the 2012 through 2021 accident years $ 10,617.5 Cumulative paid loss and LAE for the 2012 through 2021 accident years 8,146.8 Unpaid loss and LAE, net of reinsurance recoverables, for accident years prior to 2012 151.6 Unpaid loss and LAE, net of reinsurance recoverables, as of December 31, 2021 $ 2,622.3 Primarily represents the following reinsurance lines of business: ocean marine and aviation; auto liability; accident & health; mortgage reinsurance; surety; and credit.
Insurance Segment | RSUI | Property Insurance
Supplemental Information About Incurred and Paid Loss and LAE Development and Reconciliation to Consolidated Balance Sheet	Insurance Segment RSUI - Property As of Incurred Loss and LAE, Net of Reinsurance Cumulative Year Ended December 31, Number of Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 IBNR Reported (1) ($ in millions) 2012 $ 270.9 $ 262.5 $ 258.6 $ 256.1 $ 235.1 $ 236.1 $ 235.5 $ 228.3 $ 228.4 $ 228.2 $ 0.8 2,313 2013 157.3 157.2 150.4 152.1 152.4 152.5 154.3 154.4 153.5 1.1 2,395 2014 170.7 166.2 155.9 153.7 153.8 153.6 153.4 153.3 1.1 3,094 2015 140.5 136.1 142.6 141.3 140.1 140.2 140.4 1.5 3,004 2016 181.4 170.5 172.9 173.9 175.3 175.1 2.4 3,368 2017 330.7 306.5 304.1 300.0 296.7 10.6 3,696 2018 259.9 265.7 256.7 237.0 9.6 3,071 2019 204.3 200.9 205.1 13.9 3,343 2020 357.2 365.4 40.6 4,257 2021 341.5 80.6 3,193 Total Incurred Loss and LAE for the 2012 through 2021 accident years $ 2,296.2 Paid Loss and LAE, Net of Reinsurance Year Ended December 31, Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 ($ in millions) 2012 $ 62.0 $ 157.5 $ 181.9 $ 193.5 $ 202.4 $ 216.2 $ 216.7 $ 219.2 $ 219.4 $ 222.5 2013 72.7 118.7 134.0 141.1 144.0 148.7 151.5 151.8 152.1 2014 93.2 133.8 145.0 148.8 150.3 151.3 151.6 151.9 2015 70.8 106.9 120.0 129.8 136.5 138.0 138.5 2016 72.0 127.1 147.1 161.2 167.3 169.8 2017 88.6 213.3 253.3 267.3 278.5 2018 62.3 175.1 202.9 216.1 2019 79.8 145.8 167.1 2020 118.8 251.2 2021 137.2 Cumulative Paid Loss and LAE for the 2012 through 2021 accident years $ 1,885.0 Total incurred loss and LAE for the 2012 through 2021 accident years $ 2,296.2 Cumulative paid loss and LAE for the 2012 through 2021 accident years 1,885.0 Unpaid loss and LAE, net of reinsurance recoverables, for accident years prior to 2012 4.3 Unpaid loss and LAE, net of reinsurance recoverables, as of December 31, 2021 $ 415.5 Represents claims reported by insured claimants.
Insurance Segment | RSUI | Casualty Insurance
Supplemental Information About Incurred and Paid Loss and LAE Development and Reconciliation to Consolidated Balance Sheet	Insurance Segment RSUI - Casualty As of Incurred Loss and LAE, Net of Reinsurance Cumulative Year Ended December 31, Number of Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 IBNR Reported (1) ($ in millions) 2012 $ 226.3 $ 226.3 $ 230.3 $ 242.8 $ 238.9 $ 233.8 $ 231.9 $ 221.8 $ 210.2 $ 213.4 $ 12.3 7,726 2013 264.8 264.8 277.6 280.1 279.0 273.5 269.6 261.4 263.7 30.1 8,791 2014 292.0 322.7 321.1 322.4 320.3 310.9 300.3 301.7 29.7 10,293 2015 300.2 300.2 304.2 302.2 291.4 289.8 283.6 54.9 9,489 2016 290.7 293.7 301.3 312.0 317.5 317.8 56.7 9,110 2017 282.5 286.4 299.1 311.1 309.7 79.2 9,073 2018 290.0 301.5 310.0 312.8 95.8 9,441 2019 316.9 332.2 332.2 171.9 8,792 2020 393.9 393.9 291.5 7,690 2021 470.2 430.8 6,909 Total Incurred Loss and LAE for the 2012 through 2021 accident years $ 3,199.0 Paid Loss and LAE, Net of Reinsurance Year Ended December 31, Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 ($ in millions) 2012 $ 6.8 $ 38.4 $ 96.0 $ 125.5 $ 144.0 $ 159.3 $ 166.7 $ 176.1 $ 178.5 $ 180.2 2013 10.1 50.0 103.4 146.2 176.6 191.3 203.9 212.9 222.8 2014 13.0 69.5 130.1 179.1 206.5 234.6 249.1 259.7 2015 9.0 47.3 96.6 129.2 176.5 196.2 207.3 2016 13.7 69.2 123.6 197.8 220.8 239.1 2017 9.4 63.6 115.6 163.1 196.2 2018 13.0 70.4 116.8 165.6 2019 12.9 57.9 104.2 2020 12.6 45.7 2021 10.2 Cumulative Paid Loss and LAE for the 2012 through 2021 accident years $ 1,631.0 Total incurred loss and LAE for the 2012 through 2021 accident years $ 3,199.0 Cumulative paid loss and LAE for the 2012 through 2021 accident years 1,631.0 Unpaid loss and LAE, net of reinsurance recoverables, for accident years prior to 2012 80.4 Unpaid loss and LAE, net of reinsurance recoverables, as of December 31, 2021 $ 1,648.4 Represents claims reported by insured claimants.
Insurance Segment | CapSpecialty Incorporated
Supplemental Information About Incurred and Paid Loss and LAE Development and Reconciliation to Consolidated Balance Sheet	Insurance Segment CapSpecialty (1) As of Incurred Loss and LAE, Net of Reinsurance Cumulative Year Ended December 31, Number of Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 IBNR Reported (2) ($ in millions) 2012 $ 72.7 $ 71.8 $ 66.2 $ 69.3 $ 69.7 $ 68.7 $ 68.8 $ 69.1 $ 69.1 $ 68.9 $ 0.3 5,269 2013 78.7 81.4 85.2 84.4 87.2 88.6 87.4 87.4 88.1 1.1 5,181 2014 102.8 102.7 101.0 100.2 98.6 97.6 97.7 99.0 1.4 6,050 2015 111.0 111.8 109.2 109.7 112.4 115.2 118.0 3.3 5,666 2016 129.4 132.4 132.7 135.0 133.4 136.7 4.4 6,297 2017 147.3 143.7 157.6 156.2 159.9 9.7 6,561 2018 164.1 173.3 176.5 180.9 22.3 6,848 2019 193.0 188.9 185.4 58.4 6,171 2020 214.9 209.5 116.8 4,917 2021 231.7 183.7 4,616 Total Incurred Loss and LAE for the 2012 through 2021 accident years $ 1,478.1 Paid Loss and LAE, Net of Reinsurance Year Ended December 31, Accident 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 ($ in millions) 2012 $ 18.6 $ 38.6 $ 46.9 $ 57.2 $ 63.3 $ 65.0 $ 66.5 $ 67.7 $ 67.7 $ 68.2 2013 23.4 48.0 62.0 69.6 78.6 84.5 85.3 86.1 86.5 2014 34.0 56.3 71.9 83.1 89.8 93.1 94.2 95.1 2015 30.9 57.4 73.5 88.8 101.1 106.7 110.5 2016 30.3 64.0 86.6 106.1 116.3 123.2 2017 30.1 65.6 95.1 116.1 126.6 2018 31.7 72.4 102.1 130.4 2019 29.8 62.5 88.5 2020 27.8 60.9 2021 26.1 Cumulative Paid Loss and LAE for the 2012 through 2021 accident years $ 916.0 Total incurred loss and LAE for the 2012 through 2021 accident years $ 1,478.1 Cumulative paid loss and LAE for the 2012 through 2021 accident years 916.0 Unpaid loss and LAE, net of reinsurance recoverables, for accident years prior to 2012 4.4 Unpaid loss and LAE, net of reinsurance recoverables, as of December 31, 2021 $ 566.5 (1) The vast majority of the CapSpecialty’s loss and LAE reserves relate to its casualty lines of business. Represents claims reported by insured claimants.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Income Tax Expense (Benefit)	The following table presents income tax expense (benefit) for 2021, 2020 and 2019: Federal State Foreign Total ($ in millions) Year ended December 31, 2021 Current $ 141.6 $ 16.2 $ 36.3 $ 194.1 Deferred 88.2 ( 0.3 ) ( 0.1 ) 87.8 $ 229.8 $ 15.9 $ 36.2 $ 281.9 Year ended December 31, 2020 Current $ 6.9 $ 9.7 $ 58.3 $ 74.9 Deferred ( 45.8 ) 0.8 0.8 ( 44.2 ) $ ( 38.9 ) $ 10.5 $ 59.1 $ 30.7 Year ended December 31, 2019 Current $ 87.9 $ 12.0 $ 70.8 $ 170.7 Deferred 62.9 0.5 ( 0.7 ) 62.7 $ 150.8 $ 12.5 $ 70.1 $ 233.4
Difference between Federal Income Tax Rate and Effective Income Tax Rate	The following table presents the difference between the federal income tax rate and the effective income tax rate: Year Ended December 31, 2021 2020 2019 Federal income tax rate 21.0 % 21.0 % 21.0 % Foreign tax expense reduced by foreign tax credits 0.6 6.9 0.4 Income subject to dividends-received deduction ( 0.3 ) ( 1.3 ) ( 0.3 ) Tax-exempt interest ( 0.7 ) ( 6.0 ) ( 1.0 ) State taxes, net of federal tax benefit 0.9 4.9 0.9 Prior period adjustment ( 0.1 ) ( 2.6 ) 0.2 Other, net (1) ( 1.4 ) ( 3.4 ) ( 0.4 ) Effective tax rate 20.0 % 19.5 % 20.8 % _____________________________________ (1) For 2021, includes the benefit from non-controlling interests, various general business tax credits, partially offset by disallowed expense deductions primarily related to certain executive compensation paid in 2021. For 2020 , includes various general business credits and tax benefits resulting from corporate acquisitions and dispositions, partially offset by disallowed expense deductions primarily related to certain executive compensation paid in 2020.
Tax Effects of Temporary Differences that Give Rise to Significant Portions of Deferred Tax Assets and Deferred Tax Liabilities	The following table presents the tax effects of temporary differences that give rise to the deferred tax assets and deferred tax liabilities as of December 31, 2021 and 2020: As of December 31, 2021 2020 ($ in millions) Deferred tax assets: Loss and LAE reserves $ 144.5 $ 132.3 Foreign tax credit carry forward 59.2 74.1 Compensation accruals 99.7 87.5 Unearned premiums 114.1 112.2 Allowance for credit losses on available for sale securities 5.2 5.7 State net operating loss carry forward 13.2 12.5 Other 97.8 98.0 Gross deferred tax assets before valuation allowance 533.7 522.3 Valuation allowance ( 12.9 ) ( 12.5 ) Gross deferred tax assets 520.8 509.8 Deferred tax liabilities: Net unrealized gains on investments 308.4 294.7 Deferred acquisition costs 127.0 128.4 Purchase accounting adjustments 11.2 11.7 Other 131.2 118.5 Gross deferred tax liabilities 577.8 553.3 Net deferred tax (liabilities) assets $ ( 57.0 ) $ ( 43.5 )
Tax Year Returns that Remain Subject to Examination by Major Tax Jurisdiction	The following table presents the tax years of Alleghany and TransRe tax returns that remain subject to examination by major tax jurisdictions as of December 31, 2021. Major Tax Jurisdiction Open Tax Years Australia 2016 - 2021 Canada 2017 - 2021 France 2018 - 2021 Germany 2019 - 2021 Hong Kong 2015 - 2021 Japan 2019 - 2021 Luxembourg 2019 - 2021 Singapore 2017 - 2021 Switzerland 2018 - 2021 U.K. 2015 - 2021 U.S. 2018 - 2021

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2021
Stockholders' Equity Note [Abstract]
Schedule of Common Stock Repurchases	The following table presents the shares of Common Stock that Alleghany repurchased in 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 Shares repurchased 446,596 333,393 215,091 Cost of shares repurchased (in millions) $ 290.5 $ 194.8 $ 144.4 Average price per share repurchased $ 650.52 $ 584.18 $ 671.44
Reconciliation of Accumulated Other Comprehensive Income	The following table presents a reconciliation of the changes during 2021 and 2020 in accumulated other comprehensive income attributable to Alleghany stockholders: Unrealized Unrealized Retirement Total ($ in millions) Balance as of January 1, 2021 $ 564.9 $ ( 99.4 ) $ ( 13.1 ) $ 452.4 Other comprehensive income (loss), net of tax: Other comprehensive loss before reclassifications ( 253.3 ) ( 4.3 ) ( 0.5 ) ( 258.1 ) Reclassifications from accumulated other comprehensive income ( 52.5 ) — — ( 52.5 ) Total ( 305.8 ) ( 4.3 ) ( 0.5 ) ( 310.6 ) Balance as of December 31, 2021 $ 259.1 $ ( 103.7 ) $ ( 13.6 ) $ 141.8 Unrealized Unrealized Retirement (1) Total ($ in millions) Balance as of January 1, 2020 $ 321.0 $ ( 121.8 ) $ ( 27.9 ) $ 171.3 Other comprehensive income (loss), net of tax: Other comprehensive income (loss) before reclassifications 277.0 22.4 ( 0.4 ) 299.0 Reclassifications from accumulated other comprehensive income ( 33.1 ) — 15.2 ( 17.9 ) Total 243.9 22.4 14.8 281.1 Balance as of December 31, 2020 $ 564.9 $ ( 99.4 ) $ ( 13.1 ) $ 452.4 (1) See Note 15 for further information on retirement plan-related reclassifications from accumulated other comprehensive income.
Reclassifications of Accumulated Other Comprehensive Income	The following table presents unrealized appreciation of investment reclassifications out of accumulated other comprehensive income attributable to Alleghany stockholders during 2021 and 2020: Accumulated Other Year Ended December 31, Comprehensive Income Component Line in Consolidated Statement of Earnings 2021 2020 ($ in millions) Unrealized appreciation of investments: Net realized capital gains (1) $ ( 64.4 ) $ ( 49.9 ) Change in allowance for credit losses on available for sale securities ( 2.1 ) 8.0 Income taxes 14.0 8.8 Total reclassifications: Net earnings $ ( 52.5 ) $ ( 33.1 ) (1) For 2021, excludes: the 2021 Concord Remeasurement Gain. For 2020, excludes: (i) the 2020 Concord Settlement Gain; ( ii) $ 76.0 million of impairment charge from a write-down of SORC oil field assets; (iii) the Wilbert Remeasurement Gain; (iv) a $ 7.1 million realized loss as a result of an early redemption of debt; and (v) a $ 5.0 million realized gain resulting from a reduction of certain PCT contingent consideration liabilities. See Note 4(e) for additional information.
Summary of Dividends Paid to Alleghany by its Reinsurance and Insurance Subsidiaries	The following table presents the dividends paid to Alleghany by its reinsurance and insurance subsidiaries in 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 (1) ($ in millions) TransRe (2) $ 280.0 $ 210.0 $ 301.0 RSUI 150.0 225.0 100.0 Total $ 430.0 $ 435.0 $ 401.0 (1) Includes $ 101.0 million representing the July 1, 2019 carrying value of TransRe’s ownership interest in CapSpecialty, which was transferred to Alleghany. (2) In 2021, 2020 and 2019 , TRC paid cash dividends of $ 290.0 million, $ 245.0 million and $ 220.0 million, respectively, to the TransRe holding company. In addition, in 2019, TRC transferred its ownership interest in CapSpecialty to the TransRe holding company, and consequently, the TransRe holding company recorded a dividend from TRC in the amount of $ 101.0 million.
Summary of Dividends Paid to Alleghany Capital Corporation by its Subsidiaries	The following table presents the dividends paid to Alleghany Capital by its subsidiaries in 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Alleghany Capital Subsidiaries (1) $ 133.3 $ 60.9 $ 82.4 (1) Federal income taxes for most Alleghany Capital subsidiaries are incurred at the Alleghany Capital corporate level. As such, these dividends were arrived at after deducting a provision for estimated income taxes to be paid at the Alleghany Capital-level, as applicable. Income tax provisions are finalized when tax returns are filed in future periods.

Earnings Per Share of Common _2

Earnings Per Share of Common Stock (Tables)	12 Months Ended
	Dec. 31, 2021
Earnings Per Share [Abstract]
Reconciliation of Earnings and Share Data used in Basic and Diluted (Losses) Earnings per Share Computations	The following table presents a reconciliation of the earnings and share data used in the basic and diluted earnings per share computations for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions, except share amounts) Net earnings available to Alleghany stockholders $ 1,034.9 $ 101.8 $ 857.8 Effect of dilutive securities — ( 1.2 ) — Income available to common stockholders for diluted earnings per share $ 1,034.9 $ 100.6 $ 857.8 Weighted average common shares outstanding applicable to basic earnings per share 13,853,780 14,257,793 14,431,892 Effect of dilutive securities 7,167 25,825 11,584 Adjusted weighted average common shares outstanding applicable to diluted earnings per share 13,860,947 14,283,618 14,443,476 Contingently issuable shares (1) 62,264 34,148 48,468 (1) Contingently issuable shares were potentially available in the periods presented, but were not included in the diluted earnings per share computations because the impact was anti-dilutive to the earnings per share calculation.

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Consolidated Lease Liabilities And Right-Of-Use Lease Assets Related To Operating Leases	The following table presents Alleghany’s consolidated lease liabilities and right-of-use lease assets related to operating leases as of December 31, 2021: As of Maturity of lease payments, by year ($ in millions) 1 year or less $ 50.3 More than 1 year to 2 years 45.7 More than 2 years to 3 years 42.7 More than 3 years to 4 years 35.4 More than 4 years to 5 years 30.3 More than 5 years 143.3 Total lease payments (1) 347.7 Less: interest (2) ( 79.2 ) Lease liabilities (3) $ 268.5 Right-of-use l ease assets (4) $ 240.5 Prepaid lease assets, net of lease allowances and incentives 28.0 $ 268.5 (1) As of December 31, 2021, the weighted average lease term was approximately 13 y ears. (2) As of December 31, 2021, the weighted average discount rate was approximate ly 5 p ercent. (3) Represents the present val ue of expected lease payments over the remaining lease term and is reported as a component of other liabilities on Alleghany’s consolidated balance sheet. Such lease payments do not include future lease payments arising from certain leases that are yet to commence. Based on current lease contracts that are set to commence in early 2022, Alleghany will be committed to pay additional lease contracts in future years in the amount of approximately $ 30 million. (4) Reported as a component of other assets on Alleghany’s consolidated balance sheet.
Asbestos Related Illnesses and Environmental Impairment Loss and Loss Adjustment Expense Reserves	The following table presents such gross and net reserves as of December 31, 2021 and 2020: December 31, 2021 December 31, 2020 Gross Net Gross Net ($ in millions) TransRe $ 105.0 $ 101.1 $ 108.4 $ 103.6 CapSpecialty 4.5 4.5 4.6 4.6 Total $ 109.5 $ 105.6 $ 113.0 $ 108.2

Segments of Business (Tables)

Segments of Business (Tables)	12 Months Ended
	Dec. 31, 2021
Segment Reporting [Abstract]
Results for Reportable Segments and Corporate Activities	The following tables present segment results for Alleghany’s three reportable segments and for corporate activities for 2021, 2020 and 2019: Reinsurance Segment Insurance Segment Year Ended December 31, 2021 Property Casualty & (1) Total RSUI Cap Total Subtotal Alleghany Total Corporate Consolidated ($ in millions) Gross premiums written $ 1,975.2 $ 4,058.8 $ 6,034.0 $ 2,067.6 $ 475.2 $ 2,542.8 $ 8,576.8 $ — $ 8,576.8 $ ( 38.0 ) $ 8,538.8 Net premiums written 1,550.4 3,837.0 5,387.4 1,354.7 407.3 1,762.0 7,149.4 — 7,149.4 — 7,149.4 Net premiums earned 1,708.8 3,768.3 5,477.1 1,230.7 389.9 1,620.6 7,097.7 — 7,097.7 — 7,097.7 Net loss and LAE 1,444.2 2,347.4 3,791.6 805.5 237.8 1,043.3 4,834.9 — 4,834.9 — 4,834.9 Commissions, brokerage and other underwriting expenses (2) 480.1 1,176.6 1,656.7 261.1 149.7 410.8 2,067.5 — 2,067.5 — 2,067.5 Underwriting (loss) profit (3) $ ( 215.5 ) $ 244.3 $ 28.8 $ 164.1 $ 2.4 $ 166.5 195.3 — 195.3 — 195.3 Net investment income 509.0 ( 0.2 ) 508.8 31.6 540.4 Change in the fair value of equity securities 457.1 — 457.1 49.7 506.8 Net realized capital gains 57.6 7.6 65.2 2.2 67.4 Change in allowance for credit losses on available for sale securities 2.0 — 2.0 0.1 2.1 Product and service revenues 39.3 3,736.4 3,775.7 14.0 3,789.7 Other operating expenses 88.9 3,387.8 3,476.7 2.9 3,479.6 Corporate administration ( 0.1 ) — ( 0.1 ) 57.3 57.2 Amortization of intangible assets 1.8 48.1 49.9 — 49.9 Interest expense 26.9 16.2 43.1 59.2 102.3 Earnings (losses) before income taxes $ 1,142.8 $ 291.7 $ 1,434.5 $ ( 21.8 ) $ 1,412.7 Reinsurance Segment Insurance Segment Year Ended December 31, 2020 Property Casualty & (1) Total RSUI Cap Total Subtotal Alleghany Total Corporate Consolidated ($ in millions) Gross premiums written $ 1,761.7 $ 3,475.6 $ 5,237.3 $ 1,714.4 $ 411.3 $ 2,125.7 $ 7,363.0 $ — $ 7,363.0 $ ( 33.6 ) $ 7,329.4 Net premiums written 1,439.6 3,405.4 4,845.0 1,124.8 374.6 1,499.4 6,344.4 — 6,344.4 — 6,344.4 Net premiums earned 1,379.7 3,265.0 4,644.7 1,008.8 346.7 1,355.5 6,000.2 — 6,000.2 — 6,000.2 Net loss and LAE 1,130.6 2,256.3 3,386.9 738.4 213.8 952.2 4,339.1 — 4,339.1 — 4,339 .1 Commissions, brokerage and other underwriting expenses (2) 424.2 1,000.8 1,425.0 226.1 138.7 364.8 1,789.8 — 1,789.8 — 1,789.8 Underwriting (loss) profit (3) $ ( 175.1 ) $ 7.9 $ ( 167.2 ) $ 44.3 $ ( 5.8 ) $ 38.5 ( 128.7 ) — ( 128.7 ) — ( 128.7 ) Net investment income 465.7 1.9 467.6 23.3 490.9 Change in the fair value of equity securities ( 55.8 ) — ( 55.8 ) ( 54.7 ) ( 110.5 ) Net realized capital gains 37.1 35.5 72.6 ( 69.5 ) 3.1 Change in allowance for credit losses on available for sale securities ( 8.0 ) — ( 8.0 ) — ( 8.0 ) Product and service revenues 34.9 2,477.5 2,512.4 8.7 2,521.1 Other operating expenses 103.6 2,310.0 2,413.6 15.7 2,429.3 Corporate administration ( 0.3 ) — ( 0.3 ) 48.9 48.6 Amortization of intangible assets 0.8 43.4 44.2 — 44.2 Interest expense 27.0 15.5 42.5 45.7 88.2 Earnings (losses) before income taxes $ 214.1 $ 146.0 $ 360.1 $ ( 202.5 ) $ 157.6 Reinsurance Segment Insurance Segment Year Ended December 31, 2019 Property Casualty & (1) Total RSUI Cap Total Subtotal Alleghany Total Corporate Consolidated ($ in millions) Gross premiums written $ 1,700.3 $ 3,245.4 $ 4,945.7 $ 1,366.6 $ 371.8 $ 1,738.4 $ 6,684.1 $ — $ 6,684.1 $ ( 27.7 ) $ 6,656.4 Net premiums written 1,328.8 3,166.2 4,495.0 912.0 344.7 1,256.7 5,751.7 — 5,751.7 — 5,751.7 Net premiums earned 1,280.1 3,046.9 4,327.0 824.2 326.9 1,151.1 5,478.1 — 5,478.1 — 5,478.1 Net loss and LAE 942.6 2,018.5 2,961.1 503.7 221.6 725.3 3,686.4 — 3,686.4 — 3,686.4 Commissions, brokerage and other underwriting expenses (2) 424.2 982.6 1,406.8 219.2 132.7 351.9 1,758.7 — 1,758.7 — 1,758.7 Underwriting (loss) profit (3) $ ( 86.7 ) $ 45.8 $ ( 40.9 ) $ 101.3 $ ( 27.4 ) $ 73.9 33.0 — 33.0 — 33.0 Net investment income 533.2 6.3 539.5 10.7 550.2 Change in the fair value of equity securities 705.8 — 705.8 3.9 709.7 Net realized capital gains 6.0 1.0 7.0 ( 13.5 ) ( 6.5 ) Change in allowance for credit losses on available for sale securities ( 19.7 ) — ( 19.7 ) — ( 19.7 ) Product and service revenues 27.0 2,289.3 2,316.3 12.5 2,328.8 Other operating expenses 103.1 2,132.9 2,236.0 27.3 2,263.3 Corporate administration 4.1 — 4.1 70.7 74.8 Amortization of intangible assets 1.3 32.5 33.8 — 33.8 Interest expense 27.1 20.1 47.2 52.8 100.0 Earnings (losses) before income taxes $ 1,149.7 $ 111.1 $ 1,260.8 $ ( 137.2 ) $ 1,123.6 (1) Primarily consists of the following reinsurance lines of business: directors’ and officers’ liability; errors and omissions liability; general liability; medical malpractice; ocean marine and aviation; auto liability; accident & health; mortgage reinsurance; surety; and credit. (2) Includes amortization associated with deferred acquisition costs of $ 1,693.1 mil lion, $ 1,457.0 million and $ 1,392.8 million for the years ended December 31, 2021, 2020 and 2019 , respectively. (3) Underwriting profit represents net premiums earned less net loss and LAE and commissions, brokerage and other underwriting expenses, all as determined in accordance with GAAP, and does not include net investment income, change in the fair value of equity securities, net realized capital gains, change in allowance for credit losses on available for sale securities, product and service revenues, other operating expenses, corporate administration, amortization of intangible assets or interest expense. Underwriting profit does not replace earnings before income taxes determined in accordance with GAAP as a measure of profitability. Rather, Alleghany believes that underwriting profit enhances the understanding of its reinsurance and insurance segments’ operating results by highlighting net earnings attributable to their underwriting performance. Earnings before income taxes (a GAAP measure) may show a profit despite an underlying underwriting loss. Where underwriting losses persist over extended periods, a reinsurance or an insurance company’s ability to continue as an ongoing concern may be at risk. Therefore, Alleghany views underwriting profit as an important measure in the overall evaluation of performance.
Summary of Identifiable Assets and Equity	The following table presents identifiable assets, the portion of identifiable assets related to cash and invested assets, and equity attributable to Alleghany, for Alleghany’s reportable segments and for corporate activities as of December 31, 2021: Identifiable Invested Assets Equity ($ in millions) Reinsurance segment $ 19,048.2 $ 15,208.8 $ 5,398.4 Insurance segment 8,402.7 6,080.2 2,759.1 Subtotal 27,450.9 21,289.0 8,157.5 Alleghany Capital 3,368.0 165.9 1,337.9 Total segments 30,818.9 21,454.9 9,495.4 Corporate activities 1,449.7 1,394.5 ( 308.5 ) Consolidated $ 32,268.6 $ 22,849.4 $ 9,186.9
Summary of Alleghany Capital Product and Service Revenues	For Alleghany Capital’s industrial and consumer & services operations, product and service revenues consists of the sale of manufactured goods and services. The following table presents product and service revenues for the Alleghany Capital segment for 2021, 2020 and 2019: Year Ended December 31, 2021 2020 2019 ($ in millions) Industrial (1) $ 1,662.3 $ 1,220.9 $ 1,105.6 Consumer & services (2) 2,074.1 1,256.5 1,183.7 Corporate & other — 0.1 — Alleghany Capital $ 3,736.4 $ 2,477.5 $ 2,289.3 (1) For 2021, 2020 and 2019 , the vast majority of industrial product and service revenues were recognized as goods and services transferred to customers over time. (2) For 2021, 2020 and 2019 , approximately 50 percent, 59 percent and 70 percent, respectively, of consumer & services product and service revenues were recognized as services transferred to customers over time, with the remainder recognized as goods transferred at a point in time.

Quarterly Results of Operatio_2

Quarterly Results of Operations (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2021
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data	Selected quarterly financial data for 2021 and 2020 are presented below: Quarter Ended March 31 June 30 September 30 December 31 ($ in millions, except per share data) 2021 Revenues $ 2,653.7 $ 2,928.7 $ 2,866.6 $ 3,555.0 Net earnings (losses) (1) 230.0 403.7 ( 115.0 ) 516.2 Basic earnings (losses) per share of common stock (1)(2) 16.44 29.00 ( 8.31 ) 37.76 2020 Revenues $ 1,482.9 $ 2,227.4 $ 2,522.9 $ 2,663.5 Net (losses) earnings (1) ( 361.2 ) 177.4 126.5 159.1 Basic (losses) earnings per share of common stock (1)(2) ( 25.19 ) 12.39 8.86 11.28 (1) Attributable to Alleghany stockholders. (2) Earnings per share by quarter may not equal the amount for the full year due to the timing of repurchases of Common Stock, as well as rounding.

Summary of Significant Accoun_4

Summary of Significant Accounting Principles - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		Jan. 01, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Apr. 01, 2020	Jan. 01, 2019	Dec. 31, 2018
Significant Accounting Policies [Line Items]
Accretion reduced capital contribution			$ (5,300)	$ 0	$ 0
Par value of common stock outstanding			$ 1
Statutory federal income tax rate			21.00%	21.00%	21.00%
Total stockholders’ equity attributable to Alleghany stockholders			$ 9,186,882	$ 8,755,720	$ 8,776,734			$ 7,692,710
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]			Other Assets
Right-of-use asset	[1]		$ 240,500
Lease liability	[2]		268,500
Retained earnings			7,353,226	6,318,334
Cumulative Effect, Period of Adoption, Adjustment
Significant Accounting Policies [Line Items]
Total stockholders’ equity attributable to Alleghany stockholders					(3,570)
Retained Earnings
Significant Accounting Policies [Line Items]
Total stockholders’ equity attributable to Alleghany stockholders			7,353,226	6,318,334	6,435,163			5,577,362
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
Significant Accounting Policies [Line Items]
Total stockholders’ equity attributable to Alleghany stockholders					(3,570)
Accumulated Other Comprehensive Income
Significant Accounting Policies [Line Items]
Total stockholders’ equity attributable to Alleghany stockholders			$ 141,822	$ 452,402	171,350			$ (202,003)
Accumulated Other Comprehensive Income | Cumulative Effect, Period of Adoption, Adjustment
Significant Accounting Policies [Line Items]
Total stockholders’ equity attributable to Alleghany stockholders					$ 0
Accounting Standards Update 2016-02 | Cumulative Effect, Period of Adoption, Adjustment
Significant Accounting Policies [Line Items]
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]							Other Assets
Right-of-use asset							$ 200,000
Lease liability							$ 200,000
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjustment
Significant Accounting Policies [Line Items]
Allowances for credit losses on certain financial assets		$ 4,500
Retained earnings		$ (3,600)
Kentucky Trailer
Significant Accounting Policies [Line Items]
Ownership of interest held by noncontrolling partners			22.00%
Integrated Project Services LLC
Significant Accounting Policies [Line Items]
Ownership of interest held by noncontrolling partners			18.00%
Jazwares, LLC
Significant Accounting Policies [Line Items]
Ownership of interest held by noncontrolling partners			24.00%
WWSC Holdings, LLC
Significant Accounting Policies [Line Items]
Ownership of interest held by noncontrolling partners			20.00%
Concord
Significant Accounting Policies [Line Items]
Ownership of interest held by noncontrolling partners			15.00%
Wilbert Funeral Services, Inc
Significant Accounting Policies [Line Items]
Equity interest percentage acquired						55.00%
Equity interest percentage						100.00%
[1]	Reported as a component of other assets on Alleghany’s consolidated balance sheet.
[2]	Represents the present val ue of expected lease payments over the remaining lease term and is reported as a component of other liabilities on Alleghany’s consolidated balance sheet.

Summary of Significant Accoun_5

Summary of Significant Accounting Principles - Components of Net Earnings Attributable to Noncontrolling Interests (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Noncontrolling Interest [Line Items]
Accretion of redeemable noncontrolling interests	$ 23,500	$ 2,200	$ 8,800
Portion of net earnings attributable to noncontrolling interests	72,400	22,900	23,600
Total	$ 95,886	$ 25,129	$ 32,400

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Summary of Rollforward of Goodwill and Intangible Assets by Segment (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021		Dec. 31, 2020
Goodwill [Line Items]
Goodwill, beginning balance		$ 614,163	[1]	$ 523,000
Acquired	[2]	139,400		92,100
Other increase (decrease)		0		(900)
Goodwill, ending balance	[1]	753,607		614,163
Intangible assets, beginning balance		787,462	[1]	686,000
Acquired	[2]	189,400		147,000
Amortization	[3]	(49,900)		(44,200)
Other increase (decrease)		(2,600)		(1,300)
Intangible assets, ending balance	[1]	924,406		787,462
Alleghany Capital Segment
Goodwill [Line Items]
Goodwill, beginning balance		557,300	[1],[4],[5]	465,200
Acquired	[2]	139,400		92,100
Other increase (decrease)		0		0
Goodwill, ending balance	[1],[4],[5]	696,700		557,300
Intangible assets, beginning balance		646,000	[1],[4]	542,400
Acquired	[2]	189,400		147,000
Amortization	[3]	(48,100)		(43,400)
Other increase (decrease)		0		0
Intangible assets, ending balance	[1],[4]	787,300		646,000
Insurance Segment
Goodwill [Line Items]
Goodwill, beginning balance		48,100	[1],[5]	49,000
Acquired	[2]	0		0
Other increase (decrease)		0		(900)
Goodwill, ending balance	[1],[5]	48,100		48,100
Intangible assets, beginning balance		63,100	[1]	65,400
Acquired	[2]	0		0
Amortization	[3]	(700)		(1,000)
Other increase (decrease)		(1,300)		(1,300)
Intangible assets, ending balance	[1]	61,100		63,100
Reinsurance Segment
Goodwill [Line Items]
Goodwill, beginning balance		8,800	[1],[5]	8,800
Acquired	[2]	0		0
Other increase (decrease)		0		0
Goodwill, ending balance	[1],[5]	8,800		8,800
Intangible assets, beginning balance		78,400	[1]	78,200
Acquired	[2]	0		0
Amortization	[3]	(1,100)		200
Other increase (decrease)		(1,300)		0
Intangible assets, ending balance	[1]	$ 76,000		$ 78,400
[1]	Goodwill and intangible assets have been reduced by amounts written-down in prior periods, as applicable.
[2]	See description below for a summary of recent material acquisitions impacting goodwill and intangible assets.
[3]	See table below for additional information regarding amortization and useful lives by major class of intangible asset.
[4]	Represents goodwill and other intangible assets related to the acquisition of: (i) Jazwares on April 15, 2016 and its subsequent acquisitions; (ii) W&W|AFCO Steel on April 28, 2017 and its subsequent acquisition; (iii) Concord on October 1, 2018; (iv) PCT on April 26, 2012 and its subsequent acquisitions; (v) IPS on October 31, 2015 and its subsequent acquisitions; (vi) Kentucky Trailer on August 30, 2013 and its subsequent acquisitions; (vii) Wilbert on April 1, 2020 and its subsequent acquisitions; and (viii) WPS on May 10, 2021.
[5]	See N ote 13 for additional information on Alleghany’s segments of business.

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions		Oct. 14, 2021	May 10, 2021	Apr. 01, 2020	Oct. 01, 2019	Dec. 31, 2021	Dec. 31, 2020	Oct. 13, 2021	Mar. 31, 2020	Sep. 30, 2019
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill acquired	[1]					$ 139.4	$ 92.1
Alleghany Capital Corporation Segment
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill acquired	[1]					$ 139.4	$ 92.1
Jazwares, LLC
Goodwill and Intangible Assets Disclosure [Line Items]
Ownership of interest held by noncontrolling partners						24.00%
Integrated Project Services LLC
Goodwill and Intangible Assets Disclosure [Line Items]
Ownership of interest held by noncontrolling partners						18.00%
License Agreements
Goodwill and Intangible Assets Disclosure [Line Items]
Economic useful lives of significant intangible assets						8 years
Agency Relationships
Goodwill and Intangible Assets Disclosure [Line Items]
Economic useful lives of significant intangible assets						15 years
Brokerage and Reinsurance Relationships
Goodwill and Intangible Assets Disclosure [Line Items]
Economic useful lives of significant intangible assets						15 years
Renewal rights | Minimum
Goodwill and Intangible Assets Disclosure [Line Items]
Economic useful lives of significant intangible assets						3 years
Renewal rights | Maximum
Goodwill and Intangible Assets Disclosure [Line Items]
Economic useful lives of significant intangible assets						14 years
Loss and LAE reserves
Goodwill and Intangible Assets Disclosure [Line Items]
Economic useful lives of significant intangible assets						15 years
Leases
Goodwill and Intangible Assets Disclosure [Line Items]
Economic useful lives of significant intangible assets						10 years
Customer Relationships | Minimum
Goodwill and Intangible Assets Disclosure [Line Items]
Economic useful lives of significant intangible assets						5 years
Customer Relationships | Maximum
Goodwill and Intangible Assets Disclosure [Line Items]
Economic useful lives of significant intangible assets						18 years 6 months
Wilbert Funeral Services, Inc
Goodwill and Intangible Assets Disclosure [Line Items]
Ownership interest acquired				55.00%
Equity interest percentage				100.00%
Purchase price for acquisition				$ 121.3
Cash consideration paid for acquisition				46.3
Incremental debt acquired				75
Goodwill acquired				62.9
Gain on remeasurement of pre-existing equity ownership to estimated fair value				16.3
Equity interest percentage									45.00%
Wilbert Funeral Services, Inc | Trade name
Goodwill and Intangible Assets Disclosure [Line Items]
Indefinite-lived intangible assets acquired				26.2
Wilbert Funeral Services, Inc | Customer Relationship
Goodwill and Intangible Assets Disclosure [Line Items]
Finite-lived intangible assets acquired				21.5
Wilbert Funeral Services, Inc | License Agreements
Goodwill and Intangible Assets Disclosure [Line Items]
Finite-lived intangible assets acquired				$ 14.9
Wicked Cool Toys LLC Acquisition By Jazwares
Goodwill and Intangible Assets Disclosure [Line Items]
Purchase price for acquisition					$ 159
Incremental debt acquired					135.5
Goodwill acquired					39.1
Issuance of certain noncontrolling interests in Jazwares					$ 23.5
Wicked Cool Toys LLC Acquisition By Jazwares | Jazwares, LLC | Alleghany Capital Corporation Segment
Goodwill and Intangible Assets Disclosure [Line Items]
Ownership of interest held by noncontrolling partners					25.00%					23.00%
Wicked Cool Toys LLC Acquisition By Jazwares | Customer Relationship
Goodwill and Intangible Assets Disclosure [Line Items]
Finite-lived intangible assets acquired					$ 24.9
Wicked Cool Toys LLC Acquisition By Jazwares | License Agreements
Goodwill and Intangible Assets Disclosure [Line Items]
Finite-lived intangible assets acquired					$ 83.9
Linesight
Goodwill and Intangible Assets Disclosure [Line Items]
Purchase price for acquisition		$ 262.5
Cash consideration paid for acquisition		98.6
Incremental debt acquired		125.1
Goodwill acquired		102.1
Issuance of certain noncontrolling interests in Jazwares		$ 38.8
Linesight | Integrated Project Services LLC
Goodwill and Intangible Assets Disclosure [Line Items]
Ownership of interest held by noncontrolling partners		18.00%						15.00%
Linesight | Alleghany Corporation
Goodwill and Intangible Assets Disclosure [Line Items]
Contribution from Alleghany		$ 97.4
Linesight | Trade Names and Trade Marks
Goodwill and Intangible Assets Disclosure [Line Items]
Indefinite-lived intangible assets acquired		15.5
Linesight | Customer Relationship
Goodwill and Intangible Assets Disclosure [Line Items]
Finite-lived intangible assets acquired		$ 124.7
Wilbert Plastic Services
Goodwill and Intangible Assets Disclosure [Line Items]
Purchase price for acquisition			$ 93.4
Cash consideration paid for acquisition			60.4
Incremental debt acquired			33
Goodwill acquired			17.7
Wilbert Plastic Services | Customer Relationships
Goodwill and Intangible Assets Disclosure [Line Items]
Finite lived intangible assets			$ 36.3
Economic useful lives of significant intangible assets			18 years 6 months
[1]	See description below for a summary of recent material acquisitions impacting goodwill and intangible assets.

Goodwill and Intangible Asset,

Goodwill and Intangible Asset, Net of Accumulated Amortization Expense on Consolidated Balance Sheets (Detail) - USD ($) $ in Thousands		Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill, gross		$ 753,600		$ 614,200
Accumulated Amortization		0		0
Goodwill		753,607	[1]	614,163	[1]	$ 523,000
Finite lived intangible assets, accumulated amortization		496,700		446,700
Intangible assets excluding goodwill, gross		1,421,100		1,234,200
Goodwill and other intangible assets, accumulated amortization		496,700		446,700
Intangible assets excluding goodwill, net of amortization		924,406	[1]	787,462	[1]	686,000
Goodwill and other intangible assets, Gross carrying value		2,174,700		1,848,400
Goodwill and other intangible assets, Net carrying value	[1]	1,678,000		1,401,700
Insurance Segment
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill, gross	[2]	48,100		48,100
Accumulated Amortization	[2]	0		0
Goodwill		48,100	[1],[2]	48,100	[1],[2]	49,000
Finite lived intangible assets, accumulated amortization		74,800		74,100
Intangible assets excluding goodwill, gross		135,900		137,200
Goodwill and other intangible assets, accumulated amortization		74,800		74,100
Intangible assets excluding goodwill, net of amortization		61,100	[1]	63,100	[1]	65,400
Goodwill and other intangible assets, Gross carrying value		184,000		185,300
Goodwill and other intangible assets, Net carrying value	[1]	109,200		111,200
Insurance Segment | State insurance licenses
Goodwill and Intangible Assets Disclosure [Line Items]
Indefinite Lived Intangible Assets Accumulated Amortization		0		0
Indefinite lived intangible assets, gross		25,100		25,100
Indefinite lived intangible assets, net	[1]	25,100		25,100
Insurance Segment | Trade name
Goodwill and Intangible Assets Disclosure [Line Items]
Indefinite Lived Intangible Assets Accumulated Amortization		0		0
Indefinite lived intangible assets, gross		35,500		35,500
Indefinite lived intangible assets, net	[1]	35,500		35,500
Insurance Segment | Agency Relationships
Goodwill and Intangible Assets Disclosure [Line Items]
Finite lived intangible assets, gross		12,500		13,800
Finite lived intangible assets, accumulated amortization		12,100		11,600
Finite lived intangible assets, net	[1]	400		2,200
Insurance Segment | Brokerage and Reinsurance Relationships
Goodwill and Intangible Assets Disclosure [Line Items]
Finite lived intangible assets, gross		33,800		33,800
Finite lived intangible assets, accumulated amortization		33,800		33,800
Finite lived intangible assets, net	[1]	0		0
Insurance Segment | Renewal rights
Goodwill and Intangible Assets Disclosure [Line Items]
Finite lived intangible assets, gross		24,900		24,900
Finite lived intangible assets, accumulated amortization		24,800		24,600
Finite lived intangible assets, net	[1]	100		300
Insurance Segment | Other
Goodwill and Intangible Assets Disclosure [Line Items]
Finite lived intangible assets, gross		4,100		4,100
Finite lived intangible assets, accumulated amortization		4,100		4,100
Finite lived intangible assets, net	[1]	0		0
Reinsurance Segment
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill, gross	[2]	8,800		8,800
Accumulated Amortization	[2]	0		0
Goodwill		8,800	[1],[2]	8,800	[1],[2]	8,800
Finite lived intangible assets, accumulated amortization		226,700		225,500
Intangible assets excluding goodwill, gross		302,700		303,900
Goodwill and other intangible assets, accumulated amortization		226,700		225,500
Intangible assets excluding goodwill, net of amortization		76,000	[1]	78,400	[1]	78,200
Goodwill and other intangible assets, Gross carrying value		311,500		312,700
Goodwill and other intangible assets, Net carrying value	[1]	84,800		87,200
Reinsurance Segment | Trade name
Goodwill and Intangible Assets Disclosure [Line Items]
Indefinite Lived Intangible Assets Accumulated Amortization		0		0
Indefinite lived intangible assets, gross		50,000		50,000
Indefinite lived intangible assets, net	[1]	50,000		50,000
Reinsurance Segment | State and Foreign Insurance Licenses
Goodwill and Intangible Assets Disclosure [Line Items]
Indefinite Lived Intangible Assets Accumulated Amortization		0		0
Indefinite lived intangible assets, gross		19,000		19,000
Indefinite lived intangible assets, net	[1]	19,000		19,000
Reinsurance Segment | Renewal rights
Goodwill and Intangible Assets Disclosure [Line Items]
Finite lived intangible assets, gross		51,800		53,000
Finite lived intangible assets, accumulated amortization		40,400		35,200
Finite lived intangible assets, net	[1]	11,400		17,800
Reinsurance Segment | Other
Goodwill and Intangible Assets Disclosure [Line Items]
Finite lived intangible assets, gross		15,100		15,100
Finite lived intangible assets, accumulated amortization		11,600		11,200
Finite lived intangible assets, net	[1]	3,500		3,900
Reinsurance Segment | Value of business in-force
Goodwill and Intangible Assets Disclosure [Line Items]
Finite lived intangible assets, gross		291,400		291,400
Finite lived intangible assets, accumulated amortization		291,400		291,400
Finite lived intangible assets, net	[1]	0		0
Reinsurance Segment | Loss and LAE reserves
Goodwill and Intangible Assets Disclosure [Line Items]
Finite lived intangible assets, gross		(98,800)		(98,800)
Finite lived intangible assets, accumulated amortization		(90,900)		(88,600)
Finite lived intangible assets, net	[1]	(7,900)		(10,200)
Reinsurance Segment | Leases
Goodwill and Intangible Assets Disclosure [Line Items]
Finite lived intangible assets, gross		(25,800)		(25,800)
Finite lived intangible assets, accumulated amortization		(25,800)		(23,700)
Finite lived intangible assets, net	[1]	0		(2,100)
Alleghany Capital Corporation Segment
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill, gross	[2],[3]	696,700		557,300
Accumulated Amortization	[2],[3]	0		0
Goodwill		696,700	[1],[2],[3]	557,300	[1],[2],[3]	465,200
Finite lived intangible assets, accumulated amortization	[3]	195,200		147,100
Intangible assets excluding goodwill, gross	[3]	982,500		793,100
Goodwill and other intangible assets, accumulated amortization	[3]	195,200		147,100
Intangible assets excluding goodwill, net of amortization		787,300	[1],[3]	646,000	[1],[3]	$ 542,400
Goodwill and other intangible assets, Gross carrying value	[3]	1,679,200		1,350,400
Goodwill and other intangible assets, Net carrying value	[1],[3]	1,484,000		1,203,300
Alleghany Capital Corporation Segment | Trade name
Goodwill and Intangible Assets Disclosure [Line Items]
Indefinite Lived Intangible Assets Accumulated Amortization	[3]	5,200		2,700
Indefinite lived intangible assets, gross	[3]	245,300		218,200
Indefinite lived intangible assets, net	[1],[3]	240,100		215,500
Alleghany Capital Corporation Segment | Other
Goodwill and Intangible Assets Disclosure [Line Items]
Finite lived intangible assets, gross	[3]	50,000		50,000
Finite lived intangible assets, accumulated amortization	[3]	25,800		23,900
Finite lived intangible assets, net	[1],[3]	24,200		26,100
Alleghany Capital Corporation Segment | License Agreements
Goodwill and Intangible Assets Disclosure [Line Items]
Finite lived intangible assets, gross	[3]	167,100		167,100
Finite lived intangible assets, accumulated amortization	[3]	63,300		48,100
Finite lived intangible assets, net	[1],[3]	103,800		119,000
Alleghany Capital Corporation Segment | Customer Relationships
Goodwill and Intangible Assets Disclosure [Line Items]
Finite lived intangible assets, gross	[3]	520,100		357,800
Finite lived intangible assets, accumulated amortization	[3]	100,900		72,400
Finite lived intangible assets, net	[1],[3]	$ 419,200		$ 285,400
[1]	Goodwill and intangible assets have been reduced by amounts written-down in prior periods, as applicable.
[2]	See N ote 13 for additional information on Alleghany’s segments of business.
[3]	Represents goodwill and other intangible assets related to the acquisition of: (i) Jazwares on April 15, 2016 and its subsequent acquisitions; (ii) W&W|AFCO Steel on April 28, 2017 and its subsequent acquisition; (iii) Concord on October 1, 2018; (iv) PCT on April 26, 2012 and its subsequent acquisitions; (v) IPS on October 31, 2015 and its subsequent acquisitions; (vi) Kentucky Trailer on August 30, 2013 and its subsequent acquisitions; (vii) Wilbert on April 1, 2020 and its subsequent acquisitions; and (viii) WPS on May 10, 2021.

Carrying Values and Estimated F

Carrying Values and Estimated Fair Values of Consolidated Financial Instruments (Detail) - USD ($) $ in Millions		Dec. 31, 2021	Dec. 31, 2020
Assets
Investments (excluding equity method investments and loans)	[1]	$ 20,887.7	$ 19,051.9
Liabilities
Senior Notes and other debt	[2]	3,157.9	2,468.7
Carrying Value
Assets
Investments (excluding equity method investments and loans)	[1]	20,887.7	19,051.9
Liabilities
Senior Notes and other debt	[2]	$ 2,847.2	$ 2,135.9
[1]	This table includes debt and equity securities, as well as partnership and non-marketable equity investments accounted for at fair value that are included in other invested assets. This table excludes investments accounted for using the equity method and commercial mortgage loans that are accounted for at unpaid principal balance. The fair value of short-term investments approximates amortized cost.
[2]	See Note 8 for additional information on the Senior Notes and other debt.

Financial Instruments at Fair V

Financial Instruments at Fair Value and Level of Fair Value Hierarchy of Inputs (Detail) - USD ($) $ in Thousands		Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		$ 3,683,820	$ 2,718,902
Estimated fair value of available for sale debt securities		16,061,560	15,618,470
Estimated fair value of investments (excluding equity method investments and loans)	[1]	20,887,700	19,051,900
Senior Notes and other debt	[2]	3,157,900	2,468,700
Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		3,679,200	2,714,600
Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		4,600	4,300
U.S. Government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		2,050,700	1,360,100
Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		2,535,900	2,656,800
Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		854,900	879,500
U.S. corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		3,477,300	3,545,700
Foreign corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		1,226,900	1,323,100
RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities	[3]	2,009,000	2,611,400
CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		905,900	890,300
Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities	[4]	3,001,000	2,351,600
Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of investments (excluding equity method investments and loans)		1,142,300	714,200
Other invested assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of investments (excluding equity method investments and loans)		0	300	[5]
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		3,677,100	2,711,100
Estimated fair value of available for sale debt securities		0	0
Estimated fair value of investments (excluding equity method investments and loans)		3,677,100	2,711,100
Senior Notes and other debt		0	0
Level 1 | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		3,677,100	2,711,100
Level 1 | Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		0	0
Level 1 | U.S. Government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		0	0
Level 1 | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		0	0
Level 1 | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		0	0
Level 1 | U.S. corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		0	0
Level 1 | Foreign corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		0	0
Level 1 | RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities	[3]	0	0
Level 1 | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		0	0
Level 1 | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities	[4]	0	0
Level 1 | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of investments (excluding equity method investments and loans)		0	0
Level 1 | Other invested assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of investments (excluding equity method investments and loans)		0	0	[5]
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		5,400	6,500
Estimated fair value of available for sale debt securities		13,863,900	13,886,400
Estimated fair value of investments (excluding equity method investments and loans)		15,011,600	14,607,100
Senior Notes and other debt		2,377,400	1,911,800
Level 2 | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		2,100	3,500
Level 2 | Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		3,300	3,000
Level 2 | U.S. Government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		2,050,700	1,360,100
Level 2 | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		2,535,900	2,656,800
Level 2 | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		854,900	879,500
Level 2 | U.S. corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		2,807,000	2,914,100
Level 2 | Foreign corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		1,049,700	1,133,600
Level 2 | RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities	[3]	2,007,100	2,608,900
Level 2 | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		905,900	884,500
Level 2 | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities	[4]	1,652,700	1,448,900
Level 2 | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of investments (excluding equity method investments and loans)		1,142,300	714,200
Level 2 | Other invested assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of investments (excluding equity method investments and loans)		0	0	[5]
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		1,300	1,300
Estimated fair value of available for sale debt securities		2,197,700	1,732,100
Estimated fair value of investments (excluding equity method investments and loans)		2,199,000	1,733,700
Senior Notes and other debt		780,500	556,900
Level 3 | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		0	0
Level 3 | Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		1,300	1,300
Level 3 | U.S. Government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		0	0
Level 3 | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		0	0
Level 3 | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		0	0
Level 3 | U.S. corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		670,300	631,600
Level 3 | Foreign corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		177,200	189,500
Level 3 | RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities	[3]	1,900	2,500
Level 3 | CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		0	5,800
Level 3 | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities	[4]	1,348,300	902,700
Level 3 | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of investments (excluding equity method investments and loans)		0	0
Level 3 | Other invested assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of investments (excluding equity method investments and loans)		$ 0	$ 300	[5]
[1]	This table includes debt and equity securities, as well as partnership and non-marketable equity investments accounted for at fair value that are included in other invested assets. This table excludes investments accounted for using the equity method and commercial mortgage loans that are accounted for at unpaid principal balance. The fair value of short-term investments approximates amortized cost.
[2]	See Note 8 for additional information on the Senior Notes and other debt.
[3]	Primarily includes government agency pass-through securities guaranteed by a government agency or government sponsored enterprise, among other types of RMBS.
[4]	Includes $ 1,320.4 million and $ 878.4 million of collateralized loan obligations as of December 31, 2021 and 2020 , respectively.
[5]	Includes partnership investments accounted for at fair value and excludes investments accounted for using the equity method.

Financial Instruments at Fair_2

Financial Instruments at Fair Value and Level of Fair Value Hierarchy of Inputs (Parenthetical) (Detail) - USD ($) $ in Thousands		Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		$ 16,061,560	$ 15,618,470
Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities	[1]	3,001,000	2,351,600
Collateralized loan obligations | Other asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		$ 1,320,400	$ 878,400
[1]	Includes $ 1,320.4 million and $ 878.4 million of collateralized loan obligations as of December 31, 2021 and 2020 , respectively.

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers out of Level 3	$ 48.2	$ 20.7
Gross transfers into Level 3	5.8	0
Foreign corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers out of Level 3	0	6.2
Gross transfers into Level 3	0	0
Other asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers out of Level 3	37	14.5
Gross transfers into Level 3	5.8	0
CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers out of Level 3	5.8	0
Gross transfers into Level 3	0	0
U.S. corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers out of Level 3	3.7	0
Gross transfers into Level 3	0	0
Foreign government obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers out of Level 3	1.7	0
Gross transfers into Level 3	$ 0	$ 0

Reconciliation of Changes in Le

Reconciliation of Changes in Level 3 Assets Measured at Fair Value (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		$ 1,733.7	$ 1,640.4
Net realized/unrealized gains (losses) included in:
Net earnings	[1]	0.7	(13.8)
Other comprehensive income (loss)		(19.4)	35.5
Purchases		951.9	285.7
Sales		(13)	(64.5)
Issuances		0	0
Settlements		(412.5)	(128.9)
Transfers into Level 3		5.8	0
Transfers out of Level 3		(48.2)	(20.7)
Ending balance		2,199	1,733.7
Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		1.3	2
Net realized/unrealized gains (losses) included in:
Net earnings	[1]	0	(0.7)
Other comprehensive income (loss)		0	0
Purchases		0	0
Sales		0	0
Issuances		0	0
Settlements		0	0
Transfers into Level 3		0	0
Transfers out of Level 3		0	0
Ending balance		1.3	1.3
Foreign government obligations
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		0	0
Net realized/unrealized gains (losses) included in:
Net earnings	[1]	0	0
Other comprehensive income (loss)		0	0
Purchases		1.7	0
Sales		0	0
Issuances		0	0
Settlements		0	0
Transfers into Level 3		0	0
Transfers out of Level 3		(1.7)	0
Ending balance		0	0
U.S. corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		631.6	605
Net realized/unrealized gains (losses) included in:
Net earnings	[1]	0.1	(3.8)
Other comprehensive income (loss)		(20.4)	22.7
Purchases		151.2	56.4
Sales		(0.2)	(2)
Issuances		0	0
Settlements		(88.3)	(46.7)
Transfers into Level 3		0	0
Transfers out of Level 3		(3.7)	0
Ending balance		670.3	631.6
Foreign corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		189.5	168.7
Net realized/unrealized gains (losses) included in:
Net earnings	[1]	(0.1)	0.1
Other comprehensive income (loss)		(7.2)	7.3
Purchases		22.7	32
Sales		0	(0.8)
Issuances		0	0
Settlements		(27.7)	(11.6)
Transfers into Level 3		0	0
Transfers out of Level 3		0	(6.2)
Ending balance		177.2	189.5
RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		2.5	1.9
Net realized/unrealized gains (losses) included in:
Net earnings	[1]	0.1	0
Other comprehensive income (loss)		(0.1)	0.1
Purchases		0	0.9
Sales		0	0
Issuances		0	0
Settlements		(0.6)	(0.4)
Transfers into Level 3		0	0
Transfers out of Level 3		0	0
Ending balance		1.9	2.5
CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		5.8	5.8
Net realized/unrealized gains (losses) included in:
Net earnings	[1]	0	0
Other comprehensive income (loss)		0	0.1
Purchases		0	0
Sales		0	0
Issuances		0	0
Settlements		0	(0.1)
Transfers into Level 3		0	0
Transfers out of Level 3		(5.8)	0
Ending balance		0	5.8
Other asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance		902.7	856.7
Net realized/unrealized gains (losses) included in:
Net earnings	[1]	0.5	(9.4)
Other comprehensive income (loss)		8.3	5.3
Purchases		776.3	196.4
Sales		(12.4)	(61.7)
Issuances		0	0
Settlements		(295.9)	(70.1)
Transfers into Level 3		5.8	0
Transfers out of Level 3		(37)	(14.5)
Ending balance		1,348.3	902.7
Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	[2]	0.3	0.3
Net realized/unrealized gains (losses) included in:
Net earnings	[1],[2]	0.1	0
Other comprehensive income (loss)	[2]	0	0
Purchases	[2]	0	0
Sales	[2]	(0.4)	0
Issuances	[2]	0	0
Settlements	[2]	0	0
Transfers into Level 3	[2]	0	0
Transfers out of Level 3	[2]	0	0
Ending balance	[2]	$ 0	$ 0.3
[1]	There were no credit losses recorded in net earnings related to Level 3 instruments still held as of December 31, 2021 and 2020 .
[2]	Includes partnership and non-marketable equity investments accounted for at fair value.

Amortized Cost and Fair Value o

Amortized Cost and Fair Value of Available For Sale Securities (Detail) - USD ($) $ in Thousands		Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Debt securities, amortized cost		$ 15,727,143		$ 14,898,522
Debt securities, gross unrealized gains		433,800		762,200
Debt securities, gross unrealized losses		(98,800)		(39,600)
Debt securities, allowance for credit losses		(502)	[1]	(2,579)	[1]	$ 0
Debt securities, fair value		16,061,560		15,618,470
Amortized Cost or Cost		16,869,400		15,612,700
Gross Unrealized Gains		433,800		762,200
Gross Unrealized Losses		(98,800)		(39,600)
Allowance for Credit Losses	[1]	(500)		(2,600)
Fair Value		17,203,900		16,332,700
U.S. Government obligations
Schedule of Available-for-sale Securities [Line Items]
Debt securities, amortized cost		2,039,700		1,317,600
Debt securities, gross unrealized gains		27,900		44,000
Debt securities, gross unrealized losses		(16,900)		(1,500)
Debt securities, allowance for credit losses	[1]	0		0
Debt securities, fair value		2,050,700		1,360,100
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Debt securities, amortized cost		2,412,700		2,489,100
Debt securities, gross unrealized gains		127,300		168,300
Debt securities, gross unrealized losses		(4,100)		(600)
Debt securities, allowance for credit losses	[1]	0		0
Debt securities, fair value		2,535,900		2,656,800
Foreign government obligations
Schedule of Available-for-sale Securities [Line Items]
Debt securities, amortized cost		850,800		846,600
Debt securities, gross unrealized gains		12,000		33,400
Debt securities, gross unrealized losses		(7,900)		(500)
Debt securities, allowance for credit losses	[1]	0		0
Debt securities, fair value		854,900		879,500
U.S. corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Debt securities, amortized cost		3,336,900		3,262,000
Debt securities, gross unrealized gains		159,200		289,700
Debt securities, gross unrealized losses		(18,300)		(3,500)
Debt securities, allowance for credit losses	[1]	(500)		(2,500)
Debt securities, fair value		3,477,300		3,545,700
Foreign corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Debt securities, amortized cost		1,216,600		1,268,300
Debt securities, gross unrealized gains		19,900		55,600
Debt securities, gross unrealized losses		(9,600)		(700)
Debt securities, allowance for credit losses	[1]	0		(100)
Debt securities, fair value		1,226,900		1,323,100
RMBS
Schedule of Available-for-sale Securities [Line Items]
Debt securities, amortized cost		1,993,600		2,533,600
Debt securities, gross unrealized gains		37,200		78,300
Debt securities, gross unrealized losses		(21,800)		(500)
Debt securities, allowance for credit losses	[1]	0		0
Debt securities, fair value	[2]	2,009,000		2,611,400
CMBS
Schedule of Available-for-sale Securities [Line Items]
Debt securities, amortized cost		879,800		852,600
Debt securities, gross unrealized gains		28,300		45,300
Debt securities, gross unrealized losses		(2,200)		(7,600)
Debt securities, allowance for credit losses	[1]	0		0
Debt securities, fair value		905,900		890,300
Other asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Debt securities, amortized cost	[3]	2,997,000		2,328,700
Debt securities, gross unrealized gains	[3]	22,000		47,600
Debt securities, gross unrealized losses	[3]	(18,000)		(24,700)
Debt securities, allowance for credit losses	[1],[3]	0		0
Debt securities, fair value	[4]	3,001,000		2,351,600
Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost or Cost		1,142,300		714,200
Gross Unrealized Gains		0		0
Gross Unrealized Losses		0		0
Allowance for Credit Losses	[1]	0		0
Fair Value		$ 1,142,300		$ 714,200
[1]	See Note 1(r) for additional information regarding Alleghany’s adoption of new credit loss accounting guidance.
[2]	Primarily includes government agency pass-through securities guaranteed by a government agency or government sponsored enterprise, among other types of RMBS.
[3]	Includes $ 1,320.4 million and $ 878.4 million of collateralized loan obligations as of December 31, 2021 and 2020 , respectively.
[4]	Includes $ 1,320.4 million and $ 878.4 million of collateralized loan obligations as of December 31, 2021 and 2020 , respectively.

Amortized Cost and Fair Value_2

Amortized Cost and Fair Value of Available For Sale Securities (Parenthetical) (Detail) - USD ($) $ in Thousands		Dec. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value of available for sale debt securities		$ 16,061,560	$ 15,618,470
Other asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value of available for sale debt securities	[1]	3,001,000	2,351,600
Other asset-backed securities | Collateralized loan obligations
Schedule of Available-for-sale Securities [Line Items]
Estimated fair value of available for sale debt securities		$ 1,320,400	$ 878,400
[1]	Includes $ 1,320.4 million and $ 878.4 million of collateralized loan obligations as of December 31, 2021 and 2020 , respectively.

Amortized Cost and Estimated Fa

Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands		Dec. 31, 2021	Dec. 31, 2020
Investments, Debt and Equity Securities [Abstract]
Short-term investments due in one year or less, amortized cost		$ 1,142,300
Mortgage and asset-backed securities, amortized cost	[1]	5,870,400
Debt securities with maturity dates, amortized cost:
One year or less		624,200
Over one through five years		3,714,400
Over five through ten years		3,037,600
Over ten years		2,480,500
Debt securities, amortized cost		15,727,143	$ 14,898,522
Short-term investments due in one year or less, fair value		1,142,258	714,208
Mortgage and asset-backed securities, fair value	[1]	5,915,900
Debt securities with maturity dates, fair value:
One year or less		628,700
Over one through five years		3,772,700
Over five through ten years		3,106,400
Over ten years		2,637,900
Total debt securities, fair value		$ 16,061,560	$ 15,618,470
[1]	Mortgage and asset-backed securities by their nature do not generally have single maturity dates.

Net Investment Income (Detail)

Net Investment Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Investment Income, Net [Abstract]
Interest income	$ 397,700	$ 443,100	$ 499,500
Dividend income	79,400	28,000	37,900
Investment expenses	(26,500)	(28,600)	(28,900)
Partnerships and other investment results	89,800	48,400	41,700
Net investment income	$ 540,445	$ 490,856	$ 550,241

Investments - Additional Inform

Investments - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)Investment	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Investments [Line Items]
Proceeds from sale of equity securities	$ 633,111	$ 1,659,234	$ 2,296,371
Proceeds from sale of debt securities	$ 3,582,319	4,042,915	3,645,307
Securities impairment test description	Alleghany continually monitors the difference between amortized cost and the estimated fair value of its debt investments. The analysis of a security’s decline in value is performed in its functional currency. Debt securities in an unrealized loss position are evaluated for credit losses if they meet any of the following criteria: (i) they are trading at a discount of at least 20 percent to amortized cost and have a credit rating below investment grade or are not rated; (ii) there has been a negative credit or news event with respect to the issuer that could indicate the existence of a credit loss; or (iii) Alleghany intends to sell, or it is more likely than not that Alleghany will sell, the debt security before recovery of its amortized cost basis. If Alleghany intends to sell, or it is more likely than not that Alleghany will sell, a debt security before recovery of its amortized cost basis, the total amount of the unrealized loss position is recognized as a credit loss in earnings. To the extent that a debt security that is in an unrealized loss position is not impaired based on the preceding, Alleghany will consider a debt security to be impaired when it believes it to be probable that Alleghany will not be able to collect the entire amortized cost basis. For debt securities in an unrealized loss position as of the end of each quarter, Alleghany develops a best estimate of the present value of expected cash flows. If the results of the cash flow analysis indicate that Alleghany will not recover the full amount of its amortized cost basis in the debt security, Alleghany records a credit loss in earnings equal to the difference between the present value of expected cash flows and the amortized cost basis of the debt security. If applicable, the difference between the total unrealized loss position on the debt security and the total loss recognized in earnings is the non-credit related portion, which is recorded as a component of other comprehensive income.In developing the cash flow analyses for debt securities, Alleghany considers various factors for the different categories of debt securities. For municipal bonds, Alleghany takes into account the taxing power of the issuer, source of revenue, credit risk and enhancements and pre-refunding. For mortgage and asset-backed securities, Alleghany discounts its best estimate of future cash flows at an effective rate equal to the original effective yield of the security or, in the case of floating rate securities, at the current coupon. Alleghany’s models include assumptions about prepayment speeds, default and delinquency rates, underlying collateral (if any), credit ratings, credit enhancements and other observable market data. For corporate bonds, Alleghany reviews business prospects, credit ratings and available information from asset managers and rating agencies for individual securities.
Changes in allowance for credit losses (reduction) for available for sale securities	$ (2,077)	8,029
Change in allowance for credit losses on available for sale securities			$ 19,660
Other invested assets	557,800	465,153
Commercial mortgage loans	475,860	670,239
Commercial mortgage loan investments in default or in arrears	$ 0
Commercial mortgage loan principal amount description	The principal amounts of the loans were no more than approximately two-thirds of the property’s appraised value at the time the loans were made and the estimated fair value of underlying collateral was approximately double that of the commercial mortgage loan portfolio carrying value as of December 31, 2021.
Statutory deposits	$ 2,300,000
Minimum
Investments [Line Items]
Term of commercial mortgage loans	2 years
Maximum
Investments [Line Items]
Term of commercial mortgage loans	10 years
Pillar Capital Holdings Limited And Managed Funds
Investments [Line Items]
Other invested assets	$ 156,400	$ 173,300
Debt Securities
Investments [Line Items]
Number of securities in an unrealized loss position | Investment	1,644
Number of securities in an unrealized loss position continuously for 12 months or more | Investment	186

Summary of Changes in Fair Valu

Summary of Changes in Fair Value of Equity Securities (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Equity Securities, FV-NI, Gain (Loss) [Abstract]
Change in the fair value of equity securities sold during the period	$ 3,200	$ (147,400)	$ 59,100
Change in the fair value of equity securities held at the end of the period	503,600	36,900	650,600
Change in the fair value of equity securities	$ 506,769	$ (110,459)	$ 709,695

Amounts of Gross Realized Capit

Amounts of Gross Realized Capital Gains and Gross Realized Capital Losses (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Gross realized capital gains	$ 84,200	[1]	$ 134,600	[2]	$ 62,400
Gross realized capital losses	(16,800)		(131,500)	[3]	(68,900)	[4]
Net realized capital gains	$ 67,493		$ 3,098		$ (6,551)
[1]	Gross realized capital gains in 2021 include a $ 3.1 million realized gain on the remeasurement of fair value of certain outstanding contingent consideration liabilities by Alleghany Capital in connection with its 2018 acquisition of Concord (the "2021 Concord Remeasurement Gain")
[2]	Gross realized capital gains in 2020 include (i) a $ 15.0 million realized gain on a partial settlement and remeasurement of fair value of certain outstanding contingent consideration liabilities by Alleghany Capital in connection with its 2018 acquisition of Concord (the “2020 Concord Settlement Gain”); (ii) a gain of $ 16.3 million on April 1, 2020 in connection with Alleghany Capital’s acquisition of an a dditional approximately 55 percent of Wilbert that it did not previously own, and the remeasurement of its pre-existing approximately 45 percent equity ownership to estimated fair value (the “Wilbert Remeasurement Gain”); and (iii) a $ 5.0 million realized gain from a reduction of certain contingent consideration liabilities at the PCT-level in connection with its acquisition of a provider of high-performance solid carbide end mills in June 2019.
[3]	Gross realized capital losses in 2020 include (i) impairment charges of $ 76.0 million from write-downs of SORC oil field assets prior to SORC’s December 31, 2020 sale; and (ii) a $ 7.1 million realized loss as a result of an early redemption of debt (see Note 8 for additional information on this early redemption).
[4]	Gross realized capital losses in 2019 include $ 38.4 million from a derivative. Specifically, on July 18, 2019, AIHL purchased an exchange-traded equity derivative index put option (the “Put Option”) for $ 38.4 million to hedge the downside equity market risk on approximately $ 1.0 billion of Alleghany’s equity portfolio. The Put Option did not qualify for hedge accounting. The Put Option expired worthless on December 31, 2019, and the resulting $ 38.4 million decline in value of the Put Option was recorded as a gross realized capital loss. Gross realized capital losses in 2019 also includes a $ 13.6 million loss from the December 2019 sale of a privately held investment accounted for under the equity method.

Amounts of Gross Realized Cap_2

Amounts of Gross Realized Capital Gains and Gross Realized Capital Losses (Parenthetical) (Detail) - USD ($) $ in Thousands	Apr. 01, 2020	Jul. 18, 2019	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2020
Investments [Line Items]
Realized loss on early redemption of debt					$ (7,100)
Pre tax loss from sale of privately held investment accounted under equity method			$ 13,600
Net realized capital gains				$ 67,493	3,098	$ (6,551)
Insurance Segment | Put Option | Equity Contract
Investments [Line Items]
Gross realized capital loss from derivative						$ 38,400
Cost of put option		$ 38,400
Portion of equity portfolio hedged for downside equity market risk		$ 1,000,000
Concord | Alleghany Capital Corporation
Investments [Line Items]
Gain on partial settlement and remeasurement of fair value of outstanding contingent consideration liabilities				$ 3,100	15,000
Wilbert Funeral Services, Inc
Investments [Line Items]
Gain on remeasurement of pre-existing equity ownership to estimated fair value	$ 16,300
Equity interest percentage acquired	55.00%
Equity interest percentage							45.00%
Precision Cutting Technologies, Inc
Investments [Line Items]
Realized gain on reduction of contingent consideration liabilities					5,000
Stranded Oil Resources Corporation
Investments [Line Items]
Write-down of oil field assets					$ 76,000

Allowance for Credit Losses on

Allowance for Credit Losses on Available for Sale Securities (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021		Dec. 31, 2020
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance		$ 2,579	[1]	$ 0
Change in allowance for credit losses on available for sale securities		(2,077)		8,029
Charge-offs		0		(5,400)
Recoveries		0		0
Ending balance	[1]	502		2,579
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance		$ 0		0
Ending balance				$ 0
[1]	See Note 1(r) for additional information regarding Alleghany’s adoption of new credit loss accounting guidance.

Summary of Rating of Debt secur

Summary of Rating of Debt securities (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		$ 16,061,560	$ 15,618,470
Percentage of debt securities, before allowance for credit losses		100.00%
AAA / Aaa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		$ 2,406,000
Percentage of debt securities, before allowance for credit losses		15.00%
AA / Aa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		$ 7,544,400
Percentage of debt securities, before allowance for credit losses		47.00%
A
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		$ 3,259,900
Percentage of debt securities, before allowance for credit losses		20.30%
BBB / Baa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		$ 2,402,400
Percentage of debt securities, before allowance for credit losses		14.90%
Below BBB / Baa or Not Rated
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value	[1]	$ 448,900
Percentage of debt securities, before allowance for credit losses	[1]	2.80%
U.S. Government obligations
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		$ 2,050,700	1,360,100
U.S. Government obligations | AAA / Aaa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		1,400
U.S. Government obligations | AA / Aa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		2,049,300
U.S. Government obligations | A
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		0
U.S. Government obligations | BBB / Baa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		0
U.S. Government obligations | Below BBB / Baa or Not Rated
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value	[1]	0
Municipal bonds
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		2,535,900	2,656,800
Municipal bonds | AAA / Aaa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		219,000
Municipal bonds | AA / Aa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		1,756,300
Municipal bonds | A
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		469,200
Municipal bonds | BBB / Baa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		83,300
Municipal bonds | Below BBB / Baa or Not Rated
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value	[1]	8,100
Foreign government obligations
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		854,900	879,500
Foreign government obligations | AAA / Aaa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		376,500
Foreign government obligations | AA / Aa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		389,300
Foreign government obligations | A
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		87,800
Foreign government obligations | BBB / Baa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		1,100
Foreign government obligations | Below BBB / Baa or Not Rated
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value	[1]	200
U.S. corporate bonds
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		3,477,300	3,545,700
U.S. corporate bonds | AAA / Aaa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		13,900
U.S. corporate bonds | AA / Aa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		165,600
U.S. corporate bonds | A
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		1,442,900
U.S. corporate bonds | BBB / Baa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		1,485,100
U.S. corporate bonds | Below BBB / Baa or Not Rated
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value	[1]	369,800
Foreign corporate bonds
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		1,226,900	1,323,100
Foreign corporate bonds | AAA / Aaa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		184,700
Foreign corporate bonds | AA / Aa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		69,100
Foreign corporate bonds | A
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		564,100
Foreign corporate bonds | BBB / Baa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		372,800
Foreign corporate bonds | Below BBB / Baa or Not Rated
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value	[1]	36,200
RMBS
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value	[2]	2,009,000	2,611,400
RMBS | AAA / Aaa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		4,200
RMBS | AA / Aa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		1,998,400
RMBS | A
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		0
RMBS | BBB / Baa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		800
RMBS | Below BBB / Baa or Not Rated
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value	[1]	5,600
CMBS
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		905,900	890,300
CMBS | AAA / Aaa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		324,200
CMBS | AA / Aa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		355,400
CMBS | A
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		218,600
CMBS | BBB / Baa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		7,700
CMBS | Below BBB / Baa or Not Rated
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value	[1]	0
Other asset-backed securities
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value	[3]	3,001,000	$ 2,351,600
Other asset-backed securities | AAA / Aaa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		1,282,100
Other asset-backed securities | AA / Aa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		761,000
Other asset-backed securities | A
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		477,300
Other asset-backed securities | BBB / Baa
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value		451,600
Other asset-backed securities | Below BBB / Baa or Not Rated
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities, fair value	[1]	$ 29,000
[1]	Consists of $ 140.8 million of securities rated BB / Ba, $ 203.5 million of securities rated B, $ 32.0 million of securities rated CCC, $ 0.5 million of securities rated CC, $ 3.1 million of securities rated below CC and $ 69.0 million of not rated securities.
[2]	Primarily includes government agency pass-through securities guaranteed by a government agency or government sponsored enterprise, among other types of RMBS.
[3]	Includes $ 1,320.4 million and $ 878.4 million of collateralized loan obligations as of December 31, 2021 and 2020 , respectively.

Summary of Rating of Debt sec_2

Summary of Rating of Debt securities (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	$ 16,061,560	$ 15,618,470
BB / Ba
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	140,800
B
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	203,500
CCC
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	32,000
CC
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	500
Below CC
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	3,100
Not rated securities
Financing Receivable Allowance For Credit Losses [Line Items]
Debt securities	$ 69,000

Gross Unrealized Losses and Rel

Gross Unrealized Losses and Related Fair Values for AFS Securities before an Allowance for Credit Losses Grouped by Duration of Time in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Securities, less than 12 months, fair value	$ 5,968.9	$ 1,463.8
Securities, less than 12 months, gross unrealized losses	75.4	27.8
Securities, 12 months or more, fair value	695.1	560
Securities, 12 months or more, gross unrealized losses	23.4	11.8
Total, fair value	6,664	2,023.8
Total, gross unrealized losses	98.8	39.6
U.S. Government obligations
Schedule of Available-for-sale Securities [Line Items]
Securities, less than 12 months, fair value	1,196.3	255.9
Securities, less than 12 months, gross unrealized losses	11.1	1.5
Securities, 12 months or more, fair value	122.1	0
Securities, 12 months or more, gross unrealized losses	5.8	0
Total, fair value	1,318.4	255.9
Total, gross unrealized losses	16.9	1.5
Municipal bonds
Schedule of Available-for-sale Securities [Line Items]
Securities, less than 12 months, fair value	267.3	36.2
Securities, less than 12 months, gross unrealized losses	4	0.6
Securities, 12 months or more, fair value	2.8	0
Securities, 12 months or more, gross unrealized losses	0.1	0
Total, fair value	270.1	36.2
Total, gross unrealized losses	4.1	0.6
Foreign government obligations
Schedule of Available-for-sale Securities [Line Items]
Securities, less than 12 months, fair value	350	132.8
Securities, less than 12 months, gross unrealized losses	5.3	0.5
Securities, 12 months or more, fair value	73.2	0
Securities, 12 months or more, gross unrealized losses	2.6	0
Total, fair value	423.2	132.8
Total, gross unrealized losses	7.9	0.5
U.S. corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Securities, less than 12 months, fair value	814.2	168.5
Securities, less than 12 months, gross unrealized losses	12.4	3.5
Securities, 12 months or more, fair value	79.3	2.4
Securities, 12 months or more, gross unrealized losses	5.9	0
Total, fair value	893.5	170.9
Total, gross unrealized losses	18.3	3.5
Foreign corporate bonds
Schedule of Available-for-sale Securities [Line Items]
Securities, less than 12 months, fair value	460.6	36.4
Securities, less than 12 months, gross unrealized losses	8.3	0.2
Securities, 12 months or more, fair value	34.6	19.5
Securities, 12 months or more, gross unrealized losses	1.3	0.5
Total, fair value	495.2	55.9
Total, gross unrealized losses	9.6	0.7
RMBS
Schedule of Available-for-sale Securities [Line Items]
Securities, less than 12 months, fair value	1,072.8	152.6
Securities, less than 12 months, gross unrealized losses	20.5	0.5
Securities, 12 months or more, fair value	50.7	0.4
Securities, 12 months or more, gross unrealized losses	1.3	0
Total, fair value	1,123.5	153
Total, gross unrealized losses	21.8	0.5
CMBS
Schedule of Available-for-sale Securities [Line Items]
Securities, less than 12 months, fair value	197.8	133.5
Securities, less than 12 months, gross unrealized losses	0.6	7.6
Securities, 12 months or more, fair value	40.9	3.8
Securities, 12 months or more, gross unrealized losses	1.6	0
Total, fair value	238.7	137.3
Total, gross unrealized losses	2.2	7.6
Other asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Securities, less than 12 months, fair value	1,609.9	547.9
Securities, less than 12 months, gross unrealized losses	13.2	13.4
Securities, 12 months or more, fair value	291.5	533.9
Securities, 12 months or more, gross unrealized losses	4.8	11.3
Total, fair value	1,901.4	1,081.8
Total, gross unrealized losses	$ 18	$ 24.7

Allowance for Credit Losses o_2

Allowance for Credit Losses on Commercial Mortgage Loans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	$ 1.4	$ 0
Provision for credit losses	(1.2)	0.6
Charge-offs	0	0
Recoveries	0	0
Ending balance	0.2	1.4
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Financing Receivable Allowance For Credit Losses [Line Items]
Beginning balance	$ 0	0.8
Ending balance		$ 0

Reinsurance Recoverables After

Reinsurance Recoverables After Allowance for Credit Losses (Detail) - USD ($) $ in Thousands		Dec. 31, 2021		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Insurance [Abstract]
Reinsurance recoverables on paid losses		$ 173,100		$ 85,300
Ceded outstanding loss and LAE	[2]	2,026,100	[1]	1,703,700	$ 1,583,900	$ 1,857,400
Reinsurance recoverables, before allowance for credit losses		2,199,200		1,789,000
Allowance for credit losses		(3,200)		(7,900)	$ 0
Total		$ 2,195,975		$ 1,781,096
[1]	Includes unallocated LAE, which aggregate t o 1.0 perce nt of gross loss and LAE reserves as of December 31, 2021 . Net loss and LAE reserves by component are shown in the preceding tables, and consolidated gross loss and LAE reserves is presented in the consolidated balance sheets.
[2]	Reinsurance recoverables in this table include only ceded loss and LAE reserves.

Information Regarding Concentra

Information Regarding Concentration of Reinsurance Recoverables and The Ratings Profile of Our Reinsurers (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Ceded Credit Risk [Line Items]
Reinsurance recoverables, before allowance for credit losses		$ 2,199,200	$ 1,789,000
Allowance for credit losses		(3,200)	(7,900)	$ 0
Reinsurance recoverables		2,195,975	$ 1,781,096
Reinsurance Recoverable | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables, before allowance for credit losses	[1],[2]	2,199,200
Allowance for credit losses	[2]	(3,200)
Reinsurance recoverables	[2]	$ 2,196,000
Reinsurance recoverable as percentage of total reinsurance recoverables	[1],[2]	100.00%
Syndicates at Lloyd's of London | A (Excellent) | Reinsurance Recoverable | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables, before allowance for credit losses	[2],[3]	$ 154,500
Reinsurance recoverable as percentage of total reinsurance recoverables	[2],[3]	7.00%
Kane SAC Ltd, Rondout Segregated Account | Not Rated | Reinsurance Recoverable | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables, before allowance for credit losses	[2],[3],[4]	$ 154,300
Reinsurance recoverable as percentage of total reinsurance recoverables	[2],[3],[4]	7.00%
PartnerRe Limited | A (Excellent) | Reinsurance Recoverable | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables, before allowance for credit losses	[2],[3]	$ 142,700
Reinsurance recoverable as percentage of total reinsurance recoverables	[2],[3]	6.50%
RenaissanceRe Holdings Ltd | A+ (Superior) | Reinsurance Recoverable | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables, before allowance for credit losses	[2],[3]	$ 135,500
Reinsurance recoverable as percentage of total reinsurance recoverables	[2],[3]	6.20%
Fairfax Financial Holdings Ltd | A (Excellent) | Reinsurance Recoverable | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables, before allowance for credit losses	[2],[3]	$ 124,400
Reinsurance recoverable as percentage of total reinsurance recoverables	[2],[3]	5.70%
Swiss Reinsurance Company | A+ (Superior) | Reinsurance Recoverable | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables, before allowance for credit losses	[2],[3]	$ 99,200
Reinsurance recoverable as percentage of total reinsurance recoverables	[2],[3]	4.50%
Integral Reinsurance Ltd | Not Rated | Reinsurance Recoverable | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables, before allowance for credit losses	[2],[3],[4]	$ 97,400
Reinsurance recoverable as percentage of total reinsurance recoverables	[2],[3],[4]	4.40%
Chubb Ltd. | A++ (Superior) | Reinsurance Recoverable | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables, before allowance for credit losses	[2],[3]	$ 79,300
Reinsurance recoverable as percentage of total reinsurance recoverables	[2],[3]	3.60%
W.R. Berkley Corporation | A+ (Superior) | Reinsurance Recoverable | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables, before allowance for credit losses	[2],[3]	$ 77,000
Reinsurance recoverable as percentage of total reinsurance recoverables	[2],[3]	3.50%
SiriusPoint Ltd. | A- (Excellent) | Reinsurance Recoverable | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables, before allowance for credit losses	[2],[3]	$ 73,600
Reinsurance recoverable as percentage of total reinsurance recoverables	[2],[3]	3.30%
All other reinsurers | Reinsurance Recoverable | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables, before allowance for credit losses	[2]	$ 1,061,300
Reinsurance recoverable as percentage of total reinsurance recoverables	[2]	48.30%
Ceded Credit Risk, Secured | Reinsurance Recoverable | Reinsurer Concentration Risk
Ceded Credit Risk [Line Items]
Reinsurance recoverables	[2],[4]	$ 967,700
Reinsurance recoverable as percentage of total reinsurance recoverables	[2],[4]	44.00%
[1]	Approximately 66 percent of Alleghany’s reinsurance recoverables balance as of December 31, 2021 was due from reinsurers having an A.M. Best Company, Inc. financial strength rating of A (Excellent) or higher, with a majority of the other reinsurance recoverables being secured by funds held, trust agreements or letters of credit.
[2]	Reinsurance recoverables reflect amounts due from one or more reinsurance subsidiaries of the listed company.
[3]	Represents the A.M. Best Company, Inc. financial strength rating for the applicable reinsurance subsidiary or subsidiaries from which the reinsurance recoverable is due.
[4]	Represents reinsurance recoverables secured by funds held, trust agreements or letters of credit.

Information Regarding Concent_2

Information Regarding Concentration of Reinsurance Recoverables and The Ratings Profile of Our Reinsurers (Parenthetical) (Detail) - Reinsurance Recoverable - Reinsurer Concentration Risk	12 Months Ended
	Dec. 31, 2021
Ceded Credit Risk [Line Items]
Reinsurance recoverable as percentage of total reinsurance recoverables	100.00%	[1],[2]
Reinsurers Rated A Or Higher
Ceded Credit Risk [Line Items]
Reinsurance recoverable as percentage of total reinsurance recoverables	66.00%
[1]	Approximately 66 percent of Alleghany’s reinsurance recoverables balance as of December 31, 2021 was due from reinsurers having an A.M. Best Company, Inc. financial strength rating of A (Excellent) or higher, with a majority of the other reinsurance recoverables being secured by funds held, trust agreements or letters of credit.
[2]	Reinsurance recoverables reflect amounts due from one or more reinsurance subsidiaries of the listed company.

Allowance for Credit Losses o_3

Allowance for Credit Losses on Reinsurance Recoverables (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Allowance for Credit Losses
Beginning balance	$ 7.9	$ 0
Provision for credit losses	(4.7)	4.6
Charge-offs	0	0
Recoveries	0	0
Ending balance	3.2	7.9
Accounting Standards Update 2016-13 | Cumulative Effect, Period of Adoption, Adjusted Balance
Allowance for Credit Losses
Beginning balance	$ 0	3.3
Ending balance		$ 0

Reinsurance Ceded - Additional

Reinsurance Ceded - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017
Effects Of Reinsurance [Line Items]
Ceded loss and loss adjustment expenses incurred	$ 866.6	$ 562.7	$ 407.7
AIHL Re Limited Liability Company reinsurance of CapSpecialty Incorporated | Alleghany Corporation | Financial Guarantee
Effects Of Reinsurance [Line Items]
Guarantee amount related to reinsurance agreement	50
AIHL Re Limited Liability Company reinsurance of Pacific Compensation Insurance Company | Alleghany Corporation | Financial Guarantee
Effects Of Reinsurance [Line Items]
Guarantee amount related to reinsurance agreement				$ 150
CapSpecialty Incorporated | AIHL Re Limited Liability Company reinsurance of CapSpecialty Incorporated
Effects Of Reinsurance [Line Items]
Reinsurance coverage before co-participation	$ 50
Reinsurance Segment
Effects Of Reinsurance [Line Items]
Retrocession protection term	1 year
Term of catastrophe bonds	4 years

Property and Casualty Premiums

Property and Casualty Premiums Written and Earned (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Premiums Written and Earned [Abstract]
Gross premiums written – direct	$ 2,704,300	$ 2,214,600	$ 1,800,300
Gross premiums written – assumed	5,834,500	5,114,800	4,856,100
Ceded premiums written	(1,389,400)	(985,000)	(904,700)
Net premiums written	7,149,400	6,344,400	5,751,700
Gross premiums earned – direct	3,005,700	2,370,400	2,114,100
Gross premiums earned – assumed	5,364,800	4,582,900	4,268,800
Ceded premiums earned	(1,272,800)	(953,100)	(904,800)
Net premiums earned	$ 7,097,653	$ 6,000,161	$ 5,478,143

Activity in the Liability for L

Activity in the Liability for Loss and Loss Adjustment Expense (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021		Dec. 31, 2020	Dec. 31, 2019
Activity in liability for loss and loss adjustment expense
Reserves as of January 1		$ 12,970,626		$ 11,928,400	$ 12,250,300
Less: reinsurance recoverables	[1]	1,703,700		1,583,900	1,857,400
Net reserves as of January 1		11,266,900		10,344,500	10,392,900
Other adjustments		100		(4,000)	(2,300)
Incurred loss and LAE, net of reinsurance, related to:
Current year		5,084,600		4,559,900	3,871,100
Prior years		(249,700)		(220,800)	(184,700)
Total incurred loss and LAE, net of reinsurance		4,834,935		4,339,046	3,686,435
Paid loss and LAE, net of reinsurance, related to:
Current year	[2]	1,032,800		931,700	884,600
Prior years	[2]	2,655,900		2,571,800	2,839,900
Total paid loss and LAE, net of reinsurance	[2]	3,688,700		3,503,500	3,724,500
Foreign currency exchange rate effect		(81,700)		90,800	(8,000)
Net reserves as of December 31		12,331,500	[3]	11,266,900	10,344,500
Reinsurance recoverables as of December 31	[1]	2,026,100	[3]	1,703,700	1,583,900
Reserves as of December 31		$ 14,357,635	[3]	$ 12,970,626	$ 11,928,400
[1]	Reinsurance recoverables in this table include only ceded loss and LAE reserves.
[2]	Includes paid loss and LAE, net of reinsurance, related to commutations.
[3]	Includes unallocated LAE, which aggregate t o 1.0 perce nt of gross loss and LAE reserves as of December 31, 2021 . Net loss and LAE reserves by component are shown in the preceding tables, and consolidated gross loss and LAE reserves is presented in the consolidated balance sheets.

Liability for Loss and LAE - Ad

Liability for Loss and LAE - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses incurred, net of reinsurance	$ 4,834,935	$ 4,339,046	$ 3,686,435
COVID-19 Global Pandemic
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses incurred, net of reinsurance		415,200
Hurricane Laura
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses incurred, net of reinsurance		114,200
Hurricane Sally
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses incurred, net of reinsurance		92,600
Earthquakes | Puerto Rico
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses incurred, net of reinsurance		$ 19,100
Hurricane Ida
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses incurred, net of reinsurance	268,700
Winter Storm Uri and Other Storms
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses incurred, net of reinsurance	252,800
Severe Flooding in Northwestern and Central Europe
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses incurred, net of reinsurance	125,200
Midwest Tornadoes
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses incurred, net of reinsurance	$ 18,500

(Favorable) Unfavorable Prior A

(Favorable) Unfavorable Prior Accident Year Loss Reserve Development (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Claims Development [Line Items]
Claims incurred related to prior years		$ (249.7)		$ (220.8)		$ (184.7)
Reinsurance Segment
Claims Development [Line Items]
Claims incurred related to prior years		(249.6)		(206.9)		(195.8)
Reinsurance Segment | Property
Claims Development [Line Items]
Claims incurred related to prior years		(23.8)		(76.9)		(46.2)
Reinsurance Segment | Property | Catastrophe Events (Excluding Pandemic)
Claims Development [Line Items]
Claims incurred related to prior years		(35.5)	[1]	(43.3)	[2]	(6.8)	[3]
Reinsurance Segment | Property | Pandemic
Claims Development [Line Items]
Claims incurred related to prior years		62.6		0		0
Reinsurance Segment | Property | Non-catastrophe
Claims Development [Line Items]
Claims incurred related to prior years		(50.9)	[4]	(33.6)	[5]	(39.4)	[6]
Reinsurance Segment | Casualty & Specialty
Claims Development [Line Items]
Claims incurred related to prior years		(225.8)		(130)		(149.6)
Reinsurance Segment | Casualty & Specialty | Catastrophe Events (Excluding Pandemic)
Claims Development [Line Items]
Claims incurred related to prior years		(0.4)		(5.9)		(4.4)
Reinsurance Segment | Casualty & Specialty | Pandemic
Claims Development [Line Items]
Claims incurred related to prior years		(48.9)		0		0
Reinsurance Segment | Casualty & Specialty | Non-catastrophe
Claims Development [Line Items]
Claims incurred related to prior years		(176.5)	[7]	(124.1)	[8]	(145.2)	[9]
Insurance Segment | RSUI
Claims Development [Line Items]
Claims incurred related to prior years		(6.1)		(12.8)		(17.5)
Insurance Segment | RSUI | Casualty Insurance
Claims Development [Line Items]
Claims incurred related to prior years		5	[10]	1.8	[11]	(16.3)	[12]
Insurance Segment | RSUI | Property and Other Insurance
Claims Development [Line Items]
Claims incurred related to prior years		(11.1)	[13]	(14.6)	[14]	(1.2)	[15]
Insurance Segment | CapSpecialty Incorporated
Claims Development [Line Items]
Claims incurred related to prior years		6		(1.1)		28.6
Insurance Segment | CapSpecialty Incorporated | Ongoing Lines Of Business
Claims Development [Line Items]
Claims incurred related to prior years		6.1	[16]	(2)	[17]	26.1	[18]
Insurance Segment | CapSpecialty Incorporated | Terminated Program Business
Claims Development [Line Items]
Claims incurred related to prior years	[19]	(0.1)		0.9		3
Insurance Segment | CapSpecialty Incorporated | Asbestos and Environmental
Claims Development [Line Items]
Claims incurred related to prior years		$ 0		$ 0		$ (0.5)
[1]	Primarily reflects favorable prior accident year loss reserve development related to catastrophic events in the 2018 accident year, partially offset by unfavorable prior accident year loss reserve development related to Hurricane Laura and Sally in the 2020 accident year.
[2]	Primarily reflects favorable prior accident year loss reserve development related to Typhoon Hagibis in the 2019 accident year and wildfires in California in the 2017 and 2018 accident years, partially offset by unfavorable prior accident year loss reserve development related to Hurricane Irma in the 2017 accident year and Typhoon Faxai in the 2019 accident year.
[3]	Primarily reflects favorable prior accident year loss reserve development related to wildfires in California in the 2018 accident year, partially offset by unfavorable prior accident year loss reserve development related to Typhoon Jebi in the 2018 accident year and Hurricane Irma in the 2017 accident year.
[4]	Primarily reflects favorable prior accident year loss reserve development in the 2020 accident year.
[5]	Primarily reflects favorable prior accident year loss reserve development in the 2017 accident year.
[6]	Primarily reflects favorable prior accident year loss reserve development in the 2016 and 2017 accident years, partially offset by unfavorable prior accident year loss reserve development in the 2018 accident year.
[7]	Primarily reflects favorable prior accident year loss reserve development in the shorter-tailed lines of business in the 2020 accident year and in both the longer- and shorter-tailed lines of business in the 2015 and earlier accident years, partially offset by unfavorable prior accident year loss reserve development in the longer-tailed lines of business in the 2016 to 2018 accident years.
[8]	Primarily reflects favorable prior accident year loss reserve development in the longer-tailed casualty lines of business in the 2014 and prior accident years and, to a lesser extent, shorter-tailed lines of business in the 2014 and prior accident years, partially offset by unfavorable prior accident year loss reserve development in the marine and aviation lines of business in the 2018 accident year.
[9]	Primarily reflects favorable prior accident year loss reserve development in the longer-tailed casualty lines of business in the 2014 and prior accident years and, to a lesser extent, shorter-tailed lines of business in the 2014 and prior accident years, partially offset by unfavorable prior accident year loss reserve development in the marine and aviation lines of business in the 2018 accident year.
[10]	Primarily reflects unfavorable prior accident year loss reserve development in the directors’ and officers’ liability lines of business in the 2012 and 2014 accident years and, to a lesser extent, the general liability and binding authority lines of business in earlier accident years, partially offset by favorable prior accident year loss reserve development in the umbrella/excess lines of business in the 2005 through 2015 accident years.
[11]	Primarily reflects unfavorable prior accident year loss reserve development in the professional liability lines of business in the 2 017 through 2019 accident years, partially offset by favorable prior accident year loss reserve development in the directors’ and officers’ liability and umbrella/excess lines of business in the 2011 through 2015 accident years.
[12]	Primarily reflects favorable prior accident year loss reserve development in the directors’ and officers’ liability and umbrella/excess lines of business in the 2011 through 2015 accident years, partially offset by unfavorable prior accident year loss reserve development in the professional liability lines of business in the 2016 through 2018 accident years.
[13]	Primarily reflects favorable prior accident year loss reserve development related to losses not classified as catastrophes in recent accident years and, to a lesser extent, catastrophes in the 2017, 2018 and 2019 accident years, partially offset by unfavorable prior accident year loss reserve development related to catastrophes in the 2020 accident year.
[14]	Primarily reflects favorable prior accident year loss reserve development related to U.S. catastrophe losses in the 2018 accident year and, to a lesser extent, favorable prior accident year loss reserve development related to the assumed property reinsurance lines of business from catastrophe losses in the 2019 and 2018 accident years.
[15]	Primarily reflects favorable prior accident year loss reserve development related to Superstorm Sandy in the 2012 accident year, Hurricanes Florence and Michael in the 2018 accident year and Hurricanes Harvey and Maria in the 2017 accident year, partially offset by unfavorable prior accident year loss reserve development related to assumed property reinsurance lines of business from both catastrophe and non-catastrophe losses in the 2018 accident year.
[16]	Primarily reflects unfavorable prior accident year loss reserve development in the healthcare, construction liability and other casualty lines of business in the 2015 through 2017 accident years.
[17]	Primarily reflects favorable prior acciden t year loss reserve development in the surety lines of business in recent accident years.
[18]	Primarily reflects unfavorable prior accident loss reserve development related to the professional liability and other casualty lines of business in the 2015 through 2018 accident years.
[19]	Represents certain specialty lines of business written through a program administrator in connection with a terminated program in the 2010 and 2009 accident years and reflects favorable loss emergence compared with loss emergence patterns assumed in earlier periods for such business.

Information About Incurred and

Information About Incurred and Paid Loss and LAE Development - Reinsurance Segment - Property (Detail) - 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
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables		$ 12,331.5	[1]	$ 11,266.9	$ 10,344.5	$ 10,392.9
Reinsurance Segment
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables	[1]	9,701.1
Reinsurance Segment | Property
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables, prior to 2012		19.7
Unpaid loss and LAE, net of reinsurance recoverables	[1]	1,958.3
Reinsurance Segment | Property | Accident Year 2012
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		456.1		454.9	460.3	462.5	$ 469.4	$ 478.1	$ 495.6	$ 530.3	$ 579.1	$ 697.2
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		0
Paid Loss and LAE, Net of Reinsurance		466.6		461.1	460.1	451.2	448	438	416.7	377.8	268.9	$ 90.3
Reinsurance Segment | Property | Accident Year 2013
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		394		394.7	398.1	403.6	406.8	422.1	444.6	470.6	501.2
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		0
Paid Loss and LAE, Net of Reinsurance		403.9		403	401.4	399.7	396.7	389.8	361	277.4	$ 113.1
Reinsurance Segment | Property | Accident Year 2014
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		416.2		419.7	425.1	429.8	435.2	451.3	464.8	496.4
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		0
Paid Loss and LAE, Net of Reinsurance		399.4		398.4	397.3	394	382.9	360	297.6	$ 109.4
Reinsurance Segment | Property | Accident Year 2015
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		295.5		297.9	301.9	306.3	320.6	332	368.8
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		1.4
Paid Loss and LAE, Net of Reinsurance		311.9		308.8	307.6	303.1	278.3	217.7	$ 96
Reinsurance Segment | Property | Accident Year 2016
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		578.1		577.8	587.9	596.7	647.2	684.1
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		2.6
Paid Loss and LAE, Net of Reinsurance		563.9		552.2	535.1	504.8	429.8	$ 210.5
Reinsurance Segment | Property | Accident Year 2017
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		1,114.8		1,127.7	1,148.3	1,179.5	1,174.6
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		20.2
Paid Loss and LAE, Net of Reinsurance		1,039.9		1,023	977.9	818.5	$ 324.5
Reinsurance Segment | Property | Accident Year 2018
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		1,116.8		1,147.8	1,169.4	1,152.7
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		49.1
Paid Loss and LAE, Net of Reinsurance		1,002.3		944.2	811.8	$ 309.5
Reinsurance Segment | Property | Accident Year 2019
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		972.2		981.5	988.7
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		56
Paid Loss and LAE, Net of Reinsurance		793.2		645.5	$ 265.1
Reinsurance Segment | Property | Accident Year 2020
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		1,253.5		1,207.5
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		297.1
Paid Loss and LAE, Net of Reinsurance		732.1		$ 301.1
Reinsurance Segment | Property | Accident Year 2021
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		1,468.1
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		640.3
Paid Loss and LAE, Net of Reinsurance		413.5
Reinsurance Segment | Property | Accident Year 2012 Through 2021
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		8,065.3
Paid Loss and LAE, Net of Reinsurance		$ 6,126.7
[1]	Includes unallocated LAE, which aggregate t o 1.0 perce nt of gross loss and LAE reserves as of December 31, 2021 . Net loss and LAE reserves by component are shown in the preceding tables, and consolidated gross loss and LAE reserves is presented in the consolidated balance sheets.

Information About Incurred an_2

Information About Incurred and Paid Loss and LAE Development - Reinsurance Segment - Casualty & Specialty - Longer-Tailed Lines of Business (Detail) - 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
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables		$ 12,331.5	[1]	$ 11,266.9	$ 10,344.5	$ 10,392.9
Reinsurance Segment
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables	[1]	9,701.1
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables, prior to 2012	[2]	793.5
Unpaid loss and LAE, net of reinsurance recoverables	[1],[2]	5,120.5
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business | Accident Year 2012
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	802.3		819.7	826.4	832.4	$ 829.8	$ 833.1	$ 860.8	$ 875.9	$ 877.5	$ 877.5
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	60.9
Paid Loss and LAE, Net of Reinsurance	[2]	677.8		648.7	624.4	587	521.3	435.7	316.6	201.1	106.8	$ 46.9
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business | Accident Year 2013
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	726.8		740.5	767.4	783	776.7	777.5	799.2	802.2	798.6
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	100.8
Paid Loss and LAE, Net of Reinsurance	[2]	558.8		528.5	494.6	452.7	378	296.4	176.6	85.1	$ 22.2
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business | Accident Year 2014
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	764		771.7	784.8	790.3	793.9	794.3	791.1	801.8
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	126.2
Paid Loss and LAE, Net of Reinsurance	[2]	619.2		580.6	522.7	444.7	342.9	229.6	107.5	$ 29.8
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business | Accident Year 2015
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	798.2		799.6	799.1	793.7	797	799	794.8
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	123
Paid Loss and LAE, Net of Reinsurance	[2]	595.9		536.5	455.8	325.8	205	100.4	$ 32.2
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business | Accident Year 2016
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	862.9		842.2	807.8	787.4	776.8	776.7
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	126
Paid Loss and LAE, Net of Reinsurance	[2]	573.6		491.1	370	242.9	121.8	$ 34.8
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business | Accident Year 2017
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	824		800.1	783.4	765.7	764.4
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	180.3
Paid Loss and LAE, Net of Reinsurance	[2]	447.9		347.5	221.8	110.6	$ 34
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business | Accident Year 2018
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	767.4		752.5	741.6	727.3
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	279.5
Paid Loss and LAE, Net of Reinsurance	[2]	324.7		206.7	104.6	$ 33
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business | Accident Year 2019
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	765.4		761.6	759.7
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	415.2
Paid Loss and LAE, Net of Reinsurance	[2]	202.5		99.7	$ 29
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business | Accident Year 2020
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	952.4		978.1
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	729.1
Paid Loss and LAE, Net of Reinsurance	[2]	127.6		$ 47.2
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business | Accident Year 2021
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	1,239.9
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	1,124
Paid Loss and LAE, Net of Reinsurance	[2]	48.3
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business | Accident Year 2012 Through 2021
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	8,503.3
Paid Loss and LAE, Net of Reinsurance	[2]	$ 4,176.3
[1]	Includes unallocated LAE, which aggregate t o 1.0 perce nt of gross loss and LAE reserves as of December 31, 2021 . Net loss and LAE reserves by component are shown in the preceding tables, and consolidated gross loss and LAE reserves is presented in the consolidated balance sheets.
[2]	Represents the following reinsurance lines of business: directors’ and officers’ liability; errors and omissions liability; general liability; and medical malpractice.

Information About Incurred an_3

Information About Incurred and Paid Loss and LAE Development - Reinsurance Segment - Casualty & Specialty - Shorter-Tailed Lines of Business (Detail) - 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
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables		$ 12,331.5	[1]	$ 11,266.9	$ 10,344.5	$ 10,392.9
Reinsurance Segment
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables	[1]	9,701.1
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables, prior to 2012	[2]	151.6
Unpaid loss and LAE, net of reinsurance recoverables	[1],[2]	2,622.3
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business | Accident Year 2012
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	929.9		933.9	941.4	948.4	$ 958.9	$ 983.9	$ 1,005.5	$ 1,056.8	$ 1,059.9	$ 1,022.3
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	6.4
Paid Loss and LAE, Net of Reinsurance	[2]	880.3		876.1	871.4	860.2	846.5	828.3	792.7	740	614.5	$ 354.8
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business | Accident Year 2013
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	764.5		769.6	780.7	790.3	804.1	823.4	838.4	868.8	850.8
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	9.2
Paid Loss and LAE, Net of Reinsurance	[2]	730.7		723.9	717.5	704.9	685.5	663	613.3	523.5	$ 265.4
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business | Accident Year 2014
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	740.8		752.5	755	772.4	784.3	808.8	833	850.4
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	15.2
Paid Loss and LAE, Net of Reinsurance	[2]	647.8		636.8	627.8	604.6	572.9	523.3	421.1	$ 251.2
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business | Accident Year 2015
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	771.9		776.2	776.7	798.4	784	768.6	763.4
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	17
Paid Loss and LAE, Net of Reinsurance	[2]	669.5		653.2	629.1	577.7	518.7	409.1	$ 218.5
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business | Accident Year 2016
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	1,085.2		1,092.6	1,100.3	1,111.6	1,124.4	1,118
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	25.7
Paid Loss and LAE, Net of Reinsurance	[2]	1,002		973.8	921.3	828.7	685.6	$ 367.2
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business | Accident Year 2017
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	989		994.5	1,026.9	1,046.3	1,095.9
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	49
Paid Loss and LAE, Net of Reinsurance	[2]	909.8		867.6	793.5	639.1	$ 342.8
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business | Accident Year 2018
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	1,267.3		1,270.7	1,266.1	1,255.4
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	89.2
Paid Loss and LAE, Net of Reinsurance	[2]	1,033.3		952.2	774.4	$ 397.9
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business | Accident Year 2019
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	1,400.7		1,411.8	1,408.6
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	159.8
Paid Loss and LAE, Net of Reinsurance	[2]	1,051.3		881.3	$ 462
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business | Accident Year 2020
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	1,335.1		1,408.2
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	325.8
Paid Loss and LAE, Net of Reinsurance	[2]	810.7		$ 418
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business | Accident Year 2021
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	1,333.1
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	729
Paid Loss and LAE, Net of Reinsurance	[2]	411.4
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business | Accident Year 2012 Through 2021
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	10,617.5
Paid Loss and LAE, Net of Reinsurance	[2]	$ 8,146.8
[1]	Includes unallocated LAE, which aggregate t o 1.0 perce nt of gross loss and LAE reserves as of December 31, 2021 . Net loss and LAE reserves by component are shown in the preceding tables, and consolidated gross loss and LAE reserves is presented in the consolidated balance sheets.
[2]	Primarily represents the following reinsurance lines of business: ocean marine and aviation; auto liability; accident & health; mortgage reinsurance; surety; and credit.

Information About Incurred an_4

Information About Incurred and Paid Loss and LAE Development - Insurance Segment - RSUI - Property (Detail) $ in Millions		Dec. 31, 2021USD ($)Claim		Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables		$ 12,331.5	[1]	$ 11,266.9	$ 10,344.5	$ 10,392.9
Insurance Segment
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables	[1]	2,630.4
Insurance Segment | RSUI
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables	[1]	2,063.9
Insurance Segment | RSUI | Property Insurance
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables, prior to 2012		4.3
Unpaid loss and LAE, net of reinsurance recoverables	[1]	415.5
Insurance Segment | RSUI | Property Insurance | Accident Year 2012
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		228.2		228.4	228.3	235.5	$ 236.1	$ 235.1	$ 256.1	$ 258.6	$ 262.5	$ 270.9
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 0.8
Cumulative Number of Reported Claims | Claim	[2]	2,313
Paid Loss and LAE, Net of Reinsurance		$ 222.5		219.4	219.2	216.7	216.2	202.4	193.5	181.9	157.5	$ 62
Insurance Segment | RSUI | Property Insurance | Accident Year 2013
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		153.5		154.4	154.3	152.5	152.4	152.1	150.4	157.2	157.3
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 1.1
Cumulative Number of Reported Claims | Claim	[2]	2,395
Paid Loss and LAE, Net of Reinsurance		$ 152.1		151.8	151.5	148.7	144	141.1	134	118.7	$ 72.7
Insurance Segment | RSUI | Property Insurance | Accident Year 2014
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		153.3		153.4	153.6	153.8	153.7	155.9	166.2	170.7
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 1.1
Cumulative Number of Reported Claims | Claim	[2]	3,094
Paid Loss and LAE, Net of Reinsurance		$ 151.9		151.6	151.3	150.3	148.8	145	133.8	$ 93.2
Insurance Segment | RSUI | Property Insurance | Accident Year 2015
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		140.4		140.2	140.1	141.3	142.6	136.1	140.5
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 1.5
Cumulative Number of Reported Claims | Claim	[2]	3,004
Paid Loss and LAE, Net of Reinsurance		$ 138.5		138	136.5	129.8	120	106.9	$ 70.8
Insurance Segment | RSUI | Property Insurance | Accident Year 2016
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		175.1		175.3	173.9	172.9	170.5	181.4
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 2.4
Cumulative Number of Reported Claims | Claim	[2]	3,368
Paid Loss and LAE, Net of Reinsurance		$ 169.8		167.3	161.2	147.1	127.1	$ 72
Insurance Segment | RSUI | Property Insurance | Accident Year 2017
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		296.7		300	304.1	306.5	330.7
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 10.6
Cumulative Number of Reported Claims | Claim	[2]	3,696
Paid Loss and LAE, Net of Reinsurance		$ 278.5		267.3	253.3	213.3	$ 88.6
Insurance Segment | RSUI | Property Insurance | Accident Year 2018
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		237		256.7	265.7	259.9
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 9.6
Cumulative Number of Reported Claims | Claim	[2]	3,071
Paid Loss and LAE, Net of Reinsurance		$ 216.1		202.9	175.1	$ 62.3
Insurance Segment | RSUI | Property Insurance | Accident Year 2019
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		205.1		200.9	204.3
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 13.9
Cumulative Number of Reported Claims | Claim	[2]	3,343
Paid Loss and LAE, Net of Reinsurance		$ 167.1		145.8	$ 79.8
Insurance Segment | RSUI | Property Insurance | Accident Year 2020
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		365.4		357.2
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 40.6
Cumulative Number of Reported Claims | Claim	[2]	4,257
Paid Loss and LAE, Net of Reinsurance		$ 251.2		$ 118.8
Insurance Segment | RSUI | Property Insurance | Accident Year 2021
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		341.5
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 80.6
Cumulative Number of Reported Claims | Claim	[2]	3,193
Paid Loss and LAE, Net of Reinsurance		$ 137.2
Insurance Segment | RSUI | Property Insurance | Accident Year 2012 Through 2021
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		2,296.2
Paid Loss and LAE, Net of Reinsurance		$ 1,885
[1]	Includes unallocated LAE, which aggregate t o 1.0 perce nt of gross loss and LAE reserves as of December 31, 2021 . Net loss and LAE reserves by component are shown in the preceding tables, and consolidated gross loss and LAE reserves is presented in the consolidated balance sheets.
[2]	Represents claims reported by insured claimants.

Information About Incurred an_5

Information About Incurred and Paid Loss and LAE Development - Insurance Segment - RSUI - Casualty (Detail) $ in Millions		Dec. 31, 2021USD ($)Claim		Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables		$ 12,331.5	[1]	$ 11,266.9	$ 10,344.5	$ 10,392.9
Insurance Segment
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables	[1]	2,630.4
Insurance Segment | RSUI
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables	[1]	2,063.9
Insurance Segment | RSUI | Casualty Insurance
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables, prior to 2012		80.4
Unpaid loss and LAE, net of reinsurance recoverables	[1]	1,648.4
Insurance Segment | RSUI | Casualty Insurance | Accident Year 2012
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		213.4		210.2	221.8	231.9	$ 233.8	$ 238.9	$ 242.8	$ 230.3	$ 226.3	$ 226.3
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 12.3
Cumulative Number of Reported Claims | Claim	[2]	7,726
Paid Loss and LAE, Net of Reinsurance		$ 180.2		178.5	176.1	166.7	159.3	144	125.5	96	38.4	$ 6.8
Insurance Segment | RSUI | Casualty Insurance | Accident Year 2013
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		263.7		261.4	269.6	273.5	279	280.1	277.6	264.8	264.8
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 30.1
Cumulative Number of Reported Claims | Claim	[2]	8,791
Paid Loss and LAE, Net of Reinsurance		$ 222.8		212.9	203.9	191.3	176.6	146.2	103.4	50	$ 10.1
Insurance Segment | RSUI | Casualty Insurance | Accident Year 2014
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		301.7		300.3	310.9	320.3	322.4	321.1	322.7	292
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 29.7
Cumulative Number of Reported Claims | Claim	[2]	10,293
Paid Loss and LAE, Net of Reinsurance		$ 259.7		249.1	234.6	206.5	179.1	130.1	69.5	$ 13
Insurance Segment | RSUI | Casualty Insurance | Accident Year 2015
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		283.6		289.8	291.4	302.2	304.2	300.2	300.2
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 54.9
Cumulative Number of Reported Claims | Claim	[2]	9,489
Paid Loss and LAE, Net of Reinsurance		$ 207.3		196.2	176.5	129.2	96.6	47.3	$ 9
Insurance Segment | RSUI | Casualty Insurance | Accident Year 2016
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		317.8		317.5	312	301.3	293.7	290.7
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 56.7
Cumulative Number of Reported Claims | Claim	[2]	9,110
Paid Loss and LAE, Net of Reinsurance		$ 239.1		220.8	197.8	123.6	69.2	$ 13.7
Insurance Segment | RSUI | Casualty Insurance | Accident Year 2017
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		309.7		311.1	299.1	286.4	282.5
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 79.2
Cumulative Number of Reported Claims | Claim	[2]	9,073
Paid Loss and LAE, Net of Reinsurance		$ 196.2		163.1	115.6	63.6	$ 9.4
Insurance Segment | RSUI | Casualty Insurance | Accident Year 2018
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		312.8		310	301.5	290
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 95.8
Cumulative Number of Reported Claims | Claim	[2]	9,441
Paid Loss and LAE, Net of Reinsurance		$ 165.6		116.8	70.4	$ 13
Insurance Segment | RSUI | Casualty Insurance | Accident Year 2019
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		332.2		332.2	316.9
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 171.9
Cumulative Number of Reported Claims | Claim	[2]	8,792
Paid Loss and LAE, Net of Reinsurance		$ 104.2		57.9	$ 12.9
Insurance Segment | RSUI | Casualty Insurance | Accident Year 2020
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		393.9		393.9
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 291.5
Cumulative Number of Reported Claims | Claim	[2]	7,690
Paid Loss and LAE, Net of Reinsurance		$ 45.7		$ 12.6
Insurance Segment | RSUI | Casualty Insurance | Accident Year 2021
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		470.2
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves		$ 430.8
Cumulative Number of Reported Claims | Claim	[2]	6,909
Paid Loss and LAE, Net of Reinsurance		$ 10.2
Insurance Segment | RSUI | Casualty Insurance | Accident Year 2012 Through 2021
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance		3,199
Paid Loss and LAE, Net of Reinsurance		$ 1,631
[1]	Includes unallocated LAE, which aggregate t o 1.0 perce nt of gross loss and LAE reserves as of December 31, 2021 . Net loss and LAE reserves by component are shown in the preceding tables, and consolidated gross loss and LAE reserves is presented in the consolidated balance sheets.
[2]	Represents claims reported by insured claimants.

Information About Incurred an_6

Information About Incurred and Paid Loss and LAE Development - Insurance Segment - CapSpecialty (Detail) $ in Millions		Dec. 31, 2021USD ($)Claim		Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Dec. 31, 2012USD ($)
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables		$ 12,331.5	[1]	$ 11,266.9	$ 10,344.5	$ 10,392.9
Insurance Segment
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables	[1]	2,630.4
Insurance Segment | CapSpecialty Incorporated
Claims Development [Line Items]
Unpaid loss and LAE, net of reinsurance recoverables, prior to 2012	[2]	4.4
Unpaid loss and LAE, net of reinsurance recoverables	[1],[2]	566.5
Insurance Segment | CapSpecialty Incorporated | Accident Year 2012
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	68.9		69.1	69.1	68.8	$ 68.7	$ 69.7	$ 69.3	$ 66.2	$ 71.8	$ 72.7
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	$ 0.3
Cumulative Number of Reported Claims | Claim	[2],[3]	5,269
Paid Loss and LAE, Net of Reinsurance	[2]	$ 68.2		67.7	67.7	66.5	65	63.3	57.2	46.9	38.6	$ 18.6
Insurance Segment | CapSpecialty Incorporated | Accident Year 2013
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	88.1		87.4	87.4	88.6	87.2	84.4	85.2	81.4	78.7
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	$ 1.1
Cumulative Number of Reported Claims | Claim	[2],[3]	5,181
Paid Loss and LAE, Net of Reinsurance	[2]	$ 86.5		86.1	85.3	84.5	78.6	69.6	62	48	$ 23.4
Insurance Segment | CapSpecialty Incorporated | Accident Year 2014
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	99		97.7	97.6	98.6	100.2	101	102.7	102.8
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	$ 1.4
Cumulative Number of Reported Claims | Claim	[2],[3]	6,050
Paid Loss and LAE, Net of Reinsurance	[2]	$ 95.1		94.2	93.1	89.8	83.1	71.9	56.3	$ 34
Insurance Segment | CapSpecialty Incorporated | Accident Year 2015
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	118		115.2	112.4	109.7	109.2	111.8	111
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	$ 3.3
Cumulative Number of Reported Claims | Claim	[2],[3]	5,666
Paid Loss and LAE, Net of Reinsurance	[2]	$ 110.5		106.7	101.1	88.8	73.5	57.4	$ 30.9
Insurance Segment | CapSpecialty Incorporated | Accident Year 2016
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	136.7		133.4	135	132.7	132.4	129.4
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	$ 4.4
Cumulative Number of Reported Claims | Claim	[2],[3]	6,297
Paid Loss and LAE, Net of Reinsurance	[2]	$ 123.2		116.3	106.1	86.6	64	$ 30.3
Insurance Segment | CapSpecialty Incorporated | Accident Year 2017
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	159.9		156.2	157.6	143.7	147.3
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	$ 9.7
Cumulative Number of Reported Claims | Claim	[2],[3]	6,561
Paid Loss and LAE, Net of Reinsurance	[2]	$ 126.6		116.1	95.1	65.6	$ 30.1
Insurance Segment | CapSpecialty Incorporated | Accident Year 2018
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	180.9		176.5	173.3	164.1
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	$ 22.3
Cumulative Number of Reported Claims | Claim	[2],[3]	6,848
Paid Loss and LAE, Net of Reinsurance	[2]	$ 130.4		102.1	72.4	$ 31.7
Insurance Segment | CapSpecialty Incorporated | Accident Year 2019
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	185.4		188.9	193
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	$ 58.4
Cumulative Number of Reported Claims | Claim	[2],[3]	6,171
Paid Loss and LAE, Net of Reinsurance	[2]	$ 88.5		62.5	$ 29.8
Insurance Segment | CapSpecialty Incorporated | Accident Year 2020
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	209.5		214.9
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	$ 116.8
Cumulative Number of Reported Claims | Claim	[2],[3]	4,917
Paid Loss and LAE, Net of Reinsurance	[2]	$ 60.9		$ 27.8
Insurance Segment | CapSpecialty Incorporated | Accident Year 2021
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	231.7
Incurred But Not Reported Loss and Loss Adjustment Expense Reserves	[2]	$ 183.7
Cumulative Number of Reported Claims | Claim	[2],[3]	4,616
Paid Loss and LAE, Net of Reinsurance	[2]	$ 26.1
Insurance Segment | CapSpecialty Incorporated | Accident Year 2012 Through 2021
Claims Development [Line Items]
Incurred Loss and LAE, net of reinsurance	[2]	1,478.1
Paid Loss and LAE, Net of Reinsurance	[2]	$ 916
[1]	Includes unallocated LAE, which aggregate t o 1.0 perce nt of gross loss and LAE reserves as of December 31, 2021 . Net loss and LAE reserves by component are shown in the preceding tables, and consolidated gross loss and LAE reserves is presented in the consolidated balance sheets.
[2]	The vast majority of the CapSpecialty’s loss and LAE reserves relate to its casualty lines of business.
[3]	Represents claims reported by insured claimants.

Loss and LAE Reserve Summary an

Loss and LAE Reserve Summary and Reconciliation to Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands		Dec. 31, 2021		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Gross Loss and LAE Reserves		$ 14,357,635	[1]	$ 12,970,626	$ 11,928,400	$ 12,250,300
Reinsurance Recoverables on Unpaid Losses	[2]	2,026,100	[1]	1,703,700	1,583,900	1,857,400
Net Loss and LAE Reserves		12,331,500	[1]	$ 11,266,900	$ 10,344,500	$ 10,392,900
Eliminations
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Gross Loss and LAE Reserves	[1]	(76,600)
Reinsurance Recoverables on Unpaid Losses	[1]	(76,600)
Net Loss and LAE Reserves		0
Reinsurance Segment
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Gross Loss and LAE Reserves	[1]	10,748,200
Reinsurance Recoverables on Unpaid Losses	[1]	1,047,100
Net Loss and LAE Reserves	[1]	9,701,100
Reinsurance Segment | Property
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Gross Loss and LAE Reserves	[1]	2,599,400
Reinsurance Recoverables on Unpaid Losses	[1]	641,100
Net Loss and LAE Reserves	[1]	1,958,300
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Gross Loss and LAE Reserves	[1]	5,264,900
Reinsurance Recoverables on Unpaid Losses	[1]	144,400
Net Loss and LAE Reserves	[1],[3]	5,120,500
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Gross Loss and LAE Reserves	[1]	2,883,900
Reinsurance Recoverables on Unpaid Losses	[1]	261,600
Net Loss and LAE Reserves	[1],[4]	2,622,300
Insurance Segment
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Gross Loss and LAE Reserves	[1]	3,686,000
Reinsurance Recoverables on Unpaid Losses	[1]	1,055,600
Net Loss and LAE Reserves	[1]	2,630,400
Insurance Segment | RSUI
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Gross Loss and LAE Reserves	[1]	3,016,200
Reinsurance Recoverables on Unpaid Losses	[1]	952,300
Net Loss and LAE Reserves	[1]	2,063,900
Insurance Segment | RSUI | Property Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Gross Loss and LAE Reserves	[1]	617,000
Reinsurance Recoverables on Unpaid Losses	[1]	201,500
Net Loss and LAE Reserves	[1]	415,500
Insurance Segment | RSUI | Casualty Insurance
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Gross Loss and LAE Reserves	[1]	2,399,200
Reinsurance Recoverables on Unpaid Losses	[1]	750,800
Net Loss and LAE Reserves	[1]	1,648,400
Insurance Segment | CapSpecialty Incorporated
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Gross Loss and LAE Reserves	[1]	669,800
Reinsurance Recoverables on Unpaid Losses	[1]	103,300
Net Loss and LAE Reserves	[1],[5]	$ 566,500
[1]	Includes unallocated LAE, which aggregate t o 1.0 perce nt of gross loss and LAE reserves as of December 31, 2021 . Net loss and LAE reserves by component are shown in the preceding tables, and consolidated gross loss and LAE reserves is presented in the consolidated balance sheets.
[2]	Reinsurance recoverables in this table include only ceded loss and LAE reserves.
[3]	Represents the following reinsurance lines of business: directors’ and officers’ liability; errors and omissions liability; general liability; and medical malpractice.
[4]	Primarily represents the following reinsurance lines of business: ocean marine and aviation; auto liability; accident & health; mortgage reinsurance; surety; and credit.
[5]	The vast majority of the CapSpecialty’s loss and LAE reserves relate to its casualty lines of business.

Loss and LAE Reserve Summary _2

Loss and LAE Reserve Summary and Reconciliation to Consolidated Balance Sheet (Parenthetical) (Detail)	Dec. 31, 2021
Policyholders Account In Life Insurance Business [Abstract]
Unallocated LAE as a percentage of gross loss and LAE reserves	1.00%

Average Historical Loss and LAE

Average Historical Loss and LAE Duration, Net of Reinsurance (Detail)	Dec. 31, 2021
Reinsurance Segment | Property
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year One	28.00%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Two	40.90%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Three	16.90%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Four	6.30%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Five	2.50%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Six	1.20%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Seven	0.60%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Eight	0.90%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Nine	0.20%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Ten	1.20%
Reinsurance Segment | Casualty & Specialty | Longer Tailed Lines of Business
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year One	4.20%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Two	9.00%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Three	13.50%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Four	15.20%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Five	13.60%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Six	10.20%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Seven	7.20%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Eight	4.80%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Nine	3.60%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Ten	3.60%
Reinsurance Segment | Casualty & Specialty | Shorter Tailed Lines Of Business
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year One	33.00%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Two	28.60%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Three	13.50%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Four	7.00%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Five	4.50%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Six	2.70%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Seven	1.60%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Eight	1.20%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Nine	0.70%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Ten	0.50%
Insurance Segment | RSUI | Property Insurance
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year One	34.70%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Two	13.90%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Three	6.10%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Four	3.10%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Five	2.50%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Six	0.80%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Seven	0.60%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Eight	0.10%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Nine	0.20%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Ten	1.30%
Insurance Segment | RSUI | Casualty Insurance
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year One	14.40%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Two	17.80%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Three	17.30%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Four	13.00%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Five	10.70%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Six	6.30%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Seven	5.10%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Eight	3.60%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Nine	3.90%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Ten	1.90%
Insurance Segment | CapSpecialty Incorporated
Short-duration Insurance Contracts, Historical Claims Duration [Line Items]
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year One	19.10%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Two	21.60%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Three	15.60%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Four	13.30%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Five	8.20%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Six	4.60%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Seven	1.90%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Eight	1.10%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Nine	0.30%
Average Annual Percentage Payout of Loss and LAE Incurred, Net of Reinsurance Year Ten	0.70%

Credit Agreements - Additional

Credit Agreements - Additional Information (Detail) - Alleghany Corporation - Revolving Credit Facility - USD ($)	Jul. 31, 2017	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Revolving credit facility, initiation date	Jul. 31, 2017
Line of credit facility, term	5 years
Revolving credit facility, maximum borrowing capacity	$ 300,000,000
Revolving credit facility expiration date	Jul. 31, 2022
Borrowings		$ 0	$ 0	$ 0
Credit facility borrowings outstanding		$ 0

Debt - Additional Information (

Debt - Additional Information (Detail) - USD ($) $ in Thousands	Oct. 14, 2021	Aug. 13, 2021	May 18, 2020	Jan. 15, 2020	Sep. 09, 2014	Jun. 26, 2012	Sep. 20, 2010	Nov. 23, 2009	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Interest paid									$ 94,540	$ 91,832	$ 97,016
Loss on early redemption of debt										(7,100)
Senior Notes and other debt									2,847,199	2,135,946
Operating Segments | Alleghany Capital Corporation Segment
Debt Instrument [Line Items]
Senior Notes and other debt									$ 780,500	556,900
Alleghany Corporation | 2051 Senior Notes
Debt Instrument [Line Items]
Senior notes, face value		$ 500,000
Senior notes, maturity date		Aug. 15, 2051
Senior notes, frequency of interest payment									Interest on the 2051 Senior Notes is payable semi-annually in arrears on February 15 and August 15 of each year, commencing February 15, 2022.
Senior notes, interest rate		3.25%
Senior notes, issuance rate		98.60%
Proceeds from issuance of Senior notes		$ 487,500
Senior notes, effective yield		3.32%
Deferred underwriting discount, commission and other expenses		$ 5,700
Alleghany Corporation | 2030 Senior Notes
Debt Instrument [Line Items]
Senior notes, face value			$ 500,000
Senior notes, maturity date			May 15, 2030
Senior notes, frequency of interest payment									Interest on the 2030 Senior Notes is payable semi-annually in arrears on May 15 and November 15 of each year.
Senior notes, interest rate			3.625%
Senior notes, issuance rate			99.90%
Proceeds from issuance of Senior notes			$ 494,800
Senior notes, effective yield			3.64%
Deferred underwriting discount, commission and other expenses			$ 4,600
Alleghany Corporation | 2044 Senior Notes
Debt Instrument [Line Items]
Senior notes, face value					$ 300,000
Senior notes, maturity date					Sep. 15, 2044
Senior notes, frequency of interest payment									Interest on the 2044 Senior Notes is payable semi-annually on March 15 and September 15 of each year.
Senior notes, interest rate					4.90%
Senior notes, issuance rate					99.30%
Proceeds from issuance of Senior notes					$ 294,300
Senior notes, effective yield					5.00%
Alleghany Corporation | 2022 Senior Notes
Debt Instrument [Line Items]
Senior notes, face value						$ 400,000
Senior notes, frequency of interest payment									Interest on the 2022 Senior Notes is payable semi-annually on June 27 and December 27 of each year.
Senior notes, interest rate		4.95%
Senior notes, issuance rate						99.90%
Proceeds from issuance of Senior notes						$ 396,000
Senior notes, effective yield						5.05%
Alleghany Corporation | 2020 Senior Notes
Debt Instrument [Line Items]
Senior notes, face value							$ 300,000
Senior notes, maturity date							Sep. 15, 2020
Senior notes, frequency of interest payment									Interest on the 2020 Senior Notes is payable semi-annually on March 15 and September 15 of each year.
Senior notes, interest rate							5.625%
Senior notes, issuance rate							99.60%
Proceeds from issuance of Senior notes							$ 298,900
Senior notes, effective yield							5.67%
Cost of senior note redemption				$ 312,700
Aggregate principal amount redeemed				300,000
Redemption premium				7,100
Interest paid				$ 5,600
Loss on early redemption of debt										$ (7,100)
Transatlantic Holdings Incorporated | 2039 Notes
Debt Instrument [Line Items]
Senior notes, face value								$ 350,000
Senior notes, maturity date								Nov. 30, 2039
Senior notes, frequency of interest payment									semi-annually
Senior notes, interest rate								8.00%
WWSC Holdings, LLC | Operating Segments | Alleghany Capital Corporation Segment
Debt Instrument [Line Items]
Senior Notes and other debt									$ 83,500
Wilbert Funeral Services, Inc | Operating Segments | Alleghany Capital Corporation Segment
Debt Instrument [Line Items]
Senior Notes and other debt									73,400
Kentucky Trailer | Operating Segments | Alleghany Capital Corporation Segment
Debt Instrument [Line Items]
Senior Notes and other debt									55,300
Piedmont Manufacturing Group, LLC | Operating Segments | Alleghany Capital Corporation Segment
Debt Instrument [Line Items]
Senior Notes and other debt									31,800
Integrated Project Services LLC | Operating Segments | Alleghany Capital Corporation Segment
Debt Instrument [Line Items]
Senior Notes and other debt									162,900
Precision Cutting Technologies, Inc | Operating Segments | Alleghany Capital Corporation Segment
Debt Instrument [Line Items]
Senior Notes and other debt									24,400
Concord | Operating Segments | Alleghany Capital Corporation Segment | Floating Rate Debt Funded by Alleghany Corporation
Debt Instrument [Line Items]
Senior Notes and other debt											$ 33,000
Jazwares, LLC | Operating Segments | Alleghany Capital Corporation Segment
Debt Instrument [Line Items]
Senior Notes and other debt									349,200
Linesight
Debt Instrument [Line Items]
Incremental debt acquired	$ 125,100
Linesight | Integrated Project Services LLC | Operating Segments | Alleghany Capital Corporation Segment
Debt Instrument [Line Items]
Senior Notes and other debt									$ 125,000

Income Tax Expense (Benefit) (D

Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of Provision of Income Taxes [Line Items]
Current	$ 194,100	$ 74,900	$ 170,700
Deferred	87,800	(44,200)	62,700
Income taxes	281,925	30,734	233,435
Federal
Reconciliation of Provision of Income Taxes [Line Items]
Current	141,600	6,900	87,900
Deferred	88,200	(45,800)	62,900
Income taxes	229,800	(38,900)	150,800
State
Reconciliation of Provision of Income Taxes [Line Items]
Current	16,200	9,700	12,000
Deferred	(300)	800	500
Income taxes	15,900	10,500	12,500
Foreign
Reconciliation of Provision of Income Taxes [Line Items]
Current	36,300	58,300	70,800
Deferred	(100)	800	(700)
Income taxes	$ 36,200	$ 59,100	$ 70,100

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Earnings (losses) before income taxes, domestic	$ 1,208.7	$ (21)	$ 952.4
Earnings (losses) before Income Taxes, Foreign	$ 204	178.6	$ 171.2
Foreign tax credit carryforwards expiration beginning year	2028
State net operating loss carry forward	$ 13.2	12.5
Valuation allowance	12.9	$ 12.5
Interest or penalties accrued for uncertain tax positions	$ 0

Difference between Federal Inco

Difference between Federal Income Tax Rate and Effective Income Tax Rate (Detail)		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Federal income tax rate		21.00%	21.00%	21.00%
Foreign tax expense reduced by foreign tax credits		0.60%	6.90%	0.40%
Income subject to dividends-received deduction		(0.30%)	(1.30%)	(0.30%)
Tax-exempt interest		(0.70%)	(6.00%)	(1.00%)
State taxes, net of federal tax benefit		0.90%	4.90%	0.90%
Prior period adjustment		(0.10%)	(2.60%)	0.20%
Other, net	[1]	(1.40%)	(3.40%)	(0.40%)
Effective tax rate		20.00%	19.50%	20.80%
[1]	For 2021, includes the benefit from non-controlling interests, various general business tax credits, partially offset by disallowed expense deductions primarily related to certain executive compensation paid in 2021. For 2020 , includes various general business credits and tax benefits resulting from corporate acquisitions and dispositions, partially offset by disallowed expense deductions primarily related to certain executive compensation paid in 2020.

Tax Effects of Temporary Differ

Tax Effects of Temporary Differences that Give Rise to Significant Portions of Deferred Tax Assets and Deferred Tax Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Loss and LAE reserves	$ 144,500	$ 132,300
Foreign tax credit carry forward	59,200	74,100
Compensation accruals	99,700	87,500
Unearned premiums	114,100	112,200
Allowance for credit losses on available for sale securities	5,200	5,700
State net operating loss carry forward	13,200	12,500
Other	97,800	98,000
Gross deferred tax assets before valuation allowance	533,700	522,300
Valuation allowance	(12,900)	(12,500)
Gross deferred tax assets	520,800	509,800
Deferred tax liabilities:
Net unrealized gains on investments	308,400	294,700
Deferred acquisition costs	127,000	128,400
Purchase accounting adjustments	11,200	11,700
Other	131,200	118,500
Gross deferred tax liabilities	577,800	553,300
Net deferred tax (liabilities)	$ (56,958)	$ (43,547)

Tax Year Returns that Remain Su

Tax Year Returns that Remain Subject to Examination by Major Tax Jurisdiction (Detail)	12 Months Ended
	Dec. 31, 2021
Australia | Earliest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2016
Australia | Latest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2021
Canada | Earliest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2017
Canada | Latest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2021
France | Earliest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2018
France | Latest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2021
GERMANY | Earliest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2019
GERMANY | Latest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2021
HONG KONG | Earliest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2015
HONG KONG | Latest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2021
Japan | Earliest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2019
Japan | Latest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2021
Luxembourg | Earliest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2019
Luxembourg | Latest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2021
SINGAPORE | Earliest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2017
SINGAPORE | Latest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2021
SWITZERLAND | Earliest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2018
SWITZERLAND | Latest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2021
U.K. | Earliest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2015
U.K. | Latest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2021
U.S. | Earliest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2018
U.S. | Latest Tax Year
Income Tax Examination [Line Items]
Open Tax Year	2021

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	Mar. 16, 2020	Feb. 29, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
Stockholders Equity Note [Line Items]
Remaining authorized repurchases under share repurchase program			$ 141,900,000
Amount of equity unavailable for dividends or advances from subsidiaries			7,300,000,000
Stockholders' equity attributable to Alleghany stockholders			9,186,882,000	$ 8,755,720,000	$ 8,776,734,000		$ 7,692,710,000
Amount available for dividends or advances, parent level			1,900,000,000
Dividends paid			$ 0	215,013,000	0
Dividend Declared in 2020
Stockholders Equity Note [Line Items]
Dividends paid	$ 215,000,000
Special dividend declared per share		$ 15
Dividend record date		Mar. 5, 2020
Dividend payable nature			special
Operating Segments
Stockholders Equity Note [Line Items]
Stockholders' equity attributable to Alleghany stockholders			$ 9,495,400,000
Operating Segments | Reinsurance Segment and Insurance Segment
Stockholders Equity Note [Line Items]
Stockholders' equity attributable to Alleghany stockholders			8,157,500,000
Statutory net income of insurance operating units			681,400,000	274,800,000
Combined statutory capital and surplus of insurance operating unit			7,200,000,000	6,800,000,000
Transatlantic Reinsurance Company
Stockholders Equity Note [Line Items]
Amount of dividend that can be declared without regulatory approval			108,600,000
Dividends paid			$ 290,000,000	$ 245,000,000	$ 220,000,000
Stock Repurchase Programs 2018
Stockholders Equity Note [Line Items]
Aggregate amount of common stock authorized for repurchase								$ 400,000,000
Stock Repurchase Programs 2019
Stockholders Equity Note [Line Items]
Aggregate amount of common stock authorized for repurchase						$ 500,000,000

Schedule of Common Stock Repurc

Schedule of Common Stock Repurchases (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stockholders' Equity Note [Abstract]
Shares repurchased	446,596	333,393	215,091
Cost of shares repurchased	$ 290,521	$ 194,762	$ 144,422
Average price per share repurchased	$ 650.52	$ 584.18	$ 671.44

Reconciliation of Accumulated O

Reconciliation of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		$ 8,755,720	$ 8,776,734
Other comprehensive income (loss), net of tax:
Ending Balance		9,186,882	8,755,720
Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			(3,570)
Unrealized Appreciation of Investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		564,900	321,000
Other comprehensive income (loss), net of tax:
Other comprehensive income (loss) before reclassifications		(253,300)	277,000
Reclassifications from accumulated other comprehensive income		(52,500)	(33,100)
Total		(305,800)	243,900
Ending Balance		259,100	564,900
Unrealized Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(99,400)	(121,800)
Other comprehensive income (loss), net of tax:
Other comprehensive income (loss) before reclassifications		(4,300)	22,400
Reclassifications from accumulated other comprehensive income		0	0
Total		(4,300)	22,400
Ending Balance		(103,700)	(99,400)
Retirement Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	[1]	(13,100)	(27,900)
Other comprehensive income (loss), net of tax:
Other comprehensive income (loss) before reclassifications		(500)	(400)	[1]
Reclassifications from accumulated other comprehensive income		0	15,200	[1]
Total		(500)	14,800	[1]
Ending Balance		(13,600)	(13,100)	[1]
Accumulated Other Comprehensive Income (loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		452,402	171,350
Other comprehensive income (loss), net of tax:
Other comprehensive income (loss) before reclassifications		(258,100)	299,000
Reclassifications from accumulated other comprehensive income		(52,500)	(17,900)
Total		(310,600)	281,100
Ending Balance		$ 141,822	452,402
Accumulated Other Comprehensive Income (loss) | Cumulative Effect, Period of Adoption, Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance			$ 0
[1]	See Note 15 for further information on retirement plan-related reclassifications from accumulated other comprehensive income.

Reclassifications of Accumulate

Reclassifications of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains		$ (67,493)	$ (3,098)	$ 6,551
Change in allowance for credit losses on available for sale securities		(2,077)	8,029
Income taxes		281,925	30,734	$ 233,435
Unrealized Appreciation of Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications		(52,500)	(33,100)
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Appreciation of Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains	[1]	(64,400)	(49,900)
Change in allowance for credit losses on available for sale securities		(2,100)	8,000
Income taxes		$ 14,000	$ 8,800
[1]	For 2021, excludes: the 2021 Concord Remeasurement Gain. For 2020, excludes: (i) the 2020 Concord Settlement Gain; ( ii) $ 76.0 million of impairment charge from a write-down of SORC oil field assets; (iii) the Wilbert Remeasurement Gain; (iv) a $ 7.1 million realized loss as a result of an early redemption of debt; and (v) a $ 5.0 million realized gain resulting from a reduction of certain PCT contingent consideration liabilities. See Note 4(e) for additional information.

Reclassifications of Accumula_2

Reclassifications of Accumulated Other Comprehensive Income (Parenthetical) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss on early redemption of debt	$ (7.1)
Alleghany Corporation | 2020 Senior Notes
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Loss on early redemption of debt	(7.1)
Stranded Oil Resources Corporation
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Write-down of oil field assets	76
Precision Cutting Technologies, Inc
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Realized gain on reduction of contingent consideration liabilities	$ 5

Summary of Dividends Paid to Al

Summary of Dividends Paid to Alleghany by Operating Subsidiaries (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Dividends Payable [Line Items]
Dividends paid		$ 0	$ 215,013	$ 0
TransRe
Dividends Payable [Line Items]
Dividends paid	[1]	280,000	210,000	301,000	[2]
RSUI
Dividends Payable [Line Items]
Dividends paid		150,000	225,000	100,000	[2]
Transatlantic Holdings Incorporated And Rsui Group Incorporated
Dividends Payable [Line Items]
Dividends paid		$ 430,000	$ 435,000	$ 401,000	[2]
[1]	In 2021, 2020 and 2019 , TRC paid cash dividends of $ 290.0 million, $ 245.0 million and $ 220.0 million, respectively, to the TransRe holding company. In addition, in 2019, TRC transferred its ownership interest in CapSpecialty to the TransRe holding company, and consequently, the TransRe holding company recorded a dividend from TRC in the amount of $ 101.0 million.
[2]	Includes $ 101.0 million representing the July 1, 2019 carrying value of TransRe’s ownership interest in CapSpecialty, which was transferred to Alleghany.

Summary of Dividends Paid to _2

Summary of Dividends Paid to Alleghany by Operating Subsidiaries (Parenthetical) (Detail) - USD ($) $ in Thousands		Jul. 01, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Dividends Payable [Line Items]
Dividends paid			$ 0	$ 215,013	$ 0
Transatlantic Reinsurance Company
Dividends Payable [Line Items]
Dividends paid			290,000	245,000	220,000
Dividend of Ownership Interest in CapSpecialty, Inc. | Transatlantic Reinsurance Company
Dividends Payable [Line Items]
Dividends paid					101,000
TransRe
Dividends Payable [Line Items]
Dividends paid	[1]		$ 280,000	$ 210,000	$ 301,000	[2]
TransRe | Dividend of Ownership Interest in CapSpecialty, Inc.
Dividends Payable [Line Items]
Dividends paid		$ 101,000
[1]	In 2021, 2020 and 2019 , TRC paid cash dividends of $ 290.0 million, $ 245.0 million and $ 220.0 million, respectively, to the TransRe holding company. In addition, in 2019, TRC transferred its ownership interest in CapSpecialty to the TransRe holding company, and consequently, the TransRe holding company recorded a dividend from TRC in the amount of $ 101.0 million.
[2]	Includes $ 101.0 million representing the July 1, 2019 carrying value of TransRe’s ownership interest in CapSpecialty, which was transferred to Alleghany.

Summary of Dividends Paid to _3

Summary of Dividends Paid to Alleghany Capital Corporation by its Subsidiaries (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Dividends Payable [Line Items]
Payments of Dividends		$ 0	$ 215,013	$ 0
Alleghany Capital Corporation Subsidiaries
Dividends Payable [Line Items]
Payments of Dividends	[1]	$ 133,300	$ 60,900	$ 82,400
[1]	Federal income taxes for most Alleghany Capital subsidiaries are incurred at the Alleghany Capital corporate level. As such, these dividends were arrived at after deducting a provision for estimated income taxes to be paid at the Alleghany Capital-level, as applicable. Income tax provisions are finalized when tax returns are filed in future periods.

Reconciliation of Earnings and

Reconciliation of Earnings and Share Data used in Basic and Diluted Earnings per Share Computations (Detail) - USD ($) $ in Thousands		3 Months Ended																12 Months Ended
		Dec. 31, 2021	[1]	Sep. 30, 2021	[1]	Jun. 30, 2021	[1]	Mar. 31, 2021	[1]	Dec. 31, 2020	[1]	Sep. 30, 2020	[1]	Jun. 30, 2020	[1]	Mar. 31, 2020	[1]	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net earnings available to Alleghany stockholders		$ 516,200		$ (115,000)		$ 403,700		$ 230,000		$ 159,100		$ 126,500		$ 177,400		$ (361,200)		$ 1,034,892	$ 101,754	$ 857,801
Effect of dilutive securities																		0	(1,200)	0
Income available to common stockholders for diluted earnings per share																		$ 1,034,900	$ 100,600	$ 857,800
Weighted average common shares outstanding applicable to basic earnings per share																		13,853,780	14,257,793	14,431,892
Effect of dilutive securities																		7,167	25,825	11,584
Adjusted weighted average common shares outstanding applicable to diluted earnings per share																		13,860,947	14,283,618	14,443,476
Contingently issuable shares	[2]																	62,264	34,148	48,468
[1]	Attributable to Alleghany stockholders.
[2]	Contingently issuable shares were potentially available in the periods presented, but were not included in the diluted earnings per share computations because the impact was anti-dilutive to the earnings per share calculation.

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Commitments and Contingencies Disclosure [Line Items]
Rent expense	$ 53,700	$ 45,400	$ 40,000
Investment in other invested asset	$ 557,800	$ 465,153
Maximum
Commitments and Contingencies Disclosure [Line Items]
Non-cancelable operating leases, expiration date	2040
Hotel Development Projects
Commitments and Contingencies Disclosure [Line Items]
Investment in other invested asset	$ 5,400
Hotel Development Projects | Maximum
Commitments and Contingencies Disclosure [Line Items]
Guaranteed debt of entities	$ 5,300

Consolidated Lease Liabilities

Consolidated Lease Liabilities And Right-Of-Use Lease Assets Related To Operating Leases (Detail) $ in Millions	Dec. 31, 2021USD ($)
Maturity of lease payments, by year
1 year or less	$ 50.3
More than 1 year to 2 years	45.7
More than 2 years to 3 years	42.7
More than 3 years to 4 years	35.4
More than 4 years to 5 years	30.3
More than 5 years	143.3
Total lease payments	347.7	[1]
Less: interest	(79.2)	[2]
Lease liabilities	$ 268.5	[3]
Operating Lease, Liability, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesMember
Right-of-use lease assets	$ 240.5	[4]
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other Assets
Prepaid lease assets, net of lease allowances and incentives	$ 28
Right-of-use lease assets and prepaid lease assets, net of lease allowances and incentives	$ 268.5
[1]	As of December 31, 2021, the weighted average lease term was approximately 13 y ears.
[2]	As of December 31, 2021, the weighted average discount rate was approximate ly 5 p ercent.
[3]	Represents the present val ue of expected lease payments over the remaining lease term and is reported as a component of other liabilities on Alleghany’s consolidated balance sheet.
[4]	Reported as a component of other assets on Alleghany’s consolidated balance sheet.

Consolidated Lease Liabilitie_2

Consolidated Lease Liabilities And Right-Of-Use Lease Assets Related To Operating Leases (Parenthetical) (Detail) $ in Millions	Dec. 31, 2021USD ($)
Leases [Abstract]
Weighted average discount rate	5.00%
Weighted average lease term	13 years
Lease commitments on lease contracts that are set to commence in early 2022	$ 30

Asbestos Related Illnesses and

Asbestos Related Illnesses and Environmental Impairment Loss and Loss Adjustment Expense Reserves (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Commitments and Contingencies [Line Items]
Gross asbestos-related illness and environmental impairment reserves	$ 109.5	$ 113
Net asbestos-related illness and environmental impairment reserves	105.6	108.2
Reinsurance Segment
Commitments and Contingencies [Line Items]
Gross asbestos-related illness and environmental impairment reserves	105	108.4
Net asbestos-related illness and environmental impairment reserves	101.1	103.6
Insurance Segment | CapSpecialty Incorporated
Commitments and Contingencies [Line Items]
Gross asbestos-related illness and environmental impairment reserves	4.5	4.6
Net asbestos-related illness and environmental impairment reserves	$ 4.5	$ 4.6

Segments of Business - Addition

Segments of Business - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2021USD ($)Segment	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment	3
Gross premiums written	$ 8,538,800	$ 7,329,400	$ 6,656,400
Net premiums earned	$ 7,097,653	$ 6,000,161	$ 5,478,143
Reinsurance Segment | Largest Broker Concentration Risk | Gross Premiums Written
Segment Reporting Information [Line Items]
Percentage of gross premiums written	30.00%	27.00%	26.00%
Reinsurance Segment | Second Largest Broker Concentration Risk | Gross Premiums Written
Segment Reporting Information [Line Items]
Percentage of gross premiums written	23.00%	19.00%	17.00%
Reinsurance Segment | Third Largest Broker Concentration Risk | Gross Premiums Written
Segment Reporting Information [Line Items]
Percentage of gross premiums written	10.00%	14.00%	16.00%
Reinsurance Segment | Large Whole Account Quota Share Treaty | Gross Premiums Written
Segment Reporting Information [Line Items]
Percentage of gross premiums written	8.00%	13.00%	14.00%
Operating Segments
Segment Reporting Information [Line Items]
Gross premiums written	$ 8,576,800	$ 7,363,000	$ 6,684,100
Net premiums earned	7,097,700	6,000,200	5,478,100
Operating Segments | Alleghany Capital Corporation Segment
Segment Reporting Information [Line Items]
Gross premiums written	0	0	0
Net premiums earned	0	0	0
Operating Segments | Reinsurance Segment
Segment Reporting Information [Line Items]
Gross premiums written	6,034,000	5,237,300	4,945,700
Net premiums earned	5,477,100	4,644,700	4,327,000
Operating Segments | Reinsurance Segment | Non-US
Segment Reporting Information [Line Items]
Gross premiums written	1,700,000	1,700,000	1,700,000
Net premiums earned	1,600,000	1,600,000	1,500,000
Operating Segments | Reinsurance Segment | U.K.
Segment Reporting Information [Line Items]
Net premiums earned	$ 756,600	$ 699,600	$ 615,600

Results for Reportable Segments

Results for Reportable Segments and Corporate Activities (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Gross premiums written		$ 8,538,800	$ 7,329,400	$ 6,656,400
Net premiums written		7,149,400	6,344,400	5,751,700
Net premiums earned		7,097,653	6,000,161	5,478,143
Net loss and LAE		4,834,935	4,339,046	3,686,435
Commissions, brokerage and other underwriting expenses	[1]	2,067,501	1,789,820	1,758,698
Underwriting (loss) profit	[2]	195,300	(128,700)	33,000
Net investment income		540,445	490,856	550,241
Change in the fair value of equity securities		506,769	(110,459)	709,695
Net realized capital gains		67,493	3,098	(6,551)
Change in allowance for credit losses on available for sale securities		2,077	(8,029)
Change in allowance for credit losses on available for sale securities				(19,660)
Product and service revenues		3,789,668	2,521,092	2,328,848
Other operating expenses		3,479,528	2,429,262	2,263,326
Corporate administration		57,218	48,581	74,830
Amortization of intangible assets		49,912	44,241	33,834
Interest expense		102,308	88,152	99,957
Earnings (losses) before income taxes		1,412,703	157,617	1,123,636
Operating Segments
Segment Reporting Information [Line Items]
Gross premiums written		8,576,800	7,363,000	6,684,100
Net premiums written		7,149,400	6,344,400	5,751,700
Net premiums earned		7,097,700	6,000,200	5,478,100
Net loss and LAE		4,834,900	4,339,100	3,686,400
Commissions, brokerage and other underwriting expenses	[1]	2,067,500	1,789,800	1,758,700
Underwriting (loss) profit	[2]	195,300	(128,700)	33,000
Net investment income		508,800	467,600	539,500
Change in the fair value of equity securities		457,100	(55,800)	705,800
Net realized capital gains		65,200	72,600	7,000
Change in allowance for credit losses on available for sale securities		2,000	(8,000)
Change in allowance for credit losses on available for sale securities				(19,700)
Product and service revenues		3,775,700	2,512,400	2,316,300
Other operating expenses		3,476,700	2,413,600	2,236,000
Corporate administration		(100)	(300)	4,100
Amortization of intangible assets		49,900	44,200	33,800
Interest expense		43,100	42,500	47,200
Earnings (losses) before income taxes		1,434,500	360,100	1,260,800
Operating Segments | Reinsurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		6,034,000	5,237,300	4,945,700
Net premiums written		5,387,400	4,845,000	4,495,000
Net premiums earned		5,477,100	4,644,700	4,327,000
Net loss and LAE		3,791,600	3,386,900	2,961,100
Commissions, brokerage and other underwriting expenses	[1]	1,656,700	1,425,000	1,406,800
Underwriting (loss) profit	[2]	28,800	(167,200)	(40,900)
Operating Segments | Reinsurance Segment | Property
Segment Reporting Information [Line Items]
Gross premiums written		1,975,200	1,761,700	1,700,300
Net premiums written		1,550,400	1,439,600	1,328,800
Net premiums earned		1,708,800	1,379,700	1,280,100
Net loss and LAE		1,444,200	1,130,600	942,600
Commissions, brokerage and other underwriting expenses	[1]	480,100	424,200	424,200
Underwriting (loss) profit	[2]	(215,500)	(175,100)	(86,700)
Operating Segments | Reinsurance Segment | Casualty & Specialty
Segment Reporting Information [Line Items]
Gross premiums written	[3]	4,058,800	3,475,600	3,245,400
Net premiums written	[3]	3,837,000	3,405,400	3,166,200
Net premiums earned	[3]	3,768,300	3,265,000	3,046,900
Net loss and LAE	[3]	2,347,400	2,256,300	2,018,500
Commissions, brokerage and other underwriting expenses	[1],[3]	1,176,600	1,000,800	982,600
Underwriting (loss) profit	[2],[3]	244,300	7,900	45,800
Operating Segments | Insurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		2,542,800	2,125,700	1,738,400
Net premiums written		1,762,000	1,499,400	1,256,700
Net premiums earned		1,620,600	1,355,500	1,151,100
Net loss and LAE		1,043,300	952,200	725,300
Commissions, brokerage and other underwriting expenses	[1]	410,800	364,800	351,900
Underwriting (loss) profit	[2]	166,500	38,500	73,900
Operating Segments | Insurance Segment | RSUI
Segment Reporting Information [Line Items]
Gross premiums written		2,067,600	1,714,400	1,366,600
Net premiums written		1,354,700	1,124,800	912,000
Net premiums earned		1,230,700	1,008,800	824,200
Net loss and LAE		805,500	738,400	503,700
Commissions, brokerage and other underwriting expenses	[1]	261,100	226,100	219,200
Underwriting (loss) profit	[2]	164,100	44,300	101,300
Operating Segments | Insurance Segment | CapSpecialty Incorporated
Segment Reporting Information [Line Items]
Gross premiums written		475,200	411,300	371,800
Net premiums written		407,300	374,600	344,700
Net premiums earned		389,900	346,700	326,900
Net loss and LAE		237,800	213,800	221,600
Commissions, brokerage and other underwriting expenses	[1]	149,700	138,700	132,700
Underwriting (loss) profit	[2]	2,400	(5,800)	(27,400)
Operating Segments | Reinsurance Segment and Insurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		8,576,800	7,363,000	6,684,100
Net premiums written		7,149,400	6,344,400	5,751,700
Net premiums earned		7,097,700	6,000,200	5,478,100
Net loss and LAE		4,834,900	4,339,100	3,686,400
Commissions, brokerage and other underwriting expenses	[1]	2,067,500	1,789,800	1,758,700
Underwriting (loss) profit	[2]	195,300	(128,700)	33,000
Net investment income		509,000	465,700	533,200
Change in the fair value of equity securities		457,100	(55,800)	705,800
Net realized capital gains		57,600	37,100	6,000
Change in allowance for credit losses on available for sale securities		2,000	(8,000)
Change in allowance for credit losses on available for sale securities				(19,700)
Product and service revenues		39,300	34,900	27,000
Other operating expenses		88,900	103,600	103,100
Corporate administration		(100)	(300)	4,100
Amortization of intangible assets		1,800	800	1,300
Interest expense		26,900	27,000	27,100
Earnings (losses) before income taxes		1,142,800	214,100	1,149,700
Operating Segments | Alleghany Capital Corporation Segment
Segment Reporting Information [Line Items]
Gross premiums written		0	0	0
Net premiums written		0	0	0
Net premiums earned		0	0	0
Net loss and LAE		0	0	0
Commissions, brokerage and other underwriting expenses	[1]	0	0	0
Underwriting (loss) profit	[2]	0	0	0
Net investment income		(200)	1,900	6,300
Change in the fair value of equity securities		0	0	0
Net realized capital gains		7,600	35,500	1,000
Change in allowance for credit losses on available for sale securities		0	0
Change in allowance for credit losses on available for sale securities				0
Product and service revenues		3,736,400	2,477,500	2,289,300
Other operating expenses		3,387,800	2,310,000	2,132,900
Corporate administration		0	0	0
Amortization of intangible assets		48,100	43,400	32,500
Interest expense		16,200	15,500	20,100
Earnings (losses) before income taxes		291,700	146,000	111,100
Corporate activities
Segment Reporting Information [Line Items]
Gross premiums written		(38,000)	(33,600)	(27,700)
Net premiums written		0	0	0
Net premiums earned		0	0	0
Net loss and LAE		0	0	0
Commissions, brokerage and other underwriting expenses	[1]	0	0	0
Underwriting (loss) profit	[2]	0	0	0
Net investment income		31,600	23,300	10,700
Change in the fair value of equity securities		49,700	(54,700)	3,900
Net realized capital gains		2,200	(69,500)	(13,500)
Change in allowance for credit losses on available for sale securities		100	0
Change in allowance for credit losses on available for sale securities				0
Product and service revenues		14,000	8,700	12,500
Other operating expenses		2,900	15,700	27,300
Corporate administration		57,300	48,900	70,700
Amortization of intangible assets		0	0	0
Interest expense		59,200	45,700	52,800
Earnings (losses) before income taxes		$ (21,800)	$ (202,500)	$ (137,200)
[1]	Includes amortization associated with deferred acquisition costs of $ 1,693.1 mil lion, $ 1,457.0 million and $ 1,392.8 million for the years ended December 31, 2021, 2020 and 2019 , respectively.
[2]	Underwriting profit represents net premiums earned less net loss and LAE and commissions, brokerage and other underwriting expenses, all as determined in accordance with GAAP, and does not include net investment income, change in the fair value of equity securities, net realized capital gains, change in allowance for credit losses on available for sale securities, product and service revenues, other operating expenses, corporate administration, amortization of intangible assets or interest expense. Underwriting profit does not replace earnings before income taxes determined in accordance with GAAP as a measure of profitability. Rather, Alleghany believes that underwriting profit enhances the understanding of its reinsurance and insurance segments’ operating results by highlighting net earnings attributable to their underwriting performance. Earnings before income taxes (a GAAP measure) may show a profit despite an underlying underwriting loss. Where underwriting losses persist over extended periods, a reinsurance or an insurance company’s ability to continue as an ongoing concern may be at risk. Therefore, Alleghany views underwriting profit as an important measure in the overall evaluation of performance.
[3]	Primarily consists of the following reinsurance lines of business: directors’ and officers’ liability; errors and omissions liability; general liability; medical malpractice; ocean marine and aviation; auto liability; accident & health; mortgage reinsurance; surety; and credit.

Results for Reportable Segmen_2

Results for Reportable Segments and Corporate Activities (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting [Abstract]
Amortization associated with deferred acquisition costs	$ 1,693.1	$ 1,457	$ 1,392.8

Summary of Identifiable Assets

Summary of Identifiable Assets and Equity (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Identifiable Assets	$ 32,268,675	$ 28,927,010
Invested Assets and Cash	22,849,400
Equity Attributable to Alleghany	9,186,882	$ 8,755,720	$ 8,776,734	$ 7,692,710
Operating Segments
Segment Reporting Information [Line Items]
Identifiable Assets	30,818,900
Invested Assets and Cash	21,454,900
Equity Attributable to Alleghany	9,495,400
Operating Segments | Reinsurance Segment
Segment Reporting Information [Line Items]
Identifiable Assets	19,048,200
Invested Assets and Cash	15,208,800
Equity Attributable to Alleghany	5,398,400
Operating Segments | Insurance Segment
Segment Reporting Information [Line Items]
Identifiable Assets	8,402,700
Invested Assets and Cash	6,080,200
Equity Attributable to Alleghany	2,759,100
Operating Segments | Reinsurance Segment and Insurance Segment
Segment Reporting Information [Line Items]
Identifiable Assets	27,450,900
Invested Assets and Cash	21,289,000
Equity Attributable to Alleghany	8,157,500
Operating Segments | Alleghany Capital Corporation Segment
Segment Reporting Information [Line Items]
Identifiable Assets	3,368,000
Invested Assets and Cash	165,900
Equity Attributable to Alleghany	1,337,900
Corporate activities
Segment Reporting Information [Line Items]
Identifiable Assets	1,449,700
Invested Assets and Cash	1,394,500
Equity Attributable to Alleghany	$ (308,500)

Summary of Alleghany Capital Pr

Summary of Alleghany Capital Product and Service Revenues (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Other Revenues [Line Items]
Product and service revenues		$ 3,789,668	$ 2,521,092	$ 2,328,848
Operating Segments
Other Revenues [Line Items]
Product and service revenues		3,775,700	2,512,400	2,316,300
Operating Segments | Alleghany Capital Corporation Segment
Other Revenues [Line Items]
Product and service revenues		3,736,400	2,477,500	2,289,300
Operating Segments | Alleghany Capital Corporation Segment | Industrial Segment
Other Revenues [Line Items]
Product and service revenues	[1]	1,662,300	1,220,900	1,105,600
Operating Segments | Alleghany Capital Corporation Segment | Non-industrial Segment
Other Revenues [Line Items]
Product and service revenues	[2]	2,074,100	1,256,500	1,183,700
Operating Segments | Alleghany Capital Corporation Segment | Corporate & Other
Other Revenues [Line Items]
Product and service revenues		$ 0	$ 100	$ 0
[1]	For 2021, 2020 and 2019 , the vast majority of industrial product and service revenues were recognized as goods and services transferred to customers over time.
[2]	For 2021, 2020 and 2019 , approximately 50 percent, 59 percent and 70 percent, respectively, of consumer & services product and service revenues were recognized as services transferred to customers over time, with the remainder recognized as goods transferred at a point in time.

Summary of Alleghany Capital _2

Summary of Alleghany Capital Product and Service Revenues (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Segments | Alleghany Capital Corporation Segment | Non-Industrial Segment | Transferred over Time [Member]
Other Revenues [Line Items]
Product and service revenue percentage	50.00%	59.00%	70.00%

Long-Term Compensation Plans -

Long-Term Compensation Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
RSUI
Executive Compensation Plan Expense [Line Items]
Compensation expense recognized	$ 37.3	$ 29	$ 37.4
Income tax (expenses) benefit related to share based compensation expense	7.8	6.1	7.8
Parent Company
Executive Compensation Plan Expense [Line Items]
Compensation expense recognized	21.5	4.3	38.7
Income tax (expenses) benefit related to share based compensation expense	4.5	0.9	8.1
Fair value of common stocks issued to satisfy share based compensations	2.5	5	2.4
Compensation costs paid in cash	8.4	12.8	2.2
Reinsurance Segment
Executive Compensation Plan Expense [Line Items]
Compensation expense recognized	36.1	44.3	48.7
Income tax (expenses) benefit related to share based compensation expense	$ 7.6	$ 9.3	$ 10.2

Employee Retirement Benefit P_2

Employee Retirement Benefit Plans - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Other comprehensive loss reclassed to expenses	$ 57,218	$ 48,581	$ 74,830
Other comprehensive loss reclassed to expenses	3,479,528	2,429,262	2,263,326
Parent Company
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	3,900	3,900
Fair value of plan assets	3,700	3,800
Other comprehensive loss reclassed to expenses	57,301	48,849	70,692
Executive Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		57,000
Other comprehensive losses attributable to retirement plans		3,800	$ 15,400
Executive Retirement Plans | Reclassification out of Accumulated Other Comprehensive Income | Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Other comprehensive loss reclassed to expenses		19,200
Executive Retirement Plans | Reclassification out of Accumulated Other Comprehensive Income | Retirement Plans | Reinsurance Segment
Defined Benefit Plan Disclosure [Line Items]
Other comprehensive loss reclassed to expenses		5,600
Executive Retirement Plans | Reclassification out of Accumulated Other Comprehensive Income | Retirement Plans | Parent Company
Defined Benefit Plan Disclosure [Line Items]
Other comprehensive loss reclassed to expenses		13,600
Transatlantic Holdings Incorporated
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	68,700	72,200
Fair value of plan assets	$ 60,300	$ 63,700

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2021		Sep. 30, 2021		Jun. 30, 2021		Mar. 31, 2021		Dec. 31, 2020		Sep. 30, 2020		Jun. 30, 2020		Mar. 31, 2020		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 3,555,000		$ 2,866,600		$ 2,928,700		$ 2,653,700		$ 2,663,500		$ 2,522,900		$ 2,227,400		$ 1,482,900		$ 12,004,105	$ 8,896,719	$ 9,040,716
Net earnings (losses)	$ 516,200	[1]	$ (115,000)	[1]	$ 403,700	[1]	$ 230,000	[1]	$ 159,100	[1]	$ 126,500	[1]	$ 177,400	[1]	$ (361,200)	[1]	$ 1,034,892	$ 101,754	$ 857,801
Basic earnings (losses) per share of common stock	$ 37.76	[1],[2]	$ (8.31)	[1],[2]	$ 29	[1],[2]	$ 16.44	[1],[2]	$ 11.28	[1],[2]	$ 8.86	[1],[2]	$ 12.39	[1],[2]	$ (25.19)	[1],[2]	$ 74.70	$ 7.14	$ 59.44
[1]	Attributable to Alleghany stockholders.
[2]	Earnings per share by quarter may not equal the amount for the full year due to the timing of repurchases of Common Stock, as well as rounding.

Summary of Investments Other Th

Summary of Investments Other Than Investments in Related Parties (Detail) $ in Millions	Dec. 31, 2021USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$ 20,455.8
Fair Value	21,921.4
Amount at which shown in Balance sheet	21,921.4
U.S. Government obligations
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,039.7
Fair Value	2,050.7
Amount at which shown in Balance sheet	2,050.7
Municipal bonds
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,412.7
Fair Value	2,535.9
Amount at which shown in Balance sheet	2,535.9
Foreign government obligations
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	850.8
Fair Value	854.9
Amount at which shown in Balance sheet	854.9
U.S. corporate bonds
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	3,336.9
Fair Value	3,477.3
Amount at which shown in Balance sheet	3,477.3
Foreign corporate bonds
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,216.6
Fair Value	1,226.9
Amount at which shown in Balance sheet	1,226.9
RMBS
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,993.6
Fair Value	2,009
Amount at which shown in Balance sheet	2,009
CMBS
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	879.8
Fair Value	905.9
Amount at which shown in Balance sheet	905.9
Other asset-backed securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,997
Fair Value	3,001
Amount at which shown in Balance sheet	3,001
Fixed Maturities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	15,727.1
Fair Value	16,061.6
Amount at which shown in Balance sheet	16,061.6
Public utilities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	179.2
Fair Value	189.6
Amount at which shown in Balance sheet	189.6
Banks, trust and insurance companies
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	353
Fair Value	483.2
Amount at which shown in Balance sheet	483.2
Industrial, miscellaneous and all other
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,015.2
Fair Value	3,006.4
Amount at which shown in Balance sheet	3,006.4
Nonredeemable preferred stocks
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	5.3
Fair Value	4.6
Amount at which shown in Balance sheet	4.6
Equity Securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,552.7
Fair Value	3,683.8
Amount at which shown in Balance sheet	3,683.8
Commercial mortgage loans
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	475.9
Fair Value	475.9
Amount at which shown in Balance sheet	475.9
Other invested assets
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	557.8
Fair Value	557.8
Amount at which shown in Balance sheet	557.8
Short-term Investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,142.3
Fair Value	1,142.3
Amount at which shown in Balance sheet	$ 1,142.3

Condensed Balance Sheets (Detai

Condensed Balance Sheets (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets
Equity securities	$ 3,683,820	$ 2,718,902
Debt securities	16,061,560	15,618,470
Short-term investments	1,142,258	714,208
Other invested assets	557,800	465,153
Cash	927,966	791,442
Property and equipment at cost, net of accumulated depreciation and amortization	304,452	267,872
Other assets	2,010,335	1,559,245
Current taxes receivable	0	3,189
Total assets	32,268,675	28,927,010
Liabilities, Redeemable Noncontrolling Interests and Stockholders’ Equity
Senior notes	2,847,199	2,135,946
Other liabilities	1,965,943	1,594,918
Current taxes payable	34,297	0
Total liabilities	22,764,447	19,937,481
Redeemable noncontrolling interest	317,346	233,809	$ 204,753	$ 169,762
Total stockholders’ equity attributable to Alleghany stockholders	9,186,882	8,755,720	$ 8,776,734	$ 7,692,710
Total liabilities, redeemable noncontrolling interests and stockholders’ equity	32,268,675	28,927,010
Parent Company
Assets
Equity securities	741,620	571,314
Debt securities	0	48,753
Short-term investments	452,549	76,259
Other invested assets	165,931	91,873
Cash	21,847	17,243
Property and equipment at cost, net of accumulated depreciation and amortization	3,561	3,707
Other assets	55,581	60,089
Net deferred tax assets	5,240	21,060
Current taxes receivable	4,296	17,649
Investment in subsidiaries	9,843,147	9,361,261
Total assets	11,293,772	10,269,208
Liabilities, Redeemable Noncontrolling Interests and Stockholders’ Equity
Senior notes	1,678,964	1,190,192
Other liabilities	110,580	89,487
Total liabilities	1,789,544	1,279,679
Redeemable noncontrolling interest	317,346	233,809
Total stockholders’ equity attributable to Alleghany stockholders	9,186,882	8,755,720
Total liabilities, redeemable noncontrolling interests and stockholders’ equity	$ 11,293,772	$ 10,269,208

Condensed Balance Sheets (Paren

Condensed Balance Sheets (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Condensed Balance Sheet Statements Captions [Line Items]
Equity securities, cost	$ 2,552,722		$ 2,051,996
Debt securities, amortized cost	15,727,143		14,898,522
Allowance for credit losses	502	[1]	2,579	[1]	$ 0
Parent Company
Condensed Balance Sheet Statements Captions [Line Items]
Equity securities, cost	$ 681,375		587,418
Debt securities, amortized cost			47,397
Allowance for credit losses			$ 57
[1]	See Note 1(r) for additional information regarding Alleghany’s adoption of new credit loss accounting guidance.

Condensed Statements of Earning

Condensed Statements of Earnings (Detail) - USD ($) $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2021		Sep. 30, 2021		Jun. 30, 2021		Mar. 31, 2021		Dec. 31, 2020		Sep. 30, 2020		Jun. 30, 2020		Mar. 31, 2020		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenues
Net investment income																	$ 540,445	$ 490,856	$ 550,241
Change in the fair value of equity securities																	506,769	(110,459)	709,695
Net realized capital gains																	67,493	3,098	(6,551)
Change in allowance for credit losses on available for sale securities																	2,077	(8,029)
Change in allowance for credit losses on available for sale securities																			(19,660)
Product and service revenues																	3,789,668	2,521,092	2,328,848
Total revenues	$ 3,555,000		$ 2,866,600		$ 2,928,700		$ 2,653,700		$ 2,663,500		$ 2,522,900		$ 2,227,400		$ 1,482,900		12,004,105	8,896,719	9,040,716
Costs and Expenses
Interest expense																	102,308	88,152	99,957
Corporate administration																	57,218	48,581	74,830
Total costs and expenses																	10,591,402	8,739,102	7,917,080
Earnings (losses) before income taxes																	1,412,703	157,617	1,123,636
Income taxes																	281,925	30,734	233,435
Net earnings																	1,130,778	126,883	890,201
Net earnings attributable to noncontrolling interest																	95,886	25,129	32,400
Net earnings attributable to Alleghany stockholders	$ 516,200	[1]	$ (115,000)	[1]	$ 403,700	[1]	$ 230,000	[1]	$ 159,100	[1]	$ 126,500	[1]	$ 177,400	[1]	$ (361,200)	[1]	1,034,892	101,754	857,801
Parent Company
Revenues
Net investment income																	32,778	24,448	10,790
Change in the fair value of equity securities																	49,715	(54,647)	3,937
Net realized capital gains																	2,322	6,522	(13,497)
Change in allowance for credit losses on available for sale securities																	57	(57)
Change in allowance for credit losses on available for sale securities																			0
Product and service revenues																	81	771	85
Total revenues																	84,953	(22,963)	1,315
Costs and Expenses
Interest expense																	60,379	46,811	52,908
Corporate administration																	57,301	48,849	70,692
Total costs and expenses																	117,680	95,660	123,600
(Losses) before equity in earnings of consolidated subsidiaries and income taxes																	(32,727)	(118,623)	(122,285)
Equity in earnings of consolidated subsidiaries																	1,445,430	276,240	1,245,921
Earnings (losses) before income taxes																	1,412,703	157,617	1,123,636
Income taxes																	281,925	30,734	233,435
Net earnings																	1,130,778	126,883	890,201
Net earnings attributable to noncontrolling interest																	95,886	25,129	32,400
Net earnings attributable to Alleghany stockholders																	$ 1,034,892	$ 101,754	$ 857,801
[1]	Attributable to Alleghany stockholders.

Condensed Statements of Cash Fl

Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net earnings	$ 1,130,778	$ 126,883	$ 890,201
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization	178,031	160,002	119,513
Change in the fair value of equity securities	(506,769)	110,459	(709,695)
Net realized capital (gains) losses	(67,493)	(3,098)	6,551
Change in allowance for credit losses on available for sale securities	(2,077)	8,029
Change in allowance for credit losses on available for sale securities			19,660
Net adjustments	729,455	909,951	(175,796)
Net cash provided by (used in) operating activities	1,860,233	1,036,834	714,405
Cash flows from investing activities
Purchases of equity securities	(1,092,926)	(1,974,625)	(520,961)
Purchases of debt securities	(6,737,728)	(6,721,073)	(6,726,809)
Sales of debt securities	3,582,319	4,042,915	3,645,307
Maturities and redemptions of debt securities	2,240,302	1,664,285	1,166,841
Sales of equity securities	633,111	1,659,234	2,296,371
Net (purchase) sale of short-term investments	(432,422)	208,263	(21,564)
Purchases of property and equipment	(59,651)	(37,519)	(47,572)
Other, net	(33,039)	(12,973)	(40,218)
Net cash provided by (used in) investing activities	(2,009,130)	(1,284,447)	(476,539)
Cash flows from financing activities
Repayment of senior notes	0	(307,095)	0
Treasury stock acquisitions	(290,521)	(194,762)	(144,422)
Proceeds from issuance of senior notes	493,195	499,335	0
Debt issue costs paid	(5,675)	(4,550)	0
Cash dividends paid	0	(215,013)	0
Other, net	(82,178)	(27,912)	(40,530)
Net cash provided by (used in) financing activities	304,570	(164,008)	(103,214)
Net (decrease) increase in cash	136,524	(387,656)	140,335
Cash at beginning of period	791,442	1,179,098	1,038,763
Cash at end of period	927,966	791,442	1,179,098
Cash paid during the period for:
Interest paid	94,540	91,832	97,016
Income taxes paid (refunds received)	162,336	90,828	61,786
Parent Company
Cash flows from operating activities
Net earnings	1,130,778	126,883	890,201
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Equity in undistributed net (earnings) losses of consolidated subsidiaries	(1,157,344)	(226,590)	(989,486)
Depreciation and amortization	1,976	4,064	2,249
Change in the fair value of equity securities	(49,715)	54,647	(3,937)
Net realized capital (gains) losses	(2,322)	(6,522)	13,497
Change in allowance for credit losses on available for sale securities	(57)	57
Change in allowance for credit losses on available for sale securities			0
Increase (decrease) in other liabilities and taxes payable	47,462	(56,298)	24,593
Net adjustments	(1,160,000)	(230,642)	(953,084)
Net cash provided by (used in) operating activities	(29,222)	(103,759)	(62,883)
Cash flows from investing activities
Purchases of equity securities	(220,914)	(763,986)	0
Purchases of debt securities	0	(497,058)	(194,706)
Sales of debt securities	45,786	606,110	1,186
Maturities and redemptions of debt securities	3,049	32,383	13,344
Sales of equity securities	100,324	142,065	64,016
Net (purchase) sale of short-term investments	(376,290)	49,154	162,161
Purchases of property and equipment	(395)	(9)	(124)
Other, net	(64,345)	(8,731)	(33,245)
Net cash provided by (used in) investing activities	(512,785)	(440,072)	12,632
Cash flows from financing activities
Repayment of senior notes	0	(307,095)	0
Treasury stock acquisitions	(290,521)	(194,762)	(144,422)
Proceeds from issuance of senior notes	493,195	499,335	0
Debt issue costs paid	(5,675)	(4,550)	0
Cash dividends paid	0	(215,013)	0
Capital contributions to consolidated subsidiaries	(140,000)	(87,323)	(15,267)
Distributions from consolidated subsidiaries	488,500	865,000	215,000
Other, net	1,112	4,798	(4,707)
Net cash provided by (used in) financing activities	546,611	560,390	50,604
Net (decrease) increase in cash	4,604	16,559	353
Cash at beginning of period	17,243	684	331
Cash at end of period	21,847	17,243	684
Cash paid during the period for:
Interest paid	52,652	49,036	51,375
Income taxes paid (refunds received)	$ 94,001	$ 17,255	$ (4,189)

Supplemental Insurance Inform_2

Supplemental Insurance Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reinsurance Segment
Supplementary Insurance Information By Segment [Line Items]
Deferred Policy Acquisition Costs	$ 434.3	$ 460.7	$ 406.7
Future Policy Benefits, Losses, Claims and Loss Expenses	10,748.2	9,814	9,323.8
Unearned Premiums	1,848.1	1,873.7	1,668.1
Other Policy Claims and Benefits Payable	0	0	0
Premium Revenue	5,477.1	4,644.7	4,327
Net Investment Income	347.8	330.2	371.9
Benefits, Claims, Losses and Settlement Expenses	3,791.6	3,386.9	2,961.1
Amortization of Deferred Policy Acquisition Costs	1,429.3	1,225.3	1,178.7
Other Operating Expenses	227.4	199.7	228.1
Premiums Written	5,387.4	4,845	4,495
Insurance Segment
Supplementary Insurance Information By Segment [Line Items]
Deferred Policy Acquisition Costs	152.5	134.4	115.9
Future Policy Benefits, Losses, Claims and Loss Expenses	3,686	3,226.9	2,670.3
Unearned Premiums	1,347.8	1,124.2	910.1
Other Policy Claims and Benefits Payable	0	0	0
Premium Revenue	1,620.6	1,355.5	1,151.1
Net Investment Income	161.2	135.5	161.3
Benefits, Claims, Losses and Settlement Expenses	1,043.3	952.2	725.3
Amortization of Deferred Policy Acquisition Costs	263.8	231.7	214.1
Other Operating Expenses	147	133.1	137.8
Premiums Written	$ 1,762	$ 1,499.4	$ 1,256.7

Reinsurance (Detail)

Reinsurance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount	$ 3,005,700	$ 2,370,400	$ 2,114,100
Ceded to Other Companies	1,272,800	953,100	904,800
Assumed from Other Companies	5,364,800	4,582,900	4,268,800
Net Amount	7,097,653	6,000,161	5,478,143
Property and Casualty Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross Amount	3,005,700	2,370,400	2,114,100
Ceded to Other Companies	1,272,800	953,100	904,800
Assumed from Other Companies	5,364,800	4,582,900	4,268,800
Net Amount	$ 7,097,700	$ 6,000,200	$ 5,478,100
Percentage of Amount Assumed to Net	75.60%	76.40%	77.90%

Valuation and Qualifying Acco_2

Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Allowance for Credit Losses for Reinsurance Recoverable
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 7.9	$ 0	$ 0
Charged to Costs and Expenses	0	4.6	0
Charged to Other Accounts	0	3.3	0
Deductions	4.7	0	0
Ending Balance	3.2	7.9	0
Allowance for Credit Losses for Premiums Receivable
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning Balance	2.2	0.7	0.4
Charged to Costs and Expenses	0	1.1	0.9
Charged to Other Accounts	0	0.4	0
Deductions	1.2	0	0.6
Ending Balance	$ 1	$ 2.2	$ 0.7

Supplemental Information Conc_2

Supplemental Information Concerning Insurance Operations (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-18, Supplemental Information, Property-Casualty Insurance Underwriters [Abstract]
Deferred Policy Acquisition Costs	$ 586.8	$ 595.1	$ 522.6
Reserves for Unpaid Claims and Claim Adjustment Expenses	14,357.6	12,970.6	11,928.4
Discount if Any Deducted, in Reserves for Unpaid Claims and Claim Adjustment Expenses	0	0	0
Unearned Premiums	3,179.5	2,984.1	2,566.2
Earned Premiums	7,097.7	6,000.2	5,478.1
Net Investment Income	509	465.7	533.2
Claims and Claim Adjustment Expenses Incurred Related to Current Year	5,084.6	4,559.9	3,871.1
Claims incurred related to prior years	(249.7)	(220.8)	(184.7)
Amortization of Deferred Policy Acquisition Costs	1,693.1	1,457	1,392.8
Paid Claims and Claim Adjustment Expenses	3,688.7	3,503.5	3,724.5
Premiums Written	$ 7,149.4	$ 6,344.4	$ 5,751.7