Alleghany (Y) 10-Q 2 Aug 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 26, 2018
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Trading Symbol	Y
Entity Registrant Name	ALLEGHANY CORP /DE
Entity Central Index Key	775,368
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		14,936,675

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Securities at fair value:
Available for sale equity securities (cost: 2018 - $3,705,364; 2017 - $3,170,673)		$ 4,099,467
Equity securities (cost: 2018 - $3,705,364; 2017 - $3,170,673)	$ 4,714,079
Debt securities (amortized cost: 2018 - $12,206,035; 2017 - $12,536,772)	12,155,866	12,721,399
Short-term investments	472,830	578,054
Marketable Securities, Total	17,342,775	17,398,920
Other invested assets	605,477	743,358
Total investments	18,644,024	18,800,642
Cash	623,223	838,375
Accrued investment income	97,347	105,877
Premium balances receivable	831,989	797,346
Reinsurance recoverables	1,602,600	1,746,488
Ceded unearned premiums	208,534	190,252
Deferred acquisition costs	468,243	453,346
Property and equipment at cost, net of accumulated depreciation and amortization	197,678	125,337
Goodwill	346,270	334,905
Intangible assets, net of amortization	463,544	459,037
Current taxes receivable	68,396	31,085
Net deferred tax assets	61,806	136,489
Funds held under reinsurance agreements	719,360	706,042
Other assets	752,873	659,096
Total assets	25,085,887	25,384,317
Liabilities, Redeemable Noncontrolling Interests and Stockholders' Equity
Loss and loss adjustment expenses	11,515,493	11,871,250
Unearned premiums	2,279,810	2,182,294
Senior Notes and other debt	1,569,367	1,484,897
Reinsurance payable	159,944	156,376
Other liabilities	1,021,512	1,068,907
Total liabilities	16,546,126	16,763,724
Redeemable noncontrolling interests	135,372	106,530
Common stock (shares authorized: 2018 and 2017 - 22,000,000; shares issued: 2018 and 2017 - 17,459,961)	17,460	17,460
Contributed capital	3,612,615	3,612,109
Accumulated other comprehensive (loss) income	(172,307)	618,118
Treasury stock, at cost (2018 - 2,465,282 shares; 2017 - 2,069,461 shares)	(1,057,885)	(824,906)
Retained earnings	6,004,506	5,091,282
Total stockholders' equity attributable to Alleghany stockholders	8,404,389	8,514,063
Total liabilities, redeemable noncontrolling interest and stockholders' equity	25,085,887	25,384,317
Commercial Mortgage Loan Portfolio
Securities at fair value:
Commercial mortgage loans	$ 695,772	$ 658,364

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Available for sale equity securities, cost		$ 3,170,673
Equity securities, cost	$ 3,705,364
Debt securities, amortized cost	$ 12,206,035	$ 12,536,772
Common stock, Shares authorized	22,000,000	22,000,000
Common stock, Shares issued	17,459,961	17,459,961
Treasury stock, shares	2,465,282	2,069,461

Consolidated Statements of Earn

Consolidated Statements of Earnings and Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues
Net premiums earned	$ 1,236,959	$ 1,243,929	$ 2,444,815	$ 2,453,117
Net investment income	126,273	101,656	250,399	217,194
Change in the fair value of equity securities	185,245		142,596
Net realized capital gains	6,462	9,268	50,967	68,919
Other than temporary impairment losses		(3,747)		(6,964)
Other than temporary impairment losses			(511)
Total revenues	1,897,664	1,553,918	3,482,618	3,086,370
Costs and Expenses
Net loss and loss adjustment expenses	738,210	734,886	1,408,788	1,434,191
Commissions, brokerage and other underwriting expenses	402,083	413,737	808,378	822,252
Other operating expenses	343,165	225,170	608,062	400,308
Corporate administration	14,119	14,405	21,904	31,290
Amortization of intangible assets	5,966	4,611	11,230	8,375
Interest expense	22,277	20,989	43,808	41,924
Total costs and expenses	1,525,820	1,413,798	2,902,170	2,738,340
Earnings (losses) before income taxes	371,844	140,120	580,448	348,030
Income taxes	73,440	37,461	110,862	96,011
Net earnings	298,404	102,659	469,586	252,019
Net earnings attributable to noncontrolling interest	3,288	848	2,895	1,032
Net earnings attributable to Alleghany stockholders	295,116	101,811	466,691	250,987
Net earnings	298,404	102,659	469,586	252,019
Other comprehensive income:
Change in unrealized gains (losses), net of deferred taxes of ($8,853) and $76,300 for the three months ended June 30, 2018 and 2017, respectively; and of ($47,758) and $143,570 for the six months ended June 30, 2018 and 2017, respectively	(33,305)	141,701	(179,663)	266,630
Less: reclassification for net realized capital gains and other than temporary impairments, net of taxes of ($1,357) and ($1,932) for the three months ended June 30, 2018 and 2017, respectively; and of ($991) and ($21,684) for the six months ended June 30, 2018 and 2017, respectively	(5,105)	(3,589)	(3,726)	(40,271)
Change in unrealized currency translation adjustment, net of deferred taxes of ($2,797) and $5,364 for the three months ended June 30, 2018 and 2017, respectively; and of ($1,442) and $8,083 for the six months ended June 30, 2018 and 2017, respectively	(10,523)	9,962	(5,423)	15,011
Retirement plans	209	98	(1,113)	(297)
Comprehensive income	249,680	250,831	279,661	493,092
Comprehensive income attributable to noncontrolling interests	3,288	848	2,895	1,032
Comprehensive income attributable to Alleghany stockholders	$ 246,392	$ 249,983	$ 276,766	$ 492,060
Basic earnings per share attributable to Alleghany stockholders	$ 19.44	$ 6.60	$ 30.53	$ 16.28
Diluted earnings per share attributable to Alleghany stockholders	$ 19.44	$ 6.60	$ 30.52	$ 16.27
Noninsurance Revenue
Revenues
Noninsurance revenue	$ 342,725	$ 202,812	$ 594,352	$ 354,104

Consolidated Statements of Ear5

Consolidated Statements of Earnings and Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Change in unrealized gains (losses), deferred taxes	$ (8,853)	$ 76,300	$ (47,758)	$ 143,570
Reclassification for net realized capital gains and other than temporary impairments,taxes	(1,357)	(1,932)	(991)	(21,684)
Change in unrealized currency translation adjustment, deferred taxes	$ (2,797)	$ 5,364	$ (1,442)	$ 8,083

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities
Net earnings	$ 469,586	$ 252,019
Adjustments to reconcile net earnings to net cash provided by (used in) operating activities:
Depreciation and amortization	64,510	69,723
Change in the fair value of equity securities	(142,596)
Net realized capital (gains) losses	(50,967)	(68,919)
Other than temporary impairment losses		6,964
Other than temporary impairment losses	511
(Increase) decrease in reinsurance recoverables, net of reinsurance payable	147,456	109,287
(Increase) decrease in premium balances receivable	(34,643)	(109,073)
(Increase) decrease in ceded unearned premiums	(18,282)	4,057
(Increase) decrease in deferred acquisition costs	(14,897)	(20,683)
(Increase) decrease in funds held under reinsurance agreements	(13,318)	(50,281)
Increase (decrease) in unearned premiums	97,516	78,592
Increase (decrease) in loss and loss adjustment expenses	(355,757)	(26,960)
Change in unrealized foreign currency exchange rate losses (gains)	48,228	(86,834)
Other, net	(48,172)	45,989
Net adjustments	(320,411)	(48,138)
Net cash provided by (used in) operating activities	149,175	203,881
Cash flows from investing activities
Purchases of debt securities	(2,301,614)	(3,313,484)
Purchases of equity securities		(1,849,990)
Purchase of equity securities	(533,842)
Sales of debt securities	1,667,526	2,193,147
Maturities and redemptions of debt securities	886,970	907,309
Sales of equity securities		1,972,117
Sales of equity securities	269,567
Net (purchases) sales of short-term investments	104,728	73,725
Net (purchases) sales and maturities of commercial mortgage loans	(37,408)	(41,659)
(Purchases) sales of property and equipment	(13,164)	16,006
Purchases of affiliates and subsidiaries, net of cash acquired	(108,386)	(164,528)
Other, net	50,415	84,585
Net cash provided by (used in) investing activities	(15,208)	(122,772)
Cash flows from financing activities
Treasury stock acquisitions	(236,103)
Increase (decrease) in other debt	38,452	(26,098)
Cash dividends paid	(153,967)
Other, net	5,317	(15,238)
Net cash provided by (used in) financing activities	(346,301)	(41,336)
Effect of foreign currency exchange rate changes on cash	(2,818)	9,821
Net increase (decrease) in cash	(215,152)	49,594
Cash at beginning of period	838,375	594,091
Cash at end of period	623,223	643,685
Cash paid during period for:
Interest paid	42,562	41,207
Income taxes paid (refund received)	$ 22,135	$ 31,242

Summary of Significant Accounti

Summary of Significant Accounting Principles	6 Months Ended
	Jun. 30, 2018
Summary of Significant Accounting Principles	1. Summary of Significant Accounting Principles (a) Principles of Financial Statement Presentation This Quarterly Report on Form 10-Q 10-Q”) Form 10-K 10-K”) 10-Q Alleghany Corporation, a Delaware corporation, owns and manages certain operating subsidiaries and investments, anchored by a core position in property and casualty reinsurance and insurance. Through its wholly-owned subsidiary Transatlantic Holdings, Inc. (“TransRe”), Alleghany is engaged in the property and casualty reinsurance business. TransRe has been a subsidiary of Alleghany since March 2012. Through its wholly-owned subsidiary Alleghany Insurance Holdings LLC (“AIHL”) and its subsidiaries, 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 has been a subsidiary of AIHL since July 2003 and CapSpecialty has been a subsidiary of AIHL since January 2002. 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. Prior to December 31, 2017, AIHL’s insurance operations also included Pacific Compensation Corporation (“PacificComp”). On September 12, 2017, AIHL signed a definitive agreement to sell PacificComp to CopperPoint Mutual Insurance Company (“CopperPoint”) for total cash consideration of approximately $158 million. The transaction closed on December 31, 2017, at which time: (i) approximately $442 million of PacificComp assets, consisting primarily of debt securities, and approximately $316 million of PacificComp liabilities, consisting primarily of loss and loss adjustment expenses (“LAE”) reserves, were transferred to CopperPoint; and (ii) AIHL recorded an after-tax pre-acquisition Although Alleghany’s primary sources of revenues and earnings are its reinsurance and insurance operations and investments, Alleghany also sources, executes, manages and monitors certain private investments primarily through its wholly-owned subsidiary Alleghany Capital Corporation (“Alleghany Capital”). Alleghany Capital’s investments include: • Bourn & Koch, Inc. (“Bourn & Koch”), a manufacturer/remanufacturer of specialty machine tools and supplier of replacement parts, accessories and services for a variety of cutting technologies, headquartered in Rockford, Illinois; • 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 • Jazwares, LLC (together with its affiliates, “Jazwares”), a global toy, entertainment and musical instrument company, headquartered in Sunrise, Florida; • WWSC Holdings, LLC (“W&W|AFCO Steel”), a structural steel fabricator and erector, headquartered in Oklahoma City, Oklahoma; and • a 45 percent equity interest in 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. The results of W&W|AFCO Steel have been included in Alleghany’s consolidated results beginning with its acquisition by Alleghany Capital on April 28, 2017. On February 7, 2018, W&W|AFCO Steel acquired Hirschfeld Holdings, LP (“Hirschfeld”). Wilbert is accounted for under the equity method of accounting and is included in other invested assets. The results of Wilbert have been included in Alleghany’s consolidated results beginning with its acquisition by Alleghany Capital on August 1, 2017. In addition, Alleghany owns certain other holding-company investments. Alleghany’s wholly-owned subsidiary, Stranded Oil Resources Corporation (“SORC”) is an exploration and production company focused on enhanced oil recovery, headquartered in Golden, Colorado. 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. 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 and the Consolidated Statements of Earnings and Comprehensive Income as noncontrolling interests. Because all noncontrolling interests have the option to sell their ownership interests to Alleghany in the future (generally through 2024), the portion of stockholders’ equity that is not attributable to Alleghany stockholders is presented on the Consolidated Balance Sheets as redeemable noncontrolling interests for all periods presented. During the first six months of 2018, the noncontrolling interests outstanding were approximately as follows: Bourn & Koch - 11 percent; Kentucky Trailer - 21 percent; IPS - 16 percent; Jazwares - 23 percent; and W&W|AFCO Steel - 20 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 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) Other Significant Accounting Principles Alleghany’s significant accounting principles can be found in Note 1 to Notes to Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of the 2017 Form 10-K. (c) Recent Accounting Standards Recently Adopted In February 2018, the Financial Accounting Standards Board (the “FASB”) issued guidance on certain tax effects caused by the Tax Cuts and Jobs Act of 2017 (the “Tax Act”), which was signed into law on December 22, 2017. The Tax Act, among other things, reduced the U.S. corporate federal income tax rate from 35.0 percent to 21.0 percent, effective January 1, 2018 for the 2018 tax year. Under such circumstances, GAAP requires that the value of deferred tax assets and liabilities be reduced through tax expense. The new guidance provides an option to reclassify any stranded tax amounts that remain in accumulated other comprehensive income to retained earnings, either retrospectively or at the beginning of the period in which the adoption is elected. This guidance became effective in the first quarter of 2018 for public entities, with early adoption permitted in 2017. Alleghany adopted this new guidance in the first quarter of 2018 and has elected to reclassify stranded tax amounts that remain in accumulated other comprehensive income, in the amount of approximately $135 million, to retained earnings as of January 1, 2018. See Note 7(b) of this Form 10-Q 10-K In March 2017, the FASB issued guidance that reduces the amortization period for the premium on certain purchased callable debt securities to the earliest call date. The guidance applies specifically to noncontingent call features that are callable at a predetermined and fixed price and date. The accounting for purchased callable debt securities held at a discount is not affected. This guidance is effective in the first quarter of 2019 for public entities with early adoption permitted. Alleghany adopted this guidance in the fourth quarter of 2017 and recorded a cumulative effect reduction of approximately $13 million directly to opening 2017 retained earnings and an offsetting increase in opening 2017 accumulated other comprehensive income. The implementation did not have a material impact on Alleghany’s results of operations and financial condition. See Note 7(b) of this Form 10-Q In May 2014, the FASB, together with the International Accounting Standards Board, issued guidance on the recognition of revenue from contracts with customers. Under this guidance, revenue is recognized as the transfer of goods and services to customers takes place and in amounts that reflect the payment or payments that are expected to be received from the customers for those goods and services. This guidance also requires new disclosures about revenue. Revenues related to insurance and reinsurance contracts and revenues from investments are not impacted by this guidance, whereas noninsurance revenues arising from the sale of manufactured goods and services is generally included within the scope of this guidance. This guidance, and all related amendments, became effective in the first quarter of 2018 for public entities, with early adoption permitted in 2017. Alleghany adopted this guidance in the first quarter of 2018 using the modified retrospective transition approach and the implementation did not have a material impact on its results of operations and financial condition. See Note 10 of this Form 10-Q In January 2016, the FASB issued guidance that changes the recognition and measurement of certain financial instruments. This guidance requires investments in equity securities (except those accounted for under the equity method of accounting, but including partnership investments not accounted for under the equity method) to be measured at fair value with changes in fair value recognized in net earnings. For equity securities that do not have readily determinable fair values, measurement may be at cost, adjusted for any impairment and changes resulting from observable price changes for a similar investment of the same issuer. This guidance also changes the presentation and disclosure of financial instruments by: (i) requiring that financial instrument disclosures of fair value use the exit price notion; (ii) requiring separate presentation of financial assets and financial liabilities by measurement category and form, either on the balance sheet or the accompanying notes to the financial statements; (iii) requiring separate presentation in other comprehensive income for the portion of the change in a liability’s fair value resulting from instrument-specific credit risk when an election has been made to measure the liability at fair value; and (iv) eliminating the requirement to disclose the methods and significant assumptions used to estimate the fair value for financial instruments measured at amortized cost on the balance sheet. This guidance is effective for fiscal years beginning after December 15, 2017 for public entities, including interim periods within those fiscal years. Except for the change in presentation for instrument-specific credit risk, this guidance does not permit early adoption. Alleghany adopted this guidance in the first quarter of 2018. As of January 1, 2018, approximately $736 million of net unrealized gains of equity securities, net of deferred taxes, were reclassified from accumulated other comprehensive income to retained earnings. Subsequently, all changes in unrealized gains or losses of equity securities, net of deferred taxes, were presented in the Consolidated Statements of Earnings rather than the Consolidated Statements of Comprehensive Income, under the caption “change in the fair value of equity securities.” Results arising from partnership investments, whether accounted for under the equity method or at fair value, continue to be reported as a component of net investment income. The implementation did not have a material impact on Alleghany’s financial condition. See Note 3 of this Form 10-Q 10-Q Future Application of Accounting Standards In February 2016, the FASB issued guidance on leases. Under this guidance, a lessee is required to recognize lease liabilities and corresponding right-of-use 10-K 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. Estimates of expected credit losses are to be based on historical experience, current conditions and reasonable and supportable forecasts. Credit losses for securities accounted for on an available-for-sale 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 is effective in the first quarter of 2020 for public entities, with early adoption permitted. Alleghany will adopt this guidance in the first quarter of 2020 and does not currently believe that the implementation will have a material impact on its results of operations and financial condition. See Note 2 to Notes to Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of the 2017 Form 10-K In August 2017, the FASB issued guidance that simplifies the requirements to achieve hedge accounting, better reflects the economic results of hedging in the financial statements and improves the alignment between hedge accounting and a company’s risk management activities. This guidance is effective in the first quarter of 2019 for public entities, with early adoption permitted. Alleghany will adopt this guidance in the first quarter of 2019 and does not currently believe that the implementation will have a material impact on its results of operations and financial condition.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	6 Months Ended
	Jun. 30, 2018
Fair Value of Financial Instruments	2. Fair Value of Financial Instruments The following table presents the carrying value and estimated fair value of Alleghany’s consolidated financial instruments as of June 30, 2018 and December 31, 2017: June 30, 2018 December 31, 2017 Carrying Value Fair Value Carrying Value Fair Value ($ in millions) Assets Investments (excluding equity method investments and loans) (1) $ 17,401.1 $ 17,401.1 $ 17,406.5 $ 17,406.5 Liabilities Senior Notes and other debt (2) $ 1,569.4 $ 1,697.6 $ 1,484.9 $ 1,614.6 (1) This table includes debt and equity securities, as well as partnership and non-marketable (2) See Note 8 to Notes to Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of the 2017 Form 10-K The following tables present Alleghany’s financial instruments measured at fair value and the level of the fair value hierarchy of inputs used as of June 30, 2018 and December 31, 2017: Level 1 Level 2 Level 3 Total ($ in millions) As of June 30, 2018 Equity securities: Common stock $ 4,704.2 $ 3.6 $ - $ 4,707.8 Preferred stock - - 6.3 6.3 Total equity securities 4,704.2 3.6 6.3 4,714.1 Debt securities: U.S. Government obligations - 993.6 - 993.6 Municipal bonds - 2,842.5 - 2,842.5 Foreign government obligations - 932.9 - 932.9 U.S. corporate bonds - 2,040.6 367.8 2,408.4 Foreign corporate bonds - 1,317.6 94.8 1,412.4 Mortgage and asset-backed securities: Residential mortgage-backed securities (“RMBS”) (1) - 1,160.7 - 1,160.7 Commercial mortgage-backed securities (“CMBS”) - 540.6 - 540.6 Other asset-backed securities (2) - 640.8 1,224.0 1,864.8 Total debt securities - 10,469.3 1,686.6 12,155.9 Short-term investments - 472.8 - 472.8 Other invested assets (3) - - 58.3 58.3 Total investments (excluding equity method investments and loans) $ 4,704.2 $ 10,945.7 $ 1,751.2 $ 17,401.1 Senior Notes and other debt $ - $ 1,512.2 $ 185.4 $ 1,697.6 Level 1 Level 2 Level 3 Total ($ in millions) As of December 31, 2017 Equity securities: Common stock $ 4,090.7 $ 3.8 $ - $ 4,094.5 Preferred stock - 3.1 1.9 5.0 Total equity securities 4,090.7 6.9 1.9 4,099.5 Debt securities: U.S. Government obligations - 948.0 - 948.0 Municipal bonds - 3,682.1 - 3,682.1 Foreign government obligations - 1,006.6 - 1,006.6 U.S. corporate bonds - 2,173.0 260.0 2,433.0 Foreign corporate bonds - 1,424.6 75.2 1,499.8 Mortgage and asset-backed securities: RMBS (1) - 833.8 161.8 995.6 CMBS - 550.1 1.6 551.7 Other asset-backed securities (2) - 503.3 1,101.3 1,604.6 Total debt securities - 11,121.5 1,599.9 12,721.4 Short-term investments - 578.1 - 578.1 Other invested assets (3) - - 7.5 7.5 Total investments (excluding equity method investments and loans) $ 4,090.7 $ 11,706.5 $ 1,609.3 $ 17,406.5 Senior Notes and other debt $ - $ 1,513.6 $ 101.0 $ 1,614.6 (1) Primarily includes government agency pass-through securities guaranteed by a government agency or government sponsored enterprise, among other types of RMBS. (2) Includes $1,224.0 million and $1,101.3 million of collateralized loan obligations as of June 30, 2018 and December 31, 2017, respectively. (3) Includes partnership and non-marketable In the three and six months ended June 30, 2018, Alleghany transferred out of Level 3 $151.9 million and $153.5 million, respectively, of financial instruments, principally due to an increase in observable inputs related to the valuation of such assets. Specifically, during the second quarter of 2018, there was a decrease in the weight given to non-binding As further described in Note 3(h), on March 15, 2018, most of AIHL’s limited partnership interests in certain subsidiaries of Ares Management LLC (“Ares”) were converted into Ares common units. As a result of the conversion, as of March 15, 2018, $208.2 million of Ares common units, classified as common stock, was transferred into Level 1, and $58.7 million of Ares limited partner interests, classified as other invested assets, was transferred into Level 3. In addition to the above, in the three and six months ended June 30, 2018, Alleghany transferred into Level 3 $1.3 million and $5.6 million, respectively, of financial instruments, principally due to a decrease in observable inputs related to the valuation of such assets and, specifically, a decrease in broker quotes. Of the $5.6 million of transfers, $4.3 million related to preferred stock, $1.2 million related to U.S. corporate bonds, and $0.1 million related to other invested assets. There were no other material transfers between Levels 1, 2 or 3 in the three and six months ended June 30, 2018. In the three and six months ended June 30, 2017, Alleghany transferred out of Level 3 $3.1 million and $7.2 million, respectively, of financial instruments that were principally due to an increase in observable inputs related to the valuation of such assets and, specifically, an increase in broker quotes. Of the $7.2 million of transfers, $4.8 million related to U.S. corporate bonds and $2.4 million related to common stock. In the three and six months ended June 30, 2017, Alleghany transferred into Level 3 $2.1 million and $4.7 million, respectively, of financial instruments that were principally due to a decrease in observable inputs related to the valuation of such assets and, specifically, a decrease in broker quotes. Of the $4.7 million of transfers, $3.0 million related to U.S. corporate bonds, $1.4 million related to common stock and $0.3 million related to foreign corporate bonds. There were no other material transfers between Levels 1, 2 or 3 in the three and six months ended June 30, 2017. The following tables present reconciliations of the changes during the six months ended June 30, 2018 and 2017 in Level 3 assets measured at fair value: Debt Securities Mortgage and asset-backed Six Months Ended June 30, 2018 Preferred U.S. Foreign RMBS CMBS Other Asset- Other (1) Total ($ in millions) Balance as of January 1, 2018 $ 1.9 $ 260.0 $ 75.2 $ 161.8 $ 1.6 $ 1,101.3 $ 7.5 $ 1,609.3 Net realized/unrealized gains (losses) included in: Net earnings (2) - - (0.1 ) (0.3 ) - 1.0 1.1 1.7 Other comprehensive income 0.2 (6.9 ) (2.2 ) (5.3 ) - (7.7 ) (3.5 ) (25.4 ) Purchases - 117.3 23.8 - - 495.1 - 636.2 Sales (0.1 ) (2.5 ) (1.9 ) (5.6 ) - (365.7 ) (5.6 ) (381.4 ) Issuances - - - - - - - - Settlements - - - - - - - - Transfers into Level 3 4.3 1.2 - - - - 58.8 64.3 Transfers out of Level 3 - (1.3 ) - (150.6 ) (1.6 ) - - (153.5 ) Balance as of June 30, 2018 $ 6.3 $ 367.8 $ 94.8 $ - $ - $ 1,224.0 $ 58.3 $ 1,751.2 Equity Securities Debt Securities Mortgage and asset-backed Six Months Ended June 30, 2017 Common Preferred U.S. Foreign RMBS CMBS Other Asset- Other (1) Total ($ in millions) Balance as of January 1, 2017 $ 4.3 $ - $ 72.9 $ 0.4 $ 5.9 $ 4.3 $ 903.8 $ 28.1 $ 1,019.7 Net realized/unrealized gains (losses) Net earnings (2) (0.1 ) - (0.3 ) - 0.1 - 2.7 10.8 13.2 Other comprehensive income 0.5 - 1.5 0.4 0.2 0.1 11.9 (10.6 ) 4.0 Purchases - 2.4 151.4 36.0 - - 578.0 - 767.8 Sales (1.8 ) (0.2 ) (4.3 ) (0.1 ) - (2.2 ) (19.7 ) (21.6 ) (49.9 ) Issuances - - - - - - - - - Settlements - - (4.4 ) - (0.7 ) (0.3 ) (315.8 ) - (321.2 ) Transfers into Level 3 1.4 - 3.0 0.3 - - - - 4.7 Transfers out of Level 3 (2.4 ) - (4.8 ) - - - - - (7.2 ) Balance as of June 30, 2017 $ 1.9 $ 2.2 $ 215.0 $ 37.0 $ 5.5 $ 1.9 $ 1,160.9 $ 6.7 $ 1,431.1 (1) Includes partnership and non-marketable (2) There were no other than temporary impairment (“OTTI”) losses recorded in net earnings related to Level 3 assets still held as of June 30, 2018 and 2017. Net unrealized losses related to Level 3 assets as of June 30, 2018 and December 31, 2017 were not material. See Note 1(c) to Notes to Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of the 2017 Form 10-K

Investments

Investments	6 Months Ended
	Jun. 30, 2018
Investments	3. Investments (a) Unrealized Gains and Losses The following tables present the amortized cost or cost and the fair value of AFS securities as of June 30, 2018 and December 31, 2017: Amortized Gross Gross Fair Value ($ in millions) As of June 30, 2018 Debt securities: U.S. Government obligations $ 1,026.0 $ 0.6 $ (33.0) $ 993.6 Municipal bonds 2,803.5 56.1 (17.1) 2,842.5 Foreign government obligations 929.3 9.3 (5.7) 932.9 U.S. corporate bonds 2,432.4 17.9 (41.9) 2,408.4 Foreign corporate bonds 1,418.5 12.9 (19.0) 1,412.4 Mortgage and asset-backed securities: RMBS 1,184.1 3.3 (26.7) 1,160.7 CMBS 545.5 2.5 (7.4) 540.6 Other asset-backed securities (1) 1,866.7 4.9 (6.8) 1,864.8 Total debt securities 12,206.0 107.5 (157.6) 12,155.9 Short-term investments 472.8 - - 472.8 Total investments $ 12,678.8 $ 107.5 $ (157.6) $ 12,628.7 Amortized Gross Gross Fair Value ($ in millions) As of December 31, 2017 Equity securities: Common stock $ 3,165.8 $ 932.5 $ (3.8) $ 4,094.5 Preferred stock 4.9 0.1 - 5.0 Total equity securities 3,170.7 932.6 (3.8) 4,099.5 Debt securities: U.S. Government obligations 963.9 1.7 (17.6) 948.0 Municipal bonds 3,578.9 109.8 (6.6) 3,682.1 Foreign government obligations 1,000.1 11.2 (4.7) 1,006.6 U.S. corporate bonds 2,381.1 61.6 (9.7) 2,433.0 Foreign corporate bonds 1,481.8 24.5 (6.5) 1,499.8 Mortgage and asset-backed securities: RMBS 993.9 6.3 (4.6) 995.6 CMBS 545.0 9.0 (2.3) 551.7 Other asset-backed securities (1) 1,592.1 13.8 (1.3) 1,604.6 Total debt securities 12,536.8 237.9 (53.3) 12,721.4 Short-term investments 578.1 - - 578.1 Total investments $ 16,285.6 $ 1,170.5 $ (57.1) $ 17,399.0 (1) Includes $1,224.0 million and $1,101.3 million of collateralized loan obligations as of June 30, 2018 and December 31, 2017, respectively. (b) Contractual Maturity The following table presents the amortized cost or cost and estimated fair value of debt securities by contractual maturity as of June 30, 2018. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. Amortized Fair Value ($ in millions) As of June 30, 2018 Short-term investments due in one year or less $ 472.8 $ 472.8 Mortgage and asset-backed securities (1) 3,596.3 3,566.1 Debt securities with maturity dates: One year or less 348.2 348.2 Over one through five years 3,042.6 3,024.8 Over five through ten years 2,997.0 2,973.6 Over ten years 2,221.9 2,243.2 Total debt securities $ 12,206.0 $ 12,155.9 (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 the three and six months ended June 30, 2018 and 2017: Three Months Ended Six Months Ended June 30, June 30, 2018 2017 2018 2017 ($ in millions) Interest income $ 104.8 $ 102.5 $ 206.8 $ 201.7 Dividend income 22.3 11.8 38.6 21.2 Investment expenses (6.6 ) (6.9 ) (18.6 ) (14.3 ) Pillar Investments (1) 1.9 3.2 1.9 6.6 Limited partnership interests in certain subsidiaries of Ares (1) (0.7 ) (12.6 ) 13.2 (7.4 ) Other investment results 4.6 3.7 8.5 9.4 Total $ 126.3 $ 101.7 $ 250.4 $ 217.2 (1) See Note 3(h) of this Form 10-Q As of June 30, 2018, non-income (d) Change in the Fair Value of Equity Securities In the first quarter of 2018, Alleghany adopted new investment accounting guidance, which requires changes in the fair value of equity securities, except those accounted for under the equity method, to be recognized in net earnings. In earlier periods, equity securities were considered to be AFS and were included in the analysis of OTTI. See Note 1(c) of this Form 10-Q The following table presents increases in the fair value of equity securities for the three and six months ended June 30, 2018: Three Months Ended Six Months Ended June 30, 2018 June 30, 2018 ($ in millions) Change in the fair value of equity securities sold during the period $ 4.4 $ 16.0 Change in the fair value of equity securities held at the end of the period 180.8 126.6 Change in the fair value of equity securities $ 185.2 $ 142.6 (e) Realized Gains and Losses The proceeds from sales of debt and equity securities were $0.8 billion and $1.5 billion for the three months ended June 30, 2018 and 2017, respectively, and $1.9 billion and $4.2 billion for the six months ended June 30, 2018 and 2017, respectively. Realized capital gains and losses for the three months ended June 30, 2018 primarily reflect the sale of debt securities. Realized capital gains and losses for the first six months of 2018 primarily reflect a $45.7 million gain on AIHL’s conversion of its limited partnership interests in certain subsidiaries of Ares into Ares common units. See Note 3(h) of this Form 10-Q Realized capital gains and losses for the three and six months ended June 30, 2017 primarily reflect the sale of equity securities. Realized capital gains for the first six months of 2017 also include the sale of certain equity securities resulting from a partial restructuring of the equity portfolio. The following table presents amounts of gross realized capital gains and gross realized capital losses for the three and six months ended June 30, 2018 and 2017: Three Months Ended Six Months Ended June 30, 2018 2017 2018 2017 ($ in millions) Gross realized capital gains $ 6.5 $ 34.0 $ 66.4 $ 142.7 Gross realized capital losses - (24.7) (15.4) (73.8) Net realized capital gains $ 6.5 $ 9.3 $ 51.0 $ 68.9 Gross realized loss amounts exclude OTTI losses, as discussed below. (f) OTTI Losses Alleghany holds its debt securities as AFS and, as such, these securities are recorded at fair value. Alleghany continually monitors the difference between amortized cost and the estimated fair value of its debt investments, which involves uncertainty as to whether declines in value are temporary in nature. The analysis of a security’s decline in value is performed in its functional currency. If the decline is deemed temporary, Alleghany records the decline as an unrealized loss in stockholders’ equity. If the decline is deemed to be other than temporary, Alleghany writes its amortized cost-basis down to the fair value of the security and records an OTTI loss on its statement of earnings. In addition, any portion of such decline 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. Debt securities in an unrealized loss position are evaluated for OTTI if they meet any of the following criteria: (i) they are trading at a discount of at least 20 percent to amortized cost for an extended period of time (nine consecutive months or more); (ii) there has been a negative credit or news event with respect to the issuer that could indicate the existence of an OTTI; 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 an OTTI 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 an OTTI 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 OTTI loss recognized in earnings is the non-credit 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. OTTI losses in the first six months of 2018 reflect $0.5 million of unrealized losses on debt securities that were deemed to be other than temporary and, as such, were required to be charged against earnings. Of the $0.5 million of OTTI losses, none were incurred in the second quarter of 2018. OTTI losses in the first six months of 2017 reflect $7.0 million of unrealized losses that were deemed to be other than temporary and, as such, were required to be charged against earnings. Of the $7.0 million of OTTI losses, $6.8 million related to equity securities, primarily in the retail sector, and $0.2 million related to debt securities. The determination that unrealized losses on the securities were other than temporary was primarily due to the duration of the decline in the fair value of equity and debt securities relative to their costs. Of the $7.0 million of OTTI losses, $3.8 million was incurred in the second quarter of 2017. Upon the ultimate disposition of the securities for which OTTI losses have been recorded, a portion of the loss may be recoverable depending on market conditions at the time of disposition. After adjusting the amortized cost basis of securities for the recognition of OTTI losses, the remaining gross unrealized investment losses for debt securities as of June 30, 2018 were deemed to be temporary, based on, among other factors: (i) the duration of time and the relative magnitude to which the fair value of these investments had been below cost were not indicative of an OTTI loss; (ii) the absence of compelling evidence that would cause Alleghany to call into question the financial condition or near-term business prospects of the issuer of the security; and (iii) Alleghany’s ability and intent to hold the security for a period of time sufficient to allow for any anticipated recovery. Alleghany may ultimately record a realized loss after having originally concluded that the decline in value was temporary. Risks and uncertainties are inherent in the methodology. Alleghany’s methodology for assessing other than temporary declines in value contains inherent risks and uncertainties which could include, but are not limited to, incorrect assumptions about financial condition, liquidity or future prospects, inadequacy of any underlying collateral and unfavorable changes in economic conditions or social trends, interest rates or credit ratings. (g) Aging of Gross Unrealized Losses The following tables present gross unrealized losses and related fair values for Alleghany’s AFS securities, grouped by duration of time in a continuous unrealized loss position, as of June 30, 2018 and December 31, 2017: Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross ($ in millions) As of June 30, 2018 Debt securities: U.S. Government obligations $ 532.8 $ 12.7 $ 390.1 $ 20.3 $ 922.9 $ 33.0 Municipal bonds 543.2 8.2 215.2 8.9 758.4 17.1 Foreign government obligations 189.9 2.1 130.5 3.6 320.4 5.7 U.S. corporate bonds 1,355.7 32.1 174.1 9.8 1,529.8 41.9 Foreign corporate bonds 656.7 12.7 189.2 6.3 845.9 19.0 Mortgage and asset-backed securities: RMBS 887.3 21.3 116.5 5.4 1,003.8 26.7 CMBS 277.9 4.6 32.3 2.8 310.2 7.4 Other asset-backed securities 982.2 6.4 27.7 0.4 1,009.9 6.8 Total temporarily impaired securities $ 5,425.7 $ 100.1 $ 1,275.6 $ 57.5 $ 6,701.3 $ 157.6 Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross ($ in millions) As of December 31, 2017 Equity securities: Common stock $ 145.7 $ 3.8 $ - $ - $ 145.7 $ 3.8 Preferred stock - - - - - - Total equity securities 145.7 3.8 - - 145.7 3.8 Debt securities: U.S. Government obligations 447.8 4.4 416.6 13.2 864.4 17.6 Municipal bonds 240.0 1.5 267.3 5.1 507.3 6.6 Foreign government obligations 321.9 2.7 72.2 2.0 394.1 4.7 U.S. corporate bonds 568.8 6.1 207.3 3.6 776.1 9.7 Foreign corporate bonds 417.4 3.0 159.4 3.5 576.8 6.5 Mortgage and asset-backed securities: RMBS 284.2 1.6 131.5 3.0 415.7 4.6 CMBS 112.2 0.5 34.7 1.8 146.9 2.3 Other asset-backed securities 211.1 0.9 65.7 0.4 276.8 1.3 Total debt securities 2,603.4 20.7 1,354.7 32.6 3,958.1 53.3 Total temporarily impaired securities $ 2,749.1 $ 24.5 $ 1,354.7 $ 32.6 $ 4,103.8 $ 57.1 As of June 30, 2018, Alleghany held a total of 1,995 debt securities that were in an unrealized loss position, of which 430 securities were in an unrealized loss position continuously for 12 months or more. The unrealized losses associated with these debt securities consisted primarily of losses related primarily to U.S. Government obligations, U.S. corporate bonds, municipal bonds, foreign corporate bonds and RMBS. As of June 30, 2018, the vast majority of Alleghany’s debt securities were rated investment grade, with 4.3 percent of debt securities having issuer credit ratings that were below investment grade or not rated, compared with 5.3 percent as of December 31, 2017. (h) 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 invested $175.0 million and AIHL invested $25.0 million 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 June 30, 2018, Alleghany’s carrying value in the Pillar Investments, as determined under the equity method of accounting, was $219.8 million, which is net of returns of capital received from the Pillar Investments. In July 2013, AIHL invested $250.0 million in Ares, an asset manager, in exchange for a 6.25 percent equity stake in Ares, with an agreement to engage Ares to manage up to $1.0 billion in certain investment strategies. In May 2014, Ares completed an initial public offering of its common units. Upon completion of the initial public offering, Alleghany’s equity investment in Ares converted into limited partner interests in certain Ares subsidiaries that were convertible into Ares common units. On March 15, 2018, most of AIHL’s limited partner interests were converted into Ares common units. As a result of the conversion and with respect to the limited partnership interests that were converted into Ares common units, AIHL: (i) reclassified its converted interests from other invested assets to equity securities; (ii) increased its carrying value to $208.2 million to reflect the fair value of Ares common units; and (iii) recorded the $45.7 million increase in carrying value as a realized capital gain as of March 15, 2018. As a result of the conversion and with respect to the unconverted limited partnership interests, AIHL: (i) changed its accounting from the equity method to fair value; (ii) increased its carrying value to $58.7 million to reflect the fair value of Ares limited partnership interests; and (iii) recorded the $12.9 million increase in carrying value as a component of net investment income as of March 15, 2018. (i) Investments in Commercial Mortgage Loans As of June 30, 2018, the carrying value of Alleghany’s commercial mortgage loan portfolio was $695.8 million, representing the unpaid principal balance on the loans. As of June 30, 2018, there was no allowance for loan losses. 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, mature in two to ten years from loan origination and the principal amounts of the loans were no more than approximately two-thirds

Reinsurance Ceded

Reinsurance Ceded	6 Months Ended
	Jun. 30, 2018
Reinsurance Ceded	4. Reinsurance Ceded 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 purchase reinsurance and retrocessional coverages from highly-rated third-party reinsurers. 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. TransRe enters into retrocession arrangements, including property catastrophe retrocession arrangements, in order to reduce the effect of individual or aggregate exposure to losses, reduce volatility in specific lines of business, improve risk-adjusted portfolio returns and increase gross premium writings and risk capacity without requiring additional capital. RSUI reinsures its property lines of business through a program consisting of surplus share treaties, facultative placements, per risk and catastrophe excess of loss treaties. RSUI’s catastrophe reinsurance program and property per risk reinsurance program run on an annual basis from May 1 to the following April 30 and portions expired on April 30, 2018. Both programs were renewed on May 1, 2018 with substantially similar terms as the expired programs.

Liability for Loss and LAE

Liability for Loss and LAE	6 Months Ended
	Jun. 30, 2018
Liability for Loss and LAE	5. Liability for Loss and LAE (a) Liability Rollforward The following table presents the activity in the liability for loss and LAE in the six months ended June 30, 2018 and 2017: Six Months Ended 2018 2017 ($ in millions) Reserves as of January 1 $ 11,871.3 $ 11,087.2 Less: reinsurance recoverables (1) 1,650.1 1,236.2 Net reserves as of January 1 10,221.2 9,851.0 Other adjustments 2.0 - Incurred loss and LAE, net of reinsurance, related to: Current year 1,546.7 1,545.6 Prior years (137.9 ) (111.4 ) Total incurred loss and LAE, net of reinsurance 1,408.8 1,434.2 Paid loss and LAE, net of reinsurance, related to: (2) Current year 237.6 242.7 Prior years 1,366.1 1,190.1 Total paid loss and LAE, net of reinsurance 1,603.7 1,432.8 Foreign currency exchange rate effect (24.2 ) 55.4 Net reserves as of June 30 10,004.1 9,907.8 Reinsurance recoverables as of June 30 (1) 1,511.4 1,152.4 Reserves as of June 30 $ 11,515.5 $ 11,060.2 (1) Reinsurance recoverables in this table include only ceded loss and LAE reserves. (2) Includes paid losses, net of reinsurance, related to commutations. Gross loss and LAE reserves and reinsurance recoverables as of June 30, 2018 decreased from December 31, 2017, primarily reflecting payments on catastrophe losses incurred in 2017 and favorable prior accident year loss reserve development. The decrease in net loss and LAE reserves was partially offset by the collection of reinsurance recoverables related to catastrophe losses incurred in 2017. (b) Liability Development The following table presents the (favorable) unfavorable prior accident year loss reserve development for the three and six months ended June 30, 2018 and 2017: Three Months Ended Six Months Ended 2018 2017 2018 2017 ($ in millions) Reinsurance Segment Property: Catastrophe events $ 5.1 ( 1) $ (4.0) (2) $ (25.3) (3) $ (4.4) (2) Non-catastrophe (18.8) (4) (18.9) (5) (29.8) (4) (50.0) (5) Total property (13.7) (22.9) (55.1) (54.4) Casualty & other: Malpractice Treaties (6) (3.4) (2.0) (3.4) (2.0) Ogden rate impact (7) - - - 24.4 Other (33.6) (8) (27.7) (9) (63.8) (10) (58.9) (9) Total casualty & other (37.0) (29.7) (67.2) (36.5) Total Reinsurance Segment (50.7) (52.6) (122.3) (90.9) Insurance Segment RSUI: Casualty (1.5) (11) (9.5) (12) (12.5) (13) (21.6) (12) Property and other 0.1 (0.8) - 2.9 ( 14) Total RSUI (1.4) (10.3) (12.5) (18.7) CapSpecialty (0.1) (0.2) (15) (3.1) (16) (0.8) (15) PacificComp - (0.5) (17) - (1.0) (17) Total incurred related to prior years $ (52.2) $ (63.6) $ (137.9) $ (111.4) (1) Primarily reflects unfavorable prior accident year loss reserve development related to Hurricane Maria that occurred in the 2017 accident year, partially offset by favorable prior accident year loss reserve development related to Hurricane Harvey that occurred in the 2017 accident year and catastrophes that occurred in the 2016 accident year. (2) Primarily reflects favorable prior accident year loss reserve development related to catastrophes that occurred in the 2010 through 2016 accident years. (3) Primarily reflects favorable prior accident year loss reserve development related to Hurricanes Harvey and Maria that occurred in the 2017 accident year and catastrophes that occurred in the 2016 accident year. (4) Primarily reflects favorable prior accident year loss reserve development in the 2016 and 2017 accident years. (5) Primarily reflects favorable prior accident year loss reserve development in the 2013 through 2016 accident years. (6) Represents certain medical malpractice treaties pursuant to which the increased underwriting profits created by the favorable prior accident year loss reserve development are largely retained by the cedants. As a result, the favorable prior accident year loss reserve development is largely offset by an increase in profit commission expense incurred when such favorable prior accident year loss reserve development occurs. (7) Represents unfavorable prior accident year loss reserve development related to the U.K. Ministry of Justice’s significant reduction in the discount rate, referred to as the Ogden rate, used to calculate lump-sum (8) Primarily reflects favorable prior accident year loss reserve development in the shorter-tailed casualty lines of business in the 2015 and 2017 accident years and the longer-tailed lines of business in the 2008 through 2010 accident years. (9) Primarily reflects favorable prior accident year loss reserve development in the longer-tailed U.S. professional liability lines of business in the 2005 through 2014 accident years, partially offset by unfavorable development in the shorter-tailed casualty lines of business in the 2015 accident year in the U.S. and in the U.K. (10) Primarily reflects favorable prior accident year loss reserve development in the shorter-tailed casualty lines of business in the 2016 and 2017 accident years and the longer-tailed lines of business in the 2008 through 2010 accident years. (11) Primarily reflects favorable prior accident year loss reserve development in the umbrella/excess lines of business in the 2005 through 2012 accident years, partially offset by unfavorable prior accident year loss reserve development in the directors’ and officers’ liability lines of business in the 2012 accident year. (12) Primarily reflects favorable prior accident year loss reserve development in the umbrella/excess lines of business in the 2005 through 2011 accident years. (13) Primarily reflects favorable prior accident year loss reserve development in the umbrella/excess lines of business in the 2005 through 2012 accident years, partially offset by unfavorable prior accident year loss reserve development in the directors’ and officers’ liability lines of business in the 2009 and 2012 accident years. (14) Primarily reflects unfavorable prior accident year property loss reserve development in the binding authority lines of business in the 2015 and 2016 accident years. (15) Primarily reflects favorable prior accident year loss reserve development in the casualty lines of business in the 2010 and 2015 accident years. (16) Primarily reflects favorable prior accident year loss reserve development in the surety lines of business in the 2016 and 2017 accident years. (17) Primarily reflects favorable prior accident year loss reserve development in the 2013 and prior accident years.

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2018
Income Taxes	6. Income Taxes The effective tax rate on earnings before income taxes for the first six months of 2018 was 19.1 percent, compared with 27.6 percent for the first six months of 2017. The decrease in the effective tax rate in the first six months of 2018 from the first six months of 2017 primarily reflects the decrease in the U.S. corporate federal income tax rate from 35.0 percent to 21.0 percent due to the Tax Act, partially offset by new limitations on certain deductions as a result of the Tax Act. There continues to be a degree of uncertainty as to how certain provisions of the Tax Act will be interpreted and implemented in practice in the future. Alleghany believes that, as of June 30, 2018, 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 June 30, 2018.

Stockholders' Equity

Stockholders' Equity	6 Months Ended
	Jun. 30, 2018
Stockholders' Equity	7. Stockholders’ Equity (a) Common Stock Repurchases In November 2015, the Alleghany Board of Directors authorized the repurchase of shares of common stock of Alleghany, par value $1.00 per share (“Common Stock”), at such times and at prices as management determines to be advisable, up to an aggregate of $400.0 million (the “2015 Repurchase Program”). In June 2018, the Alleghany Board of Directors authorized, upon the completion of the 2015 Repurchase Program, 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. As of June 30, 2018, Alleghany had $527.1 million remaining under both share repurchase authorization programs. The following table presents the shares of Common Stock that Alleghany repurchased in the three and six months ended June 30, 2018 and 2017 pursuant to the 2015 Repurchase Program: Three Months Ended Six Months Ended June 30, June 30, 2018 2017 2018 2017 Shares repurchased 368,551 - 403,623 - Cost of shares repurchased (in millions) $ 214.8 $ - $ 236.1 $ - Average price per share repurchased $ 582.92 $ - $ 584.96 $ - (b) Accumulated Other Comprehensive Income (loss) The following table presents a reconciliation of the changes during the six months ended June 30, 2018 and 2017 in accumulated other comprehensive income (loss) attributable to Alleghany stockholders: Unrealized Unrealized Retirement Total ($ in millions) Balance as of January 1, 2018 $ 718.2 $ (84.6 ) $ (15.5 ) $ 618.1 Cumulative effect of adoption of new accounting pronouncements (1) Reclassification of net unrealized gains on equity securities, net of tax (735.6 ) - - (735.6 ) Reclassification of stranded taxes 156.6 (18.2 ) (3.3 ) 135.1 Total (579.0 ) (18.2 ) (3.3 ) (600.5 ) Other comprehensive income (loss), net of tax: Other comprehensive income (loss) before reclassifications (179.7 ) (5.4 ) (1.1 ) (186.2 ) Reclassifications from accumulated other comprehensive income (3.7 ) - - (3.7 ) Total (183.4 ) (5.4 ) (1.1 ) (189.9 ) Balance as of June 30, 2018 $ (44.2 ) $ (108.2 ) $ (19.9 ) $ (172.3 ) Unrealized Unrealized Retirement Total ($ in millions) Balance as of January 1, 2017 $ 232.2 $ (111.2 ) $ (11.7 ) $ 109.3 Cumulative effect of adoption of new accounting pronouncements (1) 12.9 - - 12.9 Other comprehensive income (loss), net of tax: Other comprehensive income (loss) before reclassifications 266.7 15.0 (0.3 ) 281.4 Reclassifications from accumulated other comprehensive income (40.3 ) - - (40.3 ) Total 226.4 15.0 (0.3 ) 241.1 Balance as of June 30, 2017 $ 471.5 $ (96.2 ) $ (12.0 ) $ 363.3 (1) See Note 1(c) of this Form 10-Q The following table presents reclassifications out of accumulated other comprehensive income attributable to Alleghany stockholders during the three and six months ended June 30, 2018 and 2017: Accumulated Other Three Months Ended June 30, Six Months Ended June 30, Comprehensive Income Component Line in Consolidated Statement of Earnings 2018 2017 2018 2017 ($ in millions) Unrealized appreciation of investments: Net realized capital gains (1) $ (6.5 ) $ (9.3 ) $ (5.3 ) $ (68.9 ) Other than temporary impairment losses - 3.8 0.5 7.0 Income taxes 1.4 1.9 1.1 21.6 Total reclassifications: Net earnings $ (5.1 ) $ (3.6 ) $ (3.7 ) $ (40.3 ) (1) For the six month period ended June 30, 2018, excludes a $45.7 million pre-tax 10-Q (c) Special Dividend In February 2018, the Alleghany Board of Directors declared a special dividend of $10 per share for stockholders of record on March 5, 2018. On March 15, 2018, Alleghany paid dividends to stockholders totaling $154.0 million.

Earnings Per Share of Common St

Earnings Per Share of Common Stock	6 Months Ended
	Jun. 30, 2018
Earnings Per Share of Common Stock	8. 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 the three and six months ended June 30, 2018 and 2017: Three Months Ended Six Months Ended June 30, June 30, 2018 2017 2018 2017 ($ in millions, except share amounts) Net earnings available to Alleghany stockholders $ 295.1 $ 101.8 $ 466.7 $ 251.0 Effect of dilutive securities - - - - Income available to common stockholders for diluted earnings per share $ 295.1 $ 101.8 $ 466.7 $ 251.0 Weighted average common shares outstanding applicable to 15,180,075 15,419,034 15,284,679 15,416,366 Effect of dilutive securities - - 4,915 5,703 Adjusted weighted average common shares outstanding 15,180,075 15,419,034 15,289,594 15,422,069 57,766 and 75,035 contingently issuable shares were potentially available during the first six months of 2018 and 2017, respectively, 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	6 Months Ended
	Jun. 30, 2018
Commitments and Contingencies	9. 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, furniture and equipment under long-term lease agreements. Additional information about leases can be found in Note 12(b) to Notes to Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of the 2017 Form 10-K. (c) Energy Holdings As of June 30, 2018, Alleghany had holdings in energy sector businesses of $920.0 million, comprised of $289.6 million of debt securities, $487.1 million of equity securities and $143.3 million of Alleghany’s equity attributable to SORC.

Segments of Business

Segments of Business	6 Months Ended
	Jun. 30, 2018
Segments of Business	10. Segments of Business (a) Overview Alleghany’s segments are reported in a manner consistent with the way management evaluates the business. As such, Alleghany classifies its business into three reportable segments – reinsurance, insurance and Alleghany Capital. Alleghany determined that Alleghany Capital qualified as a reportable segment in the first quarter of 2018, reflecting the increased significance of Alleghany Capital’s business to Alleghany and its projected growth. Reinsurance and insurance underwriting activities are evaluated separately from investment and other activities. Segment accounting policies are described in Note 1 to Notes to Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of the 2017 Form 10-K. 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 & other. TransRe provides property and casualty reinsurance to insurers and reinsurers through brokers and on a direct basis to ceding companies. TransRe also writes a modest amount of 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 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, CapSpecialty and, prior to its sale on December 31, 2017, PacificComp. 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, non-industrial Non-industrial On February 7, 2018, W&W|AFCO Steel acquired the outstanding equity of Hirschfeld, a fabricator of steel bridges and structural steel for stadiums, airports and other large commercial and industrial projects, for $111.3 million, consisting of $96.6 million in cash and $14.7 million of incremental debt. The acquisition-date consideration transferred and purchase price allocation to the acquired assets and assumed liabilities of Hirschfeld were based on estimated fair values that have not been finalized. As a result, the fair value recorded for these items is a provisional estimate and may be subject to adjustment. Once completed, any adjustment resulting from the valuations may impact the individual amounts recorded for acquired assets and assumed liabilities, as well as the residual goodwill. The acquisition accounting for Hirschfeld is expected to be finalized later in 2018. Corporate activities are not classified as a segment. The primary components of corporate activities are Alleghany Properties, SORC and activities at the Alleghany parent company. In addition, corporate activities include interest expense associated with the senior notes issued by Alleghany, whereas interest expense associated with senior notes issued by TransRe is included in “Total Segments” and interest expense associated with other debt is included in Alleghany Capital. Information related to the senior notes and other debt can be found in Note 8 to Notes to Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of the 2017 Form 10-K. (b) Results The following tables present the results for Alleghany’s three reportable segments and for corporate activities for the three and six months ended June 30, 2018 and 2017: Reinsurance Segment Insurance Segment Three Months Ended Property Casualty (1) Total RSUI Cap Total Subtotal Alleghany Total Corporate (2) Consolidated ($ in millions) Gross premiums written $ 345.1 $ 726.6 $ 1,071.7 $ 318.8 $ 88.7 $ 407.5 $ 1,479.2 $ - $ 1,479.2 $ (6.5 ) $ 1,472.7 Net premiums written 275.9 700.7 976.6 216.9 82.3 299.2 1,275.8 - 1,275.8 - 1,275.8 Net premiums earned 292.1 689.2 981.3 184.7 71.0 255.7 1,237.0 - 1,237.0 - 1,237.0 Net loss and LAE 153.5 440.0 593.5 105.7 39.0 144.7 738.2 - 738.2 - 738.2 Commissions, brokerage and other 94.8 223.2 318.0 53.7 30.4 84.1 402.1 - 402.1 - 402.1 Underwriting profit (3) $ 43.8 $ 26.0 $ 69.8 $ 25.3 $ 1.6 $ 26.9 96.7 - 96.7 - 96.7 Net investment income 121.1 1.2 122.3 4.0 126.3 Change in the fair value of equity securities 146.8 - 146.8 38.4 185.2 Net realized capital gains 6.8 (0.1 ) 6.7 (0.2 ) 6.5 Other than temporary impairment losses - - - - - Noninsurance revenue 4.7 329.0 333.7 9.0 342.7 Other operating expenses 19.9 314.5 334.4 8.8 343.2 Corporate administration 0.8 - 0.8 13.3 14.1 Amortization of intangible assets 0.2 5.8 6.0 - 6.0 Interest expense 6.9 2.3 9.2 13.1 22.3 Earnings before income taxes $ 348.3 $ 7.5 $ 355.8 $ 16.0 $ 371.8 Reinsurance Segment Insurance Segment Three Months Ended June 30, 2017 Property Casualty (1) Total RSUI Cap Pacific Total Subtotal Alleghany Total Corporate (2) Consolidated ($ in millions) Gross premiums written $ 369.1 $ 676.3 $ 1,045.4 $ 295.1 $ 73.3 $ 41.9 $ 410.3 $ 1,455.7 $ - $ 1,455.7 $ (5.7 ) $ 1,450.0 Net premiums written 317.2 661.6 978.8 204.6 68.4 41.3 314.3 1,293.1 - 1,293.1 - 1,293.1 Net premiums earned 270.5 686.9 957.4 178.5 64.1 43.9 286.5 1,243.9 - 1,243.9 - 1,243.9 Net loss and LAE 122.9 450.1 573.0 93.8 35.6 32.5 161.9 734.9 - 734.9 - 734.9 Commissions, brokerage and other underwriting expenses 87.9 234.3 322.2 53.0 27.2 11.3 91.5 413.7 - 413.7 - 413.7 Underwriting profit (3) $ 59.7 $ 2.5 $ 62.2 $ 31.7 $ 1.3 $ 0.1 $ 33.1 95.3 - 95.3 - 95.3 Net investment income 98.0 0.2 98.2 3.5 101.7 Change in the fair value of equity securities - - - - - Net realized capital gains 9.2 0.2 9.4 (0.1 ) 9.3 Other than temporary impairment losses (3.8 ) - (3.8 ) - (3.8 ) Noninsurance revenue 3.3 192.8 196.1 6.7 202.8 Other operating expenses 25.9 189.4 215.3 9.9 225.2 Corporate administration 0.8 - 0.8 13.6 14.4 Amortization of intangible assets (0.4 ) 5.0 4.6 - 4.6 Interest expense 6.8 1.0 7.8 13.2 21.0 Earnings (losses) before income taxes $ 168.9 $ (2.2 ) $ 166.7 $ (26.6 ) $ 140.1 Reinsurance Segment Insurance Segment Six Months Ended June 30, 2018 Property Casualty (1) Total RSUI Cap Total Subtotal Alleghany Total Corporate (2) Consolidated ($ in millions) Gross premiums written $ 742.3 $ 1,445.0 $ 2,187.3 $ 593.4 $ 163.2 $ 756.6 $ 2,943.9 $ - $ 2,943.9 $ (12.4 ) $ 2,931.5 Net premiums written 581.0 1,392.7 1,973.7 403.8 151.7 555.5 2,529.2 - 2,529.2 - 2,529.2 Net premiums earned 567.2 1,374.3 1,941.5 365.6 137.7 503.3 2,444.8 - 2,444.8 - 2,444.8 Net loss and LAE 250.1 882.8 1,132.9 202.6 73.3 275.9 1,408.8 - 1,408.8 - 1,408.8 Commissions, brokerage and other underwriting expenses 187.9 452.1 640.0 107.2 61.2 168.4 808.4 - 808.4 - 808.4 Underwriting profit (3) $ 129.2 $ 39.4 $ 168.6 $ 55.8 $ 3.2 $ 59.0 227.6 - 227.6 - 227.6 Net investment income 239.4 3.1 242.5 7.9 250.4 Change in the fair value of equity securities 132.7 - 132.7 9.9 142.6 Net realized capital gains 50.7 0.5 51.2 (0.2 ) 51.0 Other than temporary impairment losses (0.5 ) - (0.5 ) - (0.5 ) Noninsurance revenue 10.4 571.7 582.1 12.3 594.4 Other operating expenses 37.0 554.4 591.4 16.7 608.1 Corporate administration 0.5 - 0.5 21.4 21.9 Amortization of intangible assets - 11.2 11.2 - 11.2 Interest expense 13.6 3.6 17.2 26.6 43.8 Earnings (losses) before income taxes $ 609.2 $ 6.1 $ 615.3 $ (34.8 ) $ 580.5 Reinsurance Segment Insurance Segment Six Months Ended June 30, 2017 Property Casualty (1) Total RSUI Cap Pacific Total Subtotal Alleghany Total Corporate (2) Consolidated ($ in millions) Gross premiums written $ 744.5 $ 1,356.6 $ 2,101.1 $ 559.6 $ 138.8 $ 82.6 $ 781.0 $ 2,882.1 $ - $ 2,882.1 $ (11.2 ) $ 2,870.9 Net premiums written 602.4 1,325.8 1,928.2 387.2 129.4 81.4 598.0 2,526.2 - 2,526.2 - 2,526.2 Net premiums earned 557.3 1,326.2 1,883.5 361.2 126.2 82.2 569.6 2,453.1 - 2,453.1 - 2,453.1 Net loss and LAE 244.7 885.4 1,130.1 174.4 68.7 61.0 304.1 1,434.2 - 1,434.2 - 1,434.2 Commissions, brokerage and other underwriting expenses 178.7 459.0 637.7 107.9 54.9 21.7 184.5 822.2 - 822.2 - 822.2 Underwriting profit (loss) (3) $ 133.9 $ (18.2 ) $ 115.7 $ 78.9 $ 2.6 $ (0.5 ) $ 81.0 196.7 - 196.7 - 196.7 Net investment income 210.3 0.5 210.8 6.4 217.2 Change in the fair value of equity securities - - - - - Net realized capital gains 69.4 0.1 69.5 (0.6 ) 68.9 Other than temporary impairment losses (7.0 ) - (7.0 ) - (7.0 ) Noninsurance revenue 5.8 337.6 343.4 10.7 354.1 Other operating expenses 49.1 331.0 380.1 20.2 400.3 Corporate administration 1.6 - 1.6 29.7 31.3 Amortization of intangible assets (0.9 ) 9.3 8.4 - 8.4 Interest expense 13.6 1.8 15.4 26.5 41.9 Earnings (losses) before income taxes $ 411.8 $ (3.9 ) $ 407.9 $ (59.9 ) $ 348.0 (1) Primarily consists of the following assumed reinsurance lines of business: directors’ and officers’ liability; errors and omissions liability; general liability; medical malpractice; ocean marine and aviation; auto liability; accident and health; surety; and credit. (2) Includes elimination of minor reinsurance activity between segments. (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, OTTI losses, noninsurance revenue, 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) 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 three reportable segments and for corporate activities as of June 30, 2018: Identifiable Invested Assets Equity ($ in millions) Reinsurance segment $ 16,356.9 $ 13,387.8 $ 5,208.5 Insurance segment 6,837.9 5,263.3 2,891.5 Subtotal 23,194.8 18,651.1 8,100.0 Alleghany Capital 1,328.3 130.5 777.2 Total segments 24,523.1 18,781.6 8,877.2 Corporate activities 562.8 485.6 (472.8) Consolidated $ 25,085.9 $ 19,267.2 $ 8,404.4 Included in Alleghany Capital is debt associated with its operating subsidiaries, which totaled $185.4 million as of June 30, 2018. The $185.4 million includes $95.0 million of borrowings by W&W|AFCO Steel under its available credit facility and term loans (including borrowings incurred and assumed from its acquisition of Hirschfeld), $41.0 million of borrowings by Jazwares under its available credit facility, $19.1 million of term loans at Kentucky Trailer primarily related to borrowings to finance small acquisitions and borrowings under its available credit facility, $15.7 million of borrowings by IPS under its available credit facility, and $14.6 million of term loans at Bourn & Koch related to borrowings to finance an acquisition and borrowings under its available credit facility. None of these liabilities are guaranteed by Alleghany or Alleghany Capital. (d) Alleghany Capital Noninsurance Revenue For Alleghany Capital’s industrial and non-industrial Three Months Ended Six Months Ended 2018 2017 2018 2017 ($ in millions) Industrial (1) $ 221.9 $ 74.5 $ 367.4 $ 116.4 Non-industrial (2) 107.1 118.3 204.2 221.2 Corporate & other - - 0.1 - Alleghany Capital $ 329.0 $ 192.8 $ 571.7 $ 337.6 (1) For the three and six months ended June 30, 2018, the vast majority of noninsurance revenues were recognized as goods and services transferred to customers over time. For the three and six months ended June 30, 2017, approximately 66 percent and 57 percent, respectively, of noninsurance revenues were recognized as services were transferred to customers over time, with the remainder recognized as goods transferred at a point in time. See Note 1(c) of this Form 10-Q (2) For the three and six months ended June 30, 2018, approximately 70 percent of noninsurance revenues were recognized as services transferred to customers over time, with the remainder recognized as goods transferred at a point in time. For the three and six months ended June 30, 2017, approximately 75 percent and 78 percent, respectively, of noninsurance revenues were recognized as services were transferred to customers over time, with the remainder recognized as goods were transferred at a point in time. See Note 1(c) of this Form 10-Q

Summary of Significant Accoun17

Summary of Significant Accounting Principles (Policies)	6 Months Ended
	Jun. 30, 2018
Principles of Financial Statement Presentation	(a) Principles of Financial Statement Presentation This Quarterly Report on Form 10-Q 10-Q”) Form 10-K 10-K”) 10-Q Alleghany Corporation, a Delaware corporation, owns and manages certain operating subsidiaries and investments, anchored by a core position in property and casualty reinsurance and insurance. Through its wholly-owned subsidiary Transatlantic Holdings, Inc. (“TransRe”), Alleghany is engaged in the property and casualty reinsurance business. TransRe has been a subsidiary of Alleghany since March 2012. Through its wholly-owned subsidiary Alleghany Insurance Holdings LLC (“AIHL”) and its subsidiaries, 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 has been a subsidiary of AIHL since July 2003 and CapSpecialty has been a subsidiary of AIHL since January 2002. 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. Prior to December 31, 2017, AIHL’s insurance operations also included Pacific Compensation Corporation (“PacificComp”). On September 12, 2017, AIHL signed a definitive agreement to sell PacificComp to CopperPoint Mutual Insurance Company (“CopperPoint”) for total cash consideration of approximately $158 million. The transaction closed on December 31, 2017, at which time: (i) approximately $442 million of PacificComp assets, consisting primarily of debt securities, and approximately $316 million of PacificComp liabilities, consisting primarily of loss and loss adjustment expenses (“LAE”) reserves, were transferred to CopperPoint; and (ii) AIHL recorded an after-tax pre-acquisition Although Alleghany’s primary sources of revenues and earnings are its reinsurance and insurance operations and investments, Alleghany also sources, executes, manages and monitors certain private investments primarily through its wholly-owned subsidiary Alleghany Capital Corporation (“Alleghany Capital”). Alleghany Capital’s investments include: • Bourn & Koch, Inc. (“Bourn & Koch”), a manufacturer/remanufacturer of specialty machine tools and supplier of replacement parts, accessories and services for a variety of cutting technologies, headquartered in Rockford, Illinois; • 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 • Jazwares, LLC (together with its affiliates, “Jazwares”), a global toy, entertainment and musical instrument company, headquartered in Sunrise, Florida; • WWSC Holdings, LLC (“W&W|AFCO Steel”), a structural steel fabricator and erector, headquartered in Oklahoma City, Oklahoma; and • a 45 percent equity interest in 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. The results of W&W|AFCO Steel have been included in Alleghany’s consolidated results beginning with its acquisition by Alleghany Capital on April 28, 2017. On February 7, 2018, W&W|AFCO Steel acquired Hirschfeld Holdings, LP (“Hirschfeld”). Wilbert is accounted for under the equity method of accounting and is included in other invested assets. The results of Wilbert have been included in Alleghany’s consolidated results beginning with its acquisition by Alleghany Capital on August 1, 2017. In addition, Alleghany owns certain other holding-company investments. Alleghany’s wholly-owned subsidiary, Stranded Oil Resources Corporation (“SORC”) is an exploration and production company focused on enhanced oil recovery, headquartered in Golden, Colorado. 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. 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 and the Consolidated Statements of Earnings and Comprehensive Income as noncontrolling interests. Because all noncontrolling interests have the option to sell their ownership interests to Alleghany in the future (generally through 2024), the portion of stockholders’ equity that is not attributable to Alleghany stockholders is presented on the Consolidated Balance Sheets as redeemable noncontrolling interests for all periods presented. During the first six months of 2018, the noncontrolling interests outstanding were approximately as follows: Bourn & Koch - 11 percent; Kentucky Trailer - 21 percent; IPS - 16 percent; Jazwares - 23 percent; and W&W|AFCO Steel - 20 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 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) Other Significant Accounting Principles Alleghany’s significant accounting principles can be found in Note 1 to Notes to Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of the 2017 Form 10-K.
Recent Accounting Standards	(c) Recent Accounting Standards Recently Adopted In February 2018, the Financial Accounting Standards Board (the “FASB”) issued guidance on certain tax effects caused by the Tax Cuts and Jobs Act of 2017 (the “Tax Act”), which was signed into law on December 22, 2017. The Tax Act, among other things, reduced the U.S. corporate federal income tax rate from 35.0 percent to 21.0 percent, effective January 1, 2018 for the 2018 tax year. Under such circumstances, GAAP requires that the value of deferred tax assets and liabilities be reduced through tax expense. The new guidance provides an option to reclassify any stranded tax amounts that remain in accumulated other comprehensive income to retained earnings, either retrospectively or at the beginning of the period in which the adoption is elected. This guidance became effective in the first quarter of 2018 for public entities, with early adoption permitted in 2017. Alleghany adopted this new guidance in the first quarter of 2018 and has elected to reclassify stranded tax amounts that remain in accumulated other comprehensive income, in the amount of approximately $135 million, to retained earnings as of January 1, 2018. See Note 7(b) of this Form 10-Q 10-K In March 2017, the FASB issued guidance that reduces the amortization period for the premium on certain purchased callable debt securities to the earliest call date. The guidance applies specifically to noncontingent call features that are callable at a predetermined and fixed price and date. The accounting for purchased callable debt securities held at a discount is not affected. This guidance is effective in the first quarter of 2019 for public entities with early adoption permitted. Alleghany adopted this guidance in the fourth quarter of 2017 and recorded a cumulative effect reduction of approximately $13 million directly to opening 2017 retained earnings and an offsetting increase in opening 2017 accumulated other comprehensive income. The implementation did not have a material impact on Alleghany’s results of operations and financial condition. See Note 7(b) of this Form 10-Q In May 2014, the FASB, together with the International Accounting Standards Board, issued guidance on the recognition of revenue from contracts with customers. Under this guidance, revenue is recognized as the transfer of goods and services to customers takes place and in amounts that reflect the payment or payments that are expected to be received from the customers for those goods and services. This guidance also requires new disclosures about revenue. Revenues related to insurance and reinsurance contracts and revenues from investments are not impacted by this guidance, whereas noninsurance revenues arising from the sale of manufactured goods and services is generally included within the scope of this guidance. This guidance, and all related amendments, became effective in the first quarter of 2018 for public entities, with early adoption permitted in 2017. Alleghany adopted this guidance in the first quarter of 2018 using the modified retrospective transition approach and the implementation did not have a material impact on its results of operations and financial condition. See Note 10 of this Form 10-Q In January 2016, the FASB issued guidance that changes the recognition and measurement of certain financial instruments. This guidance requires investments in equity securities (except those accounted for under the equity method of accounting, but including partnership investments not accounted for under the equity method) to be measured at fair value with changes in fair value recognized in net earnings. For equity securities that do not have readily determinable fair values, measurement may be at cost, adjusted for any impairment and changes resulting from observable price changes for a similar investment of the same issuer. This guidance also changes the presentation and disclosure of financial instruments by: (i) requiring that financial instrument disclosures of fair value use the exit price notion; (ii) requiring separate presentation of financial assets and financial liabilities by measurement category and form, either on the balance sheet or the accompanying notes to the financial statements; (iii) requiring separate presentation in other comprehensive income for the portion of the change in a liability’s fair value resulting from instrument-specific credit risk when an election has been made to measure the liability at fair value; and (iv) eliminating the requirement to disclose the methods and significant assumptions used to estimate the fair value for financial instruments measured at amortized cost on the balance sheet. This guidance is effective for fiscal years beginning after December 15, 2017 for public entities, including interim periods within those fiscal years. Except for the change in presentation for instrument-specific credit risk, this guidance does not permit early adoption. Alleghany adopted this guidance in the first quarter of 2018. As of January 1, 2018, approximately $736 million of net unrealized gains of equity securities, net of deferred taxes, were reclassified from accumulated other comprehensive income to retained earnings. Subsequently, all changes in unrealized gains or losses of equity securities, net of deferred taxes, were presented in the Consolidated Statements of Earnings rather than the Consolidated Statements of Comprehensive Income, under the caption “change in the fair value of equity securities.” Results arising from partnership investments, whether accounted for under the equity method or at fair value, continue to be reported as a component of net investment income. The implementation did not have a material impact on Alleghany’s financial condition. See Note 3 of this Form 10-Q 10-Q Future Application of Accounting Standards In February 2016, the FASB issued guidance on leases. Under this guidance, a lessee is required to recognize lease liabilities and corresponding right-of-use 10-K 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. Estimates of expected credit losses are to be based on historical experience, current conditions and reasonable and supportable forecasts. Credit losses for securities accounted for on an available-for-sale 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 is effective in the first quarter of 2020 for public entities, with early adoption permitted. Alleghany will adopt this guidance in the first quarter of 2020 and does not currently believe that the implementation will have a material impact on its results of operations and financial condition. See Note 2 to Notes to Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of the 2017 Form 10-K In August 2017, the FASB issued guidance that simplifies the requirements to achieve hedge accounting, better reflects the economic results of hedging in the financial statements and improves the alignment between hedge accounting and a company’s risk management activities. This guidance is effective in the first quarter of 2019 for public entities, with early adoption permitted. Alleghany will adopt this guidance in the first quarter of 2019 and does not currently believe that the implementation will have a material impact on its results of operations and financial condition.

Fair Value of Financial Instr18

Fair Value of Financial Instruments (Tables)	6 Months Ended
	Jun. 30, 2018
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 June 30, 2018 and December 31, 2017: June 30, 2018 December 31, 2017 Carrying Value Fair Value Carrying Value Fair Value ($ in millions) Assets Investments (excluding equity method investments and loans) (1) $ 17,401.1 $ 17,401.1 $ 17,406.5 $ 17,406.5 Liabilities Senior Notes and other debt (2) $ 1,569.4 $ 1,697.6 $ 1,484.9 $ 1,614.6 (1) This table includes debt and equity securities, as well as partnership and non-marketable (2) See Note 8 to Notes to Consolidated Financial Statements set forth in Part II, Item 8, “Financial Statements and Supplementary Data” of the 2017 Form 10-K
Financial Instruments Measured at Fair Value and Level of Fair Value Hierarchy of Inputs	The following tables present Alleghany’s financial instruments measured at fair value and the level of the fair value hierarchy of inputs used as of June 30, 2018 and December 31, 2017: Level 1 Level 2 Level 3 Total ($ in millions) As of June 30, 2018 Equity securities: Common stock $ 4,704.2 $ 3.6 $ - $ 4,707.8 Preferred stock - - 6.3 6.3 Total equity securities 4,704.2 3.6 6.3 4,714.1 Debt securities: U.S. Government obligations - 993.6 - 993.6 Municipal bonds - 2,842.5 - 2,842.5 Foreign government obligations - 932.9 - 932.9 U.S. corporate bonds - 2,040.6 367.8 2,408.4 Foreign corporate bonds - 1,317.6 94.8 1,412.4 Mortgage and asset-backed securities: Residential mortgage-backed securities (“RMBS”) (1) - 1,160.7 - 1,160.7 Commercial mortgage-backed securities (“CMBS”) - 540.6 - 540.6 Other asset-backed securities (2) - 640.8 1,224.0 1,864.8 Total debt securities - 10,469.3 1,686.6 12,155.9 Short-term investments - 472.8 - 472.8 Other invested assets (3) - - 58.3 58.3 Total investments (excluding equity method investments and loans) $ 4,704.2 $ 10,945.7 $ 1,751.2 $ 17,401.1 Senior Notes and other debt $ - $ 1,512.2 $ 185.4 $ 1,697.6 Level 1 Level 2 Level 3 Total ($ in millions) As of December 31, 2017 Equity securities: Common stock $ 4,090.7 $ 3.8 $ - $ 4,094.5 Preferred stock - 3.1 1.9 5.0 Total equity securities 4,090.7 6.9 1.9 4,099.5 Debt securities: U.S. Government obligations - 948.0 - 948.0 Municipal bonds - 3,682.1 - 3,682.1 Foreign government obligations - 1,006.6 - 1,006.6 U.S. corporate bonds - 2,173.0 260.0 2,433.0 Foreign corporate bonds - 1,424.6 75.2 1,499.8 Mortgage and asset-backed securities: RMBS (1) - 833.8 161.8 995.6 CMBS - 550.1 1.6 551.7 Other asset-backed securities (2) - 503.3 1,101.3 1,604.6 Total debt securities - 11,121.5 1,599.9 12,721.4 Short-term investments - 578.1 - 578.1 Other invested assets (3) - - 7.5 7.5 Total investments (excluding equity method investments and loans) $ 4,090.7 $ 11,706.5 $ 1,609.3 $ 17,406.5 Senior Notes and other debt $ - $ 1,513.6 $ 101.0 $ 1,614.6 (1) Primarily includes government agency pass-through securities guaranteed by a government agency or government sponsored enterprise, among other types of RMBS. (2) Includes $1,224.0 million and $1,101.3 million of collateralized loan obligations as of June 30, 2018 and December 31, 2017, respectively. (3) Includes partnership and non-marketable
Reconciliations of Changes in Level Three Assets Measured at Fair Value	The following tables present reconciliations of the changes during the six months ended June 30, 2018 and 2017 in Level 3 assets measured at fair value: Debt Securities Mortgage and asset-backed Six Months Ended June 30, 2018 Preferred U.S. Foreign RMBS CMBS Other Asset- Other (1) Total ($ in millions) Balance as of January 1, 2018 $ 1.9 $ 260.0 $ 75.2 $ 161.8 $ 1.6 $ 1,101.3 $ 7.5 $ 1,609.3 Net realized/unrealized gains (losses) included in: Net earnings (2) - - (0.1 ) (0.3 ) - 1.0 1.1 1.7 Other comprehensive income 0.2 (6.9 ) (2.2 ) (5.3 ) - (7.7 ) (3.5 ) (25.4 ) Purchases - 117.3 23.8 - - 495.1 - 636.2 Sales (0.1 ) (2.5 ) (1.9 ) (5.6 ) - (365.7 ) (5.6 ) (381.4 ) Issuances - - - - - - - - Settlements - - - - - - - - Transfers into Level 3 4.3 1.2 - - - - 58.8 64.3 Transfers out of Level 3 - (1.3 ) - (150.6 ) (1.6 ) - - (153.5 ) Balance as of June 30, 2018 $ 6.3 $ 367.8 $ 94.8 $ - $ - $ 1,224.0 $ 58.3 $ 1,751.2 Equity Securities Debt Securities Mortgage and asset-backed Six Months Ended June 30, 2017 Common Preferred U.S. Foreign RMBS CMBS Other Asset- Other (1) Total ($ in millions) Balance as of January 1, 2017 $ 4.3 $ - $ 72.9 $ 0.4 $ 5.9 $ 4.3 $ 903.8 $ 28.1 $ 1,019.7 Net realized/unrealized gains (losses) Net earnings (2) (0.1 ) - (0.3 ) - 0.1 - 2.7 10.8 13.2 Other comprehensive income 0.5 - 1.5 0.4 0.2 0.1 11.9 (10.6 ) 4.0 Purchases - 2.4 151.4 36.0 - - 578.0 - 767.8 Sales (1.8 ) (0.2 ) (4.3 ) (0.1 ) - (2.2 ) (19.7 ) (21.6 ) (49.9 ) Issuances - - - - - - - - - Settlements - - (4.4 ) - (0.7 ) (0.3 ) (315.8 ) - (321.2 ) Transfers into Level 3 1.4 - 3.0 0.3 - - - - 4.7 Transfers out of Level 3 (2.4 ) - (4.8 ) - - - - - (7.2 ) Balance as of June 30, 2017 $ 1.9 $ 2.2 $ 215.0 $ 37.0 $ 5.5 $ 1.9 $ 1,160.9 $ 6.7 $ 1,431.1 (1) Includes partnership and non-marketable (2) There were no other than temporary impairment (“OTTI”) losses recorded in net earnings related to Level 3 assets still held as of June 30, 2018 and 2017.

Investments (Tables)

Investments (Tables)	6 Months Ended
	Jun. 30, 2018
Amortized Cost or Cost and Fair Value of Available For Sale Securities	The following tables present the amortized cost or cost and the fair value of AFS securities as of June 30, 2018 and December 31, 2017: Amortized Gross Gross Fair Value ($ in millions) As of June 30, 2018 Debt securities: U.S. Government obligations $ 1,026.0 $ 0.6 $ (33.0) $ 993.6 Municipal bonds 2,803.5 56.1 (17.1) 2,842.5 Foreign government obligations 929.3 9.3 (5.7) 932.9 U.S. corporate bonds 2,432.4 17.9 (41.9) 2,408.4 Foreign corporate bonds 1,418.5 12.9 (19.0) 1,412.4 Mortgage and asset-backed securities: RMBS 1,184.1 3.3 (26.7) 1,160.7 CMBS 545.5 2.5 (7.4) 540.6 Other asset-backed securities (1) 1,866.7 4.9 (6.8) 1,864.8 Total debt securities 12,206.0 107.5 (157.6) 12,155.9 Short-term investments 472.8 - - 472.8 Total investments $ 12,678.8 $ 107.5 $ (157.6) $ 12,628.7 Amortized Gross Gross Fair Value ($ in millions) As of December 31, 2017 Equity securities: Common stock $ 3,165.8 $ 932.5 $ (3.8) $ 4,094.5 Preferred stock 4.9 0.1 - 5.0 Total equity securities 3,170.7 932.6 (3.8) 4,099.5 Debt securities: U.S. Government obligations 963.9 1.7 (17.6) 948.0 Municipal bonds 3,578.9 109.8 (6.6) 3,682.1 Foreign government obligations 1,000.1 11.2 (4.7) 1,006.6 U.S. corporate bonds 2,381.1 61.6 (9.7) 2,433.0 Foreign corporate bonds 1,481.8 24.5 (6.5) 1,499.8 Mortgage and asset-backed securities: RMBS 993.9 6.3 (4.6) 995.6 CMBS 545.0 9.0 (2.3) 551.7 Other asset-backed securities (1) 1,592.1 13.8 (1.3) 1,604.6 Total debt securities 12,536.8 237.9 (53.3) 12,721.4 Short-term investments 578.1 - - 578.1 Total investments $ 16,285.6 $ 1,170.5 $ (57.1) $ 17,399.0 (1) Includes $1,224.0 million and $1,101.3 million of collateralized loan obligations as of June 30, 2018 and December 31, 2017, respectively.
Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity	The following table presents the amortized cost or cost and estimated fair value of debt securities by contractual maturity as of June 30, 2018. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties. Amortized Fair Value ($ in millions) As of June 30, 2018 Short-term investments due in one year or less $ 472.8 $ 472.8 Mortgage and asset-backed securities (1) 3,596.3 3,566.1 Debt securities with maturity dates: One year or less 348.2 348.2 Over one through five years 3,042.6 3,024.8 Over five through ten years 2,997.0 2,973.6 Over ten years 2,221.9 2,243.2 Total debt securities $ 12,206.0 $ 12,155.9 (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 the three and six months ended June 30, 2018 and 2017: Three Months Ended Six Months Ended June 30, June 30, 2018 2017 2018 2017 ($ in millions) Interest income $ 104.8 $ 102.5 $ 206.8 $ 201.7 Dividend income 22.3 11.8 38.6 21.2 Investment expenses (6.6 ) (6.9 ) (18.6 ) (14.3 ) Pillar Investments (1) 1.9 3.2 1.9 6.6 Limited partnership interests in certain subsidiaries of Ares (1) (0.7 ) (12.6 ) 13.2 (7.4 ) Other investment results 4.6 3.7 8.5 9.4 Total $ 126.3 $ 101.7 $ 250.4 $ 217.2 (1) See Note 3(h) of this Form 10-Q
Summary of Increases in Fair Value of Equity Securities	The following table presents increases in the fair value of equity securities for the three and six months ended June 30, 2018: Three Months Ended Six Months Ended June 30, 2018 June 30, 2018 ($ in millions) Change in the fair value of equity securities sold during the period $ 4.4 $ 16.0 Change in the fair value of equity securities held at the end of the period 180.8 126.6 Change in the fair value of equity securities $ 185.2 $ 142.6
Amounts of Gross Realized Capital Gains and Gross Realized Capital Losses of Available For Sale Securities	The following table presents amounts of gross realized capital gains and gross realized capital losses for the three and six months ended June 30, 2018 and 2017: Three Months Ended Six Months Ended June 30, 2018 2017 2018 2017 ($ in millions) Gross realized capital gains $ 6.5 $ 34.0 $ 66.4 $ 142.7 Gross realized capital losses - (24.7) (15.4) (73.8) Net realized capital gains $ 6.5 $ 9.3 $ 51.0 $ 68.9
Gross Unrealized Losses and Related Fair Values for AFS Securities 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, grouped by duration of time in a continuous unrealized loss position, as of June 30, 2018 and December 31, 2017: Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross ($ in millions) As of June 30, 2018 Debt securities: U.S. Government obligations $ 532.8 $ 12.7 $ 390.1 $ 20.3 $ 922.9 $ 33.0 Municipal bonds 543.2 8.2 215.2 8.9 758.4 17.1 Foreign government obligations 189.9 2.1 130.5 3.6 320.4 5.7 U.S. corporate bonds 1,355.7 32.1 174.1 9.8 1,529.8 41.9 Foreign corporate bonds 656.7 12.7 189.2 6.3 845.9 19.0 Mortgage and asset-backed securities: RMBS 887.3 21.3 116.5 5.4 1,003.8 26.7 CMBS 277.9 4.6 32.3 2.8 310.2 7.4 Other asset-backed securities 982.2 6.4 27.7 0.4 1,009.9 6.8 Total temporarily impaired securities $ 5,425.7 $ 100.1 $ 1,275.6 $ 57.5 $ 6,701.3 $ 157.6 Less Than 12 Months 12 Months or More Total Fair Value Gross Fair Value Gross Fair Value Gross ($ in millions) As of December 31, 2017 Equity securities: Common stock $ 145.7 $ 3.8 $ - $ - $ 145.7 $ 3.8 Preferred stock - - - - - - Total equity securities 145.7 3.8 - - 145.7 3.8 Debt securities: U.S. Government obligations 447.8 4.4 416.6 13.2 864.4 17.6 Municipal bonds 240.0 1.5 267.3 5.1 507.3 6.6 Foreign government obligations 321.9 2.7 72.2 2.0 394.1 4.7 U.S. corporate bonds 568.8 6.1 207.3 3.6 776.1 9.7 Foreign corporate bonds 417.4 3.0 159.4 3.5 576.8 6.5 Mortgage and asset-backed securities: RMBS 284.2 1.6 131.5 3.0 415.7 4.6 CMBS 112.2 0.5 34.7 1.8 146.9 2.3 Other asset-backed securities 211.1 0.9 65.7 0.4 276.8 1.3 Total debt securities 2,603.4 20.7 1,354.7 32.6 3,958.1 53.3 Total temporarily impaired securities $ 2,749.1 $ 24.5 $ 1,354.7 $ 32.6 $ 4,103.8 $ 57.1

Liability for Loss and LAE (Tab

Liability for Loss and LAE (Tables)	6 Months Ended
	Jun. 30, 2018
Activity in Liability for Loss and Loss Adjustment Expense	The following table presents the activity in the liability for loss and LAE in the six months ended June 30, 2018 and 2017: Six Months Ended 2018 2017 ($ in millions) Reserves as of January 1 $ 11,871.3 $ 11,087.2 Less: reinsurance recoverables (1) 1,650.1 1,236.2 Net reserves as of January 1 10,221.2 9,851.0 Other adjustments 2.0 - Incurred loss and LAE, net of reinsurance, related to: Current year 1,546.7 1,545.6 Prior years (137.9 ) (111.4 ) Total incurred loss and LAE, net of reinsurance 1,408.8 1,434.2 Paid loss and LAE, net of reinsurance, related to: (2) Current year 237.6 242.7 Prior years 1,366.1 1,190.1 Total paid loss and LAE, net of reinsurance 1,603.7 1,432.8 Foreign currency exchange rate effect (24.2 ) 55.4 Net reserves as of June 30 10,004.1 9,907.8 Reinsurance recoverables as of June 30 (1) 1,511.4 1,152.4 Reserves as of June 30 $ 11,515.5 $ 11,060.2 (1) Reinsurance recoverables in this table include only ceded loss and LAE reserves. (2) Includes paid losses, 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 the three and six months ended June 30, 2018 and 2017: Three Months Ended Six Months Ended 2018 2017 2018 2017 ($ in millions) Reinsurance Segment Property: Catastrophe events $ 5.1 ( 1) $ (4.0) (2) $ (25.3) (3) $ (4.4) (2) Non-catastrophe (18.8) (4) (18.9) (5) (29.8) (4) (50.0) (5) Total property (13.7) (22.9) (55.1) (54.4) Casualty & other: Malpractice Treaties (6) (3.4) (2.0) (3.4) (2.0) Ogden rate impact (7) - - - 24.4 Other (33.6) (8) (27.7) (9) (63.8) (10) (58.9) (9) Total casualty & other (37.0) (29.7) (67.2) (36.5) Total Reinsurance Segment (50.7) (52.6) (122.3) (90.9) Insurance Segment RSUI: Casualty (1.5) (11) (9.5) (12) (12.5) (13) (21.6) (12) Property and other 0.1 (0.8) - 2.9 ( 14) Total RSUI (1.4) (10.3) (12.5) (18.7) CapSpecialty (0.1) (0.2) (15) (3.1) (16) (0.8) (15) PacificComp - (0.5) (17) - (1.0) (17) Total incurred related to prior years $ (52.2) $ (63.6) $ (137.9) $ (111.4) (1) Primarily reflects unfavorable prior accident year loss reserve development related to Hurricane Maria that occurred in the 2017 accident year, partially offset by favorable prior accident year loss reserve development related to Hurricane Harvey that occurred in the 2017 accident year and catastrophes that occurred in the 2016 accident year. (2) Primarily reflects favorable prior accident year loss reserve development related to catastrophes that occurred in the 2010 through 2016 accident years. (3) Primarily reflects favorable prior accident year loss reserve development related to Hurricanes Harvey and Maria that occurred in the 2017 accident year and catastrophes that occurred in the 2016 accident year. (4) Primarily reflects favorable prior accident year loss reserve development in the 2016 and 2017 accident years. (5) Primarily reflects favorable prior accident year loss reserve development in the 2013 through 2016 accident years. (6) Represents certain medical malpractice treaties pursuant to which the increased underwriting profits created by the favorable prior accident year loss reserve development are largely retained by the cedants. As a result, the favorable prior accident year loss reserve development is largely offset by an increase in profit commission expense incurred when such favorable prior accident year loss reserve development occurs. (7) Represents unfavorable prior accident year loss reserve development related to the U.K. Ministry of Justice’s significant reduction in the discount rate, referred to as the Ogden rate, used to calculate lump-sum (8) Primarily reflects favorable prior accident year loss reserve development in the shorter-tailed casualty lines of business in the 2015 and 2017 accident years and the longer-tailed lines of business in the 2008 through 2010 accident years. (9) Primarily reflects favorable prior accident year loss reserve development in the longer-tailed U.S. professional liability lines of business in the 2005 through 2014 accident years, partially offset by unfavorable development in the shorter-tailed casualty lines of business in the 2015 accident year in the U.S. and in the U.K. (10) Primarily reflects favorable prior accident year loss reserve development in the shorter-tailed casualty lines of business in the 2016 and 2017 accident years and the longer-tailed lines of business in the 2008 through 2010 accident years. (11) Primarily reflects favorable prior accident year loss reserve development in the umbrella/excess lines of business in the 2005 through 2012 accident years, partially offset by unfavorable prior accident year loss reserve development in the directors’ and officers’ liability lines of business in the 2012 accident year. (12) Primarily reflects favorable prior accident year loss reserve development in the umbrella/excess lines of business in the 2005 through 2011 accident years. (13) Primarily reflects favorable prior accident year loss reserve development in the umbrella/excess lines of business in the 2005 through 2012 accident years, partially offset by unfavorable prior accident year loss reserve development in the directors’ and officers’ liability lines of business in the 2009 and 2012 accident years. (14) Primarily reflects unfavorable prior accident year property loss reserve development in the binding authority lines of business in the 2015 and 2016 accident years. (15) Primarily reflects favorable prior accident year loss reserve development in the casualty lines of business in the 2010 and 2015 accident years. (16) Primarily reflects favorable prior accident year loss reserve development in the surety lines of business in the 2016 and 2017 accident years. (17) Primarily reflects favorable prior accident year loss reserve development in the 2013 and prior accident years.

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	6 Months Ended
	Jun. 30, 2018
Schedule of Common Stock Repurchases	The following table presents the shares of Common Stock that Alleghany repurchased in the three and six months ended June 30, 2018 and 2017 pursuant to the 2015 Repurchase Program: Three Months Ended Six Months Ended June 30, June 30, 2018 2017 2018 2017 Shares repurchased 368,551 - 403,623 - Cost of shares repurchased (in millions) $ 214.8 $ - $ 236.1 $ - Average price per share repurchased $ 582.92 $ - $ 584.96 $ -
Reconciliation of Accumulated Other Comprehensive Income (Loss)	The following table presents a reconciliation of the changes during the six months ended June 30, 2018 and 2017 in accumulated other comprehensive income (loss) attributable to Alleghany stockholders: Unrealized Unrealized Retirement Total ($ in millions) Balance as of January 1, 2018 $ 718.2 $ (84.6 ) $ (15.5 ) $ 618.1 Cumulative effect of adoption of new accounting pronouncements (1) Reclassification of net unrealized gains on equity securities, net of tax (735.6 ) - - (735.6 ) Reclassification of stranded taxes 156.6 (18.2 ) (3.3 ) 135.1 Total (579.0 ) (18.2 ) (3.3 ) (600.5 ) Other comprehensive income (loss), net of tax: Other comprehensive income (loss) before reclassifications (179.7 ) (5.4 ) (1.1 ) (186.2 ) Reclassifications from accumulated other comprehensive income (3.7 ) - - (3.7 ) Total (183.4 ) (5.4 ) (1.1 ) (189.9 ) Balance as of June 30, 2018 $ (44.2 ) $ (108.2 ) $ (19.9 ) $ (172.3 ) Unrealized Unrealized Retirement Total ($ in millions) Balance as of January 1, 2017 $ 232.2 $ (111.2 ) $ (11.7 ) $ 109.3 Cumulative effect of adoption of new accounting pronouncements (1) 12.9 - - 12.9 Other comprehensive income (loss), net of tax: Other comprehensive income (loss) before reclassifications 266.7 15.0 (0.3 ) 281.4 Reclassifications from accumulated other comprehensive income (40.3 ) - - (40.3 ) Total 226.4 15.0 (0.3 ) 241.1 Balance as of June 30, 2017 $ 471.5 $ (96.2 ) $ (12.0 ) $ 363.3 (1) See Note 1(c) of this Form 10-Q
Reclassifications of Accumulated Other Comprehensive Income	The following table presents reclassifications out of accumulated other comprehensive income attributable to Alleghany stockholders during the three and six months ended June 30, 2018 and 2017: Accumulated Other Three Months Ended June 30, Six Months Ended June 30, Comprehensive Income Component Line in Consolidated Statement of Earnings 2018 2017 2018 2017 ($ in millions) Unrealized appreciation of investments: Net realized capital gains (1) $ (6.5 ) $ (9.3 ) $ (5.3 ) $ (68.9 ) Other than temporary impairment losses - 3.8 0.5 7.0 Income taxes 1.4 1.9 1.1 21.6 Total reclassifications: Net earnings $ (5.1 ) $ (3.6 ) $ (3.7 ) $ (40.3 ) (1) For the six month period ended June 30, 2018, excludes a $45.7 million pre-tax 10-Q

Earnings Per Share of Common 22

Earnings Per Share of Common Stock (Tables)	6 Months Ended
	Jun. 30, 2018
Reconciliation of Earnings and Share Data used in Basic and Diluted 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 the three and six months ended June 30, 2018 and 2017: Three Months Ended Six Months Ended June 30, June 30, 2018 2017 2018 2017 ($ in millions, except share amounts) Net earnings available to Alleghany stockholders $ 295.1 $ 101.8 $ 466.7 $ 251.0 Effect of dilutive securities - - - - Income available to common stockholders for diluted earnings per share $ 295.1 $ 101.8 $ 466.7 $ 251.0 Weighted average common shares outstanding applicable to 15,180,075 15,419,034 15,284,679 15,416,366 Effect of dilutive securities - - 4,915 5,703 Adjusted weighted average common shares outstanding 15,180,075 15,419,034 15,289,594 15,422,069

Segments of Business (Tables)

Segments of Business (Tables)	6 Months Ended
	Jun. 30, 2018
Results for Reportable Segments and Corporate Activities	The following tables present the results for Alleghany’s three reportable segments and for corporate activities for the three and six months ended June 30, 2018 and 2017: Reinsurance Segment Insurance Segment Three Months Ended Property Casualty (1) Total RSUI Cap Total Subtotal Alleghany Total Corporate (2) Consolidated ($ in millions) Gross premiums written $ 345.1 $ 726.6 $ 1,071.7 $ 318.8 $ 88.7 $ 407.5 $ 1,479.2 $ - $ 1,479.2 $ (6.5 ) $ 1,472.7 Net premiums written 275.9 700.7 976.6 216.9 82.3 299.2 1,275.8 - 1,275.8 - 1,275.8 Net premiums earned 292.1 689.2 981.3 184.7 71.0 255.7 1,237.0 - 1,237.0 - 1,237.0 Net loss and LAE 153.5 440.0 593.5 105.7 39.0 144.7 738.2 - 738.2 - 738.2 Commissions, brokerage and other 94.8 223.2 318.0 53.7 30.4 84.1 402.1 - 402.1 - 402.1 Underwriting profit (3) $ 43.8 $ 26.0 $ 69.8 $ 25.3 $ 1.6 $ 26.9 96.7 - 96.7 - 96.7 Net investment income 121.1 1.2 122.3 4.0 126.3 Change in the fair value of equity securities 146.8 - 146.8 38.4 185.2 Net realized capital gains 6.8 (0.1 ) 6.7 (0.2 ) 6.5 Other than temporary impairment losses - - - - - Noninsurance revenue 4.7 329.0 333.7 9.0 342.7 Other operating expenses 19.9 314.5 334.4 8.8 343.2 Corporate administration 0.8 - 0.8 13.3 14.1 Amortization of intangible assets 0.2 5.8 6.0 - 6.0 Interest expense 6.9 2.3 9.2 13.1 22.3 Earnings before income taxes $ 348.3 $ 7.5 $ 355.8 $ 16.0 $ 371.8 Reinsurance Segment Insurance Segment Three Months Ended June 30, 2017 Property Casualty (1) Total RSUI Cap Pacific Total Subtotal Alleghany Total Corporate (2) Consolidated ($ in millions) Gross premiums written $ 369.1 $ 676.3 $ 1,045.4 $ 295.1 $ 73.3 $ 41.9 $ 410.3 $ 1,455.7 $ - $ 1,455.7 $ (5.7 ) $ 1,450.0 Net premiums written 317.2 661.6 978.8 204.6 68.4 41.3 314.3 1,293.1 - 1,293.1 - 1,293.1 Net premiums earned 270.5 686.9 957.4 178.5 64.1 43.9 286.5 1,243.9 - 1,243.9 - 1,243.9 Net loss and LAE 122.9 450.1 573.0 93.8 35.6 32.5 161.9 734.9 - 734.9 - 734.9 Commissions, brokerage and other underwriting expenses 87.9 234.3 322.2 53.0 27.2 11.3 91.5 413.7 - 413.7 - 413.7 Underwriting profit (3) $ 59.7 $ 2.5 $ 62.2 $ 31.7 $ 1.3 $ 0.1 $ 33.1 95.3 - 95.3 - 95.3 Net investment income 98.0 0.2 98.2 3.5 101.7 Change in the fair value of equity securities - - - - - Net realized capital gains 9.2 0.2 9.4 (0.1 ) 9.3 Other than temporary impairment losses (3.8 ) - (3.8 ) - (3.8 ) Noninsurance revenue 3.3 192.8 196.1 6.7 202.8 Other operating expenses 25.9 189.4 215.3 9.9 225.2 Corporate administration 0.8 - 0.8 13.6 14.4 Amortization of intangible assets (0.4 ) 5.0 4.6 - 4.6 Interest expense 6.8 1.0 7.8 13.2 21.0 Earnings (losses) before income taxes $ 168.9 $ (2.2 ) $ 166.7 $ (26.6 ) $ 140.1 Reinsurance Segment Insurance Segment Six Months Ended June 30, 2018 Property Casualty (1) Total RSUI Cap Total Subtotal Alleghany Total Corporate (2) Consolidated ($ in millions) Gross premiums written $ 742.3 $ 1,445.0 $ 2,187.3 $ 593.4 $ 163.2 $ 756.6 $ 2,943.9 $ - $ 2,943.9 $ (12.4 ) $ 2,931.5 Net premiums written 581.0 1,392.7 1,973.7 403.8 151.7 555.5 2,529.2 - 2,529.2 - 2,529.2 Net premiums earned 567.2 1,374.3 1,941.5 365.6 137.7 503.3 2,444.8 - 2,444.8 - 2,444.8 Net loss and LAE 250.1 882.8 1,132.9 202.6 73.3 275.9 1,408.8 - 1,408.8 - 1,408.8 Commissions, brokerage and other underwriting expenses 187.9 452.1 640.0 107.2 61.2 168.4 808.4 - 808.4 - 808.4 Underwriting profit (3) $ 129.2 $ 39.4 $ 168.6 $ 55.8 $ 3.2 $ 59.0 227.6 - 227.6 - 227.6 Net investment income 239.4 3.1 242.5 7.9 250.4 Change in the fair value of equity securities 132.7 - 132.7 9.9 142.6 Net realized capital gains 50.7 0.5 51.2 (0.2 ) 51.0 Other than temporary impairment losses (0.5 ) - (0.5 ) - (0.5 ) Noninsurance revenue 10.4 571.7 582.1 12.3 594.4 Other operating expenses 37.0 554.4 591.4 16.7 608.1 Corporate administration 0.5 - 0.5 21.4 21.9 Amortization of intangible assets - 11.2 11.2 - 11.2 Interest expense 13.6 3.6 17.2 26.6 43.8 Earnings (losses) before income taxes $ 609.2 $ 6.1 $ 615.3 $ (34.8 ) $ 580.5 Reinsurance Segment Insurance Segment Six Months Ended June 30, 2017 Property Casualty (1) Total RSUI Cap Pacific Total Subtotal Alleghany Total Corporate (2) Consolidated ($ in millions) Gross premiums written $ 744.5 $ 1,356.6 $ 2,101.1 $ 559.6 $ 138.8 $ 82.6 $ 781.0 $ 2,882.1 $ - $ 2,882.1 $ (11.2 ) $ 2,870.9 Net premiums written 602.4 1,325.8 1,928.2 387.2 129.4 81.4 598.0 2,526.2 - 2,526.2 - 2,526.2 Net premiums earned 557.3 1,326.2 1,883.5 361.2 126.2 82.2 569.6 2,453.1 - 2,453.1 - 2,453.1 Net loss and LAE 244.7 885.4 1,130.1 174.4 68.7 61.0 304.1 1,434.2 - 1,434.2 - 1,434.2 Commissions, brokerage and other underwriting expenses 178.7 459.0 637.7 107.9 54.9 21.7 184.5 822.2 - 822.2 - 822.2 Underwriting profit (loss) (3) $ 133.9 $ (18.2 ) $ 115.7 $ 78.9 $ 2.6 $ (0.5 ) $ 81.0 196.7 - 196.7 - 196.7 Net investment income 210.3 0.5 210.8 6.4 217.2 Change in the fair value of equity securities - - - - - Net realized capital gains 69.4 0.1 69.5 (0.6 ) 68.9 Other than temporary impairment losses (7.0 ) - (7.0 ) - (7.0 ) Noninsurance revenue 5.8 337.6 343.4 10.7 354.1 Other operating expenses 49.1 331.0 380.1 20.2 400.3 Corporate administration 1.6 - 1.6 29.7 31.3 Amortization of intangible assets (0.9 ) 9.3 8.4 - 8.4 Interest expense 13.6 1.8 15.4 26.5 41.9 Earnings (losses) before income taxes $ 411.8 $ (3.9 ) $ 407.9 $ (59.9 ) $ 348.0 (1) Primarily consists of the following assumed reinsurance lines of business: directors’ and officers’ liability; errors and omissions liability; general liability; medical malpractice; ocean marine and aviation; auto liability; accident and health; surety; and credit. (2) Includes elimination of minor reinsurance activity between segments. (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, OTTI losses, noninsurance revenue, 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 three reportable segments and for corporate activities as of June 30, 2018: Identifiable Invested Assets Equity ($ in millions) Reinsurance segment $ 16,356.9 $ 13,387.8 $ 5,208.5 Insurance segment 6,837.9 5,263.3 2,891.5 Subtotal 23,194.8 18,651.1 8,100.0 Alleghany Capital 1,328.3 130.5 777.2 Total segments 24,523.1 18,781.6 8,877.2 Corporate activities 562.8 485.6 (472.8) Consolidated $ 25,085.9 $ 19,267.2 $ 8,404.4
Summary of Alleghany Capital Noninsurance Revenue	The following table presents noninsurance revenue for the Alleghany Capital segment for the three and six months ended June 30, 2018 and 2017: Three Months Ended Six Months Ended 2018 2017 2018 2017 ($ in millions) Industrial (1) $ 221.9 $ 74.5 $ 367.4 $ 116.4 Non-industrial (2) 107.1 118.3 204.2 221.2 Corporate & other - - 0.1 - Alleghany Capital $ 329.0 $ 192.8 $ 571.7 $ 337.6

Summary of Significant Accoun24

Summary of Significant Accounting Principles - Additional Information (Detail) - USD ($) $ in Millions		6 Months Ended		12 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Jan. 01, 2018	Aug. 01, 2017	Jan. 01, 2017
Significant Accounting Policies [Line Items]
Statutory federal income tax rate		21.00%	35.00%	35.00%
Accumulated Other Comprehensive Income
Significant Accounting Policies [Line Items]
Cumulative effective of adoption of new accounting pronouncements	[1]				$ (600.5)		$ 12.9
Accounting Standards Update 2018-02 | Accumulated Other Comprehensive Income
Significant Accounting Policies [Line Items]
Cumulative effective of adoption of new accounting pronouncements	[1]				135.1
Accounting Standards Update 2018-02 | Retained Earnings
Significant Accounting Policies [Line Items]
Cumulative effective of adoption of new accounting pronouncements					(135.1)
Accounting Standards Update 2017-08 | Accumulated Other Comprehensive Income
Significant Accounting Policies [Line Items]
Cumulative effective of adoption of new accounting pronouncements							13
Accounting Standards Update 2017-08 | Retained Earnings
Significant Accounting Policies [Line Items]
Cumulative effective of adoption of new accounting pronouncements							$ (13)
Accounting Standards Update 2016-01 | Accumulated Other Comprehensive Income
Significant Accounting Policies [Line Items]
Cumulative effective of adoption of new accounting pronouncements	[1]				(735.6)
Accounting Standards Update 2016-01 | Retained Earnings
Significant Accounting Policies [Line Items]
Cumulative effective of adoption of new accounting pronouncements					$ 735.6
Wilbert Funeral Services, Inc
Significant Accounting Policies [Line Items]
Equity interest percentage		45.00%				45.00%
Pacific Comp
Significant Accounting Policies [Line Items]
Cash consideration from sale				$ 158
Disposal date				Dec. 31, 2017
Assets disposed of				$ 442
Liabilities disposed of				316
Gain on sale of business, after tax				16
Alleghany Corporation | Financial Guarantee | AIHL Re Limited Liability Company reinsurance of Pacific Compensation Insurance Company
Significant Accounting Policies [Line Items]
Guaranteed obligation, aggregate limit				150
Aihl Re Limited Liability Company | AIHL Re Limited Liability Company reinsurance of Pacific Compensation Insurance Company
Significant Accounting Policies [Line Items]
Aggregate limit				$ 150
Final commutation and settlement date				Dec. 31, 2024
WWSC Holdings, LLC
Significant Accounting Policies [Line Items]
Ownership of interest held by noncontrolling partners		20.00%
Kentucky Trailer
Significant Accounting Policies [Line Items]
Ownership of interest held by noncontrolling partners		21.00%
Integrated Project Services LLC
Significant Accounting Policies [Line Items]
Ownership of interest held by noncontrolling partners		16.00%
Bourn & Koch, Inc.
Significant Accounting Policies [Line Items]
Ownership of interest held by noncontrolling partners		11.00%
Jazwares, LLC
Significant Accounting Policies [Line Items]
Ownership of interest held by noncontrolling partners		23.00%
WWSC Holdings, LLC
Significant Accounting Policies [Line Items]
Business acquisition date		Apr. 28, 2017
Hirschfeld Holdings, LP | WWSC Holdings, LLC
Significant Accounting Policies [Line Items]
Business acquisition date		Feb. 7, 2018
[1]	See Note 1(c) of this Form 10-Q for additional information regarding Alleghany's adoption of new investment accounting guidance and new guidance on certain tax effects caused by the Tax Act.

Carrying Value and Estimated Fa

Carrying Value and Estimated Fair Value of Consolidated Financial Instruments (Detail) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Assets
Investments (excluding equity method investments and loans)	[1]	$ 17,401.1	$ 17,406.5
Liabilities
Senior Notes and other debt	[2]	1,697.6	1,614.6
Carrying Value
Assets
Investments (excluding equity method investments and loans)	[1]	17,401.1	17,406.5
Liabilities
Senior Notes and other debt	[2]	$ 1,569.4	$ 1,484.9
[1]	This table includes debt and equity securities, as well as partnership and non-marketable equity investments carried 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 carried at unpaid principal balance. The fair value of short-term investments approximates amortized cost. The fair value of all other categories of investments is discussed below.
[2]	See Note 8 to Notes to Consolidated Financial Statements set forth in Part II, Item 8, "Financial Statements and Supplementary Data" of the 2017 Form 10-K for additional information on the senior notes and other debt.

Financial Instruments Measured

Financial Instruments Measured at Fair Value and Level of Fair Value Hierarchy of Inputs (Detail) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		$ 4,714,079
Estimated fair value of available for sale debt securities		12,155,866	$ 12,721,399
Estimated fair value of investments (excluding equity method investments and loans)	[1]	17,401,100	17,406,500
Senior Notes and other debt	[2]	1,697,600	1,614,600
Estimated fair value of equities			4,099,467
Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		4,707,800
Estimated fair value of equities			4,094,500
Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		6,300
Estimated fair value of equities			5,000
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		993,600	948,000
Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		2,842,500	3,682,100
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		932,900	1,006,600
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		2,408,400	2,433,000
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		1,412,400	1,499,800
RMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities	[3]	1,160,700	995,600
CMBS
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		540,600	551,700
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]	1,864,800	1,604,600
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)		472,800	578,100
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)	[5]	58,300	7,500
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		4,704,200
Estimated fair value of investments (excluding equity method investments and loans)		4,704,200	4,090,700
Estimated fair value of equities			4,090,700
Level 1 | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		4,704,200
Estimated fair value of equities			4,090,700
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		3,600
Estimated fair value of available for sale debt securities		10,469,300	11,121,500
Estimated fair value of investments (excluding equity method investments and loans)		10,945,700	11,706,500
Senior Notes and other debt		1,512,200	1,513,600
Estimated fair value of equities			6,900
Level 2 | Common Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		3,600
Estimated fair value of equities			3,800
Level 2 | Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities			3,100
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		993,600	948,000
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		2,842,500	3,682,100
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		932,900	1,006,600
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		2,040,600	2,173,000
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		1,317,600	1,424,600
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]	1,160,700	833,800
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		540,600	550,100
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]	640,800	503,300
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)		472,800	578,100
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		6,300
Estimated fair value of available for sale debt securities		1,686,600	1,599,900
Estimated fair value of investments (excluding equity method investments and loans)		1,751,200	1,609,300
Senior Notes and other debt		185,400	101,000
Estimated fair value of equities			1,900
Level 3 | Preferred Stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of equities		6,300
Estimated fair value of equities			1,900
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		367,800	260,000
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		94,800	75,200
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]		161,800
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			1,600
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]	1,224,000	1,101,300
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)	[5]	$ 58,300	$ 7,500
[1]	This table includes debt and equity securities, as well as partnership and non-marketable equity investments carried 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 carried at unpaid principal balance. The fair value of short-term investments approximates amortized cost. The fair value of all other categories of investments is discussed below.
[2]	See Note 8 to Notes to Consolidated Financial Statements set forth in Part II, Item 8, "Financial Statements and Supplementary Data" of the 2017 Form 10-K 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 $1,224.0 million and $1,101.3 million of collateralized loan obligations as of June 30, 2018 and December 31, 2017, respectively.
[5]	Includes partnership and non-marketable equity investments accounted for at fair value, and excludes investments accounted for using the equity method.

Financial Instruments Measure27

Financial Instruments Measured at Fair Value and Level of Fair Value Hierarchy of Inputs (Parenthetical) (Detail) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of available for sale debt securities		$ 12,155,866	$ 12,721,399
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]	1,864,800	1,604,600
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		$ 1,224,000	$ 1,101,300
[1]	Includes $1,224.0 million and $1,101.3 million of collateralized loan obligations as of June 30, 2018 and December 31, 2017, respectively.

Fair Value of Financial Instr28

Fair Value of Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions		Mar. 15, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers out of Level 3			$ 151.9		$ 3.1	$ 153.5	$ 7.2
Gross transfers into Level 3					$ 2.1	64.3	4.7
All investment issuers other than Ares
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers into Level 3			1.3			5.6
CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers out of Level 3				$ 1.6		1.6
U.S. corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers out of Level 3			1.3			1.3	4.8
Gross transfers into Level 3						1.2	3
Foreign corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers into Level 3							0.3
Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers out of Level 3							2.4
Gross transfers into Level 3							$ 1.4
Common Stock | Ares | Insurance Segment
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers into Level 1		$ 208.2
Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers into Level 3						4.3
Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers into Level 3	[1]					58.8
Other invested assets | Limited partnership interests in certain subsidiaries of Ares | Insurance Segment
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers into Level 3		$ 58.7
Other invested assets | All investment issuers other than Ares
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers into Level 3						0.1
RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross transfers out of Level 3			$ 150.6			$ 150.6
[1]	Includes partnership and non-marketable equity investments accounted for at fair value.

Reconciliations of Changes in L

Reconciliations of Changes in Level Three Assets Measured at Fair Value (Detail) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance			$ 1,609.3		$ 1,609.3	$ 1,019.7
Net realized/unrealized gains (losses) included in:
Net earnings	[1]				1.7	13.2
Other comprehensive income					(25.4)	4
Purchases					636.2	767.8
Sales					(381.4)	(49.9)
Issuances					0	0
Settlements						(321.2)
Transfers into Level 3				$ 2.1	64.3	4.7
Transfers out of Level 3		$ (151.9)		(3.1)	(153.5)	(7.2)
Ending balance		1,751.2		1,431.1	1,751.2	1,431.1
Preferred Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance			1.9		1.9
Net realized/unrealized gains (losses) included in:
Other comprehensive income					0.2
Purchases						2.4
Sales					(0.1)	(0.2)
Issuances					0	0
Transfers into Level 3					4.3
Ending balance		6.3		2.2	6.3	2.2
Common Stock
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance						4.3
Net realized/unrealized gains (losses) included in:
Net earnings	[1]					(0.1)
Other comprehensive income						0.5
Sales						(1.8)
Issuances						0
Transfers into Level 3						1.4
Transfers out of Level 3						(2.4)
Ending balance				1.9		1.9
U.S. corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance			260		260	72.9
Net realized/unrealized gains (losses) included in:
Net earnings	[1]					(0.3)
Other comprehensive income					(6.9)	1.5
Purchases					117.3	151.4
Sales					(2.5)	(4.3)
Issuances					0	0
Settlements						(4.4)
Transfers into Level 3					1.2	3
Transfers out of Level 3		(1.3)			(1.3)	(4.8)
Ending balance		367.8		215	367.8	215
Foreign corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance			75.2		75.2	0.4
Net realized/unrealized gains (losses) included in:
Net earnings	[1]				(0.1)
Other comprehensive income					(2.2)	0.4
Purchases					23.8	36
Sales					(1.9)	(0.1)
Issuances					0	0
Transfers into Level 3						0.3
Ending balance		94.8		37	94.8	37
RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance			161.8		161.8	5.9
Net realized/unrealized gains (losses) included in:
Net earnings	[1]				(0.3)	0.1
Other comprehensive income					(5.3)	0.2
Sales					(5.6)
Issuances					0	0
Settlements						(0.7)
Transfers out of Level 3		(150.6)			(150.6)
Ending balance				5.5		5.5
CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance			1.6		1.6	4.3
Net realized/unrealized gains (losses) included in:
Other comprehensive income						0.1
Sales						(2.2)
Issuances					0	0
Settlements						(0.3)
Transfers out of Level 3			(1.6)		(1.6)
Ending balance				1.9		1.9
Other asset-backed securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance			1,101.3		1,101.3	903.8
Net realized/unrealized gains (losses) included in:
Net earnings	[1]				1	2.7
Other comprehensive income					(7.7)	11.9
Purchases					495.1	578
Sales					(365.7)	(19.7)
Issuances					0	0
Settlements						(315.8)
Ending balance		1,224		1,160.9	1,224	1,160.9
Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	[2]		$ 7.5		7.5	28.1
Net realized/unrealized gains (losses) included in:
Net earnings	[1],[2]				1.1	10.8
Other comprehensive income	[2]				(3.5)	(10.6)
Sales	[2]				(5.6)	(21.6)
Issuances	[2]				0	0
Transfers into Level 3	[2]				58.8
Ending balance	[2]	$ 58.3		$ 6.7	$ 58.3	$ 6.7
[1]	There were no other than temporary impairment ("OTTI") losses recorded in net earnings related to Level 3 assets still held as of June 30, 2018 and 2017.
[2]	Includes partnership and non-marketable equity investments accounted for at fair value.

Amortized Cost or Cost and Fair

Amortized Cost or Cost and Fair Value of Available For Sale Securities (Detail) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Available-for-sale [Line Items]
Amortized Cost or Cost		$ 12,678,800	$ 16,285,600
Gross Unrealized Gains		107,500	1,170,500
Gross Unrealized Losses		(157,600)	(57,100)
Fair Value		12,628,700	17,399,000
Equity securities, cost			3,170,673
Equity securities, gross unrealized gains			932,600
Equity securities, gross unrealized losses			(3,800)
Equity securities, fair value			4,099,467
Debt securities, amortized cost		12,206,035	12,536,772
Debt securities, gross unrealized gains		107,500	237,900
Debt securities, gross unrealized losses		(157,600)	(53,300)
Debt securities, fair value		12,155,866	12,721,399
U.S. Government obligations
Available-for-sale [Line Items]
Debt securities, amortized cost		1,026,000	963,900
Debt securities, gross unrealized gains		600	1,700
Debt securities, gross unrealized losses		(33,000)	(17,600)
Debt securities, fair value		993,600	948,000
Municipal bonds
Available-for-sale [Line Items]
Debt securities, amortized cost		2,803,500	3,578,900
Debt securities, gross unrealized gains		56,100	109,800
Debt securities, gross unrealized losses		(17,100)	(6,600)
Debt securities, fair value		2,842,500	3,682,100
Foreign government obligations
Available-for-sale [Line Items]
Debt securities, amortized cost		929,300	1,000,100
Debt securities, gross unrealized gains		9,300	11,200
Debt securities, gross unrealized losses		(5,700)	(4,700)
Debt securities, fair value		932,900	1,006,600
U.S. corporate bonds
Available-for-sale [Line Items]
Debt securities, amortized cost		2,432,400	2,381,100
Debt securities, gross unrealized gains		17,900	61,600
Debt securities, gross unrealized losses		(41,900)	(9,700)
Debt securities, fair value		2,408,400	2,433,000
Foreign corporate bonds
Available-for-sale [Line Items]
Debt securities, amortized cost		1,418,500	1,481,800
Debt securities, gross unrealized gains		12,900	24,500
Debt securities, gross unrealized losses		(19,000)	(6,500)
Debt securities, fair value		1,412,400	1,499,800
RMBS
Available-for-sale [Line Items]
Debt securities, amortized cost		1,184,100	993,900
Debt securities, gross unrealized gains		3,300	6,300
Debt securities, gross unrealized losses		(26,700)	(4,600)
Debt securities, fair value	[1]	1,160,700	995,600
CMBS
Available-for-sale [Line Items]
Debt securities, amortized cost		545,500	545,000
Debt securities, gross unrealized gains		2,500	9,000
Debt securities, gross unrealized losses		(7,400)	(2,300)
Debt securities, fair value		540,600	551,700
Other asset-backed securities
Available-for-sale [Line Items]
Debt securities, amortized cost	[2]	1,866,700	1,592,100
Debt securities, gross unrealized gains	[2]	4,900	13,800
Debt securities, gross unrealized losses	[2]	(6,800)	(1,300)
Debt securities, fair value	[2]	1,864,800	1,604,600
Common Stock
Available-for-sale [Line Items]
Equity securities, cost			3,165,800
Equity securities, gross unrealized gains			932,500
Equity securities, gross unrealized losses			(3,800)
Equity securities, fair value			4,094,500
Preferred Stock
Available-for-sale [Line Items]
Equity securities, cost			4,900
Equity securities, gross unrealized gains			100
Equity securities, fair value			5,000
Short-term Investments
Available-for-sale [Line Items]
Amortized Cost or Cost		472,800	578,100
Fair Value		$ 472,800	$ 578,100
[1]	Primarily includes government agency pass-through securities guaranteed by a government agency or government sponsored enterprise, among other types of RMBS.
[2]	Includes $1,224.0 million and $1,101.3 million of collateralized loan obligations as of June 30, 2018 and December 31, 2017, respectively.

Amortized Cost or Cost and Fa31

Amortized Cost or Cost and Fair Value of Available For Sale Securities (Parenthetical) (Detail) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Available-for-sale [Line Items]
Estimated fair value of available for sale debt securities		$ 12,155,866	$ 12,721,399
Other asset-backed securities
Available-for-sale [Line Items]
Estimated fair value of available for sale debt securities	[1]	1,864,800	1,604,600
Collateralized loan obligations | Other asset-backed securities
Available-for-sale [Line Items]
Estimated fair value of available for sale debt securities		$ 1,224,000	$ 1,101,300
[1]	Includes $1,224.0 million and $1,101.3 million of collateralized loan obligations as of June 30, 2018 and December 31, 2017, respectively.

Amortized Cost and Estimated Fa

Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Detail) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Available-for-sale [Line Items]
Short-term investments due in one year or less, amortized cost or cost		$ 472,800
Mortgage and asset-backed securities, amortized cost or cost	[1]	3,596,300
Debt securities with maturity dates, amortized cost or cost:
One year or less		348,200
Over one through five years		3,042,600
Over five through ten years		2,997,000
Over ten years		2,221,900
Debt securities, amortized cost		12,206,035	$ 12,536,772
Short-term investments due in one year or less, fair value		472,830	578,054
Mortgage and asset-backed securities, fair value	[1]	3,566,100
Debt securities with maturity dates, fair value:
One year or less		348,200
Over one through five years		3,024,800
Over five through ten years		2,973,600
Over ten years		2,243,200
Debt securities, fair value		$ 12,155,866	$ 12,721,399
[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		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net Investment Income [Line Items]
Interest income		$ 104,800	$ 102,500	$ 206,800	$ 201,700
Dividend income		22,300	11,800	38,600	21,200
Investment expenses		(6,600)	(6,900)	(18,600)	(14,300)
Other investment results		4,600	3,700	8,500	9,400
Net investment income		126,273	101,656	250,399	217,194
Limited partnership interests in certain subsidiaries of Ares
Net Investment Income [Line Items]
Equity results	[1]	(700)	(12,600)	13,200	(7,400)
Pillar Capital Holdings Limited And Managed Funds
Net Investment Income [Line Items]
Equity results	[1]	$ 1,900	$ 3,200	$ 1,900	$ 6,600
[1]	See Note 3(h) of this Form 10-Q for discussion of the Pillar Investments, as defined therein, and limited partnership interests in certain subsidiaries of Ares.

Investments - Summary of Increa

Investments - Summary of Increases in Fair Value of Equity Securities (Detail) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Equity Securities, FV-NI, Gain (Loss) [Abstract]
Change in the fair value of equity securities sold during the period	$ 4.4	$ 16
Change in the fair value of equity securities held at the end of the period	180.8	126.6
Change in the fair value of equity securities	$ 185.2	$ 142.6

Investments - Additional Inform

Investments - Additional Information (Detail)	Mar. 15, 2018USD ($)	Jul. 31, 2013USD ($)	Dec. 31, 2012USD ($)	Jun. 30, 2018USD ($)Investment	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)Investment	Jun. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Investment [Line Items]
Proceeds from sales of debt and equity securities				$ 800,000,000	$ 1,500,000,000	$ 1,900,000,000	$ 4,200,000,000
Net realized capital gains				$ 6,462,000	9,268,000	$ 50,967,000	68,919,000
Securities impairment test description						Debt securities in an unrealized loss position are evaluated for OTTI if they meet any of the following criteria: (i) they are trading at a discount of at least 20 percent to amortized cost for an extended period of time (nine consecutive months or more); (ii) there has been a negative credit or news event with respect to the issuer that could indicate the existence of an OTTI; 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 an OTTI 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 an OTTI 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 OTTI 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.
Other than temporary impairment losses						$ 511,000
Other than temporary impairment losses					3,747,000		6,964,000
Percentage of debt securities owned with credit rating below investment grade or not rated				4.30%		4.30%		5.30%
Other invested assets				$ 605,477,000		$ 605,477,000		$ 743,358,000
Fair value of common units				4,714,079,000		4,714,079,000
Fair value of investment				12,628,700,000		12,628,700,000		17,399,000,000
Net investment income				126,273,000	$ 101,656,000	250,399,000	217,194,000
Pillar Capital Holdings Limited And Managed Funds
Investment [Line Items]
Other invested assets				219,800,000		219,800,000
Pillar Capital Holdings Limited And Managed Funds | Reinsurance Segment
Investment [Line Items]
Investment in other invested asset			$ 175,000,000
Pillar Capital Holdings Limited And Managed Funds | Insurance Segment
Investment [Line Items]
Investment in other invested asset			$ 25,000,000
Limited partnership interests in certain subsidiaries of Ares | Insurance Segment
Investment [Line Items]
Net investment income	$ 12,900,000
Ares
Investment [Line Items]
Net realized capital gains						45,700,000
Ares | Insurance Segment
Investment [Line Items]
Net realized capital gains	45,700,000					45,700,000
Investment in other invested asset		$ 250,000,000
Percentage of equity stake		6.25%
Commercial Mortgage Loan Portfolio
Investment [Line Items]
Commercial mortgage loans				695,772,000		695,772,000		$ 658,364,000
Allowance for loan losses on commercial mortgage loans				0		0
Equity Securities
Investment [Line Items]
Other than temporary impairment losses							6,800,000
Debt Securities
Investment [Line Items]
Other than temporary impairment losses				$ 0		$ 500,000
Other than temporary impairment losses							$ 200,000
Number of securities in an unrealized loss position | Investment				1,995		1,995
Number of securities in an unrealized loss position for 12 months or more | Investment				430		430
Other invested assets | Limited partnership interests in certain subsidiaries of Ares | Insurance Segment
Investment [Line Items]
Fair value of investment	58,700,000
Common Stock
Investment [Line Items]
Fair value of common units				$ 4,707,800,000		$ 4,707,800,000
Common Stock | Ares | Insurance Segment
Investment [Line Items]
Fair value of common units	$ 208,200,000
Minimum | Commercial Mortgage Loan Portfolio
Investment [Line Items]
Term of commercial mortgage loans						2 years
Minimum | Debt Securities
Investment [Line Items]
Percentage of unrealized loss to cost where a security would be evaluated for other than temporarily impairment						20.00%
Maximum | Ares | Insurance Segment
Investment [Line Items]
Investment commitment in investment fund		$ 1,000,000,000
Maximum | Commercial Mortgage Loan Portfolio
Investment [Line Items]
Term of commercial mortgage loans						10 years
Percentage of principal amounts of loans to the property's appraised value						0.667%

Amounts of Gross Realized Capit

Amounts of Gross Realized Capital Gains and Gross Realized Capital Losses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Schedule of Gross Gains (Losses) [Line Items]
Gross realized capital gains	$ 6,500	$ 34,000	$ 66,400	$ 142,700
Gross realized capital losses		(24,700)	(15,400)	(73,800)
Net realized capital gains	$ 6,462	$ 9,268	$ 50,967	$ 68,919

Gross Unrealized Losses and Rel

Gross Unrealized Losses and Related Fair Values for AFS Securities Grouped by Duration of Time in Continuous Unrealized Loss Position (Detail) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Available-for-sale [Line Items]
Securities, less than 12 months, fair value	$ 5,425.7
Securities, less than 12 months, gross unrealized losses	100.1
Securities, 12 months or more, fair value	1,275.6
Securities, 12 months or more, gross unrealized losses	57.5
Total, fair value	6,701.3
Total, gross unrealized losses	157.6
Securities, less than 12 months, fair value		$ 2,749.1
Securities, less than 12 months, gross unrealized losses		24.5
Securities, 12 months or more, fair value		1,354.7
Securities, 12 months or more, gross unrealized losses		32.6
Total, fair value		4,103.8
Total, gross unrealized losses		57.1
U.S. Government obligations
Available-for-sale [Line Items]
Securities, less than 12 months, fair value	532.8
Securities, less than 12 months, gross unrealized losses	12.7
Securities, 12 months or more, fair value	390.1
Securities, 12 months or more, gross unrealized losses	20.3
Total, fair value	922.9
Total, gross unrealized losses	33
Securities, less than 12 months, fair value		447.8
Securities, less than 12 months, gross unrealized losses		4.4
Securities, 12 months or more, fair value		416.6
Securities, 12 months or more, gross unrealized losses		13.2
Total, fair value		864.4
Total, gross unrealized losses		17.6
Municipal bonds
Available-for-sale [Line Items]
Securities, less than 12 months, fair value	543.2
Securities, less than 12 months, gross unrealized losses	8.2
Securities, 12 months or more, fair value	215.2
Securities, 12 months or more, gross unrealized losses	8.9
Total, fair value	758.4
Total, gross unrealized losses	17.1
Securities, less than 12 months, fair value		240
Securities, less than 12 months, gross unrealized losses		1.5
Securities, 12 months or more, fair value		267.3
Securities, 12 months or more, gross unrealized losses		5.1
Total, fair value		507.3
Total, gross unrealized losses		6.6
Foreign government obligations
Available-for-sale [Line Items]
Securities, less than 12 months, fair value	189.9
Securities, less than 12 months, gross unrealized losses	2.1
Securities, 12 months or more, fair value	130.5
Securities, 12 months or more, gross unrealized losses	3.6
Total, fair value	320.4
Total, gross unrealized losses	5.7
Securities, less than 12 months, fair value		321.9
Securities, less than 12 months, gross unrealized losses		2.7
Securities, 12 months or more, fair value		72.2
Securities, 12 months or more, gross unrealized losses		2
Total, fair value		394.1
Total, gross unrealized losses		4.7
U.S. corporate bonds
Available-for-sale [Line Items]
Securities, less than 12 months, fair value	1,355.7
Securities, less than 12 months, gross unrealized losses	32.1
Securities, 12 months or more, fair value	174.1
Securities, 12 months or more, gross unrealized losses	9.8
Total, fair value	1,529.8
Total, gross unrealized losses	41.9
Securities, less than 12 months, fair value		568.8
Securities, less than 12 months, gross unrealized losses		6.1
Securities, 12 months or more, fair value		207.3
Securities, 12 months or more, gross unrealized losses		3.6
Total, fair value		776.1
Total, gross unrealized losses		9.7
Foreign corporate bonds
Available-for-sale [Line Items]
Securities, less than 12 months, fair value	656.7
Securities, less than 12 months, gross unrealized losses	12.7
Securities, 12 months or more, fair value	189.2
Securities, 12 months or more, gross unrealized losses	6.3
Total, fair value	845.9
Total, gross unrealized losses	19
Securities, less than 12 months, fair value		417.4
Securities, less than 12 months, gross unrealized losses		3
Securities, 12 months or more, fair value		159.4
Securities, 12 months or more, gross unrealized losses		3.5
Total, fair value		576.8
Total, gross unrealized losses		6.5
RMBS
Available-for-sale [Line Items]
Securities, less than 12 months, fair value	887.3
Securities, less than 12 months, gross unrealized losses	21.3
Securities, 12 months or more, fair value	116.5
Securities, 12 months or more, gross unrealized losses	5.4
Total, fair value	1,003.8
Total, gross unrealized losses	26.7
Securities, less than 12 months, fair value		284.2
Securities, less than 12 months, gross unrealized losses		1.6
Securities, 12 months or more, fair value		131.5
Securities, 12 months or more, gross unrealized losses		3
Total, fair value		415.7
Total, gross unrealized losses		4.6
CMBS
Available-for-sale [Line Items]
Securities, less than 12 months, fair value	277.9
Securities, less than 12 months, gross unrealized losses	4.6
Securities, 12 months or more, fair value	32.3
Securities, 12 months or more, gross unrealized losses	2.8
Total, fair value	310.2
Total, gross unrealized losses	7.4
Securities, less than 12 months, fair value		112.2
Securities, less than 12 months, gross unrealized losses		0.5
Securities, 12 months or more, fair value		34.7
Securities, 12 months or more, gross unrealized losses		1.8
Total, fair value		146.9
Total, gross unrealized losses		2.3
Other asset-backed securities
Available-for-sale [Line Items]
Securities, less than 12 months, fair value	982.2
Securities, less than 12 months, gross unrealized losses	6.4
Securities, 12 months or more, fair value	27.7
Securities, 12 months or more, gross unrealized losses	0.4
Total, fair value	1,009.9
Total, gross unrealized losses	$ 6.8
Securities, less than 12 months, fair value		211.1
Securities, less than 12 months, gross unrealized losses		0.9
Securities, 12 months or more, fair value		65.7
Securities, 12 months or more, gross unrealized losses		0.4
Total, fair value		276.8
Total, gross unrealized losses		1.3
Debt Securities
Available-for-sale [Line Items]
Securities, less than 12 months, fair value		2,603.4
Securities, less than 12 months, gross unrealized losses		20.7
Securities, 12 months or more, fair value		1,354.7
Securities, 12 months or more, gross unrealized losses		32.6
Total, fair value		3,958.1
Total, gross unrealized losses		53.3
Common Stock
Available-for-sale [Line Items]
Securities, less than 12 months, fair value		145.7
Securities, less than 12 months, gross unrealized losses		3.8
Total, fair value		145.7
Total, gross unrealized losses		3.8
Equity Securities
Available-for-sale [Line Items]
Securities, less than 12 months, fair value		145.7
Securities, less than 12 months, gross unrealized losses		3.8
Total, fair value		145.7
Total, gross unrealized losses		$ 3.8

Activity in the Liability for L

Activity in the Liability for Loss and Loss Adjustment Expense (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Liability for Claims and Claims Adjustment Expense [Line Items]
Reserves as of January 1				$ 11,871,250	$ 11,087,200
Less: reinsurance recoverables	[1]			1,650,100	1,236,200
Net reserves as of January 1				10,221,200	9,851,000
Other adjustments				2,000
Incurred loss and LAE, net of reinsurance, related to:
Current year				1,546,700	1,545,600
Prior years		$ (52,200)	$ (63,600)	(137,900)	(111,400)
Total incurred loss and LAE, net of reinsurance		738,210	734,886	1,408,788	1,434,191
Paid loss and LAE, net of reinsurance, related to:
Current year	[2]			237,600	242,700
Prior years	[2]			1,366,100	1,190,100
Total paid loss and LAE, net of reinsurance	[2]			1,603,700	1,432,800
Foreign currency exchange rate effect				(24,200)	55,400
Net reserves as of June 30		10,004,100	9,907,800	10,004,100	9,907,800
Reinsurance recoverables as of June 30	[1]	1,511,400	1,152,400	1,511,400	1,152,400
Reserves as of June 30		$ 11,515,493	$ 11,060,200	$ 11,515,493	$ 11,060,200
[1]	Reinsurance recoverables in this table include only ceded loss and LAE reserves.
[2]	Includes paid losses, net of reinsurance, related to commutations.

(Favorable) Unfavorable Prior A

(Favorable) Unfavorable Prior Accident Year Loss Reserve Development (Detail) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017
Claims Development [Line Items]
Claims incurred related to prior years		$ (52.2)		$ (63.6)		$ (137.9)		$ (111.4)
Reinsurance Segment
Claims Development [Line Items]
Claims incurred related to prior years		(50.7)		(52.6)		(122.3)		(90.9)
Reinsurance Segment | Property
Claims Development [Line Items]
Claims incurred related to prior years		(13.7)		(22.9)		(55.1)		(54.4)
Reinsurance Segment | Property | Property Catastrophe
Claims Development [Line Items]
Claims incurred related to prior years		5.1	[1]	(4)	[2]	(25.3)	[3]	(4.4)	[2]
Reinsurance Segment | Property | Property Non-catastrophe
Claims Development [Line Items]
Claims incurred related to prior years		(18.8)	[4]	(18.9)	[5]	(29.8)	[4]	(50)	[5]
Reinsurance Segment | Casualty & Other
Claims Development [Line Items]
Claims incurred related to prior years		(37)		(29.7)		(67.2)		(36.5)
Reinsurance Segment | Casualty & Other | Ogden Rate Impact
Claims Development [Line Items]
Claims incurred related to prior years	[6]							24.4
Reinsurance Segment | Casualty & Other | Malpractice Treaties
Claims Development [Line Items]
Claims incurred related to prior years	[7]	(3.4)		(2)		(3.4)		(2)
Reinsurance Segment | Casualty & Other | All Other Casualty and Other
Claims Development [Line Items]
Claims incurred related to prior years		(33.6)	[8]	(27.7)	[9]	(63.8)	[10]	(58.9)	[9]
Insurance Segment | RSUI
Claims Development [Line Items]
Claims incurred related to prior years		(1.4)		(10.3)		(12.5)		(18.7)
Insurance Segment | RSUI | Casualty Insurance
Claims Development [Line Items]
Claims incurred related to prior years		(1.5)	[11]	(9.5)	[12]	(12.5)	[13]	(21.6)	[12]
Insurance Segment | RSUI | Property and Other Insurance
Claims Development [Line Items]
Claims incurred related to prior years		0.1		(0.8)				2.9	[14]
Insurance Segment | CapSpecialty Incorporated
Claims Development [Line Items]
Claims incurred related to prior years		$ (0.1)		(0.2)	[15]	$ (3.1)	[16]	(0.8)	[15]
Insurance Segment | Pacific Comp
Claims Development [Line Items]
Claims incurred related to prior years	[17]			$ (0.5)				$ (1)
[1]	Primarily reflects unfavorable prior accident year loss reserve development related to Hurricane Maria that occurred in the 2017 accident year, partially offset by favorable prior accident year loss reserve development related to Hurricane Harvey that occurred in the 2017 accident year and catastrophes that occurred in the 2016 accident year.
[2]	Primarily reflects favorable prior accident year loss reserve development related to catastrophes that occurred in the 2010 through 2016 accident years.
[3]	Primarily reflects favorable prior accident year loss reserve development related to Hurricanes Harvey and Maria that occurred in the 2017 accident year and catastrophes that occurred in the 2016 accident year.
[4]	Primarily reflects favorable prior accident year loss reserve development in the 2016 and 2017 accident years.
[5]	Primarily reflects favorable prior accident year loss reserve development in the 2013 through 2016 accident years.
[6]	Represents unfavorable prior accident year loss reserve development related to the U.K. Ministry of Justice's significant reduction in the discount rate, referred to as the Ogden rate, used to calculate lump-sum bodily injury payouts in personal injury insurance claims in the U.K to negative 0.75 percent as of March 20, 2017 from 2.50 percent.
[7]	Represents certain medical malpractice treaties pursuant to which the increased underwriting profits created by the favorable prior accident year loss reserve development are largely retained by the cedants. As a result, the favorable prior accident year loss reserve development is largely offset by an increase in profit commission expense incurred when such favorable prior accident year loss reserve development occurs.
[8]	Primarily reflects favorable prior accident year loss reserve development in the shorter-tailed casualty lines of business in the 2015 and 2017 accident years and the longer-tailed lines of business in the 2008 through 2010 accident years.
[9]	Primarily reflects favorable prior accident year loss reserve development in the longer-tailed U.S. professional liability lines of business in the 2005 through 2014 accident years, partially offset by unfavorable development in the shorter-tailed casualty lines of business in the 2015 accident year in the U.S. and in the U.K.
[10]	Primarily reflects favorable prior accident year loss reserve development in the shorter-tailed casualty lines of business in the 2016 and 2017 accident years and the longer-tailed lines of business in the 2008 through 2010 accident years.
[11]	Primarily reflects favorable prior accident year loss reserve development in the umbrella/excess lines of business in the 2005 through 2012 accident years, partially offset by unfavorable prior accident year loss reserve development in the directors' and officers' liability lines of business in the 2012 accident year.
[12]	Primarily reflects favorable prior accident year loss reserve development in the umbrella/excess lines of business in the 2005 through 2011 accident years.
[13]	Primarily reflects favorable prior accident year loss reserve development in the umbrella/excess lines of business in the 2005 through 2012 accident years, partially offset by unfavorable prior accident year loss reserve development in the directors' and officers' liability lines of business in the 2009 and 2012 accident years.
[14]	Primarily reflects unfavorable prior accident year property loss reserve development in the binding authority lines of business in the 2015 and 2016 accident years.
[15]	Primarily reflects favorable prior accident year loss reserve development in the casualty lines of business in the 2010 and 2015 accident years.
[16]	Primarily reflects favorable prior accident year loss reserve development in the surety lines of business in the 2016 and 2017 accident years.
[17]	Primarily reflects favorable prior accident year loss reserve development in the 2013 and prior accident years.

(Favorable) Unfavorable Prior40

(Favorable) Unfavorable Prior Accident Year Loss Reserve Development (Parenthetical) (Detail)	Mar. 20, 2017	Mar. 19, 2017
Claims Development [Line Items]
Ogden discount rate	(0.75%)	2.50%

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income Taxes [Line Items]
Effective income tax rate	19.10%	27.60%
Statutory federal income tax rate	21.00%	35.00%	35.00%
Interest or penalties accrued for uncertain tax positions	$ 0

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	Mar. 15, 2018	Feb. 28, 2018	Jun. 30, 2018	Nov. 30, 2015
Stockholders Equity Note [Line Items]
Par value of common stock			$ 1
Dividends paid	$ 154,000		$ 153,967
Dividend Declared [Member]
Stockholders Equity Note [Line Items]
Dividend record date		Mar. 5, 2018
Special dividend per share		$ 10
Dividend payable nature		Special
2015 Repurchase Program
Stockholders Equity Note [Line Items]
Aggregate amount of common stock authorized for repurchase				$ 400,000
2018 Repurchase Program
Stockholders Equity Note [Line Items]
Aggregate amount of common stock authorized for repurchase			400,000
2015 Repurchase Program and 2018 Repurchase Program
Stockholders Equity Note [Line Items]
Remaining authorized repurchases under share repurchase program			$ 527,100

Schedule of Common Stock Repurc

Schedule of Common Stock Repurchases (Detail) - 2015 Repurchase Program - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Schedule Of Common Share Purchase [Line Items]
Shares repurchased	368,551	403,623
Cost of shares repurchased (in millions)	$ 214.8	$ 236.1
Average price per share repurchased	$ 582.92	$ 584.96

Reconciliation of Accumulated O

Reconciliation of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Jan. 01, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance				$ 8,514,063
Other comprehensive income (loss), net of tax:
Reclassifications from accumulated other comprehensive income		$ (5,100)	$ (3,600)	(3,700)	$ (40,300)
Ending Balance		8,404,389		8,404,389
Accumulated Other Comprehensive Income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance				618,100	109,300
Cumulative effect of adoption of new accounting pronouncements	[1]					$ (600,500)	$ 12,900
Other comprehensive income (loss), net of tax:
Other comprehensive income (loss) before reclassifications				(186,200)	281,400
Reclassifications from accumulated other comprehensive income				(3,700)	(40,300)
Total				(189,900)	241,100
Ending Balance		(172,300)	363,300	(172,300)	363,300
Accumulated Other Comprehensive Income | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of adoption of new accounting pronouncements	[1]					(735,600)
Accumulated Other Comprehensive Income | Accounting Standards Update 2018-02
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of adoption of new accounting pronouncements	[1]					135,100
Accumulated Unrealized Gain (Loss) on Investments in Available-For-Sale Debt and Equity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance					232,200
Cumulative effect of adoption of new accounting pronouncements	[1]						$ 12,900
Other comprehensive income (loss), net of tax:
Other comprehensive income (loss) before reclassifications					266,700
Reclassifications from accumulated other comprehensive income					(40,300)
Total					226,400
Ending Balance			471,500		471,500
Unrealized Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance				(84,600)	(111,200)
Cumulative effect of adoption of new accounting pronouncements	[1]					(18,200)
Other comprehensive income (loss), net of tax:
Other comprehensive income (loss) before reclassifications				(5,400)	15,000
Total				(5,400)	15,000
Ending Balance		(108,200)	(96,200)	(108,200)	(96,200)
Unrealized Currency Translation Adjustment | Accounting Standards Update 2018-02
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of adoption of new accounting pronouncements	[1]					(18,200)
Retirement Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance				(15,500)	(11,700)
Cumulative effect of adoption of new accounting pronouncements	[1]					(3,300)
Other comprehensive income (loss), net of tax:
Other comprehensive income (loss) before reclassifications				(1,100)	(300)
Total				(1,100)	(300)
Ending Balance		(19,900)	$ (12,000)	(19,900)	$ (12,000)
Retirement Plans | Accounting Standards Update 2018-02
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of adoption of new accounting pronouncements	[1]					(3,300)
Unrealized Appreciation of Investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance				718,200
Cumulative effect of adoption of new accounting pronouncements	[1]					(579,000)
Other comprehensive income (loss), net of tax:
Other comprehensive income (loss) before reclassifications				(179,700)
Reclassifications from accumulated other comprehensive income				(3,700)
Total				(183,400)
Ending Balance		$ (44,200)		$ (44,200)
Unrealized Appreciation of Investments | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of adoption of new accounting pronouncements	[1]					(735,600)
Unrealized Appreciation of Investments | Accounting Standards Update 2018-02
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cumulative effect of adoption of new accounting pronouncements	[1]					$ 156,600
[1]	See Note 1(c) of this Form 10-Q for additional information regarding Alleghany's adoption of new investment accounting guidance and new guidance on certain tax effects caused by the Tax Act.

Reclassifications of Accumulate

Reclassifications of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains		$ (6,462)	$ (9,268)	$ (50,967)	$ (68,919)
Other than temporary impairment losses				511
Other than temporary impairment losses			3,747		6,964
Income taxes		73,440	37,461	110,862	96,011
Total reclassifications		(5,100)	(3,600)	(3,700)	(40,300)
Accumulated Unrealized Gain (Loss) on Investments in Available-For-Sale Debt and Equity Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications					(40,300)
Unrealized Appreciation of Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications				(3,700)
Reclassification out of Accumulated Other Comprehensive Income | Accumulated Unrealized Gain (Loss) on Investments in Available-For-Sale Debt and Equity Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains	[1]		(9,300)		(68,900)
Other than temporary impairment losses			3,800		7,000
Income taxes			$ 1,900		$ 21,600
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]	(6,500)		(5,300)
Other than temporary impairment losses				500
Income taxes		$ 1,400		$ 1,100
[1]	For the six month period ended June 30, 2018, excludes a $45.7 million pre-tax gain from AIHL's conversion of its limited partnership interests in certain subsidiaries of Ares into Ares common units. See Note 3(h) of this Form 10-Q for additional information.

Reclassifications of Accumula46

Reclassifications of Accumulated Other Comprehensive Income (Parenthetical) (Detail) - USD ($) $ in Thousands	Mar. 15, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains		$ 6,462	$ 9,268	$ 50,967	$ 68,919
Ares
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains				45,700
Ares | Insurance Segment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains	$ 45,700			$ 45,700

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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share Disclosure [Line Items]
Net earnings available to Alleghany stockholders	$ 295,116	$ 101,811	$ 466,691	$ 250,987
Effect of dilutive securities	0	0	0	0
Income available to common stockholders for diluted earnings per share	$ 295,100	$ 101,800	$ 466,700	$ 251,000
Weighted average common shares outstanding applicable to basic earnings per share	15,180,075	15,419,034	15,284,679	15,416,366
Effect of dilutive securities			4,915	5,703
Adjusted weighted average common shares outstanding applicable to diluted earnings per share	15,180,075	15,419,034	15,289,594	15,422,069

Earnings Per Share of Common 48

Earnings Per Share of Common Stock - Additional Information (Detail) - shares	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Line Items]
Shares excluded in diluted earnings per share computation	57,766	75,035

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Line Items]
Investments, debt securities	$ 12,155,866	$ 12,721,399
Investments, equity securities	4,714,079
Stockholders' equity	8,404,389	$ 8,514,063
Energy Sector Business
Commitments and Contingencies Disclosure [Line Items]
Investments and equity in consolidated subsidiaries	920,000
Investments, debt securities	289,600
Investments, equity securities	487,100
Energy Sector Business | Stranded Oil Resources Corporation
Commitments and Contingencies Disclosure [Line Items]
Stockholders' equity	$ 143,300

Segments of Business - Addition

Segments of Business - Additional Information (Detail) $ in Thousands	Feb. 07, 2018USD ($)	Jun. 30, 2018USD ($)Segment	Dec. 31, 2017USD ($)	Aug. 01, 2017	Apr. 28, 2017
Segment Reporting Information [Line Items]
Number of reportable segments | Segment		3
Debt amount		$ 1,569,367	$ 1,484,897
WWSC Holdings, LLC
Segment Reporting Information [Line Items]
Business acquisition date		Apr. 28, 2017
WWSC Holdings, LLC | Hirschfeld Holdings, LP
Segment Reporting Information [Line Items]
Business acquisition date		Feb. 7, 2018
Wilbert Funeral Services, Inc
Segment Reporting Information [Line Items]
Equity interest percentage		45.00%		45.00%
Operating Segments | Alleghany Capital Corporation Segment
Segment Reporting Information [Line Items]
Debt amount		$ 185,400
Operating Segments | Alleghany Capital Corporation Segment | WWSC Holdings, LLC
Segment Reporting Information [Line Items]
Business acquisition date		Apr. 28, 2017
Ownership interest acquired					80.00%
Operating Segments | Alleghany Capital Corporation Segment | WWSC Holdings, LLC
Segment Reporting Information [Line Items]
Debt amount		$ 95,000
Operating Segments | Alleghany Capital Corporation Segment | WWSC Holdings, LLC | Hirschfeld Holdings, LP
Segment Reporting Information [Line Items]
Business acquisition date	Feb. 7, 2018
Purchase price for acquisition	$ 111,300
Cash consideration for acquisition	96,600
Incremental debt acquired	$ 14,700
Operating Segments | Alleghany Capital Corporation Segment | Jazwares, LLC
Segment Reporting Information [Line Items]
Debt amount		41,000
Operating Segments | Alleghany Capital Corporation Segment | Bourn & Koch, Inc.
Segment Reporting Information [Line Items]
Debt amount		14,600
Operating Segments | Alleghany Capital Corporation Segment | Integrated Project Services LLC
Segment Reporting Information [Line Items]
Debt amount		15,700
Operating Segments | Alleghany Capital Corporation Segment | Kentucky Trailer
Segment Reporting Information [Line Items]
Debt amount		$ 19,100
Pacific Comp
Segment Reporting Information [Line Items]
Disposal date			Dec. 31, 2017

Results for Reportable Segments

Results for Reportable Segments and Corporate Activities (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Gross premiums written		$ 1,472,700	$ 1,450,000	$ 2,931,500	$ 2,870,900
Net premiums written		1,275,800	1,293,100	2,529,200	2,526,200
Net premiums earned		1,236,959	1,243,929	2,444,815	2,453,117
Net loss and LAE		738,210	734,886	1,408,788	1,434,191
Commissions, brokerage and other underwriting expenses		402,083	413,737	808,378	822,252
Underwriting (loss) profit	[1]	96,700	95,300	227,600	196,700
Net investment income		126,273	101,656	250,399	217,194
Change in the fair value of equity securities		185,245		142,596
Net realized capital gains		6,462	9,268	50,967	68,919
Other than temporary impairment losses				(511)
Other than temporary impairment losses			(3,747)		(6,964)
Other operating expenses		343,165	225,170	608,062	400,308
Corporate administration		14,119	14,405	21,904	31,290
Amortization of intangible assets		5,966	4,611	11,230	8,375
Interest expense		22,277	20,989	43,808	41,924
Earnings (losses) before income taxes		371,844	140,120	580,448	348,030
Noninsurance Revenue
Segment Reporting Information [Line Items]
Noninsurance revenue		342,725	202,812	594,352	354,104
Operating Segments
Segment Reporting Information [Line Items]
Gross premiums written		1,479,200	1,455,700	2,943,900	2,882,100
Net premiums written		1,275,800	1,293,100	2,529,200	2,526,200
Net premiums earned		1,237,000	1,243,900	2,444,800	2,453,100
Net loss and LAE		738,200	734,900	1,408,800	1,434,200
Commissions, brokerage and other underwriting expenses		402,100	413,700	808,400	822,200
Underwriting (loss) profit	[1]	96,700	95,300	227,600	196,700
Net investment income		122,300	98,200	242,500	210,800
Change in the fair value of equity securities		146,800		132,700
Net realized capital gains		6,700	9,400	51,200	69,500
Other than temporary impairment losses				(500)
Other than temporary impairment losses			(3,800)		(7,000)
Other operating expenses		334,400	215,300	591,400	380,100
Corporate administration		800	800	500	1,600
Amortization of intangible assets		6,000	4,600	11,200	8,400
Interest expense		9,200	7,800	17,200	15,400
Earnings (losses) before income taxes		355,800	166,700	615,300	407,900
Operating Segments | Noninsurance Revenue
Segment Reporting Information [Line Items]
Noninsurance revenue		333,700	196,100	582,100	343,400
Operating Segments | Reinsurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		1,071,700	1,045,400	2,187,300	2,101,100
Net premiums written		976,600	978,800	1,973,700	1,928,200
Net premiums earned		981,300	957,400	1,941,500	1,883,500
Net loss and LAE		593,500	573,000	1,132,900	1,130,100
Commissions, brokerage and other underwriting expenses		318,000	322,200	640,000	637,700
Underwriting (loss) profit	[1]	69,800	62,200	168,600	115,700
Operating Segments | Reinsurance Segment | Property
Segment Reporting Information [Line Items]
Gross premiums written		345,100	369,100	742,300	744,500
Net premiums written		275,900	317,200	581,000	602,400
Net premiums earned		292,100	270,500	567,200	557,300
Net loss and LAE		153,500	122,900	250,100	244,700
Commissions, brokerage and other underwriting expenses		94,800	87,900	187,900	178,700
Underwriting (loss) profit	[1]	43,800	59,700	129,200	133,900
Operating Segments | Reinsurance Segment | Casualty & Other
Segment Reporting Information [Line Items]
Gross premiums written	[2]	726,600	676,300	1,445,000	1,356,600
Net premiums written	[2]	700,700	661,600	1,392,700	1,325,800
Net premiums earned	[2]	689,200	686,900	1,374,300	1,326,200
Net loss and LAE	[2]	440,000	450,100	882,800	885,400
Commissions, brokerage and other underwriting expenses	[2]	223,200	234,300	452,100	459,000
Underwriting (loss) profit	[1],[2]	26,000	2,500	39,400	(18,200)
Operating Segments | Insurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		407,500	410,300	756,600	781,000
Net premiums written		299,200	314,300	555,500	598,000
Net premiums earned		255,700	286,500	503,300	569,600
Net loss and LAE		144,700	161,900	275,900	304,100
Commissions, brokerage and other underwriting expenses		84,100	91,500	168,400	184,500
Underwriting (loss) profit	[1]	26,900	33,100	59,000	81,000
Operating Segments | Insurance Segment | RSUI
Segment Reporting Information [Line Items]
Gross premiums written		318,800	295,100	593,400	559,600
Net premiums written		216,900	204,600	403,800	387,200
Net premiums earned		184,700	178,500	365,600	361,200
Net loss and LAE		105,700	93,800	202,600	174,400
Commissions, brokerage and other underwriting expenses		53,700	53,000	107,200	107,900
Underwriting (loss) profit	[1]	25,300	31,700	55,800	78,900
Operating Segments | Insurance Segment | CapSpecialty Incorporated
Segment Reporting Information [Line Items]
Gross premiums written		88,700	73,300	163,200	138,800
Net premiums written		82,300	68,400	151,700	129,400
Net premiums earned		71,000	64,100	137,700	126,200
Net loss and LAE		39,000	35,600	73,300	68,700
Commissions, brokerage and other underwriting expenses		30,400	27,200	61,200	54,900
Underwriting (loss) profit	[1]	1,600	1,300	3,200	2,600
Operating Segments | Insurance Segment | Pacific Comp
Segment Reporting Information [Line Items]
Gross premiums written			41,900		82,600
Net premiums written			41,300		81,400
Net premiums earned			43,900		82,200
Net loss and LAE			32,500		61,000
Commissions, brokerage and other underwriting expenses			11,300		21,700
Underwriting (loss) profit	[1]		100		(500)
Operating Segments | Reinsurance Segment and Insurance Segment
Segment Reporting Information [Line Items]
Gross premiums written		1,479,200	1,455,700	2,943,900	2,882,100
Net premiums written		1,275,800	1,293,100	2,529,200	2,526,200
Net premiums earned		1,237,000	1,243,900	2,444,800	2,453,100
Net loss and LAE		738,200	734,900	1,408,800	1,434,200
Commissions, brokerage and other underwriting expenses		402,100	413,700	808,400	822,200
Underwriting (loss) profit	[1]	96,700	95,300	227,600	196,700
Net investment income		121,100	98,000	239,400	210,300
Change in the fair value of equity securities		146,800		132,700
Net realized capital gains		6,800	9,200	50,700	69,400
Other than temporary impairment losses				(500)
Other than temporary impairment losses			(3,800)		(7,000)
Other operating expenses		19,900	25,900	37,000	49,100
Corporate administration		800	800	500	1,600
Amortization of intangible assets		200	(400)		(900)
Interest expense		6,900	6,800	13,600	13,600
Earnings (losses) before income taxes		348,300	168,900	609,200	411,800
Operating Segments | Reinsurance Segment and Insurance Segment | Noninsurance Revenue
Segment Reporting Information [Line Items]
Noninsurance revenue		4,700	3,300	10,400	5,800
Operating Segments | Alleghany Capital
Segment Reporting Information [Line Items]
Net investment income		1,200	200	3,100	500
Net realized capital gains		(100)	200	500	100
Other operating expenses		314,500	189,400	554,400	331,000
Amortization of intangible assets		5,800	5,000	11,200	9,300
Interest expense		2,300	1,000	3,600	1,800
Earnings (losses) before income taxes		7,500	(2,200)	6,100	(3,900)
Operating Segments | Alleghany Capital | Noninsurance Revenue
Segment Reporting Information [Line Items]
Noninsurance revenue		329,000	192,800	571,700	337,600
Corporate Activities
Segment Reporting Information [Line Items]
Gross premiums written	[3]	(6,500)	(5,700)	(12,400)	(11,200)
Net investment income	[3]	4,000	3,500	7,900	6,400
Change in the fair value of equity securities	[3]	38,400		9,900
Net realized capital gains	[3]	(200)	(100)	(200)	(600)
Other operating expenses	[3]	8,800	9,900	16,700	20,200
Corporate administration	[3]	13,300	13,600	21,400	29,700
Interest expense	[3]	13,100	13,200	26,600	26,500
Earnings (losses) before income taxes	[3]	16,000	(26,600)	(34,800)	(59,900)
Corporate Activities | Noninsurance Revenue
Segment Reporting Information [Line Items]
Noninsurance revenue	[3]	$ 9,000	$ 6,700	$ 12,300	$ 10,700
[1]	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, OTTI losses, noninsurance revenue, 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.
[2]	Primarily consists of the following assumed reinsurance lines of business: directors' and officers' liability; errors and omissions liability; general liability; medical malpractice; ocean marine and aviation; auto liability; accident and health; surety; and credit.
[3]	Includes elimination of minor reinsurance activity between segments.

Summary of Identifiable Assets

Summary of Identifiable Assets and Equity (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Identifiable Assets	$ 25,085,887	$ 25,384,317
Invested Assets and Cash	19,267,200
Equity attributable to Alleghany	8,404,389	$ 8,514,063
Operating Segments
Segment Reporting Information [Line Items]
Identifiable Assets	24,523,100
Invested Assets and Cash	18,781,600
Equity attributable to Alleghany	8,877,200
Operating Segments | Reinsurance Segment
Segment Reporting Information [Line Items]
Identifiable Assets	16,356,900
Invested Assets and Cash	13,387,800
Equity attributable to Alleghany	5,208,500
Operating Segments | Insurance Segment
Segment Reporting Information [Line Items]
Identifiable Assets	6,837,900
Invested Assets and Cash	5,263,300
Equity attributable to Alleghany	2,891,500
Operating Segments | Reinsurance Segment and Insurance Segment
Segment Reporting Information [Line Items]
Identifiable Assets	23,194,800
Invested Assets and Cash	18,651,100
Equity attributable to Alleghany	8,100,000
Operating Segments | Alleghany Capital
Segment Reporting Information [Line Items]
Identifiable Assets	1,328,300
Invested Assets and Cash	130,500
Equity attributable to Alleghany	777,200
Corporate Activities
Segment Reporting Information [Line Items]
Identifiable Assets	562,800
Invested Assets and Cash	485,600
Equity attributable to Alleghany	$ (472,800)

Summary of Alleghany Capital No

Summary of Alleghany Capital Non-Insurance Revenue (Detail) - Noninsurance Revenue - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other Revenues [Line Items]
Noninsurance revenue		$ 342,725	$ 202,812	$ 594,352	$ 354,104
Operating Segments
Other Revenues [Line Items]
Noninsurance revenue		333,700	196,100	582,100	343,400
Operating Segments | Alleghany Capital
Other Revenues [Line Items]
Noninsurance revenue		329,000	192,800	571,700	337,600
Operating Segments | Alleghany Capital | Industrial Segment
Other Revenues [Line Items]
Noninsurance revenue	[1]	221,900	74,500	367,400	116,400
Operating Segments | Alleghany Capital | Non-industrial Segment
Other Revenues [Line Items]
Noninsurance revenue	[2]	$ 107,100	$ 118,300	204,200	$ 221,200
Operating Segments | Alleghany Capital | Corporate & Other
Other Revenues [Line Items]
Noninsurance revenue				$ 100
[1]	For the three and six months ended June 30, 2018, the vast majority of noninsurance revenues were recognized as goods and services transferred to customers over time. For the three and six months ended June 30, 2017, approximately 66 percent and 57 percent, respectively, of noninsurance revenues were recognized as services were transferred to customers over time, with the remainder recognized as goods transferred at a point in time. See Note 1(c) of this Form 10-Q for additional information regarding Alleghany's adoption of new revenue recognition accounting guidance effective in the first quarter of 2018.
[2]	For the three and six months ended June 30, 2018, approximately 70 percent of noninsurance revenues were recognized as services transferred to customers over time, with the remainder recognized as goods transferred at a point in time. For the three and six months ended June 30, 2017, approximately 75 percent and 78 percent, respectively, of noninsurance revenues were recognized as services were transferred to customers over time, with the remainder recognized as goods were transferred at a point in time. See Note 1(c) of this Form 10-Q for additional information regarding Alleghany's adoption of new revenue recognition accounting guidance effective in the first quarter of 2018.

Summary of Alleghany Capital 54

Summary of Alleghany Capital Non-Insurance Revenue (Parenthetical) (Detail) - Operating Segments - Alleghany Capital - Transferred over Time [Member]	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Industrial Segment
Other Revenues [Line Items]
Noninsurance revenue percentage		66.00%		57.00%
Non-industrial Segment
Other Revenues [Line Items]
Noninsurance revenue percentage	70.00%	75.00%	70.00%	78.00%