Markel (MKL) 10-Q 2 Nov 21 2021 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 26, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-15811
Entity Registrant Name	MARKEL CORPORATION
Entity Incorporation, State or Country Code	VA
Entity Tax Identification Number	54-1959284
Entity Address, Address Line One	4521 Highwoods Parkway
Entity Address, City or Town	Glen Allen
Entity Address, State or Province	VA
Entity Address, Postal Zip Code	23060-6148
City Area Code	804
Local Phone Number	747-0136
Title of 12(b) Security	Common Stock, no par value
Trading Symbol	MKL
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		13,668,248
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001096343
Current Fiscal Year End Date	--12-31

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets [Abstract]
Fixed maturities, available-for-sale (amortized cost of $11,324,144 in 2021 and $9,655,261 in 2020)	$ 11,962,587	$ 10,681,734
Equity securities (cost of $2,823,310 in 2021 and $2,732,998 in 2020)	8,220,874	6,994,110
Short-term investments, available-for-sale (estimated fair value approximates cost)	2,757,798	2,034,099
Total Investments	22,941,259	19,709,943
Cash and cash equivalents	3,938,626	4,341,736
Restricted cash and cash equivalents	568,385	874,913
Receivables	2,320,987	1,930,211
Reinsurance recoverables	6,944,636	5,989,337
Deferred policy acquisition costs	772,127	630,794
Prepaid reinsurance premiums	1,920,184	1,451,858
Goodwill	2,695,164	2,604,624
Intangible assets	1,719,609	1,782,718
Other assets	2,875,459	2,393,920
Total Assets	46,696,436	41,710,054
Liabilities and Equity [Abstract]
Unpaid losses and loss adjustment expenses	17,611,199	16,222,376
Life and annuity benefits	925,958	1,069,986
Unearned premiums	5,511,392	4,433,245
Payables to insurance and reinsurance companies	579,905	493,470
Senior long-term debt and other debt (estimated fair value of $4,956,000 in 2021 and $4,367,000 in 2020)	4,268,290	3,484,023
Other liabilities	3,527,555	2,946,631
Total Liabilities	32,424,299	28,649,731
Redeemable noncontrolling interests	231,912	245,642
Commitments and contingencies
Shareholders' equity:
Preferred Stock	591,891	591,891
Common stock	3,455,129	3,428,340
Retained earnings	9,650,355	8,195,182
Accumulated other comprehensive income	319,389	584,376
Total Shareholders' Equity	14,016,764	12,799,789
Noncontrolling interests	23,461	14,892
Total Equity	14,040,225	12,814,681
Total Liabilities and Equity	$ 46,696,436	$ 41,710,054

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fixed maturities, available-for-sale amortized cost	$ 11,324,144	$ 9,655,261
Equity securities, cost	2,823,310	2,732,998
Senior long-term debt and other debt (estimated fair value)	$ 4,956,000	$ 4,367,000

Consolidated Statements Of Inco

Consolidated Statements Of Income (Loss) And Comprehensive Income - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2021		Sep. 30, 2020		Sep. 30, 2021		Sep. 30, 2020
OPERATING REVENUES
Earned premiums	$ 1,630,500		$ 1,394,428		$ 4,696,232		$ 4,085,311
Net investment income	91,264		90,384		284,095		274,242
Net investment gains (losses)	(25,833)		539,302		1,175,791		(230,896)
Products revenues	405,711		342,039		1,327,144		1,117,781
Services and other revenues	585,712		545,582		1,605,058		1,132,978
Total Operating Revenues	2,687,354		2,911,735		9,088,320		6,379,416
OPERATING EXPENSES
Losses and loss adjustment expenses	948,241		863,247		2,643,114		2,652,811
Underwriting, acquisition and insurance expenses	569,756		492,824		1,644,863		1,477,349
Products expenses	374,407		296,371		1,173,135		974,925
Services and other expenses	513,994		522,237		1,442,342		1,024,733
Amortization of intangible assets	39,268	[1]	44,664	[1]	118,550	[2]	120,276	[1]
Total Operating Expenses	2,445,666		2,219,343		7,022,004		6,250,094
Operating Income	241,688		692,392		2,066,316		129,322
Interest expense	(46,455)		(42,744)		(135,412)		(133,201)
Net foreign exchange gains (losses)	48,850		(65,577)		61,677		(8,736)
Income (Loss) Before Income Taxes	244,083		584,071		1,992,581		(12,615)
Income tax expense	(54,415)		(130,028)		(419,898)		(3,047)
Net Income (Loss)	189,668		454,043		1,572,683		(15,662)
Net income attributable to noncontrolling interests	(1,598)		(1,317)		(18,809)		(15,607)
Net Income (Loss) to Shareholders	188,070		452,726		1,553,874		(31,269)
Preferred stock dividends	0		0		(18,000)		0
Net Income (Loss) to Common Stockholders	188,070		452,726		1,535,874		(31,269)
OTHER COMPREHENSIVE INCOME (LOSS)
Net holding gains (losses) arising during the period	(104,238)		64,449		(262,679)		301,487
Reclassification adjustments for net gains included in net income (loss)	224		(3,362)		(3,807)		(3,560)
Change in net unrealized gains on available-for-sale investments, net of taxes	(104,014)		61,087		(266,486)		297,927
Change in foreign currency translation adjustments, net of taxes	(4,437)		5,756		(330)		(8,383)
Change in net actuarial pension loss, net of taxes	586		538		1,832		1,422
Total Other Comprehensive Income (Loss)	(107,865)		67,381		(264,984)		290,966
Comprehensive Income (Loss)	81,803		521,424		1,307,699		275,304
Comprehensive income attributable to noncontrolling interests	(1,567)		(1,335)		(18,812)		(15,631)
Comprehensive Income to Shareholders	$ 80,236		$ 520,089		$ 1,288,887		$ 259,673
NET INCOME (LOSS) PER COMMON SHARE
Basic	$ 15.12		$ 31.07		$ 114.39		$ (3.76)
Diluted	$ 15.09		$ 31.03		$ 114.20		$ (3.76)	[3]
[1]	Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments.
[2]	Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments.
[3]	The impact of restricted stock units and restricted stock of 13 thousand shares was excluded from the computation of diluted earnings per common share for the nine months ended September 30, 2020 because the effect would have been anti-dilutive.

Consolidated Statements Of Chan

Consolidated Statements Of Changes In Equity - USD ($) $ in Thousands	Total	Total Equity [Member]	Total Shareholders' Equity [Member]	Preferred Stock [Member]	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Noncontrolling Interests [Member]	Redeemable Noncontrolling Interests [Member]	Redeemable Noncontrolling Interests [Member]Acquisition of Lansing	Redeemable Noncontrolling Interests [Member]Acquisition of Buckner
Balance at Dec. 31, 2019		$ 11,078,416	$ 11,070,867	$ 0	$ 3,404,919	$ 7,457,176	$ 208,772	$ 7,549
Balance, redeemable noncontrolling interests at Dec. 31, 2019									$ 177,562
Net Income (Loss)	$ (15,662)	(27,068)	(31,269)			(31,269)	0	4,201	11,406
Other comprehensive income (loss)	290,966	290,942	290,942			0	290,942	0	24
Comprehensive Income (Loss)	275,304	263,874	259,673					4,201	11,430
Issuance of preferred stock		591,891	591,891	591,891	0	0	0	0	0
Repurchase of common stock		(23,943)	(23,943)	0	0	(23,943)	0	0	0
Restricted stock units expensed		26,386	26,386	0	26,386	0	0	0	0
Acquisitions		0	0	0	0	0	0	0		$ 43,566
Adjustment of redeemable noncontrolling interests		(20,681)	(20,681)	0	0	(20,681)	0	0	20,681
Purchase of noncontrolling interest		(6,131)	(6,131)	0	(6,131)	0	0	0	(7,029)
Other		1,773	(288)	0	73	(361)	0	2,061	(5,190)
Balance at Sep. 30, 2020		11,907,758	11,893,947	591,891	3,425,247	7,377,095	499,714	13,811
Balance, redeemable noncontrolling interests at Sep. 30, 2020									241,020
Balance at Jun. 30, 2020		11,410,248	11,394,553	591,891	3,421,845	6,948,466	432,351	15,695
Balance, redeemable noncontrolling interests at Jun. 30, 2020									214,653
Net Income (Loss)	454,043	450,333	452,726			452,726	0	(2,393)	3,710
Other comprehensive income (loss)	67,381	67,363	67,363			0	67,363	0	18
Comprehensive Income (Loss)	521,424	517,696	520,089					(2,393)	3,728
Restricted stock units expensed		3,402	3,402	0	3,402	0	0	0	0
Adjustment of redeemable noncontrolling interests		(23,621)	(23,621)	0	0	(23,621)	0	0	23,621
Other		33	(476)	0	0	(476)	0	509	(982)
Balance at Sep. 30, 2020		11,907,758	11,893,947	591,891	3,425,247	7,377,095	499,714	13,811
Balance, redeemable noncontrolling interests at Sep. 30, 2020									241,020
Balance at Dec. 31, 2020	12,814,681	12,814,681	12,799,789	591,891	3,428,340	8,195,182	584,376	14,892
Balance, redeemable noncontrolling interests at Dec. 31, 2020	245,642								245,642
Net Income (Loss)	1,572,683	1,561,834	1,553,874			1,553,874	0	7,960	10,849
Other comprehensive income (loss)	(264,984)	(264,987)	(264,987)			0	(264,987)	0	3
Comprehensive Income (Loss)	1,307,699	1,296,847	1,288,887					7,960	10,852
Repurchase of common stock		(122,377)	(122,377)	0	0	(122,377)	0	0	0
Preferred stock dividends		(18,000)	(18,000)	0	0	(18,000)	0	0	0
Restricted stock units expensed		27,783	27,783	0	27,783	0	0	0	0
Acquisitions		0	0	0	0	0	0	0			$ 26,438
Adjustment of redeemable noncontrolling interests		41,553	41,553	0	0	41,553	0	0	(41,553)
Purchase of noncontrolling interest		(1,551)	(1,551)	0	(1,551)	0	0	0	(1,179)
Other		1,289	680	0	557	123	0	609	(8,288)
Balance at Sep. 30, 2021	14,040,225	14,040,225	14,016,764	591,891	3,455,129	9,650,355	319,389	23,461
Balance, redeemable noncontrolling interests at Sep. 30, 2021	231,912								231,912
Balance at Jun. 30, 2021		13,998,049	13,974,971	591,891	3,451,968	9,503,889	427,223	23,078
Balance, redeemable noncontrolling interests at Jun. 30, 2021									228,401
Net Income (Loss)	189,668	188,628	188,070			188,070	0	558	1,040
Other comprehensive income (loss)	(107,865)	(107,834)	(107,834)			0	(107,834)	0	(31)
Comprehensive Income (Loss)	81,803	80,794	80,236					558	1,009
Repurchase of common stock		(61,551)	(61,551)	0	0	(61,551)	0	0	0
Restricted stock units expensed		4,181	4,181	0	4,181	0	0	0	0
Acquisitions		0	0	0	0	0	0	0			$ 26,438
Adjustment of redeemable noncontrolling interests		19,930	19,930	0	0	19,930	0	0	(19,930)
Purchase of noncontrolling interest		(1,020)	(1,020)	0	(1,020)	0	0	0	(1,032)
Other		(158)	17	0	0	17	0	(175)	(2,974)
Balance at Sep. 30, 2021	14,040,225	$ 14,040,225	$ 14,016,764	$ 591,891	$ 3,455,129	$ 9,650,355	$ 319,389	$ 23,461
Balance, redeemable noncontrolling interests at Sep. 30, 2021	$ 231,912								$ 231,912

Condensed Consolidated Statemen

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
OPERATING ACTIVITIES
Net income (loss)	$ 1,572,683	$ (15,662)
Adjustments to reconcile net income (loss) to net cash provided by operating activities	49,759	1,277,250
Net Cash Provided By Operating Activities	1,622,442	1,261,588
INVESTING ACTIVITIES
Proceeds from sales of fixed maturities and equity securities	182,040	1,544,501
Proceeds from maturities, calls and prepayments of fixed maturities	467,170	507,480
Cost of fixed maturities and equity securities purchased	(2,379,990)	(764,823)
Net change in short-term investments	(727,366)	(697,580)
Additions to property and equipment	(80,758)	(72,771)
Acquisitions, net of cash acquired	(241,210)	(547,847)
Other	47,623	53,531
Net Cash Provided (Used) By Investing Activities	(2,732,491)	22,491
FINANCING ACTIVITIES
Additions to senior long-term debt and other debt	989,067	189,846
Repayment of senior long-term debt and other debt	(370,157)	(227,692)
Repurchases of common stock	(122,377)	(23,943)
Issuance of preferred stock, net	0	591,891
Dividends paid on preferred stock	(18,000)	0
Other	(39,149)	(54,481)
Net Cash Provided By Financing Activities	439,384	475,621
Effect of foreign currency rate changes on cash, cash equivalents, restricted cash and restricted cash equivalents	(38,973)	2,500
Increase (decrease) in cash, cash equivalents, restricted cash and restricted cash equivalents	(709,638)	1,762,200
Cash, cash equivalents, restricted cash and restricted cash equivalents at beginning of period	5,216,649	3,500,353
CASH, CASH EQUIVALENTS, RESTRICTED CASH AND RESTRICTED CASH EQUIVALENTS AT END OF PERIOD	$ 4,507,011	$ 5,262,553

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary Of Significant Accounting Policies	Summary of Significant Accounting Policies Markel Corporation is a diverse financial holding company serving a variety of niche markets. Markel Corporation's principal business markets and underwrites specialty insurance products. Through its wholly owned subsidiary, Markel Ventures, Inc. (Markel Ventures), Markel Corporation also owns interests in various businesses that operate outside of the specialty insurance marketplace. See note 2 for details regarding reportable segments. a) Basis of Presentation. The consolidated balance sheet as of September 30, 2021 and the related consolidated statements of income (loss) and comprehensive income and changes in equity for the quarters and nine months ended September 30, 2021 and 2020, and the condensed consolidated statements of cash flows for the nine months ended September 30, 2021 and 2020 are unaudited. In the opinion of management, all adjustments necessary for fair presentation of such consolidated financial statements have been included. Such adjustments consist only of normal, recurring items. Interim results are not necessarily indicative of results of operations for the entire year. The consolidated balance sheet as of December 31, 2020 was derived from Markel Corporation's audited annual consolidated financial statements. The accompanying consolidated financial statements have been prepared in accordance with United States (U.S.) generally accepted accounting principles (GAAP) and include the accounts of Markel Corporation and its consolidated subsidiaries, as well as any variable interest entities (VIEs) that meet the requirements for consolidation (the Company). All significant intercompany balances and transactions have been eliminated in consolidation. The Company consolidates the results of its Markel Ventures subsidiaries on a one-month lag, with the exception of significant transactions or events that occur during the intervening period. Certain prior period amounts have been reclassified to conform to the current period presentation. The preparation of financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities. Actual results may differ materially from the estimates and assumptions used in preparing the consolidated financial statements. The consolidated financial statements and notes are presented as permitted by Form 10-Q and do not contain certain information included in the Company's annual consolidated financial statements and notes. Readers are urged to review the Company's 2020 Annual Report on Form 10-K for a more complete description of the Company's business and accounting policies, as well as a description of the risks and uncertainties associated with the COVID-19 pandemic on the Company's businesses and results of operations, financial condition and cash flows, including in note 20 of the notes to consolidated financial statements included under Item 8 Financial Statements and Supplementary Data. There were no material changes in the Company's assessment of the risks and uncertainties associated with the COVID-19 pandemic during the nine months ended September 30, 2021. b) Recent Accounting Pronouncements Accounting Standards Adopted in 2021 The Company adopted Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes , effective January 1, 2021. Adoption of this standard did not have a material impact on the Company's financial position, results of operations or cash flows. Accounting Standards Not Yet Adopted In August 2018, the FASB issued ASU No. 2018-12, Financial Services—Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts. The FASB subsequently issued several ASUs as amendments to ASU No. 2018-12. The standard requires insurance entities with long duration contracts to: (1) review and, if there is a change, update the assumptions used to measure expected cash flows at least annually; (2) update the discount rate assumption at each reporting date; (3) measure all market risk benefits associated with deposit (or account balance) contracts at fair value; and (4) disclose liability rollforwards and information about significant inputs, judgments, assumptions and methods used to measure the liability, including changes thereto and the effect of those changes on measurement. ASU No. 2018-12 becomes effective for the Company during the first quarter of 2023. The standard will, among other things, impact the discount rate used in estimating reserves for the Company's life and annuity reinsurance portfolio, which is in runoff. Currently, the discount rate assumption is locked-in for the life of the contracts, unless there is a loss recognition event. The Company is currently evaluating ASU No. 2018-12 to determine the impact that adopting this standard will have on its consolidated financial statements.

Segment Reporting Disclosures

Segment Reporting Disclosures	9 Months Ended
	Sep. 30, 2021
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]
Segment Reporting Disclosures	Segment Reporting Disclosures The chief operating decision maker reviews the Company's ongoing underwriting operations on a global basis in the following two segments: Insurance and Reinsurance. In determining how to allocate resources and assess the performance of the Company's underwriting results, management considers many factors, including the nature of the insurance product sold, the type of account written and the type of customer served. The Insurance segment includes all direct business and facultative placements written within the Company's underwriting operations. The Reinsurance segment includes all treaty reinsurance written within the Company's underwriting operations. All investing activities related to the Company's insurance operations are included in the Investing segment. The chief operating decision maker reviews and assesses Markel Ventures' performance in the aggregate, as a single operating segment. The Markel Ventures segment primarily consists of controlling interests in a diverse portfolio of businesses that operate in various industries. The Company's other operations primarily consist of the results of the Company's insurance-linked securities operations and program services business. Other operations also include results for lines of business discontinued prior to, or in conjunction with, acquisitions, including development on asbestos and environmental loss reserves and results attributable to the run-off of life and annuity reinsurance business, which are monitored separately from the Company's ongoing underwriting operations. For purposes of segment reporting, none of these other operations are considered to be reportable segments. Segment profit for each of the Company's underwriting segments is measured by underwriting profit. The property and casualty insurance industry commonly defines underwriting profit as earned premiums net of losses and loss adjustment expenses and underwriting, acquisition and insurance expenses. Underwriting profit does not replace operating income or net income computed in accordance with U.S. GAAP as a measure of profitability. Underwriting profit or loss provides a basis for management to evaluate the Company's underwriting performance. Segment profit for the Company's underwriting segments may also include other revenues and expenses that are attributable to the Company's underwriting operations that are not captured in underwriting profit. Segment profit for the Investing segment is measured by net investment income and net investment gains. Segment profit for the Markel Ventures segment is measured by operating income. For management reporting purposes, the Company allocates assets to its underwriting operations and to its Investing and Markel Ventures segments and certain of its other operations, including its insurance-linked securities and program services operations. Underwriting assets include assets attributed to the Company's Insurance and Reinsurance segments, discontinued underwriting lines of business, as well as assets that are not specifically allocated to the Company's other operations. Generally, the Company manages its underwriting assets in the aggregate and therefore does not allocate assets to individual underwriting segments. a) The following tables summarize the Company's segment disclosures. Quarter Ended September 30, 2021 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 1,899,592 $ 180,673 $ — $ — $ 888,337 $ 2,968,602 Net written premiums 1,545,428 141,642 — — (2,260) 1,684,810 Earned premiums 1,381,235 250,962 — — (1,697) 1,630,500 Losses and loss adjustment expenses: Current accident year (866,481) (221,872) — — — (1,088,353) Prior accident years 124,133 16,292 — — (313) 140,112 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (289,201) (63,723) — — — (352,924) Other operating expenses (202,961) (12,101) — — (1,770) (216,832) Underwriting profit (loss) 146,725 (30,442) — — (3,780) 112,503 Net investment income — — 91,261 3 — 91,264 Net investment losses — — (25,833) — — (25,833) Products revenues — — — 405,711 — 405,711 Services and other revenues — — — 502,471 83,241 585,712 Products expenses — — — (374,407) — (374,407) Services and other expenses — — — (465,268) (48,726) (513,994) Amortization of intangible assets (3) — — — (13,541) (25,727) (39,268) Segment profit (loss) $ 146,725 $ (30,442) $ 65,428 $ 54,969 $ 5,008 $ 241,688 Interest expense (46,455) Net foreign exchange gains 48,850 Income before income taxes $ 244,083 U.S. GAAP combined ratio (4) 89 % 112 % NM (5) 93 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $15.8 million for the quarter ended September 30, 2021. (2) Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $10.3 million for the quarter ended September 30, 2021, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments. (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful Quarter Ended September 30, 2020 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 1,514,002 $ 222,066 $ — $ — $ 536,666 $ 2,272,734 Net written premiums 1,220,054 178,994 — — (1,772) 1,397,276 Earned premiums 1,173,758 222,369 — — (1,699) 1,394,428 Losses and loss adjustment expenses: Current accident year (817,174) (213,325) — — — (1,030,499) Prior accident years 137,312 30,681 — — (741) 167,252 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (239,096) (56,997) — — — (296,093) Other operating expenses (179,840) (17,609) — — 718 (196,731) Underwriting profit (loss) 74,960 (34,881) — — (1,722) 38,357 Net investment income — — 90,380 4 — 90,384 Net investment gains — — 539,302 — — 539,302 Products revenues — — — 342,039 — 342,039 Services and other revenues — — — 482,089 63,493 545,582 Products expenses — — — (296,371) — (296,371) Services and other expenses — — — (432,294) (89,943) (522,237) Amortization of intangible assets (3) — — — (15,862) (28,802) (44,664) Segment profit (loss) $ 74,960 $ (34,881) $ 629,682 $ 79,605 $ (56,974) $ 692,392 Interest expense (42,744) Net foreign exchange losses (65,577) Income before income taxes $ 584,071 U.S. GAAP combined ratio (4) 94 % 116 % NM (5) 97 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $15.3 million for the quarter ended September 30, 2020. (2) Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $10.4 million for the quarter ended September 30, 2020, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments. (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful Nine Months Ended September 30, 2021 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 5,359,293 $ 992,635 $ — $ — $ 2,305,539 $ 8,657,467 Net written premiums 4,427,301 893,082 — — (3,052) 5,317,331 Earned premiums 3,928,824 770,031 — — (2,623) 4,696,232 Losses and loss adjustment expenses: Current accident year (2,448,034) (561,226) — — — (3,009,260) Prior accident years 397,723 (34,104) — — 2,527 366,146 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (814,623) (193,697) — — — (1,008,320) Other operating expenses (594,880) (39,676) — — (1,987) (636,543) Underwriting profit (loss) 469,010 (58,672) — — (2,083) 408,255 Net investment income — — 284,087 8 — 284,095 Net investment gains — — 1,175,791 — — 1,175,791 Products revenues — — — 1,327,144 — 1,327,144 Services and other revenues — — — 1,363,141 241,917 1,605,058 Products expenses — — — (1,173,135) — (1,173,135) Services and other expenses — 109 — (1,260,957) (181,494) (1,442,342) Amortization of intangible assets (3) — — — (41,104) (77,446) (118,550) Segment profit (loss) $ 469,010 $ (58,563) $ 1,459,878 $ 215,097 $ (19,106) $ 2,066,316 Interest expense (135,412) Net foreign exchange gains 61,677 Income before income taxes $ 1,992,581 U.S. GAAP combined ratio (4) 88 % 108 % NM (5) 91 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $47.7 million for the nine months ended September 30, 2021. (2) Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $31.1 million for the nine months ended September 30, 2021, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments. (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful Nine Months Ended September 30, 2020 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 4,482,149 $ 958,529 $ — $ — $ 1,528,072 $ 6,968,750 Net written premiums 3,683,767 820,573 — — (4,191) 4,500,149 Earned premiums 3,400,760 688,884 — — (4,333) 4,085,311 Losses and loss adjustment expenses: Current accident year (2,554,010) (534,218) — — — (3,088,228) Prior accident years 404,649 29,049 — — 1,719 435,417 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (717,300) (176,799) — — — (894,099) Other operating expenses (530,440) (51,001) — — (1,809) (583,250) Underwriting profit (loss) 3,659 (44,085) — — (4,423) (44,849) Net investment income — — 274,000 242 — 274,242 Net investment losses — — (230,896) — — (230,896) Products revenues — — — 1,117,781 — 1,117,781 Services and other revenues — — — 895,469 237,509 1,132,978 Products expenses — — — (974,925) — (974,925) Services and other expenses — — — (798,502) (226,231) (1,024,733) Amortization of intangible assets (3) — — — (39,299) (80,977) (120,276) Segment profit (loss) $ 3,659 $ (44,085) $ 43,104 $ 200,766 $ (74,122) $ 129,322 Interest expense (133,201) Net foreign exchange losses (8,736) Loss before income taxes $ (12,615) U.S. GAAP combined ratio (4) 100 % 106 % NM (5) 101 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $43.5 million for the nine months ended September 30, 2020. (2) Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $31.5 million for the nine months ended September 30, 2020, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments. (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful b) The following table reconciles segment assets to the Company's consolidated balance sheets. (dollars in thousands) September 30, 2021 December 31, 2020 Segment assets: Investing $ 27,327,180 $ 24,781,946 Underwriting 8,151,380 7,228,297 Markel Ventures 4,336,021 3,636,060 Total segment assets 39,814,581 35,646,303 Other operations 6,881,855 6,063,751 Total assets $ 46,696,436 $ 41,710,054

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2021
Business Combination and Asset Acquisition [Abstract]
Acquisitions	Acquisitions In August 2021, the Company acquired 90% of the holding company for the Buckner HeavyLift Cranes companies (Buckner), a provider of crane rental services for large commercial contractors. Under the terms of the acquisition agreement, the Company has the option to acquire the remaining equity interests and the remaining equity holders have the option to sell their interests to the Company in the future. The redemption value of the remaining equity interests is generally based on Buckner's earnings in specified periods preceding the redemption dates. Total consideration for the transaction was $237.9 million, all of which was cash. The purchase price was preliminarily allocated to the acquired assets and liabilities of Buckner based on estimated fair value at the acquisition date. The Company recognized goodwill of $91.9 million, intangible assets of $60.0 million and fixed assets of $306.6 million, primarily related to cranes. Goodwill is primarily attributable to expected future earnings and cash flow potential of Buckner, and it is not expected to be deductible for income tax purposes. Intangible assets include $50.0 million of customer relationships and $10.0 million of trade names, which are expected to be amortized over 7 years and 15 years, respectively. Additionally, the Company assumed long-term debt of $165.1 million and recognized redeemable noncontrolling interests of $26.4 million. Results attributable to Buckner will be included in the Company's Markel Ventures segment. The Company has not completed the process of determining the fair value of the assets acquired and liabilities assumed. These valuations are required to be completed within 12 months from the acquisition date. As a result, the fair value recorded for these items is a provisional estimate and is subject to adjustment. Once completed, any adjustments resulting from the valuations may impact the individual amounts recorded for assets acquired and liabilities assumed, as well as the residual goodwill.

Investments

Investments	9 Months Ended
	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Investments	Investments a) The following tables summarize the Company's available-for-sale investments. Commercial and residential mortgage-backed securities include securities issued by U.S. government-sponsored enterprises and U.S. government agencies. The net unrealized holding gains in the tables below are presented before taxes and any reserve deficiency adjustments for life and annuity benefit reserves. See note 9. September 30, 2021 (dollars in thousands) Amortized Gross Gross Estimated Fixed maturity securities: U.S. Treasury securities $ 1,900,911 $ 3,907 $ (7,466) $ 1,897,352 U.S. government-sponsored enterprises 750,038 31,417 (4,423) 777,032 Obligations of states, municipalities and political subdivisions 3,866,173 292,948 (5,656) 4,153,465 Foreign governments 1,383,586 153,795 (5,576) 1,531,805 Commercial mortgage-backed securities 1,945,261 93,916 (5,143) 2,034,034 Residential mortgage-backed securities 740,380 36,057 (73) 776,364 Asset-backed securities 3,403 79 — 3,482 Corporate bonds 734,392 57,462 (2,801) 789,053 Total fixed maturity securities 11,324,144 669,581 (31,138) 11,962,587 Short-term investments 2,757,235 2,365 (1,802) 2,757,798 Investments, available-for-sale $ 14,081,379 $ 671,946 $ (32,940) $ 14,720,385 December 31, 2020 (dollars in thousands) Amortized Gross Gross Estimated Fixed maturity securities: U.S. Treasury securities $ 580,716 $ 9,091 $ (507) $ 589,300 U.S. government-sponsored enterprises 500,053 51,593 (92) 551,554 Obligations of states, municipalities and political subdivisions 3,903,292 386,784 (235) 4,289,841 Foreign governments 1,352,616 275,450 (57) 1,628,009 Commercial mortgage-backed securities 1,736,257 149,359 (34) 1,885,582 Residential mortgage-backed securities 811,732 58,742 (29) 870,445 Asset-backed securities 5,812 154 — 5,966 Corporate bonds 764,783 96,257 (3) 861,037 Total fixed maturity securities 9,655,261 1,027,430 (957) 10,681,734 Short-term investments 2,030,460 3,645 (6) 2,034,099 Investments, available-for-sale $ 11,685,721 $ 1,031,075 $ (963) $ 12,715,833 b) The following tables summarize gross unrealized investment losses on available-for-sale investments by the length of time that securities have continuously been in an unrealized loss position. September 30, 2021 Less than 12 months 12 months or longer Total (dollars in thousands) Estimated Gross Estimated Gross Estimated Gross Fixed maturity securities: U.S. Treasury securities $ 1,529,225 $ (5,438) $ 53,457 $ (2,028) $ 1,582,682 $ (7,466) U.S. government-sponsored enterprises 256,872 (3,602) 14,028 (821) 270,900 (4,423) Obligations of states, municipalities and political subdivisions 283,201 (5,182) 21,491 (474) 304,692 (5,656) Foreign governments 255,067 (5,576) — — 255,067 (5,576) Commercial mortgage-backed securities 306,557 (5,143) — — 306,557 (5,143) Residential mortgage-backed securities 5,928 (70) 92 (3) 6,020 (73) Corporate bonds 101,607 (2,801) — — 101,607 (2,801) Total fixed maturity securities 2,738,457 (27,812) 89,068 (3,326) 2,827,525 (31,138) Short-term investments 2,450,158 (1,802) — — 2,450,158 (1,802) Total $ 5,188,615 $ (29,614) $ 89,068 $ (3,326) $ 5,277,683 $ (32,940) At September 30, 2021, the Company held 203 available-for-sale securities in an unrealized loss position with a total estimated fair value of $5.3 billion and gross unrealized losses of $32.9 million. Of these 203 securities, 10 securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $89.1 million and gross unrealized losses of $3.3 million. The Company does not intend to sell or believe it will be required to sell these available-for-sale securities before recovery of their amortized cost. December 31, 2020 Less than 12 months 12 months or longer Total (dollars in thousands) Estimated Gross Estimated Gross Estimated Gross Fixed maturity securities: U.S. Treasury securities $ 66,220 $ (507) $ — $ — $ 66,220 $ (507) U.S. government-sponsored enterprises 14,878 (92) — — 14,878 (92) Obligations of states, municipalities and political subdivisions 28,037 (223) 2,960 (12) 30,997 (235) Foreign governments 20,790 (57) — — 20,790 (57) Commercial mortgage-backed securities 13,178 (26) 2,526 (8) 15,704 (34) Residential mortgage-backed securities 3,345 (29) — — 3,345 (29) Corporate bonds 92 (3) — — 92 (3) Total fixed maturity securities 146,540 (937) 5,486 (20) 152,026 (957) Short-term investments 349,978 (6) — — 349,978 (6) Total $ 496,518 $ (943) $ 5,486 $ (20) $ 502,004 $ (963) At December 31, 2020, the Company held 36 available-for-sale securities in an unrealized loss position with a total estimated fair value of $502.0 million and gross unrealized losses of $963 thousand. Of these 36 securities, six securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $5.5 million and gross unrealized losses of $20 thousand. The Company completes a detailed analysis each quarter to assess whether the decline in the fair value of any investment below its cost basis is the result of a credit loss. All available-for-sale securities with unrealized losses are reviewed. The Company considers many factors in completing its quarterly review of securities with unrealized losses for credit-related impairment to determine whether a credit loss exists, including the extent to which fair value is below cost, the implied yield to maturity, rating downgrades of the security and whether or not the issuer has failed to make scheduled principal or interest payments. The Company also takes into consideration information about the financial condition of the issuer and industry factors that could negatively impact the capital markets. If the decline in fair value of an available-for-sale security below its amortized cost is considered to be the result of a credit loss, the Company compares the estimated present value of the cash flows expected to be collected to the amortized cost of the security. The extent to which the estimated present value of the cash flows expected to be collected is less than the amortized cost of the security represents the credit loss, which is recorded as an allowance and recognized in net income. The allowance is limited to the difference between the fair value and the amortized cost of the security. Any remaining decline in fair value represents the non-credit portion of the impairment, which is recognized in other comprehensive income. The Company did not have an allowance for credit losses as of September 30, 2021 or December 31, 2020. Quarterly, the Company also considers whether it intends to sell an available-for-sale security or if it is more likely than not that it will be required to sell the security before recovery of its amortized cost. In these instances, a decline in fair value is recognized in net income based on the fair value of the security at the time of assessment, resulting in a new cost basis for the security. c) The amortized cost and estimated fair value of fixed maturity securities at September 30, 2021 are shown below by contractual maturity. (dollars in thousands) Amortized Estimated Due in one year or less $ 391,678 $ 395,422 Due after one year through five years 3,407,996 3,507,926 Due after five years through ten years 2,576,383 2,706,530 Due after ten years 2,259,043 2,538,829 8,635,100 9,148,707 Commercial mortgage-backed securities 1,945,261 2,034,034 Residential mortgage-backed securities 740,380 776,364 Asset-backed securities 3,403 3,482 Total fixed maturity securities $ 11,324,144 $ 11,962,587 d) The following table presents the components of net investment income. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2021 2020 2021 2020 Interest: Tax-exempt municipal bonds $ 14,293 $ 15,693 $ 43,631 $ 48,451 Taxable municipal bonds 16,320 16,456 49,236 50,185 Other taxable bonds 39,705 38,788 119,718 118,376 Short-term investments, including overnight deposits 633 894 2,179 13,516 Dividends on equity securities 23,400 20,282 68,583 66,916 Income (loss) from equity method investments 882 2,483 13,825 (11,849) Other (335) (365) (947) 438 94,898 94,231 296,225 286,033 Investment expenses (3,634) (3,847) (12,130) (11,791) Net investment income $ 91,264 $ 90,384 $ 284,095 $ 274,242 e) The following table presents the components of net investment gains (losses) and the change in net unrealized gains included in other comprehensive income (loss). Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2021 2020 2021 2020 Fixed maturity securities: Realized gains $ 92 $ 5,292 $ 4,967 $ 12,025 Realized losses (390) (1,209) (471) (7,480) Change in allowance for expected credit losses — 202 — — Short-term investments: Realized gains 16 655 324 1,756 Realized losses (294) (43) (1,021) (399) Other investment gains (losses) (2,002) 38 1,434 5,959 Net realized investment gains (losses) (2,578) 4,935 5,233 11,861 Equity securities: Change in fair value of securities sold during the period (400) 16,090 22,254 (453,258) Change in fair value of securities held at the end of the period (22,855) 518,277 1,148,304 210,501 Total change in fair value (23,255) 534,367 1,170,558 (242,757) Net investment gains (losses) $ (25,833) $ 539,302 $ 1,175,791 $ (230,896) Change in net unrealized gains on available-for-sale investments included in other comprehensive income (loss): Fixed maturity securities $ (133,244) $ 96,723 $ (391,528) $ 431,811 Short-term investments (4,855) 1,425 (3,076) (2,153) Reserve deficiency adjustment for life and annuity benefit reserves (see note 9) 6,428 (20,625) 56,690 (56,237) Net increase (decrease) $ (131,671) $ 77,523 $ (337,914) $ 373,421

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements ASC 820, Fair Value Measurements and Disclosures, establishes a three-level hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. The fair value hierarchy gives the highest priority to quoted prices in active markets for identical assets or liabilities (Level 1) and the lowest priority to unobservable inputs (Level 3). If the inputs used to measure the assets or liabilities fall within different levels of the hierarchy, the classification is based on the lowest level input that is significant to the fair value measurement of the asset or liability. Classification of assets and liabilities within the hierarchy considers the markets in which the assets and liabilities are traded and the reliability and transparency of the assumptions used to determine fair value. The hierarchy requires the use of observable market data when available. The levels of the hierarchy are defined as follows: • Level 1 – Inputs to the valuation methodology are quoted prices (unadjusted) for identical assets or liabilities traded in active markets. • Level 2 – Inputs to the valuation methodology include quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability and market-corroborated inputs. • Level 3 – Inputs to the valuation methodology are unobservable for the asset or liability and are significant to the fair value measurement. In accordance with ASC 820, the Company determines fair value based on the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. In determining fair value, the Company uses various methods, including the market, income and cost approaches. The Company uses valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs. The following section describes the valuation methodologies used by the Company to measure assets and liabilities at fair value, including an indication of the level within the fair value hierarchy in which each asset or liability is generally classified. Available-for-sale investments and equity securities. Available-for-sale investments and equity securities are recorded at fair value on a recurring basis. Available-for-sale investments include fixed maturity securities and short-term investments. Short-term investments include certificates of deposit, commercial paper, discount notes and treasury bills with original maturities of one year or less. Fair value is determined by the Company after considering various sources of information, including information provided by a third-party pricing service. The pricing service provides prices for substantially all of the Company's fixed maturity securities and equity securities. In determining fair value, the Company generally does not adjust the prices obtained from the pricing service. The Company obtains an understanding of the pricing service's valuation methodologies and related inputs, which include, but are not limited to, reported trades, benchmark yields, issuer spreads, bids, offers, duration, credit ratings, estimated cash flows and prepayment speeds. The Company validates prices provided by the pricing service by reviewing prices from other pricing sources and analyzing pricing data in certain instances. The Company has evaluated the various types of securities in its investment portfolio to determine an appropriate fair value hierarchy level based upon trading activity and the observability of market inputs. Level 1 investments include those traded on an active exchange, such as the New York Stock Exchange. Level 2 investments include U.S. Treasury securities, U.S. government-sponsored enterprises, municipal bonds, foreign government bonds, commercial mortgage-backed securities, residential mortgage-backed securities, asset-backed securities and corporate debt securities. Level 3 investments include the Company's investments in certain insurance-linked securities funds that are not traded on an active exchange and are valued using unobservable inputs. Fair value for available-for-sale investments and equity securities is measured based upon quoted prices in active markets, if available. Due to variations in trading volumes and the lack of quoted market prices, fixed maturity securities are classified as Level 2 investments. The fair value of fixed maturity securities is normally derived through recent reported trades for identical or similar securities, making adjustments through the reporting date based upon available market observable data previously described. If there are no recent reported trades, the fair value of fixed maturity securities may be derived through the use of matrix pricing or model processes, where future cash flow expectations are developed based upon collateral performance and discounted at an estimated market rate. Significant inputs used to determine the fair value of obligations of states, municipalities and political subdivisions, corporate bonds and obligations of foreign governments include reported trades, benchmark yields, issuer spreads, bids, offers, credit information and estimated cash flows. Significant inputs used to determine the fair value of commercial mortgage-backed securities, residential mortgage-backed securities and asset-backed securities include the type of underlying assets, benchmark yields, prepayment speeds, collateral information, tranche type and volatility, estimated cash flows, credit information, default rates, recovery rates, issuer spreads and the year of issue. Due to the significance of unobservable inputs required in measuring the fair value of the Company's investments in insurance-linked securities funds, these investments are classified as Level 3 within the fair value hierarchy. The fair value of the securities are derived using their reported net asset value (NAV) as the primary input, as well as other observable and unobservable inputs as deemed necessary by management. Management has obtained an understanding of the inputs, assumptions, process and controls used to determine NAV, which is calculated by an independent third party. Unobservable inputs to the NAV calculations include assumptions around premium earnings patterns and loss reserve estimates for the underlying securitized reinsurance contracts. The Company's valuation policies and procedures for Level 3 investments are determined by management. Fair value measurements are analyzed quarterly to ensure the change in fair value from prior periods is reasonable relative to management's understanding of the underlying investments, recent market trends and external market data. Senior long-term debt and other debt. Senior long-term debt and other debt is carried at amortized cost with the estimated fair value disclosed on the consolidated balance sheets. Senior long-term debt and other debt is classified as Level 2 within the fair value hierarchy due to variations in trading volumes and the lack of quoted market prices. Fair value is generally derived through recent reported trades for identical securities, making adjustments through the reporting date, if necessary, based upon available market observable data including U.S. Treasury securities and implied credit spreads. Significant inputs used to determine the fair value of senior long-term debt and other debt include reported trades, benchmark yields, issuer spreads, bids and offers. The following tables present the balances of assets measured at fair value on a recurring basis by level within the fair value hierarchy. September 30, 2021 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments: Fixed maturity securities, available-for-sale: U.S. Treasury securities $ — $ 1,897,352 $ — $ 1,897,352 U.S. government-sponsored enterprises — 777,032 — 777,032 Obligations of states, municipalities and political subdivisions — 4,153,465 — 4,153,465 Foreign governments — 1,531,805 — 1,531,805 Commercial mortgage-backed securities — 2,034,034 — 2,034,034 Residential mortgage-backed securities — 776,364 — 776,364 Asset-backed securities — 3,482 — 3,482 Corporate bonds — 789,053 — 789,053 Total fixed maturity securities, available-for-sale — 11,962,587 — 11,962,587 Equity securities: Insurance, banks and other financial institutions 3,032,545 — 56,625 3,089,170 Industrial, consumer and all other 5,131,704 — — 5,131,704 Total equity securities 8,164,249 — 56,625 8,220,874 Short-term investments, available-for-sale 2,599,116 158,682 — 2,757,798 Total investments $ 10,763,365 $ 12,121,269 $ 56,625 $ 22,941,259 December 31, 2020 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments: Fixed maturity securities, available-for-sale: U.S. Treasury securities $ — $ 589,300 $ — $ 589,300 U.S. government-sponsored enterprises — 551,554 — 551,554 Obligations of states, municipalities and political subdivisions — 4,289,841 — 4,289,841 Foreign governments — 1,628,009 — 1,628,009 Commercial mortgage-backed securities — 1,885,582 — 1,885,582 Residential mortgage-backed securities — 870,445 — 870,445 Asset-backed securities — 5,966 — 5,966 Corporate bonds — 861,037 — 861,037 Total fixed maturity securities, available-for-sale — 10,681,734 — 10,681,734 Equity securities: Insurance, banks and other financial institutions 2,516,361 — 58,493 2,574,854 Industrial, consumer and all other 4,419,256 — — 4,419,256 Total equity securities 6,935,617 — 58,493 6,994,110 Short-term investments, available-for-sale 1,922,459 111,640 — 2,034,099 Total investments $ 8,858,076 $ 10,793,374 $ 58,493 $ 19,709,943 The following table summarizes changes in Level 3 investments measured at fair value on a recurring basis. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2021 2020 2021 2020 Equity securities, beginning of period $ 41,066 $ 115,648 $ 58,493 $ 45,992 Purchases 18,900 — 18,900 90,000 Sales — (13,472) (15,015) (31,365) Net investment losses (3,341) (126) (5,753) (2,577) Equity securities, end of period $ 56,625 $ 102,050 $ 56,625 $ 102,050 Level 3 investments include the Company's investments in insurance-linked securities funds managed by Markel CATCo Investment Management Ltd. (MCIM). See note 11 for further details regarding investments managed by MCIM. In connection with the run-off of one of the funds managed by MCIM and to facilitate the return of capital to third-party investors, the Company invested $90.0 million in that fund effective January 1, 2020. This investment replaced collateral previously provided by other investors for risk exposures within the underlying reinsurance contracts in which the fund is invested related to loss events that occur after December 31, 2019 and through the expiration of the reinsurance contracts. All of these reinsurance contracts expired or were commuted in 2020, resulting in the subsequent return of a portion of the Company's capital. However, the Company continues to have exposure to adverse loss development on 2020 exposures under any unsettled contracts through its remaining investment in the fund ($40.9 million at September 30, 2021). Except as disclosed in note 3, the Company did not have any assets or liabilities measured at fair value on a non-recurring basis during the nine months ended September 30, 2021 and 2020.

Products, Services and Other Re

Products, Services and Other Revenues	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Products, Services and Other Revenues	Products, Services and Other Revenues The amount of revenues from contracts with customers was $933.0 million and $839.2 million for the quarters ended September 30, 2021 and 2020, respectively, and $2.8 billion and $2.1 billion for the nine months ended September 30, 2021 and 2020, respectively. The following tables present revenues from contracts with customers by segment and type, all of which are included in products revenues and services and other revenues in the consolidated statements of income (loss) and comprehensive income, along with a reconciliation to total products revenues and services and other revenues. Quarter Ended September 30, 2021 2020 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 394,444 $ — $ 394,444 $ 332,584 $ — $ 332,584 Services 487,942 30,027 517,969 467,377 18,136 485,513 Investment management — 20,571 20,571 — 21,066 21,066 Total revenues from contracts with customers 882,386 50,598 932,984 799,961 39,202 839,163 Program services and other fronting — 32,298 32,298 — 23,395 23,395 Other 25,796 345 26,141 24,167 896 25,063 Total $ 908,182 $ 83,241 $ 991,423 $ 824,128 $ 63,493 $ 887,621 Nine Months Ended September 30, 2021 2020 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 1,294,407 $ — $ 1,294,407 $ 1,085,338 $ — $ 1,085,338 Services 1,313,054 95,908 1,408,962 850,861 86,143 937,004 Investment management — 57,693 57,693 — 75,898 75,898 Total revenues from contracts with customers 2,607,461 153,601 2,761,062 1,936,199 162,041 2,098,240 Program services and other fronting — 87,314 87,314 — 73,889 73,889 Other 82,824 1,002 83,826 77,051 1,579 78,630 Total $ 2,690,285 $ 241,917 $ 2,932,202 $ 2,013,250 $ 237,509 $ 2,250,759 Receivables from contracts with customers were $490.0 million and $406.4 million as of September 30, 2021 and December 31, 2020, respectively.

Unpaid Losses And Loss Adjustme

Unpaid Losses And Loss Adjustment Expenses	9 Months Ended
	Sep. 30, 2021
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Unpaid Losses And Loss Adjustment Expenses	Unpaid Losses and Loss Adjustment Expenses The following table presents a reconciliation of consolidated beginning and ending reserves for losses and loss adjustment expenses. Nine Months Ended September 30, (dollars in thousands) 2021 2020 Net reserves for losses and loss adjustment expenses, beginning of year $ 10,485,717 $ 9,475,261 Effect of foreign currency rate changes on beginning of year balance (52,117) (25,659) Effect of adoption of ASU No. 2016-13 — 3,849 Adjusted net reserves for losses and loss adjustment expenses, beginning of year 10,433,600 9,453,451 Incurred losses and loss adjustment expenses: Current accident year 3,009,260 3,088,228 Prior accident years (366,171) (435,467) Total incurred losses and loss adjustment expenses 2,643,089 2,652,761 Payments: Current accident year 365,640 469,447 Prior accident years 1,678,164 1,407,641 Total payments 2,043,804 1,877,088 Effect of foreign currency rate changes on current year activity (1,339) (220) Net reserves for losses and loss adjustment expenses of insurance companies sold (2,762) — Net reserves for losses and loss adjustment expenses, end of period 11,028,784 10,228,904 Reinsurance recoverables on unpaid losses 6,582,415 5,494,327 Gross reserves for losses and loss adjustment expenses, end of period $ 17,611,199 $ 15,723,231 For the nine months ended September 30, 2021, current accident year losses and loss adjustment expenses included $182.3 million of net losses and loss adjustment expenses from Winter Storm Uri, European Floods and Hurricane Ida (2021 Catastrophes). The net losses and loss adjustment expenses from the 2021 Catastrophes as of September 30, 2021 represent the Company's best estimates based upon information currently available. The estimates for these losses are based on claims received to date, detailed policy and reinsurance contract level reviews, preliminary industry loss estimates and output from both industry and proprietary models, as well as analysis of the Company's ceded reinsurance contracts. Due to limited claims activity, these estimates are based on various assumptions about coverage, liability and reinsurance and are therefore subject to change. While the Company believes its reserves for the 2021 Catastrophes as of September 30, 2021 are adequate, it continues to closely monitor reported claims and will adjust estimates of gross and net losses as new information becomes available. For the nine months ended September 30, 2020, current accident year losses and loss adjustment expenses included $371.8 million of net losses and loss adjustment expenses attributed to the COVID-19 pandemic, including $356.8 million for which COVID-19 was identified as the proximate, or direct, cause of loss and $15.0 million that were indirectly attributable to COVID-19. Current accident year losses and loss adjustment expenses for the nine months ended September 30, 2020 also included $101.8 million of net losses and loss adjustment expenses from Hurricanes Laura, Sally and Isaias as well as the derecho in Iowa and wildfires in the western U.S. (2020 Catastrophes).

Reinsurance

Reinsurance	9 Months Ended
	Sep. 30, 2021
Reinsurance Disclosures [Abstract]
Reinsurance	Reinsurance The following table summarizes the effect of reinsurance and retrocessional reinsurance on premiums written and earned. Quarter Ended September 30, 2021 2020 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 1,776,716 $ 303,551 $ (393,195) $ 1,687,072 $ 1,420,067 $ 315,774 $ (337,181) $ 1,398,660 Earned 1,599,931 363,665 (331,397) 1,632,199 1,323,451 362,539 (290,058) 1,395,932 Program services and other fronting: Written 711,182 177,153 (890,597) (2,262) 518,921 17,972 (538,277) (1,384) Earned 634,520 103,008 (739,227) (1,699) 491,524 14,489 (507,517) (1,504) Consolidated: Written 2,487,898 480,704 (1,283,792) 1,684,810 1,938,988 333,746 (875,458) 1,397,276 Earned $ 2,234,451 $ 466,673 $ (1,070,624) $ 1,630,500 $ 1,814,975 $ 377,028 $ (797,575) $ 1,394,428 Nine Months Ended September 30, 2021 2020 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 5,082,494 $ 1,269,578 $ (1,031,546) $ 5,320,526 $ 4,229,398 $ 1,211,335 $ (936,342) $ 4,504,391 Earned 4,542,680 1,081,494 (925,176) 4,698,998 3,886,390 1,035,501 (832,196) 4,089,695 Program services and other fronting: Written 2,056,328 249,067 (2,308,590) (3,195) 1,475,709 52,308 (1,532,259) (4,242) Earned 1,800,489 141,676 (1,944,931) (2,766) 1,535,248 54,800 (1,594,432) (4,384) Consolidated: Written 7,138,822 1,518,645 (3,340,136) 5,317,331 5,705,107 1,263,643 (2,468,601) 4,500,149 Earned $ 6,343,169 $ 1,223,170 $ (2,870,107) $ 4,696,232 $ 5,421,638 $ 1,090,301 $ (2,426,628) $ 4,085,311 Substantially all of the premiums written and earned in the Company's program services and other fronting operations for the quarter and nine months ended September 30, 2021 and 2020 were ceded. The percentage of consolidated ceded earned premiums to gross earned premiums was 40% and 38% for the quarter and nine months ended September 30, 2021, respectively, and 36% and 37% for the quarter and nine months September 30, 2020, respectively. The percentage of consolidated assumed earned premiums to net earned premiums was 29% and 26% and for the quarter and nine months ended September 30, 2021, respectively, and 27% for both the quarter and nine months September 30, 2020. Substantially all of the incurred losses and loss adjustment expenses in the Company's program services and other fronting operations, which totaled $620.1 million and $1.7 billion for the quarter and nine months ended September 30, 2021, respectively, and $412.7 million and $1.1 billion for the quarter and nine months ended September 30, 2020, respectively, were ceded. The following table summarizes the effect of reinsurance and retrocessional reinsurance on losses and loss adjustment expenses in the Company's underwriting operations. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2021 2020 2021 2020 Gross $ 1,238,974 $ 1,023,479 $ 3,306,035 $ 3,135,105 Ceded (290,834) (160,387) (660,479) (481,874) Net losses and loss adjustment expenses $ 948,140 $ 863,092 $ 2,645,556 $ 2,653,231

Life and Annuity Benefits Life

Life and Annuity Benefits Life and Annuity Benefits	9 Months Ended
	Sep. 30, 2021
Liability for Future Policy Benefit, before Reinsurance [Abstract]
Liability for Future Policy Benefits and Unpaid Claims Disclosure [Text Block]	Life and Annuity Benefits Life and annuity benefits are compiled on a reinsurance contract-by-contract basis and are discounted using standard actuarial techniques and cash flow models. Since the development of the life and annuity reinsurance reserves is based upon cash flow projection models, the Company must make estimates and assumptions based on cedent experience, industry mortality tables, and expense and investment experience, including a provision for adverse deviation. The assumptions used to determine policy benefit reserves are generally locked-in for the life of the contract unless an unlocking event occurs. Loss recognition testing is performed to determine if existing policy benefit reserves, together with the present value of future gross premiums and expected investment income earned thereon, are adequate to cover the present value of future benefits, settlement and maintenance costs. If the existing policy benefit reserves are not sufficient, the locked-in assumptions are revised to current best estimate assumptions and a charge to earnings for life and annuity benefits is recognized at that time. Life and annuity benefits are also adjusted to the extent unrealized gains on the investments supporting the policy benefit reserves would result in a reserve deficiency if those gains were realized. As of September 30, 2021 and December 31, 2020, the cumulative adjustment to life and annuity benefits attributable to unrealized gains on the underlying investment portfolio totaled $62.9 million and $119.6 million, respectively. During the quarter and nine months ended September 30, 2021, the Company decreased life and annuity benefits by $6.4 million and $56.7 million, respectively, reflecting an increase in the market yield on the investment portfolio supporting the policy benefit reserves, and increased the change in net unrealized holding gains included in other comprehensive loss by a corresponding amount. During the quarter and nine months ended September 30, 2020, the Company increased life and annuity benefits by $20.6 million and $56.2 million, respectively, as a result of decreases in the market yield on the investment portfolio supporting the policy benefit reserves, and decreased the change in net unrealized holding gains included in other comprehensive income by a corresponding amount.

Senior Long-Term Debt and Other

Senior Long-Term Debt and Other Debt	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Senior Long-Term Debt and Other Debt	Senior Long-Term Debt and Other DebtIn May 2021, the Company issued $600 million of 3.45% unsecured senior notes due May 2052. Net proceeds to the Company were $591.4 million, before expenses. The Company expects to use a portion of these proceeds to retire its 4.9% unsecured senior notes due July 1, 2022 ($350.0 million aggregate principal outstanding at September 30, 2021) and the remainder for general corporate purposes.

Variable Interest Entities

Variable Interest Entities	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities	Variable Interest Entities MCIM, a wholly-owned consolidated subsidiary of the Company, is an insurance-linked securities investment fund manager and reinsurance manager headquartered in Bermuda. Results attributable to MCIM are not included in a reportable segment. MCIM serves as the insurance manager for Markel CATCo Re Ltd. (Markel CATCo Re), a Bermuda Class 3 reinsurance company, and as the investment manager for Markel CATCo Reinsurance Fund Ltd., a Bermuda exempted mutual fund company comprised of multiple segregated accounts (Markel CATCo Funds). The Markel CATCo Funds issued multiple classes of nonvoting, redeemable preference shares to investors, and the Markel CATCo Funds are primarily invested in nonvoting preference shares of Markel CATCo Re. The underwriting results of Markel CATCo Re are attributed to the Markel CATCo Funds through those nonvoting preference shares. Voting shares in Markel CATCo Reinsurance Fund Ltd. and Markel CATCo Re are held by MCIM. The Markel CATCo Funds and Markel CATCo Re are considered VIEs, as their preference shareholders have no voting rights. MCIM has the power to direct the activities that most significantly impact the economic performance of these entities, but does not have a variable interest in any of the entities. With the exception of an investment in one of the Markel CATCo Funds ($40.9 million and $58.5 million as of September 30, 2021 and December 31, 2020, respectively), the Company's involvement is generally limited to that of an investment or insurance manager, receiving fees that are at market and commensurate with the level of effort required. The Company is not the primary beneficiary of the Markel CATCo Funds or Markel CATCo Re and therefore does not consolidate these entities. The Company's exposure to risk from unconsolidated Markel CATCo Funds and Markel CATCo Re is generally limited to its investment and any earned but uncollected fees. The Company has not issued any investment performance guarantees to these VIEs or their investors. As of September 30, 2021 and December 31, 2020, net assets under management of MCIM for unconsolidated VIEs were $781.2 million and $929.2 million, respectively. In July 2019, both the Markel CATCo Funds and Markel CATCo Re were placed into run-off. See note 14 for further details regarding developments in the Company's Markel CATCo operations.

Related Party Transactions Rela

Related Party Transactions Related Party Transactions	9 Months Ended
	Sep. 30, 2021
Related Party Transactions [Abstract]
Related Party Transactions Disclosure [Text Block]	Related Party Transactions The Company engages in certain related party transactions in the normal course of business at arm's length. Insurance-Linked Securities Within the Company's insurance-linked securities operations, the Company provides investment and insurance management services through Nephila Holdings Ltd. (together with its consolidated subsidiaries, Nephila). Nephila serves as the investment manager to several Bermuda, Ireland and U.S. based private funds (the Nephila Funds). To provide access for the Nephila Funds to the insurance, reinsurance and weather markets, Nephila also provides managing general agent services and acts as an insurance manager to certain Bermuda Class 3 and 3A reinsurance companies and Lloyd's Syndicate 2357 (Syndicate 2357) (collectively, the Nephila Reinsurers), as well as other unaffiliated insurance entities. Nephila receives management fees for investment and insurance management services provided through its insurance-linked securities operations based on the net asset value of the accounts managed, and, for certain funds, incentive fees based on the annual performance of the funds managed. Nephila also receives commissions from the Nephila Reinsurers, which are based on the direct written premiums of the insurance contracts placed. For the quarter and nine months ended September 30, 2021, total revenues attributed to unconsolidated entities managed by Nephila were $32.8 million and $103.5 million, respectively. For the quarter and nine months ended September 30, 2020, total revenues attributed to unconsolidated entities managed by Nephila were $29.8 million and $113.5 million, respectively. Through the Company's program services operations and other fronting arrangements, the Company has programs with Nephila through which the Company writes insurance policies that are ceded to Syndicate 2357 and certain other Nephila Reinsurers. Through these programs, Nephila utilizes certain of the Company's licensed insurance companies to write U.S. catastrophe-exposed property risk that is then ceded to Nephila Reinsurers. Gross premiums written through these programs with Nephila were $283.7 million and $587.7 million for the quarter and nine months ended September 30, 2021, respectively, and $119.2 million and $332.6 million for the quarter and nine months ended September 30, 2020, respectively, all of which were ceded to Nephila Reinsurers. As of September 30, 2021 and December 31, 2020, reinsurance recoverables on the consolidated balance sheets included $601.9 million and $353.8 million, respectively, due from Nephila Reinsurers. Under these programs, the Company bears underwriting risk for annual aggregate agreement year losses in excess of a limit the Company believes is unlikely to be exceeded. To the extent losses under these programs exceed the prescribed limits, the Company is obligated to pay such losses to the cedents without recourse to the Nephila Reinsurers. While the Company believes losses under these programs are unlikely, those losses, if incurred, could be material to the Company's consolidated results of operations and financial condition. The Company has also entered into other assumed and ceded reinsurance transactions with the Nephila Reinsurers in the normal course of business, which are not material to the Company's consolidated financial statements. The Hagerty Group, LLC The Company holds a minority ownership interest in The Hagerty Group, LLC, which is accounted for under the equity method. Hagerty Group primarily operates as a managing general agent under the names Hagerty Insurance Agency and Hagerty Classic Marine Insurance Agency (collectively, Hagerty). Hagerty Group also includes Hagerty Re, a Bermuda Class 3 reinsurance company. Essentia Insurance Company (Essentia), one of the Company's insurance subsidiaries, is the exclusive insurance underwriter for Hagerty in the U.S., and a portion of this insurance is ceded to Hagerty Re. For the quarter and nine months ended September 30, 2021, gross written premiums attributable to Hagerty written on Essentia were $167.6 million and $464.3 million, respectively, of which $94.8 million and $263.2 million, respectively, were ceded to Hagerty Re. For the quarter and nine months ended September 30, 2020 gross written premiums attributable to Hagerty written on Essentia were $144.8 million and $399.7 million, respectively, of which $68.4 million and $189.0 million, respectively, were ceded to Hagerty Re.

Shareholders' Equity

Shareholders' Equity	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity Note [Abstract]
Shareholders' Equity Note Disclosure	Shareholders' Equity a) The Company has 50,000,000 shares of no par value common stock authorized. The following table presents a rollforward of changes in common shares issued and outstanding. Quarter Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Issued and outstanding common shares, beginning of period 13,734 13,776 13,783 13,794 Issuance of common shares 1 2 4 5 Repurchase of common shares (50) — (102) (21) Issued and outstanding common shares, end of period 13,685 13,778 13,685 13,778 b) The Company has 10,000,000 shares of no par value preferred stock authorized, of which 600,000 shares were issued and outstanding at September 30, 2021 and December 31, 2020. The outstanding preferred shares were issued in May 2020 for an aggregate initial purchase price of $600 million and net proceeds of $591.9 million. The Company declared and paid dividends on preferred shares of $18.0 million, or $30 per share, in the second quarter of 2021. c) Net income (loss) per common share was determined by dividing adjusted net income (loss) to common shareholders by the applicable weighted average common shares outstanding. Basic common shares outstanding include restricted stock units that are no longer subject to any contingencies for issuance, but for which corresponding shares have not been issued. Diluted net income (loss) per common share is computed by dividing adjusted net income (loss) to common shareholders by the weighted average number of common shares and dilutive potential common shares outstanding during the period. Quarter Ended September 30, Nine Months Ended September 30, (in thousands, except per share amounts) 2021 2020 2021 2020 Net income (loss) to common shareholders $ 188,070 $ 452,726 $ 1,535,874 $ (31,269) Adjustment of redeemable noncontrolling interests 19,930 (23,621) 41,553 (20,681) Adjusted net income (loss) to common shareholders $ 208,000 $ 429,105 $ 1,577,427 $ (51,950) Basic common shares outstanding 13,758 13,809 13,790 13,811 Dilutive potential common shares from restricted stock units and restricted stock (1) 27 18 23 — Diluted common shares outstanding 13,785 13,827 13,813 13,811 Basic net income (loss) per common share $ 15.12 $ 31.07 $ 114.39 $ (3.76) Diluted net income (loss) per common share (1) $ 15.09 $ 31.03 $ 114.20 $ (3.76) (1) The impact of restricted stock units and restricted stock of 13 thousand shares was excluded from the computation of diluted earnings per common share for the nine months ended September 30, 2020 because the effect would have been anti-dilutive.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Loss Contingency [Abstract]
Commitments and Contingencies	Commitments and Contingencies a) Late in the fourth quarter of 2018, the Company was contacted by and received inquiries from the U.S. Department of Justice (DOJ), U.S. Securities and Exchange Commission (SEC) and Bermuda Monetary Authority (BMA) (collectively, Governmental Authorities) into loss reserves recorded in late 2017 and early 2018 at Markel CATCo Re (the Markel CATCo Inquiries), an unconsolidated subsidiary managed by MCIM. As a result, the Company engaged outside counsel to conduct an internal review. The internal review was completed in April 2019 and found no evidence that MCIM personnel acted in bad faith in exercising business judgment in the setting of reserves and making related disclosures during late 2017 and early 2018. The Company's outside counsel met with the Governmental Authorities and reported the findings from the internal review. On September 27, 2021, the SEC notified the Company that it has concluded its investigation and it does not intend to recommend an enforcement action against MCIM. On September 28, 2021, the Company was advised by the DOJ that it has concluded its investigation and will not take any action against MCIM. Throughout the Markel CATCo Inquiries, the Company has proactively kept the BMA informed of the status of the SEC and DOJ investigations, including the recent conclusion of those investigations. There are currently no pending requests from the BMA, and it has been over a year since the BMA has contacted the Company in relation to the Markel CATCo Inquiries. Matters related to or arising from the Company's Markel CATCo operations, including matters of which the Company is currently unaware, could result in additional claims, litigation, investigations, enforcement actions or proceedings. For example, litigation may be filed by investors in the Markel CATCo Funds. The Company also could become subject to increased regulatory scrutiny, investigations or proceedings in any of the jurisdictions where it operates. If any regulatory authority takes action against the Company or the Company enters into an agreement to settle a matter, the Company may incur sanctions or be required to pay substantial fines or implement remedial measures that could prove costly or disruptive to its businesses and operations. An unfavorable outcome could have a material adverse effect on the Company's results of operations and financial condition. Even if an unfavorable outcome does not materialize, these matters could have an adverse impact on the Company's reputation and result in substantial expense and disruption. Costs associated with the Markel CATCo Inquiries, as well as legal costs incurred in connection with any related litigation or disputes, are being expensed as incurred. In addition, the Company may take steps to mitigate potential risks or liabilities related to or arising from the Company's Markel CATCo operations. For example, in September and October 2021, the Company announced the terms of a proposed transaction that would allow the acceleration of a full return of remaining capital to investors in the Markel CATCo Funds, which are currently in run-off. Under the terms of the proposed transaction, the Company would provide cash funding that is not expected to exceed $270 million and tail risk cover of $100 million to Markel CATCo Re in exchange for the Markel CATCo Funds' interests in Markel CATCo Re. The Company would also make $75 million in payments to or for the benefit of investors, which would be an expense to the Company. These amounts are estimates and are subject to change based on the NAV of the Markel CATCo Funds at the closing of the transaction, the amount of capital available for distribution from the Markel CATCo Funds at the closing of the transaction and the ultimate level of tail risk cover provided by the Company. As a result of the transaction, the Company would have exposure to adverse loss development on reinsurance contracts written by Markel CATCo Re for loss events that occurred in 2020 and prior years. However, subsequent favorable development on loss reserves held by Markel CATCo Re, less estimated transaction costs and operating expenses, would be distributed to investors. As a condition to this transaction, all investors in the Markel CATCo Funds, the Markel CATCo Group Companies (MCIM, the Markel CATCo Funds and Markel CATCo Re), Markel Corporation and each of their related parties, among others, would grant mutual releases of all claims related to the transaction, the Markel CATCo Group Companies' businesses and the investors' investments in the Funds. Over 90% of investors in the Markel CATCo Funds have indicated support for the proposed transaction, but it is still subject to formal investor approval and is also subject to court approvals in both Bermuda and the United States. If all required approvals are obtained, the transaction is expected to close in the fourth quarter of 2021. Other steps the Company may take to mitigate potential risks or liabilities related to or arising from the Company's Markel CATCo operations could have a material impact on the Company's results of operations or financial condition. b) In 2019, the Company established Lodgepine Capital Management Limited (LCM), a new retrocessional insurance-linked securities investment fund manager in Bermuda. LCM's initial product offering is Lodgepine Fund Limited (Lodgepine Fund), a property catastrophe retrocessional investment fund, and subject to certain conditions, the Company has committed to invest up to $100 million in Lodgepine Fund. Lodgepine Fund launched July 1, 2021 with initial investor capital of $98.9 million, including an initial investment by the Company of $18.9 million. c) Contingencies arise in the normal course of the Company's operations and are not expected to have a material impact on the Company's financial condition or results of operations.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation. The consolidated balance sheet as of September 30, 2021 and the related consolidated statements of income (loss) and comprehensive income and changes in equity for the quarters and nine months ended September 30, 2021 and 2020, and the condensed consolidated statements of cash flows for the nine months ended September 30, 2021 and 2020 are unaudited. In the opinion of management, all adjustments necessary for fair presentation of such consolidated financial statements have been included. Such adjustments consist only of normal, recurring items. Interim results are not necessarily indicative of results of operations for the entire year. The consolidated balance sheet as of December 31, 2020 was derived from Markel Corporation's audited annual consolidated financial statements. The accompanying consolidated financial statements have been prepared in accordance with United States (U.S.) generally accepted accounting principles (GAAP) and include the accounts of Markel Corporation and its consolidated subsidiaries, as well as any variable interest entities (VIEs) that meet the requirements for consolidation (the Company). All significant intercompany balances and transactions have been eliminated in consolidation. The Company consolidates the results of its Markel Ventures subsidiaries on a one-month lag, with the exception of significant transactions or events that occur during the intervening period. Certain prior period amounts have been reclassified to conform to the current period presentation. The preparation of financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingent assets and liabilities. Actual results may differ materially from the estimates and assumptions used in preparing the consolidated financial statements. The consolidated financial statements and notes are presented as permitted by Form 10-Q and do not contain certain information included in the Company's annual consolidated financial statements and notes. Readers are urged to review the Company's 2020 Annual Report on Form 10-K for a more complete description of the Company's business and accounting policies, as well as a description of the risks and uncertainties associated with the COVID-19 pandemic on the Company's businesses and results of operations, financial condition and cash flows, including in note 20 of the notes to consolidated financial statements included under Item 8 Financial Statements and Supplementary Data. There were no material changes in the Company's assessment of the risks and uncertainties associated with the COVID-19 pandemic during the nine months ended September 30, 2021.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Accounting Standards Adopted in 2021 The Company adopted Financial Accounting Standards Board (FASB) Accounting Standards Update (ASU) No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes , effective January 1, 2021. Adoption of this standard did not have a material impact on the Company's financial position, results of operations or cash flows. Accounting Standards Not Yet Adopted In August 2018, the FASB issued ASU No. 2018-12, Financial Services—Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts. The FASB subsequently issued several ASUs as amendments to ASU No. 2018-12. The standard requires insurance entities with long duration contracts to: (1) review and, if there is a change, update the assumptions used to measure expected cash flows at least annually; (2) update the discount rate assumption at each reporting date; (3) measure all market risk benefits associated with deposit (or account balance) contracts at fair value; and (4) disclose liability rollforwards and information about significant inputs, judgments, assumptions and methods used to measure the liability, including changes thereto and the effect of those changes on measurement. ASU No. 2018-12 becomes effective for the Company during the first quarter of 2023. The standard will, among other things, impact the discount rate used in estimating reserves for the Company's life and annuity reinsurance portfolio, which is in runoff. Currently, the discount rate assumption is locked-in for the life of the contracts, unless there is a loss recognition event. The Company is currently evaluating ASU No. 2018-12 to determine the impact that adopting this standard will have on its consolidated financial statements.

Segment Reporting Disclosures (

Segment Reporting Disclosures (Tables)	9 Months Ended
	Sep. 30, 2021
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]
Company's Segment Disclosures	The following tables summarize the Company's segment disclosures. Quarter Ended September 30, 2021 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 1,899,592 $ 180,673 $ — $ — $ 888,337 $ 2,968,602 Net written premiums 1,545,428 141,642 — — (2,260) 1,684,810 Earned premiums 1,381,235 250,962 — — (1,697) 1,630,500 Losses and loss adjustment expenses: Current accident year (866,481) (221,872) — — — (1,088,353) Prior accident years 124,133 16,292 — — (313) 140,112 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (289,201) (63,723) — — — (352,924) Other operating expenses (202,961) (12,101) — — (1,770) (216,832) Underwriting profit (loss) 146,725 (30,442) — — (3,780) 112,503 Net investment income — — 91,261 3 — 91,264 Net investment losses — — (25,833) — — (25,833) Products revenues — — — 405,711 — 405,711 Services and other revenues — — — 502,471 83,241 585,712 Products expenses — — — (374,407) — (374,407) Services and other expenses — — — (465,268) (48,726) (513,994) Amortization of intangible assets (3) — — — (13,541) (25,727) (39,268) Segment profit (loss) $ 146,725 $ (30,442) $ 65,428 $ 54,969 $ 5,008 $ 241,688 Interest expense (46,455) Net foreign exchange gains 48,850 Income before income taxes $ 244,083 U.S. GAAP combined ratio (4) 89 % 112 % NM (5) 93 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $15.8 million for the quarter ended September 30, 2021. (2) Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $10.3 million for the quarter ended September 30, 2021, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments. (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful Quarter Ended September 30, 2020 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 1,514,002 $ 222,066 $ — $ — $ 536,666 $ 2,272,734 Net written premiums 1,220,054 178,994 — — (1,772) 1,397,276 Earned premiums 1,173,758 222,369 — — (1,699) 1,394,428 Losses and loss adjustment expenses: Current accident year (817,174) (213,325) — — — (1,030,499) Prior accident years 137,312 30,681 — — (741) 167,252 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (239,096) (56,997) — — — (296,093) Other operating expenses (179,840) (17,609) — — 718 (196,731) Underwriting profit (loss) 74,960 (34,881) — — (1,722) 38,357 Net investment income — — 90,380 4 — 90,384 Net investment gains — — 539,302 — — 539,302 Products revenues — — — 342,039 — 342,039 Services and other revenues — — — 482,089 63,493 545,582 Products expenses — — — (296,371) — (296,371) Services and other expenses — — — (432,294) (89,943) (522,237) Amortization of intangible assets (3) — — — (15,862) (28,802) (44,664) Segment profit (loss) $ 74,960 $ (34,881) $ 629,682 $ 79,605 $ (56,974) $ 692,392 Interest expense (42,744) Net foreign exchange losses (65,577) Income before income taxes $ 584,071 U.S. GAAP combined ratio (4) 94 % 116 % NM (5) 97 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $15.3 million for the quarter ended September 30, 2020. (2) Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $10.4 million for the quarter ended September 30, 2020, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments. (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful Nine Months Ended September 30, 2021 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 5,359,293 $ 992,635 $ — $ — $ 2,305,539 $ 8,657,467 Net written premiums 4,427,301 893,082 — — (3,052) 5,317,331 Earned premiums 3,928,824 770,031 — — (2,623) 4,696,232 Losses and loss adjustment expenses: Current accident year (2,448,034) (561,226) — — — (3,009,260) Prior accident years 397,723 (34,104) — — 2,527 366,146 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (814,623) (193,697) — — — (1,008,320) Other operating expenses (594,880) (39,676) — — (1,987) (636,543) Underwriting profit (loss) 469,010 (58,672) — — (2,083) 408,255 Net investment income — — 284,087 8 — 284,095 Net investment gains — — 1,175,791 — — 1,175,791 Products revenues — — — 1,327,144 — 1,327,144 Services and other revenues — — — 1,363,141 241,917 1,605,058 Products expenses — — — (1,173,135) — (1,173,135) Services and other expenses — 109 — (1,260,957) (181,494) (1,442,342) Amortization of intangible assets (3) — — — (41,104) (77,446) (118,550) Segment profit (loss) $ 469,010 $ (58,563) $ 1,459,878 $ 215,097 $ (19,106) $ 2,066,316 Interest expense (135,412) Net foreign exchange gains 61,677 Income before income taxes $ 1,992,581 U.S. GAAP combined ratio (4) 88 % 108 % NM (5) 91 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $47.7 million for the nine months ended September 30, 2021. (2) Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $31.1 million for the nine months ended September 30, 2021, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments. (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful Nine Months Ended September 30, 2020 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 4,482,149 $ 958,529 $ — $ — $ 1,528,072 $ 6,968,750 Net written premiums 3,683,767 820,573 — — (4,191) 4,500,149 Earned premiums 3,400,760 688,884 — — (4,333) 4,085,311 Losses and loss adjustment expenses: Current accident year (2,554,010) (534,218) — — — (3,088,228) Prior accident years 404,649 29,049 — — 1,719 435,417 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (717,300) (176,799) — — — (894,099) Other operating expenses (530,440) (51,001) — — (1,809) (583,250) Underwriting profit (loss) 3,659 (44,085) — — (4,423) (44,849) Net investment income — — 274,000 242 — 274,242 Net investment losses — — (230,896) — — (230,896) Products revenues — — — 1,117,781 — 1,117,781 Services and other revenues — — — 895,469 237,509 1,132,978 Products expenses — — — (974,925) — (974,925) Services and other expenses — — — (798,502) (226,231) (1,024,733) Amortization of intangible assets (3) — — — (39,299) (80,977) (120,276) Segment profit (loss) $ 3,659 $ (44,085) $ 43,104 $ 200,766 $ (74,122) $ 129,322 Interest expense (133,201) Net foreign exchange losses (8,736) Loss before income taxes $ (12,615) U.S. GAAP combined ratio (4) 100 % 106 % NM (5) 101 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $43.5 million for the nine months ended September 30, 2020. (2) Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $31.5 million for the nine months ended September 30, 2020, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments. (3) Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments. (4) The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums. (5) NM - Ratio is not meaningful
Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets	The following table reconciles segment assets to the Company's consolidated balance sheets. (dollars in thousands) September 30, 2021 December 31, 2020 Segment assets: Investing $ 27,327,180 $ 24,781,946 Underwriting 8,151,380 7,228,297 Markel Ventures 4,336,021 3,636,060 Total segment assets 39,814,581 35,646,303 Other operations 6,881,855 6,063,751 Total assets $ 46,696,436 $ 41,710,054

Investments (Tables)

Investments (Tables)	6 Months Ended	9 Months Ended
	Jun. 30, 2021	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Available-For-Sale Investments		The following tables summarize the Company's available-for-sale investments. Commercial and residential mortgage-backed securities include securities issued by U.S. government-sponsored enterprises and U.S. government agencies. The net unrealized holding gains in the tables below are presented before taxes and any reserve deficiency adjustments for life and annuity benefit reserves. See note 9. September 30, 2021 (dollars in thousands) Amortized Gross Gross Estimated Fixed maturity securities: U.S. Treasury securities $ 1,900,911 $ 3,907 $ (7,466) $ 1,897,352 U.S. government-sponsored enterprises 750,038 31,417 (4,423) 777,032 Obligations of states, municipalities and political subdivisions 3,866,173 292,948 (5,656) 4,153,465 Foreign governments 1,383,586 153,795 (5,576) 1,531,805 Commercial mortgage-backed securities 1,945,261 93,916 (5,143) 2,034,034 Residential mortgage-backed securities 740,380 36,057 (73) 776,364 Asset-backed securities 3,403 79 — 3,482 Corporate bonds 734,392 57,462 (2,801) 789,053 Total fixed maturity securities 11,324,144 669,581 (31,138) 11,962,587 Short-term investments 2,757,235 2,365 (1,802) 2,757,798 Investments, available-for-sale $ 14,081,379 $ 671,946 $ (32,940) $ 14,720,385 December 31, 2020 (dollars in thousands) Amortized Gross Gross Estimated Fixed maturity securities: U.S. Treasury securities $ 580,716 $ 9,091 $ (507) $ 589,300 U.S. government-sponsored enterprises 500,053 51,593 (92) 551,554 Obligations of states, municipalities and political subdivisions 3,903,292 386,784 (235) 4,289,841 Foreign governments 1,352,616 275,450 (57) 1,628,009 Commercial mortgage-backed securities 1,736,257 149,359 (34) 1,885,582 Residential mortgage-backed securities 811,732 58,742 (29) 870,445 Asset-backed securities 5,812 154 — 5,966 Corporate bonds 764,783 96,257 (3) 861,037 Total fixed maturity securities 9,655,261 1,027,430 (957) 10,681,734 Short-term investments 2,030,460 3,645 (6) 2,034,099 Investments, available-for-sale $ 11,685,721 $ 1,031,075 $ (963) $ 12,715,833
Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position	December 31, 2020 Less than 12 months 12 months or longer Total (dollars in thousands) Estimated Gross Estimated Gross Estimated Gross Fixed maturity securities: U.S. Treasury securities $ 66,220 $ (507) $ — $ — $ 66,220 $ (507) U.S. government-sponsored enterprises 14,878 (92) — — 14,878 (92) Obligations of states, municipalities and political subdivisions 28,037 (223) 2,960 (12) 30,997 (235) Foreign governments 20,790 (57) — — 20,790 (57) Commercial mortgage-backed securities 13,178 (26) 2,526 (8) 15,704 (34) Residential mortgage-backed securities 3,345 (29) — — 3,345 (29) Corporate bonds 92 (3) — — 92 (3) Total fixed maturity securities 146,540 (937) 5,486 (20) 152,026 (957) Short-term investments 349,978 (6) — — 349,978 (6) Total $ 496,518 $ (943) $ 5,486 $ (20) $ 502,004 $ (963)	The following tables summarize gross unrealized investment losses on available-for-sale investments by the length of time that securities have continuously been in an unrealized loss position. September 30, 2021 Less than 12 months 12 months or longer Total (dollars in thousands) Estimated Gross Estimated Gross Estimated Gross Fixed maturity securities: U.S. Treasury securities $ 1,529,225 $ (5,438) $ 53,457 $ (2,028) $ 1,582,682 $ (7,466) U.S. government-sponsored enterprises 256,872 (3,602) 14,028 (821) 270,900 (4,423) Obligations of states, municipalities and political subdivisions 283,201 (5,182) 21,491 (474) 304,692 (5,656) Foreign governments 255,067 (5,576) — — 255,067 (5,576) Commercial mortgage-backed securities 306,557 (5,143) — — 306,557 (5,143) Residential mortgage-backed securities 5,928 (70) 92 (3) 6,020 (73) Corporate bonds 101,607 (2,801) — — 101,607 (2,801) Total fixed maturity securities 2,738,457 (27,812) 89,068 (3,326) 2,827,525 (31,138) Short-term investments 2,450,158 (1,802) — — 2,450,158 (1,802) Total $ 5,188,615 $ (29,614) $ 89,068 $ (3,326) $ 5,277,683 $ (32,940)
Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturity Securities By Contractual Maturity Date		The amortized cost and estimated fair value of fixed maturity securities at September 30, 2021 are shown below by contractual maturity. (dollars in thousands) Amortized Estimated Due in one year or less $ 391,678 $ 395,422 Due after one year through five years 3,407,996 3,507,926 Due after five years through ten years 2,576,383 2,706,530 Due after ten years 2,259,043 2,538,829 8,635,100 9,148,707 Commercial mortgage-backed securities 1,945,261 2,034,034 Residential mortgage-backed securities 740,380 776,364 Asset-backed securities 3,403 3,482 Total fixed maturity securities $ 11,324,144 $ 11,962,587
Components Of Net Investment Income		The following table presents the components of net investment income. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2021 2020 2021 2020 Interest: Tax-exempt municipal bonds $ 14,293 $ 15,693 $ 43,631 $ 48,451 Taxable municipal bonds 16,320 16,456 49,236 50,185 Other taxable bonds 39,705 38,788 119,718 118,376 Short-term investments, including overnight deposits 633 894 2,179 13,516 Dividends on equity securities 23,400 20,282 68,583 66,916 Income (loss) from equity method investments 882 2,483 13,825 (11,849) Other (335) (365) (947) 438 94,898 94,231 296,225 286,033 Investment expenses (3,634) (3,847) (12,130) (11,791) Net investment income $ 91,264 $ 90,384 $ 284,095 $ 274,242
Summary Of Net Investment Gains (Losses) And The Change In Net Unrealized Gains On Available-For-Sale Investments		The following table presents the components of net investment gains (losses) and the change in net unrealized gains included in other comprehensive income (loss). Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2021 2020 2021 2020 Fixed maturity securities: Realized gains $ 92 $ 5,292 $ 4,967 $ 12,025 Realized losses (390) (1,209) (471) (7,480) Change in allowance for expected credit losses — 202 — — Short-term investments: Realized gains 16 655 324 1,756 Realized losses (294) (43) (1,021) (399) Other investment gains (losses) (2,002) 38 1,434 5,959 Net realized investment gains (losses) (2,578) 4,935 5,233 11,861 Equity securities: Change in fair value of securities sold during the period (400) 16,090 22,254 (453,258) Change in fair value of securities held at the end of the period (22,855) 518,277 1,148,304 210,501 Total change in fair value (23,255) 534,367 1,170,558 (242,757) Net investment gains (losses) $ (25,833) $ 539,302 $ 1,175,791 $ (230,896) Change in net unrealized gains on available-for-sale investments included in other comprehensive income (loss): Fixed maturity securities $ (133,244) $ 96,723 $ (391,528) $ 431,811 Short-term investments (4,855) 1,425 (3,076) (2,153) Reserve deficiency adjustment for life and annuity benefit reserves (see note 9) 6,428 (20,625) 56,690 (56,237) Net increase (decrease) $ (131,671) $ 77,523 $ (337,914) $ 373,421

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Balances Of Assets Measured At Fair Value On A Recurring Basis	The following tables present the balances of assets measured at fair value on a recurring basis by level within the fair value hierarchy. September 30, 2021 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments: Fixed maturity securities, available-for-sale: U.S. Treasury securities $ — $ 1,897,352 $ — $ 1,897,352 U.S. government-sponsored enterprises — 777,032 — 777,032 Obligations of states, municipalities and political subdivisions — 4,153,465 — 4,153,465 Foreign governments — 1,531,805 — 1,531,805 Commercial mortgage-backed securities — 2,034,034 — 2,034,034 Residential mortgage-backed securities — 776,364 — 776,364 Asset-backed securities — 3,482 — 3,482 Corporate bonds — 789,053 — 789,053 Total fixed maturity securities, available-for-sale — 11,962,587 — 11,962,587 Equity securities: Insurance, banks and other financial institutions 3,032,545 — 56,625 3,089,170 Industrial, consumer and all other 5,131,704 — — 5,131,704 Total equity securities 8,164,249 — 56,625 8,220,874 Short-term investments, available-for-sale 2,599,116 158,682 — 2,757,798 Total investments $ 10,763,365 $ 12,121,269 $ 56,625 $ 22,941,259 December 31, 2020 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments: Fixed maturity securities, available-for-sale: U.S. Treasury securities $ — $ 589,300 $ — $ 589,300 U.S. government-sponsored enterprises — 551,554 — 551,554 Obligations of states, municipalities and political subdivisions — 4,289,841 — 4,289,841 Foreign governments — 1,628,009 — 1,628,009 Commercial mortgage-backed securities — 1,885,582 — 1,885,582 Residential mortgage-backed securities — 870,445 — 870,445 Asset-backed securities — 5,966 — 5,966 Corporate bonds — 861,037 — 861,037 Total fixed maturity securities, available-for-sale — 10,681,734 — 10,681,734 Equity securities: Insurance, banks and other financial institutions 2,516,361 — 58,493 2,574,854 Industrial, consumer and all other 4,419,256 — — 4,419,256 Total equity securities 6,935,617 — 58,493 6,994,110 Short-term investments, available-for-sale 1,922,459 111,640 — 2,034,099 Total investments $ 8,858,076 $ 10,793,374 $ 58,493 $ 19,709,943
Summary Of Changes In Level 3 Investments Measured At Fair Value On A Recurring Basis	The following table summarizes changes in Level 3 investments measured at fair value on a recurring basis. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2021 2020 2021 2020 Equity securities, beginning of period $ 41,066 $ 115,648 $ 58,493 $ 45,992 Purchases 18,900 — 18,900 90,000 Sales — (13,472) (15,015) (31,365) Net investment losses (3,341) (126) (5,753) (2,577) Equity securities, end of period $ 56,625 $ 102,050 $ 56,625 $ 102,050

Products, Services and Other _2

Products, Services and Other Revenues (Tables)	9 Months Ended
	Sep. 30, 2021
Revenue from Contract with Customer [Abstract]
Schedule Of Revenues From Contracts With Customers By Type	The following tables present revenues from contracts with customers by segment and type, all of which are included in products revenues and services and other revenues in the consolidated statements of income (loss) and comprehensive income, along with a reconciliation to total products revenues and services and other revenues. Quarter Ended September 30, 2021 2020 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 394,444 $ — $ 394,444 $ 332,584 $ — $ 332,584 Services 487,942 30,027 517,969 467,377 18,136 485,513 Investment management — 20,571 20,571 — 21,066 21,066 Total revenues from contracts with customers 882,386 50,598 932,984 799,961 39,202 839,163 Program services and other fronting — 32,298 32,298 — 23,395 23,395 Other 25,796 345 26,141 24,167 896 25,063 Total $ 908,182 $ 83,241 $ 991,423 $ 824,128 $ 63,493 $ 887,621 Nine Months Ended September 30, 2021 2020 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 1,294,407 $ — $ 1,294,407 $ 1,085,338 $ — $ 1,085,338 Services 1,313,054 95,908 1,408,962 850,861 86,143 937,004 Investment management — 57,693 57,693 — 75,898 75,898 Total revenues from contracts with customers 2,607,461 153,601 2,761,062 1,936,199 162,041 2,098,240 Program services and other fronting — 87,314 87,314 — 73,889 73,889 Other 82,824 1,002 83,826 77,051 1,579 78,630 Total $ 2,690,285 $ 241,917 $ 2,932,202 $ 2,013,250 $ 237,509 $ 2,250,759

Unpaid Losses And Loss Adjust_2

Unpaid Losses And Loss Adjustment Expenses (Tables)	9 Months Ended
	Sep. 30, 2021
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Reconciliation Of Consolidated Reserves For Losses And Loss Adjustment Expenses	The following table presents a reconciliation of consolidated beginning and ending reserves for losses and loss adjustment expenses. Nine Months Ended September 30, (dollars in thousands) 2021 2020 Net reserves for losses and loss adjustment expenses, beginning of year $ 10,485,717 $ 9,475,261 Effect of foreign currency rate changes on beginning of year balance (52,117) (25,659) Effect of adoption of ASU No. 2016-13 — 3,849 Adjusted net reserves for losses and loss adjustment expenses, beginning of year 10,433,600 9,453,451 Incurred losses and loss adjustment expenses: Current accident year 3,009,260 3,088,228 Prior accident years (366,171) (435,467) Total incurred losses and loss adjustment expenses 2,643,089 2,652,761 Payments: Current accident year 365,640 469,447 Prior accident years 1,678,164 1,407,641 Total payments 2,043,804 1,877,088 Effect of foreign currency rate changes on current year activity (1,339) (220) Net reserves for losses and loss adjustment expenses of insurance companies sold (2,762) — Net reserves for losses and loss adjustment expenses, end of period 11,028,784 10,228,904 Reinsurance recoverables on unpaid losses 6,582,415 5,494,327 Gross reserves for losses and loss adjustment expenses, end of period $ 17,611,199 $ 15,723,231

Reinsurance (Tables)

Reinsurance (Tables)	9 Months Ended
	Sep. 30, 2021
Reinsurance Disclosures [Abstract]
Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned	The following table summarizes the effect of reinsurance and retrocessional reinsurance on premiums written and earned. Quarter Ended September 30, 2021 2020 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 1,776,716 $ 303,551 $ (393,195) $ 1,687,072 $ 1,420,067 $ 315,774 $ (337,181) $ 1,398,660 Earned 1,599,931 363,665 (331,397) 1,632,199 1,323,451 362,539 (290,058) 1,395,932 Program services and other fronting: Written 711,182 177,153 (890,597) (2,262) 518,921 17,972 (538,277) (1,384) Earned 634,520 103,008 (739,227) (1,699) 491,524 14,489 (507,517) (1,504) Consolidated: Written 2,487,898 480,704 (1,283,792) 1,684,810 1,938,988 333,746 (875,458) 1,397,276 Earned $ 2,234,451 $ 466,673 $ (1,070,624) $ 1,630,500 $ 1,814,975 $ 377,028 $ (797,575) $ 1,394,428 Nine Months Ended September 30, 2021 2020 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 5,082,494 $ 1,269,578 $ (1,031,546) $ 5,320,526 $ 4,229,398 $ 1,211,335 $ (936,342) $ 4,504,391 Earned 4,542,680 1,081,494 (925,176) 4,698,998 3,886,390 1,035,501 (832,196) 4,089,695 Program services and other fronting: Written 2,056,328 249,067 (2,308,590) (3,195) 1,475,709 52,308 (1,532,259) (4,242) Earned 1,800,489 141,676 (1,944,931) (2,766) 1,535,248 54,800 (1,594,432) (4,384) Consolidated: Written 7,138,822 1,518,645 (3,340,136) 5,317,331 5,705,107 1,263,643 (2,468,601) 4,500,149 Earned $ 6,343,169 $ 1,223,170 $ (2,870,107) $ 4,696,232 $ 5,421,638 $ 1,090,301 $ (2,426,628) $ 4,085,311
Effect Of Reinsurance And Retrocessional Reinsurance On Losses	The following table summarizes the effect of reinsurance and retrocessional reinsurance on losses and loss adjustment expenses in the Company's underwriting operations. Quarter Ended September 30, Nine Months Ended September 30, (dollars in thousands) 2021 2020 2021 2020 Gross $ 1,238,974 $ 1,023,479 $ 3,306,035 $ 3,135,105 Ceded (290,834) (160,387) (660,479) (481,874) Net losses and loss adjustment expenses $ 948,140 $ 863,092 $ 2,645,556 $ 2,653,231

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2021
Stockholders' Equity Note [Abstract]
Schedule of Common Stock Outstanding Roll Forward	The Company has 50,000,000 shares of no par value common stock authorized. The following table presents a rollforward of changes in common shares issued and outstanding. Quarter Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Issued and outstanding common shares, beginning of period 13,734 13,776 13,783 13,794 Issuance of common shares 1 2 4 5 Repurchase of common shares (50) — (102) (21) Issued and outstanding common shares, end of period 13,685 13,778 13,685 13,778
Schedule Of Net Income (Loss) Per Common Share	Quarter Ended September 30, Nine Months Ended September 30, (in thousands, except per share amounts) 2021 2020 2021 2020 Net income (loss) to common shareholders $ 188,070 $ 452,726 $ 1,535,874 $ (31,269) Adjustment of redeemable noncontrolling interests 19,930 (23,621) 41,553 (20,681) Adjusted net income (loss) to common shareholders $ 208,000 $ 429,105 $ 1,577,427 $ (51,950) Basic common shares outstanding 13,758 13,809 13,790 13,811 Dilutive potential common shares from restricted stock units and restricted stock (1) 27 18 23 — Diluted common shares outstanding 13,785 13,827 13,813 13,811 Basic net income (loss) per common share $ 15.12 $ 31.07 $ 114.39 $ (3.76) Diluted net income (loss) per common share (1) $ 15.09 $ 31.03 $ 114.20 $ (3.76) (1) The impact of restricted stock units and restricted stock of 13 thousand shares was excluded from the computation of diluted earnings per common share for the nine months ended September 30, 2020 because the effect would have been anti-dilutive.

Segment Reporting Disclosures_2

Segment Reporting Disclosures (Company's Segment Disclosures) (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2021		Sep. 30, 2020		Sep. 30, 2021		Sep. 30, 2020
Segment Reporting Information [Line Items]
Gross premium volume	$ 2,968,602		$ 2,272,734		$ 8,657,467		$ 6,968,750
Net written premiums	1,684,810		1,397,276		5,317,331		4,500,149
Earned premiums	1,630,500		1,394,428		4,696,232		4,085,311
Losses and loss adjustment expenses, current accident year	(1,088,353)		(1,030,499)		(3,009,260)		(3,088,228)
Losses and loss adjustment expenses, prior accident year	140,112		167,252		366,146		435,417
Amortization of policy acquisition costs	(352,924)		(296,093)		(1,008,320)		(894,099)
Other operating expenses	(216,832)		(196,731)		(636,543)		(583,250)
Underwriting profit (loss)	112,503		38,357		408,255		(44,849)
Net investment income	91,264		90,384		284,095		274,242
Net investment gains (losses)	(25,833)		539,302		1,175,791		(230,896)
Products revenues	405,711		342,039		1,327,144		1,117,781
Services and other revenues	585,712		545,582		1,605,058		1,132,978
Products expenses	(374,407)		(296,371)		(1,173,135)		(974,925)
Services and other expenses	(513,994)		(522,237)		(1,442,342)		(1,024,733)
Amortization of intangible assets	(39,268)	[1]	(44,664)	[1]	(118,550)	[2]	(120,276)	[1]
Segment profit (loss)	241,688		692,392		2,066,316		129,322
Interest expense	(46,455)		(42,744)		(135,412)		(133,201)
Net foreign exchange gains	48,850		(65,577)		61,677		(8,736)
Income (Loss) before income taxes	$ 244,083		$ 584,071		$ 1,992,581		$ (12,615)
U.S. GAAP combined ratio	93.00%	[3]	97.00%	[3]	91.00%	[4]	101.00%	[3]
Insurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume	$ 1,899,592		$ 1,514,002		$ 5,359,293		$ 4,482,149
Net written premiums	1,545,428		1,220,054		4,427,301		3,683,767
Earned premiums	1,381,235		1,173,758		3,928,824		3,400,760
Losses and loss adjustment expenses, current accident year	(866,481)		(817,174)		(2,448,034)		(2,554,010)
Losses and loss adjustment expenses, prior accident year	124,133		137,312		397,723		404,649
Amortization of policy acquisition costs	(289,201)		(239,096)		(814,623)		(717,300)
Other operating expenses	(202,961)		(179,840)		(594,880)		(530,440)
Underwriting profit (loss)	146,725		74,960		469,010		3,659
Net investment income	0		0		0		0
Net investment gains (losses)	0		0		0		0
Products revenues	0		0		0		0
Services and other revenues	0		0		0		0
Products expenses	0		0		0		0
Services and other expenses	0		0		0		0
Amortization of intangible assets	0	[1]	0	[1]	0	[2]	0	[1]
Segment profit (loss)	$ 146,725		$ 74,960		$ 469,010		$ 3,659
U.S. GAAP combined ratio	89.00%	[3]	94.00%	[3]	88.00%	[4]	100.00%	[3]
Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume	$ 180,673		$ 222,066		$ 992,635		$ 958,529
Net written premiums	141,642		178,994		893,082		820,573
Earned premiums	250,962		222,369		770,031		688,884
Losses and loss adjustment expenses, current accident year	(221,872)		(213,325)		(561,226)		(534,218)
Losses and loss adjustment expenses, prior accident year	16,292		30,681		(34,104)		29,049
Amortization of policy acquisition costs	(63,723)		(56,997)		(193,697)		(176,799)
Other operating expenses	(12,101)		(17,609)		(39,676)		(51,001)
Underwriting profit (loss)	(30,442)		(34,881)		(58,672)		(44,085)
Net investment income	0		0		0		0
Net investment gains (losses)	0		0		0		0
Products revenues	0		0		0		0
Services and other revenues	0		0		0		0
Products expenses	0		0		0		0
Services and other expenses	0		0		109		0
Amortization of intangible assets	0	[1]	0	[1]	0	[2]	0	[1]
Segment profit (loss)	$ (30,442)		$ (34,881)		$ (58,563)		$ (44,085)
U.S. GAAP combined ratio	112.00%	[3]	116.00%	[3]	108.00%	[4]	106.00%	[3]
Investing [Member]
Segment Reporting Information [Line Items]
Gross premium volume	$ 0		$ 0		$ 0		$ 0
Net written premiums	0		0		0		0
Earned premiums	0		0		0		0
Losses and loss adjustment expenses, current accident year	0		0		0		0
Losses and loss adjustment expenses, prior accident year	0		0		0		0
Amortization of policy acquisition costs	0		0		0		0
Other operating expenses	0		0		0		0
Underwriting profit (loss)	0		0		0		0
Net investment income	91,261		90,380		284,087		274,000
Net investment gains (losses)	(25,833)		539,302		1,175,791		(230,896)
Products revenues	0		0		0		0
Services and other revenues	0		0		0		0
Products expenses	0		0		0		0
Services and other expenses	0		0		0		0
Amortization of intangible assets	0	[1]	0	[1]	0	[2]	0	[1]
Segment profit (loss)	65,428		629,682		1,459,878		43,104
Markel Ventures [Member]
Segment Reporting Information [Line Items]
Gross premium volume	0	[5]	0	[5]	0	[6]	0	[5]
Net written premiums	0	[5]	0	[5]	0	[6]	0	[5]
Earned premiums	0	[5]	0	[5]	0	[6]	0	[5]
Losses and loss adjustment expenses, current accident year	0	[5]	0	[5]	0	[6]	0	[5]
Losses and loss adjustment expenses, prior accident year	0	[5]	0	[5]	0	[6]	0	[5]
Amortization of policy acquisition costs	0	[5]	0	[5]	0	[6]	0	[5]
Other operating expenses	0	[5]	0	[5]	0	[6]	0	[5]
Underwriting profit (loss)	0	[5]	0	[5]	0	[6]	0	[5]
Net investment income	3	[5]	4	[5]	8	[6]	242	[5]
Net investment gains (losses)	0	[5]	0	[5]	0	[6]	0	[5]
Products revenues	405,711	[5]	342,039	[5]	1,327,144	[6]	1,117,781	[5]
Services and other revenues	502,471	[5]	482,089	[5]	1,363,141	[6]	895,469	[5]
Products expenses	(374,407)	[5]	(296,371)	[5]	(1,173,135)	[6]	(974,925)	[5]
Services and other expenses	(465,268)	[5]	(432,294)	[5]	(1,260,957)	[6]	(798,502)	[5]
Amortization of intangible assets	(13,541)	[1],[5]	(15,862)	[1],[5]	(41,104)	[2],[6]	(39,299)	[1],[5]
Segment profit (loss)	54,969	[5]	79,605	[5]	215,097	[6]	200,766	[5]
Depreciation	15,800		15,300		47,700	[6]	43,500	[5]
Underwriting Segments [Member]
Segment Reporting Information [Line Items]
Amortization of intangible assets	10,300		10,400		31,100	[7]	31,500	[8]
Other [Member]
Segment Reporting Information [Line Items]
Gross premium volume	888,337	[8]	536,666	[8]	2,305,539	[7]	1,528,072	[8]
Net written premiums	(2,260)	[8]	(1,772)	[8]	(3,052)	[7]	(4,191)	[8]
Earned premiums	(1,697)	[8]	(1,699)	[8]	(2,623)	[7]	(4,333)	[8]
Losses and loss adjustment expenses, current accident year	0	[8]	0	[8]	0	[7]	0	[8]
Losses and loss adjustment expenses, prior accident year	(313)	[8]	(741)	[8]	2,527	[7]	1,719	[8]
Amortization of policy acquisition costs	0	[8]	0	[8]	0	[7]	0	[8]
Other operating expenses	(1,770)	[8]	718	[8]	(1,987)	[7]	(1,809)	[8]
Underwriting profit (loss)	(3,780)	[8]	(1,722)	[8]	(2,083)	[7]	(4,423)	[8]
Net investment income	0	[8]	0	[8]	0	[7]	0	[8]
Net investment gains (losses)	0	[8]	0	[8]	0	[7]	0	[8]
Products revenues	0	[8]	0	[8]	0	[7]	0	[8]
Services and other revenues	83,241	[8]	63,493	[8]	241,917	[7]	237,509	[8]
Products expenses	0	[8]	0	[8]	0	[7]	0	[8]
Services and other expenses	(48,726)	[8]	(89,943)	[8]	(181,494)	[7]	(226,231)	[8]
Amortization of intangible assets	(25,727)	[1],[8]	(28,802)	[1],[8]	(77,446)	[2],[7]	(80,977)	[1],[8]
Segment profit (loss)	$ 5,008	[8]	$ (56,974)	[8]	$ (19,106)	[7]	$ (74,122)	[5]
[1]	Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments.
[2]	Segment profit for the Markel Ventures segment includes amortization of intangible assets attributable to Markel Ventures. Amortization of intangible assets is not allocated to the Company's Insurance and Reinsurance segments.
[3]	The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.
[4]	The U.S. GAAP combined ratio is a measure of underwriting performance and represents the relationship of incurred losses, loss adjustment expenses and underwriting, acquisition and insurance expenses to earned premiums.
[5]	Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $43.5 million for the nine months ended September 30, 2020.
[6]	Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $47.7 million for the nine months ended September 30, 2021.
[7]	Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $31.1 million for the nine months ended September 30, 2021, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments.
[8]	Other represents the total profit (loss) attributable to the Company's operations that are not included in a reportable segment as well as any amortization of intangible assets that is not allocated to a reportable segment. Amortization of intangible assets attributable to the Company's underwriting segments was $31.5 million for the nine months ended September 30, 2020, however, the Company does not allocate amortization of intangible assets between the Insurance and Reinsurance segments.

Segment Reporting Disclosures_3

Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Assets	$ 46,696,436	$ 41,710,054
Other [Member]
Segment Reporting Information [Line Items]
Assets	6,881,855	6,063,751
Segment assets [Member]
Segment Reporting Information [Line Items]
Assets	39,814,581	35,646,303
Segment assets [Member] | Investing [Member]
Segment Reporting Information [Line Items]
Assets	27,327,180	24,781,946
Segment assets [Member] | Underwriting [Member]
Segment Reporting Information [Line Items]
Assets	8,151,380	7,228,297
Segment assets [Member] | Markel Ventures [Member]
Segment Reporting Information [Line Items]
Assets	$ 4,336,021	$ 3,636,060

Acquisitions (Narratives) (Deta

Acquisitions (Narratives) (Details) - Buckner HeavyLift Cranes [Member] $ in Thousands	Aug. 31, 2021USD ($)
Business Acquisition [Line Items]
Percentage acquired	90.00%
Total purchase consideration	$ 237,900
Cash consideration	237,900
Goodwill recognized	91,900
Finite-lived intangible assets	60,000
Fixed assets	306,600
Long-term debt	165,100
Redeemable noncontrolling interest from business acquisition	26,400
Customer relationships [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets	$ 50,000
Definite-lived intangible assets, weighted-average amortization period	7 years
Trade names [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets	$ 10,000
Definite-lived intangible assets, weighted-average amortization period	15 years

Investments (Narrative) (Detail

Investments (Narrative) (Details) $ in Thousands	Sep. 30, 2021USD ($)securities	Dec. 31, 2020USD ($)securities
Schedule of Investments [Line Items]
Available-for-sale fixed maturity securities in unrealized loss position, number of positions | securities	203	36
Available-for-sale securities, estimated fair value	$ 5,277,683	$ 502,004
Available-for-sale securities, gross unrealized holding losses	$ (32,940)	$ (963)
Number of available-for-sale fixed maturity securities positions in a continuous unrealized loss position for one year or longer at period end | securities	10	6
Available-for-sale securities, estimated fair value, 12 months or longer	$ 89,068	$ 5,486
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(3,326)	(20)
Available-for-sale, allowance for credit losses	0	0
Fixed Maturities [Member]
Schedule of Investments [Line Items]
Available-for-sale securities, estimated fair value	2,827,525	152,026
Available-for-sale securities, gross unrealized holding losses	(31,138)	(957)
Available-for-sale securities, estimated fair value, 12 months or longer	89,068	5,486
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	$ (3,326)	$ (20)

Investments (Available-For-Sale

Investments (Available-For-Sale Investments) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	$ 11,324,144	$ 9,655,261
Available-for-sale fixed maturity investments, gross unrealized holding gains	669,581	1,027,430
Available-for-sale fixed maturity investments, gross unrealized holding losses	(31,138)	(957)
Available-for-sale fixed maturity investments, estimated fair value	11,962,587	10,681,734
Short-term investments, available-for-sale, amortized cost	2,757,235	2,030,460
Short-term investments, available-for-sale, gross unrealized holding gains	2,365	3,645
Short-term investments, available-for-sale, gross unrealized holding losses	(1,802)	(6)
Short-term investments, available-for-sale, estimated fair value	2,757,798	2,034,099
Investments, available-for-sale, amortized cost	14,081,379	11,685,721
Investments, available-for-sale, gross unrealized holding gains	671,946	1,031,075
Investments, available-for-sale, gross unrealized holding losses	(32,940)	(963)
Investments, available-for-sale, estimated fair value	14,720,385	12,715,833
U.S. Treasury securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	1,900,911	580,716
Available-for-sale fixed maturity investments, gross unrealized holding gains	3,907	9,091
Available-for-sale fixed maturity investments, gross unrealized holding losses	(7,466)	(507)
Available-for-sale fixed maturity investments, estimated fair value	1,897,352	589,300
U.S. government-sponsored enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	750,038	500,053
Available-for-sale fixed maturity investments, gross unrealized holding gains	31,417	51,593
Available-for-sale fixed maturity investments, gross unrealized holding losses	(4,423)	(92)
Available-for-sale fixed maturity investments, estimated fair value	777,032	551,554
Obligations of states, municipalities and political subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	3,866,173	3,903,292
Available-for-sale fixed maturity investments, gross unrealized holding gains	292,948	386,784
Available-for-sale fixed maturity investments, gross unrealized holding losses	(5,656)	(235)
Available-for-sale fixed maturity investments, estimated fair value	4,153,465	4,289,841
Foreign governments [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	1,383,586	1,352,616
Available-for-sale fixed maturity investments, gross unrealized holding gains	153,795	275,450
Available-for-sale fixed maturity investments, gross unrealized holding losses	(5,576)	(57)
Available-for-sale fixed maturity investments, estimated fair value	1,531,805	1,628,009
Commercial mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	1,945,261	1,736,257
Available-for-sale fixed maturity investments, gross unrealized holding gains	93,916	149,359
Available-for-sale fixed maturity investments, gross unrealized holding losses	(5,143)	(34)
Available-for-sale fixed maturity investments, estimated fair value	2,034,034	1,885,582
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	740,380	811,732
Available-for-sale fixed maturity investments, gross unrealized holding gains	36,057	58,742
Available-for-sale fixed maturity investments, gross unrealized holding losses	(73)	(29)
Available-for-sale fixed maturity investments, estimated fair value	776,364	870,445
Asset-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	3,403	5,812
Available-for-sale fixed maturity investments, gross unrealized holding gains	79	154
Available-for-sale fixed maturity investments, gross unrealized holding losses	0	0
Available-for-sale fixed maturity investments, estimated fair value	3,482	5,966
Corporate bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	734,392	764,783
Available-for-sale fixed maturity investments, gross unrealized holding gains	57,462	96,257
Available-for-sale fixed maturity investments, gross unrealized holding losses	(2,801)	(3)
Available-for-sale fixed maturity investments, estimated fair value	$ 789,053	$ 861,037

Investments (Summary Of Gross U

Investments (Summary Of Gross Unrealized Investment Losses By Length Of Time That Securities Have Continuously Been In An Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	$ 5,188,615	$ 496,518
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(29,614)	(943)
Available-for-sale securities, estimated fair value, 12 months or longer	89,068	5,486
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(3,326)	(20)
Available-for-sale securities, estimated fair value	5,277,683	502,004
Available-for-sale securities, gross unrealized holding losses	(32,940)	(963)
Short-term investments, estimated fair value, less than 12 months	2,450,158	349,978
Short-term investments, gross unrealized holding losses, less than 12 months	(1,802)	(6)
Short-term investments, estimated fair value, 12 months or longer	0	0
Short-term investments, gross unrealized holding losses, 12 months or longer	0	0
Short-term investments, estimated fair value	2,450,158	349,978
Short-term investments, gross unrealized holding losses	(1,802)	(6)
U.S. Treasury securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	1,529,225	66,220
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(5,438)	(507)
Available-for-sale securities, estimated fair value, 12 months or longer	53,457	0
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(2,028)	0
Available-for-sale securities, estimated fair value	1,582,682	66,220
Available-for-sale securities, gross unrealized holding losses	(7,466)	(507)
U.S. government-sponsored enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	256,872	14,878
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(3,602)	(92)
Available-for-sale securities, estimated fair value, 12 months or longer	14,028	0
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(821)	0
Available-for-sale securities, estimated fair value	270,900	14,878
Available-for-sale securities, gross unrealized holding losses	(4,423)	(92)
Obligations of states, municipalities and political subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	283,201	28,037
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(5,182)	(223)
Available-for-sale securities, estimated fair value, 12 months or longer	21,491	2,960
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(474)	(12)
Available-for-sale securities, estimated fair value	304,692	30,997
Available-for-sale securities, gross unrealized holding losses	(5,656)	(235)
Foreign governments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	255,067	20,790
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(5,576)	(57)
Available-for-sale securities, estimated fair value, 12 months or longer	0	0
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	0	0
Available-for-sale securities, estimated fair value	255,067	20,790
Available-for-sale securities, gross unrealized holding losses	(5,576)	(57)
Commercial mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	306,557	13,178
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(5,143)	(26)
Available-for-sale securities, estimated fair value, 12 months or longer	0	2,526
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	0	(8)
Available-for-sale securities, estimated fair value	306,557	15,704
Available-for-sale securities, gross unrealized holding losses	(5,143)	(34)
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	5,928	3,345
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(70)	(29)
Available-for-sale securities, estimated fair value, 12 months or longer	92	0
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(3)	0
Available-for-sale securities, estimated fair value	6,020	3,345
Available-for-sale securities, gross unrealized holding losses	(73)	(29)
Corporate bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	101,607	92
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(2,801)	(3)
Available-for-sale securities, estimated fair value, 12 months or longer	0	0
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	0	0
Available-for-sale securities, estimated fair value	101,607	92
Available-for-sale securities, gross unrealized holding losses	(2,801)	(3)
Total fixed maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	2,738,457	146,540
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(27,812)	(937)
Available-for-sale securities, estimated fair value, 12 months or longer	89,068	5,486
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(3,326)	(20)
Available-for-sale securities, estimated fair value	2,827,525	152,026
Available-for-sale securities, gross unrealized holding losses	$ (31,138)	$ (957)

Investments (Schedule Of Amorti

Investments (Schedule Of Amortized Cost And Estimated Fair Value Of Fixed Maturity Securities By Contractual Maturity Date) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, amortized cost	$ 391,678
Due after one year through five years, amortized cost	3,407,996
Due after five years through ten years, amortized cost	2,576,383
Due after ten years, amortized cost	2,259,043
Amortized cost, sub-total	8,635,100
Total fixed maturities, amortized cost	11,324,144	$ 9,655,261
Due in one year or less, estimated fair value	395,422
Due after one year through five years, estimated fair value	3,507,926
Due after five years through ten years, estimated fair value	2,706,530
Due after ten years, estimated fair value	2,538,829
Estimated fair value, sub-total	9,148,707
Total fixed maturities, estimated fair value	11,962,587	10,681,734
Commercial mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	1,945,261
Total fixed maturities, amortized cost	1,945,261	1,736,257
Fixed maturities, estimated fair value	2,034,034
Total fixed maturities, estimated fair value	2,034,034	1,885,582
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	740,380
Total fixed maturities, amortized cost	740,380	811,732
Fixed maturities, estimated fair value	776,364
Total fixed maturities, estimated fair value	776,364	870,445
Asset-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	3,403
Total fixed maturities, amortized cost	3,403	5,812
Fixed maturities, estimated fair value	3,482
Total fixed maturities, estimated fair value	$ 3,482	$ 5,966

Investments (Components Of Net

Investments (Components Of Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Tax-exempt municipal bonds	$ 14,293	$ 15,693	$ 43,631	$ 48,451
Short-term investments, including overnight deposits	633	894	2,179	13,516
Dividends on equity securities	23,400	20,282	68,583	66,916
Income (loss) from equity method investments	882	2,483	13,825	(11,849)
Other	(335)	(365)	(947)	438
Total investment income	94,898	94,231	296,225	286,033
Investment expenses	(3,634)	(3,847)	(12,130)	(11,791)
Net investment income	91,264	90,384	284,095	274,242
Taxable municipal bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	16,320	16,456	49,236	50,185
Other taxable bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	$ 39,705	$ 38,788	$ 119,718	$ 118,376

Investments (Summary Of Net Inv

Investments (Summary Of Net Investment Gains (Losses) And The Change In Net Unrealized Gains On Investments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Gain (Loss) on Securities [Line Items]
Net realized investment gains	$ (2,578)	$ 4,935	$ 5,233	$ 11,861
Equity securities, Change in fair value of securities sold during the period	(400)	16,090	22,254	(453,258)
Equity securities, Change in fair value of securities held at the end of the period	(22,855)	518,277	1,148,304	210,501
Total change in fair value of equity securities	(23,255)	534,367	1,170,558	(242,757)
Net investment gains (losses)	(25,833)	539,302	1,175,791	(230,896)
Change in net unrealized gains on available-for-sale investments included in other comprehensive income	(131,671)	77,523	(337,914)	373,421
Reserve deficiency adjustment for life and annuity benefit reserves	6,428	(20,625)	56,690	(56,237)
Sales of fixed maturities [Member]
Gain (Loss) on Securities [Line Items]
Fixed maturity securities, realized gains	92	5,292	4,967	12,025
Fixed maturity securities, realized losses	(390)	(1,209)	(471)	(7,480)
Change in allowance for expected credit losses	0	202	0	0
Sales of short-term investments [Member]
Gain (Loss) on Securities [Line Items]
Short-term investments, available-for-sale, realized gains	16	655	324	1,756
Short-term investments, available-for-sale, realized losses	(294)	(43)	(1,021)	(399)
Sales of Other Investments [Member]
Gain (Loss) on Securities [Line Items]
Other investment gains (losses)	(2,002)	38	1,434	5,959
Fixed Maturities [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains on available-for-sale investments included in other comprehensive income	(133,244)	96,723	(391,528)	431,811
Short-term investments [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains on available-for-sale investments included in other comprehensive income	$ (4,855)	$ 1,425	$ (3,076)	$ (2,153)

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net investment gains (losses)	$ (25,833)	$ 539,302	$ 1,175,791	$ (230,896)
Equity securities	8,220,874		8,220,874		$ 6,994,110
Fair value, recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, level 1 to level 2 transfers, amount			0	0
Fair value, level 2 to level 1 transfers, amount			0	0
Equity securities	8,220,874		8,220,874		$ 6,994,110
Fair value, nonrecurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis	0	0	0	0
Liabilities measured at fair value on a nonrecurring basis	$ 0	$ 0	$ 0	$ 0

Fair Value Measurements (Balanc

Fair Value Measurements (Balances Of Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	$ 11,962,587	$ 10,681,734
Equity securities	8,220,874	6,994,110
Short-term investments, available-for-sale	2,757,798	2,034,099
Total Investments	22,941,259	19,709,943
U.S. Treasury securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	1,897,352	589,300
U.S. government-sponsored enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	777,032	551,554
Obligations of states, municipalities and political subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	4,153,465	4,289,841
Foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	1,531,805	1,628,009
Commercial mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	2,034,034	1,885,582
Residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	776,364	870,445
Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	3,482	5,966
Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	789,053	861,037
Fair value, recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	11,962,587	10,681,734
Equity securities	8,220,874	6,994,110
Short-term investments, available-for-sale	2,757,798	2,034,099
Total Investments	22,941,259	19,709,943
Fair value, recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Equity securities	8,164,249	6,935,617
Short-term investments, available-for-sale	2,599,116	1,922,459
Total Investments	10,763,365	8,858,076
Fair value, recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	11,962,587	10,681,734
Equity securities	0	0
Short-term investments, available-for-sale	158,682	111,640
Total Investments	12,121,269	10,793,374
Fair value, recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Equity securities	56,625	58,493
Short-term investments, available-for-sale	0	0
Total Investments	56,625	58,493
Fair value, recurring [Member] | U.S. Treasury securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	1,897,352	589,300
Fair value, recurring [Member] | U.S. Treasury securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | U.S. Treasury securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	1,897,352	589,300
Fair value, recurring [Member] | U.S. Treasury securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | U.S. government-sponsored enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	777,032	551,554
Fair value, recurring [Member] | U.S. government-sponsored enterprises [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | U.S. government-sponsored enterprises [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	777,032	551,554
Fair value, recurring [Member] | U.S. government-sponsored enterprises [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | Obligations of states, municipalities and political subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	4,153,465	4,289,841
Fair value, recurring [Member] | Obligations of states, municipalities and political subdivisions [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | Obligations of states, municipalities and political subdivisions [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	4,153,465	4,289,841
Fair value, recurring [Member] | Obligations of states, municipalities and political subdivisions [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | Foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	1,531,805	1,628,009
Fair value, recurring [Member] | Foreign governments [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | Foreign governments [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	1,531,805	1,628,009
Fair value, recurring [Member] | Foreign governments [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | Commercial mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	2,034,034	1,885,582
Fair value, recurring [Member] | Commercial mortgage-backed securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | Commercial mortgage-backed securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	2,034,034	1,885,582
Fair value, recurring [Member] | Commercial mortgage-backed securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | Residential mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	776,364	870,445
Fair value, recurring [Member] | Residential mortgage-backed securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | Residential mortgage-backed securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	776,364	870,445
Fair value, recurring [Member] | Residential mortgage-backed securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	3,482	5,966
Fair value, recurring [Member] | Asset-backed securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | Asset-backed securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	3,482	5,966
Fair value, recurring [Member] | Asset-backed securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	789,053	861,037
Fair value, recurring [Member] | Corporate bonds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | Corporate bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	789,053	861,037
Fair value, recurring [Member] | Corporate bonds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale fixed maturity investments, estimated fair value	0	0
Fair value, recurring [Member] | Insurance, banks and other financial institutions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	3,089,170	2,574,854
Fair value, recurring [Member] | Insurance, banks and other financial institutions [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	3,032,545	2,516,361
Fair value, recurring [Member] | Insurance, banks and other financial institutions [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Fair value, recurring [Member] | Insurance, banks and other financial institutions [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	56,625	58,493
Fair value, recurring [Member] | Industrial, consumer and all other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	5,131,704	4,419,256
Fair value, recurring [Member] | Industrial, consumer and all other [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	5,131,704	4,419,256
Fair value, recurring [Member] | Industrial, consumer and all other [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	0	0
Fair value, recurring [Member] | Industrial, consumer and all other [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	$ 0	$ 0

Fair Value Measurements (Summar

Fair Value Measurements (Summary Of Changes In Level 3 Investments Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands	Jan. 01, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Purchases		$ 18,900	$ 0	$ 18,900	$ 90,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		56,625	102,050	56,625	102,050	$ 58,493
Equity securities, beginning of period	$ 45,992	41,066	115,648	58,493	45,992
Purchases		18,900	0	18,900	90,000
Sales		0	(13,472)	(15,015)	(31,365)
Net investment gains (losses) on Level 3 investments		(3,341)	(126)	(5,753)	(2,577)
Equity securities, end of period		56,625	$ 102,050	56,625	$ 102,050
Unconsolidated Markel CATCo Fund 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Purchases	90,000
Variable interest entity, consolidated, carrying amount, investment in one of the unconsolidated funds		$ 40,900		$ 40,900		$ 58,500
Purchases	$ 90,000

Products, Services and Other _3

Products, Services and Other Revenues (Schedule Of Revenues From Contracts With Customers By Type) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Other revenues	$ 991,423	$ 887,621	$ 2,932,202	$ 2,250,759
Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	932,984	839,163	2,761,062	2,098,240
Products [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	394,444	332,584	1,294,407	1,085,338
Services [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	517,969	485,513	1,408,962	937,004
Investment management [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	20,571	21,066	57,693	75,898
Program services and other fronting [Member]
Disaggregation of Revenue [Line Items]
Other revenues	32,298	23,395	87,314	73,889
Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	26,141	25,063	83,826	78,630
Markel Ventures [Member]
Disaggregation of Revenue [Line Items]
Other revenues	908,182	824,128	2,690,285	2,013,250
Markel Ventures [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	882,386	799,961	2,607,461	1,936,199
Markel Ventures [Member] | Products [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	394,444	332,584	1,294,407	1,085,338
Markel Ventures [Member] | Services [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	487,942	467,377	1,313,054	850,861
Markel Ventures [Member] | Investment management [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	0	0	0	0
Markel Ventures [Member] | Program services and other fronting [Member]
Disaggregation of Revenue [Line Items]
Other revenues	0	0	0	0
Markel Ventures [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	25,796	24,167	82,824	77,051
Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	83,241	63,493	241,917	237,509
Other [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	50,598	39,202	153,601	162,041
Other [Member] | Products [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	0	0	0	0
Other [Member] | Services [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	30,027	18,136	95,908	86,143
Other [Member] | Investment management [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	20,571	21,066	57,693	75,898
Other [Member] | Program services and other fronting [Member]
Disaggregation of Revenue [Line Items]
Other revenues	32,298	23,395	87,314	73,889
Other [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	$ 345	$ 896	$ 1,002	$ 1,579

Products, Services and Other _4

Products, Services and Other Revenues (Schedule Of Receivables And Customer Deposits Related To Contracts With Customers) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Receivables and Customer Deposits [Line Items]
Other revenues	$ 991,423	$ 887,621	$ 2,932,202	$ 2,250,759
Contracts with customers [Member]
Receivables and Customer Deposits [Line Items]
Trade and Other Receivables, Net	490,000		490,000		$ 406,400
Revenue from contracts with customers [Member]
Receivables and Customer Deposits [Line Items]
Other revenues	$ 932,984	$ 839,163	$ 2,761,062	$ 2,098,240

Unpaid Losses And Loss Adjust_3

Unpaid Losses And Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred losses and loss adjustment expenses, current accident years	$ 1,088,353	$ 1,030,499	$ 3,009,260	$ 3,088,228
Favorable (adverse) development on prior years' loss reserves			366,171	435,467
General Liab Prof Liab And Workers Comp Insurance Segment and Property Reinsurance Segment
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable (adverse) development on prior years' loss reserves				294,900
2021 Catastrophes [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred losses and loss adjustment expenses, current accident years			182,300
COVID-19 Pandemic [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred losses and loss adjustment expenses, current accident years				371,800
COVID-19 Pandemic Direct Effect [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred losses and loss adjustment expenses, current accident years				356,800
COVID-19 Pandemic Indirect Effect [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred losses and loss adjustment expenses, current accident years				15,000
2020 Catastrophes [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred losses and loss adjustment expenses, current accident years				101,800
Insurance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred losses and loss adjustment expenses, current accident years	866,481	817,174	2,448,034	2,554,010
Insurance [Member] | General Liab Prop Worker's Comp Professional Liab and Marine & Energy Insurance Segment
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable (adverse) development on prior years' loss reserves			324,800
Reinsurance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred losses and loss adjustment expenses, current accident years	$ 221,872	$ 213,325	561,226	$ 534,218
Reinsurance [Member] | Property
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable (adverse) development on prior years' loss reserves			$ (30,600)

Unpaid Losses And Loss Adjust_4

Unpaid Losses And Loss Adjustment Expenses (Reconciliation Of Consolidated Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Net reserves for losses and loss adjustment expenses, beginning of year			$ 10,485,717	$ 9,475,261
Effect of foreign currency rate changes on beginning of year balance	$ (52,117)	$ (25,659)	(52,117)	(25,659)
Effect of adoption of ASU No. 2016-13	0	3,849	0	3,849
Adjusted net reserves for losses and loss adjustment expenses, beginning of year			10,433,600	9,453,451
Incurred losses and loss adjustment expenses, current accident years	1,088,353	1,030,499	3,009,260	3,088,228
Incurred losses and loss adjustment expenses, prior accident years			(366,171)	(435,467)
Total incurred losses and loss adjustment expenses			2,643,089	2,652,761
Payments, current accident year			365,640	469,447
Payments, prior accident years			1,678,164	1,407,641
Total payments			2,043,804	1,877,088
Effect of foreign currency rate changes on current year activity			(1,339)	(220)
Net reserves for losses and loss adjustment expenses of insurance companies sold			(2,762)	0
Net reserves for losses and loss adjustment expenses, end of period	11,028,784	10,228,904	11,028,784	10,228,904
Reinsurance recoverable on unpaid losses	6,582,415	5,494,327	6,582,415	5,494,327
Gross reserves for losses and loss adjustment expenses, end of period	$ 17,611,199	$ 15,723,231	$ 17,611,199	$ 15,723,231

Reinsurance (Narrative) (Detail

Reinsurance (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Percentage of ceded earned premiums to gross earned premiums	40.00%	36.00%	38.00%	37.00%
Percentage of assumed earned premiums to net earned premiums	29.00%	27.00%	26.00%	27.00%
Program services and other fronting [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Policyholder Benefits and Claims Incurred, Gross	$ 620.1	$ 412.7	$ 1,700	$ 1,100
Reinsurance recoverables	$ (620)	$ (412.5)	$ (1,700)	$ (1,115.6)

Reinsurance (Effect Of Reinsura

Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Effects of Reinsurance [Line Items]
Direct premiums written	$ 2,487,898	$ 1,938,988	$ 7,138,822	$ 5,705,107
Direct premiums earned	2,234,451	1,814,975	6,343,169	5,421,638
Assumed premiums written	480,704	333,746	1,518,645	1,263,643
Assumed premiums earned	466,673	377,028	1,223,170	1,090,301
Ceded premiums written	(1,283,792)	(875,458)	(3,340,136)	(2,468,601)
Ceded premiums earned	(1,070,624)	(797,575)	(2,870,107)	(2,426,628)
Net premiums written	1,684,810	1,397,276	5,317,331	4,500,149
Net premiums earned	1,630,500	1,394,428	4,696,232	4,085,311
Underwriting [Member]
Effects of Reinsurance [Line Items]
Direct premiums written	1,776,716	1,420,067	5,082,494	4,229,398
Direct premiums earned	1,599,931	1,323,451	4,542,680	3,886,390
Assumed premiums written	303,551	315,774	1,269,578	1,211,335
Assumed premiums earned	363,665	362,539	1,081,494	1,035,501
Ceded premiums written	(393,195)	(337,181)	(1,031,546)	(936,342)
Ceded premiums earned	(331,397)	(290,058)	(925,176)	(832,196)
Net premiums written	1,687,072	1,398,660	5,320,526	4,504,391
Net premiums earned	1,632,199	1,395,932	4,698,998	4,089,695
Program services and other fronting [Member]
Effects of Reinsurance [Line Items]
Direct premiums written	711,182	518,921	2,056,328	1,475,709
Direct premiums earned	634,520	491,524	1,800,489	1,535,248
Assumed premiums written	177,153	17,972	249,067	52,308
Assumed premiums earned	103,008	14,489	141,676	54,800
Ceded premiums written	(890,597)	(538,277)	(2,308,590)	(1,532,259)
Ceded premiums earned	(739,227)	(507,517)	(1,944,931)	(1,594,432)
Net premiums written	(2,262)	(1,384)	(3,195)	(4,242)
Net premiums earned	$ (1,699)	$ (1,504)	$ (2,766)	$ (4,384)

Reinsurance Reinsurance (Effect

Reinsurance Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Losses) (Details) - Underwriting [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Effects of Reinsurance [Line Items]
Gross	$ 1,238,974	$ 1,023,479	$ 3,306,035	$ 3,135,105
Ceded	(290,834)	(160,387)	(660,479)	(481,874)
Net losses and loss adjustment expenses	$ 948,140	$ 863,092	$ 2,645,556	$ 2,653,231

Life and Annuity Benefits Lif_2

Life and Annuity Benefits Life and Annuity Benefits (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Liability for Future Policy Benefit, before Reinsurance [Abstract]
Cumulative adjustment to life and annuity benefits	$ 62.9		$ 62.9		$ 119.6
Adjustment to life and annuity benefits	$ (6.4)	$ 20.6	$ (56.7)	$ 56.2

Debt (Details)

Debt (Details) - USD ($) $ in Thousands	May 04, 2021	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Senior long-term debt and other debt (estimated fair value)		$ 4,956,000	$ 4,367,000
Three Point Four Five Percent Unsecured Senior Notes Due May 2052
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 600,000
Debt Instrument, Interest Rate, Stated Percentage	3.45%
Proceeds from Debt, Net of Issuance Costs	$ 591,400
Four Point Nine Percent Unsecured Senior Notes Due July 2022
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.90%
Senior long-term debt and other debt (estimated fair value)		$ 350,000

Variable Interest Entities (Nar

Variable Interest Entities (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Unconsolidated Markel CATCo Fund 2 [Member]
Variable Interest Entity [Line Items]
Variable interest entity, consolidated, carrying amount, investment in one of the unconsolidated funds	$ 40.9	$ 58.5
Unconsolidated Markel CATCo Funds [Member]
Variable Interest Entity [Line Items]
Net assets under management of MCIM for unconsolidated VIEs	$ 781.2	$ 929.2

Related Party Transactions Re_2

Related Party Transactions Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Services and other revenues	$ 585,712	$ 545,582	$ 1,605,058	$ 1,132,978
Gross premium volume	2,968,602	2,272,734	8,657,467	6,968,750
Ceded premiums written	1,283,792	875,458	3,340,136	2,468,601
Reinsurance recoverables	6,944,636		6,944,636		$ 5,989,337
Syndicate 2357 and certain other Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Gross premium volume	283,700	119,200	587,700	332,600
Ceded premiums written	283,700	119,200	587,700	332,600
Reinsurance recoverables	601,900		601,900		$ 353,800
Hagerty Group, LLC [Member]
Related Party Transaction [Line Items]
Gross premium volume	167,600	144,800	464,300	399,700
Ceded premiums written	94,800	68,400	263,200	189,000
Insurance-linked Securities Operations [Member] | Unconsolidated entities managed by Nephila [Member]
Related Party Transaction [Line Items]
Services and other revenues	$ 32,800	$ 29,800	$ 103,500	$ 113,500

Shareholders' Equity (Details)

Shareholders' Equity (Details) - USD ($)	May 27, 2020	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Stockholders' Equity Note [Abstract]
Issuance of preferred stock, net					$ 0	$ 591,891,000
Preferred stock, no par value		$ 0			$ 0
Earnings Per Share [Line Items]
Preferred stock, no par value		$ 0			$ 0
Issuance of preferred stock, net					$ 0	591,891,000
Common stock, shares authorized		50,000,000			50,000,000
Common stock, no par value		$ 0			$ 0
Preferred stock, shares authorized		10,000,000			10,000,000
Common Stock [Member]
Stockholders' Equity Note [Abstract]
Issuance of stock						0
Earnings Per Share [Line Items]
Issuance of stock						$ 0
Shares, issued		13,685,000	13,734,000	13,778,000	13,685,000	13,778,000	13,783,000	13,776,000	13,794,000
Repurchase of common stock, shares		(50,000)		0	(102,000)	(21,000)
Shares, outstanding		13,685,000	13,734,000	13,778,000	13,685,000	13,778,000	13,783,000	13,776,000	13,794,000
Preferred stock dividends					$ 0
Series A preferred stock [Member]
Stockholders' Equity Note [Abstract]
Preferred stock, shares issued		600,000			600,000		600,000
Issuance of preferred stock, net	$ 591,900,000
Issuance of stock	600,000,000
Earnings Per Share [Line Items]
Preferred stock, shares issued		600,000			600,000		600,000
Preferred stock, shares outstanding		600,000			600,000		600,000
Issuance of stock	600,000,000
Issuance of preferred stock, net	$ 591,900,000
Preferred stock dividends			$ 18,000,000
Preferred stock, dividend rate, per-dollar-amount			$ 30
Common Stock [Member] | Common Stock [Member]
Earnings Per Share [Line Items]
Issuance of stock, shares		1,000		2,000	4,000	5,000

Shareholders' Equity (Schedule

Shareholders' Equity (Schedule Of Net Income (Loss) Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Line Items]
Net income (loss) to common stockholders	$ 188,070	$ 452,726	$ 1,535,874	$ (31,269)
Adjustment of redeemable noncontrolling interests	19,930	(23,621)	41,553	(20,681)
Adjusted net income (loss) to common shareholders	$ 208,000	$ 429,105	$ 1,577,427	$ (51,950)
Basic common shares outstanding	13,758	13,809	13,790	13,811
Diluted shares outstanding	13,785	13,827	13,813	13,811
Basic net income (loss) per common share	$ 15.12	$ 31.07	$ 114.39	$ (3.76)
Diluted net income (loss) per common share	$ 15.09	$ 31.03	$ 114.20	$ (3.76)	[1]
Restricted Stock Units (RSUs) [Member]
Earnings Per Share [Line Items]
Dilutive potential common shares from restricted stock units and restricted stock	27	18	23	0	[1]
Potential incremental common shares attributable to share-based payment arrangements				13
[1]	The impact of restricted stock units and restricted stock of 13 thousand shares was excluded from the computation of diluted earnings per common share for the nine months ended September 30, 2020 because the effect would have been anti-dilutive.

Commitments and Contingencies (

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Jul. 01, 2021
Loss Contingencies [Line Items]
Investor Capital in Lodgepine Fund Limited		$ 98.9
Investment in Lodgepine Fund Limited		$ 18.9
Tail risk cover in proposed CATCo transaction	$ 100
Payments to investors in proposed CATCo transaction	75
Lodgepine Fund Limited [Member]
Loss Contingencies [Line Items]
Other commitment	100
Markel CatCo Re
Loss Contingencies [Line Items]
Other commitment	$ 270

Uncategorized Items - mkl-20210

Label	Element	Value
Parent [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	mkl_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance	$ 11,067,040,000
Cumulative Effect of Adoption of ASU No 2016-13, Net of Taxes	mkl_CumulativeEffectofAdoptionofASUNo201613NetofTaxes	(3,827,000)
Retained Earnings [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	mkl_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance	7,453,349,000
Cumulative Effect of Adoption of ASU No 2016-13, Net of Taxes	mkl_CumulativeEffectofAdoptionofASUNo201613NetofTaxes	(3,827,000)
Redeemable Noncontrolling Interests, Temporary Equity [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	mkl_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance	177,562,000
Cumulative Effect of Adoption of ASU No 2016-13, Net of Taxes	mkl_CumulativeEffectofAdoptionofASUNo201613NetofTaxes	0
Total Equity [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	mkl_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance	11,074,589,000
Cumulative Effect of Adoption of ASU No 2016-13, Net of Taxes	mkl_CumulativeEffectofAdoptionofASUNo201613NetofTaxes	(3,827,000)
Preferred Stock [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	mkl_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance	0
Common Stock [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	mkl_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance	3,404,919,000
Noncontrolling Interest [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	mkl_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance	7,549,000
Cumulative Effect of Adoption of ASU No 2016-13, Net of Taxes	mkl_CumulativeEffectofAdoptionofASUNo201613NetofTaxes	0
AOCI Attributable to Parent [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	mkl_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance	208,772,000
Cumulative Effect of Adoption of ASU No 2016-13, Net of Taxes	mkl_CumulativeEffectofAdoptionofASUNo201613NetofTaxes	$ 0