Markel (MKL) 10-Q 3 Aug 21 2021 Q2 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Jul. 27, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 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		13,724,847
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
Entity Central Index Key	0001096343
Current Fiscal Year End Date	--12-31

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Assets [Abstract]
Fixed maturities, available-for-sale (amortized cost of $10,667,968 in 2021 and $9,655,261 in 2020)	$ 11,439,655	$ 10,681,734
Equity securities (cost of $2,771,057 in 2021 and $2,732,998 in 2020)	8,205,708	6,994,110
Short-term investments, available-for-sale (estimated fair value approximates cost)	3,263,073	2,034,099
Total Investments	22,908,436	19,709,943
Cash and cash equivalents	3,679,433	4,341,736
Restricted cash and cash equivalents	672,385	874,913
Receivables	2,627,218	1,930,211
Reinsurance recoverables	6,484,269	5,989,337
Deferred policy acquisition costs	766,736	630,794
Prepaid reinsurance premiums	1,708,240	1,451,858
Goodwill	2,606,138	2,604,624
Intangible assets	1,696,748	1,782,718
Other assets	2,491,910	2,393,920
Total Assets	45,641,513	41,710,054
Liabilities and Equity [Abstract]
Unpaid losses and loss adjustment expenses	16,999,816	16,222,376
Life and annuity benefits	975,499	1,069,986
Unearned premiums	5,261,649	4,433,245
Payables to insurance and reinsurance companies	671,820	493,470
Senior long-term debt and other debt (estimated fair value of $4,868,000 in 2021 and $4,367,000 in 2020)	4,160,175	3,484,023
Other liabilities	3,346,104	2,946,631
Total Liabilities	31,415,063	28,649,731
Redeemable noncontrolling interests	228,401	245,642
Commitments and contingencies
Shareholders' equity:
Preferred Stock	591,891	591,891
Common stock	3,451,968	3,428,340
Retained earnings	9,503,889	8,195,182
Accumulated other comprehensive income	427,223	584,376
Total Shareholders' Equity	13,974,971	12,799,789
Noncontrolling interests	23,078	14,892
Total Equity	13,998,049	12,814,681
Total Liabilities and Equity	$ 45,641,513	$ 41,710,054

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Fixed maturities, available-for-sale amortized cost	$ 10,667,968	$ 9,655,261
Equity securities, cost	2,771,057	2,732,998
Senior long-term debt and other debt (estimated fair value)	$ 4,868,000	$ 4,367,000

Consolidated Statements Of Inco

Consolidated Statements Of Income (Loss) And Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021		Jun. 30, 2020		Jun. 30, 2021		Jun. 30, 2020
OPERATING REVENUES
Earned premiums	$ 1,568,037		$ 1,360,174		$ 3,065,732		$ 2,690,883
Net investment income	96,261		95,615		192,831		183,858
Net investment gains (losses)	674,753		911,243		1,201,624		(770,198)
Products revenues	592,601		423,581		921,433		775,742
Services and other revenues	569,120		341,402		1,019,346		587,396
Total Operating Revenues	3,500,772		3,132,015		6,400,966		3,467,681
OPERATING EXPENSES
Losses and loss adjustment expenses	814,955		713,216		1,694,873		1,789,564
Underwriting, acquisition and insurance expenses	548,364		489,362		1,075,107		984,525
Products expenses	502,202		364,483		798,728		678,554
Services and other expenses	516,251		284,940		928,348		502,496
Amortization of intangible assets	39,729	[1]	37,754	[1]	79,282	[2]	75,612	[1]
Total Operating Expenses	2,421,501		1,889,755		4,576,338		4,030,751
Operating Income (Loss)	1,079,271		1,242,260		1,824,628		(563,070)
Interest expense	(46,568)		(45,427)		(88,957)		(90,457)
Net foreign exchange gains (losses)	(12,257)		(21,460)		12,827		56,841
Income (Loss) Before Income Taxes	1,020,446		1,175,373		1,748,498		(596,686)
Income tax (expense) benefit	(217,112)		(243,702)		(365,483)		126,981
Net Income (Loss)	803,334		931,671		1,383,015		(469,705)
Net income attributable to noncontrolling interests	(11,224)		(9,903)		(17,211)		(14,290)
Net Income (Loss) to Shareholders	792,110		921,768		1,365,804		(483,995)
Preferred stock dividends	(18,000)		0		(18,000)		0
Net Income (Loss) to Common Stockholders	774,110		921,768		1,347,804		(483,995)
OTHER COMPREHENSIVE INCOME (LOSS)
Net holding gains (losses) arising during the period	55,935		172,661		(158,441)		237,038
Reclassification adjustments for net gains included in net income (loss)	(3,943)		(1,385)		(4,031)		(198)
Change in net unrealized gains on available-for-sale investments, net of taxes	51,992		171,276		(162,472)		236,840
Change in foreign currency translation adjustments, net of taxes	4,915		(1,405)		4,107		(14,139)
Change in net actuarial pension loss, net of taxes	654		884		1,246		884
Total Other Comprehensive Income (Loss)	57,561		170,755		(157,119)		223,585
Comprehensive Income (Loss)	860,895		1,102,426		1,225,896		(246,120)
Comprehensive income attributable to noncontrolling interests	(11,241)		(10,033)		(17,245)		(14,296)
Comprehensive Income (Loss) to Shareholders	$ 849,654		$ 1,092,393		$ 1,208,651		$ (260,416)
NET INCOME (LOSS) PER COMMON SHARE
Basic	$ 57.12		$ 65.81		$ 99.19		$ (34.83)
Diluted	$ 57.02		$ 65.75		$ 99.03		$ (34.83)	[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 11 thousand shares was excluded from the computation of diluted earnings per common share for the six months ended June 30, 2020 because the effect would have been anti-dilutive.

Consolidated Statements Of Chan

Consolidated Statements Of Changes In Equity - USD ($) shares in Thousands, $ 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 [Member]
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)	$ (469,705)	(477,401)	(483,995)			(483,995)	0	6,594	7,696
Other comprehensive income (loss)	223,585	223,579	223,579			0	223,579	0	6
Comprehensive Income (Loss)	(246,120)	(253,822)	(260,416)					6,594	7,702
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		$ 22,984	$ 22,984	$ 0	$ 22,984	$ 0	$ 0	$ 0	0
Acquisitions		0	0	0	0	0	0	0		43,566
Adjustment of redeemable noncontrolling interests		$ 2,940	$ 2,940	$ 0	$ 0	$ 2,940	$ 0	$ 0	(2,940)
Purchase of noncontrolling interest		(6,131)	(6,131)	0	(6,131)	0	0	0	(7,029)
Other		1,740	188	0	73	115	0	1,552	(4,208)
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
Balance at Mar. 31, 2020		9,732,330	9,720,728	0	3,419,528	6,039,474	261,726	11,602
Balance, redeemable noncontrolling interests at Mar. 31, 2020									155,417
Net Income (Loss)	931,671	925,061	921,768			921,768	0	3,293	6,610
Other comprehensive income (loss)	170,755	170,625	170,625			0	170,625	0	130
Comprehensive Income (Loss)	1,102,426	1,095,686	1,092,393					3,293	6,740
Issuance of preferred stock		591,891	591,891	591,891	0	0	0	0	0
Repurchase of common stock		(78)	(78)	0	0	(78)	0	0	0
Restricted stock units expensed		$ 3,615	$ 3,615	$ 0	$ 3,615	$ 0	$ 0	$ 0	0
Acquisitions		0	0	0	0	0	0	0		43,566
Adjustment of redeemable noncontrolling interests		$ (13,073)	$ (13,073)	$ 0	$ 0	$ (13,073)	$ 0	$ 0	13,073
Purchase of noncontrolling interest		(1,298)	(1,298)	0	(1,298)	0	0	0	(1,777)
Other		1,175	375	0	0	375	0	800	(2,366)
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
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)	1,383,015	1,373,206	1,365,804			1,365,804	0	7,402	9,809
Other comprehensive income (loss)	(157,119)	(157,153)	(157,153)			0	(157,153)	0	34
Comprehensive Income (Loss)	1,225,896	1,216,053	1,208,651					7,402	9,843
Repurchase of common stock		(60,826)	(60,826)	0	0	(60,826)	0	0	0
Preferred stock dividends		(18,000)	(18,000)	0	0	(18,000)	0	0	0
Restricted stock units expensed		23,602	23,602	0	23,602	0	0	0	0
Adjustment of redeemable noncontrolling interests		21,623	21,623	0	0	21,623	0	0	(21,623)
Purchase of noncontrolling interest		(531)	(531)	0	(531)	0	0	0	(147)
Other		1,447	663	0	557	106	0	784	(5,314)
Balance at Jun. 30, 2021	13,998,049	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								228,401
Balance at Mar. 31, 2021		13,185,164	13,163,944	591,891	3,447,614	8,754,760	369,679	21,220
Balance, redeemable noncontrolling interests at Mar. 31, 2021									234,654
Net Income (Loss)	803,334	792,837	792,110			792,110	0	727	10,497
Other comprehensive income (loss)	57,561	57,544	57,544			0	57,544	0	17
Comprehensive Income (Loss)	860,895	850,381	849,654					727	10,514
Repurchase of common stock		(38,803)	(38,803)	0	0	(38,803)	0	0	0
Preferred stock dividends		(18,000)	(18,000)	0	0	(18,000)	0	0	0
Restricted stock units expensed		4,442	4,442	0	4,442	0	0	0	0
Adjustment of redeemable noncontrolling interests		13,717	13,717	0	0	13,717	0	0	(13,717)
Other		1,148	17	0	(88)	105	0	1,131	(3,050)
Balance at Jun. 30, 2021	13,998,049	$ 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								$ 228,401

Condensed Consolidated Statemen

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
OPERATING ACTIVITIES
Net income (loss)	$ 1,383,015	$ (469,705)
Adjustments to reconcile net income (loss) to net cash provided by operating activities	(569,843)	958,446
Net Cash Provided By Operating Activities	813,172	488,741
INVESTING ACTIVITIES
Proceeds from sales of fixed maturities and equity securities	138,414	1,426,776
Proceeds from maturities, calls and prepayments of fixed maturities	271,450	359,062
Cost of fixed maturities and equity securities purchased	(1,410,308)	(448,997)
Net change in short-term investments	(1,227,644)	268,343
Additions to property and equipment	(55,738)	(50,668)
Acquisitions, net of cash acquired	0	(547,847)
Other	46,487	46,987
Net Cash Provided (Used) By Investing Activities	(2,237,339)	1,053,656
FINANCING ACTIVITIES
Additions to senior long-term debt and other debt	893,575	162,935
Repayment of senior long-term debt and other debt	(217,348)	(92,304)
Repurchases of common stock	(60,826)	(23,943)
Issuance of preferred stock, net	0	591,891
Dividends paid on preferred stock	(18,000)	0
Other	(33,120)	(31,049)
Net Cash Provided By Financing Activities	564,281	607,530
Effect of foreign currency rate changes on cash, cash equivalents, restricted cash and restricted cash equivalents	(4,945)	(22,908)
Increase (decrease) in cash, cash equivalents, restricted cash and restricted cash equivalents	(864,831)	2,127,019
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	$ 4,351,818	$ 5,627,372

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	6 Months Ended
	Jun. 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 June 30, 2021 and the related consolidated statements of income (loss) and comprehensive income (loss) and changes in equity for the quarters and six months ended June 30, 2021 and 2020, and the consolidated statements of cash flows for the six months ended June 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 six months ended June 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	6 Months Ended
	Jun. 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 its 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 June 30, 2021 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 1,821,374 $ 279,444 $ — $ — $ 783,195 $ 2,884,013 Net written premiums 1,494,443 257,355 — — (347) 1,751,451 Earned premiums 1,303,562 264,982 — — (507) 1,568,037 Losses and loss adjustment expenses: Current accident year (783,306) (166,853) — — — (950,159) Prior accident years 154,526 (21,741) — — 2,419 135,204 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (264,823) (67,986) — — — (332,809) Other operating expenses (204,622) (13,414) — — 2,481 (215,555) Underwriting profit (loss) 205,337 (5,012) — — 4,393 204,718 Net investment income — — 96,259 2 — 96,261 Net investment gains — — 674,753 — — 674,753 Products revenues — — — 592,601 — 592,601 Services and other revenues — — — 482,903 86,217 569,120 Products expenses — — — (502,202) — (502,202) Services and other expenses — 109 — (450,781) (65,579) (516,251) Amortization of intangible assets (3) — — — (13,858) (25,871) (39,729) Segment profit (loss) $ 205,337 $ (4,903) $ 771,012 $ 108,665 $ (840) $ 1,079,271 Interest expense (46,568) Net foreign exchange losses (12,257) Income before income taxes $ 1,020,446 U.S. GAAP combined ratio (4) 84 % 102 % NM (5) 87 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $15.8 million for the quarter ended June 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 $10.4 million for the quarter ended June 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 June 30, 2020 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 1,553,436 $ 223,277 $ — $ — $ 596,479 $ 2,373,192 Net written premiums 1,267,976 188,830 — — (411) 1,456,395 Earned premiums 1,120,151 240,555 — — (532) 1,360,174 Losses and loss adjustment expenses: Current accident year (730,201) (147,163) — — — (877,364) Prior accident years 151,205 12,280 — — 663 164,148 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (238,784) (63,411) — — — (302,195) Other operating expenses (167,298) (17,506) — — (2,363) (187,167) Underwriting profit (loss) 135,073 24,755 — — (2,232) 157,596 Net investment income — — 95,561 54 — 95,615 Net investment gains — — 911,243 — — 911,243 Products revenues — — — 423,581 — 423,581 Services and other revenues — — — 254,504 86,898 341,402 Products expenses — — — (364,483) — (364,483) Services and other expenses — — — (222,656) (62,284) (284,940) Amortization of intangible assets (3) — — — (11,596) (26,158) (37,754) Segment profit (loss) $ 135,073 $ 24,755 $ 1,006,804 $ 79,404 $ (3,776) $ 1,242,260 Interest expense (45,427) Net foreign exchange losses (21,460) Income before income taxes $ 1,175,373 U.S. GAAP combined ratio (4) 88 % 90 % NM (5) 88 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $14.3 million for the quarter ended June 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 $10.7 million for the quarter ended June 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 Six Months Ended June 30, 2021 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 3,459,701 $ 811,962 $ — $ — $ 1,417,202 $ 5,688,865 Net written premiums 2,881,873 751,440 — — (792) 3,632,521 Earned premiums 2,547,589 519,069 — — (926) 3,065,732 Losses and loss adjustment expenses: Current accident year (1,581,553) (339,354) — — — (1,920,907) Prior accident years 273,590 (50,396) — — 2,840 226,034 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (525,422) (129,974) — — — (655,396) Other operating expenses (391,919) (27,575) — — (217) (419,711) Underwriting profit (loss) 322,285 (28,230) — — 1,697 295,752 Net investment income — — 192,826 5 — 192,831 Net investment gains — — 1,201,624 — — 1,201,624 Products revenues — — — 921,433 — 921,433 Services and other revenues — — — 860,670 158,676 1,019,346 Products expenses — — — (798,728) — (798,728) Services and other expenses — 109 — (795,689) (132,768) (928,348) Amortization of intangible assets (3) — — — (27,563) (51,719) (79,282) Segment profit (loss) $ 322,285 $ (28,121) $ 1,394,450 $ 160,128 $ (24,114) $ 1,824,628 Interest expense (88,957) Net foreign exchange gains 12,827 Income before income taxes $ 1,748,498 U.S. GAAP combined ratio (4) 87 % 105 % NM (5) 90 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $31.8 million for the six months ended June 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 $20.8 million for the six months ended June 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 Six Months Ended June 30, 2020 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 2,968,147 $ 736,463 $ — $ — $ 991,406 $ 4,696,016 Net written premiums 2,463,713 641,579 — — (2,419) 3,102,873 Earned premiums 2,227,002 466,515 — — (2,634) 2,690,883 Losses and loss adjustment expenses: Current accident year (1,736,836) (320,893) — — — (2,057,729) Prior accident years 267,337 (1,632) — — 2,460 268,165 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (478,204) (119,802) — — — (598,006) Other operating expenses (350,600) (33,392) — — (2,527) (386,519) Underwriting loss (71,301) (9,204) — — (2,701) (83,206) Net investment income — — 183,620 238 — 183,858 Net investment losses — — (770,198) — — (770,198) Products revenues — — — 775,742 — 775,742 Services and other revenues — — — 413,380 174,016 587,396 Products expenses — — — (678,554) — (678,554) Services and other expenses — — — (366,208) (136,288) (502,496) Amortization of intangible assets (3) — — — (23,437) (52,175) (75,612) Segment profit (loss) $ (71,301) $ (9,204) $ (586,578) $ 121,161 $ (17,148) $ (563,070) Interest expense (90,457) Net foreign exchange gains 56,841 Loss before income taxes $ (596,686) U.S. GAAP combined ratio (4) 103 % 102 % NM (5) 103 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $28.1 million for the six months ended June 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 $21.1 million for the six months ended June 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) June 30, 2021 December 31, 2020 Segment assets: Investing $ 27,208,704 $ 24,781,946 Underwriting 8,049,139 7,228,297 Markel Ventures 3,793,058 3,636,060 Total segment assets 39,050,901 35,646,303 Other operations 6,590,612 6,063,751 Total assets $ 45,641,513 $ 41,710,054

Investments

Investments	6 Months Ended
	Jun. 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 8. June 30, 2021 (dollars in thousands) Amortized Gross Gross Estimated Fixed maturity securities: U.S. Treasury securities $ 1,400,765 $ 5,063 $ (4,613) $ 1,401,215 U.S. government-sponsored enterprises 725,412 38,428 (3,075) 760,765 Obligations of states, municipalities and political subdivisions 3,862,463 321,796 (3,565) 4,180,694 Foreign governments 1,423,017 194,614 (2,270) 1,615,361 Commercial mortgage-backed securities 1,736,946 107,924 (1,778) 1,843,092 Residential mortgage-backed securities 776,119 43,117 (94) 819,142 Asset-backed securities 3,505 99 — 3,604 Corporate bonds 739,741 77,578 (1,537) 815,782 Total fixed maturity securities 10,667,968 788,619 (16,932) 11,439,655 Short-term investments 3,257,655 5,551 (133) 3,263,073 Investments, available-for-sale $ 13,925,623 $ 794,170 $ (17,065) $ 14,702,728 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. June 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 $ 1,014,543 $ (4,613) $ — $ — $ 1,014,543 $ (4,613) U.S. government-sponsored enterprises 176,254 (3,075) — — 176,254 (3,075) Obligations of states, municipalities and political subdivisions 230,831 (3,560) 2,892 (5) 233,723 (3,565) Foreign governments 146,779 (2,270) — — 146,779 (2,270) Commercial mortgage-backed securities 84,621 (1,778) — — 84,621 (1,778) Residential mortgage-backed securities 8,582 (91) 130 (3) 8,712 (94) Corporate bonds 77,424 (1,537) — — 77,424 (1,537) Total fixed maturity securities 1,739,034 (16,924) 3,022 (8) 1,742,056 (16,932) Short-term investments 3,095,980 (133) — — 3,095,980 (133) Total $ 4,835,014 $ (17,057) $ 3,022 $ (8) $ 4,838,036 $ (17,065) At June 30, 2021, the Company held 139 available-for-sale securities with a total estimated fair value of $4.8 billion and gross unrealized losses of $17.1 million. Of these 139 securities, three securities had been in a continuous unrealized loss position for one year or longer and had a total estimated fair value of $3.0 million and gross unrealized losses of $8 thousand. 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 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 June 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 June 30, 2021 are shown below by contractual maturity. (dollars in thousands) Amortized Estimated Due in one year or less $ 419,585 $ 425,283 Due after one year through five years 2,849,923 2,972,522 Due after five years through ten years 2,570,434 2,748,079 Due after ten years 2,311,456 2,627,933 8,151,398 8,773,817 Commercial mortgage-backed securities 1,736,946 1,843,092 Residential mortgage-backed securities 776,119 819,142 Asset-backed securities 3,505 3,604 Total fixed maturity securities $ 10,667,968 $ 11,439,655 d) The following table presents the components of net investment income. Quarter Ended June 30, Six Months Ended June 30, (dollars in thousands) 2021 2020 2021 2020 Interest: Tax-exempt municipal bonds $ 14,102 $ 16,157 $ 29,338 $ 32,758 Taxable municipal bonds 16,421 16,834 32,916 33,729 Other taxable bonds 40,618 39,616 80,013 79,588 Short-term investments, including overnight deposits 874 2,379 1,546 12,622 Dividends on equity securities 19,798 18,020 45,183 46,634 Income (loss) from equity method investments 9,018 5,647 12,943 (14,332) Other (417) 46 (612) 803 100,414 98,699 201,327 191,802 Investment expenses (4,153) (3,084) (8,496) (7,944) Net investment income $ 96,261 $ 95,615 $ 192,831 $ 183,858 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 June 30, Six Months Ended June 30, (dollars in thousands) 2021 2020 2021 2020 Fixed maturity securities: Realized gains $ 4,792 $ 5,348 $ 4,875 $ 6,733 Realized losses (81) (5,126) (81) (6,271) Change in allowance for expected credit losses — 1,537 — (202) Short-term investments: Realized gains 278 1,002 308 1,100 Realized losses (633) (184) (727) (356) Cost-method investments: Realized gains — — 4,722 11,167 Other investment gains (losses) 46 (5,389) (1,286) (5,245) Net realized investment gains (losses) 4,402 (2,812) 7,811 6,926 Equity securities: Change in fair value of securities sold during the period 1,345 82,523 3,971 (450,907) Change in fair value of securities held at the end of the period 669,006 831,532 1,189,842 (326,217) Total change in fair value 670,351 914,055 1,193,813 (777,124) Net investment gains (losses) $ 674,753 $ 911,243 $ 1,201,624 $ (770,198) Change in net unrealized gains on available-for-sale investments included in other comprehensive income (loss): Fixed maturity securities $ 62,948 $ 236,521 $ (258,284) $ 335,088 Short-term investments 1,095 3,128 1,779 (3,578) Reserve deficiency adjustment for life and annuity benefit reserves (see note 8) 929 (22,740) 50,262 (35,612) Net increase (decrease) $ 64,972 $ 216,909 $ (206,243) $ 295,898

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 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 for available-for-sale investments and equity securities are 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 managed by Markel CATCo Investment Management Ltd. (MCIM), a consolidated subsidiary, that are not traded on an active exchange, as further described and defined in note 10 (the Markel CATCo Funds), 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 the Markel CATCo 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 in which the Markel CATCo Funds invest. In July 2019, the Markel CATCo Funds were placed into run-off and capital is being returned to investors as it becomes available, the timing of which is impacted by contractual terms regarding release of collateral on the underlying securitized reinsurance contracts, as well as required regulatory approvals. 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 for senior long-term debt and other debt 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. June 30, 2021 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments: Fixed maturity securities, available-for-sale: U.S. Treasury securities $ — $ 1,401,215 $ — $ 1,401,215 U.S. government-sponsored enterprises — 760,765 — 760,765 Obligations of states, municipalities and political subdivisions — 4,180,694 — 4,180,694 Foreign governments — 1,615,361 — 1,615,361 Commercial mortgage-backed securities — 1,843,092 — 1,843,092 Residential mortgage-backed securities — 819,142 — 819,142 Asset-backed securities — 3,604 — 3,604 Corporate bonds — 815,782 — 815,782 Total fixed maturity securities, available-for-sale — 11,439,655 — 11,439,655 Equity securities: Insurance, banks and other financial institutions 3,049,092 — 41,066 3,090,158 Industrial, consumer and all other 5,115,550 — — 5,115,550 Total equity securities 8,164,642 — 41,066 8,205,708 Short-term investments, available-for-sale 3,145,608 117,465 — 3,263,073 Total investments $ 11,310,250 $ 11,557,120 $ 41,066 $ 22,908,436 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, all of which are attributed to the Company's investments in the Markel CATCo Funds. Quarter Ended June 30, Six Months Ended June 30, (dollars in thousands) 2021 2020 2021 2020 Equity securities, beginning of period $ 56,138 $ 131,307 $ 58,493 $ 45,992 Purchases — — — 90,000 Sales (15,015) (16,529) (15,015) (17,893) Net investment gains (losses) (57) 870 (2,412) (2,451) Equity securities, end of period $ 41,066 $ 115,648 $ 41,066 $ 115,648 In connection with the run-off of one of the Markel CATCo Funds 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, however, the Company continues to have exposure to adverse loss development on 2020 exposures under these contracts through its investment in the fund. The Company did not have any assets or liabilities measured at fair value on a non-recurring basis during the six months ended June 30, 2021 and 2020.

Products, Services and Other Re

Products, Services and Other Revenues	6 Months Ended
	Jun. 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 $1.1 billion and $716.9 million for the quarters ended June 30, 2021 and 2020, respectively, and $1.8 billion and $1.3 billion for the six months ended June 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 (loss), along with a reconciliation to total products revenues and services and other revenues. Quarter Ended June 30, 2021 2020 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 581,321 $ — $ 581,321 $ 414,516 $ — $ 414,516 Services 468,424 37,902 506,326 240,220 37,122 277,342 Investment management — 20,785 20,785 — 25,009 25,009 Total revenues from contracts with customers 1,049,745 58,687 1,108,432 654,736 62,131 716,867 Program services and other fronting — 27,399 27,399 — 24,790 24,790 Other 25,759 131 25,890 23,349 (23) 23,326 Total $ 1,075,504 $ 86,217 $ 1,161,721 $ 678,085 $ 86,898 $ 764,983 Six Months Ended June 30, 2021 2020 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 899,963 $ — $ 899,963 $ 752,754 $ — $ 752,754 Services 825,112 65,881 890,993 383,484 68,007 451,491 Investment management — 37,122 37,122 — 54,832 54,832 Total revenues from contracts with customers 1,725,075 103,003 1,828,078 1,136,238 122,839 1,259,077 Program services and other fronting — 55,016 55,016 — 50,494 50,494 Other 57,028 657 57,685 52,884 683 53,567 Total $ 1,782,103 $ 158,676 $ 1,940,779 $ 1,189,122 $ 174,016 $ 1,363,138 Receivables from contracts with customers were $615.1 million and $406.4 million as of June 30, 2021 and December 31, 2020, respectively.

Unpaid Losses And Loss Adjustme

Unpaid Losses And Loss Adjustment Expenses	6 Months Ended
	Jun. 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. Six Months Ended June 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 5,198 (75,037) Effect of adoption of ASU No. 2016-13 — 3,849 Adjusted net reserves for losses and loss adjustment expenses, beginning of year 10,490,915 9,404,073 Incurred losses and loss adjustment expenses: Current accident year 1,920,907 2,057,729 Prior accident years (226,059) (268,220) Total incurred losses and loss adjustment expenses 1,694,848 1,789,509 Payments: Current accident year 198,402 217,466 Prior accident years 1,190,303 1,033,176 Total payments 1,388,705 1,250,642 Effect of foreign currency rate changes on current year activity (476) (1,997) 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 10,793,820 9,940,943 Reinsurance recoverables on unpaid losses 6,205,996 5,304,562 Gross reserves for losses and loss adjustment expenses, end of period $ 16,999,816 $ 15,245,505 For the six months ended June 30, 2021, current accident year losses and loss adjustment expenses included $67.9 million of net losses and loss adjustment expenses from Winter Storm Uri. The net losses and loss adjustment expenses from Winter Storm Uri as of June 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, industry loss estimates and output from both industry and proprietary models, as well as analysis of the Company's ceded reinsurance contracts. 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 Winter Storm Uri as of June 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 six months ended June 30, 2020, current accident year losses and loss adjustment expenses included $325.0 million of net losses and loss adjustment expenses attributed to the COVID-19 pandemic. For the six months ended June 30, 2021, prior accident years losses and loss adjustment expenses included $226.1 million of favorable development on prior years loss reserves, which included $213.3 million of favorable development on the Company's general liability, workers' compensation, marine and energy, property and professional liability product lines within the Insurance segment. Favorable development on prior years loss reserves for the six months ended June 30, 2021 was partially offset by $32.8 million of adverse development on the Company's property product lines within the Reinsurance segment, due in part to an increase in our estimate of ultimate losses and loss adjustment expenses directly attributed to COVID-19 in the first quarter of 2021. The Company's estimate of ultimate losses directly attributed to COVID-19 is based on assumptions about coverage, liability and reinsurance, for which significant uncertainty still exists, and represents the Company's best estimate as of June 30, 2021 based upon information currently available. While the Company believes the net reserves for losses and loss adjustment expenses for COVID-19 as of June 30, 2021 are adequate based on information available at this time, the Company continues to closely monitor reported claims, government actions, judicial decisions and changes in the levels of worldwide social disruption and economic activity arising from the pandemic and will adjust the estimates of gross and net losses as new information becomes available. Such adjustments to the Company's reserves for COVID-19 losses and loss adjustment expenses may be material to the Company's results of operations, financial condition and cash flows.

Reinsurance

Reinsurance	6 Months Ended
	Jun. 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 June 30, 2021 2020 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 1,756,680 $ 344,279 $ (349,037) $ 1,751,922 $ 1,460,090 $ 316,905 $ (319,772) $ 1,457,223 Earned 1,511,416 351,931 (294,679) 1,568,668 1,287,268 346,262 (272,600) 1,360,930 Program services and other fronting: Written 737,110 45,944 (783,525) (471) 567,864 28,333 (597,025) (828) Earned 582,809 23,763 (607,203) (631) 498,381 26,588 (525,725) (756) Consolidated: Written 2,493,790 390,223 (1,132,562) 1,751,451 2,027,954 345,238 (916,797) 1,456,395 Earned $ 2,094,225 $ 375,694 $ (901,882) $ 1,568,037 $ 1,785,649 $ 372,850 $ (798,325) $ 1,360,174 Six Months Ended June 30, 2021 2020 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 3,305,777 $ 966,027 $ (638,350) $ 3,633,454 $ 2,809,331 $ 895,561 $ (599,161) $ 3,105,731 Earned 2,942,749 717,829 (593,779) 3,066,799 2,562,939 672,962 (542,138) 2,693,763 Program services and other fronting: Written 1,345,147 71,914 (1,417,994) (933) 956,788 34,336 (993,982) (2,858) Earned 1,165,969 38,668 (1,205,704) (1,067) 1,043,724 40,311 (1,086,915) (2,880) Consolidated: Written 4,650,924 1,037,941 (2,056,344) 3,632,521 3,766,119 929,897 (1,593,143) 3,102,873 Earned $ 4,108,718 $ 756,497 $ (1,799,483) $ 3,065,732 $ 3,606,663 $ 713,273 $ (1,629,053) $ 2,690,883 Substantially all of the premiums written and earned in the Company's program services and other fronting operations for the quarter and six months ended June 30, 2021 and 2020 were ceded. The percentage of consolidated ceded earned premiums to gross earned premiums was 37% for both the quarter and six months ended June 30, 2021 and 37% and 38% for the quarter and six months June 30, 2020, respectively. The percentage of consolidated assumed earned premiums to net earned premiums was 24% and 25% and for the quarter and six months ended June 30, 2021, respectively, and 27% for both the quarter and six months June 30, 2020. Substantially all of the incurred losses and loss adjustment expenses in the Company's program services and other fronting operations, which totaled $636.8 million and $1.1 billion for the quarter and six months ended June 30, 2021, respectively, and $394.5 million and $702.5 million for the quarter and six months ended June 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 June 30, Six Months Ended June 30, (dollars in thousands) 2021 2020 2021 2020 Gross $ 993,138 $ 868,069 $ 2,067,061 $ 2,111,626 Ceded (177,674) (154,307) (369,645) (321,487) Net losses and loss adjustment expenses $ 815,464 $ 713,762 $ 1,697,416 $ 1,790,139

Life and Annuity Benefits Life

Life and Annuity Benefits Life and Annuity Benefits	6 Months Ended
	Jun. 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 June 30, 2021 and December 31, 2020, the cumulative adjustment to life and annuity benefits attributable to unrealized gains on the underlying investment portfolio totaled $69.3 million and $119.6 million, respectively. During the quarter and six months ended June 30, 2021, the Company decreased life and annuity benefits by $0.9 million and $50.3 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 income by a corresponding amount. During the quarter and six months ended June 30, 2020, the Company increased life and annuity benefits by $22.7 million and $35.6 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 (loss) by a corresponding amount.

Senior Long-Term Debt and Other

Senior Long-Term Debt and Other Debt	6 Months Ended
	Jun. 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 June 30, 2021) and the remainder for general corporate purposes.

Variable Interest Entities

Variable Interest Entities	6 Months Ended
	Jun. 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 issue 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 ($41.1 million and $58.5 million as of June 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 June 30, 2021 and December 31, 2020, net assets under management of MCIM for unconsolidated VIEs were $726.6 million and $929.2 million, respectively. In July 2019, both the Markel CATCo Funds and Markel CATCo Re were placed into run-off, and MCIM is returning capital to investors as it becomes available. See note 13 for further details regarding developments in the Company's Markel CATCo operations.

Related Party Transactions Rela

Related Party Transactions Related Party Transactions	6 Months Ended
	Jun. 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 six months ended June 30, 2021, total revenues attributed to unconsolidated entities managed by Nephila were $42.0 million and $70.7 million, respectively. For the quarter and six months ended June 30, 2020, total revenues attributed to unconsolidated entities managed by Nephila were $42.2 million and $83.7 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 $186.7 million and $304.0 million for the quarter and six months ended June 30, 2021, respectively, and $122.9 million and $213.4 million for the quarter and six months ended June 30, 2020, respectively, all of which were ceded to Nephila Reinsurers. As of June 30, 2021 and December 31, 2020, reinsurance recoverables on the consolidated balance sheets included $466.7 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 six months ended June 30, 2021, gross written premiums attributable to Hagerty written on Essentia were $176.8 million and $296.7 million, respectively, of which $100.5 million and $168.4 million, respectively, were ceded to Hagerty Re. For the quarter and six months ended June 30, 2020 gross written premiums attributable to Hagerty written on Essentia were $154.0 million and $254.9 million, respectively, of which $72.8 million and $120.6 million, respectively, were ceded to Hagerty Re.

Shareholders' Equity

Shareholders' Equity	6 Months Ended
	Jun. 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 June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Issued and outstanding common shares, beginning of period 13,765 13,775 13,783 13,794 Issuance of common shares 2 1 3 3 Repurchase of common shares (33) — (52) (21) Issued and outstanding common shares, end of period 13,734 13,776 13,734 13,776 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 June 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. For the quarter and six months ended June 30, 2021, total dividends declared and paid on preferred shares were $18.0 million, or $30 per share. 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 June 30, Six Months Ended June 30, (in thousands, except per share amounts) 2021 2020 2021 2020 Net income (loss) to common shareholders $ 774,110 $ 921,768 $ 1,347,804 $ (483,995) Adjustment of redeemable noncontrolling interests 13,717 (13,073) 21,623 2,940 Adjusted net income (loss) to common shareholders $ 787,827 $ 908,695 $ 1,369,427 $ (481,055) Basic common shares outstanding 13,793 13,808 13,806 13,812 Dilutive potential common shares from restricted stock units and restricted stock (1) 24 13 22 — Diluted common shares outstanding 13,817 13,821 13,828 13,812 Basic net income (loss) per common share $ 57.12 $ 65.81 $ 99.19 $ (34.83) Diluted net income (loss) per common share (1) $ 57.02 $ 65.75 $ 99.03 $ (34.83) (1) The impact of restricted stock units and restricted stock of 11 thousand shares was excluded from the computation of diluted earnings per common share for the six months ended June 30, 2020 because the effect would have been anti-dilutive.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 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, U.S. Securities and Exchange Commission and Bermuda Monetary Authority (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 has met with the Governmental Authorities and reported the findings from the internal review. The Company cannot currently predict the duration, scope or result of the Markel CATCo Inquiries. The Markel CATCo Inquiries, as well as other matters related to or arising from the Markel CATCo Inquiries, including matters of which the Company is currently unaware, could result in additional claims, litigation, investigations, enforcement actions or proceedings. For example, additional 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. Costs associated with the Markel CATCo Inquiries, as well as legal costs incurred in connection with any existing or future litigation or disputes, are being expensed as incurred. An unfavorable outcome in one or more of these matters, and others the Company cannot anticipate, could have a material adverse effect on the Company's results of operations and financial condition. In addition, the Company may take further steps to mitigate potential risks or liabilities that may arise from the Markel CATCo Inquiries and related developments and some of those steps may have a material impact on the Company's results of operations or financial condition. Even if an unfavorable outcome does not materialize, these matters, and actions the Company may take in response, could have an adverse impact on the Company's reputation and result in substantial expense and disruption. b) In 2019, the Company established Lodgepine Capital Management Limited (Lodgepine), a new retrocessional insurance-linked securities fund manager in Bermuda. Lodgepine'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, which includes 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)	6 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation. The consolidated balance sheet as of June 30, 2021 and the related consolidated statements of income (loss) and comprehensive income (loss) and changes in equity for the quarters and six months ended June 30, 2021 and 2020, and the consolidated statements of cash flows for the six months ended June 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 six months ended June 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)	6 Months Ended
	Jun. 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 June 30, 2021 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 1,821,374 $ 279,444 $ — $ — $ 783,195 $ 2,884,013 Net written premiums 1,494,443 257,355 — — (347) 1,751,451 Earned premiums 1,303,562 264,982 — — (507) 1,568,037 Losses and loss adjustment expenses: Current accident year (783,306) (166,853) — — — (950,159) Prior accident years 154,526 (21,741) — — 2,419 135,204 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (264,823) (67,986) — — — (332,809) Other operating expenses (204,622) (13,414) — — 2,481 (215,555) Underwriting profit (loss) 205,337 (5,012) — — 4,393 204,718 Net investment income — — 96,259 2 — 96,261 Net investment gains — — 674,753 — — 674,753 Products revenues — — — 592,601 — 592,601 Services and other revenues — — — 482,903 86,217 569,120 Products expenses — — — (502,202) — (502,202) Services and other expenses — 109 — (450,781) (65,579) (516,251) Amortization of intangible assets (3) — — — (13,858) (25,871) (39,729) Segment profit (loss) $ 205,337 $ (4,903) $ 771,012 $ 108,665 $ (840) $ 1,079,271 Interest expense (46,568) Net foreign exchange losses (12,257) Income before income taxes $ 1,020,446 U.S. GAAP combined ratio (4) 84 % 102 % NM (5) 87 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $15.8 million for the quarter ended June 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 $10.4 million for the quarter ended June 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 June 30, 2020 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 1,553,436 $ 223,277 $ — $ — $ 596,479 $ 2,373,192 Net written premiums 1,267,976 188,830 — — (411) 1,456,395 Earned premiums 1,120,151 240,555 — — (532) 1,360,174 Losses and loss adjustment expenses: Current accident year (730,201) (147,163) — — — (877,364) Prior accident years 151,205 12,280 — — 663 164,148 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (238,784) (63,411) — — — (302,195) Other operating expenses (167,298) (17,506) — — (2,363) (187,167) Underwriting profit (loss) 135,073 24,755 — — (2,232) 157,596 Net investment income — — 95,561 54 — 95,615 Net investment gains — — 911,243 — — 911,243 Products revenues — — — 423,581 — 423,581 Services and other revenues — — — 254,504 86,898 341,402 Products expenses — — — (364,483) — (364,483) Services and other expenses — — — (222,656) (62,284) (284,940) Amortization of intangible assets (3) — — — (11,596) (26,158) (37,754) Segment profit (loss) $ 135,073 $ 24,755 $ 1,006,804 $ 79,404 $ (3,776) $ 1,242,260 Interest expense (45,427) Net foreign exchange losses (21,460) Income before income taxes $ 1,175,373 U.S. GAAP combined ratio (4) 88 % 90 % NM (5) 88 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $14.3 million for the quarter ended June 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 $10.7 million for the quarter ended June 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 Six Months Ended June 30, 2021 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 3,459,701 $ 811,962 $ — $ — $ 1,417,202 $ 5,688,865 Net written premiums 2,881,873 751,440 — — (792) 3,632,521 Earned premiums 2,547,589 519,069 — — (926) 3,065,732 Losses and loss adjustment expenses: Current accident year (1,581,553) (339,354) — — — (1,920,907) Prior accident years 273,590 (50,396) — — 2,840 226,034 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (525,422) (129,974) — — — (655,396) Other operating expenses (391,919) (27,575) — — (217) (419,711) Underwriting profit (loss) 322,285 (28,230) — — 1,697 295,752 Net investment income — — 192,826 5 — 192,831 Net investment gains — — 1,201,624 — — 1,201,624 Products revenues — — — 921,433 — 921,433 Services and other revenues — — — 860,670 158,676 1,019,346 Products expenses — — — (798,728) — (798,728) Services and other expenses — 109 — (795,689) (132,768) (928,348) Amortization of intangible assets (3) — — — (27,563) (51,719) (79,282) Segment profit (loss) $ 322,285 $ (28,121) $ 1,394,450 $ 160,128 $ (24,114) $ 1,824,628 Interest expense (88,957) Net foreign exchange gains 12,827 Income before income taxes $ 1,748,498 U.S. GAAP combined ratio (4) 87 % 105 % NM (5) 90 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $31.8 million for the six months ended June 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 $20.8 million for the six months ended June 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 Six Months Ended June 30, 2020 (dollars in thousands) Insurance Reinsurance Investing Markel Ventures (1) Other (2) Consolidated Gross premium volume $ 2,968,147 $ 736,463 $ — $ — $ 991,406 $ 4,696,016 Net written premiums 2,463,713 641,579 — — (2,419) 3,102,873 Earned premiums 2,227,002 466,515 — — (2,634) 2,690,883 Losses and loss adjustment expenses: Current accident year (1,736,836) (320,893) — — — (2,057,729) Prior accident years 267,337 (1,632) — — 2,460 268,165 Underwriting, acquisition and insurance expenses: Amortization of policy acquisition costs (478,204) (119,802) — — — (598,006) Other operating expenses (350,600) (33,392) — — (2,527) (386,519) Underwriting loss (71,301) (9,204) — — (2,701) (83,206) Net investment income — — 183,620 238 — 183,858 Net investment losses — — (770,198) — — (770,198) Products revenues — — — 775,742 — 775,742 Services and other revenues — — — 413,380 174,016 587,396 Products expenses — — — (678,554) — (678,554) Services and other expenses — — — (366,208) (136,288) (502,496) Amortization of intangible assets (3) — — — (23,437) (52,175) (75,612) Segment profit (loss) $ (71,301) $ (9,204) $ (586,578) $ 121,161 $ (17,148) $ (563,070) Interest expense (90,457) Net foreign exchange gains 56,841 Loss before income taxes $ (596,686) U.S. GAAP combined ratio (4) 103 % 102 % NM (5) 103 % (1) Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $28.1 million for the six months ended June 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 $21.1 million for the six months ended June 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) June 30, 2021 December 31, 2020 Segment assets: Investing $ 27,208,704 $ 24,781,946 Underwriting 8,049,139 7,228,297 Markel Ventures 3,793,058 3,636,060 Total segment assets 39,050,901 35,646,303 Other operations 6,590,612 6,063,751 Total assets $ 45,641,513 $ 41,710,054

Investments (Tables)

Investments (Tables)	3 Months Ended	6 Months Ended
	Mar. 31, 2021	Jun. 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 8. June 30, 2021 (dollars in thousands) Amortized Gross Gross Estimated Fixed maturity securities: U.S. Treasury securities $ 1,400,765 $ 5,063 $ (4,613) $ 1,401,215 U.S. government-sponsored enterprises 725,412 38,428 (3,075) 760,765 Obligations of states, municipalities and political subdivisions 3,862,463 321,796 (3,565) 4,180,694 Foreign governments 1,423,017 194,614 (2,270) 1,615,361 Commercial mortgage-backed securities 1,736,946 107,924 (1,778) 1,843,092 Residential mortgage-backed securities 776,119 43,117 (94) 819,142 Asset-backed securities 3,505 99 — 3,604 Corporate bonds 739,741 77,578 (1,537) 815,782 Total fixed maturity securities 10,667,968 788,619 (16,932) 11,439,655 Short-term investments 3,257,655 5,551 (133) 3,263,073 Investments, available-for-sale $ 13,925,623 $ 794,170 $ (17,065) $ 14,702,728 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. June 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 $ 1,014,543 $ (4,613) $ — $ — $ 1,014,543 $ (4,613) U.S. government-sponsored enterprises 176,254 (3,075) — — 176,254 (3,075) Obligations of states, municipalities and political subdivisions 230,831 (3,560) 2,892 (5) 233,723 (3,565) Foreign governments 146,779 (2,270) — — 146,779 (2,270) Commercial mortgage-backed securities 84,621 (1,778) — — 84,621 (1,778) Residential mortgage-backed securities 8,582 (91) 130 (3) 8,712 (94) Corporate bonds 77,424 (1,537) — — 77,424 (1,537) Total fixed maturity securities 1,739,034 (16,924) 3,022 (8) 1,742,056 (16,932) Short-term investments 3,095,980 (133) — — 3,095,980 (133) Total $ 4,835,014 $ (17,057) $ 3,022 $ (8) $ 4,838,036 $ (17,065)
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 June 30, 2021 are shown below by contractual maturity. (dollars in thousands) Amortized Estimated Due in one year or less $ 419,585 $ 425,283 Due after one year through five years 2,849,923 2,972,522 Due after five years through ten years 2,570,434 2,748,079 Due after ten years 2,311,456 2,627,933 8,151,398 8,773,817 Commercial mortgage-backed securities 1,736,946 1,843,092 Residential mortgage-backed securities 776,119 819,142 Asset-backed securities 3,505 3,604 Total fixed maturity securities $ 10,667,968 $ 11,439,655
Components Of Net Investment Income		The following table presents the components of net investment income. Quarter Ended June 30, Six Months Ended June 30, (dollars in thousands) 2021 2020 2021 2020 Interest: Tax-exempt municipal bonds $ 14,102 $ 16,157 $ 29,338 $ 32,758 Taxable municipal bonds 16,421 16,834 32,916 33,729 Other taxable bonds 40,618 39,616 80,013 79,588 Short-term investments, including overnight deposits 874 2,379 1,546 12,622 Dividends on equity securities 19,798 18,020 45,183 46,634 Income (loss) from equity method investments 9,018 5,647 12,943 (14,332) Other (417) 46 (612) 803 100,414 98,699 201,327 191,802 Investment expenses (4,153) (3,084) (8,496) (7,944) Net investment income $ 96,261 $ 95,615 $ 192,831 $ 183,858
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 June 30, Six Months Ended June 30, (dollars in thousands) 2021 2020 2021 2020 Fixed maturity securities: Realized gains $ 4,792 $ 5,348 $ 4,875 $ 6,733 Realized losses (81) (5,126) (81) (6,271) Change in allowance for expected credit losses — 1,537 — (202) Short-term investments: Realized gains 278 1,002 308 1,100 Realized losses (633) (184) (727) (356) Cost-method investments: Realized gains — — 4,722 11,167 Other investment gains (losses) 46 (5,389) (1,286) (5,245) Net realized investment gains (losses) 4,402 (2,812) 7,811 6,926 Equity securities: Change in fair value of securities sold during the period 1,345 82,523 3,971 (450,907) Change in fair value of securities held at the end of the period 669,006 831,532 1,189,842 (326,217) Total change in fair value 670,351 914,055 1,193,813 (777,124) Net investment gains (losses) $ 674,753 $ 911,243 $ 1,201,624 $ (770,198) Change in net unrealized gains on available-for-sale investments included in other comprehensive income (loss): Fixed maturity securities $ 62,948 $ 236,521 $ (258,284) $ 335,088 Short-term investments 1,095 3,128 1,779 (3,578) Reserve deficiency adjustment for life and annuity benefit reserves (see note 8) 929 (22,740) 50,262 (35,612) Net increase (decrease) $ 64,972 $ 216,909 $ (206,243) $ 295,898

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 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. June 30, 2021 (dollars in thousands) Level 1 Level 2 Level 3 Total Assets: Investments: Fixed maturity securities, available-for-sale: U.S. Treasury securities $ — $ 1,401,215 $ — $ 1,401,215 U.S. government-sponsored enterprises — 760,765 — 760,765 Obligations of states, municipalities and political subdivisions — 4,180,694 — 4,180,694 Foreign governments — 1,615,361 — 1,615,361 Commercial mortgage-backed securities — 1,843,092 — 1,843,092 Residential mortgage-backed securities — 819,142 — 819,142 Asset-backed securities — 3,604 — 3,604 Corporate bonds — 815,782 — 815,782 Total fixed maturity securities, available-for-sale — 11,439,655 — 11,439,655 Equity securities: Insurance, banks and other financial institutions 3,049,092 — 41,066 3,090,158 Industrial, consumer and all other 5,115,550 — — 5,115,550 Total equity securities 8,164,642 — 41,066 8,205,708 Short-term investments, available-for-sale 3,145,608 117,465 — 3,263,073 Total investments $ 11,310,250 $ 11,557,120 $ 41,066 $ 22,908,436 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, all of which are attributed to the Company's investments in the Markel CATCo Funds. Quarter Ended June 30, Six Months Ended June 30, (dollars in thousands) 2021 2020 2021 2020 Equity securities, beginning of period $ 56,138 $ 131,307 $ 58,493 $ 45,992 Purchases — — — 90,000 Sales (15,015) (16,529) (15,015) (17,893) Net investment gains (losses) (57) 870 (2,412) (2,451) Equity securities, end of period $ 41,066 $ 115,648 $ 41,066 $ 115,648

Products, Services and Other _2

Products, Services and Other Revenues (Tables)	6 Months Ended
	Jun. 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 (loss), along with a reconciliation to total products revenues and services and other revenues. Quarter Ended June 30, 2021 2020 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 581,321 $ — $ 581,321 $ 414,516 $ — $ 414,516 Services 468,424 37,902 506,326 240,220 37,122 277,342 Investment management — 20,785 20,785 — 25,009 25,009 Total revenues from contracts with customers 1,049,745 58,687 1,108,432 654,736 62,131 716,867 Program services and other fronting — 27,399 27,399 — 24,790 24,790 Other 25,759 131 25,890 23,349 (23) 23,326 Total $ 1,075,504 $ 86,217 $ 1,161,721 $ 678,085 $ 86,898 $ 764,983 Six Months Ended June 30, 2021 2020 (dollars in thousands) Markel Ventures Other Total Markel Ventures Other Total Products $ 899,963 $ — $ 899,963 $ 752,754 $ — $ 752,754 Services 825,112 65,881 890,993 383,484 68,007 451,491 Investment management — 37,122 37,122 — 54,832 54,832 Total revenues from contracts with customers 1,725,075 103,003 1,828,078 1,136,238 122,839 1,259,077 Program services and other fronting — 55,016 55,016 — 50,494 50,494 Other 57,028 657 57,685 52,884 683 53,567 Total $ 1,782,103 $ 158,676 $ 1,940,779 $ 1,189,122 $ 174,016 $ 1,363,138

Unpaid Losses And Loss Adjust_2

Unpaid Losses And Loss Adjustment Expenses (Tables)	6 Months Ended
	Jun. 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. Six Months Ended June 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 5,198 (75,037) Effect of adoption of ASU No. 2016-13 — 3,849 Adjusted net reserves for losses and loss adjustment expenses, beginning of year 10,490,915 9,404,073 Incurred losses and loss adjustment expenses: Current accident year 1,920,907 2,057,729 Prior accident years (226,059) (268,220) Total incurred losses and loss adjustment expenses 1,694,848 1,789,509 Payments: Current accident year 198,402 217,466 Prior accident years 1,190,303 1,033,176 Total payments 1,388,705 1,250,642 Effect of foreign currency rate changes on current year activity (476) (1,997) 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 10,793,820 9,940,943 Reinsurance recoverables on unpaid losses 6,205,996 5,304,562 Gross reserves for losses and loss adjustment expenses, end of period $ 16,999,816 $ 15,245,505

Reinsurance (Tables)

Reinsurance (Tables)	6 Months Ended
	Jun. 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 June 30, 2021 2020 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 1,756,680 $ 344,279 $ (349,037) $ 1,751,922 $ 1,460,090 $ 316,905 $ (319,772) $ 1,457,223 Earned 1,511,416 351,931 (294,679) 1,568,668 1,287,268 346,262 (272,600) 1,360,930 Program services and other fronting: Written 737,110 45,944 (783,525) (471) 567,864 28,333 (597,025) (828) Earned 582,809 23,763 (607,203) (631) 498,381 26,588 (525,725) (756) Consolidated: Written 2,493,790 390,223 (1,132,562) 1,751,451 2,027,954 345,238 (916,797) 1,456,395 Earned $ 2,094,225 $ 375,694 $ (901,882) $ 1,568,037 $ 1,785,649 $ 372,850 $ (798,325) $ 1,360,174 Six Months Ended June 30, 2021 2020 (dollars in thousands) Direct Assumed Ceded Net Premiums Direct Assumed Ceded Net Premiums Underwriting: Written $ 3,305,777 $ 966,027 $ (638,350) $ 3,633,454 $ 2,809,331 $ 895,561 $ (599,161) $ 3,105,731 Earned 2,942,749 717,829 (593,779) 3,066,799 2,562,939 672,962 (542,138) 2,693,763 Program services and other fronting: Written 1,345,147 71,914 (1,417,994) (933) 956,788 34,336 (993,982) (2,858) Earned 1,165,969 38,668 (1,205,704) (1,067) 1,043,724 40,311 (1,086,915) (2,880) Consolidated: Written 4,650,924 1,037,941 (2,056,344) 3,632,521 3,766,119 929,897 (1,593,143) 3,102,873 Earned $ 4,108,718 $ 756,497 $ (1,799,483) $ 3,065,732 $ 3,606,663 $ 713,273 $ (1,629,053) $ 2,690,883
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 June 30, Six Months Ended June 30, (dollars in thousands) 2021 2020 2021 2020 Gross $ 993,138 $ 868,069 $ 2,067,061 $ 2,111,626 Ceded (177,674) (154,307) (369,645) (321,487) Net losses and loss adjustment expenses $ 815,464 $ 713,762 $ 1,697,416 $ 1,790,139

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	6 Months Ended
	Jun. 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 June 30, Six Months Ended June 30, (in thousands) 2021 2020 2021 2020 Issued and outstanding common shares, beginning of period 13,765 13,775 13,783 13,794 Issuance of common shares 2 1 3 3 Repurchase of common shares (33) — (52) (21) Issued and outstanding common shares, end of period 13,734 13,776 13,734 13,776
Schedule Of Net Income (Loss) Per Common Share	Quarter Ended June 30, Six Months Ended June 30, (in thousands, except per share amounts) 2021 2020 2021 2020 Net income (loss) to common shareholders $ 774,110 $ 921,768 $ 1,347,804 $ (483,995) Adjustment of redeemable noncontrolling interests 13,717 (13,073) 21,623 2,940 Adjusted net income (loss) to common shareholders $ 787,827 $ 908,695 $ 1,369,427 $ (481,055) Basic common shares outstanding 13,793 13,808 13,806 13,812 Dilutive potential common shares from restricted stock units and restricted stock (1) 24 13 22 — Diluted common shares outstanding 13,817 13,821 13,828 13,812 Basic net income (loss) per common share $ 57.12 $ 65.81 $ 99.19 $ (34.83) Diluted net income (loss) per common share (1) $ 57.02 $ 65.75 $ 99.03 $ (34.83) (1) The impact of restricted stock units and restricted stock of 11 thousand shares was excluded from the computation of diluted earnings per common share for the six months ended June 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				6 Months Ended
	Jun. 30, 2021		Jun. 30, 2020		Jun. 30, 2021		Jun. 30, 2020
Segment Reporting Information [Line Items]
Gross premium volume	$ 2,884,013		$ 2,373,192		$ 5,688,865		$ 4,696,016
Net written premiums	1,751,451		1,456,395		3,632,521		3,102,873
Earned premiums	1,568,037		1,360,174		3,065,732		2,690,883
Losses and loss adjustment expenses, current accident year	(950,159)		(877,364)		(1,920,907)		(2,057,729)
Losses and loss adjustment expenses, prior accident year	135,204		164,148		226,034		268,165
Amortization of policy acquisition costs	(332,809)		(302,195)		(655,396)		(598,006)
Other operating expenses	(215,555)		(187,167)		(419,711)		(386,519)
Underwriting profit (loss)	204,718		157,596		295,752		(83,206)
Net investment income	96,261		95,615		192,831		183,858
Net investment gains (losses)	674,753		911,243		1,201,624		(770,198)
Products revenues	592,601		423,581		921,433		775,742
Services and other revenues	569,120		341,402		1,019,346		587,396
Products expenses	(502,202)		(364,483)		(798,728)		(678,554)
Services and other expenses	(516,251)		(284,940)		(928,348)		(502,496)
Amortization of intangible assets	(39,729)	[1]	(37,754)	[1]	(79,282)	[2]	(75,612)	[1]
Segment profit (loss)	1,079,271		1,242,260		1,824,628		(563,070)
Interest expense	(46,568)		(45,427)		(88,957)		(90,457)
Net foreign exchange gains	(12,257)		(21,460)		12,827		56,841
Income (Loss) before income taxes	$ 1,020,446		$ 1,175,373		$ 1,748,498		$ (596,686)
U.S. GAAP combined ratio	87.00%	[3]	88.00%	[3]	90.00%	[4]	103.00%	[3]
Insurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume	$ 1,821,374		$ 1,553,436		$ 3,459,701		$ 2,968,147
Net written premiums	1,494,443		1,267,976		2,881,873		2,463,713
Earned premiums	1,303,562		1,120,151		2,547,589		2,227,002
Losses and loss adjustment expenses, current accident year	(783,306)		(730,201)		(1,581,553)		(1,736,836)
Losses and loss adjustment expenses, prior accident year	154,526		151,205		273,590		267,337
Amortization of policy acquisition costs	(264,823)		(238,784)		(525,422)		(478,204)
Other operating expenses	(204,622)		(167,298)		(391,919)		(350,600)
Underwriting profit (loss)	205,337		135,073		322,285		(71,301)
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)	$ 205,337		$ 135,073		$ 322,285		$ (71,301)
U.S. GAAP combined ratio	84.00%	[3]	88.00%	[3]	87.00%	[4]	103.00%	[3]
Reinsurance [Member]
Segment Reporting Information [Line Items]
Gross premium volume	$ 279,444		$ 223,277		$ 811,962		$ 736,463
Net written premiums	257,355		188,830		751,440		641,579
Earned premiums	264,982		240,555		519,069		466,515
Losses and loss adjustment expenses, current accident year	(166,853)		(147,163)		(339,354)		(320,893)
Losses and loss adjustment expenses, prior accident year	(21,741)		12,280		(50,396)		(1,632)
Amortization of policy acquisition costs	(67,986)		(63,411)		(129,974)		(119,802)
Other operating expenses	(13,414)		(17,506)		(27,575)		(33,392)
Underwriting profit (loss)	(5,012)		24,755		(28,230)		(9,204)
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	109		0		109		0
Amortization of intangible assets	0	[1]	0	[1]	0	[2]	0	[1]
Segment profit (loss)	$ (4,903)		$ 24,755		$ (28,121)		$ (9,204)
U.S. GAAP combined ratio	102.00%	[3]	90.00%	[3]	105.00%	[4]	102.00%	[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	96,259		95,561		192,826		183,620
Net investment gains (losses)	674,753		911,243		1,201,624		(770,198)
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)	771,012		1,006,804		1,394,450		(586,578)
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	2	[5]	54	[5]	5	[6]	238	[5]
Net investment gains (losses)	0	[5]	0	[5]	0	[6]	0	[5]
Products revenues	592,601	[5]	423,581	[5]	921,433	[6]	775,742	[5]
Services and other revenues	482,903	[5]	254,504	[5]	860,670	[6]	413,380	[5]
Products expenses	(502,202)	[5]	(364,483)	[5]	(798,728)	[6]	(678,554)	[5]
Services and other expenses	(450,781)	[5]	(222,656)	[5]	(795,689)	[6]	(366,208)	[5]
Amortization of intangible assets	(13,858)	[1],[5]	(11,596)	[1],[5]	(27,563)	[2],[6]	(23,437)	[1],[5]
Segment profit (loss)	108,665	[5]	79,404	[5]	160,128	[6]	121,161	[5]
Depreciation	15,800		14,300		31,800	[6]	28,100	[5]
Underwriting Segments [Member]
Segment Reporting Information [Line Items]
Amortization of intangible assets	10,400		10,700		20,800	[7]	21,100	[8]
Other [Member]
Segment Reporting Information [Line Items]
Gross premium volume	783,195	[8]	596,479	[8]	1,417,202	[7]	991,406	[8]
Net written premiums	(347)	[8]	(411)	[8]	(792)	[7]	(2,419)	[8]
Earned premiums	(507)	[8]	(532)	[8]	(926)	[7]	(2,634)	[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	2,419	[8]	663	[8]	2,840	[7]	2,460	[8]
Amortization of policy acquisition costs	0	[8]	0	[8]	0	[7]	0	[8]
Other operating expenses	2,481	[8]	(2,363)	[8]	(217)	[7]	(2,527)	[8]
Underwriting profit (loss)	4,393	[8]	(2,232)	[8]	1,697	[7]	(2,701)	[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	86,217	[8]	86,898	[8]	158,676	[7]	174,016	[8]
Products expenses	0	[8]	0	[8]	0	[7]	0	[8]
Services and other expenses	(65,579)	[8]	(62,284)	[8]	(132,768)	[7]	(136,288)	[8]
Amortization of intangible assets	(25,871)	[1],[8]	(26,158)	[1],[8]	(51,719)	[2],[7]	(52,175)	[1],[8]
Segment profit (loss)	$ (840)	[8]	$ (3,776)	[8]	$ (24,114)	[7]	$ (17,148)	[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 $28.1 million for the six months ended June 30, 2020.
[6]	Products expenses and services and other expenses for the Markel Ventures segment include depreciation expense of $31.8 million for the six months ended June 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 $20.8 million for the six months ended June 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 $21.1 million for the six months ended June 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	Jun. 30, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Assets	$ 45,641,513	$ 41,710,054
Other [Member]
Segment Reporting Information [Line Items]
Assets	6,590,612	6,063,751
Segment assets [Member]
Segment Reporting Information [Line Items]
Assets	39,050,901	35,646,303
Segment assets [Member] | Investing [Member]
Segment Reporting Information [Line Items]
Assets	27,208,704	24,781,946
Segment assets [Member] | Underwriting [Member]
Segment Reporting Information [Line Items]
Assets	8,049,139	7,228,297
Segment assets [Member] | Markel Ventures [Member]
Segment Reporting Information [Line Items]
Assets	$ 3,793,058	$ 3,636,060

Investments (Narrative) (Detail

Investments (Narrative) (Details) $ in Thousands	Jun. 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	139	36
Available-for-sale securities, estimated fair value	$ 4,838,036	$ 502,004
Available-for-sale securities, gross unrealized holding losses	$ (17,065)	$ (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	3	6
Available-for-sale securities, estimated fair value, 12 months or longer	$ 3,022	$ 5,486
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(8)	(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	1,742,056	152,026
Available-for-sale securities, gross unrealized holding losses	(16,932)	(957)
Available-for-sale securities, estimated fair value, 12 months or longer	3,022	5,486
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	$ (8)	$ (20)

Investments (Available-For-Sale

Investments (Available-For-Sale Investments) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	$ 10,667,968	$ 9,655,261
Available-for-sale fixed maturity investments, gross unrealized holding gains	788,619	1,027,430
Available-for-sale fixed maturity investments, gross unrealized holding losses	(16,932)	(957)
Available-for-sale fixed maturity investments, estimated fair value	11,439,655	10,681,734
Short-term investments, available-for-sale, amortized cost	3,257,655	2,030,460
Short-term investments, available-for-sale, gross unrealized holding gains	5,551	3,645
Short-term investments, available-for-sale, gross unrealized holding losses	(133)	(6)
Short-term investments, available-for-sale, estimated fair value	3,263,073	2,034,099
Investments, available-for-sale, amortized cost	13,925,623	11,685,721
Investments, available-for-sale, gross unrealized holding gains	794,170	1,031,075
Investments, available-for-sale, gross unrealized holding losses	(17,065)	(963)
Investments, available-for-sale, estimated fair value	14,702,728	12,715,833
U.S. Treasury securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	1,400,765	580,716
Available-for-sale fixed maturity investments, gross unrealized holding gains	5,063	9,091
Available-for-sale fixed maturity investments, gross unrealized holding losses	(4,613)	(507)
Available-for-sale fixed maturity investments, estimated fair value	1,401,215	589,300
U.S. government-sponsored enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	725,412	500,053
Available-for-sale fixed maturity investments, gross unrealized holding gains	38,428	51,593
Available-for-sale fixed maturity investments, gross unrealized holding losses	(3,075)	(92)
Available-for-sale fixed maturity investments, estimated fair value	760,765	551,554
Obligations of states, municipalities and political subdivisions [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	3,862,463	3,903,292
Available-for-sale fixed maturity investments, gross unrealized holding gains	321,796	386,784
Available-for-sale fixed maturity investments, gross unrealized holding losses	(3,565)	(235)
Available-for-sale fixed maturity investments, estimated fair value	4,180,694	4,289,841
Foreign governments [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	1,423,017	1,352,616
Available-for-sale fixed maturity investments, gross unrealized holding gains	194,614	275,450
Available-for-sale fixed maturity investments, gross unrealized holding losses	(2,270)	(57)
Available-for-sale fixed maturity investments, estimated fair value	1,615,361	1,628,009
Commercial mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	1,736,946	1,736,257
Available-for-sale fixed maturity investments, gross unrealized holding gains	107,924	149,359
Available-for-sale fixed maturity investments, gross unrealized holding losses	(1,778)	(34)
Available-for-sale fixed maturity investments, estimated fair value	1,843,092	1,885,582
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	776,119	811,732
Available-for-sale fixed maturity investments, gross unrealized holding gains	43,117	58,742
Available-for-sale fixed maturity investments, gross unrealized holding losses	(94)	(29)
Available-for-sale fixed maturity investments, estimated fair value	819,142	870,445
Asset-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	3,505	5,812
Available-for-sale fixed maturity investments, gross unrealized holding gains	99	154
Available-for-sale fixed maturity investments, gross unrealized holding losses	0	0
Available-for-sale fixed maturity investments, estimated fair value	3,604	5,966
Corporate bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, available-for-sale amortized cost	739,741	764,783
Available-for-sale fixed maturity investments, gross unrealized holding gains	77,578	96,257
Available-for-sale fixed maturity investments, gross unrealized holding losses	(1,537)	(3)
Available-for-sale fixed maturity investments, estimated fair value	$ 815,782	$ 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	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	$ 4,835,014	$ 496,518
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(17,057)	(943)
Available-for-sale securities, estimated fair value, 12 months or longer	3,022	5,486
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(8)	(20)
Available-for-sale securities, estimated fair value	4,838,036	502,004
Available-for-sale securities, gross unrealized holding losses	(17,065)	(963)
Short-term investments, estimated fair value, less than 12 months	3,095,980	349,978
Short-term investments, gross unrealized holding losses, less than 12 months	(133)	(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	3,095,980	349,978
Short-term investments, gross unrealized holding losses	(133)	(6)
U.S. Treasury securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	1,014,543	66,220
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(4,613)	(507)
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	1,014,543	66,220
Available-for-sale securities, gross unrealized holding losses	(4,613)	(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	176,254	14,878
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(3,075)	(92)
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	176,254	14,878
Available-for-sale securities, gross unrealized holding losses	(3,075)	(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	230,831	28,037
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(3,560)	(223)
Available-for-sale securities, estimated fair value, 12 months or longer	2,892	2,960
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(5)	(12)
Available-for-sale securities, estimated fair value	233,723	30,997
Available-for-sale securities, gross unrealized holding losses	(3,565)	(235)
Foreign governments [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	146,779	20,790
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(2,270)	(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	146,779	20,790
Available-for-sale securities, gross unrealized holding losses	(2,270)	(57)
Commercial mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	84,621	13,178
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(1,778)	(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	84,621	15,704
Available-for-sale securities, gross unrealized holding losses	(1,778)	(34)
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	8,582	3,345
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(91)	(29)
Available-for-sale securities, estimated fair value, 12 months or longer	130	0
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(3)	0
Available-for-sale securities, estimated fair value	8,712	3,345
Available-for-sale securities, gross unrealized holding losses	(94)	(29)
Corporate bonds [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	77,424	92
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(1,537)	(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	77,424	92
Available-for-sale securities, gross unrealized holding losses	(1,537)	(3)
Total fixed maturities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale securities, estimated fair value, less than 12 months	1,739,034	146,540
Available-for-sale securities, gross unrealized holding losses, less than 12 months	(16,924)	(937)
Available-for-sale securities, estimated fair value, 12 months or longer	3,022	5,486
Available-for-sale securities, gross unrealized holding losses, 12 months or longer	(8)	(20)
Available-for-sale securities, estimated fair value	1,742,056	152,026
Available-for-sale securities, gross unrealized holding losses	$ (16,932)	$ (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	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Due in one year or less, amortized cost	$ 419,585
Due after one year through five years, amortized cost	2,849,923
Due after five years through ten years, amortized cost	2,570,434
Due after ten years, amortized cost	2,311,456
Amortized cost, sub-total	8,151,398
Total fixed maturities, amortized cost	10,667,968	$ 9,655,261
Due in one year or less, estimated fair value	425,283
Due after one year through five years, estimated fair value	2,972,522
Due after five years through ten years, estimated fair value	2,748,079
Due after ten years, estimated fair value	2,627,933
Estimated fair value, sub-total	8,773,817
Total fixed maturities, estimated fair value	11,439,655	10,681,734
Commercial mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	1,736,946
Total fixed maturities, amortized cost	1,736,946	1,736,257
Fixed maturities, estimated fair value	1,843,092
Total fixed maturities, estimated fair value	1,843,092	1,885,582
Residential mortgage-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	776,119
Total fixed maturities, amortized cost	776,119	811,732
Fixed maturities, estimated fair value	819,142
Total fixed maturities, estimated fair value	819,142	870,445
Asset-backed securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fixed maturities, amortized cost	3,505
Total fixed maturities, amortized cost	3,505	5,812
Fixed maturities, estimated fair value	3,604
Total fixed maturities, estimated fair value	$ 3,604	$ 5,966

Investments (Components Of Net

Investments (Components Of Net Investment Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Tax-exempt municipal bonds	$ 14,102	$ 16,157	$ 29,338	$ 32,758
Short-term investments, including overnight deposits	874	2,379	1,546	12,622
Dividends on equity securities	19,798	18,020	45,183	46,634
Income (loss) from equity method investments	9,018	5,647	12,943	(14,332)
Other	(417)	(46)	612	(803)
Total investment income	100,414	98,699	201,327	191,802
Investment expenses	(4,153)	(3,084)	(8,496)	(7,944)
Net investment income	96,261	95,615	192,831	183,858
Taxable municipal bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	16,421	16,834	32,916	33,729
Other taxable bonds [Member]
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Taxable bonds	$ 40,618	$ 39,616	$ 80,013	$ 79,588

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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Gain (Loss) on Securities [Line Items]
Cost method investments, realized gains	$ 0	$ 0	$ 4,722	$ 11,167
Net realized investment gains	4,402	(2,812)	7,811	6,926
Equity securities, Change in fair value of securities sold during the period	1,345	82,523	3,971	(450,907)
Equity securities, Change in fair value of securities held at the end of the period	669,006	831,532	1,189,842	(326,217)
Total change in fair value of equity securities	670,351	914,055	1,193,813	(777,124)
Net investment gains (losses)	674,753	911,243	1,201,624	(770,198)
Change in net unrealized gains on available-for-sale investments included in other comprehensive income	64,972	216,909	(206,243)	295,898
Reserve deficiency adjustment for life and annuity benefit reserves	929	(22,740)	50,262	(35,612)
Sales of fixed maturities [Member]
Gain (Loss) on Securities [Line Items]
Fixed maturity securities, realized gains	4,792	5,348	4,875	6,733
Fixed maturity securities, realized losses	(81)	(5,126)	(81)	(6,271)
Change in allowance for expected credit losses	0	1,537	0	(202)
Sales of short-term investments [Member]
Gain (Loss) on Securities [Line Items]
Short-term investments, available-for-sale, realized gains	278	1,002	308	1,100
Short-term investments, available-for-sale, realized losses	(633)	(184)	(727)	(356)
Sales of Other Investments
Gain (Loss) on Securities [Line Items]
Other investment gains (losses)	46	(5,389)	(1,286)	(5,245)
Fixed Maturities [Member]
Gain (Loss) on Securities [Line Items]
Change in net unrealized gains on available-for-sale investments included in other comprehensive income	62,948	236,521	(258,284)	335,088
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	$ 1,095	$ 3,128	$ 1,779	$ (3,578)

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net investment gains (losses)	$ 674,753	$ 911,243	$ 1,201,624	$ (770,198)
Equity securities	8,205,708		8,205,708		$ 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	8,205,708		8,205,708		$ 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	Jun. 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	$ 11,439,655	$ 10,681,734
Equity securities	8,205,708	6,994,110
Short-term investments, available-for-sale	3,263,073	2,034,099
Total Investments	22,908,436	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	1,401,215	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	760,765	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	4,180,694	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	1,615,361	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	1,843,092	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	819,142	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	3,604	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	815,782	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	11,439,655	10,681,734
Equity securities	8,205,708	6,994,110
Short-term investments, available-for-sale	3,263,073	2,034,099
Total Investments	22,908,436	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	8,164,642	6,935,617
Short-term investments, available-for-sale	3,145,608	1,922,459
Total Investments	11,310,250	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	11,439,655	10,681,734
Equity securities	0	0
Short-term investments, available-for-sale	117,465	111,640
Total Investments	11,557,120	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	41,066	58,493
Short-term investments, available-for-sale	0	0
Total Investments	41,066	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	1,401,215	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	1,401,215	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	760,765	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	760,765	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	4,180,694	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	4,180,694	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	1,615,361	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	1,615,361	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	1,843,092	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	1,843,092	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	819,142	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	819,142	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	3,604	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	3,604	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	815,782	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	815,782	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	3,090,158	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	3,049,092	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	41,066	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	5,115,550	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	5,115,550	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	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Purchases	$ 90,000	$ 0	$ 0	$ 0	$ 90,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		41,066	115,648	41,066	115,648
Equity securities, beginning of period	45,992	56,138	131,307	58,493	45,992
Purchases	$ 90,000	0	0	0	90,000
Sales		(15,015)	(16,529)	(15,015)	(17,893)
Net investment gains (losses) on Level 3 investments		(57)	870	(2,412)	(2,451)
Equity securities, end of period		41,066	115,648	41,066	115,648
Sales of fixed maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fixed maturity securities, realized gains		$ 4,792	$ 5,348	$ 4,875	$ 6,733

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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Other revenues	$ 1,161,721	$ 764,983	$ 1,940,779	$ 1,363,138
Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	1,108,432	716,867	1,828,078	1,259,077
Products [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	581,321	414,516	899,963	752,754
Services [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	506,326	277,342	890,993	451,491
Investment management [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	20,785	25,009	37,122	54,832
Program services and other fronting [Member]
Disaggregation of Revenue [Line Items]
Other revenues	27,399	24,790	55,016	50,494
Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	25,890	23,326	57,685	53,567
Markel Ventures [Member]
Disaggregation of Revenue [Line Items]
Other revenues	1,075,504	678,085	1,782,103	1,189,122
Markel Ventures [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	1,049,745	654,736	1,725,075	1,136,238
Markel Ventures [Member] | Products [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	581,321	414,516	899,963	752,754
Markel Ventures [Member] | Services [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	468,424	240,220	825,112	383,484
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	25,759	23,349	57,028	52,884
Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	86,217	86,898	158,676	174,016
Other [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	58,687	62,131	103,003	122,839
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	37,902	37,122	65,881	68,007
Other [Member] | Investment management [Member] | Revenue from contracts with customers [Member]
Disaggregation of Revenue [Line Items]
Other revenues	20,785	25,009	37,122	54,832
Other [Member] | Program services and other fronting [Member]
Disaggregation of Revenue [Line Items]
Other revenues	27,399	24,790	55,016	50,494
Other [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Other revenues	$ 131	$ (23)	$ 657	$ 683

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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Receivables and Customer Deposits [Line Items]
Receivables	$ 2,627,218		$ 2,627,218		$ 1,930,211
Other revenues	1,161,721	$ 764,983	1,940,779	$ 1,363,138
Contracts with customers [Member]
Receivables and Customer Deposits [Line Items]
Trade and Other Receivables, Net	615,100		615,100		$ 406,400
Revenue from contracts with customers [Member]
Receivables and Customer Deposits [Line Items]
Other revenues	$ 1,108,432	$ 716,867	$ 1,828,078	$ 1,259,077

Unpaid Losses And Loss Adjust_3

Unpaid Losses And Loss Adjustment Expenses (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred losses and loss adjustment expenses, current accident years	$ 950,159	$ 877,364	$ 1,920,907	$ 2,057,729
Favorable (adverse) development on prior years' loss reserves			226,059	268,220
Prof Liab General Liab And Workers Comp Insurance Segment and Property and General Liab Reinsurance Segment
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable (adverse) development on prior years' loss reserves				206,600
2021 Catastrophes [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred losses and loss adjustment expenses, current accident years			67,900
COVID-19 Pandemic [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred losses and loss adjustment expenses, current accident years				325,000
Insurance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred losses and loss adjustment expenses, current accident years	783,306	730,201	1,581,553	1,736,836
Insurance [Member] | General Liab Workers Comp Marine & Energy Property And Professional Liab Insurance Segment
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable (adverse) development on prior years' loss reserves			213,300
Reinsurance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Incurred losses and loss adjustment expenses, current accident years	$ 166,853	$ 147,163	339,354	$ 320,893
Reinsurance [Member] | Property
Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Favorable (adverse) development on prior years' loss reserves			$ (32,800)

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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 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	$ 5,198	$ (75,037)	5,198	(75,037)
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			10,490,915	9,404,073
Incurred losses and loss adjustment expenses, current accident years	950,159	877,364	1,920,907	2,057,729
Incurred losses and loss adjustment expenses, prior accident years			(226,059)	(268,220)
Total incurred losses and loss adjustment expenses			1,694,848	1,789,509
Payments, current accident year			198,402	217,466
Payments, prior accident years			1,190,303	1,033,176
Total payments			1,388,705	1,250,642
Effect of foreign currency rate changes on current year activity			(476)	(1,997)
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	10,793,820	9,940,943	10,793,820	9,940,943
Reinsurance recoverable on unpaid losses	6,205,996	5,304,562	6,205,996	5,304,562
Gross reserves for losses and loss adjustment expenses, end of period	$ 16,999,816	$ 15,245,505	$ 16,999,816	$ 15,245,505

Reinsurance (Narrative) (Detail

Reinsurance (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Percentage of ceded earned premiums to gross earned premiums	37.00%	37.00%	37.00%	38.00%
Percentage of assumed earned premiums to net earned premiums	24.00%	27.00%	25.00%	27.00%
Program services and other fronting [Member]
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Policyholder Benefits and Claims Incurred, Gross	$ 636.8	$ 394.5	$ 1,100	$ 702.5
Reinsurance recoverables	$ (637.3)	$ (395)	$ (1,100)	$ (703.1)

Reinsurance (Effect Of Reinsura

Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Premiums Written And Earned) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Effects of Reinsurance [Line Items]
Direct premiums written	$ 2,493,790	$ 2,027,954	$ 4,650,924	$ 3,766,119
Direct premiums earned	2,094,225	1,785,649	4,108,718	3,606,663
Assumed premiums written	390,223	345,238	1,037,941	929,897
Assumed premiums earned	375,694	372,850	756,497	713,273
Ceded premiums written	(1,132,562)	(916,797)	(2,056,344)	(1,593,143)
Ceded premiums earned	(901,882)	(798,325)	(1,799,483)	(1,629,053)
Net premiums written	1,751,451	1,456,395	3,632,521	3,102,873
Net premiums earned	1,568,037	1,360,174	3,065,732	2,690,883
Underwriting [Member]
Effects of Reinsurance [Line Items]
Direct premiums written	1,756,680	1,460,090	3,305,777	2,809,331
Direct premiums earned	1,511,416	1,287,268	2,942,749	2,562,939
Assumed premiums written	344,279	316,905	966,027	895,561
Assumed premiums earned	351,931	346,262	717,829	672,962
Ceded premiums written	(349,037)	(319,772)	(638,350)	(599,161)
Ceded premiums earned	(294,679)	(272,600)	(593,779)	(542,138)
Net premiums written	1,751,922	1,457,223	3,633,454	3,105,731
Net premiums earned	1,568,668	1,360,930	3,066,799	2,693,763
Program services and other fronting [Member]
Effects of Reinsurance [Line Items]
Direct premiums written	737,110	567,864	1,345,147	956,788
Direct premiums earned	582,809	498,381	1,165,969	1,043,724
Assumed premiums written	45,944	28,333	71,914	34,336
Assumed premiums earned	23,763	26,588	38,668	40,311
Ceded premiums written	(783,525)	(597,025)	(1,417,994)	(993,982)
Ceded premiums earned	(607,203)	(525,725)	(1,205,704)	(1,086,915)
Net premiums written	(471)	(828)	(933)	(2,858)
Net premiums earned	$ (631)	$ (756)	$ (1,067)	$ (2,880)

Reinsurance Reinsurance (Effect

Reinsurance Reinsurance (Effect Of Reinsurance And Retrocessional Reinsurance On Losses) (Details) - Underwriting [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Effects of Reinsurance [Line Items]
Gross	$ 993,138	$ 868,069	$ 2,067,061	$ 2,111,626
Ceded	(177,674)	(154,307)	(369,645)	(321,487)
Net losses and loss adjustment expenses	$ 815,464	$ 713,762	$ 1,697,416	$ 1,790,139

Life and Annuity Benefits Lif_2

Life and Annuity Benefits Life and Annuity Benefits (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Liability for Future Policy Benefit, before Reinsurance [Abstract]
Adjustment to life and annuity benefits	$ (0.9)	$ 22.7	$ (50.3)	$ 35.6
Cumulative adjustment to life and annuity benefits	$ 69.3		$ 69.3		$ 119.6

Debt (Details)

Debt (Details) - USD ($) $ in Thousands	May 04, 2021	Jun. 30, 2021	Dec. 31, 2020
Debt Disclosure [Abstract]
Senior long-term debt and other debt (estimated fair value)		$ 4,868,000	$ 4,367,000
Debt Instrument [Line Items]
Senior long-term debt and other debt (estimated fair value)		$ 4,868,000	$ 4,367,000
Three Point Four Five Percent Unsecured Senior Notes Due May 2052
Debt Disclosure [Abstract]
Debt Instrument, Face Amount	$ 600,000
Debt Instrument, Interest Rate, Stated Percentage	3.45%
Proceeds from Debt, Net of Issuance Costs	$ 591,400
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 Disclosure [Abstract]
Debt Instrument, Interest Rate, Stated Percentage		4.90%
Senior long-term debt and other debt (estimated fair value)		$ 350,000
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	Jun. 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	$ 41.1	$ 58.5
Unconsolidated Markel CATCo Funds [Member]
Variable Interest Entity [Line Items]
Net assets under management of MCIM for unconsolidated VIEs	$ 726.6	$ 929.2

Related Party Transactions Re_2

Related Party Transactions Related Party Transactions (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Services and other revenues	$ 569,120	$ 341,402	$ 1,019,346	$ 587,396
Gross premium volume	2,884,013	2,373,192	5,688,865	4,696,016
Ceded premiums written	1,132,562	916,797	2,056,344	1,593,143
Reinsurance recoverables	6,484,269		6,484,269		$ 5,989,337
Syndicate 2357 and certain other Nephila Reinsurers [Member]
Related Party Transaction [Line Items]
Gross premium volume	186,700	122,900	304,000	213,400
Ceded premiums written			304,000	213,400
Reinsurance recoverables	466,700		466,700		$ 353,800
Hagerty Group, LLC [Member]
Related Party Transaction [Line Items]
Gross premium volume	176,800	154,000	296,700	254,900
Ceded premiums written	100,500	72,800	168,400	120,600
Insurance-linked Securities Operations [Member] | Unconsolidated entities managed by Nephila [Member]
Related Party Transaction [Line Items]
Services and other revenues	$ 42,000	$ 42,200	$ 70,700	$ 83,700

Shareholders' Equity (Details)

Shareholders' Equity (Details) - USD ($)	May 27, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 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		0
Earnings Per Share [Line Items]
Issuance of stock			$ 0		$ 0
Shares, Issued		13,734,000	13,776,000	13,734,000	13,776,000	13,765,000	13,783,000	13,775,000	13,794,000
Repurchase of common stock, shares		(33,000)	0	(52,000)	(21,000)
Shares, Outstanding		13,765,000	13,775,000	13,765,000	13,775,000		13,783,000		13,794,000
Preferred stock dividends		$ 0		$ 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		2,000	1,000	3,000	3,000

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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Line Items]
Net income (loss) to common stockholders	$ 774,110	$ 921,768	$ 1,347,804	$ (483,995)
Adjustment of redeemable noncontrolling interests	13,717	(13,073)	21,623	2,940
Adjusted net income (loss) to common shareholders	$ 787,827	$ 908,695	$ 1,369,427	$ (481,055)
Basic common shares outstanding	13,793	13,808	13,806	13,812
Diluted shares outstanding	13,817	13,821	13,828	13,812
Basic net income (loss) per common share	$ 57.12	$ 65.81	$ 99.19	$ (34.83)
Diluted net income (loss) per common share	$ 57.02	$ 65.75	$ 99.03	$ (34.83)	[1]
Restricted Stock Units (RSUs) [Member]
Earnings Per Share [Line Items]
Dilutive potential common shares from restricted stock units and restricted stock	24	13	22	0	[1]
Potential incremental common shares attributable to share-based payment arrangements				11
[1]	The impact of restricted stock units and restricted stock of 11 thousand shares was excluded from the computation of diluted earnings per common share for the six months ended June 30, 2020 because the effect would have been anti-dilutive.

Commitments and Contingencies (

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	Jul. 01, 2021	Jun. 30, 2021
Subsequent Event
Loss Contingencies [Line Items]
Investor Capital in Lodgepine Fund Limited	$ 98.9
Investment in Lodgepine Fund Limited	$ 18.9
Lodgepine Fund Limited [Member]
Loss Contingencies [Line Items]
Other commitment		$ 100

Uncategorized Items - mkl-20210

Label	Element	Value
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
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)
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
Common Stock [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	mkl_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance	3,404,919,000
Preferred Stock [Member]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	mkl_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterestAdjustedBalance	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)
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
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)