Consolidated Statements Of Changes In Equity - USD ($) $ in Thousands	Total	Total Equity [Member]	Total Shareholders' Equity [Member]	Preferred Stock [Member]	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Noncontrolling Interests [Member]	Redeemable Noncontrolling Interests [Member]
Balance at Dec. 31, 2022		$ 13,213,885	$ 13,151,094	$ 591,891	$ 3,493,893	$ 9,832,804	$ (767,494)	$ 62,791
Balance, redeemable noncontrolling interests at Dec. 31, 2022									$ 523,154
Net Income	$ 1,306,997	1,282,694	1,226,754			1,226,754	0	55,940	24,303
Other comprehensive income (loss)	(123,257)	(123,340)	(123,340)			0	(123,340)	0	83
Comprehensive Income (Loss)	1,183,740	1,159,354	1,103,414					55,940	24,386
Repurchase of common stock		(269,593)	(269,593)	0	0	(269,593)	0	0	0
Preferred stock dividends		(18,000)	(18,000)	0	0	(18,000)	0	0	0
Equity awards expensed		31,477	31,477	0	31,477	0	0	0	0
Adjustment of redeemable noncontrolling interests		7,087	7,087	0	0	7,087	0	0	(7,087)
Purchase of noncontrolling interest		(5,464)	(5,464)	0	(5,464)	0	0	0	(48,907)
Redemption of Markel CATCo Re noncontrolling interests	(88,997)	(62,646)	0	0	0	0	0	(62,646)	0
Other		(857)	(856)	0	(372)	(485)	1	(1)	(24,160)
Balance at Sep. 30, 2023		14,055,243	13,999,159	591,891	3,519,534	10,778,567	(890,833)	56,084
Balance, redeemable noncontrolling interests at Sep. 30, 2023									467,386
Balance at Jun. 30, 2023		14,239,081	14,185,499	591,891	3,515,362	10,818,989	(740,743)	53,582
Balance, redeemable noncontrolling interests at Jun. 30, 2023									464,442
Net Income	53,268	45,093	42,591			42,591	0	2,502	8,175
Other comprehensive income (loss)	(150,019)	(150,091)	(150,091)			0	(150,091)	0	72
Comprehensive Income (Loss)	(96,751)	(104,998)	(107,500)					2,502	8,247
Repurchase of common stock		(82,432)	(82,432)	0	0	(82,432)	0	0	0
Equity awards expensed		4,949	4,949	0	4,949	0	0	0	0
Adjustment of redeemable noncontrolling interests		(628)	(628)	0	0	(628)	0	0	628
Purchase of noncontrolling interest		(776)	(776)	0	(776)	0	0	0	570
Other		47	47	0	(1)	47	1	0	(6,501)
Balance at Sep. 30, 2023		14,055,243	13,999,159	591,891	3,519,534	10,778,567	(890,833)	56,084
Balance, redeemable noncontrolling interests at Sep. 30, 2023									467,386
Balance at Dec. 31, 2023	15,056,208	15,056,208	14,983,928	591,891	3,517,146	11,353,101	(478,210)	72,280
Balance, redeemable noncontrolling interests at Dec. 31, 2023	469,685								469,685
Net Income	2,285,974	2,253,837	2,197,844			2,197,844	0	55,993	32,137
Other comprehensive income (loss)	284,451	284,355	284,355			0	284,355	0	96
Comprehensive Income (Loss)	2,570,425	2,538,192	2,482,199					55,993	32,233
Repurchase of common stock		(389,089)	(389,089)	0	0	(389,089)	0	0	0
Preferred stock dividends		(18,000)	(18,000)	0	0	(18,000)	0	0	0
Equity awards expensed		46,275	46,275	0	46,275	0	0	0	0
Adjustment of redeemable noncontrolling interests		(81,267)	(81,267)	0	0	(81,267)	0	0	81,267
Purchase of noncontrolling interest		(9,596)	(9,596)	0	(9,596)	0	0	0	(36,896)
Redemption of Markel CATCo Re noncontrolling interests	0
Other		4,612	(211)	0	(1,025)	814	0	4,823	(30,796)
Balance at Sep. 30, 2024	17,147,335	17,147,335	17,014,239	591,891	3,552,800	13,063,403	(193,855)	133,096
Balance, redeemable noncontrolling interests at Sep. 30, 2024	515,493								515,493
Balance at Jun. 30, 2024		15,948,554	15,850,024	591,891	3,546,661	12,329,827	(618,355)	98,530
Balance, redeemable noncontrolling interests at Jun. 30, 2024									476,518
Net Income	946,942	937,525	904,959			904,959	0	32,566	9,417
Other comprehensive income (loss)	424,523	424,499	424,499			0	424,499	0	24
Comprehensive Income (Loss)	1,371,465	1,362,024	1,329,458					32,566	9,441
Repurchase of common stock		(128,897)	(128,897)	0	0	(128,897)	0	0	0
Equity awards expensed		7,164	7,164	0	7,164	0	0	0	0
Adjustment of redeemable noncontrolling interests		(42,565)	(42,565)	0	0	(42,565)	0	0	42,565
Other		1,055	(945)	0	(1,025)	79	1	2,000	(13,031)
Balance at Sep. 30, 2024	17,147,335	$ 17,147,335	$ 17,014,239	$ 591,891	$ 3,552,800	$ 13,063,403	$ (193,855)	$ 133,096
Balance, redeemable noncontrolling interests at Sep. 30, 2024	$ 515,493								$ 515,493