Unpaid Losses And Loss Adjustment Expenses (Reconciliation Of Consolidated Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Gross reserves for losses and loss adjustment expenses, beginning of year	$ 23,483,321	$ 20,947,898	$ 18,178,894
Reinsurance recoverables on unpaid losses, beginning of year	8,820,567	7,994,884	6,876,317
Net reserves for losses and loss adjustment expenses, beginning of year	14,662,754	12,953,014	11,302,577
Effect of foreign currency rate changes on beginning of year balance	(78,702)	70,344	(160,622)
Adjusted net reserves for losses and loss adjustment expenses, beginning of year	14,584,052	13,023,358	11,141,955
Incurred losses and loss adjustment expenses, current accident year	5,508,059	5,360,559	4,613,035
Incurred losses and loss adjustment expenses, prior accident years (including deposit liability)	(455,310)	(38,550)	(167,446)
Total incurred losses and loss adjustment expenses	5,052,749	5,322,009	4,445,589
Payments, current accident year	720,178	729,895	580,537
Payments, prior accident years	3,239,999	2,663,165	2,396,446
Total payments	3,960,177	3,393,060	2,976,983
Effect of foreign currency rate changes on current year activity	(3,934)	(1,532)	(5,468)
Net reserves for losses and loss adjustment expenses of Markel CATCo Re	(159,963)	(162,954)	347,921
Reinsurance Recoverable, Retroactive Reinsurance Transaction	0	(125,067)	0
Net reserves for losses and loss adjustment expenses, end of year	15,512,727	14,662,754	12,953,014
Reinsurance recoverables on unpaid losses, end of year	11,120,367	8,820,567	7,994,884
Gross reserves for losses and loss adjustment expenses, end of year	$ 26,633,094	$ 23,483,321	$ 20,947,898

The liability as of the balance sheet date for amounts representing estimated cost of settling unpaid claims under the terms of the underlying insurance policies, less estimated reinsurance recoveries on such claims, adjusted for foreign currency movements, commutations and other events. The liability includes an estimate for claims which have been incurred but not reported. Claim adjustment expenses represent the costs estimated to be incurred in the settlement of unpaid claims.

No definition available.