Unpaid Losses And Loss Adjustment Expenses (Reconciliation Of Consolidated Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Gross reserves for losses and loss adjustment expenses, beginning of year	$ 30,857,453	$ 26,633,094
Reinsurance recoverable on unpaid losses, beginning of year	14,150,484	11,120,367
Net reserves for losses and loss adjustment expenses, beginning of year	16,706,969	15,512,727
Effect of foreign currency rate changes on beginning of year balance	(36,345)	56,701
Adjusted net reserves for losses and loss adjustment expenses, beginning of year	16,670,624	15,569,428
Incurred losses and loss adjustment expenses, current accident year	1,270,880	1,404,772
Incurred losses and loss adjustment expenses, prior accident years	(104,063)	(150,107)
Total incurred losses and loss adjustment expenses	1,166,817	1,254,665
Payments, current accident year	35,061	50,284
Payments, prior accident years	1,099,676	901,098
Total payments	1,134,737	951,382
Effect of foreign currency rate changes on current year activity	(582)	54
Net reserves for losses and loss adjustment expenses of Markel CATCo Re	0	(121)
Retroactive reinsurance transaction with Hagerty Re, net losses and loss adjustment expenses	(62,202)	0
Net reserves for losses and loss adjustment expenses, end of period	16,639,920	15,872,644
Reinsurance recoverable on unpaid losses	14,730,616	12,015,613
Gross reserves for losses and loss adjustment expenses, end of period	$ 31,370,536	$ 27,888,257

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.