Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Segment Reporting Information [Line Items]
Assets	$ 68,602,357	$ 68,905,050
Corporate and eliminations
Segment Reporting Information [Line Items]
Assets	4,268,430	4,397,391
Segment assets [Member]
Segment Reporting Information [Line Items]
Assets	64,333,927	64,507,659
Segment assets [Member] \| Markel Insurance
Segment Reporting Information [Line Items]
Assets	43,473,248	44,314,601
Segment assets [Member] \| Industrial
Segment Reporting Information [Line Items]
Assets	3,989,709	3,965,449
Segment assets [Member] \| Financial
Segment Reporting Information [Line Items]
Assets	15,057,582	14,444,426
Segment assets [Member] \| Consumer and Other
Segment Reporting Information [Line Items]
Assets	$ 1,813,388	$ 1,783,183

Amount of asset recognized for present right to economic benefit.

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+ Details