Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2025	Dec. 31, 2024
Segment Reporting Information [Line Items]
Assets	$ 66,791,177	$ 61,897,982
Other Insurance Operations [Member]
Segment Reporting Information [Line Items]
Assets	12,290,158	11,070,570
Segment assets [Member]
Segment Reporting Information [Line Items]
Assets	54,501,019	50,827,412
Segment assets [Member] \| Investing [Member]
Segment Reporting Information [Line Items]
Assets	35,365,983	34,272,049
Segment assets [Member] \| Markel Insurance
Segment Reporting Information [Line Items]
Assets	13,092,554	10,731,134
Segment assets [Member] \| Markel Ventures [Member]
Segment Reporting Information [Line Items]
Assets	$ 6,042,482	$ 5,824,229

Amount of asset recognized for present right to economic benefit.

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+ Details