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Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Assets	$ 61,897,982	$ 55,045,710
Investing [Member]
Segment Reporting Information [Line Items]
Assets	34,272,049	30,542,282
Underwriting Operations [Member]
Segment Reporting Information [Line Items]
Assets	10,784,528	9,897,689
Markel Ventures [Member]
Segment Reporting Information [Line Items]
Assets	5,824,229	5,519,542
Other Insurance Operations
Segment Reporting Information [Line Items]
Assets	11,017,176	9,086,197
Segment Assets [Member]
Segment Reporting Information [Line Items]
Assets	$ 50,880,806	$ 45,959,513

X

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Amount of asset recognized for present right to economic benefit.

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