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Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Assets	$ 57,286,385	$ 55,045,710
Other Insurance Operations [Member]
Segment Reporting Information [Line Items]
Assets	9,645,732	9,086,197
Segment assets [Member]
Segment Reporting Information [Line Items]
Assets	47,640,653	45,959,513
Segment assets [Member] | Investing [Member]
Segment Reporting Information [Line Items]
Assets	31,699,863	30,542,282
Segment assets [Member] | Underwriting Segments [Member]
Segment Reporting Information [Line Items]
Assets	10,317,034	9,897,689
Segment assets [Member] | Markel Ventures [Member]
Segment Reporting Information [Line Items]
Assets	$ 5,623,756	$ 5,519,542

X

- Definition

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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