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Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Assets	$ 52,748,716	$ 49,791,259
Other [Member]
Segment Reporting Information [Line Items]
Assets	8,898,006	8,639,743
Segment assets [Member]
Segment Reporting Information [Line Items]
Assets	43,850,710	41,151,516
Segment assets [Member] | Investing [Member]
Segment Reporting Information [Line Items]
Assets	28,522,052	26,982,280
Segment assets [Member] | Underwriting [Member]
Segment Reporting Information [Line Items]
Assets	9,884,553	8,853,559
Segment assets [Member] | Markel Ventures [Member]
Segment Reporting Information [Line Items]
Assets	$ 5,444,105	$ 5,315,677

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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