Segment Reporting Disclosures (Reconciliation Of Segment Assets To The Company's Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Segment Reporting [Line Items]
Assets	$ 71,263,146	$ 68,905,050
Corporate and eliminations
Segment Reporting [Line Items]
Assets	3,867,405	4,397,391
Segment assets [Member]
Segment Reporting [Line Items]
Assets	67,395,741	64,507,659
Segment assets [Member] \| Markel Insurance
Segment Reporting [Line Items]
Assets	46,220,751	44,314,601
Segment assets [Member] \| Industrial
Segment Reporting [Line Items]
Assets	4,068,516	3,965,449
Segment assets [Member] \| Financial
Segment Reporting [Line Items]
Assets	15,235,325	14,444,426
Segment assets [Member] \| Consumer and Other
Segment Reporting [Line Items]
Assets	$ 1,871,149	$ 1,783,183

Amount of asset recognized for present right to economic benefit.

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+ Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details