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Segment Reporting Disclosures (Narrative) (Details) - segment | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Segment Reporting Information [Line Items] |  |  |
Number of Reportable Segments | 4 |  |
Segment Reporting, CODM, Individual Title and Position or Group Name [Extensible Enumeration] | Chief Executive Officer [Member] |  |
Segment Reporting, CODM, Profit (Loss) Measure, How Used, Description | The chief operating decision maker uses segment operating income to assess the performance of each segment and determine how to allocate capital. The chief operating decision maker allocates capital where he believes it will earn an appropriate return. |  |
Underwriting Operations [Member] | United States [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Percentage of gross premiums written | 75.00% | 75.00% | 75.00%
Markel Ventures [Member] | United States [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Percentage of revenue attributable to U.S. | 94.00% | 95.00% | 96.00%

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- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 47 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482785/280-10-55-47 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 54 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482785/280-10-55-54 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-18 + Details
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- Definition Indicates title and position of individual or name of group identified as chief operating decision maker (CODM) for segment reporting. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 54 -Subparagraph (f) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482785/280-10-55-54 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 47 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482785/280-10-55-47 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 280 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 21 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482810/280-10-50-21 + Details
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