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v3.25.0.1

Senior Long-Term Debt And Other Debt (Narrative) (Details) - USD ($) $ in Thousands |  | 12 Months Ended
--- | --- | ---
May 15, 2024 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Debt Instrument [Line Items] |  |  |  |
Senior long-term debt and other debt |  | $ 4,330,341 | $ 3,779,796 |
Senior long-term debt and other debt, estimated fair value |  | $ 3,800,000 | 3,400,000 |
Line of credit facility, initiation date |  | Jun. 23, 2023 |  |
Line of credit facility, expiration date |  | Jun. 23, 2028 |  |
Interest on senior long-term debt and other debt |  | $ 197,400 | 187,800 | $ 197,300
Revolving Credit Facility [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Line of credit facility, increase (decrease), net |  | $ 200,000 |  |
Line of credit facility, unused capacity, commitment fee percentage |  | 0.20% |  |
Borrowings outstanding under the facility |  | $ 0 | 0 |
Revolving Credit Facility [Member] | Markel Ventures [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Line of credit facility, capacity available |  | 692,000 |  |
Borrowings outstanding under the facility |  | 150,000 | 169,500 |
Revolving Credit Facility [Member] | Secured Letters Of Credit [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Line of credit facility, capacity available |  | 200,000 |  |
Previous line of credit facility |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Line of credit facility, capacity available |  | 300,000 |  |
Unsecured Senior Notes [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Senior long-term debt and other debt |  | 4,032,959 |  |
Other Debt [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Senior long-term debt and other debt |  | 297,382 | 340,597 |
Other Debt [Member] | Markel Ventures [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Senior long-term debt and other debt |  | $ 297,400 | 339,000 |
7.35% Unsecured Senior Notes Due August 15, 2034 [Member] | Unsecured Senior Notes [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt instrument, interest rate |  | 7.35% |  |
3.625% Unsecured Senior Notes Due March 30, 2023 [Member] | Unsecured Senior Notes [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt instrument, face amount |  |  | $ 250,000 |
Debt instrument, interest rate |  |  | 3.625% |
6.0% Unsecured Senior Notes due May 16 2054 |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Net proceeds from issuance of unsecured senior notes | $ 592,600 |  |  |
6.0% Unsecured Senior Notes due May 16 2054 | Unsecured Senior Notes [Member] |  |  |  |
Debt Instrument [Line Items] |  |  |  |
Debt instrument, face amount | $ 600,000 |  |  |
Debt instrument, interest rate | 6.00% | 6.00% |  |

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