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Markel Group (Parent Company Only) Financial Information (Narrative) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Revolving Credit Facility [Member]    
Condensed Financial Statements, Captions [Line Items]    
Borrowings outstanding under the facility $ 0.0 $ 0.0
Markel Ventures [Member]    
Condensed Financial Statements, Captions [Line Items]    
Debt Guaranteed by Parent 788.0 738.0
Markel Ventures [Member] | Revolving Credit Facility [Member]    
Condensed Financial Statements, Captions [Line Items]    
Borrowings outstanding under the facility $ 150.0 $ 169.5