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Loss and Loss Adjustment Expense Reserves (Loss and LAE Activity) (Narrative) (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Loss And Loss Adjustment Expense Reserves [Line Items]      
Weighted average risk-free rate used to discount claim liability 4.50% 3.97%  
Lae [Member]      
Loss And Loss Adjustment Expense Reserves [Line Items]      
Losses and loss adjustment $ 17 $ 6 $ 3
Loss and loss adjustment expense reserves $ 19 $ 8  
Changes in Loss and LAE Reserves one-year