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Loss And Loss Adjustment Expense Reserves (Loss And LAE Activity) (Narrative) (Detail) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2022
Sep. 30, 2021
Sep. 30, 2022
Sep. 30, 2021
Dec. 31, 2021
Loss And Loss Adjustment Expense Reserves [Line Items]          
Weighted average risk-free rate used to discount claim liability     3.90%    
Percentage of voters voted by the deadline     27.00%    
Lae [Member]          
Loss And Loss Adjustment Expense Reserves [Line Items]          
Losses and loss adjustment $ 1 $ 4 $ 4 $ 17  
Loss and loss adjustment expense reserves $ 18   $ 18   $ 38
Changes in Loss and LAE Reserves     one-year