v3.26.3
Loss and Loss Adjustment Expense Reserves (Schedule of Losses and Loss Adjustment Expenses Reserves and Recoveries) (Detail) - USD ($)
$ in Millions
Sep. 30, 2026
Dec. 31, 2025
Loss And Lae Reserves [Member]    
Loss And Loss Adjustment Expense Reserves [Line Items]    
Loss and loss adjustment expense reserves [1] $ 399 $ 454
Insurance Loss Recoverable [Member]    
Loss And Loss Adjustment Expense Reserves [Line Items]    
Insurance Loss Recoverable 74 43
Non Variable Interest Entity [Member]    
Loss And Loss Adjustment Expense Reserves [Line Items]    
Insurance Loss Recoverable 74 43
Loss and loss adjustment expense reserves 399 454
US Public Finance Insurance [Member]    
Loss And Loss Adjustment Expense Reserves [Line Items]    
Insurance Loss Recoverable 53 22
Loss and loss adjustment expense reserves [1] 184 219
International And Structured Finance Insurance [Member]    
Loss And Loss Adjustment Expense Reserves [Line Items]    
Insurance Loss Recoverable 21 21
Loss and loss adjustment expense reserves [1] 210 229
International And Structured Finance Insurance [Member] | Non Variable Interest Entity [Member]    
Loss And Loss Adjustment Expense Reserves [Line Items]    
Insurance Loss Recoverable 21 21
Loss and loss adjustment expense reserves [1] 215 235
Consolidation Elimination [Member] | International And Structured Finance Insurance [Member] | Variable Interest Entity, Primary Beneficiary [Member]    
Loss And Loss Adjustment Expense Reserves [Line Items]    
Insurance Loss Recoverable 0 0
Loss and loss adjustment expense reserves [1] $ 5 $ 6
[1] Amounts are net of estimated recoveries of expected future claims.