v3.26.1
Loss and Loss Adjustment Expense Reserves (Schedule of Losses and Loss Adjustment Expenses Reserves and Recoveries) (Detail) - USD ($)
$ in Millions
Mar. 31, 2026
Dec. 31, 2025
Loss And Lae Reserves [Member]    
Loss And Loss Adjustment Expense Reserves [Line Items]    
Loss and loss adjustment expense reserves [1] $ 437 $ 454
Insurance Loss Recoverable [Member]    
Loss And Loss Adjustment Expense Reserves [Line Items]    
Insurance Loss Recoverable 47 43
Non Variable Interest Entity [Member]    
Loss And Loss Adjustment Expense Reserves [Line Items]    
Insurance Loss Recoverable 47 43
Loss and loss adjustment expense reserves 437 454
US Public Finance Insurance [Member]    
Loss And Loss Adjustment Expense Reserves [Line Items]    
Insurance Loss Recoverable 25 22
Loss and loss adjustment expense reserves [1] 208 219
International And Structured Finance Insurance [Member]    
Loss And Loss Adjustment Expense Reserves [Line Items]    
Insurance Loss Recoverable 22 21
Loss and loss adjustment expense reserves [1] 223 229
International And Structured Finance Insurance [Member] | Non Variable Interest Entity [Member]    
Loss And Loss Adjustment Expense Reserves [Line Items]    
Insurance Loss Recoverable 22 21
Loss and loss adjustment expense reserves [1] 229 235
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] $ 6 $ 6
[1] Amounts are net of estimated recoveries of expected future claims.