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Investments (Securities Held In Unrealized Loss Position And Insured By Financial Guarantor) (Detail) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Schedule Of Investments [Line Items]    
Fair value $ 740 $ 854
Financial Guarantee [Member]    
Schedule Of Investments [Line Items]    
Fair value 95  
Unrealized loss (50)  
Insurance loss reserve [1] 24  
Mortgage-backed [Member] | Financial Guarantee [Member]    
Schedule Of Investments [Line Items]    
Fair value 21  
Unrealized loss (5)  
Insurance loss reserve [1] 24  
Corporate Obligations [Member]    
Schedule Of Investments [Line Items]    
Fair value 327 $ 354
Corporate Obligations [Member] | Financial Guarantee [Member]    
Schedule Of Investments [Line Items]    
Fair value 74  
Unrealized loss (45)  
Insurance loss reserve [1] $ 0  
[1] Insurance loss reserve estimates are based on the proportion of par value owned to the total amount of par value insured and are discounted using a discount rate equal to the risk-free rate applicable to the currency and weighted average remaining life of the insurance contract and may differ from the fair value.