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Investments (Narrative) (Detail)
$ in Millions
 12 Months Ended
Dec. 31, 2024
USD ($)
Security
Dec. 31, 2023
USD ($)
Security
Dec. 31, 2022
USD ($)
Schedule Of Investments [Line Items]      
Fair value of securities on deposit with various regulatory authorities $ 11 $ 11  
Number of securities in unrealized loss position for a continuous 12 month period | Security 366 450  
Rate that a security's fair value is below book value 5.00% 5.00%  
Increase decrease in other net realized (gains) losses $ 13 $ 29 $ (11)
Asset Pledged as Collateral [Member]      
Schedule Of Investments [Line Items]      
Fair value of securities pledged as collateral $ 213 $ 241  
Securities In Unrealized Loss Position [Member]      
Schedule Of Investments [Line Items]      
Weighted average contractual maturity period in years for securities in an unrealized loss position 15 years 14 years  
Increase decrease in other net realized (gains) losses   $ 8 $ 21
Fair Value Below Book Value Greater Than Five Percent [Member]      
Schedule Of Investments [Line Items]      
Number of securities in unrealized loss position for a continuous 12 month period | Security 318 365