v3.26.1
Investments (Narrative) (Detail)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2026
USD ($)
Security
Dec. 31, 2025
USD ($)
Security
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 240 247
Rate that a security's fair value is below book value 5.00% 5.00%
Asset Pledged as Collateral [Member]    
Schedule Of Investments [Line Items]    
Fair value of securities pledged as collateral | $ $ 181 $ 183
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 13 years 14 years
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 212 200