Investments (Narrative) (Detail) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023 USD ($) Security	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) Security	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) Security
Schedule Of Investments [Line Items]
Fair value of securities on deposit with various regulatory authorities	$ 10		$ 10		$ 10
Number of securities in unrealized loss position for a continuous 12 month period | Security	589		589		210
Rate that a security's fair value is below book value	5.00%		5.00%		5.00%
Increase decrease in other net realized (gains) losses			$ 30	$ 13
Asset Pledged as Collateral [Member]
Schedule Of Investments [Line Items]
Fair value of securities pledged as collateral	$ 209		$ 209		$ 251
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
Increase decrease in other net realized (gains) losses	$ 8	$ 2	$ 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	509		509		190