Investments (Narrative) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) Security	Dec. 31, 2022 USD ($) Security	Dec. 31, 2021 USD ($)
Schedule Of Investments [Line Items]
Fair value of securities on deposit with various regulatory authorities	$ 11	$ 10
Number of securities in unrealized loss position for a continuous 12 month period | Security	450	210
Rate that a security's fair value is below book value	5.00%	5.00%
Increase decrease in other net realized (gains) losses	$ 30	$ (7)	$ 21
Asset Pledged as Collateral [Member]
Schedule Of Investments [Line Items]
Fair value of securities pledged as collateral	$ 241	$ 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	14 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	365	190