Investments (Narrative) (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) security	Dec. 31, 2021 USD ($) security	Dec. 31, 2020 USD ($)
Schedule Of Investments [Line Items]
Fair value of securities on deposit with various regulatory authorities	$ 10	$ 11
Number of securities in unrealized loss position for a continuous 12 month period | security	210	36
Rate that a security's fair value is below book value	5.00%	5.00%
Increase Decrease In Other Net Realized Gains Losses	$ (7)	$ 21	$ (37)
Asset Pledged as Collateral [Member]
Schedule Of Investments [Line Items]
Fair value of securities pledged as collateral	$ 251	$ 280
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	11 years
Increase Decrease In Other Net Realized Gains Losses	$ 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	190	7