Investments (Narrative) (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2023 USD ($) security	Dec. 31, 2022 USD ($) security
Schedule Of Investments [Line Items]
Fair value of securities on deposit with various regulatory authorities | $	$ 10	$ 10
Number of securities in unrealized loss position for a continuous 12 month period | security	495	210
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 | $	$ 228	$ 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
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	444	190