Investments (Narrative) (Detail) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2022 USD ($) security	Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) security
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	140		36
Rate that a security's fair value is below book value	5.00%		5.00%
Increase Decrease In Other Net Realized Gains Losses	$ 13	$ 14
Asset Pledged as Collateral [Member]
Schedule Of Investments [Line Items]
Fair value of securities pledged as collateral	$ 282		$ 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	$ 2
Debt securities intent to sell impairment	$ 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	135		7