Investments (Securities Held In Unrealized Loss Position And Insured By Financial Guarantor) (Detail) - Financial Guarantee [Member] $ in Millions	Sep. 30, 2022 USD ($)
Schedule Of Investments [Line Items]
Total available-for-sale, fair value	$ 173
Gross unrealized losses	(48)
Loss and loss adjustment expense reserves	111
Mortgage-backed [Member]
Schedule Of Investments [Line Items]
Total available-for-sale, fair value	93
Gross unrealized losses	(17)
Loss and loss adjustment expense reserves	111
Corporate Obligations [Member]
Schedule Of Investments [Line Items]
Total available-for-sale, fair value	74
Gross unrealized losses	(31)
Loss and loss adjustment expense reserves	0
Other [Member]
Schedule Of Investments [Line Items]
Total available-for-sale, fair value	$ 6