Investments (Securities Held In Unrealized Loss Position And Insured By Financial Guarantor) (Detail) - Financial Guarantee [Member] $ in Millions	Sep. 30, 2023 USD ($)
Schedule Of Investments [Line Items]
Fair value	$ 100
Unrealized loss	(47)
Insurance loss reserve	20	[1]
Mortgage-backed [Member]
Schedule Of Investments [Line Items]
Fair value	16
Unrealized loss	(5)
Insurance loss reserve	20	[1]
Corporate Obligations [Member]
Schedule Of Investments [Line Items]
Fair value	77
Unrealized loss	(42)
Insurance loss reserve	0	[1]
Other [Member]
Schedule Of Investments [Line Items]
Fair value	7
Unrealized loss	0
Insurance loss reserve	$ 0	[1]

[1] Insurance loss reserve estimates are based on the proportion of par value owned to the total amount of par value insured and are discounted using a discount rate equal to the risk-free rate applicable to the currency and weighted average remaining life of the insurance contract and may differ from the fair value.