Investments (Securities Held In Unrealized Loss Position And Insured By Financial Guarantor) (Detail) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Schedule of Investments [Line Items]
Fair value		$ 870	$ 854
Financial Guarantee [Member]
Schedule of Investments [Line Items]
Fair value		95
Unrealized loss		(43)
Insurance loss reserve	[1]	22
Mortgage-backed [Member] | Financial Guarantee [Member]
Schedule of Investments [Line Items]
Fair value		17
Unrealized loss		(4)
Insurance loss reserve	[1]	22
Corporate Obligations [Member]
Schedule of Investments [Line Items]
Fair value		359	$ 354
Corporate Obligations [Member] | Financial Guarantee [Member]
Schedule of Investments [Line Items]
Fair value		78
Unrealized loss		(39)
Insurance loss reserve	[1]	$ 0

[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.