Investments (Securities Held In Unrealized Loss Position And Insured By Financial Guarantor) (Detail) - Financial Guarantee [Member] $ in Millions	Mar. 31, 2022 USD ($)
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	$ 29
Gross unrealized losses	0
Loss and loss adjustment expense reserves	18	[1]
Mortgage-backed [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	18
Gross unrealized losses	0
Loss and loss adjustment expense reserves	18	[1]
Corporate Obligations [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	11
Gross unrealized losses	0
Loss and loss adjustment expense reserves	$ 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.