Investments (Securities Held In Unrealized Loss Position And Insured By Financial Guarantor) (Detail) - Financial Guarantee [Member]	Jun. 30, 2020 USD ($)
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	$ 15
Gross unrealized losses	(6)
Loss and loss adjustment expense reserves	21	[1]
MBS [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	9
Gross unrealized losses	(6)
Loss and loss adjustment expense reserves	21	[1]
Corporate Obligations [Member]
Schedule Of Investments [Line Items]
Total Available-For-Sale, Fair Value	6
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.