Derivative Instruments (Effect Of Derivative Instruments On Consolidated Statements Of Operations) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative [Line Items]
Net gain/(loss) recognized in income	$ 37	$ (50)
Unrealized Gains Losses On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	0	(1)
Net gains (losses) on financial instruments at fair value and foreign exchange [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	35	(56)
Net gains (losses) on financial instruments at fair value and foreign exchange [Member] | Currency Swaps Vie [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	2	10
Net gains (losses) on financial instruments at fair value and foreign exchange [Member] | All Other [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	$ 0	$ (3)