Derivative Instruments (Effect Of Derivative Instruments On Consolidated Statements Of Operations) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative [Line Items]
Net gain/(loss) recognized in income	$ 4	$ (48)	$ (54)	$ (104)
Unrealized Gains Losses On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	0	9	(1)	23
Realized Gains Losses And Other Settlements On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	0	(10)	0	(11)
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	6	(30)	(53)	(85)
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	(1)	(3)	4	(8)
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	$ (1)	$ (14)	$ (4)	$ (23)