Derivative Instruments (Effect Of Derivative Instruments On Consolidated Statements Of Operations) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative [Line Items]
Net gain/(loss) recognized in income	$ (8)	$ (46)	$ (58)	$ (56)
Unrealized Gains Losses On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	0	1	(1)	14
Realized Gains Losses And Other Settlements On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	0	(1)	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	(3)	(35)	(59)	(55)
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	(5)	(2)	5	(5)
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	$ (9)	$ (3)	$ (9)