Derivative Instruments (Effect Of Derivative Instruments On Consolidated Statements Of Operations) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative [Line Items]
Net gain/(loss) recognized in income	$ (46)	$ 0	$ (56)	$ 8
Unrealized Gains Losses On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	1	18	14	32
Realized Gains Losses And Other Settlements On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	(1)	(25)	(1)	(44)
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)	7	(55)	25
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	(9)	0	(9)	0
Net gains (losses) on financial instruments at fair value and foreign exchange-VIE [Member] | Currency Swaps Vie [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	$ (2)	$ 0	$ (5)	$ (5)