Derivative Instruments (Effect Of Derivative Instruments On Consolidated Statements Of Operations) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative [Line Items]
Net gain/(loss) recognized in income	$ (48)	$ 2	$ (104)	$ 11
Unrealized Gains Losses On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	9	4	23	36
Realized Gains Losses And Other Settlements On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	(10)	(5)	(11)	(49)
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	(30)	7	(85)	33
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	(14)	(4)	(23)	(4)
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	$ (3)	$ 0	$ (8)	$ (5)