Derivative Instruments (Effect Of Derivative Instruments On Consolidated Statements Of Operations) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Net gain/(loss) recognized in income	$ (85)	$ (27)	$ (68)
Unrealized Gains Losses On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	25	31	0
Realized Gains Losses And Other Settlements On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	(10)	(56)	(51)
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	(66)	4	3
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	(26)	(4)	(19)
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	$ (8)	$ (2)	$ (1)