Derivative Instruments (Effect Of Derivative Instruments On Consolidated Statements Of Operations) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Net gain/(loss) recognized in income	$ (68)	$ (15)	$ 69
Unrealized Gains Losses On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	0	21	157
Realized Gains Losses And Other Settlements On Insured Derivatives [Member] | Credit Default Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	(51)	(40)	(28)
Foreign Exchange And Other Derivative Financial Instruments [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	3	(11)	(108)
Foreign Exchange And Other Derivative Financial Instruments [Member] | All Other [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	(19)	(2)	7
Foreign Exchange And Other Derivative Financial Instruments Attributable To V I E [Member] | Interest Rate Swaps V I E [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	0	8	31
Foreign Exchange And Other Derivative Financial Instruments Attributable To V I E [Member] | Currency Swaps Vie [Member]
Derivative [Line Items]
Net gain/(loss) recognized in income	$ (1)	$ 9	$ 10