Derivative Financial Instruments - Gains and Losses on Derivative Instruments Designated and Qualifying As Hedging Instruments in Cash Flow Hedges (Detail) (Interest rate contracts [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI on Derivative (Effective Portion)	$ 14	$ (205)	$ 4	$ (219)
Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Loss Reclassified from AOCI into Income (Effective Portion)	(4)	(4)	(12)	(9)
Loss Recognized in Income on the Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)		$ (6)		$ (7)