Derivative Financial Instruments - Gain or Loss Recorded on Derivatives Related to Fair Value Option Debt Primarily Due to Changes in Interest Rates (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Total Amount of Gain (Loss) Recognized in Derivative Related Income (Expense)	$ (23)	$ 62	$ (52)	$ 66
Interest rate component [Member] | Gain (loss) on debt designated at fair value and related derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest rate contracts, Gain (loss) on debt designated at fair value and related derivatives, Amount of Gain (loss) Recognzied in Derivative Related Income (Expense)	(6)	25	(7)	40
Currency contracts [Member] | Gain (loss) on debt designated at fair value and related derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Currency contracts, Gain (loss) on debt designated at fair value and related derivatives, Amount of Gain (Loss) Recognzied in Derivative Related Income (Expense)	$ (17)	$ 37	$ (45)	$ 26