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
	Mar. 31, 2013	Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Total Amount of Gain (Loss) Recognized in Derivative Related Income (Expense)	$ (29)	$ 4
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)	(1)	15
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)	$ (28)	$ (11)