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, 2015	Mar. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Total Amount of Gain (Loss) Recognized in Derivative Related Income (Expense)	$ (16)	$ 11
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) Recognized in Derivative Related Income (Expense)	2	3
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) Recognized in Derivative Related Income (Expense)	$ (18)	$ 8