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	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Total	$ 143	$ 523	$ 901
Interest rate component [Member] | Gain (loss) on debt designated at fair value and related derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Interest Rate Derivative Fair value Gain (Loss)	70	263	719
Currency contracts [Member] | Gain (loss) on debt designated at fair value and related derivatives [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Foreign Currency Derivative Fair Value Gain (Loss)	$ 73	$ 260	$ 182