Derivative Financial Instruments - Gain or Loss Recorded on Our Cash Flow Hedging Relationships (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
Derivatives, Fair Value [Line Items]
Gain (Loss) Recognized in AOCI on Derivative (Effective Portion)	$ 55	$ (14)	$ 112	$ 65
Gain (Loss) Reclassed From AOCI into Income (Effective Portion)	(3)	(6)	(208)	(15)
Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Gain (Loss) Recognized in AOCI, Interest Rate Swaps	32	(53)	74	37
Currency swaps [Member]
Derivatives, Fair Value [Line Items]
Gain (Loss) Recognized in AOCI on Derivative (Effective Portion), Currency Swaps	23	39	38	28
Interest Expense [Member] | Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Gain (Loss) Reclassed from AOCI into Income (Effective Portion), Interest Rate Swaps	0	(1)	(1)	(4)
Interest Expense [Member] | Currency swaps [Member]
Derivatives, Fair Value [Line Items]
Gain (Loss) Reclassed from AOCI into Income (Effective Portion), Currency swaps	(3)	(5)	(8)	(11)
Derivative related income (loss) [Member]
Derivatives, Fair Value [Line Items]
Loss on cash flow hedge reclassified to income	0	0	(199)	0
Gain (Loss) Recognized In Income on Derivative (Ineffective Portion)	5	(4)	21	(1)
Derivative related income (loss) [Member] | Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Gain (Loss) Recognized in Income on Derivative (Ineffective Portion), Interest Rate Swaps	0	(1)	2	0
Derivative related income (loss) [Member] | Currency swaps [Member]
Derivatives, Fair Value [Line Items]
Gain (Loss) Recognized in Income on Derivative (Ineffective Portion, Currency swaps)	$ 5	$ (3)	$ 19	$ (1)