Derivative Financial Instruments - Gains and Losses on Derivative Instruments Designated and Qualifying As Hedging Instruments in Cash Flow Hedges (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI on Derivative (Effective Portion)	$ 34	$ 14	$ 153	$ 4
Gain (Loss) Reclassed From AOCI into Income (Effective Portion)	(2)	(4)	(9)	(12)
Gain (Loss) Recognized in Income on the Derivative (Ineffective Portion)	0	0	0	0
Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on the Derivative (Ineffective Portion)	4	17	16	(3)
Foreign exchange contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI on Derivative (Effective Portion)	2	0	3	0
Foreign exchange contracts [Member] | Interest Income Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassed From AOCI into Income (Effective Portion)	0	0	0	0
Foreign exchange contracts [Member] | Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on the Derivative (Ineffective Portion)	0	0	0	0
Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in AOCI on Derivative (Effective Portion)	32	14	150	4
Interest rate contracts [Member] | Interest Income Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Reclassed From AOCI into Income (Effective Portion)	(2)	(4)	(9)	(12)
Interest rate contracts [Member] | Other Income [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss) Recognized in Income on the Derivative (Ineffective Portion)	$ 0	$ 0	$ 0	$ 0