Derivative Instruments - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jul. 31, 2014
Derivative [Line Items]
Net derivative gains to be reclassified into earnings within the next 12 months	$ 109		$ 109
Derivative asset offset against collateral	51		51
Derivative liability offset against collateral	51		51
Net derivative assets	109		109
Net derivative liabilities	10		10
Gain (loss) recognized from derivative contracts in the condensed consolidated statement of income	(33)	$ 39	(129)	$ 70
Interest Rate Swap | Fair Value Hedging | Designated as Hedging Instrument
Derivative [Line Items]
Derivative liability					$ 2,400
Interest and Other, Net | Foreign Exchange Contract | Not Designated as Hedging Instrument
Derivative [Line Items]
Gain (loss) recognized from derivative contracts in the condensed consolidated statement of income	41	$ 12	15	$ 22
Interest and Other, Net | Future | Foreign Exchange Contract | Not Designated as Hedging Instrument
Derivative [Line Items]
Gain (loss) recognized from derivative contracts in the condensed consolidated statement of income	$ 15		$ 15