Derivative Financial Instruments - Summary of Activity in Other Comprehensive Income Related to Derivative Instruments Classified as Cash Flow Hedges and as a Net Investment Hedge (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income Derivatives Qualifying as Hedges, Net of Tax [Roll Forward]
Accumulated gain (loss) included in other comprehensive income (loss) at beginning of the period	$ (929)	$ (589)	$ (552)
Increase in fair value of derivatives that qualify for hedge accounting, net of tax	(290)	(308)	(77)
Accumulated gain (loss) included in other comprehensive income (loss) at end of the period	(1,219)	(929)	(589)
Derivatives designated as hedging instruments | Derivatives in cash flow hedging and net investment hedging relationships
Accumulated Other Comprehensive Income Derivatives Qualifying as Hedges, Net of Tax [Roll Forward]
Accumulated gain (loss) included in other comprehensive income (loss) at beginning of the period	37	(12)	(21)
Accumulated gain (loss) included in other comprehensive income (loss) at end of the period	86	37	(12)
Derivatives designated as hedging instruments | Derivatives in cash flow hedging and net investment hedging relationships | Foreign currency translation adjustment
Accumulated Other Comprehensive Income Derivatives Qualifying as Hedges, Net of Tax [Roll Forward]
Increase in fair value of derivatives that qualify for hedge accounting, net of tax	$ 49	$ 49	$ 9