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	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income Derivatives Qualifying as Hedges, Net of Tax [Roll Forward]
Accumulated gain included in other comprehensive income (loss) at beginning of the period			$ (1,219)
Increase (decrease) in fair value of derivatives that qualify for hedge accounting, net of tax	$ (41)	$ 37	(105)	$ (136)
Accumulated gain included in other comprehensive income (loss) at end of the period	(1,325)		(1,325)
Accumulated net gain (loss) from cash flow hedges
Accumulated Other Comprehensive Income Derivatives Qualifying as Hedges, Net of Tax [Roll Forward]
Accumulated gain included in other comprehensive income (loss) at beginning of the period	81	79	86	37
Increase (decrease) in fair value of derivatives that qualify for hedge accounting, net of tax	19	(22)	14	20
Accumulated gain included in other comprehensive income (loss) at end of the period	$ 100	$ 57	$ 100	$ 57