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, 2016	Dec. 31, 2015	Dec. 31, 2014
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	$ (1,219)
Increase in fair value of derivatives that qualify for hedge accounting, net of tax	(153)	$ (290)	$ (308)
Accumulated gain included in other comprehensive income at end of the period	(1,326)	(1,219)
Fair value of derivatives that qualify for hedge accounting, tax	23	30	31
Accumulated net gain (loss) from cash flow hedges
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	86	37	(12)
Increase in fair value of derivatives that qualify for hedge accounting, net of tax	38	49	49
Accumulated gain included in other comprehensive income at end of the period	$ 124	$ 86	$ 37