Derivative Instruments - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Maximum maturity of foreign currency exchange contracts	18 months
Net derivative losses related to cash flow hedges to be reclassified into earnings within the next 12 months	$ 111
Derivative asset, offset	56	$ 44
Derivative liability, offset	53	$ 44
Derivative liability, collateral, right to reclaim cash, offset	$ 38