Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 197	$ 188	$ 159
Amortization expense relating to capitalized computer software	$ 95	$ 87	$ 61