CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 273	$ 966	$ 892
Other comprehensive income (loss):
Foreign currency translation adjustments	36	(29)	(326)
Unrealized gains (losses) on forward contracts designated as hedges, net of tax	(44)	33	(4)
Unrealized gains (losses) on investments, net of tax	(1)	0	0
Total other comprehensive income (loss)	(9)	4	(330)
Comprehensive income	$ 264	$ 970	$ 562