Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 9,119
Ending balance	9,967
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(659)	$ (630)
Other comprehensive income (loss) before reclassifications	20	(20)
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	16	0
Ending balance	(623)	(650)
Unrealized gain (loss) on forward contracts
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	29	(4)
Other comprehensive income (loss) before reclassifications	(38)	(1)
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	(7)	1
Ending balance	(16)	(4)
Unrealized gain (loss) on available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	1	1
Other comprehensive income (loss) before reclassifications	(2)	0
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	(2)	0
Ending balance	(3)	1
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(629)	(633)
Other comprehensive income (loss) before reclassifications	(20)	(21)
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	7	1
Ending balance	$ (642)	$ (653)