Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 9,119
Ending balance	9,715
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(659)	$ (630)
Other comprehensive income (loss) before reclassifications	11	(20)
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	16	0
Ending balance	(632)	(650)
Unrealized gain (loss) on forward contracts
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	29	(4)
Other comprehensive income (loss) before reclassifications	(28)	2
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	(9)	2
Ending balance	(8)	0
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	1	0
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	(2)	0
Ending balance	0	1
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(629)	(633)
Other comprehensive income (loss) before reclassifications	(16)	(18)
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	5	2
Ending balance	$ (640)	$ (649)