Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ 9,119
Ending balance	9,436
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(659)	$ (630)
Other comprehensive income (loss) before reclassifications	3	(5)
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	16	0
Ending balance	(640)	(635)
Unrealized gain (loss) on forward contracts
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	29	(4)
Other comprehensive income (loss) before reclassifications	(9)	(6)
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	(6)	1
Ending balance	14	(9)
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	0	0
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	0	0
Ending balance	1	1
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(629)	(633)
Other comprehensive income (loss) before reclassifications	(6)	(11)
Amounts reclassified from accumulated other comprehensive income (loss) into earnings	10	1
Ending balance	$ (625)	$ (643)