Accumulated Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (913)	$ (724)	$ (995)	$ (897)
Other comprehensive income/(loss) before reclassifications	144	(71)	212	100
Amounts reclassified from accumulated other comprehensive (income)/loss	16	4	30	6
Other comprehensive income/(loss)	160	(67)	242	106
Balance at end of period	(753)	(791)	(753)	(791)
Foreign currency translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(914)	(725)	(994)	(897)
Other comprehensive income/(loss) before reclassifications	158	(65)	238	107
Amounts reclassified from accumulated other comprehensive (income)/loss	0	0	0	0
Other comprehensive income/(loss)	158	(65)	238	107
Balance at end of period	(756)	(790)	(756)	(790)
Derivative financial instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	1	1	(1)	0
Other comprehensive income/(loss) before reclassifications	(15)	(4)	(27)	(5)
Amounts reclassified from accumulated other comprehensive (income)/loss	16	4	30	6
Other comprehensive income/(loss)	1	0	3	1
Balance at end of period	2	1	2	1
Available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	0	0	0	0
Other comprehensive income/(loss) before reclassifications	1	(2)	1	(2)
Amounts reclassified from accumulated other comprehensive (income)/loss	0	0	0	0
Other comprehensive income/(loss)	1	(2)	1	(2)
Balance at end of period	$ 1	$ (2)	$ 1	$ (2)