Accumulated Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (753)	$ (791)	$ (995)	$ (897)
Other comprehensive income/(loss) before reclassifications	136	(14)	348	86
Amounts reclassified from accumulated other comprehensive (income)/loss	11	7	41	13
Other comprehensive income/(loss)	147	(7)	389	99
Balance at end of period	(606)	(798)	(606)	(798)
Foreign currency translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(756)	(790)	(994)	(897)
Other comprehensive income/(loss) before reclassifications	151	(5)	389	102
Amounts reclassified from accumulated other comprehensive (income)/loss	0	0	0	0
Other comprehensive income/(loss)	151	(5)	389	102
Balance at end of period	(605)	(795)	(605)	(795)
Derivative financial instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	2	1	(1)	0
Other comprehensive income/(loss) before reclassifications	(14)	(10)	(41)	(15)
Amounts reclassified from accumulated other comprehensive (income)/loss	11	7	41	13
Other comprehensive income/(loss)	(3)	(3)	0	(2)
Balance at end of period	(1)	(2)	(1)	(2)
Available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	1	(2)	0	0
Other comprehensive income/(loss) before reclassifications	(1)	1	0	(1)
Amounts reclassified from accumulated other comprehensive (income)/loss	0	0	0	0
Other comprehensive income/(loss)	(1)	1	0	(1)
Balance at end of period	$ 0	$ (1)	$ 0	$ (1)