Accumulated Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (784)	$ (753)	$ (592)	$ (995)
Other comprehensive income/(loss) before reclassifications	(2)	136	(118)	348
Amounts reclassified from accumulated other comprehensive (income)/loss	(42)	11	(118)	41
Other comprehensive income/(loss)	(44)	147	(236)	389
Balance at end of period	(828)	(606)	(828)	(606)
Foreign currency translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(776)	(756)	(587)	(994)
Other comprehensive income/(loss) before reclassifications	(44)	151	(233)	389
Amounts reclassified from accumulated other comprehensive (income)/loss	0	0	0	0
Other comprehensive income/(loss)	(44)	151	(233)	389
Balance at end of period	(820)	(605)	(820)	(605)
Derivative financial instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(8)	2	(5)	(1)
Other comprehensive income/(loss) before reclassifications	42	(14)	115	(41)
Amounts reclassified from accumulated other comprehensive (income)/loss	(42)	11	(118)	41
Other comprehensive income/(loss)	0	(3)	(3)	0
Balance at end of period	(8)	(1)	(8)	(1)
Available-for-sale securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	0	1	0	0
Other comprehensive income/(loss) before reclassifications	0	(1)	0	0
Amounts reclassified from accumulated other comprehensive (income)/loss	0	0	0	0
Other comprehensive income/(loss)	0	(1)	0	0
Balance at end of period	$ 0	$ 0	$ 0	$ 0