Accumulated Other Comprehensive Income/(Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of year	$ (592)	$ (995)	$ (897)
Other comprehensive income/(loss) before reclassifications	(204)	358	(82)
Amounts reclassified from accumulated other comprehensive (income)/loss	(129)	45	(16)
Other comprehensive income/(loss)	(333)	403	(98)
Balance at end of year	(925)	(592)	(995)
Foreign currency translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of year	(587)	(994)	(897)
Other comprehensive income/(loss) before reclassifications	(302)	407	(97)
Amounts reclassified from accumulated other comprehensive (income)/loss	0	0	0
Other comprehensive income/(loss)	(302)	407	(97)
Balance at end of year	(889)	(587)	(994)
Derivative financial instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of year	(5)	(1)	0
Other comprehensive income/(loss) before reclassifications	98	(49)	15
Amounts reclassified from accumulated other comprehensive (income)/loss	(129)	45	(16)
Other comprehensive income/(loss)	(31)	(4)	(1)
Balance at end of year	$ (36)	$ (5)	$ (1)