Stockholders' Equity - Accumulated other comprehensive income/ (loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ (629)
Other comprehensive (loss)/gain, net of tax	(97)	$ (124)	$ 95
Ending balance	(726)	(629)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	2,708	2,185	1,786	$ 1,499
Accumulated Other Comprehensive (Loss)/ Income
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive (loss)/gain, net of tax	(97)	(124)	93
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(726)	(629)	(505)	(598)
Derivatives Net Unrealized Losses
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive (loss)/gain, net of tax	4	(1)	(11)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	0	(4)	(3)	$ 8
Accumulated Other Comprehensive Income (Loss), Derivative Qualifying as Hedge, Excluded Component, Including Portion Attributable to Noncontrolling Interest [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	9	0	0
Other comprehensive (loss)/gain, net of tax	12	9	0
Ending balance	21	9	0
Currency Translation Adjustment, Net Unrealized Losses
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(620)	(487)	(583)
Other comprehensive (loss)/gain, net of tax	(104)	(133)	96
Ending balance	(724)	(620)	(487)
Benefit Plans, Actuarial Gains/ (Losses)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(14)	(15)	(23)
Other comprehensive (loss)/gain, net of tax	(9)	1	8
Ending balance	$ (23)	$ (14)	$ (15)