Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of unrecognized tax benefits
Unrecognized tax benefits as of January 1,	$ 17	$ 23	$ 20
Gross increases and decreases - tax positions taken during a prior period	1	2	0
Gross increases and decreases—tax positions taken during the current period	0	0	1
Decreases related to settlements of amounts due to tax authorities	0	0	0
Reductions resulting from the lapse of statutes of limitation	(2)	(7)	0
Foreign currency movements			2
Foreign currency movements	0	(1)
Unrecognized tax benefits as of December 31,	$ 16	$ 17	$ 23