Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Unrecognized tax benefits roll forward
Gross unrecognized tax benefits at beginning of period	$ (20)	$ (13)	$ (11)
Increases in tax positions for current year		(9)	(1)
Increases in tax positions for prior years	0	0	(4)
Decreases in tax positions for prior years	0	0	3
Lapse in statute of limitations		2	0
Gross unrecognized tax benefits at end of period	$ (20)	$ (20)	$ (13)