Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Unrecognized Tax Benefits
Unrecognized tax benefits	$ 34	$ 34	$ 28	$ 28
Unrecognized tax benefit, if recognized, would have an impact on effective tax rate				$ 28
Activity for unrecognized tax benefits [Roll Forward]
Balance at beginning of period	34	22	28
Tax positions related to current year additions	1	11	2
Additions for tax positions of prior years	0	2	0
Tax positions related to prior years reductions	0	0	(7)
Reductions due to lapse of statute of limitations on tax positions	(7)	(1)	0
Settlements	0	0	(1)
Balance at end of period	$ 28	$ 34	$ 22