Income Taxes - Components of the Provision (Benefit) for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current
Federal									$ 17	$ 0	$ 2
State									6	1	0
Total current income tax expense									23	1	2
Deferred
Federal									39	47	66
Federal impact of tax reform									0	0	80
State									(14)	(3)	0
Total deferred income tax expense (benefit)									25	44	146
Total income tax expense	$ 11	$ 15	$ 14	$ 8	$ 12	$ 12	$ 12	$ 9	$ 48	$ 45	$ 148