Income Taxes - Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	5 Months Ended	7 Months Ended	12 Months Ended
	Dec. 31, 2018	Jul. 31, 2018	Dec. 31, 2020	Dec. 31, 2019
Current Income Taxes
Federal	$ 0	$ (14)	$ (3)	$ 19
State	0	(1)	92	74
Total current income taxes	0	(15)	89	93
Deferred Income Taxes
Federal	(1,015)	54	86	(298)
State	(6)	9	(83)	(68)
Total deferred income taxes	(1,021)	63	3	(366)
Total income tax expense (benefit)	$ (1,021)	$ 48	$ 92	$ (273)