Income Taxes - Income Taxes at Federal Statutory Rate (Details) - USD ($) $ in Millions	1 Months Ended	2 Months Ended	3 Months Ended							5 Months Ended	7 Months Ended	12 Months Ended
	Jul. 31, 2018	Sep. 30, 2018	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Jul. 31, 2018	Dec. 31, 2019	Dec. 31, 2017
Amount
Tax (Benefit) Expense at Federal Statutory Rate										$ (29)	$ 42	$ (1)	$ 15
State taxes, net of federal benefit										(6)	8	5	1
Non-controlling interests										0	0	1	0
Change in valuation allowance										(990)	0	(285)	(1)
Deferred adjustments										3	(1)	2	0
Nondeductible items										1	7	4	1
Federal tax reform impact										0	0	0	(5)
Current payable adjustments										0	(1)	0	0
Adjustments related to uncertain tax positions										0	0	0	1
Other, net										0	(7)	1	1
Total income tax (benefit) expense	$ (19)	$ (979)	$ (221)	$ 24	$ (29)	$ (47)	$ (42)	$ 21	$ 46	$ (1,021)	$ 48	$ (273)	$ 13
Percent
Tax (Benefit) Expense at Federal Statutory Rate										21.00%	21.00%	21.00%	35.00%
State taxes, net of federal benefit										4.20%	3.80%	(141.20%)	1.90%
Non-controlling interests										(0.00%)	(0.00%)	(21.10%)	(0.30%)
Change in valuation allowance										720.00%	0.00%	8066.40%	(1.20%)
Deferred adjustments										(1.80%)	(0.50%)	(64.10%)	0.00%
Nondeductible items										(1.00%)	3.30%	(136.50%)	3.20%
Federal tax reform impact										0.00%	0.00%	0.00%	(12.60%)
Current payable adjustments										(0.00%)	(0.50%)	(0.00%)	(0.00%)
Adjustments related to uncertain tax positions										0.00%	0.00%	0.00%	2.40%
Other, net										0.00%	(3.30%)	(5.70%)	0.50%
Total income tax (benefit) expense										742.40%	23.80%	7718.80%	28.90%