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, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Jul. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Amount
Tax (Benefit) Expense at Federal Statutory Rate										$ (29)
State taxes, net of federal benefit										(6)
Non-controlling interests										0
Decrease of federal valuation allowance										(990)
Deferred adjustments										3
Federal tax reform impact										0
Current payable adjustments										0
Adjustments related to uncertain tax positions										0
Other, net										1
Total income tax (benefit) expense		$ (979)	$ (42)							$ (1,021)
Percent
Tax (Benefit) Expense at Federal Statutory Rate			21.00%							21.00%
State taxes, net of federal benefit										4.20%
Non-controlling interests										(0.00%)
Decrease of federal valuation allowance										720.00%
Deferred adjustments										(1.80%)
Federal tax reform impact										0.00%
Current payable adjustments										(0.00%)
Adjustments related to uncertain tax positions										0.00%
Other, net										(1.00%)
Total income tax (benefit) expense										742.40%
Predecessor
Amount
Tax (Benefit) Expense at Federal Statutory Rate											$ 42	$ 15	$ 10
State taxes, net of federal benefit											8	1	1
Non-controlling interests											0	0	1
Decrease of federal valuation allowance											0	(1)	0
Deferred adjustments											(1)	0	1
Federal tax reform impact											0	(5)	0
Current payable adjustments											(1)	0	1
Adjustments related to uncertain tax positions											0	1	0
Other, net											0	2	(1)
Total income tax (benefit) expense	$ (19)			$ 21	$ 46	$ 17	$ 5	$ (10)	$ 1		$ 48	$ 13	$ 13
Percent
Tax (Benefit) Expense at Federal Statutory Rate											21.00%	35.00%	35.00%
State taxes, net of federal benefit											3.80%	1.90%	5.00%
Non-controlling interests											(0.00%)	(0.30%)	3.40%
Decrease of federal valuation allowance											0.00%	(1.20%)	0.00%
Deferred adjustments											(0.50%)	0.00%	2.30%
Federal tax reform impact											0.00%	(12.60%)	0.00%
Current payable adjustments											(0.50%)	(0.00%)	1.90%
Adjustments related to uncertain tax positions											0.00%	2.40%	0.00%
Other, net											0.00%	3.70%	(2.40%)
Total income tax (benefit) expense											23.80%	28.90%	45.20%