Income Taxes - Unrecognized Tax Benefits Rollforward (Details) - USD ($) $ in Millions	5 Months Ended	7 Months Ended	12 Months Ended
	Dec. 31, 2018	Jul. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance - beginning of period	$ 0
Increases in tax positions of current year	0
Increases in tax positions of prior years	0
Decreases in tax positions of prior years	0
Settlements	0
Balance - end of period	0	$ 0
Predecessor
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance - beginning of period	$ 0	17	$ 0	$ 0
Increases in tax positions of current year		0	1	0
Increases in tax positions of prior years		0	20	0
Decreases in tax positions of prior years		(17)	0	0
Settlements		0	(4)	0
Balance - end of period		$ 0	$ 17	$ 0