Earnings Per Share - Basic and Diluted EPS (Details) $ / shares in Units, shares in Thousands, $ in Millions		1 Months Ended	2 Months Ended	3 Months Ended							5 Months Ended	7 Months Ended	12 Months Ended
	Oct. 10, 2018	Jul. 31, 2018 USD ($) $ / shares	Sep. 30, 2018 USD ($) $ / shares	Dec. 31, 2019 USD ($) $ / shares	Sep. 30, 2019 USD ($) $ / shares	Jun. 30, 2019 USD ($) $ / shares	Mar. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares shares	Jul. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Earnings Per Share [Abstract]
Reverse stock split ratio	0.0833
Net income | $		$ (64)	$ 1,020	$ 463	$ 84	$ (87)	$ (186)	$ (136)	$ 58	$ 160	$ 884	$ 154	$ 274	$ 30
Less: Undistributed earnings attributable to participating stockholders | $		0	9	4	1	0	0	0	0	0	8	0	2	0
Net income attributable to common stockholders | $		$ (64)	$ 1,011	$ 459	$ 83	$ (87)	$ (186)	$ (136)	$ 58	$ 160	$ 876	$ 154	$ 272	$ 30
Net income (loss) per common share attributable to Successor/Predecessor:
Basic (in dollars per share) | $ / shares		$ (0.65)	$ 11.13	$ 5.03	$ 0.91	$ (0.96)	$ (2.05)	$ (1.50)	$ 0.59	$ 1.63	$ 9.65	$ 1.57	$ 2.99	$ 0.31
Diluted (in dollars per share) | $ / shares		$ (0.65)	$ 10.99	$ 4.95	$ 0.90	$ (0.96)	$ (2.05)	$ (1.50)	$ 0.59	$ 1.61	$ 9.54	$ 1.55	$ 2.95	$ 0.30
Weighted average shares of common stock outstanding (in thousands):
Basic (in shares)											90,813	98,046	91,035	97,696
Dilutive effect of stock awards (in shares)											178	1,091	270	1,107
Dilutive effect of participating securities (in shares)											839	0	839	0
Diluted (in shares)											91,830	99,137	92,144	98,803