Earnings Per Share (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, 2018 USD ($) $ / shares	Jun. 30, 2018 USD ($) $ / shares	Mar. 31, 2018 USD ($) $ / shares	Dec. 31, 2017 USD ($) $ / shares	Sep. 30, 2017 USD ($) $ / shares	Jun. 30, 2017 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares shares	Jul. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Reverse stock split ratio	0.0833
Net income attributable to Successor/Predecessor | $			$ 1,020	$ (136)							$ 884
Less: Undistributed earnings attributable to participating stockholders | $			9	0							8
Net income attributable to common stockholders | $			$ 1,011	$ (136)							$ 876
Net income (loss) per common share attributable to Successor/Predecessor:
Basic (in dollars per share) | $ / shares			$ 11.13	$ (1.50)							$ 9.65
Diluted (in dollars per share) | $ / shares			$ 10.99	$ (1.50)							$ 9.54
Weighted average shares of common stock outstanding (in thousands):
Basic (in shares)											90,813
Dilutive effect of stock awards (in shares)											178
Dilutive effect of participating securities (in shares)											839
Diluted (in shares)											91,830
Predecessor
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income attributable to Successor/Predecessor | $		$ (64)			$ 58	$ 160	$ 41	$ 7	$ (20)	$ 2		$ 154	$ 30	$ 19
Less: Undistributed earnings attributable to participating stockholders | $		0			0	0						0	0	0
Net income attributable to common stockholders | $		$ (64)			$ 58	$ 160						$ 154	$ 30	$ 19
Net income (loss) per common share attributable to Successor/Predecessor:
Basic (in dollars per share) | $ / shares		$ (0.65)			$ 0.59	$ 1.63	$ 0.42	$ 0.07	$ (0.20)	$ 0.02		$ 1.57	$ 0.31	$ 0.19
Diluted (in dollars per share) | $ / shares		$ (0.65)			$ 0.59	$ 1.61	$ 0.41	$ 0.07	$ (0.20)	$ 0.02		$ 1.55	$ 0.30	$ 0.19
Weighted average shares of common stock outstanding (in thousands):
Basic (in shares)												98,046	97,696	99,765
Dilutive effect of stock awards (in shares)												1,091	1,107	880
Dilutive effect of participating securities (in shares)												0	0	0
Diluted (in shares)												99,137	98,803	100,645