Earnings Per Share (Details) $ / shares in Units, shares in Thousands, $ in Millions		1 Months Ended	2 Months Ended	3 Months Ended	7 Months Ended	9 Months Ended
	Oct. 10, 2018	Jul. 31, 2018 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares	Jul. 31, 2018 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) $ / shares shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income (loss) attributable to Successor/Predecessor | $			$ 1,020
Less: Undistributed earnings attributable to participating stockholders | $			9
Net income (loss) attributable to common stockholders | $			$ 1,011
Net income (loss) per common share attributable to Successor/Predecessor:
Basic (in dollars per share) | $ / shares			$ 11.13
Diluted (in dollars per share) | $ / shares			$ 10.99
Weighted average shares of common stock outstanding (in thousands):
Basic (in shares)			90,808
Dilutive effect of stock awards (in shares)			345
Dilutive effect of participating securities (in shares)			839
Diluted (in shares)			91,992
Predecessor
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income (loss) attributable to Successor/Predecessor | $		$ (64)		$ 7	$ 154	$ (11)
Less: Undistributed earnings attributable to participating stockholders | $		0		0	0	0
Net income (loss) attributable to common stockholders | $		$ (64)		$ 7	$ 154	$ (11)
Net income (loss) per common share attributable to Successor/Predecessor:
Basic (in dollars per share) | $ / shares		$ (0.65)		$ 0.07	$ 1.57	$ (0.11)
Diluted (in dollars per share) | $ / shares		$ (0.65)		$ 0.07	$ 1.55	$ (0.11)
Weighted average shares of common stock outstanding (in thousands):
Basic (in shares)		98,164		97,706	98,046	97,685
Dilutive effect of stock awards (in shares)		0		988	1,091	0
Dilutive effect of participating securities (in shares)		0		0	0	0
Diluted (in shares)		98,164		98,694	99,137	97,685
Subsequent Event
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Reverse stock split ratio	0.0833