Issuance of Equity Securities (Details) $ / shares in Units, $ in Millions		2 Months Ended	9 Months Ended	12 Months Ended		21 Months Ended
	Apr. 01, 2017 USD ($) days $ / shares shares	Feb. 15, 2019 shares	Dec. 31, 2017 shares	Dec. 31, 2018 shares	Dec. 31, 2017 shares	Dec. 31, 2018 shares	Jan. 31, 2018 shares	Jul. 03, 2017
Warrant | Effect of Plan
Fresh-Start Adjustment [Line Items]
Number of securities called by each right	1
Exercise price | $ / shares	$ 0.01
Warrants issued (in shares)	6,200,000
Warrants unexercised, percent								0.10%
Series A Preferred Stock | Preferred Stock | Effect of Plan
Fresh-Start Adjustment [Line Items]
Preferred stock, dividend rate	8.50%
Preferred stock, conversion price (in dollars per share) | $ / shares	$ 16.25
Discount percent of common stock value	35.00%
Threshold price of common stock | $ / shares	$ 32.50
Threshold trading days | days	45
Threshold consecutive trading days | days	60
Threshold last trading days in consecutive trading period | days	20
Conversion period threshold after initial issuance	3 years
Section 1145 Securities | Effect of Plan
Fresh-Start Adjustment [Line Items]
Stock issued | $	$ 704.4
Section 1145 Securities | Common Stock | Effect of Plan
Fresh-Start Adjustment [Line Items]
New shares issued (in shares)	51,200,000
Section 1145 Securities | Warrant | Effect of Plan
Fresh-Start Adjustment [Line Items]
New shares issued (in shares)	2,900,000
Parties to Private Placement and Backstop Commitment Agreement | Section 4(a)(2) Securities | Common Stock | Effect of Plan
Fresh-Start Adjustment [Line Items]
New shares issued (in shares)	4,800,000
Parties to Private Placement and Backstop Commitment Agreement | Section 4(a)(2) Securities | Warrant | Effect of Plan
Fresh-Start Adjustment [Line Items]
New shares issued (in shares)	3,100,000
Parties to Private Placement Agreement | Section 4(a)(2) Securities | Preferred Stock | Effect of Plan
Fresh-Start Adjustment [Line Items]
Stock issued | $	$ 750.0
Parties to Private Placement Agreement | Section 4(a)(2) Securities | Series A Preferred Stock | Preferred Stock | Effect of Plan
Fresh-Start Adjustment [Line Items]
New shares issued (in shares)	30,000,000
Parties to Backstop Commitment Agreement | Section 4(a)(2) Securities | Effect of Plan
Fresh-Start Adjustment [Line Items]
Stock issued | $	$ 45.6
Parties to Backstop Commitment Agreement | Section 4(a)(2) Securities | Common Stock | Effect of Plan
Fresh-Start Adjustment [Line Items]
New shares issued (in shares)	3,300,000
Parties to Backstop Commitment Agreement | Section 4(a)(2) Securities | Warrant | Effect of Plan
Fresh-Start Adjustment [Line Items]
New shares issued (in shares)	200,000
Allowed Claims In Classes 2A, 2B, 2C, 2D And 5B | Rights Offering | Effect of Plan
Fresh-Start Adjustment [Line Items]
Units authorized	54,500,000.0
Number of securities called by each right	1
Exercise price | $ / shares	$ 13.75
Rights offering, units purchased	51,200,000
Allowed Claims In Classes 2A, 2B, 2C, 2D And 5B | Section 1145 Securities | Common Stock | Effect of Plan
Fresh-Start Adjustment [Line Items]
New shares issued (in shares)	11,600,000
Allowed Claims In Classes 2A, 2B, 2C, 2D And 5B | Parties to Backstop Commitment Agreement | Rights Offering | Effect of Plan
Fresh-Start Adjustment [Line Items]
Rights offering, units purchased	3,300,000
Subsequent Event
Fresh-Start Adjustment [Line Items]
Treasury stock, shares, acquired		2,300,000
Successor
Fresh-Start Adjustment [Line Items]
Treasury stock, shares, acquired				21,100,000	5,800,000	26,900,000
Conversion of Stock, Shares Converted			(17,200,000)	(13,500,000)
Successor | Effect of Plan
Fresh-Start Adjustment [Line Items]
Common stock, outstanding (in shares)	70,900,000
Discount percent of common stock value	35.00%
Convertible preferred stock, shares issued upon conversion	46,200,000
Successor | Common Stock | Effect of Plan
Fresh-Start Adjustment [Line Items]
Stock issued | $	$ 70.9
Successor | Series A Preferred Stock | Effect of Plan
Fresh-Start Adjustment [Line Items]
Preferred Stock, shares issued (in shares)	30,000,000.0
Successor | Convertible Preferred Stock
Fresh-Start Adjustment [Line Items]
Preferred Stock, shares issued (in shares)			30,000,000	0	30,000,000	0	30,000,000
Successor | Common Stock
Fresh-Start Adjustment [Line Items]
Common stock, outstanding (in shares)			111,800,000	137,700,000	111,800,000	137,700,000
Successor | Common Stock | Common Stock
Fresh-Start Adjustment [Line Items]
Convertible preferred stock, shares issued upon conversion							59,300,000