Basis of Presentation and Significant Accounting Policies, Voluntary Reorganization under Chapter 11 Cases - Voluntary Reorganization under Chapter 11 Proceedings Narrative (Details) - USD ($)			12 Months Ended
	Oct. 18, 2019	Sep. 14, 2019	Dec. 31, 2019	Dec. 31, 2018	Nov. 25, 2019	Sep. 03, 2019	Aug. 15, 2019
Restructuring Cost and Reserve [Line Items]
Equity Rights Offering amount backstopped	$ 463,000,000
Debtor-in-possession financing, borrowings outstanding			$ 148,000,000	$ 0
Maximum borrowing capacity	629,000,000
Reorganization items			65,000,000	0
Liabilities subject to compromise			2,932,000,000	0
Liabilities subject to compromise, debt			2,780,000,000	0
Contractual interest expense on prepetition liabilities			235,000,000
Interest expense on prepetition liabilities recognized in Statement of Operations			211,000,000
Senior Secured Notes due February 15, 2025
Restructuring Cost and Reserve [Line Items]
Cash interest payment due, not paid							$ 40,000,000
Purchase price of new common shares	325,000,000
Principal amount issued	$ 138,000,000
Senior Unsecured Notes due September 1, 2022
Restructuring Cost and Reserve [Line Items]
Cash interest payment due, not paid						$ 7,000,000
Debtor-In-Possession Senior Secured Superpriority Revolving Credit Facility
Restructuring Cost and Reserve [Line Items]
Principal amount issued					$ 629,000,000
Debtor-in-possession financing, amount arranged					315,000,000
Debtor-in possession financing, remaining borrowing capacity			150,000,000
Debtor-in-possession financing, borrowings outstanding			148,000,000	$ 0
Senior Secured Notes
Restructuring Cost and Reserve [Line Items]
Liabilities subject to compromise, debt			2,092,000,000
Senior Unsecured Notes
Restructuring Cost and Reserve [Line Items]
Liabilities subject to compromise, debt			688,000,000
Letter of Credit
Restructuring Cost and Reserve [Line Items]
Debtor-in possession financing, maximum borrowing capacity					$ 50,000,000
Debtor-in-possession financing, letters of credit outstanding			$ 17,000,000
Beneficial Owner | Senior Secured Notes due February 15, 2025
Restructuring Cost and Reserve [Line Items]
Percent of aggregate principal amount		70.00%
Beneficial Owner | Senior Secured Notes due November 29, 2024
Restructuring Cost and Reserve [Line Items]
Percent of aggregate principal amount	52.00%
Beneficial Owner | Senior Secured Note due May 1, 2024
Restructuring Cost and Reserve [Line Items]
Percent of aggregate principal amount	79.30%