Debt - Additional Information (Details) - USD ($) $ in Millions		1 Months Ended	12 Months Ended
	Nov. 25, 2019	Jan. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Oct. 18, 2019	Sep. 03, 2019	Aug. 15, 2019
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt			$ 10	$ 73
Debtor-in possession financing, loans outstanding			148	0
Senior Secured Note due May 1, 2024
Debt Instrument [Line Items]
Principal amount issued		$ 1,100
Gain (loss) on extinguishment/modification of debt		(12)
Gain (loss) on extinguishment of debt		$ 53
Unsecured Debt
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt			10	32
Repayments of outstanding amount			40	49
Aggregate principal amount repurchased			50	84
Senior Secured Notes due February 15, 2025
Debt Instrument [Line Items]
Principal amount issued					$ 138
Cash interest payment due, not paid							$ 40
Senior Unsecured Notes due September 1, 2022
Debt Instrument [Line Items]
Cash interest payment due, not paid						$ 7
Debtor-In-Possession Senior Secured Superpriority Revolving Credit Facility
Debt Instrument [Line Items]
Principal amount issued	$ 629
Debtor-in-possession financing, amount arranged	315
Debtor-in possession financing, remaining borrowing capacity			150
Debtor-in possession financing, loans outstanding			148	$ 0
Letter of Credit
Debt Instrument [Line Items]
Debtor-in-possession financing, amount arranged	$ 50
Debtor-in-possession letter of credit outstanding			$ 17
LIBOR | Debtor-In-Possession Senior Secured Superpriority Revolving Credit Facility
Debt Instrument [Line Items]
Debtor-in possession financing, basis spread on variable rate	3.50%
Debt Instrument Variable Rate Alternate Base Rate | Debtor-In-Possession Senior Secured Superpriority Revolving Credit Facility
Debt Instrument [Line Items]
Debtor-in possession financing, basis spread on variable rate	2.50%
Debtor-in possession financing, unused capacity, commitment fee percentage	0.50%