BASIS OF PRESENTATION - Liabilities Subject to Compromise – Liabilities Subject to Compromise – Pre-petition Debt (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Debt instrument
Accrued interest on long-term debt	$ 164
Liabilities Subject to Compromise, Total	4,516	$ 0
2017 Credit Agreement
Debt instrument
Liabilities subject to compromise gross	1,300
2016 Credit Agreement
Debt instrument
Liabilities subject to compromise gross	1,000
Second Lien Notes
Debt instrument
Liabilities subject to compromise gross	1,808
Senior Notes (Unsecured) | 5.5% Senior Notes due 2021
Debt instrument
Liabilities subject to compromise gross	$ 100
Debt instrument, interest rate, stated percentage	5.50%
Senior Notes (Unsecured) | 6% Senior Notes due 2024
Debt instrument
Liabilities subject to compromise gross	$ 144
Debt instrument, interest rate, stated percentage	6.00%