Chapter 11 Proceedings and Ability to continue as a Going Concern - Reorganziation Items (Details) - USD ($) $ in Millions	1 Months Ended	11 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 13, 2019	Dec. 31, 2020	Dec. 31, 2018
Reorganizations [Abstract]
Debtor Reorganization Items, Discharge of Claims and Liabilities	$ 0	$ 4,297	$ 0
Debtor Reorganization Items, Revaluation of Assets and Liabilities	0	1,434	0
Debtor Reorganization Items subtotal for Gain on Settlement of LSTC and Fair Value Adjustment	0	5,731	0
Unamortized Debt Issuance and Discount Expensed	0	(128)	0
Unamortized Interest Rate Derivative Loss Expensed	0	(8)	0
Reorganization Items	0	(136)	0
Backstop Commitment Fees	0	(81)	0
DIP Financing Fees	0	(56)	0
Professional Fees	(4)	(69)	(9)
Reorganization Items (Fees)	(4)	(206)	(9)
Total Reorganization Items	(4)	5,389	(9)	$ 0
Reorganization Items (Fees) Unpaid	30	30	0
Reorganization Items (Fees) Paid	$ 4	$ 176	$ 39