Chapter 11 Proceedings and Ability to continue as a Going Concern - Reorganziation Items (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		11 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Sep. 30, 2019	Dec. 13, 2019	Dec. 31, 2018	Dec. 31, 2017
Reorganizations [Abstract]
Debtor Reorganization Items, Discharge of Claims and Liabilities	$ 0			$ 4,297
Debtor Reorganization Items, Revaluation of Assets and Liabilities	0			1,434
Debtor Reorganization Items subtotal for Gain on Settlement of LSTC and Fair Value Adjustment	0			5,731
Unamortized Debt Issuance and Discount Expensed	0			(128)
Unamortized Interest Rate Derivative Loss Expensed	0			(8)
Reorganization Items	0			(136)
Backstop Commitment Fees	0			(81)
DIP Financing Fees	0			(56)
Professional Fees	(4)			(69)
Reorganization Items (Fees)	(4)			(206)
Total Reorganization Items	(4)	$ (5,700)	$ (303)	5,389	$ 0	$ 0
Reorganization Items (Fees) Unpaid	30			30
Reorganization Items (Fees) Paid	$ 4			$ 176