Chapter 11 Proceedings and Ability to continue as a Going Concern - Schedule of Debtor in Possession Consolidated Financial Statements (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	Dec. 12, 2019
Revenues [Abstract]
Revenues	$ 261	$ 4,954	$ 3,685	$ 5,744
Operating Expenses	(260)	(6,136)	(5,171)	(7,828)
Operating Loss	1	(1,182)	(1,486)	(2,084)
Other Expense:
Reorganization Items	(4)	5,389	(9)	0
Interest Expense, Net	(12)	(362)	(266)	(614)
Income (Loss) Before Income Taxes	(15)	3,819	(1,814)	(2,757)
Income Tax Provision	(9)	(135)	(85)	(34)
Net Income (Loss)	(24)	3,684	(1,899)	(2,791)
Liabilities:
Liabilities Subject to Compromise					$ 7,600
Cash Flows from Operating Activities:
Net Income (Loss)	(24)	3,684	(1,899)	(2,791)
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Reorganization Items	0	136	0
Other Assets and Liabilities, Net	(76)	11	(96)	111
Net Cash Provided by (Used in) Operating Activities	61	(747)	210	(242)
Cash Flows From Financing Activities:
Borrowings from Debtor in Possession Credit Facility, net	0	1,529	0	0
Debtor in Possession Financing Payments and Payments on Backstop Agreement	0	(137)	0	0
Borrowings (Repayments) of Short-term Debt, Net	(1)	(347)	(27)	158
Other Financing Activities Among Subsidiaries	0	(49)	(45)	(74)
Net Cash Provided by (Used in) Financing Activities, Total	(2)	749	348	168
Cash and Cash Equivalents at Beginning of Period		$ 602	800	613
Cash, Cash Equivalents and Restricted Cash at End of Period	$ 800		$ 1,285	$ 602