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	3 Months Ended								11 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 13, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 12, 2019
Revenues [Abstract]
Revenues	$ 261	$ 985	$ 1,314	$ 1,309	$ 1,346	$ 1,429	$ 1,444	$ 1,448	$ 1,423	$ 4,954	$ 4,954	$ 5,744	$ 5,699
Operating Expenses	(260)									(6,136)		(7,828)	(7,869)
Operating Loss	1									(1,182)		(2,084)	(2,170)
Other Expense:
Reorganization Items	(4)	(5,700)	$ (303)							5,389		0	0
Interest Expense, Net	(12)									(362)		(614)	(579)
Income (Loss) Before Income Taxes	(15)									3,819		(2,757)	(2,656)
Income Tax (Provision)	(9)									(135)		(34)	(137)
Net Income (Loss)	(24)									3,684		(2,791)	(2,793)
Liabilities:
Liabilities Subject to Compromise														$ 7,600
Cash Flows from Operating Activities:
Net Income (Loss)	(24)									3,684		(2,791)	(2,793)
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Reorganization Items	0									136
Other Assets and Liabilities, Net	73									31		(116)	(25)
Net Cash Provided by (Used in) Operating Activities	61									(747)		(242)	(388)
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)		158	(128)
Other Financing Activities Among Subsidiaries	0									(49)		(40)	(33)
Net Cash Provided by (Used in) Financing Activities	(2)									$ 749		168	20
Cash and Cash Equivalents at Beginning of Period									$ 613			$ 613
Cash, Cash Equivalents and Restricted Cash at End of Period	$ 800	$ 800									$ 800		$ 613