Shareholders' Equity Narrative (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 13, 2019	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Jun. 30, 2020	Nov. 21, 2016
Class of Warrant or Right [Line Items]
Additional Paid in Capital, Common Stock		$ 2,897		$ 2,897	$ 2,897
Class of Warrant or Right, Unissued							1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right	7,777,779					84,500,000
Class of Warrant or Right, Exercise Price of Warrants or Rights	$ 99.96	$ 99.96			$ 99.96	$ 6.43
Adjustments to Additional Paid in Capital, Stock Issued, Own-share Lending Arrangement, Issuance Costs					$ 2,900
Common Stock
Class of Warrant or Right [Line Items]
Stock Issued During Period, Shares, New Issues	69,999,954	0		0
Additional Paid-in Capital [Member]
Class of Warrant or Right [Line Items]
Stock Issued During Period, Shares, New Issues			84,500,000
Warrant [Member]
Class of Warrant or Right [Line Items]
Additional Paid in Capital, Common Stock	$ 31
Reorganization Adjustments
Class of Warrant or Right [Line Items]
Fresh-Start Adjustment, Issuance Of Successor Common Stock To Creditors		$ 2,837			$ 2,837