Reorganization Adjustments - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019	Jul. 01, 2019
Reorganizations [Abstract]
Reorganization Adjustments, Escrow Cash Receivable			$ 3
Reorganization Items, Current Portion of Secured Debt			7
Debtor reorganization item, equity backstop	$ 24	$ 24
Debtor reorganization items, debt backstop	$ 80	$ 80
Reorganization Items, Other Current Liabilities			13
Reorganization Items, Secured Term Loan			1,208
Reorganization Items, Secured Notes			450
Debt Instrument, Unamortized Discount			12
Reorganization Items, Debt Issuance Costs Paid			$ 17