Commitments and Contingencies - General (Details) - USD ($) $ in Millions |
2 Months Ended | 10 Months Ended | 12 Months Ended | |
|---|---|---|---|---|
Dec. 15, 2017 |
Sep. 30, 2018 |
Sep. 30, 2017 |
Sep. 30, 2016 |
|
| Loss Contingencies [Line Items] | ||||
| Legal costs | $ 0 | |||
| Predecessor | ||||
| Loss Contingencies [Line Items] | ||||
| Legal costs | $ 37 | $ 64 | $ 106 | |