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Commitments and Contingencies - Legal Proceedings (Details) - USD ($) $ in Millions | 12 Months Ended
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Sep. 30, 2023 | Sep. 30, 2022
Legal Proceedings |  |
Possible additional future costs for compliance with CCR requirements | $ 1,600 |
Contribution related to TVARS case | 4 | $ 4
Possible additional future costs for compliance with Clean Water requirements. | 190 |
Amount remaining to be spent under environmental agreements | 8 |
General |  |
Legal Proceedings |  |
Legal loss contingency accrual | 28 |
Environmental Agreements |  |
Legal Proceedings |  |
Amount to be invested in certain environmental projects | 290 |
Amount invested in certain environmental projects | 283 |
Other long-term liabilities | General |  |
Legal Proceedings |  |
Legal loss contingency accrual | 10 |
Accounts payable and accrued liabilities | General |  |
Legal Proceedings |  |
Legal loss contingency accrual | $ 18 |

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