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Commitments and Contingencies - Legal Proceedings (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Legal Proceedings
Contribution related to TVARS case	$ 5	$ 4
Amount remaining to be spent under environmental agreements	7
General
Legal Proceedings
Legal loss contingency accrual	10
Environmental Agreements
Legal Proceedings
Amount to be invested in certain environmental projects	290
Amount invested in certain environmental projects	284
Other long-term liabilities | General
Legal Proceedings
Legal loss contingency accrual	9
Accounts payable and accrued liabilities | General
Legal Proceedings
Legal loss contingency accrual	$ 1

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