Fair Value Measurements - Summary of Fair Values of Outstanding Natural Gas Derivatives (Details) - Commodity Contract [Member] - USD ($) $ in Millions	Mar. 31, 2026	Sep. 30, 2025
Accounts Receivable [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Commodity derivative assets	$ 1	$ 1
Notional contract values	2	6
Accrued Expenses and Other Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional contract values	9	7
Commodity derivative liabilities	$ 1	$ 1

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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