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Litigation, Claims and Contingencies - Schedule of Progression of Activity in the Asbestos Reserve (Parenthetical) (Details) - USD ($) $ in Millions | Mar. 31, 2025 | Sep. 30, 2024 | Mar. 31, 2024 | Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2021
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Ashland [Member] |  |  |  |  |  |  |  |  |  |  |
Asbestos reserve [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asbestos reserve | $ 256 | [1] | $ 274 | [1] | $ 263 | [1] | $ 281 | [1] | $ 305 | [1] | $ 320
Ashland [Member] | Other Current Liabilities [Member] |  |  |  |  |  |  |  |  |  |  |
Asbestos reserve [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asbestos reserve | 28 |  | 28 |  |  |  |  |  |  |  |
Hercules [Member] |  |  |  |  |  |  |  |  |  |  |
Asbestos reserve [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asbestos reserve | 180 | [2] | 185 | [2] | $ 180 | [2] | $ 191 | [2] | $ 213 | [2] | $ 217
Hercules [Member] | Other Current Liabilities [Member] |  |  |  |  |  |  |  |  |  |  |
Asbestos reserve [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Asbestos reserve | $ 17 |  | $ 17 |  |  |  |  |  |  |  |
[1] | Includes $28 million classified in accrued expenses and other liabilities on the Condensed Consolidated Balance Sheets as of March 31, 2025 and September 30, 2024.
[2] | Includes $17 million classified in accrued expenses and other liabilities on the Condensed Consolidated Balance Sheets at March 31, 2025 and September 30, 2024.

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