Litigation, Claims and Contingencies - Schedule of Progression of Activity in the Asbestos Reserve (Parenthetical) (Details) - USD ($) $ in Millions |
Jun. 30, 2026 |
Sep. 30, 2025 |
Jun. 30, 2025 |
Sep. 30, 2024 |
Sep. 30, 2023 |
Sep. 30, 2022 |
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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Ashland [Member] | |||||||||||||||
| Asbestos reserve [Roll Forward] | |||||||||||||||
| Asbestos reserve | $ 262 | [1] | $ 258 | [1] | $ 265 | [1] | $ 274 | [1] | $ 281 | [1] | $ 305 | ||||
| Ashland [Member] | Other Current Liabilities [Member] | |||||||||||||||
| Asbestos reserve [Roll Forward] | |||||||||||||||
| Asbestos reserve | 29 | 29 | |||||||||||||
| Hercules [Member] | |||||||||||||||
| Asbestos reserve [Roll Forward] | |||||||||||||||
| Asbestos reserve | 183 | [2] | 177 | [2] | $ 185 | [2] | $ 185 | [2] | $ 191 | [2] | $ 213 | ||||
| Hercules [Member] | Other Current Liabilities [Member] | |||||||||||||||
| Asbestos reserve [Roll Forward] | |||||||||||||||
| Asbestos reserve | $ 17 | $ 17 | |||||||||||||
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