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Litigation, Claims and Contingencies - Summary of Progression of Insurance Receivable (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] |  |  |  |  |  |  |  |  |  |  |
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Insurance receivable | $ 95 | [1] | $ 97 | [1] | $ 91 | [1] | $ 95 | [1] | $ 101 | [1] | $ 100
Total allowance for credit losses | 1 |  | 1 |  |  |  |  |  |  |  |
Ashland [Member] | Accounts Receivable [Member] |  |  |  |  |  |  |  |  |  |  |
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Insurance receivable | 9 |  | 9 |  |  |  |  |  |  |  |
Hercules [Member] |  |  |  |  |  |  |  |  |  |  |
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Insurance receivable | 46 | [2] | 50 | [2] | $ 45 | [2] | $ 47 | [2] | $ 52 | [2] | $ 47
Total allowance for credit losses | 1 |  | 1 |  |  |  |  |  |  |  |
Hercules [Member] | Accounts Receivable [Member] |  |  |  |  |  |  |  |  |  |  |
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward] |  |  |  |  |  |  |  |  |  |  |
Insurance receivable | $ 6 |  | $ 6 |  |  |  |  |  |  |  |
[1] | Includes $9 million classified in accounts receivable, net on the Condensed Consolidated Balance Sheets at March 31, 2025 and September 30, 2024.
[2] | Includes $6 million classified in accounts receivable, net on the Condensed Consolidated Balance Sheets at March 31, 2025 and September 30, 2024.

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- Definition Loss contingency reserve allowance for credit losses. + References No definition available. + Details
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- Definition Amount of receivable related to a loss contingency accrual. For example, an insurance recovery receivable. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 460 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482425/460-10-50-3 + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Details
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