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Litigation, Claims and Contingencies - Additional Information (Details) $ in Millions | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Mar. 31, 2025 USD ($) Facility ServiceStationProperty Site | Mar. 31, 2025 USD ($) Facility ServiceStationProperty Site | Mar. 31, 2024 USD ($) | Sep. 30, 2024 USD ($) | Sep. 30, 2023 USD ($) | Sep. 30, 2022 USD ($) | Sep. 30, 2021 USD ($)
Asbestos litigation cost projection [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Years Included in Asbestos Assumption |  |  | 40 years |  |  |  |  |  |  |  |  |  |
Environmental Remediation Costs Recognized [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Number of sites were company is identified as a potentially responsible party under the superfund or similar state law | Site | 53 |  | 53 |  |  |  |  |  |  |  |  |  |
Number of current and former operating facilities subject to various environmental laws | Facility | 108 |  | 108 |  |  |  |  |  |  |  |  |  |
Total number of service station properties subject to various environmental laws | ServiceStationProperty | 1,225 |  | 1,225 |  |  |  |  |  |  |  |  |  |
Number of service stations being actively remediated | ServiceStationProperty | 14 |  | 14 |  |  |  |  |  |  |  |  |  |
Environmental Loss Contingency, Statement of Financial Position [Extensible Enumeration] | Other liabilities |  | Other liabilities |  |  |  |  |  |  |  |  |  |
Accrual for environmental loss contingencies | $ 207 |  | $ 207 |  | $ 198 |  | $ 221 |  | $ 214 |  |  |  |
Accrued environmental loss contingencies, noncurrent | 150 |  | 150 |  |  |  | 164 |  |  |  |  |  |
Recorded third-party environmental recoveries receivables | 12 |  | 12 |  |  |  | 13 |  |  |  |  |  |
Recorded third-party environmental recoveries, noncurrent | 10 |  | $ 10 |  |  |  | 11 |  |  |  |  |  |
Environmental exit costs, reasonably possible additional loss | $ 465 |  |  |  |  |  |  |  |  |  |  |  |
Maximum reserve for remediation reserve related to any one site (in hundredths) | 22.00% |  | 22.00% |  |  |  |  |  |  |  |  |  |
Ashland [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Asbestos reserve [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in asbestos related reserve |  |  | $ 0 |  | 0 |  | 24 |  | 9 |  | $ 16 |  |
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance receivable | $ 95 | [1] | 95 | [1] | 91 | [1] | 97 | [1] | 95 | [1] | 101 | [1] | $ 100
Receivable adjustment |  |  |  |  |  |  | 11 |  |  |  |  |  |
Asbestos litigation cost projection [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Possible total future litigation defense and claim settlement costs | 410 |  | 410 |  |  |  |  |  |  |  |  |  |
Total reserves for asbestos claims | 256 | [2] | 256 | [2] | 263 | [2] | 274 | [2] | 281 | [2] | 305 | [2] | 320
Hercules [Member] |  |  |  |  |  |  |  |  |  |  |  |  |
Asbestos reserve [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (decrease) in asbestos related reserve |  |  | 0 |  | 0 |  | 14 |  | (2) |  | 15 |  |
Movement in Loss Contingency Receivable, Increase (Decrease) [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |
Insurance receivable | 46 | [3] | 46 | [3] | 45 | [3] | 50 | [3] | 47 | [3] | 52 | [3] | 47
Receivable adjustment |  |  |  |  |  |  | 6 |  |  |  |  |  |
Asbestos litigation cost projection [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |
Possible total future litigation defense and claim settlement costs | 276 |  | 276 |  |  |  |  |  |  |  |  |  |
Total reserves for asbestos claims | $ 180 | [4] | $ 180 | [4] | $ 180 | [4] | $ 185 | [4] | $ 191 | [4] | $ 213 | [4] | $ 217
[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 $28 million classified in accrued expenses and other liabilities on the Condensed Consolidated Balance Sheets as of March 31, 2025 and September 30, 2024.
[3] | Includes $6 million classified in accounts receivable, net on the Condensed Consolidated Balance Sheets at March 31, 2025 and September 30, 2024.
[4] | 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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