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Financial Information by Segment & Geographic Area - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022
Segment Reporting Information [Line Items] |  |  |
Revenues | $ 3,994 | $ 3,931 | $ 4,321
Depreciation and amortization | 151 | 144 | 146
Income (Loss) from Equity Method Investments | 6 | 5 | 10
Income (loss) from operations before income taxes | 529 | 451 | 335
Assets | 3,736 | 3,604 | 3,525
Total expenditures for additions to long-lived assets | 249 | 265 | 221
Operating Segments [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenues | 3,860 | 3,788 | 4,158
Depreciation and amortization | 144 | 142 | 145
Income (Loss) from Equity Method Investments | 6 | 5 | 10
Income (loss) from operations before income taxes | 701 | 607 | 642
Assets | 3,245 | 3,105 | 3,149
Total expenditures for additions to long-lived assets | 241 | 257 | 217
Unallocated and Other [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenues | 134 | 143 | 163
Depreciation and amortization | 7 | 2 | 1
Income (loss) from operations before income taxes | (172) | (156) | (307)
Assets | 491 | 499 | 376
Total expenditures for additions to long-lived assets | 8 | 8 | 4
Reinforcement Materials [Member] | Operating Segments [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenues | 2,610 | 2,563 | 2,673
Depreciation and amortization | 66 | 70 | 70
Income (Loss) from Equity Method Investments | 2 | 2 | 4
Income (loss) from operations before income taxes | 537 | 482 | 408
Assets | 1,751 | 1,632 | 1,691
Total expenditures for additions to long-lived assets | 165 | 149 | 114
Performance Chemicals [Member] | Operating Segments [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenues | 1,250 | 1,225 | 1,388
Depreciation and amortization | 78 | 72 | 72
Income (Loss) from Equity Method Investments | 4 | 3 | 5
Income (loss) from operations before income taxes | 164 | 125 | 234
Assets | 1,494 | 1,473 | 1,458
Total expenditures for additions to long-lived assets | $ 76 | $ 108 | 100
Purification Solutions [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenues |  |  | 97
Purification Solutions [Member] | Operating Segments [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenues |  |  | 97
Depreciation and amortization |  |  | 3
Income (Loss) from Equity Method Investments |  |  | 1
Total expenditures for additions to long-lived assets |  |  | $ 3

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