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v3.26.1

Financial Information by Segment - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Jun. 30, 2026 | Jun. 30, 2025 | Jun. 30, 2026 | Jun. 30, 2025
Segment Reporting Information [Line Items] |  |  |  |
Revenues from external customers | $ 982 | $ 923 | $ 2,735 | $ 2,814
Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues from external customers | 950 | 893 | 2,642 | 2,720
Unallocated and Other [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues from external customers | 32 | 30 | 93 | 94
Reinforcement Materials [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues from external customers | 599 | 573 | 1,663 | 1,778
Performance Chemicals [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues from external customers | $ 351 | $ 320 | $ 979 | $ 942

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