Financial Information by Segment & Geographic Area - Financial Information by Reportable Segment (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Segment Reporting Information [Line Items]
Revenues	$ 3,931	$ 4,321	$ 3,409
Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Revenues		98	57
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Revenues		$ 16	$ 8

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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+ Details