Subsequent Event	9 Months Ended
Jun. 30, 2025
Subsequent Events [Abstract]
Subsequent Event	L. Subsequent Event On August 4, 2025, Cabot entered into agreements with Bridgestone Corporation to purchase its carbon black manufacturing facility in Tamaulipas, Mexico, Mexico Carbon Manufacturing, S.A. de C.V., for approximately $70 million, which will be subject to customary closing adjustments. The acquisition is expected to close in the first half of fiscal 2026, subject to regulatory approval.

The entire disclosure for significant events or transactions that occurred after the balance sheet date through the date the financial statements were issued or the date the financial statements were available to be issued. Examples include: the sale of a capital stock issue, purchase of a business, settlement of litigation, catastrophic loss, significant foreign exchange rate changes, loans to insiders or affiliates, and transactions not in the ordinary course of business.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 855
-Name Accounting Standards Codification
-Publisher FASB
-URI https://asc.fasb.org/855/tableOfContent

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 855
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483399/855-10-50-2

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