| Document and Entity Information | Feb. 05, 2024 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 05, 2024 |
| Entity Registrant Name | Cabot Corporation |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-05667 |
| Entity Tax Identification Number | 04-2271897 |
| Entity Address, Address Line One | 2 Seaport Lane |
| Entity Address, Address Line Two | Suite 1400 |
| Entity Address, City or Town | Boston |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02210-2019 |
| City Area Code | 617 |
| Local Phone Number | 345-0100 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000016040 |
| Title of 12(b) Security | Common Stock, $1 par value per share |
| Trading Symbol | CBT |
| Security Exchange Name | NYSE |
