| Document and Entity Information | Sep. 13, 2023 |
| Cover [Abstract] | |
| Entity Registrant Name | CABOT CORP |
| Entity Incorporation State Country Code | DE |
| Entity Address, State or Province | MA |
| Amendment Flag | false |
| Entity Central Index Key | 0000016040 |
| Document Type | 8-K |
| Document Period End Date | Sep. 13, 2023 |
| Entity File Number | 1-5667 |
| Entity Tax Identification Number | 04-2271897 |
| Entity Address, Address Line One | TWO SEAPORT LANE |
| Entity Address, Address Line Two | SUITE 1400 |
| Entity Address, City or Town | BOSTON |
| 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 |
| Security 12b Title | Common Stock, $1 par value per share |
| Trading Symbol | CBT |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
