| Document and Entity Information Document and Entity Information | Jun. 11, 2021 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Jun. 11, 2021 |
| Entity Registrant Name | GREIF INC |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-00566 |
| Entity Tax Identification Number | 31-4388903 |
| Entity Address, Address Line One | 425 Winter Road |
| Entity Address, City or Town | Delaware |
| Entity Address, State or Province | OH |
| Entity Address, Postal Zip Code | 43015 |
| City Area Code | 740 |
| Local Phone Number | 549-6000 |
| Entity Emerging Growth Company | false |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Central Index Key | 0000043920 |
| Amendment Flag | false |
| Common Class A | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Class A Common Stock |
| Trading Symbol | GEF |
| Security Exchange Name | NYSE |
| Common Class B | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Class B Common Stock |
| Trading Symbol | GEF-B |
| Security Exchange Name | NYSE |
