| Cover | Dec. 01, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Dec. 1, 2020 |
| Entity File Number | 1-14204 |
| Entity Registrant Name | FUELCELL ENERGY, INC. |
| Entity Central Index Key | 0000886128 |
| Entity Tax Identification Number | 06-0853042 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 3 Great Pasture Road |
| Entity Address, City or Town | Danbury |
| Entity Address, State or Province | CT |
| Entity Address, Postal Zip Code | 06810 |
| City Area Code | 203 |
| Local Phone Number | 825-6000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.0001 par value per share |
| Trading Symbol | FCEL |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
