| Cover Page | Jun. 29, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jun. 29, 2021 |
| Entity File Number | 333-21011 |
| Entity Registrant Name | FIRSTENERGY CORP |
| Entity Tax Identification Number | 34-1843785 |
| Entity Incorporation, State or Country Code | OH |
| Entity Address, Address Line One | 76 South Main Street |
| Entity Address, City or Town | Akron |
| Entity Address, State or Province | OH |
| Entity Address, Postal Zip Code | 44308 |
| City Area Code | (800) |
| Local Phone Number | 736-3402 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.10 par value per share |
| Trading Symbol | FE |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001031296 |
| Amendment Flag | false |
| Document Information [Line Items] | |
| Document Type | 8-K |
