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Cover Page - USD ($)
 12 Months Ended
Dec. 31, 2021
Jan. 31, 2022
Jun. 30, 2021
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2021    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
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    
Title of 12(b) Security Common Stock, $0.10 par value per share    
Trading Symbol FE    
Security Exchange Name NYSE    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Entity Shell Company false    
Entity Public Float     $ 20,228,791,176
Entity Common Stock Shares Outstanding   570,344,389  
Documents Incorporated by Reference
Documents Incorporated By Reference
 PART OF FORM 10-K INTO WHICH
DOCUMENTDOCUMENT IS INCORPORATED
Proxy Statement for 2022 Annual Meeting of Shareholders of FirstEnergy Corp. to be held May 17, 2022Part III
    
Entity Central Index Key 0001031296    
Document Fiscal Year Focus 2021    
Document Fiscal Period Focus FY    
Amendment Flag false