SHORT-TERM BORROWINGS AND BANK LINES OF CREDIT - Narrative (Details)			12 Months Ended
	Oct. 20, 2023 USD ($)	Oct. 18, 2021 USD ($) agreement	Dec. 31, 2023 USD ($)	Dec. 31, 2021	Dec. 31, 2022 USD ($)
Short-term Debt [Line Items]
Short-term debt, weighted average interest rate, at point in time			6.96%		3.93%
Short-term borrowings			$ 775,000,000		$ 100,000,000
Minimum | Available for Issuance of Letters of Credit
Short-term Debt [Line Items]
Cross-default provision for other indebtedness			$ 100,000,000
Maximum | Money Pool
Short-term Debt [Line Items]
Debt term			364 days
Revolving Credit Facility | Line of Credit
Short-term Debt [Line Items]
Maximum amount borrowed under revolving credit facility	$ 1,000,000,000.0	$ 4,500,000,000
Line of credit facility, remaining borrowing capacity			$ 5,000,000,000
Number of agreements | agreement		6
Revolving Credit Facility | Line of Credit | Parent, FET, the Utilities and the Transmission Companies
Short-term Debt [Line Items]
Debt term		5 years
Revolving Credit Facility | Line of Credit | Ohio Companies
Short-term Debt [Line Items]
Maximum amount borrowed under revolving credit facility	800,000,000
Revolving Credit Facility | Line of Credit | Pennsylvania Companies
Short-term Debt [Line Items]
Maximum amount borrowed under revolving credit facility	950,000,000
Revolving Credit Facility | Line of Credit | JCP&L
Short-term Debt [Line Items]
Maximum amount borrowed under revolving credit facility	500,000,000
Revolving Credit Facility | Line of Credit | MP and PE
Short-term Debt [Line Items]
Maximum amount borrowed under revolving credit facility	400,000,000
Revolving Credit Facility | Line of Credit | Transmission companies
Short-term Debt [Line Items]
Maximum amount borrowed under revolving credit facility	850,000,000
Revolving Credit Facility | Line of Credit | KATCo
Short-term Debt [Line Items]
Maximum amount borrowed under revolving credit facility	$ 150,000,000
Debt term	364 days
Revolving Credit Facility | Line of Credit | FET, the Utilities and the Transmission Companies
Short-term Debt [Line Items]
Coverage ratio				250.00%
Revolving Credit Facility | Line of Credit | FET
Short-term Debt [Line Items]
Maximum amount borrowed under revolving credit facility	$ 1,000,000,000.0
Revolving Credit Facility | Line of Credit | Minimum | FET, the Utilities and the Transmission Companies
Short-term Debt [Line Items]
Consolidated debt to total capitalization ratio (percent)				65.00%
Revolving Credit Facility | Line of Credit | Maximum | Parent, FET, the Utilities and the Transmission Companies
Short-term Debt [Line Items]
Debt term				364 days
Revolving Credit Facility | Line of Credit | Maximum | FET, the Utilities and the Transmission Companies
Short-term Debt [Line Items]
Consolidated debt to total capitalization ratio (percent)				75.00%
Letter of Credit | Line of Credit
Short-term Debt [Line Items]
Debt term			1 year
Letter of Credit | Line of Credit | FE
Short-term Debt [Line Items]
Outstanding borrowings			$ 4,000,000