COMMITMENTS, GUARANTEES AND CONTINGENCIES - Climate Change, Clean Water Act, Regulation of Waste Disposal and Other Legal Proceedings (Details) $ in Thousands				12 Months Ended
	Feb. 09, 2022 USD ($)	Jul. 21, 2021 USD ($)	Feb. 20, 2018 USD ($)	Dec. 31, 2021 USD ($)	Oct. 29, 2020 director
Loss Contingencies [Line Items]
Number of additional executives terminated | director					2
Climate change
Loss Contingencies [Line Items]
Proposed reduction in power plants carbon pollution (percent)				30.00%
Smith v FirstEnergy Corp et al., Buldas v FirstEnergy Corp. et al., and Hudock and Cameo Countertops, Inc. v. FirstEnergy Corp. et al.
Loss Contingencies [Line Items]
Loss contingency accrual				$ 37,500
Emmons v. FirstEnergy Corp. et al.
Loss Contingencies [Line Items]
Loss contingency accrual				37,500
Shareholder Derivative Lawsuit | Subsequent Event
Loss Contingencies [Line Items]
Settlement payment awarded	$ 180,000
U.S. Attorney's Office | United States v. Householder, et al.
Loss Contingencies [Line Items]
Term of DPA		3 years
Loss in period		$ 230,000
Term of payments		60 days
United States Treasury | United States v. Householder, et al.
Loss Contingencies [Line Items]
Proposed penalty		$ 115,000
Ohio Development Service | United States v. Householder, et al.
Loss Contingencies [Line Items]
Proposed penalty		$ 115,000
Clean Water Act | EPA
Loss Contingencies [Line Items]
Proposed penalty			$ 610
Regulation of Waste Disposal
Loss Contingencies [Line Items]
Accrual for environmental loss contingencies				110,000
Environmental liabilities former gas facilities				$ 70,000