REGULATORY MATTERS - Pennsylvania and West Virginia (Details) $ in Millions							3 Months Ended
	Jan. 13, 2023 USD ($)	Aug. 25, 2022 USD ($) MW	May 01, 2022 USD ($)	Mar. 17, 2022	Nov. 22, 2021 site MW	Jan. 16, 2020 USD ($)	Mar. 31, 2023 USD ($) proposal
FERC | Regulated Transmission
Regulatory Matters [Line Items]
Pre-tax impairment of regulatory asset							$ 25.0
FERC | Transmission Related Vegetation Management Programs | FirstEnergy
Regulatory Matters [Line Items]
Customer refund							45.0
Customer refund, net							34.0
Capital assets							195.0
Operating expense							90.0
Operating expense, net							67.0
Reduction in operating expense							$ 160.0
Pennsylvania | DSP June 2019- May 2023
Regulatory Matters [Line Items]
Number of RFP's | proposal							2
RFP term							2 years
Pennsylvania | Three month period | DSP June 2019- May 2023
Regulatory Matters [Line Items]
Term of energy contract							3 months
Pennsylvania | Twelve month period | DSP June 2019- May 2023
Regulatory Matters [Line Items]
Term of energy contract							12 months
Pennsylvania | Twenty-four month period | DSP June 2019- May 2023
Regulatory Matters [Line Items]
Term of energy contract							24 months
Pennsylvania | Pennsylvania Companies | PPUC | New LTIIPs
Regulatory Matters [Line Items]
Recovery period						5 years
Amount of requested rate increase (decrease)						$ 572.0
Pennsylvania | ME | PPUC | EE&C Phase IV
Regulatory Matters [Line Items]
Demand reduction targets							2.90%
Energy consumption reduction targets							3.10%
Pennsylvania | PN | PPUC | EE&C Phase IV
Regulatory Matters [Line Items]
Demand reduction targets							3.30%
Energy consumption reduction targets							3.00%
Pennsylvania | Penn | PPUC | EE&C Phase IV
Regulatory Matters [Line Items]
Demand reduction targets							2.00%
Energy consumption reduction targets							2.70%
Pennsylvania | WP | PPUC | EE&C Phase IV
Regulatory Matters [Line Items]
Demand reduction targets							2.50%
Energy consumption reduction targets							2.40%
West Virginia | MP and PE | WVPSC
Regulatory Matters [Line Items]
Requested amount of annual depreciation expense	$ 75.5
West Virginia | MP and PE | WVPSC | ENEC
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)		$ 183.8
Under recovered amount, percent		12.20%
Supplemental requested decrease		$ 145.0
Approved amount of annual increase		$ 92.0
Approved ROE		4.00%
Plant capacity (in MW's) | MW		1,200
West Virginia | MP and PE | WVPSC | Solar Generation Project
Regulatory Matters [Line Items]
Plant capacity (in MW's) | MW					50
Percent of subscriptions required prior to commencement of construction				85.00%
Number of proposed solar sites | site					3
Number of solar sites | site					5
Expected cost of the program			$ 110.0