Regulatory Matters - Pennsylvania and West Virginia (Details) $ in Millions												3 Months Ended	9 Months Ended
	May 17, 2022 USD ($)	May 01, 2022 USD ($)	Mar. 17, 2022	Dec. 29, 2021 USD ($)	Dec. 27, 2021 USD ($)	Dec. 17, 2021 USD ($)	Nov. 22, 2021 MW	Nov. 18, 2021 USD ($)	Aug. 27, 2021 USD ($)	Dec. 30, 2020 USD ($)	Jan. 16, 2020 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2022 proposal	Sep. 30, 2021 USD ($)	Jun. 18, 2020
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
FERC | Transmission Related Vegetation Management Programs | Other Nonoperating Income (Expense) | FirstEnergy
Regulatory Matters [Line Items]
Pre-tax impairment of regulatory asset														$ 21.0
ATSI | FERC | Transmission Related Vegetation Management Programs | Regulated Transmission
Regulatory Matters [Line Items]
Pre-tax impairment of regulatory asset														48.0
ATSI | FERC | Transmission Related Vegetation Management Programs | Regulated Distribution
Regulatory Matters [Line Items]
Pre-tax impairment of regulatory asset														$ 27.0
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 | PPUC
Regulatory Matters [Line Items]
Amended amount of rate increase								$ 61.0
Pennsylvania | PPUC | Regulated Distribution
Regulatory Matters [Line Items]
Pre-tax charges												$ 61.0
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]
Interim amount of approved rate increase	$ 94.0
West Virginia | MP and PE | WVPSC | Ft. Martin and Harrison Power Stations
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)						$ 142.0
Requested annual rate increase						$ 3.0
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%
Expected cost of the program		$ 100.0
West Virginia | MP and PE | WVPSC | ENEC
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)									$ 19.6	$ (2.6)
Approved amount of annual increase										$ (7.7)
Amount of requested rate increase (decrease) (percent)									1.50%
Supplemental requested decrease									$ (7.7)
Expected cost of the program				$ 2.9
West Virginia | MP and PE | WVPSC | Integrated Resource Plan
Regulatory Matters [Line Items]
Approved amount of annual increase				$ 19.6
West Virginia | MP and PE | WVPSC | VMS
Regulatory Matters [Line Items]
Approved amount of annual increase					$ 16.0
Surcharge period					2 years