Regulatory Matters - Pennsylvania and West Virginia (Details) $ in Millions					1 Months Ended	3 Months Ended
	Dec. 30, 2020 USD ($) MW	Aug. 28, 2020 USD ($)	May 01, 2020 USD ($)	Aug. 30, 2019 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2021 proposal	Jun. 18, 2020
ATSI | FERC | Transmission Related Vegetation Management Programs
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)			$ 19.0
Amended amount of rate increase			$ 85.0
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 | EE&C Phase III
Regulatory Matters [Line Items]
Approved amount of annual increase					$ 390.0
Pennsylvania | Pennsylvania Companies | PPUC | New LTIIPs
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)				$ 572.0
Recovery period				5 years
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 | ENEC
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)		$ (55.0)
Amount of requested rate increase (decrease) (percent)		(4.00%)
Recovery of deferred, incremental uncollectible and other related costs		$ 10.5
Amount of requested rate decrease	$ 2.6
West Virginia | MP and PE | WVPSC | Modernization and Improvement Program For Coal-Fired Boilers
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)		$ 5.0
West Virginia | MP and PE | WVPSC | Integrated Resource Plan
Regulatory Matters [Line Items]
Project period	15 years
Capacity of plant to be constructed (in MW's) | MW	50