Regulatory Matters - Pennsylvania and West Virginia (Details) $ in Millions					1 Months Ended	3 Months Ended	6 Months Ended
	Mar. 12, 2020	Mar. 11, 2020	Aug. 30, 2019 USD ($)	Aug. 21, 2019 USD ($)	Mar. 31, 2016 USD ($)	Mar. 31, 2020	Jun. 30, 2020 USD ($) proposal	Jun. 18, 2020	Dec. 31, 2019 USD ($)	Oct. 11, 2019 MW
ATSI | FERC
Regulatory Matters [Line Items]
Regulatory Assets							$ 76.0		$ 73.0
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 | Pennsylvania Companies | PPUC | Wavier of DSIC Cap
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease) (percent)			11.81%
Approved ROE		5.00%
Temporary increase in rate cap	7.50%
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)				$ (6.1)
Amount of requested rate increase (decrease) (percent)				(0.40%)
West Virginia | MP and PE | WVPSC | Termination Agreement of PURPA Power Purchase Agreement
Regulatory Matters [Line Items]
Proposed plant disposal capacity (in MW's) | MW										50
West Virginia | MP and PE | WVPSC | VMS
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)				$ 7.6
Amount of requested rate increase (decrease) (percent)				0.05%
Maintenance cycle						4 years	5 years