Regulatory Matters - Pennsylvania and West Virginia (Details) $ in Millions				1 Months Ended	9 Months Ended
	Aug. 30, 2019 USD ($)	Aug. 21, 2019 USD ($)	Jan. 18, 2019 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2019 proposal	Oct. 11, 2019 MW
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
Pennsylvania | Pennsylvania Companies | PPUC | Wavier of DSIC Cap
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease) (percent)	11.81%
Pennsylvania | ME
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)			$ 45.0
Pennsylvania | Penn
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)			26.0
Pennsylvania | WP
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)			51.0
Pennsylvania | PN
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)			$ 25.0
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 | VMS
Regulatory Matters [Line Items]
Amount of requested rate increase (decrease)		$ 7.6
Amount of requested rate increase (decrease) (percent)		0.05%
Subsequent Event | 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