Regulatory Matters (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Regulatory Assets, Noncurrent		$ 175.8	$ 173.8
Unbilled Revenue		15.9	19.4
Due from PJM transmission settlement		1.8	1.8
Subsidiaries [Member]
Regulatory Assets, Noncurrent		175.8	173.8
Unbilled Revenue		15.9	19.4
Due from PJM transmission settlement		$ 1.8	$ 1.8
Scenario, Forecast [Member]
Increase in revenues from proposed transmission rate change to a formula rate	$ 4.1
Scenario, Forecast [Member] | Subsidiaries [Member]
Increase in revenues from proposed transmission rate change to a formula rate	$ 4.1