Rate Matters (Details) - USD ($) $ in Millions	1 Months Ended			12 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2017	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2018
Tax Cuts and Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Return of tax credit					$ 3.2		$ 8.2
PSCW [Member] | MGE [Member]
Rate Proceedings [Abstract]
Approved equity capital structure, percentage				56.10%	56.60%	57.20%
Authorized return on equity, percentage				9.80%	9.80%	9.80%
Fuel Rules [Abstract]
Fuel rules, bandwidth					2.00%
Fuel rules, electric fuel costs, deferral, upper threshold					102.00%
Fuel rules, electric fuel costs, deferral, lower threshold					98.00%
Deferred fuel rules monitored costs					$ 1.5
Public Utilities Fuel Surcharge Amount					$ 0.5
Public Utilities Fuel Surcharge Percentage					0.13%
PSCW [Member] | Fuel Rules Refund, 2015/2016 [Member] | MGE [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total			$ 6.2
PSCW [Member] | Fuel Rules Refund, 2017 [Member] | MGE [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total		$ 4.2
PSCW [Member] | Fuel Rules Refund 2018 [Member] | MGE [Member]
Fuel Rules [Abstract]
Return of electric fuel credit, total	$ 9.5
Electric Rate Proceeding [Member] | PSCW [Member] | MGE [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage				(0.84%)	(2.24%)	(0.80%)
Authorized rate increase (decrease), amount				$ (3.4)	$ (9.2)	$ (3.3)
Gas Rate Proceeding [Member] | PSCW [Member] | MGE [Member]
Rate Proceedings [Abstract]
Authorized rate increase (decrease), percentage				1.46%	1.06%	1.90%
Authorized rate increase (decrease), amount				$ 2.4	$ 1.7	$ 3.1