Taxes (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Reconciliation of tax provision to statutory federal income tax rate [Abstract]
Statutory federal income tax rate		21.00%	21.00%
State income taxes, net of federal benefit		6.30%	6.30%
Amortized investment tax credits		(0.10%)	(0.10%)
Credit for electricity from wind energy		(6.90%)	(5.90%)
AFUDC equity, net		(1.60%)	(0.20%)
Amortization of utility excess deferred tax - tax reform	[1]	(2.60%)	(2.40%)
Other, net, individually significant		0.00%	0.50%
Effective income tax rate		16.10%	19.20%
Excess Deferred Taxes, Tax Cuts And Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Excess deferred tax - Income statement effect		$ 0.7	$ 0.6
MGE [Member]
Reconciliation of tax provision to statutory federal income tax rate [Abstract]
Statutory federal income tax rate		21.00%	21.00%
State income taxes, net of federal benefit		6.30%	6.20%
Amortized investment tax credits		(0.10%)	(0.10%)
Credit for electricity from wind energy		(7.50%)	(6.50%)
AFUDC equity, net		(1.70%)	(0.20%)
Amortization of utility excess deferred tax - tax reform	[1]	(2.80%)	(2.60%)
Other, net, individually significant		(0.10%)	0.50%
Effective income tax rate		15.10%	18.30%

[1] Included are impacts of the Tax Cuts and Jobs Act for the regulated utility for excess deferred taxes recognized using a normalization method of accounting. For the three months ended March 31, 2020 and 2019, MGE recognized $0.7 million and $0.6 million, respectively. The amount and timing of the cash impacts will depend on the period over which certain income tax benefits are provided to customers, which will be determined by the PSCW.