Taxes (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2024	Mar. 31, 2023
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax rate		21.00%	21.00%
State income taxes, net of federal benefit		6.20%	6.30%
Amortized investment tax credits		(2.20%)	(0.80%)
Credit for electricity from renewable energy		(10.20%)	(6.00%)
AFUDC equity, net		(0.60%)	(0.50%)
Amortization of utility excess deferred tax - tax reform	[1]	(6.20%)	(1.80%)
Other, net, individually significant		(0.30%)	(0.20%)
Effective income tax rate		7.70%	18.00%
Excess Deferred Taxes, Tax Cuts And Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Excess deferred tax - Income statement effect		$ 0.9	$ 0.9
Return of unprotected excess deferred taxes		$ 1.0
Deficient Deferred Taxes, Tax Cuts And Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Collection of unprotected deficient deferred taxes			$ 0.3
MGE [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax rate		21.00%	21.00%
State income taxes, net of federal benefit		6.20%	6.20%
Amortized investment tax credits		(2.40%)	(0.80%)
Credit for electricity from renewable energy		(11.20%)	(6.50%)
AFUDC equity, net		(0.70%)	(0.50%)
Amortization of utility excess deferred tax - tax reform	[1]	(6.70%)	(1.90%)
Other, net, individually significant		(0.40%)	(0.30%)
Effective income tax rate		5.80%	17.20%

[1] Included are impacts of the 2017 Tax Act for the regulated utility for excess deferred taxes recognized using a normalization method of accounting in recognition of IRS rules that restrict the rate at which the excess deferred taxes may be returned to utility customers. For both the three months ended March 31, 2024 and 2023, MGE recognized $0.9 million. For the three months ended March 31, 2024, MGE recognized $1.0 million of deferred taxes not restricted by IRS normalization rules, compared to a net collection from customers of $0.3 million for the three months ended March 31, 2023.