Taxes (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2025	Mar. 31, 2024
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		(1.40%)	(2.20%)
Credit for electricity from renewable energy		(9.60%)	(10.20%)
AFUDC equity, net		(0.60%)	(0.60%)
Amortization of utility excess deferred tax - tax reform	[1]	(2.60%)	(6.20%)
Other, net, individually insignificant		0.10%	(0.30%)
Effective income tax rate		13.10%	7.70%
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
Deficient Deferred Taxes, Tax Cuts And Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Collection of unprotected deficient deferred taxes			$ 1.0
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		(1.50%)	(2.40%)
Credit for electricity from renewable energy		(10.50%)	(11.20%)
AFUDC equity, net		(0.70%)	(0.70%)
Amortization of utility excess deferred tax - tax reform	[1]	(2.80%)	(6.70%)
Other, net, individually insignificant		0.10%	(0.40%)
Effective income tax rate		11.80%	5.80%

[1] Included are impacts of the Tax Cut and Jobs Act of 2017 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, 2025 and 2024, 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.