Taxes (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax rate		21.00%	21.00%	21.00%	21.00%
State income taxes, net of federal benefit		6.40%	6.20%	6.30%	6.20%
Amortized investment tax credits		(1.30%)	(2.40%)	(1.30%)	(2.30%)
Credit for electricity from renewable energy		(13.20%)	(11.70%)	(11.00%)	(10.80%)
AFUDC equity, net		(0.50%)	(0.70%)	(0.60%)	(0.70%)
Amortization of utility excess deferred tax - tax reform	[1]	(2.50%)	(6.80%)	(2.50%)	(6.40%)
Other, net, individually insignificant		0.20%	0.20%	0.10%	(0.10%)
Effective income tax rate		10.10%	5.80%	12.00%	6.90%
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	$ 1.8	$ 1.8
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		$ 2.1
MGE [Member]
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax rate		21.00%	21.00%	21.00%	21.00%
State income taxes, net of federal benefit		6.20%	6.20%	6.20%	6.20%
Amortized investment tax credits		(1.40%)	(2.60%)	(1.50%)	(2.50%)
Credit for electricity from renewable energy		(14.40%)	(12.90%)	(11.90%)	(11.90%)
AFUDC equity, net		(0.50%)	(0.70%)	(0.60%)	(0.70%)
Amortization of utility excess deferred tax - tax reform	[1]	(2.70%)	(7.50%)	(2.80%)	(7.00%)
Other, net, individually insignificant		0.20%	0.10%	0.10%	(0.20%)
Effective income tax rate		8.40%	3.60%	10.50%	4.90%

[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 June 30, 2025 and 2024, MGE recognized $0.9 million. For both the six months ended June 30, 2025 and 2024, MGE recognized $1.8 million. For the three and six months ended June 30, 2024, MGE recognized $1.0 million and $2.1 million, respectively, of deferred taxes not restricted by IRS normalization rules.