Taxes (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
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%	6.30%	6.20%
Amortized investment tax credits		(0.60%)	(0.60%)	(0.70%)	(0.70%)
Credit for electricity from renewable energy		(4.90%)	(4.90%)	(5.40%)	(5.30%)
AFUDC equity, net		(0.90%)	(0.40%)	(0.60%)	(0.40%)
Amortization of utility excess deferred tax - tax reform	[1]	(1.40%)	(1.70%)	(1.60%)	(1.80%)
Other, net, individually significant		(0.50%)	(0.10%)	(0.20%)	(0.10%)
Effective income tax rate		18.90%	19.50%	18.80%	18.90%
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	$ 1.0	$ 2.7	$ 2.9
Deficient Deferred Taxes, Tax Cuts And Jobs Act [Member]
Effects Of The Tax Cuts And Jobs Act [Abstract]
Collection of unprotected deficient deferred taxes		$ 0.3	$ 0.3	$ 1.0	$ 1.0
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%	6.30%	6.20%
Amortized investment tax credits		(0.60%)	(0.70%)	(0.70%)	(0.70%)
Credit for electricity from renewable energy		(5.20%)	(5.20%)	(5.70%)	(5.70%)
AFUDC equity, net		(1.00%)	(0.40%)	(0.70%)	(0.50%)
Amortization of utility excess deferred tax - tax reform	[1]	(1.50%)	(1.80%)	(1.70%)	(1.90%)
Other, net, individually significant		(0.50%)	(0.20%)	(0.30%)	(0.20%)
Effective income tax rate		18.40%	18.90%	18.20%	18.20%

[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 the three months ended September 30, 2023 and 2022, MGE recognized $0.9 million and $1.0 million, respectively. For the nine months ended September 30, 2023 and 2022, MGE recognized $2.7 million and $2.9 million, respectively. Included in the 2022 and 2023 rate settlement was a net collection from customers of the gas portion of deficient deferred taxes related to the 2017 Tax Act not restricted by IRS normalization rules. For both the three months ended September 30, 2023 and 2022, MGE recognized $0.3 million. For both the nine months ended September 30, 2023 and 2022, MGE recognized $1.0 million.