Joint Plant Ownership (Details) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2022 USD ($) MW	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) MW	Jun. 30, 2021 USD ($)
Red Barn Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Projected renewable project costs	[1],[2]	$ 18.0		$ 18.0
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	[1],[2]	$ 0.6		$ 0.6
Red Barn Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	[2]	10.00%		10.00%
Jointly owned utility plant, plant capacity (in MW) | MW	[2]	9.16		9.16
Badger Hollow II Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Projected renewable project costs	[1],[3],[4]	$ 76.0		$ 76.0
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	[1],[4],[5]	$ 47.5		$ 47.5
Badger Hollow II Units [Member] | Public Service Commission of Wisconsin [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate - Signficiant projects (100%)				100.00%
Badger Hollow II Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	[4]	33.00%		33.00%
Jointly owned utility plant, plant capacity (in MW) | MW	[4]	50		50
Paris Units [Member]
Jointly Owned Utility Plant Interests [Line Items]
Projected renewable project costs	[1],[3],[6]	$ 51.0		$ 51.0
Public Utilities, Property, Plant and Equipment, Construction Work in Progress	[1],[6]	$ 15.4		$ 15.4
Paris Units [Member] | Public Service Commission of Wisconsin [Member]
Allowance for Funds Used During Construction
Authorized AFUDC rate - Signficiant projects (100%)				100.00%
Paris Units [Member] | MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly owned utility plant, ownership interest	[6]	10.00%		10.00%
Jointly owned utility plant, plant capacity (in MW) | MW	[6]	31		31
Badger Hollow II and Paris Units [Member]
Allowance for Funds Used During Construction
AFUDC		$ 0.6	$ 0.1	$ 1.0	$ 0.2

[1] Excluding AFUDC.

[2] The Red Barn Wind Farm is located in the Towns of Wingville and Clifton in Grant County, Wisconsin.

[3] In 2022, MGE notified the PSCW of increases in projected costs at Badger Hollow II and Paris. The main drivers were increases in the costs of key commodities, labor, and solar modules resulting from supply chain and market disruptions. MGE expects to recover the incremental costs through future rates.

[4] The Badger Hollow II solar farm is located in southwestern Wisconsin in Iowa County, near the villages of Montfort and Cobb.

[5] Includes an allocation of common facilities at Badger Hollow placed in service in November 2021.

[6] Paris Solar-Battery Park is located in the Town of Paris in Kenosha County, Wisconsin.