Jointly Owned Utility Facilities (Details) $ in Millions	Dec. 31, 2020 USD ($) MW
Elm Road Generating Station Units 1 and 2 | We Power
Jointly owned utility facilities
Ownership (as a percentage)	83.34%
Share of capacity (MW) | MW	1,059.4
Property, plant, and equipment	$ 2,436.5
Accumulated depreciation	(447.2)
Construction work in progress	$ 2.2
Weston Unit 4 | WPS
Jointly owned utility facilities
Ownership (as a percentage)	70.00%
Share of capacity (MW) | MW	385.0
Property, plant, and equipment	$ 613.5
Accumulated depreciation	(218.6)
Construction work in progress	$ 3.8
Columbia Energy Center Units 1 and 2 | WPS
Jointly owned utility facilities
Ownership (as a percentage)	27.50%
Share of capacity (MW) | MW	311.1
Property, plant, and equipment	$ 422.3
Accumulated depreciation	(145.5)
Construction work in progress	$ 2.3
Forward Wind Energy Center | WPS
Jointly owned utility facilities
Ownership (as a percentage)	44.60%
Share of capacity (MW) | MW	61.5
Property, plant, and equipment	$ 118.9
Accumulated depreciation	(49.6)
Construction work in progress	$ 0.0
Two Creeks | WPS
Jointly owned utility facilities
Ownership (as a percentage)	66.70%
Share of capacity (MW) | MW	100.0
Property, plant, and equipment	$ 136.0
Accumulated depreciation	(0.7)
Construction work in progress	$ 0.0
Badger Hollow I | WPS
Jointly owned utility facilities
Ownership (as a percentage)	66.70%
Share of capacity (MW) | MW	100
Construction work in progress	$ 115.3
Badger Hollow II | WE
Jointly owned utility facilities
Ownership (as a percentage)	66.70%
Share of capacity (MW) | MW	100
Construction work in progress	$ 10.8