Jointly Owned Utility Facilities (Details) $ in Millions	Dec. 31, 2018 USD ($) MW
Oak Creek Expansion Units 1 and 2 | We Power
Jointly Owned Electric Generating Facilities
Ownership (as a percentage)	83.34%
Share of rated capacity (MW) (1) | MW	1,056.8
Property, plant, and equipment	$ 2,450.6
Accumulated depreciation	(394.1)
Construction Work in Progress	$ 1.8
Weston 4 | WPS
Jointly Owned Electric Generating Facilities
Ownership (as a percentage)	70.00%
Share of rated capacity (MW) (1) | MW	384.9
Property, plant, and equipment	$ 615.4
Accumulated depreciation	(205.2)
Construction Work in Progress	$ 1.9
Columbia Energy Center Units 1 and 2 | WPS
Jointly Owned Electric Generating Facilities
Future Ownership Interest of Columbia	27.50%
Ownership (as a percentage)	28.10%
Share of rated capacity (MW) (1) | MW	314.8
Property, plant, and equipment	$ 438.8
Accumulated depreciation	(132.2)
Construction Work in Progress	$ 0.3
Forward Wind Energy Center | WPS
Jointly Owned Electric Generating Facilities
Ownership (as a percentage)	44.60%
Share of rated capacity (MW) (1) | MW	8.7
Property, plant, and equipment	$ 123.7
Accumulated depreciation	(43.7)
Construction Work in Progress	$ 0.1