COMMITMENTS AND CONTINGENCIES - ENVIRONMENTAL MATTERS (Details) T in Millions, $ in Millions	1 Months Ended							12 Months Ended
	Jan. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Aug. 31, 2014	Jun. 30, 2013 USD ($)	Apr. 30, 2013	Mar. 31, 2013 USD ($)	Feb. 28, 2011	Dec. 31, 2015 USD ($) T	Dec. 31, 2014 USD ($) T	Jun. 01, 2015 USD ($)
Mercury and other hazardous air pollutants | Electric utility
Air Quality
Percentage mercury emission reduction required by the State of Wisconsin's mercury rule		90.00%						90.00%
Mercury and other hazardous air pollutants | Electric utility | Wisconsin Electric
Air Quality
Term of MATS compliance extension					1 year
Mercury and other hazardous air pollutants | Electric utility | WPS
Air Quality
Term of MATS compliance extension								1 year
Climate Change | Electric utility
Air Quality
Percentage greenhouse gas emission reduction nationwide								32.00%
Percentage greenhouse gas emission reduction for retirement of a nuclear plant								10.00%
Carbon dioxide emissions | T								31.0
Climate Change | Electric utility | Wisconsin Energy
Air Quality
Carbon dioxide emissions | T									23.3
Climate Change | Electric utility | Wisconsin
Air Quality
Percentage greenhouse gas emission reduction by state								41.00%
Climate Change | Electric utility | Michigan
Air Quality
Percentage greenhouse gas emission reduction by state								39.00%
Term of extension for Federal Plan and Model Trading Rule		2 years
Climate Change | Natural gas utility
Air Quality
Carbon dioxide emissions | T								27.1
Climate Change | Natural gas utility | Wisconsin Energy
Air Quality
Carbon dioxide emissions | T									10.8
Clean Water Act Cooling Water Intake Structure Rule | Electric utility
Water Quality
Number of compliance options available to meet standard			7
Steam Electric Effluent Guidelines | Electric utility | Subsequent event
Environmental Matters
Renewal period for facility permits	5 years
Steam Electric Effluent Guidelines | Electric utility | Minimum | Subsequent event
Water Quality
Expected environmental costs to achieve required emission reductions	$ 70.0
Steam Electric Effluent Guidelines | Electric utility | Maximum | Subsequent event
Water Quality
Expected environmental costs to achieve required emission reductions	$ 100.0
Renewables, Efficiency, and Conservation | Electric utility | Wisconsin
Renewables, Efficiency, and Conservation
Percent goal of electricity consumption		10.00%						10.00%
Percent of annual operating revenues								1.20%
Renewables, Efficiency, and Conservation | Electric utility | Wisconsin | Wisconsin Electric
Renewables, Efficiency, and Conservation
Renewable energy percent required		8.27%						8.27%
Renewables, Efficiency, and Conservation | Electric utility | Wisconsin | WPS
Renewables, Efficiency, and Conservation
Renewable energy percent required		9.74%						9.74%
Renewables, Efficiency, and Conservation | Electric utility | Michigan
Renewables, Efficiency, and Conservation
Percent goal of electricity consumption		10.00%						10.00%
Renewables, Efficiency, and Conservation | Electric utility | Maximum | Michigan
Renewables, Efficiency, and Conservation
Renewable energy percent required		1.00%						1.00%
Manufactured Gas Plant Remediation | Natural gas utility
Manufactured Gas Plant Remediation
Regulatory assets recorded for cash and estimated future remediation expenditures		$ 697.0						$ 697.0	$ 45.9
Liabilities estimated and accrued for future undiscounted investigation and cleanup costs for all sites		$ 628.0						$ 628.0	$ 32.6
Valley Power Plant | Electric utility | Wisconsin Electric
Environmental Matters
Renewal period for facility permits							5 years
Weston and Pulliam Consent Decree | Electric utility
Consent Decrees
Regulatory asset for undepreciated book value of retired plants										$ 11.5
Weston and Pulliam Consent Decree | Electric utility | WPS
Consent Decrees
Beneficial environmental project amount						$ 6.0
Civil penalty						$ 1.2
Joint Ownership Power Plants Consent Decree - Columbia and Edgewater | Electric utility | WPS
Consent Decrees
Beneficial environmental project amount				$ 1.3
Civil penalty				$ 0.4