COMMITMENTS AND CONTINGENCIES - ENVIRONMENTAL MATTERS (Details) T in Millions, $ in Millions	1 Months Ended						12 Months Ended
	Sep. 30, 2016	Jan. 31, 2016	Dec. 31, 2015 USD ($)	Aug. 31, 2014	Jun. 30, 2013 USD ($)	Mar. 31, 2013 USD ($)	Dec. 31, 2016 USD ($) T	Dec. 31, 2015 USD ($) T	Jun. 01, 2015 USD ($)
Electric | Cross-State Air Pollution Rule
Air Quality
Number Of States Impacted By Cross State Air Pollution Rule	23
Electric | Mercury And Other Hazardous Air Pollutants
Air Quality
Percentage Mercury Emission Reduction							90.00%
Electric | Climate Change
Air Quality
Percentage greenhouse gas emission reduction nationwide								32.00%
Interim requirement greenhouse gas emissions reductions								0.667
Percentage carbon dioxide emission reduction company goal							40.00%
Carbon dioxide emissions | T							5.7	5.7
Electric | Clean Water Act Cooling Water Intake Structure Rule [Member]
Water Quality
Number of compliance options available to meet standard				7
Electric | Steam Electric Effluent Guidelines
Water Quality
Renewal period for facility permits		5 years
Electric | Steam Electric Effluent Guidelines | Minimum
Water Quality
Expected environmental costs to achieve required emission reductions							$ 25.0
Electric | Steam Electric Effluent Guidelines | Maximum
Water Quality
Expected environmental costs to achieve required emission reductions							$ 35.0
Electric | Weston and Pulliam Consent Decree
Consent Decrees
Beneficial environmental project amount						$ 6.0
Civil penalty						$ 1.2
Regulatory asset for undepreciated book value of retired plants									$ 11.5
Electric | Joint Ownership Power Plants Consent Decree - Columbia and Edgewater
Consent Decrees
Beneficial environmental project amount					$ 1.3
Civil penalty					$ 0.4
Natural gas | Climate Change
Air Quality
Carbon dioxide emissions | T							3.6	3.5
Natural gas | Manufactured gas plant remediation
Manufactured Gas Plant Remediation
Regulatory assets recorded for remediation of manufactured gas plant sites			$ 104.4				$ 116.0	$ 104.4
Reserves recorded for remediation of manufactured gas plant sites			$ 83.5				$ 97.2	$ 83.5
MICHIGAN | Electric | Renewables, efficiency, and conservation
Renewables, Efficiency, and Conservation
Percent goal of electricity consumption							10.00%
Energy optimization target							1.00%
WISCONSIN | Electric | Climate Change
Air Quality
Percentage greenhouse gas emission reduction state								41.00%
Percentage greenhouse gas emission reduction for retirement of a nuclear plant			10.00%
WISCONSIN | Electric | Renewables, efficiency, and conservation
Renewables, Efficiency, and Conservation
Percent goal of electricity consumption							10.00%
Renewable energy percent required							9.74%
Percent of annual operating revenues							1.20%