Commitments and Contingencies - Environmental Matters (Details) T in Millions, $ in Millions	1 Months Ended		12 Months Ended
	Jun. 30, 2013 USD ($)	Mar. 31, 2013 USD ($)	Dec. 31, 2018 USD ($) generating_units degreecelsius T MW	Dec. 31, 2017 USD ($) T	Jun. 01, 2015 USD ($)
Climate Change | Electric
Air Quality
Company goal for percentage of carbon dioxide emissions reductions by 2030			40.00%
Company goal for percentage of carbon dioxide emissions reduction by 2050			80.00%
Capacity of coal generation expected to be retired by 2020 | MW			1,800
Carbon dioxide emissions | T			26.4	29.2
Climate Change | Electric | Maximum
Air Quality
Global temperature increases limit | degreecelsius			2
Climate Change | Natural gas
Air Quality
Carbon dioxide emissions | T			29.5	26.5
Steam Electric Effluent Guidelines | Electric
Water Quality
Total units of OCPP and ERGS | generating_units			6
Expected cost to achieve required emission reductions			$ 70.0
Manufactured Gas Plant Remediation | Natural gas
Manufactured Gas Plant Remediation
Regulatory assets recorded for remediation of manufactured gas plant sites			687.1	$ 676.6
Reserves recorded for remediation of manufactured gas plant sites			$ 616.4	$ 617.2
Renewables, Efficiency, and Conservation | Electric | Wisconsin
Renewables, Efficiency, and Conservation
State renewable portfolio requirement for years 2016 through 2018, as a percent			10.00%
Percent of annual operating revenues used to fund renewable program			1.20%
Renewables, Efficiency, and Conservation | Electric | Wisconsin | WE
Renewables, Efficiency, and Conservation
Renewable energy percent			8.27%
Renewables, Efficiency, and Conservation | Electric | Wisconsin | WPS
Renewables, Efficiency, and Conservation
Renewable energy percent			9.74%
Renewables, Efficiency, and Conservation | Electric | Michigan
Renewables, Efficiency, and Conservation
State renewable portfolio requirement for years 2016 through 2018, as a percent			10.00%
State renewable portfolio requirement for years 2019 through 2020, as a percent			12.50%
State renewable portfolio requirement for 2021, as a percent			15.00%
Renewables, Efficiency, and Conservation | Electric | Michigan | Maximum
Renewables, Efficiency, and Conservation
Energy optimization target, as a percent			1.00%
WPS Consent Decree - Weston and Pulliam Power Plants | Electric | WPS
Consent Decrees
Beneficial environmental project amount		$ 6.0
Civil penalty		$ 1.2
Regulatory asset for undepreciated book value of retired plants					$ 11.5
Joint Ownership Power Plants Consent Decree - Columbia and Edgewater | Electric | WPS
Consent Decrees
Beneficial environmental project amount	$ 1.3
Civil penalty	$ 0.4