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Commitments and Contingencies - Environmental Matters (Details) T in Millions, $ in Millions | 1 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Oct. 31, 2014 compliance_option | Jun. 30, 2013 USD ($) | Mar. 31, 2013 USD ($) | Dec. 31, 2017 USD ($) T MW | Dec. 31, 2016 USD ($) T | Dec. 31, 2015 | Sep. 30, 2016 Case | Jun. 01, 2015 USD ($)
Climate Change | Electric |  |  |  |  |  |  |  |
Air Quality |  |  |  |  |  |  |  |
Number of legal cases heard by a court | Case |  |  |  |  |  |  | 1 |
Percentage of nationwide greenhouse gas emissions reduction |  |  |  |  |  | 32.00% |  |
Interim goal for greenhouse gas emissions reductions (fraction) |  |  |  |  |  | 0.667 |  |
Company goal for percentage of carbon dioxide emissions reductions |  |  |  | 40.00% |  |  |  |
Capacity of coal generation expected to be retired by 2020 | MW |  |  |  | 1,800 |  |  |  |
Carbon dioxide emissions | T |  |  |  | 29.2 | 29.1 |  |  |
Climate Change | Electric | Wisconsin |  |  |  |  |  |  |  |
Air Quality |  |  |  |  |  |  |  |
Percentage of greenhouse gas emissions reduction by state |  |  |  |  |  | 41.00% |  |
Climate Change | Electric | Michigan |  |  |  |  |  |  |  |
Air Quality |  |  |  |  |  |  |  |
Percentage of greenhouse gas emissions reduction by state |  |  |  |  |  | 39.00% |  |
Climate Change | Natural gas |  |  |  |  |  |  |  |
Air Quality |  |  |  |  |  |  |  |
Carbon dioxide emissions | T |  |  |  | 26.4 | 26.8 |  |  |
Clean Water Act Cooling Water Intake Structure Rule | Electric |  |  |  |  |  |  |  |
Water Quality |  |  |  |  |  |  |  |
Number of compliance options available to meet standard | compliance_option | 7 |  |  |  |  |  |  |
Steam Electric Effluent Guidelines | Electric |  |  |  |  |  |  |  |
Water Quality |  |  |  |  |  |  |  |
Renewal period for facility permits |  |  |  | 5 years |  |  |  |
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 |  |  |  | 676.6 | $ 702.7 |  |  |
Reserves recorded for remediation of manufactured gas plant sites |  |  |  | $ 617.2 | $ 633.4 |  |  |
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 |  |  |  |  |  |

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