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OPERATING REVENUES - DISAGGREGATION OF OPERATING REVENUES (Details) $ in Millions | 3 Months Ended
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Mar. 31, 2018 USD ($) contract performance_obligations | Mar. 31, 2017 USD ($)
Disaggregation of Operating Revenues |  |
Revenues | $ 2,286.5 | $ 2,304.5
Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 2,290.0 |
Other operating revenues |  |
Disaggregation of Operating Revenues |  |
Revenues | $ (3.5) |
Electric |  |
Disaggregation of Operating Revenues |  |
Number of contracts | contract | 1 |
Number of performance obligations | performance_obligations | 2 |
Number of days payment is due | 30 days |
Electric | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | $ 1,067.7 |
Natural gas |  |
Disaggregation of Operating Revenues |  |
Number of days payment is due | 30 days |
Natural gas | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | $ 1,210.7 |
Natural gas | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 1,198.3 |
Natural gas | Transferred over time | Revenues from contracts with customers | Residential |  |
Disaggregation of Operating Revenues |  |
Revenues | 812.5 |
Natural gas | Transferred over time | Revenues from contracts with customers | Total retail |  |
Disaggregation of Operating Revenues |  |
Revenues | 1,174.5 |
Natural gas | Transferred over time | Revenues from contracts with customers | Commercial and industrial |  |
Disaggregation of Operating Revenues |  |
Revenues | 362.0 |
Natural gas | Transferred over time | Revenues from contracts with customers | Transport |  |
Disaggregation of Operating Revenues |  |
Revenues | 108.6 |
Natural gas | Transferred over time | Revenues from contracts with customers | Other utility |  |
Disaggregation of Operating Revenues |  |
Revenues | (84.8) |
Total utility revenues | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 2,278.4 |
Other non-utility revenues | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 11.6 |
Public Utility |  |
Disaggregation of Operating Revenues |  |
Revenues | 2,266.3 |
Public Utility | Other operating revenues |  |
Disaggregation of Operating Revenues |  |
Revenues | (3.6) |
Public Utility | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 2,269.9 |
Public Utility | Electric | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 1,067.7 |
Public Utility | Natural gas | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 1,198.3 |
Public Utility | Total utility revenues | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 2,266.0 |
Public Utility | Other non-utility revenues | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 3.9 |
Wisconsin | Natural gas | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 518.0 |
Wisconsin | Natural gas | Transferred over time | Revenues from contracts with customers | Residential |  |
Disaggregation of Operating Revenues |  |
Revenues | 356.7 |
Wisconsin | Natural gas | Transferred over time | Revenues from contracts with customers | Total retail |  |
Disaggregation of Operating Revenues |  |
Revenues | 544.6 |
Wisconsin | Natural gas | Transferred over time | Revenues from contracts with customers | Commercial and industrial |  |
Disaggregation of Operating Revenues |  |
Revenues | 187.9 |
Wisconsin | Natural gas | Transferred over time | Revenues from contracts with customers | Transport |  |
Disaggregation of Operating Revenues |  |
Revenues | 21.0 |
Wisconsin | Natural gas | Transferred over time | Revenues from contracts with customers | Other utility |  |
Disaggregation of Operating Revenues |  |
Revenues | (47.6) |
Wisconsin | Public Utility |  |
Disaggregation of Operating Revenues |  |
Revenues | 1,589.1 |
Wisconsin | Public Utility | Other operating revenues |  |
Disaggregation of Operating Revenues |  |
Revenues | 3.4 |
Wisconsin | Public Utility | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 1,585.7 |
Wisconsin | Public Utility | Electric | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 1,067.7 |
Wisconsin | Public Utility | Electric | Transferred over time | Revenues from contracts with customers | Residential |  |
Disaggregation of Operating Revenues |  |
Revenues | 384.3 |
Wisconsin | Public Utility | Electric | Transferred over time | Revenues from contracts with customers | Small commercial and industrial |  |
Disaggregation of Operating Revenues |  |
Revenues | 330.7 |
Wisconsin | Public Utility | Electric | Transferred over time | Revenues from contracts with customers | Large commercial and industrial |  |
Disaggregation of Operating Revenues |  |
Revenues | 203.9 |
Wisconsin | Public Utility | Electric | Transferred over time | Revenues from contracts with customers | Other |  |
Disaggregation of Operating Revenues |  |
Revenues | 7.7 |
Wisconsin | Public Utility | Electric | Transferred over time | Revenues from contracts with customers | Total retail |  |
Disaggregation of Operating Revenues |  |
Revenues | 926.6 |
Wisconsin | Public Utility | Electric | Transferred over time | Revenues from contracts with customers | Wholesale |  |
Disaggregation of Operating Revenues |  |
Revenues | 54.9 |
Wisconsin | Public Utility | Electric | Transferred over time | Revenues from contracts with customers | Resale |  |
Disaggregation of Operating Revenues |  |
Revenues | 73.8 |
Wisconsin | Public Utility | Electric | Transferred over time | Revenues from contracts with customers | Steam |  |
Disaggregation of Operating Revenues |  |
Revenues | 9.7 |
Wisconsin | Public Utility | Electric | Transferred over time | Revenues from contracts with customers | Other utility |  |
Disaggregation of Operating Revenues |  |
Revenues | 2.7 |
Wisconsin | Public Utility | Natural gas | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 518.0 |
Wisconsin | Public Utility | Total utility revenues | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 1,585.7 |
Wisconsin | Public Utility | Other non-utility revenues | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Illinois | Natural gas | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 507.6 |
Illinois | Natural gas | Transferred over time | Revenues from contracts with customers | Residential |  |
Disaggregation of Operating Revenues |  |
Revenues | 332.6 |
Illinois | Natural gas | Transferred over time | Revenues from contracts with customers | Total retail |  |
Disaggregation of Operating Revenues |  |
Revenues | 442.0 |
Illinois | Natural gas | Transferred over time | Revenues from contracts with customers | Commercial and industrial |  |
Disaggregation of Operating Revenues |  |
Revenues | 109.4 |
Illinois | Natural gas | Transferred over time | Revenues from contracts with customers | Transport |  |
Disaggregation of Operating Revenues |  |
Revenues | 77.7 |
Illinois | Natural gas | Transferred over time | Revenues from contracts with customers | Other utility |  |
Disaggregation of Operating Revenues |  |
Revenues | (12.1) |
Illinois | Public Utility |  |
Disaggregation of Operating Revenues |  |
Revenues | 507.3 |
Illinois | Public Utility | Other operating revenues |  |
Disaggregation of Operating Revenues |  |
Revenues | (0.3) |
Illinois | Public Utility | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 507.6 |
Illinois | Public Utility | Electric | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Illinois | Public Utility | Natural gas | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 507.6 |
Illinois | Public Utility | Total utility revenues | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 507.6 |
Illinois | Public Utility | Other non-utility revenues | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Other States | Natural gas | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 172.7 |
Other States | Natural gas | Transferred over time | Revenues from contracts with customers | Residential |  |
Disaggregation of Operating Revenues |  |
Revenues | 123.2 |
Other States | Natural gas | Transferred over time | Revenues from contracts with customers | Total retail |  |
Disaggregation of Operating Revenues |  |
Revenues | 187.9 |
Other States | Natural gas | Transferred over time | Revenues from contracts with customers | Commercial and industrial |  |
Disaggregation of Operating Revenues |  |
Revenues | 64.7 |
Other States | Natural gas | Transferred over time | Revenues from contracts with customers | Transport |  |
Disaggregation of Operating Revenues |  |
Revenues | 9.9 |
Other States | Natural gas | Transferred over time | Revenues from contracts with customers | Other utility |  |
Disaggregation of Operating Revenues |  |
Revenues | (25.1) |
Other States | Public Utility |  |
Disaggregation of Operating Revenues |  |
Revenues | 169.9 |
Other States | Public Utility | Other operating revenues |  |
Disaggregation of Operating Revenues |  |
Revenues | (6.7) |
Other States | Public Utility | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 176.6 |
Other States | Public Utility | Electric | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Other States | Public Utility | Natural gas | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 172.7 |
Other States | Public Utility | Total utility revenues | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 172.7 |
Other States | Public Utility | Other non-utility revenues | Transferred over time | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 3.9 |
Electric Transmission |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Electric Transmission | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Electric Transmission | Other operating revenues |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Electric Transmission | Electric | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Electric Transmission | Natural gas | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Electric Transmission | Total utility revenues | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Electric Transmission | Other non-utility revenues | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Non-Utility Energy Infrastructure |  |
Disaggregation of Operating Revenues |  |
Revenues | 118.1 |
Non-Utility Energy Infrastructure | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 22.0 |
Non-Utility Energy Infrastructure | Other operating revenues |  |
Disaggregation of Operating Revenues |  |
Revenues | 96.1 |
Non-Utility Energy Infrastructure | Electric | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Non-Utility Energy Infrastructure | Natural gas | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 14.9 |
Non-Utility Energy Infrastructure | Total utility revenues | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 14.9 |
Non-Utility Energy Infrastructure | Other non-utility revenues | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 7.1 |
Corporate and Other |  |
Disaggregation of Operating Revenues |  |
Revenues | 1.4 |
Corporate and Other | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 1.3 |
Corporate and Other | Other operating revenues |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.1 |
Corporate and Other | Electric | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Corporate and Other | Natural gas | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Corporate and Other | Total utility revenues | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Corporate and Other | Other non-utility revenues | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 1.3 |
Reconciling Eliminations |  |
Disaggregation of Operating Revenues |  |
Revenues | (99.3) |
Reconciling Eliminations | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | (3.2) |
Reconciling Eliminations | Other operating revenues |  |
Disaggregation of Operating Revenues |  |
Revenues | (96.1) |
Reconciling Eliminations | Electric | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | 0.0 |
Reconciling Eliminations | Natural gas | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | (2.5) |
Reconciling Eliminations | Total utility revenues | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | (2.5) |
Reconciling Eliminations | Other non-utility revenues | Revenues from contracts with customers |  |
Disaggregation of Operating Revenues |  |
Revenues | $ (0.7) |

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