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OPERATING REVENUES - DISAGGREGATION OF NATURAL GAS UTILITY OPERATING REVENUES BY CUSTOMER CLASS (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 30, 2017
Disaggregation of Operating Revenues |  |  |  |
Revenues | $ 1,672.5 | $ 1,631.5 | $ 3,959.0 | $ 3,936.0
Natural gas |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Number of days payment is due |  |  | 30 days |
Public Utility |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 1,665.9 |  | $ 3,932.2 |
Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 1,673.6 |  | 3,963.6 |
Revenues from contracts with customers | Natural gas |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 576.4 |  | 1,787.1 |
Revenues from contracts with customers | Public Utility | Transferred over time |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 1,667.3 |  | 3,937.2 |
Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 579.1 |  | 1,777.4 |
Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Residential |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 329.7 |  | 1,142.2 |
Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Commercial and industrial |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 129.5 |  | 491.5 |
Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Total retail revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 459.2 |  | 1,633.7 |
Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Transport |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 77.8 |  | 186.4 |
Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Other utility revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 42.1 |  | (42.7) |
Wisconsin | Public Utility |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 1,325.5 |  | 2,914.6 |
Wisconsin | Revenues from contracts with customers | Public Utility | Transferred over time |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 1,320.6 |  | 2,906.3 |
Wisconsin | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 236.4 |  | 754.4 |
Wisconsin | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Residential |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 128.1 |  | 484.8 |
Wisconsin | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Commercial and industrial |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 63.5 |  | 251.4 |
Wisconsin | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Total retail revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 191.6 |  | 736.2 |
Wisconsin | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Transport |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 16.4 |  | 37.4 |
Wisconsin | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Other utility revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 28.4 |  | (19.2) |
Illinois | Public Utility |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 268.0 |  | 775.3 |
Illinois | Revenues from contracts with customers | Public Utility | Transferred over time |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 273.9 |  | 781.5 |
Illinois | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 273.8 |  | 781.4 |
Illinois | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Residential |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 163.7 |  | 496.3 |
Illinois | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Commercial and industrial |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 47.3 |  | 156.7 |
Illinois | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Total retail revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 211.0 |  | 653.0 |
Illinois | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Transport |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 54.6 |  | 132.3 |
Illinois | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Other utility revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 8.2 |  | (3.9) |
Other States | Public Utility |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 72.4 |  | 242.3 |
Other States | Revenues from contracts with customers | Public Utility | Transferred over time |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 72.8 |  | 249.4 |
Other States | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 68.9 |  | 241.6 |
Other States | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Residential |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 37.9 |  | 161.1 |
Other States | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Commercial and industrial |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 18.7 |  | 83.4 |
Other States | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Total retail revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 56.6 |  | 244.5 |
Other States | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Transport |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | 6.8 |  | 16.7 |
Other States | Revenues from contracts with customers | Public Utility | Natural gas | Transferred over time | Other utility revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues | $ 5.5 |  | $ (19.6) |

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