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OPERATING REVENUES - DISAGGREGATION OF OPERATING REVENUES BY SEGMENT (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | $ 1,643.7 | $ 1,657.5 | $ 5,602.7 | $ 5,593.5
Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 1,635.7 |  | 5,599.3 |
Other operating revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 8.0 |  | 3.4 |
Total utility revenues | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 1,622.1 |  | 5,561.1 |
Electric | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 1,218.3 |  | 3,370.2 |
Natural gas | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 403.8 |  | 2,190.9 |
Natural gas | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 406.5 |  | 2,183.9 |
Other non-utility revenues | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 13.6 |  | 38.2 |
Total Utility Operations |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 1,636.8 |  | 5,569.0 |
Total Utility Operations | Other operating revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 7.9 |  | 2.9 |
Total Utility Operations | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 1,628.9 |  | 5,566.1 |
Total Utility Operations | Total utility revenues | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 1,624.8 |  | 5,554.1 |
Total Utility Operations | Electric | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 1,218.3 |  | 3,370.2 |
Total Utility Operations | Natural gas | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 406.5 |  | 2,183.9 |
Total Utility Operations | Other non-utility revenues | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 4.1 |  | 12.0 |
Wisconsin |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 1,388.7 |  | 4,303.3 |
Wisconsin | Other operating revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 3.0 |  | 11.3 |
Wisconsin | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 1,385.7 |  | 4,292.0 |
Wisconsin | Total utility revenues | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 1,385.7 |  | 4,292.0 |
Wisconsin | Electric | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 1,218.3 |  | 3,370.2 |
Wisconsin | Natural gas | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 167.4 |  | 921.8 |
Wisconsin | Other non-utility revenues | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.0 |  | 0.0 |
Illinois |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 197.9 |  | 973.2 |
Illinois | Other operating revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 4.6 |  | (1.6) |
Illinois | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 193.3 |  | 974.8 |
Illinois | Total utility revenues | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 193.2 |  | 974.6 |
Illinois | Electric | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.0 |  | 0.0 |
Illinois | Natural gas | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 193.2 |  | 974.6 |
Illinois | Other non-utility revenues | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.1 |  | 0.2 |
Other States |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 50.2 |  | 292.5 |
Other States | Other operating revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 0.3 |  | (6.8) |
Other States | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 49.9 |  | 299.3 |
Other States | Total utility revenues | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 45.9 |  | 287.5 |
Other States | Electric | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.0 |  | 0.0 |
Other States | Natural gas | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 45.9 |  | 287.5 |
Other States | Other non-utility revenues | Transferred over time | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 4.0 |  | 11.8 |
Electric Transmission |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 0.0 |  | 0.0 |
Electric Transmission | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.0 |  | 0.0 |
Electric Transmission | Other operating revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 0.0 |  | 0.0 |
Electric Transmission | Total utility revenues | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.0 |  | 0.0 |
Electric Transmission | Electric | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.0 |  | 0.0 |
Electric Transmission | Natural gas | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.0 |  | 0.0 |
Electric Transmission | Other non-utility revenues | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.0 |  | 0.0 |
Non-Utility Energy Infrastructure |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 115.2 |  | 350.3 |
Non-Utility Energy Infrastructure | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 17.9 |  | 59.2 |
Non-Utility Energy Infrastructure | Other operating revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 97.3 |  | 291.1 |
Non-Utility Energy Infrastructure | Total utility revenues | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 10.0 |  | 34.9 |
Non-Utility Energy Infrastructure | Electric | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.0 |  | 0.0 |
Non-Utility Energy Infrastructure | Natural gas | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 10.0 |  | 34.9 |
Non-Utility Energy Infrastructure | Other non-utility revenues | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 7.9 |  | 24.3 |
Corporate and Other |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 2.4 |  | 6.9 |
Corporate and Other | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 2.3 |  | 6.4 |
Corporate and Other | Other operating revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | 0.1 |  | 0.5 |
Corporate and Other | Total utility revenues | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.0 |  | 0.0 |
Corporate and Other | Electric | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.0 |  | 0.0 |
Corporate and Other | Natural gas | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.0 |  | 0.0 |
Corporate and Other | Other non-utility revenues | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 2.3 |  | 6.4 |
Reconciling Eliminations |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | (110.7) |  | (323.5) |
Reconciling Eliminations | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | (13.4) |  | (32.4) |
Reconciling Eliminations | Other operating revenues |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Operating revenues | (97.3) |  | (291.1) |
Reconciling Eliminations | Total utility revenues | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | (12.7) |  | (27.9) |
Reconciling Eliminations | Electric | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | 0.0 |  | 0.0 |
Reconciling Eliminations | Natural gas | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | (12.7) |  | (27.9) |
Reconciling Eliminations | Other non-utility revenues | Revenues from contracts with customers |  |  |  |
Disaggregation of Operating Revenues |  |  |  |
Revenues from contracts with customers | $ (0.7) |  | $ (4.5) |

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