OPERATING REVENUES - DISAGGREGATION OF OPERATING REVENUES BY SEGMENT (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended |
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018 |
Disaggregation of Operating Revenues | | | | |
Operating revenues | $ 1,590.2 | $ 1,672.5 | $ 3,967.6 | $ 3,959 |
Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 1,563.9 | 1,673.6 | 3,940.4 | 3,963.6 |
Other operating revenues | | | | |
Disaggregation of Operating Revenues | | | | |
Other operating revenues | 26.3 | (1.1) | 27.2 | (4.6) |
Total utility revenues | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 1,546.7 | 1,660.6 | 3,904.9 | 3,939 |
Electric | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 1,021.9 | 1,084.2 | 2,083.7 | 2,151.9 |
Natural gas | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 524.8 | 576.4 | 1,821.2 | 1,787.1 |
Natural gas | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 524.1 | 579.1 | 1,818.8 | 1,777.4 |
Other non-utility revenues | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 17.2 | 13 | 35.5 | 24.6 |
Total Utility Operations | | | | |
Disaggregation of Operating Revenues | | | | |
Operating revenues | 1,565 | 1,665.9 | 3,920.1 | 3,932.2 |
Total Utility Operations | Other operating revenues | | | | |
Disaggregation of Operating Revenues | | | | |
Other operating revenues | 14.8 | (1.4) | 9.2 | (5) |
Total Utility Operations | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 1,550.2 | 1,667.3 | 3,910.9 | 3,937.2 |
Total Utility Operations | Total utility revenues | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 1,546 | 1,663.3 | 3,902.5 | 3,929.3 |
Total Utility Operations | Electric | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 1,021.9 | 1,084.2 | 2,083.7 | 2,151.9 |
Total Utility Operations | Natural gas | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 524.1 | 579.1 | 1,818.8 | 1,777.4 |
Total Utility Operations | Other non-utility revenues | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 4.2 | 4 | 8.4 | 7.9 |
Wisconsin | | | | |
Disaggregation of Operating Revenues | | | | |
Operating revenues | 1,253.3 | 1,325.5 | 2,886.7 | 2,914.6 |
Wisconsin | Other operating revenues | | | | |
Disaggregation of Operating Revenues | | | | |
Other operating revenues | 4.1 | 4.9 | 10.8 | 8.3 |
Wisconsin | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 1,249.2 | 1,320.6 | 2,875.9 | 2,906.3 |
Wisconsin | Total utility revenues | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 1,249.2 | 1,320.6 | 2,875.9 | 2,906.3 |
Wisconsin | Electric | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 1,021.9 | 1,084.2 | 2,083.7 | 2,151.9 |
Wisconsin | Natural gas | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 227.3 | 236.4 | 792.2 | 754.4 |
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 | 242.9 | 268 | 779.4 | 775.3 |
Illinois | Other operating revenues | | | | |
Disaggregation of Operating Revenues | | | | |
Other operating revenues | 10.1 | (5.9) | 1.9 | (6.2) |
Illinois | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 232.8 | 273.9 | 777.5 | 781.5 |
Illinois | Total utility revenues | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 232.8 | 273.8 | 777.4 | 781.4 |
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 | 232.8 | 273.8 | 777.4 | 781.4 |
Illinois | Other non-utility revenues | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 0 | 0.1 | 0.1 | 0.1 |
Other States | | | | |
Disaggregation of Operating Revenues | | | | |
Operating revenues | 68.8 | 72.4 | 254 | 242.3 |
Other States | Other operating revenues | | | | |
Disaggregation of Operating Revenues | | | | |
Other operating revenues | 0.6 | (0.4) | (3.5) | (7.1) |
Other States | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 68.2 | 72.8 | 257.5 | 249.4 |
Other States | Total utility revenues | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 64 | 68.9 | 249.2 | 241.6 |
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 | 64 | 68.9 | 249.2 | 241.6 |
Other States | Other non-utility revenues | Transferred over time | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 4.2 | 3.9 | 8.3 | 7.8 |
Non-Utility Energy Infrastructure | | | | |
Disaggregation of Operating Revenues | | | | |
Operating revenues | 123.3 | 117 | 251.1 | 235.1 |
Non-Utility Energy Infrastructure | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 25.1 | 19.3 | 54.8 | 41.3 |
Non-Utility Energy Infrastructure | Other operating revenues | | | | |
Disaggregation of Operating Revenues | | | | |
Other operating revenues | 98.2 | 97.7 | 196.3 | 193.8 |
Non-Utility Energy Infrastructure | Total utility revenues | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 9.8 | 10 | 26.2 | 24.9 |
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 | 9.8 | 10 | 26.2 | 24.9 |
Non-Utility Energy Infrastructure | Other non-utility revenues | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 15.3 | 9.3 | 28.6 | 16.4 |
Corporate and Other | | | | |
Disaggregation of Operating Revenues | | | | |
Operating revenues | 0.9 | 3.1 | 2.6 | 4.5 |
Corporate and Other | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | 0.8 | 2.8 | 2.3 | 4.1 |
Corporate and Other | Other operating revenues | | | | |
Disaggregation of Operating Revenues | | | | |
Other operating revenues | 0.1 | 0.3 | 0.3 | 0.4 |
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 | 0.8 | 2.8 | 2.3 | 4.1 |
Reconciling Eliminations | | | | |
Disaggregation of Operating Revenues | | | | |
Operating revenues | (99) | (113.5) | (206.2) | (212.8) |
Reconciling Eliminations | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | (12.2) | (15.8) | (27.6) | (19) |
Reconciling Eliminations | Other operating revenues | | | | |
Disaggregation of Operating Revenues | | | | |
Other operating revenues | (86.8) | (97.7) | (178.6) | (193.8) |
Reconciling Eliminations | Total utility revenues | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | (9.1) | (12.7) | (23.8) | (15.2) |
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 | (9.1) | (12.7) | (23.8) | (15.2) |
Reconciling Eliminations | Other non-utility revenues | Revenues from contracts with customers | | | | |
Disaggregation of Operating Revenues | | | | |
Revenues from contracts with customers | $ (3.1) | $ (3.1) | $ (3.8) | $ (3.8) |