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Disaggregation of Revenues (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disaggregation of Revenue [Line Items] |  |  |
Revenues | $ 3,534.5 | $ 3,382.2 | $ 3,320.0
IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 2,042.3 | 1,870.3 | 1,820.4
WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 1,452.6 | 1,472.8 | 1,459.1
Electric [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 3,000.3 | 2,894.7 | 2,875.5
Electric [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 1,731.1 | 1,598.9 | 1,569.7
Electric [Member] | WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 1,269.2 | 1,295.8 | 1,305.8
Electric [Member] | Retail - Residential [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 1,063.4 | 1,006.2 | 1,001.1
Electric [Member] | Retail - Residential [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 590.6 | 535.6 | 536.7
Electric [Member] | Retail - Residential [Member] | WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 472.8 | 470.6 | 464.4
Electric [Member] | Retail - Commercial [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 735.6 | 710.3 | 712.6
Electric [Member] | Retail - Commercial [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 486.8 | 452.7 | 445.4
Electric [Member] | Retail - Commercial [Member] | WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 248.8 | 257.6 | 267.2
Electric [Member] | Retail - Industrial [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 888.8 | 853.1 | 851.1
Electric [Member] | Retail - Industrial [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 500.8 | 459.7 | 460.4
Electric [Member] | Retail - Industrial [Member] | WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 388.0 | 393.4 | 390.7
Electric [Member] | Wholesale [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 188.4 | 238.4 | 256.6
Electric [Member] | Wholesale [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 71.2 | 95.5 | 94.2
Electric [Member] | Wholesale [Member] | WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 117.2 | 142.9 | 162.4
Electric [Member] | Other Customer [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 124.1 | 86.7 | 54.1
Electric [Member] | Other Customer [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 81.7 | 55.4 | 33.0
Electric [Member] | Other Customer [Member] | WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 42.4 | 31.3 | 21.1
Gas [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 446.6 | 400.9 | 355.4
Gas [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 266.2 | 226.0 | 204.0
Gas [Member] | WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 180.4 | 174.9 | 151.4
Gas [Member] | Retail - Residential [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 254.4 | 224.7 | 197.6
Gas [Member] | Retail - Residential [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 152.3 | 123.2 | 110.6
Gas [Member] | Retail - Residential [Member] | WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 102.1 | 101.5 | 87.0
Gas [Member] | Retail - Commercial [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 133.0 | 123.2 | 109.6
Gas [Member] | Retail - Commercial [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 75.9 | 67.9 | 61.9
Gas [Member] | Retail - Commercial [Member] | WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 57.1 | 55.3 | 47.7
Gas [Member] | Retail - Industrial [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 14.9 | 16.7 | 15.2
Gas [Member] | Retail - Industrial [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 10.2 | 11.1 | 10.6
Gas [Member] | Retail - Industrial [Member] | WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 4.7 | 5.6 | 4.6
Gas [Member] | Other Customer [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 44.3 | 36.3 | 33.0
Gas [Member] | Other Customer [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 27.8 | 23.8 | 20.9
Gas [Member] | Other Customer [Member] | WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 16.5 | 12.5 | 12.1
Other Utility [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 48.0 | 47.5 | 48.6
Other Utility [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 45.0 | 45.4 | 46.7
Other Utility [Member] | WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 3.0 | 2.1 | 1.9
Other Utility [Member] | Other Customer [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 12.8 | 12.9 | 14.7
Other Utility [Member] | Other Customer [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 9.8 | 10.8 | 12.8
Other Utility [Member] | Other Customer [Member] | WPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 3.0 | 2.1 | 1.9
Other Utility [Member] | Steam [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 35.2 | 34.6 | 33.9
Other Utility [Member] | Steam [Member] | IPL [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 35.2 | 34.6 | 33.9
Other Segments [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | 39.6 | 39.1 | 40.5
Other Segments [Member] | Other Customer [Member] |  |  |
Disaggregation of Revenue [Line Items] |  |  |
Revenues | $ 39.6 | $ 39.1 | $ 40.5

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