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Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019
Segment Reporting Information [Line Items] |  |  |  |
Revenues | $ 763.1 | $ 790.2 | $ 1,678.8 | $ 1,777.4
Operating income (loss) | 168.1 | 149.8 | 356.4 | 326.6
Net income attributable to common shareowners | 134.4 | 94.6 | 304.4 | 219.7
Net income | 136.9 | 97.1 | 309.5 | 224.8
IPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 431.9 | 441.2 | 950.8 | 996.3
Operating income (loss) | 88.7 | 74.5 | 185.4 | 148.0
Net income attributable to common shareowners | 59.8 | 45.0 | 142.4 | 98.3
Net income | 62.3 | 47.5 | 147.5 | 103.4
WPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 312.3 | 326.1 | 687.5 | 741.3
Operating income (loss) | 71.7 | 67.0 | 165.5 | 165.1
Net income | 57.6 | 42.0 | 147.2 | 107.7
Electric [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 675.2 | 691.2 | 1,405.5 | 1,434.6
Operating income (loss) | 152.1 | 132.9 | 298.3 | 259.3
Electric [Member] | IPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 388.4 | 392.3 | 813.2 | 812.1
Operating income (loss) | 82.1 | 68.9 | 149.1 | 115.7
Electric [Member] | WPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 286.8 | 298.9 | 592.3 | 622.5
Operating income (loss) | 70.0 | 64.0 | 149.2 | 143.6
Gas [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 58.9 | 65.2 | 211.1 | 281.0
Operating income (loss) | 7.1 | 7.2 | 48.7 | 52.4
Gas [Member] | IPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 33.9 | 38.4 | 116.9 | 163.0
Operating income (loss) | 5.2 | 4.2 | 32.5 | 30.5
Gas [Member] | WPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 25.0 | 26.8 | 94.2 | 118.0
Operating income (loss) | 1.9 | 3.0 | 16.2 | 21.9
Other Utility [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 10.1 | 10.9 | 21.7 | 22.0
Operating income (loss) | 1.2 | 1.4 | 3.9 | 1.4
Other Utility [Member] | IPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 9.6 | 10.5 | 20.7 | 21.2
Operating income (loss) | 1.4 | 1.4 | 3.8 | 1.8
Other Utility [Member] | WPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 0.5 | 0.4 | 1.0 | 0.8
Operating income (loss) | (0.2) | 0.0 | 0.1 | (0.4)
Utility Business [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 744.2 | 767.3 | 1,638.3 | 1,737.6
Operating income (loss) | 160.4 | 141.5 | 350.9 | 313.1
Net income attributable to common shareowners | 117.4 | 87.0 | 289.6 | 206.0
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 18.9 | 22.9 | 40.5 | 39.8
Operating income (loss) | 7.7 | 8.3 | 5.5 | 13.5
Net income attributable to common shareowners | $ 17.0 | $ 7.6 | $ 14.8 | $ 13.7

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