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Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2019 | Jun. 30, 2018 | Jun. 30, 2019 | Jun. 30, 2018
Segment Reporting Information [Line Items] |  |  |  |
Revenues | $ 790.2 | $ 816.1 | $ 1,777.4 | $ 1,732.4
Operating income (loss) | 149.8 | 151.2 | 326.6 | 316.9
Net income attributable to common shareowners | 94.6 | 100.4 | 219.7 | 221.3
IPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 441.2 | 474.8 | 996.3 | 1,000.6
Operating income (loss) | 74.5 | 77.7 | 148.0 | 153.3
Net income attributable to common shareowners | 45.0 | 51.7 | 98.3 | 98.4
WPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 326.1 | 330.8 | 741.3 | 712.5
Operating income (loss) | 67.0 | 63.4 | 165.1 | 147.4
Net income attributable to common shareowners | 42.0 | 39.8 | 107.7 | 93.8
Electric [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 691.2 | 726.3 | 1,434.6 | 1,435.0
Operating income (loss) | 132.9 | 134.8 | 259.3 | 261.5
Electric [Member] | IPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 392.3 | 422.1 | 812.1 | 827.8
Operating income (loss) | 68.9 | 73.5 | 115.7 | 131.0
Electric [Member] | WPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 298.9 | 304.2 | 622.5 | 607.2
Operating income (loss) | 64.0 | 61.3 | 143.6 | 130.5
Gas [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 65.2 | 68.6 | 281.0 | 254.2
Operating income (loss) | 7.2 | 5.4 | 52.4 | 36.9
Gas [Member] | IPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 38.4 | 42.2 | 163.0 | 150.3
Operating income (loss) | 4.2 | 2.5 | 30.5 | 19.4
Gas [Member] | WPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 26.8 | 26.4 | 118.0 | 103.9
Operating income (loss) | 3.0 | 2.9 | 21.9 | 17.5
Other Utility [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 10.9 | 10.7 | 22.0 | 23.9
Operating income (loss) | 1.4 | 0.9 | 1.4 | 2.3
Other Utility [Member] | IPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 10.5 | 10.5 | 21.2 | 22.5
Operating income (loss) | 1.4 | 1.7 | 1.8 | 2.9
Other Utility [Member] | WPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 0.4 | 0.2 | 0.8 | 1.4
Operating income (loss) | 0.0 | (0.8) | (0.4) | (0.6)
Utility Business [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 767.3 | 805.6 | 1,737.6 | 1,713.1
Operating income (loss) | 141.5 | 141.1 | 313.1 | 300.7
Net income attributable to common shareowners | 87.0 | 91.5 | 206.0 | 192.2
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 22.9 | 10.5 | 39.8 | 19.3
Operating income (loss) | 8.3 | 10.1 | 13.5 | 16.2
Net income attributable to common shareowners | $ 7.6 | $ 8.9 | $ 13.7 | $ 29.1

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