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Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2019 | Mar. 31, 2018
Segment Reporting Information [Line Items] |  |
Revenues | $ 987.2 | $ 916.3
Operating income (loss) | 176.8 | 165.7
Net income attributable to common shareowners | 125.1 | 120.9
IPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 555.1 | 525.8
Operating income (loss) | 73.5 | 75.6
Net income attributable to common shareowners | 53.3 | 46.7
WPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 415.2 | 381.7
Operating income (loss) | 98.1 | 84.0
Net income attributable to common shareowners | 65.7 | 54.0
Electric [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 743.4 | 708.7
Operating income (loss) | 126.4 | 126.7
Electric [Member] | IPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 419.8 | 405.7
Operating income (loss) | 46.8 | 57.5
Electric [Member] | WPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 323.6 | 303.0
Operating income (loss) | 79.6 | 69.2
Gas [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 215.8 | 185.6
Operating income (loss) | 45.2 | 31.5
Gas [Member] | IPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 124.6 | 108.1
Operating income (loss) | 26.3 | 16.9
Gas [Member] | WPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 91.2 | 77.5
Operating income (loss) | 18.9 | 14.6
Other Utility [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 11.1 | 13.2
Operating income (loss) | 0.0 | 1.4
Other Utility [Member] | IPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 10.7 | 12.0
Operating income (loss) | 0.4 | 1.2
Other Utility [Member] | WPL [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 0.4 | 1.2
Operating income (loss) | (0.4) | 0.2
Utility Business [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 970.3 | 907.5
Operating income (loss) | 171.6 | 159.6
Net income attributable to common shareowners | 119.0 | 100.7
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member] |  |
Segment Reporting Information [Line Items] |  |
Revenues | 16.9 | 8.8
Operating income (loss) | 5.2 | 6.1
Net income attributable to common shareowners | $ 6.1 | $ 20.2

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