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Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Segment Reporting Information [Line Items] |  |  |  |
Revenues | $ 928.6 | $ 906.9 | $ 2,661.0 | $ 2,526.1
Operating income (loss) | 256.1 | 236.3 | 573.0 | 537.2
Income from continuing operations, net of tax | 205.5 | 168.8 | 426.8 | 362.1
Income from discontinued operations, net of tax | 0.0 | 0.0 | 0.0 | 1.4
Net income attributable to common shareowners | 205.5 | 168.8 | 426.8 | 363.5
IPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 547.6 | 527.4 | 1,548.2 | 1,398.1
Operating income (loss) | 143.1 | 133.8 | 296.4 | 253.2
Net income attributable to common shareowners | 126.5 | 120.4 | 224.9 | 200.4
WPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 370.7 | 370.2 | 1,083.2 | 1,098.1
Operating income (loss) | 104.2 | 93.5 | 251.6 | 258.3
Net income attributable to common shareowners | 76.3 | 49.8 | 170.1 | 133.4
Electric [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 861.2 | 840.6 | 2,296.2 | 2,199.1
Operating income (loss) | 248.7 | 236.7 | 510.2 | 486.9
Electric [Member] | IPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 509.2 | 489.0 | 1,337.0 | 1,217.6
Operating income (loss) | 144.7 | 140.0 | 275.7 | 239.2
Electric [Member] | WPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 352.0 | 351.6 | 959.2 | 981.5
Operating income (loss) | 104.0 | 96.7 | 234.5 | 247.7
Gas [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 44.8 | 45.8 | 299.0 | 262.7
Operating income (loss) | (2.0) | (1.7) | 34.9 | 31.3
Gas [Member] | IPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 26.7 | 27.4 | 177.0 | 147.2
Operating income (loss) | (3.1) | (1.8) | 16.3 | 15.4
Gas [Member] | WPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 18.1 | 18.4 | 122.0 | 115.5
Operating income (loss) | 1.1 | 0.1 | 18.6 | 15.9
Other Utility [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 12.3 | 11.2 | 36.2 | 34.4
Operating income (loss) | 0.6 | (7.7) | 2.9 | (6.7)
Other Utility [Member] | IPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 11.7 | 11.0 | 34.2 | 33.3
Operating income (loss) | 1.5 | (4.4) | 4.4 | (1.4)
Other Utility [Member] | WPL [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 0.6 | 0.2 | 2.0 | 1.1
Operating income (loss) | (0.9) | (3.3) | (1.5) | (5.3)
Utility Business [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 918.3 | 897.6 | 2,631.4 | 2,496.2
Operating income (loss) | 247.3 | 227.3 | 548.0 | 511.5
Income from continuing operations, net of tax |  |  |  | 333.8
Income from discontinued operations, net of tax |  |  |  | 0.0
Net income attributable to common shareowners | 202.8 | 170.2 | 395.0 | 333.8
Non-Utility [Member] | ATC Holdings, Non-Utility, Parent and Other [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenues | 10.3 | 9.3 | 29.6 | 29.9
Operating income (loss) | 8.8 | 9.0 | 25.0 | 25.7
Income from continuing operations, net of tax |  |  |  | 28.3
Income from discontinued operations, net of tax |  |  |  | 1.4
Net income attributable to common shareowners | $ 2.7 | $ (1.4) | $ 31.8 | $ 29.7

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