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Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2017 | Sep. 30, 2016 | Sep. 30, 2017 | Sep. 30, 2016
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues |  | $ 906.9 | $ 924.6 | $ 2,526.1 | $ 2,523.0
Operating income (loss) |  | 231.5 | 162.6 | 523.7 | 437.1
Income (loss) from continuing operations, net of tax |  | 168.8 | 128.8 | 362.1 | 310.8
Income (loss) from discontinued operations, net of tax |  | 0.0 | (0.4) | 1.4 | (2.0)
Net income (loss) attributable to common shareowners |  | 168.8 | 128.4 | 363.5 | 308.8
IPL [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues |  | 527.4 | 516.2 | 1,398.1 | 1,385.9
Operating income (loss) |  | 131.8 | 125.9 | 247.7 | 235.9
Net income (loss) attributable to common shareowners |  | 120.4 | 114.1 | 200.4 | 191.6
WPL [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues |  | 370.2 | 397.0 | 1,098.1 | 1,106.9
Operating income (loss) |  | 90.7 | 115.0 | 250.4 | 268.8
Net income (loss) attributable to common shareowners |  | 49.8 | 69.0 | 133.4 | 158.7
Electric [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues | [1] | 840.6 | 864.3 | 2,199.1 | 2,209.1
Operating income (loss) | [1] | 232.6 | 244.2 | 475.4 | 473.3
Electric [Member] | IPL [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues |  | 489.0 | 483.2 | 1,217.6 | 1,209.2
Operating income (loss) |  | 138.3 | 125.9 | 234.5 | 213.8
Electric [Member] | WPL [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues |  | 351.6 | 381.1 | 981.5 | 999.9
Operating income (loss) |  | 94.3 | 118.3 | 240.9 | 259.5
Gas [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues | [1] | 45.8 | 39.5 | 262.7 | 248.7
Operating income (loss) | [1] | (2.4) | (3.7) | 29.5 | 27.0
Gas [Member] | IPL [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues |  | 27.4 | 23.9 | 147.2 | 142.6
Operating income (loss) |  | (2.1) | (1.4) | 14.7 | 15.3
Gas [Member] | WPL [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues |  | 18.4 | 15.6 | 115.5 | 106.1
Operating income (loss) |  | (0.3) | (2.3) | 14.8 | 11.7
Other Utility [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues | [1] | 11.2 | 9.4 | 34.4 | 35.0
Operating income (loss) | [1] | (7.7) | 0.4 | (6.8) | 4.4
Other Utility [Member] | IPL [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues |  | 11.0 | 9.1 | 33.3 | 34.1
Operating income (loss) |  | (4.4) | 1.4 | (1.5) | 6.8
Other Utility [Member] | WPL [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues |  | 0.2 | 0.3 | 1.1 | 0.9
Operating income (loss) |  | (3.3) | (1.0) | (5.3) | (2.4)
Utility Business [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues | [1] | 897.6 | 913.2 | 2,496.2 | 2,492.8
Operating income (loss) | [1] | 222.5 | 240.9 | 498.1 | 504.7
Income (loss) from continuing operations, net of tax | [1] |  | 183.1 | 353.5 | 350.3
Income (loss) from discontinued operations, net of tax | [1] |  | 0.0 | 0.0 | 0.0
Net income (loss) attributable to common shareowners | [1] | 176.3 | 183.1 | 353.5 | 350.3
Non-Regulated [Member] | Other Segments [Member] |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Operating revenues |  | 9.3 | 11.4 | 29.9 | 30.2
Operating income (loss) |  | 9.0 | (78.3) | 25.6 | (67.6)
Income (loss) from continuing operations, net of tax |  |  | (54.3) | 8.6 | (39.5)
Income (loss) from discontinued operations, net of tax |  |  | (0.4) | 1.4 | (2.0)
Net income (loss) attributable to common shareowners |  | $ (7.5) | $ (54.7) | $ 10.0 | $ (41.5)
[1] | Alliant Energy’s utility business segments include: a) utility electric operations, which include Alliant Energy’s entire investment in ATC; b) utility gas operations; and c) utility other, which includes steam operations and the unallocated portions of the utility business.

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