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Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2017 | Mar. 31, 2016
Segment Reporting Information [Line Items] |  |  |
Operating revenues |  | $ 853.9 | $ 843.8
Operating income (loss) |  | 142.9 | 145.9
Income from continuing operations, net of tax |  | 99.0 | 97.6
Income (loss) from discontinued operations, net of tax |  | 1.4 | (1.1)
Net income attributable to common shareowners |  | 100.4 | 96.5
IPL [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Operating revenues |  | 450.5 | 458.7
Operating income (loss) |  | 49.6 | 62.0
Net income attributable to common shareowners |  | 37.2 | 45.6
WPL [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Operating revenues |  | 393.1 | 375.6
Operating income (loss) |  | 86.0 | 78.8
Net income attributable to common shareowners |  | 45.5 | 46.5
Electric [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Operating revenues | [1] | 677.6 | 668.9
Operating income (loss) | [1] | 107.2 | 109.8
Electric [Member] | IPL [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Operating revenues |  | 356.2 | 361.6
Operating income (loss) |  | 33.8 | 43.4
Electric [Member] | WPL [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Operating revenues |  | 321.4 | 307.3
Operating income (loss) |  | 73.4 | 66.4
Gas [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Operating revenues | [1] | 154.3 | 152.2
Operating income (loss) | [1] | 28.0 | 28.8
Gas [Member] | IPL [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Operating revenues |  | 83.1 | 84.2
Operating income (loss) |  | 14.4 | 15.8
Gas [Member] | WPL [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Operating revenues |  | 71.2 | 68.0
Operating income (loss) |  | 13.6 | 13.0
Other Utilities [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Operating revenues | [1] | 11.7 | 13.2
Operating income (loss) | [1] | 0.4 | 2.2
Other Utilities [Member] | IPL [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Operating revenues |  | 11.2 | 12.9
Operating income (loss) |  | 1.4 | 2.8
Other Utilities [Member] | WPL [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Operating revenues |  | 0.5 | 0.3
Operating income (loss) |  | (1.0) | (0.6)
Utility Business [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Operating revenues | [1] | 843.6 | 834.3
Operating income (loss) | [1] | 135.6 | 140.8
Income from continuing operations, net of tax | [1] | 89.6 | 92.1
Income (loss) from discontinued operations, net of tax | [1] | 0.0 | 0.0
Net income attributable to common shareowners | [1] | 89.6 | 92.1
Non-Regulated [Member] | Other Segments [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Operating revenues |  | 10.3 | 9.5
Operating income (loss) |  | 7.3 | 5.1
Income from continuing operations, net of tax |  | 9.4 | 5.5
Income (loss) from discontinued operations, net of tax |  | 1.4 | (1.1)
Net income attributable to common shareowners |  | $ 10.8 | $ 4.4
[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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