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Consolidated Statements of Common Equity - USD ($) $ in Millions | Total | IPL [Member] | WPL [Member] | Common Stock [Member] | Common Stock [Member] IPL [Member] | Common Stock [Member] WPL [Member] | Additional Paid-in Capital [Member] | Additional Paid-in Capital [Member] IPL [Member] | Additional Paid-in Capital [Member] WPL [Member] | Retained Earnings [Member] | Retained Earnings [Member] IPL [Member] | Retained Earnings [Member] WPL [Member] | Accumulated Other Comprehensive Income (Loss) [Member] | Shares in Deferred Compensation Trust [Member] | Noncontrolling Interest [Member] WPL [Member]
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Beginning balance at Dec. 31, 2014 | $ 3,438.7 | $ 1,784.3 |  | $ 2.2 | $ 33.4 | $ 66.2 | $ 1,508.0 | $ 1,242.8 | $ 959.0 | $ 1,938.0 | $ 508.1 | $ 681.7 | $ (0.6) | $ (8.9) | $ 8.5
Beginning balance at Dec. 31, 2014 |  |  | $ 1,715.4 |  |  |  |  |  |  |  |  |  |  |  |
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net income (loss) attributable to common shareowners | 378.2 | 186.0 | 176.3 |  |  |  |  |  |  | 378.2 | 186.0 | 176.3 |  |  | 1.3
Net income | 388.4 | 196.2 | 177.6 |  |  |  |  |  |  |  |  |  |  |  |
Common stock dividends | (247.3) | (140.0) | (126.9) |  |  |  |  |  |  | (247.3) | (140.0) | (126.9) |  |  |
Common stock issued, net | 151.2 |  |  | 0.1 |  |  | 151.1 |  |  |  |  |  |  |  |
Capital contributions from parent |  | 165.0 | 0.0 |  |  |  |  | 165.0 |  |  |  |  |  |  |
Contributions from noncontrolling interest |  |  | 3.4 |  |  |  |  |  |  |  |  |  |  |  | 3.4
Distributions to noncontrolling interest |  |  | (1.9) |  |  |  |  |  |  |  |  |  |  |  | (1.9)
Transfer of investment in ATC to ATI |  |  | 0.0 |  |  |  |  |  |  |  |  |  |  |  |
Other | 3.1 |  |  |  |  |  | 2.7 |  |  |  |  |  |  | 0.4 |
Other comprehensive income (loss), net of tax | 0.2 | 0.0 | 0.0 |  |  |  |  |  |  |  |  |  | 0.2 |  |
Ending balance at Dec. 31, 2015 | 3,724.1 | 1,995.3 |  | 2.3 | 33.4 | 66.2 | 1,661.8 | 1,407.8 | 959.0 | 2,068.9 | 554.1 | 731.1 | (0.4) | (8.5) | 11.3
Ending balance at Dec. 31, 2015 |  |  | 1,767.6 |  |  |  |  |  |  |  |  |  |  |  |
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net income (loss) attributable to common shareowners | 371.5 | 215.6 | 190.4 |  |  |  |  |  |  | 371.5 | 215.6 | 190.4 |  |  | 2.4
Net income | 381.7 | 225.8 | 192.8 |  |  |  |  |  |  |  |  |  |  |  |
Common stock dividends | (266.5) | (151.9) | (135.0) |  |  |  |  |  |  | (266.5) | (151.9) | (135.0) |  |  |
Common stock issued, net | 26.6 |  |  |  |  |  | 26.6 |  |  |  |  |  |  |  |
Capital contributions from parent |  | 190.0 | 60.0 |  |  |  |  | 190.0 | 60.0 |  |  |  |  |  |
Contributions from noncontrolling interest |  |  | 11.5 |  |  |  |  |  |  |  |  |  |  |  | 11.5
Distributions to noncontrolling interest |  |  | (2.5) |  |  |  |  |  |  |  |  |  |  |  | (2.5)
Transfer of investment in ATC to ATI |  |  | (163.6) |  |  |  |  |  |  |  |  | (140.9) |  |  | (22.7)
Other | 6.3 |  |  |  |  |  | 4.7 |  |  | 3.1 |  |  |  | (1.5) |
Other comprehensive income (loss), net of tax | 0.0 | 0.0 | 0.0 |  |  |  |  |  |  |  |  |  |  |  |
Ending balance at Dec. 31, 2016 | 3,862.0 | 2,249.0 | 1,730.8 | 2.3 | 33.4 | 66.2 | 1,693.1 | 1,597.8 | 1,019.0 | 2,177.0 | 617.8 | 645.6 | (0.4) | (10.0) | 0.0
Ending balance at Dec. 31, 2016 | 4,062.0 | 2,449.0 | 1,730.8 |  |  |  |  |  |  |  |  |  |  |  |
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net income (loss) attributable to common shareowners | 457.3 | 216.8 | 186.6 |  |  |  |  |  |  | 457.3 | 216.8 | 186.6 |  |  |
Net income | 467.5 | 227.0 | 186.6 |  |  |  |  |  |  |  |  |  |  |  |
Common stock dividends | (288.3) | (156.1) | (125.9) |  |  |  |  |  |  | (288.3) | (156.1) | (125.9) |  |  |
Common stock issued, net | 149.6 |  |  |  |  |  | 149.6 |  |  |  |  |  |  |  |
Capital contributions from parent |  | 200.0 | 90.0 |  |  |  |  | 200.0 | 90.0 |  |  |  |  |  |
Transfer of investment in ATC to ATI |  |  | 0.0 |  |  |  |  |  |  |  |  |  |  |  |
Other | 1.7 |  |  |  |  |  | 2.8 |  |  |  |  |  |  | (1.1) |
Other comprehensive income (loss), net of tax | (0.1) | 0.0 | 0.0 |  |  |  |  |  |  |  |  |  | (0.1) |  |
Ending balance at Dec. 31, 2017 | 4,182.2 | 2,509.7 | 1,881.5 | $ 2.3 | $ 33.4 | $ 66.2 | $ 1,845.5 | $ 1,797.8 | $ 1,109.0 | $ 2,346.0 | $ 678.5 | $ 706.3 | $ (0.5) | $ (11.1) | $ 0.0
Ending balance at Dec. 31, 2017 | $ 4,382.2 | $ 2,709.7 | $ 1,881.5 |  |  |  |  |  |  |  |  |  |  |  |

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