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Consolidated Statements of Common Equity (USD $) In Millions, unless otherwise specified | 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] | Deferred Compensation, Share-based Payments [Member]
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Beginning balance at Dec. 31, 2010 | $ 2,893.6 | $ 1,389.8 | $ 1,369.3 | $ 1.1 | $ 33.4 | $ 66.2 | $ 1,506.8 | $ 974.0 | $ 844.0 | $ 1,394.7 | $ 382.4 | $ 459.1 | $ (1.4) | $ (7.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net income attributable to Alliant Energy common shareowners | 303.6 | 124.3 | 160.2 |  |  |  |  |  |  | 303.6 | 124.3 | 160.2 |  |
Common stock dividends | (188.1) | (73.4) | (112.1) |  |  |  |  |  |  | (188.1) | (73.4) | (112.1) |  |
Capital contributions from parent |  | 54.0 | 25.0 |  |  |  |  | 54.0 | 25.0 |  |  |  |  |
Repayment of capital to parent |  | (100.7) |  |  |  |  |  | (100.7) |  |  |  |  |  |
Other | 3.3 | 0.4 |  |  |  |  | 4.0 | 0.4 |  |  |  |  |  | (0.7)
Other comprehensive income, net of tax | 0.6 |  |  |  |  |  |  |  |  |  |  |  | 0.6 |
Ending balance at Dec. 31, 2011 | 3,013.0 | 1,394.4 | 1,442.4 | 1.1 | 33.4 | 66.2 | 1,510.8 | 927.7 | 869.0 | 1,510.2 | 433.3 | 507.2 | (0.8) | (8.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net income attributable to Alliant Energy common shareowners | 34.9 | (4.7) | 31.1 |  |  |  |  |  |  |  |  |  |  |
Ending balance at Mar. 31, 2012 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance at Dec. 31, 2011 | 3,013.0 | 1,394.4 | 1,442.4 | 1.1 | 33.4 | 66.2 | 1,510.8 | 927.7 | 869.0 | 1,510.2 | 433.3 | 507.2 |  | (8.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net income attributable to Alliant Energy common shareowners | 319.8 | 137.6 | 162.4 |  |  |  |  |  |  | 319.8 | 137.6 | 162.4 |  |
Common stock dividends | (199.3) | (122.9) | (112.0) |  |  |  |  |  |  | (199.3) | (122.9) | (112.0) |  |
Capital contributions from parent |  | 110.0 | 90.0 |  |  |  |  | 110.0 | 90.0 |  |  |  |  |
Other | 1.4 | 0.1 | 0.2 |  |  |  | 0.4 | 0.1 | 0.2 |  |  |  |  | 1.0
Ending balance at Dec. 31, 2012 | 3,134.9 | 1,519.2 | 1,583.0 | 1.1 | 33.4 | 66.2 | 1,511.2 | 1,037.8 | 959.2 | 1,630.7 | 448.0 | 557.6 |  | (7.3)
Beginning balance at Sep. 30, 2012 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net income attributable to Alliant Energy common shareowners | 68.3 | 22.4 | 40.2 |  |  |  |  |  |  |  |  |  |  |
Ending balance at Dec. 31, 2012 | 3,134.9 | 1,519.2 | 1,583.0 | 1.1 | 33.4 | 66.2 |  |  |  |  |  |  |  |
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net income attributable to Alliant Energy common shareowners | 69.9 | 22.9 | 42.0 |  |  |  |  |  |  |  |  |  |  |
Ending balance at Mar. 31, 2013 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance at Dec. 31, 2012 | 3,134.9 | 1,519.2 | 1,583.0 | 1.1 | 33.4 | 66.2 | 1,511.2 | 1,037.8 | 959.2 | 1,630.7 | 448.0 | 557.6 | (0.8) | (7.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net income attributable to Alliant Energy common shareowners | 358.3 | 173.6 | 175.9 |  |  |  |  |  |  | 358.3 | 173.6 | 175.9 |  |
Common stock dividends | (208.3) | (128.1) | (116.3) |  |  |  |  |  |  | (208.3) | (128.1) | (116.3) |  |
Capital contributions from parent |  | 120.0 | 0 |  |  |  |  | 120.0 |  |  |  |  |  |
Preferred stock issuance costs | (5.4) | (5.4) |  |  |  |  | (5.4) | (5.4) |  |  |  |  |  |
Other | 1.3 | 0.4 | (0.2) |  |  |  | 2.0 | 0.4 | (0.2) |  |  |  |  | (0.7)
Other comprehensive income, net of tax | 0.6 |  |  |  |  |  |  |  |  |  |  |  | 0.6 |
Ending balance at Dec. 31, 2013 | 3,281.4 | 1,679.7 | 1,642.4 | 1.1 | 33.4 | 66.2 | 1,507.8 | 1,152.8 | 959.0 | 1,780.7 | 493.5 | 617.2 | (0.2) | (8.0)
Beginning balance at Sep. 30, 2013 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase (Decrease) in Stockholders' Equity [Roll Forward] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Net income attributable to Alliant Energy common shareowners | 65.5 | 18.5 | 38.2 |  |  |  |  |  |  |  |  |  |  |
Ending balance at Dec. 31, 2013 | $ 3,281.4 | $ 1,679.7 | $ 1,642.4 | $ 1.1 | $ 33.4 | $ 66.2 |  |  |  |  |  |  |  |

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