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Common Equity (Tables) | 12 Months Ended
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Dec. 31, 2015
Schedule of Common Equity [Line Items] |
Common Stock Activity | A summary of Alliant Energy’s common stock activity was as follows:
| 2015 |  | 2014 |  | 2013
Shares outstanding, January 1 | 110,935,680 |  |  | 110,943,669 |  |  | 110,987,400 |
At-the-market offering program | 2,186,617 |  |  | — |  |  | — |
Shareowner Direct Plan issuances | 303,005 |  |  | — |  |  | — |
Equity-based compensation plans (Note 12(b)) | 56,378 |  |  | 35,547 |  |  | (23,374 | )
Other | (22,464 | ) |  | (43,536 | ) |  | (20,357 | )
Shares outstanding, December 31 | 113,459,216 |  |  | 110,935,680 |  |  | 110,943,669 |
Schedule of Restricted Net Assets of Subsidiaries | As of December 31, the amount of net assets of IPL and WPL that were not available to be transferred to their parent company, Alliant Energy, in the form of loans, advances or cash dividends without the consent of IPL’s and WPL’s regulatory authorities was as follows (in billions):
| 2015 |  | 2014
IPL |  | $1.4 |  |  |  | $1.3 |
WPL | 1.6 |  |  | 1.6 |
Capital Transactions with Subsidiaries | IPL, WPL and Resources paid common stock dividends and repayments of capital to their parent company, Alliant Energy, as follows (in millions):
| IPL |  | WPL |  | Resources
| 2015 |  | 2014 |  | 2013 |  | 2015 |  | 2014 |  | 2013 |  | 2015 |  | 2014 |  | 2013
Common stock dividends |  | $140.0 |  |  |  | $140.0 |  |  |  | $128.1 |  |  |  | $126.9 |  |  |  | $118.7 |  |  |  | $116.3 |  |  |  | $— |  |  |  | $— |  |  |  | $— |
Repayments of capital | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 50.0 |  |  | 95.0 |
Total distributions from common equity |  | $140.0 |  |  |  | $140.0 |  |  |  | $128.1 |  |  |  | $126.9 |  |  |  | $118.7 |  |  |  | $116.3 |  |  |  | $— |  |  |  | $50.0 |  |  |  | $95.0 |
Schedule of Capital Contributions | IPL received capital contributions from its parent company, Alliant Energy, as follows (in millions):
2015 |  | 2014 |  | 2013
| $165.0 |  |  |  | $90.0 |  |  |  | $120.0 |
IPL [Member] |
Schedule of Common Equity [Line Items] |
Schedule of Restricted Net Assets of Subsidiaries | As of December 31, the amount of net assets of IPL and WPL that were not available to be transferred to their parent company, Alliant Energy, in the form of loans, advances or cash dividends without the consent of IPL’s and WPL’s regulatory authorities was as follows (in billions):
| 2015 |  | 2014
IPL |  | $1.4 |  |  |  | $1.3 |
WPL | 1.6 |  |  | 1.6 |
Capital Transactions with Subsidiaries | IPL, WPL and Resources paid common stock dividends and repayments of capital to their parent company, Alliant Energy, as follows (in millions):
| IPL |  | WPL |  | Resources
| 2015 |  | 2014 |  | 2013 |  | 2015 |  | 2014 |  | 2013 |  | 2015 |  | 2014 |  | 2013
Common stock dividends |  | $140.0 |  |  |  | $140.0 |  |  |  | $128.1 |  |  |  | $126.9 |  |  |  | $118.7 |  |  |  | $116.3 |  |  |  | $— |  |  |  | $— |  |  |  | $— |
Repayments of capital | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 50.0 |  |  | 95.0 |
Total distributions from common equity |  | $140.0 |  |  |  | $140.0 |  |  |  | $128.1 |  |  |  | $126.9 |  |  |  | $118.7 |  |  |  | $116.3 |  |  |  | $— |  |  |  | $50.0 |  |  |  | $95.0 |
Schedule of Capital Contributions | IPL received capital contributions from its parent company, Alliant Energy, as follows (in millions):
2015 |  | 2014 |  | 2013
| $165.0 |  |  |  | $90.0 |  |  |  | $120.0 |
WPL [Member] |
Schedule of Common Equity [Line Items] |
Schedule of Restricted Net Assets of Subsidiaries | As of December 31, the amount of net assets of IPL and WPL that were not available to be transferred to their parent company, Alliant Energy, in the form of loans, advances or cash dividends without the consent of IPL’s and WPL’s regulatory authorities was as follows (in billions):
| 2015 |  | 2014
IPL |  | $1.4 |  |  |  | $1.3 |
WPL | 1.6 |  |  | 1.6 |
Capital Transactions with Subsidiaries | IPL, WPL and Resources paid common stock dividends and repayments of capital to their parent company, Alliant Energy, as follows (in millions):
| IPL |  | WPL |  | Resources
| 2015 |  | 2014 |  | 2013 |  | 2015 |  | 2014 |  | 2013 |  | 2015 |  | 2014 |  | 2013
Common stock dividends |  | $140.0 |  |  |  | $140.0 |  |  |  | $128.1 |  |  |  | $126.9 |  |  |  | $118.7 |  |  |  | $116.3 |  |  |  | $— |  |  |  | $— |  |  |  | $— |
Repayments of capital | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 50.0 |  |  | 95.0 |
Total distributions from common equity |  | $140.0 |  |  |  | $140.0 |  |  |  | $128.1 |  |  |  | $126.9 |  |  |  | $118.7 |  |  |  | $116.3 |  |  |  | $— |  |  |  | $50.0 |  |  |  | $95.0 |

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