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Common Equity (Tables) | 3 Months Ended
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Mar. 31, 2019
Schedule of Capitalization, Equity [Line Items] |
Common Share Activity | A summary of Alliant Energy’s common stock activity was as follows:
Shares outstanding, January 1, 2019 | 236,063,279 |
Equity forward agreements | 1,090,300 |
Shareowner Direct Plan issuances | 142,090 |
Equity-based compensation plans | 101,478 |
Other | (2,738 | )
Shares outstanding, March 31, 2019 | 237,394,409 |
Changes in Shareowners' Equity | A summary of changes in shareowners’ equity was as follows (in millions):
Alliant Energy | Total Alliant Energy Common Equity |  |  |  |
|  |  |  |  |  |  | Accumulated |  | Shares in |  | Cumulative |  |
|  |  | Additional |  |  |  | Other |  | Deferred |  | Preferred |  |
| Common |  | Paid-In |  | Retained |  | Comprehensive |  | Compensation |  | Stock |  | Total
| Stock |  | Capital |  | Earnings |  | Income (Loss) |  | Trust |  | of IPL |  | Equity
Three Months Ended March 31, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $2.4 |  |  |  | $2,045.5 |  |  |  | $2,545.9 |  |  |  | $1.7 |  |  |  | ($9.8 | ) |  |  | $200.0 |  |  |  | $4,785.7 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  | 125.1 |  |  |  |  |  |  |  |  | 125.1 |
Common stock dividends ($0.355 per share) |  |  |  |  | (83.7 | ) |  |  |  |  |  |  |  | (83.7 | )
Equity forward settlements and Shareowner Direct Plan issuances |  |  |  | 54.6 |  |  |  |  |  |  |  |  |  |  | 54.6 |
Equity-based compensation plans and other |  |  | (0.1 | ) |  |  |  |  |  | 0.1 |  |  |  |  | — |
Other comprehensive income, net of tax |  |  |  |  |  |  | 0.7 |  |  |  |  |  |  | 0.7 |
Ending balance, March 31 |  | $2.4 |  |  |  | $2,100.0 |  |  |  | $2,587.3 |  |  |  | $2.4 |  |  |  | ($9.7 | ) |  |  | $200.0 |  |  |  | $4,882.4 |
Three Months Ended March 31, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $2.3 |  |  |  | $1,845.5 |  |  |  | $2,346.0 |  |  |  | ($0.5 | ) |  |  | ($11.1 | ) |  |  | $200.0 |  |  |  | $4,382.2 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  | 120.9 |  |  |  |  |  |  |  |  | 120.9 |
Common stock dividends ($0.335 per share) |  |  |  |  | (77.5 | ) |  |  |  |  |  |  |  | (77.5 | )
Shareowner Direct Plan issuances |  |  | 6.3 |  |  |  |  |  |  |  |  |  |  | 6.3 |
Equity-based compensation plans |  |  | (0.4 | ) |  |  |  |  |  |  |  |  |  | (0.4 | )
Ending balance, March 31 |  | $2.3 |  |  |  | $1,851.4 |  |  |  | $2,389.4 |  |  |  | ($0.5 | ) |  |  | ($11.1 | ) |  |  | $200.0 |  |  |  | $4,431.5 |
IPL | Total IPL Common Equity |  |  |  |
|  |  | Additional |  |  |  | Cumulative |  |
| Common |  | Paid-In |  | Retained |  | Preferred |  | Total
| Stock |  | Capital |  | Earnings |  | Stock |  | Equity
Three Months Ended March 31, 2019 |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $33.4 |  |  |  | $2,222.8 |  |  |  | $774.5 |  |  |  | $200.0 |  |  |  | $3,230.7 |
Earnings available for common stock |  |  |  |  | 53.3 |  |  |  |  | 53.3 |
Common stock dividends |  |  |  |  | (42.0 | ) |  |  |  | (42.0 | )
Capital contribution from parent |  |  | 100.0 |  |  |  |  |  |  | 100.0 |
Ending balance, March 31 |  | $33.4 |  |  |  | $2,322.8 |  |  |  | $785.8 |  |  |  | $200.0 |  |  |  | $3,342.0 |
Three Months Ended March 31, 2018 |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $33.4 |  |  |  | $1,797.8 |  |  |  | $678.5 |  |  |  | $200.0 |  |  |  | $2,709.7 |
Earnings available for common stock |  |  |  |  | 46.7 |  |  |  |  | 46.7 |
Common stock dividends |  |  |  |  | (41.9 | ) |  |  |  | (41.9 | )
Ending balance, March 31 |  | $33.4 |  |  |  | $1,797.8 |  |  |  | $683.3 |  |  |  | $200.0 |  |  |  | $2,714.5 |
WPL |  |  | Additional |  |  |  | Total
| Common |  | Paid-In |  | Retained |  | Common
| Stock |  | Capital |  | Earnings |  | Equity
Three Months Ended March 31, 2019 |  |  |  |  |  |  |
Beginning balance, January 1 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $774.3 |  |  |  | $2,149.5 |
Earnings available for common stock |  |  |  |  | 65.7 |  |  | 65.7 |
Common stock dividends |  |  |  |  | (36.0 | ) |  | (36.0 | )
Ending balance, March 31 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $804.0 |  |  |  | $2,179.2 |
Three Months Ended March 31, 2018 |  |  |  |  |  |  |
Beginning balance, January 1 |  | $66.2 |  |  |  | $1,109.0 |  |  |  | $706.3 |  |  |  | $1,881.5 |
Earnings available for common stock |  |  |  |  | 54.0 |  |  | 54.0 |
Common stock dividends |  |  |  |  | (35.0 | ) |  | (35.0 | )
Ending balance, March 31 |  | $66.2 |  |  |  | $1,109.0 |  |  |  | $725.3 |  |  |  | $1,900.5 |
IPL [Member] |
Schedule of Capitalization, Equity [Line Items] |
Changes in Shareowners' Equity | A summary of changes in shareowners’ equity was as follows (in millions):
Alliant Energy | Total Alliant Energy Common Equity |  |  |  |
|  |  |  |  |  |  | Accumulated |  | Shares in |  | Cumulative |  |
|  |  | Additional |  |  |  | Other |  | Deferred |  | Preferred |  |
| Common |  | Paid-In |  | Retained |  | Comprehensive |  | Compensation |  | Stock |  | Total
| Stock |  | Capital |  | Earnings |  | Income (Loss) |  | Trust |  | of IPL |  | Equity
Three Months Ended March 31, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $2.4 |  |  |  | $2,045.5 |  |  |  | $2,545.9 |  |  |  | $1.7 |  |  |  | ($9.8 | ) |  |  | $200.0 |  |  |  | $4,785.7 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  | 125.1 |  |  |  |  |  |  |  |  | 125.1 |
Common stock dividends ($0.355 per share) |  |  |  |  | (83.7 | ) |  |  |  |  |  |  |  | (83.7 | )
Equity forward settlements and Shareowner Direct Plan issuances |  |  |  | 54.6 |  |  |  |  |  |  |  |  |  |  | 54.6 |
Equity-based compensation plans and other |  |  | (0.1 | ) |  |  |  |  |  | 0.1 |  |  |  |  | — |
Other comprehensive income, net of tax |  |  |  |  |  |  | 0.7 |  |  |  |  |  |  | 0.7 |
Ending balance, March 31 |  | $2.4 |  |  |  | $2,100.0 |  |  |  | $2,587.3 |  |  |  | $2.4 |  |  |  | ($9.7 | ) |  |  | $200.0 |  |  |  | $4,882.4 |
Three Months Ended March 31, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $2.3 |  |  |  | $1,845.5 |  |  |  | $2,346.0 |  |  |  | ($0.5 | ) |  |  | ($11.1 | ) |  |  | $200.0 |  |  |  | $4,382.2 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  | 120.9 |  |  |  |  |  |  |  |  | 120.9 |
Common stock dividends ($0.335 per share) |  |  |  |  | (77.5 | ) |  |  |  |  |  |  |  | (77.5 | )
Shareowner Direct Plan issuances |  |  | 6.3 |  |  |  |  |  |  |  |  |  |  | 6.3 |
Equity-based compensation plans |  |  | (0.4 | ) |  |  |  |  |  |  |  |  |  | (0.4 | )
Ending balance, March 31 |  | $2.3 |  |  |  | $1,851.4 |  |  |  | $2,389.4 |  |  |  | ($0.5 | ) |  |  | ($11.1 | ) |  |  | $200.0 |  |  |  | $4,431.5 |
IPL | Total IPL Common Equity |  |  |  |
|  |  | Additional |  |  |  | Cumulative |  |
| Common |  | Paid-In |  | Retained |  | Preferred |  | Total
| Stock |  | Capital |  | Earnings |  | Stock |  | Equity
Three Months Ended March 31, 2019 |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $33.4 |  |  |  | $2,222.8 |  |  |  | $774.5 |  |  |  | $200.0 |  |  |  | $3,230.7 |
Earnings available for common stock |  |  |  |  | 53.3 |  |  |  |  | 53.3 |
Common stock dividends |  |  |  |  | (42.0 | ) |  |  |  | (42.0 | )
Capital contribution from parent |  |  | 100.0 |  |  |  |  |  |  | 100.0 |
Ending balance, March 31 |  | $33.4 |  |  |  | $2,322.8 |  |  |  | $785.8 |  |  |  | $200.0 |  |  |  | $3,342.0 |
Three Months Ended March 31, 2018 |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $33.4 |  |  |  | $1,797.8 |  |  |  | $678.5 |  |  |  | $200.0 |  |  |  | $2,709.7 |
Earnings available for common stock |  |  |  |  | 46.7 |  |  |  |  | 46.7 |
Common stock dividends |  |  |  |  | (41.9 | ) |  |  |  | (41.9 | )
Ending balance, March 31 |  | $33.4 |  |  |  | $1,797.8 |  |  |  | $683.3 |  |  |  | $200.0 |  |  |  | $2,714.5 |
WPL |  |  | Additional |  |  |  | Total
| Common |  | Paid-In |  | Retained |  | Common
| Stock |  | Capital |  | Earnings |  | Equity
Three Months Ended March 31, 2019 |  |  |  |  |  |  |
Beginning balance, January 1 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $774.3 |  |  |  | $2,149.5 |
Earnings available for common stock |  |  |  |  | 65.7 |  |  | 65.7 |
Common stock dividends |  |  |  |  | (36.0 | ) |  | (36.0 | )
Ending balance, March 31 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $804.0 |  |  |  | $2,179.2 |
Three Months Ended March 31, 2018 |  |  |  |  |  |  |
Beginning balance, January 1 |  | $66.2 |  |  |  | $1,109.0 |  |  |  | $706.3 |  |  |  | $1,881.5 |
Earnings available for common stock |  |  |  |  | 54.0 |  |  | 54.0 |
Common stock dividends |  |  |  |  | (35.0 | ) |  | (35.0 | )
Ending balance, March 31 |  | $66.2 |  |  |  | $1,109.0 |  |  |  | $725.3 |  |  |  | $1,900.5 |
WPL [Member] |
Schedule of Capitalization, Equity [Line Items] |
Changes in Shareowners' Equity | A summary of changes in shareowners’ equity was as follows (in millions):
Alliant Energy | Total Alliant Energy Common Equity |  |  |  |
|  |  |  |  |  |  | Accumulated |  | Shares in |  | Cumulative |  |
|  |  | Additional |  |  |  | Other |  | Deferred |  | Preferred |  |
| Common |  | Paid-In |  | Retained |  | Comprehensive |  | Compensation |  | Stock |  | Total
| Stock |  | Capital |  | Earnings |  | Income (Loss) |  | Trust |  | of IPL |  | Equity
Three Months Ended March 31, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $2.4 |  |  |  | $2,045.5 |  |  |  | $2,545.9 |  |  |  | $1.7 |  |  |  | ($9.8 | ) |  |  | $200.0 |  |  |  | $4,785.7 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  | 125.1 |  |  |  |  |  |  |  |  | 125.1 |
Common stock dividends ($0.355 per share) |  |  |  |  | (83.7 | ) |  |  |  |  |  |  |  | (83.7 | )
Equity forward settlements and Shareowner Direct Plan issuances |  |  |  | 54.6 |  |  |  |  |  |  |  |  |  |  | 54.6 |
Equity-based compensation plans and other |  |  | (0.1 | ) |  |  |  |  |  | 0.1 |  |  |  |  | — |
Other comprehensive income, net of tax |  |  |  |  |  |  | 0.7 |  |  |  |  |  |  | 0.7 |
Ending balance, March 31 |  | $2.4 |  |  |  | $2,100.0 |  |  |  | $2,587.3 |  |  |  | $2.4 |  |  |  | ($9.7 | ) |  |  | $200.0 |  |  |  | $4,882.4 |
Three Months Ended March 31, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $2.3 |  |  |  | $1,845.5 |  |  |  | $2,346.0 |  |  |  | ($0.5 | ) |  |  | ($11.1 | ) |  |  | $200.0 |  |  |  | $4,382.2 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  | 120.9 |  |  |  |  |  |  |  |  | 120.9 |
Common stock dividends ($0.335 per share) |  |  |  |  | (77.5 | ) |  |  |  |  |  |  |  | (77.5 | )
Shareowner Direct Plan issuances |  |  | 6.3 |  |  |  |  |  |  |  |  |  |  | 6.3 |
Equity-based compensation plans |  |  | (0.4 | ) |  |  |  |  |  |  |  |  |  | (0.4 | )
Ending balance, March 31 |  | $2.3 |  |  |  | $1,851.4 |  |  |  | $2,389.4 |  |  |  | ($0.5 | ) |  |  | ($11.1 | ) |  |  | $200.0 |  |  |  | $4,431.5 |
IPL | Total IPL Common Equity |  |  |  |
|  |  | Additional |  |  |  | Cumulative |  |
| Common |  | Paid-In |  | Retained |  | Preferred |  | Total
| Stock |  | Capital |  | Earnings |  | Stock |  | Equity
Three Months Ended March 31, 2019 |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $33.4 |  |  |  | $2,222.8 |  |  |  | $774.5 |  |  |  | $200.0 |  |  |  | $3,230.7 |
Earnings available for common stock |  |  |  |  | 53.3 |  |  |  |  | 53.3 |
Common stock dividends |  |  |  |  | (42.0 | ) |  |  |  | (42.0 | )
Capital contribution from parent |  |  | 100.0 |  |  |  |  |  |  | 100.0 |
Ending balance, March 31 |  | $33.4 |  |  |  | $2,322.8 |  |  |  | $785.8 |  |  |  | $200.0 |  |  |  | $3,342.0 |
Three Months Ended March 31, 2018 |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $33.4 |  |  |  | $1,797.8 |  |  |  | $678.5 |  |  |  | $200.0 |  |  |  | $2,709.7 |
Earnings available for common stock |  |  |  |  | 46.7 |  |  |  |  | 46.7 |
Common stock dividends |  |  |  |  | (41.9 | ) |  |  |  | (41.9 | )
Ending balance, March 31 |  | $33.4 |  |  |  | $1,797.8 |  |  |  | $683.3 |  |  |  | $200.0 |  |  |  | $2,714.5 |
WPL |  |  | Additional |  |  |  | Total
| Common |  | Paid-In |  | Retained |  | Common
| Stock |  | Capital |  | Earnings |  | Equity
Three Months Ended March 31, 2019 |  |  |  |  |  |  |
Beginning balance, January 1 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $774.3 |  |  |  | $2,149.5 |
Earnings available for common stock |  |  |  |  | 65.7 |  |  | 65.7 |
Common stock dividends |  |  |  |  | (36.0 | ) |  | (36.0 | )
Ending balance, March 31 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $804.0 |  |  |  | $2,179.2 |
Three Months Ended March 31, 2018 |  |  |  |  |  |  |
Beginning balance, January 1 |  | $66.2 |  |  |  | $1,109.0 |  |  |  | $706.3 |  |  |  | $1,881.5 |
Earnings available for common stock |  |  |  |  | 54.0 |  |  | 54.0 |
Common stock dividends |  |  |  |  | (35.0 | ) |  | (35.0 | )
Ending balance, March 31 |  | $66.2 |  |  |  | $1,109.0 |  |  |  | $725.3 |  |  |  | $1,900.5 |

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