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Common Equity (Tables) | 9 Months Ended
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Sep. 30, 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 | 3,790,300 |
Shareowner Direct Plan | 390,630 |
Equity-based compensation plans | 101,478 |
Other | (2,738 | )
Shares outstanding, September 30, 2019 | 240,342,949 |
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 September 30, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance, July 1 |  | $2.4 |  |  |  | $2,108.4 |  |  |  | $2,597.8 |  |  |  | $1.0 |  |  |  | ($10.0 | ) |  |  | $200.0 |  |  |  | $4,899.6 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  | 226.0 |  |  |  |  |  |  |  |  | 226.0 |
Common stock dividends ($0.355 per share) |  |  |  |  | (84.7 | ) |  |  |  |  |  |  |  | (84.7 | )
Equity forward settlements and Shareowner Direct Plan issuances |  |  |  | 124.8 |  |  |  |  |  |  |  |  |  |  | 124.8 |
Equity-based compensation plans and other |  |  | 3.7 |  |  |  |  |  |  | (0.2 | ) |  |  |  | 3.5 |
Ending balance, September 30 |  | $2.4 |  |  |  | $2,236.9 |  |  |  | $2,739.1 |  |  |  | $1.0 |  |  |  | ($10.2 | ) |  |  | $200.0 |  |  |  | $5,169.2 |
Three Months Ended September 30, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance, July 1 |  | $2.3 |  |  |  | $1,947.2 |  |  |  | $2,412.5 |  |  |  | $0.1 |  |  |  | ($11.4 | ) |  |  | $200.0 |  |  |  | $4,550.7 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  | 205.5 |  |  |  |  |  |  |  |  | 205.5 |
Common stock dividends ($0.335 per share) |  |  |  |  | (78.5 | ) |  |  |  |  |  |  |  | (78.5 | )
At-the-market offering program and Shareowner Direct Plan issuances | 0.1 |  |  | 91.1 |  |  |  |  |  |  |  |  |  |  | 91.2 |
Equity-based compensation plans and other |  |  | (0.1 | ) |  |  |  |  |  | 1.9 |  |  |  |  | 1.8 |
Other comprehensive loss, net of tax |  |  |  |  |  |  | (0.3 | ) |  |  |  |  |  | (0.3 | )
Ending balance, September 30 |  | $2.4 |  |  |  | $2,038.2 |  |  |  | $2,539.5 |  |  |  | ($0.2 | ) |  |  | ($9.5 | ) |  |  | $200.0 |  |  |  | $4,770.4 |
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
Nine Months Ended September 30, 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 |  |  |  |  | 445.7 |  |  |  |  |  |  |  |  | 445.7 |
Common stock dividends ($1.065 per share) |  |  |  |  | (252.5 | ) |  |  |  |  |  |  |  | (252.5 | )
Equity forward settlements and Shareowner Direct Plan issuances |  |  |  | 185.4 |  |  |  |  |  |  |  |  |  |  | 185.4 |
Equity-based compensation plans and other |  |  | 6.0 |  |  |  |  |  |  | (0.4 | ) |  |  |  | 5.6 |
Other comprehensive loss, net of tax |  |  |  |  |  |  | (0.7 | ) |  |  |  |  |  | (0.7 | )
Ending balance, September 30 |  | $2.4 |  |  |  | $2,236.9 |  |  |  | $2,739.1 |  |  |  | $1.0 |  |  |  | ($10.2 | ) |  |  | $200.0 |  |  |  | $5,169.2 |
Nine Months Ended September 30, 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 |  |  |  |  | 426.8 |  |  |  |  |  |  |  |  | 426.8 |
Common stock dividends ($1.005 per share) |  |  |  |  | (233.3 | ) |  |  |  |  |  |  |  | (233.3 | )
At-the-market offering program and Shareowner Direct Plan issuances | 0.1 |  |  | 191.2 |  |  |  |  |  |  |  |  |  |  | 191.3 |
Equity-based compensation plans and other |  |  | 1.5 |  |  |  |  |  |  | 1.6 |  |  |  |  | 3.1 |
Other comprehensive income, net of tax |  |  |  |  |  |  | 0.3 |  |  |  |  |  |  | 0.3 |
Ending balance, September 30 |  | $2.4 |  |  |  | $2,038.2 |  |  |  | $2,539.5 |  |  |  | ($0.2 | ) |  |  | ($9.5 | ) |  |  | $200.0 |  |  |  | $4,770.4 |
IPL | Total IPL Common Equity |  |  |  |
|  |  | Additional |  |  |  | Cumulative |  |
| Common |  | Paid-In |  | Retained |  | Preferred |  | Total
| Stock |  | Capital |  | Earnings |  | Stock |  | Equity
Three Months Ended September 30, 2019 |  |  |  |  |  |  |  |  |
Beginning balance, July 1 |  | $33.4 |  |  |  | $2,322.8 |  |  |  | $788.9 |  |  |  | $200.0 |  |  |  | $3,345.1 |
Earnings available for common stock |  |  |  |  | 141.1 |  |  |  |  | 141.1 |
Common stock dividends |  |  |  |  | (42.1 | ) |  |  |  | (42.1 | )
Ending balance, September 30 |  | $33.4 |  |  |  | $2,322.8 |  |  |  | $887.9 |  |  |  | $200.0 |  |  |  | $3,444.1 |
Three Months Ended September 30, 2018 |  |  |  |  |  |  |  |  |
Beginning balance, July 1 |  | $33.4 |  |  |  | $1,927.8 |  |  |  | $692.9 |  |  |  | $200.0 |  |  |  | $2,854.1 |
Earnings available for common stock |  |  |  |  | 126.5 |  |  |  |  | 126.5 |
Common stock dividends |  |  |  |  | (41.9 | ) |  |  |  | (41.9 | )
Capital contributions from parent |  |  | 100.0 |  |  |  |  |  |  | 100.0 |
Ending balance, September 30 |  | $33.4 |  |  |  | $2,027.8 |  |  |  | $777.5 |  |  |  | $200.0 |  |  |  | $3,038.7 |
IPL | Total IPL Common Equity |  |  |  |
|  |  | Additional |  |  |  | Cumulative |  |
| Common |  | Paid-In |  | Retained |  | Preferred |  | Total
| Stock |  | Capital |  | Earnings |  | Stock |  | Equity
Nine Months Ended September 30, 2019 |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $33.4 |  |  |  | $2,222.8 |  |  |  | $774.5 |  |  |  | $200.0 |  |  |  | $3,230.7 |
Earnings available for common stock |  |  |  |  | 239.4 |  |  |  |  | 239.4 |
Common stock dividends |  |  |  |  | (126.0 | ) |  |  |  | (126.0 | )
Capital contributions from parent |  |  | 100.0 |  |  |  |  |  |  | 100.0 |
Ending balance, September 30 |  | $33.4 |  |  |  | $2,322.8 |  |  |  | $887.9 |  |  |  | $200.0 |  |  |  | $3,444.1 |
Nine Months Ended September 30, 2018 |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $33.4 |  |  |  | $1,797.8 |  |  |  | $678.5 |  |  |  | $200.0 |  |  |  | $2,709.7 |
Earnings available for common stock |  |  |  |  | 224.9 |  |  |  |  | 224.9 |
Common stock dividends |  |  |  |  | (125.9 | ) |  |  |  | (125.9 | )
Capital contributions from parent |  |  | 230.0 |  |  |  |  |  |  | 230.0 |
Ending balance, September 30 |  | $33.4 |  |  |  | $2,027.8 |  |  |  | $777.5 |  |  |  | $200.0 |  |  |  | $3,038.7 |
WPL |  |  | Additional |  |  |  | Total
| Common |  | Paid-In |  | Retained |  | Common
| Stock |  | Capital |  | Earnings |  | Equity
Three Months Ended September 30, 2019 |  |  |  |  |  |  |
Beginning balance, July 1 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $810.0 |  |  |  | $2,185.2 |
Earnings available for common stock |  |  |  |  | 75.5 |  |  | 75.5 |
Common stock dividends |  |  |  |  | (35.9 | ) |  | (35.9 | )
Capital contributions from parent |  |  | 100.0 |  |  |  |  | 100.0 |
Ending balance, September 30 |  | $66.2 |  |  |  | $1,409.0 |  |  |  | $849.6 |  |  |  | $2,324.8 |
Three Months Ended September 30, 2018 |  |  |  |  |  |  |
Beginning balance, July 1 |  | $66.2 |  |  |  | $1,259.0 |  |  |  | $730.0 |  |  |  | $2,055.2 |
Earnings available for common stock |  |  |  |  | 76.3 |  |  | 76.3 |
Common stock dividends |  |  |  |  | (34.9 | ) |  | (34.9 | )
Capital contributions from parent |  |  | 50.0 |  |  |  |  | 50.0 |
Ending balance, September 30 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $771.4 |  |  |  | $2,146.6 |
WPL |  |  | Additional |  |  |  | Total
| Common |  | Paid-In |  | Retained |  | Common
| Stock |  | Capital |  | Earnings |  | Equity
Nine Months Ended September 30, 2019 |  |  |  |  |  |  |
Beginning balance, January 1 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $774.3 |  |  |  | $2,149.5 |
Earnings available for common stock |  |  |  |  | 183.2 |  |  | 183.2 |
Common stock dividends |  |  |  |  | (107.9 | ) |  | (107.9 | )
Capital contributions from parent |  |  | 100.0 |  |  |  |  | 100.0 |
Ending balance, September 30 |  | $66.2 |  |  |  | $1,409.0 |  |  |  | $849.6 |  |  |  | $2,324.8 |
Nine Months Ended September 30, 2018 |  |  |  |  |  |  |
Beginning balance, January 1 |  | $66.2 |  |  |  | $1,109.0 |  |  |  | $706.3 |  |  |  | $1,881.5 |
Earnings available for common stock |  |  |  |  | 170.1 |  |  | 170.1 |
Common stock dividends |  |  |  |  | (105.0 | ) |  | (105.0 | )
Capital contributions from parent |  |  | 200.0 |  |  |  |  | 200.0 |
Ending balance, September 30 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $771.4 |  |  |  | $2,146.6 |
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 September 30, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance, July 1 |  | $2.4 |  |  |  | $2,108.4 |  |  |  | $2,597.8 |  |  |  | $1.0 |  |  |  | ($10.0 | ) |  |  | $200.0 |  |  |  | $4,899.6 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  | 226.0 |  |  |  |  |  |  |  |  | 226.0 |
Common stock dividends ($0.355 per share) |  |  |  |  | (84.7 | ) |  |  |  |  |  |  |  | (84.7 | )
Equity forward settlements and Shareowner Direct Plan issuances |  |  |  | 124.8 |  |  |  |  |  |  |  |  |  |  | 124.8 |
Equity-based compensation plans and other |  |  | 3.7 |  |  |  |  |  |  | (0.2 | ) |  |  |  | 3.5 |
Ending balance, September 30 |  | $2.4 |  |  |  | $2,236.9 |  |  |  | $2,739.1 |  |  |  | $1.0 |  |  |  | ($10.2 | ) |  |  | $200.0 |  |  |  | $5,169.2 |
Three Months Ended September 30, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance, July 1 |  | $2.3 |  |  |  | $1,947.2 |  |  |  | $2,412.5 |  |  |  | $0.1 |  |  |  | ($11.4 | ) |  |  | $200.0 |  |  |  | $4,550.7 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  | 205.5 |  |  |  |  |  |  |  |  | 205.5 |
Common stock dividends ($0.335 per share) |  |  |  |  | (78.5 | ) |  |  |  |  |  |  |  | (78.5 | )
At-the-market offering program and Shareowner Direct Plan issuances | 0.1 |  |  | 91.1 |  |  |  |  |  |  |  |  |  |  | 91.2 |
Equity-based compensation plans and other |  |  | (0.1 | ) |  |  |  |  |  | 1.9 |  |  |  |  | 1.8 |
Other comprehensive loss, net of tax |  |  |  |  |  |  | (0.3 | ) |  |  |  |  |  | (0.3 | )
Ending balance, September 30 |  | $2.4 |  |  |  | $2,038.2 |  |  |  | $2,539.5 |  |  |  | ($0.2 | ) |  |  | ($9.5 | ) |  |  | $200.0 |  |  |  | $4,770.4 |
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
Nine Months Ended September 30, 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 |  |  |  |  | 445.7 |  |  |  |  |  |  |  |  | 445.7 |
Common stock dividends ($1.065 per share) |  |  |  |  | (252.5 | ) |  |  |  |  |  |  |  | (252.5 | )
Equity forward settlements and Shareowner Direct Plan issuances |  |  |  | 185.4 |  |  |  |  |  |  |  |  |  |  | 185.4 |
Equity-based compensation plans and other |  |  | 6.0 |  |  |  |  |  |  | (0.4 | ) |  |  |  | 5.6 |
Other comprehensive loss, net of tax |  |  |  |  |  |  | (0.7 | ) |  |  |  |  |  | (0.7 | )
Ending balance, September 30 |  | $2.4 |  |  |  | $2,236.9 |  |  |  | $2,739.1 |  |  |  | $1.0 |  |  |  | ($10.2 | ) |  |  | $200.0 |  |  |  | $5,169.2 |
Nine Months Ended September 30, 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 |  |  |  |  | 426.8 |  |  |  |  |  |  |  |  | 426.8 |
Common stock dividends ($1.005 per share) |  |  |  |  | (233.3 | ) |  |  |  |  |  |  |  | (233.3 | )
At-the-market offering program and Shareowner Direct Plan issuances | 0.1 |  |  | 191.2 |  |  |  |  |  |  |  |  |  |  | 191.3 |
Equity-based compensation plans and other |  |  | 1.5 |  |  |  |  |  |  | 1.6 |  |  |  |  | 3.1 |
Other comprehensive income, net of tax |  |  |  |  |  |  | 0.3 |  |  |  |  |  |  | 0.3 |
Ending balance, September 30 |  | $2.4 |  |  |  | $2,038.2 |  |  |  | $2,539.5 |  |  |  | ($0.2 | ) |  |  | ($9.5 | ) |  |  | $200.0 |  |  |  | $4,770.4 |
IPL | Total IPL Common Equity |  |  |  |
|  |  | Additional |  |  |  | Cumulative |  |
| Common |  | Paid-In |  | Retained |  | Preferred |  | Total
| Stock |  | Capital |  | Earnings |  | Stock |  | Equity
Three Months Ended September 30, 2019 |  |  |  |  |  |  |  |  |
Beginning balance, July 1 |  | $33.4 |  |  |  | $2,322.8 |  |  |  | $788.9 |  |  |  | $200.0 |  |  |  | $3,345.1 |
Earnings available for common stock |  |  |  |  | 141.1 |  |  |  |  | 141.1 |
Common stock dividends |  |  |  |  | (42.1 | ) |  |  |  | (42.1 | )
Ending balance, September 30 |  | $33.4 |  |  |  | $2,322.8 |  |  |  | $887.9 |  |  |  | $200.0 |  |  |  | $3,444.1 |
Three Months Ended September 30, 2018 |  |  |  |  |  |  |  |  |
Beginning balance, July 1 |  | $33.4 |  |  |  | $1,927.8 |  |  |  | $692.9 |  |  |  | $200.0 |  |  |  | $2,854.1 |
Earnings available for common stock |  |  |  |  | 126.5 |  |  |  |  | 126.5 |
Common stock dividends |  |  |  |  | (41.9 | ) |  |  |  | (41.9 | )
Capital contributions from parent |  |  | 100.0 |  |  |  |  |  |  | 100.0 |
Ending balance, September 30 |  | $33.4 |  |  |  | $2,027.8 |  |  |  | $777.5 |  |  |  | $200.0 |  |  |  | $3,038.7 |
IPL | Total IPL Common Equity |  |  |  |
|  |  | Additional |  |  |  | Cumulative |  |
| Common |  | Paid-In |  | Retained |  | Preferred |  | Total
| Stock |  | Capital |  | Earnings |  | Stock |  | Equity
Nine Months Ended September 30, 2019 |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $33.4 |  |  |  | $2,222.8 |  |  |  | $774.5 |  |  |  | $200.0 |  |  |  | $3,230.7 |
Earnings available for common stock |  |  |  |  | 239.4 |  |  |  |  | 239.4 |
Common stock dividends |  |  |  |  | (126.0 | ) |  |  |  | (126.0 | )
Capital contributions from parent |  |  | 100.0 |  |  |  |  |  |  | 100.0 |
Ending balance, September 30 |  | $33.4 |  |  |  | $2,322.8 |  |  |  | $887.9 |  |  |  | $200.0 |  |  |  | $3,444.1 |
Nine Months Ended September 30, 2018 |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $33.4 |  |  |  | $1,797.8 |  |  |  | $678.5 |  |  |  | $200.0 |  |  |  | $2,709.7 |
Earnings available for common stock |  |  |  |  | 224.9 |  |  |  |  | 224.9 |
Common stock dividends |  |  |  |  | (125.9 | ) |  |  |  | (125.9 | )
Capital contributions from parent |  |  | 230.0 |  |  |  |  |  |  | 230.0 |
Ending balance, September 30 |  | $33.4 |  |  |  | $2,027.8 |  |  |  | $777.5 |  |  |  | $200.0 |  |  |  | $3,038.7 |
WPL |  |  | Additional |  |  |  | Total
| Common |  | Paid-In |  | Retained |  | Common
| Stock |  | Capital |  | Earnings |  | Equity
Three Months Ended September 30, 2019 |  |  |  |  |  |  |
Beginning balance, July 1 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $810.0 |  |  |  | $2,185.2 |
Earnings available for common stock |  |  |  |  | 75.5 |  |  | 75.5 |
Common stock dividends |  |  |  |  | (35.9 | ) |  | (35.9 | )
Capital contributions from parent |  |  | 100.0 |  |  |  |  | 100.0 |
Ending balance, September 30 |  | $66.2 |  |  |  | $1,409.0 |  |  |  | $849.6 |  |  |  | $2,324.8 |
Three Months Ended September 30, 2018 |  |  |  |  |  |  |
Beginning balance, July 1 |  | $66.2 |  |  |  | $1,259.0 |  |  |  | $730.0 |  |  |  | $2,055.2 |
Earnings available for common stock |  |  |  |  | 76.3 |  |  | 76.3 |
Common stock dividends |  |  |  |  | (34.9 | ) |  | (34.9 | )
Capital contributions from parent |  |  | 50.0 |  |  |  |  | 50.0 |
Ending balance, September 30 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $771.4 |  |  |  | $2,146.6 |
WPL |  |  | Additional |  |  |  | Total
| Common |  | Paid-In |  | Retained |  | Common
| Stock |  | Capital |  | Earnings |  | Equity
Nine Months Ended September 30, 2019 |  |  |  |  |  |  |
Beginning balance, January 1 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $774.3 |  |  |  | $2,149.5 |
Earnings available for common stock |  |  |  |  | 183.2 |  |  | 183.2 |
Common stock dividends |  |  |  |  | (107.9 | ) |  | (107.9 | )
Capital contributions from parent |  |  | 100.0 |  |  |  |  | 100.0 |
Ending balance, September 30 |  | $66.2 |  |  |  | $1,409.0 |  |  |  | $849.6 |  |  |  | $2,324.8 |
Nine Months Ended September 30, 2018 |  |  |  |  |  |  |
Beginning balance, January 1 |  | $66.2 |  |  |  | $1,109.0 |  |  |  | $706.3 |  |  |  | $1,881.5 |
Earnings available for common stock |  |  |  |  | 170.1 |  |  | 170.1 |
Common stock dividends |  |  |  |  | (105.0 | ) |  | (105.0 | )
Capital contributions from parent |  |  | 200.0 |  |  |  |  | 200.0 |
Ending balance, September 30 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $771.4 |  |  |  | $2,146.6 |
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 September 30, 2019 |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance, July 1 |  | $2.4 |  |  |  | $2,108.4 |  |  |  | $2,597.8 |  |  |  | $1.0 |  |  |  | ($10.0 | ) |  |  | $200.0 |  |  |  | $4,899.6 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  | 226.0 |  |  |  |  |  |  |  |  | 226.0 |
Common stock dividends ($0.355 per share) |  |  |  |  | (84.7 | ) |  |  |  |  |  |  |  | (84.7 | )
Equity forward settlements and Shareowner Direct Plan issuances |  |  |  | 124.8 |  |  |  |  |  |  |  |  |  |  | 124.8 |
Equity-based compensation plans and other |  |  | 3.7 |  |  |  |  |  |  | (0.2 | ) |  |  |  | 3.5 |
Ending balance, September 30 |  | $2.4 |  |  |  | $2,236.9 |  |  |  | $2,739.1 |  |  |  | $1.0 |  |  |  | ($10.2 | ) |  |  | $200.0 |  |  |  | $5,169.2 |
Three Months Ended September 30, 2018 |  |  |  |  |  |  |  |  |  |  |  |  |
Beginning balance, July 1 |  | $2.3 |  |  |  | $1,947.2 |  |  |  | $2,412.5 |  |  |  | $0.1 |  |  |  | ($11.4 | ) |  |  | $200.0 |  |  |  | $4,550.7 |
Net income attributable to Alliant Energy common shareowners |  |  |  |  | 205.5 |  |  |  |  |  |  |  |  | 205.5 |
Common stock dividends ($0.335 per share) |  |  |  |  | (78.5 | ) |  |  |  |  |  |  |  | (78.5 | )
At-the-market offering program and Shareowner Direct Plan issuances | 0.1 |  |  | 91.1 |  |  |  |  |  |  |  |  |  |  | 91.2 |
Equity-based compensation plans and other |  |  | (0.1 | ) |  |  |  |  |  | 1.9 |  |  |  |  | 1.8 |
Other comprehensive loss, net of tax |  |  |  |  |  |  | (0.3 | ) |  |  |  |  |  | (0.3 | )
Ending balance, September 30 |  | $2.4 |  |  |  | $2,038.2 |  |  |  | $2,539.5 |  |  |  | ($0.2 | ) |  |  | ($9.5 | ) |  |  | $200.0 |  |  |  | $4,770.4 |
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
Nine Months Ended September 30, 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 |  |  |  |  | 445.7 |  |  |  |  |  |  |  |  | 445.7 |
Common stock dividends ($1.065 per share) |  |  |  |  | (252.5 | ) |  |  |  |  |  |  |  | (252.5 | )
Equity forward settlements and Shareowner Direct Plan issuances |  |  |  | 185.4 |  |  |  |  |  |  |  |  |  |  | 185.4 |
Equity-based compensation plans and other |  |  | 6.0 |  |  |  |  |  |  | (0.4 | ) |  |  |  | 5.6 |
Other comprehensive loss, net of tax |  |  |  |  |  |  | (0.7 | ) |  |  |  |  |  | (0.7 | )
Ending balance, September 30 |  | $2.4 |  |  |  | $2,236.9 |  |  |  | $2,739.1 |  |  |  | $1.0 |  |  |  | ($10.2 | ) |  |  | $200.0 |  |  |  | $5,169.2 |
Nine Months Ended September 30, 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 |  |  |  |  | 426.8 |  |  |  |  |  |  |  |  | 426.8 |
Common stock dividends ($1.005 per share) |  |  |  |  | (233.3 | ) |  |  |  |  |  |  |  | (233.3 | )
At-the-market offering program and Shareowner Direct Plan issuances | 0.1 |  |  | 191.2 |  |  |  |  |  |  |  |  |  |  | 191.3 |
Equity-based compensation plans and other |  |  | 1.5 |  |  |  |  |  |  | 1.6 |  |  |  |  | 3.1 |
Other comprehensive income, net of tax |  |  |  |  |  |  | 0.3 |  |  |  |  |  |  | 0.3 |
Ending balance, September 30 |  | $2.4 |  |  |  | $2,038.2 |  |  |  | $2,539.5 |  |  |  | ($0.2 | ) |  |  | ($9.5 | ) |  |  | $200.0 |  |  |  | $4,770.4 |
IPL | Total IPL Common Equity |  |  |  |
|  |  | Additional |  |  |  | Cumulative |  |
| Common |  | Paid-In |  | Retained |  | Preferred |  | Total
| Stock |  | Capital |  | Earnings |  | Stock |  | Equity
Three Months Ended September 30, 2019 |  |  |  |  |  |  |  |  |
Beginning balance, July 1 |  | $33.4 |  |  |  | $2,322.8 |  |  |  | $788.9 |  |  |  | $200.0 |  |  |  | $3,345.1 |
Earnings available for common stock |  |  |  |  | 141.1 |  |  |  |  | 141.1 |
Common stock dividends |  |  |  |  | (42.1 | ) |  |  |  | (42.1 | )
Ending balance, September 30 |  | $33.4 |  |  |  | $2,322.8 |  |  |  | $887.9 |  |  |  | $200.0 |  |  |  | $3,444.1 |
Three Months Ended September 30, 2018 |  |  |  |  |  |  |  |  |
Beginning balance, July 1 |  | $33.4 |  |  |  | $1,927.8 |  |  |  | $692.9 |  |  |  | $200.0 |  |  |  | $2,854.1 |
Earnings available for common stock |  |  |  |  | 126.5 |  |  |  |  | 126.5 |
Common stock dividends |  |  |  |  | (41.9 | ) |  |  |  | (41.9 | )
Capital contributions from parent |  |  | 100.0 |  |  |  |  |  |  | 100.0 |
Ending balance, September 30 |  | $33.4 |  |  |  | $2,027.8 |  |  |  | $777.5 |  |  |  | $200.0 |  |  |  | $3,038.7 |
IPL | Total IPL Common Equity |  |  |  |
|  |  | Additional |  |  |  | Cumulative |  |
| Common |  | Paid-In |  | Retained |  | Preferred |  | Total
| Stock |  | Capital |  | Earnings |  | Stock |  | Equity
Nine Months Ended September 30, 2019 |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $33.4 |  |  |  | $2,222.8 |  |  |  | $774.5 |  |  |  | $200.0 |  |  |  | $3,230.7 |
Earnings available for common stock |  |  |  |  | 239.4 |  |  |  |  | 239.4 |
Common stock dividends |  |  |  |  | (126.0 | ) |  |  |  | (126.0 | )
Capital contributions from parent |  |  | 100.0 |  |  |  |  |  |  | 100.0 |
Ending balance, September 30 |  | $33.4 |  |  |  | $2,322.8 |  |  |  | $887.9 |  |  |  | $200.0 |  |  |  | $3,444.1 |
Nine Months Ended September 30, 2018 |  |  |  |  |  |  |  |  |
Beginning balance, January 1 |  | $33.4 |  |  |  | $1,797.8 |  |  |  | $678.5 |  |  |  | $200.0 |  |  |  | $2,709.7 |
Earnings available for common stock |  |  |  |  | 224.9 |  |  |  |  | 224.9 |
Common stock dividends |  |  |  |  | (125.9 | ) |  |  |  | (125.9 | )
Capital contributions from parent |  |  | 230.0 |  |  |  |  |  |  | 230.0 |
Ending balance, September 30 |  | $33.4 |  |  |  | $2,027.8 |  |  |  | $777.5 |  |  |  | $200.0 |  |  |  | $3,038.7 |
WPL |  |  | Additional |  |  |  | Total
| Common |  | Paid-In |  | Retained |  | Common
| Stock |  | Capital |  | Earnings |  | Equity
Three Months Ended September 30, 2019 |  |  |  |  |  |  |
Beginning balance, July 1 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $810.0 |  |  |  | $2,185.2 |
Earnings available for common stock |  |  |  |  | 75.5 |  |  | 75.5 |
Common stock dividends |  |  |  |  | (35.9 | ) |  | (35.9 | )
Capital contributions from parent |  |  | 100.0 |  |  |  |  | 100.0 |
Ending balance, September 30 |  | $66.2 |  |  |  | $1,409.0 |  |  |  | $849.6 |  |  |  | $2,324.8 |
Three Months Ended September 30, 2018 |  |  |  |  |  |  |
Beginning balance, July 1 |  | $66.2 |  |  |  | $1,259.0 |  |  |  | $730.0 |  |  |  | $2,055.2 |
Earnings available for common stock |  |  |  |  | 76.3 |  |  | 76.3 |
Common stock dividends |  |  |  |  | (34.9 | ) |  | (34.9 | )
Capital contributions from parent |  |  | 50.0 |  |  |  |  | 50.0 |
Ending balance, September 30 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $771.4 |  |  |  | $2,146.6 |
WPL |  |  | Additional |  |  |  | Total
| Common |  | Paid-In |  | Retained |  | Common
| Stock |  | Capital |  | Earnings |  | Equity
Nine Months Ended September 30, 2019 |  |  |  |  |  |  |
Beginning balance, January 1 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $774.3 |  |  |  | $2,149.5 |
Earnings available for common stock |  |  |  |  | 183.2 |  |  | 183.2 |
Common stock dividends |  |  |  |  | (107.9 | ) |  | (107.9 | )
Capital contributions from parent |  |  | 100.0 |  |  |  |  | 100.0 |
Ending balance, September 30 |  | $66.2 |  |  |  | $1,409.0 |  |  |  | $849.6 |  |  |  | $2,324.8 |
Nine Months Ended September 30, 2018 |  |  |  |  |  |  |
Beginning balance, January 1 |  | $66.2 |  |  |  | $1,109.0 |  |  |  | $706.3 |  |  |  | $1,881.5 |
Earnings available for common stock |  |  |  |  | 170.1 |  |  | 170.1 |
Common stock dividends |  |  |  |  | (105.0 | ) |  | (105.0 | )
Capital contributions from parent |  |  | 200.0 |  |  |  |  | 200.0 |
Ending balance, September 30 |  | $66.2 |  |  |  | $1,309.0 |  |  |  | $771.4 |  |  |  | $2,146.6 |

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