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Common Equity | 12 Months Ended
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Dec. 31, 2017
Schedule of Common Equity [Line Items] |
Common Equity | COMMON EQUITY Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows:
| 2017 |  | 2016 |  | 2015
Shares outstanding, January 1 | 227,673,654 |  |  | 226,918,432 |  |  | 221,871,360 |
At-the-market offering programs | 3,074,931 |  |  | — |  |  | 4,373,234 |
Shareowner Direct Plan issuances | 640,723 |  |  | 732,814 |  |  | 606,010 |
Equity-based compensation plans (Note 12(b)) | 5,185 |  |  | 22,408 |  |  | 112,756 |
Other | (45,847 | ) |  | — |  |  | (44,928 | )
Shares outstanding, December 31 | 231,348,646 |  |  | 227,673,654 |  |  | 226,918,432 |
At December 31, 2017, Alliant Energy had a total of 12.4 million shares available for issuance in the aggregate, pursuant to its Amended and Restated OIP, Shareowner Direct Plan and 401(k) Savings Plan. At-the-Market Offering Programs - In 2017 and 2015, Alliant Energy filed prospectus supplements under which it could sell up to $125 million and $150 million of its common stock, respectively, through at-the-market offering programs. In 2017, Alliant Energy issued 3,074,931 shares of common stock through this program and received cash proceeds of $124 million, net of $1 million in commissions and fees. In 2015, Alliant Energy issued 4,373,234 shares of common stock through this program and received cash proceeds of $133 million, net of $2 million in commissions and fees. The proceeds from the issuances of common stock were used for general corporate purposes. The 2015 at-the-market offering program expired in 2016, and Alliant Energy currently has no plans to issue any additional common stock through the 2017 at-the-market offering program. Shareowner Direct Plan - Alliant Energy satisfies its requirements under the Shareowner Direct Plan (dividend reinvestment and stock purchase plan) by acquiring Alliant Energy common stock through original issue, rather than on the open market. Shareowner Rights Agreement - Alliant Energy previously established an amended and restated Shareowner Rights Agreement. The rights under this agreement were exercisable if a person or group acquired, or announced an intention to acquire, 15% or more of Alliant Energy’s outstanding common stock. In January 2018, Alliant Energy’s Board of Directors authorized the redemption of the rights, which were redeemed to shareowners as of the close of business on January 31, 2018. Dividend Restrictions - Alliant Energy does not have any significant common stock dividend restrictions. IPL and WPL each have common stock dividend restrictions based on applicable regulatory limitations. IPL also has common stock dividend restrictions based on the terms of its outstanding preferred stock. As of December 31, 2017, IPL and WPL were in compliance with all such dividend restrictions. IPL is restricted from paying common stock dividends to its parent company, Alliant Energy, if for any past or current dividend period, dividends on its preferred stock have not been paid, or declared and set apart for payment. IPL has paid all dividends on its preferred stock through 2017. Under the Federal Power Act, IPL may not pay dividends to its parent company in excess of the current amount of its retained earnings. As of December 31, 2017, IPL’s amount of retained earnings that were free of dividend restrictions was $679 million. If IPL’s actual 13-month average common equity ratio (calculated on a financial basis consistent with IPL’s rate reviews) falls below 42% of total capitalization, IPL is required to notify the IUB. Pursuant to a December 2016 PSCW order, WPL has a regulatory limitation on distributions to its parent company. WPL is prohibited from paying annual common stock dividends to its parent company in excess of forecasted dividend levels of $140 million in 2018 if WPL’s actual 13-month average common equity ratio (calculated on a financial basis consistent with WPL’s rate reviews) would fall below 51.00% for 2018. As of December 31, 2017, WPL’s amount of retained earnings that were free of dividend restrictions was $140 million for 2018. Restricted Net Assets of Subsidiaries - IPL and WPL do not have regulatory authority to lend or advance any amounts to their parent company. As of December 31, 2017, the amount of IPL’s and WPL’s net assets 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 $1.8 billion and $1.7 billion, respectively. Comprehensive Income - In 2017, 2016 and 2015, Alliant Energy’s other comprehensive income (loss) was ($0.1) million, $0 million and $0.2 million, respectively; therefore, its comprehensive income was substantially equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was substantially equal to its net income attributable to Alliant Energy common shareowners for such periods. In 2017, 2016 and 2015, IPL and WPL had no other comprehensive income; therefore their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.
IPL [Member] |
Schedule of Common Equity [Line Items] |
Common Equity | COMMON EQUITY Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows:
| 2017 |  | 2016 |  | 2015
Shares outstanding, January 1 | 227,673,654 |  |  | 226,918,432 |  |  | 221,871,360 |
At-the-market offering programs | 3,074,931 |  |  | — |  |  | 4,373,234 |
Shareowner Direct Plan issuances | 640,723 |  |  | 732,814 |  |  | 606,010 |
Equity-based compensation plans (Note 12(b)) | 5,185 |  |  | 22,408 |  |  | 112,756 |
Other | (45,847 | ) |  | — |  |  | (44,928 | )
Shares outstanding, December 31 | 231,348,646 |  |  | 227,673,654 |  |  | 226,918,432 |
At December 31, 2017, Alliant Energy had a total of 12.4 million shares available for issuance in the aggregate, pursuant to its Amended and Restated OIP, Shareowner Direct Plan and 401(k) Savings Plan. At-the-Market Offering Programs - In 2017 and 2015, Alliant Energy filed prospectus supplements under which it could sell up to $125 million and $150 million of its common stock, respectively, through at-the-market offering programs. In 2017, Alliant Energy issued 3,074,931 shares of common stock through this program and received cash proceeds of $124 million, net of $1 million in commissions and fees. In 2015, Alliant Energy issued 4,373,234 shares of common stock through this program and received cash proceeds of $133 million, net of $2 million in commissions and fees. The proceeds from the issuances of common stock were used for general corporate purposes. The 2015 at-the-market offering program expired in 2016, and Alliant Energy currently has no plans to issue any additional common stock through the 2017 at-the-market offering program. Shareowner Direct Plan - Alliant Energy satisfies its requirements under the Shareowner Direct Plan (dividend reinvestment and stock purchase plan) by acquiring Alliant Energy common stock through original issue, rather than on the open market. Shareowner Rights Agreement - Alliant Energy previously established an amended and restated Shareowner Rights Agreement. The rights under this agreement were exercisable if a person or group acquired, or announced an intention to acquire, 15% or more of Alliant Energy’s outstanding common stock. In January 2018, Alliant Energy’s Board of Directors authorized the redemption of the rights, which were redeemed to shareowners as of the close of business on January 31, 2018. Dividend Restrictions - Alliant Energy does not have any significant common stock dividend restrictions. IPL and WPL each have common stock dividend restrictions based on applicable regulatory limitations. IPL also has common stock dividend restrictions based on the terms of its outstanding preferred stock. As of December 31, 2017, IPL and WPL were in compliance with all such dividend restrictions. IPL is restricted from paying common stock dividends to its parent company, Alliant Energy, if for any past or current dividend period, dividends on its preferred stock have not been paid, or declared and set apart for payment. IPL has paid all dividends on its preferred stock through 2017. Under the Federal Power Act, IPL may not pay dividends to its parent company in excess of the current amount of its retained earnings. As of December 31, 2017, IPL’s amount of retained earnings that were free of dividend restrictions was $679 million. If IPL’s actual 13-month average common equity ratio (calculated on a financial basis consistent with IPL’s rate reviews) falls below 42% of total capitalization, IPL is required to notify the IUB. Pursuant to a December 2016 PSCW order, WPL has a regulatory limitation on distributions to its parent company. WPL is prohibited from paying annual common stock dividends to its parent company in excess of forecasted dividend levels of $140 million in 2018 if WPL’s actual 13-month average common equity ratio (calculated on a financial basis consistent with WPL’s rate reviews) would fall below 51.00% for 2018. As of December 31, 2017, WPL’s amount of retained earnings that were free of dividend restrictions was $140 million for 2018. Restricted Net Assets of Subsidiaries - IPL and WPL do not have regulatory authority to lend or advance any amounts to their parent company. As of December 31, 2017, the amount of IPL’s and WPL’s net assets 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 $1.8 billion and $1.7 billion, respectively. Comprehensive Income - In 2017, 2016 and 2015, Alliant Energy’s other comprehensive income (loss) was ($0.1) million, $0 million and $0.2 million, respectively; therefore, its comprehensive income was substantially equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was substantially equal to its net income attributable to Alliant Energy common shareowners for such periods. In 2017, 2016 and 2015, IPL and WPL had no other comprehensive income; therefore their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.
WPL [Member] |
Schedule of Common Equity [Line Items] |
Common Equity | COMMON EQUITY Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows:
| 2017 |  | 2016 |  | 2015
Shares outstanding, January 1 | 227,673,654 |  |  | 226,918,432 |  |  | 221,871,360 |
At-the-market offering programs | 3,074,931 |  |  | — |  |  | 4,373,234 |
Shareowner Direct Plan issuances | 640,723 |  |  | 732,814 |  |  | 606,010 |
Equity-based compensation plans (Note 12(b)) | 5,185 |  |  | 22,408 |  |  | 112,756 |
Other | (45,847 | ) |  | — |  |  | (44,928 | )
Shares outstanding, December 31 | 231,348,646 |  |  | 227,673,654 |  |  | 226,918,432 |
At December 31, 2017, Alliant Energy had a total of 12.4 million shares available for issuance in the aggregate, pursuant to its Amended and Restated OIP, Shareowner Direct Plan and 401(k) Savings Plan. At-the-Market Offering Programs - In 2017 and 2015, Alliant Energy filed prospectus supplements under which it could sell up to $125 million and $150 million of its common stock, respectively, through at-the-market offering programs. In 2017, Alliant Energy issued 3,074,931 shares of common stock through this program and received cash proceeds of $124 million, net of $1 million in commissions and fees. In 2015, Alliant Energy issued 4,373,234 shares of common stock through this program and received cash proceeds of $133 million, net of $2 million in commissions and fees. The proceeds from the issuances of common stock were used for general corporate purposes. The 2015 at-the-market offering program expired in 2016, and Alliant Energy currently has no plans to issue any additional common stock through the 2017 at-the-market offering program. Shareowner Direct Plan - Alliant Energy satisfies its requirements under the Shareowner Direct Plan (dividend reinvestment and stock purchase plan) by acquiring Alliant Energy common stock through original issue, rather than on the open market. Shareowner Rights Agreement - Alliant Energy previously established an amended and restated Shareowner Rights Agreement. The rights under this agreement were exercisable if a person or group acquired, or announced an intention to acquire, 15% or more of Alliant Energy’s outstanding common stock. In January 2018, Alliant Energy’s Board of Directors authorized the redemption of the rights, which were redeemed to shareowners as of the close of business on January 31, 2018. Dividend Restrictions - Alliant Energy does not have any significant common stock dividend restrictions. IPL and WPL each have common stock dividend restrictions based on applicable regulatory limitations. IPL also has common stock dividend restrictions based on the terms of its outstanding preferred stock. As of December 31, 2017, IPL and WPL were in compliance with all such dividend restrictions. IPL is restricted from paying common stock dividends to its parent company, Alliant Energy, if for any past or current dividend period, dividends on its preferred stock have not been paid, or declared and set apart for payment. IPL has paid all dividends on its preferred stock through 2017. Under the Federal Power Act, IPL may not pay dividends to its parent company in excess of the current amount of its retained earnings. As of December 31, 2017, IPL’s amount of retained earnings that were free of dividend restrictions was $679 million. If IPL’s actual 13-month average common equity ratio (calculated on a financial basis consistent with IPL’s rate reviews) falls below 42% of total capitalization, IPL is required to notify the IUB. Pursuant to a December 2016 PSCW order, WPL has a regulatory limitation on distributions to its parent company. WPL is prohibited from paying annual common stock dividends to its parent company in excess of forecasted dividend levels of $140 million in 2018 if WPL’s actual 13-month average common equity ratio (calculated on a financial basis consistent with WPL’s rate reviews) would fall below 51.00% for 2018. As of December 31, 2017, WPL’s amount of retained earnings that were free of dividend restrictions was $140 million for 2018. Restricted Net Assets of Subsidiaries - IPL and WPL do not have regulatory authority to lend or advance any amounts to their parent company. As of December 31, 2017, the amount of IPL’s and WPL’s net assets 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 $1.8 billion and $1.7 billion, respectively. Comprehensive Income - In 2017, 2016 and 2015, Alliant Energy’s other comprehensive income (loss) was ($0.1) million, $0 million and $0.2 million, respectively; therefore, its comprehensive income was substantially equal to its net income and its comprehensive income attributable to Alliant Energy common shareowners was substantially equal to its net income attributable to Alliant Energy common shareowners for such periods. In 2017, 2016 and 2015, IPL and WPL had no other comprehensive income; therefore their comprehensive income was equal to their net income and their comprehensive income available for common stock was equal to their earnings available for common stock for such periods.

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