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Common Equity | 12 Months Ended
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Dec. 31, 2020
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:
| 2020 |  | 2019 |  | 2018
Shares outstanding, January 1 | 245,022,800 |  |  | 236,063,279 |  |  | 231,348,646 |
Equity forward agreements | 4,275,127 |  |  | 8,358,973 |  |  | — |
At-the-market offering programs | — |  |  | — |  |  | 4,171,013 |
Shareowner Direct Plan | 472,283 |  |  | 501,808 |  |  | 576,965 |
Equity-based compensation plans | 98,205 |  |  | 101,478 |  |  | 5,078 |
Other | — |  |  | (2,738) |  |  | (38,423) |
Shares outstanding, December 31 | 249,868,415 |  |  | 245,022,800 |  |  | 236,063,279 |
At December 31, 2020, Alliant Energy had a total of 15 million shares available for issuance in the aggregate, pursuant to its 2020 OIP, Shareowner Direct Plan and 401(k) Savings Plan. Equity Forward Agreements - In 2018, Alliant Energy entered into forward sale agreements with various counterparties in connection with a public offering of 8,358,973 shares of Alliant Energy common stock. In 2019, Alliant Energy settled $366 million under the forward sale agreements by delivering 8,358,973 shares of newly issued Alliant Energy common stock at a weighted average forward sale price of $43.75 per share. Alliant Energy used the net proceeds from the settlements for general corporate purposes. In 2019, Alliant Energy entered into forward sale agreements with a counterparty in connection with a public offering of 4,275,127 shares of Alliant Energy common stock. In 2020, Alliant Energy settled $222 million under the forward sale agreements by delivering 4,275,127 shares of newly issued Alliant Energy common stock at a weighted average forward sale price of $51.98 per share. Alliant Energy used the net proceeds from the settlements for general corporate purposes. At-the-Market Offering Program - In 2018, Alliant Energy filed a prospectus supplement under which it could sell up to $175 million of its common stock through an at-the-market offering program. In 2018, Alliant Energy issued 4,171,013 shares of common stock through this program and received cash proceeds of $173 million, net of $2 million in commissions and fees. The 2018 at-the-market offering program has expired. 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.

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- Definition The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(e)(1)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -URI http://asc.fasb.org/topic&trid=2208762 + Details
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