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Investments (Tables) | 3 Months Ended
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Mar. 31, 2021
Schedule of Equity Method Investments [Line Items] |
Unconsolidated Equity Investments | Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three months ended March 31 was as follows (in millions):
| 2021 |  | 2020 |  |  |  |
ATC Holdings | ($11) |  | ($11) |  |  |  |
Other | (4) |  | (2) |  |  |  |
| ($15) |  | ($13) |  |  |  |

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