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Investments (Tables) | 3 Months Ended
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Mar. 31, 2018
Schedule of 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):
| 2018 |  | 2017
ATC Holdings |  | ($8.7 | ) |  |  | ($11.5 | )
Non-utility wind farm in Oklahoma | (12.1 | ) |  | — |
Other | (0.5 | ) |  | — |
|  | ($21.3 | ) |  |  | ($11.5 | )

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