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Investments (Tables) | 12 Months Ended
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Dec. 31, 2018
Investment [Line Items] |
Unconsolidated Equity Investments | Unconsolidated investments accounted for under the equity method of accounting are as follows (in millions):
| Ownership Interest at |  | Carrying Value at December 31, |  | Equity (Income) / Loss
| December 31, 2018 |  | 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2016
Alliant Energy |  |  |  |  |  |  |  |  |  |  |
ATC Holdings (a) | 16%-20% |  |  | $293.6 |  |  |  | $274.2 |  |  |  | ($38.1 | ) |  |  | ($42.4 | ) |  |  | ($39.1 | )
Non-utility wind farm in Oklahoma | 50% |  | 105.1 |  |  | 98.3 |  |  | (15.6 | ) |  | (1.8 | ) |  | — |
Other | Various |  | 22.6 |  |  | 8.9 |  |  | (0.9 | ) |  | (0.6 | ) |  | (0.5 | )
|  |  |  | $421.3 |  |  |  | $381.4 |  |  |  | ($54.6 | ) |  |  | ($44.8 | ) |  |  | ($39.6 | )
WPL |  |  |  |  |  |  |  |  |  |  |
ATC | —% |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | ($39.1 | )
Wisconsin River Power Company | 50% |  | 8.1 |  |  | 8.3 |  |  | (0.9 | ) |  | (0.7 | ) |  | (0.7 | )
|  |  |  | $8.1 |  |  |  | $8.3 |  |  |  | ($0.9 | ) |  |  | ($0.7 | ) |  |  | ($39.8 | )
(a) | As of December 31, 2018, Alliant Energy’s interest in ATC Holdings is comprised of a 16% ownership interest in ATC and a 20% ownership interest in ATC Holdco LLC, which are described below. Alliant Energy currently has the ability to exercise significant influence over ATC’s and ATC Holdco LLC’s financial and operating policies through its participation on ATC’s Board of Directors.
Summary Aggregate Financial Information | Summary aggregate financial information from the financial statements of these holdings is as follows (in millions):
| Alliant Energy |  | WPL
| 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016
Revenues |  | $724 |  |  |  | $741 |  |  |  | $658 |  |  |  | $8 |  |  |  | $8 |  |  |  | $658 |
Operating income | 325 |  |  | 374 |  |  | 331 |  |  | 2 |  |  | 4 |  |  | 331 |
Net income | 217 |  |  | 267 |  |  | 232 |  |  | 1 |  |  | 2 |  |  | 234 |
As of December 31: |  |  |  |  |  |  |  |  |  |  |
Current assets | 144 |  |  | 104 |  |  |  |  | 4 |  |  | 7 |  |  |
Non-current assets | 5,498 |  |  | 5,041 |  |  |  |  | 19 |  |  | 20 |  |  |
Current liabilities | 644 |  |  | 770 |  |  |  |  | 1 |  |  | 2 |  |  |
Non-current liabilities | 2,315 |  |  | 2,038 |  |  |  |  | 6 |  |  | 8 |  |  |
Noncontrolling interest | 223 |  |  | 255 |  |  |  |  | — |  |  | — |  |  |
WPL [Member] |
Investment [Line Items] |
Unconsolidated Equity Investments | Unconsolidated investments accounted for under the equity method of accounting are as follows (in millions):
| Ownership Interest at |  | Carrying Value at December 31, |  | Equity (Income) / Loss
| December 31, 2018 |  | 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2016
Alliant Energy |  |  |  |  |  |  |  |  |  |  |
ATC Holdings (a) | 16%-20% |  |  | $293.6 |  |  |  | $274.2 |  |  |  | ($38.1 | ) |  |  | ($42.4 | ) |  |  | ($39.1 | )
Non-utility wind farm in Oklahoma | 50% |  | 105.1 |  |  | 98.3 |  |  | (15.6 | ) |  | (1.8 | ) |  | — |
Other | Various |  | 22.6 |  |  | 8.9 |  |  | (0.9 | ) |  | (0.6 | ) |  | (0.5 | )
|  |  |  | $421.3 |  |  |  | $381.4 |  |  |  | ($54.6 | ) |  |  | ($44.8 | ) |  |  | ($39.6 | )
WPL |  |  |  |  |  |  |  |  |  |  |
ATC | —% |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | ($39.1 | )
Wisconsin River Power Company | 50% |  | 8.1 |  |  | 8.3 |  |  | (0.9 | ) |  | (0.7 | ) |  | (0.7 | )
|  |  |  | $8.1 |  |  |  | $8.3 |  |  |  | ($0.9 | ) |  |  | ($0.7 | ) |  |  | ($39.8 | )
(a) | As of December 31, 2018, Alliant Energy’s interest in ATC Holdings is comprised of a 16% ownership interest in ATC and a 20% ownership interest in ATC Holdco LLC, which are described below. Alliant Energy currently has the ability to exercise significant influence over ATC’s and ATC Holdco LLC’s financial and operating policies through its participation on ATC’s Board of Directors.
Summary Aggregate Financial Information | Summary aggregate financial information from the financial statements of these holdings is as follows (in millions):
| Alliant Energy |  | WPL
| 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016
Revenues |  | $724 |  |  |  | $741 |  |  |  | $658 |  |  |  | $8 |  |  |  | $8 |  |  |  | $658 |
Operating income | 325 |  |  | 374 |  |  | 331 |  |  | 2 |  |  | 4 |  |  | 331 |
Net income | 217 |  |  | 267 |  |  | 232 |  |  | 1 |  |  | 2 |  |  | 234 |
As of December 31: |  |  |  |  |  |  |  |  |  |  |
Current assets | 144 |  |  | 104 |  |  |  |  | 4 |  |  | 7 |  |  |
Non-current assets | 5,498 |  |  | 5,041 |  |  |  |  | 19 |  |  | 20 |  |  |
Current liabilities | 644 |  |  | 770 |  |  |  |  | 1 |  |  | 2 |  |  |
Non-current liabilities | 2,315 |  |  | 2,038 |  |  |  |  | 6 |  |  | 8 |  |  |
Noncontrolling interest | 223 |  |  | 255 |  |  |  |  | — |  |  | — |  |  |

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