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Investments (Tables) | 12 Months Ended
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Dec. 31, 2017
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, 2017 |  | 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2015
Alliant Energy |  |  |  |  |  |  |  |  |  |  |
ATC Investment (a) | 16%-20% |  |  | $274.2 |  |  |  | $317.6 |  |  |  | ($42.4 | ) |  |  | ($39.1 | ) |  |  | ($34.2 | )
Wind Investment in Oklahoma | 50% |  | 98.3 |  |  | — |  |  | (1.8 | ) |  | — |  |  | — |
Other | Various |  | 8.9 |  |  | 8.4 |  |  | (0.6 | ) |  | (0.5 | ) |  | 0.4 |
|  |  |  | $381.4 |  |  |  | $326.0 |  |  |  | ($44.8 | ) |  |  | ($39.6 | ) |  |  | ($33.8 | )
WPL |  |  |  |  |  |  |  |  |  |  |
ATC | —% |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | ($39.1 | ) |  |  | ($34.2 | )
Wisconsin River Power Company | 50% |  | 8.3 |  |  | 7.7 |  |  | (0.7 | ) |  | (0.7 | ) |  | (0.9 | )
|  |  |  | $8.3 |  |  |  | $7.7 |  |  |  | ($0.7 | ) |  |  | ($39.8 | ) |  |  | ($35.1 | )
(a) | As of December 31, 2017, Alliant Energy’s ATC Investment is comprised of a 16% ownership interest in ATC and a 20% ownership interest in ATC Holdco LLC, which are described below. In 2017, Alliant Energy’s investment in ATC decreased due to the impacts of Tax Reform. Refer to Note 11 for further discussion. Alliant Energy currently has the ability to exercise significant influence over ATC’s financial and operating policies through its participation on ATC’s Board of Directors. Refer to Note 18 for information regarding related party transactions with ATC.
Summary Aggregate Financial Information | Summary aggregate financial information from the financial statements of these investments is as follows (in millions):
| Alliant Energy |  | WPL
| 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Operating revenues |  | $741 |  |  |  | $658 |  |  |  | $624 |  |  |  | $8 |  |  |  | $658 |  |  |  | $624 |
Operating income | 374 |  |  | 331 |  |  | 299 |  |  | 4 |  |  | 331 |  |  | 299 |
Net income | 267 |  |  | 232 |  |  | 186 |  |  | 2 |  |  | 234 |  |  | 202 |
As of December 31: |  |  |  |  |  |  |  |  |  |  |
Current assets | 104 |  |  | 82 |  |  |  |  | 7 |  |  | 6 |  |  |
Non-current assets | 5,041 |  |  | 4,340 |  |  |  |  | 20 |  |  | 19 |  |  |
Current liabilities | 770 |  |  | 498 |  |  |  |  | 2 |  |  | 3 |  |  |
Non-current liabilities | 2,038 |  |  | 2,144 |  |  |  |  | 8 |  |  | 7 |  |  |
Minority interest | 255 |  |  | — |  |  |  |  | — |  |  | — |  |  |
Cash Surrender Value of Life Insurance Policies | At December 31, the cash surrender value of these investments was as follows (in millions):
| Alliant Energy |  | WPL
| 2017 |  | 2016 |  | 2017 |  | 2016
Cash surrender value | $10.4 |  | $10.6 |  | $5.6 |  | $5.8
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, 2017 |  | 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2015
Alliant Energy |  |  |  |  |  |  |  |  |  |  |
ATC Investment (a) | 16%-20% |  |  | $274.2 |  |  |  | $317.6 |  |  |  | ($42.4 | ) |  |  | ($39.1 | ) |  |  | ($34.2 | )
Wind Investment in Oklahoma | 50% |  | 98.3 |  |  | — |  |  | (1.8 | ) |  | — |  |  | — |
Other | Various |  | 8.9 |  |  | 8.4 |  |  | (0.6 | ) |  | (0.5 | ) |  | 0.4 |
|  |  |  | $381.4 |  |  |  | $326.0 |  |  |  | ($44.8 | ) |  |  | ($39.6 | ) |  |  | ($33.8 | )
WPL |  |  |  |  |  |  |  |  |  |  |
ATC | —% |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | ($39.1 | ) |  |  | ($34.2 | )
Wisconsin River Power Company | 50% |  | 8.3 |  |  | 7.7 |  |  | (0.7 | ) |  | (0.7 | ) |  | (0.9 | )
|  |  |  | $8.3 |  |  |  | $7.7 |  |  |  | ($0.7 | ) |  |  | ($39.8 | ) |  |  | ($35.1 | )
(a) | As of December 31, 2017, Alliant Energy’s ATC Investment is comprised of a 16% ownership interest in ATC and a 20% ownership interest in ATC Holdco LLC, which are described below. In 2017, Alliant Energy’s investment in ATC decreased due to the impacts of Tax Reform. Refer to Note 11 for further discussion. Alliant Energy currently has the ability to exercise significant influence over ATC’s financial and operating policies through its participation on ATC’s Board of Directors. Refer to Note 18 for information regarding related party transactions with ATC.
Summary Aggregate Financial Information | Summary aggregate financial information from the financial statements of these investments is as follows (in millions):
| Alliant Energy |  | WPL
| 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Operating revenues |  | $741 |  |  |  | $658 |  |  |  | $624 |  |  |  | $8 |  |  |  | $658 |  |  |  | $624 |
Operating income | 374 |  |  | 331 |  |  | 299 |  |  | 4 |  |  | 331 |  |  | 299 |
Net income | 267 |  |  | 232 |  |  | 186 |  |  | 2 |  |  | 234 |  |  | 202 |
As of December 31: |  |  |  |  |  |  |  |  |  |  |
Current assets | 104 |  |  | 82 |  |  |  |  | 7 |  |  | 6 |  |  |
Non-current assets | 5,041 |  |  | 4,340 |  |  |  |  | 20 |  |  | 19 |  |  |
Current liabilities | 770 |  |  | 498 |  |  |  |  | 2 |  |  | 3 |  |  |
Non-current liabilities | 2,038 |  |  | 2,144 |  |  |  |  | 8 |  |  | 7 |  |  |
Minority interest | 255 |  |  | — |  |  |  |  | — |  |  | — |  |  |
Cash Surrender Value of Life Insurance Policies | At December 31, the cash surrender value of these investments was as follows (in millions):
| Alliant Energy |  | WPL
| 2017 |  | 2016 |  | 2017 |  | 2016
Cash surrender value | $10.4 |  | $10.6 |  | $5.6 |  | $5.8

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