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Investments | 12 Months Ended
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Dec. 31, 2020
Schedule of Equity Method Investments [Line Items] |
Investments | INVESTMENTS Unconsolidated Equity Investments - Alliant Energy’s 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, 2020 |  | 2020 |  | 2019 |  | 2020 |  | 2019 |  | 2018
ATC Holdings | 16%, 20% |  | $331 |  | $320 |  | ($47) |  | ($45) |  | ($38)
Non-utility wind farm in Oklahoma | 50% |  | 103 |  | 105 |  | (8) |  | (5) |  | (16)
Other | Various |  | 42 |  | 33 |  | (6) |  | (3) |  | (1)
|  |  | $476 |  | $458 |  | ($61) |  | ($53) |  | ($55)
Summary aggregate financial information from the financial statements of these holdings is as follows (in millions):
| Alliant Energy |  |
| 2020 |  | 2019 |  | 2018 |  |  |  |  |  |
Revenues | $801 |  |  | $783 |  |  | $724 |  |  |  |  |  |  |
Operating income | 376 |  |  | 359 |  |  | 325 |  |  |  |  |  |  |
Net income | 343 |  |  | 340 |  |  | 217 |  |  |  |  |  |  |
As of December 31: |  |  |  |  |  |  |  |  |  |  |
Current assets | 121 |  |  | 139 |  |  |  |  |  |  |  |  |
Non-current assets | 6,388 |  |  | 5,964 |  |  |  |  |  |  |  |  |
Current liabilities | 317 |  |  | 507 |  |  |  |  |  |  |  |  |
Non-current liabilities | 2,997 |  |  | 2,659 |  |  |  |  |  |  |  |  |
Noncontrolling interest | 192 |  |  | 208 |  |  |  |  |  |  |  |  |
ATC Holdings - As of December 31, 2020, Alliant Energy has a 16% ownership interest in ATC and a 20% ownership interest in ATC Holdco LLC, collectively referred to as ATC Holdings. ATC is an independent, for-profit, transmission-only company. ATC Holdco LLC holds Duke-American Transmission Company, LLC, a joint venture between Duke Energy Corporation and ATC, that owns electric transmission infrastructure in North America. Non-utility Wind Farm in Oklahoma - The non-utility wind farm located in Oklahoma provides electricity to a third-party under a long-term PPA, and has both cash and tax equity ownership. The equity income recognized in 2018 was primarily related to the impacts of Federal Tax Reform. The liquidation method utilized to recognize Alliant Energy’s share of the wind farm’s earnings includes utilizing the federal income tax rate in effect as of the end of the measurement period. The lower federal income tax rate effective as of January 1, 2018 resulted in an acceleration of earnings attributable to Alliant Energy’s interest in the Oklahoma wind farm. This increase in earnings is expected to reverse over time. Alliant Energy does not maintain or operate the wind farm, and provided a parent guarantee of its subsidiary’s indemnification obligations under the operating agreement and PPA. Refer to Note 17(d) for discussion of the guarantee.

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