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Investments | 12 Months Ended
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Dec. 31, 2018
Schedule of Equity Method Investments [Line Items] |
Investments | INVESTMENTS 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 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 |  |  |  |  | — |  |  | — |  |  |
Interest in ATC and WPL’s Noncontrolling Interest - Prior to 2014, WPL owned 100% of WPL Transco, which held Alliant Energy’s interest in ATC. In 2014, WPL Transco’s operating agreement was amended to allow ATI, a wholly-owned subsidiary of AEF, to become a member of WPL Transco in addition to WPL. Prior to the transfer of the interest in ATC to ATI discussed below, WPL consolidated WPL Transco, and ATI’s ownership in WPL Transco was recorded as a noncontrolling interest in total equity on WPL’s balance sheets. On December 31, 2016, pursuant to a PSCW order, WPL Transco was liquidated and WPL transferred its interest in ATC to ATI. As a result, WPL no longer records equity income from its prior interest in ATC. In conjunction with the transfer of the interest in ATC, a deferred intercompany tax gain recognized by WPL was assumed by ATI. The impact of WPL’s transfer of the interest in ATC Holdings, including the assumption of such intercompany tax gain by ATI, was recorded as a net reduction in total equity of $163.6 million on WPL’s balance sheet. WPL’s income statement includes all of the equity earnings from ATC through December 31, 2016, the date of transfer. There were no impacts of this transfer to Alliant Energy’s consolidated financial statements. As of December 31, 2016, ATI owns Alliant Energy’s entire interest in ATC Holdings. Interest in ATC Holdco LLC - In 2011, Duke Energy Corporation and ATC announced the creation of Duke-American Transmission Company, LLC, a joint venture that is expected to acquire, build, own and operate new electric transmission infrastructure in North America. In 2017, ATC transferred a portion of its interest in Duke-American Transmission Company, LLC to ATC Holdco LLC, and as a result, Alliant Energy contributed additional equity capital funding based on its ownership interest in ATC Holdco LLC. A portion of the proceeds from the transfer was distributed to all ATC Holdco LLC’s owners based on their ATC ownership percentage. Non-utility Wind Farm in Oklahoma - In July 2017, a wholly-owned subsidiary of AEF acquired 50% of a cash equity ownership interest in a 225 MW non-utility wind farm located in Oklahoma, which started commercial operations in December 2016. The wind farm 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.
WPL [Member] |
Schedule of Equity Method Investments [Line Items] |
Investments | INVESTMENTS 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 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 |  |  |  |  | — |  |  | — |  |  |
Interest in ATC and WPL’s Noncontrolling Interest - Prior to 2014, WPL owned 100% of WPL Transco, which held Alliant Energy’s interest in ATC. In 2014, WPL Transco’s operating agreement was amended to allow ATI, a wholly-owned subsidiary of AEF, to become a member of WPL Transco in addition to WPL. Prior to the transfer of the interest in ATC to ATI discussed below, WPL consolidated WPL Transco, and ATI’s ownership in WPL Transco was recorded as a noncontrolling interest in total equity on WPL’s balance sheets. On December 31, 2016, pursuant to a PSCW order, WPL Transco was liquidated and WPL transferred its interest in ATC to ATI. As a result, WPL no longer records equity income from its prior interest in ATC. In conjunction with the transfer of the interest in ATC, a deferred intercompany tax gain recognized by WPL was assumed by ATI. The impact of WPL’s transfer of the interest in ATC Holdings, including the assumption of such intercompany tax gain by ATI, was recorded as a net reduction in total equity of $163.6 million on WPL’s balance sheet. WPL’s income statement includes all of the equity earnings from ATC through December 31, 2016, the date of transfer. There were no impacts of this transfer to Alliant Energy’s consolidated financial statements. As of December 31, 2016, ATI owns Alliant Energy’s entire interest in ATC Holdings. Interest in ATC Holdco LLC - In 2011, Duke Energy Corporation and ATC announced the creation of Duke-American Transmission Company, LLC, a joint venture that is expected to acquire, build, own and operate new electric transmission infrastructure in North America. In 2017, ATC transferred a portion of its interest in Duke-American Transmission Company, LLC to ATC Holdco LLC, and as a result, Alliant Energy contributed additional equity capital funding based on its ownership interest in ATC Holdco LLC. A portion of the proceeds from the transfer was distributed to all ATC Holdco LLC’s owners based on their ATC ownership percentage.

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