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Property, Plant and Equipment | 9 Months Ended
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Sep. 30, 2025
Property, Plant and Equipment [Line Items] |
Property, Plant and Equipment | PROPERTY, PLANT AND EQUIPMENT Construction costs associated with WPL’s approximately 1,100 MW of new solar generation exceeded the construction cost estimates previously approved by the PSCW by approximately $205 million. In September 2025, WPL filed a settlement agreement with the PSCW for the 2026/2027 forward-looking Test Period. In November 2025, the PSCW issued an oral decision approving the settlement, which includes a full return of and on these solar generation construction costs from WPL’s retail electric customers. As a result, Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of September 30, 2025. A written order from the PSCW is currently expected by the end of 2025. As of December 31, 2024, WPL planned to cease coal operations at Columbia Units 1 and 2 by the end of 2029, and Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment. WPL currently plans to continue coal operations at Columbia Units 1 and 2 at least through 2029 as well as evaluate the potential conversion of Columbia Unit 1 and/or Unit 2 to natural gas. As a result, as of September 30, 2025, Alliant Energy and WPL concluded that Columbia Units 1 and 2 (net book value of $398 million) no longer meet the criteria to be considered probable of abandonment.
WPL [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant and Equipment | PROPERTY, PLANT AND EQUIPMENT Construction costs associated with WPL’s approximately 1,100 MW of new solar generation exceeded the construction cost estimates previously approved by the PSCW by approximately $205 million. In September 2025, WPL filed a settlement agreement with the PSCW for the 2026/2027 forward-looking Test Period. In November 2025, the PSCW issued an oral decision approving the settlement, which includes a full return of and on these solar generation construction costs from WPL’s retail electric customers. As a result, Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of September 30, 2025. A written order from the PSCW is currently expected by the end of 2025. As of December 31, 2024, WPL planned to cease coal operations at Columbia Units 1 and 2 by the end of 2029, and Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment. WPL currently plans to continue coal operations at Columbia Units 1 and 2 at least through 2029 as well as evaluate the potential conversion of Columbia Unit 1 and/or Unit 2 to natural gas. As a result, as of September 30, 2025, Alliant Energy and WPL concluded that Columbia Units 1 and 2 (net book value of $398 million) no longer meet the criteria to be considered probable of abandonment.

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