Property, Plant and Equipment	9 Months Ended
Sep. 30, 2024
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT WPL currently expects construction costs associated with its approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $195 million. In February 2024, the PSCW issued an order approving deferral of the incremental solar generation construction costs. The PSCW’s order did not authorize a deferral for the return on such costs. In March 2024, WPL filed for judicial review of the PSCW’s retail electric rate review order (2024/2025 forward-looking Test Period) and solar generation construction cost deferral order related to the recovery and deferral of the return on the incremental solar generation construction costs in 2024 and 2025. In September 2024, the PSCW issued an order modifying its February 2024 order and approving the deferral of the return on the incremental solar generation construction costs, and in October 2024, WPL withdrew its filing for judicial review. Alliant Energy and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of September 30, 2024 given construction costs were reasonably and prudently incurred. In September 2024, the IUC approved IPL’s settlement agreement with certain stakeholders for its retail electric rate review for the October 2024 through September 2025 forward-looking Test Period. The settlement agreement allows IPL to recover construction costs associated with its 400 MW of new solar generation, including allowance for funds used during construction and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt. In May 2024, WPL announced updated plans to convert the coal-fired Edgewater Unit 5 to natural gas in 2028, subject to regulatory approvals. WPL previously planned to retire the EGU by June 1, 2025. As a result, as of September 30, 2024, Alliant Energy and WPL concluded Edgewater Unit 5 (net book value of $493 million) no longer meets the criteria to be considered probable of abandonment, and $794 million was reclassified to utility electric generation plant in service from utility electric plant anticipated to be retired early. WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In May 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In June 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements for the nine months ended September 30, 2024. As a result of these transactions, WPL’s undivided current ownership interest in West Riverside is 56.6%.
IPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT WPL currently expects construction costs associated with its approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $195 million. In February 2024, the PSCW issued an order approving deferral of the incremental solar generation construction costs. The PSCW’s order did not authorize a deferral for the return on such costs. In March 2024, WPL filed for judicial review of the PSCW’s retail electric rate review order (2024/2025 forward-looking Test Period) and solar generation construction cost deferral order related to the recovery and deferral of the return on the incremental solar generation construction costs in 2024 and 2025. In September 2024, the PSCW issued an order modifying its February 2024 order and approving the deferral of the return on the incremental solar generation construction costs, and in October 2024, WPL withdrew its filing for judicial review. Alliant Energy and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of September 30, 2024 given construction costs were reasonably and prudently incurred. In September 2024, the IUC approved IPL’s settlement agreement with certain stakeholders for its retail electric rate review for the October 2024 through September 2025 forward-looking Test Period. The settlement agreement allows IPL to recover construction costs associated with its 400 MW of new solar generation, including allowance for funds used during construction and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt. In May 2024, WPL announced updated plans to convert the coal-fired Edgewater Unit 5 to natural gas in 2028, subject to regulatory approvals. WPL previously planned to retire the EGU by June 1, 2025. As a result, as of September 30, 2024, Alliant Energy and WPL concluded Edgewater Unit 5 (net book value of $493 million) no longer meets the criteria to be considered probable of abandonment, and $794 million was reclassified to utility electric generation plant in service from utility electric plant anticipated to be retired early. WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In May 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In June 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements for the nine months ended September 30, 2024. As a result of these transactions, WPL’s undivided current ownership interest in West Riverside is 56.6%.
WPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT WPL currently expects construction costs associated with its approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $195 million. In February 2024, the PSCW issued an order approving deferral of the incremental solar generation construction costs. The PSCW’s order did not authorize a deferral for the return on such costs. In March 2024, WPL filed for judicial review of the PSCW’s retail electric rate review order (2024/2025 forward-looking Test Period) and solar generation construction cost deferral order related to the recovery and deferral of the return on the incremental solar generation construction costs in 2024 and 2025. In September 2024, the PSCW issued an order modifying its February 2024 order and approving the deferral of the return on the incremental solar generation construction costs, and in October 2024, WPL withdrew its filing for judicial review. Alliant Energy and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of September 30, 2024 given construction costs were reasonably and prudently incurred. In September 2024, the IUC approved IPL’s settlement agreement with certain stakeholders for its retail electric rate review for the October 2024 through September 2025 forward-looking Test Period. The settlement agreement allows IPL to recover construction costs associated with its 400 MW of new solar generation, including allowance for funds used during construction and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt. In May 2024, WPL announced updated plans to convert the coal-fired Edgewater Unit 5 to natural gas in 2028, subject to regulatory approvals. WPL previously planned to retire the EGU by June 1, 2025. As a result, as of September 30, 2024, Alliant Energy and WPL concluded Edgewater Unit 5 (net book value of $493 million) no longer meets the criteria to be considered probable of abandonment, and $794 million was reclassified to utility electric generation plant in service from utility electric plant anticipated to be retired early. WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In May 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In June 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements for the nine months ended September 30, 2024. As a result of these transactions, WPL’s undivided current ownership interest in West Riverside is 56.6%.

PROPERTY, PLANT AND EQUIPMENT

WPL currently expects construction costs associated with its approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $195 million. In February 2024, the PSCW issued an order approving deferral of the incremental solar generation construction costs. The PSCW’s order did not authorize a deferral for the return on such costs. In March 2024, WPL filed for judicial review of the PSCW’s retail electric rate review order (2024/2025 forward-looking Test Period) and solar generation construction cost deferral order related to the recovery and deferral of the return on the incremental solar generation construction costs in 2024 and 2025. In September 2024, the PSCW issued an order modifying its February 2024 order and approving the deferral of the return on the incremental solar generation construction costs, and in October 2024, WPL withdrew its filing for judicial review. Alliant Energy and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of September 30, 2024 given construction costs were reasonably and prudently incurred.

In September 2024, the IUC approved IPL’s settlement agreement with certain stakeholders for its retail electric rate review for the October 2024 through September 2025 forward-looking Test Period. The settlement agreement allows IPL to recover construction costs associated with its 400 MW of new solar generation, including allowance for funds used during construction and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt.

In May 2024, WPL announced updated plans to convert the coal-fired Edgewater Unit 5 to natural gas in 2028, subject to regulatory approvals. WPL previously planned to retire the EGU by June 1, 2025. As a result, as of September 30, 2024, Alliant Energy and WPL concluded Edgewater Unit 5 (net book value of $493 million) no longer meets the criteria to be considered probable of abandonment, and $794 million was reclassified to utility electric generation plant in service from utility electric plant anticipated to be retired early.

WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In May 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining.

In June 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements for the nine months ended September 30, 2024. As a result of these transactions, WPL’s undivided current ownership interest in West Riverside is 56.6%.

Property, Plant and Equipment [Line Items]

Property, Plant and Equipment

PROPERTY, PLANT AND EQUIPMENT

WPL currently expects construction costs associated with its approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $195 million. In February 2024, the PSCW issued an order approving deferral of the incremental solar generation construction costs. The PSCW’s order did not authorize a deferral for the return on such costs. In March 2024, WPL filed for judicial review of the PSCW’s retail electric rate review order (2024/2025 forward-looking Test Period) and solar generation construction cost deferral order related to the recovery and deferral of the return on the incremental solar generation construction costs in 2024 and 2025. In September 2024, the PSCW issued an order modifying its February 2024 order and approving the deferral of the return on the incremental solar generation construction costs, and in October 2024, WPL withdrew its filing for judicial review. Alliant Energy and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of September 30, 2024 given construction costs were reasonably and prudently incurred.

In September 2024, the IUC approved IPL’s settlement agreement with certain stakeholders for its retail electric rate review for the October 2024 through September 2025 forward-looking Test Period. The settlement agreement allows IPL to recover construction costs associated with its 400 MW of new solar generation, including allowance for funds used during construction and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt.

In May 2024, WPL announced updated plans to convert the coal-fired Edgewater Unit 5 to natural gas in 2028, subject to regulatory approvals. WPL previously planned to retire the EGU by June 1, 2025. As a result, as of September 30, 2024, Alliant Energy and WPL concluded Edgewater Unit 5 (net book value of $493 million) no longer meets the criteria to be considered probable of abandonment, and $794 million was reclassified to utility electric generation plant in service from utility electric plant anticipated to be retired early.

WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In May 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining.

In June 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements for the nine months ended September 30, 2024. As a result of these transactions, WPL’s undivided current ownership interest in West Riverside is 56.6%.