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Property, Plant and Equipment (Tables) | 12 Months Ended
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Dec. 31, 2024
Property, Plant and Equipment [Line Items] |
Property, Plant and Equipment | At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Utility: |  |  |  |  |  |  |  |  |  |  |
Electric plant: |  |  |  |  |  |  |  |  |  |  |
Generation in service (a)(b) | $11,156 |  |  | $9,180 |  |  | $5,924 |  |  | $5,025 |  |  | $5,232 |  |  | $4,155 |
Distribution in service | 7,811 |  |  | 7,314 |  |  | 4,344 |  |  | 4,091 |  |  | 3,467 |  |  | 3,223 |
Other in service | 595 |  |  | 567 |  |  | 385 |  |  | 356 |  |  | 210 |  |  | 211 |
Anticipated to be retired early (c) | 784 |  |  | 1,629 |  |  | — |  |  | — |  |  | 784 |  |  | 1,629 |
Total electric plant | 20,346 |  |  | 18,690 |  |  | 10,653 |  |  | 9,472 |  |  | 9,693 |  |  | 9,218 |
Gas plant in service | 1,863 |  |  | 1,791 |  |  | 981 |  | 951 |  |  | 882 |  |  | 840 |
Other plant in service (d) | 734 |  |  | 653 |  |  | 456 |  | 411 |  |  | 278 |  |  | 242 |
Accumulated depreciation (c) | (6,229) |  |  | (5,924) |  |  | (3,360) |  |  | (3,180) |  |  | (2,869) |  |  | (2,744) |
Net plant | 16,714 |  |  | 15,210 |  |  | 8,730 |  |  | 7,654 |  |  | 7,984 |  |  | 7,556 |
Leased Sheboygan Falls Energy Facility, net (e) | — |  |  | — |  |  | — |  |  | — |  |  | 74 |  |  | 79 |
Leased land for solar generation, net | 189 |  |  | 172 |  |  | 53 |  |  | 33 |  |  | 136 |  |  | 139 |
Construction work in progress | 1,215 |  |  | 1,245 |  |  | 548 |  | 605 |  |  | 667 |  |  | 640 |
Other, net | 5 |  |  | 7 |  |  | 5 |  |  | 6 |  |  | — |  |  | 1 |
Total utility | 18,123 |  |  | 16,634 |  |  | 9,336 |  |  | 8,298 |  |  | 8,861 |  |  | 8,415 |
Non-utility and other: |  |  |  |  |  |  |  |  |  |  |
Non-utility Generation, net (f) | 103 |  |  | 68 |  |  | — |  |  | — |  |  | — |  |  | — |
Corporate Services and other, net (g) | 475 |  | 455 |  |  | — |  |  | — |  |  | — |  |  | — |
Total non-utility and other | 578 |  |  | 523 |  |  | — |  |  | — |  |  | — |  |  | — |
Total property, plant and equipment | $18,701 |  |  | $17,157 |  |  | $9,336 |  |  | $8,298 |  |  | $8,861 |  |  | $8,415 |
(a)Alliant Energy and WPL currently expect construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $205 million. In 2024, the PSCW issued orders approving deferral of, and the deferral of a return on, the incremental solar generation construction costs in 2024 and 2025. Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2024 given construction costs were reasonably and prudently incurred. (b)In September 2024, the IUC approved IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period, which allows IPL to recover construction costs associated with its 400 MW of new solar generation, including AFUDC 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. (c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2, and Edgewater Unit 5. WPL currently plans to cease coal operations at Columbia Units 1 and 2 by the end of 2029, as well as evaluate the conversion of Columbia Unit 1 and/or Unit 2 to natural gas. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2024. As of December 31, 2024 and 2023, the net book value of Columbia Units 1 and 2 in aggregate was $413 million and $428 million, respectively. As of December 31, 2023, WPL anticipated retiring Edgewater Unit 5 by June 1, 2025, and Alliant Energy and WPL concluded that Edgewater Unit 5 met the criteria to be considered probable of abandonment. In May 2024, WPL announced updated plans to convert Edgewater Unit 5 to natural gas by 2028, subject to regulatory approvals. As a result, as of December 31, 2024, Alliant Energy and WPL concluded that Edgewater Unit 5 no longer meets the criteria to be considered probable of abandonment. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, as of December 31, 2024, Alliant Energy and WPL concluded that no disallowance was probable. (d)Includes IPL’s steam service assets, which are fully depreciated as of December 31, 2024. IPL’s steam customers are each under contract through 2025 for taking minimum quantities of annual steam usage, with certain conditions. (e)Less accumulated amortization of $116 million and $112 million for WPL as of December 31, 2024 and 2023, respectively. Refer to Note 9 for discussion of WPL’s renewal of this lease in 2024. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment. (f)Less accumulated depreciation of $78 million and $75 million for Alliant Energy as of December 31, 2024 and 2023, respectively. (g)Less accumulated depreciation of $289 million and $275 million for Alliant Energy as of December 31, 2024 and 2023, respectively.
Allowance For Funds Used During Construction | The amount of AFUDC generated by equity and debt components was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Equity | $54 |  | $74 |  | $44 |  | $31 |  | $15 |  | $8 |  | $23 |  | $59 |  | $36
Debt | 21 |  | 26 |  | 16 |  | 12 |  | 6 |  | 3 |  | 9 |  | 20 |  | 13
| $75 |  | $100 |  | $60 |  | $43 |  | $21 |  | $11 |  | $32 |  | $79 |  | $49
IPL [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant and Equipment | At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Utility: |  |  |  |  |  |  |  |  |  |  |
Electric plant: |  |  |  |  |  |  |  |  |  |  |
Generation in service (a)(b) | $11,156 |  |  | $9,180 |  |  | $5,924 |  |  | $5,025 |  |  | $5,232 |  |  | $4,155 |
Distribution in service | 7,811 |  |  | 7,314 |  |  | 4,344 |  |  | 4,091 |  |  | 3,467 |  |  | 3,223 |
Other in service | 595 |  |  | 567 |  |  | 385 |  |  | 356 |  |  | 210 |  |  | 211 |
Anticipated to be retired early (c) | 784 |  |  | 1,629 |  |  | — |  |  | — |  |  | 784 |  |  | 1,629 |
Total electric plant | 20,346 |  |  | 18,690 |  |  | 10,653 |  |  | 9,472 |  |  | 9,693 |  |  | 9,218 |
Gas plant in service | 1,863 |  |  | 1,791 |  |  | 981 |  | 951 |  |  | 882 |  |  | 840 |
Other plant in service (d) | 734 |  |  | 653 |  |  | 456 |  | 411 |  |  | 278 |  |  | 242 |
Accumulated depreciation (c) | (6,229) |  |  | (5,924) |  |  | (3,360) |  |  | (3,180) |  |  | (2,869) |  |  | (2,744) |
Net plant | 16,714 |  |  | 15,210 |  |  | 8,730 |  |  | 7,654 |  |  | 7,984 |  |  | 7,556 |
Leased Sheboygan Falls Energy Facility, net (e) | — |  |  | — |  |  | — |  |  | — |  |  | 74 |  |  | 79 |
Leased land for solar generation, net | 189 |  |  | 172 |  |  | 53 |  |  | 33 |  |  | 136 |  |  | 139 |
Construction work in progress | 1,215 |  |  | 1,245 |  |  | 548 |  | 605 |  |  | 667 |  |  | 640 |
Other, net | 5 |  |  | 7 |  |  | 5 |  |  | 6 |  |  | — |  |  | 1 |
Total utility | 18,123 |  |  | 16,634 |  |  | 9,336 |  |  | 8,298 |  |  | 8,861 |  |  | 8,415 |
Non-utility and other: |  |  |  |  |  |  |  |  |  |  |
Non-utility Generation, net (f) | 103 |  |  | 68 |  |  | — |  |  | — |  |  | — |  |  | — |
Corporate Services and other, net (g) | 475 |  | 455 |  |  | — |  |  | — |  |  | — |  |  | — |
Total non-utility and other | 578 |  |  | 523 |  |  | — |  |  | — |  |  | — |  |  | — |
Total property, plant and equipment | $18,701 |  |  | $17,157 |  |  | $9,336 |  |  | $8,298 |  |  | $8,861 |  |  | $8,415 |
(a)Alliant Energy and WPL currently expect construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $205 million. In 2024, the PSCW issued orders approving deferral of, and the deferral of a return on, the incremental solar generation construction costs in 2024 and 2025. Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2024 given construction costs were reasonably and prudently incurred. (b)In September 2024, the IUC approved IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period, which allows IPL to recover construction costs associated with its 400 MW of new solar generation, including AFUDC 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. (c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2, and Edgewater Unit 5. WPL currently plans to cease coal operations at Columbia Units 1 and 2 by the end of 2029, as well as evaluate the conversion of Columbia Unit 1 and/or Unit 2 to natural gas. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2024. As of December 31, 2024 and 2023, the net book value of Columbia Units 1 and 2 in aggregate was $413 million and $428 million, respectively. As of December 31, 2023, WPL anticipated retiring Edgewater Unit 5 by June 1, 2025, and Alliant Energy and WPL concluded that Edgewater Unit 5 met the criteria to be considered probable of abandonment. In May 2024, WPL announced updated plans to convert Edgewater Unit 5 to natural gas by 2028, subject to regulatory approvals. As a result, as of December 31, 2024, Alliant Energy and WPL concluded that Edgewater Unit 5 no longer meets the criteria to be considered probable of abandonment. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, as of December 31, 2024, Alliant Energy and WPL concluded that no disallowance was probable. (d)Includes IPL’s steam service assets, which are fully depreciated as of December 31, 2024. IPL’s steam customers are each under contract through 2025 for taking minimum quantities of annual steam usage, with certain conditions. (e)Less accumulated amortization of $116 million and $112 million for WPL as of December 31, 2024 and 2023, respectively. Refer to Note 9 for discussion of WPL’s renewal of this lease in 2024. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment. (f)Less accumulated depreciation of $78 million and $75 million for Alliant Energy as of December 31, 2024 and 2023, respectively. (g)Less accumulated depreciation of $289 million and $275 million for Alliant Energy as of December 31, 2024 and 2023, respectively.
Allowance For Funds Used During Construction | The amount of AFUDC generated by equity and debt components was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Equity | $54 |  | $74 |  | $44 |  | $31 |  | $15 |  | $8 |  | $23 |  | $59 |  | $36
Debt | 21 |  | 26 |  | 16 |  | 12 |  | 6 |  | 3 |  | 9 |  | 20 |  | 13
| $75 |  | $100 |  | $60 |  | $43 |  | $21 |  | $11 |  | $32 |  | $79 |  | $49
WPL [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant and Equipment | At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Utility: |  |  |  |  |  |  |  |  |  |  |
Electric plant: |  |  |  |  |  |  |  |  |  |  |
Generation in service (a)(b) | $11,156 |  |  | $9,180 |  |  | $5,924 |  |  | $5,025 |  |  | $5,232 |  |  | $4,155 |
Distribution in service | 7,811 |  |  | 7,314 |  |  | 4,344 |  |  | 4,091 |  |  | 3,467 |  |  | 3,223 |
Other in service | 595 |  |  | 567 |  |  | 385 |  |  | 356 |  |  | 210 |  |  | 211 |
Anticipated to be retired early (c) | 784 |  |  | 1,629 |  |  | — |  |  | — |  |  | 784 |  |  | 1,629 |
Total electric plant | 20,346 |  |  | 18,690 |  |  | 10,653 |  |  | 9,472 |  |  | 9,693 |  |  | 9,218 |
Gas plant in service | 1,863 |  |  | 1,791 |  |  | 981 |  | 951 |  |  | 882 |  |  | 840 |
Other plant in service (d) | 734 |  |  | 653 |  |  | 456 |  | 411 |  |  | 278 |  |  | 242 |
Accumulated depreciation (c) | (6,229) |  |  | (5,924) |  |  | (3,360) |  |  | (3,180) |  |  | (2,869) |  |  | (2,744) |
Net plant | 16,714 |  |  | 15,210 |  |  | 8,730 |  |  | 7,654 |  |  | 7,984 |  |  | 7,556 |
Leased Sheboygan Falls Energy Facility, net (e) | — |  |  | — |  |  | — |  |  | — |  |  | 74 |  |  | 79 |
Leased land for solar generation, net | 189 |  |  | 172 |  |  | 53 |  |  | 33 |  |  | 136 |  |  | 139 |
Construction work in progress | 1,215 |  |  | 1,245 |  |  | 548 |  | 605 |  |  | 667 |  |  | 640 |
Other, net | 5 |  |  | 7 |  |  | 5 |  |  | 6 |  |  | — |  |  | 1 |
Total utility | 18,123 |  |  | 16,634 |  |  | 9,336 |  |  | 8,298 |  |  | 8,861 |  |  | 8,415 |
Non-utility and other: |  |  |  |  |  |  |  |  |  |  |
Non-utility Generation, net (f) | 103 |  |  | 68 |  |  | — |  |  | — |  |  | — |  |  | — |
Corporate Services and other, net (g) | 475 |  | 455 |  |  | — |  |  | — |  |  | — |  |  | — |
Total non-utility and other | 578 |  |  | 523 |  |  | — |  |  | — |  |  | — |  |  | — |
Total property, plant and equipment | $18,701 |  |  | $17,157 |  |  | $9,336 |  |  | $8,298 |  |  | $8,861 |  |  | $8,415 |
(a)Alliant Energy and WPL currently expect construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $205 million. In 2024, the PSCW issued orders approving deferral of, and the deferral of a return on, the incremental solar generation construction costs in 2024 and 2025. Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2024 given construction costs were reasonably and prudently incurred. (b)In September 2024, the IUC approved IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period, which allows IPL to recover construction costs associated with its 400 MW of new solar generation, including AFUDC 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. (c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2, and Edgewater Unit 5. WPL currently plans to cease coal operations at Columbia Units 1 and 2 by the end of 2029, as well as evaluate the conversion of Columbia Unit 1 and/or Unit 2 to natural gas. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2024. As of December 31, 2024 and 2023, the net book value of Columbia Units 1 and 2 in aggregate was $413 million and $428 million, respectively. As of December 31, 2023, WPL anticipated retiring Edgewater Unit 5 by June 1, 2025, and Alliant Energy and WPL concluded that Edgewater Unit 5 met the criteria to be considered probable of abandonment. In May 2024, WPL announced updated plans to convert Edgewater Unit 5 to natural gas by 2028, subject to regulatory approvals. As a result, as of December 31, 2024, Alliant Energy and WPL concluded that Edgewater Unit 5 no longer meets the criteria to be considered probable of abandonment. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, as of December 31, 2024, Alliant Energy and WPL concluded that no disallowance was probable. (d)Includes IPL’s steam service assets, which are fully depreciated as of December 31, 2024. IPL’s steam customers are each under contract through 2025 for taking minimum quantities of annual steam usage, with certain conditions. (e)Less accumulated amortization of $116 million and $112 million for WPL as of December 31, 2024 and 2023, respectively. Refer to Note 9 for discussion of WPL’s renewal of this lease in 2024. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment. (f)Less accumulated depreciation of $78 million and $75 million for Alliant Energy as of December 31, 2024 and 2023, respectively. (g)Less accumulated depreciation of $289 million and $275 million for Alliant Energy as of December 31, 2024 and 2023, respectively.
Allowance For Funds Used During Construction | The amount of AFUDC generated by equity and debt components was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Equity | $54 |  | $74 |  | $44 |  | $31 |  | $15 |  | $8 |  | $23 |  | $59 |  | $36
Debt | 21 |  | 26 |  | 16 |  | 12 |  | 6 |  | 3 |  | 9 |  | 20 |  | 13
| $75 |  | $100 |  | $60 |  | $43 |  | $21 |  | $11 |  | $32 |  | $79 |  | $49

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