XML 44 R10.htm IDEA: XBRL DOCUMENT
v3.25.0.1

Property, Plant and Equipment | 12 Months Ended
--- | ---
Dec. 31, 2024
Property, Plant and Equipment [Line Items] |
Property, Plant and Equipment | 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. AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. The concurrent credit for the amount of AFUDC capitalized is recorded as “Allowance for funds used during construction” in the income statements. 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
Non-utility and Other - The non-utility and other property, plant and equipment recorded on Alliant Energy’s balance sheets include the following: Non-utility Generation - The Sheboygan Falls Energy Facility was placed in service in 2005 and is depreciated using the straight-line method over a 35-year period. Corporate Services and Other - Property, plant and equipment related to Corporate Services include computer software, and the corporate headquarters building located in Madison, Wisconsin. The majority of the software is amortized over a 5-year period. Other property, plant and equipment include Travero assets (a short-line rail freight service in Iowa; a Mississippi River barge, rail and truck freight terminal in Illinois; wind turbine blade recycling services; and a rail-served warehouse in Iowa). All Corporate Services and Other property, plant and equipment are depreciated using the straight-line method over periods ranging from 5 to 30 years.
IPL [Member] |
Property, Plant and Equipment [Line Items] |
Property, Plant and Equipment | 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. AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. The concurrent credit for the amount of AFUDC capitalized is recorded as “Allowance for funds used during construction” in the income statements. 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 | 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. AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. The concurrent credit for the amount of AFUDC capitalized is recorded as “Allowance for funds used during construction” in the income statements. 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

X
- Definition The entire disclosure for long-lived, physical asset used in normal conduct of business and not intended for resale. Includes, but is not limited to, work of art, historical treasure, and similar asset classified as collections. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 360 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org/360/tableOfContent Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 6 -SubTopic 360 -Topic 958 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477798/958-360-50-6 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d) -SubTopic 360 -Topic 958 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477798/958-360-50-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 7 -SubTopic 360 -Topic 958 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477798/958-360-50-7 + Details
Name: | us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 842 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 7A -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147478964/842-20-50-7A + Details
Name: | us-gaap_PropertyPlantAndEquipmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |