XML 78 R44.htm IDEA: XBRL DOCUMENT
v3.25.0.1

Asset Retirement Obligations (Tables) | 12 Months Ended
--- | ---
Dec. 31, 2024
Schedule of Asset Retirement Obligations [Line Items] |
Reconciliation Of Changes In Asset Retirement Obligations (AROs) | A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Balance, January 1 | $246 |  |  | $279 |  |  | $148 |  |  | $195 |  |  | $98 |  |  | $84 |
Revisions in estimated cash flows | (3) |  |  | (6) |  |  | (1) |  |  | (9) |  |  | (2) |  |  | 3 |
Liabilities settled | (8) |  |  | (51) |  |  | (6) |  |  | (44) |  |  | (2) |  |  | (7) |
Liabilities incurred (a) | 409 |  |  | 16 |  |  | 201 |  |  | 1 |  |  | 208 |  |  | 15 |
Accretion expense | 19 |  |  | 8 |  |  | 8 |  |  | 5 |  |  | 11 |  |  | 3 |
Balance, December 31 | $663 |  |  | $246 |  |  | $350 |  |  | $148 |  |  | $313 |  |  | $98 |
(a)In 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL initially recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts initially recorded in 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
IPL [Member] |
Schedule of Asset Retirement Obligations [Line Items] |
Reconciliation Of Changes In Asset Retirement Obligations (AROs) | A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Balance, January 1 | $246 |  |  | $279 |  |  | $148 |  |  | $195 |  |  | $98 |  |  | $84 |
Revisions in estimated cash flows | (3) |  |  | (6) |  |  | (1) |  |  | (9) |  |  | (2) |  |  | 3 |
Liabilities settled | (8) |  |  | (51) |  |  | (6) |  |  | (44) |  |  | (2) |  |  | (7) |
Liabilities incurred (a) | 409 |  |  | 16 |  |  | 201 |  |  | 1 |  |  | 208 |  |  | 15 |
Accretion expense | 19 |  |  | 8 |  |  | 8 |  |  | 5 |  |  | 11 |  |  | 3 |
Balance, December 31 | $663 |  |  | $246 |  |  | $350 |  |  | $148 |  |  | $313 |  |  | $98 |
(a)In 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL initially recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts initially recorded in 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
WPL [Member] |
Schedule of Asset Retirement Obligations [Line Items] |
Reconciliation Of Changes In Asset Retirement Obligations (AROs) | A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2024 |  | 2023 |  | 2024 |  | 2023
Balance, January 1 | $246 |  |  | $279 |  |  | $148 |  |  | $195 |  |  | $98 |  |  | $84 |
Revisions in estimated cash flows | (3) |  |  | (6) |  |  | (1) |  |  | (9) |  |  | (2) |  |  | 3 |
Liabilities settled | (8) |  |  | (51) |  |  | (6) |  |  | (44) |  |  | (2) |  |  | (7) |
Liabilities incurred (a) | 409 |  |  | 16 |  |  | 201 |  |  | 1 |  |  | 208 |  |  | 15 |
Accretion expense | 19 |  |  | 8 |  |  | 8 |  |  | 5 |  |  | 11 |  |  | 3 |
Balance, December 31 | $663 |  |  | $246 |  |  | $350 |  |  | $148 |  |  | $313 |  |  | $98 |
(a)In 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL initially recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts initially recorded in 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.

X
- Definition [Line Items] for Schedule of Asset Retirement Obligations [Table] + References No definition available. + Details
Name: | lnt_ScheduleOfAssetRetirementObligationsLineItems
Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481850/410-20-50-1 + Details
Name: | us-gaap_ScheduleOfChangeInAssetRetirementObligationTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
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: |