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Regulatory Matters | 9 Months Ended
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Sep. 30, 2025
Public Utilities, General Disclosures [Line Items] |
Regulatory Matters | REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2025 |  | December 31, 2024 |  | September 30, 2025 |  | December 31, 2024 |  | September 30, 2025 |  | December 31, 2024
Tax-related | $1,069 |  | $989 |  | $932 |  | $870 |  | $137 |  | $119
AROs | 441 |  | 401 |  | 304 |  | 281 |  | 137 |  | 120
Pension and OPEB costs | 301 |  | 315 |  | 151 |  | 157 |  | 150 |  | 158
Assets retired early | 162 |  | 180 |  | 153 |  | 168 |  | 9 |  | 12
Non-service pension and OPEB costs | 55 |  | 51 |  | 20 |  | 19 |  | 35 |  | 32
Derivatives | 51 |  | 60 |  | 12 |  | 15 |  | 39 |  | 45
WPL’s Western Wisconsin gas distribution expansion investments | 40 |  | 42 |  | — |  | — |  | 40 |  | 42
Commodity cost recovery | 33 |  | 68 |  | 8 |  | 2 |  | 25 |  | 66
Other | 151 |  | 168 |  | 52 |  | 74 |  | 99 |  | 94
| $2,303 |  | $2,274 |  | $1,632 |  | $1,586 |  | $671 |  | $688
Assets retired early - IPL was previously allowed a full recovery of and a full return on the Lansing Generating Station from both its retail and wholesale customers. The IUC’s September 2024 order for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period included a return of the remaining net book value of Lansing, but did not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value was no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2024. Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2025 |  | December 31, 2024 |  | September 30, 2025 |  | December 31, 2024 |  | September 30, 2025 |  | December 31, 2024
Tax-related | $658 |  | $582 |  | $301 |  | $286 |  | $357 |  | $296
Cost of removal obligations | 351 |  | 347 |  | 206 |  | 205 |  | 145 |  | 142
Derivatives | 49 |  | 53 |  | 25 |  | 29 |  | 24 |  | 24
Other | 76 |  | 46 |  | 26 |  | 26 |  | 50 |  | 20
| $1,134 |  | $1,028 |  | $558 |  | $546 |  | $576 |  | $482
Tax-related - The increase in Alliant Energy’s and WPL’s tax-related regulatory liabilities was primarily due to tax benefits resulting from investment tax credits recognized by WPL for certain energy storage facilities in 2025.
IPL [Member] |
Public Utilities, General Disclosures [Line Items] |
Regulatory Matters | REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2025 |  | December 31, 2024 |  | September 30, 2025 |  | December 31, 2024 |  | September 30, 2025 |  | December 31, 2024
Tax-related | $1,069 |  | $989 |  | $932 |  | $870 |  | $137 |  | $119
AROs | 441 |  | 401 |  | 304 |  | 281 |  | 137 |  | 120
Pension and OPEB costs | 301 |  | 315 |  | 151 |  | 157 |  | 150 |  | 158
Assets retired early | 162 |  | 180 |  | 153 |  | 168 |  | 9 |  | 12
Non-service pension and OPEB costs | 55 |  | 51 |  | 20 |  | 19 |  | 35 |  | 32
Derivatives | 51 |  | 60 |  | 12 |  | 15 |  | 39 |  | 45
WPL’s Western Wisconsin gas distribution expansion investments | 40 |  | 42 |  | — |  | — |  | 40 |  | 42
Commodity cost recovery | 33 |  | 68 |  | 8 |  | 2 |  | 25 |  | 66
Other | 151 |  | 168 |  | 52 |  | 74 |  | 99 |  | 94
| $2,303 |  | $2,274 |  | $1,632 |  | $1,586 |  | $671 |  | $688
Assets retired early - IPL was previously allowed a full recovery of and a full return on the Lansing Generating Station from both its retail and wholesale customers. The IUC’s September 2024 order for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period included a return of the remaining net book value of Lansing, but did not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value was no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2024. Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2025 |  | December 31, 2024 |  | September 30, 2025 |  | December 31, 2024 |  | September 30, 2025 |  | December 31, 2024
Tax-related | $658 |  | $582 |  | $301 |  | $286 |  | $357 |  | $296
Cost of removal obligations | 351 |  | 347 |  | 206 |  | 205 |  | 145 |  | 142
Derivatives | 49 |  | 53 |  | 25 |  | 29 |  | 24 |  | 24
Other | 76 |  | 46 |  | 26 |  | 26 |  | 50 |  | 20
| $1,134 |  | $1,028 |  | $558 |  | $546 |  | $576 |  | $482
Tax-related - The increase in Alliant Energy’s and WPL’s tax-related regulatory liabilities was primarily due to tax benefits resulting from investment tax credits recognized by WPL for certain energy storage facilities in 2025.
WPL [Member] |
Public Utilities, General Disclosures [Line Items] |
Regulatory Matters | REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2025 |  | December 31, 2024 |  | September 30, 2025 |  | December 31, 2024 |  | September 30, 2025 |  | December 31, 2024
Tax-related | $1,069 |  | $989 |  | $932 |  | $870 |  | $137 |  | $119
AROs | 441 |  | 401 |  | 304 |  | 281 |  | 137 |  | 120
Pension and OPEB costs | 301 |  | 315 |  | 151 |  | 157 |  | 150 |  | 158
Assets retired early | 162 |  | 180 |  | 153 |  | 168 |  | 9 |  | 12
Non-service pension and OPEB costs | 55 |  | 51 |  | 20 |  | 19 |  | 35 |  | 32
Derivatives | 51 |  | 60 |  | 12 |  | 15 |  | 39 |  | 45
WPL’s Western Wisconsin gas distribution expansion investments | 40 |  | 42 |  | — |  | — |  | 40 |  | 42
Commodity cost recovery | 33 |  | 68 |  | 8 |  | 2 |  | 25 |  | 66
Other | 151 |  | 168 |  | 52 |  | 74 |  | 99 |  | 94
| $2,303 |  | $2,274 |  | $1,632 |  | $1,586 |  | $671 |  | $688
Assets retired early - IPL was previously allowed a full recovery of and a full return on the Lansing Generating Station from both its retail and wholesale customers. The IUC’s September 2024 order for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period included a return of the remaining net book value of Lansing, but did not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value was no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2024. Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2025 |  | December 31, 2024 |  | September 30, 2025 |  | December 31, 2024 |  | September 30, 2025 |  | December 31, 2024
Tax-related | $658 |  | $582 |  | $301 |  | $286 |  | $357 |  | $296
Cost of removal obligations | 351 |  | 347 |  | 206 |  | 205 |  | 145 |  | 142
Derivatives | 49 |  | 53 |  | 25 |  | 29 |  | 24 |  | 24
Other | 76 |  | 46 |  | 26 |  | 26 |  | 50 |  | 20
| $1,134 |  | $1,028 |  | $558 |  | $546 |  | $576 |  | $482
Tax-related - The increase in Alliant Energy’s and WPL’s tax-related regulatory liabilities was primarily due to tax benefits resulting from investment tax credits recognized by WPL for certain energy storage facilities in 2025.

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