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Income Taxes (Tables) | 9 Months Ended
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Sep. 30, 2025
Income Taxes [Line Items] |
Schedule Of Effective Income Tax Rates | Overall effective income tax rates for the three and nine months ended September 30, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the nine months ended September 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generating Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the AROs allocated to IPL’s steam business discussed in Note 1(d). Alliant Energy’s, IPL’s and WPL’s effective income tax rates for the three and nine months ended September 30, 2025 were also impacted by additional tax credits in 2025 from renewable generation and energy storage projects placed in service in 2024 and/or expected to be placed in service in 2025.
| Alliant Energy |  | IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Overall income tax rate | (7%) |  | (27%) |  | (19%) |  | (24%) |  | (15%) |  | (56%) |  | (36%) |  | (70%) |  | 1% |  | 3% |  | (3%) |  | 5%
Summary Of Tax Credit Carryforwards | At September 30, 2025, the carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
State net operating losses | 2025-2045 |  | $249 |  | $7 |  | $1
Federal tax credits | 2034-2045 |  | 741 |  | 464 |  | 263
IPL [Member] |
Income Taxes [Line Items] |
Schedule Of Effective Income Tax Rates | Overall effective income tax rates for the three and nine months ended September 30, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the nine months ended September 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generating Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the AROs allocated to IPL’s steam business discussed in Note 1(d). Alliant Energy’s, IPL’s and WPL’s effective income tax rates for the three and nine months ended September 30, 2025 were also impacted by additional tax credits in 2025 from renewable generation and energy storage projects placed in service in 2024 and/or expected to be placed in service in 2025.
| Alliant Energy |  | IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Overall income tax rate | (7%) |  | (27%) |  | (19%) |  | (24%) |  | (15%) |  | (56%) |  | (36%) |  | (70%) |  | 1% |  | 3% |  | (3%) |  | 5%
Summary Of Tax Credit Carryforwards | At September 30, 2025, the carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
State net operating losses | 2025-2045 |  | $249 |  | $7 |  | $1
Federal tax credits | 2034-2045 |  | 741 |  | 464 |  | 263
WPL [Member] |
Income Taxes [Line Items] |
Schedule Of Effective Income Tax Rates | Overall effective income tax rates for the three and nine months ended September 30, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the nine months ended September 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generating Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the AROs allocated to IPL’s steam business discussed in Note 1(d). Alliant Energy’s, IPL’s and WPL’s effective income tax rates for the three and nine months ended September 30, 2025 were also impacted by additional tax credits in 2025 from renewable generation and energy storage projects placed in service in 2024 and/or expected to be placed in service in 2025.
| Alliant Energy |  | IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Overall income tax rate | (7%) |  | (27%) |  | (19%) |  | (24%) |  | (15%) |  | (56%) |  | (36%) |  | (70%) |  | 1% |  | 3% |  | (3%) |  | 5%
Summary Of Tax Credit Carryforwards | At September 30, 2025, the carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
State net operating losses | 2025-2045 |  | $249 |  | $7 |  | $1
Federal tax credits | 2034-2045 |  | 741 |  | 464 |  | 263

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