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Income Taxes
 3 Months Ended
Mar. 31, 2025
Income Taxes [Line Items]  
Income Taxes INCOME TAXES
Income Tax Rates - Overall effective income tax rates for the three months ended March 31, 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. Alliant Energy’s, IPL’s and WPL’s effective income tax rates were lower in the first quarter of 2025 compared to the same period in 2024 primarily due to the additional tax credits from renewable generation and energy storage projects placed in service in 2024 and/or expected to be placed in service in 2025.
Alliant EnergyIPLWPL
202520242025202420252024
Overall income tax rate(28%)(7%)(57%)(19%)(5%)6%

Deferred Tax Assets and Liabilities -
Carryforwards - At March 31, 2025, the carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2045$336$7$1
Federal tax credits2033-2045701473215
IPL [Member]  
Income Taxes [Line Items]  
Income Taxes INCOME TAXES
Income Tax Rates - Overall effective income tax rates for the three months ended March 31, 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. Alliant Energy’s, IPL’s and WPL’s effective income tax rates were lower in the first quarter of 2025 compared to the same period in 2024 primarily due to the additional tax credits from renewable generation and energy storage projects placed in service in 2024 and/or expected to be placed in service in 2025.
Alliant EnergyIPLWPL
202520242025202420252024
Overall income tax rate(28%)(7%)(57%)(19%)(5%)6%

Deferred Tax Assets and Liabilities -
Carryforwards - At March 31, 2025, the carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2045$336$7$1
Federal tax credits2033-2045701473215
WPL [Member]  
Income Taxes [Line Items]  
Income Taxes INCOME TAXES
Income Tax Rates - Overall effective income tax rates for the three months ended March 31, 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. Alliant Energy’s, IPL’s and WPL’s effective income tax rates were lower in the first quarter of 2025 compared to the same period in 2024 primarily due to the additional tax credits from renewable generation and energy storage projects placed in service in 2024 and/or expected to be placed in service in 2025.
Alliant EnergyIPLWPL
202520242025202420252024
Overall income tax rate(28%)(7%)(57%)(19%)(5%)6%

Deferred Tax Assets and Liabilities -
Carryforwards - At March 31, 2025, the carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2045$336$7$1
Federal tax credits2033-2045701473215