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Income Taxes
 9 Months Ended
Sep. 30, 2022
Income Taxes [Line Items]  
Income Taxes INCOME TAXESIncome Tax Rates - Overall effective income tax rates, 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, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The increases in Alliant Energy’s and WPL’s overall effective income tax rates for the three
and nine months ended September 30, 2022 compared to the same periods in 2021 were primarily due to decreased amortization of excess deferred taxes primarily at WPL.
Alliant EnergyIPLWPL
Three MonthsNine Months Three MonthsNine Months Three MonthsNine Months
202220212022202120222021202220212022202120222021
Overall income tax rate6%(9%)4%(13%)(12%)(8%)(14%)(11%)15%(19%)17%(24%)

Deferred Tax Assets and Liabilities -
Carryforwards - In the third quarter of 2022, Alliant Energy, IPL and WPL fully utilized their respective federal net operating losses carryforwards. At September 30, 2022, the remaining carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2022-2042$500$9$2
Federal tax credits2022-2042655437208

Iowa Tax Reform - In March 2022, Iowa tax reform was enacted. Annually, and by each November 1, the Iowa Department of Revenue will establish corporate income tax rates for the next tax year based on net corporate income tax receipts for the prior tax year, and reduce such rates if certain state income tax revenue triggers are satisfied. These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5%, compared to the current 9.8% Iowa corporate income tax rate. In September 2022, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4%, effective January 1, 2023. Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the announcement of the new Iowa corporate income tax rate, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured based upon the new rate effective January 1, 2023, which resulted in a $76 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a decrease in their deferred tax liabilities in the third quarter of 2022. The reduction in tax-related regulatory assets is expected to provide cost benefits to IPL’s customers in the future. Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rate effective January 1, 2023, which resulted in a charge of $8 million recorded to income tax expense in Alliant Energy’s income statement and a decrease in deferred income tax assets on Alliant Energy’s balance sheet in the third quarter of 2022. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.
IPL [Member]  
Income Taxes [Line Items]  
Income Taxes INCOME TAXESIncome Tax Rates - Overall effective income tax rates, 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, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The increases in Alliant Energy’s and WPL’s overall effective income tax rates for the three
and nine months ended September 30, 2022 compared to the same periods in 2021 were primarily due to decreased amortization of excess deferred taxes primarily at WPL.
Alliant EnergyIPLWPL
Three MonthsNine Months Three MonthsNine Months Three MonthsNine Months
202220212022202120222021202220212022202120222021
Overall income tax rate6%(9%)4%(13%)(12%)(8%)(14%)(11%)15%(19%)17%(24%)

Deferred Tax Assets and Liabilities -
Carryforwards - In the third quarter of 2022, Alliant Energy, IPL and WPL fully utilized their respective federal net operating losses carryforwards. At September 30, 2022, the remaining carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2022-2042$500$9$2
Federal tax credits2022-2042655437208

Iowa Tax Reform - In March 2022, Iowa tax reform was enacted. Annually, and by each November 1, the Iowa Department of Revenue will establish corporate income tax rates for the next tax year based on net corporate income tax receipts for the prior tax year, and reduce such rates if certain state income tax revenue triggers are satisfied. These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5%, compared to the current 9.8% Iowa corporate income tax rate. In September 2022, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4%, effective January 1, 2023. Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the announcement of the new Iowa corporate income tax rate, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured based upon the new rate effective January 1, 2023, which resulted in a $76 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a decrease in their deferred tax liabilities in the third quarter of 2022. The reduction in tax-related regulatory assets is expected to provide cost benefits to IPL’s customers in the future. Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rate effective January 1, 2023, which resulted in a charge of $8 million recorded to income tax expense in Alliant Energy’s income statement and a decrease in deferred income tax assets on Alliant Energy’s balance sheet in the third quarter of 2022. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.
WPL [Member]  
Income Taxes [Line Items]  
Income Taxes INCOME TAXESIncome Tax Rates - Overall effective income tax rates, 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, amortization of excess deferred taxes and the effect of rate-making on property-related differences. The increases in Alliant Energy’s and WPL’s overall effective income tax rates for the three
and nine months ended September 30, 2022 compared to the same periods in 2021 were primarily due to decreased amortization of excess deferred taxes primarily at WPL.
Alliant EnergyIPLWPL
Three MonthsNine Months Three MonthsNine Months Three MonthsNine Months
202220212022202120222021202220212022202120222021
Overall income tax rate6%(9%)4%(13%)(12%)(8%)(14%)(11%)15%(19%)17%(24%)

Deferred Tax Assets and Liabilities -
Carryforwards - In the third quarter of 2022, Alliant Energy, IPL and WPL fully utilized their respective federal net operating losses carryforwards. At September 30, 2022, the remaining carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2022-2042$500$9$2
Federal tax credits2022-2042655437208

Iowa Tax Reform - In March 2022, Iowa tax reform was enacted. Annually, and by each November 1, the Iowa Department of Revenue will establish corporate income tax rates for the next tax year based on net corporate income tax receipts for the prior tax year, and reduce such rates if certain state income tax revenue triggers are satisfied. These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5%, compared to the current 9.8% Iowa corporate income tax rate. In September 2022, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4%, effective January 1, 2023. Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the announcement of the new Iowa corporate income tax rate, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured based upon the new rate effective January 1, 2023, which resulted in a $76 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a decrease in their deferred tax liabilities in the third quarter of 2022. The reduction in tax-related regulatory assets is expected to provide cost benefits to IPL’s customers in the future. Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rate effective January 1, 2023, which resulted in a charge of $8 million recorded to income tax expense in Alliant Energy’s income statement and a decrease in deferred income tax assets on Alliant Energy’s balance sheet in the third quarter of 2022. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.