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Income Taxes | 9 Months Ended
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Sep. 30, 2023
Income Taxes [Line Items] |
Income Taxes | INCOME TAXESIncome 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, amortization of excess deferred taxes and the effect of rate-making on property-related differences.
| Alliant Energy |  | IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022
Overall income tax rate | 2% |  | 6% |  | 1% |  | 4% |  | (22%) |  | (12%) |  | (20%) |  | (14%) |  | 16% |  | 15% |  | 15% |  | 17%
Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2023, the carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
State net operating losses | 2025-2043 |  | $431 |  | $6 |  | $1
Federal tax credits | 2031-2043 |  | 737 |  | 520 |  | 208
Iowa Tax Reform - Pursuant to Iowa tax reform enacted in 2022, in September 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 7.1%, effective January 1, 2024. 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, 2024, which resulted in a $73 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in the third quarter of 2023. 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, 2024, which resulted in a charge of $8 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred tax liabilities on Alliant Energy’s balance sheet in the third quarter of 2023. Based on the remeasurement of Alliant Energy parent company’s deferred tax assets in the third quarter of 2022 for the Iowa corporate income tax rate of 8.4% effective January 1, 2023, a charge of $8 million was recorded to income tax expense in Alliant Energy’s income statement 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 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, amortization of excess deferred taxes and the effect of rate-making on property-related differences.
| Alliant Energy |  | IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022
Overall income tax rate | 2% |  | 6% |  | 1% |  | 4% |  | (22%) |  | (12%) |  | (20%) |  | (14%) |  | 16% |  | 15% |  | 15% |  | 17%
Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2023, the carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
State net operating losses | 2025-2043 |  | $431 |  | $6 |  | $1
Federal tax credits | 2031-2043 |  | 737 |  | 520 |  | 208
Iowa Tax Reform - Pursuant to Iowa tax reform enacted in 2022, in September 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 7.1%, effective January 1, 2024. 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, 2024, which resulted in a $73 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in the third quarter of 2023. 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, 2024, which resulted in a charge of $8 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred tax liabilities on Alliant Energy’s balance sheet in the third quarter of 2023. Based on the remeasurement of Alliant Energy parent company’s deferred tax assets in the third quarter of 2022 for the Iowa corporate income tax rate of 8.4% effective January 1, 2023, a charge of $8 million was recorded to income tax expense in Alliant Energy’s income statement 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 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, amortization of excess deferred taxes and the effect of rate-making on property-related differences.
| Alliant Energy |  | IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022 |  | 2023 |  | 2022
Overall income tax rate | 2% |  | 6% |  | 1% |  | 4% |  | (22%) |  | (12%) |  | (20%) |  | (14%) |  | 16% |  | 15% |  | 15% |  | 17%
Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2023, the carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
State net operating losses | 2025-2043 |  | $431 |  | $6 |  | $1
Federal tax credits | 2031-2043 |  | 737 |  | 520 |  | 208
Iowa Tax Reform - Pursuant to Iowa tax reform enacted in 2022, in September 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 7.1%, effective January 1, 2024. 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, 2024, which resulted in a $73 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in the third quarter of 2023. 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, 2024, which resulted in a charge of $8 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred tax liabilities on Alliant Energy’s balance sheet in the third quarter of 2023. Based on the remeasurement of Alliant Energy parent company’s deferred tax assets in the third quarter of 2022 for the Iowa corporate income tax rate of 8.4% effective January 1, 2023, a charge of $8 million was recorded to income tax expense in Alliant Energy’s income statement in the third quarter of 2022. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.

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