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Income Taxes (Tables) | 3 Months Ended
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Mar. 31, 2021
Income Taxes [Line Items] |
Schedule Of Effective Income 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 decreases in Alliant Energy’s and WPL’s overall effective income tax rates for the three months ended March 31, 2021 compared to the same period in 2020 were primarily due to increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2021 increased revenue requirements.
| Alliant Energy |  | IPL |  | WPL
Three Months Ended March 31 | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Overall income tax rate | (19%) |  | (12%) |  |  |  |  |  | (17%) |  | (19%) |  |  |  |  |  | (29%) |  | (10%) |  |  |  |
Summary Of Tax Credit Carryforwards | At March 31, 2021, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2037 |  | $331 |  | $306 |  | $3
State net operating losses | 2021-2041 |  | 627 |  | 16 |  | 2
Federal tax credits | 2022-2041 |  | 481 |  | 280 |  | 180
IPL [Member] |
Income Taxes [Line Items] |
Schedule Of Effective Income 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 decreases in Alliant Energy’s and WPL’s overall effective income tax rates for the three months ended March 31, 2021 compared to the same period in 2020 were primarily due to increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2021 increased revenue requirements.
| Alliant Energy |  | IPL |  | WPL
Three Months Ended March 31 | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Overall income tax rate | (19%) |  | (12%) |  |  |  |  |  | (17%) |  | (19%) |  |  |  |  |  | (29%) |  | (10%) |  |  |  |
Summary Of Tax Credit Carryforwards | At March 31, 2021, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2037 |  | $331 |  | $306 |  | $3
State net operating losses | 2021-2041 |  | 627 |  | 16 |  | 2
Federal tax credits | 2022-2041 |  | 481 |  | 280 |  | 180
WPL [Member] |
Income Taxes [Line Items] |
Schedule Of Effective Income 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 decreases in Alliant Energy’s and WPL’s overall effective income tax rates for the three months ended March 31, 2021 compared to the same period in 2020 were primarily due to increased amortization of excess deferred taxes primarily at WPL, which were used to offset increases in WPL’s 2021 increased revenue requirements.
| Alliant Energy |  | IPL |  | WPL
Three Months Ended March 31 | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Overall income tax rate | (19%) |  | (12%) |  |  |  |  |  | (17%) |  | (19%) |  |  |  |  |  | (29%) |  | (10%) |  |  |  |
Summary Of Tax Credit Carryforwards | At March 31, 2021, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2037 |  | $331 |  | $306 |  | $3
State net operating losses | 2021-2041 |  | 627 |  | 16 |  | 2
Federal tax credits | 2022-2041 |  | 481 |  | 280 |  | 180

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- Definition Tabular disclosure of the reconciliation using percentage or dollar amounts of the reported amount of income tax expense attributable to continuing operations for the year to the amount of income tax expense that would result from applying domestic federal statutory tax rates to pretax income from continuing operations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32687-109319 + Details
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- Definition Tabular disclosure of tax credit carryforwards available to reduce future taxable income, including amounts, expiration dates, limitations on use and the related deferred tax assets and valuation allowances. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32559-109319 + Details
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