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Income Taxes | 3 Months Ended
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Mar. 31, 2021
Income Taxes [Line Items] |
Income Taxes | INCOME TAXES 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%) |  |  |  |
Deferred Tax Assets and Liabilities - 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] |
Income Taxes | INCOME TAXES 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%) |  |  |  |
Deferred Tax Assets and Liabilities - 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] |
Income Taxes | INCOME TAXES 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%) |  |  |  |
Deferred Tax Assets and Liabilities - 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 The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 21 -URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32857-109319 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB Topic 11.C) -URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330215-122817 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 17 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32809-109319 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I.5.Q1) -URI http://asc.fasb.org/extlink&oid=122134291&loc=d3e330036-122817 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32705-109319 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 270 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6424409&loc=d3e44925-109338 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -URI http://asc.fasb.org/topic&trid=2144680 Reference 8: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(h)(2)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690 + Details
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