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Income Taxes (Tables) | 3 Months Ended
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Mar. 31, 2018
Income Taxes [Line Items] |
Schedule Of Effective Income Tax Rates | The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
| Alliant Energy |  | IPL |  | WPL
Three Months Ended March 31 | 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Statutory federal income tax rate | 21.0 | % |  | 35.0 | % |  | 21.0 | % |  | 35.0 | % |  | 21.0 | % |  | 35.0 | %
State income taxes, net of federal benefits | 7.5 |  |  | 5.4 |  |  | 8.5 |  |  | 6.3 |  |  | 6.2 |  |  | 5.1 |
Effect of rate-making on property-related differences | (7.4 | ) |  | (7.5 | ) |  | (13.5 | ) |  | (17.9 | ) |  | (2.4 | ) |  | (1.7 | )
Production tax credits | (5.5 | ) |  | (5.9 | ) |  | (5.4 | ) |  | (6.6 | ) |  | (6.7 | ) |  | (7.0 | )
IPL’s tax benefit riders | (2.2 | ) |  | (7.8 | ) |  | (4.7 | ) |  | (19.4 | ) |  | — |  |  | — |
Other items, net | (1.4 | ) |  | (4.4 | ) |  | — |  |  | (7.6 | ) |  | (0.3 | ) |  | (0.4 | )
Overall income tax rate | 12.0 | % |  | 14.8 | % |  | 5.9 | % |  | (10.2 | %) |  | 17.8 | % |  | 31.0 | %
Summary Of Tax Credit Carryforwards | At March 31, 2018, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2030-2037 |  |  | $774 |  |  |  | $497 |  |  |  | $176 |
State net operating losses | 2018-2038 |  | 707 |  |  | 13 |  |  | 2 |
Federal tax credits | 2022-2038 |  | 277 |  |  | 123 |  |  | 136 |
IPL [Member] |
Income Taxes [Line Items] |
Schedule Of Effective Income Tax Rates | The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
| Alliant Energy |  | IPL |  | WPL
Three Months Ended March 31 | 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Statutory federal income tax rate | 21.0 | % |  | 35.0 | % |  | 21.0 | % |  | 35.0 | % |  | 21.0 | % |  | 35.0 | %
State income taxes, net of federal benefits | 7.5 |  |  | 5.4 |  |  | 8.5 |  |  | 6.3 |  |  | 6.2 |  |  | 5.1 |
Effect of rate-making on property-related differences | (7.4 | ) |  | (7.5 | ) |  | (13.5 | ) |  | (17.9 | ) |  | (2.4 | ) |  | (1.7 | )
Production tax credits | (5.5 | ) |  | (5.9 | ) |  | (5.4 | ) |  | (6.6 | ) |  | (6.7 | ) |  | (7.0 | )
IPL’s tax benefit riders | (2.2 | ) |  | (7.8 | ) |  | (4.7 | ) |  | (19.4 | ) |  | — |  |  | — |
Other items, net | (1.4 | ) |  | (4.4 | ) |  | — |  |  | (7.6 | ) |  | (0.3 | ) |  | (0.4 | )
Overall income tax rate | 12.0 | % |  | 14.8 | % |  | 5.9 | % |  | (10.2 | %) |  | 17.8 | % |  | 31.0 | %
Summary Of Tax Credit Carryforwards | At March 31, 2018, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2030-2037 |  |  | $774 |  |  |  | $497 |  |  |  | $176 |
State net operating losses | 2018-2038 |  | 707 |  |  | 13 |  |  | 2 |
Federal tax credits | 2022-2038 |  | 277 |  |  | 123 |  |  | 136 |
WPL [Member] |
Income Taxes [Line Items] |
Schedule Of Effective Income Tax Rates | The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
| Alliant Energy |  | IPL |  | WPL
Three Months Ended March 31 | 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Statutory federal income tax rate | 21.0 | % |  | 35.0 | % |  | 21.0 | % |  | 35.0 | % |  | 21.0 | % |  | 35.0 | %
State income taxes, net of federal benefits | 7.5 |  |  | 5.4 |  |  | 8.5 |  |  | 6.3 |  |  | 6.2 |  |  | 5.1 |
Effect of rate-making on property-related differences | (7.4 | ) |  | (7.5 | ) |  | (13.5 | ) |  | (17.9 | ) |  | (2.4 | ) |  | (1.7 | )
Production tax credits | (5.5 | ) |  | (5.9 | ) |  | (5.4 | ) |  | (6.6 | ) |  | (6.7 | ) |  | (7.0 | )
IPL’s tax benefit riders | (2.2 | ) |  | (7.8 | ) |  | (4.7 | ) |  | (19.4 | ) |  | — |  |  | — |
Other items, net | (1.4 | ) |  | (4.4 | ) |  | — |  |  | (7.6 | ) |  | (0.3 | ) |  | (0.4 | )
Overall income tax rate | 12.0 | % |  | 14.8 | % |  | 5.9 | % |  | (10.2 | %) |  | 17.8 | % |  | 31.0 | %
Summary Of Tax Credit Carryforwards | At March 31, 2018, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2030-2037 |  |  | $774 |  |  |  | $497 |  |  |  | $176 |
State net operating losses | 2018-2038 |  | 707 |  |  | 13 |  |  | 2 |
Federal tax credits | 2022-2038 |  | 277 |  |  | 123 |  |  | 136 |

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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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319 + Details
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