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Income Taxes (Tables) | 3 Months Ended
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Mar. 31, 2013
Income Tax [Line Items] |
Schedule Of Effective Income Tax Rates | The effective income tax rates shown in the following table for the three months ended March 31 were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
| 2013 |  | 2012
Alliant Energy | 12.7 | % |  | 39.0 | %
IPL | (24.0 | %) |  | 125.4 | %
WPL | 32.0 | % |  | 44.1 | %
Production Tax Credits (Net Of State Tax Impacts) | For the three months ended March 31, production tax credits (net of state tax impacts) resulting from these wind projects were as follows (in millions):
| 2013 |  | 2012
Cedar Ridge (WPL) |  | $1.2 |  |  |  | $1.3 |
Bent Tree - Phase I (WPL) | 3.5 |  |  | 1.5 |
Subtotal (WPL) | 4.7 |  |  | 2.8 |
Whispering Willow - East (IPL) | 3.9 |  |  | 3.6 |
|  | $8.6 |  |  |  | $6.4 |
Summary Of Tax Credit Carryforwards | At March 31, 2013, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (in millions):
Alliant Energy | Carryforward Amount |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $863 |  |  |  | $296 |  |  | 2029
State net operating losses | 808 |  |  | 43 |  |  | 2019
Federal tax credits | 146 |  |  | 144 |  |  | 2022
|  |  |  | $483 |  |  |
IPL | Carryforward Amount |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $400 |  |  |  | $137 |  |  | 2029
State net operating losses | 238 |  |  | 14 |  |  | 2018
Federal tax credits | 43 |  |  | 42 |  |  | 2022
|  |  |  | $193 |  |  |
WPL | Carryforward Amount |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $349 |  |  |  | $120 |  |  | 2029
State net operating losses | 148 |  |  | 7 |  |  | 2018
Federal tax credits | 46 |  |  | 45 |  |  | 2022
|  |  |  | $172 |  |  |
IPL [Member] |
Income Tax [Line Items] |
Schedule Of Effective Income Tax Rates | The effective income tax rates shown in the following table for the three months ended March 31 were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
| 2013 |  | 2012
Alliant Energy | 12.7 | % |  | 39.0 | %
IPL | (24.0 | %) |  | 125.4 | %
WPL | 32.0 | % |  | 44.1 | %
Production Tax Credits (Net Of State Tax Impacts) | For the three months ended March 31, production tax credits (net of state tax impacts) resulting from these wind projects were as follows (in millions):
| 2013 |  | 2012
Cedar Ridge (WPL) |  | $1.2 |  |  |  | $1.3 |
Bent Tree - Phase I (WPL) | 3.5 |  |  | 1.5 |
Subtotal (WPL) | 4.7 |  |  | 2.8 |
Whispering Willow - East (IPL) | 3.9 |  |  | 3.6 |
|  | $8.6 |  |  |  | $6.4 |
Summary Of Tax Credit Carryforwards | At March 31, 2013, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (in millions):
Alliant Energy | Carryforward Amount |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $863 |  |  |  | $296 |  |  | 2029
State net operating losses | 808 |  |  | 43 |  |  | 2019
Federal tax credits | 146 |  |  | 144 |  |  | 2022
|  |  |  | $483 |  |  |
IPL | Carryforward Amount |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $400 |  |  |  | $137 |  |  | 2029
State net operating losses | 238 |  |  | 14 |  |  | 2018
Federal tax credits | 43 |  |  | 42 |  |  | 2022
|  |  |  | $193 |  |  |
WPL | Carryforward Amount |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $349 |  |  |  | $120 |  |  | 2029
State net operating losses | 148 |  |  | 7 |  |  | 2018
Federal tax credits | 46 |  |  | 45 |  |  | 2022
|  |  |  | $172 |  |  |
WPL [Member] |
Income Tax [Line Items] |
Schedule Of Effective Income Tax Rates | The effective income tax rates shown in the following table for the three months ended March 31 were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
| 2013 |  | 2012
Alliant Energy | 12.7 | % |  | 39.0 | %
IPL | (24.0 | %) |  | 125.4 | %
WPL | 32.0 | % |  | 44.1 | %
Production Tax Credits (Net Of State Tax Impacts) | For the three months ended March 31, production tax credits (net of state tax impacts) resulting from these wind projects were as follows (in millions):
| 2013 |  | 2012
Cedar Ridge (WPL) |  | $1.2 |  |  |  | $1.3 |
Bent Tree - Phase I (WPL) | 3.5 |  |  | 1.5 |
Subtotal (WPL) | 4.7 |  |  | 2.8 |
Whispering Willow - East (IPL) | 3.9 |  |  | 3.6 |
|  | $8.6 |  |  |  | $6.4 |
Summary Of Tax Credit Carryforwards | At March 31, 2013, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (in millions):
Alliant Energy | Carryforward Amount |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $863 |  |  |  | $296 |  |  | 2029
State net operating losses | 808 |  |  | 43 |  |  | 2019
Federal tax credits | 146 |  |  | 144 |  |  | 2022
|  |  |  | $483 |  |  |
IPL | Carryforward Amount |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $400 |  |  |  | $137 |  |  | 2029
State net operating losses | 238 |  |  | 14 |  |  | 2018
Federal tax credits | 43 |  |  | 42 |  |  | 2022
|  |  |  | $193 |  |  |
WPL | Carryforward Amount |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $349 |  |  |  | $120 |  |  | 2029
State net operating losses | 148 |  |  | 7 |  |  | 2018
Federal tax credits | 46 |  |  | 45 |  |  | 2022
|  |  |  | $172 |  |  |

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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=6907707&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=6907707&loc=d3e32559-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 17 -Subparagraph a -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 43 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Carryforwards -URI http://asc.fasb.org/extlink&oid=6506874 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 48 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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