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Income Taxes | 3 Months Ended
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Mar. 31, 2013
Income Tax [Line Items] |
Income Taxes | INCOME TAXES Income Tax Rates - The provision for income taxes for earnings from continuing operations is based on an estimated annual effective income tax rate that excludes the impact of significant unusual or infrequently occurring items, discontinued operations or extraordinary items. The effective income tax rates for Alliant Energy, IPL and WPL differ from the federal statutory rate of 35% generally due to effects of enacted tax legislation, utility rate-making, including IPL’s tax benefit riders, tax credits, state income taxes and certain non-deductible expenses. Changes in state apportionment rates caused by the planned sale of Alliant Energy’s RMT business also impacted the effective income tax rates in 2012 for Alliant Energy, IPL and WPL. 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 | %
State apportionment change due to planned sale of RMT - Alliant Energy, IPL and WPL utilize state apportionment projections to record their deferred tax assets and liabilities each reporting period. Deferred tax assets and liabilities for temporary differences between the tax basis of assets and liabilities and the amounts reported in the condensed consolidated financial statements are recorded utilizing currently enacted tax rates and estimates of future state apportionment rates expected to be in effect at the time the temporary differences reverse. These state apportionment projections are most significantly impacted by the estimated amount of revenues expected in the future from each state jurisdiction for Alliant Energy’s consolidated tax groups, including both its regulated and its non-regulated operations. In the first quarter of 2012, Alliant Energy, IPL and WPL recorded $15 million, $8 million and $7 million, respectively, of deferred income tax expense due to changes in state apportionment projections caused by the planned sale of Alliant Energy’s RMT business. These income tax expense amounts recognized during the three months ended March 31, 2012 increased Alliant Energy’s, IPL’s and WPL’s effective income tax rates for continuing operations for such period by 21.4%, 137.3% and 12.3%, respectively. IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates for the three months ended March 31, 2013 and 2012 include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing the tax benefit riders. The tax impacts of the tax benefit riders decreased Alliant Energy’s and IPL’s effective income tax rates for continuing operations by 12.8% and 37.3%, respectively, for the three months ended March 31, 2013 and by 12.2% and 37.5%, respectively, for the three months ended March 31, 2012. Refer to Note 1(b) for additional details of IPL’s tax benefit riders. Production tax credits - Alliant Energy has three wind projects that are currently generating production tax credits: WPL’s 68 MW Cedar Ridge wind project, which began generating electricity in late 2008; IPL’s 200 MW Whispering Willow - East wind project, which began generating electricity in late 2009; and WPL’s 200 MW Bent Tree - Phase I wind project, which began generating electricity in late 2010. 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 |
Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s effective income tax rates are impacted by certain property-related differences at IPL for which deferred tax is not recognized in the income statement pursuant to Iowa rate-making principles. The tax impacts of the effect of rate-making on property-related differences decreased Alliant Energy’s and IPL’s effective income tax rates for continuing operations by 5.0% and 14.0%, respectively, for the three months ended March 31, 2013 and by 1.7% and 2.1%, respectively, for the three months ended March 31, 2012. The primary factor contributing to the increase in the current tax benefits recorded for the effect of rate-making on property-related differences during the three months ended March 31, 2013 was repair expenditures at IPL. Deferred Tax Assets and Liabilities - For the three months ended March 31, 2013, Alliant Energy’s, IPL’s and WPL’s current deferred tax assets decreased $77.7 million, $20.6 million and $63.0 million, respectively, and Alliant Energy’s, IPL’s and WPL’s non-current deferred tax liabilities decreased $32.8 million, $7.7 million and $32.9 million, respectively. These decreases were primarily due to a transfer of deferred tax assets from current to non-current during the three months ended March 31, 2013 caused by a decrease in the amount of federal net operating loss carryforwards expected to be utilized during the next 12 months. The decrease in the amount of net operating loss carryforwards expected to be utilized during the next 12 months was impacted by the extension of bonus depreciation deductions in the first quarter of 2013. In January 2013, the American Taxpayer Relief Act of 2012 (ATR Act) was enacted. The most significant provision of the ATR Act for Alliant Energy, IPL and WPL relates to the extension of bonus depreciation deductions for certain expenditures for property that are incurred through December 31, 2013. 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 |  |  |
Uncertain Tax Positions - In 2013, statutes of limitations will expire for Alliant Energy’s, IPL’s and WPL’s tax returns in multiple state jurisdictions. The expiration of the statutes of limitations will not have any impact on Alliant Energy’s, IPL’s and WPL’s uncertain tax positions in 2013. As of March 31, 2013, it is reasonably possible that Alliant Energy, IPL and WPL could have material changes to their unrecognized tax benefits during the next 12 months as a result of the issuance of revenue procedures clarifying the treatment of repair expenditures for electric generation and gas distribution property in 2013. An estimate of the expected changes during the next 12 months cannot be determined at this time.
IPL [Member] |
Income Tax [Line Items] |
Income Taxes | INCOME TAXES Income Tax Rates - The provision for income taxes for earnings from continuing operations is based on an estimated annual effective income tax rate that excludes the impact of significant unusual or infrequently occurring items, discontinued operations or extraordinary items. The effective income tax rates for Alliant Energy, IPL and WPL differ from the federal statutory rate of 35% generally due to effects of enacted tax legislation, utility rate-making, including IPL’s tax benefit riders, tax credits, state income taxes and certain non-deductible expenses. Changes in state apportionment rates caused by the planned sale of Alliant Energy’s RMT business also impacted the effective income tax rates in 2012 for Alliant Energy, IPL and WPL. 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 | %
State apportionment change due to planned sale of RMT - Alliant Energy, IPL and WPL utilize state apportionment projections to record their deferred tax assets and liabilities each reporting period. Deferred tax assets and liabilities for temporary differences between the tax basis of assets and liabilities and the amounts reported in the condensed consolidated financial statements are recorded utilizing currently enacted tax rates and estimates of future state apportionment rates expected to be in effect at the time the temporary differences reverse. These state apportionment projections are most significantly impacted by the estimated amount of revenues expected in the future from each state jurisdiction for Alliant Energy’s consolidated tax groups, including both its regulated and its non-regulated operations. In the first quarter of 2012, Alliant Energy, IPL and WPL recorded $15 million, $8 million and $7 million, respectively, of deferred income tax expense due to changes in state apportionment projections caused by the planned sale of Alliant Energy’s RMT business. These income tax expense amounts recognized during the three months ended March 31, 2012 increased Alliant Energy’s, IPL’s and WPL’s effective income tax rates for continuing operations for such period by 21.4%, 137.3% and 12.3%, respectively. IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates for the three months ended March 31, 2013 and 2012 include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing the tax benefit riders. The tax impacts of the tax benefit riders decreased Alliant Energy’s and IPL’s effective income tax rates for continuing operations by 12.8% and 37.3%, respectively, for the three months ended March 31, 2013 and by 12.2% and 37.5%, respectively, for the three months ended March 31, 2012. Refer to Note 1(b) for additional details of IPL’s tax benefit riders. Production tax credits - Alliant Energy has three wind projects that are currently generating production tax credits: WPL’s 68 MW Cedar Ridge wind project, which began generating electricity in late 2008; IPL’s 200 MW Whispering Willow - East wind project, which began generating electricity in late 2009; and WPL’s 200 MW Bent Tree - Phase I wind project, which began generating electricity in late 2010. 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 |
Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s effective income tax rates are impacted by certain property-related differences at IPL for which deferred tax is not recognized in the income statement pursuant to Iowa rate-making principles. The tax impacts of the effect of rate-making on property-related differences decreased Alliant Energy’s and IPL’s effective income tax rates for continuing operations by 5.0% and 14.0%, respectively, for the three months ended March 31, 2013 and by 1.7% and 2.1%, respectively, for the three months ended March 31, 2012. The primary factor contributing to the increase in the current tax benefits recorded for the effect of rate-making on property-related differences during the three months ended March 31, 2013 was repair expenditures at IPL. Deferred Tax Assets and Liabilities - For the three months ended March 31, 2013, Alliant Energy’s, IPL’s and WPL’s current deferred tax assets decreased $77.7 million, $20.6 million and $63.0 million, respectively, and Alliant Energy’s, IPL’s and WPL’s non-current deferred tax liabilities decreased $32.8 million, $7.7 million and $32.9 million, respectively. These decreases were primarily due to a transfer of deferred tax assets from current to non-current during the three months ended March 31, 2013 caused by a decrease in the amount of federal net operating loss carryforwards expected to be utilized during the next 12 months. The decrease in the amount of net operating loss carryforwards expected to be utilized during the next 12 months was impacted by the extension of bonus depreciation deductions in the first quarter of 2013. In January 2013, the American Taxpayer Relief Act of 2012 (ATR Act) was enacted. The most significant provision of the ATR Act for Alliant Energy, IPL and WPL relates to the extension of bonus depreciation deductions for certain expenditures for property that are incurred through December 31, 2013. 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 |  |  |
Uncertain Tax Positions - In 2013, statutes of limitations will expire for Alliant Energy’s, IPL’s and WPL’s tax returns in multiple state jurisdictions. The expiration of the statutes of limitations will not have any impact on Alliant Energy’s, IPL’s and WPL’s uncertain tax positions in 2013. As of March 31, 2013, it is reasonably possible that Alliant Energy, IPL and WPL could have material changes to their unrecognized tax benefits during the next 12 months as a result of the issuance of revenue procedures clarifying the treatment of repair expenditures for electric generation and gas distribution property in 2013. An estimate of the expected changes during the next 12 months cannot be determined at this time.
WPL [Member] |
Income Tax [Line Items] |
Income Taxes | INCOME TAXES Income Tax Rates - The provision for income taxes for earnings from continuing operations is based on an estimated annual effective income tax rate that excludes the impact of significant unusual or infrequently occurring items, discontinued operations or extraordinary items. The effective income tax rates for Alliant Energy, IPL and WPL differ from the federal statutory rate of 35% generally due to effects of enacted tax legislation, utility rate-making, including IPL’s tax benefit riders, tax credits, state income taxes and certain non-deductible expenses. Changes in state apportionment rates caused by the planned sale of Alliant Energy’s RMT business also impacted the effective income tax rates in 2012 for Alliant Energy, IPL and WPL. 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 | %
State apportionment change due to planned sale of RMT - Alliant Energy, IPL and WPL utilize state apportionment projections to record their deferred tax assets and liabilities each reporting period. Deferred tax assets and liabilities for temporary differences between the tax basis of assets and liabilities and the amounts reported in the condensed consolidated financial statements are recorded utilizing currently enacted tax rates and estimates of future state apportionment rates expected to be in effect at the time the temporary differences reverse. These state apportionment projections are most significantly impacted by the estimated amount of revenues expected in the future from each state jurisdiction for Alliant Energy’s consolidated tax groups, including both its regulated and its non-regulated operations. In the first quarter of 2012, Alliant Energy, IPL and WPL recorded $15 million, $8 million and $7 million, respectively, of deferred income tax expense due to changes in state apportionment projections caused by the planned sale of Alliant Energy’s RMT business. These income tax expense amounts recognized during the three months ended March 31, 2012 increased Alliant Energy’s, IPL’s and WPL’s effective income tax rates for continuing operations for such period by 21.4%, 137.3% and 12.3%, respectively. IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates for the three months ended March 31, 2013 and 2012 include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing the tax benefit riders. The tax impacts of the tax benefit riders decreased Alliant Energy’s and IPL’s effective income tax rates for continuing operations by 12.8% and 37.3%, respectively, for the three months ended March 31, 2013 and by 12.2% and 37.5%, respectively, for the three months ended March 31, 2012. Refer to Note 1(b) for additional details of IPL’s tax benefit riders. Production tax credits - Alliant Energy has three wind projects that are currently generating production tax credits: WPL’s 68 MW Cedar Ridge wind project, which began generating electricity in late 2008; IPL’s 200 MW Whispering Willow - East wind project, which began generating electricity in late 2009; and WPL’s 200 MW Bent Tree - Phase I wind project, which began generating electricity in late 2010. 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 |
Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s effective income tax rates are impacted by certain property-related differences at IPL for which deferred tax is not recognized in the income statement pursuant to Iowa rate-making principles. The tax impacts of the effect of rate-making on property-related differences decreased Alliant Energy’s and IPL’s effective income tax rates for continuing operations by 5.0% and 14.0%, respectively, for the three months ended March 31, 2013 and by 1.7% and 2.1%, respectively, for the three months ended March 31, 2012. The primary factor contributing to the increase in the current tax benefits recorded for the effect of rate-making on property-related differences during the three months ended March 31, 2013 was repair expenditures at IPL. Deferred Tax Assets and Liabilities - For the three months ended March 31, 2013, Alliant Energy’s, IPL’s and WPL’s current deferred tax assets decreased $77.7 million, $20.6 million and $63.0 million, respectively, and Alliant Energy’s, IPL’s and WPL’s non-current deferred tax liabilities decreased $32.8 million, $7.7 million and $32.9 million, respectively. These decreases were primarily due to a transfer of deferred tax assets from current to non-current during the three months ended March 31, 2013 caused by a decrease in the amount of federal net operating loss carryforwards expected to be utilized during the next 12 months. The decrease in the amount of net operating loss carryforwards expected to be utilized during the next 12 months was impacted by the extension of bonus depreciation deductions in the first quarter of 2013. In January 2013, the American Taxpayer Relief Act of 2012 (ATR Act) was enacted. The most significant provision of the ATR Act for Alliant Energy, IPL and WPL relates to the extension of bonus depreciation deductions for certain expenditures for property that are incurred through December 31, 2013. 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 |  |  |
Uncertain Tax Positions - In 2013, statutes of limitations will expire for Alliant Energy’s, IPL’s and WPL’s tax returns in multiple state jurisdictions. The expiration of the statutes of limitations will not have any impact on Alliant Energy’s, IPL’s and WPL’s uncertain tax positions in 2013. As of March 31, 2013, it is reasonably possible that Alliant Energy, IPL and WPL could have material changes to their unrecognized tax benefits during the next 12 months as a result of the issuance of revenue procedures clarifying the treatment of repair expenditures for electric generation and gas distribution property in 2013. An estimate of the expected changes during the next 12 months cannot be determined at this time.

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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/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 136, 172 -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)) -URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Article 4 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 109 -Paragraph 43, 44, 45, 46, 47, 48, 49 -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 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32537-109319 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32639-109319 Reference 8: 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 + Details
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