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Income Taxes | 3 Months Ended
--- | ---
Mar. 31, 2016
Income Taxes [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 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 | 2016 |  | 2015 |  | 2016 |  | 2015 |  | 2016 |  | 2015
Statutory federal income tax rate | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | %
IPL’s tax benefit riders | (8.7 | ) |  | (9.9 | ) |  | (20.7 | ) |  | (25.2 | ) |  | — |  |  | — |
Effect of rate-making on property-related differences | (6.8 | ) |  | (6.1 | ) |  | (15.2 | ) |  | (14.6 | ) |  | (0.8 | ) |  | (0.6 | )
Production tax credits | (6.3 | ) |  | (6.2 | ) |  | (6.7 | ) |  | (7.1 | ) |  | (6.5 | ) |  | (6.2 | )
Other items, net | 4.5 |  |  | 4.3 |  |  | 5.9 |  |  | 4.8 |  |  | 4.8 |  |  | 4.4 |
Overall income tax rate | 17.7 | % |  | 17.1 | % |  | (1.7 | %) |  | (7.1 | %) |  | 32.5 | % |  | 32.6 | %
IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing IPL’s tax benefit riders. Refer to Note 2 for additional details of the tax benefit riders. Deferred Tax Assets and Liabilities - For the three months ended March 31, 2016, Alliant Energy’s, IPL’s and WPL’s non-current deferred tax liabilities increased $43.4 million, $30.9 million and $19.7 million, respectively. These increases in non-current deferred tax liabilities were primarily due to property-related differences recorded during the three months ended March 31, 2016. Carryforwards - At March 31, 2016, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
|  |  | Alliant Energy |  | IPL |  | WPL
| Earliest Expiration Date |  | Tax Carryforwards |  | Deferred Tax Assets |  | Tax Carryforwards |  | Deferred Tax Assets |  | Tax Carryforwards |  | Deferred Tax Assets
Federal net operating losses | 2030 |  |  | $733 |  |  |  | $252 |  |  |  | $330 |  |  |  | $111 |  |  |  | $298 |  |  |  | $104 |
State net operating losses | 2018 |  | 748 |  |  | 39 |  |  | 20 |  |  | 1 |  |  | 47 |  |  | 2 |
Federal tax credits | 2022 |  | 250 |  |  | 246 |  |  | 89 |  |  | 86 |  |  | 101 |  |  | 101 |
|  |  |  |  |  | $537 |  |  |  |  |  | $198 |  |  |  |  |  | $207 |
IPL [Member] |
Income Taxes [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 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 | 2016 |  | 2015 |  | 2016 |  | 2015 |  | 2016 |  | 2015
Statutory federal income tax rate | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | %
IPL’s tax benefit riders | (8.7 | ) |  | (9.9 | ) |  | (20.7 | ) |  | (25.2 | ) |  | — |  |  | — |
Effect of rate-making on property-related differences | (6.8 | ) |  | (6.1 | ) |  | (15.2 | ) |  | (14.6 | ) |  | (0.8 | ) |  | (0.6 | )
Production tax credits | (6.3 | ) |  | (6.2 | ) |  | (6.7 | ) |  | (7.1 | ) |  | (6.5 | ) |  | (6.2 | )
Other items, net | 4.5 |  |  | 4.3 |  |  | 5.9 |  |  | 4.8 |  |  | 4.8 |  |  | 4.4 |
Overall income tax rate | 17.7 | % |  | 17.1 | % |  | (1.7 | %) |  | (7.1 | %) |  | 32.5 | % |  | 32.6 | %
IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing IPL’s tax benefit riders. Refer to Note 2 for additional details of the tax benefit riders. Deferred Tax Assets and Liabilities - For the three months ended March 31, 2016, Alliant Energy’s, IPL’s and WPL’s non-current deferred tax liabilities increased $43.4 million, $30.9 million and $19.7 million, respectively. These increases in non-current deferred tax liabilities were primarily due to property-related differences recorded during the three months ended March 31, 2016. Carryforwards - At March 31, 2016, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
|  |  | Alliant Energy |  | IPL |  | WPL
| Earliest Expiration Date |  | Tax Carryforwards |  | Deferred Tax Assets |  | Tax Carryforwards |  | Deferred Tax Assets |  | Tax Carryforwards |  | Deferred Tax Assets
Federal net operating losses | 2030 |  |  | $733 |  |  |  | $252 |  |  |  | $330 |  |  |  | $111 |  |  |  | $298 |  |  |  | $104 |
State net operating losses | 2018 |  | 748 |  |  | 39 |  |  | 20 |  |  | 1 |  |  | 47 |  |  | 2 |
Federal tax credits | 2022 |  | 250 |  |  | 246 |  |  | 89 |  |  | 86 |  |  | 101 |  |  | 101 |
|  |  |  |  |  | $537 |  |  |  |  |  | $198 |  |  |  |  |  | $207 |
WPL [Member] |
Income Taxes [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 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 | 2016 |  | 2015 |  | 2016 |  | 2015 |  | 2016 |  | 2015
Statutory federal income tax rate | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | %
IPL’s tax benefit riders | (8.7 | ) |  | (9.9 | ) |  | (20.7 | ) |  | (25.2 | ) |  | — |  |  | — |
Effect of rate-making on property-related differences | (6.8 | ) |  | (6.1 | ) |  | (15.2 | ) |  | (14.6 | ) |  | (0.8 | ) |  | (0.6 | )
Production tax credits | (6.3 | ) |  | (6.2 | ) |  | (6.7 | ) |  | (7.1 | ) |  | (6.5 | ) |  | (6.2 | )
Other items, net | 4.5 |  |  | 4.3 |  |  | 5.9 |  |  | 4.8 |  |  | 4.8 |  |  | 4.4 |
Overall income tax rate | 17.7 | % |  | 17.1 | % |  | (1.7 | %) |  | (7.1 | %) |  | 32.5 | % |  | 32.6 | %
IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing IPL’s tax benefit riders. Refer to Note 2 for additional details of the tax benefit riders. Deferred Tax Assets and Liabilities - For the three months ended March 31, 2016, Alliant Energy’s, IPL’s and WPL’s non-current deferred tax liabilities increased $43.4 million, $30.9 million and $19.7 million, respectively. These increases in non-current deferred tax liabilities were primarily due to property-related differences recorded during the three months ended March 31, 2016. Carryforwards - At March 31, 2016, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (dollars in millions):
|  |  | Alliant Energy |  | IPL |  | WPL
| Earliest Expiration Date |  | Tax Carryforwards |  | Deferred Tax Assets |  | Tax Carryforwards |  | Deferred Tax Assets |  | Tax Carryforwards |  | Deferred Tax Assets
Federal net operating losses | 2030 |  |  | $733 |  |  |  | $252 |  |  |  | $330 |  |  |  | $111 |  |  |  | $298 |  |  |  | $104 |
State net operating losses | 2018 |  | 748 |  |  | 39 |  |  | 20 |  |  | 1 |  |  | 47 |  |  | 2 |
Federal tax credits | 2022 |  | 250 |  |  | 246 |  |  | 89 |  |  | 86 |  |  | 101 |  |  | 101 |
|  |  |  |  |  | $537 |  |  |  |  |  | $198 |  |  |  |  |  | $207 |

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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 Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 2: 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 3: 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 4: 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 5: 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 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Article 4 + Details
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