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Income Taxes | 9 Months Ended
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Sep. 30, 2017
Income Taxes [Line Items] |
Income Taxes | INCOME TAXES 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 September 30 | 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Statutory federal income tax rate | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | %
Effect of rate-making on property-related differences | (10.1 | ) |  | (11.9 | ) |  | (22.6 | ) |  | (16.5 | ) |  | (1.9 | ) |  | (0.7 | )
IPL’s tax benefit riders | (8.3 | ) |  | (13.1 | ) |  | (20.9 | ) |  | (20.1 | ) |  | — |  |  | — |
Production tax credits | (6.2 | ) |  | (9.0 | ) |  | (7.0 | ) |  | (6.0 | ) |  | (7.0 | ) |  | (5.7 | )
Other items, net | 2.8 |  |  | 4.4 |  |  | 2.3 |  |  | 5.4 |  |  | 5.5 |  |  | 4.0 |
Overall income tax rate | 13.2 | % |  | 5.4 | % |  | (13.2 | %) |  | (2.2 | %) |  | 31.6 | % |  | 32.6 | %
| Alliant Energy |  | IPL |  | WPL
Nine Months Ended September 30 | 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Statutory federal income tax rate | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | %
Effect of rate-making on property-related differences | (9.1 | ) |  | (8.2 | ) |  | (20.6 | ) |  | (14.8 | ) |  | (1.8 | ) |  | (0.8 | )
IPL’s tax benefit riders | (8.1 | ) |  | (10.2 | ) |  | (20.1 | ) |  | (19.6 | ) |  | — |  |  | — |
Production tax credits | (6.0 | ) |  | (7.2 | ) |  | (6.8 | ) |  | (6.1 | ) |  | (7.0 | ) |  | (6.1 | )
Other items, net | 3.1 |  |  | 3.5 |  |  | 2.7 |  |  | 4.2 |  |  | 4.9 |  |  | 4.4 |
Overall income tax rate | 14.9 | % |  | 12.9 | % |  | (9.8 | %) |  | (1.3 | %) |  | 31.1 | % |  | 32.5 | %
Deferred Tax Assets and Liabilities - For the nine months ended September 30, 2017, Alliant Energy’s, IPL’s and WPL’s deferred tax liabilities increased $204.5 million, $131.7 million and $63.6 million, respectively. These increases were primarily due to property-related differences recorded during the nine months ended September 30, 2017. Alliant Energy’s and IPL’s increases were partially offset by the generation of federal net operating losses recorded during the nine months ended September 30, 2017, which are primarily due to accelerated tax depreciation associated with Marshalltown. Carryforwards - At September 30, 2017, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2030-2037 |  |  | $815 |  |  |  | $500 |  |  |  | $208 |
State net operating losses | 2018-2037 |  | 701 |  |  | 14 |  |  | 2 |
Federal tax credits | 2022-2037 |  | 297 |  |  | 110 |  |  | 125 |
IPL [Member] |
Income Taxes [Line Items] |
Income Taxes | INCOME TAXES 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 September 30 | 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Statutory federal income tax rate | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | %
Effect of rate-making on property-related differences | (10.1 | ) |  | (11.9 | ) |  | (22.6 | ) |  | (16.5 | ) |  | (1.9 | ) |  | (0.7 | )
IPL’s tax benefit riders | (8.3 | ) |  | (13.1 | ) |  | (20.9 | ) |  | (20.1 | ) |  | — |  |  | — |
Production tax credits | (6.2 | ) |  | (9.0 | ) |  | (7.0 | ) |  | (6.0 | ) |  | (7.0 | ) |  | (5.7 | )
Other items, net | 2.8 |  |  | 4.4 |  |  | 2.3 |  |  | 5.4 |  |  | 5.5 |  |  | 4.0 |
Overall income tax rate | 13.2 | % |  | 5.4 | % |  | (13.2 | %) |  | (2.2 | %) |  | 31.6 | % |  | 32.6 | %
| Alliant Energy |  | IPL |  | WPL
Nine Months Ended September 30 | 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Statutory federal income tax rate | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | %
Effect of rate-making on property-related differences | (9.1 | ) |  | (8.2 | ) |  | (20.6 | ) |  | (14.8 | ) |  | (1.8 | ) |  | (0.8 | )
IPL’s tax benefit riders | (8.1 | ) |  | (10.2 | ) |  | (20.1 | ) |  | (19.6 | ) |  | — |  |  | — |
Production tax credits | (6.0 | ) |  | (7.2 | ) |  | (6.8 | ) |  | (6.1 | ) |  | (7.0 | ) |  | (6.1 | )
Other items, net | 3.1 |  |  | 3.5 |  |  | 2.7 |  |  | 4.2 |  |  | 4.9 |  |  | 4.4 |
Overall income tax rate | 14.9 | % |  | 12.9 | % |  | (9.8 | %) |  | (1.3 | %) |  | 31.1 | % |  | 32.5 | %
Deferred Tax Assets and Liabilities - For the nine months ended September 30, 2017, Alliant Energy’s, IPL’s and WPL’s deferred tax liabilities increased $204.5 million, $131.7 million and $63.6 million, respectively. These increases were primarily due to property-related differences recorded during the nine months ended September 30, 2017. Alliant Energy’s and IPL’s increases were partially offset by the generation of federal net operating losses recorded during the nine months ended September 30, 2017, which are primarily due to accelerated tax depreciation associated with Marshalltown. Carryforwards - At September 30, 2017, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2030-2037 |  |  | $815 |  |  |  | $500 |  |  |  | $208 |
State net operating losses | 2018-2037 |  | 701 |  |  | 14 |  |  | 2 |
Federal tax credits | 2022-2037 |  | 297 |  |  | 110 |  |  | 125 |
WPL [Member] |
Income Taxes [Line Items] |
Income Taxes | INCOME TAXES 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 September 30 | 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Statutory federal income tax rate | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | %
Effect of rate-making on property-related differences | (10.1 | ) |  | (11.9 | ) |  | (22.6 | ) |  | (16.5 | ) |  | (1.9 | ) |  | (0.7 | )
IPL’s tax benefit riders | (8.3 | ) |  | (13.1 | ) |  | (20.9 | ) |  | (20.1 | ) |  | — |  |  | — |
Production tax credits | (6.2 | ) |  | (9.0 | ) |  | (7.0 | ) |  | (6.0 | ) |  | (7.0 | ) |  | (5.7 | )
Other items, net | 2.8 |  |  | 4.4 |  |  | 2.3 |  |  | 5.4 |  |  | 5.5 |  |  | 4.0 |
Overall income tax rate | 13.2 | % |  | 5.4 | % |  | (13.2 | %) |  | (2.2 | %) |  | 31.6 | % |  | 32.6 | %
| Alliant Energy |  | IPL |  | WPL
Nine Months Ended September 30 | 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Statutory federal income tax rate | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | %
Effect of rate-making on property-related differences | (9.1 | ) |  | (8.2 | ) |  | (20.6 | ) |  | (14.8 | ) |  | (1.8 | ) |  | (0.8 | )
IPL’s tax benefit riders | (8.1 | ) |  | (10.2 | ) |  | (20.1 | ) |  | (19.6 | ) |  | — |  |  | — |
Production tax credits | (6.0 | ) |  | (7.2 | ) |  | (6.8 | ) |  | (6.1 | ) |  | (7.0 | ) |  | (6.1 | )
Other items, net | 3.1 |  |  | 3.5 |  |  | 2.7 |  |  | 4.2 |  |  | 4.9 |  |  | 4.4 |
Overall income tax rate | 14.9 | % |  | 12.9 | % |  | (9.8 | %) |  | (1.3 | %) |  | 31.1 | % |  | 32.5 | %
Deferred Tax Assets and Liabilities - For the nine months ended September 30, 2017, Alliant Energy’s, IPL’s and WPL’s deferred tax liabilities increased $204.5 million, $131.7 million and $63.6 million, respectively. These increases were primarily due to property-related differences recorded during the nine months ended September 30, 2017. Alliant Energy’s and IPL’s increases were partially offset by the generation of federal net operating losses recorded during the nine months ended September 30, 2017, which are primarily due to accelerated tax depreciation associated with Marshalltown. Carryforwards - At September 30, 2017, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2030-2037 |  |  | $815 |  |  |  | $500 |  |  |  | $208 |
State net operating losses | 2018-2037 |  | 701 |  |  | 14 |  |  | 2 |
Federal tax credits | 2022-2037 |  | 297 |  |  | 110 |  |  | 125 |

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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=65882285&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=65882285&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=65882285&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=65882285&loc=d3e32537-109319 + Details
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