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Income Taxes (Tables) | 12 Months Ended
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Dec. 31, 2017
Income Tax [Line Items] |
Schedule Of Impacts Of the Tax Cuts And Jobs Act of 2017 | Alliant Energy, IPL and WPL have completed their assessment of the applicable provisions of Tax Reform, and the impacts to their 2017 balance sheets and income statements are as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Balance Sheet |  |  |  |  |
Other current assets |  | $— |  |  |  | $4.7 |  |  |  | ($1.4 | )
Investments: |  |  |  |  |
ATC Investment | (75.0 | ) |  | — |  |  | — |
Other assets: |  |  |  |  |
Regulatory assets | (387.6 | ) |  | (375.0 | ) |  | (12.7 | )
Deferred charges and other | 41.0 |  |  | — |  |  | — |
Total Tax Reform impact on assets |  | ($421.6 | ) |  |  | ($370.3 | ) |  |  | ($14.1 | )
Other liabilities: |  |  |  |  |
Deferred tax liabilities |  | ($1,331.9 | ) |  |  | ($757.2 | ) |  |  | ($523.8 | )
Regulatory liabilities | 885.9 |  |  | 390.7 |  |  | 495.2 |
Other | 6.3 |  |  | — |  |  | — |
Total Tax Reform impact on liabilities |  | ($439.7 | ) |  |  | ($366.5 | ) |  |  | ($28.6 | )
Income Statement |  |  |  |  |
Income tax expense (benefit) |  | ($18.1 | ) |  |  | $3.8 |  |  |  | ($14.5 | )
Schedule of Components of Income Tax Expense (Benefit) | The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal |  | ($41.0 | ) |  |  | $1.8 |  |  |  | $2.0 |  |  |  | ($27.9 | ) |  |  | ($12.8 | ) |  |  | ($14.1 | ) |  |  | $5.5 |  |  |  | ($22.3 | ) |  |  | $4.7 |
State | 8.5 |  |  | 17.2 |  |  | 3.2 |  |  | 1.6 |  |  | 15.5 |  |  | 11.5 |  |  | 2.5 |  |  | 1.1 |  |  | 0.6 |
IPL’s tax benefit riders | (40.4 | ) |  | (44.2 | ) |  | (49.0 | ) |  | (40.4 | ) |  | (44.2 | ) |  | (49.0 | ) |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 159.5 |  |  | 112.8 |  |  | 120.8 |  |  | 72.5 |  |  | 59.1 |  |  | 40.7 |  |  | 55.0 |  |  | 112.3 |  |  | 76.8 |
State | 12.3 |  |  | 4.9 |  |  | 27.9 |  |  | (2.2 | ) |  | (9.0 | ) |  | 3.3 |  |  | 16.6 |  |  | 20.8 |  |  | 20.2 |
Production tax credits | (31.1 | ) |  | (31.8 | ) |  | (33.1 | ) |  | (14.1 | ) |  | (14.0 | ) |  | (14.5 | ) |  | (17.0 | ) |  | (17.8 | ) |  | (18.6 | )
Investment tax credits | (1.1 | ) |  | (1.3 | ) |  | (1.4 | ) |  | (0.4 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.7 | ) |  | (0.8 | ) |  | (0.8 | )
|  | $66.7 |  |  |  | $59.4 |  |  |  | $70.4 |  |  |  | ($10.9 | ) |  |  | ($5.9 | ) |  |  | ($22.7 | ) |  |  | $61.9 |  |  |  | $93.3 |  |  |  | $82.9 |
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
| 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Statutory federal income tax rate | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | %
State income taxes, net of federal benefits | 5.5 |  |  | 5.4 |  |  | 5.2 |  |  | 6.5 |  |  | 6.4 |  |  | 6.2 |  |  | 5.1 |  |  | 5.1 |  |  | 5.1 |
Effect of rate-making on property-related differences | (8.5 | ) |  | (8.5 | ) |  | (6.8 | ) |  | (19.1 | ) |  | (16.2 | ) |  | (17.2 | ) |  | (1.7 | ) |  | (0.7 | ) |  | (0.5 | )
IPL’s tax benefit riders | (7.6 | ) |  | (10.0 | ) |  | (10.6 | ) |  | (18.7 | ) |  | (20.1 | ) |  | (28.3 | ) |  | — |  |  | — |  |  | — |
Production tax credits | (6.1 | ) |  | (7.2 | ) |  | (7.2 | ) |  | (6.7 | ) |  | (6.3 | ) |  | (8.3 | ) |  | (7.1 | ) |  | (6.2 | ) |  | (7.1 | )
Impact of Tax Reform | (3.4 | ) |  | — |  |  | — |  |  | 1.7 |  |  | — |  |  | — |  |  | (5.8 | ) |  | — |  |  | — |
Other items, net | (2.4 | ) |  | (1.3 | ) |  | (0.3 | ) |  | (3.7 | ) |  | (1.5 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.6 | ) |  | (0.7 | )
Overall income tax rate | 12.5 | % |  | 13.4 | % |  | 15.3 | % |  | (5.0 | %) |  | (2.7 | %) |  | (13.1 | %) |  | 24.9 | % |  | 32.6 | % |  | 31.8 | %
Schedule of Deferred Tax Assets and Liabilities | The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property |  | $1,852.7 |  |  |  | $2,919.0 |  |  |  | $1,102.6 |  |  |  | $1,677.0 |  |  |  | $674.2 |  |  |  | $1,124.5 |
ATC Investment | 86.4 |  |  | 153.1 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 75.9 |  |  | 95.1 |  |  | 63.4 |  |  | 71.4 |  |  | 36.5 |  |  | 58.8 |
Total deferred tax liabilities | 2,015.0 |  |  | 3,167.2 |  |  | 1,166.0 |  |  | 1,748.4 |  |  | 710.7 |  |  | 1,183.3 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 260.7 |  |  | 268.4 |  |  | 113.1 |  |  | 95.9 |  |  | 131.0 |  |  | 112.9 |
Net operating losses carryforwards - federal | 174.4 |  |  | 173.3 |  |  | 107.4 |  |  | 69.6 |  |  | 43.7 |  |  | 75.4 |
Regulatory liability - IPL’s tax benefit riders | 7.4 |  |  | 34.7 |  |  | 7.4 |  |  | 34.7 |  |  | — |  |  | — |
Net operating losses carryforwards - state | 41.3 |  |  | 32.9 |  |  | 0.9 |  |  | 0.6 |  |  | 0.2 |  |  | 0.1 |
Other | 61.8 |  |  | 87.9 |  |  | 27.1 |  |  | 35.8 |  |  | 14.7 |  |  | 23.6 |
Subtotal deferred tax assets | 545.6 |  |  | 597.2 |  |  | 255.9 |  |  | 236.6 |  |  | 189.6 |  |  | 212.0 |
Valuation allowance | (9.0 | ) |  | (0.2 | ) |  | (0.6 | ) |  | — |  |  | (1.3 | ) |  | (0.3 | )
Total deferred tax assets | 536.6 |  |  | 597.0 |  |  | 255.3 |  |  | 236.6 |  |  | 188.3 |  |  | 211.7 |
Total deferred tax liabilities, net |  | $1,478.4 |  |  |  | $2,570.2 |  |  |  | $910.7 |  |  |  | $1,511.8 |  |  |  | $522.4 |  |  |  | $971.6 |
Summary Of Tax Credit Carryforwards | At December 31, 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 |  |  | $852 |  |  |  | $537 |  |  |  | $208 |
State net operating losses | 2018-2037 |  | 700 |  |  | 13 |  |  | 2 |
Federal tax credits | 2022-2037 |  | 267 |  |  | 119 |  |  | 131 |
Schedule Of Open Tax Years | Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a) | 2014 | - | 2016
Consolidated Iowa income tax returns (b) | 2014 | - | 2016
Wisconsin combined tax returns (c) | 2013 | - | 2016
(a) | These federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.
(b) | The statute of limitations for these Iowa tax returns expires three years from each filing date.
(c) | The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.
IPL [Member] |
Income Tax [Line Items] |
Schedule Of Impacts Of the Tax Cuts And Jobs Act of 2017 | Alliant Energy, IPL and WPL have completed their assessment of the applicable provisions of Tax Reform, and the impacts to their 2017 balance sheets and income statements are as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Balance Sheet |  |  |  |  |
Other current assets |  | $— |  |  |  | $4.7 |  |  |  | ($1.4 | )
Investments: |  |  |  |  |
ATC Investment | (75.0 | ) |  | — |  |  | — |
Other assets: |  |  |  |  |
Regulatory assets | (387.6 | ) |  | (375.0 | ) |  | (12.7 | )
Deferred charges and other | 41.0 |  |  | — |  |  | — |
Total Tax Reform impact on assets |  | ($421.6 | ) |  |  | ($370.3 | ) |  |  | ($14.1 | )
Other liabilities: |  |  |  |  |
Deferred tax liabilities |  | ($1,331.9 | ) |  |  | ($757.2 | ) |  |  | ($523.8 | )
Regulatory liabilities | 885.9 |  |  | 390.7 |  |  | 495.2 |
Other | 6.3 |  |  | — |  |  | — |
Total Tax Reform impact on liabilities |  | ($439.7 | ) |  |  | ($366.5 | ) |  |  | ($28.6 | )
Income Statement |  |  |  |  |
Income tax expense (benefit) |  | ($18.1 | ) |  |  | $3.8 |  |  |  | ($14.5 | )
Schedule of Components of Income Tax Expense (Benefit) | The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal |  | ($41.0 | ) |  |  | $1.8 |  |  |  | $2.0 |  |  |  | ($27.9 | ) |  |  | ($12.8 | ) |  |  | ($14.1 | ) |  |  | $5.5 |  |  |  | ($22.3 | ) |  |  | $4.7 |
State | 8.5 |  |  | 17.2 |  |  | 3.2 |  |  | 1.6 |  |  | 15.5 |  |  | 11.5 |  |  | 2.5 |  |  | 1.1 |  |  | 0.6 |
IPL’s tax benefit riders | (40.4 | ) |  | (44.2 | ) |  | (49.0 | ) |  | (40.4 | ) |  | (44.2 | ) |  | (49.0 | ) |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 159.5 |  |  | 112.8 |  |  | 120.8 |  |  | 72.5 |  |  | 59.1 |  |  | 40.7 |  |  | 55.0 |  |  | 112.3 |  |  | 76.8 |
State | 12.3 |  |  | 4.9 |  |  | 27.9 |  |  | (2.2 | ) |  | (9.0 | ) |  | 3.3 |  |  | 16.6 |  |  | 20.8 |  |  | 20.2 |
Production tax credits | (31.1 | ) |  | (31.8 | ) |  | (33.1 | ) |  | (14.1 | ) |  | (14.0 | ) |  | (14.5 | ) |  | (17.0 | ) |  | (17.8 | ) |  | (18.6 | )
Investment tax credits | (1.1 | ) |  | (1.3 | ) |  | (1.4 | ) |  | (0.4 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.7 | ) |  | (0.8 | ) |  | (0.8 | )
|  | $66.7 |  |  |  | $59.4 |  |  |  | $70.4 |  |  |  | ($10.9 | ) |  |  | ($5.9 | ) |  |  | ($22.7 | ) |  |  | $61.9 |  |  |  | $93.3 |  |  |  | $82.9 |
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
| 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Statutory federal income tax rate | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | %
State income taxes, net of federal benefits | 5.5 |  |  | 5.4 |  |  | 5.2 |  |  | 6.5 |  |  | 6.4 |  |  | 6.2 |  |  | 5.1 |  |  | 5.1 |  |  | 5.1 |
Effect of rate-making on property-related differences | (8.5 | ) |  | (8.5 | ) |  | (6.8 | ) |  | (19.1 | ) |  | (16.2 | ) |  | (17.2 | ) |  | (1.7 | ) |  | (0.7 | ) |  | (0.5 | )
IPL’s tax benefit riders | (7.6 | ) |  | (10.0 | ) |  | (10.6 | ) |  | (18.7 | ) |  | (20.1 | ) |  | (28.3 | ) |  | — |  |  | — |  |  | — |
Production tax credits | (6.1 | ) |  | (7.2 | ) |  | (7.2 | ) |  | (6.7 | ) |  | (6.3 | ) |  | (8.3 | ) |  | (7.1 | ) |  | (6.2 | ) |  | (7.1 | )
Impact of Tax Reform | (3.4 | ) |  | — |  |  | — |  |  | 1.7 |  |  | — |  |  | — |  |  | (5.8 | ) |  | — |  |  | — |
Other items, net | (2.4 | ) |  | (1.3 | ) |  | (0.3 | ) |  | (3.7 | ) |  | (1.5 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.6 | ) |  | (0.7 | )
Overall income tax rate | 12.5 | % |  | 13.4 | % |  | 15.3 | % |  | (5.0 | %) |  | (2.7 | %) |  | (13.1 | %) |  | 24.9 | % |  | 32.6 | % |  | 31.8 | %
Schedule of Deferred Tax Assets and Liabilities | The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property |  | $1,852.7 |  |  |  | $2,919.0 |  |  |  | $1,102.6 |  |  |  | $1,677.0 |  |  |  | $674.2 |  |  |  | $1,124.5 |
ATC Investment | 86.4 |  |  | 153.1 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 75.9 |  |  | 95.1 |  |  | 63.4 |  |  | 71.4 |  |  | 36.5 |  |  | 58.8 |
Total deferred tax liabilities | 2,015.0 |  |  | 3,167.2 |  |  | 1,166.0 |  |  | 1,748.4 |  |  | 710.7 |  |  | 1,183.3 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 260.7 |  |  | 268.4 |  |  | 113.1 |  |  | 95.9 |  |  | 131.0 |  |  | 112.9 |
Net operating losses carryforwards - federal | 174.4 |  |  | 173.3 |  |  | 107.4 |  |  | 69.6 |  |  | 43.7 |  |  | 75.4 |
Regulatory liability - IPL’s tax benefit riders | 7.4 |  |  | 34.7 |  |  | 7.4 |  |  | 34.7 |  |  | — |  |  | — |
Net operating losses carryforwards - state | 41.3 |  |  | 32.9 |  |  | 0.9 |  |  | 0.6 |  |  | 0.2 |  |  | 0.1 |
Other | 61.8 |  |  | 87.9 |  |  | 27.1 |  |  | 35.8 |  |  | 14.7 |  |  | 23.6 |
Subtotal deferred tax assets | 545.6 |  |  | 597.2 |  |  | 255.9 |  |  | 236.6 |  |  | 189.6 |  |  | 212.0 |
Valuation allowance | (9.0 | ) |  | (0.2 | ) |  | (0.6 | ) |  | — |  |  | (1.3 | ) |  | (0.3 | )
Total deferred tax assets | 536.6 |  |  | 597.0 |  |  | 255.3 |  |  | 236.6 |  |  | 188.3 |  |  | 211.7 |
Total deferred tax liabilities, net |  | $1,478.4 |  |  |  | $2,570.2 |  |  |  | $910.7 |  |  |  | $1,511.8 |  |  |  | $522.4 |  |  |  | $971.6 |
Summary Of Tax Credit Carryforwards | At December 31, 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 |  |  | $852 |  |  |  | $537 |  |  |  | $208 |
State net operating losses | 2018-2037 |  | 700 |  |  | 13 |  |  | 2 |
Federal tax credits | 2022-2037 |  | 267 |  |  | 119 |  |  | 131 |
Schedule Of Open Tax Years | Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a) | 2014 | - | 2016
Consolidated Iowa income tax returns (b) | 2014 | - | 2016
Wisconsin combined tax returns (c) | 2013 | - | 2016
(a) | These federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.
(b) | The statute of limitations for these Iowa tax returns expires three years from each filing date.
(c) | The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.
WPL [Member] |
Income Tax [Line Items] |
Schedule Of Impacts Of the Tax Cuts And Jobs Act of 2017 | Alliant Energy, IPL and WPL have completed their assessment of the applicable provisions of Tax Reform, and the impacts to their 2017 balance sheets and income statements are as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Balance Sheet |  |  |  |  |
Other current assets |  | $— |  |  |  | $4.7 |  |  |  | ($1.4 | )
Investments: |  |  |  |  |
ATC Investment | (75.0 | ) |  | — |  |  | — |
Other assets: |  |  |  |  |
Regulatory assets | (387.6 | ) |  | (375.0 | ) |  | (12.7 | )
Deferred charges and other | 41.0 |  |  | — |  |  | — |
Total Tax Reform impact on assets |  | ($421.6 | ) |  |  | ($370.3 | ) |  |  | ($14.1 | )
Other liabilities: |  |  |  |  |
Deferred tax liabilities |  | ($1,331.9 | ) |  |  | ($757.2 | ) |  |  | ($523.8 | )
Regulatory liabilities | 885.9 |  |  | 390.7 |  |  | 495.2 |
Other | 6.3 |  |  | — |  |  | — |
Total Tax Reform impact on liabilities |  | ($439.7 | ) |  |  | ($366.5 | ) |  |  | ($28.6 | )
Income Statement |  |  |  |  |
Income tax expense (benefit) |  | ($18.1 | ) |  |  | $3.8 |  |  |  | ($14.5 | )
Schedule of Components of Income Tax Expense (Benefit) | The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal |  | ($41.0 | ) |  |  | $1.8 |  |  |  | $2.0 |  |  |  | ($27.9 | ) |  |  | ($12.8 | ) |  |  | ($14.1 | ) |  |  | $5.5 |  |  |  | ($22.3 | ) |  |  | $4.7 |
State | 8.5 |  |  | 17.2 |  |  | 3.2 |  |  | 1.6 |  |  | 15.5 |  |  | 11.5 |  |  | 2.5 |  |  | 1.1 |  |  | 0.6 |
IPL’s tax benefit riders | (40.4 | ) |  | (44.2 | ) |  | (49.0 | ) |  | (40.4 | ) |  | (44.2 | ) |  | (49.0 | ) |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 159.5 |  |  | 112.8 |  |  | 120.8 |  |  | 72.5 |  |  | 59.1 |  |  | 40.7 |  |  | 55.0 |  |  | 112.3 |  |  | 76.8 |
State | 12.3 |  |  | 4.9 |  |  | 27.9 |  |  | (2.2 | ) |  | (9.0 | ) |  | 3.3 |  |  | 16.6 |  |  | 20.8 |  |  | 20.2 |
Production tax credits | (31.1 | ) |  | (31.8 | ) |  | (33.1 | ) |  | (14.1 | ) |  | (14.0 | ) |  | (14.5 | ) |  | (17.0 | ) |  | (17.8 | ) |  | (18.6 | )
Investment tax credits | (1.1 | ) |  | (1.3 | ) |  | (1.4 | ) |  | (0.4 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.7 | ) |  | (0.8 | ) |  | (0.8 | )
|  | $66.7 |  |  |  | $59.4 |  |  |  | $70.4 |  |  |  | ($10.9 | ) |  |  | ($5.9 | ) |  |  | ($22.7 | ) |  |  | $61.9 |  |  |  | $93.3 |  |  |  | $82.9 |
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
| 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015 |  | 2017 |  | 2016 |  | 2015
Statutory federal income tax rate | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | % |  | 35.0 | %
State income taxes, net of federal benefits | 5.5 |  |  | 5.4 |  |  | 5.2 |  |  | 6.5 |  |  | 6.4 |  |  | 6.2 |  |  | 5.1 |  |  | 5.1 |  |  | 5.1 |
Effect of rate-making on property-related differences | (8.5 | ) |  | (8.5 | ) |  | (6.8 | ) |  | (19.1 | ) |  | (16.2 | ) |  | (17.2 | ) |  | (1.7 | ) |  | (0.7 | ) |  | (0.5 | )
IPL’s tax benefit riders | (7.6 | ) |  | (10.0 | ) |  | (10.6 | ) |  | (18.7 | ) |  | (20.1 | ) |  | (28.3 | ) |  | — |  |  | — |  |  | — |
Production tax credits | (6.1 | ) |  | (7.2 | ) |  | (7.2 | ) |  | (6.7 | ) |  | (6.3 | ) |  | (8.3 | ) |  | (7.1 | ) |  | (6.2 | ) |  | (7.1 | )
Impact of Tax Reform | (3.4 | ) |  | — |  |  | — |  |  | 1.7 |  |  | — |  |  | — |  |  | (5.8 | ) |  | — |  |  | — |
Other items, net | (2.4 | ) |  | (1.3 | ) |  | (0.3 | ) |  | (3.7 | ) |  | (1.5 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.6 | ) |  | (0.7 | )
Overall income tax rate | 12.5 | % |  | 13.4 | % |  | 15.3 | % |  | (5.0 | %) |  | (2.7 | %) |  | (13.1 | %) |  | 24.9 | % |  | 32.6 | % |  | 31.8 | %
Schedule of Deferred Tax Assets and Liabilities | The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2017 |  | 2016 |  | 2017 |  | 2016 |  | 2017 |  | 2016
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property |  | $1,852.7 |  |  |  | $2,919.0 |  |  |  | $1,102.6 |  |  |  | $1,677.0 |  |  |  | $674.2 |  |  |  | $1,124.5 |
ATC Investment | 86.4 |  |  | 153.1 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 75.9 |  |  | 95.1 |  |  | 63.4 |  |  | 71.4 |  |  | 36.5 |  |  | 58.8 |
Total deferred tax liabilities | 2,015.0 |  |  | 3,167.2 |  |  | 1,166.0 |  |  | 1,748.4 |  |  | 710.7 |  |  | 1,183.3 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 260.7 |  |  | 268.4 |  |  | 113.1 |  |  | 95.9 |  |  | 131.0 |  |  | 112.9 |
Net operating losses carryforwards - federal | 174.4 |  |  | 173.3 |  |  | 107.4 |  |  | 69.6 |  |  | 43.7 |  |  | 75.4 |
Regulatory liability - IPL’s tax benefit riders | 7.4 |  |  | 34.7 |  |  | 7.4 |  |  | 34.7 |  |  | — |  |  | — |
Net operating losses carryforwards - state | 41.3 |  |  | 32.9 |  |  | 0.9 |  |  | 0.6 |  |  | 0.2 |  |  | 0.1 |
Other | 61.8 |  |  | 87.9 |  |  | 27.1 |  |  | 35.8 |  |  | 14.7 |  |  | 23.6 |
Subtotal deferred tax assets | 545.6 |  |  | 597.2 |  |  | 255.9 |  |  | 236.6 |  |  | 189.6 |  |  | 212.0 |
Valuation allowance | (9.0 | ) |  | (0.2 | ) |  | (0.6 | ) |  | — |  |  | (1.3 | ) |  | (0.3 | )
Total deferred tax assets | 536.6 |  |  | 597.0 |  |  | 255.3 |  |  | 236.6 |  |  | 188.3 |  |  | 211.7 |
Total deferred tax liabilities, net |  | $1,478.4 |  |  |  | $2,570.2 |  |  |  | $910.7 |  |  |  | $1,511.8 |  |  |  | $522.4 |  |  |  | $971.6 |
Summary Of Tax Credit Carryforwards | At December 31, 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 |  |  | $852 |  |  |  | $537 |  |  |  | $208 |
State net operating losses | 2018-2037 |  | 700 |  |  | 13 |  |  | 2 |
Federal tax credits | 2022-2037 |  | 267 |  |  | 119 |  |  | 131 |
Schedule Of Open Tax Years | Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a) | 2014 | - | 2016
Consolidated Iowa income tax returns (b) | 2014 | - | 2016
Wisconsin combined tax returns (c) | 2013 | - | 2016
(a) | These federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.
(b) | The statute of limitations for these Iowa tax returns expires three years from each filing date.
(c) | The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.

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