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Income Taxes | 12 Months Ended
--- | ---
Dec. 31, 2018
Income Tax [Line Items] |
Income Taxes | INCOME TAXES Federal Tax Reform Adjustments - In December 2017, Federal Tax Reform was enacted, which had a material impact on Alliant Energy’s, IPL’s and WPL’s 2017 financial statements since changes in tax laws must be recognized in the period in which the law is enacted. The most significant provision of Federal Tax Reform that impact Alliant Energy, IPL and WPL was the reduction in the federal corporate tax rate from 35% to 21%. As a result of Federal Tax Reform, at December 31, 2017, Alliant Energy’s, IPL’s and WPL’s regulated utility operations recorded the net impacts from re-measuring deferred tax assets and liabilities as a change in regulatory liabilities or regulatory assets. Alliant Energy’s, IPL’s and WPL’s non-utility operations recorded the net change in deferred tax assets and liabilities to “Income tax expense (benefit)” in their respective income statement or as an increase to “Other liabilities” or decrease in “ATC Holdings” on Alliant Energy’s balance sheet. As a result of Federal Tax Reform, Alliant Energy, IPL and WPL recorded tax expense (benefits) in their 2017 income statements of ($18.1) million, $3.8 million, and ($14.5) million, respectively. In 2018, additional rules were issued related to Federal Tax Reform, including clarifications of the treatment of bonus depreciation deductions, which impacted the federal income tax return for the calendar year 2017. As result of these clarifying rules, Alliant Energy, IPL and WPL recorded tax benefits of $5.6 million, $1.1 million and $5.5 million, respectively, in 2018. Iowa Tax Reform - In May 2018, Iowa tax reform was enacted, resulting in a reduction in the Iowa income tax rate from 12% to 9.8%, effective January 1, 2021 and the elimination of the deduction for federal income taxes, effective January 1, 2022. Alliant Energy’s and IPL’s deferred tax assets and liabilities as of June 30, 2018 were remeasured based upon the new tax rate, and as a result, Alliant Energy’s and IPL’s tax-related regulatory assets decreased $33.7 million and tax-related regulatory liabilities increased $7.3 million in the second quarter of 2018. Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal |  | ($1.0 | ) |  |  | ($41.0 | ) |  |  | $1.8 |  |  |  | $14.9 |  |  |  | ($27.9 | ) |  |  | ($12.8 | ) |  |  | ($9.2 | ) |  |  | $5.5 |  |  |  | ($22.3 | )
State | (5.1 | ) |  | 8.5 |  |  | 17.2 |  |  | (7.1 | ) |  | 1.6 |  |  | 15.5 |  |  | (4.4 | ) |  | 2.5 |  |  | 1.1 |
IPL’s tax benefit riders | (13.2 | ) |  | (40.4 | ) |  | (44.2 | ) |  | (13.2 | ) |  | (40.4 | ) |  | (44.2 | ) |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 67.9 |  |  | 159.5 |  |  | 112.8 |  |  | 9.5 |  |  | 72.5 |  |  | 59.1 |  |  | 43.8 |  |  | 55.0 |  |  | 112.3 |
State | 29.8 |  |  | 12.3 |  |  | 4.9 |  |  | 7.3 |  |  | (2.2 | ) |  | (9.0 | ) |  | 22.1 |  |  | 16.6 |  |  | 20.8 |
Production tax credits | (29.5 | ) |  | (31.1 | ) |  | (31.8 | ) |  | (14.0 | ) |  | (14.1 | ) |  | (14.0 | ) |  | (15.5 | ) |  | (17.0 | ) |  | (17.8 | )
Investment tax credits | (1.2 | ) |  | (1.1 | ) |  | (1.3 | ) |  | (0.6 | ) |  | (0.4 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.7 | ) |  | (0.8 | )
|  | $47.7 |  |  |  | $66.7 |  |  |  | $59.4 |  |  |  | ($3.2 | ) |  |  | ($10.9 | ) |  |  | ($5.9 | ) |  |  | $36.2 |  |  |  | $61.9 |  |  |  | $93.3 |
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
| 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016
Statutory federal income tax rate | 21.0 | % |  | 35.0 | % |  | 35.0 | % |  | 21.0 | % |  | 35.0 | % |  | 35.0 | % |  | 21.0 | % |  | 35.0 | % |  | 35.0 | %
State income taxes, net of federal benefits | 7.0 |  |  | 5.5 |  |  | 5.4 |  |  | 7.7 |  |  | 6.5 |  |  | 6.4 |  |  | 6.2 |  |  | 5.1 |  |  | 5.1 |
Effect of rate-making on property-related differences | (7.6 | ) |  | (8.5 | ) |  | (8.5 | ) |  | (14.0 | ) |  | (19.1 | ) |  | (16.2 | ) |  | (2.3 | ) |  | (1.7 | ) |  | (0.7 | )
Production tax credits | (5.2 | ) |  | (6.1 | ) |  | (7.2 | ) |  | (5.2 | ) |  | (6.7 | ) |  | (6.3 | ) |  | (6.4 | ) |  | (7.1 | ) |  | (6.2 | )
IPL’s tax benefit riders | (2.3 | ) |  | (7.6 | ) |  | (10.0 | ) |  | (4.9 | ) |  | (18.7 | ) |  | (20.1 | ) |  | — |  |  | — |  |  | — |
Adjustment for prior period taxes | (2.3 | ) |  | (1.5 | ) |  | (0.8 | ) |  | (4.8 | ) |  | (3.4 | ) |  | (1.2 | ) |  | (0.2 | ) |  | — |  |  | (0.1 | )
Federal Tax Reform adjustments | (1.0 | ) |  | (3.4 | ) |  | — |  |  | (0.4 | ) |  | 1.7 |  |  | — |  |  | (2.3 | ) |  | (5.8 | ) |  | — |
Other items, net | (1.2 | ) |  | (0.9 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.3 | ) |  | (0.3 | ) |  | (1.2 | ) |  | (0.6 | ) |  | (0.5 | )
Overall income tax rate | 8.4 | % |  | 12.5 | % |  | 13.4 | % |  | (1.2 | %) |  | (5.0 | %) |  | (2.7 | %) |  | 14.8 | % |  | 24.9 | % |  | 32.6 | %
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
| 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property |  | $1,975.5 |  |  |  | $1,852.7 |  |  |  | $1,158.4 |  |  |  | $1,102.6 |  |  |  | $735.2 |  |  |  | $674.2 |
ATC Holdings | 102.4 |  |  | 86.4 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 80.5 |  |  | 75.9 |  |  | 69.4 |  |  | 63.4 |  |  | 34.4 |  |  | 36.5 |
Total deferred tax liabilities | 2,158.4 |  |  | 2,015.0 |  |  | 1,227.8 |  |  | 1,166.0 |  |  | 769.6 |  |  | 710.7 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 299.1 |  |  | 260.7 |  |  | 133.2 |  |  | 113.1 |  |  | 147.4 |  |  | 131.0 |
Net operating losses carryforwards - federal | 158.6 |  |  | 174.4 |  |  | 114.1 |  |  | 107.4 |  |  | 26.4 |  |  | 43.7 |
Net operating losses carryforwards - state | 47.0 |  |  | 41.3 |  |  | 0.9 |  |  | 0.9 |  |  | 0.5 |  |  | 0.2 |
Other | 59.8 |  |  | 69.2 |  |  | 22.8 |  |  | 34.5 |  |  | 14.1 |  |  | 14.7 |
Subtotal deferred tax assets | 564.5 |  |  | 545.6 |  |  | 271.0 |  |  | 255.9 |  |  | 188.4 |  |  | 189.6 |
Valuation allowances | (9.2 | ) |  | (9.0 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.8 | ) |  | (1.3 | )
Total deferred tax assets | 555.3 |  |  | 536.6 |  |  | 270.5 |  |  | 255.3 |  |  | 187.6 |  |  | 188.3 |
Total deferred tax liabilities, net |  | $1,603.1 |  |  |  | $1,478.4 |  |  |  | $957.3 |  |  |  | $910.7 |  |  |  | $582.0 |  |  |  | $522.4 |
Carryforwards - At December 31, 2018, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2031-2037 |  |  | $766 |  |  |  | $551 |  |  |  | $126 |
State net operating losses | 2018-2038 |  | 792 |  |  | 13 |  |  | 8 |
Federal tax credits | 2022-2038 |  | 299 |  |  | 133 |  |  | 147 |
Valuation Allowances - Due to the anticipated future reductions in revenues from utility customers due to Federal Tax Reform, Alliant Energy expects its Federal net operating losses carryforwards will not be fully utilized until 2024. Because taxable income must be reduced by net operating losses carryforwards prior to utilizing federal tax credit carryforwards, Alliant Energy currently does not expect to utilize 2002 and 2003 vintage federal credit carryforwards prior to their expiration in 2022 and 2023, respectively. As a result, Alliant Energy established valuation allowances for the 2002 and 2003 vintage federal credit carryforwards in 2017 that remain as of December 31, 2018. Uncertain Tax Positions - At December 31, 2018, 2017 and 2016, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2018, no material changes to unrecognized tax benefits are expected during the next 12 months. 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) | 2015 | - | 2017
Consolidated Iowa income tax returns (b) | 2015 | - | 2017
Wisconsin combined tax returns (c) | 2014 | - | 2017
(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] |
Income Taxes | INCOME TAXES Federal Tax Reform Adjustments - In December 2017, Federal Tax Reform was enacted, which had a material impact on Alliant Energy’s, IPL’s and WPL’s 2017 financial statements since changes in tax laws must be recognized in the period in which the law is enacted. The most significant provision of Federal Tax Reform that impact Alliant Energy, IPL and WPL was the reduction in the federal corporate tax rate from 35% to 21%. As a result of Federal Tax Reform, at December 31, 2017, Alliant Energy’s, IPL’s and WPL’s regulated utility operations recorded the net impacts from re-measuring deferred tax assets and liabilities as a change in regulatory liabilities or regulatory assets. Alliant Energy’s, IPL’s and WPL’s non-utility operations recorded the net change in deferred tax assets and liabilities to “Income tax expense (benefit)” in their respective income statement or as an increase to “Other liabilities” or decrease in “ATC Holdings” on Alliant Energy’s balance sheet. As a result of Federal Tax Reform, Alliant Energy, IPL and WPL recorded tax expense (benefits) in their 2017 income statements of ($18.1) million, $3.8 million, and ($14.5) million, respectively. In 2018, additional rules were issued related to Federal Tax Reform, including clarifications of the treatment of bonus depreciation deductions, which impacted the federal income tax return for the calendar year 2017. As result of these clarifying rules, Alliant Energy, IPL and WPL recorded tax benefits of $5.6 million, $1.1 million and $5.5 million, respectively, in 2018. Iowa Tax Reform - In May 2018, Iowa tax reform was enacted, resulting in a reduction in the Iowa income tax rate from 12% to 9.8%, effective January 1, 2021 and the elimination of the deduction for federal income taxes, effective January 1, 2022. Alliant Energy’s and IPL’s deferred tax assets and liabilities as of June 30, 2018 were remeasured based upon the new tax rate, and as a result, Alliant Energy’s and IPL’s tax-related regulatory assets decreased $33.7 million and tax-related regulatory liabilities increased $7.3 million in the second quarter of 2018. Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal |  | ($1.0 | ) |  |  | ($41.0 | ) |  |  | $1.8 |  |  |  | $14.9 |  |  |  | ($27.9 | ) |  |  | ($12.8 | ) |  |  | ($9.2 | ) |  |  | $5.5 |  |  |  | ($22.3 | )
State | (5.1 | ) |  | 8.5 |  |  | 17.2 |  |  | (7.1 | ) |  | 1.6 |  |  | 15.5 |  |  | (4.4 | ) |  | 2.5 |  |  | 1.1 |
IPL’s tax benefit riders | (13.2 | ) |  | (40.4 | ) |  | (44.2 | ) |  | (13.2 | ) |  | (40.4 | ) |  | (44.2 | ) |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 67.9 |  |  | 159.5 |  |  | 112.8 |  |  | 9.5 |  |  | 72.5 |  |  | 59.1 |  |  | 43.8 |  |  | 55.0 |  |  | 112.3 |
State | 29.8 |  |  | 12.3 |  |  | 4.9 |  |  | 7.3 |  |  | (2.2 | ) |  | (9.0 | ) |  | 22.1 |  |  | 16.6 |  |  | 20.8 |
Production tax credits | (29.5 | ) |  | (31.1 | ) |  | (31.8 | ) |  | (14.0 | ) |  | (14.1 | ) |  | (14.0 | ) |  | (15.5 | ) |  | (17.0 | ) |  | (17.8 | )
Investment tax credits | (1.2 | ) |  | (1.1 | ) |  | (1.3 | ) |  | (0.6 | ) |  | (0.4 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.7 | ) |  | (0.8 | )
|  | $47.7 |  |  |  | $66.7 |  |  |  | $59.4 |  |  |  | ($3.2 | ) |  |  | ($10.9 | ) |  |  | ($5.9 | ) |  |  | $36.2 |  |  |  | $61.9 |  |  |  | $93.3 |
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
| 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016
Statutory federal income tax rate | 21.0 | % |  | 35.0 | % |  | 35.0 | % |  | 21.0 | % |  | 35.0 | % |  | 35.0 | % |  | 21.0 | % |  | 35.0 | % |  | 35.0 | %
State income taxes, net of federal benefits | 7.0 |  |  | 5.5 |  |  | 5.4 |  |  | 7.7 |  |  | 6.5 |  |  | 6.4 |  |  | 6.2 |  |  | 5.1 |  |  | 5.1 |
Effect of rate-making on property-related differences | (7.6 | ) |  | (8.5 | ) |  | (8.5 | ) |  | (14.0 | ) |  | (19.1 | ) |  | (16.2 | ) |  | (2.3 | ) |  | (1.7 | ) |  | (0.7 | )
Production tax credits | (5.2 | ) |  | (6.1 | ) |  | (7.2 | ) |  | (5.2 | ) |  | (6.7 | ) |  | (6.3 | ) |  | (6.4 | ) |  | (7.1 | ) |  | (6.2 | )
IPL’s tax benefit riders | (2.3 | ) |  | (7.6 | ) |  | (10.0 | ) |  | (4.9 | ) |  | (18.7 | ) |  | (20.1 | ) |  | — |  |  | — |  |  | — |
Adjustment for prior period taxes | (2.3 | ) |  | (1.5 | ) |  | (0.8 | ) |  | (4.8 | ) |  | (3.4 | ) |  | (1.2 | ) |  | (0.2 | ) |  | — |  |  | (0.1 | )
Federal Tax Reform adjustments | (1.0 | ) |  | (3.4 | ) |  | — |  |  | (0.4 | ) |  | 1.7 |  |  | — |  |  | (2.3 | ) |  | (5.8 | ) |  | — |
Other items, net | (1.2 | ) |  | (0.9 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.3 | ) |  | (0.3 | ) |  | (1.2 | ) |  | (0.6 | ) |  | (0.5 | )
Overall income tax rate | 8.4 | % |  | 12.5 | % |  | 13.4 | % |  | (1.2 | %) |  | (5.0 | %) |  | (2.7 | %) |  | 14.8 | % |  | 24.9 | % |  | 32.6 | %
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
| 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property |  | $1,975.5 |  |  |  | $1,852.7 |  |  |  | $1,158.4 |  |  |  | $1,102.6 |  |  |  | $735.2 |  |  |  | $674.2 |
ATC Holdings | 102.4 |  |  | 86.4 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 80.5 |  |  | 75.9 |  |  | 69.4 |  |  | 63.4 |  |  | 34.4 |  |  | 36.5 |
Total deferred tax liabilities | 2,158.4 |  |  | 2,015.0 |  |  | 1,227.8 |  |  | 1,166.0 |  |  | 769.6 |  |  | 710.7 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 299.1 |  |  | 260.7 |  |  | 133.2 |  |  | 113.1 |  |  | 147.4 |  |  | 131.0 |
Net operating losses carryforwards - federal | 158.6 |  |  | 174.4 |  |  | 114.1 |  |  | 107.4 |  |  | 26.4 |  |  | 43.7 |
Net operating losses carryforwards - state | 47.0 |  |  | 41.3 |  |  | 0.9 |  |  | 0.9 |  |  | 0.5 |  |  | 0.2 |
Other | 59.8 |  |  | 69.2 |  |  | 22.8 |  |  | 34.5 |  |  | 14.1 |  |  | 14.7 |
Subtotal deferred tax assets | 564.5 |  |  | 545.6 |  |  | 271.0 |  |  | 255.9 |  |  | 188.4 |  |  | 189.6 |
Valuation allowances | (9.2 | ) |  | (9.0 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.8 | ) |  | (1.3 | )
Total deferred tax assets | 555.3 |  |  | 536.6 |  |  | 270.5 |  |  | 255.3 |  |  | 187.6 |  |  | 188.3 |
Total deferred tax liabilities, net |  | $1,603.1 |  |  |  | $1,478.4 |  |  |  | $957.3 |  |  |  | $910.7 |  |  |  | $582.0 |  |  |  | $522.4 |
Carryforwards - At December 31, 2018, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2031-2037 |  |  | $766 |  |  |  | $551 |  |  |  | $126 |
State net operating losses | 2018-2038 |  | 792 |  |  | 13 |  |  | 8 |
Federal tax credits | 2022-2038 |  | 299 |  |  | 133 |  |  | 147 |
Valuation Allowances - Due to the anticipated future reductions in revenues from utility customers due to Federal Tax Reform, Alliant Energy expects its Federal net operating losses carryforwards will not be fully utilized until 2024. Because taxable income must be reduced by net operating losses carryforwards prior to utilizing federal tax credit carryforwards, Alliant Energy currently does not expect to utilize 2002 and 2003 vintage federal credit carryforwards prior to their expiration in 2022 and 2023, respectively. As a result, Alliant Energy established valuation allowances for the 2002 and 2003 vintage federal credit carryforwards in 2017 that remain as of December 31, 2018. Uncertain Tax Positions - At December 31, 2018, 2017 and 2016, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2018, no material changes to unrecognized tax benefits are expected during the next 12 months. 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) | 2015 | - | 2017
Consolidated Iowa income tax returns (b) | 2015 | - | 2017
Wisconsin combined tax returns (c) | 2014 | - | 2017
(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] |
Income Taxes | INCOME TAXES Federal Tax Reform Adjustments - In December 2017, Federal Tax Reform was enacted, which had a material impact on Alliant Energy’s, IPL’s and WPL’s 2017 financial statements since changes in tax laws must be recognized in the period in which the law is enacted. The most significant provision of Federal Tax Reform that impact Alliant Energy, IPL and WPL was the reduction in the federal corporate tax rate from 35% to 21%. As a result of Federal Tax Reform, at December 31, 2017, Alliant Energy’s, IPL’s and WPL’s regulated utility operations recorded the net impacts from re-measuring deferred tax assets and liabilities as a change in regulatory liabilities or regulatory assets. Alliant Energy’s, IPL’s and WPL’s non-utility operations recorded the net change in deferred tax assets and liabilities to “Income tax expense (benefit)” in their respective income statement or as an increase to “Other liabilities” or decrease in “ATC Holdings” on Alliant Energy’s balance sheet. As a result of Federal Tax Reform, Alliant Energy, IPL and WPL recorded tax expense (benefits) in their 2017 income statements of ($18.1) million, $3.8 million, and ($14.5) million, respectively. In 2018, additional rules were issued related to Federal Tax Reform, including clarifications of the treatment of bonus depreciation deductions, which impacted the federal income tax return for the calendar year 2017. As result of these clarifying rules, Alliant Energy, IPL and WPL recorded tax benefits of $5.6 million, $1.1 million and $5.5 million, respectively, in 2018. Iowa Tax Reform - In May 2018, Iowa tax reform was enacted, resulting in a reduction in the Iowa income tax rate from 12% to 9.8%, effective January 1, 2021 and the elimination of the deduction for federal income taxes, effective January 1, 2022. Alliant Energy’s and IPL’s deferred tax assets and liabilities as of June 30, 2018 were remeasured based upon the new tax rate, and as a result, Alliant Energy’s and IPL’s tax-related regulatory assets decreased $33.7 million and tax-related regulatory liabilities increased $7.3 million in the second quarter of 2018. Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal |  | ($1.0 | ) |  |  | ($41.0 | ) |  |  | $1.8 |  |  |  | $14.9 |  |  |  | ($27.9 | ) |  |  | ($12.8 | ) |  |  | ($9.2 | ) |  |  | $5.5 |  |  |  | ($22.3 | )
State | (5.1 | ) |  | 8.5 |  |  | 17.2 |  |  | (7.1 | ) |  | 1.6 |  |  | 15.5 |  |  | (4.4 | ) |  | 2.5 |  |  | 1.1 |
IPL’s tax benefit riders | (13.2 | ) |  | (40.4 | ) |  | (44.2 | ) |  | (13.2 | ) |  | (40.4 | ) |  | (44.2 | ) |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 67.9 |  |  | 159.5 |  |  | 112.8 |  |  | 9.5 |  |  | 72.5 |  |  | 59.1 |  |  | 43.8 |  |  | 55.0 |  |  | 112.3 |
State | 29.8 |  |  | 12.3 |  |  | 4.9 |  |  | 7.3 |  |  | (2.2 | ) |  | (9.0 | ) |  | 22.1 |  |  | 16.6 |  |  | 20.8 |
Production tax credits | (29.5 | ) |  | (31.1 | ) |  | (31.8 | ) |  | (14.0 | ) |  | (14.1 | ) |  | (14.0 | ) |  | (15.5 | ) |  | (17.0 | ) |  | (17.8 | )
Investment tax credits | (1.2 | ) |  | (1.1 | ) |  | (1.3 | ) |  | (0.6 | ) |  | (0.4 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.7 | ) |  | (0.8 | )
|  | $47.7 |  |  |  | $66.7 |  |  |  | $59.4 |  |  |  | ($3.2 | ) |  |  | ($10.9 | ) |  |  | ($5.9 | ) |  |  | $36.2 |  |  |  | $61.9 |  |  |  | $93.3 |
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
| 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016 |  | 2018 |  | 2017 |  | 2016
Statutory federal income tax rate | 21.0 | % |  | 35.0 | % |  | 35.0 | % |  | 21.0 | % |  | 35.0 | % |  | 35.0 | % |  | 21.0 | % |  | 35.0 | % |  | 35.0 | %
State income taxes, net of federal benefits | 7.0 |  |  | 5.5 |  |  | 5.4 |  |  | 7.7 |  |  | 6.5 |  |  | 6.4 |  |  | 6.2 |  |  | 5.1 |  |  | 5.1 |
Effect of rate-making on property-related differences | (7.6 | ) |  | (8.5 | ) |  | (8.5 | ) |  | (14.0 | ) |  | (19.1 | ) |  | (16.2 | ) |  | (2.3 | ) |  | (1.7 | ) |  | (0.7 | )
Production tax credits | (5.2 | ) |  | (6.1 | ) |  | (7.2 | ) |  | (5.2 | ) |  | (6.7 | ) |  | (6.3 | ) |  | (6.4 | ) |  | (7.1 | ) |  | (6.2 | )
IPL’s tax benefit riders | (2.3 | ) |  | (7.6 | ) |  | (10.0 | ) |  | (4.9 | ) |  | (18.7 | ) |  | (20.1 | ) |  | — |  |  | — |  |  | — |
Adjustment for prior period taxes | (2.3 | ) |  | (1.5 | ) |  | (0.8 | ) |  | (4.8 | ) |  | (3.4 | ) |  | (1.2 | ) |  | (0.2 | ) |  | — |  |  | (0.1 | )
Federal Tax Reform adjustments | (1.0 | ) |  | (3.4 | ) |  | — |  |  | (0.4 | ) |  | 1.7 |  |  | — |  |  | (2.3 | ) |  | (5.8 | ) |  | — |
Other items, net | (1.2 | ) |  | (0.9 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.3 | ) |  | (0.3 | ) |  | (1.2 | ) |  | (0.6 | ) |  | (0.5 | )
Overall income tax rate | 8.4 | % |  | 12.5 | % |  | 13.4 | % |  | (1.2 | %) |  | (5.0 | %) |  | (2.7 | %) |  | 14.8 | % |  | 24.9 | % |  | 32.6 | %
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
| 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property |  | $1,975.5 |  |  |  | $1,852.7 |  |  |  | $1,158.4 |  |  |  | $1,102.6 |  |  |  | $735.2 |  |  |  | $674.2 |
ATC Holdings | 102.4 |  |  | 86.4 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 80.5 |  |  | 75.9 |  |  | 69.4 |  |  | 63.4 |  |  | 34.4 |  |  | 36.5 |
Total deferred tax liabilities | 2,158.4 |  |  | 2,015.0 |  |  | 1,227.8 |  |  | 1,166.0 |  |  | 769.6 |  |  | 710.7 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 299.1 |  |  | 260.7 |  |  | 133.2 |  |  | 113.1 |  |  | 147.4 |  |  | 131.0 |
Net operating losses carryforwards - federal | 158.6 |  |  | 174.4 |  |  | 114.1 |  |  | 107.4 |  |  | 26.4 |  |  | 43.7 |
Net operating losses carryforwards - state | 47.0 |  |  | 41.3 |  |  | 0.9 |  |  | 0.9 |  |  | 0.5 |  |  | 0.2 |
Other | 59.8 |  |  | 69.2 |  |  | 22.8 |  |  | 34.5 |  |  | 14.1 |  |  | 14.7 |
Subtotal deferred tax assets | 564.5 |  |  | 545.6 |  |  | 271.0 |  |  | 255.9 |  |  | 188.4 |  |  | 189.6 |
Valuation allowances | (9.2 | ) |  | (9.0 | ) |  | (0.5 | ) |  | (0.6 | ) |  | (0.8 | ) |  | (1.3 | )
Total deferred tax assets | 555.3 |  |  | 536.6 |  |  | 270.5 |  |  | 255.3 |  |  | 187.6 |  |  | 188.3 |
Total deferred tax liabilities, net |  | $1,603.1 |  |  |  | $1,478.4 |  |  |  | $957.3 |  |  |  | $910.7 |  |  |  | $582.0 |  |  |  | $522.4 |
Carryforwards - At December 31, 2018, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2031-2037 |  |  | $766 |  |  |  | $551 |  |  |  | $126 |
State net operating losses | 2018-2038 |  | 792 |  |  | 13 |  |  | 8 |
Federal tax credits | 2022-2038 |  | 299 |  |  | 133 |  |  | 147 |
Valuation Allowances - Due to the anticipated future reductions in revenues from utility customers due to Federal Tax Reform, Alliant Energy expects its Federal net operating losses carryforwards will not be fully utilized until 2024. Because taxable income must be reduced by net operating losses carryforwards prior to utilizing federal tax credit carryforwards, Alliant Energy currently does not expect to utilize 2002 and 2003 vintage federal credit carryforwards prior to their expiration in 2022 and 2023, respectively. As a result, Alliant Energy established valuation allowances for the 2002 and 2003 vintage federal credit carryforwards in 2017 that remain as of December 31, 2018. Uncertain Tax Positions - At December 31, 2018, 2017 and 2016, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2018, no material changes to unrecognized tax benefits are expected during the next 12 months. 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) | 2015 | - | 2017
Consolidated Iowa income tax returns (b) | 2015 | - | 2017
Wisconsin combined tax returns (c) | 2014 | - | 2017
(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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- 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 740 -URI http://asc.fasb.org/topic&trid=2144680 + Details
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