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Income Taxes | 12 Months Ended
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Dec. 31, 2017
Income Tax [Line Items] |
Income Taxes | INCOME TAXES Tax Reform - In December 2017, Tax Reform was enacted. Substantially all of the provisions of Tax Reform are effective for taxable years beginning after December 31, 2017. The most significant provisions of Tax Reform that impact Alliant Energy, IPL and WPL were the reduction in the federal corporate tax rate from 35% to 21%, the repeal of the federal corporate alternative minimum tax (AMT), and the elimination of bonus depreciation deductions on utility property placed in service after September 27, 2017 unless a binding contract existed as of that date. The enactment of Tax Reform in December 2017 had a material impact on Alliant Energy’s, IPL’s and WPL’s 2017 financial statements as the tax effects of the changes in tax laws must be recognized in the period in which the law is enacted. 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 | )
Deferred Tax Liabilities - Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the enactment of Tax Reform in December 2017, Alliant Energy’s, IPL’s and WPL’s deferred tax assets and liabilities at December 31, 2017 were re-measured based upon the new corporate tax rate. Alliant Energy’s utility operations in IPL and WPL recorded the net changes from re-measuring deferred tax assets and liabilities as a change in regulatory liabilities or regulatory assets as described in further detail below. 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 Investment” on Alliant Energy’s balance sheet. Regulatory Assets and Regulatory Liabilities - Tax Reform requires regulated utilities to account for certain changes in deferred taxes related to accelerated depreciation and net operating losses using a normalization method of accounting. This method of accounting requires regulated utilities to record the normalized changes in deferred tax liabilities and assets to a regulatory liability or regulatory asset. For other changes to regulatory assets and regulatory liabilities resulting from Tax Reform, IPL and WPL are awaiting decisions from the IUB, PCSW and FERC to determine the appropriate regulatory treatment. IPL and WPL have recorded the offset to the changes in utility deferred tax liabilities and assets in a regulatory liability or regulatory asset to be reflected in future customer billings. Future changes may occur based on decisions received from the IUB, PSCW and FERC. In January 2018, the IUB issued an order initiating investigation of the impacts of Tax Reform. The order requires IPL to track all calculated differences since January 1, 2018 resulting from Tax Reform, such that any over-collections can be refunded to its customers at a future date, if appropriate. In January 2018, the PSCW issued an order directing WPL to defer and to accrue carrying costs on the revenue requirement impacts resulting from Tax Reform since its inception. ATC Investment - Tax Reform required a re-measurement of deferred tax assets and liabilities associated with Alliant Energy’s ATC Investment. These deferred tax assets and liabilities have been utilized to determine the amount of costs billed by ATC to its customers. Due to the regulated nature of ATC and FERC policy on income tax allowances, Alliant Energy expects the changes in deferred taxes that have been collected in ATC’s customers’ rates to be returned to such customers over the regulatory life of ATC’s assets. As a result, Alliant Energy has reduced the deferred tax liabilities associated with the ATC Investment and recorded the offset to “ATC Investment” on its balance sheet. Starting in 2018, the adjustment as a result of the change in deferred taxes will be amortized as a reduction in deferred tax expense over the remaining life of ATC’s assets. Deferred Charges and Other - Tax Reform repealed corporate federal AMT and allows unutilized AMT credits to be refunded over the next four tax years beginning with the U.S. federal tax return for calendar year 2018. As a result of these changes, Alliant Energy reclassified $41 million of unutilized AMT credits from a deferred tax asset into a long-term tax receivable in 2017 in anticipation of future refunds of such tax credits. The long-term tax receivable is included in “Deferred charges and other” on Alliant Energy’s balance sheet. Income Tax Expense (Benefit) -The changes in deferred taxes for Alliant Energy’s, IPL’s and WPL’s non-utility operations were primarily recorded in the income statements. In addition, Alliant Energy recognized valuation allowances for certain tax credit carryforwards as a result of Tax Reform that are discussed in more detail below. 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 |
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 | %
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 |
The decreases in deferred tax liabilities were primarily due to the reduction in the federal corporate tax rate from 35% to 21% as a result of Tax Reform, as discussed above. Property - The decrease in property-related deferred tax liabilities from Tax Reform was partially offset by bonus depreciation deductions from property placed in service in 2017, including IPL’s Marshalltown Generating Station. Alliant Energy currently estimates its total bonus depreciation deductions to be claimed on its U.S. federal income tax return for calendar year 2017 will be approximately $670 million ($500 million for IPL and $140 million for WPL). Carryforwards - The decrease in Alliant Energy’s federal credit carryforwards was due to the reclassification of AMT credits to a long-term tax receivable as a result of Tax Reform, partially offset by production tax credits generated in 2017. The increase in Alliant Energy’s and IPL’s federal net operating losses carryforwards was primarily due to bonus depreciation deductions for property placed in service in 2017, including IPL’s Marshalltown Generating Station, largely offset by the impacts of Tax Reform. 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 |
Valuation Allowances - Due to the anticipated future reductions in revenues from utility customers due to Tax Reform, Alliant Energy expects a reduction in its future consolidated taxable income, which will extend the period to which prior unutilized operating losses will be utilized. Taxable income must be reduced by net operating losses carryforwards prior to utilizing federal tax credit carryforwards. Alliant Energy expects to utilize its net operating losses carryforwards by 2024 and therefore, currently does not expect to utilize 2002 and 2003 vintage federal credit carryforwards prior to their expiration in 2022 and 2023, respectively. This has resulted in valuation allowance charges recorded to “Income tax expense (benefit)” on the income statements as noted in the table above. Uncertain Tax Positions - At December 31, 2017, 2016 and 2015, there were no uncertain tax positions or penalties accrued related to uncertain tax positions, and interest accrued and tax positions favorably impacting future effective tax rates for continuing operations were not material. As of December 31, 2017, 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) | 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] |
Income Taxes | INCOME TAXES Tax Reform - In December 2017, Tax Reform was enacted. Substantially all of the provisions of Tax Reform are effective for taxable years beginning after December 31, 2017. The most significant provisions of Tax Reform that impact Alliant Energy, IPL and WPL were the reduction in the federal corporate tax rate from 35% to 21%, the repeal of the federal corporate alternative minimum tax (AMT), and the elimination of bonus depreciation deductions on utility property placed in service after September 27, 2017 unless a binding contract existed as of that date. The enactment of Tax Reform in December 2017 had a material impact on Alliant Energy’s, IPL’s and WPL’s 2017 financial statements as the tax effects of the changes in tax laws must be recognized in the period in which the law is enacted. 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 | )
Deferred Tax Liabilities - Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the enactment of Tax Reform in December 2017, Alliant Energy’s, IPL’s and WPL’s deferred tax assets and liabilities at December 31, 2017 were re-measured based upon the new corporate tax rate. Alliant Energy’s utility operations in IPL and WPL recorded the net changes from re-measuring deferred tax assets and liabilities as a change in regulatory liabilities or regulatory assets as described in further detail below. 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 Investment” on Alliant Energy’s balance sheet. Regulatory Assets and Regulatory Liabilities - Tax Reform requires regulated utilities to account for certain changes in deferred taxes related to accelerated depreciation and net operating losses using a normalization method of accounting. This method of accounting requires regulated utilities to record the normalized changes in deferred tax liabilities and assets to a regulatory liability or regulatory asset. For other changes to regulatory assets and regulatory liabilities resulting from Tax Reform, IPL and WPL are awaiting decisions from the IUB, PCSW and FERC to determine the appropriate regulatory treatment. IPL and WPL have recorded the offset to the changes in utility deferred tax liabilities and assets in a regulatory liability or regulatory asset to be reflected in future customer billings. Future changes may occur based on decisions received from the IUB, PSCW and FERC. In January 2018, the IUB issued an order initiating investigation of the impacts of Tax Reform. The order requires IPL to track all calculated differences since January 1, 2018 resulting from Tax Reform, such that any over-collections can be refunded to its customers at a future date, if appropriate. In January 2018, the PSCW issued an order directing WPL to defer and to accrue carrying costs on the revenue requirement impacts resulting from Tax Reform since its inception. ATC Investment - Tax Reform required a re-measurement of deferred tax assets and liabilities associated with Alliant Energy’s ATC Investment. These deferred tax assets and liabilities have been utilized to determine the amount of costs billed by ATC to its customers. Due to the regulated nature of ATC and FERC policy on income tax allowances, Alliant Energy expects the changes in deferred taxes that have been collected in ATC’s customers’ rates to be returned to such customers over the regulatory life of ATC’s assets. As a result, Alliant Energy has reduced the deferred tax liabilities associated with the ATC Investment and recorded the offset to “ATC Investment” on its balance sheet. Starting in 2018, the adjustment as a result of the change in deferred taxes will be amortized as a reduction in deferred tax expense over the remaining life of ATC’s assets. Deferred Charges and Other - Tax Reform repealed corporate federal AMT and allows unutilized AMT credits to be refunded over the next four tax years beginning with the U.S. federal tax return for calendar year 2018. As a result of these changes, Alliant Energy reclassified $41 million of unutilized AMT credits from a deferred tax asset into a long-term tax receivable in 2017 in anticipation of future refunds of such tax credits. The long-term tax receivable is included in “Deferred charges and other” on Alliant Energy’s balance sheet. Income Tax Expense (Benefit) -The changes in deferred taxes for Alliant Energy’s, IPL’s and WPL’s non-utility operations were primarily recorded in the income statements. In addition, Alliant Energy recognized valuation allowances for certain tax credit carryforwards as a result of Tax Reform that are discussed in more detail below. 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 |
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 | %
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 |
The decreases in deferred tax liabilities were primarily due to the reduction in the federal corporate tax rate from 35% to 21% as a result of Tax Reform, as discussed above. Property - The decrease in property-related deferred tax liabilities from Tax Reform was partially offset by bonus depreciation deductions from property placed in service in 2017, including IPL’s Marshalltown Generating Station. Alliant Energy currently estimates its total bonus depreciation deductions to be claimed on its U.S. federal income tax return for calendar year 2017 will be approximately $670 million ($500 million for IPL and $140 million for WPL). Carryforwards - The decrease in Alliant Energy’s federal credit carryforwards was due to the reclassification of AMT credits to a long-term tax receivable as a result of Tax Reform, partially offset by production tax credits generated in 2017. The increase in Alliant Energy’s and IPL’s federal net operating losses carryforwards was primarily due to bonus depreciation deductions for property placed in service in 2017, including IPL’s Marshalltown Generating Station, largely offset by the impacts of Tax Reform. 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 |
Valuation Allowances - Due to the anticipated future reductions in revenues from utility customers due to Tax Reform, Alliant Energy expects a reduction in its future consolidated taxable income, which will extend the period to which prior unutilized operating losses will be utilized. Taxable income must be reduced by net operating losses carryforwards prior to utilizing federal tax credit carryforwards. Alliant Energy expects to utilize its net operating losses carryforwards by 2024 and therefore, currently does not expect to utilize 2002 and 2003 vintage federal credit carryforwards prior to their expiration in 2022 and 2023, respectively. This has resulted in valuation allowance charges recorded to “Income tax expense (benefit)” on the income statements as noted in the table above. Uncertain Tax Positions - At December 31, 2017, 2016 and 2015, there were no uncertain tax positions or penalties accrued related to uncertain tax positions, and interest accrued and tax positions favorably impacting future effective tax rates for continuing operations were not material. As of December 31, 2017, 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) | 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] |
Income Taxes | INCOME TAXES Tax Reform - In December 2017, Tax Reform was enacted. Substantially all of the provisions of Tax Reform are effective for taxable years beginning after December 31, 2017. The most significant provisions of Tax Reform that impact Alliant Energy, IPL and WPL were the reduction in the federal corporate tax rate from 35% to 21%, the repeal of the federal corporate alternative minimum tax (AMT), and the elimination of bonus depreciation deductions on utility property placed in service after September 27, 2017 unless a binding contract existed as of that date. The enactment of Tax Reform in December 2017 had a material impact on Alliant Energy’s, IPL’s and WPL’s 2017 financial statements as the tax effects of the changes in tax laws must be recognized in the period in which the law is enacted. 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 | )
Deferred Tax Liabilities - Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the enactment of Tax Reform in December 2017, Alliant Energy’s, IPL’s and WPL’s deferred tax assets and liabilities at December 31, 2017 were re-measured based upon the new corporate tax rate. Alliant Energy’s utility operations in IPL and WPL recorded the net changes from re-measuring deferred tax assets and liabilities as a change in regulatory liabilities or regulatory assets as described in further detail below. 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 Investment” on Alliant Energy’s balance sheet. Regulatory Assets and Regulatory Liabilities - Tax Reform requires regulated utilities to account for certain changes in deferred taxes related to accelerated depreciation and net operating losses using a normalization method of accounting. This method of accounting requires regulated utilities to record the normalized changes in deferred tax liabilities and assets to a regulatory liability or regulatory asset. For other changes to regulatory assets and regulatory liabilities resulting from Tax Reform, IPL and WPL are awaiting decisions from the IUB, PCSW and FERC to determine the appropriate regulatory treatment. IPL and WPL have recorded the offset to the changes in utility deferred tax liabilities and assets in a regulatory liability or regulatory asset to be reflected in future customer billings. Future changes may occur based on decisions received from the IUB, PSCW and FERC. In January 2018, the IUB issued an order initiating investigation of the impacts of Tax Reform. The order requires IPL to track all calculated differences since January 1, 2018 resulting from Tax Reform, such that any over-collections can be refunded to its customers at a future date, if appropriate. In January 2018, the PSCW issued an order directing WPL to defer and to accrue carrying costs on the revenue requirement impacts resulting from Tax Reform since its inception. ATC Investment - Tax Reform required a re-measurement of deferred tax assets and liabilities associated with Alliant Energy’s ATC Investment. These deferred tax assets and liabilities have been utilized to determine the amount of costs billed by ATC to its customers. Due to the regulated nature of ATC and FERC policy on income tax allowances, Alliant Energy expects the changes in deferred taxes that have been collected in ATC’s customers’ rates to be returned to such customers over the regulatory life of ATC’s assets. As a result, Alliant Energy has reduced the deferred tax liabilities associated with the ATC Investment and recorded the offset to “ATC Investment” on its balance sheet. Starting in 2018, the adjustment as a result of the change in deferred taxes will be amortized as a reduction in deferred tax expense over the remaining life of ATC’s assets. Deferred Charges and Other - Tax Reform repealed corporate federal AMT and allows unutilized AMT credits to be refunded over the next four tax years beginning with the U.S. federal tax return for calendar year 2018. As a result of these changes, Alliant Energy reclassified $41 million of unutilized AMT credits from a deferred tax asset into a long-term tax receivable in 2017 in anticipation of future refunds of such tax credits. The long-term tax receivable is included in “Deferred charges and other” on Alliant Energy’s balance sheet. Income Tax Expense (Benefit) -The changes in deferred taxes for Alliant Energy’s, IPL’s and WPL’s non-utility operations were primarily recorded in the income statements. In addition, Alliant Energy recognized valuation allowances for certain tax credit carryforwards as a result of Tax Reform that are discussed in more detail below. 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 |
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 | %
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 |
The decreases in deferred tax liabilities were primarily due to the reduction in the federal corporate tax rate from 35% to 21% as a result of Tax Reform, as discussed above. Property - The decrease in property-related deferred tax liabilities from Tax Reform was partially offset by bonus depreciation deductions from property placed in service in 2017, including IPL’s Marshalltown Generating Station. Alliant Energy currently estimates its total bonus depreciation deductions to be claimed on its U.S. federal income tax return for calendar year 2017 will be approximately $670 million ($500 million for IPL and $140 million for WPL). Carryforwards - The decrease in Alliant Energy’s federal credit carryforwards was due to the reclassification of AMT credits to a long-term tax receivable as a result of Tax Reform, partially offset by production tax credits generated in 2017. The increase in Alliant Energy’s and IPL’s federal net operating losses carryforwards was primarily due to bonus depreciation deductions for property placed in service in 2017, including IPL’s Marshalltown Generating Station, largely offset by the impacts of Tax Reform. 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 |
Valuation Allowances - Due to the anticipated future reductions in revenues from utility customers due to Tax Reform, Alliant Energy expects a reduction in its future consolidated taxable income, which will extend the period to which prior unutilized operating losses will be utilized. Taxable income must be reduced by net operating losses carryforwards prior to utilizing federal tax credit carryforwards. Alliant Energy expects to utilize its net operating losses carryforwards by 2024 and therefore, currently does not expect to utilize 2002 and 2003 vintage federal credit carryforwards prior to their expiration in 2022 and 2023, respectively. This has resulted in valuation allowance charges recorded to “Income tax expense (benefit)” on the income statements as noted in the table above. Uncertain Tax Positions - At December 31, 2017, 2016 and 2015, there were no uncertain tax positions or penalties accrued related to uncertain tax positions, and interest accrued and tax positions favorably impacting future effective tax rates for continuing operations were not material. As of December 31, 2017, 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) | 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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