XML 136 R18.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Income Taxes | 12 Months Ended
--- | ---
Dec. 31, 2014
Income Tax [Line Items] |
Income Taxes | INCOME TAXES Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal |  | $36.6 |  |  |  | $4.4 |  |  |  | ($29.3 | ) |  |  | $11.3 |  |  |  | $11.7 |  |  |  | ($7.7 | ) |  |  | $0.6 |  |  |  | ($5.7 | ) |  |  | $7.2 |
State | 9.3 |  |  | (3.6 | ) |  | 11.6 |  |  | 3.4 |  |  | (0.1 | ) |  | 9.1 |  |  | 4.4 |  |  | 6.0 |  |  | (0.9 | )
IPL’s tax benefit riders | (56.7 | ) |  | (52.9 | ) |  | (48.3 | ) |  | (56.7 | ) |  | (52.9 | ) |  | (48.3 | ) |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 83.5 |  |  | 123.9 |  |  | 157.8 |  |  | 11.1 |  |  | 20.0 |  |  | 37.4 |  |  | 88.9 |  |  | 92.7 |  |  | 81.1 |
State | 4.6 |  |  | 15.6 |  |  | 23.9 |  |  | (6.2 | ) |  | (0.8 | ) |  | 3.2 |  |  | 10.1 |  |  | 11.8 |  |  | 20.3 |
Production tax credits | (31.3 | ) |  | (31.0 | ) |  | (24.8 | ) |  | (14.0 | ) |  | (14.4 | ) |  | (12.5 | ) |  | (17.3 | ) |  | (16.6 | ) |  | (12.3 | )
Investment tax credits | (1.6 | ) |  | (1.6 | ) |  | (1.7 | ) |  | (0.6 | ) |  | (0.6 | ) |  | (0.6 | ) |  | (1.0 | ) |  | (1.0 | ) |  | (1.1 | )
Provision recorded as a change in uncertain tax positions: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Current | — |  |  | — |  |  | 8.0 |  |  | — |  |  | — |  |  | 8.1 |  |  | — |  |  | — |  |  | (0.1 | )
Deferred | — |  |  | (0.4 | ) |  | (7.6 | ) |  | — |  |  | — |  |  | (8.2 | ) |  | — |  |  | (0.4 | ) |  | 0.6 |
Provision recorded as a change in accrued interest | (0.1 | ) |  | (0.5 | ) |  | (0.2 | ) |  | — |  |  | (0.8 | ) |  | (0.3 | ) |  | (0.1 | ) |  | 0.4 |  |  | (0.2 | )
|  | $44.3 |  |  |  | $53.9 |  |  |  | $89.4 |  |  |  | ($51.7 | ) |  |  | ($37.9 | ) |  |  | ($19.8 | ) |  |  | $85.6 |  |  |  | $87.2 |  |  |  | $94.6 |
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
| 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012
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 | 5.4 |  |  | 5.7 |  |  | 5.7 |  |  | 5.0 |  |  | 5.4 |  |  | 5.8 |  |  | 5.5 |  |  | 6.0 |  |  | 5.5 |
IPL’s tax benefit riders | (12.9 | ) |  | (12.1 | ) |  | (11.2 | ) |  | (39.6 | ) |  | (34.8 | ) |  | (37.0 | ) |  | — |  |  | — |  |  | — |
Effect of rate-making on property-related differences | (7.5 | ) |  | (6.0 | ) |  | (5.0 | ) |  | (21.9 | ) |  | (15.9 | ) |  | (14.2 | ) |  | (0.7 | ) |  | (0.8 | ) |  | (1.1 | )
Production tax credits | (7.1 | ) |  | (7.1 | ) |  | (5.8 | ) |  | (9.8 | ) |  | (9.5 | ) |  | (9.6 | ) |  | (6.5 | ) |  | (6.3 | ) |  | (4.7 | )
Adjustment of prior period taxes | (1.3 | ) |  | (1.3 | ) |  | — |  |  | (3.5 | ) |  | (3.6 | ) |  | 0.2 |  |  | (0.1 | ) |  | (0.1 | ) |  | (0.3 | )
State apportionment change due to announced sale of RMT | — |  |  | — |  |  | 3.5 |  |  | — |  |  | — |  |  | 6.2 |  |  | — |  |  | — |  |  | 2.7 |
Other items, net | (1.5 | ) |  | (1.8 | ) |  | (1.4 | ) |  | (1.4 | ) |  | (1.5 | ) |  | (1.6 | ) |  | (1.1 | ) |  | (0.9 | ) |  | (0.8 | )
Overall income tax rate | 10.1 | % |  | 12.4 | % |  | 20.8 | % |  | (36.2 | %) |  | (24.9 | %) |  | (15.2 | %) |  | 32.1 | % |  | 32.9 | % |  | 36.3 | %
IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing the tax benefit riders. Refer to Note 2 for additional details on IPL’s tax benefit riders. Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s income tax expense and benefits are impacted by certain property-related differences at IPL for which deferred tax is not recognized in the income statement pursuant to Iowa rate-making principles. For example, tax expenses and benefits related to mixed service costs and repairs expenditures at IPL are recorded as a component of income tax expense pursuant to Iowa rate-making principles. In 2013, the primary factor contributing to the increase in the current tax benefits recorded for the effect of rate-making on property-related differences was increased repairs expenditures and the equity component of AFUDC at IPL. In 2014, the increased benefits from property-related differences were primarily due to additional repairs deductions and additional deductions from the allocation of mixed service costs related to Marshalltown. Production tax credits - Production tax credits are earned from owned and operated wind projects. Production tax credits are based on the electricity generated by each wind project during the first 10 years of operation. Details regarding production tax credits (net of state tax impacts) related to various wind projects are as follows (dollars in millions):
| End of Production |  | Nameplate |  |  |  |  |
| Tax Credit Generation |  | Capacity in MW | 2014 |  | 2013 |  | 2012
Cedar Ridge (WPL) | December 2018 |  | 68 |  | $4.0 |  |  |  | $4.1 |  |  |  | $4.0 |
Bent Tree (WPL) | February 2021 |  | 201 | 13.3 |  |  | 12.5 |  |  | 8.3 |
Subtotal (WPL) |  |  |  | 17.3 |  |  | 16.6 |  |  | 12.3 |
Whispering Willow - East (IPL) | December 2019 |  | 200 | 14.0 |  |  | 14.4 |  |  | 12.5 |
|  |  |  |  | $31.3 |  |  |  | $31.0 |  |  |  | $24.8 |
State apportionment change due to announced sale of RMT - State apportionment projections are utilized to record deferred tax assets and liabilities each reporting period. Deferred tax assets and liabilities for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements are recorded utilizing currently enacted tax rates and estimates of future state apportionment rates expected to be in effect at the time the temporary differences reverse. These state apportionment projections are most significantly impacted by the estimated amount of revenues expected in the future from each state jurisdiction for Alliant Energy’s consolidated tax groups, including both its regulated and its non-regulated operations. In 2012, Alliant Energy, IPL and WPL recorded $15 million, $8 million and $7 million, respectively, of deferred income tax expense due to changes in state apportionment projections caused by the announced sale of Alliant Energy’s RMT business. Deferred Tax Assets and Liabilities - The deferred income tax (assets) and liabilities included on Alliant Energy’s balance sheets at December 31 arise from the following temporary differences (in millions):
| 2014 |  | 2013
| Deferred | Deferred Tax |  |  | Deferred | Deferred Tax |
Alliant Energy | Tax Assets | Liabilities | Net |  | Tax Assets | Liabilities | Net
Property |  | $— |  |  | $2,627.8 |  |  | $2,627.8 |  |  |  | $— |  |  | $2,316.3 |  |  | $2,316.3 |
Investment in ATC | — |  | 131.6 |  | 131.6 |  |  | — |  | 120.7 |  | 120.7 |
Net operating losses carryforwards - state | (45.7 | ) | — |  | (45.7 | ) |  | (35.3 | ) | — |  | (35.3 | )
Regulatory liability - IPL’s tax benefit riders | (100.9 | ) | — |  | (100.9 | ) |  | (107.8 | ) | — |  | (107.8 | )
Federal credit carryforwards | (201.0 | ) | — |  | (201.0 | ) |  | (167.8 | ) | — |  | (167.8 | )
Net operating losses carryforwards - federal | (332.8 | ) | — |  | (332.8 | ) |  | (251.9 | ) | — |  | (251.9 | )
Other | (88.1 | ) | 180.1 |  | 92.0 |  |  | (108.9 | ) | 210.7 |  | 101.8 |
Subtotal |  | ($768.5 | ) |  | $2,939.5 |  |  | $2,171.0 |  |  |  | ($671.7 | ) |  | $2,647.7 |  |  | $1,976.0 |
| 2014 |  | 2013
Current deferred tax assets |  | ($150.1 | ) |  |  | ($136.7 | )
Non-current deferred tax liabilities | 2,321.1 |  |  | 2,112.7 |
Total net deferred tax liabilities |  | $2,171.0 |  |  |  | $1,976.0 |
The deferred income tax (assets) and liabilities included on IPL’s balance sheets at December 31 arise from the following temporary differences (in millions):
| 2014 |  | 2013
| Deferred | Deferred Tax |  |  | Deferred | Deferred Tax |
IPL | Tax Assets | Liabilities | Net |  | Tax Assets | Liabilities | Net
Property |  | $— |  |  | $1,531.0 |  |  | $1,531.0 |  |  |  | $— |  |  | $1,338.1 |  |  | $1,338.1 |
Federal credit carryforwards | (67.7 | ) | — |  | (67.7 | ) |  | (52.9 | ) | — |  | (52.9 | )
Regulatory liability - tax benefit riders | (100.9 | ) | — |  | (100.9 | ) |  | (107.8 | ) | — |  | (107.8 | )
Net operating losses carryforwards - federal | (160.6 | ) | — |  | (160.6 | ) |  | (111.3 | ) | — |  | (111.3 | )
Other | (47.2 | ) | 81.9 |  | 34.7 |  |  | (64.0 | ) | 103.2 |  | 39.2 |
|  | ($376.4 | ) |  | $1,612.9 |  |  | $1,236.5 |  |  |  | ($336.0 | ) |  | $1,441.3 |  |  | $1,105.3 |
| 2014 |  | 2013
Current deferred tax assets |  | ($104.9 | ) |  |  | ($87.7 | )
Non-current deferred tax liabilities | 1,341.4 |  |  | 1,193.0 |
Total net deferred tax liabilities |  | $1,236.5 |  |  |  | $1,105.3 |
The deferred income tax (assets) and liabilities included on WPL’s balance sheets at December 31 arise from the following temporary differences (in millions):
| 2014 |  | 2013
| Deferred | Deferred Tax |  |  | Deferred | Deferred Tax |
WPL | Tax Assets | Liabilities | Net |  | Tax Assets | Liabilities | Net
Property |  | $— |  |  | $964.4 |  |  | $964.4 |  |  |  | $— |  |  | $859.1 |  |  | $859.1 |
Investment in ATC | — |  | 131.6 |  | 131.6 |  |  | — |  | 120.7 |  | 120.7 |
Federal credit carryforwards | (75.2 | ) | — |  | (75.2 | ) |  | (57.1 | ) | — |  | (57.1 | )
Net operating losses carryforwards - federal | (128.9 | ) | — |  | (128.9 | ) |  | (106.9 | ) | — |  | (106.9 | )
Other | (40.3 | ) | 80.9 |  | 40.6 |  |  | (37.6 | ) | 75.6 |  | 38.0 |
|  | ($244.4 | ) |  | $1,176.9 |  |  | $932.5 |  |  |  | ($201.6 | ) |  | $1,055.4 |  |  | $853.8 |
| 2014 |  | 2013
Current deferred tax assets |  | ($37.5 | ) |  |  | ($43.3 | )
Non-current deferred tax liabilities | 970.0 |  |  | 897.1 |
Total net deferred tax liabilities |  | $932.5 |  |  |  | $853.8 |
Property - Property-related differences were primarily related to accelerated depreciation, including bonus depreciation. In December 2014, the FTIP Act was enacted. The most significant provisions of the FTIP Act for Alliant Energy, IPL and WPL are related to the extension of bonus depreciation deductions for certain expenditures for property that were incurred through December 31, 2014. As a result, Alliant Energy currently estimates its total bonus depreciation deductions to be claimed on its U.S. federal income tax return for calendar year 2014 will be approximately $450 million ($245 million for IPL and $190 million for WPL). Property-related differences also related to tax accounting method changes for cost of removal expenditures and repair expenditures for electric generation property, which are discussed in Note 2. Investment in ATC - WPL Transco has a partial ownership interest in ATC, which has generated deferred tax liabilities primarily from tax depreciation deductions taken at ATC in excess of book depreciation. The increase in deferred tax liabilities in 2014 was primarily due to bonus depreciation deductions estimated at ATC. Carryforwards - At December 31, 2014, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (in millions):
Alliant Energy | Tax Carryforwards |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $970 |  |  |  | $333 |  |  | 2029
State net operating losses (a) | 881 |  |  | 46 |  |  | 2018
Federal tax credits | 204 |  |  | 201 |  |  | 2022
|  |  |  | $580 |  |  |
IPL | Tax Carryforwards |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $468 |  |  |  | $161 |  |  | 2029
State net operating losses (b) | 291 |  |  | 16 |  |  | 2018
Federal tax credits | 69 |  |  | 68 |  |  | 2022
|  |  |  | $245 |  |  |
WPL | Tax Carryforwards |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $376 |  |  |  | $129 |  |  | 2029
State net operating losses (c) | 171 |  |  | 9 |  |  | 2018
Federal tax credits | 77 |  |  | 75 |  |  | 2022
|  |  |  | $213 |  |  |
(a) | At December 31, 2014, Alliant Energy’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2033 with 98% expiring after 2024.
(b) | At December 31, 2014, IPL’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2031 with 96% expiring after 2024.
(c) | At December 31, 2014, WPL’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2031 with 99% expiring after 2024.
Regulatory liability - tax benefit riders - Refer to Note 2 for discussion of regulatory liabilities associated with IPL’s tax benefit riders. Uncertain Tax Positions - A reconciliation of the beginning and ending amounts of uncertain tax positions, excluding interest, is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012
Balance, January 1 |  | $— |  |  |  | $0.7 |  |  |  | $23.5 |  |  |  | $— |  |  |  | $— |  |  |  | $10.9 |  |  |  | $— |  |  |  | $0.7 |  |  |  | $12.6 |
Additions based on tax positions related to the current year | — |  |  | — |  |  | 0.7 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 0.7 |
Reductions for tax positions of prior years (a) | — |  |  | (0.7 | ) |  | (23.5 | ) |  | — |  |  | — |  |  | (10.9 | ) |  | — |  |  | (0.7 | ) |  | (12.6 | )
Balance, December 31 |  | $— |  |  |  | $— |  |  |  | $0.7 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $0.7 |
(a) | In 2012, the reductions for tax positions of prior years were due to the finalization of Alliant Energy’s federal income tax return audits for calendar years 2005 through 2009.
At December 31, 2014, 2013 and 2012, there were no 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, 2014, 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 are as follows:
| Alliant Energy |  | IPL |  | WPL
Consolidated federal income tax returns (a) | 2011 | - | 2013 |  | 2011 | - | 2013 |  | 2011 | - | 2013
Consolidated Iowa income tax returns (b) | 2011 | - | 2013 |  | 2011 | - | 2013 |  | 2011 | - | 2013
Wisconsin combined tax returns (c) | 2010 | - | 2013 |  | 2010 | - | 2013 |  | 2010 | - | 2013
(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 Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal |  | $36.6 |  |  |  | $4.4 |  |  |  | ($29.3 | ) |  |  | $11.3 |  |  |  | $11.7 |  |  |  | ($7.7 | ) |  |  | $0.6 |  |  |  | ($5.7 | ) |  |  | $7.2 |
State | 9.3 |  |  | (3.6 | ) |  | 11.6 |  |  | 3.4 |  |  | (0.1 | ) |  | 9.1 |  |  | 4.4 |  |  | 6.0 |  |  | (0.9 | )
IPL’s tax benefit riders | (56.7 | ) |  | (52.9 | ) |  | (48.3 | ) |  | (56.7 | ) |  | (52.9 | ) |  | (48.3 | ) |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 83.5 |  |  | 123.9 |  |  | 157.8 |  |  | 11.1 |  |  | 20.0 |  |  | 37.4 |  |  | 88.9 |  |  | 92.7 |  |  | 81.1 |
State | 4.6 |  |  | 15.6 |  |  | 23.9 |  |  | (6.2 | ) |  | (0.8 | ) |  | 3.2 |  |  | 10.1 |  |  | 11.8 |  |  | 20.3 |
Production tax credits | (31.3 | ) |  | (31.0 | ) |  | (24.8 | ) |  | (14.0 | ) |  | (14.4 | ) |  | (12.5 | ) |  | (17.3 | ) |  | (16.6 | ) |  | (12.3 | )
Investment tax credits | (1.6 | ) |  | (1.6 | ) |  | (1.7 | ) |  | (0.6 | ) |  | (0.6 | ) |  | (0.6 | ) |  | (1.0 | ) |  | (1.0 | ) |  | (1.1 | )
Provision recorded as a change in uncertain tax positions: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Current | — |  |  | — |  |  | 8.0 |  |  | — |  |  | — |  |  | 8.1 |  |  | — |  |  | — |  |  | (0.1 | )
Deferred | — |  |  | (0.4 | ) |  | (7.6 | ) |  | — |  |  | — |  |  | (8.2 | ) |  | — |  |  | (0.4 | ) |  | 0.6 |
Provision recorded as a change in accrued interest | (0.1 | ) |  | (0.5 | ) |  | (0.2 | ) |  | — |  |  | (0.8 | ) |  | (0.3 | ) |  | (0.1 | ) |  | 0.4 |  |  | (0.2 | )
|  | $44.3 |  |  |  | $53.9 |  |  |  | $89.4 |  |  |  | ($51.7 | ) |  |  | ($37.9 | ) |  |  | ($19.8 | ) |  |  | $85.6 |  |  |  | $87.2 |  |  |  | $94.6 |
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
| 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012
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 | 5.4 |  |  | 5.7 |  |  | 5.7 |  |  | 5.0 |  |  | 5.4 |  |  | 5.8 |  |  | 5.5 |  |  | 6.0 |  |  | 5.5 |
IPL’s tax benefit riders | (12.9 | ) |  | (12.1 | ) |  | (11.2 | ) |  | (39.6 | ) |  | (34.8 | ) |  | (37.0 | ) |  | — |  |  | — |  |  | — |
Effect of rate-making on property-related differences | (7.5 | ) |  | (6.0 | ) |  | (5.0 | ) |  | (21.9 | ) |  | (15.9 | ) |  | (14.2 | ) |  | (0.7 | ) |  | (0.8 | ) |  | (1.1 | )
Production tax credits | (7.1 | ) |  | (7.1 | ) |  | (5.8 | ) |  | (9.8 | ) |  | (9.5 | ) |  | (9.6 | ) |  | (6.5 | ) |  | (6.3 | ) |  | (4.7 | )
Adjustment of prior period taxes | (1.3 | ) |  | (1.3 | ) |  | — |  |  | (3.5 | ) |  | (3.6 | ) |  | 0.2 |  |  | (0.1 | ) |  | (0.1 | ) |  | (0.3 | )
State apportionment change due to announced sale of RMT | — |  |  | — |  |  | 3.5 |  |  | — |  |  | — |  |  | 6.2 |  |  | — |  |  | — |  |  | 2.7 |
Other items, net | (1.5 | ) |  | (1.8 | ) |  | (1.4 | ) |  | (1.4 | ) |  | (1.5 | ) |  | (1.6 | ) |  | (1.1 | ) |  | (0.9 | ) |  | (0.8 | )
Overall income tax rate | 10.1 | % |  | 12.4 | % |  | 20.8 | % |  | (36.2 | %) |  | (24.9 | %) |  | (15.2 | %) |  | 32.1 | % |  | 32.9 | % |  | 36.3 | %
IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing the tax benefit riders. Refer to Note 2 for additional details on IPL’s tax benefit riders. Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s income tax expense and benefits are impacted by certain property-related differences at IPL for which deferred tax is not recognized in the income statement pursuant to Iowa rate-making principles. For example, tax expenses and benefits related to mixed service costs and repairs expenditures at IPL are recorded as a component of income tax expense pursuant to Iowa rate-making principles. In 2013, the primary factor contributing to the increase in the current tax benefits recorded for the effect of rate-making on property-related differences was increased repairs expenditures and the equity component of AFUDC at IPL. In 2014, the increased benefits from property-related differences were primarily due to additional repairs deductions and additional deductions from the allocation of mixed service costs related to Marshalltown. Production tax credits - Production tax credits are earned from owned and operated wind projects. Production tax credits are based on the electricity generated by each wind project during the first 10 years of operation. Details regarding production tax credits (net of state tax impacts) related to various wind projects are as follows (dollars in millions):
| End of Production |  | Nameplate |  |  |  |  |
| Tax Credit Generation |  | Capacity in MW | 2014 |  | 2013 |  | 2012
Cedar Ridge (WPL) | December 2018 |  | 68 |  | $4.0 |  |  |  | $4.1 |  |  |  | $4.0 |
Bent Tree (WPL) | February 2021 |  | 201 | 13.3 |  |  | 12.5 |  |  | 8.3 |
Subtotal (WPL) |  |  |  | 17.3 |  |  | 16.6 |  |  | 12.3 |
Whispering Willow - East (IPL) | December 2019 |  | 200 | 14.0 |  |  | 14.4 |  |  | 12.5 |
|  |  |  |  | $31.3 |  |  |  | $31.0 |  |  |  | $24.8 |
State apportionment change due to announced sale of RMT - State apportionment projections are utilized to record deferred tax assets and liabilities each reporting period. Deferred tax assets and liabilities for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements are recorded utilizing currently enacted tax rates and estimates of future state apportionment rates expected to be in effect at the time the temporary differences reverse. These state apportionment projections are most significantly impacted by the estimated amount of revenues expected in the future from each state jurisdiction for Alliant Energy’s consolidated tax groups, including both its regulated and its non-regulated operations. In 2012, Alliant Energy, IPL and WPL recorded $15 million, $8 million and $7 million, respectively, of deferred income tax expense due to changes in state apportionment projections caused by the announced sale of Alliant Energy’s RMT business. Deferred Tax Assets and Liabilities - The deferred income tax (assets) and liabilities included on Alliant Energy’s balance sheets at December 31 arise from the following temporary differences (in millions):
| 2014 |  | 2013
| Deferred | Deferred Tax |  |  | Deferred | Deferred Tax |
Alliant Energy | Tax Assets | Liabilities | Net |  | Tax Assets | Liabilities | Net
Property |  | $— |  |  | $2,627.8 |  |  | $2,627.8 |  |  |  | $— |  |  | $2,316.3 |  |  | $2,316.3 |
Investment in ATC | — |  | 131.6 |  | 131.6 |  |  | — |  | 120.7 |  | 120.7 |
Net operating losses carryforwards - state | (45.7 | ) | — |  | (45.7 | ) |  | (35.3 | ) | — |  | (35.3 | )
Regulatory liability - IPL’s tax benefit riders | (100.9 | ) | — |  | (100.9 | ) |  | (107.8 | ) | — |  | (107.8 | )
Federal credit carryforwards | (201.0 | ) | — |  | (201.0 | ) |  | (167.8 | ) | — |  | (167.8 | )
Net operating losses carryforwards - federal | (332.8 | ) | — |  | (332.8 | ) |  | (251.9 | ) | — |  | (251.9 | )
Other | (88.1 | ) | 180.1 |  | 92.0 |  |  | (108.9 | ) | 210.7 |  | 101.8 |
Subtotal |  | ($768.5 | ) |  | $2,939.5 |  |  | $2,171.0 |  |  |  | ($671.7 | ) |  | $2,647.7 |  |  | $1,976.0 |
| 2014 |  | 2013
Current deferred tax assets |  | ($150.1 | ) |  |  | ($136.7 | )
Non-current deferred tax liabilities | 2,321.1 |  |  | 2,112.7 |
Total net deferred tax liabilities |  | $2,171.0 |  |  |  | $1,976.0 |
The deferred income tax (assets) and liabilities included on IPL’s balance sheets at December 31 arise from the following temporary differences (in millions):
| 2014 |  | 2013
| Deferred | Deferred Tax |  |  | Deferred | Deferred Tax |
IPL | Tax Assets | Liabilities | Net |  | Tax Assets | Liabilities | Net
Property |  | $— |  |  | $1,531.0 |  |  | $1,531.0 |  |  |  | $— |  |  | $1,338.1 |  |  | $1,338.1 |
Federal credit carryforwards | (67.7 | ) | — |  | (67.7 | ) |  | (52.9 | ) | — |  | (52.9 | )
Regulatory liability - tax benefit riders | (100.9 | ) | — |  | (100.9 | ) |  | (107.8 | ) | — |  | (107.8 | )
Net operating losses carryforwards - federal | (160.6 | ) | — |  | (160.6 | ) |  | (111.3 | ) | — |  | (111.3 | )
Other | (47.2 | ) | 81.9 |  | 34.7 |  |  | (64.0 | ) | 103.2 |  | 39.2 |
|  | ($376.4 | ) |  | $1,612.9 |  |  | $1,236.5 |  |  |  | ($336.0 | ) |  | $1,441.3 |  |  | $1,105.3 |
| 2014 |  | 2013
Current deferred tax assets |  | ($104.9 | ) |  |  | ($87.7 | )
Non-current deferred tax liabilities | 1,341.4 |  |  | 1,193.0 |
Total net deferred tax liabilities |  | $1,236.5 |  |  |  | $1,105.3 |
The deferred income tax (assets) and liabilities included on WPL’s balance sheets at December 31 arise from the following temporary differences (in millions):
| 2014 |  | 2013
| Deferred | Deferred Tax |  |  | Deferred | Deferred Tax |
WPL | Tax Assets | Liabilities | Net |  | Tax Assets | Liabilities | Net
Property |  | $— |  |  | $964.4 |  |  | $964.4 |  |  |  | $— |  |  | $859.1 |  |  | $859.1 |
Investment in ATC | — |  | 131.6 |  | 131.6 |  |  | — |  | 120.7 |  | 120.7 |
Federal credit carryforwards | (75.2 | ) | — |  | (75.2 | ) |  | (57.1 | ) | — |  | (57.1 | )
Net operating losses carryforwards - federal | (128.9 | ) | — |  | (128.9 | ) |  | (106.9 | ) | — |  | (106.9 | )
Other | (40.3 | ) | 80.9 |  | 40.6 |  |  | (37.6 | ) | 75.6 |  | 38.0 |
|  | ($244.4 | ) |  | $1,176.9 |  |  | $932.5 |  |  |  | ($201.6 | ) |  | $1,055.4 |  |  | $853.8 |
| 2014 |  | 2013
Current deferred tax assets |  | ($37.5 | ) |  |  | ($43.3 | )
Non-current deferred tax liabilities | 970.0 |  |  | 897.1 |
Total net deferred tax liabilities |  | $932.5 |  |  |  | $853.8 |
Property - Property-related differences were primarily related to accelerated depreciation, including bonus depreciation. In December 2014, the FTIP Act was enacted. The most significant provisions of the FTIP Act for Alliant Energy, IPL and WPL are related to the extension of bonus depreciation deductions for certain expenditures for property that were incurred through December 31, 2014. As a result, Alliant Energy currently estimates its total bonus depreciation deductions to be claimed on its U.S. federal income tax return for calendar year 2014 will be approximately $450 million ($245 million for IPL and $190 million for WPL). Property-related differences also related to tax accounting method changes for cost of removal expenditures and repair expenditures for electric generation property, which are discussed in Note 2. Investment in ATC - WPL Transco has a partial ownership interest in ATC, which has generated deferred tax liabilities primarily from tax depreciation deductions taken at ATC in excess of book depreciation. The increase in deferred tax liabilities in 2014 was primarily due to bonus depreciation deductions estimated at ATC. Carryforwards - At December 31, 2014, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (in millions):
Alliant Energy | Tax Carryforwards |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $970 |  |  |  | $333 |  |  | 2029
State net operating losses (a) | 881 |  |  | 46 |  |  | 2018
Federal tax credits | 204 |  |  | 201 |  |  | 2022
|  |  |  | $580 |  |  |
IPL | Tax Carryforwards |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $468 |  |  |  | $161 |  |  | 2029
State net operating losses (b) | 291 |  |  | 16 |  |  | 2018
Federal tax credits | 69 |  |  | 68 |  |  | 2022
|  |  |  | $245 |  |  |
WPL | Tax Carryforwards |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $376 |  |  |  | $129 |  |  | 2029
State net operating losses (c) | 171 |  |  | 9 |  |  | 2018
Federal tax credits | 77 |  |  | 75 |  |  | 2022
|  |  |  | $213 |  |  |
(a) | At December 31, 2014, Alliant Energy’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2033 with 98% expiring after 2024.
(b) | At December 31, 2014, IPL’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2031 with 96% expiring after 2024.
(c) | At December 31, 2014, WPL’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2031 with 99% expiring after 2024.
Regulatory liability - tax benefit riders - Refer to Note 2 for discussion of regulatory liabilities associated with IPL’s tax benefit riders. Uncertain Tax Positions - A reconciliation of the beginning and ending amounts of uncertain tax positions, excluding interest, is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012
Balance, January 1 |  | $— |  |  |  | $0.7 |  |  |  | $23.5 |  |  |  | $— |  |  |  | $— |  |  |  | $10.9 |  |  |  | $— |  |  |  | $0.7 |  |  |  | $12.6 |
Additions based on tax positions related to the current year | — |  |  | — |  |  | 0.7 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 0.7 |
Reductions for tax positions of prior years (a) | — |  |  | (0.7 | ) |  | (23.5 | ) |  | — |  |  | — |  |  | (10.9 | ) |  | — |  |  | (0.7 | ) |  | (12.6 | )
Balance, December 31 |  | $— |  |  |  | $— |  |  |  | $0.7 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $0.7 |
(a) | In 2012, the reductions for tax positions of prior years were due to the finalization of Alliant Energy’s federal income tax return audits for calendar years 2005 through 2009.
At December 31, 2014, 2013 and 2012, there were no 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, 2014, 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 are as follows:
| Alliant Energy |  | IPL |  | WPL
Consolidated federal income tax returns (a) | 2011 | - | 2013 |  | 2011 | - | 2013 |  | 2011 | - | 2013
Consolidated Iowa income tax returns (b) | 2011 | - | 2013 |  | 2011 | - | 2013 |  | 2011 | - | 2013
Wisconsin combined tax returns (c) | 2010 | - | 2013 |  | 2010 | - | 2013 |  | 2010 | - | 2013
(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 Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal |  | $36.6 |  |  |  | $4.4 |  |  |  | ($29.3 | ) |  |  | $11.3 |  |  |  | $11.7 |  |  |  | ($7.7 | ) |  |  | $0.6 |  |  |  | ($5.7 | ) |  |  | $7.2 |
State | 9.3 |  |  | (3.6 | ) |  | 11.6 |  |  | 3.4 |  |  | (0.1 | ) |  | 9.1 |  |  | 4.4 |  |  | 6.0 |  |  | (0.9 | )
IPL’s tax benefit riders | (56.7 | ) |  | (52.9 | ) |  | (48.3 | ) |  | (56.7 | ) |  | (52.9 | ) |  | (48.3 | ) |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 83.5 |  |  | 123.9 |  |  | 157.8 |  |  | 11.1 |  |  | 20.0 |  |  | 37.4 |  |  | 88.9 |  |  | 92.7 |  |  | 81.1 |
State | 4.6 |  |  | 15.6 |  |  | 23.9 |  |  | (6.2 | ) |  | (0.8 | ) |  | 3.2 |  |  | 10.1 |  |  | 11.8 |  |  | 20.3 |
Production tax credits | (31.3 | ) |  | (31.0 | ) |  | (24.8 | ) |  | (14.0 | ) |  | (14.4 | ) |  | (12.5 | ) |  | (17.3 | ) |  | (16.6 | ) |  | (12.3 | )
Investment tax credits | (1.6 | ) |  | (1.6 | ) |  | (1.7 | ) |  | (0.6 | ) |  | (0.6 | ) |  | (0.6 | ) |  | (1.0 | ) |  | (1.0 | ) |  | (1.1 | )
Provision recorded as a change in uncertain tax positions: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Current | — |  |  | — |  |  | 8.0 |  |  | — |  |  | — |  |  | 8.1 |  |  | — |  |  | — |  |  | (0.1 | )
Deferred | — |  |  | (0.4 | ) |  | (7.6 | ) |  | — |  |  | — |  |  | (8.2 | ) |  | — |  |  | (0.4 | ) |  | 0.6 |
Provision recorded as a change in accrued interest | (0.1 | ) |  | (0.5 | ) |  | (0.2 | ) |  | — |  |  | (0.8 | ) |  | (0.3 | ) |  | (0.1 | ) |  | 0.4 |  |  | (0.2 | )
|  | $44.3 |  |  |  | $53.9 |  |  |  | $89.4 |  |  |  | ($51.7 | ) |  |  | ($37.9 | ) |  |  | ($19.8 | ) |  |  | $85.6 |  |  |  | $87.2 |  |  |  | $94.6 |
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
| 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012
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 | 5.4 |  |  | 5.7 |  |  | 5.7 |  |  | 5.0 |  |  | 5.4 |  |  | 5.8 |  |  | 5.5 |  |  | 6.0 |  |  | 5.5 |
IPL’s tax benefit riders | (12.9 | ) |  | (12.1 | ) |  | (11.2 | ) |  | (39.6 | ) |  | (34.8 | ) |  | (37.0 | ) |  | — |  |  | — |  |  | — |
Effect of rate-making on property-related differences | (7.5 | ) |  | (6.0 | ) |  | (5.0 | ) |  | (21.9 | ) |  | (15.9 | ) |  | (14.2 | ) |  | (0.7 | ) |  | (0.8 | ) |  | (1.1 | )
Production tax credits | (7.1 | ) |  | (7.1 | ) |  | (5.8 | ) |  | (9.8 | ) |  | (9.5 | ) |  | (9.6 | ) |  | (6.5 | ) |  | (6.3 | ) |  | (4.7 | )
Adjustment of prior period taxes | (1.3 | ) |  | (1.3 | ) |  | — |  |  | (3.5 | ) |  | (3.6 | ) |  | 0.2 |  |  | (0.1 | ) |  | (0.1 | ) |  | (0.3 | )
State apportionment change due to announced sale of RMT | — |  |  | — |  |  | 3.5 |  |  | — |  |  | — |  |  | 6.2 |  |  | — |  |  | — |  |  | 2.7 |
Other items, net | (1.5 | ) |  | (1.8 | ) |  | (1.4 | ) |  | (1.4 | ) |  | (1.5 | ) |  | (1.6 | ) |  | (1.1 | ) |  | (0.9 | ) |  | (0.8 | )
Overall income tax rate | 10.1 | % |  | 12.4 | % |  | 20.8 | % |  | (36.2 | %) |  | (24.9 | %) |  | (15.2 | %) |  | 32.1 | % |  | 32.9 | % |  | 36.3 | %
IPL’s tax benefit riders - Alliant Energy’s and IPL’s effective income tax rates include the impact of reducing income tax expense with offsetting reductions to regulatory liabilities as a result of implementing the tax benefit riders. Refer to Note 2 for additional details on IPL’s tax benefit riders. Effect of rate-making on property-related differences - Alliant Energy’s and IPL’s income tax expense and benefits are impacted by certain property-related differences at IPL for which deferred tax is not recognized in the income statement pursuant to Iowa rate-making principles. For example, tax expenses and benefits related to mixed service costs and repairs expenditures at IPL are recorded as a component of income tax expense pursuant to Iowa rate-making principles. In 2013, the primary factor contributing to the increase in the current tax benefits recorded for the effect of rate-making on property-related differences was increased repairs expenditures and the equity component of AFUDC at IPL. In 2014, the increased benefits from property-related differences were primarily due to additional repairs deductions and additional deductions from the allocation of mixed service costs related to Marshalltown. Production tax credits - Production tax credits are earned from owned and operated wind projects. Production tax credits are based on the electricity generated by each wind project during the first 10 years of operation. Details regarding production tax credits (net of state tax impacts) related to various wind projects are as follows (dollars in millions):
| End of Production |  | Nameplate |  |  |  |  |
| Tax Credit Generation |  | Capacity in MW | 2014 |  | 2013 |  | 2012
Cedar Ridge (WPL) | December 2018 |  | 68 |  | $4.0 |  |  |  | $4.1 |  |  |  | $4.0 |
Bent Tree (WPL) | February 2021 |  | 201 | 13.3 |  |  | 12.5 |  |  | 8.3 |
Subtotal (WPL) |  |  |  | 17.3 |  |  | 16.6 |  |  | 12.3 |
Whispering Willow - East (IPL) | December 2019 |  | 200 | 14.0 |  |  | 14.4 |  |  | 12.5 |
|  |  |  |  | $31.3 |  |  |  | $31.0 |  |  |  | $24.8 |
State apportionment change due to announced sale of RMT - State apportionment projections are utilized to record deferred tax assets and liabilities each reporting period. Deferred tax assets and liabilities for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements are recorded utilizing currently enacted tax rates and estimates of future state apportionment rates expected to be in effect at the time the temporary differences reverse. These state apportionment projections are most significantly impacted by the estimated amount of revenues expected in the future from each state jurisdiction for Alliant Energy’s consolidated tax groups, including both its regulated and its non-regulated operations. In 2012, Alliant Energy, IPL and WPL recorded $15 million, $8 million and $7 million, respectively, of deferred income tax expense due to changes in state apportionment projections caused by the announced sale of Alliant Energy’s RMT business. Deferred Tax Assets and Liabilities - The deferred income tax (assets) and liabilities included on Alliant Energy’s balance sheets at December 31 arise from the following temporary differences (in millions):
| 2014 |  | 2013
| Deferred | Deferred Tax |  |  | Deferred | Deferred Tax |
Alliant Energy | Tax Assets | Liabilities | Net |  | Tax Assets | Liabilities | Net
Property |  | $— |  |  | $2,627.8 |  |  | $2,627.8 |  |  |  | $— |  |  | $2,316.3 |  |  | $2,316.3 |
Investment in ATC | — |  | 131.6 |  | 131.6 |  |  | — |  | 120.7 |  | 120.7 |
Net operating losses carryforwards - state | (45.7 | ) | — |  | (45.7 | ) |  | (35.3 | ) | — |  | (35.3 | )
Regulatory liability - IPL’s tax benefit riders | (100.9 | ) | — |  | (100.9 | ) |  | (107.8 | ) | — |  | (107.8 | )
Federal credit carryforwards | (201.0 | ) | — |  | (201.0 | ) |  | (167.8 | ) | — |  | (167.8 | )
Net operating losses carryforwards - federal | (332.8 | ) | — |  | (332.8 | ) |  | (251.9 | ) | — |  | (251.9 | )
Other | (88.1 | ) | 180.1 |  | 92.0 |  |  | (108.9 | ) | 210.7 |  | 101.8 |
Subtotal |  | ($768.5 | ) |  | $2,939.5 |  |  | $2,171.0 |  |  |  | ($671.7 | ) |  | $2,647.7 |  |  | $1,976.0 |
| 2014 |  | 2013
Current deferred tax assets |  | ($150.1 | ) |  |  | ($136.7 | )
Non-current deferred tax liabilities | 2,321.1 |  |  | 2,112.7 |
Total net deferred tax liabilities |  | $2,171.0 |  |  |  | $1,976.0 |
The deferred income tax (assets) and liabilities included on IPL’s balance sheets at December 31 arise from the following temporary differences (in millions):
| 2014 |  | 2013
| Deferred | Deferred Tax |  |  | Deferred | Deferred Tax |
IPL | Tax Assets | Liabilities | Net |  | Tax Assets | Liabilities | Net
Property |  | $— |  |  | $1,531.0 |  |  | $1,531.0 |  |  |  | $— |  |  | $1,338.1 |  |  | $1,338.1 |
Federal credit carryforwards | (67.7 | ) | — |  | (67.7 | ) |  | (52.9 | ) | — |  | (52.9 | )
Regulatory liability - tax benefit riders | (100.9 | ) | — |  | (100.9 | ) |  | (107.8 | ) | — |  | (107.8 | )
Net operating losses carryforwards - federal | (160.6 | ) | — |  | (160.6 | ) |  | (111.3 | ) | — |  | (111.3 | )
Other | (47.2 | ) | 81.9 |  | 34.7 |  |  | (64.0 | ) | 103.2 |  | 39.2 |
|  | ($376.4 | ) |  | $1,612.9 |  |  | $1,236.5 |  |  |  | ($336.0 | ) |  | $1,441.3 |  |  | $1,105.3 |
| 2014 |  | 2013
Current deferred tax assets |  | ($104.9 | ) |  |  | ($87.7 | )
Non-current deferred tax liabilities | 1,341.4 |  |  | 1,193.0 |
Total net deferred tax liabilities |  | $1,236.5 |  |  |  | $1,105.3 |
The deferred income tax (assets) and liabilities included on WPL’s balance sheets at December 31 arise from the following temporary differences (in millions):
| 2014 |  | 2013
| Deferred | Deferred Tax |  |  | Deferred | Deferred Tax |
WPL | Tax Assets | Liabilities | Net |  | Tax Assets | Liabilities | Net
Property |  | $— |  |  | $964.4 |  |  | $964.4 |  |  |  | $— |  |  | $859.1 |  |  | $859.1 |
Investment in ATC | — |  | 131.6 |  | 131.6 |  |  | — |  | 120.7 |  | 120.7 |
Federal credit carryforwards | (75.2 | ) | — |  | (75.2 | ) |  | (57.1 | ) | — |  | (57.1 | )
Net operating losses carryforwards - federal | (128.9 | ) | — |  | (128.9 | ) |  | (106.9 | ) | — |  | (106.9 | )
Other | (40.3 | ) | 80.9 |  | 40.6 |  |  | (37.6 | ) | 75.6 |  | 38.0 |
|  | ($244.4 | ) |  | $1,176.9 |  |  | $932.5 |  |  |  | ($201.6 | ) |  | $1,055.4 |  |  | $853.8 |
| 2014 |  | 2013
Current deferred tax assets |  | ($37.5 | ) |  |  | ($43.3 | )
Non-current deferred tax liabilities | 970.0 |  |  | 897.1 |
Total net deferred tax liabilities |  | $932.5 |  |  |  | $853.8 |
Property - Property-related differences were primarily related to accelerated depreciation, including bonus depreciation. In December 2014, the FTIP Act was enacted. The most significant provisions of the FTIP Act for Alliant Energy, IPL and WPL are related to the extension of bonus depreciation deductions for certain expenditures for property that were incurred through December 31, 2014. As a result, Alliant Energy currently estimates its total bonus depreciation deductions to be claimed on its U.S. federal income tax return for calendar year 2014 will be approximately $450 million ($245 million for IPL and $190 million for WPL). Property-related differences also related to tax accounting method changes for cost of removal expenditures and repair expenditures for electric generation property, which are discussed in Note 2. Investment in ATC - WPL Transco has a partial ownership interest in ATC, which has generated deferred tax liabilities primarily from tax depreciation deductions taken at ATC in excess of book depreciation. The increase in deferred tax liabilities in 2014 was primarily due to bonus depreciation deductions estimated at ATC. Carryforwards - At December 31, 2014, tax carryforwards and associated deferred tax assets and expiration dates were estimated as follows (in millions):
Alliant Energy | Tax Carryforwards |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $970 |  |  |  | $333 |  |  | 2029
State net operating losses (a) | 881 |  |  | 46 |  |  | 2018
Federal tax credits | 204 |  |  | 201 |  |  | 2022
|  |  |  | $580 |  |  |
IPL | Tax Carryforwards |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $468 |  |  |  | $161 |  |  | 2029
State net operating losses (b) | 291 |  |  | 16 |  |  | 2018
Federal tax credits | 69 |  |  | 68 |  |  | 2022
|  |  |  | $245 |  |  |
WPL | Tax Carryforwards |  | Deferred Tax Assets |  | Earliest Expiration Date
Federal net operating losses |  | $376 |  |  |  | $129 |  |  | 2029
State net operating losses (c) | 171 |  |  | 9 |  |  | 2018
Federal tax credits | 77 |  |  | 75 |  |  | 2022
|  |  |  | $213 |  |  |
(a) | At December 31, 2014, Alliant Energy’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2033 with 98% expiring after 2024.
(b) | At December 31, 2014, IPL’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2031 with 96% expiring after 2024.
(c) | At December 31, 2014, WPL’s state net operating losses carryforwards had expiration dates ranging from 2018 to 2031 with 99% expiring after 2024.
Regulatory liability - tax benefit riders - Refer to Note 2 for discussion of regulatory liabilities associated with IPL’s tax benefit riders. Uncertain Tax Positions - A reconciliation of the beginning and ending amounts of uncertain tax positions, excluding interest, is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012
Balance, January 1 |  | $— |  |  |  | $0.7 |  |  |  | $23.5 |  |  |  | $— |  |  |  | $— |  |  |  | $10.9 |  |  |  | $— |  |  |  | $0.7 |  |  |  | $12.6 |
Additions based on tax positions related to the current year | — |  |  | — |  |  | 0.7 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 0.7 |
Reductions for tax positions of prior years (a) | — |  |  | (0.7 | ) |  | (23.5 | ) |  | — |  |  | — |  |  | (10.9 | ) |  | — |  |  | (0.7 | ) |  | (12.6 | )
Balance, December 31 |  | $— |  |  |  | $— |  |  |  | $0.7 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $0.7 |
(a) | In 2012, the reductions for tax positions of prior years were due to the finalization of Alliant Energy’s federal income tax return audits for calendar years 2005 through 2009.
At December 31, 2014, 2013 and 2012, there were no 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, 2014, 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 are as follows:
| Alliant Energy |  | IPL |  | WPL
Consolidated federal income tax returns (a) | 2011 | - | 2013 |  | 2011 | - | 2013 |  | 2011 | - | 2013
Consolidated Iowa income tax returns (b) | 2011 | - | 2013 |  | 2011 | - | 2013 |  | 2011 | - | 2013
Wisconsin combined tax returns (c) | 2010 | - | 2013 |  | 2010 | - | 2013 |  | 2010 | - | 2013
(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.

X
- Details
Name: | lnt_IncomeTaxLineItems
Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- 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 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(h)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 08 -Paragraph h -Article 4 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32639-109319 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32537-109319 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 + Details
Name: | us-gaap_IncomeTaxDisclosureTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |