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Income Taxes
 12 Months Ended
Dec. 31, 2016
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
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
Current tax expense (benefit):
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Federal

$1.8

 

$2.0

 

$36.6

 

($12.8
)
 

($14.1
)
 

$8.9

 

($22.3
)
 

$4.7

 

$2.0

State
17.2

 
3.2

 
9.3

 
15.5

 
11.5

 
10.4

 
1.1

 
0.6

 
0.8

IPL’s tax benefit riders
(44.2
)
 
(49.0
)
 
(56.7
)
 
(44.2
)
 
(49.0
)
 
(56.7
)
 
—

 
—

 
—

Deferred tax expense (benefit):
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Federal
112.8

 
120.8

 
83.5

 
59.1

 
40.7

 
10.8

 
112.3

 
76.8

 
81.1

State
4.9

 
27.9

 
4.6

 
(9.0
)
 
3.3

 
(7.9
)
 
20.8

 
20.2

 
20.0

Production tax credits
(31.8
)
 
(33.1
)
 
(31.3
)
 
(14.0
)
 
(14.5
)
 
(13.8
)
 
(17.8
)
 
(18.6
)
 
(17.5
)
Investment tax credits
(1.3
)
 
(1.4
)
 
(1.6
)
 
(0.5
)
 
(0.6
)
 
(0.6
)
 
(0.8
)
 
(0.8
)
 
(1.0
)
Provision recorded as a change in accrued interest
—

 
—

 
(0.1
)
 
—

 
—

 
—

 
—

 
—

 
(0.1
)
 

$59.4

 

$70.4

 

$44.3

 

($5.9
)
 

($22.7
)
 

($48.9
)
 

$93.3

 

$82.9

 

$85.3



Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
 
Alliant Energy
 
IPL
 
WPL
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
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

 
5.2

 
5.4

 
6.4

 
6.2

 
6.1

 
5.1

 
5.1

 
5.1

IPL’s tax benefit riders
(10.0
)
 
(10.6
)
 
(12.9
)
 
(20.1
)
 
(28.3
)
 
(39.6
)
 
—

 
—

 
—

Effect of rate-making on property-related differences
(8.5
)
 
(6.8
)
 
(7.5
)
 
(16.2
)
 
(17.2
)
 
(21.9
)
 
(0.7
)
 
(0.5
)
 
(0.7
)
Production tax credits
(7.2
)
 
(7.2
)
 
(7.1
)
 
(6.3
)
 
(8.3
)
 
(9.6
)
 
(6.2
)
 
(7.1
)
 
(6.6
)
Adjustment of prior period taxes
(0.8
)
 
0.8

 
(1.3
)
 
(1.2
)
 
0.7

 
(3.0
)
 
(0.1
)
 
0.1

 
—

Other items, net
(0.5
)
 
(1.1
)
 
(1.5
)
 
(0.3
)
 
(1.2
)
 
(1.2
)
 
(0.5
)
 
(0.8
)
 
(0.8
)
Overall income tax rate
13.4
%
 
15.3
%
 
10.1
%
 
(2.7
%)
 
(13.1
%)
 
(34.2
%)
 
32.6
%
 
31.8
%
 
32.0
%


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
 
2016
 
2015
 
2016
 
2015
 
2016
 
2015
Deferred tax liabilities:
 
 
 
 
 
 
 
 
 
 
 
Property

$2,919.0

 

$2,762.9

 

$1,677.0

 

$1,587.8

 

$1,124.5

 

$1,027.0

Investment in ATC
153.1

 
138.1

 
—

 
—

 
—

 
138.9

Other
95.3

 
157.3

 
71.4

 
87.8

 
59.1

 
67.9

Total deferred tax liabilities
3,167.4

 
3,058.3

 
1,748.4

 
1,675.6

 
1,183.6

 
1,233.8

Deferred tax assets:
 
 
 
 
 
 
 
 
 
 
 
Federal credit carryforwards
268.4

 
236.4

 
95.9

 
81.7

 
112.9

 
95.5

Net operating losses carryforwards - federal
173.3

 
250.9

 
69.6

 
113.1

 
75.4

 
105.1

Regulatory liability - IPL’s tax benefit riders
34.7

 
66.1

 
34.7

 
66.1

 
—

 
—

Net operating losses carryforwards - state
32.9

 
38.3

 
0.6

 
1.1

 
0.1

 
3.6

Other
87.9

 
85.4

 
35.8

 
35.6

 
23.6

 
24.2

Total deferred tax assets
597.2

 
677.1

 
236.6

 
297.6

 
212.0

 
228.4

Total deferred tax liabilities, net

$2,570.2

 

$2,381.2

 

$1,511.8

 

$1,378.0

 

$971.6

 

$1,005.4



Property - Property-related differences were primarily related to accelerated depreciation, including bonus depreciation. In 2015, the PATH Act was enacted. The most significant provisions of the PATH Act for Alliant Energy, IPL and WPL relate to the extension of bonus depreciation deductions for certain expenditures for property incurred through December 31, 2019 and placed in service prior to December 31, 2020. Alliant Energy currently estimates its total bonus depreciation deductions to be claimed on its U.S. federal income tax return for calendar year 2016 will be approximately $350 million ($100 million for IPL and $200 million for WPL).

Carryforwards - At December 31, 2016, carryforwards and expiration dates were estimated as follows (in millions):
 
Range of Expiration Dates
 
Alliant Energy
 
IPL
 
WPL
Federal net operating losses
2030-2034
 

$506

 

$206

 

$215

State net operating losses
2018-2034
 
673

 
12

 
2

Federal tax credits
2022-2036
 
274

 
100

 
113



Uncertain Tax Positions - At December 31, 2016, 2015 and 2014, 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, 2016, 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)
2013
-
2015
Consolidated Iowa income tax returns (b)
2013
-
2015
Wisconsin combined tax returns (c)
2012
-
2015

(a)
The federal tax returns for 2013 and 2014 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
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
Current tax expense (benefit):
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Federal

$1.8

 

$2.0

 

$36.6

 

($12.8
)
 

($14.1
)
 

$8.9

 

($22.3
)
 

$4.7

 

$2.0

State
17.2

 
3.2

 
9.3

 
15.5

 
11.5

 
10.4

 
1.1

 
0.6

 
0.8

IPL’s tax benefit riders
(44.2
)
 
(49.0
)
 
(56.7
)
 
(44.2
)
 
(49.0
)
 
(56.7
)
 
—

 
—

 
—

Deferred tax expense (benefit):
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Federal
112.8

 
120.8

 
83.5

 
59.1

 
40.7

 
10.8

 
112.3

 
76.8

 
81.1

State
4.9

 
27.9

 
4.6

 
(9.0
)
 
3.3

 
(7.9
)
 
20.8

 
20.2

 
20.0

Production tax credits
(31.8
)
 
(33.1
)
 
(31.3
)
 
(14.0
)
 
(14.5
)
 
(13.8
)
 
(17.8
)
 
(18.6
)
 
(17.5
)
Investment tax credits
(1.3
)
 
(1.4
)
 
(1.6
)
 
(0.5
)
 
(0.6
)
 
(0.6
)
 
(0.8
)
 
(0.8
)
 
(1.0
)
Provision recorded as a change in accrued interest
—

 
—

 
(0.1
)
 
—

 
—

 
—

 
—

 
—

 
(0.1
)
 

$59.4

 

$70.4

 

$44.3

 

($5.9
)
 

($22.7
)
 

($48.9
)
 

$93.3

 

$82.9

 

$85.3



Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
 
Alliant Energy
 
IPL
 
WPL
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
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

 
5.2

 
5.4

 
6.4

 
6.2

 
6.1

 
5.1

 
5.1

 
5.1

IPL’s tax benefit riders
(10.0
)
 
(10.6
)
 
(12.9
)
 
(20.1
)
 
(28.3
)
 
(39.6
)
 
—

 
—

 
—

Effect of rate-making on property-related differences
(8.5
)
 
(6.8
)
 
(7.5
)
 
(16.2
)
 
(17.2
)
 
(21.9
)
 
(0.7
)
 
(0.5
)
 
(0.7
)
Production tax credits
(7.2
)
 
(7.2
)
 
(7.1
)
 
(6.3
)
 
(8.3
)
 
(9.6
)
 
(6.2
)
 
(7.1
)
 
(6.6
)
Adjustment of prior period taxes
(0.8
)
 
0.8

 
(1.3
)
 
(1.2
)
 
0.7

 
(3.0
)
 
(0.1
)
 
0.1

 
—

Other items, net
(0.5
)
 
(1.1
)
 
(1.5
)
 
(0.3
)
 
(1.2
)
 
(1.2
)
 
(0.5
)
 
(0.8
)
 
(0.8
)
Overall income tax rate
13.4
%
 
15.3
%
 
10.1
%
 
(2.7
%)
 
(13.1
%)
 
(34.2
%)
 
32.6
%
 
31.8
%
 
32.0
%


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
 
2016
 
2015
 
2016
 
2015
 
2016
 
2015
Deferred tax liabilities:
 
 
 
 
 
 
 
 
 
 
 
Property

$2,919.0

 

$2,762.9

 

$1,677.0

 

$1,587.8

 

$1,124.5

 

$1,027.0

Investment in ATC
153.1

 
138.1

 
—

 
—

 
—

 
138.9

Other
95.3

 
157.3

 
71.4

 
87.8

 
59.1

 
67.9

Total deferred tax liabilities
3,167.4

 
3,058.3

 
1,748.4

 
1,675.6

 
1,183.6

 
1,233.8

Deferred tax assets:
 
 
 
 
 
 
 
 
 
 
 
Federal credit carryforwards
268.4

 
236.4

 
95.9

 
81.7

 
112.9

 
95.5

Net operating losses carryforwards - federal
173.3

 
250.9

 
69.6

 
113.1

 
75.4

 
105.1

Regulatory liability - IPL’s tax benefit riders
34.7

 
66.1

 
34.7

 
66.1

 
—

 
—

Net operating losses carryforwards - state
32.9

 
38.3

 
0.6

 
1.1

 
0.1

 
3.6

Other
87.9

 
85.4

 
35.8

 
35.6

 
23.6

 
24.2

Total deferred tax assets
597.2

 
677.1

 
236.6

 
297.6

 
212.0

 
228.4

Total deferred tax liabilities, net

$2,570.2

 

$2,381.2

 

$1,511.8

 

$1,378.0

 

$971.6

 

$1,005.4



Property - Property-related differences were primarily related to accelerated depreciation, including bonus depreciation. In 2015, the PATH Act was enacted. The most significant provisions of the PATH Act for Alliant Energy, IPL and WPL relate to the extension of bonus depreciation deductions for certain expenditures for property incurred through December 31, 2019 and placed in service prior to December 31, 2020. Alliant Energy currently estimates its total bonus depreciation deductions to be claimed on its U.S. federal income tax return for calendar year 2016 will be approximately $350 million ($100 million for IPL and $200 million for WPL).

Carryforwards - At December 31, 2016, carryforwards and expiration dates were estimated as follows (in millions):
 
Range of Expiration Dates
 
Alliant Energy
 
IPL
 
WPL
Federal net operating losses
2030-2034
 

$506

 

$206

 

$215

State net operating losses
2018-2034
 
673

 
12

 
2

Federal tax credits
2022-2036
 
274

 
100

 
113



Uncertain Tax Positions - At December 31, 2016, 2015 and 2014, 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, 2016, 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)
2013
-
2015
Consolidated Iowa income tax returns (b)
2013
-
2015
Wisconsin combined tax returns (c)
2012
-
2015

(a)
The federal tax returns for 2013 and 2014 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
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
Current tax expense (benefit):
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Federal

$1.8

 

$2.0

 

$36.6

 

($12.8
)
 

($14.1
)
 

$8.9

 

($22.3
)
 

$4.7

 

$2.0

State
17.2

 
3.2

 
9.3

 
15.5

 
11.5

 
10.4

 
1.1

 
0.6

 
0.8

IPL’s tax benefit riders
(44.2
)
 
(49.0
)
 
(56.7
)
 
(44.2
)
 
(49.0
)
 
(56.7
)
 
—

 
—

 
—

Deferred tax expense (benefit):
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Federal
112.8

 
120.8

 
83.5

 
59.1

 
40.7

 
10.8

 
112.3

 
76.8

 
81.1

State
4.9

 
27.9

 
4.6

 
(9.0
)
 
3.3

 
(7.9
)
 
20.8

 
20.2

 
20.0

Production tax credits
(31.8
)
 
(33.1
)
 
(31.3
)
 
(14.0
)
 
(14.5
)
 
(13.8
)
 
(17.8
)
 
(18.6
)
 
(17.5
)
Investment tax credits
(1.3
)
 
(1.4
)
 
(1.6
)
 
(0.5
)
 
(0.6
)
 
(0.6
)
 
(0.8
)
 
(0.8
)
 
(1.0
)
Provision recorded as a change in accrued interest
—

 
—

 
(0.1
)
 
—

 
—

 
—

 
—

 
—

 
(0.1
)
 

$59.4

 

$70.4

 

$44.3

 

($5.9
)
 

($22.7
)
 

($48.9
)
 

$93.3

 

$82.9

 

$85.3



Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
 
Alliant Energy
 
IPL
 
WPL
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
 
2016
 
2015
 
2014
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

 
5.2

 
5.4

 
6.4

 
6.2

 
6.1

 
5.1

 
5.1

 
5.1

IPL’s tax benefit riders
(10.0
)
 
(10.6
)
 
(12.9
)
 
(20.1
)
 
(28.3
)
 
(39.6
)
 
—

 
—

 
—

Effect of rate-making on property-related differences
(8.5
)
 
(6.8
)
 
(7.5
)
 
(16.2
)
 
(17.2
)
 
(21.9
)
 
(0.7
)
 
(0.5
)
 
(0.7
)
Production tax credits
(7.2
)
 
(7.2
)
 
(7.1
)
 
(6.3
)
 
(8.3
)
 
(9.6
)
 
(6.2
)
 
(7.1
)
 
(6.6
)
Adjustment of prior period taxes
(0.8
)
 
0.8

 
(1.3
)
 
(1.2
)
 
0.7

 
(3.0
)
 
(0.1
)
 
0.1

 
—

Other items, net
(0.5
)
 
(1.1
)
 
(1.5
)
 
(0.3
)
 
(1.2
)
 
(1.2
)
 
(0.5
)
 
(0.8
)
 
(0.8
)
Overall income tax rate
13.4
%
 
15.3
%
 
10.1
%
 
(2.7
%)
 
(13.1
%)
 
(34.2
%)
 
32.6
%
 
31.8
%
 
32.0
%


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
 
2016
 
2015
 
2016
 
2015
 
2016
 
2015
Deferred tax liabilities:
 
 
 
 
 
 
 
 
 
 
 
Property

$2,919.0

 

$2,762.9

 

$1,677.0

 

$1,587.8

 

$1,124.5

 

$1,027.0

Investment in ATC
153.1

 
138.1

 
—

 
—

 
—

 
138.9

Other
95.3

 
157.3

 
71.4

 
87.8

 
59.1

 
67.9

Total deferred tax liabilities
3,167.4

 
3,058.3

 
1,748.4

 
1,675.6

 
1,183.6

 
1,233.8

Deferred tax assets:
 
 
 
 
 
 
 
 
 
 
 
Federal credit carryforwards
268.4

 
236.4

 
95.9

 
81.7

 
112.9

 
95.5

Net operating losses carryforwards - federal
173.3

 
250.9

 
69.6

 
113.1

 
75.4

 
105.1

Regulatory liability - IPL’s tax benefit riders
34.7

 
66.1

 
34.7

 
66.1

 
—

 
—

Net operating losses carryforwards - state
32.9

 
38.3

 
0.6

 
1.1

 
0.1

 
3.6

Other
87.9

 
85.4

 
35.8

 
35.6

 
23.6

 
24.2

Total deferred tax assets
597.2

 
677.1

 
236.6

 
297.6

 
212.0

 
228.4

Total deferred tax liabilities, net

$2,570.2

 

$2,381.2

 

$1,511.8

 

$1,378.0

 

$971.6

 

$1,005.4



Property - Property-related differences were primarily related to accelerated depreciation, including bonus depreciation. In 2015, the PATH Act was enacted. The most significant provisions of the PATH Act for Alliant Energy, IPL and WPL relate to the extension of bonus depreciation deductions for certain expenditures for property incurred through December 31, 2019 and placed in service prior to December 31, 2020. Alliant Energy currently estimates its total bonus depreciation deductions to be claimed on its U.S. federal income tax return for calendar year 2016 will be approximately $350 million ($100 million for IPL and $200 million for WPL).

Carryforwards - At December 31, 2016, carryforwards and expiration dates were estimated as follows (in millions):
 
Range of Expiration Dates
 
Alliant Energy
 
IPL
 
WPL
Federal net operating losses
2030-2034
 

$506

 

$206

 

$215

State net operating losses
2018-2034
 
673

 
12

 
2

Federal tax credits
2022-2036
 
274

 
100

 
113



Uncertain Tax Positions - At December 31, 2016, 2015 and 2014, 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, 2016, 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)
2013
-
2015
Consolidated Iowa income tax returns (b)
2013
-
2015
Wisconsin combined tax returns (c)
2012
-
2015

(a)
The federal tax returns for 2013 and 2014 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.