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Income Taxes
 6 Months Ended
Jun. 30, 2018
Income Taxes [Line Items]  
Income Taxes
INCOME TAXES
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
Three Months Ended June 30
2018
 
2017
 
2018
 
2017
 
2018
 
2017
Statutory federal income tax rate
21.0
 %
 
35.0
 %
 
21.0
%
 
35.0
%
 
21.0
 %
 
35.0
 %
State income taxes, net of federal benefits
6.5

 
5.5

 
7.0

 
6.5

 
6.2

 
5.1

Effect of rate-making on property-related differences
(6.7
)
 
(9.0
)
 
(11.5
)
 
(18.0
)
 
(2.7
)
 
(1.9
)
Production tax credits
(5.4
)
 
(5.9
)
 
(5.3
)
 
(6.2
)
 
(6.8
)
 
(7.1
)
IPL’s tax benefit riders
(2.1
)
 
(7.8
)
 
(4.3
)
 
(18.6
)
 
—

 
—

Other items, net
(1.6
)
 
0.2

 
(2.8
)
 
—

 
(4.2
)
 
(0.6
)
Overall income tax rate
11.7
%
 
18.0
%
 
4.1
%
 
(1.3
%)
 
13.5
%
 
30.5
%

 
Alliant Energy
 
IPL
 
WPL
Six Months Ended June 30
2018
 
2017
 
2018
 
2017
 
2018
 
2017
Statutory federal income tax rate
21.0
 %
 
35.0
 %
 
21.0
%
 
35.0
%
 
21.0
 %
 
35.0
 %
State income taxes, net of federal benefits
7.1

 
5.5

 
7.7

 
6.4

 
6.2

 
5.1

Effect of rate-making on property-related differences
(7.2
)
 
(8.0
)
 
(12.4
)
 
(18.0
)
 
(2.5
)
 
(1.8
)
Production tax credits
(5.5
)
 
(5.9
)
 
(5.3
)
 
(6.4
)
 
(6.7
)
 
(7.0
)
IPL’s tax benefit riders
(2.2
)
 
(7.8
)
 
(4.5
)
 
(19.0
)
 
—

 
—

Other items, net
(1.4
)
 
(2.4
)
 
(1.5
)
 
(3.3
)
 
(2.0
)
 
(0.6
)
Overall income tax rate
11.8
%
 
16.4
%
 
5.0
%
 
(5.3
%)
 
16.0
%
 
30.7
%


Deferred Tax Assets and Liabilities - For the six months ended June 30, 2018, Alliant Energy’s, IPL’s and WPL’s deferred tax liabilities increased (decreased) $28.8 million, ($7.8) million and $17.6 million, respectively. Alliant Energy’s and WPL’s increases were primarily due to property-related differences and the utilization of federal net operating losses, which were partially offset by an increase in federal credit carryforwards. Alliant Energy’s increase was also partially offset by the effects of Iowa tax reform, which is discussed in Note 2. IPL’s decrease was primarily due to the effects of Iowa tax reform and an increase in federal credit carryforwards, which were partially offset by property-related differences and the utilization of federal net operating losses.

Carryforwards - At June 30, 2018, carryforwards and expiration dates were estimated as follows (in millions):
 
Range of Expiration Dates
 
Alliant Energy
 
IPL
 
WPL
Federal net operating losses
2030-2037
 

$759

 

$490

 

$170

State net operating losses
2018-2038
 
732

 
13

 
22

Federal tax credits
2022-2038
 
284

 
127

 
140
IPL [Member]  
Income Taxes [Line Items]  
Income Taxes
INCOME TAXES
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
Three Months Ended June 30
2018
 
2017
 
2018
 
2017
 
2018
 
2017
Statutory federal income tax rate
21.0
 %
 
35.0
 %
 
21.0
%
 
35.0
%
 
21.0
 %
 
35.0
 %
State income taxes, net of federal benefits
6.5

 
5.5

 
7.0

 
6.5

 
6.2

 
5.1

Effect of rate-making on property-related differences
(6.7
)
 
(9.0
)
 
(11.5
)
 
(18.0
)
 
(2.7
)
 
(1.9
)
Production tax credits
(5.4
)
 
(5.9
)
 
(5.3
)
 
(6.2
)
 
(6.8
)
 
(7.1
)
IPL’s tax benefit riders
(2.1
)
 
(7.8
)
 
(4.3
)
 
(18.6
)
 
—

 
—

Other items, net
(1.6
)
 
0.2

 
(2.8
)
 
—

 
(4.2
)
 
(0.6
)
Overall income tax rate
11.7
%
 
18.0
%
 
4.1
%
 
(1.3
%)
 
13.5
%
 
30.5
%

 
Alliant Energy
 
IPL
 
WPL
Six Months Ended June 30
2018
 
2017
 
2018
 
2017
 
2018
 
2017
Statutory federal income tax rate
21.0
 %
 
35.0
 %
 
21.0
%
 
35.0
%
 
21.0
 %
 
35.0
 %
State income taxes, net of federal benefits
7.1

 
5.5

 
7.7

 
6.4

 
6.2

 
5.1

Effect of rate-making on property-related differences
(7.2
)
 
(8.0
)
 
(12.4
)
 
(18.0
)
 
(2.5
)
 
(1.8
)
Production tax credits
(5.5
)
 
(5.9
)
 
(5.3
)
 
(6.4
)
 
(6.7
)
 
(7.0
)
IPL’s tax benefit riders
(2.2
)
 
(7.8
)
 
(4.5
)
 
(19.0
)
 
—

 
—

Other items, net
(1.4
)
 
(2.4
)
 
(1.5
)
 
(3.3
)
 
(2.0
)
 
(0.6
)
Overall income tax rate
11.8
%
 
16.4
%
 
5.0
%
 
(5.3
%)
 
16.0
%
 
30.7
%


Deferred Tax Assets and Liabilities - For the six months ended June 30, 2018, Alliant Energy’s, IPL’s and WPL’s deferred tax liabilities increased (decreased) $28.8 million, ($7.8) million and $17.6 million, respectively. Alliant Energy’s and WPL’s increases were primarily due to property-related differences and the utilization of federal net operating losses, which were partially offset by an increase in federal credit carryforwards. Alliant Energy’s increase was also partially offset by the effects of Iowa tax reform, which is discussed in Note 2. IPL’s decrease was primarily due to the effects of Iowa tax reform and an increase in federal credit carryforwards, which were partially offset by property-related differences and the utilization of federal net operating losses.

Carryforwards - At June 30, 2018, carryforwards and expiration dates were estimated as follows (in millions):
 
Range of Expiration Dates
 
Alliant Energy
 
IPL
 
WPL
Federal net operating losses
2030-2037
 

$759

 

$490

 

$170

State net operating losses
2018-2038
 
732

 
13

 
22

Federal tax credits
2022-2038
 
284

 
127

 
140
WPL [Member]  
Income Taxes [Line Items]  
Income Taxes
INCOME TAXES
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
Three Months Ended June 30
2018
 
2017
 
2018
 
2017
 
2018
 
2017
Statutory federal income tax rate
21.0
 %
 
35.0
 %
 
21.0
%
 
35.0
%
 
21.0
 %
 
35.0
 %
State income taxes, net of federal benefits
6.5

 
5.5

 
7.0

 
6.5

 
6.2

 
5.1

Effect of rate-making on property-related differences
(6.7
)
 
(9.0
)
 
(11.5
)
 
(18.0
)
 
(2.7
)
 
(1.9
)
Production tax credits
(5.4
)
 
(5.9
)
 
(5.3
)
 
(6.2
)
 
(6.8
)
 
(7.1
)
IPL’s tax benefit riders
(2.1
)
 
(7.8
)
 
(4.3
)
 
(18.6
)
 
—

 
—

Other items, net
(1.6
)
 
0.2

 
(2.8
)
 
—

 
(4.2
)
 
(0.6
)
Overall income tax rate
11.7
%
 
18.0
%
 
4.1
%
 
(1.3
%)
 
13.5
%
 
30.5
%

 
Alliant Energy
 
IPL
 
WPL
Six Months Ended June 30
2018
 
2017
 
2018
 
2017
 
2018
 
2017
Statutory federal income tax rate
21.0
 %
 
35.0
 %
 
21.0
%
 
35.0
%
 
21.0
 %
 
35.0
 %
State income taxes, net of federal benefits
7.1

 
5.5

 
7.7

 
6.4

 
6.2

 
5.1

Effect of rate-making on property-related differences
(7.2
)
 
(8.0
)
 
(12.4
)
 
(18.0
)
 
(2.5
)
 
(1.8
)
Production tax credits
(5.5
)
 
(5.9
)
 
(5.3
)
 
(6.4
)
 
(6.7
)
 
(7.0
)
IPL’s tax benefit riders
(2.2
)
 
(7.8
)
 
(4.5
)
 
(19.0
)
 
—

 
—

Other items, net
(1.4
)
 
(2.4
)
 
(1.5
)
 
(3.3
)
 
(2.0
)
 
(0.6
)
Overall income tax rate
11.8
%
 
16.4
%
 
5.0
%
 
(5.3
%)
 
16.0
%
 
30.7
%


Deferred Tax Assets and Liabilities - For the six months ended June 30, 2018, Alliant Energy’s, IPL’s and WPL’s deferred tax liabilities increased (decreased) $28.8 million, ($7.8) million and $17.6 million, respectively. Alliant Energy’s and WPL’s increases were primarily due to property-related differences and the utilization of federal net operating losses, which were partially offset by an increase in federal credit carryforwards. Alliant Energy’s increase was also partially offset by the effects of Iowa tax reform, which is discussed in Note 2. IPL’s decrease was primarily due to the effects of Iowa tax reform and an increase in federal credit carryforwards, which were partially offset by property-related differences and the utilization of federal net operating losses.

Carryforwards - At June 30, 2018, carryforwards and expiration dates were estimated as follows (in millions):
 
Range of Expiration Dates
 
Alliant Energy
 
IPL
 
WPL
Federal net operating losses
2030-2037
 

$759

 

$490

 

$170

State net operating losses
2018-2038
 
732

 
13

 
22

Federal tax credits
2022-2038
 
284

 
127

 
140