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Income Taxes (Tables)
 6 Months Ended
Jun. 30, 2017
Income Taxes [Line Items]  
Schedule Of Effective 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
2017
 
2016
 
2017
 
2016
 
2017
 
2016
Statutory federal income tax rate
35.0
 %
 
35.0
 %
 
35.0
%
 
35.0
%
 
35.0
 %
 
35.0
 %
Effect of rate-making on property-related differences
(9.0
)
 
(4.9
)
 
(18.0
)
 
(8.8
)
 
(1.9
)
 
(1.0
)
IPL’s tax benefit riders
(7.8
)
 
(7.9
)
 
(18.6
)
 
(16.6
)
 
—

 
—

Production tax credits
(5.9
)
 
(5.7
)
 
(6.2
)
 
(5.3
)
 
(7.1
)
 
(6.3
)
Other items, net
5.7

 
0.7

 
6.5

 
(2.0
)
 
4.5

 
4.5

Overall income tax rate
18.0
%
 
17.2
%
 
(1.3
%)
 
2.3
%
 
30.5
%
 
32.2
%

 
Alliant Energy
 
IPL
 
WPL
Six Months Ended June 30
2017
 
2016
 
2017
 
2016
 
2017
 
2016
Statutory federal income tax rate
35.0
 %
 
35.0
 %
 
35.0
%
 
35.0
%
 
35.0
 %
 
35.0
 %
Effect of rate-making on property-related differences
(8.0
)
 
(5.9
)
 
(18.0
)
 
(12.5
)
 
(1.8
)
 
(0.9
)
IPL’s tax benefit riders
(7.8
)
 
(8.4
)
 
(19.0
)
 
(19.0
)
 
—

 
—

Production tax credits
(5.9
)
 
(6.0
)
 
(6.4
)
 
(6.1
)
 
(7.0
)
 
(6.4
)
Other items, net
3.1

 
2.8

 
3.1

 
2.6

 
4.5

 
4.7

Overall income tax rate
16.4
%
 
17.5
%
 
(5.3
%)
 
—
%
 
30.7
%
 
32.4
%
Summary Of Tax Credit Carryforwards
At June 30, 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
 

$736

 

$412

 

$217

State net operating losses
2018-2037
 
707

 
14

 
2

Federal tax credits
2022-2037
 
292

 
108

 
123
IPL [Member]  
Income Taxes [Line Items]  
Schedule Of Effective 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
2017
 
2016
 
2017
 
2016
 
2017
 
2016
Statutory federal income tax rate
35.0
 %
 
35.0
 %
 
35.0
%
 
35.0
%
 
35.0
 %
 
35.0
 %
Effect of rate-making on property-related differences
(9.0
)
 
(4.9
)
 
(18.0
)
 
(8.8
)
 
(1.9
)
 
(1.0
)
IPL’s tax benefit riders
(7.8
)
 
(7.9
)
 
(18.6
)
 
(16.6
)
 
—

 
—

Production tax credits
(5.9
)
 
(5.7
)
 
(6.2
)
 
(5.3
)
 
(7.1
)
 
(6.3
)
Other items, net
5.7

 
0.7

 
6.5

 
(2.0
)
 
4.5

 
4.5

Overall income tax rate
18.0
%
 
17.2
%
 
(1.3
%)
 
2.3
%
 
30.5
%
 
32.2
%

 
Alliant Energy
 
IPL
 
WPL
Six Months Ended June 30
2017
 
2016
 
2017
 
2016
 
2017
 
2016
Statutory federal income tax rate
35.0
 %
 
35.0
 %
 
35.0
%
 
35.0
%
 
35.0
 %
 
35.0
 %
Effect of rate-making on property-related differences
(8.0
)
 
(5.9
)
 
(18.0
)
 
(12.5
)
 
(1.8
)
 
(0.9
)
IPL’s tax benefit riders
(7.8
)
 
(8.4
)
 
(19.0
)
 
(19.0
)
 
—

 
—

Production tax credits
(5.9
)
 
(6.0
)
 
(6.4
)
 
(6.1
)
 
(7.0
)
 
(6.4
)
Other items, net
3.1

 
2.8

 
3.1

 
2.6

 
4.5

 
4.7

Overall income tax rate
16.4
%
 
17.5
%
 
(5.3
%)
 
—
%
 
30.7
%
 
32.4
%
Summary Of Tax Credit Carryforwards
At June 30, 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
 

$736

 

$412

 

$217

State net operating losses
2018-2037
 
707

 
14

 
2

Federal tax credits
2022-2037
 
292

 
108

 
123
WPL [Member]  
Income Taxes [Line Items]  
Schedule Of Effective 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
2017
 
2016
 
2017
 
2016
 
2017
 
2016
Statutory federal income tax rate
35.0
 %
 
35.0
 %
 
35.0
%
 
35.0
%
 
35.0
 %
 
35.0
 %
Effect of rate-making on property-related differences
(9.0
)
 
(4.9
)
 
(18.0
)
 
(8.8
)
 
(1.9
)
 
(1.0
)
IPL’s tax benefit riders
(7.8
)
 
(7.9
)
 
(18.6
)
 
(16.6
)
 
—

 
—

Production tax credits
(5.9
)
 
(5.7
)
 
(6.2
)
 
(5.3
)
 
(7.1
)
 
(6.3
)
Other items, net
5.7

 
0.7

 
6.5

 
(2.0
)
 
4.5

 
4.5

Overall income tax rate
18.0
%
 
17.2
%
 
(1.3
%)
 
2.3
%
 
30.5
%
 
32.2
%

 
Alliant Energy
 
IPL
 
WPL
Six Months Ended June 30
2017
 
2016
 
2017
 
2016
 
2017
 
2016
Statutory federal income tax rate
35.0
 %
 
35.0
 %
 
35.0
%
 
35.0
%
 
35.0
 %
 
35.0
 %
Effect of rate-making on property-related differences
(8.0
)
 
(5.9
)
 
(18.0
)
 
(12.5
)
 
(1.8
)
 
(0.9
)
IPL’s tax benefit riders
(7.8
)
 
(8.4
)
 
(19.0
)
 
(19.0
)
 
—

 
—

Production tax credits
(5.9
)
 
(6.0
)
 
(6.4
)
 
(6.1
)
 
(7.0
)
 
(6.4
)
Other items, net
3.1

 
2.8

 
3.1

 
2.6

 
4.5

 
4.7

Overall income tax rate
16.4
%
 
17.5
%
 
(5.3
%)
 
—
%
 
30.7
%
 
32.4
%
Summary Of Tax Credit Carryforwards
At June 30, 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
 

$736

 

$412

 

$217

State net operating losses
2018-2037
 
707

 
14

 
2

Federal tax credits
2022-2037
 
292

 
108

 
123