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Income Taxes (Tables)
 9 Months Ended
Sep. 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 September 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
(10.1
)
 
(11.9
)
 
(22.6
)
 
(16.5
)
 
(1.9
)
 
(0.7
)
IPL’s tax benefit riders
(8.3
)
 
(13.1
)
 
(20.9
)
 
(20.1
)
 
—

 
—

Production tax credits
(6.2
)
 
(9.0
)
 
(7.0
)
 
(6.0
)
 
(7.0
)
 
(5.7
)
Other items, net
2.8

 
4.4

 
2.3

 
5.4

 
5.5

 
4.0

Overall income tax rate
13.2
%
 
5.4
%
 
(13.2
%)
 
(2.2
%)
 
31.6
%
 
32.6
%

 
Alliant Energy
 
IPL
 
WPL
Nine Months Ended September 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
(9.1
)
 
(8.2
)
 
(20.6
)
 
(14.8
)
 
(1.8
)
 
(0.8
)
IPL’s tax benefit riders
(8.1
)
 
(10.2
)
 
(20.1
)
 
(19.6
)
 
—

 
—

Production tax credits
(6.0
)
 
(7.2
)
 
(6.8
)
 
(6.1
)
 
(7.0
)
 
(6.1
)
Other items, net
3.1

 
3.5

 
2.7

 
4.2

 
4.9

 
4.4

Overall income tax rate
14.9
%
 
12.9
%
 
(9.8
%)
 
(1.3
%)
 
31.1
%
 
32.5
%
Summary Of Tax Credit Carryforwards
At September 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
 

$815

 

$500

 

$208

State net operating losses
2018-2037
 
701

 
14

 
2

Federal tax credits
2022-2037
 
297

 
110

 
125
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 September 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
(10.1
)
 
(11.9
)
 
(22.6
)
 
(16.5
)
 
(1.9
)
 
(0.7
)
IPL’s tax benefit riders
(8.3
)
 
(13.1
)
 
(20.9
)
 
(20.1
)
 
—

 
—

Production tax credits
(6.2
)
 
(9.0
)
 
(7.0
)
 
(6.0
)
 
(7.0
)
 
(5.7
)
Other items, net
2.8

 
4.4

 
2.3

 
5.4

 
5.5

 
4.0

Overall income tax rate
13.2
%
 
5.4
%
 
(13.2
%)
 
(2.2
%)
 
31.6
%
 
32.6
%

 
Alliant Energy
 
IPL
 
WPL
Nine Months Ended September 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
(9.1
)
 
(8.2
)
 
(20.6
)
 
(14.8
)
 
(1.8
)
 
(0.8
)
IPL’s tax benefit riders
(8.1
)
 
(10.2
)
 
(20.1
)
 
(19.6
)
 
—

 
—

Production tax credits
(6.0
)
 
(7.2
)
 
(6.8
)
 
(6.1
)
 
(7.0
)
 
(6.1
)
Other items, net
3.1

 
3.5

 
2.7

 
4.2

 
4.9

 
4.4

Overall income tax rate
14.9
%
 
12.9
%
 
(9.8
%)
 
(1.3
%)
 
31.1
%
 
32.5
%
Summary Of Tax Credit Carryforwards
At September 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
 

$815

 

$500

 

$208

State net operating losses
2018-2037
 
701

 
14

 
2

Federal tax credits
2022-2037
 
297

 
110

 
125
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 September 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
(10.1
)
 
(11.9
)
 
(22.6
)
 
(16.5
)
 
(1.9
)
 
(0.7
)
IPL’s tax benefit riders
(8.3
)
 
(13.1
)
 
(20.9
)
 
(20.1
)
 
—

 
—

Production tax credits
(6.2
)
 
(9.0
)
 
(7.0
)
 
(6.0
)
 
(7.0
)
 
(5.7
)
Other items, net
2.8

 
4.4

 
2.3

 
5.4

 
5.5

 
4.0

Overall income tax rate
13.2
%
 
5.4
%
 
(13.2
%)
 
(2.2
%)
 
31.6
%
 
32.6
%

 
Alliant Energy
 
IPL
 
WPL
Nine Months Ended September 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
(9.1
)
 
(8.2
)
 
(20.6
)
 
(14.8
)
 
(1.8
)
 
(0.8
)
IPL’s tax benefit riders
(8.1
)
 
(10.2
)
 
(20.1
)
 
(19.6
)
 
—

 
—

Production tax credits
(6.0
)
 
(7.2
)
 
(6.8
)
 
(6.1
)
 
(7.0
)
 
(6.1
)
Other items, net
3.1

 
3.5

 
2.7

 
4.2

 
4.9

 
4.4

Overall income tax rate
14.9
%
 
12.9
%
 
(9.8
%)
 
(1.3
%)
 
31.1
%
 
32.5
%
Summary Of Tax Credit Carryforwards
At September 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
 

$815

 

$500

 

$208

State net operating losses
2018-2037
 
701

 
14

 
2

Federal tax credits
2022-2037
 
297

 
110

 
125