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Income Taxes (Tables)
 3 Months Ended
Mar. 31, 2018
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 March 31
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
7.5

 
5.4

 
8.5

 
6.3

 
6.2

 
5.1

Effect of rate-making on property-related differences
(7.4
)
 
(7.5
)
 
(13.5
)
 
(17.9
)
 
(2.4
)
 
(1.7
)
Production tax credits
(5.5
)
 
(5.9
)
 
(5.4
)
 
(6.6
)
 
(6.7
)
 
(7.0
)
IPL’s tax benefit riders
(2.2
)
 
(7.8
)
 
(4.7
)
 
(19.4
)
 
—

 
—

Other items, net
(1.4
)
 
(4.4
)
 
—

 
(7.6
)
 
(0.3
)
 
(0.4
)
Overall income tax rate
12.0
%
 
14.8
%
 
5.9
%
 
(10.2
%)
 
17.8
%
 
31.0
%
Summary Of Tax Credit Carryforwards
At March 31, 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
 

$774

 

$497

 

$176

State net operating losses
2018-2038
 
707

 
13

 
2

Federal tax credits
2022-2038
 
277

 
123

 
136
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 March 31
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
7.5

 
5.4

 
8.5

 
6.3

 
6.2

 
5.1

Effect of rate-making on property-related differences
(7.4
)
 
(7.5
)
 
(13.5
)
 
(17.9
)
 
(2.4
)
 
(1.7
)
Production tax credits
(5.5
)
 
(5.9
)
 
(5.4
)
 
(6.6
)
 
(6.7
)
 
(7.0
)
IPL’s tax benefit riders
(2.2
)
 
(7.8
)
 
(4.7
)
 
(19.4
)
 
—

 
—

Other items, net
(1.4
)
 
(4.4
)
 
—

 
(7.6
)
 
(0.3
)
 
(0.4
)
Overall income tax rate
12.0
%
 
14.8
%
 
5.9
%
 
(10.2
%)
 
17.8
%
 
31.0
%
Summary Of Tax Credit Carryforwards
At March 31, 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
 

$774

 

$497

 

$176

State net operating losses
2018-2038
 
707

 
13

 
2

Federal tax credits
2022-2038
 
277

 
123

 
136
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 March 31
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
7.5

 
5.4

 
8.5

 
6.3

 
6.2

 
5.1

Effect of rate-making on property-related differences
(7.4
)
 
(7.5
)
 
(13.5
)
 
(17.9
)
 
(2.4
)
 
(1.7
)
Production tax credits
(5.5
)
 
(5.9
)
 
(5.4
)
 
(6.6
)
 
(6.7
)
 
(7.0
)
IPL’s tax benefit riders
(2.2
)
 
(7.8
)
 
(4.7
)
 
(19.4
)
 
—

 
—

Other items, net
(1.4
)
 
(4.4
)
 
—

 
(7.6
)
 
(0.3
)
 
(0.4
)
Overall income tax rate
12.0
%
 
14.8
%
 
5.9
%
 
(10.2
%)
 
17.8
%
 
31.0
%
Summary Of Tax Credit Carryforwards
At March 31, 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
 

$774

 

$497

 

$176

State net operating losses
2018-2038
 
707

 
13

 
2

Federal tax credits
2022-2038
 
277

 
123

 
136