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Income Taxes (Tables)
 9 Months Ended
Sep. 30, 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 September 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
6.9

 
5.7

 
7.7

 
6.5

 
6.2

 
5.2

Effect of rate-making on property-related differences
(6.3
)
 
(10.1
)
 
(11.5
)
 
(22.6
)
 
(2.1
)
 
(1.9
)
Production tax credits
(5.4
)
 
(6.2
)
 
(5.5
)
 
(7.0
)
 
(6.4
)
 
(7.0
)
Adjustment for prior period taxes
(5.7
)
 
(2.0
)
 
(10.2
)
 
(3.5
)
 
—

 
0.8

IPL’s tax benefit riders
(2.3
)
 
(8.3
)
 
(4.8
)
 
(20.9
)
 
—

 
—

Federal Tax Reform adjustments
(2.5
)
 
—

 
(0.9
)
 
—

 
(6.4
)
 
—

Other items, net
(0.4
)
 
(0.9
)
 
(0.6
)
 
(0.7
)
 
(0.5
)
 
(0.5
)
Overall income tax rate
5.3
%
 
13.2
%
 
(4.8
%)
 
(13.2
%)
 
11.8
%
 
31.6
%

 
Alliant Energy
 
IPL
 
WPL
Nine Months Ended September 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
6.9

 
5.6

 
7.7

 
6.5

 
6.2

 
5.1

Effect of rate-making on property-related differences
(6.7
)
 
(9.1
)
 
(12.0
)
 
(20.6
)
 
(2.3
)
 
(1.8
)
Production tax credits
(5.4
)
 
(6.0
)
 
(5.4
)
 
(6.8
)
 
(6.6
)
 
(7.0
)
Adjustment for prior period taxes
(2.6
)
 
(1.3
)
 
(5.4
)
 
(3.3
)
 
—

 
0.3

IPL’s tax benefit riders
(2.2
)
 
(8.1
)
 
(4.6
)
 
(20.1
)
 
—

 
—

Federal Tax Reform adjustments
(1.2
)
 
—

 
(0.5
)
 
—

 
(2.8
)
 
—

Other items, net
(1.0
)
 
(1.2
)
 
(1.0
)
 
(0.5
)
 
(1.3
)
 
(0.5
)
Overall income tax rate
8.8
%
 
14.9
%
 
(0.2
%)
 
(9.8
%)
 
14.2
%
 
31.1
%
Summary Of Tax Credit Carryforwards
At September 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
 

$804

 

$563

 

$144

State net operating losses
2018-2038
 
765

 
13

 
2

Federal tax credits
2022-2038
 
290

 
129

 
143
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
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
6.9

 
5.7

 
7.7

 
6.5

 
6.2

 
5.2

Effect of rate-making on property-related differences
(6.3
)
 
(10.1
)
 
(11.5
)
 
(22.6
)
 
(2.1
)
 
(1.9
)
Production tax credits
(5.4
)
 
(6.2
)
 
(5.5
)
 
(7.0
)
 
(6.4
)
 
(7.0
)
Adjustment for prior period taxes
(5.7
)
 
(2.0
)
 
(10.2
)
 
(3.5
)
 
—

 
0.8

IPL’s tax benefit riders
(2.3
)
 
(8.3
)
 
(4.8
)
 
(20.9
)
 
—

 
—

Federal Tax Reform adjustments
(2.5
)
 
—

 
(0.9
)
 
—

 
(6.4
)
 
—

Other items, net
(0.4
)
 
(0.9
)
 
(0.6
)
 
(0.7
)
 
(0.5
)
 
(0.5
)
Overall income tax rate
5.3
%
 
13.2
%
 
(4.8
%)
 
(13.2
%)
 
11.8
%
 
31.6
%

 
Alliant Energy
 
IPL
 
WPL
Nine Months Ended September 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
6.9

 
5.6

 
7.7

 
6.5

 
6.2

 
5.1

Effect of rate-making on property-related differences
(6.7
)
 
(9.1
)
 
(12.0
)
 
(20.6
)
 
(2.3
)
 
(1.8
)
Production tax credits
(5.4
)
 
(6.0
)
 
(5.4
)
 
(6.8
)
 
(6.6
)
 
(7.0
)
Adjustment for prior period taxes
(2.6
)
 
(1.3
)
 
(5.4
)
 
(3.3
)
 
—

 
0.3

IPL’s tax benefit riders
(2.2
)
 
(8.1
)
 
(4.6
)
 
(20.1
)
 
—

 
—

Federal Tax Reform adjustments
(1.2
)
 
—

 
(0.5
)
 
—

 
(2.8
)
 
—

Other items, net
(1.0
)
 
(1.2
)
 
(1.0
)
 
(0.5
)
 
(1.3
)
 
(0.5
)
Overall income tax rate
8.8
%
 
14.9
%
 
(0.2
%)
 
(9.8
%)
 
14.2
%
 
31.1
%
Summary Of Tax Credit Carryforwards
At September 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
 

$804

 

$563

 

$144

State net operating losses
2018-2038
 
765

 
13

 
2

Federal tax credits
2022-2038
 
290

 
129

 
143
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
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
6.9

 
5.7

 
7.7

 
6.5

 
6.2

 
5.2

Effect of rate-making on property-related differences
(6.3
)
 
(10.1
)
 
(11.5
)
 
(22.6
)
 
(2.1
)
 
(1.9
)
Production tax credits
(5.4
)
 
(6.2
)
 
(5.5
)
 
(7.0
)
 
(6.4
)
 
(7.0
)
Adjustment for prior period taxes
(5.7
)
 
(2.0
)
 
(10.2
)
 
(3.5
)
 
—

 
0.8

IPL’s tax benefit riders
(2.3
)
 
(8.3
)
 
(4.8
)
 
(20.9
)
 
—

 
—

Federal Tax Reform adjustments
(2.5
)
 
—

 
(0.9
)
 
—

 
(6.4
)
 
—

Other items, net
(0.4
)
 
(0.9
)
 
(0.6
)
 
(0.7
)
 
(0.5
)
 
(0.5
)
Overall income tax rate
5.3
%
 
13.2
%
 
(4.8
%)
 
(13.2
%)
 
11.8
%
 
31.6
%

 
Alliant Energy
 
IPL
 
WPL
Nine Months Ended September 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
6.9

 
5.6

 
7.7

 
6.5

 
6.2

 
5.1

Effect of rate-making on property-related differences
(6.7
)
 
(9.1
)
 
(12.0
)
 
(20.6
)
 
(2.3
)
 
(1.8
)
Production tax credits
(5.4
)
 
(6.0
)
 
(5.4
)
 
(6.8
)
 
(6.6
)
 
(7.0
)
Adjustment for prior period taxes
(2.6
)
 
(1.3
)
 
(5.4
)
 
(3.3
)
 
—

 
0.3

IPL’s tax benefit riders
(2.2
)
 
(8.1
)
 
(4.6
)
 
(20.1
)
 
—

 
—

Federal Tax Reform adjustments
(1.2
)
 
—

 
(0.5
)
 
—

 
(2.8
)
 
—

Other items, net
(1.0
)
 
(1.2
)
 
(1.0
)
 
(0.5
)
 
(1.3
)
 
(0.5
)
Overall income tax rate
8.8
%
 
14.9
%
 
(0.2
%)
 
(9.8
%)
 
14.2
%
 
31.1
%
Summary Of Tax Credit Carryforwards
At September 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
 

$804

 

$563

 

$144

State net operating losses
2018-2038
 
765

 
13

 
2

Federal tax credits
2022-2038
 
290

 
129

 
143