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Income Taxes (Tables)
 6 Months Ended
Jun. 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 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
%
Summary Of Tax Credit 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]  
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
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
%
Summary Of Tax Credit 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]  
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
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
%
Summary Of Tax Credit 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