XML 50 R27.htm IDEA: XBRL DOCUMENT
v3.8.0.1

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 |

X
- Definition Income tax + References No definition available. + Details
Name: | lnt_IncomeTaxLineItems
Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the reconciliation using percentage or dollar amounts of the reported amount of income tax expense attributable to continuing operations for the year to the amount of income tax expense that would result from applying domestic federal statutory tax rates to pretax income from continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32687-109319 + Details
Name: | us-gaap_ScheduleOfEffectiveIncomeTaxRateReconciliationTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of tax credit carryforwards available to reduce future taxable income, including amounts, expiration dates, limitations on use and the related deferred tax assets and valuation allowances. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Carryforwards -URI http://asc.fasb.org/extlink&oid=6506874 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=65882285&loc=d3e32559-109319 + Details
Name: | us-gaap_SummaryOfTaxCreditCarryforwardsTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |