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v3.6.0.2

Income Taxes (Narrative) (Details) - Scenario, Forecast [Member] $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($)
Income Tax [Line Items] |
Deductions in income tax return | $ 350
IPL [Member] |
Income Tax [Line Items] |
Deductions in income tax return | 100
WPL [Member] |
Income Tax [Line Items] |
Deductions in income tax return | $ 200

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- Definition The difference between tax and book deductions that are expected to be reflected on income tax returns as applicable federal and state laws allow. + References No definition available. + Details
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Balance Type: | credit
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- Definition Income tax + References No definition available. + Details
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Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |