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v3.10.0.1

Debt (Schedule Of Debt-To-Capital Ratios) (Details) | Dec. 31, 2018
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Actual debt-to-capital ratio | 55.00%
IPL [Member] |
Actual debt-to-capital ratio | 45.00%
WPL [Member] |
Actual debt-to-capital ratio | 48.00%
Maximum [Member] |
Requirement, not to exceed | 65.00%
Maximum [Member] | IPL [Member] |
Requirement, not to exceed | 65.00%
Maximum [Member] | WPL [Member] |
Requirement, not to exceed | 65.00%

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- Definition Debt to capital ratios actual status + References No definition available. + Details
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Namespace Prefix: | lnt_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Debt to capital ratios base percentage + References No definition available. + Details
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Namespace Prefix: | lnt_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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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_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |