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Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
401(k) costs | $ 26 | $ 25 | $ 25
IPL [Member] |  |  |
401(k) costs | 13 | 13 | 13
WPL [Member] |  |  |
401(k) costs | $ 12 | $ 12 | $ 12

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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | debit
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_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |