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Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Accounts Receivable [Line Items] |  |
Fair value of deferred proceeds | $ 188 | $ 188
IPL [Member] |  |
Accounts Receivable [Line Items] |  |
Fair value of deferred proceeds | 188 | 188
Financing Receivable [Member] | IPL [Member] |  |
Accounts Receivable [Line Items] |  |
Customer accounts receivable | 114 | 125
Unbilled utility revenues | 92 | 95
Other receivables | 0 | 1
Receivables sold to third party | 206 | 221
Less: cash proceeds | 1 | 27
Deferred proceeds | 205 | 194
Less: allowance for expected credit losses | 17 | 6
Fair value of deferred proceeds | 188 | 188
Outstanding receivables past due | $ 27 | $ 26

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Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Cash Proceeds From Receivables Sold + References No definition available. + Details
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Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition Customer Accounts Receivable Sold, Amount + References No definition available. + Details
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Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Deferred proceeds of receivables sold + References No definition available. + Details
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Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Receivables sold + References No definition available. + Details
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Namespace Prefix: | lnt_
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Balance Type: | debit
Period Type: | instant

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- Definition Unbilled Utility Revenues Sold, Amount + References No definition available. + Details
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Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Balance Type: | na
Period Type: | duration

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- Definition Amount of financing receivable past due. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 55 -Paragraph 80 -URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922355-210448 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919253-210447 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7A -URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953401-111524 + Details
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- Details
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Namespace Prefix: |
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- Details
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