XML 104 R70.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items] |  |  |
Collections reinvested in receivables | $ 1,647.1 | $ 1,818.1 | $ 1,812.9
Write-offs, net of recoveries | $ 17.7 | $ 4.8 | $ 8.8

X
- Definition Collections reinvested related to sales of accounts receivable program. + References No definition available. + Details
Name: | lnt_CollectionsReinvestedInReceivables
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Credit losses, net of recoveries related to sales of accounts receivable program. + References No definition available. + Details
Name: | lnt_CreditLossesNetOfRecoveries
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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
Name: | us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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