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v2.4.1.9

Regulatory Matters (Customer Billing Credits) (Details) (IPL [Member], USD $) In Millions, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2015
IPL [Member] |
Regulatory Liabilities [Line Items] |
Customer billing credits | $ 6 lnt_CustomerBillingCredits / dei_LegalEntityAxis = lnt_IplMember

X
- Definition Customer Billing Credits + References No definition available. + Details
Name: | lnt_CustomerBillingCredits
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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