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v2.4.1.9

Related Parties (Service Agreements) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Corporate Service Billings [Member] | IPL [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts billed between related parties | $ 148 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_IplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_CorporateServiceBillingsMember | $ 140 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_IplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_CorporateServiceBillingsMember | $ 129 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_IplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_CorporateServiceBillingsMember
Corporate Service Billings [Member] | WPL [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts billed between related parties | 116 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_WplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_CorporateServiceBillingsMember | 103 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_WplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_CorporateServiceBillingsMember | 102 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_WplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_CorporateServiceBillingsMember
Sales Credited [Member] | IPL [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts billed between related parties | 8 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_IplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_ScoaSalesCreditedMember | 7 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_IplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_ScoaSalesCreditedMember | 10 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_IplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_ScoaSalesCreditedMember
Sales Credited [Member] | WPL [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts billed between related parties | 6 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_WplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_ScoaSalesCreditedMember | 12 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_WplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_ScoaSalesCreditedMember | 14 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_WplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_ScoaSalesCreditedMember
Purchases Billed [Member] | IPL [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts billed between related parties | 422 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_IplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_ScoaPurchasesBilledMember | 365 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_IplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_ScoaPurchasesBilledMember | 301 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_IplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_ScoaPurchasesBilledMember
Purchases Billed [Member] | WPL [Member] |  |  |
Related Party Transaction [Line Items] |  |  |
Amounts billed between related parties | $ 125 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_WplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_ScoaPurchasesBilledMember | $ 68 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_WplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_ScoaPurchasesBilledMember | $ 61 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = lnt_WplMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = lnt_ScoaPurchasesBilledMember

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- Definition Amount of transactions with related party during the financial reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39622-107864 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864 + Details
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Balance Type: | debit
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- Details
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- Details
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- Details
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- Details
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Data Type: | na
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