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Commitments And Contingencies (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | $ 2,360 us-gaap_LongTermPurchaseCommitmentAmount |
Performance guarantees outstanding | 251 lnt_PerformanceGuaranteesOutstanding |
Present value abandonment obligation | 35 lnt_PresentValueAbandonmentObligation |
Minimum [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Warranty period | 12 months |
Maximum [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Warranty period | 60 months |
Performance guarantees outstanding, 2015 [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Performance guarantees outstanding | 128 lnt_PerformanceGuaranteesOutstanding / lnt_PerformanceGuaranteesOutstandingByExpirationPeriodAxis = lnt_PerformanceGuaranteesOutstandingYearOneMember |
Performance guarantees outstanding, 2016 [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Performance guarantees outstanding | 48 lnt_PerformanceGuaranteesOutstanding / lnt_PerformanceGuaranteesOutstandingByExpirationPeriodAxis = lnt_PerformanceGuaranteesOutstandingYearTwoMember |
Performance guarantees outstanding, 2017 [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Performance guarantees outstanding | 75 lnt_PerformanceGuaranteesOutstanding / lnt_PerformanceGuaranteesOutstandingByExpirationPeriodAxis = lnt_PerformanceGuaranteesOutstandingYearThreeMember |
Capital Purchase Obligation [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 25 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CapitalPurchaseObligationMember |
DAEC IPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 1,538 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_DaecIplMember | [1],[2]
IPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 1,859 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember |
Number of sites monitoring and/or remediating (in sites) | 25 lnt_Numberofsitesremediatingandmonitoring / dei_LegalEntityAxis = lnt_IplMember |
IPL [Member] | Capital Purchase Obligation [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 6 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_IplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CapitalPurchaseObligationMember |
WPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 499 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember |
Number of sites monitoring and/or remediating (in sites) | 5 lnt_Numberofsitesremediatingandmonitoring / dei_LegalEntityAxis = lnt_WplMember |
WPL [Member] | Capital Purchase Obligation [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Minimum future commitments | 19 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis = lnt_CapitalPurchaseObligationMember |
Environmental Issue [Member] | WPL [Member] |  |
Long-term Purchase Commitment [Line Items] |  |
Damages awarded | $ 7 us-gaap_LossContingencyDamagesAwardedValue / dei_LegalEntityAxis = lnt_WplMember / us-gaap_LitigationCaseAxis = us-gaap_EnvironmentalIssueMember |
[1] | Includes commitments incurred under a PPA, which grants IPL rights to purchase up to 431 MWs of capacity and the resulting energy from DAEC for a term through December 31, 2025. If energy delivered is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s fuel adjustment clause.
[2] | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. Refer to Note 18 for additional information on purchased power transactions.

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- Definition Amount of damages awarded to the plaintiff in the legal matter. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349 + Details
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