XML 32 R112.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Benefit Plans (Regulatory Assets and Regulatory Liabilities) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
--- | --- | ---
IPL [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Regulatory assets | $ 38.2 lnt_DefinedBenefitPlanRegulatoryAssetAllocatedFromCorporateServices / dei_LegalEntityAxis = lnt_IplMember | $ 26.5 lnt_DefinedBenefitPlanRegulatoryAssetAllocatedFromCorporateServices / dei_LegalEntityAxis = lnt_IplMember
Regulatory liabilities | 0 lnt_DefinedBenefitPlanRegulatoryLiabilitiesAllocatedFromCorporateServices / dei_LegalEntityAxis = lnt_IplMember | 1.7 lnt_DefinedBenefitPlanRegulatoryLiabilitiesAllocatedFromCorporateServices / dei_LegalEntityAxis = lnt_IplMember
WPL [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Regulatory assets | 28.0 lnt_DefinedBenefitPlanRegulatoryAssetAllocatedFromCorporateServices / dei_LegalEntityAxis = lnt_WplMember | 19.8 lnt_DefinedBenefitPlanRegulatoryAssetAllocatedFromCorporateServices / dei_LegalEntityAxis = lnt_WplMember
Regulatory liabilities | $ 0 lnt_DefinedBenefitPlanRegulatoryLiabilitiesAllocatedFromCorporateServices / dei_LegalEntityAxis = lnt_WplMember | $ 1.3 lnt_DefinedBenefitPlanRegulatoryLiabilitiesAllocatedFromCorporateServices / dei_LegalEntityAxis = lnt_WplMember

X
- Definition Defined Benefit Plan Regulatory Asset Allocated From Corporate Services + References No definition available. + Details
Name: | lnt_DefinedBenefitPlanRegulatoryAssetAllocatedFromCorporateServices
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Defined Benefit Plan Regulatory Liabilities Allocated From Corporate Services + References No definition available. + Details
Name: | lnt_DefinedBenefitPlanRegulatoryLiabilitiesAllocatedFromCorporateServices
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
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: |

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