XML 109 R55.htm IDEA: XBRL DOCUMENT
v2.4.0.8

Benefit Plans (Schedule Of Qualified and Non-qualified Pension And Other Postretirement Benefits Costs (Credits)) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2013 | Jun. 30, 2012 | Jun. 30, 2013 | Jun. 30, 2012
Defined benefit pension plans [Member] | IPL [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefits costs (credits) associated with Corporate Services employees | $ 0.5 | $ 0.5 | $ 1.0 | $ 1.0
Defined benefit pension plans [Member] | WPL [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefits costs (credits) associated with Corporate Services employees | 0.4 | 0.3 | 0.7 | 0.6
Other Postretirement Benefits Costs (Credits) [Member] | IPL [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefits costs (credits) associated with Corporate Services employees | 0 | 0.1 | (0.1) | 0.1
Other Postretirement Benefits Costs (Credits) [Member] | WPL [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefits costs (credits) associated with Corporate Services employees | $ (0.1) | $ 0 | $ (0.1) | $ 0

X
- Definition Pension and other postretirement benefits plans costs allocated from Corporate Services. + References No definition available. + Details
Name: | lnt_DefinedBenefitPlanPensionAndOtherPostretirementBenefitsPlansCostsAllocatedFromCorporateServices
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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