XML 154 R122.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Benefit Plans (Carrying Value Of Entity's Deferred Compensation Obligations Interest And Equity Accounts) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items] |  |
Carrying value of deferred compensation obligations | $ 18.3 | $ 17.8
IPL [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Carrying value of deferred compensation obligations | $ 5.0 | $ 5.2

X
- Definition Carrying value of entity deferred compensation obligations interest and equity accounts + References No definition available. + Details
Name: | lnt_CarryingValueOfEntityDeferredCompensationObligationsInterestAndEquityAccounts
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + 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: |