XML 58 R110.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Benefit Plans (Carrying Value And Fair Market Value Of The Deferred Compensation Obligation for Company Stock Account) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items] |  |
Carrying value of deferred compensation obligation | $ 10.0 | $ 9.8
Fair market value of deferred compensation obligation | $ 20.9 | $ 16.2

X
- Definition Carrying value of deferred compensation + References No definition available. + Details
Name: | lnt_CarryingValueOfDeferredCompensation
Namespace Prefix: | lnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Fair market value of deferred compensation + References No definition available. + Details
Name: | lnt_FairMarketValueOfDeferredCompensation
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