XML 68 R59.htm IDEA: XBRL DOCUMENT
v3.2.0.727

Benefit Plans (Defined Contribution Retirement Plans) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2015 | Jun. 30, 2014 | Jun. 30, 2015 | Jun. 30, 2014
401(k) costs |  | $ 5.6 | $ 6.1 | $ 12.3 | $ 12.0
IPL [Member] |  |  |  |  |
401(k) costs | [1] | 2.9 | 2.6 | 6.3 | 5.7
WPL [Member] |  |  |  |  |
401(k) costs | [1] | $ 2.6 | $ 3.3 | $ 5.5 | $ 5.9
[1] | IPL’s and WPL’s amounts include allocated costs associated with Corporate Services employees.

X
- Definition The amount of the cost recognized during the period for defined contribution plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942 + Details
Name: | us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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: |