XML 146 R114.htm IDEA: XBRL DOCUMENT
v3.3.1.900

Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
401(k) costs | $ 24.9 | $ 22.5 | $ 19.2
IPL [Member] |  |  |
401(k) costs | 12.7 | 11.1 | 9.9
WPL [Member] |  |  |
401(k) costs | $ 11.2 | $ 10.5 | $ 8.5

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: |