XML 185 R74.htm IDEA: XBRL DOCUMENT
v2.4.1.9

Investments (Narrative) (Details) | Dec. 31, 2014 | Dec. 31, 2013
--- | --- | ---
WPL [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
WPL's ownership interest in WPL Transco | 95.00%us-gaap_MinorityInterestOwnershipPercentageByParent / dei_LegalEntityAxis = lnt_WplMember | 100.00%us-gaap_MinorityInterestOwnershipPercentageByParent / dei_LegalEntityAxis = lnt_WplMember
ATI [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
ATI's ownership interest in WPL Transco | 5.00%us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners / dei_LegalEntityAxis = lnt_AtiMember |

X
- Definition The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity. + References No definition available. + Details
Name: | us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The parent entity's interest in net assets of the subsidiary, expressed as a percentage. + References No definition available. + Details
Name: | us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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

X
- Details
Name: | dei_LegalEntityAxis=lnt_AtiMember
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: |