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