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Electric utility segment Related-Party Transactions (Details) (Hawaiian Electric Industries, Inc., HECO, USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Hawaiian Electric Industries, Inc. | HECO
      
Related Party Transaction [Line Items]      
Amount charged to subsidiaries for general management and administrative services $ 7.0us-gaap_RelatedPartyTransactionAmountsOfTransaction
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_ParentCompanyMember		 $ 6.2us-gaap_RelatedPartyTransactionAmountsOfTransaction
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_ParentCompanyMember		 $ 6.1us-gaap_RelatedPartyTransactionAmountsOfTransaction
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_ParentCompanyMember
Effective interest rate basis term 30 days    
Line of credit facility basis point spread (as a percent) 0.15%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
/ us-gaap_RelatedPartyTransactionsByRelatedPartyAxis
= us-gaap_ParentCompanyMember