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Bank segment - Contingencies (Details) (USD $)
In Millions, unless otherwise specified
 1 Months Ended
Dec. 31, 2014
Mar. 31, 2015
March 2011 Class Action Lawsuit    
Loss Contingencies [Line Items]    
Litigation Settlement, Amount $ (2.0)us-gaap_LitigationSettlementAmount
/ us-gaap_LitigationCaseAxis
= he_March2011ClassActionLawsuitMember		  
Loss Contingency Accrual   2.0us-gaap_LossContingencyAccrualAtCarryingValue
/ us-gaap_LitigationCaseAxis
= he_March2011ClassActionLawsuitMember
American Savings Bank (ASB)    
Loss Contingencies [Line Items]    
Unfunded commitments to fund the company's LIHTC $ 14.8he_QualifiedAffordableHousingProjectInvestmentsCommitment
/ dei_LegalEntityAxis
= he_AmericanSavingsBankFSBMember		 $ 12.5he_QualifiedAffordableHousingProjectInvestmentsCommitment
/ dei_LegalEntityAxis
= he_AmericanSavingsBankFSBMember