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Electric utility subsidiary - Commitments and contingencies (Details) (USD $)
 0 Months Ended 1 Months Ended 3 Months Ended 1 Months Ended 3 Months Ended 0 Months Ended
Mar. 31, 2015
Jan. 20, 2015
Feb. 16, 2012
generation_unit
Aug. 31, 2014
Apr. 30, 2014
order
Mar. 31, 2015
Oct. 31, 1988
Mar. 31, 2014
Apr. 15, 2015
Mar. 23, 2015
Mar. 31, 2012
Feb. 07, 2014
Mar. 01, 2014
Dec. 31, 2014
Environmental regulation                            
Number of EGUs impacted by proposed rules of MATS     14he_NumberOfUtilitiesImpactedByProposedRulesOfMACT                      
Period for which operations was stopped prior to merger           4 years                
Changes in the asset retirement obligation liability                            
Number of orders from regulatory agency         4he_PublicUtilitiesOrdersfromRegulatoryAgencyNumber                  
Percent of energy production from renewable energy sources       65.00%he_PublicUtilitiesPercentOfEnergyProductionFromRenewableEnergySources                    
Requested approval period for motion   60 days                        
Public Utilities, Phase-in Plans [Abstract]                            
Annual incremental RAM adjusted revenues $ 31,600,000he_PublicUtilityAnnualIncrementalRateAdjustmentMechanismAdjustedRevenue                          
Hawaiian Electric Company                            
Environmental regulation                            
Period of extension resulting in MATS compliance date             1 year              
Maui Electric                            
Environmental regulation                            
Additional accrued investigation and estimated cleanup costs 3,600,000he_ReserveForAdditionalInvestigationAndEstimatedCleanupCosts
/ dei_LegalEntityAxis
= he_MauiElectricCompanyLimitedMember		         3,600,000he_ReserveForAdditionalInvestigationAndEstimatedCleanupCosts
/ dei_LegalEntityAxis
= he_MauiElectricCompanyLimitedMember		         3,100,000he_ReserveForAdditionalInvestigationAndEstimatedCleanupCosts
/ dei_LegalEntityAxis
= he_MauiElectricCompanyLimitedMember		      
Hawaiian Electric Company, Inc. and Subsidiaries                            
Environmental regulation                            
Percentage of reduction in GHG emissions by 2020 16.00%he_RequiredReductionOfGreenhouseGasEmissionsMandatedByRegulationsPercentage
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		         16.00%he_RequiredReductionOfGreenhouseGasEmissionsMandatedByRegulationsPercentage
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		                
Estimated annual fee for greenhouse gas emissions           500,000he_RequiredReductionOfGreenhouseGasEmissionsMandatedByRegulationsEstimatedAnnualFee
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		                
Impact on earnings from recognition of AROs           0he_AssetRetirementObligationsRecognitionImpactOnEarnings
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		                
Changes in the asset retirement obligation liability                            
Balance, beginning of period         41,236,000us-gaap_AssetRetirementObligation
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		 29,419,000us-gaap_AssetRetirementObligation
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		   43,106,000us-gaap_AssetRetirementObligation
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		            
Accretion expense           6,000us-gaap_AssetRetirementObligationAccretionExpense
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		   370,000us-gaap_AssetRetirementObligationAccretionExpense
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		            
Liabilities settled           (1,614,000)us-gaap_AssetRetirementObligationLiabilitiesSettled
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		   (2,240,000)us-gaap_AssetRetirementObligationLiabilitiesSettled
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		            
Revisions in estimated cash flows           0us-gaap_AssetRetirementObligationRevisionOfEstimate
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		   0us-gaap_AssetRetirementObligationRevisionOfEstimate
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		            
Balance, end of period 27,811,000us-gaap_AssetRetirementObligation
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		         27,811,000us-gaap_AssetRetirementObligation
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		   41,236,000us-gaap_AssetRetirementObligation
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		            
Proposed rate base adjustment, percent of previous rate base adjustment                       90.00%he_PublicUtilitiesProposedRateBaseAdjustmentPercentofPreviousRateBaseAdjustment
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		    
Effective interest rate, revenue balancing account                       6.00%he_PublicUtilitesEffectiveInterestRateRevenueBalancingAccount
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember		    
Period to file required plan         120 days                  
Period to file implementation plan         60 days                  
Period for full implementation of plan         180 days                  
Period to file action plan         30 days                  
Proposal to file implementation proposal         120 days                  
Period to file demand response portfolio plan         90 days                  
Minimum | Hawaiian Electric Company, Inc. and Subsidiaries                            
Changes in the asset retirement obligation liability                            
Proposed effective interest rate, revenue balancing account                         1.25%he_PublicUtilitiesProposedEffectiveInterestRateRevenueBalancingAccount
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Maximum | Hawaiian Electric Company, Inc. and Subsidiaries                            
Changes in the asset retirement obligation liability                            
Proposed effective interest rate, revenue balancing account                         3.25%he_PublicUtilitiesProposedEffectiveInterestRateRevenueBalancingAccount
/ dei_LegalEntityAxis
= he_HawaiianElectricCompanyAndSubsidiariesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Reserve for Environmental Costs                            
Environmental regulation                            
Additional reserve for investigation                           800,000us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_ReserveForEnvironmentalCostsMember
Subsequent Event                            
Changes in the asset retirement obligation liability                            
Regulatory filing period for initial briefing                 60 days          
Regulatory filing period for reply briefing                 75 days          
Public Utilities, Phase-in Plans [Abstract]                            
Annual incremental RAM adjusted revenues                 26,200,000he_PublicUtilityAnnualIncrementalRateAdjustmentMechanismAdjustedRevenue
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Net annual incremental amount to be collected under the tariffs                 14,700,000he_PublicUtilityNetReceivableUnderTariff
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Subsequent Event | Hawaiian Electric Company                            
Public Utilities, Phase-in Plans [Abstract]                            
Annual incremental RAM adjusted revenues                 20,300,000he_PublicUtilityAnnualIncrementalRateAdjustmentMechanismAdjustedRevenue
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Annual change in accrued earnings sharing credits to be refunded                 0he_PublicUtilityIncreaseDecreaseInAccruedEarningsSharingCreditsToBeRefunded
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Annual change in accrued RBA balance as of December 31, 2014 (and associated revenue taxes) to be collected                 (9,200,000)he_PublicUtilityIncreaseDecreaseInAccruedRevenueBalancingAccountToBeCollected
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Net annual incremental amount to be collected under the tariffs                 11,100,000he_PublicUtilityNetReceivableUnderTariff
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Impact on typical residential customer monthly bill                 560,000he_PublicUtilitiesIncreaseDecreaseInCustomerMonthlyBill
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Monthly utility usage assumption (in kilowatts per hour)                 600he_PublicUtilitiesMonthlyUtilityUsageAssumption
/ dei_LegalEntityAxis
= us-gaap_SubsidiariesMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Subsequent Event | Hawaii Electric Light Company, Inc. (HELCO)                            
Public Utilities, Phase-in Plans [Abstract]                            
Annual incremental RAM adjusted revenues                 2,400,000he_PublicUtilityAnnualIncrementalRateAdjustmentMechanismAdjustedRevenue
/ dei_LegalEntityAxis
= he_HawaiiElectricLightCompanyIncMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Annual change in accrued earnings sharing credits to be refunded                 0he_PublicUtilityIncreaseDecreaseInAccruedEarningsSharingCreditsToBeRefunded
/ dei_LegalEntityAxis
= he_HawaiiElectricLightCompanyIncMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Annual change in accrued RBA balance as of December 31, 2014 (and associated revenue taxes) to be collected                 100,000he_PublicUtilityIncreaseDecreaseInAccruedRevenueBalancingAccountToBeCollected
/ dei_LegalEntityAxis
= he_HawaiiElectricLightCompanyIncMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Net annual incremental amount to be collected under the tariffs                 2,500,000he_PublicUtilityNetReceivableUnderTariff
/ dei_LegalEntityAxis
= he_HawaiiElectricLightCompanyIncMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Impact on typical residential customer monthly bill                 1,100,000he_PublicUtilitiesIncreaseDecreaseInCustomerMonthlyBill
/ dei_LegalEntityAxis
= he_HawaiiElectricLightCompanyIncMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Monthly utility usage assumption (in kilowatts per hour)                 500he_PublicUtilitiesMonthlyUtilityUsageAssumption
/ dei_LegalEntityAxis
= he_HawaiiElectricLightCompanyIncMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Subsequent Event | Maui Electric                            
Public Utilities, Phase-in Plans [Abstract]                            
Annual incremental RAM adjusted revenues                 3,400,000he_PublicUtilityAnnualIncrementalRateAdjustmentMechanismAdjustedRevenue
/ dei_LegalEntityAxis
= he_MauiElectricCompanyLimitedMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Annual change in accrued earnings sharing credits to be refunded                 (100,000)he_PublicUtilityIncreaseDecreaseInAccruedEarningsSharingCreditsToBeRefunded
/ dei_LegalEntityAxis
= he_MauiElectricCompanyLimitedMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Annual change in accrued RBA balance as of December 31, 2014 (and associated revenue taxes) to be collected                 (2,200,000)he_PublicUtilityIncreaseDecreaseInAccruedRevenueBalancingAccountToBeCollected
/ dei_LegalEntityAxis
= he_MauiElectricCompanyLimitedMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Net annual incremental amount to be collected under the tariffs                 1,100,000he_PublicUtilityNetReceivableUnderTariff
/ dei_LegalEntityAxis
= he_MauiElectricCompanyLimitedMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Impact on typical residential customer monthly bill                 $ 600,000he_PublicUtilitiesIncreaseDecreaseInCustomerMonthlyBill
/ dei_LegalEntityAxis
= he_MauiElectricCompanyLimitedMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
Monthly utility usage assumption (in kilowatts per hour)                 600he_PublicUtilitiesMonthlyUtilityUsageAssumption
/ dei_LegalEntityAxis
= he_MauiElectricCompanyLimitedMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember		          
PCB Contamination | Waiau Power Plant                            
Environmental regulation                            
Period For Submission Of Plan To EPA                   45 days