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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 |  |  |  |
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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 |  |  | 14 he_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 |  |  |  |  | 4 he_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 | $ 31,600,000 he_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 | 3,600,000 he_ReserveForAdditionalInvestigationAndEstimatedCleanupCosts / dei_LegalEntityAxis = he_MauiElectricCompanyLimitedMember |  |  |  |  | 3,600,000 he_ReserveForAdditionalInvestigationAndEstimatedCleanupCosts / dei_LegalEntityAxis = he_MauiElectricCompanyLimitedMember |  |  |  |  | 3,100,000 he_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 |  |  |  |  |  | 500,000 he_RequiredReductionOfGreenhouseGasEmissionsMandatedByRegulationsEstimatedAnnualFee / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember |  |  |  |  |  |  |  |
Impact on earnings from recognition of AROs |  |  |  |  |  | 0 he_AssetRetirementObligationsRecognitionImpactOnEarnings / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |
Balance, beginning of period |  |  |  |  | 41,236,000 us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | 29,419,000 us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember |  | 43,106,000 us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember |  |  |  |  |  |
Accretion expense |  |  |  |  |  | 6,000 us-gaap_AssetRetirementObligationAccretionExpense / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember |  | 370,000 us-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 |  |  |  |  |  | 0 us-gaap_AssetRetirementObligationRevisionOfEstimate / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember |  | 0 us-gaap_AssetRetirementObligationRevisionOfEstimate / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember |  |  |  |  |  |
Balance, end of period | 27,811,000 us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember |  |  |  |  | 27,811,000 us-gaap_AssetRetirementObligation / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember |  | 41,236,000 us-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 |  |  |  |  |  |  |  |  |  |  |  |  |  | 800,000 us-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 |  |  |  |  |  |  |  |  | 26,200,000 he_PublicUtilityAnnualIncrementalRateAdjustmentMechanismAdjustedRevenue / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Net annual incremental amount to be collected under the tariffs |  |  |  |  |  |  |  |  | 14,700,000 he_PublicUtilityNetReceivableUnderTariff / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Subsequent Event | Hawaiian Electric Company |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public Utilities, Phase-in Plans [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual incremental RAM adjusted revenues |  |  |  |  |  |  |  |  | 20,300,000 he_PublicUtilityAnnualIncrementalRateAdjustmentMechanismAdjustedRevenue / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Annual change in accrued earnings sharing credits to be refunded |  |  |  |  |  |  |  |  | 0 he_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 |  |  |  |  |  |  |  |  | 11,100,000 he_PublicUtilityNetReceivableUnderTariff / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Impact on typical residential customer monthly bill |  |  |  |  |  |  |  |  | 560,000 he_PublicUtilitiesIncreaseDecreaseInCustomerMonthlyBill / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Monthly utility usage assumption (in kilowatts per hour) |  |  |  |  |  |  |  |  | 600 he_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 |  |  |  |  |  |  |  |  | 2,400,000 he_PublicUtilityAnnualIncrementalRateAdjustmentMechanismAdjustedRevenue / dei_LegalEntityAxis = he_HawaiiElectricLightCompanyIncMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Annual change in accrued earnings sharing credits to be refunded |  |  |  |  |  |  |  |  | 0 he_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 |  |  |  |  |  |  |  |  | 100,000 he_PublicUtilityIncreaseDecreaseInAccruedRevenueBalancingAccountToBeCollected / dei_LegalEntityAxis = he_HawaiiElectricLightCompanyIncMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Net annual incremental amount to be collected under the tariffs |  |  |  |  |  |  |  |  | 2,500,000 he_PublicUtilityNetReceivableUnderTariff / dei_LegalEntityAxis = he_HawaiiElectricLightCompanyIncMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Impact on typical residential customer monthly bill |  |  |  |  |  |  |  |  | 1,100,000 he_PublicUtilitiesIncreaseDecreaseInCustomerMonthlyBill / dei_LegalEntityAxis = he_HawaiiElectricLightCompanyIncMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Monthly utility usage assumption (in kilowatts per hour) |  |  |  |  |  |  |  |  | 500 he_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 |  |  |  |  |  |  |  |  | 3,400,000 he_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 |  |  |  |  |  |  |  |  | 1,100,000 he_PublicUtilityNetReceivableUnderTariff / dei_LegalEntityAxis = he_MauiElectricCompanyLimitedMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Impact on typical residential customer monthly bill |  |  |  |  |  |  |  |  | $ 600,000 he_PublicUtilitiesIncreaseDecreaseInCustomerMonthlyBill / dei_LegalEntityAxis = he_MauiElectricCompanyLimitedMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |
Monthly utility usage assumption (in kilowatts per hour) |  |  |  |  |  |  |  |  | 600 he_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 |  |  |  |

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- Definition The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Asset Retirement Obligation -URI http://asc.fasb.org/extlink&oid=6505190 + Details
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