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Income taxes Additional Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Expense (Benefit) [Line Items]
Reconciliation percentage of amount of income taxes computed at federal statutory rate	35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Amount of decrease in deferred taxes related to tax gross-up of AFUDC-equity		$ 3.5he_EffectiveIncomeTaxRateReconciliationAllowanceforFundsUsedDuringConstructionTaxEffect
Out-of-period income tax benefit		3.1us-gaap_RestatementOfPriorYearIncomeTaxEffects
Out-of-period tax benefit related to utilities		2.7he_RestatementofPriorYearIncomeTaxEffectsUtilities
Credit adjustments to interest expense on income taxes	1.7us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense	0.3us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense	1.4us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense
Amount of accrued interest related to uncertain tax positions		0.4us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued
Hawaiian Electric Company, Inc. and Subsidiaries
Income Tax Expense (Benefit) [Line Items]
Net operating loss carryforwards	52us-gaap_OperatingLossCarryforwards / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember
Credit adjustments to interest expense on income taxes	$ 0.7us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember	$ 0.3us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember	$ 0.5us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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