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Income taxes Additional Information (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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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 |  | $ 3.5 he_EffectiveIncomeTaxRateReconciliationAllowanceforFundsUsedDuringConstructionTaxEffect |
Out-of-period income tax benefit |  | 3.1 us-gaap_RestatementOfPriorYearIncomeTaxEffects |
Out-of-period tax benefit related to utilities |  | 2.7 he_RestatementofPriorYearIncomeTaxEffectsUtilities |
Credit adjustments to interest expense on income taxes | 1.7 us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense | 0.3 us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense | 1.4 us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense
Amount of accrued interest related to uncertain tax positions |  | 0.4 us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued |
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Income Tax Expense (Benefit) [Line Items] |  |  |
Net operating loss carryforwards | 52 us-gaap_OperatingLossCarryforwards / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember |  |
Credit adjustments to interest expense on income taxes | $ 0.7 us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | $ 0.3 us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | $ 0.5 us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember

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- Definition Effective Income Tax Rate Reconciliation, Allowance for Funds Used During Construction, Tax Effect + References No definition available. + Details
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- Definition Restatement of Prior Year Income, Tax Effects, Utilities + References No definition available. + Details
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- Definition Percentage of domestic federal statutory tax rate applicable to pretax income (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 + Details
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- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 + Details
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- Definition The tax effect of the restatement to correct an error in net income of prior periods for the year in which any adjustments are first made. In statements containing more than one period, disclose the effects for each period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=28359718&loc=d3e22663-107794 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=28359718&loc=d3e22658-107794 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=28359718&loc=d3e22644-107794 + Details
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- Definition Amount of interest expense accrued for an underpayment of income taxes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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- Definition Amount of interest expense for an underpayment of income taxes. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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