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Income taxes Changes in Unrecognized Tax Benefits (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Changes in total unrecognized tax benefits |  |  |
Unrecognized tax benefits, at the beginning of the period | $ 0.9 us-gaap_UnrecognizedTaxBenefits | $ 0.8 us-gaap_UnrecognizedTaxBenefits | $ 5.7 us-gaap_UnrecognizedTaxBenefits
Additions based on tax positions taken during the year | 0 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions | 0 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions | 0.3 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions
Reductions based on tax positions taken during the year | 0 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromCurrentPeriodTaxPositions | 0 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromCurrentPeriodTaxPositions | 0 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromCurrentPeriodTaxPositions
Additions for tax positions of prior years | 0.1 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions | 0.5 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions | 0 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions
Reductions for tax positions of prior years | 0 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions | (0.4)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions | (4.1)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions
Settlements | (1.0)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities | 0 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities | 0 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities
Lapses of statute of limitations | 0 us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations | 0 us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations | (1.1)us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations
Unrecognized tax benefits, at the end of the period | 0 us-gaap_UnrecognizedTaxBenefits | 0.9 us-gaap_UnrecognizedTaxBenefits | 0.8 us-gaap_UnrecognizedTaxBenefits
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Changes in total unrecognized tax benefits |  |  |
Unrecognized tax benefits, at the beginning of the period | 0.5 us-gaap_UnrecognizedTaxBenefits / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | 0.4 us-gaap_UnrecognizedTaxBenefits / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | 3.7 us-gaap_UnrecognizedTaxBenefits / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember
Additions based on tax positions taken during the year | 0 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | 0 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | 0.3 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember
Reductions based on tax positions taken during the year | 0 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromCurrentPeriodTaxPositions / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | 0 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromCurrentPeriodTaxPositions / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | 0 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromCurrentPeriodTaxPositions / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember
Additions for tax positions of prior years | 0.1 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | 0.5 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | 0 us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember
Reductions for tax positions of prior years | 0 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | (0.4)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | (3.6)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromPriorPeriodTaxPositions / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember
Settlements | (0.6)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | 0 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | 0 us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember
Lapses of statute of limitations | 0 us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | 0 us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | 0 us-gaap_UnrecognizedTaxBenefitsReductionsResultingFromLapseOfApplicableStatuteOfLimitations / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember
Unrecognized tax benefits, at the end of the period | $ 0 us-gaap_UnrecognizedTaxBenefits / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | $ 0.5 us-gaap_UnrecognizedTaxBenefits / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember | $ 0.4 us-gaap_UnrecognizedTaxBenefits / dei_LegalEntityAxis = he_HawaiianElectricCompanyAndSubsidiariesMember

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- Definition Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Unrecognized Tax Benefit -URI http://asc.fasb.org/extlink&oid=6527854 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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- Definition Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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- Definition Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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