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Electric utility segment Major Customers (Details) (Operating revenues, Customer concentration, Various federal government agencies, USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Operating revenues | Customer concentration | Various federal government agencies |  |  |
Major customers |  |  |
Operating revenues percentage | 12.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = he_RegulatedOperatingRevenueElectricNonNuclearMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = he_FederalGovernmentAgenciesMember | 11.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = he_RegulatedOperatingRevenueElectricNonNuclearMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = he_FederalGovernmentAgenciesMember | 11.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = he_RegulatedOperatingRevenueElectricNonNuclearMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = he_FederalGovernmentAgenciesMember
Operating revenues amount | $ 350 he_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = he_RegulatedOperatingRevenueElectricNonNuclearMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = he_FederalGovernmentAgenciesMember | $ 340 he_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = he_RegulatedOperatingRevenueElectricNonNuclearMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = he_FederalGovernmentAgenciesMember | $ 349 he_ConcentrationRiskAmount / us-gaap_ConcentrationRiskByBenchmarkAxis = he_RegulatedOperatingRevenueElectricNonNuclearMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember / us-gaap_MajorCustomersAxis = he_FederalGovernmentAgenciesMember

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