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Electric utility segment Related-Party Transactions (Details) (Hawaiian Electric Industries, Inc., HECO, USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Hawaiian Electric Industries, Inc. | HECO |  |  |
Related Party Transaction [Line Items] |  |  |
Amount charged to subsidiaries for general management and administrative services | $ 7.0 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = us-gaap_ParentCompanyMember | $ 6.2 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = us-gaap_ParentCompanyMember | $ 6.1 us-gaap_RelatedPartyTransactionAmountsOfTransaction / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = us-gaap_ParentCompanyMember
Effective interest rate basis term | 30 days |  |
Line of credit facility basis point spread (as a percent) | 0.15%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1 / dei_LegalEntityAxis = us-gaap_SubsidiariesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = us-gaap_ParentCompanyMember |  |

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