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Bank segment - Contingencies (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
American Savings Bank (ASB)
Loss Contingencies [Line Items]
Unfunded commitments to fund the company's LIHTC	$ 20.6	$ 15.8

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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- Definition

Amount of commitment or contingent commitments to qualified affordable housing project investments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=114775393&loc=SL49122993-202985

+ Details

Name:	us-gaap_QualifiedAffordableHousingProjectInvestmentsCommitment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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- Details

Name:	dei_LegalEntityAxis=he_AmericanSavingsBankFSBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: