Bank segment (HEI only) - Loans Receivable, Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Bank Segment Disclosure [Abstract]
Percentage of benchmark loan to appraisal ratio in excess of which mortgage insurance is required	80.00%
Real estate loans for investors	$ 1,200.0	$ 1,200.0	$ 1,200.0
Loans pledged as collateral to secure advances from the FHLB of Des Moines	2,700.0	2,400.0
Loans to directors, executive directors, affiliates and any related interest of such individuals	24.0	23.8
Loan balances, related interests of individuals who are directors	$ 18.3	$ 18.7

Bank Segment Disclosure [Abstract]

No definition available.

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- Definition

Represents the amount of Loan balances, which are related to interests of individuals who are directors of bank.

+ References

No definition available.

+ Details

Name:	he_LoanBalancesRelatedToInterestOfIndividualDirectors
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the amount of Loan balances, which are related to interests of individuals who are directors of bank, executive officers and related interests.

+ References

No definition available.

+ Details

Name:	he_LoanBalancesRelatedToInterestOfIndividualDirectorsExecutiveOfficersAndRelatedInterests
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Balance Type:	debit
Period Type:	instant

- Definition

Represents the minimum benchmark percentage of loan to appraisal ratio which mortgage insurance is required as per the policy of the reporting entity.

+ References

No definition available.

+ Details

Name:	he_MinimumBenchmarkPercentageofLoantoAppraisalRatiowhichMortgageInsuranceisRequired
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- Definition

Real estate loans serviced for investors.

+ References

No definition available.

+ Details

Name:	he_RealEstateLoansServicedForInvestors
Namespace Prefix:	he_
Data Type:	xbrli:monetaryItemType
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- Definition

Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant