Bank segment - Loan modifications (Details) - Troubled debt restructurings real estate loans $ in Thousands	3 Months Ended
Mar. 31, 2020 USD ($) contract	Mar. 31, 2019 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts \| contract	7	12
Outstanding recorded investment	$ 17,488	$ 1,842
Net increase in allowance	$ 4,567	$ 45
Residential 1-4 family
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts \| contract	1	8
Outstanding recorded investment	$ 148	$ 1,048
Net increase in allowance	$ 8	$ 5
Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts \| contract	2	0
Outstanding recorded investment	$ 16,584	$ 0
Net increase in allowance	$ 4,281	$ 0
Home equity line of credit
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts \| contract	0	2
Outstanding recorded investment	$ 0	$ 264
Net increase in allowance	$ 0	$ 23
Residential land
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts \| contract	0	1
Outstanding recorded investment	$ 0	$ 335
Net increase in allowance	$ 0	$ 0
Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts \| contract	0	0
Outstanding recorded investment	$ 0	$ 0
Net increase in allowance	$ 0	$ 0
Residential construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts \| contract	0	0
Outstanding recorded investment	$ 0	$ 0
Net increase in allowance	$ 0	$ 0
Commercial loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts \| contract	4	1
Outstanding recorded investment	$ 756	$ 195
Net increase in allowance	$ 278	$ 17
Consumer loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts \| contract	0	0
Outstanding recorded investment	$ 0	$ 0
Net increase in allowance	$ 0	$ 0

Amount of increase (decrease) of allowance reserve for credit loss.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_AllowanceForLoanAndLeaseLossesPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before troubled debt restructuring, of financing receivable to be modified.

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsPreModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	he_FinancingReceivableTroubledDebtRestructuringsAndTroubledDebtRestructuringsThatSubsequentlyDefaultedAxis=he_FinancingReceivableTroubledDebtRestructuringsRealEstateLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=he_Residential1To4FamilyPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_HomeEquityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=he_ResidentialLandPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=he_ResidentialConstructionPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_CommercialLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_ConsumerLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: