Bank segment - Troubled debt restructuring - narrative (Details) - Troubled debt restructurings real estate loans - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Troubled debt restructurings
Financing receivable modifications minimum, period of payment default of loans determined to be TDRs (in days)	90 days	90 days
Commitments to lend additional funds to borrows with impaired or modified loans	$ 0.0	$ 0.0	$ 0.0
Consumer mortgage loans collateralized by residential real estate property in foreclosure process	$ 3.0	$ 3.0	$ 3.5

Financial Receivables, Loans Collateralized by Real Estate in Foreclosure

No definition available.

Name:	he_FinancialReceivablesLoansCollateralizedbyRealEstateinForeclosure
Namespace Prefix:	he_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the minimum period of payment default of loans determined to be troubled debt restructurings.

+ References

No definition available.

+ Details

Name:	he_FinancingReceivableModificationsMinimumPeriodOfPaymentDefaultOfLoansDeterminedToBeTroubledDebtRestructurings
Namespace Prefix:	he_
Data Type:	xbrli:durationItemType
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_FinancingReceivableImpairedLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of restructured debt contingently payable based on the occurrence of future events or circumstances.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 60
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6402221&loc=d3e15765-112638

+ Details

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

- Details

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