Bank segment (HEI only) - Securities Sold Under Agreements to Repurchase (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Securities sold under agreements to repurchase
Repurchase liability	$ 89,670	$ 115,110
Weighted-average interest rate	0.02%	0.98%
Collateralized by mortgage-related securities and federal agency obligations
Securities sold under agreements to repurchase
Collateralized by mortgage-backed securities and federal agency obligations at fair value plus accrued interest	$ 92,478	$ 129,527
Overnight
Securities sold under agreements to repurchase
Repurchase liability	$ 89,670	$ 115,110
Weighted-average interest rate	0.02%	0.98%
Overnight \| Collateralized by mortgage-related securities and federal agency obligations
Securities sold under agreements to repurchase
Collateralized by mortgage-backed securities and federal agency obligations at fair value plus accrued interest	$ 92,478	$ 129,527
1 to 29 days
Securities sold under agreements to repurchase
Repurchase liability	$ 0	$ 0
Weighted-average interest rate	0.00%	0.00%
1 to 29 days \| Collateralized by mortgage-related securities and federal agency obligations
Securities sold under agreements to repurchase
Collateralized by mortgage-backed securities and federal agency obligations at fair value plus accrued interest	$ 0	$ 0
30 to 90 days
Securities sold under agreements to repurchase
Repurchase liability	$ 0	$ 0
Weighted-average interest rate	0.00%	0.00%
30 to 90 days \| Collateralized by mortgage-related securities and federal agency obligations
Securities sold under agreements to repurchase
Collateralized by mortgage-backed securities and federal agency obligations at fair value plus accrued interest	$ 0	$ 0
Over 90 days
Securities sold under agreements to repurchase
Repurchase liability	$ 0	$ 0
Weighted-average interest rate	0.00%	0.00%
Over 90 days \| Collateralized by mortgage-related securities and federal agency obligations
Securities sold under agreements to repurchase
Collateralized by mortgage-backed securities and federal agency obligations at fair value plus accrued interest	$ 0	$ 0

Assets Sold Under Agreements To Repurchase Fair Value Plus Accrued Interest

No definition available.

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

- Definition

Interest rate on the amount to be repaid to the counterparty to the repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(1)(i)(A)(ii))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Name:	us-gaap_AssetsSoldUnderAgreementsToRepurchaseInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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

- Definition

Amount to be repaid to the counterparty to the repurchase agreement when the carrying amount (or market value, if higher than the carrying amount) of securities or other assets sold under the repurchase agreement exceeds 10 percent of total assets.

+ References

+ Details

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

- Details

Name:	us-gaap_AssetsSoldUnderAgreementsToRepurchaseAxis=he_USGovernmentAgenciesDebtSecuritiesAndMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis=us-gaap_MaturityOvernightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis=us-gaap_MaturityUpTo30DaysMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis=us-gaap_Maturity30To90DaysMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AssetsSoldUnderAgreementsToRepurchaseMaturityPeriodsAxis=us-gaap_MaturityOver90DaysMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: