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Fair value measurements - Narrative (Details) | Jun. 30, 2021
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Discount rate |
Fair Value Measurement Inputs and Valuation Techniques [Line Items] |
Mortgage revenue bonds, measurement input | 0.0205

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- Definition Asset Backed Securities, Measurement Input + References No definition available. + Details
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Namespace Prefix: | he_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

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

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- Details
Name: | us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |