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Bank segment (HEI only) - TDR Narrative (Details) - Residential land | 12 Months Ended
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Dec. 31, 2018
Troubled debt restructurings |
Period of interest-only monthly payment term loan | 3 years
Maximum |
Troubled debt restructurings |
Extension of maturity date | 5 years

X
- Definition Represents the extension of maturity period of troubled debt under the troubled debt restructuring plan. + References No definition available. + Details
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Namespace Prefix: | he_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the period of interest-only monthly payment term loan under the troubled debt restructuring plan. + References No definition available. + Details
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Namespace Prefix: | he_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- 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

X
- Details
Name: | us-gaap_LoanRestructuringModificationAxis=he_ResidentialLandPortfolioSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |