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Significant group concentrations of credit risk (Details) | 12 Months Ended
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Dec. 31, 2018
Risks and Uncertainties [Abstract] |
Percentage of benchmark loan to appraisal ratio in excess of which mortgage insurance is required | 80.00%

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- Definition Represents the minimum benchmark percentage of loan to appraisal ratio which mortgage insurance is required as per the policy of the reporting entity. + References No definition available. + Details
Name: | he_MinimumBenchmarkPercentageofLoantoAppraisalRatiowhichMortgageInsuranceisRequired
Namespace Prefix: | he_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_RisksAndUncertaintiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration