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

X

- 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