Significant group concentrations of credit risk (Details)	12 Months Ended
Dec. 31, 2019
Risks and Uncertainties [Abstract]
Percentage of benchmark loan to appraisal ratio in excess of which mortgage insurance is required	80.00%

Represents the minimum benchmark percentage of loan to appraisal ratio which mortgage insurance is required as per the policy of the reporting entity.

No definition available.

Name:	he_MinimumBenchmarkPercentageofLoantoAppraisalRatiowhichMortgageInsuranceisRequired
Namespace Prefix:	he_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration