Electric utility segment - Rate proceedings (Details) - USD ($) $ in Thousands	Oct. 22, 2020	May 13, 2020	Nov. 13, 2019	Apr. 18, 2018	Sep. 30, 2020	Dec. 31, 2019
Regulatory Projects and Legal Obligations [Line Items]
Regulatory assets					$ 677,683	$ 715,080
Hawaiian Electric (parent only)
Regulatory Projects and Legal Obligations [Line Items]
Multi-year rate plan, term				5 years
Timeframe to acquire annual savings		3 years
Proposed annual savings		$ 25,000
Proposed annual savings, capital, percentage		80.00%
Proposed annual savings, operations and maintenance, percentage		20.00%
Hawaiian Electric (parent only) | Subsequent Event
Regulatory Projects and Legal Obligations [Line Items]
Effective interest rate of return	7.37%
Stipulated ROACE rate	9.50%
Period to file revised tariffs	15 days
Common equity capitalization rate	58.00%
HELCO
Regulatory Projects and Legal Obligations [Line Items]
Interim revenue requirement			$ 387,000
Rate base			$ 534,000
Effective interest rate of return			7.52%
Stipulated ROACE rate			9.50%
Common equity capitalization rate			58.00%
Amortization period for state investment tax credit			10 years
Risk sharing percentage, ratepayer			98.00%
Maximum exposure cap			$ 600
Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory Projects and Legal Obligations [Line Items]
Regulatory assets					$ 12,400