Share-based compensation - Fair Value Assumptions (Details) - LTIP linked to TRS - $ / shares	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Risk-free interest rate	4.37%	4.25%
Expected life in years	3 years	3 years
Expected volatility	64.70%	52.50%
Range of expected volatility for Peer Group, minimum rate	15.30%	12.30%
Range of expected volatility for Peer Group, maximum rate	64.70%	52.50%
Grant-date fair value (in dollars per share)	$ 11.39	$ 17.28
Hawaiian Electric Company, Inc. and Subsidiaries
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Grant-date fair value (in dollars per share)	$ 11.12	$ 17.28