Share-based compensation - Share-Based Compensation Expense and Related Income Tax Benefit (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Share-based compensation
Share-based compensation expense	$ 3.9	$ 3.5	$ 5.9	$ 5.6
Income tax benefit	0.8	0.8	1.1	1.1
Hawaiian Electric Company, Inc. and Subsidiaries
Share-based compensation
Share-based compensation expense	1.1	1.0	1.7	1.6
Income tax benefit	$ 0.2	$ 0.3	$ 0.4	$ 0.4