Share-based compensation - Share-Based Compensation Expense and Related Income Tax Benefit (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based compensation
Share-based compensation expense	$ 2.4	$ 1.7	$ 8.3	$ 7.3
Income tax benefit	0.5	0.4	1.6	1.5
Hawaiian Electric Company, Inc. and Subsidiaries
Share-based compensation
Share-based compensation expense	0.7	0.6	2.5	2.1
Income tax benefit	$ 0.1	$ 0.1	$ 0.5	$ 0.5