Retirement benefits - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Vested percentage of interest of each affected participant after participating employer terminates participation	100.00%
Number of years for which regulatory asset/liability for each utility will be amortized, beginning with respective utility's next rate case	5 years
Executive life and nonqualified pension plan expenses	$ 900,000	$ 700,000
Regulatory asset charges pretax	(85,800,000)	(11,100,000)
Expected cash funding for qualified defined benefit plans
Defined contribution plan, expenses recognized	8,000,000	6,000,000	$ 4,000,000
Hawaiian Electric Company, Inc. and Subsidiaries
Expected cash funding for qualified defined benefit plans
Defined contribution plan, expenses recognized	$ 7,000,000	6,000,000	4,000,000
Employer contribution, percent of annual compensation	10.00%
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Expected rate of return on plan assets	7.25%
Actual net return on plan assets	6.70%
Pension expense	$ 47,000,000	43,000,000	47,000,000
Expected cash funding for qualified defined benefit plans
Estimate of contributions to postretirement benefit plans in next fiscal year	9,000,000
Expected benefits to be paid, year one	111,000,000
Expected benefits to be paid, year two	115,000,000
Expected benefits to be paid, year three	119,000,000
Expected benefits to be paid, year four	122,000,000
Expected benefits to be paid, year five	126,000,000
Expected benefits to be paid, after year five for next five years	677,000,000
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined Benefit Plan Disclosure [Line Items]
Pension expense	45,000,000	$ 42,000,000	45,000,000
Expected cash funding for qualified defined benefit plans
Estimate of contributions to postretirement benefit plans in next fiscal year	9,000,000
Expected benefits to be paid, year one	106,000,000
Expected benefits to be paid, year two	111,000,000
Expected benefits to be paid, year three	114,000,000
Expected benefits to be paid, year four	117,000,000
Expected benefits to be paid, year five	121,000,000
Expected benefits to be paid, after year five for next five years	$ 652,000,000
Other benefits
Defined Benefit Plan Disclosure [Line Items]
Assumed health care trend rate for medical in next fiscal year	7.00%	6.25%
Assumed health care trend rate for grading down in next eight fiscal years thereafter	5.00%
Assumed health care trend rate for medical, post-65 in next fiscal year	6.50%
Assumed health care trend rate for grading down plan in six fiscal years thereafter	5.00%	5.00%
Assumed health care trend rate for dental in next fiscal year	5.00%	5.00%
Assumed health care trend rate for vision in next fiscal year	4.00%	4.00%
Postretirement benefits other than pension expense	$ (200,000)	$ (100,000)	(100,000)
Expected cash funding for qualified defined benefit plans
Estimate of contributions to postretirement benefit plans in next fiscal year	0
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Defined Benefit Plan Disclosure [Line Items]
Postretirement benefits other than pension expense	(300,000)	$ (300,000)	$ (100,000)
Expected cash funding for qualified defined benefit plans
Estimate of contributions to postretirement benefit plans in next fiscal year	$ 0