Electric utility segment - Annual Decoupling Filings (Details) - USD ($) $ in Millions		12 Months Ended
	Oct. 28, 2024	Dec. 31, 2024
Regulatory Projects and Legal Obligations [Line Items]
2025 ARA revenues	$ 22.9
Management Audit savings commitment	(6.6)
Net 2025 ARA revenues	16.3
2025 ARA revenues		$ 22.9
Annual change in accrued RBA balance through September 30, 2024 (and associated revenue taxes)		(1.9)
Incremental Performance Incentive Mechanisms (net)		0.0
Net incremental amount to be collected under the RBA rate tariffs		21.0
Hawaiian Electric
Regulatory Projects and Legal Obligations [Line Items]
2025 ARA revenues	15.4
Management Audit savings commitment	(4.6)
Net 2025 ARA revenues	10.8
2025 ARA revenues		15.4
Annual change in accrued RBA balance through September 30, 2024 (and associated revenue taxes)		(7.0)
Incremental Performance Incentive Mechanisms (net)		(0.1)
Net incremental amount to be collected under the RBA rate tariffs		8.3
Hawaii Electric Light
Regulatory Projects and Legal Obligations [Line Items]
2025 ARA revenues	3.8
Management Audit savings commitment	(1.0)
Net 2025 ARA revenues	2.8
2025 ARA revenues		3.8
Annual change in accrued RBA balance through September 30, 2024 (and associated revenue taxes)		(1.3)
Incremental Performance Incentive Mechanisms (net)		0.1
Net incremental amount to be collected under the RBA rate tariffs		2.6
Maui Electric
Regulatory Projects and Legal Obligations [Line Items]
2025 ARA revenues	3.7
Management Audit savings commitment	(1.0)
Net 2025 ARA revenues	$ 2.7
2025 ARA revenues		3.7
Annual change in accrued RBA balance through September 30, 2024 (and associated revenue taxes)		6.4
Incremental Performance Incentive Mechanisms (net)		0.0
Net incremental amount to be collected under the RBA rate tariffs		$ 10.1