Electric utility segment - Schedule of Annual Decoupling Filings (Details) - USD ($) $ in Millions		7 Months Ended
	Oct. 31, 2025	Oct. 31, 2025
Regulatory Projects and Legal Obligations [Line Items]
2026 ARA revenues	$ 30.3
Management Audit savings commitment	(6.6)
Net 2026 ARA revenues	23.7
2026 ARA revenues		$ 30.3
Annual change in accrued RBA balance through September 30, 2025 (and associated revenue taxes)		(30.6)
Incremental Performance Incentive Mechanisms (net)		0.2
Net incremental amount to be collected under the RBA rate tariffs		(0.1)
Hawaiian Electric
Regulatory Projects and Legal Obligations [Line Items]
2026 ARA revenues	20.4
Management Audit savings commitment	(4.6)
Net 2026 ARA revenues	15.8
2026 ARA revenues		20.4
Annual change in accrued RBA balance through September 30, 2025 (and associated revenue taxes)		(18.6)
Incremental Performance Incentive Mechanisms (net)		0.0
Net incremental amount to be collected under the RBA rate tariffs		1.8
Hawaii Electric Light
Regulatory Projects and Legal Obligations [Line Items]
2026 ARA revenues	5.0
Management Audit savings commitment	(1.0)
Net 2026 ARA revenues	4.0
2026 ARA revenues		5.0
Annual change in accrued RBA balance through September 30, 2025 (and associated revenue taxes)		(1.3)
Incremental Performance Incentive Mechanisms (net)		(0.1)
Net incremental amount to be collected under the RBA rate tariffs		3.6
Maui Electric
Regulatory Projects and Legal Obligations [Line Items]
2026 ARA revenues	4.9
Management Audit savings commitment	(1.0)
Net 2026 ARA revenues	$ 3.9
2026 ARA revenues		4.9
Annual change in accrued RBA balance through September 30, 2025 (and associated revenue taxes)		(10.7)
Incremental Performance Incentive Mechanisms (net)		0.3
Net incremental amount to be collected under the RBA rate tariffs		$ (5.5)