Electric utility segment - Annual Decoupling Filings Summary (Details) - USD ($) $ in Millions		3 Months Ended
	Mar. 28, 2024	Mar. 31, 2024
Regulatory Projects and Legal Obligations [Line Items]
Recovery of COVID-19 related costs	$ 3.2
Return of ERP benefit liability	(3.2)
Net 2024 ARA revenues	0.0
Incremental RAM revenues and ARA revenues		$ 0.0
Incremental PIMs (net)		(2.6)
Incremental MPIR/EPRM revenue adjustment		4.9
Incremental Pilot Process cost recovery		2.7
Net incremental amount to be collected under the RBA rate tariffs		5.0
Hawaiian Electric, Parent
Regulatory Projects and Legal Obligations [Line Items]
Recovery of COVID-19 related costs	2.2
Return of ERP benefit liability	0.0
Net 2024 ARA revenues	2.2
Incremental RAM revenues and ARA revenues		2.2
Incremental PIMs (net)		(1.3)
Incremental MPIR/EPRM revenue adjustment		3.0
Incremental Pilot Process cost recovery		1.9
Net incremental amount to be collected under the RBA rate tariffs		5.8
Hawaii Electric Light
Regulatory Projects and Legal Obligations [Line Items]
Recovery of COVID-19 related costs	0.5
Return of ERP benefit liability	(1.3)
Net 2024 ARA revenues	(0.8)
Incremental RAM revenues and ARA revenues		(0.8)
Incremental PIMs (net)		(1.1)
Incremental MPIR/EPRM revenue adjustment		0.7
Incremental Pilot Process cost recovery		0.3
Net incremental amount to be collected under the RBA rate tariffs		(0.9)
Maui Electric
Regulatory Projects and Legal Obligations [Line Items]
Recovery of COVID-19 related costs	0.5
Return of ERP benefit liability	(1.9)
Net 2024 ARA revenues	$ (1.4)
Incremental RAM revenues and ARA revenues		(1.4)
Incremental PIMs (net)		(0.2)
Incremental MPIR/EPRM revenue adjustment		1.2
Incremental Pilot Process cost recovery		0.5
Net incremental amount to be collected under the RBA rate tariffs		$ 0.1