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Electric utility segment - Utility projects (Details) - USD ($) $ in Millions		3 Months Ended
	Jun. 10, 2019	Mar. 31, 2022	Oct. 31, 2018
ERP/EAM Implementation Project
Public Utilities, General Disclosures [Line Items]
ERP/EAM project service period (in years)	12 years
Future O&M expense reductions	$ 150.0
Future cost avoidance related to capital cost and tax costs	$ 96.0
Hawaiian Electric Company, Inc. and Subsidiaries | ERP/EAM Implementation Project
Public Utilities, General Disclosures [Line Items]
ERP/EAM project service period (in years)		12 years
ERP/EAM project service, savings over 12 years			$ 246.0
Regulatory liability for O&M expense reductions		$ 9.1
Hawaiian Electric, Parent | PCB Contamination
Public Utilities, General Disclosures [Line Items]
Valuation allowances and reserves		10.1
Hawaiian Electric, Parent | ERP/EAM Implementation Project
Public Utilities, General Disclosures [Line Items]
Regulatory liability for O&M expense reductions		5.1
HELCO | ERP/EAM Implementation Project
Public Utilities, General Disclosures [Line Items]
Regulatory liability for O&M expense reductions		1.6
Maui Electric
Public Utilities, General Disclosures [Line Items]
Additional accrued investigation and estimated cleanup costs		2.7
Maui Electric | ERP/EAM Implementation Project
Public Utilities, General Disclosures [Line Items]
Regulatory liability for O&M expense reductions		$ 2.4
Regulatory liability, amortization period		5 years

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