Electric utility segment - Utility projects (Details) - USD ($) $ in Millions		1 Months Ended		6 Months Ended
	Jun. 10, 2019	Nov. 30, 2020	Jan. 31, 2020	Jun. 30, 2021	Dec. 31, 2020
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, Parent | PCB Contamination
Public Utilities, General Disclosures [Line Items]
Valuation allowances and reserves				$ 10.5
Hawaiian Electric, Parent | ERP/EAM Implementation Project
Public Utilities, General Disclosures [Line Items]
ERP/EAM project service period (in years)		12 years
Regulatory liability for O&M expense reductions				6.1
Hawaiian Electric Company, Inc. and Subsidiaries | ERP/EAM Implementation Project
Public Utilities, General Disclosures [Line Items]
Regulatory liability for O&M expense reductions				11.1
HELCO | ERP/EAM Implementation Project
Public Utilities, General Disclosures [Line Items]
ERP/EAM project service period (in years)			12 years
Regulatory liability for O&M expense reductions				2.0
Regulatory liability to be flowed through to customers					$ 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				$ 3.0
Regulatory liability, amortization period				5 years
Regulatory liability to be flowed through to customers					$ 2.3