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Electric utility segment - Commitments and contingencies (Details) $ in Millions			1 Months Ended					12 Months Ended
	Nov. 06, 2020	Jun. 10, 2019 USD ($)	Jan. 31, 2020	Jul. 31, 2018 MW	Jun. 30, 2015 MW	May 31, 2012 MW	Mar. 31, 1988 MW	Dec. 31, 1988 MW	Sep. 30, 2020 USD ($)
Regulatory Projects and Legal Obligations [Line Items]
ERP/EAM project service period (in years)		12 years
Project costs, accrued carrying costs once put into service | $									$ 59.5
Project costs, amortization | $									0.5
Future O&M expense reductions | $		$ 150.0
Future cost avoidance related to capital cost and tax costs | $		$ 96.0
AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchase commitment, period (in years)							30 years
Minimum power volume required (in megawatts) | MW							180
Additional capacity requirement (in megawatts) | MW					9
Hu Honua Bioenergy, LLC
Regulatory Projects and Legal Obligations [Line Items]
Minimum power volume required (in megawatts) | MW						21.5
Molokai New Energy Partners
Regulatory Projects and Legal Obligations [Line Items]
Total contracted PV capacity (in megawatts) | MW				4.88
Total contracted battery energy storage system capacity | MW				3
Maximum power volume to be delivered (in megawatts) | MW				2.64
Hawaiian Electric (parent only) | Subsequent Event
Regulatory Projects and Legal Obligations [Line Items]
ERP/EAM project service period (in years)	12 years
Hawaiian Electric (parent only) | PCB Contamination
Environmental regulation
Valuation allowances and reserves | $									4.6
HELCO
Regulatory Projects and Legal Obligations [Line Items]
ERP/EAM project service period (in years)			12 years
Maui Electric
Environmental regulation
Additional accrued investigation and estimated cleanup costs | $									2.7
ERP/EAM Implementation Project | Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory Projects and Legal Obligations [Line Items]
Regulatory liability for O&M expense reductions | $									$ 9.7
Kalaeloa | Hawaiian Electric (parent only)
Regulatory Projects and Legal Obligations [Line Items]
Increased power purchase commitment capacity (in megawatts) | MW								208

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Aggregate of Power Purchase Capacity Increases from Initial Capacity

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Public Utilities, ERP/EAM Implementation Project Costs, Accrued Carrying Costs Once Put Into Service

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Period covered by the long-term purchase commitment, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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