Summary of significant accounting policies - General, Cash, and PPE (Details) $ in Thousands			1 Months Ended	12 Months Ended
	Feb. 02, 2018 MWh MW	Nov. 24, 2017 MW	Sep. 30, 2020 MW	Dec. 31, 2021 USD ($) MWh branch MW	Dec. 31, 2020 USD ($)	Dec. 31, 2019
Significant Accounting Policies [Line Items]
Number of branches				42
Restricted cash | $				$ 5,900	$ 17,600
Oahu
Significant Accounting Policies [Line Items]
Number of branches				29
Maui
Significant Accounting Policies [Line Items]
Number of branches				6
Kauai
Significant Accounting Policies [Line Items]
Number of branches				2
Hawaii
Significant Accounting Policies [Line Items]
Number of branches				4
Molokai
Significant Accounting Policies [Line Items]
Number of branches				1
Hawaiian Electric Company, Inc. and Subsidiaries
Significant Accounting Policies [Line Items]
Composite annual depreciation rate				3.20%	3.20%	3.20%
Minimum
Significant Accounting Policies [Line Items]
Estimated useful life under production plant (in years)				16 years
Estimated useful life under transmission and distribution plant (in years)				10 years
Estimated useful life under general plant (in years)				5 years
Maximum
Significant Accounting Policies [Line Items]
Estimated useful life under production plant (in years)				51 years
Estimated useful life under transmission and distribution plant (in years)				79 years
Estimated useful life under general plant (in years)				50 years
Hamakua Energy
Significant Accounting Policies [Line Items]
Power produced by power plants (in megawatts) | MW		60		60
Mauo, LLC
Significant Accounting Policies [Line Items]
Power produced by power plants (in megawatts) | MW	8.6			8.6
Power storage capacity (in megawatt hours) | MWh	42.3			42.3
American Savings Bank (ASB)
Significant Accounting Policies [Line Items]
Reserve requirement | $					$ 0
Hawaiian Electric Company, Inc. and Subsidiaries
Significant Accounting Policies [Line Items]
Restricted cash | $				$ 3,089	$ 15,966
Ka‘ie‘ie Waho Company, LLC
Significant Accounting Policies [Line Items]
Photovoltaic system power amount (in megawatts) | MW			6