Summary of significant accounting policies - Accounts Receivable and Additional Information (Details)	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Goodwill and other intangibles
Goodwill	$ 82,190,000	$ 82,190,000
Valuation, Income Approach | Measurement Input, Terminal Value
Goodwill and other intangibles
Goodwill impairment, measurement input	0.75
Valuation, Publicly Traded Company Method
Goodwill and other intangibles
Goodwill impairment, measurement input	0.20
Valuation, Sale Transaction Method
Goodwill and other intangibles
Goodwill impairment, measurement input	0.05
American Savings Bank (ASB)
Loans modified in a troubled debt restructuring
Number of consecutive months of repayment required for loans to be removed from nonaccrual status	6 months
Goodwill and other intangibles
Goodwill	$ 82,190,000	82,190,000
Goodwill impairment	0	0	$ 0
Low-income housing investments	111,000,000	83,400,000
Commitments to fund affordable housing investments	$ 62,800,000	41,000,000
American Savings Bank (ASB) | Measurement Band A
Goodwill and other intangibles
Risks inherent in servicing assets and servicing liabilities band percent for risk categorization	0.50%
American Savings Bank (ASB) | Measurement Band B
Goodwill and other intangibles
Risks inherent in servicing assets and servicing liabilities band percent for risk categorization	1.00%
American Savings Bank (ASB) | Loans receivable
Nonperforming loans
Period for classification as delinquent	90 days
American Savings Bank (ASB) | Mortgage receivable
Nonperforming loans
Period for classification as delinquent	180 days
American Savings Bank (ASB) | Consumer
Nonperforming loans
Period for write-off	120 days
Hawaiian Electric Company, Inc. and Subsidiaries
Accounts Receivable
Allowance for customer accounts receivable, accrued unbilled revenues and other accounts receivable	$ 26,100,000	$ 17,800,000
Electric utility revenues
Weighted average AFUDC rate	7.10%	7.10%	7.40%