Summary of significant accounting policies - Accounts Receivable and Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2020	Dec. 31, 2016
Allowance for Credit Losses
Allowance for credit losses	$ 53,355,000	$ 52,119,000	$ 53,637,000		$ 55,533,000
Retained earnings	622,042,000	543,623,000
Accounts Receivable
Allowance for customer accounts receivable, accrued unbilled revenues and other accounts receivable	1,400,000	1,500,000
Goodwill and other intangibles
Goodwill	82,190,000	82,190,000
American Savings Bank (ASB)
Allowance for Credit Losses
Retained earnings	358,259,000	325,286,000
Investment Securities
Other than temporary impairment, investments	$ 0	0	0
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	66,302,000	67,626,000
Commitments to fund affordable housing investments	$ 23,400,000	$ 18,100,000
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
Electric utility revenues
Weighted average AFUDC rate	7.40%	7.30%	7.70%
Forecast [Member] | ASU 2016-13 | Minimum
Allowance for Credit Losses
Allowance for credit losses				$ 18,000,000
Retained earnings				18,000,000
Forecast [Member] | ASU 2016-13 | Maximum
Allowance for Credit Losses
Allowance for credit losses				22,000,000
Retained earnings				$ 22,000,000