Fair value measurements - Summary of financial assets and liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Financial assets
Available-for-sale investment securities	$ 2,444,267	$ 2,574,618
Held-to-maturity investment securities	440,023
Financial liabilities
Short-term borrowings—other than bank	124,017	53,998
Other bank borrowings	241,610	88,305
Carrying or notional amount
Financial assets
Available-for-sale investment securities	2,444,267	2,574,618
Held-to-maturity investment securities	513,767	522,270
Loans, net	5,361,277	5,150,388
Mortgage-servicing rights	9,696	9,950
Derivative assets	22,689	57,377
Financial liabilities
Deposit liabilities	407,972	423,976
Short-term borrowings—other than bank	124,017	53,998
Other bank borrowings	241,610	88,305
Long-term debt, net	2,374,500	2,321,937
Derivative liabilities	124,000	57,000
Carrying or notional amount | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,736,508	1,676,402
Short-term borrowings	54,987
Estimated fair value
Financial assets
Available-for-sale investment securities	2,444,267	2,574,618
Held-to-maturity investment securities	440,023	510,474
Loans, net	5,099,980	5,228,524
Mortgage-servicing rights	17,201	14,480
Derivative assets	1,101	909
Financial liabilities
Deposit liabilities	397,909	442,361
Short-term borrowings—other than bank	124,017	53,998
Other bank borrowings	241,606	88,304
Long-term debt, net	2,222,491	2,624,130
Derivative liabilities	810	5,282
Estimated fair value | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,622,996	1,955,710
Short-term borrowings	54,987
Estimated fair value | Quoted prices in active markets for identical assets (Level 1)
Financial assets
Available-for-sale investment securities	0	0
Held-to-maturity investment securities	0	0
Loans, net	0	0
Mortgage-servicing rights	0	0
Derivative assets	27	0
Financial liabilities
Deposit liabilities	0	0
Short-term borrowings—other than bank	0	0
Other bank borrowings	0	0
Long-term debt, net	0	0
Derivative liabilities	0	11
Estimated fair value | Quoted prices in active markets for identical assets (Level 1) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	0	0
Short-term borrowings	0
Estimated fair value | Significant  other observable  inputs (Level 2)
Financial assets
Available-for-sale investment securities	2,429,102	2,559,191
Held-to-maturity investment securities	440,023	510,474
Loans, net	3,737	10,403
Mortgage-servicing rights	0	0
Derivative assets	1,074	909
Financial liabilities
Deposit liabilities	397,909	442,361
Short-term borrowings—other than bank	124,017	53,998
Other bank borrowings	241,606	88,304
Long-term debt, net	2,222,491	2,624,130
Derivative liabilities	810	5,271
Estimated fair value | Significant  other observable  inputs (Level 2) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	1,622,996	1,955,710
Short-term borrowings	54,987
Estimated fair value | Significant unobservable inputs (Level 3)
Financial assets
Available-for-sale investment securities	15,165	15,427
Held-to-maturity investment securities	0	0
Loans, net	5,096,243	5,218,121
Mortgage-servicing rights	17,201	14,480
Derivative assets	0	0
Financial liabilities
Deposit liabilities	0	0
Short-term borrowings—other than bank	0	0
Other bank borrowings	0	0
Long-term debt, net	0	0
Derivative liabilities	0	0
Estimated fair value | Significant unobservable inputs (Level 3) | Hawaiian Electric Company, Inc. and Subsidiaries
Financial liabilities
Long-term debt, net	0	$ 0
Short-term borrowings	$ 0