Long-term debt - Schedule of Long-Term Debt and Maturities (Details) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Less unamortized debt issuance costs	$ (2,249,000)	$ (2,350,000)
Long-term debt, net—other than bank	2,119,129,000	1,964,365,000
Aggregate principal payments, fiscal year maturity:
2021	55,000,000
2022	241,000,000
2023	162,000,000
2024	6,000,000
2025	103,000,000
Hawaiian Electric Company, Inc. and Subsidiaries
Debt Instrument [Line Items]
Gross long-term debt	1,569,000,000	1,505,000,000
Aggregate principal payments, fiscal year maturity:
2021	0
2022	52,000,000
2023	100,000,000
2024	0
2025	47,000,000
Special purpose revenue bonds issued on behalf of electric utility subsidiaries
Debt Instrument [Line Items]
Long-term debt, net—other than bank	1,561,302,000	1,497,667,000
Senior notes \| Hawaiian Electric Company, Inc. and Subsidiaries
Debt Instrument [Line Items]
Gross long-term debt	1,027,000,000	963,000,000
Senior notes \| HEI 5.67% senior notes, due 2021
Debt Instrument [Line Items]
Gross long-term debt	$ 50,000,000	50,000,000
Debt instrument, stated interest rate	5.67%
Senior notes \| HEI 3.99% senior notes, due 2023
Debt Instrument [Line Items]
Gross long-term debt	$ 50,000,000	50,000,000
Debt instrument, stated interest rate	3.99%
Senior notes \| HEI 4.58% senior notes, due 2025
Debt Instrument [Line Items]
Gross long-term debt	$ 50,000,000	50,000,000
Debt instrument, stated interest rate	4.58%
Senior notes \| HEI 4.72% senior notes, due 2028
Debt Instrument [Line Items]
Gross long-term debt	$ 100,000,000	100,000,000
Debt instrument, stated interest rate	4.72%
Senior notes \| Hamakua Energy 4.02% notes, due 2030, secured by real and personal property of Hamakua Energy, LLC
Debt Instrument [Line Items]
Gross long-term debt	$ 56,030,000	59,699,000
Debt instrument, stated interest rate	4.02%
Senior notes \| Senior Notes 2.98 Percent Due 2030
Debt Instrument [Line Items]
Gross long-term debt	$ 50,000,000	0
Debt instrument, stated interest rate	2.98%
Term Loan \| HEI 2.99% term loan, due 2022
Debt Instrument [Line Items]
Gross long-term debt	$ 150,000,000	150,000,000
Debt instrument, stated interest rate	2.99%
Term Loan \| Ka'ie'ie Waho Company, LLC 2.79% non-recourse loan, due 2031
Debt Instrument [Line Items]
Gross long-term debt	$ 13,000,000	0
Debt instrument, stated interest rate	2.79%
Unsecured Debt \| Mauo LIBOR + 1.375% loan, due 2023
Debt Instrument [Line Items]
Gross long-term debt	$ 41,046,000	$ 9,349,000
Paydown of loan balance, maximum balance	$ 7,000,000
Unsecured Debt \| Mauo LIBOR + 1.375% loan, due 2023 \| LIBOR
Debt Instrument [Line Items]
Line of credit facility basis point spread	1.375%

Debt Instrument, Covenant, Paydown Of Loan Balance, Maximum Balance

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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