Electric utility segment - Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Regulatory assets
Regulatory assets	$ 766,708	$ 715,080
Regulatory liabilities
Regulatory liabilities	$ 959,786	972,310
Minimum | Income taxes
Regulatory liabilities
Authorized amortization or recovery periods	1 year
Minimum | Decoupling revenue balancing account and RAM
Regulatory liabilities
Authorized amortization or recovery periods	1 year
Maximum | Income taxes
Regulatory liabilities
Authorized amortization or recovery periods	55 years
Maximum | Decoupling revenue balancing account and RAM
Regulatory liabilities
Authorized amortization or recovery periods	2 years
Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory assets
Regulatory assets	$ 766,708	715,080
Regulatory liabilities
Regulatory liabilities	959,786	972,310
Hawaiian Electric Company, Inc. and Subsidiaries | Cost of removal in excess of salvage value
Regulatory liabilities
Regulatory liabilities	541,730	521,977
Hawaiian Electric Company, Inc. and Subsidiaries | Income taxes
Regulatory liabilities
Regulatory liabilities	360,426	386,990
Hawaiian Electric Company, Inc. and Subsidiaries | Decoupling revenue balancing account and RAM
Regulatory liabilities
Regulatory liabilities	1,957	16,370
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans
Regulatory liabilities
Regulatory liabilities	29,759	21,707
Hawaiian Electric Company, Inc. and Subsidiaries | Other
Regulatory liabilities
Regulatory liabilities	$ 25,914	25,266
Hawaiian Electric Company, Inc. and Subsidiaries | Minimum | Cost of removal in excess of salvage value
Regulatory liabilities
Authorized amortization or recovery periods	1 year
Hawaiian Electric Company, Inc. and Subsidiaries | Minimum | Other
Regulatory liabilities
Remaining amortization or recovery periods	1 year
Hawaiian Electric Company, Inc. and Subsidiaries | Maximum | Cost of removal in excess of salvage value
Regulatory liabilities
Authorized amortization or recovery periods	79 years
Hawaiian Electric Company, Inc. and Subsidiaries | Maximum | Other
Regulatory liabilities
Remaining amortization or recovery periods	18 years
Hawaiian Electric Company, Inc. and Subsidiaries | Current assets
Regulatory assets
Regulatory assets	$ 30,435	30,710
Hawaiian Electric Company, Inc. and Subsidiaries | Long-term assets
Regulatory assets
Regulatory assets	736,273	684,370
Hawaiian Electric Company, Inc. and Subsidiaries | Current liabilities
Regulatory liabilities
Regulatory liabilities	37,301	30,724
Hawaiian Electric Company, Inc. and Subsidiaries | Long-term liabilities
Regulatory liabilities
Regulatory liabilities	922,485	941,586
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans (balance primarily varies with plans’ funded statuses)
Regulatory assets
Regulatory assets	592,644	554,485
Hawaiian Electric Company, Inc. and Subsidiaries | Income taxes
Regulatory assets
Regulatory assets	$ 96,171	102,612
Hawaiian Electric Company, Inc. and Subsidiaries | Income taxes | Minimum
Regulatory assets
Authorized amortization or recovery periods	1 year
Hawaiian Electric Company, Inc. and Subsidiaries | Income taxes | Maximum
Regulatory assets
Authorized amortization or recovery periods	55 years
Hawaiian Electric Company, Inc. and Subsidiaries | Decoupling revenue balancing account and RAM
Regulatory assets
Regulatory assets	$ 10,432	0
Hawaiian Electric Company, Inc. and Subsidiaries | Decoupling revenue balancing account and RAM | Minimum
Regulatory assets
Authorized amortization or recovery periods	1 year
Hawaiian Electric Company, Inc. and Subsidiaries | Decoupling revenue balancing account and RAM | Maximum
Regulatory assets
Authorized amortization or recovery periods	2 years
Hawaiian Electric Company, Inc. and Subsidiaries | Unamortized expense and premiums on retired debt and equity issuances
Regulatory assets
Regulatory assets	$ 8,654	10,228
Hawaiian Electric Company, Inc. and Subsidiaries | Unamortized expense and premiums on retired debt and equity issuances | Minimum
Regulatory assets
Authorized amortization or recovery periods	1 year
Remaining amortization or recovery periods	1 year
Hawaiian Electric Company, Inc. and Subsidiaries | Unamortized expense and premiums on retired debt and equity issuances | Maximum
Regulatory assets
Authorized amortization or recovery periods	19 years
Remaining amortization or recovery periods	18 years
Hawaiian Electric Company, Inc. and Subsidiaries | Vacation earned, but not yet taken
Regulatory assets
Regulatory assets	$ 15,665	12,535
Authorized amortization or recovery periods	1 year
Hawaiian Electric Company, Inc. and Subsidiaries | COVID-19 related costs (to be determined by PUC)
Regulatory assets
Regulatory assets	$ 18,032	0
Hawaiian Electric Company, Inc. and Subsidiaries | Other
Regulatory assets
Regulatory assets	$ 25,110	$ 35,220
Hawaiian Electric Company, Inc. and Subsidiaries | Other | Minimum
Regulatory assets
Remaining amortization or recovery periods	1 year
Hawaiian Electric Company, Inc. and Subsidiaries | Other | Maximum
Regulatory assets
Remaining amortization or recovery periods	39 years