Electric utility segment - Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Regulatory assets
Regulatory assets	$ 715,080	$ 833,426
Regulatory liabilities
Regulatory liabilities	$ 972,310	950,236
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	$ 715,080	833,426
Regulatory liabilities
Regulatory liabilities	972,310	950,236
Hawaiian Electric Company, Inc. and Subsidiaries | Cost of removal in excess of salvage value
Regulatory liabilities
Regulatory liabilities	521,977	491,006
Hawaiian Electric Company, Inc. and Subsidiaries | Income taxes
Regulatory liabilities
Regulatory liabilities	386,990	413,339
Hawaiian Electric Company, Inc. and Subsidiaries | Decoupling revenue balancing account and RAM
Regulatory liabilities
Regulatory liabilities	16,370	0
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans
Regulatory liabilities
Regulatory liabilities	21,707	19,129
Hawaiian Electric Company, Inc. and Subsidiaries | Other
Regulatory liabilities
Regulatory liabilities	$ 25,266	26,762
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	60 years
Hawaiian Electric Company, Inc. and Subsidiaries | Maximum | Other
Regulatory liabilities
Remaining amortization or recovery periods	19 years
Hawaiian Electric Company, Inc. and Subsidiaries | Current assets
Regulatory assets
Regulatory assets	$ 30,710	71,016
Hawaiian Electric Company, Inc. and Subsidiaries | Long-term assets
Regulatory assets
Regulatory assets	684,370	762,410
Hawaiian Electric Company, Inc. and Subsidiaries | Current liabilities
Regulatory liabilities
Regulatory liabilities	30,724	17,977
Hawaiian Electric Company, Inc. and Subsidiaries | Long-term liabilities
Regulatory liabilities
Regulatory liabilities	941,586	932,259
Hawaiian Electric Company, Inc. and Subsidiaries | Retirement benefit plans (balance primarily varies with plans’ funded statuses)
Regulatory assets
Regulatory assets	554,485	624,126
Hawaiian Electric Company, Inc. and Subsidiaries | Income taxes
Regulatory assets
Regulatory assets	$ 102,612	114,076
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	$ 0	49,560
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	$ 10,228	10,065
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	20 years
Remaining amortization or recovery periods	19 years
Hawaiian Electric Company, Inc. and Subsidiaries | Vacation earned, but not yet taken
Regulatory assets
Regulatory assets	$ 12,535	10,820
Authorized amortization or recovery periods	1 year
Hawaiian Electric Company, Inc. and Subsidiaries | Other
Regulatory assets
Regulatory assets	$ 35,220	$ 24,779
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