Electric utility segment - Most Recent Proceedings (Details) - USD ($) $ in Millions	Nov. 13, 2019	Aug. 21, 2019	Mar. 18, 2019	Dec. 14, 2018
Hawaiian Electric
Regulatory Projects and Legal Obligations [Line Items]
General rate increase, revenue, percent		4.10%
Revenue, calculation assumption, rate of return		8.00%
Stipulated return on average common equity rate		10.50%
General rate increase, revenue		$ 77.6
Maui Electric
Regulatory Projects and Legal Obligations [Line Items]
Stipulated return on average common equity rate			9.50%
Interim general rate increase			$ 12.2
Interim general rate increase, effective interest rate of return			7.43%
Interim general rate increase, common equity capitalization			57.00%
Interim general rate increase, rate base			$ 454.0
General rate increase, risk sharing percentage, ratepayer			98.00%
General rate increase, risk sharing percentage, utility			2.00%
General rate increase, maximum exposure cap			$ 0.6
Hawaii Electric Light
Regulatory Projects and Legal Obligations [Line Items]
General rate increase, revenue, percent				3.40%
Revenue, calculation assumption, rate of return				8.30%
Stipulated return on average common equity rate	9.50%			10.50%
Interim general rate increase, effective interest rate of return	7.52%
Interim general rate increase, common equity capitalization	58.00%
Interim general rate increase, rate base	$ 534.0
General rate increase, revenue				$ 13.4
Interim revenue requirement	$ 387.0