Electric utility segment - Major Customers (Details) - Hawaiian Electric Company, Inc. and Subsidiaries - Operating revenues - Customer concentration - Various federal government agencies - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Major customers
Operating revenues percentage	11.00%	11.00%	11.00%
Operating revenues amount	$ 281	$ 273	$ 239