Electric utility segment - Taxes (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Hawaiian Electric Company, Inc. and Subsidiaries
Revenue taxes
Revenue taxes included in operating revenues and in taxes other than income taxes expense	$ 61	$ 54	$ 166	$ 150

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