Electric utility segment - Power purchase agreements (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 176	$ 177	$ 472	$ 478
Hawaiian Electric (parent only) | Kalaeloa
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	58	62	159	154
Hawaiian Electric (parent only) | AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	38	38	102	107
Hawaiian Electric (parent only) | HPOWER
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	20	19	57	51
Hawaiian Electric (parent only) | Puna Geothermal Venture
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	0	0	0	15
Hawaiian Electric (parent only) | Hamakua Energy
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	17	17	51	39
Hawaiian Electric (parent only) | Wind IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	30	31	73	84
Hawaiian Electric (parent only) | Solar IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	11	8	26	22
Hawaiian Electric (parent only) | Other IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 2	$ 2	$ 4	$ 6