Electric utility segment - Power purchase agreements (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 134	$ 140
Hawaiian Electric (parent only) | Kalaeloa Partners, L.P. (Kalaeloa)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	40	40
Hawaiian Electric (parent only) | AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	32	37
Hawaiian Electric (parent only) | HPOWER
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	18	15
Hawaiian Electric (parent only) | Puna Geothermal Venture
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	0	11
Hawaiian Electric (parent only) | Hamakua Energy Partners, L.P. (HEP)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	16	7
Hawaiian Electric (parent only) | Wind IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	20	22
Hawaiian Electric (parent only) | Solar IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	7	6
Hawaiian Electric (parent only) | Other IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 1	$ 2