Electric utility segment - Power purchase agreements (Details) - Hawaiian Electric (parent only) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 140	$ 134
Kalaeloa
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	38	40
AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	31	32
HPOWER
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	17	18
Hamakua Energy
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	13	16
Wind IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	28	20
Solar IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	11	7
Other IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 2	$ 1