Electric utility segment - Power purchase agreements (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 162	$ 161	$ 296	$ 301
Hawaiian Electric (parent only) | Kalaeloa
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	61	52	101	92
Hawaiian Electric (parent only) | AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	32	32	64	69
Hawaiian Electric (parent only) | HPOWER
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	19	17	37	32
Hawaiian Electric (parent only) | Puna Geothermal Venture
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	0	4	0	15
Hawaiian Electric (parent only) | Hamakua Energy
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	18	15	34	22
Hawaiian Electric (parent only) | Wind IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	23	31	43	53
Hawaiian Electric (parent only) | Solar IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	8	8	15	14
Hawaiian Electric (parent only) | Other IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 1	$ 2	$ 2	$ 4