Electric utility segment - Power purchase agreements (Details) - Hawaiian Electric (parent only) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 137	$ 162	$ 277	$ 296
Kalaeloa
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	34	61	72	101
AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	32	32	63	64
HPOWER
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	17	19	34	37
Hamakua Energy
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	11	18	24	34
Wind IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	25	23	53	43
Solar IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	17	8	28	15
Other IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 1	$ 1	$ 3	$ 2