Electric utility segment - Power Purchase Agreements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 639	$ 587	$ 563
Kalaeloa Partners, L.P. (Kalaeloa)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	216	180	152
AES Hawaii, Inc. (AES Hawaii)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	140	140	149
HPOWER
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	69	67	71
Puna Geothermal Venture
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	15	38	28
Hamakua Energy Partners, L.P. (HEP)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	56	35	29
Hawaiian Commercial & Sugar (HC&S)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	0	0	1
Wind IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	107	97	113
Solar IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	29	27	15
Other IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 7	$ 3	$ 5