Electric utility segment - Power Purchase Agreements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 587	$ 563	$ 594
Kalaeloa Partners, L.P. (Kalaeloa)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	180	152	187
AES Hawaii, Inc. (AES Hawaii)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	140	149	134
HPOWER
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	67	71	66
Puna Geothermal Venture
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	38	28	29
Hamakua Energy Partners, L.P. (HEP)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	35	29	44
Hawaiian Commercial & Sugar (HC&S)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	0	1	8
Other IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 127	$ 133	$ 126