Cash flows (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Supplemental disclosures of cash flow information
Interest paid to non-affiliates	$ 19	$ 19
Income taxes paid (including refundable credits)	3	4
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	3	0
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	48	27
Loans transferred from held for investment to held for sale (investing)	1	9
Common stock issued (gross) for director and executive/management compensation (financing)	3	9
Transfer of retail repurchase agreements to deposit liabilities (financing)	102	0
Hawaiian Electric Company, Inc. and Subsidiaries
Supplemental disclosures of cash flow information
Interest paid to non-affiliates	12	13
Income taxes paid (including refundable credits)	5	2
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	3	0
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	$ 29	$ 26