Cash flows (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	$ 21	$ 19
Income taxes paid (including refundable credits)	4	3
Income taxes refunded (including refundable credits)	4	0
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	0	3
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	36	48
Loans transferred from held for investment to held for sale (investing)	0	1
Common stock issued (gross) for director and executive/management compensation (financing)	3	3
Real estate transferred from property, plant and equipment to other assets held-for-sale (investing)	9	0
Transfer of retail repurchase agreements to deposit liabilities (financing)	0	102
Hawaiian Electric Company, Inc. and Subsidiaries
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	12	12
Income taxes paid (including refundable credits)	5	5
Income taxes refunded (including refundable credits)	4	0
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	0	3
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	$ 29	$ 29