Cash flows (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Supplemental disclosures of cash flow information
Interest paid to non-affiliates	$ 67	$ 62
Income taxes paid (including refundable credits)	50	32
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	6	3
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	42	35
Loans transferred from held for investment to held for sale (investing)	1	41
Common stock issued (gross) for director and executive/management compensation (financing)	4	11
Obligations to fund low income housing investments (investing)	12	10
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	44	45
Income taxes paid (including refundable credits)	47	9
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	6	3
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	$ 28	$ 32