Cash flows (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Supplemental disclosures of cash flow information
Interest paid to non-affiliates	$ 62	$ 61
Income taxes paid (including refundable credits)	32	19
Income taxes refunded (including refundable credits)	0	45
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	3	12
Unpaid invoices and accruals for capital expenditures (investing)
Change during the period	31	(6)
Balance, end of period	116	64
Common stock dividends reinvested in HEI common stock (financing)	0	17
Loans transferred from held for investment to held for sale (investing)	41	14
Common stock issued (gross) for director and executive/management compensation (financing)	11	7
Obligations to fund low income housing investments (investing)	10	0
Hawaiian Electric Company, Inc. and Subsidiaries
Supplemental disclosures of cash flow information
Interest paid to non-affiliates	45	43
Income taxes paid (including refundable credits)	9	0
Income taxes refunded (including refundable credits)	0	20
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	3	12
Unpaid invoices and accruals for capital expenditures (investing)
Change during the period	29	(7)
Balance, end of period	$ 113	$ 63