Cash flows (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	$ 75	$ 67
Income taxes paid (including refundable credits)	55	50
Income taxes refunded (including refundable credits)	4	0
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	7	6
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	37	42
Common stock issued (gross) for director and executive/management compensation (financing)	5	4
Real estate transferred from property, plant and equipment to other assets held-for-sale (investing)	9	0
Obligations to fund low income housing investments (investing)	6	12
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	45	44
Income taxes paid (including refundable credits)	55	47
Income taxes refunded (including refundable credits)	4	0
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	7	6
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	$ 34	$ 28