Cash flows (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	$ 53	$ 45
Income taxes paid (including refundable credits)	46	36
Income taxes refunded (including refundable credits)	4	0
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	1	5
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	30	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	6
Transfer of retail repurchase agreements to deposit liabilities (financing)	0	102
Unsettled trades to purchase investment securities (investing)	0	10
Hawaiian Electric Company, Inc. and Subsidiaries
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	34	32
Income taxes paid (including refundable credits)	46	35
Income taxes refunded (including refundable credits)	4	0
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	1	5
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	$ 27	$ 28