Cash flows (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	$ 64	$ 75
Income taxes paid (including refundable credits)	23	55
Income taxes refunded (including refundable credits)	0	4
Supplemental disclosures of noncash activities
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	32	37
Reduction of long-term debt from funds previously transferred for repayment (financing)	82	0
Right-of-use assets obtained in exchange for operating lease obligations (investing)	22	5
Common stock issued (gross) for director and executive/management compensation (financing)	16	5
Real estate transferred from property, plant and equipment to other assets held-for-sale (investing)	0	9
Obligations to fund low income housing investments (investing)	10	6
Hawaiian Electric Company, Inc. and Subsidiaries
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	39	45
Income taxes paid (including refundable credits)	29	55
Income taxes refunded (including refundable credits)	0	4
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	9	7
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	28	34
Reduction of long-term debt from funds previously transferred for repayment (financing)	82	0
Right-of-use assets obtained in exchange for operating lease obligations (investing)	$ 16	$ 1