Cash flows (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	$ 51	$ 50
Income taxes paid (including refundable credits)	14	0
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	1	3
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	31	34
Reduction of long-term debt from funds previously transferred for repayment (financing)	0	82
Right-of-use assets obtained in exchange for operating lease obligations (investing)	38	20
Common stock issued (gross) for director and executive/management compensation (financing)	7	16
Obligations to fund low income housing investments (investing)	9	0
Loans transferred from held for investment to held for sale (investing)	62	0
Hawaiian Electric Company, Inc. and Subsidiaries
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	37	32
Income taxes paid (including refundable credits)	20	0
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	1	3
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	27	30
Reduction of long-term debt from funds previously transferred for repayment (financing)	0	82
Right-of-use assets obtained in exchange for operating lease obligations (investing)	$ 38	$ 16