Cash flows (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	$ 15	$ 18
Income taxes paid (including refundable credits)	0	0
Income taxes refunded (including refundable credits)	0	0
Supplemental disclosures of noncash activities
Property, plant and equipment unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	28	32
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)	28	19
Common stock issued (gross) for director and executive/management compensation (financing)	6	14
Hawaiian Electric Company, Inc. and Subsidiaries
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	9	9
Income taxes paid (including refundable credits)	0	0
Income taxes refunded (including refundable credits)	0	0
Supplemental disclosures of noncash activities
Property, plant and equipment unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	24	27
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)	$ 28	$ 16