Cash flows (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	$ 18	$ 21
Income taxes paid (including refundable credits)	0	4
Income taxes refunded (including refundable credits)	0	4
Supplemental disclosures of noncash activities
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)	19	0
Common stock issued (gross) for director and executive/management compensation (financing)	14	3
Real estate transferred from property, plant and equipment to other assets held-for-sale (investing)	0	9
Property, plant and equipment-unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	32	36
Hawaiian Electric Company, Inc. and Subsidiaries
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	9	12
Income taxes paid (including refundable credits)	0	5
Income taxes refunded (including refundable credits)	0	4
Supplemental disclosures of noncash activities
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	0
Property, plant and equipment-unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	$ 27	$ 29