Cash flows (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Continuing Operations
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	$ 71	$ 84
Interest paid on finance lease obligations	29	23
Income taxes paid (including refundable credits)	28	30
Income taxes refunded (including refundable credits)	4	0
Supplemental disclosures of noncash activities
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	66	33
Right-of-use assets obtained in exchange for finance lease obligations (financing)	51	108
Common stock issued (gross) for nonemployee director and executive/management compensation (financing)	2	2
Debt assumed by buyer - sale of subsidiaries (financing)	67	0
Discontinued Operations
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	0	91
Income taxes paid (including refundable credits)	0	4
Supplemental disclosures of noncash activities
Common stock issued (gross) for nonemployee director and executive/management compensation (financing)	0	1
Loans transferred from held for investment to held for sale (investing)	0	29
Right-of-use assets obtained in exchange for operating lease obligations (investing)	0	4
HEI consolidated (continuing operations) and Hawaiian Electric consolidated
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	5	9
Reduction of long-term debt from funds previously transferred for repayment (financing)	47	0
Hawaiian Electric Company, Inc. and Subsidiaries
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	53	59
Interest paid on finance lease obligations	29	23
Income taxes paid (including refundable credits)	39	53
Income taxes refunded (including refundable credits)	5	0
Supplemental disclosures of noncash activities
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	66	33
Right-of-use assets obtained in exchange for finance lease obligations (financing)	51	107
Capital contribution from parent of a membership interest in an unconsolidated affiliate (financing)	$ 287	$ 0