Cash flows (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	$ 175	$ 104
Income taxes paid (including refundable credits)	34	28
Income taxes refunded (including refundable credits)	0	1
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	9	9
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	33	45
Right-of-use assets obtained in exchange for finance lease obligations (financing)	108	76
Right-of-use assets obtained in exchange for operating lease obligations (investing)	4	1
Common stock issued (gross) for director and executive/management compensation (financing)	3	8
Obligations to fund low income housing investments (investing)	0	7
Loans transferred from held for investment to held for sale (investing)	29	95
Transfer of retail repurchase agreements to deposit liabilities (financing)	0	98
Hawaiian Electric Company, Inc. and Subsidiaries
Supplemental disclosures of cash flow information
Interest paid to non-affiliates, net of amounts capitalized	59	45
Income taxes paid (including refundable credits)	53	38
Income taxes refunded (including refundable credits)	0	2
Supplemental disclosures of noncash activities
Estimated fair value of noncash contributions in aid of construction (investing)	9	9
Unpaid invoices and accruals for capital expenditures, balance, end of period (investing)	33	43
Right-of-use assets obtained in exchange for finance lease obligations (financing)	$ 107	$ 76