Credit agreements, long-term debt and changes in long-term debt - Schedule of Line of Credit Facilities (Details) - Revolving Credit Facility - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Line of Credit Facility [Line Items]
Capacity	$ 650	$ 664
Outstanding	144	389
Undrawn	506	275
Hawaiian Electric Company, Inc. and Subsidiaries
Line of Credit Facility [Line Items]
Capacity	550	564
Outstanding	93	216
Undrawn	457	348
Unsecured revolving line of credit
Line of Credit Facility [Line Items]
Capacity	175	175
Outstanding	51	173
Undrawn	124	2
Unsecured revolving line of credit | Hawaiian Electric Company, Inc. and Subsidiaries
Line of Credit Facility [Line Items]
Capacity	200	200
Outstanding	43	166
Undrawn	157	34
ABL Facility | Hawaiian Electric Company, Inc. and Subsidiaries
Line of Credit Facility [Line Items]
Capacity	225	239
Outstanding	0	0
Undrawn	225	239
Borrowing from HEI - standing commitment letter | Hawaiian Electric Company, Inc. and Subsidiaries
Line of Credit Facility [Line Items]
Capacity	75	75
Outstanding	0	0
Undrawn	75	75
Short-term loan credit facility | Hawaiian Electric Company, Inc. and Subsidiaries
Line of Credit Facility [Line Items]
Capacity	50	50
Outstanding	50	50
Undrawn	$ 0	$ 0