Credit agreements and changes in debt - Narrative (Details)					9 Months Ended
	Jun. 26, 2024 USD ($) payment	May 17, 2024 USD ($) extensionOption	May 14, 2023 USD ($) institution extensionOption	Feb. 18, 2022 USD ($) extensionOption	Sep. 30, 2024 USD ($)	Jun. 27, 2024 USD ($)	Dec. 08, 2023 USD ($)	Aug. 23, 2023 USD ($)	May 14, 2021 USD ($) institution
Mahipapa
Credit agreement
Number of deferred payments | payment	2
Deferred payments	$ 3,000,000
Credit Facilities | Hawaiian Electric Company, Inc. and Subsidiaries
Credit agreement
Number of financial institutions | institution			9						9
Number of financial institutions with extended termination date | institution			8
HEI Facility
Credit agreement
Credit agreement			$ 175,000,000					$ 175,000,000	$ 175,000,000
Credit agreement, remaining borrowing capacity			157,000,000
Hawaiian Electric Facility
Credit agreement
Credit agreement			200,000,000
Credit agreement, remaining borrowing capacity			$ 180,000,000
Hawaiian Electric Facility | Hawaiian Electric Company, Inc. and Subsidiaries
Credit agreement
Credit agreement				$ 275,000,000				$ 200,000,000	$ 200,000,000
Number of extension options | extensionOption			2	2
Extension period			1 year	1 year
Hawaiian Electric Facility | Hawaiian Electric Company, Inc. and Subsidiaries | Letter of Credit
Credit agreement
Credit agreement							$ 75,000,000
ABL Credit Facility Agreement | Hawaiian Electric Company, Inc. and Subsidiaries | Revolving Credit Facility | Line of credit facility
Credit agreement
Credit agreement		$ 250,000,000
Number of extension options | extensionOption		3
Extension period		1 year
Credit facility period		364 days
Automatic extension expiration period		3 years
Short-term borrowings						$ 250,000,000
Draw down of debt					$ 90,000,000