Electric utility segment - Utility Projects (Details) $ in Millions		1 Months Ended
	Jan. 31, 2024 USD ($)	Jul. 31, 2025	Dec. 31, 2023 USD ($)	Sep. 30, 2020 MW	Sep. 30, 2025 USD ($)	Aug. 07, 2024 USD ($)
Hawaiian Electric Company, Inc. and Subsidiaries
Public Utilities, General Disclosures [Line Items]
Public utilities, project cost recovery cap						$ 95.0
Project costs incurred					$ 34.2
Waena Battery Energy Storage System Project
Public Utilities, General Disclosures [Line Items]
Total contracted battery energy storage system capacity | MW				40
Waena Battery Energy Storage System Project | Hawaiian Electric Company, Inc. and Subsidiaries
Public Utilities, General Disclosures [Line Items]
Renewable energy generation project, approved funds			$ 82.1
Renewable energy generation project, incurred cost					$ 18.1
Public utilities, approved estimated capital costs (as percent)		20.00%
Climate Adaptation Transmission And Distribution Resilience Program | Hawaiian Electric Company, Inc. and Subsidiaries
Public Utilities, General Disclosures [Line Items]
Public utilities, electric grid project, approved funds	$ 189.7
Project period (in years)	5 years