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Electric utility segment - Utility Projects (Details)
$ in Millions
 1 Months Ended 3 Months Ended
Jan. 31, 2024
USD ($)
Sep. 30, 2020
MW
Mar. 31, 2025
USD ($)
Aug. 07, 2024
USD ($)
Dec. 31, 2023
USD ($)
Hawaiian Electric Company, Inc. and Subsidiaries          
Public Utilities, General Disclosures [Line Items]          
Public utilities, project cost recovery cap       $ 95.0  
Project costs incurred     $ 17.1    
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     $ 8.8    
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