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Electric utility segment - Commitments and contingencies (Details)
 1 Months Ended 12 Months Ended 36 Months Ended
Aug. 11, 2016
Jun. 30, 2017
USD ($)
$ / kWh
MW
Jun. 30, 2015
MW
May 31, 2012
MW
Mar. 31, 1988
MW
Dec. 31, 1988
MW
Jun. 30, 2019
USD ($)
Jun. 10, 2019
USD ($)
Regulatory Projects and Legal Obligations [Line Items]                
AFUDC rate 1.75%              
Project costs, accrued carrying costs once put into service             $ 58,900,000  
Future O&M expense reductions               $ 150,000,000
Future cost avoidance related to capital cost and tax costs               $ 96,000,000
ERP/EAM project service period (in years) 12 years              
Regulatory liability for O&M expense reductions             500,000  
West Lock PV Project, energy generated (in megawatts) | MW   20            
West Lock PV Project, cost cap   $ 67,000,000            
West Lock PV Project, maximum energy cost (in dollars per kilowatt hours) | $ / kWh   0.0956            
West Lock PV Project, project costs incurred             46,500,000  
PCB Contamination                
Environmental regulation                
Valuation allowances and reserves             4,700,000  
AES Hawaii                
Regulatory Projects and Legal Obligations [Line Items]                
Purchase commitment, period (in years)         30 years      
Minimum power volume required (in megawatts) | MW         180      
Additional capacity requirement (in megawatts) | MW     9          
Hu Honua Bioenergy, LLC                
Regulatory Projects and Legal Obligations [Line Items]                
Minimum power volume required (in megawatts) | MW       21.5        
Maui Electric                
Environmental regulation                
Additional accrued investigation and estimated cleanup costs             $ 2,700,000  
Kalaeloa | Hawaiian Electric (parent only)                
Regulatory Projects and Legal Obligations [Line Items]                
Increased power purchase commitment capacity (in megawatts) | MW           208