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Electric utility segment - Regulatory Proceedings (Details)
 1 Months Ended 9 Months Ended 12 Months Ended
Sep. 15, 2020
agreement
Jun. 05, 2020
USD ($)
Apr. 27, 2017
USD ($)
Dec. 31, 2019
USD ($)
Sep. 30, 2020
USD ($)
Dec. 31, 2019
USD ($)
agreement
Dec. 31, 2018
$ / kWh
Oct. 22, 2020
Jul. 09, 2020
entity
Regulatory Projects and Legal Obligations [Line Items]                  
Decoupling order, service reliability performance, historical measurement period (in years)         10 years        
Service reliability, pending adjusted maximum penalty amount         $ 6,800,000        
Dead band percentage above or below the target         3.00%        
Call center performance, pending adjusted maximum penalty         $ 1,400,000        
Energy price, renewable projects with storage capacity (in dollars per kilowatt hour) | $ / kWh             0.115    
Energy price, renewable energy-only projects (in dollars per kilowatt hour) | $ / kWh             0.095    
Hawaiian Electric Company, Inc. and Subsidiaries                  
Regulatory Projects and Legal Obligations [Line Items]                  
Threshold of capital expenditures in excess of contributions     $ 2,500,000            
MPIR requested amount   $ 23,600,000       $ 19,800,000      
Percentage cap on cost recovery       90.00%   90.00%      
Maximum penalty, percent of ROE         0.20%        
Call center performance, maximum penalty percentage         0.08%        
Call center performance, maximum penalty amount       $ 300,000          
Performance incentive mechanism, incentive cap           $ 3,500,000      
Number of power purchase agreements (PPAs) (in agreements) | agreement 8         7      
Incentives accrued       $ 1,700,000   $ 1,700,000      
Number of grid service purchase agreements | entity                 2
Number of power purchase agreements qualifying for potential payout | agreement 1                
Hawaiian Electric Company, Inc. and Subsidiaries | Subsequent Event                  
Regulatory Projects and Legal Obligations [Line Items]                  
Percentage cap on cost recovery               90.00%  
Percentage of allowed project costs to flow through MPIR mechanism               100.00%  
Schofield Generation Station | Hawaiian Electric Company, Inc. and Subsidiaries                  
Regulatory Projects and Legal Obligations [Line Items]                  
MPIR requested amount   19,200,000              
West Loch PV Project | Hawaiian Electric Company, Inc. and Subsidiaries                  
Regulatory Projects and Legal Obligations [Line Items]                  
MPIR requested amount   3,800,000              
Grid Modernization Strategy Phase 1 Project | Hawaiian Electric Company, Inc. and Subsidiaries                  
Regulatory Projects and Legal Obligations [Line Items]                  
MPIR requested amount   $ 600,000