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Electric utility segment - Annual Decoupling Filings Summary (Details) - USD ($)
$ in Millions
 9 Months Ended
Oct. 31, 2023
Sep. 30, 2023
Regulatory Projects and Legal Obligations [Line Items]    
Incremental RAM revenues and ARA revenues   $ 24.9
Annual change in accrued RBA balance through September 30, 2023 (and associated revenue taxes)   3.4
Incremental Performance Incentive Mechanisms (net)   0.1
Net incremental amount to be collected under the RBA rate tariffs   28.4
Subsequent Event    
Regulatory Projects and Legal Obligations [Line Items]    
2024 ARA revenues $ 24.7  
Management Audit savings commitment (6.6)  
Enterprise Resource Planning system benefits savings (3.2)  
COVID-19 related cost recovery 3.4  
Net 2024 ARA revenues 18.3  
Hawaiian Electric, Parent    
Regulatory Projects and Legal Obligations [Line Items]    
Incremental RAM revenues and ARA revenues   19.2
Annual change in accrued RBA balance through September 30, 2023 (and associated revenue taxes)   3.6
Incremental Performance Incentive Mechanisms (net)   0.1
Net incremental amount to be collected under the RBA rate tariffs   22.9
Hawaiian Electric, Parent | Subsequent Event    
Regulatory Projects and Legal Obligations [Line Items]    
2024 ARA revenues 16.6  
Management Audit savings commitment (4.6)  
Enterprise Resource Planning system benefits savings 0.0  
COVID-19 related cost recovery 2.6  
Net 2024 ARA revenues 14.6  
Hawaii Electric Light    
Regulatory Projects and Legal Obligations [Line Items]    
Incremental RAM revenues and ARA revenues   3.0
Annual change in accrued RBA balance through September 30, 2023 (and associated revenue taxes)   (0.3)
Incremental Performance Incentive Mechanisms (net)   0.0
Net incremental amount to be collected under the RBA rate tariffs   2.7
Hawaii Electric Light | Subsequent Event    
Regulatory Projects and Legal Obligations [Line Items]    
2024 ARA revenues 4.1  
Management Audit savings commitment (1.0)  
Enterprise Resource Planning system benefits savings (1.3)  
COVID-19 related cost recovery 0.2  
Net 2024 ARA revenues 2.0  
Maui Electric    
Regulatory Projects and Legal Obligations [Line Items]    
Incremental RAM revenues and ARA revenues   2.7
Annual change in accrued RBA balance through September 30, 2023 (and associated revenue taxes)   0.1
Incremental Performance Incentive Mechanisms (net)   0.0
Net incremental amount to be collected under the RBA rate tariffs   $ 2.8
Maui Electric | Subsequent Event    
Regulatory Projects and Legal Obligations [Line Items]    
2024 ARA revenues 4.0  
Management Audit savings commitment (1.0)  
Enterprise Resource Planning system benefits savings (1.9)  
COVID-19 related cost recovery 0.6  
Net 2024 ARA revenues $ 1.7