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Electric utility segment - Annual Decoupling Filings Summary (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2025
Regulatory Projects and Legal Obligations [Line Items]    
Recovery of COVID-19 related costs $ 3.2  
Return of ERP benefit liability (3.3)  
Net 2025 ARA revenues (0.1)  
Incremental Performance Incentive Mechanisms (net)   $ 5.2
Incremental MPIR/EPRM revenue adjustment   (2.3)
Incremental Pilot Process cost recovery   (0.9)
Net incremental amount to be collected under the RBA rate tariffs   1.9
Hawaiian Electric, Parent    
Regulatory Projects and Legal Obligations [Line Items]    
Recovery of COVID-19 related costs 2.2  
Return of ERP benefit liability 0.0  
Net 2025 ARA revenues 2.2  
Incremental Performance Incentive Mechanisms (net)   1.3
Incremental MPIR/EPRM revenue adjustment   (1.4)
Incremental Pilot Process cost recovery   (0.7)
Net incremental amount to be collected under the RBA rate tariffs   (0.8)
Hawaii Electric Light    
Regulatory Projects and Legal Obligations [Line Items]    
Recovery of COVID-19 related costs 0.5  
Return of ERP benefit liability (1.3)  
Net 2025 ARA revenues (0.8)  
Incremental Performance Incentive Mechanisms (net)   3.9
Incremental MPIR/EPRM revenue adjustment   (0.6)
Incremental Pilot Process cost recovery   0.0
Net incremental amount to be collected under the RBA rate tariffs   3.2
Maui Electric    
Regulatory Projects and Legal Obligations [Line Items]    
Recovery of COVID-19 related costs 0.5  
Return of ERP benefit liability (2.0)  
Net 2025 ARA revenues $ (1.4)  
Incremental Performance Incentive Mechanisms (net)   0.0
Incremental MPIR/EPRM revenue adjustment   (0.3)
Incremental Pilot Process cost recovery   (0.1)
Net incremental amount to be collected under the RBA rate tariffs   $ (0.5)