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Electric utility segment - Annual decoupling filings summary (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2021
USD ($)
Regulatory Projects and Legal Obligations [Line Items]  
2021 Annual incremental RAM adjusted revenues and ARA revenues $ (21.7)
Annual change in accrued RBA balance as of December 31, 2020 (and associated revenue taxes) 25.0
Incremental Performance Incentive Mechanisms (net) 0.7
Incremental MPIR/EPRM Revenue Adjustment 12.8
Incremental Affiliate Transaction Refund/PUC Ordered Adjustment 2.0
Net annual incremental amount to be collected under the tariffs 18.7
Hawaiian Electric (parent only)  
Regulatory Projects and Legal Obligations [Line Items]  
2021 Annual incremental RAM adjusted revenues and ARA revenues (13.8)
Annual change in accrued RBA balance as of December 31, 2020 (and associated revenue taxes) 10.4
Incremental Performance Incentive Mechanisms (net) 0.0
Incremental MPIR/EPRM Revenue Adjustment 12.6
Incremental Affiliate Transaction Refund/PUC Ordered Adjustment 0.0
Net annual incremental amount to be collected under the tariffs 9.1
Hawaii Electric Light  
Regulatory Projects and Legal Obligations [Line Items]  
2021 Annual incremental RAM adjusted revenues and ARA revenues (2.0)
Annual change in accrued RBA balance as of December 31, 2020 (and associated revenue taxes) 5.7
Incremental Performance Incentive Mechanisms (net) 0.2
Incremental MPIR/EPRM Revenue Adjustment 0.1
Net annual incremental amount to be collected under the tariffs 4.0
Maui Electric  
Regulatory Projects and Legal Obligations [Line Items]  
2021 Annual incremental RAM adjusted revenues and ARA revenues (5.9)
Annual change in accrued RBA balance as of December 31, 2020 (and associated revenue taxes) 8.9
Incremental Performance Incentive Mechanisms (net) 0.5
Incremental MPIR/EPRM Revenue Adjustment 0.1
Incremental Affiliate Transaction Refund/PUC Ordered Adjustment 2.0
Net annual incremental amount to be collected under the tariffs $ 5.6