Electric utility segment - Annual decoupling filings summary (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($)
Regulatory Projects and Legal Obligations [Line Items]
Incremental accrued RBA balance through September 30, 2021 (and associated revenue taxes)	$ (8.3)
Incremental Performance Incentive Mechanisms (net)	2.7
Incremental MPIR/EPRM Revenue Adjustment	2.8
Other	(0.1)
Net incremental amount to be collected under the RBA rate tariffs	(2.9)
Hawaiian Electric, Parent
Regulatory Projects and Legal Obligations [Line Items]
Incremental accrued RBA balance through September 30, 2021 (and associated revenue taxes)	(5.7)
Incremental Performance Incentive Mechanisms (net)	1.9
Incremental MPIR/EPRM Revenue Adjustment	1.3
Other	(0.1)
Net incremental amount to be collected under the RBA rate tariffs	(2.6)
Hawaii Electric Light
Regulatory Projects and Legal Obligations [Line Items]
Incremental accrued RBA balance through September 30, 2021 (and associated revenue taxes)	2.1
Incremental Performance Incentive Mechanisms (net)	0.4
Incremental MPIR/EPRM Revenue Adjustment	0.8
Other	0.0
Net incremental amount to be collected under the RBA rate tariffs	3.3
Maui Electric
Regulatory Projects and Legal Obligations [Line Items]
Incremental accrued RBA balance through September 30, 2021 (and associated revenue taxes)	(4.7)
Incremental Performance Incentive Mechanisms (net)	0.4
Incremental MPIR/EPRM Revenue Adjustment	0.7
Other	0.0
Net incremental amount to be collected under the RBA rate tariffs	$ (3.6)