Electric utility segment - Regulatory proceedings (Details) $ in Millions					3 Months Ended		12 Months Ended
	Mar. 31, 2022 USD ($) project contract	Nov. 12, 2021	Feb. 16, 2021 agreement	Dec. 23, 2020 USD ($)	Mar. 31, 2022 USD ($) MWh project contract	Nov. 30, 2021 agreement	Dec. 31, 2021 USD ($)	Dec. 31, 2019 USD ($) agreement	Feb. 28, 2022 USD ($)	Jun. 01, 2021 mechanism	Mar. 23, 2021 mechanism	Jul. 09, 2020 entity
Regulatory Projects and Legal Obligations [Line Items]
Propose pilots annual cap				$ 10.0
Potential total annual maximum reward	$ 2.0				$ 2.0
Advanced metering infrastructure term					3 years
Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory Projects and Legal Obligations [Line Items]
Multi-year rate period				5 years
Customer dividend, negative adjustment percentage				0.22%
Savings commitment liability, annual rate				$ 6.6
Earnings sharing mechanism, actual return on equity, dead band percentage above or below target					3.00%
Approved return on equity, percentage					9.50%
Earnings sharing mechanism, actual earning, above or below dead band					1.50%
MPIR requested amount	$ 25.9
EPRM approved projects | contract	2				2
EPRM approved projects, capital costs					$ 41.0
Number of projects | project	5				5
Estimated capital costs					$ 264.0
Development period		3 years
2021 deferred costs to be reviewed by the PUC									$ 0.1
Decoupling order, service reliability performance, historical measurement period (in years)					10 years
Maximum penalty, percent of ROE					0.20%
Service reliability, pending adjusted maximum penalty amount					$ 6.8
Service reliability, estimated penalties					$ 0.2
Dead band percentage above or below the target					3.00%
Call center performance, maximum penalty percentage					0.08%
Call center performance, pending adjusted maximum penalty					$ 1.4
Number of power purchase agreements (PPAs) (in agreements) | agreement			1					7
Incentives accrued							$ 0.1	$ 1.7
Number of grid service purchase agreements | entity												2
Number of PPAs approved | agreement						2
Number of performance incentive mechanisms | mechanism										3	2
Interpolated RPS rate goal, year one and two (dollars per MWh) | MWh					20
Interpolated RPS rate goal, year three (dollars per MWh) | MWh					15
Interpolated RPS rate goal, after year three (dollars per MWh) | MWh					10
Failure to meet RPS targets, penalty rate (dollars per MWh) | MWh					20
Estimated rewards							1.0
Potential total annual maximum reward	$ 1.5				$ 1.5
Potential total annual maximum reward	3.0				3.0
Total annual maximum penalty	0.9				0.9
Interconnection approval PIM, accrued estimated rewards					2.8
Performance incentive mechanism, maximum reward	2.0				$ 2.0
Performance incentive mechanism, term					3 years
Accrued estimated rewards, net of penalties							3.7
Hawaiian Electric, Parent
Regulatory Projects and Legal Obligations [Line Items]
Accrued estimated rewards, net of penalties							2.8
HELCO
Regulatory Projects and Legal Obligations [Line Items]
Accrued estimated rewards, net of penalties							0.4
Maui Electric
Regulatory Projects and Legal Obligations [Line Items]
Accrued estimated rewards, net of penalties							$ 0.5
Schofield Generation Station | Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory Projects and Legal Obligations [Line Items]
MPIR requested amount	16.5
West Loch PV Project | Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory Projects and Legal Obligations [Line Items]
MPIR requested amount	3.3
Grid Modernization Strategy Phase 1 Project | Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory Projects and Legal Obligations [Line Items]
MPIR requested amount	$ 6.1