Electric utility segment - Regulatory proceedings (Details)						1 Months Ended	9 Months Ended	12 Months Ended
	May 26, 2021 USD ($)	Feb. 16, 2021 agreement	Dec. 23, 2020 USD ($)	Sep. 15, 2020 agreement	Apr. 27, 2017 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2021 USD ($) MWh project	Dec. 31, 2019 USD ($) agreement	Jun. 01, 2021 mechanism	Mar. 23, 2021 mechanism	Jul. 09, 2020 entity
Regulatory Projects and Legal Obligations [Line Items]
Propose pilots annual cap			$ 10,000,000
Potential total annual maximum reward							$ 2,000,000
Advanced metering infrastructure term							3 years
Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory Projects and Legal Obligations [Line Items]
Customer dividend, negative adjustment percentage			0.22%
Savings commitment liability, annual rate			$ 6,600,000
ERP system benefits savings liability			$ 3,900,000
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%
Threshold of capital expenditures in excess of customer contributions for qualification for major project interim recovery					$ 2,500,000
MPIR requested amount	$ 21,800,000
Number of projects | project							8
Estimated capital costs							$ 324,000,000
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							$ 6,800,000
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							$ 1,400,000
Call center performance, maximum penalty amount						$ 900,000
Number of power purchase agreements (PPAs) (in agreements) | agreement		1		8				7
Incentives accrued							$ 100,000	$ 1,700,000
Number of grid service purchase agreements | entity											2
Number of power purchase agreements qualifying for potential payout | agreement				1
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
Potential total annual maximum reward							$ 1,500,000
Potential total annual maximum reward							3,000,000
Total annual maximum penalty							900,000
Performance incentive mechanism, maximum reward							$ 2,000,000
Performance incentive mechanism, term							3 years
Schofield Generation Station | Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory Projects and Legal Obligations [Line Items]
MPIR requested amount	17,600,000
West Loch PV Project | Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory Projects and Legal Obligations [Line Items]
MPIR requested amount	3,300,000
Grid Modernization Strategy Phase 1 Project | Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory Projects and Legal Obligations [Line Items]
MPIR requested amount	$ 900,000