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Electric utility segment - Regulatory Proceedings (Details) |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |  |
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Apr. 30, 2021 USD ($) project | Feb. 16, 2021 agreement | Dec. 23, 2020 USD ($) | Sep. 15, 2020 agreement | Apr. 27, 2017 USD ($) | Dec. 31, 2020 USD ($) | Feb. 28, 2019 USD ($) | Mar. 31, 2021 USD ($) MWh | Dec. 31, 2019 USD ($) agreement | Jun. 01, 2021 mechanism | Mar. 23, 2021 mechanism | Jul. 09, 2020 entity
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Potential total annual maximum reward |  |  |  |  |  |  |  | $ 2,000,000.0 |  |  |  |
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Customer dividend, negative adjustment percentage |  |  | 22.00% |  |  |  |  |  |  |  |  |
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 |  |  |  |  |  |  |  | 950.00% |  |  |  |
Earnings share mechanism, sharing between customers and utilities, percentage |  |  |  |  |  |  |  | 0.5 |  |  |  |
Earnings share mechanism, percentage sharing for any further difference |  |  |  |  |  |  |  | 9 |  |  |  |
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 |  |  |  |  |
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 |  |  |  |  |  |  |  |  | $ 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 |  |  |  |  |  |  |  |  |  |  | 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 |  |  |  |  |  |  |  | 3,000,000.0 |  |  |  |
Total annual maximum penalty |  |  |  |  |  |  |  | 900,000 |  |  |  |
Performance incentive mechanism, maximum reward |  |  |  |  |  |  |  | $ 2,000,000.0 |  |  |  |
Performance incentive mechanism, term |  |  |  |  |  |  |  | 3 years |  |  |  |
Hawaiian Electric Company, Inc. and Subsidiaries | Forecast |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of performance incentive mechanisms | mechanism |  |  |  |  |  |  |  |  |  | 3 |  |
Hawaiian Electric Company, Inc. and Subsidiaries | Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Estimated capital costs | $ 95,000,000 |  |  |  |  |  |  |  |  |  |  |
Number of projects | project | 4 |  |  |  |  |  |  |  |  |  |  |
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 |  |  |  |  |

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