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Electric utility segment - Commitments and contingencies (Details) |  |  |  |  |  |  |  |  |  |  | 1 Months Ended | 3 Months Ended |  |  |  |  |  |
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Apr. 27, 2017 USD ($) | Dec. 23, 2016 island | Aug. 11, 2016 USD ($) | Feb. 18, 2016 contract | Jan. 05, 2016 USD ($) | Dec. 22, 2015 USD ($) | Aug. 01, 2015 air_quality_monitoring_station | Oct. 14, 2014 facility | May 31, 2013 | Feb. 16, 2012 generation_unit | Oct. 31, 2016 customer | Sep. 30, 2015 USD ($) | Jun. 30, 2015 MW | Aug. 31, 2014 | Apr. 30, 2014 order | Aug. 31, 2012 MW | May 31, 2012 MW | Mar. 31, 1988 MW | Mar. 31, 2017 USD ($) agreement contract MW | Mar. 31, 2016 USD ($) | Sep. 30, 2015 USD ($) | Dec. 31, 2045 | Dec. 31, 2016 USD ($) | Jul. 31, 2014 USD ($) | Jun. 20, 2014 | Mar. 01, 2014 | Feb. 07, 2014
Regulatory projects and legal obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase commitment, period (in years) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30 years |  |  |  |  |  |  |  |  |
Minimum power volume required (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 186 |  | 180 |  |  |  |  |  |  |  |  |
Additional capacity requirement (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  | 9 |  |  |  |  |  |  |  |  |  |  |  |  |  |
ERP/EAM Project, expected costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 82,400,000 |  |  |
SAP software costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 4,800,000 |  |  |  |  |  |
ERP/EAM cost recovery cap |  |  | $ 77,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utility, ERP/EAM required pass through savings to customers |  |  | $ 244,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ERP/EAM project service period (in years) |  |  | 12 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Schofield generating station facility capacity (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50 |  |  |  |  |  |  |  |  |  |  |
Schofield generating station project, budgetary cap |  |  |  |  | $ 157,300,000 |  |  |  |  |  |  | $ 167,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percent of costs recoverable through recovery mechanisms other than base rates (as a percent) |  |  |  |  |  |  |  |  |  |  |  | 90.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in project costs |  |  |  |  | $ 9,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Project lease term (in years) |  |  |  |  | 35 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of power plants affected by CWA section 316(b) (in facilities) | facility |  |  |  |  |  |  |  | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Environmental regulation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of EGUs impacted by proposed rules of MATS (in generation units) | generation_unit |  |  |  |  |  |  |  |  |  | 14 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of additional air quality monitor stations (in air quality monitoring stations) | air_quality_monitoring_station |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts receivable and unbilled revenues, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 252,416,000 |  |  |  | $ 237,950,000 |  |  |  |
Number of orders from regulatory agency (in orders) | order |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 |  |  |  |  |  |  |  |  |  |  |  |
Percent of energy production from renewable energy sources (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  | 65.00% |  |  |  |  |  |  |  |  |  |  |  |  |
PSIPs, Number of years covered (in years) |  | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PSIPs, Number of geographic regions covered (in islands) | island |  | 5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, duration of Time of Use Program (in years) |  |  |  |  |  |  |  |  |  |  | 2 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utilities, number of customers impacted by Time Of Use Program (in customers) | customer |  |  |  |  |  |  |  |  |  |  | 5,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Designated as Hedging Instrument | Window forward contract | Cash Flow Hedging |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Notional amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 15,838,000 |  |  |  | 20,734,000 |  |  |  |
Fair Value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (277,000) |  |  |  | $ (743,000) |  |  |  |
Scenario, Forecast |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Expected portfolio standard (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |  |  |  |  |
Subsequent Event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decoupling order, service reliability performance, historical measurement period (in years) | 10 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum penalty as a percent of equity (as a percent) | 20.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Service reliability, maximum penalty | $ 3,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Call center performance, maximum penalty | $ 1,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Average annual performance, measurement period (in days) | 730 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Dead band percentage above or below the target (as a percent) | 3.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum incentive, percent of return on equity (as a percent) | 8.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period to file proposed tariffs (in days) | 30 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decoupling order, comment period for proposed tariffs (in days) | 60 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Threshold of capital expenditures in excess of customer contributions for qualification for major project interim recovery | $ 2,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PCB Contamination |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Environmental regulation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Valuation allowances and reserves |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 5,000,000 |  |  |  |  |  |  |  |
Hawaii Electric Light Company, Inc. (HELCO) | Hamakua Energy Partners, L.P. (HEP) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory projects and legal obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Potential purchase price |  |  |  |  |  | $ 84,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Hawaii Electric Light Company, Inc. (HELCO) | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory projects and legal obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Power purchase capacity that Increases from initial capacity (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 60 |  |  |  |  |  |  |  |
Hamakua Energy Partners, L.P. (HEP) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory projects and legal obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percent of island's generating capacity (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 23.00% |  |  |  |  |  |  |  |
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Environmental regulation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of reduction in GHG emissions by 2020 (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 16.00% |  |
Estimated annual fee for greenhouse gas emissions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 500,000 |  |  |  |  |  |  |  |
Impact on earnings from recognition of AROs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Balance, beginning of period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25,589,000 | $ 26,848,000 |  |  |  |  |  |  |
Accretion expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,000 | 3,000 |  |  |  |  |  |  |
Liabilities incurred |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 | 0 |  |  |  |  |  |  |
Liabilities settled |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (403,000) | (138,000) |  |  |  |  |  |  |
Revisions in estimated cash flows |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 | 0 |  |  |  |  |  |  |
Balance, end of period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 25,189,000 | $ 26,713,000 |  |  |  |  |  |  |
Decoupling implementation experience, period (in years) |  |  |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed rate base adjustment, percent of previous rate base adjustment (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90.00%
Effective interest rate, revenue balancing account (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6.00%
Hawaiian Electric Company, Inc. and Subsidiaries | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed effective interest rate, revenue balancing account (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.25% |
Hawaiian Electric Company, Inc. and Subsidiaries | Minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proposed effective interest rate, revenue balancing account (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.25% |
Hawaiian Electric Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory projects and legal obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of power purchase agreements (PPAs) (in agreements) | agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 |  |  |  |  |  |  |  |
Environmental regulation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of extension resulting in MATS compliance date (in years) |  |  |  |  |  |  |  |  |  | 1 year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maui Electric |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Environmental regulation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional accrued investigation and estimated cleanup costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,600,000 |  |  |  |  |  |  |  |
Biodiesel Fuel |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory projects and legal obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of power purchase agreements (PPAs) (in agreements) | contract |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 |  |  |  |  |  |  |  |
Chevron |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory projects and legal obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of power purchase agreements (PPAs) (in agreements) | contract |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pacific Biodiesel Technologies, LLC | Biodiesel Fuel |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory projects and legal obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of power purchase agreements (PPAs) (in agreements) | contract |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |
PPA extension period (in years) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 year |  |  |  |  |  |  |  |
REG Marketing & Logistics, LLC | Biodiesel Fuel |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory projects and legal obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of power purchase agreements (PPAs) (in agreements) | contract |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |
PPA extension period (in years) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 year |  |  |  |  |  |  |  |
Hu Honua Bioenergy, LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory projects and legal obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum power volume required (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 21.5 |  |  |  |  |  |  |  |  |  |
Hawaiian Telcom |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts receivable and unbilled revenues, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 21,700,000 |  |  |  |  |  |  |  |
Reserve for interest accrued |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,500,000 |  |  |  |  |  |  |  |
Hawaiian Telcom | Hawaii Electric Light Company, Inc. (HELCO) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts receivable and unbilled revenues, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,900,000 |  |  |  |  |  |  |  |
Hawaiian Telcom | Hawaiian Electric Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts receivable and unbilled revenues, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 14,500,000 |  |  |  |  |  |  |  |
Hawaiian Telcom | Maui Electric |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts receivable and unbilled revenues, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,300,000 |  |  |  |  |  |  |  |

X
- Definition Represents the entity's aggregate capacity utilized under power purchase agreements (PPAs). + References No definition available. + Details
Name: | he_AggregateofPowerPurchaseCapacity
Namespace Prefix: | he_
Data Type: | num:powerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the amount of impact on earnings from recognition of asset retirement obligations (AROs). + References No definition available. + Details
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Namespace Prefix: | he_
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