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Electric utility segment - Commitments and contingencies (Details) |  |  |  |  |  |  |  |  |  |  |  |  | 1 Months Ended | 3 Months Ended | 12 Months Ended | 20 Months Ended | 21 Months Ended | 31 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Mar. 29, 2018 USD ($) | Mar. 05, 2018 USD ($) | Feb. 16, 2018 USD ($) | Jan. 19, 2018 USD ($) | Dec. 15, 2017 USD ($) | Oct. 12, 2017 USD ($) | Aug. 21, 2017 USD ($) | Jul. 11, 2017 | Apr. 27, 2017 USD ($) | Aug. 11, 2016 USD ($) | May 23, 2016 | Jan. 05, 2016 USD ($) | Jun. 30, 2017 USD ($) $ / kWh | Jul. 31, 2016 MW | Sep. 30, 2015 USD ($) | Jun. 30, 2015 MW | Aug. 31, 2012 MW | May 31, 2012 MW | Mar. 31, 1988 MW | Mar. 31, 2018 USD ($) $ / kWh | Dec. 31, 1988 MW | Mar. 31, 2018 USD ($) | Mar. 31, 2018 USD ($) | Mar. 31, 2018 USD ($) | Mar. 27, 2018 USD ($) | Feb. 26, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 18, 2017 USD ($)
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues with respect to interim orders related to general rate increase requests |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 7,000,000 |  |  |  |  |  |  |  |
Power purchase agreement, termination period |  |  |  |  |  |  |  |  |  |  | 60 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ERP/EAM cost recovery cap |  |  |  |  |  |  |  |  |  | $ 77,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Public utility, ERP/EAM required pass through savings to customers |  |  |  |  |  |  |  |  |  | $ 244,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 244,000,000
ERP/EAM project service period (in years) |  |  |  |  |  |  |  |  |  | 12 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
AFUDC rate |  |  |  |  |  |  |  |  |  | 1.75% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
ERP/EAM implementation project costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 47,700,000 |  |  |  |  |  |
ERP/EAM implementation project, operations and management |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8,600,000 |  |  |  |  |  |
ERP/EAM implementation project, capital costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,600,000 |  |  |  |  |  |
ERP/EAM implementation project, deferred costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 36,500,000 |  |  |  |  |  |
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 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90.00% |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in project costs |  |  |  |  |  |  |  |  |  |  |  | $ 9,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Project lease term (in years) |  |  |  |  |  |  |  |  |  |  |  | 35 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Project cost incurred |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 131,600,000 |  |  |  |
West Lock PV Project, energy generated (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  | 20 |  |  |  |  |  |  |  |  |  |  |  |  |  |
West Lock PV Project, cost cap |  |  |  |  |  |  |  |  |  |  |  |  | $ 67,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
West Lock PV Project, maximum energy cost (in dollars per kilowatt hours) | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  | 0.0956 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
West Lock PV Project, project costs incurred |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 7,000,000 |  |  |  |  |
Accounts receivable and unbilled revenues, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 266,336,000 |  | 266,336,000 | 266,336,000 | 266,336,000 |  |  | $ 263,209,000 |
Environmental regulation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Threshold of capital expenditures in excess of customer contributions for qualification for major project interim recovery |  |  |  |  |  |  |  |  | $ 2,500,000.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decoupling order, service reliability performance, historical measurement period (in years) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 years |  |  |  |  |  |  |  |
Maximum penalty as a percent of equity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20.00% |  |  |  |  |  |  |  |
Service reliability, maximum penalty |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 6,200,000 |  |  |  |  |  |  |  |
Dead band percentage above or below the target |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.00% |  |  |  |  |  |  |  |
Call center performance, maximum penalty, percent |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 8.00% |  |  |  |  |  |  |  |
Call center performance, maximum penalty |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,200,000 |  |  |  |  |  |  |  |
Demand response, award percentage of annual maintenance costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5.00% |  |  |  |  |  |  |  |
Demand response, maximum award |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 500,000 |  |  |  |  |  |  |  |
Demand response, penalty |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 0 |  |  |  |  |  |  |  |
Expected savings, percent |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20.00% |  |  |  |  |  |  |  |
Energy price, renewable projects with storage capacity (in dollars per kilowatt hour) | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.115 |  |  |  |  |  |  |  |
Energy price, energy-only renewable projects (in dollars per kilowatt hour) | $ / kWh |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.095 |  |  |  |  |  |  |  |
Performance incentive mechanism, incentive cap |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,500,000 |  |  |  |  |  |  |  |
Performance incentive mechanism penalty |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0 |  |  |  |  |  |  |  |
Revenue calculation assumptions, rate of return |  |  |  | 7.57% | 7.57% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue calculation assumptions, percentage of return on average common equity |  | 9.50% |  | 9.50% | 9.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General rate increase, revenue, calculation assumptions, rate of return, common equity capitalization percentage |  |  |  | 57.00% | 57.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interim D&O, reduction in revenue requirement, baseline plant additions |  |  |  |  | $ 5,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interim D&O, Reduction in revenue requirement of pension regulatory asset |  |  |  |  | $ 6,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Statement of probable entitlement, interim increase |  |  | $ 36,000,000 | $ 36,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining settlement, reduction in revenue requirement |  | $ 38,300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining settlement, reduction in O&M expenses |  | 5,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining settlement, hold-back amount |  | $ 5,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
PCB Contamination |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Environmental regulation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Valuation allowances and reserves |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,700,000 |  | 4,700,000 | 4,700,000 | 4,700,000 |  |  |  |
AES Hawaii |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase commitment, period (in years) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30 years |  |  |  |  |  |  |  |  |
Minimum power volume required (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 186 |  | 180 |  |  |  |  |  |  |  |  |
Additional capacity requirement (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9 |  |  |  |  |  |  |  |  |  |  |  |
Hu Honua Bioenergy, LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum power volume required (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 21.5 |  |  |  |  |  |  |  |  |  |
Hawaiian Telcom |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts receivable and unbilled revenues, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 22,400,000 |  | 22,400,000 | 22,400,000 | 22,400,000 |  |  |  |
Hawaiian Electric Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Environmental regulation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decoupling filing, change in income taxes | $ 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Hawaiian Electric Company | Hawaiian Telcom |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts receivable and unbilled revenues, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 15,100,000 |  | 15,100,000 | 15,100,000 | 15,100,000 |  |  |  |
Hawaiian Telcom |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts receivable and unbilled revenues, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 48,000,000 |  | 48,000,000 | 48,000,000 | 48,000,000 |  |  |  |
Hawaii Electric Light Company, Inc. (HELCO) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Environmental regulation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decoupling filing, change in income taxes | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stipulated ROACE rate |  |  |  |  |  |  | 9.50% | 9.75% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General rate increase, ROACE, percentage decrease |  |  |  |  |  |  |  | 25.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interim general rate increase granted |  |  |  |  |  |  | $ 9,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in test year revenue requirement, tax act |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 9,500,000 |  |  |
Hawaii Electric Light Company, Inc. (HELCO) | Hawaiian Telcom |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts receivable and unbilled revenues, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6,000,000 |  | 6,000,000 | 6,000,000 | 6,000,000 |  |  |  |
Maui Electric |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Environmental regulation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional accrued investigation and estimated cleanup costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,700,000 |  | 2,700,000 | 2,700,000 | 2,700,000 |  |  |  |
Decoupling filing, change in income taxes | $ 2,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General rate increase, revenue, calculation assumptions, rate of return, common equity capitalization percentage |  |  |  |  |  | 56.90% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General rate increase, revenue |  |  |  |  |  | $ 30,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General rate increase, revenue, percent |  |  |  |  |  | 9.30% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General rate increase, revenue, calculation assumptions, rate of return |  |  |  |  |  | 8.05% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General rate increase, revenue, calculation assumptions, rate of return, ROACE |  |  |  |  |  | 10.60% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
General rate increase, revenue, calculation assumptions, rate base |  |  |  |  |  | $ 473,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conditional general rate increase, revenue |  |  |  |  |  | $ 46,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Conditional general rate increase, revenue, percentage |  |  |  |  |  | 14.30% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rate case, income tax expense reduction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 8,100,000 |  |
Rate case, annual amortization credit |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 500,000 |  |
Rate case, increase in rate base resulting from decrease in accumulated deferred income tax |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 7,100,000 |  |
Maui Electric | Hawaiian Telcom |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accounts receivable and unbilled revenues, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,300,000 |  | $ 1,300,000 | $ 1,300,000 | $ 1,300,000 |  |  |  |
Kalaeloa Partners, L.P. (Kalaeloa) | Hawaiian Electric Company |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increased power purchase commitment capacity (in megawatts) | MW |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 208 |  |  |  |  |  |  |

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