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Commitments and contingencies - (Details) - HECO (USD $) | 3 Months Ended | 6 Months Ended |  | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended | 3 Months Ended | 6 Months Ended |  |  | 6 Months Ended |  | 3 Months Ended |  | 1 Months Ended | 6 Months Ended | 12 Months Ended |
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Jun. 30, 2012 | Jun. 30, 2011 | Jun. 30, 2012 Y item | Jun. 30, 2011 | Jun. 30, 2012 Electric utility | Jan. 31, 2011 Hawaiian Electric Company, Inc. and Subsidiaries Y | Jun. 30, 2012 Hawaiian Electric Company, Inc. and Subsidiaries | Jun. 30, 2011 Hawaiian Electric Company, Inc. and Subsidiaries | Jun. 30, 2012 Hawaiian Electric Company, Inc. and Subsidiaries mW | Jun. 30, 2011 Hawaiian Electric Company, Inc. and Subsidiaries | Dec. 31, 2013 Hawaiian Electric Company, Inc. and Subsidiaries | Dec. 31, 2012 Hawaiian Electric Company, Inc. and Subsidiaries | Dec. 31, 2011 Hawaiian Electric Company, Inc. and Subsidiaries | Jun. 30, 2012 MECO | Jun. 30, 2011 MECO | Jun. 30, 2012 MECO | Jun. 30, 2011 MECO | Dec. 31, 2012 MECO | Mar. 31, 2012 MECO | Jun. 30, 2012 Campbell Industrial Park 110MW combustion turbine and transmission line Hawaiian Electric Company, Inc. and Subsidiaries | Jun. 30, 2012 East Oahu transmission project | Dec. 31, 2011 East Oahu transmission project Hawaiian Electric Company, Inc. and Subsidiaries | Jun. 30, 2012 East Oahu Transmission Project Phase 1 | Jun. 30, 2012 East Oahu Transmission Project Phase 1 Hawaiian Electric Company, Inc. and Subsidiaries | Jun. 30, 2012 East Oahu Transmission Project Phase 2 | Apr. 30, 2010 East Oahu Transmission Project Phase 2 Hawaiian Electric Company, Inc. and Subsidiaries | Jun. 30, 2012 East Oahu Transmission Project Phase 2 Hawaiian Electric Company, Inc. and Subsidiaries | Jun. 30, 2012 Customer Information System Project | Dec. 31, 2005 Customer Information System Project Hawaiian Electric Company, Inc. and Subsidiaries | Jun. 30, 2012 Customer Information System Project Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory projects and legal obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred cost to be recovered subject to PUC approval |  |  |  |  |  |  |  |  | $ 3,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Balance at the beginning of the period |  |  |  |  |  | 48,630,000 |  |  | 50,871,000 | 48,630,000 |  | 50,871,000 | 48,630,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accretion expense |  |  |  |  |  |  |  |  | 862,000 | 1,134,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Liabilities settled |  |  |  |  |  |  |  |  | (2,217,000) | (573,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Balance at the end of the period |  |  |  |  |  |  | 49,516,000 | 49,191,000 | 49,516,000 | 49,191,000 |  |  | 50,871,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Integration from renewable energy sources (in megawatts) |  |  |  |  |  |  |  |  | 200 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Collective bargaining agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of employees who are members of the International Brotherhood of Electrical Workers |  |  |  |  | 53.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Non-compounded wage increase (as a percent) |  |  |  |  |  |  |  |  |  |  | 3.00% | 2.50% | 1.75% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional deferred cost to be recovered subject to PUC approval |  |  |  |  |  |  |  |  | 555,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum deferred cost recovery |  |  |  |  |  |  |  |  | 5,890,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period for deferred cost recovery |  |  |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Integration from dispatchable renewable geothermal sources (in megawatts) |  |  |  |  |  |  |  |  | 50 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenue recognized with respect to interim rate increase order |  |  |  |  |  |  |  |  | 1,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated project cost above PUC approval |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 32,000,000 |  |  |  | 43,000,000 |  |  |  |  |  |
Limitation on deferred project operation and maintenance expenses |  |  |  |  |  |  |  |  |  |  |  | 2,300,000 | 2,300,000 |  |  |  |  | 600,000 |  |  |  |  |  |  |  |  |  |  |  |
Project cost incurred |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 195,000,000 |  |  |  |  |  |  |  |  |  |
Allowance for funds used during construction | (893,000) | (553,000) | (1,763,000) | (1,073,000) |  |  | (760,000) | (412,000) | (1,485,000) | (820,000) |  |  |  | (69,000) | (39,000) | (163,000) | (118,000) |  |  | 9,000,000 |  |  |  |  |  |  |  |  |  |
Cost of project recoverable from increase in annual revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 163,000,000 |  |  |  |  |  |  |  |  |  |
Estimated cost of project upon completion |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 56,000,000 |  | 42,000,000 |  | 14,000,000 |  |  |  |  |
Accumulated project cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 59,000,000 |  |  |  |  |  |
Estimated project cost subject to decision and order issued |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 16,000,000 |  |  |  |  |  |
Write-off project cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9,500,000 |  |  |  |  |  |
Cost of settlement agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6,000,000 |  |  |  |  |  |  |  |
Annual interim increase in cost of settlement agreement, subject to PUC approval |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,000,000 |  |  |  |  |  |  |  |
Annual interim increase to rate base in cost of settlement agreement, subject to PUC approval |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 31,000,000 |  |  |  |  |  |  |  |
Net estimated cost of using smart grid technology |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10,000,000 |  |  |  |
Estimated cost of smart grid technology |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 15,000,000 |  |  |  |
Estimated statutory funding for smart grid technology |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,000,000 |  |  |  |
Net actual cost of using smart grid technology |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10,000,000 |  |  |
Cost of smart grid technology |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 14,000,000 |  |  |
Statutory funding for smart grid technology |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,000,000 |  |  |
Amount authorized for the project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 20,000,000 |
Amount authorized for project attributable to capital and deferred costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 18,000,000 |  |
Deferred and capital cost estimate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 58,600,000
Deferred and capital cost recorded |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 58,400,000
Environmental regulation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of steam generating units on the island of Hawaii |  |  | 5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of periods allowed for compliance of EPA regulation (in years) |  |  | 8 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of EGUs impacted by proposed rules of MATS |  |  | 14 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of periods allowed for compliance of MATS rules (in years) |  |  | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of extensions allowed for installation of emission control technology |  |  | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Extension periods allowed for installation of emission control technology (in years) |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferral period for GHG permitting requirements for carbon dioxide emissions (in years) |  |  |  |  |  | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional accrued investigation and estimated cleanup costs |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,600,000 |  | $ 3,600,000 |  |  | $ 3,100,000 |  |  |  |  |  |  |  |  |  |  |
Period for which operations was stopped prior to merger |  |  | 4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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- Definition Represents the annual interim increase in cost of settlement agreement, subject to PUC approval which is based on additional revenue requirements. + References No definition available. + Details
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- Definition Represents the annual interim increase to rate base in cost of settlement agreement, subject to PUC approval which is based on additional revenue requirements. + References No definition available. + Details
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- Definition Represents the capacity integration from dispatchable renewable geothermal sources. + References No definition available. + Details
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- Definition Represents the capacity integration to the grid from renewable energy sources, including solar, biomass, wind, ocean thermal energy conversion, wave and others. + References No definition available. + Details
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- Details
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- Definition Represents the percentage of annual non-compounded wage increase under the collective bargaining agreement. + References No definition available. + Details
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- Definition Represents the amount authorized by the appropriate authority for the project. + References No definition available. + Details
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- Definition Represents the amount authorized by the appropriate authority for the project attributable to capital and deferred costs. + References No definition available. + Details
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- Definition Represents the actual cost of project modification. + References No definition available. + Details
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- Definition The portion of the settlement agreement to allow deferral of certain costs. + References No definition available. + Details
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- Definition Represents the actual statutory funding for the project modification through the Smart Grid Investment Grant Program of the American Recovery and Reinvestment Act of 2009. + References No definition available. + Details
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- Definition Represents the cost written-off related to the project. + References No definition available. + Details
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- Definition Represents the estimated cost to complete the project as of balance sheet date. + References No definition available. + Details
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- Definition Represents the cost to the project above the PUC approval. + References No definition available. + Details
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- Definition Represents the estimated cost of project modification. + References No definition available. + Details
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- Definition Represents the net estimated cost of project modification. + References No definition available. + Details
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- Definition Represents the estimated statutory funding for the project modification through the Smart Grid Investment Grant Program of the American Recovery and Reinvestment Act of 2009. + References No definition available. + Details
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- Definition Represents the cost to the project, which are subject to the decision and order issued. + References No definition available. + Details
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- Definition Represents the deferral years for GHG permitting requirements for carbon dioxide emissions. + References No definition available. + Details
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- Definition Represents the amount of limitation on deferred project operation and maintenance expenses. + References No definition available. + Details
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- Definition Represents number of 1-year extensions allowed for installation of emission control technology under MACT rules. + References No definition available. + Details
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- Definition Represents the extension periods allowed for installation of emission control technology under the MACT rules. + References No definition available. + Details
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- Definition Represents the number of periods allowed for compliance of the EPA regulation. + References No definition available. + Details
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- Definition Represents the number of periods allowed for the compliance of the MATS rules. + References No definition available. + Details
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- Definition Represents the number of steam generating units. + References No definition available. + Details
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- Definition Represents the number of electrical generating units for which the proposed rules of MATS are applicable. + References No definition available. + Details
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- Definition Represents the percentage of employees of the entity who are members of the International Brotherhood of Electrical Workers, AFL-CIO, Local 1260, Unit 8. + References No definition available. + Details
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- Definition Represents the period for deferred cost recovery of the wind project according to the PUC approval. + References No definition available. + Details
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- Definition Represents the period for which operations was stopped prior to merger. + References No definition available. + Details
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- Definition Represents the cost of the project which is recoverable from the annual rate increase. + References No definition available. + Details
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- Definition Represents the amount of additional accrued investigation and estimated cleanup costs. + References No definition available. + Details
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- Definition Represents the revenue recognized by the entity with respect to interim orders related to general rate increase requests. + References No definition available. + Details
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- Definition Represents the accumulated costs of the project as of the balance sheet date. + References No definition available. + Details
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- Definition Represents the additional deferred cost of the wind project to be recovered by the entity subject to the PUC approval. + References No definition available. + Details
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- Definition Represents the estimated total deferred and capital cost for the project. + References No definition available. + Details
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- Definition Represents the deferred and capital cost recorded by the entity as of the balance sheet date. + References No definition available. + Details
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- Definition Represents the deferred cost of the wind project to be recovered by the entity subject to the PUC approval. + References No definition available. + Details
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- Definition Represents the deferred cost of the wind project to be recovered by the entity per year according to the PUC approval. + References No definition available. + Details
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- Definition The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 3, 10, 22 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Asset Retirement Obligation -URI http://asc.fasb.org/extlink&oid=6505190 + Details
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- Definition Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 13, 14 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 22 -Subparagraph c(3) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848 + Details
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- Definition Costs incurred to prepare, construct, and develop the infrastructure necessary to deliver utilities (for example, land improvements, construction of property developments). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2(b)) -URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688 + Details
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- Definition The component of the allowance for funds used during construction during the period comprised of interest on borrowed funds used in financing the construction of regulated assets, which may be reflected as a reduction of interest expense. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 71 -Paragraph 15 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433 + Details
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