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Commitments and contingencies (Details) - HECO (USD $) | 9 Months Ended | 0 Months Ended | 1 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended |  | 0 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended |  |  | 0 Months Ended
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Sep. 30, 2013 item | May 31, 2013 Hawaiian Electric Company, Inc. and Subsidiaries | Oct. 19, 2012 Hawaiian Electric Company, Inc. and Subsidiaries | Jun. 30, 2013 Hawaiian Electric Company, Inc. and Subsidiaries item | Apr. 30, 2013 Hawaiian Electric Company, Inc. and Subsidiaries item | Nov. 30, 2011 Hawaiian Electric Company, Inc. and Subsidiaries | Sep. 30, 2013 Hawaiian Electric Company, Inc. and Subsidiaries | Sep. 30, 2012 Hawaiian Electric Company, Inc. and Subsidiaries | Sep. 30, 2013 Hawaiian Electric Company, Inc. and Subsidiaries kW | Sep. 30, 2012 Hawaiian Electric Company, Inc. and Subsidiaries | Sep. 30, 2013 Maui Electric Company, Limited (MECO) | Sep. 30, 2012 Maui Electric Company, Limited (MECO) | Sep. 30, 2013 Maui Electric Company, Limited (MECO) | Sep. 30, 2012 Maui Electric Company, Limited (MECO) | Mar. 31, 2012 Maui Electric Company, Limited (MECO) | Jan. 28, 2013 Hawaii Electric Light Company, Inc. (HELCO) | Sep. 30, 2013 Hawaii Electric Light Company, Inc. (HELCO) | Sep. 30, 2012 Hawaii Electric Light Company, Inc. (HELCO) | Sep. 30, 2013 Hawaii Electric Light Company, Inc. (HELCO) | Sep. 30, 2012 Hawaii Electric Light Company, Inc. (HELCO) | Sep. 30, 2013 Hawaiian Electric Company, Inc. and Subsidiaries | Sep. 30, 2012 Hawaiian Electric Company, Inc. and Subsidiaries | Sep. 30, 2013 Hawaiian Electric Company, Inc. and Subsidiaries | Sep. 30, 2012 Hawaiian Electric Company, Inc. and Subsidiaries | Dec. 31, 2012 East Oahu transmission project Hawaiian Electric Company, Inc. and Subsidiaries | Dec. 31, 2012 Customer Information System Project Maui Electric Company, Limited (MECO) | Dec. 31, 2012 Customer Information System Project Hawaii Electric Light Company, Inc. (HELCO) | Dec. 31, 2012 Customer Information System Project Group of subsidiaries | Jan. 28, 2013 Customer Information System Project Group of subsidiaries | Dec. 31, 2012 CIP CT-1 and CIS projects Group of subsidiaries | Nov. 07, 2013 Subsequent Event Hawaiian Electric Company, Inc. and Subsidiaries item
Regulatory projects and legal obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Project costs to be written off, subject to approval by PUC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 40,000,000 |  |
After-tax charge to net income due to write-off of project costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 17,100,000 | 3,200,000 | 3,400,000 | 24,000,000 |  |  |
Remaining recoverable project costs included in rate base, in accordance with the settlement agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 52,000,000 |
Term of cycle, within which rate case can not be filed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of renewable energy as per State's Renewable Portfolio Standard (RPS), which is committed to be achieved |  |  |  |  |  |  |  |  | 40.00% |  |  |  |  |  |  |  |  |  |  |  |  |  | 40.00% |  |  |  |  |  |  |  |
Deferred cost to be recovered subject to PUC approval |  |  |  |  | 3,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period for deferred cost recovery |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accrual rate of carrying cost per annum (as a percent) |  |  |  |  | 1.75% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred cost to be recovered for additional studies subject to PUC approval |  |  |  |  |  | 555,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Integration from renewable energy sources (in kilowatts) |  |  |  |  |  |  |  |  | 200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  | 200,000 |  |  |  |  |  |  |  |
Maximum deferred cost recovery |  |  |  |  |  |  |  |  | 5,890,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Integration from firm renewable geothermal dispatchable energy (in kilowatts) |  |  |  |  |  |  |  |  | 50,000 |  |  |  |  |  |  |  |  |  |  |  |  |  | 50,000 |  |  |  |  |  |  |  |
Number of bids received |  |  |  |  | 6 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of projects for bidding subject to PUC approval |  |  |  | 5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6
Number of photovoltaic projects for bidding subject to PUC approval |  |  |  | 4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6
Number of wind projects for bidding subject to PUC approval |  |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Environmental regulation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of EGUs impacted by proposed rules of MATS | 14 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period of extension resulting in MATS compliance date |  |  |  |  |  |  |  |  | 1 year |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 year |  |  |  |  |  |  |  |
Additional accrued investigation and estimated cleanup costs |  |  |  |  |  |  |  |  |  |  | 3,600,000 |  | 3,600,000 |  | 3,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of reduction in GHG emissions by 2020 |  |  | 25.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period for which operations was stopped prior to merger | 4 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Annual revenue |  | 5,300,000 |  |  |  |  | 547,310,000 | 579,464,000 | 1,574,869,000 | 1,677,604,000 | 108,699,000 | 111,249,000 | 313,740,000 | 324,664,000 |  |  | 107,924,000 | 108,490,000 | 320,314,000 | 332,558,000 | 763,933,000 | 799,203,000 | 2,208,923,000 | 2,334,826,000 |  |  |  |  |  |  |
Reductions from the interim D&O relate primarily to: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Lower ROACE |  |  |  |  |  |  |  |  |  |  |  |  | 4,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Customer Information System expenses |  |  |  |  |  |  |  |  |  |  |  |  | 300,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Pension and OPEB expense based on 3-year average |  |  |  |  |  |  |  |  |  |  |  |  | 1,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Integrated resource planning expenses |  |  |  |  |  |  |  |  |  |  |  |  | 900,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operational and Renewable Energy Integration study costs |  |  |  |  |  |  |  |  |  |  |  |  | 1,100,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total adjustment |  |  |  |  |  |  |  |  |  |  |  |  | 7,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stipulated ROACE (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  | 10.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Final approved ROACE (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  | 9.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Final approved ROACE allocated to lower interest rate (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  | 0.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Final approved ROACE allocated for over curtailment of renewable energy (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  | 0.50% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period for calculating average pension costs |  |  |  |  |  |  |  |  |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred IRP cost allowed by PUC order |  |  |  |  |  |  |  |  |  |  |  |  | 800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Charge recorded net of revenue taxes |  |  |  |  |  |  |  |  |  |  | 7,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount to be refunded to customers |  |  |  |  |  |  |  |  |  |  |  |  | 9,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Decrease in employee benefits expenses |  |  |  |  |  |  |  |  |  |  | 1,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred IRP cost reclassified to deferred accounts |  |  |  |  |  |  |  |  |  |  |  |  | 700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Asset retirement obligations |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Impact on earnings from recognition of AROs |  |  |  |  |  |  |  |  | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Changes in the asset retirement obligation liability |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Balance at the beginning of the period |  |  |  |  |  |  |  |  | 48,431,000 | 50,871,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accretion expense |  |  |  |  |  |  |  |  | 833,000 | 1,233,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Liabilities settled |  |  |  |  |  |  |  |  | (1,165,000) | (2,788,000) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revisions in estimated cash flows |  |  |  |  |  |  |  |  | (916,000) | 0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Balance at the end of the period |  |  |  |  |  |  | $ 47,183,000 | $ 49,316,000 | $ 47,183,000 | $ 49,316,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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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 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848 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)(3) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 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 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. + Details
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- Definition Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset. + 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)(2) -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 22 -Subparagraph c(2) -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. + Details
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