Commitments and contingencies (Details) - HECO (USD $)	6 Months Ended	0 Months Ended		1 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			0 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended
	Jun. 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	Jun. 30, 2013 Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2012 Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2013 Hawaiian Electric Company, Inc. and Subsidiaries MW	Jun. 30, 2012 Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2013 Maui Electric Company, Limited (MECO)	Jun. 30, 2012 Maui Electric Company, Limited (MECO)	Jun. 30, 2013 Maui Electric Company, Limited (MECO)	Jun. 30, 2012 Maui Electric Company, Limited (MECO)	Mar. 31, 2012 Maui Electric Company, Limited (MECO)	Jan. 28, 2013 Hawaii Electric Light Company, Inc. (HELCO)	Jun. 30, 2013 Hawaii Electric Light Company, Inc. (HELCO)	Jun. 30, 2012 Hawaii Electric Light Company, Inc. (HELCO)	Jun. 30, 2013 Hawaii Electric Light Company, Inc. (HELCO)	Jun. 30, 2012 Hawaii Electric Light Company, Inc. (HELCO)	Jun. 30, 2013 Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2012 Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2013 Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 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
Regulatory projects and legal obligations
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
Integration from renewable energy sources (in megawatts)									200														200
Maximum deferred cost recovery									5,890,000
Integration from firm renewable geothermal dispatchable energy (in megawatts)									50														50
Number of bids received					6
Number of projects for bidding subject to PUC approval				5
Number of photovoltaic projects for bidding subject to PUC approval				4
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					521,730,000	567,527,000	1,027,559,000	1,098,140,000	100,689,000	108,417,000	205,041,000	213,415,000			106,374,000	111,741,000	212,390,000	224,068,000	728,793,000	787,685,000	1,444,990,000	1,535,623,000
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													700,000
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
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									363,000	862,000
Liabilities settled									(1,506,000)	(2,217,000)
Revisions in estimated cash flows									(916,000)
Balance at the end of the period				46,372,000			46,372,000	49,516,000	46,372,000	49,516,000
Subsequent event
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