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
	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