Commitments and contingencies - (Details) - HECO (USD $)	3 Months Ended		9 Months Ended						1 Months Ended			12 Months Ended		9 Months Ended	1 Months Ended				3 Months Ended		9 Months Ended		12 Months Ended			9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 years EGUs statements months contracts days	Sep. 30, 2010	Sep. 30, 2011 Hawaiian Electric Company, Inc. and Subsidiaries Campbell Industrial Park 110MW combustion turbine and transmission line mW	Sep. 30, 2011 East Oahu transmission project	Sep. 30, 2011 Hawaiian Electric Company, Inc. and Subsidiaries East Oahu Transmission Project Phase 1	Sep. 30, 2011 East Oahu Transmission Project Phase 1	Apr. 30, 2010 Hawaiian Electric Company, Inc. and Subsidiaries East Oahu Transmission Project Phase 2	Sep. 30, 2011 Hawaiian Electric Company, Inc. and Subsidiaries East Oahu Transmission Project Phase 2	Sep. 30, 2011 East Oahu Transmission Project Phase 2	Dec. 31, 2005 Hawaiian Electric Company, Inc. and Subsidiaries Customer Information System Project	Sep. 30, 2011 Hawaiian Electric Company, Inc. and Subsidiaries Customer Information System Project	Sep. 30, 2011 Customer Information System Project	Jun. 30, 2010 Hawaiian Electric Company, Inc. and Subsidiaries Honolulu power plant	Aug. 31, 2010 Hawaiian Electric Company, Inc. and Subsidiaries Waiau power plant	Jan. 31, 2011 Hawaiian Electric Company, Inc. and Subsidiaries years	Sep. 30, 2009 Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2011 Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2010 Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2011 Hawaiian Electric Company, Inc. and Subsidiaries kW agreements mW institutions	Sep. 30, 2010 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	Sep. 30, 2011 Hawaii Electric Light Company, Inc. (HELCO)	Sep. 30, 2011 Maui Electric Company, Limited (MECO)	Sep. 30, 2011 Electric utility
Regulatory projects and legal obligations
Deferred cost to be recovered subject to PUC approval																					$ 3,900,000
Integration from renewable energy sources (in megawatts)																					200
Revenue recognized with respect to interim rate increase order																					24,000,000
Estimated project cost above PUC approval					32,000,000		43,000,000
Capacity of projects (in megawatts)					110
Cost of project recoverable from increase in annual revenue					163,000,000
Estimated project cost						56,000,000		42,000,000			14,000,000
Project cost incurred					195,000,000
Allowance for funds used during construction	(658,000)	(492,000)	(1,731,000)	(2,061,000)	9,000,000														(658,000)	(492,000)	(1,731,000)	(2,061,000)				(189,000)	(204,000)
Estimated project cost subject to decision and order issued							16,000,000
Amount authorized for the project												20,000,000
Amount authorized for project attributable to capital and deferred costs														18,000,000
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
Accumulated project cost							59,000,000			9,000,000
Accumulated project planning and permitting cost							12,000,000
Accumulated project planning and permitting cost after denial of permit							24,000,000
Accumulated cost for allowance for funds used during construction							23,000,000
Deferred and capital cost													57,000,000
Deferred and capital cost recorded													36,000,000
Environmental regulation
Number of periods allowed for compliance of EPA regulation (in years)			8
Number of EGUs impacted by proposed rules of MACT			14
Number of periods allowed for compliance of MACT rules (in years)			3
Number of 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
Asset retirement obligations
Asset retirement obligation related to removal of retired generating units															11,000,000	12,000,000		23,000,000
Changes in the asset retirement obligation liability
Balance at the beginning of the period																	48,630,000				48,630,000	23,746,000			48,630,000
Accretion expense																					1,641,000	1,714,000
Liabilities incurred																						11,949,000
Liabilities settled																					(681,000)	(499,000)
Revisions in estimated cash flows																					390,000	11,141,000
Balance at the end of the period																			$ 49,980,000	$ 48,051,000	$ 49,980,000	$ 48,051,000
Collective bargaining agreement
Percentage of employees who are members of the International Brotherhood of Electrical Workers (as a percent)																												53.00%
Non-compounded wage increase (as a percent)																							3.00%	2.50%	1.75%