Commitments and contingencies (Details) - HECO (USD $)	3 Months Ended				0 Months Ended	1 Months Ended			3 Months Ended		12 Months Ended								3 Months Ended			0 Months Ended	3 Months Ended											12 Months Ended	3 Months Ended
	Mar. 31, 2013 item	Mar. 31, 2012	Feb. 06, 2013 item	Apr. 01, 2013 Electric utility	Oct. 19, 2012 Hawaiian Electric Company, Inc. and Subsidiaries	Apr. 30, 2013 Hawaiian Electric Company, Inc. and Subsidiaries	Nov. 30, 2011 Hawaiian Electric Company, Inc. and Subsidiaries	Jan. 31, 2011 Hawaiian Electric Company, Inc. and Subsidiaries	Mar. 31, 2013 Hawaiian Electric Company, Inc. and Subsidiaries MW	Mar. 31, 2012 Hawaiian Electric Company, Inc. and Subsidiaries	Dec. 31, 2018 Hawaiian Electric Company, Inc. and Subsidiaries	Dec. 31, 2017 Hawaiian Electric Company, Inc. and Subsidiaries	Dec. 31, 2016 Hawaiian Electric Company, Inc. and Subsidiaries	Dec. 31, 2015 Hawaiian Electric Company, Inc. and Subsidiaries	Dec. 31, 2014 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	Mar. 31, 2013 Maui Electric Company, Limited (MECO)	Mar. 31, 2012 Maui Electric Company, Limited (MECO)	Dec. 31, 2012 Maui Electric Company, Limited (MECO)	Jan. 28, 2013 Hawaii Electric Light Company, Inc. (HELCO)	Mar. 31, 2013 Hawaii Electric Light Company, Inc. (HELCO)	Mar. 31, 2012 Hawaii Electric Light Company, Inc. (HELCO)	Mar. 31, 2013 Hawaiian Electric Company, Inc. and Subsidiaries	Mar. 31, 2012 Hawaiian Electric Company, Inc. and Subsidiaries	Mar. 31, 2013 Campbell Industrial Park 110MW combustion turbine and transmission line Hawaiian Electric Company, Inc. and Subsidiaries	Dec. 31, 2012 East Oahu transmission project Hawaiian Electric Company, Inc. and Subsidiaries	Mar. 31, 2013 East Oahu Transmission Project Phase 2 Hawaiian Electric Company, Inc. and Subsidiaries	Mar. 31, 2013 Customer Information System Project	Mar. 31, 2013 Customer Information System 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, 2005 Customer Information System Project Hawaiian Electric Company, Inc. and Subsidiaries	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
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
Revenue recognized with respect to interim rate increase order									3,000,000
Project cost incurred																											195,000,000
Allowance for funds used during construction	(730,000)	(870,000)							(568,000)	(725,000)									(70,000)	(94,000)			(92,000)	(51,000)	(730,000)	(870,000)	9,000,000
Estimated project cost above PUC approval																											32,000,000
Adjustment to project costs																											0		0		0
Amount authorized for the project																															20,000,000			20,000,000
Number of hours for development of implementation plans as per EPA guidance			1
Project costs to be written off, subject to approval by PUC																															18,000,000					40,000,000
Amount authorized for project attributable to capital and deferred costs																														18,000,000
Limitation on deferred project operation and maintenance expenses																	2,300,000	2,300,000			600,000
Project costs included in rate base																															0
Environmental regulation
Number of EGUs impacted by proposed rules of MATS	14
Deferral period for GHG permitting requirements for carbon dioxide emissions								3 years
Additional accrued investigation and estimated cleanup costs																			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
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						48,431,000
Accretion expense									124,000	451,000
Liabilities settled									(642,000)	(210,000)
Balance at the end of the period									47,913,000	51,112,000
Collective bargaining agreement
Percentage of employees who are members of the International Brotherhood of Electrical Workers				52.00%
Non-compounded wage increase (as a percent)											3.00%	3.00%	3.25%	3.00%	3.00%	3.00%
Subsequent event
Project costs to be written off, subject to approval by PUC																															18,000,000					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