Electric utility subsidiary - Commitments and contingencies (Details) (USD $)	1 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended		9 Months Ended
	Apr. 30, 2014 order	Sep. 30, 2014 item	Sep. 30, 2014 Hawaiian Electric Company	Sep. 30, 2013 Hawaiian Electric Company	Sep. 30, 2014 Hawaiian Electric Company	Sep. 30, 2013 Hawaiian Electric Company	Sep. 30, 2014 Maui Electric Company (MECO)	Sep. 30, 2013 Maui Electric Company (MECO)	Sep. 30, 2014 Maui Electric Company (MECO)	Sep. 30, 2013 Maui Electric Company (MECO)	Mar. 31, 2012 Maui Electric Company (MECO)	Sep. 30, 2014 Hawaii Electric Light Company, Inc. (HELCO)	Sep. 30, 2013 Hawaii Electric Light Company, Inc. (HELCO)	Sep. 30, 2014 Hawaii Electric Light Company, Inc. (HELCO)	Sep. 30, 2013 Hawaii Electric Light Company, Inc. (HELCO)	Apr. 30, 2014 Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2014 Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2013 Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2014 Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2013 Hawaiian Electric Company, Inc. and Subsidiaries	Feb. 07, 2014 Hawaiian Electric Company, Inc. and Subsidiaries	Oct. 31, 2013 Hawaiian Electric Company, Inc. and Subsidiaries	Mar. 01, 2014 Maximum Hawaiian Electric Company, Inc. and Subsidiaries	Mar. 01, 2014 Minimum Hawaiian Electric Company, Inc. and Subsidiaries
Environmental regulation
Number of EGUs impacted by proposed rules of MATS		14
Period of extension resulting in MATS compliance date					1 year
Period for which operations was stopped prior to merger		4 years
Additional accrued investigation and estimated cleanup costs							$ 3,600,000		$ 3,600,000		$ 3,100,000
Percentage of reduction in GHG emissions by 2020																	16.00%		16.00%
Estimated annual fee for greenhouse gas emissions																			500,000
Annual revenue			579,777,000	547,434,000	1,623,223,000	1,576,068,000	112,656,000	108,699,000	319,265,000	313,725,000		111,154,000	107,957,000	319,629,000	320,330,000		803,565,000	764,054,000	2,262,056,000	2,210,020,000
Asset retirement obligations
Impact on earnings from recognition of AROs																			0
Changes in the asset retirement obligation liability
Balance, beginning of period																			43,106,000	48,431,000
Accretion expense																			816,000	833,000
Liabilities settled																			(11,338,000)	(1,165,000)
Revisions in estimated cash flows																			0	(916,000)
Balance, end of period																	32,584,000	47,183,000	32,584,000	47,183,000
Baseline capital project value to determine revenue adjustment																						$ 2,500,000
Proposed rate base adjustment, percent of previous rate base adjustment																					90.00%
Proposed effective interest rate, revenue balancing account																							3.25%	1.25%
Effective interest rate, revenue balancing account																					6.00%
Number of orders from regulatory agency	4
Period to file required plan																120 days
Period to file demand response portfolio plan																90 days
Period to file implementation plan																60 days
Period for full implementation of plan																180 days
Period to file action plan																30 days
Proposal to file implementation proposal																120 days