Electric utility subsidiary - Commitments and contingencies (Details)										1 Months Ended					6 Months Ended
	Jun. 18, 2015	May. 28, 2015 USD ($) kWh	Apr. 15, 2015 USD ($)	Mar. 31, 2015 USD ($)	Mar. 23, 2015	Jan. 20, 2015	Dec. 19, 2014 memorandum	May. 31, 2013	Feb. 16, 2012 generation_unit	Jun. 30, 2015 USD ($) MW	Aug. 31, 2014	Apr. 30, 2014 order	Aug. 31, 2012 MW	Mar. 31, 1988 MW	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Mar. 01, 2014	Feb. 07, 2014	Mar. 31, 2012 USD ($)
Regulatory projects and legal obligations
Purchase commitment, period														30 years
Long-term Purchase Commitment, Minimum Power Volume Required | MW													186	180
Environmental regulation
Number of EGUs impacted by proposed rules of MATS | generation_unit									14
Period for which operations was stopped prior to merger															4 years
Number of memoranda issued | memorandum							2
Decrease in GHG emission level regulatory requirements	16.00%
Changes in the asset retirement obligation liability
Number of orders from regulatory agency | order												4
Percent of energy production from renewable energy sources											65.00%
Requested approval period for motion						60 days
Public Utilities, Phase-in Plans [Abstract]
Annual incremental RAM adjusted revenues		$ 11,100,000	$ 26,200,000	$ 31,600,000
Net annual incremental amount to be collected under the tariffs		400,000	$ 14,700,000
Long Term Purchase Commitment, Additional Capacity Requirement | MW										9
Hawaiian Electric Company
Environmental regulation
Period of extension resulting in MATS compliance date									1 year
Public Utilities, Phase-in Plans [Abstract]
Annual incremental RAM adjusted revenues		8,100,000
Annual change in accrued earnings sharing credits to be refunded		0
Annual change in accrued RBA balance as of December 31, 2014 (and associated revenue taxes) to be collected		(9,200,000)
Net annual incremental amount to be collected under the tariffs		(1,100,000)
Impact on typical residential customer monthly bill		$ (90,000)
Monthly utility usage assumption (in kilowatts per hour) | kWh		500
Lanai and Molokai [Member]
Public Utilities, Phase-in Plans [Abstract]
Impact on typical residential customer monthly bill		$ 0.11
Monthly utility usage assumption (in kilowatts per hour) | kWh		400
Hawaii Electric Light Company, Inc. (HELCO)
Public Utilities, Phase-in Plans [Abstract]
Annual incremental RAM adjusted revenues		$ 1,500,000
Annual change in accrued earnings sharing credits to be refunded		0
Annual change in accrued RBA balance as of December 31, 2014 (and associated revenue taxes) to be collected		100,000
Net annual incremental amount to be collected under the tariffs		1,500,000
Impact on typical residential customer monthly bill		$ 880,000
Monthly utility usage assumption (in kilowatts per hour) | kWh		500
Maui Electric
Environmental regulation
Additional accrued investigation and estimated cleanup costs										$ 3,600,000					$ 3,600,000					$ 3,100,000
Public Utilities, Phase-in Plans [Abstract]
Annual incremental RAM adjusted revenues		$ 1,500,000
Annual change in accrued earnings sharing credits to be refunded		(100,000)
Annual change in accrued RBA balance as of December 31, 2014 (and associated revenue taxes) to be collected		(2,200,000)
Net annual incremental amount to be collected under the tariffs		(800,000)
Impact on typical residential customer monthly bill		$ (130,000)
Hawaiian Electric Company, Inc. and Subsidiaries
Environmental regulation
Percentage of reduction in GHG emissions by 2020										16.00%					16.00%
Estimated annual fee for greenhouse gas emissions															$ 500,000
Impact on earnings from recognition of AROs															0
Changes in the asset retirement obligation liability
Balance, beginning of period															29,419,000	$ 43,106,000
Accretion expense															12,000	643,000
Liabilities incurred															0	0
Liabilities settled															(1,881,000)	(6,052,000)
Revisions in estimated cash flows															0	0
Balance, end of period										$ 27,550,000					$ 27,550,000	$ 37,697,000
Decoupling implementation experience, period								3 years
Proposed rate base adjustment, percent of previous rate base adjustment																			90.00%
Effective interest rate, revenue balancing account																			6.00%
Period to file required plan												120 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
Period to file demand response portfolio plan												90 days
Minimum | Hawaiian Electric Company, Inc. and Subsidiaries
Changes in the asset retirement obligation liability
Proposed effective interest rate, revenue balancing account																		1.25%
Maximum | Hawaiian Electric Company, Inc. and Subsidiaries
Changes in the asset retirement obligation liability
Proposed effective interest rate, revenue balancing account																		3.25%
Reserve for Environmental Costs
Environmental regulation
Additional reserve for investigation																	$ 800,000
PCB Contamination | Waiau Power Plant
Environmental regulation
Period for submissions to EPA					45 days