Electric utility subsidiary - Commitments and contingencies (Details)						1 Months Ended			3 Months Ended
	Apr. 15, 2015 USD ($) kWh	Mar. 31, 2015 USD ($)	Mar. 23, 2015	Jan. 20, 2015	Feb. 16, 2012 generation_unit	Aug. 31, 2014	Apr. 30, 2014 USD ($) order	Oct. 31, 1988	Mar. 31, 2015 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2014 USD ($)	Mar. 01, 2014	Feb. 07, 2014	Mar. 31, 2012 USD ($)
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
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		$ 31,600,000
Hawaiian Electric Company
Environmental regulation
Period of extension resulting in MATS compliance date								1 year
Maui Electric
Environmental regulation
Additional accrued investigation and estimated cleanup costs		$ 3,600,000							$ 3,600,000					$ 3,100,000
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							$ 41,236,000		29,419,000	$ 43,106,000
Accretion expense									6,000	370,000
Liabilities settled									(1,614,000)	(2,240,000)
Revisions in estimated cash flows									0	0
Balance, end of period		$ 27,811,000							$ 27,811,000	$ 41,236,000
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
Subsequent Event
Changes in the asset retirement obligation liability
Regulatory filing period for initial briefing	60 days
Regulatory filing period for reply briefing	75 days
Public Utilities, Phase-in Plans [Abstract]
Annual incremental RAM adjusted revenues	$ 26,200,000
Net annual incremental amount to be collected under the tariffs	14,700,000
Subsequent Event | Hawaiian Electric Company
Public Utilities, Phase-in Plans [Abstract]
Annual incremental RAM adjusted revenues	20,300,000
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	11,100,000
Impact on typical residential customer monthly bill	$ 560,000
Monthly utility usage assumption (in kilowatts per hour) | kWh	600
Subsequent Event | Hawaii Electric Light Company, Inc. (HELCO)
Public Utilities, Phase-in Plans [Abstract]
Annual incremental RAM adjusted revenues	$ 2,400,000
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	2,500,000
Impact on typical residential customer monthly bill	$ 1,100,000
Monthly utility usage assumption (in kilowatts per hour) | kWh	500
Subsequent Event | Maui Electric
Public Utilities, Phase-in Plans [Abstract]
Annual incremental RAM adjusted revenues	$ 3,400,000
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	1,100,000
Impact on typical residential customer monthly bill	$ 600,000
Monthly utility usage assumption (in kilowatts per hour) | kWh	600
PCB Contamination | Waiau Power Plant
Environmental regulation
Period For Submission Of Plan To EPA			45 days