Electric utility segment Additional Information (Details)												1 Months Ended													3 Months Ended	12 Months Ended			22 Months Ended
	Jan. 05, 2016 USD ($)	Nov. 13, 2015 MW	Oct. 30, 2015 USD ($)	Oct. 26, 2015 USD ($)	Aug. 03, 2015 state	May. 28, 2015 USD ($) kWh	Apr. 15, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jun. 30, 2014	May. 31, 2013	Feb. 16, 2012 generation_unit	Nov. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jul. 31, 2015 USD ($)	Jun. 30, 2015 MW	Oct. 31, 2014 bidder	Aug. 31, 2014	Jul. 31, 2014 USD ($)	Nov. 30, 2013 USD ($)	Feb. 28, 2013 bid	Aug. 31, 2012 MW	May. 31, 2012 MW	Feb. 28, 2012 USD ($) MW	Mar. 31, 1988 MW	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) agreement MW	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2013 USD ($)	Jun. 20, 2014 facility	Feb. 07, 2014
Regulatory projects and legal obligations
Period for which Operations was Stopped Prior to Merger																										4 years
Public Utility, Annual Incremental Rate Adjustment Mechanism Adjusted Revenue						$ 11,100,000	$ 26,200,000	$ 31,600,000
Power purchase agreements
Number of power purchase agreements (PPAs) | agreement																										5
Purchase commitment, period																								30 years
Purchase commitment, minimum power volume required to be purchased | MW																					186			180
Purchase commitment, arbitration, additional capacity requirement | MW		9													9
Decoupling
Public Utility, Net Receivable Under Tariff						400,000	$ 14,700,000
Public Utility, Enterprise Resource Management System Project, Costs																		$ 82,400,000
Public Utility, Enterprise Resource Management System Project, Difference In Cost Between Replacing System And Utilizing Potential Merger Subsidiary's Existing System														$ 20,800,000
Software Acquisition Expense																									$ 4,800,000
Public Utility, Project Facility Capacity | MW																					50
Public Utility, Maximum Project Budget													$ 167,000,000
Public Utility, Project, Percent Of Cost Recoverable Through Recovery Mechanisms Other Than Base Rates													90.00%
Number Of States Included In Interim State-wide Emission Limits | state					48
PSIP, percent of energy coming from renewable sources																	65.00%
Revenue Requirement Associated With Plant Additions				$ 40,300,000
PCB Contamination
Decoupling
Accrual for Environmental Loss Contingencies																										$ 4,700,000
Subsequent event
Decoupling
Public Utility, Maximum Project Budget	$ 157,300,000
Public Utility, Decrease In Project Costs	$ 9,700,000
Hawaiian Electric Company, Inc (HECO)
Regulatory projects and legal obligations
Public Utility, Annual Incremental Rate Adjustment Mechanism Adjusted Revenue						8,100,000
Power purchase agreements
Number of power purchase agreements (PPAs) | agreement																										5
Purchased power																										$ 440,983,000	$ 537,821,000	$ 527,839,000
Renewable projects
Recovery of annual deferred costs, recovery period														4 months
Number of Generating Units Subject to New Regulation | generation_unit											14
Period of Extension Resulting in Mercury and Air Toxics Standards Compliance Date											1 year
D&O
Revenues																										1,644,181,000	2,142,245,000	2,124,174,000
Decoupling
Public Utility, Increase (Decrease) In Accrued Earnings Sharing Credits To Be Refunded						0
Public Utility, Increase (Decrease) In Accrued Revenue Balancing Account To Be Collected						(9,200,000)
Public Utility, Net Receivable Under Tariff						$ (1,100,000)
Public Utilities, Monthly Utility Usage Assumption | kWh						500
Public Utilities, Increase (Decrease) In Customer Monthly Bill						$ (90,000)
Lanai and Molokai
Decoupling
Public Utilities, Monthly Utility Usage Assumption | kWh						400
Public Utilities, Increase (Decrease) In Customer Monthly Bill						$ 0.11
Hawaii Electric Light Company, Inc. (HELCO)
Power purchase agreements
Purchased power																										97,503,000	123,226,000	128,368,000
D&O
Revenues																										345,549,000	422,200,000	431,517,000
Maui Electric Company, Limited (MECO)
Power purchase agreements
Purchased power																										55,610,000	60,961,000	54,474,000
Environmental regulation
Additional accrued investigation and estimated cleanup costs																										3,600,000
D&O
Revenues																										345,517,000	422,965,000	424,603,000
Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory projects and legal obligations
Decoupling Implementation Experience, Period										3 years
Asset Retirement Obligations, Recognition Impact on Earnings																										0
Fuel contracts
Estimated cost of minimum purchase within 2015 year																										245,000,000
Estimated cost of minimum purchase in 2016 year																										4,000,000
Estimated cost of minimum purchase in 2017 year																										0
Cost of purchases																										$ 600,000,000	1,100,000,000	1,100,000,000
Power purchase agreements
Power purchase capacity excluding agreements with smaller IPPs (in megawatts) | MW																										551
Purchased power																										$ 594,096,000	722,008,000	710,681,000
Expected fixed capacity charges per year for 2015 through 2019, minimum																										100,000,000
Expected fixed capacity charges from 2019 through 2033																										500,000,000
Renewable projects
Recovery of annual deferred costs contingent on approval																			$ 405,000
Maximum deferred cost recovery - inter-island project support costs																							$ 5,890,000
Maximum deferred cost recovery, contractor service costs																													$ 3,100,000
Integration from renewable energy sources (in megawatts) | MW																							200
Maximum deferred cost recover, contractor service costs, amortization period																							3 years
Integration from firm renewable geothermal dispatchable energy (in megawatts) | MW																						50
Maximum deferred cost recovery - geothermal dispatchable energy costs												$ 2,100,000
Number of bids received | bid																				6
Number of eligible bidders | bidder																5
Environmental regulation
Percentage of reduction in GHG emissions by 2020									16.00%
Estimated annual fee, emissions regulation																										500,000
D&O
Revenues																										2,335,166,000	2,987,323,000	2,980,172,000
Changes in the asset retirement obligation liability
Balance at the beginning of the period																										29,419,000	43,106,000
Accretion expense																										24,000	890,000
Liabilities incurred																										0	0
Liabilities settled																										(2,595,000)	(14,577,000)
Revisions in estimated cash flows																										0	0
Balance at the end of the period																										$ 26,848,000	$ 29,419,000	$ 43,106,000	$ 43,106,000
Decoupling
Public Utilities, proposed rate base adjustment, percent of previous rate base adjustment																															90.00%
Public Utilities, effective interest rate, revenue balancing account																										6.00%
Required Reduction Of Greenhouse Gas Emissions Mandated By Regulations, Percentage																														16.00%
Required Reduction Of Greenhouse Gas Emissions Mandated By Regulations, Number Of Facilities Impacted | facility																														11
Hawaiian Electric Company, Inc. and Subsidiaries | Minimum
Decoupling
Public Utilities, proposed effective interest rate, revenue balancing account																															1.25%
Hawaiian Electric Company, Inc. and Subsidiaries | Maximum
Decoupling
Public Utilities, proposed effective interest rate, revenue balancing account																															3.25%
HELCO
Regulatory projects and legal obligations
Public Utility, Annual Incremental Rate Adjustment Mechanism Adjusted Revenue						1,500,000
Decoupling
Public Utility, Increase (Decrease) In Accrued Earnings Sharing Credits To Be Refunded						0
Public Utility, Increase (Decrease) In Accrued Revenue Balancing Account To Be Collected						100,000
Public Utility, Net Receivable Under Tariff						1,500,000
Public Utilities, Increase (Decrease) In Customer Monthly Bill						880,000
MECO
Regulatory projects and legal obligations
Public Utility, Annual Incremental Rate Adjustment Mechanism Adjusted Revenue						1,500,000
Renewable projects
Recovery of annual deferred costs, recovery period														2 years
Decoupling
Public Utility, Increase (Decrease) In Accrued Earnings Sharing Credits To Be Refunded						(100,000)
Public Utility, Increase (Decrease) In Accrued Revenue Balancing Account To Be Collected						(2,200,000)
Public Utility, Net Receivable Under Tariff						(800,000)
Public Utilities, Increase (Decrease) In Customer Monthly Bill						$ (130,000)
Revenue Requirement Associated With Plant Additions			$ 4,300,000