Electric utility segment - Additional Information (Details)									1 Months Ended									7 Months Ended	12 Months Ended			29 Months Ended	30 Months Ended
	Dec. 14, 2018 USD ($)	Sep. 26, 2018 USD ($)	Aug. 09, 2018 USD ($)	Jun. 22, 2018 USD ($)	May 01, 2018 USD ($)	Feb. 16, 2018 USD ($)	Apr. 27, 2017 USD ($)	Aug. 11, 2016 USD ($)	Feb. 28, 2019 USD ($)	Jun. 30, 2018 USD ($) MW	May 31, 2018 MW	Aug. 31, 2017 USD ($)	Jun. 30, 2017 USD ($) $ / kWh MW	Jun. 30, 2015 MW	Aug. 31, 2012 MW	May 31, 2012 MW	Mar. 31, 1988 MW	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) agreement $ / kWh MW	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Fuel contracts
Revenue subject to refund																			$ 10,000,000
Power purchase agreements
Number of power purchase agreements (PPAs) | agreement																			4
Renewable projects
ERP/EAM cost recovery cap								$ 77,600,000
ERP/EAM required pass-through savings								$ 244,000,000
ERP/EAM project service period (in years)								12 years
Weighted average AFUDC rate								1.75%
ERP/EAM implementation project costs																						$ 77,500,000
ERP/EAM implementation project costs, operations and management																						16,700,000
ERP/EAM implementation project costs, capital costs																						2,600,000
ERP/EAM implementation project costs, deferred costs																						58,200,000
ERP/EAM implementation project costs, accrued carrying costs once put into service																		$ 200,000	$ 200,000			200,000	$ 200,000
Project facility capacity (in mW) | MW										50
Project, lease term (in years)										35 years
Maximum project budget										$ 157,300,000
Percent of costs recoverable through recovery mechanisms other than base rates										90.00%
Total project costs incurred																		144,900,000
Amount recoverable through the major project interim recovery										$ 141,600,000								141,600,000	141,600,000			141,600,000	141,600,000
Environmental regulation
Solar project, energy production (in megawatts) | MW													20
Solar project, project cap													$ 67,000,000
Solar project, maximum energy costs (in dollars per KWH) | $ / kWh													9.56
Solar project, cost incurred																							38,600,000
Accounts receivable and unbilled revenues, net																		325,672,000	325,672,000	$ 263,209,000		325,672,000	325,672,000
Environmental remediation, estimated cost		$ 3,400,000
Decoupling
Threshold of capital expenditures in excess of customer contributions for qualification for major project interim recovery							$ 2,500,000.0
Major project interim recovery requested amount							$ 3,400,000
Major product interim recovered amount																			$ 500,000
Target performance historical measurement period																			10 years
Service reliability, maximum penalty, percent of return on equity																			20.00%
Maximum penalty, pending adjusted amount																			$ 6,700,000
Dead band percentage above or below target																			3.00%
Call center performance, maximum penalty, percent																			8.00%
Call center performance, maximum penalty, pending adjusted amount																			$ 1,300,000
Call center performance, maximum penalty amount																			$ 2,100,000
Performance incentive mechanism, demand response, award percentage of annual maintenance costs																			5.00%
Performance incentive mechanism, demand response, maximum award																			$ 500,000
Performance incentive mechanism, demand response, penalty																			$ 0
Performance incentive mechanism, savings calculation, energy price, renewable projects with storage capacity | $ / kWh																			0.115
Performance incentive mechanism, savings calculation, energy price, renewable energy-only projects | $ / kWh																			0.095
Performance incentive mechanism, expected savings percentage, phase 1																			20.00%
Performance incentive mechanism, savings calculation, incentive cap phase 1																			$ 3,500,000
Performance incentive mechanism, expected savings in Phase 2, January 2019																			15.00%
Performance incentive mechanism, expected savings in Phase 2, February 2019																			10.00%
Performance incentive mechanism, expected savings in Phase 2, March 2019																			5.00%
Performance incentive mechanism, savings calculation, incentive cap																			$ 3,000,000
Performance incentive mechanism, penalty																			0
Statement of probable entitlement, interim increase						$ 36,000,000
Rate increase before tax act impact				$ 37,700,000
Tax act impact on rate				$ 38,300,000
Revenue, calculation assumptions, rate of return, return on average common equity				9.50%
Revenue, calculation assumption, rate of return				7.57%
General rate increase, risk sharing percentage, ratepayer				98.00%
General rate increase, risk sharing percentage, utility				2.00%
General rate increase, maximum exposure cap				$ 2,500,000
PCB Contamination
Environmental regulation
Accrual for environmental loss contingencies																		4,800,000	$ 4,800,000			4,800,000	4,800,000
Subsequent Event
Renewable projects
ERP/EAM required pass-through savings									$ 244,000,000
ERP/EAM project service period (in years)									12 years
ERP/EAM implementation project, expected future O&M expense reductions									$ 141,000,000
ERP/EAM implementation project, future cost avoidance related to capital costs and tax costs									$ 103,000,000
Hawaiian Electric Company, Inc (HECO)
Power purchase agreements
Number of power purchase agreements (PPAs) | agreement																			4
Hawaiian Electric Company, Inc. and Subsidiaries
Fuel contracts
Estimated cost of minimum purchase within 2018 year																			$ 140,000,000
Cost of purchases																			$ 700,000,000	600,000,000	$ 400,000,000
Power purchase agreements
Power purchase capacity excluding agreements with smaller IPPs (in megawatts) | MW																			516.5
Expected fixed capacity charges per year for 2018 through 2022, minimum																			$ 100,000,000
Expected fixed capacity charges from 2023 through 2033																			300,000,000
Environmental regulation
ARO, recognition impact on earnings																			0	0
Changes in the asset retirement obligation liability
Balance at the beginning of the period																			6,035,000	25,589,000
Accretion expense																			282,000	10,000
Liabilities incurred																			1,058,000	5,370,000
Liabilities settled																			(74,000)	(527,000)
Revisions in estimated cash flows																			1,125,000	(24,407,000)
Balance at the end of the period																		8,426,000	8,426,000	$ 6,035,000	$ 25,589,000	8,426,000	8,426,000
Hawaiian Telcom
Environmental regulation
Accounts receivable and unbilled revenues, net																		48,000,000	48,000,000			48,000,000	48,000,000
PGV Facility
Power purchase agreements
Power purchase capacity excluding agreements with smaller IPPs (in megawatts) | MW											34.6
HELCO
Decoupling
Interim general rate increase												$ 9,900,000
Stipulated return on average common equity rate	10.50%											9.50%
Interim rate increase (decrease), amount					$ (9,900,000)
General rate increase, revenue	$ 13,400,000
General rate increase, revenue, percent	3.40%
General rate increase, return on average common equity percent decrease	8.30%
MECO
Decoupling
Interim general rate increase			$ 12,500,000
Interim general rate increase, effective interest rate of return			7.43%
Stipulated return on average common equity rate			9.50%
Interim general rate increase, common equity capitalization			57.00%
Interim general rate increase, rate base			$ 462,000,000
Maui Electric Company, Limited (MECO)
Environmental regulation
Additional accrued investigation and estimated cleanup costs																		2,700,000	$ 2,700,000			2,700,000	2,700,000
Island Energy Services, LLC (IES)
Fuel contracts
Period prior to year end for written notice for cancellation																			120 days
AES Hawaii, Inc. (AES Hawaii)
Power purchase agreements
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
Hu Honua Bioenergy
Power purchase agreements
Purchase commitment, minimum power volume required to be purchased | MW																21.5
Hawaiian Telcom
Environmental regulation
Accounts receivable and unbilled revenues, net																		19,100,000	$ 19,100,000			19,100,000	19,100,000
Hawaiian Telcom | Hawaiian Electric Company, Inc (HECO)
Environmental regulation
Accounts receivable and unbilled revenues, net																		12,300,000	12,300,000			12,300,000	12,300,000
Hawaiian Telcom | HELCO
Environmental regulation
Accounts receivable and unbilled revenues, net																		5,500,000	5,500,000			5,500,000	5,500,000
Hawaiian Telcom | MECO
Environmental regulation
Accounts receivable and unbilled revenues, net																		$ 1,300,000	$ 1,300,000			$ 1,300,000	$ 1,300,000