Electric utility segment - Commitments and contingencies (Details)		1 Months Ended				12 Months Ended		39 Months Ended
	Jun. 10, 2019 USD ($)	Jun. 30, 2017 USD ($) $ / kWh MW	Jun. 30, 2015 MW	May 31, 2012 MW	Mar. 31, 1988 MW	Dec. 31, 2017	Dec. 31, 1988 MW	Sep. 30, 2019 USD ($)
Regulatory Projects and Legal Obligations [Line Items]
AFUDC rate						1.75%
Project costs, accrued carrying costs once put into service								$ 59,100,000
Future O&M expense reductions	$ 150,000,000
Future cost avoidance related to capital cost and tax costs	$ 96,000,000
ERP/EAM project service period (in years)	12 years
Regulatory liability for O&M expense reductions								1,400,000
West Lock PV Project, energy generated (in megawatts) | MW		20
West Lock PV Project, cost cap		$ 67,000,000
West Lock PV Project, maximum energy cost (in dollars per kilowatt hours) | $ / kWh		0.0956
West Lock PV Project, project costs incurred								49,300,000
PCB Contamination
Environmental regulation
Valuation allowances and reserves								4,400,000
AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchase commitment, period (in years)					30 years
Minimum power volume required (in megawatts) | MW					180
Additional capacity requirement (in megawatts) | MW			9
Hu Honua Bioenergy, LLC
Regulatory Projects and Legal Obligations [Line Items]
Minimum power volume required (in megawatts) | MW				21.5
Maui Electric
Environmental regulation
Additional accrued investigation and estimated cleanup costs								$ 2,700,000
Kalaeloa | Hawaiian Electric (parent only)
Regulatory Projects and Legal Obligations [Line Items]
Increased power purchase commitment capacity (in megawatts) | MW							208