Electric utility segment - Commitments and contingencies (Details) $ in Millions		1 Months Ended				12 Months Ended
	Jun. 10, 2019 USD ($)	Jan. 31, 2020	Jun. 30, 2015 MW	May 31, 2012 MW	Mar. 31, 1988 MW	Dec. 31, 1988 MW	Jun. 30, 2020 USD ($)
Regulatory Projects and Legal Obligations [Line Items]
ERP/EAM project service period (in years)	12 years	12 years
Project costs, accrued carrying costs once put into service							$ 59.4
Project costs, amortization							0.3
Future O&M expense reductions	$ 150.0
Future cost avoidance related to capital cost and tax costs	$ 96.0
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
Hawaiian Electric (parent only) | PCB Contamination
Environmental regulation
Valuation allowances and reserves							4.8
Maui Electric
Environmental regulation
Additional accrued investigation and estimated cleanup costs							2.7
ERP/EAM Implementation Project | Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory Projects and Legal Obligations [Line Items]
Regulatory liability for O&M expense reductions							$ 7.2
Kalaeloa | Hawaiian Electric (parent only)
Regulatory Projects and Legal Obligations [Line Items]
Increased power purchase commitment capacity (in megawatts) | MW						208