Electric utility segment - Power purchase agreements (Details) $ in Millions	1 Months Ended				3 Months Ended		9 Months Ended		12 Months Ended
	Oct. 31, 2021	Jul. 31, 2018 MW	May 31, 2012 MW	Mar. 31, 1988 MW	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) MW	Sep. 30, 2020 USD ($)	Dec. 31, 1988 MW
Kalaeloa | Subsequent Event
Regulatory Projects and Legal Obligations [Line Items]
Purchase commitment, extension period	10 years
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
Molokai New Energy Partners
Regulatory Projects and Legal Obligations [Line Items]
Total contracted PV capacity (in megawatts) | MW		4.88
Total contracted battery energy storage system capacity | MW		3
Maximum power volume to be delivered (in megawatts) | MW		2.64
Hawaiian Electric, Parent
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					$ 186	$ 149	$ 491	$ 426
Hawaiian Electric, Parent | Kalaeloa
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					56	39	142	111
Increased power purchase commitment capacity (in megawatts) | MW									208
Hawaiian Electric, Parent | AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					32	33	98	96
Hawaiian Electric, Parent | HPOWER
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					20	18	51	52
Hawaiian Electric, Parent | Hamakua Energy
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					15	12	38	36
Hawaiian Electric, Parent | Puna Geothermal Venture
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					9	0	20	0
Hawaiian Electric, Parent | Wind IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					38	30	95	83
Hawaiian Electric, Parent | Solar IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					12	17	40	45
Hawaiian Electric, Parent | Other IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					$ 4	$ 0	$ 7	$ 3