Electric utility segment - Power purchase agreements (Details) $ in Millions	1 Months Ended			3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 31, 2018 MW	May 31, 2012 MW	Mar. 31, 1988 MW	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) MW	Jun. 30, 2020 USD ($)	Dec. 31, 1988 MW
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
Kalaeloa
Regulatory Projects and Legal Obligations [Line Items]
PPA termination period						60 days
Hawaiian Electric, Parent
Regulatory Projects and Legal Obligations [Line Items]
Purchased power				$ 163	$ 137	$ 305	$ 277
Hawaiian Electric, Parent | Kalaeloa
Regulatory Projects and Legal Obligations [Line Items]
Purchased power				49	34	86	72
Increased power purchase commitment capacity (in megawatts) | MW								208
Hawaiian Electric, Parent | AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchased power				36	32	66	63
Hawaiian Electric, Parent | HPOWER
Regulatory Projects and Legal Obligations [Line Items]
Purchased power				14	17	31	34
Hawaiian Electric, Parent | Hamakua Energy
Regulatory Projects and Legal Obligations [Line Items]
Purchased power				12	11	23	24
Hawaiian Electric, Parent | Puna Geothermal Venture
Regulatory Projects and Legal Obligations [Line Items]
Purchased power				7	0	11	0
Hawaiian Electric, Parent | Wind IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power				28	25	57	53
Hawaiian Electric, Parent | Solar IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power				16	17	28	28
Hawaiian Electric, Parent | Other IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power				$ 1	$ 1	$ 3	$ 3