Segment financial information - Narrative (Details) $ in Millions			1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2024 segment subsidiary	Dec. 30, 2024	Sep. 30, 2020 a MW	Sep. 30, 2024 USD ($)	Dec. 31, 2024 segment subsidiary	Dec. 30, 2024 segment	Dec. 31, 2018 MWh MW	Dec. 31, 2017 MW	Jul. 31, 2022 MW
Segment financial information
Number of reportable segments | segment	1					2
Hamakua Energy
Segment financial information
Power produced by power plants (in megawatts)								60
Mauo, LLC
Segment financial information
Power produced by power plants (in megawatts)							8.1
Power storage capacity (in megawatt hours) | MWh							42.6
Power purchase agreement term (in years)							15 years
Power purchase agreement extension term (in years)							5 years
Ka‘ie‘ie Waho Company, LLC
Segment financial information
Photovoltaic system power amount (in megawatts)			6
Area of land (in acres) | a			20
Mahipapa, LLC | Green Energy Team, LLC
Segment financial information
Unit of renewable energy (in mega watts)									7.5
HEI and Pacific
Segment financial information
Asset impairment charges | $				$ 35.2
Hamakua Holdings, LLC
Segment financial information
Number of wholly-owned subsidiaries | subsidiary	2				2
Hawaiian Electric Company, Inc. and Subsidiaries
Segment financial information
Number of reportable segments | segment					1
American Savings Bank (ASB) | ASB Hawaii, Inc
Segment financial information
Minority ownership percentage	9.90%	9.90%			9.90%	9.90%
Discontinued Operations, Disposed of by Sale | American Savings Bank (ASB)
Segment financial information
Ownership percentage disposed		90.10%