Long-term debt - Narrative (Details) $ in Millions	Jun. 26, 2024 USD ($) payment	Dec. 31, 2024 USD ($)
Debt Instrument [Line Items]
Long-term debt payments, year one		$ 110
Long-term debt payments, year two		153
Long-term debt payments, year three		435
Long-term debt payments, year four		274
Long-term debt payments, year five		51
Hawaiian Electric Company, Inc. and Subsidiaries
Debt Instrument [Line Items]
Long-term debt payments, year one		47
Long-term debt payments, year two		125
Long-term debt payments, year three		266
Long-term debt payments, year four		68
Long-term debt payments, year five		$ 35
Mahipapa, LLC
Debt Instrument [Line Items]
Number of deferred payments | payment	3
Deferred payments	$ 5