Credit agreements and changes in debt - Note Purchase Agreements (Details) - Senior Notes	May 14, 2020 USD ($)
Unsecured Senior Notes Series 2020A
Debt Instrument [Line Items]
Aggregate principal amount	$ 80,000,000
Unsecured Senior Notes Series 2020A | Hawaiian Electric (parent only)
Debt Instrument [Line Items]
Aggregate principal amount	$ 50,000,000
Fixed coupon interest rate	3.31%
Unsecured Senior Notes Series 2020A | HELCO
Debt Instrument [Line Items]
Aggregate principal amount	$ 10,000,000
Fixed coupon interest rate	3.96%
Unsecured Senior Notes Series 2020A | Maui Electric
Debt Instrument [Line Items]
Aggregate principal amount	$ 20,000,000
Fixed coupon interest rate	3.31%
Unsecured Senior Notes Series 2020B
Debt Instrument [Line Items]
Aggregate principal amount	$ 60,000,000
Unsecured Senior Notes Series 2020B | Hawaiian Electric (parent only)
Debt Instrument [Line Items]
Aggregate principal amount	$ 40,000,000
Fixed coupon interest rate	3.31%
Unsecured Senior Notes Series 2020B | Maui Electric
Debt Instrument [Line Items]
Aggregate principal amount	$ 20,000,000
Fixed coupon interest rate	3.96%
Unsecured Senior Notes Series 2020C
Debt Instrument [Line Items]
Aggregate principal amount	$ 20,000,000
Unsecured Senior Notes Series 2020C | Hawaiian Electric (parent only)
Debt Instrument [Line Items]
Aggregate principal amount	$ 20,000,000
Fixed coupon interest rate	3.96%