Bank segment (HEI only) - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 1988
Hawaiian Electric (parent only)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash dividends paid	$ 172.0	$ 145.0	$ 157.0
Hawaiian Electric (parent only) | Consolidated subsidiary | American Savings Bank (ASB) | Management and administrative services
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Revenue from related party	2.1	2.3	$ 2.3
Hawaiian Electric (parent only) | Maximum
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Obligation to contribute additional capital under the Capital Maintenance Agreement				$ 65.1
Reduction in obligation to contribute additional capital under the Capital Maintenance Agreement	28.3
American Savings Bank (ASB)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash dividends paid	$ 59.0	$ 31.0