Bank segment (HEI only) - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 1988
Parent Company
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash dividends paid	$ 157.0	$ 154.0	$ 125.0
Parent Company | Consolidated subsidiary | American Savings Bank (ASB) | Management and administrative services
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Revenue from related party	2.3	2.2	$ 2.1
Parent Company | 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	$ 56.0	$ 50.0