Retirement benefits - ABO and PBO in Excess of Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined benefit plans with PBOs in excess of plan assets
Defined contribution plan, expenses recognized	$ 6	$ 7	$ 7
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plans - ABOs	2,300	2,300
Defined benefit plans with ABO in excess of plan assets
ABOs	0	2,100
Fair value of plan assets	0	2,000
Defined benefit plans with PBOs in excess of plan assets
PBOs	2,500	2,500
Fair value of plan assets	2,200	2,000
Hawaiian Electric Company, Inc. and Subsidiaries
Defined benefit plans with PBOs in excess of plan assets
Defined contribution plan, expenses recognized	3	3	$ 3
Hawaiian Electric Company, Inc. and Subsidiaries | Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plans - ABOs	2,100	2,100
Defined benefit plans with ABO in excess of plan assets
ABOs	0	2,100
Fair value of plan assets	0	1,900
Defined benefit plans with PBOs in excess of plan assets
PBOs	2,500	2,400
Fair value of plan assets	$ 2,100	$ 1,900