Retirement benefits - ABO and PBO in Excess of Plan Assets (Details) - Pension benefits - USD ($) $ in Billions	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plans - ABOs	$ 2.0	$ 1.7
Defined benefit plans with ABO in excess of plan assets
ABOs	1.9	1.6
Fair value of plan assets	1.7	1.4
Defined benefit plans with PBOs in excess of plan assets
PBOs	2.2	1.9
Fair value of plan assets	1.7	1.4
Hawaiian Electric Company, Inc. and Subsidiaries
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plans - ABOs	1.8	1.6
Defined benefit plans with ABO in excess of plan assets
ABOs	1.8	1.6
Fair value of plan assets	1.6	1.3
Defined benefit plans with PBOs in excess of plan assets
PBOs	2.1	1.8
Fair value of plan assets	$ 1.6	$ 1.3

Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level.

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