PENSION PLANS AND POST-RETIREMENT BENEFITS - APBO (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
ABO for all defined benefit pension plans	$ 2,534.1	$ 2,390.5
Pension plans with the PBO in excess of plan assets
Projected benefit obligation	2,901.1	2,718.2
Fair value of plan assets	1,799.1	1,732.8
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated benefit obligation	2,534.1	2,390.5
Fair value of plan assets	1,799.1	1,732.8
Post-Retirement Benefits
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated benefit obligation	280.4	264.3
Fair value of plan assets	248.3	239.9
Evergy Metro | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
ABO for all defined benefit pension plans	1,227.4	1,170.2
Pension plans with the PBO in excess of plan assets
Projected benefit obligation	1,446.5	1,371.4
Fair value of plan assets	912.1	890.7
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated benefit obligation	1,227.4	1,170.2
Fair value of plan assets	912.1	890.7
Evergy Metro | Post-Retirement Benefits
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated benefit obligation	133.6	125.6
Fair value of plan assets	122.5	119.4
Evergy Kansas Central | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
ABO for all defined benefit pension plans	1,281.6	1,196.8
Pension plans with the PBO in excess of plan assets
Projected benefit obligation	1,429.6	1,323.4
Fair value of plan assets	887.0	842.1
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated benefit obligation	1,281.6	1,196.8
Fair value of plan assets	887.0	842.1
Evergy Kansas Central | Post-Retirement Benefits
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated benefit obligation	146.8	138.7
Fair value of plan assets	$ 125.8	$ 120.5