PENSION PLANS AND POST-RETIREMENT BENEFITS - APBO (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
ABO for all defined benefit pension plans	$ 2,390.5	$ 2,257.9
Pension plans with the PBO in excess of plan assets
Projected benefit obligation	2,718.2	2,553.4
Fair value of plan assets	1,732.8	1,603.4
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated benefit obligation	2,390.5	2,257.9
Fair value of plan assets	1,732.8	1,603.4
Post-Retirement Benefits
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated benefit obligation	264.3	249.3
Fair value of plan assets	239.9	223.3
Evergy Metro | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
ABO for all defined benefit pension plans	1,170.2	1,096.7
Pension plans with the PBO in excess of plan assets
Projected benefit obligation	1,371.4	1,272.4
Fair value of plan assets	890.7	798.8
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated benefit obligation	1,170.2	1,096.7
Fair value of plan assets	890.7	798.8
Evergy Metro | Post-Retirement Benefits
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated benefit obligation	125.6	57.7
Fair value of plan assets	119.4	38.2
Evergy Kansas Central | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
ABO for all defined benefit pension plans	1,196.8	1,139.1
Pension plans with the PBO in excess of plan assets
Projected benefit obligation	1,323.4	1,258.9
Fair value of plan assets	842.1	804.6
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated benefit obligation	1,196.8	1,139.1
Fair value of plan assets	842.1	804.6
Evergy Kansas Central | Post-Retirement Benefits
Other post-retirement benefit plans with the APBO in excess of plan assets
Accumulated benefit obligation	138.7	133.6
Fair value of plan assets	$ 120.5	$ 109.7