PENSION PLANS AND POST-RETIREMENT BENEFITS - Schedule of Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 20.1	$ 19.1	$ 59.2	$ 57.3
Interest cost	24.0	27.5	72.9	82.4
Expected return on plan assets	(26.3)	(27.0)	(79.7)	(80.9)
Prior service cost	0.4	0.5	1.3	1.5
Recognized net actuarial (gain) loss	12.1	6.9	34.8	20.6
Settlement and special termination benefits	10.0	14.5	10.0	14.5
Net periodic benefit costs before regulatory adjustment and intercompany allocations	40.3	41.5	98.5	95.4
Regulatory adjustment	(0.4)	4.9	18.6	30.4
Intercompany allocations	0.0	0.0	0.0	0.0
Net periodic benefit costs	39.9	46.4	117.1	125.8
Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.7	0.6	2.1	1.9
Interest cost	2.3	2.6	6.9	7.9
Expected return on plan assets	(2.4)	(2.5)	(7.0)	(7.5)
Prior service cost	0.1	0.1	0.3	0.3
Recognized net actuarial (gain) loss	0.1	(0.3)	0.2	(0.9)
Settlement and special termination benefits	0.0	0.0	0.0	0.0
Net periodic benefit costs before regulatory adjustment and intercompany allocations	0.8	0.5	2.5	1.7
Regulatory adjustment	(1.0)	(0.8)	(2.9)	(2.5)
Intercompany allocations	0.0	0.0	0.0	0.0
Net periodic benefit costs	(0.2)	(0.3)	(0.4)	(0.8)
Evergy Kansas Central | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	6.8	7.3	20.4	21.8
Interest cost	11.7	13.4	35.2	40.3
Expected return on plan assets	(13.3)	(13.7)	(39.9)	(41.1)
Prior service cost	0.4	0.5	1.2	1.3
Recognized net actuarial (gain) loss	8.5	6.2	25.4	19.0
Settlement and special termination benefits	0.0	0.0	0.0	0.0
Net periodic benefit costs before regulatory adjustment and intercompany allocations	14.1	13.7	42.3	41.3
Regulatory adjustment	0.4	0.5	1.1	1.5
Intercompany allocations	1.6	0.0	(0.1)	0.0
Net periodic benefit costs	16.1	14.2	43.3	42.8
Evergy Kansas Central | Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.3	0.2	0.9	0.8
Interest cost	1.2	1.4	3.6	4.2
Expected return on plan assets	(1.7)	(1.7)	(5.0)	(5.0)
Prior service cost	0.1	0.1	0.3	0.3
Recognized net actuarial (gain) loss	0.0	(0.1)	0.0	(0.4)
Settlement and special termination benefits	0.0	0.0	0.0	0.0
Net periodic benefit costs before regulatory adjustment and intercompany allocations	(0.1)	(0.1)	(0.2)	(0.1)
Regulatory adjustment	(0.7)	(0.7)	(2.1)	(2.2)
Intercompany allocations	0.1	0.0	0.1	0.0
Net periodic benefit costs	(0.7)	(0.8)	(2.2)	(2.3)
Evergy Metro | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	13.3	11.8	38.8	35.5
Interest cost	12.1	14.1	37.1	42.1
Expected return on plan assets	(13.5)	(12.3)	(41.5)	(36.9)
Prior service cost	0.2	0.2	0.6	0.7
Recognized net actuarial (gain) loss	11.6	12.2	34.2	36.7
Settlement and special termination benefits	12.7	20.8	12.7	20.8
Net periodic benefit costs before regulatory adjustment and intercompany allocations	36.4	46.8	81.9	98.9
Regulatory adjustment	(11.3)	(14.7)	(9.2)	(15.9)
Intercompany allocations	(5.8)	(13.6)	(17.0)	(27.6)
Net periodic benefit costs	19.3	18.5	55.7	55.4
Evergy Metro | Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.4	0.4	1.2	1.1
Interest cost	1.1	1.2	3.3	3.7
Expected return on plan assets	(0.7)	(0.8)	(2.0)	(2.5)
Prior service cost	0.0	0.0	0.0	0.0
Recognized net actuarial (gain) loss	(0.1)	(0.3)	(0.4)	(1.1)
Settlement and special termination benefits	0.0	0.0	0.0	0.0
Net periodic benefit costs before regulatory adjustment and intercompany allocations	0.7	0.5	2.1	1.2
Regulatory adjustment	(0.2)	0.1	(0.3)	0.3
Intercompany allocations	(0.1)	(0.2)	(0.1)	(0.3)
Net periodic benefit costs	$ 0.4	$ 0.4	$ 1.7	$ 1.2