PENSION PLANS AND POST-RETIREMENT BENEFITS PENSION PLANS AND POST-RETIREMENT BENEFITS - Schedule of Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 21.2	$ 19.5	$ 42.3	$ 39.1
Interest cost	21.3	24.5	42.6	48.9
Expected return on plan assets	(26.8)	(26.7)	(53.6)	(53.4)
Prior service cost	0.5	0.5	1.0	0.9
Recognized net actuarial (gain) loss	14.7	11.3	29.5	22.7
Net periodic benefit costs before regulatory adjustment and intercompany allocations	30.9	29.1	61.8	58.2
Regulatory adjustment	6.6	9.1	13.7	19.0
Intercompany allocations	0.0	0.0	0.0	0.0
Net periodic benefit costs (income)	37.5	38.2	75.5	77.2
Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.9	0.7	1.7	1.4
Interest cost	1.9	2.3	3.9	4.6
Expected return on plan assets	(2.2)	(2.3)	(4.4)	(4.6)
Prior service cost	0.2	0.1	0.3	0.2
Recognized net actuarial (gain) loss	0.3	0.0	0.6	0.1
Net periodic benefit costs before regulatory adjustment and intercompany allocations	1.1	0.8	2.1	1.7
Regulatory adjustment	(1.3)	(1.0)	(2.5)	(1.9)
Intercompany allocations	0.0	0.0	0.0	0.0
Net periodic benefit costs (income)	(0.2)	(0.2)	(0.4)	(0.2)
Evergy Kansas Central | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	7.5	6.8	14.9	13.6
Interest cost	10.4	11.7	20.7	23.5
Expected return on plan assets	(13.5)	(13.3)	(27.1)	(26.6)
Prior service cost	0.5	0.4	1.0	0.8
Recognized net actuarial (gain) loss	9.5	8.5	19.3	16.9
Net periodic benefit costs before regulatory adjustment and intercompany allocations	14.4	14.1	28.8	28.2
Regulatory adjustment	0.1	0.3	(0.8)	0.7
Intercompany allocations	0.8	(1.7)	1.2	(1.7)
Net periodic benefit costs (income)	15.3	12.7	29.2	27.2
Evergy Kansas Central | Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.4	0.3	0.8	0.6
Interest cost	1.0	1.2	2.0	2.4
Expected return on plan assets	(1.5)	(1.6)	(3.1)	(3.3)
Prior service cost	0.1	0.1	0.2	0.2
Recognized net actuarial (gain) loss	0.1	0.0	0.3	0.0
Net periodic benefit costs before regulatory adjustment and intercompany allocations	0.1	0.0	0.2	(0.1)
Regulatory adjustment	(0.8)	(0.7)	(1.6)	(1.4)
Intercompany allocations	0.0	0.0	0.0	0.0
Net periodic benefit costs (income)	(0.7)	(0.7)	(1.4)	(1.5)
Evergy Metro | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	13.7	12.7	27.4	25.5
Interest cost	10.8	12.4	21.6	25.0
Expected return on plan assets	(14.4)	(13.9)	(28.9)	(28.0)
Prior service cost	0.0	0.2	0.0	0.4
Recognized net actuarial (gain) loss	11.1	11.3	22.3	22.6
Net periodic benefit costs before regulatory adjustment and intercompany allocations	21.2	22.7	42.4	45.5
Regulatory adjustment	1.6	0.7	4.6	2.1
Intercompany allocations	(6.3)	(5.0)	(12.2)	(11.2)
Net periodic benefit costs (income)	16.5	18.4	34.8	36.4
Evergy Metro | Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.5	0.4	0.9	0.8
Interest cost	0.9	1.1	1.9	2.2
Expected return on plan assets	(0.6)	(0.6)	(1.3)	(1.3)
Prior service cost	(0.2)	0.0	(0.5)	0.0
Recognized net actuarial (gain) loss	(0.1)	(0.2)	(0.1)	(0.3)
Net periodic benefit costs before regulatory adjustment and intercompany allocations	0.5	0.7	0.9	1.4
Regulatory adjustment	0.0	(0.1)	0.1	(0.1)
Intercompany allocations	(0.1)	(0.2)	(0.2)	0.0
Net periodic benefit costs (income)	$ 0.4	$ 0.4	$ 0.8	$ 1.3