PENSION PLANS AND POST-RETIREMENT BENEFITS - Schedule of Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 19.6	$ 19.1
Interest cost	24.4	27.5
Expected return on plan assets	(26.7)	(27.1)
Prior service cost	0.4	0.5
Recognized net actuarial (gain) loss	11.4	6.9
Net periodic benefit costs before regulatory adjustment and intercompany allocations	29.1	26.9
Regulatory adjustment	9.9	(0.1)
Intercompany allocations	0.0	0.0
Net periodic benefit costs	39.0	26.8
Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.7	0.6
Interest cost	2.3	2.6
Expected return on plan assets	(2.3)	(2.4)
Prior service cost	0.1	0.1
Recognized net actuarial (gain) loss	0.1	(0.3)
Net periodic benefit costs before regulatory adjustment and intercompany allocations	0.9	0.6
Regulatory adjustment	(0.9)	(0.7)
Intercompany allocations	0.0	0.0
Net periodic benefit costs	0.0	(0.1)
Evergy Kansas Central | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	6.8	7.3
Interest cost	11.8	13.4
Expected return on plan assets	(13.3)	(13.7)
Prior service cost	0.4	0.4
Recognized net actuarial (gain) loss	8.4	6.4
Net periodic benefit costs before regulatory adjustment and intercompany allocations	14.1	13.8
Regulatory adjustment	0.4	0.5
Intercompany allocations	0.0	0.0
Net periodic benefit costs	14.5	14.3
Evergy Kansas Central | Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.3	0.3
Interest cost	1.2	1.4
Expected return on plan assets	(1.7)	(1.7)
Prior service cost	0.1	0.1
Recognized net actuarial (gain) loss	0.0	(0.1)
Net periodic benefit costs before regulatory adjustment and intercompany allocations	(0.1)	0.0
Regulatory adjustment	(0.7)	(0.8)
Intercompany allocations	0.0	0.0
Net periodic benefit costs	(0.8)	(0.8)
Evergy Metro | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	12.8	11.8
Interest cost	12.6	14.1
Expected return on plan assets	(14.1)	(12.3)
Prior service cost	0.2	0.2
Recognized net actuarial (gain) loss	11.3	12.2
Net periodic benefit costs before regulatory adjustment and intercompany allocations	22.8	26.0
Regulatory adjustment	1.4	(0.6)
Intercompany allocations	(6.2)	(6.9)
Net periodic benefit costs	18.0	18.5
Evergy Metro | Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.4	0.3
Interest cost	1.1	1.2
Expected return on plan assets	(0.7)	(0.7)
Prior service cost	0.0	0.0
Recognized net actuarial (gain) loss	(0.1)	(0.4)
Net periodic benefit costs before regulatory adjustment and intercompany allocations	0.7	0.4
Regulatory adjustment	0.0	0.1
Intercompany allocations	0.2	(0.1)
Net periodic benefit costs	$ 0.9	$ 0.4