PENSION PLANS AND POST-RETIREMENT BENEFITS PENSION PLANS AND POST-RETIREMENT BENEFITS - Schedule of Components of Net Periodic Benefit Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	$ 47.0	$ 3.0	$ 0.0
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	79.1	60.7	28.7
Interest cost	108.0	82.5	52.4
Expected return on plan assets	(106.3)	(86.4)	(53.6)
Prior service cost	1.9	0.7	0.7
Recognized net actuarial (gain) loss	33.0	32.6	26.9
Settlement and special termination benefits	15.6		0.4
Net periodic benefit costs before regulatory adjustment and intercompany allocations	131.3	90.1	55.5
Regulatory adjustment	37.4	8.3	14.5
Net periodic benefit costs	168.7	98.4	70.0
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	34.2	47.3	19.5
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	202.9	145.7	89.5
Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2.5	2.3	1.2
Interest cost	10.5	8.0	5.5
Expected return on plan assets	(10.0)	(8.8)	(6.9)
Prior service cost	0.5	0.5	0.5
Recognized net actuarial (gain) loss	(1.2)	(0.6)	(0.8)
Settlement and special termination benefits	0.0		0.0
Net periodic benefit costs before regulatory adjustment and intercompany allocations	2.3	1.4	(0.5)
Regulatory adjustment	(3.4)	(1.7)	(1.9)
Net periodic benefit costs	(1.1)	(0.3)	(2.4)
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	1.6	5.0	(5.5)
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	0.5	4.7	(7.9)
Evergy Kansas Central | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	29.0	32.2	28.7
Interest cost	53.7	50.7	52.4
Expected return on plan assets	(54.8)	(55.9)	(53.6)
Prior service cost	1.7	0.7	0.7
Recognized net actuarial (gain) loss	25.5	32.6	26.9
Settlement and special termination benefits	0.0		0.4
Net periodic benefit costs before regulatory adjustment and intercompany allocations	55.1	60.3	55.5
Regulatory adjustment	3.0	8.8	14.5
Intercompany allocations	0.0	0.0	0.0
Net periodic benefit costs	58.1	69.1	70.0
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	17.4	(35.1)	19.5
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	75.5	34.0	89.5
Evergy Kansas Central | Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.1	1.3	1.2
Interest cost	5.6	5.0	5.5
Expected return on plan assets	(6.7)	(7.0)	(6.9)
Prior service cost	0.5	0.5	0.5
Recognized net actuarial (gain) loss	(0.6)	(0.6)	(0.8)
Settlement and special termination benefits	0.0		0.0
Net periodic benefit costs before regulatory adjustment and intercompany allocations	(0.1)	(0.8)	(0.5)
Regulatory adjustment	(3.0)	(2.0)	(1.9)
Intercompany allocations	0.0	0.0	0.0
Net periodic benefit costs	(3.1)	(2.8)	(2.4)
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	(3.7)	11.8	(5.5)
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	(6.8)	9.0	(7.9)
Evergy Metro
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	(0.7)	(3.7)	(4.6)
Evergy Metro | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	50.1	48.6	44.2
Interest cost	53.3	49.9	52.6
Expected return on plan assets	(48.9)	(55.5)	(51.2)
Prior service cost	0.9	0.7	0.7
Recognized net actuarial (gain) loss	49.8	45.1	49.0
Settlement and special termination benefits	23.0		16.3
Net periodic benefit costs before regulatory adjustment and intercompany allocations	128.2	88.8	111.6
Regulatory adjustment	(19.2)	0.7	(9.2)
Intercompany allocations	(34.4)	(21.6)	(37.1)
Net periodic benefit costs	74.6	67.9	65.3
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	(37.8)	(17.9)	5.7
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	36.8	50.0	71.0
Evergy Metro | Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.4	2.0	2.1
Interest cost	4.9	4.8	5.4
Expected return on plan assets	(3.3)	(2.8)	(2.5)
Prior service cost	0.0	0.1	0.0
Recognized net actuarial (gain) loss	(1.4)	(0.2)	(0.5)
Settlement and special termination benefits	0.0		0.0
Net periodic benefit costs before regulatory adjustment and intercompany allocations	1.6	3.9	4.5
Regulatory adjustment	0.4	(0.1)	1.3
Intercompany allocations	(0.4)	(1.1)	(1.5)
Net periodic benefit costs	1.6	2.7	4.3
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	6.1	(13.9)	3.5
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	7.7	(11.2)	7.8
Actuarial (gain) loss | Pension Benefits
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Other comprehensive income (loss) before reclassifications	84.7	67.2	47.1
Amounts reclassified from accumulated other comprehensive loss	(48.6)	(32.6)	(26.9)
Actuarial (gain) loss | Post-Retirement Benefits
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Other comprehensive income (loss) before reclassifications	0.9	4.9	(5.8)
Amounts reclassified from accumulated other comprehensive loss	1.2	0.6	0.8
Actuarial (gain) loss | Evergy Kansas Central | Pension Benefits
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Other comprehensive income (loss) before reclassifications	44.6	(13.2)	47.1
Amounts reclassified from accumulated other comprehensive loss	(25.5)	(32.6)	(26.9)
Actuarial (gain) loss | Evergy Kansas Central | Post-Retirement Benefits
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Other comprehensive income (loss) before reclassifications	(3.8)	11.7	(5.8)
Amounts reclassified from accumulated other comprehensive loss	0.6	0.6	0.8
Actuarial (gain) loss | Evergy Metro | Pension Benefits
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Other comprehensive income (loss) before reclassifications	35.9	25.9	71.3
Amounts reclassified from accumulated other comprehensive loss	(72.8)	(45.1)	(64.9)
Actuarial (gain) loss | Evergy Metro | Post-Retirement Benefits
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Other comprehensive income (loss) before reclassifications	4.7	(14.0)	3.0
Amounts reclassified from accumulated other comprehensive loss	1.4	0.2	0.5
Prior service cost | Pension Benefits
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Other comprehensive income (loss) before reclassifications		13.4
Amounts reclassified from accumulated other comprehensive loss	(1.9)	(0.7)	(0.7)
Prior service cost | Post-Retirement Benefits
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Other comprehensive income (loss) before reclassifications		0.0
Amounts reclassified from accumulated other comprehensive loss	(0.5)	(0.5)	(0.5)
Prior service cost | Evergy Kansas Central | Pension Benefits
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Other comprehensive income (loss) before reclassifications		11.4
Amounts reclassified from accumulated other comprehensive loss	(1.7)	(0.7)	(0.7)
Prior service cost | Evergy Kansas Central | Post-Retirement Benefits
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Other comprehensive income (loss) before reclassifications		0.0
Amounts reclassified from accumulated other comprehensive loss	(0.5)	(0.5)	(0.5)
Prior service cost | Evergy Metro | Pension Benefits
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Other comprehensive income (loss) before reclassifications		2.0
Amounts reclassified from accumulated other comprehensive loss	(0.9)	(0.7)	(0.7)
Prior service cost | Evergy Metro | Post-Retirement Benefits
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Other comprehensive income (loss) before reclassifications		0.0
Amounts reclassified from accumulated other comprehensive loss	$ 0.0	$ (0.1)	$ 0.0