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, 2020	Dec. 31, 2019	Dec. 31, 2018
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	$ (0.6)	$ 47.0	$ 3.0
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	78.9	79.1	60.7
Interest cost	96.8	108.0	82.5
Expected return on plan assets	(105.6)	(106.3)	(86.4)
Prior service cost	1.8	1.9	0.7
Recognized net actuarial (gain) loss	46.4	33.0	32.6
Settlement and special termination benefits	11.2	15.6
Net periodic benefit costs before regulatory adjustment and intercompany allocations	129.5	131.3	90.1
Regulatory adjustment	29.6	37.4	8.3
Net periodic benefit costs (income)	159.1	168.7	98.4
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	112.8	34.2	47.3
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	271.9	202.9	145.7
Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	2.7	2.5	2.3
Interest cost	9.2	10.5	8.0
Expected return on plan assets	(9.3)	(10.0)	(8.8)
Prior service cost	0.5	0.5	0.5
Recognized net actuarial (gain) loss	0.2	(1.2)	(0.6)
Settlement and special termination benefits	0.0	0.0
Net periodic benefit costs before regulatory adjustment and intercompany allocations	3.3	2.3	1.4
Regulatory adjustment	(4.0)	(3.4)	(1.7)
Net periodic benefit costs (income)	(0.7)	(1.1)	(0.3)
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	8.4	1.6	5.0
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	7.7	0.5	4.7
Evergy Kansas Central | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	27.1	29.0	32.2
Interest cost	47.0	53.7	50.7
Expected return on plan assets	(53.1)	(54.8)	(55.9)
Prior service cost	1.6	1.7	0.7
Recognized net actuarial (gain) loss	33.9	25.5	32.6
Settlement and special termination benefits	0.0	0.0
Net periodic benefit costs before regulatory adjustment and intercompany allocations	56.5	55.1	60.3
Regulatory adjustment	5.9	3.0	8.8
Intercompany allocations	(0.2)	0.0	0.0
Net periodic benefit costs (income)	62.2	58.1	69.1
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	53.1	17.4	(35.1)
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	115.3	75.5	34.0
Evergy Kansas Central | Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.1	1.1	1.3
Interest cost	4.8	5.6	5.0
Expected return on plan assets	(6.6)	(6.7)	(7.0)
Prior service cost	0.5	0.5	0.5
Recognized net actuarial (gain) loss	0.0	(0.6)	(0.6)
Settlement and special termination benefits	0.0	0.0
Net periodic benefit costs before regulatory adjustment and intercompany allocations	(0.2)	(0.1)	(0.8)
Regulatory adjustment	(3.0)	(3.0)	(2.0)
Intercompany allocations	0.1	0.0	0.0
Net periodic benefit costs (income)	(3.1)	(3.1)	(2.8)
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	3.9	(3.7)	11.8
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	0.8	(6.8)	9.0
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	0.2	(0.7)	(3.7)
Evergy Metro | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	51.8	50.1	48.6
Interest cost	49.1	53.3	49.9
Expected return on plan assets	(54.7)	(48.9)	(55.5)
Prior service cost	0.8	0.9	0.7
Recognized net actuarial (gain) loss	45.7	49.8	45.1
Settlement and special termination benefits	14.3	23.0
Net periodic benefit costs before regulatory adjustment and intercompany allocations	107.0	128.2	88.8
Regulatory adjustment	(11.6)	(19.2)	0.7
Intercompany allocations	(22.6)	(34.4)	(21.6)
Net periodic benefit costs (income)	72.8	74.6	67.9
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	24.6	(37.8)	(17.9)
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	97.4	36.8	50.0
Evergy Metro | Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.6	1.4	2.0
Interest cost	4.4	4.9	4.8
Expected return on plan assets	(2.7)	(3.3)	(2.8)
Prior service cost	0.0	0.0	0.1
Recognized net actuarial (gain) loss	(0.6)	(1.4)	(0.2)
Settlement and special termination benefits	0.0	0.0
Net periodic benefit costs before regulatory adjustment and intercompany allocations	2.7	1.6	3.9
Regulatory adjustment	(0.2)	0.4	(0.1)
Intercompany allocations	(0.3)	(0.4)	(1.1)
Net periodic benefit costs (income)	2.2	1.6	2.7
Other changes in plan assets and benefit obligations recognized in OCI or regulatory assets/liabilities
Total recognized in OCI or regulatory asset/liability	5.3	6.1	(13.9)
Total recognized in net periodic benefit costs and OCI or regulatory asset/liability	7.5	7.7	(11.2)
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, Net of Tax	169.7	84.7	67.2
Amounts reclassified from accumulated other comprehensive loss	(59.2)	(48.6)	(32.6)
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, Net of Tax	8.2	0.9	4.9
Amounts reclassified from accumulated other comprehensive loss	(0.2)	1.2	0.6
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, Net of Tax	80.4	44.6	(13.2)
Amounts reclassified from accumulated other comprehensive loss	(33.8)	(25.5)	(32.6)
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, Net of Tax	3.9	(3.8)	11.7
Amounts reclassified from accumulated other comprehensive loss	0.0	0.6	0.6
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, Net of Tax	89.3	35.9	25.9
Amounts reclassified from accumulated other comprehensive loss	(60.0)	(72.8)	(45.1)
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, Net of Tax	4.3	4.7	(14.0)
Amounts reclassified from accumulated other comprehensive loss	0.6	1.4	0.2
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, Net of Tax	(4.1)		13.4
Amounts reclassified from accumulated other comprehensive loss	(1.8)	(1.9)	(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, Net of Tax	(0.9)		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, Net of Tax	(8.1)		11.4
Amounts reclassified from accumulated other comprehensive loss	(1.6)	(1.7)	(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, Net of Tax	(0.5)		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, Net of Tax	3.9		2.0
Amounts reclassified from accumulated other comprehensive loss	(0.8)	(0.9)	(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, Net of Tax	(0.4)		0.0
Amounts reclassified from accumulated other comprehensive loss	$ 0.0	$ 0.0	$ (0.1)