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PENSION PLANS AND POST-RETIREMENT BENEFITS - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Settlement and special termination benefits	$ 30.4	$ 10.0	$ 30.4	$ 10.0
Contributions by employer			41.7
Contributions to plans remainder of year	68.2		68.2
Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Settlement and special termination benefits	0.0	0.0	0.0	0.0
Contributions by employer			1.2
Contributions to plans remainder of year	3.7		3.7
Evergy Kansas Central \| Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Settlement and special termination benefits	22.5	0.0	22.5	0.0
Contributions by employer			26.2
Contributions to plans remainder of year	11.1		11.1
Evergy Kansas Central \| Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Settlement and special termination benefits	0.0	0.0	0.0	0.0
Contributions by employer			0.6
Contributions to plans remainder of year	0.5		0.5
Evergy Metro \| Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Settlement and special termination benefits	12.5	12.7	12.5	12.7
Contributions by employer			15.5
Contributions to plans remainder of year	57.1		57.1
Evergy Metro \| Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Settlement and special termination benefits	0.0	$ 0.0	0.0	$ 0.0
Contributions by employer			0.6
Contributions to plans remainder of year	$ 3.2		$ 3.2
Wolf Creek
Defined Benefit Plan Disclosure [Line Items]
Jointly owned utility plant, proportionate ownership share	94.00%		94.00%
Wolf Creek \| Evergy Kansas South Inc
Defined Benefit Plan Disclosure [Line Items]
Jointly owned utility plant, proportionate ownership share	47.00%		47.00%
Wolf Creek \| Evergy Metro
Defined Benefit Plan Disclosure [Line Items]
Jointly owned utility plant, proportionate ownership share	47.00%		47.00%