EQUITY COMPENSATION - Income Tax Benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	$ 15.5	$ 15.5	$ 30.7
Income tax benefit	2.2	3.0	1.4
Evergy Kansas Central
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	7.6	6.7	24.8
Income tax benefit	1.6	1.9	1.4
Evergy Metro
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	5.7	5.7	6.5
Income tax benefit	$ 0.2	$ 0.3	$ 0.1