EQUITY COMPENSATION - Income Tax Benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	$ 15.5	$ 30.7	$ 8.9
Income tax benefit	3.0	1.4	3.5
Evergy Kansas Central
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	6.7	24.8	8.9
Income tax benefit	1.9	1.4	3.5
Evergy Metro
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity compensation expense	5.7	6.5	4.2
Income tax benefit	$ 0.3	$ 0.1	$ 1.6