ORGANIZATION AND BASIS OF PRESENTATION - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Income
Net income	$ 367.5	$ 136.3	$ 72.2	$ 370.9	$ 144.6	$ 103.4	$ 576.0	$ 618.9
Less: Net income attributable to noncontrolling interests	3.0			4.1			8.7	12.9
Net income attributable to Evergy, Inc.	$ 364.5			$ 366.8			$ 567.3	$ 606.0
Common Shares Outstanding
Weighted average equivalent common shares outstanding - basic (in shares)	227.3			234.6			227.2	243.5
Add: effect of dilutive securities (in shares)	0.2			0.4			0.3	0.3
Diluted average number of common shares outstanding (in shares)	227.5			235.0			227.5	243.8
Earnings Per Share, Basic	$ 1.60			$ 1.56			$ 2.50	$ 2.49
Earnings Per Share, Diluted	$ 1.60			$ 1.56			$ 2.49	$ 2.49