SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash paid for (received from):
Interest on financing activities, net of amount capitalized	$ 329.5	$ 255.9	$ 153.9
Income taxes, net of refunds	(5.2)	(0.9)	(12.7)
Non-cash investing transactions:
Property, plant and equipment additions (reductions)	186.0	(7.8)	158.8
Deconsolidation of property, plant and equipment of VIE	0.0	0.0	(72.9)
Non-cash financing transactions:
Issuance of stock for compensation and reinvested dividends	(0.3)	0.5	5.1
Deconsolidation of VIE	0.0	0.0	(83.1)
Evergy Kansas Central
Cash paid for (received from):
Interest on financing activities, net of amount capitalized	143.0	155.3	153.9
Income taxes, net of refunds	29.9	37.5	(12.7)
Non-cash investing transactions:
Property, plant and equipment additions (reductions)	92.1	(32.5)	158.8
Non-cash financing transactions:
Issuance of stock for compensation and reinvested dividends	0.0	0.0	5.1
Deconsolidation of VIE	0.0	0.0	(83.1)
Evergy Metro
Cash paid for (received from):
Interest on financing activities, net of amount capitalized	118.4	129.4	128.0
Income taxes, net of refunds	77.0	31.2	38.8
Non-cash investing transactions:
Property, plant and equipment additions (reductions)	80.7	19.2	36.6
Variable Interest Entities
Cash paid for (received from):
Interest on financing activities of VIEs	1.6	2.3	3.1
Variable Interest Entities | Evergy Kansas Central
Cash paid for (received from):
Interest on financing activities of VIEs	1.6	2.3	3.1
Non-cash investing transactions:
Deconsolidation of property, plant and equipment of VIE	$ 0.0	$ 0.0	$ (72.9)