ORGANIZATION AND BASIS OF PRESENTATION - Summary of Property, Plant and Equipment (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	$ 19,624.1	$ 19,184.4
Electric plant in service
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	28,670.5	27,768.8
Property, plant and equipment, adjustment	724.3	740.6
Accumulated depreciation	(10,849.4)	(10,293.7)
Property, plant and equipment, net	18,545.4	18,215.7
Construction work in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	946.6	839.2
Nuclear fuel, net
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	131.2	128.5
Plant to be retired, net
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	0.9	1.0
Evergy Kansas Central
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	10,054.8	9,864.9
Evergy Kansas Central | Electric plant in service
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	13,947.2	13,538.1
Property, plant and equipment, adjustment	724.3	740.6
Accumulated depreciation	(5,210.0)	(4,951.5)
Property, plant and equipment, net	9,461.5	9,327.2
Evergy Kansas Central | Construction work in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	527.1	472.8
Evergy Kansas Central | Nuclear fuel, net
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	65.3	63.9
Evergy Kansas Central | Plant to be retired, net
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	0.9	1.0
Evergy Metro
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	7,027.1	6,839.0
Evergy Metro | Electric plant in service
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	11,110.9	10,776.5
Property, plant and equipment, adjustment	0.0	0.0
Accumulated depreciation	(4,487.3)	(4,272.0)
Property, plant and equipment, net	6,623.6	6,504.5
Evergy Metro | Construction work in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	337.6	269.9
Evergy Metro | Nuclear fuel, net
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	65.9	64.6
Evergy Metro | Plant to be retired, net
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net	$ 0.0	$ 0.0