SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Depreciation rates average	3.00%
Regulatory assets	$ 1,972.2	$ 2,061.8
Depreciation expense reflected in retail rates	$ 9.0
Minimum
Property, Plant and Equipment [Line Items]
Generating facilities	8 years
Transmission facilities	15 years
Distribution facilities	8 years
Other	5 years
Maximum
Property, Plant and Equipment [Line Items]
Generating facilities	87 years
Transmission facilities	94 years
Distribution facilities	73 years
Other	84 years
Evergy Kansas Central
Property, Plant and Equipment [Line Items]
Regulatory assets	$ 823.7	797.5
Evergy Kansas Central | Minimum
Property, Plant and Equipment [Line Items]
Generating facilities	8 years
Transmission facilities	36 years
Distribution facilities	19 years
Other	7 years
Evergy Kansas Central | Maximum
Property, Plant and Equipment [Line Items]
Generating facilities	87 years
Transmission facilities	94 years
Distribution facilities	73 years
Other	84 years
Evergy Metro
Property, Plant and Equipment [Line Items]
Regulatory assets	$ 559.8	626.1
Evergy Metro | Minimum
Property, Plant and Equipment [Line Items]
Generating facilities	20 years
Transmission facilities	15 years
Distribution facilities	8 years
Other	5 years
Evergy Metro | Maximum
Property, Plant and Equipment [Line Items]
Generating facilities	60 years
Transmission facilities	70 years
Distribution facilities	55 years
Other	50 years
Retired Generation Facilities
Property, Plant and Equipment [Line Items]
Regulatory assets	$ 130.5	159.9
Retired Generation Facilities | Evergy Kansas Central
Property, Plant and Equipment [Line Items]
Regulatory assets	0.0	0.0
Retired Generation Facilities | Evergy Metro
Property, Plant and Equipment [Line Items]
Regulatory assets	$ 0.0	$ 0.0