MERGER OF GREAT PLAINS ENERGY AND EVERGY KANSAS CENTRAL - Narrative (Details) $ in Millions		1 Months Ended	12 Months Ended
	Jun. 04, 2018	May 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Anticipated Merger With Westar Energy, Inc. [Line Items]
Conversion ratio			0.5981
Merger Settlement Agreement | Kansas Corporation Commission
Anticipated Merger With Westar Energy, Inc. [Line Items]
One-time bill credits		$ 30.6
Additional bill credits		46.0
Additional bill credits, annual amount		11.5
Merger-related savings on current rate cases		$ 30.0
Return on equity refund		50.00%
Charitable contributions period		5 years
Merger transaction costs, recovery amount		$ 30.9
Merger Settlement Agreement | Missouri Public Service Commission
Anticipated Merger With Westar Energy, Inc. [Line Items]
One-time bill credits		$ 29.1
Charitable contributions period		5 years
Merger transaction costs, recovery amount		$ 16.9
One-time bill credits, period		120 days
Support to promote low-income weatherization, amount		$ 3.0
Support to promote low-income weatherization, period		10 years
Evergy Kansas Central | Merger Settlement Agreement | Kansas Corporation Commission
Anticipated Merger With Westar Energy, Inc. [Line Items]
One-time bill credits		$ 23.1
Additional bill credits, annual amount		8.7
Merger-related savings on current rate cases		$ 22.5
Base rate moratorium period		5 years
Merger transaction costs, recovery amount		$ 23.2
Evergy Metro | Merger Settlement Agreement | Kansas Corporation Commission
Anticipated Merger With Westar Energy, Inc. [Line Items]
One-time bill credits		7.5
Additional bill credits, annual amount		2.8
Merger-related savings on current rate cases		$ 7.5
Base rate moratorium period		5 years
Merger transaction costs, recovery amount		$ 7.7
Merger transaction costs, recovery period		10 years
Evergy Metro | Merger Settlement Agreement | Missouri Public Service Commission
Anticipated Merger With Westar Energy, Inc. [Line Items]
One-time bill credits		$ 14.9
Merger transaction costs, recovery amount		$ 9.7
Evergy Missouri West Inc | Merger Settlement Agreement | Kansas Corporation Commission
Anticipated Merger With Westar Energy, Inc. [Line Items]
Merger transaction costs, recovery period		10 years
Evergy Missouri West Inc | Merger Settlement Agreement | Missouri Public Service Commission
Anticipated Merger With Westar Energy, Inc. [Line Items]
One-time bill credits		$ 14.2
Merger transaction costs, recovery amount		$ 7.2
Evergy Kansas Central
Anticipated Merger With Westar Energy, Inc. [Line Items]
Conversion ratio	1
Great Plains Energy
Anticipated Merger With Westar Energy, Inc. [Line Items]
Conversion ratio	0.5981
Goodwill decrease from recognition of deferred tax assets			$ 2.3
Revenue of acquiree since acquisition				$ 1,661.1
Earnings or loss of acquiree since acquisition date, actual				236.2
Merger-related costs				$ 148.0	$ 11.9