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MERGER OF GREAT PLAINS ENERGY AND EVERGY KANSAS CENTRAL - Narrative (Details)
$ in Millions
12 Months Ended
Jun. 04, 2018
Dec. 31, 2018
USD ($)
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  
Revenue of acquiree since acquisition   $ 1,661.1
Earnings or loss of acquiree since acquisition date, actual   236.2
Merger-related costs   $ 148.0