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RATE MATTERS AND REGULATION - Narrative (Details)
$ in Millions
1 Months Ended 12 Months Ended
May 31, 2020
USD ($)
Apr. 30, 2020
USD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Regulatory Proceedings [Line Items]        
Regulatory liabilities     $ 2,664.9 $ 2,311.6
Pension and post-retirement costs        
Regulatory Proceedings [Line Items]        
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided     806.3  
Regulatory asset representing differences between pension and post retirement costs for GAAP and for ratemaking     250.1  
Analog meter unrecovered investment        
Regulatory Proceedings [Line Items]        
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided     $ 15.8  
Regulatory Asset, Amortization Period     5 years  
Deferred Customer Programs [Member]        
Regulatory Proceedings [Line Items]        
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided     $ 10.6  
Kansas property tax surcharge        
Regulatory Proceedings [Line Items]        
Regulatory Asset, Amortization Period     1 year  
Fuel recovery mechanisms        
Regulatory Proceedings [Line Items]        
Regulatory Asset, Amortization Period     1 year  
Evergy Kansas Central        
Regulatory Proceedings [Line Items]        
Regulatory liabilities     $ 1,472.9 1,174.8
Evergy Kansas Central | Pension and post-retirement costs        
Regulatory Proceedings [Line Items]        
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided     412.9  
Regulatory asset representing differences between pension and post retirement costs for GAAP and for ratemaking     (27.5)  
Evergy Kansas Central | Analog meter unrecovered investment        
Regulatory Proceedings [Line Items]        
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided     $ 15.8  
Regulatory Asset, Amortization Period     5 years  
Evergy Metro        
Regulatory Proceedings [Line Items]        
Regulatory liabilities     $ 907.4 803.6
Evergy Metro | Pension and post-retirement costs        
Regulatory Proceedings [Line Items]        
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided     333.6  
Regulatory asset representing differences between pension and post retirement costs for GAAP and for ratemaking     137.6  
Evergy Metro | Deferred Customer Programs [Member]        
Regulatory Proceedings [Line Items]        
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided     8.6  
Revenues Probable Of Refund        
Regulatory Proceedings [Line Items]        
Regulatory liabilities     18.4 10.2
Revenues Probable Of Refund | Evergy Kansas Central        
Regulatory Proceedings [Line Items]        
Regulatory liabilities     0.0 0.0
Revenues Probable Of Refund | Evergy Metro        
Regulatory Proceedings [Line Items]        
Regulatory liabilities     0.0 0.0
Purchase power agreement        
Regulatory Proceedings [Line Items]        
Regulatory liabilities     $ 6.3 7.4
Regulatory Liability, Amortization Period     5 years  
Purchase power agreement | Evergy Kansas Central        
Regulatory Proceedings [Line Items]        
Regulatory liabilities     $ 6.3 7.4
Purchase power agreement | Evergy Metro        
Regulatory Proceedings [Line Items]        
Regulatory liabilities     0.0 0.0
Fuel recovery mechanisms        
Regulatory Proceedings [Line Items]        
Regulatory liabilities     $ 1.3 34.1
Regulatory Liability, Amortization Period     1 year  
Fuel recovery mechanisms | Evergy Kansas Central        
Regulatory Proceedings [Line Items]        
Regulatory liabilities     $ 0.0 30.2
Fuel recovery mechanisms | Evergy Metro        
Regulatory Proceedings [Line Items]        
Regulatory liabilities     $ 0.0 $ 0.0
La Cygne Station | Evergy Kansas South Inc        
Regulatory Proceedings [Line Items]        
VIE ownership percentage     50.00%  
Transmission delivery charge | Evergy Kansas Central | Kansas Corporation Commission        
Regulatory Proceedings [Line Items]        
Annual revenue increase (decrease) approved   $ 3.5    
Transmission delivery charge | Evergy Metro | Kansas Corporation Commission        
Regulatory Proceedings [Line Items]        
Annual revenue increase (decrease) approved $ (2.7)      
2018 Rate Case Proceedings | Evergy Kansas Central | Kansas Corporation Commission        
Regulatory Proceedings [Line Items]        
Refund percent on earnings over approved return on equity     0.50  
Approved return on equity, percentage     9.30%  
2018 Rate Case Proceedings | Evergy Metro | Kansas Corporation Commission        
Regulatory Proceedings [Line Items]        
Refund percent on earnings over approved return on equity     0.50  
Approved return on equity, percentage     9.30%  
2018 MPSC OPC MECG Petition        
Regulatory Proceedings [Line Items]        
Annual estimated loss contingency portion not accrued (up to)     $ 12.0  
2018 MPSC OPC MECG Petition | Revenues Probable Of Refund        
Regulatory Proceedings [Line Items]        
Regulatory liabilities     18.4  
FERC 2021 TFR Proceeding | Evergy Kansas Central | Federal Energy Regulatory Commission        
Regulatory Proceedings [Line Items]        
Annual transmissions revenue estimated amount of increase (decrease) over prior year     32.4  
FERC 2021 TFR Proceeding | Evergy Metro | Federal Energy Regulatory Commission        
Regulatory Proceedings [Line Items]        
Annual transmissions revenue estimated amount of increase (decrease) over prior year     (3.9)  
FERC 2020 TFR Proceeding | Evergy Kansas Central | Federal Energy Regulatory Commission        
Regulatory Proceedings [Line Items]        
Annual transmissions revenue estimated amount of increase (decrease) over prior year     6.8  
FERC 2020 TFR Proceeding | Evergy Metro | Federal Energy Regulatory Commission        
Regulatory Proceedings [Line Items]        
Annual transmissions revenue estimated amount of increase (decrease) over prior year     (1.7)  
FERC 2019 TFR Proceeding | Evergy Kansas Central | Federal Energy Regulatory Commission        
Regulatory Proceedings [Line Items]        
Annual transmissions revenue estimated amount of increase (decrease) over prior year     (11.2)  
FERC 2019 TFR Proceeding | Evergy Metro | Federal Energy Regulatory Commission        
Regulatory Proceedings [Line Items]        
Annual transmissions revenue estimated amount of increase (decrease) over prior year     $ (2.8)