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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) |

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