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RATE MATTERS AND REGULATION - Regulatory Matters Asset (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Regulatory Assets [Line Items] |  |
Regulatory Assets | $ 2,074.4 | $ 1,972.2
Less: current portion | (206.2) | (231.7)
Total noncurrent regulatory assets | 1,868.2 | 1,740.5
Pension and post-retirement costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 867.8 | 795.9
Debt reacquisition costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 98.9 | 105.8
Debt fair value adjustment |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 104.0 | 112.0
Asset retirement obligations fair value adjustment |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 116.2 | 114.3
Depreciation |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 70.0 | 55.3
Cost of removal |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 183.4 | 129.3
Asset retirement obligations |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 170.8 | 167.1
Analog meter unrecovered investment |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 24.1 | 29.9
Treasury yield hedges |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 21.5 | 22.6
Iatan No. 1 and common facilities |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 6.9 | 7.1
Iatan No. 2 construction accounting costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 25.4 | 26.1
Kansas property tax surcharge |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 28.9 | 21.7
Disallowed plant costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 14.5 | 14.8
La Cygne environmental costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 12.4 | 13.7
Deferred customer programs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 16.3 | 18.0
Fuel recovery mechanisms |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 26.2 | 34.7
Solar rebates |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 25.9 | 39.8
Wolf Creek outage |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 10.0 | 31.0
Pension and other post-retirement benefit non-service costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 49.8 | 31.8
Retired generation facilities |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 128.4 | 130.5
Merger transition costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 37.6 | 42.3
Other regulatory liabilities |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 35.4 | 28.5
Evergy Kansas Central |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 896.3 | 823.7
Less: current portion | (96.2) | (93.3)
Total noncurrent regulatory assets | 800.1 | 730.4
Evergy Kansas Central | Pension and post-retirement costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 412.9 | 359.9
Evergy Kansas Central | Debt reacquisition costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 91.3 | 97.3
Evergy Kansas Central | Debt fair value adjustment |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 0.0 | 0.0
Evergy Kansas Central | Asset retirement obligations fair value adjustment |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 0.0 | 0.0
Evergy Kansas Central | Depreciation |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 52.7 | 55.3
Evergy Kansas Central | Cost of removal |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 125.7 | 94.4
Evergy Kansas Central | Asset retirement obligations |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 55.0 | 52.8
Evergy Kansas Central | Analog meter unrecovered investment |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 24.1 | 29.9
Evergy Kansas Central | Treasury yield hedges |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 21.5 | 22.6
Evergy Kansas Central | Iatan No. 1 and common facilities |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 0.0 | 0.0
Evergy Kansas Central | Iatan No. 2 construction accounting costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 0.0 | 0.0
Evergy Kansas Central | Kansas property tax surcharge |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 23.7 | 18.7
Evergy Kansas Central | Disallowed plant costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 14.5 | 14.8
Evergy Kansas Central | La Cygne environmental costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 10.1 | 11.2
Evergy Kansas Central | Deferred customer programs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 5.7 | 6.2
Evergy Kansas Central | Fuel recovery mechanisms |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 1.2 | 0.0
Evergy Kansas Central | Solar rebates |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 0.0 | 0.0
Evergy Kansas Central | Wolf Creek outage |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 5.0 | 15.5
Evergy Kansas Central | Pension and other post-retirement benefit non-service costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 12.8 | 7.4
Evergy Kansas Central | Retired generation facilities |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 0.0 | 0.0
Evergy Kansas Central | Merger transition costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 18.0 | 20.3
Evergy Kansas Central | Other regulatory liabilities |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 22.1 | 17.4
Evergy Metro |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 615.5 | 559.8
Less: current portion | (82.0) | (95.4)
Total noncurrent regulatory assets | 533.5 | 464.4
Evergy Metro | Pension and post-retirement costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 359.9 | 330.7
Evergy Metro | Debt reacquisition costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 6.8 | 7.5
Evergy Metro | Debt fair value adjustment |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 0.0 | 0.0
Evergy Metro | Asset retirement obligations fair value adjustment |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 0.0 | 0.0
Evergy Metro | Depreciation |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 9.4 | 0.0
Evergy Metro | Cost of removal |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 57.7 | 34.9
Evergy Metro | Asset retirement obligations |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 84.0 | 79.4
Evergy Metro | Analog meter unrecovered investment |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 0.0 | 0.0
Evergy Metro | Treasury yield hedges |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 0.0 | 0.0
Evergy Metro | Iatan No. 1 and common facilities |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 2.8 | 2.8
Evergy Metro | Iatan No. 2 construction accounting costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 12.7 | 13.1
Evergy Metro | Kansas property tax surcharge |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 5.2 | 3.0
Evergy Metro | Disallowed plant costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 0.0 | 0.0
Evergy Metro | La Cygne environmental costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 2.3 | 2.5
Evergy Metro | Deferred customer programs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 8.6 | 8.3
Evergy Metro | Fuel recovery mechanisms |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 17.7 | 16.6
Evergy Metro | Solar rebates |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 1.5 | 9.0
Evergy Metro | Wolf Creek outage |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 5.0 | 15.5
Evergy Metro | Pension and other post-retirement benefit non-service costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 23.4 | 15.6
Evergy Metro | Retired generation facilities |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 0.0 | 0.0
Evergy Metro | Merger transition costs |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 13.9 | 15.6
Evergy Metro | Other regulatory liabilities |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | $ 4.6 | $ 5.3

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