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FAIR VALUE MEASUREMENTS - NAV (Details) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2019 USD ($) fund extension | Dec. 31, 2018 USD ($)
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Unfunded Commitments | $ 4.0 | $ 4.3
Westar Energy | Alternative investments fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Unfunded Commitments | $ 0.0 | 0.0
Length of Settlement | 65 days |
Westar Energy | Real estate securities fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Unfunded Commitments | $ 0.0 | 0.0
Length of Settlement | 65 days |
Westar Energy | Nuclear decommissioning trust: |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | $ 41.8 |
Unfunded Commitments | 4.0 | 4.3
Westar Energy | Core bond fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Unfunded Commitments | 0.0 | 0.0
Westar Energy | Combination debt/equity/other fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Unfunded Commitments | 0.0 | 0.0
Westar Energy | Rabbi trust: |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Unfunded Commitments | 0.0 | 0.0
Other Evergy |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Unfunded Commitments | 0.0 | 0.0
Domestic | Westar Energy | Equity securities |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Unfunded Commitments | $ 4.0 | 4.3
NAV, Number of funds | fund | 5 |
NAV, Number of funds making distributions | fund | 3 |
Domestic | Westar Energy | Equity Securities - Fourth Fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Length of Settlement | 15 years |
NAV, Extension term | 1 year |
NAV, Number of extensions | extension | 3 |
Domestic | Westar Energy | Equity Securities - Fifth Fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Length of Settlement | 15 years |
Fair Value, Measurements, Recurring |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | $ 518.3 | 472.1
Total rabbi trust | 44.6 | 43.8
Total Assets | 575.5 | 528.3
Fair Value, Measurements, Recurring | Westar Energy |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | 248.4 | 227.5
Total rabbi trust | 31.1 | 30.6
Total Assets | 279.5 | 258.1
Fair Value, Measurements, Recurring | Westar Energy | Alternative investments fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | 23.3 | 24.1
Fair Value, Measurements, Recurring | Westar Energy | Real estate securities fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | 12.0 | 11.8
Fair Value, Measurements, Recurring | Westar Energy | Core bond fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | 34.6 | 37.5
Total rabbi trust | 24.7 | 24.8
Fair Value, Measurements, Recurring | Westar Energy | Combination debt/equity/other fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | 14.7 | 12.9
Total rabbi trust | 6.2 | 5.6
Fair Value, Measurements, Recurring | Other Evergy |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total rabbi trust | 13.5 | 13.2
Fair Value, Measurements, Recurring | Domestic | Westar Energy | Equity securities |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | 80.1 | 70.6
NAV | Fair Value, Measurements, Recurring |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | 41.8 | 42.6
Total rabbi trust | 44.0 | 43.6
Total Assets | 85.8 | 86.2
NAV | Fair Value, Measurements, Recurring | Westar Energy |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | 41.8 | 42.6
Total rabbi trust | 30.9 | 30.4
Total Assets | 72.7 | 73.0
NAV | Fair Value, Measurements, Recurring | Westar Energy | Alternative investments fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | 23.3 | 24.1
NAV | Fair Value, Measurements, Recurring | Westar Energy | Real estate securities fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | 12.0 | 11.8
NAV | Fair Value, Measurements, Recurring | Westar Energy | Nuclear decommissioning trust: |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust |  | 42.6
NAV | Fair Value, Measurements, Recurring | Westar Energy | Core bond fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 24.7 | 24.8
NAV | Fair Value, Measurements, Recurring | Westar Energy | Combination debt/equity/other fund |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | 0.0 | 0.0
Total rabbi trust | 6.2 | 5.6
NAV | Fair Value, Measurements, Recurring | Westar Energy | Rabbi trust: |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total rabbi trust | 30.9 | 30.4
NAV | Fair Value, Measurements, Recurring | Other Evergy |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total rabbi trust | 13.1 | 13.2
NAV | Fair Value, Measurements, Recurring | Domestic | Westar Energy | Equity securities |  |
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items] |  |
Total nuclear decommissioning trust | $ 6.5 | $ 6.7

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