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COMMITMENTS AND CONTINGENCIES - Contingencies (Details) - USD ($) $ in Millions | Jun. 30, 2020 | Dec. 31, 2019
--- | --- | ---
Loss Contingencies [Line Items] |  |
Environmental obligations | $ 41.4 | $ 2.0
Less current portion | 6.5 | 0.3
Long-term environmental obligations | 34.9 | $ 1.7
Hamilton Plant [Member] |  |
Loss Contingencies [Line Items] |  |
Environmental obligations | 0.7 |
Ashland Works Coke Plant [Member] |  |
Loss Contingencies [Line Items] |  |
Environmental obligations | $ 1.4 |

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