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DERIVATIVE INSTRUMENTS - DERIVATIVE ASSETS AND LIABILITIES (Details) - USD ($) $ in Millions | Jun. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Derivative Asset |  |
Other current derivative assets | $ 23.2 | $ 11.8
Other long-term derivative assets | 0.5 | 0.6
Derivative asset | 23.7 | 12.4
Derivative Liability |  |
Other current derivative liabilities | 2.1 | 10.0
Other long-term derivative liabilities | 0.5 | 1.6
Derivative liability | 2.6 | 11.6
Natural gas contracts |  |
Derivative Asset |  |
Other current derivative assets | 5.6 | 5.6
Other long-term derivative assets | 0.4 | 0.1
Derivative Liability |  |
Other current derivative liabilities | 1.8 | 9.4
Other long-term derivative liabilities | 0.5 | 1.4
Petroleum products contracts |  |
Derivative Asset |  |
Other current derivative assets | 0.4 | 1.2
Derivative Liability |  |
Other current derivative liabilities | 0.0 | 0.0
FTRs |  |
Derivative Asset |  |
Other current derivative assets | 16.7 | 4.4
Derivative Liability |  |
Other current derivative liabilities | 0.0 | 0.0
Coal contracts |  |
Derivative Asset |  |
Other current derivative assets | 0.5 | 0.6
Other long-term derivative assets | 0.1 | 0.5
Derivative Liability |  |
Other current derivative liabilities | 0.3 | 0.6
Other long-term derivative liabilities | $ 0.0 | $ 0.2

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