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Derivative Financial Instruments - Schedule of Gains (Losses) on Derivatives and Current Period Settlements (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]        
Current period settlements on derivative contracts $ (0.1) $ 7.1 $ 1.1 $ 28.5
Gain (loss) on derivatives, net $ 0.0 $ (1.9) $ 12.2 $ (3.1)