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Derivative Financial Instruments - Schedule of Gains (Losses) on Derivatives and Current Period Settlements (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]    
Current period settlements on derivative contracts $ 1.2 $ 21.4
Gain (loss) on derivatives, net $ 12.2 $ (1.2)