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Derivative Financial Instruments - Schedule of Gains (Losses) on Derivatives and Current Period Settlements (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]        
Current period settlements on derivative contracts $ 0.0 $ 6.7 $ 1.1 $ 35.2
Loss on derivatives, net $ (17.0) $ (1.7) $ (4.8) $ (4.8)