Derivative Instruments - Realized and Unrealized (Losses) Gains Associated with Derivatives Not Designated as Hedging Instruments (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
(Loss) gain on derivative contracts		$ (12.5)	$ (74.0)	$ 0.4
Foreign exchange and metals contracts | (Loss) gain on derivative contracts | Derivatives not designated as hedging instruments:
Derivative Instruments, Gain (Loss) [Line Items]
(Loss) gain on derivative contracts	$ (74.0)	$ (12.5)		$ 0.4