Losses (Gains) and Other Expenses, net (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary of Losses (Gains) and Other Expenses, net
Realized losses (gains) on settled futures contracts	$ (0.1)	$ (1.5)	$ 3.7
Net change in unrealized (gains) losses on unsettled futures contracts	3.8	(0.6)	(7.1)
Gain on disposal of a business, net	(0.1)	(0.1)	(4.1)
Losses (gains) on disposals of fixed assets	(0.8)	0.1	(0.1)
Special legal contingency charge	(0.4)	6.8
Acquisition expenses	1.0	4.8
Foreign currency exchange losses (gains)	1.4	0.4	0.7
Other items, net	0.2	0.3	0.3
Losses (gains) and other expenses, net	$ 5.0	$ 10.2	$ (6.6)