Derivative Instruments and Hedging Activities (Details) (Commodity contracts [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Asset Derivatives
Fair Value of Derivative Instruments, Assets	$ 35.3	$ 47.7
Liability Derivatives
Fair Value of Derivative Instruments, Liabilities	(35.3)	(11.9)
Current assets [Member]
Asset Derivatives
Fair Value of Derivative Instruments, Assets	24.4	25.2
Current liabilities [Member]
Liability Derivatives
Fair Value of Derivative Instruments, Liabilities	(27.3)	(11.1)
Long-term assets [Member]
Asset Derivatives
Fair Value of Derivative Instruments, Assets	10.9	22.5
Long-term liabilities [Member]
Liability Derivatives
Fair Value of Derivative Instruments, Liabilities	$ (8.0)	$ (0.8)