Fair Value Measurements Unobservable Input Reconciliation (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation Calculation [Roll Forward]
Level 3 Asset Value, End of Period	$ 54.3	$ 52.4
Commodity Contract [Member] | Commodity Contrtacts, Liabilities [Member]
Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation Calculation [Roll Forward]
Level 3 Liability Value, Beginning of Period	0	14.7
Total gains or losses included in other comprehensive income	0	0
Settlements	0	(14.7)
Level 3 Liability Value, End of Period	0	0
Commodity Contract [Member] | Commodity Contracts, Assets [Member]
Fair Value Assets and Liabilities Measured on Recurring Basis Unobservable Input Reconciliation Calculation [Roll Forward]
Level 3 Asset Value, Beginning of Period	13.3	49.0
Total gains or losses included in other comprehensive income	(5.4)	(10.0)
Settlements	(7.9)	(25.7)
Level 3 Asset Value, End of Period	$ 0	$ 13.3