Fair Value Measurements Unobservable Input Reconciliation (Details) (Commodity Contract [Member], USD $) In Millions	3 Months Ended
	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010
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	$ 2.5	$ 5.2	$ 13.3	$ 42.1	$ 41.0	$ 49.0
Total gains or losses included in other comprehensive income	0.4	(1.0)	(4.8)	(8.5)	7.2	(3.9)
Settlements	(1.4)	(1.7)	(3.3)	(6.7)	(6.1)	(4.1)
Level 3 Asset Value, End of Period	1.5	2.5	5.2	26.9	42.1	41.0
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	0	0	1.8	8.2	14.7
Total gains or losses included in other comprehensive income	0	0	0	2.3	(3.7)	(5.1)
Settlements	0	0	0	(0.9)	(2.7)	(1.4)
Level 3 Liability Value, End of Period	$ 0	$ 0	$ 0	$ 3.2	$ 1.8	$ 8.2