Commitments And Contingencies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			3 Months Ended		0 Months Ended
	Mar. 31, 2012 Y	Mar. 31, 2011	Dec. 31, 2011	Mar. 31, 2012 Minimum [Member]	Mar. 31, 2012 Maximum [Member]	Nov. 04, 2011 MF Global Holdings Ltd. Bankruptcy [Member]	Mar. 31, 2012 Other Accounts Receivables [Member]	Dec. 31, 2011 Other Accounts Receivables [Member]	Mar. 31, 2012 Long-Term Receivables [Member]	Dec. 31, 2011 Long-Term Receivables [Member]
Commitments And Contingencies [Line Items]
Estimated fees for excess emissions, accrued	$ 10.8			$ 6.4	$ 13.7
Amount owed on transfer of existing trading positions						29.4
Amount received from existing trading positions						21.2
Remaining amount owed						8.2
Liabilities recognized for estimated environmental costs	47.5		49.6
Estimated environmental liabilities, years	10
Environmental expenses	2.5	3.9
Receivables from insurance carriers related to environmental matters	7.7		7.7				4.8	5.2	2.9	2.5
Unrecognized product overages	$ 6.8