Alternative Energy Tax Credits (Details) (USD $)	3 Months Ended			6 Months Ended		3 Months Ended	6 Months Ended	9 Months Ended
	Mar. 31, 2010	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2011 Alternative Fuel Mixture Credits [Member]	Dec. 31, 2009 Alternative Fuel Mixture Credits [Member]	Dec. 31, 2010 Cellulosic Biofuel Tax Credits [Member]	Jun. 30, 2011 Cellulosic Biofuel Tax Credits [Member]	Sep. 30, 2010 Cellulosic Biofuel Tax Credits [Member]	Jun. 30, 2010 Cellulosic Biofuel Tax Credits [Member]
Refundable tax credit per gallon					$ 0.50				$ 1.01
Alternative fuel mixture tax credit reserve	9,200,000
Alternative fuels produced claimed for alternative energy tax credits				33.00%			66.00%
Cellulosic biofuel producer credits before reserves for uncertain tax positions						107,000,000
Net income impact from the alternative energy tax credits						5,000,000		33,400,000
Uncertain tax positions			102,000,000
Tax credits used to offset future cash tax payment		$ 179,000,000