Derivatives (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2012 Swap [Member] gal	Mar. 31, 2011 Swap [Member] gal	Mar. 31, 2012 Swap [Member] Prepaid Expenses And Other Assets [Member]	Dec. 31, 2011 Swap [Member] Prepaid Expenses And Other Assets [Member]	Mar. 31, 2012 Swap [Member] Accrued Expenses And Other Liabilities [Member]	Dec. 31, 2011 Swap [Member] Accrued Expenses And Other Liabilities [Member]	Mar. 31, 2012 Maximum [Member] Swap [Member] Accumulated Other Comprehensive Income [Member]	Dec. 31, 2011 Maximum [Member] Swap [Member] Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Fixed price swap contract (in gallons)		3,000,000
Derivative asset				$ 1	$ 0
Derivative liability						0	1
Derivative accumulated other comprehensive income								1	1
Threshold for inclusion	$ 1
Purchases of diesel covered by the fixed price swaps (in gallons)		1,200,000	900,000