Fair Value Measurements (Narrative) (Details) (Swap [Member], USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Fixed price swap contract (in gallons)	8,600,000
Average contract price (in dollars per gallon)	3.87
Average forward price (in dollars per gallon)	3.93
Prepaid Expenses And Other Assets [Member]
Derivative [Line Items]
Derivative asset (Less than $1 as of December 31, 2012)	$ 1	$ 1
Accrued Expenses And Other Liabilities [Member]
Derivative [Line Items]
Derivative liability (Less than $1 as of March 31, 2013 and December 31, 2012)	$ 1	$ 1