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Contingencies (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
9 Months Ended
Sep. 30, 2012
Dec. 31, 2011
Aug. 25, 2011
Aug. 13, 2007
Sep. 30, 2012
Maximum [Member]
Sep. 30, 2012
Minimum [Member]
Purchase replacement coal       $ 100    
Aggregate amount of past and future damages         377.0 228.0
Damages and interest awarded     104.1      
Appeal Bond 124.9          
Amount accrued 32.3 117.2        
Amount accrued current portion $ 4.3 $ 6.3