Quarterly report pursuant to Section 13 or 15(d)

Inventories (Narrative) (Detail)

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Inventories (Narrative) (Detail) (North American Coal [Member], USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2012
North American Coal [Member]
   
Inventories [Line Items]    
Cost or market inventory charges $ 8.6 $ 9.9