Quarterly report pursuant to Section 13 or 15(d)

Inventories (Narrative) (Detail)

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Inventories (Narrative) (Detail) (USD $)
In Millions, unless otherwise specified
9 Months Ended 3 Months Ended 9 Months Ended
Sep. 30, 2011
Sep. 30, 2012
North American Coal [Member]
Sep. 30, 2012
North American Coal [Member]
Inventories [Line Items]      
Cost or market inventory charges    $ 8.0 $ 17.9