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Derivative Instruments - Additional Information (Detail) (Energy Hedges [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Energy Hedges [Member]
Derivative [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ 1

Fair value of derivative liability, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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