Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Parenthetical) (Detail) (Aluminum Contracts [Member], USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Aluminum Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Decrease in Fair value of assets and liabilities	$ 3