Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2013
Aluminum Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Beginning balance	$ 432	$ 547
Fair value measurement, Assets, Sales	(1)	(4)
Fair value measurement, Assets, Cost of goods sold	(49)	(151)
Fair value measurement, Assets, Other income, net	4	20
Fair value measurement, Assets, Other comprehensive loss	(12)	4
Fair value measurement, Assets, Purchases, sales, issuances, and settlements*
Fair value measurement, Assets, Transfers into and (or) out of Level 3*
Fair value measurement, Assets, Foreign currency translation	7	(35)
Fair value measurement, Assets, Ending balance	381	381
Fair value measurement, Assets, Sales
Fair value measurement, Assets, Cost of goods sold
Fair value measurement, Assets, Other income, net	4	20
Fair value measurement, Liabilities, Beginning balance	395	608
Fair value measurement, Liabilities, Sales	(5)	(19)
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other comprehensive loss	61	(138)
Fair value measurement, Liabilities, Purchases, sales, issuances, and settlements*
Fair value measurement, Liabilities, Transfers into and (or) out of Level 3*
Fair value measurement, Liabilities, Foreign currency translation
Fair value measurement, Liabilities, Ending balance	451	451
Fair value measurement, Liabilities, Sales
Fair value measurement, Liabilities, Cost of goods sold
Embedded Credit Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities, Beginning balance	39	30
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other income, net	(11)	(2)
Fair value measurement, Liabilities, Purchases, sales, issuances, and settlements*
Fair value measurement, Liabilities, Transfers into and (or) out of Level 3*
Fair value measurement, Liabilities, Foreign currency translation
Fair value measurement, Liabilities, Ending balance	28	28
Fair value measurement, Liabilities, Sales
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other income, net	(11)	(2)
Energy Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Beginning balance		3
Fair value measurement, Assets, Other comprehensive loss	4	1
Fair value measurement, Assets, Purchases, sales, issuances, and settlements*
Fair value measurement, Assets, Transfers into and (or) out of Level 3*
Fair value measurement, Assets, Ending balance	4	4
Fair value measurement, Assets, Sales
Fair value measurement, Assets, Cost of goods sold