Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2013
Aluminum Contracts [Member] | Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	$ 522	$ 547
Sales	(1)	(3)
Cost of goods sold	(50)	(102)
Other income (expenses), net	(1)	16
Other comprehensive loss	9	16
Purchases, sales, issuances, and settlements
Transfers into and (or) out of Level 3
Foreign currency translation	(47)	(42)
Ending balance	432	432
Sales
Cost of goods sold
Other income (expenses), net	(1)	16
Aluminum Contracts [Member] | Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	478	608
Sales	(6)	(14)
Other comprehensive loss	(77)	(199)
Purchases, sales, issuances, and settlements
Transfers into and (or) out of Level 3
Ending balance	395	395
Sales
Cost of goods sold
Energy Contracts [Member] | Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	8	3
Other comprehensive loss	(8)	(3)
Purchases, sales, issuances, and settlements
Transfers into and (or) out of Level 3
Sales
Cost of goods sold
Embedded Credit Derivative [Member] | Liabilities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning balance	32	30
Other income (expenses), net	7	9
Purchases, sales, issuances, and settlements
Transfers into and (or) out of Level 3
Ending balance	39	39
Sales
Cost of goods sold
Other income (expenses), net	$ 7	$ 9