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, 2014	Jun. 30, 2014
Aluminum Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Beginning balance	$ 326	$ 349
Fair value measurement, Assets, Sales
Fair value measurement, Assets, Cost of goods sold	(53)	(111)
Fair value measurement, Assets, Other expenses, net		(1)
Fair value measurement, Assets, Other comprehensive income	(9)
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	17	44
Fair value measurement, Assets, Ending balance	281	281
Fair value measurement, Assets, Sales
Fair value measurement, Assets, Cost of goods sold
Fair value measurement, Assets, Other expenses, net		(1)
Fair value measurement, Liabilities, Beginning balance	384	410
Fair value measurement, Liabilities, Sales	(6)	(11)
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other income, net
Fair value measurement, Liabilities, Other comprehensive income	44	23
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	422	422
Fair value measurement, Liabilities, Sales
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other income, net
Embedded Credit Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities, Beginning balance	20	21
Fair value measurement, Liabilities, Sales
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other income, net	(6)	(7)
Fair value measurement, Liabilities, Other comprehensive income
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	14	14
Fair value measurement, Liabilities, Sales
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other income, net	(6)	(7)
Energy Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Beginning balance	11	6
Fair value measurement, Assets, Sales
Fair value measurement, Assets, Cost of goods sold
Fair value measurement, Assets, Other expenses, net	5	5
Fair value measurement, Assets, Other comprehensive income	7	12
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	1	1
Fair value measurement, Assets, Ending balance	24	24
Fair value measurement, Assets, Sales
Fair value measurement, Assets, Cost of goods sold
Fair value measurement, Assets, Other expenses, net	$ 5	$ 5