Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Embedded Aluminum Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Beginning balance	$ 266
Fair value measurement, Assets, Sales	6
Fair value measurement, Assets, Cost of goods sold	(21)
Fair value measurement, Assets, Other income, net	1
Fair value measurement, Assets, Other comprehensive loss	(43)
Fair value measurement, Assets, Purchases, sales, issuances, and settlements	0
Fair value measurement, Assets, Transfers into and/or out of Level 3	0
Fair value measurement, Assets, Foreign currency translation	(8)
Fair value measurement, Assets, Ending balance	201
Fair value measurement, Assets, Sales	0
Fair value measurement, Assets, Cost of goods sold	0
Fair value measurement, Assets, Other income, net	1
Fair value measurement, Liabilities, Beginning balance	376
Fair value measurement, Liabilities, Sales	(6)
Fair value measurement, Liabilities, Cost of goods sold	0
Fair value measurement, Liabilities, Other comprehensive loss	55
Fair value measurement, Liabilities, Purchases, sales, issuances, and settlements	0
Fair value measurement, Liabilities, Transfers into and/or out of Level 3	0
Fair value measurement, Liabilities, Foreign currency translation	0
Fair value measurement, Liabilities, Ending balance	425
Fair value measurement, Liabilities, Sales	0
Fair value measurement, Liabilities, Cost of goods sold	0
Embedded Credit Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities, Beginning balance	18
Fair value measurement, Liabilities, Cost of goods sold	0
Fair value measurement, Liabilities, Other income, net	(2)
Fair value measurement, Liabilities, Purchases, sales, issuances, and settlements	0
Fair value measurement, Liabilities, Transfers into and/or out of Level 3	0
Fair value measurement, Liabilities, Foreign currency translation	0
Fair value measurement, Liabilities, Ending balance	16
Fair value measurement, Liabilities, Sales	0
Fair value measurement, Liabilities, Cost of goods sold	0
Fair value measurement, Liabilities, Other income, net	(2)
Energy Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Beginning balance	2
Fair value measurement, Assets, Other comprehensive loss	6
Fair value measurement, Assets, Purchases, sales, issuances, and settlements	0
Fair value measurement, Assets, Transfers into and/or out of Level 3	0
Fair value measurement, Assets, Ending balance	8
Fair value measurement, Assets, Sales	0
Fair value measurement, Assets, Cost of goods sold	$ 0