Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Embedded Aluminum Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of year	$ 349	$ 547
Fair value measurement, Assets, Sales	(1)	2
Fair value measurement, Assets, Cost of goods sold	(163)	(202)
Fair value measurement, Assets, Other expenses, net	(15)	28
Fair value measurement, Assets, Other comprehensive loss	71	17
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	23	(43)
Balance at end of year	266	349
Fair value measurement, Assets, Sales	0	0
Fair value measurement, Assets, Cost of goods sold	0	0
Fair value measurement, Assets, Other expenses, net	(15)	28
Fair value measurement, Liabilities, Beginning balance	410	608
Fair value measurement, Liabilities, Sales	(27)	(25)
Fair value measurement, Liabilities, Cost of goods sold
Fair value measurement, Liabilities, Other income, net
Fair value measurement, Liabilities, Other comprehensive loss	(7)	(173)
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	376	410
Fair value measurement, Liabilities, Sales	0	0
Fair value measurement, Liabilities, Cost of goods sold	0	0
Embedded Credit Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of year	6	3
Fair value measurement, Assets, Sales
Fair value measurement, Assets, Cost of goods sold
Fair value measurement, Assets, Other expenses, net
Fair value measurement, Assets, Other comprehensive loss		3
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
Balance at end of year		6
Fair value measurement, Assets, Sales		0
Fair value measurement, Assets, Cost of goods sold		0
Fair value measurement, Assets, Other expenses, net
Fair value measurement, Liabilities, Beginning balance	21	30
Fair value measurement, Liabilities, Sales
Fair value measurement, Liabilities, Cost of goods sold	(1)	(1)
Fair value measurement, Liabilities, Other income, net	(2)	(8)
Fair value measurement, Liabilities, Other comprehensive loss
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	18	21
Fair value measurement, Liabilities, Sales	0	0
Fair value measurement, Liabilities, Cost of goods sold	0	0
Fair value measurement, Liabilities, Other expense, net	(2)	(8)
Energy Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of year	6
Fair value measurement, Assets, Other comprehensive loss	(4)
Balance at end of year	2
Fair value measurement, Assets, Sales	0
Fair value measurement, Assets, Cost of goods sold	$ 0