Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail)	3 Months Ended
	Mar. 31, 2016 USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Purchases, sales, issuances, and settlements	$ 0
Embedded Aluminum Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Beginning balance	1,135,000,000
Fair value measurement, Assets, Sales	(7,000,000)
Fair value measurement, Assets, Cost of goods sold	(31,000,000)
Fair value measurement, Assets, Other expenses (income), net	(4,000,000)
Fair value measurement, Assets, Other comprehensive income (loss)	(121,000,000)
Fair value measurement, Assets, Transfers into and/or out of Level 3	0
Fair value measurement, Assets, Foreign currency translation	16,000,000
Fair value measurement, Assets, Ending balance	988,000,000
Fair value measurement, Assets, Sales	0
Fair value measurement, Assets, Cost of goods sold	0
Fair value measurement, Assets, Other expenses (income), net	(4,000,000)
Fair value measurement, Liabilities, Beginning balance	169,000,000
Fair value measurement, Liabilities, Sales	(2,000,000)
Fair value measurement, Liabilities, Other comprehensive income (loss)	(6,000,000)
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	161,000,000
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	35,000,000
Fair value measurement, Liabilities, Cost of goods sold	(1,000,000)
Fair value measurement, Liabilities, Other expenses (income), net	(1,000,000)
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	33,000,000
Fair value measurement, Liabilities, Sales	0
Fair value measurement, Liabilities, Cost of goods sold	0
Fair value measurement, Liabilities, Other expenses (income), net	(1,000,000)
Energy Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Beginning balance	2,000,000
Fair value measurement, Assets, Other expenses (income), net	2,000,000
Fair value measurement, Assets, Other comprehensive income (loss)	2,000,000
Fair value measurement, Assets, Transfers into and/or out of Level 3	0
Fair value measurement, Assets, Ending balance	6,000,000
Fair value measurement, Assets, Sales	0
Fair value measurement, Assets, Cost of goods sold	0
Fair value measurement, Assets, Other expenses (income), net	2,000,000
Fair value measurement, Liabilities, Beginning balance	4,000,000
Fair value measurement, Liabilities, Other expenses (income), net	(1,000,000)
Fair value measurement, Liabilities, Other comprehensive income (loss)	8,000,000
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	11,000,000
Fair value measurement, Liabilities, Sales	0
Fair value measurement, Liabilities, Cost of goods sold	0
Fair value measurement, Liabilities, Other expenses (income), net	$ (1,000,000)