Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Nov. 30, 2014	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Purchases, sales, issuances, and settlements	$ 0	$ 0
Embedded Aluminum Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of year		266,000,000	$ 349,000,000
Fair value measurement, Assets, Sales		5,000,000	(1,000,000)
Fair value measurement, Assets, Cost of goods sold		(99,000,000)	163,000,000
Fair value measurement, Assets, Other expenses, net		(8,000,000)	15,000,000
Fair value measurement, Assets, Other comprehensive loss		964,000,000	71,000,000
Fair value measurement, Assets, Transfers into and/or out of Level 3		0	0
Fair value measurement, Assets, Foreign currency translation		7,000,000	23,000,000
Balance at end of year		1,135,000,000	266,000,000
Fair value measurement, Assets, Sales		0	0
Fair value measurement, Assets, Cost of goods sold		0	0
Fair value measurement, Assets, Other expenses, net		(8,000,000)	15,000,000
Fair value measurement, Liabilities, Beginning balance		376,000,000	410,000,000
Fair value measurement, Liabilities, Sales		(16,000,000)	(27,000,000)
Fair value measurement, Liabilities, Other comprehensive loss		(191,000,000)	(7,000,000)
Fair value measurement, Liabilities, Purchases, sales, issuances, and settlements		0	0
Fair value measurement, Liabilities, Transfers into and/or out of Level 3		0	0
Fair value measurement, Liabilities, Foreign currency translation		0	0
Fair value measurement, Liabilities, Ending balance		169,000,000	376,000,000
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]
Fair value measurement, Liabilities, Beginning balance		18,000,000	21,000,000
Fair value measurement, Liabilities, Cost of goods sold			(1,000,000)
Fair value measurement, Liabilities, Other expenses, net		17,000,000	(2,000,000)
Fair value measurement, Liabilities, Purchases, sales, issuances, and settlements		0	0
Fair value measurement, Liabilities, Transfers into and/or out of Level 3		0	0
Fair value measurement, Liabilities, Foreign currency translation		0	0
Fair value measurement, Liabilities, Ending balance		35,000,000	18,000,000
Fair value measurement, Liabilities, Sales		0	0
Fair value measurement, Liabilities, Cost of goods sold		0	0
Fair value measurement, Liabilities, Other expenses, net		(17,000,000)	(2,000,000)
Energy Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of year		2,000,000	6,000,000
Fair value measurement, Assets, Other expenses, net		(2,000,000)
Fair value measurement, Assets, Other comprehensive loss		(1,000,000)	(4,000,000)
Fair value measurement, Assets, Transfers into and/or out of Level 3		0	0
Fair value measurement, Assets, Foreign currency translation		1,000,000
Balance at end of year		2,000,000	2,000,000
Fair value measurement, Assets, Sales		0	0
Fair value measurement, Assets, Cost of goods sold		0	$ 0
Fair value measurement, Assets, Other expenses, net		(2,000,000)
Fair value measurement, Liabilities, Other expenses, net		1,000,000
Fair value measurement, Liabilities, Other comprehensive loss		3,000,000
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		4,000,000
Fair value measurement, Liabilities, Sales		0
Fair value measurement, Liabilities, Cost of goods sold		0
Fair value measurement, Liabilities, Other expenses, net		$ 1,000,000