Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Financial Contracts [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Beginning balance	$ 132	$ 112
Other comprehensive income (loss)	7	89
Fair value measurement, Assets, Other	(1)	(4)
Fair value measurement, Assets, Ending balance	119	119
Financial Contracts [Member] | Sales [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets	0	0
Financial Contracts [Member] | Cost of Goods Sold [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets	(19)	(78)
Financial Contracts [Member] | Other Expense [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets	0	0
Embedded Aluminum Derivative [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets, Beginning balance		41
Other comprehensive income (loss)		(41)
Fair value measurement, Assets, Other		0
Fair value measurement, Assets, Ending balance	0	0
Fair value measurement, Liabilities, Beginning balance	515	269
Fair value measurement, Liabilities, Cost of goods sold	0	0
Fair value measurement, Liabilities	(97)	181
Fair value measurement, Liabilities, Other	0	(5)
Fair value measurement, Liabilities, Ending balance	409	409
Embedded Aluminum Derivative [Member] | Sales [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets		0
Fair value measurement, Liabilities	(9)	(34)
Embedded Aluminum Derivative [Member] | Cost of Goods Sold [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets		0
Embedded Aluminum Derivative [Member] | Other Expense [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Assets		0
Fair value measurement, Liabilities	0	(2)
Fair value measurement, Liabilities, Other expenses, net		(2)
Embedded Credit Derivative [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities, Beginning balance	20	20
Fair value measurement, Liabilities, Cost of goods sold	(1)	(3)
Fair value measurement, Liabilities	0	0
Fair value measurement, Liabilities, Other	0	0
Fair value measurement, Liabilities, Ending balance	18	18
Embedded Credit Derivative [Member] | Sales [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities	0	0
Embedded Credit Derivative [Member] | Other Expense [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value measurement, Liabilities	(1)	1
Fair value measurement, Liabilities, Other expenses, net	$ (1)	$ 1