Derivatives and Other Financial Instruments - Schedule of Fair Values and Corresponding Level of Fair Value Hierarchy of Outstanding Derivative Contracts Recorded as Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Fair value liability derivatives	$ 594	$ 679
Level 1 [Member]
Derivative [Line Items]
Fair value liability derivatives	68	15
Level 3 [Member]
Derivative [Line Items]
Fair value liability derivatives	510	638
Level 2 [Member]
Derivative [Line Items]
Fair value liability derivatives	16	26
Derivatives designated as hedging instruments [Member]
Derivative [Line Items]
Fair value liability derivatives	542	622
Derivatives designated as hedging instruments [Member] | Other current liabilities [Member] | Aluminum contracts [Member] | Level 1 [Member]
Derivative [Line Items]
Fair value liability derivatives	49	13
Derivatives designated as hedging instruments [Member] | Other current liabilities [Member] | Aluminum contracts [Member] | Level 3 [Member]
Derivative [Line Items]
Fair value liability derivatives	27	35
Derivatives designated as hedging instruments [Member] | Other noncurrent liabilities and deferred credits [Member] | Aluminum contracts [Member] | Level 1 [Member]
Derivative [Line Items]
Fair value liability derivatives	15	1
Derivatives designated as hedging instruments [Member] | Other noncurrent liabilities and deferred credits [Member] | Aluminum contracts [Member] | Level 3 [Member]
Derivative [Line Items]
Fair value liability derivatives	451	573
Derivatives not designated as hedging instruments [Member]
Derivative [Line Items]
Fair value liability derivatives	52	57
Derivatives not designated as hedging instruments [Member] | Other current liabilities [Member] | Aluminum contracts [Member] | Level 1 [Member]
Derivative [Line Items]
Fair value liability derivatives	3	1
Derivatives not designated as hedging instruments [Member] | Other current liabilities [Member] | Aluminum contracts [Member] | Level 2 [Member]
Derivative [Line Items]
Fair value liability derivatives	16	21
Derivatives not designated as hedging instruments [Member] | Other current liabilities [Member] | Embedded credit derivative [Member] | Level 3 [Member]
Derivative [Line Items]
Fair value liability derivatives	3	3
Derivatives not designated as hedging instruments [Member] | Other noncurrent liabilities and deferred credits [Member] | Aluminum contracts [Member] | Level 1 [Member]
Derivative [Line Items]
Fair value liability derivatives	1
Derivatives not designated as hedging instruments [Member] | Other noncurrent liabilities and deferred credits [Member] | Aluminum contracts [Member] | Level 2 [Member]
Derivative [Line Items]
Fair value liability derivatives		5
Derivatives not designated as hedging instruments [Member] | Other noncurrent liabilities and deferred credits [Member] | Embedded credit derivative [Member] | Level 3 [Member]
Derivative [Line Items]
Fair value liability derivatives	$ 29	$ 27