Inventories - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014
Inventory Disclosure [Abstract]
Inventories valued on a LIFO basis	$ 1,169us-gaap_LIFOInventoryAmount		$ 1,514us-gaap_LIFOInventoryAmount
Total inventories valued on an average-cost basis	691us-gaap_InventoryLIFOReserve		767us-gaap_InventoryLIFOReserve
Recognition of income caused by partial liquidations of the lower cost LIFO inventory base, gross	26	1
Recognition of income caused by partial liquidations of the lower cost LIFO inventory base, after tax	$ 17	$ 1

Recognition of income caused by partial liquidations of the lower cost LIFO inventory base gross.

No definition available.

Name:	aa_RecognitionOfIncomeCausedByPartialLiquidationsOfLowerCostLifoInventoryBaseGross
Namespace Prefix:	aa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Recognition of income caused by partial liquidations of lower cost LIFO inventory base net.

+ References

No definition available.

+ Details

Name:	aa_RecognitionOfIncomeCausedByPartialLiquidationsOfLowerCostLifoInventoryBaseNet
Namespace Prefix:	aa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_InventoryDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of difference between inventory at lower of LIFO cost or market and inventory at lower of other inventory accounting method cost or market, for example, but not limited to, FIFO or average cost.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.6(c))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 6

-Subparagraph c

-Article 5

+ Details

Name:	us-gaap_InventoryLIFOReserve
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of LIFO (last in first out) inventory present at the reporting date when inventory is also valued using different valuation methods.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6361739&loc=d3e7789-107766

+ Details

Name:	us-gaap_LIFOInventoryAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant