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Segment and Geographic Area Information - Sales by Major Product Grouping (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Product Information [Line Items]
Consolidated sales	$ 6,377us-gaap_SalesRevenueGoodsNet	$ 6,239us-gaap_SalesRevenueGoodsNet	$ 5,836us-gaap_SalesRevenueGoodsNet	$ 5,454us-gaap_SalesRevenueGoodsNet	$ 5,585us-gaap_SalesRevenueGoodsNet	$ 5,765us-gaap_SalesRevenueGoodsNet	$ 5,849us-gaap_SalesRevenueGoodsNet	$ 5,833us-gaap_SalesRevenueGoodsNet	$ 23,906us-gaap_SalesRevenueGoodsNet	$ 23,032us-gaap_SalesRevenueGoodsNet	$ 23,700us-gaap_SalesRevenueGoodsNet
Alumina [Member]
Product Information [Line Items]
Consolidated sales									3,401us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_AluminaMember	3,151us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_AluminaMember	2,962us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_AluminaMember
Primary Aluminum [Member]
Product Information [Line Items]
Consolidated sales									6,011us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_PrimaryAluminumMember	6,194us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_PrimaryAluminumMember	7,121us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_PrimaryAluminumMember
Flat-Rolled Aluminum [Member]
Product Information [Line Items]
Consolidated sales									7,351us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_FlatRolledAluminumMember	7,106us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_FlatRolledAluminumMember	7,378us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_FlatRolledAluminumMember
Investment Castings [Member]
Product Information [Line Items]
Consolidated sales									1,784us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_InvestmentCastingsMember	1,807us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_InvestmentCastingsMember	1,747us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_InvestmentCastingsMember
Alcoa Fastening Systems [Member]
Product Information [Line Items]
Consolidated sales									1,647us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_AlcoaFasteningSystemsMember	1,505us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_AlcoaFasteningSystemsMember	1,414us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_AlcoaFasteningSystemsMember
Architectural Aluminum Systems [Member]
Product Information [Line Items]
Consolidated sales									1,002us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_ArchitecturalAluminumSystemsMember	977us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_ArchitecturalAluminumSystemsMember	970us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_ArchitecturalAluminumSystemsMember
Aluminum Wheels [Member]
Product Information [Line Items]
Consolidated sales									786us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_AluminumWheelsMember	702us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_AluminumWheelsMember	692us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_AluminumWheelsMember
Other Extruded Aluminum and Forged Products [Member]
Product Information [Line Items]
Consolidated sales									1,019us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_OtherExtrudedAluminumAndForgedProductsMember	1,015us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_OtherExtrudedAluminumAndForgedProductsMember	955us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_OtherExtrudedAluminumAndForgedProductsMember
Other [Member]
Product Information [Line Items]
Consolidated sales									$ 905us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_OtherGroupMember	$ 575us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_OtherGroupMember	$ 461us-gaap_SalesRevenueGoodsNet / us-gaap_ProductOrServiceAxis = aa_OtherGroupMember

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- Definition

Aggregate revenue during the period from the sale of goods in the normal course of business, after deducting returns, allowances and discounts.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1(a))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688



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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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