Segment Information - Schedule of Operating Results of Alcoa's Reportable Segment (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Segment Reporting Information [Line Items]
Total sales	$ 5,819us-gaap_SalesRevenueGoodsNet	$ 5,454us-gaap_SalesRevenueGoodsNet
Equity loss	(19)	(38)
Depreciation, depletion, and amortization	305	319
Income taxes	264	154
After-tax operating income (ATOI)	633	325
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	6,998	6,676
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	1,229	1,287
Third-Party Sales [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	5,769	5,389
Alumina [Member]
Segment Reporting Information [Line Items]
Equity loss	(7)	(5)
Depreciation, depletion, and amortization	80	97
Income taxes	92	40
After-tax operating income (ATOI)	221	92
Alumina [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	1,388	1,355
Alumina [Member] \| Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	501	510
Alumina [Member] \| Third-Party Sales [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	887	845
Primary Metals [Member]
Segment Reporting Information [Line Items]
Equity loss	(3)	(28)
Depreciation, depletion, and amortization	109	124
Income taxes	57	(11)
After-tax operating income (ATOI)	187	(15)
Primary Metals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	2,264	2,158
Primary Metals [Member] \| Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	692	734
Primary Metals [Member] \| Third-Party Sales [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,572	1,424
Global Rolled Products [Member]
Segment Reporting Information [Line Items]
Equity loss	(9)	(5)
Depreciation, depletion, and amortization	56	58
Income taxes	26	34
After-tax operating income (ATOI)	34	59
Global Rolled Products [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	1,657	1,720
Global Rolled Products [Member] \| Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment sales	36	43
Global Rolled Products [Member] \| Third-Party Sales [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	1,621	1,677
Engineered Products and Solutions [Member]
Segment Reporting Information [Line Items]
Depreciation, depletion, and amortization	60	40
Income taxes	89	91
After-tax operating income (ATOI)	191	189
Engineered Products and Solutions [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Total sales	1,689	1,443
Engineered Products and Solutions [Member] \| Third-Party Sales [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Third-party sales	$ 1,689	$ 1,443

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Equity in net income of equity method investees of segment total.

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Segment reporting information income tax expense benefit total.

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Segment reporting information intersegment revenue total.

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Segment reporting information profit loss total.

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Segment reporting information revenue from external customers total.

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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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