Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended					12 Months Ended
	Dec. 31, 2012	Jul. 31, 2012	Sep. 30, 2011	Jan. 31, 2011	Jan. 31, 2010	Dec. 31, 2012 Reporting_Unit Y	Dec. 31, 2011	Dec. 31, 2010	Mar. 31, 2010
Summary Of Significant Accounting Policies [Line Items]
Percent of equity investments in other entity, maximum	50.00%					50.00%
Original maturity of cash equivalents						3 months
Number of reporting units being subjected to goodwill impairment test						9
Minimum number of reporting units being subjected for goodwill impairment test						3
Percentage of total goodwill allocated to reporting units						90.00%
Goodwill	$ 5,170					$ 5,170	$ 5,157	$ 5,028
Minimum percentage of estimated fair value of reporting unit to be less than carrying amount of goodwill			50.00%
Market capitalization of common stock	9,263
Maximum hedging contracts period, in years						5
Change in functional currency of certain Brazilian operations					309
Businesses expected to be disposed within, years						1
Goodwill impairment threshold, maximum		50.00%	50.00%	50.00%
Effect of change in accounting principle presented on financial statement, before tax									250
Alcoa World Alumina and Chemicals [Member]
Summary Of Significant Accounting Policies [Line Items]
Percent of equity investments in other entity, maximum					60.00%
Alcoa Fastening Systems [Member]
Summary Of Significant Accounting Policies [Line Items]
Goodwill	1,160					1,160
Alcoa Power and Propulsion [Member]
Summary Of Significant Accounting Policies [Line Items]
Goodwill	1,628					1,628
Primary Metals [Member]
Summary Of Significant Accounting Policies [Line Items]
Goodwill	997					997
Estimated fair value exceeded percentage on carrying value						9.20%
Engineered Products and Solutions [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units						5
Minimum [Member] | Bauxite mining [Member]
Summary Of Significant Accounting Policies [Line Items]
Period of mining						1 year
Maximum [Member] | Bauxite mining [Member]
Summary Of Significant Accounting Policies [Line Items]
Period of mining						5 years
Alumina [Member]
Summary Of Significant Accounting Policies [Line Items]
Goodwill	10					10	11	12
Estimated fair value exceeded percentage on carrying value						7.40%
Alumina [Member] | Alcoa World Alumina and Chemicals [Member]
Summary Of Significant Accounting Policies [Line Items]
Percent of equity investments in other entity, maximum					40.00%
Alumina [Member] | Primary Metals [Member]
Summary Of Significant Accounting Policies [Line Items]
Number of reporting units						4
Global Rolled Products [Member]
Summary Of Significant Accounting Policies [Line Items]
Goodwill	$ 214					$ 214	$ 208	$ 207
Estimated fair value exceeded percentage on carrying value						150.00%