Investments - Additional Information (Detail) $ in Millions, SAR in Billions	1 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2015 USD ($) Project Subsidiary kt	Dec. 31, 2015 SAR Project Subsidiary kt	Dec. 31, 2014 USD ($) Project Subsidiary	Dec. 31, 2013 USD ($)	Dec. 31, 2012 kt
Schedule of Equity Method Investments [Line Items]
Percent of equity investments in other entity				40.00%
Dividends from equity investments		$ 152		$ 86	$ 89
Expanded capacity amount of processed bauxite, in Kmt | kt						100
Outstanding receivable for labor and other employee-related expenses		19		30
Equity investments		1,476		1,780
Guarantee issued on behalf of smelting and rolling mill companies		320
Other investments		$ 209		164
Ma'aden Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Joint venture shareholders agreement period, years		30 years	30 years
Joint venture shareholders agreement, automatic extension additional period, years		20 years	20 years
Ownership interest in joint venture		74.90%	74.90%
Payment for pro rata share of pre-incorporation costs		$ 56
Alcoa Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest in joint venture		25.10%	25.10%
Initial investment		$ 80
Maaden Alcoa Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest in joint venture at fair market value		14.90%	14.90%
Period Bracket To Exercise Option		6 months	6 months
Period To Open Option Exercise Bracket From Commercial Production Date		5 years	5 years
Amount invested by Alcoa and Aluminum Financing Limited		$ 10,800	SAR 40.5
Capital investment commitment paid-to-date		29		120
Equity investments		928		983
Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member]
Schedule of Equity Method Investments [Line Items]
Project financing Investment		4,311
Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] | Other Noncurrent Liabilities and Deferred Credits [Member]
Schedule of Equity Method Investments [Line Items]
Guarantee issued on behalf of smelting and rolling mill companies		7		8
Maaden Alcoa Joint Venture Mine And Refinery Company [Member] | Other Noncurrent Liabilities and Deferred Credits [Member]
Schedule of Equity Method Investments [Line Items]
Guarantee issued on behalf of smelting and rolling mill companies		$ 3		4
Alumina Limited [Member]
Schedule of Equity Method Investments [Line Items]
Percentage of amount required to be contributed in the event Alcoa would be required to make payments under the guarantees		40.00%	40.00%
Fixed Income Securities [Member]
Schedule of Equity Method Investments [Line Items]
Other investments		$ 193
Equity Securities [Member]
Schedule of Equity Method Investments [Line Items]
Other investments				$ 153
Saudi Arabia Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Joint venture agreement period	20 years
Canada [Member]
Schedule of Equity Method Investments [Line Items]
Number of wholly-owned subsidiaries | Subsidiary		2	2	2
Brazil [Member]
Schedule of Equity Method Investments [Line Items]
Number of hydroelectric power projects | Project		2	2	2
Financial Guarantee [Member] | Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member]
Schedule of Equity Method Investments [Line Items]
Debt service requirements, principal		$ 142
Debt service requirements, interest maximum		50
Financial Guarantee [Member] | Maaden Alcoa Joint Venture Mine And Refinery Company [Member]
Schedule of Equity Method Investments [Line Items]
Debt service requirements, principal		120
Debt service requirements, interest maximum		30
Alcoa [Member] | Maaden Alcoa Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Amount invested by Alcoa and Aluminum Financing Limited		1,100
Capital investment commitment paid-to-date		981
Alcoa [Member] | Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member]
Schedule of Equity Method Investments [Line Items]
Project financing Investment		142
Alcoa [Member] | Maaden Alcoa Joint Venture Mine And Refinery Company [Member]
Schedule of Equity Method Investments [Line Items]
Project financing Investment		$ 2,232
Halco Mining, Inc. [Member] | Boke Investment Company [Member]
Schedule of Equity Method Investments [Line Items]
Minority interest percentage held by equity interest		100.00%		100.00%
Compagnie Des Bauxites De Guinee [Member] | Boke Investment Company [Member]
Schedule of Equity Method Investments [Line Items]
Minority interest percentage held by equity interest		51.00%		51.00%
Scenario Two [Member] | Saudi Arabia Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Potential forfeiture of letter of credit		$ 60
Canadian Subsidiaries [Member] | Becancour Smelter [Member]
Schedule of Equity Method Investments [Line Items]
Percent of equity investments in other entity		49.90%		49.90%
Smelter Sites [Member] | Canada [Member] | Pechiney Reynolds Quebec, Inc. [Member]
Schedule of Equity Method Investments [Line Items]
Percent of equity investments in other entity		50.00%		50.00%
Smelter Sites [Member] | Pechiny Reynolds Quebec Subsidiary [Member]
Schedule of Equity Method Investments [Line Items]
Percent of equity investments in other entity		50.10%		50.10%
Smelter Sites [Member] | Pechiny Reynolds Quebec Subsidiary [Member] | Becancour Smelter [Member]
Schedule of Equity Method Investments [Line Items]
Percent of equity investments in other entity		25.05%		25.05%
Bauxite Mining [Member]
Schedule of Equity Method Investments [Line Items]
Projected capacity amount of processed bauxite, in kmt | kt		4,000	4,000
Bauxite Mining [Member] | Brazil [Member] | Minerao Rio Do Norte S.A. [Member]
Schedule of Equity Method Investments [Line Items]
Percent of equity investments in other entity		18.20%		18.20%
Bauxite Mining [Member] | Halco Mining, Inc. [Member] | GUINEA
Schedule of Equity Method Investments [Line Items]
Percent of equity investments in other entity		45.00%		45.00%
Hydroelectric Power [Member] | Canada [Member] | Manicouagan Power Limited Partnership [Member]
Schedule of Equity Method Investments [Line Items]
Percent of equity investments in other entity		40.00%		40.00%
Alumina Refinery [Member]
Schedule of Equity Method Investments [Line Items]
Projected capacity amount of processed bauxite, in kmt | kt		1,800	1,800
Primary Aluminum Smelter [Member]
Schedule of Equity Method Investments [Line Items]
Projected capacity amount of processed bauxite, in kmt | kt		740	740
Rolling Mill [Member]
Schedule of Equity Method Investments [Line Items]
Projected capacity amount of processed bauxite, in kmt | kt		380	380
Alcoa World Alumina and Chemicals [Member]
Schedule of Equity Method Investments [Line Items]
Percent of equity investments in other entity				55.00%
Alcoa World Alumina and Chemicals [Member] | Alcoa Joint Venture [Member]
Schedule of Equity Method Investments [Line Items]
Percent of equity investments in other entity		60.00%		60.00%
Alcoa World Alumina and Chemicals [Member] | Maaden Alcoa Joint Venture Mine And Refinery Company [Member]
Schedule of Equity Method Investments [Line Items]
Project financing Investment		$ 560
Alcoa World Alumina and Chemicals [Member] | Alumina Limited [Member]
Schedule of Equity Method Investments [Line Items]
Percent of equity investments in other entity		40.00%		40.00%