Contingencies and Commitments - Additional Information - 2 (Detail) € in Millions, BRL in Millions, SAR in Billions					1 Months Ended									3 Months Ended			6 Months Ended	12 Months Ended							36 Months Ended	93 Months Ended
	Feb. 27, 2014 EUR (€)	Feb. 27, 2014 USD ($)	Apr. 08, 2013 USD ($)	Apr. 08, 2013 BRL	Apr. 30, 2016 USD ($)	Apr. 30, 2016 AUD	Mar. 31, 2016 USD ($)	Apr. 30, 2015 USD ($) Installment Refinery	Jan. 31, 2014	Oct. 31, 2013 USD ($)	Mar. 31, 2013 USD ($)	May. 31, 2012 USD ($)	May. 31, 2012 BRL	Mar. 31, 2016 USD ($)	Mar. 31, 2016 AUD	Mar. 31, 2016 SAR	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2014 AUD	Dec. 31, 2012 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2004 USD ($)	Dec. 31, 2004 AUD	Dec. 31, 2002 t	Sep. 30, 2011 USD ($)	Sep. 30, 2011 AUD	Mar. 31, 2016 EUR (€)	Mar. 31, 2016 USD ($)	Mar. 31, 2016 BRL	Mar. 31, 2016 AUD	Dec. 31, 2015 AUD	Apr. 08, 2013 BRL	Mar. 31, 2013 BRL
Loss Contingencies [Line Items]
Increase in remediation reserve							$ 1,000,000							$ 7,000,000
Revised project cost submitted to reflect the removal of a larger volume of contaminated soil														7,000,000
Total combined assessments																												€ 241	$ 273,000,000
State and Local Jurisdiction [Member]
Loss Contingencies [Line Items]
Total combined assessments																													38,000,000	BRL 137
Maaden Alcoa Joint Venture [Member]
Loss Contingencies [Line Items]
Required plan contributions														10,800,000,000		SAR 40.5
Capital investment														1,000,000
Equity investments																		$ 928,000,000											906,000,000
Maaden Alcoa Joint Venture [Member] | Alcoa [Member]
Loss Contingencies [Line Items]
Required plan contributions														1,100,000,000
Capital investment														$ 982,000,000
Ma'aden Joint Venture [Member]
Loss Contingencies [Line Items]
Ownership interest in joint venture														74.90%	74.90%	74.90%
Alcoa Joint Venture [Member]
Loss Contingencies [Line Items]
Ownership interest in joint venture														25.10%	25.10%	25.10%
Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member]
Loss Contingencies [Line Items]
Project financing Investment																													4,311,000,000
Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] | Other Noncurrent Liabilities and Deferred Credits [Member]
Loss Contingencies [Line Items]
Guarantee issued on behalf of smelting and rolling mill companies																		7,000,000											7,000,000
Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] | Financial Guarantee [Member]
Loss Contingencies [Line Items]
Debt service requirements, principal														$ 142,000,000
Debt service requirements, interest maximum														40,000,000
Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] | Alcoa [Member]
Loss Contingencies [Line Items]
Project financing Investment																													142,000,000
Maaden Alcoa Joint Venture Mine And Refinery Company [Member] | Other Noncurrent Liabilities and Deferred Credits [Member]
Loss Contingencies [Line Items]
Guarantee issued on behalf of smelting and rolling mill companies																		$ 3,000,000											3,000,000
Maaden Alcoa Joint Venture Mine And Refinery Company [Member] | Financial Guarantee [Member]
Loss Contingencies [Line Items]
Debt service requirements, principal														120,000,000
Debt service requirements, interest maximum														$ 30,000,000
Maaden Alcoa Joint Venture Mine And Refinery Company [Member] | AWAC [Member]
Loss Contingencies [Line Items]
Project financing Investment																													560,000,000
Maaden Alcoa Joint Venture Mine And Refinery Company [Member] | Alcoa [Member]
Loss Contingencies [Line Items]
Project financing Investment																													2,232,000,000
Alumina Limited [Member]
Loss Contingencies [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%	40.00%
Ligestra [Member]
Loss Contingencies [Line Items]
Costs and payments	€ 12	$ 17,000,000
Costs and payments related to damages	6	9,000,000
Payment period														10 years	10 years	10 years
Ligestra [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Percentage of payments and remediation costs									50.00%
Ligestra [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Percentage of payments and remediation costs									80.00%
Italian Ministry of Environment and Protection of Land and Sea[Member]
Loss Contingencies [Line Items]
Soil remediation project, estimated cost	24	33,000,000
Payments for emergency action and natural resource damages	€ 18	$ 25,000,000
Alcoa World Alumina Brasil [Member]
Loss Contingencies [Line Items]
Disallowed tax credits											$ 110,000,000																							BRL 220
Percentage of penalty of the gross disallowed amount			50.00%	50.00%							50.00%
Value added tax receivable												$ 41,000,000	BRL 82
Estimated range of reasonably possible loss, minimum | BRL				BRL 103
Alcoa World Alumina Brasil [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Estimated range of reasonably possible loss, minimum			$ 0
Alcoa World Alumina Brasil [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Estimated range of reasonably possible loss, minimum			29,000,000
Alcoa World Alumina Brasil [Member] | Fixed Assets [Member]
Loss Contingencies [Line Items]
Disallowed tax credits | BRL																																	BRL 117
Alcoa World Alumina Brasil [Member] | Fixed Assets [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Disallowed tax credits			0
Alcoa World Alumina Brasil [Member] | Fixed Assets [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Disallowed tax credits			$ 32,000,000
Alcoa Aluminio [Member]
Loss Contingencies [Line Items]
Metal sold per month | t																									2,000
Majority-Owned Subsidiary | AofA [Member] | Service Agreements [Member]
Loss Contingencies [Line Items]
Gas supply agreement period																		12 years
Number of alumina refineries to be powered under supplied agreement | Refinery								3
Number of installments | Installment								2
Gas supply agreement prepayment amount								$ 500,000,000
Majority-Owned Subsidiary | AofA [Member] | Service Agreements [Member] | First Installment [Member]
Loss Contingencies [Line Items]
Gas supply agreement prepayment amount								300,000,000
Asset included in other noncurrent assets																		$ 288,000,000											304,000,000		AUD 395,000,000	AUD 395,000,000
Majority-Owned Subsidiary | AofA [Member] | Service Agreements [Member] | Second Installment [Member]
Loss Contingencies [Line Items]
Gas supply agreement prepayment amount								$ 200,000,000
Fusina [Member]
Loss Contingencies [Line Items]
Increase in remediation reserve										$ 0												$ 12,000,000
Portovesme [Member]
Loss Contingencies [Line Items]
Increase in remediation reserve																			$ 3,000,000			$ 3,000,000
Baie Comeau Smelter [Member]
Loss Contingencies [Line Items]
Increase in remediation reserve																					$ 25,000,000
Mosjoen [Member]
Loss Contingencies [Line Items]
Increase in remediation reserve																	$ 11,000,000				$ 20,000,000
Dampier to Bunbury Natural Gas Pipeline [Member]
Loss Contingencies [Line Items]
Capital investment																							$ 17,000,000	AUD 24,000,000
Dampier to Bunbury Natural Gas Pipeline [Member] | AofA [Member]
Loss Contingencies [Line Items]
Capital investment																										$ 141,000,000	AUD 176,000,000
Investment percentage														30.00%	30.00%	30.00%							20.00%	20.00%
Percentage of ownership sold														20.00%	20.00%	20.00%
Cash received on sale of ownership														$ 154,000,000	AUD 205,000,000
Dampier to Bunbury Natural Gas Pipeline [Member] | Subsequent Event [Member] | AofA [Member]
Loss Contingencies [Line Items]
Percentage of ownership sold					20.00%	20.00%
Cash received on sale of ownership					$ 154,000,000	AUD 205,000,000
Dampier to Bunbury Natural Gas Pipeline [Member] | Three-Year Equity Call Plan [Member]
Loss Contingencies [Line Items]
Required plan contributions																			39,000,000	AUD 40,000,000
Dampier to Bunbury Natural Gas Pipeline [Member] | Three-Year Equity Call Plan [Member] | AofA [Member]
Loss Contingencies [Line Items]
Prepayments made under the agreement for future gas transmission services																													284,000,000		369,000,000
Range of reasonable possible loss, maximum																													$ 400,000,000		AUD 520,000,000
Dampier to Bunbury Natural Gas Pipeline [Member] | New Equity Call Plan [Member]
Loss Contingencies [Line Items]
Required plan contributions														3,000,000	5,000,000				$ 30,000,000	AUD 36,000,000
Capital investment														$ 20,000,000	AUD 27,000,000