Contingencies and Commitments - Additional Information - 2 (Detail) BRL in Millions, SAR in Billions						1 Months Ended					3 Months Ended			6 Months Ended				12 Months Ended						36 Months Ended	93 Months Ended
	Apr. 08, 2015 USD ($) Installment Refinery	Feb. 27, 2014 EUR (€)	Feb. 27, 2014 USD ($)	Apr. 08, 2013 USD ($)	Apr. 08, 2013 BRL	Jan. 31, 2014	Oct. 31, 2013 USD ($)	Mar. 31, 2013 USD ($)	May. 31, 2012 USD ($)	May. 31, 2012 BRL	Jun. 30, 2015 USD ($)	Jun. 30, 2015 AUD	Mar. 31, 2015 USD ($)	Jun. 30, 2015 USD ($) MWh Entity	Jun. 30, 2015 BRL MWh Entity	Jun. 30, 2015 AUD MWh Entity	Jun. 30, 2015 SAR MWh Entity	Dec. 31, 2014 USD ($)	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	Jun. 30, 2015 EUR (€)	Jun. 30, 2015 USD ($)	Jun. 30, 2015 BRL	Jun. 30, 2015 AUD	Apr. 08, 2013 BRL	Mar. 31, 2013 BRL	Jun. 30, 2012 EUR (€) Installment	Jun. 30, 2012 USD ($) Installment
Loss Contingencies [Line Items]
Revised project cost submitted to reflect the removal of a larger volume of contaminated soil													$ 7,000,000
Total combined assessments																											€ 228,000,000	$ 253,000,000
Range of reasonable possible loss, maximum																																	€ 303,000,000	$ 337,000,000
Number of installments | Installment																																	5	5
State and Local Jurisdiction [Member]
Loss Contingencies [Line Items]
Total combined assessments																												$ 41,000,000	BRL 130
Maaden Alcoa Joint Venture [Member]
Loss Contingencies [Line Items]
Ownership interest issued as guarantee for Saudi Arabian Joint Venture																											25.10%	25.10%	25.10%	25.10%
Number of companies in Saudi Arabian joint venture | Entity														3	3	3	3
Amount invested by Alcoa and Aluminum Financing Limited														$ 10,800,000,000			SAR 40.5
Capital investment											$ 5,000,000			9,000,000
Equity method investment, carrying value																		$ 983,000,000										$ 952,000,000
Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member]
Loss Contingencies [Line Items]
Capital investment																												1,133,000,000
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																		8,000,000										8,000,000
Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] | Financial Guarantee [Member]
Loss Contingencies [Line Items]
Debt service requirements, principal														176,000,000
Debt service requirements, interest maximum														$ 50,000,000
Maaden Alcoa Joint Venture Mine And Refinery Company [Member]
Loss Contingencies [Line Items]
Capital investment																												560,000,000
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%	40.00%
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																		4,000,000										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
Alcoa [Member] | Maaden Alcoa Joint Venture [Member]
Loss Contingencies [Line Items]
Amount invested by Alcoa and Aluminum Financing Limited														1,100,000,000
Capital investment														$ 961,000,000
Alcoa [Member] | Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member]
Loss Contingencies [Line Items]
Capital investment																												4,515,000,000
Alcoa [Member] | Maaden Alcoa Joint Venture Mine And Refinery Company [Member]
Loss Contingencies [Line Items]
Capital investment																												$ 2,232,000,000
Ligestra [Member]
Loss Contingencies [Line Items]
Costs and payments		€ 12,000,000	$ 17,000,000
Costs and payments related to damages		6,000,000	9,000,000
Payment period														10 years	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		24,000,000	33,000,000
Payments for emergency action and natural resource damages		€ 18,000,000	$ 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 155
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				50,000,000
Alcoa World Alumina Brasil [Member] | Fixed Assets [Member]
Loss Contingencies [Line Items]
Disallowed tax credits | BRL																															BRL 175
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				$ 55,000,000
Alcoa Aluminio [Member]
Loss Contingencies [Line Items]
Metal sold per month | t																								2,000
Maaden Company [Member] | Maaden Alcoa Joint Venture [Member]
Loss Contingencies [Line Items]
Percent of guarantee issued by co-venturing entity																											74.90%	74.90%	74.90%	74.90%
Estreito Project [Member]
Loss Contingencies [Line Items]
Investment percentage														25.49%	25.49%	25.49%	25.49%
Assured power from installed capacity | MWh														150	150	150	150
Estimated project costs														$ 1,650,000,000	BRL 5,170
Aluminio's share of project														420,000,000	1,320
Commitment expended on the project														$ 400,000,000	BRL 1,270
Majority-Owned Subsidiary | Alcoa Of Australia Limited [Member] | Service Agreements [Member]
Loss Contingencies [Line Items]
Gas supply agreement period														12 years	12 years	12 years	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 | Alcoa Of Australia Limited [Member] | Service Agreements [Member] | First Installment [Member]
Loss Contingencies [Line Items]
Gas supply agreement prepayment amount	300,000,000
Majority-Owned Subsidiary | Alcoa Of Australia Limited [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 [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		$ 141,000,000	AUD 176,000,000
Investment percentage																						20.00%	20.00%
Dampier to Bunbury Natural Gas Pipeline [Member] | Three-Year Equity Call Plan [Member]
Loss Contingencies [Line Items]
Amount invested by Alcoa and Aluminum Financing Limited																		$ 39,000,000	AUD 40,000,000
Capital investment											$ 5,000,000	AUD 6,000,000		$ 8,000,000		AUD 11,000,000
Prepayments made under the agreement for future gas transmission services																												$ 280,000,000		AUD 364,000,000
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]
Amount invested by Alcoa and Aluminum Financing Limited														30,000,000		36,000,000
Capital investment														$ 9,000,000		AUD 12,000,000