Contingencies and Commitments - Additional Information - 2 (Detail)	3 Months Ended						3 Months Ended						3 Months Ended				3 Months Ended	0 Months Ended		3 Months Ended	1 Months Ended		0 Months Ended			1 Months Ended				0 Months Ended					36 Months Ended		3 Months Ended			3 Months Ended		12 Months Ended				1 Months Ended	12 Months Ended			93 Months Ended		3 Months Ended		12 Months Ended		3 Months Ended
	Mar. 31, 2015 USD ($)	Mar. 31, 2015 EUR (€)	Jun. 12, 2012 USD ($)	Jun. 12, 2012 EUR (€)	Mar. 31, 2015 State and Local Jurisdiction [Member] USD ($)	Mar. 31, 2015 State and Local Jurisdiction [Member] BRL	Mar. 31, 2015 Maaden Alcoa Joint Venture [Member] USD ($) Entity	Mar. 31, 2015 Maaden Alcoa Joint Venture [Member] SAR	Dec. 31, 2014 Maaden Alcoa Joint Venture [Member] USD ($)	Mar. 31, 2015 Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] USD ($)	Mar. 31, 2015 Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] Other Noncurrent Liabilities and Deferred Credits [Member] USD ($)	Dec. 31, 2014 Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] Other Noncurrent Liabilities and Deferred Credits [Member] USD ($)	Mar. 31, 2015 Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] Financial Guarantee [Member] USD ($)	Mar. 31, 2015 Maaden Alcoa Joint Venture Mine And Refinery Company [Member] USD ($)	Mar. 31, 2015 Maaden Alcoa Joint Venture Mine And Refinery Company [Member] Other Noncurrent Liabilities and Deferred Credits [Member] USD ($)	Dec. 31, 2014 Maaden Alcoa Joint Venture Mine And Refinery Company [Member] Other Noncurrent Liabilities and Deferred Credits [Member] USD ($)	Mar. 31, 2015 Maaden Alcoa Joint Venture Mine And Refinery Company [Member] Financial Guarantee [Member] USD ($)	Feb. 27, 2014 Ligestra [Member] USD ($)	Feb. 27, 2014 Ligestra [Member] EUR (€)	Mar. 31, 2015 Ligestra [Member]	Jan. 31, 2014 Ligestra [Member] Minimum [Member]	Jan. 31, 2014 Ligestra [Member] Maximum [Member]	Feb. 27, 2014 Italian Ministry of Environment and Protection of Land and Sea[Member] USD ($)	Feb. 27, 2014 Italian Ministry of Environment and Protection of Land and Sea[Member] EUR (€)	Apr. 08, 2013 Alcoa World Alumina Brasil [Member] BRL	Mar. 31, 2013 Alcoa World Alumina Brasil [Member] USD ($)	Mar. 31, 2013 Alcoa World Alumina Brasil [Member] BRL	May 31, 2012 Alcoa World Alumina Brasil [Member] USD ($)	May 31, 2012 Alcoa World Alumina Brasil [Member] BRL	Apr. 08, 2013 Alcoa World Alumina Brasil [Member] Minimum [Member] USD ($)	Apr. 08, 2013 Alcoa World Alumina Brasil [Member] Maximum [Member] USD ($)	Apr. 08, 2013 Alcoa World Alumina Brasil [Member] Fixed Assets [Member] BRL	Apr. 08, 2013 Alcoa World Alumina Brasil [Member] Fixed Assets [Member] Minimum [Member] USD ($)	Apr. 08, 2013 Alcoa World Alumina Brasil [Member] Fixed Assets [Member] Maximum [Member] USD ($)	Dec. 31, 2002 Alcoa Aluminio [Member] t	Mar. 31, 2015 Maaden Company [Member] Maaden Alcoa Joint Venture [Member]	Mar. 31, 2015 Alcoa [Member] Maaden Alcoa Joint Venture [Member] USD ($)	Mar. 31, 2015 Alcoa [Member] Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] USD ($)	Mar. 31, 2015 Alcoa [Member] Maaden Alcoa Joint Venture Mine And Refinery Company [Member] USD ($)	Mar. 31, 2015 Estreito Project [Member] USD ($) MWh	Mar. 31, 2015 Estreito Project [Member] BRL	Dec. 31, 2014 Portovesme [Member] USD ($)	Dec. 31, 2009 Portovesme [Member] USD ($)	Dec. 31, 2012 Baie Comeau [Member] USD ($)	Dec. 31, 2012 Mosjoen [Member] USD ($)	Oct. 31, 2013 Fusina [Member] USD ($)	Dec. 31, 2009 Fusina [Member] USD ($)	Dec. 31, 2004 Dampier to Bunbury Natural Gas Pipeline [Member] USD ($)	Dec. 31, 2004 Dampier to Bunbury Natural Gas Pipeline [Member] AUD	Sep. 30, 2011 Dampier to Bunbury Natural Gas Pipeline [Member] USD ($)	Sep. 30, 2011 Dampier to Bunbury Natural Gas Pipeline [Member] AUD	Mar. 31, 2015 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] USD ($)	Mar. 31, 2015 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] AUD	Dec. 31, 2014 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] USD ($)	Dec. 31, 2014 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] AUD	Mar. 31, 2015 Dampier to Bunbury Natural Gas Pipeline [Member] New Equity Call Plan [Member] USD ($)	Mar. 31, 2015 Dampier to Bunbury Natural Gas Pipeline [Member] New Equity Call Plan [Member] AUD
Loss Contingencies [Line Items]
Increase in remediation reserve																																										$ 3,000,000	$ 3,000,000	$ 25,000,000	$ 20,000,000	$ 0	$ 12,000,000
Percentage of payments and remediation costs																					50.00%	80.00%
Soil remediation project, estimated cost																							33,000,000	24,000,000
Payments for emergency action and natural resource damages																							25,000,000	18,000,000
Costs and payments																		17,000,000	12,000,000
Costs and payments related to damages																		9,000,000	6,000,000
Payment period																				10 years
Revised project cost submitted to reflect the removal of a larger volume of contaminated soil	7,000,000
Total combined assessments	247,000,000	228,000,000			40,000,000	130,000,000
Disallowed tax credits																										110,000,000	220,000,000					175,000,000	0	55,000,000
Percentage of penalty of the gross disallowed amount																									50.00%	50.00%	50.00%
Value added tax receivable																												41,000,000	82,000,000
Estimated range of reasonably possible loss, minimum																									155,000,000					0	50,000,000
Administrative appeal, assessment period																									2 years
Metal sold per month																																			2,000
Ownership interest issued as guarantee for Saudi Arabian Joint Venture																																				74.90%
Ownership interest issued as guarantee for Saudi Arabian Joint Venture							25.10%	25.10%
Number of companies in Saudi Arabian joint venture							3	3
Amount invested by Alcoa and Aluminum Financing Limited							10,800,000,000	40,500,000,000																													1,100,000,000																	39,000,000	40,000,000	30,000,000	36,000,000
Capital investment							4,000,000																														956,000,000											17,000,000	24,000,000	141,000,000	176,000,000	3,000,000	5,000,000			4,000,000	6,000,000
Equity method investment, carrying value							969,000,000		983,000,000
Capital investment										1,133,000,000				560,000,000																								4,515,000,000	2,232,000,000
Debt service requirements, principal													176,000,000				120,000,000
Debt service requirements, interest maximum													60,000,000				30,000,000
Guarantee issued on behalf of smelting and rolling mill companies											8,000,000	8,000,000			4,000,000	4,000,000
Percentage of amount required to be contributed in the event Alcoa would be required to make payments under the guarantees														40.00%
Investment percentage																																								25.49%	25.49%							20.00%	20.00%
Assured power from installed capacity																																								150	150
Estimated project costs																																								1,590,000,000	5,170,000,000
Aluminio's share of project																																								400,000,000	1,320,000,000
Commitment expended on the project																																								390,000,000	1,270,000,000
Prepayments made under the agreement for future gas transmission services																																																				279,000,000	362,000,000
Range of reasonable possible loss, maximum			$ 329,000,000	€ 303,000,000																																																$ 400,000,000	520,000,000