Contingencies and Commitments - Additional Information - 2 (Detail) In Millions, unless otherwise specified	6 Months Ended								3 Months Ended	6 Months Ended	60 Months Ended			6 Months Ended		12 Months Ended		93 Months Ended		6 Months Ended								6 Months Ended				3 Months Ended		6 Months Ended		33 Months Ended		0 Months Ended	1 Months Ended				0 Months Ended					36 Months Ended	0 Months Ended		6 Months Ended	1 Months Ended		0 Months Ended			12 Months Ended			3 Months Ended	12 Months Ended
	Jun. 30, 2014 USD ($)	Jun. 30, 2014 EUR (€)	Jun. 30, 2012 USD ($)	Jun. 30, 2012 EUR (€)	Jun. 30, 2014 Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] USD ($)	Jun. 30, 2014 Maaden Alcoa Joint Venture Mine And Refinery Company [Member] USD ($)	Jan. 31, 2014 Maaden Alcoa Joint Venture Mine And Refinery Company [Member] USD ($)	Jun. 30, 2014 Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] USD ($)	Jun. 30, 2014 Maaden Alcoa Joint Venture [Member] USD ($)	Jun. 30, 2014 Maaden Alcoa Joint Venture [Member] USD ($) Agency	Jun. 30, 2014 Maaden Alcoa Joint Venture [Member] USD ($)	Mar. 31, 2014 Maaden Alcoa Joint Venture [Member]	Dec. 31, 2013 Maaden Alcoa Joint Venture [Member] USD ($)	Jun. 30, 2014 Maaden Alcoa Joint Venture Mine And Refinery Company [Member] USD ($)	Jan. 31, 2014 Maaden Alcoa Joint Venture Mine And Refinery Company [Member] USD ($)	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	Jun. 30, 2014 Maaden Alcoa Joint Venture [Member] USD ($) Entity	Jun. 30, 2014 Maaden Alcoa Joint Venture [Member] SAR	Jun. 30, 2014 Other Noncurrent Liabilities and Deferred Credits [Member] Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] USD ($)	Dec. 31, 2013 Other Noncurrent Liabilities and Deferred Credits [Member] Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] USD ($)	Jun. 30, 2014 Other Noncurrent Liabilities and Deferred Credits [Member] Maaden Alcoa Joint Venture Mine And Refinery Company [Member] USD ($)	Dec. 31, 2013 Other Noncurrent Liabilities and Deferred Credits [Member] Maaden Alcoa Joint Venture Mine And Refinery Company [Member] USD ($)	Jun. 30, 2014 State and Local Jurisdiction [Member] USD ($)	Jun. 30, 2014 State and Local Jurisdiction [Member] BRL	Jun. 30, 2014 Financial Guarantee [Member] Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] USD ($)	Jun. 30, 2014 Financial Guarantee [Member] Maaden Alcoa Joint Venture Mine And Refinery Company [Member] USD ($)	Jun. 30, 2014 Estreito Project [Member] USD ($) MWh	Jun. 30, 2014 Estreito Project [Member] BRL	Jun. 30, 2014 Three-Year Equity Call Plan [Member] Dampier to Bunbury Natural Gas Pipeline [Member] USD ($)	Jun. 30, 2014 Three-Year Equity Call Plan [Member] Dampier to Bunbury Natural Gas Pipeline [Member] AUD	Jun. 30, 2014 Three-Year Equity Call Plan [Member] Dampier to Bunbury Natural Gas Pipeline [Member] USD ($)	Jun. 30, 2014 Three-Year Equity Call Plan [Member] Dampier to Bunbury Natural Gas Pipeline [Member] AUD	Jun. 30, 2014 Three-Year Equity Call Plan [Member] Dampier to Bunbury Natural Gas Pipeline [Member] USD ($)	Jun. 30, 2014 Three-Year Equity Call Plan [Member] Dampier to Bunbury Natural Gas Pipeline [Member] AUD	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	Feb. 27, 2014 Ligestra [Member] USD ($)	Feb. 27, 2014 Ligestra [Member] EUR (€)	Jun. 30, 2014 Ligestra [Member]	Jan. 31, 2014 Ligestra [Member] Minimum [Member]	Jan. 31, 2014 Ligestra [Member] Maximum [Member]	Feb. 27, 2014 Italian Ministry of Environment and Protection of Land and Sea[Member] USD ($)	Feb. 27, 2014 Italian Ministry of Environment and Protection of Land and Sea[Member] EUR (€)	Jun. 30, 2014 Maaden Company [Member] Maaden Alcoa Joint Venture [Member]	Dec. 31, 2009 Fusina [Member] USD ($)	Dec. 31, 2012 Baie Comeau [Member] USD ($)	Dec. 31, 2012 Mosjoen [Member] USD ($)	Jun. 30, 2014 Portovesme [Member] USD ($)	Dec. 31, 2009 Portovesme [Member] USD ($)
Loss Contingencies [Line Items]
Increase in remediation reserve	$ 38																																																								$ 12	$ 25	$ 20	$ 3	$ 3
Percentage of payments and remediation costs																																																				50.00%	80.00%
Soil remediation project, estimated cost																																																						33	24
Payments for emergency action and natural resource damages																																																						25	18
Costs and payments																																																	17	12
Costs and payments related to damages																																																	9	6
Payment period																																																			10 years
Total combined assessments	330	242																								57	125
Disallowed tax credits																																							110	220					175	0	80
Percentage of penalty of the gross disallowed amount																																							50.00%	50.00%
Value added tax receivable																																									41	82
Estimated range of reasonably possible loss, minimum																																						155					0	70
Administrative appeal, assessment period																																						2 years
Metal sold per month																																																2,000
Ownership interest issued as guarantee for Saudi Arabian Joint Venture																																																								74.90%
Investment percentage in Australian Project									25.10%	25.10%	25.10%					20.00%	20.00%
Number of companies in Saudi Arabian joint venture																				3	3
Amount invested by Alcoa and Aluminum Financing Limited										1,100										10,800	40,500															40	40
Additional contributions									29	83	915					17	24	141	176													1	2	3	4	32	33
Equity method investment, carrying value									968	968	968		951
Capital investment					4,515	1,992	240	1,133						500	60
Debt service requirements, principal																												121	67
Debt service requirements, interest maximum																												60	30
Guarantee issued on behalf of smelting and rolling mill companies																						8	10	3	4
Percentage of amount required to be contributed in the event Alcoa would be required to make payments under the guarantees														40.00%
Number of agencies needed to downgrade Alcoa's credit rating below investment grade in order to require Alcoa to provide a letter of credit or fund an escrow account										2
Minimum percentage of equity commitment required									67.00%	67.00%	67.00%	67.00%
Investment percentage in Brazilian project																														25.49%	25.49%
Assured power from installed capacity																														150	150
Estimated project costs																														2,350	5,170
Aluminio's share of project																														600	1,320
Commitment expended on the project																														580	1,270
Prepayments made under the agreement for future gas transmission services																																335	356	335	356	335	356
Alcoa's maximum exposure to loss in projects			$ 413	€ 303																												$ 470	500	$ 470	500	$ 470	500