Contingencies and Commitments - Additional Information - 2 (Detail) € in Millions, BRL in Millions							1 Months Ended						6 Months Ended	12 Months Ended									36 Months Ended	93 Months Ended
	Apr. 08, 2015 USD ($) Installment Refinery	Feb. 27, 2014 EUR (€)	Feb. 27, 2014 USD ($)	Sep. 30, 2013 MW	Apr. 08, 2013 USD ($)	Apr. 08, 2013 BRL	Sep. 30, 2015 USD ($)	Jan. 31, 2014	Oct. 31, 2013 USD ($)	Mar. 31, 2013 USD ($)	May. 31, 2012 USD ($)	May. 31, 2012 BRL	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) MWh	Dec. 31, 2015 AUD MWh	Dec. 31, 2014 USD ($)	Dec. 31, 2014 AUD	Dec. 31, 2013 USD ($) MW	Dec. 31, 2012 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2004 USD ($)	Dec. 31, 2004 AUD	Dec. 31, 2002 t	Sep. 30, 2011 USD ($)	Sep. 30, 2011 AUD	Dec. 31, 2015 EUR (€)	Dec. 31, 2015 USD ($)	Dec. 31, 2015 BRL	Dec. 31, 2015 AUD	Dec. 31, 2014 BRL	Apr. 08, 2013 BRL	Mar. 31, 2013 BRL	Jun. 30, 2012 Installment
Loss Contingencies [Line Items]
Increase in remediation reserve							$ 1,000,000							$ 115,000,000
Revised project cost submitted to reflect the removal of a larger volume of contaminated soil														7,000,000
Total combined assessments																										€ 241	$ 263,000,000
Investment percentage under equity method																40.00%														40.00%
Percentage of power self-sufficiency upon completion of project with full operating capacity				70.00%
Total energy demand | MW				690
Temporarily declined in energy demand | MW				675														675
Number of installments | Installment																																	5
Asset included in other noncurrent assets																											288,000,000
Purchase obligations due in 2016																											74,000,000
Purchase obligations due in 2017																											130,000,000
Purchase obligations due in 2018																											133,000,000
Purchase obligations due in 2019																											126,000,000
Purchase obligations due in 2020																											129,000,000
Purchase obligations due thereafter																											1,711,000,000
Purchase obligations expenditures														131,000,000		$ 178,000,000		$ 163,000,000
Operating leases, expense														$ 210,000,000		227,000,000		$ 232,000,000
Long-term operating leases, minimum annual rentals due in 2015																											243,000,000
Long-term operating leases, minimum annual rentals due in 2016																											168,000,000
Long-term operating leases, minimum annual rentals due in 2017																											130,000,000
Long-term operating leases, minimum annual rentals due in 2018																											100,000,000
Long-term operating leases, minimum annual rentals due in 2019																											74,000,000
Long-term operating leases, minimum annual rentals due thereafter																											138,000,000
Guarantees of third party related to project financing																											478,000,000
Guarantees, total amount committed																											320,000,000
Letters of credit, total amount committed																											510,000,000
Letters of credit, expiration date														2016	2016
Total amount committed under outstanding surety bonds																											159,000,000
Surety bonds, expiration date														2016	2016
Gas Supply Contract [Member]
Loss Contingencies [Line Items]
Letters of credit, total amount committed																											$ 200,000,000
Minimum [Member]
Loss Contingencies [Line Items]
Expiration date of unconditional purchase obligations for energy														2018	2018
Guarantees, expiration date														2017	2017
Minimum [Member] | Outstanding bank guarantees [Member]
Loss Contingencies [Line Items]
Guarantees, expiration date														2016	2016
Maximum [Member]
Loss Contingencies [Line Items]
Investment percentage under equity method																										50.00%	50.00%	50.00%	50.00%
Expiration date of unconditional purchase obligations for energy														2036	2036
Guarantees, expiration date														2024	2024
Maximum [Member] | Outstanding bank guarantees [Member]
Loss Contingencies [Line Items]
Guarantees, expiration date														2023	2023
Energy, Raw Materials, and Other Goods and Services [Member]
Loss Contingencies [Line Items]
Purchase obligations due in 2016																											$ 3,015,000,000
Purchase obligations due in 2017																											1,807,000,000
Purchase obligations due in 2018																											1,569,000,000
Purchase obligations due in 2019																											1,496,000,000
Purchase obligations due in 2020																											1,401,000,000
Purchase obligations due thereafter																											13,251,000,000
State and Local Jurisdiction [Member]
Loss Contingencies [Line Items]
Total combined assessments																											$ 35,000,000	BRL 135
Machadinho and Barra Grande [Member]
Loss Contingencies [Line Items]
Commitment to taking share of output in associated projects at cost, in years														30 years	30 years
Serrado Facao and Estreito Projects [Member]
Loss Contingencies [Line Items]
Commitment to taking share of output in associated projects at cost, in years														26 years	26 years
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
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					27,000,000
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					$ 30,000,000
Barra Grande [Member]
Loss Contingencies [Line Items]
Assured power from installed capacity | MWh														160	160
Investment percentage under equity method																										42.18%	42.18%	42.18%	42.18%
Total investment in project																132,000,000											$ 94,000,000	BRL 374		BRL 355
Estreito Project [Member]
Loss Contingencies [Line Items]
Investment percentage														25.49%	25.49%
Assured power from installed capacity | MWh														150	150
Alcoa Aluminio [Member]
Loss Contingencies [Line Items]
Metal sold per month | t																							2,000
Majority-Owned Subsidiary | Alcoa Of Australia Limited [Member] | Service Agreements [Member]
Loss Contingencies [Line Items]
Gas supply agreement period														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
Asset included in other noncurrent assets																										€ 395	$ 288,000,000
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 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	$ 12,000,000					$ 20,000,000
Machadinho [Member]
Loss Contingencies [Line Items]
Investment percentage														30.99%	30.99%
Assured power from installed capacity | MWh														120	120
Serra Do Facao Project [Member]
Loss Contingencies [Line Items]
Assured power from installed capacity | MWh														65	65
Investment percentage under equity method																										34.97%	34.97%	34.97%	34.97%
Total investment in project																66,000,000											$ 52,000,000	BRL 208		BRL 178
Dampier to Bunbury Natural Gas Pipeline [Member]
Loss Contingencies [Line Items]
Investment percentage																					20.00%	20.00%
Capital investment																					$ 17,000,000	AUD 24,000,000		$ 141,000,000	AUD 176,000,000
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
Prepayments made under the agreement for future gas transmission services																											268,000,000		AUD 368,000,000
Range of reasonable possible loss, maximum																											$ 380,000,000		AUD 520,000,000
Dampier to Bunbury Natural Gas Pipeline [Member] | New Equity Call Plan [Member]
Loss Contingencies [Line Items]
Capital investment														$ 17,000,000	AUD 22,000,000
Required plan contributions																$ 30,000,000	AUD 36,000,000