Contingencies and Commitments - Additional Information (Detail)	1 Months Ended			3 Months Ended		12 Months Ended									3 Months Ended	0 Months Ended		3 Months Ended		12 Months Ended			3 Months Ended		12 Months Ended			1 Months Ended	12 Months Ended							0 Months Ended		12 Months Ended
	Jul. 31, 2012 Plant	Jun. 12, 2012 USD ($) Installment	Jun. 12, 2012 EUR (€)	Dec. 31, 2013 USD ($)	Jun. 30, 2013 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Mar. 26, 2012 USD ($)	Mar. 26, 2012 EUR (€)	Sep. 30, 2010 t	Feb. 21, 2013 Minimum [Member] USD ($)	Feb. 21, 2013 Maximum [Member] USD ($)	Feb. 21, 2013 Maximum [Member] EUR (€)	Jun. 30, 2013 Aluminium Bahrain [Member] USD ($)	Oct. 09, 2012 Alba [Member] USD ($) Installment	Feb. 27, 2008 Alba [Member] USD ($)	Sep. 30, 2012 Alba [Member] USD ($)	Jun. 30, 2012 Alba [Member] USD ($)	Dec. 31, 2014 Alba [Member]	Oct. 09, 2013 Alba [Member] USD ($)	Oct. 09, 2012 Alba [Member] USD ($)	Dec. 31, 2013 Department of Justice and Securities Exchange Commission [Member] USD ($)	Jun. 30, 2013 Department of Justice and Securities Exchange Commission [Member] USD ($)	Dec. 31, 2014 Department of Justice [Member] USD ($) Installment	Dec. 31, 2014 Securities and Exchange Commission [Member] USD ($) Installment	Dec. 31, 2014 Alcoa World Alumina and Chemicals [Member] Country	Nov. 30, 2006 Curtis v. Alcoa Inc. [Member] Person	Dec. 31, 2014 Alcoa [Member] USD ($)	Dec. 31, 2014 Alcoa [Member] EUR (€)	Dec. 31, 2014 Alcoa [Member] Alcoa World Alumina and Chemicals [Member]	Dec. 31, 2014 Alumina [Member]	Dec. 31, 2014 Alumina [Member] Alcoa World Alumina and Chemicals [Member]	Feb. 21, 2013 Alcoa Trasformazioni [Member] USD ($)	Feb. 21, 2013 Alcoa Trasformazioni [Member] EUR (€)	Nov. 19, 2009 Italian Government [Member] USD ($) Plant	Nov. 19, 2009 Italian Government [Member] EUR (€) Plant	Dec. 31, 2014 Italian Government [Member]	Dec. 31, 2012 Portovesme [Member] t
Loss Contingencies [Line Items]
Period of alleged conspiracy, years																	15 years
Damages claimed, value																	$ 1,000,000,000
Agreed amount payable on settlement																85,000,000									223,000,000	175,000,000
Litigation settlement number of installments																2
Contingency settlement agreement amount paid																					42,500,000	42,500,000
Contingency settlement agreement future payable date																				October 9, 2013					AWA agreed to pay a total of $223, including a fine of $209 payable in five equal installments over four years. The first installment of $41.8, plus a one-time administrative forfeiture of $14, will be paid in the first quarter of 2014 (paid on January 22, 2014), and the remaining installments of $41.8 each will be paid in the first quarters of 2015-2018 (the second installment was paid on January 9, 2015)	The Company agreed to a settlement amount of $175, but will be given credit for the $14 one-time forfeiture payment, which is part of the DOJ resolution, resulting in a total cash payment to the SEC of $161 payable in five equal installments over four years. The first installment of $32.2 will be paid to the SEC in the first quarter of 2014 (paid on January 22, 2014), and the remaining installments of $32.2 each will be paid in the first quarters of 2015-2018.
Cash payment for suit settlement															103,000,000			40,000,000								161,000,000
Restructuring and other charges						1,168,000,000	782,000,000	172,000,000							103,000,000				45,000,000
Amount of settlement offer rejected					60,000,000
Charges recorded of settlement amount				288,000,000	0																		288,000,000
Agreement settlement effective date																									Jan. 09, 2014
Number of installments																									5
Number of years in which installments is payable																									4 years	4 years
Fine payable over four years period																									209,000,000
Installments payable in first quarters of 2014																									41,800,000	32,200,000
One-time administrative forfeiture amount																									14,000,000	14,000,000
Installments payable in first quarters of 2015																									41,800,000	32,200,000
Installments payable in first quarters of 2016																									41,800,000	32,200,000
Installments payable in first quarters of 2017																									41,800,000	32,200,000
Installments payable in first quarters of 2018																									41,800,000	32,200,000
Number of installments																										5
Legal costs							391,000,000	85,000,000															7,000,000
Charges in respect of the investigations																								103,000,000
Number of countries																											7
Percentage owns on settlement																															60.00%		40.00%
Civil settlement						85,000,000
Government investigations and legal charges						384,000,000
Percentage to allocate cost of Alba civil settlement and all legal fees																													85.00%	85.00%		15.00%
Percentage of civil settlement and all legal costs associated with civil suit and government investigations																													60.00%	60.00%		40.00%
Retired former employees involved in class action																												13,000
Trial length, number of days						8 days
Management estimate for maximum exposure from class action									110,000,000	85,000,000																								97,000,000	76,000,000
Provision for contract losses												0	97,000,000	76,000,000
Number of years operating under a power supply structure																																						10 years
Charge related to European Commission announcement																																				250,000,000	173,000,000
Number of smelters	2																																			2	2
Write-off of receivable																																				20,000,000	14,000,000
Establishment reserve																																				230,000,000	159,000,000
Recovery amount		375,000,000	303,000,000
Owed by the Italian Government		65,000,000	53,000,000																										64,000,000	53,000,000
Payments to Italian Government		310,000,000	250,000,000
Payments to Italian Government, installments amount		69,000,000	50,000,000
Number of installments, litigation payment		5	5
Litigation reserve		193,000,000	159,000,000																										0
Range of reasonable possible loss, minimum		193,000,000	159,000,000
Range of reasonable possible loss, maximum		369,000,000	303,000,000
Noncurrent asset																													$ 111,000,000	€ 91,000,000
Amount of curtailment, metric-tons-per-year											44,000																												150,000