Debt - Additional Information (Detail) In Millions, unless otherwise specified	1 Months Ended		12 Months Ended						12 Months Ended	1 Months Ended				12 Months Ended			12 Months Ended			1 Months Ended	12 Months Ended		2 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended		1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended				12 Months Ended					12 Months Ended																		3 Months Ended		12 Months Ended		6 Months Ended		12 Months Ended												1 Months Ended	12 Months Ended
	Jan. 31, 2012 USD ($)	May 31, 2011 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 2012 BRL	Dec. 31, 2011 USD ($)	Dec. 31, 2011 BRL	Dec. 31, 2010 USD ($)	Jul. 25, 2011 USD ($)	Dec. 31, 2012 Aluminio [Member] USD ($) D	May 31, 2011 Debt Principal [Member] USD ($)	May 31, 2011 Debt Accrued And Unpaid Interest [Member] USD ($)	Dec. 31, 2012 Second Loan Agreement [Member] First Loans [Member] USD ($)	Dec. 31, 2012 Second Loan Agreement [Member] First Loans [Member] BRL	Dec. 31, 2012 Commercial Paper [Member] USD ($)	Dec. 31, 2011 Commercial Paper [Member] USD ($)	Dec. 31, 2010 Commercial Paper [Member]	Dec. 31, 2012 First Loan Agreement [Member] USD ($)	Mar. 31, 2008 First Loan Agreement [Member] First Loans [Member] USD ($)	Mar. 31, 2008 First Loan Agreement [Member] First Loans [Member] BRL	Dec. 31, 2012 Two Term Loan Agreements [Member] USD ($)	Dec. 31, 2012 Two Term Loan Agreements [Member]	Jan. 31, 2012 Two Term Loan Agreements [Member] USD ($)	Nov. 30, 2012 Third Loan Agreement [Member] USD ($)	Dec. 31, 2012 Third Loan Agreement [Member] USD ($)	Dec. 31, 2012 Minimum [Member] Commercial Paper [Member]	Dec. 31, 2012 Maximum [Member] Commercial Paper [Member]	Apr. 30, 2011 5.40% Notes, due 2021 [Member] USD ($)	Dec. 31, 2012 5.40% Notes, due 2021 [Member]	Apr. 30, 2011 5.40% Notes, due 2021 [Member] Brazil Bauxite Mine [Member] USD ($)	Dec. 31, 2012 5.40% Notes, due 2021 [Member] Minimum [Member] D	Dec. 31, 2012 5.40% Notes, due 2021 [Member] Maximum [Member] D	May 31, 2011 5.375% Notes, due 2013 [Member] USD ($)	Dec. 31, 2012 5.375% Notes, due 2013 [Member]	May 31, 2011 6% Notes, due 2013 [Member] USD ($)	Dec. 31, 2012 6% Notes, due 2013 [Member]	Dec. 31, 2011 6% Notes, due 2013 [Member] USD ($)	Dec. 31, 2012 Two Of The Subloans [Member] Second Loan Agreement [Member] First Loans [Member]	Dec. 31, 2012 Two Of The Subloans [Member] Loan Agreement With BNDES [Member] BRL	Dec. 31, 2012 Two Of The Subloans [Member] Loan Agreement With BNDES [Member] First Loans [Member] USD ($)	Dec. 31, 2012 Two Of The Subloans [Member] Loan Agreement With BNDES [Member] First Loans [Member] BRL	Dec. 31, 2012 Third Subloan [Member] Second Loan Agreement [Member] First Loans [Member] USD ($)	Dec. 31, 2012 Third Subloan [Member] Second Loan Agreement [Member] First Loans [Member] BRL	Dec. 31, 2012 Third Subloan [Member] Loan Agreement With BNDES [Member] BRL	Dec. 31, 2012 Revolving Credit Agreement [Member] USD ($) Y	Dec. 31, 2012 Revolving Credit Agreement [Member] Second Loan Agreement [Member] USD ($)	Dec. 31, 2012 Revolving Credit Agreement [Member] First Loan Agreement [Member] USD ($)	Dec. 31, 2012 Revolving Credit Agreement [Member] Two Term Loan Agreements [Member] Agreement	Dec. 31, 2012 Revolving Credit Agreement [Member] Third Loan Agreement [Member] USD ($)	Dec. 31, 2012 Revolving Credit Agreement [Member] Fourth Loan Agreement [Member] USD ($)	Dec. 31, 2012 Revolving Credit Agreement [Member] Fifth Loan Agreement [Member] USD ($)	Dec. 31, 2012 Revolving Credit Agreement [Member] Sixth Loan Agreement Member USD ($)	Dec. 31, 2011 Subloan Of $233 [Member] First Loans [Member]	Dec. 31, 2012 Subloan Of $233 [Member] First Loan Agreement [Member] First Loans [Member] USD ($)	Dec. 31, 2012 Subloan Of $233 [Member] First Loan Agreement [Member] First Loans [Member] BRL	Dec. 31, 2011 Subloan Of $233 [Member] First Loan Agreement [Member] First Loans [Member] USD ($)	Dec. 31, 2011 Subloan Of $233 [Member] First Loan Agreement [Member] First Loans [Member] BRL	Dec. 31, 2011 Subloan Of $15 [Member] First Loans [Member]	Dec. 31, 2012 Subloan Of $15 [Member] First Loan Agreement [Member] First Loans [Member] USD ($)	Dec. 31, 2012 Subloan Of $15 [Member] First Loan Agreement [Member] First Loans [Member] BRL	Dec. 31, 2011 Subloan Of $15 [Member] First Loan Agreement [Member] First Loans [Member] USD ($)	Dec. 31, 2011 Subloan Of $15 [Member] First Loan Agreement [Member] First Loans [Member] BRL	Mar. 31, 2008 Four Of The Subloans [Member] First Loan Agreement [Member] First Loans [Member] USD ($)	Mar. 31, 2008 Four Of The Subloans [Member] First Loan Agreement [Member] First Loans [Member] BRL	Dec. 31, 2012 Four Of The Subloans [Member] First Loan Agreement [Member] First Loans [Member]	Dec. 31, 2011 Four Of The Subloans [Member] First Loan Agreement [Member] First Loans [Member]	Jun. 30, 2008 Fifth Subloan [Member] First Loan Agreement [Member] First Loans [Member] USD ($)	Jun. 30, 2008 Fifth Subloan [Member] First Loan Agreement [Member] First Loans [Member] BRL	Dec. 31, 2012 Fifth Subloan [Member] First Loan Agreement [Member] First Loans [Member]	Dec. 31, 2011 Fifth Subloan [Member] First Loan Agreement [Member] First Loans [Member]	Dec. 31, 2012 Subloan Of $339 [Member] Second Loan Agreement [Member] First Loans [Member] USD ($)	Dec. 31, 2012 Subloan Of $339 [Member] Second Loan Agreement [Member] First Loans [Member] BRL	Dec. 31, 2011 Subloan Of $339 [Member] Second Loan Agreement [Member] First Loans [Member] USD ($)	Dec. 31, 2011 Subloan Of $339 [Member] Second Loan Agreement [Member] First Loans [Member] BRL	Dec. 31, 2012 Subloan Of $35 [Member] Second Loan Agreement [Member] First Loans [Member] USD ($)	Dec. 31, 2012 Subloan Of $35 [Member] Second Loan Agreement [Member] First Loans [Member] BRL	Dec. 31, 2011 Subloan Of $35 [Member] Second Loan Agreement [Member] First Loans [Member] USD ($)	Dec. 31, 2011 Subloan Of $35 [Member] Second Loan Agreement [Member] First Loans [Member] BRL	Jun. 30, 2008 Three Of The Subloans [Member] Loan Agreement With BNDES [Member] USD ($)	Jun. 30, 2008 Three Of The Subloans [Member] Loan Agreement With BNDES [Member] BRL	Aug. 31, 2012 Midwestern Disaster Area Revenue Bonds Series 2012 Due 2042 [Member] USD ($)	Dec. 31, 2012 Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Principal amount of long-term debt maturing in year 2013			$ 465
Principal amount of long-term debt maturing in year 2014			661
Principal amount of long-term debt maturing in year 2015			34
Principal amount of long-term debt maturing in year 2016			33
Principal amount of long-term debt maturing in year 2017			780
Payments on long-term debt	322	972	1,489		1,194		1,757			881	17
Interest rate of bonds	6.00%		4.75%	4.75%																								5.40%					5.375%		6.00%	6.00%
Debt instruments agreement date																																																																																August 2012
Proceeds from issuance of bonds																																																																																250
Restricted cash																																																																																248
Debt instruments maturity date																																																																																2042
Restricted cash, current			171
Debt instrument frequency of periodic payment			Semi-annually	Semi-annually
Redemption date of Bonds			Alcoa has the option through the loan agreement to redeem the Bonds, as a whole or in part, on or after August 1, 2022, on at least 30 days, but not more than 60 days	Alcoa has the option through the loan agreement to redeem the Bonds, as a whole or in part, on or after August 1, 2022, on at least 30 days, but not more than 60 days
Percentage of principal amount repayment			100.00%	100.00%
Senior debt securities issued under shelf registration statement			1,250		1,250																						1,250
Net proceeds received from public debt offering			972		1,256		1,126																				1,241
Debt instrument, maturity date																												2021					2013		2013																																														July 25, 2016
Early repayment of outstanding notes																											881		101			284
Option to redeem notes, period prior to notice to holders, days																														30	60
Debt repurchase price, percentage of aggregate principal																												101.00%
Tender offer completed, debt amount																																		400
Aggregate outstanding principal amount								500							224																	269		328		422																	233	470	233	470		15	30	15	30									339	589			35	61
Purchase premiums repaid recorded as interest expense		74
Interest rate swaps terminated, notional amount	315		550		550		825
Gain resulting from termination of interest rate swaps, recorded as interest expense			33
Commitment on loan agreement			85	177								374	650					248	500																																																											397	687
Interest on subloans																																							339	589	35	61																				233	470			15	30
Long-term interest rate												2.02%	2.02%	0.80%	0.60%	0.70%																					1.99%																											5.00%	6.00%			2.40%										1.48%	1.48%
Weighted-average margin on long term debt																																																																2.13%
Percentage of average cost incurred in raising capital																																																																				3.56%	3.59%
Early repayment of outstanding borrowings			20	38	5	9																																															51	102	131	209		3	7	7	11									176	356	67	113	22	46	7	11
Line of credit facility amount outstanding			311	637	355	661		3,750	280								100					350		150																															55	102				3	7											191	356			23	42
Weighted-average interest rate			6.49%	6.49%	7.50%	7.50%			2.32%																																											8.13%					5.99%															7.99%	7.99%			5.61%	5.61%
Principal and interest																																						667					20
Additional borrowing amount			7	13	5	8
Interest rate margin			1.55%	1.55%
Outstanding borrowings			86	177
Interest rate of outstanding borrowings			6.55%	6.55%
Average outstanding commercial paper														354	197
Debt instrument maturity date, description														Matures at various times within one year
Revolving credit facility, term																																												5
Letters of credit sublimit under credit facility								1,000
Extension of maturity period			1 year	1 year
Agreed credit Facility amount			3,700
Approved credit facility amount			50
Extended credit facility maturity date			July 25, 2017	July 25, 2017
Fees paid to maintain credit facility														0.25%
Applicable margin on LIBOR loans																									0.50%	1.50%
Outstanding borrowings														3,275
Short-term borrowings			53		62
Accounts payable settlement arrangements			48		53
Number of revolving credit facility agreements																																															6
Agreed credit facility amount																																												640
Pension contributions			561		336		113
Applicable margin on LIBOR																	1.25%				1.50%			1.375%
Repayment of term loans																				200			150
Revolving credit expiration amount																																													$ 100	$ 150		$ 100	$ 140	$ 100	$ 50
Line of credit facility, expiration date																																													Sep. 30, 2013	Mar. 31, 2013		Sep. 30, 2013	Oct. 31, 2013	Dec. 31, 2013	Dec. 31, 2015
Weighted-average maturity days									172