Income Taxes (Reconciliation Of The U.S. Federal Statutory Rate To Alcoa's Effective Tax Rate For Continuing Operations) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Income Taxes [Abstract]
U.S. federal statutory rate	35.00%		35.00%		35.00%
Taxes on foreign operations	(8.40%)		(3.50%)		(4.80%)
Permanent differences on restructuring charges and asset disposals			0.70%		1.10%
Audit and other adjustments to prior years' accruals	(1.10%)		1.20%		(0.70%)
Noncontrolling interests	0.80%		2.60%
Statutory tax rate and law changes	0.80%		(5.10%)		4.20%
Reorganization of equity investment					4.70%
Items related to smelter operations in Italy		[1]		[1]	(9.30%)	[1]
Tax law change related to Medicare Part D			14.40%
Release of valuation allowances	(0.30%)		(10.60%)		2.30%
Amortization of goodwill	(2.80%)		(5.20%)		3.50%
Other			(2.60%)		2.30%
Effective tax rate	24.00%		26.90%		38.30%
Income tax benefit for operational losses related to certain foreign jurisdictions that are excluded from the estimated annual effective tax rate calculation	$ 8,300				$ 250
Charge for environmental remediation					15
Restructuring charge for layoffs					15
Valuation allowance placed on existing deferred tax assets					$ 41

[1] * Includes items not tax benefitted as follows: a $250 charge related to a 2009 decision by the European Commission on electricity pricing (see Note N), a $15 charge for environmental remediation, and a $15 restructuring charge for layoffs. Also includes a $41 valuation allowance placed on existing deferred tax assets.