Preferred and Common Stock - Schedule of Unrecognized Compensation Expense (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012
Compensating Balances [Line Items]
2013	$ 38
2014	18
2015	1
Totals	$ 57

Share Based Compensation, Unrecognized Compensation Expense Expected To Be Recognized In Year Three

No definition available.

Name:	aa_ShareBasedCompensationUnrecognizedCompensationExpenseExpectedToBeRecognizedInYearThree
Namespace Prefix:	aa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration