Income Taxes - Reconciliation of U.S. Federal Statutory Rate to Alcoa's Effective Tax Rate (Parenthetical) (Detail)	12 Months Ended
	Nov. 30, 2014
Reconciliation Of Effective Income Tax Rate [Line Items]
Corporate tax rate	30.00%
Tax Year Two Thousand And Fifteen [Member]
Reconciliation Of Effective Income Tax Rate [Line Items]
Corporate tax rate	28.00%
Tax Year Two Thousand And Sixteen [Member]
Reconciliation Of Effective Income Tax Rate [Line Items]
Corporate tax rate	25.00%