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Segment And Geographic Area Information (Schedule Of Segment Reporting Information To Consolidate Net Income (Loss) Attributable To Alcoa) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2010
Sep. 30, 2010
Jun. 30, 2010
Mar. 31, 2010
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Segment Reporting Information [Line Items]                      
Total segment ATOI                 $ 1,893 $ 1,424 $ (234)
Interest expense                 (524) (494) (470)
Noncontrolling interests                 194 138 61
Discontinued operations                 (3) (8) (166)
Consolidated net income (loss) attributable to Alcoa (191) 172 322 308 258 61 136 (201) 611 254 (1,151)
Unallocated Amounts (Net Of Tax) [Member]
                      
Segment Reporting Information [Line Items]                      
Impact of LIFO                 (38) (16) 235
Interest expense                 (340) (321) (306)
Noncontrolling interests                 (194) (138) (61)
Corporate expense                 (290) (291) (304)
Restructuring and other charges                 (196) (134) (155)
Discontinued operations                 (3) (8) (166)
Other                 $ (221) $ (262) $ (160)