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Segment Information - Schedule of Operating Results of Alcoa's Reportable Segment (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2014 | Sep. 30, 2013 | Sep. 30, 2014 | Sep. 30, 2013
Segment Reporting Information [Line Items] |  |  |  |
Total sales | $ 6,239 | $ 5,765 | $ 17,529 | $ 17,447
Equity loss | (15) | (18) | (83) | (40)
Depreciation, depletion, and amortization | 326 | 327 | 973 | 1,009
Income taxes | 263 | 124 | 584 | 377
After-tax operating income (ATOI) | 619 | 338 | 1,362 | 993
Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 7,436 | 6,939 | 21,136 | 21,186
Intersegment Eliminations [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment sales | 1,264 | 1,251 | 3,793 | 3,925
Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | 6,172 | 5,688 | 17,343 | 17,261
Alumina [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Equity loss | (7) | (2) | (19) | (2)
Depreciation, depletion, and amortization | 100 | 100 | 297 | 324
Income taxes | 26 | 17 | 78 | 45
After-tax operating income (ATOI) | 62 | 67 | 192 | 189
Alumina [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 1,368 | 1,359 | 3,964 | 4,183
Alumina [Member] | Intersegment Eliminations [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment sales | 482 | 513 | 1,472 | 1,689
Alumina [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | 886 | 846 | 2,492 | 2,494
Primary Metals [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Equity loss |  | (13) | (45) | (29)
Depreciation, depletion, and amortization | 124 | 131 | 377 | 398
Income taxes | 95 | (16) | 114 | (40)
After-tax operating income (ATOI) | 245 | 8 | 327 | 15
Primary Metals [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 2,595 | 2,291 | 7,130 | 7,073
Primary Metals [Member] | Intersegment Eliminations [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment sales | 730 | 691 | 2,182 | 2,095
Primary Metals [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | 1,865 | 1,600 | 4,948 | 4,978
Global Rolled Products [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Equity loss | (8) | (3) | (19) | (9)
Depreciation, depletion, and amortization | 62 | 56 | 178 | 168
Income taxes | 42 | 32 | 99 | 103
After-tax operating income (ATOI) | 103 | 71 | 241 | 231
Global Rolled Products [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 1,978 | 1,852 | 5,602 | 5,602
Global Rolled Products [Member] | Intersegment Eliminations [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment sales | 52 | 47 | 139 | 141
Global Rolled Products [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | 1,926 | 1,805 | 5,463 | 5,461
Engineered Products and Solutions [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Depreciation, depletion, and amortization | 40 | 40 | 121 | 119
Income taxes | 100 | 91 | 293 | 269
After-tax operating income (ATOI) | 209 | 192 | 602 | 558
Engineered Products and Solutions [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 1,495 | 1,437 | 4,440 | 4,328
Engineered Products and Solutions [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | $ 1,495 | $ 1,437 | $ 4,440 | $ 4,328

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