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Segment Information - Schedule of Operating Results of Alcoa's Reportable Segment (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2015 | Jun. 30, 2014 | Jun. 30, 2015 | Jun. 30, 2014
Segment Reporting Information [Line Items] |  |  |  |
Total sales | $ 5,897 | $ 5,836 | $ 11,716 | $ 11,290
Equity loss | (23) | (30) | (42) | (68)
Depreciation, depletion, and amortization | 306 | 328 | 611 | 647
Income taxes | 217 | 161 | 492 | 309
After-tax operating income (ATOI) | 568 | 407 | 1,224 | 725
Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 6,886 | 7,024 | 13,884 | 13,700
Intersegment Eliminations [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment sales | 1,027 | 1,242 | 2,256 | 2,529
Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | 5,859 | 5,782 | 11,628 | 11,171
Alumina [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Equity loss | (11) | (7) | (18) | (12)
Depreciation, depletion, and amortization | 77 | 100 | 157 | 197
Income taxes | 87 | 12 | 179 | 52
After-tax operating income (ATOI) | 215 | 38 | 436 | 130
Alumina [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 1,355 | 1,241 | 2,743 | 2,596
Alumina [Member] | Intersegment Eliminations [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment sales | 431 | 480 | 932 | 990
Alumina [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | 924 | 761 | 1,811 | 1,606
Primary Metals [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Equity loss | (5) | (17) | (8) | (45)
Depreciation, depletion, and amortization | 109 | 129 | 218 | 253
Income taxes | 6 | 30 | 63 | 19
After-tax operating income (ATOI) | 67 | 97 | 254 | 82
Primary Metals [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 2,096 | 2,377 | 4,360 | 4,535
Primary Metals [Member] | Intersegment Eliminations [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment sales | 562 | 718 | 1,254 | 1,452
Primary Metals [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | 1,534 | 1,659 | 3,106 | 3,083
Global Rolled Products [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Equity loss | (7) | (6) | (16) | (11)
Depreciation, depletion, and amortization | 56 | 58 | 112 | 116
Income taxes | 25 | 18 | 61 | 47
After-tax operating income (ATOI) | 76 | 70 | 130 | 124
Global Rolled Products [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 1,702 | 1,904 | 3,359 | 3,624
Global Rolled Products [Member] | Intersegment Eliminations [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment sales | 34 | 44 | 70 | 87
Global Rolled Products [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | 1,668 | 1,860 | 3,289 | 3,537
Engineered Products and Solutions [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Depreciation, depletion, and amortization | 64 | 41 | 124 | 81
Income taxes | 99 | 101 | 189 | 191
After-tax operating income (ATOI) | 210 | 202 | 404 | 389
Engineered Products and Solutions [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 1,733 | 1,502 | 3,422 | 2,945
Engineered Products and Solutions [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | $ 1,733 | $ 1,502 | $ 3,422 | $ 2,945

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