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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, 2016 | Jun. 30, 2015 | Jun. 30, 2016 | Jun. 30, 2015
Segment Reporting Information [Line Items] |  |  |  |
Equity (loss) income |  | $ (23) | $ (38) | $ (42)
Total sales | $ 5,295 | 5,897 | 10,242 | 11,716
Depreciation, depletion, and amortization | 296 | 307 | 593 | 613
Income taxes | 173 | 216 | 288 | 491
After-tax operating income (ATOI) | 444 | 567 | 735 | 1,223
Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 6,097 | 6,924 | 11,836 | 13,961
Intersegment Eliminations [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment sales | 802 | 1,027 | 1,598 | 2,256
Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | 5,295 | 5,897 | 10,238 | 11,705
Alumina [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Equity (loss) income |  | (11) | (21) | (18)
Depreciation, depletion, and amortization | 66 | 77 | 129 | 157
Income taxes | 40 | 87 | 45 | 179
After-tax operating income (ATOI) | 109 | 215 | 117 | 436
Alumina [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 994 | 1,355 | 1,831 | 2,743
Alumina [Member] | Intersegment Eliminations [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment sales | 300 | 431 | 592 | 932
Alumina [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | 694 | 924 | 1,239 | 1,811
Primary Metals [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Equity (loss) income |  | (5) | 4 | (8)
Depreciation, depletion, and amortization | 101 | 109 | 203 | 218
Income taxes |  | 6 | (16) | 63
After-tax operating income (ATOI) | 41 | 67 | 55 | 254
Primary Metals [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 1,592 | 2,096 | 3,190 | 4,360
Primary Metals [Member] | Intersegment Eliminations [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment sales | 473 | 562 | 948 | 1,254
Primary Metals [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | 1,119 | 1,534 | 2,242 | 3,106
Global Rolled Products [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Equity (loss) income |  | (7) | (21) | (16)
Depreciation, depletion, and amortization | 55 | 56 | 111 | 112
Income taxes | 28 | 25 | 62 | 61
After-tax operating income (ATOI) | 68 | 76 | 136 | 130
Global Rolled Products [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 1,579 | 1,702 | 3,005 | 3,359
Global Rolled Products [Member] | Intersegment Eliminations [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Intersegment sales | 29 | 34 | 58 | 70
Global Rolled Products [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | 1,550 | 1,668 | 2,947 | 3,289
Engineered Products and Solutions [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Depreciation, depletion, and amortization | 62 | 54 | 127 | 105
Income taxes | 87 | 81 | 165 | 157
After-tax operating income (ATOI) | 180 | 165 | 342 | 321
Engineered Products and Solutions [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 1,465 | 1,279 | 2,914 | 2,536
Engineered Products and Solutions [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | 1,465 | 1,279 | 2,914 | 2,536
Transportation and Construction Solutions [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Depreciation, depletion, and amortization | 12 | 11 | 23 | 21
Income taxes | 18 | 17 | 32 | 31
After-tax operating income (ATOI) | 46 | 44 | 85 | 82
Transportation and Construction Solutions [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Total sales | 467 | 492 | 896 | 963
Transportation and Construction Solutions [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Third-party sales | $ 467 | $ 492 | $ 896 | $ 963

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