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Restructuring and Other Charges - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended | 12 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended | 9 Months Ended | 12 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 12 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended
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Sep. 30, 2014 | Mar. 31, 2014 t | Sep. 30, 2013 t Location | Sep. 30, 2014 Employees t | Sep. 30, 2013 Employees Location | Dec. 31, 2013 | Sep. 30, 2014 Engineered Products and Solutions [Member] Employees | Sep. 30, 2013 Engineered Products and Solutions [Member] Employees | Sep. 30, 2014 Global Rolled Products Segment [Member] Employees | Sep. 30, 2014 Alumina and Primary Metals Segments [Member] Employees | Sep. 30, 2014 Primary Metals [Member] Employees | Sep. 30, 2013 Primary Metals [Member] Employees | Sep. 30, 2014 Global Rolled Products [Member] Employees | Sep. 30, 2013 Global Rolled Products [Member] Employees | Sep. 30, 2014 Alumina [Member] Employees | Mar. 31, 2014 Fusina and Massena East [Member] t | Sep. 30, 2013 Fusina and Massena East [Member] | Sep. 30, 2013 Fusina and Massena East [Member] | Mar. 31, 2014 Point Henry Smelter [Member] t | Sep. 30, 2014 Pocos De Caldas Refinery [Member] t | Sep. 30, 2014 Australia [Member] Facilities | Sep. 30, 2014 Baie Comeau [Member] Potline | Jun. 30, 2013 Baie Comeau [Member] Potline t | Sep. 30, 2014 Quebec Canada [Member] t | Jun. 30, 2013 Quebec Canada [Member] t | Sep. 30, 2014 Fusina Italy [Member] t | Jun. 30, 2013 Fusina Italy [Member] t | Sep. 30, 2014 Portovesme [Member] t | Sep. 30, 2014 Other Exit Costs [Member] | Sep. 30, 2013 Other Exit Costs [Member] | Sep. 30, 2014 Other Exit Costs [Member] | Sep. 30, 2013 Other Exit Costs [Member] | Dec. 31, 2013 Other Exit Costs [Member] | Sep. 30, 2013 Legal Matter [Member] | Sep. 30, 2014 Asset Impairment [Member] | Sep. 30, 2013 Asset Impairment [Member] | Sep. 30, 2014 Layoff Costs [Member] | Sep. 30, 2013 Layoff Costs [Member] | Dec. 31, 2013 Layoff Costs [Member] | Sep. 30, 2014 Layoff Costs [Member] Primary Metals [Member] | Sep. 30, 2014 Layoff Costs [Member] Primary Metals [Member] | Sep. 30, 2014 Other Miscellaneous Items [Member] | Sep. 30, 2013 Other Miscellaneous Items [Member] | Sep. 30, 2013 Other Miscellaneous Items [Member] | Sep. 30, 2014 Small Layoff Reserves Related to Prior Periods [Member] | Sep. 30, 2013 Small Layoff Reserves Related to Prior Periods [Member] | Sep. 30, 2014 Small Layoff Reserves Related to Prior Periods [Member] | Sep. 30, 2013 Small Layoff Reserves Related to Prior Periods [Member] | Sep. 30, 2014 Permanent Shutdown and Planned Demolition of Idled Structures [Member] | Sep. 30, 2013 Permanent Shutdown and Planned Demolition of Idled Structures [Member] | Sep. 30, 2014 Permanent Shutdown and Planned Demolition of Idled Structures [Member] | Sep. 30, 2013 Permanent Shutdown and Planned Demolition of Idled Structures [Member] | Sep. 30, 2014 Operating Supplies [Member] | Sep. 30, 2013 Operating Supplies [Member] | Sep. 30, 2014 Operating Supplies [Member] | Sep. 30, 2013 Operating Supplies [Member] | Sep. 30, 2014 Asset Retirement Obligations [Member] | Sep. 30, 2013 Asset Retirement Obligations [Member] | Sep. 30, 2014 Asset Retirement Obligations [Member] | Sep. 30, 2013 Asset Retirement Obligations [Member] | Dec. 31, 2013 Asset Retirement Obligations [Member] | Sep. 30, 2014 Environmental Remediation [Member] | Sep. 30, 2013 Environmental Remediation [Member] | Sep. 30, 2014 Environmental Remediation [Member] | Sep. 30, 2013 Environmental Remediation [Member] | Dec. 31, 2013 Environmental Remediation [Member] | Sep. 30, 2014 Smelter Curtailments [Member] Employees | Sep. 30, 2014 Supplier And Customer Contract [Member] | Sep. 30, 2013 Supplier And Customer Contract [Member] | Sep. 30, 2014 Supplier And Customer Contract [Member] | Sep. 30, 2013 Supplier And Customer Contract [Member] | Sep. 30, 2014 Restructuring Programs Layoffs 2014 [Member] Employees | Sep. 30, 2014 Restructuring Programs Layoffs 2014 [Member] Employees | Sep. 30, 2013 Pension Costs [Member] | Sep. 30, 2014 Pension Costs [Member] | Sep. 30, 2013 Pension Costs [Member] | Dec. 31, 2013 Pension Costs [Member] | Sep. 30, 2014 Restructuring Programs Layoffs 2013 [Member] Employees | Sep. 30, 2014 Restructuring Programs Layoffs 2013 [Member] Employees | Sep. 30, 2013 Exit Costs [Member] | Sep. 30, 2013 Exit Costs [Member] | Sep. 30, 2013 Exit Costs [Member] Primary Metals [Member] Employees | Sep. 30, 2013 Exit Costs [Member] Primary Metals [Member] Employees | Sep. 30, 2014 Corporate [Member] | Sep. 30, 2013 Corporate [Member] | Sep. 30, 2014 Corporate [Member] Employees | Sep. 30, 2013 Corporate [Member] Employees | Sep. 30, 2014 Corporate [Member] Other Miscellaneous Items [Member] | Sep. 30, 2014 Rolling Mill [Member] Plant | Mar. 31, 2014 Rolling Mill [Member] Plant | Sep. 30, 2014 Rolling Mill [Member] Plant | Sep. 30, 2014 Smelter [Member] Plant | Sep. 30, 2014 Smelter [Member] Plant | Sep. 30, 2014 Refinery [Member] Smelter Curtailments [Member] Plant
Restructuring Cost and Reserve [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restructuring and other charges | $ 209 |  | $ 151 | $ 780 | $ 402 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 220 | $ 152 | $ 663 | $ 238 |  | $ 103 | $ 33 | $ 29 | $ 18 | $ 27 |  | $ 60 | $ 197 | $ 4 | $ 1 | $ 9 | $ 10 | $ 2 | $ 17 | $ 4 |  |  |  |  |  |  |  |  |  |  | $ 95 |  | $ 58 |  |  | $ 47 |  | $ 12 | $ 67 |  |  |  |  |  |  |  |  |  |  |  |  | $ 107 | $ 107 |  |  | $ 2 | $ 1 | $ 34 | $ 126 | $ 16 |  |  |  |  |  |
Restructuring and other charges, after-tax and noncontrolling interest | 175 |  | 108 | 503 | 283 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 186 | 109 | 426 | 179 |  | 62 | 26 | 19 | 11 | 20 |  |  |  | 2 | 1 | 6 | 9 | 2 | 13 | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 44 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9 |  |  |  |  |  |
Number of plants permanently shut down and demolished |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 | 2 | 2 | 2 | 3 |
Restructuring and other charges, gain on sale of assets | 5 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Restructuring and other charges, gain on sale of assets after-tax | 4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of plants temporarily curtailed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 | 1
Number of employees associated with layoff costs |  |  |  |  | 510 |  | 115 | 170 | 30 | 10 |  | 120 |  | 190 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 245 |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 520 | 520 |  |  | 90 | 30 |  |  |  |  |  |  |
Reduction in production - result of market conditions, in metric tons per year |  |  | 460,000 | 460,000 |  |  |  |  |  |  |  |  |  |  |  | 84,000 |  |  | 190,000 | 200,000 |  |  |  |  |  | 84,000 |  | 150,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining smelting capacity subject to review |  |  |  | 62,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional smelting capacity subject to review |  |  |  | 85,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reduction in combined capacity |  | 200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of employees associated with layoff costs |  |  |  | 1,780 |  |  |  |  |  |  | 1,200 |  | 470 |  | 80 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 30 |  |  |  |  |  |  |  |
Other layoff cost including reclassification in pension cost |  |  |  | 216 |  | 185 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 176 |  | 84 |  |  |  | 40 |  | 101 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 78 | 18 | 78 | 92 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Accelerated depreciation | 40 |  | 35 | 190 | 58 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other asset impairment charges | 74 |  |  | 165 |  |  |  |  |  |  |  |  |  |  |  |  | 4 | 18 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other exit costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 45 | 6 | 178 | 55 |  |  |  |  | 40 | 48 | 95 | 48 |  | 4 | 5 | 42 | 5 |  |  | 1 | 2 | 41 | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Inventory write-down - permanent shutdown and planned demolition of idled structures |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 33 | 2 | 67 | 9 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Inventory write-down, after-tax and non-controlling interests |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 27 | 1 | 47 | 6 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional charges related to shutdown actions |  |  |  | 25 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of facilities accelerated depreciation write off |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of non-U.S. locations permanently shutdown and demolished |  |  | 2 |  | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of potlines to be shutdown and demolished |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 | 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reduction in production - result of market conditions, in mt per year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 105,000 | 41,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Reduction in production - result of market conditions, in mt per year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 280,000 |  | 44,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capacity of lines under review period |  |  | 15 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total number of employees already laid off |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,300 | 1,300 |  |  |  |  | 1,390 | 1,390 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of positions separated |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,025 |  |  |  |  |  | 1,620 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash payments made against the layoff reserves |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 66 | 89 |  |  |  |  | 4 | 36 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum amount of cash payments expected to be paid beyond the end of the current annual period |  |  |  | 75 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum amount of cash payments expected to be paid beyond the end of the current annual period |  |  |  | $ 80 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

X
- Definition Accelerated depreciation related to written off of lines. + References No definition available. + Details
Name: | aa_AcceleratedDepreciationRelatedToWrittenOffOfLines
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Additional capacity of line under review for which temporary curtailment was initiated. + References No definition available. + Details
Name: | aa_AdditionalCapacityOfLineUnderReviewForWhichTemporaryCurtailmentWasInitiated
Namespace Prefix: | aa_
Data Type: | num:massItemType
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