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Summary of Significant Accounting Policies - Additional Information (Details) | 3 Months Ended | 12 Months Ended |  |  |  |  |  |
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Dec. 31, 2018 USD ($) | Jun. 30, 2018 USD ($) | Dec. 31, 2019 USD ($) reporting_unit | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) | Dec. 31, 2016 reporting_unit | Sep. 30, 2019 USD ($) | Jun. 30, 2019 USD ($) | Mar. 31, 2019 USD ($) | Jan. 01, 2019 USD ($) | Jan. 01, 2018 USD ($) | Jan. 01, 2017 USD ($)
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of reporting units | reporting_unit |  |  | 7 |  |  | 7 |  |  |  |  |  |
Segment allocation, goodwill recognized | $ 4,500,000,000 |  | $ 4,493,000,000 | $ 4,500,000,000 | $ 4,535,000,000 |  |  |  |  |  |  |
Minimum percentage of estimated fair value of reporting unit to be less than carrying amount of goodwill |  |  | 50.00% |  |  |  |  |  |  |  |  |
Percentage of fair value in excess of carrying amount |  |  | 50.00% |  |  |  |  |  |  |  |  |
Impairment of goodwill (A and N) |  |  | $ 0 | 0 | $ 719,000,000 |  |  |  |  |  |  |
Period required for impairment testing of reporting units |  |  | 3 years |  |  |  |  |  |  |  |  |
Businesses expected to be disposed within, years |  |  | 1 year |  |  |  |  |  |  |  |  |
Right-of-use assets |  |  | $ 252,000,000 |  |  |  |  |  |  | $ 320,000,000 |  |
Revenue, terms of payment, period |  |  | 30 days |  |  |  |  |  |  |  |  |
Cash proceed from Other noncurrent liabilities |  |  |  |  |  |  |  |  |  | 119,000,000 |  |
Properties, plants, and equipment, net | 5,704,000,000 |  | $ 5,463,000,000 | 5,704,000,000 |  |  |  |  |  | 24,000,000 |  |
Cash proceeds from Other noncurrent assets | 416,000,000 |  | 514,000,000 | 416,000,000 |  |  |  |  |  | 22,000,000 |  |
Cumulative effect adjustment |  |  |  |  |  |  |  |  |  | 73,000,000 | $ 0 | $ 0
Amount of stranded tax effects in accumulated other comprehensive income reclassified to accumulated deficit | 367,000,000 |  |  |  |  |  |  |  |  |  |  |
Engineered Products and Forgings |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of reporting units | reporting_unit |  |  |  |  |  | 4 |  |  |  |  |  |
Segment allocation, goodwill recognized | 4,186,000,000 |  | 4,067,000,000 | 4,186,000,000 |  |  | $ 7,000,000 |  |  |  |  |
Impairment of goodwill (A and N) |  |  |  | 719,000,000 |  |  |  |  |  |  |  |
Engineered Products and Forgings | Alcoa Forging and Extrusions |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Impairment of goodwill (A and N) |  |  |  | 719,000,000 |  |  |  |  |  |  |  |
Transportation and Construction Solutions |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Number of reporting units | reporting_unit |  |  |  |  |  | 3 |  |  |  |  |  |
Global Rolled Products |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Segment allocation, goodwill recognized | $ 314,000,000 |  | $ 426,000,000 | $ 314,000,000 |  |  | $ 68,000,000 |  |  |  |  |
Minimum | Engineered Products and Forgings |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Percentage of total goodwill allocated to two reporting units |  |  | 90.00% |  |  |  |  |  |  |  |  |
Aluminum extrusions |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Segment allocation, goodwill recognized |  |  |  |  |  |  |  |  | $ 110,000,000 |  |  |
Engine products |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Segment allocation, goodwill recognized |  |  |  |  |  |  |  | $ 105,000,000 |  |  |  |
Arconic Engines |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Segment allocation, goodwill recognized |  |  | $ 2,164,000,000 |  |  |  |  |  |  |  |  |
Percentage of fair value in excess of carrying amount |  | 13.00% |  |  |  |  |  |  |  |  |  |
Fastening systems |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Segment allocation, goodwill recognized |  |  | 1,607,000,000 |  |  |  |  |  |  |  |  |
Arconic Engineered Structures |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Segment allocation, goodwill recognized |  |  | 289,000,000 |  |  |  |  |  |  |  |  |
Forged wheels |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Segment allocation, goodwill recognized |  |  | $ 7,000,000 |  |  |  |  |  |  |  |  |
Disks Asset Group |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Impairment of goodwill (A and N) |  | $ 0 |  |  |  |  |  |  |  |  |  |
ASU 2017-12 |  |  |  |  |  |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Cumulative effect adjustment |  |  |  |  |  |  |  |  |  | $ 2,000,000 |  |

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