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Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Details) - USD ($) shares in Millions, $ in Millions |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Oct. 15, 2019 | Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Net income from continuing operations attributable to common shareholders: |  | $ 106 | $ 36 | $ (84) | $ 153 | $ 118 | $ 58 | $ (136) | $ 86 | $ 211 | $ 126 | $ 309
Less: preferred stock dividends declared |  |  |  |  |  |  |  |  |  | 2 | 2 | 2
Net income from continuing operations attributable to common shareholders: |  |  |  |  |  |  |  |  |  | 209 | 124 | 307
Income from discontinued operations |  |  |  |  |  |  |  |  |  | 50 | 344 | 333
Net income available to Howmet Aerospace common shareholders - basic |  |  |  |  |  |  |  |  |  | 259 | 468 | 640
Add: interest expense related to convertible notes |  |  |  |  |  |  |  |  |  | 0 | 9 | 11
Net income available to Howmet common shareholders - diluted |  |  |  |  |  |  |  |  |  | $ 259 | $ 477 | $ 651
Average shares outstanding - basic (in shares) |  |  |  |  |  |  |  |  |  | 435 | 446 | 483
Effect of dilutive securities: |  |  |  |  |  |  |  |  |  |  |  |
Stock options (in shares) |  |  |  |  |  |  |  |  |  | 0 | 1 | 1
Stock and performance awards (in shares) |  |  |  |  |  |  |  |  |  | 4 | 5 | 5
Convertible notes (in shares) |  |  |  |  |  |  |  |  |  | 0 | 11 | 14
Average shares outstanding - diluted (in shares) |  |  |  |  |  |  |  |  |  | 439 | 463 | 503
Convertible notes |  |  |  |  |  |  |  |  |  |  |  |
Effect of dilutive securities: |  |  |  |  |  |  |  |  |  |  |  |
Number of anti-dilutive securities (in shares) | 15 |  |  |  |  |  |  |  |  | 0 | 0 | 0

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