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Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Detail) - USD ($)
shares in Millions, $ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Earnings Per Share [Abstract]    
Net income $ 143 $ 322
Less: Preferred stock dividends declared (1) (17)
Net income available to Arconic common shareholders - basic 142 305
Add: Interest expense related to convertible notes 3 2
Add: Dividends related to mandatory convertible preferred stock 0 17
Net income available to Arconic common shareholders - diluted $ 145 $ 324
Average shares outstanding - basic (in shares) 482 440
Effect of dilutive securities:    
Stock options (in shares) 5 1
Stock and performance awards (in shares) 2 5
Mandatory convertible preferred stock (in shares) 0 39
Convertible notes (in shares) 14 14
Weighted average shares outstanding - diluted (in shares) 503 499