Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income	$ 187	$ 143
Less: preferred stock dividends declared	(1)	(1)
Net income available to Arconic common shareholders - basic	186	142
Add: Interest expense related to convertible notes	4	3
Net income available to Arconic common shareholders - diluted	$ 190	$ 145
Average shares outstanding - basic (in shares)	471	482
Effect of dilutive securities:
Stock options (in shares)	0	5
Stock and performance awards (in shares)	4	2
Convertible notes (in shares)	14	14
Weighted average shares outstanding - diluted (in shares)	489	503
Common stock outstanding	453	483
Incremental common shares attributable to dilutive effect of accelerated share repurchase agreements	32

Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Amount after tax of income (loss) from continuing operations including portion attributable to the noncontrolling interest.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of accelerated share repurchase agreements. An accelerated share repurchase program is a combination of transactions that permits an entity to purchase a targeted number of shares immediately with the final purchase price of those shares determined by an average market price over a fixed period of time.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of convertible debt securities using the if-converted method.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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