Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net (loss) income	$ (121)	$ 120	$ 66	$ 263
Less: preferred stock dividends declared	0	0	(1)	(1)
Net (loss) income available to Arconic common shareholders - basic	(121)	120	65	262
Add: Interest expense related to convertible notes	0	3	0	6
Net (loss) income available to Arconic common shareholders - diluted	$ (121)	$ 123	$ 65	$ 268
Average shares outstanding - basic (in shares)	445	483	458	483
Effect of dilutive securities:
Stock options (in shares)	0	0	0	0
Stock and performance awards (in shares)	0	5	4	5
Convertible notes (in shares)	0	14	0	14
Average shares outstanding - diluted (in shares)	445	502	462	502
Common stock outstanding (in shares)	440	483	440	483
Incremental common shares attributable to dilutive effect of accelerated share repurchase agreements (in shares)			45

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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