Subsequent Events	12 Months Ended
Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Management evaluated all activity of Arconic and concluded that no subsequent events have occurred that would require recognition in the Consolidated Financial Statements or disclosure in the Notes to the Consolidated Financial Statements, except as noted below: In January 2018, the Company announced the freeze of its U.S. defined benefit pension plans for salaried and non-bargained hourly employees, effective April 1, 2018. Benefit accruals for future service and compensation under all of the Company’s qualified and non-qualified defined benefit pension plans for U.S. salaried and non-bargained hourly employees (the “Pension Plans”) will cease. In connection with this change, effective April 1, 2018, impacted employees will commence receiving an employer contribution of 3% of eligible compensation under the Arconic Salaried Retirement Savings Plan, and, for the period from April 1, 2018 through December 31, 2018, an additional transition employer contribution of 3% of eligible compensation. In January 2018, management announced a change in the organizational structure of the Engineered Products and Solutions segment, from four business units to three business units, with a focus on aligning its internal structure to core markets and customers and reducing cost. As a result of this change, goodwill will be reallocated to the three new reporting units and evaluated for impairment during the first quarter of 2018. The Company does not expect any goodwill impairment as a result of the realignment. In February 2018, the Company announced that its Board of Directors authorized a share repurchase program of up to $500 of its outstanding common stock and a $500 early debt reduction. Under the share repurchase program, the Company may repurchase shares from time to time, in amounts, at prices, and at such times as the Company deems appropriate. Repurchases will be subject to market conditions, legal requirements and other considerations. Arconic is not obligated to repurchase any specific number of shares or to do so at any particular time, and the share repurchase program may be suspended, modified or terminated at any time without prior notice. For the early debt reduction, Arconic intends to redeem in March 2018 all of its outstanding 5.72% Notes due in 2019. Beginning in the first quarter of 2018, the Company's primary measure of segment performance will change from Adjusted EBITDA to Operating income, which more closely aligns segment performance with Operating income as presented in the Statement of Consolidated Operations. As part of this change, LIFO and metal price lag will be included in the Operating income of the segments.

Subsequent Events

Management evaluated all activity of Arconic and concluded that no subsequent events have occurred that would require recognition in the Consolidated Financial Statements or disclosure in the Notes to the Consolidated Financial Statements, except as noted below:

In January 2018, the Company announced the freeze of its U.S. defined benefit pension plans for salaried and non-bargained hourly employees, effective April 1, 2018. Benefit accruals for future service and compensation under all of the Company’s qualified and non-qualified defined benefit pension plans for U.S. salaried and non-bargained hourly employees (the “Pension Plans”) will cease. In connection with this change, effective April 1, 2018, impacted employees will commence receiving an employer contribution of 3% of eligible compensation under the Arconic Salaried Retirement Savings Plan, and, for the period from April 1, 2018 through December 31, 2018, an additional transition employer contribution of 3% of eligible compensation.

In January 2018, management announced a change in the organizational structure of the Engineered Products and Solutions segment, from four business units to three business units, with a focus on aligning its internal structure to core markets and customers and reducing cost. As a result of this change, goodwill will be reallocated to the three new reporting units and evaluated for impairment during the first quarter of 2018. The Company does not expect any goodwill impairment as a result of the realignment.

In February 2018, the Company announced that its Board of Directors authorized a share repurchase program of up to $500 of its outstanding common stock and a $500 early debt reduction. Under the share repurchase program, the Company may repurchase shares from time to time, in amounts, at prices, and at such times as the Company deems appropriate. Repurchases will be subject to market conditions, legal requirements and other considerations. Arconic is not obligated to repurchase any specific number of shares or to do so at any particular time, and the share repurchase program may be suspended, modified or terminated at any time without prior notice. For the early debt reduction, Arconic intends to redeem in March 2018 all of its outstanding 5.72% Notes due in 2019.

Beginning in the first quarter of 2018, the Company's primary measure of segment performance will change from Adjusted EBITDA to Operating income, which more closely aligns segment performance with Operating income as presented in the Statement of Consolidated Operations. As part of this change, LIFO and metal price lag will be included in the Operating income of the segments.