Contingencies and Commitments	3 Months Ended
Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Contingencies and Commitments	Contingencies and Commitments Contingencies Environmental Matters Arconic participates in environmental assessments and cleanups at more than 100 locations. These include owned or operating facilities and adjoining properties, previously owned or operating facilities and adjoining properties, and waste sites, including Superfund (Comprehensive Environmental Response, Compensation and Liability Act (CERCLA)) sites. A liability is recorded for environmental remediation when a cleanup program becomes probable and the costs can be reasonably estimated. As assessments and cleanups proceed, the liability is adjusted based on progress made in determining the extent of remedial actions and related costs. The liability can change substantially due to factors such as the nature and extent of contamination, changes in remedial requirements, and technological changes, among others. Arconic’s remediation reserve balance was $292 at March 31, 2018 and $294 at December 31, 2017 (of which $40 and $41, respectively, was classified as a current liability), and reflects the most probable costs to remediate identified environmental conditions for which costs can be reasonably estimated. Payments related to remediation expenses applied against the reserve were $3 in the quarter ended March 31, 2018. This amount includes expenditures currently mandated, as well as those not required by any regulatory authority or third party. Included in annual operating expenses are the recurring costs of managing hazardous substances and environmental programs. These costs are estimated to be approximately 1% or less of cost of goods sold. The following discussion provides details regarding the current status of the most significant remediation reserves related to a current Arconic site. Massena West, NY—Arconic has an ongoing remediation project related to the Grasse River, which is adjacent to Arconic’s Massena plant site. Many years ago, it was determined that sediments and fish in the river contain varying levels of polychlorinated biphenyls (PCBs). The project, which was selected by the U.S. Environmental Protection Agency (EPA) in a Record of Decision issued in April 2013, is aimed at capping PCB contaminated sediments with concentration in excess of one part per million in the main channel of the river and dredging PCB contaminated sediments in the near-shore areas where total PCBs exceed one part per million. At March 31, 2018 and December 31, 2017, the reserve balance associated with this matter was $213 and $215, respectively. Arconic is in the planning and design phase of the project, which is expected to be completed in 2018. Following the submittal of the final design and EPA approval, the actual remediation fieldwork is expected to commence and take approximately four years. The majority of the project funding is expected to be incurred between 2018 and 2022. Tax Pursuant to the Tax Matters Agreement entered into between Arconic and Alcoa Corporation in connection with the separation transaction with Alcoa Corporation, Arconic shares responsibility with Alcoa Corporation, and Alcoa Corporation has agreed to partially indemnify Arconic, with respect to the following matter. As previously reported, in July 2013, following a corporate income tax audit covering the 2006 through 2009 tax years, an assessment was received as a result of Spain’s tax authorities disallowing certain interest deductions claimed by a Spanish consolidated tax group owned by the Company. The assessment is $161 (€130), including interest. In August 2013, the Company filed an appeal of this assessment in Spain’s Central Tax Administrative Court, which was denied in January 2015. Arconic filed another appeal in Spain’s National Court in March 2015. Spain’s National Court has not yet rendered a decision related to the assessment. The Company believes it has meritorious arguments to support its tax position and intends to continue to vigorously litigate the assessment. However, in the event the Company is unsuccessful, a portion of the assessment may be offset with existing net operating losses available to the Spanish consolidated tax group, which would be shared between the Company and Alcoa Corporation as provided for in the Tax Matters Agreement. Additionally, while the tax years 2010 through 2013 are closed to audit, it is possible that the Company may receive similar assessments for tax years subsequent to 2013. At this time, the Company is unable to reasonably predict an ultimate outcome for this matter. Reynobond PE Howard v. Arconic Inc. et al. As previously reported, a purported class action complaint related to the Grenfell Tower fire was filed on August 11, 2017 in the United States District Court for the Western District of Pennsylvania against Arconic Inc., and Klaus Kleinfeld. A related purported class action complaint was filed in the United States District Court for the Western District of Pennsylvania on August 25, 2017, under the caption Sullivan v. Arconic Inc. et al., against Arconic Inc., two former Arconic executives, several current and former Arconic directors, and banks that acted as underwriters for Arconic’s September 18, 2014 preferred stock offering (the “Preferred Offering”). The plaintiff in Sullivan had previously filed a purported class action against the same defendants on July 18, 2017 in the Southern District of New York and, on August 25, 2017, voluntarily dismissed that action without prejudice. On February 7, 2018, on motion from certain putative class members, the court consolidated Howard and Sullivan, closed Sullivan, and appointed lead plaintiffs in the consolidated case. On April 9, 2018, the lead plaintiffs in the consolidated purported class action filed a consolidated amended complaint. The consolidated amended complaint alleges that the registration statement for the Preferred Offering contained false and misleading statements and omitted to state material information, including by allegedly failing to disclose material uncertainties and trends resulting from sales of Reynobond PE for unsafe uses and by allegedly expressing a belief that appropriate risk management and compliance programs had been adopted while concealing the risks posed by Reynobond PE sales. The consolidated amended complaint also alleges that between November 4, 2013 and June 23, 2017 Arconic and Kleinfeld made false and misleading statements and failed to disclose material information about the Company’s commitment to safety, business and financial prospects, and the risks of the Reynobond PE product, including in Arconic’s Form 10-Ks for the fiscal years ended December 31, 2013, 2014, 2015 and 2016, its Form 10-Qs and quarterly financial press releases from the fourth quarter of 2013 through the first quarter of 2017, its 2013, 2014, 2015 and 2016 Annual Reports, and its 2016 Annual Highlights Report. The consolidated amended complaint seeks, among other things, unspecified compensatory damages and an award of attorney and expert fees and expenses. While the Company believes that this case is without merit and intends to challenge it vigorously, there can be no assurances regarding the ultimate resolution of this matter. Given the preliminary nature of this matter and the uncertainty of litigation, the Company cannot reasonably estimate at this time the likelihood of an unfavorable outcome or the possible loss or range of losses in the event of an unfavorable outcome. The Board of Directors has also received letters, purportedly sent on behalf of shareholders, reciting allegations similar to those made in the federal court lawsuit and demanding that the Board authorize the Company to initiate litigation against members of management, the Board and others. The Board of Directors has appointed a Special Litigation Committee of the Board to review these shareholder demand letters and consider the appropriate course of action. In addition, lawsuits are pending in state court in New York and federal court in Pennsylvania, initiated, respectively, by another purported shareholder and by the Company, concerning the shareholder’s claimed right, which the Company contests, to inspect the Company’s books and records related to the Grenfell Tower fire and Reynobond PE. Other In addition to the matters discussed above, various other lawsuits, claims, and proceedings have been or may be instituted or asserted against Arconic, including those pertaining to environmental, product liability, safety and health, employment, and tax matters. While the amounts claimed in these other matters may be substantial, the ultimate liability cannot currently be determined because of the considerable uncertainties that exist. Therefore, it is possible that the Company’s liquidity or results of operations in a period could be materially affected by one or more of these other matters. However, based on facts currently available, management believes that the disposition of these other matters that are pending or asserted will not have a material adverse effect, individually or in the aggregate, on the results of operations, financial position or cash flows of the Company. Commitments Guarantees At March 31, 2018, Arconic had outstanding bank guarantees related to tax matters, outstanding debt, workers’ compensation, environmental obligations, energy contracts, and customs duties, among others. The total amount committed under these guarantees, which expire at various dates between 2018 and 2026, was $27 at March 31, 2018. Pursuant to the Separation and Distribution Agreement between Arconic and Alcoa Corporation, Arconic was required to provide certain guarantees for Alcoa Corporation, which had a combined fair value of $7 and $8 at March 31, 2018 and December 31, 2017, respectively, and were included in Other noncurrent liabilities and deferred credits on the accompanying Consolidated Balance Sheet. Arconic was required to provide payment guarantees for Alcoa Corporation issued on behalf of a third party, and amounts outstanding under these payment guarantees were $169 and $197 at March 31, 2018 and December 31, 2017, respectively. These guarantees expire at various times between 2018 and 2024, and relate to project financing for Alcoa Corporation’s aluminum complex in Saudi Arabia. Furthermore, Arconic was required to provide a guarantee up to an estimated present value amount of approximately $1,188 and $1,297 at March 31, 2018 and December 31, 2017, respectively, related to a long-term supply agreement for energy for an Alcoa Corporation facility in the event of an Alcoa Corporation payment default. For each guarantee, subject to its respective provisions, Arconic is secondarily liable in the event of a payment default by Alcoa Corporation. Arconic currently views the risk of an Alcoa Corporation payment default on its obligations under the respective contracts to be remote. Letters of Credit Arconic has outstanding letters of credit, primarily related to workers’ compensation, energy contracts and leasing obligations. The total amount committed under these letters of credit, which automatically renew or expire at various dates, mostly in 2018, was $126 at March 31, 2018. Pursuant to the Separation and Distribution Agreement, Arconic was required to retain letters of credit of $53 that had previously been provided related to both Arconic and Alcoa Corporation workers’ compensation claims which occurred prior to November 1, 2016. Alcoa Corporation workers’ compensation claims and letter of credit fees paid by Arconic are being proportionally billed to and are being fully reimbursed by Alcoa Corporation. Surety Bonds Arconic has outstanding surety bonds, primarily related to tax matters, contract performance, workers’ compensation, environmental-related matters, and customs duties. The total amount committed under these surety bonds, which expire at various dates, primarily in 2018, was $55 at March 31, 2018. Pursuant to the Separation and Distribution Agreement, Arconic was required to provide surety bonds related to Alcoa Corporation workers’ compensation claims which occurred prior to November 1, 2016 and, as a result, Arconic has $25 in outstanding surety bonds relating to these liabilities. Alcoa Corporation workers’ compensation claims and surety bond fees paid by Arconic are being proportionately billed to and are being fully reimbursed by Alcoa Corporation.

Contingencies and Commitments

Contingencies

Environmental Matters

Arconic participates in environmental assessments and cleanups at more than 100 locations. These include owned or operating facilities and adjoining properties, previously owned or operating facilities and adjoining properties, and waste sites, including Superfund (Comprehensive Environmental Response, Compensation and Liability Act (CERCLA)) sites.

A liability is recorded for environmental remediation when a cleanup program becomes probable and the costs can be reasonably estimated. As assessments and cleanups proceed, the liability is adjusted based on progress made in determining the extent of remedial actions and related costs. The liability can change substantially due to factors such as the nature and extent of contamination, changes in remedial requirements, and technological changes, among others.

Arconic’s remediation reserve balance was $292 at March 31, 2018 and $294 at December 31, 2017 (of which $40 and $41, respectively, was classified as a current liability), and reflects the most probable costs to remediate identified environmental conditions for which costs can be reasonably estimated.

Payments related to remediation expenses applied against the reserve were $3 in the quarter ended March 31, 2018. This amount includes expenditures currently mandated, as well as those not required by any regulatory authority or third party.

Included in annual operating expenses are the recurring costs of managing hazardous substances and environmental programs. These costs are estimated to be approximately 1% or less of cost of goods sold.

The following discussion provides details regarding the current status of the most significant remediation reserves related to a current Arconic site.

Massena West, NY—Arconic has an ongoing remediation project related to the Grasse River, which is adjacent to Arconic’s Massena plant site. Many years ago, it was determined that sediments and fish in the river contain varying levels of polychlorinated biphenyls (PCBs). The project, which was selected by the U.S. Environmental Protection Agency (EPA) in a Record of Decision issued in April 2013, is aimed at capping PCB contaminated sediments with concentration in excess of one part per million in the main channel of the river and dredging PCB contaminated sediments in the near-shore areas where total PCBs exceed one part per million. At March 31, 2018 and December 31, 2017, the reserve balance associated with this matter was $213 and $215, respectively. Arconic is in the planning and design phase of the project, which is expected to be completed in 2018. Following the submittal of the final design and EPA approval, the actual remediation fieldwork is expected to commence and take approximately four years. The majority of the project funding is expected to be incurred between 2018 and 2022.

Tax

Pursuant to the Tax Matters Agreement entered into between Arconic and Alcoa Corporation in connection with the separation transaction with Alcoa Corporation, Arconic shares responsibility with Alcoa Corporation, and Alcoa Corporation has agreed to partially indemnify Arconic, with respect to the following matter.

As previously reported, in July 2013, following a corporate income tax audit covering the 2006 through 2009 tax years, an assessment was received as a result of Spain’s tax authorities disallowing certain interest deductions claimed by a Spanish consolidated tax group owned by the Company. The assessment is $161 (€130), including interest. In August 2013, the Company filed an appeal of this assessment in Spain’s Central Tax Administrative Court, which was denied in January 2015. Arconic filed another appeal in Spain’s National Court in March 2015. Spain’s National Court has not yet rendered a decision related to the assessment.

The Company believes it has meritorious arguments to support its tax position and intends to continue to vigorously litigate the assessment. However, in the event the Company is unsuccessful, a portion of the assessment may be offset with existing net operating losses available to the Spanish consolidated tax group, which would be shared between the Company and Alcoa Corporation as provided for in the Tax Matters Agreement. Additionally, while the tax years 2010 through 2013 are closed to audit, it is possible that the Company may receive similar assessments for tax years subsequent to 2013. At this time, the Company is unable to reasonably predict an ultimate outcome for this matter.

Reynobond PE

Howard v. Arconic Inc. et al. As previously reported, a purported class action complaint related to the Grenfell Tower fire was filed on August 11, 2017 in the United States District Court for the Western District of Pennsylvania against Arconic Inc., and Klaus Kleinfeld. A related purported class action complaint was filed in the United States District Court for the Western District of Pennsylvania on August 25, 2017, under the caption Sullivan v. Arconic Inc. et al., against Arconic Inc., two former Arconic executives, several current and former Arconic directors, and banks that acted as underwriters for Arconic’s September 18, 2014 preferred stock offering (the “Preferred Offering”). The plaintiff in Sullivan had previously filed a purported class action against the same defendants on July 18, 2017 in the Southern District of New York and, on August 25, 2017, voluntarily dismissed that action without prejudice. On February 7, 2018, on motion from certain putative class members, the court consolidated Howard and Sullivan, closed Sullivan, and appointed lead plaintiffs in the consolidated case. On April 9, 2018, the lead plaintiffs in the consolidated purported class action filed a consolidated amended complaint. The consolidated amended complaint alleges that the registration statement for the Preferred Offering contained false and misleading statements and omitted to state material information, including by allegedly failing to disclose material uncertainties and trends resulting from sales of Reynobond PE for unsafe uses and by allegedly expressing a belief that appropriate risk management and compliance programs had been adopted while concealing the risks posed by Reynobond PE sales. The consolidated amended complaint also alleges that between November 4, 2013 and June 23, 2017 Arconic and Kleinfeld made false and misleading statements and failed to disclose material information about the Company’s commitment to safety, business and financial prospects, and the risks of the Reynobond PE product, including in Arconic’s Form 10-Ks for the fiscal years ended December 31, 2013, 2014, 2015 and 2016, its Form 10-Qs and quarterly financial press releases from the fourth quarter of 2013 through the first quarter of 2017, its 2013, 2014, 2015 and 2016 Annual Reports, and its 2016 Annual Highlights Report. The consolidated amended complaint seeks, among other things, unspecified compensatory damages and an award of attorney and expert fees and expenses.

While the Company believes that this case is without merit and intends to challenge it vigorously, there can be no assurances regarding the ultimate resolution of this matter. Given the preliminary nature of this matter and the uncertainty of litigation, the Company cannot reasonably estimate at this time the likelihood of an unfavorable outcome or the possible loss or range of losses in the event of an unfavorable outcome. The Board of Directors has also received letters, purportedly sent on behalf of shareholders, reciting allegations similar to those made in the federal court lawsuit and demanding that the Board authorize the Company to initiate litigation against members of management, the Board and others. The Board of Directors has appointed a Special Litigation Committee of the Board to review these shareholder demand letters and consider the appropriate course of action. In addition, lawsuits are pending in state court in New York and federal court in Pennsylvania, initiated, respectively, by another purported shareholder and by the Company, concerning the shareholder’s claimed right, which the Company contests, to inspect the Company’s books and records related to the Grenfell Tower fire and Reynobond PE.

Other

In addition to the matters discussed above, various other lawsuits, claims, and proceedings have been or may be instituted or asserted against Arconic, including those pertaining to environmental, product liability, safety and health, employment, and tax matters. While the amounts claimed in these other matters may be substantial, the ultimate liability cannot currently be determined because of the considerable uncertainties that exist. Therefore, it is possible that the Company’s liquidity or results of operations in a period could be materially affected by one or more of these other matters. However, based on facts currently available, management believes that the disposition of these other matters that are pending or asserted will not have a material adverse effect, individually or in the aggregate, on the results of operations, financial position or cash flows of the Company.

Commitments

Guarantees

At March 31, 2018, Arconic had outstanding bank guarantees related to tax matters, outstanding debt, workers’ compensation, environmental obligations, energy contracts, and customs duties, among others. The total amount committed under these guarantees, which expire at various dates between 2018 and 2026, was $27 at March 31, 2018.

Pursuant to the Separation and Distribution Agreement between Arconic and Alcoa Corporation, Arconic was required to provide certain guarantees for Alcoa Corporation, which had a combined fair value of $7 and $8 at March 31, 2018 and December 31, 2017, respectively, and were included in Other noncurrent liabilities and deferred credits on the accompanying Consolidated Balance Sheet. Arconic was required to provide payment guarantees for Alcoa Corporation issued on behalf of a third party, and amounts outstanding under these payment guarantees were $169 and $197 at March 31, 2018 and December 31, 2017, respectively. These guarantees expire at various times between 2018 and 2024, and relate to project financing for Alcoa Corporation’s aluminum complex in Saudi Arabia. Furthermore, Arconic was required to provide a guarantee up to an estimated present value amount of approximately $1,188 and $1,297 at March 31, 2018 and December 31, 2017, respectively, related to a long-term supply agreement for energy for an Alcoa Corporation facility in the event of an Alcoa Corporation payment default. For each guarantee, subject to its respective provisions, Arconic is secondarily liable in the event of a payment default by Alcoa Corporation. Arconic currently views the risk of an Alcoa Corporation payment default on its obligations under the respective contracts to be remote.

Letters of Credit

Arconic has outstanding letters of credit, primarily related to workers’ compensation, energy contracts and leasing obligations. The total amount committed under these letters of credit, which automatically renew or expire at various dates, mostly in 2018, was $126 at March 31, 2018.

Pursuant to the Separation and Distribution Agreement, Arconic was required to retain letters of credit of $53 that had previously been provided related to both Arconic and Alcoa Corporation workers’ compensation claims which occurred prior to November 1, 2016. Alcoa Corporation workers’ compensation claims and letter of credit fees paid by Arconic are being proportionally billed to and are being fully reimbursed by Alcoa Corporation.

Surety Bonds

Arconic has outstanding surety bonds, primarily related to tax matters, contract performance, workers’ compensation, environmental-related matters, and customs duties. The total amount committed under these surety bonds, which expire at various dates, primarily in 2018, was $55 at March 31, 2018.

Pursuant to the Separation and Distribution Agreement, Arconic was required to provide surety bonds related to Alcoa Corporation workers’ compensation claims which occurred prior to November 1, 2016 and, as a result, Arconic has $25 in outstanding surety bonds relating to these liabilities. Alcoa Corporation workers’ compensation claims and surety bond fees paid by Arconic are being proportionately billed to and are being fully reimbursed by Alcoa Corporation.