Contingencies and Commitments	12 Months Ended
Dec. 31, 2017
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 $294 at December 31, 2017 and $308 at December 31, 2016 (of which $41 and $48, 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. In 2017, the remediation reserve increased by $5 due to a net charge associated with a number of sites and was recorded in Costs of goods sold on the accompanying Statement of Consolidated Operations. The change in the reserve also reflects an increase of $8 due to a reclassification of amounts included in other reserves within Other noncurrent liabilities and deferred credits on the accompanying Consolidated Balance Sheet, and a decrease of $1 due to the effects of foreign currency translation. Payments related to remediation expenses applied against the reserve were $26 in 2017 and include 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 reserve 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 December 31, 2017 and December 31, 2016, the reserve balance associated with this matter was $215 and $228, respectively. Arconic is in the planning and design phase of the project, which phase is now expected to be completed in 2018. Originally, the design was scheduled to be completed and approved by the EPA in 2017, but in the third quarter of 2017, the New York State Department of Environmental Conservation (DEC) sent a letter to EPA requesting revisions to the draft design. That caused EPA to delay their review and comment on the draft design. EPA has now responded to the DEC letter and while issues remain, Arconic is now able to recommence work on the final design. Following 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 (see Note C), dated as of October 31, 2016, entered into between the Company and Alcoa Corporation in connection with the Separation, the Company shares responsibility with Alcoa Corporation for, and Alcoa Corporation has agreed to partially indemnify the Company with respect to the following matter. As previously reported, in September 2010, following a corporate income tax audit covering the 2003 through 2005 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. An appeal of this assessment in Spain’s Central Tax Administrative Court by the Company was denied in October 2013. In December 2013, the Company filed an appeal of the assessment in Spain’s National Court. On January 16, 2017, Spain’s National Court issued a decision in favor of the Company related to the assessment received in September 2010. The Spanish Tax Administration did not file an appeal within the applicable period. Based on this decision and recent confirming correspondence from the Spanish Tax Administration, the matter is now closed. The Company will not be responsible for any assessment related to the 2003 through 2005 tax years. Additionally, following a corporate income tax audit of the same Spanish tax group for the 2006 through 2009 tax years, Spain’s tax authorities issued an assessment in July 2013 similarly disallowing certain interest deductions. In August 2013, the Company filed an appeal of this second assessment in Spain’s Central Tax Administrative Court, which was denied in January 2015. The Company filed an appeal of this second assessment in Spain’s National Court in March 2015. Spain’s National Court has not yet rendered a decision related to the assessment received in July 2013. The assessment for the 2006 through 2009 tax years is $155 (€130), including interest. The Company believes it has meritorious arguments to support its tax position and intends to vigorously litigate the assessments through Spain’s court system. However, in the event the Company is unsuccessful, a portion of the assessments 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. As previously reported, on June 13, 2017, the Grenfell Tower in London, UK caught fire resulting in fatalities, injuries and damage. A French subsidiary of Arconic, Arconic Architectural Products SAS (AAP SAS), supplied a product, Reynobond PE, to its customer, a cladding system fabricator, which used the product as one component of the overall cladding system on Grenfell Tower. The fabricator supplied its portion of the cladding system to the façade installer, who then completed and installed the system under the direction of the general contractor. Neither Arconic nor AAP SAS was involved in the design or installation of the system used at the Grenfell Tower, nor did it have a role in any other aspect of the building’s refurbishment or original design. Regulatory investigations into the overall Grenfell Tower matter are being conducted, including a criminal investigation by the London Metro Police, a Public Inquiry by the British government and a consumer protection inquiry by a French public authority. AAP SAS sought and received core participant status in the Public Inquiry. The Company will no longer sell the PE product for architectural use on buildings. In August and September 2017, two purported class action complaints were filed against Arconic and certain officers, directors and/or other parties, alleging that, in light of the Grenfell Tower fire, certain Company filings with the Securities and Exchange Commission contained false and misleading disclosures and omissions in violation of the federal securities laws. Those cases remain pending. While the Company believes that these cases are without merit and intends to challenge them vigorously, there can be no assurances regarding the ultimate resolution of these matters. Given the preliminary nature of these matters 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 lawsuits 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 to review these shareholder demand letters and is considering 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 Purchase Obligations. Arconic has entered into purchase commitments for raw materials, energy and other goods and services, which total $861 in 2018, $176 in 2019, $74 in 2020, $13 in 2021, $6 in 2022, and $5 thereafter. Operating Leases. Certain land and buildings, plant equipment, vehicles, and computer equipment are under operating lease agreements. Total expense for all leases was $113 in 2017, $110 in 2016, and $112 in 2015. Under long-term operating leases, minimum annual rentals are $108 in 2018, $88 in 2019, $62 in 2020, $46 in 2021, $38 in 2022, and $100 thereafter. Guarantees. At December 31, 2017, Arconic has 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 $29 at December 31, 2017. Pursuant to the Separation and Distribution Agreement, Arconic was required to provide certain guarantees for Alcoa Corporation, which had a combined fair value of $8 and $35 at December 31, 2017 and 2016, 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 $197 and $354 at December 31, 2017 and 2016, 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 guarantees related to two long-term supply agreements for energy for Alcoa Corporation facilities in the event of an Alcoa Corporation payment default. In October 2017, Alcoa Corporation announced that it had terminated one of the two agreements, the electricity contract with Luminant Generation Company LLC that was tied to its Rockdale Operations, effective as of October 1, 2017. As a result of the termination of the Rockdale electricity contract, Arconic recorded income of $25 in the fourth quarter of 2017 associated with reversing the fair value of the electricity contract guarantee. For the remaining long-term supply agreement, Arconic is required to provide a guarantee up to an estimated present value amount of approximately $1,297. Arconic was also required to provide guarantees of $50 related to two Alcoa Corporation energy supply contracts. These guarantees expired in March 2017. Additionally, Arconic was required to provide guarantees of $53 related to certain Alcoa Corporation environmental liabilities. Notification of a change in guarantor to Alcoa Corporation was made to the appropriate environmental agencies and as such, Arconic no longer provides these guarantees. In December 2016, Arconic entered into a one-year claims purchase agreement with a bank covering claims up to $245 related to the Saudi Arabian joint venture and two long-term energy supply agreements. The majority of the premium was paid by Alcoa Corporation. The agreement matured in December 2017 and was not renewed in 2018 due to the decline in exposure to guarantee claims including a substantial reduction in the guarantees related to the Saudi Arabian joint venture and also the elimination of the guarantee related to the Rockdale energy contract. The decision to enter into a claims purchase agreement will be made on an annual basis going forward. 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 $120 at December 31, 2017. Pursuant to the Separation and Distribution Agreement, Arconic was required to retain letters of credit of $62 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. Additionally, Arconic was required to provide letters of credit for certain Alcoa Corporation equipment leases and energy contracts and, as a result, Arconic had $103 of outstanding letters of credit relating to these liabilities. The entire $103 of outstanding letters of credit were canceled in 2017 when Alcoa Corporation issued its own letters of credit to cover these obligations. 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 bonds, which automatically renew or expire at various dates, mostly in 2018, was $54 at December 31, 2017. 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 $294 at December 31, 2017 and $308 at December 31, 2016 (of which $41 and $48, 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. In 2017, the remediation reserve increased by $5 due to a net charge associated with a number of sites and was recorded in Costs of goods sold on the accompanying Statement of Consolidated Operations. The change in the reserve also reflects an increase of $8 due to a reclassification of amounts included in other reserves within Other noncurrent liabilities and deferred credits on the accompanying Consolidated Balance Sheet, and a decrease of $1 due to the effects of foreign currency translation. Payments related to remediation expenses applied against the reserve were $26 in 2017 and include 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 reserve 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 December 31, 2017 and December 31, 2016, the reserve balance associated with this matter was $215 and $228, respectively. Arconic is in the planning and design phase of the project, which phase is now expected to be completed in 2018. Originally, the design was scheduled to be completed and approved by the EPA in 2017, but in the third quarter of 2017, the New York State Department of Environmental Conservation (DEC) sent a letter to EPA requesting revisions to the draft design. That caused EPA to delay their review and comment on the draft design. EPA has now responded to the DEC letter and while issues remain, Arconic is now able to recommence work on the final design. Following 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 (see Note C), dated as of October 31, 2016, entered into between the Company and Alcoa Corporation in connection with the Separation, the Company shares responsibility with Alcoa Corporation for, and Alcoa Corporation has agreed to partially indemnify the Company with respect to the following matter.

As previously reported, in September 2010, following a corporate income tax audit covering the 2003 through 2005 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. An appeal of this assessment in Spain’s Central Tax Administrative Court by the Company was denied in October 2013. In December 2013, the Company filed an appeal of the assessment in Spain’s National Court.

On January 16, 2017, Spain’s National Court issued a decision in favor of the Company related to the assessment received in September 2010. The Spanish Tax Administration did not file an appeal within the applicable period. Based on this decision and recent confirming correspondence from the Spanish Tax Administration, the matter is now closed. The Company will not be responsible for any assessment related to the 2003 through 2005 tax years.

Additionally, following a corporate income tax audit of the same Spanish tax group for the 2006 through 2009 tax years, Spain’s tax authorities issued an assessment in July 2013 similarly disallowing certain interest deductions. In August 2013, the Company filed an appeal of this second assessment in Spain’s Central Tax Administrative Court, which was denied in January 2015. The Company filed an appeal of this second assessment in Spain’s National Court in March 2015. Spain’s National Court has not yet rendered a decision related to the assessment received in July 2013. The assessment for the 2006 through 2009 tax years is $155 (€130), including interest.

The Company believes it has meritorious arguments to support its tax position and intends to vigorously litigate the assessments through Spain’s court system. However, in the event the Company is unsuccessful, a portion of the assessments 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. As previously reported, on June 13, 2017, the Grenfell Tower in London, UK caught fire resulting in fatalities, injuries and damage. A French subsidiary of Arconic, Arconic Architectural Products SAS (AAP SAS), supplied a product, Reynobond PE, to its customer, a cladding system fabricator, which used the product as one component of the overall cladding system on Grenfell Tower. The fabricator supplied its portion of the cladding system to the façade installer, who then completed and installed the system under the direction of the general contractor. Neither Arconic nor AAP SAS was involved in the design or installation of the system used at the Grenfell Tower, nor did it have a role in any other aspect of the building’s refurbishment or original design. Regulatory investigations into the overall Grenfell Tower matter are being conducted, including a criminal investigation by the London Metro Police, a Public Inquiry by the British government and a consumer protection inquiry by a French public authority. AAP SAS sought and received core participant status in the Public Inquiry. The Company will no longer sell the PE product for architectural use on buildings.

In August and September 2017, two purported class action complaints were filed against Arconic and certain officers, directors and/or other parties, alleging that, in light of the Grenfell Tower fire, certain Company filings with the Securities and Exchange Commission contained false and misleading disclosures and omissions in violation of the federal securities laws. Those cases remain pending.

While the Company believes that these cases are without merit and intends to challenge them vigorously, there can be no assurances regarding the ultimate resolution of these matters. Given the preliminary nature of these matters 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 lawsuits 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 to review these shareholder demand letters and is considering 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

Purchase Obligations. Arconic has entered into purchase commitments for raw materials, energy and other goods and services, which total $861 in 2018, $176 in 2019, $74 in 2020, $13 in 2021, $6 in 2022, and $5 thereafter.

Operating Leases. Certain land and buildings, plant equipment, vehicles, and computer equipment are under operating lease agreements. Total expense for all leases was $113 in 2017, $110 in 2016, and $112 in 2015. Under long-term operating leases, minimum annual rentals are $108 in 2018, $88 in 2019, $62 in 2020, $46 in 2021, $38 in 2022, and $100 thereafter.

Guarantees. At December 31, 2017, Arconic has 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 $29 at December 31, 2017.

Pursuant to the Separation and Distribution Agreement, Arconic was required to provide certain guarantees for Alcoa Corporation, which had a combined fair value of $8 and $35 at December 31, 2017 and 2016, 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 $197 and $354 at December 31, 2017 and 2016, 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 guarantees related to two long-term supply agreements for energy for Alcoa Corporation facilities in the event of an Alcoa Corporation payment default. In October 2017, Alcoa Corporation announced that it had terminated one of the two agreements, the electricity contract with Luminant Generation Company LLC that was tied to its Rockdale Operations, effective as of October 1, 2017. As a result of the termination of the Rockdale electricity contract, Arconic recorded income of $25 in the fourth quarter of 2017 associated with reversing the fair value of the electricity contract guarantee. For the remaining long-term supply agreement, Arconic is required to provide a guarantee up to an estimated present value amount of approximately $1,297.

Arconic was also required to provide guarantees of $50 related to two Alcoa Corporation energy supply contracts. These guarantees expired in March 2017. Additionally, Arconic was required to provide guarantees of $53 related to certain Alcoa Corporation environmental liabilities. Notification of a change in guarantor to Alcoa Corporation was made to the appropriate environmental agencies and as such, Arconic no longer provides these guarantees.

In December 2016, Arconic entered into a one-year claims purchase agreement with a bank covering claims up to $245 related to the Saudi Arabian joint venture and two long-term energy supply agreements. The majority of the premium was paid by Alcoa Corporation. The agreement matured in December 2017 and was not renewed in 2018 due to the decline in exposure to guarantee claims including a substantial reduction in the guarantees related to the Saudi Arabian joint venture and also the elimination of the guarantee related to the Rockdale energy contract. The decision to enter into a claims purchase agreement will be made on an annual basis going forward.

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 $120 at December 31, 2017.

Pursuant to the Separation and Distribution Agreement, Arconic was required to retain letters of credit of $62 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. Additionally, Arconic was required to provide letters of credit for certain Alcoa Corporation equipment leases and energy contracts and, as a result, Arconic had $103 of outstanding letters of credit relating to these liabilities. The entire $103 of outstanding letters of credit were canceled in 2017 when Alcoa Corporation issued its own letters of credit to cover these obligations.

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 bonds, which automatically renew or expire at various dates, mostly in 2018, was $54 at December 31, 2017.

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.