Recently Adopted and Recently Issued Accounting Guidance	6 Months Ended
Jun. 30, 2018
Accounting Policies [Abstract]
Recently Adopted and Recently Issued Accounting Guidance	Recently Adopted and Recently Issued Accounting Guidance Adopted In May 2014, the FASB issued changes to the recognition of revenue from contracts with customers. These changes created a comprehensive framework for all entities in all industries to apply in the determination of when to recognize revenue and, therefore, supersede virtually all existing revenue recognition requirements and guidance. This framework is expected to result in less complex guidance in application while providing a consistent and comparable methodology for revenue recognition. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve this principle, an entity should apply the following steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract(s), (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract(s), and (v) recognize revenue when, or as, the entity satisfies a performance obligation. These changes became effective for Arconic on January 1, 2018. Arconic adopted this new guidance using the modified retrospective transition approach applied to those contracts that were not completed as of January 1, 2018. There was no cumulative effect adjustment to the opening balance of retained earnings in the Consolidated Balance Sheet in the first quarter of 2018, as the adoption did not result in a change to our timing of revenue recognition, which continues to be at a point in time. See Note C for further details. In January 2016, the FASB issued changes to equity investments. These changes require equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. However, an entity may choose to measure equity investments that do not have readily determinable fair values using the measurement alternative of cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or similar investment of the same issuer. Also, the impairment assessment of equity investments without readily determinable fair values has been simplified by requiring a qualitative assessment to identify impairment. Also, the new guidance required changes in fair value of equity securities to be recognized immediately as a component of net income instead of being reported in accumulated other comprehensive loss until the gain (loss) is realized. These changes became effective for Arconic on January 1, 2018 and have been applied on a prospective basis. Arconic elected the measurement alternative for its equity investments that do not have readily determinable fair values. The adoption of this guidance did not have a material impact on the Consolidated Financial Statements. In August 2016, the FASB issued changes to the classification of certain cash receipts and cash payments within the statement of cash flows. The guidance identifies eight specific cash flow items and the sections where they must be presented within the statement of cash flows. These changes became effective for Arconic on January 1, 2018 and have been be applied retrospectively. As of result of the adoption, Arconic reclassified cash received related to beneficial interest in previously transferred trade accounts receivables from operating activities to investing activities in the Statement of Consolidated Cash Flows. This new accounting standard does not reflect a change in our underlying business or activities. The reclassification of cash received related to beneficial interest in previously transferred trade accounts receivables was $285 for the six months ended June 30, 2017. In addition, Arconic reclassified $52 of cash paid for debt prepayments including extinguishment costs from operating activities to financing activities for the six months ended June 30, 2017. In November 2016, the FASB issued changes to the classification of cash and cash equivalents within the statement of cash flow. Restricted cash and cash equivalents will be included within the cash and cash equivalents line on the cash flow statement and a reconciliation must be prepared to the statement of financial position. Transfers between restricted cash and cash equivalents and cash and cash equivalents will no longer be presented as cash flow activities in the Statement of Consolidated Cash Flows and for material balances of restricted cash and restricted cash equivalents Arconic will disclose information regarding the nature of the restrictions. These changes became effective for Arconic on January 1, 2018 and have been applied retrospectively. Management has determined that the adoption of this guidance did not have a material impact on the Statement of Consolidated Cash Flows. Restricted cash was $5, $4 and $5 at June 30, 2018, December 31, 2017 and June 30, 2017, respectively. In March 2017, the FASB issued changes to the presentation of net periodic pension cost and net periodic postretirement benefit cost. The new guidance requires registrants to present the service cost component of net periodic benefit cost in the same income statement line item or items as other employee compensation costs arising from services rendered during the period. Also, only the service cost component will be eligible for asset capitalization. Registrants will present the other components of net periodic benefit cost separately from the service cost component; and, the line item or items used in the income statement to present the other components of net periodic benefit cost must be disclosed. These changes became effective for Arconic on January 1, 2018 and were adopted retrospectively for the presentation of the service cost component and the other components of net periodic benefit cost in the Statement of Consolidated Operations, and prospectively for the asset capitalization of the service cost component of net periodic benefit cost. The Company recorded the service related net periodic benefit cost within Cost of goods sold, Selling, general administrative, and other expenses and Research and development expenses and recorded the non-service related net periodic benefit cost (except for the curtailment cost which was recorded in Restructuring and other charges) separately from service cost in Other expense (income), net within the Statement of Consolidated Operations. The impact of the retrospective adoption of this guidance was an increase to consolidated Operating income of $39 and $77 while there was no impact to consolidated Net income for the second quarter or six months ended June 30, 2017, respectively. In May 2017, the FASB issued clarification to guidance on the modification accounting criteria for share-based payment awards. The new guidance requires registrants to apply modification accounting unless three specific criteria are met. The three criteria are 1) the fair value of the award is the same before and after the modification, 2) the vesting conditions are the same before and after the modification and 3) the classification as a debt or equity award is the same before and after the modification. These changes became effective for Arconic on January 1, 2018 and were applied prospectively to new awards modified after adoption. The adoption of this guidance did not have a material impact on the Consolidated Financial Statements. Issued In February 2016, the FASB issued changes to the accounting and presentation of leases. These changes require lessees to recognize a right of use asset and lease liability on the balance sheet for all leases with terms longer than 12 months. For leases with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize a right of use asset and lease liability. Also, when measuring assets and liabilities arising from a lease, optional payments should be included only if the lessee is reasonably certain to exercise an option to extend the lease, exercise a purchase option, or not exercise an option to terminate the lease. As originally released, the standards update required application at the beginning of the earliest comparative period presented at the time of adoption. However, in July 2018, the FASB provided entities the option to instead apply the provisions of the new leases guidance at the effective date, without adjusting the comparative periods presented. These changes become effective for Arconic on January 1, 2019. Arconic’s current operating lease portfolio is primarily comprised of land and buildings, plant equipment, vehicles, and computer equipment. A cross-functional implementation team is in the process of determining the scope of arrangements that will be subject to this standard as well as assessing the impact to the Company’s systems, processes and internal controls. Arconic has contracted with a third-party vendor to implement a software solution. Concurrently, Arconic is compiling lease data to be uploaded into the software solution to account for leases under the new standard. Management is evaluating the impact of these changes on the Consolidated Balance Sheet, which will require right of use assets and lease liabilities be recorded for operating leases; therefore, an estimate of the impact is not currently determinable. However, the adoption is not expected to have a material impact on the Statement of Consolidated Operations or Statement of Consolidated Cash Flows. In June 2016, the FASB added a new impairment model (known as the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of expected credit losses. The CECL model applies to most debt instruments, trade receivables, lease receivables, financial guarantee contracts, and other loan commitments. The CECL model does not have a minimum threshold for recognition of impairment losses and entities will need to measure expected credit losses on assets that have a low risk of loss. These changes become effective for Arconic on January 1, 2020. Management is currently evaluating the potential impact of these changes on the Consolidated Financial Statements. In August 2017, the FASB issued guidance that will make more financial and nonfinancial hedging strategies eligible for hedge accounting. It also amends the presentation and disclosure requirements and changes how companies assess effectiveness. It is intended to more closely align hedge accounting with companies’ risk management strategies, simplify the application of hedge accounting, and increase transparency as to the scope and results of hedging programs. These changes become effective for Arconic on January 1, 2019. For cash flow and net investment hedges existing at the date of adoption, Arconic will apply a cumulative-effect adjustment related to eliminating the separate measurement of ineffectiveness to accumulated other comprehensive income with a corresponding adjustment to the opening balance of retained earnings as of the beginning of the fiscal year in which the amendment is adopted. The amended presentation and disclosure guidance is required only prospectively. Management is currently evaluating the potential impact of this guidance on the Consolidated Financial Statements. In February 2018, the FASB issued guidance that allows an optional reclassification from Accumulated other comprehensive loss to Accumulated deficit for stranded tax effects resulting from the Tax Cuts and Jobs Act enacted on December 22, 2017. These changes become effective for Arconic on January 1, 2019. Management is currently evaluating the potential impact of this guidance on the Consolidated Financial Statements.

Recently Adopted and Recently Issued Accounting Guidance

Adopted

In May 2014, the FASB issued changes to the recognition of revenue from contracts with customers. These changes created a comprehensive framework for all entities in all industries to apply in the determination of when to recognize revenue and, therefore, supersede virtually all existing revenue recognition requirements and guidance. This framework is expected to result in less complex guidance in application while providing a consistent and comparable methodology for revenue recognition. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve this principle, an entity should apply the following steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract(s), (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract(s), and (v) recognize revenue when, or as, the entity satisfies a performance obligation. These changes became effective for Arconic on January 1, 2018. Arconic adopted this new guidance using the modified retrospective transition approach applied to those contracts that were not completed as of January 1, 2018. There was no cumulative effect adjustment to the opening balance of retained earnings in the Consolidated Balance Sheet in the first quarter of 2018, as the adoption did not result in a change to our timing of revenue recognition, which continues to be at a point in time. See Note C for further details.

In January 2016, the FASB issued changes to equity investments. These changes require equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. However, an entity may choose to measure equity investments that do not have readily determinable fair values using the measurement alternative of cost minus impairment, if any, plus or minus changes resulting from observable price changes in orderly transactions for the identical or similar investment of the same issuer. Also, the impairment assessment of equity investments without readily determinable fair values has been simplified by requiring a qualitative assessment to identify impairment. Also, the new guidance required changes in fair value of equity securities to be recognized immediately as a component of net income instead of being reported in accumulated other comprehensive loss until the gain (loss) is realized. These changes became effective for Arconic on January 1, 2018 and have been applied on a prospective basis. Arconic elected the measurement alternative for its equity investments that do not have readily determinable fair values. The adoption of this guidance did not have a material impact on the Consolidated Financial Statements.

In August 2016, the FASB issued changes to the classification of certain cash receipts and cash payments within the statement of cash flows. The guidance identifies eight specific cash flow items and the sections where they must be presented within the statement of cash flows. These changes became effective for Arconic on January 1, 2018 and have been be applied retrospectively. As of result of the adoption, Arconic reclassified cash received related to beneficial interest in previously transferred trade accounts receivables from operating activities to investing activities in the Statement of Consolidated Cash Flows. This new accounting standard does not reflect a change in our underlying business or activities. The reclassification of cash received related to beneficial interest in previously transferred trade accounts receivables was $285 for the six months ended June 30, 2017. In addition, Arconic reclassified $52 of cash paid for debt prepayments including extinguishment costs from operating activities to financing activities for the six months ended June 30, 2017.

In November 2016, the FASB issued changes to the classification of cash and cash equivalents within the statement of cash flow. Restricted cash and cash equivalents will be included within the cash and cash equivalents line on the cash flow statement and a reconciliation must be prepared to the statement of financial position. Transfers between restricted cash and cash equivalents and cash and cash equivalents will no longer be presented as cash flow activities in the Statement of Consolidated Cash Flows and for material balances of restricted cash and restricted cash equivalents Arconic will disclose information regarding the nature of the restrictions. These changes became effective for Arconic on January 1, 2018 and have been applied retrospectively. Management has determined that the adoption of this guidance did not have a material impact on the Statement of Consolidated Cash Flows. Restricted cash was $5, $4 and $5 at June 30, 2018, December 31, 2017 and June 30, 2017, respectively.

In March 2017, the FASB issued changes to the presentation of net periodic pension cost and net periodic postretirement benefit cost. The new guidance requires registrants to present the service cost component of net periodic benefit cost in the same income statement line item or items as other employee compensation costs arising from services rendered during the period. Also, only the service cost component will be eligible for asset capitalization. Registrants will present the other components of net periodic benefit cost separately from the service cost component; and, the line item or items used in the income statement to present the other components of net periodic benefit cost must be disclosed. These changes became effective for Arconic on January 1, 2018 and were adopted retrospectively for the presentation of the service cost component and the other components of net periodic benefit cost in the Statement of Consolidated Operations, and prospectively for the asset capitalization of the service cost component of net periodic benefit cost. The Company recorded the service related net periodic benefit cost within Cost of goods sold, Selling, general administrative, and other expenses and Research and development expenses and recorded the non-service related net periodic benefit cost (except for the curtailment cost which was recorded in Restructuring and other charges) separately from service cost in Other expense (income), net within the Statement of Consolidated Operations. The impact of the retrospective adoption of this guidance was an increase to consolidated Operating income of $39 and $77 while there was no impact to consolidated Net income for the second quarter or six months ended June 30, 2017, respectively.

In May 2017, the FASB issued clarification to guidance on the modification accounting criteria for share-based payment awards. The new guidance requires registrants to apply modification accounting unless three specific criteria are met. The three criteria are 1) the fair value of the award is the same before and after the modification, 2) the vesting conditions are the same before and after the modification and 3) the classification as a debt or equity award is the same before and after the modification. These changes became effective for Arconic on January 1, 2018 and were applied prospectively to new awards modified after adoption. The adoption of this guidance did not have a material impact on the Consolidated Financial Statements.

Issued

In February 2016, the FASB issued changes to the accounting and presentation of leases. These changes require lessees to recognize a right of use asset and lease liability on the balance sheet for all leases with terms longer than 12 months. For leases with a term of 12 months or less, a lessee is permitted to make an accounting policy election by class of underlying asset not to recognize a right of use asset and lease liability. Also, when measuring assets and liabilities arising from a lease, optional payments should be included only if the lessee is reasonably certain to exercise an option to extend the lease, exercise a purchase option, or not exercise an option to terminate the lease. As originally released, the standards update required application at the beginning of the earliest comparative period presented at the time of adoption. However, in July 2018, the FASB provided entities the option to instead apply the provisions of the new leases guidance at the effective date, without adjusting the comparative periods presented. These changes become effective for Arconic on January 1, 2019. Arconic’s current operating lease portfolio is primarily comprised of land and buildings, plant equipment, vehicles, and computer equipment. A cross-functional implementation team is in the process of determining the scope of arrangements that will be subject to this standard as well as assessing the impact to the Company’s systems, processes and internal controls. Arconic has contracted with a third-party vendor to implement a software solution. Concurrently, Arconic is compiling lease data to be uploaded into the software solution to account for leases under the new standard. Management is evaluating the impact of these changes on the Consolidated Balance Sheet, which will require right of use assets and lease liabilities be recorded for operating leases; therefore, an estimate of the impact is not currently determinable. However, the adoption is not expected to have a material impact on the Statement of Consolidated Operations or Statement of Consolidated Cash Flows.

In June 2016, the FASB added a new impairment model (known as the current expected credit loss (CECL) model) that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of expected credit losses. The CECL model applies to most debt instruments, trade receivables, lease receivables, financial guarantee contracts, and other loan commitments. The CECL model does not have a minimum threshold for recognition of impairment losses and entities will need to measure expected credit losses on assets that have a low risk of loss. These changes become effective for Arconic on January 1, 2020. Management is currently evaluating the potential impact of these changes on the Consolidated Financial Statements.

In August 2017, the FASB issued guidance that will make more financial and nonfinancial hedging strategies eligible for hedge accounting. It also amends the presentation and disclosure requirements and changes how companies assess effectiveness. It is intended to more closely align hedge accounting with companies’ risk management strategies, simplify the application of hedge accounting, and increase transparency as to the scope and results of hedging programs. These changes become effective for Arconic on January 1, 2019. For cash flow and net investment hedges existing at the date of adoption, Arconic will apply a cumulative-effect adjustment related to eliminating the separate measurement of ineffectiveness to accumulated other comprehensive income with a corresponding adjustment to the opening balance of retained earnings as of the beginning of the fiscal year in which the amendment is adopted. The amended presentation and disclosure guidance is required only prospectively. Management is currently evaluating the potential impact of this guidance on the Consolidated Financial Statements.

In February 2018, the FASB issued guidance that allows an optional reclassification from Accumulated other comprehensive loss to Accumulated deficit for stranded tax effects resulting from the Tax Cuts and Jobs Act enacted on December 22, 2017. These changes become effective for Arconic on January 1, 2019. Management is currently evaluating the potential impact of this guidance on the Consolidated Financial Statements.