Summary of Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2018
Accounting Policies [Abstract]
Principles of Consolidation and Basis of Presentation	Principles of Consolidation and Basis of Presentation. The accompanying unaudited consolidated financial statements include the accounts of our wholly owned subsidiaries and are prepared in accordance with United States generally accepted accounting principles ("GAAP") and the rules and regulations of the Securities and Exchange Commission ("SEC") applicable for interim periods and, therefore, do not include all information and footnotes required by GAAP for complete financial statements. In management's opinion, all adjustments (which include normal recurring adjustments) considered necessary for a fair presentation have been included. The results of operations for our interim periods are not necessarily indicative of the results of operations that may be achieved for the entire 2018 fiscal year. The financial information as of December 31, 2017 is derived from our audited consolidated financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2017. We have reclassified certain amounts in prior-period financial statements to conform to the current period’s presentation. On the Statements of Consolidated Income, prior period presentation of Unrealized (gain) loss on derivative instruments is now contained within "Cost of products sold, excluding depreciation and amortization and other items." See Note 5 for additional details. See Note 14 for changes relating to the consolidation of the All Other business unit into the Fabricated Products reporting segment.
Use of Estimates in the Preparation of Financial Statements	Use of Estimates in the Preparation of Financial Statements. The preparation of financial statements in accordance with GAAP requires the use of estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities known to exist as of the date the financial statements are published and the reported amounts of revenues and expenses during the reporting period. Uncertainties with respect to such estimates and assumptions are inherent in the preparation of our consolidated financial statements; accordingly, it is possible that the actual results could differ from these estimates and assumptions, which could have a material effect on the reported amounts of our consolidated financial position and results of operations.
Fair Value Measurements	Fair Value Measurements. We apply the fair value hierarchy established by GAAP for the recognition and measurement of certain financial assets and liabilities. An asset or liability's fair value classification within the hierarchy is determined based on the lowest level input that is significant to the fair value measurement. In determining fair value, we utilize valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible and consider counterparty risk in our assessment of fair value. We also review the underlying inputs that are significant to the fair value measurement of financial instruments to determine if a transfer among hierarchy levels is appropriate. We historically have not had significant transfers into or out of each hierarchy level. Financial assets and liabilities that we measure at fair value each period include our derivative instruments, equity investments related to our deferred compensation plan and debt investment securities classified as available for sale securities (see Note 4). Additionally, we measure at fair value once each year at December 31 the plan assets of the Salaried VEBA (defined in Note 4) and our Canadian defined benefit pension plan. We record our remaining financial assets and liabilities at carrying value. For a majority of our non-financial assets and liabilities, which include goodwill, intangible assets, inventories and property, plant and equipment, we are not required to measure their fair value on a recurring basis. However, if certain triggering events occur (or at least annually for goodwill), an evaluation of the affected non-financial asset or liability will be required, which could result in a reduction to the carrying amount of such asset or liability. See Note 3 for a discussion of our business acquisition during the quarter ended September 30, 2018, as well as the goodwill impairment charge recorded during the quarter ended June 30, 2017 related to the operations at our Chandler, Arizona (Extrusion) facility. None of our non-financial assets and liabilities subject to fair value assessments on a non-recurring basis required a material adjustment to the carrying amount of such assets and liabilities for the quarter and nine months ended September 30, 2018.
Inventories	Inventories. Inventories are stated at the lower of cost or market value. Finished products, work-in-process and raw material inventories are stated on the last-in, first-out ("LIFO") basis. At September 30, 2018 and December 31, 2017, the current cost of our inventory exceeded its stated LIFO value by $42.9 million and $24.3 million, respectively. Other inventories are stated on the first-in, first-out basis and consist of operating supplies, which are materials and supplies to be consumed during the production process. Inventory costs consist of material, labor and manufacturing overhead, including depreciation. Abnormal costs, such as idle facility expenses, freight, handling costs and spoilage, are accounted for as current period charges (see Note 2 for the components of inventories).
Replacement Parts	Replacement Parts. Replacement parts consist of preventative maintenance and capital spare parts, which are stated on the first-in, first-out basis. Replacement parts are recorded within Prepaid expenses and other current assets or Other assets depending on whether or not the expected utilization of the replacement parts is to occur within the current operating cycle.
Property, Plant and Equipment - Net	Property, Plant and Equipment, Net. Property, plant and equipment, net is recorded at cost and includes construction in progress (see Note 2). Interest related to the construction of qualifying assets is capitalized as part of the construction costs. The amount of interest expense capitalized as construction in progress was $0.4 million and $0.7 million during the quarters ended September 30, 2018 and September 30, 2017, respectively. The amount of interest expense capitalized as construction in progress was $1.3 million and $1.9 million during the nine months ended September 30, 2018 and September 30, 2017, respectively. Depreciation is computed using the straight-line method at rates based on the estimated useful lives of the various classes of assets. Capital lease assets and leasehold improvements are depreciated on a straight-line basis over the shorter of the estimated useful lives of the assets or the lease term. We classify assets as held for sale only when an asset is being actively marketed and expected to sell within 12 months. Assets held for sale are initially measured at the lesser of the assets' carrying amount and the fair value less costs to sell.
Derivative Financial Instruments	Derivative Financial Instruments. Consistent with guidelines established by management and approved by our Board of Directors, we use derivative financial instruments to mitigate our exposure to changes in the market price of aluminum, alloying metals, energy, and, to a lesser extent, foreign currency exchange rates. We do not use derivative financial instruments for trading or other speculative purposes. Hedging transactions are executed centrally on behalf of all of our operations to minimize transaction costs, monitor consolidated net exposures and allow for increased responsiveness to changes in market factors. We reflect the fair value of all of our derivative instruments on our Consolidated Balance Sheets (see Note 5). The fair value of hedges settling within one year is included in Prepaid expenses and other current assets or Other accrued liabilities. The fair value of hedges settling beyond one year is included in Other assets or Long-term liabilities. Prior to our adoption of ASU 2017-12 (as defined below under "Adoption of New Accounting Standards"), we did not meet the documentation requirements for hedge (deferral) accounting related to our aluminum and energy derivatives. Accordingly, we recorded unrealized gain or loss associated with these hedges in the Statements of Consolidated Income. Subsequent to our adoption of ASU 2017-12 on January 1, 2018, our aluminum and energy derivatives qualified for hedge (deferral) accounting and, as such, we designated such hedges as cash flow hedges. Forward swap contracts for zinc and copper ("Alloying Metals") used in our fabrication operations are also designated as cash flow hedges. Unrealized gains and losses associated with our cash flow hedges are deferred in Other comprehensive income, net of tax and reclassified to Cost of products sold, excluding depreciation and amortization and other items when such hedges settle (see Note 5). From time to time, we enter into foreign currency forward contracts to protect the value of anticipated foreign currency expenses associated with cash commitments for equipment purchases. We do not meet the documentation requirements for hedge (deferral) accounting related to foreign currency derivatives and, as such, gains and losses (both unrealized and realized) related to our foreign currency forward contracts are reflected as an increase or reduction in Other income, net.
Self Insurance of Workers' Compensation and Employee Healthcare Liabilities	Self Insurance of Workers' Compensation and Employee Healthcare Liabilities. We self-insure the majority of the costs of workers' compensation benefits and employee healthcare benefits and rely on insurance coverage to protect us from large losses on individual claims. Workers' compensation liabilities are based on a combination of estimates for: (i) incurred-but-not-reported claims and (ii) the ultimate expense of incurred claims. Such estimates are based on judgment, using our historical claims data and information and analysis provided by actuarial and claims advisors, our insurance carriers and other professionals. Our undiscounted workers' compensation liabilities were estimated at $27.9 million and $24.8 million as of September 30, 2018 and December 31, 2017, respectively. However, we account for our workers' compensation accrued liability on a discounted basis, using a discount rate of 3.00% and 2.25% at September 30, 2018 and December 31, 2017, respectively. Accrued liabilities for employee healthcare benefits, which are estimates of unpaid incurred medical and prescription drug costs as provided by our healthcare administrators, were $3.1 million and $3.5 million as of September 30, 2018 and December 31, 2017, respectively.
Short-Term Incentive Plans (STI Plans)	Short-Term Incentive Plans ("STI Plans"). We have annual short-term incentive compensation plans for senior management and certain other employees payable at our election in cash, shares of common stock, or a combination of cash and shares of common stock. Amounts earned under STI Plans are based on our adjusted earnings before interest, taxes, depreciation and amortization ("Adjusted EBITDA"), modified for certain safety, quality, delivery, cost and individual performance factors. The Adjusted EBITDA targets are determined based on the return on adjusted net assets. Most of our production facilities have similar programs for both hourly and salaried employees. As of September 30, 2018, we had a liability of $10.6 million recorded within Accrued salaries, wages and related expenses for estimated probable future payments relating to the nine month performance period of our 2018 STI Plan.
Long-Term Incentive Programs (LTI Programs)	Long-Term Incentive Programs ("LTI Programs"). Executive officers and other key employees of the Company, as well as non-employee directors of the Company, are eligible to participate in the Kaiser Aluminum Corporation 2016 Equity and Incentive Compensation Plan approved by stockholders on May 26, 2016 ("2016 Plan"). At September 30, 2018, 577,300 shares were available for awards under the 2016 Plan. We issue new shares of our common stock upon vesting under the 2016 Plan.
New Accounting Pronouncements	Adoption of New Accounting Pronouncements Accounting Standards Update ("ASU") No. 2014-09, Revenue from Contracts with Customers (Topic 606) ("ASU 2014-09") was issued in May 2014 and requires an entity to 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. We adopted ASU 2014-09, including its subsequent amendments as codified under Accounting Standards Codification Topic 606 ("ASC 606"), during the quarter ended March 31, 2018. Upon adoption under the modified retrospective method, we elected to apply the guidance only to contracts that were not completed at the date of initial application, which resulted in a cumulative-effect increase of $10.1 million (see Note 9) to our Retained earnings (net of a $3.3 million tax impact) on January 1, 2018. Comparative information in this report has not been adjusted and continues to be reported under previous revenue recognition guidance within Accounting Standards Codification Topic 605 ("ASC 605"). See Statement of Consolidated Stockholders' Equity and Note 9 for details of the significant changes and quantitative impacts of the changes, as well as our policy on revenue recognition. ASU No. 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities ("ASU 2016-01"), was issued in January 2016. The amendments in ASU 2016-01 require equity investments to be measured at fair value with changes in fair value recognized in net income. Equity investments related to our deferred compensation plan that had previously been accounted for as available for sale securities are now accounted for as equity investments with changes in fair value recorded within net income. As such, we recorded a cumulative-effect increase of $0.4 million to our Retained earnings (net of a $0.2 million tax impact) on January 1, 2018 to remove the balance of mark-to-market adjustments recorded within Accumulated other comprehensive income at December 31, 2017. See Note 4 for additional details on our deferred compensation plan, including the fair value of related equity investments. ASU No. 2017-07, Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost ("ASU 2017-07"), was issued in March 2017. ASU 2017-07 amends the requirements related to the income statement presentation of the components of net periodic benefit cost for our defined benefit pension and other postretirement plans. Specifically, ASU 2017-07 requires us to: (i) disaggregate the current-service-cost component from the "other components" of net benefit cost and present it with other current compensation costs for related employees in the income statement and (ii) present the other components elsewhere in the income statement and outside of income from operations. As a result of our retrospective adoption of ASU 2017-07, we reclassified amounts that had previously been presented within Selling, general, administrative, research and development to Other income (expense), net in the Statements of Consolidated Income. See Note 4 for further discussion of our defined benefit pension and other postretirement plans. ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities ("ASU 2017-12"), was issued in August 2017. The amendments under ASU 2017-12 refine and expand hedge accounting requirements for both financial (e.g., interest rate) and commodity risks. Its provisions create more transparency around how economic results are presented, both on the face of the financial statements and in the related notes. It also makes certain targeted improvements to simplify the application of hedge accounting guidance. There was no cumulative effect adjustment to record as a result of early adopting ASU 2017-12 in the quarter ended March 31, 2018; however, we designated all of our outstanding commodity hedges as cash flow hedges beginning January 1, 2018. We therefore have significantly reduced the mark-to-market adjustments that have historically been recorded within the Statements of Consolidated Income. These adjustments have instead been recorded within Other comprehensive income, net of tax beginning in the quarter ended March 31, 2018. See Note 5 for further discussion of our derivatives and hedging programs. There were no material impacts on our consolidated financial statements resulting from our adoption in the quarter ended March 31, 2018 of ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting. Accounting Pronouncements Issued But Not Yet Adopted ASU No. 2016-02, Leases (Topic 842): Amendments to the Financial Accounting Standards Board Accounting Standards Codification ("ASU 2016-02"), was issued in February 2016. Under ASU 2016-02, lessees will need to recognize a right-of-use asset and a lease liability for virtually all of their leases (other than leases that meet the definition of a short-term lease). For income statement purposes, a dual model was retained, requiring leases to be classified as either operating or finance. Operating leases will result in straight-line expense (similar to current operating leases) while finance leases will result in a front-loaded expense pattern (similar to current capital leases). ASU 2016-02 was subsequently amended by three additional pronouncements: (i) ASU No. 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842; (ii) ASU No. 2018-10, Codification Improvements to Topic 842, Leases; and (iii) ASU No. 2018-11, Leases (Topic 842): Targeted Improvements. ASU 2016-02 and its subsequent amendments (together "ASC 842") become effective for us in the first quarter of 2019. We are currently assessing the impact and expect the adoption of ASC 842 in 2019 to have a material impact on our consolidated financial statements. We plan to apply the optional transition method allowed by ASU 2018-11 upon adoption of ASC 842 in the first quarter of 2019. ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"), was issued in June 2016. Under ASU 2016-13, existing guidance on reporting credit losses for trade and other receivables and available for sale debt securities will be replaced with a new forward-looking "expected loss" model that generally will result in the earlier recognition of allowances for losses. We are currently in the process of evaluating the impact of adopting ASU 2016-13 in 2020, but do not expect it to have a material impact on our consolidated financial statements. ASU No. 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract ("ASU 2018-15"), was issued in August 2018. Under ASU 2018-15, requirements for capitalizing implementation costs incurred in a hosting arrangement (cloud computing) that is a service contract, are to be aligned with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. We are currently in the process of evaluating the impact of adopting ASU 2018-15 in 2020, but do not expect it to have a material impact on our consolidated financial statements. We do not anticipate any material impact on our consolidated financial statements upon the adoption of the following accounting pronouncements: (i) ASU No. 2018-07, Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting; (ii) ASU No. 2018-08, Not-for-Profit Entities (Topic 958): Clarifying the Scope and the Accounting Guidance for Contributions Received and Contributions Made; (iii) ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement; and (iv) ASU 2018-14, Compensation - Retirement Benefits - Defined Benefit Plans - General (Subtopic 715-20): Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans.
Revenue Recognition	Prior to the Adoption of ASC 606. Prior to our adoption of ASC 606 on January 1, 2018, we recognized revenue on a gross basis when all of the following criteria were met: (i) persuasive evidence of an arrangement existed; (ii) title, ownership and risk of loss had passed to the customer; (iii) the price to the customer was fixed or determinable; and (iv) collection of the resulting receivable was reasonably assured. Provisions for estimated sales returns from and allowances to customers were made in the same period as the related revenues were recognized, based on historical experience or the specific identification of an event necessitating a reserve. Subsequent to the Adoption of ASC 606. Subsequent to our adoption of ASC 606 on January 1, 2018 (see "New Accounting Pronouncements" in Note 1), we recognize revenue as we fulfill our performance obligations and transfer control of products to our customers. For products that have an alternative use and/or for which we do not have an enforceable right to payment (including a reasonable profit) during the production process, we recognize revenue at a point in time. For products that have no alternative use and for which we have an enforceable right to payment (including a reasonable profit) throughout the production process, we recognize revenue over time. In general, a majority of our Aero/HS products and our Automotive Extrusions are recognized over time, with the remainder of our products recognized at a point in time. For the majority of our business, contracts with customers begin when we acknowledge a purchase order for a specific customer order of product to be delivered in the near term. These purchase orders are short term in nature, although they may reference a longer term "blanket purchase order" or a "terms and conditions" agreement, both of which may span multiple years. For revenue recognized at a point in time, transfer of control usually occurs upon shipment or upon customer receipt of the product, depending on shipping terms. For contracts recognized over time, control transfer occurs incrementally during our production process as progress is made on fulfilling the performance obligation. We use the input method of determining our progress, capturing direct costs beginning at the point that billet or cast ingot is introduced into production at either the extrusion phase or the rolling phase, respectively. We believe the input method more accurately reflects the transfer of control as it represents the best information available of work completed to date for which we have an enforceable right to payment. For products in production, we recognize revenue using estimates of the cost incurred to date plus a reasonable margin. As the duration of our contracts for accounting purposes is typically less than one year, we do not present quantitative information about the aggregate transaction price allocated to unsatisfied performance obligations at the end of the reporting period. We adjust the amount of revenue recognized on all products, regardless of timing of revenue recognition, for variable price consideration, which could include metal market price adjustments, volume rebates and sales discounts. We estimate rebate and discount values based on forecasted order data and historical payment trends for specific customers, adjusted as necessary at each reporting period. Accounts receivable is recorded when our right to consideration becomes unconditional. Payment terms for a majority of our domestic customers are 30 days after invoice date. To accommodate shipping time to overseas locations, payment terms for foreign customers are typically several weeks longer than domestic terms. As such, we do not adjust the promised amount of consideration for the effects of a significant financing component as we do not expect the period between the transfer of control of products to our customers and receipt of payment will be greater than one year. Contract assets primarily relate to our enforceable right to consideration for work completed but not billed at the reporting date on contracts for products recognized over time. Contract assets also include amounts related to our contractual right to consideration for finished goods recognized over time that were in transit as of period end. Incremental Costs of Obtaining a Contract. We expense the costs of obtaining a contract as incurred as the amortization period of the asset that we otherwise would have recognized is one year or less. Shipping and Handling Activities. We account for shipping and handling activities that occur after the customer has obtained control of a product as fulfillment activities (i.e., an expense) rather than as a promised service (i.e., a revenue element).

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2018

Principles of Consolidation and Basis of Presentation

Principles of Consolidation and Basis of Presentation. The accompanying unaudited consolidated financial statements include the accounts of our wholly owned subsidiaries and are prepared in accordance with United States generally accepted accounting principles ("GAAP") and the rules and regulations of the Securities and Exchange Commission ("SEC") applicable for interim periods and, therefore, do not include all information and footnotes required by GAAP for complete financial statements. In management's opinion, all adjustments (which include normal recurring adjustments) considered necessary for a fair presentation have been included. The results of operations for our interim periods are not necessarily indicative of the results of operations that may be achieved for the entire 2018 fiscal year. The financial information as of December 31, 2017 is derived from our audited consolidated financial statements and footnotes included in our Annual Report on Form 10-K for the year ended December 31, 2017. We have reclassified certain amounts in prior-period financial statements to conform to the current period’s presentation. On the Statements of Consolidated Income, prior period presentation of Unrealized (gain) loss on derivative instruments is now contained within "Cost of products sold, excluding depreciation and amortization and other items." See Note 5 for additional details. See Note 14 for changes relating to the consolidation of the All Other business unit into the Fabricated Products reporting segment.

Use of Estimates in the Preparation of Financial Statements

Use of Estimates in the Preparation of Financial Statements. The preparation of financial statements in accordance with GAAP requires the use of estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities known to exist as of the date the financial statements are published and the reported amounts of revenues and expenses during the reporting period. Uncertainties with respect to such estimates and assumptions are inherent in the preparation of our consolidated financial statements; accordingly, it is possible that the actual results could differ from these estimates and assumptions, which could have a material effect on the reported amounts of our consolidated financial position and results of operations.

Fair Value Measurements

Fair Value Measurements. We apply the fair value hierarchy established by GAAP for the recognition and measurement of certain financial assets and liabilities. An asset or liability's fair value classification within the hierarchy is determined based on the lowest level input that is significant to the fair value measurement. In determining fair value, we utilize valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible and consider counterparty risk in our assessment of fair value. We also review the underlying inputs that are significant to the fair value measurement of financial instruments to determine if a transfer among hierarchy levels is appropriate. We historically have not had significant transfers into or out of each hierarchy level.

Financial assets and liabilities that we measure at fair value each period include our derivative instruments, equity investments related to our deferred compensation plan and debt investment securities classified as available for sale securities (see Note 4). Additionally, we measure at fair value once each year at December 31 the plan assets of the Salaried VEBA (defined in Note 4) and our Canadian defined benefit pension plan. We record our remaining financial assets and liabilities at carrying value.

For a majority of our non-financial assets and liabilities, which include goodwill, intangible assets, inventories and property, plant and equipment, we are not required to measure their fair value on a recurring basis. However, if certain triggering events occur (or at least annually for goodwill), an evaluation of the affected non-financial asset or liability will be required, which could result in a reduction to the carrying amount of such asset or liability. See Note 3 for a discussion of our business

acquisition during the quarter ended September 30, 2018, as well as the goodwill impairment charge recorded during the quarter ended June 30, 2017 related to the operations at our Chandler, Arizona (Extrusion) facility.

None of our non-financial assets and liabilities subject to fair value assessments on a non-recurring basis required a material adjustment to the carrying amount of such assets and liabilities for the quarter and nine months ended September 30, 2018.

Inventories

Inventories. Inventories are stated at the lower of cost or market value. Finished products, work-in-process and raw material inventories are stated on the last-in, first-out ("LIFO") basis. At September 30, 2018 and December 31, 2017, the current cost of our inventory exceeded its stated LIFO value by $42.9 million and $24.3 million, respectively. Other inventories are stated on the first-in, first-out basis and consist of operating supplies, which are materials and supplies to be consumed during the production process. Inventory costs consist of material, labor and manufacturing overhead, including depreciation. Abnormal costs, such as idle facility expenses, freight, handling costs and spoilage, are accounted for as current period charges (see Note 2 for the components of inventories).

Replacement Parts

Replacement Parts. Replacement parts consist of preventative maintenance and capital spare parts, which are stated on the first-in, first-out basis. Replacement parts are recorded within Prepaid expenses and other current assets or Other assets depending on whether or not the expected utilization of the replacement parts is to occur within the current operating cycle.

Property, Plant and Equipment - Net

Property, Plant and Equipment, Net. Property, plant and equipment, net is recorded at cost and includes construction in progress (see Note 2). Interest related to the construction of qualifying assets is capitalized as part of the construction costs. The amount of interest expense capitalized as construction in progress was $0.4 million and $0.7 million during the quarters ended September 30, 2018 and September 30, 2017, respectively. The amount of interest expense capitalized as construction in progress was $1.3 million and $1.9 million during the nine months ended September 30, 2018 and September 30, 2017, respectively.

Depreciation is computed using the straight-line method at rates based on the estimated useful lives of the various classes of assets. Capital lease assets and leasehold improvements are depreciated on a straight-line basis over the shorter of the estimated useful lives of the assets or the lease term.

We classify assets as held for sale only when an asset is being actively marketed and expected to sell within 12 months. Assets held for sale are initially measured at the lesser of the assets' carrying amount and the fair value less costs to sell.

Derivative Financial Instruments

Derivative Financial Instruments. Consistent with guidelines established by management and approved by our Board of Directors, we use derivative financial instruments to mitigate our exposure to changes in the market price of aluminum, alloying metals, energy, and, to a lesser extent, foreign currency exchange rates. We do not use derivative financial instruments for trading or other speculative purposes. Hedging transactions are executed centrally on behalf of all of our operations to minimize transaction costs, monitor consolidated net exposures and allow for increased responsiveness to changes in market factors.

We reflect the fair value of all of our derivative instruments on our Consolidated Balance Sheets (see Note 5). The fair value of hedges settling within one year is included in Prepaid expenses and other current assets or Other accrued liabilities. The fair value of hedges settling beyond one year is included in Other assets or Long-term liabilities.

Prior to our adoption of ASU 2017-12 (as defined below under "Adoption of New Accounting Standards"), we did not meet the documentation requirements for hedge (deferral) accounting related to our aluminum and energy derivatives. Accordingly, we recorded unrealized gain or loss associated with these hedges in the Statements of Consolidated Income. Subsequent to our adoption of ASU 2017-12 on January 1, 2018, our aluminum and energy derivatives qualified for hedge (deferral) accounting and, as such, we designated such hedges as cash flow hedges. Forward swap contracts for zinc and copper ("Alloying Metals") used in our fabrication operations are also designated as cash flow hedges. Unrealized gains and losses associated with our cash flow hedges are deferred in Other comprehensive income, net of tax and reclassified to Cost of products sold, excluding depreciation and amortization and other items when such hedges settle (see Note 5).

From time to time, we enter into foreign currency forward contracts to protect the value of anticipated foreign currency expenses associated with cash commitments for equipment purchases. We do not meet the documentation requirements for hedge (deferral) accounting related to foreign currency derivatives and, as such, gains and losses (both unrealized and realized) related to our foreign currency forward contracts are reflected as an increase or reduction in Other income, net.

Self Insurance of Workers' Compensation and Employee Healthcare Liabilities

Self Insurance of Workers' Compensation and Employee Healthcare Liabilities. We self-insure the majority of the costs of workers' compensation benefits and employee healthcare benefits and rely on insurance coverage to protect us from large losses on individual claims. Workers' compensation liabilities are based on a combination of estimates for: (i) incurred-but-not-reported claims and (ii) the ultimate expense of incurred claims. Such estimates are based on judgment, using our historical claims data and information and analysis provided by actuarial and claims advisors, our insurance carriers and other professionals. Our undiscounted workers' compensation liabilities were estimated at $27.9 million and $24.8 million as of September 30, 2018 and December 31, 2017, respectively. However, we account for our workers' compensation accrued liability on a discounted basis, using a discount rate of 3.00% and 2.25% at September 30, 2018 and December 31, 2017, respectively. Accrued liabilities for employee healthcare benefits, which are estimates of unpaid incurred medical and prescription drug costs as provided by our healthcare administrators, were $3.1 million and $3.5 million as of September 30, 2018 and December 31, 2017, respectively.

Short-Term Incentive Plans (STI Plans)

Short-Term Incentive Plans ("STI Plans"). We have annual short-term incentive compensation plans for senior management and certain other employees payable at our election in cash, shares of common stock, or a combination of cash and shares of common stock. Amounts earned under STI Plans are based on our adjusted earnings before interest, taxes, depreciation and amortization ("Adjusted EBITDA"), modified for certain safety, quality, delivery, cost and individual performance factors. The Adjusted EBITDA targets are determined based on the return on adjusted net assets. Most of our production facilities have similar programs for both hourly and salaried employees. As of September 30, 2018, we had a liability of $10.6 million recorded within Accrued salaries, wages and related expenses for estimated probable future payments relating to the nine month performance period of our 2018 STI Plan.

Long-Term Incentive Programs (LTI Programs)

Long-Term Incentive Programs ("LTI Programs"). Executive officers and other key employees of the Company, as well as non-employee directors of the Company, are eligible to participate in the Kaiser Aluminum Corporation 2016 Equity and Incentive Compensation Plan approved by stockholders on May 26, 2016 ("2016 Plan"). At September 30, 2018, 577,300 shares were available for awards under the 2016 Plan. We issue new shares of our common stock upon vesting under the 2016 Plan.

New Accounting Pronouncements

Adoption of New Accounting Pronouncements

Accounting Standards Update ("ASU") No. 2014-09, Revenue from Contracts with Customers (Topic 606) ("ASU 2014-09") was issued in May 2014 and requires an entity to 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. We adopted ASU 2014-09, including its subsequent amendments as codified under Accounting Standards Codification Topic 606 ("ASC 606"), during the quarter ended March 31, 2018. Upon adoption under the modified retrospective method, we elected to apply the guidance only to contracts that were not completed at the date of initial application, which resulted in a cumulative-effect increase of $10.1 million (see Note 9) to our Retained earnings (net of a $3.3 million tax impact) on January 1, 2018. Comparative information in this report has not been adjusted and continues to be reported under previous revenue recognition guidance within Accounting Standards Codification Topic 605 ("ASC 605"). See Statement of Consolidated Stockholders' Equity and Note 9 for details of the significant changes and quantitative impacts of the changes, as well as our policy on revenue recognition.

ASU No. 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities ("ASU 2016-01"), was issued in January 2016. The amendments in ASU 2016-01 require equity investments to be measured at fair value with changes in fair value recognized in net income. Equity investments related to our deferred compensation plan that had previously been accounted for as available for sale securities are now accounted for as equity investments with changes in fair value recorded within net income. As such, we recorded a cumulative-effect increase of $0.4 million to our Retained earnings (net of a $0.2 million tax impact) on January 1, 2018 to remove the balance of mark-to-market adjustments recorded within Accumulated other comprehensive income at December 31, 2017. See Note 4 for additional details on our deferred compensation plan, including the fair value of related equity investments.

ASU No. 2017-07, Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost ("ASU 2017-07"), was issued in March 2017. ASU 2017-07 amends the requirements related to the income statement presentation of the components of net periodic benefit cost for our defined benefit pension and other postretirement plans. Specifically, ASU 2017-07 requires us to: (i) disaggregate the current-service-cost component from the "other components" of net benefit cost and present it with other current compensation costs for related employees in the income statement and (ii) present the other components elsewhere in the income statement and outside of

income from operations. As a result of our retrospective adoption of ASU 2017-07, we reclassified amounts that had previously been presented within Selling, general, administrative, research and development to Other income (expense), net in the Statements of Consolidated Income. See Note 4 for further discussion of our defined benefit pension and other postretirement plans.

ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities ("ASU 2017-12"), was issued in August 2017. The amendments under ASU 2017-12 refine and expand hedge accounting requirements for both financial (e.g., interest rate) and commodity risks. Its provisions create more transparency around how economic results are presented, both on the face of the financial statements and in the related notes. It also makes certain targeted improvements to simplify the application of hedge accounting guidance. There was no cumulative effect adjustment to record as a result of early adopting ASU 2017-12 in the quarter ended March 31, 2018; however, we designated all of our outstanding commodity hedges as cash flow hedges beginning January 1, 2018. We therefore have significantly reduced the mark-to-market adjustments that have historically been recorded within the Statements of Consolidated Income. These adjustments have instead been recorded within Other comprehensive income, net of tax beginning in the quarter ended March 31, 2018. See Note 5 for further discussion of our derivatives and hedging programs.

There were no material impacts on our consolidated financial statements resulting from our adoption in the quarter ended March 31, 2018 of ASU No. 2017-09, Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting.

Accounting Pronouncements Issued But Not Yet Adopted

ASU No. 2016-02, Leases (Topic 842): Amendments to the Financial Accounting Standards Board Accounting Standards Codification ("ASU 2016-02"), was issued in February 2016. Under ASU 2016-02, lessees will need to recognize a right-of-use asset and a lease liability for virtually all of their leases (other than leases that meet the definition of a short-term lease). For income statement purposes, a dual model was retained, requiring leases to be classified as either operating or finance. Operating leases will result in straight-line expense (similar to current operating leases) while finance leases will result in a front-loaded expense pattern (similar to current capital leases). ASU 2016-02 was subsequently amended by three additional pronouncements: (i) ASU No. 2018-01, Leases (Topic 842): Land Easement Practical Expedient for Transition to Topic 842; (ii) ASU No. 2018-10, Codification Improvements to Topic 842, Leases; and (iii) ASU No. 2018-11, Leases (Topic 842): Targeted Improvements. ASU 2016-02 and its subsequent amendments (together "ASC 842") become effective for us in the first quarter of 2019. We are currently assessing the impact and expect the adoption of ASC 842 in 2019 to have a material impact on our consolidated financial statements. We plan to apply the optional transition method allowed by ASU 2018-11 upon adoption of ASC 842 in the first quarter of 2019.

ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments ("ASU 2016-13"), was issued in June 2016. Under ASU 2016-13, existing guidance on reporting credit losses for trade and other receivables and available for sale debt securities will be replaced with a new forward-looking "expected loss" model that generally will result in the earlier recognition of allowances for losses. We are currently in the process of evaluating the impact of adopting ASU 2016-13 in 2020, but do not expect it to have a material impact on our consolidated financial statements.

ASU No. 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer's Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract ("ASU 2018-15"), was issued in August 2018. Under ASU 2018-15, requirements for capitalizing implementation costs incurred in a hosting arrangement (cloud computing) that is a service contract, are to be aligned with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. We are currently in the process of evaluating the impact of adopting ASU 2018-15 in 2020, but do not expect it to have a material impact on our consolidated financial statements.

We do not anticipate any material impact on our consolidated financial statements upon the adoption of the following accounting pronouncements: (i) ASU No. 2018-07, Compensation-Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting; (ii) ASU No. 2018-08, Not-for-Profit Entities (Topic 958): Clarifying the Scope and the Accounting Guidance for Contributions Received and Contributions Made; (iii) ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework - Changes to the Disclosure Requirements for Fair Value Measurement; and (iv) ASU 2018-14, Compensation - Retirement Benefits - Defined Benefit Plans - General (Subtopic 715-20): Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans.

Revenue Recognition

Prior to the Adoption of ASC 606. Prior to our adoption of ASC 606 on January 1, 2018, we recognized revenue on a gross basis when all of the following criteria were met: (i) persuasive evidence of an arrangement existed; (ii) title, ownership and risk of loss had passed to the customer; (iii) the price to the customer was fixed or determinable; and (iv) collection of the resulting receivable was reasonably assured. Provisions for estimated sales returns from and allowances to customers were made in the same period as the related revenues were recognized, based on historical experience or the specific identification of an event necessitating a reserve.

Subsequent to the Adoption of ASC 606. Subsequent to our adoption of ASC 606 on January 1, 2018 (see "New Accounting Pronouncements" in Note 1), we recognize revenue as we fulfill our performance obligations and transfer control of products to our customers. For products that have an alternative use and/or for which we do not have an enforceable right to payment (including a reasonable profit) during the production process, we recognize revenue at a point in time. For products that have no alternative use and for which we have an enforceable right to payment (including a reasonable profit) throughout the production process, we recognize revenue over time. In general, a majority of our Aero/HS products and our Automotive Extrusions are recognized over time, with the remainder of our products recognized at a point in time.

For the majority of our business, contracts with customers begin when we acknowledge a purchase order for a specific customer order of product to be delivered in the near term. These purchase orders are short term in nature, although they may reference a longer term "blanket purchase order" or a "terms and conditions" agreement, both of which may span multiple years. For revenue recognized at a point in time, transfer of control usually occurs upon shipment or upon customer receipt of the product, depending on shipping terms. For contracts recognized over time, control transfer occurs incrementally during our production process as progress is made on fulfilling the performance obligation. We use the input method of determining our progress, capturing direct costs beginning at the point that billet or cast ingot is introduced into production at either the extrusion phase or the rolling phase, respectively. We believe the input method more accurately reflects the transfer of control as it represents the best information available of work completed to date for which we have an enforceable right to payment. For products in production, we recognize revenue using estimates of the cost incurred to date plus a reasonable margin. As the duration of our contracts for accounting purposes is typically less than one year, we do not present quantitative information about the aggregate transaction price allocated to unsatisfied performance obligations at the end of the reporting period.

We adjust the amount of revenue recognized on all products, regardless of timing of revenue recognition, for variable price consideration, which could include metal market price adjustments, volume rebates and sales discounts. We estimate rebate and discount values based on forecasted order data and historical payment trends for specific customers, adjusted as necessary at each reporting period. Accounts receivable is recorded when our right to consideration becomes unconditional. Payment terms for a majority of our domestic customers are 30 days after invoice date. To accommodate shipping time to overseas locations, payment terms for foreign customers are typically several weeks longer than domestic terms. As such, we do not adjust the promised amount of consideration for the effects of a significant financing component as we do not expect the period between the transfer of control of products to our customers and receipt of payment will be greater than one year.

Contract assets primarily relate to our enforceable right to consideration for work completed but not billed at the reporting date on contracts for products recognized over time. Contract assets also include amounts related to our contractual right to consideration for finished goods recognized over time that were in transit as of period end.

Incremental Costs of Obtaining a Contract. We expense the costs of obtaining a contract as incurred as the amortization period of the asset that we otherwise would have recognized is one year or less.

Shipping and Handling Activities. We account for shipping and handling activities that occur after the customer has obtained control of a product as fulfillment activities (i.e., an expense) rather than as a promised service (i.e., a revenue element).