Summary of Significant Accounting Policies	9 Months Ended
Sep. 30, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies This Quarterly Report on Form 10-Q (this "Report") should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2014. Unless the context otherwise requires, references in these notes to interim consolidated financial statements - unaudited to "Kaiser Aluminum Corporation," "we," "us," "our," "the Company" and "our Company" refer to Kaiser Aluminum Corporation and its consolidated subsidiaries. Organization and Nature of Operations. Kaiser Aluminum Corporation specializes in the production of semi-fabricated specialty aluminum products, such as aluminum sheet and plate and extruded and drawn products, primarily used in aerospace/high strength, automotive, general engineering and other industrial end market applications. Our business is organized into one operating segment, Fabricated Products. See Note 11 for additional information regarding our reportable segment and business unit. 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 2015 fiscal year. The financial information as of December 31, 2014 is derived from our audited consolidated financial statements and footnotes for the year ended December 31, 2014 included in our Annual Report on Form 10-K. 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. 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. The (shortfalls) excesses of current cost over the stated LIFO value of inventory at September 30, 2015 and December 31, 2014 was $(13.4) million and $37.6 million, respectively. The net realizable value of our inventory was approximately the stated LIFO value as of September 30, 2015. Other inventories, principally operating supplies and repair and maintenance parts, are stated at average cost. 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. All of our inventories at September 30, 2015 and December 31, 2014 were included in the Fabricated Products segment (see Note 2 for the components of inventories). Property, Plant and Equipment – Net. Property, plant and equipment is recorded at cost (see Note 2). Construction in progress is included within Property, plant and equipment – net on the Consolidated Balance Sheets. Interest related to the construction of qualifying assets is capitalized as part of the construction costs. The aggregate amount of interest capitalized is limited to the interest expense incurred in the period. The amount of interest expense capitalized as construction in progress was $0.4 million and $0.3 million during the quarters ended September 30, 2015 and September 30, 2014, respectively. The amount of interest expense capitalized as construction in progress was $1.1 million and $2.2 million during the nine months ended September 30, 2015 and September 30, 2014, respectively. We recorded impairment charges of $1.3 million and $1.5 million during the quarter and nine months ended September 30, 2014, respectively, to reflect the scrap value of idled assets we determined not to deploy for future use. Asset impairment charges are included in Other operating charges, net, in the Statements of Consolidated Income and are included in the Fabricated Products segment. 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. Depreciation expense is not included in Cost of products sold, excluding depreciation and amortization and other items, but is included in Depreciation and amortization on the Statements of Consolidated Income. For the quarters ended September 30, 2015 and September 30, 2014, we recorded depreciation expense of $7.5 million and $7.4 million, respectively, relating to our operating facilities in the Fabricated Products segment. For the nine months ended September 30, 2015 and September 30, 2014, we recorded depreciation expense of $22.6 million and $21.5 million, respectively, relating to our operating facilities in the Fabricated Products segment. An immaterial amount of depreciation expense was also recorded within All Other for all periods presented in this Report. 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. Concentration of Labor Subject to Collective Bargaining Agreements. At September 30, 2015, approximately 63% of our employees were covered by collective bargaining agreements and 5% of our employees were covered by collective bargaining agreements with expiration dates occurring within one year from September 30, 2015. Dividends. When we expect to be in a capital surplus position by the end of a fiscal year, cash dividends and dividend equivalents paid are charged against (Accumulated deficit) retained earnings; otherwise, dividends and dividend equivalents paid are charged against Additional paid in capital. Foreign Currency Risk Management. 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. These derivative instruments are designated and qualify for cash flow hedge accounting and are adjusted to current market values each reporting period. Both realized and unrealized periodic gains and losses of derivative instruments designated as cash flow hedges are deferred in Accumulated other comprehensive loss until depreciation on the underlying equipment commences. Upon commencement, realized gains and losses are recorded in Net income (loss) as an adjustment to depreciation expense in the period in which depreciation is recognized on the underlying equipment. Depending on the time to maturity and asset or liability position, the carrying values of cash flow hedges are included in Prepaid expenses and other current assets, Other assets, Other accrued liabilities or Long-term liabilities. Our policy requires that derivative instruments used as hedges must be effective at reducing the risk associated with the exposure being hedged and must be designated as a hedge at the inception of the instrument contract. Hedge effectiveness is assessed periodically. Any derivative instrument not designated as a hedge, or so designated but ineffective, is adjusted to market value and recognized in net income immediately. If a cash flow hedge ceases to qualify for hedge accounting treatment or is terminated, the derivative instrument would continue to be carried on the balance sheet at fair value until settled and future adjustments to the derivative instrument’s fair value would be recognized in earnings immediately. If a forecasted equipment purchase was no longer probable to occur, amounts previously deferred in accumulated other comprehensive income would be recognized immediately in earnings. See Note 8 for additional information. We are exposed to counterparty credit risk on all of our derivative instruments. Accordingly, we have established and maintained strict counterparty credit guidelines and entered into hedges only with major financial institutions that are investment grade or better. We do not have significant exposure to any one counterparty and management believes the risk of loss is remote and in any event would not be material. Additionally, we do not require collateral under these agreements. New Accounting Pronouncements. Accounting Standards Update ("ASU") No. 2014-12, Compensation - Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period - Consensus of the FASB Emerging Issues Task Force ("ASU 2014-12"), was issued in June 2014. ASU 2014-12 requires an entity to treat a performance target that affects vesting and that could be achieved after the requisite service period as a performance condition. Our adoption of this ASU in the first quarter of 2015 did not have a material impact on our consolidated financial statements. ASU No. 2015-03, Interest - Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs ("ASU 2015-03"), was issued in April 2015. ASU 2015-03 requires debt issuance costs related to a recognized debt liability to be presented in an entity’s balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts, instead of being presented as a deferred charge in the balance sheet. In August 2015, ASU No. 2015-15, Interest - Imputation of Interest (Subtopic 835-30) - Presentation and Subsequent Measurement of Debt Issuance Costs Associated with Line-of-Credit Arrangements ("ASU 2015-15") was issued to address the presentation and subsequent measurement of debt issuance costs related to line-of-credit arrangements. The recognition and measurement guidance for debt issuance costs is not affected by ASU 2015-03 and ASU 2015-15. An entity is required to adopt ASU 2015-03 and ASU 2015-15 for reporting periods beginning on or after December 15, 2015. We do not expect the adoption of these ASUs to have a material impact on our consolidated financial statements. ASU No. 2015-05, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement ("ASU 2015-05"), was issued in April 2015. The ASU requires companies to perform the same assessment that vendors currently perform under ASC 985-605; that is, companies must determine whether an arrangement with its vendor contains a software license element. If so, the related fees paid are accounted for as an internal-use software intangible under ASC 350-40; if not, the arrangement is accounted for as a service contract. As a result of the issuance of ASU 2015-05, all software licenses within the scope of Subtopic 350-40 will be accounted for consistent with other licenses of intangible assets. An entity is required to adopt ASU 2015-05 for reporting periods beginning on or after December 15, 2015. We do not expect the adoption of this ASU to have a material impact on our consolidated financial statements. ASU No. 2015-07, Fair Value Measurement (Topic 820): Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent) ("ASU 2015-07"), was issued in May 2015. This ASU removes the requirement to categorize within the fair value hierarchy table investments without readily determinable fair values in entities that elect to measure fair value using net asset value per share ("NAV") or its equivalent. ASU 2015-07 requires that these investments continue to be shown in the fair value disclosure in order to allow the disclosure to reconcile to the investment amount presented in the balance sheet. We expect to early adopt ASU 2015-07 in the quarter ending December 31, 2015 with retrospective application. We expect to modify our presentation of assets valued using NAV in the voluntary employees’ beneficiary association ("VEBA") postretirement benefit plan and Canadian Pension Plan section of our fair value hierarchy table when we adopt ASU 2015-07. ASU No. 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date ("ASU 2015-14"), was issued in August 2015. ASU 2015-14 defers the effective date of ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which 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, by one year for all entities and permits early adoption on a limited basis. We expect to adopt ASU 2014-09 for the fiscal year ending December 31, 2018 and will continue to assess the impact of the adoption on our consolidated financial statements.

Summary of Significant Accounting Policies

This Quarterly Report on Form 10-Q (this "Report") should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2014. Unless the context otherwise requires, references in these notes to interim consolidated financial statements - unaudited to "Kaiser Aluminum Corporation," "we," "us," "our," "the Company" and "our Company" refer to Kaiser Aluminum Corporation and its consolidated subsidiaries.

Organization and Nature of Operations. Kaiser Aluminum Corporation specializes in the production of semi-fabricated specialty aluminum products, such as aluminum sheet and plate and extruded and drawn products, primarily used in aerospace/high strength, automotive, general engineering and other industrial end market applications. Our business is organized into one operating segment, Fabricated Products. See Note 11 for additional information regarding our reportable segment and business unit.

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 2015 fiscal year. The financial information as of December 31, 2014 is derived from our audited consolidated financial statements and footnotes for the year ended December 31, 2014 included in our Annual Report on Form 10-K.

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.

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. The (shortfalls) excesses of current cost over the stated LIFO value of inventory at September 30, 2015 and December 31, 2014 was $(13.4) million and $37.6 million, respectively. The net realizable value of our inventory was approximately the stated LIFO value as of September 30, 2015. Other inventories, principally operating supplies and repair and maintenance parts, are stated at average cost. 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. All of our inventories at September 30, 2015 and December 31, 2014 were included in the Fabricated Products segment (see Note 2 for the components of inventories).

Property, Plant and Equipment – Net. Property, plant and equipment is recorded at cost (see Note 2). Construction in progress is included within Property, plant and equipment – net on the Consolidated Balance Sheets. Interest related to the construction of qualifying assets is capitalized as part of the construction costs. The aggregate amount of interest capitalized is limited to the interest expense incurred in the period. The amount of interest expense capitalized as construction in progress was $0.4 million and $0.3 million during the quarters ended September 30, 2015 and September 30, 2014, respectively. The amount of interest expense capitalized as construction in progress was $1.1 million and $2.2 million during the nine months ended September 30, 2015 and September 30, 2014, respectively.

We recorded impairment charges of $1.3 million and $1.5 million during the quarter and nine months ended September 30, 2014, respectively, to reflect the scrap value of idled assets we determined not to deploy for future use. Asset impairment charges are included in Other operating charges, net, in the Statements of Consolidated Income and are included in the Fabricated Products segment.

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. Depreciation expense is not included in Cost of products sold, excluding depreciation and amortization and other items, but is included in Depreciation and amortization on the Statements of Consolidated Income. For the quarters ended September 30, 2015 and September 30, 2014, we recorded depreciation expense of $7.5 million and $7.4 million, respectively, relating to our operating facilities in the Fabricated Products segment. For the nine months ended September 30, 2015 and September 30, 2014, we recorded depreciation expense of $22.6 million and $21.5 million, respectively, relating to our operating facilities in the Fabricated Products segment. An immaterial amount of depreciation expense was also recorded within All Other for all periods presented in this Report.

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.

Concentration of Labor Subject to Collective Bargaining Agreements. At September 30, 2015, approximately 63% of our employees were covered by collective bargaining agreements and 5% of our employees were covered by collective bargaining agreements with expiration dates occurring within one year from September 30, 2015.

Dividends. When we expect to be in a capital surplus position by the end of a fiscal year, cash dividends and dividend equivalents paid are charged against (Accumulated deficit) retained earnings; otherwise, dividends and dividend equivalents paid are charged against Additional paid in capital.

Foreign Currency Risk Management. 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. These derivative instruments are designated and qualify for cash flow hedge accounting and are adjusted to current market values each reporting period. Both realized and unrealized periodic gains and losses of derivative instruments designated as cash flow hedges are deferred in Accumulated other comprehensive loss until depreciation on the underlying equipment commences. Upon commencement, realized gains and losses are recorded in Net income (loss) as an adjustment to depreciation expense in the period in which depreciation is recognized on the underlying equipment. Depending on the time to maturity and asset or liability position, the carrying values of cash flow hedges are included in Prepaid expenses and other current assets, Other assets, Other accrued liabilities or Long-term liabilities.

Our policy requires that derivative instruments used as hedges must be effective at reducing the risk associated with the exposure being hedged and must be designated as a hedge at the inception of the instrument contract. Hedge effectiveness is assessed periodically. Any derivative instrument not designated as a hedge, or so designated but ineffective, is adjusted to market value and recognized in net income immediately. If a cash flow hedge ceases to qualify for hedge accounting treatment or is terminated, the derivative instrument would continue to be carried on the balance sheet at fair value until settled and future adjustments to the derivative instrument’s fair value would be recognized in earnings immediately. If a forecasted equipment purchase was no longer probable to occur, amounts previously deferred in accumulated other comprehensive income would be recognized immediately in earnings. See Note 8 for additional information.

We are exposed to counterparty credit risk on all of our derivative instruments. Accordingly, we have established and maintained strict counterparty credit guidelines and entered into hedges only with major financial institutions that are investment grade or better. We do not have significant exposure to any one counterparty and management believes the risk of loss is remote and in any event would not be material. Additionally, we do not require collateral under these agreements.

New Accounting Pronouncements. Accounting Standards Update ("ASU") No. 2014-12, Compensation - Stock Compensation (Topic 718): Accounting for Share-Based Payments When the Terms of an Award Provide That a Performance Target Could Be Achieved after the Requisite Service Period - Consensus of the FASB Emerging Issues Task Force ("ASU 2014-12"), was issued in June 2014. ASU 2014-12 requires an entity to treat a performance target that affects vesting and that could be achieved after the requisite service period as a performance condition. Our adoption of this ASU in the first quarter of 2015 did not have a material impact on our consolidated financial statements.

ASU No. 2015-03, Interest - Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs ("ASU 2015-03"), was issued in April 2015. ASU 2015-03 requires debt issuance costs related to a recognized debt liability to be presented in an entity’s balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts, instead of being presented as a deferred charge in the balance sheet. In August 2015, ASU No. 2015-15, Interest - Imputation of Interest (Subtopic 835-30) - Presentation and Subsequent Measurement of Debt Issuance Costs Associated with Line-of-Credit Arrangements ("ASU 2015-15") was issued to address the presentation and subsequent measurement of debt issuance costs related to line-of-credit arrangements. The recognition and measurement guidance for debt issuance costs is not affected by ASU 2015-03 and ASU 2015-15. An entity is required to adopt ASU 2015-03 and ASU 2015-15 for reporting periods beginning on or after December 15, 2015. We do not expect the adoption of these ASUs to have a material impact on our consolidated financial statements.

ASU No. 2015-05, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Fees Paid in a Cloud Computing Arrangement ("ASU 2015-05"), was issued in April 2015. The ASU requires companies to perform the same assessment that vendors currently perform under ASC 985-605; that is, companies must determine whether an arrangement with its vendor contains a software license element. If so, the related fees paid are accounted for as an internal-use software intangible under ASC 350-40; if not, the arrangement is accounted for as a service contract. As a result of the issuance of ASU 2015-05, all software licenses within the scope of Subtopic 350-40 will be accounted for consistent with other licenses of intangible assets. An entity is required to adopt ASU 2015-05 for reporting periods beginning on or after December 15, 2015. We do not expect the adoption of this ASU to have a material impact on our consolidated financial statements.

ASU No. 2015-07, Fair Value Measurement (Topic 820): Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent) ("ASU 2015-07"), was issued in May 2015. This ASU removes the requirement to categorize within the fair value hierarchy table investments without readily determinable fair values in entities that elect to measure fair value using net asset value per share ("NAV") or its equivalent. ASU 2015-07 requires that these investments continue to be shown in the fair value disclosure in order to allow the disclosure to reconcile to the investment amount presented in the balance sheet. We expect to early adopt ASU 2015-07 in the quarter ending December 31, 2015 with retrospective application. We expect to modify our presentation of assets valued using NAV in the voluntary employees’ beneficiary association ("VEBA") postretirement benefit plan and Canadian Pension Plan section of our fair value hierarchy table when we adopt ASU 2015-07.

ASU No. 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date ("ASU 2015-14"), was issued in August 2015. ASU 2015-14 defers the effective date of ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which 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, by one year for all entities and permits early adoption on a limited basis. We expect to adopt ASU 2014-09 for the fiscal year ending December 31, 2018 and will continue to assess the impact of the adoption on our consolidated financial statements.