Summary of Significant Accounting Policies	3 Months Ended
Mar. 31, 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 excesses of current cost over the stated LIFO value of inventory at March 31, 2015 and December 31, 2014 was $24.7 million and $37.6 million, respectively. 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 March 31, 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 $0.3 million and $1.1 million during the quarters ended March 31, 2015 and March 31, 2014, 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. 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 March 31, 2015 and March 31, 2014, we recorded depreciation expense of $7.5 million and $6.8 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. Concentration of Labor Subject to Collective Bargaining Agreements. At March 31, 2015, approximately 63% of our employees were covered by collective bargaining agreements and 2% of our employees were covered by collective bargaining agreements with expiration dates occurring within the remainder of 2015. Dividends. To the extent we expect to be in a capital surplus position by the end of the 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. New Accounting Pronouncements. ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) ("ASU 2014-09"), was issued in May 2014. ASU 2014-09 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. To achieve this core principle, the guidance provides that an entity should apply the following steps: (1) identify the contract(s) with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when, or as, the entity satisfies a performance obligation. We expect to adopt ASU 2014-09 for the fiscal year ending December 31, 2017, unless the adoption date is extended by the Financial Accounting Standard Board, and will continue to assess the impact on our consolidated financial statements. 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. The performance target should not be reflected in estimating the grant-date fair value of the award. Additionally, compensation cost should be recognized in the period in which it becomes probable that the performance target will be achieved, and should represent the compensation cost attributable to the period(s) for which the requisite service has already been rendered; if the performance target becomes probable of being achieved before the end of the requisite service period, then the remaining unrecognized compensation cost should be recognized prospectively over the remaining requisite service period. Finally, the total amount of compensation cost recognized during and after the requisite service period should reflect the number of awards that are expected to vest, and should be adjusted to reflect those awards that ultimately vest. Our adoption of ASU 2014-12 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. Significantly, the recognition and measurement guidance for debt issuance costs are not affected by ASU 2015-03. An entity is required to adopt ASU 2015-03 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. 2015-05, 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 this ASU, 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 2015-03 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.

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 excesses of current cost over the stated LIFO value of inventory at March 31, 2015 and December 31, 2014 was $24.7 million and $37.6 million, respectively. 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 March 31, 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 $0.3 million and $1.1 million during the quarters ended March 31, 2015 and March 31, 2014, 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. 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 March 31, 2015 and March 31, 2014, we recorded depreciation expense of $7.5 million and $6.8 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.

Concentration of Labor Subject to Collective Bargaining Agreements. At March 31, 2015, approximately 63% of our employees were covered by collective bargaining agreements and 2% of our employees were covered by collective bargaining agreements with expiration dates occurring within the remainder of 2015.

Dividends. To the extent we expect to be in a capital surplus position by the end of the 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.

New Accounting Pronouncements. ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) ("ASU 2014-09"), was issued in May 2014. ASU 2014-09 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. To achieve this core principle, the guidance provides that an entity should apply the following steps: (1) identify the contract(s) with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when, or as, the entity satisfies a performance obligation. We expect to adopt ASU 2014-09 for the fiscal year ending December 31, 2017, unless the adoption date is extended by the Financial Accounting Standard Board, and will continue to assess the impact on our consolidated financial statements.

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. The performance target should not be reflected in estimating the grant-date fair value of the award. Additionally, compensation cost should be recognized in the period in which it becomes probable that the performance target will be achieved, and should represent the compensation cost attributable to the period(s) for which the requisite service has already been rendered; if the performance target becomes probable of being achieved before the end of the requisite service period, then the remaining unrecognized compensation cost should be recognized prospectively over the remaining requisite service period. Finally, the total amount of compensation cost recognized during and after the requisite service period should reflect the number of awards that are expected to vest, and should be adjusted to reflect those awards that ultimately vest. Our adoption of ASU 2014-12 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. Significantly, the recognition and measurement guidance for debt issuance costs are not affected by ASU 2015-03. An entity is required to adopt ASU 2015-03 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. 2015-05, 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 this ASU, 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 2015-03 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.