Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2016
Accounting Policies [Abstract]
Organization and Nature of Operations	Organization and Nature of Operations. Kaiser Aluminum Corporation specializes in the production of semi-fabricated specialty aluminum products, such as aluminum plate and sheet 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	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 2016 fiscal year. The financial information as of December 31, 2015 is derived from our audited consolidated financial statements and footnotes for the year ended December 31, 2015 included in our Annual Report on Form 10-K. See New Accounting Pronouncements below for a discussion of new accounting pronouncements we adopted during the quarter ended March 31, 2016 requiring cumulative-effect adjustments that impacted our consolidated financial statements and footnotes for the year ended December 31, 2015.
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.
Inventories	Inventories. Inventories are stated at the lower of cost or market value. On March 31, 2016, we recorded an inventory write-down of $4.9 million to reflect the net realizable value as of that date. The net realizable value reflected commitments as of that date from customers to purchase our inventory at prices that exceeded the Midwest Transaction Price ("Midwest Price"), which reflects the primary aluminum supply/demand dynamics in North America, reduced by an approximate normal profit margin. If we encounter a further decrease in our net realizable value of inventory, we may be subject to additional inventory lower of cost or market value adjustments. Finished products, work-in-process and raw material inventories are stated on the last-in, first-out ("LIFO") basis. At March 31, 2016, after adjusting for the inventory write down discussed above, the stated LIFO value of the inventory represented its net realizable value (less a normal profit margin) and exceeded the current cost of our inventory by $17.7 million. Additionally, during the quarter ended March 31, 2016, we decremented a prior year, higher cost LIFO layer, which resulted in an insignificant charge. The excess of current cost over the stated LIFO value of inventory at December 31, 2015 was $24.1 million. 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, 2016 and December 31, 2015 were included in the Fabricated Products segment (see Note 2 for the components of inventories).
Property, Plant and Equipment - Net	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 $0.9 million and $0.3 million during the quarters ended March 31, 2016 and March 31, 2015, 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 (Loss). For the quarters ended March 31, 2016 and March 31, 2015, we recorded depreciation expense of $8.2 million and $7.5 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.
Derivatives, Policy [Policy Text Block]	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 income 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. We report the effective portion of our cash flow hedges in the same financial statement line item as changes in the fair value of the hedged item. In order to qualify for hedge accounting treatment, derivative instruments 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, 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 Net income (loss) immediately. If a forecasted equipment purchase was no longer probable to occur, amounts previously deferred in Accumulated other comprehensive income (loss) would be recognized immediately in Net income (loss). 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	New Accounting Pronouncements. Accounting Standards Update ("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. The recognition and measurement guidance for debt issuance costs is not affected by ASU 2015-03. During the quarter ended March 31, 2016, we retrospectively adopted ASU 2015-03, which resulted in a reclassification of $3.2 million of debt issuance costs related to our Senior Notes (as defined in Note 3) from Other assets to Long-term debt as of December 31, 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 in August 2015 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 2015-15. Our adoption of this ASU in the first quarter of 2016 did not 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. Our retrospective adoption of this ASU in the first quarter of 2016 did not have a material impact on our consolidated financial statements. 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; however, based on our assessments to date, we do not expect the adoption of this ASU to have a material impact on our consolidated financial statements. ASU No. 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes ("ASU 2015-17"), was issued in November 2015. ASU 2015-17 requires that all deferred tax assets and liabilities, along with any related valuation allowance, be classified as noncurrent on the balance sheet. This ASU does not, however, change the existing requirement that deferred tax liabilities and assets of a tax-paying component of an entity be offset and presented as a single amount. During the quarter ended March 31, 2016, we early adopted this ASU on a prospective basis. As such, prior periods were not retrospectively adjusted. 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 becomes effective for us in the first quarter of 2019. We are currently evaluating whether to early adopt the standard and what impact it will have on our consolidated financial statements, which we expect will be material. ASU No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting ("ASU 2016-09"), was issued in March 2016. ASU 2016-09 eliminates additional paid in capital ("APIC") pools and requires excess tax benefits and tax deficiencies to be recorded in the income statement when the awards vest or are settled. The accounting for an employee's use of shares to satisfy the employer's statutory income tax withholding obligation and the accounting for forfeitures is also changing. ASU 2016-09 becomes effective for us in the first quarter of 2017. We early adopted ASU 2016-09 during the quarter ended March 31, 2016. See Note 4 and Note 6 for a discussion on the impact of our adoption of ASU 2016-09.

Disclosure of accounting policy for major classes of inventories, bases of stating inventories (for example, lower of cost or market), methods by which amounts are added and removed from inventory classes (for example, FIFO, LIFO, or average cost), loss recognition on impairment of inventories, and situations in which inventories are stated above cost. If inventory is carried at cost, this disclosure includes the nature of the cost elements included in inventory.