Basis of Presentation, Economic Conditions and Recent Accounting Pronouncements	6 Months Ended
Jun. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation, Economic Conditions and Recent Accounting Pronouncements	1. Basis of Presentation, Economic Conditions and Recent Accounting Pronouncements 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, 2019. 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 collectively to Kaiser Aluminum Corporation and its subsidiaries. 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 2020 fiscal year. The financial information as of December 31, 2019 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, 2019. Coronavirus Disease 2019 ("COVID-19") Pandemic. Beginning in March 2020, the COVID-19 pandemic significantly impacted our industry, causing demand for our products, primarily in our aerospace and automotive end markets, to decline. We instituted operational measures in response to financial impacts caused by the reduced demand. In March 2020, we suspended repurchases of our common stock. During the quarter ended June 30, 2020, we: (i) began limiting capital spending to critical sustaining projects (see Note 2 for discussion of idled projects); (ii) early settled firm commitments with corresponding fair value hedges and reduced forecasts with respect to purchase transactions with corresponding cash flow hedges (see Note 5); (iii) settled all outstanding available for sale securities (see Note 5); (iv) issued $350.0 million of new unsecured senior notes (see Note 6); and (v) initiated a plan of restructuring (see Note 9). For additional discussion related to the COVID-19 pandemic, see Item 2. Management's Discussion and Analysis of Financial Condition and Results of Operations and Item 1A. Risk Factors, both of which are included in this Report. 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. The severity, magnitude and duration, as well as the economic consequences of the COVID-19 pandemic, are uncertain, rapidly changing and difficult to predict. Therefore, our accounting estimates and assumptions may change over time in response to the COVID-19 pandemic and may change materially in future periods. Adoption of New Accounting Pronouncements Accounting Standards Update ("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 have been replaced with a new forward-looking "expected loss" model that has resulted in the earlier recognition of allowances for losses. Our adoption of ASU 2016-13 during the quarter ended March 31, 2020 using the modified retrospective transition approach did not result in a material impact on our consolidated financial statements. As part of our assessment of the adequacy of our allowances for credit losses, we consider a number of factors including, but not limited to, customer credit ratings, bankruptcy filings, published or estimated credit default rates, age of receivables, expected loss rates and collateral exposures. 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 adopted ASU 2018-15 during the quarter ended March 31, 2020 using the prospective transition approach. The implementation costs we capitalized during the six months ended June 30, 2020 were included in both Prepaid expenses and other current assets and Other assets in our Consolidated Balance Sheets. The corresponding cash flows related to these arrangements were included in Net cash provided by operating activities in our Statements of Consolidated Cash Flows. Accounting Pronouncements Issued But Not Yet Adopted ASU No. 2019-12, Simplifying the Accounting for Income Taxes ("ASU 2019-12"), was issued in December 2019. Under ASU 2019-12, the accounting for income taxes is simplified by eliminating certain exceptions and implementing additional requirements which result in a more consistent application of ASC 740 Income Taxes. We are currently in the process of evaluating the impact of adopting ASU 2019-12 in 2021, but do not expect it to have a material impact on our consolidated financial statements.

Basis of Presentation, Economic Conditions and Recent Accounting Pronouncements

6 Months Ended

Jun. 30, 2020

Basis of Presentation, Economic Conditions and Recent Accounting Pronouncements

1. Basis of Presentation, Economic Conditions and Recent Accounting Pronouncements

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, 2019. 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 collectively to Kaiser Aluminum Corporation and its subsidiaries.

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 2020 fiscal year. The financial information as of December 31, 2019 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, 2019.

Coronavirus Disease 2019 ("COVID-19") Pandemic. Beginning in March 2020, the COVID-19 pandemic significantly impacted our industry, causing demand for our products, primarily in our aerospace and automotive end markets, to decline. We instituted operational measures in response to financial impacts caused by the reduced demand. In March 2020, we suspended repurchases of our common stock. During the quarter ended June 30, 2020, we: (i) began limiting capital spending to critical sustaining projects (see Note 2 for discussion of idled projects); (ii) early settled firm commitments with corresponding fair value hedges and reduced forecasts with respect to purchase transactions with corresponding cash flow hedges (see Note 5); (iii) settled all outstanding available for sale securities (see Note 5); (iv) issued $350.0 million of new unsecured senior notes (see Note 6); and (v) initiated a plan of restructuring (see Note 9). For additional discussion related to the COVID-19 pandemic, see Item 2. Management's Discussion and Analysis of Financial Condition and Results of Operations and Item 1A. Risk Factors, both of which are included in this Report.

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. The severity, magnitude and duration, as well as the economic consequences of the COVID-19 pandemic, are uncertain, rapidly changing and difficult to predict. Therefore, our accounting estimates and assumptions may change over time in response to the COVID-19 pandemic and may change materially in future periods.

Adoption of New Accounting Pronouncements

Accounting Standards Update ("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 have been replaced with a new forward-looking "expected loss" model that has resulted in the earlier recognition of allowances for losses. Our adoption of ASU 2016-13 during the quarter ended March 31, 2020 using the modified retrospective transition approach did not result in a material impact on our consolidated financial statements. As part of our assessment of the adequacy of our allowances for credit losses, we consider a number of factors including, but not limited to, customer credit ratings, bankruptcy filings, published or estimated credit default rates, age of receivables, expected loss rates and collateral exposures.

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 adopted ASU 2018-15 during the quarter ended March 31, 2020 using the prospective transition approach. The implementation costs we capitalized during the six months ended June 30, 2020 were included in both Prepaid expenses and other current assets and Other assets in our Consolidated Balance Sheets. The corresponding cash flows related to these arrangements were included in Net cash provided by operating activities in our Statements of Consolidated Cash Flows.

Accounting Pronouncements Issued But Not Yet Adopted

ASU No. 2019-12, Simplifying the Accounting for Income Taxes ("ASU 2019-12"), was issued in December 2019. Under ASU 2019-12, the accounting for income taxes is simplified by eliminating certain exceptions and implementing additional requirements which result in a more consistent application of ASC 740 Income Taxes. We are currently in the process of evaluating the impact of adopting ASU 2019-12 in 2021, but do not expect it to have a material impact on our consolidated financial statements.