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Cover Page - USD ($)
$ in Billions
 12 Months Ended
Dec. 31, 2019
Feb. 14, 2020
Jun. 30, 2019
Cover page.      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2019    
Document Transition Report false    
Entity File Number 1-09447    
Entity Registrant Name KAISER ALUMINUM CORPORATION    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 94-3030279    
Entity Address, Address Line One 27422 Portola Parkway    
Entity Address, Address Line Two Suite 200    
Entity Address, City or Town Foothill Ranch    
Entity Address, State or Province CA    
Entity Address, Postal Zip Code 92610-2831    
City Area Code (949)    
Local Phone Number 614-1740    
Title of 12(b) Security Common stock, par value $0.01 per share    
Trading Symbol KALU    
Security Exchange Name NASDAQ    
Entity Well Known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 1.5
Entity Common Stock, Shares Outstanding   15,854,182  
Documents Incorporated by Reference
Documents Incorporated by Reference. Certain portions of the registrant's definitive proxy statement related to the registrant's 2020 annual meeting of stockholders are incorporated by reference into Part III of this Annual Report on Form 10-K.
    
Entity Central Index Key 0000811596    
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2019    
Document Fiscal Period Focus FY    
Amendment Flag false