| Document and Entity Information | Mar. 05, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Mar. 5, 2022 |
| Entity Registrant Name | KAISER ALUMINUM CORP |
| Entity Central Index Key | 0000811596 |
| Entity Emerging Growth Company | false |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 1-09447 |
| Entity Tax Identification Number | 94-3030279 |
| Entity Address, Address Line One | 1550 West McEwen |
| Entity Address, Address Line Two | Suite 500 |
| Entity Address, City or Town | Franklin |
| Entity Address, State or Province | TN |
| Entity Address, Postal Zip Code | 37067 |
| City Area Code | (626) |
| Local Phone Number | 252-7040 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.01 per share |
| Trading Symbol | KALU |
| Security Exchange Name | NASDAQ |
