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Other Income, Net - Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023
Other Income and Expenses [Abstract] |  |
Trade accounts receivable sold | $ 1,078.6 | $ 1,240.6
Net discount fees recognized | $ 24.8 | $ 29.7

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- Definition Discount fees recognized. + References No definition available. + Details
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Namespace Prefix: | kalu_
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Balance Type: | credit
Period Type: | duration

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- Definition Amount of decrease from sale of accounts receivable. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 11 -Subparagraph (i) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-11 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration