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Business, Product, and Geographical Area Information - Schedule of Significant Segment Expenses Provided to CODM (Parenthetical) (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2025 | Mar. 31, 2024
Segment Reporting [Abstract] |  |
Hedged cost realized gains (losses) upon settlement | $ 4.6 | $ (3.5)

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- Definition Hedged cost realized gains (losses) upon settlement. + References No definition available. + Details
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Namespace Prefix: | kalu_
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