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Employee Benefits - Expected Benefit Payments (Parenthetical) (Details) | 12 Months Ended
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Dec. 31, 2023 USD ($)
Postretirement Health Coverage | Salaried VEBA |
Defined Benefit Plan Disclosure [Line Items] |
Maximum contribution threshold | $ 2,900,000

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- Definition Defined Benefit Plan, Maximum Annual Employer Contributions, Amount + References No definition available. + Details
Name: | kalu_DefinedBenefitPlanMaximumPeriodicEmployerContributionsAmount
Namespace Prefix: | kalu_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_DefinedBenefitPostretirementHealthCoverageMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RetirementPlanNameAxis=kalu_SalariedVEBAMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |