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Business Combinations, Goodwill and Intangible Assets - Additional Information (Details) - Alcoa Warrick LLC [Member] - USD ($) $ in Millions |  | 3 Months Ended
--- | --- | ---
Mar. 31, 2021 | Mar. 31, 2021
Finite Lived Intangible Assets [Line Items] |  |
Business combination, purchase price | $ 670.0 |
Acquisition costs |  | $ 11.0

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- Definition Amount of consideration to be transferred on the date of acquisition consisting of acquisition-date fair value of assets transferred by the acquirer and liabilities incurred by the acquirer. + 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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- Definition This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=116868678&loc=d3e1043-128460 + Details
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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
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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |