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Summary of Significant Accounting Policies - Additional Information (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2021 USD ($) Segment | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Significant Accounting Policies [Line Items] |  |  |
Number of operating segments | Segment | 1 |  |
Trade accounts receivable sold | $ 1,102.8 |  |
Net discount fees recognized | 6.2 |  |
Effect of LIFO Inventory Liquidation on Income | 0.2 |  |
Excess of current cost over the stated LIFO value of inventory | 137.1 | $ 8.4 |
Interest expense capitalized as construction in progress | $ 1.2 | 1.0 | $ 1.6
Non-cash asset impairment charges |  | 0.5 | 26.1
Software amortization period | 9 years |  |
Amortization expenses of cloud computing software | $ 0.1 | 0.0 |
Workers' compensation charge |  | 0.6 |
Accrued employee healthcare benefits | 9.0 | 3.1 |
Advertising costs | 0.1 | 0.2 | 0.4
Research and development costs | $ 9.3 | 9.1 | 10.5
ASU No. 2019-12 |  |  |
Significant Accounting Policies [Line Items] |  |  |
Change in Accounting Principle, Accounting Standards Update, Adopted | true |  |
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect | true |  |
ASU No. 2021-08 |  |  |
Significant Accounting Policies [Line Items] |  |  |
Change in Accounting Principle, Accounting Standards Update, Immaterial Effect | true |  |
Change in Accounting Principle, Accounting Standards Update, Early Adopted | true |  |
Prepaid Expenses and Other Current Assets |  |  |
Significant Accounting Policies [Line Items] |  |  |
Hosting arrangement, service contract, implementation cost recognized | $ 1.1 | 0.4 |
Other Assets |  |  |
Significant Accounting Policies [Line Items] |  |  |
Hosting arrangement, service contract, implementation cost recognized | 6.7 | 2.7 |
Fabricated Products | Idled Equipment |  |  |
Significant Accounting Policies [Line Items] |  |  |
Non-cash asset impairment charges | $ 0.0 | 0.5 | $ 0.9
Minimum |  |  |
Significant Accounting Policies [Line Items] |  |  |
Number of days in maturity for debt investment securities to be classified as available for sale securities | 90 days |  |
Period over which accounts receivable is due, days | 30 days |  |
Maximum |  |  |
Significant Accounting Policies [Line Items] |  |  |
Period over which accounts receivable is due, days | 90 days |  |
Kaiser Aluminum Canada Limited |  |  |
Significant Accounting Policies [Line Items] |  |  |
Government grants income recognized from other operating charges (income), net |  | $ 1.3 |

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