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Income Taxes - Changes in Valuation Allowance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance, valuation allowance	$ 537.6	$ 487.9	$ 485.8
Remeasurement of deferred tax assets	0.0	0.0	0.0
Release of valuation allowance	0.0	0.0	0.0
Expiration of net operating losses	(6.1)	(7.2)	(15.4)
Other change in valuation allowance	(27.1)	56.9	17.5
Balance, valuation allowance	$ 504.4	$ 537.6	$ 487.9

X

- Definition

Valuation Allowance, Deferred Tax Asset, Decrease Due To Tax Cuts And Jobs Act

+ References

No definition available.

+ Details

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X

- Definition

Valuation Allowance, Deferred Tax Asset, Expiration of Net Operating Losses

+ References

No definition available.

+ Details

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X

- Definition

Valuation Allowance, Deferred Tax Asset, Release of Valuation Allowance

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
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X

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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X

- Definition

Amount of increase (decrease) in the valuation allowance for a specified deferred tax asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-2

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X

- Definition

Amount of valuation and qualifying accounts and reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09(Column B))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-4

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 4
-Subparagraph (SX 210.12-09(Column E))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480678/235-10-S99-4

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