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Subsequent Events (Details) - Casthouse Facility - USD ($) $ in Millions		9 Months Ended
	Oct. 27, 2025	Sep. 30, 2025	Sep. 30, 2024
Subsequent Event [Line Items]
Repayments under Grundartangi casthouse debt facility		$ 6.8	$ 4.5
Subsequent Event | Foreign line of credit
Subsequent Event [Line Items]
Repayments under Grundartangi casthouse debt facility	$ 116.4
Repayments of interest on debt	$ 1.9

X

- Definition

Repayments Of Accrued Interest On Debt

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
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Balance Type:	credit
Period Type:	duration

X

- Definition

The cash outflow to repay long-term debt that is wholly or partially secured by collateral. Excludes repayments of tax exempt secured debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 15
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-15

+ Details

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X

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 830
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481674/830-30-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 855
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483399/855-10-50-2

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- Details

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- Details

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- Details

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