XML 55 R44.htm IDEA: XBRL DOCUMENT v3.23.3

Fair Value Measurements - Level 3 Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
LME forward financial sales contracts
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning	$ 1.6	$ 1.8	$ 0.0
Total realized/unrealized gains (losses)
Included in net income	1.6		1.6
Transfers into Level 3	0.0		1.6
Transfers out of Level 3		(1.8)	0.0
Balance, ending	3.2	0.0	3.2
Change in unrealized gains (losses)	1.6	0.0	1.6
LME forward financial sales contracts
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning	(3.8)	(4.6)	(5.1)
Total realized/unrealized gains (losses)
Included in net income	1.5		5.3
Transfers into Level 3	0.0		(2.5)
Transfers out of Level 3		4.6	0.0
Balance, ending	(2.3)	0.0	(2.3)
Change in unrealized gains (losses)	1.5	$ 0.0	5.3
Casthouse currency hedges
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning	0.0		0.0
Total realized/unrealized gains (losses)
Included in net income	0.0		0.0
Transfers into Level 3	0.0		0.0
Transfers out of Level 3			0.0
Balance, ending	0.0		0.0
Change in unrealized gains (losses)	0.0		0.0
Nord Pool Swaps
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning			0.2
Total realized/unrealized gains (losses)
Included in net income			0.0
Transfers into Level 3			0.0
Transfers out of Level 3			(0.2)
Balance, ending	0.0		0.0
Change in unrealized gains (losses)			0.0
FX Swaps
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance, beginning			(0.2)
Total realized/unrealized gains (losses)
Included in net income			0.0
Transfers into Level 3			0.0
Transfers out of Level 3			0.2
Balance, ending	$ 0.0		0.0
Change in unrealized gains (losses)			$ 0.0

X

- Definition

Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Total Realized/Unrealized Gains (Losses) [Abstract]

+ References

No definition available.

+ Details

Name:	cenx_FairValueNetDerivativeAssetLiabilityMeasuredonRecurringBasisUnobservableInputsReconciliationTotalRealizedUnrealizedGainsLossesAbstract
Namespace Prefix:	cenx_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Unrealized Gains (Losses)

+ References

No definition available.

+ Details

Name:	cenx_FairValueNetDerivativeAssetLiabilityMeasuredonRecurringBasisUnobservableInputsReconciliationUnrealizedGainsLosses
Namespace Prefix:	cenx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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

Name:	us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputReconciliationRollForward
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of gain (loss) recognized in income from derivative asset (liability) after deduction of derivative liability (asset), measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-3

+ Details

Name:	us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationGainLossIncludedInEarnings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of transfers of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset) into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-3

+ Details

Name:	us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersIntoLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Amount of transfers of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset) out of level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-3

+ Details

Name:	us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisUnobservableInputsReconciliationTransfersOutOfLevel3
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-SubTopic 10
-Topic 820
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-3

+ Details

Name:	us-gaap_FairValueNetDerivativeAssetLiabilityMeasuredOnRecurringBasisWithUnobservableInputs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cenx_FixedToVariableLondonMetalsExchangeSwapAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cenx_FixedtoVariableLondonMetalsExchangeSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cenx_CasthouseHedgesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cenx_NordpoolPowerPriceSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cenx_FXSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: