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Derivatives (Details) € in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019 EUR (€) MWh t	Dec. 31, 2017
LME Swap [Member]
Derivative [Line Items]
Other forward delivery contracts to sell primary aluminum, open (in tonnes)	96,506
Midwest Premium (MWP) [Member]
Derivative [Line Items]
Open position to offset fixed prices	122,500
Hawesville L4 Power Price Swaps [Member]
Derivative [Line Items]
Power available | MWh	790,560
Price Swap [Member]
Derivative [Line Items]
Open position to offset fixed prices	10,097
Nordpool Power Price Swap [Member] | Grundartangi [Member]
Derivative [Line Items]
Power available | MWh	256,200
Percentage of power purchases included in forward price contract (percent)		4.00%
FX Swap [Member]
Derivative [Line Items]
Derivative asset | €	€ 5.6

X

- Definition

Derivative, Financial Contract, Percentage

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Total amount of primary aluminum committed to be supplied under existing contracts or agreements outside of major long-term supply commitments.

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
Data Type:	num:massItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Underlying, Derivative Energy, Available

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
Data Type:	num:energyItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- 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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Data Type:	xbrli:stringItemType
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X

- Definition

Nominal mass used to calculate payments on a derivative instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:massItemType
Balance Type:	na
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X

- Details

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

X

- Details

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

X

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cenx_HawesvilleL4PowerPriceSwapsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

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

X

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

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Namespace Prefix:
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Balance Type:
Period Type: