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Derivatives (Details) € in Millions	6 Months Ended
	Jun. 30, 2020 EUR (€) MMBTU MWh t
LME Swap [Member]
Derivative [Line Items]
Other forward delivery contracts to sell primary aluminum, open (in tonnes) | t	104,740
Midwest Premium (MWP) [Member]
Derivative [Line Items]
Open position to offset fixed prices | t	151,500
Fixed For Floating Swaps [Member]
Derivative [Line Items]
Open position to offset fixed prices | t	14,596
Hawesville L4 Power Price Swaps [Member]
Derivative [Line Items]
Power available | MWh	395,280
NYMEX Henry Hub Natural Gas Price Swaps [Member]
Derivative [Line Items]
Power available | MMBTU	1,170,000
MISO Indiana Hub Power Price Swaps [Member]
Derivative [Line Items]
Power available | MWh	735,660
Nordpool Power Price Swap [Member] | Grundartangi [Member]
Derivative [Line Items]
Power available | MWh	1,340,992
FX Swap [Member]
Derivative [Line Items]
Derivative asset | €	€ 35.6

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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Balance Type:	na
Period Type:	instant

X

- Definition

Underlying, Derivative Energy, Available

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
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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=121572278&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

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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.

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- Definition

Nominal mass used to calculate payments on a derivative instrument.

+ References

No definition available.

+ Details

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X

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

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

X

- Details

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X

- Details

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X

- Details

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X

- Details

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X

- Details

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- Details

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