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Pension and Other Postretirement Benefits Weighted average assumptions used to determine net periodic benefit cost (Details)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Pension Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Measurement date	12/31/2012		12/31/2011		12/31/2010
Fiscal year end	12/31/2013		12/31/2012		12/31/2011
Discount rate	4.00%		4.25%		5.49%
Rate of compensation increase, group 1	3.00%	[1]	3.00%	[1]	3.00%	[1]
Rate of compensation increase, group 2	4.00%	[1]	4.00%	[1]	3.00%	[1]
Rate of compensation increase, group 3	4.00%	[1]	4.00%	[1]	4.00%	[1]
Expected return on plan assets	7.25%		8.00%		8.00%
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Measurement date	12/31/2012		12/31/2011		12/31/2010
Fiscal year end	12/31/2013		12/31/2012		12/31/2011
Discount rate	4.01%		3.83%		5.23%
Rate of compensation increase, group 1	3.00%	[1]	3.00%	[1]	3.00%	[1]
Rate of compensation increase, group 2	4.00%	[1]	4.00%	[1]	3.00%	[1]
Rate of compensation increase, group 3	4.00%	[1]	4.00%	[1]	4.00%	[1]
Expected return on plan assets	0.00%		0.00%		0.00%
[1] For 2013 and 2012, the rate of compensation increase is 3% per year for first five years and 4% per year for year six and thereafter. For 2011, the rate of compensation increase is for 3% per year for years 1 and 2 and 4% per year for year 3 and thereafter.

X

- Definition

Year end for fiscal year

+ References

No definition available.

+ Details

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X

- Definition

The date(s) used to measure (at least the majority of) plan assets and benefit obligations for defined benefit pension and other postretirement benefit plans.

+ References

No definition available.

+ Details

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X

- Definition

The maximum expected rate of compensation increases (for pay-related plans).

+ References

No definition available.

+ Details

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X

- Definition

The mid expected rate of compensation increases (for pay-related plans).

+ References

No definition available.

+ Details

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Namespace Prefix:	cenx_
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X

- Definition

The interest rate used to adjust for the time value of money.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (k)(1)

-URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920

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X

- Definition

An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Glossary Expected Long-Term Rate of Return on Plan Assets

-URI http://asc.fasb.org/extlink&oid=6512013



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (k)(3)

-URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920

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X

- Definition

Expected rate of compensation increases (for pay-related plans).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (k)(2)

-URI http://asc.fasb.org/extlink&oid=28361610&loc=d3e1928-114920

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