XML 97 R76.htm IDEA: XBRL DOCUMENT v3.3.1.900

Pension and other postretirement benefits - Weighted Average assumptions used in calculating benefit obligations (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Pension Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Discount rate	4.44%	4.05%
Rate of compensation increase, minimum	3.00%	3.00%
Rate of compensation increase, maximum	4.00%	4.00%
Measurement date	12/31/2015	12/31/2014
Other Postretirement Benefit Plans [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Discount rate	4.50%	4.00%
Rate of compensation increase, minimum	3.00%	3.00%
Rate of compensation increase, maximum	4.00%	4.00%
Measurement date	12/31/2015	12/31/2014

X

- Definition

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

+ References

No definition available.

+ Details

Name:	cenx_BenefitObligationRateOfCompensationIncreaseMax
Namespace Prefix:	cenx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

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

+ 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=58740216&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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=58740216&loc=d3e1928-114920

+ Details

Name:	us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationRateOfCompensationIncrease
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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

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

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. Disclosure required by FAS 132R paragraph 5k prior to being amended by FAS 158.

+ References

No definition available.

+ Details

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

X

- Details

Name:	us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: