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: |