XML 39 R87.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Income Taxes (Details) - USD ($) $ in Millions | 12 Months Ended |  |  |
--- | --- | --- | --- | ---
Dec. 31, 2017 | Dec. 31, 2019 | Jan. 01, 2019 | Dec. 31, 2018
Operating Loss Carryforwards [Line Items] |  |  |  |
Decrease in deferred tax assets | $ 205.2 |  |  |
Valuation allowance |  | $ 492.4 |  | $ 552.5
Impact of ASU 2018-02 |  |  | $ (1.3) |
All U.S. and Portion of Icelandic Deferred Tax Assets [Member] |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |
Valuation allowance |  | $ 492.4 |  |
Accounting Standards Update 2018-02 [Member] |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |
Impact of ASU 2018-02 |  |  | $ 1.3 |

X
- Definition Tax Cuts and Jobs Act of 2017, Increase (Decrease) In Deferred Tax Asset + References No definition available. + Details
Name: | cenx_TaxCutsandJobsActof2017IncreaseDecreaseInDeferredTaxAsset
Namespace Prefix: | cenx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption. + References No definition available. + Details
Name: | us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
Name: | us-gaap_DeferredTaxAssetsValuationAllowance
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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_OperatingLossCarryforwardsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_ValuationAllowanceByDeferredTaxAssetAxis=cenx_AllU.S.andPortionofIcelandicDeferredTaxAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201802Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |