XML 43 R31.htm IDEA: XBRL DOCUMENT
v3.20.2

Components of Net Periodic Benefit Cost (Tables) | 6 Months Ended
--- | ---
Jun. 30, 2020
Components of net periodic benefit cost [Abstract] |
Schedule of net periodic benefit cost |
| Pension Benefits |  |  |  |  |  |  |  |  |  |
| Three months ended June 30, |  |  |  | Six months ended June 30, |  |  |  |  |  |
| 2020 |  | 2019 |  | 2020 |  | 2019 |  |  |  |
Service cost | $ | 1.1 |  |  | $ | 0.5 |  |  | $ | 2.4 |  |  | $ | 1.5 |  |  |  |  |
Interest cost | 2.8 |  |  | 3.4 |  |  | 5.6 |  |  | 6.7 |  |  |  |  |
Expected return on plan assets | (5.2) |  |  | (4.3) |  |  | (10.3) |  |  | (9.1) |  |  |  |  |
Amortization of prior service costs | 0.0 |  |  | 0.5 |  |  | 0.0 |  |  | 0.5 |  |  |  |  |
Amortization of net loss | 1.8 |  |  | 2.2 |  |  | 3.3 |  |  | 3.3 |  |  |  |  |
Net periodic benefit cost | $ | 0.5 |  |  | $ | 2.3 |  |  | $ | 1.0 |  |  | $ | 2.9 |  |  |  |  |
| Other Postretirement Benefits ("OPEB") |  |  |  |  |  |  |  |  |  |
| Three months ended June 30, |  |  |  | Six months ended June 30, |  |  |  |  |  |
| 2020 |  | 2019 |  | 2020 |  | 2019 |  |  |  |
Service cost | $ | 0.1 |  |  | $ | 0.7 |  |  | $ | 0.2 |  |  | $ | 0.7 |  |  |  |  |
Interest cost | 0.7 |  |  | 1.2 |  |  | 1.5 |  |  | 2.3 |  |  |  |  |
Amortization of prior service cost | (0.8) |  |  | (1.8) |  |  | (1.6) |  |  | (3.1) |  |  |  |  |
Amortization of net loss | 0.1 |  |  | 0.4 |  |  | 1.1 |  |  | 1.1 |  |  |  |  |
Net periodic benefit cost | $ | 0.1 |  |  | $ | 0.5 |  |  | $ | 1.2 |  |  | $ | 1.0 |  |  |  |  |

X
- Definition Components of net periodic benefit cost [Abstract] + References No definition available. + Details
Name: | cenx_ComponentsOfNetPeriodicBenefitCostAbstract
Namespace Prefix: | cenx_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
Name: | us-gaap_ScheduleOfNetBenefitCostsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration