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Derivatives (Details) € in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 EUR (€) MWh t | Dec. 31, 2017
LME Swap [Member] |  |
Derivative [Line Items] |  |
Other forward delivery contracts to sell primary aluminum (in tonnes) | 66,506 |
Midwest Premium (MWP) [Member] |  |
Derivative [Line Items] |  |
Open position to offset fixed prices | 104,250 |
Price Swap [Member] |  |
Derivative [Line Items] |  |
Open position to offset fixed prices | 12,093 |
Power Price Swap [Member] | Grundartangi [Member] |  |
Derivative [Line Items] |  |
Percentage of power purchases included in forward price contract (percent) |  | 4.00%
Power available | MWh | 256,200 |
FX Swap [Member] |  |
Derivative [Line Items] |  |
Derivative asset | € | € 5.6 |

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- Definition Total amount of primary aluminum committed to be supplied under existing contracts or agreements outside of major long-term supply commitments. + References No definition available. + Details
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- Definition Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226008-175313 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312 + Details
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- 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
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- Definition Nominal mass used to calculate payments on a derivative instrument. + References No definition available. + Details
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- Details
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- Details
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- Details
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- Details
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