Derivatives, Hedging Programs and Other Financial Instruments, Material Derivative Positions (Details) - Designated as Hedging Instrument mmlbs in Millions	Jun. 30, 2018 EUR (€) MMBTU MWH mmlbs
Aluminum \| Purchase
Derivative [Line Items]
Derivative non-monetary notional amount	163.4
Aluminum \| Sales
Derivative [Line Items]
Derivative non-monetary notional amount	2.4
Midwest premium swap contracts \| Purchase
Derivative [Line Items]
Derivative non-monetary notional amount	130.7
Alloy Metal Hedge \| Purchase
Derivative [Line Items]
Derivative non-monetary notional amount	6.6
Natural Gas \| Purchase
Derivative [Line Items]
Derivative non-monetary notional amount \| MMBTU	3,210,000
Electricity \| Purchase
Derivative [Line Items]
Derivative non-monetary notional amount \| MWH	175,680
Foreign Exchange Contract \| Purchase
Derivative [Line Items]
Derivative notional amount \| €	€ 53,324

- Definition

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ 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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- Details

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- Details

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