Derivative Financial Instruments and Related Hedging Programs, Notional Quantity Table (Details) mmlbs in Millions	Dec. 31, 2017 EUR (€) mmlbs MMBTU
Not Designated as Hedging Instrument \| Aluminum \| Purchase
Derivative [Line Items]
Derivative Notional Amount (Non-Monetary)	165.3
Not Designated as Hedging Instrument \| Aluminum \| Sale
Derivative [Line Items]
Derivative Notional Amount (Non-Monetary)	1.4
Not Designated as Hedging Instrument \| Midwest premium swap contracts \| Purchase
Derivative [Line Items]
Derivative Notional Amount (Non-Monetary)	163.9
Not Designated as Hedging Instrument \| Natural Gas Member \| Purchase
Derivative [Line Items]
Derivative Notional Amount (Non-Monetary) \| MMBTU	3,600,000
Not Designated as Hedging Instrument \| Electricity \| Purchase
Derivative [Line Items]
Derivative Notional Amount (Non-Monetary) \| MMBTU	131,760
Not Designated as Hedging Instrument \| Foreign Exchange Contract \| Purchase
Derivative [Line Items]
Derivative, Notional Amount (Monetary) \| €	€ 301,304
Designated as Hedging Instrument \| Alloy Metal Hedge \| Purchase
Derivative [Line Items]
Derivative Notional Amount (Non-Monetary)	2.7

- 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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