Segment and Geographical Area Information, Textuals (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Segment Reporting Information [Line Items]
Charges relating to LTI programs and certain short-term incentive plans		$ 0.6		$ 2.4
Non-cash LIFO benefits (charges)	7.1	2.0	(12.8)	(6.2)
Unrealized (losses) gains on derivatives	(12.7)	10.9	(19.8)	(7.1)
Metal related gains(losses) on internal hedging activities	2.3	(0.8)	11.6	(2.7)
Fabricated Products [Member]
Segment Reporting Information [Line Items]
Environmental expenses included in operating results	0.1	13.1	0.6	13.5
Unrealized (losses) gains on derivatives	(2.0)	(2.4)	(0.6)	(5.2)
All Other [Member]
Segment Reporting Information [Line Items]
Unrealized (losses) gains on derivatives	$ (14.8)	$ 17.1	$ (21.4)	$ 1.1
Anglesey Aluminum Limited [Member]
Segment Reporting Information [Line Items]
Ownership holding in Anglesey	49.00%		49.00%

The charge against earnings in the period for known or estimated future costs arising from requirements to perform environmental remediation activities.

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-Publisher AICPA

-Name Statement of Position (SOP)

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-Paragraph 147, 148, 149, 150

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Statement of Position (SOP)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9, 10

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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+ Details