Derivative Financial Instruments and Related Hedging Programs, Hedging Discussion (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012 mmlbs	Dec. 31, 2011 mmlbs	Dec. 31, 2010 mmlbs	Dec. 31, 2012 2013 mmlbs	Dec. 31, 2012 2014 mmlbs	Dec. 31, 2012 2015 mmlbs	Mar. 29, 2010 Convertible Notes
Derivative Financial Instruments and Related Hedging Programs (Textuals) [Abstract]
Total fabricated products shipments containing fixed price terms	178.8	157.0	97.0
Firm price customer sales contracts containing price risk on anticipated purchases of primary aluminum				56.9	0.8	0.8
Principal amount of notes	$ 225.0	$ 0					$ 175.0

The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

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

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant