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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

Reference 2: 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 3: 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

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

Derivative Financial Instruments and Related Hedging Programs, Textuals (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2011 years mmlbs	Sep. 30, 2010 mmlbs	Mar. 29, 2010 Convertible Debt [Member]	Sep. 30, 2011 Remainder of 2011 mmlbs	Sep. 30, 2011 2012 mmlbs	Sep. 30, 2011 2013 mmlbs
Derivative Financial Instruments and Related Hedging Programs (Textuals) [Abstract]
Total fabricated products shipments containing fixed price terms	112.1	72.3
Firm price customer sales contracts containing price risk on anticipated purchases of primary aluminum				57.2	31.9	0.4
Aggregate principal amount of notes			$ 175.0
Percentage Of Natural Gas Purchases For Which The Companys Exposure To Fluctuations In Gas Prices Have Been Reduced				96.00%	74.00%	46.00%