Derivatives And Other Financial Instruments (Narrative) (Details)	3 Months Ended								3 Months Ended
	Mar. 31, 2012 USD ($) Y	Dec. 31, 2009 USD ($)	Dec. 31, 2009 CAD	Mar. 31, 2012 Level 3 [Member] USD ($)	Mar. 31, 2012 Level 1 [Member] USD ($)	Dec. 31, 2011 Level 1 [Member] USD ($)	Mar. 31, 2012 Level 2 [Member] USD ($)	Dec. 31, 2011 Level 2 [Member] USD ($)	Mar. 31, 2012 Six-Year Natural Gas Supply Contract [Member] USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net unrealized loss on derivative contracts				$ 704,000,000					$ 5,000,000
Other derivative contracts estimated term of quoted market prices, in years	10
Supply contract duration									6 years
Amount of aluminum kmt designated as fair value hedges	407
Face amount of debt the hedges effectively convert from fixed to floating through 2018	200,000,000
Contracts expiration date	September 2011
Forward contract to purchase to mitigate the foreign currency risk related to a Canadian-denominated loan due in 2014		58,000,000	58,000,000
Long-term debt, fair value					$ 8,844,000,000	$ 8,576,000,000	$ 674,000,000	$ 698,000,000