Segment and Geographical Area Information, Textuals (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Segment Reporting Information [Line Items]
Decrease in Fabricated Products segment operating income relating to primary aluminum hedging activities		$ 8.9		$ 5.6
Increase in Fabricated Products segment asset related to primary aluminum hedging activities					0.6
Net non-cash LIFO (benefits) charges	(4.9)	5.0	(7.8)	19.9
Unrealized (losses) gains on derivatives	0.6	(13.1)	4.2	(7.1)
Fabricated Products
Segment Reporting Information [Line Items]
Unrealized (losses) gains on derivatives	$ (0.1)	$ (9.5)	$ 3.0	$ (5.2)