Segment and Geographical Area Information, Financial Information by Operating Segment Table (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011
Net Sales:
Total net sales	$ 335.5		$ 322.3		$ 1,046.1		$ 983.7
Segment Operating Income (Loss):
Total operating income (loss)	56.2		4.9		142.0		39.4
Interest expense	(9.2)		(4.3)		(19.8)		(13.2)
Other income, net	0.4		3.9		2.2		2.2
Income before income taxes	47.4		4.5		124.4		28.4
Depreciation and Amortization:
Depreciation and amortization	6.7		6.2		19.6		18.9
Capital expenditures:
Capital expenditures	8.8		8.8		25.7		22.9
Income Taxes Paid:
Income taxes paid	0.4		0.4		0.9		1.4
Segment assets:
Total assets	1,694.3				1,694.3				1,320.6
Fabricated Products
Net Sales:
Total net sales	335.5		322.3		1,046.1		983.7
Segment Operating Income (Loss):
Total operating income (loss)	62.5	[1],[2]	10.3	[1],[2]	161.7	[1],[2]	61.3	[1],[2]
Depreciation and Amortization:
Depreciation and amortization	6.6		6.2		19.3		18.6
Capital expenditures:
Capital expenditures	8.8		8.7		25.5		22.8
Segment assets:
Total assets	790.5				790.5				637.0
Fabricated Products | United States
Income Taxes Paid:
Income taxes paid	0		0.2		0.1		1.0
Fabricated Products | Canada
Income Taxes Paid:
Income taxes paid	0.4		0.2		0.8		0.4
All Other
Segment Operating Income (Loss):
Total operating income (loss)	(6.3)	[3]	(5.4)	[3]	(19.7)	[3]	(21.9)	[3]
Depreciation and Amortization:
Depreciation and amortization	0.1		0		0.3		0.3
Capital expenditures:
Capital expenditures	0		0.1		0.2		0.1
Segment assets:
Total assets	$ 903.8	[4]			$ 903.8	[4]			$ 683.6	[4]

[1] Operating results in the Fabricated Products segment for the quarters ended September 30, 2012 and September 30, 2011 included LIFO inventory benefits of $5.7 and $7.1, respectively. Operating results in the Fabricated Products segment for the nine months ended September 30, 2012 and September 30, 2011 included LIFO inventory (benefits) charges of $(13.5) and $12.8, respectively.

[2] Fabricated Products segment results include non-cash mark-to-market gains on primary aluminum, natural gas and electricity hedging activities totaling $12.3 and $15.3 for the quarter and nine months ended September 30, 2012. Fabricated Products segment results include non-cash mark-to-market losses on primary aluminum, natural gas and electricity hedging activities totaling $16.8 and $22.0 for the quarter and nine months ended September 30, 2011 . For further discussion regarding mark-to-market matters, see Note 10.

[3] Operating results in All Other represent operating expenses in the Corporate and Other business unit.

[4] Assets in All Other represent primarily all of the Company’s cash and cash equivalents, short-term investments, financial derivative assets, net assets in respect of VEBAs and net deferred income tax assets.