Segment and Geographical Area Information, Financial Information by Reporting Segment Table (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012
Net Sales:
Net sales	$ 337.4		$ 365.4
Segment Operating Income (Loss):
Operating income (loss)	50.0		46.2
Interest expense	(9.3)		(4.1)
Other income, net	1.0		0.7
Income before income taxes	41.7		42.8
Depreciation and Amortization:
Depreciation and amortization	7.0		6.3
Capital expenditures:
Capital expenditures	9.3		9.0
Income Taxes Paid:
Income taxes paid	0.7		0.2
Assets:
Assets	1,764.4				1,752.5
Fabricated Products
Net Sales:
Net sales	337.4		365.4
Segment Operating Income (Loss):
Operating income (loss)	55.2	[1],[2]	54.1	[1],[2]
Depreciation and Amortization:
Depreciation and amortization	6.9		6.2
Capital expenditures:
Capital expenditures	8.9		8.8
Assets:
Assets	812.9				771.2
Fabricated Products | United States
Income Taxes Paid:
Income taxes paid	0.4		0
Fabricated Products | Canada
Income Taxes Paid:
Income taxes paid	0.3		0.2
All Other
Segment Operating Income (Loss):
Operating income (loss)	(5.2)	[3]	(7.9)	[3]
Depreciation and Amortization:
Depreciation and amortization	0.1		0.1
Capital expenditures:
Capital expenditures	0.4		0.2
Assets:
Assets	$ 951.5	[4]			$ 981.3	[4]

[1] Fabricated Products segment results include non-cash mark-to-market (losses) gains on primary aluminum, natural gas, electricity and foreign currency hedging activities totaling $(0.7) and $3.1 for the quarters ended March 31, 2013 and March 31, 2012, respectively. For further discussion regarding mark-to-market matters, see Note 8.

[2] Operating results in the Fabricated Products segment for the quarters ended March 31, 2013 and March 31, 2012 included net non-cash LIFO benefits of $3.7 and $2.9, respectively.

[3] Operating results in All Other represent operating expenses in the Corporate and Other business unit. Operating results of All Other include VEBA net periodic pension benefit income of $5.6 and $3.0 for the quarters ended March 31, 2013 and March 31, 2012, respectively.

[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 VEBA(s) and net deferred income tax assets.