Segment and Geographical Area Information, Financial Information by Reporting Segment Table (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Net Sales:
Net sales	$ 311.3		$ 319.9	$ 328.9	$ 337.4	$ 314.0		$ 335.5	$ 345.2	$ 365.4	$ 1,297.5		$ 1,360.1		$ 1,301.3
Segment Operating Income (Loss):
Total operating income (loss)	41.6		41.6	40.1	50.0	23.9		56.2	39.6	46.2	173.3		165.9		55.0
Interest expense											(35.7)		(29.1)		(18.0)
Other income, net											5.6		2.8		4.3
Income before income taxes											143.2		139.6		41.3
Depreciation and Amortization:
Depreciation and amortization											28.1		26.5		25.2
Capital expenditures:
Capital expenditures											70.4		44.1		32.5
Segment assets:
Total	1,770.9					1,752.5					1,770.9		1,752.5		1,320.6
Fabricated Products
Net Sales:
Net sales											1,297.5		1,360.1		1,301.3
Segment Operating Income (Loss):
Total operating income (loss)											188.6	[1],[2]	190.8	[1],[2]	83.6	[1],[2]
Depreciation and Amortization:
Depreciation and amortization											27.6		26.0		24.8
Capital expenditures:
Capital expenditures											69.8		43.8		32.1
Segment assets:
Total	852.5					771.2					852.5		771.2		637.0
All Other
Segment Operating Income (Loss):
Total operating income (loss)											(15.3)	[3]	(24.9)	[3]	(28.6)	[3]
Depreciation and Amortization:
Depreciation and amortization											0.5		0.5		0.4
Capital expenditures:
Capital expenditures											0.6		0.3		0.4
Segment assets:
Total	$ 918.4	[4]				$ 981.3	[4]				$ 918.4	[4]	$ 981.3	[4]	$ 683.6	[4]

[1] Operating results in the Fabricated Products segment for 2013, 2012 and 2011 included non-cash LIFO inventory benefits of $24.1, $4.9 and $7.1, respectively. Also included in the Fabricated Products segment operating results for 2013, 2012 and 2011 were $4.0, $1.1 and $1.7, respectively, of environmental expense. Fabricated Products segment operating results for 2012 also included $4.4 of asset impairment charge relating to certain property, plant and equipment.

[2] Fabricated Products segment results for 2013, 2012 and 2011 include non-cash mark-to-market gains (losses) on primary aluminum, natural gas, electricity and foreign currency hedging activities totaling $0.7, $15.2 and $(29.9), respectively. For further discussion regarding mark-to-market matters, see Note 11.

[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 $22.5, $11.9 and $6.0 for 2013, 2012 and 2011, 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.