Segment and Geographical Area Information, Financial Information by Operating Segment Table (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended										12 Months Ended
	Dec. 31, 2011		Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010		Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Net Sales:
Total net sales	$ 317.6		$ 322.3	$ 338.8	$ 322.6	$ 265.8		$ 263.4	$ 282.4	$ 267.5	$ 1,301.3	[1]	$ 1,079.1		$ 987.0
Segment Operating Income (Loss):
Total operating income (loss)	15.6		4.9	14.7	19.8	11.6		12.3	3.2	14.0	55.0		41.1		118.7
Interest expense											(18.0)		(11.8)		0
Other income (expense), net											4.3		(4.2)		(0.1)
Income before income taxes											41.3		25.1		118.6
Depreciation and Amortization:
Depreciation and Amortization											25.2		19.8		16.4
Capital Expenditures:
Capital expenditures											32.5		38.9		59.2
Segment assets:
Total assets	1,320.6					1,318.9					1,320.6		1,318.9
Segment Reporting Information, Additional Information
Lower of cost or market inventory write-down											0		0		9.3
Restructuring Charges											(0.3)		(0.3)		5.4
Environmental expenses included in operating results											3.9		13.9		2.4
Impairment charge											0		4.6		2.3
Unrealized (losses) gains on derivatives											(25.9)		(5.6)		80.5
Impairment of investment in Anglesey											0		0		(1.8)
Fabricated Products
Net Sales:
Total net sales											1,301.3		1,078.8		897.1
Segment Operating Income (Loss):
Total operating income (loss)											108.6	[2],[3],[4]	78.6	[2],[3],[4]	73.6	[2],[3],[4]
Depreciation and Amortization:
Depreciation and Amortization											24.8		19.4		16.2
Capital Expenditures:
Capital expenditures											32.1		38.0		58.5
Segment assets:
Total assets	636.4					496.7					636.4		496.7
Segment Reporting Information, Additional Information
Non-cash LIFO inventory (benefits) charges											7.1		(16.5)		(8.7)
Lower of cost or market inventory write-down															9.3
Restructuring Charges											(0.3)				5.4
Environmental expenses included in operating results											1.7		13.6		0.7
Impairment charge													3.9
Unrealized (losses) gains on derivatives											(3.4)		(4.3)		4.9
Internal hedging gain (loss) metal											8.1		(0.1)		(42.8)
All Other
Net Sales:
Total net sales											0		0.3	[5]	89.9	[5]
Segment Operating Income (Loss):
Total operating income (loss)											(53.6)	[2],[6]	(37.5)	[2],[6]	45.1	[2],[6]
Depreciation and Amortization:
Depreciation and Amortization											0.4		0.4		0.2
Capital Expenditures:
Capital expenditures											0.4		0.9		0.7
Segment assets:
Total assets	684.2	[7]				822.2	[7]				684.2	[7]	822.2	[7]
Segment Reporting Information, Additional Information
Impairment of investment in Anglesey															(1.8)
Anglesey Aluminum Limited
Segment Reporting Information, Additional Information
Ownership Percentage of Anglesey	49.00%										49.00%
Aluminum
Segment Reporting Information, Additional Information
Unrealized (losses) gains on derivatives											(26.5)		3.6		61.2
Aluminum | All Other
Segment Reporting Information, Additional Information
Unrealized (losses) gains on derivatives											(26.5)		3.6		61.2
Foreign Currency
Segment Reporting Information, Additional Information
Unrealized (losses) gains on derivatives											0		0.1		15.6
Foreign Currency | All Other
Segment Reporting Information, Additional Information
Unrealized (losses) gains on derivatives															$ 14.4

[1] The combined results presented for year ended December 31, 2011 are the actual results presented in the Statements of Consolidated Income, as the operating results for the Chandler, Arizona (Extrusion) facility were included in the Company's consolidated operating results commencing January 1, 2011 (see Note 1).

[2] Operating results of the Fabricated Products segment and All Other include gains and losses on intercompany hedging activities related to metal. At the time the Fabricated Products segment enters into a firm-price customer contract, the Hedging business unit and Fabricated Products segment enter into an “internal hedge” so that metal price risk resides in the Hedging business unit under All Other. The Hedging business unit uses third-party hedging instruments to limit exposure to metal price risks related to firm-price customer sales contracts. Results from internal hedging activities between the Fabricated Products segment and Hedging business unit eliminate in consolidation. Internal hedging gains (losses) in the Fabricated Products segment were $8.1, $(0.1) and $(42.8) for 2011, 2010 and 2009, respectively. All Other included the same amounts as (losses) gains for 2011, 2010 and 2009, respectively.

[3] Fabricated Products segment results for 2011, 2010 and 2009 include non-cash mark-to-market (losses) gains on natural gas, electricity and foreign currency hedging activities totaling $(3.4), $(4.3) and $4.9, respectively. For further discussion regarding mark-to-market matters, see Note 12.

[4] Operating results in the Fabricated Products segment for 2011, 2010 and 2009 included non-cash LIFO inventory (benefits) charges of $(7.1), $16.5 and $8.7, respectively. Also included in the Fabricated Products segment operating results for 2009 were $9.3 of lower of cost or market inventory write-down and $5.4 of restructuring charges relating to the restructuring plans involving the Company's Tulsa, Oklahoma and Bellwood, Virginia facilities. Restructuring charges in 2011 and 2010 were not material. Also included in the Fabricated Products segment operating results for 2011, 2010 and 2009 were $1.7, $13.6 and $0.7, respectively, of environmental expense. Fabricated Products segment operating results for 2010 also included $3.9 of asset impairment charge relating to certain Property, plant and equipment.

[5] Net sales in All Other in 2010 represent residual activity involving primary aluminum purchased by the Company from Anglesey while it continued its smelting operations, prior to September 30, 2009, and resold by the Company in the first quarter of 2010. In connection with Anglesey’s remelt operations beginning in the fourth quarter of 2009, the Company changed its basis of revenue recognition from gross to a net basis (see Note 1).

[6] Operating results of All Other for 2011, 2010 and 2009 include non-cash mark-to-market (losses) gains on primary aluminum hedging activities totaling $(26.5), $3.6 and $61.2 respectively. The non-cash mark-to-market gain on foreign currency derivatives for 2009 was $14.4. Non-cash mark-to-market gains (losses) on foreign currency derivatives for 2011 and 2010 were immaterial. Also included in the operating income of All Other were $1.8 of impairment charges in 2009 relating to the Company's investment in Anglesey.

[7] Assets in All Other represent primarily all of the Company’s cash and cash equivalents, metal and financial derivative assets, net assets in respect of VEBA(s) and net deferred income tax assets.