Curtailment of operations Ravenswood and Hawesville (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended	12 Months Ended
	Mar. 31, 2009	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Curtailment of operations - Ravenswood and Hawesville [Abstract]
Number of potlines curtailed	1
Number of potlines at Hawesville	5
Curtailment of potlines reduced aluminum production by approximately (in metric tons)	49,000
Restructuring Costs [Abstract]
Total curtailment expense (benefit)		$ (3,806)	$ (37,386)	$ 41,710
Total cash curtailment cost		22,966	17,429	46,700
Severance - Employee Related Cost [Member]
Restructuring Costs [Abstract]
Total curtailment expense (benefit)		1,038	455	22,049
Alumina Contract [Member]
Restructuring Costs [Abstract]
Total curtailment expense (benefit)		0	0	7,448
Power And Other Contract Termination Costs [Member]
Restructuring Costs [Abstract]
Total curtailment expense (benefit)		0	0	6,332
Ongoing Site Costs [Member]
Restructuring Costs [Abstract]
Total curtailment expense (benefit)		12,313	14,332	18,233
Pension Plan Curtailment Adjustment [Member]
Restructuring Costs [Abstract]
Total curtailment expense (benefit)		1,147	4,555	2,478
OPEB Plan Curtailment Adjustment [Member]
Restructuring Costs [Abstract]
Total curtailment expense (benefit)		(18,304)	(56,728)	(14,830)
Curtailment At Ravenswood and Hawesville [Member]
Restructuring Costs [Abstract]
Total cash curtailment cost		13,502	10,078	22,300
Ravenswood Ongoing Idling Costs [Member]
Restructuring Costs [Abstract]
Total cash curtailment cost		9,464	7,351	9,300
Contract Termination and Amendment Costs [Member]
Restructuring Costs [Abstract]
Total cash curtailment cost		$ 0	$ 0	$ 15,100