Quarterly report pursuant to Section 13 or 15(d)

Income Taxes (Details)

v2.4.0.6
Income Taxes (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Mar. 31, 2012
Lower Limit [Member]
Mar. 31, 2012
Upper Limit [Member]
Jul. 01, 2012
Scenario, Forecast [Member]
Iron Ore And Coal Mining Profits [Member]
Mar. 31, 2012
United States [Member]
Mar. 31, 2012
Canada [Member]
Mar. 31, 2012
Australia [Member]
Income tax provision $ (210.8) $ 142.2            
Effective income tax rate (112.40%) 25.30%            
Effective income tax rate before discrete items 23.20%              
U.S. statutory tax rate 35.00%              
Increased valuation allowance against deferred tax assets 51.8              
Expected tax rate         22.50%      
Unrecognized tax benefits 78.5              
Change in unrecognized tax benefits     27.2 29.5        
Additional accrued interest relating to unrecognized tax benefits 0.1              
Effect of MRRT, increase in effective tax rate each year over the life of mines     3.00% 4.00%        
Tax years that remain subject to examination           2009 and forward 2005 and forward 2007 and forward
Cost to settle audit 23.9              
Net deferred tax assets 314.7              
Increase to the balance of deferred tax assets resulting from settlements with MRRT 334.6              
Valuation allowance $ 19.9