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Stock Compensation (Maximum Future Value of Performance Shares) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2012
Feb. 25, 2012
Stock Compensation [Abstract]    
2010 Award $ 21  
2011 Award 24  
2012 Award 27  
2012 performance share grant target distribution 251,000  
Performance share based awards cumulative target period, in years 3  
Grant-date fair value of shares that correspond with target grants $ 47  
Number of performance shares that could be issued on the vesting date, minimum 0.00%  
Number of performance shares that could be issued on the vesting date, maximum 200.00%  
2009 Performance share award settlement in terms of original target   82.00%
2009 Performance share award settlement in dollars   $ 7