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Stock-Based Compensation (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]    
Stock-based compensation expense $ 28 $ 17
Tax benefit 11 6
Stock-based compensation cost capitalized in property, plant and equipment $ 2 $ 1