v2.4.0.6
Stock-Based Compensation (Schedule of Non-qualified Stock Option Activity) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
 3 Months Ended 12 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]    
Options, Outstanding 17,280,425 17,862,501
Options, Outstanding, Weighted Average Exercise Price $ 17.36 $ 17.30
Options, Outstanding, Weighted Average Remaining Contractual Term 3 years 8 months 12 days 4 years
Options, Outstanding, Intrinsic Value $ 69 $ 42
Options, Grants in Period, Gross 11,299  
Options, Grants in Period, Weighted Average Exercise Price $ 18.34  
Options, Exercises in Period 580,975  
Options, Exercises in Period, Weighted Average Exercise Price $ 15.75  
Options, Forfeitures in Period 0  
Options, Forfeitures in Period, Weighted Average Exercise Price $ 0.00  
Options, Expirations in Period 12,400  
Options, Expirations in Period, Weighted Average Exercise Price $ 17.77  
Options, Exercisable 10,344,468  
Options, Exercisable, Weighted Average Exercise Price $ 18.82  
Options, Exercisable, Weighted Average Remaining Contractual Term 3 years 6 months  
Options, Exercisable, Intrinsic Value 29  
Options, Vested and Expected to Vest, Outstanding 17,051,325  
Options, Vested and Expected to Vest, Outstanding, Weighted Average Exercise Price $ 17.39  
Options, Vested and Expected to Vest, Outstanding, Weighted Average Remaining Contractual Term 3 years 7 months 6 days  
Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value $ 68