v2.4.0.6
Share-Based Compensation (Summary of Stock Option Activity) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
 3 Months Ended 12 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Number of Stock Options Outstanding, Beginning of period 7,545,777 [1]    
Number of Stock Options, Exercised 377,425 [1] 100,299  
Number of Stock Options, Forfeited or expired 42,604 [1]    
Number of Stock Options Outstanding, End of period 7,125,748 [1]   7,545,777 [1]
Stock options, exercisable 4,902,865 [1] 5,700,000  
Weighted-Average Exercise Price, Outstanding Beginning of period $ 21.10    
Weighted-Average Exercise Price, Exercised $ 14.68    
Weighted-Average Exercise Price, Forfeited or expired $ 23.77    
Weighted-Average Exercise Price, Outstanding End of period $ 21.41   $ 21.10
Weighted-average exercise price $ 20.93 $ 15.10  
Options Outstanding, Weighted-Average Remaining Contractual Term, outstanding (in years) 4 years 9 months 18 days   5 years
Aggregate Intrinsic Value, Options Outstanding $ 83   $ 45
Options Outstanding, Weighted-Average Remaining Contractual Term, exercisable (in years) 3 years 8 months 12 days    
Aggregate Intrinsic Value, Exercisable $ 62    
[1] No stock option awards were granted during the three months ended March 31, 2013.