v2.4.0.8
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, 2014
Mar. 31, 2013
Dec. 31, 2013
Share-Based Compensation [Abstract]      
Number of Stock Options Outstanding, Beginning of period 4,926,522 [1]    
Number of Stock Options, Exercised (367,115) [1] (377,425)  
Number of Stock Options, Forfeited or expired (27,401) [1]    
Number of Stock Options Outstanding, End of period 4,532,006 [1]   4,926,522 [1]
Stock options, exercisable 4,472,845 [1] 4,900,000  
Weighted-Average Exercise Price, Outstanding Beginning of period $ 25.21    
Weighted-Average Exercise Price, Exercised $ 19.39    
Weighted-Average Exercise Price, Forfeited or expired $ 22.67    
Weighted-Average Exercise Price, Outstanding End of period $ 25.70   $ 25.21
Weighted-average exercise price $ 25.72 $ 20.93  
Options Outstanding, Weighted-Average Remaining Contractual Term, outstanding (in years) 4 years 9 months 4 days   4 years 11 months 19 days
Aggregate Intrinsic Value, Options Outstanding $ 52   $ 73
Options Outstanding, Weighted-Average Remaining Contractual Term, exercisable (in years) 4 years 8 months 23 days    
Aggregate Intrinsic Value, Exercisable $ 51    
Stock options, granted 0    
[1] No stock option awards were granted during the three months ended March 31, 2014.