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 9 Months Ended 12 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Dec. 31, 2012
Share-Based Compensation [Abstract]          
Number of Stock Options Outstanding, Beginning of period     7,545,777 [1]    
Number of Stock Options, Exercised 171,458 159,282 1,730,647 [1] 318,406  
Number of Stock Options, Forfeited or expired     161,492 [1]    
Number of Stock Options Outstanding, End of period 5,653,638 [1]   5,653,638 [1]   7,545,777 [1]
Stock options, exercisable 3,765,289 [1] 5,700,000 3,765,289 [1] 5,700,000  
Weighted-Average Exercise Price, Outstanding Beginning of period     $ 21.10    
Weighted-Average Exercise Price, Exercised     $ 10.25    
Weighted-Average Exercise Price, Forfeited or expired     $ 25.15    
Weighted-Average Exercise Price, Outstanding End of period $ 24.29   $ 24.29   $ 21.10
Weighted-average exercise price $ 25.06 $ 15.47 $ 25.06 $ 15.47  
Options Outstanding, Weighted-Average Remaining Contractual Term, outstanding (in years)     4 years 10 months 24 days   5 years
Aggregate Intrinsic Value, Options Outstanding $ 50   $ 50   $ 45
Options Outstanding, Weighted-Average Remaining Contractual Term, exercisable (in years)     4 years    
Aggregate Intrinsic Value, Exercisable $ 32   $ 32    
Stock options, granted 0   0    
[1] No stock option awards were granted during the three and nine months ended September 30, 2013.