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Stock-Based Compensation - Company's Stock Option Activity (Detail) (USD $)
In Millions, except Per Share data, unless otherwise specified
 3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]    
Option shares outstanding 30 36
Weighted average exercise price $ 21 $ 21
Option shares granted 1 1
Weighted average exercise price $ 20 $ 12
Option shares exercised 2  
Aggregate intrinsic value on date of exercise $ 17 $ 1
Weighted average exercise price $ 11 $ 8
Option shares forfeited   2
Weighted average exercise price $ 19 $ 18
Option shares outstanding 29 35
Weighted average exercise price $ 22 $ 21
Weighted average remaining option term (in years) 4 years 5 years
Option shares vested and expected to vest 29 35
Weighted average exercise price $ 22 $ 21
Aggregate intrinsic value 82 26
Weighted average remaining option term (in years) 4 years 5 years
Option shares exercisable (vested) 23 25
Weighted average exercise price $ 24 $ 23
Aggregate intrinsic value $ 45 $ 14
Weighted average remaining option term (in years) 4 years 4 years