Stock-Based Compensation - Company's Stock Option Activity (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Option shares outstanding, Beginning balance	30	36
Weighted average exercise price	$ 21	$ 21
Option shares granted, including restoration options	1	1
Weighted average exercise price	$ 20	$ 12
Option shares exercised	3	1
Aggregate intrinsic value on date of exercise	$ 22	$ 4
Weighted average exercise price	$ 12	$ 9
Option shares forfeited	1	3
Weighted average exercise price	$ 23	$ 18
Option shares outstanding, Ending balance	27	33
Weighted average exercise price	$ 22	$ 21
Weighted average remaining option term (in years)	4 years	5 years
Option shares vested and expected to vest, Ending balance	27	33
Weighted average exercise price	$ 22	$ 21
Aggregate intrinsic value	91	39
Weighted average remaining option term (in years)	4 years	5 years
Option shares exercisable (vested), Ending balance	22	25
Weighted average exercise price	$ 24	$ 24
Aggregate intrinsic value	$ 51	$ 17
Weighted average remaining option term (in years)	3 years	4 years