Share-based Compensation - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Companies
Vesting period for stock options from the date of grant	3 years
Option term (in years)	10 years
Vesting period for outstanding restricted common stock from the date of grant	3 years
Number of predetermined peer companies	15
Performance of predetermined peer companies	3 years
Minimum PSU award payout	0.00%
Maximum PSU award payout	200.00%
Unearned compensation expense, before income taxes due 2013	$ 69
Unearned compensation expense, before income taxes due 2014	43
Unearned compensation expense, before income taxes due 2015	8
Intrinsic value for exercisable options	32
Intrinsic value for outstanding options	$ 32
Weighted average remaining term of exercisable options	5 years
Long-term Incentive Plan [Member]
Available for future awards of restricted stock, stock options and PSUs	12.4
Common stock authorized for issuance	29