Net Income Per Common Share - Calculations for Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Numerator:
Net income-basic and diluted	$ 154	$ 86
Denominator:
Weighted-average common shares outstanding (in shares)	163,133	162,277
Adjusted diluted weighted-average shares (in shares)	164,924	163,145
Earnings per share:
Basic (in USD per share)	$ 0.95	$ 0.53
Diluted (in USD per share)	$ 0.94	$ 0.53
Number of anti-dilutive stock-based awards (in shares)	2,056	6,215
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	783	541
Stock Options
Denominator:
Effect of stock-based awards (in shares)	1,008	327