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		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator:
Net income-basic and diluted	$ 110	$ 32	$ 264	$ 118
Denominator:
Weighted-average common shares outstanding (in shares)	163,512	162,425	163,323	162,351
Adjusted diluted weighted-average shares (in shares)	165,442	163,514	165,151	163,328
Earnings per share:
Basic (in USD per share)	$ 0.67	$ 0.20	$ 1.62	$ 0.73
Diluted (in USD per share)	$ 0.66	$ 0.20	$ 1.60	$ 0.72
Number of anti-dilutive stock-based awards (in shares)	340	6,059	393	6,072
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	1,239	419	1,098	375
Stock Options
Denominator:
Effect of stock-based awards (in shares)	691	670	730	602