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		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator:
Net income-basic and diluted	$ 131	$ 111	$ 395	$ 229
Denominator:
Weighted-average common shares outstanding (in shares)	163,710	162,555	163,454	162,419
Adjusted diluted weighted-average shares (in shares)	165,601	163,857	165,304	163,507
Earnings per share:
Basic (in USD per share)	$ 0.80	$ 0.69	$ 2.42	$ 1.41
Diluted (in USD per share)	$ 0.79	$ 0.68	$ 2.39	$ 1.40
Number of anti-dilutive stock-based awards (in shares)	335	5,045	390	6,000
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	1,184	563	1,131	441
Stock Options
Denominator:
Effect of stock-based awards (in shares)	707	739	719	647