Net Income Per Common Share - Calculations for Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Numerator:
Net income-basic and diluted	$ 91	$ 154
Denominator:
Weighted-average common shares outstanding (in shares)	163.4	163.1
Adjusted diluted weighted-average shares (in shares)	165.0	164.9
Earnings per share:
Basic (in USD per share)	$ 0.56	$ 0.95
Diluted (in USD per share)	$ 0.55	$ 0.94
Number of anti-dilutive stock-based awards (in shares)	0.7	2.1
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.6	0.8
Stock Options
Denominator:
Effect of stock-based awards (in shares)	1.0	1.0