Net Income Per Common Share - Calculations for Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Numerator:
Net income-basic and diluted	$ 188	$ 128
Denominator:
Basic weighted-average common shares outstanding (in shares)	164.2	164.0
Diluted weighted-average shares	166.0	165.6
Earnings per share:
Basic (in USD per share)	$ 1.14	$ 0.78
Diluted (in USD per share)	$ 1.13	$ 0.77
Number of anti-dilutive stock-based awards (in shares)	0.4	0.7
Stock Options
Denominator:
Effect of stock-based awards (in shares)	1.0	1.0
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.8	0.6