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		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Numerator:
Net income-basic and diluted	$ 174	$ 183	$ 478	$ 358
Denominator:
Basic weighted-average common shares outstanding (in shares)	164.0	163.5	164.1	163.5
Diluted weighted-average shares	165.5	165.0	165.5	165.0
Earnings per share:
Basic (in USD per share)	$ 1.06	$ 1.12	$ 2.91	$ 2.19
Diluted (in USD per share)	$ 1.05	$ 1.11	$ 2.89	$ 2.17
Number of anti-dilutive stock-based awards (in shares)	0.3	0.7	0.7	0.7
Stock Options
Denominator:
Effect of stock-based awards (in shares)	1.0	0.9	0.9	0.9
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.5	0.6	0.5	0.6