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, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Net income-basic and diluted	$ 180	$ 174	$ 491	$ 478
Denominator:
Basic weighted-average common shares outstanding (in shares)	164.6	164.0	164.5	164.1
Diluted weighted-average shares	166.8	165.5	166.5	165.5
Earnings per share:
Basic (in USD per share)	$ 1.09	$ 1.06	$ 2.98	$ 2.91
Diluted (in USD per share)	$ 1.08	$ 1.05	$ 2.95	$ 2.89
Number of anti-dilutive stock-based awards (in shares)	0.0	0.3	0.3	0.7
Stock Options
Denominator:
Effect of stock-based awards (in shares)	1.2	1.0	1.1	0.9
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	1.0	0.5	0.9	0.5