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		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net income-basic and diluted	$ 100	$ 123	$ 301	$ 311
Denominator:
Basic weighted-average common shares outstanding (in shares)	164.3	164.5	164.4	164.4
Diluted weighted-average shares	166.0	166.5	166.2	166.3
Earnings per share:
Basic (in USD per share)	$ 0.61	$ 0.75	$ 1.83	$ 1.89
Diluted (in USD per share)	$ 0.60	$ 0.74	$ 1.81	$ 1.87
Number of anti-dilutive stock-based awards (in shares)	0.6	0.3	0.7	0.4
Stock Options
Denominator:
Effect of stock-based awards (in shares)	1.0	1.1	1.1	1.1
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.7	0.9	0.7	0.8