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, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerator:
Net income-basic and diluted	$ 123	$ 176	$ 311	$ 304
Denominator:
Basic weighted-average common shares outstanding (in shares)	164.5	164.1	164.4	164.1
Diluted weighted-average shares	166.5	165.5	166.3	165.5
Earnings per share:
Basic (in USD per share)	$ 0.75	$ 1.07	$ 1.89	$ 1.85
Diluted (in USD per share)	$ 0.74	$ 1.06	$ 1.87	$ 1.84
Number of anti-dilutive stock-based awards (in shares)	0.3	0.7	0.4	0.7
Stock Options
Denominator:
Effect of stock-based awards (in shares)	1.1	0.9	1.1	0.9
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.9	0.5	0.8	0.5