Net Income Per Common Share - Calculations for Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Numerator:
Net income-basic and diluted	$ 84	$ 110	$ 175	$ 264
Denominator:
Weighted-average common shares outstanding (in shares)	163.5	163.5	163.5	163.3
Adjusted diluted weighted-average shares (in shares)	165.1	165.4	165.1	165.2
Earnings per share:
Basic (in USD per share)	$ 0.51	$ 0.67	$ 1.07	$ 1.62
Diluted (in USD per share)	$ 0.51	$ 0.66	$ 1.06	$ 1.60
Number of anti-dilutive stock-based awards (in shares)	0.7	0.3	0.7	0.4
Stock Options
Denominator:
Effect of stock-based awards (in shares)	1.0	1.2	1.0	1.1
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.6	0.7	0.6	0.7