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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Numerator:
Net income-basic and diluted	$ 183	$ 131	$ 358	$ 395
Denominator:
Basic weighted-average common shares outstanding (in shares)	163.5	163.7	163.5	163.5
Adjusted diluted weighted-average shares (in shares)	165.0	165.6	165.0	165.3
Earnings per share:
Basic (in USD per share)	$ 1.12	$ 0.80	$ 2.19	$ 2.42
Diluted (in USD per share)	$ 1.11	$ 0.79	$ 2.17	$ 2.39
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)	0.9	1.2	0.9	1.1
Nonvested shares
Denominator:
Effect of stock-based awards (in shares)	0.6	0.7	0.6	0.7