Components of 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, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Schedule of Earnings Per Share, Basic and Diluted, by Common Class
Net income available for common stockholders	$ 108	$ 112	$ 167	$ 203
Weighted average outstanding shares of common stock	163.4	168.7	164.4	168.3
Dilutive effect of employee stock options and restricted stock	2.9	3.6	3.0	3.7
Common stock and common stock equivalents	166.3	172.3	167.4	172.0
Basic	$ 0.66	$ 0.66	$ 1.02	$ 1.21
Diluted	$ 0.65	$ 0.65	$ 1.00	$ 1.18