Earnings Per Share - Components of Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income available for common stockholders	$ 22	$ 59
Weighted average outstanding shares of common stock (in shares)	145.2	158.4
Dilutive effect of employee stock options, restricted stock and other stock awards (in shares)	2.5	2.5
Common stock and common stock equivalents (in shares)	147.7	160.9
Earnings per share:
Basic (in dollars per share)	$ 0.15	$ 0.37
Diluted (in dollars per share)	$ 0.15	$ 0.37