Schedule of Details Supporting Computation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income available for common stockholders	$ 234	$ 430
Weighted average outstanding shares of common stock used to compute basic earnings per common share	149,161	150,490
Shares used to compute diluted earnings per common share	150,554	152,349
Basic earnings per common share (in dollars per share)	$ 1.57	$ 2.86
Diluted earnings per common share (in dollars per share)	$ 1.56	$ 2.82
Number of antidilutive stock options and restricted stock excluded from computation	1,273	718
Employee Stock Options
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of employee stock options and restricted stock	169	218
Restricted Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of employee stock options and restricted stock	1,224	1,641