Schedule of Details Supporting Computation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income available for common stockholders	$ 314	$ 290	$ 1,175	$ 1,002
Weighted average outstanding shares of common stock used to compute basic earnings per common share	148,889	154,502	149,617	155,006
Shares used to compute diluted earnings per common share	150,466	156,230	151,321	156,641
Basic earnings per common share (in dollars per share)	$ 2.11	$ 1.87	$ 7.85	$ 6.46
Diluted earnings per common share (in dollars per share)	$ 2.09	$ 1.85	$ 7.77	$ 6.39
Number of antidilutive stock options and restricted stock excluded from computation	320	43	451	420
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	182	203	198	233
Restricted Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of employee stock options and restricted stock	1,395	1,525	1,506	1,402