Schedule of Details Supporting Computation of Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income available for common stockholders	$ 431	$ 344	$ 861	$ 712
Weighted average outstanding shares of common stock used to compute basic earnings per common share	149,473	155,423	149,982	155,257
Shares used to compute diluted earnings per common share	151,148	157,046	151,748	156,846
Basic earnings per common share (in dollars per share)	$ 2.88	$ 2.22	$ 5.74	$ 4.59
Diluted earnings per common share (in dollars per share)	$ 2.85	$ 2.19	$ 5.67	$ 4.54
Number of antidilutive stock options and restricted stock excluded from computation	314	245	516	609
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	193	227	205	248
Restricted Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of employee stock options and restricted stock	1,482	1,396	1,561	1,341