Schedule of Details Supporting Computation of Earnings Per Share (Detail) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income available for common stockholders	$ 430	$ 368
Weighted average outstanding shares of common stock used to compute basic earnings per common share	150,490	155,091
Shares used to compute diluted earnings per common share	152,349	156,647
Basic earnings per common share (in dollars per share)	$ 2.86	$ 2.37
Diluted earnings per common share (in dollars per share)	$ 2.82	$ 2.35
Number of antidilutive stock options and restricted stock excluded from computation	718	972
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	218	268
Restricted Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of employee stock options and restricted stock	1,641	1,288