Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Basic earnings per share:
Net Income	$ 656	$ 506
Weighted average shares outstanding	263.3	274.2
Basic earnings per share	$ 2.49	$ 1.85
Diluted earnings per share:
Net Income	$ 656	$ 506
Weighted average shares outstanding	263.3	274.2
Additional shares from assumed issuance of shares under stock-based compensation awards	1.5	2.0
Weighted average shares and potential shares assumed outstanding for computing diluted earnings per share	264.8	276.2
Diluted earnings per share	$ 2.48	$ 1.83