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		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Basic earnings per share:
Net income	$ 533	$ 298	$ 1,443	$ 1,226
Weighted average shares outstanding	267.3	285.7	271.0	292.6
Basic earnings per share	$ 1.99	$ 1.04	$ 5.32	$ 4.19
Diluted earnings per share:
Net income	$ 533	$ 298	$ 1,443	$ 1,226
Weighted average shares outstanding	267.3	285.7	271.0	292.6
Additional shares from assumed issuance of shares under stock-based compensation awards	1.9	2.1	1.9	1.8
Weighted average shares and potential shares assumed outstanding for computing diluted earnings per share	269.2	287.8	272.9	294.4
Diluted earnings per share	$ 1.98	$ 1.04	$ 5.29	$ 4.16