Earnings per Share - Computation of Basic and Diluted Earnings per Share (EPS) (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
Basic EPS:
Net income	$ 1,693	$ 942	$ 4,329	$ 2,285
Weighted-average common shares outstanding	661,869	719,067	682,337	721,213
Basic EPS	$ 2.56	$ 1.31	$ 6.34	$ 3.17
Diluted EPS:
Net income	$ 1,693	$ 942	$ 4,329	$ 2,285
Change in fair value of conversion feature on 7.25% convertible senior notes				3
Net income for purposes of computing diluted EPS	$ 1,693	$ 942	$ 4,329	$ 2,288
Share computation for diluted earnings per share (in thousands):
Weighted-average shares outstanding	661,869	719,067	682,337	721,213
Dilutive effect of stock awards	18,870	16,129	19,423	14,610
Assumed conversion of convertible senior notes				1,277
Weighted average common shares outstanding	680,739	735,196	701,760	737,100
Diluted EPS	$ 2.49	$ 1.28	$ 6.17	$ 3.10
Stock options, SARs and RSUs because inclusion would be antidilutive	1,094	248	667	288