Earnings Per Share of Common Stock - Computation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Number of shares on which basic earnings per share is calculated:
Weighted-average shares outstanding during period	929,437,441	953,995,828	935,600,777	957,693,385
Add - Incremental shares under stock-based compensation plans (in shares)	2,236,234	2,357,365	3,213,758	2,258,854
Add - Incremental shares associated with contingently issuable shares (in shares)	1,553,754	964,091	1,394,930	771,943
Number of shares on which diluted earnings per share is calculated	933,227,429	957,317,284	940,209,466	960,724,182
Net income on which basic earnings per share is calculated:
Income from continuing operations	$ 2,726	$ 2,854	$ 6,811	$ 7,375
Loss from discontinued operations, net of tax	0	(1)	(3)	(4)
Net income on which basic earnings per share is calculated	2,726	2,853	6,807	7,371
Net income on which diluted earnings per share is calculated:
Income from continuing operations	2,726	2,854	6,811	7,375
Net income applicable to contingently issuable shares	0		(2)
Income from continuing operations on which diluted earnings per share is calculated	2,726	2,854	6,809	7,375
Loss from discontinued operations, net of tax, on which basic and diluted earnings per share is calculated	0	(1)	(3)	(4)
Net income on which diluted earnings per share is calculated	$ 2,726	$ 2,853	$ 6,806	$ 7,371
Assuming dilution
Continuing operations (in dollars per share)	$ 2.92	$ 2.98	$ 7.24	$ 7.67
Discontinued operations (in dollars per share)	0.00	0.00	0.00	0.00
Total (in dollars per share)	2.92	2.98	7.24	7.67
Basic
Continuing operations (in dollars per share)	2.93	2.99	7.28	7.70
Discontinued operations (in dollars per share)	0.00	0.00	0.00	0.00
Total (in dollars per share)	$ 2.93	$ 2.99	$ 7.28	$ 7.70