Earnings Per Share of Common Stock - Computation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Number of shares on which basic earnings per share is calculated:
Weighted-average shares outstanding during period	911,152,848	929,437,441	915,632,501	935,600,777
Add - Incremental shares under stock-based compensation plans (in shares)	2,566,139	2,236,234	3,000,429	3,213,758
Add - Incremental shares associated with contingently issuable shares (in shares)	1,493,644	1,553,754	1,373,960	1,394,930
Number of shares on which diluted earnings per share is calculated	915,212,631	933,227,429	920,006,890	940,209,466
Net income on which basic earnings per share is calculated:
Income from continuing operations	$ 2,692	$ 2,726	$ 6,770	$ 6,811
Income/(loss) from discontinued operations, net of tax	2	0	7	(3)
Net income on which basic earnings per share is calculated	2,694	2,726	6,777	6,807
Net income on which diluted earnings per share is calculated:
Income from continuing operations	2,692	2,726	6,770	6,811
Net income applicable to contingently issuable shares		0	(1)	(2)
Income from continuing operations on which diluted earnings per share is calculated	2,692	2,726	6,769	6,809
Income/(loss) from discontinued operations, net of tax, on which basic and diluted earnings per share is calculated	2	0	7	(3)
Net income on which diluted earnings per share is calculated	$ 2,694	$ 2,726	$ 6,776	$ 6,806
Assuming dilution
Continuing operations (in dollars per share)	$ 2.94	$ 2.92	$ 7.36	$ 7.24
Discontinued operations (in dollars per share)	0.00	0.00	0.01	0.00
Total (in dollars per share)	2.94	2.92	7.37	7.24
Basic
Continuing operations (in dollars per share)	2.95	2.93	7.39	7.28
Discontinued operations (in dollars per share)	0.00	0.00	0.01	0.00
Total (in dollars per share)	$ 2.95	$ 2.93	$ 7.40	$ 7.28