Earnings Per Share of Common Stock - Computation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Number of shares on which basic earnings per share is calculated:
Weighted-average shares outstanding during period	915,064,434	934,923,989	917,872,328	938,682,445
Add - Incremental shares under stock-based compensation plans (in shares)	2,882,043	3,191,783	3,217,574	3,702,521
Add - Incremental shares associated with contingently issuable shares (in shares)	1,452,129	1,448,989	1,314,118	1,315,518
Number of shares on which diluted earnings per share is calculated	919,398,606	939,564,761	922,404,020	943,700,484
Net income on which basic earnings per share is calculated:
Income from continuing operations	$ 2,402	$ 2,332	$ 4,078	$ 4,085
Income/(loss) from discontinued operations, net of tax	1	(1)	5	(3)
Net income on which basic earnings per share is calculated	2,404	2,331	4,083	4,082
Net income on which diluted earnings per share is calculated:
Income from continuing operations	2,402	2,332	4,078	4,085
Net income applicable to contingently issuable shares	(1)	(2)	(1)	(2)
Income from continuing operations on which diluted earnings per share is calculated	2,401	2,331	4,077	4,083
Income/(loss) from discontinued operations, net of tax, on which basic and diluted earnings per share is calculated	1	(1)	5	(3)
Net income on which diluted earnings per share is calculated	$ 2,403	$ 2,330	$ 4,082	$ 4,080
Assuming dilution
Continuing operations (in dollars per share)	$ 2.61	$ 2.48	$ 4.42	$ 4.32
Discontinued operations (in dollars per share)	0.00	0.00	0.01	0.00
Total (in dollars per share)	2.61	2.48	4.43	4.32
Basic
Continuing operations (in dollars per share)	2.63	2.49	4.44	4.35
Discontinued operations (in dollars per share)	0.00	0.00	0.01	0.00
Total (in dollars per share)	$ 2.63	$ 2.49	$ 4.45	$ 4.35