Earnings Per Share of Common Stock - Computation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Number of shares on which basic earnings per share is calculated:
Weighted-average shares outstanding during period	920,680,222	942,440,901
Add - Incremental shares under stock-based compensation plans (in shares)	3,553,104	4,213,258
Add - Incremental shares associated with contingently issuable shares (in shares)	1,176,108	1,182,047
Number of shares on which diluted earnings per share is calculated	925,409,434	947,836,207
Net income on which basic earnings per share is calculated:
Income from continuing operations	$ 1,675	$ 1,753
Income/(loss) from discontinued operations, net of tax	4	(3)
Net income on which basic earnings per share is calculated	1,679	1,750
Net income on which diluted earnings per share is calculated:
Income from continuing operations	1,675	1,753
Income from continuing operations on which diluted earnings per share is calculated	1,675	1,753
Income/(loss) from discontinued operations, net of tax, on which basic and diluted earnings per share is calculated	4	(3)
Net income on which diluted earnings per share is calculated	$ 1,679	$ 1,750
Assuming dilution
Continuing operations (in dollars per share)	$ 1.81	$ 1.85
Discontinued operations (in dollars per share)	0.00	0.00
Total (in dollars per share)	1.81	1.85
Basic
Continuing operations (in dollars per share)	1.82	1.86
Discontinued operations (in dollars per share)	0.00	0.00
Total (in dollars per share)	$ 1.82	$ 1.86