Basis of Presentation and Significant Accounting Policies and Practices - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Basic EPS:
Net income	$ 1,217	$ 1,366
Income allocated to RSUs	(8)	(11)
Income allocated to common stock for basic EPS	$ 1,209	$ 1,355
Weighted average number of shares outstanding, basic (in shares)	939	983
Basic earnings per common share	$ 1.29	$ 1.38
Dilutive effect of stock compensation plans	17	22
Diluted EPS:
Net income	$ 1,217	$ 1,366
Income allocated to RSUs	(8)	(11)
Income allocated to common stock for diluted EPS	$ 1,209	$ 1,355
Weighted average number of shares outstanding, diluted (in shares)	956	1,005
Diluted earnings per common share	$ 1.26	$ 1.35