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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic EPS:
Net income	$ 1,570	$ 1,285	$ 4,341	$ 3,338
Income allocated to RSUs	(12)	(11)	(34)	(32)
Income allocated to common stock for basic EPS	$ 1,558	$ 1,274	$ 4,307	$ 3,306
Weighted average number of shares outstanding, basic (in shares)	969	988	976	993
Basic earnings per common share	$ 1.61	$ 1.29	$ 4.41	$ 3.33
Adjustment for dilutive shares:
Stock compensation plans	20	20	21	21
Diluted EPS:
Net income	$ 1,570	$ 1,285	$ 4,341	$ 3,338
Income allocated to RSUs	(11)	(11)	(34)	(31)
Income allocated to common stock for diluted EPS	$ 1,559	$ 1,274	$ 4,307	$ 3,307
Weighted average number of shares outstanding, diluted (in shares)	989	1,008	997	1,014
Diluted earnings per common share	$ 1.58	$ 1.26	$ 4.32	$ 3.26