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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Basic EPS:
Net income	$ 1,405	$ 1,056	$ 2,771	$ 2,053
Income allocated to RSUs	(11)	(10)	(23)	(20)
Income allocated to common stock for basic EPS	$ 1,394	$ 1,046	$ 2,748	$ 2,033
Weighted average number of shares outstanding, basic (in shares)	977	994	980	996
Basic earnings per common share	$ 1.43	$ 1.05	$ 2.80	$ 2.04
Adjustment for dilutive shares:
Stock compensation plans	20	21	21	21
Diluted EPS:
Net income	$ 1,405	$ 1,056	$ 2,771	$ 2,053
Income allocated to RSUs	(11)	(10)	(22)	(20)
Income allocated to common stock for diluted EPS	$ 1,394	$ 1,046	$ 2,749	$ 2,033
Weighted average number of shares outstanding, diluted (in shares)	997	1,015	1,001	1,017
Diluted earnings per common share	$ 1.40	$ 1.03	$ 2.75	$ 2.00