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, 2018	Mar. 31, 2017
Basic EPS:
Net income	$ 1,366	$ 997
Income allocated to RSUs	(11)	(10)
Income allocated to common stock for basic EPS	$ 1,355	$ 987
Weighted average number of shares outstanding, basic (in shares)	983	998
Basic earnings per common share	$ 1.38	$ 0.99
Adjustment for dilutive shares:
Stock compensation plans	22	21
Diluted EPS:
Net income	$ 1,366	$ 997
Income allocated to RSUs	(11)	(10)
Income allocated to common stock for diluted EPS	$ 1,355	$ 987
Weighted average number of shares outstanding, diluted (in shares)	1,005	1,019
Diluted earnings per common share	$ 1.35	$ 0.97