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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Basic EPS:
Net income	$ 1,285	$ 1,018	$ 3,338	$ 2,548
Income allocated to RSUs	(11)	(12)	(32)	(31)
Income allocated to common stock for basic EPS calculation	$ 1,274	$ 1,006	$ 3,306	$ 2,517
Weighted average number of shares outstanding, basic (in shares)	988	1,003	993	1,004
Basic earnings per common share	$ 1.29	$ 1.00	$ 3.33	$ 2.51
Adjustment for dilutive shares:
Stock compensation plans	20	20	21	18
Diluted EPS:
Net income	$ 1,285	$ 1,018	$ 3,338	$ 2,548
Income allocated to RSUs	(11)	(11)	(31)	(31)
Income allocated to common stock for diluted EPS	$ 1,274	$ 1,007	$ 3,307	$ 2,517
Weighted average number of shares outstanding, diluted (in shares)	1,008	1,023	1,014	1,022
Diluted earnings per common share	$ 1.26	$ 0.98	$ 3.26	$ 2.46