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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic EPS:
Net income	$ 1,056	$ 819	$ 2,053	$ 1,530
Income allocated to RSUs	(10)	(10)	(20)	(19)
Income allocated to common stock for basic EPS calculation	$ 1,046	$ 809	$ 2,033	$ 1,511
Weighted average number of shares outstanding, basic (in shares)	994	1,004	996	1,005
Basic earnings per common share	$ 1.05	$ 0.81	$ 2.04	$ 1.50
Adjustment for dilutive shares:
Stock compensation plans	21	16	21	16
Diluted EPS:
Net income	$ 1,056	$ 819	$ 2,053	$ 1,530
Income allocated to RSUs	(10)	(10)	(20)	(19)
Income allocated to common stock for diluted EPS	$ 1,046	$ 809	$ 2,033	$ 1,511
Weighted average number of shares outstanding, diluted (in shares)	1,015	1,020	1,017	1,021
Diluted earnings per common share	$ 1.03	$ 0.79	$ 2.00	$ 1.48