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								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic EPS:
Net income	$ 1,239	$ 1,570	$ 1,405	$ 1,366	$ 344	$ 1,285	$ 1,056	$ 997	$ 5,580	$ 3,682	$ 3,595
Income allocated to RSUs									(43)	(34)	(45)
Income allocated to common stock for basic EPS									$ 5,537	$ 3,648	$ 3,550
Weighted average number of shares outstanding, basic (in shares)									970	991	1,003
Basic earnings per common share	$ 1.29	$ 1.61	$ 1.43	$ 1.38	$ 0.35	$ 1.29	$ 1.05	$ 0.99	$ 5.71	$ 3.68	$ 3.54
Dilutive effect of stock compensation plans									20	21	18
Diluted EPS:
Net income	$ 1,239	$ 1,570	$ 1,405	$ 1,366	$ 344	$ 1,285	$ 1,056	$ 997	$ 5,580	$ 3,682	$ 3,595
Income allocated to RSUs									(42)	(33)	(44)
Income allocated to common stock for diluted EPS									$ 5,538	$ 3,649	$ 3,551
Weighted average number of shares outstanding, diluted (in shares)									990	1,012	1,021
Diluted earnings per common share	$ 1.27	$ 1.58	$ 1.40	$ 1.35	$ 0.34	$ 1.26	$ 1.03	$ 0.97	$ 5.59	$ 3.61	$ 3.48