Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic
Income from continuing operations	$ 2,418	$ 2,390	$ 4,575	$ 3,506
Less: cumulative dividends on subsidiary preferred stock	(37)	(15)	(75)	(29)
Income from continuing operations attributable to common stockholders	2,381	2,375	4,500	3,477
Loss from discontinued operations, net of tax	0	0	0	70
Net income attributable to common stockholders	$ 2,381	$ 2,375	$ 4,500	$ 3,407
Weighted-average common shares outstanding - basic (in shares)	1,420	1,410	1,419	1,409
Basic earnings per common share – continuing operations (in dollars per share)	$ 1.68	$ 1.68	$ 3.17	$ 2.47
Basic loss per common share – discontinued operations (in dollars per share)	0	0	0	0.05
Basic earnings per common share (in dollars per share)	$ 1.68	$ 1.68	$ 3.17	$ 2.42
Diluted
Income from continuing operations attributable to common stockholders – diluted	$ 2,381	$ 2,375	$ 4,500	$ 3,477
Loss from discontinued operations, net of tax – diluted	0	0	0	70
Net income attributable to common stockholders – diluted	$ 2,381	$ 2,375	$ 4,500	$ 3,407
Weighted-average common shares outstanding - basic (in shares)	1,420	1,410	1,419	1,409
Dilutive effect of warrants and awards under stock incentive plans (in shares)	18	21	18	21
Weighted-average common shares outstanding - diluted (in shares)	1,438	1,431	1,437	1,430
Diluted earnings per common share – continuing operations (in dollars per share)	$ 1.66	$ 1.66	$ 3.13	$ 2.43
Diluted loss per common share – discontinued operations (in dollars per share)	0	0	0	0.05
Diluted earnings per common share (in dollars per share)	$ 1.66	$ 1.66	$ 3.13	$ 2.38
Potentially dilutive securities (in shares)	7	4	7	4