Earnings Per Common Share - Schedule of Computation of Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Income from continuing operations, net of tax	$ 1,329	$ 1,501	$ 4,355	$ 4,761
Income (loss) from discontinued operations, net of tax	4	1	15	(7)
Net income	1,333	1,502	4,370	4,754
Dividends and undistributed earnings allocated to participating securities	(10)	(9)	(34)	(32)
Preferred stock dividends	(53)	(53)	(185)	(185)
Net income available to common stockholders	$ 1,270	$ 1,440	$ 4,151	$ 4,537
Total weighted-average basic shares outstanding	469.5	477.8	469.9	483.2
Effect of dilutive securities:
Stock options	1.3	1.5	1.2	1.8
Other contingently issuable shares	1.0	1.1	1.0	1.1
Warrants	0.0	0.5	0.0	0.6
Total effect of dilutive securities	2.3	3.1	2.2	3.5
Total weighted-average diluted shares outstanding	471.8	480.9	472.1	486.7
Basic earnings per common share:
Net income from continuing operations (in dollars per share)	$ 2.70	$ 3.01	$ 8.80	$ 9.40
Income (loss) from discontinued operations (in dollars per share)	0.01	0.00	0.03	(0.01)
Net income per basic common share (in dollars per share)	2.71	3.01	8.83	9.39
Diluted earnings per common share:
Net income from continuing operations (in dollars per share)	2.68	2.99	8.76	9.33
Income (loss) from discontinued operations (in dollars per share)	0.01	0.00	0.03	(0.01)
Net income per diluted common share (in dollars per share)	$ 2.69	$ 2.99	$ 8.79	$ 9.32