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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Basic earnings per common share:
Income from continuing operations, net of tax	$ 1,118	$ 1,125	$ 3,104	$ 3,453
Income (loss) from discontinued operations, net of tax	(4)	(44)	26	(24)
Net income	1,114	1,081	3,130	3,429
Dividends and undistributed earnings allocated to participating securities	(6)	(5)	(16)	(14)
Preferred stock dividends	(29)	(20)	(90)	(46)
Net income available to common stockholders	$ 1,079	$ 1,056	$ 3,024	$ 3,369
Net income from continuing operations (in dollars per share)	$ 2.01	$ 1.97	$ 5.49	$ 5.99
Income (loss) from discontinued operations (in dollars per share)	(0.01)	(0.08)	0.05	(0.04)
Net income per basic common share (in dollars per share)	$ 2.00	$ 1.89	$ 5.54	$ 5.95
Weighted Average Number of Shares Outstanding, Basic	540.6	559.9	545.5	566.1
Diluted earnings per common share:
Net income available to common stockholders	$ 1,079	$ 1,056	$ 3,024	$ 3,369
Net income from continuing operations (in dollars per share)	$ 1.99	$ 1.94	$ 5.43	$ 5.90
Income (loss) from discontinued operations (in dollars per share)	(0.01)	(0.08)	0.05	(0.04)
Net income per diluted common share (in dollars per share)	$ 1.98	$ 1.86	$ 5.48	$ 5.86
Effect of dilutive securities:
Stock options	2.5	2.8	2.6	2.7
Other contingently issuable shares	1.2	1.6	1.3	1.5
Warrants	2.0	3.6	2.5	4.9
Total effect of dilutive securities	5.7	8.0	6.4	9.1
Total weighted-average diluted shares outstanding	546.3	567.9	551.9	575.2