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								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Income from continuing operations, net of tax	$ 908	$ 1,118	$ 852	$ 1,134	$ 970	$ 1,125	$ 1,204	$ 1,124	$ 4,012	$ 4,423	$ 4,354
Income (loss) from discontinued operations, net of tax	12	(4)	11	19	29	(44)	(10)	30	38	5	(233)
Net income	920	1,114	863	1,153	999	1,081	1,194	1,154	4,050	4,428	4,121
Dividends and undistributed earnings allocated to participating securities	(4)	(6)	(4)	(6)	(4)	(5)	(4)	(5)	(20)	(18)	(17)
Preferred stock dividends	(68)	(29)	(29)	(32)	(21)	(20)	(13)	(13)	(158)	(67)	(53)
Net income available to common stockholders	$ 848	$ 1,079	$ 830	$ 1,115	$ 974	$ 1,056	$ 1,177	$ 1,136	$ 3,872	$ 4,343	$ 4,051
Total weighted-average basic shares outstanding	530.8	540.6	545.6	550.2	554.3	559.9	567.5	571.0	541.8	563.1	579.7
Effect of dilutive securities:
Stock options									2.6	2.7	2.2
Other contingently issuable shares									1.3	1.6	1.5
Warrants									2.3	4.5	4.2
Total effect of dilutive securities									6.2	8.8	7.9
Total weighted-average diluted shares outstanding	536.3	546.3	552.0	557.2	561.8	567.9	577.6	580.3	548.0	571.9	587.6
Basic earnings per common share:
Net income from continuing operations (in dollars per share)	$ 1.58	$ 2.01	$ 1.50	$ 2.00	$ 1.71	$ 1.97	$ 2.09	$ 1.94	$ 7.08	$ 7.70	$ 7.39
Income (loss) from discontinued operations (in dollars per share)	0.02	(0.01)	0.02	0.03	0.05	(0.08)	(0.02)	0.05	0.07	0.01	(0.40)
Net income per basic common share (in dollars per share)	1.60	2.00	1.52	2.03	1.76	1.89	2.07	1.99	7.15	7.71	6.99
Diluted earnings per common share:
Net income from continuing operations (in dollars per share)	1.56	1.99	1.48	1.97	1.68	1.94	2.06	1.91	7.00	7.58	7.28
Income (loss) from discontinued operations (in dollars per share)	0.02	(0.01)	0.02	0.03	0.05	(0.08)	(0.02)	0.05	0.07	0.01	(0.39)
Net income per diluted common share (in dollars per share)	$ 1.58	$ 1.98	$ 1.50	$ 2.00	$ 1.73	$ 1.86	$ 2.04	$ 1.96	$ 7.07	$ 7.59	$ 6.89