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, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Income from continuing operations, net of tax	$ 793	$ 1,016	$ 943	$ 1,018	$ 908	$ 1,118	$ 852	$ 1,134	$ 3,770	$ 4,012	$ 4,423
Income (loss) from discontinued operations, net of tax	(2)	(11)	(1)	(5)	12	(4)	11	19	(19)	38	5
Net income	791	1,005	942	1,013	920	1,114	863	1,153	3,751	4,050	4,428
Dividends and undistributed earnings allocated to participating securities	(6)	(6)	(6)	(6)	(4)	(6)	(4)	(6)	(24)	(20)	(18)
Preferred stock dividends	(75)	(37)	(65)	(37)	(68)	(29)	(29)	(32)	(214)	(158)	(67)
Net income available to common stockholders	$ 710	$ 962	$ 871	$ 970	$ 848	$ 1,079	$ 830	$ 1,115	$ 3,513	$ 3,872	$ 4,343
Total weighted-average basic shares outstanding	483.5	501.1	511.7	523.5	530.8	540.6	545.6	550.2	504.9	541.8	563.1
Effect of dilutive securities:
Stock options									2.0	2.6	2.7
Other contingently issuable shares									1.3	1.3	1.6
Warrants									1.6	2.3	4.5
Total effect of dilutive securities									4.9	6.2	8.8
Total weighted-average diluted shares outstanding	489.2	505.9	516.5	528.0	536.3	546.3	552.0	557.2	509.8	548.0	571.9
Basic earnings per common share:
Net income from continuing operations (in dollars per share)	$ 1.47	$ 1.94	$ 1.70	$ 1.86	$ 1.58	$ 2.01	$ 1.50	$ 2.00	$ 7.00	$ 7.08	$ 7.70
Income (loss) from discontinued operations (in dollars per share)	0.00	(0.02)	0.00	(0.01)	0.02	(0.01)	0.02	0.03	(0.04)	0.07	0.01
Net income per basic common share (in dollars per share)	1.47	1.92	1.70	1.85	1.60	2.00	1.52	2.03	6.96	7.15	7.71
Diluted earnings per common share:
Net income from continuing operations (in dollars per share)	1.45	1.92	1.69	1.85	1.56	1.99	1.48	1.97	6.93	7.00	7.58
Income (loss) from discontinued operations (in dollars per share)	0.00	(0.02)	0.00	(0.01)	0.02	(0.01)	0.02	0.03	(0.04)	0.07	0.01
Net income per diluted common share (in dollars per share)	$ 1.45	$ 1.90	$ 1.69	$ 1.84	$ 1.58	$ 1.98	$ 1.50	$ 2.00	$ 6.89	$ 7.07	$ 7.59