CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (USD $) In Millions, except Share data, unless otherwise specified	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance at Dec. 31, 2012	$ 40,425		$ 6	$ 26,188	$ 16,779	$ 739	$ (3,287)
Beginning balance (shares) at Dec. 31, 2012			631,806,585
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	2,510				4,121	(1,611)
Cash dividends—common stock	(555)				(555)
Cash dividends - preferred series	(53)				(53)
Purchases of treasury stock	(1,033)						(1,033)
Issuances of common stock and restricted stock, net of forfeitures (in shares)			3,049,705
Issuances of common stock and restricted stock, net of forfeitures	81		0	81
Exercise of stock options and warrants, tax benefits of exercises and restricted stock vesting (in shares)			2,295,510
Exercise of stock options and warrants, tax benefits of exercises and restricted stock vesting	114		0	114
Compensation expense for restricted stock awards and stock options	143			143
Ending balance at Dec. 31, 2013	41,632		6	26,526	20,292	(872)	(4,320)
Ending balance (shares) at Dec. 31, 2013			637,151,800
Beginning balance at Dec. 31, 2011	29,617	0	5	19,274	13,413	169	(3,244)
Beginning balance (shares) at Dec. 31, 2011		0	508,594,308
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	4,062				3,492	570
Cash dividends—common stock	(111)				(111)
Cash dividends - preferred series	(15)				(15)
Purchases of treasury stock	(43)						(43)
Issuances of common stock and restricted stock, net of forfeitures (in shares)			67,368,854
Issuances of common stock and restricted stock, net of forfeitures	3,233		0	3,233
Issuance of common stock related to acquisition (in shares)			54,028,086
Issuance of common stock related to acquisition	2,638		1	2,637
Exercise of stock options and warrants, tax benefits of exercises and restricted stock vesting (in shares)			1,815,337
Exercise of stock options and warrants, tax benefits of exercises and restricted stock vesting	80		0	80
Issuances of preferred stock (in shares)		875,000
Issuance of preferred stock	853	0		853
Compensation expense for restricted stock awards and stock options	111			111
Ending balance at Dec. 31, 2012	40,425	0	6	26,188	16,779	739	(3,287)
Ending balance (shares) at Dec. 31, 2012		875,000	631,806,585
Beginning balance at Dec. 31, 2013	41,632	0	6	26,526	20,292	(872)	(4,320)
Beginning balance (shares) at Dec. 31, 2013		875,000	637,151,800
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	4,870				4,428	442
Cash dividends—common stock	(680)				(680)
Cash dividends - preferred series	(67)				(67)
Purchases of treasury stock	(2,045)						(2,045)
Issuances of common stock and restricted stock, net of forfeitures (in shares)			1,373,725
Issuances of common stock and restricted stock, net of forfeitures	100		0	100
Exercise of stock options and warrants, tax benefits of exercises and restricted stock vesting (in shares)			5,031,523
Exercise of stock options and warrants, tax benefits of exercises and restricted stock vesting	146		0	146
Issuances of preferred stock (in shares)		1,000,000
Issuance of preferred stock	969	0		969
Compensation expense for restricted stock awards and stock options	128			128
Ending balance at Dec. 31, 2014	$ 45,053	$ 0	$ 6	$ 27,869	$ 23,973	$ (430)	$ (6,365)
Ending balance (shares) at Dec. 31, 2014		1,875,000	643,557,048