CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance at Dec. 31, 2014	$ 45,053	$ 0	$ 6	$ 27,869	$ 23,973	$ (430)	$ (6,365)
Beginning balance (shares) at Dec. 31, 2014		1,875,000	643,557,048
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	3,864				4,050	(186)
Common Stock Dividends, Shares			46,846
Dividends, Common Stock	(816)		$ 0		(820)
Dividends, Share-based Compensation, Stock				4
Cash dividends - preferred series	(158)				(158)
Purchases of treasury stock	(2,441)						(2,441)
Issuances of common stock and restricted stock, shares, net of forfeitures			2,603,953
Issuances of common stock and restricted stock, value, net of forfeitures	111		$ 0	111
Exercise of stock options and warrants, tax effects of exercises and restricted stock vesting, shares			2,109,548
Exercise of stock options and warrants, tax effects of exercises and restricted stock vesting, value	71		$ 0	71
Stock Issued During Period, Shares, New Issues		1,500,000
Stock Issued During Period, Value, New Issues	1,472	$ 0		1,472
Compensation expense for restricted stock awards, restricted stock units and stock options	128			128
Ending balance at Dec. 31, 2015	47,284	$ 0	$ 6	29,655	27,045	(616)	(8,806)
Ending balance (shares) at Dec. 31, 2015		3,375,000	648,317,395
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	3,418				3,751	(333)
Common Stock Dividends, Shares			52,338
Dividends, Common Stock	(812)		$ 0		(816)
Dividends, Share-based Compensation, Stock				4
Cash dividends - preferred series	(214)				(214)
Purchases of treasury stock	(3,661)						(3,661)
Issuances of common stock and restricted stock, shares, net of forfeitures			3,272,745
Issuances of common stock and restricted stock, value, net of forfeitures	131		$ 1	130
Exercise of stock options and warrants, tax effects of exercises and restricted stock vesting, shares			2,094,129
Exercise of stock options and warrants, tax effects of exercises and restricted stock vesting, value	102		$ 0	102
Stock Issued During Period, Shares, New Issues		1,100,000
Stock Issued During Period, Value, New Issues	1,066	$ 0		1,066
Compensation expense for restricted stock awards, restricted stock units and stock options	200			200
Ending balance at Dec. 31, 2016	47,514	$ 0	$ 7	31,157	29,766	(949)	(12,467)
Ending balance (shares) at Dec. 31, 2016		4,475,000	653,736,607
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	2,005				1,982	23
Common Stock Dividends, Shares			42,613
Dividends, Common Stock	(780)		$ 0		(783)
Dividends, Share-based Compensation, Stock				3
Cash dividends - preferred series	(265)				(265)
Purchases of treasury stock	(240)						(240)
Issuances of common stock and restricted stock, shares, net of forfeitures			4,057,555
Issuances of common stock and restricted stock, value, net of forfeitures	164		$ 0	164
Exercise of stock options and warrants, tax effects of exercises and restricted stock vesting, shares			3,888,152
Exercise of stock options and warrants, tax effects of exercises and restricted stock vesting, value	124		$ 0	124
Compensation expense for restricted stock awards, restricted stock units and stock options	208			208
Ending balance at Dec. 31, 2017	$ 48,730	$ 0	$ 7	$ 31,656	$ 30,700	$ (926)	$ (12,707)
Ending balance (shares) at Dec. 31, 2017		4,475,000	661,724,927