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	Cumulative effects from adoption of new accounting standards	Cumulative effects from adoption of new accounting standards Retained Earnings	Cumulative effects from adoption of new accounting standards Accumulated Other Comprehensive Income (Loss)
Beginning balance (shares) at Dec. 31, 2019			4,975,000	672,969,391
Beginning balance at Dec. 31, 2019		$ 58,011	$ 0	$ 7	$ 32,980	$ 40,340	$ 1,156	$ (16,472)	$ (2,192)	$ (2,184)	$ (8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income		1,191				(1,340)	2,531
Dividends, common stock (shares)	[1]			23,213
Dividends, common stock	[1]	(185)		$ 0	2	(187)
Dividends, preferred stock		(55)				(55)
Purchases of treasury stock		(386)						(386)
Issuances of common stock and restricted stock, net of forfeitures (shares)				2,618,628
Issuances of common stock and restricted stock, net of forfeitures		63		$ 0	63
Exercises of stock options (shares)				559,333
Exercises of stock options		20		$ 0	20
Issuances of preferred stock (shares)			1,250,000
Issuances of preferred stock		1,209	$ 0		1,209
Redemptions of preferred stock (shares)			(875,000)
Redemptions of preferred stock		(875)	$ 0		(853)	(22)
Compensation expense for restricted stock units and stock options		29			29
Ending balance (shares) at Mar. 31, 2020			5,350,000	676,170,565
Ending balance at Mar. 31, 2020		56,830	$ 0	$ 7	33,450	36,552	3,679	(16,858)
Beginning balance (shares) at Dec. 31, 2020			4,975,000	679,932,837
Beginning balance at Dec. 31, 2020		60,204	$ 0	$ 7	33,480	40,088	3,494	(16,865)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income		1,614				3,325	(1,711)
Dividends, common stock (shares)	[1]			13,356
Dividends, common stock	[1]	(184)		$ 0	1	(185)
Dividends, preferred stock		(61)				(61)
Purchases of treasury stock		(575)						(575)
Issuances of common stock and restricted stock, net of forfeitures (shares)				2,531,966
Issuances of common stock and restricted stock, net of forfeitures		60		$ 0	60
Exercises of stock options (shares)				283,398
Exercises of stock options		19		$ 0	19
Compensation expense for restricted stock units and stock options		111			111
Ending balance (shares) at Mar. 31, 2021			4,975,000	682,761,557
Ending balance at Mar. 31, 2021		$ 61,188	$ 0	$ 7	$ 33,671	$ 43,167	$ 1,783	$ (17,440)

[1] We declared dividends per share on our common stock of 0.40 in both the first quarters of 2021 and 2020.