CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (unaudited) - USD ($) $ in Millions	Total	Series I Preferred Stock	Series J Preferred Stock	Series K Preferred Stock	Series L Preferred Stock	Class B, Series A Preferred Stock	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, Adjusted Balance	Common Stock	Preferred Stock	Capital Surplus	Retained Earnings	Retained Earnings Series I Preferred Stock	Retained Earnings Series J Preferred Stock	Retained Earnings Series K Preferred Stock	Retained Earnings Series L Preferred Stock	Retained Earnings Class B, Series A Preferred Stock	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Retained Earnings Cumulative Effect, Period of Adoption, Adjusted Balance	Accumulated Other Comprehensive Income	Treasury Stock
Beginning Balance at Dec. 31, 2019	$ 21,203						$ (472)	$ 20,731	$ 2,051	$ 1,770	$ 3,599	$ 18,315						$ (472)	$ 17,843	$ 1,192	$ (5,724)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	46											46
Other comprehensive income (loss), net of tax	1,285																			1,285
Cash dividends declared:
Common stock	(195)											(195)
Preferred stock		$ (7)	$ (4)	$ (3)		$ (3)							$ (7)	$ (4)	$ (3)		$ (3)
Impact of stock transactions under stock compensation plans, net	23										(2)										25
Ending Balance at Mar. 31, 2020	21,873								2,051	1,770	3,597	17,677								2,477	(5,699)
Beginning Balance at Dec. 31, 2020	23,111								2,051	2,116	3,635	18,384								2,601	(5,676)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	694											694
Other comprehensive income (loss), net of tax	(809)																			(809)
Cash dividends declared:
Common stock	(195)											(195)
Preferred stock		$ (7)	$ (3)	$ (3)	$ (4)	$ (3)							$ (7)	$ (3)	$ (3)	$ (4)	$ (3)
Shares acquired for treasury	(180)																				(180)
Impact of stock transactions under stock compensation plans, net	(6)										(43)										37
Ending Balance at Mar. 31, 2021	$ 22,595								$ 2,051	$ 2,116	$ 3,592	$ 18,863								$ 1,792	$ (5,819)