Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Preferred Shares [Member]	Common Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]	Series B Preferred Stock [Member]	Series B Preferred Stock [Member] Retained Earnings [Member]	Series C Preferred Stock [Member]	Series C Preferred Stock [Member] Retained Earnings [Member]
Beginning Balance at Dec. 31, 2018	$ 22,290	$ 0	$ 170	$ 12,218	$ (2,597)	$ 12,499
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,550					1,550
Other comprehensive loss	(2)				(2)	0
Repurchase of common shares	(1,245)		(3)	(267)		(975)
Other changes, primarily employee plans	(27)		1	12		(40)
Cash dividends declared preferred									$ (21)	$ (21)
Cash dividends declared common	(327)					(327)
Ending Balance at Mar. 31, 2019	22,218	0	168	11,963	(2,599)	12,686
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock, dividend per share (in dollars per share)									$ 24.50
Beginning Balance at Dec. 31, 2019	23,071	0	163	11,774	(2,737)	13,871
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of new accounting guidance, net of tax | Accounting Standards Update 2016-13 [Member]	1,170
Impact of new accounting guidance, tax | Accounting Standards Update 2016-13 [Member]	288
Beginning Balance at Dec. 31, 2019	23,071	0	163	11,774	(2,737)	13,871
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	367					367
Other comprehensive loss	(259)				(259)	0
Repurchase of common shares	(875)		(2)	(105)		(768)
Other changes, primarily employee plans	(36)		0	11		(47)
Cash dividends declared preferred							$ (11)	$ (11)	$ (21)	$ (21)
Cash dividends declared common	(348)					(348)
Ending Balance at Mar. 31, 2020	21,006	$ 0	$ 161	$ 11,680	$ (2,996)	$ 12,161
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Preferred stock, dividend per share (in dollars per share)							$ 14.09		$ 24.50
Cumulative effect of change in accounting principle - Reserve for Credit Losses	$ (882)