Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Cumulative effect of change in accounting principle - Reserve for Credit Losses	Preferred Shares [Member]	Common Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]	Retained Earnings [Member] Cumulative effect of change in accounting principle - Reserve for Credit Losses	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	3,311						3,311
Other comprehensive loss	(9)					(9)	0
Repurchase of common shares	(1,875)			(4)	(347)		(1,524)
Other changes, primarily employee plans	69			1	109		(41)
Cash dividends declared preferred									$ (19)	$ (19)	$ (21)	$ (21)
Cash dividends declared common	(654)						(654)
Ending Balance at Jun. 30, 2019	23,092		0	167	11,980	(2,606)	13,551
Beginning Balance at Mar. 31, 2019	22,218		0	168	11,963	(2,599)	12,686
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,761						1,761
Other comprehensive loss	(7)					(7)	0
Repurchase of common shares	(630)			(1)	(80)		(549)
Other changes, primarily employee plans	96				97		(1)
Cash dividends declared preferred									(19)	(19)
Cash dividends declared common	(327)						(327)
Ending Balance at Jun. 30, 2019	23,092		0	167	11,980	(2,606)	13,551
Beginning Balance at Dec. 31, 2019	$ 23,071	$ (882)	0	163	11,774	(2,737)	13,871	$ (882)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Ending Balance at Jan. 01, 2020								(882)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of new accounting guidance, tax		288
Beginning Balance at Dec. 31, 2019	$ 23,071	(882)	0	163	11,774	(2,737)	13,871	$ (882)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	624						624
Other comprehensive loss	(174)					(174)	0
Repurchase of common shares	(875)			(2)	(105)		(768)
Other changes, primarily employee plans	43				91		(48)
Cash dividends declared preferred									(20)	(20)	(29)	(29)
Cash dividends declared common	(696)						(696)
Ending Balance at Jun. 30, 2020	21,062		0	161	11,760	(2,911)	12,052
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Impact of new accounting guidance, net of tax		$ 1,170
Beginning Balance at Mar. 31, 2020	21,006		0	161	11,680	(2,996)	12,161
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	257						257
Other comprehensive loss	85					85	0
Other changes, primarily employee plans	79				80		(1)
Cash dividends declared preferred									$ (9)	$ (9)	$ (8)	$ (8)
Cash dividends declared common	(348)						(348)
Ending Balance at Jun. 30, 2020	$ 21,062		$ 0	$ 161	$ 11,760	$ (2,911)	$ 12,052