Consolidated Statements of Shareholders' Equity - USD ($) $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	[1]	Preferred Shares	Common Shares	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Series B Preferred Stock	Series B Preferred Stock Retained Earnings	Series C Preferred Stock	Series C Preferred Stock Retained Earnings
Beginning Balance at Dec. 31, 2019	$ 23,071	$ (882)		$ 0	$ 163	$ 11,774	$ (2,737)	$ 13,871
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	624							624
Other comprehensive income (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]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
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 income (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
Beginning Balance at Dec. 31, 2020	22,984			0	161	11,881	(2,895)	13,837
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	4,515							4,515
Other comprehensive income (loss)	14						14	0
Repurchase of common shares	(1,346)				(2)	(134)		(1,210)
Other changes, primarily employee plans	94				1	111		(18)
Cash dividends declared preferred									(14)	(14)	(15)	(15)
Cash dividends declared common	(693)							(693)
Ending Balance at Jun. 30, 2021	25,539			0	160	11,858	(2,881)	16,402
Beginning Balance at Mar. 31, 2021	24,449			0	161	11,878	(2,898)	15,308
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,280							2,280
Other comprehensive income (loss)	17						17	0
Repurchase of common shares	(908)				(1)	(85)		(822)
Other changes, primarily employee plans	62					65		(3)
Cash dividends declared preferred									$ (7)	$ (7)	$ (8)	$ (8)
Cash dividends declared common	(346)							(346)
Ending Balance at Jun. 30, 2021	$ 25,539			$ 0	$ 160	$ 11,858	$ (2,881)	$ 16,402

[1] Represents $1,170 million, net of tax of $288 million, related to the impact as of January 1, 2020 of adopting the current expected credit loss methodology for the recognition of credit losses on certain financial instruments.