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	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	[1]	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	$ (882)
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)					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
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	2,235							2,235
Other comprehensive loss	(3)						(3)	0
Repurchase of common shares	(438)				(1)	(49)		(388)
Other changes, primarily employee plans	32				1	46		(15)
Cash dividends declared preferred											$ (7)	$ (7)	$ (7)	$ (7)
Cash dividends declared common	(347)							(347)
Ending Balance at Mar. 31, 2021	$ 24,449			$ 0	$ 161	$ 11,878	$ (2,898)	$ 15,308

[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.