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	Series D Preferred Stock	Series D 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	1,697							1,697
Other comprehensive income (loss)	(135)						(135)	0
Repurchase of common shares	(875)				(2)	(105)		(768)
Other changes, primarily employee plans	102					149		(47)
Cash dividends declared preferred									$ (27)	$ (27)	$ (38)	$ (38)
Cash dividends declared common	(1,044)							(1,044)
Ending Balance at Sep. 30, 2020	21,869			0	161	11,818	(2,872)	12,762
Beginning Balance at Jun. 30, 2020	21,062			0	161	11,760	(2,911)	12,052
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,073							1,073
Other comprehensive income (loss)	39						39	0
Other changes, primarily employee plans	59					58		1
Cash dividends declared preferred									(7)	(7)	(9)	(9)
Cash dividends declared common	(348)							(348)
Ending Balance at Sep. 30, 2020	21,869			0	161	11,818	(2,872)	12,762
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	6,341							6,341
Other comprehensive income (loss)	(68)						(68)
Preferred shares issued	1,584					1,584
Redemption of preferred shares	(850)					(841)		(9)
Repurchase of common shares	(4,646)				(6)	(400)		(4,240)
Other changes, primarily employee plans	160				1	177		(18)
Cash dividends declared preferred									(21)	(21)	(22)	(22)	$ (6)	$ (6)
Cash dividends declared common	(1,030)							(1,030)
Ending Balance at Sep. 30, 2021	24,426			0	156	12,401	(2,963)	14,832
Beginning Balance at Jun. 30, 2021	25,539			0	160	11,858	(2,881)	16,402
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,826							1,826
Other comprehensive income (loss)	(82)						(82)
Preferred shares issued	1,584					1,584
Redemption of preferred shares	(850)					(841)		(9)
Repurchase of common shares	(3,300)				(4)	(266)		(3,030)
Other changes, primarily employee plans	66					66
Cash dividends declared preferred									$ (7)	$ (7)	$ (7)	$ (7)	$ (6)	$ (6)
Cash dividends declared common	(337)							(337)
Ending Balance at Sep. 30, 2021	$ 24,426			$ 0	$ 156	$ 12,401	$ (2,963)	$ 14,832

[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.