Common, Preferred and Treasury Stock - Share Activity within Common, Preferred and Treasury Stock (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Value
Beginning balance	$ 21,203	$ 16,250	$ 16,220
Impact of MB Financial, Inc. acquisition		3,356
Shares acquired for treasury		(1,763)	(1,453)
Impact of stock transactions under stock compensation plans, net	82	72	65
Other	0	4	(22)
Ending balance	23,111	21,203	16,250
Common Stock
Value
Beginning balance	2,051	2,051	2,051
Ending balance	$ 2,051	$ 2,051	$ 2,051
Shares
Beginning balance (in shares)	923,892,581	923,892,581	923,892,581
Ending balance (in shares)	923,892,581	923,892,581	923,892,581
Preferred Stock
Value
Beginning balance	$ 1,770	$ 1,331	$ 1,331
Issuance of preferred shares	346	242
Conversion of outstanding preferred stock issued by a Bancorp subsidiary		197
Ending balance	$ 2,116	$ 1,770	$ 1,331
Shares
Beginning balance (in shares)	264,000	54,000	54,000
Issuance of preferred shares (in shares)	14,000	10,000
Conversion of outstanding preferred stock issued by a Bancorp subsidiary (in shares)		200,000
Ending balance (in shares)	278,000	264,000	54,000
Treasury Stock
Value
Beginning balance	$ (5,724)	$ (6,471)	$ (5,002)
Impact of MB Financial, Inc. acquisition		2,447
Shares acquired for treasury		(1,763)	(1,494)
Impact of stock transactions under stock compensation plans, net	46	56	23
Other	2	7	2
Ending balance	$ (5,676)	$ (5,724)	$ (6,471)
Shares
Beginning balance (in shares)	214,976,952	277,261,724	230,087,688
Shares acquired for treasury (in shares)		64,601,891	49,967,134
Impact of MB Financial, Inc. acquisition (in shares)		(122,848,442)
Impact of stock transactions under stock compensation plans, net (in shares)	(3,818,518)	(4,258,132)	(2,698,451)
Other (in shares)	(26,178)	219,911	(94,647)
Ending balance (in shares)	211,132,256	214,976,952	277,261,724