Common, Preferred and Treasury Stock (Share Acitivity within Common, Preferred and Treasury Stock) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Values
Beginning Balance	$ 16,250	$ 16,220	$ 16,081
Issuance of preferred shares, Series K	1,770	1,331
Impact of MB Financial, Inc. acquisition	3,356
Shares acquired for treasury	(1,763)	(1,453)	(1,605)
Impact of stock transactions under stock compensation plans, net	72	65	67
Other	4	(22)	(6)
Ending Balance	21,203	16,250	16,220
Common Stock
Values
Beginning Balance	2,051	2,051	2,051
Ending Balance	$ 2,051	$ 2,051	$ 2,051
Shares
Beginning balance	923,892,581	923,892,581	923,892,581
Ending balance	923,892,581	923,892,581	923,892,581
Preferred Stock
Values
Beginning Balance	$ 1,331	$ 1,331	$ 1,331
Conversion of outstanding preferred stock	197
Ending Balance	$ 1,770	$ 1,331	$ 1,331
Shares
Beginning balance	54,000	54,000	54,000
Conversion of outstanding preferred stock	200,000
Ending balance	264,000	54,000	54,000
Treasury Stock
Values
Beginning Balance	$ (6,471)	$ (5,002)	$ (3,433)
Impact of MB Financial, Inc. acquisition	2,447
Shares acquired for treasury	(1,763)	(1,494)	(1,588)
Impact of stock transactions under stock compensation plans, net	56	23	16
Other	7	2	3
Ending Balance	$ (5,724)	$ (6,471)	$ (5,002)
Shares
Beginning balance	277,261,724	230,087,688	173,413,282
Shares acquired for treasury	64,601,891	49,967,134	58,493,506
Impact of MB Financial, Inc. acquisition	(122,848,442)
Impact of stock transactions under stock compensation plans, net	(4,258,132)	(2,698,451)	(1,693,503)
Other	219,911	(94,647)	(125,597)
Ending balance	214,976,952	277,261,724	230,087,688
Preferred Stock Series K
Values
Issuance of preferred shares, Series K	$ 242
Shares
Issuance of preferred shares, Series K	10,000