Parent Company (Statement of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Return on investment in subsidiaries	$ 6,444
Other	684	$ (341)	$ 32
Net cash provided (used) by operating activities	4,659	7,363	7,840
Investing Activities
Other	(1,264)	(705)	(1,684)
Net cash provided (used) by investing activities	(51,122)	(24,990)	(3,969)
Financing Activities
Net change in commercial paper			(100)
Preferred stock redemptions	(480)
Acquisition of treasury stock	(1,624)	(3,578)	(2,877)
Preferred stock cash dividends paid	(229)	(236)	(236)
Common stock cash dividends paid	(1,980)	(1,895)	(1,601)
Net Increase (Decrease) In Cash And Due From Banks And Restricted Cash	1,956	(547)	359
Net cash provided by discontinued operations	11,542	299	264
Net cash provided (used) by continuing operations	(9,586)	(846)	95
Cash and due from banks and restricted cash at beginning of period	5,061	5,608	5,249
Cash and due from banks and restricted cash at end of period	7,017	5,061	5,608
Parent Company
Operating Activities
Net income	7,517	5,369	5,301
Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]
Equity in undistributed net earnings of subsidiaries		(1,363)	(2,307)
Other	237	218	155
Net cash provided (used) by operating activities	14,198	4,224	3,149
Investing Activities
Net change in loans and securities from affiliates	(2,808)	664	540
Net change in nonrestricted interest-earning deposits	7,024	(2,369)	1,145
Other		(8)	2
Net cash provided (used) by investing activities	4,216	(1,713)	1,687
Financing Activities
Net change in other borrowed funds from affiliates	473	228	(29)
Proceeds from long-term borrowings	1,986	4,180	498
Repayments of long-term borrowings	(1,750)	(1,300)	(553)
Net change in commercial paper			(100)
Preferred stock redemptions	(480)
Common and treasury stock issuances	65	90	69
Acquisition of treasury stock	(1,624)	(3,578)	(2,877)
Preferred stock cash dividends paid	(229)	(236)	(236)
Common stock cash dividends paid	(1,979)	(1,895)	(1,603)
Net cash provided (used) by financing activities	(3,538)	(2,511)	(4,831)
Net Increase (Decrease) In Cash And Due From Banks And Restricted Cash	14,876		5
Net cash provided (used) by continuing operations	3,334	(299)	(259)
Cash and due from banks and restricted cash at beginning of period	181	181	176
Cash and due from banks and restricted cash at end of period	$ 15,057	$ 181	$ 181