Parent Company Financial Statements - Condensed Statement of Cash Flow - Parent Company Only (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating Activities
Net Income	$ 1,427	$ 2,512	$ 2,193
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for (benefit from) deferred income taxes	(162)	(246)	30
Equity in undistributed earnings	0	(2)	(1)
Net change in:
Equity securities	12	(29)	132
Other assets	(855)	20	303
Net Cash Provided by Operating Activities	371	1,824	2,856
Investing Activities
Other short-term investments and federal funds sold	(31,446)	(612)	928
Net Cash Used in Investing Activities	(31,902)	(797)	(4,141)
Financing Activities
Dividends paid on common and preferred stock	(858)	(753)	(565)
Proceeds from issuance of long-term debt	2,557	3,866	2,438
Repayment of long-term debt	(2,799)	(4,212)	(2,884)
Issuance of preferred stock	346	242	0
Repurchase of treasury stock and related forward contract	0	(1,763)	(1,453)
Other, net	(47)	(58)	(69)
Net Cash Provided by (Used in) Financing Activities	31,400	(430)	1,452
Cash and Due from Banks at Beginning of Period	3,278	2,681	2,514
Cash and Due from Banks at End of Period	3,147	3,278	2,681
Parent Company
Operating Activities
Net Income	1,427	2,512	2,193
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization and accretion	7	7	4
Provision for (benefit from) deferred income taxes	0	(11)	3
Securities gains, net	(1)	(2)	0
Equity in undistributed earnings	(351)	(594)	(474)
Net change in:
Equity securities	0	(49)	0
Other assets	(1)	(80)	61
Accrued expenses and other liabilities	0	127	(120)
Net Cash Provided by Operating Activities	1,081	1,910	1,667
Investing Activities
Other short-term investments and federal funds sold	(855)	(1,081)	(149)
Loans to nonbank subsidiaries	94	127	272
Net cash paid on acquisition	0	(469)	0
Net Cash Used in Investing Activities	(761)	(1,423)	123
Financing Activities
Net change in other short-term borrowings	91	106	(62)
Dividends paid on common and preferred stock	(858)	(753)	(565)
Proceeds from issuance of long-term debt	1,243	2,235	895
Repayment of long-term debt	(1,100)	(500)	(500)
Issuance of preferred stock	346	242	0
Repurchase of treasury stock and related forward contract	0	(1,763)	(1,453)
Other, net	(40)	(56)	(65)
Net Cash Provided by (Used in) Financing Activities	(318)	(489)	(1,750)
Increase (Decrease) in Cash	2	(2)	40
Cash and Due from Banks at Beginning of Period	118	120	80
Cash and Due from Banks at End of Period	$ 120	$ 118	$ 120