Parent Company Financial Statements - Condensed Statement of Cash Flow - Parent Company Only (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Activities
Net Income	$ 2,349	$ 2,446	$ 2,770
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, amortization and accretion	462	436	349
Provision for (benefit from) deferred income taxes	(106)	(60)	(14)
Securities (gains) losses, net	(31)	84	16
Equity in undistributed earnings	(52)	(22)	(30)
Net change in:
Equity securities	(128)	70	15
Other assets	326	646	(37)
Net Cash Provided by Operating Activities	4,509	6,428	2,704
Investing Activities
Proceeds from maturities of securities issued by subsidiary	4,235	4,495	6,079
Other short-term investments	(13,731)	26,224	(1,172)
Net Cash Used in Investing Activities	(9,488)	(4,871)	(7,968)
Financing Activities
Proceeds from long-term debt issuances/advances	4,286	4,026	562
Repayment of long-term debt	(1,657)	(1,762)	(3,603)
Dividends paid on common and preferred stock	(1,060)	(927)	(897)
Repurchase of treasury stock and related forward contract	(200)	(100)	(1,393)
Other, net	(55)	(85)	(99)
Net Cash Provided by (Used in) Financing Activities	4,655	(1,085)	5,111
(Decrease) Increase in Cash and Due from Banks	(324)	472	(153)
Parent Company
Operating Activities
Net Income	2,349	2,446	2,770
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, amortization and accretion	7	7	7
Provision for (benefit from) deferred income taxes	1	(3)	(1)
Securities (gains) losses, net	(4)	9	(1)
Equity in undistributed earnings	(915)	(2,533)	64
Net change in:
Equity securities	4	6	1
Other assets	147	(115)	(40)
Accrued expenses and other liabilities	(126)	45	(80)
Net Cash Provided by Operating Activities	1,463	(138)	2,720
Investing Activities
Proceeds from maturities of securities issued by subsidiary	1,000	0	0
Purchase of securities issued by subsidiary	(1,000)	(1,000)	0
Other short-term investments	(833)	567	(656)
Loans to nonbank subsidiaries	60	132	158
Net Cash Used in Investing Activities	(773)	(301)	(498)
Financing Activities
Net change in other short-term borrowings	(121)	(240)	(89)
Proceeds from long-term debt issuances/advances	1,244	2,986	498
Repayment of long-term debt	(500)	(1,200)	(250)
Dividends paid on common and preferred stock	(1,060)	(927)	(897)
Repurchase of treasury stock and related forward contract	(200)	(100)	(1,393)
Other, net	(53)	(82)	(89)
Net Cash Provided by (Used in) Financing Activities	(690)	437	(2,220)
(Decrease) Increase in Cash and Due from Banks	0	(2)	2
Cash and Due from Banks at Beginning of Period	120	122	120
Cash and Due from Banks at End of Period	$ 120	$ 120	$ 122