LOANS - Corporate Loans (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) category	Dec. 31, 2022 USD ($)
Loans and Leases Receivable Disclosure [Abstract]
Number of loan categories | category	2
Loans
Loans, net of unearned income	$ 689,362	$ 657,221
Unallocated portfolio layer cumulative basis adjustments	$ 93
Accrued interest receivable, location	Other assets	Other assets
Lease financing
Loans
Loans, net of unearned income	$ 300	$ 400
Corporate
Loans
Loans, net of unearned income	300,165	289,154
Corporate loans, net of unearned income, excluding portfolio layer cumulative basis adjustments	300,072	289,154
Unallocated portfolio layer cumulative basis adjustments	93	0
Unearned income	(917)	(797)
Accrued interest receivable	2,000	2,000
Loans sold and/or reclassified to held-for-sale	5,700	5,000
Corporate | Commercial and industrial
Loans
Loans, net of unearned income	151,451	147,803
Corporate | Financial institutions
Loans
Loans, net of unearned income	65,060	64,907
Corporate | Mortgage and real estate
Loans
Loans, net of unearned income	24,938	21,949
Corporate | Lease financing
Loans
Loans, net of unearned income	275	354
In U.S. offices | Corporate
Loans
Loans, net of unearned income	141,776	141,479
In U.S. offices | Corporate | Commercial and industrial
Loans
Loans, net of unearned income	61,008	56,176
In U.S. offices | Corporate | Financial institutions
Loans
Loans, net of unearned income	39,393	43,399
In U.S. offices | Corporate | Mortgage and real estate
Loans
Loans, net of unearned income	17,813	17,829
In U.S. offices | Corporate | Installment and other
Loans
Loans, net of unearned income	23,335	23,767
In U.S. offices | Corporate | Lease financing
Loans
Loans, net of unearned income	227	308
In offices outside the U.S. | Corporate
Loans
Loans, net of unearned income	158,296	147,675
In offices outside the U.S. | Corporate | Commercial and industrial
Loans
Loans, net of unearned income	93,402	93,967
In offices outside the U.S. | Corporate | Financial institutions
Loans
Loans, net of unearned income	26,143	21,931
In offices outside the U.S. | Corporate | Mortgage and real estate
Loans
Loans, net of unearned income	7,197	4,179
In offices outside the U.S. | Corporate | Installment and other
Loans
Loans, net of unearned income	27,907	23,347
In offices outside the U.S. | Corporate | Lease financing
Loans
Loans, net of unearned income	48	46
In offices outside the U.S. | Corporate | Governments and official institutions
Loans
Loans, net of unearned income	$ 3,599	$ 4,205