FAIR VALUE MEASUREMENT - Estimate Fair Value of Financial Instruments Not Carried at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Assets
Loans	$ 8,165	$ 8,040
Liabilities
Deposits	1,316,410	1,284,458
Allowance for credit losses	18,726	18,574	$ 18,296	$ 18,145
Loans, net of unearned income	702,056	694,488
Corporate loans
Assets
Loans	7,887	7,759
Liabilities
Allowance for credit losses	2,725	2,556	$ 2,772	$ 2,714
Loans, net of unearned income	315,744	301,386
Lease financing
Liabilities
Loans, net of unearned income	300	300
Carrying value
Assets
HTM debt securities, net of allowance(1)	225,600	247,600
Securities borrowed and purchased under agreements to resell	125,300	133,200
Loans	674,900	667,600
Other financial assets	400,200	362,200
Liabilities
Deposits	1,312,200	1,280,900
Securities loaned and sold under agreements to repurchase	244,100	205,600
Long-term debt	178,400	174,500
Other financial liabilities	145,400	137,700
Allowance for credit losses	18,700	18,600
Estimated fair value
Assets
HTM debt securities, net of allowance(1)	210,500	229,800
Securities borrowed and purchased under agreements to resell	125,300	133,200
Loans	684,500	673,500
Other financial assets	400,200	362,200
Liabilities
Deposits	1,312,200	1,280,900
Securities loaned and sold under agreements to repurchase	244,100	205,600
Long-term debt	181,200	178,000
Other financial liabilities	145,400	137,700
Estimated fair value | Corporate loans
Liabilities
Loans, net of unearned income	7,887	7,759
Estimated fair value | Level 1
Assets
HTM debt securities, net of allowance(1)	101,400	120,200
Securities borrowed and purchased under agreements to resell	0	0
Loans	0	0
Other financial assets	289,300	260,600
Liabilities
Deposits	0	0
Securities loaned and sold under agreements to repurchase	0	0
Long-term debt	0	0
Other financial liabilities	0	0
Estimated fair value | Level 2
Assets
HTM debt securities, net of allowance(1)	106,900	107,400
Securities borrowed and purchased under agreements to resell	125,300	133,200
Loans	0	0
Other financial assets	19,100	15,900
Liabilities
Deposits	1,312,200	1,280,900
Securities loaned and sold under agreements to repurchase	244,100	205,600
Long-term debt	176,100	162,100
Other financial liabilities	28,800	34,700
Estimated fair value | Level 3
Assets
HTM debt securities, net of allowance(1)	2,200	2,200
Securities borrowed and purchased under agreements to resell	0	0
Loans	684,500	673,500
Other financial assets	91,800	85,700
Liabilities
Deposits	0	0
Securities loaned and sold under agreements to repurchase	0	0
Long-term debt	5,100	15,900
Other financial liabilities	116,600	103,000
Estimated fair value | Level 3 | Corporate loans
Fair value measurements additional disclosures
Unfunded lending commitments	$ 10,900	$ 13,500