LOANS - Corporate Loan Delinquency (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 674,578	$ 689,362
Loans at fair value	8,854	7,594
Unallocated portfolio layer cumulative basis adjustments	(113)	93
Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	300	300
Corporate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	543	594
Total non-accrual	1,489	1,882
Loans net of unearned income, before adjustments	292,822	300,072
Loans, net of unearned income	292,819	300,165
Loans at fair value	8,551	7,281
Unallocated portfolio layer cumulative basis adjustments	(3)	93
Corporate loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	424	426
Total non-accrual	551	717
Loans net of unearned income, before adjustments	148,028
Loans, net of unearned income		151,451
Corporate loans | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	20	16
Total non-accrual	43	51
Loans net of unearned income, before adjustments	64,096
Loans, net of unearned income		65,060
Corporate loans | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	35	69
Total non-accrual	811	868
Loans net of unearned income, before adjustments	25,146
Loans, net of unearned income		24,938
Corporate loans | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	0	0
Total non-accrual	0	0
Loans net of unearned income, before adjustments	274
Loans, net of unearned income		275
Corporate loans | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	64	83
Total non-accrual	84	246
Loans net of unearned income, before adjustments	46,727
Loans, net of unearned income		51,067
Corporate loans | 30–89 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	370	449
Corporate loans | 30–89 days past due | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	306	308
Corporate loans | 30–89 days past due | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	11	9
Corporate loans | 30–89 days past due | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	4	66
Corporate loans | 30–89 days past due | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	0	0
Corporate loans | 30–89 days past due | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	49	66
Corporate loans | Equal to and greater than 90 days past due and accruing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	173	145
Corporate loans | Equal to and greater than 90 days past due and accruing | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	118	118
Corporate loans | Equal to and greater than 90 days past due and accruing | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	9	7
Corporate loans | Equal to and greater than 90 days past due and accruing | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	31	3
Corporate loans | Equal to and greater than 90 days past due and accruing | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	0	0
Corporate loans | Equal to and greater than 90 days past due and accruing | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	15	17
Corporate loans | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Loans net of unearned income, before adjustments	282,239
Loans, net of unearned income		290,315
Corporate loans | Current | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans net of unearned income, before adjustments	147,053
Loans, net of unearned income		150,308
Corporate loans | Current | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Loans net of unearned income, before adjustments	64,033
Loans, net of unearned income		64,993
Corporate loans | Current | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans net of unearned income, before adjustments	24,300
Loans, net of unearned income		24,001
Corporate loans | Current | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans net of unearned income, before adjustments	274
Loans, net of unearned income		275
Corporate loans | Current | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans net of unearned income, before adjustments	$ 46,579
Loans, net of unearned income		$ 50,738