LOANS - Corporate Loan Delinquency (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 666,348	$ 657,221
Loans at fair value	7,411	5,360
Cumulative basis adjustments	(171)
Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	300	400
Corporate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	894	1,898
Total non-accrual	1,975	1,122
Loans net of unearned income, before adjustments	288,805
Loans, net of unearned income	288,634	289,154
Loans at fair value	7,189	5,123
Cumulative basis adjustments	(171)	0
Corporate loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	585	1,357
Total non-accrual	903	860
Loans net of unearned income, before adjustments	150,395
Loans, net of unearned income		147,803
Corporate loans | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	111	335
Total non-accrual	87	152
Loans net of unearned income, before adjustments	60,146
Loans, net of unearned income		64,907
Corporate loans | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	108	42
Total non-accrual	821	33
Loans net of unearned income, before adjustments	23,861
Loans, net of unearned income		21,949
Corporate loans | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	0	1
Total non-accrual	0	10
Loans net of unearned income, before adjustments	271
Loans, net of unearned income		354
Corporate loans | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	90	163
Total non-accrual	164	67
Loans net of unearned income, before adjustments	46,943
Loans, net of unearned income		49,018
Corporate loans | 30–89 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	586	1,171
Corporate loans | 30–89 days past due | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	402	763
Corporate loans | 30–89 days past due | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	106	233
Corporate loans | 30–89 days past due | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	8	30
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	70	145
Corporate loans | Equal to and greater than 90 days past due and accruing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	308	727
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	183	594
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	5	102
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	100	12
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	1
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	20	18
Corporate loans | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Loans net of unearned income, before adjustments	278,747
Loans, net of unearned income		281,011
Corporate loans | Current | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans net of unearned income, before adjustments	148,907
Loans, net of unearned income		145,586
Corporate loans | Current | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Loans net of unearned income, before adjustments	59,948
Loans, net of unearned income		64,420
Corporate loans | Current | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans net of unearned income, before adjustments	22,932
Loans, net of unearned income		21,874
Corporate loans | Current | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans net of unearned income, before adjustments	271
Loans, net of unearned income		343
Corporate loans | Current | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans net of unearned income, before adjustments	$ 46,689
Loans, net of unearned income		$ 48,788