LOANS - Corporate Loan Delinquency (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 659,669	$ 667,767
Loans held at fair value	5,732	6,082
Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	400	500
Corporate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	2,390	1,895
Total non-accrual	1,866	1,553
Loans, net of unearned income	309,341	291,233
Loans held at fair value	5,722	6,070
Corporate | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	1,563	1,311
Total non-accrual	1,519	1,263
Loans, net of unearned income	163,361	147,004
Corporate | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	591	486
Total non-accrual	52	2
Loans, net of unearned income	75,242	71,767
Corporate | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	150	2
Total non-accrual	119	136
Loans, net of unearned income	22,190	20,291
Corporate | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	0	0
Total non-accrual	15	14
Loans, net of unearned income	426	455
Corporate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	86	96
Total non-accrual	161	138
Loans, net of unearned income	42,400	45,646
Corporate | 30 to 89 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	1,403	1,470
Corporate | 30 to 89 days past due | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	932	1,072
Corporate | 30 to 89 days past due | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	380	320
Corporate | 30 to 89 days past due | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	50	1
Corporate | 30 to 89 days past due | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	0	0
Corporate | 30 to 89 days past due | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	41	77
Corporate | Equal to and greater than 90 days past due and accruing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	987	425
Corporate | 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	631	239
Corporate | Equal to and greater than 90 days past due and accruing | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	211	166
Corporate | 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	1
Corporate | 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 | Equal to and greater than 90 days past due and accruing | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	45	19
Corporate | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	299,363	281,715
Corporate | Current | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	160,279	144,430
Corporate | Current | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	74,599	71,279
Corporate | Current | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	21,921	20,153
Corporate | Current | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	411	441
Corporate | Current | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 42,153	$ 45,412