LOANS - Corporate Loan Delinquency (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 665,988	$ 675,883
Loans at fair value	7,525	6,854
Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	600	700
Corporate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	2,226	2,144
Total non-accrual	3,106	3,527
Total current	379,112	374,533
Loans, net of unearned income	391,954	387,044
Loans at fair value	7,510	6,840
Corporate | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	700	509
Total non-accrual	2,465	2,795
Total current	148,635	153,036
Loans, net of unearned income	151,800	156,340
Corporate | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	1,143	733
Total non-accrual	36	92
Total current	90,339	86,864
Loans, net of unearned income	91,518	87,689
Corporate | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	273	697
Total non-accrual	496	505
Total current	71,373	70,836
Loans, net of unearned income	72,142	72,038
Corporate | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	28	74
Total non-accrual	27	24
Total current	540	640
Loans, net of unearned income	595	738
Corporate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	82	131
Total non-accrual	82	111
Total current	68,225	63,157
Loans, net of unearned income	68,389	63,399
Corporate | 30 to 89 Days Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	1,838	1,692
Corporate | 30 to 89 Days Past Due | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	582	400
Corporate | 30 to 89 Days Past Due | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	969	668
Corporate | 30 to 89 Days Past Due | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	189	450
Corporate | 30 to 89 Days Past Due | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	28	62
Corporate | 30 to 89 Days Past Due | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	70	112
Corporate | Equal to and greater than 90 days past due and accruing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	388	452
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	118	109
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	174	65
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	84	247
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	12
Corporate | Equal to and greater than 90 days past due and accruing | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	$ 12	$ 19