LOANS - Corporate Loan Delinquency (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 676,834	$ 675,883
Loans held at fair value	7,707	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	2,305	2,144
Total non-accrual	2,576	3,527
Loans, net of unearned income	400,939	387,044
Loans held at fair value	7,693	6,840
Corporate | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	939	509
Total non-accrual	1,878	2,795
Loans, net of unearned income	152,134	156,340
Corporate | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	801	733
Total non-accrual	39	92
Loans, net of unearned income	100,989	87,689
Corporate | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	231	697
Total non-accrual	458	505
Loans, net of unearned income	73,156	72,038
Corporate | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	26	74
Total non-accrual	22	24
Loans, net of unearned income	602	738
Corporate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	308	131
Total non-accrual	179	111
Loans, net of unearned income	66,365	63,399
Corporate | 30 to 89 Days Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	1,602	1,692
Corporate | 30 to 89 Days Past Due | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	818	400
Corporate | 30 to 89 Days Past Due | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	477	668
Corporate | 30 to 89 Days Past Due | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	210	450
Corporate | 30 to 89 Days Past Due | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	26	62
Corporate | 30 to 89 Days Past Due | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	71	112
Corporate | Equal to and greater than 90 days past due and accruing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	703	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	121	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	324	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	21	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	237	19
Corporate | Current
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	388,365	374,533
Corporate | Current | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	149,317	153,036
Corporate | Current | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	100,149	86,864
Corporate | Current | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	72,467	70,836
Corporate | Current | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	554	640
Corporate | Current | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 65,878	$ 63,157