LOANS - Corporate Loan Delinquency (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 666,911	$ 699,483
Loans at fair value	5,524	4,085
Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	800	1,400
Corporate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	2,254	2,380
Total non-accrual	3,584	2,188
Total current	375,538	381,300
Loans, net of unearned income	386,886	389,935
Loans at fair value	$ 5,510	4,067
Number of days past due, non-accrual status	90 days
Loans less than this number of days past due are considered current	30 days
Corporate | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	$ 705	769
Total non-accrual	2,784	1,828
Total current	161,546	164,249
Loans, net of unearned income	165,035	166,846
Corporate | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	489	794
Total non-accrual	165	50
Total current	84,259	91,008
Loans, net of unearned income	84,913	91,852
Corporate | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	775	538
Total non-accrual	486	188
Total current	68,500	62,425
Loans, net of unearned income	69,761	63,151
Corporate | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	34	67
Total non-accrual	37	41
Total current	696	1,277
Loans, net of unearned income	767	1,385
Corporate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	251	212
Total non-accrual	112	81
Total current	60,537	62,341
Loans, net of unearned income	60,900	62,634
Corporate | 30 to 89 Days Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	1,909	2,249
Corporate | 30 to 89 Days Past Due | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	648	676
Corporate | 30 to 89 Days Past Due | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	405	791
Corporate | 30 to 89 Days Past Due | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	641	534
Corporate | 30 to 89 Days Past Due | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	18	58
Corporate | 30 to 89 Days Past Due | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	197	190
Corporate | Equal to and greater than 90 days past due and accruing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	345	131
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	57	93
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	84	3
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	134	4
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	16	9
Corporate | Equal to and greater than 90 days past due and accruing | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	$ 54	$ 22