LOANS - Corporate Loan Delinquency (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 685,292	$ 699,483
Loans at fair value	5,799	4,085
Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	900	1,400
Corporate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	3,560	2,380
Total non-accrual	4,016	2,188
Total current	390,820	381,300
Loans, net of unearned income	404,179	389,935
Loans at fair value	$ 5,783	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	$ 1,079	769
Total non-accrual	3,202	1,828
Total current	178,084	164,249
Loans, net of unearned income	182,365	166,846
Corporate | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	1,098	794
Total non-accrual	244	50
Total current	85,884	91,008
Loans, net of unearned income	87,226	91,852
Corporate | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	1,207	538
Total non-accrual	455	188
Total current	66,484	62,425
Loans, net of unearned income	68,146	63,151
Corporate | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	3	67
Total non-accrual	36	41
Total current	896	1,277
Loans, net of unearned income	935	1,385
Corporate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	173	212
Total non-accrual	79	81
Total current	59,472	62,341
Loans, net of unearned income	59,724	62,634
Corporate | 30 to 89 Days Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	3,131	2,249
Corporate | 30 to 89 Days Past Due | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	971	676
Corporate | 30 to 89 Days Past Due | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	1,031	791
Corporate | 30 to 89 Days Past Due | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	986	534
Corporate | 30 to 89 Days Past Due | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	0	58
Corporate | 30 to 89 Days Past Due | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	143	190
Corporate | Equal to and greater than 90 days past due and accruing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	429	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	108	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	67	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	221	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	3	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	$ 30	$ 22