LOANS - Corporate Loan Delinquency (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 721,020	$ 699,483
Loans at fair value	3,999	4,085
Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,100	1,400
Corporate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	3,396	2,380
Total non-accrual	2,484	2,188
Total current	422,729	381,300
Loans, net of unearned income	432,590	389,935
Loans at fair value	$ 3,981	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	$ 1,329	769
Total non-accrual	1,814	1,828
Total current	197,154	164,249
Loans, net of unearned income	200,297	166,846
Corporate | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	1,229	794
Total non-accrual	29	50
Total current	94,748	91,008
Loans, net of unearned income	96,006	91,852
Corporate | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	615	538
Total non-accrual	204	188
Total current	64,398	62,425
Loans, net of unearned income	65,217	63,151
Corporate | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	36	67
Total non-accrual	41	41
Total current	983	1,277
Loans, net of unearned income	1,060	1,385
Corporate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	187	212
Total non-accrual	396	81
Total current	65,446	62,341
Loans, net of unearned income	66,029	62,634
Corporate | 30 to 89 Days Past Due
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	3,130	2,249
Corporate | 30 to 89 Days Past Due | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	1,166	676
Corporate | 30 to 89 Days Past Due | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	1,178	791
Corporate | 30 to 89 Days Past Due | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	591	534
Corporate | 30 to 89 Days Past Due | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	28	58
Corporate | 30 to 89 Days Past Due | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	167	190
Corporate | Equal to and greater than 90 days past due and accruing
Financing Receivable, Credit Quality Indicator [Line Items]
Past due and accruing	266	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	163	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	51	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	24	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	8	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	$ 20	$ 22