LOANS - Corporate Loan Delinquency (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Loans receivable
Loans, net of unearned income	$ 684,196	$ 667,034
Loans at fair value	$ 3,223	4,374
Corporate
Loans receivable
Number of days past due, non-accrual status	90 days
Number of days past due for reversal of accrued interest and charging to earnings	90 days
Total loans past due and accruing	$ 852	735
Loans, total non-accrual	1,311	1,942
Loans, total current	348,343	326,352
Loans, net of unearned income	353,709	333,378
Loans at fair value	$ 3,203	4,349
Loans less than this number of days past due are considered current	30 days
Corporate | Commercial and industrial
Loans receivable
Total loans past due and accruing	$ 407	262
Loans, total non-accrual	919	1,506
Loans, total current	143,960	139,554
Loans, net of unearned income	145,286	141,322
Corporate | Financial institutions
Loans receivable
Total loans past due and accruing	94	108
Loans, total non-accrual	102	92
Loans, total current	83,672	73,557
Loans, net of unearned income	83,868	73,757
Corporate | Mortgage and real estate
Loans receivable
Total loans past due and accruing	133	206
Loans, total non-accrual	215	195
Loans, total current	57,116	51,563
Loans, net of unearned income	57,464	51,964
Corporate | Leases
Loans receivable
Total loans past due and accruing	15	76
Loans, total non-accrual	0	46
Loans, total current	1,516	1,533
Loans, net of unearned income	1,531	1,655
Corporate | Other
Loans receivable
Total loans past due and accruing	203	83
Loans, total non-accrual	75	103
Loans, total current	62,079	60,145
Loans, net of unearned income	62,357	60,331
30 to 89 Days Past Due | Corporate
Loans receivable
Total loans past due and accruing	736	627
30 to 89 Days Past Due | Corporate | Commercial and industrial
Loans receivable
Total loans past due and accruing	365	249
30 to 89 Days Past Due | Corporate | Financial institutions
Loans receivable
Total loans past due and accruing	87	93
30 to 89 Days Past Due | Corporate | Mortgage and real estate
Loans receivable
Total loans past due and accruing	128	147
30 to 89 Days Past Due | Corporate | Leases
Loans receivable
Total loans past due and accruing	5	68
30 to 89 Days Past Due | Corporate | Other
Loans receivable
Total loans past due and accruing	151	70
Equal to greater than 90 days past due | Corporate
Loans receivable
Total loans past due and accruing	116	108
Equal to greater than 90 days past due | Corporate | Commercial and industrial
Loans receivable
Total loans past due and accruing	42	13
Equal to greater than 90 days past due | Corporate | Financial institutions
Loans receivable
Total loans past due and accruing	7	15
Equal to greater than 90 days past due | Corporate | Mortgage and real estate
Loans receivable
Total loans past due and accruing	5	59
Equal to greater than 90 days past due | Corporate | Leases
Loans receivable
Total loans past due and accruing	10	8
Equal to greater than 90 days past due | Corporate | Other
Loans receivable
Total loans past due and accruing	$ 52	$ 13