LOANS - Corporate Loans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Loans
Loans, net of unearned income	$ 684,196	$ 667,034
Corporate
Loans
Total loans	354,531	334,141
Net unearned income (loss)	(822)	(763)
Loans, net of unearned income	353,709	333,378
Loans sold and/or reclassified to held-for-sale	1,000	1,000
Corporate | Commercial and industrial
Loans
Loans, net of unearned income	145,286	141,322
Corporate | Financial institutions
Loans
Loans, net of unearned income	83,868	73,757
Corporate | Mortgage and real estate
Loans
Loans, net of unearned income	57,464	51,964
Corporate | Lease financing
Loans
Loans, net of unearned income	1,531	1,655
In U.S. offices | Corporate
Loans
Total loans	185,310	169,781
In U.S. offices | Corporate | Commercial and industrial
Loans
Total loans	52,063	51,319
In U.S. offices | Corporate | Financial institutions
Loans
Total loans	48,447	39,128
In U.S. offices | Corporate | Mortgage and real estate
Loans
Total loans	50,124	44,683
In U.S. offices | Corporate | Installment, revolving credit and other
Loans
Total loans	33,247	33,181
In U.S. offices | Corporate | Lease financing
Loans
Total loans	1,429	1,470
In offices outside the U.S. | Corporate
Loans
Total loans	169,221	164,360
In offices outside the U.S. | Corporate | Commercial and industrial
Loans
Total loans	94,701	93,750
In offices outside the U.S. | Corporate | Financial institutions
Loans
Total loans	36,837	35,273
In offices outside the U.S. | Corporate | Mortgage and real estate
Loans
Total loans	7,376	7,309
In offices outside the U.S. | Corporate | Installment, revolving credit and other
Loans
Total loans	25,684	22,638
In offices outside the U.S. | Corporate | Lease financing
Loans
Total loans	103	190
In offices outside the U.S. | Corporate | Government and official institutions
Loans
Total loans	$ 4,520	$ 5,200