LOANS - Corporate Loans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Loans
Loans, net of unearned income	$ 699,483	$ 684,196
Corporate
Loans
Loans, net of unearned income	389,935	381,836
Unearned income	(814)	(855)
Loans sold and/or reclassified to held-for-sale	2,600	1,000
Corporate | Commercial and industrial
Loans
Loans, net of unearned income	166,846	174,890
Corporate | Financial institutions
Loans
Loans, net of unearned income	91,852	85,284
Corporate | Mortgage and real estate
Loans
Loans, net of unearned income	63,151	57,500
Corporate | Lease financing
Loans
Loans, net of unearned income	1,385	1,532
In U.S. offices | Corporate
Loans
Total loans	195,750	193,286
In U.S. offices | Corporate | Commercial and industrial
Loans
Total loans	55,929	60,861
In U.S. offices | Corporate | Financial institutions
Loans
Total loans	53,922	48,447
In U.S. offices | Corporate | Mortgage and real estate
Loans
Total loans	53,371	50,124
In U.S. offices | Corporate | Installment, revolving credit and other
Loans
Total loans	31,238	32,425
In U.S. offices | Corporate | Lease financing
Loans
Total loans	1,290	1,429
In offices outside the U.S. | Corporate
Loans
Total loans	194,185	188,550
In offices outside the U.S. | Corporate | Commercial and industrial
Loans
Total loans	112,668	114,029
In offices outside the U.S. | Corporate | Financial institutions
Loans
Total loans	40,211	36,837
In offices outside the U.S. | Corporate | Mortgage and real estate
Loans
Total loans	9,780	7,376
In offices outside the U.S. | Corporate | Installment, revolving credit and other
Loans
Total loans	27,303	25,685
In offices outside the U.S. | Corporate | Lease financing
Loans
Total loans	95	103
In offices outside the U.S. | Corporate | Government and official institutions
Loans
Total loans	$ 4,128	$ 4,520