LOANS - Corporate Loans Credit Quality Indicators (Details) - USD ($) $ in Millions	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]
Loans, net of unearned income	404,179	389,935
Total non-accrual	4,016	2,188
Loans at fair value	5,783	4,067
Corporate | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	182,365	166,846
Total non-accrual	3,202	1,828
Corporate | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	87,226	91,852
Total non-accrual	244	50
Corporate | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	68,146	63,151
Total non-accrual	455	188
Corporate | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	935	1,385
Total non-accrual	36	41
Corporate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	59,724	62,634
Total non-accrual	79	81
Corporate | Non-rated private bank loans managed on a delinquency basis
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,461
2019	7,597
2018	3,822
2017	4,171
2016	4,604
Prior	9,232
Revolving line of credit arrangements	0
Loans, net of unearned income	33,887	31,590
Corporate | Corporate loans, net of unearned income
Financing Receivable, Credit Quality Indicator [Line Items]
2020	86,519
2019	43,568
2018	35,384
2017	20,510
2016	12,324
Prior	42,968
Revolving line of credit arrangements	157,123
Loans, net of unearned income	404,179	389,935
Loans at fair value	5,783	4,067
Corporate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2020	54,154
2019	24,703
2018	22,208
2017	11,180
2016	5,833
Prior	23,965
Revolving line of credit arrangements	116,742
Loans, net of unearned income	258,785	277,056
Corporate | Investment grade | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	35,627
2019	9,480
2018	7,242
2017	5,035
2016	2,233
Prior	10,162
Revolving line of credit arrangements	36,478
Loans, net of unearned income	106,257	110,797
Corporate | Investment grade | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8,131
2019	5,359
2018	4,125
2017	1,626
2016	1,458
Prior	4,941
Revolving line of credit arrangements	47,425
Loans, net of unearned income	73,065	80,533
Corporate | Investment grade | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3,614
2019	6,267
2018	5,622
2017	3,207
2016	1,436
Prior	3,017
Revolving line of credit arrangements	3,086
Loans, net of unearned income	26,249	27,571
Corporate | Investment grade | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	6,782
2019	3,597
2018	5,219
2017	1,312
2016	706
Prior	5,845
Revolving line of credit arrangements	29,753
Loans, net of unearned income	53,214	58,155
Corporate | Non-investment grade, accrual | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	18,097
2019	7,045
2018	5,922
2017	3,431
2016	1,061
Prior	6,022
Revolving line of credit arrangements	31,045
Loans, net of unearned income	72,623	54,220
Corporate | Non-investment grade, accrual | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
2020	7,189
2019	1,343
2018	742
2017	337
2016	39
Prior	1,562
Revolving line of credit arrangements	2,705
Loans, net of unearned income	13,917	11,269
Corporate | Non-investment grade, accrual | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,217
2019	1,193
2018	2,031
2017	1,025
2016	512
Prior	941
Revolving line of credit arrangements	920
Loans, net of unearned income	7,839	3,811
Corporate | Non-investment grade, accrual | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,179
2019	1,567
2018	603
2017	160
2016	197
Prior	783
Revolving line of credit arrangements	2,840
Loans, net of unearned income	7,329	5,734
Corporate | Non-investment grade, non-accrual | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	207
2019	108
2018	54
2017	181
2016	72
Prior	343
Revolving line of credit arrangements	2,237
Total non-accrual	3,202	1,828
Corporate | Non-investment grade, non-accrual | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	26
Revolving line of credit arrangements	218
Total non-accrual	244	50
Corporate | Non-investment grade, non-accrual | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2
2019	4
2018	2
2017	10
2016	6
Prior	52
Revolving line of credit arrangements	379
Total non-accrual	455	188
Corporate | Non-investment grade, non-accrual | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	13
2019	8
2018	0
2017	15
2016	0
Prior	42
Revolving line of credit arrangements	37
Total non-accrual	115	122
Corporate | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2020	27,904
2019	11,268
2018	9,354
2017	5,159
2016	1,887
Prior	9,771
Revolving line of credit arrangements	40,381
Loans, net of unearned income	$ 105,724	$ 77,222