LOANS - Corporate Loans Credit Quality Indicators (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 666,911	$ 699,483
Loans at fair value	5,524	4,085
Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	800	1,400
Corporate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	386,886	389,935
Total non-accrual	3,584	2,188
Loans at fair value	5,510	4,067
Corporate | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	165,035	166,846
Total non-accrual	2,784	1,828
Corporate | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	84,913	91,852
Total non-accrual	165	50
Corporate | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	69,761	63,151
Total non-accrual	486	188
Corporate | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	767	1,385
Total non-accrual	37	41
Corporate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	60,900	62,634
Total non-accrual	112	81
Corporate | Non-rated private bank loans managed on a delinquency basis
Financing Receivable, Credit Quality Indicator [Line Items]
2020	7,244
2019	7,368
2018	3,676
2017	3,839
2016	4,448
Prior	8,572
Revolving line of credit arrangements	0
Loans, net of unearned income	35,147	31,590
Corporate | Corporate loans, net of unearned income
Financing Receivable, Credit Quality Indicator [Line Items]
2020	99,089
2019	39,954
2018	32,988
2017	18,538
2016	11,461
Prior	32,203
Revolving line of credit arrangements	147,143
Loans, net of unearned income	386,886	389,935
Loans at fair value	5,510	4,067
Corporate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2020	56,698
2019	22,198
2018	19,612
2017	9,272
2016	4,900
Prior	18,170
Revolving line of credit arrangements	115,121
Loans, net of unearned income	245,971	277,056
Corporate | Investment grade | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	33,735
2019	8,471
2018	6,379
2017	4,440
2016	2,092
Prior	8,506
Revolving line of credit arrangements	30,601
Loans, net of unearned income	94,224	110,797
Corporate | Investment grade | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
2020	9,205
2019	3,403
2018	2,603
2017	760
2016	820
Prior	2,090
Revolving line of credit arrangements	52,564
Loans, net of unearned income	71,445	80,533
Corporate | Investment grade | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	5,283
2019	6,931
2018	5,511
2017	2,896
2016	1,342
Prior	2,193
Revolving line of credit arrangements	1,916
Loans, net of unearned income	26,072	27,571
Corporate | Investment grade | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8,475
2019	3,393
2018	5,119
2017	1,176
2016	646
Prior	5,381
Revolving line of credit arrangements	30,040
Loans, net of unearned income	54,230	58,155
Corporate | Non-investment grade, accrual | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	24,224
2019	6,284
2018	5,806
2017	3,175
2016	1,187
Prior	3,621
Revolving line of credit arrangements	23,394
Loans, net of unearned income	67,691	54,220
Corporate | Non-investment grade, accrual | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
2020	7,245
2019	1,137
2018	806
2017	755
2016	93
Prior	152
Revolving line of credit arrangements	3,302
Loans, net of unearned income	13,490	11,269
Corporate | Non-investment grade, accrual | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,470
2019	1,648
2018	2,239
2017	1,059
2016	596
Prior	861
Revolving line of credit arrangements	518
Loans, net of unearned income	8,391	3,811
Corporate | Non-investment grade, accrual | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,015
2019	1,179
2018	744
2017	229
2016	163
Prior	408
Revolving line of credit arrangements	2,364
Loans, net of unearned income	7,102	5,734
Corporate | Non-investment grade, non-accrual | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	135
2019	130
2018	81
2017	162
2016	68
Prior	343
Revolving line of credit arrangements	1,865
Total non-accrual	2,784	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	1
Revolving line of credit arrangements	164
Total non-accrual	165	50
Corporate | Non-investment grade, non-accrual | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	6
2019	1
2018	7
2017	28
2016	6
Prior	52
Revolving line of credit arrangements	386
Total non-accrual	486	188
Corporate | Non-investment grade, non-accrual | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	52
2019	9
2018	17
2017	19
2016	0
Prior	23
Revolving line of credit arrangements	29
Total non-accrual	149	122
Corporate | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2020	35,147
2019	10,388
2018	9,700
2017	5,427
2016	2,113
Prior	5,461
Revolving line of credit arrangements	32,022
Loans, net of unearned income	$ 100,258	$ 77,222