LOANS - Corporate Loans Credit Quality Indicators (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 721,020	$ 699,483
Loans at fair value	3,999	4,085
Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,100	1,400
Corporate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	432,590	389,935
Total non-accrual	2,484	2,188
Loans at fair value	3,981	4,067
Corporate | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	200,297	166,846
Total non-accrual	1,814	1,828
Corporate | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	96,006	91,852
Total non-accrual	29	50
Corporate | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	65,217	63,151
Total non-accrual	204	188
Corporate | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	1,060	1,385
Total non-accrual	41	41
Corporate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	66,029	62,634
Total non-accrual	396	81
Corporate | Non-rated private bank loans managed on a delinquency basis
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,032
2019	7,782
2018	3,971
2017	4,200
2016	4,831
Prior	9,912
Revolving line of credit arrangements	0
Loans, net of unearned income	32,728	31,590
Corporate | Corporate loans, net of unearned income
Financing Receivable, Credit Quality Indicator [Line Items]
2020	79,513
2019	56,944
2018	37,140
2017	22,701
2016	14,138
Prior	48,855
Revolving line of credit arrangements	169,318
Loans, net of unearned income	432,590	389,935
Loans at fair value	3,981	4,067
Corporate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2020	57,213
2019	34,400
2018	24,408
2017	13,590
2016	7,206
Prior	29,090
Revolving line of credit arrangements	130,352
Loans, net of unearned income	296,259	277,056
Corporate | Investment grade | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	31,204
2019	14,056
2018	8,343
2017	6,340
2016	2,838
Prior	11,737
Revolving line of credit arrangements	51,963
Loans, net of unearned income	126,481	110,797
Corporate | Investment grade | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
2020	14,705
2019	7,338
2018	4,327
2017	1,897
2016	1,777
Prior	6,563
Revolving line of credit arrangements	47,013
Loans, net of unearned income	83,620	80,533
Corporate | Investment grade | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2,717
2019	7,406
2018	6,391
2017	3,904
2016	1,809
Prior	3,164
Revolving line of credit arrangements	1,668
Loans, net of unearned income	27,059	27,571
Corporate | Investment grade | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	8,587
2019	5,600
2018	5,347
2017	1,449
2016	782
Prior	7,626
Revolving line of credit arrangements	29,708
Loans, net of unearned income	59,099	58,155
Corporate | Non-investment grade, accrual | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	14,634
2019	9,193
2018	5,929
2017	3,488
2016	1,400
Prior	6,277
Revolving line of credit arrangements	30,827
Loans, net of unearned income	71,748	54,220
Corporate | Non-investment grade, accrual | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
2020	4,233
2019	3,494
2018	580
2017	213
2016	67
Prior	1,305
Revolving line of credit arrangements	2,466
Loans, net of unearned income	12,358	11,269
Corporate | Non-investment grade, accrual | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	258
2019	813
2018	1,405
2017	845
2016	375
Prior	490
Revolving line of credit arrangements	1,292
Loans, net of unearned income	5,478	3,811
Corporate | Non-investment grade, accrual | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,130
2019	1,181
2018	771
2017	165
2016	175
Prior	1,199
Revolving line of credit arrangements	2,933
Loans, net of unearned income	7,554	5,734
Corporate | Non-investment grade, non-accrual | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	11
2019	81
2018	68
2017	155
2016	79
Prior	431
Revolving line of credit arrangements	989
Total non-accrual	1,814	1,828
Corporate | Non-investment grade, non-accrual | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	4
2017	0
2016	0
Prior	24
Revolving line of credit arrangements	1
Total non-accrual	29	50
Corporate | Non-investment grade, non-accrual | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2
2019	0
2018	2
2017	9
2016	5
Prior	68
Revolving line of credit arrangements	118
Total non-accrual	204	188
Corporate | Non-investment grade, non-accrual | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	2
2017	36
2016	0
Prior	59
Revolving line of credit arrangements	340
Total non-accrual	437	122
Corporate | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
2020	20,268
2019	14,762
2018	8,761
2017	4,911
2016	2,101
Prior	9,853
Revolving line of credit arrangements	38,966
Loans, net of unearned income	$ 99,622	$ 77,222