LOANS - Corporate Loans Credit Quality Indicators (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	$ 665,988	$ 675,883
Loans at fair value	7,525	6,854
Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	600	700
Corporate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	391,954	387,044
Total non-accrual	3,106	3,527
Loans at fair value	7,510	6,840
Corporate | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	151,800	156,340
Total non-accrual	2,465	2,795
Corporate | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	91,518	87,689
Total non-accrual	36	92
Corporate | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	72,142	72,038
Total non-accrual	496	505
Corporate | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	595	738
Total non-accrual	27	24
Corporate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans, net of unearned income	68,389	63,399
Total non-accrual	82	111
Corporate | Non-rated private bank loans managed on a delinquency basis
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	2,313	9,823
One year prior to current fiscal year	9,755	7,121
Two years prior to current fiscal year	6,839	3,533
Three years prior to current fiscal year	3,359	3,674
Four years prior to current fiscal year	3,488	4,300
Prior	10,994	7,942
Revolving line of credit arrangements	0	0
Loans, net of unearned income	36,748	36,393
Corporate | Corporate loans, net of unearned income
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	71,832	107,122
One year prior to current fiscal year	50,085	36,513
Two years prior to current fiscal year	31,780	29,628
Three years prior to current fiscal year	26,688	17,059
Four years prior to current fiscal year	15,536	11,340
Prior	39,709	32,195
Revolving line of credit arrangements	148,814	146,347
Loans, net of unearned income	391,954	387,044
Loans at fair value	7,510	6,840
Corporate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	51,010	66,625
One year prior to current fiscal year	29,453	20,851
Two years prior to current fiscal year	16,988	17,806
Three years prior to current fiscal year	16,308	8,211
Four years prior to current fiscal year	7,252	4,767
Prior	21,965	17,709
Revolving line of credit arrangements	120,033	115,311
Loans, net of unearned income	263,009	251,280
Corporate | Investment grade | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	29,070	38,398
One year prior to current fiscal year	11,833	7,607
Two years prior to current fiscal year	6,534	5,929
Three years prior to current fiscal year	5,311	3,909
Four years prior to current fiscal year	3,416	2,094
Prior	10,120	8,670
Revolving line of credit arrangements	26,712	25,819
Loans, net of unearned income	92,996	92,426
Corporate | Investment grade | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	10,473	10,560
One year prior to current fiscal year	5,551	2,964
Two years prior to current fiscal year	2,242	2,106
Three years prior to current fiscal year	1,582	782
Four years prior to current fiscal year	1,025	681
Prior	2,254	2,030
Revolving line of credit arrangements	58,910	56,239
Loans, net of unearned income	82,037	75,362
Corporate | Investment grade | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	2,473	6,793
One year prior to current fiscal year	5,494	6,714
Two years prior to current fiscal year	5,820	5,174
Three years prior to current fiscal year	4,827	2,568
Four years prior to current fiscal year	2,205	1,212
Prior	2,847	1,719
Revolving line of credit arrangements	1,728	1,557
Loans, net of unearned income	25,394	25,737
Corporate | Investment grade | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	8,994	10,874
One year prior to current fiscal year	6,575	3,566
Two years prior to current fiscal year	2,392	4,597
Three years prior to current fiscal year	4,588	952
Four years prior to current fiscal year	606	780
Prior	6,744	5,290
Revolving line of credit arrangements	32,683	31,696
Loans, net of unearned income	62,582	57,755
Corporate | Non-investment grade, accrual | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	12,897	19,683
One year prior to current fiscal year	6,422	4,794
Two years prior to current fiscal year	4,266	4,645
Three years prior to current fiscal year	3,991	2,883
Four years prior to current fiscal year	2,850	1,182
Prior	4,167	4,533
Revolving line of credit arrangements	21,746	23,400
Loans, net of unearned income	56,339	61,120
Corporate | Non-investment grade, accrual | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	3,196	7,413
One year prior to current fiscal year	2,395	700
Two years prior to current fiscal year	629	654
Three years prior to current fiscal year	555	274
Four years prior to current fiscal year	98	141
Prior	274	197
Revolving line of credit arrangements	2,298	2,855
Loans, net of unearned income	9,445	12,234
Corporate | Non-investment grade, accrual | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	944	1,882
One year prior to current fiscal year	1,319	1,919
Two years prior to current fiscal year	2,117	2,058
Three years prior to current fiscal year	1,755	1,457
Four years prior to current fiscal year	1,415	697
Prior	1,376	837
Revolving line of credit arrangements	578	551
Loans, net of unearned income	9,504	9,401
Corporate | Non-investment grade, accrual | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,384	1,407
One year prior to current fiscal year	528	918
Two years prior to current fiscal year	682	725
Three years prior to current fiscal year	541	370
Four years prior to current fiscal year	299	186
Prior	591	657
Revolving line of credit arrangements	2,268	1,986
Loans, net of unearned income	6,293	6,249
Corporate | Non-investment grade, non-accrual | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	81	260
One year prior to current fiscal year	197	203
Two years prior to current fiscal year	227	192
Three years prior to current fiscal year	86	143
Four years prior to current fiscal year	106	57
Prior	286	223
Revolving line of credit arrangements	1,482	1,717
Total non-accrual	2,465	2,795
Corporate | Non-investment grade, non-accrual | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	1
One year prior to current fiscal year	0	0
Two years prior to current fiscal year	0	0
Three years prior to current fiscal year	0	0
Four years prior to current fiscal year	0	0
Prior	0	0
Revolving line of credit arrangements	36	91
Total non-accrual	36	92
Corporate | Non-investment grade, non-accrual | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	13
One year prior to current fiscal year	12	4
Two years prior to current fiscal year	8	3
Three years prior to current fiscal year	55	18
Four years prior to current fiscal year	18	8
Prior	30	32
Revolving line of credit arrangements	373	427
Total non-accrual	496	505
Corporate | Non-investment grade, non-accrual | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	7	15
One year prior to current fiscal year	4	3
Two years prior to current fiscal year	24	12
Three years prior to current fiscal year	38	29
Four years prior to current fiscal year	10	2
Prior	26	65
Revolving line of credit arrangements	0	9
Total non-accrual	109	135
Corporate | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	18,509	30,674
One year prior to current fiscal year	10,877	8,541
Two years prior to current fiscal year	7,953	8,289
Three years prior to current fiscal year	7,021	5,174
Four years prior to current fiscal year	4,796	2,273
Prior	6,750	6,544
Revolving line of credit arrangements	28,781	31,036
Loans, net of unearned income	$ 84,687	$ 92,531