LOANS - Corporate Loans Credit Quality Indicators (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	$ 664,764	$ 675,883
Loans at fair value	7,159	6,854
Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	500	700
Corporate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	400,514	387,044
Total non-accrual	2,400	3,527
Loans at fair value	7,146	6,840
Corporate | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	155,985	156,340
Total non-accrual	1,751	2,795
Corporate | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	95,820	87,689
Total non-accrual	53	92
Corporate | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	74,261	72,038
Total non-accrual	418	505
Corporate | Lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	472	738
Total non-accrual	18	24
Corporate | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	66,830	63,399
Total non-accrual	160	111
Corporate | Non-rated private bank loans managed on a delinquency basis
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	8,007	9,823
One year prior to current fiscal year	9,233	7,121
Two years prior to current fiscal year	6,277	3,533
Three years prior to current fiscal year	3,074	3,674
Four years prior to current fiscal year	3,087	4,300
Prior	9,395	7,942
Revolving line of credit arrangements	0	0
Total loans, net of unearned income	39,073	36,393
Corporate | Corporate loans, net of unearned income
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	107,041	107,122
One year prior to current fiscal year	35,029	36,513
Two years prior to current fiscal year	27,207	29,628
Three years prior to current fiscal year	21,526	17,059
Four years prior to current fiscal year	12,754	11,340
Prior	37,756	32,195
Revolving line of credit arrangements	152,055	146,347
Total loans, net of unearned income	400,514	387,044
Loans at fair value	7,146	6,840
Corporate | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	73,234	66,625
One year prior to current fiscal year	20,025	20,851
Two years prior to current fiscal year	14,637	17,806
Three years prior to current fiscal year	13,270	8,211
Four years prior to current fiscal year	6,664	4,767
Prior	22,028	17,709
Revolving line of credit arrangements	124,105	115,311
Total loans, net of unearned income	273,963	251,280
Corporate | Investment grade | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	44,949	38,398
One year prior to current fiscal year	6,818	7,607
Two years prior to current fiscal year	5,187	5,929
Three years prior to current fiscal year	4,218	3,909
Four years prior to current fiscal year	3,358	2,094
Prior	9,826	8,670
Revolving line of credit arrangements	29,013	25,819
Total loans, net of unearned income	103,369	92,426
Corporate | Investment grade | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	13,440	10,560
One year prior to current fiscal year	3,115	2,964
Two years prior to current fiscal year	1,650	2,106
Three years prior to current fiscal year	1,147	782
Four years prior to current fiscal year	631	681
Prior	2,439	2,030
Revolving line of credit arrangements	61,610	56,239
Total loans, net of unearned income	84,032	75,362
Corporate | Investment grade | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	3,357	6,793
One year prior to current fiscal year	5,754	6,714
Two years prior to current fiscal year	5,970	5,174
Three years prior to current fiscal year	3,759	2,568
Four years prior to current fiscal year	2,122	1,212
Prior	3,312	1,719
Revolving line of credit arrangements	1,525	1,557
Total loans, net of unearned income	25,799	25,737
Corporate | Investment grade | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	11,488	10,874
One year prior to current fiscal year	4,338	3,566
Two years prior to current fiscal year	1,830	4,597
Three years prior to current fiscal year	4,146	952
Four years prior to current fiscal year	553	780
Prior	6,451	5,290
Revolving line of credit arrangements	31,957	31,696
Total loans, net of unearned income	60,763	57,755
Corporate | Non-investment grade, accrual | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	15,208	19,683
One year prior to current fiscal year	3,298	4,794
Two years prior to current fiscal year	3,073	4,645
Three years prior to current fiscal year	2,883	2,883
Four years prior to current fiscal year	1,670	1,182
Prior	4,009	4,533
Revolving line of credit arrangements	20,724	23,400
Total loans, net of unearned income	50,865	61,120
Corporate | Non-investment grade, accrual | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	6,467	7,413
One year prior to current fiscal year	535	700
Two years prior to current fiscal year	507	654
Three years prior to current fiscal year	193	274
Four years prior to current fiscal year	91	141
Prior	619	197
Revolving line of credit arrangements	3,325	2,855
Total loans, net of unearned income	11,737	12,234
Corporate | Non-investment grade, accrual | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,661	1,882
One year prior to current fiscal year	1,339	1,919
Two years prior to current fiscal year	2,009	2,058
Three years prior to current fiscal year	1,469	1,457
Four years prior to current fiscal year	857	697
Prior	1,027	837
Revolving line of credit arrangements	610	551
Total loans, net of unearned income	8,972	9,401
Corporate | Non-investment grade, accrual | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	2,416	1,407
One year prior to current fiscal year	434	918
Two years prior to current fiscal year	582	725
Three years prior to current fiscal year	433	370
Four years prior to current fiscal year	240	186
Prior	460	657
Revolving line of credit arrangements	1,797	1,986
Total loans, net of unearned income	6,362	6,249
Corporate | Non-investment grade, non-accrual | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	11	260
One year prior to current fiscal year	142	203
Two years prior to current fiscal year	99	192
Three years prior to current fiscal year	104	143
Four years prior to current fiscal year	108	57
Prior	167	223
Revolving line of credit arrangements	1,120	1,717
Total non-accrual	1,751	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	5	0
Revolving line of credit arrangements	46	91
Total non-accrual	51	92
Corporate | Non-investment grade, non-accrual | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	16	13
One year prior to current fiscal year	12	4
Two years prior to current fiscal year	4	3
Three years prior to current fiscal year	81	18
Four years prior to current fiscal year	11	8
Prior	26	32
Revolving line of credit arrangements	267	427
Total non-accrual	417	505
Corporate | Non-investment grade, non-accrual | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	21	15
One year prior to current fiscal year	11	3
Two years prior to current fiscal year	19	12
Three years prior to current fiscal year	19	29
Four years prior to current fiscal year	26	2
Prior	20	65
Revolving line of credit arrangements	61	9
Total non-accrual	177	135
Corporate | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	25,800	30,674
One year prior to current fiscal year	5,771	8,541
Two years prior to current fiscal year	6,293	8,289
Three years prior to current fiscal year	5,182	5,174
Four years prior to current fiscal year	3,003	2,273
Prior	6,333	6,544
Revolving line of credit arrangements	27,950	31,036
Total loans, net of unearned income	$ 80,332	$ 92,531