LOANS - Corporate Loans Credit Quality Indicators (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	$ 674,578	$ 689,362
Loans at fair value	8,854	7,594
Unallocated portfolio layer cumulative basis adjustments	(113)	93
Corporate loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income	292,819	300,165
Total non-accrual	1,489	1,882
Loans at fair value	8,551	7,281
Unallocated portfolio layer cumulative basis adjustments	(3)	93
Corporate loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income		151,451
Total non-accrual	551	717
Corporate loans | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income		65,060
Total non-accrual	43	51
Corporate loans | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income		24,938
Total non-accrual	811	868
Corporate loans | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans, net of unearned income		51,067
Total non-accrual	84	246
Corporate loans | Corporate loans, net of unearned income(7)
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	49,389	90,737
One year prior to current fiscal year	40,878	27,788
Two years prior to current fiscal year	25,029	15,899
Three years prior to current fiscal year	15,661	8,869
Four years prior to current fiscal year	7,799	7,313
Prior	24,740	20,008
Revolving line of credit arrangements	120,775	122,177
Total loans, net of unearned income	292,822	300,072
Loans at fair value	8,551	7,281
Corporate loans | Investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	35,700	67,094
One year prior to current fiscal year	28,935	20,308
Two years prior to current fiscal year	18,104	11,142
Three years prior to current fiscal year	10,657	6,276
Four years prior to current fiscal year	5,731	5,211
Prior	18,811	15,638
Revolving line of credit arrangements	99,103	101,072
Total loans, net of unearned income	217,041	226,741
Corporate loans | Investment grade | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	28,244	47,811
One year prior to current fiscal year	16,153	7,738
Two years prior to current fiscal year	6,978	3,641
Three years prior to current fiscal year	3,548	2,279
Four years prior to current fiscal year	2,067	2,604
Prior	8,147	6,907
Revolving line of credit arrangements	35,962	34,956
Total loans, net of unearned income	101,099	105,936
Corporate loans | Investment grade | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	5,534	11,002
One year prior to current fiscal year	5,570	2,356
Two years prior to current fiscal year	2,103	2,834
Three years prior to current fiscal year	2,442	424
Four years prior to current fiscal year	369	557
Prior	2,293	1,847
Revolving line of credit arrangements	37,160	36,715
Total loans, net of unearned income	55,471	55,735
Corporate loans | Investment grade | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	439	3,628
One year prior to current fiscal year	3,720	4,433
Two years prior to current fiscal year	3,955	3,595
Three years prior to current fiscal year	3,470	2,544
Four years prior to current fiscal year	2,447	1,238
Prior	2,577	1,582
Revolving line of credit arrangements	257	66
Total loans, net of unearned income	16,865	17,086
Corporate loans | Investment grade | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,483	4,653
One year prior to current fiscal year	3,492	5,781
Two years prior to current fiscal year	5,068	1,072
Three years prior to current fiscal year	1,197	1,029
Four years prior to current fiscal year	848	812
Prior	5,794	5,302
Revolving line of credit arrangements	25,724	29,335
Total loans, net of unearned income	43,606	47,984
Corporate loans | Non-investment grade
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	13,689	23,643
One year prior to current fiscal year	11,943	7,480
Two years prior to current fiscal year	6,925	4,757
Three years prior to current fiscal year	5,004	2,593
Four years prior to current fiscal year	2,068	2,102
Prior	5,929	4,370
Revolving line of credit arrangements	21,672	21,105
Total loans, net of unearned income	67,230	66,050
Corporate loans | Non-investment grade, accrual | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	11,407	17,570
One year prior to current fiscal year	7,834	4,785
Two years prior to current fiscal year	4,529	1,914
Three years prior to current fiscal year	2,036	1,359
Four years prior to current fiscal year	949	732
Prior	2,912	2,526
Revolving line of credit arrangements	16,711	15,912
Total loans, net of unearned income	46,378	44,798
Corporate loans | Non-investment grade, accrual | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,667	4,207
One year prior to current fiscal year	2,011	748
Two years prior to current fiscal year	624	1,084
Three years prior to current fiscal year	1,044	56
Four years prior to current fiscal year	43	194
Prior	442	260
Revolving line of credit arrangements	2,750	2,725
Total loans, net of unearned income	8,581	9,274
Corporate loans | Non-investment grade, accrual | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	251	1,034
One year prior to current fiscal year	1,162	1,234
Two years prior to current fiscal year	1,337	1,378
Three years prior to current fiscal year	1,507	947
Four years prior to current fiscal year	923	755
Prior	1,688	1,016
Revolving line of credit arrangements	602	620
Total loans, net of unearned income	7,470	6,984
Corporate loans | Non-investment grade, accrual | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	362	653
One year prior to current fiscal year	813	434
Two years prior to current fiscal year	140	248
Three years prior to current fiscal year	304	158
Four years prior to current fiscal year	109	211
Prior	385	155
Revolving line of credit arrangements	1,199	1,253
Total loans, net of unearned income	3,312	3,112
Corporate loans | Non-investment grade, non-accrual | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	53
One year prior to current fiscal year	83	46
Two years prior to current fiscal year	31	84
Three years prior to current fiscal year	65	35
Four years prior to current fiscal year	8	45
Prior	63	93
Revolving line of credit arrangements	301	361
Total non-accrual	551	717
Corporate loans | Non-investment grade, non-accrual | Financial institutions
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1	0
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	42	51
Total non-accrual	43	51
Corporate loans | Non-investment grade, non-accrual | Mortgage and real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1	118
One year prior to current fiscal year	40	233
Two years prior to current fiscal year	264	8
Three years prior to current fiscal year	32	38
Four years prior to current fiscal year	36	110
Prior	376	308
Revolving line of credit arrangements	62	53
Total non-accrual	811	868
Corporate loans | Non-investment grade, non-accrual | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	8
One year prior to current fiscal year	0	0
Two years prior to current fiscal year	0	41
Three years prior to current fiscal year	16	0
Four years prior to current fiscal year	0	55
Prior	63	12
Revolving line of credit arrangements	5	130
Total non-accrual	$ 84	$ 246