ALLOWANCE FOR CREDIT LOSSES, NONACCRUAL LOANS AND LEASES, AND CONCENTRATIONS OF CREDIT RISK - Amortized Cost Basis by Credit Quality Indicator (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Total	$ 154,688		$ 156,662
Gross charge-offs
Total	171	$ 101
Commercial
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	2,076		14,715
Year two	14,454		15,843
Year three	15,166		6,633
Year four	6,174		6,280
Year five	5,824		4,245
Prior to year five	10,455		7,076
Within the Revolving Period	26,568		27,221
Converted to Term	149		167
Total	80,866		82,180
Gross charge-offs
Year one	0
Year two	0
Year three	27
Year four	4
Year five	1
Prior to year five	3
Within the Revolving Period	24
Converted to Term	0
Total	59	14
Commercial \| Pass
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	2,019		14,334
Year two	13,280		15,274
Year three	14,427		6,113
Year four	5,346		5,239
Year five	4,678		3,607
Prior to year five	8,336		5,833
Within the Revolving Period	25,265		26,099
Converted to Term	133		151
Total	73,484		76,650
Commercial \| Special Mention
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	3		129
Year two	683		313
Year three	343		225
Year four	440		470
Year five	291		148
Prior to year five	475		269
Within the Revolving Period	393		426
Converted to Term	0		0
Total	2,628		1,980
Commercial \| Substandard
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	36		242
Year two	449		240
Year three	372		285
Year four	379		511
Year five	760		449
Prior to year five	1,519		959
Within the Revolving Period	836		620
Converted to Term	12		14
Total	4,363		3,320
Commercial \| Doubtful
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	18		10
Year two	42		16
Year three	24		10
Year four	9		60
Year five	95		41
Prior to year five	125		15
Within the Revolving Period	74		76
Converted to Term	4		2
Total	391		230
Commercial \| Commercial and industrial
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	1,411		8,588
Year two	8,177		8,890
Year three	8,154		2,548
Year four	2,178		2,408
Year five	1,966		1,522
Prior to year five	3,472		2,468
Within the Revolving Period	24,947		25,248
Converted to Term	145		164
Total	50,450		51,836
Gross charge-offs
Year one	0
Year two	0
Year three	27
Year four	4
Year five	0
Prior to year five	0
Within the Revolving Period	24
Converted to Term	0
Total	55
Commercial \| Commercial and industrial \| Pass
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	1,357		8,304
Year two	7,665		8,469
Year three	7,610		2,224
Year four	1,832		2,074
Year five	1,766		1,334
Prior to year five	2,791		1,952
Within the Revolving Period	23,680		24,211
Converted to Term	129		148
Total	46,830		48,716
Commercial \| Commercial and industrial \| Special Mention
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	0		124
Year two	192		189
Year three	242		120
Year four	127		74
Year five	15		48
Prior to year five	196		153
Within the Revolving Period	382		364
Converted to Term	0		0
Total	1,154		1,072
Commercial \| Commercial and industrial \| Substandard
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	36		150
Year two	286		218
Year three	279		203
Year four	216		255
Year five	178		99
Prior to year five	397		349
Within the Revolving Period	811		597
Converted to Term	12		14
Total	2,215		1,885
Commercial \| Commercial and industrial \| Doubtful
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	18		10
Year two	34		14
Year three	23		1
Year four	3		5
Year five	7		41
Prior to year five	88		14
Within the Revolving Period	74		76
Converted to Term	4		2
Total	251		163
Commercial \| Commercial real estate
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	603		5,860
Year two	6,026		6,581
Year three	6,664		3,830
Year four	3,759		3,764
Year five	3,763		2,594
Prior to year five	6,559		4,260
Within the Revolving Period	1,621		1,973
Converted to Term	4		3
Total	28,999		28,865
Gross charge-offs
Year one	0
Year two	0
Year three	0
Year four	0
Year five	1
Prior to year five	3
Within the Revolving Period	0
Converted to Term	0
Total	4
Commercial \| Commercial real estate \| Pass
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	603		5,767
Year two	5,375		6,442
Year three	6,486		3,639
Year four	3,284		3,066
Year five	2,827		2,145
Prior to year five	5,124		3,536
Within the Revolving Period	1,585		1,888
Converted to Term	4		3
Total	25,288		26,486
Commercial \| Commercial real estate \| Special Mention
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	0		1
Year two	489		119
Year three	95		103
Year four	309		390
Year five	274		99
Prior to year five	279		113
Within the Revolving Period	11		62
Converted to Term	0		0
Total	1,457		887
Commercial \| Commercial real estate \| Substandard
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	0		92
Year two	154		18
Year three	82		79
Year four	160		253
Year five	574		350
Prior to year five	1,119		610
Within the Revolving Period	25		23
Converted to Term	0		0
Total	2,114		1,425
Commercial \| Commercial real estate \| Doubtful
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	0		0
Year two	8		2
Year three	1		9
Year four	6		55
Year five	88		0
Prior to year five	37		1
Within the Revolving Period	0		0
Converted to Term	0		0
Total	140		67
Commercial \| Leases
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	62		267
Year two	251		372
Year three	348		255
Year four	237		108
Year five	95		129
Prior to year five	424		348
Within the Revolving Period	0		0
Converted to Term	0		0
Total	1,417		1,479
Gross charge-offs
Year one	0
Year two	0
Year three	0
Year four	0
Year five	0
Prior to year five	0
Within the Revolving Period	0
Converted to Term	0
Total	0
Commercial \| Leases \| Pass
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	59		263
Year two	240		363
Year three	331		250
Year four	230		99
Year five	85		128
Prior to year five	421		345
Within the Revolving Period	0		0
Converted to Term	0		0
Total	1,366		1,448
Commercial \| Leases \| Special Mention
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	3		4
Year two	2		5
Year three	6		2
Year four	4		6
Year five	2		1
Prior to year five	0		3
Within the Revolving Period	0		0
Converted to Term	0		0
Total	17		21
Commercial \| Leases \| Substandard
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	0		0
Year two	9		4
Year three	11		3
Year four	3		3
Year five	8		0
Prior to year five	3		0
Within the Revolving Period	0		0
Converted to Term	0		0
Total	34		10
Commercial \| Leases \| Doubtful
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	0		0
Year two	0		0
Year three	0		0
Year four	0		0
Year five	0		0
Prior to year five	0		0
Within the Revolving Period	0		0
Converted to Term	0		0
Total	0		0
Retail
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	1,399		11,158
Year two	11,147		18,251
Year three	17,545		11,083
Year four	10,554		5,223
Year five	4,891		2,457
Prior to year five	11,226		9,401
Within the Revolving Period	15,984		15,803
Converted to Term	1,076		1,106
Total	73,822		74,482
Gross charge-offs
Year one	5
Year two	24
Year three	18
Year four	11
Year five	10
Prior to year five	20
Within the Revolving Period	24
Converted to Term	0
Total	112	$ 87
Retail \| Residential mortgages
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	583		5,421
Year two	5,588		9,071
Year three	9,059		5,519
Year four	5,454		2,432
Year five	2,397		1,017
Prior to year five	7,281		6,461
Within the Revolving Period	0		0
Converted to Term	0		0
Total	30,362		29,921
Gross charge-offs
Year one	0
Year two	0
Year three	0
Year four	0
Year five	0
Prior to year five	1
Within the Revolving Period	0
Converted to Term	0
Total	1
Retail \| Home equity
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	0		7
Year two	6		9
Year three	9		8
Year four	8		36
Year five	35		57
Prior to year five	519		496
Within the Revolving Period	12,496		12,340
Converted to Term	1,062		1,090
Total	14,135		14,043
Gross charge-offs
Year one	0
Year two	0
Year three	0
Year four	0
Year five	0
Prior to year five	1
Within the Revolving Period	1
Converted to Term	0
Total	2
Retail \| Automobile
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	500		3,276
Year two	3,041		5,141
Year three	4,685		2,028
Year four	1,799		1,160
Year five	991		474
Prior to year five	519		213
Within the Revolving Period	0		0
Converted to Term	0		0
Total	11,535		12,292
Gross charge-offs
Year one	0
Year two	7
Year three	11
Year four	4
Year five	4
Prior to year five	4
Within the Revolving Period	0
Converted to Term	0
Total	30
Retail \| Education
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	243		1,712
Year two	1,866		3,586
Year three	3,446		3,131
Year four	2,977		1,400
Year five	1,319		820
Prior to year five	2,783		2,159
Within the Revolving Period	0		0
Converted to Term	0		0
Total	12,634		12,808
Gross charge-offs
Year one	0
Year two	2
Year three	3
Year four	4
Year five	3
Prior to year five	11
Within the Revolving Period	0
Converted to Term	0
Total	23
Retail \| Other retail
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	73		742
Year two	646		444
Year three	346		397
Year four	316		195
Year five	149		89
Prior to year five	124		72
Within the Revolving Period	3,488		3,463
Converted to Term	14		16
Total	5,156		5,418
Gross charge-offs
Year one	5
Year two	15
Year three	4
Year four	3
Year five	3
Prior to year five	3
Within the Revolving Period	23
Converted to Term	0
Total	56
Greater than 800 \| Retail
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	318		3,516
Year two	3,972		8,226
Year three	8,264		5,389
Year four	5,324		2,251
Year five	2,153		924
Prior to year five	4,958		4,340
Within the Revolving Period	5,432		5,449
Converted to Term	257		267
Total	30,678		30,362
Greater than 800 \| Retail \| Residential mortgages
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	133		2,132
Year two	2,528		4,943
Year three	5,105		3,143
Year four	3,202		1,180
Year five	1,167		363
Prior to year five	3,289		3,081
Within the Revolving Period	0		0
Converted to Term	0		0
Total	15,424		14,842
Greater than 800 \| Retail \| Home equity
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	0		4
Year two	4		5
Year three	5		2
Year four	2		5
Year five	5		6
Prior to year five	108		110
Within the Revolving Period	4,957		4,958
Converted to Term	257		267
Total	5,338		5,357
Greater than 800 \| Retail \| Automobile
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	95		650
Year two	625		1,453
Year three	1,362		584
Year four	524		324
Year five	276		120
Prior to year five	130		54
Within the Revolving Period	0		0
Converted to Term	0		0
Total	3,012		3,185
Greater than 800 \| Retail \| Education
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	74		548
Year two	652		1,720
Year three	1,710		1,567
Year four	1,522		694
Year five	668		410
Prior to year five	1,391		1,068
Within the Revolving Period	0		0
Converted to Term	0		0
Total	6,017		6,007
Greater than 800 \| Retail \| Other retail
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	16		182
Year two	163		105
Year three	82		93
Year four	74		48
Year five	37		25
Prior to year five	40		27
Within the Revolving Period	475		491
Converted to Term	0		0
Total	887		971
740-799 \| Retail
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	613		4,305
Year two	4,069		6,084
Year three	5,635		3,557
Year four	3,270		1,539
Year five	1,415		695
Prior to year five	2,838		2,422
Within the Revolving Period	5,272		5,324
Converted to Term	264		275
Total	23,376		24,201
740-799 \| Retail \| Residential mortgages
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	344		2,376
Year two	2,225		2,991
Year three	2,850		1,660
Year four	1,566		638
Year five	628		257
Prior to year five	1,747		1,635
Within the Revolving Period	0		0
Converted to Term	0		0
Total	9,360		9,557
740-799 \| Retail \| Home equity
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	0		2
Year two	1		2
Year three	2		1
Year four	1		4
Year five	4		6
Prior to year five	98		97
Within the Revolving Period	4,306		4,350
Converted to Term	263		274
Total	4,675		4,736
740-799 \| Retail \| Automobile
Financing Receivable, Excluding Accrued Interest, before Allowance for Credit Loss, by Origination Year [Abstract]
Year one	141		962
Year two	877		1,606
Year three	1,434		649
Year four	567		343
Year five	290		134
Prior to year five	141		56
Within the Revolving Period	0		0
Converted to Term	0		0

ALLOWANCE FOR CREDIT LOSSES, NONACCRUAL LOANS AND LEASES, AND CONCENTRATIONS OF CREDIT RISK - Amortized Cost Basis by Credit Quality Indicator (Details) - USD ($)
$ in Millions