ALLOWANCE FOR CREDIT LOSSES, NONACCRUAL LOANS AND LEASES, AND CONCENTRATIONS OF CREDIT RISK - Amortized Cost Basis by Credit Quality Indicator (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 156,172	$ 128,163
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	8,143	13,660
Year two	17,026	6,289
Year three	7,403	7,499
Year four	7,409	4,775
Year five	5,221	2,327
Prior to year five	8,929	3,878
Within the Revolving Period	27,204	21,777
Converted to Term	110	145
Total	81,445	60,350
Commercial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	8,037	13,431
Year two	16,703	6,015
Year three	7,122	6,914
Year four	6,593	4,184
Year five	4,721	2,118
Prior to year five	7,774	3,441
Within the Revolving Period	26,277	20,857
Converted to Term	93	125
Total	77,320	57,085
Commercial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	4	102
Year two	151	128
Year three	143	268
Year four	381	219
Year five	122	71
Prior to year five	210	159
Within the Revolving Period	371	316
Converted to Term	1	1
Total	1,383	1,264
Commercial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	94	125
Year two	166	128
Year three	115	308
Year four	431	350
Year five	369	128
Prior to year five	919	260
Within the Revolving Period	467	530
Converted to Term	13	17
Total	2,574	1,846
Commercial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	8	2
Year two	6	18
Year three	23	9
Year four	4	22
Year five	9	10
Prior to year five	26	18
Within the Revolving Period	89	74
Converted to Term	3	2
Total	168	155
Commercial | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	4,745	10,363
Year two	10,080	3,528
Year three	3,166	3,978
Year four	3,279	2,501
Year five	2,127	1,527
Prior to year five	3,275	2,144
Within the Revolving Period	25,022	20,317
Converted to Term	107	142
Total	51,801	44,500
Commercial | Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	4,730	10,218
Year two	9,806	3,336
Year three	2,974	3,599
Year four	2,830	2,284
Year five	1,972	1,426
Prior to year five	2,845	1,863
Within the Revolving Period	24,106	19,406
Converted to Term	90	122
Total	49,353	42,254
Commercial | Commercial and industrial | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	4	47
Year two	127	71
Year three	66	155
Year four	113	114
Year five	17	41
Prior to year five	116	64
Within the Revolving Period	369	316
Converted to Term	1	1
Total	813	809
Commercial | Commercial and industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	3	97
Year two	142	112
Year three	112	215
Year four	332	81
Year five	129	50
Prior to year five	290	201
Within the Revolving Period	458	521
Converted to Term	13	17
Total	1,479	1,294
Commercial | Commercial and industrial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	8	1
Year two	5	9
Year three	14	9
Year four	4	22
Year five	9	10
Prior to year five	24	16
Within the Revolving Period	89	74
Converted to Term	3	2
Total	156	143
Commercial | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	3,284	2,839
Year two	6,532	2,468
Year three	3,951	3,382
Year four	4,002	2,123
Year five	2,943	731
Prior to year five	5,173	1,258
Within the Revolving Period	2,182	1,460
Converted to Term	3	3
Total	28,070	14,264
Commercial | Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	3,193	2,766
Year two	6,487	2,417
Year three	3,867	3,181
Year four	3,638	1,756
Year five	2,602	626
Prior to year five	4,449	1,119
Within the Revolving Period	2,171	1,451
Converted to Term	3	3
Total	26,410	13,319
Commercial | Commercial real estate | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0	45
Year two	21	42
Year three	75	113
Year four	268	100
Year five	102	27
Prior to year five	93	79
Within the Revolving Period	2	0
Converted to Term	0	0
Total	561	406
Commercial | Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	91	27
Year two	23	0
Year three	0	88
Year four	96	267
Year five	239	78
Prior to year five	629	59
Within the Revolving Period	9	9
Converted to Term	0	0
Total	1,087	528
Commercial | Commercial real estate | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0	1
Year two	1	9
Year three	9	0
Year four	0	0
Year five	0	0
Prior to year five	2	1
Within the Revolving Period	0	0
Converted to Term	0	0
Total	12	11
Commercial | Leases
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	114	458
Year two	414	293
Year three	286	139
Year four	128	151
Year five	151	69
Prior to year five	481	476
Within the Revolving Period	0	0
Converted to Term	0	0
Total	1,574	1,586
Commercial | Leases | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	114	447
Year two	410	262
Year three	281	134
Year four	125	144
Year five	147	66
Prior to year five	480	459
Within the Revolving Period	0	0
Converted to Term	0	0
Total	1,557	1,512
Commercial | Leases | Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0	10
Year two	3	15
Year three	2	0
Year four	0	5
Year five	3	3
Prior to year five	1	16
Within the Revolving Period	0	0
Converted to Term	0	0
Total	9	49
Commercial | Leases | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0	1
Year two	1	16
Year three	3	5
Year four	3	2
Year five	1	0
Prior to year five	0	0
Within the Revolving Period	0	0
Converted to Term	0	0
Total	8	24
Commercial | Leases | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
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	1
Within the Revolving Period	0	0
Converted to Term	0	0
Total	0	1
Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	7,487	19,683
Year two	19,928	13,715
Year three	12,320	7,020
Year four	6,011	3,366
Year five	2,905	3,083
Prior to year five	10,544	7,094
Within the Revolving Period	14,343	12,688
Converted to Term	1,189	1,164
Total	74,727	67,813
Retail | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	3,529	7,700
Year two	9,133	5,669
Year three	5,757	2,637
Year four	2,566	995
Year five	1,090	1,468
Prior to year five	7,013	4,353
Within the Revolving Period	0	0
Converted to Term	0	0
Total	29,088	22,822
Retail | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	7	0
Year two	9	9
Year three	10	43
Year four	41	66
Year five	62	63
Prior to year five	581	589
Within the Revolving Period	11,239	10,100
Converted to Term	1,173	1,145
Total	13,122	12,015
Retail | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	2,465	7,469
Year two	6,184	3,227
Year three	2,543	2,065
Year four	1,549	1,000
Year five	699	561
Prior to year five	428	227
Within the Revolving Period	0	0
Converted to Term	0	0
Total	13,868	14,549
Retail | Education
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	1,046	3,487
Year two	3,840	3,899
Year three	3,393	1,798
Year four	1,544	1,071
Year five	908	890
Prior to year five	2,410	1,852
Within the Revolving Period	0	0
Converted to Term	0	0
Total	13,141	12,997
Retail | Other retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	440	1,027
Year two	762	911
Year three	617	477
Year four	311	234
Year five	146	101
Prior to year five	112	73
Within the Revolving Period	3,104	2,588
Converted to Term	16	19
Total	5,508	5,430
Greater than 800 | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	1,837	5,912
Year two	7,655	5,833
Year three	5,528	2,735
Year four	2,417	1,170
Year five	1,018	1,323
Prior to year five	4,499	3,239
Within the Revolving Period	5,154	4,780
Converted to Term	301	281
Total	28,409	25,273
Greater than 800 | Retail | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	953	2,431
Year two	4,170	3,017
Year three	3,049	1,230
Year four	1,156	342
Year five	343	672
Prior to year five	3,023	2,139
Within the Revolving Period	0	0
Converted to Term	0	0
Total	12,694	9,831
Greater than 800 | Retail | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	2	0
Year two	3	2
Year three	2	5
Year four	6	5
Year five	6	3
Prior to year five	122	134
Within the Revolving Period	4,714	4,394
Converted to Term	301	281
Total	5,156	4,824
Greater than 800 | Retail | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	505	1,887
Year two	1,587	829
Year three	707	538
Year four	423	244
Year five	178	148
Prior to year five	112	57
Within the Revolving Period	0	0
Converted to Term	0	0
Total	3,512	3,703
Greater than 800 | Retail | Education
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	288	1,361
Year two	1,703	1,771
Year three	1,623	840
Year four	751	514
Year five	450	470
Prior to year five	1,201	880
Within the Revolving Period	0	0
Converted to Term	0	0
Total	6,016	5,836
Greater than 800 | Retail | Other retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	89	233
Year two	192	214
Year three	147	122
Year four	81	65
Year five	41	30
Prior to year five	41	29
Within the Revolving Period	440	386
Converted to Term	0	0
Total	1,031	1,079
740-799 | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	3,353	8,311
Year two	7,520	4,801
Year three	4,249	2,210
Year four	1,868	994
Year five	869	836
Prior to year five	3,003	1,806
Within the Revolving Period	4,908	4,278
Converted to Term	292	280
Total	26,062	23,516
740-799 | Retail | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	1,987	4,015
Year two	3,723	1,876
Year three	1,936	746
Year four	738	246
Year five	315	360
Prior to year five	2,049	1,086
Within the Revolving Period	0	0
Converted to Term	0	0
Total	10,748	8,329
740-799 | Retail | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	4	0
Year two	5	1
Year three	2	4
Year four	5	5
Year five	6	7
Prior to year five	117	122
Within the Revolving Period	4,017	3,514
Converted to Term	291	278
Total	4,447	3,931
740-799 | Retail | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	760	2,418
Year two	1,984	1,051
Year three	816	615
Year four	463	288
Year five	198	156
Prior to year five	115	58
Within the Revolving Period	0	0
Converted to Term	0	0
Total	4,336	4,586
740-799 | Retail | Education
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	474	1,555
Year two	1,563	1,577
Year three	1,299	672
Year four	553	371
Year five	299	275
Prior to year five	683	514
Within the Revolving Period	0	0
Converted to Term	0	0
Total	4,871	4,964
740-799 | Retail | Other retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	128	323
Year two	245	296
Year three	196	173
Year four	109	84
Year five	51	38
Prior to year five	39	26
Within the Revolving Period	891	764
Converted to Term	1	2
Total	1,660	1,706
680-739 | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	1,598	3,842
Year two	3,248	2,114
Year three	1,726	1,193
Year four	943	596
Year five	493	441
Prior to year five	1,569	1,041
Within the Revolving Period	2,804	2,447
Converted to Term	249	248
Total	12,630	11,922
680-739 | Retail | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	525	1,116
Year two	1,037	572
Year three	558	335
Year four	313	152
Year five	169	172
Prior to year five	1,005	585
Within the Revolving Period	0	0
Converted to Term	0	0
Total	3,607	2,932
680-739 | Retail | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	1	0
Year two	1	1
Year three	2	7
Year four	7	14
Year five	14	16
Prior to year five	137	134
Within the Revolving Period	1,940	1,738
Converted to Term	245	243
Total	2,347	2,153
680-739 | Retail | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	699	1,968
Year two	1,537	827
Year three	610	500
Year four	352	234
Year five	157	123
Prior to year five	89	48
Within the Revolving Period	0	0
Converted to Term	0	0
Total	3,444	3,700
680-739 | Retail | Education
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	254	512
Year two	489	474
Year three	395	229
Year four	190	140
Year five	118	107
Prior to year five	316	262
Within the Revolving Period	0	0
Converted to Term	0	0
Total	1,762	1,724
680-739 | Retail | Other retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	119	246
Year two	184	240
Year three	161	122
Year four	81	56
Year five	35	23
Prior to year five	22	12
Within the Revolving Period	864	709
Converted to Term	4	5
Total	1,470	1,413
620-679 | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	576	1,339
Year two	1,114	696
Year three	550	517
Year four	443	296
Year five	258	231
Prior to year five	751	523
Within the Revolving Period	833	662
Converted to Term	166	172
Total	4,691	4,436
620-679 | Retail | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	59	111
Year two	149	130
Year three	135	161
Year four	185	93
Year five	108	107
Prior to year five	463	276
Within the Revolving Period	0	0
Converted to Term	0	0
Total	1,099	878
620-679 | Retail | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0	0
Year two	0	3
Year three	2	11
Year four	9	19
Year five	17	17
Prior to year five	110	112
Within the Revolving Period	448	363
Converted to Term	162	167
Total	748	692
620-679 | Retail | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	412	1,029
Year two	787	378
Year three	273	257
Year four	183	131
Year five	90	72
Prior to year five	57	32
Within the Revolving Period	0	0
Converted to Term	0	0
Total	1,802	1,899
620-679 | Retail | Education
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	26	50
Year two	74	66
Year three	61	45
Year four	38	34
Year five	30	28
Prior to year five	114	99
Within the Revolving Period	0	0
Converted to Term	0	0
Total	343	322
620-679 | Retail | Other retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	79	149
Year two	104	119
Year three	79	43
Year four	28	19
Year five	13	7
Prior to year five	7	4
Within the Revolving Period	385	299
Converted to Term	4	5
Total	699	645
Less than 620 | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	113	225
Year two	386	258
Year three	261	364
Year four	336	310
Year five	263	252
Prior to year five	657	423
Within the Revolving Period	262	191
Converted to Term	180	182
Total	2,458	2,205
Less than 620 | Retail | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	5	24
Year two	51	66
Year three	77	164
Year four	170	162
Year five	151	157
Prior to year five	456	257
Within the Revolving Period	0	0
Converted to Term	0	0
Total	910	830
Less than 620 | Retail | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0	0
Year two	0	2
Year three	2	16
Year four	14	23
Year five	19	20
Prior to year five	95	87
Within the Revolving Period	120	91
Converted to Term	174	176
Total	424	415
Less than 620 | Retail | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	86	164
Year two	289	142
Year three	137	155
Year four	128	103
Year five	76	62
Prior to year five	55	32
Within the Revolving Period	0	0
Converted to Term	0	0
Total	771	658
Less than 620 | Retail | Education
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	2	5
Year two	11	11
Year three	15	12
Year four	12	12
Year five	11	10
Prior to year five	48	45
Within the Revolving Period	0	0
Converted to Term	0	0
Total	99	95
Less than 620 | Retail | Other retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	20	32
Year two	35	37
Year three	30	17
Year four	12	10
Year five	6	3
Prior to year five	3	2
Within the Revolving Period	142	100
Converted to Term	6	6
Total	254	207
No FICO available | Retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	10	54
Year two	5	13
Year three	6	1
Year four	4	0
Year five	4	0
Prior to year five	65	62
Within the Revolving Period	382	330
Converted to Term	1	1
Total	477	461
No FICO available | Retail | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	0	3
Year two	3	8
Year three	2	1
Year four	4	0
Year five	4	0
Prior to year five	17	10
Within the Revolving Period	0	0
Converted to Term	0	0
Total	30	22
No FICO available | Retail | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	3	3
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	3	3
No FICO available | Retail | Education
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	2	4
Year two	0	0
Year three	0	0
Year four	0	0
Year five	0	0
Prior to year five	48	52
Within the Revolving Period	0	0
Converted to Term	0	0
Total	50	56
No FICO available | Retail | Other retail
Financing Receivable, Credit Quality Indicator [Line Items]
Year one	5	44
Year two	2	5
Year three	4	0
Year four	0	0
Year five	0	0
Prior to year five	0	0
Within the Revolving Period	382	330
Converted to Term	1	1
Total	$ 394	$ 380