LOANS AND LEASES - Origination Year (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	$ 5,102	$ 7,565
Fiscal year before current fiscal year	4,854	4,429
Two years before current fiscal year	3,596	2,837
Three years before current fiscal year	2,194	2,281
Four years before current fiscal year	1,718	1,800
Prior	4,501	3,917
Revolving Loans Amortized Cost Basis	2,751	2,630
Total Loans and Leases	24,716	25,459
Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	24,539	25,201
Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	177	258
Total Commercial Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	2,969	5,402
Fiscal year before current fiscal year	2,986	3,109
Two years before current fiscal year	2,720	2,001
Three years before current fiscal year	1,663	1,603
Four years before current fiscal year	1,285	1,217
Prior	3,109	2,659
Revolving Loans Amortized Cost Basis	1,669	1,479
Total Loans and Leases	16,401	17,470
Total Commercial Loans [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	16,298	17,315
Total Commercial Loans [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	103	155
Total Commercial Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,305	1,892
Fiscal year before current fiscal year	1,841	1,916
Two years before current fiscal year	1,785	1,244
Three years before current fiscal year	1,113	1,166
Four years before current fiscal year	956	1,074
Prior	2,718	2,266
Revolving Loans Amortized Cost Basis	153	173
Total Loans and Leases	9,871	9,731
Total Commercial Loans [Member] | Commercial Real Estate [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	9,810	9,633
Total Commercial Loans [Member] | Commercial Real Estate [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	61	98
Total Commercial Loans [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,290	1,879
Fiscal year before current fiscal year	1,817	1,854
Two years before current fiscal year	1,706	1,135
Three years before current fiscal year	964	927
Four years before current fiscal year	797	888
Prior	2,385	1,911
Revolving Loans Amortized Cost Basis	148	163
Total Loans and Leases	9,107	8,757
Total Commercial Loans [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	15	9
Fiscal year before current fiscal year	16	30
Two years before current fiscal year	45	80
Three years before current fiscal year	111	158
Four years before current fiscal year	115	70
Prior	175	163
Revolving Loans Amortized Cost Basis	2	4
Total Loans and Leases	479	514
Total Commercial Loans [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	4
Fiscal year before current fiscal year	8	32
Two years before current fiscal year	34	29
Three years before current fiscal year	38	81
Four years before current fiscal year	44	116
Prior	158	192
Revolving Loans Amortized Cost Basis	3	6
Total Loans and Leases	285	460
Total Commercial Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,502	3,324
Fiscal year before current fiscal year	1,017	1,056
Two years before current fiscal year	825	668
Three years before current fiscal year	488	376
Four years before current fiscal year	283	136
Prior	378	383
Revolving Loans Amortized Cost Basis	1,467	1,271
Total Loans and Leases	5,960	7,214
Total Commercial Loans [Member] | Commercial and Industrial [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	5,924	7,162
Total Commercial Loans [Member] | Commercial and Industrial [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	36	52
Total Commercial Loans [Member] | Commercial and Industrial [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	1,500	3,286
Fiscal year before current fiscal year	980	1,007
Two years before current fiscal year	788	590
Three years before current fiscal year	422	304
Four years before current fiscal year	200	120
Prior	293	311
Revolving Loans Amortized Cost Basis	1,335	1,095
Total Loans and Leases	5,518	6,713
Total Commercial Loans [Member] | Commercial and Industrial [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	30
Fiscal year before current fiscal year	31	23
Two years before current fiscal year	15	13
Three years before current fiscal year	5	28
Four years before current fiscal year	18	10
Prior	64	35
Revolving Loans Amortized Cost Basis	35	79
Total Loans and Leases	168	218
Total Commercial Loans [Member] | Commercial and Industrial [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	2	8
Fiscal year before current fiscal year	6	26
Two years before current fiscal year	22	65
Three years before current fiscal year	61	44
Four years before current fiscal year	65	6
Prior	21	37
Revolving Loans Amortized Cost Basis	97	97
Total Loans and Leases	274	283
Total Commercial Loans [Member] | Commercial Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	139	186
Fiscal year before current fiscal year	128	137
Two years before current fiscal year	110	89
Three years before current fiscal year	62	61
Four years before current fiscal year	46	7
Prior	4	5
Revolving Loans Amortized Cost Basis	0	0
Total Loans and Leases	489	485
Total Commercial Loans [Member] | Commercial Leases [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	484	481
Total Commercial Loans [Member] | Commercial Leases [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	5	4
Total Commercial Loans [Member] | Commercial Leases [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	139	178
Fiscal year before current fiscal year	124	134
Two years before current fiscal year	107	83
Three years before current fiscal year	58	56
Four years before current fiscal year	43	5
Prior	2	3
Revolving Loans Amortized Cost Basis	0	0
Total Loans and Leases	473	459
Total Commercial Loans [Member] | Commercial Leases [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	1
Fiscal year before current fiscal year	0	1
Two years before current fiscal year	0	4
Three years before current fiscal year	2	4
Four years before current fiscal year	3	1
Prior	2	2
Revolving Loans Amortized Cost Basis	0	0
Total Loans and Leases	7	13
Total Commercial Loans [Member] | Commercial Leases [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	7
Fiscal year before current fiscal year	4	2
Two years before current fiscal year	3	2
Three years before current fiscal year	2	1
Four years before current fiscal year	0	1
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Total Loans and Leases	9	13
Total Commercial Loans [Member] | Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	23	0
Fiscal year before current fiscal year	0	0
Two years before current fiscal year	0	0
Three years before current fiscal year	0	0
Four years before current fiscal year	0	0
Prior	9	5
Revolving Loans Amortized Cost Basis	49	35
Total Loans and Leases	81	40
Total Commercial Loans [Member] | Other [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	80	39
Total Commercial Loans [Member] | Other [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	1	1
Total Commercial Loans [Member] | Other [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	23	0
Fiscal year before current fiscal year	0	0
Two years before current fiscal year	0	0
Three years before current fiscal year	0	0
Four years before current fiscal year	0	0
Prior	9	4
Revolving Loans Amortized Cost Basis	49	35
Total Loans and Leases	81	39
Total Commercial Loans [Member] | Other [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Two years before current fiscal year	0	0
Three years before current fiscal year	0	0
Four years before current fiscal year	0	0
Prior	0	1
Revolving Loans Amortized Cost Basis	0	0
Total Loans and Leases	0	1
Total Consumer Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	2,133	2,163
Fiscal year before current fiscal year	1,868	1,320
Two years before current fiscal year	876	836
Three years before current fiscal year	531	678
Four years before current fiscal year	433	583
Prior	1,392	1,258
Revolving Loans Amortized Cost Basis	1,082	1,151
Total Loans and Leases	8,315	7,989
Total Consumer Loan [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	8,241	7,886
Total Consumer Loan [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	74	103
Total Consumer Loan [Member] | Direct Installment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	707	706
Fiscal year before current fiscal year	585	338
Two years before current fiscal year	241	202
Three years before current fiscal year	142	144
Four years before current fiscal year	106	173
Prior	469	456
Revolving Loans Amortized Cost Basis	0	1
Total Loans and Leases	2,250	2,020
Total Consumer Loan [Member] | Direct Installment [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	707	706
Fiscal year before current fiscal year	585	337
Two years before current fiscal year	240	200
Three years before current fiscal year	141	143
Four years before current fiscal year	106	171
Prior	458	442
Revolving Loans Amortized Cost Basis	0	1
Total Loans and Leases	2,237	2,000
Total Consumer Loan [Member] | Direct Installment [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	1
Two years before current fiscal year	1	2
Three years before current fiscal year	1	1
Four years before current fiscal year	0	2
Prior	11	14
Revolving Loans Amortized Cost Basis	0	0
Total Loans and Leases	13	20
Total Consumer Loan [Member] | Residential Mortgages [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	996	1,080
Fiscal year before current fiscal year	988	712
Two years before current fiscal year	449	290
Three years before current fiscal year	171	382
Four years before current fiscal year	243	336
Prior	739	632
Revolving Loans Amortized Cost Basis	2	1
Total Loans and Leases	3,588	3,433
Total Consumer Loan [Member] | Residential Mortgages [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	996	1,079
Fiscal year before current fiscal year	986	707
Two years before current fiscal year	445	283
Three years before current fiscal year	167	378
Four years before current fiscal year	240	330
Prior	715	603
Revolving Loans Amortized Cost Basis	2	1
Total Loans and Leases	3,551	3,381
Total Consumer Loan [Member] | Residential Mortgages [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	1
Fiscal year before current fiscal year	2	5
Two years before current fiscal year	4	7
Three years before current fiscal year	4	4
Four years before current fiscal year	3	6
Prior	24	29
Revolving Loans Amortized Cost Basis	0	0
Total Loans and Leases	37	52
Total Consumer Loan [Member] | Indirect Installment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	417	373
Fiscal year before current fiscal year	292	263
Two years before current fiscal year	182	336
Three years before current fiscal year	212	149
Four years before current fiscal year	81	69
Prior	46	28
Revolving Loans Amortized Cost Basis	0	0
Total Loans and Leases	1,230	1,218
Total Consumer Loan [Member] | Indirect Installment [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	415	372
Fiscal year before current fiscal year	290	260
Two years before current fiscal year	180	332
Three years before current fiscal year	210	147
Four years before current fiscal year	80	67
Prior	45	27
Revolving Loans Amortized Cost Basis	0	0
Total Loans and Leases	1,220	1,205
Total Consumer Loan [Member] | Indirect Installment [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	2	1
Fiscal year before current fiscal year	2	3
Two years before current fiscal year	2	4
Three years before current fiscal year	2	2
Four years before current fiscal year	1	2
Prior	1	1
Revolving Loans Amortized Cost Basis	0	0
Total Loans and Leases	10	13
Total Consumer Loan [Member] | Consumer Lines of Credit [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	13	4
Fiscal year before current fiscal year	3	7
Two years before current fiscal year	4	8
Three years before current fiscal year	6	3
Four years before current fiscal year	3	5
Prior	138	142
Revolving Loans Amortized Cost Basis	1,080	1,149
Total Loans and Leases	1,247	1,318
Total Consumer Loan [Member] | Consumer Lines of Credit [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	13	4
Fiscal year before current fiscal year	3	7
Two years before current fiscal year	4	8
Three years before current fiscal year	6	3
Four years before current fiscal year	3	5
Prior	126	127
Revolving Loans Amortized Cost Basis	1,078	1,146
Total Loans and Leases	1,233	1,300
Total Consumer Loan [Member] | Consumer Lines of Credit [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Current fiscal year	0	0
Fiscal year before current fiscal year	0	0
Two years before current fiscal year	0	0
Three years before current fiscal year	0	0
Four years before current fiscal year	0	0
Prior	12	15
Revolving Loans Amortized Cost Basis	2	3
Total Loans and Leases	$ 14	$ 18