LOANS AND LEASES - Origination Year (Details) $ in Millions	Mar. 31, 2020 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	$ 1,310
2019	5,388
2018	3,893
2017	3,020
2016	2,225
Prior	4,946
Revolving Loans Amortized Cost Basis	3,089
Total Loans and Leases	23,871
Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	329
2019	1,832
2018	1,402
2017	1,352
2016	1,215
Prior	2,805
Revolving Loans Amortized Cost Basis	191
Total Loans and Leases	9,126
Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	329
2019	1,823
2018	1,363
2017	1,285
2016	1,117
Prior	2,521
Revolving Loans Amortized Cost Basis	182
Total Loans and Leases	8,620
Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	6
2018	26
2017	44
2016	53
Prior	144
Revolving Loans Amortized Cost Basis	3
Total Loans and Leases	276
Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	3
2018	13
2017	23
2016	45
Prior	140
Revolving Loans Amortized Cost Basis	6
Total Loans and Leases	230
Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	0
Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	439
2019	1,424
2018	896
2017	551
2016	207
Prior	512
Revolving Loans Amortized Cost Basis	1,615
Total Loans and Leases	5,644
Commercial and Industrial [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	437
2019	1,392
2018	843
2017	497
2016	186
Prior	456
Revolving Loans Amortized Cost Basis	1,435
Total Loans and Leases	5,246
Commercial and Industrial [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	2
2019	29
2018	33
2017	30
2016	15
Prior	28
Revolving Loans Amortized Cost Basis	78
Total Loans and Leases	215
Commercial and Industrial [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	3
2018	20
2017	24
2016	6
Prior	28
Revolving Loans Amortized Cost Basis	102
Total Loans and Leases	183
Commercial and Industrial [Member] | Doubtful [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	0
Commercial Leases [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	51
2019	176
2018	120
2017	76
2016	14
Prior	7
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	444
Commercial Leases [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	41
2019	173
2018	117
2017	75
2016	13
Prior	6
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	425
Commercial Leases [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	10
2019	1
2018	1
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	12
Commercial Leases [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	2
2018	2
2017	1
2016	1
Prior	1
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	7
Commercial Leases [Member] | Doubtful [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	0
Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3
2019	0
2018	0
2017	0
2016	0
Prior	5
Revolving Loans Amortized Cost Basis	38
Total Loans and Leases	46
Other [Member] | Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3
2019	0
2018	0
2017	0
2016	0
Prior	5
Revolving Loans Amortized Cost Basis	38
Total Loans and Leases	46
Other [Member] | Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	0
Other [Member] | Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	0
Other [Member] | Doubtful [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	0
Total Commercial Loans [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	822
2019	3,432
2018	2,418
2017	1,979
2016	1,436
Prior	3,329
Revolving Loans Amortized Cost Basis	1,844
Total Loans and Leases	15,260
Direct Installment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	163
2019	433
2018	277
2017	194
2016	224
Prior	588
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	1,879
Direct Installment [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	163
2019	433
2018	276
2017	193
2016	223
Prior	573
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	1,861
Direct Installment [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	1
2017	1
2016	1
Prior	15
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	18
Residential Mortgages [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	201
2019	894
2018	525
2017	565
2016	434
Prior	824
Revolving Loans Amortized Cost Basis	2
Total Loans and Leases	3,445
Residential Mortgages [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	201
2019	891
2018	521
2017	559
2016	431
Prior	797
Revolving Loans Amortized Cost Basis	2
Total Loans and Leases	3,402
Residential Mortgages [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	3
2018	4
2017	6
2016	3
Prior	27
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	43
Indirect Installment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	123
2019	620
2018	659
2017	277
2016	125
Prior	59
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	1,863
Indirect Installment [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	123
2019	615
2018	653
2017	273
2016	122
Prior	57
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	1,843
Indirect Installment [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	5
2018	6
2017	4
2016	3
Prior	2
Revolving Loans Amortized Cost Basis	0
Total Loans and Leases	20
Consumer Lines of Credit [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1
2019	9
2018	14
2017	5
2016	6
Prior	146
Revolving Loans Amortized Cost Basis	1,243
Total Loans and Leases	1,424
Consumer Lines of Credit [Member] | Current [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1
2019	9
2018	14
2017	5
2016	5
Prior	132
Revolving Loans Amortized Cost Basis	1,240
Total Loans and Leases	1,406
Consumer Lines of Credit [Member] | Past Due [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	1
Prior	14
Revolving Loans Amortized Cost Basis	3
Total Loans and Leases	18
Consumer Loan [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
2020	488
2019	1,956
2018	1,475
2017	1,041
2016	789
Prior	1,617
Revolving Loans Amortized Cost Basis	1,245
Total Loans and Leases	$ 8,611