LOANS AND LEASES - Age Analysis of Past Due Loans (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Total Loans	$ 22,543	$ 22,153
Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Total Loans	8,832	8,786
Commercial and Industrial [Member]
Financing Receivable, Past Due [Line Items]
Total Loans	5,028	4,556
Commercial Leases [Member]
Financing Receivable, Past Due [Line Items]
Total Loans	385	373
Other [Member]
Financing Receivable, Past Due [Line Items]
Total Loans	37	46
Total Commercial Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Loans	14,282	13,761
Direct Installment [Member]
Financing Receivable, Past Due [Line Items]
Total Loans	1,758	1,764
Residential Mortgages [Member]
Financing Receivable, Past Due [Line Items]
Total Loans	3,022	3,113
Indirect Installment [Member]
Financing Receivable, Past Due [Line Items]
Total Loans	1,968	1,933
Consumer Lines of Credit [Member]
Financing Receivable, Past Due [Line Items]
Total Loans	1,513	1,582
Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Total Loans	8,261	8,392
Originated Loans and Leases [Member]
Financing Receivable, Past Due [Line Items]
Past Due	126	116
Non- Accrual	68	58
Current	18,924	17,946
Total Loans	19,050	18,062
Originated Loans and Leases [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	54	53
Originated Loans and Leases [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	4	5
Originated Loans and Leases [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Past Due	34	24
Non- Accrual	27	17
Current	6,567	6,147
Total Loans	6,601	6,171
Originated Loans and Leases [Member] | Commercial Real Estate [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	7	7
Originated Loans and Leases [Member] | Commercial Real Estate [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Originated Loans and Leases [Member] | Commercial and Industrial [Member]
Financing Receivable, Past Due [Line Items]
Past Due	24	24
Non- Accrual	17	19
Current	4,684	4,116
Total Loans	4,708	4,140
Originated Loans and Leases [Member] | Commercial and Industrial [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	7	5
Originated Loans and Leases [Member] | Commercial and Industrial [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Originated Loans and Leases [Member] | Commercial Leases [Member]
Financing Receivable, Past Due [Line Items]
Past Due	6	3
Non- Accrual	2	2
Current	379	370
Total Loans	385	373
Originated Loans and Leases [Member] | Commercial Leases [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	4	1
Originated Loans and Leases [Member] | Commercial Leases [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Originated Loans and Leases [Member] | Other [Member]
Financing Receivable, Past Due [Line Items]
Past Due	1	1
Non- Accrual	1	1
Current	36	45
Total Loans	37	46
Originated Loans and Leases [Member] | Other [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Originated Loans and Leases [Member] | Other [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Originated Loans and Leases [Member] | Total Commercial Loans [Member]
Financing Receivable, Past Due [Line Items]
Past Due	65	52
Non- Accrual	47	39
Current	11,666	10,678
Total Loans	11,731	10,730
Originated Loans and Leases [Member] | Total Commercial Loans [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	18	13
Originated Loans and Leases [Member] | Total Commercial Loans [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	0	0
Originated Loans and Leases [Member] | Direct Installment [Member]
Financing Receivable, Past Due [Line Items]
Past Due	14	16
Non- Accrual	7	8
Current	1,665	1,652
Total Loans	1,679	1,668
Originated Loans and Leases [Member] | Direct Installment [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	6	8
Originated Loans and Leases [Member] | Direct Installment [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	1	0
Originated Loans and Leases [Member] | Residential Mortgages [Member]
Financing Receivable, Past Due [Line Items]
Past Due	26	25
Non- Accrual	8	6
Current	2,547	2,587
Total Loans	2,573	2,612
Originated Loans and Leases [Member] | Residential Mortgages [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	16	16
Originated Loans and Leases [Member] | Residential Mortgages [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	2	3
Originated Loans and Leases [Member] | Indirect Installment [Member]
Financing Receivable, Past Due [Line Items]
Past Due	12	14
Non- Accrual	2	2
Current	1,956	1,919
Total Loans	1,968	1,933
Originated Loans and Leases [Member] | Indirect Installment [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	10	11
Originated Loans and Leases [Member] | Indirect Installment [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	0	1
Originated Loans and Leases [Member] | Consumer Lines of Credit [Member]
Financing Receivable, Past Due [Line Items]
Past Due	9	9
Non- Accrual	4	3
Current	1,090	1,110
Total Loans	1,099	1,119
Originated Loans and Leases [Member] | Consumer Lines of Credit [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	4	5
Originated Loans and Leases [Member] | Consumer Lines of Credit [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	1	1
Originated Loans and Leases [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Past Due	61	64
Non- Accrual	21	19
Current	7,258	7,268
Total Loans	7,319	7,332
Originated Loans and Leases [Member] | Consumer Loan [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	36	40
Originated Loans and Leases [Member] | Consumer Loan [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	4	5
Acquired Loans [Member]
Financing Receivable, Past Due [Line Items]
Past Due	88	120
Non- Accrual	5	21
Current	3,607	4,193
(Discount) Premium	(202)	(222)
Total Loans	3,493	4,091
Acquired Loans [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	40	46
Acquired Loans [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	43	53
Acquired Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Past Due	53	60
Non- Accrual	3	3
Current	2,332	2,723
(Discount) Premium	(154)	(168)
Total Loans	2,231	2,615
Acquired Loans [Member] | Commercial Real Estate [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	19	19
Acquired Loans [Member] | Commercial Real Estate [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	31	38
Acquired Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Past Due [Line Items]
Past Due	7	24
Non- Accrual	2	17
Current	336	420
(Discount) Premium	(23)	(28)
Total Loans	320	416
Acquired Loans [Member] | Commercial and Industrial [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	1	3
Acquired Loans [Member] | Commercial and Industrial [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	4	4
Acquired Loans [Member] | Total Commercial Loans [Member]
Financing Receivable, Past Due [Line Items]
Past Due	60	84
Non- Accrual	5	20
Current	2,668	3,143
(Discount) Premium	(177)	(196)
Total Loans	2,551	3,031
Acquired Loans [Member] | Total Commercial Loans [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	20	22
Acquired Loans [Member] | Total Commercial Loans [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	35	42
Acquired Loans [Member] | Direct Installment [Member]
Financing Receivable, Past Due [Line Items]
Past Due	2	5
Non- Accrual	0	0
Current	77	91
(Discount) Premium	0	0
Total Loans	79	96
Acquired Loans [Member] | Direct Installment [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	1	3
Acquired Loans [Member] | Direct Installment [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	1	2
Acquired Loans [Member] | Residential Mortgages [Member]
Financing Receivable, Past Due [Line Items]
Past Due	16	19
Non- Accrual	0	0
Current	449	498
(Discount) Premium	(16)	(16)
Total Loans	449	501
Acquired Loans [Member] | Residential Mortgages [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	12	13
Acquired Loans [Member] | Residential Mortgages [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	4	6
Acquired Loans [Member] | Consumer Lines of Credit [Member]
Financing Receivable, Past Due [Line Items]
Past Due	10	12
Non- Accrual	0	1
Current	413	461
(Discount) Premium	(9)	(10)
Total Loans	414	463
Acquired Loans [Member] | Consumer Lines of Credit [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	7	8
Acquired Loans [Member] | Consumer Lines of Credit [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	3	3
Acquired Loans [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Past Due	28	36
Non- Accrual	0	1
Current	939	1,050
(Discount) Premium	(25)	(26)
Total Loans	942	1,060
Acquired Loans [Member] | Consumer Loan [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	20	24
Acquired Loans [Member] | Consumer Loan [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	$ 8	$ 11