LOANS AND LEASES - Age Analysis of Past Due Loans (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 22,620	$ 22,153
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	8,835	8,786
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	4,889	4,556
Commercial Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	374	373
Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	49	46
Total Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	14,147	13,761
Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,744	1,764
Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	3,233	3,113
Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,950	1,933
Consumer Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,546	1,582
Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	8,473	8,392
Originated Loans and Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	118	116
Non- Accrual	61	58
Current	18,694	17,946
Total Loans	18,812	18,062
Originated Loans and Leases [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	51	53
Originated Loans and Leases [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	6	5
Originated Loans and Leases [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	28	24
Non- Accrual	20	17
Current	6,384	6,147
Total Loans	6,412	6,171
Originated Loans and Leases [Member] | Commercial Real Estate [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	8	7
Originated Loans and Leases [Member] | Commercial Real Estate [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Originated Loans and Leases [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	27	24
Non- Accrual	18	19
Current	4,482	4,116
Total Loans	4,509	4,140
Originated Loans and Leases [Member] | Commercial and Industrial [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	9	5
Originated Loans and Leases [Member] | Commercial and Industrial [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Originated Loans and Leases [Member] | Commercial Leases [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3	3
Non- Accrual	2	2
Current	371	370
Total Loans	374	373
Originated Loans and Leases [Member] | Commercial Leases [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1	1
Originated Loans and Leases [Member] | Commercial Leases [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Originated Loans and Leases [Member] | Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1	1
Non- Accrual	1	1
Current	48	45
Total Loans	49	46
Originated Loans and Leases [Member] | Other [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, 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, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Originated Loans and Leases [Member] | Total Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	59	52
Non- Accrual	41	39
Current	11,285	10,678
Total Loans	11,344	10,730
Originated Loans and Leases [Member] | Total Commercial Loans [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, 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, Recorded Investment, Past Due [Line Items]
Past Due	0	0
Originated Loans and Leases [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	15	16
Non- Accrual	8	8
Current	1,642	1,652
Total Loans	1,657	1,668
Originated Loans and Leases [Member] | Direct Installment [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, 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, Recorded Investment, Past Due [Line Items]
Past Due	1	0
Originated Loans and Leases [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	24	25
Non- Accrual	7	6
Current	2,731	2,587
Total Loans	2,755	2,612
Originated Loans and Leases [Member] | Residential Mortgages [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	13	16
Originated Loans and Leases [Member] | Residential Mortgages [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	4	3
Originated Loans and Leases [Member] | Indirect Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	11	14
Non- Accrual	2	2
Current	1,939	1,919
Total Loans	1,950	1,933
Originated Loans and Leases [Member] | Indirect Installment [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	9	11
Originated Loans and Leases [Member] | Indirect Installment [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	0	1
Originated Loans and Leases [Member] | Consumer Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	9	9
Non- Accrual	3	3
Current	1,097	1,110
Total Loans	1,106	1,119
Originated Loans and Leases [Member] | Consumer Lines of Credit [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	5	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, Recorded Investment, Past Due [Line Items]
Past Due	1	1
Originated Loans and Leases [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	59	64
Non- Accrual	20	19
Current	7,409	7,268
Total Loans	7,468	7,332
Originated Loans and Leases [Member] | Consumer Loan [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	33	40
Originated Loans and Leases [Member] | Consumer Loan [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	6	5
Acquired Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	102	120
Non- Accrual	17	21
Current	3,917	4,193
(Discount) Premium	(211)	(222)
Total Loans	3,808	4,091
Acquired Loans [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	36	46
Acquired Loans [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	49	53
Acquired Loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	54	60
Non- Accrual	3	3
Current	2,530	2,723
(Discount) Premium	(161)	(168)
Total Loans	2,423	2,615
Acquired Loans [Member] | Commercial Real Estate [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	14	19
Acquired Loans [Member] | Commercial Real Estate [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	37	38
Acquired Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	18	24
Non- Accrual	13	17
Current	387	420
(Discount) Premium	(25)	(28)
Total Loans	380	416
Acquired Loans [Member] | Commercial and Industrial [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, 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, Recorded Investment, Past Due [Line Items]
Past Due	4	4
Acquired Loans [Member] | Total Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	72	84
Non- Accrual	16	20
Current	2,917	3,143
(Discount) Premium	(186)	(196)
Total Loans	2,803	3,031
Acquired Loans [Member] | Total Commercial Loans [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	15	22
Acquired Loans [Member] | Total Commercial Loans [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	41	42
Acquired Loans [Member] | Direct Installment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	3	5
Non- Accrual	0	0
Current	84	91
(Discount) Premium	0	0
Total Loans	87	96
Acquired Loans [Member] | Direct Installment [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2	3
Acquired Loans [Member] | Direct Installment [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	1	2
Acquired Loans [Member] | Residential Mortgages [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	18	19
Non- Accrual	0	0
Current	476	498
(Discount) Premium	(16)	(16)
Total Loans	478	501
Acquired Loans [Member] | Residential Mortgages [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	13	13
Acquired Loans [Member] | Residential Mortgages [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	5	6
Acquired Loans [Member] | Consumer Lines of Credit [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	9	12
Non- Accrual	1	1
Current	440	461
(Discount) Premium	(9)	(10)
Total Loans	440	463
Acquired Loans [Member] | Consumer Lines of Credit [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	6	8
Acquired Loans [Member] | Consumer Lines of Credit [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	2	3
Acquired Loans [Member] | Consumer Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	30	36
Non- Accrual	1	1
Current	1,000	1,050
(Discount) Premium	(25)	(26)
Total Loans	1,005	1,060
Acquired Loans [Member] | Consumer Loan [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	21	24
Acquired Loans [Member] | Consumer Loan [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Past Due	$ 8	$ 11