LOANS AND LEASES - Age Analysis of Past Due Loans (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	$ 25,532	$ 25,459
Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	9,799	9,731
Commercial and Industrial [Member]
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	7,401	7,214
Commercial Leases [Member]
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	471	485
Other [Member]
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	25	40
Total Commercial Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	17,696	17,470
Direct Installment [Member]
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	2,025	2,020
Residential Mortgages [Member]
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	3,329	3,433
Indirect Installment [Member]
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	1,201	1,218
Consumer Lines of Credit [Member]
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	1,281	1,318
Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Total Loans and Leases	7,836	7,989
Loans and Leases [Member]
Financing Receivable, Past Due [Line Items]
Past Due	205	258
Non-accrual loans	157	170
Current	25,327	25,201
Total Loans and Leases	25,532	25,459
Non-accrual with No ACL	45	52
Loans and Leases [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	38	72
Loans and Leases [Member] | Equal to Greater than 90 Days Past Due and Still Accruing [Member]
Financing Receivable, Past Due [Line Items]
Past Due	10	16
Loans and Leases [Member] | Commercial Real Estate [Member]
Financing Receivable, Past Due [Line Items]
Past Due	86	98
Non-accrual loans	78	85
Current	9,713	9,633
Total Loans and Leases	9,799	9,731
Non-accrual with No ACL	30	36
Loans and Leases [Member] | Commercial Real Estate [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	8	13
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
Loans and Leases [Member] | Commercial and Industrial [Member]
Financing Receivable, Past Due [Line Items]
Past Due	38	52
Non-accrual loans	36	44
Current	7,363	7,162
Total Loans and Leases	7,401	7,214
Non-accrual with No ACL	15	16
Loans and Leases [Member] | Commercial and Industrial [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	2	8
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
Loans and Leases [Member] | Commercial Leases [Member]
Financing Receivable, Past Due [Line Items]
Past Due	5	4
Non-accrual loans	2	2
Current	466	481
Total Loans and Leases	471	485
Non-accrual with No ACL	0	0
Loans and Leases [Member] | Commercial Leases [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	3	2
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
Loans and Leases [Member] | Other [Member]
Financing Receivable, Past Due [Line Items]
Past Due	0	1
Non-accrual loans	0	1
Current	25	39
Total Loans and Leases	25	40
Non-accrual with No ACL	0	0
Loans and Leases [Member] | Other [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	0	0
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
Loans and Leases [Member] | Total Commercial Loans [Member]
Financing Receivable, Past Due [Line Items]
Past Due	129	155
Non-accrual loans	116	132
Current	17,567	17,315
Total Loans and Leases	17,696	17,470
Non-accrual with No ACL	45	52
Loans and Leases [Member] | Total Commercial Loans [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	13	23
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
Loans and Leases [Member] | Direct Installment [Member]
Financing Receivable, Past Due [Line Items]
Past Due	17	20
Non-accrual loans	11	11
Current	2,008	2,000
Total Loans and Leases	2,025	2,020
Non-accrual with No ACL	0	0
Loans and Leases [Member] | Direct Installment [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	5	7
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	2
Loans and Leases [Member] | Residential Mortgages [Member]
Financing Receivable, Past Due [Line Items]
Past Due	39	52
Non-accrual loans	21	18
Current	3,290	3,381
Total Loans and Leases	3,329	3,433
Non-accrual with No ACL	0	0
Loans and Leases [Member] | Residential Mortgages [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	12	23
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	6	11
Loans and Leases [Member] | Indirect Installment [Member]
Financing Receivable, Past Due [Line Items]
Past Due	6	13
Non-accrual loans	2	2
Current	1,195	1,205
Total Loans and Leases	1,201	1,218
Non-accrual with No ACL	0	0
Loans and Leases [Member] | Indirect Installment [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	4	10
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
Loans and Leases [Member] | Consumer Lines of Credit [Member]
Financing Receivable, Past Due [Line Items]
Past Due	14	18
Non-accrual loans	7	7
Current	1,267	1,300
Total Loans and Leases	1,281	1,318
Non-accrual with No ACL	0	0
Loans and Leases [Member] | Consumer Lines of Credit [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	4	9
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	3	2
Loans and Leases [Member] | Consumer Loan [Member]
Financing Receivable, Past Due [Line Items]
Past Due	76	103
Non-accrual loans	41	38
Current	7,760	7,886
Total Loans and Leases	7,836	7,989
Non-accrual with No ACL	0	0
Loans and Leases [Member] | Consumer Loan [Member] | 30-89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Past Due	25	49
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	$ 10	$ 16