ALLOWANCE FOR CREDIT LOSSES - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	$ 180	$ 175
Charge- Offs	(10)	(13)
Recoveries	2	3
Net Charge- Offs	(8)	(10)
Provision for credit losses	14	14
Balance at End of Period	186	179
Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	173	168
Charge- Offs	(7)	(13)
Recoveries	2	3
Net Charge- Offs	(5)	(10)
Provision for credit losses	9	14
Balance at End of Period	177	172
Loans Acquired in a Business Combination [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	7	7
Charge- Offs	(3)	0
Recoveries	0	0
Net Charge- Offs	(3)	0
Provision for credit losses	5	0
Balance at End of Period	9	7
Commercial Real Estate [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	55	50
Charge- Offs	(1)	0
Recoveries	0	1
Net Charge- Offs	(1)	1
Provision for credit losses	3	3
Balance at End of Period	57	54
Commercial Real Estate [Member] | Loans Acquired in a Business Combination [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	2
Balance at End of Period	2
Commercial and Industrial [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	49	52
Charge- Offs	(1)	(6)
Recoveries	1	1
Net Charge- Offs	0	(5)
Provision for credit losses	3	6
Balance at End of Period	52	53
Commercial and Industrial [Member] | Loans Acquired in a Business Combination [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	4
Balance at End of Period	5
Commercial Leases [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	8	5
Charge- Offs	0	0
Recoveries	0	0
Net Charge- Offs	0	0
Provision for credit losses	0	1
Balance at End of Period	8	6
Other [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	2	2
Charge- Offs	(1)	(1)
Recoveries	0	0
Net Charge- Offs	(1)	(1)
Provision for credit losses	1	1
Balance at End of Period	2	2
Total Commercial Loans and Leases [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	114	109
Charge- Offs	(3)	(7)
Recoveries	1	2
Net Charge- Offs	(2)	(5)
Provision for credit losses	7	11
Balance at End of Period	119	115
Total Commercial Loans and Leases [Member] | Loans Acquired in a Business Combination [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	6
Balance at End of Period	7
Direct Installment [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	14	21
Charge- Offs	(1)	(3)
Recoveries	0	0
Net Charge- Offs	(1)	(3)
Provision for credit losses	(1)	2
Balance at End of Period	12	20
Direct Installment [Member] | Loans Acquired in a Business Combination [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	1
Balance at End of Period	1
Residential Mortgages [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	20	16
Charge- Offs	0	0
Recoveries	0	0
Net Charge- Offs	0	0
Provision for credit losses	(1)	(1)
Balance at End of Period	19	15
Residential Mortgages [Member] | Loans Acquired in a Business Combination [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	0
Balance at End of Period	1
Indirect Installment [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	15	12
Charge- Offs	(3)	(3)
Recoveries	1	1
Net Charge- Offs	(2)	(2)
Provision for credit losses	4	2
Balance at End of Period	17	12
Consumer Lines of Credit [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	10	10
Charge- Offs	0	0
Recoveries	0	0
Net Charge- Offs	0	0
Provision for credit losses	0	0
Balance at End of Period	10	10
Consumer Loan [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	59	59
Charge- Offs	(4)	(6)
Recoveries	1	1
Net Charge- Offs	(3)	(5)
Provision for credit losses	2	3
Balance at End of Period	58	57
Consumer Loan [Member] | Loans Acquired in a Business Combination [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	1
Balance at End of Period	2
Purchased Credit-Impaired Loans [Member] | Loans Acquired in a Business Combination [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	1	1
Charge- Offs	0	0
Recoveries	0	0
Net Charge- Offs	0	0
Provision for credit losses	0	0
Balance at End of Period	1	1
Other Loans Acquired In A Business Combination [Member] | Loans Acquired in a Business Combination [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	6	6
Charge- Offs	(3)	0
Recoveries	0	0
Net Charge- Offs	(3)	0
Provision for credit losses	5	0
Balance at End of Period	$ 8	$ 6