ALLOWANCE FOR CREDIT LOSSES - Changes in Allowance for Credit Losses (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	$ 186	$ 179	$ 180	$ 175
Charge- Offs	(13)	(23)	(23)	(36)
Recoveries	4	5	6	8
Net Charge- Offs	(9)	(18)	(17)	(28)
Provision for credit losses	11	16	25	30
Balance at End of Period	188	177	188	177
Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	177	172	173	168
Charge- Offs	(9)	(19)	(16)	(31)
Recoveries	3	4	5	6
Net Charge- Offs	(6)	(15)	(11)	(25)
Provision for credit losses	12	16	21	30
Balance at End of Period	183	173	183	173
Acquired Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	9	7
Charge- Offs	(4)	(4)
Recoveries	1	1
Net Charge- Offs	(3)	(3)
Provision for credit losses	(1)	0
Balance at End of Period	5	4	5	4
Loans Acquired in a Business Combination [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period			7	7
Charge- Offs			(7)	(5)
Recoveries			1	2
Net Charge- Offs			(6)	(3)
Provision for credit losses			4	0
Balance at End of Period	5	4	5	4
Commercial Real Estate [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	57	54	55	50
Charge- Offs	(1)	(5)	(2)	(4)
Recoveries	1	1	1	1
Net Charge- Offs	0	(4)	(1)	(3)
Provision for credit losses	4	0	7	3
Balance at End of Period	61	50	61	50
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		2
Commercial and Industrial [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	52	53	49	52
Charge- Offs	(3)	(6)	(4)	(12)
Recoveries	1	1	2	1
Net Charge- Offs	(2)	(5)	(2)	(11)
Provision for credit losses	2	6	5	13
Balance at End of Period	52	54	52	54
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	1		1
Commercial Leases [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	8	6	8	5
Charge- Offs	0	0	0	0
Recoveries	0	0	0	0
Net Charge- Offs	0	0	0	0
Provision for credit losses	1	1	1	2
Balance at End of Period	9	7	9	7
Other [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	2	2	2	2
Charge- Offs	(1)	(2)	(2)	(3)
Recoveries	0	0	0	1
Net Charge- Offs	(1)	(2)	(2)	(2)
Provision for credit losses	0	2	1	2
Balance at End of Period	1	2	1	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	119	115	114	109
Charge- Offs	(5)	(13)	(8)	(19)
Recoveries	2	2	3	3
Net Charge- Offs	(3)	(11)	(5)	(16)
Provision for credit losses	7	9	14	20
Balance at End of Period	123	113	123	113
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	3		3
Direct Installment [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	12	20	14	21
Charge- Offs	0	(3)	(1)	(6)
Recoveries	0	1	0	1
Net Charge- Offs	0	(2)	(1)	(5)
Provision for credit losses	1	3	0	5
Balance at End of Period	13	21	13	21
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		1
Residential Mortgages [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	19	15	20	16
Charge- Offs	(1)	0	(1)	(1)
Recoveries	0	0	0	0
Net Charge- Offs	(1)	0	(1)	(1)
Provision for credit losses	2	0	1	0
Balance at End of Period	20	15	20	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		1
Indirect Installment [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	17	12	15	12
Charge- Offs	(2)	(2)	(5)	(4)
Recoveries	1	1	2	2
Net Charge- Offs	(1)	(1)	(3)	(2)
Provision for credit losses	2	3	6	4
Balance at End of Period	18	14	18	14
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	10	10
Charge- Offs	(1)	(1)	(1)	(1)
Recoveries	0	0	0	0
Net Charge- Offs	(1)	(1)	(1)	(1)
Provision for credit losses	0	1	0	1
Balance at End of Period	9	10	9	10
Consumer Loan [Member] | Originated Loans and Leases [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	58	57	59	59
Charge- Offs	(4)	(6)	(8)	(12)
Recoveries	1	2	2	3
Net Charge- Offs	(3)	(4)	(6)	(9)
Provision for credit losses	5	7	7	10
Balance at End of Period	60	60	60	60
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		2
Purchased Credit-Impaired Loans [Member] | Acquired Loans [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	1	1
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	1	1
Other Acquired Loans [Member] | Acquired Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at Beginning of Period	8	6
Charge- Offs	(4)	(4)
Recoveries	1	1
Net Charge- Offs	(3)	(3)
Provision for credit losses	(1)	0
Balance at End of Period	4	3	4	3
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			(7)	(5)
Recoveries			1	2
Net Charge- Offs			(6)	(3)
Provision for credit losses			4	0
Balance at End of Period	$ 4	$ 3	$ 4	$ 3