ALLOWANCE FOR CREDIT LOSSES - Individual and Collective Allowance for Credit Losses (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Valuation Allowance [Line Items]
Originated loans and leases outstanding, loans and leases	$ 22,620	$ 22,153
Commercial Real Estate [Member]
Valuation Allowance [Line Items]
Originated loans and leases outstanding, loans and leases	8,835	8,786
Commercial and Industrial [Member]
Valuation Allowance [Line Items]
Originated loans and leases outstanding, loans and leases	4,889	4,556
Commercial Leases [Member]
Valuation Allowance [Line Items]
Originated loans and leases outstanding, loans and leases	374	373
Other [Member]
Valuation Allowance [Line Items]
Originated loans and leases outstanding, loans and leases	49	46
Total Commercial Loans and Leases [Member]
Valuation Allowance [Line Items]
Originated loans and leases outstanding, loans and leases	14,147	13,761
Direct Installment [Member]
Valuation Allowance [Line Items]
Originated loans and leases outstanding, loans and leases	1,744	1,764
Residential Mortgages [Member]
Valuation Allowance [Line Items]
Originated loans and leases outstanding, loans and leases	3,233	3,113
Indirect Installment [Member]
Valuation Allowance [Line Items]
Originated loans and leases outstanding, loans and leases	1,950	1,933
Consumer Lines of Credit [Member]
Valuation Allowance [Line Items]
Originated loans and leases outstanding, loans and leases	1,546	1,582
Consumer Loan [Member]
Valuation Allowance [Line Items]
Originated loans and leases outstanding, loans and leases	8,473	8,392
Originated Loans and Leases [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment	6	4
Originated allowance, collectively evaluated for impairment	171	173
Originated loans and leases outstanding, loans and leases	18,812	18,062
Originated loans and leases outstanding, individually evaluated for impairment	17	18
Originated loans and leases outstanding, collectively evaluated for impairment	18,795	18,044
Originated Loans and Leases [Member] | Commercial Real Estate [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment	0	0
Originated allowance, collectively evaluated for impairment	57	55
Originated loans and leases outstanding, loans and leases	6,412	6,171
Originated loans and leases outstanding, individually evaluated for impairment	7	7
Originated loans and leases outstanding, collectively evaluated for impairment	6,405	6,164
Originated Loans and Leases [Member] | Commercial and Industrial [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment	6	4
Originated allowance, collectively evaluated for impairment	46	49
Originated loans and leases outstanding, loans and leases	4,509	4,140
Originated loans and leases outstanding, individually evaluated for impairment	10	11
Originated loans and leases outstanding, collectively evaluated for impairment	4,499	4,129
Originated Loans and Leases [Member] | Commercial Leases [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment	0	0
Originated allowance, collectively evaluated for impairment	8	9
Originated loans and leases outstanding, loans and leases	374	373
Originated loans and leases outstanding, individually evaluated for impairment	0	0
Originated loans and leases outstanding, collectively evaluated for impairment	374	373
Originated Loans and Leases [Member] | Other [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment	0	0
Originated allowance, collectively evaluated for impairment	2	2
Originated loans and leases outstanding, loans and leases	49	46
Originated loans and leases outstanding, individually evaluated for impairment	0	0
Originated loans and leases outstanding, collectively evaluated for impairment	49	46
Originated Loans and Leases [Member] | Total Commercial Loans and Leases [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment	6	4
Originated allowance, collectively evaluated for impairment	113	115
Originated loans and leases outstanding, loans and leases	11,344	10,730
Originated loans and leases outstanding, individually evaluated for impairment	17	18
Originated loans and leases outstanding, collectively evaluated for impairment	11,327	10,712
Originated Loans and Leases [Member] | Direct Installment [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment	0	0
Originated allowance, collectively evaluated for impairment	12	14
Originated loans and leases outstanding, loans and leases	1,657	1,668
Originated loans and leases outstanding, individually evaluated for impairment	0	0
Originated loans and leases outstanding, collectively evaluated for impairment	1,657	1,668
Originated Loans and Leases [Member] | Residential Mortgages [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment	0	0
Originated allowance, collectively evaluated for impairment	19	19
Originated loans and leases outstanding, loans and leases	2,755	2,612
Originated loans and leases outstanding, individually evaluated for impairment	0	0
Originated loans and leases outstanding, collectively evaluated for impairment	2,755	2,612
Originated Loans and Leases [Member] | Indirect Installment [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment	0	0
Originated allowance, collectively evaluated for impairment	17	15
Originated loans and leases outstanding, loans and leases	1,950	1,933
Originated loans and leases outstanding, individually evaluated for impairment	0	0
Originated loans and leases outstanding, collectively evaluated for impairment	1,950	1,933
Originated Loans and Leases [Member] | Consumer Lines of Credit [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment	0	0
Originated allowance, collectively evaluated for impairment	10	10
Originated loans and leases outstanding, loans and leases	1,106	1,119
Originated loans and leases outstanding, individually evaluated for impairment	0	0
Originated loans and leases outstanding, collectively evaluated for impairment	1,106	1,119
Originated Loans and Leases [Member] | Consumer Loan [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment	0	0
Originated allowance, collectively evaluated for impairment	58	58
Originated loans and leases outstanding, loans and leases	7,468	7,332
Originated loans and leases outstanding, individually evaluated for impairment	0	0
Originated loans and leases outstanding, collectively evaluated for impairment	$ 7,468	$ 7,332