ALLOWANCE FOR CREDIT LOSSES - Individual and Collective Allowance for Credit Losses (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Valuation Allowance [Line Items]
Amortized cost loans and leases, carrying amount	$ 26,162	$ 23,289
Commercial Real Estate [Member]
Valuation Allowance [Line Items]
Amortized cost loans and leases, carrying amount	9,305	8,960
Commercial and Industrial [Member]
Valuation Allowance [Line Items]
Amortized cost loans and leases, carrying amount	7,709	5,308
Commercial Leases [Member]
Valuation Allowance [Line Items]
Amortized cost loans and leases, carrying amount	497	432
Other [Member]
Valuation Allowance [Line Items]
Amortized cost loans and leases, carrying amount	40	21
Total Commercial Loans and Leases [Member]
Valuation Allowance [Line Items]
Amortized cost loans and leases, carrying amount	17,551	14,721
Direct Installment [Member]
Valuation Allowance [Line Items]
Amortized cost loans and leases, carrying amount	1,947	1,821
Residential Mortgages [Member]
Valuation Allowance [Line Items]
Amortized cost loans and leases, carrying amount	3,520	3,374
Indirect Installment [Member]
Valuation Allowance [Line Items]
Amortized cost loans and leases, carrying amount	1,767	1,922
Consumer Lines of Credit [Member]
Valuation Allowance [Line Items]
Amortized cost loans and leases, carrying amount	1,377	1,451
Consumer Loan [Member]
Valuation Allowance [Line Items]
Amortized cost loans and leases, carrying amount	$ 8,611	8,568
Originated Loans And Leases [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment		4
Originated allowance, collectively evaluated for impairment		185
Amortized cost loans and leases, carrying amount		20,397
Originated loans and leases outstanding, individually evaluated for impairment		30
Originated loans and leases outstanding, collectively evaluated for impairment		20,367
Originated Loans And Leases [Member] | Commercial Real Estate [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment		2
Originated allowance, collectively evaluated for impairment		58
Amortized cost loans and leases, carrying amount		7,114
Originated loans and leases outstanding, individually evaluated for impairment		13
Originated loans and leases outstanding, collectively evaluated for impairment		7,101
Originated Loans And Leases [Member] | Commercial and Industrial [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment		2
Originated allowance, collectively evaluated for impairment		51
Amortized cost loans and leases, carrying amount		5,063
Originated loans and leases outstanding, individually evaluated for impairment		17
Originated loans and leases outstanding, collectively evaluated for impairment		5,046
Originated Loans And Leases [Member] | Commercial Leases [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment		0
Originated allowance, collectively evaluated for impairment		11
Amortized cost loans and leases, carrying amount		432
Originated loans and leases outstanding, individually evaluated for impairment		0
Originated loans and leases outstanding, collectively evaluated for impairment		432
Originated Loans And Leases [Member] | Other [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment		0
Originated allowance, collectively evaluated for impairment		2
Amortized cost loans and leases, carrying amount		21
Originated loans and leases outstanding, individually evaluated for impairment		0
Originated loans and leases outstanding, collectively evaluated for impairment		21
Originated Loans And Leases [Member] | Total Commercial Loans and Leases [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment		4
Originated allowance, collectively evaluated for impairment		122
Amortized cost loans and leases, carrying amount		12,630
Originated loans and leases outstanding, individually evaluated for impairment		30
Originated loans and leases outstanding, collectively evaluated for impairment		12,600
Originated Loans And Leases [Member] | Direct Installment [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment		0
Originated allowance, collectively evaluated for impairment		13
Amortized cost loans and leases, carrying amount		1,758
Originated loans and leases outstanding, individually evaluated for impairment		0
Originated loans and leases outstanding, collectively evaluated for impairment		1,758
Originated Loans And Leases [Member] | Residential Mortgages [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment		0
Originated allowance, collectively evaluated for impairment		22
Amortized cost loans and leases, carrying amount		2,995
Originated loans and leases outstanding, individually evaluated for impairment		0
Originated loans and leases outstanding, collectively evaluated for impairment		2,995
Originated Loans And Leases [Member] | Indirect Installment [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment		0
Originated allowance, collectively evaluated for impairment		19
Amortized cost loans and leases, carrying amount		1,922
Originated loans and leases outstanding, individually evaluated for impairment		0
Originated loans and leases outstanding, collectively evaluated for impairment		1,922
Originated Loans And Leases [Member] | Consumer Lines of Credit [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment		0
Originated allowance, collectively evaluated for impairment		9
Amortized cost loans and leases, carrying amount		1,092
Originated loans and leases outstanding, individually evaluated for impairment		0
Originated loans and leases outstanding, collectively evaluated for impairment		1,092
Originated Loans And Leases [Member] | Consumer Loan [Member]
Valuation Allowance [Line Items]
Originated allowance, individually evaluated for impairment		0
Originated allowance, collectively evaluated for impairment		63
Amortized cost loans and leases, carrying amount		7,767
Originated loans and leases outstanding, individually evaluated for impairment		0
Originated loans and leases outstanding, collectively evaluated for impairment		$ 7,767