LOANS AND LEASES - Consumer Loans by Payment Status (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount	$ 26,162	$ 23,289
Direct Installment [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount	1,947	1,821
Residential Mortgages [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount	3,520	3,374
Indirect Installment [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount	$ 1,767	1,922
Originated Loans And Leases [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		20,397
Originated Loans And Leases [Member] | Direct Installment [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		1,758
Originated Loans And Leases [Member] | Residential Mortgages [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		2,995
Originated Loans And Leases [Member] | Indirect Installment [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		1,922
Acquired Loans [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		2,892
Acquired Loans [Member] | Direct Installment [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		63
Acquired Loans [Member] | Residential Mortgages [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		379
Consumer Loan [Member] | Originated Loans And Leases [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		7,767
Consumer Loan [Member] | Originated Loans And Leases [Member] | Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		7,728
Consumer Loan [Member] | Originated Loans And Leases [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		39
Consumer Loan [Member] | Originated Loans And Leases [Member] | Direct Installment [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		1,758
Consumer Loan [Member] | Originated Loans And Leases [Member] | Direct Installment [Member] | Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		1,745
Consumer Loan [Member] | Originated Loans And Leases [Member] | Direct Installment [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		13
Consumer Loan [Member] | Originated Loans And Leases [Member] | Residential Mortgages [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		2,995
Consumer Loan [Member] | Originated Loans And Leases [Member] | Residential Mortgages [Member] | Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		2,978
Consumer Loan [Member] | Originated Loans And Leases [Member] | Residential Mortgages [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		17
Consumer Loan [Member] | Originated Loans And Leases [Member] | Indirect Installment [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		1,922
Consumer Loan [Member] | Originated Loans And Leases [Member] | Indirect Installment [Member] | Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		1,919
Consumer Loan [Member] | Originated Loans And Leases [Member] | Indirect Installment [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		3
Consumer Loan [Member] | Originated Loans And Leases [Member] | Consumer Lines of Credit [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		1,092
Consumer Loan [Member] | Originated Loans And Leases [Member] | Consumer Lines of Credit [Member] | Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		1,086
Consumer Loan [Member] | Originated Loans And Leases [Member] | Consumer Lines of Credit [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		6
Consumer Loan [Member] | Acquired Loans [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		801
Consumer Loan [Member] | Acquired Loans [Member] | Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		800
Consumer Loan [Member] | Acquired Loans [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		1
Consumer Loan [Member] | Acquired Loans [Member] | Direct Installment [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		63
Consumer Loan [Member] | Acquired Loans [Member] | Direct Installment [Member] | Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		63
Consumer Loan [Member] | Acquired Loans [Member] | Direct Installment [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		0
Consumer Loan [Member] | Acquired Loans [Member] | Residential Mortgages [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		379
Consumer Loan [Member] | Acquired Loans [Member] | Residential Mortgages [Member] | Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		379
Consumer Loan [Member] | Acquired Loans [Member] | Residential Mortgages [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		0
Consumer Loan [Member] | Acquired Loans [Member] | Consumer Lines of Credit [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		359
Consumer Loan [Member] | Acquired Loans [Member] | Consumer Lines of Credit [Member] | Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		358
Consumer Loan [Member] | Acquired Loans [Member] | Consumer Lines of Credit [Member] | Non-Performing [Member]
Credit Quality [Line Items]
Amortized cost loans and leases, carrying amount		$ 1