LOANS AND LEASES - Additional Allowance for Credit Losses Relating to Acquired Loans (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on loans acquired in a business combination	$ 186	$ 180	$ 179	$ 175
Loans Acquired in a Business Combination [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on loans acquired in a business combination	9	7	$ 7	$ 7
Loans Acquired in a Business Combination [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on loans acquired in a business combination	2	2
Loans Acquired in a Business Combination [Member] | Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on loans acquired in a business combination	5	4
Loans Acquired in a Business Combination [Member] | Total Commercial Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on loans acquired in a business combination	7	6
Loans Acquired in a Business Combination [Member] | Direct Installment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on loans acquired in a business combination	1	1
Loans Acquired in a Business Combination [Member] | Consumer Loan [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on loans acquired in a business combination	2	1
Loans Acquired in a Business Combination [Member] | Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Total allowance on loans acquired in a business combination	$ 1	$ 0