LOANS AND LEASES - Additional Allowance for Credit Losses Relating to Acquired Loans (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss	$ 343	$ 196	$ 196	$ 186	$ 180
Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss	152	60	60
Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss	88	53	53
Total Commercial Loans [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss	254		133
Direct Installment [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss	26	13	13
Consumer Loan [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss	89		63
Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss	$ 31	$ 22	22
Loans Acquired in a Business Combination [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss			7
Loans Acquired in a Business Combination [Member] | Commercial Real Estate [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss			4
Loans Acquired in a Business Combination [Member] | Commercial and Industrial [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss			0
Loans Acquired in a Business Combination [Member] | Total Commercial Loans [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss			4
Loans Acquired in a Business Combination [Member] | Direct Installment [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss			1
Loans Acquired in a Business Combination [Member] | Consumer Loan [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss			3
Loans Acquired in a Business Combination [Member] | Residential Mortgages [Member]
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for credit loss			$ 2