FAIR VALUE MEASUREMENTS - Financial Instruments (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 564	$ 599
Debt securities available for sale	3,194	3,289
Securities held to maturity	3,179	3,275
Securities held to maturity, fair value	3,264	3,305
Net loans and leases	23,528	23,093
Derivative assets	406	154
Deposits	24,746	24,786
Short-term borrowings	3,443	3,216
Long-term borrowings	1,633	1,340
Long-term borrowings, fair value	547
Derivative liabilities	50	25
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	564	599
Debt securities available for sale	3,194	3,289
Securities held to maturity	3,179	3,275
Net loans and leases	23,610	23,144
Loan servicing rights	38	46
Derivative assets	406	154
Accrued interest receivable	88	109
Deposits	24,746	24,786
Short-term borrowings	3,443	3,216
Long-term borrowings	1,633	1,340
Derivative liabilities	50	25
Accrued interest payable	19	21
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	564	599
Debt securities available for sale	3,194	3,289
Securities held to maturity, fair value	3,264	3,305
Net loans and leases, fair value	23,538	22,930
Loan servicing rights, fair value	38	48
Derivative assets	406	154
Accrued interest receivable	88	109
Deposits, fair value	24,797	24,797
Short-term borrowings, fair value	3,450	3,219
Long-term borrowings, fair value	1,620	1,355
Derivative liabilities	50	25
Accrued interest payable	19	21
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	564	599
Debt securities available for sale	0	0
Securities held to maturity, fair value	0	0
Net loans and leases, fair value	0	0
Loan servicing rights, fair value	0	0
Derivative assets	0	0
Accrued interest receivable	88	109
Deposits, fair value	20,184	20,058
Short-term borrowings, fair value	3,450	3,219
Long-term borrowings, fair value	0	0
Derivative liabilities	0	0
Accrued interest payable	19	21
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	0	0
Debt securities available for sale	3,194	3,289
Securities held to maturity, fair value	3,264	3,305
Net loans and leases, fair value	68	41
Loan servicing rights, fair value	0	0
Derivative assets	395	151
Accrued interest receivable	0	0
Deposits, fair value	4,613	4,739
Short-term borrowings, fair value	0	0
Long-term borrowings, fair value	0	0
Derivative liabilities	50	25
Accrued interest payable	0	0
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	0	0
Debt securities available for sale	0	0
Securities held to maturity, fair value	0	0
Net loans and leases, fair value	23,470	22,889
Loan servicing rights, fair value	38	48
Derivative assets	11	3
Accrued interest receivable	0	0
Deposits, fair value	0	0
Short-term borrowings, fair value	0	0
Long-term borrowings, fair value	1,620	1,355
Derivative liabilities	0	0
Accrued interest payable	$ 0	$ 0