FAIR VALUE MEASUREMENTS - Financial Instruments (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 931	$ 599
Debt securities available for sale	3,301	3,289
Securities held to maturity	3,050	3,275
Securities held to maturity, fair value	3,162	3,305
Net loans and leases	25,797	23,093
Derivative assets	439	154
Deposits	28,395	24,786
Short-term borrowings	2,411	3,216
Long-term borrowings	1,630	1,340
Long-term borrowings, fair value	547
Derivative liabilities	47	25
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	931	599
Debt securities available for sale	3,301	3,289
Securities held to maturity	3,050	3,275
Net loans and leases	25,905	23,144
Loan servicing rights	37	46
Derivative assets	439	154
Accrued interest receivable	94	109
Deposits	28,395	24,786
Short-term borrowings	2,411	3,216
Long-term borrowings	1,630	1,340
Derivative liabilities	47	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	931	599
Debt securities available for sale	3,301	3,289
Securities held to maturity, fair value	3,162	3,305
Net loans and leases, fair value	25,627	22,930
Loan servicing rights, fair value	37	48
Derivative assets	439	154
Accrued interest receivable	94	109
Deposits, fair value	28,450	24,797
Short-term borrowings, fair value	2,416	3,219
Long-term borrowings, fair value	1,616	1,355
Derivative liabilities	47	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	931	599
Debt securities available for sale	300	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	94	109
Deposits, fair value	24,129	20,058
Short-term borrowings, fair value	2,416	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	3,001	3,289
Securities held to maturity, fair value	3,162	3,305
Net loans and leases, fair value	95	41
Loan servicing rights, fair value	0	0
Derivative assets	421	151
Accrued interest receivable	0	0
Deposits, fair value	4,321	4,739
Short-term borrowings, fair value	0	0
Long-term borrowings, fair value	0	0
Derivative liabilities	47	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	25,532	22,889
Loan servicing rights, fair value	37	48
Derivative assets	18	3
Accrued interest receivable	0	0
Deposits, fair value	0	0
Short-term borrowings, fair value	0	0
Long-term borrowings, fair value	1,616	1,355
Derivative liabilities	0	0
Accrued interest payable	$ 0	$ 0