FAIR VALUE MEASUREMENTS - Financial Instruments (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 900	$ 599
Debt securities available for sale	3,101	3,289
Securities held to maturity	2,966	3,275
Securities held to maturity, fair value	3,072	3,305
Net loans and leases	25,316	23,093
Derivative assets	423	154
Deposits	28,836	24,786
Short-term borrowings	1,899	3,216
Long-term borrowings	1,397	1,340
Long-term borrowings, fair value	547
Derivative liabilities	45	25
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	900	599
Debt securities available for sale	3,101	3,289
Securities held to maturity	2,966	3,275
Net loans and leases	25,996	23,144
Loan servicing rights	37	46
Derivative assets	423	154
Accrued interest receivable	90	109
Deposits	28,836	24,786
Short-term borrowings	1,899	3,216
Long-term borrowings	1,397	1,340
Derivative liabilities	45	25
Accrued interest payable	14	21
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	900	599
Debt securities available for sale	3,101	3,289
Securities held to maturity, fair value	3,072	3,305
Net loans and leases, fair value	25,872	22,930
Loan servicing rights, fair value	37	48
Derivative assets	423	154
Accrued interest receivable	90	109
Deposits, fair value	28,882	24,797
Short-term borrowings, fair value	1,904	3,219
Long-term borrowings, fair value	1,379	1,355
Derivative liabilities	45	25
Accrued interest payable	14	21
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents, fair value	900	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	90	109
Deposits, fair value	24,811	20,058
Short-term borrowings, fair value	1,904	3,219
Long-term borrowings, fair value	0	0
Derivative liabilities	0	0
Accrued interest payable	14	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	2,801	3,289
Securities held to maturity, fair value	3,072	3,305
Net loans and leases, fair value	138	41
Loan servicing rights, fair value	0	0
Derivative assets	401	151
Accrued interest receivable	0	0
Deposits, fair value	4,071	4,739
Short-term borrowings, fair value	0	0
Long-term borrowings, fair value	0	0
Derivative liabilities	45	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	25,734	22,889
Loan servicing rights, fair value	37	48
Derivative assets	22	3
Accrued interest receivable	0	0
Deposits, fair value	0	0
Short-term borrowings, fair value	0	0
Long-term borrowings, fair value	1,379	1,355
Derivative liabilities	0	0
Accrued interest payable	$ 0	$ 0