FAIR VALUE MEASUREMENTS - Schedule of Fair Values of Corporation's Financial Instruments (Details) - USD ($) $ in Millions		Dec. 31, 2024	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt securities available for sale		$ 3,466	$ 3,254
Debt securities held to maturity		3,644	3,593
Net loans and leases, including loans held for sale	[1]	53	45
Derivative assets		117	116
Long-term borrowings		1,115
Derivative liabilities		313	328
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents		2,419	1,576
Debt securities available for sale		3,466	3,254
Debt securities held to maturity		3,979	3,911
Net loans and leases, including loans held for sale		33,734	32,405
Loan servicing rights		72	61
Derivative assets		117	116
Accrued interest receivable		164	160
Deposits		37,107	34,711
Short-term borrowings		1,256	2,506
Long-term borrowings		3,012	1,971
Derivative liabilities		313	328
Accrued interest payable		65	69
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents		2,419	1,576
Debt securities available for sale		3,466	3,254
Debt securities held to maturity		3,644	3,593
Net loans and leases, including loans held for sale		32,648	30,641
Loan servicing rights		88	73
Derivative assets		117	116
Accrued interest receivable		164	160
Deposits		37,070	34,654
Short-term borrowings		1,256	2,505
Long-term borrowings		3,004	1,928
Derivative liabilities		313	328
Accrued interest payable		65	69
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents		2,419	1,576
Debt securities available for sale		274	420
Debt securities held to maturity		1	0
Net loans and leases, including loans held for sale		0	0
Loan servicing rights		0	0
Derivative assets		0	0
Accrued interest receivable		164	160
Deposits		29,607	28,496
Short-term borrowings		1,256	2,505
Long-term borrowings		0	0
Derivative liabilities		0	0
Accrued interest payable		65	69
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents		0	0
Debt securities available for sale		3,192	2,834
Debt securities held to maturity		3,643	3,593
Net loans and leases, including loans held for sale		214	150
Loan servicing rights		0	0
Derivative assets		116	111
Accrued interest receivable		0	0
Deposits		7,463	6,158
Short-term borrowings		0	0
Long-term borrowings		1,748	1,192
Derivative liabilities		309	328
Accrued interest payable		0	0
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents		0	0
Debt securities available for sale		0	0
Debt securities held to maturity		0	0
Net loans and leases, including loans held for sale		32,434	30,491
Loan servicing rights		88	73
Derivative assets		1	5
Accrued interest receivable		0	0
Deposits		0	0
Short-term borrowings		0	0
Long-term borrowings		1,256	736
Derivative liabilities		4	0
Accrued interest payable		$ 0	$ 0

[1] Amount represents loans for which we have elected the fair value option. See Note 25.