LOANS AND LEASES - Narrative (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable on loans and leases held for investment		$ 858		$ 858		$ 875
Loans pledged as collateral for FHLB borrowed funds	[1]	139,717		139,717		143,861
Interest income on direct financing lease		9	$ 12	20	$ 24
Retail | Residential mortgages | Pledged as collateral for FHLB borrowing capacity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral for FHLB borrowed funds		36,500		36,500		36,000
Consumer and Commercial Portfolio Segment | Education, commercial and industrial, and commercial real estate loans | Notes Payable, Other Payables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged as collateral for FHLB borrowed funds		$ 28,000		$ 28,000		$ 31,900

[1] Includes amounts in consolidated VIEs. See Note 6 for additional information.