LOANS AND LEASES - Narrative (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable on loans and leases held for investment		$ 850		$ 875
Loans pledged as collateral for FHLB borrowed funds	[1]	141,102		143,861
Interest income on direct financing lease		11	$ 12
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		36,300		36,000
Consumer and Commercial Portfolio Segment | Auto, commercial 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		$ 31,100		$ 31,900

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