LOANS AND LEASES - Narrative (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accrued interest receivable on loans and leases held for investment		$ 887		$ 887		$ 820
Loans pledged as collateral for FHLB borrowed funds	[1]	147,666		147,666		154,679
Interest income on direct financing lease		12	$ 13	36	$ 34
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		37,100		37,100		38,400
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		$ 31,100		$ 34,800

[1] Includes amounts in consolidated VIEs. See Note 7 for additional information.