CREDIT QUALITY AND THE ALLOWANCE FOR CREDIT LOSSES - Troubled Debt Restructurings (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR's that defaulted within 12 months of modification date	$ 164	$ 242
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR's that defaulted within 12 months of modification date	145
Commercial | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR's that defaulted within 12 months of modification date	43	0
Retail
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR's that defaulted within 12 months of modification date	19
Retail | Residential mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR's that defaulted within 12 months of modification date	$ 15	242
Retail | Loans Insured or Guaranteed by US Government Authorities
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR's that defaulted within 12 months of modification date		$ 187