LOANS - Corporate Loan Modifications to Borrowers Experiencing Financial Difficulty (Details) - Corporate loans - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Financing Receivable, Modified [Line Items]
Total modifications balance	$ 115	$ 76
Commitments to lend	530	368
Term extension
Financing Receivable, Modified [Line Items]
Total modifications balance	115	46
Combination: term extension and payment delay
Financing Receivable, Modified [Line Items]
Total modifications balance	0	30
Commercial and industrial
Financing Receivable, Modified [Line Items]
Total modifications balance	$ 61	$ 70
Weighted average term extension	12 months	15 months
Commercial and industrial | Term extension
Financing Receivable, Modified [Line Items]
Total modifications balance	$ 61	$ 40
Commercial and industrial | Combination: term extension and payment delay
Financing Receivable, Modified [Line Items]
Total modifications balance	0	30
Financial institutions
Financing Receivable, Modified [Line Items]
Total modifications balance	0	0
Financial institutions | Term extension
Financing Receivable, Modified [Line Items]
Total modifications balance	0	0
Financial institutions | Combination: term extension and payment delay
Financing Receivable, Modified [Line Items]
Total modifications balance	0	0
Mortgage and real estate
Financing Receivable, Modified [Line Items]
Total modifications balance	$ 54	$ 6
Weighted average term extension	18 months	4 months
Mortgage and real estate | Term extension
Financing Receivable, Modified [Line Items]
Total modifications balance	$ 54	$ 6
Mortgage and real estate | Combination: term extension and payment delay
Financing Receivable, Modified [Line Items]
Total modifications balance	0	0
Other
Financing Receivable, Modified [Line Items]
Total modifications balance	0	0
Other | Term extension
Financing Receivable, Modified [Line Items]
Total modifications balance	0	0
Other | Combination: term extension and payment delay
Financing Receivable, Modified [Line Items]
Total modifications balance	$ 0	$ 0