LOANS - Schedule of Purchased Credit Deteriorated Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Credit cards
Financing Receivable, Purchased with Credit Deterioration, Amount at Purchase Price [Abstract]
Purchase price	$ 0	$ 0	$ 4
Allowance for credit losses at acquisition date	0	0	4
Discount or premium attributable to non-credit factors	0	0	0
Par value (amortized cost basis)	0	0	8
Mortgages
Financing Receivable, Purchased with Credit Deterioration, Amount at Purchase Price [Abstract]
Purchase price	3	12	9
Allowance for credit losses at acquisition date	0	0	0
Discount or premium attributable to non-credit factors	0	0	0
Par value (amortized cost basis)	3	12	9
Installment and other
Financing Receivable, Purchased with Credit Deterioration, Amount at Purchase Price [Abstract]
Purchase price	0	0	0
Allowance for credit losses at acquisition date	0	0	0
Discount or premium attributable to non-credit factors	0	0	0
Par value (amortized cost basis)	$ 0	$ 0	$ 0